Fabrication And Lithium Adsorption Properties Of Ti-based Lithium-ion Sieves

The growing global energy demand and environmental pollution drive the desire for the sustainable development of clean energy and storage technology.Rechargeable battery,as an attractive energy storage technology,is experiencing unprecedented rapid development.In particular,the demand for lithium-ion batteries（LIBs）in hybrid electric vehicles and electric vehicles is enormous,leading to lithium in short supply.At present,extracting lithium from ore consumes large amounts acid,which leads to serious environmental problems.The development and utilization of liquid lithium resources have been a research hotspot home and abroad.Adsorption method has the advantages of green,simple process,high selectivity,and high recovery rate.The selection of appropriate adsorbent is a crucial factor.Lithium-ion sieve（LIS）is considered to be one of the most promising adsorbents for extracting lithium from liquid lithium resources.In this thesis,several methods for improving lithium adsorption performance and assistant recovery strategy were proposed based on H₂TiO₃,and H₄Ti₅O₁₂ LISs.The main contents and results are as follows:1.The amorphous TiO₂ prepared by hydrolysis of isopropyl titanate was used as the titanium source,and then to prepare H₂TiO₃（HTO-Am）ion sieve by solid-state reaction with lithium titanate.The effect of time on the lithium adsorption performance of HTO-Am was investigated.The results showed that HTO-Am could reach the adsorption equilibrium within 4 h.The process is in accordance with the pseudo-second-order kinetic model,which indicates that the adsorption process is mainly chemical adsorption.The adsorption isotherms of HTO-Am at different initial lithium concentration solutions were studied.The results showed that the adsorption process was more consistent with the Langmuir adsorption isotherm model,indicating that the adsorption of lithium by HTO-Am was monolayer adsorption.In the presence of coexisting ions,the selectivity of HTO-Am follows the sequence of Li⁺>K⁺>Na⁺>Mg²⁺,showing good adsorption selectivity for Li⁺.HTO-Am has good cycling performance.After five adsorption-desorption cycles,the lithium adsorption capacity decreases from 30.03 mg·g^-1 to 28.65 mg·g^-1,and the average lithium adsorption capacity is 29.02 mg·g^-1,which proves the structural stability of HTO-Am.2.The relationship of wettability and adsorption properties between TiO₂ crystal phase and the prepared lithium-ion sieve was investigated.The different crystalline phases of TiO₂were prepared by the sol-gel method,and the H₂TiO₃（HTO）ion sieve with strong hydrophilicity was obtained by the solid-state reaction of as-prepared TiO₂ and Li₂CO₃coupling with the acid pickling.Through the wettability experiments,it is concluded that the ion sieve prepared by anatase phase TiO₂（HTO-400）shows the strongest hydrophilicity,which makes Li⁺easy to transport and exchange with H⁺,thus realizing the effective contact between HTO-400 ion sieve and Li⁺and showing the maximum lithium adsorption capacity.The mechanism of lithium adsorption on HTO-400 was studied by adsorption kinetics,adsorption isotherm,and adsorption thermodynamics.The results showed that the process of lithium adsorption by HTO-400 is chemical adsorption and monolayer adsorption,which is an endothermic reaction.The adsorption capacity of HTO-400 for Li⁺in the simulated mother liquor of lithium precipitation is 30.11 mg·g^-1,and the presence of Na⁺and K⁺has little effect on the adsorption performance,which proves a high adsorption selectivity for Li⁺of HTO-400.The HTO-400 adsorbed Li⁺was regenerated by HCl.Even after eight adsorption-desorption cycles,the lithium adsorption capacity of HTO-400 remained at about 31 mg·g^-1 with almost no attenuation.The dissolution loss rate of Ti remains below0.31 wt%.This shows that the prepared HTO-400 has good chemical stability and lithium recovery performance.3.The Li₂TiO₃ precursor hollow sphere ion sieve was prepared by dissolving and hydrolyzing of MXene in alkaline conditions and calcining at high temperature.HTO ion sieve with a fast adsorption rate was obtained by acid pickling.The particle size of LTO hollow spheres can be controlled by adjusting the amount of ammonia.With the increase of ammonia volume,the particle size decreases significantly,from microspheres to nanospheres,and then to nanoparticles.The ion sieve prepared with 8 m L ammonia（8N-HTO）showed excellent lithium adsorption performance,which may be due to its smaller nano size and hollow structure,shortening the Li⁺transport path and promoting Li-H ion exchange.Compared with HTO-400（k₂=0.0220）,8N-HTO has a faster adsorption rate（k₂=0.3759）,which indicates that the hollow structure can effectively improve the adsorption rate.In the presence of coexisting ions,HTO hollow sphere maintains excellent lithium adsorption selectivity;the experimental results of cycling performance show that the adsorption capacity of 8N-HTO hollow nanosphere has almost no change after 5 adsorption-desorption cycles,indicating that it has excellent cycling performance and shows broad application prospects.4.The hierarchical porous Li₄Ti₅O₁₂（M-LTO）microspheres were constructed to further improve the adsorption capacity and adsorption rate of Ti-based LIS.Firstly,MXene was alkalized and oxidized into NTO nanobelts with urchin-like microspheres;secondly,the self-assembled hierarchical Li₄Ti₅O₁₂（M-LTO）microspheres composed of ultrathin nanosheets were obtained by the strategy of spontaneous-dissolution regeneration of NTO.M-HTO microspheres were prepared by acid pickling and used for selective adsorption of lithium.The composition and structure of the M-HTO microspheres were characterized by modern characterization method,and the formation mechanism of the adsorbent was proposed.It was proved that M-HTO had a highly open pore structure with a specific surface area of 182.0 m²·g^-1,and was a microsphere assembled by ultrathin nanosheets.The prepared M-HTO was used to adsorb lithium in lithium-containing solutions.The porous structure of M-HTO microspheres increases the contact area between Li⁺and adsorbents,promotes the adsorption of Li⁺,thus enhancing its adsorption performance.The theoretical adsorption capacity of M-HTO microspheres is as high as 52.97 mg·g^-1,which is superior to other commonly used ion sieves.In the presence of coexisting ions and a high Mg/Li ratio,M-HTO microspheres show high adsorption selectivity for Li⁺.Besides,the adsorption capacity of M-HTO microspheres did not decrease significantly after five cycles in a mixed ionic solution,and maintained a high adsorption selectivity.5.A magnetic separation Fe doped H₄Ti₅O₁₂（Fe doped HTO）was prepared by one-step hydrothermal reaction method to reduce the difficulty of solid-liquid separation of powder LIS.The composition and structure of the adsorbent are determined by XRD,SEM,and XPS.It was proved that Fe was incorporated into the lattice structure of LTO.At the same time,the introduction of Fe changed the original morphology of LTO,and the microspheres made up of nanosheets changed into stacked nanosheets.The prepared undoped HTO and Fe doped HTO are used for the adsorption of lithium,it is proved that introducing Fe into HTO can enhance the lithium adsorption capacity,and the lower Fe doping shows a better lithium adsorption performance.Among them,Fe-HTO-2 has the highest lithium adsorption capacity(54.4 mg·g^-1),and can be magnetically separated.The selectivity experiment showed that the Fe doped HTO had excellent lithium adsorption selectivity,and the lithium distribution coefficient reaches 177.66,and the separation factors of Li⁺for Na⁺,K⁺,and Mg²⁺are greater than 1.The adsorption-desorption experiments showed that the Fe doped HTO had excellent cycling performance,and the desorption efficiency E_Li and adsorption capacity had not changed significantly.Meanwhile,the dissolution loss rate of Fe decreases with the increase of cycle times,and finally maintains at about 0.7%.It shows that the structure of Fe doped HTO is relatively stable.