Low-expansion silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a low-expansion silicon-carbon negative electrode material and a preparation method thereof, and belongs to the technical field of secondary batteries. The invention relates to a preparation method of a low-expansion silicon-carbon negative electrode material. The preparation method comprises the following steps: S1, depositing SiO2: depositing porous carbon for the first time by adopting silane with at least two ethyoxyl groups or methoxyl groups; then calcining to obtain a SiO2 deposition layer; s2, silicon deposition: carrying out secondary deposition on the material obtained in the step S1 by adopting monosilane, disilane and / or trichlorosilane; and S3, carbon coating: carrying out carbon coating on the material obtained in the step S2 by using a carbon source gas. According to the low-expansion silicon-carbon negative electrode material disclosed by the invention, porous carbon is firstly subjected to deposition modification by utilizing SiO2 deposition, so that the overall structural strength of a framework is improved; after silane deposition, silicon of the second deposition layer and silicon dioxide of the first deposition layer can react to generate SiO, and volume expansion of silicon crystal grains can be relieved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of secondary batteries, in particular to a low-expansion silicon-carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] Secondary batteries (i.e. rechargeable batteries) play a vital role in modern society, and the core advantage thereof is that the secondary batteries can be repeatedly charged and discharged. Compared with disposable batteries (primary batteries), the secondary batteries have the advantages of high economy, good environmental protection, convenience, superior performance and sustainable development, so that the secondary batteries become the mainstream choice for energy storage and utilization in modern society. With the development of industries such as unmanned aerial vehicles, electric aircrafts and electric vehicles, people have higher and higher requirements for the energy density of the secondary batteries.

[0003] The negative electrode material of the secondary battery plays a decisive role in the energy density thereof. As the main body of lithium ion intercalation / deintercalation, the theoretical specific capacity of the negative electrode material directly determines the maximum number of lithium ions that can be stored by the battery, thereby greatly affecting the total capacity of the battery. The higher the specific capacity is, the more energy can be theoretically stored.

[0004] The graphite negative electrode has already approached its theoretical specific capacity, and cannot further improve the energy density of the battery. Therefore, a series of new negative electrodes of conversion type and alloy type are paid more and more attention, and the silicon negative electrode is expected to be first commercialized on a large scale due to reasons such as element abundance, high specific capacity and suitable electrochemical potential. However, the silicon negative electrode currently still has defects such as large expansion rate and poor cycle performance. At present, the silicon negative electrode material has developed from sand milling silicon-carbon and silicon-oxygen material to the latest gas-phase deposition silicon-carbon. The development path is basically along the direction of reducing the expansion of the silicon negative electrode, and the expansion of the gas-phase deposition silicon-carbon is the smallest among the three types, but is still much higher than that of graphite. Therefore, the further development of the silicon negative electrode cannot be separated from the reduction of the expansion rate of the material, and the root cause of the poor cycle performance of the secondary battery is also due to the expansion of the material itself during the cycle process. SUMMARY

[0005] The application aims to provide a preparation method of a low-expansion silicon-carbon negative electrode material, and another object of the application is to provide a low-expansion silicon-carbon negative electrode material.

[0006] The application discloses a preparation method of a low-expansion silicon-carbon negative electrode material, which comprises the following steps:

[0007] S1, depositing SiO2: a silane with at least two ethoxy groups or methoxy groups is used to perform first deposition on porous carbon; then calcination is performed to obtain a SiO2 deposition layer;

[0008] S2, depositing silicon: silane, disilane and / or trichlorosilane are used to perform second deposition on the material obtained in step S1;

[0009] S3 Carbon coating: Carbon coating is performed on the material obtained in step S2 using a carbon source gas.

[0010] The porous carbon is selected from one of resin-based porous carbon, bio-based porous carbon, petroleum coke-based porous carbon.

[0011] Further, the specific surface area of the porous carbon is 1400-2200 m 2 / g, the pore volume is 0.6-1.2 cm 3 / g, and the mesopore ratio is >20%.

[0012] Such porous carbon has an ultrahigh specific surface area, can provide a large number of active sites, greatly improves the adsorption capacity and electrochemical activity. The moderate pore volume ensures a high specific surface area while avoiding the collapse of the skeleton caused by excessive activation. The high mesopore ratio significantly improves the material diffusion efficiency.

[0013] Further, the silane having at least two ethoxy groups or methoxy groups is selected from at least one of tetraethoxysilane, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane.

[0014] Further, the conditions for the first deposition are that the deposition is performed in an inert atmosphere selected from one of nitrogen, argon, and helium, and the deposition method can be rotary furnace CVD deposition or fluidized bed CVD deposition, and the deposition temperature is 100-500°C.

[0015] Further, the conditions for the calcination are that the calcination is performed in an inert atmosphere, the calcination temperature is 500-1200°C, and the calcination time is 1-6h.

[0016] The silane having at least two ethoxy groups or methoxy groups is deposited in the pores of the porous carbon by the first deposition, and is then decomposed into SiO2 by high-temperature calcination. SiO2 is an inert substance and does not swell in volume during charging and discharging. First, SiO2 is deposited on the porous carbon, which is beneficial to reducing the ultra-micropores of the porous carbon itself, adjusting the pore structure of the porous carbon, and enhancing the overall skeleton strength of the porous carbon.

[0017] Further, the mass of the SiO2 deposition is 0.1%-10% of the mass of the porous carbon.

[0018] Controlling the deposition amount of SiO2 within this range helps to reduce the ultra-micropores of the porous carbon itself, while not filling the mesopores of the porous carbon.

[0019] Further, the conditions for the second deposition are that the deposition is performed in an inert atmosphere, and the deposition temperature is 400-800°C.

[0020] The deposition method can be rotary furnace CVD deposition or fluidized bed CVD deposition.

[0021] After the deposition of silicon, the silicon is reacted with the silicon dioxide of the first deposition layer at high temperature to form SiO, and the SiO layer is formed in the contact layer between the silicon dioxide layer and the silicon layer.

[0022] Further, the mass of the second deposited silicon is 40-60% of the mass of the porous carbon.

[0023] The deposition amount is controlled within the range, so that the capacity and the cycle performance are balanced, the low deposition amount leads to low capacity of the negative electrode material, and the high deposition amount leads to poor cycle performance.

[0024] Further, the carbon source gas is selected from at least one of acetylene, methane, ethylene and benzene.

[0025] Further, the carbon coating condition is that the carbon coating is performed by chemical vapor deposition, and the coating temperature is 500-1000 DEG C.

[0026] Further, the thickness of the carbon layer of the carbon coating is 2-50nm.

[0027] The application further discloses a low-expansion silicon-carbon negative electrode material obtained by the preparation method.

[0028] The low-expansion silicon-carbon negative electrode material disclosed by the application is modified by SiO2 deposition to improve the overall structural strength of the skeleton; after the deposition of silane, the silicon of the second deposition layer can be reacted with the silicon dioxide of the first deposition layer to generate SiO, which is beneficial to relieve the volume expansion of the silicon grains. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a preparation process schematic diagram of the low-expansion silicon-carbon negative electrode material. DETAILED DESCRIPTION

[0030] In order to make the technical scheme of the application clearer, the application is further described in detail below with reference to the drawings and specific embodiments.

[0031] Embodiment 1

[0032] The silicon-carbon negative electrode material for lithium ion batteries in the embodiment is prepared by the following method:

[0033] 1) 1kg of resin-based porous carbon is selected as a matrix, and the specific surface area is 1800m 2 / g, and the pore volume is 1.0cm 3 / g, using tetraethoxysilane as the source material for CVD deposition in a rotating furnace at a flow rate of 1 g / min, a deposition temperature of 300°C, and calcination at 1000°C. The SiO2 mass deposited was 5% of the mass of the porous carbon.

[0034] 2) The intermediate product particles obtained in step 2) were subjected to silicon vapor deposition in a rotating furnace, using silane gas (SiH4) as the silicon source, at a deposition temperature of 500°C. The mass of silicon deposited was 48% of the mass of the porous carbon.

[0035] 3) The intermediate product particles obtained in step 2) were subjected to CVD carbon coating in a rotating furnace, using acetylene gas as the carbon source, at a deposition temperature of 600°C. The thickness of the carbon coating layer was 20 nm.

[0036] Example 2

[0037] The silicon-carbon anode material for lithium ion batteries of this example was prepared by the following method:

[0038] 1) 1 kg of resin-based porous carbon was selected as the substrate, with a specific surface area of 1800 m 2 / g, and a pore volume of 1.0 cm 3 / g, using tetraethoxysilane as the source material for CVD deposition in a rotating furnace at a flow rate of 1 g / min, a deposition temperature of 300°C, and calcination at 1000°C. The SiO2 mass deposited was 2% of the mass of the porous carbon.

[0039] 2) The intermediate product particles obtained in step 2) were subjected to silicon vapor deposition in a rotating furnace, using silane gas (SiH4) as the silicon source, at a deposition temperature of 500°C. The mass of silicon deposited was 48% of the mass of the porous carbon.

[0040] 3) The intermediate product particles obtained in step 2) were subjected to CVD carbon coating in a rotating furnace, using acetylene gas as the carbon source, at a deposition temperature of 600°C. The thickness of the carbon coating layer was 20 nm.

[0041] Example 3

[0042] The silicon-carbon anode material for lithium ion batteries of this example was prepared by the following method:

[0043] 1) 1 kg of resin-based porous carbon was selected as the substrate, with a specific surface area of 1800 m 2 / g, and a pore volume of 1.0 cm 3 / g, using tetraethoxysilane as the source material for CVD deposition in a rotating furnace at a flow rate of 1 g / min, a deposition temperature of 300°C, and calcination at 1000°C. The SiO2 mass deposited was 15% of the mass of the porous carbon.

[0044] 2) The intermediate product particles obtained in step 2) were subjected to silicon vapor deposition in a rotating furnace, using silane gas (SiH4) as the silicon source, at a deposition temperature of 500°C. The mass of silicon deposited was 48% of the mass of the porous carbon.

[0045] 3) The intermediate product particles obtained in step 2) are subjected to CVD carbon coating in a rotary furnace, the carbon source is acetylene gas, the deposition temperature is 600°C, and the carbon coating layer thickness is 20 nm.

[0046] Example 4

[0047] The silicon-carbon negative electrode material for lithium ion batteries of the present example is prepared by the following method:

[0048] 1) 1 kg of resin-based porous carbon is selected as the substrate, the specific surface area is 850 m 2 / g, and the pore volume is 1.1 cm 3 / g, rotary furnace CVD deposition is performed thereon at a flow rate of 1 g / min using tetraethoxysilane, the deposition temperature is 300°C, calcination is performed at 1000°C, and the mass of SiO2 deposited is 2% of the mass of the porous carbon.

[0049] 2) The intermediate product particles obtained in step 2) are subjected to vapor-phase silicon deposition in a rotary furnace, the silicon source is silane gas, the deposition temperature is 500°C, and the mass of silicon deposited is 48% of the mass of the porous carbon.

[0050] 3) The intermediate product particles obtained in step 2) are subjected to CVD carbon coating in a rotary furnace, the carbon source is acetylene gas, the deposition temperature is 600°C, and the carbon coating layer thickness is 20 nm.

[0051] Example 5

[0052] The silicon-carbon negative electrode material for lithium ion batteries of the present example is prepared by the following method:

[0053] 1) 1 kg of resin-based porous carbon is selected as the substrate, the specific surface area is 800 m 2 / g, and the pore volume is 1.0 cm 3 / g, rotary furnace CVD deposition is performed thereon at a flow rate of 1 g / min using tetraethoxysilane, the deposition temperature is 300°C, calcination is performed at 1000°C, and the mass of SiO2 deposited is 2% of the mass of the porous carbon.

[0054] 2) The intermediate product particles obtained in step 2) are subjected to vapor-phase silicon deposition in a rotary furnace, the silicon source is silane gas, the deposition temperature is 500°C, and the mass of silicon deposited is 65% of the mass of the porous carbon.

[0055] 3) The intermediate product particles obtained in step 2) are subjected to CVD carbon coating in a rotary furnace, the carbon source is acetylene gas, the deposition temperature is 600°C, and the carbon coating layer thickness is 20 nm.

[0056] Example 6

[0057] The silicon-carbon negative electrode material for lithium ion batteries of the present example is prepared by the following method:

[0058] 1) Select 1 kg of resin-based porous carbon as the substrate, specific surface area 1800 m 2 / g, pore volume 1.0 cm 3 / g, rotary furnace CVD deposition with tetraethoxysilane at a flow rate of 1 g / min, deposition temperature 300°C, calcination 1000°C, and the mass of SiO2 deposited is 2% of the mass of the porous carbon.

[0059] 2) Perform gas-phase silicon deposition on the intermediate product particles obtained in step 2) in a rotary furnace, with a silicon source of silane gas, at a deposition temperature of 500°C, and the mass of silicon deposited is 48% of the mass of the porous carbon.

[0060] 3) Perform CVD carbon coating on the intermediate product particles obtained in step 2) in a rotary furnace, with a carbon source of acetylene gas, at a deposition temperature of 600°C, and the thickness of the carbon coating layer is 10 nm.

[0061] Example 7

[0062] The silicon-carbon negative electrode material for lithium ion batteries of this example is prepared by the following method:

[0063] 1) Select 1 kg of resin-based porous carbon as the substrate, specific surface area 1200 m 2 / g, pore volume 0.7 cm 3 / g, rotary furnace CVD deposition with tetraethoxysilane at a flow rate of 1 g / min, deposition temperature 300°C, calcination 1000°C, and the mass of SiO2 deposited is 2% of the mass of the porous carbon.

[0064] 2) Perform gas-phase silicon deposition on the intermediate product particles obtained in step 2) in a rotary furnace, with a silicon source of silane gas, at a deposition temperature of 500°C, and the mass of silicon deposited is 48% of the mass of the porous carbon.

[0065] 3) Perform CVD carbon coating on the intermediate product particles obtained in step 2) in a rotary furnace, with a carbon source of acetylene gas, at a deposition temperature of 600°C, and the thickness of the carbon coating layer is 20 nm.

[0066] Example 8

[0067] The silicon-carbon negative electrode material for lithium ion batteries of this example is prepared by the following method:

[0068] 1) Select 1 kg of resin-based porous carbon as the substrate, specific surface area 2300 m 2 / g, pore volume 1.2 cm 3 / g, rotary furnace CVD deposition with tetraethoxysilane at a flow rate of 1 g / min, deposition temperature 300°C, calcination 1000°C, and the mass of SiO2 deposited is 2% of the mass of the porous carbon.

[0069] 2) The intermediate product particles obtained in step 2) were subjected to silicon vapor deposition in a rotary furnace, the silicon source was silane gas, the deposition temperature was 500°C, and the mass of silicon deposition was 48% of the mass of the porous carbon.

[0070] 3) The intermediate product particles obtained in step 2) were subjected to CVD carbon coating in a rotary furnace, the carbon source was acetylene gas, the deposition temperature was 600°C, and the thickness of the carbon coating layer was 20 nm.

[0071] Comparative Example 1

[0072] The silicon-carbon negative electrode material for lithium ion batteries of the present example was prepared by the following method:

[0073] 1) 1 kg of resin-based porous carbon was selected as the substrate, the specific surface area was 1800 m 2 / g, the pore volume was 1.0 cm 3 / g, the silicon source was silane gas, the deposition temperature was 500°C, and the mass of silicon deposition was 48% of the mass of the porous carbon.

[0074] 2) The intermediate product particles obtained in step 2) were subjected to CVD carbon coating in a rotary furnace, the carbon source was acetylene gas, the deposition temperature was 600°C, and the thickness of the carbon coating layer was 20 nm.

[0075] Comparative Example 2

[0076] The silicon-carbon negative electrode material for lithium ion batteries of the present example was prepared by the following method:

[0077] 1) 1 kg of resin-based porous carbon was selected as the substrate, the specific surface area was 1800 m 2 / g, the pore volume was 1.0 cm 3 / g, the silicon source was silane gas, the deposition temperature was 500°C, and the mass of silicon deposition was 48% of the mass of the porous carbon.

[0078] 2) Tetraethoxysilane was used for rotary furnace CVD deposition at a flow rate of 1 g / min, the deposition temperature was 300°C, and calcination was performed at 1000°C. The mass of SiO2 deposition was 2% of the mass of the porous carbon.

[0079] 3) The intermediate product particles obtained in step 2) were subjected to CVD carbon coating in a rotary furnace, the carbon source was acetylene gas, the deposition temperature was 600°C, and the thickness of the carbon coating layer was 20 nm.

[0080] Performance test:

[0081] The silicon-carbon negative electrode materials provided by the examples and comparative examples were assembled into button cells according to the same preparation process. The button cell assembly process is as follows.

[0082] The silicon-carbon material prepared by the example or the comparative example was used as a negative active material. The silicon-carbon composite negative active material, carboxymethyl cellulose and Super P were weighed in a mass ratio of 90:5:5, and then added with an appropriate amount of deionized water and ball-milled for 2 h using a planetary ball mill. The slurry after ball-milling was coated on a current collector, and the coated current collector was vacuum-dried at 80°C for 12 h and then cut into a negative electrode sheet with a diameter of 12 mm. A lithium metal was used as a counter electrode and a reference electrode, and a LiPF6 solution with a concentration of 1 mol / L was used as an electrolyte, and a mixed solution of diethyl carbonate and ethylene carbonate (volume ratio of 1:1) was used as a solvent. The coin cell was assembled in an argon glove box.

[0083] The coin cell assembled by the example and the comparative example was subjected to a coin cell test and a negative electrode sheet expansion rate test, and the test methods are described below, and the test results are shown in Table 1.

[0084] 1. Coin cell test

[0085] The porous carbon loaded nanosilicon negative electrode obtained by the example was cut into a negative electrode sheet with a diameter of 12 mm using a tablet press, and weighed for use.

[0086] Battery assembly: The positive electrode shell, sample electrode sheet, separator, lithium sheet, nickel mesh and negative electrode shell were stacked and assembled in the glove box. An appropriate amount of electrolyte was added dropwise in the middle of each sample. A total of 100 μL was added. The assembled coin cell was placed on the tablet press and pressed at 50 MPa for 10 s to obtain the coin cell prepared by the sample.

[0087] Battery test: The battery test was performed on a blue electric multifunctional battery test system, and the device model was CT2000A. The test steps are as follows:

[0088] Rest: 12 h;

[0089] Constant current discharge: 0.2 C, (1C = 1000 mAh), to 0.005 V;

[0090] Rest: 30 min;

[0091] Constant current charge: 0.2 C, (1C = 1000 mAh), to 1.5 V;

[0092] Rest: 30 min.

[0093] 2. Negative electrode sheet expansion rate test

[0094] Full charge expansion test: The thickness D1 of the negative electrode sheet of the coin cell after rolling was tested, and then the negative electrode sheet of the coin cell was dissected at 100% SOC, and the thickness D2 of the negative electrode sheet was tested, and then the full charge expansion rate was calculated as (D2-D1) / D1*100%.

[0095] Table 1 performance test results

[0096] 0.8 V capacity (mAh / g) 0.8 V initial efficiency (%) Pole piece expansion rate (%) Example 1 1705 82.79 70 Example 2 1761 84.02 72 Example 3 1648 81.96 67 Example 4 1777 84.11 68 Example 5 2014 84.83 86 Example 6 1775 84.00 77 Example 7 1589 83.78 109 Example 8 1755 82.51 68 Comparative Example 1 1699 83.05 130 Comparative Example 2 77 68 9

[0097] As shown in Table 1, compared with Comparative Example 1, Examples 1-8 can effectively improve the capacity, initial efficiency of lithium ion battery and reduce the expansion rate of the pole piece by depositing SiO2 first and then depositing Si.

[0098] Compared with Comparative Example 2, Examples 1-8, depositing Si first and then depositing SiO2, the high-temperature treatment required for depositing SiO2 makes the first-step deposited Si ineffective, thus greatly reducing the silicon capacity.

[0099] Compared with Example 2 and Example 3, the higher the deposited amount of silicon dioxide, the lower the capacity and initial efficiency, and the lower the pole piece expansion rate. This is because during the charging and discharging process, the side reaction between silicon dioxide and lithium affects the initial efficiency.

[0100] Compared with other examples, the specific surface area and pore volume of the porous carbon in Example 7 are small, and during vapor deposition, silicon and silicon dioxide are difficult to deposit in the deep part of the pore diameter, and part of the active material is only deposited on the surface of the porous carbon, affecting the activity of the active material.

[0101] Compared with other examples, Example 8 shows that the increase of pore volume also affects the initial efficiency. When the pore volume increases, the remaining pore volume will also consume lithium after the deposition of silicon decreases, thereby affecting the initial efficiency.

[0102] Compared with Example 2, in Example 5, the silicon deposition rate is high under the condition of the same silicon dioxide deposition rate, thereby the capacity and initial efficiency are high; but the pole piece expansion rate is larger, because the more silicon deposited, the higher the expansion rate of the pole piece.

[0103] Compared with Example 2, in Example 6, the thickness of the carbon layer is thinned, which shortens the lithium ion diffusion path and has a beneficial effect on capacity improvement; but the carbon layer is too thin, which will lead to insufficient strain resistance, thereby weakening the anti-expansion ability.

[0104] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the present patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present patent should be subject to the appended claims.

Claims

1. A method for preparing a low-expansion silicon-carbon anode material, characterized in that, Includes the following steps: S1 SiO2 deposition: Porous carbon is deposited for the first time using a silane with at least two ethoxy or methoxy groups; then calcined to obtain a SiO2 deposition layer; S2 Silicon Deposition: The material obtained in step S1 is deposited a second time using silane, silane and / or trichlorosilane; S3 Carbon Coating: Carbon coating is performed on the material obtained in step S2 using a carbon source gas. The porous carbon is selected from one of resin-based porous carbon, bio-based porous carbon, and petroleum coke-based porous carbon.

2. The method for preparing a low-expansion silicon-carbon anode material according to claim 1, characterized in that, The specific surface area of ​​the porous carbon is 1400-2200 m². 2 / g, pore volume between 0.6-1.2cm 3 / g, mesoporous ratio >20%.

3. The method for preparing a low-expansion silicon-carbon anode material according to claim 1, characterized in that, The silane having at least two ethoxy or methoxy groups is selected from at least one of tetraethoxysilane, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane.

4. The method for preparing a low-expansion silicon-carbon anode material according to claim 3, characterized in that, The conditions for the first deposition are as follows: deposition is carried out in an inert atmosphere, which is selected from nitrogen, argon, and helium. The deposition method can be rotary kiln CVD deposition or fluidized bed CVD deposition, and the deposition temperature is 100-500℃.

5. The method for preparing a low-expansion silicon-carbon anode material according to claim 4, characterized in that, The calcination conditions are as follows: calcination is carried out under an inert atmosphere, the calcination temperature is 500-1200℃, and the calcination time is 1-6h.

6. The method for preparing a low-expansion silicon-carbon anode material according to claim 5, characterized in that, The mass of the SiO2 deposited is 0.1%-10% of the mass of porous carbon.

7. The method for preparing a low-expansion silicon-carbon anode material according to claim 1, characterized in that, The conditions for the second deposition are: deposition is carried out in an inert atmosphere at a temperature of 400-800℃.

8. The method for preparing a low-expansion silicon-carbon anode material according to claim 1, characterized in that, The mass of the silicon deposited in the second deposition is 40-60% of the mass of the porous carbon.

9. The method for preparing a low-expansion silicon-carbon anode material according to claim 1, characterized in that, The carbon source gas is selected from at least one of acetylene, methane, ethylene, and benzene; carbon coating is performed by chemical vapor deposition at a coating temperature of 500-1000℃; and the thickness of the carbon coating layer is 2-50 nm.

10. A low-expansion silicon-carbon anode material, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

Images