CN115566196A - Binder for silicon negative electrode of lithium battery, silicon negative electrode pole piece and lithium battery - Google Patents

Abstract

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

Description

Binder for lithium battery silicon negative pole, silicon negative pole piece and lithium battery

technical field

The invention belongs to the technical field of lithium batteries, and in particular relates to a binder for a silicon negative electrode of a lithium battery, a silicon negative pole piece and a lithium battery.

Background technique

Due to the advantages of high theoretical specific capacity, abundant reserves, controllable cost, and the ability to increase the energy density of batteries, silicon materials are increasingly being used as anode materials for lithium batteries. In the process of preparing the silicon negative electrode, it is an essential step to use a binder to bond the components of the silicon negative electrode together; however, the currently used binders for the silicon negative electrode mainly include PVA (polypropylene alcohol) adhesive There are two types of binders and PAA binders (acrylic binders); and because of the lithium transfer characteristics of PAA and PVA, lithium ions can hop between adjacent carboxyl and hydroxyl positions, so multiple or more particles are formed on the surface of silicon particles Or less thin coatings play the role of artificial SEI to transport ions; among them, there are only hydroxyl groups and no carboxyl groups in the PVA binder, so the ion transmission is poor, and the PAA binder, although there are The existence of a large number of carboxyl groups, but this makes the PAA binder very easy to absorb water, and the excessive hydrogen bonds generated between the carboxyl groups hinder the free rotation of the molecular chain, making the polymer too poor in flexibility, which is not conducive to bearing the volume expansion of the active material. Stress affects the improvement of battery performance, and the linear long-chain structure of PAA makes it easy to slide between molecular chains, and is prone to permanent deformation after being stressed, resulting in the agglomeration of active materials and reducing the specific capacity of the pole piece. Therefore, in the chain segment design process of PAA, the number of carboxyl chain segments is usually controlled, which limits the effect of PAA binder on ion transfer and limits the faster transmission of lithium ions in the binder; It is also because of the performance limitations of these two types of binders in ion transfer that the prepared lithium batteries have high electrochemical impedance and poor electrochemical performance.

Contents of the invention

The purpose of the present invention is to overcome the defects in the prior art, and provide a binder for silicon negative electrodes of lithium batteries, which can improve the ion transfer performance of the binder, greatly reduce the electrochemical impedance of lithium batteries, and improve the performance of lithium batteries. Electrochemical performance of the battery.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

Technical solution one:

A binder for silicon negative electrodes of lithium batteries, comprising at least component A and component B; wherein, the component A is an acrylic multi-polymer; the component B is tannic acid;

In parts by weight, the A component is 100 parts, and the B component is 1-50 parts by weight.

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 Parts, 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.), when the B component is 10-15 parts by weight, the improvement effect on lithium battery ESI is the best.

As a preferred technical solution, the tannic acid adopts vitex tannic acid composed of a resorcinol type A ring.

As a preferred technical solution, the component A is a terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid.

Technical solution two:

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

Step 1, adding the B component into deionized water to prepare an aqueous solution of tannic acid;

Step 2. Add the binder polymer containing the component A into the aqueous solution of tannic acid prepared in step 1, and disperse mechanically until uniform.

As a preferred technical solution, the solid content of the binder polymer containing the A component is 5%.

As a preferred technical solution, in terms of mass fraction, the mass concentration of the tannic acid aqueous solution prepared in step 1 is 4% to 20%.

As a preferred technical solution, the rotational speed of the mechanical dispersion is 500-1500 rpm. The rotating speed of described mechanical dispersion is 500 turns/min, 600 turns/min, 700 turns/min, 800 turns/min, 900 turns/min, 1000 turns/min, 1100 turns/min, 1200 turns/min, 1300 turns/min min, 1400 rpm or 1500 rpm, etc., among which the dispersing effect is the best at the speed of 1000 rpm.

Technical solution three:

A silicon negative pole piece, containing the binder for the lithium battery silicon negative pole;

Technical solution four:

A lithium battery contains the silicon negative electrode sheet.

Compared with prior art, the beneficial effect of the present invention is:

The present invention uses acrylic multi-polymer as the binder system, and by adding tannic acid to it, utilizes polar structures such as phenolic hydroxyl groups and carbonyl groups of tannic acid to interact with the acrylic multi-polymer to form ion transport The channel improves the ion transfer effect of the lithium battery, thereby reducing the electrochemical impedance of the lithium battery and improving its electrochemical performance. In addition, the polyphenolic hydroxyl groups of tannic acid can also form hydrogen bonds with the polypropylene chain segments in the binder, and use hydrogen bonds to build a polymer cross-linked network structure, and tannic acid can be used as a "dynamic bond". agent", which improves the cohesiveness of the binder, thereby improving the peel strength and cycle stability of the negative electrode material.

Description of drawings

Fig. 1 is the electrochemical impedance spectrogram of lithium battery of the present invention;

Fig. 2 is a graph showing the relationship between the capacity retention rate and the charge-discharge cycle time of the lithium battery of the present invention.

detailed description

In the present invention,

Vitex tannic acid: purchased from Shanghai McLean Biochemical Technology Co., Ltd.;

The chemical structural formula of Vitex tannic acid is as follows:

PVA powder (Mw≈195000): purchased from Shanghai Macklin Biochemical Technology Co., Ltd.;

Si-C composite material containing Si and C (silicon-carbon negative electrode main material), silicon base with a gram capacity of 600mAh/g: purchased from Zhejiang Lichen New Material Technology Co., Ltd.;

PE/PP diaphragm: purchased from Shanghai Enjie New Material Technology Co., Ltd.;

The binder polymer used in the present invention adopts the binder polymer containing the terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid, and its preparation method comprises the steps:

Step a. Add 350 parts of pure water to the reactor, stir at 100 rpm, feed nitrogen gas at a flow rate of 2000 L/h, remove water-soluble oxygen for 1.5 hours, then add 55 parts of monomeric acrylic acid, 5 parts of monomeric N,N- Diethylacrylamide, 40 parts of monomeric acrylonitrile, continuously blowing nitrogen, stirring for 3 hours, to obtain a solution.

Step b. Continuously feed nitrogen, heat the solution to 55° C. at a heating rate of 1° C./min, add 0.5 parts of benzoyl peroxide as an initiator solution with a mass fraction of 10%, and initiate the reaction for 10 hours to obtain a polymerization product.

Step c, depressurize the polymer product at 60° C. with a vacuum pump until the vacuum degree is lower than 0.1 MPa, remove residual monomers, and obtain a polymer product with a solid content of 40%.

Step d, take 500g of the polymer product with a solid content of 40% and neutralize it with 3500g of lithium hydroxide alkali aqueous solution to pH 7.5 at 50°C to obtain a viscous binder polymer; The solid content of the terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid in the binder polymer was 5%.

Below in conjunction with embodiment the present invention is described in further detail.

In the following examples, the terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid in component A is added by adding a binder polymer, and component B is The addition of niacin is done by adding an aqueous solution of tannic acid, and the actual amount of components A and B added is calculated by the following formula:

A component = binder polymer addition amount × A component solid content;

Component B = added amount of tannic acid aqueous solution × mass fraction of component B.

Example 1:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous tannic acid solution: take 10 g of Vitex tannic acid solids, put them into 90 g of deionized water, and prepare an aqueous tannic acid solution with a mass concentration of 10%;

Step 2, blending: 100g of binder polymer (solid content 5%) is added to 2.63g of the tannic acid aqueous solution prepared in step 1 with a mass concentration of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for silicon negative electrodes of lithium batteries in this embodiment is 2.563‰.

A silicon negative pole piece, its preparation method comprises the steps:

Step A, after mixing the Si-C composite material containing Si and C (silicon base with a gram capacity of 600mAh/g), conductive carbon black, and the binder for the silicon negative electrode, add deionized water, disperse evenly and pass A 100-mesh sieve 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, and the conductive carbon black accounts for 2.0 wt% of the total solid content; The binder for the silicon negative electrode accounts for 2.5wt% of the total solid content in terms of solid content;

Step B. Coat the silicon negative electrode slurry on a 10 μm thick copper foil as a current collector, and then dry it at 120°C for ⁵ minutes. The silicon negative electrode sheet was obtained by calendering under load.

A lithium battery, the preparation method of which is as follows:

The silicon negative pole piece is used as the negative electrode, nickel-cobalt lithium manganese oxide NCM523 is used as the positive electrode, and ethylene carbonate EC: ethyl methyl carbonate EMC: diethyl carbonate DEC is used as a mixed solvent in a mass ratio of 3:2:5, containing 1M LiPF ₆ is used as the electrolyte, and the PE/PP diaphragm is used as the diaphragm to make a P383450 lithium battery.

Example 2:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous tannic acid solution: take 10 g of Vitex tannic acid solids, put them into 90 g of deionized water, and prepare an aqueous tannic acid solution with a mass concentration of 10%;

Step 2, blending: 100g of binder polymer (solid content 5%) is added to 5.56g of the tannic acid aqueous solution prepared in step 1 with a mass concentration of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for silicon negative electrodes of lithium batteries in this embodiment is 5.267‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Example 3:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous tannic acid solution: take 10 g of Vitex tannic acid solids, put them into 90 g of deionized water, and prepare an aqueous tannic acid solution with a mass concentration of 10%;

Step 2, blending: 100g of binder polymer (solid content 5%) is added to 8.82g of the tannic acid aqueous solution prepared in step 1 with a mass concentration of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for the silicon negative electrode of the lithium battery in this embodiment is 8.105‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Example 4:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous solution of tannic acid: take 10 g of Vitexia tannic acid solids and put them into 90 g of deionized water to prepare a 10% aqueous solution of tannic acid;

Step 3, blending: 100g of binder polymer (solid content 5%) is added to 12.5g of the tannic acid aqueous solution prepared in step 1 with a mass concentration of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for the silicon negative electrode of the lithium battery in this embodiment is 11.11‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Example 5:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous solution of tannic acid: take 10 g of Vitexia tannic acid solids and put them into 90 g of deionized water to prepare a 10% aqueous solution of tannic acid;

Step 3, blending: 100g of binder polymer (solid content 5%) is added to 0.5g of the tannic acid aqueous solution with a mass concentration prepared in step 1 of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for silicon negative electrodes of lithium batteries in this embodiment is 0.4975‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Embodiment 6:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous solution of tannic acid: take 10 g of Vitexia tannic acid solids and put them into 90 g of deionized water to prepare a 10% aqueous solution of tannic acid;

Step 3, blending: 100g of binder polymer (solid content 5%) is added to 20.0g of the tannic acid aqueous solution with a mass concentration prepared in step 1 of 10%, and a disperser is used at a speed of 1000 rpm/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for silicon negative electrodes of lithium batteries in this embodiment is 16.67‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Embodiment 7:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous solution of tannic acid: take 10 g of Vitexia tannic acid solids and put them into 90 g of deionized water to prepare a 10% aqueous solution of tannic acid;

Step 3, blending: 100g of binder polymer (solid content 5%) is added to 25.0g of the tannic acid aqueous solution with a mass concentration prepared in step 1 of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for silicon negative electrodes of lithium batteries in this embodiment is 20.00‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Embodiment 8:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous solution of tannic acid: take 10 g of Vitexia tannic acid solids and put them into 90 g of deionized water to prepare a 10% aqueous solution of tannic acid;

Step 3, blending: 100g of binder polymer (solid content 5%) is added to 15.0g of the tannic acid aqueous solution prepared in step 1 with a mass concentration of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for silicon negative electrodes of lithium batteries in this embodiment is 13.04‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Embodiment 9:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous solution of tannic acid: take 10 g of Vitexia tannic acid solids and put them into 90 g of deionized water to prepare a 10% aqueous solution of tannic acid;

Step 3, blending: 100g binder polymer (solid content 5%) joins 3.5g the mass concentration that step 1 prepares is 10% in the tannic acid aqueous solution, adopts disperser under the rotating speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for silicon negative electrodes of lithium batteries in this embodiment is 3.382‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Example 10:

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous solution of tannic acid: take 10 g of Vitexia tannic acid solids and put them into 90 g of deionized water to prepare a 10% aqueous solution of tannic acid;

Step 3, blending: 100g of binder polymer (solid content 5%) is added to 1.5g of the tannic acid aqueous solution prepared in step 1 with a mass concentration of 10%, and a disperser is used at a speed of 1000 rev/min Disperse mechanically for 30 minutes until uniform.

According to calculation, the solid content of tannic acid in the binder for the silicon negative electrode of the lithium battery in this embodiment is 1.478‰.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Comparative example 1

A binder for the silicon negative electrode of a lithium battery adopts a binder polymer containing a terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid, with a solid content of 5%.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Comparative example 2

A kind of binder for silicon negative electrode of lithium battery, its preparation method comprises the following steps:

Step 1, preparing an aqueous tannic acid solution: take 10 g of pine tannic acid solids, put them into 90 g of deionized water, and prepare an aqueous tannic acid solution with a mass concentration of 10%;

Step 2, preparation of PVA binder: take 5g of commercialized PVA powder (McLean, Mw≈195000), add 95g of deionized water, heat to 60°C to completely dissolve the PVA, and obtain the PVA binder;

Step 3, blending: the PVA binder prepared in step 2 was added to 5.56 g of the 10% tannic acid aqueous solution prepared in step 1, and mechanically dispersed at a speed of 1000 rpm for 30 minutes until uniform by using a disperser. Instantly.

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Comparative example 3

A kind of binding agent for silicon negative electrode of lithium battery adopts PVA binding agent, and its preparation method comprises the following steps:

Take 5g of commercialized PVA powder (McLean, Mw≈195000), add 95g of deionized water, heat to 60°C to completely dissolve the PVA, and obtain a PVA binder;

A silicon negative pole piece, its preparation method: same as embodiment 1.

A kind of lithium battery, its preparation method: with embodiment 1.

Effect example 1: Electrochemical performance

The lithium batteries prepared in Examples 1-4 and Comparative Examples 1-3 were tested for electrochemical performance;

Test method: charge and discharge the lithium battery at 25°C, 2.5-4.2V voltage range, 0.5C, and use the constant current method to test the first Coulombic efficiency of the charge-discharge cycle and the Coulombic efficiency and capacity after 50 cycles Retention rate, after 55 cycles of charging and discharging, the results of capacity retention rate are shown in Figure 2. The results of the EIS test are shown in Figure 1.

As can be seen from Figure 1: after vitex tannic acid is added to the polypropylene binder, the EIS is improved to a certain extent, indicating that the silicon negative electrode binder of the present invention is more conducive to the electrochemical process of lithium batteries In the ion transfer in the example 2, the solid content of the B component in Example 2 is 5.267‰, which has the best effect on improving the EIS of the lithium battery. From the comparison of Comparative Example 2 and Comparative Example 3, it can be seen that in the PVA system, even if tannic acid is added, the effect of improving the ion transfer in the electrochemical process cannot be achieved. obvious advantage.

It can be seen from Figure 2 that the addition of tannic acid in Examples 1-4 of the present invention can improve the cycle stability of lithium batteries, and the solid content of component B in Example 2 is 5.267‰, the effect is the best.

Effect example 2: Peel strength

Cut the electrode pole pieces of the embodiment and the comparative example into strips of 20 cm × 2.5 cm, glue a steel plate with a thickness of 1 mm on the side of the current collector, stick a transparent tape on the side of the coating layer, and use a tensile tester to Peel in a direction of 180° at a speed of 100mm/min, and measure the peel stress. The test results are shown in Table 1.

Table 1

specific embodiment Peel force(N/m) specific embodiment 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

The implementation manners described above are only preferred embodiments of the present invention, rather than an exhaustive list of feasible implementations of the present invention. For those skilled in the art, any obvious changes made without departing from the principle and spirit of the present invention should be considered to be included in the protection scope of the claims of the present invention.

Claims (9)

1. A binder for silicon negative electrodes of lithium batteries, characterized in that it includes at least component A and component B; wherein, component A is an acrylic multi-polymer; component B is tannic acid ; In parts by weight, the A component is 100 parts, and the B component is 1-50 parts by weight. 2. a kind of binder for lithium battery silicon negative electrode according to claim 1, is characterized in that, The B component is 5-30 parts by weight. 3. a kind of binder for lithium battery silicon negative electrode according to claim 1, is characterized in that, The tannic acid adopts vitex tannic acid composed of resorcinol type A ring. 4. a kind of binder for lithium battery silicon negative electrode according to claim 1, is characterized in that, The A component is a terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid. 5. A preparation method for the lithium battery silicon negative electrode as claimed in any one of claims 1-4, characterized in that, comprising the following steps: Step 1, adding the B component into deionized water to prepare an aqueous solution of tannic acid; Step 2. Add the aqueous solution of tannic acid prepared in step 1 to the binder polymer containing the component A, and mechanically disperse until uniform. 6. the preparation method of a kind of lithium battery silicon negative electrode binder according to claim 5, is characterized in that, In terms of mass fraction, the mass concentration of the tannic acid aqueous solution prepared in step 1 is 4% to 20%. 7. the preparation method of a kind of lithium battery silicon negative electrode binder according to claim 5, is characterized in that, The rotating speed of the mechanical dispersion is 500-1500 rpm. 8. A silicon negative electrode sheet, characterized in that it contains the binder for silicon negative electrodes of lithium batteries as described in any one of claims 1-4. 9. A lithium battery, characterized in that it is provided with the silicon negative pole piece as claimed in claim 8.

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