Li Metal‐Free Rechargeable LiMn2 O 4 / Carbon Cells: Their Understanding and Optimization

So‐called "rocking‐chair" rechargeable batteries that use lithium intercalation compounds for the positive and negative electrodes should be safer than batteries that contain free‐lithium metal. Such a cell, using the spinel as the positive electrode and carbon as the negative electrode, was optimized as a function of various operating parameters. These cells reversibly insert 0.32 Li atoms per Mn at an average output voltage of 3.7 V, yielding an effective specific energy of 250 mWh/g of electrode materials (3 times that of Ni‐Cd). They can sustain high current rates similar to Ni‐Cd batteries, and can be discharged to 0 V without any degradation of their operating conditions. By systematically studying the stability of several electrolyte systems, we were able to minimize electrolyte decomposition (by controlling drastically the charge cut‐off voltage) so that these cells show a promising cycle life even at 55°C while maintaining 75% of their initial capacity.