Construction And Electrochemical Properties Of Electrode Materials For Sodium/potassium Ion Batteries With High-performance

Due to the limited resources and uneven distribution of lithium in the Earth's crust,the sustainable development and large-scale application of lithium-ion batteries(LIBs)have imposed significant challenges.Thus,it is highly desirable to develop new secondary battery systems as the alternative to LIBs.Sodium and potassium,belongs to alkali metal element family,have similar chemical properties but much higher abundance and lower price compared to lithium.Therefore,sodium/potassium-ion batteries(NIBs/KIBs)are considered as one of the most promising next-generation battery technologies for low-cost and large-scale energy storage applications.However,the larger radius of Na⁺/K⁺ions causes larger volume change,sluggish kinetic and even different electrochemical reaction mechanism,which leads to significant challenges in realizing practical NIBs/KIBs.In this dissertation,a series of high-performance electrode materials for rechargeable NIBs/KIBs were designed and synthesized.Their electrochemical performance,storage mechanisms and structure-function relationship were systematically investigated.The findings are summarized as following:(1)Bismuth nanoparticle@carbon(Bi@C)composite with core-shell structure was prepared via a facile annealing method using a commercial coordination compound precursor of bismuth citrate.The Bi@C composite presents outstanding sodium storage performance with an ultra-long cycle life of 30000 cycles and a capacity retention of95%at a high current density of 8 A g^-1,and excellent rate capability of 71%capacity retention at an ultra-high current rate of 60 A g^-1.(2)Highly graphitized nitrogen-doped carbon nanotubes(NCNTs)with an edge-open layer-alignment structure was synthesized using a simple and scalable approach of pyrolyzing zeolitic imidazolate framework compound.The unique structure enables a facile and fast intercalation of K⁺ions.As anodes for KIBs,the NCNTs shows a good stability of over 500 cycles at 2000 mA g^-1 and a superior rate capability by presenting a high capacity retention of 102 mA h g^-1 at 2000 mA g^-1.(3)A composite nanosheet with nanosized bismuth-antimony alloy particles embedded in porous carbon matrix(Bi Sb@C)was synthesized via a facile pyrolysis process using a mixture precursor of bismuth potassium citrate and potassium antimonyl tartrate sesquihydrate.As the anode for KIBs,the Bi Sb@C composite presents markedly improved cycling performance,compared with fast capacity decay of single alloy electrodes.Further operando X-ray diffraction results unveiled that the storage mechanism of Bi Sb@C composite is based on the potassiation/depotassiation reaction process within the bimetal solid solution,that is,(Bi,Sb)?K(Bi,Sb)?K₃(Bi,Sb).(4)A novel nanocomposite was designed and synthesized by anchoring red P nanoparticles on a 3D carbon nanosheet(red P@CN)framework via the vaporization-condensation strategy.As an anode material for KIBs,the red P@CN composite demonstrated a superior electrochemical performance with a high reversible capacity of 655 mA h g^-1 at 100 mA g^-1 and a good rate capability remaining 323.7 mA h g^-1 at2000 mA g^-1.In addition,the experimental characterizations and theoretical calculation results suggest KP is the final potassiation product,corresponding to a theoretical capacity of 843 mA h g^-1.(5)The microporous C/S composite was synthesized by utilizing a microporous carbon-confined small-molecule sulfur.As the cathode in KIBs,the microporous C/S composite delivered a reversible capacity of 1198.3 mA h g^-1 and retains 72.5%after150 cycles,which is attributed to the sulfur stabilization effect of microporous carbon.The potassium-storage mechanism was further investigated by experimental analysis and theoretical calculations,which unveil that K₂S is the final potassiation product,giving a theoretical capacity of 1675 mA h g^-1.