Investigation of the relationship between the cycle performance and the electronic structure in LiAlxMn2−xO4 (x = 0 and 0.2) using soft X-ray spectroscopy

Abstract

Al doping into LiMn₂O₄ is one of the well-known methods to improve the cycle performance of the LiMn₂O₄ cathode. We carried out soft X-ray emission spectroscopy (XES) for LiMn₂O₄ and LiAl_0.2Mn_1.8O₄ to elucidate the relationship between the Mn 3d electronic structures and cycle performances. After the first cycle, the XES spectra of LiAl_0.2Mn_1.8O₄ are almost unchanged compared to the initial state. In contrast, charge-transfer excitation for the XES of LiMn₂O₄ is significantly reduced, indicating that the Mn 3d-O 2p hybridization in LiMn₂O₄ should be easily weakened by charge–discharge. In LiAl_0.2Mn_1.8O₄, the Mn–O bond becomes more stable due to the decrease of Mn³⁺ ions with Jahn–Teller distortion by Al³⁺ doping, resulting in the improved cycle performance.