mixture of ethylene carbonate dimethylcarbonate the sample electrodes formed test cells which were subjected to charge discharge cycling over the range of 3 4 4 5v at a c 5 rate full cycle over 5 hours the capacity of each cell was traced during a period of up to 35 cycles to provide an indication as seen in fig3 of the rate of change of that property i e the cycling stability of the cell with extended recharging traces 31 36 reflect the above stated increasing levels of fluorine substitution z from 0 05 to 0 5 a comparison of the results depicted in fig2 and 3 graphically confirms the general tendency toward loss of both capacity and cycling stability with an increase in a axis dimension above the preferred limit of about 8 23 u00e5 a series of unsubstituted intercalation compounds of the prior art varying only in li i e li 1 x m y mn 2 x y o 4 z f z where x 0 05 0 075 and 0 1 y 0 and z 0 was prepared and tested in similar manner to provide an indication of the effect of that variable on the capacity and cycling stability of resulting cells as may be seen in fig4 as traces 41 43 of increasing li content that variance alone improves cycling stability but significantly reduces cell capacity the performance of an additional cell prepared with the oxy fluoride x 0 1 z 0 1 compound of example 1 is also represented in fig4.