A sulfidized polyacrylonitrile positive electrode binder and electrode preparation method

Abstract

The application discloses a water-soluble binder suitable for sulfidized polyacrylonitrile (SPAN) and a preparation method of an electrode. + Form directional transmission, accelerate Li + Transport rate in thick electrodes; metal M ions can form M-S bonds with SPAN in situ during electrode drying, improve positive electrode electronic conductivity, and accelerate electrode reaction kinetics; at the same time, the binder can form an interpenetrating network through supramolecular interaction and has a certain self-repairing ability, so as to buffer the volume change of the SPAN positive electrode during charging and discharging and avoid electrode structure damage. The SPAN positive electrode with high load can be prepared by using the binder, the problems of poor conductivity and easy falling of active particles of the SPAN positive electrode in the prior art are solved, and the rate capability and cycle stability of the high-load SPAN positive electrode sheet are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium batteries, and particularly relates to a sulfidized polyacrylonitrile positive electrode binder and an electrode preparation method. BACKGROUND

[0002] Lithium ion batteries have been widely used in various fields, such as portable electronic products such as mobile phones, computers and tablets, and gradually applied in new energy vehicles, large-scale energy storage and other fields. However, the energy density of lithium ion batteries at the present stage has approached its theoretical value, and cannot meet the demand for higher mileage. Lithium-sulfur batteries use sulfur positive electrode (1672 mAh / g) and metal lithium negative electrode (3860 mAh / g) with abundant reserves, and the theoretical energy density can reach 2600 Wh / kg, which has broad application prospects. However, lithium-sulfur batteries also have many problems in practical application, such as the dissolution and shuttling of intermediate products polysulfides in the charging and discharging process, which leads to the loss of active materials and the reduction of coulombic efficiency, affecting the stability of the battery.

[0003] Sulfidized polyacrylonitrile (SPAN) realizes solid-solid conversion by covalently connecting small molecules S to the conjugated PAN skeleton, avoids the generation of intermediate phase polysulfides, and further improves the cycle stability of the battery. However, the volume expansion of SPAN during the cycle process of about 40% may cause the active material to fall off due to excessive stress and deformation during the cycle process of the electrode, especially the high-loading electrode, and further cause the rapid capacity decay of the battery. At the same time, the electronic conductivity of SPAN is slightly lower than that of the traditional lithium ion battery electrode material, and the nano-structured feature further leads to high tortuosity and long charge transport distance, resulting in poor rate performance of thick electrodes and low active material utilization.

[0004] At present, the positive electrode loading of SPAN is generally low (<6 mg / cm 2 When the loading is increased, the electrode sheet is prone to cracking, material falling off, or volume expansion leading to the separation of the electrode film and the current collector when the battery is deintercalated lithium, and the capacity of the battery is greatly attenuated. As an important component of the electrode, the binder not only needs to maintain good electrical contact between the active material and the conductive additive, but also needs to have excellent mechanical properties to resist deformation during the charging and discharging process of the electrode. At the same time, in thick electrodes, the binder also needs to have the ability of fast ion transport to improve the cycle stability of the electrode. Although commercial polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose-styrene butadiene rubber (CMC-SBR) and the like have relatively high strength, they have poor deformation adaptability and are difficult to realize high loading and guarantee high active material utilization.

[0005] Therefore, it is of great significance to develop a high-performance SPAN positive electrode binder and accelerate the solid-solid conversion kinetics of SPAN. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art, and provides a sulfidized polyacrylonitrile positive electrode binder and an electrode preparation method, the binder has the functions of bonding and ion / electron conduction, can buffer the volume change of SPAN during the charging and discharging process, maintain the structural integrity of the electrode, and form Li + The fast transfer channel can further accelerate the electron transmission in the electrode preparation process, and improve the rate performance and cycle stability of the battery.

[0007] To achieve the above purpose, the present application adopts the following technical solutions:

[0008] One of the purposes of the present application is to provide a binder, which is mixed by a water-soluble cyclodextrin derivative, a linear ion-conducting polymer and a divalent / trivalent metal salt.

[0009] In the present application, the mass percentage of the cyclodextrin is 30% to 80%, and the mass percentage of the metal salt is 5% to 20% in the total mass of the water-soluble cyclodextrin derivative, the linear ion-conducting polymer and the divalent / trivalent metal salt.

[0010] In the present application, the water-soluble cyclodextrin derivative includes one or a combination of cyclodextrin polymers and carbonylated cyclodextrins.

[0011] In the present application, the linear ion-conducting polymer includes one or a combination of polyacrylic acid, polyethylene oxide and polyvinyl alcohol.

[0012] In the present application, the divalent / trivalent metal salt cation includes one or several of magnesium, calcium, iron, cobalt, nickel, copper, zinc and aluminum; and the anion includes one or several of halogen ions, sulfate ions and nitrate ions.

[0013] The binder is added into the SPAN positive electrode, the supramolecular interaction between the cyclodextrin inner cavity and the linear polymer can buffer the volume expansion of the SPAN positive electrode, thereby avoiding the phenomena such as powdering and peeling of the electrode particles; the linear ion-conducting polymer forms Li + The oriented transfer channel can accelerate the Li + transport in the thick electrode; the in-situ formed M-S bond between the metal salt and the SPAN can improve the electronic conductivity of the electrode and accelerate the reaction kinetics.

[0014] The second object of the present application is to provide a SPAN positive electrode tab, dissolving water-soluble cyclodextrin derivatives, linear ion-conducting polymers and metal salts in deionized water, mixing uniformly to obtain a binder glue solution, then adding a conductive agent and SPAN particles, continuing to mix uniformly, coating on a conductive current collector, and heating and drying the obtained positive electrode tab at a heating temperature of 60-150 DEG C, and the metal salt and SPAN form M-S bonds in situ at high temperature.

[0015] Compared with the prior art, the present application has the following gain effects:

[0016] The binder prepared by water-soluble cyclodextrin derivatives, linear ion-conducting polymers and metal salts can buffer the volume expansion of SPAN particles during charging and discharging, thereby reducing the pulverization and shedding of the electrode; the linear polymer provides Li + in the cyclodextrin cavity, the oriented transmission channel accelerates ion transport; the metal salt and SPAN form M-S bonds in situ to improve electronic conductivity and accelerate reaction kinetics; the binder is water-soluble, the raw materials are simple and easy to obtain, green and environmentally friendly, and has a wide range of applications, and the SPAN positive electrode prepared from the binder can achieve excellent rate performance and cycle stability at high load. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the hardness and modulus data graph of the SPAN positive electrode prepared in Example 1 and Comparative Example 1 by nanoindentation testing.

[0018] Figure 2 is the electronic conductivity of the SPAN positive electrode tab described in Example 1 and Comparative Example 1.

[0019] Figure 3 is the 0.2C cycle effect graph of the binder and SPAN positive electrode tab described in Example 1 at 15.6mg / cm 2 . DETAILED DESCRIPTION

[0020] The present application will be further described in detail below in conjunction with examples, but the embodiments of the present application are not limited thereto. Any changes, modifications, substitutions, combinations or simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods, and all shall be included in the protection scope of the present application.

[0021] Example 1

[0022] The preparation method of the SPAN positive electrode of the present embodiment comprises the following steps:

[0023] (1) Preparation of the cyclodextrin polymer: 5 g of a-cyclodextrin was added to 8 mL of a 33% by mass NaOH solution, and mechanically stirred at room temperature overnight. The mixture was heated to 30°C, and then epichlorohydrin was rapidly added. After stirring for 4 h, the reaction was terminated by adding acetone. The acetone was removed by decantation, and the pH was lowered to 12 using 6N hydrochloric acid. The mixture was then maintained at 50°C overnight, and then neutralized using 6N hydrochloric acid after cooling. Finally, the solution was subjected to diafiltration using a membrane with a cut-off of 3500 at a pressure of 2 bar, and the solvent was evaporated to obtain a white solid a-CDp.

[0024] (2) Preparation of the binder: 0.8 g of a-CDp, 0.15 g of polyacrylic acid, and 0.05 g of copper sulfate were dissolved in deionized water, and mixed and stirred to obtain the binder solution.

[0025] (3) Preparation of the SPAN positive electrode: 8 g of SPAN powder and 1 g of conductive carbon black were added to the binder solution, and mixed and stirred to obtain an electrode slurry. The electrode slurry was coated on a carbon-coated aluminum foil, and dried in a forced air oven at 80°C for 12 h. The electrode was then roll-pressed and sliced to obtain the SPAN positive electrode.

[0026] Example 2

[0027] The method for preparing the SPAN positive electrode of this example includes the following steps:

[0028] (1) Preparation of the cyclodextrin derivative: 5 g of β-cyclodextrin was dissolved in 15 g of a 30% by mass H2O2 aqueous solution, and magnetically stirred at 80°C for 24 h. The product was then placed in a forced air oven at 80°C to evaporate the solvent and obtain a white solid C-β-CD.

[0029] (2) Preparation of the binder: 0.3 g of C-β-CD, 0.5 g of polyethylene oxide, and 0.2 g of magnesium nitrate were dissolved in deionized water, and mixed and stirred to obtain the binder solution.

[0030] (3) Preparation of the SPAN positive electrode: 8 g of SPAN powder and 1 g of Ketjen black were added to the binder solution, and mixed and stirred to obtain an electrode slurry. The electrode slurry was coated on an aluminum foil, and dried in a forced air oven at 60°C for 12 h. The electrode was then roll-pressed and sliced to obtain the SPAN positive electrode.

[0031] Example 3

[0032] (1) Preparation of cyclodextrin polymer: 5 g of β-cyclodextrin was added to 8 mL of 33% by mass NaOH solution, mechanically stirred overnight at room temperature, the mixture was heated to 30°C, then quickly added with epichlorohydrin, continued to stir for 4 h, then added with acetone to terminate the reaction. The acetone was removed by decantation, the pH was reduced to 12 using 6N hydrochloric acid, then kept at 50°C overnight, after cooling, neutralized with 6N hydrochloric acid. Finally, the solution was subjected to diafiltration using a membrane with a cut-off of 3500 at a pressure of 2 bar, and the solvent was evaporated to obtain a white solid β-CDp.

[0033] (2) Preparation of binder: 0.8 g of β-CDp, 0.15 g of polyacrylic acid and 0.05 g of calcium chloride were dissolved in deionized water, mixed and stirred uniformly to obtain the binder solution.

[0034] (3) Preparation of SPAN positive electrode: 8 g of SPAN powder and 1 g of graphene were added to the above binder solution, and the mixture was continuously stirred uniformly to obtain an electrode slurry; the electrode slurry was coated on carbon cloth, dried in a blast oven at 100°C for 12 h, rolled and sliced to obtain a SPAN positive electrode.

[0035] Example 4

[0036] The preparation method of the SPAN positive electrode of the present example comprises the following steps:

[0037] (1) Preparation of cyclodextrin derivative: 5 g of γ-cyclodextrin was dissolved in 15 g of 30% by mass H2O2 aqueous solution, magnetically stirred at 80°C for 24 h, then the product was placed in a blast oven at 80°C to evaporate the solvent to obtain a white solid C-γ-CD.

[0038] (2) Preparation of binder: 0.3 g of C-γ-CD, 0.5 g of polyvinyl alcohol and 0.2 g of copper nitrate were dissolved in deionized water, mixed and stirred uniformly to obtain the binder solution.

[0039] (3) Preparation of SPAN positive electrode: 8 g of SPAN powder and 1 g of carbon nanotube were added to the above binder solution, and the mixture was continuously stirred uniformly to obtain an electrode slurry; the electrode slurry was coated on a foam nickel, dried in a blast oven at 150°C for 12 h, rolled and sliced to obtain a SPAN positive electrode.

[0040] Comparative Example 1

[0041] The preparation method of the SPAN positive electrode of the present example comprises the following steps:

[0042] (1) Preparation of binder: 0.5 g of sodium carboxymethyl cellulose was dissolved in 25 g of deionized water, mixed and stirred uniformly, then 1 g of 50% by mass butadiene-styrene rubber was added, and the mixture was continuously mixed and stirred uniformly to obtain the binder solution.

[0043] (2) Preparation of SPAN positive electrode: 8 g SPAN powder and 1 g conductive carbon black were added to the above binder solution, and stirring was continued until uniform, obtaining electrode slurry; the electrode slurry was coated on a carbon-coated aluminum foil, dried in a blast oven at 80°C for 12 h, roll-pressed and sliced, obtaining a SPAN positive electrode.

[0044] Comparative Example 2

[0045] The preparation method of the SPAN positive electrode of the present example comprises the following steps:

[0046] (1) Preparation of binder: 1 g polyvinylidene fluoride was dissolved in 19 g N-methylpyrrolidone, and stirring was continued until uniform, obtaining the binder solution.

[0047] (2) Preparation of SPAN positive electrode: 8 g SPAN powder and 1 g Ketjen black were added to the above binder solution, and stirring was continued until uniform, obtaining electrode slurry; the electrode slurry was coated on a carbon-coated aluminum foil, dried in a blast oven at 80°C for 12 h, roll-pressed and sliced, obtaining a SPAN positive electrode.

[0048] Comparative Example 3

[0049] The preparation method of the SPAN positive electrode of the present example comprises the following steps:

[0050] (1) Preparation of cyclodextrin polymer: 5 g a-cyclodextrin was added to 8 mL 33% mass fraction NaOH solution, and mechanical stirring was continued overnight at room temperature; the mixture was heated to 30°C, and then epoxy chloropropane was quickly added; after 4 h of continuous stirring, the reaction was terminated by adding acetone. The acetone was removed by decantation, the pH was reduced to 12 using 6N hydrochloric acid, and then it was kept at 50°C overnight after cooling; finally, it was neutralized using 6N hydrochloric acid. Finally, the white solid a-CDp was obtained by diafiltration using a membrane with a cut-off of 3500 under a pressure of 2 bar, and the solvent was evaporated.

[0051] (2) Preparation of binder: 0.8 g a-CDp and 0.2 g polyacrylic acid were dissolved in deionized water, and stirring was continued until uniform, obtaining the binder solution.

[0052] (3) Preparation of SPAN positive electrode: 8 g SPAN powder and 1 g carbon nanotube were added to the above binder solution, and stirring was continued until uniform, obtaining electrode slurry; the electrode slurry was coated on an aluminum foil, dried in a blast oven at 60°C for 12 h, roll-pressed and sliced, obtaining a SPAN positive electrode.

[0053] The SPAN positive electrodes prepared in the examples and comparative examples were respectively assembled into batteries, and then the batteries were subjected to cycle testing, with a test temperature of 25°C and a charge-discharge voltage interval of 1-3 V.

Claims

1. A vulcanized polyacrylonitrile positive electrode binder, characterized by: The binder is obtained by mixing water-soluble cyclodextrin derivatives, linear ion-conducting polymers and divalent / trivalent metal salts, wherein the mass percentage of the water-soluble cyclodextrin derivatives is 30-80% and the mass percentage of the metal salts is 5-20% based on the total mass of the water-soluble cyclodextrin derivatives, the linear ion-conducting polymers and the metal salts.

2. The sulfϊded polyacrylonitrile cathode binder of claim 1, wherein, The water-soluble cyclodextrin derivatives include one or a combination of cyclodextrin polymers and carbonylated cyclodextrins.

3. The sulfϊded polyacrylonitrile cathode binder of claim 1, wherein, The linear ion-conducting polymers include one or a combination of polyacrylic acid, polyethylene oxide and polyvinyl alcohol.

4. The sulfϊded polyacrylonitrile cathode binder of claim 1, wherein, The divalent / trivalent metal salt cations include one or a combination of magnesium, calcium, iron, cobalt, nickel, copper, zinc and aluminum; and the anions include one or a combination of halide ions, sulfate ions and nitrate ions.

5. A process for the production of the binder as claimed in any one of claims 1 to 4, characterized in that, The method comprises the following steps: (1) preparing water-soluble cyclodextrin derivatives; (2) mixing the linear ion-conducting polymers, the divalent / trivalent metal salts and the prepared water-soluble cyclodextrin derivatives in deionized water in a certain proportion and stirring uniformly.

6. A sulfidized polyacrylonitrile positive electrode, characterized by, The sulfidized polyacrylonitrile positive electrode comprises a conductive current collector and a positive electrode film attached to at least one side of the current collector, wherein the positive electrode film comprises 80-96% of sulfidized polyacrylonitrile positive electrode material, 2-10% of conductive agent and 2-10% of the binder according to any one of claims 1-4.

7. The method of producing the sulfidized polyacrylonitrile positive electrode according to claim 6, characterized by, The preparation method comprises the following steps: (1) mixing water-soluble cyclodextrin derivatives, linear ion-conducting polymers and divalent / trivalent metal salts in a certain mass ratio to obtain a glue solution in deionized water; (2) adding sulfidized polyacrylonitrile and conductive agent to the glue solution and adding an appropriate amount of deionized water to obtain a positive electrode slurry after stirring uniformly; (3) uniformly coating the positive electrode slurry on a conductive current collector and drying at 60-150°C to obtain a sulfidized polyacrylonitrile positive electrode.

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