Green, Template-Less Synthesis Of Micron-Sized Three-dimensional Porous Electrode Materials And Their Li/K Storage Performance

Lithium-ion batteries(LIBs)have been realized the miniaturization,portablility,and wirelessness of electronic devices due to their high energy density,green,and polluting-free advantages.At present,with the technological maturity of wind power generation,solar power generation and other technologies,as well as their large-scale application,the demand for large-scale energy storage devices is increasing day by day.Owing to the scarcity of resources and high price,LIBs are gradually unable to meet the above-mentioned demand for large-scale energy storage.Potassium-ion batteries(PIBs)are emerging as the ideal choice for new generation energy storage systems because of its abundant resources and low cost.As the core component of energy devices,the electrode material greatly influences the key parameters such as energy density,power density,and service life of energy devices.Thus,it is especially important to develop and design electrode materials with high energy density and long cycle stability.Elemental materials such as red phosphorus,tellurium,selenium,and antimony are promising electrode materials due to their high lithium/potassium ion storage capacity.However,after insertion of Li/K ion,the volume of the products increases grammatically,thus the structure staibility is servely affected during cycling and the performance of batteries cannot meet the requirements of the application.Nowaday,the main approach is nanotechnology strategies which can buffer the volume change.But when reducing the size of materials,the viod ratio will be larger and the tap density will be lower owing to the agglomeration,especially after nanosizing,the energy density of batteries will be greatly reduced.The free pore space of the porous structure is able to buffer the volume expansion of active materials.On the other hand,the pore channle can effectively accelerate the infiltration of electrolyte and offer a short diffusion distance of alkali metal ion.Therefore,combining the advantages of micron size and porous structure,the design of micron-sized porous electrode materials has important implications for improving the energy density,ensuring the structural stability of electrode materials,and enhancing the overall performance of batteries.However,the preparation methods of micon-sized porous elemental materials are extremely limited and complxed,and only applicable to a single material.Therefore,developing a simple and universal approach to fabricate micron-sized porous elemental materials are of great importance for the commercial application of porous bulk elements in energy storage.In this thesis,we develop a green,template-less hydrothermal/water-bath method to prepare a series of micron-sized porous elemental materials,including porous red phorphorus,Te,Se,and Sb.Besides,to improve the electrical conductivity of porous red phosphorus,Bi(Sb)nanoparticles are anchored on the surface and pore channel of porous red phosphorus by low-temperature solvothermal menthod.Moreover,the morphology and the formation mechanism of porous structure,Li/K storage performance and structureactivity relationship are further characterizated and researched.The main research of this thesis is as follows.(1)We successfully fabricate a honeycomb-like porous micron-sized red phosphorus(HPRP)with a controlled pore structure via a green and template-less hydrothermal strategy.It is demonstrated that dissolved oxygen in the solution can accelerate the destruction of P9 cages of RP,thus forming abundant active defects with a faster reaction rate,so the fast corrosion forms the honeycomb-like porous structure.Owing to the free volume,interconnected porous structure,and strong robustness,the optimized HPRP-36 can mitigate drastic volume variation and prevent pulverization during cycling resulting in tiny particlelevel outward expansion,demonstrated by in-situ TEM and ex-situ SEM analysis.Thus,the HPRP-36 anode delivers a large reversible capacity(2587.4 m Ah g-1 at 0.05 A g-1)and longcycling stability with over 500 cycles(?81.9% capacity retention at 0.5 A g-1)in lithium-ion batteries.This generally scalable,green strategy and deep insights provide a good entry point in designing honeycomb-like porous micron-sized materials for high-performance electrochemical energy storage and conversion.(2)The three-dimensional porous red phosphorus/metal bismuth(or antimony)nanoparticles composites(HPRP@Bi(Sb))were obtained through a simple low-temperature solvothermalmethod method,where bismuth(or antimony)nanoparticles with high electrical conductivity and high specific capacity were uniformly anchored and confined in the threedimensional porous red phosphorus,and the electronic conductivity of the three-dimensional porous red phosphorus was greatly improved while maintaining the three-dimensional porous structure of red phosphorus.The porous channels of the 3D porous red phosphorus have good buffering effect on the volume expansion of bismuth(or antimony)monomers during cycling,so the composite has an excellent structural stability.HPRP@Bi anode delivers a high discharge capacity of 465.6 m Ah g-1 at 0.05 A g-1,high capacity retention of 76.4% after 100 cycles,and outshanding fast charge/discharge ability(106.4 m Ah g-1 at 3 A g-1)in potassium ion batteries.Ex-situ XRD,Raman and TEM analysis further elucidated the potassium storage mechanism of HPRP@Bi anode,i.e.,the amorphization of the nano metallic bismuth loaded on the 3D porous red phosphorus during the insertion/extraction process of potassium and are uniformly distributed and limited in the stable porous red phosphorus skeleton.This amorphous structure can accommodate the volume expansion of bismuth nanoparticles during cycling,together with the excellent electrical conductivity of bismuth metal,the HPRP@Bi composite has good structural integrity and fast kinetics when used as anode material for potassium ion batteries,so achieving stable cycling performance and excellent multiplicative performance.(3)Inspired by the preparation mechanism of HPRP,we further propose a universal template-free strategy to fabricate a series of sponge-like,interconnected porous micronsized Te and Se through H2O2-assisted water bath.The formation mechanism of porous structure is demonstrated,originating from the non-homogeneous and continuous corrosion due to the preferential intergranular corrosion of polycrystalline particles and the soluble reaction products that do not passivate the corrosion interface.The as-obtained sponge-like porous elements present large reversible gravimetric and volumetric capacities and long stable lifespans.Specifically,the porous Te electrode delivers a high reversible capacity of 392.7 m Ah g-1(volumetric capacity: 1531.5 m Ah cm-3)with 93.5% utilization ratio of active materials at 0.1 A g-1 and a long-stable lifespan with 500 cycles at 1.0 A g-1 in Li-Te batteries.Besides,in-situ TEM and ex-situ SEM observations demonstrate a small volume expansion and strong structural robustness of porous Te during cycling,stemming from its inward expansion mechanism and 3D stable interconnected porous structure.This work demonstrates a simple and universal strategy to design sponge-like porous materials for energy storage.(4)The above template-less water bath method was successfully extended to the preparation of porous antimony(p-Sb),and the morphology of porous antimony was characterized and investigated in detail.When used directly as the anode material for potassium ion batteries,the p-Sb anode delivers a high discharge capacity of 658.2 m Ah g-1 at a current density of 0.05 A g-1,and retained a high specific capacity of 495.2 m Ah g-1 after 50 cycles.Moreover,p-Sb anode exhibits a K storage capacity of 141.5 m Ah g-1 at a high current density of 5 A g-1.Therefore,the p-Sb shows much better K storage performance than r-Sb,which fully proves the advantages of porous structure design and the universality of our template-less menthod.