Enhancement of the reversible capacity and cycling stability of sodium cathode materials by Li+ reversible migration

Abstract

Sodium-ion batteries, because of their sustainability and low cost, provide an attractive alternative to Li-ion technology for large-scale energy storage. However, their applicability still faces a large challenge due to the lack of high energy density and cycling-stable Na-based positive materials. Here, we design and synthesize a P2-type Na_0.7Li_0.1Mg_0.2Mn_0.7O₂ material exhibiting synergistic anionic and cationic redox activity. This material exhibits a high reversible capacity of 217 mA h g⁻¹ which is attributed to Mn³⁺ − e⁻ = Mn⁴⁺ and O²⁻ − ne⁻ = O⁽²⁻ⁿ⁾⁻ demonstrated by combined spectrum and DFT calculations. Not only high energy density, NLMMO also exhibits high cycling stability with a reversible capacity of 183 mA h g⁻¹ (84.3%) for 50 cycles. These findings, rationalized by DFT calculations, reveal the effect of interlayer Li⁺ migration on regulating structural stability, achieving a high reversible capacity. The present study offers a new strategy for designing high-performance cathode materials with synergistic anionic and cationic redox reactions.