CN111162254A

CN111162254A - Preparation method of silicon-carbon composite negative electrode material

Info

Publication number: CN111162254A
Application number: CN201911380568.XA
Authority: CN
Inventors: 郭华彬; 张正; 胡海玲; 李武义; 王诚文; 姚曼
Original assignee: Yinlong New Energy Co Ltd
Current assignee: Yinlong New Energy Co Ltd
Priority date: 2019-12-27
Filing date: 2019-12-27
Publication date: 2020-05-15

Abstract

The invention provides a preparation method of a silicon-carbon composite negative electrode material. The preparation method comprises the following steps: step S1, removing dissolved oxygen in water to obtain oxygen-free water; step S2, performing wet ball milling on the silicon material and the surfactant to obtain nano silicon slurry; step S3, mixing graphite, a binder and the nano-silicon slurry to form precursor slurry; step S4, spray drying the precursor slurry to obtain black powder; step S5, mixing the black powder with a carbon source to form a mixture; and step S6, roasting the mixture to obtain the silicon-carbon composite negative electrode material, wherein the water used in the step S2 is the oxygen-free water obtained in the step S1, and when the water is used in the step S3, the water used is the oxygen-free water obtained in the step S1. The defect of silicon oxidation caused by dissolved oxygen in water is overcome by removing the dissolved oxygen in the water, and the wet ball milling, mixing and other process treatment modes adopted by mixing are simple.

Description

Preparation method of silicon-carbon composite negative electrode material

Technical Field

The invention relates to the technical field of negative electrode materials for lithium batteries, in particular to a preparation method of a silicon-carbon composite negative electrode material.

Background

The silicon has the theoretical lithium intercalation capacity of up to 4200mAh/g and the lithium intercalation potential of 0.2V vs. Li/Li⁺And the silicon reserves are abundant, the cost advantage is obvious, it is the most promising negative pole material of lithium ion battery. The current bottlenecks restricting the development of silicon cathode materials mainly lie in two points: on the one hand, a volume change of up to 300% occurs during the lithium deintercalation of silicon, which leads to a fragmentation, pulverization of the silicon particles, and thus to the exposure of new surfaces, which consume large amounts of electrolyte. At the same time, the contact with the copper foil is lost, and the loss of the contact between the silicon and the foil greatly increases the transmission distance of electrons, which leads to the great reduction of the service life of the silicon material. On the other hand, silicon is a semiconductor material, the electronic conductivity of the silicon is relatively low, the electron transmission speed is low, and a battery prepared by adopting the silicon cathode material has high internal resistance and poor rate capability. In this regard, it is common in the academia and industry to modify silicon by both silicon nanocrystallization and carbon recombination. On one hand, the silicon nanocrystallization can reduce the volume effect of silicon; on the other hand, the composite material is prepared from the silicon material and the carbon material with good conductivity, so that the stress action of silicon in the charging and discharging process is relieved, and the electronic conductivity of the silicon material is improved.

In the grinding process, the size of silicon particles is reduced, more fresh surfaces without oxide layers are exposed, the hydrophobicity is stronger, and small silicon particles are easy to float upwards and are layered with graphite. Patent application with application publication number CN107785541A discloses a silicon-carbon composite material and a preparation method thereof, wherein the method comprises the following steps: (1) carrying out wet grinding on a graphite material and a silicon material respectively with a dispersant and a solvent to obtain graphite slurry and silicon slurry, and mixing the two slurries to obtain graphite/silicon mixed slurry; or carrying out wet grinding on the graphite material and the silicon material, the dispersant and the solvent simultaneously to obtain graphite/silicon mixed slurry; (2) preparing a high molecular polymer solution, dissolving a first carbon precursor by using a solvent, adding the dissolved first carbon precursor and the high molecular polymer solution into the slurry prepared in the step (1), and carrying out wet grinding to obtain graphite/silicon/high molecular polymer/first carbon precursor mixed slurry; or dissolving the first carbon precursor by using a solvent, adding the dissolved first carbon precursor and high polymer powder into the slurry prepared in the step (1) together, and carrying out wet grinding to obtain graphite/silicon/high polymer/first carbon precursor mixed slurry; (3) drying and granulating the mixed slurry obtained in the step (2), and then carrying out high-temperature carbonization treatment in a non-oxidizing atmosphere; (4) performing second carbon precursor coating treatment on the product obtained in the step (3), and then performing high-temperature carbonization in a non-oxidizing atmosphere; (5) and (4) crushing, screening and demagnetizing the product obtained in the step (4) to obtain the silicon-carbon composite material. And (3) adding a high molecular polymer in the form of solution or powder in the step (2), reducing the rotating speed of a sand mill, not damaging the molecular chain structure of the high molecular polymer, uniformly dispersing the high molecular polymer in a graphite/silicon/organic solvent system, forming a huge network structure on the surfaces of graphite and silicon, further inhibiting the floating and agglomeration of the silicon by utilizing the steric hindrance effect of the large network structure, and realizing the effective compounding of the silicon and the graphite.

The patent application with the application publication number of CN108232141 discloses a silicon-carbon composite material and a preparation method thereof, the method comprises the steps of 1) mixing and ball-milling a silicon-based material, polydiallyldimethylammonium chloride and water, and obtaining slurry A with positive charges on the surfaces of silicon-based material particles after the silicon-based material, the polydiallyldimethylammonium chloride and the water are combined; 2) mixing and ball-milling a carbon material, a surfactant and water to obtain slurry B with negative charges on the surface of the carbon material; 3) mixing the slurry A and the slurry B, adding an adhesive, performing ball milling, adding a proper amount of water, adjusting to a proper solid content, and performing spray drying to obtain black powder; 4) and (3) performing high-temperature pyrolysis on the black powder, performing surface coating treatment, and performing pyrolysis to obtain the high-compaction lithium ion battery silicon-carbon composite negative electrode material. In order to uniformly mix the silicon-based material and the carbon material, the preparation method adopts the high molecular polymer to modify the silicon-based material and adopts the surfactant to modify the carbon material to form the slurry with opposite charge performance. On the other hand, the cracked carbon obtained by direct high-temperature cracking of the carbon source is not in close contact with graphite, a coating layer is easy to fall off when the pole piece is manufactured, and the material modification effect is not obvious.

Therefore, in the prior art, in order to improve the mixing uniformity of the silicon material and the carbon material, organic materials are generally adopted, particularly high molecular polymers are adopted, but the adopted organic solvents such as methanol, acetone, tetrahydrofuran, toluene, dimethylformamide and the like have high toxicity, human body contact has great influence on human health, and the waste liquid recovery and treatment cost is very high. The high molecular polymer suitable for the organic solvent system is usually insoluble in water, so that the high molecular polymer needs to be subjected to grinding treatment when in use, even if the modification effect of the high molecular polymer on the silicon-based material is difficult to control, the improvement of the mixing uniformity of the silicon material and the carbon material in the water system by the high molecular polymer is difficult to ensure.

Disclosure of Invention

The invention mainly aims to provide a preparation method of a silicon-carbon composite negative electrode material, which aims to solve the problem that the silicon-carbon composite negative electrode material in the prior art is complex to process.

In order to achieve the above object, according to an aspect of the present invention, there is provided a method of preparing a silicon-carbon composite anode material, the method comprising: step S1, removing dissolved oxygen in water to obtain oxygen-free water; step S2, performing wet ball milling on the silicon material and the surfactant to obtain nano silicon slurry; step S3, mixing graphite, a binder and the nano-silicon slurry to form precursor slurry; step S4, spray drying the precursor slurry to obtain black powder; step S5, mixing the black powder with a carbon source to form a mixture; and step S6, roasting the mixture to obtain the silicon-carbon composite negative electrode material, wherein the water used in the step S2 is the oxygen-free water obtained in the step S1, and when the water is used in the step S3, the water used is the oxygen-free water obtained in the step S1.

Further, the step S1 includes removing dissolved oxygen in water by a physical method and/or a chemical method, the physical method includes introducing nitrogen gas into water to replace the dissolved oxygen in water, the chemical method includes adding a reducing agent into water to reduce the dissolved oxygen, the reducing agent is preferably any one or more of hydrazine, hydrazine hydrate, carbohydrazide and erythorbic acid, and the mass amount of the reducing agent relative to water is more preferably 0.01-2.0: 100, and more preferably 1.0-2.0: 100.

Further, in step S2, the surfactant is one or more selected from the group consisting of sodium hexadecyl diphenyl ether disulfonate, methyl acrylate-acrylic acid, fatty alcohol-polyoxyethylene ether, hexadecyl trimethyl ammonium bromide, sodium polyacrylate, ammonium polyacrylate, and sodium polyphosphate-ammonium polymethacrylate, and preferably, the silicon material is micron-sized silicon powder.

Further, in the step S2, the mass ratio of the silicon material, the surfactant and the grinding balls is 1: (0.01-1.0): (1-5); preferably, the solid content of the nano silicon slurry is 5-50%; preferably, the ball mill used in step S2 has a stirring speed of 500 to 2000rpm and a stirring time of 10 to 30 hours.

Further, in the step S3, the binder is one or more selected from the group consisting of polyvinyl alcohol, polyimide, chitosan, carboxymethyl chitosan, polyvinylpyrrolidone, polyacrylic acid and sodium salt thereof, carboxymethyl cellulose and sodium salt thereof, alginic acid and sodium salt thereof, and preferably, the mass ratio of the silicon material, graphite and the binder is 1: (1-9): (0.01 to 0.5); and preferably, the solid content of the precursor slurry is adjusted to be 5-50% by adopting oxygen-free water.

Further, in the step S3, the precursor slurry is formed by stirring, wherein the stirring speed is 1000-5000 rpm, and the stirring time is 10-20 hours.

Further, in the step S4, the inlet temperature of spray drying is 300-800 ℃, the outlet temperature is 50-250 ℃, the feeding speed of the precursor slurry is preferably 0.1-5L/min, and the rotating speed of the spray atomizing disk is 1000-50000 rpm.

Further, in the step S5, the carbon source is selected from one or more of coal pitch, petroleum pitch, natural pitch, phenolic resin, and epoxy resin, and the mass ratio of the carbon source to the black powder is preferably (0.01 to 1): 1.

further, the roasting of the step S6 comprises two-stage roasting, wherein the first-stage roasting temperature is 200-500 ℃, and the first-stage roasting time is 0.5-4 hours; the second-stage roasting temperature is 550-1200 ℃, the second-stage roasting time is 1-6 h, and the preferable temperature rise rate of reaching the first-stage roasting temperature and the temperature rise rate of reaching the second-stage roasting temperature are respectively and independently 1-20 ℃/min.

Further, the preparation method also comprises a process of mechanical fusion of the silicon-carbon composite negative electrode material, preferably, the rotation speed of a fusion machine is 1000-3000 rpm, and the fusion time is 0.5-2.5 h during the mechanical fusion.

By applying the technical scheme of the invention, water is used as a solvent, so that the problem of environmental safety caused by volatilization of an organic solvent is avoided; and the defect of silicon oxidation caused by dissolved oxygen in water is overcome by removing the dissolved oxygen in the water. In material mixing, the application adopts the high molecular polymer suitable for a water solvent system, and improves the silicon-carbon mixing uniformity through the following treatment modes: the silicon material and the surfactant are subjected to wet ball milling, the addition of the surfactant prevents nano-silicon agglomeration formed by the wet ball milling, and the graphite is not subjected to refining treatment such as ball milling, so that the graphite has a large continuous surface for adsorption of nano-silicon particles, and the uniformity of distribution of the nano-silicon particles on the surface of the graphite is ensured when the graphite, the binder and the nano-silicon slurry are mixed in the step S3. All the steps adopted by the mixing process are processes of wet ball milling, mixing and the like commonly used for silicon materials and carbon materials in the preparation of the negative electrode materials, so that the treatment mode of the materials is simple. And tests prove that the capacitance ratio cycle performance of the obtained silicon-carbon composite negative electrode material can completely meet the application of a lithium battery.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

fig. 1 shows an SEM image of a silicon carbon composite material prepared according to example 1 of the present invention;

fig. 2 shows an SEM partial enlarged view of a silicon carbon composite material prepared according to example 1 of the present invention;

FIG. 3 shows an SEM image of a silicon carbon composite prepared according to comparative example 1 of the present invention;

fig. 4 shows a graph of the normal temperature cycle performance of the silicon carbon materials prepared according to example 1 of the present invention and comparative examples 1 to 4.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

As analyzed in the background art of the present application, in order to improve the mixing uniformity of the silicon material and the carbon material in the prior art, an organic material is usually adopted, especially by means of a high molecular polymer, and the adopted organic solvent such as methanol, acetone, tetrahydrofuran, toluene, dimethylformamide and the like has high toxicity, human body contact has a great influence on human health, and the waste liquid recovery and treatment cost is very high. However, the high molecular polymer suitable for the organic solvent is mostly insoluble in water, so that the high molecular polymer needs to be ground when a water solvent system is used, even if the modification effect of the high molecular polymer on the silicon-based material is difficult to control, the improvement of the mixing uniformity of the silicon material and the carbon material in the water system by the high molecular polymer is difficult to ensure. That is to say, high molecular polymer need carry out the crocus pretreatment when using, leads to the material processing complicated, in order to solve this problem, this application provides a preparation method of silicon carbon composite negative pole material.

In an exemplary embodiment of the present application, there is provided a method of preparing a silicon-carbon composite anode material, the method including: step S1, removing dissolved oxygen in water to obtain oxygen-free water; step S2, performing wet ball milling on the silicon material and the surfactant to obtain nano silicon slurry; step S3, mixing graphite, a binder and the nano-silicon slurry to form precursor slurry; step S4, spray drying the precursor slurry to obtain black powder; step S5, mixing the black powder with a carbon source to form a mixture; and step S6, roasting the mixture to obtain the silicon-carbon composite negative electrode material, wherein the water used in the step S2 is the oxygen-free water obtained in the step S1, and when the water is used in the step S3, the water used is the oxygen-free water obtained in the step S1.

The application adopts water as the solvent, thereby avoiding the environmental safety problem caused by the volatilization of the organic solvent; and the defect of silicon oxidation caused by dissolved oxygen in water is overcome by removing the dissolved oxygen in the water. In the material mixing method, the high molecular polymer suitable for the water solvent system is adopted, and the silicon-carbon mixing uniformity is improved by the following treatment modes: the silicon material and the surfactant are subjected to wet ball milling, the addition of the surfactant prevents nano-silicon agglomeration formed by the wet ball milling, and the graphite is not subjected to refining treatment such as ball milling, so that the graphite has a large continuous surface for adsorption of nano-silicon particles, and the uniformity of distribution of the nano-silicon particles on the surface of the graphite is ensured when the graphite, the binder and the nano-silicon slurry are mixed in the step S3. All the steps adopted by the mixing process are processes of wet ball milling, mixing and the like commonly used for silicon materials and carbon materials in the preparation of the negative electrode materials, so that the treatment mode of the materials is simple. And tests prove that the capacitance ratio cycle performance of the obtained silicon-carbon composite negative electrode material can completely meet the application of a lithium battery.

There are various ways for removing dissolved oxygen, such as heating, but this method is energy intensive and inefficient. In the present application, preferably, the step S1 includes removing dissolved oxygen in water by a physical method and/or a chemical method, the physical method includes introducing nitrogen gas into water to replace dissolved oxygen in water, and preferably, the flow rate of high-purity nitrogen gas is controlled to be 0.1 to 1L/min, and the time is controlled to be 0.1 to 2 hours. The chemical method includes adding a reducing agent to water to reduce dissolved oxygen, and the physical method and the chemical method may be used simultaneously. Physical methods of removing dissolved oxygen do not introduce other components into the water, but are relatively inefficient. The chemical method for removing dissolved oxygen is efficient, but other components are introduced, and in order to avoid the influence of reduction products, the reducing agent is preferably any one or more of hydrazine, hydrazine hydrate, carbohydrazide and erythorbic acid, and the product generated after the reducing agent is oxidized can be volatilized or burnt out in subsequent spray drying and roasting. In order to further improve the reduction efficiency, the mass amount of the reducing agent to water is more preferably 0.01 to 2.0:100, and preferably 1.0 to 2.0: 100.

The purpose of adding the surfactant in step S2 is to promote the dispersion of the silicon material in the oxygen-free water, and effectively avoid the nano-silicon agglomeration formed by wet ball milling. Preferably, in step S2, the surfactant is one or more selected from the group consisting of sodium hexadecyl diphenyl ether disulfonate, methyl acrylate-acrylic acid, fatty alcohol-polyoxyethylene ether, hexadecyl trimethyl ammonium bromide, sodium polyacrylate, ammonium polyacrylate, and sodium polyphosphate-ammonium polymethacrylate, and the silicon material is preferably micron-sized silicon powder.

The grinding balls for wet ball milling in step S2 of the present application are made of grinding balls made of materials commonly used in the prior art, such as zirconia grinding balls, yttria-toughened zirconia grinding balls, zirconium silicate grinding balls, alumina grinding balls, silicon-aluminum composite material grinding balls, and stainless steel grinding balls, or may be a mixture of the above grinding balls made of multiple materials. In order to improve the ball milling efficiency, it is preferable that the mass ratio of the silicon material, the surfactant and the milling balls in the step S2 is 1: (0.01-1.0): (1-5); preferably, the solid content of the nano silicon slurry is 5-50%; preferably, the ball mill used in step S2 has a stirring speed of 500 to 2000rpm and a stirring time of 10 to 30 hours.

The binder used in step S3 of the present application may be a binder commonly used in the art, and in order to achieve a high binding effect and improve dispersibility of the silicon material and graphite in the binder, it is preferable that in step S3, the binder is selected from one or more of polyvinyl alcohol, polyimide, chitosan, carboxymethyl chitosan, polyvinylpyrrolidone, polyacrylic acid and its sodium salt, carboxymethyl cellulose and its sodium salt, alginic acid and its sodium salt, and the mass ratio of the silicon material, graphite and binder is preferably 1: (1-9): (0.01-0.5). In addition, the graphite in the application can be made of graphite materials commonly used in the field, and preferably, graphite powder with the median particle size of 5-25 mu m is adopted.

On the premise of ensuring the uniform mixing of the silicon material, the graphite and the binder, in order to ensure the high-efficiency spray drying in the next step, the solid content of the precursor slurry is preferably adjusted to be 5-50% by adopting oxygen-free water.

The mixing mode of the nano silicon slurry, the graphite and the binder can be stirring, shaking, rotating and the like, preferably, the precursor slurry is formed in the step S3 in a stirring mode, the stirring speed is 1000-5000 rpm, and the stirring time is 10-20 hours, so that a proper shearing action is generated on the binder, and the silicon material and the graphite are efficiently dispersed in the binder.

The aim of spray drying is to remove moisture in the precursor slurry and obtain particles with silicon uniformly dispersed on the graphite surface, and the moisture removal cannot be too fast in the spray drying process, otherwise, local silicon agglomeration is easily caused, so that in the step S4, the inlet temperature of the spray drying is 300-800 ℃, the outlet temperature is 50-250 ℃, the feeding rate of the precursor slurry is preferably 0.1-5L/min, and the rotation speed of the spray atomizing disc is 1000-50000 rpm.

The carbon source used in the present application may be a carbon source commonly used in the art, and preferably, in the above step S5, the carbon source is one or more selected from the group consisting of coal pitch, petroleum pitch, natural pitch, phenol resin, and epoxy resin. In order to achieve coating as complete as possible, the mass ratio of the carbon source to the black powder is preferably (0.01-1): 1.

in the present invention, the roasting of step S6 refers to high-temperature roasting of the cracked carbon source and the binder to obtain the cracked coated carbon. The firing of step S6 can be accomplished by solid phase firing, which is well known to those skilled in the art. According to the application, the roasting of the step S6 preferably comprises two-stage roasting according to the use amounts of the carbon source and the binder, wherein the first-stage roasting temperature is 200-500 ℃, and the first-stage roasting time is 0.5-4 h; the second-stage roasting temperature is 550-1200 ℃, the second-stage roasting time is 1-6 h, and the preferable temperature rise rate of reaching the first-stage roasting temperature and the temperature rise rate of reaching the second-stage roasting temperature are respectively and independently 1-20 ℃/min. The first stage of roasting aims at melting and uniformly coating the carbon source on the surface of graphite at a lower temperature, and the second stage of roasting aims at cracking the carbon source.

After the firing is completed, in order to enable the obtained silicon-carbon composite anode material to be directly applied, it is preferable that the preparation method further includes a process of mechanically fusing the silicon-carbon composite anode material. In the mechanical fusion process, the proportion of amorphous carbon pores formed by roasting can be reduced, so that the exposure of nano silicon is reduced, and the stability of the cathode material is further improved. In order to reduce the number of the gaps, the rotation speed of the fusion machine is preferably 1000-3000 rpm and the fusion time is preferably 0.5-2.5 h during mechanical fusion.

The advantageous effects of the present application will be further described below with reference to examples and comparative examples.

Example 1

Step S1 desolventizing oxygen: adding 0.02Kg of reducing agent erythorbic acid into 2Kg of deionized water, and simultaneously introducing high-purity nitrogen for 2 hours at the flow rate of 0.1L/min to remove trace oxygen dissolved in the water to obtain the oxygen-free water. (repeating the step when oxygen-free water is required in the subsequent step)

Step S2 silicon nanocrystallization: and (3) weighing 1Kg of micron-sized silicon powder, 0.01Kg of surfactant methyl acrylate-acrylic acid and 1Kg of yttrium oxide toughened zirconia grinding balls, adding the micron-sized silicon powder, the surfactant methyl acrylate-acrylic acid and the yttrium oxide toughened zirconia grinding balls into the oxygen-free water obtained in the step S1 to prepare a suspension with the micron-sized silicon content of 50%, and performing ball milling at the rotating speed of 2000rpm for 10 hours until the median particle size of silicon particles is less than 200nm to form the nano-silicon slurry.

Step S3 precursor preparation: and weighing 9Kg of artificial graphite with the median particle size of 5-25 mu m, 0.5Kg of binder carboxymethyl chitosan and 6.5Kg of deionized water with dissolved oxygen removed, adding the weighed materials into the nano silicon slurry obtained in the step S2, and stirring the materials at 1000rpm for 20 hours to prepare precursor slurry with the solid content of 50%.

Step S4 spray granulation: and (3) carrying out spray granulation on the precursor slurry under the conditions of the feeding speed of 0.1L/min, the rotating speed of a spraying disc of 50000rpm, the inlet temperature of 300 ℃ and the outlet temperature of 100 ℃ to form black solid powder with the median particle size of 5-40 mu m.

Step S5 carbon source mixture: 10.5Kg of solid powder obtained by spray granulation in step S4 and 0.105Kg of coal pitch as a carbon source were weighed and mixed for 3 hours.

Step S6 roasting and carbonizing: heating to 200 ℃ at room temperature at a heating rate of 20 ℃/min, preserving heat for 4h, heating to 1200 ℃ at a heating rate of 1 ℃/min, preserving heat for 1h, and roasting a carbon source and a binder at a high temperature to form cracked carbon to coat on the surface of silicon-graphite to form the silicon-carbon composite material.

Step S7 mechanofusion: and adding the silicon-carbon composite material formed in the S6 into a fusion machine, and fusing for 0.5h at 3000rpm to obtain the silicon-carbon composite negative electrode material.

Example 2

Unlike example 1, the step S1 of removing dissolved oxygen is as follows: 0.04Kg of reducing agent erythorbic acid is added into 2Kg of deionized water, and trace oxygen dissolved in the water is removed to obtain oxygen-free water.

Example 3

Unlike example 1, the step S1 of removing dissolved oxygen is as follows: adding 0.02Kg of hydrazine hydrate into 2Kg of deionized water, and simultaneously introducing high-purity nitrogen for 2 hours (end value is 2) at the flow rate of 0.1L/min to remove trace oxygen dissolved in the water, thereby obtaining the oxygen-free water.

Example 4

Unlike example 1, the step S1 of removing dissolved oxygen is as follows: adding carbohydrazide 0.02Kg into deionized water 2Kg, and simultaneously introducing high purity nitrogen for 2h at the flow rate of 0.1L/min to remove trace oxygen dissolved in water to obtain oxygen-free water.

Example 5

Unlike example 1, the step S1 of removing dissolved oxygen is as follows: 0.02Kg of sodium sulfite is added into 2Kg of deionized water, and high-purity nitrogen is introduced for 2 hours at the same time at the flow rate of 0.1L/min, so that trace oxygen dissolved in the water is removed, and the oxygen-free water is obtained.

Example 6

The difference from example 1 is that step S2 silicon nanocrystallization: and (3) weighing 1Kg of micron-sized silicon powder, 0.01Kg of surfactant cetyl diphenyl ether disulfonic acid sodium and 5Kg of zirconia grinding balls, adding the micron-sized silicon powder, the surfactant cetyl diphenyl ether disulfonic acid sodium and the zirconia grinding balls into the oxygen-free water obtained in the step S1 to prepare suspension with the content of micron silicon of 50%, and performing ball milling for 30 hours at the rotating speed of 500rpm until the median particle size of silicon particles is less than 200nm to form the nano-silicon slurry.

Example 7

The difference from example 1 is that in step S3 precursor preparation: and (3) weighing 1Kg of artificial graphite, 0.01Kg of polyimide as a binder and deionized water with dissolved oxygen removed, adding the deionized water into the nano silicon slurry obtained in the step S2, and stirring the mixture at 1000rpm for 20 hours to prepare precursor slurry with the solid content of 50%.

Example 8

The difference from example 1 is that the solid content of the precursor slurry in step S3 is 5%, and the spray granulation in step S4: and (3) carrying out spray granulation on the precursor slurry at the loading speed of 5L/min, the rotating speed of an atomizing disc of 1000rpm, the inlet temperature of 800 ℃ and the outlet temperature of 250 ℃ to form black solid powder with the median particle size of 15-25 mu m.

Example 9

The difference from example 1 is that step S5 mixes the carbon source: 10.5Kg of solid powder obtained by spray granulation in step S4 and 10.5Kg of coal pitch as a carbon source were weighed and mixed for 5 hours.

Step S6 roasting and carbonizing: heating to 500 ℃ at room temperature at a heating rate of 20 ℃/min, preserving heat for 4h, heating to 1200 ℃ at a heating rate of 1 ℃/min, preserving heat for 6h, and roasting a carbon source and a binder at a high temperature to form cracked carbon to coat on the surface of silicon-graphite to form the silicon-carbon composite material.

Example 10

The difference from example 1 is that step S6 calcines and carbonizes: heating to 500 ℃ at room temperature at a heating rate of 5 ℃/min, preserving heat for 0.5h, then heating to 550 ℃ at a heating rate of 15 ℃/min, preserving heat for 6h, and roasting a carbon source and a binder at a high temperature to form cracked carbon to coat on the surface of silicon-graphite to form the silicon-carbon composite material.

Example 11

The difference from example 1 is that step S6 calcines and carbonizes: heating to 400 ℃ at room temperature at a heating rate of 10 ℃/min, preserving heat for 2h, heating to 800 ℃ at a heating rate of 10 ℃/min, preserving heat for 3h, and roasting a carbon source and a binder at high temperature to form cracked carbon to coat on the surface of silicon-graphite to form the silicon-carbon composite material.

Example 12

The difference from example 1 is that step S6 calcines and carbonizes: heating to 800 ℃ at room temperature at a heating rate of 10 ℃/min, keeping the temperature for 6h, roasting the carbon source and the binder at high temperature to form cracking carbon, and coating the cracking carbon on the surface of the silicon-graphite to form the silicon-carbon composite material.

Example 13

The difference from embodiment 1 is that step S7 is mechanically fused: and adding the silicon-carbon composite material formed in the S6 into a fusion machine, and fusing for 2.5h at 1000rpm to obtain the silicon-carbon composite negative electrode material.

Example 14

The difference from example 1 is that an equivalent amount of AEO-9 fatty alcohol polyoxyethylene ether was used as the surfactant instead of the methyl acrylate-acrylic acid of example 1.

Example 15

Except for using 1.0Kg of methyl acrylate-acrylic acid as a surfactant in example 1.

Comparative example 1

Step S1 silicon nanocrystallization: weighing 1Kg of micron-sized silicon powder, 0.01Kg of surfactant methyl acrylate-acrylic acid and 1Kg of yttrium oxide toughened zirconia grinding balls, adding the micron-sized silicon powder, the surfactant methyl acrylate-acrylic acid and the 1Kg of yttrium oxide toughened zirconia grinding balls into 2Kg of deionized water without removing trace dissolved oxygen to prepare suspension with the micron-sized silicon content of 50%, and performing ball milling at 2000rpm for 10 hours until the median particle size of silicon particles is less than 200nm to form nano-silicon slurry.

Step S2 precursor preparation: and (3) weighing 9Kg of artificial graphite, 0.5Kg of binder carboxymethyl chitosan and 6.5Kg of deionized water without removing dissolved oxygen, adding the weighed materials into the nano silicon slurry obtained in the step S2, and stirring the materials at 1000rpm for 20 hours to prepare precursor slurry with the solid content of 50%.

Step S3 spray granulation: and (3) carrying out spray granulation on the precursor slurry under the conditions of the feeding speed of 0.1L/min, the rotating speed of a spraying disc of 50000rpm, the inlet temperature of 300 ℃ and the outlet temperature of 100 ℃ to form black solid powder.

Step S4 carbon source mixture: 10.5Kg of the solid powder spray-granulated in step S4 and 0.105Kg of coal pitch as a carbon source were weighed and mixed for 3 hours.

Step S5 carbonization: heating to 200 ℃ at room temperature at a heating rate of 20 ℃/min, preserving heat for 4h, heating to 1200 ℃ at a heating rate of 1 ℃/min, preserving heat for 1h, and roasting a carbon source and a binder at a high temperature to form cracked carbon to coat on the surface of silicon-graphite to form the silicon-carbon composite material.

Step S6 mechanofusion: and adding the silicon-carbon composite material formed in the S5 into a fusion machine, and fusing for 0.5h at 3000rpm to obtain the silicon-carbon composite negative electrode material.

Comparative example 2

Unlike comparative example 1, no binder was added during the preparation of the precursor of step S2.

Comparative example 3

Unlike comparative example 1, no surfactant was added when the silicon was nanocrystallized in step S1.

Comparative example 4

Unlike comparative example 1, there is no mechanical fusion of step S6.

The silicon-carbon composite negative electrode materials obtained in example 1 and comparative example 1 were subjected to morphology test, and the morphology of the silicon-carbon composite material was analyzed by using a heliotrope scanning electron microscope Regulus8220, fig. 1 is a scanning electron microscope photograph of the silicon-carbon composite negative electrode material prepared in example 1, fig. 2 is a partially enlarged view, it is seen from fig. 1 that the composite material is spheroidal, and it is seen from fig. 2 that the carbon coating layer of the composite material is dense in surface and has no graphite surface exposed. Fig. 3 is a scanning electron microscope photograph of the silicon-carbon composite negative electrode material prepared in the comparative example 1, and it can be seen from fig. 3 that the surface of the material of the comparative example has many pores, and under the same compaction density, the pole piece prepared by using the material of the comparative example 1 is easy to expose silicon due to the breakage of material particles, thereby deteriorating the performance of the battery.

The electrochemical cycling performance of the material was tested using the following method: the silicon-carbon composite negative electrode materials obtained in the examples and the comparative examples, the compound graphite, the mixed binder CMC and the SBR are mixed according to the proportion that 20: 60: 10: 10, adding a proper amount of deionized water as a dispersing agent to prepare slurry, coating the slurry on a copper foil, and carrying out vacuum baking and rolling to prepare the negative pole piece. The ternary positive electrode material, the binder PVDF and the conductive graphite are mixed according to the mass ratio of 90:5:5, a proper amount of N-methyl pyrrolidone is added to be used as a dispersing agent to prepare slurry, the slurry is coated on an aluminum foil, and the aluminum foil is subjected to vacuum baking and rolling to prepare a positive electrode plate. Using a polyolefin separator, 1mol/L LiPF₆And assembling the electrolyte into a full battery, wherein the test condition of the full battery is 25 ℃, the charge-discharge multiplying power is 1C, and the charge-discharge voltage is 2.8-4.2V. The test results are shown in Table 1. Among them, the results of the cycle test of example 1 and comparative examples 1 to 4 are shown in fig. 4. As can be seen from the figure, the implementationThe capacity retention rate of the material in the example 1 after 1000 cycles is 87%, the capacity retention rate of the material in the comparative example 1 after 1000 cycles is 77%, and the material in the example 1 has excellent cycle stability.

The tap densities of the composite materials of each example and comparative example were measured 3000 times with a Dandongbaut BT-303 tap density tester, and the normal temperature cycle properties and the volume expansion rate (cell thickness change) of the batteries prepared in each example and comparative example were recorded in Table 1.

TABLE 1

From the comparative ratios and the performance data of example 1, it can be seen that when a silicon-carbon composite material is prepared by using an aqueous solvent, the addition of a binder, a surfactant and the mechanical fusion of the silicon-carbon composite material can improve the tap density of the material, which is beneficial to improving the volume energy density of a battery. The dissolved oxygen removal can inhibit the battery expansion by 20.0 percent and improve the cycle retention rate of 1000 weeks by 10.1 percent. The carboxymethyl chitosan added as the binder can inhibit the expansion of the battery by 22.1 percent and improve the cycle retention rate of 1000 weeks by 10.6 percent. The addition of the surfactant methyl acrylate-acrylic acid can inhibit the battery expansion by 20.6 percent and improve the cycle retention rate of 1000 weeks by 11.5 percent. The mechanical fusion can inhibit the battery from expanding by 23.0 percent and improve the cycle retention rate of 1000 weeks by 7.8 percent.

From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by 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 preparation method of the silicon-carbon composite anode material is characterized by comprising the following steps of:

step S1, removing dissolved oxygen in water to obtain oxygen-free water;

step S2, performing wet ball milling on the silicon material and the surfactant to obtain nano silicon slurry;

step S3, mixing graphite, a binder and the nano-silicon slurry to form precursor slurry;

step S4, spray drying the precursor slurry to obtain black powder;

step S5, mixing the black powder with a carbon source to form a mixture; and

step S6, roasting the mixture to obtain the silicon-carbon composite negative electrode material,

wherein the water used in step S2 is the oxygen-free water obtained in step S1, and when the water is used in step S3, the water used is the oxygen-free water obtained in step S1.

2. The method according to claim 1, wherein the step S1 comprises removing dissolved oxygen in water by a physical method and/or a chemical method, the physical method comprises introducing nitrogen gas into the water to replace the dissolved oxygen in the water, the chemical method comprises adding a reducing agent to the water to reduce the dissolved oxygen, the reducing agent is preferably any one or more of hydrazine, hydrazine hydrate, carbohydrazide and erythorbic acid, and the mass usage amount of the reducing agent relative to the water is preferably 0.01-2.0: 100, and preferably 1.0-2.0: 100.

3. The method as claimed in claim 1, wherein in the step S2, the surfactant is selected from one or more of sodium hexadecyl diphenyl ether disulfonate, methyl acrylate-acrylic acid, fatty alcohol-polyoxyethylene ether, hexadecyl trimethyl ammonium bromide, sodium polyacrylate, ammonium polyacrylate, and sodium polyphosphate ammonium polymethacrylate, and preferably, the silicon material is micron-sized silicon powder.

4. The method according to claim 1, wherein in the step S2, the mass ratio of the silicon material, the surfactant and the grinding balls is 1: (0.01-1.0): (1-5); preferably, the solid content of the nano silicon slurry is 5-50%; the stirring speed of the ball mill used in the step S2 is preferably 500-2000 rpm, and the stirring time is preferably 10-30 hours.

5. The method as claimed in claim 1, wherein in step S3, the binder is selected from one or more of polyvinyl alcohol, polyimide, chitosan, carboxymethyl chitosan, polyvinyl pyrrolidone, polyacrylic acid and its sodium salt, carboxymethyl cellulose and its sodium salt, alginic acid and its sodium salt, and preferably the silicon material, the graphite and the binder are mixed in a mass ratio of 1: (1-9): (0.01 to 0.5); preferably, the solid content of the precursor slurry is adjusted to be 5-50% by adopting the oxygen-free water.

6. The preparation method according to claim 1, wherein the precursor slurry is formed in step S3 by stirring, the stirring speed is 1000-5000 rpm, and the stirring time is 10-20 h.

7. The preparation method according to claim 1, wherein in the step S4, the inlet temperature of the spray drying is 300-800 ℃, the outlet temperature is 50-250 ℃, preferably the feeding rate of the precursor slurry is 0.1-5L/min, and the rotation speed of the spray atomizing disk is 1000-50000 rpm.

8. The method according to claim 1, wherein in step S5, the carbon source is selected from one or more of coal pitch, petroleum pitch, natural pitch, phenolic resin, and epoxy resin, and the mass ratio of the carbon source to the black powder is (0.01-1): 1.

9. the preparation method according to claim 1, wherein the roasting of the step S6 comprises two-stage roasting, wherein the first-stage roasting temperature is 200-500 ℃, and the first-stage roasting time is 0.5-4 h; the second-stage roasting temperature is 550-1200 ℃, the second-stage roasting time is 1-6 h, and preferably, the temperature rising rate reaching the first-stage roasting temperature and the temperature rising rate reaching the second-stage roasting temperature are respectively and independently 1-20 ℃/min.

10. The preparation method according to claim 1, further comprising a process of mechanically fusing the silicon-carbon composite negative electrode material, preferably, when the mechanical fusion is performed, the rotating speed of a fusion machine is 1000-3000 rpm, and the fusion time is 0.5-2.5 h.