WO2022237534A1

WO2022237534A1 - Composite adhesive and preparation method therefor and application thereof

Info

Publication number: WO2022237534A1
Application number: PCT/CN2022/089437
Authority: WO
Inventors: 刘颖; 支岩辉; 姚洋洋; 窦洋; 娄帅宾
Original assignee: 蜂巢能源科技股份有限公司
Priority date: 2021-05-08
Filing date: 2022-04-27
Publication date: 2022-11-17
Also published as: CN112909261A; CN112909261B

Abstract

The present disclosure provides a composite adhesive and a preparation method therefor and an application thereof. The composite adhesive comprises a rubber, a nitrile compound, and a dispersant, and the mass ratio of the rubber to the nitrile compound is 1:2 to 1:10; in the composite adhesive, the mass fraction of the dispersant is 8-10%. The composite adhesive is particularly suitable for a silicon-oxygen system, and can increase the energy density and significantly improve the low-temperature cycle performance of a battery.

Description

A kind of composite binder and its preparation method and application

technical field

The disclosure relates to the technical field of lithium-ion batteries, and relates to a composite binder and a preparation method and application thereof.

Background technique

With the development of the battery industry, the energy density of the battery cell is required to increase. Due to the obvious advantages of high gram capacity, silicon-oxygen materials (SiOx, where 0<x<2) have been added to negative electrode graphite as additives in small amounts to improve the energy of the battery cell. Density provides ideas; however, the dynamic performance of silicon-oxygen materials is significantly worse in low-temperature environments, so adding a small amount of silicon-oxygen materials will also make the low-temperature performance of the battery worse, and lithium will be precipitated during low-temperature cycling.

Traditional lithium-ion battery negative electrodes often use styrene-butadiene rubber and sodium carboxymethyl cellulose as binders, and in the process of use, in addition to the binding effect of the binder, the impedance of the binder itself will have a negative impact on the battery impedance. Influence; during the battery cycle, with the charging and discharging process of the battery, the pole piece expands and contracts accordingly, and the binding force of the binder on the expansion of the pole piece is weak, which leads to the destruction of the SEI film, the continuous formation process, and the battery impedance increases significantly , have an adverse effect on the life of the battery cell, and even directly cause diving.

It is of great significance to provide a technical solution to improve the energy density and low-temperature cycle performance of the battery.

public content

The present disclosure provides a kind of composite binder in one embodiment, described composite binder comprises rubber, nitrile compound and dispersant, and the mass ratio of described rubber and nitrile compound is 1:2-1:10 ; In the composite binder, the mass fraction of the dispersant is 8-10%.

In the present disclosure, the mass ratio of the rubber to the nitrile compound can be 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1: 10 etc. The mass fraction of the dispersant is, for example, 8%, 8.2%, 8.4%, 8.6%, 8.8%, 9%, 9.2%, 9.4%, 9.6%, 9.8% or 10%.

Rubber (such as styrene-butadiene rubber) lacks enough functional groups on the surface, and the interaction force between the active material, the conductive agent and the current collector is poor, and in the silicon-oxygen system, the expansion of the pole piece is large, and pure rubber is used as the The binding force of the binder to the pole piece is weak, and the binding effect is significantly reduced in the later stage of the cycle, causing the active material to fall off and affecting the cycle life of the battery cell.

Nitrile compounds (such as acrylonitrile copolymers) contain cyano groups, have a strong binding ability to the pole piece, and have low self-impedance, especially in low temperature environments.

In an embodiment provided by the present disclosure, by mixing the flexible binder and the rigid binder, it is ensured that the binder has sufficient binding effect during the expansion of silicon-oxygen to ensure that the active material does not fall off, and at the same time It also avoids the problem of easy cracking during processing caused by the rigidity of the pole piece when purely using a rigid binder; at the same time, it improves the charging capacity of the silicon-oxygen system in a low-temperature environment, ensuring that the system does not precipitate lithium in a low-temperature environment . At the same time, the dispersant with a mass fraction of 8-10% plays a thickening and dispersing role in the homogenization process, and can disperse the solid particles of the negative electrode, so that the slurry can maintain a relatively stable state during use. If the amount of dispersant added is too low, it will easily lead to sedimentation during the use of the slurry, which will affect the processing of the pole piece. If the amount of dispersant added is too high, it will increase the impedance of the pole piece itself, and using too much dispersant will reduce the active material content of the main material and affect the energy density of the cell.

In the binder provided by an embodiment of the present disclosure, if the proportion of rubber is high, the flexibility of the battery cell is better, but the binding force on the expansion of the battery cell is poor. The large expansion of the pole piece leads to the continuous destruction and formation of the SEI film, which not only consumes the active lithium, but also leads to a significant increase in the resistance of the battery cell, resulting in cyclic diving. At the same time, if the proportion of rubber is too high, the low-temperature performance of the battery will deteriorate; if the proportion of nitrile compounds is too high, it will cause the pole pieces of the battery to be brittle and less flexible. Around the position, the active material of the pole piece is easy to fall off, which has an adverse effect on the life of the battery cell.

In an embodiment of the present disclosure, the composite binder is applied to the silicon-oxygen system, which not only maintains the good flexibility of the styrene-butadiene rubber binder pole piece, but also retains the strong ion transport effect of the acrylonitrile copolymer binder , the advantage of low resistance of the binder, while increasing the energy density, the low-temperature cycle of the battery is significantly improved.

In one embodiment, the mass ratio of the rubber to the nitrile compound is 1:3.5-1:4.5. If the rubber and nitrile compounds are in this range, the composite binder can achieve more excellent effects.

In one embodiment, the rubber includes styrene-butadiene rubber.

In one embodiment, the nitrile compound includes acrylonitrile copolymer. The acrylonitrile copolymer may be an LA type binder.

In one embodiment, the dispersant includes sodium carboxymethylcellulose. The use of sodium carboxymethyl cellulose in combination with rubber and nitrile compounds can better balance the effects of improving battery energy density and low-temperature performance.

In one embodiment, the present disclosure provides a method for preparing the above-mentioned composite binder, the method comprising the following steps:

The rubber, nitrile compound and dispersant are mixed to obtain the composite binder.

In one embodiment, the present disclosure provides a negative electrode sheet, the negative electrode sheet includes a current collector and a negative electrode coating coated on the current collector, the negative electrode coating includes the above-mentioned composite binder, conductive agent and Negative electrode active material, the negative electrode active material includes silicon-oxygen material.

The binder provided by an embodiment of the present disclosure is particularly suitable for negative electrode systems containing silicon-oxygen materials, which can significantly improve the low-temperature cycle of the battery while increasing the energy density.

In one embodiment, the negative electrode active material includes graphite material and silicon oxide material.

In an embodiment of the present disclosure, the negative electrode active material includes graphite, and at the same time, silicon-oxygen material with high gram capacity is added to increase the energy density of the battery. The chemical formula of the silicon-oxygen material is SiOx (0<x<2).

In one embodiment, the silicon-oxygen material is a mixture of carbon-coated SiOx (0<x≤1.2) and carbon-coated SiOx (1.2<x<2), and the carbon-coated silicon-oxygen material is selected from resin polymers The material and the silicon-oxygen material are obtained through high-temperature carbonization at 1500°C-2200°C, and the thickness of the carbon coating layer is 1-10nm.

In one embodiment, the resin polymer material is selected from phenolic resin, epoxy resin, urea-formaldehyde resin, or the coated carbon is selected from other polymer materials such as polyacrylonitrile, polyvinyl alcohol, polydopamine, etc. after high-temperature carbonization get.

In one embodiment, the thickness of the carbon coating layer in the carbon-coated silicon-oxygen material is 1-5 nm.

In one embodiment, the mass fraction of the silicon-oxygen material in the negative electrode active material is less than 5%, such as 5%, 4% or 3%.

In the negative electrode sheet provided by an embodiment of the present disclosure, silicon-oxygen material exists in the negative-electrode active material, but the mass fraction of silicon-oxygen material cannot be too high, because a higher content of silicon-oxygen material is added, and the cell will There will be a more obvious increase in expansion. In some embodiments, the binding force of the binder content in the binder formula to the silicon-oxygen expansion is not enough, which will also cause the battery cell to expand too much in the later stage of the cycle process, resulting in the battery cell cycle diving.

In one embodiment, in the negative electrode coating, the mass fraction of the negative electrode active material is 95-97%, such as 95%, 95.5%, 96%, 96.5% or 97%.

In an embodiment of the present disclosure, the negative electrode sheet can effectively solve the phenomenon of poor low-temperature charging ability caused by adding silicon-oxygen materials when the negative electrode material increases the energy density by using the above-mentioned composite binder. At the same time, in this system , the acrylonitrile copolymer blended with styrene-butadiene rubber not only improves the low-temperature charging ability, but also has the characteristics of both normal temperature cycle and high temperature cycle, and has no obvious deterioration effect on high temperature cycle. The composite binder provided by an embodiment of the present disclosure has a 25°C discharge DCR as low as 11.55mΩ, a 25°C charge DCR as low as 11.96mΩ, a -20°C discharge DCR as low as 144.96mΩ, and a -20°C charge resistance as low as To 376.38mΩ, disassembly after 50 cycles at -20°C can keep the interface normal.

In one embodiment, the conductive agent includes any one or a combination of at least two of conductive carbon black, acetylene black or Ketjen black.

In one embodiment, the mass fraction of the conductive agent is 0.5-1.5%, such as 0.5%, 0.8%, 1%, 1.2% or 1.5%.

In one embodiment, the mass fraction of the composite binder is 1.5-4.5%, such as 1.5%, 2%, 2.5%, 3%, 3.5% or 4%.

In one embodiment, the current collector is copper foil.

In one embodiment, the present disclosure provides a method for preparing the above-mentioned negative electrode sheet, and the method includes the following steps:

The solvent is mixed with the composite binder, the negative electrode active material and the conductive agent to obtain the negative electrode slurry, and the negative electrode slurry is coated on the current collector and dried to obtain the negative electrode sheet.

In one embodiment, the solvent includes water.

In one embodiment, the present disclosure provides a lithium-ion battery, the lithium-ion battery includes the above-mentioned negative electrode sheet.

Description of drawings

The accompanying drawings are used to provide a further understanding of the technical solutions of the present disclosure, and constitute a part of the description, and are used together with the embodiments of the application to explain the technical solutions of the present disclosure, and do not constitute limitations to the technical solutions of the present disclosure.

Figure 1 is a photo of the full-power disassembly of the negative electrode sheet provided in Example 1 after being prepared into a battery at -20°C and 0.05C for 50 cycles;

Figure 2 is a photo of the full-power disassembly after the negative electrode sheet provided in Comparative Example 1 was prepared into a battery at -20°C and 0.05C for 50 cycles;

Fig. 3 is a full-power disassembly photo of the negative electrode sheet provided in Comparative Example 2 prepared into a battery at -20°C and 0.05C for 50 cycles;

Fig. 4 is the normal temperature 25 ℃ cycle curve of embodiment 1, comparative example 1 and comparative example 2;

Fig. 5 is the high temperature 45°C cycle curves of Example 1, Comparative Example 1 and Comparative Example 2.

specific embodiment

The technical solutions of the present disclosure will be further described below in conjunction with the accompanying drawings and through specific implementation methods. It should be clear to those skilled in the art that the embodiments are only for helping to understand the present disclosure, and should not be regarded as specific limitations on the present disclosure.

Example 1

This embodiment provides a composite binder, which is composed of styrene-butadiene rubber, acrylonitrile copolymer (LA-type binder LA133) and sodium carboxymethyl cellulose. Wherein, the mass ratio of styrene-butadiene rubber to acrylonitrile copolymer is 6:25, and the mass fraction of sodium carboxymethyl cellulose in the composite binder is 8.8%.

This embodiment also provides a negative electrode sheet, which includes a copper foil current collector and a negative electrode coating coated on the current collector. The negative electrode coating is composed of the composite binder and conductive agent (SP) provided by this embodiment. ) and the negative electrode active material. The negative electrode active material is composed of graphite negative electrode material and silicon-oxygen material, and the mass fraction of silicon-oxygen material in the negative electrode active material is 5%.

In the negative electrode coating, the mass fraction of the composite binder is 3.4%, the mass fraction of the conductive agent is 1%, and the mass fraction of the negative electrode active material is 95.6%.

The compacted density of the negative electrode sheet is 1.60 g/cm ³ .

The preparation method of the composite binder provided in this example is as follows: mixing the styrene-butadiene rubber and the acrylonitrile copolymer in the formulated amount, adding sodium carboxymethyl cellulose and continuing mixing to obtain the binder.

The preparation method of the negative electrode sheet provided in this example is as follows: mixing water with the composite binder, negative electrode active material and conductive agent in the formulated amount to obtain the negative electrode slurry, coating the negative electrode slurry on the current collector, and drying to obtain The negative electrode sheet.

Example 2

This embodiment provides a composite binder, which is composed of styrene-butadiene rubber, acrylonitrile copolymer (LA-type binder LA133) and sodium carboxymethyl cellulose. Wherein, the mass ratio of styrene-butadiene rubber to acrylonitrile copolymer is 1:3.5, and the mass fraction of sodium carboxymethyl cellulose in the composite binder is 8%.

This embodiment also provides a negative electrode sheet, which includes a copper foil current collector and a negative electrode coating coated on the current collector. The negative electrode coating is composed of the composite binder and conductive agent (SP) provided by this embodiment. ) and the negative electrode active material. The negative electrode active material is composed of graphite negative electrode material and silicon-oxygen material, and the mass fraction of silicon-oxygen material in the negative electrode active material is 4.8%.

In the negative electrode coating, the mass fraction of the composite binder is 4%, the mass fraction of the conductive agent is 1%, and the mass fraction of the negative electrode active material is 95%.

The compacted density of the negative electrode sheet is 1.60 g/cm ³ .

Example 3

This embodiment provides a composite binder, which is composed of styrene-butadiene rubber, acrylonitrile copolymer (LA-type binder LA133) and sodium carboxymethyl cellulose. Wherein, the mass ratio of styrene-butadiene rubber to acrylonitrile copolymer is 1:4.5, and the mass fraction of sodium carboxymethyl cellulose in the composite binder is 10%.

This embodiment also provides a negative electrode sheet, which includes a copper foil current collector and a negative electrode coating coated on the current collector. The negative electrode coating is composed of the composite binder and conductive agent (SP) provided by this embodiment. ) and the negative electrode active material. The negative electrode active material is composed of graphite negative electrode material and silicon-oxygen material, and the mass fraction of silicon-oxygen material in the negative electrode active material is 4.9%.

In the negative electrode coating, the mass fraction of the composite binder is 3%, the mass fraction of the conductive agent is 1.5%, and the mass fraction of the negative electrode active material is 95.5%.

The compacted density of the negative electrode sheet is 1.60 g/cm ³ .

Example 4

This embodiment provides a composite binder, which is composed of styrene-butadiene rubber, acrylonitrile copolymer (LA-type binder LA133) and sodium carboxymethyl cellulose. Wherein, the mass ratio of styrene-butadiene rubber to acrylonitrile copolymer is 1:3.8, and the mass fraction of sodium carboxymethyl cellulose in the composite binder is 9%.

This embodiment also provides a negative electrode sheet, which includes a copper foil current collector and a negative electrode coating coated on the current collector. The negative electrode coating is composed of the composite binder and conductive agent (SP) provided by this embodiment. ) and the negative electrode active material. The negative electrode active material is composed of graphite negative electrode material and silicon-oxygen material, and the mass fraction of silicon-oxygen material in the negative electrode active material is 5.0%.

In the negative electrode coating, the mass fraction of the composite binder is 3.6%, the mass fraction of the conductive agent is 0.8%, and the mass fraction of the negative electrode active material is 95.6%.

The compacted density of the negative electrode sheet is 1.60 g/cm ³ .

Example 5

The difference between the negative electrode sheet provided in this example and the negative electrode sheet provided in Example 1 is that the mass ratio of styrene-butadiene rubber to acrylonitrile copolymer in the composite binder used is 1:2.

Example 6

The only difference between the negative electrode sheet provided in this example and the negative electrode sheet provided in Example 1 is that the mass ratio of styrene-butadiene rubber to acrylonitrile copolymer in the composite binder used is 1:10.

Comparative example 1

This comparative example provides a composite binder, which is composed of styrene-butadiene rubber and sodium carboxymethyl cellulose. The mass fraction of sodium carboxymethylcellulose in the composite binder is 35%.

Except that the composite binder provided in this comparative example is the composite binder provided in this comparative example, the difference from Example 1 is that in the negative electrode coating, the mass fraction of the composite binder is The mass fraction of the conductive agent is 1%, and the mass fraction of the negative electrode active material is 96.2%.

Comparative example 2

This comparative example provides a composite binder, which is composed of acrylonitrile copolymer (LA type binder LA133) and sodium carboxymethylcellulose. The mass fraction of sodium carboxymethylcellulose in the composite binder is 8.8%.

The difference between the negative electrode sheet provided in this comparative example and Example 1 is only that the composite binder used is the composite binder provided in this comparative example.

testing method

The positive electrode NCM613 active material, conductive agent and binder are mixed according to the ratio of 96.3%: 2.5%, 1.2%, and then made into a positive electrode slurry, which is coated on an aluminum foil, dried and made into a pole roll, and passed through a die-cut The machine die-cuts the pole roll into a size of 50.2mm*95.6mm to make pole pieces, and laminates the negative pole pieces and separators provided in the examples and comparative examples to make soft-pack batteries. Ceramic and double-sided 3μm adhesive layer, the battery cell is baked, liquid injected, pre-charged and other steps to complete the production of the pouch battery; the above test battery is used to discharge the DC resistance (DCR) at 25 °C, and charge the DC resistance (DCR) at 25 °C ( DCR), -20°C discharge DC resistance (DCR), -20°C charge DC resistance (DCR) test.

1C/1C 25°C normal temperature cycle test and 1C/1C 45°C high temperature cycle test were carried out with the above test battery, as shown in Figure 4 and Figure 5.

Use the above-mentioned test battery for low temperature -20°C, 0.05C cycle for 50 weeks and full power disassembly to observe whether lithium precipitation occurs.

Table 1

Figures 1-3 are photos of different binder formulation test schemes (Example 1, Comparative Example 1, and Comparative Example 2) in the silicon-oxygen system at a low temperature of -20°C and 0.05C cycle for 50 weeks. It can be seen that when the binder is pure styrene-butadiene rubber (comparative example 1), there is obvious lithium precipitation on the surface of the pole piece, and it is more obvious at the four corners of the pole piece, while the LA type water-based binder scheme (comparative example 2) And the blending scheme (embodiment 1) of styrene-butadiene rubber and LA water-based binder, the surface of the pole piece is normal, and there is no lithium phenomenon;

Figure 4 and Figure 5 are the normal temperature and high temperature cycle curves of different binder formulation schemes (Example 1 and Comparative Example 1, Comparative Example 2) in the silicon-oxygen system, as can be seen from the cycle curves, wherein the mixed binder scheme (Example 1) between styrene-butadiene rubber and LA-type binder, the cycle trend is basically normal, 1500 cycles at normal temperature, 88% capacity retention, 1260 cycles at high temperature, 82% capacity retention; then in the silicon-oxygen system Among them, styrene-butadiene rubber mixed with LA-type binder can achieve both high-temperature and normal-temperature cycles, improve low-temperature charging capabilities, and ensure that the battery does not decompose lithium during low-temperature cycles.

Combined with Table 1, it can be seen from the above examples and comparative examples that the composite binders provided in Examples 1-4 aim at the silicon-oxygen system, which not only maintains the good flexibility of the styrene-butadiene rubber binder pole piece, but also retains the acrylic The nitrile copolymer binder has a strong effect on ion transmission and has the advantages of low binder impedance. While increasing the energy density, it can significantly improve the low-temperature cycle of the battery. Significantly worsening effect.

In Example 5, because the proportion of styrene-butadiene rubber is relatively high (at a boundary value), the binder itself has a relatively high resistance during the low-temperature cycle, so it is slightly inferior to Example 1 in terms of low-temperature DCR.

In Example 6, because the proportion of the acrylonitrile copolymer is relatively high (in the boundary value), it is difficult to process the pole piece of the battery cell, the pole piece is relatively stiff, and the edges are easy to drop and crack.

In Comparative Example 1, because it does not contain acrylonitrile copolymer, the performance of the battery cell at low temperature is poor, and lithium deposition is more serious in low temperature cycle.

Comparative example 2 does not contain styrene-butadiene rubber, resulting in poor flexibility of the pole piece. During the cycle, the corners of the pole piece are prone to material drop, which causes the active material of the pole piece to fall off and affects the cycle life of the battery.

Claims

A kind of composite binder, it is characterized in that, described composite binder comprises rubber, nitrile compound and dispersant, and the mass ratio of described rubber and nitrile compound is 1:2-1:10;

In the composite binder, the mass fraction of the dispersant is 8-10%.
The composite binder according to claim 1, wherein the mass ratio of the rubber to the nitrile compound is 1:3.5-1:4.5.
A kind of preparation method of composite binder as claimed in claim 1 or 2, is characterized in that, described method comprises the following steps:

The compound adhesive is obtained by mixing the formulated amount of rubber and nitrile compounds.
A negative electrode sheet, characterized in that, the negative electrode sheet includes a current collector and a negative electrode coating coated on the current collector, the negative electrode coating includes the composite binder as claimed in claim 1 or 2, conductive Agent and negative electrode active material, the negative electrode active material includes silicon-oxygen material.
The negative electrode sheet according to claim 4, wherein the negative electrode active material comprises graphite material and silicon oxide material.
The negative electrode sheet according to claim 4 or 5, characterized in that, the compacted density of the negative electrode sheet is below 1.6 g/cm 3 .
The preparation method of the negative electrode sheet according to any one of claims 4-6, characterized in that the method comprises the following steps:

The solvent is mixed with the composite binder, the negative electrode active material and the conductive agent to obtain the negative electrode slurry, and the negative electrode slurry is coated on the current collector and dried to obtain the negative electrode sheet.
A lithium ion battery, characterized in that the lithium ion battery comprises the negative electrode sheet according to any one of claims 4-7.