Synthesis of Lithium Iron Phosphate Materials via an All-in-One Integrated Liquid Phase Method

Lithium iron phosphate (LiFePO₄) (LFP) has emerged as the most popular cathode material in the current lithium battery market because of its stable charge-discharge cycle performance, low cost, and high safety. Moreover, this material does not require scarce resources such as nickel and cobalt, which alleviates supply chain conflicts and reduces the environmental and health impacts associated with Ni and Co. In this study, a cost-effective preparation method is implemented to synthesize a series of all-element integrated LiFePO₄ precursors using precursor solutions with varying concentrations of oxalic acid. The final LFP materials are subsequently obtained through a one-step heat treatment. To evaluate the advantages of this method, we compare the structural and electrochemical properties of the obtained LFP materials with those synthesized via the traditional solid-phase method. The experimental results reveal that the LFP material synthesized using an oxalic acid solution with a concentration of 0.125 mol L^-1 exhibits optimal performance. This material has a grain size in the range of 300-500 nm, which is smaller and more uniform than those of the other samples. This initial specific discharge capacity of the designed LFP is 150.3 mAh·g^-1, with an initial coulombic efficiency of 88%. Notably, the material maintains a high capacity of 98 mAh·g^-1 even at -20 °C and achieves a discharge capacity of 98.7 mAh·g^-1 at a high discharge rate of 5 C. The lithium-ion diffusion coefficient was determined to be 7.1 × 10^-12 cm² s^-1, which is approximately 2.5 times greater than that of the material synthesized via the solid-phase ball-milling method. These results highlight the significant improvements in both the structural and electrochemical properties of LFP materials synthesized through this novel liquid-phase method.