2002 Volume 70 Issue 8 Pages 590-594
We analyzed the states of lithium intercalated into carbon and of lithium compounds on the surface of carbon by 7Li nuclear magnetic resonance (NMR) spectroscopy. In the case of graphite-coke hybrid carbon, the ratio of the relative peak area of inactive lithium after 500 cycles to that after 10 cycles was a smaller than that in the case of graphite or coke. The quantity of inactive lithium, which did not include the lithium compounds produced at initial charging, in graphite, coke, and graphite-coke hybrid carbon significantly differed after 500 charge/discharge cycles. In order to clarify the voltage region in which inactive lithium is produced, we carried out charge/discharge cycle tests in the higher and the lower voltage regions, respectively, and analyzed the electrodes by 7Li NMR spectroscopy. In the case of a coke negative electrode, the electrode deterioration was large after the cycle test in the higher voltage region, but was almost non-existent after that in the lower voltage region. Conversely, in the case of a graphite negative electrode, the electrode deterioration was significantly larger after the lower voltage region cycles. A battery using graphite-coke hybrid carbon as the negative electrode performed better with a reduced generation amount of inactive lithium under charge/discharge cycle.
