Tuning the electrochemical behaviors of N-doped LiMnxFe1–xPO4/C via cation engineering with metal-organic framework-templated strategy

Abstract

LiFePO4, as a prevailing cathode material for lithium-ion batteries (LIBs), still encounters issues such as intrinsic poor electronic conductivity, inferior Li-ion diffusion kinetic, and two-phase transformation mechanism involving substantial structural rearrangements, resulting in unsatisfactory rate performance. Carbon coating, cation doping, and morphological control have been widely employed to reconcile these issues. Inspired by these, we propose a synthetic route with metal–organic frameworks (MOFs) as self-sacrificial templates to simultaneously realize shape modulation, Mn doping, and N-doped carbon coating for enhanced electrochemical performances. The as-synthesized LiMnxFe1–xPO4/C (x = 0, 0.25, and 0.5) deliver tunable electrochemical behaviors induced by the MOF templates, among which LiMn0.25Fe0.75PO4/C outperforms its counterparts in cyclability (164.7 mA h g−1 after 200 cycles at 0.5 C) and rate capability (116.3 mA h g−1 at 10 C). Meanwhile, the ex-situ XRD reveals a dominant single-phase solid solution mechanism of LiMn0.25Fe0.75PO4/C during delithiation, contrary to the pristine LiFePO4, without major structural reconstruction, which helps to explain the superior rate performance. Furthermore, the density functional theory (DFT) calculations verify the effects of Mn doping and embody the superiority of LiMn0.25Fe0.75PO4/C as a LIB cathode, which well supports the experimental observations. This work provides insightful guidance for the design of tunable MOF-derived mixed transition-metal systems for advanced LIBs.