Enhancing the performance of LiMnPO4/C composites through Cr doping

•Two step sol–gel method to synthesize nano-sized LiMn1−xCrxPO4/C composite.•Defect chemistry in the lattice could balance the valence after Cr3+ doping.•Aging test reveals lower surface reactivity of the LiMn0.94Cr0.06PO4/C composite.

Cr-doped lithium manganese phosphate (LiMnPO4), with a small particle size of 50 nm in diameter, is successfully prepared using a two-step technique. TEM analysis reveals that LiMn1−xCrxPO4 (x = 0, 0.03, 0.06, and 0.1) particles coated with a 4-nm-thick carbon layer are embedded in a carbon matrix. The results from XRD patterns and the d-spacings calculated from HRTEM characterization both reveal that Cr3+ is successfully doped into the lattice. Among the samples prepared in this study, LiMn0.94Cr0.06PO4/C exhibits the best electrochemical behavior in terms of specific capacities and reversibility. Furthermore, doping the composites with Cr3+ could stabilize the electrolyte/carbon interface because of low reactivity of oxygen atoms in doped LiMPO4 compounds, and the result shows that the 6% Cr3+ doped sample gives the best combination.