Magnetic Field‐induced Disordered Phase of Spinel Oxides for High Battery Performance

The disordered phase of spinel LiMn_1.5Ni_0.5O₄ (LNMO) is more appealing as high-voltage cathode due to its superior electrochemical performance compared to its ordered counterpart. Various methods are developed to induce a phase transition. However, the resulting materials often suffer from capacity degradation due to the adverse influence of accompanying Mn³⁺ ions. This study presents the utilization of local magnetic fields generated by a magnetic Fe₃O₄ shell to induce a disordered phase transition in LNMO at lower temperature, transitioning it from an order state without significantly increasing the Mn³⁺ content. The pivotal role played by the local magnetic fields is evidenced through comparisons with samples with nonmagnetic Al₂O₃ shell, samples subjected to sole heat treatment, and samples heat-treated within magnetic fields. The key finding is that magnetic fields can initiate a radical pair mechanism, enabling the induction of order-disorder phase transition even at lower temperatures. The disordered spinal LNMO with a magnetic Fe₃O₄ shell exhibits excellent cycling stability and kinetic properties in electrochemical characterization as a result. This innovation not only unravels the intricate interplay between the disordered phase and Mn³⁺ content in the cathode spinel but also pioneers the use of magnetic field effects for manipulating material phases.