Construction Of Novel Hollow Structure Composites Based On Internal/External Interface Engineering For Energy Storage Applications

Lithium-ion batteries have been widely used in portable electronic devices,electric vehicles and smart grids in the past three decades because of their high energy density,long cycle life and green environmental protection.As a commercial lithium-ion battery anode material,the theoretical specific capacity of graphite is only 372 m A h g^-1,and when it is used as the negative electrode of potassium ion battery,its theoretical specific capacity is279 m A h g^-1,so the graphite negative electrode is difficult to meet the development needs of the next generation of high-performance battery system.Transition metal chalcogenide compounds（oxides,sulfides,selenides,etc.）are regarded as potential high-performance anode materials because of their theoretical specific capacity,environmental friendliness and low price.However,the intrinsic conductivity of metal chalcogenide compounds is low,and great volume changes will occur in the process of charge and discharge,which will lead to the collapse of electrode structure,the sharp decrease of battery capacity and the attenuation of rate performance.In order to solve the above problems,the construction of hollow metal chalcogenide/carbon nanocomposites can effectively improve the conductivity and cache the volume change,and obtain the battery negative electrode with excellent performance,which is the mainstream strategy adopted by the current researchers.In this paper,aiming at the problem of weak charge transfer in traditional hollow composites,the anode material of lithium/sodium/potassium ion battery with both long cycle and excellent rate is realized by adjusting the outer coating and building an internal efficient charge transfer network.the following three research work is mainly carried out:1.Monodisperse single-walled carbon nanotubes（SWNTs）are used as construction units.A porous SWNTs layer is coated on the surface of hollow Fe₃O₄ by electrostatic adsorption,thus effectively improving the conductivity of Fe₃O₄,and its porous structure is conducive to the rapid intercalation of lithium ions.The prepared Fe₃O₄@SWNTs shows high lithium storage capacity and long-range cycle performance,and the capacity is 408 m A h g^-1 after1000 cycles at 8 A g^-1.Compared with graphene-coated samples,SWNT-coated Fe₃O₄ and Fe Se₂ composites showed significantly improved rate performance and cycle stability in Li/Na/K ion batteries.2.Using Ni-based metal-organic framework（MIL-77）as precursor,Ni S_1.03/C@C composites with bell-like structure were constructed by Si O₂ hard template method.Ni S_1.03/C converted from MIL-77 as internal active material can effectively improve the internal charge transfer efficiency of bell-like structure,thus showing excellent potassium storage performance.The reversible capacity of 212 m A h g^-1 can be maintained after 2000 cycles at 1 A g^-1 current density,and the rate capacity is 205m A h g^-1 at the current density of 20 A g^-1.3.The Co S₂/C@C composite with bell-like structure is constructed based on coordination polymer（Co-NTA）,in which the Co S₂/C converted from Co-NTA is uniformly filled in the hollow carbon shell and has abundant internal voids.As the negative electrode of sodium/potassium ion battery,it can effectively buffer the volume change of Co S₂ during charge and discharge and improve the charge transfer efficiency of the bell-shaped structure.The capacity is maintained at 271 m A h g^-1 after1000 cycles at the current density of 1 A g^-1,and the rate capacity is 277 m A h g^-1 at 20 A g^-1.As a negative electrode of potassium ion battery,Co S₂/C@C also showed good cycle stability(232 m A h g^-1)and rate performance(220 m A h g^-1 at 20 A g^-1).