Thermal Properties of Lithium‐Ion Battery and Components

Experimental thermal property data of the Sony US-18650 lithium-ion battery and components are presented, as well as thermal property measuring techniques. The properties in question are specific heat capacity (Csub p), thermal diffusivity (alpha), and thermal conductivity (kappa), in the presence and absence of electrolyte 1 M LiPFsub 6 in ethylene carbonate-dimethyl carbonate (EC: DMC, 1: 1 wt %). The heat capacity of the battery, Csub p, is 0. 96 +- 0. 02 J/g K at an open-circuit voltage (OCV) of 2. 75 V, and 1. 04 +- 0. 02 J/g K at 3. 75 V. The thermal conductivity, kappa, was calculated from kappa identicalₜo alpharhoCsub p where alpha was measured by a xenon-flash technique. In the absence of electrolyte, kappa increases with OCV, for both the negative electrode (NE) and the positive electrode (PE). For the NE, the increase is 26% as the OCV increases from 2. 75 to 3. 75 V, whereas for the PE the increase is only 5 to 6%. The dependence of both Csub p and kappa on OCV is explained qualitatively by considering the effect of lithiation and delithiation on the electron carrier density, which leads to n-type semiconduction in the graphitic NE material, but a change from semiconducting to metallic character in Lisubmore » xCoOsub 2 PE material. The overall effect is an increase of Csub p and kappa with OCV. For kappa this dependence is eliminated by electrolyte addition, which, however, greatly increases the effective kappa of the layered battery components by lowering the thermal contact resistance. For both NE and PE, the in-plane kappa value (measured along layers) is nearly one order of magnitude higher than the cross-plane kappa. This is ascribed mostly to the high thermal conductivity of the current collectors and to a lesser extent to the orientation of particles in the layers of electrodes. « less