Abstract
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 , thermal diffusivity (α), and thermal conductivity (k), in the presence and absence of electrolyte [1 M in ethylene carbonate‐dimethyl carbonate EC:DMC, 1:1 wt %)]: The heat capacity of the battery, , is at an open‐circuit voltage (OCV) of 2.75 V and at 3.75 V. The thermal conductivity, k, was calculated from where α was measured by a xenon‐flash technique. In the absence of electrolyte, k 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 and k 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 PE material. The overall effect is an increase of and k with OCV. For k this dependence is eliminated by electrolyte addition, which, however, greatly increases the effective k of the layered battery components by lowering the thermal contact resistance. For both NE and PE, the in‐plane k value (measured along layers) is nearly one order of magnitude higher than the cross‐plane k. 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. © 1999 The Electrochemical Society. All rights reserved.