Lithium-rich layered oxides (LROs) are promising cathode materials for high-energy lithium-ion batteries because of their high specific capacity and energy density. However, oxygen release, stress accumulation, and interfacial degradation during high-voltage cycling still hinder their practical application. Here, an aqueous-processed polyimide/carbon hybrid coating is designed to stabilize LROs. The coating is constructed from a polyimide and a conductive carbon network composed of carbon nanotubes and Super P. The hybrid coating layer provides surface protection, while the carbon components form continuous electron-transport pathways. During post-treatment, mild carbothermal reactions further induce surface oxygen vacancies, which help regulate oxygen-related surface reactions. The modified cathode delivers discharge capacities of 246.6 mAh g⁻¹ at 1 C, with a capacity retention of 94.9% after 200 cycles at 25 °C. This work provides a practical aqueous interfacial coating strategy for improving the durability of high-energy LROs.

The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal (TM) oxide studies in various fields, especially on the fervent topic of oxygen redox states in battery electrodes. However, critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions, which has been a popular practice in the battery field. This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements, structures, and electrochemical states through combined experimental and theoretical analyses. It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states. Furthermore, the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window, leading to a summary map of the relative energy positions of the low-lying TM states, with higher TM oxidation states at lower energies, corresponding to higher electrochemical potentials. The results naturally clarify some unusual redox reactions, such as Cr^3+/6+. This work provides a critical clarification on O-K pre-edge interpretation and more importantly a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.