In addition to expensive pricing, low driving ranges, and insufficient charging and switching infrastructure, the safety of the ion lithium power pack is a major worry for customers and experts throughout the development of new energy vehicles. This problem also has an impact on promoting the energy of the ion lithium power pack. The key to dealing with the safety of the power ups lithium ion battery is the creation of short-circuit-proof, overcharge-proof, thermal runaway-proof, combustion-proof, and non-flammable electrolytes.
1. In addition to the regular charging and discharging events, the ion lithium power pack contains several possible exothermic side reactions. These exothermic side reactions are easily initiated when the temperature of the ups lithium ion battery or the charging voltage is too high.
2. Important ups lithium ion battery overheating side effects include: at temperatures over 130°C, the SEI coating decomposes, causing the electrolyte to disintegrate and release substantial amounts of heat in the exposed highly activated carbon cathode surface. Meanwhile, the temperature of the in ups lithium ion battery increases. This is the source of the battery's thermal runaway.
3. The exothermic thermal breakdown of the positive electrode charging state, together with subsequent electrolyte decomposition driven by active oxygen, increased the accumulation of heat within the ups lithium ion battery, encouraging thermal runaway.
4. Thermal degradation of the electrolyte results in exothermic decomposition of the electrolyte, causing the battery temperature to rise faster, so that the ups lithium ion battery binder reacts with the highly reactive negative electrode. The reaction between LixC6 and PVDF starts at around 240°C, with a peak temperature of 290°C and a reaction heat of 1500 J/g. The oxidative degradation of the organic electrolyte and the development of organic small molecules gas, which result in an increase in the battery's internal pressure and temperature, are key overcharge side reactions.
5. When the heat generation rate of the exothermic side reaction exceeds the heat dissipation rate of the ion lithium power pack, the internal temperature of the battery rapidly rises and enters a state of uncontrollable self-heating, referred to as thermal runaway, which leads to battery combustion. The slower the heat dissipation is, the greater the heat output of a thicker and bigger battery is, and the more probable it is to pose safety issues.
The following three circumstances are the most common causes of short circuits:
1) ion lithium power pack diaphragm surface conductive dust, positive and negative electrode misalignment, electrode burr, uneven electrolyte distribution, and other process factors;
2) metal impurities in the material;
3) low temperature charging, high current charging, negative electrode performance decay too fast resulting in lithium precipitation on the negative electrode surface, vibration or collision, and other application processes.
There are other overcharging issues including local overcharging of an ion lithium power pack induced by high current charging, local overcharging caused by uneven electrode coating and electrolyte distribution, and overcharging factors such rapid deterioration of positive electrode performance.
For the safety of the ion lithium power pack, because the thermal breakdown of the cathode material is just a part of the thermal runaway reaction, iron phosphate ups lithium ion battery is not completely safe from a theoretical standpoint. Large-capacity batteries installed in cars should be cautious.
Second, because of the probability of battery detection, even the ion lithium power pack that passes the safety testing cannot be guaranteed to be completely safe. Batteries that have been subjected to low temperature charging, as well as battery modules and packs, should all be evaluated for safety after a set number of weeks of full charge and discharge cycles.
Furthermore, manufacturers try to keep the ambient temperature of the ion lithium power pack in the range of 2045°C as much as possible during the use of the power pack, which not only improves battery life and reliability, but also prevents short circuit and high temperature thermal runaway problems caused by low temperature lithium precipitation.