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

The disordered phase of spinel LiMn1.5Ni0.5O4 (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.