Preparation of Cubic Spinel Type Copper Manganites Cu₂-Mn₃_3.O4 (1. 0xl. 5) and Their Lithium Intercalation Properties

Copper manganites, Cu_xMn₃__a,0₄, with a cubic spinel structure were prepared by thermal decomposition in a range of 1.0x1. 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=l. 2 and 1.4, whereas it was mixedw ith a tetragonal phase for x=1.0 and with CuO for x=l. 5. They had a d. c. resistivity of 30—55 ωCm at room temperature which decreased with an increasing copper content up to x=l. 4. The open circuit voltage (O.C.V.) was found to decrease slowly with lithium content (y in Li|_/Cu_a.Mn₃__xO₄) up to y=0.7 for x=1.2 and to y=0.85 for x=l.4, respectively. Thereafter, O. C. V. decreased more rapidly. As rhe discharge proceeded, their lattice slightly expanded and became distorted, suggesting that lithium was intercalated electroche-mically 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 Mn³⁺ according to high O.C.V. values (22.5V). For 0. 3<y< z (2=0.7 for x=l. 2, z=0.85 for x=l.4), intercalated lithium was considered to push Cu out of the host lattice onto the surface, where metallic copper formed.