Phase-purity-engineered spinel-type LiMxMn2−xO4 (M = Ni, Al; 0 ≤ x ≤ 1) with a single high-voltage plateau: design, synthesis and electrochemical mechanism

Abstract

Spinel LiMn₂O₄ (LMO) is a cost-effective cobalt-free cathode, but its practical deployment is hindered by the rapid capacity fade stemming from Mn³⁺ Jahn–Teller distortion and dissolution. Through systematic DFT screening of transition-metal doping paths, Ni-doped LiNi_0.5Mn_1.5O₄ (LNMO) is identified as the optimal composition, suppressing the structural distortion while circumventing the Al³⁺ doping-induced capacity loss. Capitalizing on the 22% lower Li⁺ migration barrier (0.35 eV) predicted for the ordered P4₃32 phase than that for the disordered Fdm (0.45 eV), surfactant-free high-energy ball milling combined with 700 °C calcination synthesizes nanoparticulate ordered o-LNMO with shortened Li⁺ diffusion paths. This phase-purity-engineered material achieves precise Mn³⁺/Mn⁴⁺ regulation (0.48 ratio), significantly mitigating parasitic reactions to enable a single stable 4.7 V plateau via exclusive Ni²⁺/Ni⁴⁺ redox activity. Electrochemically, o-LNMO delivers 127.8 mAh g⁻¹ at 1C (3.0–5.0 V) and maintains 96.1 mAh g⁻¹ after 200 cycles, demonstrating superior cycling robustness over conventional LMO. Structural integrity and plateau stability are confirmed by in situ XRD and 3D TOF-SIMS, establishing a composition-structure-phase purity paradigm for high-energy lithium-ion batteries.