A polymer composite solid electrolyte, its preparation method, and a lithium-ion battery

Abstract

This invention provides a polymer composite solid electrolyte, its preparation method, and a lithium-ion battery. The polymer composite solid electrolyte comprises a first polymer, a second polymer, and an electrolyte salt; the weight-average molecular weight of the first polymer is not less than 600,000; the weight-average molecular weight of the second polymer is not more than 6,000; the first polymer is polyethylene oxide; and the second polymer is polyethylene glycol. This invention improves the ionic conductivity and mechanical strength of the polymer composite solid electrolyte by combining a high-molecular-weight first polymer with a low-molecular-weight second polymer.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte materials technology, specifically relating to a polymer composite solid electrolyte, its preparation method, and a lithium-ion battery. Background Technology

[0002] Traditional lithium-ion batteries mostly use liquid electrolytes, which pose risks of short circuits, leaks, and even combustion and explosion. Therefore, using solid electrolytes to replace liquid electrolytes is one way to solve these problems. Among them, polyethylene oxide (PEO) solid electrolyte materials are considered one of the most promising solid electrolyte materials for lithium-ion batteries due to their excellent lithium salt dissociation ability, flexibility, and low production cost.

[0003] However, due to the high crystallinity of PEO and the poor chain segment movement in its structure, the ionic conductivity of pure PEO-based polymer solid electrolytes is limited. Existing PEO polymer solid electrolytes exhibit low ionic conductivity (<10 Ω·cm) at room temperature. -5 (S / cm). Currently, researchers have employed several methods to address the problems encountered by solid polymer electrolytes in their applications. One approach is to add inorganic fillers to the polymer electrolyte to further improve its ionic conductivity. However, inorganic fillers are prone to aggregation, thus reducing their interaction with Lewis acids and bases, resulting in lower ionic conductivity. Another technical approach involves optimizing the composition and content of the polymer solid electrolyte to increase its amorphous regions, thereby reducing the crystallinity of the PEO polymer electrolyte and providing more lithium-ion channels and improving the electrochemical performance of lithium-ion batteries.

[0004] Therefore, there is an urgent need in this field to develop a polymer solid electrolyte that not only has high ionic conductivity and good mechanical properties, but also produces lithium-ion batteries with good electrochemical performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a polymer composite solid electrolyte, its preparation method, and a lithium-ion battery. The present invention improves the ionic conductivity and mechanical strength of the polymer composite solid electrolyte by combining a first polymer with a high molecular weight with a second polymer with a low molecular weight.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a polymer composite solid electrolyte, the polymer composite solid electrolyte comprising a first polymer, a second polymer and an electrolyte salt;

[0008] The weight-average molecular weight of the first polymer is not less than 600,000;

[0009] The weight-average molecular weight of the second polymer is not higher than 6000;

[0010] The first polymer is polyethylene oxide;

[0011] The second polymer is polyethylene glycol.

[0012] This invention combines a high-molecular-weight first polymer with a low-molecular-weight second polymer. The first polymer, with a molecular weight of at least 600,000, possesses good mechanical strength and can provide self-support. Simultaneously, the second polymer, with a molecular weight of at least 6,000, exhibits a synergistic effect with the first polymer, comprehensively improving the ionic conductivity of the polymer composite solid electrolyte.

[0013] Furthermore, by adjusting the weight-average molecular weight of the first and second polymers, this invention enables polymers containing -CH2-CH2-O- groups of different molecular weights to form a complex effect, thereby improving the overall performance of the polymer composite solid electrolyte.

[0014] Preferably, the weight-average molecular weight of the first polymer is 600,000 to 800,000, for example, it can be 600,000, 700,000, 800,000, etc.

[0015] Preferably, the weight-average molecular weight of the second polymer is 5000-6000, for example, 5000, 5500, 6000, etc.

[0016] Preferably, the polymer composite solid electrolyte further includes a third polymer.

[0017] Preferably, the weight-average molecular weight of the third polymer is 90-266, for example, it can be 90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 266, etc.

[0018] Preferably, the third polymer is polyethylene glycol dimethyl ether.

[0019] In this invention, by introducing polyethylene glycol dimethyl ether into the polymer composite solid electrolyte, the overall performance of the polymer composite solid electrolyte composed of high molecular weight polyethylene oxide and low molecular weight polyethylene glycol is harmonized.

[0020] Preferably, the electrolyte salt includes a lithium salt.

[0021] Preferably, the lithium salt comprises any one or a combination of at least two of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(difluorosulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide.

[0022] Preferably, the polymer composite solid electrolyte further includes a fourth polymer, which is polyethylene oxide with a weight-average molecular weight of 90,000 to 110,000, for example, 90,000, 100,000, 110,000, etc.

[0023] Preferably, the molar ratio of the -CH2-CH2-O- group in the structure of the combination of the first polymer, the second polymer, the third polymer and the fourth polymer to the metal ion in the electrolyte salt is (6-8):1, for example, it can be 6:1, 6.2:1, 6.5:1, 6.8:1, 7:1, 7.2:1, 7.5:1, 7.8:1, 8:1, etc.

[0024] In this invention, by adjusting the molar ratio of -CH2-CH2-O- groups in the structure of the combination of the first polymer, the second polymer, the third polymer and the fourth polymer to the metal ions in the electrolyte salt, the ratio of -CH2-CH2-O- groups to metal ions in the polymer solid electrolyte is kept within a suitable range, which is beneficial to improving the overall performance of the polymer composite solid electrolyte.

[0025] Preferably, the polymer composite solid electrolyte may further include an aerogel material.

[0026] Preferably, the aerogel material includes any one or a combination of at least two of SiO2 aerogel, Al2O3-SiO2 aerogel, B2O5-SiO2 aerogel, or MgO-SiO2-Al2O3 aerogel.

[0027] Preferably, the mass percentage of the aerogel material is 10-15% based on the total mass of the first polymer being 100%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, etc.

[0028] In this invention, by adjusting the mass percentage of the aerogel material, the performance of the polymer composite solid electrolyte is made more stable.

[0029] In a second aspect, the present invention provides a method for preparing a polymer composite solid electrolyte according to the first aspect, the method comprising the following steps:

[0030] The first polymer, the second polymer, the electrolyte salt and the solvent are mixed to obtain a slurry, which is then coated on the surface of a substrate and dried to obtain the polymer composite solid electrolyte.

[0031] This invention does not have any particular requirements for the type of solvent. Without departing from the inventive concept of this invention, any known type of solvent can be used in this invention. As an implementable approach, the solvent may be, for example, acetonitrile.

[0032] Preferably, before mixing, any one or a combination of at least two of the third polymer, aerogel material, or fourth polymer may be added.

[0033] Preferably, the weight-average molecular weight of the third polymer is 90-266, for example, it can be 90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 266, etc.

[0034] Preferably, the third polymer is any one or a combination of at least two of polyethylene glycol dimethyl ether.

[0035] Preferably, the aerogel material includes any one or a combination of at least two of SiO2 aerogel, Al2O3-SiO2 aerogel, B2O5-SiO2 aerogel, or MgO-SiO2-Al2O3 aerogel.

[0036] Preferably, the fourth polymer is polyethylene oxide with a weight-average molecular weight of 90,000 to 110,000, and the weight-average molecular weight can be, for example, 90,000, 100,000, 110,000, etc.

[0037] Preferably, the mixing is performed by stirring at room temperature.

[0038] Preferably, the coating includes scraping.

[0039] Preferably, the substrate comprises aluminum foil.

[0040] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the electrolyte comprises a polymer composite solid electrolyte according to the first aspect.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] This invention provides a polymer composite solid electrolyte, which is produced by combining a first polymer with a high molecular weight with a second polymer with a low molecular weight. The first polymer, with a molecular weight of not less than 600,000, possesses good mechanical strength and can provide self-support. Simultaneously, the second polymer, with a molecular weight of not more than 6,000, has a synergistic effect with the first polymer, comprehensively improving the ionic conductivity of the polymer composite solid electrolyte. Attached Figure Description

[0043] Figure 1The image shown is a scanning electron microscope image of the polymer composite solid electrolyte provided in Example 2, with a scale bar of 100 μm. Detailed Implementation

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0045] Example 1

[0046] This embodiment provides a polymer composite solid electrolyte, which includes polyethylene oxide (PEO) with a weight average molecular weight of 600,000, polyethylene oxide with a weight average molecular weight of 100,000, polyethylene glycol (PEG) with a weight average molecular weight of 6,000, polyethylene glycol dimethyl ether (PEGDME) with a weight average molecular weight of 202, lithium bis(trifluoromethanesulfonyl)imide, and silica aerogel.

[0047] This embodiment also provides a method for preparing the above-mentioned polymer composite solid electrolyte, which includes the following steps:

[0048] PEO(M) W =600000), PEO(M W =100000), PEG(M) W =6000) and PEGDME were weighed at a mass ratio of 1:1:1:1, 2g each, and added to 25g of acetonitrile solution. Then, lithium bis(trifluoromethanesulfonyl)imide was added, wherein the molar ratio of -CH2-CH2-O- groups to lithium ions in all polymer structures was 8:1. Silica aerogel (in the form of polyethylene oxide (M)) was then added. W A slurry was prepared by mixing a total mass of 600,000 (100% of the total mass, with a mass percentage of 15 wt.%), and then stirring the slurry at 500 rpm at room temperature for 24 h. The resulting slurry was then cast onto aluminum foil, and the thickness was controlled to 50 μm using a scraper. The resulting electrolyte membrane was dried in a vacuum drying oven at 60 °C for 24 h to remove excess solvent, yielding a polymer composite solid electrolyte.

[0049] Example 2

[0050] This embodiment provides a polymer composite solid electrolyte, which includes polyethylene oxide (PEO) with a weight average molecular weight of 600,000, polyethylene oxide with a weight average molecular weight of 100,000, polyethylene glycol (PEG) with a weight average molecular weight of 6,000, and lithium bis(trifluoromethanesulfonyl)imide.

[0051] This embodiment also provides a method for preparing the above-mentioned polymer composite solid electrolyte, which includes the following steps:

[0052] PEO(M) W =600000), PEO(M W =100000) and PEG(M W =6000) Weigh 2g of the solution according to a 1:1:1 mass ratio and add it to 25g of acetonitrile solution. Then add lithium bis(trifluoromethanesulfonyl)imide, wherein the molar ratio of -CH2-CH2-O- groups to lithium ions in all polymer structures is 8:1 to obtain a slurry. The slurry is then stirred at 500rpm at room temperature for 24h. The obtained slurry is cast onto aluminum foil, and the thickness is controlled to 50μm using a scraper. The resulting electrolyte membrane is dried in a vacuum drying oven at 60℃ for 24h to remove excess solvent, yielding a polymer composite solid electrolyte.

[0053] Figure 1 This indicates that the surface of the polymer composite solid electrolyte provided in this embodiment is smooth and has no obvious defects.

[0054] Example 3

[0055] The difference between this embodiment and Embodiment 1 is that the polyethylene oxide with a weight-average molecular weight of 100,000 is replaced with an equal mass of polyethylene oxide with a weight-average molecular weight of 600,000; all other aspects are the same as in Embodiment 1.

[0056] Example 4

[0057] The difference between this embodiment and Embodiment 1 is that the polyethylene oxide with a weight average molecular weight of 600,000 is replaced with an equal mass of polyethylene oxide with a weight average molecular weight of 100,000; all other aspects are the same as in Embodiment 1.

[0058] Example 5

[0059] The difference between this embodiment and Example 1 is that polyethylene glycol with a weight average molecular weight of 6000 is replaced with an equal mass of polyethylene glycol with a weight average molecular weight of 12000; otherwise, they are the same as in Example 1.

[0060] Example 6

[0061] The difference between this embodiment and Example 1 is that the molar ratio of -CH2-CH2-O- groups to lithium ions in all polymer structures is 2:1, while all other aspects are the same as in Example 1.

[0062] Example 7

[0063] The difference between this embodiment and Example 1 is that the molar ratio of -CH2-CH2-O- groups to lithium ions in all polymer structures is 12:1, while all other aspects are the same as in Example 1.

[0064] Example 8

[0065] The difference between this embodiment and Embodiment 1 is that polyethylene oxide (M) is used. W The total mass of (600,000) is 100%, and the mass percentage of silica aerogel is 2 wt.%. Everything else is the same as in Example 1.

[0066] Example 9

[0067] The difference between this embodiment and Embodiment 1 is that polyethylene oxide (M) is used. W The total mass of (600,000) is 100%, and the mass percentage of silica aerogel is 20 wt.%. Everything else is the same as in Example 1.

[0068] Application Examples 1 to 9

[0069] Lithium-ion batteries were prepared using the polymer composite solid electrolytes provided in Examples 1 to 9, and the preparation methods are as follows:

[0070] Preparation of cathode mixture: The active material is a single-crystal ternary cathode material LiNi. 0.5 Co 0.2 Mn 0.3 O2, with LiNi in a mass ratio of 50:38:6:2:4 0.5 Co 0.2 Mn 0.3 O2, halide solid electrolyte, VGCF, Super P, and PTFE were ball-milled to obtain a positive electrode mixture;

[0071] In a solid-state battery test mold with a diameter of 10 mm, 6 mg of polymer composite solid electrolyte powder is first added and pressed into a sheet at a pressure of 400 MPa, with a thickness of about 30 μm. Then, the mold is opened, and 10 mg of positive electrode mixture is spread evenly on one side of the pressed composite electrolyte. The sheet is then pressed again at a pressure of 400 MPa. The battery mold is then disassembled, and a lithium sheet with a thickness of 500 μm is attached to the other side of the polymer composite solid electrolyte. The mold is then reassembled, thus obtaining a solid-state battery.

[0072] The lithium-ion batteries provided in Application Examples 1 to 9 were tested, and the cycle performance test method is as follows:

[0073] The solid-state battery prepared above was subjected to cycle testing using a Blue Electric test system with a voltage range of 3-4.3V and a test temperature of 25℃. The first two cycles were performed at a low rate of 0.05C, and the rate was adjusted to 0.1C from the third cycle onwards. The capacity after 32 cycles was recorded, and the cycle capacity retention rate was obtained by dividing the capacity of the 32nd cycle by the capacity of the 3rd cycle, which was used to evaluate the interfacial stability of the electrolyte system.

[0074] The test results are shown in Table 1:

[0075] Table 1

[0076]

[0077]

[0078] As shown in Table 1, this application uses three different molecular weights of PEO or polyethylene glycol containing -CH2-CH2-O- groups to prepare polymer composite solid electrolytes, forming a good synergistic effect. Furthermore, by using polyethylene glycol dimethyl ether, which also contains -CH2-CH2-O- groups, and a specific amount of silica aerogel, a lithium-ion polymer solid battery with good cycle performance was obtained.

[0079] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A polymer composite solid electrolyte, characterized in that, The polymer composite solid electrolyte comprises a first polymer, a second polymer, a third polymer, a fourth polymer, and an electrolyte salt; The weight-average molecular weight of the first polymer is 600,000 to 800,000; The weight-average molecular weight of the second polymer is not higher than 6000; The first polymer is polyethylene oxide; The second polymer is polyethylene glycol; The weight-average molecular weight of the third polymer is 90-266; The third polymer is polyethylene glycol dimethyl ether; The fourth polymer is polyethylene oxide with a weight-average molecular weight of 90,000 to 110,000; The molar ratio of the -CH2-CH2-O- groups in the structure of the combination of the first polymer, the second polymer, the third polymer and the fourth polymer to the metal ions in the electrolyte salt is (6-8):

1.

2. The polymer composite solid electrolyte according to claim 1, characterized in that, The weight-average molecular weight of the second polymer is 5000-6000.

3. The polymer composite solid electrolyte according to claim 1, characterized in that, The electrolyte salt includes lithium salt; The lithium salt includes any one or a combination of at least two of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(difluorosulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide.

4. The polymer composite solid electrolyte according to claim 1, characterized in that, The polymer composite solid electrolyte also includes aerogel materials; The aerogel material includes any one or a combination of at least two of SiO2 aerogel, Al2O3-SiO2 aerogel, B2O5-SiO2 aerogel or MgO-SiO2-Al2O3 aerogel. With the total mass of the first polymer being 100%, the mass percentage of the aerogel material is 10-15%.

5. A method for preparing the polymer composite solid electrolyte of claim 1, characterized in that, The method includes the following steps: The first polymer, the second polymer, the third polymer, the fourth polymer, the electrolyte salt and the solvent are mixed to obtain a slurry, which is then coated on the surface of a substrate and dried to obtain the polymer composite solid electrolyte.

6. A method for preparing the polymer composite solid electrolyte of claim 4, characterized in that, The method includes the following steps: The first polymer, the second polymer, the third polymer, the fourth polymer, the aerogel, the electrolyte salt and the solvent are mixed to obtain a slurry, which is then coated on the surface of the substrate and dried to obtain the polymer composite solid electrolyte.

7. The method for preparing polymer composite solid electrolytes according to any one of claims 5-6, characterized in that, The solvent is acetonitrile; The mixture is stirred at room temperature; The coating includes scraping; The substrate includes aluminum foil.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The electrolyte includes a polymer composite solid electrolyte according to any one of claims 1-4, or a polymer composite solid electrolyte prepared by any one of claims 5-7.

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