The influence of iron site doping lithium iron phosphate on the low temperature properties and the diffusion mechanism of lithium ion

Abstract

Lithium iron phosphate (LiFePO₄) is emerging as a key cathode material for the next generation of high-performance lithium-ion batteries, owing to its unparalleled combination of affordability, stability, and extended cycle life. However, its low lithium-ion diffusion and electronic conductivity, which are critical for charging speed and low-temperature performance, have become the primary constraints on its broader application. This study addresses these challenges by investigating the impact of Mn, Ti, and V doping on the low-temperature discharge characteristics of LiFePO₄. The article presents the synthesis of LiFe_0.95V_0.05PO₄, LiFe_0.95Ti_0.05PO₄, and LiFe_0.95Mn_0.05PO₄, which have demonstrated impressive discharge capacities of 88%, 80%, and 76% at − 20 °C compared to their performance at 25 °C. The vanadium doping strategy has been found to encourage the spherical growth of lithium iron phosphate material, resulting in nano-spherical particles with a balanced transverse and longitudinal growth rate. This growth pattern is attributed to the interplay between the “Mosaic models” and “Radial models” of lithium ion diffusion. The electronic and ionic transport properties have been analyzed using density functional theory, revealing that it possesses low formation energy at the Fe site. This characteristic allows for stable doping at the Fe site, leading to the formation of Mn–O, Ti–O, and V–O chemical bonds. The doping with vanadium significantly lowers the migration energy barrier and activation energy for lithium ions, thereby enhancing their transmission rate. These findings indicate that vanadium doping is an effective strategy to improve the low-temperature discharge performance of LiFePO₄ cathode materials.