Shigeki Matsuta

Impurities in LiFePO4 and Their Influence on Material Characteristics

Li 3 PO 4 impurity was found in hydrothermally grown LiFePO 4 samples made with excess Li. The impurity dissociates in water, leading to an apparent alkaline nature of the LiFePO 4 sample. The impurity can be removed by washing the sample in a neutral buffer solution, after which an increase in specific capacity of the LiFePO 4 sample was observed. Li 3 PO 4 , as an inactive component within the active material, reduces the energy density of LiFePO 4 . Additional experiments were performed to study the reactivity of LiFePO 4 in different environments. It is found that LiFePO 4 decomposes in a strong alkaline solution and the decomposition can be slowed down by carbon coating the material. After prolonged storage in water, the specific capacity of carbon-coated LiFePO 4 is reduced and Fe dissolution is observed. Material degradation is thought to be due to interactions among LiFePO 4 , impurities, and water.

Study on Sn–Co Alloy Anodes for Lithium Secondary Batteries I. Amorphous System

An amorphous Sn-Co alloy film electro-codeposited on rough Cu foil was found in our previous works to self-organize a microisland structure, which is a crucial factor to improve Sn alloy anodes for cyclability. This work focused on the electrochemical properties, film morphology, and phase structure, and the behavior of Co atoms was analyzed by extended X-ray absorption fine structure and magnetic susceptibility measurements. Cycle performance up to 20 cycles, in which the capacity anomalously fluctuated, is discussed based on these results, where the capacity change is explained by the morphological and phase structural changes. The stabilization process of the phase is clarified in connection with formation of ferromagnetic face-centered cubic Co particles.

Electron-Spin-Resonance Study of the Reaction of Electrolytic Solutions on the Positive Electrode for Lithium-Ion Secondary Batteries

Electron spin resonance is used to investigate an intermediate cation radical structure in the reaction between a positive elec trode and an electrolytic solution as well as one of the mechanisms for capacity fade of the positive electrode during storage. The i ntermediate cation radical structures of the oxidation reaction in carbonate group solvents have a delocalized radical on the OCO b ond, and neighboring solvent molecules are coordinated with the cation radical species. We measure the radical quantity of nonaqueou s solvents (ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate) in contact with the charged positive electrode.