N-Methyl-2-pyrrolidone-assisted solvothermal synthesis of nanosize orthorhombic lithium iron phosphate with improved Li-storage performance

Abstract

Exploring an efficient and effective way for synthesis of lithium iron phosphate (LiFePO₄) with good Li-storage performance is a good way to fully demonstrate their applications for Li-ion batteries. In this contribution, LiFePO₄ nanoparticles were synthesized by a facile solvothermal process with water/N-methyl-2-pyrrolidone (NMP) solvent system at a moderate temperature of 180 °C. The product was determined as single-phase orthorhombic LiFePO₄, and the presence of crystal growth inhibitor NMP was favourable for the formation of smaller-sized LiFePO₄ particles with improved electrochemical properties. After a carbon coating process, the LiFePO₄/C sample afforded a reversible capacity of 140 mA h g⁻¹ at 0.5 C, 106 mA h g⁻¹ at 5.0 C at room temperature, and 163 mA h g⁻¹ at 0.5 C, 153 mA h g⁻¹ at 5.0 C at the higher temperature of 60 °C, respectively. The long cycle test at 0.2 C showed that no noticeable capacity fading was observed. The present LiFePO₄ obtained by the facile solvothermal process had good thermal and electrochemical stability, which were attributed to facile Li ion diffusion and a good electron transfer pathway in the solvothermal LiFePO₄ product.