Graphene-doped porous carbon material, preparation method and application thereof, silicon-carbon negative electrode material and battery

Abstract

The invention relates to a graphene-doped porous carbon material, a preparation method and application thereof, a silicon-carbon negative electrode material and a battery, and belongs to the technical field of methods or devices for directly converting chemical energy into electric energy. The preparation method of the graphene-doped porous carbon material comprises the following steps: performing reduction reaction on a copper-carbon composite material in a reducing gas atmosphere at the temperature of 300-500 DEG C, and then introducing carbon source gas at the temperature of 700-1100 DEG C for catalytic reaction to obtain the graphene-doped porous carbon material, the copper-carbon composite material comprises porous carbon and nanometer copper oxide located in pores of the porous carbon. The graphene-doped porous carbon material can effectively inhibit silicon expansion in a silicon-carbon negative electrode material and enhance conductivity, so that the cycle performance of a battery is improved.

Description

Technical Field

[0001] This invention relates to the field of methods or apparatus for directly converting chemical energy into electrical energy, and particularly to a graphene-doped porous carbon material, its preparation method and application, silicon-carbon anode materials, and batteries. Background Technology

[0002] Graphite, as a mainstream anode material, has a theoretical specific capacity of only 372 mAh / g, and its actual capacity in practical applications is already close to the theoretical capacity, making it difficult to meet the range requirements of consumer electronics and electric vehicles. Silicon, on the other hand, has a theoretical specific capacity as high as 4200 mAh / g, more than 10 times that of graphite. However, its volume expansion rate during charge and discharge reaches 300%, which can easily lead to structural collapse of the anode material, resulting in a sharp reduction in battery cycle life. To address this problem, existing technologies generally solve it by combining porous carbon with silicon. Silicon is deposited using porous carbon as a framework to form a silicon-carbon composite material, and a carbon layer is coated on the surface of the silicon-carbon composite material to enhance conductivity. However, the conductivity of this silicon-carbon composite material is still low, and the buffering effect of porous carbon on the volume expansion of silicon is limited, resulting in high internal resistance and poor cycle performance of the battery. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a graphene-doped porous carbon material, its preparation method and application, silicon-carbon anode material, and battery.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a graphene-doped porous carbon material, comprising the following steps: In a reducing gas atmosphere at 300°C to 500°C, a copper-carbon composite material is subjected to a reduction reaction, and then a catalytic reaction is carried out at 700°C to 1100°C with a carbon source gas introduced to obtain a graphene-doped porous carbon material; the copper-carbon composite material includes porous carbon and nano-copper oxide located in the pores of the porous carbon.

[0005] This invention utilizes a reducing gas to reduce nano-copper oxide located within the pores of porous carbon to elemental copper. The copper then catalyzes the formation of a graphene layer on the inner surface of the porous carbon pores. This graphene layer acts as a buffer layer between the porous carbon support and nano-silicon in the silicon-carbon anode material, effectively preventing the structure of the porous carbon support from being destroyed by the expansion of the nano-silicon, thereby enhancing the structural stability of the silicon-carbon anode material. Simultaneously, the graphene layer also improves the overall conductivity of the silicon-carbon anode material, reducing the battery's internal resistance and significantly improving the battery's cycle performance.

[0006] In some embodiments, the reducing gas in the above preparation method may include, but is not limited to, hydrogen (H2), carbon monoxide (CO), etc.; the carbon source gas is an alkane, olefin, or alkyne gas, such as, but not limited to, acetylene, methane, propane, cyclohexane, etc.

[0007] In some embodiments, the temperature of the reduction reaction in the above preparation method may be, but is not limited to, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, or 500°C, or fall within the range of any two of the above values. If the reduction reaction temperature is too low, some copper oxide will not be completely reduced, thus affecting the formation of graphene in the subsequent catalytic reaction; if the reduction reaction temperature is too high, the generated copper nanoparticles will aggregate and block the pores of the porous carbon.

[0008] In some embodiments, the temperature of the catalytic reaction in the above preparation method may be, but is not limited to, 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃, 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, or 1100℃, or falls within the range of any two of the above values. If the catalytic reaction temperature is too low, the diffusion ability of carbon atoms will be weak, easily leading to the formation of amorphous carbon; if the catalytic reaction temperature is too high, the nano-copper particles will continue to grow, reducing catalytic activity and thus hindering the formation of graphene.

[0009] In a preferred embodiment of the method for preparing the graphene-doped porous carbon material of the present invention, the mass ratio of the porous carbon to the nano-copper oxide is 1:0.05 to 1:0.15, for example, but not limited to 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14 or 1:0.15, or within any two of the above values. By controlling the mass ratio of porous carbon to nano-copper oxide in the copper-carbon composite material within the above range, it is more conducive to catalyzing the formation of graphene layers by carbon source gas on the inner wall surface of the porous carbon pores. When the mass ratio of porous carbon to nano-copper oxide is large (i.e., less nano-copper oxide), it will affect the formation of graphene, and thus affect the construction of the graphene layer. When the mass ratio of porous carbon to nano-copper oxide is small (i.e., more nano-copper oxide), the generated nano-copper will occupy more of the pore space of the porous carbon, affecting the distribution of the generated graphene (making the generated graphene on the periphery), and thus affecting the deposition of nano-silicon in the subsequent preparation of silicon-carbon anode materials.

[0010] In a preferred embodiment of the preparation method of the graphene-doped porous carbon material of the present invention, the porous carbon has a specific surface area of ​​2000 m². 2 / g to 2200m 2 / g, and / or pore volume of 0.8cm 3 / g to 1.2cm 3 / g, and / or average pore size of 1.8nm to 2.2nm.

[0011] Preferably, the porous carbon has a specific surface area of ​​2050 m². 2 / g to 2150m 2 / g, pore volume 0.9cm 3 / g to 1.1cm 3 / g, with an average pore size of 1.9nm to 2.1nm; more preferably, the porous carbon has a specific surface area of ​​2105m². 2 / g, pore volume 0.97cm 3 / g, with an average pore size of 1.98nm.

[0012] In a preferred embodiment of the method for preparing graphene-doped porous carbon materials according to the present invention, the average particle size of the nano-copper oxide is less than 1.5 nm, for example, but not limited to 1.5 nm, 1.4 nm, 1.3 nm, 1.2 nm, 1.1 nm, 1 nm, 0.9 nm, 0.8 nm, 0.7 nm, 0.6 nm, or 0.5 nm, or within any two of the above values. By controlling the average particle size of the nano-copper oxide within the above range, it is more conducive to the nano-copper oxide entering the pores of porous carbon and being reduced to nano-copper elemental of suitable particle size, thereby further promoting the formation of graphene and the construction of graphene layers on the inner walls of the pores of porous carbon.

[0013] In a preferred embodiment of the method for preparing the graphene-doped porous carbon material of the present invention, the porous carbon undergoes an activation treatment, which includes the following steps: activating the porous carbon with water vapor at 700°C to 1000°C for 120 min to 360 min. By controlling the temperature and time of the activation treatment within the above range, the specific surface area and pore volume of the porous carbon can be better adjusted.

[0014] In some embodiments, the activation temperature may be, but is not limited to, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C, 980°C, or 1000°C, or fall within the range of any two of the above values.

[0015] In some embodiments, the activation treatment time may be, but is not limited to, 120 min, 140 min, 160 min, 180 min, 200 min, 220 min, 240 min, 260 min, 280 min, 300 min, 320 min, 340 min, or 360 min, or fall within the range of any two of the above values.

[0016] In a preferred embodiment of the method for preparing the graphene-doped porous carbon material of the present invention, the reaction time of the reduction reaction is 60 min to 240 min, and / or the reaction time of the catalytic reaction is 5 min to 30 min.

[0017] In some embodiments, the reduction reaction time may be, but is not limited to, 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, 200 min, 220 min or 240 min, or within the range of any two of the above values.

[0018] In some embodiments, the time for the catalytic reaction may be, but is not limited to, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min, or fall within the range of any two of the above values.

[0019] Secondly, the present invention provides a porous carbon material doped with graphene prepared by the above-described preparation method.

[0020] Thirdly, the present invention provides an application of the above-mentioned graphene-doped porous carbon material in the preparation of silicon-carbon anode materials.

[0021] Fourthly, the present invention provides a silicon-carbon anode material, comprising a silicon-carbon composite material and a carbon coating layer located on at least a portion of the surface of the silicon-carbon composite material; The silicon-carbon composite material includes the above-mentioned graphene-doped porous carbon material and nano-silicon, wherein the nano-silicon is located within the pores of the graphene-doped porous carbon material.

[0022] In some embodiments, nano-silicon is located not only within the pores of the graphene-doped porous carbon material, but also partially on the surface of the graphene-doped porous carbon material.

[0023] As a preferred embodiment of the silicon-carbon anode material of the present invention, based on the total mass of the silicon-carbon anode material, the mass percentage of nano-silicon is 45% to 55%, preferably 50% to 52%, for example, but not limited to 45%, 45.5%, 46%, 46.5%, 47%, 47.5%, 48%, 48.5%, 49%, 49.5%, 50%, 50.5%, 51%, 51.5% or 52%, or within the range of any two of the above values.

[0024] Fifthly, the present invention provides a battery comprising the aforementioned silicon-carbon anode material.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a reducing gas to reduce nano-copper oxide located within the pores of porous carbon to elemental copper. The elemental copper then acts as a catalyst on the inner surface of the porous carbon pores, directly catalyzing the formation of a graphene layer from the carbon source gas. This graphene layer serves as a buffer layer between the porous carbon support and nano-silicon in a silicon-carbon anode material, effectively preventing the structure of the porous carbon support from being destroyed by the expansion of the nano-silicon, thereby enhancing the structural stability of the silicon-carbon anode material. Simultaneously, the graphene layer also improves the overall conductivity of the silicon-carbon anode material to reduce the battery's internal resistance, thus significantly improving the battery's cycle performance. Attached Figure Description

[0026] The embodiments of this invention are not limited to the drawings described below, which are only some embodiments of this invention. Those skilled in the art can obtain drawings of other embodiments based on the content of this invention.

[0027] Figure 1 This is a SEM image of a graphene-doped porous carbon material according to one embodiment of the present invention. Figure 2 This is an XRD pattern of a silicon-carbon anode material according to one embodiment of the present invention. Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0029] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0030] <Test Methods and Equipment> 1. Resistivity Testing Tested according to standard GB / T 1552-1995.

[0031] 2. Testing of first-cycle charging capacity, first-cycle coulombic efficiency, and capacity retention. Under room temperature (25℃) conditions, first discharge at a current density of 0.1C to the cutoff voltage of 0.005V; then charge at a current density of 0.1C to the cutoff voltage of 2V. This is one cycle. Repeat this cycle 50 times to obtain the first cycle charging capacity, the first cycle coulombic efficiency, and the 50th cycle charging capacity. The 50th cycle capacity retention rate (%) = (50th cycle charging capacity / first cycle charging capacity) × 100%; To ensure the accuracy of the above test results, five samples were taken for each embodiment and comparative example, and the average value was taken as the test result.

[0032] 3. Test of zero full-charge expansion rate in the first cycle The thickness of the negative electrode sheet before it is assembled into a coin cell is measured as H1; At room temperature (25℃), the battery was first discharged at a current density of 0.1C to the cutoff voltage of 0.005V, then charged at a current density of 0.1C to the cutoff voltage of 2V, and then discharged at a current density of 0.1C to the cutoff voltage of 0.005V. The button cell was then disassembled in a glove box, and the thickness of the negative electrode was measured to be H2. First-cycle zero-full-charge expansion rate (%) = (H2-H1) / H1×100%; To ensure the accuracy of the above test results, five samples were taken for each embodiment and comparative example, and the average value was taken as the test result.

[0033] Example 1 <Preparation of Nano Copper Oxide> Step 1: Dissolve copper nitrate in ethylene glycol and add a small amount of water to initiate hydrolysis. At the same time, add citric acid and stir at 70°C to form a transparent sol (control the sol particle size to be around 1 nm). Step 2: Freeze-dry the sol at low temperature (-65℃) to obtain a dry gel powder, and then calcine it at low temperature (150℃) to remove the organic ligands, thereby obtaining nano-copper oxide particles with an average particle size of 1nm.

[0034] <Preparation of Porous Carbon> Step 1: Place the phenolic resin in an oven and bake at 100℃ for 4 hours, then raise the temperature to 120℃ and keep it warm for 4 hours. Step 2: Then, the dried phenolic resin is placed in a rotary kiln and heated to 700℃ under nitrogen protection. It is then held at this temperature for 2 hours to obtain carbonized material. The carbonized material is then crushed to a particle size Dv50 of about 20μm. Step 3: Place the crushed carbonized material into a rotary kiln, heat it to 900°C under nitrogen protection, and then introduce steam for activation for 5 hours to obtain porous carbon material. Step 4: The porous carbon material is crushed in an air jet mill to obtain a porous carbon material with a particle size Dv50 of 7.8 μm (specific surface area of ​​2105 m²). 2 / g, pore volume is 0.97cm 3 / g, with an average pore size of 1.98nm).

[0035] <Preparation of Graphene-Doped Porous Carbon Materials> Step 1: Place the above porous carbon material and nano copper oxide in a beaker at a mass ratio of 1:0.1 and add an appropriate amount of water and stir (stirring time is 8h). Then filter with a filter screen with a pore size of 5μm and dry to obtain copper-carbon composite material. Step 2: The copper-carbon composite material is placed in a fluidized bed, and nitrogen (30 L / min) is used as a protective gas. After heating to 400℃, hydrogen (flow rate 2 L / min) is introduced to carry out a reduction reaction for 2 hours, replacing copper oxide with elemental copper. Then, the temperature is further increased to 700℃, and acetylene gas (flow rate 0.5 L / min) is introduced to carry out a catalytic reaction for 30 minutes, so that under the catalysis of nano-copper, the acetylene gas generates a graphene layer on the inner wall of the pores of porous carbon. Step 3: Place the product obtained in Step 2 into a 0.1 mol / L dilute nitric acid solution, heat to 50℃ and stir for 2 hours. Then, repeatedly wash and filter using a 5 μm pore size filter, and dry to obtain a graphene-doped porous carbon material (e.g., Figure 1 (As shown).

[0036] <Preparation of Silicon-Carbon Anode Materials> The above-mentioned graphene-doped porous carbon material was placed in a fluidized bed and purged with nitrogen at a flow rate of 5 L / min to remove air. The temperature was then increased to 550°C at a rate of 10°C / min, followed by the introduction of silane gas at a rate of 2 L / min for 300 min. The silane gas was then cut off, and the temperature was increased to 620°C at a rate of 10°C / min, followed by the introduction of acetylene gas at a rate of 2 L / min for 150 min. The acetylene gas was then cut off, and the equipment was allowed to cool naturally to room temperature. The material was then sieved through a 400-mesh sieve and demagnetized using a demagnetizer to obtain the silicon-carbon anode material. The XRD pattern of the silicon-carbon anode material is shown below. Figure 2 As shown, there are no obvious silicon peaks in the XRD pattern, and the carbon coating is complete.

[0037] <Preparation of Negative Electrode Sheets> The silicon-carbon anode material, binder (polyvinylidene fluoride), and conductive agent (acetylene black) were weighed at a mass ratio of 80:10:10. The silicon-carbon anode material and conductive agent were then added to the binder solution (a 5% N-methylpyrrolidone solution of polyvinylidene fluoride). The mixture was stirred to form a paste, yielding the anode slurry. This slurry was then coated onto aluminum foil, dried at 120°C for 2 hours, and finally pressed into tablets (tablet density of 2.0 g / cm³). 3 ), thus obtaining the negative electrode sheet.

[0038] <Preparation of Electrolyte> The electrolyte is 1 mol / L LiPF6, in which the solvent is composed of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7.

[0039] <Battery Manufacturing> The positive electrode (lithium metal sheet), the separator (PE film with a thickness of 100μm), the negative electrode and the electrolyte are assembled into a CR2032 coin cell.

[0040] Example 2 Except for the mass ratio of porous carbon material to nano-copper oxide of 1:0.05 in step one of the <Preparation of Graphene-Doped Porous Carbon Material>, the rest is the same as in Example 1.

[0041] Example 3 Except for the mass ratio of porous carbon material to nano-copper oxide in step one of the <Preparation of Graphene-Doped Porous Carbon Material>, which is 1:0.15, the rest is the same as in Example 1.

[0042] Example 4 Except for the acetylene gas flow rate of 0.3 L / min in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, the rest is the same as in Example 1.

[0043] Example 5 Except for the acetylene gas flow rate of 0.8 L / min in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, the rest is the same as in Example 1.

[0044] Example 6 Except for the reduction reaction temperature of 300°C in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, the rest is the same as in Example 1.

[0045] Example 7 Except for the reduction reaction temperature of 500℃ in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, the rest is the same as in Example 1.

[0046] Example 8 Except for the temperature of the catalytic reaction in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, which is 900°C, the rest is the same as in Example 1.

[0047] Comparative Example 1 The preparation of nano-copper oxide and the preparation of graphene-doped porous carbon materials are omitted. The graphene-doped porous carbon in the preparation of silicon-carbon anode materials is replaced with porous carbon (undoped graphene). The rest is the same as in Example 1.

[0048] Comparative Example 2 Except for the reduction reaction temperature of 200°C in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, the rest is the same as in Example 1.

[0049] Comparative Example 3 Except for the reduction reaction temperature of 600℃ in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, the rest is the same as in Example 1.

[0050] Comparative Example 4 Except for the temperature of the catalytic reaction in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, which is 600°C, the rest is the same as in Example 1.

[0051] Comparative Example 5 Except for the temperature of the catalytic reaction in step two of the <Preparation of Graphene-Doped Porous Carbon Materials>, which is 1200℃, the rest is the same as in Example 1.

[0052] The test performance of the silicon-carbon anode materials and CR2032 coin cells corresponding to the graphene-doped porous carbon materials in each embodiment and comparative example is shown in Table 1.

[0053] Table 1 According to the data in Table 1, the CR2032 coin cells corresponding to the graphene-doped porous carbon materials in Examples 1 to 8 all achieved an initial charge capacity of over 1802 mAh / g, an initial coulombic efficiency of over 90.01%, a resistivity of less than or equal to 0.94 Ω·cm for the silicon-carbon anode material, an initial full-charge expansion rate of less than or equal to 69%, and a 50-cycle capacity retention rate of over 95.33%. This indicates that the graphene-doped porous carbon material of the present invention can effectively suppress silicon expansion in the silicon-carbon anode material and enhance its conductivity, thereby improving the cycle performance of the battery. Meanwhile, as can be seen from Example 1 and Comparative Example 1, when conventional porous carbon is used instead of the graphene-doped porous carbon of the present invention as the carrier for silicon deposition in silicon-carbon anode materials, it is difficult to effectively suppress the volume expansion of nano-silicon, resulting in poor battery cycle performance. As can be seen from Comparative Examples 2 to 5, if the temperature of the reduction reaction is too low or too high, or the temperature of the catalytic reaction is too low or too high, it is difficult to effectively improve the battery cycle performance.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a graphene-doped porous carbon material, characterized in that, Includes the following steps: In a reducing gas atmosphere at 300°C to 500°C, a copper-carbon composite material is subjected to a reduction reaction, and then a catalytic reaction is carried out at 700°C to 1100°C with a carbon source gas introduced to obtain a graphene-doped porous carbon material; the copper-carbon composite material includes porous carbon and nano-copper oxide located in the pores of the porous carbon.

2. The preparation method according to claim 1, characterized in that, The mass ratio of porous carbon to nano-copper oxide is 1:0.05 to 1:0.

15.

3. The preparation method according to claim 1, characterized in that, The porous carbon has a specific surface area of ​​2000 m². 2 / g to 2200m 2 / g, and / or pore volume of 0.8cm 3 / g to 1.2cm 3 / g, and / or average pore size of 1.8nm to 2.2nm.

4. The preparation method according to claim 1, characterized in that, The average particle size of the nano-copper oxide is less than 1.5 nm.

5. The preparation method according to claim 1, characterized in that, The porous carbon undergoes an activation treatment, which includes the following steps: activating the porous carbon with water vapor at 700°C to 1000°C for 120 min to 360 min.

6. The preparation method according to claim 1, characterized in that, The reduction reaction takes 60 min to 240 min, and / or the catalytic reaction takes 5 min to 30 min.

7. A porous carbon material doped with graphene prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the graphene-doped porous carbon material according to claim 7 in the preparation of silicon-carbon anode materials.

9. A silicon-carbon anode material, characterized in that, Includes a silicon-carbon composite material and a carbon coating layer located on at least a portion of the surface of the silicon-carbon composite material; The silicon-carbon composite material includes the graphene-doped porous carbon material of claim 7 and nano-silicon, wherein the nano-silicon is located within the pores of the graphene-doped porous carbon material.

10. A battery, characterized in that, Including the silicon-carbon anode material as described in claim 9.

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