Ion / electron conduction enhanced binder of lithium ion battery and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium batteries, and discloses an ion / electron conduction enhanced binder of a lithium ion battery as well as a preparation method and application of the ion / electron conduction enhanced binder, the ion / electron conduction enhanced binder is a LiPAA / PEDOT: PSS / PEI binder, and the preparation method comprises the following steps: dissolving polyacrylic acid powder in deionized water, and stirring uniformly; adding a lithium hydroxide solution to lithiate polyacrylic acid; adding poly (3, 4-ethylenedioxythiophene) / polystyrene sulfonate, stirring until the mixture is completely and uniformly mixed, and finally adding polyethyleneimine dissolved with isopropanol to form a colloidal solution. The lithium ion battery binder has the advantages of simple synthesis conditions and easily available raw materials, has good ion and electron conduction capability, can effectively solve the problem of poor ion and electron transmission performance of a SiOx negative electrode material, enables a SiOx negative electrode to show good cycle performance and rate capability, and has good application prospects in lithium ion battery silicon-based negative electrode materials.

Description

Technical Field

[0001] The invention relates to the field of binder synthesis and electrochemical technology, and in particular to an ion / electron conduction enhanced binder for lithium ion batteries and a preparation method and application thereof. Background Art

[0002] With the continuous development of portable mobile devices and new energy electric vehicles, silicon-based anodes have become the most promising alternative to commercial graphite anodes. Silicon has a theoretical specific capacity more than ten times that of graphite anodes (4200mAh / g vs. 372mAh / g), and has the advantages of high natural abundance, environmental friendliness, and relatively low lithiation potential (<0.4VvsLi / Li+). However, as an anode material, silicon has problems such as excessive volume expansion (up to 300-400%) during cycling, which leads to repeated growth of solid electrolyte interface (SEI), shedding and pulverization of active materials. Relatively speaking, SiOx (0<x<2) has a smaller volume change (100~200%), but SiOx still has problems such as low intrinsic conductivity and low lithium ion diffusion rate. The existence of these problems will lead to low electrode surface capacity, poor rate performance, and reduced battery capacity when SiOx is used as an active material.

[0003] In order to solve these problems, a variety of methods have been proposed. For example, the surface of silicon materials can be coated and modified to improve their surface properties and reduce side reactions with electrolytes; or silicon materials can be prepared into nanoparticles to reduce material pulverization and cracking. However, these methods often have problems such as complex processes, high costs, and difficulty in industrial production, which makes it difficult to achieve large-scale application.

[0004] For silicon-based negative electrodes, although the binder only accounts for a small part of the electrode material, it plays an important role in adhering the active material and the conductive agent to the current collector and maintaining the integrity of the electrode. Traditional polyvinylidene fluoride (PVDF) binders are used in graphite negative electrodes due to their good adhesion and electrochemical stability, but the linear structure of PVDF cannot withstand the drastic volume expansion of silicon-based negative electrodes, and the high cost and serious environmental pollution also make PVDF unsuitable as a binder for silicon-based negative electrodes. To solve the above problems, a new water-soluble binder CMC / SBR was developed, which has better adaptability to the volume expansion of silicon-based negative electrodes. However, CMC / SBR still cannot solve the problems of low electronic conductivity and ion transfer rate in silicon-based negative electrodes.

[0005] Therefore, there is an urgent need for a new type of binder that can improve the electronic conductivity and ion transfer rate in silicon-based negative electrodes, thereby effectively improving the rate performance and cycle performance of the electrode, and providing support for the commercial application of silicon-based negative electrodes. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a functionalized ion / electron enhanced binder with a fast electron and ion transmission network and its preparation method and application. Through the binder of the present invention, the active material, the conductive agent and the current collector can be connected to reduce the poor electron and ion transmission rate caused by interface incompatibility and agglomeration. The ion / electron enhanced binder of the present invention can not only effectively improve the ion and electron conduction of the SiOx negative electrode, but also alleviate the volume expansion of the SiOx negative electrode at the same time, thereby improving the rate performance and cycle performance of the SiOx negative electrode.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows.

[0008] A first aspect of the present invention provides a method for preparing an ion / electron enhanced binder for a lithium ion battery, the preparation method comprising the following steps:

[0009] Step S1, completely dissolving polyacrylic acid powder in deionized water to obtain a polyacrylic acid solution, adding LiOH solution and stirring until the reaction is complete to obtain a polyacrylate lithium solution;

[0010] Step S2, adding the poly (3,4-ethylenedioxythiophene) / polystyrene sulfonate solution into the polyacrylate lithium solution, stirring to form a uniform solution, and obtaining a pre-solution;

[0011] Step S3, adding the isopropanol solution containing polyethyleneimine into the pre-solution, stirring and dispersing the solution sufficiently to form a colloidal solution, thereby obtaining an ion / electron enhanced adhesive.

[0012] Furthermore, in the step S1, the mass ratio of the polyacrylic acid powder to the deionized water is 1:9, and the mass ratio of the polyacrylic acid solution to the LiOH solution is (2-6): (1-2).

[0013] Furthermore, the concentration of the LiOH solution in step S1 is 5-6 wt %.

[0014] Furthermore, in step S2, the mass ratio of the lithium polyacrylate solution to the poly (3,4-ethylenedioxythiophene) / polystyrene sulfonate solution is (3-7): (3-7).

[0015] Furthermore, in the step S3, the mass ratio of polyethyleneimine to isopropanol in the isopropanol solution containing polyethyleneimine is 1:99, and the mass ratio of the isopropanol solution containing polyethyleneimine to the pre-solution is (1-3):20.

[0016] Furthermore, the reaction time in step S1 is 24 to 48 hours; the stirring time in step S2 is 30 to 45 minutes; and the stirring time in step S3 is 24 to 48 hours.

[0017] The second aspect of the present invention provides an ion / electron enhanced binder for lithium ion batteries, which is prepared by the above-mentioned method for preparing the ion / electron enhanced binder for lithium ion batteries.

[0018] Furthermore, the infrared spectrum of the ion / electron enhanced adhesive is at 1564 and 1412 cm -1 The symmetric and asymmetric vibration peaks of the C=O bond in lithium carboxylate are shown respectively.

[0019] The ion / electron enhanced binder can effectively improve the ion and electron conduction of the SiOx negative electrode, while alleviating the volume expansion of the SiOx negative electrode, thereby improving the rate performance and cycle performance of the SiOx negative electrode.

[0020] The third aspect of the present invention provides the use of the above-mentioned ion / electron enhanced binder for lithium ion batteries in silicon-based negative electrodes of lithium ion batteries.

[0021] Furthermore, the silicon-based negative electrode material of the lithium-ion battery is SiOx, 0<x<2.

[0022] In the present invention, when the ion / electron enhanced binder is mixed with SiOx and a conductive agent in a certain proportion, the obtained half-cell exhibits excellent cycle performance and rate performance.

[0023] The polyethyleneimine (PEI) used in the present invention can form a bond with polystyrene sulfonate (PSS) and improve the conductivity of poly (3,4-ethylenedioxythiophene) (PEDOT) by doping. + The coordination between ions and the amine groups of PEI reduces the oxidation of PEDOT by PEI and forms Li 3 N improves the lithium ion transmission capacity of the SEI layer. This ion / electron enhanced binder has good ion and electron conductivity, as well as excellent bonding ability and mechanical strength. It can enhance the rate performance and cycle performance of the silicon-based negative electrode of lithium-ion batteries and has good commercial prospects.

[0024] The specific application method of the ion / electron enhanced adhesive of the present invention is as follows:

[0025] The active material SiOx, the conductive agent SuperP (conductive carbon black) and the mixed solution of polyacrylate lithium / poly 3,4-ethylenedioxythiophene / polystyrene sulfonate are mixed in a mass ratio of (7-8): (2-1): 1, and after adding an appropriate amount of deionized water, the mixture is placed in a degassing machine and stirred for 30 minutes to obtain a uniformly dispersed slurry. The obtained slurry is coated on a copper foil, dried in an 80°C blast oven for 2 hours, and then taken out. The PEI / IPA solution is evenly coated on the surface of the copper foil, dried in an 80°C vacuum oven for 12 hours, and then taken out and cut into a circular electrode with a diameter of 14 mm. The dried electrode is placed in a glove box filled with argon for battery assembly. The lithium sheet in the battery is used as the counter electrode, the electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) as the solute, and ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 are used as solvents, among which 10wt% fluoroethylene carbonate (FEC) and 1wt% ethylene carbonate (VC) are used as additives, and CR2032 button batteries are used for assembly.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The SiOx negative electrode ion / electronic enhanced binder of the present invention forms a bond between PEI and PSS and improves the conductivity of PEDOT by doping. + The coordination between ions and the amine groups of PEI reduces the oxidation of PEDOT by PEI and forms Li 3 N improves the lithium ion transmission capacity of the SEI layer, effectively solving the problem of poor ion and electron transmission performance of silicon-based negative electrodes.

[0028] 2. The ion / electron enhanced binder of the present invention is applied to the silicon-based negative electrode of lithium-ion batteries, which effectively enhances the cycle performance and rate performance of the silicon-based negative electrode of lithium-ion batteries. The cycle performance of SiOx electrodes was tested using LiPAA / PEDOT:PSS / PEI and PAA binders. x The first coulombic efficiency of the PSS / PEI electrode reached 66.93%, while that of the SiOx@PAA electrode was only 62.07%. -1 Two cycles of activation, at 0.5Ag -1 After 100 cycles, SiOx@LiPAA / PEDOT:PSS / PEI has the best cycling stability, and the discharge capacity remains at 1122.9 mAh g -1 , while the discharge capacity of SiOx@PAA dropped to 845.5 mAhg -1 .

[0029] 3. The ion / electron enhanced binder of the present invention is applied to the silicon-based negative electrode of lithium-ion batteries and exhibits excellent rate performance. The electrodes are at current densities of 0.5, 1, 2, and 4 Ag, respectively. -1 The reversible capacities were 1066.71, 830.59, 589.98, and 329.06 mAh g -1 When the current density was adjusted to 0.5Ag-1, the capacity of the electrode recovered to 1069.66mAhg -1 , showing excellent rate performance.

[0030] 4. The ion / electron enhanced binder of the present invention has simple synthesis conditions, low-cost and readily available raw materials, and has good ion and electron conduction rates. The SiOx negative electrode using the ion / electron enhanced binder has a low binder content (0-20wt%), a high SiOx content (60-90wt%) and a high SiOx mass loading (1-2mgcm -2 ), which indicates that the binder has great application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the infrared spectra of the ion / electron enhanced adhesive and the polyacrylic acid adhesive in Example 1 of the present invention.

[0032] Figure 2 This is a cycle performance diagram of the SiOx electrode using the ion / electron enhanced binder and the polyacrylic acid binder as binders in Example 2 of the present invention.

[0033] Figure 3 This is a rate performance diagram of the SiOx electrode using the ion / electron enhanced binder and the polyacrylic acid binder as binders in Example 2 of the present invention. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are further described below. It should be noted that the content of the present invention is further described below in conjunction with specific examples, but it should not be construed as reality of the present invention. If not specifically indicated, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0035] Example 1: Ion / electron enhanced adhesive and preparation method thereof

[0036] This embodiment is used to provide a method for preparing the ion / electron enhanced binder of the present invention, comprising the following steps:

[0037] Step S1, dissolving 0.2 g of polyacrylic acid (PAA) powder in 1.8 g of deionized water to obtain a polyacrylic acid solution; adding 1 g of a 5 wt% LiOH solution to lithiate the polyacrylic acid, stirring at room temperature for 48 h until the reaction is complete, to obtain a lithium polyacrylate (LiPAA) solution;

[0038] Step S2, adding 10.71 g of PEDOT:PSS solution to the LiPAA solution, stirring at room temperature for 30 min to obtain an ion / electron enhanced binder pre-solution;

[0039] Step S3, adding 1 g of 1 wt% PEI / IPA solution, stirring at room temperature for 48 hours to obtain the ion / electron enhanced binder of the present invention, namely LiPAA / PEDOT:PSS / PEI binder.

[0040] In the present invention, PEDOT:PSS is a common conductive polymer aqueous solution, which is composed of two substances, PEDOT and PSS. PEDOT is a polymer of EDOT (3,4-ethylenedioxythiophene) monomer, and PSS is polystyrene sulfonate. Aqueous solutions with different conductivity can be obtained by different ratios. PEI / IPA solution is an isopropyl alcohol (IPA) solution in which polyethyleneimine (PEI) is dissolved. PAA is a common water-soluble polymer, which is a homopolymer of acrylic acid. Lithiated polyacrylic acid has good lithium ion conductivity.

[0041] Comparative Example 1

[0042] 0.5 g of polyacrylic acid (PAA) powder was dissolved in 4.5 g of deionized water and stirred thoroughly to obtain a PAA binder with a concentration of 10 wt%.

[0043] Figure 1 : The infrared spectra of the LiPAA / PEDOT:PSS / PEI binder of the present invention and the PAA binder of Comparative Example 1. Figure 1 It can be seen that compared with the PAA binder of Comparative Example 1, the infrared spectrum of the LiPAA / PEDOT:PSS / PEII binder of the present invention is at 1564 and 1412 cm -1 The symmetric and asymmetric vibration peaks of the C=O bond in lithium carboxylate are shown at the positions, respectively, which indicates the lithiation of PAA.

[0044] Example 2: Application of ion / electron enhanced binder in lithium ion battery

[0045] The active material SiOx and the conductive agent SuperP in a mass ratio of 7:2:1 were mixed with the ion / electronic enhanced adhesive pre-solution of Example 1, 400-600 mL of deionized water were added, and the mixture was placed in a degassing machine and stirred for 30-45 min to obtain a uniformly dispersed slurry. The obtained slurry was coated on a copper foil, dried at 80°C for 2 h, and then taken out. The PEI / IPA solution was evenly coated on the surface of the copper foil, dried in a vacuum oven at 80°C for 12 h, and then taken out and cut into circular electrodes with a diameter of 14 mm.

[0046] The electrode is then transferred to an argon-filled glove box for assembly. The lithium sheet in the battery is used as the counter electrode, the electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) as the solute, and the volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) is 1:1 as the solvent, wherein 10wt% fluoroethylene carbonate (FEC) and 1wt% ethylene carbonate (VC) are used as additives, and CR2032 button batteries are used for assembly to obtain the SiOx electrode (0<x<2) of the ion / electronic enhanced binder of the present invention, namely SiOx@LiPAA / PEDOT:PSS / PEI electrode.

[0047] Comparative Example 2

[0048] The active material SiOx, the conductive agent SuperP and the binder in a mass ratio of 7:2:1 were mixed and placed in a degassing machine for stirring for 30 minutes to obtain a uniformly dispersed electrode slurry. The electrode slurry was coated on a copper foil, dried in a vacuum oven at 80°C for 12 hours, and then taken out and cut into circular electrodes with a diameter of 14 mm.

[0049] The electrode was then transferred to an argon-filled glove box for assembly. The lithium sheet in the battery was used as the counter electrode, the electrolyte was 1 mol / L lithium hexafluorophosphate (LiPF6) as the solute, and the volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) was 1:1 as the solvent, of which 10wt% fluoroethylene carbonate (FEC) and 1wt% ethylene carbonate (VC) were used as additives. CR2032 button cells were used for assembly to obtain SiOx@PAA electrodes.

[0050] Figure 2 Graph showing the cycle performance of the SiOx@LiPAA / PEDOT:PSS / PEI electrode of the present invention and the SiOx@PAA electrode of Comparative Example 2. Figure 2It can be seen that compared with the SiOx@PAA electrode in Comparative Example 2, the first coulombic efficiency of the SiOx@LiPAA / PEDOT:PSS / PEI electrode reached 66.93%, while that of the SiOx@PAA electrode was only 62.07%; after two cycles of activation at 0.2Ag-1 and 100 cycles at 0.5Ag-1, the SiOx@LiPAA / PEDOT:PSS / PEI electrode had the best cycle stability, and the discharge specific capacity remained at 1122.9mAhg-1, while the discharge specific capacity of the SiOx@PAA electrode dropped to 845.5mAhg-1.

[0051] Figure 3 Figure 2 is a rate performance diagram of the SiOx@LiPAA / PEDOT:PSS / PEI electrode of the present invention and the SiOx@PAA electrode of Comparative Example 2. Figure 3 It can be seen that compared with the SiOx@PAA electrode of Comparative Example 2, the SiOx@LiPAA / PEDOT:PSS / PEI electrode of the present invention has a current density of 0.5, 1, 2, and 4A respectively. -1 The reversible capacities were 1066.71, 830.59, 589.98, and 329.06 mAh g -1 When the current density is adjusted to 0.5Ag -1 When the electrode capacity is restored to 1069.66 mAhg -1 , showing excellent rate performance.

[0052] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A method for preparing an ion / electron enhanced binder for a lithium ion battery, characterized in that: The preparation method comprises the following steps: Step S1, completely dissolving polyacrylic acid powder in deionized water to obtain a polyacrylic acid solution, adding LiOH solution and stirring until the reaction is complete to obtain a polyacrylate lithium solution; Step S2, adding the poly (3,4-ethylenedioxythiophene) / polystyrene sulfonate solution into the polyacrylate lithium solution, stirring to form a uniform solution, and obtaining a pre-solution; Step S3, adding the isopropanol solution containing polyethyleneimine into the pre-solution, stirring and dispersing the solution sufficiently to form a colloidal solution, thereby obtaining an ion / electron enhanced adhesive.

2. The method for preparing the ion / electron enhanced binder for lithium ion batteries according to claim 1, characterized in that: In the step S1, the mass ratio of the polyacrylic acid powder to the deionized water is 1:9, and the mass ratio of the polyacrylic acid solution to the LiOH solution is (2-6): (1-2).

3. The method for preparing the ion / electron enhanced binder for lithium ion batteries according to claim 1, characterized in that: The concentration of the LiOH solution in step S1 is 5-6 wt %.

4. The method for preparing the ion / electron enhanced binder for lithium ion batteries according to claim 1, characterized in that: The mass ratio of the lithium polyacrylate solution to the poly (3,4-ethylenedioxythiophene) / polystyrene sulfonate solution in step S2 is (3-7): (3-7).

5. The method for preparing the ion / electron enhanced binder for lithium ion batteries according to claim 1, characterized in that: In the step S3, the mass ratio of polyethyleneimine to isopropanol in the isopropanol solution containing polyethyleneimine is 1:99, and the mass ratio of the isopropanol solution containing polyethyleneimine to the pre-solution is (1-3):

20.

6. The method for preparing the ion / electron enhanced binder for lithium ion batteries according to claim 1, characterized in that: The reaction time in step S1 is 24 to 48 hours; the stirring time in step S2 is 30 to 45 minutes; and the stirring time in step S3 is 24 to 48 hours.

7. An ion / electron enhanced binder for lithium ion batteries, characterized in that: The adhesive is prepared by the method for preparing the ion / electron enhanced adhesive for lithium ion batteries according to any one of claims 1 to 6.

8. The ion / electron enhanced binder for lithium ion batteries according to claim 7, characterized in that: The infrared spectrum of the ion / electron enhanced binder is at 1564 and 1412 cm -1 The symmetric and asymmetric vibration peaks of the C=O bond in lithium carboxylate are shown respectively.

9. Use of the ion / electron enhanced binder for lithium ion batteries as claimed in claim 7 or 8 in a silicon-based negative electrode of a lithium ion battery.

10. The use of the ion / electron enhanced binder for lithium ion batteries according to claim 9, characterized in that: The silicon-based negative electrode material of the lithium-ion battery is SiOx, 0<x<2.

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