Enhanced Fast-Discharging Performance and Cyclability in Oxygen-Redox-Based P3-Type Na-Layered Cathode via Vacancies in TM layers

Abstract

Oxygen redox in layered oxide cathodes for Na-ion batteries is considered a promising approach for improving the energy density. However, oxygen-redox-based cathodes suffer from sluggish kinetics and undesirable structural change during charge/discharge, leading to poor electrochemical performances. Herein, introducing vacancies (□) in the transition metal layers enables the enhanced oxygen redox-based electrochemical performances in the P3-type Mn-based layered oxide cathode is demonstrated. The vacancies can play a role of the local distortion buffers, resulting in the enhanced oxygen redox kinetics and the suppressed structural deformation such as P3-O3(II) phase transition. The oxygen-redox-based P3-type Na_0.56[Ni_0.1Mn_0.81□_0.09]O₂ exhibits the large discharge capacity of ≈140.95 mAh g⁻¹ at 26 mA g⁻¹ with a high average discharge voltage of ≈3.54 V (vs Na⁺/Na). Even at 650 mA g⁻¹, its discharge capacity and average operation voltages delivered ≈122.06 mAh g⁻¹ and ≈3.22 V, respectively. Especially, the small gap of average discharge voltage indicates both improves power-capability and enhanced kinetics of oxygen redox in P3-type Na_0.56[Ni_0.1Mn_0.81□_0.09]O₂. Moreover, the vacancy buffer in the transition metal layers results in the stable cycle-performance of P3-type Na_0.56[Ni_0.1Mn_0.81□_0.09]O₂ with the capacity retention of ≈80.80% for 100 cycles, due to the suppressed P3-O3(II) phase transition.