Study On Construction And Lithium Storage Performance Of Titanium-based Oxide Composites

New energy storage technologies offer ways to solve the storage and conversion of renewable energy,which is an effective strategy to deal with the energy crisis and environmental issues caused by the continuous consumption of fossil fuels.Lithium-ion batteries have become the most widely used energy storage and conversion equipments standing out from various energy storage devices due to their large energy density,long cycle life,no memory effect and environmental friendliness.With the rising development of new energy vehicles and smart grids,lithium-ion battery energy storage technology needs further innovation and progress.The electrode material of lithium ion batteries is a key factor in determining its lithium storage performance.Traditional graphite anode has poor rate and safety issues,so the development of high-performance anode materials has become a research hot point.Titanium-based oxides are ideal candidate anode materials for power lithium-ion batteries due to their better structural stability and higher safety performance.The poor conductivities hinder their practical applications,however.In order to solve the above problems,in this work a series of titanium-based oxide composite materials are prepared through rational design of composite structure,such as composition with carbon materials,coating with uniform carbon layer and introducing second phase of titanium-based oxide.Finally,the electrode system conductivity is improved,and anode materials with excellent electrochemical performance are achieved.In addition,the material characterization and electrochemical performance of titanium-based oxide composites are investigated,and the influence factors between material structure and electrochemical reaction are discussed in detail.Li4Ti5O12/TiO2 dual-phase composites are prepared by using solvothermal combined supercritical fluid technology.The rich interface between Li4Ti5O12 and TiO2 could connect the channel of lithium ion transport,and increase additional lithium storage sites in Li4Ti5Oi2/TiO2 composites.In addition,the reduced particle size might shorten the transport path,and the increased oxygen vacancies could promote the rapid insertion/extraction of lithium ions.In the unique solvothermal reaction process,Li4Ti5O12 and TiO2 are in-situ composited,resulting in enhanced synergistic effect and enabling improved rate and cycle performance for Li4Ti5O12/TiO2 composite anode materials.The initial discharge capacity of Li4Ti5O12/TiO2 electrode is 191 mA h g-1 at a current density of 100 mA g-1,and the reversible capacity of 154 mA h g-1 is achieved at a current density of 1600 mA g-1.After 500 cycles at the current density of 1000 mA g-1,the remaining lithium storage capacity is 142 mA h g-1 with a capacity retention of 90.7%.Li2TiSiO5/soft carbon composites are prepared by one-step method using pitch as soft carbon source.Interconnected soft carbon skeletons in the composites act as intermediary between Li2TiSiO5 particles and connect the channels for lithium ion transport.The reduced particle size might shorten the path of lithium ion transport,and the increase of specific surface area is conducive to the transfer of lithium ion at the interface between electrode and electrolyte.The formation of Li2TiSiO5 and soft carbon occurred simultaneously,and the electron interaction between them enables the composite materials producing more adaptive oxygen vacancies,which effectively improves the conductivity.Since Li2TiSiO5 and soft carbon component are combined in situ in a small scale though the one-step synthesis process,Li2TiSiO5/soft carbon composite electrodes exhibit excellent capacity,cycling and rate performance due to the unique structure and synergistic effect.Li2TiSiO5/soft carbon electrode delivers a high initial discharge capacity of 443 mA h g-1 at a current density of 100 mA g-1,and presents a reversible capacity of 165 mA h g-1 and 127 mA h g-1 at the current density of 1600 mA g-1 and 3200 mA g-1 respectively.The long-life cycling is achieved with a capacity retention of 273 mA h g-1 after 1500 cycles under a current density of 500 mA g-1.Li2TiSiO5@C composites with stable heterogeneous interface are constructed,and the effects of structure and composition of the composites under different heating temperatures on the electrochemical performance are investigated.The carbon layer with uniform and controllable thickness in Li2TiSiO5@C composite provides a stable and continuous channel for lithium ion transport and diffusion,thus promoting lithiation/delithiation process and enhancing the reaction rate.Moreover,the carbon layer can weaken the side reaction between electrode material and electrolyte.Importantly,the heating temperature could affect concentration of oxygen vacancies and defect degree of carbon layer in composites.Appropriate heating treatment would build the optimal interface to reduce the interfacial transfer resistance,thus promoting the transfer of lithium ions at the interface between electrode and electrolyte.The Li2TiSiO5@C electrode exhibits an optimized lithium storage capacity of 345 mA h g-1 after 500 cycles at a current density of 100 mA g-1,and a reversible capacity of 210 mA h g-1 after 1100 cycles at a current density of 500 mA g-1.At higher current density of 1600 mA g-1 and 3200 mA g-1,the reversible capacity reaches 197 mA h g-1 and 149 mA h g-1,respectively.