Preparation And Electrochemical Performance Of Gel Composite Electrodes For Secondary Battery

Lithium ion battery and sodium ion battery have been the major choice for the energy storage system because of its many advantages,such as high specific energy,low self-discharge rate,long cycling life,no memory effect and no pollution.However,the low capacity of electrode material can't meet the requirement of high performance storage decvices,seeking a kind of high energy density and long cycle life electrode is becoming urgent.Three dimensional porous carbon aerogel has high specific surface area and abundant pore structure.This special porous structure can provide continuous channel for ion transportion,shorten the ion diffusion path,ensureing good electrical contact,which is a very promising candidate for energy storage electrode materials.Aiming at these problems,the carbon aerogels,reduced graphene oxide aerogels and metal compounds are used as the main body in this paper,doping and compositing strategies are taken to enhance the electrochemical performance of advanced electrode materials,further study the electrode structure-activity relationship of composite materials,investigate the relevant electrochemical mechanism of secondary battery based on gel composite electrode.The main research content are summarized as following.(1)A facile sol-gel polymerization and impregnation route is developed to fabricate the novel mesoporous 3D interconnected NiCo-NiCoO2/carbon xerogel(CX)hybrids with a homogeneous carbon coating layer on the surface of NiCo and NiCoO2 nanoparticles,the metallic NiCo nanoparticles are introduced in the NiCo-NiCoO2/CX hybrids via a partially reducing chemical reaction at a high annealing temperature.The result of Nitrogen adsorption/desorption and cycling voltammograms test show that smaller NiCo particles increase the specific surface of composite and provide more active sites.The highly dispersed NiCo particles can effectively facilitate the decomposition of Li2O during the charge-discharge process,thus greatly enhance the electrochemical performance.The elastic nature of CX matrices and carbon layer coating on the surfaces of NiCo and NiCoO2 nanoparticles,renders the NiCo-NiCoO2/CX hybrids very effective in accommodating the volume strain and enhance the rate performance,greatly improve the NiCo-NiCoO2 electronic conductivity and ionic diffusion rate.The mesoporous 3D interconnected NiCo-NiCoO2/CX hybrids show significantly improved electrochemical performance,which can be attributed to their unique microstructure characteristics.After 100 cycles,the NiCo-NiCoO2/CX hybrids anode can still get a reversible capacity of 861 mAh g-1 at current density of 100mA g-1,which is 2.8 and 1.9 times higher than that of the CX(305 mAh g-1)and NiCoO2/CX hybrid(456 mAh g-1),respectively.(2)To effectively alleviate the severe volume expansion,pulverization and aggregation of anodes during the charge and discharge processes,we designed novel three-dimensional porous Sn@PVP-CX composites as anodes for lithium ion batteries(LIBs),in which Sn nanoparticles(NPs)are wrapped with outer layer of polyvinyl pyrrolidone(PVP),and the Sn@PVP core-shell nanostructures are homogenously loaded on mesoporous carbon xerogel(CX)matrix.Introducing a flexible and stable layer of PVP on surface of Sn NPs can effectively prevent the aggregation of Sn NPs and counteract the pulverization of Sn NPs due to the large volume changes generated during the lithiation-delithiation processes.CX acted as a conductive matrix,displaying porous structure with merits of continuous porosity,interconnected 3D porous structure and large interfacial surface area,can effectively alleviate the strain and stress from volume changes,provide the sufficient channel for Li ions and electrons,shorten the diffusion path of Li ions.The unique Sn@PVP-CX with Sn@PVP NPs homogenously loaded on the CX matrix can show improved structure stability as LIBs anodes.The LIBs based on Sn@PVP-CX composite anode display greatly improved electrochemical performance,showing a capacity of 757 mA h g-1 at a current density of 100 mA g-1 after 100 cycles.After 10 cycles as anode material in LIBs,the TEM images find the micro structure of PVP coated Sn particles reserved ery well.This may be used to explain the reseason of Sn@PVP-CX with more stable cyclic performance compared to Sn-CX composite electrode material.(3)Propylene epoxide as ring opening agent,Mn-doped Co2(OH)3Cl 3D mesoporous xerogels assembled from nanoparticles was developed via a one-step sol-gel method.Because of Co2(OH)3Cl incorporates both chlorine and hydroxyl functional groups simultaneously,which shows high theoretical capacity and excellent cycling stability.The uniquely special 3D hierarchically porous interconnected xerogel structure is composed of nanoparticles,showing high surface area.After TEM,N2 adsorption/desorption and EIS tests,the effect of Mn doping on the microstructures,surface area,charge transfer kinetics,and electrochemical performance of Mn-doped Co2(OH)3Cl xerogels was systematically investigated.It was observed that proper metal doping improve electronic conductivity and structure stability,increase the active sites.4%Mn-doped Co2(OH)3Cl xerogels display excellent electrochemical performance,with a superior capacity of 1377 mA h g-1 after 50 cycles at a current density of 100 mA g-1.Even when the current density was increased to 1600 mA g-1,it still retained a capacity of 824 mA h g-1.(4)A new type of hierarchically reduced graphene oxide wrapped NiCo2S4 composite composed of reduced graphene oxide(RGO)matrix is developed by template and the charge adsorption method and investigated as anode material for Li-ion and Na-ion storage.The hollow NiCo2S4 prisms consisting of interconnected nanoparticles possess a lot of pores,providing sufficient electrode/electrolyte contact area,as well as acting as cushion spaces for the huge volume changes during discharge-charge processes.The three dimensional RGO backboned matrix not only enhance the electrode conductivity,but also acts as a confinement layer to prevent the NiCo2S4 nanoparticles from aggregating,buffer the volume change effect during charge/discharge processes,assure the stability of the fragile hollow structure.EX-XRD was conducted to research electrochemical reaction mechanism.As a consequence,the RGO-NiCo2S4 anode exhibits an impressive reversible capacity of 903 mAh g-1 after 80 cycles at 500 mA g-1 for Li-ion storage.Moreover,a reversible Na-ion storage capacity of 530.2 mAh g-1 with negligible fading is also achieved after 70 cycles at 50 mA g-1.(5)Based on a simple liquid reduction and high tempreture phosphorization method,we fabricate CNT@carbon aerogel-Sn4P3 composites as anode material for sodium ion battery and investigate the electrochemical performance..Hard carbon materials have high specific capacity,low voltage sodium storage and good cycle stability.Carbon nanotubes as conductive substrate with a special tubular structure is beneficial to the transition of electrolyte and electrons.The Sn4P3 and carbon nanotube composites can effectively alleviate the huge volume change of anode material during charge and discharge processes,suppress Sn4P3 nanoparticles aggregation and improve the electric conductivity.By CV test,the sodium ion storage mechanism of Sn4P3-C was researched.After 50 cycles,the discharge capacity can still retain 513 mAh g-1 at a current density of 50 mA g-1.Even when the current density increases to 300 mA g-1,we can get capacity of 360 mAh g-1 after 400 cycles,showing an excellent electrochemical performance.