A gel polymer electrolyte, a preparation method and application thereof

Abstract

The application belongs to the technical field of battery electrolyte, and particularly relates to a gel polymer electrolyte and a preparation method and application thereof. The gel polymer electrolyte is prepared by in-situ polymerization, and the electrolyte is composed of monomers, a crosslinking agent, an initiator, an organic solvent and a lithium salt. The monomers are selected from fluorine-containing monomers such as trifluoroethyl acrylate and 2,2,3,3-tetrafluoropropyl methacrylate, and the crosslinking agent is selected from NH-containing crosslinking agents such as N,N'-methylene bisacrylamide and hexamethylene bisacrylamide. The fluorine-containing functional groups in the side chains of the polymer are formed in-situ to interact with lithium ions, thereby promoting the transmission of lithium ions. The NH functional groups in the main chains limit the migration of anions, thereby improving the ion migration number. Therefore, the gel polymer electrolyte copolymerized with the fluorine-containing monomers and the nitrogen-containing crosslinking agent in the application enables the battery to exhibit good discharge specific capacity and cycle stability under high current density.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery electrolyte, and particularly relates to a gel polymer electrolyte and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries provide high-performance energy storage solutions with excellent characteristics such as high energy density, safety and environmental protection, and are widely used in portable electronic devices, electric vehicles, renewable energy storage and other fields. In order to improve the energy density of the battery, researchers have developed many new electrode materials, such as nickel-cobalt-manganese oxide or nickel-cobalt-aluminum oxide positive electrode materials. However, the increase in energy density and voltage also exacerbates the side reactions of the electrolyte on the positive electrode surface, further accelerating the destruction of the positive electrode particles, and ultimately leading to the decline of the cycle life of the battery. In addition, the decomposition of the electrolyte on the negative electrode surface forms organic lithium salt, hindering the migration of lithium ions at the interface. Moreover, the lithium ion battery electrolyte based on carbonate has a low flash point, and there is a risk of leakage and combustion during the cycle process, thereby causing safety hazards of the battery.

[0003] Gel polymer electrolyte combines the advantages of solid and liquid electrolytes. The electrolyte is sealed in the polymer framework, reducing the safety hazards of electrolyte leakage, and the polymer skeleton structure can inhibit the growth of lithium dendrites. Compared with solid polymer electrolyte, lithium ions can quickly migrate in the liquid phase, exhibiting excellent properties, including high ionic conductivity, good interface performance and excellent chemical stability. With the increasing demand for batteries in society, fast charging capability has also become one of the standards for measuring the practical application potential of batteries. However, compared with liquid electrolyte, the presence of polymer to some extent hinders the migration of lithium ions, so the gel polymer electrolyte lithium ion battery cannot usually exhibit high discharge specific capacity at high current density. SUMMARY

[0004] In view of the deficiencies in the prior art, the application provides a gel polymer electrolyte and a preparation method and application thereof. The purpose of the application is to provide a gel polymer electrolyte used at high current density, further improving the in-situ polymerization interface stability and ion transmission rate.

[0005] The first aspect of the present application is to provide a gel polymer that can be stably used at a high current density, the polymer framework being polymerized from a monomer, a crosslinking agent and an initiator, the monomer being a fluorine-containing monomer including one or two of trifluoroethyl acrylate (TFEA), 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA), 1H,1H-perfluoropropyl methacrylate (PFPMA), hexafluorobutyl acrylate (HFBA), 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane (OFHDA) and 2-(perfluorohexyl)ethyl methacrylate (PFEMA), the crosslinking agent being a nitrogen-containing monomer including one of N,N'-methylenebisacrylamide (MBA), hexamethylenebisacrylamide (HABA) and N,N'-vinylbisacrylamide (EBA).

[0006] The monomer and the crosslinking agent are shown in structural formulas 1 to 9:

[0007]

[0008] The structural formula of the polymer framework is shown in formula 10:

[0009]

[0010] In formula 10, R1 is a fluorinated ester group, R2 is -CH3 or -H, and R3 is an amide group.

[0011] For example, the combination of the monomer and the crosslinking agent can be a combination of trifluoroethyl acrylate and N,N'-methylenebisacrylamide, or a combination of 2-(perfluorohexyl)ethyl methacrylate and 2-acrylic acid (2,2-dimethyl-1,3-propanediyl) ester, but is not limited to the listed combinations, and other unlisted combinations within the scope of the monomer are also applicable.

[0012] Further, in the present application, the lithium salt is selected from any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bistrifluoromethylsulfonylimide, lithium difluoro(oxalato)borate, lithium perchlorate and lithium bistrifluorosulfonylimide.

[0013] Further, in the present application, the initiator is any one of azobisisobutyronitrile, dicumyl peroxide, dibenzoyl peroxide or azobisisoheptane, and the addition amount is 0.01 to 5 wt% based on the mass of the polymer precursor.

[0014] Further, in the present application, the organic solvent is selected from any one or more than one of ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and fluorinated ethylene carbonate, which are blended in any volume ratio.

[0015] Furthermore, in the present invention, the thermal initiation conditions are: polymerization temperature is 50 to 80° C., and polymerization time is 0.5 to 4 hours.

[0016] The second aspect of the present invention is to provide a method for preparing the above-mentioned gel polymer, wherein a precursor electrolyte containing a monomer, a cross-linking agent, an initiator, an organic solvent and a lithium salt is heated at a temperature of 50 to 80°C for 0.5 to 4 hours to convert the precursor electrolyte from a liquid state into a gel state to obtain a gel polymer electrolyte.

[0017] The third aspect of the present invention is to provide the use of the gel polymer in a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, a separator and the gel polymer electrolyte.

[0018] Furthermore, in the gel polymer lithium-ion battery provided by the present invention: the positive electrode is one of a nickel-cobalt-manganese ternary positive electrode, a nickel-cobalt-aluminum positive electrode, a lithium cobaltate positive electrode, and a lithium iron-manganese phosphate positive electrode; the negative electrode is one of a graphite negative electrode, lithium titanate, a silicon-carbon negative electrode, and metallic lithium; and the diaphragm is one of a polypropylene diaphragm, a polyethylene diaphragm, a cellulose diaphragm, and a glass fiber diaphragm.

[0019] Furthermore, in the present invention, the positive electrode material includes a positive electrode active material, conductive carbon black and a binder, wherein the positive electrode active material accounts for 80-95% of the positive electrode material, the conductive carbon black accounts for 2.5-10% of the positive electrode material, and the binder accounts for 2.5-10% of the positive electrode material.

[0020] Furthermore, in the present invention, the negative electrode material includes a negative electrode active material, conductive carbon black, a binder and a thickener, wherein the negative electrode active material accounts for 90 to 96.5% of the negative electrode material, the conductive carbon black accounts for 1.5 to 3% of the negative electrode material, the binder accounts for 1.5 to 3% of the negative electrode material, and the thickener accounts for 1.5 to 3% of the negative electrode material.

[0021] Beneficial effects

[0022] The present invention provides a polymer skeleton in formula 10, introduces NH-containing functional groups into the main chain, and uses fluorine-containing short chains as side groups. The present invention forms in situ the fluorine-containing functional groups on the polymer side chains to interact with lithium ions, thereby promoting lithium ion transport; while the NH-containing functional groups on the main chain restrict the migration of anions, thereby increasing the ion migration number. Therefore, the gel polymer electrolyte of the copolymerized fluorine-containing monomer and nitrogen-containing crosslinker in the present invention enables the battery to exhibit good discharge specific capacity and cycle stability at high current density. Therefore, the lithium-ion battery based on the gel polymer electrolyte of the present invention has excellent performance at high current density and is particularly suitable for application scenarios requiring fast charging and discharging, such as electric vehicles and high-power electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1The thermogravimetric analysis curve of Example 1 and Comparative Example 1.

[0024] Figure 2 The electrochemical window test analysis result graph of Example 1 and Comparative Example 1.

[0025] Figure 3 The steady-state current method test result graph of Example 1.

[0026] Figure 4 The steady-state current method test result graph of Comparative Example 1.

[0027] Figure 5 The charge-discharge voltage curve of lithium battery of Example 1 and Comparative Example 1 under long-time cycle.

[0028] Figure 6 The cycle performance graph of full battery of Example 1 and Comparative Example 1 at 3C, 25℃.

[0029] Figure 7 The scanning electron microscope (SEM) graph of the positive electrode surface of the full battery of Example 1 after 400 cycles.

[0030] Figure 8 The scanning electron microscope (SEM) graph of the positive electrode surface of the full battery of Comparative Example 1 after 400 cycles.

[0031] Figure 9 The scanning electron microscope (SEM) graph of the negative electrode surface of the full battery of Example 1 after 400 cycles.

[0032] Figure 10 The scanning electron microscope (SEM) graph of the negative electrode surface of the full battery of Comparative Example 1 after 400 cycles. DETAILED DESCRIPTION

[0033] The present application will be further clarified by the following examples, which are intended to be exemplary of the present application, and are not intended to limit a scope of the present application.

[0034] Example 1

[0035] This example provides a gel polymer electrolyte lithium ion battery, which is prepared by the following steps:

[0036] Step 1: 0.025g TFEA and 0.025g MBA are added to the lithium ion battery electrolyte containing 1mol / L LiPF6 in EC / DEC / DMC (V:V:V = 1:1:1), 0.0015g of initiator azobisisobutyronitrile is added and mixed uniformly to obtain a precursor electrolyte.

[0037] Step 2: 30 μL of the precursor electrolyte was injected into a coin cell, which was assembled in a glove box. The coin cell was of CR2032 series, and the positive electrode used was a 15 mm NCM811 single-sided electrode, the negative electrode used was a 16 mm diameter graphite negative electrode, and the separator used was a 19 mm diameter polypropylene separator. After assembly, the electrolyte was allowed to fully soak the separator at room temperature for 2 hours, and then polymerized at 75°C for 0.5 hours to obtain the gel polymer electrolyte.

[0038] Example 2

[0039] This example provides a gel polymer electrolyte lithium ion battery, which is prepared by the following steps:

[0040] Step 1: 0.028 g of TFPMA and 0.025 g of MBA were added to a lithium ion battery electrolyte containing 1 mol / L LiPF6 in EC / DEC / DMC (V:V:V = 1:1:1), and 0.0017 g of initiator azobisisobutyronitrile was added and mixed uniformly to obtain a precursor electrolyte.

[0041] Step 2: 30 μL of the precursor electrolyte was injected into a coin cell, which was assembled in a glove box. The coin cell was of CR2032 series, and the positive electrode used was a 15 mm NCM811 single-sided electrode, the negative electrode used was a 16 mm diameter graphite negative electrode, and the separator used was a 19 mm diameter polypropylene separator. After assembly, the electrolyte was allowed to fully soak the separator at room temperature for 2 hours, and then polymerized at 75°C for 0.5 hours to obtain the gel polymer electrolyte.

[0042] Example 3

[0043] This example provides a gel polymer electrolyte lithium ion battery, which is prepared by the following steps:

[0044] Step 1: 0.03 g of PFPMA and 0.025 g of MBA were added to a lithium ion battery electrolyte containing 1 mol / L LiPF6 in EC / DEC / DMC (V:V:V = 1:1:1), and 0.002 g of initiator azobisisobutyronitrile was added and mixed uniformly to obtain a precursor electrolyte.

[0045] Step 2: 30 μL of the precursor electrolyte was injected into a coin cell, which was assembled in a glove box. The coin cell was of CR2032 series, and the positive electrode used was a 15 mm NCM811 single-sided electrode, the negative electrode used was a 16 mm diameter graphite negative electrode, and the separator used was a 19 mm diameter polypropylene separator. After assembly, the electrolyte was allowed to fully soak the separator at room temperature for 2 hours, and then polymerized at 75°C for 0.5 hours to obtain the gel polymer electrolyte.

[0046] Example 4

[0047] This example provides a gel polymer electrolyte lithium ion battery, which is prepared by the following steps:

[0048] Step 1: 0.034 g of HFBA, 0.025 g of N,N'-methylenebisacrylamide were added to the lithium ion battery electrolyte containing 1 mol / L LiPF6 in EC / DEC / DMC (V:V:V = 1:1:1), 0.002 g of initiator azobisisobutyronitrile was added and mixed uniformly to obtain a precursor electrolyte.

[0049] Step 2: 30 μL of the precursor electrolyte was injected into a coin cell for assembly, the coin cell was CR2032 series battery, the size of the positive electrode used was 15 mm NCM811 single-sided pole piece, the negative electrode used was a graphite negative electrode with a diameter of 16 mm, and the separator used was a polypropylene separator with a diameter of 19 mm. After assembly, the electrolyte was allowed to fully soak into the separator at room temperature for 1 hour, and then polymerized at 75°C for 0.5 hours to obtain a gel polymer electrolyte.

[0050] Example 5

[0051] This example provides a gel polymer electrolyte lithium ion battery, which is prepared by the following steps:

[0052] Step 1: 0.038 g of OFHDA, 0.025 g of MBA were added to the lithium ion battery electrolyte containing 1 mol / L LiPF6 in EC / DEC / DMC (V:V:V = 1:1:1), 0.0022 g of initiator azobisisobutyronitrile was added and mixed uniformly to obtain a precursor electrolyte.

[0053] Step 2: 30 μL of the precursor electrolyte was injected into a coin cell for assembly, the coin cell was CR2032 series battery, the size of the positive electrode used was 15 mm NCM811 single-sided pole piece, the negative electrode used was a graphite negative electrode with a diameter of 16 mm, and the separator used was a polypropylene separator with a diameter of 19 mm. After assembly, the electrolyte was allowed to fully soak into the separator at room temperature for 1 hour, and then polymerized at 75°C for 0.5 hours to obtain a gel polymer electrolyte.

[0054] Example 6

[0055] This example provides a gel polymer electrolyte lithium ion battery, which is prepared by the following steps:

[0056] Step 1: 0.043 g PFEMA, 0.025 g MBA amine were added into the lithium ion battery electrolyte containing 1 mol / L LiPF6 in EC / DEC / DMC (V:V:V = 1:1:1), 0.0025 g of initiator azobisisobutyronitrile was added and mixed uniformly to obtain a precursor electrolyte.

[0057] Step 2: 30 μL of the precursor electrolyte was injected into a coin cell for assembly, the coin cell was a CR2032 series battery, the positive electrode used was a 15 mm NCM811 single-sided electrode, the negative electrode used was a 16 mm diameter graphite negative electrode, and the separator used was a 19 mm diameter polypropylene separator. After assembly, the electrolyte was allowed to fully soak into the separator at room temperature for 2 hours, and then polymerized at 70°C for 40 minutes to obtain a gel polymer electrolyte.

[0058] The preparation method of the coin lithium ion battery is as follows:

[0059] (1) Preparation of positive electrode sheet: single crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 ternary positive electrode material, conductive agent carbon black (Super-P) and binder (PVDF) were dissolved in N-methyl pyrrolidone at a mass ratio of 8:1:1, mixed uniformly to prepare a positive electrode slurry, then the positive electrode slurry was uniformly coated on the current collector aluminum foil, and finally dried at 80°C under vacuum conditions for 12h to prepare the positive electrode sheet of the lithium ion battery;

[0060] (2) Preparation of negative electrode sheet: graphite negative electrode material, conductive agent carbon black (Super-P), thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were dissolved in deionized water at a mass ratio of 95.5:1.5:1.5:1.5, mixed uniformly to prepare a negative electrode slurry, then the negative electrode slurry was uniformly coated on the current collector copper foil, and finally dried at 80°C under vacuum conditions for 12h to prepare the negative electrode sheet of the lithium ion battery;

[0061] (3) Assembly of lithium ion battery: assembled in a glove box with an argon content of 99.999%, an actual oxygen content <0.1 ppm, and a moisture content <0.1 ppm; the battery was assembled in the order of positive electrode shell, positive electrode, precursor solution, separator, precursor solution, negative electrode, gasket, spring, and negative electrode shell.

[0062] Comparative Example 1

[0063] A lithium ion battery electrolyte containing 1 mol / L LiPF6 in EC / DEC / DMC (V:V:V = 1:1:1) was prepared, and 30 μL of the electrolyte was injected into a button cell for assembly. The button cell was of CR2032 series, and the positive electrode used was a 15 mm NCM811 single-sided pole piece, the negative electrode used was a 16 mm diameter graphite negative electrode, and the separator used was a 19 mm diameter polypropylene separator.

[0064] Comparative Example 2

[0065] A lithium ion battery electrolyte containing 0.5 mol / L LiDFOB and 1 mol / L LiPF6 in EC / EMC (V:V = 3:7) was prepared, and 30 μL of the electrolyte was injected into a button cell for assembly. The button cell was of CR2032 series, and the positive electrode used was a 15 mm NCM811 single-sided pole piece, the negative electrode used was a 16 mm diameter graphite negative electrode, and the separator used was a 19 mm diameter polypropylene separator.

[0066] The button cells prepared in Examples 1-6 and Comparative Examples 1 and 2 were subjected to electrochemical performance tests, including electrochemical window tests and long cycle tests (0.1C activation for 2 cycles at room temperature, and long cycle tests at 3C, with a charge-discharge range of 2.7-4.5V). The specific test results are shown in Table 1.

[0067] Table 1

[0068]

[0069] The results show that Examples 1-6 have higher electrochemical windows and higher first cycle efficiencies than Comparative Examples 1 and 2, indicating that the obtained gel polymer electrolyte has better electrochemical stability, and has a higher capacity retention rate after 100 cycles, indicating better long cycle stability at high current density.

[0070] The thermal gravimetric curves of the electrolytes of Example 1 and Comparative Example 1 were tested, as shown in Figure 1 It was found that Comparative Example 1 began to rapidly lose weight from room temperature, while Example 1 began to show significant thermal weight loss only at 130°C, indicating that the polymerized electrolyte has better thermal stability and anti-oxidative decomposition ability.

[0071] The electrochemical windows of Example 1 and Comparative Example 1 were tested, as shown in Figure 2 Comparative Example 1 began to polarize severely near 4.5V, while Example 1 began to polarize only around 5.0V, indicating that the gel polymer electrolyte has higher electrochemical stability.

[0072] The electrochemical windows of Example 1 and Comparative Example 1 were tested, as shown inFigure 3 and Figure 4 As shown, the ion migration number of Example 1 is 0.67, while the ion migration number of Comparative Example 1 is 0.33, which indicates that the combination of the introduced fluorine-containing side chain and the main chain containing the NH functional group can effectively promote the migration of lithium ions and effectively limit the migration of anions.

[0073] Assemble the lithium battery, Figure 5 It can be seen that at 0.2 mA cm -2 At this current density, Example 1 showed no significant polarization after 1400 hours of cycling, while Comparative Example 1 began to show a significant increase in polarization voltage after 700 hours of cycling. This indicates that the gel polymer electrolyte has superior long-term cycling stability.

[0074] The long cycle performance of the lithium ion batteries of Example 1 and Comparative Example 1 was tested. Figure 6 As shown. In Example 1, the initial discharge capacity of the battery at 3C is 145.8 mAh g -1 , the capacity retention rate after 300 cycles is 73.2%. The initial discharge capacity of the battery in comparative example 1 at 3C is 148.9 mAh g -1 , the capacity retention rate after 300 cycles is 33.3%, which shows that the gel polymer electrolyte has better long-term cycle stability at high current density.

[0075] The SEM images of the positive electrodes of the lithium ion batteries of Example 1 and Comparative Example 1 after 400 cycles are as follows: Figure 7 and Figure 8 As shown, it can be found that the positive electrode particles of Example 1 maintain a relatively complete morphology after cycling, while the positive electrode particles of Comparative Example 1 are more broken, which indicates that the integrity of the positive electrode can be effectively protected by in situ polymerization.

[0076] The SEM images of the negative electrodes of the lithium ion batteries of Example 1 and Comparative Example 1 after 400 cycles are as follows: Figure 9 and Figure 10 As shown, it can be found that the surface of the negative electrode of Example 1 is relatively smooth after cycling, while the surface of the negative electrode of Comparative Example 1 is uneven, which indicates that a uniform solid electrolyte interface layer can be formed by introducing fluorine-containing and nitrogen-containing polymers, thereby promoting uniform deposition of lithium ions.

[0077] The above embodiments are exemplary and intended to illustrate the technical concepts and features of the present invention so that those skilled in the art can understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A gel polymer electrolyte, characterized by: A polymer framework comprising the following structure: wherein R1 is a fluorinated ester group, R2 is -CH3 or -H, and R3 is an amide group; The raw materials of the polymer electrolyte include a monomer, a crosslinking agent, an initiator, an organic solvent and a lithium salt; the monomer is any one or a combination of two of trifluoroethyl acrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 1H,1H-perfluoropropyl methacrylate, hexafluorobutyl acrylate, 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane and 2-(perfluorohexyl)ethyl methacrylate; the crosslinking agent is one of N,N'-methylene bisacrylamide, hexamethylene bisacrylamide and N,N'-vinyl bisacrylamide; the monomer accounts for 0.1-10wt% of the mass of the electrolyte, and the crosslinking agent accounts for 0.1-10wt% of the mass of the electrolyte.

2. The gel polymer electrolyte according to claim 1, characterized by: The initiator is any one of azobisisobutyronitrile, dicumyl peroxide, dibenzoyl peroxide and azobisisoheptane.

3. The gel polymer electrolyte of claim 1, wherein: The organic solvent is a mixed organic solvent formed by blending any two or more of vinyl carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and fluorinated vinyl carbonate.

4. The gel polymer electrolyte of claim 1, wherein: The lithium salt is any one or a combination of multiple of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluoro(oxalato)borate, lithium perchlorate and lithium bis(trifluorosulfonyl)imide.

5. The gel polymer electrolyte of claim 1, wherein: The initiator accounts for 0.001-0.5wt% of the mass of the electrolyte.

6. The gel polymer electrolyte according to any one of claims 1 to 5, characterized in that: The concentration of the lithium salt in the electrolyte is between 0.5-2mol / L.

7. The method of claim 1-6, wherein the gel polymer electrolyte is prepared by the steps of: The precursor electrolyte containing the monomer, the crosslinking agent, the initiator, the organic solvent and the lithium salt is heated to react at a temperature of 50-80℃ for 0.5-4 hours, so that the precursor electrolyte is converted from a liquid state to a gel state, and the gel polymer electrolyte is obtained.

8. Use of a gel polymer electrolyte in a lithium ion battery, characterized in that: The lithium ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the gel polymer electrolyte according to any one of claims 1-6.

9. Use of the gel polymer electrolyte according to claim 8 in a lithium-ion battery, characterized in that: The positive electrode is one of a nickel-cobalt-manganese ternary positive electrode, a nickel-cobalt-aluminum positive electrode, a lithium cobaltate positive electrode and a lithium iron manganese phosphate positive electrode; the negative electrode is one of a graphite negative electrode, a lithium titanate, a silicon-carbon negative electrode and a metal lithium negative electrode; and the separator is one of a polypropylene separator, a polyethylene separator, a cellulose separator and a glass fiber separator.

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