Lithium battery safety

In order to avoid over discharging or overcharging 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, and when the temperature is too high, the power supply will automatically stop; The second is to select an appropriate separator material. When the temperature rises to a certain value, the micron sized micropores on the separator will automatically dissolve, preventing lithium ions from passing through and stopping the internal reaction of the battery; The third is to set a safety valve (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.
Sometimes, although the battery itself has safety control measures, due to certain reasons, the control fails, there is a lack of safety valves, or the gas cannot be released through the safety valves in time, and the internal pressure of the battery can rise sharply, causing an explosion.
In general, the total energy stored by lithium ion batteries is inversely proportional to their safety. As the battery capacity increases, the battery size also increases, and its heat dissipation performance deteriorates, resulting in a significant increase in the likelihood of accidents. For lithium ion batteries for 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 adopt forced cooling.
Choosing a safer electrode material and lithium manganate ensures a fully charged state in terms of molecular structure. The lithium ions in the positive electrode have been completely embedded in the carbon pores of the negative electrode, fundamentally avoiding the generation of dendrites. At the same time, the stable structure of lithium manganate makes its oxidation performance far lower than that of lithium cobalt oxide, and the decomposition temperature exceeds 100 ℃ of lithium cobalt oxide. Even if internal short circuits (acupuncture), external short circuits, and overcharging occur due to external forces, the danger of combustion and explosion caused by the precipitation of metal lithium can be completely avoided.
In addition, the use of lithium manganate materials can also 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. Select a membrane with good thermal shutdown performance. The function of the membrane is to isolate the positive and negative electrodes of the battery while allowing the passage of lithium ions. When the temperature rises, it is closed before the membrane melts, thereby increasing the internal resistance to 2000 ohms and stopping the internal reaction.
When the internal pressure or temperature reaches a preset standard, the explosion-proof valve will open and begin to relieve pressure to prevent excessive accumulation of internal gas, causing deformation, and ultimately causing the shell to burst.
Improving control sensitivity, selecting more sensitive control parameters, and adopting joint control with multiple parameters (especially important for large capacity batteries). For large capacity lithium ion battery packs, they are composed of multiple battery cells in series/parallel. For example, if the voltage of a notebook computer is above 10V, and the capacity is large, it is generally possible to use 3-4 single batteries in series to meet the voltage requirements, and then connect 2-3 battery packs in series 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: Level 1 protection IC (to prevent overcharge, over discharge, and short circuit of the battery), Level 2 protection IC (to prevent the 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 notebook computer, the notebook battery can only be switched to the automatic protection state. If the situation is not serious, it can often work 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 summary, 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.