Magnetite Nanoparticle Coating Enables High Voltage Stability in Ni-Rich Cathodes for High Energy Lithium-Ion Batteries

The widespread application of rechargeable batteries necessitates high-performance and cost-effective solutions. Nickel-rich cathodes such as LiNi_0.8Co_0.1Mn_0.1O₂(NMC 811) are of great interest in academia and industries given their high theoretical capacity (~ 200 mAh g^-1for NMC 811) and lower economic and environmental costs associated with the cobalt mining. However, deleterious side reaction on the surface of these cathode active particles inhibits their stable electrochemical cycling performance. These reactions are worsened during high voltage cycling, as the Ni cation in the cathode material experiences an increase in oxidation state, which can lead to Li/Ni cation intermixing. This also triggers phase changes from hexagonal to disordered spinel or even rock-salt structure, resulting in an irreversible loss of active material. Herein, we developed a coating of Magnetite nanoparticles over the micro NMC811 particles using a facile surfactant-assisted strategy using an aqueous medium. A notably higher cycle stability, rate performance, and overall energy density was realized for the coated cathode in a conventional liquid electrolyte system. To prove the versatility of the chemistry, pellet-stacked solid-state cells with Li₆PS₅Cl as the electrolyte was deployed and the coated NMC 811 showed superior cycling stability than its uncoated counterpart.