Fires caused by lithium batteries have been reported many times, and the safety hazards are all around us. How does the risk of spontaneous combustion of lithium batteries arise? Is there any improvement program to make it much lower risk of spontaneous combustion?
Why lithium batteries are prone to spontaneous combustion
When the internal temperature of the lithium battery reaches about 70 ℃, the negative electrolyte membrane begins to decompose, self-exothermic reaction occurs, as the temperature rises further, a number of side reactions affect each other, so the battery produces bulging, expansion until thermal runaway.
However, the current development of high security, high energy density semi-solid state, all-solid state lithium batteries, due to the existence of harsh production environment requirements, the production process is cumbersome and complex, low yield, expensive and other issues, delayed production. If the old battery internal wiring arrangement appears aging, loose, and then bumps in the transportation process, will also lead to line short circuit, battery abnormal heat release, thermal runaway.
Common methods to prevent lithium battery explosion
In order to control the risk of lithium battery explosion, according to the regulations, the rated energy more than 160Wh charging treasure can not be carried on the airplane. When traveling on high-speed railways, rechargeable batteries need to meet the requirements that the logo is clearly visible and the rated energy of a single piece does not exceed 100Wh. Passengers traveling by passenger shuttle bus when carrying the rechargeable treasure, lithium batteries shall not exceed 5, single rated capacity shall not exceed 20000mAh. According to experts: "the use of battery management system to monitor the battery's voltage, current, temperature and other conditions, once found that a cell abnormalities, the battery should be disconnected immediately from the system and the system's connection and alarm. At present, to prevent lithium battery explosion there are battery cooling system, fine water mist thermal runaway protection, pressure relief suppression system and battery thermal insulation system four methods."
Aerogel felt heat insulation "star"
Compared with other thermal insulation materials, aerogel felt with lower thermal conductivity, better high temperature performance stands out as the current mainstream battery insulation piece "new favorite". In addition, a professor said that the composite phase change material can absorb the heat emitted by the battery thermal runaway, and also has a significant effect on slowing down the spread of thermal runaway.
Experts said that the high energy density of high nickel ternary lithium batteries in high-end electric vehicles in the application of the gradual increase. But high nickel ternary safety is poor, in the thermal runaway its maximum temperature can exceed 1000 ℃. Aerogel is a kind of heat insulation material to block the heat spread of the battery, but ordinary silicone-based aerogel can generally only isolate the temperature of about 600 ℃, not applicable to high-nickel ternary lithium battery.
A team developed and mass-produced 1200 ℃ high temperature resistant silicon oxide aerogel material has been successfully applied to lithium-ion power battery core group between the heat insulation. "The material for the core group constructed a high-performance 'firewall', well blocked the thermal runaway process of heat spreading, equivalent to the lithium battery to wear a safe 'heat insulation suit', but also for the safety of people's lives to wear a 'protective suit'. 'protective clothing'." The relevant members said.
Aerogel nanoscale mesh bone structure holes in more than 99% of the gap filled by air, air is a poor conductor of heat, and aerogel air in the grid tripped "feet" can not flow, so the thermal conductivity of the air is lower, to become a heat insulation "star".
Professionals said that if this accident in the battery using the aerogel felt insulation material, a single battery thermal runaway release of limited energy will be blocked, will not quickly heat spread to neighboring batteries triggering deflagration, is expected to give passengers enough time to escape. The fire may even be extinguished at an early stage without causing spontaneous combustion of the electric bus, resulting in major personal safety and property accidents. They are particularly looking forward to the new technology they have developed to play a strong protective role in their lives as soon as possible.
