Countering the Voltage Decay in High Capacity xLi2MnO3•(1–x)LiMO2Electrodes (M=Mn, Ni, Co) for Li+-Ion Batteries

A new approach to synthesizing high capacity lithium-metal-oxide cathodes for lithium-ion batteries from a Li2MnO3 precursor is described. The technique, which is simple and versatile, can be used to prepare a variety of integrated 'composite' electrode structures, such as 'layered-layered' xLi2MnO3•(1–x)LiMO2, 'layered–spinel' xLi2MnO3•(1–x)LiM2O4, 'layered-rocksalt' xLi2MnO3• (1–x)MO and more complex arrangements, in which M is typically Mn, Ni, and/or Co. Early indications are that electrodes prepared by this method are effective in 1) countering the voltage decay that occurs on cycling 'layered-layered' xLi2MnO3•(1–x)LiMO2 electrodes without compromising capacity, and 2) reducing the extent of electrochemical activation required above 4.5 V on the initial charge. In particular, a 0.5Li2MnO3•0.5LiMn0.5Ni0.5O2 electrode, after activation at 4.6 V, delivers a steady capacity of 245 mAh/g between 4.4 and 2.5 V at 15 mA/g (∼C/15 rate) with little change to the voltage profile; a first cycle capacity loss of 12%, which is significantly less than usually observed for 'layered-layered' electrodes, has been achieved with a manganese-rich 0.1Li2MnO3•0.9LiMn0.50Ni0.37Co0.13O2 electrode. These results have implications for enhancing the performance of the next generation of high-energy lithium-ion batteries. The flexibility of the method and the variation in electrochemical properties of various composite electrode structures and compositions are demonstrated.