Yoshihiro Kadoma

Enhancement of Rate Capability in Graphite Anode by Surface Modification with Zirconia

Department of Applied Chemistry, Graduate School of Science and Engineering,Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, JapanZirconia coating the graphite was examined with a view to enhance the cycling stability of the graphite anode in Li-ion batteries.A thin zirconia film was produced on the graphite surface using an alkoxide precursor solution, followed by the conversion of thewet film into an oxide film by thermal annealing. The anode consisting of zirconia-treated graphite, acetylene black, and the binder~8:1:1! exhibits a capacity exceeding the theoretical value and a pronounced stability upon cycling even at a charge-dischargecurrent rate as high as 3C. It is suggested that the combination of nanocrystalline-zirconia and thein situ formed surface filmsbetter protects graphite from destruction upon cycling.© 2002 The Electrochemical Society. @DOI: 10.1149/1.1516410# All rights reserved.Manuscript submitted May 20, 2002; revised manuscript received August 17, 2002. Available electronically October 4, 2002.

High-Rate-Capable Lithium-Ion Battery Based on Surface-Modified Natural Graphite Anode and Substituted Spinel Cathode for Hybrid Electric Vehicles

Zirconia-treated natural graphite (C Z r ) anode and cobalt-substituted spinel (LiMn 1 . 8 Co 0 . 2 O 4 ) cathode have previously been shown to have significant rate capability and cycle stability as half-cells in Li-ion batteries. We report attempts made to optimize the electrochemical performance of the Li-ion battery based on the above anode and cathode as a potential candidate for hybrid electric vehicles. A novel approach was taken to construct the full cell which is applicable to common Li-ion batteries, i.e., precycling of the graphite electrode at slower rate vs Li metal prior to assembling against LiMn 1 . 8 Co 0 . 2 O 4 . Precycling was found to be effective in delivering high steady capacity on subsequent cycling as a full cell. A Li-ion cell composed of precycled C Z r as anode and LiMn 1 . 8 Co 0 . 2 O 4 as cathode shows pronounced cycle stability and high rate capability. The high cycle stability of C Z r anode was recognized as being due to the high stability of the surface film on graphite consisting of ZrO 2 .