Effect of Ti‐Substitution on the Properties of P3 Structure Na_2/3Mn_0.8Li_0.2O₂ Showing a Ribbon Superlattice

Abstract

Oxygen anion redox offers an effective strategy to enhance the energy density of layered oxide positive electrodes for sodium‐ and lithium‐ion batteries. However, lattice oxygen loss and irreversible structural transformations over the first cycle may result in large voltage hysteresis, thereby impeding practical application. Herein, ribbon superstructure ordering of Li/transition‐metal‐ions was applied to suppress the voltage hysteresis combined with Ti‐substitution to improve the cycling stability for P3‐Na0.67Li0.2Ti0.15Mn0.65O2. When both cation and anion redox reactions are utilized, Na0.67Li0.2Ti0.15Mn0.65O2 delivers a reversible capacity of 172 mA h g−1 after 25 cycles at 10 mA g−1 between 1.6–4.4 V vs. Na+/Na. Ex‐situ X‐ray diffraction data reveal that the ribbon superstructure is retained with negligible unit cell volume expansion/contraction upon sodiation/desodiation. The performance as a positive electrode for Li‐ion batteries was also evaluated and P3‐Na0.67Li0.2Ti0.15Mn0.65O2 delivers a reversible capacity of 180 mA h g−1 after 25 cycles at 10 mA g−1 when cycled vs. Li+/Li between 2.0–4.8 V.

Effects of Particle Size and Polytype on the Redox Reversibility of the Layered Na0.76Ni0.38Mn0.62O2 Electrode

“…The mixed powders were heated at 700, 800, and 900 °C in air for 14 h with a heating rate of 5 °C min –1 and then quenched directly into an Ar-filled glovebox. Of note, a slightly higher temperature − is applied to achieve a highly crystalline P3 phase and quenching − is applied to avoid vacancies in transition metal layers. The nomenclature of samples is given in Table .…”