Compositional Gradient Design of Ni-Rich Co-Poor Cathodes Enhanced Cyclability and Safety in High-Voltage Li-Ion Batteries

Developing cost-effective high-voltage Ni-rich cathodes has reached a consensus to replace conventional ultrahigh Ni counterparts for high-energy Li-ion batteries, but more rigorous requirements are put forward for their mechanical and chemical stability. Herein, we report the design and synthesis of a full concentration gradient LiNi_0.75Mn_0.20Co_0.05O₂ cathode with a Mn-rich Ni-poor surface, which has been realized by in situ forming a PO₄^3- gradient distribution to retard the transition-metal ions' interdiffusion during the high-temperature lithiation process. This design mitigates the mechanical stress concentration at the source with high morphological integrity and refrains the lattice oxygen loss under 4.5 V high-voltage operation. After Li_0.1B_0.967PO₄ is coated, the surface parasitic reactions are further ameliorated with stable interface chemistry. The resultant Ni-rich cathodes deliver a reversible capacity as high as 212.6 mAh g^-1 at 2.7-4.5 V with an energy density of >800 Wh kg^-1_cathode, almost equivalent to the state-of-the-art Ni-content 90% cathodes at 2.7-4.3 V. In commercial-grade full cells, a superior cycle life of 80.5% capacity retention is achieved at 1C within 2.7-4.5 V after 1700 cycles, exhibiting promising opportunities in compositional gradient design for Ni-rich cathodes.