Solid-State Lithium-Polymer Batteries Using Lithiated MnO[sub 2] Cathodes

We have used a lithiated MnO 2 , Li 0.33 MnO 2 , with ordered alternating one‐dimensional [1 × 2] and [1 × 1] channels as a cathode material in solid‐state lithium/polymer cells. An optimized cell can operate at moderate temperatures (40–80°C). Li 0.33 MnO 2 delivers a rechargeable capacity of 160 mAh/g with a flat potential plateau at ca . 3.0 V vs . Li / Li + at the C/3 rate and 65°C, corresponding to a specific energy of 450 Wh/kg of the pure oxide. Cells show good rate capability and excellent cyclability when cycled between 2.7 and 3.5 V at 80% depth of discharge, whereas a capacity decline was observed when cycled between 2.0 and 3.5 V. Capacity fading upon cycling is believed to be due to the formation of a thin layer of spinel phase (transformation to Li 0.5 MnO 2 from Li 0.33 MnO 2 ) on the particle surfaces, as well as to increased cell resistance during charge/discharge cycling. The cell self‐discharge at high temperature and the thermal stability of Li 0.33 MnO 2 in contact with the polymer electrolyte are also discussed.