Sodium-doped LiFe0.5Mn0.5PO4 using sodium gluconate as both reducing agent and a doping source in Lithium-ion batteries

Abstract

LiFexMn1-xPO4 (LFMP) cathode materials faces developmental challenges because Fe2+ and Mn2+ ions are prone to oxidation during the synthesis process and exhibit low electronic and ionic conductivities. We propose employing a multifunctional sodium gluconate that simultaneously acts as a reducing agent and dopant. XPS analysis shows an increased ratio of Fe2+ and Mn2+ ions within LFMP following the introduction of the reducing agent. Rietveld refinement indicates an expanded b-axis lattice space at an appropriate amount of Na-doped LFMP/C, which results in enhancement the Li+ diffusivity. SEM and TEM-EDS mapping confirm the morphology and elemental distribution of the LFMP materials. Electrochemical properties show the introduction of sodium gluconate enhanced the electrochemical properties of LFMP materials. This result demonstrates that the reducing agent prevents oxidation of transition metals during synthesis and Na doping significantly increases the Li+ diffusion coefficient. The Li0.97Na0.03Fe0.5Mn0.5PO4/C sample, when combined with a reducing agent, exhibits an outstanding rate performance of 122.6 mAh/g at 1C, 113.4 mAh/g at 5C, and 85.1 mAh/g at 20C. The enhancements in both electronic and ionic conductivities of LFMP cathodes are mainly ascribed to the incorporation of a reducing agent and Na doping.