Investigation on lithium-ion battery electrochemical and thermal characteristic based on electrochemical-thermal coupled model

A lithium-ion battery consists of numerous electrochemical cell units, and is treated as an assembly of one dimensional (1D) cell unit connected in parallel. The electrochemical and thermal characteristics of 1D cell unit have a great influence on battery performance. The thermal behavior and the dynamic evolution of electrochemical reaction in the cell are simulated. At lower discharge rate, reversible heat dominates the heat generation, but the proportion of irreversible heat gradually increases with the discharge rate. Non-uniform distribution of heat generation and electrochemical reaction rate in the cell increase with the discharge rate. Temperature has little effect on average heat generation rate and mainly influences the distribution uniformity of electrochemical reaction rate and heat generation in the cell. The temperature distribution in a battery is researched based on multi-cell 1D model. It is found that temperature in the battery presents a parabolic distribution in the laminated direction and the temperature gradient significantly increases with the cells number, which is mainly induced from the lower heat conductivity in the laminated direction. The bulk temperature will be decreased and safety of battery will be improved with the increase of cooling strength, but the temperature difference within the battery will be significant increased simultaneously. The number of cell can't exceed 80 for a monomer battery with this electrode thickness and an active battery thermal management system (such as forced air cooling and liquid cooling system) is also indispensable to keep the temperature difference and surface temperature in the reasonable range at 5C discharge rate. At the same time, the thickness of the battery need to be chosen based on the application.