Yuzo Kozono

X-ray photoelectron spectroscopy analyses of lithium intercalation and alloying reactions on graphite electrodes

Abstract Electrochemical lithium intercalation reactions occurring in silver-supported graphite anodes were investigated by X-ray photoelectron spectroscopy (XPS). The binding energy of Li(1s) of intercalating lithium was higher than that of lithium metal, which suggests that lithium exists in the form of a positive ion in the graphite layers. The core level of the C(1s) signal of lithium intercalated graphite was higher than that of graphite, which implies that the carbon in lithium-intercalated graphite has a negative charge. This finding agrees with previous XPS studies indicating that carbon has a negative charge in a graphite-intercalation compound produced by a molten lithium intercalation reaction to graphite. Lithium carbonate, lithium fluoride and organic compounds were produced on the graphite surfaces in charge/discharge reactions in 1 M LiPF 6 /EC—DMC electrolytic solution. It was also confirmed that the initial charge current supplied to the graphite electrode with a potential between 2.8 and 0.6 V did not cause a lithium-intercalation reaction. It caused, however, other reactions such as decomposition of the electrolytic solution and production of passivating films.

Design and performance of 10 Wh rechargeable lithium batteries

Abstract New metal—carbon composite anodes were developed by a chemical deposition method of metal particles onto graphite powder. Silver—graphite composites consisted of ultrafine silver particles on a graphite surface, exhibiting a large specific volume capacity of 468–505 Ah/l which may be due to Li Ag alloy formation. The Ag—graphite anodes also showed excellent cycleability over 700 charge/discharge cycles with only 3% capacity loss. 10 Wh class rechargeable lithium batteries with energy densities of 270–300 Wh/l were manufactured using Ag—graphite anodes and cathodes of LiNiO 2 or LiCoO 2 . Little capacity loss in these batteries was found even after 250 cycles because of the highly durable Ag—graphite anodes.

Spinel-type lithium–manganese oxide cathodes for rechargeable lithium batteries

Dissolution of Mn ions and capacity loss of spinel-type Li–Mn oxide cathodes in LiPF6-containing electrolytic solutions at 60°C were investigated. The amounts of dissolved Mn decreased with the increase in the Li/Mn molar ratios in Li–Mn oxides. The dissolution reaction of Mn ions was enhanced on charged cathodes, resulting in a cathode capacity loss and a contraction of the lattice parameter. An increase of the polarization voltage was considered to cause a capacity loss on the charged cathodes during the course of immersion at 60°C, as well as the dissolution of Mn ions.