CN112768674A

CN112768674A - Silicon-based composite negative electrode material and preparation method thereof, and negative electrode and preparation method thereof

Info

Publication number: CN112768674A
Application number: CN202110176423.9A
Authority: CN
Inventors: 彭工厂; 胡语芯; 刘文静; 谢正伟; 乔英钧; 瞿美臻
Original assignee: Chengdu Organic Chemicals Co Ltd of CAS
Current assignee: Chengdu Organic Chemicals Co Ltd of CAS
Priority date: 2021-02-09
Filing date: 2021-02-09
Publication date: 2021-05-07

Abstract

The invention belongs to the technical field of lithium ion batteries, and discloses a silicon-based composite anode material, which comprises secondary spherical particles and a conductive material; the secondary spherical particles are prepared from raw materials comprising silicon and a water-soluble high-molecular polymer; the conductive material is coated outside the secondary spherical particles or dispersed inside the secondary spherical particles. The silicon-based composite negative electrode material has high specific capacity, first coulombic efficiency, and good cycle performance and rate capability. The invention also discloses a preparation method of the silicon-based composite negative electrode material, a negative electrode prepared from the silicon-based composite negative electrode material and a preparation method of the negative electrode.

Description

Silicon-based composite negative electrode material and preparation method thereof, and negative electrode and preparation method thereof

Technical Field

The invention relates to the technical field of lithium ion battery cathode materials, in particular to a silicon-based composite cathode material and a preparation method thereof, and a cathode and a preparation method thereof.

Background

Lithium ion batteries are currently the most widely used energy storage devices. The appearance of the lithium ion battery greatly improves the life quality of people, people have higher and higher requirements on the performance of the lithium ion battery, and a large amount of continuous research is carried out on the anode material and the cathode material of the lithium ion battery.

In the existing anode material, silicon has lower working voltage (relative to Li/Li) due to the fact that the theoretical capacity (about 3579mAh/g) of silicon is ten times higher than that of commercial graphite⁺About 0.3V) and abundant reserves, has proven to be the most promising negative electrode material for next generation high energy density batteries. However, silicon is accompanied by huge volume expansion (about 300%) during charging and discharging, so that the damage and thickening of an SEI film and side reactions are increased, an electrode material is easy to pulverize and crack, the caking property is poor, and the electrode material finally falls off from a current collector, so that the electrode cycle performance is poor. Meanwhile, the silicon material has the problem of low electronic conductivity, and the commercial application of the silicon cathode is greatly limited.

The existing preparation methods of the silicon-based negative electrode material mainly comprise the following steps:

(1) in the current commercial application, a common technology is used, a small amount of nano silicon is compounded with carbon, and then extra binder, conductive agent and the like are added to be ground and mixed into slurry to prepare the negative pole piece. The technology has the problems of complicated preparation process, low content of active substances, low capacity, poor dispersibility of the silicon-carbon composite material, large specific surface area of nano silicon, more side reactions, limited volume expansion capability of carbon material buffering silicon, non-uniform bonding with a current collector and the like, and causes unobvious capacity improvement and quick battery performance attenuation.

(2) For example, patent CN107230781A, a three-dimensional spherical silicon-carbon composite negative electrode material and a preparation method thereof, discloses a silicon-based composite material composed of graphite, silicon and amorphous carbon, wherein the graphite and the silicon are wrapped in an amorphous carbon layer. The preparation method comprises the steps of dispersing nano-silicon and a carbon source in an organic solvent, carrying out spray drying to obtain a Si @ C precursor, carrying out carbonization to obtain a Si material, effectively relieving the volume expansion effect of silicon by using a surface carbon layer, dispersing the Si @ C material, graphite and the carbon source in the organic solvent, carrying out spray drying to obtain a silicon-carbon composite anode material precursor, and carrying out carbonization to obtain the three-dimensional spherical silicon-carbon composite anode material. The double-layer amorphous carbon layer can effectively relieve the volume expansion effect of silicon in the charging and discharging processes, the outer amorphous carbon layer enables the material to have a low specific surface area, large irreversible capacity loss is avoided, and the obtained material has high specific capacity, high first efficiency and excellent cycling stability. However, the method has the disadvantages of complex process steps, low active substance ratio and limited capacity exertion, and the polymer structure in the system is damaged due to the calcination effect, so that the prepared three-microsphere structure has poor stability, poor structural strength and toughness and is easy to damage, thereby influencing the use effect.

(3) For example, patent CN 111916745 a-silicon negative electrode material, a preparation method thereof, and an electrochemical cell disclose a silicon negative electrode material, wherein the silicon negative electrode material is a secondary composite particle, the secondary composite particle comprises a silicon particle, a conductive agent, and a thermosetting high polymer, the thermosetting high polymer is at least arranged on the outer layer of the secondary composite particle, the patent technology utilizes the thermosetting high polymer to process, crosslink and mold, and then the secondary composite particle cannot be processed again, the shape is not changed, and the thermosetting high polymer has better strength and toughness performance, so that the silicon negative electrode material can maintain the inherent shape and structure in the charging and discharging process of the electrochemical cell, and plays a role of supporting the secondary composite particle. Although the secondary composite particles which are relatively stable can be formed in the mode, the formed particles have no deformation performance due to the inherent characteristics of the shape structure of the thermosetting resin, so that the buffering performance of the formed particles on the volume expansion of silicon is limited, and the electrochemical performance of the obtained product is poor.

In conclusion, the prior art can not effectively solve the problem of poor electrode cycle performance caused by volume expansion of the silicon-based negative electrode material in the charging and discharging processes by adopting a simple method; and the problem of low electronic conductivity of silicon materials.

Disclosure of Invention

The first purpose of the invention is to provide a silicon-based negative electrode material and a preparation method thereof, wherein the preparation method is simple, efficient and easy to industrialize, and the lithium ion battery negative electrode material with high specific capacity, first coulombic efficiency, good cycle performance and rate capability can be obtained by one step.

The second purpose of the invention is to provide the negative electrode prepared from the silicon-based negative electrode material and the preparation method thereof, the operation is simple, and the negative electrode has high specific capacity, first coulombic efficiency, good cycle performance and rate capability when being applied to a battery.

A third object of the present invention is to provide a battery comprising the above negative electrode material, which has excellent electrochemical properties.

The invention is realized by the following technical scheme:

the invention firstly provides a silicon-based composite anode material, which comprises secondary spherical particles and a conductive material; the secondary spherical particles are prepared from raw materials comprising silicon and a water-soluble high-molecular polymer; the conductive material is coated outside the secondary spherical particles or dispersed inside the secondary spherical particles.

According to the invention, the secondary spherical particles are prepared by taking silicon and a water-soluble high molecular polymer as raw materials, the silicon can be uniformly dispersed among the water-soluble high molecular polymers to form silicon and polymer integrated spherical particles, the formed spherical particles not only can generate an internal gap structure and provide silicon expansion gaps, but also more importantly, the water-soluble high molecular polymer has good flexibility and viscoelasticity, the flexibility can deform along with the silicon integrated with the water-soluble high molecular polymer when expanding, so that a good buffering effect is achieved, and the viscoelasticity can enable the formed silicon-based composite negative electrode material to be well bonded with a current collector without adding an additional adhesive when a negative electrode plate is prepared subsequently.

In addition, the conductive material disclosed by the invention is coated outside the secondary spherical particles or dispersed inside the secondary spherical particles, and whether coated outside or dispersed inside the secondary spherical particles, the conductive material disclosed by the invention can be stably and uniformly dispersed outside or inside the secondary spherical particles due to the adhesive property, water solubility and net structure of the water-soluble high polymer, so that the utilization rate of the conductive material is high, and the conductivity is fully exerted.

Through the above functions, the silicon-based composite negative electrode material provided by the invention has high specific capacity, first coulombic efficiency, and good cycle performance and rate capability when being applied to a lithium ion battery.

Preferably, the secondary spherical particles have a particle diameter of 1 to 20 μm.

The mass percentage of the selected silicon, the water-soluble high molecular polymer and the conductive material is (50-90%) (10-50%) (0.5-20%); and the sum of the mass percentages of the silicon, the water-soluble high molecular polymer and the conductive material in the silicon-based composite negative electrode material is 100%.

According to the invention, by reasonably controlling the proportion of the silicon, the water-soluble high molecular polymer and the conductive material, the silicon and the conductive material can be uniformly and stably dispersed in the water-soluble high molecular polymer to form a stable charge-discharge structure, and the utilization rate of the conductive material can be improved.

The addition of silicon in high mass proportion also ensures the high specific capacity of the material.

Preferably, the water-soluble high molecular polymer is a high molecular polymer having a hydrophilic group, and specifically, one or more of polyacrylamide, carboxymethyl chitosan, carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone can be selected.

The conductive material of the present application is preferably one or more of acetylene black, Super P, mesocarbon microbeads, graphite, graphene, carbon nanotubes, carbon nanofibers, polyacetylene, polypyrrole, and polyaniline.

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

when the conductive material is coated outside the secondary spherical particles, the method comprises the following steps:

s1, uniformly dispersing silicon and a water-soluble high molecular polymer in water to form a mixed aqueous solution;

s2, carrying out spray drying granulation on the mixed aqueous solution obtained in the step S1 to obtain secondary spherical particles;

s3, mixing the secondary spherical particles prepared in the step S2 with a conductive material to obtain the silicon-based composite negative electrode material;

when the conductive material is dispersed in the secondary spherical particles, the method comprises the following steps:

s1, uniformly dispersing silicon, a water-soluble high molecular polymer and a conductive material in water to form a mixed aqueous solution;

and S2, carrying out spray drying granulation on the mixed aqueous solution obtained in the step S1 to obtain the silicon-based composite negative electrode material.

The invention fully disperses silicon and water-soluble high molecular polymer in water to ensure that the silicon and the water-soluble high molecular polymer can be well dispersed and silicon particles are nested between grids of the polymer, and then secondary spherical particles are formed by spray drying, the appearance of the secondary spherical particles is tightly connected by nano silicon particles, and the interior of the secondary spherical particles is provided with pore space to buffer the volume expansion of the secondary spherical particles.

According to the method, the nano silicon particles are micronized, and compared with nano silicon, the secondary spherical particles have the advantages that the specific surface area is reduced, the side reaction is reduced, an internal gap structure is formed, and further, a silicon expansion space is provided; in addition, in the secondary spherical particles, silicon and the polymer form an integrated structure, and the polymer with flexibility and viscoelasticity can also deform along with the volume expansion of the silicon, so that a good buffering effect is achieved.

No matter the mode of adopting the conducting material to coat the outside or the mode of adopting the conducting material to disperse inside, because of the existence of the water-soluble high molecular polymer, the conducting material can be well bonded on the secondary spherical particles to form a stable silicon-based composite negative electrode material, and further the conductivity of the material is effectively improved.

The preparation method has simple steps, is convenient and easy to operate and control, and is easy to realize industrialization.

Preferably, the average particle size of silicon in step S1 is 30nm to 500 nm.

The smaller the particle size, the more easily the silicon is uniformly dispersed and embedded in the polymer, but the smaller the particle size, the agglomeration phenomenon may occur, and therefore, the particle size of silicon is preferably 30 to 500nm in the present application.

Preferably, the solid content of the mixed aqueous solution in the step S1 is 1-20%.

If the solid content is too low, the product has large pores and unstable structure and is not favorable for production; if the solid content is too high, the viscosity of the mixed aqueous solution increases, which is disadvantageous in spray granulation.

Preferably, the spray drying temperature in step S2 is 130 to 220 ℃.

Reasonably controlling the temperature of spray drying, and avoiding the damage of viscoelasticity of the water-soluble high molecular polymer caused by overhigh temperature.

The application also provides a cathode prepared from the silicon-based composite cathode material, and the preparation method of the cathode comprises the following steps:

and mixing the silicon-based composite negative electrode material with water or a binder aqueous solution to prepare slurry, uniformly stirring, coating the slurry on the surface of a negative current collector, and drying to obtain the negative electrode.

Specifically, the mass of water or a binder aqueous solution in the slurry is 2-5 times of that of the silicon-based composite negative electrode material, the stirring temperature is 15-40 ℃, the stirring time is 0.5-6 h, and the drying mode is drying for 6-24 h at the temperature of 60-105 ℃ in a vacuum and inert atmosphere.

Because the silicon-based composite negative electrode material of the application contains the viscoelastic high molecular polymer, and the viscoelasticity of the high molecular polymer is not damaged in the preparation process of the whole silicon-based composite negative electrode material, the application can prepare the slurry with good binding property with the current collector without adding a binder in the slurry when preparing the negative electrode plate, thereby greatly saving the operation steps, reducing the addition of auxiliary materials and ensuring the addition of silicon and conductive materials. And the secondary ball particle structure is not damaged after the pole piece is prepared, so that the electrical property of silicon can be maintained.

In another embodiment, a binder may be further added to the slurry of the present application, specifically, the mass percentage of the binder in the binder aqueous solution is 1% to 5%.

Under the condition of additionally adding the binder, the silicon-based composite negative electrode material and the binder have a synergistic effect, the structural integrity of the electrode is maintained in the charging and discharging processes, and the performance stability is improved.

The invention also provides application of the cathode, and the cathode is used in a lithium ion battery and used as a cathode of the lithium ion battery.

In conclusion, the water-soluble high molecular polymer can be dissolved or swelled in water to form an aqueous solution, and the aqueous solution has viscosity and still has good fluidity after being mixed with silicon particles; in the secondary spherical particles, water-soluble polymers are distributed between silicon and silicon particles or on the surfaces of the silicon particles, and the structure of the secondary particles is stabilized by using the viscoelasticity of the water-soluble polymers, so that the material is prevented from falling off from a current collector; different from other researches, the self characteristics of the water-soluble polymer are not influenced by the spray drying temperature, the silicon-based composite negative electrode material and water are stirred and mixed, the slurry has viscosity, and the structure of the secondary spherical particles is not damaged after the pole piece is prepared.

The invention has the beneficial effects that:

1. the silicon-based negative electrode composite material has high specific capacity, first coulombic efficiency, and good cycle performance and rate capability.

2. The preparation method of the silicon-based composite negative electrode material is simple and easy to implement, is simple and convenient when being applied to the preparation of a negative electrode plate, can be used for preparing a negative electrode by directly adding water and mixing slurry, is simple to operate, has low cost and is easy to industrialize.

Drawings

FIG. 1 is a scanning electron micrograph of a secondary spherical particle obtained in example 1 of the present invention;

FIG. 2 is a scanning electron microscope image of a negative plate made of the silicon-based composite negative electrode material in example 1 of the present invention;

FIG. 3 is a scanning electron microscope image of the silicon-based composite anode material obtained in example 2 of the present invention;

fig. 4 is a graph comparing the rate performance of the batteries of example 1 of the present invention and comparative examples 1 to 3.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the present invention is further described with reference to specific embodiments below.

Example 1

S1, forming a dispersion liquid of nano silicon particles with the D50 of 50nm and carboxymethyl cellulose in water, and carrying out ultrasonic treatment for 30 min. In the dispersion, the mass fraction of nano silicon is 3%, the mass fraction of carboxymethyl cellulose is 0.5%, and the balance is water.

S2, spray drying the dispersion liquid obtained in the step S1 at 160-200 ℃ to obtain secondary spherical particles, wherein the average particle size of the particles is about 6 mu m.

And S3, mixing the secondary spherical particles with the Super P to obtain the silicon-based composite negative electrode material, wherein the mass ratio of the secondary spherical particles to the Super P is 9: 1.

And S4, mixing the silicon-based composite negative electrode material obtained in the step S3 with water according to the mass ratio of 2:5, stirring for 40min, coating the mixture on a copper foil, and performing vacuum drying at 105 ℃ for 12 hours to obtain a negative electrode sheet.

Example 2

S1, forming a dispersion liquid of nano silicon particles with D50 of 50nm, carboxymethyl cellulose and carbon nano tubes in water, and carrying out ultrasonic treatment for 30 min. In the dispersion, the mass fraction of nano silicon is 3%, the mass fraction of carboxymethyl cellulose is 0.5%, the mass fraction of carbon nano tubes is 0.3%, and the balance is water.

And S2, spray drying the dispersion liquid obtained in the step S1 at 160-200 ℃ to obtain the silicon-based composite negative electrode material, wherein the average particle size of the particles is about 6 microns.

And S3, mixing the silicon-based composite negative electrode material obtained in the step S2 with water according to the mass ratio of 2:4, stirring for 30min, coating the mixture on a copper foil, and performing vacuum drying at 105 ℃ for 12 hours to obtain a negative electrode sheet.

Example 3

The difference from example 1 is that: and (4) mixing and stirring the silicon-based composite negative electrode material obtained in the step S3 with a 1% binder aqueous solution to prepare a negative plate.

Example 4

The difference from example 2 is that: and (4) mixing and stirring the silicon-based composite negative electrode material obtained in the step S2 with a 1% binder aqueous solution to prepare a negative plate.

Example 5

The difference from example 1 is that: carboxymethyl cellulose is replaced by polyacrylamide.

Example 6

The difference from example 2 is that: carboxymethyl cellulose was replaced with polyvinylpyrrolidone.

Comparative example 1

The difference from the preparation method of the example is that: in step S1, silicon and carboxymethyl cellulose are dispersed in a small amount of water to form a dispersion liquid, wherein the mass ratio of silicon to carboxymethyl cellulose is 6:1, and the dispersion liquid is subjected to ultrasonic treatment for 30min and then is dried in vacuum at 80 ℃ until the water solvent is completely evaporated without a spray drying process.

Comparative example 2

Re-dispersing the secondary spherical particles obtained in step S2 in example 1 in a small amount of water, subjecting the aqueous solution to ultrasonic treatment for 30min, and vacuum-drying at 80 ℃ until the aqueous solvent is completely evaporated to obtain mixed particles; the mixed particles and Super P are mixed according to the mass ratio of 9:1 to obtain a silicon-based composite negative electrode material, and then a negative electrode plate is prepared according to the step S4 in the example 1.

Comparative example 3

The difference from example 1 is that: in step S1, no carboxymethyl cellulose was added, and the dispersion contained only 3% by mass of nano-silicon particles.

Comparative example 4

The difference from example 1 is that: replacing carboxymethyl cellulose with phenolic resin, and fully emulsifying in water to form emulsion.

Experimental example 1 electrochemical experiment

The negative pole pieces obtained in the above examples 1 to 4 and comparative examples 1 to 4 are used as positive poles, then the lithium pieces are used as negative poles to assemble the button type half cell, the electrochemical performance is carried out on a Xinwei cell test system, the charging and discharging voltage range is 0.01V to 2.0V, the first two circles of tests are activated under the current density of 100mA/g, and then the test is carried out under the current density of 500 mA/g. The test results are shown in table 1 below:

TABLE 1 electrochemical Properties of examples and comparative examples

FIG. 4 shows a comparison of the properties of example 1 and comparative examples 1-4 at different rates.

As can be seen from the data in Table 1 and FIG. 4, the discharge capacity, the first charge-discharge efficiency, the capacity retention rate of 100 cycles and the rate capability of the silicon-based composite anode materials prepared in the examples 1 to 4 of the invention are obviously superior to those of the comparative examples 1 to 4.

The results of comparative examples 1 to 4 and comparative examples 1 to 3 show that the water-soluble high molecular polymer rather hinders the capacity development without spray drying or breaking the secondary particle structure. The reasons for this are mainly: the synergistic effect among the high silicon content, the internal pore structure and the viscoelasticity of the water-soluble polymer of the secondary spherical particles obtained by spray drying not only buffers the volume expansion of silicon and reduces the side reaction with electrolyte, but also enhances the bonding effect with a conductive material and a current collector and enhances the electronic conductivity.

The results of comparative examples 1 to 4 and comparative example 4 show that the use of a water-insoluble thermosetting polymer as the polymer not only does not allow good buffer effect during charging and discharging but also allows stable adhesion between the conductive material and the current collector, thereby affecting the conductivity.

Experimental example 2: scanning electron microscope

1. The secondary spherical particles prepared in example 1 were subjected to a scanning electron microscope test, and the test results are shown in fig. 1.

As can be seen from fig. 1: the secondary spherical particles obtained by spray drying the nano silicon particles and the water-soluble polymer have good spherical shape and high dispersibility. The silicon particles and the water-soluble polymer are tightly combined, and the particle surface is compact.

2. Scanning electron microscope tests are carried out on the negative plate prepared from the silicon-based composite negative electrode material obtained in the example 1, and the results are shown in the attached figure 2.

As can be seen from fig. 2: in the negative plate prepared by only adding water and mixing slurry, the spherical structure of the silicon-based composite negative material is complete, the particles are uniformly dispersed and filled, and the cracks of the plate are fewer, which shows that the method for preparing the negative plate has less influence on the structure of the material and is feasible and effective.

3. Scanning electron microscope tests are carried out on the silicon-based composite negative electrode material obtained in the example 2, and the results are shown in the attached figure 3.

As can be seen from fig. 3: the nano silicon particles, the water-soluble polymer and the carbon nano tubes are subjected to spray drying to form integrated secondary spherical particles with good spherical shape, and the carbon nano tubes serving as conductive materials are uniformly distributed in the secondary spherical particles and are tightly connected with the silicon particles through the water-soluble polymer.

In conclusion, the silicon-based composite negative electrode material has good electrochemical performance, and the preparation method is simple and easy to realize industrialization.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The silicon-based composite anode material is characterized by comprising secondary spherical particles and a conductive material; the secondary spherical particles are prepared from raw materials comprising silicon and a water-soluble high-molecular polymer; the conductive material is coated outside the secondary spherical particles or dispersed inside the secondary spherical particles.

2. The silicon-based composite anode material according to claim 1, wherein the secondary sphere particles have a particle size of 1 μm to 20 μm.

3. The silicon-based composite anode material as claimed in claim 1, wherein the mass percentages of the silicon, the water-soluble high molecular polymer and the conductive material are (50-90%) (10-50%) (0.5-20%); and the sum of the mass percentages of the silicon, the water-soluble high molecular polymer and the conductive material in the silicon-based composite negative electrode material is 100%.

4. The silicon-based composite anode material according to claim 1 to 3, wherein the water-soluble high polymer is one or more of polyacrylamide, carboxymethyl chitosan, carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone.

5. The silicon-based composite anode material according to claims 1 to 3, wherein the conductive material is one or more of acetylene black, Super P, mesocarbon microbeads, graphite, graphene, carbon nanotubes, carbon nanofibers, polyacetylene, polypyrrole and polyaniline.

6. The preparation method of the silicon-based composite anode material as claimed in any one of claims 1 to 5, wherein when the conductive material is coated outside the secondary spherical particles, the method comprises the following steps:

7. The method for preparing the silicon-based composite anode material according to claim 6, wherein the average particle size of the silicon in the step S1 is 30nm to 500 nm.

8. The method for preparing the silicon-based composite anode material as claimed in claim 6, wherein the spray drying temperature in the step S2 is 130 ℃ to 220 ℃.

9. A negative electrode is characterized by being prepared from the silicon-based composite negative electrode material as claimed in any one of claims 1 to 5.

10. The preparation method of the negative electrode according to claim 9, wherein the silicon-based composite negative electrode material is mixed with water or a binder aqueous solution to prepare slurry, the slurry is uniformly stirred and then coated on the surface of a negative electrode current collector, and the negative electrode is obtained after drying.