In Situ XAFS Study of the Effect of Dopants in Li[sub 1+x]Ni[sub (1−3x)∕2]Mn[sub (3+x)∕2]O[sub 4] (0≤x≤1∕3), a Li-Ion Battery Cathode Material

Spinel-type Li1+xNi(1-3x)/2Mn(3+x)/2O4 (0 <= x <= 1/3) cathode materials, which exhibit Ni2+/4+ as a redox species, were synthesized via a solid state reaction. The electrochemical properties of the materials and their potential use as high-power storage materials were examined. These materials show three electrochemical plateaus around 4.1, 4.7, and 4.9 V. We investigated the fundamental roles of the Li and metal ions for these materials using the in situ transmission X-ray absorption fine structure (XAFS) technique in the range of 3.5-5.0 V. The XAFS analyses revealed that Mn did not participate in any of the redox reactions. However, the 4.7 V capacity was highly dependent on the Ni2+/4+ redox reaction, which led to a significant variation in the interatomic distances between the Ni and oxygen atoms. In addition, it was discovered that the capacities around 4.1 and 4.9 V were not associated with a change in the oxidation states of the Mn and Ni ions. It is suggested that the origin of these capacities stems from the oxidation of the oxygen ion accompanied by the extraction of the Li+ from the 16d and the 8a sites, respectively. (c) 2008 The Electrochemical Society.