Optimization of Comprehensive Properties in LiFePO4/C Cathodes via Doping with Diverse Aluminum Sources

To improve the inherently low electronic and ionic conductivity of lithium iron phosphate (LFP) cathode materials, the synergistic modification of Al doping and carbon coating has been proven to be an effective strategy. However, the doping effects of different aluminum (Al) sources have not been systematically compared, and the mechanism of the synergistic effect between the characteristics of the Al source and the synthesis process remains poorly understood. To address this, the present study systematically investigated the effects of three Al sources on the structure and electrochemical performance of LFP/C composites under two sintering processes: static and dynamic. Phase and microstructure characterizations confirmed the successful doping of Al3+ and the formation of an effective carbon coating. Electrochemical tests indicated that the choice of Al source and sintering process was strongly coupled: in the dynamic fluidized-bed process, which is highly characterized by efficient mass and heat transfer, Al(OH)3, due to its lower thermal decomposition temperature and the release of active H2O, promoted uniform Al3+ doping and optimized the quality of the carbon coating, thereby achieving the best overall performance. By contrast, under the sluggish reaction kinetics of static sintering, the chemically stable Al2O3 achieved ordered doping through slow solid-state diffusion, demonstrating the best cycling stability. In both processes, the overly stable AlPO4 failed to release Al3+ effectively, resulting in limited performance improvement. This work reveals the key principle that the intrinsic reactivity of the Al source must be matched with the kinetics of the sintering process, deepens mechanistic understanding of the doping modification, and provides clear experimental evidence for the selection of the optimal Al source under different synthesis processes.