Polymer electrolyte with high interface stability and preparation method and application thereof

Abstract

The invention provides a polymer electrolyte with high interface stability and a preparation method and application thereof. The polymer electrolyte comprises a polymer matrix, a porous support material, a lithium salt, a solvent and an initiator. The polymer matrix is formed by in-situ copolymerization of a methacrylate polymer monomer as a rigid skeleton monomer and a methacrylate polymer monomer with a functional group as a functional monomer. The polymer electrolyte prepared by an in-situ curing method has high room-temperature ionic conductivity, a wide electrochemical window (gt; 5.3 V) and excellent cycling stability. The functional monomer is helpful for forming a high-stability SEI film rich in inorganic components on a positive electrode and a lithium metal / electrolyte interface, the stability of the electrode / electrolyte interface is improved, and the growth of lithium dendrites is inhibited, so that the mechanical property and the safety performance are improved. The polymer electrolyte can be widely applied to battery systems such as high-voltage lithium ion batteries, high-specific-energy lithium ion batteries and high-safety lithium ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrolytes, and in particular to a polymer electrolyte with high interface stability and innovative technologies in preparation and application thereof. Background Art

[0002] In the context of today's rapid technological development, rechargeable lithium batteries have become one of the ideal choices for meeting the development needs of efficient and portable energy storage devices due to their high specific capacity and energy density. With the continuous evolution of electronic devices, the pursuit of higher energy density and Coulombic efficiency has become increasingly urgent, which has prompted researchers to devote themselves to the development of excellent electrode and electrolyte materials to achieve lithium batteries with excellent electrochemical performance.

[0003] Lithium-ion batteries have been widely studied and commercialized in the past. They usually use lithium salts as electrolytes, carbon as anodes, and lithium-ion embedded compounds (such as LiCoO2, LiMn2O4, and LiFePO4) as cathodes. However, currently large-scale commercial lithium-ion secondary batteries generally use organic carbonate liquid electrolytes, which have serious safety hazards such as easy leakage, easy combustion, and easy explosion, which greatly restricts the further development and application of lithium-ion batteries.

[0004] In contrast, polymer electrolytes in solid electrolytes have become a research hotspot due to their advantages such as high safety, viscoelasticity and good interfacial compatibility. However, in practical applications, polymer electrolytes still face many key problems. From the perspective of long-term application, it is urgent to develop a simpler and faster preparation method; in terms of polymer matrix applications, the modification of ordinary matrices and the research and development of new matrices are still insufficient; in addition, practical applications have high requirements on the comprehensive performance of polymer electrolytes, which must have good mechanical stability, thermal stability, and excellent ability to inhibit lithium dendrites, while also meeting low cost and environmental protection conditions. Therefore, the development of polymer electrolytes prepared by in-situ curing methods is of great significance for promoting the commercialization of high-safety and high-energy-density lithium-ion batteries.

[0005] Patent CN201911339978.X discloses a polymer electrolyte and a lithium-ion battery including the polymer electrolyte. The preparation method of the polymer electrolyte comprises: (1) dissolving a functional polymer in an organic solvent and mixing them uniformly to obtain a system A, wherein the mass proportion of the functional polymer in the system A is 0.2% to 30%; (2) uniformly mixing the system A, a lithium salt and a functional additive to obtain a mixed solution; (3) in-situ polymerizing the mixed solution to obtain a polymer electrolyte. However, the addition of boron-containing polymer monomers to the electrolyte makes the electrolyte unstable and increases the cost of the electrolyte. Patent 201811419047.6 discloses a method for preparing a cross-linked polymer electrolyte, a semi-solid polymer battery and a preparation method, and uses a cyclic borate ester with alkenyl groups at both ends as a cross-linking agent, so that the polymer monomer and the like are polymerized in situ on the supporting material to obtain a cross-linked polymer electrolyte. However, the patent requires the preparation of a cross-linked polymer electrolyte first and then the battery is assembled, which has the problem of complicated processing. Secondly, the cross-linking agent used in the patent is a diene cyclic borate ester structure, which has a high cost and is difficult to meet industrial production requirements. Summary of the invention

[0006] In order to solve the problems existing in the background technology, the present invention provides a polymer electrolyte with high interface stability and its preparation method and application. The polymer electrolyte of the present invention is simple to prepare, non-flammable and has a wide electrochemical window, high ionic conductivity and good cycle performance. It has high room temperature conductivity and can be used as an electrolyte for lithium ion batteries.

[0007] In order to achieve the above-mentioned object, the present invention provides a polymer electrolyte with high interface stability, characterized in that it includes a polymer matrix, a porous supporting material, a lithium salt, a solvent and an initiator, wherein the polymer matrix is ​​formed by an in-situ copolymerization reaction of a methacrylate polymer monomer as a rigid skeleton monomer and a methacrylate polymer monomer with a functional group as a functional monomer; by mass percentage, the polymer electrolyte includes 10-80% of the polymer matrix, 4%-60% of the porous supporting material, 10-80% of the lithium salt and the solvent, and 0.01%-1% of the initiator. Furthermore, the methacrylate polymer monomer is one or both of glycidyl methacrylate and methyl methacrylate; and the methacrylate polymer monomer with a functional group is a mixture of isocyanoethyl methacrylate and trifluoroethyl methacrylate.

[0008] Furthermore, in the polymer matrix, the mass ratio of the rigid skeleton monomer to the functional monomer is 1:1-2.

[0009] Furthermore, the porous supporting material is one of a polypropylene non-woven membrane, a glass fiber non-woven membrane, a cellulose non-woven membrane, and a polyethylene non-woven membrane.

[0010] Furthermore, the lithium salt is one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium trifluoromethanesulfonate.

[0011] Furthermore, the solvent is one or more of ethyl methyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, and vinylene carbonate.

[0012] Furthermore, the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and benzoyl peroxide.

[0013] Furthermore, the solvent accounts for 20% to 80% of the mass of the lithium salt and the solvent.

[0014] The present invention also provides a method for preparing the above-mentioned polymer electrolyte with high interface stability, comprising the following steps: S1, mixing monomers, lithium salt and solvent used to form a polymer matrix into a uniform solution; S2, adding an initiator to the above solution to obtain a mixed solution; S3, placing the porous support material between the positive and negative electrodes of the lithium-ion battery, and then injecting the prepared mixed solution into the lithium-ion battery; S4, generating the polymer electrolyte with high interface stability through in-situ solid-state reaction at 30-60°C for 3-24h.

[0015] Another aspect of the present invention further provides a use of the above-mentioned highly interfacially stable polymer electrolyte or the highly interfacially stable polymer electrolyte prepared by the above-mentioned method in the preparation of a lithium ion battery.

[0016] The beneficial effects of the present invention are: (1) By using methacrylate polymer monomers as rigid skeleton monomers and methacrylate polymer monomers with functional groups as functional monomers, the polymer electrolyte forms a highly stable SEI film rich in inorganic components at the positive electrode and lithium metal / electrolyte interface, significantly improving the stability of the electrode / electrolyte interface. This interfacial stability helps to inhibit the growth of lithium dendrites, thereby improving the safety and cycle life of the battery.

[0017] (2) The polymer electrolyte has high room temperature ionic conductivity. By regulating the mass ratio of rigid skeleton monomers and functional monomers, the prepared polymer electrolyte can effectively support the rapid transmission of lithium ions. The oxidative decomposition potential is >5.3V, and it has a wide electrochemical window. It can operate stably at high voltage and is suitable for high-voltage lithium-ion batteries.

[0018] (3) A lithium-ion battery assembled using the polymer electrolyte of the present invention with lithium metal as the negative electrode and ternary 811 material as the positive electrode can -1 ) after 400 cycles at a current density of 1.5 200 W, it still has a high capacity retention rate and has excellent cycle stability. This polymer electrolyte is not only suitable for lithium metal batteries, but also can be used in other types of lithium-ion batteries. This polymer electrolyte can be widely used in battery systems such as high-voltage lithium-ion batteries, high-energy lithium-ion batteries and high-safety lithium-ion batteries, meeting the needs of modern society for efficient and safe energy storage devices, and has a wide range of application scenarios and versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work. In the drawings: Figure 1 is the conductivity curve of the polymer electrolyte of Example 1 of the present invention; Figure 2 is the linear sweep voltammetry curve of the polymer electrolyte of Example 1 of the present invention; Figure 3 The ternary 811 lithium metal full battery assembled with the polymer electrolyte of Example 1 of the present invention is charged at 0.5C (1C = 200 mAh g -1 ) Cycling performance diagram at room temperature under current density; Figure 4 This is a long cycle performance diagram of a lithium-lithium symmetric battery assembled with a polymer electrolyte according to Example 1 of the present invention at a current density of 0.1 mAcm-2. DETAILED DESCRIPTION

[0020] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0021] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections.

[0022] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0023] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0024] In the embodiments shown in the drawings, the indications of directions (such as up, down, left, right, front and back) used to explain the structure and movement of the various components of the present invention are not absolute but relative. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, the indications of these directions also change accordingly.

[0025] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0026] Example 1 The raw material ratio for preparing the polymer electrolyte is shown in Table 1. An electrolyte solution of a mixture of lithium salt and solvent is prepared in a glove box filled with argon. After the monomers used to form the polymer matrix are added, an in-situ curing initiator is added. After complete dissolution, the solution is injected into a lithium-ion battery containing positive and negative electrode materials and a battery separator (porous support material), placed at 60°C for in-situ polymerization, and the desired polymer electrolyte lithium-ion battery is obtained after 6 hours.

[0027] Table 1

[0028] The conductivity of the polymer electrolyte prepared in this example was tested by using a stainless steel inert electrode as the working electrode and a stainless steel inert electrode as the counter electrode to form a button cell. The test frequency was 1 MHz to 100 MHz and the test was performed using an EC-lab electrochemical workstation. The test results are shown in Figure 1 From the figure, we can see that the room temperature conductivity of the electrolyte is 10-4 Scm -1 .

[0029] The polymer electrolyte prepared in this example was subjected to an electrochemical window test. The test method was as follows: a button cell was formed using a stainless steel inert electrode as the working electrode and a lithium sheet as the counter electrode. The test voltage range was 0-6 V at room temperature and the scan rate was 1 mV / s. The test was performed using an EC-lab electrochemical workstation. The test results are shown in Table 1. Figure 2 ,As can be seen from the figure, the electrolyte has an electrochemical window of >5.3 V, indicating that the polymer electrolyte has high electrochemical stability and has the potential to operate at high voltage.

[0030] The polymer electrolyte prepared in this embodiment is used to assemble a lithium metal battery. The specific method is as follows: dissolve polyvinylidene fluoride with a concentration of 0.1~1.5 mol / L in N-methylpyrrolidone. Mix polyvinylidene fluoride, conductive carbon black (acetylene black or SuperP, etc.), and nickel-cobalt-manganese 811 ternary active materials in a mass ratio of 10:10:80, grind, and stir at room temperature for 24 hours. Scrape the positive electrode material slurry obtained in the previous step evenly on aluminum foil or carbon-coated aluminum foil, then dry in a vacuum oven at 60~120℃, roll, and slice, and put it in a glove box for use. After purchasing lithium metal foil, put it in a glove box for use. The prepared separator, lithium metal sheet, and ternary 811 positive electrode sheet were placed in the 2016 button battery shell in sequence, and then the electrolyte solution mixed with lithium salt and solvent was injected. After the polymer monomer was added, the in-situ curing initiator was added. After complete dissolution, the solution was injected into the lithium-ion battery containing the positive and negative electrode materials and the battery separator, and placed at 60°C for in-situ polymerization. After 6 hours, the required polymer electrolyte lithium-ion battery was obtained. After assembly, it was heated at room temperature at 0.5C (1C = 200 mAh g -1 ) Constant current charge to 4.3 V and then discharge to 2.7 V for long cycle charge and discharge test. The test results are shown in Figure 3 As can be seen from the figure, the assembled full battery can stably cycle for more than 400 cycles, indicating that the polymer electrolyte prepared in this embodiment has high cycle stability and can be used in high-performance lithium-ion batteries. The polymer electrolyte prepared in this embodiment is tested for lithium-lithium symmetric batteries. The test method is as follows: a button cell is formed with a lithium sheet electrode as the working electrode and a lithium sheet as the counter electrode. At room temperature, the battery is charged at 0.1 mA cm -2 The current density and constant current charge and discharge time are both 1 hour. The test is carried out using the Blue Battery Test System. The test results are shown in Figure 4 ,As can be seen from the figure, the assembled Li-Li symmetric battery can ,cycle stably for more than 2000 h, which shows that it has extremely high ,stability to lithium and can be perfectly applied to lithium metal batteries.

[0031] Example 2 The raw material ratio for preparing the polymer electrolyte is shown in Table 2. An electrolyte solution of a mixture of lithium salt and solvent is prepared in a glove box filled with argon. After adding the monomers used to form the polymer matrix and the in-situ curing initiator, the solution is injected into a lithium-ion battery containing positive and negative electrode materials and a battery separator (porous support material) after complete dissolution. The solution is placed at 50°C for in-situ polymerization. After 8 hours, the desired polymer electrolyte lithium-ion battery is obtained.

[0032] Table 2

[0033] Taking the polymer electrolyte obtained in this embodiment as an example, when used as a lithium ion battery electrolyte, the electrochemical performance is similar to that of Embodiment 1.

[0034] Example 3 The raw material ratio for preparing the polymer electrolyte is shown in Table 2. An electrolyte solution of a mixture of lithium salt and solvent is prepared in a glove box filled with argon. After adding the monomers used to form the polymer matrix and the in-situ curing initiator, the solution is injected into a lithium-ion battery containing positive and negative electrode materials and a battery separator (porous support material) after complete dissolution. The solution is placed at 50°C for in-situ polymerization. After 8 hours, the desired polymer electrolyte lithium-ion battery is obtained.

[0035] Table 3

[0036] Taking the polymer electrolyte obtained in this embodiment as an example, when used as a lithium ion battery electrolyte, the electrochemical performance is similar to that of Embodiment 1.

[0037] Example 4 The raw material ratio for preparing the polymer electrolyte is shown in Table 4. A mixed electrolyte solution of lithium salt and solvent is prepared in a glove box filled with argon. After adding the monomers used to form the polymer matrix and the in-situ curing initiator, the solution is injected into a lithium-ion battery containing positive and negative electrode materials and a battery separator (porous support material) after complete dissolution. The solution is placed at 70°C for in-situ polymerization. After 12 hours, the desired polymer electrolyte lithium-ion battery is obtained.

[0038] Table 4

[0039] Taking the polymer electrolyte obtained in this embodiment as an example, when used as a lithium ion battery electrolyte, the ionic conductivity can reach 10 -4 S cm -1 , with an electrochemical window close to 5 V.

[0040] Example 5 The proportions of the raw materials used to prepare the polymer electrolyte are shown in Table 5. The electrolyte solution mixed with the lithium salt and the solvent was prepared in a glove box filled with argon. After adding the monomers used to form the polymer matrix, the in-situ curing initiator was added. After complete dissolution, the solution was injected into a lithium-ion battery containing positive and negative electrode materials and a battery separator (porous support material), and placed at 70 ° C for in-situ polymerization. After 12 h, the desired polymer electrolyte lithium-ion battery was obtained.

[0041] Table 5

[0042] Taking the polymer electrolyte obtained in this embodiment as an example, when used as a lithium ion battery electrolyte, the electrochemical performance is similar to that of Embodiment 4.

[0043] Example 6 The proportions of the raw materials used to prepare the polymer electrolyte are shown in Table 6. The electrolyte solution mixed with the lithium salt and the solvent was prepared in a glove box filled with argon. After adding the monomers used to form the polymer matrix, the in-situ curing initiator was added. After complete dissolution, the solution was injected into a lithium-ion battery containing positive and negative electrode materials and a battery separator (porous support material), and placed at 80 ° C for in-situ polymerization. After 10 h, the desired polymer electrolyte lithium-ion battery was obtained.

[0044] Table 6

[0045] Taking the polymer electrolyte obtained in this embodiment as an example, when used as a lithium ion battery electrolyte, the electrochemical performance is similar to that of Embodiment 4.

[0046] Example 7 The raw material ratio for preparing the polymer electrolyte is shown in Table 7. A mixed electrolyte solution of lithium salt and solvent is prepared in a glove box filled with argon. After adding the monomers used to form the polymer matrix and the in-situ curing initiator, the solution is injected into a lithium-ion battery containing positive and negative electrode materials and a battery separator (porous support material) after complete dissolution. The solution is placed at 80°C for in-situ polymerization. After 10 hours, the desired polymer electrolyte lithium-ion battery is obtained.

[0047] Table 7

[0048] Taking the polymer electrolyte obtained in this embodiment as an example, when used as a lithium ion battery electrolyte, the electrochemical performance is similar to that of Embodiment 4.

[0049] Examples 1-7 show that the polymer matrix involved in the present invention can be homopolymerized or copolymerized by an in-situ solidification method to prepare a high-performance polymer electrolyte. This preparation method is not only simple to operate, but also has higher safety than traditional liquid electrolytes. In the application of lithium-ion batteries, the polymer electrolyte exhibits excellent electrochemical properties, especially in the electrochemical window, which is close to 5V or above 5V, and has outstanding performance in terms of interface stability and ion transmission efficiency.

[0050] Specifically, the comparative experiments of Examples 1-3 and 4-7 show that when the mass ratio of polymer skeleton monomers to polymer functional monomers is controlled between 1:1 and 1:2, the electrochemical window of the prepared polymer electrolyte is significantly improved, reaching above 5.4V. This result shows that within this ratio range, the performance of the polymer electrolyte is even better. By regulating the polymerization reaction of the polymer matrix, the obtained polymer electrolyte can participate in the construction of a solid electrolyte interface (SEI film) with stronger mechanochemical stability. This interface can not only effectively inhibit the further decomposition of the electrolyte, but also promote the lithium ion (Li ⁺ ) for fast transfer on the interface.

[0051] As a preferred example, the polymer electrolyte prepared by the in-situ curing method of Example 1 is simple to prepare, has high room temperature ionic conductivity, and has an oxidative decomposition potential of >5.3V. The functional monomer helps to form a highly stable SEI film rich in inorganic components at the positive electrode and lithium metal / electrolyte interface, thereby improving the stability of the electrode / electrolyte interface and inhibiting the growth of lithium dendrites, thereby greatly improving the mechanical properties and safety performance. The lithium-ion battery assembled using the polymer electrolyte of the present invention with lithium metal as the negative electrode and the ternary 811 material as the positive electrode can be charged at 0.5 C (1C=200 mAh g -1 After 400 cycles at a current density of 1.5 200V, it still has a high capacity retention rate and has excellent cycle stability. It can be used in battery systems such as high-voltage lithium-ion batteries, high-energy lithium-ion batteries, and high-safety lithium-ion batteries.

[0052] Therefore, the polymer electrolyte prepared by the present invention has the following significant advantages: Higher electrochemical stability window: The electrochemical window reaches above 5.3V, which significantly improves the operating voltage range of the battery and is suitable for high-voltage lithium-ion battery systems. Lower interface transmission energy barrier: By optimizing the ratio of polymer skeleton monomers to functional monomers, the energy barrier of lithium ions in the interface transmission process is effectively reduced, and the ion transmission efficiency is improved. Excellent cycle stability and rate performance: In lithium-ion batteries, the polymer electrolyte exhibits good cycle stability and high-rate charge and discharge performance, which can meet the application requirements of high energy density and high power density.

[0053] In summary, the polymer electrolyte prepared by the in-situ curing method of the present invention is not only superior to the traditional liquid electrolyte in terms of safety, but also shows significant advantages in electrochemical performance. Its high electrochemical window, low interface transport energy barrier and excellent cycle stability make it have a wide range of application prospects in high-performance lithium-ion batteries.

[0054] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A polymer electrolyte with high interfacial stability, characterized in that: The invention comprises a polymer matrix, a porous support material, a lithium salt, a solvent and an initiator, wherein the polymer matrix is ​​formed by an in-situ copolymerization reaction of a methacrylate polymer monomer as a rigid skeleton monomer and a methacrylate polymer monomer with a functional group as a functional monomer; and the polymer electrolyte comprises, by mass percentage, 10-80% of the polymer matrix, 4%-60% of the porous support material, 10-80% of the lithium salt and the solvent, and 0.01%-1% of the initiator.

2. The highly interfacially stable polymer electrolyte according to claim 1, characterized in that: The methacrylate polymer monomer is one or both of glycidyl methacrylate and methyl methacrylate; the methacrylate polymer monomer with functional groups is a mixture of isocyanoethyl methacrylate and trifluoroethyl methacrylate.

3. The highly interfacially stable polymer electrolyte according to claim 1, characterized in that: In the polymer matrix, the mass ratio of the rigid skeleton monomer to the functional monomer is 1:1-2.

4. The highly interfacially stable polymer electrolyte according to claim 1, characterized in that: The porous supporting material is one of a polypropylene non-woven membrane, a glass fiber non-woven membrane, a cellulose non-woven membrane, and a polyethylene non-woven membrane.

5. The highly interfacially stable polymer electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium trifluoromethanesulfonate.

6. The highly interfacially stable polymer electrolyte according to claim 1, characterized in that: The solvent is one or more of ethyl methyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and vinylene carbonate.

7. The highly interfacially stable polymer electrolyte according to claim 1, characterized in that: The initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate and benzoyl peroxide.

8. The highly interfacially stable polymer electrolyte according to claim 1, characterized in that: The solvent accounts for 20% to 80% of the mass of the lithium salt and the solvent.

9. A method for preparing a polymer electrolyte with high interfacial stability as claimed in any one of claims 1 to 8, characterized in that: The following steps are involved: S1, mixing monomers, lithium salt and solvent used to form a polymer matrix into a uniform solution; S2, adding an initiator to the above solution to obtain a mixed solution; S3, placing the porous support material between the positive and negative electrodes of the lithium-ion battery, and then injecting the prepared mixed solution into the lithium-ion battery; S4, generating the polymer electrolyte with high interface stability through in-situ solid-state reaction at 30-60°C for 3-24h.

10. Use of the highly interfacially stable polymer electrolyte according to any one of claims 1 to 8 or the highly interfacially stable polymer electrolyte prepared by the method according to claim 9 in preparing a lithium ion battery.

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