Preparation method of silicon-based negative electrode binder and negative electrode slurry

Abstract

The application discloses a preparation method of a silicon-based negative electrode binder, which comprises the following steps: adding chitosan into a sodium hydroxide isopropanol solution, stirring at room temperature, then adding 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide, stirring and reacting under temperature rising, dropping into an ice water bath after cooling to precipitate, washing the precipitate with ethanol, drying to obtain modified chitosan, dispersing the modified chitosan into DMF, then adding propyl triethoxysilane isocyanate and dibutyl tin dilaurate, stirring and reacting, precipitating the product in an ice water bath, filtering, washing with diethyl ether and drying to obtain an intermediate, and adding an additive to the intermediate after free proton hydrogen treatment to obtain the silicon-based negative electrode binder; the application further discloses a battery negative electrode slurry; the binder prepared by the method has high peeling strength, can effectively buffer the volume change of the silicon-based negative electrode in the process of lithium extraction and embedding, thereby effectively ensuring the integrity of the electrode structure and improving the cycle performance of the silicon-based negative electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a preparation method of a binder for a silicon-based negative electrode and a negative electrode slurry. BACKGROUND

[0002] In recent years, in the face of higher requirements in the fields of long-range electric vehicles, portable electronic products, aerospace and high-end military equipment, high specific capacity and low cost lithium ion batteries have become the research focus. Among them, high specific capacity positive and negative electrode materials are the key factors to improve the energy density of lithium ion batteries. The current commercialized lithium ion battery negative electrode material is mainly graphite-based carbon negative electrode material, and its theoretical specific capacity is only 372 mAh / g, which seriously limits the further development of lithium ion batteries.

[0003] Silicon-based materials are the highest theoretical specific capacity research system among the researched negative electrode materials, with a theoretical specific capacity of up to 4200 mAh / g. Because of its low lithium intercalation potential, low atomic mass, high energy density and high Li molar fraction in Li-Si alloy, and the fact that the material is abundant and low in price, it is considered to be a substitute for carbon negative electrode materials. However, the silicon negative electrode has serious volume expansion and contraction during the intercalation and deintercalation of lithium, causing the destruction of the material structure and mechanical crushing, resulting in poor cycle performance of the electrode, so a suitable binder needs to be found to improve its cycle performance.

[0004] The binder is a non-active component in the lithium ion battery electrode sheet and is one of the important materials for preparing the lithium ion battery electrode sheet. The main function of the binder is to connect the electrode active material, the conductive agent and the electrode current collector, so that they have overall connectivity. In the charging and discharging process, the binder effectively maintains the integrity of the electrode structure and ensures that the electrode material can repeatedly intercalate and deintercalate lithium, so the binder is a crucial factor for the normal operation of the lithium ion battery and also plays an important role in improving the cycle performance of the silicon-based negative electrode material.

[0005] In the prior art, common binders include PAA, CMC / SBR, sodium alginate, chitosan, PI, PAI, etc. Chinese patent document CN201810873435.5 discloses a modified chitosan as a lithium ion battery negative electrode binder and a preparation method of a negative electrode sheet containing the binder. The binder is prepared by the following method: an isopropyl alcohol solution of sodium hydroxide with a mass fraction of 5.0-10% is prepared, a certain amount of chitosan is weighed and slowly added under magnetic stirring, the temperature is raised to 70°C, and after complete dissolution, a dispersion liquid with a mass fraction of 1.5-3.5% is obtained, then chloroalkane is added dropwise, the mass ratio of RCl to CS is 1:3-1:10, stirring is continued for 4-6 h, and the product is repeatedly washed with diethyl ether and then dried to obtain the modified chitosan negative electrode binder.

[0006] However, the existing silicon-based negative electrode material binder cannot well inhibit the volume change of the silicon-based negative electrode material during the charging and discharging process, and cannot effectively improve the cycle stability of the battery. SUMMARY

[0007] In order to solve the problems existing in the prior art, one of the purposes of the present application is to provide a preparation method of a silicon-based negative electrode binder, which has high peel strength and can effectively buffer the volume change of the silicon-based negative electrode during the lithium extraction process, thereby effectively ensuring the integrity of the electrode structure and improving the cycle performance of the silicon-based negative electrode.

[0008] The technical scheme adopted by the present application to solve its technical problems is: a preparation method of a silicon-based negative electrode binder, comprising the following steps:

[0009] (1) 10g of chitosan is added to 50-80g of sodium hydroxide isopropyl alcohol solution, stirred at room temperature, then 32-47g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-oxypolypropylene is added, heated and stirred, the reaction liquid is cooled, precipitated in an ice water bath, the precipitate is washed with ethanol, and dried to obtain modified chitosan; the specific reaction process is as follows:

[0010] .

[0011] (2) 5g of modified chitosan is dispersed in 50-80g of DMF, then 1-3g of propyl triethoxysilane isocyanate and 0.01-0.2g of dibutyltin dilaurate are added, and stirred at 80-100℃ for 10-14h, the product is precipitated in an ice water bath, filtered, washed with diethyl ether, and dried to obtain a binder intermediate; the specific reaction process is as follows: .

[0012] (3) The binder intermediate is treated to remove free proton hydrogen, then an additive Li3YCl6 is added and mixed uniformly to obtain a silicon-based negative electrode binder.

[0013] Further, the viscosity of the chitosan in step (1) is 200-800cp, and the degree of deacetylation is ≥90%; the mass fraction of the sodium hydroxide isopropyl alcohol solution is 10-20%.

[0014] Further, the mass ratio of chitosan, sodium hydroxide isopropyl alcohol solution and 3-(2,2,3,3-tetrafluoropropoxy)-1,2-oxypolypropylene in step (1) is 10:50-80:32-47.

[0015] Further, the mass ratio of the modified chitosan, DMF, propyl triethoxysilane isocyanate and dibutyl tin dilaurate in step (2) is 5: 50-80: 1-3: 0.01-0.2.

[0016] Further, in step (1), the stirring is carried out at room temperature for 1-2 h at 420-500 r / min, and then the temperature is raised to 50-70 DEG C and the stirring is carried out for 3-5 h at 420-500 r / min, and in step (2), the stirring reaction condition is that the stirring is carried out for 10-14 h at 80-100 DEG C.

[0017] Further, in step (3), the water content is tested by Karl Fischer method after the treatment of removing free proton hydrogen, and the overall water content of the additive is less than or equal to 35 ppm, and the additive accounts for 5-10 wt% of the binder.

[0018] The second purpose of the present application is to provide a battery negative electrode slurry, which is composed of a silicon-based active material, a conductive agent and the above-mentioned silicon-based negative electrode binder with a mass ratio of 80-90: 5-10: 5-10.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1) The present application uses widely available chitosan as raw material, and 3-(2, 2, 3, 3-tetrafluoropropoxy)-1, 2-propylene oxide and propyl triethoxysilane isocyanate are grafted onto the molecular chain of chitosan to obtain a functional bonding segment, which can improve the flexibility of the binder, avoid shrinkage during drying of the adhesive film, improve the Young's modulus and elongation at break of the binder, effectively buffer the volume change of the silicon-based negative electrode during the process of deintercalating lithium, and effectively ensure the integrity of the electrode structure and improve the cycle performance of the silicon-based negative electrode.

[0021] 2) The present invention first 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-containing chain segment into the binder to obtain modified chitosan, which can reduce the hydrogen bonding between chitosan and water molecules, increase its dispersibility, enable the active material to fully contact with the electrode, and improve the conductivity of the prepared slurry; then, under the catalysis of dibutyltin dilaurate, the isocyanate group of isocyanatepropyltriethoxysilane reacts with the active hydroxyl group in chitosan , a siloxane chain segment is introduced to obtain an intermediate, and the intermediate is processed and additives are added to obtain a binder. When the binder is compounded with a silicon-based active material and a conductive agent to prepare a negative electrode slurry, the siloxane chain segment of the binder can undergo a condensation reaction with the silicon-based active material and the hydroxyl group on the surface of the current collector after hydrolysis, so that the binder can tightly combine the negative electrode active material and the current collector through chemical bonds, effectively enhancing the interfacial bonding strength, and giving the binder a strong ability to adapt to the volume expansion effect during the cycle of the silicon-based negative electrode, thereby significantly improving the electrochemical performance of the battery. DETAILED DESCRIPTION

[0022] 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.

[0023] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased from commercial sources or synthesized from commercially purchased raw materials. Example 1

[0024] This embodiment discloses a method for preparing a binder for a silicon-based negative electrode, comprising the following steps.

[0025] (1) 10 g of chitosan was added to 80 g of 20 wt% sodium hydroxide isopropanol solution and stirred at room temperature for 2 h. Then, 47 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide was added and stirred at 70 °C and 500 r / min for 5 h. 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 modified chitosan; wherein the viscosity of the chitosan was 200-800 cp and the degree of deacetylation was ≥90%.

[0026] (2) Disperse 5 g of modified chitosan 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 a binder intermediate.

[0027] (3) The binder intermediate is treated to remove free proton hydrogen until the water content is ≤20 ppm by Karl Fischer method, then the additive Li3YCl6 is added, the total water content of the additive is ≤35 ppm, the additive is added in an amount of 10 wt% of the binder, and the mixture is uniformly mixed to obtain a silicon-based negative electrode binder.

[0028] When the negative electrode slurry composed of the silicon-based active material, the conductive agent, and the silicon-based negative electrode binder prepared by the above preparation method in a mass ratio of 80-90:5-10:5-10 is applied in a battery, the following steps are included:

[0029] (1) The prepared binder is configured as a 5 wt% binder aqueous solution, uniformly mixed according to a mass ratio of nano-silicon: conductive carbon black: binder = 8:1:1, and ball milled and ultrasonically oscillated to uniformly mix to prepare a slurry.

[0030] (2) The slurry obtained in step (1) is coated on a copper foil, vacuum dried at 60°C for 10 h, and then punched to obtain a 14 mm diameter circular electrode sheet after rolling. 2 .

[0031] (3) The electrode sheet obtained in step (2) is dried at 100°C in a vacuum to completely remove water, and a half-cell is assembled in an argon-filled glove box using a lithium sheet as a counter electrode, 1M LiPF6 (FEC:DMC = 1:1, V / V) as an electrolyte, and Celgard 3501 separator as a separator. Example 2

[0032] The preparation method of the silicon-based negative electrode binder disclosed in this embodiment includes the following steps.

[0033] (1) 10 g of chitosan is added to 70 g of a 15 wt% sodium hydroxide isopropanol solution, stirred at room temperature for 1.5 h, then 43 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide is added, and stirred at 65°C and 480 r / min for 4.5 h. The reaction liquid is cooled, precipitated by dropwise addition to an ice water bath, washed with ethanol, and dried to obtain modified chitosan.

[0034] (2) 5 g of modified chitosan is dispersed in 70 g of DMF, then 2.5 g of propyl triethoxysilane isocyanate and 0.15 g of dibutyltin dilaurate are added, and stirred at 90°C for 12 h. The product is precipitated in an ice water bath, filtered, washed with diethyl ether, and dried to obtain a binder intermediate.

[0035] (3) The binder intermediate is treated to remove free proton hydrogen until the water content is less than or equal to 20 ppm by Karl Fischer method, then the additive Li3YCl6 is added, the overall water content of the additive is less than or equal to 35 ppm, the additive is added in an amount of 10 wt% of the binder, and the mixture is uniformly mixed to obtain the binder for the silicon-based negative electrode.

[0036] The solid-state battery and the preparation method of the pole piece are the same as those in Embodiment 1. Embodiment 3

[0037] The preparation method of the binder for the silicon-based negative electrode disclosed in this embodiment includes the following steps.

[0038] (1) 10 g of chitosan is added to 60 g of 15 wt% sodium hydroxide isopropyl alcohol solution, stirred at room temperature for 1.5 h, then 39 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide is added, stirred at 60°C and 450 r / min for 4 h, the reaction liquid is cooled, and then added dropwise into an ice water bath for precipitation, the precipitate is washed with ethanol, and dried to obtain modified chitosan.

[0039] (2) 5 g of the modified chitosan is dispersed into 60 g of DMF, then 2 g of propyl triethoxysilane isocyanate and 0.02 g of dibutyltin dilaurate are added, stirred at 90°C for 11 h, the product is precipitated in an ice water bath, filtered, washed with diethyl ether, and dried to obtain a binder intermediate.

[0040] (3) The binder intermediate is treated to remove free proton hydrogen until the water content is less than or equal to 20 ppm by Karl Fischer method, then the additive Li3YCl6 is added, the overall water content of the additive is less than or equal to 35 ppm, the additive is added in an amount of 10 wt% of the binder, and the mixture is uniformly mixed to obtain the binder for the silicon-based negative electrode.

[0041] The solid-state battery and the preparation method of the pole piece are the same as those in Embodiment 1. Embodiment 4

[0042] The preparation method of the binder for the silicon-based negative electrode disclosed in this embodiment includes the following steps.

[0043] (1) 10 g of chitosan is added to 50 g of 10 wt% sodium hydroxide isopropyl alcohol solution, stirred at room temperature for 1 h, then 32 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide is added, stirred at 50°C and 420 r / min for 3 h, the reaction liquid is cooled, and then added dropwise into an ice water bath for precipitation, the precipitate is washed with ethanol, and dried to obtain modified chitosan.

[0044] (2) Disperse 5 g of modified chitosan in 50 g of DMF, then add 1 g of isocyanatepropyltriethoxysilane and 0.01 g of dibutyltin dilaurate, and stir the mixture at 80 °C for 10 h. The product is precipitated in an ice-water bath, filtered, washed with ether, and dried to obtain a binder intermediate.

[0045] (3) The binder intermediate is treated to remove free proton hydrogen until the moisture content is ≤20 ppm as measured by the Karl Fischer method, and then the additive Li3YCl6 is added, the overall moisture content of the additive is ≤35 ppm, and the amount of the additive added accounts for 10 wt% of the binder. The mixture is mixed evenly to obtain a binder for a silicon-based negative electrode.

[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 a silicon-based negative electrode, 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 modified chitosan.

[0049] (2) Addition of additive Li3YC to phase-modified chitosan l6 The overall moisture content of the additive is ≤35ppm, the added amount of the additive accounts for 10wt% of the binder, and the mixture is mixed evenly to obtain the binder.

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

[0051] Comparative Example 2: Application of a binder in a silicon-based negative electrode comprises the following steps.

[0052] (1) The prepared binder is configured as a 5 wt% binder aqueous solution, mixed according to the mass ratio of nano-silicon: conductive carbon black: binder = 8:1:1, and then ball milled and ultrasonically vibrated to mix evenly to prepare a slurry.

[0053] (2) The slurry obtained in step (1) was coated on copper foil, vacuum dried at 60°C for 10 hours, and then rolled to obtain a circular electrode with a diameter of 14 mm. The density of the nano-silicon particles on the copper foil was controlled to 1 mg / cm by controlling the height of the coating scraper. 2 .

[0054] (3) The pole piece obtained in step (2) was dried at 100°C in vacuum to remove water completely, and then a half battery was assembled in an argon-filled glove box using lithium as a contrast electrode, 1M LiPF6 (FEC:DMC=1:1, V / V) as an electrolyte, and Celgard 3501 diaphragm as a diaphragm.

[0055] The batteries prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to performance testing, and the charge-discharge performance of the batteries was detected using a LAND-CT2001A tester according to GB / T 31484-2015 "Cyclic Life Requirements and Test Methods for Power Storage Batteries for Electric Vehicles", with a current density of 200 mA / g and a voltage range of 0.02-1.5 V.

[0056] The peeling strength was tested using a universal tensile testing machine according to GB / T 2790-1995 "180 Degree Peel Strength Test Method for Adhesives for Flexible Materials on Rigid Materials", and the test method was as follows: two copper foil pieces with a size of 40 mm x 100 mm were taken out and cleaned with alcohol before use; during testing, sufficient electrode paste was applied to one end of the two copper foils, with a coating area of 5.5 cm x 1.3 cm, and after coating, the sample was placed in a 60°C oven for 2 h to dry; finally, one end of the sample was fixed to the tensile probe, and a 180° peeling was performed at a constant speed of 10 mm / min, and the peeling force during peeling was used to represent the bonding strength of the adhesive. The specific data are shown in the table below.

[0057] The peeling force and cycle performance of the adhesives prepared in the examples were superior to those of the comparative examples, indicating that the chitosan was modified with 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide and propyl triethoxysilane, which on the one hand reduced the side reaction between the electrode and the electrolyte, improved the initial coulombic efficiency, and on the other hand effectively improved the cohesion of the electrode active coating. The use of the adhesive provided by the present application in the battery can effectively reduce the possibility of thickening, cracking, and pulverization of the SEI layer during the charge-discharge cycle of the battery, and significantly improve the electrochemical performance of the battery.

[0058] The above examples are preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for preparing a silicon-based negative electrode binder, characterized in that: Includes 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 modified chitosan. (2) Dispersing the modified chitosan in DMF, then adding isocyanatepropyltriethoxysilane and dibutyltin dilaurate and stirring to react, precipitating the product in an ice-water bath, filtering, washing with ether, and drying to obtain a binder intermediate; (3) The binder intermediate is treated to remove free proton hydrogen, and then the additive Li3YCl6 is added and mixed evenly to obtain a binder for silicon-based negative electrode.

2. The method for preparing a silicon-based negative electrode binder according to claim 1, wherein: In the step (1), the viscosity of chitosan is 200-800 cp, and the degree of deacetylation is ≥90%; the mass fraction of the sodium hydroxide isopropanol solution is 10-20%.

3. The method for preparing a silicon-based negative electrode binder according to claim 1, wherein: In the step (1), 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 the silicon-based negative electrode binder according to claim 1, 2 or 3, wherein: The mass ratio of the modified chitosan, DMF, isocyanatepropyltriethoxysilane and dibutyltin dilaurate in the step (2) is 5:50-80:1-3:0.01-0.

2.

5. The method for preparing a silicon-based negative electrode binder according to claim 4, wherein: In step (1), the mixture is stirred at room temperature at 420-500 r / min for 1-2 hours, then heated to 50-70° C. and stirred at 420-500 r / min for 3-5 hours. In step (2), the mixture is stirred at 80-100° C. for 10-14 hours.

6. The method for preparing a silicon-based negative electrode binder according to claim 5, wherein: After the free proton hydrogen removal treatment in step (3), the moisture content is ≤20ppm as measured by the Karl Fischer method, and the overall moisture content of the additive is ≤35ppm. The amount of the additive added accounts for 5-10wt% of the binder.

7. A battery negative electrode slurry, characterized in that: The invention is composed of a silicon-based active material, a conductive agent and a silicon-based negative electrode binder prepared by the preparation method according to claim 6 in a mass ratio of 80-90:5-10:5-10.

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