Effect of transition metal substitution on elastoplastic properties of LiMn₂O₄ spinel

LiMn₂O₄ (LMO) derivatives partially substituted with transition metals (e.g., Ni) have received attention for their higher energy density achieved at higher charge voltage than pure LMO, and may be attractive cathode candidates for emerging all solid state batteries. Accurate mechanical properties of these high voltage spinels are required for prediction of electrode and electrolyte fracture that may compromise battery lifetime and performance. Here, we quantified the Young’s elastic modulus E and hardness H for LMO, LiMn_1.5Ni_0.5O₄ (LMNO), and LiMn_1.5Ni_0.42Fe_0.08O₄ (LMNFO) spinel microparticles via instrumented grid nanoindentation. Elastic modulus E and hardness H increased by more than 40% (up to 145 and 11 GPa, respectively) as a result of Ni or Ni/Fe substitution; such substitution also reduces the lattice parameter and increases the oxidization state of Mn. These results demonstrate how changes in transition metal occupancy can significantly affect the mechanical properties of LMO spinel, and provide critical parameters for designing against fracture in all solid state batteries.