A binder for solid-state batteries and its preparation method and application

Abstract

The invention discloses a binder for solid-state batteries, which is composed of 10 to 20 parts of polycaprolactone, 12 to 18 parts of dimethyl carbonate, 8 to 16 parts of modified chitosan, and 60 to 80 parts of a solvent. The preparation method comprises the following steps: adding polycaprolactone, dimethyl carbonate, and modified chitosan to a solvent, stirring and ultrasonicating for 0.5 to 1 hour, and then stirring at 40 to 80°C for 6 to 12 hours. The binder prepared by the invention can improve the wettability between the interface between the electrode and the solid electrolyte, improve the lithium ion conduction mechanism of the solid electrolyte, and simultaneously has excellent bonding performance and flexibility, can buffer the volume change of the electrode during the lithium insertion and deinsertion process, ensure the integrity of the electrode structure, inhibit contact deterioration caused by expansion of the electrode material, and improve the cycle performance of the solid-state battery.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and in particular to a binder for solid-state batteries, as well as a preparation method and application thereof. Background Art

[0002] With the continuous development of society and the economy, low-carbon, environmentally friendly new energy industries are gaining increasing attention. Lithium batteries, particularly solid-state lithium batteries, have been a hot topic in recent years. To avoid the safety issues associated with electrolyte leakage in traditional lithium batteries, lithium secondary battery electrolyte systems are evolving to solid-state electrolytes. Compared to liquid electrolytes, solid-state electrolytes are non-volatile, flame-retardant, and reduce side reactions caused by electrolytes, significantly improving battery safety. Furthermore, solid-state electrolytes are lightweight, possess a certain mechanical strength, are easily designed, and have a longer lifespan, better meeting production and application requirements. This will facilitate the development of future energy storage devices towards lightweight, environmentally friendly, and miniaturized designs.

[0003] All-solid-state batteries replace traditional separators and electrolytes with solid-state electrolyte membranes, improving battery safety while increasing energy density. Traditional liquid batteries use coated positive and negative electrodes, with lithium ions transferred by injecting electrolyte into the pores. However, solid-state batteries, due to their solid electrolyte membranes, require electrolytes to create ion pathways between the positive and negative electrodes.

[0004] The interface problem of solid-state batteries is currently recognized by the academic community as the most important difficulty affecting the performance of solid-state batteries. Both solid-state lithium-ion and sodium-ion batteries face the challenge of improving the compatibility between the electrode and the solid electrolyte layer. The interface in solid-state batteries changes from the solid-liquid contact interface in traditional liquid batteries to a solid-solid contact interface. In most cases, it is a point contact with a small contact area. In a few battery systems, the interface can initially be a surface contact. However, as the battery cycles, the electrode material inevitably expands in volume, deteriorating the originally good contact, resulting in a reduction in ion transmission pathways, increased interfacial impedance, and continued deterioration of battery performance.

[0005] Chinese patent document CN201611047441.2 discloses a method for preparing solid-state lithium battery electrodes using PEO as a binder. The manufacturing method is as follows: electrode materials, PEO, lithium salt, inorganic filler, etc. are dissolved in acetonitrile solvent in a certain proportion, and after stirring evenly, they are coated on a current collector to obtain an electrode using PEO as a binder.

[0006] Existing adhesives exhibit poor viscosity, which causes the electrodes to easily shed powder and crack, or although they have strong bonding ability, they cannot contribute to ion conduction, affecting battery performance. Summary of the Invention

[0007] In order to address the deficiencies in the prior art, one of the objectives of the present invention is to provide a binder for solid-state batteries.

[0008] The technical solution adopted by the present invention to solve its technical problem is: a binder for solid-state batteries, which is made of the following components, calculated by weight: 10 to 20 parts of polycaprolactone, 12 to 18 parts of dimethyl carbonate, 8 to 16 parts of modified chitosan, and 60 to 80 parts of a solvent; the solvent is one or more of acetone, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0009] The second object of the present invention is to provide a method for preparing a binder for solid-state batteries. The prepared binder can improve the wettability between the interface of the electrode and the solid electrolyte, improve the lithium ion conduction mechanism of the solid electrolyte, and at the same time has excellent bonding performance, Young's modulus and elongation at break. It can buffer the volume change of the electrode during lithium insertion and deintercalation, ensure the integrity of the electrode structure, inhibit the contact deterioration caused by the expansion of the electrode material, and improve the cycle performance of the solid-state battery. The method comprises the following steps: adding 10 to 20 g of polycaprolactone, 12 to 18 g of dimethyl carbonate and 8 to 16 g of modified chitosan to 60 to 80 g of solvent, stirring and ultrasonicating for 0.5 to 1 hour, and then stirring at 40 to 80 ° C for 6 to 12 hours to obtain a binder for solid-state batteries.

[0010] Furthermore, the preparation steps of the modified chitosan are as follows:

[0011] (1) Add 10 g of chitosan to 50-80 g of sodium hydroxide isopropanol solution and stir at room temperature for 1-2 h. Then add 32-47 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide and stir at 50-70 ° C and 420-500 r / min for 3-5 h. Cool the reaction solution and add it dropwise to an ice water bath for precipitation. Wash the precipitate with ethanol and dry it to obtain the intermediate modified chitosan. The specific reaction process is as follows:

[0012] .

[0013] (2) Disperse 5 g of the intermediate modified chitosan in 50-80 g of DMF, then add 1-3 g of isocyanatepropyltriethoxysilane and 0.01-0.2 g of dibutyltin dilaurate and stir to react. The product is precipitated in an ice-water bath, filtered, washed with ether, and dried to obtain modified chitosan. The specific reaction process is as follows:

[0014] .

[0015] Furthermore, in step (1), the mass fraction of the sodium hydroxide isopropanol solution is 10-20%; the mass ratio of chitosan, sodium hydroxide isopropanol solution and 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide is 10:50-80:32-47.

[0016] Furthermore, in step (2), the mass ratio of the intermediate, DMF, isocyanatepropyltriethoxysilane and dibutyltin dilaurate is 5:50-80:1-3:0.01-0.2; the stirring reaction condition is 80-100° C. and the stirring reaction is performed for 10-14 hours; and the modified chitosan is further subjected to a treatment for removing free proton hydrogen until the moisture content is ≤20 ppm as tested by the Karl Fischer method.

[0017] Furthermore, in step (1), the mixture is stirred at room temperature at 420-500 r / min for 1-2 hours, and then heated to 50-70° C. and stirred at 420-500 r / min for 3-5 hours.

[0018] A third object of the present invention is to provide the above-mentioned solid-state battery binder for use in a solid-state battery electrode slurry. When the electrode slurry is a negative electrode slurry, the binder comprises an active material, a solid electrolyte, a conductive agent, and the solid-state battery binder according to claim 1 in a mass ratio of 50-75:10-30:1-10:1-15. The active material is selected from one or more of Si / C450, graphite, and LiCoO2; the solid electrolyte is selected from one or more of LPSC651, LPS314, and Li2S-P2S5; and the conductive agent is selected from one or more of VGCF, CNTs, and Super P.

[0019] A fourth object of the present invention is to provide a solid-state battery binder for use in a solid-state battery electrode slurry. When the electrode slurry is a positive electrode slurry, the binder comprises an active material, a solid electrolyte, a conductive agent, and the solid-state battery binder of claim 1 in a mass ratio of 50-80:10-30:1-5:1-10. The active material is selected from one or more of NCM811, NCM523, NCM622, and LiFePO4; the solid electrolyte is selected from one or more of LPSC651, LPS314, and Li2S-P2S5; and the conductive agent is selected from one or more of VGCF, CNTs, and Super P.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The solid-state battery binder of the present invention uses polycaprolactone, dimethyl carbonate, and modified chitosan as raw materials, wherein polycaprolactone has excellent stability and electrochemical window, can wet the solid electrolyte electrolytic interface, and will not react with the positive electrode active material to form an undesirable inert interface layer; dimethyl carbonate can also improve the wettability between the electrode and the solid electrolyte interface, and can also effectively improve the lithium ion conduction mechanism of the solid electrolyte, reduce the interface impedance between the electrode and the solid electrolyte membrane, and improve the ionic conductivity of the binder; the modified chitosan is modified by grafting functionalized adhesive chain segments, which can improve the bonding performance and flexibility of the binder, thereby effectively buffering the volume change of the electrode during the lithium insertion and deintercalation process, ensuring the integrity of the electrode structure, inhibiting the contact deterioration caused by the expansion of the electrode material, and improving the cycle performance of the solid-state battery.

[0022] 2) The modified chitosan of the present invention firstly utilizes the epoxy group of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide to react with the active amino group on the chitosan chain segment in an alkaline environment to generate a ring-opening reaction, and introduces the fluorine chain segment into the binder to obtain an intermediate, thereby improving the dispersibility of the chitosan in the binder matrix. At the same time, the introduced chain segment has a suitable glass transition temperature, which can improve the flexibility of the binder and avoid shrinkage during drying of the adhesive film. Then, under the catalysis of dibutyltin dilaurate, propyl triethoxy isocyanate is catalyzed by dibutyltin dilaurate. The isocyanate group of silane reacts with the active hydroxyl groups in chitosan to introduce siloxane chain segments to obtain modified chitosan. After the modified chitosan is compounded with polycaprolactone and dimethyl carbonate to prepare a binder, its siloxane segments can undergo condensation reaction with the hydroxyl groups on the surface of the active material and the current collector, so that the binder can tightly combine the active material, the conductive agent and the current collector through chemical bonds, effectively enhancing the interfacial bonding strength, enabling the binder to effectively adapt to the volume expansion of the active material during the cycle, and significantly improving the electrochemical performance of the solid-state battery. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0024] Unless otherwise specified, the chemical reagents and materials used in the present invention were purchased from commercial sources or synthesized from commercially available raw materials. Chitosan had a viscosity of 200-800 cp and a degree of deacetylation of ≥90%. Polycaprolactone was purchased from Shandong Liang New Materials Technology Co., Ltd., model LA1444.

[0025] The present invention will be further described below with reference to specific examples. Example 1

[0026] This embodiment discloses a method for preparing a binder for solid-state batteries, comprising the following steps.

[0027] (1) Add 10 g of chitosan to 80 g of 20 wt% sodium hydroxide isopropanol solution and stir at room temperature for 2 h. Then add 47 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide and stir at 70 °C and 500 r / min for 5 h. Cool the reaction solution and add it dropwise to an ice-water bath for precipitation. Wash the precipitate with ethanol and dry it to obtain the intermediate.

[0028] (2) Disperse 5 g of the intermediate in 80 g of DMF, then add 3 g of isocyanatepropyltriethoxysilane and 0.2 g of dibutyltin dilaurate, and stir the mixture at 100 °C for 14 h. The product is precipitated in an ice-water bath, filtered, washed with ether, and dried to obtain modified chitosan. The modified chitosan is treated to remove free proton hydrogen until the moisture content is ≤20 ppm as tested by the Karl Fischer method.

[0029] (3) 20 g of polycaprolactone, 18 g of dimethyl carbonate, and 16 g of modified chitosan were added to 80 g of DMF, stirred and ultrasonicated for 1 h, and then stirred at 80° C. for 12 h to obtain the binder for solid-state batteries.

[0030] The preparation method of the solid-state battery negative electrode plate based on the above-mentioned binder comprises the following steps: taking 0.6 g of negative electrode active material Si / C450, 0.2 g of solid electrolyte LPS314, 0.05 g of conductive agent CNTs and 0.15 g of the binder prepared in Example 1, mixing them in a micro ball mill at a speed of 1000 r / min for 30 min, and then coating them on stainless steel foil with a 300 μm SQZ four-sided preparation device, and drying them at 60°C for 12 h.

[0031] The preparation method of the solid-state battery includes the following steps: cutting the prepared negative electrode into 10mm small discs, weighing 85mg of LPS314 in the glove box and pouring it into the mold, pressing it twice at 300MPa, adding the negative electrode piece at one end, pressing it twice under the same conditions, and then adding a lithium sheet with a diameter of 10mm. After sealing, the mold frame is tightened with a 3.5N torque wrench. Example 2

[0032] This embodiment discloses a method for preparing a binder for solid-state batteries, comprising the following steps.

[0033] (1) Add 10 g of chitosan to 70 g of 15 wt% sodium hydroxide isopropanol solution and stir at room temperature for 1.5 h. Then add 43 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide and stir at 65 °C and 480 r / min for 4.5 h. Cool the reaction solution and add it dropwise to an ice-water bath for precipitation. Wash the precipitate with ethanol and dry it to obtain the intermediate.

[0034] (2) Disperse 5 g of the intermediate in 70 g of DMF, then add 2.5 g of isocyanatepropyltriethoxysilane and 0.15 g of dibutyltin dilaurate, and stir the reaction at 90 °C for 12 h. The product is precipitated in an ice-water bath, filtered, washed with ether, and dried to obtain modified chitosan. The modified chitosan is treated to remove free proton hydrogen until the moisture content is ≤20 ppm as tested by the Karl Fischer method.

[0035] (3) 18 g of polycaprolactone, 16 g of dimethyl carbonate, and 14 g of modified chitosan were added to 70 g of acetone, stirred and ultrasonicated for 1 hour, and then stirred at 70° C. for 10 hours to obtain the binder for solid-state batteries.

[0036] The preparation method of the solid-state battery and the electrode is the same as that in Example 1. Example 3

[0037] This embodiment discloses a method for preparing a binder for solid-state batteries, comprising the following steps.

[0038] (1) Add 10 g of chitosan to 60 g of a 15 wt% sodium hydroxide isopropanol solution and stir at room temperature for 1.5 h. Then add 39 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide and stir at 60 °C and 450 r / min for 4 h. Cool the reaction solution and add it dropwise to an ice-water bath for precipitation. Wash the precipitate with ethanol and dry it to obtain the intermediate.

[0039] (2) Disperse 5 g of the intermediate in 60 g of DMF, then add 2 g of isocyanatepropyltriethoxysilane and 0.02 g of dibutyltin dilaurate, and stir the reaction at 90 °C for 11 h. The product is precipitated in an ice-water bath, filtered, washed with ether, and dried to obtain modified chitosan. The modified chitosan is treated to remove free proton hydrogen until the moisture content is ≤20 ppm as tested by the Karl Fischer method.

[0040] (3) 16 g of polycaprolactone, 14 g of dimethyl carbonate, and 12 g of modified chitosan were added to 65 g of N-methylpyrrolidone, stirred and ultrasonicated for 1 hour, and then stirred at 60° C. for 8 hours to obtain the binder for solid-state batteries.

[0041] The preparation method of the solid-state battery and the electrode is the same as that in Example 1. Example 4

[0042] This embodiment discloses a method for preparing a binder for solid-state batteries, comprising the following steps.

[0043] (1) Add 10 g of chitosan to 50 g of a 10 wt% sodium hydroxide isopropanol solution and stir at room temperature for 1 h. Then add 32 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide and stir at 50 °C and 420 r / min for 3 h. Cool the reaction solution and add it dropwise to an ice-water bath for precipitation. Wash the precipitate with ethanol and dry it to obtain the intermediate.

[0044] (2) Disperse 5 g of the intermediate in 50 g of DMF, then add 1 g of isocyanatepropyltriethoxysilane and 0.01 g of dibutyltin dilaurate, and stir the reaction at 80 °C for 10 h. The product is precipitated in an ice-water bath, filtered, washed with ether, and dried to obtain modified chitosan. The modified chitosan is treated to remove free proton hydrogen until the moisture content is ≤20 ppm as tested by the Karl Fischer method.

[0045] (3) 10 g of polycaprolactone, 12 g of dimethyl carbonate, and 8 g of modified chitosan were added to 60 g of N,N-dimethylacetamide or dimethyl sulfoxide, stirred and ultrasonicated for 1 h, and then stirred at 40° C. for 6 h to obtain the binder for solid-state batteries.

[0046] The preparation method of the solid-state battery and the electrode is the same as that in Example 1.

[0047] Comparative Example 1: A method for preparing a binder for solid-state batteries, comprising the following steps.

[0048] (1) Add 10 g of chitosan to 80 g of 20 wt% sodium hydroxide isopropanol solution and stir at room temperature for 2 h. Then add 47 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide and stir at 70 ° C and 500 r / min for 5 h. The reaction solution is cooled and added dropwise to an ice water bath for precipitation. The precipitate is washed with ethanol and dried to obtain an intermediate. The intermediate is treated to remove free proton hydrogen until the moisture content is ≤20 ppm as tested by the Karl Fischer method.

[0049] (2) 20 g of polycaprolactone, 18 g of dimethyl carbonate, and 16 g of the intermediate were added to 80 g of DMF, stirred and ultrasonicated for 1 hour, and then stirred at 80° C. for 12 hours to obtain the binder for solid-state batteries.

[0050] The preparation method of the solid-state battery and the electrode is the same as that in Example 1.

[0051] Comparative Example 2: A method for preparing a binder for solid-state batteries, comprising the following steps: adding 20 g of polycaprolactone, 18 g of dimethyl carbonate, and 16 g of chitosan to 80 g of DMF, stirring and ultrasonicating for 1 hour, and then stirring at 80°C for 12 hours to obtain a binder for solid-state batteries.

[0052] The preparation method of the solid-state battery and the electrode is the same as that in Example 1.

[0053] The peel strength of the adhesives prepared in the Examples and Comparative Examples was tested using a universal tensile testing machine, referring to GB / T2790-1995 "Test method for 180-degree peel strength of adhesives - Flexible material to rigid material." The testing method involves: taking two pieces of copper foil measuring 40 mm x 100 mm and cleaning them with alcohol before use; applying enough electrode slurry to one end of each piece of copper foil to cover an area of ​​5.5 cm x 1.3 cm and drying them in a 60°C oven for 2 hours; finally, securing one end of the sample to a tensile probe and peeling the sample through 180° at a constant speed of 10 mm / min. The peel force during the test indicates the adhesive's strength. Specific data are shown in the table below.

[0054]

[0055] The solid-state batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to performance tests. The charge and discharge performance of the batteries was tested using a LAND-CT2001A tester at 70°C and 0.2C, with a voltage range of 2.8 to 4.2V and a constant current charge and discharge method.

[0056] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A binder for solid-state batteries, characterized in that: The invention is composed of 10-20 parts of polycaprolactone, 12-18 parts of dimethyl carbonate, 8-16 parts of modified chitosan, and 60-80 parts of a solvent; the solvent is one or more of acetone, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the modified chitosan is prepared by the following steps: (1) Chitosan was added to a sodium hydroxide isopropanol solution and stirred at room temperature. Then 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide was added and the temperature was raised and stirred. The reaction solution was cooled and added dropwise to an ice water bath for precipitation. The precipitate was washed with ethanol and dried to obtain an intermediate. (2) The intermediate was dispersed in DMF, and then propyltriethoxysilane and dibutyltin dilaurate were added and stirred for reaction. The product was precipitated in an ice-water bath, filtered, washed with ether, and dried to obtain modified chitosan.

2. A method for preparing a binder for solid-state batteries according to claim 1, characterized in that: The method comprises the following steps: adding polycaprolactone, dimethyl carbonate and modified chitosan into a solvent, stirring and ultrasonicating for 0.5 to 1 hour, and then stirring at 40 to 80° C. for 6 to 12 hours to obtain a binder for solid-state batteries.

3. The method for preparing a binder for solid-state batteries according to claim 2, wherein: The mass fraction of the sodium hydroxide isopropanol solution in step (1) is 10-20%; the mass ratio of chitosan, sodium hydroxide isopropanol solution and 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide is 10:50-80:32-47.

4. The method for preparing a binder for solid-state batteries according to claim 3, wherein: In the step (2), the mass ratio of the intermediate, DMF, isocyanatepropyltriethoxysilane and dibutyltin dilaurate is 5:50-80:1-3:0.01-0.2, and the stirring reaction conditions are 80-100° C. and the stirring reaction is carried out for 10-14 hours; the modified chitosan is further subjected to a treatment for removing free proton hydrogen until the moisture content is ≤20 ppm as tested by the Karl Fischer method.

5. The method for preparing a binder for solid-state batteries according to claim 4, wherein: In the step (1), the mixture is stirred at room temperature for 1 to 2 hours, and then stirred at 50 to 70°C at 420 to 500 r / min for 3 to 5 hours.

6. A use of the solid-state battery binder according to claim 1 in a solid-state battery negative electrode slurry, characterized in that: The negative electrode slurry is composed of an active material, a solid electrolyte, a conductive agent and the binder for a solid-state battery according to claim 1 in a mass ratio of 50 to 75:10 to 30:1 to 10:1 to 15.

7. The use according to claim 6, characterized in that The active material is selected from one or more of Si / C450, graphite, and LiCoO2; the solid electrolyte is selected from one or more of LPSC651, LPS314, and Li2S-P2S5; and the conductive agent is selected from one or more of VGCF, CNTs, and Super P.

8. A use of the solid-state battery binder according to claim 1 in a solid-state battery positive electrode slurry, characterized in that: The positive electrode slurry is composed of an active material, a solid electrolyte, a conductive agent and the binder for a solid-state battery according to claim 1 in a mass ratio of 50 to 80:10 to 30:1 to 5:1 to 10.

9. The use according to claim 8, characterized in that The active material is selected from one or more of NCM811, NCM523, NCM622, and LiFePO4; the solid electrolyte is selected from one or more of LPSC651, LPS314, and Li2S-P2S5; and the conductive agent is selected from one or more of VGCF, CNTs, and Super P.

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