Method for producing metallic titanium and nanocarbon material by molten salt electrolysis

Abstract

The application provides a method for preparing metal titanium and nanocarbon material by molten salt electrolysis, and the method comprises the following steps: mixing a titanium-based raw material, a sulfur-based raw material and a carbon-based raw material, sequentially performing ball milling, briquetting and sintering to obtain Ti2SC powder; sequentially performing briquetting and sintering on the Ti2SC powder to obtain a block Ti2SC; and performing electrolysis reaction on the block Ti2SC as an anode in molten salt to obtain preliminary metal titanium and preliminary nanocarbon material. The method can greatly improve the competitiveness of the molten salt electrolysis for extracting titanium by taking into account the current efficiency of the cathode and the anode.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium extraction by molten salt electrolysis, and in particular to a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. Background Art

[0002] Titanium, with its numerous excellent properties, including light weight, high specific strength, strong corrosion resistance, and non-toxicity, has become an indispensable metallic material in scientific and technological fields such as aerospace, national defense, and deep-sea exploration. In recent years, its applications have gradually expanded to civilian applications, playing an increasingly important role in the medical, chemical, and electronic information sectors, earning it the nickname "the metal of the future." Although titanium is abundant in the Earth's crust, its extraction is relatively difficult. Existing industrial production of titanium primarily relies on the Kroll process (magnesium-thermal reduction of TiCl₄). TiO₂ is first subjected to boiling chlorination in a fluidized bed furnace to produce crude TiCl₄. Refined TiCl₄ is then obtained in a distillation column. This refined TiCl₄ is then passed into a reactor at a constant flow rate to react with molten magnesium metal. The byproduct, MgCl₂, can be electrolyzed to produce Mg metal and Cl₂ for recycling. However, this method suffers from issues such as discontinuous production and high energy consumption, resulting in high prices for titanium metal and limiting its large-scale application. The development of new, low-cost titanium extraction technologies is urgently needed.

[0003] Molten salt electrolysis (FFC) uses metal oxides as cathodes and directly produces metals from them through electro-deoxidation. Based on the FFC method, numerous other methods have been developed, including the OS method, EMR method, and SOM method. However, due to the poor conductivity of oxides, the tendency of metallic titanium obtained by surface reduction to sinter, and the limited mass transfer in the later stages of electrolysis, these methods are unable to address the deep reduction of oxides, resulting in low current efficiency.

[0004] Beijing University of Science and Technology has proposed a new electrolytic strategy for electrolysis of anode materials and cathode titanium extraction - USTB method. TiO2 is reduced by carbon thermal reduction to obtain TiC with good conductivity. x O y, using it as the anode material for electrolysis. Titanium not only enters the molten salt at a lower valence state, but the material is also soluble during the electrolysis process, successfully solving the problem of the raw material's inability to undergo deep reduction (see "Improved USTB titanium production with a Ti2CO anode formed by casting", Jiao Shuqiang et al., Journal of The Electrochemical Society, Vol. 8, No. 166, pp. E226-E230). However, although this method can produce metallic titanium at the cathode, no product is obtained at the anode, and the anode current efficiency is zero, resulting in a production cost that has no significant advantage over the Kroll method. Furthermore, the CO or CO2 generated at the anode does not meet the requirements of current low-carbon development.

[0005] CN106591888A discloses a method and device for preparing a low-valence titanium ion molten salt electrolyte. The preparation method comprises the following steps: under the protection of an inert atmosphere, heating and melting a halide salt and a titanium sponge placed on the surface of the halide salt to obtain a molten salt; adding TiCl under a vacuum degree of 0.015 to 0.025 MPa, and reacting for 30 to 60 minutes under inert gas stirring to obtain a molten salt electrolyte; sampling and analyzing the titanium ion concentration in the molten salt electrolysis, and when the titanium ion concentration is equal to the titanium ion concentration threshold, a low-valence titanium ion molten salt electrolyte is obtained; when the titanium ion concentration is less than the titanium ion concentration threshold, additional TiCl is added until the titanium ion concentration is equal to the titanium ion concentration threshold; when the titanium ion concentration in the molten salt electrolyte is higher than the titanium ion concentration threshold, additional halide is added until the titanium ion concentration is equal to the titanium ion concentration threshold. However, although this method can obtain metallic titanium at the cathode, no product is obtained at the anode, and the anode current efficiency is zero.

[0006] CN106757167A discloses a method and device for preparing titanium by molten salt pulse current electrolysis. The method comprises: under the protection of inert gas, connecting the positive and negative electrodes of a pulse power supply to the anode titanium sponge and molten salt respectively, so that the titanium generated by electrolysis of the molten salt containing titanium ions under the pulse current is deposited on the cathode, thereby producing low-oxygen high-purity titanium. However, although this method can obtain metallic titanium at the cathode, no product is obtained at the anode, and the anode current efficiency is zero.

[0007] CN110079837A discloses a method for preparing titanium metal by electrolyzing soluble titanate in a water-soluble fluoride salt system molten salt. The method comprises placing a composite fluoride molten salt containing 1-10% titanate by mass in a graphite crucible, heating it to 300°C in a sealed steel reactor under a nitrogen or argon atmosphere, and maintaining the temperature for 24 hours to remove moisture from the molten salt. The temperature is then raised to 900-1100°C, and electrolysis is performed at a constant voltage of 3.3-5.0V using graphite as the anode and a titanium plate as the cathode, to obtain titanium metal powder on the cathode surface. After the electrolysis is completed, the cathode is removed from the molten salt, cooled to room temperature, and the product on the cathode surface is separated and washed sequentially with deionized water, 2-5% hydrochloric acid, 1-5% hydrofluoric acid, and deionized water, followed by drying to obtain titanium metal powder. However, although titanium metal can be obtained at the cathode, no product is obtained at the anode, resulting in a zero anode current efficiency.

[0008] Therefore, it is necessary to develop a method of using molten salt electrolysis to not only reduce titanium metal to the cathode, but also obtain high-value products at the anode at the same time. The titanium metal obtained at the cathode can even be regarded as a by-product in comparison. This method that takes into account the current efficiency of both the cathode and the cathode will greatly enhance the competitiveness of titanium extraction by molten salt electrolysis. Summary of the Invention

[0009] In view of the problems existing in the prior art, the present invention provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, the method comprising: mixing titanium-based raw materials, sulfur-based raw materials and carbon-based raw materials, ball milling, briquetting, sintering and crushing to obtain Ti2SC powder; briquetting and sintering the Ti2SC powder in sequence to obtain bulk Ti2SC; the bulk Ti2SC acts as an anode to undergo an electrolytic reaction in molten salt to obtain preliminary metallic titanium and preliminary nano-carbon materials. The method takes into account the current efficiency of both the cathode and anode, which will greatly enhance the competitiveness of titanium extraction by molten salt electrolysis.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] The present invention provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, the method comprising the following steps:

[0012] (1) mixing titanium-based raw materials, sulfur-based raw materials, and carbon-based raw materials, and sequentially performing ball milling, briquetting, sintering, and crushing to obtain Ti2SC powder;

[0013] (2) briquetting and sintering the Ti2SC powder in step (1) to obtain Ti2SC blocks;

[0014] (3) The bulk Ti2SC in step (2) is used as an anode to undergo electrolysis reaction in molten salt to obtain preliminary metallic titanium and preliminary nanocarbon material.

[0015] The present invention uses a special structure MAX phase Ti2SC as the anode material. Through molten salt electrolysis, not only metallic titanium is reduced at the cathode, but also shell nano-carbon materials are obtained at the anode, achieving a balance between the current efficiency of the cathode and the cathode in the process of molten salt electrolysis for titanium extraction, and greatly improving the competitiveness of molten salt electrolysis for the preparation of metallic titanium. Electrochemical etching and stratification of the multi-faceted layered structure Ti2SC on the anode breaks the existing research understanding that the MAX phase is a highly oriented crystal structure. Using electrons as an etchant, the sulfur between the layers of the wrapped Ti2SC structure is first reduced to elemental sulfur. Elemental sulfur has a low boiling point and quickly turns into sulfur vapor in the molten salt. The sulfur vapor expands the carbon shell that has been separated from the precursor but is still wrapped on the precursor, and eventually breaks and separates from the precursor, solving the problem of difficulty in synchronizing the etching and separation of layered materials. The sulfur vapor can be collected and further used as a raw material for the preparation of Ti2SC to achieve full quantitative utilization of the element. The carbon shell has undergone a more dramatic volume expansion and is rich in defects. At the same time, some sulfur that has not been completely removed enters the crystal lattice as the volume of the carbon shell expands to form doping. This defect-rich and doped nanocarbon shell provides broad prospects for long-cycle and highly stable carbon negative electrode materials for lithium-ion batteries. In addition, this material can be expanded to other fields such as supercapacitors and water purification.

[0016] Preferably, the titanium-based raw material in step (1) comprises any one or a combination of at least two of TiO2, TiC, Ti, TiS2 or TiS, wherein typical but non-limiting combinations are: a combination of TiO2 and TiC, a combination of TiC and Ti, a combination of Ti and TiS2, a combination of TiS2 and TiS, or a combination of Ti, TiS2 and TiS, etc.

[0017] Preferably, the sulfur-based raw material in step (1) comprises any one of S, TiS2, TiS, FeS2 or FeS, or a combination of at least two thereof, wherein typical but non-limiting combinations are: a combination of S and TiS2, a combination of TiS2 and TiS, a combination of TiS and FeS2, a combination of FeS2 and FeS, or a combination of TiS, FeS2 and FeS, etc.

[0018] Preferably, the carbon-based raw material in step (1) comprises any one or a combination of at least two of TiC, graphite or activated carbon, wherein typical but non-limiting combinations are: a combination of TiC and graphite, a combination of graphite and activated carbon, a combination of TiC and activated carbon, or a combination of TiC, graphite and activated carbon, etc.

[0019] The purity of the titanium-based raw material, the sulfur-based raw material and the carbon-based raw material in the present invention is all above 99wt%.

[0020] Preferably, the mixing in step (1) comprises mixing the titanium-based raw material, the sulfur-based raw material and the carbon-based raw material in an atomic ratio of titanium, sulfur and carbon of 2:1:1.

[0021] Preferably, the crushing in step (1) further comprises grinding, pickling and drying in sequence. Preferably, the Ti2SC powder in step (1) comprises polyhedral layered Ti2SC powder.

[0022] Preferably, the average particle size of the Ti2SC powder is 0.5-2 μm, for example, 0.5 μm, 0.7 μm, 0.9 μm, 1.2 μm, 1.5 μm, 1.8 μm or 2 μm.

[0023] Preferably, the briquetting in step (2) comprises pressing Ti2SC powder in a mold.

[0024] Preferably, the mold comprises a stainless steel mold.

[0025] Preferably, the molding pressure of the briquetting is 5-50 Kg / cm 2 , for example, it can be 5Kg / cm 2 , 8Kg / cm 2 、10Kg / cm 2 、15Kg / cm 2 , 20Kg / cm 2 , 25Kg / cm 2 、30Kg / cm 2 、35Kg / cm 2 , 40Kg / cm 2 , 45Kg / cm 2 or 50Kg / cm 2 wait.

[0026] The present invention sets the molding pressure of the briquetting to 5-50Kg / cm 2 , which can not only ensure that the block has sufficient strength, but also avoid the block being too dense during the electrolysis process, resulting in low current efficiency.

[0027] Preferably, the sintering temperature in step (2) is 1000-1600°C, for example, it can be 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C or 1600°C.

[0028] The sintering temperature of the present invention is 1000-1600° C., which can not only ensure that the sintered block has sufficient strength during electrolysis in molten salt, but also avoid the block from undergoing phase change due to excessively high sintering temperature.

[0029] Preferably, the sintering time is 1 to 8 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0030] Preferably, the density of the Ti2SC block in step (2) is 4.2-4.6 g / cm 3 , for example, it can be 4.2g / cm 3 , 4.25g / cm 3 , 4.3g / cm 3 , 4.35g / cm 3 , 4.4g / cm 3 , 4.45g / cm 3 , 4.5g / cm 3 , 4.55g / cm 3 or 4.6g / cm 3 wait.

[0031] Preferably, the shape of the bulk Ti2SC includes cylinder, cuboid or flake.

[0032] Preferably, the bulk Ti2SC comprises MAX phase Ti2SC.

[0033] Preferably, the molten salt in step (3) comprises a combination of at least two of LiCl, NaCl, KCl, CaCl2, MgCl2, CsCl, AlCl3, InCl, ZnCl, CdCl, CuCl, NdCl, LiF, NaF or KF, wherein typical but non-limiting combinations are: a combination of LiCl, NaCl and KCl, a combination of CaCl2, MgCl2 and CsCl, a combination of AlCl3, InCl and ZnCl, a combination of ZnCl, CdCl and CuCl or a combination of NdCl, LiF, NaF and KF, etc.

[0034] Preferably, the electrolysis reaction in step (3) comprises constant current or constant pressure.

[0035] Preferably, the current density of the constant current is 0.05-0.3 A / cm 2 , for example, it can be 0.05A / cm 2 , 0.1A / cm 2 , 0.13A / cm 2 , 0.15A / cm 2 , 0.18A / cm 2 , 0.2A / cm 2 , 0.23A / cm 2 , 0.25A / cm 2 , 0.28A / cm 2 or 0.3A / cm 2 wait.

[0036] Preferably, the constant voltage is 1-3V, for example, 1V, 1.2V, 1.4V, 1.6V, 1.8V, 2V, 2.2V, 2.4V, 2.6V, 2.8V or 3V.

[0037] Preferably, the electrolysis reaction time is 0.5 to 6 hours, for example, it can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours.

[0038] Preferably, the temperature of the electrolysis reaction is 450-950°C, for example, it can be 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C or 950°C.

[0039] Preferably, the cathode of the electrolytic reaction comprises a graphite rod.

[0040] Preferably, after the electrolysis reaction, the preliminary metallic titanium and preliminary nano-carbon material are separated from the molten salt and cooled.

[0041] Preferably, the cooling is performed under an argon atmosphere.

[0042] Preferably, the method further comprises step (4): grinding, pickling, filtering and drying the preliminary metallic titanium and preliminary nano-carbon material in step (3) respectively and in sequence to obtain metallic titanium and nano-carbon material.

[0043] Preferably, the average particle size of the titanium metal after grinding in step (4) is 1 to 10 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0044] Preferably, the average particle size of the nanocarbon material after grinding in step (4) is 1 to 3 μm, for example, it can be 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm or 3.0 μm.

[0045] Preferably, the pickling solution in the pickling comprises any one of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, oxalic acid or aqua regia, or a combination of at least two of them, wherein typical but non-limiting combinations are: a combination of sulfuric acid and hydrochloric acid, a combination of hydrochloric acid and nitric acid, a combination of nitric acid and hydrofluoric acid, a combination of oxalic acid and aqua regia, or a combination of hydrofluoric acid, oxalic acid and aqua regia, etc.

[0046] Preferably, the concentration of hydrogen ions in the pickling solution is 0.1-5 mol / L, for example, it can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, etc.

[0047] Preferably, the purity of the metal titanium is ≥99 wt%, for example, it can be 99.1 wt%, 99.15 wt%, 99.2 wt%, 99.25 wt%, 99.3 wt%, 99.35 wt%, 99.4 wt%, 99.45 wt% or 99.5 wt%, etc.

[0048] Preferably, the shape of the nanocarbon material includes shell-like and / or sheet-like.

[0049] As a preferred technical solution of the present application, the method comprises the following steps:

[0050] (1) The titanium-based raw material, sulfur-based raw material and carbon-based raw material are mixed according to the atomic ratio of titanium, sulfur and carbon being 2:1:1, and sequentially subjected to ball milling, briquetting, sintering, crushing, grinding, pickling and drying to obtain polyhedral layered Ti2SC powder with an average particle size of 0.5-2.0 μm;

[0051] (2) The Ti2SC powder of step (1) is briquetted in a mold, and the briquetting forming pressure is 5-50 Kg / cm 2 , and after briquetting, sintering is carried out at 1000-1600 ℃ for 1-8 h to obtain bulk Ti2SC with a density of 4.2-4.6 g / cm 3 ;

[0052] (3) The bulk Ti2SC of step (2) is used as an anode, and a graphite rod is used as a cathode to carry out a constant-current or constant-voltage electrolysis reaction in a molten salt at 450-950 ℃ for 0.5-6 h, the current density of the constant-current is 0.05-0.3 A / cm 2 , and the voltage of the constant-voltage is 1-3 V, to obtain preliminary metal titanium and preliminary nanocarbon material, and the preliminary metal titanium and preliminary nanocarbon material are separated from the molten salt and cooled in an argon atmosphere;

[0053] (4) The preliminary metal titanium and preliminary nanocarbon material of step (3) are respectively and sequentially ground, the average particle size of the metal titanium after grinding is 1-10 μm, the average particle size of the nanocarbon material after grinding is 1-3 μm, and pickling, suction filtration and drying are carried out in a pickling solution with a concentration of hydrogen ions of 0.1-5 mol / L to obtain metal titanium with a purity of ≥99 wt% and nanocarbon material with a shell-like and / or sheet-like shape.

[0054] Compared with the prior art, the present invention has at least the following beneficial effects:

[0055] (1) The present invention provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method fully considers the current efficiency of the cathode and anode of the molten salt electrolysis process, and simultaneously obtains high value-added products at the cathode and anode, thereby greatly improving the competitiveness of the electrolytic method for preparing metallic titanium and effectively promoting the large-scale application of electrolytic titanium extraction.

[0056] (2) The present invention provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The shell nano-carbon material prepared by the method exhibits high capacity and excellent cycle stability when used as a negative electrode for a lithium battery. The purity of the metallic titanium obtained by the method is ≥99.1%, and the nano-shell carbon material as a negative electrode for a lithium battery has a coulombic efficiency of ≥33% and a capacity of ≥256.9 mAh g -1 Under optimal conditions, the purity of titanium metal is ≥99.2%, the coulombic efficiency of nanoshell carbon material as lithium battery negative electrode is ≥43%, and the capacity is ≥404.2mAh·g -1 ;

[0057] (3) The present invention provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, which has simple operation steps and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a scanning electron microscope image of the polyhedral layered Ti2SC in Example 1 of the present invention.

[0059] Figure 2 is the X-ray diffraction spectrum of the polyhedral layered Ti2SC in Example 1 of the present invention.

[0060] Figure 3 This is a scanning electron microscope image of the nanoshell carbon material in Example 1 of the present invention.

[0061] Figure 4 These are the transmission electron microscope images and X-ray energy spectrum images of the nanoshell carbon material in Example 1 of the present invention.

[0062] Figure 5 These are the transmission electron microscope images and X-ray energy spectrum images of the layer-by-layer exfoliation of the polyhedral layered Ti2SC in Example 1 of the present invention.

[0063] Figure 6 This is the X-ray diffraction spectrum of metallic titanium in Example 1 of the present invention.

[0064] Figure 7 This is a graph showing the cycling performance of the nanoshell carbon material used as the negative electrode of a lithium battery in Example 1 of the present invention. DETAILED DESCRIPTION

[0065] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0066] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0067] 1. Implementation

[0068] Example 1

[0069] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, the method comprising the following steps:

[0070] (1) TiC, TiS2, and graphite, each with a purity of 99 wt%, were mixed in an atomic ratio of titanium, sulfur, and carbon of 2:1:1, ball-milled in a ball mill, and then briquetting, sintering, crushing, grinding, pickling, and drying to obtain a polyhedral layered Ti2SC powder with an average particle size of 0.5 μm.

[0071] (2) The Ti2SC powder in step (1) was pressed into a stainless steel mold at a molding pressure of 5 kg / cm 2 After briquetting, the sintering was carried out at 1000℃ for 8h to obtain a density of 4.2g / cm 3 Bulk Ti2SC;

[0072] (3) The Ti2SC block in step (2) was used as the anode and the graphite rod was used as the cathode in the LiCl-KCl eutectic salt at 450°C for 6 h at a constant current electrolysis reaction with a current density of 0.05 A / cm 2 After the electrolysis is completed, the two electrodes are separated from the LiCl-KCl eutectic salt and fixed, and cooled to room temperature under an argon atmosphere to obtain preliminary metallic titanium and preliminary nanocarbon materials;

[0073] (4) The preliminary metallic titanium and the preliminary nano-carbon material described in step (3) are ground in sequence, and the average particle size of the metallic titanium after grinding is 1 μm, and the average particle size of the nano-carbon material after grinding is 1 μm. The ground metallic titanium and the ground nano-carbon material are pickled in a hydrochloric acid solution with a hydrogen ion concentration of 0.1 mol / L, filtered and dried to obtain metallic titanium and nano-shell carbon material.

[0074] Figure 1 The microstructure of Ti2SC obtained after sintering is observed under a scanning electron microscope (SEM). It can be seen that the Ti2SC has uniform size and a very obvious polyhedral structure.

[0075] Figure 2represents the X-ray diffraction spectrum of Ti2SC obtained after sintering, where It represents the Ti2SC standard card. The main diffraction peak is completely consistent with the Ti2SC standard card. The purity of the obtained Ti2SC is greater than 99%.

[0076] Figure 3 The microscopic morphology of the hollow shell material obtained by molten salt electrolysis observed under a scanning electron microscope (SEM) shows that the shell particle size is uniform and the thickness is about 20 to 35 nm.

[0077] Figure 4 The microscopic morphology and X-ray energy spectrum of the hollow shell obtained by molten salt electrolysis observed under a transmission electron microscope (TEM) are compared with the O, C, S and Ti images on the right. It can be found that the main component of the shell is carbon, with very small amounts of titanium and sulfur that have not been completely removed.

[0078] Figure 5 The microstructure and X-ray energy spectrum of the polyhedral layered Ti2SC observed under a scanning electron microscope (SEM) after 10 minutes of molten salt electrolysis. Compared with the images of C, S and Ti, it can be found that the shell is obviously observed to fall off from the precursor, and the energy spectrum shows that the main component of the shell is carbon.

[0079] Figure 6 represents the X-ray diffraction spectrum of metallic titanium obtained by molten salt electrolysis, wherein It represents the Ti2SC standard card. By comparing it with the X-ray diffraction spectrum of analytical grade titanium powder, it can be seen that the purity of the titanium metal obtained by electrolysis is very high.

[0080] Figure 7 The cycling performance of nanoshell carbon materials as negative electrodes for lithium-ion batteries is shown in Figure 2. The current density of the materials is 5A·g -1 and 10A·g -1 The upper line shows a higher capacity and long-term cycle stability, where the current density is 5A·g -1 The lines below are current densities of 10 A g -1 After 1000 cycles, the current density is 5A·g -1 Capacity is 582.1 mAh g -1 , current density is 10A·g -1 Capacity is 322.3 mAh g -1 .

[0081] Example 2

[0082] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, the method comprising the following steps:

[0083] (1) Ti, FeS2, and TiC, each with a purity of 99 wt%, were mixed in a titanium, sulfur, and carbon atomic ratio of 2:1:1, ball-milled in a ball mill, briquetting, sintering, crushing, grinding, and the ground powder was pickled in a 5 mol / L hydrochloric acid solution. The resulting powder was dried to obtain a polyhedral layered Ti2SC powder with an average particle size of 2.0 μm.

[0084] (2) The Ti2SC powder in step (1) was heated to 50 kg / cm 2 The molded pieces were pressed into blocks under a forming pressure, heated to 1600°C in a tube furnace and kept warm for 1 hour;

[0085] (3) The Ti2SC block in step (2) was used as the anode and the graphite rod was used as the cathode in the CaCl2-NaCl eutectic salt at 950°C for 0.5h at a constant current density of 0.3A / cm 2 After the electrolysis is completed, the two electrodes are separated from the CaCl2-NaCl eutectic salt and fixed, and cooled to room temperature under an argon atmosphere to obtain preliminary metallic titanium and preliminary nanocarbon materials;

[0086] (4) The preliminary metallic titanium and the preliminary nano-carbon material described in step (3) are ground in sequence, respectively. The average particle size of the metallic titanium after grinding is 10 μm, and the average particle size of the nano-carbon material after grinding is 3 μm. The ground metallic titanium and the ground nano-carbon material are pickled in a hydrochloric acid solution with a hydrogen ion concentration of 5 mol / L, filtered and dried to obtain metallic titanium and nano-shell carbon material.

[0087] Example 3

[0088] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, the method comprising the following steps:

[0089] (1) Ti, TiS, and graphite, each with a purity of 99 wt%, were mixed in an atomic ratio of titanium, sulfur, and carbon of 2:1:1, ball-milled in a ball mill, and then briquetting, sintering, crushing, grinding, pickling, and drying to obtain a polyhedral layered Ti2SC powder with an average particle size of 1.5 μm.

[0090] (2) The Ti2SC powder in step (1) was pressed into a stainless steel mold at a molding pressure of 25 kg / cm 2 After briquetting, the sintering was carried out at 1300℃ for 4h to obtain a density of 4.4g / cm 3 Bulk Ti2SC;

[0091] (3) The bulk Ti2SC in step (2) was used as the anode and the graphite rod was used as the cathode in NaCl-CsCl eutectic salt at 750°C for 3.0 h. The constant current density was 0.15 A / cm 2 After the electrolysis is completed, the two electrodes are separated from the NaCl-CsCl eutectic salt and fixed, and cooled to room temperature under an argon atmosphere to obtain preliminary metallic titanium and preliminary nanocarbon materials;

[0092] (4) The preliminary metallic titanium and the preliminary nano-carbon material described in step (3) are ground in sequence, respectively. The average particle size of the metallic titanium after grinding is 5 μm, and the average particle size of the nano-carbon material after grinding is 2.0 μm. The ground metallic titanium and the ground nano-carbon material are pickled in an oxalic acid solution with a hydrogen ion concentration of 2.5 mol / L, filtered and dried to obtain metallic titanium and nano-shell carbon material.

[0093] Example 4

[0094] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, the method comprising the following steps:

[0095] (1) TiO2, S, and activated carbon, each with a purity of 99 wt%, were mixed in an atomic ratio of titanium, sulfur, and carbon of 2:1:1 and ball-milled in a ball mill to obtain a polyhedral layered Ti2SC powder with an average particle size of 1.0 μm;

[0096] (2) The Ti2SC powder described in step (1) was pressed into a stainless steel mold at a molding pressure of 40 kg / cm 2 After briquetting, the sintering was carried out at 1400℃ for 3h to obtain a density of 4.5g / cm 3 Bulk Ti2SC;

[0097] (3) The Ti2SC block in step (2) was used as the anode and the graphite rod was used as the cathode in NaF-KF eutectic salt at 800°C for 6 h. The constant current density was 0.05 A / cm 2 After the electrolysis is completed, the two electrodes are separated from the NaF-KF eutectic salt and fixed, and cooled to room temperature under an argon atmosphere to obtain preliminary metallic titanium and preliminary nanocarbon materials;

[0098] (4) The preliminary metallic titanium and the preliminary nano-carbon material described in step (3) are ground in sequence, respectively. The average particle size of the metallic titanium after grinding is 4 μm, and the average particle size of the nano-carbon material after grinding is 1.5 μm. The ground metallic titanium and the ground nano-carbon material are pickled in a hydrofluoric acid solution with a hydrogen ion concentration of 2 mol / L, filtered and dried to obtain metallic titanium and nano-shell carbon material.

[0099] Example 5

[0100] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method differs from Example 1 only in that step (3) electrolysis adopts constant voltage, the constant voltage is 1V, and the electrolysis reaction time is 6h. The rest is the same as Example 1.

[0101] Example 6

[0102] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method differs from Example 1 only in that step (3) electrolysis adopts constant voltage, the constant voltage is 3V, and the electrolysis reaction time is 3.0h. The rest is the same as Example 1.

[0103] Example 7

[0104] This embodiment provides a method for preparing titanium metal and nano-carbon materials by molten salt electrolysis. The difference between the method and embodiment 1 is that the molding pressure of the briquetting in step (2) is 2 kg / cm 2 , the rest are the same as in Example 1.

[0105] In this embodiment, since the molding pressure is too low, the strength of the sintered block is obviously insufficient, and a large area of ​​falling occurs during the electrode preparation process; when electrolysis is carried out in the molten salt, most of the blocks are scattered in the molten salt, and only a small part participates in the electrolysis, resulting in an extremely low yield of titanium and nano-carbon materials.

[0106] Example 8

[0107] This embodiment provides a method for preparing titanium metal and nano-carbon materials by molten salt electrolysis. The difference between the method and embodiment 1 is that the molding pressure of the briquetting in step (2) is 55Kg / cm 2 , the rest are the same as in Example 1.

[0108] In this embodiment, since the molding pressure is too high, the density of the sintered block is too high, deep electrolysis cannot be completed, and a large amount of Ti2SC still exists inside the electrode block.

[0109] Example 9

[0110] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method is different from that of Example 1 only in that the sintering temperature in step (2) is 900° C., and the rest is the same as that of Example 1.

[0111] In this embodiment, since the sintering temperature is too low, the strength of the sintered block is obviously insufficient, and most of it falls off during the electrode preparation process; when electrolysis is carried out in the molten salt, the block is partially scattered in the molten salt, and the yield of titanium and nano-carbon materials is low.

[0112] Example 10

[0113] This embodiment provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method is different from that of Example 1 only in that the sintering temperature in step (2) is 1700° C., and the rest is the same as that of Example 1.

[0114] In this embodiment, since the sintering temperature is too high, the Ti2SC on the surface of the block undergoes a phase change, and a large amount of TiO2 is generated on the surface. The presence of this TiO2 greatly reduces the current efficiency of the two electrodes and the yield of the anode and cathode products.

[0115] 2. Comparative Example

[0116] Comparative Example 1

[0117] This comparative example provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method differs from Example 1 only in that TiS2 is not added in step (1), and the rest is the same as Example 1.

[0118] In this embodiment, since no sulfur source was added, Ti2SC was not generated and electrolysis could not be carried out.

[0119] Comparative Example 2

[0120] This comparative example provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method differs from Example 1 only in that graphite is not added in step (1), and the rest is the same as Example 1.

[0121] In this embodiment, the purity of Ti2SC in the sintered product is significantly low, which greatly reduces the current efficiency of the two electrodes and the yield of the anode and cathode products.

[0122] Comparative Example 3

[0123] This comparative example provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method is different from Example 1 only in that sintering is not performed in step (3). The rest is the same as Example 1.

[0124] The unsintered blocks in this embodiment are obviously not strong enough to prepare a complete electrode; and when electrolysis is carried out in molten salt, most of the blocks are scattered in the molten salt, and only a small part participates in the electrolysis, resulting in an extremely low yield of titanium and nano-carbon materials.

[0125] 3. Test and Results

[0126] Testing method for the cycling performance of nanocarbon materials as lithium battery anodes: The prepared nanocarbon material, acetylene black, and binder were thoroughly mixed in a mass ratio of 8:1:1 and used as the anode material for lithium-ion batteries. A metal lithium sheet was used as the counter electrode, Celgard 2325 was used as the separator, 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and dimethyl carbonate in a 1:1 volume ratio) was used as the electrolyte, and CR2032 button cell shells were assembled in an argon-protected glove box. Charge and discharge cycling performance tests were conducted at 5000 mA / g and 10000 mA / g, with a voltage range of 0.01 to 3 V. The coulombic efficiency and capacity of the nanoshell carbon material as a lithium battery anode were determined.

[0127] Scanning electron microscopy images were obtained using a JSM-7800 scanning electron microscope, transmission electron microscopy images were obtained using a JEM-2100F transmission electron microscope, and X-ray diffraction spectra were obtained using an X'Pert PRO MPD X-ray diffractometer.

[0128] Testing method for the purity of titanium metal: The purity of titanium metal obtained by electrolysis is tested by atomic absorption spectroscopy. The principle is to use flame combustion to quickly heat up a small amount of the test sample to complete the sample atomization process. Then, based on the absorption of the characteristic spectral lines by the ground state atomic vapor of the titanium element, the characteristic spectral lines and the degree of attenuation of the spectral lines are used to qualitatively and quantitatively analyze the titanium element.

[0129] The test results of the above embodiments and comparative examples are shown in Table 1.

[0130] Table 1

[0131]

[0132] From Table 1 we can see several points:

[0133] (1) The present invention provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, the method comprising: mixing titanium-based raw materials, sulfur-based raw materials and carbon-based raw materials, ball milling, briquetting, sintering and crushing to obtain Ti2SC powder; briquetting and sintering the Ti2SC powder in sequence to obtain bulk Ti2SC; the bulk Ti2SC acts as an anode to undergo electrolysis in molten salt to obtain preliminary metallic titanium and preliminary nano-carbon materials. The method takes into account the current efficiency of both the cathode and anode, which will greatly enhance the competitiveness of titanium extraction by molten salt electrolysis. Specifically, the purity of metallic titanium in Examples 1 to 10 is ≥99.1%, the coulombic efficiency of the nanoshell carbon material as the negative electrode of the lithium battery is ≥33%, and the capacity is ≥256.9 mAh·g -1Under optimal conditions, the purity of titanium metal is ≥99.2%, the coulombic efficiency of nanoshell carbon material as lithium battery negative electrode is ≥43%, and the capacity is ≥404.2mAh·g -1 ;

[0134] (2) Combining Example 1 and Examples 7 to 8, it can be seen that the molding pressure of the briquetting in step (2) of Example 1 is 5Kg / cm 2 , compared with the molding pressure of the briquetting in step (2) in Examples 7 to 8, which is 2 Kg / cm 2 and 55Kg / cm 2 In Example 1, the purity of titanium metal is 99.5%, the coulombic efficiency of the nanoshell carbon material as the negative electrode of the lithium battery is 45%, and the capacity is 464.3 mAh·g -1 , while the purity of titanium metal in Examples 7 and 8 was 99.1% and 99.3% respectively, and the coulombic efficiency of the nanoshell carbon material as the negative electrode of the lithium battery was 33% and 40% respectively, and the capacity was 256.9 mAh g -1 and 321.2mAh·g -1 , which shows that the present invention controls the molding pressure of the briquetting in step (2) within a certain range, which can further improve the purity of the prepared metallic titanium and further improve the coulombic efficiency and capacity of the nano-carbon material as the negative electrode of the lithium battery;

[0135] (3) Combining Example 1 with Examples 9 and 10, it can be seen that the sintering temperature in step (2) of Example 1 is 1000°C. Compared with the sintering temperatures of 900°C and 1700°C in Step (2) of Examples 9 and 10, respectively, the purity of the titanium metal in Example 1 is 99.5%, the coulombic efficiency of the nanoshell carbon material as the negative electrode of the lithium battery is 45%, and the capacity is 464.3 mAh·g -1 , while the purity of titanium metal in Examples 9 and 10 was 99.2% and 99.3% respectively, and the coulombic efficiency of the nanoshell carbon material as the negative electrode of the lithium battery was 42% and 39% respectively, and the capacity was 322.5 mAh g -1 and 367.5mAh·g -1 , which shows that the present invention controls the sintering temperature in step (2) within a certain range, which can further improve the purity of the prepared metallic titanium and further improve the coulombic efficiency and capacity of the nano-carbon material as the negative electrode of the lithium battery;

[0136] (4) Combining Example 1 and Comparative Examples 1 to 2, it can be seen that in Example 1, step (1) of mixing TiC, TiS2 and graphite is compared with Comparative Examples 1 to 3 in which no TiS2 and graphite are added in step (1). In Example 1, the purity of metallic titanium is 99.5%, the coulombic efficiency of the nanoshell carbon material as the negative electrode of the lithium battery is 45%, and the capacity is 464.3 mAh g -1 In Comparative Example 1, no metallic titanium and nano-carbon materials were obtained. In Comparative Example 2, the purity of metallic titanium was 99.1%, and the coulombic efficiency of the nano-shell carbon material as the negative electrode of the lithium battery was 35%, and the capacity was 252.1 mAh g -1 , which shows that the present invention mixes titanium-based raw materials, sulfur-based raw materials and carbon-based raw materials, which can improve the purity of the prepared metallic titanium and also improve the coulombic efficiency and capacity of the nano-carbon material as the negative electrode of the lithium battery;

[0137] (5) Combining Example 1 and Comparative Example 3, it can be seen that the purity of the titanium metal in Example 1 is 99.5%, the coulombic efficiency of the nanoshell carbon material as the negative electrode of the lithium battery is 45%, and the capacity is 464.3 mAh·g, compared with the case where step (3) in Example 1 is not sintered. -1 , while metallic titanium and nano-carbon materials could not be obtained in Comparative Example 3, which shows that sintering in step (3) of the present invention is an indispensable step in the method, and the purity of metallic titanium that can be prepared is high.

[0138] In summary, the present invention provides a method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis. The method takes into account the current efficiency of both the cathode and anode, which will greatly improve the competitiveness of titanium extraction by molten salt electrolysis. The purity of the obtained metallic titanium is ≥99.1%, and the coulombic efficiency of the nano-shell carbon material as the negative electrode of the lithium battery is ≥33%, and the capacity is ≥256.9 mAh g -1 Under optimal conditions, the purity of titanium metal is ≥99.2%, the coulombic efficiency of nanoshell carbon material as lithium battery negative electrode is ≥43%, and the capacity is ≥404.2mAh·g -1 .

[0139] The applicant declares that the present invention is intended to illustrate the detailed structural features of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed structural features. This does not mean that the present invention must rely on the above-described detailed structural features in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific embodiments, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing metallic titanium and nano-carbon materials by molten salt electrolysis, characterized in that: The method comprises the following steps: (1) mixing titanium-based raw materials, sulfur-based raw materials, and carbon-based raw materials, and sequentially performing ball milling, briquetting, sintering, and crushing to obtain Ti2SC powder; (2) briquetting and sintering the Ti2SC powder in step (1) to obtain Ti2SC blocks; (3) The bulk Ti2SC in step (2) is used as an anode to perform an electrolytic reaction in a molten salt to obtain preliminary metallic titanium and preliminary nanocarbon materials; The molding pressure of the briquetting is 5-50 Kg / cm 2 The sintering temperature is 1000-1600°C; the electrolysis reaction temperature is 450-950°C; Part of the sulfur that is not completely removed during the electrolysis reaction enters the crystal lattice as the volume of the carbon shell expands to form doping; The method further comprises step (4): grinding, pickling, filtering and drying the preliminary metallic titanium and preliminary nano-carbon material in step (3) respectively and in sequence to obtain metallic titanium and nano-carbon material; the shape of the nano-carbon material includes a shell shape.

2. The method according to claim 1, characterized in that The titanium-based raw material in step (1) includes any one of TiO2, TiC, Ti, TiS2 or TiS, or a combination of at least two of them.

3. The method according to claim 1, characterized in that The sulfur-based raw material in step (1) includes any one of S, TiS2, TiS, FeS2 or FeS, or a combination of at least two of them.

4. The method according to claim 1, wherein The carbon-based raw material in step (1) includes any one of TiC, graphite or activated carbon, or a combination of at least two of them.

5. The method according to claim 1, wherein The mixing in step (1) includes mixing a titanium-based raw material, a sulfur-based raw material and a carbon-based raw material according to an atomic ratio of titanium, sulfur and carbon of 2:1:

1.

6. The method according to claim 1, characterized in that After the crushing in step (1), the process further includes grinding, pickling and drying.

7. The method according to claim 1, characterized in that The Ti2SC powder in step (1) includes polyhedral layered Ti2SC powder.

8. The method according to claim 7, characterized in that The average particle size of the Ti2SC powder is 0.5-2 μm.

9. The method according to claim 1, characterized in that The briquetting in step (2) includes pressing Ti2SC powder in a mold.

10. The method according to claim 1, characterized in that The sintering time is 1 to 8 hours.

11. The method according to claim 1, wherein The density of the Ti2SC block in step (2) is 4.2-4.6 g / cm 3 .

12. The method according to claim 1, characterized in that The shape of the bulk Ti2SC includes cylinder, cuboid or flake.

13. The method according to claim 1, wherein The bulk Ti2SC includes MAX phase Ti2SC.

14. The method according to claim 1, wherein The molten salt in step (3) includes a combination of at least two of LiCl, NaCl, KCl, CaCl2, MgCl2, CsCl, AlCl3, InCl, ZnCl, CdCl, CuCl, NdCl, LiF, NaF or KF.

15. The method according to claim 1, wherein The electrolysis reaction in step (3) includes constant current or constant pressure.

16. The method according to claim 15, characterized in that The current density of the constant current is 0.05-0.3A / cm 2 .

17. The method according to claim 15, characterized in that The constant voltage is 1-3V.

18. The method according to claim 1, wherein The electrolysis reaction time is 0.5 to 6 hours.

19. The method according to claim 1, wherein The cathode of the electrolytic reaction includes a graphite rod.

20. The method according to claim 1, wherein After the electrolysis reaction, the preliminary metallic titanium and the preliminary nano-carbon material are separated from the molten salt and cooled.

21. The method according to claim 20, characterized in that The cooling was performed under an argon atmosphere.

22. The method according to claim 1, wherein The average particle size of the titanium metal after grinding in step (4) is 1 to 10 μm.

23. The method according to claim 1, wherein The average particle size of the nano-carbon material after grinding in step (4) is 1 to 3 μm.

24. The method according to claim 1, wherein The pickling solution in the pickling process includes any one of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, oxalic acid or aqua regia, or a combination of at least two of them.

25. The method according to claim 1, wherein The concentration of hydrogen ions in the pickling solution is 0.1 to 5 mol / L.

26. The method according to claim 1, wherein The purity of the metallic titanium is ≥99 wt%.

27. The method according to claim 1, wherein The method comprises the following steps: (1) A titanium-based raw material, a sulfur-based raw material, and a carbon-based raw material are mixed according to an atomic ratio of titanium, sulfur, and carbon of 2:1:1, and the mixture is subjected to ball milling, briquetting, sintering, crushing, grinding, pickling, and drying in sequence to obtain a polyhedral layered Ti2SC powder with an average particle size of 0.5 to 2 μm; (2) The Ti2SC powder of step (1) is pressed into a mold at a pressure of 5 to 50 kg / cm 2 After briquetting, the briquetting is carried out at 1000-1600℃ for 1-8h to obtain a density of 4.2-4.6g / cm 3 Bulk Ti2SC; (3) In step (2), the Ti2SC block is used as the anode and the graphite rod is used as the cathode in a molten salt at 450-950°C for a constant current or constant voltage electrolysis reaction for 0.5-6 hours. The constant current density is 0.05-0.3 A / cm 2 , the constant voltage is 1 to 3 V, to obtain preliminary metallic titanium and preliminary nano-carbon materials, and to separate the preliminary metallic titanium and preliminary nano-carbon materials from the molten salt and to cool them in an argon atmosphere; (4) The preliminary metallic titanium and preliminary nano-carbon material described in step (3) are ground respectively in sequence, wherein the average particle size of the metallic titanium after grinding is 1 to 10 μm, and the average particle size of the nano-carbon material after grinding is 1 to 3 μm. The metallic titanium and the preliminary nano-carbon material are pickled in an acid pickling solution with a hydrogen ion concentration of 0.1 to 5 mol / L, filtered and dried to obtain metallic titanium with a purity of ≥99 wt% and shell-shaped and / or lamellar nano-carbon materials.

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