Tunning the linkage of structure units to enable stable spinel-based cathode in the wide potential window

Abstract

The low practical capacity (<140 mA h g −1 ) of spinel phase LiMn 2−x Ni x O 4 (0 < x < 1) excludes it from high energy density lithium ion batteries (LIBs) for powering electric vehicles. Extending the operating potential window from 3.0 to 4.8 V to 2.0–4.8 V can double the capacity, but result in fast capacity decay due to the drastic cubic-tetragonal phase transition below 3.0 V, induced by serious Jahn-Teller (J-T) distortion of structure units (Mn 3+ )O 6 octahedra. Herein, we propose a novel strategy to suppress J-T distortion by tuning the linkage of structure units MnO 6 octahedra. The original full-vertex-sharing LiO 4 tetrahedra around MnO 6 octahedra in spinel phase are partially replaced by edge-sharing LiO 6 octahedra, which relate Mn-O bonds along the dz 2 direction with those along the d xy plane, thus significantly mitigating J-T distortion and suppressing the phase transition when discharged to 2.0 V. Following this strategy, the prepared spinel-based cathode achieves a high reversible capacity of about 290 mA h g −1 and an energy density up to 957 W h kg −1 with improved cycling stability. This work finds a new opportunity for the traditional spinel cathode towards applications in high energy density LIBs in a low cost and sustainable manner. Tunning the linkage of structure units MnO 6 octahedra in spinel-based cathode from full-vertex-sharing mode to partial-edge-sharing mode, greatly restricts Jahn-Teller distortion when discharged below 3 V and delivers a high capacity with decent cycling stability, which makes spinel cathode potential to power electric vehicles. • The structural origin for the Jahn-Teller effect in spinel phase was revealed based on the linkage way of MnO 6 octahedra. • Through a spinel/layered complex strategy, the local structure linkage of MnO 6 octahedra was partially converted to edge-sharing. • The change in the local structure linkage greatly suppressed the Jahn-Teller distortion and improved the cycling stability.