Preparation method of intrinsic safe polymer electrolyte and solid-state battery of intrinsic safe polymer electrolyte

Abstract

The invention discloses a preparation method of an intrinsically safe polymer electrolyte and a solid-state battery thereof, and belongs to the field of preparation of solid-state lithium metal batteries. The solid polymer electrolyte is of a 1M (xA + yB) + (z1C + z2D) type, x accounts for 14-15 wt%, y accounts for 1-2 wt%, z1 accounts for 70-72 wt%, z2 accounts for 11-12 wt%, A and B are lithium salts, C is a fluorine-containing monomer, D is a cross-linking agent, the fluorine-rich monomer, the cross-linking agent and the lithium salts are mixed, no electrolyte is added, an in-situ thermal polymerization method is adopted to prepare the intrinsic safe solid polymer electrolyte with high safety and high voltage resistance, and meanwhile, the electrolyte is of a three-dimensional chain network structure. Therefore, the safety performance of the electrolyte is effectively enhanced, the migration activation energy of lithium ions is reduced, and the ionic conductivity is improved. The core problems that an existing traditional battery is poor in safety performance, poor in high-voltage tolerance, large in interface impedance, out-of-control in lithium dendrite growth and the like are solved.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of solid-state lithium metal batteries, and specifically relates to a preparation method of an intrinsically safe polymer electrolyte and a solid-state battery thereof. An intrinsically safe polymer electrolyte battery with high safety and high voltage resistance is in-situ grown by an in-situ thermal polymerization method. Background Art

[0002] The large-scale consumption of fossil energy not only leads to resource depletion, but also is accompanied by the emission of a large amount of greenhouse gases (such as CO2, SO2) and harmful substances, exacerbating the deterioration of the ecological environment and seriously threatening the sustainable development of human society. To promote the transformation of the green and low-carbon economy, countries around the world are accelerating the layout of renewable clean energy technologies such as wind energy and solar energy. However, such energy sources have significant characteristics of intermittency, regionality and instability, and there is an urgent need to build an efficient, safe and long-life energy storage system to achieve stable storage and flexible allocation of energy.

[0003] With the transformation of the global energy structure towards cleaner and lower-carbon, secondary batteries represented by lithium-ion batteries have become the core supporting technologies for energy storage systems. However, traditional lithium-ion batteries rely on liquid electrolyte systems and have safety hazards such as flammability, easy leakage, and frequent interfacial side reactions, which severely restrict their applications in high energy density scenarios. In contrast, solid-state batteries can significantly improve the battery safety and the upper limit of energy density. Currently, solid electrolytes mainly include inorganic ceramics, polymers and composite electrolytes. Solid polymer electrolytes stand out due to their unique flexibility, excellent interfacial compatibility and lithium dendrite inhibition ability.

[0004] Although solid polymer electrolytes have significant advantages, electrolytes synthesized by conventional methods often have defects such as low ionic conductivity, insufficient mechanical strength and loose interfacial layers, resulting in poor high voltage resistance performance and limited cycle life of the battery. In addition, the problems of electrolyte decomposition and lithium metal interface passivation under high voltage working conditions have not been effectively solved. Based on this, developing high-safety and high-voltage-resistant solid polymer electrolyte batteries based on in-situ polymerization technology has important strategic significance. This technology can not only promote the development of long-life and high-voltage-resistant energy storage devices, but also provide support for the efficient storage of renewable energy and the construction of smart grids. Summary of the Invention

[0005] The purpose of the present invention is to propose a preparation method of an intrinsically safe polymer electrolyte and a solid-state battery thereof for the problems of low safety, low ionic conductivity, low voltage resistance and poor battery cycle stability existing in the existing solid polymer electrolyte lithium metal batteries mentioned in the background art. The present invention uses fluorine-rich monomers and cross-linking agents to in-situ generate an intrinsically safe polymer electrolyte with a three-dimensional chain network structure for solid-state batteries, enhancing the high voltage resistance performance of the battery while improving the battery safety performance.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A preparation method of an intrinsically safe polymer electrolyte and a solid-state battery thereof, comprising the following steps: Step 1. Take 5 - 10 mL of fluorine-rich monomer, dehydrate it through a molecular sieve, and store it for use at 2 - 8 °C. Step 2. Take 16 - 18 parts by mass of the monomer dried in Step 1 and mix it with 2 - 4 parts by mass of a crosslinking agent to obtain a mixed solution A after uniform mixing. Step 3. Add 3 - 4 parts by mass of a lithium salt to the mixed solution A prepared in Step 2, and stir well for 15 - 30 min to obtain a mixed solution B. Step 4. Add 0.09 - 0.17 parts by mass of an initiator to the mixed solution B prepared in Step 3, stir for 15 - 30 min to obtain an electrolyte precursor, and store it at 2 - 8 °C for assembling into a battery. Step 5. In a glove box, assemble the cleaned and dried battery positive and negative electrode cases, gaskets, shrapnel, positive electrode sheets, separators, and lithium metal sheets in the order of positive electrode case, positive electrode, separator, lithium metal sheet, gasket, shrapnel, negative electrode case. Drop 50 - 60 mL of the electrolyte precursor obtained in Step 4 on both sides of the separator, perform in-situ polymerization at 70 °C for 2 - 4 h, and let it stand at room temperature for 10 - 14 h to obtain the solid-state battery.

[0007] Among them, the fluorine-rich monomer is one or more of 2,2,2-trifluoroethyl acrylate, hexafluorobutyl acrylate, fluoroalkyl acrylate, hexafluoroisopropyl methacrylate, perfluoroalkyl ethyl acrylate, 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxy-4-methylpentyl methacrylate, 2-methyl-2-(trifluoromethylsulfonamide)propyl methacrylate, 2,2,3,3-tetrafluoropropyl acrylate, and trifluoroethyl methacrylate.

[0008] Among them, the lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), and lithium tetrafluoroborate (LiBF4).

[0009] Among them, the crosslinking agent is an acrylic acid-based or methacrylic acid-based crosslinking agent.

[0010] Among them, the initiator is one or more of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, benzoyl peroxide, and lithium iodide.

[0011] Among them, the diaphragm is one of an electrospun polyimide membrane, a glass fiber membrane, a polyethylene diaphragm, a polypropylene diaphragm, and an electrospun polyvinylidene fluoride membrane; the active material of the positive electrode sheet is one of high-voltage lithium cobaltate and nickel cobalt manganese ternary positive electrode.

[0012] A preparation method of an intrinsically safe polymer electrolyte and a solid-state battery provided by the present invention, the structural characteristics of one of the obtained typical three-dimensional chain network structure solid polymer electrolytes are as Figure 1 .

[0013] Compared with the prior art, the beneficial effects of the present invention are: A preparation method of an intrinsically safe polymer electrolyte and a solid-state battery provided by the present invention constructs a fluorinated intrinsically safe solid polymer electrolyte system with a three-dimensional chain network structure through gradient in-situ polymerization of a fluorinated rigid backbone and a flexible chain segment. The high electronegativity and chemical inertness of fluorine elements can significantly enhance the antioxidant capacity and thermal stability of the electrolyte, while the interpenetrating network design forms continuous fast lithium-ion transport channels through the synergistic effect of rigid-flexible domains. This effectively enhances the safety performance of the electrolyte, reduces the activation energy of lithium-ion migration, and improves the ionic conductivity. In addition, the battery can effectively cycle about 100 times under the high-voltage working condition of 4.4V. By designing an intrinsically safe solid polymer electrolyte, the present invention synchronously overcomes the core problems of traditional batteries such as poor safety performance, poor high-voltage tolerance, large interfacial impedance, and out-of-control growth of lithium dendrites, and provides a solution for developing the next-generation energy storage devices with both high energy density and high safety. Description of the Drawings

[0014] Figure 1 It is the polymerization principle diagram of Example 2; Figure 2 It is the photo after polymerization of Example 1; Figure 3 It is the AC impedance curve of the intrinsically safe solid polymer electrolyte battery obtained in Example 1 and Comparative Example 1; Figure 4 It is the rate performance test result of the intrinsically safe solid polymer electrolyte battery obtained in Example 2; Figure 5 It is the charge-discharge cycle performance of the intrinsically safe solid polymer electrolyte battery obtained in Example 2 at 4.4V and 0.5 C rate; Figure 6 It is the manufacturing flow chart of the intrinsically safe polymer solid electrolyte battery. Detailed Embodiments

[0015] The present invention will be further elaborated below in combination with some comparative examples and examples. It should be noted that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] A preparation method of an intrinsically safe polymer electrolyte and its solid-state battery, comprising the following steps: Example 1

[0017] Step 1: Prepare the pre-polymerization electrolyte in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm); 1.1 Take 16 parts by mass of pre-dehydrated 2,2,2-trifluoroethyl acrylate and 3 parts by mass of polyethylene glycol diacrylate, mix them evenly to obtain a mixed solution A; 1.2 Add 3.2 parts by mass of lithium bis(trifluoromethanesulfonyl)imide and 0.6 parts by mass of lithium difluoro(oxalato)borate to the mixed solution A, stir for 30 min to mix evenly, and obtain a mixed solution B; 1.3 Add 0.12 parts by mass of azobisisobutyronitrile to the mixed solution B in 1.2, mix evenly to obtain the electrolyte precursor, seal it with sealing tape, and store it at 2 - 8 °C for later use.

[0018] Step 2: Assemble a high-pressure-resistant solid-state battery in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm); 2.1 Put the pre-cleaned and dried battery case, shrapnel, gasket, etc. into the glove box, cut the high-pressure-resistant lithium cobaltate positive electrode sheet in advance, dry it and put it into the glove box for later use; 2.2 Assemble in the order of positive electrode case, high-pressure-resistant lithium cobaltate electrode sheet, electrospun polyimide membrane, lithium metal sheet, gasket, shrapnel, negative electrode case. Among them, 50 - 60 mL of the pre-polymerization electrolyte obtained in Step 1 is dropped on both sides of the separator, and it is pressed and sealed.

[0019] Step 3: Put the assembled battery into an oven, heat it at 70 °C for 3 h to ensure complete polymerization of the electrolyte, and place it at room temperature for 12 h for testing.

[0020] The lithium metal battery obtained in Example 1 was first activated for 3 cycles at 0.1 C on a LAND charge and discharge instrument, and then cycled at 0.5 C. The average Coulombic efficiency was 99.5%, and the cycle life was 89 cycles. Example 2

[0021] Step 1: Prepare the pre-polymerization electrolyte in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm); 1.1 Take 17 parts by mass of pre-dehydrated butyl hexafluoracrylate and 2.8 parts by mass of polyethylene glycol diacrylate, mix them evenly to obtain a mixed solution A; 1.2 Add 3.4 parts by mass of lithium bis(trifluoromethanesulfonyl)imide and 0.4 part by mass of lithium difluoro(oxalato)borate to the mixed solution A, stir for 30 min to mix evenly, and obtain the mixed solution B; 1.3 Add 0.17 part by mass of azobisisobutyronitrile to the mixed solution B in 1.2, mix evenly to obtain the electrolyte precursor, seal it with a sealing tape, and store it at 2 - 8 °C for later use.

[0022] Step 2: Assemble a high - voltage resistant solid - state battery in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm); 2.1 Put the pre - cleaned and dried battery case, shrapnel, gasket, etc. into the glove box, cut the high - voltage resistant lithium cobaltate cathode sheet in advance, and put it into the glove box after drying for later use; 2.2 Assemble in the order of the positive electrode case, high - voltage resistant lithium cobaltate electrode sheet, electrospun polyimide membrane, lithium metal sheet, gasket, shrapnel, and negative electrode case. Drop 50 - 60 mL of the pre - polymerized electrolyte obtained in Step 1 on both sides of the separator, and press and seal tightly.

[0023] Step 3: Put the assembled battery into an oven, heat it at 70 °C for 3 h to ensure complete polymerization of the electrolyte, and place it at room temperature for 12 h for testing.

[0024] The lithium - metal battery obtained in Example 2 was first activated for 3 cycles at 0.1 C on a LAND charge - discharge instrument, and then subjected to long - term cycling at 0.5 C. The average Coulombic efficiency was 99.8%, and the cycle life was 94 cycles. Example 3

[0025] Step 1: Prepare the pre - polymerized electrolyte in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm); 1.1 Take 18 parts by mass of hexafluoroisopropyl methacrylate that has been pre - dehydrated and 3.6 parts by mass of polyethylene glycol diacrylate, mix them evenly to obtain the mixed solution A; 1.2 Add 3.3 parts by mass of lithium bis(trifluoromethanesulfonyl)imide and 0.5 part by mass of lithium difluoro(oxalato)borate to the mixed solution A, stir for 30 min to mix evenly, and obtain the mixed solution B; 1.3 Add 0.14 part by mass of azobisisobutyronitrile to the mixed solution B in 1.2, mix evenly to obtain the electrolyte precursor, seal it with a sealing tape, and store it at 2 - 8 °C for later use.

[0026] Step 2: Assemble a high - voltage resistant solid - state battery in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm); 2.1 Put the pre-cleaned and dried battery cases, shrapnel, gaskets, etc. into the glove box. Cut the high-voltage-resistant lithium cobalt oxide positive electrode sheets in advance and put them into the glove box for use after drying. 2.2 Assemble in the order of positive electrode case, high-voltage-resistant lithium cobalt oxide electrode sheet, electrospun polyimide film, lithium metal sheet, gasket, shrapnel, and negative electrode case. Drop 50 - 60 mL of the pre-polymerization electrolyte obtained in step 1 on both sides of the separator, and press and seal.

[0027] Step 3: Put the assembled battery into the oven and heat it at 70 °C for 3 h to ensure complete polymerization of the electrolyte. Place it at room temperature for 12 h for testing.

[0028] The lithium metal battery obtained in Example 3 was first activated for 3 cycles at 0.1 C on a LAND charge and discharge instrument, and then subjected to long cycling at 0.5 C. The average Coulombic efficiency was 99.81% and the cycle life was 90 cycles. Example 4

[0029] Step 1: Prepare the pre-polymerization electrolyte in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm). 1.1 Take 17.3 parts by mass of pre-dehydrated perfluoroalkyl ethyl acrylate and 3.1 parts by mass of polyethylene glycol diacrylate, mix them evenly to obtain mixture A. 1.2 Add 3.5 parts by mass of lithium bis(trifluoromethanesulfonyl)imide and 0.3 parts by mass of lithium difluoro(oxalato)borate to mixture A, stir for 30 min to mix evenly, and obtain mixture B. 1.3 Add 0.13 parts by mass of azobisisobutyronitrile to mixture B in 1.2 and mix evenly to obtain the electrolyte precursor. Seal it with sealing tape and store it at 2 - 8 °C for use.

[0030] Step 2: Assemble the high-voltage-resistant solid-state battery in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm). 2.1 Put the pre-cleaned and dried battery cases, shrapnel, gaskets, etc. into the glove box. Cut the high-voltage-resistant lithium cobalt oxide positive electrode sheets in advance and put them into the glove box for use after drying. 2.2 Assemble in the order of positive electrode case, high-voltage-resistant lithium cobalt oxide electrode sheet, electrospun polyimide film, lithium metal sheet, gasket, shrapnel, and negative electrode case. Drop 50 - 60 mL of the pre-polymerization electrolyte obtained in step 1 on both sides of the separator, and press and seal.

[0031] Step 3: Put the assembled battery into the oven and heat it at 70 °C for 3 h to ensure complete polymerization of the electrolyte. Place it at room temperature for 12 h for testing.

[0032] The lithium metal battery obtained in Example 4 was first activated at 0.1 C for 3 cycles on a LAND charge and discharge instrument, and then subjected to long cycling at 0.5 C. The average Coulombic efficiency was 99.3%, and the cycle life was 88 cycles.

[0033] Comparative Example 1 Comparative Example 1 was set up to illustrate that the intrinsically safe solid polymer electrolyte with a three-dimensional chain-like network structure of the present invention can improve the ionic conductivity of the battery.

[0034] Compared with Example 1, the difference in Comparative Example 1 is that the cross-linking agent polyethylene glycol diacrylate in Example 1 is not added, and the remaining steps are the same as those in Example 1.

[0035] The lithium metal battery obtained in Comparative Example 1 was first activated at 0.1 C for 3 cycles on a LAND charge and discharge instrument, and then subjected to long cycling at 0.5 C. The average Coulombic efficiency was 99.0%, and the cycle life was 67 cycles.

[0036] Comparative Example 2 Comparative Example 2 was set up to prove that the fluorinated intrinsically safe solid polymer electrolyte can effectively improve the electrochemical window, enhance the high-voltage resistance performance and cycling stability performance of the battery.

[0037] Compared with Example 2, the difference in Comparative Example 2 is that the fluorinated monomer is not used, and butyl acrylate is used instead. The remaining steps are the same as those in Example 2.

[0038] The lithium metal battery obtained in Comparative Example 2 was first activated at 0.1 C for 3 cycles on a LAND charge and discharge instrument, and then subjected to long cycling at 0.5 C. The average Coulombic efficiency was 98.87%, and the cycle life was 45 cycles.

[0039] Figure 1 It is a photo after polymerization of Example 1, from Figure 1 it can be seen that after polymerization in Example 1, it presents a transparent solid state without flowing liquid. Figure 2 It is the AC impedance curves of Example 1 and Comparative Example 1. The ionic conductivity of the example increased several times compared with the comparative example, indicating that the fluorinated three-dimensional chain-like network structure in the example can form a fast ion conductor, thereby further improving the ionic conductivity performance of the battery. Figure 3 It is the rate performance test of the intrinsically safe solid polymer electrolyte battery obtained in Example 2. From Figure 3 it can be seen that this example has excellent rate performance. Figure 4 It is the charge and discharge cycle performance of the high-voltage resistant solid battery obtained in Example 2 at a rate of 0.5 C. From Figure 4 it can be seen that this example has excellent cycling stability performance.

Claims

1. A method for preparing an intrinsically safe polymer electrolyte and a solid-state battery thereof, characterized in that: It is of the 1M(xA+yB)+(z1C+z2D) type, in which x accounts for 14~15wt%, y accounts for 1~2wt%, z1 accounts for 70~72wt%, and z2 accounts for 11~12wt%. A and B are lithium salts, C is a fluorine-containing monomer, and D is a cross-linking agent. The fluorine-rich monomer, cross-linking agent and lithium salt are mixed without adding any electrolyte. An in-situ polymerization method is used to obtain a solid polymer electrolyte with high safety and high voltage resistance. At the same time, the electrolyte presents a three-dimensional chain network structure.

2. The method for preparing an intrinsically safe polymer electrolyte and a solid-state battery thereof according to claim 1, characterized in that: The following steps are involved: Step 1. Take 5-10 mL of fluorine-rich monomer, remove water through molecular sieves, and store at 2-8°C for later use; Step 2. Take 16-18 parts by weight of the monomer dried in step 1 and mix with 2-4 parts by weight of the cross-linking agent, and mix well to obtain a mixed solution A; Step 3. Add 3 to 4 parts by weight of lithium salt to the mixed solution A obtained in step 2, and stir for 15 to 30 minutes to obtain a mixed solution B; Step 4. Add 0.09-0.17 parts by mass of an initiator to the mixed solution B obtained in step 3, stir for 15-30 minutes to obtain an electrolyte precursor, and store at 2-8°C to be assembled into a battery; Step 5. In a glove box, assemble the cleaned and dried battery positive and negative electrode shells, gaskets, shrapnel, positive electrode sheet, diaphragm and lithium metal sheet in the order of positive electrode shell, positive electrode, diaphragm, lithium metal sheet, gasket, shrapnel and negative electrode shell, wherein 50-60 mL of the electrolyte precursor obtained in step 4 is dripped on both sides of the diaphragm, in-situ polymerized at 70°C for 2-4 hours, and allowed to stand at room temperature for 10-14 hours to obtain the solid-state battery.

3. The method for preparing an intrinsically safe polymer electrolyte according to claim 2, characterized in that: The fluorine-rich monomer is one or more of 2,2,2-trifluoroethyl acrylate, hexafluorobutyl acrylate, fluoroalkyl acrylate, hexafluoroisopropyl methacrylate, perfluoroalkylethyl acrylate, 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxy-4-pentyl methacrylate, 2-methyl-2-(trifluoromethylsulfonamide)propyl methacrylate, 2,2,3,3-tetrafluoropropyl acrylate, and trifluoroethyl methacrylate.

4. The method for preparing an intrinsically safe polymer electrolyte according to claim 2, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), and lithium tetrafluoroborate (LiBF4).

5. The method for preparing an intrinsically safe polymer electrolyte according to claim 2, characterized in that: The cross-linking agent is an acrylic acid or methacrylic acid cross-linking agent.

6. The method for preparing an intrinsically safe polymer electrolyte according to claim 2, characterized in that: The initiator is one or more of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, benzoyl peroxide and lithium iodide.

7. The method for preparing an intrinsically safe polymer electrolyte battery according to claim 2, characterized in that: The diaphragm is one of electrospun polyimide film, glass fiber film, polyethylene diaphragm, polypropylene diaphragm and electrospun polyvinylidene fluoride film; the active material of the positive electrode plate is one of high-voltage lithium cobalt oxide and nickel-cobalt-manganese ternary positive electrode.

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