Gradient polymer electrolyte, preparation method thereof and solid-state battery

Abstract

The application provides a gradient polymer electrolyte and a preparation method and a solid-state battery thereof, and particularly relates to the technical field of electrolytes. The preparation method comprises the following steps: firstly, dissolving positive and negative electrode side polymer electrolytes in organic solvents respectively, and preparing positive and negative electrode side polymer electrolyte solutions; secondly, coating the positive and negative electrode side polymer electrolyte solutions on a substrate to obtain a composite preformed film; and thirdly, placing the composite preformed film in a uniform electric field, and diffusing and drying the composite preformed film in a vacuum environment at a certain temperature, so that the gradient distribution is fully performed to obtain a gradient polymer solid-state electrolyte. The solid-state electrolyte prepared by the application can solve the interface impedance problem and improve the cycle performance of the solid-state battery.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, specifically to a gradient polymer electrolyte, its preparation method, and a solid-state battery. Background Technology

[0002] As a medium for storing electrical energy, the demand for batteries is constantly increasing, and with the continuous development of the new energy field, higher requirements are being placed on the energy density and storage capacity of batteries. At the same time, battery safety issues are arising. Most secondary battery thermal runaways are caused by short circuits inside the battery, generating a large amount of heat, leading to the decomposition of the internal electrolyte. Solid-state batteries, because they do not contain flammable liquid electrolytes, can greatly improve battery safety. Furthermore, solid-state batteries also possess high energy density, making them widely recognized as the preferred choice for next-generation power batteries.

[0003] Solid electrolytes are an important component of solid-state batteries. Currently, solid electrolytes mainly include oxide solid electrolytes, polymer solid electrolytes, and inorganic-organic composite solid electrolytes. Among them, oxide solid electrolytes have poor interfacial contact with the battery active components and are prone to breakage during battery cycling due to internal stress, making it impossible to manufacture large-capacity cells. Polymer solid electrolytes have many problems in terms of ionic conductivity, interfacial impedance, and high-voltage resistance, which seriously hinder the commercial application of solid-state batteries. In the existing technology, multi-level composite solid electrolytes with multiple layers have also been disclosed for use in lithium batteries. Although the design of multi-layer composite structures has improved and solved the different requirements of positive and negative electrodes in the entire lithium battery system to a certain extent, the multi-layer film composite also results in the lack of continuous transition characteristics at the interface between the positive and negative electrodes and the electrolyte layer. There is still a step gradient, which greatly increases the interfacial impedance, leads to poor low-temperature performance, and thus reduces battery performance.

[0004] Therefore, there is an urgent need to provide a new solid electrolyte to improve the above problems. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a gradient polymer electrolyte, a method for preparing the same, and a solid-state battery. While ensuring the safety of the solid-state battery, it can be highly matched with the positive and negative electrode materials, solve the impedance problem between interfaces, and thus improve the performance of the polymer electrolyte solid-state battery.

[0006] To achieve the above and other related objectives, the present invention provides a method for preparing a gradient polymer electrolyte, comprising the following steps:

[0007] The positive-side polymeric electrolyte and the negative-side polymeric electrolyte are dissolved in an organic solvent with lithium salt to prepare the positive-side polymeric electrolyte solution and the negative-side polymeric electrolyte solution, respectively.

[0008] The positive electrode polymer electrolyte solution and the negative electrode polymer electrolyte solution are sequentially coated onto a substrate to obtain a composite pre-film.

[0009] The composite preform is placed in a uniform electric field and diffused and dried in a vacuum environment at 20–100°C to allow it to fully undergo gradient distribution. The direction of the electric field in the uniform electric field is consistent with the direction of the electric field in the battery.

[0010] After the composite pre-film drying process is completed, the substrate is peeled off to obtain a gradient polymer electrolyte.

[0011] In one example of the present invention, the mass ratio of the positive electrode polymer electrolyte to the lithium salt is 5:1 to 30:1, and the concentration of the positive electrode polymer electrolyte in the positive electrode polymer electrolyte solution is 1 to 15 g / ml; the mass ratio of the negative electrode polymer electrolyte to the lithium salt is 5:1 to 30:1, and the concentration of the negative electrode polymer electrolyte in the negative electrode polymer electrolyte solution is 1 to 15 g / ml.

[0012] In one example of the present invention, the positive electrode side polymer electrolyte is a fluorinated polymer and / or a polysulfonic acid and / or a polyamic acid.

[0013] Preferably, the positive electrode side polymer electrolyte comprises one or more of polystyrene sulfonic acid (PSSA), sodium polybenzene sulfonate, lithium polystyrene sulfonate, fluorinated polyvinyl carbonate (PVCA), fluorinated polycyanoacrylate (PECA), fluorinated polymethyl methacrylate (PMMA), fluorinated polyacrylonitrile (PAN), polymaleic anhydride (PMA), polyimide, polypyrrole, and poly(3,4-ethylenedioxythiophene).

[0014] In one example of the present invention, the polymer electrolyte on the negative electrode side includes one or more of polyethylene oxide (PEO), polypropylene oxide (PPO), polypropylene carbonate (PPC), polyethylene carbonate (PEC), and polyethylene oxide-propylene oxide (PEO-PPO).

[0015] In one example of the present invention, the organic solvent includes one or more of N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, and dichloromethane.

[0016] In one example of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(oxalate-borate) (LiBOB), lithium difluorooxalate-borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiFTSI), and lithium bis(fluorosulfonyl)imide (LiTFSI).

[0017] In one example of the present invention, the coating thickness of the polymer electrolyte solution on the positive electrode side is 10-300 μm; the coating thickness of the polymer electrolyte solution on the negative electrode side is 10-300 μm.

[0018] In one example of the present invention, the composite preform is placed in a uniform electric field and diffused and dried in a vacuum environment at 20–100°C, which includes: first drying the composite preform in a vacuum environment at 20–50°C for 0.5–1 h; then increasing the temperature by 2–5°C every 10–30 minutes until the temperature reaches 50–100°C; and then adjusting the temperature to 40–60°C and maintaining it for 1–4 h.

[0019] In one example of the present invention, the intensity of the uniform electric field is controlled by applying a DC voltage of 40 to 700V to the electric field.

[0020] Another aspect of the present invention provides a gradient polymer electrolyte, which is prepared using the preparation method of the present invention.

[0021] The present invention also provides a solid-state battery comprising the gradient polymer solid-state electrolyte of the present invention or a gradient polymer electrolyte prepared by the preparation method of the present invention.

[0022] In one embodiment of the present invention, the cathode material of the solid-state battery includes any one or a combination of at least two of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese aluminum oxide high-nickel ternary materials or even quaternary materials.

[0023] In one embodiment of the present invention, the negative electrode material of the solid-state battery includes lithium metal, silicon / carbon composite material and / or silicon oxide / carbon composite material.

[0024] This invention provides a method for preparing a gradient polymer electrolyte. The method involves pre-forming polymer electrolytes on the positive and negative electrode sides into films, and then placing these films in a uniform electric field and at a specific temperature. Through the induction effect of the electric field on the polymer electrolytes, a continuous concentration gradient is formed between the positive and negative electrode sides, resulting in a continuous and uniform gradient polymer solid electrolyte. This solid electrolyte effectively solves the interfacial impedance problem and improves the cycle performance of polymer solid electrolyte batteries. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of the preparation method of the gradient polymer solid electrolyte of the present invention;

[0027] Figure 2 for Figure 1 A flowchart of step S3 in one embodiment;

[0028] Figure 3 This is a schematic diagram illustrating the gradient change of the gradient polymer solid electrolyte of the present invention;

[0029] Figure 4 This is a schematic diagram of the solid-state battery structure of the present invention;

[0030] Figure 5 This is an EDS characterization diagram of the gradient interface of the gradient polymer solid electrolyte of the present invention.

[0031] Component designation

[0032] 1. Positive electrode; 2. Negative electrode; 3. Electrolyte layer. Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of the present invention is for describing specific implementation schemes and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0034] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" used in this specification are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as part of the scope of the invention.

[0035] Please see Figures 1 to 5 This invention provides a gradient polymer electrolyte, its preparation method, and a solid-state battery, which enables the polymer electrolyte on the positive and negative electrode sides to form a continuous and uniform gradient transition, solving the interfacial impedance problem while improving the cycle performance of the solid-state battery.

[0036] Please see Figure 1 This invention provides a method for preparing a gradient polymer solid electrolyte, comprising the following steps:

[0037] S1. Dissolve the positive electrode polymeric electrolyte and the negative electrode polymeric electrolyte in an organic solvent with lithium salt to prepare positive and negative electrode polymeric electrolyte solutions.

[0038] S2. The positive electrode side polymer electrolyte solution and the negative electrode side polymer electrolyte solution are sequentially coated onto the substrate to obtain a composite pre-film.

[0039] S3. The composite preform is placed in a uniform electric field and diffused and dried in a vacuum environment at 20-100°C to allow it to fully undergo gradient distribution, wherein the direction of the electric field in the uniform electric field is consistent with the direction of the electric field in the battery.

[0040] S4. After the composite pre-film drying process is completed, the substrate is peeled off to obtain the gradient polymer electrolyte.

[0041] Please see Figure 1 Specifically, step S1, preparing the positive electrode-side polymer electrolyte solution, includes placing the positive electrode-side polymer electrolyte and lithium salt in a sample vial at a certain ratio, adding a certain amount of organic solvent to the sample vial, and mixing and stirring evenly to obtain the positive electrode-side polymer electrolyte solution. The mass ratio of the positive electrode-side polymer electrolyte to the lithium salt is 5:1 to 30:1, for example, any ratio within the range of 5:1, 10:1, 20:1, or 30:1. The concentration of the positive electrode-side polymer electrolyte in the positive electrode-side polymer electrolyte solution is 1 to 15 g / ml, for example, any value within the range of 1 g / ml, 5 g / ml, 10 g / ml, or 15 g / ml. The stirring method is not limited here; conventional mixing and stirring methods in the art can be used, such as magnetic stirring until the electrolyte and lithium salt are evenly dispersed; or ultrasonic dispersion followed by magnetic stirring until the electrolyte and lithium salt are evenly dispersed.

[0042] Similarly, to prepare the negative electrode polymer electrolyte solution, the negative electrode polymer electrolyte and lithium salt are placed in a sample vial at a certain ratio, and a certain amount of organic solvent is added to the sample vial and mixed and stirred evenly to obtain the negative electrode polymer electrolyte solution. The mass ratio of the negative electrode polymer electrolyte to the lithium salt is 5:1 to 30:1, for example, any ratio within the range of 5:1, 10:1, 20:1, 30:1, etc. The concentration of the negative electrode polymer electrolyte in the negative electrode polymer electrolyte solution is 1 to 15 g / ml, for example, any value within the range of 1 g / ml, 5 g / ml, 10 g / ml, or 15 g / ml, etc. The stirring method is not limited here; conventional mixing and stirring methods in the art can be used, such as magnetic stirring until the electrolyte and lithium salt are evenly dispersed; or ultrasonic dispersion followed by magnetic stirring until the electrolyte and lithium salt are evenly dispersed.

[0043] The positive electrode polymer electrolyte is a high-voltage resistant polymer electrolyte. Preferably, the positive electrode polymer electrolyte includes fluorinated polymers and / or polysulfonic acids and / or polyamic acids. Further, the positive electrode polymer electrolyte includes one or more of polystyrene sulfonic acid, sodium polybenzene sulfonate, lithium polystyrene sulfonate, fluorinated polyvinyl carbonate, fluorinated polycyanoacrylate, fluorinated polymethacrylate, fluorinated polyacrylonitrile, polymaleic anhydride, polyimide, polypyrrole, and poly(3,4-ethylenedioxythiophene). That is, the positive electrode polymer electrolyte can be any one of the electrolyte types listed above, such as polystyrene sulfonate, sodium polybenzene sulfonate, lithium polystyrene sulfonate, fluorinated polyvinyl carbonate, fluorinated polycyanoacrylate, fluorinated polymethacrylate, fluorinated polyacrylonitrile, polymaleic anhydride, polyimide, polypyrrole, or poly(3,4-ethylenedioxythiophene). The positive electrode polymer electrolyte can also be any combination of two or more of the electrolyte types listed above, such as a combination of polystyrene sulfonate and sodium polybenzene sulfonate, or a combination of lithium polystyrene sulfonate, fluorinated polyvinyl carbonate, and fluorinated polycyanoacrylate, or a combination of fluorinated polycyanoacrylate, fluorinated polymethacrylate, and fluorinated polyacrylonitrile, or a combination of fluorinated polymethacrylate, fluorinated polyacrylonitrile, polymaleic anhydride, and polyimide, etc., etc. When the positive electrode polymer electrolyte is a combination of several components, there is no restriction on the proportion of each component in the composition; they can be mixed in any proportion. Positive electrode polymer electrolytes include, but are not limited to, the types listed above; other lithium salts with the same effect may also be used.

[0044] The negative electrode polymer electrolyte is a polymer electrolyte with high ionic conductivity. Further, the negative electrode polymer electrolyte includes one or more of polyethylene oxide (PEO), polypropylene oxide (PPO), polypropylene carbonate (PPC), polyethylene carbonate (PEC), and polyethylene oxide-propylene oxide (PEO-PPO). The negative electrode polymer electrolyte can be any of the polymers listed above, such as polyethylene oxide (PEO), polypropylene oxide (PPO), polypropylene carbonate (PPC), polyvinyl carbonate (PEC), or polyethylene oxide-propylene oxide (PEO-PPO). It can also be any combination of two or more of the polymers listed above, such as a combination of polyethylene oxide (PEO) and polypropylene oxide (PPO), or a combination of polypropylene carbonate (PPC) and polyvinyl carbonate (PEC), or a combination of polyethylene oxide (PEO) and polyethylene oxide-propylene oxide (PEO-PPO), or a combination of polyethylene oxide (PEO), polypropylene oxide (PPO), and polypropylene carbonate (PPC), etc., and so on. When the negative electrode polymer electrolyte is a combination of several polymers, there is no restriction on the proportion of each component in the composition; they can be mixed in any proportion. Of course, the type of negative electrode polymer electrolyte is not limited to those listed above; other electrolytes with equivalent effects are also acceptable.

[0045] The organic solvent includes one or more of N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, and dichloromethane. That is, the organic solvent can be any one of the listed types, for example, N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, or dichloromethane. The organic solvent can also be any combination of two or more of the listed types, such as a combination of N,N-dimethylformamide and acetonitrile, or a combination of N-methylpyrrolidone and dimethyl sulfoxide, or a combination of N-methylpyrrolidone, dimethyl sulfoxide, and dichloromethane, etc., etc. When several organic solvents are combined, the proportions of the components in the composition are limited, and they can be mixed in any proportion. Of course, the organic solvent includes, but is not limited to, the types listed above; any organic solvent not listed in this application can also be selected, as long as it can sufficiently disperse the electrolyte and lithium salt.

[0046] Lithium salts include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiFTSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). That is, the lithium salt can be any of the types listed above, such as lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), or lithium bis(trifluoromethanesulfonyl)imide. Lithium (LiFTSI) or lithium bis(fluorosulfonyl)imide (LiTFSI); the lithium salt can also be any combination of two or more of the types listed above, such as a combination of lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4), or a combination of lithium tetrafluoroborate (LiBF4) and lithium perchlorate (LiClO4), or a combination of lithium bis(oxalato)borate (LiBOB) and lithium difluorooxalato)borate (LiDFOB), or a combination of lithium bis(oxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiFTSI), and lithium bis(fluorosulfonyl)imide (LiTFSI), etc., etc., which will not be listed here. When there are several combinations of lithium salts, there is no restriction on the proportion of each component in the composition, and they can be mixed in any proportion. Of course, lithium salts include, but are not limited to, the types listed above, and other lithium salts with the same effect can also be used.

[0047] Please see Figure 1 In step S2, the positive electrode polymer electrolyte solution is first coated onto the substrate and dried in a vacuum environment at 20°C for 30–60 minutes. Then, the negative electrode polymer electrolyte solution is coated onto the upper surface of the positive electrode electrolyte solution. After coating, the negative electrode electrolyte adheres tightly to the upper side of the positive electrode polymer electrolyte, forming a composite pre-film. The coating thickness of the positive electrode polymer electrolyte is 10–300 μm, for example, any value within the range of 10 μm, 20 μm, 50 μm, 100 μm, 200 μm, or 300 μm; the coating thickness of the negative electrode polymer electrolyte solution is also 10–300 μm, any value within the range of 10 μm, 20 μm, 50 μm, 100 μm, 200 μm, or 300 μm. In one embodiment, the substrate can be a glass plate. During coating, a custom mold can be used to define the coating range and thickness. This mold is a hollow stainless steel frame with the ability to maintain its thickness at 3 MPa. The thickness of the stainless steel frame border is 10 to 300 μm. For example, the border thickness can be 10 μm, 20 μm, 50 μm, 100 μm, 200 μm or 300 μm. The border thickness can be selected according to the coating thickness.

[0048] In some embodiments, oxide electrolytes may be introduced into the polymer electrolyte solutions on both the positive and negative electrode sides to improve the performance of the polymer electrolyte. Oxide electrolytes include any one or a combination of at least two of the following: garnet-type LLZO electrolyte, perovskite-type LLTO electrolyte, NASICON-type LATP electrolyte, LLZTO electrolyte, and LAGP electrolyte. That is, the oxide electrolyte can be any one of the above types, or any combination of two or more of them. For example, the oxide electrolyte can be an LLZO electrolyte, or an LLZTO electrolyte, or an LAGP electrolyte, or a combination of LLTO and LATP electrolytes, or a combination of LLTO, LATP, and LLZTO electrolytes, etc., and so on. The amount of oxide electrolyte added can be set according to the specific requirements of the electrolyte and is not limited here.

[0049] Please see Figure 1 and Figure 2 Step S3 specifically includes:

[0050] S31. Place the composite preform obtained in step S2 in a uniform electric field and dry it in a vacuum environment at 20-50°C for 30-60 minutes.

[0051] S32. Gradually increase the ambient temperature, raising it by 2-5°C every 10-30 minutes until it reaches 50-100°C;

[0052] S33. Then adjust the ambient temperature to 40-60℃ and maintain it for 1-4 hours.

[0053] The uniform electric field in step S31 can be adjusted by regulating the magnitude of the DC voltage applied to it. The DC voltage is 40–700V, for example, any value within the range of 40V, 100V, 300V, 500V, or 700V. The direction of the uniform electric field is from high potential to low potential from top to bottom, consistent with the direction of the polymer electrolyte in the battery. Since the composite pre-film is not completely dry, to prevent the polymer electrolyte from flowing, it is first dried in a vacuum environment at 20–50°C, for example, any value within the range of 20°C, 30°C, 40°C, or 50°C, for 30–60 minutes, for example, 30 minutes, 40 minutes, 50 minutes, or 60 minutes.

[0054] Step S32, Heating Stage: Increase the temperature every 10–30 minutes, for example, at intervals of 10, 20, or 30 minutes, with each increase being 2–5°C, such as 2°C, 3°C, 4°C, or 5°C, until the temperature reaches 50–100°C, such as 50°C, 70°C, 90°C, or 100°C. After each heating, invert the electric field device and the composite pre-film sample once to allow for sufficient gradient distribution under the influence of the electric field and gravity.

[0055] After the heating stage in step S33 is completed, adjust the temperature to 40-60℃, such as 40℃, 50℃ or 60℃, and maintain it at this temperature for 1-4 hours, such as any value within the above range, such as 1 hour, 2 hours, 3 hours or 4 hours.

[0056] Please see Figure 1 In step S4, after the processing in step S3 is completed, the substrate is peeled off and compacted to obtain the gradient polymer electrolyte.

[0057] This invention utilizes an electric field to induce the preparation of a polymer electrolyte with a continuous and uniform gradient. The two sides of this polymer electrolyte can respectively match the high voltage resistance of the positive electrode and the compatibility of the negative electrode interface, effectively solving the interface problem and improving the cycle performance of solid-state batteries. Moreover, the preparation process is simple and can be industrialized for large-scale production.

[0058] Please see Figure 3 In another aspect, the present invention provides a gradient polymer electrolyte prepared using the above-described preparation method. The gradient polymer electrolyte comprises a positive electrode-side polymer electrolyte and a negative electrode-side polymer electrolyte. The concentration of the positive electrode-side polymer electrolyte exhibits a continuous gradient change from 100% to 0% from the side closest to the positive electrode of the solid-state battery to the negative electrode side, and the concentration of the negative electrode-side polymer electrolyte exhibits a continuous gradient change from 100% to 0% from the side closest to the negative electrode of the solid-state battery to the positive electrode side. A relatively fast and high gradient distribution exists between the two phases, and as the contact deepens, the gradient composition changes of each phase gradually decrease, and the change curve is continuously differentiable.

[0059] Please see Figure 4 The present invention provides a solid-state battery, including a positive electrode 1, a negative electrode 2 and an electrolyte layer 3 located between the positive electrode 1 and the negative electrode 2. The electrolyte layer 3 is a gradient polymer electrolyte of the present invention or a gradient polymer electrolyte prepared by the preparation method of the present invention.

[0060] The positive electrode 1 material in the aforementioned solid-state battery includes any one or a combination of at least two of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and high-nickel ternary or quaternary materials of lithium nickel cobalt manganese aluminum oxide; the negative electrode 2 material includes lithium metal, silicon / carbon composite material, and / or silicon oxide / carbon composite material. The electrolyte layer 3 includes a polymer electrolyte on the positive electrode side and a polymer electrolyte on the negative electrode side. The concentration of the polymer electrolyte on the positive electrode side changes continuously from 100% to 0% from the side closest to the positive electrode of the solid-state battery to the side closest to the negative electrode, and the concentration of the polymer electrolyte on the negative electrode side changes continuously from 100% to 0% from the side closest to the negative electrode of the solid-state battery to the side closest to the positive electrode.

[0061] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments thereof. The described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0062] Example 1

[0063] The positive electrode polymer electrolyte is lithium polystyrene sulfonate, with N,N-dimethylformamide (DMF) as the solvent; the negative electrode polymer electrolyte is polyvinyl carbonate (PEC), with acetonitrile as the solvent; and the lithium salt is lithium hexafluorophosphate (LiPF6).

[0064] Step 1: Dissolve lithium polystyrene sulfonate and LiPF6 in DMF at a mass ratio of 9:1 to prepare a positive electrode side polymer electrolyte solution, wherein the concentration of lithium polystyrene sulfonate in the positive electrode side polymer electrolyte solution is 4 g / mL. -1 .

[0065] PEC and LiPF6 were dissolved in acetonitrile at a mass ratio of 7:1 to prepare a polymer electrolyte solution for the negative electrode side, wherein the concentration of PEC in the polymer electrolyte solution for the negative electrode side was 3 g / mL. -1 ;

[0066] Step 2: Pour the positive electrode polymer electrolyte solution onto the glass substrate. A 100μm mold is provided on the outer side of the substrate. Use a doctor blade to scrape the film to form a 100μm coating layer on the glass substrate. Dry in a vacuum environment at 20℃ for 1 hour. Pour the negative electrode polymer electrolyte solution onto the pre-treated film. Then, use a 300μm thick mold and doctor blade to scrape the film to form a 300μm negative electrode electrolyte coating, thus forming a composite pre-formed film.

[0067] Step 3: Place the pre-formed composite film obtained in Step 2 into a uniform electric field with a vertical downward voltage of 600V. First, dry and diffuse the film in a vacuum environment at 40℃ for 1 hour. Then, increase the temperature by 5℃ every 30 minutes until the temperature reaches 70℃. At the same time, rotate the sample and the electric field up and down each time the temperature is adjusted. After holding at 60℃ for 2 hours, take it out, glass the glass substrate, and roll it to obtain a 100μm thick continuous uniform gradient polymer solid electrolyte.

[0068] Example 2

[0069] The positive electrode polymer electrolyte is selected as follows: fluorinated polyacrylonitrile (PAN) with N,N-dimethylformamide (DMF) as the solvent; the negative electrode polymer electrolyte is selected as: polyoxyethylene (PEO) with acetonitrile as the solvent; and the lithium salt is lithium tetrafluoroborate (LiBF4).

[0070] Step 1: Dissolve PAN and LiBF4 in DMF at a mass ratio of 15:1 to prepare the positive electrode side polymer electrolyte solution, wherein the concentration of lithium polystyrene sulfonate in the positive electrode side polymer electrolyte solution is 10 g / mL. -1 .

[0071] PEO and LiBF4 were dissolved in acetonitrile at a mass ratio of 15:1 to prepare a polymer electrolyte solution for the negative electrode side, wherein the concentration of PEO in the polymer electrolyte solution for the negative electrode side was 8 g / mL. -1 ;

[0072] Step 2: Pour the positive electrode polymer electrolyte solution onto the glass substrate. A 200μm mold is provided on the outer side of the substrate. Use a doctor blade to scrape the film to form a 200μm coating layer on the glass substrate. Dry in a vacuum environment at 20℃ for 1 hour. Pour the negative electrode polymer electrolyte solution onto the pre-treated film. Then, use a 200μm thick mold and doctor blade to scrape the film to form a 200μm negative electrode electrolyte coating, thus forming a composite pre-formed film.

[0073] Step 3: Place the pre-formed composite film obtained in Step 2 into a 300V vertically downward uniform electric field, and first dry and diffuse it in a vacuum environment at 50℃ for 30 minutes to form a film; then increase the temperature by 3℃ every 20 minutes until the temperature reaches 100℃, while flipping the sample and electric field up and down each time the temperature is adjusted; after holding at 60℃ for 2 hours, take it out, glass the glass substrate, and roll it to obtain a 100μm thick continuous uniform gradient polymer solid electrolyte.

[0074] Example 3

[0075] The positive electrode polymer electrolyte is selected as sodium polybenzenesulfonate, with N,N-dimethylformamide (DMF) as the solvent; the negative electrode polymer electrolyte is polypropylene carbonate (PPC), with acetonitrile as the solvent; and the lithium salt is lithium bis(oxalato)borate (LiBOB).

[0076] Step 1: Dissolve sodium polystyrene sulfonate and LiBOB in DMF at a mass ratio of 30:1 to prepare a positive electrode side polymer electrolyte solution, wherein the concentration of lithium polystyrene sulfonate in the positive electrode side polymer electrolyte solution is 15 g / mL. -1 .

[0077] PPC and LiBOB were dissolved in acetonitrile at a mass ratio of 30:1 to prepare a polymer electrolyte solution for the negative electrode side, wherein the concentration of PPC in the polymer electrolyte solution for the negative electrode side was 15 g / mL. -1 ;

[0078] Step 2: Pour the positive electrode polymer electrolyte solution onto the glass substrate. A 100μm mold is provided on the outer side of the substrate. Use a doctor blade to scrape the film to form a 100μm coating layer on the glass substrate. Dry in a vacuum environment at 20℃ for 1 hour. Pour the negative electrode polymer electrolyte solution onto the pre-treated film. Then, use a 300μm thick mold and doctor blade to scrape the film to form a 300μm negative electrode electrolyte coating, thus forming a composite pre-formed film.

[0079] Step 3: Place the pre-formed composite film obtained in Step 2 into a uniform electric field with a vertical downward voltage of 700V. First, dry and diffuse the film in a vacuum environment at 20℃ for 1 hour. Then, increase the temperature by 2℃ every 10 minutes until the temperature reaches 50℃. At the same time, rotate the sample and the electric field up and down each time the temperature is adjusted. After holding at 50℃ for 4 hours, take it out, glass the glass substrate, and roll it to obtain a 100μm thick continuous uniform gradient polymer solid electrolyte.

[0080] Example 4

[0081] The positive electrode polymer electrolyte is selected as sodium polybenzenesulfonate, with N-methylpyrrolidone (NMP) as the solvent; the negative electrode polymer electrolyte is polyvinyl carbonate (PEC), with dimethyl sulfoxide (DMSO) as the solvent; and the lithium salt is lithium hexafluorophosphate (LiPF6).

[0082] Step 1: Dissolve sodium polystyrene sulfonate and LiPF6 in NMP at a mass ratio of 5:1 to prepare a positive electrode side polymer electrolyte solution, wherein the concentration of lithium polystyrene sulfonate in the positive electrode side polymer electrolyte solution is 1 g / mL. -1 .

[0083] PEC and LiPF6 were dissolved in DMSO at a mass ratio of 5:1 to prepare a polymer electrolyte solution for the negative electrode side, wherein the concentration of PEC in the polymer electrolyte solution for the negative electrode side was 1 g / mL. -1 ;

[0084] Step 2: Pour the positive electrode polymer electrolyte solution onto the glass substrate. A 100μm mold is provided on the outer side of the substrate. Use a doctor blade to scrape the film to form a 100μm coating layer on the glass substrate. Dry in a vacuum environment at 20℃ for 1 hour. Pour the negative electrode polymer electrolyte solution onto the pre-treated film. Then, use a 300μm thick mold and doctor blade to scrape the film to form a 300μm negative electrode electrolyte coating, thus forming a composite pre-formed film.

[0085] Step 3: Place the pre-formed composite film obtained in Step 2 into a uniform electric field with a vertical downward voltage of 100V. First, dry and diffuse the film in a vacuum environment at 40℃ for 1 hour. Then, increase the temperature by 2℃ every 10 minutes until the temperature reaches 70℃. At the same time, rotate the sample and the electric field up and down each time the temperature is adjusted. After holding at 60℃ for 3 hours, take it out, glass the glass substrate, and roll it to obtain a 100μm thick continuous uniform gradient polymer solid electrolyte.

[0086] Comparative Example 1

[0087] The positive electrode polymer electrolyte is lithium polystyrene sulfonate, with DMF as the solvent; the negative electrode polymer electrolyte is polyvinyl carbonate (PEC), with acetonitrile as the solvent; and the lithium salt is lithium hexafluorophosphate (LiPF6).

[0088] Step 1: Dissolve lithium polystyrene sulfonate and LiPF6 in DMF at a mass ratio of 9:1 to prepare a positive electrode side polymer electrolyte solution, wherein the concentration of lithium polystyrene sulfonate in the positive electrode side polymer electrolyte solution is 4 g / mL. -1 .

[0089] PEC and LiPF6 were dissolved in acetonitrile at a mass ratio of 7:1 to prepare a polymer electrolyte solution for the negative electrode side, wherein the concentration of PEC in the polymer electrolyte solution for the negative electrode side was 3 g / mL. -1 ;

[0090] Step 2: Pour the positive electrode polymer electrolyte solution onto a glass substrate. A 100μm mold is provided on the outer side of the substrate. Use a doctor blade to scrape the film onto the glass substrate to form a 100μm coating layer. Dry at 60℃ for 2 hours. Pour the negative electrode polymer electrolyte solution onto the pre-treated film. Then, use a 300μm thick mold and doctor blade to scrape the film to form a 300μm negative electrode electrolyte coating. Dry at 60℃ for 4 hours. After peeling off the glass substrate, roll it to obtain a simple composite polymer electrolyte.

[0091] Comparative Example 2

[0092] The positive electrode polymer electrolyte is selected as follows: fluorinated polyacrylonitrile (PAN) with DMF as the solvent; the negative electrode polymer electrolyte is selected as: polyoxyethylene (PEO) with acetonitrile as the solvent; and the lithium salt is lithium tetrafluoroborate (LiBF4).

[0093] Step 1: Dissolve PAN and LiBF4 in DMF at a mass ratio of 15:1 to prepare the positive electrode side polymer electrolyte solution, wherein the concentration of lithium polystyrene sulfonate in the positive electrode side polymer electrolyte solution is 10 g / mL. -1 .

[0094] PEO and LiBF4 were dissolved in acetonitrile at a mass ratio of 15:1 to prepare a polymer electrolyte solution for the negative electrode side, wherein the concentration of PEO in the polymer electrolyte solution for the negative electrode side was 8 g / mL. -1 ;

[0095] Step 2: Pour the positive electrode polymer electrolyte solution onto a glass substrate. A 200μm mold is provided on the outer side of the substrate. Use a doctor blade to scrape the film onto the glass substrate to form a 200μm coating layer. Dry at 60℃ for 2 hours. Pour the negative electrode polymer electrolyte solution onto the pre-treated film. Then, use a 200μm thick mold and doctor blade to scrape the film to form a 200μm negative electrode electrolyte coating. After drying at 60℃ for 4 hours, peel off the glass substrate and roll it to obtain a simple composite polymer electrolyte.

[0096] Comparative Example 3

[0097] The positive electrode polymer electrolyte is selected as sodium polybenzenesulfonate, with DMF as the solvent; the negative electrode polymer electrolyte is polypropylene carbonate (PPC), with acetonitrile as the solvent; and the lithium salt is lithium bis(oxalato)borate (LiBOB).

[0098] Step 1: Dissolve sodium polystyrene sulfonate and LiBOB in DMF at a mass ratio of 30:1 to prepare a positive electrode side polymer electrolyte solution, wherein the concentration of lithium polystyrene sulfonate in the positive electrode side polymer electrolyte solution is 15 g / mL. -1 .

[0099] PPC and LiBOB were dissolved in acetonitrile at a mass ratio of 30:1 to prepare a polymer electrolyte solution for the negative electrode side, wherein the concentration of PPC in the polymer electrolyte solution for the negative electrode side was 15 g / mL. -1 ;

[0100] Step 2: Pour the positive electrode polymer electrolyte solution onto a glass substrate. A 100μm mold is provided on the outer side of the substrate. Use a doctor blade to scrape the film onto the glass substrate to form a 100μm coating layer. Dry at 60℃ for 2 hours. Pour the negative electrode polymer electrolyte solution onto the pre-treated film. Then, use a 300μm thick mold and doctor blade to scrape the film to form a 300μm negative electrode electrolyte coating. After drying at 60℃ for 4 hours, peel off the glass substrate and roll it to obtain a simple composite polymer electrolyte.

[0101] The electrical properties of the polymer solid electrolytes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were tested respectively, and the test results are shown in Table 1.

[0102] Table 1: Electrical properties of polymer solid electrolytes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 at 25°C

[0103]

[0104] The test results show that, compared with the polymer solid electrolyte prepared by simple composite in the comparative example, the polymer solid electrolyte prepared by the method of the present invention has significantly improved ionic conductivity, significantly reduced interfacial resistance, and correspondingly widened electrochemical window.

[0105] Please see Figure 5 The gradient cross section of the gradient polymer solid electrolyte prepared by the present invention was scanned by EDS. The figure shows that the brightness of the EDS elemental distribution map gradually darkens, indicating that the elemental distribution gradually decreases, that is, the polymer electrolyte changes in a gradient from the positive electrode side to the negative electrode side.

[0106] This invention places a composite pre-formed film composed of a positive-side polymer electrolyte and a negative-side polymer electrolyte in a uniform electric field. At a certain temperature, the electric field induces a continuous concentration gradient between the positive and negative sides of the polymer electrolyte, resulting in a continuous and uniform gradient polymer solid electrolyte. This solid electrolyte effectively solves the interfacial impedance problem and improves the cycle performance of polymer solid electrolyte batteries. Therefore, this invention effectively overcomes some practical problems in the prior art, thus having high utilization value and application significance.

[0107] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a gradient polymer electrolyte, characterized in that, Includes the following steps: The positive electrode polymer electrolyte and the negative electrode polymer electrolyte are dissolved with lithium salt in an organic solvent to prepare the positive electrode polymer electrolyte solution and the negative electrode polymer electrolyte solution, respectively. The positive electrode polymer electrolyte solution and the negative electrode polymer electrolyte solution are sequentially coated onto a substrate to obtain a composite pre-film. The composite preform is placed in a uniform electric field and diffused and dried in a vacuum environment at 20–100°C to allow it to fully undergo gradient distribution. The direction of the electric field in the uniform electric field is consistent with the direction of the electric field in the battery. After the composite pre-film treatment and drying process is completed, the substrate is peeled off to obtain a gradient polymer solid electrolyte. The process of placing the composite preform in a uniform electric field and diffusing it in a vacuum environment at 20–100°C includes: first drying the composite preform in a vacuum environment at 20–50°C for 0.5–1 hour; then increasing the temperature by 2–5°C every 10–30 minutes until the temperature reaches 50–100°C; and then adjusting the temperature to 40–60°C and maintaining it for 1–4 hours.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the positive electrode polymer electrolyte to the lithium salt is 5:1 to 30:1, and the concentration of the positive electrode polymer electrolyte in the positive electrode polymer electrolyte solution is 1 to 15 g / ml; the mass ratio of the negative electrode polymer electrolyte to the lithium salt is 5:1 to 30:1, and the concentration of the negative electrode polymer electrolyte in the negative electrode polymer electrolyte solution is 1 to 15 g / ml.

3. The preparation method according to claim 1, characterized in that, The positive electrode side polymer electrolyte is a fluorinated polymer and / or a polysulfonic acid and / or a polyamic acid, and the positive electrode side polymer electrolyte includes one or more of polystyrene sulfonic acid, sodium polybenzene sulfonate, lithium polystyrene sulfonate, fluorinated polyvinyl carbonate, fluorinated polycyanoacrylate, fluorinated polymethacrylate, fluorinated polyacrylonitrile, polymaleic anhydride, polyimide, polypyrrole, and poly(3,4-ethylenedioxythiophene).

4. The preparation method according to claim 1, characterized in that, The polymer of the negative electrode side polymer electrolyte includes one or more of polyoxyethylene, polyoxypropylene, polypropylene carbonate, polyethylene carbonate, and polyoxyethylene-oxypropylene.

5. The preparation method according to claim 1, characterized in that, The organic solvent includes one or more of N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethyl sulfoxide, and dichloromethane; the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

6. The preparation method according to claim 1, characterized in that, The coating thickness of the polymer electrolyte solution on the positive electrode side is 10–300 μm; the coating thickness of the polymer electrolyte solution on the negative electrode side is 10–300 μm.

7. The preparation method according to claim 1, characterized in that, The intensity of the uniform electric field is controlled by a DC voltage applied to the electric field, wherein the DC voltage is 40–700V.

8. A gradient polymer electrolyte, characterized in that, It is prepared by the preparation method described in claim 1.

9. A solid-state battery, characterized in that, This includes the gradient polymer electrolyte as described in claim 8 or the gradient polymer electrolyte prepared by the preparation method described in claim 1.

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