LiNi0.8Co0.2O2 blending was investigated as a way to overcome the problems associated with lithium ion rechargeable batteries that use manganese spinel as a cathode material. LiNi0.8Co0.2O2 is a useful additive for preventing HF-generation and Li-loss in electrolytes during storage at elevated temperatures. In experiments, the Mn dissolution from the spinel structure into the electrolyte was decreased by adding LiNi0.8Co0.2O2. This dissolution was almost completely eliminated by 15wt.% LiNi0.8Co0.2O2 blending. As a result, this blending technique can prevent the decline in capacity caused by storage at elevated temperatures.