Of Ticl <sub> 4 </ Sub> Aqueous Solution Stability And In Situ Hydrolysis Of Synthetic Li <sub> 4 </ Sub> Ti <sub> 5 </ Sub> O <sub> 12 </ Sub>,

Spinel Li₄Ti₅O₁₂ has become one of the most promising Li-ion battery anode materials due to its distinct characteristics of zero-strain insertion, satisfactory safety, long cycle life and environmental friendliness. At present, Li₄Ti₅O₁₂ is mainly prepared by solid-state or wet chemical reactions, both synthesis methods using TiO₂ as main raw material, which, however, increases the cost and results in low homogeneity and poor crystallinity. Therefore, exploring new raw materials and technology for the production of Li₄Ti₅O₁₂ has become an intensive research topic. In order to solve the problem, the stability of aqueous TiCl₄ solution was investigated and then the synthesis of nano-sized Li₄Ti₅O₁₂ powders via in-situ hydrolysis process was carried out using inexpensive aqueous TiCl₄ solution as Ti raw material and LiOH·H₂O as the inducer. The experiments and obtained results are reported in this paper.The stability of aqueous TiCl₄ solution and the mechanism of TiCl₄ hydrolysis have been studied. Based on experimental observation and some fundamental for generating particles from homogenous, the intermediates for the hydrolysis of aqueous TiCl₄ solution are proposed as follows: [Ti(OH)_n(H₂O)_6-n]^(4-n)+ as the main species at low Ti(Ⅳ) concentration and TiOCl_n^(2-n)+ as the major species at high Ti(Ⅳ) concentration. Larger polymeric clusters are formed by further hydrolysis of these intermediates and consequent condensation of the polymerization. When the polymer cluster grows and reach critical nucleus size, TiO₂ particles generate. The stability of aqueous TiCl₄ solution increases with increasing Ti(Ⅳ) concentration. and decreases with increasing hydrolysis temperature. The hydrolysis of aqueous TiCl₄ solution is inhibited by adding LiCl and HCl, which increases the stability. At the initial stage, the induced period is prolonged, the stability is increased accordingly. However, LiCl or HCl has minor effects on the stability at the later stage.Spinel Li₄Ti₅O₁₂ procursor was synthesized via in-situ hydrolysis from aqueous TiCl₄ solution and LiOH·H₂O. The optimal synthetic condition were established as follows: acidic milieu, stoichiometry Li/Ti(mol ratio)=4.8, stirring rate 250 rpm, reaction temperation 60℃, reaction time 2h, washing with ethanol and sintering 6 h at 800℃. Also, the optimal time for the hydrolysis preparation of Li₄Ti₅O₁₂ from various Ti(Ⅳ) concentrations were found to be as follows: 1h hydrolysis for 0.5 mol/L aqueous TiCl₄ solution (Ti-0.5), 3h for 0.5 mol/L aqueous TiCl₄ solution with adding 1.0 mol/L LiCl(Li-1.0) and 5 h for both 1.0 mol/L(Ti-1.0) and 1.5 mol/L(Ti-1.5) aqueous TiCl₄ solution. Agglomeration was found in the products obtained from high Ti(Ⅳ) concentration(Ti-1.0 and Ti-1.5). Products prepared from low Ti(Ⅳ) concentration(Ti-0.5 and Li-1.0) have octahedral spherical shape and a uniform particle size of 200nm as well as well-distribution. Thus, it is possible to recycle the LiCl produced from Li₄Ti₅O₁₂ preparation, and thereby achieving zero release.The electrochemical property tests at 0.1 C show that the Li₄Ti₅O₁₂ material prepared from high Ti(Ⅳ) concentration (Ti-1.0 and Ti-1.5) has low first discharge capacity and serious polarization. In comparison, the material obtained from low Ti(Ⅳ) concentration of Ti-0.5 and Li-1.0 has high first discharge capacity of 140.3 and 100.3 mAh/g, respectively, and shows good recycle performance and charge-discharge plateau close to 1.56 V, exhibiting representative electrochemical performance of typical spinel Li₄Ti₅O₁₂. After secondary Li-doping, Li_4.555Ti₅O₁₂ demonstrates better first discharge capacity and recycle performance.