TiCl₄水溶液稳定性及原位水解合成Li₄Ti₅O₁₂的研究

【作者】 陈盼盼；

【导师】 李运姣； 习小明；

【作者基本信息】 中南大学 ， 有色金属冶金， 2009， 硕士

【摘要】 尖晶石Li₄Ti₅O₁₂因其零应变、安全性能好、使用寿命长、环境友好等突出特点,成为现今倍受人们青睐的最理想的锂离子电池负极材料之一。目前Li₄Ti₅O₁₂的合成无论是固相法还是水热法都离不开以TiO₂或其水合物为钛源,其原料来源有限且制备成本高。因此寻求新的合成方法是Li₄Ti₅O₁₂材料研究的热点。针对这一问题,本文在对TiCl₄水溶液稳定性研究的基础上,系统地研究了以廉价的TiCl₄水溶液为钛源,以LiOH·H₂O为锂源及水解诱导剂,在水溶液中采用水解-原位相转化法由TiCl₄直接合成Li₄Ti₅O₁₂。对TiCl₄水溶液水解机制与稳定性进行研究表明:低浓度钛液水解中间产物主要是[Ti（OH）_n（H₂O）_6-n]^（4-n）+,高浓度钛液为TiOCl_n^（2-n）+。这些中间产物进一步水解,发生缩聚反应形成较大的聚合物团簇。当聚合物团簇长大到一定尺寸,达到临界晶核尺寸时,产生晶核。通过晶核的生长形成水合TiO₂一次粒子。TiCl₄水溶液稳定性随TiCl₄浓度的增加而增大,随温度的升高而降低。溶液中LiCl或HCl的存在有利于提高TiCl₄水溶液的稳定性,抑制Ti的水解。水解初期,随溶液中LiCl或HCl浓度的增加,稳定性增大;但水解后期,LiCl或HCl的影响不大。以TiCl₄水溶液和LiOH·H₂O为原料,原位水解合成了尖晶石Li₄Ti₅O₁₂。制备纯净尖晶石Li₄Ti₅O₁₂的适宜条件为:酸性环境、加料Li/Ti摩尔比4.8、搅拌速度250 rpm、反应温度60℃、反应2h后得到的产物用无水乙醇洗涤后,经800℃热处理6h。不同浓度TiCl4水溶液最有利于合成Li₄Ti₅O₁₂的水解时间分别是:0.5 mol/L TiCl₄水溶液（Ti-0.5）水解1h、添加1.0 mol/L LiCl的0.5 mol/L TiCl₄水溶液（Li-1.0）水解3h、1.0 mol/L（Ti-1.0）与1.5 mol/LTiCl₄水溶液（Ti-1.5）水解5h。高浓度TiCl₄水溶液（Ti-1.0与Ti-1.5）的合成产物团聚相对严重,而低浓度TiCl₄水溶液（Ti-0.5与Li-1.0）的合成Li₄Ti₅O₁₂分散性较好,平均粒径约为200 nm左右。电性能分析表明,0.1C倍率下,由高浓度TiCl₄水溶液（Ti-1.0与Ti-1.5）合成的Li₄Ti₅O₁₂首次充放电比容量低,电极极化严重;而低浓度TiCl₄水溶液（Ti-0.5与Li-1.0）合成的Li₄Ti₅O₁₂首次放电容量分别为140.3和100.3 mAh/g,循环性能较好,充放电平台与1.56V接近,该材料具有尖晶石Li₄Ti₅O₁₂典型电性能特性。二次配锂样品中以Li_4.555Ti₅O₁₂性能较佳。更多还原

【Abstract】 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.更多还原