Investigation Of Microstructure And Electrochemical Li/Na Ion-storage Performance Of Spherical TiO₂/Carbon And Li₄Ti₅O₁₂/Carbon

As anode materials for Li/Na ion batteries,anatase TiO₂and spinel Li₄Ti₅O₁₂have theoretical specific capacities of 335 m Ah g^-1and 175 m Ah g^-1,respectively,and have the advantages of low volume expansion,abundant reserves,and environmental friendliness.However,both materials have the problems of poor electrical conductivity and low mass diffusion rate,resulting in poor Li/Na ion-storage performance.In this thesis,excessive carbon was added in the starting materials with purpose to suppress Ostwald ripening of the TiO₂particles.Pitaya flesh-structured TiO₂/carbon with TiO₂size of 3.3 nm（3.3-TO/C）and Li₄Ti₅O₁₂/carbon（LTO/C）spherical composite materials were fabricated through spray-pyrolysis and carbonization A variety of structural and electrochemical methods have been employed to analyze their microstructure and electrochemical Li/Na ion-storage performance,and the following conclusions have been obtained:（1）3.3 nm-sized TiO2 particles are embedded in the carbon matrix of the pitaya flesh-structured 3.3-TO/C.The abundant pore structure and size effect-induced pseudocapacitance endow 3.3-TO/C with excellent Li ion-storage performance.The reversible capacity reaches 371 m Ah g^-1after 600 charge-discharge cycles at 2 C,which is still higher than the theoretical capacity of anatase TiO₂.The reversible capacity retention reaches 92.3%.Even at a current density of 80 C,the reversible capacity still can maintain ca.200 m Ah g^-1.The pseudo-capacitance effect of3.3-TO/C is significant,and the differential capacitance reaches 558 F g^-1at 2 C current density.（2）3.3-TO/C also has excellent Na ion-storage performance.Its reversible capacity can maintain 170 m Ah g^-1after 2,500 charge-discharge cycles at a current density of 2 C.In addition,3.3-TO/C exhibits obvious pseudocapacitance effect,which accounts for ca.75%of the total charge storage at a CV scan rate of 5 m V s^-1.（3）Li₄Ti₅O₁₂nanoparticles are embedded in the carbon matrix in LTO/C.LTO/C-5 obtained at a carbonization temperature of 500℃has the best electrochemical Li ion-storage performance in a voltage window of 0.01-2.5V.At a current density of 0.5 A g^-1,the specific intercalation/delithiation capacities maintain 282.5/274m Ah g^-1after 500 charge-discharge cycles.At a CV scan rate of 5m V s^-1,the pseudocapacitance accounts for ca.81%of the total charge storage.（4）LTO/C-8 obtained at a carbonization temperature of 800℃has the best electrochemical Li ion-storage performance in a voltage window of 1-2.5V.At a current density of 0.5 A g^-1,the specific intercalation/delithiation capacities reach157/156 m Ah g^-1after 500 charge-discharge cycles.Even at a current density of 80C(14 A g^-1),a reversible specific capacity of 120 m Ah g^-1can be obtained,which is ca.69%of the theoretical capacity of Li₄Ti₅O₁₂.