A lithium battery silicon negative electrode binder, a silicon negative electrode sheet and a lithium battery

Abstract

The present application relates to a kind of lithium battery silicon negative electrode binder, silicon negative pole piece and lithium battery, at least including A component and B component;Wherein, the A component is acrylic polyco polymer;The B component is tannic acid;The A component is 100 parts by weight, and B component is 1-50 weight parts by weight portion.The present application improves the ion transfer performance of binder, greatly reduces the electrochemical impedance of lithium battery, improves the electrochemical performance of lithium battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a binder for a silicon negative electrode of a lithium battery, a silicon negative electrode pole piece and a lithium battery. BACKGROUND

[0002] Silicon material is more and more used as a negative electrode material of a lithium battery due to the advantages of high theoretical specific capacity, rich reserves, controllable cost and improved energy density of the battery. In the process of preparing the silicon negative electrode, it is necessary to use a binder to bond the components of the silicon negative electrode together. However, the binders currently used for the silicon negative electrode mainly include PVA (polyvinyl alcohol) binders and PAA binders (acrylic acid binders). Due to the lithium transfer characteristics of PAA and PVA, lithium ions can jump between adjacent carboxyl and hydroxyl positions, so that a more or less thin coating is formed on the surface of silicon particles to play the role of artificial SEI to transfer ions. In the PVA binder, only hydroxyl groups are present without carboxyl groups, so the ion transfer is poor. Although a large number of carboxyl groups exist in the PAA chain segment, this leads to easy water absorption of the PAA binder, and too many hydrogen bonds generated between the carboxyl groups hinder the free rotation of the molecular chain, so that the flexibility of the polymer is poor, which is not conducive to bearing the stress generated by the volume expansion of the active material, affects the improvement of the battery performance, and the linear long-chain structure of PAA makes the molecular chains easy to slide, so that permanent deformation occurs after stress to cause the aggregation of the active material and reduce the specific capacity of the pole piece. Therefore, the number of carboxyl chain segments is usually controlled in the design process of the PAA chain segment, which limits the effect of the PAA binder on ion transfer and limits the faster transfer of lithium ions in the binder. Due to the performance limitation of the two types of binders in ion transfer, the prepared lithium battery has high electrochemical impedance and poor electrochemical performance. SUMMARY

[0003] The purpose of the present application is to overcome the defects in the prior art, and to provide a binder for a silicon negative electrode of a lithium battery, which can improve the ion transfer performance of the binder, greatly reduce the electrochemical impedance of the lithium battery and improve the electrochemical performance of the lithium battery.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] Technical scheme one:

[0006] A binder for a silicon negative electrode of a lithium battery, at least comprising A component and B component; wherein the A component is an acrylic acid copolymer; and the B component is tannic acid.

[0007] The A component is 100 parts by weight, and the B component is 1-50 parts by weight.

[0008] As a preferred technical solution, the B component is 5-30 parts by weight (such as: 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, etc.), and when the B component is 10-15 parts by weight, the improvement effect on lithium battery ESI is best.

[0009] As a preferred technical solution, the A component adopts a terpolymer of acrylonitrile, 2-acrylamide-2-phenyl ethanesulfonic acid and methacrylic acid.

[0010] Technical solution two:

[0011] A preparation method of a lithium battery silicon negative electrode adhesive, comprising the following steps:

[0012] Step 1, adding the B component to deionized water to prepare a tannic acid aqueous solution;

[0013] Step 2, adding the adhesive polymer containing the A component to the tannic acid aqueous solution prepared in step 1 and mechanically dispersing to uniformity.

[0014] As a preferred technical solution, the solid content of the adhesive polymer containing the A component is 5%.

[0015] As a preferred technical solution, the mass concentration of the tannic acid aqueous solution prepared in step 1 is 4%-20% by mass fraction.

[0016] As a preferred technical solution, the rotation speed of the mechanical dispersion is 500-1500 rpm. The rotation speed of the mechanical dispersion is 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm or 1500 rpm, etc., and the dispersion effect is best at a rotation speed of 1000 rpm.

[0017] Technical solution three:

[0018] A silicon negative electrode sheet containing the lithium battery silicon negative electrode adhesive;

[0019] Technical solution four:

[0020] A lithium battery containing the silicon negative electrode sheet.

[0021] Compared with the prior art, the present application has the beneficial effects that:

[0022] The present application uses acrylic multi-copolymer as the binder system, and by adding tannic acid thereto, the ion transfer channel is formed by the interaction between the polar structure such as phenolic hydroxyl and carbonyl of tannic acid and the acrylic multi-copolymer, the ion transfer effect of the lithium battery is improved, thereby the electrochemical impedance of the lithium battery is reduced, and the electrochemical performance is improved. In addition, the polyphenolic hydroxyl of tannic acid can also form hydrogen bonds with the polypropylene segment in the binder, and the hydrogen bonds are used to construct a high molecular crosslinked network structure, and the tannic acid can act as a "dynamic binder" in the structure, thereby the adhesion of the binder is improved, and the peeling strength and cycle stability of the negative electrode material are improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The electrochemical impedance spectrum of the lithium battery of the present application;

[0024] Figure 2 The relationship diagram of the capacity retention rate and the charge-discharge cycle time of the lithium battery of the present application. DETAILED DESCRIPTION

[0025] In the present application,

[0026] Tannic acid: purchased from Shanghai Maikelin Biotechnology Co., Ltd.;

[0027] The chemical structure of tannic acid is as follows:

[0028]

[0029] PVA powder (Mw≈195000): purchased from Shanghai Maikelin Biotechnology Co., Ltd.;

[0030] Si-C composite material (silicon-carbon negative electrode main material) containing Si and C, silicon-based with a specific capacity of 600 mAh / g: purchased from Zhejiang Lixian New Material Technology Co., Ltd.;

[0031] PE / PP separator: purchased from Shanghai Enxin New Material Technology Co., Ltd.;

[0032] The binder polymer used in the present application is a binder polymer containing a terpolymer of acrylonitrile, 2-acrylamide-2-phenyl ethanesulfonic acid and methacrylic acid, and the preparation method comprises the following steps:

[0033] Step a, 350 parts of pure water are added into a reaction kettle, stirred at 100 rpm, nitrogen is introduced, the flow rate is 2000 L / h, water-soluble oxygen is removed for 1.5 hours, then 55 parts of monomer acrylic acid, 5 parts of monomer N,N-diethyl acrylamide and 40 parts of monomer acrylonitrile are added, nitrogen is continuously introduced, and stirring is carried out for 3 h to obtain a solution.

[0034] Step b, continuously passing nitrogen, the solution is heated to 55℃ at a temperature rise rate of 1℃ / min, 0.5 parts of 10% mass fraction initiator solution benzoyl peroxide is added, and the reaction is initiated for 10 hours to obtain a polymerization product.

[0035] Step c, the polymerization product is removed at 60℃ under reduced pressure to a vacuum degree of less than 0.1 MPa by a vacuum pump to remove residual monomers to obtain a polymerization product with a solid content of 40%.

[0036] Step d, 500g of the polymerization product with a solid content of 40% is neutralized to pH 7.5 at 50℃ with 3500g of lithium hydroxide aqueous solution to obtain a viscous adhesive polymer; it is determined that the solid content of the ternary copolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid in the obtained adhesive polymer is 5%.

[0037] The application is further described in detail in combination with the following examples.

[0038] In the following examples, the addition of the A component ternary copolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid is in the form of an adhesive polymer, and the addition of the B component tannic acid is in the form of a tannic acid aqueous solution, and the actual addition amount of the A component and the B component is calculated by the following formula:

[0039] A component = adhesive polymer addition amount x A component solid content;

[0040] B component = tannic acid aqueous solution addition amount x B component mass fraction.

[0041] Example 1:

[0042] A lithium battery silicon negative electrode adhesive, the preparation method comprising the following steps:

[0043] Step 1, prepare a tannic acid aqueous solution: take 10g of tannic acid solid and put it into 90g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%;

[0044] Step 2, blending: 100g of adhesive polymer (solid content 5%) is added to 2.63g of the tannic acid aqueous solution with a mass concentration of 10% prepared in step 1, and mechanically dispersed at a speed of 1000r / min for 30min by a disperser until uniform, and then obtained.

[0045] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode adhesive of the present example is 2.563‰.

[0046] A silicon negative electrode sheet, the preparation method comprising the following steps:

[0047] Step A, Si-C composite material (Si-based with a capacity of 600 mAh / g) containing Si and C, conductive carbon black, and the binder for the silicon negative electrode are mixed, deionized water is added, and the mixture is uniformly dispersed and then passed through a 100-mesh screen to obtain a silicon negative electrode slurry with a total solid content of 45%; in the silicon negative electrode slurry, the silicon negative electrode material accounts for 95.5 wt% of the total solid content, the conductive carbon black accounts for 2.0 wt% of the total solid content, and the binder for the silicon negative electrode accounts for 2.5 wt% of the total solid content in terms of solid content;

[0048] Step B, the silicon negative electrode slurry is coated on a 10-μm-thick copper foil as a current collector, and then placed in a drying oven at 120°C for 5 minutes, and then naturally cooled to room temperature in the oven, and then calendered at a unit length load of 10×10 4 N / m to obtain a silicon negative electrode sheet.

[0049] A lithium battery is prepared by the following method:

[0050] The silicon negative electrode sheet is used as the negative electrode, lithium nickel cobalt manganese oxide NCM523 is used as the positive electrode, a mixed solvent of ethylene carbonate EC, methyl ethyl carbonate EMC, and diethyl carbonate DEC in a mass ratio of 3:2:5 is used as the electrolyte, 1M LiPF6 is used as the electrolyte, and PE / PP is used as the separator to make a P383450 lithium battery.

[0051] Example 2:

[0052] A binder for a silicon negative electrode of a lithium battery is prepared by the following method:

[0053] Step 1, preparing a tannic acid aqueous solution: 10 g of tannic acid solid is added to 90 g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%;

[0054] Step 2, blending: 100 g of the binder polymer (with a solid content of 5%) is added to 5.56 g of the tannic acid aqueous solution prepared in step 1 with a mass concentration of 10%, and the mixture is mechanically dispersed at a speed of 1000 rpm for 30 minutes until uniform, thereby obtaining the binder.

[0055] It is calculated that the solid content of tannic acid in the binder for the silicon negative electrode of the lithium battery of the present embodiment is 5.267‰.

[0056] A silicon negative electrode sheet is prepared by the method of Example 1.

[0057] A lithium battery is prepared by the method of Example 1.

[0058] Example 3:

[0059] A binder for a silicon negative electrode of a lithium battery is prepared by the following method:

[0060] Step 1, preparation of tannic acid aqueous solution: take 10 g of tannic acid solid, put into 90 g of deionized water to prepare 10% tannic acid aqueous solution;

[0061] Step 2, blending: 100 g of binder polymer (solid content 5%) is added to 8.82 g of 10% tannic acid aqueous solution prepared in step 1, and mechanically dispersed at a speed of 1000 rpm for 30 min to uniformity by using a disperser.

[0062] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the embodiment is 8.105 ‰.

[0063] A silicon negative electrode sheet, the preparation method is the same as that of example 1.

[0064] A lithium battery, the preparation method is the same as that of example 1.

[0065] Example 4:

[0066] A lithium battery silicon negative electrode binder, the preparation method comprises the following steps:

[0067] Step 1, preparation of tannic acid aqueous solution: take 10 g of tannic acid solid, put into 90 g of deionized water to prepare 10% tannic acid aqueous solution;

[0068] Step 3, blending: 100 g of binder polymer (solid content 5%) is added to 12.5 g of 10% tannic acid aqueous solution prepared in step 1, and mechanically dispersed at a speed of 1000 rpm for 30 min to uniformity by using a disperser.

[0069] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the embodiment is 11.11 ‰.

[0070] A silicon negative electrode sheet, the preparation method is the same as that of example 1.

[0071] A lithium battery, the preparation method is the same as that of example 1.

[0072] Example 5:

[0073] A lithium battery silicon negative electrode binder, the preparation method comprises the following steps:

[0074] Step 1, preparation of tannic acid aqueous solution: take 10 g of tannic acid solid, put into 90 g of deionized water to prepare 10% tannic acid aqueous solution;

[0075] Step 3, blending: 100 g of the binder polymer (solid content 5%) is added to 20.0 g of the tannic acid aqueous solution with a mass concentration of 10% prepared in step 1, and mechanically dispersed at a speed of 1000 r / min for 30 min by a disperser until uniform, and thus obtained.

[0076] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the embodiment is 16.67 ‰.

[0077] A silicon negative electrode sheet, and the preparation method thereof is the same as that in embodiment 1.

[0078] A lithium battery, and the preparation method thereof is the same as that in embodiment 1.

[0079] Embodiment 6:

[0080] A lithium battery silicon negative electrode binder, and the preparation method thereof comprises the following steps:

[0081] Step 1, preparation of tannic acid aqueous solution: 10 g of tannic acid solid is put into 90 g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%;

[0082] Step 3, blending: 100 g of the binder polymer (solid content 5%) is added to 20.0 g of the tannic acid aqueous solution with a mass concentration of 10% prepared in step 1, and mechanically dispersed at a speed of 1000 r / min for 30 min by a disperser until uniform, and thus obtained.

[0083] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the embodiment is 16.67 ‰.

[0084] A silicon negative electrode sheet, and the preparation method thereof is the same as that in embodiment 1.

[0085] A lithium battery, and the preparation method thereof is the same as that in embodiment 1.

[0086] Embodiment 7:

[0087] A lithium battery silicon negative electrode binder, and the preparation method thereof comprises the following steps:

[0088] Step 1, preparation of tannic acid aqueous solution: 10 g of tannic acid solid is put into 90 g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%;

[0089] Step 3, blending: 100 g of the binder polymer (solid content 5%) is added to 20.0 g of the tannic acid aqueous solution with a mass concentration of 10% prepared in step 1, and mechanically dispersed at a speed of 1000 r / min for 30 min by a disperser until uniform, and thus obtained.

[0090] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the embodiment is 16.67 ‰.

[0091] A silicon negative electrode tab, the preparation method of which is as follows.

[0092] A lithium battery, the preparation method of which is as follows.

[0093] Example 8:

[0094] A lithium battery silicon negative electrode binder, the preparation method of which comprises the following steps:

[0095] Step 1, preparing a tannic acid aqueous solution: taking 10 g of tannic acid solid and putting it into 90 g of deionized water to prepare a 10% tannic acid aqueous solution;

[0096] Step 3, blending: adding 100 g of binder polymer (solid content 5%) into 15.0 g of the 10% tannic acid aqueous solution prepared in step 1, and mechanically dispersing at a speed of 1000 r / min for 30 min until uniform by using a disperser, and then obtaining the product.

[0097] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the present example is 13.04 ‰.

[0098] A silicon negative electrode tab, the preparation method of which is as follows.

[0099] A lithium battery, the preparation method of which is as follows.

[0100] Example 9:

[0101] A lithium battery silicon negative electrode binder, the preparation method of which comprises the following steps:

[0102] Step 1, preparing a tannic acid aqueous solution: taking 10 g of tannic acid solid and putting it into 90 g of deionized water to prepare a 10% tannic acid aqueous solution;

[0103] Step 3, blending: adding 100 g of binder polymer (solid content 5%) into 3.5 g of the 10% tannic acid aqueous solution prepared in step 1, and mechanically dispersing at a speed of 1000 r / min for 30 min until uniform by using a disperser, and then obtaining the product.

[0104] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the present example is 3.382 ‰.

[0105] A silicon negative electrode tab, the preparation method of which is as follows.

[0106] A lithium battery, the preparation method of which is as follows.

[0107] Example 10:

[0108] A binder for a lithium battery silicon negative electrode, the preparation method thereof comprising the following steps:

[0109] Step 1, preparing a tannic acid aqueous solution: taking 10 g of tannic acid solid and putting it into 90 g of deionized water to prepare a 10% tannic acid aqueous solution;

[0110] Step 3, blending: adding 100 g of the binder polymer (solid content 5%) into 1.5 g of the 10% tannic acid aqueous solution prepared in step 1, and mechanically dispersing at a speed of 1000 rpm for 30 min until uniform by using a disperser.

[0111] It is calculated that the solid content of tannic acid in the lithium battery silicon negative electrode binder of the embodiment is 1.478 ‰.

[0112] A silicon negative electrode sheet, the preparation method thereof being the same as that of Example 1.

[0113] A lithium battery, the preparation method thereof being the same as that of Example 1.

[0114] Comparative Example 1

[0115] A binder for a lithium battery silicon negative electrode, the binder polymer being a terpolymer containing acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid, and the solid content being 5%.

[0116] A silicon negative electrode sheet, the preparation method thereof being the same as that of Example 1.

[0117] A lithium battery, the preparation method thereof being the same as that of Example 1.

[0118] Comparative Example 2

[0119] A binder for a lithium battery silicon negative electrode, the preparation method thereof comprising the following steps:

[0120] Step 1, preparing a tannic acid aqueous solution: taking 10 g of pine tannic acid solid and putting it into 90 g of deionized water to prepare a 10% tannic acid aqueous solution;

[0121] Step 2, preparing a PVA binder: taking 5 g of commercial PVA powder (Macklin, Mw≈195000) and adding 95 g of deionized water, and heating to 60℃ to completely dissolve the PVA to obtain a PVA binder;

[0122] Step 3, blending: adding the PVA binder prepared in step 2 into 5.56 g of the 10% tannic acid aqueous solution prepared in step 1, and mechanically dispersing at a speed of 1000 rpm for 30 min until uniform by using a disperser.

[0123] A silicon negative electrode sheet, the preparation method thereof being the same as that of Example 1.

[0124] A lithium battery, the preparation method of which is the same as in Example 1.

[0125] Comparative Example 3

[0126] A binder for silicon anodes in lithium-ion batteries, using PVA binder, is prepared by the following steps:

[0127] Take 5g of commercially available PVA powder (Maclean, Mw≈195000), add 95g of deionized water, heat to 60℃ to dissolve all PVA, and obtain PVA adhesive;

[0128] A silicon negative electrode sheet, the preparation method of which is the same as in Example 1.

[0129] A lithium battery, the preparation method of which is the same as in Example 1.

[0130] Example 1: Electrochemical performance

[0131] The electrochemical performance of the lithium batteries prepared in Examples 1-4 and Comparative Examples 1-3 was tested respectively.

[0132] Test method: The lithium battery was charged and discharged at 25℃, within a voltage range of 2.5~4.2V, and at 0.5C. The coulombic efficiency of the first charge-discharge cycle and the coulombic efficiency and capacity retention after 50 cycles were tested using the constant current method. The capacity retention results after 55 charge-discharge cycles are shown in the figure. Figure 2 The EIS results were tested as follows: Figure 1 As shown.

[0133] Depend on Figure 1 As can be seen, the addition of tannic acid to the polypropylene binder improved the EIS to a certain extent, indicating that the binder for the silicon anode of the present invention is more conducive to ion transfer in the electrochemical process of lithium batteries. Among them, the solid content of component B in Example 2, at 5.267‰, showed the best improvement effect on the EIS of lithium batteries. A comparison between Comparative Examples 2 and 3 shows that in the PVA system, even the addition of tannic acid cannot improve the ion transfer effect in the electrochemical process; there is no significant advantage in EIS improvement between adding and not adding tannic acid.

[0134] Depend on Figure 2 As can be seen from the above, the addition of tannic acid in Examples 1-4 of the present invention can improve the cycle stability of lithium batteries, among which the solid content of component B in Example 2 is 5.267‰, which has the best effect.

[0135] Example 2: Peel strength

[0136] The electrode tabs of the examples and comparative examples were cut into 20 cm x 2.5 cm strips, a 1 mm thick steel plate was attached to the current collector side with double-sided tape, a transparent tape was attached to the coating layer side, and the peeling stress was measured by peeling in the 180° direction at a speed of 100 mm / min using a tensile tester. The test results are shown in Table 1.

[0137] Table 1

[0138] Specific embodiments Peel force (N / m) Specific embodiments Peel force (N / m) Example 1 38.15 Example 2 45.07 Example 3 48.75 Example 4 51.07 Example 5 30.56 Example 6 60.25 Example 7 57.78 Example 8 53.43 Example 9 41.44 Example 10 39.78 Comparative Example 1 29.72 Comparative Example 2 22.34 Comparative Example 3 20.75

[0139] The above-described embodiments are merely preferred embodiments of the present application and are not intended to exhaustively enumerate the possible implementations of the present application. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present application should be considered to be within the scope of the claims of the present application.

Claims

1. A binder for silicon anodes in lithium batteries, characterized in that, It includes at least component A and component B; wherein component A is an acrylic multi-component copolymer; and component B is tannic acid; By weight, component A comprises 100 parts and component B comprises 1-50 parts by weight; The structure of the tannic acid is shown in Formula 1: Component A is a terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid.

2. The binder for a silicon anode in a lithium battery according to claim 1, characterized in that, The B component is 5-30 parts by weight.

3. A method for preparing a binder for a lithium battery silicon anode as described in any one of claims 1-2, characterized in that, Includes the following steps: Step 1: Add component B to deionized water to prepare an aqueous solution of tannic acid; Step 2: Add the tannic acid aqueous solution prepared in Step 1 to the binder polymer containing component A, and mechanically disperse until uniform, to obtain the final product.

4. The method for preparing a binder for a lithium battery silicon anode according to claim 3, characterized in that, The mass concentration of the tannic acid aqueous solution prepared in step 1 is 4% to 20% by mass fraction.

5. The method for preparing a binder for a silicon anode in a lithium battery according to claim 3, characterized in that, The rotational speed of the mechanical dispersion is 500-1500 rpm.

6. A silicon negative electrode sheet, characterized in that, Contains a binder for a silicon anode in a lithium battery as described in any one of claims 1-2.

7. A lithium battery, characterized in that, The device is equipped with a silicon negative electrode as described in claim 6.

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