High-entropy modulation and surface engineering promising 4.8 V-tolerant practical Co-free ultrahigh-Ni cathodes
High-Ni (Ni ≥ 0.9) layered cathodes are being developed to endure high-voltage operations above 4.5 V to boost energy density. However, they face exacerbated chemo-mechanical and electrochemical degradation under high-voltage operation, primarily due to excessive lattice strain and phase distortion during cycling. Here, we engineer a high-Ni, Co-free cathode featuring a multicomponent complex doping-modulated bulk structure, coupled with surface modification via a multifunctional atomic layer deposition-coated LiAlO2 layer. Such a unique framework achieved by surface-to-bulk integrated modification can not only greatly prevent lattice stress-induced mechanical degradation but also effectively mitigate the accumulation of by-products due to surface side-reactions. Moreover, the LiAlO2 nanoshell with exceptional ion conductivity markedly enhances the sur-/interfacial Li-ion migration kinetics, thus rendering low electron/ion-diffusion resistance. The developed cathode breaks through existing voltage constraints without compromising on performance, achieving an exceptional balance between capacity and cycle stability during operation at 4.8 V. Notably, the pouch-type cells utilizing graphite and Li metal anodes demonstrate excellent cyclability under demanding conditions, even operating at high charging cut-off voltages of 4.5 and 4.6 V, respectively.