Mg–B–O Coated P2-Type Hexagonal Na0.5Mn0.95Ni0.05O2 as a High-Performance Cathode for Sodium-Ion Batteries

P2-type Na0.5Mn0.95Ni0.05O2 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 Na0.5Mn0.95Ni0.05O2 microspheres have been synthesized via a liquid-phase method based on solvothermal synthesized Na0.5Mn0.95Ni0.05O2. 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 Na0.5Mn0.95Ni0.05O2 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.