XAS Investigation of Inhomogeneous Metal-Oxygen Bond Covalency in Bulk and Surface for Charge Compensation in Li-Ion Battery Cathode LiNi[sub 1∕3Cosub 1∕3Mnsub 1∕3]Osub 2 Material

Layered was prepared by ultrasonic spray pyrolysis. The discharge capacity increases linearly with increases of the upper cutoff voltage limit. Layered attained a high discharge capacity of over between 2.8 and 4.6 V with an excellent cyclability. An in situ transition metal (TM) K-edge X-ray absorption spectroscopic (XAS) study was carried out to investigate the electronic and the local structures of the delithiated-relithiated system compared with surface-sensitive soft XAS of oxygen K-edge and TM L-edges. The bulk-sensitive TM K-edge XAS analysis shows that the charge compensation is made through the formation of and during the delithiation-relithiation process. However, the soft TM L-edges XAS indicate that the in the electrochemical untreated sample prefers to be oxidized to , not , in the surface region of delithiated material. The bond covalency between TM and oxygen, especially the oxygen 2p hole state by ligand-to-metal charge transfer, plays an important role in the charge compensation. The TM K- and L-edge XAS results suggest that an inhomogeneous chemical state was induced along direction of electrochemical reaction.