Cyclic Voltammetry of Pulsed Laser Deposited Li_xMn₂O₄ Thin Films

Electrochemical properties of thin films of LiMn₂O₄ spinel prepared by pulsed laser deposition were studied using constant current cycling and cyclic voltammetry. Films have been cycled more than 220 times with no significant capacity fading. The shape of the cyclic voltammogram is very sensitive to the composition and morphology of the film. The diffusion process for the Li_xMn₂O₄ thin films with an excess of lithium (x > 1) appears to be slower than for lithium-deficient films. Films were subjected to overcharge (5 V vs. Li/Li⁺) and overdischarge (2 V vs. Li/Li⁺). Overcharge does not significantly affect the structure of the film. Overdischarge leads to changes in the shape of the cyclic voltammogram: (i) loss of resolution of the two oxidation peaks at 4.1 and 4.2 V which are the signatures of the spinel structure, and (ii) loss of capacity. These changes in the electrochemical behavior may be correlated to the structural disorder associated with the phase transition when more than one lithium is intercalated in LiMn₂O₄. It is a reversible phenomenon.