The use of li ion customized battery packs in low battery temperature environments is limited. In addition to the serious decline in discharge capacity, lithium batteries cannot be charged at low battery temperature. When charging at low battery temperature, the intercalation and lithium plating reactions of lithium ions on the graphite electrode of the battery exist simultaneously and compete with each other.

The diffusion of lithium ions in graphite is inhibited under low battery temperature conditions, and the conductivity of the electrolyte decreases, resulting in a decrease in the intercalation rate and the lithium plating reaction is more likely to occur on the graphite surface. The main reasons for the decline in the life of lithium-ion batteries when they are used at low battery temperature are the increase in internal impedance and the loss of capacity due to the precipitation of lithium ions.

1.Effect of low battery temperature on battery discharge capacity

Capacity is one of the most important parameters of lithium batteries, and its size varies with temperature. For AGM replacement battery, the charge end voltage is 3.65±0.05V, and the discharge end voltage is 2±0.05V. The two curves are the temperature capacity curves obtained by discharging the battery at different temperatures at 0.1C and 0.3C respectively.

2.Effect of low battery temperature on battery internal resistance

The relationship between li ion customized battery packs temperature and resistance is shown in the figure below. Different curves represent different charge levels of the battery itself. Under any charge, the internal resistance of the battery increases significantly as the temperature decreases. The lower the charge, the greater the internal resistance, and this trend remains unchanged as the temperature changes.

At low battery temperature, in the cathode and anode materials, the diffusion and movement ability of charged ions becomes poor, and it becomes difficult to pass through the passivation film between the electrode and the electrolyte. The speed of transfer in the electrolyte is also reduced, and a lot of heat is additionally generated during the transfer.

After lithium ions reach the anode, the diffusion inside the anode material also becomes unsmooth. During the whole process, the movement of charged ions becomes very difficult. From the outside, it means that the internal resistance of the battery cell has increased.

3. Effect of low battery temperature on battery charge and discharge efficiency

The lower curve is the curve of charging efficiency changing with temperature. We can observe that the charging efficiency at -20°C is only 65% of that at 15°C.

The low battery temperature brings about the changes in the various electrochemical performances described above, and the internal resistance increases significantly. During the discharge process, a large amount of electric energy is consumed on the internal resistance to generate heat.

4. Internal side reactions of lithium-ion batteries at low battery temperatures

The performance of li ion customized battery packs degrades severely at low battery temperatures, and some side reactions will occur during the charging and discharging process of lithium-ion batteries. These side reactions are mainly the irreversible reaction between lithium ions and the electrolyte, which will cause the capacity of the lithium battery to decline and further deteriorate the battery performance.

The consumption of conductive active material causes capacity fading. Considering the potentials of the cathode and anode in the battery, these side reactions are more likely to occur on the anode side than the cathode side. Because the potential of the anode material is much lower than that of the cathode material, the deposits of side reactions of ions and electrolyte solvents are deposited on the electrode surface, forming an SEI film. The impedance of the SEI film is one of the factors that cause the overpotential of the anode reaction.

When the battery is further cycled and aged, due to the continuous insertion and extraction of lithium ions on the anode during continuous cycles, the expansion and contraction of the electrode caused by the continuous cycle will cause the SEI film to rupture. The cracks after the rupture of the SEI film provide a direct contact channel between the electrolyte and the electrode, thereby forming a new SEI film to fill the crack and increase the thickness of the SEI film.

These reaction processes are constantly repeated as the battery is continuously charged and discharged, so that lithium ions are continuously reduced in the reaction, resulting in a decline in the discharge capacity of the lithium-ion battery.

During charging, deposits form on the surface of the active material, increasing the electrical resistance. The effective surface area of the active particles is reduced and the ionic resistance is increased. The usable capacity and energy of lithium batteries decline simultaneously. Lithium batteries are more prone to side reactions during charging.

At the beginning of lithium battery charging, lithium ions move to the anode through the electrolyte, so the potential difference between the electrode and the electrolyte decreases, making it easier for lithium ions to undergo irreversible side reactions with the substances in the electrolyte. The different electrode materials of lithium-ion batteries have different relationship curves between the potential and the lithium intercalation concentration fraction of the electrode material.

Lithium battery low temperature preheating technology

Faced with the limited use of lithium batteries at low battery temperature, the technicians found a countermeasure to charge and preheat. Although it is an expedient measure, it has a significant effect on improving the discharge capacity and long-term life of lithium batteries.

Before charging or using a lithium battery in a low battery temperature environment, the battery must be preheated. The way the battery management system (BMS) heats the battery can be roughly divided into two categories: external heating and internal heating.

Compared with external heating methods, internal heating avoids long-path heat conduction and the formation of local hot spots close to the heating device. Therefore, internal heating can heat the battery more uniformly for better heating with higher efficiency and is easier to implement.

At present, most of the research on the internal AC preheating scheme focuses on the heating speed and efficiency, and there is little clear consideration of the heating strategy to prevent the occurrence of side reactions such as lithium deposition.

In order to prevent the generation of lithium deposition during the preheating process, it is necessary for the BMS to estimate and control the conditions of lithium deposition in real time. A model-based controlled battery heating technique at low battery temperature is required to achieve the above functions.

With the development of new energy, the use of power li ion customized battery packs is also increasing day by day. The use of lithium batteries at low battery temperature urgently needs to solve the problem of battery warm-up. This is a field that is very close to practical applications. In addition, AC heating, mobilizing electrochemical substances to generate movement, and the impact on battery life have not yet been seen. It is also a problem worthy of continuous attention.

If you have any question, please feel free to contact us:

• Name: Dawn Zeng (Director)
• E-mail address: sales@himaxelectronics.com

In addition to custom lithium battery pack being popular, manganese-based cathode materials are ushering in the second wave of peaks. Manganese-based batteries were first promoted during the heyday of the Nissan Leaf. As a second-generation product of manganese-based materials, lithium iron manganese phosphate has entered the early stages of mass production and has attracted much attention from the industry.

Companies such as AVIC lithium battery, Guoxuan Hi-Tech, and REPT have all mentioned some progress in iron manganese super phosphate lithium batteries.For example, from 2023 to 2024, the energy density of REPT’s lithium iron manganese phosphate will reach 500Wh/L, supporting a battery life of 800 kilometers for pure electric vehicles; AVIC Lithium Battery will reduce lithium consumption by 15% through lithium iron manganese phosphate batteries. In addition to the above-mentioned companies, many power battery manufacturers such as CATL, BYD, and EVE Lithium Energy among the top ten power battery companies have also begun to carry out related research and development and layout of iron manganese phosphate lithium batteries.

Among them, the lithium iron manganese phosphate produced by many companies has passed battery pilot tests in the first half of this year and is sending samples to car companies for testing. CATL will mass-produce M3P batteries in the second half of the year. Another potential product, lithium-rich manganese-based batteries, is still in the development stage. At present, the lithium-rich manganese-based material has reached 400mAh/g in the laboratory stage, and is expected to reach 400mAh/g in mass production. The battery energy density can reach 400Wh/kg.

Lithium iron manganese phosphate has obvious advantages and disadvantages

The application of manganese in custom lithium battery pack cathode materials is currently mainly lithium manganate and lithium nickel cobalt manganate (ternary materials). With the advancement of material modification technology, manganese-based cathode materials lithium iron manganese phosphate and lithium-rich manganese-based technology have developed rapidly.

Lithium iron manganese phosphate has become a transition product between lithium iron phosphate and ternary batteries. It is characterized by higher energy density than lithium iron phosphate and lower cost than ternary lithium batteries.

Lithium iron manganese phosphate has the same olivine structure as lithium iron phosphate, and the structure is more stable during charge and discharge. Even if all lithium ions are embedded during charging, the structure will not collapse, making it safer. Specifically, you will find that the advantages and disadvantages of lithium iron manganese phosphate are very obvious.

First, the energy density is better. The voltage platform of lithium iron manganese phosphate is as high as 4.1V, which is higher than the 3.4V of lithium iron phosphate. The high voltage brings an increase in energy density. The theoretical energy density is 15%-20% higher than that of lithium iron phosphate, and can basically reach the level of ternary battery NCM523.

Second, the low temperature performance is better. Lithium iron manganese phosphate has better low-temperature performance than lithium iron phosphate, and the capacity retention rate at -20°C can reach about 75%. Third, it has the characteristics of lithium iron phosphate batteries and is safer than ternary batteries. Lithium iron manganese phosphate has an olivine structure and has better safety and cycle stability than ternary.

Fourth, manganese ore resources are abundant and the cost is low. The cost of lithium iron manganese phosphate is only about 5%-10% higher than that of lithium iron phosphate. Taking into account the improvement in the energy density of lithium iron-manganese phosphate, in terms of battery installed cost, the cost per watt-hour of lithium iron-manganese phosphate is slightly lower than that of custom lithium battery pack , and significantly lower than that of ternary batteries.

The disadvantage of lithium iron manganese phosphate battery is that its conductivity and lithium ion diffusion speed are low, which will make it difficult to fully utilize its capacity advantage and poor rate performance. However, in the opinion of Guoxuan Hi-Tech personnel, lithium iron manganese phosphate is basically an insulator. “Japan’s Sony Corporation has calculated that the band gap of general lithium iron phosphate materials is about 0.3eV, which is a semiconductor, but lithium iron manganese phosphate is 2eV, which is basically an insulator and does not conduct electricity.”

Improvement plan for lithium iron manganese phosphate materials

Compared with custom lithium battery pack , due to the addition of manganese, the dissolution of manganese will cause its cycle life to be reduced. In view of the above reasons, when manganese is used as a single active material, doping, carbon coating, nanotechnology modification and other methods are often used to improve the performance of lithium iron manganese phosphate materials.

This conductive network cannot be formed if it is not on the nanoscale. But once nanosized, it is not easy to combine the slurry and the coating is not easy to apply. It is difficult to use as a lithium iron manganese phosphate battery alone, and many problems need to be solved. Zhongchuang Aviation’s solution is to consider how to gradient design the manganese element. The inside and outside are not necessarily uniform, there may be a gradient design. It can be more on the outside and less on the inside, so that the entire conductive path will be smoother.

Secondly, it is doped with many other transition metal elements to give it a better balance of energy and conductivity. Then there is a problem on the interface, and coating the interface will solve the conductive problem of the interface on the one hand. On the other hand, it also effectively solves the problem of life decay caused by the phase change of the lithium manganese material itself.

REPT, one of China’s top ten lithium marine battery manufacturers, also mentioned lithium iron manganese phosphate. Their goal is to achieve an energy density of 500Wh/L for lithium iron manganese phosphate batteries and a driving range of 800 kilometers in 2023-2024. In addition to the above-mentioned companies, CATL’s M3P batteries are also iron manganese phosphate lithium batteries, which are called phosphate-based ternary batteries. CATL will invest in Lithitech in November 2021, holding 60% of the shares. Among them, Lithitech’s main business is lithium iron manganese phosphate materials, with a production capacity of 2,000 tons/year.

The direction given by researchers from China Electronics Technology Group for the application of lithium iron manganese phosphate is that it can be mixed with ternary materials to improve the safety of ternary material batteries; or mixed with lithium iron phosphate to increase the energy density of custom lithium battery pack.

The past and future of manganese-based batteries

The currently hotly debated lithium iron manganese phosphate is a second-generation manganese-based battery, a transitional product through material modification. The first generation of manganese-based batteries were lithium manganate batteries. Lithium manganate cathode material was invented 20 years ago and was used in the first generation of new energy vehicles in Japan and South Korea.

Lithium manganese oxide batteries in Japan and South Korea mainly use single crystal particle doping. Among them, the master was the Japanese battery company AESC at the time. Early model Nissan Leafs were known for their battery safety. But the shortcomings are also obvious. Due to low energy density, the driving range is only 200 kilometers. However, at present, AESC still takes ternary batteries as the mainstream development direction.

Lithium iron manganese phosphate is not a new direction either. As early as 2013, BYD considered lithium iron manganese phosphate as an upgrade route for lithium iron phosphate and began to apply for relevant patents. However, due to the subsidy policy tilting towards ternary materials with higher energy density, and BYD’s failure to solve the problems of low cycle life and excessive internal resistance of lithium iron manganese phosphate batteries, this route has not become mainstream. BYD once stopped phosphoric acid Iron, manganese and lithium exploration.

However, starting in 2020, BYD has begun to have relevant patent application records. Guoxuan Hi-Tech is also an early company that developed iron manganese phosphate lithium batteries. According to Xu Xingwu, Guoxuan Hi-Tech was also developing lithium iron manganese phosphate batteries in 2013, and obtained new product certificates for lithium iron manganese phosphate batteries in 2014 and 2017 respectively. As early as 2014, AVIC Aluminum began to try and explore on the road to high manganese.

In 2014, AVIC lithium battery has adopted lithium iron manganese phosphate and ternary batteries as composite material systems and has achieved mass production. At that time, it was a station wagon, and the shipments were actually quite large. Starting in 2021, raw material prices will skyrocket. Against this background, lithium iron manganese phosphate batteries have once again attracted the attention of enterprises, and reports on related layouts have also continued to increase.

The next highly anticipated cathode material is lithium-rich manganese-based material. Lithium-rich manganese-based materials have high specific capacity, low cost and good safety. Lithium-rich manganese-based cathode materials can be considered to be composed of two components, Li2MnO3 and LiMO2, which are uniformly compounded on the atomic scale to form lithium-rich manganese-based materials.

Lithium-rich manganese-based materials are mainly composed of cheaper manganese elements and contain less precious metals. Compared with commonly used lithium cobalt oxide and nickel cobalt manganese ternary cathode materials, they are not only lower in cost, but also safer. The advantages are outstanding, but there are also many disadvantages. Lithium-rich manganese-based materials have shortcomings such as initial irreversible capacity loss, poor rate performance, and voltage attenuation during cycling.

For manganese-rich lithium-based materials, there are great advantages and great difficulties. It can achieve 400mAh/g, but there is a problem of voltage attenuation. There is no better way to lose oxygen during the circulation process, and the challenge is still relatively large. Professionals believe that lithium-rich manganese-based material batteries can reach the level of 300mAh/g after mass production, and can achieve 400Wh/kg batteries when paired with silicon carbon.

At present, we see many companies making arrangements in the field of lithium-rich manganese-based materials. According to relevant company announcements, cathode material companies such as Rongbai Technology and Dangsheng Technology have planned the research and development of lithium-rich manganese-based materials in advance.

It has now entered the small trial stage and is actively cooperating with relevant customers to carry out product performance optimization and process amplification experiments on the company’s existing production lines.

In addition, Zhenhua New Materials, Zhongwei, Kungong Technology, Tianyuan Group, DFD and other companies have also carried out research and development projects on lithium-rich manganese-based materials (precursors) and are currently actively exploring the feasibility of their commercialization.

final thoughts

New manganese-based cathode materials are rapidly emerging, and their improved permeability is expected to increase the use of manganese in the custom lithium battery pack industry by more than 10 times between 2021 and 2035, and is expected to become one of the main cathode materials for power batteries.

Source：https://www.takomabattery.com/manganese-based-batteries-will-usher-in-another-peak/

If you have any question, please feel free to contact us:

• Name: Dawn Zeng (Director)
• E-mail address: sales@himaxelectronics.com

With the development of science and technology, batteries have become an indispensable part of our daily life. Among them, 18650 Li-ion battery pack, as a kind of high energy density and long life battery, is widely used in electronic equipment, electric vehicles, aviation and other fields. This article will introduce the principle, characteristics, applications and safety precautions of 18650 lithium-ion battery pack.

First, the working principle of 18650 lithium-ion battery packs

18650 lithium-ion battery pack is composed of positive pole, negative pole, diaphragm, electrolyte and shell. Its working principle is

• when the external circuit through the current, the lithium atoms on the positive electrode is transferred to the negative electrode, forming lithium ions, thus realizing the mutual conversion of electric energy and chemical energy. This process is controlled by the interaction between the lithium ions and the electrolyte, and the lithium ions migrate between the positive and negative electrodes, thus maintaining the voltage balance of the battery.

Second, the characteristics of 18650 lithium-ion battery packs

• 18650 lithium-ion battery pack has the advantages of high energy density, long life and no memory effect. Its energy density is more than three times that of traditional lead-acid batteries, so it can provide higher power in a smaller volume. Meanwhile, due to its no memory effect, users can charge it anywhere and anytime, which is convenient. In addition, it also has the advantages of good high temperature performance, light weight, easy mass production.

Third, 18650 lithium-ion battery pack application areas

• 18650 battery pack has a wide range of applications, including electronic equipment, electric vehicles, aviation and so on. In terms of electronic equipment, it is widely used in camcorders, digital cameras, tablet PCs and other fields to provide reliable energy security. In the field of electric vehicles, it replaces lead-acid batteries and improves the range and performance of electric vehicles. In the field of aviation, it is widely used in airplanes, providing reliable energy security for airplanes.

Fourth, safety precautions

Although 18650 lithium-ion battery packs have many advantages, it is still necessary to pay attention to safety in the process of use. First, use lithium-ion battery packs produced by regular manufacturers, avoid using low-quality or counterfeit products. Secondly, please do not put the battery in a high temperature environment when charging, high temperature will damage the battery performance. In addition, please do not disassemble, invert or shake the battery during charging to avoid arcing or short-circuiting. Using 18650 Li-ion battery packs in high temperature and high humidity environments may cause safety problems, so it is recommended to use them in a moderate temperature environment.

 

If you have any question, please feel free to contact us:

• Name: Dawn Zeng (Director)
• E-mail address: sales@himaxelectronics.com

Inconsistencies in custom lithium battery pack parameters mainly refer to inconsistencies in capacity, internal resistance, and open circuit voltage. Inconsistencies in cell performance are formed during the production process and deepen during use. Today, the editor will take you to understand the issue of consistency of lithium battery packs.

1.Definition of co-nsistency

The consistency of custom lithium battery pack refers to the convergence of a group of important characteristic parameters of lithium batteries. It is a relative concept. There is no most consistent, only more consistent. For multiple strings of cells in the same battery pack, it is best for each parameter to be within a smaller range for better consistency.

Adding the time dimension, consistency refers to the consistency of all characteristic parameters of all cells in the battery pack throughout their life cycle, taking into account inconsistencies in capacity attenuation, internal resistance growth, and aging rates. The life of the entire battery pack is our ultimate focus on consistency.

The purpose of pursuing consistency is not only to maximize the capabilities of the custom lithium battery pack (including maximum power, maximum current, and maximum available capacity) in the current state, but also to maintain such capabilities for as long as possible.

2.The concept of inconsistency

Inconsistencies in custom lithium battery pack parameters mainly refer to inconsistencies in capacity, internal resistance, and open circuit voltage. The voltage is the initial voltage of the battery when assembled. The internal resistance is the AC internal resistance when fully charged, and the capacity is the discharge capacity of the battery cell after it is fully charged.

Accumulation occurs with the continuous charge and discharge cycles of the battery during use, resulting in greater differences in the status (SOC, voltage, etc.) of each individual battery;

The usage environment in the lithium battery pack also affects every single cell. This leads to the inconsistency of single cells gradually amplifying during use, which in some cases accelerates the degradation of the performance of some single cells, and ultimately causes premature failure of the lithium battery pack.

Supplement: SOC is used to describe the remaining power of the battery and is one of the important parameters during battery use. SOC estimation is the basis for judging whether the battery is overcharged or discharged.

The open circuit voltage of lithium batteries has a clear and monotonic correspondence with the battery’s charge. As long as the accurate open circuit voltage is obtained, the battery’s charge can be calculated.

3.Causes of inconsistency

The inconsistency of the custom lithium battery pack is a continuous accumulation process. The longer the time, the greater the difference between the single cells; and the custom lithium battery pack will also be affected by the use environment, and the single cells will be inconsistent in the future use process. The characteristics will be gradually amplified, causing the performance of some individual batteries to decline at an accelerated rate, and ultimately causing the battery to become useless.

The inconsistency of lithium battery packs is mainly affected by time. The reasons mainly include two aspects:

1. First of all, there are process problems and uneven materials in the manufacturing process, which make the materials and materials of lithium batteries slightly different. After the lithium battery pack is put into use, the electrolyte density of each battery in the battery pack will have a difference. and temperature and ventilation conditions, self-discharge degree charging and discharging processes, etc.as well, there may be differences in capacity and internal resistance of batteries of the same model shipped from the same batch.
2. When used in a vehicle, the electrolyte density, temperature and ventilation conditions, self-discharge degree and charging and discharging process of each battery in the lithium battery pack are affected by differences.

4. Scope of consistency evaluation

Personally, I understand that the consistency of all cells used as power, regardless of series or parallel relationship. Give a simple example.

 

Parallel connection situation

The battery cell with low discharge capacity (code B) is connected in parallel with other normal battery cells to form a parallel module D. For example, this module has 10 batteries connected in parallel. Each parallel module must provide the same current, such as 100A, to discharge the system. For other normal parallel modules, each battery discharges 10A; B can only discharge a maximum current of 1A, and the other 9 batteries each need to discharge 11A. Generally speaking, these cells will age faster than other parallel modules due to long-term overloading. One day, this parallel module’s overall maximum discharge capacity cannot reach the designed maximum capacity. This parallel battery pack has become a bottleneck in the discharge capacity of the entire battery pack.

Series connection

According to the general situation, the series connection relationship is mainly between modules. Continuing the previous plot of the parallel connection situation, there is a battery pack D that is more aged than other battery packs in the entire battery pack. D has a small capacity and a large internal resistance. Reflected on the curve between SOC and open circuit voltage, the open circuit voltage corresponding to the same SOC has a higher voltage at D terminal. When the entire battery pack is charged, D reaches the charging cut-off voltage first, and the battery pack stops charging. The other modules haven’t eaten enough, and he is already about to burst his belly, because it is getting smaller with age.

Therefore, cell consistency is not a matter within a module that is welded together, but is a requirement for all power batteries.

What hazards and problems will occur if the lithium battery pack is inconsistent?

Poor consistency may lead to uneven real-time voltage distribution of each battery cell during charging and discharging, causing overvoltage charging or undervoltage discharging, causing safety issues.

details as follows:

① Capacity loss.

The cells form a custom lithium battery pack. The capacity conforms to the “barrel principle”. The capacity of the worst cell determines the capacity of the entire battery pack.

② Loss of life.

If a small-capacity battery is fully discharged every time and the output is too strong, it is likely to reach the end of its life first. When the life of the battery core ends, a group of battery cores welded together will also end their life.

③The internal resistance increases.

With different internal resistances, the same current flows, and the battery core with large internal resistance generates relatively more heat. If the battery temperature is too high, the degradation rate will be accelerated, and the internal resistance will further increase. Internal resistance and temperature rise form a pair of negative feedback, which accelerates the degradation of high internal resistance cells.

Lithium batteries use protective circuit systems during use to ensure safety. The intuitive performance of the consistency of lithium batteries during use is the difference in voltage consistency (voltage difference), and the detection of the protection system is based on voltage monitoring. When the voltage of one of the single cells reaches the protection condition, the battery circuit will be cut off, regardless of whether the other single cells are fully charged or discharged. After continuous charging and discharging, this difference will become larger and larger until the battery pack loses its use value. Safety issues can occur when combined with factors such as individual protection system failures or failures.

If you have any question, please feel free to contact us:

• Name: Dawn Zeng (Director)
• E-mail address: sales@himaxelectronics.com

The consistency of self-discharge is an important part of the influencing factors. Batteries with inconsistent self-discharge will have large SOC differences after being stored for a period of time, which will greatly affect its capacity and safety. Studying it will help improve the overall level of our custom lithium battery pack products, obtain a higher lifespan, and reduce the defective rate of products.

A battery containing a certain amount of electricity will lose part of its capacity after being stored at a certain temperature for a period of time. This is called self-discharge. To simply understand, self-discharge is the loss of battery capacity when it is not in use, such as the negative electrode’s power returning to the positive electrode or the battery’s power being lost through side reactions.

The importance of self-discharge

Custom lithium battery pack is currently used more and more widely in various digital devices such as notebooks, digital cameras, and digital camcorders. In addition, they also have broad prospects in automobiles, mobile base stations, energy storage power stations, etc. In this case, the use of batteries no longer appears individually as in mobile phones, but more in the form of battery packs connected in series or parallel.

The capacity and life of the battery pack are not only related to each individual battery, but also to the consistency between each battery. Poor consistency will greatly drag down the performance of the battery pack.

The consistency of self-discharge is an important part of the influencing factors. Custom lithium battery pack with inconsistent self-discharge will have large differences in SOC after being stored for a period of time, which will greatly affect its capacity and safety. Studying it will help improve the overall level of our battery packs, obtain a higher lifespan, and reduce the defective rate of products.

 

 

Self-discharge mechanism

The lithium cobalt graphite battery electrode reaction is as follows:

When the battery is open circuit, the above reaction does not occur, but the power will still decrease. This is mainly due to the self-discharge of the battery. The main causes of self-discharge are:

a. Internal electron leakage caused by local electron conduction in the electrolyte or other internal short circuits.

b. External electronic leakage caused by poor insulation of the battery seal or gasket or insufficient resistance between the external lead cases (external conductors, humidity).

c. Electrode/electrolyte reaction, such as corrosion of the anode or reduction of the cathode due to electrolyte and impurities.

d. Local decomposition of electrode active material.

e. Passivation of the electrode due to decomposition products (insoluble matter and adsorbed gas).

f. The electrode is mechanically worn or the resistance between the electrode and the current collector increases.

The self-discharge of metal impurities causes the aperture of the separator to be blocked, or even pierces the separator to cause a local short circuit, endangering the safety of the battery.

Self-discharge causes the SOC difference between batteries to increase and the battery pack capacity to decrease.

Due to the inconsistent self-discharge of the custom lithium battery pack, the SOC of the batteries in the battery pack will differ after storage, and the battery performance will decrease. Customers often find performance degradation after receiving a battery pack that has been stored for a period of time. When the SOC difference reaches about 20%, only 60% to 70% of the capacity of the combined battery remains.

Large differences in SOC can easily lead to overcharge and overdischarge of the battery.

If you have any question, please feel free to contact us:

• Name: Dawn Zeng (Director)
• E-mail address: sales@himaxelectronics.com