Doping LiFePO4 with Al3+: Suppression of Anti-Site Defects and Implications for Battery Recycling

In this study, a group of aluminum-doped lithium iron phosphate (LFP) with varying dopant concentrations (Li_1-3x Al _x FePO₄/C, where x = 0.01-0.03) was synthesized via a solid-state reaction. Comprehensive analysis revealed that the aluminum dopant was uniformly distributed across the crystals of the synthesized samples. Notably, minor doping (x ≤ 0.01) helped reduce the formation of antisite defects within the LFP structure, lowering the defect content to 1.67% compared to 2.04% in undoped LFP. Further examination corroborated the presence of antisite defects and confirmed their reduced concentration in aluminum-doped LFP. Electrochemically, LAFP01 with x = 0.01 (or 1% aluminum doping) demonstrated an increased lithium-ion diffusion coefficient and superior electrochemical performance, achieving a discharge capacity of 155.6 mA h/g at a 0.1 C rate and surpassing that of undoped LFP. The performance improvement was more evident under rapid charge and discharge conditions, where LAFP01 maintained a higher specific capacity (86 mA h/g compared to 78 mA h/g for undoped LFP) at a current density of 5 C or greater. This study suggests that the reduced antisite defects with small aluminum doping could potentially contribute to the improved electrochemical characteristics of LFP cathodes, offering insights into enhancing lithium-ion battery performance and managing aluminum impurities in battery recycling processes.