New manganese dioxides for lithium batteries

Lithium/manganese dioxide primary batteries use heat treated manganese dioxide (HEMD), a defect pyrolusite structure material as the cathode active material. Ion exchange of the structural protons in electrolytic manganese dioxide (EMD) with lithium before heating results in formation of a lithium containing γ-MnO₂. Increased lithium hydroxide concentration and increased temperature lead to increased lithium levels. At 80 °C with a combination of LiOH and LiBr, almost all of the structural protons in MnO₂ are replaced by lithium resulting in a γ-MnO₂ phase substantially free of protons and containing about 1.8% Li. This highly substituted lithium containing MnO₂ is reduced at between 3.5 and 1.8 V and has a capacity of 250 mAh g⁻¹. There are two reduction processes, one at 3.25 and the other at 2.9 V. TGA studies reveal two processes during heat treatment. Heating the lithium substituted MnO₂ to 350–400 °C results in a partially ordered HEMD-like MnO₂ (LiMD) phase with higher running voltage and superior discharge kinetics. Continued heating of the lithiated manganese dioxide to 450–480 °C under oxygen partial pressure can result in formation of a mixed phase containing both HEMD and a new, ordered MnO₂ phase (OMD). The intimately mixed HEMD/OMD composition has a discharge voltage near 2.9 V with a capacity about 220 mAh g⁻¹. Heating exhaustively lithiated MnO₂ to 350–400 °C results in formation of the partially ordered LiMD MnO₂ phase as with the previous partially lithium substituted MnO₂. Additional heating of the highly lithium substituted MnO₂ to 450–480 °C under oxygen results in formation of the new OMD phase in substantially pure form. Discharge of the new OMD phase shows it has a discharge capacity near 200 mAh g⁻¹ between 3.4 and 2.4 V versus lithium in a single, well-defined discharge process. OMD demonstrated good cycling against Li with no indication of formation of LiMn₂O₄ spinel after 80 deep discharge cycles.