Preparation And Electrochemical Performance Of Titania-Based Composite Anode For Lithium-Ion Batteries

Lithium ion battery has been widely used in portable electronic devices,automotive systems due to high capacity,high power,good cycling performance and low toxicity,etc.The anode material is an important component of lithium ion battery.Graphite is used as anode in commercial lithium ion battery,but the low theoretical capacity and poor safety can not meet the requirement of high energy density.It is essential to develop alternative lithium-ion battery anode materials.Titanium dioxide?TiO2?is considered as a promising anode material due to high voltage profile and limited volumetric effect,which endows excellent cyclic stability and operation safety.Nevertheless,the low theoretical specific capacity,poor lithium ionic and electronic conductivity significantly hampered its practical applications.Large amount of research has been devoted to tackling these issues in the last few decades.The strategies developed include synthesizing nanoscale TiO2,compositing with other materials and constructing different architectures.The lithium ionic and electronic conductivity and electrochemical performance of TiO2 are significantly enhanced with these strategies.In this thesis,it is focused to modify the structures and improve the electrochemical performance of the TiO2 based lithium-ion battery anodes based on organic/inorganic composition strategies,where comprehensive structure characterization and fundamental mechanism are investigated.The main research results are as follows:?1?Ultra-small TiO2/Ni/C nanocomposites with different Nickel amounts are synthesized using difunctional thermoset resin monomers are used as solvent and carbon source,isopropyl titanate as titanium dioxide precursor and the complex of nickel acetate and acrylic acid as nickel precursor,coupled with photo polymerization and calcination in argon atmosphere.Due to synergistic effects of the ultra-small nanoparticles,metal nanoparticle incorporation,and carbon matrix,rate performance and cyclic stability of the TiO2 anode material are significantly enhanced.The specific capacity of the TiO2/Ni/C nanocomposites keeps at 101 mAh g^-1 at the current density of 6.7 A g^-1,which is only 15 mAh g^-1 for the bare TiO₂/C nanocomposites.The TiO2/Ni/C also demonstrates good electrochemical performance as sodium-ion battery anode,where the specific capacity remains at 46 mAh g^-1 at 670 mA g^-1,which is 2.5times higher than that of bare TiO2/C.The temperature dependent I-V profiles of the TiO2/Ni/C nanocomposites with different nickel contents prove that the nickel nanoparticles provide additional charge carrier transportation paths,where the charge carrier mobility is enhanced and the conductivity and rate performance are improved.As an extension of the above mentioned work,MnO/metal/C nanocomposites are synthesized as demonstrated by the MnO/Ni/C and MnO/Ag/C.Similar as previous work,thermosetting resin monomers are used as solvent and carbon source,where metal salts are dissolved and in istu converted to element metal nanoparticles through a carbonization reduction process.The incorporation of the metal nanoparticles significantly increases the reversible capacities,which are 1.5 times higher than that of the metal free MnO/C nanocomposites.The electrochemical kinetics is enhanced due to metal nanoparticles as indicated by the increased coefficient from the cyclic voltammetry measurement.The charge carrier mobility is also accelerated as revealed by temperature dependent I-V profiles of the MnO/Metal/C nanocomposites.?2?Ultra-fine titanium dioxide nanoparticles and amorphous SiOx are uniformly embedded in the in situ formed carbon matrix by using difunctional methacrylate monomers as solvent and carbon source.The SiOx phase effectively lifts the overall reversible specific capacity;while the ultra-small TiO2 nanoparticles and carbon matrix relieve mechanical stress generated by lithiation of SiOx to achieve excellent cyclic stability.The A good balance among high reversible capacity,high capacity retention,and excellent rate performance with respect to the TiO2/SiOx/C nanocomposites is realized are by tuning the SiOx content and mesoporous structure within the carbon matrix.?3?Porous super-small SnO2/Sn/C nanocomposites are synthesized and used as lithium-ion battery anodes.Thermosetting resin monomers continue to be used as solvent and carbon source,where TEOS is used as the pore precursor.The combination of photo polymerization,high temperature calcination,and selective etching treatment allow good control over the microstructure and electrochemical performance of the SnO2/Sn/C nanocomposites.The BET surface area is drastically increased after HF etching.The specific capacity of the porous SnO2/Sn/C is 1185mAh g^-1 after 500 cycles at the current density of 200 mA g^-1.Moreover,the morphology and electrochemical properties of the porous SnO2/Sn/C can be tuned by varying the HF exposure time.It is found that the HF etching time of 120 min generates the best electrochemical performance in terms of reversible capacities,capacity retention,and rate performance,where the SiOx is removed completely with partial removal of element tin.On the basis of the above work,porous TiO2/SnO2/Sn/C is synthesized by introducing the precursors of TiO2,SiOx,and tin species together into the thermosetting resin monomer solution,coupled with consecutive polymerization,calcination,and HF treatment.The specific capacity of porous TiO2/SnO2/Sn/C nanocomposites is twice than that of the sample before etching after 450 cycles with the current density of 200 mA g^-1.The super small SnO2nanoparticles effectively improve the reversible specific capacity.The porous structure promotes electrochemical kinetic and improves the rate performance;the TiO2 nanoparticles and porous structure relief the volume effect to achieve a stable cycling performance.