Electrical and thermal characterisation of Lithium-Ion cells under isothermal conditions for optimal lifetime performance

Abstract

Lithium-Ion cell performance is sensitive to the cell temperature. An experimental approach is taken to identify the optimal cell isothermal condition. Previous studies investigated a cell’s performance under adiabatic or controlled environmental temperature (i.e. isoperibolic) conditions. Notably, these conditions do not impose a uniform cell surface temperature or a controlled cooling rate, as an active Thermal Management System (TMS) would. A novel experimental approach is proposed, replicating an active TMS for testing cells in isothermal conditions. The test rig maintains a stable cell surface temperature and minimises temperature variance for discharge rates of up to 2C and temperatures between 0oC - 40oC. The electrical, thermal, electrochemical performance and ageing of a 300mAh LCO Li-Ion pouch cell are investigated. An optimal isothermal condition which maximises the cell electrochemical efficiency and minimises its ageing is identified in the range of 25oC-35oC. A passive TMS based on Phase Change Materials (PCM) integrated with a Direct-Metal-Laser-Sintered (DMLS) aluminium heat exchanger is designed to keep the cell at the identified optimal temperature. The DMLS HEX is proposed to enhance the thermal conductivity of the TMS. The results show that PCMs have significant potential as passive TMS but the optimisation of the PCM-TMS is case-dependent