Factors affecting the stabilization of Mn spinel capacity upon storing and cycling at high temperatures

Doped and undoped Mn spinels have been evaluated at 55 degrees C in terms of capacity losses upon cycling and storage. The influence of such factors as doping, electrolyte nature, voltage range and constant- or floating-potential storage have been evaluated. Spinels of composition Li1.02M0.05Mn1.95O4 (M = Ga or Cr) exhibit fade rates of 0.15 to 0.20 mAh/g cycle vs. 0.28 mAh/g cycle for the undoped spinel. This reduction may still be unsatisfactory from a practical standpoint, but it is enhanced by two different approaches: (i) storing a cell for some days at 55 degrees C in, e.g., LiBF4-EC/PC; (ii) making a double substitution in the spinel, e.g., with Ga and Cr. The first approach brings the ab.e rate to 0.07 mAh/g cycle for both Ga-doped (2.5 mol %) and undoped spinel, whereas the second one allows a reduction to 0.05 mAh/g cycle, that is less than 0.05%/cycle. These rates of capacity loss are the lowest reported thus far at 55 degrees C. By properly tuning the Li, Ga, and Cr content of the spinel, it seems possible to have simultaneously good average capacities (similar to 110 mAh/g in 100 cycles) and limited fade rates at 55 degrees C.