Coated silicon-carbon negative electrode material, preparation method thereof and lithium ion battery

Abstract

This invention provides a coated silicon-carbon anode material, its preparation method, and a lithium-ion battery. The preparation method of the coated silicon-carbon anode material includes: heating and mixing a silicon source, graphite, and a carbon source in a kneading device to obtain a pretreated material; and carbonizing the pretreated material to obtain the coated silicon-carbon anode material. Before the carbonization process, the silicon source, graphite, and carbon source are first heated and mixed in a kneading device to form the pretreated material. Compared to conventional mixing methods, heating while mixing in a kneading device can significantly improve the kneading and coating degree of the silicon source, carbon source, and graphite. After the carbonization process, the carbon source and silicon are coated on the graphite surface. Due to the softness of graphite, this can reduce the expansion rate of silicon during charge and discharge to a certain extent, thereby improving the cycle performance of the silicon-carbon material. Furthermore, the above preparation method is simple, easy to implement, low in cost, and readily suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery negative electrode material preparation, in particular to a coated silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] The specific capacity of Si-based negative electrode material is as high as 3500 mAh / g or more. Compared with graphite negative electrode material, the theoretical energy density of the coated silicon-carbon negative electrode material is more than 10 times higher. However, the coated silicon-carbon negative electrode material has a natural defect, i.e., lithium insertion into the silicon cell will cause serious expansion of the silicon material, which will cause rapid capacity decline. In order to improve the cycle stability of the silicon-based negative electrode material, the existing silicon-carbon materials mainly include coated type, embedded type and doped type, but the preparation methods thereof are relatively complex.

[0003] In view of the above problems, it is necessary to provide a preparation method of a coated silicon-carbon negative electrode material with simple process, high cycle stability and high cycle capacity. SUMMARY

[0004] The main purpose of the present application is to provide a coated silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery, so as to solve the problem that the existing coated silicon-carbon negative electrode material cannot simultaneously meet the problems of simple process, high cycle stability and high cycle capacity.

[0005] In order to achieve the above purpose, the present application provides a preparation method of a coated silicon-carbon negative electrode material, which comprises: heating and mixing silicon source, graphite and carbon source in a kneading device to obtain pretreated material; carbonizing the pretreated material to obtain the coated silicon-carbon negative electrode material.

[0006] Further, the shear rate of the kneading device is 10-22 r / min, the heating and mixing process is 1-5 h, and the heating process is 50-120℃.

[0007] Further, the weight ratio of the silicon source, graphite and carbon source is 1:(2-10):(2-20).

[0008] Further, the carbon source is selected from one or more of the group consisting of sucrose, glucose, polyacrylic acid, polyvinyl chloride, polyethylene glycol, hydroxymethyl cellulose, sodium alginate, coal tar pitch and phenolic resin; the silicon source is selected from silicon powder and / or silicon nanowire, preferably, the particle size of the silicon powder is 30-150 nm, the diameter of the silicon nanowire is 30-100 nm, and the length is 20-100 μm.

[0009] Further, the carbonization process comprises: heating at 2-10℃ / min under an inert atmosphere, and after being heated to 500-900℃, holding for 2-4 hours, and then naturally cooling to room temperature to obtain the coated silicon-carbon negative electrode material; preferably, the inert atmosphere is argon.

[0010] Further, after the carbonization process, the preparation method comprises: grinding the product obtained after the carbonization process to obtain the coated silicon-carbon negative electrode material; preferably, the particle size d50 of the coated silicon-carbon negative electrode material is 5-12μm.

[0011] Another aspect of the present application also provides a coated silicon-carbon negative electrode material prepared by the preparation method provided by the present application.

[0012] Further, the porosity of the coated silicon-carbon negative electrode material is 30%-70%, and the bulk density is 0.2-0.6g / cm 3 .

[0013] Still another aspect of the present application also provides a lithium ion battery comprising a negative electrode material, wherein the negative electrode material comprises the coated silicon-carbon negative electrode material provided by the present application.

[0014] According to the technical solution of the present application, in the above preparation method, before the carbonization process, the silicon source, the graphite and the carbon source are heated and mixed by using a kneading device to form a pretreated material. Compared with the conventional mixing method, the kneading and coating degree of the silicon source, the carbon source and the graphite can be greatly improved by heating while mixing in the kneading device. After the carbonization process, the carbon source and the silicon source are coated on the surface of the graphite. Since the graphite has a certain softness, the expansion rate of the silicon during the charging and discharging process can be reduced to some extent, thereby improving the cycle performance of the carbon-silicon material. At the same time, the above preparation method is simple and easy to implement, has low cost, and is easy to be industrialized. In summary, the coated silicon-carbon composite material prepared by the above preparation method has low expansion rate, good cycle performance and high cycle capacity, and the preparation process is simple, has low cost and is easy to be industrialized. BRIEF DESCRIPTION OF DRAWINGS

[0015] The drawings constituting a part of the specification illustrate the present application and, together with the description, serve to explain the principles of the application. In the drawings:

[0016] Figure 1 Fig. 1 shows the SEM image of the coated silicon-carbon negative electrode material prepared in Example 1 of the present application at 10000 times;

[0017] Figure 2The cycle number-discharge specific capacity curve of the lithium ion battery made of the coated silicon-carbon negative electrode material prepared in Embodiment 1 of the present application is shown. DETAILED DESCRIPTION

[0018] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0019] As described in the background, the existing coated silicon-carbon negative electrode material cannot simultaneously meet the problems of simple process, high cycle stability and high cycle capacity. In order to solve the above technical problems, the present application provides a preparation method of a coated silicon-carbon negative electrode material, which comprises: in a kneading device, heating and mixing silicon source, graphite and carbon source to obtain pretreated material; carbonizing the pretreated material to obtain the coated silicon-carbon negative electrode material.

[0020] In the above preparation method, before the carbonization process, the kneading device is used to heat and mix the silicon source, graphite and carbon source to form the pretreated material. Compared with the conventional mixing method, the mixing in the kneading device is accompanied by heating, which can greatly improve the kneading and coating degree of the silicon source, carbon source and graphite. After the carbonization process, the carbon source and silicon are coated on the surface of the graphite. Since the graphite has a certain softness, it can reduce the expansion rate of silicon to some extent during the charging and discharging process, thereby improving the cycle performance of the carbon-silicon material. At the same time, the above preparation method is simple, low in cost and easy to industrialize. In summary, the coated silicon-carbon composite material prepared by the above preparation method has low expansion rate, good cycle performance and high cycle capacity, and the preparation process is simple, low in cost and easy to industrialize.

[0021] In order to further improve the kneading degree of the carbon source, silicon source and graphite, and the porosity of the subsequently formed silicon-carbon negative electrode material, preferably, the shear rate of the kneading device is 10-22 r / min, the heating and mixing process is 1-5 h, and the heating process is 50-120℃.

[0022] In a preferred embodiment, the weight ratio of the silicon source, graphite and carbon source is 1:(2-10):(2-20). The weight ratio of the silicon source, graphite and carbon source includes but is not limited to the above range, and it is beneficial to further improve the cycle capacity of the silicon-carbon negative electrode material to limit it in the above range.

[0023] In the above preparation method, the silicon source and the carbon source can be selected from the commonly used types in the art. For example, the carbon source includes but is not limited to one or more of the group consisting of sucrose, glucose, polyacrylic acid, polyvinyl chloride, polyethylene glycol, hydroxymethyl cellulose, sodium alginate, coal tar pitch and phenolic resin; the silicon source includes but is not limited to silicon powder and / or silicon nanowire. In order to further improve the coating property of the carbon source, preferably, the particle size of the silicon powder is 30-150 nm, the diameter of the silicon nanowire is 30-100 nm, and the length of the silicon nanowire is 20-100 μm.

[0024] The above carbonization process can use the commonly used processes and devices in the art. Preferably, in the above carbonization process, the pretreated material is placed in a quartz pot and subjected to carbonization treatment in a high-temperature tube furnace.

[0025] The carbonization treatment of the pretreated material can coat the carbon source and the silicon source on the surface of the graphite. Since the graphite has a certain softness, this can to some extent alleviate the expansion of silicon during the charging and discharging process. More preferably, the carbonization process includes: heating at 2-10 ℃ / min under an inert atmosphere, rising to 500-900 ℃, and then maintaining the temperature for 2-4 hours, and then naturally cooling to room temperature to obtain the coated silicon-carbon negative electrode material. The carbonization treatment of the pretreated material using the above process is beneficial to improve the porosity of the silicon-carbon negative electrode material, thereby being beneficial to further reduce the expansion rate of silicon during the charging and discharging process, and thereby improving the cycle performance and structural stability of the carbon-silicon material. Preferably, the inert atmosphere is argon.

[0026] In order to further improve the structural stability of the carbon-silicon negative electrode material, preferably, after the carbonization process, the above preparation method includes: grinding the product obtained after the carbonization process to obtain the coated silicon-carbon negative electrode material; more preferably, the above grinding process is carried out in a star-shaped ball mill, the ball-to-material ratio is (1-15):1, and the particle size d50 of the coated silicon-carbon negative electrode material obtained after grinding is 5-12 μm.

[0027] Another aspect of the present application also provides a coated silicon-carbon negative electrode material, which is prepared by the preparation method provided in the present application.

[0028] In the above preparation method, the silicon source, graphite and carbon source are heated and mixed to form a pretreated material before the carbonization process. Compared with the conventional mixing method, the kneading and coating degree of the silicon source, carbon source and graphite can be greatly improved by heating while mixing in the kneading device. After the carbonization process, the carbon source and silicon source are coated on the surface of the graphite. Since the graphite has a certain softness, the expansion rate of silicon during charging and discharging can be reduced to some extent, thereby improving the cycle performance of the carbon-silicon material. Meanwhile, the above preparation method is simple and easy to implement, and has low cost. In summary, the coated silicon-carbon composite material prepared by the above preparation method has low expansion rate, good cycle performance and high cycle capacity, and the preparation process is simple and has low cost.

[0029] To further improve the comprehensive performance of the coated silicon-carbon negative electrode material, more preferably, the porosity of the coated silicon-carbon negative electrode material is 30-70%, and the bulk density is 0.2-0.6 g / cm 3 .

[0030] Another aspect of the present application also provides a lithium ion battery comprising a negative electrode material, wherein the negative electrode material comprises the coated silicon-carbon negative electrode material provided by the present application.

[0031] The coated silicon-carbon composite material prepared by the above preparation method has low expansion rate, good cycle performance and high cycle capacity, and thus the lithium ion battery prepared by using the coated silicon-carbon negative electrode material provided by the present application also has very excellent rate performance and structural stability.

[0032] The present application will be further described in detail below in combination with specific examples, which cannot be understood as limiting the scope of the present application.

[0033] Example 1

[0034] A preparation method of a coated silicon-carbon negative electrode material comprises:

[0035] In the kneading pot, the silicon source (silicon powder, 60 nm), artificial graphite and sucrose are heated and mixed at a weight ratio of 1:8.5:16 to obtain a pretreated material, wherein the heating temperature is 120°C, the stirring speed of the kneading pot is 20 r / min, and the stirring time is 3 h.

[0036] The uniformly stirred silicon powder, artificial graphite and carbon source are hot transferred into a quartz pot, the quartz pot is placed in a high-temperature tube furnace, and the carbonization treatment is carried out according to the following firing curve: the temperature is raised at a rate of 2°C / min, and after rising to 860°C, it is kept for 3 h, and then naturally cooled to room temperature. The whole process is protected by argon gas at a flow rate of 50 ml / min.

[0037] The carbonized product in the high-temperature tube furnace is placed in a zirconium ball jar and ball milled on a planetary ball mill at a ball-to-material ratio of 10:1 and a rotation speed of 550 r / min. The sample is sieved through a 400-mesh sieve after ball milling to obtain the desired carbon-silicon negative electrode material. The SEM electron micrograph is shown in Figure 1 .

[0038] The obtained silicon-carbon negative electrode material is mixed with conductive carbon black and polyvinylidene fluoride at a weight ratio of 90:5:5 to prepare a slurry, which is then coated, rolled, and sheeted to obtain an electrode sheet. The electrode sheet is prepared into a button cell and tested. The cycle number-capacity graph is shown in Figure 2 . The first capacity is 603.3 mAh / g, the first efficiency is 94.8%, and the capacity retention rate after 50 cycles is 93.1%.

[0039] Example 2

[0040] The difference from Example 1 is that in the mixing kettle, the silicon source (silicon powder, 60 nm), artificial graphite, and sucrose are heated and mixed at a weight ratio of 1:2:20 to obtain a pretreated material, wherein the heating temperature is 120°C, the stirring blade rotation speed of the mixing kettle is 10 r / min, and the stirring time is 5 h.

[0041] The first capacity is 1405 mAh / g, the first efficiency is 85%, and the capacity retention rate after 50 cycles is 82%.

[0042] Example 3

[0043] The difference from Example 1 is that in the mixing kettle, the silicon source (silicon powder, 60 nm), artificial graphite, and sucrose are heated and mixed at a weight ratio of 1:10:2 to obtain a pretreated material, wherein the heating temperature is 120°C, the stirring blade rotation speed of the mixing kettle is 22 r / min, and the stirring time is 1 h. The first capacity is 580 mAh / g, the first efficiency is 93%, and the capacity retention rate after 50 cycles is 92.1%.

[0044] Example 4

[0045] The difference from Example 2 is that in the mixing kettle, the silicon source (silicon powder, 60 nm), artificial graphite, and sucrose are heated and mixed at a weight ratio of 1:5:10 to obtain a pretreated material, wherein the heating temperature is 120°C, the stirring blade rotation speed of the mixing kettle is 10 r / min, and the stirring time is 5 h.

[0046] The first capacity is 820 mAh / g, the first efficiency is 89.9%, and the capacity retention rate after 50 cycles is 89.1%.

[0047] Example 5

[0048] The difference from Example 2 is that in the heating and mixing process, the heating temperature is 50°C and the stirring speed is 10 r / min.

[0049] The first capacity is 1385 mAh / g, the first efficiency is 84.5%, and the capacity retention rate after 50 cycles is 81.9%.

[0050] Example 6

[0051] The difference from Example 2 is that the heating temperature in the heating and mixing process is 100°C, and the stirring speed is 20 r / min.

[0052] The first capacity is 1398 mAh / g, the first efficiency is 84.8%, and the capacity retention rate after 50 cycles is 82.7%.

[0053] Example 7

[0054] The difference from Example 2 is that the heating temperature in the heating and mixing process is 80°C, and the stirring speed is 15 r / min.

[0055] The first capacity is 1390 mAh / g, the first efficiency is 84%, and the capacity retention rate after 50 cycles is 82%.

[0056] Example 8

[0057] The difference from Example 2 is that in the mixing kettle, the silicon source (silicon powder, 60 nm), artificial graphite, and sucrose are heated and mixed at a weight ratio of 1:1:1 to obtain a pretreated material, wherein the heating temperature is 140°C, the stirring speed of the mixing kettle is 30 r / min, and the stirring time is 5 h.

[0058] The first capacity is 1890 mAh / g, the first efficiency is 81.6%, and the capacity retention rate after 50 cycles is 79.2%.

[0059] Example 9

[0060] The difference from Example 1 is that the carbonization temperature is 500°C.

[0061] The first capacity is 560.8 mAh / g, the first efficiency is 89.7%, and the capacity retention rate after 50 cycles is 86.7%.

[0062] Example 10

[0063] The difference from Example 1 is that the carbonization temperature is 700°C.

[0064] The first capacity is 590.6 mAh / g, the first efficiency is 92.4%, and the capacity retention rate after 50 cycles is 90.2%.

[0065] Example 11

[0066] The difference from Example 1 is that the carbonization temperature is 1100°C.

[0067] The initial capacity is 520 mAh / g, the initial efficiency is 84.0%, and the capacity retention rate after 50 cycles is 80.5%.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that the mixture of the silicon source (silicon powder, 60 nm), artificial graphite, sucrose and water is stirred, and then spray-dried to obtain a pretreated material, and the temperature of spray-drying is 120°C. Then, carbonization treatment and grinding are sequentially performed to obtain a carbon-silicon negative electrode material. The performance thereof is tested by the same method as in Example 1, and the test results show that the initial capacity of the button cell prepared thereby is 518 mAh / g, the initial efficiency is 79.5%, and the capacity retention rate after 50 cycles is 75.2%.

[0070] The porosity of the coated silicon-carbon negative electrode material prepared in Examples 1 to 11 is 30% to 70%, and the bulk density is 0.2 to 0.6 g / cm 3 , which is much higher than the porosity of the carbon-silicon negative electrode material prepared in Comparative Example 1, and the bulk density is smaller. From the above description, it can be seen that the above-mentioned examples of the present application achieve the following technical effects: the coated silicon-carbon composite material prepared by the above-mentioned preparation method has a low expansion rate, good cycle performance and high cycle capacity, and the preparation process is simple, the cost is low, and it is easy to industrialize production and has other advantages.

[0071] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the terms thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that described herein.

[0072] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a coated silicon-carbon negative electrode material, characterized in that, The preparation method of the coated silicon-carbon negative electrode material comprises the following steps: In a kneading device, a silicon source, graphite and a carbon source are heated and mixed to obtain a pretreated material; The pretreated material is carbonized to obtain the coated silicon-carbon negative electrode material; The shear rate of the kneading device is 10-22 r / min, the heating and mixing process is performed for 1-5 h, and the heating process is performed at 50-120°C; The carbonization process comprises the following steps: under an inert atmosphere, the temperature is raised at a rate of 2-10°C / min, raised to 500-900°C, and then kept for 2-4 hours, and then naturally cooled to room temperature to obtain the coated silicon-carbon negative electrode material; the inert atmosphere is argon; The weight ratio of the silicon source, the graphite and the carbon source is 1:(2-10):(2-20).

2. The method for preparing a coated silicon-carbon negative electrode material according to claim 1, characterized in that, The carbon source is selected from one or more of the group consisting of sucrose, glucose, polyacrylic acid, polyvinyl chloride, polyethylene glycol, hydroxymethyl cellulose, sodium alginate, coal tar pitch and phenolic resin; The silicon source is selected from silicon powder and / or silicon nanowires.

3. The method for preparing a coated silicon-carbon negative electrode material according to claim 2, characterized in that, The particle size of the silicon powder is 30-150 nm, and the diameter of the silicon nanowires is 30-100 nm and the length is 20-100 μm.

4. The method for preparing the coated silicon-carbon anode material according to claim 1, characterized in that, After the carbonization process, the preparation method comprises the following step: the product obtained after the carbonization process is ground to obtain the coated silicon-carbon negative electrode material.

5. The method for preparing a coated silicon-carbon negative electrode material according to claim 4, characterized in that, The particle size d50 of the coated silicon-carbon negative electrode material is 5-12 μm.

6. A coated silicon-carbon negative electrode material, characterized in that The coated silicon-carbon negative electrode material is prepared by the preparation method of any one of claims 1-5.

7. The coated silicon-carbon anode material of claim 6, wherein, The porosity of the coated silicon-carbon negative electrode material is 30% to 70%, and the bulk density is 0.2 to 0.6 g / cm 3 .

8. A lithium-ion battery comprising a negative electrode material, characterized in that, The negative electrode material comprises the coated silicon-carbon negative electrode material of claim 6 or 7.

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