Lithium battery packs do not have memory effect, why do they still bulge?
Lithium battery packs, due to their inherent characteristics, do not have memory effects and can be charged and discharged at will. However, why are there still so many accidents of lithium battery explosions and bulges? After research, it was found that the internal diaphragm was damaged, causing gas to be generated inside the battery. Or the charger used for the lithium battery pack does not meet the requirements, causing the battery to bulge. Now let's talk in detail about the reasons for lithium battery bulging.
Explanation of lithium battery pack without memory effect:
The battery memory effect refers to the reversible failure of a battery, that is, the performance of a battery that can be restored after failure The memory effect refers to the automatic retention of a specific tendency of a battery after prolonged exposure to a specific working cycle.
The memory effect is a temporary capacity loss that can be restored after several deep flushing and playback sessions. Lithium batteries do not need to be used up and recharged, they can be charged as needed. Lithium battery packs do not have this effect, but they have a similar inertia effect (which is different from the memory effect in other batteries), which refers to the chemical substances inside the battery becoming lazy after not participating in the reaction for a long time and will not react, and deep charging and discharging are also useless. So there's no need to deliberately discharge when using it, just let it go naturally without any problems. It should be noted that the lifespan of lithium battery packs is basically fixed, with one less charge per charge. In addition, if not used for a long time, 30% of the battery should be retained and placed in a dry environment at 0 degrees Celsius. This can extend the lifespan.
Why do electric vehicle lithium battery packs bulge?
Reason 1: Lithium batteries undergo a chemical reaction between lead sulfate on the positive and negative plates and water in the electrolyte during charging, resulting in the reduction of the positive plate to lead oxide and the negative plate to pure lead. The temperature of the lithium battery pack will increase, and if a large amount of gas is released, it will cause insufficient space inside the battery to store these gases, leading to battery swelling.
Reason 2: The internal resistance of lithium batteries is too high. When the internal resistance of a battery is too high and the current is constant, the voltage will be very high (voltage=current * resistance). What we can see is that during normal charging, the red light has not yet turned on and the battery is already very hot, which means that the battery has not reached the charging voltage and has already released gas in advance!
Reason 3: The electric vehicle charger does not meet the requirements. When the parameters of the electric vehicle charger we use are higher than the rated voltage and current of our battery, it is possible to overcharge the lithium battery pack!
Kind suggestion:
1： Use an electric vehicle charger that meets the requirements, and you can go to a lithium battery repair point for specialized charger testing. Nowadays, many places offer free testing.
2： Regularly check the battery and maintain the lithium battery pack, which can extend the battery life and improve the service life of the electric vehicle.
3： Not suitable for long-term overcharging.
There are two types of lithium battery pack bulging during the charging and discharging process:
1、 Bulging caused by overcharging
Overcharging can cause all lithium atoms in the positive electrode material to run into the negative electrode material, resulting in deformation and collapse of the originally full grid of the positive electrode, which is also a major reason for the decrease in battery capacity of lithium batteries. During this process, the amount of lithium ions in the negative electrode increases, and excessive accumulation causes lithium atoms to grow tree stumps and crystals, leading to battery swelling.
2、 Lithium battery bulging caused by over discharge
During the initial charging and discharging process of liquid lithium-ion batteries, the electrode material reacts with the electrolyte at the solid-liquid interface, forming a passivation layer covering the surface of the electrode material. The formed passivation layer film can effectively prevent the passage of electrolyte molecules, but Li+can freely embed and detach through the passivation layer, possessing the characteristics of a solid electrolyte. The SEI film is not static and may undergo slight changes during charging and discharging, mainly due to reversible changes in some organic compounds. After excessive discharge of the battery, the SEI film undergoes reversible damage, which protects the negative electrode material and causes the negative electrode material to collapse, resulting in the phenomenon of lithium battery bulging.
Under what circumstances will mobile phone lithium batteries swell?
1. The quality of lithium batteries is inherently inferior
With the increase in the number of mobile phones, batteries have become increasingly diverse. Many manufacturers produce batteries, and in order to pursue profits, some counterfeit and inferior batteries are produced. The most important component of a battery is the battery cell. For inferior batteries, their quality is poor, with insufficient power and false capacity labels. Generally, high-quality batteries have a smooth surface and average softness and hardness, while inferior batteries have a very hard surface;
2. Using non original chargers
The saying goes that a good horse matches a good saddle. No matter how good the lithium battery is, if there is no good charger for charging, it is easy to cause lithium battery bulging. This is because the parameters of each charger are different, especially in terms of overcharging and overcurrent power. Charging the charger for too long can damage the lithium battery pack;
3. Long term exposure to high temperature environment
To extend the lifespan of lithium battery packs, environmental temperature is the main factor, which is also an important reason for lithium battery bulging. High temperature environments can cause the battery to heat up, avoiding direct sunlight. At the same time, it is best to unplug the battery when fully charged.
Reasons for battery swelling:
1. The problem of battery manufacturing level, uneven electrode coating, and rough production process;
2. The violent reaction of a short circuit generates a large amount of heat, which in turn leads to the decomposition and gasification of the electrolyte, causing the battery to bulge.;
3. In addition, if the battery is not used for a long time, it may also experience bulging, because air is conductive to a certain extent. Therefore, if the battery is left unused for too long, it is equivalent to direct contact between the positive and negative electrodes of the battery, causing a chronic short circuit.
Will bulging of polymer lithium batteries increase battery weight?
Of course not, for batteries, there is neither an increase nor a decrease in material, only the solid or liquid substances inside the battery change state to gas and change volume, and the weight does not change according to the principle of mass conservation.
The correct charging method for lithium battery packs:
In summary, the most important reminder regarding the charging and discharging issues of lithium battery packs during use is
1. Charge according to standard time and procedures, even for the first three times;
2. When there is a low battery prompt on the machine, it is advisable to start charging as soon as possible;
3. The activation of lithium battery packs does not require special methods, and the lithium battery will naturally activate during normal machine use;
4. Try to use original chargers and qualified lithium battery chargers produced by reputable manufacturers. Do not charge for more than 10 hours at a time.
There are many reasons for lithium battery bulges, and we kindly remind everyone that if a lithium battery pack bulges, it must not be used again. Recycling is currently not very practical in China. It can only be disposed of as scrap.
