Multi-functional surface treatment enhances structural and electrochemical properties of Li-rich Mn-based cathodes for Li-ion batteries

The surface of the cathode materials is an outpost for dealing with structural degradation and unfavorable side reactions with the electrolyte, and surface engineering to improve the inherent defects of Li-rich Mn-based oxides (LRMO) is a highly promising strategy. Herein, surface functional modification of LRMO was achieved through a one-step solid-phase method using thioacetamide (TAA), which successfully introduced S doping and in situ induced spinel thin layers on the surface of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂. This integrated surface modification strategy combines the advantages of doping and coating single modifications to obtain TAAS-LRMO with superior cycling stability and rate performance. The capacity retention of TAAS-LRMO after 100 cycles is as high as 89.1% better than that of the bare LRMO (72.3%), while the average voltage decay is reduced from 7.04 mV to 4.71 mV. And the energy density retention of the modified sample rose from 60.2% to 79.5%. Experimental characterization and theoretical calculations jointly reveal that the modulation of the local electronic structure through S doping leads to enhanced transition metal‑oxygen (TM-O) covalency and an increased formation energy of oxygen vacancies. Together with the protective effect of the spinel coating, these factors improve structural stability during the cycling process. Additionally, the reduced band gap and lower lithium-ion migration energy induced by S doping and the three-dimensional lithium-ion transport channels provided by the spinel structure synergistically promote redox kinetics. This work provides a new integrated surface modification approach to commercializing Li-rich Mn-based oxide cathodes.