Gel electrolyte and preparation method and application thereof
By introducing halloysite nanotubes (HNTs) into the gel electrolyte and coating it with polymers, followed by rapid cooling, a honeycomb structure is formed, which solves the mechanical properties and conductivity problems of the gel electrolyte and improves the safety and cycle performance of lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-01-03
- Publication Date
- 2026-03-27
Smart Images
Figure CN115954540B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a kind of gel electrolyte and its preparation method, application. BACKGROUND
[0002] With the maturation of lithium ion battery technology, the application of lithium ion battery has been expanded from daily portable devices to new energy vehicles and energy storage fields. With the continuous expansion of application range, the focus of lithium ion battery research is how to realize the coexistence of high energy density and safety. The existing commercial lithium ion battery uses liquid electrolyte, which contains organic solvents that have potential risks of leakage, evaporation, combustion and explosion. The separator that separates the positive and negative electrodes also has potential risks of thermal shrinkage and being pierced by lithium dendrites, causing battery short circuit. Using solid or gel electrolyte with high mechanical strength to replace liquid electrolyte can effectively inhibit the formation of dendritic lithium and solve the safety risks brought by liquid electrolyte.
[0003] Solid electrolyte has high mechanical strength and can effectively inhibit dendrites, but has large interface resistance and is difficult to process. Gel electrolyte is a form between liquid electrolyte and solid electrolyte, which combines the characteristics of solid and liquid, has high conductivity, wide electrochemical window, good compatibility with electrodes, and can inhibit the formation and growth of lithium dendrites to some extent. Gel polymer electrolyte (GPE) is mainly obtained by confining liquid electrolyte in a polymer matrix. Because it combines the advantages of high ionic conductivity of liquid electrolyte and high safety of solid electrolyte, it has attracted more attention. There are many matrix materials that can be used to prepare GPE in traditional technology, the most commonly used ones are mainly polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN) or poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and the like.
[0004] However, the current gel electrolyte still has defects such as poor mechanical performance, low ionic conductivity and poor gel stability, which brings great trouble to practical application. This problem needs to be solved urgently. SUMMARY
[0005] The technical problem to be solved by the present application is to overcome the defects of poor mechanical performance, low ionic conductivity and poor gel stability of the gel electrolyte in the prior art, and to provide a gel electrolyte and its preparation method and application. The gel electrolyte provided by the present application has a honeycomb structure and has the effects of high stability, excellent mechanical performance and excellent electrochemical performance.
[0006] The applicant found in the research that under the effect of quenching, the membrane precursor will gradually freeze and solidify, and the HNTs will rearrange at the interface between the frozen solid and the liquid that has not yet frozen, change from a disordered state to an ordered arrangement in the vertical direction, and as the frozen layer gradually advances from bottom to top, the ordered arrangement of the HNTs in the vertical direction will continue to form in the middle between the solution layer and the frozen layer until the membrane precursor is completely frozen and formed, realizing the self-assembly of the ordered arrangement of the membrane precursor and reducing the curvature of the pores of the separator. Further, the lithium ions will be transported along the vertical channels formed by the HNTs, shortening the diffusion path of the lithium ions in the gel electrolyte.
[0007] The present application solves the above technical problems by the following technical solutions.
[0008] The present application provides a preparation method of a gel electrolyte, which comprises the following steps:
[0009] S1: coating a mixed solution of halloysite nanotubes (HNTs), polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and N-methyl pyrrolidone (NMP) on a substrate to obtain a membrane precursor;
[0010] In the mixed solution, the content of the HNTs is 1-9%, and the % refers to the mass percentage of the HNTs in the mixed solution; the content of the PVDF or the PVDF-HFP is 9-10%, and the % refers to the mass percentage of the PVDF or the PVDF-HFP in the mixed solution;
[0011] S2: cooling the substrate coated with the membrane precursor from the bottom and then moving it into a solidification bath to obtain a PVDF@HNTs composite membrane or a PVDF-HFP@HNTs composite membrane; the cooling condition is to reduce the temperature to -80 to -60℃ within 5s;
[0012] S3: immersing the PVDF@HNTs composite membrane or the PVDF-HFP@HNTs composite membrane into an electrolyte and drying.
[0013] In S1, the content of the HNTs is preferably 1%, 2%, 3% or 4%, and the % refers to the mass percentage of the HNTs in the mixed solution.
[0014] In S1, the content of the PVDF or the PVDF-HFP is preferably 6%, 7%, 8% or 9%, and the % refers to the mass percentage of the PVDF or the PVDF-HFP in the mixed solution.
[0015] In S1, the solid content in the mixed solution can be 8-15%, preferably 6-10%, for example, 10%. If the viscosity of the mixed solution is too high and the freezing speed is too fast, the HNTs will not have enough time to rearrange.
[0016] In S1, preferably, the mixed solution is prepared by first dissolving the HNTs in the NMP and then adding the PVDF or the PVDF-HFP.
[0017] The dissolving manner can be ultrasonic dispersion.
[0018] The ultrasonic dispersion time can be 10 min.
[0019] After the PVDF or the PVDF-HFP is added, the PVDF or the PVDF-HFP can also be dissolved by heating and stirring.
[0020] The heating temperature can be conventional in the art, for example, 50°C.
[0021] In S1, the coating manner can be conventional in the art, for example, doctor blade coating.
[0022] In S1, the substrate type can be conventional in the art, for example, a PTFE substrate.
[0023] In S1, the thickness of the film precursor can be 50-300 μm, for example, 100 μm. If the thickness of the film precursor is too thick, the conductivity is too low; if the thickness is too thin, the strength is poor, and the subsequent prepared battery is prone to short circuit.
[0024] In S2, the freezing can be performed by liquid nitrogen treatment or cold trap treatment.
[0025] When the liquid nitrogen treatment is used, the bottom of the substrate is contacted with the liquid nitrogen. This contacting manner can form a freezing sequence from bottom to top; if immersed in the liquid nitrogen, a solid-liquid phase interface cannot be formed in the vertical direction.
[0026] When the cold trap treatment is used, the temperature can reach a temperature at which the film precursor can be frozen.
[0027] In S2, the micro-morphology of the film precursor after the freezing treatment is similar to a honeycomb micropore.
[0028] In S2, the temperature of the coagulation bath can be -20-0°C.
[0029] In S2, the solvent of the coagulation bath can be conventional in the art, and is preferably deionized water or an organic solvent.
[0030] The type of the organic solvent can be a poor solvent of the polymer PVDF or PVDF-HFP, and is preferably isopropanol.
[0031] In S2, phase inversion process and solvent removal occur in the coagulation bath treatment. Since the phase inversion process is a rapid process, the honeycomb microporous structure formed during the freezing process can be maintained. The low temperature can prevent the frozen membrane structure from being destroyed, and the vertical arrangement of HNTs is not destroyed.
[0032] In S2, preferably, after the coagulation bath treatment, a drying operation is further performed.
[0033] In the drying operation, freeze-drying can not be used.
[0034] Preferably, the drying is first dried in an oven at 60°C for 1-2 hours, and then vacuum dried at 80°C for 12 hours. The prepared PVDF@HNTs composite membrane or PVDF-HFP@HNTs composite membrane is generally stored in a desiccator for use.
[0035] In S3, preferably, the PVDF@HNTs composite membrane or the PVDF-HFP@HNTs composite membrane further includes a cutting operation before immersion.
[0036] In S3, preferably, the electrolyte is a conventional super-concentrated electrolyte (SCE) in the art. The super-concentrated electrolyte can improve the stability of the gel electrolyte and prevent the electrolyte from precipitating.
[0037] The super-concentrated electrolyte (SCE) can include: lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the solvent is a mixed solution of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC).
[0038] The concentration of the lithium salt is preferably 2-5M, for example 3M.
[0039] In the solvent, the molar ratio of FEC to DMC is preferably 5:1-1:5, for example 1:2. The addition of FEC can prevent the corrosion of the positive current collector.
[0040] In S3, the drying is preferably vacuum drying. The vacuum environment can further promote the super-concentrated electrolyte to be immersed in the pores of the PVDF@HNTs composite membrane or the PVDF-HFP@HNTs composite membrane.
[0041] The time of the vacuum drying is preferably 1 hour. During the drying process, the PVDF@HNTs composite membrane or the PVDF-HFP@HNTs composite membrane is fully activated, and the residual solvent is removed, forming the gel electrolyte PVDF@HNTs@SCE or PVDF-HFP@HNTs@SCE.
[0042] In S3, the drying can further include a standing operation.
[0043] The standing time is preferably 6 hours.
[0044] The application further provides a gel electrolyte prepared by the preparation method of the gel electrolyte.
[0045] The application further provides a gel electrolyte comprising a PVDF@HNTs composite film or a PVDF-HFP@HNTs composite film and an electrolyte.
[0046] In the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film, the HNTs are orderly and vertically arranged on the PVDF film or the PVDF-HFP film in a honeycomb microporous structure; the distribution amount of the HNTs is 10-50%, the % refers to the mass percentage of the HNTs in the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film; the thickness of the PVDF@HNTs composite film is 50-300 μm; and the electrolyte is located in the pores of the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film.
[0047] In the application, the distribution amount of the HNTs is preferably 10-40%, for example, 10%, 20%, 30% or 40%.
[0048] In the application, the thickness of the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film is preferably 100 μm.
[0049] The application further provides the use of the gel electrolyte in a battery.
[0050] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined at will, thereby obtaining various preferred examples of the application.
[0051] The reagents and raw materials used in the application are commercially available.
[0052] The positive progress effect of the application is that:
[0053] 1. The HNTs used in the application can not only serve as a filler to improve the mechanical strength of the PVDF film or the PVDF-HFP film, but also can be orderly and vertically arranged on the freezing interface under the action of quenching to form a honeycomb structure, which is beneficial to breaking the crystalline structure of the polymer matrix, and the internal cavity of the HNTs can embed the super-concentration electrolyte, so that the super-concentration electrolyte is more easily swelled into the film. Moreover, the HNTs are a kind of natural nanotube structure material, which is moderately priced and easy to obtain.
[0054] 2、The prepared composite film comprises vertically arranged HNTs, which improves the porosity and liquid absorption rate of the composite film, reduces the pore curvature of the composite film, thereby shortens the lithium ion transmission distance, has better rate performance and cycle performance; the composite film is activated by an electrolyte, and a gel electrolyte with high stability, excellent mechanical performance and excellent electrochemical performance is formed. The gel electrolyte is not easy to precipitate electrolyte, has higher safety performance, can meet the power demand of lithium ion batteries, and is suitable for power batteries. BRIEF DESCRIPTION OF DRAWINGS
[0055] Figure 1 SEM images of the PVDF@HNTs composite film prepared in Example 1; wherein Figure 1 (a) is a plan view, Figure 1 (b) is a vertical section view.
[0056] Figure 2 The charge-discharge cycle diagram of the battery made of the PVDF@HNTs composite film prepared in Example 4 under different rates. DETAILED DESCRIPTION
[0057] The application will be further described below by way of examples, but the application is not limited in the scope of the examples. In the following examples, the experimental methods not specified in the specific conditions are selected according to the conventional methods and conditions or according to the product instructions.
[0058] Example 1
[0059] 1. HNTs were added to NMP, ultrasonic dispersion was carried out for 10 min, then a certain amount of PVDF was added, and heating and stirring were carried out at 50℃ until the PVDF was completely dissolved. In the prepared mixed slurry, the PVDF content was 9%, the HNTs content was 1%, and the solid content was 10%.
[0060] 2. The above solution was prepared into a film precursor in the form of doctor blade coating on a substrate, the substrate was a PTFE substrate, and the thickness was 100μm measured by a vernier caliper; the film precursor and the substrate were transferred to liquid nitrogen, the bottom surface of the substrate was in contact with the liquid nitrogen, and the temperature was reduced to-80~-60℃ within 5s.
[0061] 3. The frozen film precursor and the substrate were transferred together to an ice water mixed deionized water coagulation bath at-20~0℃, phase inversion process occurred and the solvent NMP was removed, then the PVDF@HNTs composite film was prepared by drying at 60℃ in an oven for 1h, and then vacuum drying at 80℃ for 12h. The PVDF@HNTs composite film was transferred to a glove box for use. The SEM images of the PVDF@HNTs composite film are shown in Figure 1 . Figure 1 (a) is a plan SEM image, and the PVDF@HNTs composite film can be seen as a honeycomb structure. Figure 1(b) For the SEM image of the longitudinal section, it can be seen that after the freezing treatment, the HNTs in the PVDF@HNTs composite membrane form an ordered vertical arrangement.
[0062] 4. Preparation of an ultra-high concentration electrolyte, wherein LiTFSI is a lithium salt electrolyte, and the solvent is a mixed solution of FEC and DMC. The lithium salt concentration is 3M, and the solvent is a mixed solution of FEC: DMC at a molar ratio of 1:2.
[0063] 5. Activation of the PVDF@HNTs composite membrane: after cutting the composite membrane, immerse it in the above-mentioned electrolyte, and treat it in a vacuum oven at room temperature for 1h, and then stand it in a glove box for 6h. After the composite membrane fully absorbs the electrolyte, a gel-like electrolyte is formed.
[0064] Example 2
[0065] Compared with Example 1, the difference is that in the prepared mixed liquid, the PVDF content is 8%, the HNTs content is 2%, and the other operations and conditions are the same as those of Example 1.
[0066] Example 3
[0067] Compared with Example 1, the difference is that in the prepared mixed liquid, the PVDF content is 7%, the HNTs content is 3%, and the other operations and conditions are the same as those of Example 1.
[0068] Example 4
[0069] Compared with Example 1, the difference is that in the prepared mixed liquid, the PVDF content is 6%, the HNTs content is 4%, and the other operations and conditions are the same as those of Example 1.
[0070] Effect Example 1
[0071] 1. The liquid absorption rate of the composite membrane before and after activation in Examples 1-4 can be calculated by weighing the composite membrane.
[0072] 2. The PVDF@HNTs@SCE gel electrolyte is assembled with a stainless steel electrode and a metal lithium sheet into a 2032 type button cell. The electrochemical workstation is used for AC impedance test, and the electrolyte ion conductivity is calculated. Specifically, the button cell is connected to the electrochemical workstation, a 10mV voltage is applied at the open circuit voltage, and the AC impedance test is carried out in the range of 0.01Hz-100000Hz. According to the test data, the intersection with the real part is the resistance of the gel electrolyte, and then the conductivity value is calculated according to the conductivity formula.
[0073] 3. The PVDF@HNTs@SCE gel electrolyte is assembled with a NCM(622) positive electrode sheet and a metal lithium sheet into a button cell, and the battery rate and cycle performance are tested. Specifically, the button half-cell is connected to the charge-discharge test system to test the electrochemical performance of the battery.
[0074] Rate performance: charge-discharge test was carried out at 0.1C, 0.2C, 0.5C, 1C, 2C, 6C rate respectively, and the voltage range was 2.8V-4.2V. Figure 2 The rate performance corresponding to the PVDF@HNTs@SCE gel electrolyte prepared in Example 4 was tested.
[0075] Cycle performance test: the button cell was subjected to charge-discharge cycle test at 0.5C rate in the voltage range of 2.8V-4.2V, and the capacity retention rate after 200 cycles was observed.
[0076] Table 1
[0077]
[0078] As can be seen from Table 1, with the increase of the distribution amount of HNTs, the gel electrolyte prepared by the application can improve the mechanical strength of the electrolyte and the cycle performance of the battery on the one hand, and the adsorbed electrolyte amount and the adsorption capacity are increased on the other hand.
Claims
1. A method for producing a gel electrolyte, characterized by, It comprises the following steps: S1: coating a mixed solution of halloysite nanotubes HNTs, polyvinylidene fluoride PVDF or polyvinylidene fluoride-hexafluoropropylene PVDF-HFP and N-methyl pyrrolidone NMP on a substrate to obtain a film precursor; In the mixed solution, the content of the HNTs is 1-9%, which means that the mass percentage of the HNTs in the mixed solution is 1-9%; the content of the PVDF or the PVDF-HFP is 9-10%, which means that the mass percentage of the PVDF or the PVDF-HFP in the mixed solution is 9-10%; S2: cooling the substrate coated with the film precursor from the bottom and then moving it into a coagulation bath to obtain a PVDF@HNTs composite film or a PVDF-HFP@HNTs composite film; the cooling condition is to reduce the temperature to-80--60℃ within 5s; S3: immersing the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film into an electrolyte and drying it.
2. The method for preparing a gel electrolyte according to claim 1, wherein In S1, the content of the HNTs is 1%, 2%, 3% or 4%; And / or, in S1, the content of the PVDF or the PVDF-HFP is 6%, 7%, 8% or 9%; And / or, in S1, the solid content in the mixed solution is 8-15%; And / or, in S1, the mixed solution is prepared by first dissolving the HNTs in the NMP and then adding the PVDF or the PVDF-HFP; And / or, in S1, the coating method is doctor blade coating; And / or, in S1, the substrate is a PTFE substrate; And / or, in S1, the thickness of the film precursor is 50-300μm.
3. The method for preparing a gel electrolyte according to claim 2, wherein In S1, the solid content in the mixed solution is 6-10%; And / or, in S1, the thickness of the film precursor is 100μm.
4. The method for preparing a gel electrolyte according to claim 3, wherein In S1, the solid content in the mixed solution is 10%.
5. The method for preparing a gel electrolyte according to claim 2, wherein the gel electrolyte is prepared by adding the electrolyte solution to the polymer gel. In S1, the dissolving method is ultrasonic dispersion; And / or, in S1, after adding the PVDF or the PVDF-HFP, the PVDF or the PVDF-HFP is dissolved by heating and stirring.
6. The method for preparing a gel electrolyte according to claim 5, wherein the gel electrolyte is prepared by adding the electrolyte solution to the polymer gel. The ultrasonic dispersion time is 10min; And / or, the heating temperature is 50℃.
7. The method for preparing a gel electrolyte according to claim 1, wherein the gel electrolyte is prepared by adding the electrolyte solution to the polymer gel. In S2, the cooling is performed by liquid nitrogen treatment or cold trap treatment; And / or, in S2, the temperature of the coagulation bath is-20-0℃; And / or, in S2, the solvent of the coagulation bath is deionized water or an organic solvent; And / or, in S2, after the coagulation bath treatment, a drying operation is further performed.
8. The method for producing a gel electrolyte according to claim 7, wherein When the liquid nitrogen treatment is adopted, the bottom of the substrate is contacted with the liquid nitrogen; when the cold trap treatment is adopted, the temperature reaches a value that can freeze the film precursor; And / or, in S2, the type of the organic solvent is a poor solvent of the polymer PVDF or PVDF-HFP; And / or, the drying is first dried in an oven at 60℃ for 1-2h and then vacuum dried at 80℃ for 12h.
9. The method for producing a gel electrolyte according to claim 8, wherein In S2, the type of the organic solvent is isopropyl alcohol.
10. The method for preparing a gel electrolyte according to claim 7, wherein the gel electrolyte is prepared by adding the electrolyte solution to the polymer gel. In S2, the drying operation does not adopt freeze drying.
11. The method for preparing a gel electrolyte according to claim 1, wherein In S3, before being immersed, the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film further comprises a cutting operation; And / or, in S3, the electrolyte is a super-high concentration electrolyte SCE; And / or, in S3, the drying is vacuum drying; And / or, in S3, the drying is further followed by a standing operation.
12. The method for preparing a gel electrolyte according to claim 11, wherein the gel electrolyte is prepared by adding the electrolyte solution to the polymer gel. The super-high concentration electrolyte SCE comprises: lithium salt is lithium bis-trifluoromethanesulfonimide LiTFSI, and the solvent is a mixed solution of fluoroethylene carbonate FEC and dimethyl carbonate DMC; And / or, the time of the vacuum drying is 1h; And / or, the time of the standing is 6h.
13. The method for producing a gel electrolyte according to claim 12, wherein The concentration of the lithium salt is 2-5M; And / or, in the solvent, the molar ratio of FEC to DMC is 5:1-1:
5.
14. The method for producing a gel electrolyte according to claim 13, wherein The concentration of the lithium salt is 3M; And / or, in the solvent, the molar ratio of FEC to DMC is 1:
2.
15. A gel electrolyte characterized by, It is prepared by the preparation method of the gel electrolyte according to any one of claims 1-14.
16. The gel electrolyte of claim 15, wherein It comprises a PVDF@HNTs composite film or a PVDF-HFP@HNTs composite film and an electrolyte; In the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film, HNTs are orderly and vertically arranged on a PVDF film or a PVDF-HFP film in a honeycomb microporous structure; the distribution amount of the HNTs is 10-50%, which refers to the mass percentage of HNTs in the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film; the thickness of the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film is 50-300μm; and the electrolyte is located in the pores of the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film.
17. The gel electrolyte of claim 16, wherein The distribution amount of the HNTs is 10-40%; And / or, the thickness of the PVDF@HNTs composite film or the PVDF-HFP@HNTs composite film is 100μm.
18. The gel electrolyte of claim 17, wherein The distribution amount of the HNTs is 10%, 20%, 30% or 40%.
19. Use of the gel electrolyte according to any one of claims 15-18 in a battery.
Citation Information
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