Structural and Electrochemical Study of Li-Al-Mn-O-F Spinel Material for Lithium Secondary Batteries

Abstract

The spinel lithium manganese oxide (LiMn2O4, Fd-3m) has many favorable properties as an active material of positive electrode such as low cost, low toxicity and environmental friendliness. However, a poor electrochemical performance at high temperatures prevents its wider use as a cathode material for lithium secondary batteries. To overcome this problem, many research groups have studied cation substituted LiMn2-xMxO4 (M=Al, Mg, Ni, Co, Cr, etc) and some of them showed improved electrochemical performance at high temperature. Also, Sun et al. and Amatucci et al. reported anion doped spinels which exhibit stable cyclability at high temperatures. The improved electrochemical performance of the twofold substituted LiAlyMn2-yO4-zFz was attributed to the combining positive effects which comes from the retention of small lattice parameters by Al substitution and reduced average Mn oxidation state by F substitution. In this work, we studied the structural and electrochemical properties of Li1.05Al0.1Mn1.85O4-zFz in the 4V region. Fluorine substitution in Li[LixAlyMn2-x-y]O4-zFz led to well developed crystallization with octahedral morphology. In addition, Li[LixAlyMn2-x-y]O4-zFz showed superior cycling performance and better thermal stability than LiMn2O4 and LiAl0.1Mn1.9O4. Fluorine substitution also suppressed Mn dissolution which led to stable cycling performance at 55 oC. The differential scanning calorimetry (DSC) results showed that the anion (F for O) and cation (Li, Al, for Mn) substituted spinel had better thermal stability than LiMn2O4, Li[AlyMn2-y]O4, or Li[LixAlyMn2-x-y]O4