Synthesis And Performance Of Metal Sulfides Anode Materials For Potassium Ion Batteries

As one of the most effective substitutes for lithium-ion batteries in large-scale energy storage,potassium-ion batteries have attracted much attention in the energy field due to their abundant resources and low cost.However,the inherent large ionic radius of potassium ions makes it easy to cause volume change or even structure collapse of electrode materials during reversible electrochemical cycle.Therefore,the development of electrode materials with high structural stability and enhanced reaction kinetics has become the main strategy to realize the practical application of potassium ion batteries in the future.Metallic chalcogenides are one of the most attractive anode materials for potassium ion batteries due to their low cost and high energy density.However,the poor conductivity,serious polysulfide shuttle effect and poor reversibility of conversion reaction of these materials greatly hinder their practical application in potassium ion batteries（PIBs）.Therefore,in order to solve the above problems,this article based on framework structure,phase composition and interface design,etc.,employed the controlled strategy of component and structure to comprehensively promote the physical and chemical properties,finally realizing the comprehensive improvement of the electrochemical performance.Notably,it provides a thought for the design and development of anode materials for potassium ion batteries with high specific energy and long service life.（1）Based on the two-dimensional layered nanostructure,aiming at the problem of poor structural stability of metal sulfide,a novel quasi-two-dimensional Bi₂O₂S@r GO composite nanosheet material was designed and prepared by room temperature chemical precipitation method in this work.Attributing to the layered structure and unique crystal framework structure of Bi₂O₂S,the Bi₂O₂S@carbon electrode has shown potential with superior potassium storage property,which delivers a capacity of223.7 m Ah·g^-1 after 100 cycles at 100 m A·g^-1 as anode for PIBs.Thus,the two-dimensional layered nanostructure design can effectively improve the structural stability and potassium ion storage reversibility of electrode materials.（2）Based on the interaction between mechanical stress and material structure,aiming at the problems of poor structural stability and capacity decline of metal sulfide,herein,an effective inner-stress-dissipative strategy is reported for core-shell Co Fe S₂/C quantum dot anodes（abbr.CFS/C）for PIBs.The rational constructed core-shell CFS/C quantum dots can not only effectively relieve the inner mechanical stress,restraining the continuous pulverization of active material,but also form the covalent interaction between internal nanodot and external carbon shell can strengthen the integrity of electrode,achieving excellent nanostructure stability with enhanced cycling lifespan.Meanwhile,due to the abundant active sites and short diffusion path of quantum dot materials,the reaction kinetics could be vastly improved.Consequently,the CFS/C electrode operates for more than 1200 cycles at 2 A g^-1 with a capacity of 205 m Ah g^-1 and achieves a desirable rate capability of 172.4 m Ah g^-1 at 10 A g^-1.This result fully demonstrates that the core-shell framework combined with quantum dot structure design strategy can effectively improve the structural stability of materials,thereof strengthen the cycling lifespan of electrode materials.（3）Based on the quantum dot structure design,aiming at the problem of poor reaction kinetics of metal sulfide and polysulfide shuttle effect,the quantum dot structure with catalytic conversion capability was synchronously introduced into the design of Fe S₂ anode materials to heighten its K⁺storage performance in this work.The constructed quantum dot structure anchored by the graphene with space-confinement effect shortens the ion diffusion path and enlarges the active area,thus accelerating the ion transmission kinetics and absorption action,respectively.The intermediate phase of formed Fe nanoclusters possesses high-active catalysis ability,which can effectively suppress the polysulfide shuttle combined with the enhanced absorption effect,fully guaranteeing the structure stability and cycling reversibility.Thus,the fabricated quantum dot Fe S₂ materials express a prominent advantage in rapid potassiation/depotassiation process(518.1 m A h g^-1,10 A g^-1)and a superior cycling lifespan with gratifying reversible capacity at superhigh rate(177.7 m A h g^-1,9000 cycles,5 A g^-1).Therefore,engineering quantum dot structure with self-induced catalysis action for detrimental polysulfide is an achievable strategy to implement high-performance sulfide electrode materials for accommodate potassium ions.（4）Based on the intrinsic characteristics of polar molecules,aiming at the problems of poor reaction reversibility of metal sulfide and polysulfide shuttle effect,this work introduces polar polysulfide VS₄ into Sn S nanosheets with constructing layered VS₄/Sn S heterostructure anchored in graphene scaffold（abbr.VS₄/Sn S@C）.In this framework,polar VS₄ with unsaturated bridging（S₂）^2-can act as the anchoring sites to stabilize intermediates K_xS_y with entrapment effects.More impressively,the layered heterostructure can maintain layered Sn S and regulate the distribution of K_xS_y with high conversion reversibility.Consequently,the VS₄/Sn S@C electrode exhibits ultra-long lifespans,which achieves a capacity of 168.4 m Ah g^-1 at high rate of 1 A g^-1 after 6000 cycles.This strategy of layered heterostructure design facilitates the comprehensive understanding of K-storage mechanisms and significantly enhances the reaction reversibility,providing a thought to address the challenges in metal sulfide anodes toward the development of high-performance PIBs.（5）Based on the conductive and catalytic characteristics of monatomic metals,and aiming at the problems of poor conductivity,serious shuttle of polysulfide and poor reversibility of transformation reaction for of metal sulfide,a rationally designed Cu₉S₅/MoS₂/C heterostructure hollow nanocage was synthesized in this work.During K-storage process,the homogeneously distributed sulfiphilic nature of Cu⁰reaction product could act as dual-functional catalyst,not only facilitates rapid charge transfer,but also effectively anchors（K_xS_y）polysulfides,thus boosting K-storage reactions reversibility during conversion reaction process.When applied as anode for PIBs,the as-prepared heterostructure exhibits excellent reversible capacity and long cycle lifespan(350.5 m Ah g^-1 at 0.1 A g^-1 and 0.04%percycle capacity decay at 1 A g^-1 after 1000cycles).The nanoarchitecture designing strategy for advanced electrode in this work can effectively improve the potassium ion storage properties,and provide vital guidance for exploiting relevant energy storage materials.