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 (square) 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 Na0.56[Ni0.1Mn0.81 square 0.09]O2 exhibits the large discharge capacity of approximate to 140.95 mAh g-1 at 26 mA g-1 with a high average discharge voltage of approximate to 3.54 V (vs Na+/Na). Even at 650 mA g-1, its discharge capacity and average operation voltages delivered approximate to 122.06 mAh g-1 and approximate to 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 Na0.56[Ni0.1Mn0.81 square 0.09]O2. Moreover, the vacancy buffer in the transition metal layers results in the stable cycle-performance of P3-type Na0.56[Ni0.1Mn0.81 square 0.09]O2 with the capacity retention of approximate to 80.80% for 100 cycles, due to the suppressed P3-O3(II) phase transition. Due to the presence of vacancies which can play a role as buffer for local distortion in transition metal layer, P3-Na0.56[Ni0.1Mn0.81 square 0.09]O2 enables stable oxygen redox reactions. The average discharge voltage difference between 26 and 650 mA g-1 is only similar to 0.32 V, and it exhibits excellent structural stability, successfully suppressing undesirable P3-O3(II) phase transitions and retaining approximate to 80.80% capacity after 100 cycles. image