Silicon-carbon negative electrode material with watermelon structure and preparation method and application thereof

Abstract

The application discloses a silicon-carbon negative electrode material with a watermelon structure and a preparation method and application thereof, and the preparation method comprises the following steps: step 1, liquid phase coating: adding nano silicon particles into a carbon source solution containing organic matter, uniformly stirring, filtering, and drying to obtain an organic carbon source coated nano silicon material; step 2, stirring and calcining the material obtained in step 1 in a protective gas atmosphere, then passing the protective gas after heating to obtain an intermediate material; step 3, passing a carbon source gas into the intermediate material obtained in step 2 to deposit carbon on the surface of the intermediate material, and collecting the product after the carbon deposition is completed, wherein the product is the silicon-carbon negative electrode material with the watermelon structure. The silicon-carbon negative electrode material has a gap between the carbon layer and the silicon, can provide space for the volume expansion of the silicon, and the carbon layer and the deposited carbon can provide buffering for the volume expansion of the silicon, thereby inhibiting the volume expansion of the silicon, forming a stable SEI film on the outside of the material, and reducing the consumption of lithium ions.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries have become an indispensable part of modern technology due to their high energy density, low self-discharge rate, long cycle life, portability, and environmental friendliness, and are applied to electric vehicles, smartphones, and other electric tools. Graphite is used as the traditional negative electrode of lithium ion batteries, but due to the low theoretical specific capacity of graphite (372 mAh / g), there is still much room for development in energy density and power density of lithium ion batteries, and they cannot currently meet the needs of electric vehicles and other electric devices.

[0003] Compared with graphite electrodes, silicon has a theoretical specific capacity of 4200 mAh / g, which is 10 times that of graphite electrodes. In addition, the electrochemical lithium intercalation potential is low. Therefore, silicon is considered to be the most promising negative electrode material for lithium ion batteries. However, silicon has some problems in terms of lithium extraction and intercalation: the volume change of silicon material is huge, the repeated formation and rupture of SEI film continuously consumes lithium ions, resulting in low battery cycle efficiency. SUMMARY

[0004] The present application aims to provide a preparation method of a silicon-carbon negative electrode material with a watermelon structure to address the problems of the prior art, such as the huge volume change of silicon material, the repeated formation and rupture of SEI film, and the continuous consumption of lithium ions, which leads to low battery cycle efficiency.

[0005] A second object of the present application is to provide a silicon-carbon negative electrode material with a watermelon structure prepared by the preparation method.

[0006] A third object of the present application is to provide a negative electrode sheet based on the silicon-carbon negative electrode material with a watermelon structure.

[0007] A fourth object of the present application is to provide a battery based on the negative electrode sheet.

[0008] To achieve the objects of the present application, the technical solutions adopted are as follows:

[0009] A preparation method of a silicon-carbon negative electrode material with a watermelon structure, comprising the following steps:

[0010] Step 1: Liquid phase coating: adding nano-silicon particles to a carbon source solution containing organic matter, stirring uniformly, filtering, and drying to obtain an organic carbon source coated nano-silicon material;

[0011] Step 2: The nano-silicon material coated with organic carbon source obtained in Step 1 is stirred and calcined at a first temperature for a first predetermined time under a protective gas atmosphere, and then heated to a second predetermined temperature and the protective gas is stopped to obtain an intermediate material.

[0012] Step 3: Introduce carbon source gas into the intermediate material obtained in Step 2, deposit carbon on the surface of the intermediate material at a second predetermined temperature, stop introducing carbon source gas after a second predetermined time, keep warm for a third predetermined time, and then collect the product at room temperature. The product is the silicon-carbon anode material with the watermelon-like structure.

[0013] In the above technical solution, the diameter of the nano-silicon particles is 5-100 nm, and the specific surface area of ​​the nano-silicon particles is 50-1000 m². 2 / g.

[0014] In the above technical solution, the stirring time in step 1 is 2-10 hours;

[0015] And / or, the mass fraction of organic matter in the carbon source solution containing organic matter is less than 15 wt%.

[0016] In the above technical solution, the organic matter in the carbon source solution containing organic matter in step 1 is one or more of polyvinylpyridinium ketone, glucose, or carboxymethyl cellulose.

[0017] In the above technical solution, the organic matter in the carbon source solution containing organic matter in step 1 is polyvinylpyridinium, glucose and carboxymethyl cellulose;

[0018] The mass fraction of the polyvinylpyridinium ketone content is not greater than 3 wt%.

[0019] And / or, the mass fraction of the glucose is not greater than 5 wt%;

[0020] And / or, the carboxymethyl cellulose content is not greater than 2.5 wt%.

[0021] In the above technical solution, the protective gas in step 2 is nitrogen, the flow rate of nitrogen is 0.2-1 L / min, the first predetermined temperature is 400-600℃, the first predetermined time is 2-6 h, the stirring speed is 2-10 Hz, and the second predetermined temperature is 600-800℃.

[0022] And / or, in step 3, the flow rate of the carbon source gas is 1-2 L / min, the second predetermined time is 6-8 h, and the third predetermined time is 0.5-1 h;

[0023] And / or, the carbon source gas is one or more of methane, ethane, propane, ethylene, acetylene, benzene, naphthalene, and anthracene.

[0024] In a second aspect, the present invention provides a silicon-carbon anode material with a watermelon-like structure, which is prepared by the aforementioned preparation method.

[0025] In the above technical solution, the particle size of the silicon-carbon anode material with the watermelon-like structure is 3μm-35μm.

[0026] A third aspect of the present invention provides a negative electrode sheet comprising the aforementioned watermelon-structured silicon-carbon negative electrode material.

[0027] A fourth aspect of the present invention provides a battery comprising the aforementioned negative electrode.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention provides a method for preparing a silicon-carbon anode material with a watermelon-like structure. First, a carbon layer is coated onto nano-silicon particles using a liquid-phase solidification method to obtain an intermediate material. Then, using a vapor-phase deposition method, several portions of the intermediate material are distributed on the deposited carbon to form a silicon-carbon anode material with a watermelon-like structure. The gaps between the carbon layer and the silicon provide space for the volume expansion of silicon. Furthermore, the carbon layer and the deposited carbon buffer the volume expansion of silicon, suppressing it. Therefore, a stable SEI film can be formed on the outer surface of the material, reducing lithium-ion consumption.

[0030] 2. In the silicon-carbon anode material of this invention, the average diameter of the nano-silicon particles is less than 100 nm, which is beneficial for the binding of lithium ions with silicon. During delithiation and lithium insertion processes, the particles will not be subjected to huge strain that could lead to particle breakage. Simultaneously, the use of an aqueous solution of polyvinylpyridinium, glucose, and carboxymethyl cellulose effectively prevents the sedimentation and agglomeration of the nano-silicon particles. After calcination, these additives carbonize to form a carbon layer, which is used to coat the nano-silicon particles. During delithiation and lithium insertion processes, the carbon layer can suppress the volume change of silicon. Furthermore, during carbonization, solvent evaporation creates pores, which provide space for the volume expansion of silicon. The deposited carbon formed in the carbon layer coating step has a uniformly distributed intermediate product inside, preventing agglomeration. Secondly, it can suppress the volume expansion of silicon during charge and discharge processes. At the same time, it can reduce the specific surface area of ​​the material, improving the initial coulombic efficiency and capacity of the battery. In addition, it is tightly connected with several intermediate materials to construct a complete conductive framework, thereby promoting the transfer of electrons and lithium ions. Attached Figure Description

[0031] Figure 1 A schematic diagram of the watermelon-inspired silicon-carbon anode material provided by this invention;

[0032] Figure 2 This is a SEM image of the watermelon-inspired silicon-carbon anode material in Embodiment 1 of the present invention;

[0033] Figure 3 This is an EDS image of a silicon-carbon anode material with a watermelon-like structure according to Embodiment 1 of the present invention;

[0034] Figure 4 This is a carbon atom distribution diagram of the watermelon-inspired silicon-carbon anode material in Embodiment 1 of the present invention;

[0035] Figure 5 This is a diagram showing the oxygen atom distribution of the watermelon-inspired silicon-carbon anode material in Embodiment 1 of the present invention.

[0036] Figure 6 This is a silicon atom distribution diagram of the watermelon-inspired silicon-carbon anode material in Embodiment 1 of the present invention;

[0037] Figure 7 This is the first charge-discharge curve of the watermelon-structured silicon-carbon anode material in Embodiment 1 of the present invention.

[0038] Figure 8 This is a graph showing the coulombic efficiency performance of the watermelon-inspired silicon-carbon anode material in Example 1 of the present invention after multiple cycles. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0040] Example 1

[0041] A silicon-carbon anode material with a watermelon-like structure, such as Figure 1 As shown, it is prepared by the following method:

[0042] Step 1, liquid phase coating: The nano-silicon particles are poured into an aqueous solution of 3 wt% polyvinylpyrrolidone, 5 wt% glucose and 2.5 wt% carboxymethyl cellulose, stirred evenly for 2 hours, filtered, and dried to obtain nano-silicon material coated with organic carbon source.

[0043] Step 2: Place the nano-silicon material coated with organic carbon source obtained in Step 1 into a rotary kiln, start the rotary kiln, introduce nitrogen gas at a flow rate of 0.2 L / min, calcine at 400℃ for 4 hours, maintain the rotation speed at 6 Hz, and after calcine, raise the temperature to 700℃ at full power, stop the nitrogen gas supply to obtain the intermediate material.

[0044] Step 3, carbon source cracking: Acetylene is introduced at a flow rate of 1.5 L / min and maintained for 8 hours. Then the carbon source gas is stopped, and the mixture is kept at the temperature for 1 hour before being cooled to room temperature. The rotary kiln is then stopped, and the product is collected to obtain the silicon-carbon anode material with the watermelon-like structure.

[0045] Table 1. Elemental content test results of the silicon-carbon anode material prepared in Example 1 of this study.

[0046] Element Line type wt% wt% σ At% C K line system 53.75 1.84 69.38 O K line system 12.20 0.89 11.82 Si K line system 34.05 1.36 18.80 Total amount 100 100

[0047] The SEM and EDS images of the watermelon-structured silicon-carbon anode material prepared in this embodiment are shown below. Figure 2 and Figure 3 As shown in Table 1, Figure 2 - Figure 6 It can be seen that the preparation method and equipment of the present invention can make silicon uniformly distributed inside carbon, realize the full composite of silicon and carbon, and obtain a silicon-carbon anode material with a watermelon-like structure.

[0048] A negative electrode sheet was prepared using a silicon-carbon negative electrode material with a watermelon-like structure, and a lithium-ion battery was assembled using this negative electrode sheet for performance testing. It can be seen that the lithium-ion battery assembled using the silicon-carbon negative electrode material prepared in this embodiment has an initial charge specific capacity of 1757.3 mAh·g. -1 The initial discharge specific capacity was 1978.1 mAh·g. -1 The initial coulombic efficiency was 88.84%, and after 250 cycles, the coulombic efficiency remained above 99%, indicating that this watermelon-like silicon-carbon anode material can effectively alleviate the volume expansion of silicon.

[0049] Example 2

[0050] In this embodiment, a silicon-carbon anode material with a watermelon-like structure is prepared by the following method:

[0051] Step 1, liquid phase coating: The nano-silicon particles are poured into an aqueous solution of 3 wt% polyvinylpyrrolidone, 5 wt% glucose and 2.5 wt% carboxymethyl cellulose, stirred evenly for 5 h, filtered, and dried to obtain nano-silicon material coated with organic carbon source.

[0052] Step 2: Place the nano-silicon material coated with organic carbon source obtained in Step 1 into a rotary kiln, start the rotary kiln, introduce nitrogen at a flow rate of 0.6 L / min, calcine at 500℃ for 6 hours, maintain the rotation speed at 8 Hz, and after calcine, raise the temperature to 600℃ at full power, stop the nitrogen flow to obtain the intermediate material.

[0053] Step 3, carbon source cracking: Acetylene is introduced at a flow rate of 2 L / min and maintained for 7 h. After that, the carbon source gas is stopped, and the temperature is maintained for 0.5 h before being cooled to room temperature. The rotary kiln is then stopped, and the product is collected to obtain the silicon-carbon anode material with the watermelon-like structure.

[0054] Example 3

[0055] In this embodiment, a silicon-carbon anode material with a watermelon-like structure is prepared by the following method:

[0056] Step 1, liquid phase coating: The nano-silicon particles are poured into an aqueous solution of 3 wt% polyvinylpyrrolidone, 5 wt% glucose and 2.5 wt% carboxymethyl cellulose, stirred evenly for 8 hours, filtered, and dried to obtain nano-silicon material coated with organic carbon source.

[0057] Step 2: Place the nano-silicon material coated with organic carbon source obtained in Step 1 into a rotary kiln, start the rotary kiln, introduce nitrogen at a flow rate of 0.9 L / min, calcine at 600℃ for 12 h, maintain the rotation speed at 9 Hz, and after calcine, raise the temperature to 700℃ at full power, stop the nitrogen flow to obtain the intermediate material.

[0058] Step 3, carbon source cracking: Acetylene is introduced at a flow rate of 1.5 L / min and maintained for 7 h. After that, the carbon source gas is stopped, and the temperature is maintained for 0.5 h before cooling to room temperature. The rotary kiln is then stopped, and the product is collected to obtain the silicon-carbon anode material with the watermelon-like structure.

[0059] Example 4

[0060] In this embodiment, a silicon-carbon anode material with a watermelon-like structure is prepared by the following method:

[0061] Step 1, liquid phase coating: The nano-silicon particles are poured into an aqueous solution of 3 wt% polyvinylpyrrolidone, 5 wt% glucose and 2.5 wt% carboxymethyl cellulose, stirred evenly for 2 hours, filtered, and dried to obtain nano-silicon material coated with organic carbon source.

[0062] Step 2: Place the nano-silicon material coated with organic carbon source obtained in Step 1 into a rotary kiln, start the rotary kiln, introduce nitrogen at a flow rate of 0.7 L / min, calcine at 450°C for 3 hours, maintain the rotation speed at 5 Hz, and after calcine, raise the temperature to 800°C at full power, stop the nitrogen flow to obtain the intermediate material.

[0063] Step 3, carbon source cracking: Acetylene is introduced at a flow rate of 2 L / min and maintained for 7 h. After that, the carbon source gas is stopped, and the mixture is kept at the temperature for 1 h before being cooled to room temperature. The rotary kiln is then stopped, and the product is collected to obtain the silicon-carbon anode material with the watermelon-like structure.

[0064] Example 5

[0065] In this embodiment, a silicon-carbon anode material with a watermelon-like structure is prepared by the following method:

[0066] Step 1, liquid phase coating: The nano-silicon particles are poured into an aqueous solution of 3 wt% polyvinylpyrrolidone, 5 wt% glucose and 2.5 wt% carboxymethyl cellulose, stirred evenly for 3 hours, filtered, and dried to obtain nano-silicon material coated with organic carbon source.

[0067] Step 2: Place the nano-silicon material coated with the organic carbon source obtained in Step 1 into a rotary kiln, start the rotary kiln, introduce nitrogen at a flow rate of 0.5 L / min, calcine at 600℃ for 4 h, maintain the rotation speed at 4 Hz, and after calcine, raise the temperature to 800℃ at full power, stop the nitrogen flow to obtain the intermediate product.

[0068] Step 3, carbon source cracking: Acetylene is introduced at a flow rate of 1.5 L / min and maintained for 6 h. After that, the carbon source gas is stopped, and the temperature is maintained for 0.5 h before cooling to room temperature. The rotary kiln is then stopped, and the product is collected to obtain the silicon-carbon anode material with the watermelon-like structure.

[0069] Example 6

[0070] In this embodiment, a silicon-carbon anode material with a watermelon-like structure is prepared by the following method:

[0071] Step 1, liquid phase coating: The nano-silicon particles are poured into an aqueous solution of 3 wt% polyvinylpyrrolidone, 5 wt% glucose and 2.5 wt% carboxymethyl cellulose, stirred evenly for 6 hours, filtered, and dried to obtain nano-silicon material coated with organic carbon source.

[0072] Step 2: Place the nano-silicon material coated with the organic carbon source obtained in Step 1 into a rotary kiln, start the rotary kiln, introduce nitrogen at a flow rate of 0.2 L / min, calcine at 500℃ for 5 h, maintain the rotary kiln speed at 10 Hz, and after calcine, raise the temperature to 600℃ at full power, stop the nitrogen flow to obtain the intermediate product.

[0073] Step 3, carbon source cracking: Acetylene is introduced at a flow rate of 1 L / min and maintained for 6 h. After that, the carbon source gas is stopped, and the mixture is kept at the same temperature for 1 h before being cooled to room temperature. The rotary kiln is then stopped, and the product is collected to obtain the silicon-carbon anode material with the watermelon-like structure.

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material with a watermelon-like structure, characterized in that, Includes the following steps: Step 1, liquid phase coating: Add nano-silicon particles to a carbon source solution containing organic matter, stir evenly, filter, and dry to obtain nano-silicon material coated with organic carbon source. The organic matter includes polyvinylpyrrolidone, glucose, and carboxymethyl cellulose. Step 2: The nano-silicon material coated with organic carbon source obtained in Step 1 is stirred and calcined at a first predetermined temperature for a first predetermined time under a protective gas atmosphere, and then heated to a second predetermined temperature and the protective gas is stopped to obtain an intermediate material. Step 3: Introduce carbon source gas into the intermediate material obtained in Step 2, deposit carbon on the surface of the intermediate material at a second predetermined temperature, stop introducing carbon source gas after a second predetermined time, keep warm for a third predetermined time, and then collect the product at room temperature. The product is the silicon-carbon anode material with the watermelon-like structure. The first predetermined temperature is 400-600℃, and the second predetermined temperature is 600-800℃.

2. The method for preparing the watermelon-inspired silicon-carbon anode material as described in claim 1, characterized in that, The diameter of the silicon nanoparticles is 5-100 nm, and the specific surface area of ​​the silicon nanoparticles is 50-1000 m². 2 / g.

3. The method for preparing the watermelon-inspired silicon-carbon anode material as described in claim 1, characterized in that, The stirring time in step 1 is 2-10 hours; And / or, the mass fraction of organic matter in the carbon source solution containing organic matter is less than 15 wt%.

4. The method for preparing the watermelon-inspired silicon-carbon anode material as described in claim 1, characterized in that, The content of organic matter in the carbon source solution containing organic matter in step 1 is: The polyvinylpyrrolidone content is no more than 3 wt%; the glucose content is no more than 5 wt%; and the carboxymethyl cellulose content is no more than 2.5 wt%.

5. The method for preparing the watermelon-inspired silicon-carbon anode material as described in claim 1, characterized in that, In step 2, the protective gas is nitrogen, the flow rate of nitrogen is 0.2-1 L / min, the first predetermined time is 2-6 h, the stirring speed is 2-10 Hz, and / or, in step 3, the flow rate of carbon source gas is 1-2 L / min, the second predetermined time is 6-8 h, and the third predetermined time is 0.5-1 h; And / or, the carbon source gas is one or more of methane, ethane, propane, ethylene, acetylene, benzene, naphthalene, and anthracene.

6. A silicon-carbon anode material with a watermelon-like structure, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The silicon-carbon anode material with a watermelon-like structure as described in claim 6, characterized in that, The silicon-carbon anode material with the watermelon-like structure has a particle size of 3-35 μm.

8. A negative electrode sheet, characterized in that, The silicon-carbon anode material with a watermelon-like structure as described in any one of claims 6-7.

9. A battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

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