Electrochemical properties of nanosized Li-rich layered oxide as positive electrode materials for Li-Ion batteries

A nanosized Li-rich layered oxide/carbon composite material is successfully prepared by simple ball milling pulverization of microsphere-shaped Li-rich layered oxide materials with conductive carbon. The nanosized Li-rich layered oxide/carbon composite electrode exhibits a high 1st discharge capacity of 250 mAh g(-1) with an excellent rate capability at high current density. The composite also reduces the internal resistance from oxygen release during the electrochemical activation of Li2MnO3. The improvement in the electrochemical performance of nanosized Li-rich layered oxide/carbon composite materials primarily occurs because the nanosized particles facilitate the diffusion of Li within the structure and provide innumerable reaction sites with lithium. Furthermore, the electronic conductivity of the active material is effectively enhanced by the carbon coating on the particles. In addition, unique effects of ball milling on the electrochemical properties of the Li-rich layered oxides are observed: (i) pre-activation of the Li2MnO3 component and (ii) gradual electrochemical activation under 4.3 V during cycling. Adverse effects on the electrochemical stability of the nanosized Li-rich layered oxide are also discussed, and these adverse effects mainly arise due to (i) the structural deformation of hexagonal ordering, (ii) the growth of the spinel component and (iii) the insufficient formation of a protective NiF2 layer on the surface of the active material.