In-situ compositing HA significantly enhancing electrochemical performance of Mn-MOF anode materials

Abstract

MOFs (metal–organic frameworks) have large specific surface area, abundant active sites, and tunable pore structures, making them highly attractive anode materials for lithium-ion batteries. However, their inadequate electrical conductivity and rate performance greatly hinder the further applications of MOFs in field of energy storage. In this study, we present a robust Mn-MOF/HA (humic acid) composite anode material with multilayer nano-sheet structures, synthesized via in-situ compositing HA with Mn-MOF in general hydrothermal reaction. The Mn-MOF derived from hydrothermal reaction shows poor electrochemical stability and low electrical conductivity. The incorporation of HA notably elevates electrochemical stability of materials, boosts both electrical and lithium-ion conductivity, and also modulates the microstructure to form ultrathin multilayer nanosheets by rationally adjusting the feed ratio of HA. The resulting HA₂₀-Mn-MOF (with a HA feed ratio of 20 %) demonstrates significant improvements in cycling stability and rate performance, with a reversible specific capacity of 1318.7mAh/g at 0.1 A/g after 100 cycles and a substantial capacity of 657.0mAh/g even after 1000 cycles at 1 A/g. An extraordinary V-shaped capacity reversal is observed for HA₂₀-Mn-MOF during cycling. Ex-situ EPR (Electron Paramagnetic Resonance) investigation reveals this capacity growth is associated with the reoxidation of active manganese during cycling, in which a notable correlation between the specific capacity and the Mn²⁺ signal intensity in EPR spectra is found. These results suggest in-situ compositing HA with MOFs can be a cost-effective strategy in regulating MOFs morphology and in achieving an optimized electrochemical performance for MOFs-based electrode materials in energy storage field.