Lithium-ion batteries will be increasingly important in next-generation energy-storage devices. However, the charge-discharge mechanism of the electrode in these batteries has not yet been revealed. It has been reported that the surface crystal structure changes when these batteries degrade, but the phase transition that occurs on the surface of the cathode material has not yet been clarified because observation of the surface of the grains is insufficient. On the other hand, it has been shown that using Ga⁺ primary ion time-of-flight secondary ion mass spectrometry (TOF-SIMS), a regularity can be observed in the fragment patterns of metal compounds that can provide information on their oxidation states and electron affinities. Therefore, in this study the spectra of various cobalt components, including LiCoO₂, CoO, and Co₃O₄ were compared, and depth profile analyses of Li-ion battery’s cathode materials were conducted using a laboratory-made TOF-SIMS apparatus. Variation in the secondary ion mass spectra was observed from the surface to the interior. Although a phase transition was not directly observed via cross-sectional analysis, it was concluded that the surface of the cathode materials comprised of CoO and/or Co₃O₄, while the interior of the cathode consisted of LiCoO₂. Moreover, it was determined that the thickness of the CoO and/or Co₃O₄ layers on the cathode materials was less than 200 nm.

　電子プローブマイクロアナライザー(EPMA)による定量分析においてZAF法は，X線の発生領域よりも大きな均一相をもつバルク状態の試料であれば，解析的手法としてほぼ確立されている．しかしながら，ZAF法の定量精度は，低加速電圧領域での測定やF以下の軽元素の測定において，Na以上の重元素の場合と比較して十分とは言い難い．そこで，モンテカルロ法で求めた発生関数を一般式化し，その発生関数が実用に供せるか否かを検討した．その結果，バルク試料において加速電圧5kVにおいては，O, S, Ga, Co, Niの定量値はMC法と同程度であった．5–25keVの加速電圧領域においては既存のZAF法と比較すると同等もしくはそれ以上の高い正確さであった．ただし，Fに関してはMC法の結果よりも定量の正確さは低かった．