The construction of metal phosphate coating layers has been widely recognized as an effective strategy for protecting high-energy cathode materials in lithium-ion batteries (LIBs). However, due to the low solubility of metal phosphates, their precipitation in aqueous solution becomes too fast to control, making it a significant challenge to ensure a heterogeneous growth process towards surface coatings. Herein, we report a solution-based synthetic process to achieve conformal metal phosphate coating through coordination-assisted precipitation, which involved the reaction between phytic acid (PA), urea, and metal ions, particularly Nb⁵⁺, in ethanol solution to achieve a well-tamed coating effect. The use of PA, a plant-derived compound known as inositol hexaphosphoric acid, was facile to form soluble phytate-metal complex, which precipitated with urea to form metal-phosphate-containing coatings with thickness controlled at high precision. This proposed synthetic protocol was applied for the surface coating of high-voltage cathode materials in the form of LiNi_0.5Mn_1.5O₄ (LNMO), leading to significantly enhanced structural and electrochemical stability for its working at 5 V. Notably, after 300 cycles, the modified LNMO was able to achieve capacity retention of 85.1% for its working at 45 °C at a current density of 1 C as compared to only 29.9% of the pristine sample. Our findings highlight the potential of solution-based processes in building conformal coatings for the stabilization of high-energy cathode materials in their LIBs application.

Charging the LiCoO₂ (LCO) cathode to a higher voltage, for example 4.5 V compared to the commonly used 4.2 V, is now intensively pursued so as to achieve a higher specific capacity. However, it suffers severe surface structural degradation and detrimental interfacial side reactions between cathode and electrolyte, which lead to the fast capacity fading during long-term cycling. Here, a surface coating strategy was developed for the protection of 4.5 V LCO by constructing a manganese oxides (MOs) nanoshell around LCO particles, which was achieved through a solution-based coating process with success in controlling the growth kinetics of the coating species. We found that the introduction of the MOs nanoshell is highly effective in alleviating the organic electrolyte decomposition at the cathode surface, thus ensuring a much more stable LiF-rich cathode-electrolyte interface and an obvious lower interfacial resistance during electrochemical cycling. Meanwhile, this protection layer can effectively improve the structural stability of the cathode by hindering the cracks formation and structural degradation of LCO particles. Therefore, the MOs modified LCO exhibited excellent rate performance and a high discharge capacity retention of 81.5% after 100 cycles at 1 C compared with the untreated LCO (55.2%), as well as the improved thermal stability and cyclability at the elevated temperature. It is expected that this discovery and fundamental understanding of the surface chemistry regulation strategy provide promising insights into improving the reversibility and stability of LCO cathode at the cut-off voltage of 4.5 V.