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 1.8V and has a capacity of 250mAhg−1. There are two reduction processes, one at 3.25 and the other at 2.9V. 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 2.9V with a capacity about 220mAhg−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 200mAhg−1 between 3.4 and 2.4V 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.