Electrochemical behavior of Li[Li0.2Co0.3Mn0.5]O2 as cathode material in Li2SO4 aqueous electrolyte

Abstract

Layered, lithium-rich Li[Li0.2Co0.3Mn0.5]O2 cathode material is synthesized by reactions under autogenic pressure at elevated temperature (RAPET) method, and its electrochemical behavior is studied in 2 M Li2SO4 aqueous solution and compared with that in a non-aqueous electrolyte. In cyclic voltammetry (CV), Li[Li0.2Co0.3Mn0.5]O2 electrode exhibits a pair of reversible redox peaks corresponding to lithium ion intercalation and deintercalation at the safe potential window without causing the electrolysis of water. CV experiments at various scan rates revealed a linear relationship between the peak current and the square root of scan rate for all peak pairs, indicating that the lithium ion intercalation–deintercalation processes are diffusion controlled. The corresponding diffusion coefficients are found to be in the order of 10−8 cm2 s−1. A typical cell employing Li[Li0.2Co0.3Mn0.5]O2 as cathode and LiTi2(PO4)3 as anode in 2 M Li2SO4 solution delivers a discharge capacity of 90 mA h g−1. Electrochemical impedance spectral data measured at various discharge potentials are analyzed to determine the kinetic parameters which characterize intercalation–deintercalation of lithium ions in Li[Li0.2Co0.3Mn0.5]O2 from 2 M Li2SO4 aqueous electrolyte.