Preparation Of Metal-based Nanoparticles And Their Applications As Anodes In Alkali Metal-ion Batteries

In recent years,with the continuous development of energy storage technology,alkali metal-ion batteries[such as lithium-ion batteries(LIBs),sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs)]as an important part of them have attracted more and more attention.In alkali metal-ion batteries,negative electrode materials play an important role,and affect the electrochemical performance of the whole battery.Metal-based materials(including metal oxides)as anodes have the characteristics of low cost,easy availability of raw materials and environmental friendliness,prompting us to carry out in-depth research on them.Here,we have selected several current metal-based hotspot materials,and are committed to solving the key problems they face in different battery devices.In LIBs,TiO₂ has attracted special attention because of its good safety,small volume change during cycling,and non-toxicity.However,the electrochemical properties of TiO₂ are limited due to its low theoretical capacity,low Li⁺mobility and conductivity,and serious agglomeration during cycling.Recently,due to the rising price of Li and the increasing demand for energy storage systems in many fields,the energy storage devices outside LIBs have been developed vigorously.Both K and Na are earth-abundant elements with low cost and rich resources.Therefore,in large-scale energy storage devices,LIBs may be replaced by SIBs and PIBs.In SIBs and PIBs,metal-based materials have the advantages of high theoretical capacity and low reaction potential,which can store electric energy by alloying with Na/K-ions,showing potential commercial application prospect.However,the volume change of alloy materials during cycling leads to the rapid capacity decreasing.In LIBs/SIBs/PIBs,small-sized nanoparticles(<20 nm)can ensure the full utilization of active materials;and accelerate stress release during cycling.Therefore,the preparation of small-sized nanoparticles helps to improve the electrochemical performances of electrode materials.Moreover,the combination of active materials and carbon materials is also considered an effective means to improve performances.The preparation of composite materials containing metal-based nanoparticles as the starting point of research has been carried out in the following three aspects:(1)Preparation of surface-amorphized TiO₂ nanoparticles/graphene(SA-TiO₂/RGO)composite and its applications in LIBsThe surface amorphous/disordered structure can reduce the size of nanoparticles and facilitate the transport of electrons and ions.The effective connection of above material and carbon substrate can further optimize the electrochemical performances of the electrode.Here,SA-TiO₂ and RGO are combined tightly through covalent C-O-Ti bonds using hydrothermal method.The prepared SA-TiO₂/RGO composite delivers outstanding rate property(135.6m Ah g^-1 at 10 A g^-1)and long cycling stability(98 m Ah g^-1 at 5 A g^-1 after 2000 cycles).The outstanding electrochemical performances of SA-TiO₂/RGO can be attributed to the ultrasmall SA-TiO₂ nanoparticles(?7 nm),high electron transport capacity of RGO and SA-TiO₂,and close combination between SA-TiO₂ and RGO.(2)Preparation of ultrasmall SnSb nanoparticles/three-dimensional N-doped nanoporous carbon frameworks(SnSb/3D-NPC)composite and its applications in SIBsAs a SIBs anode material,SnSb alloy is becoming a research hotspot.At present,how to prepare ultrasmall nanoparticles(average diameter<5 nm)and select suitable substrate for further improving the electrochemical performance of the alloy need to be solved urgently.Here,we synthesized a hybrid of ultrasmall SnSb nanoparticles(average diameter<2 nm)encapsulated in 3D-NPC via a facile chemical reduction method.Note that this method has good scalability.Sb/3D-NPC and Sn/3D-NPC composites with ultra-small nanoparticles were prepared by the same chemical reduction method though changing the salt composition in the precursor.As a SIBs anode,SnSb/3D-NPC exhibits high discharge capacity(693.6 m Ah g^-1 at0.2 A g^-1 after 100 cycles),excellent rate performance(359.1 m Ah g^-1 at 20 A g^-1)and long cycling stability(266.6 m Ah g^-1 at 5 A g^-1 after 15000 cycles).Such outstanding performance is ascribed to the well-dispersed ultrasmall SnSb nanoparticles and unique three-dimensional integrated structure.(3)Preparation of porous Sn nanospheres/N-doped carbon nanofibers frameworks(Sn/N-CNFs)composite and its applications in PIBsMetal Sn is considered as a negative electrode material with potential application value for PIBs.However,the volume change of Sn is up to 360%upon K⁺insertion/extraction,which leads to structural deterioration of electrode materials.In order to solve this problem,Sn/N-CNFs was prepared by electrospinning and subsequent carbonization.The composite exhibits excellent rate performance of 168.7 m Ah g^-1 at 2 A g^-1 and outstanding cycling stability(316.1 m Ah g^-1 at 0.1 A g^-1 after 100 cycles;198.0 m Ah g^-1 at 1 A g^-1 after 3000cycles).Such attractive electrochemical properties can be ascribed to porous Sn nanospheres composed of nanoparticles(average diameter(?)15.2 nm),carbon skeleton around Sn nanoparticles,and cross linked N-CNFs.