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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 false(Cpfalse) , thermal diffusivity (α), and thermal conductivity (k), in the presence and absence of electrolyte [1 M LiPF6 in ethylene carbonate‐dimethyl carbonate EC:DMC, 1:1 wt %)]: The heat capacity of the battery, Cp , is 0.96±0.02Jg−1 K−1 at an open‐circuit voltage (OCV) of 2.75 V and 1.04±0.02Jg−1 K−1 at 3.75 V. The thermal conductivity, k, was calculated from k≡αρCp 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 Cp 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 LixCoO2 PE material. The overall effect is an increase of Cp 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.

An accelerated rate calorimeter in combination with a battery cycler and a precision multimeter was used to measure the heat dissipation from, and heat accumulated in, commercially available lithium-ion cells during cycling over a range of operating parameters within the limits recommended by the manufacturer. An integral energy balance was used to determine the total heat generated in the test cell during cycling. From the measurements during temperature transients 1 the heat capacity of the test cell was found to be relatively independent of temperature, ranging from 0.82 to 1.07 J g-K -'. This value agrees relatively well with separate measurements using an adiabatic calorimeter which yield slightly higher values. DC current interruption technique was used to determine the time-dependent area-specific impedance, , of the cell which was well correlated with steeply increased heat dissipation rate at the end of discharge. The reversible (entropic) heat effect derived from an energy balance was found to be exothermic during discharge and endothermic during charge. Using two different methods, values were obtained for the entropy of reaction (AS) during discharge of the cell. The resulting values obtained with method II, depending on the discharge rate, varied from -41.19 to -80.98 J K -' per g mole of Li and showed a weak dependence on temperature, in the 35 to 55"C range. The rate dependence of the AS values needs further examination in a future study. By extrapolating to zero rate, the reversible entropy of the faradaic reaction for this cell was found to be -37 _ 3 J Kl per g mole of Li within the temperature range. The entropic heat effect and the heat effect associated with nonfaradaic reactions are appreciable and should be included in thermal modeling.

A novel thermal-management system that incorporates phase-change material (PCM) is proposed and investigated for electric vehicle (EV) applications. A commercial finite-element (FE) software, PDEase2D™, was used to simulate the thermal behavior of EV battery modules with a PCM thermal management system. Simulation results show that the temperature profile of the cells integrated in the module design was substantially more uniform during discharge at different rates than without PCM. The PCM system is effective in thermally sensitive batteries such as Li-ion and most Li-polymer batteries with a significant reversible heat effect. The heat generated during discharge and stored as latent heat is then largely utilized during charge, and a smaller part of it is transferred to the surroundings. The stored heat will be rejected to the module when the battery is left to relax or when its temperature drops below the melting point of the PCM. This is an important advantage for EV operation under cold conditions or in space applications where the battery temperature drops significantly when an orbiting satellite moves from the light to the dark side of the earth.

Electrochemical-calorimetric measurements, in combination with the dc current interruption technique, were used to determine the change of entropy during discharge and charge of the Panasonic Li-ion cell CGR 18650H. The entropy coefficient dE eq /dT was found to vary from Ϫ0.6 mV K Ϫ1 in the discharged state to Ϫ0.1 mV K Ϫ1 in the fully charged state. An unexpected variation of large amplitude (from Ϫ0.1 to 0.25 and Ϫ0.75 back to Ϫ0.1 mV K Ϫ1 ) was observed in a narrow range of depth of discharge (DOD) near 0.23, between 3.95 and 4.10 V, curing charge as well as discharge. Thus, changes in the reversible heat, T⌬S, appear to be mainly responsible for the transient endothermic heat effect observed during discharge of these Li-ion cells, near DOD 0.23, between 4.035 and 3.975 V. This interpretation of the calorimetric measurements is confirmed by the fact that dE eq /dT measured at 4.0 V was positive (0.14 mV K Ϫ1 ). The unexpected strong variation of dE eq /dT near DOD 0.23 is due to the nearly simultaneous occurrence of a phase change in the cathode and a structural transformation (quasi-phase change) in the graphite anode.