Controlled Construction And Sodium Storage Mechanism Of Mesoscale Composite Assembly Structures Based On Titanium

The burning of fossil fuels has resulted in a deepening energy crisis and serious environmental problems,and hence,to search for the new energy sources is the key factor required for the sustainable development of human society.The application of renewable energy,such as solar,wind power,and hydropower,is critically limited,however,by the intermittent nature of supply due to the natural conditions.Among the energy storage systems,lithium ion batteries(LIBs)have dominated the market for a myriad of portable electronic devices over the past few decades due to their light weight,high energy density,lack of a memory effect,and environmental friendliness.Sodium,the next alkali metal after lithium,presents similar chemical properties to lithium,indicating that room-temperature sodium ion batteries(SIBs)are the most promising candidates to replace LIBs.In this thesis,electrode materials with micro-nano structures have been synthesized by hydrothermal or water bath method.The formation mechanism of crystalline materials and electrochemical performance of lithium-ion batteries have been explored and investigated.The main contents are as follows:1.We devise a facile self-template,in situ recrystallization,and self-assembly method for construction of bismuth/titanium dioxide heterostructure quantum dots(Bi/TiO₂ HQDs)embedded into nitrogen-doped porous carbon 2D nanosheets(denoted as Bi/TiO₂ HQDs(?)NC).Our synthesis strategy greatly simplifies the usual synthesis,as it does not require the fussy procedures involving carbon,nitrogen,titanium,and bismuth sources through multiple-step reactions or other organic solvents.Such a novel and unique 0D and 2D(0D(?)2D)multidimensional architecture has rarely been reported,and the porous carbon sheet and the quantum-scale Bi/TiO₂ heterostructure shorten the distance of sodium ion diffusion.In addition,the unique electronic states have been engineered in quantumscale Bi/TiO₂ heterostructure,giving rise to opportunities for reducing the ion-diffusion resistance and facilitating interfacial charge transport at interface during the storage process.Under the double confinement of TiO₂ and NC,the volume expansion of Bi metal QDs is alleviated during the sodiation/desodiation process.The unique 0D(?)2D multi-dimensional assembled architecture with immobilization alignment and encapsulated configuration can effectively overcome the undesirable aggregation and endow Bi/TiO₂ HQDs(?)NC hybrids with excellent sodium storage performance.An experimental and density functional theory(DFT)proves a redistribution of interfacial charge and the reduction of bandgap as the electrons transfer at the interface of heterostructures.2.The general synergistic effect of TiO₂-based heterostructures has been discovered to improve the sodium storage of anodes,involving conversion,alloying,and insertion mechanism materials.Herein,metal sulfides(?),metallic Sb and Sn,as well as,carbon nanotubes(CNTs)are chosen as the model examples from the three kinds.The introduction of TiO₂ into the MS₂ and Sb or Sn systems induces a built-in electric field as the charge transfer force at the heterojunctions,greatly reducing the ion transfer resistance and promoting interfacial electron transfer.In the CNT/TiO₂ structure,the chemical growth of TiO₂ nanoparticles on the outer surface of CNTs makes the interface more compact than the physical blending case,offering better improvement of electrochemistry.The synergy should work via the growth of heterostructures,relying on the interface effects,which always plays the promotion role through the formation of driving force or grain boundaries and/or condense phase interface to facilitate charge transfer at the interface during the storage process.Therefore,the construction of reasonable heterostructures can endow materials with intriguing electrochemical performance based on the synergistic effect.3.Preintercalating the suitable alkali cations in the titanate oxides is an effective strategy to improve the structure stability of electrode materials.In this work,for the first time,titanium dioxide(TiO₂)pre-embedded with different alkali cations(A-TO,A=Li+,Na+and K+,denoted as LTO,NTO and KTO)were systematically studied as host structure for sodium/lithium ion reversible insertion/exaction.The relationships between the structure and electrochemical properties have been investigated in detailed.Our experiment results,theory calculation,and kinetics analyses confirmed that the capacities and capacity retention of the electrode materials are affected by the interaction between the host Ti-O layers and alien cations.NTO exhibits the best electrochemical properties,indicating the vital role of the suitable ions between the interlayers.These systematic findings provide valuable information for the reasonable development of suitable host materials with enhanced sodium/lithium storage.4.Bearing in mind,we design a convenient "self-template and recrystallization-self-assembly" tactics for the one-step preparation of TiO₂ nanoparticles(NPs)embedded into N-doped porous carbon truncated ocatahedra sheets(denoted as TiO₂cNPCTO)via a self-prepared single precursor and subsequent heat calcination under an inert atmosphere.Then,we use TiO₂(?)NPCTO as a cathode material and systematically investigate the electrochemistry to store different metal ions in alkali metal batteries.The difference for three kinds of batteries at electrochemical performance and the corresponding mechanism investigation are carefully researched.Because Na-K liquid alloy is immiscible with carbonate electrolytes,it offers the establishment of a liquid-liquid connection interface between the electrode and the electrolyte.By replacing a conventional solid-liquid interface with a liquid-liquid one,the two critical problems of sodium and potassium dendrites formation and lower ICE have been completely resolved in our new battery.Furthermore,the new liquid anode-electrolyte interface contributes to the better cyclic performance and the higher ICE than that of Na-ion or K-ion battery with pure solid anode.In other words,this work provides a new way to solve the issues of dendrites formation and efficiently improves the ICE in alkali metal batteries.