Mg-B-O Coated P2-Type Hexagonal Na_0.5Mn_0.95Ni_0.05O₂ as a High-Performance Cathode for Sodium-Ion Batteries

P2-type Na_0.5Mn_0.95Ni_0.05O₂ as the cathode for sodium-ion batteries, has a relatively high theoretical specific capacity, but its unstable crystal structure and undesirable phase transitions lead to rapid capacity decay. In this work, Mg-B-O coated Na_0.5Mn_0.95Ni_0.05O₂ microspheres have been synthesized via a liquid-phase method based on solvothermal synthesized Na_0.5Mn_0.95Ni_0.05O₂. The Mg-B-O coating layer significantly improves the electrochemical performance, including specific capacity, rate capability, and cycle stability. Within the voltage window of 2.0-4.0 V, Mg-B-O coated Na_0.5Mn_0.95Ni_0.05O₂ could exhibit an initial capacity of 93.2 mAh g^-1 at a current density of 500 mA g^-1, and maintains a capacity of 74.6 mAh g^-1 after 500 cycles, with a capacity retention rate of 80.0%. The Mg-B-O coating effectively inhibits the formation of Na₂CO₃ on the surface, enhancing air stability, reducing the Jahn-Teller effect induced by Mn³⁺, as well as ensuring fast Na⁺ diffusion kinetics. This work provides a new strategy for designing P2-type layered sodium-ion batteries with both high specific capacity and cycling stability.