Analyze the pros and cons of other battery systems and learn what the potentials are.
The media promotes wonderful new batteries that promise long runtimes, charge in minutes, are paper-thin and will one day power the electric car. While these experimental batteries produce a voltage, the downsides are seldom mentioned. The typical shortcomings are low load capacity and short cycle life. (See BU-104c: The Octagon Battery.)
As a lemon can be made into a battery, so also has seawater been tried as electrolyte, but the retrieved energy is only good to light an incandescent flashlight for a short time before corrosion buildup renders the battery unusable. Many chemical processes are being tried to generate electricity from diverse metals but only a few promise to surpass today’s lead, nickel and lithium systems.
There is much media hype, and this may be done in part to attract venture capitalists to fund research projects. Few products have incubation periods that are as long as a battery. Although glamorous and promising at first, especially if the battery promises to power the electric vehicle, investment firms are beginning to realize the high development costs, uncertainties and long gestation periods before a return can be realized. Meanwhile, universities continue publishing papers about battery breakthroughs to keep receiving government funding while private companies throw in a paper or two to appease investors and boost their own stock value.
Zinc-air (Primary & Secondary)
Zinc-air batteries generate electrical power by an oxidation process of zinc and oxygen from the air. The cell can produce 1.65V; however, cells with 1.4V and lower voltages achieve a longer lifetime. To activate the battery, the user removes a sealing tab that enables airflow. The battery reaches full operating voltage within 5 seconds. Airflow can control the rate of the reaction somewhat and once turned on, the battery cannot be reverted back to standby mode. Adding a tape to stop the airflow only slows the chemical activity and battery will soon dry out.
The Zinc-air battery shares similarities with the fuel cell (PEMFC) by using oxygen from the air to fuel the positive electrode. It is considered a primary battery and recharging versions for high-power applications have been tried. Recharging occurs by replacing the spent zinc electrodes, which can be in the form of a zinc electrolyte paste. Other zinc-air batteries use zinc pellets.
At 300–400Wh/kg, zinc-air has a high specific energy but the specific power is low. Manufacturing cost is low and in a sealed state, zinc-air has a 2 percent self-discharge per year. The battery is sensitive to hot and cold temperatures and high humidity. Pollution also affects performance; high carbon dioxide content reduces the performance by increasing the internal resistance. Typical applications are hearing aids while large systems operate remote railway signaling and safety lamps at construction sites.
Silver-zinc (Primary & Secondary)
The small silver-based batteries in button cells are typically called silver-oxide and are non-rechargeable; the higher capacity rechargeable versions are referred to as silver-zinc. Both have an open circuit voltage of 1.60 volts. Because of the high cost of silver, these batteries come in either very small sizes where the amount of silver does not contribute significantly to the overall product cost, or they are available in larger sizes for critical applications where the superior performance outweighs any cost considerations.
The primary cells are used for watches, hearing aids and memory backup; the larger rechargeable version is found in submarines, missiles and aerospace applications. Silver-zinc also powers TV cameras needing extra runtime. High cost and short service life locked the silver-zinc out of the commercial market, but it is on the verge of a rebirth with improvements.
The primary cause of failure in the original design was the decaying of the zinc electrode and separator. Cycling developed zinc dendrites that pierced through the separator, causing electrical shorts. In addition, the separator degraded by sitting in the potassium hydroxide electrolyte. This limited the calendar life to about 2 years.
Improvements in the zinc electrode and separator promise a longer service life and a 40 percent higher specific energy than Li-ion. Silver-zinc is safe, has no toxic metals and can be recycled, but the use of silver makes the battery expensive to manufacture.
Reusable Alkaline
The reusable alkaline served as an alternative to disposable batteries. Although fabrication costs were said to be similar to regular alkaline, the consumer did not accept the product.
Recharging alkaline batteries is not new. Ordinary alkaline batteries have been recharged in households for many years. Recharging is most effective if alkaline is discharged to less than 50 percent before recharging. The number of recharges depends on the depth of discharge and is limited to just a few cycles. Battery makers do not endorse this practice for safety reasons; charging ordinary alkaline batteries may generate hydrogen gas that can lead to an explosion.
The reusable alkaline overcomes some of these deficiencies, but a limited cycle count and low capacity on repeat charge are major drawbacks. Longevity is also in direct relationship to the depth of discharge. At a 50 percent depth of discharge, the battery may deliver 50 cycles, but most users run a battery empty before recharging and the manufacturer, including the inventor Karl Kordesch, overestimated the eagerness of the user wanting to recharge early. An additional limitation is its low load current of 400mA, which is only sufficient for flashlights and personal entertainment devices. NiMH in AA and AAA cells has mostly replaced the reusable alkaline.
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Become familiar with the many different types of lithium-ion batteries.
Lithium-ion is named for its active materials; the words are either written in full or shortened by their chemical symbols. A series of letters and numbers strung together can be hard to remember and even harder to pronounce, and battery chemistries are also identified in abbreviated letters.
For example, lithium cobalt oxide, one of the most common Li-ions, has the chemical symbols LiCoO2 and the abbreviation LCO. For reasons of simplicity, the short form Li-cobalt can also be used for this battery. Cobalt is the main active material that gives this battery character. Other Li-ion chemistries are given similar short-form names. This section lists six of the most common Li-ions. All readings are average estimates at time of writing.
Lithium-ion batteries can be designed for optimal capacity with the drawback of limited loading, slow charging and reduced longevity. An industrial battery may have a moderate Ah rating but the focus in on durability. Specific energy only provides part of battery performance. See also BU-501a: Discharge Characteristics of Li-ion that compares energy cells with power cells.
Lithium Cobalt Oxide(LiCoO2) — LCO
Its high specific energy makes Li-cobalt the popular choice for mobile phones, laptops and digital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon anode. The cathode has a layered structure and during discharge, lithium ions move from the anode to the cathode. The flow reverses on charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power). Figure 1 illustrates the structure.
Figure 1: Li-cobalt structure.
The cathode has a layered structure. During discharge the lithium ions move from the anode to the cathode; on charge the flow is from cathode to anode. Source: Cadex
The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power). Like other cobalt-blended Li-ion, Li-cobalt has a graphite anode that limits the cycle life by a changing solid electrolyte interface (SEI), thickening on the anode and lithium plating while fast charging and charging at low temperature. Newer systems include nickel, manganese and/or aluminum to improve longevity, loading capabilities and cost.
Li-cobalt should not be charged and discharged at a current higher than its C-rating. This means that an 18650 cell with 2,400mAh can only be charged and discharged at 2,400mA. Forcing a fast charge or applying a load higher than 2,400mA causes overheating and undue stress. For optimal fast charge, the manufacturer recommends a C-rate of 0.8C or about 2,000mA. (See BU-402: What is C-rate). The mandatory battery protection circuit limits the charge and discharge rate to a safe level of about 1C for the Energy Cell.
The hexagonal spider graphic (Figure 2) summarizes the performance of Li-cobalt in terms of specific energy or capacity that relates to runtime; specific power or the ability to deliver high current; safety; performance at hot and cold temperatures; life span reflecting cycle life and longevity; and cost. Other characteristics of interest not shown in the spider webs are toxicity, fast-charge capabilities, self-discharge and shelf life. (See BU-104c: The Octagon Battery – What makes a Battery a Battery).
The Li-cobalt is losing favor to Li-manganese, but especially NMC and NCA because of the high cost of cobalt and improved performance by blending with other active cathode materials. (See description of the NMC and NCA below.)
Figure 2: Snapshot of an average Li-cobalt battery.
Li-cobalt excels on high specific energy but offers only moderate performance specific power, safety and life span. Source: Cadex
Summary Table
Lithium Cobalt Oxide: LiCoO2 cathode (~60% Co), graphite anode
Short form: LCO or Li-cobalt.Since 1991
Voltages
3.60V nominal; typical operating range 3.0–4.2V/cell
Specific energy (capacity)
150–200Wh/kg. Specialty cells provide up to 240Wh/kg.
Charge (C-rate)
0.7–1C, charges to 4.20V (most cells); 3h charge typical. Charge current above 1C shortens battery life.
Discharge (C-rate)
1C; 2.50V cut off. Discharge current above 1C shortens battery life.
Cycle life
500–1000, related to depth of discharge, load, temperature
Thermal runaway
150°C (302°F). Full charge promotes thermal runaway
Applications
Mobile phones, tablets, laptops, cameras
Comments
2019 update:
Very high specific energy, limited specific power. Cobalt is expensive. Serves as Energy Cell. Market share has stabilized.
Early version; no longer relevant.
Table 3: Characteristics of lithium cobalt oxide.
Lithium Manganese Oxide (LiMn2O4) — LMO
Li-ion with manganese spinel was first published in the Materials Research Bulletin in 1983. In 1996, Moli Energy commercialized a Li-ion cell with lithium manganese oxide as cathode material. The architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improved current handling. A further advantage of spinel is high thermal stability and enhanced safety, but the cycle and calendar life are limited.
Low internal cell resistance enables fast charging and high-current discharging. In an 18650 package, Li-manganese can be discharged at currents of 20–30A with moderate heat buildup. It is also possible to apply one-second load pulses of up to 50A. A continuous high load at this current would cause heat buildup and the cell temperature cannot exceed 80°C (176°F). Li-manganese is used for power tools, medical instruments, as well as hybrid and electric vehicles.
Figure 4 illustrates the formation of a three-dimensional crystalline framework on the cathode of a Li-manganese battery. This spinel structure, which is usually composed of diamond shapes connected into a lattice, appears after initial formation.
Figure 4: Li-manganese structure.
The cathode crystalline formation of lithium manganese oxide has a three-dimensional framework structure that appears after initial formation. Spinel provides low resistance but has a more moderate specific energy than cobalt. Source: Cadex
Li-manganese has a capacity that is roughly one-third lower than Li-cobalt. Design flexibility allows engineers to maximize the battery for either optimal longevity (life span), maximum load current (specific power) or high capacity (specific energy). For example, the long-life version in the 18650 cell has a moderate capacity of only 1,100mAh; the high-capacity version is 1,500mAh.
Figure 5 shows the spider web of a typical Li-manganese battery. The characteristics appear marginal but newer designs have improved in terms of specific power, safety and life span. Pure Li-manganese batteries are no longer common today; they may only be used for special applications.
Figure 5: Snapshot of a pure Li-manganese battery.
Although moderate in overall performance, newer designs of Li-manganese offer improvements in specific power, safety and life span. Source: Boston Consulting Group
Most Li-manganese batteries blend with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span. This combination brings out the best in each system, and the LMO (NMC) is chosen for most electric vehicles, such as the Nissan Leaf, Chevy Volt and BMW i3. The LMO part of the battery, which can be about 30 percent, provides high current boost on acceleration; the NMC part gives the long driving range.
Li-ion research gravitates heavily towards combining Li-manganese with cobalt, nickel, manganese and/or aluminum as active cathode material. In some architecture, a small amount of silicon is added to the anode. This provides a 25 percent capacity boost; however, the gain is commonly connected with a shorter cycle life as silicon grows and shrinks with charge and discharge, causing mechanical stress.
These three active metals, as well as the silicon enhancement can conveniently be chosen to enhance the specific energy (capacity), specific power (load capability) or longevity. While consumer batteries go for high capacity, industrial applications require battery systems that have good loading capabilities, deliver a long life and provide safe and dependable service. Summary Table
Lithium Manganese Oxide: LiMn2O4 cathode. graphite anode
Short form: LMO or Li-manganese (spinel structure) Since 1996
Voltages
3.70V (3.80V) nominal; typical operating range 3.0–4.2V/cell
Specific energy (capacity)
100–150Wh/kg
Charge (C-rate)
0.7–1C typical, 3C maximum, charges to 4.20V (most cells)
Discharge (C-rate)
1C; 10C possible with some cells, 30C pulse (5s), 2.50V cut-off
Cycle life
300–700 (related to depth of discharge, temperature)
Thermal runaway
250°C (482°F) typical. High charge promotes thermal runaway
Applications
Power tools, medical devices, electric powertrains
Comments
2019 update:
High power but less capacity; safer than Li-cobalt; commonly mixed with NMC to improve performance.
Less relevant now; limited growth potential.
Table 6: Characteristics of Lithium Manganese Oxide.
One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored to serve as Energy Cells or Power Cells. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4A to 5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mAh but delivers a continuous discharge current of 20A. A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life. Silicon added to graphite has the drawback that the anode grows and shrinks with charge and discharge, making the cell mechanically unstable.
The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt in which the main ingredients, sodium and chloride, are toxic on their own but mixing them serves as seasoning salt and food preserver. Nickel is known for its high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers a low specific energy. Combining the metals enhances each other strengths.
NMC is the battery of choice for power tools, e-bikes and other electric powertrains. The cathode combination is typically one-third nickel, one-third manganese and one-third cobalt, also known as 1-1-1. Cobalt is expensive and in limited supply. Battery manufacturers are reducing the cobalt content with some compromise in performance. A successful combination is NCM532 with 5 parts nickel, 3 parts cobalt and 2 parts manganese. Other combinations are NMC622 and NMC811. Cobalt stabilizes nickel, a high energy active material
New electrolytes and additives enable charging to 4.4V/cell and higher to boost capacity. Figure 7 demonstrates the characteristics of the NMC.
Figure 7: Snapshot of NMC.
NMC has good overall performance and excels on specific energy. This battery is the preferred candidate for the electric vehicle and has the lowest self-heating rate. Source: Boston Consulting Group
There is a move towards NMC-blended Li-ion as the system can be built economically and it achieves a good performance. The three active materials of nickel, manganese and cobalt can easily be blended to suit a wide range of applications for automotive and energy storage systems (ESS) that need frequent cycling. The NMC family is growing in its diversity.
Summary Table
Lithium Nickel Manganese Cobalt Oxide: LiNiMnCoO2. cathode, graphite anode
Short form: NMC (NCM, CMN, CNM, MNC, MCN similar with different metal combinations) Since 2008
Voltages
3.60V, 3.70V nominal; typical operating range 3.0–4.2V/cell, or higher
Specific energy (capacity)
150–220Wh/kg
Charge (C-rate)
0.7–1C, charges to 4.20V, some go to 4.30V; 3h charge typical. Charge current above 1C shortens battery life.
Discharge (C-rate)
1C; 2C possible on some cells; 2.50V cut-off
Cycle life
1000–2000 (related to depth of discharge, temperature)
Thermal runaway
210°C (410°F) typical. High charge promotes thermal runaway
Cost
~$420 per kWh (Source: RWTH, Aachen)
Applications
E-bikes, medical devices, EVs, industrial
Comments
2019 update:
Provides high capacity and high power. Serves as Hybrid Cell. Favorite chemistry for many uses; market share is increasing.
Leading system; dominant cathode chemistry.
Table 8: Characteristics of lithium nickel manganese cobalt oxide (NMC).
Lithium Iron Phosphate(LiFePO4) — LFP
In 1996, the University of Texas (and other contributors) discovered phosphate as cathode material for rechargeable lithium batteries. Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused.
Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. (See BU-808: How to Prolong Lithium-based Batteries). As a trade-off, its lower nominal voltage of 3.2V/cell reduces the specific energy below that of cobalt-blended lithium-ion. With most batteries, cold temperature reduces performance and elevated storage temperature shortens the service life, and Li-phosphate is no exception. Li-phosphate has a higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. This can be mitigated by buying high quality cells and/or using sophisticated control electronics, both of which increase the cost of the pack. Cleanliness in manufacturing is of importance for longevity. There is no tolerance for moisture, lest the battery will only deliver 50 cycles. Figure 9 summarizes the attributes of Li-phosphate.
Li-phosphate is often used to replace the lead acid starter battery. Four cells in series produce 12.80V, a similar voltage to six 2V lead acid cells in series. Vehicles charge lead acid to 14.40V (2.40V/cell) and maintain a topping charge. Topping charge is applied to maintain full charge level and prevent sulfation on lead acid batteries.
With four Li-phosphate cells in series, each cell tops at 3.60V, which is the correct full-charge voltage. At this point, the charge should be disconnected but the topping charge continues while driving. Li-phosphate is tolerant to some overcharge; however, keeping the voltage at 14.40V for a prolonged time, as most vehicles do on a long road trip, could stress Li-phosphate. Time will tell how durable Li-Phosphate will be as a lead acid replacement with a regular vehicle charging system. Cold temperature also reduces performance of Li-ion and this could affect the cranking ability in extreme cases.
Figure 9: Snapshot of a typical Li-phosphate battery.
Li-phosphate has excellent safety and long life span but moderate specific energy and elevated self-discharge. Source: Cadex
Summary Table
Lithium Iron Phosphate: LiFePO4 cathode, graphite anode
Short form: LFP or Li-phosphate. LIP is also common. Since 1996
Voltages
3.20, 3.30V nominal; typical operating range 2.5–3.65V/cell
Specific energy (capacity)
90–120Wh/kg
Charge (C-rate)
1C typical, charges to 3.65V; 3h charge time typical
Discharge (C-rate)
1C, 25C on some cells; 40A pulse (2s); 2.50V cut-off (lower that 2V causes damage)
Cycle life
2000 and higher (related to depth of discharge, temperature)
Thermal runaway
270°C (518°F) Very safe battery even if fully charged
Cost
~$580 per kWh (Source: RWTH, Aachen)
Applications
Portable and stationary needing high load currents and endurance
Comments
2019 update:
Very flat voltage discharge curve but low capacity. One of safest
Li-ions. Used for special markets. Elevated self-discharge.Used primarily for energy storage, moderate growth.
Table 10: Characteristics of lithium iron phosphate.
Lithium nickel cobalt aluminum oxide battery, or NCA, has been around since 1999 for special applications. It shares similarities with NMC by offering high specific energy, reasonably good specific power and a long life span. Less flattering are safety and cost. Figure 11 summarizes the six key characteristics. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.
Figure 11: Snapshot of NCA.
High energy and power densities, as well as good life span, make NCA a candidate for EV powertrains. High cost and marginal safety are negatives. Source: Cadex
Summary Table
Lithium Nickel Cobalt Aluminum Oxide: LiNiCoAlO2 cathode (~9% Co), graphite anode
Short form: NCA or Li-aluminum. Since 1999
Voltages
3.60V nominal; typical operating range 3.0–4.2V/cell
Specific energy (capacity)
200-260Wh/kg; 300Wh/kg predictable
Charge (C-rate)
0.7C, charges to 4.20V (most cells), 3h charge typical, fast charge possible with some cells
Discharge (C-rate)
1C typical; 3.00V cut-off; high discharge rate shortens battery life
Cycle life
500 (related to depth of discharge, temperature)
Thermal runaway
150°C (302°F) typical, High charge promotes thermal runaway
Cost
~$350 per kWh (Source: RWTH, Aachen)
Applications
Medical devices, industrial, electric powertrain (Tesla)
Comments
2019 update:
Shares similarities with Li-cobalt. Serves as Energy Cell.
Mainly used by Panasonic and Tesla; growth potential.
Table 12: Characteristics of Lithium Nickel Cobalt Aluminum Oxide.
Lithium Titanate (Li2TiO3) — LTO
Batteries with lithium titanate anodes have been known since the 1980s. Li-titanate replaces the graphite in the anode of a typical lithium-ion battery and the material forms into a spinel structure. The cathode can be lithium manganese oxide or NMC. Li-titanate has a nominal cell voltage of 2.40V, can be fast charged and delivers a high discharge current of 10C, or 10 times the rated capacity. The cycle count is said to be higher than that of a regular Li-ion. Li-titanate is safe, has excellent low-temperature discharge characteristics and obtains a capacity of 80 percent at –30°C (–22°F).
LTO (commonly Li4Ti5O12) has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation and no lithium plating when fast charging and charging at low temperature. Thermal stability under high temperature is also better than other Li-ion systems; however, the battery is expensive. At only 65Wh/kg, the specific energy is low, rivalling that of NiCd. Li-titanate charges to 2.80V/cell, and the end of discharge is 1.80V/cell. Figure 13 illustrates the characteristics of the Li-titanate battery. Typical uses are electric powertrains, UPS and solar-powered street lighting.
Figure 13: Snapshot of Li-titanate.
Li-titanate excels in safety, low-temperature performance and life span. Efforts are being made to improve the specific energy and lower cost. Source: Boston Consulting Group
Summary Table
Lithium Titanate: Cathode can be lithium manganese oxide or NMC; Li2TiO3 (titanate) anode
Short form: LTO or Li-titanate Commercially available since about 2008.
Voltages
2.40V nominal; typical operating range 1.8–2.85V/cell
Specific energy (capacity)
50–80Wh/kg
Charge (C-rate)
1C typical; 5C maximum, charges to 2.85V
Discharge (C-rate)
10C possible, 30C 5s pulse; 1.80V cut-off on LCO/LTO
Cycle life
3,000–7,000
Thermal runaway
One of safest Li-ion batteries
Cost
~$1,005 per kWh (Source: RWTH, Aachen)
Applications
UPS, electric powertrain (Mitsubishi i-MiEV, Honda Fit EV),
solar-powered street lighting
Comments
2019 update:
Long life, fast charge, wide temperature range but low specific energy and expensive. Among safest Li-ion batteries.
Ability to ultra-fast charge; high cost limits to special application.
Solid-state Li-ion: High specific energy but poor loading and safety.
Lithium-sulfur: High specific energy but poor cycle life and poor loading
Lithium-air: High specific energy but poor loading, needs clean air to breath and has short life.
Figure 15 compares the specific energy of lead-, nickel- and lithium-based systems. While Li-aluminum (NCA) is the clear winner by storing more capacity than other systems, this only applies to specific energy. In terms of specific power and thermal stability, Li-manganese (LMO) and Li-phosphate (LFP) are superior. Li-titanate (LTO) may have low capacity but this chemistry outlives most other batteries in terms of life span and also has the best cold temperature performance. Moving towards the electric powertrain, safety and cycle life will gain dominance over capacity. (LCO stands for Li-cobalt, the original Li-ion.)
Figure 15: Typical specific energy of lead-, nickel- and lithium-based batteries.
NCA enjoys the highest specific energy; however, manganese and phosphate are superior in terms of specific power and thermal stability. Li-titanate has the best life span. Courtesy of Cadex
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Observe how the charge and discharge rates are scaled and why it matters.
Charge and discharge rates of a battery are governed by C-rates. The capacity of a battery is commonly rated at 1C, meaning that a fully charged battery rated at 1Ah should provide 1A for one hour. The same battery discharging at 0.5C should provide 500mA for two hours, and at 2C it delivers 2A for 30 minutes. Losses at fast discharges reduce the discharge time and these losses also affect charge times.
A C-rate of 1C is also known as a one-hour discharge; 0.5C or C/2 is a two-hour discharge and 0.2C or C/5 is a 5-hour discharge. Some high-performance batteries can be charged and discharged above 1C with moderate stress. Table 1 illustrates typical times at various C-rates.
C-rate
Time
Table 1: C-rate and service times when charging and discharging batteries of 1Ah (1,000mAh)
5C
12 min
2C
30 min
1C
1h
0.5C or C/2
2h
0.2C or C/5
5h
0.1C or C/10
10h
0.05C or C/20
20h
The battery capacity, or the amount of energy a battery can hold, can be measured with a battery analyzer. The analyzer discharges the battery at a calibrated current while measuring the time until the end-of-discharge voltage is reached. For lead acid, the end-of-discharge is typically 1.75V/cell, for NiCd/NiMH 1.0V/cell and for Li-ion 3.0V/cell. If a 1Ah battery provides 1A for one hour, an analyzer displaying the results in percentage of the nominal rating will show 100 percent. If the discharge lasts 30 minutes before reaching the end-of-discharge cut-off voltage, then the battery has a capacity of 50 percent. A new battery is sometimes overrated and can produce more than 100 percent capacity; others are underrated and never reach 100 percent, even after priming.
When discharging a battery with a battery analyzer capable of applying different C rates, a higher C rate will produce a lower capacity reading and vice versa. By discharging the 1Ah battery at the faster 2C-rate, or 2A, the battery should ideally deliver the full capacity in 30 minutes. The sum should be the same since the identical amount of energy is dispensed over a shorter time. In reality, internal losses turn some of the energy into heat and lower the resulting capacity to about 95 percent or less. Discharging the same battery at 0.5C, or 500mA over 2 hours, will likely increase the capacity to above 100 percent.
To obtain a reasonably good capacity reading, manufacturers commonly rate alkaline and lead acid batteries at a very low 0.05C, or a 20-hour discharge. Even at this slow discharge rate, lead acid seldom attains a 100 percent capacity as the batteries are overrated. Manufacturers provide capacity offsets to adjust for the discrepancies if discharged at a higher C rate than specified. Figure 2 illustrates the discharge times of a lead acid battery at various loads expressed in C-rate.
Figure 2: Typical discharge curves of lead acid as a function of C-rate.
Smaller batteries are rated at a 1C discharge rate. Due to sluggish behavior, lead acid is rated at 0.2C (5h) and 0.05C (20h).
While lead- and nickel-based batteries can be discharged at a high rate, the protection circuit prevents the Li-ion Energy Cell from discharging above 1C. The Power Cell with nickel, manganese and/or phosphate active material can tolerate discharge rates of up to 10C and the current threshold is set higher accordingly.
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Learn the key feature of each Li-ion in a summary table.
The term lithium-ion points to a family of batteries that shares similarities, but the chemistries can vary greatly. Li-cobalt, Li-manganese, NMC and Li-aluminum are similar in that they deliver high capacity and are used in portable applications. Li-phosphate and Li-titanate have lower voltages and have less capacity, but are very durable. These batteries are mainly found in wheeled and stationary uses. Table 1 summarizes the characteristics of major Li-ion batteries.
Chemistry
Lithium Cobalt Oxide
Lithium Manganese Oxide
Lithium Nickel Manganese Oxide
Lithium Iron Phosphate
Lithium Nickel Cobalt Aluminum Oxide
Lithium Titanate Oxide
Short form
Li-cobalt
Li-manganese
NMC
Li-phosphate
Li-aluminum
Li-titanate
Abbreviation
LiCoO2
(LCO)
LiMn2O4
(LMO)
LiNiMnCoO2 (NMC)
LiFePO4
(LFP)
LiNiCoAlO2 (NCA)
Li2TiO3 (common)
(LTO)
Nominal voltage
3.60V
3.70V (3.80V)
3.60V (3.70V)
3.20, 3.30V
3.60V
2.40V
Full charge
4.20V
4.20V
4.20V (or higher)
3.65V
4.20V
2.85V
Full discharge
3.00V
3.00V
3.00V
2.50V
3.00V
1.80V
Minimal voltage
2.50V
2.50V
2.50V
2.00V
2.50V
1.50V (est.)
Specific Energy
150–200Wh/kg
100–150Wh/kg
150–220Wh/kg
90–120Wh/kg
200-260Wh/kg
70–80Wh/kg
Charge rate
0.7–1C (3h)
0.7–1C (3h)
0.7–1C (3h)
1C (3h)
1C
1C (5C max)
Discharge rate
1C (1h)
1C, 10C possible
1–2C
1C (25C pule)
1C
10C possible
Cycle life (ideal)
500–1000
300–700
1000–2000
1000–2000
500
3,000–7,000
Thermal runaway
150°C (higher when empty)
250°C (higher when empty)
210°C(higher when empty)
270°C (safe at full charge)
150°C (higher when empty)
One of safest
Li-ion batteries
Maintenance
Keep cool; store partially charged; prevent full charge cycles, use moderate charge and discharge currents
Packaging (typical)
18650, prismatic and pouch cell
prismatic
18650, prismatic and pouch cell
26650, prismatic
18650
prismatic
History
1991 (Sony)
1996
2008
1996
1999
2008
Applications
Mobile phones, tablets, laptops, cameras
Power tools, medical devices, powertrains
E-bikes, medical devices, EVs, industrial
Stationary with high currents and endurance
Medical, industrial,
EV (Tesla)
UPS, EV, solar street lighting
Comments
High energy, limited power. Market share has stabilized.
High power, less capacity; safer than Li-cobalt; often mixed with NMC to improve performance.
High capacity and high power. Market share is increasing. Also NCM, CMN, MNC, MCN
Flat discharge voltage, high power low capacity, very safe; elevated self-discharge.
Highest capacity with moderate power. Similar to Li-cobalt.
Long life, fast charge, wide temperature range and safe. Low capacity, expensive.
Table 1: Summary of most common lithium-ion based batteries.
https://himaxelectronics.com/wp-content/uploads/2021/05/Summary-Table-of-Lithium-based-Batteries.jpg400800administrator/wp-content/uploads/2019/05/Himax-home-page-design-logo-z.pngadministrator2021-05-21 10:45:322024-04-29 01:35:34Summary Table of Lithium-based Batteries
Learn how to arrange batteries to increase voltage or gain higher capacity.
Batteries achieve the desired operating voltage by connecting several cells in series; each cell adds its voltage potential to derive at the total terminal voltage. Parallel connection attains higher capacity by adding up the total ampere-hour (Ah).
Some packs may consist of a combination of series and parallel connections. Laptop batteries commonly have four 3.6V Li-ion cells in series to achieve a nominal voltage 14.4V and two in parallel to boost the capacity from 2,400mAh to 4,800mAh. Such a configuration is called 4s2p, meaning four cells in series and two in parallel. Insulating foil between the cells prevents the conductive metallic skin from causing an electrical short.
Most battery chemistries lend themselves to series and parallel connection. It is important to use the same battery type with equal voltage and capacity (Ah) and never to mix different makes and sizes. A weaker cell would cause an imbalance. This is especially critical in a series configuration because a battery is only as strong as the weakest link in the chain. An analogy is a chain in which the links represent the cells of a battery connected in series (Figure 1).
Figure 1: Comparing a battery with a chain.
Chain links represent cells in series to increase voltage, doubling a link denotes parallel connection to boost current loading.
A weak cell may not fail immediately but will get exhausted more quickly than the strong ones when on a load. On charge, the low cell fills up before the strong ones because there is less to fill and it remains in over-charge longer than the others. On discharge, the weak cell empties first and gets hammered by the stronger brothers. Cells in multi-packs must be matched, especially when used under heavy loads. (See BU-803a: Cell Mismatch, Balancing).
Single Cell Applications
The single-cell configuration is the simplest battery pack; the cell does not need matching and the protection circuit on a small Li-ion cell can be kept simple. Typical examples are mobile phones and tablets with one 3.60V Li-ion cell. Other uses of a single cell are wall clocks, which typically use a 1.5V alkaline cell, wristwatches and memory backup, most of which are very low power applications.
The nominal cell voltage for a nickel-based battery is 1.2V, alkaline is 1.5V; silver-oxide is 1.6V and lead acid is 2.0V. Primary lithium batteries range between 3.0V and 3.9V. Li-ion is 3.6V; Li-phosphate is 3.2V and Li-titanate is 2.4V.
Li-manganese and other lithium-based systems often use cell voltages of 3.7V and higher. This has less to do with chemistry than promoting a higher watt-hour (Wh), which is made possible with a higher voltage. The argument goes that a low internal cell resistance keeps the voltage high under load. For operational purposes these cells go as 3.6V candidates. (See BU-303 Confusion with Voltages)
Series Connection
Portable equipment needing higher voltages use battery packs with two or more cells connected in series. Figure 2 shows a battery pack with four 3.6V Li-ion cells in series, also known as 4S, to produce 14.4V nominal. In comparison, a six-cell lead acid string with 2V/cell will generate 12V, and four alkaline with 1.5V/cell will give 6V.
Figure 2: Series connection of four cells (4s).
Adding cells in a string increases the voltage; the capacity remains the same.
Courtesy of Cadex
If you need an odd voltage of, say, 9.50 volts, connect five lead acid, eight NiMH or NiCd, or three Li-ion in series. The end battery voltage does not need to be exact as long as it is higher than what the device specifies. A 12V supply might work in lieu of 9.50V. Most battery-operated devices can tolerate some over-voltage; the end-of-discharge voltage must be respected, however.
High voltage batteries keep the conductor size small. Cordless power tools run on 12V and 18V batteries; high-end models use 24V and 36V. Most e-bikes come with 36V Li-ion, some are 48V. The car industry wanted to increase the starter battery from 12V (14V) to 36V, better known as 42V, by placing 18 lead acid cells in series. Logistics of changing the electrical components and arcing problems on mechanical switches derailed the move.
Some mild hybrid cars run on 48V Li-ion and use DC-DC conversion to 12V for the electrical system. Starting the engine is often done by a separate 12V lead acid battery. Early hybrid cars ran on a 148V battery; electric vehicles are typically 450–500V. Such a battery needs more than 100 Li-ion cells connected in series.
High-voltage batteries require careful cell matching, especially when drawing heavy loads or when operating at cold temperatures. With multiple cells connected in a string, the possibility of one cell failing is real and this would cause a failure. To prevent this from happening, a solid state switch in some large packs bypasses the failing cell to allow continued current flow, albeit at a lower string voltage.
Cell matching is a challenge when replacing a faulty cell in an aging pack. A new cell has a higher capacity than the others, causing an imbalance. Welded construction adds to the complexity of the repair, and this is why battery packs are commonly replaced as a unit.
High-voltage batteries in electric vehicles, in which a full replacement would be prohibitive, divide the pack into modules, each consisting of a specific number of cells. If one cell fails, only the affected module is replaced. A slight imbalance might occur if the new module is fitted with new cells. (See BU-910: How to Repair a Battery Pack.)
Figure 3 illustrates a battery pack in which “cell 3” produces only 2.8V instead of the full nominal 3.6V. With depressed operating voltage, this battery reaches the end-of-discharge point sooner than a normal pack. The voltage collapses and the device turns off with a “Low Battery” message.
Figure 3: Series connection with a faulty cell.
Faulty cell 3 lowers the voltage and cuts the equipment off prematurely.
Courtesy of Cadex
Batteries in drones and remote controls for hobbyist requiring high load current often exhibit an unexpected voltage drop if one cell in a string is weak. Drawing maximum current stresses frail cells, leading to a possible crash. Reading the voltage after a charge does not identify this anomaly; examining the cell-balance or checking the capacity with a battery analyzer will.
Tapping into a Series String
There is a common practice to tap into the series string of a lead acid array to obtain a lower voltage. Heavy duty equipment running on a 24V battery bank may need a 12V supply for an auxiliary operation and this voltage is conveniently available at the half-way point.
Tapping is not recommended because it creates a cell imbalance as one side of the battery bank is loaded more than the other. Unless the disparity can be corrected by a special charger, the side effect is a shorter battery life. Here is why:
When charging an imbalanced lead acid battery bank with a regular charger, the undercharged section tends to develop sulfation as the cells never receive a full charge. The high voltage section of the battery that does not receive the extra load tends to get overcharged and this leads to corrosion and loss of water due to gassing. Please note that the charger charging the entire string looks at the average voltage and terminates the charge accordingly.
Tapping is also common on Li-ion and nickel-based batteries and the results are similar to lead acid: reduced cycle life. (See BU-803a: Cell Matching and Balancing.) Newer devices use a DC-DC converter to deliver the correct voltage. Electric and hybrid vehicles, alternatively, use a separate low-voltage battery for the auxiliary system.
Parallel Connection
If higher currents are needed and larger cells are not available or do not fit the design constraint, one or more cells can be connected in parallel. Most battery chemistries allow parallel configurations with little side effect. Figure 4 illustrates four cells connected in parallel in a P4 arrangement. The nominal voltage of the illustrated pack remains at 3.60V, but the capacity (Ah) and runtime are increased fourfold.
Figure 4: Parallel connection of four cells (4p).
With parallel cells, capacity in Ah and runtime increases while the voltage stays the same.
Courtesy of Cadex
A cell that develops high resistance or opens is less critical in a parallel circuit than in a series configuration, but a failing cell will reduce the total load capability. It’s like an engine only firing on three cylinders instead of on all four. An electrical short, on the other hand, is more serious as the faulty cell drains energy from the other cells, causing a fire hazard. Most so-called electrical shorts are mild and manifest themselves as elevated self-discharge.
A total short can occur through reverse polarization or dendrite growth. Large packs often include a fuse that disconnects the failing cell from the parallel circuit if it were to short. Figure 5 illustrates a parallel configuration with one faulty cell.
Figure 5: Parallel/connection with one faulty cell.
A weak cell will not affect the voltage but provide a low runtime due to reduced capacity. A shorted cell could cause excessive heat and become a fire hazard. On larger packs a fuse prevents high current by isolating the cell.
Courtesy of Cadex
Series/parallel Connection
The series/parallel configuration shown in Figure 6 enables design flexibility and achieves the desired voltage and current ratings with a standard cell size. The total power is the sum of voltage times current; a 3.6V (nominal) cell multiplied by 3,400mAh produces 12.24Wh. Four 18650 Energy Cells of 3,400mAh each can be connected in series and parallel as shown to get 7.2V nominal and a total of 48.96Wh. A combination with 8 cells would produce 97.92Wh, the allowable limit for carry on an aircraft or shipped without Class 9 hazardous material. (See BU-704a: Shipping Lithium-based Batteries by Air) The slim cell allows flexible pack design but a protection circuit is needed.
Figure 6: Series/ parallel connection of four cells (2s2p).
This configuration provides maximum design flexibility. Paralleling the cells helps in voltage management.
Courtesy of Cadex
Li-ion lends itself well to series/parallel configurations but the cells need monitoring to stay within voltage and current limits. Integrated circuits (ICs) for various cell combinations are available to supervise up to 13 Li-ion cells. Larger packs need custom circuits, and this applies to e-bike batteries, hybrid cars and the Tesla Model 85 that devours over 7000 18650 cells to make up the 90kWh pack.
Terminology to describe Series and Parallel Connection
The battery industry specifies the number of cells in series first, followed by the cells placed in parallel. An example is 2s2p. With Li-ion, the parallel strings are always made first; the completed parallel units are then placed in series. Li-ion is a voltage based system that lends itself well for parallel formation. Combining several cells into a parallel and then adding the units serially reduces complexity in terms of voltages control for pack protection.
Building series strings first and then placing them in in parallel may be more common with NiCd packs to satisfy the chemical shuttle mechanism that balances charge at the top of charge. “2s2p” is common; white papers have been issued that refer to 2p2s when a serial string is paralleled.
Safety devices in Series and Parallel Connection
Positive Temperature Coefficient Switches (PTC) and Charge Interrupt Devices (CID) protect the battery from overcurrent and excessive pressure. While recommended for safety in a smaller 2- or 3-cell pack with serial and parallel configuration, these protection devices are often being omitted in larger multi-cell batteries, such as those for power tool.
The PTC and CID work as expected to switch of the cell on excessive current and internal cell pressure; however the shutdown occurs in cascade format. While some cells may go offline early, the load current causes excess current on the remaining cells. Such overload condition could lead to a thermal runaway before the remaining safety devices activate.
Some cells have built-in PCT and CID; these protection devices can also be added retroactively. The design engineer must be aware than any safety device is subject to failure. In addition, the PTC induces a small internal resistance that reduces the load current. (See also BU-304b: Making Lithium-ion Safe)
Simple Guidelines for Using Household Primary Batteries
Keep the battery contacts clean. A four-cell configuration has eight contacts and each contact adds resistance (cell to holder and holder to next cell).
Never mix batteries; replace all cells when weak. The overall performance is only as good as the weakest link in the chain.
Observe polarity. A reversed cell subtracts rather than adds to the cell voltage.
Remove batteries from the equipment when no longer in use to prevent leakage and corrosion. This is especially important with zinc-carbon primary cells.
Do not store loose cells in a metal box. Place individual cells in small plastic bags to prevent an electrical short. Do not carry loose cells in your pockets.
Keep batteries away from small children. In addition to being a choking hazard, the current-flow of the battery can ulcerate the stomach wall if swallowed. The battery can also rupture and cause poisoning. (See BU-703: Health Concerns with Batteries.)
Do not recharge non-rechargeable batteries; hydrogen buildup can lead to an explosion. Perform experimental charging only under supervision.
Simple Guidelines for Using Secondary Batteries
Observe polarity when charging a secondary cell. Reversed polarity can cause an electrical short, leading to a hazardous condition.
Remove fully charged batteries from the charger. A consumer charger may not apply the correct trickle charge when fully charged and the cell can overheat.
Charge only at room temperature.
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Discover familiar battery formats, some of which going back to the late 1800s.
Early batteries of the 1700s and 1800s developed in Europe were mostly encased in glass jars. As batteries grew in size, jars shifted to sealed wooden containers and composite materials. In the 1890s, battery manufacturing spread from Europe to the United States and in 1896 the National Carbon Company successfully produced a standard cell for widespread consumer use. It was the zinc-carbon Columbia Dry Cell Battery producing 1.5 volts and measuring 6 inches in length.
With the move to portability, sealed cylindrical cells emerged that led to standards sizes. The International Electrochemical Commission (IEC), a non-governmental standards organization founded in 1906, developed standards for most rechargeable batteries. In around 1917, the National Institute of Standards and Technology formalized the alphabet nomenclature that is still used today. Table 1 summarizes these historic and current battery sizes.
Size
Dimensions
History
F cell
33 x 91 mm
Introduced in 1896 for lanterns; later used for radios; only available in nickel-cadmium today.
E cell
N/A
Introduced ca. 1905 to power box lanterns and hobby applications. Discontinued ca. 1980.
D cell
34.2 x 61.5mm
Introduced in 1898 for flashlights and radios; still current.
C cell
25.5 x 50mm
Introduced ca. 1900 to attain smaller form factor.
Sub-C
22.2 x 42.9mm
16.1mL
Cordless tool battery. Other sizes are ½, 4/5 and 5/4 sub-C lengths. Mostly NiCd.
B cell
20.1 x 56.8mm
Introduced in 1900 for portable lighting, including bicycle lights in Europe; discontinued in in North America in 2001.
A cell
17 x 50mm
Available in NiCd, NiMH and primary lithium; also in 2/3 and 4/5 sizes. Popular in older laptops and hobby applications.
AA cell
14.5 x 50mm
Introduced in 1907 as penlight battery for pocket lights and spy tool in WWI; added to ANSI standard in 1947.
AAA cell
10.5 x 44.5mm
Developed in 1954 to reduce size for Kodak and Polaroid cameras. Added to ANSI standard in 1959.
AAAA cell
8.3 x 42.5mm
Offshoot of 9V, since 1990s; used for laser pointers, LED penlights, computer styli, headphone amplifiers.
4.5V battery
67 x 62
x 22mm
Three cells form a flat pack; short terminal strip is positive, long strip is negative; common in Europe, Russia.
9V battery
48.5 x 26.5
x 17.5mm
Introduced in 1956 for transistor radios; contains six prismatic or AAAA cells. Added to ANSI standard in 1959.
18650
18 x 65mm
16.5mL
Developed in the mid-1990s for lithium-ion; commonly used in laptops, e-bikes, including Tesla EV cars.
26650
26 x 65mm
34.5mL
Larger Li-ion. Some measure 26x70mm sold as 26700. Common chemistry is LiFeO4 for UPS, hobby, automotive.
14500
14x 50mm
Li-ion, similar size to AA. (Observe voltage incompatibility: NiCd/NiMH = 1.2V, alkaline = 1.5V, Li-ion = 3.6V)
21700*
21 x 70mm
New (2016), used for the Tesla Model 3 and other applications, made by Panasonic, Samsung, Molicel, etc.
32650
32 x 65mm
Primarily in LiFePO4 (Lithium Iron Phosphate)
Table 1: Common old and new battery norms. * The 21700 cell is also known as 2170. IEC norm calls for the second zero at the end to denote cylindrical format.
Standardization included primary cells, mostly in zinc-carbon; alkaline emerged only in the early 1960s. With the growing popularity of the sealed nickel-cadmium in the 1950s and 1960s, new sizes appeared, many of which were derived from the “A” and “C” sizes. Beginning in the 1990s, makers of Li-ion departed from conventional sizes and invented their own standards.
A successful standard is the 18650 cylindrical cell. Developed in the early 1990s for lithium-ion, these cells are used in laptops, electric bicycles and even electric vehicles (Tesla). The first two digits of 18650 designate the diameter in millimeters; the next three digits are the length in tenths of millimeters. The 18650 cell is 18mm in diameter and 65.0mm in length.
Other sizes are identified with a similar numbering scheme. For example, a prismatic cell carries the number 564656P. It is 5.6mm thick, 46mm wide and 56mm long. P stands for prismatic. Because of the large variety of chemistries and their diversity within, battery cells do not show the chemistry.
Few popular new standards have immerged since the 18650 appeared in ca. 1991. Several battery manufacturers started experimenting using slightly larger diameters with sizes of 20x70mm, 21x70mm and 22x70mm. Panasonic and Tesla decided on the 21×70, so has Samsung, and other manufacturers followed. The “2170” is only slightly larger than the 18650 it but has 35% more energy (by volume). This new cell is used in the Tesla Model 3 while Samsung is looking at new applications in laptops, power tools, e-bikes and more. It is said that the best diameters in terms of manufacturability is between 18mm and 26mm and the 2170 sits in between. (The 2170 is also known as the 21700.) The 26650 introduced earlier never became a best-seller.
The 32650 is primarily available in LiFePO4 (Lithium Iron Phosphate) with a nominal voltage of 3.2V/cell and a typical capacity of 5,000mAh. The dimensions are 32x65mm; true sizes may be slightly larger to allow for insulation and labels.
On the prismatic and pouch cell front, new cells are being developed for the electric vehicle (EV) and energy storage systems (ESS). Some of these formats may one day also become readily available similar to the 18650, made in high energy and high power versions, sourced by several manufacturers and sold at a competitive prices. Prismatic and pouch cells currently carry a higher price tag per Wh than the 18650.
The EV and ESS markets advance with two distinct philosophies: The use of a large number of small cells produced by an automated process as low cost, as done by Tesla, versus larger cells in the prismatic and pouch formats at a higher price per Wh for now, as done by other EV manufacturers. We have not seen clear winners of either format; time will tell.
Looking at the batteries in mobile phones and laptops, one sees a departure from established standards. This is due in part to the manufacturers’ inability to agree on a standard, meaning that most consumer devices come with custom-made cells or battery packs. Compact design and market demand are swaying manufacturers to go their own way. High volume with planned obsolescence allows the production of unique sizes in consumer products.
In the early days, a battery was perceived “big” by nature, and this is reflected in the sizing convention. While the “F” nomenclature may have been seen as mid-sized in the late 1800s, our forefathers did not anticipate that a battery resembling a credit card could power computers, phones and cameras. Running out of letters towards the smaller sizes led to the awkward numbering of AA, AAA and AAAA.
Since the introduction of the 9V battery in 1956, no new formats have emerged. Meanwhile portable devices lowered the operating voltages to between 3V and 5V. Switching six cells (6S) in series to attain 9V is expensive to manufacture, and a 3.6V alternative would serve better. This imaginary new pack would have a coding system to prevent charging primaries and select the correct charge algorithm for secondary chemistries.
Starter batteries for vehicles also follow battery norms that are based on the North American BCI, the European DIN and the Japanese JIS standards. These batteries are similar in footprint to allow swapping. Deep-cycle and stationary batteries follow no standardized norms and the replacement packs must be sourced from the original maker. The attempt to standardize electric vehicle batteries may not work and might follow the failed attempt to standardize laptop batteries in the 1990s.
Future Cell Formats
Standardization for Li-ion cell formats is diverse, especially for the electric vehicle. Research teams, including Fraunhofer,* examine and evaluate various formats and the most promising cell types until 2025 will be the pouch and the 21700 cylindrical formats. Looking further, experts predict the large-size prismatic Li-ion cell to domineer in the EV battery market. Meanwhile, Samsung and others bet on the prismatic cell, LG gravitates towards the pouch format and Panasonic is most comfortable with the 18650 and 21700 cylindrical cells.
Large battery systems for ESS, UPS, marine vessels and traction use mostly large format pouch cells stacked with light pressure to prolong longevity and prevent delamination. Thermal management is often done by plates drawing the heat between layers to the outside and liquid cooling.
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The most common drone safety issues, next to pilot error are related to battery failures. If you’ve ever experienced battery failure during charging, storage, or operation, then you understand how alarming and potentially dangerous it can be.
Over 200 injuries related to drone battery incidents were reported to the U.S. Consumer Product Safety Commission between 2012 and 2017. The reported incidents involved fire, smoke, and even explosions. It’s likely that countless other incidents went unreported because they didn’t end in an emergency room visit.
In order to ensure battery safety, it’s critical as a commercial drone operator to purchase your batteries and battery management systems from a reputable, safety-minded provider.
Why Do Drone Batteries Fail?
While some drone battery failures occur for reasons that no one could predict or discover, most incidents could have been avoided with proper care and maintenance of your battery fleet. To reduce your potential risk drone users should be well-versed in battery safety practices.
Manufacturers are also responsible for the safety of each battery. In order to provide reliable performance and increased safety, reputable battery manufacturers employ high-quality materials and precise manufacturing and quality control processes. When manufacturers cut corners, they reduce overall battery safety. Quality costs money, so when a battery price seems too good to be true, it probably is.
Choosing Batteries for Drone Safety
Know the Manufacturer
Reputable manufacturers are transparent and provide plenty of information about their company and practices. Research the quality of materials and designs used to manufacture their drone batteries. If you’re considering a discounted battery purchase but can’t find much information about the company that makes it, it’s best to reconsider. Make sure that your supplier is located within the United States, if you need support or have a question, you want to have an English speaking support staff to answer your call.
Focus on Safety Features
In the interests of the bottom line, some manufacturers strip away “expendable” safety features to create budget batteries. You might be tempted by those batteries when you’re browsing online, but be careful – always review the product description carefully and note the safety features listed. You’ll probably need to visit the manufacturer’s website to find a complete list of features and related details.
Choose the Right Charger
A top-of-the-line drone battery plugged into a low-quality charger will inevitably cause headaches and compromise battery safety. It’s best to choose a “smart” or programmable battery charger. You’re better able to manage your drone batteries when you have important charging data at your disposal. It’s also best to use batteries and chargers produced by the same manufacturer.
Best Practices for Battery Safety
How to Store
It’s recommended that you drain batteries to 40-60 percent of their full capacity before storing them for more than ten days. If you’re planning to store them for fewer than 10 days, drain them to 60-80 percent of their capacity. Partially draining batteries reduces stress on them and extends their working life. Never store your batteries for more than three months without charging them.
It’s best to store batteries in a dry location at room temperature. Before tucking those batteries away, inspect them for a puncture, puffing, or other abnormal physical features that indicate an unhealthy battery.
How to Charge
Most incidents occur while the battery is charging, which is why it’s recommended to charge your drone batteries at a 1C charge rate. To find this rate take the milliamp hour capacity rating of your battery divide it by 1000. For example, a 22,000 millamp battery should be charged at 22amps. Always monitor your batteries during the charging process and only charge your batteries on a non-flammable surface located away from any flammable materials. While battery fires are rare, a damaged battery or incorrect charge settings can cause a battery to swell, expand and worst-case scenario catch fire. Being prepared with a suitable fire extinguisher and ready to react if you see signs of trouble is critical.
How to Operate
How and where you fly your drone can impact its battery life. It’s best to avoid flying in extreme temperatures. Refer to the manufacturer’s instructions for specific information about safe flight temperatures for your drone. The generally accepted rule is to fly within the range of 14 °F to 104 °F for optimal drone safety.
Using an appropriately sized battery for your drone is critical for overall safety. Using a battery that does not provide enough power for your drone will not only adversely affect battery life but can lead to overheating of the pack and thermal runaway, a dangerous process that devours the battery. Thermal runaway is a heat-induced chemical reaction that intensifies and continues to raise internal temperatures until all the reactive agents within the cell are consumed.
How to Transport
Secure your batteries with padding during transport to prevent them from hitting against other batteries or objects. Also, make sure that any exposed leads or connectors are protected from arcing or shorting. Cover with tape or use specifically designed covers to avoid issues.You can purchase cases and backpacks designed specifically for this purpose. If you’re taking them with you on a plane, remember to pack your drone and batteries in your carry-on baggage and review the current FAA rules for batteries. Regulations for transportation of batteries are also subject to the carrier by carrier-specific rules. Always check with your airline before you try and fly with your drone or batteries.
Himax Provides Safe, Custom-Designed Batteries for Commercial Use
Himax values safety above their bottom line, which is why they offer custom-designed batteries that are produced with superior materials and high-tech safety features.
Custom-Designed Lithium-Ion Batteries for OEM Applications
Himax’s custom-designed batteries were created for professional, commercial, and industrial use. Their robust composition will withstand the most rigorous, unmanned applications without compromising on energy density and weight. They offer a wide range of custom battery designs, which ensures that you will receive a product that meets your unique and precise requirements.
Why does custom design matter for drone safety? Himax’s custom-designed batteries accommodate targeted operating temperatures and discharge voltages. When your drone battery is designed with a specific application in mind, it will operate more efficiently and safely in the conditions under which it will actually be used.
Battery Safety Certifications
Himax products are produced with high-quality materials that ensure durability, extend battery life, and prevent battery failure. Himax can assist with manufacturing to meet and exceed any required safety compliance schemes. We have experience with UN38.3, CE, RoHS, and FCC. We have multiple NRT laboratories that can provide testing services.
Safety Features
Himax’s commercial series of batteries provides the most advanced battery management system (BMS) available on the market. These “smart” batteries include an embedded BMS. This active BMS system helps extend battery life, tracks, and stores critical battery information. The system also allows for additional safety features include real-time fault detection, battery lockout protocol, five LED Indicators, and the ability to capture and store KPIs, which include:
Remaining capacity
State of charge
Cell voltage
Pack voltage
Current draw
Cell temperatures
Faults
In addition to careful construction and critical safety features, Himax inspects all products before they leave the factory to ensure each one meets their quality and safety standards.
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You walk into work one morning and find out that a battery system isn’t working. What happens? How much time will you lose trying to fix it? Getting it back online will probably cost money, but how much?
When it comes to battery malfunctions, that’s not even the worst-case scenario. What if damage to the battery system causes equipment damage further downstream or even creates a fire?
You consider eventualities like this whenever you integrate a new piece of machinery or develop a new work process, but have you gone through this process when integrating your battery system?
In this article, we’ll take a look at circuit protection and why it’s so important for industrial batteries. We’ll analyze a few of the different options you have for battery protection systems and how each system can help you to avoid battery damage and dangerous accidents.
Let’s start with the basics:
What Are Battery Protection Systems?
A battery protection system is any device that safeguards against battery malfunctions. Some are only effective against basic issues like overcharge or short circuit, while others provide complex monitoring and balancing for an entire battery system.
What Do They Protect Against?
To really understand why battery protection systems are so important, you need to know what can happen if they’re not in place:
Short Circuits
These occur when a current takes a shortcut. Electricity always wants to go back to the ground as soon as possible, but a correctly functioning circuit keeps it on the proper track. If the wiring in the circuit malfunctions, the current can escape and go back to the ground another way. That way might involve going through your equipment or one of your workers.
Overcharge
When you put too much charge into a rechargeable battery, that extra energy becomes heat. The temperature of the battery can rise beyond safe limits and reduce the battery’s lifespan.
Over Discharge
Draining too much of the charge from a battery can damage it in several ways, including decreasing the capacity of the battery, causing it to require charging more often, and causing a short circuit within the battery. If a lithium-ion battery lacks a protection system, it is highly prone to these and other malfunctions related to over-discharge.
Overcurrent
Too much current within the circuit can result from a number of malfunctions, including short circuits. If there is enough excess current, it can ignite components of the machinery and cause a fire.
Battery protection systems serve to keep the temperature and voltage balanced in your battery. Steady temperatures are critical for optimal battery life, which increases the safety of your operations and reduces your material costs.
An effective battery protection system will measure the current and temperature in your battery and adjust the circuit to provide protection if levels become unsafe. The process typically involves a thermistor, a ceramic-type semiconductor that decreases in resistance when the temperature of the battery rises. When this happens, it indicates the need for control and simultaneously acts as a battery “first aid.”
Thermistors work in conjunction with other safety mechanisms. Together, these systems provide the current and temperature control that a battery needs to stay operational. Let’s take a look at some of the most effective options:
Polymeric Positive Temperature Coefficients
The polymeric positive temperature coefficient, or PPTC, helps to balance the circuit against excess energy. Just like a standard fuse, it opens to create high resistance when there is too much current in the system. When the current decreases back to normal levels, it resets.
Unlike some types of fuses, the PPTC resets itself so that you can still use the battery after the overcurrent is corrected. It simply serves to keep the battery functional until electricity resets back to normal levels.
PPTCs are most commonly used for nickel batteries. They’re affordable, easy to install, and are compatible with most systems.
Protection Circuit Modules
Protection circuit modules, or PCMs, protect against overcharge, over-discharge, and excessively fast discharge, all of which can cause an excess of current. In lithium batteries, the PCM usually protects against these situations using a metal-oxide-semiconductor field-effect transistor, or MOSFET.
The MOSFET alters the circuit’s conduction by switching cells on if the voltage falls too quickly or off if the voltage rises to unsafe levels. It keeps the battery running while helping to avoid damage, preserving battery life in the short and long term.
Battery Management Systems
A battery management system, or BMS, is necessary when you need more precise control over multiple batteries. They provide all of the standard protection involved with simpler systems while monitoring individual cells and the system as a whole.
A BMS can do any of the following:
Preserve the life of the battery and keep it safe to use
Report the state of the battery’s charge and capacity
Indicate when the battery is in need of replacement
Warn the user when the battery needs repair or when the voltage flow is too high
The most important difference between a BMS and a simpler battery protection system is the ability of the BMS to monitor each cell as well as the full system.
Individual cell monitoring is critical for battery health because systemwide malfunctions often show themselves at the individual cell level first. By monitoring the voltage in each cell and alerting the user to voltage overages or drops, a BMS can prompt repair of issues such as corrosion or dry-out before they do extensive damage.
In addition to monitoring, a BMS provides safety protection during key processes, including charging and discharging and disconnects the battery in case of failure or safety hazard. It integrates completely with the machine’s software system, allowing the user to get battery alerts as readily as texts or emails.
The Takeaway
Battery protection systems ensure the correct flow of voltage through your batteries, protecting your machinery as well as the health and safety of your personnel.
At Himax, we understand that battery protection is an essential safety function. We offer a variety of products to meet the needs of our industrial clients, and we take pride in our ability to help you select the right product for your business.
If you’re in need of a custom battery or battery charger, contact us today to get started.
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As technology advances, portable energy solutions are becoming more available and more sophisticated. Highly specialized technologies call for highly specialized batteries.
Custom OEM batteries can help your business operate more efficiently and increase your profits. Himax has many years of experience in designing batteries for Lead-acid replacement, as well as in other industrial and commercial industries. Our custom battery solutions have the power to fulfill your mission-critical requirements and advance your company’s reputation.
How Custom OEM Batteries Benefit Your Brand
Precision Safety
High-quality custom batteries are specifically designed with your product’s application in mind. For instance, your product might be designed for operation in harsh, dirty, or dangerous conditions, in which case you need custom OEM batteries that can operate in rigorous environments for long periods of time.
Whether it’s strong winds, high altitudes, varying humidity levels, extreme temperatures, or other challenging environmental conditions, you need a custom battery that will power through without failure or malfunction. An experienced company will design and develop custom batteries to suit your product and application while implementing safety features that protect your investment and your reputation.
Optimal Performance
When you use high-quality, custom OEM batteries, you enhance your product’s performance. Precisely engineered batteries not only minimize safety hazards to people and investments, but they also reduce wasted energy. This increased energy efficiency optimizes your product’s potential, which positions you ahead of the competition.
Additionally, custom OEM batteries for drones and other high-tech applications can be used as primary power sources or as backup sources for protection in the case of a combustion engine failure or other critical issues. Many custom OEM batteries can also be used in hybrid fuel or battery systems, enhancing performance while providing flexibility.
Increased Endurance
The increased energy efficiency provided by custom OEM batteries also increases your product’s endurance. Drone batteries and other technical-use batteries have come a very long way in terms of longevity, but nothing improves endurance like a custom battery solution. When your product goes farther and lasts longer than the competition’s, it increases your brand’s credibility. That translates to boosted sales.
Targeted Testing
High-quality, custom OEM batteries undergo rigorous, application-specific testing to guarantee their performance, durability, and strength when used in your product. You’ll want to know how your custom commercial or industrial battery performs while engaged in various applications and under specific conditions.
Reputable and experienced companies ensure functionality by performing both routine and additional mechanical testing for custom battery designs. Routine tests include component inspection, in-process inspection, and final testing on the completed product. Additional tests should be performed according to your application’s requirements. Reputable companies maintain complete testing data records that can be supplied upon request.
Direct Support & Transparency
Look for a portable energy solutions company that will provide direct and continual support for your custom OEM batteries. They should be well-staffed, with after-sales support to ensure that you always receive the answers you need, when you need them.
For your custom OEM battery needs, you’ll want to partner with a company that has access to an extensive, highly vetted network with a strong global presence. Experienced and reputable companies are forthcoming about their supply chains and professional network, so be sure you ask the right questions.
Additionally, any company you partner with should be transparent concerning their security protocols, especially regarding their supply chains in Asian markets. Find out how they intend to keep your sensitive IP projects secure.
Himax Delivers Safe and Professional Custom Battery Solutions
At Himax, we value innovation and integrity. We partner with you to generate, design and implement custom battery solutions and custom charging solutions for your critical operations.
For over 15 years we’ve supplied the energy, aerospace, and automation industries with high-quality, reliable, custom OEM batteries. We’ll work closely with your design team to ensure timely delivery. We’re here to provide support throughout the process and after the sale.
If you’d like to learn more about how our custom OEM batteries can benefit your product or company, please contact us today.
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The energy density of batteries can be displayed in two different ways: gravimetric energy density and volumetric energy density.
The gravimetric energy density is the measure of how much energy a battery contains in proportion to its weight. This measurement is typically presented in Watt-hours per kilogram (W-hr / kg). The volumetric energy density, on the other hand, is compared to its volume and is usually expressed in watt-hours per liter (W-hr / L). Generally, we refer to battery energy density as gravimetric ( weight ) energy density, and watt-hour is a measure of electrical energy, equivalent to one hour, one watt of consumption.
In contrast, the power density of a battery is a measure of how fast energy can be delivered, not how much stored energy is available. Energy density is often confused with power density, so it is important to understand the difference between the two.
Calculation formula
The energy density of a battery can be simply calculated using this formula: Nominal Battery Voltage (V) x Rated Battery Capacity (Ah) / Battery Weight (kg) = Specific Energy or Energy Density (Wh / kg).
LiCo and LiFePO4 Batteries’ energy density
Generally speaking, LiCo batteries have an energy density of 150-270 Wh/kg. Their cathode is made up of cobalt oxide and the typical carbon anode with a layered structure that moves lithium-ions from anode to the cathode and back. This battery is popular for its high energy density, and it’s typically used in consumer products such as cell phones and laptops.
LiFe batteries, on the other hand, have an energy density of 100-120 Wh/kg. Although this is lower than LiCo batteries, it is still considered higher in the rechargeable battery category. LiFe batteries use iron phosphate for the cathode and a graphite electrode combined with a metallic backing for the anode. They are ideal for heavy equipment and industrial applications because of their better ability to withstand high and low temperatures.
Conclusion
As far as the single-cell is concerned, the positive and negative materials and production process of the battery will affect the energy density, so it is necessary to develop more reasonable materials and better manufacturing technology to obtain a more efficient battery.
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The most common drone safety issues, next to pilot error are related to battery failures. If you’ve ever experienced battery failure during charging, storage, or operation, then you understand how alarming and potentially dangerous it can be.
