Lithium-ion battery packs supposedly have no memory effect, so why do they still bulge? Lithium-ion battery packs are inherently designed to have no memory effect and can be charged and discharged at will. However, why are there still so many incidents of lithium-ion batteries exploding and bulging? After investigation, we found that this is caused by damage to the internal separator, leading to gas buildup inside the battery. Alternatively, it could be due to an incompatible charger being used, causing the battery to bulge. Below, we'll discuss the specific reasons for lithium-ion battery bulging.
Explanation of why lithium-ion battery packs have no memory effect:
The battery memory effect refers to the reversible failure of a battery, that is, the ability to recover its performance after failure. The memory effect means that after a battery has undergone a specific set of operating cycles over a long period of time, it automatically retains this specific characteristic.
The memory effect is a temporary capacity loss that can be recovered after several deep charge-discharge cycles. Lithium-ion batteries do not need to be completely discharged before recharging; they can be charged whenever needed. Lithium-ion battery packs do not have this memory effect, but they have a similar inertia effect (this is different from the memory effect, which all other batteries have). This refers to the chemical substances inside the battery becoming inactive over a long period of time and eventually ceasing to react, so deep charge-discharge cycles are ineffective. Therefore, avoid intentionally discharging the battery; let it run naturally. It's important to note that the lifespan of a lithium-ion battery pack is essentially fixed; each charge reduces its capacity. Additionally, if the battery will not be used for an extended period, it should retain 30% charge and be stored in a dry environment at 0 degrees Celsius. This can extend its lifespan.
Why do lithium-ion battery packs in electric vehicles bulge?
Reason one:
During charging, lithium-ion batteries undergo a chemical reaction between the lead sulfate on the positive and negative electrodes and the water in the electrolyte. This reduces the positive electrode to lead oxide and the negative electrode to pure lead. This process increases the temperature of the lithium-ion battery pack. Furthermore, if excessive gas is released, there may not be enough space inside the battery to store the gas, causing the battery to swell.
Reason 2: High internal resistance of the lithium-ion battery. When the internal resistance of a battery is too high, the voltage will be very high for a given current (voltage = current * resistance). We can see that during normal charging, the battery gets very hot before the red light switches off, meaning it's prematurely releasing gas before reaching the charging voltage!
Reason 3: The electric vehicle charger does not meet the requirements. If the parameters of the electric vehicle charger we use exceed the rated voltage and current of our battery, it may cause the lithium-ion battery pack to swell!
Helpful suggestion:
1. Use a compliant electric vehicle charger. You can have it tested at a lithium-ion battery repair shop. Many places offer free testing these days.
Second: Regularly check the battery and perform maintenance on the lithium-ion battery pack. This can extend the battery's lifespan and improve the lifespan of the electric vehicle.
Third: It is not advisable to overcharge for extended periods.
There are two types of bulging phenomena that occur in lithium-ion battery packs during charging and discharging:
1. Bulging caused by overcharging
Overcharging causes all the lithium atoms in the positive electrode material to migrate into the negative electrode material, leading to the deformation and collapse of the originally full grid in the positive electrode. This is a major reason for the decrease in the capacity of lithium-ion battery packs. During this process, the number of lithium ions in the negative electrode increases, and excessive accumulation causes lithium atoms to grow into stumps and crystals, resulting in battery swelling.
II. Lithium-ion battery swelling caused by over-discharge
During the initial charge and discharge of a liquid lithium-ion battery, the electrode material and electrolyte react at the solid-liquid interface, forming a passivation layer covering the electrode material surface. This passivation layer effectively prevents electrolyte molecules from passing through, but Li+ ions can freely insert and extract through it, exhibiting characteristics of a solid electrolyte. The SEI film is not static and undergoes slight changes during charge and discharge, primarily reversible changes in some organic components. Over-discharge causes reversible damage to the SEI film. The destruction of the SEI protecting the negative electrode material leads to its collapse, resulting in bulging of the lithium-ion battery pack.
Under what circumstances will a mobile phone lithium-ion battery bulge?
1. The lithium-ion battery itself is of poor quality.
With the increase in the number of mobile phones, batteries have also become more diverse. Many manufacturers produce batteries, and in pursuit of profit, some produce counterfeit and substandard batteries. The most crucial component of a battery is the battery cell. Inferior batteries are of poor quality, have insufficient power, and falsely advertised capacity. Generally, a good battery has a smooth surface and moderate hardness, while a lower-quality battery has a very hard surface.
2. Using a non-original charger
The saying "a good horse needs a good saddle" applies here. No matter how good a lithium-ion battery is, it can easily swell if it's not charged with a good charger. This is because the parameters of each charger are different, especially regarding overcharging, overcurrent, and overpower. Overcharging with a charger for too long can damage the lithium-ion battery pack.
3. Prolonged exposure to high temperatures
To extend the lifespan of lithium-ion battery packs, ambient temperature is a crucial factor, which is also a major reason for lithium-ion batteries bulging. High temperatures will cause the battery to heat up, so avoid direct sunlight and unplug the charger when the battery is fully charged.
Reasons for battery swelling:
1. Issues with battery manufacturing quality: uneven electrode coating and relatively rough processing.
2. The violent reaction of a short circuit generates a large amount of heat, which in turn causes the electrolyte to vaporize, causing the battery to swell.
3. In addition, batteries may bulge if they are not used for a long time. This is because air is conductive to a certain extent. Therefore, leaving the battery unused for too long is equivalent to the positive and negative terminals of the battery directly touching, resulting in a slow short circuit.
Will swelling of a polymer lithium-ion battery increase its weight?
Of course not. As far as batteries are concerned, there is neither the addition nor the subtraction of any substances. It is only that the solid or liquid substances inside the battery change state and become gaseous, thus changing their volume. In accordance with the law of conservation of mass, the weight remains unchanged.
The correct way to charge a lithium-ion battery pack:
In summary, the most important reminder regarding the charging and discharging of lithium-ion battery packs during use is...
1. Charge according to the standard time and procedure, even for the first three times;
2. When the machine displays a low battery warning, you should start charging it as soon as possible;
3. Activation of the lithium-ion battery pack does not require any special method; the lithium-ion battery will activate naturally during normal use of the machine.
4. Use the original charger whenever possible, and use qualified lithium-ion battery chargers manufactured by reputable manufacturers. Do not charge for more than 10 hours at a time.
There are many reasons why lithium-ion batteries bulge. A friendly reminder: if a lithium-ion battery pack bulges, it should never be used again. Recycling is not currently practical in my country; it must be disposed of as a waste.
