Thermally Induced Spin State Transition in LiCoO₂ and Its Effects on Battery Performance

LiCoO₂ is the most widely used and extensively studied cathode material for Li-ion batteries. The studies based on the improvement of the performance have focused on the structural and electrochemical properties of LiCoO₂. However, significantly less attention has been paid to its magnetic properties and their effects on battery performance. For the first time to our knowledge, we report a thermally induced magnetic spin state transition from low spin (LS) to intermediate spin (IS) at ∼800 K in bulk LiCoO₂ via magnetic susceptibility measurements. We quench the LiCoO₂ from above the spin state transition temperature (∼810 K) into liquid nitrogen to preserve the IS state at room temperature. We use this quenched sample (q-LiCoO₂) as an active cathode material. We observe a significant improvement (∼15% better capacity retention after 200 cycles at 1C) in cell performance of q-LiCoO₂ compared to the ref-LiCoO₂ which is used as a reference material. Our results show that it is possible to tailor the magnetic properties and electronic structure of cathode materials to achieve better battery performance.