Ti-O electronic compound, lithium-sulfur battery electrode material, preparation method and application of Ti-O electronic compound and lithium-sulfur battery electrode material

Abstract

The invention discloses a Ti-O electronic compound, a sulfur lithium battery electrode material, a preparation method and application, and belongs to the technical field of electrode material preparation. The preparation method comprises the following steps: (1) uniformly mixing Ti powder and TiO2 powder according to the stoichiometric ratio of Ti to TiO2; (2) pressing the mixed powder obtained in the step (1) under the condition of 150-250 MPa to obtain a sintered body; and (3) the sintered body is wrapped with Ti powder, then high-temperature sintering is conducted, cooling is conducted after sintering is finished, and the Ti-O electronic compound is obtained. The invention provides a simple preparation method for synthesizing a high-purity Ti-O electron compound, and a lithium-sulfur battery positive electrode based on the Ti-O electron compound as a catalytic carrier is prepared. The powder embedding high-temperature sintering synthesis of the Ti-O electronic compound is realized by controlling key parameters such as powder particle size, compaction density, sintering atmosphere and temperature, and the sulfur positive electrode of the lithium-sulfur battery with high rate performance is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode material preparation, and particularly relates to a Ti-O electron compound, a sulfur-lithium battery electrode material, a preparation method and uses thereof. Background Art

[0002] Electron compounds are a special type of ionic compounds. In their crystal structures, some excess electrons are highly localized in the lattice voids, producing an effect similar to that of anions. The regions composed of these localized electrons are called "pseudo atoms". Since these "pseudo atoms" in electron compounds are extremely easy to break free from the lattice voids that bind them and contribute to the outside, electron compounds generally have an extremely low work function (2.6 - 4.0 eV) and extremely strong reducibility, which makes them shine in fields such as catalytic reduction synthesis of ammonia and catalytic oxygen reduction reaction.

[0003] Currently, the mainly studied electron compounds include 7Al2O3·12CaO, Ca2N, LaScSi, etc., but they have been showing weakness in the expansion of synthesis and application. First of all, many electron compounds only exist under extreme conditions such as extremely high pressure (≥2 GPa), and generally have complex structures and rare element compositions, making the research and synthesis of this type of electron compounds difficult; then, the synthesis of many electron compounds requires extreme conditions such as extremely high temperature and extremely high pressure and complex processes, and has high requirements for the equipment required for the synthesis process, resulting in few scientific research institutions that can study electron compounds. The high cost and high threshold also limit the extensiveness of their research; finally, the properties of most electron compounds are too active and are extremely easy to react with external media such as air, water, and organic reagents. The conditions that need to be overcome during the experimental research of these electron compounds are harsh and difficult to control, which also greatly limits the research and application of electron compounds. Considering these factors comprehensively, the types of successfully discovered and synthesized electron compounds are still limited at present, and the most widely studied is still 7Al2O3·12CaO. It can be seen that the theoretical research on electron compounds is not yet mature at present, and the applied research is also mostly limited to only a few catalytic fields.

[0004] Ti and O elements can form electronic compounds with chemical formulas of Ti2O, Ti3O, and Ti6O, which are stable at room temperature and pressure, safe and cheap in elemental composition, and can also exist stably in many media due to the characteristics of self-passivation. In particular, Ti2O has achieved some results in the field of applied research. However, on the one hand, previous research was limited to Ti2O electronic compounds and lacked the expansion of Ti3O and Ti6O. On the other hand, in previous synthesis methods, the synthesis method of Ti2O was complicated and the purity was difficult to control. For example, high-temperature molten salt electrolysis at 800°C synthesized relatively pure Ti2O, and arc melting at 2000°C synthesized Ti2O and used to load Pt metal catalysts. These methods require special equipment or special methods such as extremely high temperature to be carried out; other methods such as laser pulse deposition and TiH2 sintering are difficult to synthesize relatively pure Ti2O. In addition to the above problems of Ti2O, Ti3O and Ti6O lack research on synthesis and experimental application.

[0005] In the field of secondary batteries, lithium-sulfur batteries are currently considered to be one of the most promising replacements for lithium-ion batteries due to their high theoretical energy density and cheap raw sulfur. However, the slow reaction kinetics of lithium polysulfide and the shuttling effect of lithium polysulfide lead to poor rate performance (difficult to reach above 1C) and poor cycle stability of lithium-sulfur batteries, which limits the further development and application of lithium-sulfur batteries. Therefore, designing catalytic positive electrode carriers for lithium-sulfur batteries has become one of the hot research directions of lithium-sulfur batteries, but there is currently no catalytic carrier associated with electronic compounds. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a Ti-O electronic compound, a sulfur-lithium battery electrode material, a preparation method and use thereof. The present invention provides a simple preparation method to synthesize a high-purity Ti-O electronic compound, and to develop a lithium-sulfur battery positive electrode using the Ti-O electronic compound as a catalytic carrier. The powder embedding and high-temperature sintering synthesis of the Ti-O electronic compound is achieved by controlling key parameters such as powder particle size, compaction density, sintering atmosphere and temperature. In addition, the sulfur positive electrode of the lithium-sulfur battery is prepared by a wet electrode process, achieving high rate performance.

[0007] To achieve the above purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0008] The object of the present invention is to provide a method for preparing a Ti-O electronic compound, comprising the following steps:

[0009] (1) mixing Ti powder and TiO2 powder uniformly according to the stoichiometric ratio of Ti and TiO2;

[0010] (2) pressing the mixed powder obtained in step (1) at a pressure of 150 to 250 MPa to obtain a sintered body;

[0011] (3) Wrap the sintered body with Ti powder, then heat it to 1000 - 1300 °C at a rate of 2 - 5 °C / min for sintering. After sintering, cool it to 400 - 500 °C at a rate of 2 - 5 °C / min, and then cool it naturally to obtain the Ti-O electron compound.

[0012] Further, in step (1), the stoichiometric ratio of Ti to TiO₂ is 3 - 11:1.

[0013] Further, in step (1), the stoichiometric ratio of Ti to TiO₂ is 3:1, 5:1 or 11:1.

[0014] Further, in step (1), the particle size of the Ti powder is 40 - 50 μm, and the particle size of the TiO₂ powder is 5 - 10 nm.

[0015] Further, in step (1), the particle size of the Ti powder is 50 μm, and the particle size of the TiO₂ powder is 5 - 10 nm.

[0016] Further, in step (3), the particle size of the Ti powder is 40 - 50 μm, and its coating thickness is not less than 1 mm.

[0017] Further, in step (3), the sintering temperature is 1250 °C, the heating rate is 5 °C / min, and after cooling to 500 °C, it is cooled naturally, and the cooling rate is 5 °C / min.

[0018] Another object of the present invention is to provide a Ti-O electron compound prepared by the above method; the Ti-O electron compound is a Ti₂O, Ti₃O or Ti₆O electron compound.

[0019] Another object of the present invention is to provide a preparation method of a lithium-sulfur battery electrode material, which is characterized by including the following steps:

[0020] (1) Grind and crush the Ti-O electron compound described in claim 7, then mix it with sulfur powder in a mass ratio of 1:2 - 4, and then heat it at 150 - 200 °C for 10 - 15 h to obtain Ti x O@S powder;

[0021] (2) Mix the Ti x O@S (x = 2, 3, 6) powder with conductive carbon black and a PVDF nmp solution, stir evenly to obtain an electrode slurry, and then coat it on the surface of the current collector, and dry it to prepare a Ti-O electron compound-based lithium-sulfur battery electrode material.

[0022] Furthermore, in step (1), the dense protective layer on the surface of the Ti-O electronic compound is removed by grinding, and the particle size after crushing is 500 nm.

[0023] Furthermore, in step (1), the mass ratio of the Ti—O electronic compound powder to the sulfur powder is 1:3.

[0024] Furthermore, the temperature in step (1) is 155° C. and the heating time is 12 h.

[0025] Furthermore, step (1) Ti x In O@S powder, x is 2, 3 or 6.

[0026] Further, the concentration of PVDF in the nmp solution was 4%.

[0027] Furthermore, Ti x The mass ratio of O@S (x=2,3,6) powder to conductive carbon black and PVDF is 7:2:1.

[0028] Furthermore, the amount of electrolyte used in step (2) should be precisely controlled, with the ratio to sulfur being 25 μL / mg.

[0029] Another object of the present invention is to provide a sulfur-lithium battery electrode material, which is prepared by the above method.

[0030] Furthermore, the prepared sulfur-lithium battery electrode material is a sulfur-lithium battery positive electrode material.

[0031] Another object of the present invention is to provide the use of the above-mentioned sulfur-lithium battery electrode material in the preparation of lithium batteries.

[0032] Beneficial effects of the present invention:

[0033] 1. The present invention has successfully developed a simple high-temperature sintering synthesis process. By mixing and compacting Ti powder and TiO2 and then sintering at high temperature, Ti2O, Ti3O, and Ti6O electronic compounds are successfully synthesized. The process uses simple raw materials (cheap Ti and TiO2 powders), the obtained samples have good purity and considerable yield, and the equipment used is simple (ordinary corundum tube furnace).

[0034] 2. The present invention suppresses the oxidation of Ti during the sintering process by the embedding method, and realizes the precise control of the oxygen content in the Ti-O electronic compound. And the compacted sheet is conducive to the solid-phase reaction and solid-phase diffusion between the sintered powders. According to this method, a single sintering preparation of tens of grams can be completed using only a tubular furnace, which is sufficient to meet most experimental research, and the output can continue to increase with the expansion of the equipment. Compared with the previous Ti2O synthesis methods such as arc melting and molten salt electrolysis, the output is greatly improved, and the process is greatly simplified, which greatly reduces the difficulty of synthesizing electronic compounds and the research threshold.

[0035] 3. Compared with other electronic compounds, Ti-O electronic compounds have higher research value and broader research prospects. Due to the self-passivation characteristics, Ti-O series electronic compounds remain stable in many media, and this characteristic greatly broadens the application research scope of electronic compounds. Most electronic compounds are difficult to synthesize, have poor stability, and are difficult to research and apply. They will react with most common media and solvents such as air, water, and organic solvents. The Ti-O electronic compounds easily synthesized by the present invention can remain stable in these media due to their self-passivation characteristics, which is also the reason why they can be expanded to lithium-sulfur batteries.

[0036] 4. Ti2O and Ti3O exhibit good performance as sulfur carriers for the positive electrode of lithium-sulfur batteries. They can effectively overcome the shuttle effect of lithium polysulfide in the sulfur positive electrode and provide highly conductive chemical adsorption carriers for sulfur species, allowing electrons to transfer quickly at the electrode, overcoming the problem of weak electronic conductivity of electrochemically active substances such as elemental sulfur and Li2S, and catalyzing and accelerating the decomposition of lithium polysulfide. The assembled lithium-sulfur battery achieved a capacity of 500mAh / g at a high rate of 4C. Compared with previous research on electronic compounds limited to the fields of oxygen reduction and ammonia reduction, this further expands the scope of application research of electronic compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the present invention in which Ti powder and TiO2 powder are mixed and then pressed into a sintered sheet;

[0038] Figure 2 The schematic diagram of the present invention is that the above-mentioned sheet to be sintered is uniformly embedded in titanium powder and placed in a graphite boat;

[0039] Figure 3 A schematic diagram of preparing a Ti-O electronic compound sintered sheet by high temperature sintering according to the present invention;

[0040] Figure 4 This is a detection diagram of the crushed Ti-O electronic compound of the present invention;

[0041] Figure 5 is the neutron diffraction spectrum of Ti-O electronic compound;

[0042] Figure 6 Ti with sulfur-coated powder surface x Detection diagram of O@S(x = 2, 3, 6);

[0043] Figure 7 Schematic diagram for electrode preparation;

[0044] Figure 8 Schematic diagram for the assembly of button cell device;

[0045] Figure 9 Detection diagram of the electrochemical performance of button cell. Detailed implementation manners

[0046] The following describes the detailed implementation manners of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed implementation manners. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

[0047] Example 1

[0048] A preparation method for the cathode of a Ti-O electron compound-based lithium-sulfur battery, and the specific process is as follows:

[0049] (1) Based on the stoichiometric ratio of Ti and O in the Ti-O electron compound, mix Ti powder and TiO2 powder evenly at a ratio of 3:1 by stoichiometric ratio; among them, the particle size of the Ti powder is 50 μm, and the particle size of the TiO2 powder is 10 nm;

[0050] (2) Under the condition of 200 MPa, press the mixed powder obtained in step (1) to form a circular sheet to obtain a sintered body;

[0051] (3) Place the sintered body in a graphite boat, completely wrap the sintered body with Ti powder, and the coating thickness is 2 mm. Then, heat it to 1250 °C at a rate of 5 °C / min for sintering. After sintering, cool it to 500 °C at a rate of 5 °C / min, and then cool it naturally to obtain the Ti2O electron compound;

[0052] (4) After taking out the Ti2O electron compound, polish its surface to remove the dense protective layer on the surface. Grind the polished sintered sheet into coarse powder in a mortar, and then ball mill it into fine powder with a particle size of 500 nm;

[0053] (5) Mix the Ti2O electronic compound powder and sulfur powder evenly at a mass ratio of 1:3 and place them in a corundum boat. In an argon atmosphere in a tube furnace, heat at 155 °C for 12 h to melt and load sulfur to obtain Ti2O@S powder;

[0054] (6) Mix the Ti2O@S powder with a conductive carbon black and PVDF N-methylpyrrolidone solution in a ratio of 7:2:1, stir evenly to obtain an electrode slurry, then coat it on the surface of an aluminum foil current collector, dry it in a vacuum oven to make an electrode sheet, and then cut the electrode sheet into different specifications as needed to obtain a cathode for a Ti-O electronic compound-based lithium-sulfur battery.

[0055] Example 2

[0056] A method for preparing a cathode for a Ti-O electronic compound-based lithium-sulfur battery, the specific process is as follows:

[0057] (1) Based on the stoichiometric ratio of Ti and O in the Ti-O electronic compound, mix Ti powder and TiO2 powder evenly at a stoichiometric ratio of 5:1; among them, the particle size of the Ti powder is 40 μm, and the particle size of the TiO2 powder is 5 nm;

[0058] (2) Under the condition of 150 MPa, press the mixed powder obtained in step (1) to form a circular sheet to obtain a sintered body;

[0059] (3) Place the sintered body in a graphite boat, completely wrap the sintered body with Ti powder, the coating thickness is 4 mm, then heat it to 1250 °C at a rate of 5 °C / min for sintering, after sintering, cool it to 500 °C at a rate of 5 °C / min, and then cool it naturally to obtain a Ti3O electronic compound;

[0060] (4) After taking out the Ti3O electronic compound, polish its surface to remove the dense protective layer on the surface, grind the polished sintered sheet into coarse powder in a mortar, and then ball mill it into fine powder with a particle size of 500 nm;

[0061] (5) Mix the Ti3O electronic compound powder and sulfur powder evenly at a mass ratio of 1:2 and place them in a corundum boat. In an argon atmosphere in a tube furnace, heat at 150 °C for 15 h to melt and load sulfur to obtain Ti3O@S powder;

[0062] (6) Mix the Ti3O@S powder with a conductive carbon black and PVDF N-methylpyrrolidone solution in a ratio of 7:2:1, stir evenly to obtain an electrode slurry, then coat it on the surface of an aluminum foil current collector, dry it in a vacuum oven to make an electrode sheet, and then cut the electrode sheet into different specifications as needed to obtain a cathode for a Ti-O electronic compound-based lithium-sulfur battery.

[0063] Example 3

[0064] A preparation method for the cathode of a lithium-sulfur battery based on a Ti-O electronic compound is as follows:

[0065] (1) Based on the stoichiometric ratio of Ti and O in the Ti-O electronic compound, mix Ti powder and TiO2 powder evenly at a stoichiometric ratio of 11:1; among them, the particle size of the Ti powder is 45 μm, and the particle size of the TiO2 powder is 10 nm;

[0066] (2) Under the condition of 250 MPa, press the mixed powder obtained in step (1) to form a circular sheet to obtain a sintered body;

[0067] (3) Place the sintered body in a graphite boat, completely wrap the sintered body with Ti powder, with a coating thickness of 2.5 mm, then heat it to 1250 °C at a rate of 5 °C / min for sintering, cool it to 500 °C at a rate of 5 °C / min after sintering, and then cool it naturally to obtain the Ti6O electronic compound;

[0068] (4) After taking out the Ti6O electronic compound, polish its surface to remove the dense protective layer on the surface, grind the polished sintered sheet into coarse powder in a mortar, and then ball-mill it into fine powder with a particle size of 500 nm;

[0069] (5) Mix the Ti6O electronic compound powder and sulfur powder evenly at a mass ratio of 1:4 and place them in a corundum boat. In an argon atmosphere in a tube furnace, heat it at 200 °C for 10 h to melt and load sulfur to obtain Ti6O@S powder;

[0070] (6) Mix the Ti6O@S powder with conductive carbon black and an N-methylpyrrolidone solution of PVDF in a ratio of 7:2:1, stir evenly to obtain an electrode slurry, then coat it on the surface of an aluminum foil current collector, dry it in a vacuum oven to obtain an electrode sheet, and then cut the electrode sheet into different specifications as needed to obtain the cathode of the lithium-sulfur battery based on the Ti-O electronic compound.

[0071] Figures 1 - 3 This is a schematic flow chart for sintering and preparing the Ti-O electronic compound of the present invention, Figure 1 This is a schematic diagram showing that after mixing Ti powder and TiO2 powder according to the ratio described in step (1) of the present invention, they are pressed into a sheet in a tablet press mold. Figure 2 This is a schematic diagram showing that the well-formed sintered sheet after the above pressing is evenly embedded in titanium powder and placed in a graphite boat. Figure 3 This is a schematic diagram showing high-temperature sintering and obtaining the Ti-O electronic compound sintered sheet.

[0072] As Figure 3As shown, it is heated to 1250 °C in an argon atmosphere in a tube furnace and then cooled to obtain a sintered sheet after sintering. However, at this time, there is still a protective film formed by a dense layer of Ti on the surface of the sheet. This film is formed by the sintering and welding of the embedded Ti on the surface at high temperature, which can effectively prevent the interior from being affected by the external atmosphere, thereby achieving precise control of the oxygen content and the precise oxygen content in the Ti-O electron compound. It should be noted that due to the limited distance of solid-phase diffusion and the limited sintering reaction rate, this layer of Ti will not affect the internal purity. The degree of polishing should be until the surface loses its luster and exposes the single-colored grayish-black substance inside.

[0073] The Ti-O electron compound prepared by the present invention is detected, and the results are shown in Figure 4 and Figure 5 . The sintered sheet of the Ti-O electron compound of the present invention is crushed and ball-milled to reach a powder with a particle size of 500 nm ( Figure 4 ), and the measured neutron diffraction spectrum is consistent with the theoretical calculation ( Figure 5 ). The above detection results prove the reliability of the process of the present invention and the purity of the synthesized Ti-O electron compound. In particular, the diffraction peaks of the oxygen layer crystal plane are complete, which indicates that an order-disorder phase transition occurs during the cooling process of the Ti-O electron compound sintered body, making the disordered oxygen atoms arranged in an orderly manner.

[0074] Figure 6 It is the detection diagram of Ti x O@S(x = 2, 3, 6) with sulfur-coated on the powder surface, Figure 7 It is the schematic diagram for electrode preparation, Figure 8 It is the schematic diagram for the assembly of the button battery device.

[0075] After cutting the electrode sheet into an appropriately sized electrode sheet, it is assembled in the order of Figure 8 . It is assembled in the order of negative electrode cap - lithium sheet - separator - drop electrolyte - positive electrode sheet - gasket - elastic sheet - positive electrode cap. The obtained button battery is subjected to electrochemical testing to evaluate the catalytic performance, and the results are shown in Figure 9 .

[0076] As shown in Figure 9As shown, the prepared Ti3O@S sulfur cathode can still maintain a high theoretical specific capacity of 500 mAh / g under a rate condition of 4C (1C = 1675 mAh / g). There is no over-polarization phenomenon in its discharge curve, which is due to the acceleration of the polysulfide decomposition reaction. The Ti2O@S cathode can achieve a relatively high specific capacity (800 - 1100 mAh / g) at a low rate (0.1C), but the capacity fades relatively quickly. The charge-discharge capacity at a higher rate (2C) is significantly lower than that of Ti3O@S. The theoretical specific capacity of Ti2O@S at 4C has dropped sharply. Ti6O@S has a relatively low specific capacity at low rates, and although it is better than Ti2O@S at a high rate of 4C, it is much lower than Ti3O@S. The above results confirm the catalytic performance of Ti-O electron compounds for the polysulfide decomposition reaction and their application prospects in lithium-sulfur batteries.

[0077] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a Ti-O electronic compound, characterized in that It includes the following steps: (1) Mix Ti powder and TiO2 powder evenly according to the stoichiometric ratio of Ti and TiO2; (2) Under the condition of 150 - 250 MPa, press the mixed powder obtained in step (1) to obtain a sintered body; (3) Wrap the sintered body with Ti powder, then heat it to 1000 - 1300 °C at a rate of 2 - 5 °C / min for sintering. After sintering, cool it to 400 - 500 °C at a rate of 2 - 5 °C / min, and then cool it naturally to obtain a Ti - O electron compound.

2. The preparation method according to claim 1, characterized in that, In step (1), the amounts of Ti and TiO2 are based on the stoichiometric ratio of Ti and O in the Ti - O electron compound, and the stoichiometric ratio is 3 - 11:

1.

3. The preparation method according to claim 2, characterized in that, In step (1), the stoichiometric ratio of Ti and TiO2 is 3:1, 5:1 or 11:

1.

4. The preparation method according to claim 1 or 2, characterized in that, In step (1), the particle size of the Ti powder is 40 - 50 μm, and the particle size of the TiO2 powder is 5 - 10 nm.

5. The preparation method according to claim 1, characterized in that, In step (3), the particle size of the Ti powder is 40 - 50 μm, and its wrapping thickness is not less than 1 mm.

6. The preparation method according to claim 1, wherein In step (3), the sintering temperature is 1250 °C, the heating rate is 5 °C / min, and after cooling to 500 °C, it is cooled naturally, and the cooling rate is 5 °C / min.

7. A Ti-O electronic compound, characterized in that, Prepared by the method described in any one of claims 1 - 6; the Ti - O electron compound is a Ti2O, Ti3O or Ti6O electron compound.

8. A preparation method of a sulfur-lithium battery electrode material, characterized in that, It includes the following steps: (1) Grind and then crush the Ti-O electronic compound according to claim 7, and then mix it with sulfur powder in a mass ratio of 1:2 to 4, and then heat it at 150 to 200 °C for 10 to 15 h to obtain Ti x O@S powder; (2) Use Ti x O@S powder to prepare the electrode slurry, and then coat it on the surface of the current collector. After drying, the electrode material of the Ti-O electronic compound-based lithium-sulfur battery is obtained.

9. The preparation method according to claim 8, wherein Step (1) Ti x In the TiOS powder, the value of x is 2, 3 or 6.

10. Use of the sulfur - lithium battery electrode material prepared by the method described in claim 8 or 9 in the preparation of a lithium battery.

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