Study On Synthesis Of Alloying Anodes And Electrochemistry Of Potassium Storage

With the development of new energy storage fields(electric vehicles and portable electronic devices),the shortage of lithium resources and uneven geographical distribution have caused increasing concern about the severe reliance on LIBs.Hence,sodium-ion batteries(NIBs)and potassium-ion batteries(KIBs)have attracted tremendous interest because of their approximate physical and chemical characteristics to those of LIBs.Among them,PIBs have received growing attention due to the extensive global abundance of potassium resources and low potential of potassium(-2.936 V vs.standardhydrogen electrode),PIBs seems to be a more prospective replacement of LIBs as large-scale energy storage systems(solar and wind energy).In the development of anode material,carbon matrix electrode material has dominated the important position.Currently,graphite is the most stable choice for commercial anode in LIBs.However,the development of NIBs still faces great challenges because sodium will be deposited on the graphite surface before forming sodium–graphite intercalation compounds.Potassium and graphite form stable KC8 in the PIBs,and its theoretical capacity is about 279 m Ah g-1 through calculation.However,the larger ionic radius and slower kinetic reaction rate of K+(1.33 nm)than that of Li+ result in significant polarization and huge volume expansion in the charge and discharge process.Therefore,the development of carbon matrix anode materials for PIBs still needs further improvement.In this paper,Three carbon matrix composites were synthesized,including phosphorus nanoparticles encapsulated in the reduced graphene oxide(P@RGO),antimony nanoparticles encapsulated in the 3D porous carbon(Sb@PC)and tin Submicron-particles encapsulated in the reduced graphene oxide(Sn@RGO)network as the electrode materials for PIBs.Based on the study of the electrochemical properties of three kinds of composite materials,The alloying mechanism and the reason of excellent performance is explained.Several feasible paths for the development of PIBs anode materials are summarized as follows:(1)The RP and RGO powders were mixed uniformly uniformly and put into a stainless-steel autoclave.In the absence of air,red phosphorus and white phosphorus can be converted to each other.After a certain time of being heated at 500 ?,the RP powder was vaporized and dispersed into the defects and surfaces of the RGO layers.Then,upon cooling(260 ?),the phosphorous vapor condensed and was deposited on the defects and surfaces of RGO.In this design,the P@RGO matrix features are RP nanoparticles uniformly distributed in the RGO matrix,which has a lamellar structure.As a result,the P@RGO matrix electrode material delivers a good reversible specific capacity,excellentcycling stability,and superior rate capability.(2)By a simple and controllable high temperature solid phase method,the insert Sb nanoparticles into the 3D porous carbon(Sb@PC)was obtained directly.As PIBs anode,the Sb@PC delivers a high specific capacity,good rate capability and stable cycling performance.The superior electrochemical performance of Sb@PC is mainly due to the hierarchically porous carbon encapsulated Sb nanoparticles,which can not only effectively avoid the direct exposure of elemental Sb to the electrolyte,but also accommodate the mechanical stress induced by the large volume expansion of Sb nanoparticles during charge and discharge process.(3)A simple synthesis strategy is reported to make the submicron metallic tin particles encapsulated in the reduced graphene oxide(RGO)network as the electrode materials for PIBs.The as-prepared Sn@RGO possesses a homogeneous dispersion and intimate contact between the Sn-based particles and RGO network,abundant structural defects and a high Brunauer-Emmett-Teller(BET)surface area(136.5 m2 g-1).To highlight the crucial effect of high surface area is conducive to the capacitance,cyclic voltammogram measurements are conducted to verify the contributions of surface-dominated K-storage.Meanwhile,the alloying phase observed in ex-situ XRD scans at the end of one K-alloying half cycle.Considering the cost-effectiveness and material sustainability,this work shows a promising development of Sn-based anode materials for PIBs.