Batteries can release high energies and the safety requirements for nickel- and lithium-based batteries and cells for portable applications are harmonized under IEC 62133. The standard came into effect in 2012 to reduce the global risk in transporting, storing and operating batteries.
The most basic safety device in a battery is a fuse that opens on high current. Some fuses open permanently and render the battery useless; others are more forgiving and reset. Figure 1 illustrates the top of an 18650 cell for Li-ion with built-in safety features. The resistance of the positive thermal coefficient (PTC) (blue) is low during normal operation and increases when the temperature rises above a critical level to reduce current flow. The PTC is reversible and returns to high conductivity when the temperature normalizes.
The current interrupt device (CID) is a fuse-type device that cuts off the electrical circuit permanently when triggered by excessive cell pressure, high temperature, or high voltage, depending on design. In Figure 1, the CID operates by pressure. When the internal pressure increases to about 1,000kPa, the scored top disk (orange) breaks, separates from the metallic foil (brown) and disconnects the current flow. This also allows gas to vent.
The last safety device is the vent that releases gas during an anomaly and can be resealed. However, the pressure of a disintegrating cell can be so large that the gases are unable to escape in an orderly way and venting with flame occurs. In some cases the top of the cell escapes like a bullet from a shotgun. Similar to a nuclear meltdown that cannot be stopped once in progress; a Li-ion battery once in disintegration should be allowed to burn out in a safe place with ventilation.
Figure 1: Typical safety mechanism of the 18650 cell cap.
PTC (blue) increases resistance by heat to reduce electrical current. The effect is reversible.
CID consists of a top disk (orange) that breaks under pressure and permanently disconnects the current flow. Source: CALCE (Center for Advanced Life Cycle Engineering)
Protection devices have a residual resistance that causes a slight decrease in overall performance due to a resistive voltage drop. Not all cells have built-in protections and the responsibility for safety in its absence falls to the Battery Management System (BMS).
Further layers of safeguards can include solid-state switches in a circuit that is attached to the battery pack to measure current and voltage and disconnect the circuit if the values are too high. Protection circuits for Li-ion packs are mandatory. (See BU-304b: Making Lithium-ion Safe.)
More information on why batteries fail, what the user can do when a battery overheats and simple guidelines using Lithium-ion Batteries are described in BU-304a: Safety Concerns with Li-ion.
Intrinsically Safe Batteries
Safety is vitally important when using electronic devices in hazardous areas. Intrinsic safety (IS) ensures harmless operation in areas where an electric spark could ignite flammable gas or dust. Hazardous areas include oil refineries, chemical plants, grain elevators and textile mills.
All electronic devices entering a hazardous area must be intrinsically safe. This includes two-way radios, mobile phones, laptops, cameras, flashlights, gas detectors, test devices and medical instruments, even when powered with primary AA and AAA cells. Intrinsically safe devices and batteries contain protection circuits that prevent excessive currents that could lead to high heat, sparks and explosion. The hazard levels are subdivided into these four disciplines.
1. Types of Hazardous Materials present
Class I Flammable gases, vapors or liquids in petroleum refineries, utility gas plants
Class II Combustible dust in grain elevators, coal preparations plants
Class III Ignitable fibers and flyings in textile mills, wood processing creating sawdust, etc.
2. Likelihood of Hazardous Materials present
Division I Hazardous materials can exist in ignitable concentrations
Division II Hazardous materials will not likely exist in ignitable concentrations
3. Potency of Hazardous Material (Groups from A to G)
A hazardous material is given a designation of: Acetylene (A), hydrogen (B), ethylene (C), propane, gasoline, etc. (D), metal dust (E), coal dust (F) and grain dust (G).
4. Temperature Codes (from T1 to T6)
The explosion danger of gases or combustible dust is affected by surface temperature. T1 is a hot 450ºC (842ºF); T6 is a moderate 85ºC (185ºF). All other temperatures fall in between.
Intrinsic safety requirements vary from country to country. North America has the Factory Mutual Research Corporation, Underwriters Laboratories (UL) and Canadian Standards Association (CSA); Europe has the ATEX directive; while other countries follow the IECEx standards. Many countries recognize harmonized IEC 60079.
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Battery users often ask: “Why does an old Li-ion lake so long to charge?” Indeed, when Li-ion gets older, the battery takes its time to charge even if there is little to fill. We call this the “old-man syndrome.” Figure 1 illustrates the charge time of a new Li-ion with a capacity of 100 percent against an aged pack delivering only 82 percent. Both take roughly 150 minutes to charge.
Figure 1: New and aged Li-ion batteries are charged.
Both packs take roughly 150 minutes to charge. The new pack charges to 1,400mAh (100%) while the aged one only goes to 1,150mAh (82%). Courtesy: Cadex Electronics Inc.
When charging Li-ion, the voltage shoots up similar to lifting a weight with a rubber band. The new pack as demonstrated in Figure 2 is “hungrier” and can take on more “food” before reaching the 4.20V/cell voltage limit compared to the aged Li-ion that hits V Limit in Stage 1 after only about 60 minutes. In terms of a rubber band analogy, the new battery has less slack than to the aged pack and can accept charge longer before going into saturation.
Figure 2: Observing charge times of a new and aged Li-ion in Stage 1.
The new Li-ion takes on full charge for 90 minutes while the aged cell reaches 4.20V/cell in 60 minutes Courtesy: Cadex Electronics Inc.
Figure 3 demonstrates the different saturation times in Stage 2 as the current trails from the fully regulated current to about 0.05C to trigger ready mode. The trailing on a good battery is short and is prolonged on an aged pack. This explains the longer charge time of an older Li-ion with less capacity. An analogy is a young athlete running a sprint with little or no slow-down towards the end, while the old man gets out of breath and begins walking, prolonging the time to reach the goal.
Figure 3: Observing saturation times of new and aged Li-ion in Stage 2 before switching to ready.
The new cell stays in full-charge longer than the old cell and has a shorter current trail. Courtesy: Cadex Electronics Inc.
A common aging effect of Li-ion is loss of charge transfer capability. This is caused by the formation of passive materials on the electrodes, which inhibits the flow of free electrons. This reduces the porosity on the electrodes, decreases the surface area, lowers the lower ionic conductivity and raises migration resistance. The aging phenomenon is permanent and cannot be reversed.
The health of a battery is based on these three fundamental attributes:
Capacity, the ability to store energy. Capacity is the leading health indicator of a battery
Internal resistance, the ability to deliver current
Self-discharge, indicator of the mechanical integrity
The charge signature reveals valuable health indicators of Li-ion. A good battery absorbs most of the charge in Stage 1 before reaching 4.20V/cell and the trailing in Stage 2 is short. “Lack of hunger” on a Li-ion can be attributed to a battery being partially charged; exceptionally long trailing times relates to a battery with low capacity, high internal resistance and/or elevated self-discharge.
Algorithms can be developed that compare Stage 1 and Stage 2 based on capacity and state-of-charge. Anomalies, such as low capacity and elevated self-discharge can be identified by setting acceptance thresholds. Cadex is developing chargers with algorithms that will provide diagnostic functions. Such advancement will promote the lone charger into a supervisory position to provide quality assurance in batteries without added logistics.
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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.
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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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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 SEI (solid electrolyte interphase) is formed on the surface of the anode from the electrochemical reduction of the electrolyte and plays a crucial role in the long-term cyclability of a lithium-based battery.
Introduction of SEI
During the first charge and discharge of a lithium-ion battery, the electrode material reacts with the electrolyte at the solid-liquid phase interface. After the reaction, a thin film forms on the surface of the electrode material, where Li+ can be embedded and removed freely while electrons cannot. The SEI is about 100-120 nm thick, and it is mainly composed of various inorganic components, such as Lithium Carbonate (Li2CO3), Lithium Fluoride (LiF), Lithium Oxide (Li2O), Lithium Hydroxide (LiOH), as well as some organic components like Lithium Alkyl Carbonates (ROCO2Li).
Source of SEI
When a lithium-ion battery starts to charge and discharge, the lithium ions are extracted from the active material of the positive electrode. At which point, they enter the electrolyte, penetrate the separator, enter the electrolyte, and finally embed themselves into the layered gap of the negative carbon material.
Electrons then come out of the positive electrode along the outer end loop and enter the negative electrode carbon material. At this point, an oxidation-reduction reaction occurs between the electrons, the solvent in the electrolyte, and the lithium ions. As the thickness of the SEI increases to the point where electrons cannot penetrate it, a passivation layer is formed, which inhibits the continuation of the redox reaction.
SEI’s impact on batteries
The formation of the SEI film has a crucial impact on the performance of electrode materials. On one hand, in the formation of the SEI film, parts of the lithium ions are consumed, which increases the irreversible capacity of batteries and reduces the charge and discharge efficiency of the electrode material.
On the other hand, the SEI is insoluble in organic solvents and can exist in stable conditions in organic electrolyte solutions. Furthermore, solvent molecules cannot pass through it, thus effectively preventing the co-embedding of the ions and avoiding damage to the electrode material. This greatly improves the cycling performance and service life of the battery.
SEI’s affecting factors
The formation of the SEI is mainly influenced by the following aspects. First, electrolytes (Li salts, solvents, admixtures, etc.), with different compositions will result in different SEI compositions and affect the stability. Next, the formation, that is, the intensity of the first charge and discharges current. High temperature will also reduce the stability of the SEI and affect the battery cycle life. In addition, the thickness of the SEI changes based on the type of negative electrode material.
Conclusion
In-depth research on the SEI with its formation mechanism, structure and stability, and further search for effective ways to improve the performance have been hot topics of research in the electrochemical community.
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The power output depends on the battery, and the battery management system (BMS) is the core of it. It is a system for monitoring and managing the battery. It controls the charge and discharge of the battery by collecting and calculating parameters such as voltage, current, temperature, and SOC. The process, the management system that realizes the protection of the battery and improves the overall performance of the battery is an important link between the battery and the battery application equipment.
BMS mainly includes three parts: hardware, bottom layer software, and application layer software.
The hardware of the battery management system (BMS)
1. Architecture
The topology of Battery Management System(BMS) hardware is divided into two types: centralized and distributed.
(1) The centralized type
The centralized type is to concentrate all the electrical components into a large board, the sampling chip channel utilization is the highest and the daisy chain communication can be adopted between the sampling chip and the main chip, the circuit design is relatively simple, the product cost is greatly reduced, but All the collection wiring harnesses will be connected to the mainboard, which poses a greater challenge to the security of the BMS, and there may also be problems in the stability of the daisy chain communication. It is more suitable for occasions where the battery pack capacity is relatively small and the module and battery pack types are relatively fixed.
(2) The Distributed type
Distributed includes a mainboard and a slave board. It is possible that a battery module is equipped with a slave board. The disadvantage of this design is that if the number of battery modules is less than 12, the sampling channel will be wasted (generally there are 12 sampling chips. Channel), or 2-3 slave boards to collect all battery modules. This structure has multiple sampling chips in one slave board. The advantages are high channel utilization, cost-saving, flexibility in system configuration, and adaptation to different capacities. Modules and battery packs of different specifications and types.
2. Function
The hardware design and specific selection should be combined with the functional requirements of the vehicle and battery system. The general functions mainly include collection functions (such as voltage, current, and temperature collection), charging port detection (CC and CC2), and charging wake-up (CP and A+) ), relay control and status diagnosis, insulation detection, high voltage interlock, collision detection, CAN communication and data storage requirements.
(1) Main controller
Process the information reported from the controller and the high-voltage controller, and at the same time judge and control the battery operating status according to the reported information, realize the BMS-related control strategy, and make the corresponding fault diagnosis and processing.
(2) High voltage controller
Collect and report the total voltage and current information of the battery in real-time, and realize timely integration through its hardware circuit, and provide accurate data for the calculation of the state of charge (SOC) and the state of health (SOH) for the motherboard. Charge detection and insulation detection function.
(3) Slave controller
Real-time collection and reporting of battery cell voltage and temperature information, feedback of the SOH and SOC of each string of cells, and a passive equalization function, effectively ensuring the consistency of cells during power use.
(4) Sampling control harness
Provide hardware support for battery information collection and information interaction between controllers, and at the same time add redundant insurance function to each voltage sampling line, effectively avoid battery short circuit caused by wiring harness or management system.
3. Communication method
There are two ways to transfer information between the sampling chip and the main chip: CAN communication and daisy chain communication. CAN communication is the most stable. However, due to the high cost of power chips and isolation circuits, daisy chain communication is actually SPI communication. The cost is very low, and the stability is relatively poor. However, as the pressure on cost control is increasing, many manufacturers are shifting to the daisy chain mode. Generally, two or more daisy chains are used to enhance communication stability.
4. Structure
BMS(Battery Management System) hardware includes power supply IC, CPU, sampling IC, high-drive IC, other IC components, isolation transformer, RTC, EEPROM, CAN module, etc. The CPU is the core component, and the functions of different models are different, and the configuration of the AUTOSAR architecture is also different. Sampling IC manufacturers mainly include Linear Technology, Maxim, Texas Instruments, etc., including collecting cell voltage, module temperature, and peripheral configuration equalization circuits.
Bottom layer software
According to the AUTOSAR architecture, it is divided into many general functional modules, which reduces the dependence on hardware, and can realize the configuration of different hardware, while the application layer software changes little. The application layer and the bottom layer need to determine the RTE interface, and consider the flexibility of DEM (fault diagnosis event management), DCM (fault diagnosis communication management), FIM (function information management), and CAN communication reserved interfaces, which are configured by the application layer.
Application layer software of the BMS
The software architecture mainly includes high and low voltage management, charging management, state estimation, balance control, and fault management, etc.
1. High and low voltage management
Generally, when the power is on normally, the VCU will wake up the BMS through the hardwire or 12V of the CAN signal. After the BMS completes the self-check and enters the standby mode, the VCU sends the high-voltage command, and the BMS controls the closed relay to complete the high-voltage. When the power is off, the VCU sends a high-voltage command and then disconnects and wakes up 12V. It can be awakened by CP or A+ signal when the gun is plugged in in the power-off state.
2. Charging management
(1) Slow charge
Slow charging uses an AC charging station (or 220V power supply) to convert AC to DC to charge the battery through an on-board charger. The charging station specifications are generally 16A, 32A, and 64A, and it can also be charged through a household power supply. The BMS can be awakened by CC or CP signal, but it should be ensured that it can sleep normally after charging. The AC charging process is relatively simple, and it can be developed in accordance with the detailed regulations of the national standard.
(2) Fast charge
Fast charging is to charge the battery with DC output from the DC charging pile, which can achieve 1C or even higher rate charging. Generally, 80% of the power can be charged in 45 minutes. Wake up by the auxiliary power A+ signal of the charging pile, the fast charging process in the national standard is more complicated, and there are two versions of 2011 and 2015 at the same time, and the different understanding of the technical details of the charging pile manufacturer’s unclear technical details of the national standard process also causes the vehicle charging adaptability A great challenge, so fast charging adaptability is a key indicator to measure the performance of BMS products.
3. Estimation function
(1) the State Of Power
SOP (State Of Power) mainly obtains the available charge and discharge power of the current battery through the temperature and SOC lookup table. The VCU determines how the current vehicle is used according to the transmitted power value. It is necessary to consider both the ability to release the battery and the protection of the battery performance, such as a partial power limit before reaching the cut-off voltage. Of course, this will have a certain impact on the driving experience of the whole vehicle.
(2) state of health
SOH (state of health) mainly characterizes the current state of health of the battery, which is a value between 0-100%. It is generally believed that the battery can no longer be used after it is lower than 80%. It can be expressed by the change of battery capacity or internal resistance. When using the capacity, the actual capacity of the current battery is estimated through the battery operating process data, and the ratio of the rated capacity to the rated capacity is the SOH. Accurate SOH will improve the estimation accuracy of other modules when the battery decays.
(3) the State Of Charge
SOC (State Of Charge) belongs to the BMS core control algorithm, which characterizes the current remaining capacity state, mainly through the ampere-hour integration method and EKF (Extended Kalman Filter) algorithm, combined with correction strategies (such as open-circuit voltage correction, full charge correction, charging End correction, capacity correction under different temperatures and SOH, etc.). The ampere-hour integration method is relatively reliable under the condition of ensuring the accuracy of current acquisition, but the robustness is not strong. Because of the error accumulation, it must be combined with a correction strategy. The EKF has strong robustness, but the algorithm is more complex and difficult to implement. Domestic mainstream manufacturers generally can achieve accuracy within 6% at room temperature, and it is difficult to estimate high and low temperatures and battery attenuation.
(4) the State Of Energy
SOE (State Of Energy) algorithm manufacturers do not develop much now or use a simpler algorithm, look up the table to get the ratio of the remaining energy to the maximum available energy in the current state. This function is mainly used to estimate the remaining cruising range.
4. Fault diagnosis
According to the different performance of the battery, it is divided into different fault levels, and in the case of different fault levels, the BMS and VCU will take different treatment measures, warning, limiting power, or directly cutting off the high voltage. Failures include data collection and rationality failures, electrical failures (sensors and actuators), communication failures, and battery status failures.
5. Balance control
The equalization function is to eliminate the inconsistency of the battery cells generated during battery use. According to the shortboard effect of the barrel, the cells with the worst performance during charging and discharging first reach the cut-off condition, and the other cells have some capabilities. It is not released, causing battery waste.
Equalization includes active equalization and passive equalization. Active equalization is the transfer of energy from more monomers to fewer monomers, which will not cause energy loss, but the structure is complex, the cost is high, and the requirements for electrical components are relatively high. Relatively passive The balance structure is simple and the cost is much lower, but the energy will be dissipated and wasted in the form of heat. Generally, the maximum balance current is about 100mA. Now many manufacturers can achieve better balance effects using passive balance.
The BMS(Battery Management System) control method, as the central control idea of the battery, directly affects the service life of the battery, the safe operation of the electric vehicle, and the performance of the entire vehicle. It has a significant impact on battery life and determines the future of new energy vehicles. A good battery management system will greatly promote the development of new energy vehicles.
https://himaxelectronics.com/wp-content/uploads/2021/03/Battery-Bms.jpg400800administrator/wp-content/uploads/2019/05/Himax-home-page-design-logo-z.pngadministrator2021-03-16 03:48:572024-04-29 01:27:58What is a Battery Management System (BMS)?
