Enhancing the performance of LiMnPO₄/C composites through Cr doping

Highlights: • Two step sol–gel method to synthesize nano-sized LiMn_1−xCr_xPO₄/C composite. • Defect chemistry in the lattice could balance the valence after Cr³⁺ doping. • Aging test reveals lower surface reactivity of the LiMn_0.94Cr_0.06PO₄/C composite. - Abstract: 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 LiMn_1−xCr_xPO₄ (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, LiMn_0.94Cr_0.06PO₄/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