Safety of lithium battery
In order to avoid over discharge or over charging of the battery due to improper use, a triple protection mechanism is set in the single lithium-ion battery.
First, the switching element is adopted. When the temperature in the battery rises, its resistance will rise. When the temperature is too high, the power supply will be automatically stopped;
Second, select appropriate separator materials. When the temperature rises to a certain value, the micron micropores on the separator will dissolve automatically, so that lithium ions cannot pass through and the internal reaction of the battery will stop;
Third, set the safety valve (i.e. the vent hole on the top of the battery). When the internal pressure of the battery rises to a certain value, the safety valve will open automatically to ensure the safety of the battery.
Sometimes, although the battery itself has safety control measures, the control fails due to some reasons. If there is no safety valve or the gas cannot be released through the safety valve, the internal pressure of the battery will rise sharply and cause an explosion.
Generally, the total energy stored by lithium-ion battery is inversely proportional to its safety. With the increase of battery capacity, the battery volume is also increasing, its heat dissipation performance becomes worse, and the possibility of accidents will increase significantly. 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 high-capacity lithium-ion batteries, especially for automobiles, it is particularly important to adopt forced heat dissipation.
Selecting safer electrode materials and lithium manganate materials ensures that the lithium ion of the positive electrode has been completely embedded into the carbon hole of the negative electrode in the fully charged state in terms of molecular structure, so as to fundamentally avoid the generation of dendrites. At the same time, the stable structure of lithium manganate makes its oxidation performance far lower than that of lithium cobaltate, and the decomposition temperature exceeds 100 ℃ of lithium cobaltate. Even if there is internal short circuit (acupuncture), external short circuit and overcharge due to external force, the danger of combustion and explosion caused by the precipitation of metal lithium can be completely avoided.
In addition, the cost can be greatly reduced by using lithium manganate material.
To improve the performance of the existing safety control technology, we must first improve the safety performance of lithium-ion battery cells, which is particularly important for high-capacity batteries. Select a diaphragm with good thermal closing performance. The function of the diaphragm is to isolate the positive and negative poles of the battery and allow the passage of lithium ions. When the temperature rises, it is closed before the diaphragm melts, so as to increase the internal resistance to 2000 ohms and stop the internal reaction.
When the internal pressure or temperature reaches the preset standard, the explosion-proof valve will open and start pressure relief to prevent excessive internal gas accumulation and deformation, resulting in shell burst.
Improve control sensitivity Select more sensitive control parameters and joint control with multiple parameters (this is particularly important for high-capacity batteries). The high-capacity lithium-ion battery pack is composed of multiple cells in series / parallel. For example, the voltage of notebook computer is more than 10V and the capacity is large. Generally, 3 ~ 4 single batteries in series can meet the voltage requirements, and then 2 ~ 3 battery packs in series can be connected in parallel to ensure large capacity.
The high-capacity battery pack itself must be equipped with relatively perfect protection function, Two circuit board modules shall also be considered: protection board PCB module and smart battery gauge board module. The complete battery protection design includes: Level 1 protection IC (to prevent battery overcharge, over discharge and short circuit), level 2 protection IC (to prevent the second overvoltage), fuse, LED indication, temperature regulation and other components.
Under the multi-level protection mechanism, even when the power charger and notebook computer are abnormal, the notebook battery can only change to the automatic protection state. If the situation is not serious, it often works normally after re plugging without explosion.
The underlying technology of lithium-ion batteries used in laptops and mobile phones is unsafe, and a safer structure needs to be considered.
In short, with the progress of material technology and people's deepening understanding of the requirements for the design, manufacture, detection and use of lithium-ion batteries, lithium-ion batteries will become safer in the future.