Preparation of Cubic Spinel Type Copper Manganites CuxMn3-x04 (1. 0≤x≤1. 5) and Their Lithium Intercalation Pro p erties

Abstract

Copper manganites, Cu1Mn304, with a cubic spinel structure were prepared by thermal decomposition in a range of 1.0≤x≤1.5, and their cathode properties in a lithium battery were investigated. Our attention was directed to their high electrical conductivity. The cubic spinel was obtained as a single phase for x=1.2 and 1.4, whereas it was mixedw ith a tetragonal phase for x=1.0 and with CuO for x=1.5. They had a d. c. resistivity of 30, --55cm at room temperature which decreased with an increasing copper content up to x= 1.4. The open circuit voltage (0. C. V. ) was found to decrease slowly with lithium content (y in Li, CusMn304) up to y=0.7 for x=1.2 and to y=0.85 for x=1.4, respectively. Thereafter, 0. C. V. decreased more rapidly. As rhe discharge proceeded, their lattice slightly expanded and became distorted, suggesting that lithium was intercalated electrochemically into the cubic spinel copper manganites. Moreover, after deep discharge (y>0.3), the concentration of copper near the cathode surface increased and metallic copper deposition was observed. Below y=0.3, the lithium intercalation seemed to proceed incorporated with the reduction of Mn4+ to Mn" according to high 0. C. V. values (2-2.5 V). For 0.3 Cy<z (z=0.7 for x=1.2, z=0.85 for x=1.4), intercalated lithium was considered to push Cu out of the host lattice onto the surface, where metallic copper formed.