N doping promotes the multiplication capability and cycling stability of cobalt-free lithium-rich layered cathode materials

Abstract

Cobalt-free lithium-rich layered oxides (LLOs) become a new hotspot in energy storage science due to their high specific capacity and high voltage. However, challenges such as the dissolution and depletion of transition metals, cycling instability due to irreversible oxygen release, and structural transformations hinder their commercial application. In this study, Li_1.2Mn_0.6N_xNi_0.2O₂ (x = 0, 0.01, 0.02, 0.03) is synthesized by de-doping the substrate material with varying amounts of N using carbonate co-precipitation and high-temperature solid-phase methods. The cathode material doped with 2 % N exhibits the best electrochemical performance. This improvement is attributed to the introduction of N, which occupies oxygen sites, enlarges the lattice spacing, mitigates the mixing of Li⁺/Ni²⁺ in the material, and enhances lattice oxygen content. This leads to better cycling stability and excellent performance during multiple cycles. The modified sample shows a 27.18 % increase in capacity retention after 0.1C 100-cycle testing, and voltage decay during cycling is limited to only 0.342V. The study introduces a novel approach for anion doping to develop high-performance, cobalt-free, lithium-rich manganese-based cathode materials with enhanced discharge efficiency and cycling stability.