Research On Self-Template Synthesis And Electrochemical Li/Al Storage Of Spherical Ti-Based Oxides

Ti is an element widely distributed on earth with a high abundance(6320 ×10-6),accounting for 0.61%of the earth’s crust weight,ranking 9th of all elements.TiO2 with abundant resources is non-toxic,harmless and low-cost and is widely used in the field of electrochemical energy storage.TiO2 has numerous morphologies,and its diversity is the largest among inorganic materials.Moreover,it is the most interesting spherical morphology,which is of great research significance.Geometrically,the symmetry of the sphere represents the isotropic structure;thermodynamically,the sphere means thermodynamically stable.TiO2 spheres are popular in the field of energy storage because of their monodisperse,close-packed arrangement and diverse primary particles.In this paper,two unconventional crystallization methods of UVC induction and microwave radiationwere used.Based on the self-template method,TiO2 and quaternary Li2ZnTi3O8 with stable submicrosphere structure were constructed from the micro-nano structure regulation,crystal phase purity optimization,conductivity and metal ion diffusion coefficient improvement.The cyclic tolerance and electrochemical energy storage mechanism of lithium/aluminum-ion batteries(LIBs/AIBs)and lithium-ion hybrid capacitors(LICs)were studied,and the electrolyte optimal configuration was carried out during the electrochemical Al storage.Specific work points are as follows:To reduce the energy consumption of TiO2 mineralization and crystallization,an unconventional crystallization method of porous biphasic TiO2 spheres under ultraviolet radiation mineralization at room temperature was proposed.Based on stabilized porous TiO2 hydrous spheres(HTS),the electrochemical Li storage activity was further enhanced through mineralization and crystallization,and energy consumption and carbon emissions were reduced.The results show that the HTS synthesized by the template method is an amorphous crystal phase.After being placed in a dispersive system with the volume ratio of methanol to deionized water at 1:1 and irradiated with ultraviolet(UVC,λmax=254 nm)for 4 h,the surface of the HTS can produce an anatase/rutile biphase crystal phase,and the crystallization degree reaches the peak.Due to its crystalline surface,high porosity and large specific surface area of 358.1 m2 g-1,the resultant mesoporous TiO2 spheres show extremely high cycle tolerance(over 1000 cycles,128.6 mA h g-1)at 1.0 C when used as anode materials for LIBs.To further improve the activity and stabilize the structure of HTS,and to cope with the reversible de-intercalation of effective ions with large radii in AIBs,microwave-assisted recrystallization was introduced to systematically optimize the phase purity and structural stability of mesoporous anatase TiO2 spheres(MATS).The large surface area and pore size provide a fast,robust and interconnected scaffold channel for the Al3+ embedding reaction,making the electrochemical reaction highly reversible.Non-aqueous aluminum ion batteries(NAIBs)exhibit excellent electrochemical performance(145.3 mA h g-1 at 0.2 C;at 1.0 C,78.0 mA h g-1 after 200 cycles,the service life>600 cycles).The study of the Al storage mechanism shows that there are reversible(Al2Ti7O15,Al2TiO5)and irreversible(Ti(AlCl4)2,Ti(ClO4)4)phase transitions of anatase TiO2 during the cyclic process,and the continuous enrichment of the latter leads to the failure of electrochemical Al storage.In addition,to further improve the stability of liquid electrolyte(AlCl3/[EMIm]Cl)of NAIBs in air and reduce corrosion,the basic polyethylene oxide(PEO)was introduced as a plasticizer to construct quasi-solid gel polymer electrolytes(GPEs:PEO@AlCl3/[EMIm]Cl),and the inorganic/organic composite cathode was prepared by mixing the optimized MATS with polyaniline(PANI)to improve compatibility with GPEs.It is found that the introduction of 20 wt.%PEO can effectively reduce the volatility,improve the defect of gas leakage,eliminate part of Al2Cl7-heavy ions,reduce corrosion,and the～1.0 V voltage platform is more stable;However,when excessive addition,the conductivity will be affected,and the reactivity of Al storage will be limited,resulting in a slight decrease in specific capacity compared with liquid electrolyte.To improve the power density of LIBs,LICs with high energy/power density were designed by using the optimized MATS as the anode of "battery type" and commercial activated carbon as the cathode of "capacitor type".The study found that:the large specific surface area(88.9 m2 g-1)and porous structure of MATS synthesized by microwave-assisted self-template provide a fast and stable channel for reversible Li+de-intercalation.Moreover,the large pseudocapacitance property provides a powerful power source for the reaction,making up for the difference in the kinetic rate of the reaction between the cathode and anode.High energy/power density(97.1 Wh kg-1/16.7 kW kg-1)was realized,and because the crystal expansion coefficient of MATS is small in the cyclic process(0.78%after 1000 discharges),the cycle life of LICs based on MATS "battery-type" anode exceeds 10,000 times.After systematically studying the electrochemical Li/Al storage performance of TiO2 spheres,to further reduce the working potential of MATS as the anode of LIBs then improve the energy density of the full-LIBs.The quaternary Ti-based oxide Li2ZnTi3O8(LZTO)with a "0" strain was prepared.To overcome the weakness of low compacting density and poor conductivity of the LZTO as the anode of LIBs,the high compaction energy density LZTO spheres were synthesized by using the optimized MATS as self-template and the solid phase self-template method combined with Ostwald curing mechanism.The gap between the spheresphere accumulations forms a porous structure,which increases the contact area with the electrolyte,thus providing a large number of electrochemical reaction sites and reducing the Li+ transport path.At the same time,Ta5+ is introduced to further improve the intrinsic conductivity of the LZTO spheres.By density functional theory calculation and electronic structure visualization analysis,it is concluded that the Ti site is the most preferred doping site(the lowest binding energy).It is found that part of Ta5+is uniformly doped into the lattice structure,and the rest is transformed into LiTaO3 with piezoelectric properties on the spherical surface,which improves the electrical contact and interface Li+transport mechanics.Insitu XRD test shows that compared with the pristine,the optimized 5%Ta5+ doped LZTO spheres have less significant peak shift within the first three cycles,that is,it has more advantages in structural stability.Finally,excellent Li+storage performance was achieved(230.2 mA h g-1 at 5 A g-1,90.2 mA h g-1 after 2000 cycles).In this paper,ultraviolet radiation and microwave radiation were used as two unconventional crystallization methods combined with the self-template method.Starting by optimizing the porous structure,crystallinity,phase purity and conductivity of electrode materials,and aiming at optimizing the practical indexes such as cycle performance,energy/power density and Coulomb-efficiency of LIBs,AIBs and LICs,a batch of submicrospherical Ti-based functional materials were prepared for the rapid and highly reversible Li+/Al3+ transport reaction.The electrochemical storage mechanism of Li/Al in the cycle was also revealed.