Briefly describe the new progress made in the research on thermal safety of automotive power batteries

　　The thermal safety of power batteries is one of the key issues affecting the driving safety of electric vehicles. In the implementation of the national key R&D plan "New Energy Vehicles" special project in 2016, "High specific energy power lithium-ion battery development and industrialization technology research", the R&D team focused on the thermal safety mechanism and safety design of high specific energy lithium-ion power batteries In-depth research has been carried out and phased progress has been made.

　　The project team focused on the heat generation process and the thermal stability of each component of the lithium-ion battery during the charging and discharging process, taking 1Ah lithium-ion battery as the research object, and obtaining the apparent thermal conductivity, anisotropic thermal conductivity, and constant pressure through experiments Specific heat capacity, temperature coefficient and internal resistance at room temperature to calculate the birth heat rate. Qualitative analysis of the thermal stability of the positive and negative materials of the battery in the two states of 100% power and 0% power and the influence of the electrolyte on its thermal stability are analyzed. In the thermal runaway part of the battery, accelerated calorimetry was used to conduct thermal runaway experiments on a 100% power soft-pack lithium-ion battery, and the starting temperature, maximum temperature and self-heating rate of the thermal runaway of the battery were determined. Relevant research results and test results provide a theoretical and data basis for the thermal safety structure design of power batteries.

　　The project team focused on the application process and technology of thermosetting polymer materials and positive temperature coefficient thermal materials (PTC materials) in battery cells, combined with physical and chemical analysis testing, electrochemical testing, electrical performance testing, and battery safety performance testing. The application process of thermosetting polymer materials in the battery is achieved, and the purpose of optimizing the application process flow is achieved; the concentration of the modification solution, the modification method and the coating thickness of the positive temperature coefficient thermosensitive material (PTC material) are studied for the electrical performance and safety of the battery. The impact of performance, and then optimize the application process and technology of PTC materials. At present, the project research results provide process and technical guidance for the application of thermoset polymer materials and PTC materials in battery cells, and solve the basic and key technologies for the application of thermoset polymer materials and PTC materials in battery cells. It has laid a good foundation to solve the problem of thermal runaway of battery cells.