Nano-Crystalline Manganese Spinel Li[MxMn2-x]O4 Prepared by Ultrasonic Spray Pyrolysis; Showing Good Cycling Performance in the 3 V Range

Abstract

Manganese spinel LiMn2O4 and its derivatives are the most attractively studied cathode materials for lithium secondary batteries because of their three dimensional Li+ diffusion, low cost, abundance, and nontoxicity [1-3]. However, disadvantage of LiMn2O4 spinel electrodes is that they lose capacity during cycling. In the LixMn2O4 spinel system (0<x<2), the Mn2O4 spinel framework provides a three dimensional interstitial space for lithium ion transport. Lithium extraction from LixMn2O4 (0<x<1) occurs at 4V versus lithium metal. The electrode cycles well over this range because the cubic structure (space group Fd3m) expands and contracts isotopically during lithium insertion and extraction. For 3V region, ie. 1<x<2, as Li+ ions are inserted into the spinel structure, a two-phase reaction occurs, which is associated with the onset of an anisotropic Jahn-Teller distortion. This crystallographic distortion, which results in a 16 % increase in the c/a ratio of the unit cell parameters, is too severe for the electrode to maintain its structural integrity during cycling. Consequently, a LixMn2O4 spinel electrode cycles poorly over the range 1<x<2, and the cell suffers a capacity loss