Polymer composite electrolyte membrane and preparation method and application thereof

Abstract

The invention relates to a polymer composite electrolyte membrane as well as a preparation method and application thereof. The raw materials comprise a polymer, a lithium salt, an additive and a solvent, wherein the mass ratio of the polymer to the lithium salt to the additive is 1: (0.05-0.5): (0.01-0.5); the structural formula of the additive is shown as a formula I. The obtained polymer composite electrolyte membrane has relatively high lithium negative electrode stability and relatively large limiting current and ionic conductivity, and the cycling stability and coulombic efficiency of a lithium battery are remarkably improved. # imgabs0 # I

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and in particular to a polymer composite electrolyte membrane and a preparation method and application thereof. Background Art

[0002] With the rapid development of electric vehicles and portable electronic devices, the demand for energy storage devices with high energy density, high safety and long cycle life is becoming increasingly urgent. Lithium metal solid-state batteries have become a research hotspot for the next generation of energy storage devices due to their high theoretical energy density and excellent safety. Among them, polyethylene oxide (PEO)-based solid electrolytes have been widely studied due to their good flexibility, excellent interfacial compatibility and easy processing.

[0003] However, there are still some urgent problems to be solved in PEO-based solid electrolytes. For example: PEO has high crystallinity, which limits the migration of lithium ions, resulting in low room temperature ionic conductivity, which is difficult to meet the needs of practical applications; the interface compatibility between PEO and electrode materials is poor, resulting in large interface impedance, affecting the battery's rate performance and cycle stability; under high current density, lithium metal negative electrodes are prone to produce lithium dendrites, which pierce the electrolyte membrane and cause battery short circuit, posing a safety hazard.

[0004] As far as current technology is concerned, the additive widely used in PEO is plasticizer. The added plasticizer can effectively reduce the crystallinity of PEO and improve its ionic conductivity to a certain extent. Typical representatives include succinonitrile (SN), carbonates, polyethylene glycols, etc. However, such additives either have an inherently unstable interface (SEI) with the lithium negative electrode, or easily lead to the degradation of the mechanical properties of the electrolyte and reduce stability. In addition, the existing plasticizer additives have a single function and are insufficient in optimizing the electrolyte interface at the negative end. Therefore, there are common practical problems of low cycle stability and coulombic efficiency, and they cannot be applied to all-solid-state lithium batteries. Summary of the invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, provide a polymer composite electrolyte membrane and a preparation method and application thereof, and solve the technical problems of low cycle stability and coulombic efficiency of the electrolyte membrane in the prior art.

[0006] In order to achieve the above technical purpose, the technical solution provided by the present invention is: In a first aspect, the present invention provides a polymer composite electrolyte membrane, wherein the raw materials include a polymer, a lithium salt, an additive and a solvent; wherein the mass ratio of the polymer, the lithium salt and the additive is 1: (0.05-0.5): (0.01-0.5); the structural formula of the additive is shown in the following formula I:

[0007] I Wherein, ring A is selected from benzene ring, , or , X includes a halogen atom, Y includes oxygen, sulfur, nitrogen, phosphorus or arsenic, R1-R7 are each independently selected from hydrogen, a halogen atom, a cyano group, an alkyl chain, a saturated ester, an unsaturated ester, a substituted ether, an alicyclic hydrocarbon, an aromatic hydrocarbon ring, a substituted aromatic hydrocarbon ring or an aromatic heterocycle, and Z includes oxygen, sulfur, nitrogen or arsenic.

[0008] In a second aspect, the present invention provides a method for preparing a polymer composite electrolyte membrane, comprising the following steps: (1) dissolving a polymer, a lithium salt and an additive in a solvent in proportion, and stirring the mixture to obtain a mixed solution; (2) allowing the mixed solution to stand until there are no bubbles, and then casting the mixed solution to form a membrane, and drying the mixed solution to obtain a polymer composite electrolyte membrane.

[0009] In a third aspect, the present invention provides a lithium battery comprising the above polymer composite electrolyte membrane.

[0010] In a fourth aspect, the present invention provides an application of an additive in the preparation of a polymer composite electrolyte membrane; the additive is as shown in Formula I.

[0011] Compared with the prior art, the beneficial effects of the present invention include: The additive used in the present invention is a green, environmentally friendly, multifunctional molecular additive. The additive mediates electrochemical reactions to generate a stable electrolyte interface layer, inhibits side reactions at the lithium negative electrode interface, and enables the resulting polymer composite electrolyte membrane to have higher lithium negative electrode stability, larger limiting current and ion conductivity, and significantly improves the cycle stability and coulombic efficiency of the lithium battery. The assembled lithium symmetrical battery can be stably cycled for more than 4,000 hours, and the coulombic efficiency is greater than 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a test graph of ion conductivity of a stainless steel||stainless steel battery assembled with a composite electrolyte membrane obtained in Example 57 of the present invention and in Comparative Example 1; Figure 2 1 is a test graph of the cycle stability of a lithium||lithium symmetrical battery assembled with a composite electrolyte membrane obtained in Example 29 of the present invention and in Comparative Example 1; Figure 3 1C rate performance comparison diagram of the composite electrolyte membrane assembled lithium iron phosphate battery obtained in Example 29 of the present invention and Comparative Example 1; Figure 4 It is a comparison chart of the limiting current of the lithium||lithium symmetrical battery assembled with the composite electrolyte membrane obtained in Example 39 of the present invention and in Comparative Example 1. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0014] In view of the defects of the electrolyte membrane in the prior art, such as low cycle stability and coulombic efficiency, the present invention provides a polymer composite electrolyte membrane and a preparation method and application thereof. The electrolyte can achieve uniform deposition of lithium and ultra-long lithium negative electrode cycle time, and can be used in lithium metal batteries to effectively improve the battery cycle stability and coulombic efficiency.

[0015] In a first aspect, the present invention provides a polymer composite electrolyte membrane, wherein the raw materials include a polymer, a lithium salt, an additive and a solvent; wherein the mass ratio of the polymer, the lithium salt and the additive is 1: (0.05-0.5): (0.01-0.5); the structural formula of the additive is shown in the following formula I:

[0016] I Wherein, ring A is selected from benzene ring, , or , X includes a halogen atom, Y includes oxygen, sulfur, nitrogen, phosphorus or arsenic, R1-R7 are each independently selected from hydrogen, a halogen atom, a cyano group, an alkyl chain, a saturated ester, an unsaturated ester, a substituted ether, an alicyclic hydrocarbon, an aromatic hydrocarbon ring, a substituted aromatic hydrocarbon ring or an aromatic heterocycle, and Z includes oxygen, sulfur, nitrogen or arsenic.

[0017] Preferably, the solvent includes at least one of dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, N,N-dimethylformamide, chloroform, acetonitrile, water and acetone; the mass volume ratio of the polymer to the solvent is 1g: (1-100)mL.

[0018] Preferably, the polymer includes at least one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyurethane (PU), polyvinyl alcohol (PVA), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and propylene carbonate (PPC).

[0019] Preferably, the lithium salt comprises lithium hexafluorophosphate (LiPF 6 ), lithium difluorooxalatoborate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF 4 ), lithium sulfide (Li 2 S), lithium perchlorate (LiClO 4 ), lithium iodide (LiI) and lithium hexafluoroarsenate (LiAsF 6) at least one of.

[0020] Preferably, in the additive, X is fluorine, Y heteroatom is oxygen or sulfur, Z heteroatom is oxygen or sulfur, and R1-R7 are selected from hydrogen, halogen atoms, cyano groups, alkyl chains within C10, saturated or unsaturated esters, substituted thioethers, alicyclic hydrocarbons, aromatic hydrocarbon rings, substituted aromatic hydrocarbon rings or aromatic heterocycles.

[0021] Preferably, the additive specifically includes one or more of the compounds represented by the following formula 1 to formula 66:

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[0040] In a second aspect, the present invention provides a method for preparing a polymer composite electrolyte membrane, comprising the following steps: (1) dissolving the polymer, lithium salt and additive in a solvent in proportion, and stirring to obtain a mixed solution; (2) The mixed solution is allowed to stand until there are no bubbles, and then cast into a membrane. After drying, a polymer composite electrolyte membrane is obtained.

[0041] Preferably, in step (1), the stirring time is 12 to 48 hours and the temperature is 55 to 60°C.

[0042] Preferably, in step (2), vacuum drying is used for drying, the drying temperature is 25 to 80° C., and the drying time is 12 to 60 hours.

[0043] In a third aspect, the present invention provides a lithium battery comprising the above polymer composite electrolyte membrane.

[0044] In a fourth aspect, the present invention provides an application of an additive in the preparation of a polymer composite electrolyte membrane; the additive is as shown in Formula I.

[0045] Preferably, the additive includes one or more of the compounds represented by Formula 1-Formula 66.

[0046] Further preferably, the additive includes one or more of the compounds represented by Formula 1-Formula 3, Formula 5-Formula 30, and Formula 32-Formula 66.

[0047] The main mechanism of action and advantages of the present invention are as follows: (1) The additive used in the present invention is a green, environmentally friendly, multifunctional molecular organic additive. It not only plays a traditional plasticizing role in improving ionic conductivity, but also has a lower LUMO energy level than the other components in the electrolyte. This characteristic enables the organic additive to preferentially participate in the reaction on the positive electrode surface to generate LiF, Li x S x The formation of the SEI layer not only reduces the direct contact between the electrolyte and the electrode, but also effectively inhibits the growth of lithium dendrites, thereby improving the safety and cycle stability of the battery. Therefore, the battery assembled with this polymer electrolyte membrane has higher ionic conductivity and more stable full battery long cycle performance than traditional PEO-based polymer solid-state batteries.

[0048] (2) The present invention provides a polymer composite electrolyte membrane, which is rich in LiF and Li x S x A stable SEI layer with high-quality SEI components.

[0049] (3) The ionic conductivity of the stainless steel||stainless steel battery assembled with the polymer composite electrolyte membrane prepared by the method proposed in the present invention is generally higher than that of the stainless steel||stainless steel battery assembled with pure PEO-based polymer solid electrolyte, the long cycle performance of the assembled lithium||lithium symmetric battery is generally higher than that of the lithium||lithium symmetric battery assembled with pure PEO-based polymer solid electrolyte, and the limiting current performance of the assembled lithium||lithium symmetric battery is generally higher than that of the lithium||lithium symmetric battery assembled with pure PEO-based polymer solid electrolyte.

[0050] (4) The functional molecular additive proposed in the present invention has the function of achieving multiple uses with one component; in addition, the molecule does not contain toxic heavy metal elements, the synthesis method is reliable, and it is environmentally friendly.

[0051] (5) The method of the present invention has simple steps, low cost and is conducive to industrialization.

[0052] The present invention is further described in detail below through specific examples. The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art. The synthesis method of the additive in the present invention is described in the paper Chem. Sci., 2020, 11, 3048–3053.

[0053] Example 1 A method for preparing a polymer composite electrolyte membrane comprises the following steps: (1) Dissolve 0.25 g of PEO (molecular weight 1 million), 0.1 g of LiTFSI, and 50 mg of the additive (the compound shown in Formula 1) in 13 mL of acetonitrile solvent and stir for 24 h to obtain a uniform polymer electrolyte mixed solution.

[0054] (2) The polymer electrolyte mixed solution is allowed to stand until there are no bubbles, poured into a polytetrafluoroethylene mold, and vacuum dried at 25°C for 48 hours, and then taken out to obtain a polymer composite electrolyte membrane.

[0055] Example 2-66 The only difference from Example 1 is that the additives are replaced by the compounds represented by Formula 2-Formula 66 respectively, and the other steps and conditions are the same as Example 1.

[0056] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no additive is added to the polymer electrolyte mixed solution, and the other steps and conditions are the same as those of Example 1.

[0057] Performance Testing 1. Stainless steel || Stainless steel battery test: The composite electrolyte membrane samples (thickness 100 μm) obtained in Example 57 (the additive is the compound shown in Formula 57) and Comparative Example 1 were assembled into a stainless steel||stainless steel battery by adding stainless steel sheets with a diameter of 15.8 mm at both ends, and the electrochemical performance test was carried out at 30-80°C. All assembly conditions of Comparative Example 1 and Example 57 are the same, and the results are shown in Figure 1 .

[0058] like Figure 1 As shown, at 30-80° C., the ionic conductivity of the battery assembled from Example 57 is much higher than that of Comparative Example 1. It can be seen that the polymer electrolyte membrane with the additive has better ionic conductivity.

[0059] 2. Lithium || Lithium symmetric battery long cycle performance test: Lithium sheets with a diameter of 12 mm were added to both ends of the composite electrolyte membrane samples (thickness of 100 μm) obtained in Example 29 (the additive is the compound shown in Formula 29) and Comparative Example 1 to assemble a lithium||lithium symmetrical battery, and the electrochemical performance test was performed at 60°C. All assembly conditions of the comparative example and the example are the same, and the results are shown in Figure 2 .

[0060] like Figure 2 As shown, at a current density of 0.1 mA cm -2 and a deposition capacity of 0.1 mAh cm -2Under the test conditions of 100 hours, the symmetrical battery assembled in Comparative Example 1 quickly short-circuited in about 100 hours, while the symmetrical battery assembled in Example 29 could stably cycle for more than 4000 hours. This shows that the polymer electrolyte membrane of the present invention can effectively inhibit the growth of lithium dendrites and improve the cycle stability of the battery.

[0061] 3. Lithium iron phosphate battery test: LiFePO4 was used as the positive electrode and the lithium metal sheet was used as the negative electrode. The composite electrolyte membrane (thickness of 100 μm) obtained in Example 29 (the additive was the compound shown in Formula 29) and Comparative Example 1 was used to assemble LiFePO4. 4 ||SPE|| Lithium full battery, electrochemical performance test at 60°C, all assembly conditions of comparative example and embodiment are consistent, the results are shown in Figure 3 .

[0062] like Figure 3 As shown in the figure, under the test condition of 1C rate, the capacity of comparative example 1 rapidly decreases to zero after 300 cycles; while example 29 remains stable after 1000 cycles, and its coulombic efficiency is greater than 99%. This shows that the lithium iron phosphate full battery composed of the polymer composite electrolyte membrane of the present invention has better battery performance.

[0063] 4. Limiting current test Lithium sheets with a diameter of 10 mm were added to both ends of the composite electrolyte membrane samples (thickness 100 μm) obtained in Example 39 (the additive is the compound shown in Formula 39) and Comparative Example 1 to assemble a lithium||lithium symmetrical battery, and the electrochemical performance test was performed at 60°C. All assembly conditions of the comparative example and the example were the same, and the charge and discharge current density was 0.1 mA cm -2 ~2 mA cm -2 ; All assembly conditions are the same, the results are shown in Table 1 and Figure 4 shown.

[0064] Table 1 Limiting current of lithium symmetric battery assembled with composite electrolyte membrane obtained in Examples 1-66

[0065] Note: The serial numbers in Table 1 are the structural formula numbers of the corresponding compounds.

[0066] As shown in Table 1, the limiting current of the lithium symmetric battery assembled with the composite electrolyte membrane obtained in the present invention can reach 0.2-1.5 mA cm -2 , and preferably the limiting current is 0.8 mA cm -2The corresponding compounds above are used as additives, such as one or more of Formula 1, Formula 3, Formula 7, Formula 11, Formula 16-Formula 19, Formula 24, Formula 26-Formula 30, Formula 33-Formula 35, Formula 37-Formula 41, Formula 45-Formula 47, Formula 49-Formula 54, Formula 56-Formula 59, Formula 61-Formula 65.

[0067] like Figure 4 As shown in the figure, under the test conditions, the symmetrical battery assembled in Comparative Example 1 short-circuited rapidly (at 0.4 mA cm -2 In contrast, the symmetrical battery assembled in Example 39 can be stably cycled at a higher current density (1.2 mA cm -2 This shows that the lithium symmetric battery assembled with the composite electrolyte membrane obtained in the present invention can obtain a larger limiting current. It can be seen from the above content that the polymer composite electrolyte membrane prepared by the present invention includes polymers, lithium salts, and organic molecular additives. The additives preferentially participate in the reaction to generate a stable electrolyte interface layer, thereby inhibiting the side reactions at the lithium negative electrode interface. The polymer composite electrolyte membrane has high lithium negative electrode stability, large limiting current and ion conductivity, significantly improves the cycle performance and safety of lithium metal batteries, and the assembled lithium battery has good cycle performance and rate performance. The preparation method of the present invention is simple, low in cost, and has good compatibility with existing industrial production processes, is conducive to industrialization, and has good application prospects.

[0068] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A polymer composite electrolyte membrane, characterized in that: The raw materials include polymer, lithium salt, additive and solvent; wherein the mass ratio of polymer, lithium salt and additive is 1: (0.05-0.5): (0.01-0.5); the structural formula of the additive is shown in the following formula I: I Wherein, ring A is selected from benzene ring, , or , X includes a halogen atom, Y includes oxygen, sulfur, nitrogen, phosphorus or arsenic, R1-R7 are each independently selected from hydrogen, a halogen atom, a cyano group, an alkyl chain, a saturated ester, an unsaturated ester, a substituted ether, an alicyclic hydrocarbon, an aromatic hydrocarbon ring, a substituted aromatic hydrocarbon ring or an aromatic heterocycle, and Z includes oxygen, sulfur, nitrogen or arsenic.

2. The polymer composite electrolyte membrane according to claim 1, characterized in that The solvent comprises at least one of dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, N,N-dimethylformamide, chloroform, acetonitrile, water and acetone; The mass volume ratio of the polymer to the solvent is 1 g: (1 to 100) mL.

3. The polymer composite electrolyte membrane according to claim 1, characterized in that: The polymer includes at least one of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyurethane, polyvinyl alcohol, polyvinylidene fluoride-hexafluoropropylene copolymer and propylene carbonate.

4. The polymer composite electrolyte membrane according to claim 1, characterized in that: The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt, lithium tetrafluoroborate, lithium sulfide, lithium perchlorate, lithium iodide and lithium hexafluoroarsenate.

5. The polymer composite electrolyte membrane according to claim 1, characterized in that: In the additive, X is fluorine, Y is oxygen or sulfur, and Z is oxygen or sulfur.

6. The polymer composite electrolyte membrane according to claim 1, characterized in that: The additive specifically includes one or more of the compounds represented by the following formula 1 to formula 66: 。 7. The method for preparing a polymer composite electrolyte membrane according to any one of claims 1 to 6, characterized in that: The steps include: (1) dissolving the polymer, lithium salt and additive in a solvent in proportion, and stirring to obtain a mixed solution; (2) The mixed solution is allowed to stand until there are no bubbles, and then cast into a membrane. After drying, a polymer composite electrolyte membrane is obtained.

8. The method for preparing a polymer composite electrolyte membrane according to claim 7, characterized in that: In step (1), the stirring time is 12 to 48 hours and the stirring temperature is 55 to 60° C.; In step (2), the drying is performed by vacuum drying, the drying temperature is 25 to 80° C., and the drying time is 12 to 60 h.

9. A lithium battery, characterized in that: The invention comprises the polymer composite electrolyte membrane as claimed in any one of claims 1 to 6.

10. Use of an additive in preparing a polymer composite electrolyte membrane, characterized in that: The additive is shown in Formula I: I Wherein, ring A is selected from benzene ring, , or , X includes a halogen atom, Y includes oxygen, sulfur, nitrogen, phosphorus or arsenic, R1-R7 are each independently selected from hydrogen, a halogen atom, a cyano group, an alkyl chain, a saturated ester, an unsaturated ester, a substituted ether, an alicyclic hydrocarbon, an aromatic hydrocarbon ring, a substituted aromatic hydrocarbon ring or an aromatic heterocycle, and Z includes oxygen, sulfur, nitrogen or arsenic.

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