Structure Design Of Anode Materials For Potassium Ion Batteries To Enhance The Potassium Storage Performance

With the rapid development of lithium-ion batteries(LIBs),their application fields have become more and more extensive and have gradually been applied to electric vehicles in recent years.And the demand for LIBs is also rapidly increasing at the same time.However,the relatively scarce lithium resources in the earth's crust(0.0017 wt%)are not enough to support the long-term use of LIBs,it is an urgent need to develop new energy storage systems(EESs)to achieve sustainable development.Potassium-ion batteries(PIBs),due to the similar electrochemical performance as LIBs,rich in potassium resources(1.5 wt%),and the low redox potential(2.93 V vs.SHE)of K⁺/K,was considered to be the next-generation large-scale EES with great potential.However,because the radius of potassium ion(1.38(?))is larger than that of lithium ion(0.76(?)),the development of PIBs has encountered several obstacles:the slow kinetics of potassium ion diffusion,the large resistance of the ion insertion/extraction electrode material,and the large change in the volume of the electrode material during charging and discharging,etc.The above factors result in the unsatisfactory electrochemical performances of PIBs.As the key component of the battery,electrode materials determine the performance of the battery to a large extent.In order to promote the development of PIBs,the design and research of high-performance PIBs electrode materials is significance.This thesis focuses on improving the potassium ion diffusion kinetics,stabilizing the electrode material structure,and improving the energy density.Particularly,conversion type and alloy type anode materials with higher theoretical specific capacity were taken the as the research objects,and realized the optimization electrochemical performance of PIBs by designing the electrode material structure.(1)A three-dimensional ordered macroporous zinc-based MOFs was used as precursors,through carbonization,sulfuration and subsequent ion exchange,a composite of copper sulfide nanoparticle embedded in three-dimensional ordered macroporous carbon framework(3DOM Cu₉S₅@C)was successfully prepared.Specifically,the interconnected three-dimensional ordered macroporous structure can provide a rapid diffusion channel for potassium ions,and also provide a large surface area for full contact between electrode material and electrolyte,which is beneficial to improve the diffusion kinetics of potassium ions.In addition,the macroporous structure can effectively alleviate the volume change of the electrode material during the discharge/charging process,improving the structural stability of the electrode material.Furthermore,the active material Cu₉S₅ nanoparticles are well embedded in the carbon framework,which significantly improves the overall conductivity of the electrode material.When used as an anode electrode material for PIBs,the prepared 3DOM Cu₉S₅@C composite exhibits excellent rate performance(reversible specific capacity of 170 m A h g^-1 at a current density of 2.0 A g^-1)and cycling stability(reversible specific capacity of 316 mA h g^-1 after200 cycles at 100 m A g^-1).(2)A novel two-dimensional material MXene as the conductive substrate,the Mo Se₂nanosheets grew on the MXene through the hydrothermal method,and then the polydopamine-derived carbon layer was uniformly coated on the Mo Se₂/MXene hybird nanosheets(Mo Se₂/MXene@C).Specifically,the Mo Se₂ nanosheets are vertically anchored on the MXene substrate to form a hierarchical two-dimensional structure,which effectively alleviates the self-stacking of the Mo Se₂ nanosheets and improves the conductivity of the composite material.Further,the carbon layer uniformly coated on the surface of the hierarchical two-dimensional structure is beneficial to improve the stability of the nanostructure and improve the conductivity of the composite.Meanwhile,chemical interactions are existed on the interface between the Mo Se₂ nanosheet and the MXene substrate,which helps to promote charge transfer kinetics and improve structural stability.When used as an anode electrode material for PIBs,Mo Se₂/MXene@C exhibits ultra-stable cycling performance:A high reversible capacity of 355m A h g^-1 is maintained after 100 cycles at a current density of 200 m A g^-1.Impressively,the prepared composite exhibits excellent rate performance with an ultra-high specific capacity of183 m A h g^-1 at 10.0 A g^-1.(3)Antimonene nanosheets prepared by the liquid phase exfoliation method are stacked with graphene through suction filtration to realize the antimonene nanosheets and the graphene layer stacking to prepare a composite film,and then heat-treated phosphorus doping to obtain the antimonene nanosheets/phosphorus doped graphene membrane(Sb NS/PG).In particular,peeling off the metal antimony into nanosheet structure can significantly increase its exposed area and shorten the diffusion distance of potassium ions to improve the electrochemical reaction kinetics.The phosphorus-doped graphene conductive network can effectively improve the conductivity of the composite.Meanwhile,with coated by the extremely flexible phosphorus-doped graphene,the structural stability of the membrane electrode during the potassium storage process has been further improved.When used as the self-supporting anode electrode of PIBs,the Sb NS/PG film shows excellent cycle stability and rate performance:A high reversible specific capacity of 477 m A h g^-1 is obtained after 50 cycles at 200 m A g^-1 with a high initial coulombic efficiency of 73.1%.Furthermore,it shows a reversible specific capacity of 403 m A h g^-1 at a high current density of 2000 mA g^-1.