The Link between room temperature (RT) cycling failure for Li1Mn2O4-type spinels and elevated temperature (ET) failure of Li1.05Mn1.95O4 materials was investigated by physical and electrochemical characterization. Failure for both ET and RT cycling occurred at the end of discharge. Substantial evidence suggesting a link based on the cooperative Jahn-Teller distortion was found. Based on this knowledge, LiAlxMn2-xO4-deltaFz materials were fabricated. These novel compounds were found to offer much improved capacity and ET performance than present generation materials. Three hundred cycles at 55 degrees C resulted in 15% capacity loss. Storage in charged and discharged state for 4 days at 70 degrees C revealed less than 1.6% irreversible capacity Boss.