Electrochemical investigations of cobalt-doped LiMn2O4 as cathode material for lithium-ion batteries

A wide range (y = 0.05-0.33) of Go-doped LiCoyMn2-yO4 spinels were synthesized and electrochemically character ized. These Go-doped spinels showed improved specific capacity and capacity retention over pure spinels. Electrochemical impedance spectroscopy and the linear polarization resistance technique were used to determine the transport and electrochemical kinetic parameters of Go-doped spinels. The presence of Co in the spinel inhibits the passivation process occurring on the surface of the cathode. Also, Co increases the exchange current density and facilitates the charge-transfer reaction of the active material. The lower self-discharge observed for Go-doped spinels was attributed to their low surface areas. The cumulative capacity loss estimated for a pure spinel resulting from self-discharge in the first 30 h was 3 and 6 times larger than those estimated for Go-doped spinels with y = 0.05 and y = 0.16 in LiCoyMn2-yO4, respectively.