Physiochemical and electrochemical means were used to characterize the failure mechanisms of the lithium manganese oxide based solid solutions utilized as positive electrodes for Li batteries. Resultant data supports a theory in which the 22 and 55 degreesC failure mechanisms are one in the same. The poor performance is exacerbated during cycling due to a mechanism linked to the symbiotic relationship between physical destruction induced by a surface Jahn-Teller distortion and the classic failure mechanisms presented for the chemical failure of the spinel at elevated temperature storage. Based on these findings, a spinel, LiAlxMn2-xO4-zFz, was fabricated which exhibits enhanced stability at elevated temperature. (C) 2001 Telcordia Technologies. All rights reserved.