Cathodes And Anodes Materials And Energy Storage Mechanism Of Sodium/Potassium Secondary Batteries Based On Three-Dimensional Network Structure Design

In recent years,with the widespread popularization of electric vehicles,power storage equipment,and smart power systems,people urgently need to seek new clean energy systems with high specific energy,long life,and low cost.Among them,lithium-ion batteries(LIBs)have been widely used in the field of electronics as an efficient and clean energy source.However,lithium resources are limited in the earth’s crust,and the reserves in my country are relatively small.Sodium(Na)and potassium(K)have similar physical and chemical properties to lithium,and have the advantages of abundant reserves and low price.Therefore,sodium/potassium secondary batteries are expected to meet the demand for sustainable large-scale energy storage.The development of anode and cathode materials with high specific energy and long life is the key to realize high-performance sodium/potassium secondary batteries.In terms of negative electrodes,sodium and potassium metal negative electrodes have problems such as interface instability and dendrite growth,which easily lead to battery attenuation and short circuit.Carbon materials are another type of negative electrode material with low cost and abundant output,but the kinetics of graphite-based negative electrode materials is slow when storing Na and K,which will lead to volume expansion and performance decline;in terms of positive electrodes,the positive electrode materials of LIBs contain cobalt and nickel.Such expensive transition metal elements,and the capacity provided is limited,it is difficult to meet the requirements of energy storage systems for key parameters such as low cost,high specific energy,and long life.As a new type of cathode material,sulfur-based materials have a higher theoretical capacity(2-5 times that of traditional cathodes)and lower costs.However,it has problems such as poor conductivity and serious shuttle effect.Selenium-based materials,which have comparable volumetric energy density and better electrical conductivity to sulfur,have also received great attention.However,selenium-based materials also face challenges such as volume expansion and shuttle effect.The three-dimensional structural network has the advantages of high conductivity and ease of volume expansion,which can effectively improve the cycle performance of the above-mentioned positive and negative electrode materials.Based on this,in this dissertation,a variety of anode and cathode materials for sodium/potassium secondary batteries with three-dimensional network structures were designed and constructed,which improved the electrochemical performance of sodium/potassium secondary batteries.The internal mechanism was revealed by means of simulation calculation and in situ spectroscopy,and the structure-activity relationship between materials and properties was clarified.Below are key research finding:In the first chapter,the research status of sodium/potassium metal secondary batteries is summarized in detail,and the basis and research content of this paper are proposed.The second chapter introduces the drugs,instruments,experimental methods and testing process used in the experiment.The third chapter introduces the preparation of Ni3S2/Ni3P heterostructure threedimensional framework and its application as Na metal anode.We theoretically predict that constructing a Ni3S2/Ni3P heterostructure with high work function can lower the Fermi level,thereby effectively suppressing the continuous electrolyte decomposition caused by electron tunneling after the electrode sodiation process.The Ni3S2/Ni3P heterostructured Na metal framework prepared on the basis of nickel foam not only provides abundant active sites to induce uniform Na+deposition and enhance ion transport kinetics,but also helps to form a stable SEI.The assembled Ni3S2/Ni3P@NF@Na symmetric cells exhibit a stable cycle life of 5000 hours.The fourth chapter introduces the construction of 3D flower-like crosslinked carbon sheets supported by BiGeSnSb amorphous alloy nanoparticles and used as Na/K metal framework.As the dominant nucleation site of sodium/potassium metal,nanoscale alloy particles continue to promote the uniform deposition of sodium/potassium;the electrode after molten sodium/potassium composite has a high Young’s modulus,which effectively inhibits dendrite growth;The three-dimensional carbon framework provides a large space for pre-storing Na/K and improves Na+ conductivity.The assembled symmetric cell still achieves reversible Na and K metal plating/stripping at high rate(10 mAh cm-2).In the fifth chapter,the construction of nitrogen-doped three-dimensional porous carbon nanosheets is introduced and used as anode materials for sodium/potassium ion batteries.Nitrogen-doped three-dimensional porous carbon nanosheets(N-CNS)were obtained by sintering the magnesium oxide template and the nitrogen-containing phenyl organic precursor at high temperature under vacuum-sealed conditions,and then etching.This 3D structure consists of 2D ultrathin nanosheet structures with hierarchical porosity,ultrahigh levels of pyridinic nitrogen/pyrrolic nitrogen,and enlarged carbon interlayer distances.Significantly enhanced the sodium/potassium ion intercalation/deintercalation kinetics,shortened the diffusion length of ions and electrons,and eased the volume change during cycling.When N-CNS is used as the anode material,it can stably cycle 10000 and 5000 times in sodium and potassium ion batteries.The sixth chapter introduces the preparation of nitrogen-doped hierarchically porous three-dimensional carbon skeleton as the carrier of selenium cathode.Multifunctional selenium-loaded frameworks(Se@N-HCNS)were designed by grafting ZIF-8-derived microporous carbons into the interior of nitrogen-doped porous carbon nanosheets.The two-dimensional ultrathin nanostructure helps electrolyte immersion and alleviates the volume change during selenium alloying,and nitrogen doping improves the adsorption capacity of polyselenides and inhibits the shuttling of polyselenides.The Se@N-HCNS electrode loaded with selenium has a specific capacity as high as 260 mAh g-1 at 1.0 A g-1.The seventh chapter introduces the strategy of using three-dimensional porous carbon skeleton/Ni-C3N4 to construct heterostructures through electrostatic assembly,thereby generating a built-in electric field to inhibit the dissolution of polysulfides and promote Kinetics.The built-in electric field induced by the unbalanced charge distribution can greatly facilitate the charge transfer at the atomic level,thereby enabling fast electrochemical reactions.Through theoretical calculations and experimental measurements,the built-in electric field between 2D porous carbon nanosheets/Ni-C3N4 not only effectively restricts the dissolution of polysulfides,but also regulates the loading of sulfur The electronic structure of the matrix lowers the reaction energy barrier for the catalytic conversion of sulfur species.Ni/CN-C@S loaded with sulfur exhibits a high specific capacity of 664 mAh g-1,which is 5 times higher than that of the electrode system without built-in electric field.The eighth chapter summarizes the whole paper,points out the innovations of this paper,and plans and looks forward to the next content of the deficiencies.