CN116190660B

CN116190660B - Adhesive, preparation method and application thereof, silicon-based negative electrode and preparation method thereof

Info

Publication number: CN116190660B
Application number: CN202310231812.6A
Authority: CN
Inventors: 窦辉; 龙江; 叶文君; 张校刚
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2023-03-10
Filing date: 2023-03-10
Publication date: 2024-01-30
Anticipated expiration: 2043-03-10
Also published as: CN116190660A

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a binder, a preparation method and application thereof, a silicon-based negative electrode and a preparation method thereof. The invention provides a binder, which is obtained by crosslinking raw materials comprising polyvinyl alcohol and a zwitterionic compound; the adhesive is in an cross-network structure. The binder provided by the invention has an alternating-current network structure, can effectively accommodate the volume change caused by the silicon negative electrode in the charge and discharge process, can effectively relieve the structural damage caused by the volume change of the silicon negative electrode in the circulation process, and further improves the specific capacity and the circulation stability of the lithium ion battery.

Description

Adhesive, preparation method and application thereof, silicon-based negative electrode and preparation method thereof

Technical Field

The invention belongs to the technical field of lithium batteries, and particularly relates to a binder, a preparation method and application thereof, a silicon-based negative electrode and a preparation method thereof.

Background

In recent years, the lithium battery industry has rapidly developed, and advanced lithium batteries have been widely used in energy storage, digital products and new energy automobiles. However, the theoretical capacity of the traditional commercial graphite lithium battery is only 372mAh/g, and the energy requirement of modern electronic products cannot be met more and more.

The silicon-based negative electrode material theoretically has specific capacity of up to 4200mAh/g, and is an ideal negative electrode material for lithium batteries currently accepted; however, the silicon-based negative electrode material is easy to generate volume deformation in the charge and discharge process, so that the negative electrode material and the current collector are layered, the specific capacity of the silicon-based negative electrode is further quickly attenuated, and the circulation stability is reduced.

Disclosure of Invention

The invention aims to provide a binder, a preparation method and application thereof, a silicon-based negative electrode and a preparation method thereof.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a binder, which is obtained by crosslinking raw materials comprising polyvinyl alcohol and a zwitterionic compound; the adhesive is in an cross-network structure.

Preferably, the zwitterionic compound comprises N, N, N-trimethylglycine.

The invention also provides a preparation method of the adhesive, which comprises the following steps:

mixing polyvinyl alcohol, a zwitterionic compound and water, and carrying out a crosslinking reaction to obtain the adhesive.

Preferably, the mass ratio of the polyvinyl alcohol to the zwitterionic compound is 80-95: 5 to 20.

Preferably, the temperature of the crosslinking reaction is 40-80 ℃ and the time is 1.5-2.5 h.

The invention also provides an application of the binder in the negative electrode of the lithium battery or the binder prepared by the preparation method in the technical scheme.

The invention also provides a silicon-based negative electrode, which comprises a current collector and a silicon-based negative electrode material loaded on the current collector; the silicon-based anode material comprises a silicon-based active material, a conductive additive and a binder, wherein the binder is prepared by the binder according to the technical scheme or the preparation method according to the technical scheme.

Preferably, the silicon-based active material comprises one or more of silicon oxide, silicon simple substance and silicon oxygen carbon;

the conductive additive comprises one or more of acetylene black, conductive carbon black and carbon nanotubes.

Preferably, the mass of the binder is 2-10% of the mass of the silicon-based anode material.

The invention also provides a preparation method of the silicon-based anode, which comprises the following steps:

and mixing the silicon-based active material, the conductive additive and the binder, coating the obtained slurry on the surface of a current collector, and drying to obtain the silicon-based negative electrode.

The invention provides a binder, which is obtained by crosslinking raw materials comprising polyvinyl alcohol and a zwitterionic compound; the adhesive is in an cross-network structure. The binder provided by the invention has an alternating-current network structure, can effectively accommodate the volume change caused by the silicon negative electrode in the charge and discharge process, can effectively relieve the structural damage caused by the volume change of the silicon negative electrode in the circulation process, and further improves the specific capacity and the circulation stability of the lithium ion battery.

Drawings

FIG. 1 is a graph showing the cycle performance of lithium batteries assembled from silicon-based negative electrodes obtained in example 2 and comparative examples 1 to 2 at a current density of 0.2A/g;

FIG. 2 is a graph showing the cycle performance of lithium batteries assembled from silicon-based negative electrodes obtained in example 2 and comparative examples 1 to 2 at a current density of 1.0A/g;

fig. 3 is a graph showing the rate performance of lithium batteries assembled from silicon-based negative electrodes obtained in example 2 and comparative examples 1 to 2;

fig. 4 is an electrochemical stability test curve of a lithium battery assembled with the silicon-based negative electrode obtained in example 2 and comparative example 1;

FIG. 5 is a peel force test curve of the silicon-based negative electrodes obtained in example 2 and comparative example 1;

FIG. 6 is an elemental distribution diagram of a silicon-based anode obtained in example 2;

FIG. 7 is a graph of the performance characterization of silica, model YOB155, where FIG. 7a is an XRD pattern; FIG. 7b is an SEM image; fig. 7c and 7d are HRTEM images.

Detailed Description

In the present invention, the zwitterionic compound preferably comprises N, N, N-trimethylglycine.

In the present invention, the weight average molecular weight of the polyvinyl alcohol is preferably 89000 to 98000.

In the present invention, all the preparation materials are commercially available products well known to those skilled in the art unless specified otherwise.

In the present invention, the mass ratio of the polyvinyl alcohol to the zwitterionic compound is preferably 80 to 95:5 to 20, more preferably 82 to 92:8 to 18, more preferably 85 to 90:10 to 15.

In the invention, the mass ratio of the polyvinyl alcohol to the water is preferably 1.8:98.

in the present invention, the mixing is preferably performed under stirring. The stirring condition parameters are not particularly limited in the present invention, and may be carried out by a process well known to those skilled in the art.

In the present invention, the mixing preferably includes:

mixing a zwitterionic compound with water to obtain a first mixture;

the first mixture is mixed with a second polyvinyl alcohol.

In the present invention, the temperature of the first mixture is preferably an ordinary temperature. In the present invention, the first mixing is preferably performed under stirring. The stirring condition parameters are not particularly limited in the present invention, and may be carried out by a process well known to those skilled in the art.

The present invention is not particularly limited in the process of the second mixing, and the polyvinyl alcohol may be directly added to the first mixture.

In the present invention, the temperature of the crosslinking reaction is preferably 40 to 80 ℃, more preferably 50 to 70 ℃, still more preferably 60 to 65 ℃; the time is preferably 1.5 to 2.5 hours, more preferably 1.8 to 2 hours.

In the present invention, the binder is preferably used in the form of an aqueous binder solution; the mass concentration of the aqueous binder solution is preferably 2 to 5%, more preferably 3 to 4%.

In the present invention, the silicon-based active material preferably includes one or more of silicon oxide, elemental silicon, and silicon oxycarbide. In the present invention, the silicon oxide preferably includes SiO _x The value range of x is preferably 1<x<2; the elemental silicon preferably comprises nano-silicon and/or micro-silicon. In a specific embodiment of the present invention, the silicon-oxygen carbon is preferably silicon oxide of model YOB155 manufactured by the product of the material science and technology of the lead batteries of the order of the number of the yang.

In the present invention, the conductive additive preferably includes one or more of acetylene black, conductive carbon black and carbon nanotubes.

In the invention, the mass ratio of the silicon-based active material to the conductive additive is preferably 7:2. in the present invention, the mass of the binder is preferably 2 to 10%, more preferably 3 to 9%, and even more preferably 4 to 8% of the mass of the silicon-based negative electrode material.

In the present invention, the mixing preferably includes:

primary mixing of a silicon-based active material and a conductive additive to obtain a primary mixture;

and mixing the primary mixture and the binder in a secondary mode.

In the present invention, the primary mixing means preferably includes grinding or ball milling, and more preferably ball milling. In the present invention, when primary mixing is performed by ball milling, the rotation speed of single ball milling is preferably 2800rmp, the ball milling time is 180s, and the process is repeated 2 times. In the present invention, the ball milling is preferably performed on a miniature ball mill shaker.

In the present invention, the binder is preferably secondarily mixed in the form of an aqueous binder solution. In the present invention, the mass concentration of the aqueous binder solution is preferably 2%.

In the present invention, the secondary mixing means preferably includes grinding or ball milling, and more preferably ball milling. In the present invention, when the secondary mixing is performed by ball milling, the rotation speed of the single ball milling is preferably 2800rmp, the ball milling time is 180s, and the process is repeated 3 times. In the present invention, the ball milling is preferably performed on a miniature ball mill shaker.

In the present invention, the current collector preferably includes copper foil. The manner of the coating is not particularly limited in the present invention, and may be carried out by a process well known to those skilled in the art.

In the present invention, the temperature of the drying is preferably 60 ℃; the time is preferably 12 hours. The drying process is not particularly limited, and may be performed by a process well known to those skilled in the art.

After the drying, the invention also preferably comprises cutting the obtained electrode sheet. The cutting process is not particularly limited, and the cutting process is performed according to the required area of the negative electrode.

In the invention, the loading amount of the silicon-based active material on the current collector is preferably 0.7-1.0 g/cm ² 。

The binder provided by the invention adopts natural polymer materials as raw materials, and the reaction condition is mild; the whole process of preparing the negative electrode also meets the requirements of green and safe production, has simple operation, easy control and high feasibility, and is suitable for industrial application.

For further explanation of the present invention, a binder, a method for preparing the same, and application thereof, a silicon-based negative electrode, and a method for preparing the same, which are provided in the present invention, are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of the present invention.

Example 1

Mixing 0.02g of N, N-trimethylglycine and 9.8g of water, and uniformly stirring at 60 ℃; then, 0.18g of polyvinyl alcohol (weight average molecular weight: 89000-98000) was added thereto, and the crosslinking reaction was carried out at 60℃for 2 hours under stirring to obtain an aqueous binder solution having a mass concentration of 2%.

Example 2

70mg of silicon-oxygen carbon (silicon oxide with the model of YOB 155) and 20mg of acetylene black are placed in a miniature ball milling oscillator, ball milling is carried out for 180s at the rotating speed of 2800rpm, after repeated ball milling for 2 times, 500mg of the aqueous binder solution obtained in the example 1 is added, ball milling is carried out for 180s at the rotating speed of 2800rpm, and ball milling is repeated for 3 times;

coating the obtained slurry on copper foil, drying in a vacuum oven at 60 ℃ for 12 hours, and cutting to obtain a silicon-based negative electrode;

in the invention, the silicon oxide with the specific model YOB155 is adopted, the silicon oxide with the model YOB155 is characterized, and the obtained test chart is shown in figure 7, wherein figure 7a is an XRD pattern; FIG. 7b is an SEM image; FIGS. 7c and 7d are HRTEM diagrams;

as can be seen from FIG. 7a, the diffraction peaks are evident at 28.4 °, 47.3 °, 56.1 °, 69.1 ° and 76.4 °, and are the diffraction peaks of silicon by comparison with the Si standard card (PDF- # -27-1402), siO ₂ And C, the corresponding diffraction peak is marked in the figure;

FIG. 7b shows that the particle size of the silicon-oxygen carbon is about 5-10 μm, and the particle size distribution is uniform;

to further reveal the microstructure of silicon-oxygen-carbon, fig. 7c and 7d are high-power transmission electron microscope (HRTEM) photographs, and it can be seen that the microstructure is a silicon-carbon composite structure, ordered lattice fringes are crystal planes of silicon, disordered lattice fringes are crystal planes of carbon, lattice fringes with a spacing of 0.31nm (d=0.31 nm) correspond to the (111) crystal plane of silicon, and lattice fringes with a spacing of 0.34nm (d=0.34 nm) correspond to the (002) crystal plane of carbon;

the characterization result proves that the silicon oxide with the model of YOB155 is a silicon-oxygen-carbon composite material.

Comparative example 1

Mixing 0.2g of polyvinyl alcohol and 9.8g of water, and continuously stirring at normal temperature to dissolve the polyvinyl alcohol to obtain a polyvinyl alcohol aqueous solution with the mass fraction of 2%;

placing 70mg of silicon-oxygen carbon (model YOB155 silicon oxide) and 20mg of acetylene black into a miniature ball milling oscillator, ball milling for 180s at 2800rpm, repeating the ball milling for 2 times, adding 500mg of the obtained polyvinyl alcohol aqueous solution, continuing ball milling for 180s at 2800rpm, and repeating the ball milling for 3 times;

the obtained slurry is coated on copper foil, then dried in a vacuum oven at 60 ℃ for 12 hours, and the silicon-based negative electrode is obtained after cutting.

Comparative example 2

Mixing 0.2g of sodium carboxymethyl cellulose (CMC) and 9.8g of water, and continuously stirring at normal temperature to dissolve the mixture to obtain CMC aqueous solution with the mass fraction of 2%;

placing 70mg of silicon-oxygen-carbon (model YOB155 silicon oxide) and 20mg of acetylene black into a miniature ball milling oscillator, ball milling for 180s at 2800rpm, repeating the ball milling for 2 times, adding 500mg of the obtained CMC aqueous solution, ball milling for 180s at 2800rpm, and repeating the ball milling for 3 times;

Performance testing

Test example 1

The silicon-based negative electrodes obtained in example 2 and comparative examples 1 to 2 were assembled into half cells for electrochemical performance testing;

the assembly method comprises the following steps: a silicon-based negative electrode is used as a working electrode of the battery, metallic lithium is used as a counter electrode, and LiPF containing 1mol/L is used ₆ (EC/DEC 1:1 by volume) is electrolyte (containing 5% fec additive), assembled into C2032 coin cell in a glove box filled with argon;

test 1: the electrochemical performance of the obtained button cell was tested at a current density of 0.2A/g; the test results obtained are shown in Table 1, and the cycle curves obtained are shown in FIG. 1;

table 1 results of testing the performance of silicon-based negative electrode constituent half cells obtained in example 2 and comparative examples 1 to 2

	Example 1	Comparative example 1	Comparative example 2
				Initial discharge capacity/mAh.g ^-1	1445.6	1632.3	1636.6
Initial coulombic efficiency/%	80.95	81.05	81.56
				Capacity after cycling/mAh.g ^-1	1113.8	415.8	240.3

As can be seen from table 1 and fig. 1, the cycle performance of the lithium ion battery assembled with the silicon-based negative electrode provided by the invention is superior to that of comparative examples 1 to 2 after 100 circles of cycles at a current density of 0.2A/g. This shows that the binder provided by the invention can improve the cycle stability of the lithium ion battery.

Test 2: the electrochemical performance of the obtained button cell was tested at a current density of 1.0A/g; the test results obtained are shown in Table 2, and the cycle curves obtained are shown in FIG. 2;

table 2 results of testing the performance of silicon-based negative electrode constituent half cells obtained in example 2 and comparative examples 1 to 2

	Example 1	Comparative example 1	Comparative example 2
				Initial discharge capacity/mAh.g ^-1	1525.8	1678	1513.5
Initial coulombic efficiency/%	80.21	75.93	81.97
				Capacity after cycling/mAh.g ^-1	646.9	120	51.9

As can be seen from table 2 and fig. 2, after 200 cycles of circulation at a current density of 1.0A/g, the circulation performance of the lithium ion battery assembled by the silicon-based negative electrode provided by the invention is superior to that of comparative examples 1-2; this shows that the binder provided by the invention can improve the cycle stability of the lithium ion battery.

Test 3: the obtained button cell is subjected to rate performance test under different current densities, the obtained rate performance curve is shown in fig. 3, and as can be seen from fig. 3, the adhesive provided by the invention is beneficial to improving the rate performance of the lithium battery.

Test 4: testing the stability of the electrochemical window of the obtained button cell, wherein the obtained test curve is shown in figure 4; as can be seen from fig. 4, the lithium ion battery assembled by the silicon-based negative electrode provided by the invention has better stability in the voltage interval of 0-4.5V, and the adhesive provided by the invention can be used for effectively improving the electrochemical stability of the lithium ion battery.

Comprehensive tests 1-4 show that the adhesive provided by the invention can effectively improve the electrochemical performance of the lithium ion battery.

Test example 2

The silicon-based cathodes obtained in example 2 and comparative example 1 were subjected to a peel force test, the cut size of the electrode sheet at the time of the test was 5cm×3cm, and the obtained test curve was shown in fig. 5; as can be seen from fig. 5, the peel force of the silicon-based negative electrode provided by the invention is obviously greater than that of comparative example 1, which indicates that the adhesive provided by the invention can well adhere the active material and the current collector together, so that the silicon-based negative electrode of the lithium ion battery shows better mechanical properties.

Test example 3

The silicon-based anode obtained in example 2 was subjected to element distribution mapping test, and the distribution diagram of four elements of Si, O, C and N obtained is shown in FIG. 6. As can be seen from FIG. 6, the binder provided by the invention is uniformly distributed in the electrode; the uniform dispersion of the electrode components is beneficial to the construction of a stable electrode structure, and can also maintain good electrical contact between the active material and the conductive agent, thereby improving the electron transmission rate of the electrode.

Although the foregoing embodiments have been described in some, but not all embodiments of the invention, other embodiments may be obtained according to the present embodiments without departing from the scope of the invention.

Claims

1. A binder is characterized by being obtained by crosslinking raw materials comprising polyvinyl alcohol and a zwitterionic compound; the adhesive is in an cross-network structure; the zwitterionic compound is N, N, N-trimethylglycine.

2. The method for preparing the adhesive according to claim 1, comprising the steps of:

mixing polyvinyl alcohol, a zwitterionic compound and water, and obtaining the binder through a crosslinking reaction; the zwitterionic compound is N, N, N-trimethylglycine.

3. The preparation method according to claim 2, wherein the mass ratio of the polyvinyl alcohol to the zwitterionic compound is 80-95: 5 to 20.

4. A method according to claim 2 or 3, wherein the cross-linking reaction is carried out at a temperature of 40 to 80 ℃ for a time of 1.5 to 2.5 hours.

5. The binder of claim 1 or the binder prepared by the preparation method of any one of claims 2 to 4, and the application of the binder in the negative electrode of a lithium battery.

6. A silicon-based anode comprising a current collector and a silicon-based anode material supported on the current collector; the silicon-based anode material comprises a silicon-based active material, a conductive additive and a binder, and is characterized in that the binder is the binder according to claim 1 or the binder prepared by the preparation method according to any one of claims 2-4.

7. The silicon-based anode according to claim 6, wherein the silicon-based active material comprises one or more of silicon oxide, elemental silicon, and silicon oxycarbide;

8. The silicon-based anode according to claim 6 or 7, wherein the mass of the binder is 2-10% of the mass of the silicon-based anode material.

9. The method for producing a silicon-based anode according to any one of claims 6 to 8, comprising the steps of: