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Abstract

First order phase transitions have been detected electrochemically in intercalation batteries. The quantity dQ/dV peaks when the phase front associated with a first order phase transition moves through an intercalation compound, where V is the cell's voltage and Q is the charge that flows. The divergence of dQ/dV is analogous to the divergence of the compressibility of a gas when a first order phase transition occurs. dQ/dV can be measured by the standard electrochemical technique of linear sweep voltammetry, but resolution and clarity are vastly improved by measuring dQ/dV at constant current, which minimizes the distortions in dQ/dV due to kinetic effects. The phase diagram of the lithium intercalated layer compound has been constructed. Applications of dQ/dV measurements to phase transitions in other intercalation systems and to single phase regions are discussed.