关键词: 热失控, 热安全, 金属锂负极, 金属锂电池

Abstract:

Lithium ion batteries have been widely used in the fields of portable energy storage devices and electric vehicles due to their high energy density and high safety, and have a profound impact on modern society. However, the frequent occurrence of battery fire and explosion accidents has caused widespread concern of thermal runaway and thermal safety issues. Many reviews have reported the measures to mitigate thermal runaway of lithium ion batteries. Due to the use of graphite with a smaller capacity as the negative electrode material, the specific energy of lithium ion batteries has approached the theoretical limit, and there is an urgent need to develop more efficient electrode materials to meet the growing demand of the energy storage market. Lithium metal anode has smaller density, higher theoretical capacity and lower potential, which is the ideal anode material for the next generation of high energy density battery system. However, the high reactivity of lithium will cause uncontrollable lithium dendrite growth during the cycle, which may penetrate the separator and cause internal short circuit of the battery, and then cause thermal runaway, fire and even explosion. Therefore, the thermal runaway of lithium metal batteries are more complicated and serious, which hinders the commercial application of batteries. Aiming at the thermal runaway problem of lithium metal batteries, this article first introduces the causes of thermal runaway, which are mainly uncontrollable exothermic reactions caused by internal short circuits. The basic process of thermal runaway is divided into three stages. By analyzing the three characteristic temperatures and heating rate, it is proved that improving the thermal stability of electrolyte and seperator can alleviate thermal runaway. Then we investigated the influence of thermodynamics on the nucleation and growth of lithium dendrites, revealing the dual effects of temperature, and proving that a uniform thermal field is beneficial to obtain uniform lithium deposition and improve battery cycle performance and safety. Secondly, a variety of strategies to improve battery thermal safety are reviewed at the material level. In terms of liquid electrolytes, the development of non-flammable electrolyte systems includes the use of flame-retardant electrolytes and ionic liquid electrolytes with lower flammability. In addition, high-concentration electrolyte and local high-concentration electrolyte can change the solvation structure of lithium ions, and improve safety by reducing the number of free solvent molecules. In terms of separators, high thermal stability separators and thermal response separators with thermal shutdown function have been developed. The flame-retardant separators can release flame retardants to inhibit combustion. In addition, the new intelligent separators have dendrite detection, early warning and elimination functions, which effectively improve the safety and cycle life of the battery. In terms of solid electrolytes, thermally responsive polymer electrolytes have been developed to avoid thermal runaway through the strain function of polymer materials. Finally, further research on the thermal runaway of lithium metal batteries in the future is prospected.

Key words: Thermal runaway, Thermal safety, Lithium metal anode, Lithium metal battery