Accelerating rate calorimetry study on the thermal stability of lithium intercalated graphite in electrolyte I. Experimental

An accelerating rate calorimeter (ARC) was used to measure the thermal stability of a lithiated mesocarbon microbead (MCMB) material in electrolyte under adiabatic conditions. Measurements were carried out to determine the effects of the lithium content and surface area of the electrode as well as the effects of the electrolyte type and the initial heating temperature on thermal stability. MCMB electrodes with both high and low surface area were reacted electrochemically to three compositions: Li0.8C6 (0.0 V), Li0.45C6 (0.89 V), and Li0.2C6 (0.127 V) in LiPF6 ethylene carbonate/diethyl carbonate (EC:DEC) (33:67) electrolyte. The low-surface-area MCMB samples were also lithiated in LiPF6 EC:DEC (50:50) and LiBF4 EC:DEC (50:50) electrolytes The results showed that self-heating of the MCMB samples depends on (i) the initial lithium content of the material; (ii) the electrolyte used; (iii) the surface area, and (iv) the initial heating temperature of the sample. Measurable self-heating in the LiPF6 EC:DEC (33:67) samples was detected at 80 degrees C, at 70 degrees C for MCMB in LiPF6 EC:DEC (1:1), and at 50 degrees C for MCMB in LiBF4 EC:DEC (1:1). The initial self-heating rate for samples containing LiPF6 EC:DEC (33:67) electrolyte could be fit by an Arrhenius relation with an activation energy of 1.4 eV. The initial form of the self-heating rate profile was a result of the conversion of metastable solid electrolyte interface (SEI) components to stable SEI components. (C) 1999 The Electrochemical Society. S0013-4651(98)10-028-9. All rights reserved.