CN110289400B

CN110289400B - Dispersing method of nano silicon

Info

Publication number: CN110289400B
Application number: CN201910443514.7A
Authority: CN
Inventors: 范珂铭
Original assignee: Sichuan Chuangneng New Energy Material Co ltd
Current assignee: Sichuan Chuangneng New Energy Material Co ltd
Priority date: 2019-05-27
Filing date: 2019-05-27
Publication date: 2021-04-06
Anticipated expiration: 2039-05-27
Also published as: CN110289400A

Abstract

The invention discloses a method for dispersing nano silicon, which comprises the following steps: (1) the coarse silicon powder is pulverized into micro silicon powder with the average particle size of 3-5 mu m by air flow; (2) dissolving micro silicon powder in a polar solvent and stirring to prepare a silicon solution with the solid content of 10-15%; (3) ball-milling the silicon solution by adopting a wet ball-milling process, adding a hexadecyl trimethyl ammonium bromide ion dispersant in the ball-milling process, and ball-milling to obtain the nano silicon powder. According to the invention, the hexadecyl trimethyl ammonium bromide ion dispersing agent is accurately added in the ball milling process, so that the fluidity of the slurry is effectively improved, the stability of the slurry is enhanced, and the ball milling efficiency is improved, so that the prepared nano silicon powder has good tabletting performance, uniform particle size and a better dispersing structure; the electrochemical performance of the prepared silicon powder is greatly improved, so that the electrochemical performance of the silicon electrode material can be effectively improved, the specific capacity and the coulombic effect of the battery are improved, and the cycle performance of the battery is improved.

Description

Dispersing method of nano silicon

Technical Field

The invention belongs to the technical field of new energy materials, and particularly relates to a method for dispersing nano silicon.

Background

In the currently researched lithium ion battery cathode material system, metal alloy materials such as Si, Sn, Al and the like can form multi-lithium alloy with Li, so that the multi-lithium alloy has a theoretical specific capacity much higher than that of the traditional graphite cathode material, and meanwhile, the lithium releasing and inserting potential of the metal alloy materials is higher than that of the traditional graphite cathode material, lithium dendrite is not easily generated in the rapid charging and discharging process, and the safety performance is excellent. Among them, simple substance silicon has the highest theoretical specific capacity of 4200mAh/g, lithium intercalation potential of 0.2V (vs. Li/Li +), good safety performance, abundant reserves and high cost performance, and has recently gained extensive attention and research in academia and industry, and is considered as the first choice of the next generation of ideal negative electrode material. However, silicon anode materials also have certain defects in practical application, which leads to slow commercialization process, because silicon is an alloy anode, each silicon atom can carry about four lithium atoms, the lithiation mechanism causes a huge volume change due to the intercalation of a large amount of lithium atoms, the volume expansion is about 420% when switching from Si to li4.4si, the large volume expansion/contraction during lithium intercalation/deintercalation causes large stress to crack and crush Si, and the pulverization and peeling of active materials on the silicon electrode cause the loss of electrical contact between silicon particles and between particles and current collectors, thereby causing the rapid attenuation of battery capacity and even complete failure.

In order to solve the problem of material pulverization, researchers propose that nano silicon-based materials with centralized and stable particle size distribution and adjustable particle size are prepared by nano silicon, the volume expansion effect of silicon can be relieved, the diffusion distance of lithium ions is shortened, good electric contact and electric conduction are provided, the transmission path of the lithium ions is shortened, the electrochemical cycle performance of the silicon-based materials is improved, and the cycle life of a battery is prolonged.

Therefore, the nano silicon substrate is prepared by adopting a wet ball milling mode, the particle size of the silicon powder particles is continuously reduced along with the continuous deepening of the ball milling, when the silicon powder particles are refined to a certain degree, the specific surface area and the specific surface energy of the silicon powder particles are gradually increased, the strength and the hardness of the silicon powder particles are also increased, the particle defects are reduced, the ball milling difficulty is increased, the particle agglomeration effect is also enhanced, and when the agglomerates are processed and used in the later stage of the powder, the agglomerates are difficult to open among molecules due to high cohesive force and are difficult to uniformly disperse in an organic solvent system and a processing matrix of a battery pole piece in the later stage, so that the performance of the material is. Therefore, the dispersing agent is added in the ball milling process, so that the interaction among particles can be effectively reduced, the degree of adhesion of fine particles on a grinding medium is reduced, the flow of grinding materials is promoted, the energy consumption of ball milling is reduced, and the product quality and the production efficiency are improved.

The dispersant is in various types, including three types, i.e., cationic, anionic, nonionic, and mixed types. Dispersants prevent agglomeration with each other in suspension by interacting with the particle surface, and their mechanism of action is roughly classified into three types: electrostatic repulsion effects, steric hindrance effects, and electrostatic steric stabilization effects.

The ionic dispersing agent is electrolyzed into charged ions or hydrophilic and lipophilic groups in a water dispersion medium, and is adsorbed on the surface of solid particles to form a charged protective barrier layer, namely a diffusion double electric layer, so that the electrostatic repulsion is increased, the particles are difficult to collide and agglomerate, and the electrostatic stable dispersing effect is achieved.

The molecular structure of the non-ionic high molecular polymer such as a hyper-dispersant comprises two parts of an anchoring group and a solvation chain, wherein the anchoring group is adsorbed on the surface of solid particles, and the solvation chain is fully expanded in a medium to form a position resistance layer to prevent the flocculation and agglomeration of the solid particles so as to achieve the effect of steric hindrance.

The molecular weight of the polymeric dispersant is generally in the range of 103-104, and when the molecular chain is too short, it is difficult to overcome the van der Waals force, and when the molecular chain is too long, it is easy to bridge and connect to perform thickening effect. The polyelectrolyte is electrolytically adsorbed on the particle surface in the water dispersion medium, and the charged polymer molecular layer can repel the peripheral ions through the electrostatic repulsion effect of the charges carried by the polymer molecular layer and can also make the particles bounce off each other by utilizing the steric hindrance of the solvation chain, so that the stabilization effect of the electrostatic steric hindrance is exerted.

At present, most of the nano-silicon is added with a common dispersing agent in the ball milling process, and the dispersing agent cannot be further screened according to the surface property of a dispersing solute.

Therefore, the selection of a proper dispersing agent under the premise of comprehensively considering the surface property of a dispersing medium and a solvent system is important for preparing stable nano silicon.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method for dispersing nano-silicon, which is directed to the deficiencies of the prior art.

The technical scheme adopted by the invention is as follows: a method for dispersing nano silicon comprises the following steps:

(1) the coarse silicon powder is pulverized into micro silicon powder with the average particle size of 3-5 mu m by air flow;

(2) dissolving micro silicon powder in a polar solvent and stirring to prepare a silicon solution with the solid content of 10-15%;

(3) ball-milling the silicon solution by adopting a wet ball-milling process, adding a hexadecyl trimethyl ammonium bromide ion dispersant in the ball-milling process, and ball-milling to obtain the nano silicon powder.

Preferably, the polar solvent used in step (2) is absolute ethanol.

Preferably, the silicon solution prepared in step (2) has a solid content of 15%.

Preferably, the ball-to-material ratio of the wet ball milling in the step (3) is 3:1, the diameter of the medium is 1mm, the ball milling rotation speed is 1200r/min, the ball milling time is 8 hours, and the ball milling temperature is controlled to be 26-30 ℃.

Preferably, the cetyl trimethyl ammonium bromide ion dispersant is added in the step (3) in an amount of 0.5-2.5% of the total amount of the silicon solution.

Preferably, the cetyl trimethyl ammonium bromide ion dispersant is added in the step (3) in an amount of 1.5% of the total amount of the silicon solution.

A nano silicon powder prepared by a nano silicon dispersion method is used for a lithium ion battery cathode material.

The invention has the beneficial effects that:

(1) the hexadecyl trimethyl ammonium bromide ion dispersing agent is added in the ball milling process, so that the prepared nano silicon powder has good sheeting performance, uniform particles and a better dispersing structure;

(2) the adding amount of the hexadecyl trimethyl ammonium bromide ion dispersing agent in the ball milling process is accurately controlled, so that the fluidity of the slurry is effectively improved, the stability of the slurry is enhanced, the ball milling efficiency is effectively improved, and the average particle size of silicon powder particles is reduced;

(3) by adding the hexadecyl trimethyl ammonium bromide ion dispersing agent, the electrochemical performance of the prepared silicon powder is greatly improved, so that the electrochemical performance of the silicon electrode material can be effectively improved, the specific capacity and the coulombic effect of the battery are improved, and the cycle performance of the battery is improved.

Drawings

FIG. 1 is a TEM image of nano-silicon powder prepared in example 1 of the present invention;

FIG. 2 is a schematic diagram showing the relationship between the amount of the hexadecyl trimethyl ammonium bromide ion dispersant and the particle size of the nano silicon powder particles after ball milling;

FIG. 3 is a TEM image of nano-silicon powder prepared in comparative example 1 of the present invention;

FIG. 4 is a TEM image of nano-silicon powder prepared in comparative example 2 of the present invention;

FIG. 5 is a TEM image of nano-silicon powder prepared in comparative example 3 of the present invention;

FIG. 6 is a TEM image of nano-silicon powder prepared in comparative example 4 of the present invention.

Detailed Description

The invention will be described in further detail with reference to the following drawings and specific embodiments.

Example 1

The method for dispersing nano silicon provided by the embodiment comprises the following steps:

(2) dissolving micro silicon powder in absolute ethyl alcohol, and stirring to prepare a silicon solution with the solid content of 15%;

(3) ball-milling the silicon solution by adopting a wet ball-milling process, wherein the ball-material ratio of ball milling is 3:1, the diameter of a ball-milling medium is 1mm, the ball-milling rotation speed is 1200r/min, the ball-milling time is 8h, the ball-milling temperature is 28 ℃, adding hexadecyl trimethyl ammonium bromide ion dispersing agent accounting for 1.5 percent of the total amount of the silicon solution in the ball-milling process, and obtaining the nano silicon powder after ball-milling. The particle diameter of the nano-silicon powder was measured to be 85nm, and the transmission electron micrograph thereof is shown in FIG. 1.

Example 2

(3) ball-milling the silicon solution by adopting a wet ball-milling process, wherein the ball-material ratio of ball milling is 3:1, the diameter of a ball-milling medium is 1mm, the ball-milling rotation speed is 1200r/min, the ball-milling time is 8h, the ball-milling temperature is 26 ℃, and a hexadecyl trimethyl ammonium bromide ion dispersant accounting for 0.5 percent of the total amount of the silicon solution is added in the ball-milling process to obtain the nano silicon powder after ball-milling.

Example 3

(3) ball-milling the silicon solution by adopting a wet ball-milling process, wherein the ball-material ratio of ball milling is 3:1, the diameter of a ball-milling medium is 1mm, the ball-milling rotation speed is 1200r/min, the ball-milling time is 8h, the ball-milling temperature is 27 ℃, and a hexadecyl trimethyl ammonium bromide ion dispersant accounting for 1 percent of the total amount of the silicon solution is added in the ball-milling process to obtain the nano silicon powder after ball-milling.

Example 4

(3) ball-milling the silicon solution by adopting a wet ball-milling process, wherein the ball-material ratio of ball milling is 3:1, the diameter of a ball-milling medium is 1mm, the ball-milling rotation speed is 1200r/min, the ball-milling time is 8h, the ball-milling temperature is 29 ℃, and a hexadecyl trimethyl ammonium bromide ion dispersant accounting for 2 percent of the total amount of the silicon solution is added in the ball-milling process to obtain the nano silicon powder after ball-milling.

Example 5

(3) ball-milling the silicon solution by adopting a wet ball-milling process, wherein the ball-material ratio of ball milling is 3:1, the diameter of a ball-milling medium is 1mm, the ball-milling rotation speed is 1200r/min, the ball-milling time is 8h, the ball-milling temperature is 30 ℃, and hexadecyl trimethyl ammonium bromide ion dispersing agents accounting for 2.5 percent of the total amount of the silicon solution are added in the ball-milling process to obtain the nano silicon powder after ball-milling.

The parameters of the ball milling process in examples 1, 2, 3, 4 and 5 are the same, wherein the ball milling temperature is within the temperature difference of 28 ± 2 ℃, but the addition amount of the cetyl trimethyl ammonium bromide ion dispersant added in each example is different, and the graph shown in fig. 2 is obtained by measuring the particle size of the silicon powder particles after grinding in each example. As shown in fig. 2, as the dosage of the cetyl trimethyl ammonium bromide ion dispersant is increased, the particle size of the nano silicon powder particles tends to decrease first and then increase.

The hexadecyl trimethyl ammonium bromide ionic dispersant is adsorbed on the surface of the particles to prevent mutual adsorption among the particles and prevent the particles from growing up, along with the increase of the content of the dispersant, the coating is more and more, the electrostatic and steric hindrance effect of the dispersant on the particles is enhanced, the fluidity of the slurry is obviously improved, the suspension force of the particles is increased, the stability of the slurry is enhanced, and the average particle size of the particles is also gradually reduced.

In the stage of 0.5% -1.5%, the average grain diameter of the silicon powder is sharply reduced along with the increase of the addition of the dispersing agent;

in the stage of 1.5% -2.5%, with the increase of the dispersing agent amount, the dispersing agent remains on the surface of the coated particles, and because the influence of the remaining non-coated dispersing agent on the particle size of the particles is not large, the dispersing agent amount is continuously increased, the supersaturation adsorption condition occurs, excessive dispersing agent molecules are mutually bridged into a network structure, the movement of the particles is greatly limited, so that the fluidity of the slurry is deteriorated, the coagulation is generated, the stability of the slurry is deteriorated, and the particle size of the particles is increased on the contrary.

At 1.5%, the minimum value is reached, the addition amount of the dispersing agent reaches a critical point, and all particles are completely coated, so that the best dispersing effect is achieved.

Therefore, the hexadecyl trimethyl ammonium bromide ion dispersant in the embodiment 1 is the optimal addition amount, and can achieve the best dispersion effect and ball milling effect, and the embodiment 1 is the optimal embodiment.

As can be seen from the study of the pH-Zeta potential diagram of the nano-silicon powder after ultrasonic treatment in high-purity water, the absolute value of the Zeta potential reaches the maximum value when the pH is 6. When the pH value is 6, the nano silicon powder can form stable colloid in water, and the surface of the powder is negatively charged. Therefore, the ionic dispersant can be selected to increase the negative charge on the surface of the particles, so that xi is increased and the electrostatic repulsion is increased; or the nonionic dispersant is selected to increase the steric hindrance effect so as to play a role in grinding aid and dispersion stabilization. Therefore, the materials can be selected from citric triamine, oleic acid, cetyl trimethyl ammonium bromide, polyvinyl alcohol and sodium hexametaphosphate.

Comparative example 1

The transmission electron microscope image of the nano-silicon prepared by ball milling in this example is as shown in fig. 3, which is basically the same as example 1 except that the cetyl trimethyl ammonium bromide dispersant is replaced by the citric triamine dispersant. When the triamine citrate is used as the ball milling dispersing agent, powder particles and polar molecules act, the particle spacing is reduced, the electrostatic attraction is used as a main acting force among the particles, the silicon powder particles are not uniformly dispersed, the crystal grains of a finished product are small, and the growth is not uniform.

Comparative example 2

The transmission electron microscope image of the nano-silicon prepared by ball milling in this example is substantially the same as that of example 1, except that the oleic acid dispersant is replaced by cetyl trimethyl ammonium bromide dispersant, as shown in fig. 4. When oleic acid is used as a ball milling dispersant, the distance between powder particles is in a proper distance, the electrostatic acting force of a liquid-solid dispersion system is small, the particles are uniformly dispersed, the crystal grains are coarse, a small amount of agglomeration exists, and the growth is uniform. However, oleic acid is formed by mixing various polar substances, has different electrostatic repulsive forces inside, can form multi-layer electrode potential layers in the same volume, and is not beneficial to powder refinement for a long time.

Comparative example 3

The transmission electron microscope image of the nano-silicon prepared by ball milling in this example is shown in fig. 5, which is basically the same as example 1 except that the cetyl trimethyl ammonium bromide dispersant is replaced by the polyvinyl alcohol dispersant. When the polyvinyl alcohol is used as a ball milling dispersing agent, hydroxyl on the polyvinyl alcohol is tightly adsorbed on the surfaces of solid particles in a hydrogen bond form, has good intermiscibility with ball milling, is fully extended in a medium to form a space steric hindrance layer, generates a steric hindrance effect among the solid particles, hinders the particles from agglomerating due to mutual collision, and prepares a nano silicon sample which is bright, large in sheet diameter and serious in agglomeration phenomenon; however, it is difficult to overcome the electrostatic effect because of the limited steric effect alone. Therefore, the dispersion stability of PVA is not strong.

Comparative example 4

The present example is substantially the same as example 1, except that cetyl trimethyl ammonium bromide dispersant is replaced by sodium hexametaphosphate dispersant, and the transmission electron microscopy image of the nano-silicon prepared by ball milling is shown in fig. 6. When sodium hexametaphosphate is used as a dispersing agent, the sodium hexametaphosphate is of an annular structure, the potential of the surface of the powder can be increased, stronger electrostatic repulsive force of an electric double layer can be generated through an electrostatic stabilization mechanism, a silicon powder system has a certain dispersing effect, the steric hindrance effect is weaker, negatively charged powder particles adsorb dispersing agent molecules with weak positive electricity, and a prepared nano silicon sample is bright, large in sheet diameter, non-uniform in particle size, caking, incomplete in particle depolymerization and non-uniform in particle distribution.

In the most preferred embodiment 1, cetyl trimethyl ammonium bromide is selected as a dispersing agent, H + ions are easily ionized by cetyl trimethyl ammonium bromide, so that silica powder particles with negatively charged surfaces interact with the dispersing agent under the driving of electrostatic effect, after dispersing agent macromolecules with opposite charges are adsorbed on the surfaces of the charged particles, charged dispersing agent molecular layers repel surrounding particles through the charges carried by the charged dispersing agent molecular layers, and the particles are prevented from moving close to each other due to steric hindrance effect, and the double effects of static electricity and steric hindrance generate a composite dispersion stabilizing effect on a silica powder system. Meanwhile, the hexadecyl trimethyl ammonium bromide has a longer hydrocarbon chain structure, and is easy to generate a winding structure on the surface of the particles, so that a good protective layer is formed, the repulsive force and the steric hindrance repulsive action of an electric double layer structure between the particles are increased, the particles can be ensured to be in a long-term suspension state without agglomeration, and as shown in figure 1, a single particle in the figure is clearly visible, the particle size distribution is relatively uniform, and no obvious agglomeration phenomenon occurs. The hexadecyl trimethyl ammonium bromide dispersing agent reduces the surface tension of the nano silicon powder, and the attractive force among particles is small, so that the dispersing agent has a good dispersing structure.

And the button cell prepared from the nano silicon powder prepared by dispersing the hexadecyl trimethyl ammonium bromide ion dispersing agent and the button cell prepared from the nano silicon powder prepared by non-dispersing are respectively subjected to electrochemical performance test by a blue electrochemical testing instrument, and the electrochemical performance of the button cell and the button cell is compared by the test experiment.

The button cell prepared from undispersed nano silicon powder has the specific first discharge capacity of 2424.7mAh/g, the specific first charge capacity of 1666.3mAh/g and the coulombic efficiency of 68.73%.

The button cell prepared from the nano silicon powder dispersed by the hexadecyl trimethyl ammonium bromide has the specific discharge capacity of 3165.9mAh/g, the specific charge capacity of 2681.2mAh/g and the coulombic efficiency of 84.69%. Compared with undispersed nano-silicon powder, the discharge efficiency is improved by 30.6%, the charging efficiency is improved by 60.9%, and the coulombic efficiency is improved by 15.96%.

Therefore, the electrochemical performance of the silicon powder is greatly improved by using the hexadecyl trimethyl ammonium bromide ion dispersing agent, because when the silicon powder is not dispersed, the particles are agglomerated to form large particles, in the charging and discharging process, the particles can be subjected to corresponding agglomeration stress action, the larger the large particle group is, the larger the stress is, and meanwhile, the larger the corresponding volume expansion effect of the silicon powder is, so that the electrode structure is damaged, and the specific capacity irreversible loss is larger. After the powder particles are dispersed and broken up, the stress on the small particles is relatively isolated, and the electrode structure is difficult to damage, so that the lithium source amount of the cyclic reaction in the electrochemical reaction is more, and the cyclic efficiency is higher, therefore, the electrochemical performance of the silicon electrode material can be effectively improved by carrying out dispersant treatment on the nano silicon powder, the specific capacity and the coulombic effect of the battery are improved, and the cyclic performance of the battery is improved.

The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any modification and replacement based on the technical solution and inventive concept provided by the present invention should be covered within the scope of the present invention.

Claims

1. A method for dispersing nano silicon is characterized in that: the method comprises the following steps:

(3) ball-milling the silicon solution by adopting a wet ball-milling process, wherein the ball-material ratio of the wet ball-milling is 3:1, the diameter of a medium is 1mm, the ball-milling rotation speed is 1200r/min, the ball-milling time is 8 hours, the ball-milling temperature is controlled to be 26-30 ℃, and hexadecyl trimethyl ammonium bromide ion dispersing agents accounting for 1.5 percent of the total amount of the silicon solution are added in the ball-milling process to obtain the nano-silicon powder after ball-milling.

2. The method for dispersing nano-silicon according to claim 1, wherein: and (3) adopting absolute ethyl alcohol as the polar solvent in the step (2).

3. The method for dispersing nano-silicon according to claim 1, wherein: the solid content of the silicon solution prepared in the step (2) is 15%.

4. The nano silicon powder prepared by any one of the nano silicon dispersion methods according to claims 1 to 3 is used as a negative electrode material of a lithium ion battery.