Lithium ion battery silicon-carbon negative electrode material and preparation and application thereof

Abstract

The preparation method comprises the following steps: weighing graphite particles, putting the graphite particles into a tubular furnace, heating under the protection of an inert atmosphere, introducing steam generated after heating a silicon-carbon-containing organic liquid into the tubular furnace, and depositing a silicon-carbon layer on the surface of the graphite particles to obtain a silicon-carbon composite material; the target product is the silicon-carbon negative electrode material. Compared with the prior art, the silicon-carbon composite material is prepared by depositing a silicon-carbon layer on the surfaces of graphite particles by using siloxane as a reaction source under a high-temperature condition by using a chemical vapor deposition (CVD) method, and the silicon-carbon composite material is used as a lithium ion battery negative electrode material, so that the first charge-discharge efficiency and the cycle stability of a battery can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery negative electrode materials and relates to a lithium ion battery silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Among the many energy storage technologies, lithium-ion batteries are widely used in electronic equipment, power vehicles and other fields because of their high energy density, large output power, high operating voltage, no memory effect and long cycle life.

[0003] However, with the rapid development of electronic energy-demanding devices, the requirements for the energy density of lithium-ion batteries are becoming higher and higher. The theoretical specific capacity of traditional graphite negative electrode materials for lithium-ion batteries is only 372mAh / g, which is difficult to meet the existing needs. The theoretical specific capacity of silicon is as high as 4200mAh / g, which is the negative electrode material with the highest theoretical capacity so far. Using silicon materials as lithium-ion negative electrode materials can effectively improve the energy density of lithium-ion batteries. However, the silicon negative electrode is accompanied by huge volume changes during the charging and discharging process, and its volume expansion rate reaches 270%. The pulverization caused by the volume change of silicon materials causes the active materials to peel off, and ultimately leads to a significant decrease in the capacity of the lithium-ion negative electrode or even complete failure. Therefore, it is urgent to provide a solution to inhibit the volume expansion of silicon materials and improve the structural stability of negative electrode materials, which is of great significance for improving the coulombic efficiency and cycle stability of lithium-ion batteries.

[0004] Chinese patent CN202110733384.8 provides a silicon-carbon negative electrode material and its preparation method and application. The preparation method includes the following steps: the vaporized product of the silicon-carbon liquid precursor is mixed with the preheated graphite to obtain a silicon oxide-carbon composite nanolayer coated graphite composite material, and then an aluminothermic reduction reaction is performed. The silicon-carbon negative electrode material prepared by this patent still has room for further improvement in terms of cycle performance and other aspects. Summary of the invention

[0005] The purpose of the present invention is to provide a lithium-ion battery silicon-carbon negative electrode material and its preparation and application, by using a chemical vapor deposition method (CVD), using siloxane as a reaction source under high temperature conditions, depositing a silicon-carbon layer on the surface of graphite particles, thereby improving the low intrinsic conductivity of the silicon negative electrode material, the large volume expansion during lithiation, and the small Li + Diffusion rate and other issues, improve the fast charging ability and stability of silicon-based negative electrodes, will have fast Li + Amorphous silicon with high transmission capacity and highly conductive carbon materials are introduced into the lithium-ion battery system to construct silicon-carbon composite materials. The fast charging capability and stability of the negative electrode of the lithium-ion battery are enhanced by optimizing the structure and composition of the silicon-carbon composite materials.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] On the one hand, the present invention provides a method for preparing a silicon-carbon negative electrode material for a lithium-ion battery, wherein graphite particles are weighed and placed in a tubular furnace, and the temperature is increased under the protection of an inert atmosphere, and then a mixed steam formed by steam generated by heating a silicon-carbon organic liquid and H2 is introduced into the tubular furnace, and a silicon-carbon layer is deposited on the surface of the graphite particles to obtain a silicon-carbon composite material, which is the target product, the silicon-carbon negative electrode material.

[0008] Furthermore, the silicon-carbon-containing organic liquid is octamethyltrisiloxane.

[0009] Furthermore, the gas providing the inert atmosphere is N2 or Ar.

[0010] Furthermore, the heating process is specifically as follows: heating to 800-1200° C. at a heating rate of 5-15° C. / min. Preferably, the heating rate is 10° C. / min; the heating temperature is 1000° C.

[0011] Furthermore, the temperature of heating the silicon-carbon organic liquid is 120-140°C, preferably 130°C.

[0012] Further, the volume flow ratio of the mixed steam to the gas providing the inert atmosphere is (3-5): 1;

[0013] In the mixed steam, the volume ratio of H2 to the steam generated by heating the silicon-carbon organic liquid is (3.5-4.5): 1. The introduction of H2 here can reduce the content of SiOx phase in the deposited layer, which can improve the specific capacity and first CE of the electrode. During the pyrolysis of OMTS, the participation of an appropriate amount of H2 makes more Si atoms in OMTS converted into amorphous Si particles, and at the same time, the C atoms in OMTS are converted into an amorphous carbon matrix.

[0014] Furthermore, the time for depositing the silicon carbon layer is 2 to 6 hours.

[0015] Furthermore, the particle size of the graphite particles used is 200 meshes. In a second aspect, the present invention provides a lithium ion battery silicon-carbon negative electrode material, which is prepared by the preparation method described in the first aspect above.

[0016] In a third aspect, the present invention also provides a use of a lithium-ion battery silicon-carbon negative electrode material as an active material in the preparation of a lithium-ion battery negative electrode sheet.

[0017] Compared with the prior art, the present invention utilizes chemical vapor deposition (CVD) to deposit a silicon-carbon layer on the surface of graphite particles using siloxane as a reaction source under high temperature conditions, thereby preparing a silicon-carbon composite material, which is used as a negative electrode material for lithium-ion batteries, and can significantly improve the initial charge and discharge efficiency and cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The SEM images of the samples obtained at different silicon carbon layer deposition times in Examples 1 to 3;

[0019] Figure 2 This is a performance diagram of the silicon-carbon composite sample prepared in Comparative Example 1;

[0020] Figure 3 TG test graphs of samples prepared at different deposition times in Examples 1 to 3;

[0021] Figure 4 The electrochemical performance diagrams of the samples prepared at different deposition times in Examples 1 to 3. DETAILED DESCRIPTION

[0022] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0023] In the following examples, commercial graphite particles were purchased from Suzhou Carbon Graphene Technology Co., Ltd., with a particle size of 200 mesh;

[0024] Styrene butadiene rubber latex was purchased from Dongguan Kelude Innovation Technology Co., Ltd., brand SBR307;

[0025] The ternary lithium-ion battery electrolyte was purchased from Dongguan KLD Innovation Technology Co., Ltd., KLD-1230-C.

[0026] The rest of the raw materials or processing techniques, unless otherwise specified, are conventional commercially available raw materials or conventional processing techniques in the art.

[0027] Embodiment 1:

[0028] A controllable heating device (this is a conventional heating device in the art, does not belong to the innovation of the present invention, and will not be described here) filled with a sufficient amount of octamethyltrisiloxane (OMTS) liquid is connected to the inlet of a tube furnace (1500 mL of solvent), and then 1 g of commercial graphite particles is placed in an alumina crucible and placed in the tube furnace. Subsequently, the tube furnace is heated to 1000°C at a heating rate of 10°C / min under a N2 atmosphere (25 mL / min). After that, the OMTS liquid is heated to 130°C and introduced into the tube furnace at a gas flow rate of 20 mL per minute, and H2 is introduced at a flow rate of 80 mL / min. Maintain this condition for 2 hours, then stop passing OMTS vapor and H2 and other gases, and change to a single pass Ar for cooling, and naturally cool to room temperature to obtain the product.

[0029] Embodiment 2:

[0030] This embodiment 2 provides a method for preparing a silicon-carbon negative electrode material for a lithium-ion battery, which is different from embodiment 1 in that the final heating time is maintained at 4 hours.

[0031] Embodiment 3:

[0032] This embodiment 3 provides a method for preparing a silicon-carbon negative electrode material for a lithium-ion battery, which is different from embodiment 1 in that the final heating time is maintained at 6 hours.

[0033] Performance Testing

[0034] The lithium ion battery silicon-based negative electrode material prepared in Examples 1 to 3 was used as the active material, and the active material, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:1:1.5:1.5, respectively, and stirred at room temperature for 6 hours to uniformly mix the components of the slurry, and then the mixed slurry was uniformly coated on the clean copper foil surface using an infrared drying flat plate coating machine (coated to a thickness of about 150 microns), and then transferred to an 80°C blast oven for drying for 15 minutes, sliced ​​using a slicer, and then the negative electrode sheet was transferred to a vacuum oven, dried under 80°C vacuum conditions for 12 hours, and then calendered. After being cut into a composite sheet with a diameter of 16 mm, a lithium sheet was used as a positive electrode sheet, a ternary lithium ion battery electrolyte was used as an electrolyte, and a polypropylene microporous membrane was used as a diaphragm, and a button lithium battery was assembled in a glove box, and the batteries in Examples 1 to 3 were respectively subjected to cycle charge and discharge tests at 25°C and 0.2C rate, and the results are shown in Table 1 below.

[0035] Table 1 Electrochemical performance test results of button lithium battery

[0036]

[0037] It can be seen from Table 1 that the lithium-ion battery using the silicon-carbon negative electrode material prepared in Example 1 has good capacity performance and cycle stability, and the capacity retention rate after 100 cycles is as high as 93.2%. Although the coating time is longer when preparing the negative electrode material in Examples 2 and 3, the bonding performance between the silicon-carbon negative electrode surface and the polymerized carbonized layer is reduced, and the cycle performance of the lithium-ion battery is reduced, which affects the utilization rate of lithium and reduces the stability of lithium on the carbonized skeleton, thereby causing a decrease in cycle performance.

[0038] By controlling the deposition time of the silicon carbon layer, i.e., 2h, 4h, and 6h, samples with different deposition amounts of the silicon carbon layer were synthesized. The reason for adjusting the deposition time of the silicon carbon layer is that if the deposition time is too short, the low Si content in the silicon carbon layer cannot effectively exert the advantages of the high specific capacity of Si and the fast ion transport of the amorphous silicon carbon structure. If the deposition time is too long, the excessive Si content in the silicon carbon layer may cause severe electrode volume expansion during the lithiation process and destroy the electrode structure. Figure 1 The SEM images of samples obtained at different deposition times show that at deposition times of 2h, 4h and 6h, the synthesized samples present similar surface morphologies.

[0039] Figure 2 In the figure, (a) is the full XPS spectrum of graphite and silicon-carbon composite sample (Comparative Example 1), from which it can be seen that the graphite sample shows a typical C1s peak; the silicon-carbon composite sample shows an obvious Si2p peak, indicating the presence of Si components; at the same time, O elements are also detected in the silicon-carbon composite sample, which are mainly due to the residual SiOx (x<2) in the silicon-carbon layer. (b) is the C1s spectrum of the silicon-carbon composite sample (Comparative Example 1). Compared with graphite, its C1s peak position obviously moves to a high binding energy position. This is because the amorphous carbon (CC, sp 2 ) is caused by the presence of C-Si bond. In addition, the peak related to C-Si bond cannot be fitted in the C1s spectrum, indicating that there is no SiC in the silicon carbon layer. (c) is the Si2p spectrum of the silicon carbon composite material (Comparative Example 1). o In addition, some Si l+ This is mainly due to the residual SiOx (x < 2) in the silicon-carbon layer. In addition, as shown in Figure (a), it is shown that in the absence of H2, the Si element in the silicon-carbon composite material exists in the form of SiOx (x < 2) compounds. Therefore, the introduction of H2 can play a reducing role in the pyrolysis process, thereby reducing the O content in the deposited layer.

[0040] The Si content in the samples prepared at different deposition times (2h, 4h and 6h) was determined by TG test. Figure 3As shown, with the increase of deposition time, the mass percentage of residual products of the obtained samples after being subjected to a high temperature of 1000°C in air gradually increases (25.3wt%, 2h; 38.2wt%, 4h; 53.6wt%, 6h). Based on this, it can be obtained that the Si content in the samples obtained when the deposition time is 2h, 4h and 6h is 11.8wt%, 17.8wt% and 25.0wt% respectively, that is, with the increase of deposition time, the Si content in the C-Si@graphite sample continues to increase. For silicon / graphite composite materials prepared by directly depositing a silicon layer on the graphite surface by CVD method, the Si content is usually not more than 10wt%, otherwise, too high Si content will cause a huge volume expansion of the electrode, thereby causing damage to the electrode structure and attenuation of the cycle life. However, this silicon-carbon layer structure coated on the surface of graphite particles can solve the above problems. That is, in the silicon-carbon layer, the uniformly dispersed amorphous Si particles can effectively avoid the stress concentration caused by the volume expansion of Si during the lithiation process, protect the electrode structure to a certain extent, and reduce the degree of damage to the electrode. In addition, the amorphous carbon matrix can play a confining role, inhibiting the volume expansion of Si during the lithiation process. At the same time, it can avoid the secondary agglomeration problem of Si during the cycle, thereby ensuring that the electrode still has good cycle stability under the condition of high Si content. More importantly, the structure of the silicon-carbon layer in which Si particles are evenly dispersed in the carbon matrix significantly increases the contact area between silicon and carbon, which can effectively improve the transmission speed of electrons in the silicon-carbon layer.

[0041] Figure 4In the figure, (a) is the first charge and discharge curve of the samples obtained at different deposition times at a rate of 0.1C. It can be seen that the first charge specific capacity of the silicon-carbon composite material gradually increases with the increase of the deposition time of the silicon-carbon layer (729.5mAhg, 2h; 972.6mAhg, 4h; 1246.3mAhg, 6h). This is because the Si content in the sample gradually increases with the increase of the deposition time of the silicon-carbon layer. (b) is the cycle performance of the silicon-carbon composite material samples obtained at different deposition times at a rate of 0.1C. It can be seen that the samples with deposition times of 2h and 4h have good cycle stability, and the capacity retention rates after 100 charge and discharge cycles are 97.7% and 98.4%, respectively. The good cycle stability of these two samples is mainly due to the relatively low Si content in the samples, which makes the electrode volume expansion smaller, the uniformly dispersed Si particles avoid the generation of stress concentration, and the confinement effect of the carbon matrix in the silicon-carbon layer inhibits the agglomeration of Si particles and the destruction of the electrode structure by volume expansion during lithiation. The specific capacity (972.6 mAh g) of the sample with a deposition time of 4 h is significantly higher than that of the C-Si@graphite sample with a deposition time of 2 h (729.5 mAh g), and the higher specific capacity helps to improve the battery energy density. When the deposition time increases to 6 h, although the first charge specific capacity (1246.3 mAh g) of the sample is significantly higher than that of the samples with a deposition time of 2 h and 4 h, its cycle stability is far inferior to that of the samples with a deposition time of 2 h and 4 h. As can be seen from the figure, under the same test conditions, its capacity retention rate after 100 charge and discharge cycles is only 74.6%, and its specific capacity after 100 cycles is only 930.6 mAh g, which is lower than the specific capacity (957.4 mAh g) of the sample with a deposition time of 4 h after 100 cycles. This is mainly because when the deposition time is 6 h, the excessive Si content in the silicon carbon layer will cause a huge volume expansion, resulting in electrode cracking and even separation of the active material from the current collector, resulting in a decrease in cycle stability.

[0042] Comparative Example 1:

[0043] Compared with Example 1, most of the steps are the same, except that during the deposition of the silicon carbon layer, the mixed steam containing H2 is replaced with steam generated by heating pure OMTS liquid, that is, the introduction of H2 is omitted.

[0044] Under the same experimental conditions, a controllable heating device containing a sufficient amount of octamethyltrisiloxane (OMTS) liquid was connected to the inlet of a tube furnace (1500 mL of solvent), and then 1 g of commercial graphite particles was placed in an alumina crucible and placed in the tube furnace. Subsequently, the tube furnace was heated to 1000°C at a heating rate of 10°C / min under a N2 atmosphere (25 mL / min). After that, the OMTS liquid was heated to 130°C and introduced into the tube furnace at a gas flow rate of 20 mL per minute. Under this condition, it was maintained for 2 hours, after which the OMTS vapor was stopped and replaced with Ar, and the product was obtained by natural cooling to room temperature.

[0045] Comparative Example 2:

[0046] Compared with Example 2, most of the steps are the same, except that during the deposition of the silicon carbon layer, the mixed steam containing H2 is replaced with steam generated by heating pure OMTS liquid, that is, the introduction of H2 is omitted.

[0047] Comparative Example 3:

[0048] Compared with Example 3, most of the steps are the same, except that during the deposition of the silicon carbon layer, the mixed steam containing H2 is replaced with steam generated by heating pure OMTS liquid, that is, the introduction of H2 is omitted.

[0049] Performance Testing

[0050] The lithium ion battery silicon-based negative electrode material prepared in Comparative Examples 1 to 3 was used as the active material, and the active material, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:1:1.5:1.5, respectively, and stirred at room temperature for 6 hours to uniformly mix the components of the slurry, and then the mixed slurry was uniformly coated on the clean copper foil surface using an infrared drying flat plate coating machine (coated to a thickness of about 150 microns), and then transferred to an 80°C blast oven for drying for 15 minutes, sliced ​​using a slicer, and then the negative electrode sheet was transferred to a vacuum oven, dried under 80°C vacuum conditions for 12 hours, and then calendered. After being cut into a composite sheet with a diameter of 16 mm, a lithium sheet was used as a positive electrode sheet, a ternary lithium ion battery electrolyte was used as an electrolyte, and a polypropylene microporous membrane was used as a diaphragm, and a button lithium battery was assembled in a glove box, and the batteries in Comparative Examples 1 to 3 were respectively subjected to cycle charge and discharge tests at 25°C and 0.2C rate, and the results are shown in Table 2 below.

[0051] Table 2 Electrochemical performance test results of button lithium battery (without H2)

[0052]

[0053] By comparing Example 1 with Comparative Example 1, it can be seen that by introducing H2 to reduce the O content in the deposition layer during the pyrolysis process and optimizing the structure of the silicon-carbon composite material, the initial charge and discharge efficiency and cycle stability of the silicon-carbon composite material during application can be effectively improved.

[0054] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-ion battery silicon-carbon negative electrode material, characterized in that: Graphite particles are weighed and placed in a tubular furnace, and the temperature is increased under the protection of an inert atmosphere. The steam generated by heating the silicon-carbon organic liquid and the mixed steam formed by H2 are then introduced into the tubular furnace to deposit a silicon-carbon layer on the surface of the graphite particles to obtain a silicon-carbon composite material, which is the target product, the silicon-carbon negative electrode material.

2. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: The silicon-carbon-containing organic liquid is octamethyltrisiloxane.

3. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: The gas providing the inert atmosphere is N2 or Ar.

4. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: The specific heating process is: heating to 800-1200° C. at a heating rate of 5-15° C. / min.

5. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: The temperature of heating the silicon-carbon organic liquid is 120-140°C.

6. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: Volume flow ratio of mixed steam to gas providing inert atmosphere (3-5): 1; In the mixed steam, the volume ratio of H2 to the steam generated by heating the silicon-carbon containing organic liquid is (3.5-4.5):

1.

7. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: The time for depositing the silicon carbon layer is 2 to 6 hours.

8. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: The particle size of the graphite particles used was 200 mesh.

9. A lithium-ion battery silicon-carbon negative electrode material, characterized in that: The method is described in any one of claims 1 to 8.

10. Use of the lithium ion battery silicon-carbon negative electrode material as claimed in claim 9 as an active material in preparing a negative electrode sheet of a lithium ion battery.

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