Construction of metal phosphate coatings for improved performance of high-voltage cathode

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.