Isocyanate Additives Improve the Low-Temperature Performance of LiNi0.8Mn0.1Co0.1O2||SiOx@Graphite Lithium-Ion Batteries

Study on the electrical-thermal properties of lithium-ion battery materials in the NCM622/graphite system

The phenomenon of fire or even explosion caused by thermal runaway of lithium-ion power batteries poses a serious threat to the safety of electric vehicles. An in-depth study of the core-material thermal runaway reaction mechanism and reaction chain is a prerequisite for proposing a mechanism to prevent battery thermal runaway and enhance battery safety. In this study, based on a 24 Ah commercial Li(Ni0.6Co0.2Mn0.2)O2/graphite soft pack battery, the heat production characteristics of different state of charge (SOC) cathode and anode materials, the separator, the electrolyte, and their combinations of the battery were investigated using differential scanning calorimetry. The results show that the reaction between the negative electrode and the electrolyte is the main mode of heat accumulation in the early stage of thermal runaway, and when the heat accumulation causes the temperature to reach a certain critical value, the violent reaction between the positive electrode and the electrolyte is triggered. The extent and timing of the heat production behaviour of the battery host material is closely related to the SOC, and with limited electrolyte content, there is a competitive relationship between the positive and negative electrodes and the electrolyte reaction, leading to different SOC batteries exhibiting different heat production characteristics. In addition, the above findings are correlated with the battery failure mechanisms through heating experiments of the battery monomer. The study of the electro-thermal properties of the main materials in this paper provides a strategy for achieving early warning and suppression of thermal runaway in batteries.

Co-Intercalation-Free Graphite Anode Enabled by an Additive Regulated Interphase in an Ether-Based Electrolyte for Low-Temperature Lithium-Ion Batteries

Graphite (Gr) anode, which is endowed with high electronic conductivity and low volume expansion after Li-ion intercalation, establishes the basis for the success of rocking-chair Li-ion batteries (LIBs). However, due to the high barrier of the Li-ion desolvation process, sluggish transport of Li ions through the solid electrolyte interphase (SEI) and the high freezing points of electrolytes, the Gr anode still suffers from great loss of capacity and severe polarization at low temperature. Here, 1,2-diethoxyethane (DEE) with an intrinsically wide liquid region and weak solvation ability is applied as an electrolyte solvent for LIBs. By rationally designing the additives of electrolytes, an intact SEI with fast Li-ion conductivity is constructed, enabling the co-intercalation-free Gr anode with long-term stability (91.8% after 500 cycles) and impressive low-temperature characteristics (82.6% capacity retention at -20 °C). Coupled with LiFePO4 and LiNi0.8Mn0.1Co0.1O2 cathodes, the optimized electrolyte also demonstrates low polarization under -20 °C. Our work offers a feasible approach to enable ether-based electrolytes for low-temperature LIBs.