Synthesis and electrochemical properties of nonstoichiometric LiAlxMn2−xO4−δ as cathode materials for rechargeable lithium ion battery

Nonstoichiometric spinel oxides, LiAlxMn2−xO4−δ (image), were synthesized under controlled partial pressure of oxygen, and their elecrochemical performances were investigated. As an Al content increases, solubility limit of the oxygen nonstoichiometry, δ, increased, while partial molar enthalpy image of the formation of oxygen nonstoichiometry decreased. Cycle performance of LiAlxMn2−xO4 showed significant improvement comparing with that of LiMn2O4 cathode. However, the decrease of theoretical capacity was accompanied with Al doping. Nonstoichiometric LiAlxMn2−xO4−δ showed the increase in capacity with keeping good cycle performances as well as stoichiometric LiAlxMn2−xO4. Although the introduction of oxygen nonstoichiometry leads to the increase of Mn3+ which is known as Jahn–Teller ion, DSC curves for LiAlxMn2−xO4−δ showed no exothermic peak due to phase transition arising from Jahn–Teller distortion around room temperature.