CN106058207A - Silicon-carbon composite material, preparation method thereof and negative pole for lithium-ion battery - Google Patents

Abstract

The invention provides a method for preparing a silicon-carbon composite material, which is characterized in that the method comprises: passing a mixed gas composed of silicon tetrachloride gas and a reducing carrier gas into a reaction chamber in which a carbon material is placed, wherein the The reducing carrier gas includes a reducing gas; the mixed gas is heated so that the reducing gas reduces the silicon tetrachloride gas to elemental silicon, and forms silicon in which the elemental silicon is deposited on the carbon material. carbon composites. The method has cheap raw materials, simple process and excellent product performance. The present invention also provides a silicon-carbon composite material and a negative electrode for a lithium-ion battery comprising the same.

Description

Method for preparing silicon-carbon composite material, silicon-carbon composite material and application to lithium ion battery negative pole of

technical field

The invention relates to the field of silicon-carbon composite materials, in particular to a method for preparing the silicon-carbon composite material, the silicon-carbon composite material prepared by the method, and a negative electrode for lithium ion batteries containing the silicon-carbon composite material.

Background technique

The improvement of electrode materials is one of the key points in the research and development of lithium-ion batteries. Silicon material has high theoretical capacity (~4200mAh/g) and low discharge potential (<0.5V, Vs.Li/Li ⁺ ) as the negative electrode of lithium-ion batteries, and is considered to be an important candidate material to replace the traditional graphite negative electrode.

However, the silicon material has a large volume change (~300%) during charge and discharge, which not only is not conducive to the formation of a stable SEI film during battery cycling, but also leads to the pulverization of the electrode material, resulting in the battery exhibiting a rapid capacity decay.

Combining silicon and carbon materials can not only effectively alleviate the problem of volume expansion of electrode materials, but also effectively improve the conductivity of electrode materials and improve the electrochemical performance of composite materials.

In order to prepare silicon-carbon composite materials, different methods have been tried and applied. One type of silicon-carbon composite material is composed of a carbonaceous material matrix and a silicon material covering it. At present, when preparing such silicon-carbon composite materials, organosilicon such as silane is generally used as the silicon source, which is expensive, and carbonaceous materials are usually made of carbon nanotubes, carbon fibers and other materials, and the cost is relatively high.

There is still a need for methods to obtain silicon carbon composites with good electrode material properties in a more inexpensive manner.

Contents of the invention

In order to solve the above problems, the present invention provides the following technical solutions.

[1] A method for preparing a silicon-carbon composite material, characterized in that the method comprises:

passing a mixed gas composed of silicon tetrachloride gas and a reducing carrier gas into the reaction chamber in which the carbon material is placed, wherein the reducing carrier gas includes a reducing gas;

The mixed gas is heated so that the reducing gas reduces the silicon tetrachloride gas to elemental silicon, and forms a silicon-carbon composite material in which the elemental silicon is deposited on the carbon material.

[2] The method according to [1], wherein the reducing gas is selected from the group consisting of acetylene, hydrogen, methane, carbon monoxide, ammonia, or combinations thereof.

[3] The method according to [1] or [2], wherein the reducing gas is acetylene.

[4] The method according to any one of [1] to [3], wherein the carbon material is graphite or a biomass-sourced carbon material obtained by pre-treating a biomass material.

[5] The method according to [4], wherein the biomass material is selected from the group consisting of straw, rice husk, bamboo leaves, corn cob, or a combination thereof.

[6] The method according to [4], wherein the pre-processing includes:

pulverizing the biomass material;

Carrying out acid cooking to the biomass material;

Carbonizing the biomass material;

The carbonized biomass material is cleaned with hydrofluoric acid to obtain a biomass source carbon material.

[7] A silicon-carbon composite material prepared by the method according to any one of [1] to [6].

[8] The silicon-carbon composite material according to [7], wherein the silicon content is in the range of 10 to 50% by weight.

[9] The silicon-carbon composite material according to [7] or [8], wherein the carbon material is graphite or a biomass-sourced carbon material obtained by pre-treating biomass materials, and the biomass The material is selected from the group consisting of straw, rice hulls, bamboo leaves, corncobs, or combinations thereof.

[10] A negative electrode for a lithium ion battery, comprising the silicon-carbon composite material according to any one of [7] to [9].

Through the above technical solution, the present invention provides a method for synthesizing carbon-silicon composite materials, the required raw materials are cheap, safe, low in equipment requirements, environmentally friendly in the preparation process, high in yield, low in production cost, and conducive to scale-up Production. The invention also provides a carbon-silicon composite material, which has excellent performance although its production cost is low. The invention also provides a negative electrode containing the carbon-silicon composite material, which can meet the requirement of being a lithium ion battery negative electrode.

Description of drawings

Fig. 1 is the X-ray diffractogram of the product that embodiment 1 obtains.

Fig. 2 is the scanning electron micrograph of the product that embodiment 1 obtains.

Fig. 3 is the X-ray diffractogram of the product that embodiment 2 obtains.

4 is an energy dispersive X-ray (EDX) detection element distribution diagram of the product obtained in Example 2.

Fig. 5 is a charge-discharge cycle diagram of the silicon-carbon composite material obtained in Example 2 when the current density is 0.4A/g.

FIG. 6 is a charge-discharge cycle diagram of the silicon-carbon composite material obtained in Example 2 at a current density of 1.2 A/g.

Fig. 7 is the X-ray diffractogram of the product obtained in Example 4.

Figure 8 is a scanning electron micrograph of the product obtained in Example 4.

FIG. 9 is a charge-discharge cycle diagram of the silicon-carbon composite material obtained in Example 4 at a current density of 0.4 A/g.

Fig. 10 is the charge-discharge cycle diagram of the silicon-carbon composite material obtained in Example 4 at a current density of 1.2 A/g.

detailed description

The first aspect of the present invention provides a method for preparing a silicon-carbon composite material, which is characterized in that the method includes: passing a mixed gas composed of silicon tetrachloride gas and reducing carrier gas into the reaction in which the carbon material is placed In the chamber, wherein the reducing carrier gas contains a reducing gas; the mixed gas is heated so that the reducing gas reduces the silicon tetrachloride gas to elemental silicon, and forms wherein the elemental silicon is deposited on the Silicon-carbon composites on carbon materials.

Using silicon tetrachloride as the source of silicon in the silicon-carbon composite material, compared with using organosilicon as the silicon source, has cheap raw materials and wide sources, an environmentally friendly preparation process, high yield, and low production cost, which is conducive to scale-up production. In particular, industrial waste silicon tetrachloride can be used, which both reduces costs and provides a way to recycle industrial waste.

The reducing carrier gas in the mixed gas of the present invention plays the role of loading silicon tetrachloride into the reaction chamber and using the reducing gas therein to reduce silicon tetrachloride to simple silicon so as to vapor-deposit it. The reducing carrier gas described herein may be a blended gas consisting only of one or more reducing gas species. The reduction carrier gas can also be a blended gas of reducing gas and inert gas, as long as the blended gas can reduce silicon tetrachloride to elemental silicon so as to make its vapor deposition effect. The reducing gas mentioned herein has the reducing property for silicon in silicon tetrachloride, that is, the reducing gas can react with silicon tetrachloride under heating conditions, and the positive tetravalent silicon in silicon tetrachloride Restored to zero-valent elemental silicon. The existence of the inert gas in the reducing carrier gas can regulate the pressure and improve the safety. Examples of the inert gas include argon and the like. Preferably, the reducing gas in the reducing carrier gas is selected from the group consisting of acetylene, hydrogen, methane, carbon monoxide, ammonia, or combinations thereof. The above-mentioned reducing gas is easy to obtain and cheap, which greatly saves the cost of raw materials. More preferably, the reducing gas is acetylene. As a reducing gas, acetylene gas can react at a lower reduction temperature. At the same time, the carbon produced by pyrolysis and the reduced silicon are co-deposited. The co-deposited carbon here plays an important role in improving the stability of the material. Still more preferably, the molar ratio of acetylene to silicon tetrachloride is 2:1.

The heating of the mixed gas of silicon tetrachloride gas and reducing carrier gas only needs to make the reducing gas react with silicon tetrachloride gas to reduce the silicon therein. The reaction temperature may be 400 to 700°C, preferably about 550°C.

The flow rate of the mixed gas can range from 1 to 100ml/min. The reaction time can be from 0.5 to 24 h, preferably about 6 h.

The reaction chamber provides a substantially closed space and is configured so long as silicon produced by the gas phase reaction can be deposited on the carbon material placed therein.

As is common for vapor deposition processes, the vapor deposition process and product properties can be tuned by adjusting conditions such as temperature, gas flow rate, gas mixture composition, reaction chamber configuration, placement of carbon materials, and the like. The method of the present invention may further include purification steps, such as impurity removal (such as acid washing, water washing), filtering, drying and the like.

The carbon material may be any carbon material. The method of the present invention can use cheap carbon materials to obtain lithium-ion battery anode silicon-carbon composite materials with excellent performance, without using carbon nanotubes, carbon fibers, graphene and other difficult and expensive carbon materials.

Preferably, the present invention can use graphite as the carbon material. Graphite can be graphite ore, such as commercially available graphite ore, which has the advantages of easy availability of raw materials and low cost. In the case of using graphite ore as the carbon material, the silicon-carbon composite material prepared by the present invention still has good electrode properties and can be used in lithium-ion batteries.

Preferably, the carbon material is a biomass-sourced carbon material obtained by pre-treating a biomass material. Biomass-derived carbon materials obtained from biomass materials through pretreatment including carbonization have a natural structure derived from biomass and have excellent performance when used as anode materials for lithium-ion batteries.

More preferably, the biomass material is selected from the group consisting of straw, rice husk, bamboo leaves, corn cob, or combinations thereof. These materials are cheap, readily available, and in plentiful supply.

Also more preferably, the pretreatment includes: pulverizing the biomass material; acid boiling the biomass material; carbonizing the biomass material; cleaning the carbonized biomass with hydrofluoric acid Materials, to obtain biomass-sourced carbon materials.

The purpose of acid cooking includes the removal of inorganic salt ion impurities. For example, 4mol/L hydrochloric acid can be used for acid boiling. The slurry needs to be heated during acid cooking, for example, it can be heated to about 150°C.

Carbonization treatment is to heat the biomass material under the protection of inert gas such as nitrogen to carbonize it. The temperature of the carbonization treatment may be between 300 and 900°C.

The function of hydrofluoric acid cleaning is to remove siliceous materials such as silicon dioxide. For example, it can be washed with 3mol/L hydrofluoric acid and stirred for 1-6h.

Common steps such as washing and drying may be included between the above steps.

A second aspect of the present invention provides a silicon-carbon composite material prepared by the method of the first aspect. The raw material of the silicon-carbon composite material is cheap, the preparation cost is low, and it has excellent properties, which meets the requirement of being used as the negative electrode of the lithium ion battery. Moreover, the silicon-carbon composite material prepared in this way is evenly compounded by the two elements of silicon and carbon.

Preferably, in the silicon-carbon composite material, the silicon content is in the range of 5-55% by weight, more preferably 10-50% by weight, even more preferably 10% by weight. When the mass ratio of silicon to carbon is 1:9, the material performance is excellent.

Preferably, the carbon material in the silicon-carbon composite material is graphite or a biomass-sourced carbon material obtained by pre-treating a biomass material, and the biomass material is selected from the group consisting of: straw, rice husk , bamboo leaves, corn cobs, or combinations thereof. A silicon-carbon composite material using graphite as a carbon material is low in cost and excellent in performance. The use of biomass-derived carbon materials as silicon-carbon composites is low-cost and has a natural structure derived from biomass, which has excellent performance when used as anode materials for lithium-ion batteries.

A third aspect of the present invention provides a negative electrode for a lithium-ion battery comprising the silicon-carbon composite material of the second aspect. The negative electrode has low cost but excellent performance. The negative electrode shows a much higher lithium storage capacity than the graphite negative electrode. Its lithium storage capacity is close to 800mA h/g, which is about 2 times higher than the 372mAh/g of the graphite negative electrode. It also has high Coulombic efficiency and long cycle stability. Long cycle life.

The high lithium storage capacity and long cycle stability of lithium-ion batteries are determined by the structure of the material. Among them, the silicon attached to the surface of the carbon material is amorphous silicon, which has a good volume expansion mitigation effect, and at the same time, due to the low silicon content, it can effectively reduce the fragmentation of the electrode material and reduce the volume expansion effect of the electrode material. Secondly, the main body of the composite material is carbon material, which has good conductivity and less volume expansion effect, which can effectively improve the conductivity of the electrode material and reduce the volume expansion effect of the material.

A specific embodiment of the method of the present invention is as follows.

Using silicon tetrachloride as the silicon source, using single-component or mixed-component reducing gas as the carrier gas, silicon tetrachloride is loaded into the reaction chamber for reaction, and the oxidation-reduction reaction occurs to obtain elemental silicon, which is deposited by vapor phase deposition. Silicon is deposited on the surface of the pre-treated carbon material to prepare the silicon-carbon composite material. The vapor deposition technology prepares silicon-carbon composite materials. The reaction raw materials are cheap and easy to obtain, and the preparation process is simple. Proper control of the reaction temperature, air flow and time can effectively control the formation of silicon carbide. At the same time, different silicon contents can be obtained by adjusting the test parameters. silicon-carbon composite material. After the vapor deposition process, no subsequent treatment is required, which is conducive to the realization of mass production of silicon-carbon composite materials.

The raw materials are as follows:

Silicon source, selected from silicon tetrachloride;

The reducing carrier gas is selected from acetylene, hydrogen, methane, carbon monoxide, ammonia or their corresponding combination gas.

The carbon material is a biomass source carbon material prepared from straw, rice husk, bamboo leaves, corncobs or their mixed materials, or graphite material.

Specific steps are as follows:

a) Preparation of biomass-sourced carbon materials: cut straw and other biomass materials into pieces, pickle at high temperature, wash and dry, then carbonize at high temperature, and finally wash with hydrofluoric acid to remove silica, then wash and dry with water Obtain biomass source carbon material. Commercial carbon materials are dried at 100 degrees Celsius.

b) Put the above-mentioned carbon material into the reactor, feed acetylene gas and silicon tetrachloride gas in proportion, heat at 400 to 700 degrees Celsius in the atmosphere of acetylene and silicon tetrachloride gas, and keep it for 0.5 to 24 hours. Silicon-carbon composite materials are available;

In the silicon-carbon composite material obtained in the present invention, the silicon element is evenly compounded on the surface of the carbon material.

Preferably, the reducing gas is acetylene gas;

Preferably, the molar ratio of silicon tetrachloride to acetylene gas is 1:2;

Preferably, the reaction temperature is 540-560 degrees Celsius, such as about 550 degrees Celsius;

Preferably, the reaction time is 4-8h, such as about 6h;

Preferably, the silicon content in the silicon-carbon composite material is 5-50%, such as 10%.

The reaction can be performed in a stainless steel reaction tube furnace.

The technical solutions of the present invention will be clearly and detailedly described below in conjunction with the embodiments. However, it should be understood that the described embodiments are only a part of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments can be obtained by those skilled in the art without making creative efforts. All belong to the protection scope of the present invention.

Example 1: Using wheat straw as raw material to prepare biomass source carbon material

1) The wheat straw material was crushed, reacted with 4 mol/L hydrochloric acid at 150 degrees Celsius for 10 h, washed three times with deionized water and dried. Then carry out carbonization treatment at 600 degrees Celsius under the protection of an inert gas such as nitrogen, and then wash with 3mol/L hydrofluoric acid and stir for 1-6h. Finally, the wheat straw biomass source carbon material is obtained by washing and drying with deionized water.

2) Adopt X-ray powder diffractometer (Philips X'Pert Super diffract meter) to carry out X-ray diffraction analysis, Fig. 1 is the X-ray diffraction spectrum of the powder obtained in this embodiment. It can be seen from the figure that there is no clear and sharp diffraction peak at 2θ in the range of 10-80 degrees in the X-ray diffraction spectrum, and a steamed bun peak appears between 20 and 30 degrees, which means that the biomass-sourced carbon material is amorphous.

3) The scanning electron microscope image (FIG. 2) of the product shows that the product has a micron-scale structure and a flat surface.

Example 2: Using the biomass-sourced carbon material prepared from wheat straw in Example 1 as a substrate, a silicon-carbon composite material was prepared by vapor deposition.

1) Put the prepared biomass-sourced carbon material into the reaction chamber. Put commercially available acetylene (mixed gas of acetylene and argon, volume ratio Ar:C ₂ H ₂ =9:1) loaded with silicon tetrachloride (volume ratio of commercially available acetylene to silicon tetrachloride is 20:1) into In the reaction chamber, heat at 550 degrees Celsius in a gas atmosphere containing acetylene and silicon tetrachloride, and keep for 8 hours. After the reaction is completed, a silicon-carbon composite material is prepared.

2) Fig. 3 is the X-ray diffraction spectrum of the powder obtained in this embodiment. The spectrogram shows that the powder is an amorphous phase, and no other impurities are formed.

3) Figure 4 is an energy dispersive X-ray detection element distribution diagram of the powder obtained in this embodiment, which shows that silicon is evenly distributed on the surface of the carbon material, and the element mass ratio of silicon to carbon is 1:9. Through X-ray energy spectrum analysis, it is determined that the mass ratio of silicon to carbon is also about 1:9.

Example 3: Applying the silicon-carbon composite material obtained in Example 2 to the performance research of lithium-ion battery anode materials

The products in the above-mentioned Example 2 were packed into CR2016 button cells (Shenzhen Pengxiang Yunda Machinery Technology Co., Ltd.), respectively, with the lithium sheet as the counter electrode, the polyolefin porous film (Celgard 2500) as the separator, and the LiPF ₆ A mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1) was used as the electrolyte, and the CR2016 battery was completed in an argon atmosphere glove box. The silicon carbon electrode is made of 60% by weight of the biomass silicon carbon composite material in Example 2, 20% by weight of sodium carboxymethylcellulose adhesive, 20% of conductive carbon black, and water. The lining of the electrode film The bottom is metal copper foil. Conduct electrical performance tests at a test temperature of 25 degrees Celsius. 5-6 are graphs showing the electrochemical lithium storage performance of the silicon-carbon composite material obtained in Example 2 above. As shown in Figure 5, the reversible specific capacity is 800 mA h/g after 500 cycles at a current density of 0.4 A/g. As shown in Figure 6, after 1000 cycles at a current density of 1.2 A/g, the reversible specific capacity remains close to 600 mA h/g.

Example 4: A silicon-carbon composite material was prepared by vapor deposition using a commercial crystalline graphite ore material as a substrate.

1) Put commercial graphite ore material (commercially purchased from Hubei Yichang Zhongke Hengda Graphite Co., Ltd.) into the reaction chamber. Put commercially available acetylene (mixed gas of acetylene and argon, volume ratio Ar:C ₂ H ₂ =9:1) loaded with silicon tetrachloride (volume ratio of commercially available acetylene to silicon tetrachloride is 20:1) into In the reaction chamber, heat at 550 degrees Celsius in a gas atmosphere containing acetylene and silicon tetrachloride, and keep for 8 hours. After the reaction is completed, a silicon-carbon composite material is prepared.

2) Figure 7 is the X-ray diffraction spectrum of the powder obtained in this embodiment. The diffraction peaks shown in the spectrum can all be indicated as hexagonal crystalline carbon materials (JCPDS NO.26-1076), and no other impurities are formed. There is an amorphous peak between 20 and 30 degrees, indicating that there is an amorphous material deposited on the crystalline carbon.

3) The scanning electron microscope image (FIG. 8) of the product shows that the product has a uniform micron-scale structure.

Example 5: Applying the silicon-carbon composite material obtained in Example 4 to research on the performance of negative electrode materials for lithium-ion batteries

The silicon-carbon composite material in the above-mentioned Example 4 was used as the lithium-ion battery negative electrode material to conduct electrochemical performance research. The products were assembled into CR2016 button batteries (Shenzhen Pengxiang Yunda Machinery Technology Co., Ltd.), and the assembly method was as described in Example 3. The silicon-carbon electrode adopts 60% by weight of the graphite-silicon-carbon composite material in Example 4, 20% by weight of sodium carboxymethyl cellulose adhesive, 20% of conductive carbon black, and water to form a mixture. The substrate of the electrode film For metal copper foil. Conduct electrical performance tests at a test temperature of 25 degrees Celsius. 9-10 are graphs showing the electrochemical lithium storage performance of the silicon-carbon composite material obtained in Example 4 above. As shown in Figure 9, the reversible specific capacity is close to 700 mA h/g after 300 cycles at a current density of 0.4 A/g. As shown in Figure 10, after 1000 cycles at a current density of 1.2 A/g, the reversible specific capacity remains close to 500 mA h/g.

The results show that the present invention can realize the preparation of silicon-carbon composite material powder by using low-cost carbon material and silicon tetrachloride as raw materials and vapor deposition. By controlling the ratio of reducing gas to silicon tetrachloride, reaction temperature, reaction time and other factors, materials with different ratios of silicon to carbon are prepared. When this material is directly used as an anode material for lithium-ion batteries, it shows a much higher lithium storage capacity and better cycle stability than graphite anodes, and can be used as a potential next-generation high-performance lithium-ion battery anode material.

Claims (10)

1. A method for preparing a silicon-carbon composite material, characterized in that the method comprises: passing a mixed gas composed of silicon tetrachloride gas and a reducing carrier gas into the reaction chamber in which the carbon material is placed, wherein the reducing carrier gas includes a reducing gas; The mixed gas is heated so that the reducing gas reduces the silicon tetrachloride gas to elemental silicon, and forms a silicon-carbon composite material in which the elemental silicon is deposited on the carbon material. 2. The method of claim 1, wherein the reducing gas is selected from the group consisting of acetylene, hydrogen, methane, carbon monoxide, ammonia, or combinations thereof. 3. The method of claim 1, wherein the reducing gas is acetylene. 4. The method according to claim 1, characterized in that the carbon material is graphite or a biomass-sourced carbon material obtained by pre-treating biomass materials. 5. The method according to claim 4, wherein the biomass material is selected from the group consisting of straw, rice husk, bamboo leaves, corn cob, or combinations thereof. 6. method according to claim 4, is characterized in that, described pretreatment comprises: pulverizing the biomass material; Carrying out acid cooking to the biomass material; Carbonizing the biomass material; The carbonized biomass material is cleaned with hydrofluoric acid to obtain a biomass source carbon material. 7. A silicon-carbon composite material prepared by the method according to claim 1. 8. The silicon-carbon composite material according to claim 7, characterized in that the silicon content is in the range of 10-50% by weight. 9. The silicon-carbon composite material according to claim 7, wherein the carbon material is graphite or a biomass-sourced carbon material obtained by pre-treating the biomass material, and the biomass material is selected from the following A group consisting of items: straw, rice husk, bamboo leaves, corn cob, or a combination thereof. 10. A negative electrode for a lithium ion battery, said negative electrode comprising the silicon-carbon composite material according to claim 7.