Kinetics of Electrochemical Insertion and Extraction of Lithium Ion at SiO

Abstract

The kinetics of the electrochemical insertion and extraction of lithium ion at silicon monoxide (SiO) were investigated by ac impedance spectroscopy. The resultant Nyquist plots showed two semicircles at high and middle frequency regions. These two semicircles were attributed to lithium-ion transport resistance in a surface film and alloying reaction resistance (charge-transfer resistance), respectively. We evaluated the activation energies of the charge-transfer reaction from the temperature dependences of the interfacial conductivities. When an ethylene-carbonate-based electrolyte was used, the activation energy of the charge transfer was 32 kJ mol−1. This activation energy was much smaller than those at graphite electrode or positive electrode materials (around 50 kJ mol−1 or more). Based on these results, the charge transfer at SiO is exceptionally fast compared to those at other insertion materials. Furthermore, the activation energies of the charge transfer at SiO remained unchanged in various electrolytes. These results suggest that the charge-transfer kinetics at SiO is not influenced by the desolvation of lithium ion from solvent molecules.