(194a) Measurement of Internal Temperature of a Li-Ion Cell at Large Discharge Rates

Lithium-ion cells [1-2] have been investigated for a variety of energy storage and conversion processes in several applications including military systems, consumer electronics and electric vehicles [3-5]. The process of conversion of electrical energy to chemical energy and vice versa inherently produces heat [6-9], which results in increased cell temperature [10-12]. The operation of a Lithium-ion cell is based on several highly coupled phenomena involving multiple physical processes. For example, exothermic electrochemical reactions produce heat [6, 9, 13], which causes temperature rise. Since temperature directly affects the rates of electrochemical reactions and electrical impedances [6], therefore, the thermal performance of the cell in turn affects electrochemical and electrical performance. Cell performance, cycle life, and system safety all depend on temperature distribution in the cell, which, in turn, depends on heat generation rate within the cell and on heat removal rate at the cell surface. 

This paper presents a method for measurement of internal temperature of a Li-ion cell. The method is based on measurement of the outside temperature and extrapolation to the internal temperature based on the linear nature of the governing energy equations, and using a priori measurements of the internal and external temperatures on one cell in which a small hole has been drilled along the axis for internal temperature measurement. Measurements are found to be in good agreement with the theoretical model presented in the paper. Results illustrate a powerful way for indirect measurement of cell temperature during operation, and may be helpful in the design of thermal management strategies for high-rate electrochemical energy conversion.