Enhancing Cycling Stability and Power Density of Ni-Rich NMC811 through CaTiO₃ Surface Coating: A Combined...

Ni-rich NMC811 layered oxide cathodes are promising candidates for high-energy lithium-ion batteries; however, their practical application under fast-charging conditions is limited by interfacial instability, oxygen release, and slow Li⁺ diffusion. In this work, calcium titanate CaTiO₃ (CTO) was introduced as a perovskite-based surface coating to enhance the structural and electrochemical stability of Ni-rich NMC811 cathodes. Structural and interfacial analyses reveal the formation of a crystalline CTO coating that preserved the layered R3̅m structure and induced slight Ti doping during the thermal treatment. The synergistic effect of the CTO coating and interfacial Ti incorporation reduces Li⁺/Ni²⁺ cation mixing, strengthens transition metal-oxygen bonding, and stabilizes lattice oxygen, thereby mitigating oxygen release and suppressing the detrimental H2 → H3 phase transition at high states of charge. As a result, the CTO coating demonstrates a notable performance enhancement, enabling the NMC811@CTO cathode to deliver a higher initial discharge capacity (200.2 mAh g^-1), improved first-cycle Coulombic efficiency (92.0%), and markedly superior rate capability, retaining 158.3 mAh g^-1 at 4C, while during asymmetric fast-charging up to 6C, it maintains 166.2 mAh g^-1 compared to 130.8 mAh g^-1 for pristine NMC811 and recovered 99.8% of its capacity when returned to C/10. These results highlight the enhanced fast-charging capability enabled by improved interfacial kinetics and structural stability. Long-term cycling at 1C further confirms improved stability, with NMC811@CTO retaining 83.1% of its capacity after 200 cycles compared to 64.1% for pristine NMC811. Electrochemical impedance spectroscopy and differential scanning calorimetry analyses reveal reduced charge-transfer resistance, improved thermal stability, and lower heat release. Density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations further show increased oxygen vacancy formation energy and reduced Li⁺ migration barriers, providing atomic-scale insight into the enhanced oxygen stability and Li⁺ transport. Overall, the CTO layer acts as both a protective interface and an ion-transport facilitator, offering an effective strategy for stabilizing Ni-rich cathodes under fast-charging conditions.