Understanding the role of Zr4+ cation in improving the cycleability of LiNi0.8Co0.15Zr0.05O2 cathodes for Li ion rechargeable batteries

Lithium nickel cobalt oxide (LNCO) has been considered as one of the most attractive cathode materials for lithium rechargeable batteries. The reported discharge capacities of LNCO are scattered and these cathodes are prone to capacity fading upon repeated charge-discharge cycling. Although, inert cation modified LNCO imparts better structural stability and partially circumvent the fading problem; the role played by such dopant in improving the electrochemical characteristics remains unclear. In the present work, we have demonstrated Zr4+ modified LNCO yields decent discharge capacity and excellent cycleability. X-ray Rietveld analyses in conjunction with micro-Raman and X-ray photoelectron spectroscopy measurements were performed to understand the role of Zr4+ cation to improve the cycleability of LNCO cathode. Based on the analyses of XRD refinement and spectroscopy data we have argued that the positive role of Zr4+ dopant are realized through its preferential occupancy in lithium site (of hexagonal layered LNCO) to impart structural stability during charge-discharge cycling. Additionally, with repeated charge-discharge cycles probably part of Zr migrates to the electrode surface to form a passive layer to inhibit Ni3+ -> Ni2+ reduction to improve the cycleability. (C) 2009 Elsevier B.V. All rights reserved.