Na-substitution induced oxygen vacancy achieving high transition metal capacity in commercial Li-rich cathode

Highlights: • Oxygen vacancies is successfully induced via substitution of two Li⁺ with one Na⁺. • Surface oxygen vacancies obviously affects the local Mn coordination environments. • Na_0.1-LLMO cathode delivers remarkable electrochemical behaviors. • Na_0.1-LLMO/graphite pouch cell exhibit an excellent energy retention rate. High-capacity and low-cost Li-rich layered Mn-based oxides (LLMOs) hold the great promise for next-generation lithium ion battery cathode but LLMOs still encounter grand challenges in voltage decay and gas release. Here, we proposed a simple but effective as well as scalable approach of creating surface oxygen vacancies (OVs) and simultaneously enhancing structural stability. A series of Li_1.2–2xNa_xMn_0.56Ni_0.16Co_0.08O₂ (x = 0, 0.05, 0.1 and 0.2) cathode materials are synthesized, based on Na-pre-embedded precursor and nonstoichiometric lithiation processes, to render the OVs confirmed by synchrotron radiation analysis. First-principles calculations suggest that the architecture induced by surface OVs obviously affects the local Mn coordination environments and enhances the structural stability. Meanwhile, enlarged Li layer spacing by Na doping enables increased Li diffusion, decreased voltage polarization, and enhanced structural stability. Accordingly, the optimized Na_0.1-LLMO cathode delivers highly initial coulombic efficiency of 84.2% compared to the pristine one (79.9%) and remarkable electrochemical behaviors in terms of cycling stability, voltage retention and rate performance. Pouch cell investigation further verifies the practical applicability of Na-doped LLMO cathode materials to scale up.