CN102013487A - Carbon/silicon composite lithium ion battery negative material and preparation method thereof - Google Patents

Abstract

The invention provides a lithium ion battery negative material. The negative material is prepared from a carbon/silicon composite material which consists of silicon and carbon in the weight ratio of 40-100:15-60, wherein the discharging specific capacity of the material is 400 to 1,500mAh/g; the primary cycle efficiency is 70 to 95 percent; and the capacity retention rate after 200 cycles is 65 to 90 percent. The invention also provides a preparation method of the carbon/silicon composite material. After asphalt or resin is uniformly mixed with silicon resin or silica gel and magnesium powder, the material is prepared by thermal treatment and a cleaning process. The carbon/silicon composite material has high lithium ion battery negative performance and a simple preparation process.

Description

Carbon/silicon composite lithium ion battery negative electrode material and preparation method thereof

technical field

The invention relates to the field of negative electrode materials for lithium ion batteries, more specifically to the preparation of a negative electrode material for a carbon/silicon composite lithium ion battery, and the invention also relates to the use of the negative electrode material for a carbon/silicon composite lithium ion battery and a preparation method thereof .

Background technique

Lithium-ion secondary battery, as a new type of power supply system, has been widely used in various fields, especially in various portable microelectronic devices. With the rapid development of the microelectronics industry, the requirements for its power supply system are also getting higher and higher. It is estimated that in the next few years, the capacity of lithium-ion batteries will have to increase twice to meet its needs.

At present, the anode material of commercial lithium-ion batteries uses graphite-like carbon materials, and its theoretical specific capacity is only 372mAh/g, which limits the further improvement of the specific energy of lithium-ion batteries and cannot meet the growing demand for high-energy portable mobile power supplies. Silicon is one of the most promising anode materials to replace carbon materials, because silicon has the highest capacity up to 4200mAh/g; and has a stable discharge platform similar to graphite. But similar to other high-capacity metals, silicon has very poor cycle performance and cannot perform normal charge-discharge cycles. When silicon is used as a negative electrode material, the reversible formation and decomposition of Li ₂ Si alloy is accompanied by a huge volume change during the charge-discharge cycle, which will cause mechanical splitting of the alloy (creating cracks and pulverization), resulting in the collapse of the material structure and The peeling of the electrode material causes the electrode material to lose electrical contact, resulting in a sharp decline in the cycle performance of the electrode, and finally leads to electrode failure, so it is difficult to be practically applied in lithium-ion batteries. Studies have shown that small particle size silicon or its alloys have greatly improved both in terms of capacity and cycle performance. When the particles of alloy materials reach the nanometer level, the volume expansion during charge and discharge will be greatly reduced, and the performance will also be improved. It will be improved, but nanomaterials have a large surface energy and are prone to agglomeration, which will reduce the charge and discharge efficiency and accelerate the decay of capacity, thereby offsetting the advantages of nanoparticles; silicon films prepared by various deposition methods can To a certain extent, the cycle life of the material can be extended, but its high initial irreversible capacity cannot be eliminated, thus restricting the practical application of this material. Another research trend to improve the performance of silicon anodes is to prepare composite materials or alloys of silicon and other materials. Among them, silicon/carbon composite materials prepared by combining the stability of carbon materials and the high specific capacity of silicon have shown huge applications. prospect. The preparation technology of silicon/carbon composite materials reported in the literature mainly includes the following aspects.

1. Mechanical ball milling

This method is to mix silicon powder with carbon or silicon carbide and directly ball mill it into a nanocomposite material. Silicon powder and carbon materials can be uniformly dispersed with each other at the nanometer scale after high-energy mechanical ball milling. Since nanometer-sized silicon powder is surrounded by carbon materials, the volume change caused by lithium intercalation and delithiation can be suppressed, and the cycle performance of silicon materials can be improved to a certain extent. With the increase of silicon content, the specific capacity of silicon/carbon composites increases, but the cycle stability becomes worse. At the same time, the crystal structure, size and compatibility of the two components in the composite determine the final properties of the material.

The main problems of the composite materials prepared by this method are: due to the large specific surface area and the inability to completely prevent the micro-oxidation during the ball milling process, the first irreversible capacity is large.

2. Polymer coated silicon powder for carbonization

This method can well disperse silicon powder in the carbon matrix and improve its cycle performance; however, since the high polymer carbonization forms amorphous carbon, it cannot fully reflect the stability and conductivity of graphite carbon materials, and may The overall performance is not ideal due to the amorphous structure that increases the first irreversible capacity of the composite.

3. Asphalt is used as a binder to bond silicon powder and graphite for carbonization

Pitch not only acts as a binder to uniformly bond graphite and silicon, but also acts as a surface coating after carbonization. However, the low-temperature carbonization products of pitch also have an amorphous structure, and the bonding effect of pitch as a binder on carbon and silicon is limited, so the properties of the prepared materials still need to be further improved.

4. CVD coating

Directly use CVD method to wrap silicon or silicon/carbon mixture with carbon film. After coating, the cycle performance of silicon is improved, but due to the small amount of coating, the role of the carbon matrix cannot be fully reflected, and the performance of the prepared material is poor, but the material prepared by this method can be used to study silicon/carbon composites for lithium storage. mechanism.

Therefore, there are many problems to be solved in the practical application of carbon/silicon anode materials, which have not been effectively solved so far.

Therefore, it is necessary to provide a carbon/silicon composite lithium-ion battery negative electrode material that is easy to industrialize, has a simple preparation process, and has high specific capacity, high first cycle efficiency and long cycle life.

Contents of the invention

The object of the present invention is to provide a carbon/silicon composite lithium ion battery negative electrode material with simple process, low cost, high specific capacity, high initial cycle efficiency and long cycle life.

Another object of the present invention is to provide a preparation method of the above carbon/silicon composite lithium ion battery negative electrode material. This preparation method can generate nano-silicon particles in situ in the carbon matrix, and due to the self-assembly of the material during the preparation process, the silicon particles and the carbon matrix can be tightly combined, endowing the carbon/silicon composite lithium-ion battery negative electrode material with carbon materials at the same time. The stability and high specific capacity characteristics of silicon.

The invention relates to a carbon/silicon composite lithium-ion battery negative electrode material, which is characterized in that its composition is as follows:

Carbon 40-100 parts by weight

Silicon 15-60 parts by weight

It is also characterized in that the silicon particles generated in situ during the preparation process are uniformly dispersed in the carbon matrix with a size of 10-100nm; its discharge specific capacity is 400-1500mAh/g, the first cycle efficiency is 70-95%, and after 200 cycles The capacity retention rate is 65-90%.

The preferred described carbon/silicon composite lithium-ion battery negative electrode material is composed as follows:

Carbon 50-90 parts by weight

Silicon 15-50 parts by weight

The composition of carbon/silicon composite lithium ion battery negative electrode material of the present invention adopts following method to measure:

According to the national standard (GB2295-80), the ash content of the carbon/silicon composite material is measured in a muffle furnace. The obtained ash is divided into silica, and the weight of the ash content is multiplied by 46.7% to be the weight of silicon. The weight of the carbon/silicon composite material and the weight of silicon The difference is the carbon weight. The size of silicon particles in carbon/silicon composite lithium-ion battery anode materials was measured by high-magnification transmission electron microscopy. The discharge specific capacity, first cycle efficiency, and capacity retention rate after 200 cycles of carbon/silicon composite lithium-ion battery negative electrode materials are measured by the following methods:

The electrochemical performance of carbon/silicon composite lithium-ion battery anode materials was tested using CR2025 button cells. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1M LiPF6/EC: DC: DMC (volume ratio 1: 1 : 1) is the electrolyte, and the separator is a PP/PE composite film, and a button cell is prepared in a glove box full of argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of carbon/silicon composite lithium-ion battery negative electrode material is measured by LAND battery tester; the first discharge capacity of the battery is the discharge specific capacity of the carbon/silicon composite lithium-ion battery negative electrode material; the discharge capacity of the battery after 200 cycles and the first discharge The ratio of capacities was used to calculate the capacity retention rate after 200 cycles.

The silicon component in the carbon/silicon composite lithium-ion battery negative electrode material should be understood in the sense of the present invention as silicon particles of 10-100 nanometers generated in situ at high temperatures by the silicon-containing precursor and magnesium powder, and the formed silicon particles It is uniformly and stably dispersed in the carbon matrix, and can stably carry out the electrochemical reaction of lithium ion insertion/extraction. The silicon particle size was determined using the method described previously.

The carbon component in the negative electrode material of the carbon/silicon composite lithium ion battery should be understood in the sense of the present invention as the carbon component formed by the carbon-containing precursor through high-temperature carbonization, and this carbon component has a network matrix structure , can tightly wrap the silicon particles generated in situ during the heat treatment process, prevent the silicon particles from agglomerating each other during the formation process, and ensure that the size of the silicon particles in the carbon/silicon composite material is 10-100 nanometers, and it can be used as a negative electrode material for lithium-ion batteries during the charge and discharge process It can effectively suppress the volume change caused by lithium intercalation/delithiation of silicon particles, and endow carbon/silicon composite lithium-ion battery anode materials with excellent first-time cycle efficiency and stable cycle performance.

In the present invention, the carbon-containing precursor is one or several carbon-containing precursors selected from coal tar pitch, petroleum residue pitch, coal tar, mesophase pitch, and phenolic resin.

The carbon-containing precursor described in the present invention is coal tar pitch and/or petroleum residue pitch.

The coal tar pitch example of the present invention is that softening point is 80 ℃ medium temperature coal tar pitch;

The example of the petroleum residue pitch in the present invention is the petroleum pitch obtained after the petroleum residue is purified.

The coal tar in the present invention is a product obtained by dry distillation of coal when the air is isolated and heated.

The mesophase pitch described in the present invention is obtained by thermal condensation reaction of cheap common pitch, heavy oil, and residual oil as raw materials; The point is 260°C and the mesophase content is more than 95% mesophase pitch.

The phenolic resin of the present invention is a resin formed by polycondensation of phenol and aldehyde. Examples of the phenolic resin are 2123, 2124, 2127, 2130, 2132 phenolic resins and the like sold by Shanghai Daowong Rubber Technology Co., Ltd.

The silicon-containing precursor described in the present invention is one or more silicon-containing precursors selected from silicone resin and silica gel. The silicon-containing precursors are silicone rubbers such as raw rubber 101, 110, and 120 from Shanghai Resin Factory, and silicone resins such as 955#, 1053#, and 1153# sold by Xinrui Silicone Co., Ltd. in Bengbu City, Anhui Province.

In the present invention, the magnesium powder is 80-325 mesh high-purity (greater than 99.9%) metallic magnesium powder. It is preferably 200-325 mesh high-purity (greater than 99.9%) metal magnesium powder. An example of the magnesium powder is the JM1-7 product sold by Beijing Yuanchuang Magnesium Industry Co., Ltd.

In addition, the present invention also relates to a method for preparing a carbon/silicon composite lithium-ion battery negative electrode material, which is characterized in that the method comprises the following steps:

(1) According to the mass ratio of carbon-containing precursor, silicon-containing precursor and magnesium powder, the ratio of the three raw materials is 1:0.5-3:0.1-1. Carrying out the thermal polycondensation reaction for 0.5-5 hours to obtain the thermal polycondensation product;

(2) Under the conditions of a carbonization temperature of 650-1100° C. and an inert atmosphere, treat the heat-shrinkable product obtained in step (1) for 0.5-5 hours to obtain the heat-treated product; the inert atmosphere is, for example, argon, Nitrogen and its mixtures.

(3) soaking the heat-treated product obtained in step (2) for 0.5-24 hours in hydrochloric acid with a concentration of 5-36%, washing with deionized water, and drying to obtain a carbon/silicon composite material.

The performance of the carbon/silicon composite lithium ion battery negative electrode material of the present invention is not affected by its shape and volume, and its shape and volume can be obtained by grinding and sieving according to actual needs.

The carbon/silicon composite lithium ion battery negative electrode material of the present invention can be used as a negative electrode material for various lithium ion secondary batteries.

Beneficial effects of the present invention:

The carbon/silicon composite lithium-ion battery negative electrode material of the present invention not only has high specific capacity and first-time cycle efficiency, so it can provide a large capacity of lithium-ion batteries, and after 200 cycles, the capacity retention rate is greater than 65%, which ensures high capacity while improving its cycle life.

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Figure 1 is the first three charge and discharge curves of the material.

Figure 2 is a graph showing the 12 cycles of the material.

Figure 3 is a graph showing the variation trend of the discharge capacity of the material with the number of cycles.

Figure 4 is the XRD pattern of the material.

Figure 5 is a graph showing the variation trend of the discharge capacity of the material with the number of cycles.

Figure 6 is a graph showing the variation trend of the discharge capacity of the material with the number of cycles.

Figure 7 is a high-magnification transmission electron microscope image of the material.

Detailed ways

The present invention can be further clearly understood through the specific examples of the present invention given below, but these examples do not limit the protection scope of the present invention.

Example 1

The first step: thermal polycondensation reaction of raw materials

Add 200g of silicone resin and 150g of magnesium powder (325 mesh) to 500g of petroleum residue asphalt, and keep a constant temperature for 4.5 hours at a temperature of 440°C and a pressure of 2.0Mpa to carry out a thermal polycondensation reaction. After the reaction is completed, a thermal polycondensation product is obtained.

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 1000°C for carbonization, then the product was cooled to room temperature, then soaked with 10% hydrochloric acid for 24 hours, washed with distilled water until neutral, and then this product was placed in the Dry at -0.1MPa and 105°C for 24 hours under vacuum to obtain 40.7g of carbon/silicon composite lithium-ion battery negative electrode material. The carbon component in the material is 60.5, the silicon component is 39.5, and the silicon particle size is 10-60nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1M LiPF6/EC: DC: DMC (volume ratio 1: 1 : 1) is the electrolyte, and the separator is a PP/PE composite film, and a button cell is prepared in a glove box full of argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery negative electrode material measured by the LAND battery tester is 78.1%, and the discharge specific capacity is 885mAh/g; the capacity retention rate after 200 cycles of the battery is 78.4%. Figure 1 shows the material The first three charge and discharge curves.

Example 2

The first step: thermal polycondensation reaction of raw materials

Add 100g of silicone resin and 80g of magnesium powder (3250 mesh) to 500g of petroleum residue asphalt, and keep a constant temperature for 2.0 hours at a temperature of 450°C and a pressure of 2.0Mpa to carry out thermal polycondensation reaction. After the reaction ends, a thermal polycondensation product is obtained.

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 900°C for carbonization, then the resulting product was cooled to room temperature, then soaked with 20% hydrochloric acid for 12 hours, washed with distilled water until neutral, and then this product was placed in the Vacuum-0.1MPa and drying at 105°C for 24 hours to obtain 41.5g of carbon/silicon composite lithium-ion battery negative electrode material. The carbon component in the material is 75, the silicon component is 25, and the silicon particle size is 10-50nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1M LiPF6/EC: DC: DMC (volume ratio 1: 1 : 1) is the electrolyte, and the separator is a PP/PE composite film, and a button cell is prepared in a glove box full of argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery negative electrode material measured by the LAND battery tester is 85.5%, and the discharge specific capacity is 635.6mAh/g; the capacity retention rate after 200 cycles of the battery is 82.9%, as shown in Figure 2 Material 12 cycle graph.

Example 3

The first step: thermal polycondensation reaction of raw materials

Add 250g silicone resin and 120g magnesium powder (325 mesh) to 500g coal tar pitch, keep constant temperature 1.5 hours under temperature 410 ℃, pressure 0.1Mpa and carry out thermal polycondensation reaction, obtain thermal polycondensation product after this reaction finishes,

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 1000°C for carbonization, then the product was cooled to room temperature, then soaked with 30% hydrochloric acid for 12 hours, washed with distilled water to neutrality, and then this product was placed in the Vacuum-0.1MPa and 105°C temperature were dried for 24 hours to obtain 41.3g of carbon/silicon composite lithium-ion battery negative electrode material. The carbon component in the material is 78.2, the silicon component is 21.8, and the silicon particle size is 10-30nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) are uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1MLiPF6/EC: DC: DMC (volume ratio 1: 1: 1) is the electrolyte, and the separator is a PP/PE composite film, and a button battery is prepared in a glove box filled with argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery negative electrode material measured by the LAND battery tester is 86.7%, and the discharge specific capacity is 582.8mAh/g; the capacity retention rate after 200 cycles of the battery is 84.6%, as shown in Figure 3 Trend diagram of the discharge capacity of the material with the number of cycles.

Example 4

The first step: thermal polycondensation reaction of raw materials

Add 550g of silicone rubber and 400g of magnesium powder (325 mesh) to 500g of coal tar pitch, keep a constant temperature for 4.5 hours at a temperature of 400°C and a pressure of 0.1Mpa to carry out a thermal polycondensation reaction. After the reaction ends, a thermal polycondensation product is obtained.

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 1100°C for carbonization, then the product was cooled to room temperature, then soaked in 20% hydrochloric acid for 12 hours, washed with distilled water to neutrality, and then this product was placed in the Vacuum-0.1MPa and 105°C temperature were dried for 24 hours, thus obtaining 38.7g of carbon/silicon composite lithium-ion battery negative electrode material. The carbon component in the material is 53, the silicon component is 47, and the silicon particle size is 10-80nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1M LiPF6/EC: DC: DMC (volume ratio 1: 1 : 1) is the electrolyte, and the separator is a PP/PE composite film, and a button cell is prepared in a glove box full of argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery negative electrode material measured by the LAND battery tester is 69.3%, and the discharge specific capacity is 1434.9mAh/g; the capacity retention rate after 200 cycles of the battery is 73.5%, as shown in Figure 4. Material XRD pattern.

Example 5

The first step: thermal polycondensation reaction of raw materials

Add 300g of silicone resin and 250g of magnesium powder (200 mesh) to 500g of petroleum residue asphalt and 200g of phenolic resin, keep a constant temperature for 3.0 hours at a temperature of 445°C and a pressure of 2.0Mpa to carry out thermal polycondensation reaction, and obtain a thermal polycondensation product after the reaction ,

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 1000°C for carbonization, then the product was cooled to room temperature, then soaked with 20% hydrochloric acid for 12 hours, washed with distilled water to neutrality, and then this product was placed in the Drying under vacuum -0.1MPa and 105° C. for 24 hours, thus obtaining 43.6 g of carbon/silicon composite lithium ion battery negative electrode material. The carbon component in the material is 89.4, the silicon component is 10.6, and the silicon particle size is 10-30nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) are uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1MLiPF6/EC: DC: DMC (volume ratio 1: 1: 1) is the electrolyte, and the separator is a PP/PE composite film, and a button battery is prepared in a glove box filled with argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery negative electrode material measured by the LAND battery tester is 92.8%, and the discharge specific capacity is 476.1mAh/g; the capacity retention rate after 200 cycles of the battery is 90.3%, as shown in Figure 5 Trend diagram of the discharge capacity of the material with the number of cycles.

Example 6

The first step: thermal polycondensation reaction of raw materials

Add 350g silicone resin and 300g magnesium powder (325 mesh) to 500g coal tar, keep constant temperature 5 hours under temperature 450 ℃, pressure 2.5Mpa and carry out thermal polycondensation reaction, obtain thermal polycondensation product after this reaction finishes,

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 1000°C for carbonization, then the product was cooled to room temperature, then soaked with 20% hydrochloric acid for 12 hours, washed with distilled water to neutrality, and then this product was placed in the Vacuum-0.1MPa and 105°C temperature were dried for 24 hours to obtain 37.7g of carbon/silicon composite lithium-ion battery negative electrode material. The carbon component in the material is 51.1, the silicon component is 48.9, and the silicon particle size is 10-100nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1M LiPF6/EC: DC: DMC (volume ratio 1: 1 : 1) is the electrolyte, and the separator is a PP/PE composite film, and a button cell is prepared in a glove box full of argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery negative electrode material measured by the LAND battery tester is 69.6%, and the discharge specific capacity is 1493mAh/g; the capacity retention rate after 200 cycles of the battery is 65.2%. Figure 6 shows the material The trend graph of the discharge capacity with the number of cycles.

Example 7

The first step: thermal polycondensation reaction of raw materials

Add 400g of silicone resin and 250g of magnesium powder (325 mesh) to 500g of coal tar pitch, keep a constant temperature for 3.5 hours at a temperature of 430°C and a pressure of 0.1Mpa to carry out thermal polycondensation reaction, and obtain a thermal polycondensation product after the reaction ends.

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 750°C for carbonization, then the resulting product was cooled to room temperature, then soaked in 20% hydrochloric acid for 12 hours, washed with distilled water until neutral, and then this product was placed in the Drying under vacuum -0.1 MPa and temperature of 105° C. for 24 hours, thus obtaining 43.4 g of carbon/silicon composite lithium ion battery negative electrode material. The carbon component in the material is 71.6, the silicon component is 28.4, and the silicon particle size is 10-30nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) are uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1MLiPF6/EC: DC: DMC (volume ratio 1: 1: 1) is the electrolyte, and the separator is a PP/PE composite film, and a button battery is prepared in a glove box filled with argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery negative electrode material measured by the LAND battery tester is 78.3%, and the discharge specific capacity is 670.2mAh/g; the capacity retention rate after 200 cycles of the battery is 75.9%, as shown in Figure 7 High magnification transmission electron microscope image of the material.

Example 8

The first step: thermal polycondensation reaction of raw materials

Add 400g of silicone resin and 250g of magnesium powder (325 mesh) to 500g of coal tar pitch, keep a constant temperature for 3.5 hours at a temperature of 430°C and a pressure of 0.1Mpa to carry out thermal polycondensation reaction, and obtain a thermal polycondensation product after the reaction ends.

The second step: preparation of carbon/silicon composite lithium-ion battery anode material

50g of the prepared thermal polycondensation product was kept at a constant temperature for 1 hour at a temperature of 1100°C for carbonization, then the product was cooled to room temperature, then soaked in 20% hydrochloric acid for 12 hours, washed with distilled water to neutrality, and then this product was placed in the Vacuum-0.1MPa and 105°C temperature were dried for 24 hours, thus obtaining 42.8g of carbon/silicon composite lithium-ion battery negative electrode material. The carbon component in the material is 70.4, the silicon component is 29.6, and the silicon particle size is 10-30nm. The positive electrode is made of materials (90%), acetylene black (5%) and polyvinylidene fluoride (5%) uniformly mixed electrode sheet, the negative electrode is a metal Li sheet, 1M LiPF6/EC: DC: DMC (volume ratio 1: 1 : 1) is the electrolyte, and the separator is a PP/PE composite film, and a button cell is prepared in a glove box full of argon. The charge and discharge test of the battery is carried out on the LAND battery test system, and the charge and discharge current density is 0.2 mA/cm ² . The first cycle efficiency of the carbon/silicon composite lithium-ion battery anode material measured by the LAND battery tester is 81.6%, and the discharge specific capacity is 692.8mAh/g; the capacity retention rate after 200 cycles of the battery is 80.2%.

Claims (10)

1. carbon/silicon composite cathode material is characterized in that it is composed as follows:

Carbon 40-100 weight portion

Silicon 15-60 weight portion

Wherein, described silicon is dispersed in the carbon base body with the size of 10-100nm, is the nano particle that silicon precursor forms with magnesium powder reaction original position in heat treatment process that contains that is selected from silicones, silica gel by one or more.Carbon is by being to be handled through the heat of carbonization and formed by one or more carbon matrix precursors that contain that are selected from coal tar pitch, petroleum residual oil pitch, coal tar, mesophase pitch, phenolic resins.

Its feature is that also its specific discharge capacity is 400-1500mAh/g, and cycle efficieny is 70-95% first, and 200 times circulation back capability retention is 65-90%.

2. carbon/silicon composite cathode material according to claim 1 is characterized in that it is composed as follows:

Carbon 50-90 weight portion

Silicon 15-50 weight portion

3. carbon/silicon composite cathode material according to claim 1, the specific discharge capacity that it is characterized in that it is 400-1500nAh/g, and cycle efficieny is 75-90% first, and 200 times circulation back capability retention is 75-85%.

4. according to the described carbon/silicon composite cathode material of each claim among the claim 1-3, it is characterized in that silicon is the nano particle that silicon precursor forms with magnesium powder reaction original position that contains that is selected from silicones, silica gel by one or more in described carbon/silicon composite cathode material in heat treatment process, be of a size of 10-100nm, be dispersed in the carbon base body.

5. according to the described carbon/silicon composite cathode material of each claim among the claim 1-3, it is characterized in that carbon is to be selected from coal tar pitch by one or more in described carbon/silicon composite cathode material, petroleum residual oil pitch, coal tar, mesophase pitch, the carbon matrix precursor that contains of phenolic resins is handled the carbon component that forms through the heat of carbonization, the network-like basal body structure of this carbon component, can closely wrap up generated in-situ silicon grain in the heat treatment process, prevent to reunite mutually in the silicon grain forming process, guarantee that silicon grain is of a size of the 10-100 nanometer in carbon/silicon composite, and in as the lithium ion battery negative material charge and discharge process, can effectively suppress to give carbon/cycle efficieny first of silicon composite lithium ion battery cathode material excellence and stable cycle performance because silicon grain is inserted lithium/take off the change in volume that lithium causes.

6. the preparation method of a lithium ion battery negative carbon/silicon composite is characterized in that this method comprises the steps:

6.1 use the carbon matrix precursor that contains be selected from coal tar pitch, petroleum residual oil pitch, coal tar, mesophase pitch, phenolic resins, be selected from the silicon precursor that contains of silicones, silica gel, with magnesium powder (400-1000 order) according to containing carbon matrix precursor, contain silicon precursor and magnesium powder mass ratio is 1: the ratio of 0.5-3: 0.1-1 in autoclave pressure reaction temperature 350-500 ℃ with pressure 0.1-5Mpa under carry out thermal polycondensation reaction 0.5-5 hour, the thermal polycondensation product that obtains;

6.2 under the carburizing temperature 650-1100 ℃ of condition with inert atmosphere, handle and obtained the thermal polycondensation product 0.5-5 hour in step 6.1, the carbonized product that obtains;

6.3 with concentration is to obtain carbon/silicon composite behind the hydrochloric acid soaking step 6.2 of 5-36% obtain heat treatment product 0.5-24 hour, washed with de-ionized water, oven dry.

7. preparation method according to claim 5 is characterized in that the described carbon matrix precursor that contains is one or more carbon matrix precursors that contain that are selected from coal tar pitch, petroleum residual oil pitch, coal tar, mesophase pitch, phenolic resins.

8. preparation method according to claim 5 is characterized in that and will contain carbon matrix precursor, contains silicon precursor and magnesium powder mass ratio is 1: the ratio of 0.5-3: 0.1-1 is carried out thermal polycondensation and is handled.

9. preparation method according to claim 5 is characterized in that carrying out step 6.2 heat treatment under the carburizing temperature 650-1100 ℃ of condition with inert atmosphere.

10. preparation method according to claim 5 is characterized in that with concentration being that the hydrochloric acid of 5-36% carries out step 6.3 clean.

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