The capacity fading of lithiated and delithiated graphite electrodes has been studied using lithium manganese oxide as a counter electrode. Higher storage temperatures and longer storage periods give larger capacity losses and larger amounts of manganese (Mn) deposition on the graphite. The capacity losses appear to be related to the amount of deposited Mn in storage experiments in dry electrolyte solutions containing various concentrations of Mn2+ ions, but definite evidence has not been found that the Mn deposit is a simple and direct cause of the capacity fading. The capacity losses estimated from quantities of Mn deposition on the graphite, assuming a Mn2+­Li+ exchange process, appear negligible when compared with the experimental findings. Scanning electron microscope and transmission electron microscope observations show the presence of some amounts of fluoride compounds accompanying some Mn contents on the graphite. The capacities of the graphites are recovered to some extent during the cycles. © 2002 The Electrochemical Society. All rights reserved.

Five types of micrometer-sized Sn and acetylene black (AB) composite powders were prepared by mechanical milling for 1, 3, 6, 12, and 24 h. The Sn/AB powders obtained, in addition to Sn-only powders were added to a binder and conductive material, and then dried under vacuum to prepare negative electrodes (anodes) for sodium-ion batteries (SIBs). SIBs were fabricated with the anodes in the form of 2032type coin cells, and were evaluated using charge-discharge tests up to 50 cycles within the cutoff voltage range of 0.005-0.65 V at a constant current of 50 mA g −1 at 25°C. Maximum discharge capacities of 614 to 651 mAh g −1 were obtained with all the anodes prepared with both the Sn-only and the Sn/AB composites. However, the discharge capacities of the Sn-only and Sn/AB composites milled for 1 and 3 h were significantly decreased as the charge-discharge cycle increased. In contrast, the Sn/AB composites milled for 6 h or more exhibited improved cycle characteristics; capacities of 635, 619, and 584 mAh g −1 were maintained during 50 cycles of testing with the Sn/AB_6h, Sn/AB_12h, and Sn/AB_24h samples, respectively, which were significantly higher than the anode prepared with the Sn-only powder (135 mAh g −1 ).

JapanEffect of hydrophilic and hydrophobic properties of gas channel including bipolar plates on cell performances at freezing temperature was developed. Cell starting performance was improved as hydrophilic properties of bipolar plates increased at freezing temperature, such as -20 º C.

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