Study On Preparation Of Telluride Anode Materials For Sodium-ion Batteries And Their Electrochemical Properties

The increasing demand for energy storage has led to the rapid development of lithium-ion batteries(LIBs),but the extremely limited lithium resources cannot meet the demand for larger-scale energy storage.Therefore,sodium-ion batteries(SIBs),which work similarly to LIBs and have abundant raw material reserves,have been widely studied.However,the large sodium ion radius(1.02(?))always leads to unstable cycling performance and slow kinetics.Therefore,finding a suitable anode material is a major challenge in the commercialization of SIBs.Metal chalcogenides have been widely studied for their satisfactory theoretical capacity among many anode materials.Among the sulfur group elements(S,Se,and Te),tellurium(Te)has higher electrical conductivity,lower electronegativity,and larger atomic radius,so theoretically metal tellurides would exhibit superior electrochemical properties.Therefore,it is necessary to apply metal tellurides to SIBs anode materials and explore the sodium storage mechanism.In various metal tellurides,the theoretical capacities of cobalt telluride(CoTe₂,341 mAh g^–1/2700 mAh cm^–3)and antimony telluride(Sb₂Te₃,513 mAh g^–1/3419 mAh cm^–3)are considerable and valuable for research.However,CoTe₂ will generate some degree of polarization and volume strain during the cycling process.Similarly,Sb₂Te₃ undergoing conversion-alloying reactions have a severe volume strain(280%)when antimony and sodium ions react to form Na₃Sb,which results in unstable electrochemical performance and rapidly decaying of the battery.However,with the help of optimization strategies such as nanosizing,compounding with carbon materials,and special structural design,CoTe₂,and Sb₂Te₃ are still expected to be high-performance anode materials for SIBs.Therefore,in this thesis,cobalt telluride(CoTe₂@3DPNC)and cobalt telluride-antimony telluride(CoTe₂/Sb₂Te₃@NCNFs)composites are studied in-depth and systematically from synthesis,characterization,electrochemical properties,kinetic process,and sodium storage mechanism.The specific ideas are as follows:(1)A three-dimensional porous composite with unique dual-type carbon confinement CoTe₂ nanoparticles(CoTe₂@3DPNC)was obtained by introducing sodium chloride as a template through freeze-drying,polyvinylpyrrolidone(PVP)coating,and high-temperature in-situ tellurization.In particular,the graded porous structure derived from the sodium chloride template and the high-temperature pyrolysis of organic matter not only allows the electrolyte to more fully infiltrate the interior of the material but also effectively shortens the diffusion distance of sodium ions,which facilitates the rapid kinetic process.The double-layer nitrogen-doped carbon layers can effectively suppress the volume change of CoTe₂ nanoparticles during the charge/discharge process and avoid the crushing,shedding,and agglomeration of CoTe₂nanoparticles,which can cause the reversible specific capacity decay.The CoTe₂@3DPNC composites have been rationally designed to exhibit excellent cycling stability(190.7 mAh g^–1/553.3 mAh cm^–3 at 1 A g^–1 after 1200 cycles,118.1 mAh g^–1/342.5 mAh cm^–3 at 5 A g^–1 after2500 cycles)and rate performance.Subsequently,we investigated the kinetic processes of CoTe₂@3DPNC composites from two perspectives of sodium ions diffusion and capacity contribution using galvanostatic intermittent titration technique(GITT)test and CV test at different scan rates,respectively.Finally,we clearly revealed the conversion type sodium storage mechanism of this material in SIBs through ex-situ characterization techniques.(2)The disordered ZIF-8 particles were subtly embedded into the interior of one-dimensional polyacrylonitrile(PAN)nanofibers by the mature high-voltage electrospinning technology,and then a unique double-layer nitrogen-doped carbon nanofibers embedded with CoTe₂ and Sb₂Te₃ nanoparticles(CoTe₂/Sb₂Te₃@NCNFs)was obtained by heat treatment,ion replacement,and in-situ tellurization.Nanofibers form an interconnected conductive network that enables the rapid transfer of electrons and ions.The successful introduction of antimony-based materials with high specific capacity by partial asymmetric ion substitution method can not only reduce the content of Coelement but also obtain more pores,which can further effectively alleviate the volume stress and particle agglomeration during cycling.Further,Sb₂Te₃ nanoparticles with high theoretical specific capacity can not only improve the reversible specific capacity of the composites but also maintain the cyclic stability of CoTe₂.After the electrochemical performance measurements,the excellent cycling capacity(301.8mAh g^–1 at 0.2 A g^–1 after 500 cycles,222.1 mAh g^–1 at 1 A g^–1 after 1000 cycles)and rate performance of CoTe₂/Sb₂Te₃@NCNFs composites demonstrate the practical application of this material in SIBs.More importantly,we clearly clarified the battery(conversion-alloying)-capacitance dual model Na-ion storage mechanism of the CoTe₂/Sb₂Te₃@NCNFs electrode by using ex-situ XRD,HRTEM,and SEAD.Finally,a Na-ion full battery(CoTe₂/Sb₂Te₃@NCNFs//P2-Na NMMT-4)was assembled and obtained excellent cycling performance and rate capability,which further proved the practicality of the anode material.