A PVDF-based organic-inorganic composite polymer solid electrolyte and its preparation method and application

Abstract

The present invention belongs to the field of solid electrolytes, and in particular to a PVDF-based organic-inorganic composite polymer solid electrolyte and its preparation method and application. The solid electrolyte includes PVDF, a lithium salt, an active filler and an organic additive, wherein the mass ratio of PVDF to lithium salt is (1-20): 1, the mass ratio of the total mass of PVDF and lithium salt to the active filler is (3-30): 1, the mass ratio of the total mass of PVDF and lithium salt to the organic additive is (2-20): 1, and the organic additive is a hydrazine compound. The present invention introduces hydrazine-based organic small molecule additives to effectively improve the ionic conductivity of PVDF-based organic-inorganic composite solid electrolytes at near room temperature. Small organic molecules and lithium salts form a high-performance interface layer in situ, significantly improving the interfacial compatibility of organic-inorganic composite solid electrolytes and lithium metal, and improving the mechanical strength of organic-inorganic composite solid electrolytes.

Description

Technical Field

[0001] The present invention belongs to the field of solid electrolytes, and in particular relates to a PVDF-based organic-inorganic composite polymer solid electrolyte and a preparation method and application thereof. Background Art

[0002] Solid-state electrolytes have been a research hotspot in battery technology in recent years. Compared to liquid electrolytes, they offer greater safety and stability. Currently, solid-state electrolytes are primarily classified into three types: polymer solid electrolytes, sulfide solid electrolytes, and oxide solid electrolytes.

[0003] Polymer solid electrolytes use a polymer as a matrix and conduct ions through lithium salts. These electrolytes have good flexibility and processability, making them suitable for fabricating thin, flexible, and bendable solid-state batteries. However, the ionic conductivity of polymer solid electrolytes is relatively low, and their performance is easily affected at high temperatures, which limits their application in high-temperature environments. Polyvinylidene fluoride (PVDF) polymer organic-inorganic composite solid electrolytes suffer from low conductivity, large interfacial impedance, and low critical current density. Polymer electrolytes primarily conduct lithium ions through the movement of chain segments in the amorphous region. To reduce crystallinity and improve ionic conductivity, commonly used methods or strategies include crosslinking, forming block copolymers, adding plasticizers, and introducing inorganic fillers. Among all these attempts, dispersing inorganic fillers in a polymer matrix to synthesize organic / inorganic composite solid electrolytes has attracted particular attention. This is because this composite approach can not only effectively improve ionic conductivity but also, to a certain extent, enhance the mechanical properties and thermal stability of the electrolyte.

[0004] In addition, by adding ionic plastic crystals, reducing the crystallinity of the polymer can also improve its lithium ion conductivity. Chinese patent document CN114204118A discloses a method for preparing a PVDF-based composite solid electrolyte, which uses the plastic crystal compound succinonitrile to reduce the crystallinity of the polymer and improve the ionic conductivity. The composite solid electrolyte product has high ionic conductivity and a wide electrochemical window as well as good mechanical properties and thermal stability. However, the addition of ionic plastic crystals is to utilize the "holes" in the lattice of the ionic plastic crystal that move with the rotation of molecules or ions, so that the plastic crystal has a higher lithium ion conductivity, but has the disadvantages of large interface resistance and low mechanical properties. Summary of the Invention

[0005] In order to solve the shortcomings of polyvinylidene fluoride (PVDF) polymer organic-inorganic composite solid electrolytes in the prior art, such as low conductivity, large interfacial impedance, poor mechanical properties, and low critical current density, the present invention provides a preparation and application of a PVDF-based organic-inorganic composite polymer solid electrolyte.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A PVDF-based organic-inorganic composite polymer solid electrolyte comprises PVDF, a lithium salt, an active filler and an organic additive, wherein the mass ratio of PVDF to the lithium salt is (1-20):1, the mass ratio of the total mass of PVDF and the lithium salt to the active filler is (3-30):1, and the mass ratio of the total mass of PVDF and the lithium salt to the organic additive is (2-20):1, and the organic additive is a hydrazine compound.

[0008] Preferably, the mass ratio of the total mass of PVDF and lithium salt to the active filler is (3-14):1, and the mass ratio of the total mass of PVDF and lithium salt to the organic additive is (2-5):1. More preferably, the mass ratio of PVDF to lithium salt is 3:1, the mass ratio of the total mass of PVDF and lithium salt to the active filler is 4:1, and the mass ratio of the total mass of PVDF and lithium salt to the organic additive is 3:1.

[0009] Preferably, the lithium salt includes one or more of LiFSI, LiTFSI, LiBOB, LiODFB, LiBF4, LiPO2F2, and LiAsF6, and more preferably LiPO2F2.

[0010] Preferably, the active filler includes one or more of lithium lanthanum zirconium tantalum oxide (LLZTO), lithium indium chloride (Li3InCl6), lithium yttrium chloride (Li3YCl6), lithium zirconium chloride (Li2ZrCl6), lithium tantalum chloride (LiTaCl6), lithium aluminum titanium phosphide (LATP), lithium aluminum germanium phosphide (LGTP), and lithium phosphorus sulfur chloride (LPSCl). More preferably, Li2ZrCl6 and LATP are used, and even more preferably, LATP is used.

[0011] Preferably, the organic additives include 3,5-dimethylphenylhydrazine hydrochloride, 2-nitrobenzylhydrazine, diphenylcarbazide, 3-cyanophenylhydrazine hydrochloride, N,N'-diacetylhydrazine, stearylhydrazine, 4-aminobenzoylhydrazine, pyrazine-2-hydrazine, 3,5-bis(trifluoromethyl)phenylhydrazine hydrochloride, 3-fluorobenzoylhydrazine, 3-(trifluoromethyl)phenylhydrazine hydrochloride, dimethylhydrazine pyridine, 1,1-dimethylhydrazine hydrochloride, crotonaldehyde 2,4-dinitro Phenylhydrazine, thiocarbohydrazide, 2-furoylhydrazine, 2,2-biphenyl-1-picrylhydrazine, 4-trifluoromethylphenylhydrazine hydrochloride, aloxidazine, (α,α,α,2,3,5,6-heptafluoro-o-tolyl) hydrazine, p-tolylhydrazine, oxalic acid bis(benzylidenehydrazine), 4-cyanophenylhydrazine hydrochloride, nicotinic acid hydrazide, maleic acid dihydrazide, 2-hydrazineylethanol, 3,4-dimethoxyphenylhydrazine hydrochloride, 2,3,5,6-tetrafluorophenylhydrazine, 2-naphthoylhydrazine. Further preferably, the organic additive is crotonaldehyde 2,4-dinitrophenylhydrazine, (α,α,α,2,3,5,6-heptafluoro-o-tolyl) hydrazine, and further preferably (α,α,α,2,3,5,6-heptafluoro-o-tolyl) hydrazine.

[0012] The present invention also provides a method for preparing the above-mentioned solid electrolyte, comprising weighing PVDF and LiTFSI according to a mass ratio, adding LLZTO powder and 3,5-dimethylphenylhydrazine hydrochloride, adding a solvent, and stirring under heating to obtain a uniformly mixed slurry, casting the slurry into a film, and vacuum drying to obtain the obtained product.

[0013] Preferably, the solid content of the slurry is 20-40%.

[0014] Preferably, the organic solvent includes one or more of acetonitrile, dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylformamide, and the like.

[0015] Preferably, the heating temperature is 20-150°C, preferably 35-85°C.

[0016] Preferably, the stirring time is 8 to 60 hours, preferably 8 to 30 hours.

[0017] Preferably, the temperature used for vacuum drying is 20-100° C., preferably 40-90° C.; the time used for vacuum drying is 2-48 hours, preferably 8-30 hours.

[0018] The present invention also provides an application of a PVDF-based organic-inorganic composite polymer solid electrolyte in the preparation of a lithium electronic battery.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention improves battery performance by adding varying amounts of organic small molecule additives to a polyvinylidene fluoride (PVDF)-based organic-inorganic composite solid electrolyte. Hydrazine-based organic small molecule compounds have strong electron-donating properties and extremely strong reducing properties. The extremely strong electron-donating properties can enhance the dissociation of lithium salts, thereby improving the lithium ion conductivity of the solid electrolyte. The extremely strong reducing properties can induce the uniform deposition of lithium ions and form a stable interface layer rich in Li3N-LiF at the interface, effectively improving the interface stability.

[0021] (2) The introduction of organic small molecule additives in the present invention can effectively improve the ionic conductivity of PVDF-based organic-inorganic composite solid electrolytes at near room temperature (up to 1.3×10 -3 S cm -1 The introduction of organic small molecules forms a high-performance interface layer with the lithium salt in situ, significantly improving the interfacial compatibility between the organic-inorganic composite solid electrolyte and lithium metal, reducing the interfacial impedance to below 20Ω. The mechanical strength of the organic-inorganic composite solid electrolyte is improved to over 6.5MPa by introducing lithium salt additives and organic small molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a test graph of the lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 1;

[0023] Figure 2 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 1;

[0024] Figure 3 This is a test graph of lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 2;

[0025] Figure 4 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 2;

[0026] Figure 5 This is a test graph of lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 3;

[0027] Figure 6 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 3;

[0028] Figure 7 This is a test graph of lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 4;

[0029] Figure 8This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 4;

[0030] Figure 9 This is a test graph of the lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 5;

[0031] Figure 10 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 5;

[0032] Figure 11 This is a test graph of lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 6;

[0033] Figure 12 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 6;

[0034] Figure 13 This is a test graph of lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 7;

[0035] Figure 14 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 7;

[0036] Figure 15 This is a test graph of lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 8;

[0037] Figure 16 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 8;

[0038] Figure 17 1 is a test graph of the lithium ion conductivity of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 1;

[0039] Figure 18 This is a graph showing the interfacial impedance of the PVDF-based organic-inorganic composite polymer electrolyte membrane obtained in Example 1. DETAILED DESCRIPTION

[0040] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] In the following examples, unless otherwise specified, all reagents used were commercially available reagents, and the PVDF used was Arkema PVDF761.

[0042] All testing methods and means used are conventional in the field. Ionic conductivity and interfacial impedance were tested at room temperature (25°C) using an electrochemical workstation. Full-cell performance was tested at room temperature (25°C) using a solid-state battery with lithium iron phosphate as the positive electrode. Mechanical strength was tested at room temperature (25°C) using a nanoindenter.

[0043] Example 1

[0044] 3g PVDF and 1g LiTFSI were weighed according to the mass ratio of PVDF:LiTFSI = 3:1, and then 0.133g LLZTO (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) powder and 0.2g of 3,5-dimethylphenylhydrazine hydrochloride. DMSO was added as a solvent and heated and stirred at 35°C for 15 hours to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 55°C for 20 hours to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested and found to be 1.7×10 -4 S / cm( Figure 1 ), and its interface impedance is 100.5Ω( Figure 2 ), the critical current density is 0.4 mA / cm 2 , and its elastic simulation can reach 4.5MPa. After 100 cycles at 0.5C, the capacity retention rate reaches 81%.

[0045] Example 2

[0046] 5g of PVDF and 0.25g of LiBOB were weighed at a mass ratio of PVDF:LiBOB = 20:1, followed by the addition of 1.75g ​​of Li3YCl6 powder and 0.525g of thiocarbazide. NMP was added as a solvent, and the mixture was heated and stirred at 55°C for 25h to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 45°C for 24h to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested, and its lithium ion conductivity was 2.9×10 -4 S / cm( Figure 3 ), and its interface impedance is 90.7Ω( Figure 4 ), the critical current density is 0.7 mA / cm 2 , and its elastic simulation can reach 5.2MPa. After 100 cycles at 0.5C, the capacity retention rate reaches 86%.

[0047] Example 3

[0048] 2g PVDF and 2g LiBF4 were weighed according to the mass ratio of PVDF:LiBF4=1:1, and then 0.4g Li3YCl6 powder and 2g stearic hydrazide were added. NMP was added as a solvent, and the mixture was heated and stirred at 85°C for 8h to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 85°C for 12h to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested, and its lithium ion conductivity was 5.1×10 -4 S / cm( Figure 5 ), and its interface impedance is 121.7Ω( Figure 6 ), the critical current density is 0.9 mA / cm 2 , and its elastic simulation can reach 5.9MPa. After 200 cycles at 0.5C, the capacity retention rate is 81.2%.

[0049] Example 4

[0050] 10g of PVDF and 0.5g of LiPO2F2 were weighed at a mass ratio of PVDF:LiPO2F2 = 20:1, and then 0.75g of Li2ZrCl6 powder and 2.1g of crotonaldehyde 2,4-dinitrophenylhydrazine were added. DMAC was added as a solvent, and the mixture was heated and stirred at 75°C for 30h to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 90°C for 8h to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested, and its lithium ion conductivity was 6.7×10 -4 S / cm( Figure 7 ), and its interface impedance is 32.4Ω( Figure 8 ), the critical current density is 1.2 mA / cm 2 , and its elastic simulation can reach 6.5MPa. After 150 cycles at 0.5C, the capacity retention rate reaches 89%.

[0051] Example 5

[0052] 3g PVDF and 1g LiPO2F2 were weighed according to the mass ratio of PVDF:LiAsF6=3:1, and then 1g LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3,) powder and 1.33g (α,α,α,2,3,5,6-heptafluoro-o-tolyl)hydrazine were added. DMAC was added as a solvent and heated and stirred at 65°C for 24 hours to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 40°C for 16 hours to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested and found to be 1.3×10-3 S / cm( Figure 9 ), and its interface impedance is 14.3Ω( Figure 10 ), the critical current density is 1.5 mA / cm 2 , and its elastic simulation can reach 7.7MPa. After 200 cycles at 0.5C, the capacity retention rate reaches 92%.

[0053] Example 6

[0054] 3g PVDF and 1g LiPO2F2 were weighed in a mass ratio of PVDF:LiAsF6=3:1, followed by the addition of 1g LATP powder and 2g (α,α,α,2,3,5,6-heptafluoro-o-tolyl) hydrazine. DMAC was added as a solvent, and the mixture was heated and stirred at 65°C for 24h to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 40°C for 16h to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested, and its lithium ion conductivity was 8.6×10 -4 S / cm( Figure 11 ), and its interface impedance is 31.5Ω( Figure 12 ), the critical current density is 1.1 mA / cm 2 , and its elastic simulation can reach 7.2MPa. After 200 cycles at 0.5C, the capacity retention rate reaches 85%.

[0055] Example 7

[0056] 3g of PVDF and 1g of LiPO2F2 were weighed in a mass ratio of PVDF:LiAsF6=3:1, followed by the addition of 1.33g of LATP powder and 1.33g of (α,α,α,2,3,5,6-heptafluoro-o-tolyl)hydrazine. DMAC was added as a solvent, and the mixture was heated and stirred at 65°C for 24h to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 40°C for 16h to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested, and its lithium ion conductivity was 7.1×10 -4 S / cm( Figure 13 ), and its interface impedance is 34.3Ω( Figure 14 ), the critical current density is 0.8 mA / cm 2 , and its elastic simulation test can reach 6.5MPa. Its solid-state battery with lithium iron phosphate as the positive electrode has a capacity retention rate of 80.7% after 200 cycles at 0.5C at room temperature.

[0057] Example 8

[0058] 3g of PVDF and 1g of LiPO2F2 were weighed in a mass ratio of PVDF:LiAsF6=3:1, followed by the addition of 1g of LATP powder and 1.33g of 4-trifluoromethylphenylhydrazine hydrochloride. DMAC was added as a solvent, and the mixture was heated and stirred at 65°C for 24h to obtain a uniformly mixed slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 40°C for 16h to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested, and its lithium ion conductivity was 6.4×10 -4 S / cm( Figure 15 ), and its interface impedance is 52.7Ω( Figure 16 ), the critical current density is 0.5 mA / cm 2 , and its elastic simulation test can reach 5.5MPa. Its solid-state battery with lithium iron phosphate as the positive electrode has a capacity retention rate of 72% after 200 cycles at 0.5C at room temperature.

[0059] Comparative Example 1

[0060] 3g of PVDF and 1g of LiPO2F2 were weighed at a mass ratio of PVDF:LiAsF6=3:1, and then 1g of LATP powder was added. DMAC was added as a solvent, and the mixture was heated and stirred at 65°C for 24 hours to obtain a uniform slurry. The slurry was then cast into a polytetrafluoroethylene mold and vacuum-dried at 40°C for 16 hours to obtain a PVDF-based organic-inorganic composite polymer electrolyte membrane. After cutting, its lithium ion conductivity was tested and found to be 9.1×10 -5 S / cm( Figure 17 ), and its interface impedance is 237.5Ω( Figure 18 ), the critical current density is 0.2 mA / cm 2 , and its elastic simulation test can reach 1.2MPa. Its solid-state battery with lithium iron phosphate as the positive electrode can maintain a capacity of 65% after 100 cycles at 0.5C at room temperature.

Claims

1. A PVDF-based organic-inorganic composite polymer solid electrolyte, characterized in that: The invention comprises PVDF, lithium salt, active filler and organic additive, wherein the mass ratio of PVDF to lithium salt is (1-20):1, the mass ratio of the total mass of PVDF and lithium salt to the active filler is (3-14):1, the mass ratio of the total mass of PVDF and lithium salt to the organic additive is (2-5):1, the active filler is one or more of lithium lanthanum zirconium tantalum oxide, lithium indium chloride, lithium yttrium chloride, lithium zirconium chloride, lithium tantalum chloride, lithium aluminum titanium phosphide, lithium aluminum germanium phosphide or lithium phosphorus sulfur chloride; the organic additive is a hydrazine compound, and the hydrazine compound is 3,5-dimethylphenylhydrazine hydrochloride, 2-nitrobenzylhydrazine, diphenylcarbazide, 3-cyanophenylhydrazine hydrochloride, N,N'-diacetylhydrazine, stearyl One or more of hydrazine, 4-aminobenzoic acid hydrazide, pyrazine-2-hydrazine, 3,5-bis(trifluoromethyl)phenylhydrazine hydrochloride, 3-fluorobenzoic acid hydrazide, 3-(trifluoromethyl)phenylhydrazine hydrochloride, dimethylhydrazine pyridine, 1,1-dimethylhydrazine hydrochloride, thiocarbohydrazide, 2-furocarboxylic acid hydrazide, 2,2-biphenyl-1-picrylhydrazyl, 4-trifluoromethylphenylhydrazine hydrochloride, alohydrazine, (α,α,α,2,3,5,6-heptafluoro-o-tolyl)hydrazine, p-tolylhydrazine, oxalic acid bis(benzylidenehydrazine), 4-cyanophenylhydrazine hydrochloride, nicotinic acid hydrazide, maleic acid dihydrazide, 2-hydrazinoethanol, 3,4-dimethoxyphenylhydrazine hydrochloride, 2,3,5,6-tetrafluorophenylhydrazine, and 2-naphthoic acid hydrazide.

2. The solid electrolyte according to claim 1, characterized in that The lithium salt includes one or more of LiFSI, LiTFSI, LiBOB, LiODFB, LiBF4, LiPO2F2, and LiAsF6.

3. The solid electrolyte according to claim 2, characterized in that The lithium salt is LiPO2F2.

4. A method for preparing a solid electrolyte, characterized in that: PVDF and LiTFSI are weighed according to the mass ratio, and then LLZTO powder and 3,5-dimethylphenylhydrazine hydrochloride are added. An organic solvent is added, and the mixture is stirred under heating to obtain a uniform slurry. The slurry is cast into a film and vacuum dried to obtain the film. Among them, the mass ratio of PVDF to LiTFSI is (1~20):1, the mass ratio of the total mass of PVDF and LiTFSI to LLZTO powder is (3~14):1, and the mass ratio of the total mass of PVDF and LiTFSI to 3,5-dimethylphenylhydrazine hydrochloride is (2~5):

1.

5. The preparation method according to claim 4, characterized in that The organic solvent includes one or more of acetonitrile, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidine, and N,N-dimethylformamide.

6. The preparation method according to claim 4, characterized in that The heating temperature is 20-150° C., and the stirring time is 8-60 hours; the vacuum drying temperature is 20-100° C., and the time is 2-48 hours.

7. The preparation method according to claim 6, characterized in that The heating temperature is 35-85° C., and the stirring time is 8-30 hours; the vacuum drying temperature is 40-90° C., and the time is 8-30 hours.

8. Use of the PVDF-based organic-inorganic composite polymer solid electrolyte according to any one of claims 1 to 3 or the PVDF-based organic-inorganic composite polymer solid electrolyte prepared by the method according to any one of claims 4 to 7 in the preparation of lithium electronic batteries.

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