Compositional gradient design and microstructural engineering enable ultra-stable quinary Ni-rich cathodes in...

Developing high-voltage Ni-rich cathodes with energy densities rivaling ultrahigh-Ni counterparts is highly attractive, but the substantial de-lithiation required under high-voltage operation significantly aggravates strain accumulation and surface degradation. Herein, an in-situ co-precipitation strategy is implemented to synthesize a quinary full-concentration-gradient cathode with Mn-rich Ni-poor surface, LiNi_0.73Co_0.05Mn_0.20Al_0.01B_0.01O₂. This design markedly enhances surface mechanical strength and effectively dissipates internal tensile and compressive stresses. Well-distributed B mitigates the de-gradient effect by suppressing heat-driven transition-metal interdiffusion. The occupation of B and Al in tetrahedral interstices of transition-metal and Li layer, respectively, synergistically stabilizes the lattice oxygen, which prevents O₂/CO₂ emission during high state-of-charge (up to 4.5 V) and alleviates structural distortion of the Ni-O coordination environment after extended cycling. The resulting cathode delivers a high capacity of 210.5 mAh g^-1 (815.4 Wh kg^-1, comparable to 95% Ni cathode) and an initial Coulombic efficiency of 90.1%. It exhibits exceptional long-term cyclability in pouch-type full cells (2.7-4.5 V), retaining 87.3% capacity after 1700 ultra-long cycles. This work presents a practical approach for synthesizing electrochemically stable gradient cathodes suitable for high-voltage operation.