CN115832617A - Intercalation composite film, preparation method thereof and lithium-sulfur battery - Google Patents

Abstract

The invention discloses an intercalation composite film, a preparation method thereof and a lithium-sulfur battery. The intercalation composite film can be applied to a lithium-sulfur battery, can be particularly clamped between a positive plate and a diaphragm of the lithium-sulfur battery, can adsorb polysulfide dissolved in electrolyte in the battery charging process, inhibits the shuttle effect of the lithium-sulfur battery, can provide good conductivity when the conductive base layer is used as a support body, can utilize the adsorbed polysulfide, and improves the utilization rate of active substances, thereby improving the performance of the lithium-sulfur battery.

Description

A kind of intercalation composite thin film and its preparation method and lithium-sulfur battery

technical field

The invention relates to the technical field of batteries, in particular to an intercalation composite thin film, a preparation method thereof and a lithium-sulfur battery.

Background technique

Lithium-sulfur batteries have extremely high theoretical specific capacity (1675mAh/g) and theoretical energy density (2600Wh kg ^-1 ), and are low in cost and environmentally friendly. Therefore, they have attracted extensive attention and research from the scientific and industrial circles. A lithium-sulfur battery is a secondary battery system in which lithium is used as a negative electrode and sulfur or a sulfur-based composite is used as a positive electrode. During the discharge process of the battery, the positive electrode sulfur-based material will form a variety of chain polysulfides during the redox reaction process. These polysulfides are soluble in the electrolyte and will pass through the electrolyte through the medium due to the concentration difference. The separator diffuses and migrates to the anode side, where it is reduced to insulating, insoluble Li ₂ S ₂ and Li ₂ S and covers the surface of the anode, causing the “shuttle effect”. This part of the substance cannot make the system obtain current, so it will reduce the utilization rate of the active material negative electrode lithium and positive electrode sulfur, thereby affecting the performance of the battery. In this regard, it is urgent to seek a solution to solve the above problems.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the present invention proposes an intercalation composite thin film, a preparation method thereof, and a lithium-sulfur battery.

According to the first aspect of the present invention, an intercalation composite film is proposed, which includes a conductive base layer, and zinc oxide is loaded inside and on the surface of the conductive base layer.

According to the embodiment of the present invention, the intercalation composite film has at least the following beneficial effects: the intercalation composite film includes a conductive base layer and zinc oxide supported inside and on the surface of the conductive base layer, and the intercalation composite film can be applied to lithium-sulfur batteries, specifically Sandwiched between the positive electrode sheet and the diaphragm of the lithium-sulfur battery, during the charging process of the battery, zinc oxide can adsorb polysulfides dissolved in the electrolyte, reducing or even avoiding the diffusion and migration of dissolved polysulfides to the negative electrode side to cause side reactions Insulating and insoluble Li ₂ S ₂ and Li ₂ S are generated to cover the surface of the negative electrode, thereby inhibiting the "shuttle effect" of lithium-sulfur batteries; moreover, the conductive base layer can be used as a support and can provide good conductivity, which can The adsorbed polysulfides are utilized to increase the utilization rate of active materials, thereby improving the performance of lithium-sulfur batteries, including improving electrochemical reversibility, rate cycle performance and cycle stability, and reducing capacity fading.

The conductive base layer has a pore structure, wherein the pores can be the interlayer pores of the conductive base layer with a layered structure, or the internal pores of other conductive base layers with a pore structure; zinc oxide is specifically loaded in the internal pores and on the surface of the conductive base layer. In some embodiments of the present invention, the conductive base layer is selected from at least one of graphite paper, carbon fiber paper, and carbon cloth. Preferably, the conductive base layer is selected from graphite paper, which has a layered structure, and zinc oxide is loaded on the interlayer (ie, between the graphite sheets) and the surface of the graphite paper.

In some embodiments of the present invention, the zinc oxide is nano zinc oxide. Preferably, the nano-zinc oxide is a flower cluster-shaped zinc oxide nano-material, and the nano-zinc oxide in this form has a larger specific surface area, thereby improving the adsorption efficiency of polysulfides. For the conductive base graphite paper with a layered structure, a zinc oxide layer can be formed between the graphite sheets and on the surface of the nano-zinc oxide-loaded graphite paper, and its thickness can be controlled at 200-500nm.

In some embodiments of the present invention, the thickness of the intercalation composite film is 15-30 μm; generally about 20 μm.

In a second aspect of the present invention, a method for preparing any intercalation composite film proposed in the first aspect of the present invention is proposed, comprising the following steps:

S1. Using the conductive base as the working electrode, cooperate with the first pair of electrodes to perform electrolysis in the first electrolyte;

S2. Electrochemically deposit metal zinc on the inside and surface of the obtained conductive base layer in step S1;

S3. Calcining the film material obtained in step S2 to convert the metal zinc into zinc oxide to prepare an intercalation composite film.

According to the preparation method of the intercalation composite film in the embodiment of the present invention, it has at least the following beneficial effects: the preparation method first conducts electrolysis on the conductive base layer to make its structure open (if it is a conductive base layer with a layered structure, it can be opened by electrolysis) sheet) to provide more sites for the attachment of zinc oxide, which is conducive to the uniform deposition of zinc ions; then through electrochemical deposition, metal zinc is uniformly deposited on the inside and surface of the conductive base layer after electrolysis, and then the metal zinc is converted into oxide by calcination. Zinc, so as to realize the uniform and stable loading of zinc oxide on the surface and inside of the conductive base layer, and the obtained zinc oxide is in a neatly arranged flower cluster structure with a large specific surface area; the above process is simple, convenient for production operation, and suitable for large-scale production; and Through the above method, the resulting product intercalation composite film can maintain the complete structure of the conductive base layer (such as the complete layered structure of graphite paper), so that the film has an independent self-supporting structure; the intercalation composite film can be applied to lithium-sulfur batteries, Specifically, it can be sandwiched between the positive electrode sheet and the separator. During the discharge process of the battery, the zinc oxide on the intercalation composite film can effectively absorb dissolved polysulfides, thereby inhibiting the "shuttle effect" of lithium-sulfur batteries; and, conductive While serving as a support, the base layer can provide good electrical conductivity, utilize the adsorbed polysulfides, improve the utilization rate of active materials, and improve the performance of lithium-sulfur batteries.

In some embodiments of the present invention, in step S1, the first electrolyte solution is selected from at least one of sulfuric acid solution, hydrochloric acid solution, and nitric acid solution. The thickness of the conductive base layer can be controlled at 10-20 μm, generally about 18 μm; the first pair of electrodes can be platinum electrodes. After electrolysis, further cleaning treatment can be carried out. Specifically, deionized water can be used to rinse the conductive base layer.

In some embodiments of the present invention, in step S2, the zinc salt solution is used as the second electrolyte, the conductive base layer is used as the second working electrode, and the electrochemical deposition is carried out in cooperation with the second pair of electrodes. Nanoscale materials can be prepared by electrochemical deposition, and the operation is simple, low cost, and high efficiency; and the uniform loading of metal zinc can be realized, and the surface of the conductive base layer can be kept complete and smooth. Wherein, the second pair of electrodes can be platinum electrodes. Specifically, a nano zinc oxide layer with a thickness of about 200-500 nm can be prepared by electrochemical deposition. If graphite paper is used as the conductive base layer, the thickness can be increased by 2-4 μm after electrolysis and electrochemical deposition in steps S1 and S2.

In some embodiments of the present invention, the zinc salt solution is selected from at least one of zinc sulfate solution, zinc chloride solution, and zinc nitrate solution.

In some embodiments of the present invention, the calcination is to use an alcohol spray gun to burn the film material in air.

In the third aspect of the present invention, a lithium-sulfur battery is proposed, including a positive electrode sheet, a separator, and a negative electrode sheet sequentially stacked; it also includes any of the above intercalation composite films or a method for preparing any of the above intercalation composite films The prepared intercalation composite film, the intercalation composite film is arranged between the positive electrode sheet and the separator.

Wherein, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer covering the surface of the positive electrode current collector. The material of the positive electrode active material layer may include a sulfur-based positive electrode active material, a conductive agent, and a binder. The sulfur-based positive electrode active material may be It is a sulfur element or a sulfur-based composite material. As a positive electrode active material, sulfur has low conductivity, which will lead to a decrease in the utilization rate of active material sulfur and a decrease in battery cycle performance. The addition of a conductive agent to fully contact the active material can improve the use efficiency of the active material. Specifically, the conductive agent can be conductive carbon black, carbon nanotubes and the like. In addition, the addition of the binder can better combine the active material with the conductive agent, enhance the conductivity, and maintain the stability of the internal structure during battery charging and discharging.

The diaphragm can be one or more composite films of polyethylene, polypropylene, and polyvinylidene fluoride, but not limited thereto, and can also be other diaphragms.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, wherein:

Fig. 1 is the preparation flow diagram of intercalation composite film in embodiment 1;

2 is a schematic diagram of the assembly structure of the lithium-sulfur battery in Example 2;

Fig. 3 is the surface SEM figure of the intercalation composite film that embodiment 1 makes;

Fig. 4 is embodiment 1 step S1 processing gained graphite paper and the contact angle test result diagram of final intercalation composite film and electrolyte;

Fig. 5 is the intercalation composite film adsorption polysulfide test result figure that the made of embodiment 1;

Fig. 6 is the test result graph of the charge-discharge cycle performance of the lithium-sulfur battery of Example 2 and Comparative Examples 1 and 2;

Fig. 7 is a graph showing the cycle performance test results of the lithium-sulfur batteries of Example 2 and Comparative Example 1 at different rates.

Detailed ways

The conception and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments, so as to fully understand the purpose, features and effects of the present invention. Apparently, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts belong to The protection scope of the present invention.

Example 1

The present embodiment has prepared a kind of intercalation composite film, as shown in Figure 1, and its preparation method is specifically as follows:

S1. Configure 0.1mol/L H ₂ SO ₄ solution, and then extract 30mL of the H ₂ SO ₄ solution and place it in a 50mL electrolytic tank A as the electrolyte; one end of the electrode clamps a 1cm×2cm graphite paper as the working electrode , and the other end uses a platinum electrode with the same area as the counter electrode; immerse the graphite paper of the working electrode and the platinum electrode of the counter electrode in the electrolyte in the electrolytic cylinder A, apply a 5V direct current for electrolysis, and electrolyze the front and back sides of the graphite paper for 40s Then rinse the electrolyzed graphite paper three times with deionized water, soak it in deionized water and save it for subsequent use;

S2, configure the _ZnSO4 solution of 0.1mol/L, then extract 30mL of this _ZnSO4 solution and place it in the electrolytic tank B of 50mL as the electrolyte; one end electrode clamps the graphite paper obtained by step S1 electrolysis, as the working electrode, and the other end with Platinum electrodes with the same area and size were used as counter electrodes; both the graphite paper for the working electrode and the platinum electrode for the counter electrode were immersed in the electrolyte in the electrolytic tank B, and a 5V direct current was applied for electrochemical deposition, and the front and back sides of the graphite paper were deposited for 1 min each; Neatly arranged clusters of metallic zinc were deposited on the graphite paper, washed three times with deionized water, and then soaked in deionized water for 10 minutes to remove excess miscellaneous ions, such as free zinc ions and sulfate ions.

S3. Put the graphite paper deposited with the elemental zinc metal obtained in step S2 in a crucible, and burn it in the air with an alcohol spray gun for 30 seconds, so that the elemental zinc metal is converted into zinc oxide, and an intercalation composite film is obtained.

Example 2

In this embodiment, a lithium-sulfur battery is prepared, and its preparation method is as follows:

S1, the preparation of positive plate, including:

(1) Weigh 150mg of battery-grade polyvinylidene fluoride (PVDF) powder into a vial, then add 9.5mL of N-methyl-2-pyrrolidone (NMP) with a 10mL syringe as a solvent, add a stir bar, and stir at room temperature for 4h Fully dissolved, set aside for later use;

(2) Weigh 700mg of positive electrode material elemental sulfur and 200mg of conductive agent Super-P, and then draw 7mL of PVDF solution with NMP as solvent from the vial with a syringe, and add them to the ball mill tank together, with the ball to material ratio of 50:1, Ball mill at a speed of 1032r/min for 3 hours, then collect the ball-milled positive electrode slurry and seal it;

(3) Take a 20×20cm glass plate, drop 0.5mL of alcohol, put the aluminum foil on the glass plate, then drop about 0.5mL of alcohol on the aluminum foil, wipe the aluminum foil until it is flat with paper; About 2mL of the positive electrode slurry prepared above is evenly coated on the aluminum foil; dried on a hot table at 60°C for 12 hours, and then pressed into tablets with a roller press at a compression ratio of 1:1.5; The slicer slices the obtained positive electrode sheet, and after weighing, select the positive electrode disc with an active material mass of about 1.1-1.2 mg/cm ² as the positive electrode sheet, and collect it in an argon glove box for later use. Among them, the mass of the active material is obtained by the following method: weigh and record the mass of the cut positive electrode sheet as m1, then cut the copper foil of the same size and weigh and record the mass of m2, the mass of the active material is equal to (m1-m2)*activity Material proportion;

S2, using a lithium sheet as the negative electrode, the diaphragm adopts a PP diaphragm, and the electrolyte adopts 1,3-dioxolane containing 1M lithium bistrifluoromethanesulfonimide (LiTFSI) and 0.2M lithium nitrate (LiNO ₃ ) (DOL) and ethylene glycol dimethyl ether (DME) (1:1, v/v) mixed solvent, and the intercalation composite film that adopts embodiment 1 to cooperate group to assemble button battery, specifically as shown in Figure 2, Put the lithium sheet 12 in the positive electrode shell 11, add an appropriate amount of electrolyte, put in the separator 13, the intercalation composite film 14 in turn, add the electrolyte dropwise, then place the positive electrode sheet 15, the gasket 16, and the shrapnel 17, and then use the negative electrode The shell 18 is compressed and assembled to form a button battery, which is the product lithium-sulfur battery.

Comparative example 1

This comparative example prepared a lithium-sulfur battery. The difference between this comparative example and Example 2 is that in this comparative example, the setting of the intercalation composite film is canceled between the separator and the positive electrode sheet in step S2, and other operations are the same as in Example 2. same.

Comparative example 2

This comparative example prepared a lithium-sulfur battery, the difference between this comparative example and Example 2 is: this comparative example cancels the setting of the intercalation composite film between the diaphragm and the positive electrode sheet in step S2; and, in the PP diaphragm One side of the surface is provided with a graphite zinc oxide coating, and the PP diaphragm provided with a graphite zinc oxide coating is used as a diaphragm, and the side of the diaphragm provided with a graphite zinc oxide coating faces the positive electrode during the battery assembly process; other operations Same as Example 2.

The preparation of the above diaphragm in this comparative example includes: mixing graphite paper and zinc oxide and placing it in a mortar for grinding, then mixing with binder and solvent to form a slurry, wherein the quality of binder, graphite paper and zinc oxide The ratio is 1:8:1, and then coated on the surface of the PP diaphragm, the coating thickness is about 20μm, and then dried to form a graphite tin oxide coating on the surface of the PP diaphragm.

Performance Testing

A scanning electron microscope (SEM) was used to observe the surface of the intercalation composite film prepared in Example 1, as shown in FIG. 3 . It can be seen from FIG. 3 that the zinc oxide layer on the surface of the intercalation composite film prepared by the preparation method in Example 1 has a neatly arranged flower cluster structure.

Take the graphite paper obtained from step S1 in Example 1 and the final intercalation composite film, add a drop of lithium-sulfur electrolyte on the surfaces of both, and then test the contact between the electrolyte and the electrolytic graphite paper and the intercalation composite film. angle, and the results are shown in Figure 4. Among Fig. 4 (a) is the test result of the contact angle of the electrolyte and graphite paper after electrolysis, and the contact angle is 34.6 °; (B) is the test result of the contact angle of the electrolyte and the intercalated composite film, and the contact angle is 23.1 °, It can be seen that the contact angle between the electrolyte and the intercalation composite film is smaller than the contact angle with the graphite paper after electrolysis, which further indicates that lithium ions can pass through more quickly, which is more conducive to the electrochemical reaction.

In order to investigate the adsorption properties of the intercalation composite film prepared by the present application to polysulfides, the intercalation composite film prepared in Example 1 was placed in a pale yellow polysulfide solution (by the molar ratio of 1:1 elemental Sulfur and lithium sulfide were prepared by reacting 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (1:1, v/v) in a solvent, and observed after standing for 1h The result is shown in Figure 5. Figure 5 (a) is the sample before adding the intercalation composite film to the polysulfide solution; (b) is the sample after adding the intercalation composite film to the polysulfide solution and standing for 1 h. The test results showed that the color of the polysulfide solution changed from initial light yellow to clear and transparent after adding the intercalation composite film, because the zinc oxide in the intercalation composite film adsorbed the polysulfide dissolved in the electrolyte.

In addition, at a rate of 0.2C, the voltage window was set to 0-2.8V, and the charge-discharge cycle performance of the lithium-sulfur batteries prepared in Example 2 and Comparative Examples 1-2 were tested, and the results are shown in FIG. 6 . It can be seen from Figure 6 that after 350 cycles of charging and discharging at a rate of 0.2C, the lithium-sulfur battery of Comparative Example 1 does not have an intercalation composite film between the PP separator and the positive electrode sheet, and its capacity is only 762.0mAh/g; Example 2 The intercalation composite film of Example 1 is sandwiched between the PP separator and the positive electrode sheet of the lithium-sulfur battery, and the capacity of the battery is still 1100.2mAh/g after 350 cycles of charging and discharging at a rate of 0.2C, and the capacity decay is significantly reduced; Comparative Example 2 The lithium-sulfur battery is equipped with a graphite zinc oxide coating on the side of the PP separator facing the positive electrode sheet. The capacity of the battery after 350 cycles of charging and discharging at a rate of 0.2C is 877.0mAh/g, which is higher than that of Comparative Example 1, but still significantly lower than that of Example 2. From the above, the lithium-sulfur battery of Example 2 interposes the intercalation composite film of Example 1 between the PP separator and the positive electrode sheet, wherein zinc oxide is loaded on the interlayer and surface of the graphite paper, and zinc oxide can absorb sulfur-based positive electrode active materials in the The oxidation-reduction process generates and dissolves polysulfides in the electrolyte, and the adsorbed polysulfides can be utilized through the good conductivity of graphite paper, thereby improving the utilization rate of active materials, improving the cycle performance of the battery, and reducing the capacity decay.

In addition, the rate cycle performance of the lithium-sulfur battery of Example 2 and Comparative Example 1 was tested at current densities of 0.2C, 0.5C, 1C, 1.5C, and 2C, and the results are shown in FIG. 7 . As shown in Figure 7, the initial discharge specific capacity of the lithium-sulfur battery of Comparative Example 1 at a current density of 0.2C was 1110.6mAh/g, and the capacity decreased significantly after 5 cycles; when the current density increased to 0.5C, 1.0C, and 1.5C And at 2.0C, the discharge capacities are 864.3mAh/g, 647.7mAh/g, 519.2mAh/g and 438.9mAh/g, respectively. However, the reversible specific capacities of the lithium-sulfur battery in Example 2 are 1238.1mAh/g, 1027.9mAh/g, 914.6mAh/g, 836.9mAh/g, and 745.1mAh at 0.2C, 0.5C, 1C, 1.5C, and 2C rates, respectively. /g. It can be seen from the comparison that the lithium-sulfur battery of Comparative Example 1 does not have an intercalation composite film between the PP separator and the positive electrode sheet, and the rate performance of the battery is significantly worse than that of the lithium-sulfur battery of Example 2, which can explain the electrochemical reaction of the electrode at a higher current density. The kinetic process is slow, and lithium polysulfide shuttling during the test process leads to serious loss of active materials, so its reversible specific capacity is low at a large current density.

The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims (10)

1. The intercalated composite film is characterized by comprising a conductive base layer, wherein zinc oxide is loaded in the conductive base layer and on the surface of the conductive base layer.

2. The intercalated composite film as claimed in claim 1, wherein the conductive substrate layer is selected from at least one of graphite paper, carbon fiber paper and carbon cloth.

3. The intercalated composite film of claim 1 wherein said zinc oxide is nano zinc oxide.

4. The intercalated composite film as claimed in any one of claims 1 to 3 wherein the thickness of the intercalated composite film is 15 to 30 μm.

5. The process for preparing an intercalated composite film according to any one of claims 1 to 4, comprising the steps of:

s1, taking a conductive base layer as a working electrode, and matching the conductive base layer and a first counter electrode in a first electrolyte for electrolysis;

s2, electrochemically depositing metal zinc in the conductive base layer obtained by the step S1 and on the surface of the conductive base layer;

and S3, calcining the membrane material obtained by the treatment in the step S2 to convert the metal zinc into zinc oxide, thereby preparing the intercalation composite membrane.

6. The method of claim 5, wherein in step S1, the first electrolyte is at least one selected from a sulfuric acid solution, a hydrochloric acid solution, and a nitric acid solution.

7. The method for preparing an intercalated composite film according to claim 5, wherein in step S2, a zinc salt solution is used as a second electrolyte, the conductive base layer is used as a second working electrode, and the conductive base layer is matched with a second counter electrode for electrochemical deposition.

8. The method for preparing the intercalated composite film according to claim 7, wherein the zinc salt solution is at least one selected from the group consisting of zinc sulfate solution, zinc chloride solution and zinc nitrate solution.

9. The method of claim 5, wherein in step S3, the calcining is performed by burning the film material in air with an alcohol spray gun.

10. A lithium-sulfur battery comprising a positive electrode sheet, a separator and a negative electrode sheet, which are stacked, characterized by further comprising the intercalation composite film according to any one of claims 1 to 4 or the intercalation composite film produced by the method according to any one of claims 5 to 9, the intercalation composite film being sandwiched between the positive electrode sheet and the separator.

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