Electrochemical behaviour of titanium(II) and titanium(III) compounds in molten lithium chloride/ potassium chloride eutectic melts

The nature of the open circuit potentials of Ti and TiC electrodes in titanium(II) and titanium(III) chloride solutions, the apparent valency of the titanium ions in the melt immediately after the anodic dissolution of TiC and Ti, as well as the anodic dissolution of Ti, have been investigated in order to explain the oxidation-reduction process of titanium in lithium chloride-potassium chloride eutectic melts. It is shown that the standard electrode potential for TiC/Ti(III) exceeds that for the oxidation of Ti(II) to Ti(III). The anodic dissolution of TiC anodes give stable Ti(III) species at the standard electrode potentials the contrary to the behaviour of Ti metal anodes where the stable species are Ti(II) ions. Titanium electrodes in TiCl₃ solutions of molten lithium chloride-potassium chloride melts behave according to the Ti(III)/Ti(II) redox electrode potential of the reaction: Ti+TiCl₃3TiCl₂. An anodic dissolution mechanism compatible with all the experimental facts is proposed.     

负极材料Li_4Ti_5O_(12)合成中优化原料组成的研究

以不同的钛源(锐钛矿型TiO2、金红石型TiO2和无定形TiO2)和不同的锂源(Li2CO3和LiOH.H2O),采用高温固相合成法合成Li4Ti5O12,并对Li4Ti5O12的合成工艺进行了优化。经试验发现,在900℃下以锐钛矿型TiO2和Li2CO3为原料合成的Li4Ti5O12具有良好的电化学性能,Li4Ti5O12材料在Li+嵌入和脱出的过程中,其晶型不发生变化。     

Synthesis and structural properties of lithium titanium oxide powder

Recently, lithium titanium oxide material has gained renewed interest in electrodes for lithium ion rechargeable batteries. We investigated the influence of excess Li on the structural characteristics of lithium titanium oxide synthesized by the conventional powder calcination method, considering the potential for mass production. The lithium excess ratio is controlled by using different weight of Li₂CO₃ powder during calcination. X-ray diffraction (XRD) measurement for the synthesized powder showed that the lithium titanium oxide material with excess lithium content had a spinel crystal structure as well as a different crystal one. In addition, high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) measurement revealed that the lithium titanium oxide powders with a lithium excess ratio of 5–20% exhibited a two phase formation. Inductively coupled plasma — atomic emission spectrometer (ICP-AES) and energy dispersive x-ray spectroscopy (EDX) measurements were used to analyze composition of the lithium titanium oxide powder. These results suggested that the conventional calcination method, considering the potential for mass production, formed two phases according to the Li excess amount in initial raw materials.     

钛系锂离子筛的制备及其吸附性能研究

以无定型水合二氧化钛和氢氧化锂分别作为钛源和锂源,通过高温固相法合成钛系锂离子筛（HTO）并进行了扫描电镜（SEM）、X射线衍射（XRD）、接触角测试等表征。研究了HTO在高镁锂比[n（Mg）/n（Li）]盐湖卤水中随时间变化对锂吸附容量的影响。结果表明,HTO在高镁锂比盐湖卤水中26 h吸附容量达到24.8 mg/g。HTO具有优异的选择性,分离系数（α^Li _Mg）达到4 813.0。经过20次吸附循环试验,HTO的锂吸附容量仅下降4.8%,且每次钛的溶损率都在0.08%以下。结果表明,HTO具有较好的循环吸附性能和稳定性。该HTO具有从高镁锂比盐湖卤水提取锂的能力,具有很广阔的市场前景。     

锂离子筛研究进展

锂离子筛（锰系、钛系）在高镁锂比（质量比）的盐湖卤水中对锂离子表现出高吸附选择性，尖晶石结构的锂离子筛的提锂机理主要有氧化还原机制、离子交换机制和复合机制，而层状结构的锂离子筛主要通过Li⁺和H⁺之间的简单离子交换实现。锂离子筛的制备工艺简单，首先经过固相燃烧法、微波燃烧法或溶胶-凝胶法、水热法、共沉淀法、熔盐合成法等方法制备出前驱体，再通过H⁺取代相应前驱体中的Li⁺即可。制备的锂离子筛可用于从储量大、品位低的盐湖卤水、海水等液态锂资源中提取锂。近年来研究热点集中于结构稳定性更高的钛锂离子筛，但要进一步提高结构稳定性、实现工程化应用，还需继续研究。     

无机盐工业面临碳达峰碳中和的挑战与创新发展机遇

传统的无机化学品均是采用独自的矿产资源分别进行加工,生产资源与能源未能实现循环经济再利用、循环和分级利用的生产原则,全生命周期能源消耗无效率高。要实现碳达峰、碳中和,满足新产业的需要,就需要开发无机盐化工资源性耦合低碳的新技术新工艺。在钛、磷、硫资源耦合生产钛白粉与湿法磷酸盐先进工艺技术模式的基础上,以储能材料磷酸铁锂为例,提出将钛铁矿-磷灰石矿-锂灰石矿三矿耦合,按“元素经济”的绿色工艺技术路线生产储能材料磷酸铁及磷酸铁锂产品,论述了磷酸铁锂三元素上游磷化工、钛化工、锂化工面临节能减碳的挑战与耦合新技术创新的机遇及市场发展前景。     

钛系锂离子筛用于盐湖提锂的研究进展

随着新能源行业在世界范围内的快速发展,金属锂因其能量密度高等优势被广泛应用,从蕴含大量锂资源的盐湖卤水中提锂是获取锂资源的重要方向。盐湖提锂的方法主要有碳化法、沉淀法、离子筛吸附法、电化学辅助法等。离子筛吸附法适合从浓度低的液相中选择性回收锂,其中钛系锂离子筛因其稳定性强、吸附容量大而成为吸附法的研究热点。本文以钛系锂离子筛技术为立足点,对全球锂资源分布现状、钛系锂离子筛提锂机理进行了分析,综述了目前钛氧化物锂离子筛的合成方法、成型方法、现存的问题等,为后续开发新型钛系锂离子筛,提高饱和吸附容量等方面提供参考。     

钛系锂离子筛盐湖提锂的研究进展

随着新能源行业的迅速发展,带动了锂需求量的显著增长,锂提取技术近年来受到广泛关注。中国是盐湖锂资源大国,盐湖锂储量约占全国锂总储量的78%。但是,中国的盐湖锂资源镁含量高,不易分离提取高纯度锂工业产品;因此,研究开发盐湖提锂技术,具有非常重要的应用价值。在众多的盐湖提锂技术当中,锂离子筛吸附提锂,因其选择性好,对镁的分离效果好,适用于镁锂比高的盐湖卤水体系,这对解决盐湖提锂问题有重要指导意义。选择近年来发展比较热的钛系锂离子筛,从提锂机理、制备方法和应用等方面的研究对钛系离子筛进行一个综述,最后对钛系离子筛的未来研究方向进行展望。     

海水提锂技术的研究进展

在陆地锂资源总量远不能满足锂远景市场需求的情况下,研究海水提锂技术十分必要。介绍了从海水中提取锂的方法,认为吸附-离子交换法是有着广阔发展前景的绿色海水提锂方法,其关键就是要找到合适的吸附剂。介绍了几种无机离子交换吸附剂的吸附机理,重点论述了尖晶石型钛氧化物、锂-锰氧化物以及复合型离子筛吸附剂的技术现状。分析了目前离子筛型吸附剂法海水提锂存在的问题,指出造粒和成膜是提锂技术工业化亟待解决的问题。     

Preparation and Application of Nano-composite Poly(vinyl alcohol) Gel Electrolyte in Electrochemical Capacitor

A nano-composite polymer gel electrolyte was prepared using titanium oxide nanowire, poly(vinyl alcohol) (PVA), lithium salt and organic solvent N-methyl-2-pyrrolidone (NMP). The obtained electrolyte has the potential for application in electrochemical capacitor, the PVA in it is in an amorphous state. The ionic conductivities of electrolytes increased after addition of the nanowire, and the electrolyte with 3%(w) of nanowire exhibited the highest ionic conductivity of 3.2 mS/cm at 20℃, as measured by electrochemical impedance spectroscopy. The temperature dependence of the conductivity was found to be in agreement with the Arrhenius equation. Functioning as separator and electrolyte, this nano-composite PVA gel electrolyte was used to assemble the electrochemical capacitor with active carbon film as electrodes. The compositing of nanowire may extend the life of electrochemical capacitors as they keep more than 90% of their capacitance after 5000 cycles of charging and discharging.     

钛白副产硫酸亚铁制备铁系超细材料的研究进展

介绍了利用钛白副产硫酸亚铁制备草酸亚铁、磷酸铁、磷酸铁锂、纳米磁性材料、氧化铁颜料等铁系超细材料的技术研究。指出加强超细铁系材料的工业化研究,对于钛白副产硫酸亚铁综合利用并增加其附加值具有十分重要的现实意义。     

Increasing the electrochemical activity of transition metal phosphates in lithium cells by treatment with intimate carbon: The case of titanium phosphate

Amorphous sodium-containing titanium phosphate (sample TiP), obtained by heating a disordered precursor at 300 °C under air, electrochemically reacts with lithium by means of non-aqueous lithium cells. Discharge curves of EC/DEC cells in the 3.5-1.5 V region, were different to that observed for NASICON titanium phosphates but the related capacity can be associated to the reduction of Ti⁴⁺ to Ti³⁺. Another sample, C-TiP, obtained by using nitrogen atmosphere during the thermal treatment, was able to provide 75% more capacity in this region. This sample contained carbon because of the incomplete pyrolysis of the surfactant present in the precursor. Carbon is supposed to stay occluded inside the pores considering the values of pores surface area, total conductivity and HRTEM measurements. These titanium phosphates were also tested as negative electrodes. Electrochemical impedance spectroscopy measurements suggest that both titanium phosphates are reduced to yield titanium, lithia and phosphorus at 0.0 V. In our opinion, the presence of carbon in C-TiP is the key factor for the enhanced reactivity in the 3.2-1.5 V region but is not enough to obtain a good electrochemical performance, in terms of cycling efficiency.     

LiFePO4/C粉体合成新方法

磷酸亚铁锂作为新型锂离子动力电池正极材料,具有热稳定性好,安全环保,成本低;还具有快速充放电性能,循环寿命长,电化学性能优异等优势。我们拟定的中试试验:在流化床热气流压力混合包覆过程中,使用过程控制剂,实现碳包覆磷酸亚铁锂和掺杂钛铝金属离子。     

Effect of Impurities on Monoclinic (II)-Cubic (I) Transformation of Lithium Sulphate

The monoclinic (II)-cubic (I) transformation of lithium sulphate is a reversible reconstructive transformation associated with high activation energy. Cationic impurities like Na⁺, K⁺, Mg²⁺, Zn²⁺, Cd²⁺ and Al³⁺ have been doped in pure lithium sulphate and their effect on the kinetics and energetics of its transformation studied. By employing d.t.a., the enthalpy and energy of activation for the transformation of pure and doped samples of lithium sulphate have been calculated and compared.     

Study of Ti(III) solutions in various molten alkali chlorides. I. Chemical and electrochemical investigation

The effect of alkali metal cations in molten chloride baths on the behaviour of Ti(III) in these melts has been studied. With caesium chloride the percentage of total dissolved titanium present as Ti(II) after 72 hours at 700° C is 0.1%, whereas in lithium chloride it is 2%. In the presence of excess titanium metal the proportion of Ti(II) is always much higher. In LiCl it depends strongly on the area of titanium exposed and may reach 85%. In CsCl, on the other hand, this factor has no effect since a fine dispersion of powdery titanium appears at the very beginning of the reaction. The amount of Ti(II) remains close to 50%. In all the baths studied, the electrochemical reduction of Ti(III) at 700° C occurs in two steps: Ti(III) + e Ti(II)E _1/2 = – 1.6V versus Cl^–/Cl₂ Ti(II) + 2e Ti(O)E _1/2=–2.1V versus Cl^–/Cl₂. These results are different from those previously obtained in CsCl-LiCl (40–60 mol%) at 400° C, where reduction is a one-step process.     

Fabrication and characterization of LATP/PAN composite fiber-based lithium-ion battery separators

Lithium aluminum titanium phosphate (LATP)/polyacrylonitrile (PAN) composite fiber-based membranes were prepared by electrospinning dispersions of LATP particles in PAN solutions. The electrolyte uptakes of the electrospun LATP/PAN composite fiber-based membranes were measured and the results showed that the electrolyte uptake increased as the LATP content increased. The lithium ion conductivity, the electrochemical oxidation limit and the interface resistance of liquid electrolyte-soaked electrospun LATP/PAN composite fiber-based membranes were also measured and it was found that as the LATP content increased, the electrospun LATP/PAN composite fiber-based membranes had higher lithium ion conductivity, better electrochemical stability, and lower interfacial resistance with lithium electrode. Additionally, lithium//1 M LiPF₆/EC/EMC//lithium iron phosphate cells using LATP/PAN composite fiber-based membranes as the separator demonstrated high charge/discharge capacity and good cycle performance.     

Kinetics of the Ostwald ripening in lithium aluminosilicate glasses containing TiO2 and ZrO2

A structural investigation is undertaken on lithium aluminosilicate glasses containing a titanium oxide or titanium and zirconium oxides. The structural transformations in the course of Ostwald ripening observed after the increase in temperature of the glasses preliminarily heat-heated to the attainment of a stable two-phase structure (catalyst phase) are studied by the small-angle X-ray scattering (SAXS) technique. In all the cases, an increase in temperature leads to the loss of stability and a partial dissolution of the phase precipitated at a lower temperature. The low-temperature heat treatment (660°C) of lithium aluminosilicate glasses containing TiO₂ and ZrO₂ brings about the precipitation of aluminotitanate phase that reaches the stable state upon prolonged heat treatments for 5000–6000 h. As the temperature increases, this phase becomes unstable, which results in its dissolution and the precipitation of a new phase containing titanium and zirconium oxides in the form of zirconium titanate microcrystals. Changes in the phase composition in the course of Ostwald ripening upon isothermal treatments of glasses containing TiO₂ and ZrO₂ are associated with different mobilities of structural elements involving titanium or zirconium ions.     

Kinetics of the Ostwald ripening in lithium aluminosilicate glasses containing TiO2 and ZrO2

A structural investigation is undertaken on lithium aluminosilicate glasses containing a titanium oxide or titanium and zirconium oxides. The structural transformations in the course of Ostwald ripening observed after the increase in temperature of the glasses preliminarily heat-heated to the attainment of a stable two-phase structure (catalyst phase) are studied by the small-angle X-ray scattering (SAXS) technique. In all the cases, an increase in temperature leads to the loss of stability and a partial dissolution of the phase precipitated at a lower temperature. The low-temperature heat treatment (660°C) of lithium aluminosilicate glasses containing TiO₂ and ZrO₂ brings about the precipitation of aluminotitanate phase that reaches the stable state upon prolonged heat treatments for 5000–6000 h. As the temperature increases, this phase becomes unstable, which results in its dissolution and the precipitation of a new phase containing titanium and zirconium oxides in the form of zirconium titanate microcrystals. Changes in the phase composition in the course of Ostwald ripening upon isothermal treatments of glasses containing TiO₂ and ZrO₂ are associated with different mobilities of structural elements involving titanium or zirconium ions.     

Electrochemical formation of lithium iron(copper)silicide alloys

The behaviour of copper silicide and of some iron silicides with different silicon contents to lithium deposited electro chemically from organic solvents is investigated. The silicide phases show marked differences. Whereas with copper silicide a time-dependent alloy formation with lithium is observed, the iron silicides exhibit a behaviour ranging from no alloy formation to very rapid alloy formation (depending on the silicon content). The alloyed lithium may be recovered during oxidation with high yields. If some lithium is deposited at the supporting grid of iron silicide electrodes with high silicon content, a rapid surface diffusion with alloy formation is observed.     

Corrosion of oxide-coated titanium (DSA) anodes in organic solvents (especially methanol)

In certain organic solvents, notably alcohols (and in particular methanol), DSA-type anodes deteriorate rapidly under anodic conditions. The active RuO₂-based layer is itself quite resistant to corrosion; however, rapid dissolution of the titanium support through pores and cracks in the active oxide coating, eventually results in detachment of the surface layer. A survey of the titanium dissolution reaction in methanol, and (to a lesser extent) other common solvents, is reported first. Reaction was quite rapid in methanolic solutions at low pH, almost negligible in solutions of high pH, and inhibited in the former case on addition of increasing quantities of water or sulphuric acid. In similar experiments with oxide-coated titanium, the rate of metal dissolution in acidified methanol was reduced by addition to TiO₂ to the RuO₂ layer, increasing the active oxide loading, increasing the water or acid content of the solvent, use of low oxide annealing temperature, and operating at low current density. If this type of anode is operated in anhydrous alcohol systems, the use of a noble metal, or noble metal clad titanium, support would be worth considering. Of the other non-alcoholic solvents investigated, acetonitrile and propylene carbonate appeared to be more resistant to oxidation than dimethyl formamide or dimethyl sulphoxide — no trace of titanium dissolution was observed with any of these solvents.