阅读说明：本技术 包覆型硅碳负极材料、其制备方法及锂离子电池 (Coated silicon-carbon negative electrode material, preparation method thereof and lithium ion battery ) 是由 杜孟衣 雷磊 赵晓磊 成信刚 于 2020-12-04 设计创作，主要内容包括：本发明提供了一种包覆型硅碳负极材料、其制备方法及锂离子电池。该包覆型硅碳负极材料的制备方法包括：在混捏装置中,将硅源、石墨和碳源进行加热及混合处理,得到预处理物料；将预处理物料进行炭化,得到包覆型硅碳负极材料。在进行炭化过程之前,先采用混捏装置对硅源、石墨和碳源进行加热及混合处理形成预处理物料。相比于常规的混合方式,在混捏装置中进行混合的同时进行加热能够大大提高硅源、碳源和石墨的捏合及包覆程度。经过炭化过程后,碳源和硅包覆在石墨表面,由于石墨具有一定的软度,这在一定程度上能够降低充放电过程中硅的膨胀率,进而提高碳硅材料的循环性能。同时上述制备方法简单易行,成本较低,易于工业化生产。(The invention provides a coated silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery. The preparation method of the coated silicon-carbon negative electrode material comprises the following steps: heating and mixing a silicon source, graphite and a carbon source in a kneading device to obtain a pretreated material; and carbonizing the pretreated material to obtain the coated silicon-carbon negative electrode material. Before the carbonization process, a kneading device is adopted to heat and mix the silicon source, the graphite and the carbon source to form a pretreatment material. Compared with the conventional mixing mode, the kneading and coating degrees of the silicon source, the carbon source and the graphite can be greatly improved by mixing and heating in the kneading device. After the carbonization process, the carbon source and the silicon are coated on the surface of the graphite, and the graphite has certain softness, so that the expansion rate of the silicon in the charge-discharge process can be reduced to a certain extent, and the cycle performance of the carbon-silicon material is further improved. Meanwhile, the preparation method is simple and easy to implement, low in cost and easy for industrial production.)

1. A preparation method of a coated silicon-carbon negative electrode material is characterized by comprising the following steps:

heating and mixing a silicon source, graphite and a carbon source in a kneading device to obtain a pretreated material;

and carbonizing the pretreated material to obtain the coated silicon-carbon negative electrode material.

2. The preparation method of the coated silicon-carbon anode material as claimed in claim 1, wherein the shearing rate of the kneading device is 10-22 r/min, the heating and mixing time is 1-5 h, and the heating time is 50-120 ℃.

3. The preparation method of the coated silicon-carbon anode material as claimed in claim 1 or 2, wherein the weight ratio of the silicon source, the graphite and the carbon source is 1 (2-10) to (2-20).

4. The preparation method of the coated silicon-carbon anode material according to claim 3, wherein the carbon source is one or more selected from the group consisting of sucrose, glucose, polyacrylic acid, polyvinyl chloride, polyethylene glycol, hydroxymethyl cellulose, sodium alginate, coal tar pitch and phenolic resin;

the silicon source is selected from silicon powder and/or silicon nanowires, preferably, the particle size of the silicon powder is 30-150 nm, the diameter of the silicon nanowires is 30-100 nm, and the length of the silicon nanowires is 20-100 microns.

5. The preparation method of the coated silicon-carbon anode material as claimed in claim 1, wherein the carbonization process comprises: heating at the speed of 2-10 ℃/min under an inert atmosphere, heating to 500-900 ℃, preserving heat for 2-4 hours, and naturally cooling to room temperature to obtain the coated silicon-carbon negative electrode material;

preferably, the inert atmosphere is argon.

6. The preparation method of the coated silicon-carbon anode material according to claim 1, wherein after the carbonization process is performed, the preparation method comprises the following steps: grinding the product obtained after the carbonization process to obtain the coated silicon-carbon negative electrode material;

preferably, the particle size d50 of the coated silicon-carbon negative electrode material is 5-12 μm.

7. A coated silicon-carbon anode material, which is prepared by the preparation method of any one of claims 1 to 6.

8. The preparation method of the coated silicon-carbon anode material as claimed in claim 7, wherein the coated silicon-carbon anode material has a porosity of 30-70% and a bulk density of 0.2-0.6 g/cm³。

9. A lithium ion battery comprising an anode material, wherein the anode material comprises the coated silicon carbon anode material of claim 7 or 8.

Technical Field

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

Background

The gram capacity of the Si-based negative electrode material is as high as 3500mAh/g, and compared with the graphite negative electrode material, the theoretical energy density of the coated silicon-carbon negative electrode material is more than 10 times higher than that of the graphite negative electrode material. However, the coated silicon-carbon negative electrode material has a natural defect that lithium is inserted into the unit cell of silicon to cause severe expansion of the silicon material, which causes rapid capacity reduction. In order to improve the cycling stability of the silicon-based negative electrode material, the existing silicon-carbon material mainly comprises a cladding type, an embedding type and a doping type, but the preparation methods are all complex.

In view of the above problems, it is necessary to provide a method for preparing a coated silicon carbon anode material with simple process, high cycle stability and high cycle capacity.

Disclosure of Invention

The invention mainly aims to provide a coated silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery, and aims to solve the problems that the conventional coated silicon-carbon negative electrode material cannot simultaneously meet the requirements of simple process, high cycle stability and high cycle capacity. To a problem of (a).

In order to achieve the above object, an aspect of the present invention provides a method for preparing a coated silicon-carbon anode material, including: heating and mixing a silicon source, graphite and a carbon source in a kneading device to obtain a pretreated material; and carbonizing the pretreated material to obtain the coated silicon-carbon negative electrode material.

Further, the shearing rate of the kneading device is 10-22 r/min, the time of the heating and mixing treatment process is 1-5 h, and the temperature of the heating process is 50-120 ℃.

Furthermore, the weight ratio of the silicon source, the graphite and the carbon source is 1 (2-10) to 2-20.

Further, the carbon source is selected from one or more of the group consisting of sucrose, glucose, polyacrylic acid, polyvinyl chloride, polyethylene glycol, hydroxymethyl cellulose, sodium alginate, coal tar pitch and phenolic resin; the silicon source is selected from silicon powder and/or silicon nanowires, preferably, the particle size of the silicon powder is 30-150 nm, the diameter of the silicon nanowires is 30-100 nm, and the length of the silicon nanowires is 20-100 microns.

Further, the carbonization process comprises: heating at the speed of 2-10 ℃/min under an inert atmosphere, heating to 500-900 ℃, preserving heat for 2-4 hours, and naturally cooling to room temperature to obtain a coated silicon-carbon negative electrode material; preferably, the inert atmosphere is argon.

Further, after the carbonization process is performed, the preparation method comprises the following steps: grinding a product obtained after the carbonization process to obtain a coated silicon-carbon negative electrode material; preferably, the particle size d50 of the coated silicon-carbon negative electrode material is 5-12 μm.

The application also provides a coated silicon-carbon negative electrode material which is prepared by the preparation method.

Furthermore, the porosity of the coated silicon-carbon negative electrode material is 30-70%, and the bulk density is 0.2-0.6 g/cm³。

Yet another aspect of the present application also provides a lithium ion battery comprising an anode material comprising the coated silicon carbon anode material provided herein.

According to the technical scheme, before the carbonization process, the silicon source, the graphite and the carbon source are heated and mixed by the kneading device to form the pretreatment material. Compared with the conventional mixing mode, the kneading and coating degrees of the silicon source, the carbon source and the graphite can be greatly improved by mixing and heating in the kneading device. After the carbonization process, the carbon source and the silicon source are coated on the surface of the graphite, and the graphite has certain softness, so that the expansion rate of silicon in the charge-discharge process can be reduced to a certain extent, and the cycle performance of the carbon-silicon material is further improved. Meanwhile, the preparation method is simple and easy to implement, low in cost and easy for industrial production. In conclusion, the coated silicon-carbon composite material prepared by the preparation method has the advantages of low expansion rate, good cycle performance, high cycle capacity, simple preparation process, low cost, easiness in industrial production and the like.

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 10000 times of a coated silicon carbon anode material prepared in example 1 of the present invention;

fig. 2 shows a cycle number-specific discharge capacity curve of a lithium ion battery made of the coated silicon-carbon negative electrode material prepared in example 1 of the present invention.

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 with reference to examples.

As described in the background art, the existing coated silicon carbon anode material cannot simultaneously satisfy the problems of simple process, high cycle stability and high cycle capacity. In order to solve the technical problem, the application provides a preparation method of a coated silicon-carbon anode material, which comprises the following steps: heating and mixing a silicon source, graphite and a carbon source in a kneading device to obtain a pretreated material; and carbonizing the pretreated material to obtain the coated silicon-carbon negative electrode material.

In the preparation method, before the carbonization process, the silicon source, the graphite and the carbon source are heated and mixed by the kneading device to form the pretreatment material. Compared with the conventional mixing mode, the kneading and coating degrees of the silicon source, the carbon source and the graphite can be greatly improved by mixing and heating in the kneading device. After the carbonization process, the carbon source and the silicon are coated on the surface of the graphite, and the graphite has certain softness, so that the expansion rate of the silicon in the charge-discharge process can be reduced to a certain extent, and the cycle performance of the carbon-silicon material is further improved. Meanwhile, the preparation method is simple and easy to implement, low in cost and easy for industrial production. In conclusion, the coated silicon-carbon composite material prepared by the preparation method has the advantages of low expansion rate, good cycle performance, high cycle capacity, simple preparation process, low cost, easiness in industrial production and the like.

In order to further improve the kneading degree of the carbon source, the silicon source and the graphite and the porosity of the subsequently formed silicon-carbon anode material, the shearing rate of the kneading device is preferably 10-22 r/min, the heating and mixing treatment process lasts for 1-5 h, and the heating process lasts for 50-120 ℃.

In a preferred embodiment, the weight ratio of the silicon source, the graphite and the carbon source is 1 (2-10) to (2-20). The weight ratio of the silicon source, graphite, and carbon source includes, but is not limited to, the above range, and limiting it to the above range is advantageous to further improve the cycle capacity of the silicon carbon anode material.

In the above preparation method, the silicon source and the carbon source may be selected from those commonly used in the art. For example, the carbon source includes, but is not limited to, one or more of the group consisting of sucrose, glucose, polyacrylic acid, polyvinyl chloride, polyethylene glycol, hydroxymethylcellulose, sodium alginate, coal tar pitch, and phenolic resin; the silicon source includes, but is not limited to, silicon powder and/or silicon nanowires. In order to further improve the carbon source coating property, the particle size of the silicon powder is preferably 30-150 nm, the diameter of the silicon nanowire is preferably 30-100 nm, and the length of the silicon nanowire is preferably 20-100 μm.

The carbonization process can adopt the process and the device which are commonly used in the field. Preferably, in the carbonization process, the pretreated material is placed in a quartz pot and carbonized in a high-temperature tube furnace.

The carbon source and the silicon source can be coated on the surface of the graphite by carbonizing the pretreated material, and the graphite has certain softness, so that the expansion of silicon in the charging and discharging process can be relieved to a certain extent. More preferably, the carbonization process comprises: heating at the speed of 2-10 ℃/min under an inert atmosphere, heating to 500-900 ℃, preserving heat for 2-4 hours, and naturally cooling to room temperature to obtain the coated silicon-carbon negative electrode material. The carbonization treatment of the pretreated material by adopting the process is favorable for improving the porosity of the silicon-carbon negative electrode material, so that the expansion rate of silicon in the charging and discharging process is further reduced, and the cycle performance and the structural stability of the carbon-silicon material are further improved. Preferably, the inert atmosphere is argon.

In order to further improve the structural stability of the carbon-silicon anode material, preferably, after the carbonization process is performed, the preparation method comprises the following steps: grinding a product obtained after the carbonization process to obtain a coated silicon-carbon negative electrode material; more preferably, the grinding process is carried out in a star ball mill, the ball-to-material ratio is (1-15): 1, and the particle size d50 of the coated silicon-carbon negative electrode material obtained after grinding is 5-12 μm.

The application also provides a coated silicon-carbon negative electrode material which is prepared by the preparation method.

In the preparation method, the silicon source, the graphite and the carbon source are heated and mixed to form a pretreatment material before the carbonization process. Compared with the conventional mixing mode, the kneading and coating degrees of the silicon source, the carbon source and the graphite can be greatly improved by mixing and heating in the kneading device. After the carbonization process, the carbon source and the silicon source are coated on the surface of the graphite, and the graphite has certain softness, so that the expansion rate of silicon in the charge-discharge process can be reduced to a certain extent, and the cycle performance of the carbon-silicon material is further improved. Meanwhile, the preparation method is simple and easy to implement and low in cost. In conclusion, the coated silicon-carbon composite material prepared by the preparation method has the advantages of low expansion rate, good cycle performance, high cycle capacity, simple preparation process, low cost and the like.

In order to further improve the comprehensive performance of the coated silicon-carbon negative electrode material, more preferably, the coated silicon-carbon negative electrode material has a porosity of 30-70% and a bulk density of 0.2-0.6 g/cm³。

Yet another aspect of the present application also provides a lithium ion battery comprising an anode material comprising the coated silicon carbon anode material provided herein.

The coated silicon-carbon composite material prepared by the preparation method has lower expansion rate, better cycle performance and higher cycle capacity, so that the lithium ion battery prepared from the coated silicon-carbon negative electrode material provided by the application also has excellent rate performance and structural stability.

The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.

Example 1

The preparation method of the coated silicon-carbon negative electrode material comprises the following steps:

heating and mixing a silicon source (silicon powder, 60nm), artificial graphite and cane sugar in a mixing kneading pot according to the weight ratio of 1:8.5:16 to obtain a pretreated material, wherein the heating temperature is 120 ℃, the rotating speed of a stirring knife of the mixing kneading pot is 20r/min, and the stirring time is 3 hours.

The uniformly stirred silicon powder, artificial graphite and carbon source are transferred into a quartz pot while the silicon powder, the artificial graphite and the carbon source are hot, the quartz pot is placed into a high-temperature tubular furnace, and carbonization treatment is carried out according to the following roasting curve: heating at the speed of 2 ℃/min, keeping the temperature for 3h after the temperature is increased to 860 ℃, naturally cooling to the room temperature, and introducing argon for protection in the whole process, wherein the volume of the argon is 50 ml/min.

And (3) placing the carbonized product in the high-temperature tubular furnace in a zirconium ball tank, ball-milling on a planetary ball mill at a ball-to-material ratio of 10:1 and a rotation speed of 550r/min, and sieving a ball-milled sample with a 400-mesh sieve to obtain the required carbon-silicon negative electrode material. The SEM is shown in FIG. 1.

Mixing the obtained silicon-carbon negative electrode material with conductive carbon black and polyvinylidene fluoride according to a weight ratio of 90: 5: 5, mixing the materials at a high speed to prepare slurry, and then coating, rolling and tabletting to obtain the electrode piece. The pole piece is prepared into a button cell and tested, and a graph of cycle times and specific capacity is shown in figure 2. The primary capacity is 603.3mAh/g, the primary efficiency is 94.8 percent, and the retention rate of 50-time circulation capacity is 93.1 percent.

Example 2

The differences from example 1 are: heating and mixing a silicon source (silicon powder, 60nm), artificial graphite and cane sugar in a mixing kneading pot according to the weight ratio of 1:2:20 to obtain a pretreated material, wherein the heating temperature is 120 ℃, the rotating speed of a stirring knife of the mixing kneading pot is 10r/min, and the stirring time is 5 hours.

The first capacity is 1405mAh/g, the first efficiency is 85 percent, and the 50-time circulation capacity retention rate is 82 percent.

Example 3

The differences from example 1 are: heating and mixing a silicon source (silicon powder, 60nm), artificial graphite and cane sugar in a weight ratio of 1:10:2 in a kneading pot to obtain a pretreated material, wherein the heating temperature is 120 ℃, the rotating speed of a stirring knife of the kneading pot is 22r/min, and the stirring time is 1 h. The first capacity is 580mAh/g, the first efficiency is 93 percent, and the retention rate of the 50-time circulation capacity is 92.1 percent.

Example 4

The differences from example 2 are: heating and mixing a silicon source (silicon powder, 60nm), artificial graphite and cane sugar in a mixing kneading pot according to the weight ratio of 1:5:10 to obtain a pretreated material, wherein the heating temperature is 120 ℃, the rotating speed of a stirring knife of the mixing kneading pot is 10r/min, and the stirring time is 5 hours.

The initial capacity is 820mAh/g, the initial efficiency is 89.9 percent, and the 50-time circulation capacity retention rate is 89.1 percent.

Example 5

The differences from example 2 are: in the heating and mixing treatment, the heating temperature is 50 ℃, and the stirring speed is 10 r/min.

The first capacity is 1385mAh/g, the first efficiency is 84.5 percent, and the capacity retention rate is 81.9 percent after 50 times of circulation.

Example 6

The differences from example 2 are: in the heating and mixing treatment, the heating temperature is 100 ℃, and the stirring speed is 20 r/min.

The primary capacity is 1398mAh/g, the primary efficiency is 84.8 percent, and the 50-time circulation capacity retention rate is 82.7 percent.

Example 7

The differences from example 2 are: in the heating and mixing treatment, the heating temperature is 80 ℃, and the stirring speed is 15 r/min.

The first capacity is 1390mAh/g, the first efficiency is 84 percent, and the 50-time circulation capacity retention rate is 82 percent.

Example 8

The differences from example 2 are: heating and mixing a silicon source (silicon powder, 60nm), artificial graphite and cane sugar in a weight ratio of 1:1:1 in a kneading pot to obtain a pretreated material, wherein the heating temperature is 140 ℃, the rotating speed of a stirring knife of the kneading pot is 30r/min, and the stirring time is 5 hours.

The initial capacity is 1890mAh/g, the initial efficiency is 81.6 percent, and the 50-time circulation capacity retention rate is 79.2 percent.

Example 9

The differences from example 1 are: the carbonization temperature was 500 ℃.

The initial capacity is 560.8mAh/g, the initial efficiency is 89.7 percent, and the 50-time circulation capacity retention rate is 86.7 percent.

Example 10

The differences from example 1 are: the carbonization temperature is 700 ℃.

The first capacity is 590.6mAh/g, the first efficiency is 92.4 percent, and the retention rate of 50-time circulation capacity is 90.2 percent.

Example 11

The differences from example 1 are: the carbonization temperature was 1100 ℃.

The first capacity is 520mAh/g, the first efficiency is 84.0 percent, and the 50-time circulation capacity retention rate is 80.5 percent.

Comparative example 1

The differences from example 1 are: stirring a mixture of a silicon source (silicon powder, 60nm), artificial graphite, sucrose and water, and then carrying out spray drying at 120 ℃ to obtain a pretreated material. And then sequentially carrying out carbonization treatment and grinding to obtain the carbon-silicon negative electrode material. The performance of the button cell is tested by the same method as that of the embodiment 1, and the test result shows that the first capacity of the button cell is 518mAh/g, the first efficiency is 79.5%, and the 50-time circulation capacity retention rate is 75.2%.

The coated silicon-carbon negative electrode materials prepared in the embodiments 1 to 11 have the porosity of 30 to 70 percent and the bulk density of 0.2 to 0.6g/cm³The porosity of the carbon-silicon anode material is far higher than that of the carbon-silicon anode material prepared in comparative example 1, and the packing density is smaller. From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects: the coated silicon-carbon composite material prepared by the preparation method has the advantages of low expansion rate, good cycle performance, high cycle capacity, simple preparation process, low cost, easy industrial production and the like.

It is noted that the terms first, second and the like in the description and in the claims of the present application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described or illustrated herein.

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.