Dilatometric investigations of graphite electrodes in nonaqueous lithium battery electrolytes

A relatively uncommon technique known as in situ electrochemical dilatometry can be used to record the macroscopic expansion (dilatation) and contraction of graphite samples during charge/discharge in Li+ cation-containing nonaqueous electrolytes. Several electrolytes based on solvent mixtures such as ethylene carbonate/dimethyl carbonate, pure propylene carbonate (PC), and PC with additional solvents (ethylene sulfite or chloroethylene carbonate) have been investigated. The dilatometer yields a clear distinction between solvated lithium intercalation/deintercalation occurring in pure PC (relative expansion of the order of >100%) and the corresponding unsolvated processes occurring in the other electrolytes (theoretical relative expansion of the order of 10%). Exfoliation of graphite due to solvated lithium intercalation may destroy the graphite sample. The penetration of electrolyte into pores or fissures of the exfoliated sample can also be monitored by dilatometry. Hence, dilatometry provides relevant information concerning the feasibility of a given electrolytic solution for rechargeable lithium-ion cells with graphite as the negative electrode. Limitations and advantages of the electrochemical dilatometer and specific experimental features of the instrument are addressed. (C) 2000 The Electrochemical Society. S0013-4651(99)08-126-4. All rights reserved.