In order to avoid over-discharge or over-charge of the battery due to improper use, a triple protection mechanism is set up in the single lithium-ion battery. First, a switch element is used. When the temperature inside the battery rises, its resistance value rises accordingly. When the temperature is too high, it will automatically stop supplying power; second, an appropriate separator material is selected. When the temperature rises to a certain value, the micron-level micropores on the separator will automatically dissolve, so that lithium ions cannot pass through and the internal reaction of the battery stops; third, a safety valve (the vent hole on the top of the battery) is set. When the internal pressure of the battery rises to a certain value, the safety valve automatically opens to ensure the safety of the battery.
Sometimes, although the battery itself has safety control measures, the control fails for some reason, the safety valve is missing or the gas is not released through the safety valve in time, and the internal pressure of the battery will rise sharply and cause an explosion.
In general, the total energy stored in a lithium-ion battery is inversely proportional to its safety. As the battery capacity increases, the battery volume also increases, its heat dissipation performance deteriorates, and the possibility of an accident will increase significantly. For lithium-ion batteries used in mobile phones, the basic requirement is that the probability of a safety accident should be less than one in a million, which is also the minimum standard acceptable to the public. For large-capacity lithium-ion batteries, especially for automobiles, it is particularly important to use forced heat dissipation.
Choose safer electrode materials, such as lithium manganate materials. In terms of molecular structure, it is ensured that the lithium ions of the positive electrode are completely embedded in the carbon pores of the negative electrode when fully charged, which fundamentally avoids the formation of dendrites. At the same time, the stable structure of lithium manganate makes its oxidation performance much lower than that of lithium cobalt oxide, and its decomposition temperature exceeds that of lithium cobalt oxide by 100°C. Even if an internal short circuit (needle puncture) or an external short circuit occurs due to external force, the danger of combustion and explosion caused by the precipitation of metallic lithium can be completely avoided during overcharging.
In addition, the use of lithium manganate materials can also greatly reduce costs.
To improve the performance of existing safety control technologies, the safety performance of lithium-ion battery cells must first be improved, which is particularly important for large-capacity batteries. Choose a diaphragm with good thermal shutdown performance. The function of the diaphragm is to allow the passage of lithium ions while isolating the positive and negative electrodes of the battery. When the temperature rises, it is closed before the diaphragm melts, so that the internal resistance rises to 2000 ohms, stopping the internal reaction.
When the internal pressure or temperature reaches the preset standard, the explosion-proof valve will open and start to release the pressure to prevent excessive internal gas accumulation, deformation, and eventually cause the shell to burst.
Improve control sensitivity, select more sensitive control parameters, and use joint control of multiple parameters (this is especially important for large-capacity batteries). For large-capacity lithium-ion battery packs, they are composed of multiple cells in series/parallel. For example, the voltage of a laptop computer is above 10V and the capacity is large. Generally, 3 to 4 single cells in series can meet the voltage requirements, and then 2 to 3 battery packs in series are connected in parallel to ensure a larger capacity.
Large-capacity battery packs themselves must be equipped with more complete protection functions, and two circuit substrate modules should also be considered: protection circuit substrate (Protection Board PCB) module and Smart Battery Gauge Board module. The complete battery protection design includes: first-level protection IC (to prevent battery overcharge, over discharge, and short circuit), second-level protection IC (to prevent the second overvoltage), fuse, LED indicator, temperature adjustment and other components.
Under the multi-level protection mechanism, even if the power charger or laptop computer has an abnormality, the laptop battery can only switch to the automatic protection state. If the situation is not serious, it can often work normally after re-plugging and will not explode.
The underlying technology used in the lithium-ion batteries used in laptops and mobile phones is unsafe, and a safer structure needs to be considered.
In short, with the advancement of material technology and people's deepening understanding of the requirements for lithium-ion battery design, manufacturing, testing and use, lithium-ion batteries will become safer in the future.