Influence of magnetic ordering and Jahn-Teller distortion on the lithiation process of LiMn₂O₄

We performed extensive first-principles studies on the magnetic ordering and Jahn-Teller (JT) distortion of spinel LiMn₂O₄, a promising candidate for cathode materials in Li-ion batteries. We find that the ground state of LiMn₂O₄ is an anti-ferromagnetic (AFM) orthorhombic spinel structure, where AFM Mn³⁺ layers and FM Mn⁴⁺ layers alternate along the [001] direction and the 90° Mn³⁺-O^2--Mn³⁺ in the Mn³⁺-(001) planes are AFM coupling, forming an indirect Kramers-Anderson superexchange. The coplanar Mn³⁺ ions maximize the JT distortion and the AFM magnetic orderings further strengthen the interaction between Mn³⁺ cations and O^2- anions, making the structure stable. Li diffusion in such a stable LiMn₂O₄ material will occur through a ring consisting of six Mn atoms, and the energy barrier of Li diffusion is dependent on the valence states of those Mn atoms. Our theoretical results give insights into exploring the ground state of related JT magnetic materials, and also provide information on the performance improvement of LiMn₂O₄ cathode materials.