Polymer composite electrolyte membrane, and preparation method and application thereof

Abstract

The application relates to a polymer composite electrolyte film and a preparation method and application thereof, raw materials comprising 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); and the structural formula of the additive is shown in the following formula I. The polymer composite electrolyte film obtained by the application has higher lithium negative electrode stability, larger limit current and ionic conductivity, and significantly improves the cycle stability and coulomb efficiency of a lithium battery.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of electric vehicles and portable electronic devices, there is an increasing demand for energy storage devices with high energy density, high safety and long cycle life. 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-state electrolytes are widely studied due to their good flexibility, excellent interface compatibility and easy processing.

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

[0004] As for the current technology, the widely used additive in PEO is plasticizer, which can effectively reduce the crystallinity of PEO and improve its ionic conductivity to a certain extent. Typical representatives include succinonitrile (SN), carbonate, polyethylene glycol, etc. However, such additives either have inherent unstable interface (SEI) with lithium negative electrode or easily lead to degradation of electrolyte mechanical properties, reducing stability. In addition, existing plasticizer additives have single function and insufficient interface optimization ability for negative electrode electrolyte, so there are common problems of low cycle stability and coulombic efficiency, which cannot be applied to all-solid-state lithium batteries. SUMMARY

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

[0006] To achieve the above technical purpose, the technical solution provided by the present application is:

[0007] In a first aspect, the present application provides a polymer composite electrolyte membrane, the raw materials of which 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); and the structure of the additive is shown in the following formula I:

[0008]

[0009] I

[0010] wherein, ring A is selected from a benzene ring, , or , X comprises a halogen atom, Y comprises oxygen, sulfur, nitrogen, phosphorus or arsenic, R1-R7 are each independently selected from a hydrogen element, a halogen atom, a cyano group, an alkyl chain, a saturated ester, an unsaturated ester, a substituted ether, an alicyclic hydrocarbon, an aromatic ring, a substituted aromatic ring or an aromatic heterocyclic ring, and Z comprises oxygen, sulfur, nitrogen or arsenic.

[0011] In a second aspect, the present application provides a preparation method of a polymer composite electrolyte film, comprising the following steps: (1) dissolving a polymer, a lithium salt and an additive in a solvent in a proportion, and stirring uniformly to obtain a mixed solution; (2) casting a film after the mixed solution is left to a bubble-free state, and obtaining the polymer composite electrolyte film after drying.

[0012] In a third aspect, the present application provides a lithium battery comprising the above polymer composite electrolyte film.

[0013] In a fourth aspect, the present application provides an application of an additive in the preparation of a polymer composite electrolyte film; the additive is shown as formula I.

[0014] Compared with the prior art, the present application has the following beneficial effects:

[0015] The additive used in the present application is a green and environmentally friendly multifunctional molecular additive. The additive mediates an electrochemical reaction to generate a stable electrolyte interface layer, and inhibits the side reaction of the lithium negative electrode interface. The obtained polymer composite electrolyte film has high lithium negative electrode stability, large limiting current and ionic conductivity, significantly improves the cycle stability and coulombic efficiency of the lithium battery, and the assembled lithium symmetric battery can be stably cycled for more than 4000 hours with a coulombic efficiency of more than 99%. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a test diagram of the ionic conductivity of the composite electrolyte film obtained from the present application example 57 and the comparative example 1 assembled in a stainless steel || stainless steel battery;

[0017] Figure 2 is a test diagram of the cycle stability of the composite electrolyte film obtained from the present application example 29 and the comparative example 1 assembled in a lithium || lithium symmetric battery;

[0018] Figure 3 is a comparison diagram of the 1C rate performance of the composite electrolyte film obtained from the present application example 29 and the comparative example 1 assembled in a lithium iron phosphate battery;

[0019] Figure 4 is a comparison diagram of the limiting current of the composite electrolyte film obtained from the present application example 39 and the comparative example 1 assembled in a lithium || lithium symmetric battery. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely intended to explain the present application and not to limit the present application.

[0021] In order to solve the problems of low cycle stability and low coulomb efficiency of the electrolyte membrane in the prior art, the present application provides a polymer composite electrolyte membrane, a preparation method and application thereof. The electrolyte can realize uniform deposition of lithium and ultra-long lithium negative electrode cycle time, and can be used in lithium metal batteries to effectively improve the cycle stability and coulomb efficiency of the batteries.

[0022] In a first aspect, the present application provides a polymer composite electrolyte membrane, raw materials of which 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); and the additive has a structural formula as shown in the following Formula I:

[0023]

[0024] I

[0025] wherein ring A is selected from a benzene ring, , or X includes a halogen atom, Y includes oxygen, sulfur, nitrogen, phosphorus or arsenic, R1-R7 are each independently selected from a hydrogen element, 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 heterocyclic ring, and Z includes oxygen, sulfur, nitrogen or arsenic.

[0026] Preferably, the solvent includes at least one of dimethyl sulfoxide, N-methyl pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, chloroform, acetonitrile, water and acetone; and the mass-volume ratio of the polymer and the solvent is 1g:(1-100)mL.

[0027] 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).

[0028] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium sulfide (Li2S), lithium perchlorate (LiClO4), lithium iodide (LiI), and lithium hexafluoroarsenate (LiAsF6).

[0029] 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 atom, cyano group, C10 or less alkyl chain, saturated or unsaturated ester, substituted sulfide, alicyclic hydrocarbon, aromatic hydrocarbon ring, substituted aromatic hydrocarbon ring, or aromatic heterocyclic ring.

[0030] Preferably, the additive specifically includes one or more of the following compounds shown in Formula 1-Formula 66:

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050] In a second aspect, the present application provides a method for preparing a polymer composite electrolyte membrane, comprising the following steps:

[0051] (1) dissolving the polymer, lithium salt and additive in the solvent in proportion, and stirring to obtain a mixed solution;

[0052] (2) After the mixed solution is allowed to stand until there are no bubbles, it is cast into a membrane and dried to obtain a polymer composite electrolyte membrane.

[0053] Preferably, in step (1), the stirring time is 12 to 48 hours and the temperature is 55 to 60°C.

[0054] Preferably, in step (2), the drying is carried out by vacuum drying, the drying temperature is 25-80℃, and the drying time is 12-60h.

[0055] Thirdly, the present invention provides a lithium battery comprising the polymer composite electrolyte membrane as described above.

[0056] Fourthly, the present invention provides an application of an additive in the preparation of a polymer composite electrolyte membrane; the additive is shown in Formula I.

[0057] Preferably, the additives include one or more of the compounds shown in Formulas 1 to 66.

[0058] More preferably, the additive includes one or more of the compounds shown in Formulas 1-3, 5-30, and 32-66.

[0059] The main mechanism of action and advantages of this invention are as follows:

[0060] (1) The additive used in this invention is a green and environmentally friendly multifunctional molecular organic additive. It not only plays the traditional role of plasticizing and improving ionic conductivity, but also has a lower LUMO energy level than other components in the electrolyte. This characteristic allows the organic additive to preferentially participate in the reaction on the positive electrode surface to generate LiF and Li x S x With high-quality SEI components, the formation of the SEI layer not only reduces the direct contact between the electrolyte and the electrode but also effectively suppresses the growth of lithium dendrites, thereby improving battery safety and cycle stability. Therefore, batteries assembled using this polymer electrolyte membrane exhibit higher ionic conductivity and more stable full-cell long-cycle performance compared to traditional PEO-based polymer solid-state batteries.

[0061] (2) This invention provides a polymer composite electrolyte membrane, which is rich in LiF and Li by means of additives. x S x A stable SEI layer with high-quality SEI components.

[0062] (3) The ion conductivity of the stainless steel | stainless steel battery assembled by the polymer composite electrolyte film prepared by the method is generally higher than that of the stainless steel | stainless steel battery assembled by the pure PEO-based polymer solid electrolyte, the long cycle performance of the lithium | lithium symmetric battery assembled is generally higher than that of the lithium | lithium symmetric battery assembled by the pure PEO-based polymer solid electrolyte, and the limiting current performance of the lithium | lithium symmetric battery assembled is generally higher than that of the lithium | lithium symmetric battery assembled by the pure PEO-based polymer solid electrolyte.

[0063] (4) The functional molecular additive provided by the application has the effect of realizing multiple purposes with one component; in addition, the molecule does not contain toxic heavy metal elements, the synthesis method is reliable, and is green and friendly to the environment.

[0064] (5) The method has simple steps and low cost, and is conducive to industrialization.

[0065] The application will be further described in detail below through specific examples. The raw materials and equipment used in the application are conventional raw materials and equipment in the art unless otherwise specified; the methods used in the application are conventional methods in the art unless otherwise specified. The synthesis method of the additive in the application is described in the paper Chem. Sci., 2020, 11, 3048-3053.

[0066] Example 1

[0067] A preparation method of a polymer composite electrolyte film, comprising the following steps:

[0068] (1) 0.25 g of PEO (molecular weight 1 million), 0.1 g of LiTFSI and 50 mg of an additive (a compound represented by Formula 1) are dissolved in 13 mL of acetonitrile solvent, and stirred for 24 h to obtain a uniform polymer electrolyte mixed solution.

[0069] (2) The polymer electrolyte mixed solution is left to a bubble-free state, poured into a polytetrafluoroethylene mold, and after vacuum drying at 25°C for 48 hours, the polymer composite electrolyte film is taken out.

[0070] Examples 2-66

[0071] The difference between Example 1 and the present application is that the additive is replaced by the compound represented by Formula 2-Formula 66, and the other steps and conditions are the same as those of Example 1.

[0072] Comparative Example 1

[0073] 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.

[0074] Performance test

[0075] 1. Stainless Steel || Stainless Steel Battery Testing:

[0076] The composite electrolyte membrane samples (100 μm thick) obtained in Example 57 (with the additive being the compound shown in Formula 57) and Comparative Example 1 were assembled into stainless steel / stainless steel batteries by adding stainless steel sheets with a diameter of 15.8 mm at both ends. Electrochemical performance was tested at 30–80°C. All assembly conditions were consistent between Comparative Example 1 and Example 57. The results are shown in [Figure 1]. Figure 1 .

[0077] like Figure 1 As shown, at temperatures ranging from 30 to 80°C, the ionic conductivity of the battery assembled in Example 57 is significantly higher than that of Comparative Example 1. This demonstrates that the polymer electrolyte membrane with added additives exhibits better ionic conductivity.

[0078] 2. Long-cycle performance test of lithium-ion symmetric batteries:

[0079] Lithium sheets with a diameter of 12 mm were added to both ends of the composite electrolyte membrane samples (100 μm thick) obtained in Example 29 (additive being the compound shown in Formula 29) and Comparative Example 1 to assemble lithium||lithium symmetric batteries, and electrochemical performance was tested at 60°C. All assembly conditions were consistent with those in the Comparative Example and the Example; the results are shown in [Figure 1]. Figure 2 .

[0080] like Figure 2 As shown, at a current density of 0.1 mA cm⁻¹ -2 And the deposition capacity is 0.1 mAh cm⁻¹ -2 Under the same test conditions, the symmetrical battery assembled in Comparative Example 1 short-circuited rapidly after about 100 hours, while the symmetrical battery assembled in Example 29 could cycle stably for more than 4000 hours. This shows that the polymer electrolyte membrane of the present invention can effectively suppress lithium dendrite growth and improve battery cycle stability.

[0081] 3. Lithium iron phosphate battery testing:

[0082] Lithium iron phosphate was used as the positive electrode, lithium metal sheet as the negative electrode, and a LiFePO4||SPE|| lithium full cell was assembled using the composite electrolyte membrane (100 μm thick) obtained in Example 29 (with the additive being the compound shown in Formula 29) and Comparative Example 1. Electrochemical performance was tested at 60 °C. All assembly conditions were consistent with those in the comparative example and the examples. The results are shown in […]. Figure 3 .

[0083] like Figure 3As shown, under the test conditions of 1C, the capacity of Comparative Example 1 rapidly decreased to zero after 300 cycles; while Example 29 remained stable after 1000 cycles, and its coulombic efficiency was greater than 99%. This indicates that the lithium iron phosphate full battery composed of the polymer composite electrolyte membrane of the present invention has better battery performance.

[0084] 4. Limiting Current Test

[0085] Lithium-ion batteries with a diameter of 10 mm were assembled by adding lithium sheets to both ends of the composite electrolyte membrane samples (100 μm thick) obtained in Example 39 (additive being the compound shown in Formula 39) and Comparative Example 1. Electrochemical performance was tested at 60°C. All assembly conditions were consistent with those in the Comparative Example and the Example, and the charge / discharge current density was 0.1 mA cm⁻¹. -2 ~2 mA cm -2 All assembly conditions were consistent, and the results are shown in Table 1 and... Figure 4 As shown.

[0086] Table 1. Limiting current of lithium-symmetric batteries assembled from composite electrolyte membranes obtained in Examples 1-66.

[0087]

[0088] Note: The serial numbers in Table 1 are the corresponding compound structural formula numbers.

[0089] As shown in Table 1, the limiting current of the lithium symmetric battery assembled with the composite electrolyte membrane obtained in this invention can reach 0.2–1.5 mA cm⁻¹. -2 Furthermore, a limiting current of 0.8 mA cm⁻¹ can be preferably used. -2 The compounds listed above are used as additives, such as one or more of the following: Formula 1, Formula 3, Formula 7, Formula 11, Formula 16-19, Formula 24, Formula 26-30, Formula 33-35, Formula 37-41, Formula 45-47, Formula 49-54, Formula 56-59, and Formula 61-65.

[0090] like Figure 4 As shown, under the test conditions, the symmetric cell assembled in Comparative Example 1 rapidly short-circuited due to uneven lithium deposition and uncontrolled dendrite growth (at 0.4 mA cm⁻¹). -2 In contrast, the symmetrical cell assembled in Example 39 can cycle stably at a higher current density (at 1.2 mA cm⁻¹). -2 (Time). This demonstrates that the lithium symmetric battery assembled with the composite electrolyte membrane obtained in this invention can achieve a larger limiting current.

[0091] From the above, the polymer composite electrolyte film prepared by the application comprises a polymer, a lithium salt and an organic molecular additive. The additive preferentially participates in the reaction to generate a stable electrolyte interface layer and inhibit the side reaction of the lithium negative electrode interface. The polymer composite electrolyte film has high lithium negative electrode stability, large limiting current and ionic conductivity, significantly improves the cycle performance and safety of the lithium metal battery, and the assembled lithium battery has good cycle performance and rate performance. The preparation method of the application is simple, low in cost, compatible with the existing industrial production process, conducive to industrialization, and has good application prospect.

[0092] The specific embodiments of the application described above do not constitute a limitation on the scope of protection of the application. Any various other corresponding changes and modifications made according to the technical concept of the application should be included in the scope of protection of the claims of the application.

Claims

1. A polymer composite electrolyte membrane, characterized by, 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 additive has a structural formula as shown in the following formula I: I wherein ring A is selected from a benzene ring, or X is fluorine, Y is oxygen or sulfur, R1-R7 are each independently selected from a hydrogen element, 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 heterocyclic ring, and Z is oxygen or sulfur; The polymer is polyethylene oxide.

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

3. The polymer composite electrolyte film according to claim 1, characterized by, The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium sulfide, lithium perchlorate, lithium iodide and lithium hexafluoroarsenate.

4. The polymer composite electrolyte membrane according to claim 1, characterized by, The additive specifically includes one or more of the following compounds as shown in the formula: 。 5. The method for preparing a polymer composite electrolyte membrane according to any one of claims 1 to 4, wherein The method comprises the following steps: (1) dissolving the polymer, the lithium salt and the additive in the solvent in proportion, stirring uniformly to obtain a mixed solution; (2) pouring and casting a film after the mixed solution is left to be free of air bubbles, and obtaining the polymer composite electrolyte film after drying.

6. The production method according to claim 5, wherein In step (1), the stirring time is 12-48h and the stirring temperature is 55-60℃; In step (2), the drying is performed by vacuum drying, the drying temperature is 25-80℃, and the drying time is 12-60h.

7. A lithium battery, characterized by The method comprises the following steps:

8. Use of an additive in the preparation of a polymer composite electrolyte membrane, characterized in that, The additive is shown in the formula I: I wherein ring A is selected from a benzene ring, or X is fluorine, Y is oxygen or sulfur, R1-R7 are each independently selected from a hydrogen element, 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 heterocyclic ring, and Z is oxygen or sulfur; The polymer is polyethylene oxide.

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