Unveiling the role of Mn-interstitial defect and particle size on the Jahn-Teller distortion of the LiMn₂O₄ cathode material

This work proposes to unveil the underlying effect of Mn-interstitial defect as well as the particle size on the Jahn Teller distortion. Mn-interstitial defects and nanometric particles were characterized by HRTEM, Rietveld fitting and microstrain XRD analysis. The research was conducted by measuring the changes of the Fermi level, entropy, enthalpy and the redox potential due to the JT transition. Other dynamic electrochemical measurements were also carried out. The structural and microstructural measurements led to propose the presence of Mn ions in distorted tetrahedral 48f positions after using irradiation to induce Mn-interstitial defects. By using the proposed methodology it was possible to experimentally observe that this defect vanishes the JT effect and diminishes the shifting of the Fermi level during the phase transition. Subtle correlations between the capacity of the 3V region and the redox potential drop of these materials were revealed and explained. The surface pressure and bonding effects were set as important factors underlying stunning electrochemical and structural changes that characterise nanometric particles below 15 nm.