CN105118996B - A kind of process for dispersing of nano-silicon - Google Patents

Abstract

The invention discloses a method for dispersing nano-silicon, which comprises the following steps: (1) dissolving nano-silicon powder in a polar solvent and stirring to form a nano-silicon liquid with a solid content of 1% to 20%; (2) using physical Dispersing and pre-dispersing the nano-silicon liquid; (3) adding a multi-anchor group polyether hyperdispersant to the pre-dispersed solution in step (2), and stirring evenly to obtain a uniformly dispersed nano-silicon dispersion. The present invention adopts the method of combining mechanical dispersion and chemical dispersion, and selects a multi-anchor group ether hyperdispersant that matches the surface of nano-silicon and the properties of the solvent, and obtains nano-silicon with good dispersibility and stability. The pre-dispersion liquid improves the serious agglomeration problem encountered in the application of nano-silicon powder in the application of silicon-carbon anode materials.

Description

A kind of dispersion method of nano-silicon

technical field

The invention relates to a method for dispersing nano-silicon, in particular to a method for dispersing nano-silicon by using a multi-anchor group polymer hyperdispersant.

Background technique

Silicon is the focus material of lithium-ion battery anode material research in recent years. Silicon has a very high theoretical capacity (up to 4200mAh/g), and is an excellent substitute for graphite materials. It is much larger than the theoretical capacity of graphite, and it is not solvated like graphite. However, it has a huge volume effect in the process of charging and discharging, up to 400%. Due to its huge volume effect during the cycle, the pure silicon material will repeatedly form an SEI film on its surface during the repeated expansion and contraction during the charging and discharging process, which consumes the electrolyte, resulting in a rapid decline in capacity, and in the process of expansion and contraction. In the process, the conductive network of the material will be destroyed, and its conductivity will deteriorate rapidly, so that the capacity will rapidly decay to almost zero.

In order to avoid the harm caused by its volume expansion to electrode materials, many solutions have emerged, such as nano-sized silicon materials, porous silicon materials, silicon-metal composite materials, and silicon-carbon composite materials. The original intention of its design is to alleviate the harm caused by the huge system effect of silicon materials. The main design ideas are mainly based on the following categories: 1) The nanometerization of silicon materials is to reduce the degree of volume expansion; 2) The "rivet effect" uses external The stress suppresses the volume effect, which leads to various coatings on the silicon surface; 3) the preparation of volume buffer materials. The idea of this type of design is that there are some soft materials around the silicon particles, which can inhibit the expansion of silicon on the electrode. destroy.

Silicon carbon material is a research hotspot at the present stage, and it is the next-generation commercial product that is expected to replace graphite anode material on a large scale. It has the advantages of excellent electrical conductivity, various synthesis methods, and relatively low cost. In the preparation process of silicon-carbon anode materials with excellent performance, one of the key points is the dispersion of nano-silicon materials. The preparation of uniformly dispersed and stable silicon pre-dispersion liquid is of great significance in the preparation process of silicon-carbon materials. If the pre-dispersion cannot be in a stable dispersion state during storage and material synthesis, then the subsequent material preparation will lead to serious agglomeration of silicon, and larger silicon agglomerated particles will appear, even after the synthesis of silicon-carbon negative electrode materials. There is a huge volume effect, which leads to poor cycle retention of battery materials and other consequences.

Chinese patent CN 102702796A, published on October 3, 2012, discloses a method for improving the dispersion performance of nano-silicon grinding fluid, which discloses that micro-silicon particles are ground into nano-silicon particles by ball milling, and an anionic dispersant is added during the grinding process to make the dispersion The adsorption of the agent on the surface of nano-silicon particles improves the dispersibility of silicon grinding fluid. Chinese patent CN 1544335A, published on November 10, 2004, discloses that different anionic dispersants are added to the titanium dioxide dispersion, all of which have achieved a certain dispersion effect. However, the above-mentioned methods all use common dispersants in the market directly, and further research on the surface properties of the solute to be dispersed and the screening of dispersants has not been carried out, and the dispersion and stabilization effects achieved are not ideal. At present, many hyperdispersants have been designed for nanomaterials, but the molecular structure design of most hyperdispersants is unreasonable, resulting in unsatisfactory effects.

Therefore, it is very important to select a suitable dispersion method and suitable dispersant under the premise of fully considering the surface properties of the dispersion medium and the solvent system in which to prepare a stable nano-silicon dispersion.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a nano-silicon dispersion method.

In order to solve the problems of the technologies described above, the technical solution proposed by the present invention is:

A method for dispersing nano-silicon, comprising the following steps:

(1) dissolving nano-silicon powder in a polar solvent and stirring to form a nano-silicon liquid with a solid content of 1% to 20%;

(2) Pre-disperse the nano-silicon liquid by using physical dispersion to open the soft agglomeration of nano-silicon;

(3) Add multi-anchor group polyether hyperdispersant to the pre-dispersed solution in step (2), and stir evenly to obtain a uniformly dispersed nano-silicon dispersion.

In the above dispersion method, preferably, the anchoring group acting group of the polyether hyperdispersant with multiple anchoring groups is a carboxyl group, and the solvation chain is a polyether chain.

In the above dispersion method, preferably, the anchoring group of the multi-anchor group polyether hyperdispersant is a polyacrylic acid chain, and its monomer structure is RCH=CH-COOH, wherein R is an alkyl group; the solvation chain It is a polyvinyl methyl ether chain, and its monomer structure is CH ₂ =CH-OCH ₃ .

In the above-mentioned dispersion method, preferably, the structural formula of the multi-anchor group polyether hyperdispersant is as follows:

In the formula, R is an alkyl group.

In the above dispersion method, preferably, the degree of polymerization of the anchoring group is 10<n<30, and the degree of polymerization of the solvated chain is 15<m<40. Appropriate degree of polymerization can ensure good dispersion effect.

The above-mentioned dispersion method, preferably, in the step (2), the method of physical dispersion is disperser treatment and/or ultrasonic dispersion treatment; wherein the rotor speed is 5000～50000r/min during the disperser treatment, and the treatment time is 0.1～ 300min; for ultrasonic dispersion treatment, the power of the instrument is 300-2000w, the temperature is controlled at 5-50°C, and the treatment time is 0.1-300min.

In the above dispersion method, preferably, in the step (1), the polar solvent is water, glycerin or dimethyl sulfoxide.

In the above-mentioned dispersion method, preferably, in the step (3), the amount of multi-anchor group ether hyperdispersant added is 1% to 50% of the mass of the nano silicon powder; the stirring time is 0.5 to 24 hours.

The present invention investigates the electrical properties of the surface of nano-silicon and the groups carried on the surface, and the results of particle surface Zeta potential measurement of several common nano-silicon powders on the market are shown in Table 1. It can be seen that various manufacturers prepare them in different ways. The surface of nano silicon powder is negatively charged.

According to the DLOV theory, if a cationic dispersant is used for the dispersion of such particles, the surface charge will be neutralized and the van der Waals force will be greater than the repulsive force, leading to rapid agglomeration; and if an anionic dispersant is used, effective repulsion cannot occur due to the mutual repulsion of the same charges. adsorption. Through the infrared spectrum analysis of the nano-silicon powder produced by the Guilin Institute of Mineral Geology, as shown in Figure 1, it can be known that the surface of the nano-silicon molecule is rich in a large number of hydroxyl groups, so the carboxyl group is selected for the anchoring group of the dispersant. Considering that the hydrogen bond between the carboxyl group and the hydroxyl group is a weak force, a single anchoring group will not be able to form a firm bond with the nano-silicon particles, so the anchoring group segment must have a structure of multiple hydroxyl groups. In the choice of solvation chain: in the water system, it must have good water solubility and good steric hindrance. Here we choose polyether chain as the solvation chain, which has strong polar functional groups. It can ensure that the long-chain structure is fully stretched in polar solvents to form sufficient steric hindrance. Therefore, the anchor chain composed of multiple carboxyl groups and the solvation chain composed of polyether are selected to fully meet the requirements of nano-silicon dispersion in polar systems. The schematic diagram of the interaction between the multi-anchor group hyperdispersant and nano-silicon particles is shown in Figure 2. The anchor groups of the hyper-dispersant and the hydroxyl groups on the surface of nano-silicon undergo hydrogen bonding, and the solvation chains of polyethers extend into the solvent to play a role. hindrance.

Table 1 Zeta potential of nano-silicon from different manufacturers

Compared with the prior art, the present invention has the advantages of:

(1) The molecular structure of the polyether hyperdispersant with multiple anchoring groups is simple and effective, and the monomer of the anchoring group is an alkenoic acid, which is simple in structure and easy to synthesize; polyvinyl methyl ether is selected on the solvation chain, and its structure Simple and highly water soluble.

(2) The present invention has adopted the method that mechanical dispersion and chemical dispersion are combined, and has selected the multi-anchor group ether hyperdispersant that matches mutually with nano-silicon surface and solvent property, has obtained dispersibility and stability all better The nano-silicon pre-dispersion liquid improves the serious agglomeration problem encountered by nano-silicon powder in the application of silicon-carbon anode materials.

(3) The entire process of the present invention is carried out in a polar solvent, which creates conditions for the subsequent low-cost and multi-selective treatment of the silicon-carbon negative electrode material.

(4) The present invention adopts multi-anchor group ether hyperdispersant to disperse nano-silicon, and the dispersion effect is much better than traditional nano-silicon dispersion method. At the same time, the dispersion method of the present invention has simple process, and only needs mechanical dispersion and super-dispersion agent can achieve good results.

Description of drawings

Figure 1 is the infrared spectrum of nano-silicon of Guilin Institute of Mineral Geology.

Fig. 2 is a schematic diagram of the effect of dispersing nano-silicon particles by using multi-anchor group ether hyperdispersant in the present invention.

FIG. 3 is an SEM image of the nano-silicon dispersion liquid prepared in Example 1 of the present invention.

FIG. 4 is an SEM image of undispersed nano-silicon in Example 1 of the present invention.

detailed description

In order to facilitate the understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, the various reagents and raw materials used in the present invention are commercially available products or products that can be prepared by known methods.

Example 1:

A method for dispersing nano-silicon of the present invention, comprising the following steps: adding nano-silicon powder (severe agglomeration, average particle is about 80nm) produced by Guilin Institute of Mineral Geology into pure water and stirred evenly to form a solid content of 1% placed in an ultrasonic cleaner to control the water temperature at 20-30°C and disperse for 20 minutes under the condition of ultrasonic power of 300w, and then add polyether hyperdispersants with multi-anchor groups (molecular weight: 2000 ), using mechanical stirring for 6h to obtain a uniformly dispersed nano-silicon dispersion. The particle size of the nano-silicon dispersion liquid was measured to be 191nm; its scanning electron microscope picture is shown in Figure 3,

The particle size of the nano-silicon dispersion prepared in this example was sealed and left for 15 days and measured to be 207 nm, and then placed in a constant temperature water bath at 80° C. for 40 hours, and the particle size was measured to be 201 nm.

The SEM image of the nano-silicon particles used in this example before being treated with a dispersant is shown in Figure 4, the particles are seriously agglomerated, and there are basically no primary particles. It can be seen from the comparison of Fig. 3 and Fig. 4 that the dispersion method of the present invention greatly improves the dispersion degree of nano-silicon.

Comparative example 1:

The specific process of nano-silicon dispersion in this comparative example is: add nano-silicon powder with a particle size of 80nm to pure aqueous solution and stir evenly to form a nano-silicon liquid with a solid content of 1%, and place it in an ultrasonic cleaner to control the water temperature at 20-30°C Disperse for 20 minutes under the condition of the silicon powder, then add hexadecyltrimethylammonium bromide with 5% weight of silicon powder, and stir for 6 hours with a mechanical stirring paddle. After standing for 30 minutes, the particle size of the nano-silicon dispersion liquid was measured to be 723nm. After standing for 4 days, the layering of the turbid liquid and a large amount of precipitation appeared at the bottom of the beaker.

Example 2:

A method for dispersing nano-silicon of the present invention, comprising the following steps: adding nano-silicon powder (severe agglomeration, average particle is about 80nm) produced by Guilin Institute of Mineral Geology into pure water and stirred evenly to form a solid content of 1% Using a high-speed disperser to disperse at a speed of 30,000r/min for 20 minutes, then add a multi-anchor group polyether hyperdispersant (molecular weight: 2000) with 10% of the mass of silicon powder, and use mechanical stirring for 6 hours to obtain a uniformly dispersed nano-silicon liquid. Silicon dispersion. The particle size of the nano-silicon dispersion was measured to be 233nm; the particle size of the nano-silicon dispersion was measured to be 231nm after being sealed and left to stand for 15 days.

Comparative example 2:

The nano-silicon dispersion process of this comparative example is as follows: the nano-silicon powder (agglomeration is serious, average particle is 80nm) produced by Guilin Institute of Mineral Geology is added to pure water and stirred evenly to form a silicon pre-dispersion with a solid content of 1%. , use a high-speed disperser to disperse at a speed of 30000r/min for 20min, then add sodium lauryl sulfate with 10% weight of silicon powder, and stir for 6h with a mechanical stirring paddle. After standing still for 30 minutes, the particle size of the nano-silicon dispersion liquid was measured to be 521nm. After standing still for 4 days, it can be seen that most of the dispersion basically settled at the bottom of the beaker, and there was a relatively obvious stratification of the turbid liquid.

Example 3:

A method for dispersing nano-silicon of the present invention, comprising the following steps: adding nano-silicon powder (severe agglomeration, average particle is about 80nm) produced by Guilin Institute of Mineral Geology into pure water and stirred evenly to form a solid content of 5% placed in an ultrasonic cleaner to control the water temperature to 20-30°C and disperse for 20 minutes under the condition of an ultrasonic power of 300w, and then add a multi-anchor group polyether hyperdispersant (molecular weight: 2000 ), using mechanical stirring for 6h to obtain a uniformly dispersed nano-silicon dispersion. The particle size of the nano-silicon dispersion was measured to be 223nm. The particle size was measured to be 231nm after being sealed and left for 15 days, and the particle size was measured to be 229nm after being placed in a constant temperature water bath at 80°C for 40 hours.

Comparative example 3:

The nano-silicon dispersion process of this comparative example is: the nano-silicon powder (agglomeration is serious, average particle is 80nm) produced by Guilin Institute of Mineral Geology is added into pure water and stirred evenly to form a silicon pre-dispersion liquid with a solid content of 5%. , placed in an ultrasonic cleaning apparatus to disperse for 20 minutes under the conditions of controlling the water temperature to 20-30°C and the ultrasonic power to 300w, then adding polyvinylpyrrolidone (molecular weight: 5000) with 20% silicon powder weight, and using a mechanical stirring paddle to stir for 6 hours. After standing still for 30 minutes, the measured particle size was 221nm. After standing still for 15 days, it can be seen that basically part of the solution settled at the bottom of the beaker, and visible stratification of turbid liquid appeared.

As can be seen from the above specific examples and comparative examples, the present invention utilizes the method of combining physical dispersion and chemical dispersion and selects a matching multi-anchor polymer hyperdispersant to obtain silicon with good dispersibility and stability. The dispersion liquid shows a better effect than the traditional dispersion method, and better solves the problem of agglomeration in the use of nano-silicon in the silicon-carbon negative electrode.

Claims (5)

1. a dispersion method of nano-silicon, is characterized in that, comprises the following steps: (1) dissolving nano-silicon powder in a polar solvent and stirring to form a nano-silicon liquid with a solid content of 1% to 20%; (2) utilize physical dispersion to carry out pre-dispersion to described nano-silicon liquid; (3) Add multi-anchor group polyether hyperdispersant in the solution after step (2) predispersion, and stir evenly, obtain the evenly dispersed nano-silicon dispersion liquid; Wherein, the anchoring group of the multi-anchor group polyether hyperdispersant is a polyacrylic acid chain, and its monomer structure is RCH=CH-COOH, wherein R is an alkyl group; the solvation chain is polyvinyl methyl ether chain, its monomer structure is CH ₂ =CH-OCH ₃ . 2. dispersion method as claimed in claim 1, is characterized in that, described multi-anchor group polyether hyperdispersant structural formula is as follows: In the formula, R is an alkyl group; The degree of polymerization of the anchoring group is 10<n<30, and the degree of polymerization of the solvated chain is 15<m<40. 3. The dispersion method according to any one of claims 1 to 2, characterized in that, in the step (2), the method of physical dispersion is disperser processing and/or ultrasonic dispersion processing; wherein the rotor is processed by disperser The speed is 5000-50000r/min, and the processing time is 0.1-300min; for ultrasonic dispersion treatment, the power of the instrument is 300-2000w, the temperature is controlled at 5-50°C, and the processing time is 0.1-300min. 4. The dispersion method according to any one of claims 1-2, characterized in that, in the step (1), the polar solvent is water, glycerin or dimethyl sulfoxide. 5. dispersion method as described in any one of claim 1～2, it is characterized in that, in described step (3), the add-on of multi-anchor group ether hyperdispersant is 1%～of nano silicon powder quality 50%; the stirring time is 0.5~24h.