A method for preparing a polymer solid electrolyte membrane and its application

Abstract

This invention provides a polymer solid electrolyte, its preparation method, and its application. The preparation method includes: first, impregnating a monomer solution into a polyimide porous membrane under an oxygen-free and anhydrous atmosphere; then, heating under an oxygen-free and anhydrous atmosphere to polymerize the monomer solution in situ, thereby obtaining the polymer solid electrolyte; the monomer solution includes a solvent, an electrolyte salt, an initiator, and at least one monomer shown in structural formulas 1-4 below. The polymer solid electrolyte prepared by this method can be applied in the actual production of batteries, improving the problem of high interfacial resistance caused by poor interfacial contact between the solid electrolyte and the positive and negative electrodes, and improving the mechanical strength of the separator.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry, and more specifically to a method for preparing a polymer solid electrolyte membrane and its application. Background Technology

[0002] Since their commercialization in 1991, traditional liquid electrolyte lithium-ion batteries have been under development for nearly 30 years. Although there is considerable research on liquid lithium batteries, safety issues such as electrolyte leakage, lithium dendrite growth, and electrolyte decomposition under high voltage have greatly limited their practical application. To fundamentally address these safety concerns and further improve battery energy density, researchers have turned their attention to all-solid-state batteries.

[0003] Compared to liquid lithium-ion batteries, all-solid-state batteries have significant advantages in terms of increasing battery energy density, widening the operating temperature range, and extending service life. However, the solid electrolyte membrane of all-solid-state batteries has three main drawbacks: first, the preparation process of solid electrolyte membranes is complex and difficult to apply to batteries in actual production; second, there are still some poor interface contacts between the solid electrolyte membrane and the positive and negative electrodes, resulting in a relatively high interface resistance; and third, the mechanical strength of the separator is insufficient. Summary of the Invention

[0004] This invention provides a method for preparing a polymer solid electrolyte. The polymer solid electrolyte prepared by this method can be applied in the actual production of batteries. It can improve the disadvantage of high interfacial resistance caused by poor interfacial contact between the solid electrolyte and the positive and negative electrodes, and improve the mechanical strength of the separator.

[0005] According to a first aspect, one embodiment provides a method for preparing a polymer solid electrolyte, comprising the following steps: first, impregnating a monomer solution into a polyimide porous membrane under an oxygen-free and anhydrous atmosphere, and then heating the monomer solution under an oxygen-free and anhydrous atmosphere to polymerize the monomer solution in situ to obtain a polymer solid electrolyte; the monomer solution includes a solvent, an electrolyte salt, an initiator, and any monomer shown in the following structural formulas 1-4.

[0006]

[0007] According to a second aspect, one embodiment provides a polymer solid electrolyte prepared using the preparation method of the first aspect of the present invention.

[0008] According to a third aspect, one embodiment provides a polymeric solid electrolyte comprising an electrolyte salt and a polymer obtained by in-situ polymerization of at least one monomer shown in structural formulas 1-4.

[0009]

[0010] According to the fourth aspect, one embodiment provides a diaphragm, at least a portion of the diaphragm's surface being coated with a polymer solid electrolyte as described in the third aspect.

[0011] According to the fifth aspect, one embodiment provides a battery comprising a polymer solid electrolyte of the third aspect, or a separator of the fourth aspect, or the battery comprising a polymer solid electrolyte prepared using the preparation method of the first aspect.

[0012] This invention provides a method for preparing a polymer solid electrolyte. Using a polyimide porous membrane with excellent mechanical properties as a rigid framework improves the mechanical strength of the membrane. The monomers shown in structural formulas 1-4 can be polymerized in situ within the polyimide porous membrane to obtain the polymer solid electrolyte membrane. The preparation method is simple and can be applied to actual battery production. Because the monomers used in this invention are cyclic small-molecule monomers containing carbon-carbon double bonds, the solid electrolyte obtained by in-situ polymerization of these monomers has low surface tension with the positive and negative electrode sheets, thereby improving interfacial wettability and effectively solving the problem of high interfacial resistance caused by poor interfacial contact between the solid electrolyte and the electrodes. Detailed Implementation

[0013] The present invention will be further described in detail below through specific embodiments. In the following embodiments, many details are described to facilitate a better understanding of this application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other materials or methods. In some cases, certain operations related to this application are not shown or described in the specification. This is to avoid obscuring the core parts of this application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0014] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification are only for clearly describing a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0015] To further illustrate this application, the following detailed description of a method for preparing a polymer solid electrolyte membrane and its application is provided in conjunction with embodiments. However, it should be understood that these embodiments are implemented based on the technical solution of this application, and detailed implementation methods and specific operating procedures are given. They are only for further illustrating the features and advantages of this application, and are not intended to limit the scope of protection of the claims of this application. The scope of protection of this application is not limited to the following embodiments.

[0016] This invention selects a rigid polyimide porous membrane as a three-dimensional gel substrate. The battery can initially form a system of positive electrode-polyimide porous membrane-negative electrode. Then, after injecting a mixture of monomer, solvent, electrolyte salt and initiator, a semi-solid lithium-ion battery is formed by in-situ thermal initiation polymerization.

[0017] This invention provides a method for preparing a polymer solid electrolyte, comprising the following steps: first, impregnating a polyimide porous membrane with a monomer solution in an oxygen-free and anhydrous atmosphere, and then heating the monomer solution in an oxygen-free and anhydrous atmosphere to polymerize the monomer solution in situ to obtain a polymer solid electrolyte. The monomer solution includes a solvent, an electrolyte salt, an initiator, and at least one monomer shown in the following structural formulas 1-4.

[0018]

[0019] In this embodiment of the invention, a polyimide porous membrane with excellent mechanical properties is used as a rigid framework to improve the mechanical strength of the separator, thereby inhibiting the growth of lithium dendrites and avoiding the problem of lithium dendrite puncture. The monomers shown in structural formulas 1-4 can be polymerized in situ in the polyimide porous membrane to obtain a polymer solid electrolyte membrane. The preparation method is simple and can also be applied to the actual production of batteries. Since the monomers used in this invention are cyclic small molecule monomers containing carbon-carbon double bonds, the solid electrolyte obtained by in-situ polymerization of this type of monomer has low surface tension with the positive and negative electrode sheets, thereby improving the interfacial wettability and effectively solving the problem of high interfacial resistance caused by poor interfacial contact between the solid electrolyte and the electrode.

[0020] In some embodiments of the present invention, the positive electrode, negative electrode, and polyimide porous membrane are wound into a battery cell using a winding process commonly used in the manufacturing industry, arranged in the order of polyimide porous membrane-negative electrode-polyimide porous membrane-positive electrode. The battery cell is then fitted into an aluminum-plastic film and sealed. The monomer solution is then injected using a vacuum injection method. Because the monomer used in the present invention has low surface tension with the positive and negative electrode sheets, the monomer solution can fully wet the positive and negative electrodes before polymerization, which can effectively solve the problem of high interface resistance caused by poor interface contact between the solid electrolyte membrane and the electrode.

[0021] Furthermore, when this battery is applied to lithium-ion batteries, lithium ions can coordinate with polar functional groups on the polymer chains of the polymer solid electrolyte. As the polymer chains move, lithium ions continuously migrate from one coordination site to another, thereby achieving lithium-ion transport. In-situ polymerization of small molecule monomers effectively increases the amorphous region. Increasing the amorphous region helps with polymer chain movement and improves ionic conductivity, further enhancing the battery's electrochemical performance.

[0022] In embodiments of the present invention, based on the total mass of the monomer solution, the monomer content is 0.1-5 wt%, the solvent content is 10-90 wt%, the initiator content is 0.001-3 wt%, and the remainder is an electrolyte salt. The concentration of the electrolyte salt is 0.5-2 mol / L.

[0023] Electrolyte salts include lithium salts. An oxygen-free and anhydrous atmosphere, including a vacuum atmosphere, is used to heat the monomer solution at temperatures ranging from 40 to 90°C for 2 to 48 hours.

[0024] Lithium salts include one of the following: organic lithium salts and inorganic lithium salts. Inorganic lithium salts include lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), or lithium hexafluorophosphate (LiPF6). Organic lithium salts include lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium bis(difluorosulfonyl)imide (LiFSI), or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0025] In embodiments of the present invention, the initiator includes at least one selected from azobisisobutyronitrile, 2,4-dimethylpentanonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, benzoyl dioxide, tert-butyl peroxide, and methyl ethyl ketone peroxide. Under certain external heating conditions, the initiator can open the carbon-carbon double bonds of the monomer to initiate the polymerization reaction.

[0026] The solvent includes at least one of ethylene carbonate (EC), diethyl carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0027] Embodiments of the present invention also provide a polymer solid electrolyte, which is prepared by the aforementioned preparation method.

[0028] Embodiments of the present invention also provide a polymer solid electrolyte comprising an electrolyte salt and a polymer obtained by in-situ polymerization of at least one monomer shown in structural formulas 1-4;

[0029]

[0030] The electrolyte salt of the solid electrolyte of the present invention includes lithium salt.

[0031] Embodiments of the present invention also provide a diaphragm, wherein at least a portion of the surface of the diaphragm is coated with a polymer solid electrolyte comprising an electrolyte salt and a polymer obtained by in-situ polymerization of at least one monomer shown in structural formulas 1-4.

[0032] Embodiments of the present invention also provide a battery comprising the aforementioned polymer solid electrolyte membrane, or the polymer solid electrolyte membrane of the battery is prepared by the aforementioned preparation method; or the battery comprises the aforementioned separator with at least a portion of its surface attached with polymer solid electrolyte.

[0033] The batteries include lithium-ion batteries, specifically primary lithium-ion batteries, secondary lithium-ion batteries, and fuel cells. More preferably, they include prismatic lithium batteries, cylindrical lithium batteries, aluminum-cased lithium batteries, steel-cased lithium batteries, and pouch batteries.

[0034] Example 1

[0035] Preparation of polyimide porous membrane: 160g of polyimide, 40g of pore-forming agent polyvinylpyrrolidone, and 800g of solvent N-methylpyrrolidone (NMP) were weighed and mixed according to a mass ratio of 16:4:80 and stirred thoroughly to obtain a mixture. The mixture was then uniformly coated onto a polytetrafluoroethylene film using a coating machine and placed in a vacuum drying oven at 80℃ for 24h. After drying, the polyimide porous membrane was obtained by slitting.

[0036] Preparation of monomer solution: Weigh 100g of DMC, 100g of DEC, and 100g of EC in a mass ratio of 1:1:1 and mix them to obtain a solvent. Then add 40.9g of LiPF6 to the solvent to make the LiPF6 concentration 1mol / L to obtain the electrolyte. Take 100g of the electrolyte and add 1g of the monomer shown in structural formula 1 and 0.15g of AIBME. Stir for 4h to completely dissolve the monomer shown in structural formula 1 and AIBME in the solvent and mix evenly to obtain the monomer solution.

[0037] Preparation of the positive electrode: Weigh out LiNi in a mass ratio of 100:1.5:3. 0.5 Co 0.2 Mn 0.3 1000g of O2, 15g of conductive carbon black (SP), and 30g of polyvinylidene fluoride (PVDF) were added to 450g of NMP and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was then coated onto both sides of an aluminum foil using a coating machine, followed by drying, rolling, slitting, and tab welding to obtain the positive electrode sheet.

[0038] Preparation of the negative electrode sheet: 1000g of artificial graphite, 15g of conductive carbon black (SP), 15g of styrene-butadiene rubber (SBR), and 25g of carboxymethyl cellulose (CMC) were weighed out according to a mass ratio of 100:1.5:1.5:2.5 and added to 800g of deionized water. The mixture was stirred evenly to obtain the negative electrode slurry. The negative electrode slurry was then uniformly coated onto both sides of aluminum foil using a coating machine. After drying, rolling, slitting, and tab welding, the negative electrode sheet was obtained.

[0039] Battery assembly: The polyimide porous membrane obtained in the polyimide porous membrane preparation step, the positive electrode obtained in the positive electrode preparation step, and the negative electrode obtained in the negative electrode preparation step are wound into a cell in the order of polyimide porous membrane-negative electrode-polyimide porous membrane-positive electrode, and then inserted into a 435573 aluminum-plastic film. After sealing, injecting monomer solution (4-10g), encapsulation, and trimming, a soft-pack 435573 battery is obtained.

[0040] In-situ gel polymerization: The monomer solution in the prepared soft-pack 435573 battery was heated to induce an in-situ polymerization reaction. The heating temperature was 60℃ and the heating time was 6h to obtain the battery.

[0041] Example 2

[0042] The difference from Example 1 is the mass of the monomer shown in Structural Formula 1 in the monomer solution preparation step. In this example, the mass of the monomer is 2g.

[0043] Example 3

[0044] The difference from Example 1 is the mass of the monomer shown in Structural Formula 1 in the monomer solution preparation step. In this example, the mass of the monomer is 3g.

[0045] Example 4

[0046] The difference from Example 1 is the mass of the monomer shown in Structural Formula 1 in the monomer solution preparation step. In this example, the mass of the monomer is 4g.

[0047] Example 5

[0048] The difference from Example 1 is the mass of the monomer shown in Structural Formula 1 in the monomer solution preparation step. In this example, the mass of the monomer is 5g.

[0049] Example 6

[0050] The difference from Example 1 lies in the mass of the monomer and the initiator AIBME in the monomer solution preparation step. In this example, the mass of the monomer is 5g and the mass of AIBME is 0.2g.

[0051] Example 7

[0052] The difference from Example 1 lies in the type and mass of the monomer in the monomer solution preparation step. The monomer in this example is the monomer shown in structural formula 2, and its mass is 2g.

[0053] Example 8

[0054] The difference from Example 7 lies in the mass of the monomer in the monomer solution preparation step. In this example, the mass of the monomer shown in structural formula 2 is 3g.

[0055] Example 9

[0056] The difference from Example 7 lies in the mass of the monomer in the monomer solution preparation step. In this example, the mass of the monomer shown in structural formula 2 is 4g.

[0057] Example 10

[0058] The difference from Example 1 lies in the type and mass of the monomer in the monomer solution preparation step. The monomer in this example is the monomer shown in structural formula 3, and its mass is 2g.

[0059] Example 11

[0060] The difference from Example 10 is the mass of the monomer. In this example, the monomer shown in structural formula 3 has a mass of 3g.

[0061] Example 12

[0062] The difference from Example 10 is the mass of the monomer. In this example, the monomer shown in Structural Formula 3 has a mass of 4g.

[0063] Comparative Example

[0064] The difference from Example 1 lies in the monomer solution preparation step. No monomer or initiator was added in this comparative example; only the electrolyte was prepared. The specific steps are as follows: 100g of DMC, 100g of DEC, and 100g of EC were weighed and mixed in a mass ratio of 1:1:1 to obtain a solvent. Then, 40.9g of LiPF6 was added to the solvent to make the LiPF6 concentration 1mol / L, and 100g of the electrolyte was obtained for later use.

[0065] The batteries prepared in Examples 1-12 and the comparative examples were tested according to the following method: First, they were charged at a constant current of 0.5C to 4.2V, then charged at this voltage until the current was less than 0.02C; after resting for 5 minutes, they were discharged at 1C to 2.75V. After 100 cycles, the capacity retention rate was obtained by comparing the capacity of the first cycle and the capacity of the 100th cycle. That is, capacity retention rate = (capacity of the 100th cycle / capacity of the first cycle) × 100%. The results are shown in Table 1 below.

[0066] Table 1

[0067]

[0068]

[0069] By adjusting the proportion of the monomers shown in Structural Formula 1, it can be seen that as the amount of monomer added increases, the battery capacity retention rate first increases and then decreases, with the highest capacity retention rate and optimal battery cycle performance observed at a concentration of 3%. This is because unreacted monomers participate in electrochemical side reactions during cycling, which can affect cycle performance to some extent. Furthermore, to verify whether insufficient initiator caused the monomers to fail to polymerize completely, comparisons of Examples 5 and 6 show that adding more initiator actually decreased cycle performance. Therefore, the decrease in capacity retention rate is not due to insufficient initiator. From Examples 2, 7, and 10 (or Examples 3, 8, and 11, or Examples 4, 9, and 12), it can be concluded that the battery using the monomers shown in Structural Formula 1 exhibits the best cycle performance. To take a step back, as shown in Examples 1-6, 8, and 11, when the monomer used is the one represented by Structural Formula 1, the cycle performance is worst at a concentration of 1%, with a capacity retention of 95.7%. When the monomer used is the one represented by Structural Formula 2 or 3, the cycle performance is best at a concentration of 3%, with 94.1% and 93.8% respectively, both lower than the cycle performance of the battery in Example 1. Therefore, using monomer 1 at a concentration of 3% can maximize the improvement of battery cycle performance.

[0070] The above examples illustrate the present invention only to aid in understanding it and are not intended to limit the scope of the invention. Those skilled in the art can make various simple deductions, modifications, or substitutions based on the principles of this invention.

Claims

1. A method for preparing a polymer solid electrolyte, characterized in that, Includes the following steps: First, a monomer solution is impregnated with a polyimide porous membrane under an oxygen-free and anhydrous atmosphere. Then, the monomer solution is heated under an oxygen-free and anhydrous atmosphere to polymerize the monomer solution in situ, thereby obtaining the polymer solid electrolyte. The monomer solution includes a solvent, an electrolyte salt, an initiator, and a monomer as shown in structural formula 1 below. ， Structural Formula 1, wherein the content of the monomer is 0.1-5 wt% based on the total mass of the monomer solution.

2. The preparation method according to claim 1, characterized in that, Based on the total mass of the monomer solution, the solvent content is 10-90 wt%, the initiator content is 0.001-3 wt%, and the remainder is an electrolyte salt; the concentration of the electrolyte salt is 0.5-2 mol / L.

3. The preparation method according to claim 1, characterized in that, The electrolyte salt includes lithium salt; the oxygen-free and anhydrous atmosphere includes a vacuum atmosphere; the monomer solution is heated at a temperature of 40-90℃ for a heating time of 2-48h.

4. The preparation method according to claim 3, characterized in that, The lithium salt includes one of organic lithium salts and inorganic lithium salts; Alternatively, the inorganic lithium salt may include lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, or lithium hexafluorophosphate; the organic lithium salt may include lithium bis(oxalate-borate), lithium difluorooxalate-borate, lithium bis(difluorosulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide.

5. The preparation method according to claim 1, characterized in that, The solvent includes at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; Alternatively, the initiator may include at least one of azobisisobutyronitrile, 2,4-dimethylpentanonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, benzoyl oxide, tert-butyl peroxide, and methyl ethyl ketone peroxide.

6. The polymer solid electrolyte prepared by any one of claims 1-5.

7. A polymer solid electrolyte, characterized in that, It contains an electrolyte salt and a polymer obtained by in-situ polymerization of the monomers shown in Formula 1; ， Structural Formula 1, wherein the content of the monomer is 0.1-5 wt%.

8. The polymer solid electrolyte as described in claim 7, characterized in that, The electrolyte salt contains a lithium salt.

9. A diaphragm, characterized in that, At least a portion of the surface of the diaphragm is coated with the polymer solid electrolyte as described in any one of claims 7-8.

10. A battery, characterized in that, The battery comprises a polymer solid electrolyte as described in any one of claims 7-8, or a separator as described in claim 9, or the battery comprises a polymer solid electrolyte prepared by the preparation method described in any one of claims 1-5.

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