Diammonium Hydrogen Citrate-Assisted Spray Pyrolysis Synthesis of Nanostructured LiCoPO₄ Microspheres as High-Voltage Cathode Material for Lithium-Ion Batteries

Nanostructured LiCoPO₄ (LCP) microspheres were successfully synthesized by one-step spray pyrolysis, adding an appropriate amount of diammonium hydrogen citrate (DHC) additive to the precursor solution. Comprehensive physical characterization confirmed that the obtained LCPs exhibited a desirable orthorhombic olivine structure with nanostructured morphology and a significant increase in specific surface area. This enhancement was attributed to the dispersion effect due to the carboxyl group and the evolution of the ammonium group of DHC during the pyrolysis process. The resultant LCP delivered a high initial discharge capacity of 132 mA h g^-1 with 63.3% capacity retention (vs 103 mA h g^-1 and 37.1% of bare-LCP) after 50 cycles at 0.1 C using the conventional electrolyte. Moreover, the electrochemical performance showed additional enhancement when a fluorinated electrolyte was introduced, resulting in initial and 50th discharge capacities of 141 and about 100 mA h g^-1, respectively, at 0.1 C.