Configurational entropy-induced phase transition in spinel LiMn₂O₄

The spinel-type LiMn_2O_4 is a promising candidate as cathode material for rechargeable Li-ion batteries due to its good thermal stability and safety. Experimentally, it is observed that in this compound there occur the structural phase transitions from cubic (Fd\bar3m) to tetragonal (I4_1/amd) phase at slightly below room temperature. To understand the phase transition mechanism, we compare the Gibbs free energy between cubic phase and tetragonal phase by including the configurational entropy. Our results show that the configurational entropy contributes substantially to the stability of the cubic phase at room temperature due to the disordered Mn^3+/Mn^4+ distribution as well as the orientation of the Jahn-Teller elongation of the Mn^3+O_6 octahedron in the the spinel phase. Meanwhile, the phase transition temperature is predicted to be 267.8 K, which is comparable to the experimentally observed temperature. These results serve as a good complement to the experimental study, and are beneficial to the improving of the electrochemical performance of LiMn_2O_4 cathode.