A composition includes an electrode made of Lithium Manganese Oxyfluoride (LMOF). A single layer separator adheres to a surface of the electrode, is a dielectric that is conductive for Lithium ions but not electrons, and has top and bottom sides. A solid polymer electrolyte (SPE) saturates the electrode so that the LMOF is between 55 percent and 85 percent by mass of a composition of the LMOF electrode and the SPE is between 7.5 percent and 20 percent by mass of the composition of the LMOF electrode. The SPE saturates the separator so that the SPE resides both on the separator top and bottom sides so that the SPE residing on the separator top side contacts the surface. The LMOF exhibits X-Ray Diffraction spectrum peaks between twenty-two and twenty-four 2-theta degrees, between forty-eight and fifty 2-theta degrees, between fifty-four and fifty-six 2-theta degrees, and between fifty-six and fifty-eight 2-theta degrees.