CN116154105A

CN116154105A - Micron silicon negative electrode, preparation method thereof and lithium ion battery

Info

Publication number: CN116154105A
Application number: CN202211720054.6A
Authority: CN
Inventors: 请求不公布姓名
Original assignee: Jiangsu Weilan New Energy Battery Co ltd
Current assignee: Jiangsu Weilan New Energy Battery Co ltd
Priority date: 2022-12-30
Filing date: 2022-12-30
Publication date: 2023-05-23

Abstract

The invention provides a micron silicon cathode, which comprises a binding structure formed by a conductive agent and micron silicon particles bound in the binding structure; the conductive agent comprises a one-dimensional conductive agent and/or a two-dimensional conductive agent; the mass ratio of the micron silicon particles to the conductive agent is (80-99): (0.5-20). According to the invention, micron-sized silicon particles and one-dimensional and/or two-dimensional conductive agents with nanoscale are used, and in the mixing process, the one-dimensional and/or two-dimensional conductive agents can be crosslinked under the action of static electricity to form a binding structure for binding the silicon particles, so that a micron silicon anode with the binding structure is realized. The invention also provides a preparation method of the micron silicon negative electrode and a lithium ion battery.

Description

Micron silicon negative electrode, preparation method thereof and lithium ion battery

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a micron silicon negative electrode, a preparation method thereof and a lithium ion battery.

Background

As the energy density of the power battery is higher and higher, the charging time is shorter and shorter, and the theoretical capacity of the graphite cathode 374mAh/g gradually limits the development of the battery to the field of high energy density. Therefore, the high-gram-capacity anode material-silicon material is applied by virtue of the theoretical capacity of 4200mAh/g, such as silicon-based, silicon-oxygen-based, silicon-carbon and other high-gram-capacity materials.

Silicon cathodes with high theoretical capacity and low operating voltage are regarded as the most promising cathode materials for high specific energy lithium ion batteries, but as the silicon cathodes expand in the process of cyclically extracting lithium, the expansion rate is up to 300%, particles are pulverized due to expansion, the cycle performance is attenuated along with the expansion, and the commercialization development of the silicon cathodes is seriously affected. Silicon powder causes the loss of electrical connection between silicon particles, which is a major cause of rapid decay of the cycle.

The current methods for controlling the expansion of silicon particles are:

(1) the silicon particles are nanocrystallized, so that a lithium ion transmission path is reduced, and the volume effect is buffered; however, the undersize of the nanometer leads to overlarge specific surface area, and a large amount of active lithium ions are consumed for forming the SEI film, so that the initial efficiency of the nanometer silicon negative electrode is poor, and the capacity is difficult to exert to exceed 3000mAh/g; the nano silicon has low compaction density, and the requirement of high volume energy density is difficult to realize; the nano-scale mixing process is difficult to disperse uniformly and difficult to realize industrial production and use, so that most of nano-silicon electrodes are selected for mixing or are prepared in a small scale in a laboratory, and the nano-silicon electrodes are difficult to use in large-scale production;

(2) the silicon is compounded with carbon materials (graphite, amorphous carbon, asphalt and the like), which is a method for delaying the negative influence of the silicon in most industries, but a large amount of carbon is added to lose the high capacity of the silicon, so that the requirement of higher energy density cannot be met;

(3) the secondary processing mode of the silicon particles is adopted to manufacture a carbon layer on the surface to remove the constraint, so that the process difficulty and the redundancy are increased;

the three methods for improving the volume expansion of silicon are only limited to improvement on the material end, and no industrialized material exists at present.

Disclosure of Invention

The invention aims to provide a micron silicon negative electrode, a preparation method thereof and a lithium ion battery, wherein the micron silicon negative electrode has a binding structure for binding silicon particles, and after a charging and discharging process, the electrical connection among the silicon particles is still maintained, so that the high specific capacity and the performance of cycle are ensured.

The invention provides a micron silicon cathode, which comprises a binding structure formed by a conductive agent and micron silicon particles bound in the binding structure;

the conductive agent comprises a one-dimensional conductive agent and/or a two-dimensional conductive agent;

the mass ratio of the micron silicon particles to the conductive agent is (80-99): (0.5-20).

Preferably, the particle size of the micrometer silicon particles is 0.5-20 μm.

Preferably, the one-dimensional conductive agent comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, silver nanofibers and copper nanofibers;

the two-dimensional conductive agent comprises graphene and/or graphite alkyne.

Preferably, the micro silicon anode further comprises a binder.

Preferably, the binder comprises one or more of polyacrylonitrile, polyvinylidene fluoride, sodium carboxymethyl cellulose-styrene butadiene rubber and polyacrylic acid;

the mass ratio of the binder to the micron silicon particles is (80-99): (0.5-20).

Preferably, the conductive agent has a size in at least one dimension that is larger than the micron silicon particles.

Preferably, the length of the one-dimensional conductive agent is greater than the particle size of the micron silicon particles; the diameter is in the nanometer level;

the length and/or width of the two-dimensional conductive agent is larger than the particle size of the micron silicon particles; the thickness is on the order of nanometers.

Preferably, the conductive agent comprises a one-dimensional conductive agent and a two-dimensional conductive agent at the same time, and the binding structure formed by the conductive agent is a three-dimensional binding structure.

The invention provides a preparation method of the micron silicon cathode, which comprises the following steps:

a) Uniformly dispersing a micron silicon particle material, a conductive agent and a binder in a solvent to obtain negative electrode coating slurry with a coating structure;

b) And coating the negative electrode coating slurry on the surface of a current collector, and drying to obtain the micron silicon negative electrode.

Preferably, the current collector is a copper foil, a carbon coated copper foil or a three-dimensional porous copper foil.

The invention provides a lithium ion battery comprising the micron silicon anode described above.

The invention provides a micron silicon cathode, which comprises a binding structure formed by a conductive agent and micron silicon particles bound in the binding structure; the conductive agent comprises a one-dimensional conductive agent and/or a two-dimensional conductive agent; the mass ratio of the micron silicon particles to the conductive agent is (80-99): (0.5-20). According to the invention, micron-sized silicon particles and one-dimensional and/or two-dimensional conductive agents with nanoscale are used, and in the mixing process, the one-dimensional and/or two-dimensional conductive agents can be crosslinked under the action of static electricity to form a binding structure for binding the silicon particles, so that a micron silicon anode with the binding structure is realized.

Compared with the prior art, the invention has the beneficial effects that:

(1) The three-dimensional binding structure with a conductive function is formed on the surface of the silicon particles by crosslinking in the process of mixing the one-dimensional and/or two-dimensional conductive agent material with the micron silicon particles, and the structure can effectively restrain negative effects caused by expansion and pulverization of the silicon particles, such as low initial charge and discharge coulomb efficiency and great capacity attenuation in the cyclic process;

(2) Compared with the prior art, the structure fully exerts the high capacity characteristic of the silicon material, the initial coulombic efficiency can reach more than 90% under the voltage range of 0.01-1.5V, the specific discharge capacity can reach more than 3000mAh/g under the current density of 0.1C, and the invention has outstanding cycle performance in both button half cells and full cells. The preparation method disclosed by the invention is simple in preparation process, free from secondary processing to realize a binding structure, controllable in preparation condition and suitable for large-scale production and development.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a micro-silicon negative electrode according to the present invention; wherein 1 is a current collector, 2 is micron silicon particles, and 3 is a binding structure consisting of a conductive agent;

FIG. 2 is an SEM image of a micrometer silicon negative electrode of example 4 of the invention;

fig. 3 is an SEM image of the micron silicon negative electrode in example 4 of the present invention after 600 cycles.

Detailed Description

In the invention, the micron silicon anode comprises a current collector and an anode coating layer compounded on the surface of the current collector, wherein the anode coating layer comprises a binding structure formed by a conductive agent and micron silicon particles bound in the binding structure.

In the present invention, the thickness of the negative electrode coating layer is preferably within 100 μm, more preferably 30 to 90 μm.

In the invention, the micron silicon particles can be pure micron silicon particles, or pure phases or composite materials such as silicon oxygen-based materials, silicon carbon-based materials and the like. In order to achieve the above-described binding structure, the particle diameter of the micro silicon particles is preferably 0.5 to 20. Mu.m, may be 10 to 20. Mu.m, may be 1 to 10. Mu.m, may be 0.5 to 1. Mu.m, such as 0.5. Mu.m, 1. Mu.m, 2. Mu.m, 3. Mu.m, 4. Mu.m, 5. Mu.m, 6. Mu.m, 7. Mu.m, 8. Mu.m, 9. Mu.m, 10. Mu.m, 12. Mu.m, 15. Mu.m, 18. Mu.m, 20. Mu.m, preferably a range having any of the above values as an upper limit or a lower limit.

In the present invention, the conductive agent preferably includes a one-dimensional conductive agent and/or a two-dimensional conductive agent, and the one-dimensional conductive agent preferably includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, silver nanofibers, and copper nanofibers; the two-dimensional conductive agent comprises graphene and/or graphite alkyne.

In the present invention, the conductive agent has a size larger than the micrometer silicon particles in at least one dimension, and in the present invention, the one-dimensional conductive agent has a length larger than the particle diameter of the micrometer silicon particles; the diameter is in the nanometer level; the length and/or width of the two-dimensional conductive agent is larger than the particle size of the micron silicon particles; the thickness is in the nanometer level; specifically, in the embodiment of the present invention, the length of the one-dimensional conductive agent is preferably greater than 5 μm, more preferably 5 to 20 μm, and most preferably 10 to 15 μm; the diameter is preferably 7 to 11nm, more preferably 9 to 10nm; the length or width of the two-dimensional conductive agent is preferably greater than 1 μm, more preferably 1 to 15 μm, and still more preferably 5 to 10 μm; the thickness is preferably 1 to 3nm, more preferably 2 to 3nm.

In the invention, the mass ratio of the micron silicon particles to the conductive agent is preferably (80-99): (0.5 to 20), more preferably (80 to 95): (1-10).

In the invention, the micron silicon electrode also comprises a binder, wherein the binder preferably comprises one or more of polyacrylonitrile, polyvinylidene fluoride, sodium carboxymethyl cellulose-styrene-butadiene rubber and polyacrylic acid; the mass ratio of the binder to the micron silicon particles is preferably (80-99): (0.5 to 20), more preferably (80 to 95): (10-15).

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

In the present invention, the types, sizes and amounts of the micro silicon particle material, the conductive agent and the binder are identical to those of the micro silicon particle material, the conductive agent and the binder described above, and the present invention is not repeated here.

In the present invention, the ratio of the micro silicon is 80 to 100%, preferably 85 to 95%, such as 80%,85%,90%,95%,100%, preferably a range value in which any of the above values is an upper limit or a lower limit, based on 100% by mass of the total of the micro silicon particles, the conductive agent and the binder; the conductive agent accounts for 0.5 to 20%, more preferably 5 to 15%, such as 0%,0.5%,5%,10%,15%,20%, preferably a range value having any of the above values as an upper limit or a lower limit; the binder content is 0 to 20%, more preferably 5 to 15%,0%, such as 5%,10%,15%,20%, preferably in a range having any of the above values as an upper limit or a lower limit.

In the mixing process of raw materials, micron-sized silicon particles and one-dimensional or two-dimensional conductive agents with nano-scale are subjected to crosslinking under the action of static electricity in the mixing process, so that one-dimensional rope net-shaped or two-dimensional paper-sheet-shaped constraint structures of the silicon particles are respectively formed, when the one-dimensional conductive agents and the two-dimensional conductive agents are added at the same time, a tighter three-dimensional constraint structure can be formed, the micron-sized silicon particles are constrained, and the crosslinking also occurs between the conductive agents and the binder. The invention can make the conductive agent become a binding structure on the surface of the silicon particles by a simple homogenate coating method, and the conductive agent is attached on the surface of the silicon particles after the coating is finished into an electrode, thereby omitting the step of secondary processing and retaining the high capacity and the high first effect of the silicon.

In the present invention, the time of mixing is preferably 3 hours or more to ensure uniformity of dispersion, and the present invention preferably adds the one-dimensional conductive agent last during mixing.

In the present invention, the solvent is preferably deionized water.

In the present invention, the current collector may be a copper foil, a carbon coated copper foil, or a three-dimensional porous copper foil.

The method of the present invention is not particularly limited, and a coating method commonly used by those skilled in the art may be used.

In the present invention, the drying temperature is preferably 70 to 120 ℃, more preferably 80 to 100 ℃, such as 70 ℃,75 ℃,80 ℃,85 ℃,90 ℃,95 ℃,100 ℃,105 ℃,110 ℃,115 ℃,120 ℃, preferably a range value in which any of the above values is the upper limit or the lower limit.

The invention also provides a lithium ion battery comprising the micron silicon anode.

In the invention, the micron silicon cathode can be applied to liquid lithium ion batteries and solid lithium ion battery systems.

Compared with the prior art, the invention has the beneficial effects that:

In order to further illustrate the present invention, the following examples are provided to describe a micron silicon anode, a preparation method thereof and a lithium ion battery in detail, but the present invention is not to be construed as being limited to the scope of protection.

Example 1

Mixing 0.9g of micron silicon particles with the particle size of 2 mu m and 1.7g of polyacrylic acid binder in 1.4g of deionized water solvent to obtain negative electrode slurry;

and coating the negative electrode slurry on the surface of a copper foil, and drying at 110 ℃ to obtain the micron silicon negative electrode.

Example 2

Mixing 0.9g of micron silicon particles with the particle size of 2 mu m, 5g of single-wall carbon nano tube dispersion liquid with the length of 5 mu m and the diameter of 10nm and 0.58g of polyacrylic acid binder in 1.16g of deionized water solvent to obtain negative electrode slurry;

Example 3

The single-walled carbon nanotube dispersion of example 2 was changed to 0.67g of graphene dispersion, 5.50g of deionized water was added, and the remainder was unchanged, to prepare a micron silicon anode.

Example 4

Mixing 0.9g of micron silicon particles with the particle size of 2 mu m, 5g of single-wall carbon nano tube dispersion liquid with the length of 5 mu m and the diameter of 10nm, 0.83g of graphene dispersion liquid and 0.25g of polyacrylic acid binder in 0.67g of deionized water solvent to obtain negative electrode slurry;

Example 5

A silicon negative electrode was prepared according to the procedure of example 4, with the micrometer silicon being changed from 2 μm to 5 μm, the remainder being unchanged.

Example 6

A silicon negative electrode was prepared according to the procedure of example 4, with the micrometer silicon being changed from 2 μm to 10 μm, the remainder being unchanged.

Example 7

A silicon negative electrode was prepared in the same manner as in example 5, increasing the addition amount of the single-walled carbon nanotube dispersion to 12.5g.

Example 8

A silicon negative electrode was prepared according to the procedure of example 5, reducing the micrometer silicon content of 5 micrometers of the host material to 0.88g, increasing the addition of the single-walled carbon nanotube dispersion to 17.5g, and leaving the rest unchanged.

Example 9

A silicon negative electrode was prepared according to the procedure of example 5, reducing the main material micrometer silicon content to 0.85g, increasing the single-walled carbon nanotube dispersion addition to 25g, and leaving the rest unchanged.

Example 10

A silicon negative electrode was prepared by following the procedure of example 5, with an additional addition of 0.1g sodium carboxymethylcellulose, the remainder unchanged.

Example 11

A silicon negative electrode was prepared according to the procedure of example 10, with the micrometer silicon being replaced by a nanometer silicon (secondary agglomerate grain size 5-10 μm, primary particle size less than 100 nm), the remainder being unchanged.

The micron silicon cathodes prepared in examples 1 to 11 were assembled into batteries, the counter electrode was a lithium sheet, the electrolyte was a commercial electrolyte, button cells were assembled, and the electrical properties of the button cells were tested.

Button cell coulombic efficiency test conditions: the assembled button cell is placed at a high temperature of 40 ℃ for one night, firstly 0.05C constant current is discharged to 0.01V, the button cell is placed for 10min, 0.05C constant current is charged to 1.5V, and the button cell is kept at constant voltage to 1/10C. Coulombic efficiency: specific charge/specific discharge capacity 100%.

The test results are shown in Table 1.

Table 1 properties of micron silicon negative electrodes in examples

Note that: "0-dimensional" in table 1 means that no one-dimensional or two-dimensional conductive agent is present, only 0-dimensional active material; "Single" refers to single-walled carbon nanotubes;

taking "2% single+2.5% graphene" as an example, the "2% single" refers to that the mass of single-walled carbon nanotubes in the single-walled carbon nanotube dispersion liquid accounts for 2% of the mass of the total solid matter, and the "2.5% graphene" refers to that the mass of graphene in the graphene dispersion liquid accounts for 2.5% of the mass of the total solid matter.

The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims

1. A micron silicon negative electrode comprising a binding structure formed of a conductive agent and micron silicon particles bound therein;

2. The micron silicon anode according to claim 1, wherein the micron silicon particles have a particle size of 0.5-20 μm.

3. The micron silicon anode according to claim 1, wherein the one-dimensional conductive agent comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, silver nanofibers and copper nanofibers;

the two-dimensional conductive agent comprises graphene and/or graphite alkyne.

4. The micron silicon negative electrode according to claim 3, wherein the micron silicon negative electrode further comprises a binder, the binder comprising one or more of polyacrylonitrile, polyvinylidene fluoride, sodium carboxymethyl cellulose-styrene butadiene rubber and polyacrylic acid;

5. The micron silicon negative electrode according to claim 1, wherein the conductive agent has a size in at least one dimension that is larger than the micron silicon particles.

6. The micron silicon negative electrode according to claim 5, wherein the one-dimensional conductive agent length is greater than the particle diameter of the micron silicon particles; the diameter is in the nanometer level;

7. The micro silicon anode according to any one of claims 1 to 6, wherein the conductive agent comprises both a one-dimensional conductive agent and a two-dimensional conductive agent, and the binding structure formed by the conductive agent is a three-dimensional binding structure.

8. The method for preparing a micron silicon anode according to claim 1, comprising the steps of:

9. The method of manufacturing according to claim 6, wherein the current collector is a copper foil, a carbon coated copper foil or a three-dimensional porous copper foil.

10. A lithium ion battery comprising the microsilica anode of any of claims 1-7.