Advanced Electrode Materials Design And Their Electrochemical Performance For Lithium-Ion And Sodium-Ion Batteries

With the rapid development of electric vehicles and smart grid,large-scale energy storage systerms have become a strategic technology to support the development of clean renewable energy.Room temperature sodium-ion batteries have been considered as a promising candidate for energy storage applications due to the worldwide sodium abundance,low cost,better safety as well as moderate energy and power density,which currently is one of the most advanced electrochemical energy storage technologies.Prussian blue analogues(PBAs)have attracted extensive interest in the context of energy storage due to their open-framework structure,high surface areas,porous structure and simple synthesis.Furthermore,an aerosol spray technique has been the most promising for functional materials processing with broad application prospect.This method could efficiently produce mono-dispersed spherical powder from either a liquid or a slurry.Particles with high-purity can be produced simply using an economical,a continuous way and a rapid process.As the most promising anode material for next-generation high-capacity lithium-ion batteries,the challenge for silicon-based negative electrode material is the rapid capacity decay,low initial charge-discharge Coulombic efficiency(CE)due to its huge volume expansion during lithiation-delithiation cycling.The thesis mainly focuses on the design and assembly of electrochemical energy storage devices:low-cost,long-life room temperature sodium ion battery and high energy lithium ion battery.The structure design and preparation of new Prussian blue analogues,high performance silicon carbon composites,charge storage mechanism as well as devices construction and optimization have been carried out systematically in our thesis,summarized as follows:1.M3?[Co?(CN)6]2(M=Co,Mn)Prussian blue analogues: a new class of anode materials for lithium ion batteries: Prussian blue analogues have recently gained attention as a new class of cathode materials for rechargeable batteries.However,the anode properties of the host framework have been very limited.Herein,we demonstrate that nanoparticles of cobalt hexacyanocobaltate and manganese hexacyanocobaltate,typical Prussian blue analogues with the chemical formula of M3II[Co III(CN)6]2·n H2O(M=Co,Mn),can be operated as novel battery anodes in an organic liquid-carbonate electrolyte.The Co3[Co(CN)6]2 material exhibits a clear electrochemical activity in the voltage range of 0.01-3 V vs.Li/Li+ with a reversible capacity of 299.1 m Ah g-1.Furthermore,superior rate capability(as the current density increasing from 20 to 2000 m A g-1,capacity retention of about 34%)could be achieved,attributing to the small particle sizes and rapid transport of Li+ ions through large channels in the open-framework.2.Flexible PBAs and PBAs with fast kinetics through electronic coupling for sodium ion batteries: The concerns about the Prussian blue analogues are their insufficient cycle life and low Efficiency in non-aqueous electrolytes for sodium-ion batteries,associated with the low electrical conductivity and structural imperfection.In this chapter,we report a significant advance in the design and preparation of Prussian blue analogues Fe Fe(CN)6·x H2 O nanoparticles on a flexible carbonfiber paper as a binder-free cathode in both organic and aqueous electrolytes.This electrode structure design with high conductive scaffold for loading electroactive materials effectively prevents loss of active mass and enhances electrical contact,which make it an ideal candidate for use in SIBs.The Na-ion insertion/extraction mechanism and significantly improved sodium storage were examined by ex situ 57 Fe M?ssbauer spectroscopy.With the merits of carbon cloth paper such as flexible structure and high conductivity,the resulting Fe Fe(CN)6·x H2 O nanocomposite electrode exhibits excellent electrochemical performance: reversible specific capacity of 82 m Ah g-1 at 0.2C,prolonged cycling performance with 81.2% capacity retention for 1000 cycles,and good high rate response up to 10 C.Furthermore,a simple and new method is demonstrated to enable Ni HCF nanocrystals to be an excellent host for sodium ion storage by functionalization with redox guest molecule.The method is achieved by using Ni HCF PBA powders infiltrated with the TCNQ solution.Experimental and ab initio calculations results suggest that TCNQ molecule bridging with Fe atoms in Ni HCF leads to electronic coupling between TCNQ molecules and Ni HCF open-framework,which functions as an electrical highway for electron motion and conductivity enhancement.Combining the merits including high electronic conductivity,open framework structure,nanocrystal,and interconnected mesopores,the Ni HCF/TCNQ shows high specific capacity,fast kinetics and good cycling stability,delivering a high specific capacity of 35 m Ah g-1 after 2000 cycles,corresponding a capacity loss of0.035% decay per cycle.3.Synthesis of nanostructured materials by using PBAs and their electrochemical properties:We demonstrate a novel and simple one-step process for preparing Li Co O2 nanocrystals by using Prussian blue analogue Co3[Co(CN)6]2 as precursors.The resultant Li Co O2 nanoparticles possess single crystalline nature and good uniformity with an average size of ca.360 nm.The unique nanostructure of Li Co O2 provides relatively shorter Li+ diffusion pathways,thus facilitating the fast kinetics of electrochemical reactions.As a consequence,a high reversible capacity,excellent cycling stability and rate capability is achieved with these nanocrystals as cathodes for lithium storage.The Li Co O2 nanocrystals deliver specific capacities of 154.5,135.8,119,and 100.3 m A h g-1 at 0.2,0.4,1,and 2C rates,respectively.Even at a high current density of 4C,a reversible capacity of 87 m A h g-1could be maintained.Importantly,capacity retention of 83.4 % after 100 cycles is achieved at a constant discharge rate of 1C.Furthermore,owing to facile control the morphology and size of Prussian blue analogues by varying process parameters,as well as the tailored design of multi-component metal-cyanide hybrid coordination polymers,with which we have successfully prepared porous Fe2O3@Nix Co3-x O4 nanocubes,one of the potential anode materials for lithium-ion batteries.4.Mesoporous silicon carbon composites by an aerosol spray method and application in lithium ion batteries: Silicon anode suffers from huge volume expansion during electrochemical cycling,resulting in disintegration of the electrode and subsequent rapid capacity fading.One effective strategy is to construct a layer of conductive shell with adaptable void space,which can effectively accommodate the volume change during cycling.Herein we report selective growth of nitrogen doped graphene cages as an ideal encapsulation onto aerosol-assisted assembly of micro-sized silicon spheres,which is achieved by using magnesiothermic reduction products as novel template and catalyst.This method allows direct growth of highly graphitic graphene over silicon microparticles without the introduction of extra catalyst.Graphene cage with high graphitic characteristic successfully improves electrode stability by confining the electrochemical reaction of silicon,and simultaneously maintains electrical connectivity of fractured silicon particles.The hybrid anode exhibits remarkable lithium storage performance in terms of significant high specific capacity,fast rate response(890 m Ah g-1 at 5 A g-1),and excellent cycling performance over 200 cycles with consistently high CE at the current density of 1 A g-1.A full battery test against Li Co O2 has demonstrated a higher energy density exceeding 329 Wh kg-1 with high CE.Polybenzimidazole was used as novel carbon sources for mesoporous silicon microspheres,which was achieved by an aerosol-assisted assembly combined with a polymer solution physisorption process.The new polymer derived carbon endows silicon with the structural and compositional characteristics of intrinsic high electronic conductivity,abundant pyrrolic nitrogen,and structure robustness.The resulting mesoporous Si-PBI carbon composite exhibits excellent lithium storage performance in terms of high reversible specific capacity of 2172 m Ah g-1,superior rate capability(1186 m Ah g-1 at 5 A g-1),and prolonged cycling life.As a result,a fabricated Si/Li Co O2 full battery demonstrates high energy density of 367 Wh kg-1 as well as good cycling stability for 100 cycles.