Masataka Wakihara

This paper presents a study on electrochemical lithiation of CoMnSb with a half-Heusler structure as anode material for Li-ion batteries. During the first electrochemical lithiation, the CoMnSb electrode showed , which corresponds to a large volumetric capacity of . Combined first principles and X-ray diffraction studies revealed that Mn atoms were extruded from the host structure, resulting in the formation of a cubic phase of during the first electrochemical lithiation. The volume expansion for the reaction from CoMnSb to (per Sb atom) is 21%. Although this first lithium insertion process is irreversible, following charge–discharge cycles showed a steady capacity of within the voltage range of 0.01 to 1.5 V.

The cobalt metal particles produced during lithium insertion into spinel, , have been investigated by Co K-edge X-ray absorption spectroscopy (XAS) from the viewpoint of local and electronic structures around the Co atom. After electrochemical lithiation up to 0.01 V, extended X-ray absorption spectroscopy analysis showed an increasing Debye-Waller factor for the first neighbor interaction and disappearance of the second one. The simulated XAS by multiple scattering theory indicated that nanometer scale cobalt metal particles were produced with electrochemical reaction. It is suggested that the formation of nanometer scale cobalt particles leads to the high-rate performance of as the battery anode.

Electronic and local structural changes in ramsdellite-type Li_2+xTi₃O₇ compound were investigated by X-ray absorption spectroscopy (XAS) measurements. Upon electrochemical Li-ion insertions, the host lattice with ramsdellite structure is retained, indicated by X-ray powder diffraction. Ti K-edge extended X-ray absorption fine structure (EXAFS) analysis shows, however, slight local structural distortions around Ti ions. The energy shifts and the changes in the peak intensity of Ti K-edge and Ti L-edge XAS reveal the reducing oxidation states of Ti ions as the amount of electrochemically-inserted Li-ion increases. Equally important, oxide ions have a significant effect on the electronic transfer process, suggested by O K-edge XAS. These results on electronic structural changes were interpreted using the Zaanen–Sawatzky–Allen scheme.

Zirconia-treated natural graphite (CZr)(CZr) anode and cobalt-substituted spinel (LiMn1.8Co0.2O4)(LiMn1.8Co0.2O4) 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 LiMn1.8Co0.2O4LiMn1.8Co0.2O4 . 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 CZrCZr as anode and LiMn1.8Co0.2O4LiMn1.8Co0.2O4 as cathode shows pronounced cycle stability and high rate capability. The high cycle stability of CZrCZr anode was recognized as being due to the high stability of the surface film on graphite consisting of ZrO2ZrO2 .