Synthesis And Performance Of Chalcogenides Anode Materials Derived From Metal-Organic Framework(MOF) For Sodium And Potassium Ion Batteries

Due to the abundant resources and low cost,rechargeable sodium/potassium ion batteries are expected to be the most attractive alternative for lithium-ion batteries in large-scale energy storage.However,in view of the increase of alkali ion radius,sodium/potassium ion batteries require the preferably reversible capacity and structural stability for electrode materials.Among many anode materials,metal chalcogenides have become the most potential candidate for anode materials of sodium/potassium ion batteries due to their advantages of high specific capacity and superior conductivity.Regrettably,this kind of materials still suffer from some intrinsic problems,such as low electron conductivity and ion diffusion kinetics,large volume variation,inferior cycling specific capacity and reversibility at superhigh rates,and so on,which block their practical applications.Therefore,in order to alleviate the above issues,this article comprehensively improves the electrochemical properties of metal chalcogenides by multidimensional component management and structure adjustment,such as the design of material composition,interface configuration,grain architecture and crystal structure,and employing the precursors of metal organic framework（MOFs）materials with structural variety and high specific surface area.This work hopes to break through the Ragone limit to synchronously acquire the high-rate and high-capacity performance,which provides theoretical support and reference for the construction of alkali ion battery anode materials with high specific energy and long-term cycling lifespan.（1）In order to address the problems of inferior electron/ionconductivity in metal chalcogenides,herein,a synergistic strategy of anion ion doping and the conduction of hollow polyhedron structure with double carbon shells was designed from the design perspective of hierarchical nanostructures.The component-optimal Co_0.85Se_1-xS_xnanoparticles wrapped by the S-doped graphene are fabricated by the in-situ sulfidation of metal organic framework（Co SSe@C/G）.Benefiting from the synergistic effect of composition and architecture regulation by S-substitution,the electrochemical kinetic behavior has been enhanced by the increased electrochemical active sites and conductivity,and the structure stability has been boosted by the mitigated volume variation.Thus,this designed material delivers prominent rate properties(266.6 m A h g^-1 at 10 A g^-1 and 195.7 m A h g^-1 at 2 A g^-1 for Na-ion and K-ion batteries,respectively),which have been verified by DFT calculation,fully demonstrating the successful improvement of electrochemical reaction rate by the synergistic strategy,and providing the reference for the design of advanced anode materials with high-rate performance.（2）In order to solve the trouble of poor ionic diffusion kinetics of metal chalcogenides at high rates,a joint modification strategy including the construction of interfacial heterostructure and the introduction of heteroatom in bulk was designed in this work according to the design idea of interface heterojunction theory.Herein,the Co S₂ materials have been synthesized by the pyrolysis of Co Fe-MOF followed by solid-sulfidation,which were with graphene coating at surface,Fe clusters anchoring at interface and Fe atoms partly substituting inner Co atoms（Fe-CFS）.Interestingly,the designed grains deliver the following advantages:the graphene combined with pyrolytic carbon forms a 3D conductive network,effectively enhancing the conductivity of the materials;the anchored Fe clusters on the surface of Co S₂ results in the formation of Schottky junction,which accelerates the potassium ions insertion/de-insertion process and restrains the dynamic polarization on the reaction interfaces;the band gap of Co S₂ has been reduced by doping Fe single atoms in the crystal lattice,which is beneficial to boost the potassium ion diffusion rate.As obtained in electrochemical performances,Fe-CFS@C exhibits a high reversible capacity of 203.1 m A h g^-1 at 5 A g^-1 after 8100 cycles,and even can still maintain 178.3 m A h g^-1 over 4000 cycles at the amplified current density of 10 A g^-1.Therefore,the interfacial engineering combined with component regulation strategy can significantly improve the ionic diffusion dynamics of metal sulfide materials,and thus achieving excellent large-rate cycling performance.（3）Aiming at the problem of structure fracture caused by stress concentration in metal chalcogenides at high rates according to the relation of structure and stress,this chapter constructs electrochemistry-isotropic amorphous metal sulfide materials by using structural design,so as to realize the stress regulation in electrochemical reaction process.The amorphous Ge S₂ materials with 2D porous nanosheets morphology are presented via the solid-sulfidation of Ge-MOF with rapid cooling process.The test results reveal that the disordered structure provides open Na⁺diffusion channels and abundant active sites,effectively restraining the volume expansion and boosting ion transmission kinetics of Ge S₂.Meanwhile,the designed structure effectively weakens the stress concentration induced by sodiation,resulting in the excellent structural tolerance.As expected,when served as the anode materials of SIBs,the amorphous Ge S₂ electrode materials express prominent reversible cycling capacity of 512.8 m A h g^-1 at a superhigh rate of 10 A g^-1,and even can still maintain 239.6 m A h g^-1 at the magnified current density of 30 A g^-1.Therefore,the results fully prove that the disordered structure design of metal sulfides can effectively relieve the generated stress during the electrochemical reaction process,and then enhance their high-rate cycling stability.（4）In view of the serious problems of volume expansion and structure collapse of metal chalcogenides at high current density,inspired by the bird’s nest structure,this study designed and synthesized（Sn Fe）S₂composite with wave-like surface morphology and cross-linked inner configuration by hydrothermal sulfidation of Sn Fe-MOF according to the perspective of confined space evolution design of hierarchical structures.The analyzed results demonstrate that the materials with rapid ion diffusion channels and stable structure deliver an excellent rate performance(389.4 m A h g^-1 at 30 A g^-1)and high-rate long-term cycling performance(627.41 m A h g^-1 at 10 A g^-1 for 800 cycles).In-situ XRD measurement combined with ex-situ TEM/HRTEM illustrates that the initial nest-like（Sn Fe）S₂ architecture can be mildly evolved into a stable sphere-like architecture,which display the synchronous self-evolution confinement effect,disperse the inner-stress and alleviate the inescapable electrode pulverization,thus fully ensuring the electrode stability and structure integrity during the repeated cycling.Thus,this designed route sheds the significant light on solving large volume-expansion type materials for high reversible capacity.（5）For resolving the problem that the power density and energy density of metal chalcogenide materials cannot be obtained synchronously,basing on the design of heterojunction interface for fast electron/ion channels,this work designs a strategy of interface bridge by building a metal-carbon bond structure at the metal sulfide-carbon interface by an interface regulation method.Herein,the designed metal sulfide enwound with graphene composite（CS@C-Bond）including the Co-C bond at interface has been constructed by a solid-sulfidation route.Benefiting from the“bridge”roles of Co-C bond,the ion/electrons have been efficiently promoted by the reduced interfacial polarization.Moreover,the formation of Co-C bridge endows CS@C-Bond materials the interfacial storage sites,which can extend the horizon of sodium storage performance.Based on these advantages,the target electrode materials achieve a superior cycling capacity at superhigh-rate(855.29m A h g^-1 at 20 A g^-1 after 1600 cycles).Given these results,the rational work fully indicates that the simultaneous increase of energy density and power density can be realized by establishing the interface bridge structure,which provides a new design concept for breaking through Ragone limitation and constructing metal sulfide anode materials with advanced high-rate performance.