The thermal stabilities of delithiated LixMn2O4 powder and with electrolyte were investigated with thermogravimetric analysis and C80 calorimeter. The thermal stabilities of LixMn2O4 and its coexisting system with 1.0 M LiPF6/EC+DEC show a decreasing trend with the state of charge increasing. The thermodynamics and kinetic parameters were obtained and it was found that both the onset temperature and the activation energy of the 1.0 M LiPF6/EC+DEC-LixMn2O4 system are much lower than that of LixMn2O4 alone, which reveals that the thermal stability of the coexisting system is much poorer than that of the single component.