High-fluorine polyurethane solid electrolyte as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-fluorine polyurethane solid electrolyte as well as a preparation method and application thereof. The high-fluorine polyurethane solid electrolyte provided by the invention comprises high-fluorine polyurethane, lithium salt and a plasticizer adsorbed in pores of the high-fluorine polyurethane, a repetitive unit of the high-fluorine polyurethane is shown as a formula I in the specification. The high-fluorine polyurethane solid electrolyte provided by the invention has high ionic conductivity and a wide electrochemical window, and can adapt to a high-voltage positive electrode material, and the stability of the high-fluorine polyurethane solid electrolyte at a high working potential is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a high-fluorine polyurethane solid electrolyte and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have the advantages of high working voltage, high specific energy, long cycle life, low self-discharge rate, no pollution, etc., and are widely used in 3C products, new energy electric vehicles, electric bicycles and the like. As an important component of lithium batteries, electrolyte plays an important role in the performance of lithium batteries. Traditional liquid organic electrolyte has poor stability, is flammable and explosive, is easy to cause lithium dendrite growth and limits the application of high-potential positive electrode materials, and a large amount of toxic substances are generated in the production and manufacturing process of liquid organic electrolyte, affecting the green and sustainable development of lithium batteries. Although solid polymer electrolyte can solve the problem of the insecurity of traditional liquid electrolyte, the poor interfacial compatibility and low lithium ion conductivity at room temperature limit its practical application in lithium batteries.

[0003] Polyurethane is a polymer electrolyte with good performance and has a two-phase microstructure. The soft segment can be solvated with alkali metals due to the presence of ether bonds, which promotes the transmission of lithium ions and improves the ionic conductivity. The hard segment can provide sufficient strength and maintain dimensional stability due to the π-π interaction and hydrogen bonding between polyurethane groups. However, commercial polyurethane cannot avoid the shortcomings of the polymer itself, such as low ionic conductivity at room temperature and narrow electrochemical window. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a high-fluorine polyurethane solid electrolyte and a preparation method and application thereof. The high-fluorine polyurethane solid electrolyte provided by the present application has high ionic conductivity and a wide electrochemical window.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions: The present application provides a high-fluorine polyurethane solid electrolyte, which comprises a high-fluorine polyurethane, a lithium salt and a plasticizer adsorbed in the pores of the high-fluorine polyurethane. The repeating unit of the high-fluorine polyurethane is shown in Formula I: Formula I; wherein R is one or more of Formula II, Formula III, Formula IV and Formula V, and R1 is Formula VI and / or Formula VII, wherein x and y are positive integers. Formula II, Formula III, Formula IV, Formula V; Formula VI, Formula VII.

[0006] Preferably, the plasticizer comprises one or more of ethylene carbonate, dimethyl carbonate, propylene carbonate, sulfolane, fluoroethylene carbonate and dimethoxyethane.

[0007] Preferably, the lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate and lithium difluoro(oxalato)borate.

[0008] Preferably, the high-fluorine polyurethane-based solid-state electrolyte comprises 30-50% of the plasticizer, 15-30% of the lithium salt and 30-50% of the high-fluorine polyurethane.

[0009] The application also provides a preparation method of the high-fluorine polyurethane solid-state electrolyte, comprising the following steps: In a glove box, the fluorine-containing diol, the lithium salt, the plasticizer and the isocyanate are mixed to obtain a precursor solution; The precursor solution is subjected to a thermal initiation crosslinking polymerization reaction to obtain the high-fluorine polyurethane solid-state electrolyte; The structure of the isocyanate is shown in Formula VIII: Formula VIII; wherein R is one or more of Formula II, Formula III, Formula IV and Formula V; Formula II, Formula III, Formula IV, Formula V; The fluorine-containing diol is Formula IX and / or Formula X, wherein x and y are positive integers; Formula IX, Formula X, The molar ratio of the fluorine-containing diol to the isocyanate is 3:2.

[0010] Preferably, the thermal initiation crosslinking polymerization reaction is performed at a temperature of 60-90°C.

[0011] Preferably, the thermal initiation crosslinking polymerization reaction is performed for 12-18 hours.

[0012] Preferably, the mixing of the fluorine-containing diol, the isocyanate, the lithium salt and the plasticizer is as follows: In a glove box, the fluorine-containing diol, the lithium salt and the plasticizer are mixed to obtain a first stirring solution, the isocyanate is added to the first stirring solution, and a second stirring is performed to obtain a precursor solution; The first stirring and the second stirring are both performed at room temperature.

[0013] The application further provides application of the high-fluorine polyurethane solid electrolyte in the lithium ion battery as an electrolyte.

[0014] The application further provides a polymer lithium battery, comprising a positive electrode, a negative electrode and an electrolyte between the positive electrode and the negative electrode; the electrolyte is the high-fluorine polyurethane solid electrolyte in the technical solution or the high-fluorine polyurethane solid electrolyte prepared by the preparation method.

[0015] The application provides a high-fluorine polyurethane solid electrolyte, comprising high-fluorine polyurethane, a lithium salt and a plasticizer adsorbed in pores of the high-fluorine polyurethane. The repeating unit of the high-fluorine polyurethane is shown in formula I: Formula I; wherein R is one or more of formula II, formula III, formula IV and formula V, R1 is formula VI and / or formula VII, wherein x and y are positive integers. Formula II, Formula III, Formula IV, Formula V; Formula VI, Formula VII.

[0016] The application is based on molecular design, and a three-dimensional high-fluorine polyurethane is formed by polymerization of triisocyanate and fluorine-containing diol as monomers, so that the high-fluorine polyurethane solid electrolyte is obtained. On one hand, the plasticizer is filled into the three-dimensional structure, which is beneficial to lithium ion transmission. On the other hand, the F group in the three-dimensional skeleton has high oxidation resistance, improves the electrochemical window, so that it can adapt to high-voltage positive electrode materials and improve the stability at high working potential. Moreover, the high-fluorine polyurethane solid electrolyte has high mechanical properties, low preparation cost, high safety and simple preparation process. The results of the examples show that the electrochemical window of the lithium ion battery assembled by the high-fluorine polyurethane solid electrolyte is 5.1 V, and the NCM81-Li button cell assembled by the high-fluorine polyurethane solid electrolyte can be stably cycled at 2.8-4.3 V. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 SEM image of the surface of the high-fluorine polyurethane solid electrolyte obtained in Example 1; Figure 2 Infrared test image of the high-fluorine polyurethane solid electrolyte obtained in Example 1; Figure 3 Impedance spectrum of the steel-steel battery assembled by the high-fluorine polyurethane solid electrolyte prepared in Example 1 and Example 2; Figure 4A graph of linear sweep voltammetry of a lithium-steel battery assembled with the high-fluorine polyurethane solid electrolyte prepared in Example 1 and the polyurethane solid electrolyte prepared in Comparative Example 1; Figure 5 A graph of room temperature cycle stability of a button cell assembled with the high-fluorine polyurethane solid electrolyte prepared in Example 1 at 0.1C and 0.2C rates in Application Example 1; Figure 6 A graph of room temperature cycle stability of a button cell assembled with the high-fluorine polyurethane solid electrolyte prepared in Example 1 at 0.2C and 0.5C rates in Application Example 1. DETAILED DESCRIPTION

[0018] The present application provides a high-fluorine polyurethane solid electrolyte, comprising a fluorine-containing diol, a cross-linked polyurethane polymerized from an isocyanate, a lithium salt and a plasticizer adsorbed in pores of the high-fluorine polyurethane solid electrolyte; The repeating unit of the high-fluorine polyurethane is shown in Formula I: Formula I; wherein R is one or more of Formula II, Formula III, Formula IV and Formula V, and R1 is Formula VI and / or Formula VII, wherein x and y are positive integers; Formula II, Formula III, Formula IV, Formula V; Formula VI, Formula VII.

[0019] Unless otherwise specified, the present application does not have special requirements for the source of the raw materials used, and commercially available products known to those skilled in the art can be used.

[0020] As an embodiment, the plasticizer comprises one or more of ethylene carbonate, dimethyl carbonate, propylene carbonate, sulfolane, fluoroethylene carbonate and dimethyl ether of ethylene glycol, and in a specific embodiment, dimethyl ether of ethylene glycol.

[0021] As an embodiment, the lithium salt comprises one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide and lithium hexafluorophosphate and lithium difluoro(oxalato)borate, and in a specific embodiment, lithium bis(trifluoromethylsulfonyl)imide.

[0022] As an embodiment, the mass percentage of the plasticizer in the high-fluorine polyurethane-based solid electrolyte is 30-50%, and in a specific embodiment, 41%, the mass percentage of the lithium salt is 15-30%, and in a specific embodiment, 22%, and the mass percentage of the high-fluorine polyurethane is 30-50%, and in a specific embodiment, 37%.

[0023] In the present application, the high-fluorine polyurethane-based solid electrolyte can effectively improve the oxidation stability, so that the electrolyte can adapt to high-voltage positive electrode materials and improve the stability under high working potential.

[0024] The present application also provides a preparation method of the high-fluorine polyurethane solid electrolyte according to the above technical solution, comprising the following steps: In a glove box, fluorine-containing diol, lithium salt, plasticizer and isocyanate are mixed to obtain a precursor solution; The precursor solution is subjected to a thermal initiation crosslinking polymerization reaction to obtain the high-fluorine polyurethane solid electrolyte; The structure of the isocyanate is shown in formula VIII, and the corresponding isocyanates are triphenylmethane triisocyanate, thiophosphoric acid triphenyl isocyanate, HDI trimer and hexane diisocyanate biuret.

[0025] Formula VIII; In formula VIII, R is one or more of formula II, formula III, formula IV and formula V; Formula II, Formula III, Formula IV, Formula V; The fluorine-containing diol is formula IX and / or formula X, wherein x and y are positive integers; Formula IX, Formula X, The molar ratio of the fluorine-containing diol and the isocyanate is 3:2.

[0026] In a specific embodiment of the present application, the structure of the isocyanate is: The structure of the fluorine-containing diol is: (2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol), 2,2'-((perfluoroethane-1,2-diyl)bis(oxy))bis(2,2-difluoroethanol) or 1H,1H,11H,11H-perfluoro-3,6,9-trioxaundecane-1,11-diol.

[0027] As an embodiment, the mixing of the fluorine-containing diol, the isocyanate, the lithium salt and the plasticizer is: In a glove box, the fluorine-containing diol, the lithium salt and the plasticizer are mixed to perform first stirring, the isocyanate is added to the obtained first stirring solution to perform second stirring, and a precursor solution is obtained.

[0028] As an implementation form, the first stirring and the second stirring are both carried out at room temperature; the room temperature is 20-30 DEG C, and in particular embodiments, it is 25 DEG C. The present application does not have special limitations on the speed and time of the first stirring and the second stirring, and the material is mixed uniformly.

[0029] As an implementation form, before the heat-induced crosslinking polymerization, the prepared precursor solution is used to assemble a CR2025 button cell, and after the cell is assembled, it is transferred to a high-temperature vacuum oven for curing to complete the heat-induced crosslinking polymerization, thereby obtaining the high-fluorine polyurethane solid electrolyte.

[0030] As an implementation form, the temperature of the heat-induced crosslinking polymerization is 60-90 DEG C, and in particular embodiments, it is 75-80 DEG C; the time of the heat-induced crosslinking polymerization is 12-18 h, and in particular embodiments, it is 14-16 h.

[0031] In the present application, the fluorine-containing diol and the isocyanate are gradually added and polymerized under heating, and the specific reaction is as follows: .

[0032] The preparation method of the high-fluorine polyurethane solid electrolyte provided by the present application has low cost, simple process and easy-to-control conditions.

[0033] The present application also provides the application of the high-fluorine polyurethane solid electrolyte as an electrolyte in a lithium ion battery.

[0034] The present application also provides a polymer lithium battery, which comprises a positive electrode, a negative electrode and an electrolyte between the positive electrode and the negative electrode; the electrolyte is the high-fluorine polyurethane solid electrolyte according to the above technical solution or the high-fluorine polyurethane solid electrolyte prepared by the preparation method according to the above technical solution.

[0035] As an implementation form, the positive electrode comprises a current collector and a positive electrode coating layer covering the surface of the current collector, and the positive electrode coating layer comprises a positive electrode active material, a conductive agent and a binder; the positive electrode active material comprises one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide and lithium iron manganese phosphate, and in particular embodiments, it is LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811); the current collector is aluminum foil; the conductive agent comprises one or more of acetylene black, ketjen black and carbon nanotube, and in particular embodiments, acetylene black; the binder comprises one or more of polytetrafluoroethylene, polyurethane and polyvinylidene fluoride, and in particular embodiments, polyvinylidene fluoride; and the mass ratio of the positive electrode active material, the conductive agent and the binder is 6-8:1-2:1-2, and in particular embodiments, 8:1:1.

[0036] As an embodiment, the negative electrode is a metal lithium sheet.

[0037] The present application does not have special requirements for the assembly method of the polymer lithium battery, and the assembly method known to those skilled in the art can be used.

[0038] The lithium ion battery provided by the present application uses the high-pressure-resistant fluorine-boron polymer solid-state electrolyte film as the electrolyte, can be stably cycled at 2.8-4.3V, and has excellent rate performance at room temperature.

[0039] The technical solutions in the present application will be described below in combination with the embodiments in the present application, but they should not be understood as limitations on the protection scope of the present application.

[0040] Example 1 The preparation of the high-fluorine polyurethane solid-state electrolyte is as follows: (1) In a glove box, 0.17g of 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol and 0.42g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were accurately weighed and placed in a 5mL transparent vial, and 1mL of ethylene glycol dimethyl ether was added as a solvent; (2) The vial was placed in a magnetic sonicator and stirred at room temperature for 12h; (3) After a homogeneous solution was formed, 0.467g of trimethylphenyl triisocyanate was added, and stirring was continued for 1h to obtain a stable precursor solution; (4) The prepared precursor solution was used to assemble a CR2025 button cell, and after the cell was assembled, it was transferred to a 70℃ vacuum oven for curing for 14h to complete the thermal initiation crosslinking polymerization reaction.

[0041] Example 2 The difference from Example 1 is that the fluorine-containing diol is replaced by 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol, and the rest is the same as in Example 1.

[0042] Example 3 The difference from Example 1 is that the fluorine-containing diol is replaced by 1H, 1H, 11H, 11H-perfluoro-3, 6, 9-trioxaundecane-1, 11-diol instead of 2, 2, 3, 3, 4, 4, 5, 5-octafluoro-1, 6-hexanediol, and the rest is the same as Example 1.

[0043] Comparative Example 1 The difference from Example 1 is that the fluorine-containing diol is replaced by polyethylene glycol (Mn = 2000) instead of 2, 2, 3, 3, 4, 4, 5, 5-octafluoro-1, 6-hexanediol, and the rest is the same as Example 1.

[0044] Comparative Example 2 The difference from Example 1 is that the fluorine-containing diol is replaced by polycaprolactone diol (Mn = 1000) instead of 2, 2, 3, 3, 4, 4, 5, 5-octafluoro-1, 6-hexanediol, and the rest is the same as Example 1.

[0045] Application Example 1 The high-fluorine polyurethane solid electrolyte obtained in Example 1 is assembled into a lithium-lithium symmetrical battery (button cell) with a positive electrode and a negative electrode. The positive electrode is a current collector (aluminum foil) and a positive electrode coating layer covering the surface of the current collector; the positive electrode active material in the positive electrode coating layer is LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), the conductive agent is acetylene black, and the binder is polyvinylidene fluoride; the mass ratio of the positive electrode active material, the conductive agent and the binder is 8:1:1; The negative electrode is a lithium metal sheet.

[0046] Performance test (1) The surface of the high-fluorine polyurethane solid electrolyte obtained in Example 1 is subjected to scanning electron microscope test, and the obtained SEM image is shown in Figure 1 .

[0047] From Figure 1 it can be seen that the high-fluorine polyurethane solid electrolyte prepared in the application has a smooth surface without any pores, indicating that it has good structural stability.

[0048] (2) The high-fluorine polyurethane solid electrolyte obtained in Example 1 is subjected to infrared test, and the results are shown in Figure 2 .

[0049] From Figure 2 it can be seen that the N-H stretching peak at 3430 cm -1 and the peaks at 1539 cm -1 and 1633 cm -1N-H bending peak indicates that the -CNO group and -OH group form polyurethane, in addition, no -CNO group characteristic peak at 2260 cm -1 and -OH group characteristic peak at 332 cm -1 , which indicates that the isocyanate and fluorine-containing diol have successfully polymerized inside the electrolyte to form a stable cross-linked network structure.

[0050] (3) Figure 3 Impedance spectra of the steel-steel batteries assembled with the high-fluorine polyurethane solid electrolyte prepared in Example 1 and Example 2.

[0051] From the results of the impedance test curve of Figure 3 , it can be calculated that the ionic conductivity of the high-fluorine polyurethane solid electrolyte prepared in Example 1 is 1.78 x 10 -4 S·cm -1 , and the ionic conductivity of the high-fluorine polyurethane solid electrolyte prepared in Example 2 is 2.25 x 10 -4 S·cm -1 , which indicates that the prepared high-fluorine polyurethane solid electrolyte has high ionic conductivity.

[0052] (4) Figure 4 Linear sweep voltammetry curve of the lithium-steel battery assembled with the high-fluorine polyurethane solid electrolyte prepared in Example 1 and the polyurethane solid electrolyte prepared in Comparative Example 1.

[0053] From the results of the linear sweep voltammetry curve of Figure 4 , it can be seen that the high-fluorine polyurethane solid electrolyte prepared in Example 1 exhibits an electrochemical window as high as 5.1 V, and the electrochemical window of the polyurethane solid electrolyte prepared in Comparative Example 1 is 4.2 V, which indicates that the high-fluorine polyurethane solid electrolyte can remain stable under high voltage conditions, has excellent oxidation resistance and interface stability, and has good adaptability to high-voltage positive electrode materials.

[0054] (5) Figure 5 , Figure 6 Room temperature cycle stability diagram of the button cell assembled with the high-fluorine polyurethane solid electrolyte prepared in Example 1 in Application Example 1, wherein Figure 5 at 0.1C and 0.2C rates, Figure 6 at 0.2C and 0.5C rates, tested at room temperature (25℃), 2.8~4.3V.

[0055] From Figure 5 , it can be seen that the discharge specific capacity at 0.1C and 0.2C rates at room temperature (25℃) is 187.7 mAh·g -1 and 178.4 mAh·g -1 , respectively.The capacity retention rate is 89.2% after 100 cycles at a rate of 0.2C.

[0056] From Figure 6 It can be seen that the specific discharge capacity is 158.4mAh·g -1 at a rate of 0.5C, and the capacity retention rate is 88.6% after 160 cycles, which proves that it can work stably at a voltage of 2.8-4.3V and has good cycle stability.

[0057] Although the above embodiment has made a detailed description of the present application, it is only a part of the embodiments of the present application but not all the embodiments, and other embodiments can be obtained according to the present embodiment without creativity, which all belong to the protection scope of the present application.

Claims

1. A high-fluorine polyurethane solid electrolyte, comprising high-fluorine polyurethane, lithium salt, and a plasticizer adsorbed in the pores of the high-fluorine polyurethane; The repeating unit of the high-fluorine polyurethane is shown in Formula I: Formula I; Where R is one or more of Equations II, III, IV and V, and R1 is Equations VI and / or VII, where x and y are both positive integers; Formula II Formula III Formula IV Formula V; Formula VI Formula VII.

2. The high-fluorine polyurethane solid electrolyte according to claim 1, characterized in that, The plasticizer includes one or more of ethylene carbonate, dimethyl carbonate, propylene carbonate, sulfolane, fluoroethylene carbonate, and ethylene glycol dimethyl ether.

3. The high-fluorine polyurethane solid electrolyte according to claim 1, characterized in that, The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium difluorooxalateborate.

4. The high-fluorine polyurethane solid electrolyte according to claim 1, characterized in that, The high-fluorine polyurethane-based solid electrolyte contains 30-50% plasticizer, 15-30% lithium salt, and 30-50% high-fluorine polyurethane by mass.

5. The method for preparing the high-fluorine polyurethane solid electrolyte according to any one of claims 1 to 4, characterized in that, Includes the following steps: Inside the glove box, fluorinated glycol, lithium salt, plasticizer and isocyanate are mixed to obtain a precursor solution; The precursor solution was subjected to a thermally initiated crosslinking polymerization reaction to obtain the high-fluorine polyurethane solid electrolyte. The structure of the isocyanate is shown in Formula VIII: Formula VIII; Where R is one or more of formulas II, III, IV and V; Formula II Formula III Formula IV Formula V; The fluorinated diol is of formula IX and / or formula X, where x and y are both positive integers; Formula IX Formula X, The molar ratio of the fluorinated diol to the isocyanate is 3:

2.

6. The preparation method according to claim 5, characterized in that, The temperature for the thermally initiated crosslinking polymerization reaction is 60~90℃.

7. The preparation method according to claim 5, characterized in that, The thermally initiated crosslinking polymerization reaction takes 12-18 hours.

8. The preparation method according to claim 5, characterized in that, The mixture of fluorinated glycol, isocyanate, lithium salt and plasticizer is as follows: Inside the glove box, fluorinated glycol, lithium salt and plasticizer are mixed and stirred for the first time. Isocyanate is added to the resulting first stirred liquid and stirred for the second time to obtain a precursor solution. Both the first and second stirring were carried out at room temperature.

9. The application of the high-fluorine polyurethane solid electrolyte according to any one of claims 1 to 4 or the high-fluorine polyurethane solid electrolyte prepared by the preparation method according to any one of claims 5 to 8 as an electrolyte in lithium-ion batteries.

10. A polymer lithium battery, comprising a positive electrode, a negative electrode, and an electrolyte located between the positive electrode and the negative electrode; wherein the electrolyte is a high-fluorine polyurethane solid electrolyte according to any one of claims 1 to 4 or a high-fluorine polyurethane solid electrolyte prepared by the preparation method according to any one of claims 5 to 8.

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