Countering the voltage decay in high capacity xLi ₂MnO ₃•(1-x)LiMO ₂ electrodes (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 Li ₂MnO ₃ 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' xLi ₂MnO ₃•(1-x)LiMO ₂, layered-spinel' xLi ₂MnO ₃• (1-x)LiM ₂O _4+δ, layered-rocksalt' xLi ₂MnO ₃ • (1-x)MO and more complex arrangements, in which M is typically Mn, Ni, andor Co. Early indications are that electrodes prepared by this method are effective in 1) countering the voltage decay that occurs on cycling layered-layered' xLi ₂MnO ₃•(1-x)LiMO ₂ electrodes without compromising capacity, and 2) reducing the extent of electrochemical activation required above 4.5 V on the initial charge. In particular, a 0.5Li ₂MnO ₃•0.5LiMn _0.5Ni _0.5O ₂ electrode, after activation at 4.6 V, delivers a steady capacity of 245 mAhg between 4.4 and 2.5 V at 15 mAg (∼C15 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 0.1Li ₂MnO ₃•0.9LiMn _0.50Ni _0.37Co _0.13O ₂ 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.