In order to avoid over discharge or overcharging of the battery due to improper use, a triple protection mechanism is installed inside the single lithium-ion battery. One is the use of switching elements. When the temperature inside the battery rises, its resistance increases accordingly. When the temperature is too high, the power supply will automatically stop; The second is to choose appropriate partition materials. When the temperature rises to a certain value, the micron sized micropores on the partition will automatically dissolve, preventing lithium ions from passing through and stopping internal reactions in the battery; The third is to set a safety valve (which is the vent hole on the top of the battery). When the internal pressure of the battery rises to a certain value, the safety valve automatically opens to ensure the safety of the battery's use.
Sometimes, although the battery itself has safety control measures, due to certain reasons, the control fails, and there is a lack of safety valve or gas cannot be released through the safety valve in time, causing the internal pressure of the battery to rise sharply and cause an explosion.
In general, the total energy stored in lithium-ion batteries is inversely proportional to their safety. As the battery capacity increases, the battery volume also increases, leading to poor heat dissipation performance and a significant increase in the likelihood of accidents. For lithium-ion batteries used in mobile phones, the basic requirement is that the probability of safety accidents 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 those used in automobiles, it is particularly important to use forced cooling.
Choosing a safer electrode material and lithium manganese oxide material ensures a fully charged state in terms of molecular structure. The lithium ions in the positive electrode are fully embedded in the negative electrode carbon pores, fundamentally avoiding the generation of dendrites. At the same time, the stable structure of lithium manganese oxide makes its oxidation performance much lower than that of lithium cobalt oxide, and the decomposition temperature exceeds 100 ℃ of lithium cobalt oxide. Even if internal short circuits (punctures), external short circuits, and overcharging occur due to external forces, the danger of combustion and explosion caused by the precipitation of lithium metal can be completely avoided.
In addition, the use of lithium manganese oxide material can significantly reduce costs.
To improve the performance of existing safety control technologies, the first step is to improve the safety performance of lithium-ion battery cells, which is particularly important for large capacity batteries. Choose a diaphragm with good thermal shutdown performance. The function of the diaphragm is to isolate the positive and negative poles of the battery while allowing the passage of lithium ions. When the temperature rises, it is closed before the diaphragm melts, causing the internal resistance to rise to 2000 ohms and stopping the internal reaction.
When the internal pressure or temperature reaches the preset standard, the explosion-proof valve will open and begin to relieve pressure to prevent excessive accumulation of internal gas and deformation, ultimately causing the shell to burst.
Improving control sensitivity, selecting more sensitive control parameters, and adopting joint control with multiple parameters (this is particularly important for large capacity batteries). For a large capacity lithium-ion battery pack, it is composed of multiple battery cells in series/parallel. For example, if the voltage of a laptop is above 10V and the capacity is large, usually 3-4 single batteries are connected in series to meet the voltage requirements. Then, 2-3 series connected battery packs are connected in parallel to ensure a larger capacity.
The large capacity battery pack itself must be equipped with relatively complete protection functions, and two types of circuit board modules should also be considered: the Protection Board PCB module and the Smart Battery Gauge Board module. The complete battery protection design includes: first level protection IC (to prevent overcharging, discharging, and short circuit of the battery), second level protection IC (to prevent second overvoltage), fuses, LED indicators, temperature regulation, and other components.
Under the multi-level protection mechanism, even in the event of an abnormality in the power charger or laptop, the laptop battery can only transition to an automatic protection state. If the situation is not serious, it often works normally after being re plugged and unplugged, without explosion.
The underlying technology used in lithium-ion batteries for laptops and mobile phones is unsafe, and a more secure structure needs to be considered.
In short, with the progress of material technology and the deepening understanding of the requirements for the design, manufacturing, testing, and use of lithium-ion batteries, future lithium-ion batteries will become safer.