A causal study of the capacity fading of Li 1.01Mn 1.99O 4 cathode at 80°C, and the suppressing substances of its fading

Abstract

Discharge capacities of the Li 1.01Mn 1.99O 4 cathode and Mn content dissolved from the cathode were examined on the addition of some chemicals, as the storage temperatures and time were changed. On the addition of 1000 ppm of H 2O to 1.0 M LiPF 6 solution in EC/DMC (1:2 in volume), 41% of capacity of the cathode was lost after 24 h storage at 80°C, in contrast to 5% loss in the case of no additive. Water would be responsible for causing the capacity fading of the cathode under such condition as elevated temperatures. In the EC/DMC solution without LiPF 6, on the contrary, no capacity fading was observed with H 2O additive at 80°C storage, while the CF 3SO 3H addition resulted in 40% of capacity fading. These results show that plausible acid derived from the reaction of LiPF 6 with H 2O causes the capacity fading on the lithium manganese oxide at 80°C, relatively high storage temperature. On the other hand, addition of 500–1000 ppm of (CH 3) 3SiNHSi(CH 3) 3 resulted in less capacity fading of the cathode and made Mn dissolution decrease drastically. Therefore, dehydration and acid-neutralization in the electrolyte solution would restrain the capacity fading of the lithium manganese oxide cathode during high temperature storage, and we confirmed it in some experiments.