Antimony-based Composites Are Used As Anode Materials For Potassium Ion Batteries

In recent decades,lithium-ion batteries have been widely used commercially due to their high energy and power density.However,the limited storage and uneven distribution of lithium resources restrict the application of lithium-ion batteries in large-scale energy storage.Considering the rich resources of potassium in the earth’s crust and similar chemical properties to lithium,potassium-ion batteries have become promising alternatives to lithium-ion batteries.However,due to the lack of suitable anode materials,the practical application of potassium ion batteries still has a long way to go.Scientists have studied a variety of anode materials,including hard carbon,soft carbon,transition metal sulfides/oxides,alloy materials,etc.for anodes of potassium ion batteries.Antimony in alloy materials has become a star anode material for potassium ion batteries due to its high theoretical capacity(600 m Ah g^-1),suitable operating voltage,low bulk density,and good conductivity.However,antimony exhibits a huge volume change（～400%）during the intercalation/deintercalation of potassium ions,leading to pulverization of antimony particles,loss of electrical contact,causing a sharp decline in capacity and reducing potassium storage performance.Existing researches have proved that nanometer antimony and compounding with conductive matrix（soft carbon,hard carbon,carbon nanotubes,etc.）can effectively adapt to volume changes and improve electrochemical performance.In this paper,two kinds of antimony-based composites were obtained by mixing and pyrolyzing the precursors of antimony with the precursors of a conductive matrix,and exhibited surprising potassium storage properties,as follows:First,this paper prepared a composite of ultrafine antimony nanocrystals in-situ in carbon nanofibers composed of nanochannel arrays by electrospinning and subsequent heat treatment（u-Sb@CNFs）.Carbon nanofiber substrates（MCNFs）composed of nanochannel arrays were obtained by electrospinning and carbonizing a polyacrylonitrile（PAN）/polystyrene（PS）mixture,and antimony nanocrystals were uniformly dispersed in a carbon matrix.Thanks to this,u-Sb@CNFs adapt well to the volume change of antimony during the potassium intercalation/depotassium process and exhibits rapid electron and ion transport capabilities.At the same time,u-Sb@CNFs is also a flexible freestanding electrode,which saves the trouble of adding conductive agent,adhesive and current collector,reduces the invalid weight,and shows better performance than Sb@s-CNFs（Sb@C nanofiber without PS）.Notably,the reversible capacities of 393 m Ah g^-1 at 0.2 A g^-1,299 m Ah g^-1at 0.5 A g^-1,225 m Ah g^-1 at 1 A g^-1,and 188 m Ah g^-1 at 2 A g^-1 are well retained after 100,1000,2000,and3000 cycles,respectively.After that,this paper used a simple physical mixing and subsequent heat treatment method to synthesize titanium carbide MXene@Antimony@Carbon（MXene@Sb@C）composite.MXene@Sb@C-M demonstrates high specific capacity,stable cycling performance and excellent rate performance.It provides a large reversible specific capacity of 475.1 m Ah g^-1 at 200 m A g^-1,and a capacity retention rate of 93.73%after100 cycles.It shows a reversible capacity of 177.7 m Ah g^-1 at a current density of 5 A g^-1.Such excellent electrochemical performance depends on the unique structure of MXene/C.MXene acts as a layered 3D matrix,which accelerates the transport of electrons and ions,which is beneficial to the infiltration of the electrolyte.The synergistic effect of MXene/antimony/carbon layer makes the compound adapt to the volume change during potassium/depotassium and has stable mechanical properties.The results above provide a possibility for the practical application of antimony-based composites for potassium storage.