Noriyuki Tamura

Advanced Structures in Electrodeposited Tin Base Negative Electrodes for Lithium Secondary Batteries

Tin anodes deposited electrochemically on a copper foil current collector are studied to develop a next-generation lithium-ion battery with higher energy density. Better cycle performance through ten initial cycles under full charge and discharge conditions was attained by annealing tin electrodeposited on a rough surface copper foil. The annealing process was found to change the main active material from Sn to Cu 6 Sn 5 with some minor compounds. Furthermore, a microcolumnar structure of the active material portion was found to he self-organized in accordance with the surface profile of the foil during the first charge-discharge cycle. Advantages of these structural features are discussed in terms of the initial charge and discharge performance. including specific capacity and coulombic efficiency measured by using a three-electrode cell.

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.

Graphene-Like-Graphite as Fast-Chargeable and High-Capacity Anode Materials for Lithium Ion Batteries

Here we propose the use of a carbon material called graphene-like-graphite (GLG) as anode material of lithium ion batteries that delivers a high capacity of 608 mAh/g and provides superior rate capability. The morphology and crystal structure of GLG are quite similar to those of graphite, which is currently used as the anode material of lithium ion batteries. Therefore, it is expected to be used in the same manner of conventional graphite materials to fabricate the cells. Based on the data obtained from various spectroscopic techniques, we propose a structural GLG model in which nanopores and pairs of C-O-C units are introduced within the carbon layers stacked with three-dimensional regularity. Three types of highly ionic lithium ions are found in fully charged GLG and stored between its layers. The oxygen atoms introduced within the carbon layers seem to play an important role in accommodating a large amount of lithium ions in GLG. Moreover, the large increase in the interlayer spacing observed for fully charged GLG is ascribed to the migration of oxygen atoms within the carbon layer introduced in the state of C-O-C to the interlayer space maintaining one of the C-O bonds.