Solid-state electrolyte and preparation method thereof, and solid-state battery

Abstract

The application discloses a solid-state electrolyte and a preparation method thereof and a solid-state battery. The solid-state electrolyte comprises a gel and a first fiber fabric; the gel coats the first fiber fabric and fills pores of the first fiber fabric; the first fiber fabric comprises first fibers interwoven together, and formation materials of the gel comprise an electrolyte and second fibers dissolved in the electrolyte; wherein the first fibers comprise polyvinylidene fluoride fibers, and the second fibers comprise polypropylene carbonate fibers. The application can improve the ion transmission capacity of the solid-state electrolyte under a liquid-poor condition, and has high safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage and power battery, and particularly relates to a solid-state electrolyte, a preparation method thereof and a solid-state battery. BACKGROUND

[0002] The solid-state battery adopts a solid-state electrolyte. The polymer electrolyte in the solid-state electrolyte has the advantages of good interface contact and strong processability, but has poor ion transmission capacity and low ionic conductivity. The gel electrolyte obtained by absorbing electrolyte in the polymer electrolyte has the safety of the solid-state electrolyte and the high ionic conductivity of the liquid electrolyte. However, the electrolyte content in the gel electrolyte is usually more than 50% of the mass of the polymer matrix, and the high electrolyte content brings safety hazards, and the gel electrolyte itself has poor mechanical strength and is difficult to resist lithium dendrite growth. Reducing the electrolyte content in the gel electrolyte will limit the ion transmission efficiency. Therefore, there is an urgent need for a technology for improving the ion transmission capacity of the gel electrolyte under the condition of low electrolyte content. SUMMARY

[0003] The present application discloses a solid-state electrolyte, a preparation method thereof and a solid-state battery, which can improve the ion transmission capacity of the solid-state electrolyte under the condition of low electrolyte content and has high safety.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0005] In a first aspect, the present application provides a solid-state electrolyte, comprising a gel and a first fiber fabric;

[0006] The gel coats the first fiber fabric and fills the pores of the first fiber fabric.

[0007] The first fiber fabric comprises first fibers interwoven, and the forming material of the gel comprises electrolyte and second fibers dissolved in the electrolyte; wherein the first fibers comprise polyvinylidene fluoride fibers, and the second fibers comprise polypropylene carbonate fibers.

[0008] The solid-state electrolyte includes a gel and a first fiber fabric, the gel coats the first fiber fabric and fills the pores of the first fiber fabric. The first fiber fabric includes first fibers interwoven, and the gel is formed by electrolyte and second fibers dissolved in the electrolyte. The first fibers include polyvinylidene fluoride fibers, and the second fibers include polypropylene carbonate fibers. In the present application, the first fibers serve as rigid skeleton supports, and the second fibers, after being dissolved in the electrolyte, coat the surface of each first fiber to form a gel-state ion transport network, creating conditions for electronic conduction and improving ion transport capacity. At the same time, the structure of the gel coating the first fiber fabric of the solid-state electrolyte in the present application can make the distribution of the second fibers more uniform, which is conducive to reducing the use amount of electrolyte and realizing the liquid-lean of the solid-state electrolyte and ensuring the safety during use.

[0009] In some embodiments, in the solid-state electrolyte, the mass of the electrolyte accounts for 5%-10% of the sum of the mass of the first fibers and the second fibers.

[0010] In some embodiments, the solid-state electrolyte further includes fluorinated boron nitride, and the fluorinated boron nitride is dispersed in the gel.

[0011] In some embodiments, the mass of the fluorinated boron nitride accounts for 10%-60% of the mass of the second fibers.

[0012] In some embodiments, the electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive.

[0013] In some embodiments, the non-aqueous organic solvent includes a cyclic carbonate and a linear carbonate.

[0014] In a second aspect, the present application provides a preparation method of a solid-state electrolyte, including:

[0015] providing a second fiber fabric including first fibers and second fibers interwoven; wherein the first fibers include polyvinylidene fluoride fibers, and the second fibers include polypropylene carbonate fibers;

[0016] dropping electrolyte onto the second fiber fabric, the second fibers being dissolved in the electrolyte and forming a gel coating the first fibers, to obtain the solid-state electrolyte.

[0017] In some embodiments, the providing a second fiber fabric including first fibers and second fibers interwoven further includes:

[0018] adopting an electrospinning process to prepare the second fiber fabric from a first electrospinning solution and a second electrospinning solution; wherein the first electrospinning solution includes a polyvinylidene fluoride solution, and the second electrospinning solution includes a polypropylene carbonate solution.

[0019] In some embodiments, the second electrospinning solution further comprises a fluorinated boron nitride solution, when the electrolyte is dropped to the second fiber fabric, the fluorinated boron nitride is dispersed in the gel.

[0020] In a third aspect, the present application provides a solid-state battery, comprising a positive electrode active material, a negative electrode active material and the solid-state electrolyte according to the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A structural schematic diagram of a solid-state electrolyte provided by an embodiment of the present application is shown in the figure;

[0022] Figure 2 A structural schematic diagram of another solid-state electrolyte provided by an embodiment of the present application is shown in the figure;

[0023] Figure 3 A flowchart of a preparation method of a solid-state electrolyte provided by an embodiment of the present application is shown in the figure;

[0024] Figure 4 A structural schematic diagram of a second fiber fabric provided by an embodiment of the present application is shown in the figure;

[0025] Figure 5 A structural schematic diagram of another second fiber fabric provided by an embodiment of the present application is shown in the figure;

[0026] Figure 6 A structural schematic diagram of another second fiber fabric provided by an embodiment of the present application is shown in the figure;

[0027] Figure 7 A structural schematic diagram of another second fiber fabric provided by an embodiment of the present application is shown in the figure;

[0028] Figure 8 A structural schematic diagram of another second fiber fabric provided by an embodiment of the present application is shown in the figure;

[0029] Figure 9 A structural schematic diagram of another second fiber fabric provided by an embodiment of the present application is shown in the figure;

[0030] Figure 10 A flowchart of a preparation method of a second fiber fabric provided by an embodiment of the present application is shown in the figure;

[0031] Figure 11 A structural schematic diagram of a solid-state battery provided by an embodiment of the present application is shown in the figure;

[0032] Figure 12 A preparation process diagram of a solid-state battery provided by an embodiment of the present application is shown in the figure;

[0033] Icon: 1, gel; 11, second fiber; 2, first fiber fabric; 21, first fiber; 3, fluorinated boron nitride; 4, battery cell. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application. In the description of the embodiments of the present application, unless otherwise specified, " / " represents the meaning of or, for example, A / B can represent A or B; the "and / or" in the text only describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0035] Among them, the terms "first", "second" are only for description purpose, and cannot be understood as implying or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the embodiments of the present application, unless otherwise specified, the meaning of "multiple" is two or more than two.

[0036] In a first aspect, as Figures 1-2 The embodiments of the present application provide a solid-state electrolyte, which includes a gel 1 and a first fiber fabric 2.

[0037] The gel 1 covers the first fiber fabric 2 and fills the pores of the first fiber fabric 2.

[0038] The first fiber fabric 2 includes first fibers 21 interwoven, and the forming material of the gel 1 includes an electrolyte and a second fiber dissolved in the electrolyte; wherein the first fiber 21 includes a polyvinylidene fluoride fiber, and the second fiber includes a polypropylene carbonate fiber.

[0039] The solid-state electrolyte includes the gel 1 and the first fiber fabric 2, the gel 1 covers the first fiber fabric 2 and fills the pores of the first fiber fabric 2. The first fiber fabric 2 includes the first fibers 21 interwoven, and the forming material of the gel 1 includes an electrolyte and second fibers dissolved in the electrolyte. The first fibers 21 include polyvinylidene fluoride fibers, and the second fibers include polypropylene carbonate fibers. In the present application, the first fibers 21 serve as rigid skeleton supports, and the second fibers, after being dissolved in the electrolyte, cover the surface of each first fiber 21 to form a gel-state ion transport network, create conditions for electronic conduction, and improve ion transport capacity. Meanwhile, the structure in which the gel 1 of the solid-state electrolyte covers the first fiber fabric 2 in the embodiments of the present application can make the distribution of the second fibers more uniform, which is conducive to reducing the use amount of the electrolyte and realizing the liquid-lean of the solid-state electrolyte and ensuring the safety during use.

[0040] In some embodiments, the mass of the electrolyte in the solid-state electrolyte accounts for 5%-10% of the sum of the mass of the first fibers 21 and the second fibers, for example, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc., and the specific mass ratio is not limited.

[0041] The embodiments of the present application can realize the liquid absorption and dissolution of the second fibers and the surface coating of the first fibers 21 by using a small amount of electrolyte, which greatly reduces the content of the electrolyte in the solid-state electrolyte, is conducive to improving the ion transport efficiency, improving the use safety, and greatly reducing the safety hazard.

[0042] In some embodiments, the solid-state electrolyte further includes fluorinated boron nitride (F-BN) 3, and the fluorinated boron nitride 3 is dispersed in the gel.

[0043] In one possible implementation manner, as shown in Figure 2 The fluorinated boron nitride 3 is uniformly dispersed in the gel 1 as a filler, and since the gel 1 covers the surface of each first fiber 21, the fluorinated boron nitride 3 also forms a coating on each first fiber 21, realizing the uniform distribution of the fluorinated boron nitride 3.

[0044] When the solid-state electrolyte of the embodiment of the present application is applied to a lithium ion battery, the fluorine groups in fluorinated boron nitride 3 and N in BN both participate in the film formation on the surface of the electrode of the battery cell, generating inorganic components containing LiF / Li3N, stabilizing the electrode interface, and being conducive to improving the cycle stability of the battery cell. At the same time, fluorinated boron nitride 3 has the characteristics of high thermal conductivity and high Young's modulus, which is conducive to the uniform dispersion of heat in the solid-state electrolyte, thereby inhibiting the growth of lithium dendrites in the local temperature hotspot area. Since fluorinated boron nitride 3 participates in the electrode interface reaction, its product is also conducive to efficient and uniform ion transmission, further ensuring that the battery has good electrochemical performance. The structure of the gel 1 of the solid-state electrolyte of the embodiment of the present application coating the first fiber fabric 2, and the synergistic effect of the fluorinated boron nitride 3 filler, can realize the liquid-lean of the solid-state electrolyte, and after being applied to the battery, it can realize the high safety and high performance operation of the battery.

[0045] In some embodiments, the mass of fluorinated boron nitride 3 accounts for 10%-60% of the mass of the second fiber, for example, 10%, 12%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc., and the specific mass ratio is not limited.

[0046] According to the actual application situation, the mass ratio of fluorinated boron nitride 3 is reasonably adjusted, so that fluorinated boron nitride 3 is uniformly dispersed in the gel of the solid-state electrolyte, which can effectively inhibit the growth of lithium dendrites in the lithium ion battery and facilitate efficient and uniform ion transmission.

[0047] In some embodiments, the electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes fluoroethylene carbonate (FEC), propylene sulfite (PS), propylene sulfite (PST), vinyl sulfate (DTD), etc.

[0048] In some embodiments, the non-aqueous organic solvent includes a cyclic carbonate and a linear carbonate. The embodiment of the present application utilizes the principle of similar compatibility of polypropylene carbonate (PPC) with ester electrolyte. After the electrolyte is added, polypropylene carbonate (PPC) is dispersed into a gel state, and together with fluorinated boron nitride (F-BN), it is coated on the surface of the interwoven framework formed by polyvinylidene fluoride (PVDF) fibers to form a continuous ion transmission network for ion transport.

[0049] In a second aspect, as shown in Figure 3 The preparation method of the solid-state electrolyte provided by the embodiment of the present application specifically includes the following steps:

[0050] S301, providing a second fiber fabric, the second fiber fabric including interwoven first fibers and second fibers; wherein the first fibers include polyvinylidene fluoride fibers, and the second fibers include polypropylene carbonate fibers;

[0051] S302, drop the electrolyte on the second fiber fabric, the second fiber dissolves in the electrolyte and forms a gel covering the first fiber, to obtain a solid electrolyte.

[0052] In the above S301, the interlacing form of the first fiber and the second fiber in the second fiber fabric can be various. For example, as shown in Figure 4 , a first fiber 21 and a second fiber 11 are first arranged side by side to form a mixed fiber, and then a plurality of fibers are interlaced horizontally and vertically to form a second fiber fabric.

[0053] For another example, as shown in Figure 5 , a first fiber 21 and two second fibers 11 are first arranged side by side to form a mixed fiber, and the two second fibers 11 are located on both sides of the first fiber, and then a plurality of fibers are interlaced horizontally and vertically to form a second fiber fabric.

[0054] For another example, as shown in Figure 6 , two first fibers 21 and a second fiber 11 are first arranged side by side to form a mixed fiber, and the two first fibers 21 are located on both sides of the second fiber 11, and then a plurality of fibers are interlaced horizontally and vertically to form a second fiber fabric.

[0055] For another example, as shown in Figure 7 , two first fibers 21 and two second fibers 11 are first arranged side by side to form a mixed fiber, and the first fiber 21 and the second fiber 11 are arranged alternately, and then a plurality of fibers are interlaced horizontally and vertically to form a second fiber fabric. Of course, a mixed fiber can also include a plurality of first fibers 21 and a plurality of second fibers 11 arranged alternately.

[0056] For another example, as shown in Figure 8 , a first fiber 21 and a second fiber 11 are directly interlaced horizontally and vertically to form a second fiber fabric, and the first fiber 21 is horizontal and the second fiber 11 is vertical. As shown in Figure 9 , a first fiber 21 and a second fiber 11 are directly interlaced horizontally and vertically to form a second fiber fabric, and the first fiber 21 and the second fiber 11 both have horizontal and vertical directions, and are arranged alternately.

[0057] It can be understood that the distribution form of the first fiber 21 and the second fiber 11 can be various, which ensures that after the electrolyte is dropped, the gel 1 formed by the second fiber 11 dissolved in the electrolyte can uniformly cover each first fiber as shown in Figure 1 .

[0058] In S302, the electrolyte is dropped onto the second fiber fabric, and the second fiber is dissolved in the electrolyte and forms a gel covering the first fiber. It can be understood that at this time, the fiber fabric is the first fiber fabric (the first fiber is interwoven), and in the completed solid electrolyte, the gel may not completely fill the pores of the first fiber fabric, but the gel covers each first fiber as much as possible to form a continuous ion transport network for ion transport.

[0059] In some embodiments, as shown in Figure 10 A second fiber fabric is provided, and the second fiber fabric includes interwoven first fibers and second fibers, and further includes:

[0060] S1001, using an electrospinning process to prepare the first electrospinning solution and the second electrospinning solution into a second fiber fabric; wherein the first electrospinning solution includes a polyvinylidene fluoride solution, and the second electrospinning solution includes a polypropylene carbonate solution.

[0061] The electrospinning process is used to prepare the second fiber fabric in the embodiments of the present application, which is beneficial to improve the uniformity of the distribution of the dissolved second fiber, improve the ion conductivity, and further reduce the amount of electrolyte used, ensure high performance and high safety,

[0062] In some embodiments, the second electrospinning solution further includes a fluorinated boron nitride solution, and when the electrolyte is dropped onto the second fiber fabric, the fluorinated boron nitride is dispersed in the gel.

[0063] In order to improve the mechanical strength of the solid electrolyte and resist the growth of lithium dendrites, the embodiments of the present application add an appropriate amount of fluorinated boron nitride to the second electrospinning solution, and the fluorinated boron nitride forms the second fiber together with the polypropylene carbonate in the electrospinning process. After the electrolyte is added, the polypropylene carbonate is dispersed into a gel state, and together with the fluorinated boron nitride, it is wrapped around the interwoven skeleton surface formed by the polyvinylidene fluoride fiber to form a continuous ion transport network for ion transport. When the solid electrolyte is applied to a battery, it is beneficial to improve the cycle performance of the battery.

[0064] In a third aspect, the embodiments of the present application provide a solid-state battery, which includes a positive electrode active material, a negative electrode active material, and a solid-state electrolyte as in the first aspect. The positive electrode active material can be lithium iron phosphate, and the negative electrode active material can be lithium metal. As shown in Figure 11 The solid-state battery can include a plurality of battery cells 4.

[0065] In order to make the scheme provided by the embodiments of the present application easier to understand, the following takes the preparation of a lithium ion battery as a specific embodiment to explain the scheme of the present application in detail.

[0066] Embodiment 1

[0067] Embodiment 1 is a preparation process of a lithium ion battery, as shown in Figure 12 The specific steps are as follows:

[0068] (1) Preparation of the second fiber fabric by electrospinning

[0069] F-BN preparation: BN solid was added into HBF4, stirred at 50 °C for 12 h, and F-BN powder was obtained after filtration, deionized water washing, and drying.

[0070] Preparation of the electrospinning solution: 1 g of PVDF powder was dissolved in 10 mL of N,N-dimethylformamide, and the first electrospinning solution was obtained after stirring for 4 h. 1 g of PPC powder was dissolved in 10 mL of acetonitrile, 200-500 mg of F-BN powder was added, and the second electrospinning solution was obtained after stirring for 4 h.

[0071] Preparation of the second fiber fabric: electrospinning was performed using side-by-side needle heads, and the second electrospinning solution (PVDF solution) and the second electrospinning solution (PPC+F-BN electrospinning solution) were injected respectively to prepare a second fiber fabric with a side-by-side structure. After electrospinning, the second fiber fabric was taken off from the roller and placed in a 80 °C air oven for drying for 8 h, and then punched into small discs with a diameter of 16 mm and placed in a glove box for use.

[0072] (2) Preparation of the solid-state electrolyte

[0073] The second fiber fabric disc with a mass of m1 was weighed, and electrolyte with a mass of m2 was added dropwise on the disc, wherein 10% ≥ m2 / m1 ≥ 5%, to obtain a solid-state electrolyte. The solid-state electrolyte was taken out from the glove box and placed in a vacuum oven for drying. Figure 11 As can be seen from the scanning electron microscope picture in FIG. 1, the gel coats the first fiber. The content of the electrolyte in the solid-state electrolyte can be obtained by thermal gravimetric analysis.

[0074] (3) Preparation of the positive electrode

[0075] First, 100 mg of PVDF binder was weighed into a stirring bottle, 1 mL of N-methyl pyrrolidone was added, and stirring was performed at room temperature for 1 h until the PVDF was completely dissolved. Then, 100 mg of conductive carbon black Super P and 1 mL of N-methyl pyrrolidone were added, and stirring was performed at room temperature for 1 h. Then, 800 mg of lithium iron phosphate positive electrode active material and 1.5 mL of N-methyl pyrrolidone were added, and stirring was performed at room temperature for more than 6 h to obtain a positive electrode slurry. Then, the positive electrode slurry was coated on an aluminum foil, dried at 80 °C for more than 6 h, and then cut into a disc with a diameter of 12 mm to obtain a lithium iron phosphate positive electrode, which was placed in a vacuum oven for drying and storage.

[0076] (4) Assembly of the battery

[0077] According to the structure of the lithium metal negative electrode, the solid-state electrolyte, and the lithium iron phosphate positive electrode, a coin cell was assembled. After standing for 2 h, performance testing was performed.

[0078] Examples 2-5, Comparative Examples 1-2

[0079] Examples 2-5 and Comparative Examples 1-2 are lithium ion batteries prepared in the same manner as Example 1, and after preparation, performance tests are performed. The battery cycle rate is 0.5C at 25°C for 200 cycles. The mass ratio of electrolyte and F-BN, and the results of the room temperature ionic conductivity test of the solid electrolyte and the battery cycle performance are shown in Table 1.

[0080] Table 1

[0081]

[0082] As can be seen from Table 1, compared with Examples 2-5 and Comparative Examples 1-2, a reasonable electrolyte ratio can significantly improve the room temperature ionic conductivity of the solid electrolyte, and the cycle capacity retention rate of the lithium ion battery. When m2 / m1 is 7%, m(F-BN) / m(PPC) is 30%, the room temperature ionic conductivity of the solid electrolyte is 7.2 x 10 -4 S / cm, the cycle capacity retention rate of the lithium ion battery is 98.6% at 25°C for 200 cycles, and the comprehensive performance is relatively excellent.

[0083] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application also intends to include these modifications and variations.

Claims

1. A method for preparing a solid electrolyte, characterized in that, include: A second fiber fabric is provided, the second fiber fabric comprising interwoven first fibers and second fibers; wherein the first fibers comprise polyvinylidene fluoride fibers and the second fibers comprise polypropylene carbonate fibers; The electrolyte is dropped onto the second fiber fabric, the second fiber dissolves in the electrolyte and forms a gel that coats the first fiber, thus obtaining the solid electrolyte; The provision of a second fiber fabric, the second fiber fabric comprising interwoven first and second fibers, further includes: The second fiber fabric is prepared by electrospinning a first electrospinning solution and a second electrospinning solution; wherein the second electrospinning solution includes a polypropylene carbonate solution. The second electrospinning solution also includes a boron fluoride nitride solution, which is dispersed in the gel after the electrolyte is dropped onto the second fiber fabric.

2. The method according to claim 1, characterized in that, The first electrospinning solution includes a polyvinylidene fluoride solution.

3. The method according to claim 1, characterized in that, In the solid electrolyte, the mass of the electrolyte accounts for 5%-10% of the sum of the masses of the first fiber and the second fiber.

4. The method according to claim 1, characterized in that, The solid electrolyte further includes boron fluoride nitride, which is dispersed in the gel.

5. The method according to claim 4, characterized in that, The mass of the fluorinated boron nitride accounts for 10%-60% of the mass of the second fiber.

6. The method according to claim 1, characterized in that, The electrolyte includes a non-aqueous organic solvent, lithium salt, and additives.

7. The method according to claim 6, characterized in that, The non-aqueous organic solvents include cyclic carbonates and linear carbonates.

8. A solid electrolyte, characterized in that, The solid electrolyte is prepared by the method for preparing solid electrolyte as described in any one of claims 1 to 7.

9. A solid-state battery, characterized in that, Solid electrolytes include positive electrode active materials, negative electrode active materials, and solid electrolytes prepared by any of the methods described in any one of claims 1 to 7.

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