Method for preparing porous carbon structure containing sub-nanoscale ionic conduction improvement layer

Abstract

The invention discloses a method for preparing a porous carbon structure containing a sub-nano-scale ion conduction improvement layer, and belongs to the technical field of porous carbon structure preparation methods, and the method comprises the following steps: loading a porous carbon substrate into a CVD tubular furnace, vacuumizing, taking nitrogen as carrier gas 1, heating to 650-850 DEG C, and carrying out heat preservation for 2-3 hours, so as to obtain the porous carbon structure containing the sub-nano-scale ion conduction improvement layer. Heating aluminum trichloride to 180-300 DEG C through a sublimator to form a gas-phase precursor, introducing nitrogen serving as carrier gas 2 into the CVD tubular furnace, controlling the mass ratio of the aluminum trichloride to the porous carbon substrate to be 1: (1-20), carrying out cracking deposition at 650-850 DEG C for 30-180 minutes, cooling, and exposing the porous carbon substrate in dry air with the humidity of 10-20% RH for 2-8 hours to obtain the porous carbon composite material. And forming a sub-nano-scale aluminum oxide ion conduction improvement layer.

Description

Technical Field

[0001] The present invention relates to a method for preparing a porous carbon structure, in particular to a method for preparing a porous carbon structure containing a sub-nanometer scale ion conduction improvement layer, and belongs to the technical field of porous carbon structure preparation methods. Background Art

[0002] At present, the main route of existing technology is to improve the contact between silicon and porous carbon, strengthen the bonding between silicon and the porous carbon substrate skeleton, and thus improve the electrochemical performance.

[0003] The main implementation method is to deposit a sub-nanoscale ion conduction improvement layer on a porous carbon substrate through atomic layer deposition (ALD). Common improvement materials include silicon carbide, aluminum phosphide, aluminum nitride, aluminum oxide, lithium phosphate, aluminum phosphate, lithium aluminum phosphate, etc. These materials are introduced into the porous carbon through various precursors (organic lithium compounds such as lithium tert-butyl lithium, phosphates such as trimethyl phosphate, organic aluminum compounds such as trimethyl aluminum, etc.) for uniform deposition. Its significant features are refined deposition, customizable deposition layer thickness such as 0.5-2nm, and uniform composition.

[0004] However, the use of this method places high demands on the accuracy of the equipment and the precursor raw materials for deposition. ALD equipment is more precise and delicate than CVD equipment, and the raw materials used are relatively expensive. The common industrial recycled trimethylaluminum (TMA) alone costs 8 yuan per gram, making it difficult to apply this method on a large scale.

[0005] In view of this, a method for preparing a porous carbon structure containing a sub-nanometer scale ion conduction improvement layer is designed to solve the above problems. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method for preparing a porous carbon structure containing a sub-nanometer scale ion conduction improvement layer.

[0007] The purpose of the present invention can be achieved by adopting the following technical solutions:

[0008] A method for preparing a porous carbon structure containing a sub-nanometer scale ion conduction improvement layer comprises the following steps:

[0009] Step 1: Place the porous carbon substrate into a CVD tube furnace, evacuate the tube, and heat to 650-850°C using nitrogen as carrier gas 1;

[0010] Step 2: heating aluminum chloride to 180-300° C. in a sublimator to form a vapor precursor, introducing nitrogen as carrier gas 2 into the CVD tube furnace, and controlling the mass ratio of aluminum chloride to porous carbon substrate to be 1:1-20;

[0011] Step 3: Pyrolysis deposition at 650-850°C for 30-180 min;

[0012] Step 4: After cooling, the porous carbon substrate is exposed to dry air with a humidity of 10%-20% RH for 2-8 hours to form a sub-nanometer-scale aluminum oxide ion conduction improvement layer.

[0013] Preferably, the carrier gas 1 and the carrier gas 2 are two independent streams of nitrogen, and the sum of the flow rates of the carrier gas 1 and the carrier gas 2 is 0.8-1.2 L / min.

[0014] Preferably, the heating temperature is 680-750°C.

[0015] Preferably, the mass ratio of the aluminum chloride to the porous carbon substrate is 1:2-10.

[0016] Preferably, the heating temperature of the aluminum chloride is 180-250°C.

[0017] Preferably, the cracking and sedimentation time is 60-150 min.

[0018] Preferably, the porous carbon substrate is soaked in 1 mol / L sodium hydroxide solution for 2 h before being loaded into the CVD tube furnace, and then washed and dried before use.

[0019] Preferably, before the temperature is raised to 650° C., the flow rate of the carrier gas is controlled at 5-15 mL / min; in the temperature range from 650° C. to the target temperature, the flow rate of the carrier gas is controlled at 10-50 mL / min.

[0020] Preferably, the sub-nanometer-scale aluminum oxide ion conduction improving layer has a thickness of 0.5-2 nm and is α-aluminum oxide.

[0021] Preferably, the CVD tube furnace is equipped with a precursor aluminum source sublimation device, and the connecting pipe between the sublimator and the CVD tube furnace adopts electric heating to prevent the precursor from condensing.

[0022] Nitrogen is used as carrier gas in both steps 1 and 2, but these come from different sources. Carrier gas 1 serves simply as a common furnace carrier gas, while carrier gas 2 is the source of agitation for the vaporized aluminum chloride in the sublimator and its entry into the CVD tube furnace. The flow rate of carrier gas 1 is determined by that of carrier gas 2, with the specific flow rate relationship being: carrier gas 1 + carrier gas 2 = 0.8-1.2 L / min.

[0023] Preferably, the lysis time in step 3 is 60-150 min.

[0024] Preferably, the exposure time in step 4 is determined by the amount of deposition, and 2-4 hours is more appropriate for a small amount (less than 30%).

[0025] Preferably, the porous carbon substrate can be pretreated by soaking it in a 1 mol / L sodium hydroxide solution for 2 hours, then washing and drying. Previous experiments have shown that pretreatment helps deposit more aluminum oxide into the pores, but acceptable results can be achieved to a certain extent without pretreatment. This step is performed according to the needs of the experimenter.

[0026] Preferably, the above steps are pilot process steps. The inventors also used miniaturized equipment (Kejing small tubular test furnace) to conduct gram-level experiments in the early stage and demonstrated them in the examples. The specific steps are:

[0027] Step 1: Place the selected porous carbon substrate and aluminum chloride into a crucible in a CVD small tube furnace, evacuate to -0.08 MPa, use nitrogen as the carrier gas with a flow rate of 10-80 mL / min, and heat to 650-850°C;

[0028] Step 2: The cracking and sedimentation time is controlled within 30-180 minutes. After the time is up, the equipment is shut down and waits for cooling;

[0029] Step 3: Take out the porous carbon from the furnace and expose it to dry air for about 2-8 hours. The air humidity needs to be slightly controlled (10% to 20% RH).

[0030] Preferably, in step 1, the porous carbon substrate and aluminum chloride are placed in the same crucible. The methods or ways include: grinding and mixing, mechanical mixing (without grinding), placing them in different crucibles and placing the crucibles in parallel or stacked, but there is no obvious effect on the experimental results.

[0031] Preferably, in step 1, the flow rate control should be at a smaller flow rate before the temperature is raised to 650°C. The preferred flow rate is: from room temperature to 650°C, the flow rate is controlled at 5-15 mL / min; from 650°C to the target temperature, the flow rate is controlled at 10-50 mL / min.

[0032] Preferably, the small device is only a confirmation test, and is only used to verify the feasibility. In order to achieve the effect, a higher proportion of aluminum chloride input is used, which is explained here as a supplement to the patent.

[0033] In the present invention, the aluminum deposition effect is evaluated by analyzing the specific surface area of the porous carbon material and the pore volume and pore size distribution using the NLDFT model. The inventors selected a 10-25% reduction in the initial specific surface area and a 2-10% increase in the deposition mass based on their own production test requirements.

[0034] The formula for deposition weight gain is: weight gain Δ = (m-m0) / m0*100%.

[0035] Note: m is the mass of porous carbon after deposition; m0 is the mass of porous carbon before deposition, which is generally set or taken as 1-2g.

[0036] Beneficial technical effects of the present invention:

[0037] The present invention provides a method for preparing a porous carbon structure containing a sub-nanometer ion conduction improvement layer. The sub-nanometer ion conduction improvement layer is aluminum oxide. A sub-nanometer ion conduction improvement layer is deposited on a porous carbon substrate by chemical vapor deposition. The porous carbon substrate adheres to the sub-nanometer ion conduction improvement layer, thereby increasing the bonding force between the porous carbon substrate and the silicon particles and the ion transport channel, and solving the problem of low ion transmission efficiency between silicon and carbon in carbon-silicon negative electrode structures. The present invention and other methods that achieve similar purposes have the following significant effects:

[0038] The process proposed in the present invention is realized by CVD and can be modified on various existing CVD furnaces. It only requires an additional steam generator, namely a sublimation furnace, with low equipment requirements, small investment and simple process.

[0039] Compared with ALD, the use of organic aluminum compounds, organic lithium compounds, phosphate compounds, etc. is avoided, and the raw materials of the process are simple, easy to obtain and cheap.

[0040] Compared to ALD, a technology for forming aluminum oxide, the present invention eliminates the dedicated oxidation process and instead uses natural exposure to air for oxidation, further reducing costs and simplifying the process.

[0041] The sub-nanometer scale ion conduction improvement layer constructed by the present invention is α-aluminum oxide and has strong electrical conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A scanning electron microscope image of a preferred embodiment of a method for preparing a porous carbon structure containing a sub-nanometer-scale ion conduction improving layer according to the present invention;

[0043] Figure 2 An X-ray energy dispersion spectrum analysis diagram of a preferred embodiment of a method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to the present invention;

[0044] Figure 3 An X-ray diffraction analysis diagram of a preferred embodiment of a method for preparing a porous carbon structure containing a sub-nanometer-scale ion conduction improving layer according to the present invention;

[0045] Figure 4 NLDFT and pore volume analysis diagrams of a preferred embodiment of a method for preparing a porous carbon structure containing a sub-nanometer ion conduction improvement layer according to the present invention;

[0046] Figure 5 It is a structural diagram of a preferred embodiment of a method for preparing a porous carbon structure containing a sub-nanometer scale ion conduction improving layer according to the present invention. DETAILED DESCRIPTION

[0047] In order to make the technical solution of the present invention more clear and specific to those skilled in the art, the present invention is further described in detail below with reference to embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0048] The following examples use Chuangming porous carbon as the substrate, and respectively demonstrate a small-scale tube furnace (Examples 1 and 2) and a pilot-scale tube furnace (Examples 3 and 4);

[0049] Example 1:

[0050] Step 1: 1g of Chuangming porous carbon substrate and 2g of aluminum chloride were simply mixed and placed in a crucible in a CVD tube furnace (Kejing, small tube furnace). The mixture was evacuated to -0.08 MPa and heated to 650°C using nitrogen as the carrier gas at a flow rate of 10 mL / min. The temperature was then raised to 720°C, with a nitrogen flow rate of 20 mL / min.

[0051] Step 2: The cracking and sedimentation time is controlled within 45 minutes. After the time is up, the equipment is shut down and waits for cooling;

[0052] Step 3: After cooling, take out the porous carbon, expose it to dry air for about 2 hours, and then dry it.

[0053] Example 2:

[0054] Step 1: 1 g of Chuangming porous carbon substrate and 1.5 g of aluminum chloride were mechanically mixed and placed in a crucible in a CVD tube furnace (Kejing, small tube furnace). The mixture was evacuated to -0.08 MPa and heated to 650°C using nitrogen as the carrier gas at a flow rate of 8 mL / min. The temperature was then raised to 750°C, with a nitrogen flow rate of 30 mL / min.

[0055] Step 2: The cracking and sedimentation time is controlled within 30 minutes. After the time is up, the equipment is shut down and waits for cooling;

[0056] Step 3: After cooling, take out the porous carbon, expose it to dry air for about 2 hours, and then dry it.

[0057] Example 3:

[0058] Step 1: Place 200 g of Chuangming porous carbon substrate into a CVD tube furnace, evacuate to -0.08 MPa, use nitrogen as carrier gas at a flow rate of 0.5 L / min, and heat to 720°C;

[0059] Step 2: 50g of aluminum chloride was heated to 220°C in a sublimator to form a vapor precursor aluminum chloride, which was then introduced into the CVD furnace body using nitrogen as carrier gas 2 at a flow rate controlled at 0.3L / min.

[0060] Step 3: The cracking and sedimentation time is controlled within 80 minutes. After the time is up, the equipment is shut down and waits for cooling;

[0061] Step 4: Open the CVD furnace or take out the porous carbon in the furnace and expose it to dry air for about 3 hours. The air humidity in the dry space is (20% RH).

[0062] Example 4:

[0063] Step 1: Place 400 g of Chuangming porous carbon substrate into a CVD tube furnace, evacuate to -0.08 MPa, use nitrogen as carrier gas at a flow rate of 0.5 L / min, and heat to 720°C;

[0064] Step 2: 80g of aluminum chloride was heated to 200°C in a sublimator to form a vapor precursor aluminum chloride, which was then introduced into the CVD furnace using nitrogen as carrier gas 2 at a flow rate of 0.3L / min.

[0065] Step 3: The cracking and sedimentation time is controlled within 80 minutes. After the time is up, the equipment is shut down and waits for cooling;

[0066] Step 4: Open the CVD furnace or take out the porous carbon in the furnace and expose it to dry air for about 3 hours. The air humidity in the dry space is (20% RH).

[0067] Figure 1 Scanning electron microscopy (SEM) was used to characterize the results;

[0068] Scanning electron microscopy showed that there was no significant difference between the treated samples and the blank samples, and no obvious impurity particles were observed on the surface of the example samples;

[0069] Figure 2 is X-ray energy dispersive spectroscopy (EDS);

[0070] The mapping results of the embodiment show that no agglomerated aluminum oxide appears, proving that the cracking of aluminum chloride by CVD method is feasible;

[0071] Figure 3 Schematic diagram of X-ray diffraction analysis (XRD);

[0072] From top to bottom are the XRD diffraction results of the samples of Examples 1-4, respectively. The aluminum oxide deposited into the interior is α-aluminum oxide.

[0073] BET test and weight gain test

[0074] Chuangming Example 1 Example 2 Example 3 Example 4 <![CDATA[Single-point BET specific surface area (m 2 / g)]]> 1670 1288 1212 1223 1257 <![CDATA[Multi-point BET specific surface area (m 2 / g)]]> 1511 1240 1166 1121 1157 <![CDATA[Total pore volume of adsorption (cm 3 / g)]]> 0.837 0.678 0.628 0.626 0.649 Average adsorption pore size (nm) 2.216 2.187 2.154 2.231 2.245 Weight gain changes 0 7.65％ 6.60％ 6.98％ 6.28％

[0075] Preferably, the blank sample contains very little ash after ignition, and the amount of alumina is essentially undetectable (≤0.03% as indicated in the specification). The blank sample has a weight gain of 0 and a weight loss on ignition of 100%. Examples 1 and 2 use the weight gain method; Examples 3 and 4 use the weight loss method, where the sample is ignited at 800°C for 2 hours and the residue is weighed again to represent the amount of alumina added. This results in a certain error, but is generally controllable.

[0076] Figure 4 It is the line graph of NLDFT and pore volume analysis;

[0077] Judging from the pore volume distribution, the micropores of all pore sizes were filled, which was reflected in the overall downward shift of the peak. This was consistent with the expected result, indicating that alumina was indeed precisely deposited into the micropores of the porous carbon substrate.

[0078] Figure 5 This is a simplified diagram of the experimental setup. The main body consists of two parts: the sublimator on the left and the CVD tube furnace on the right. To prevent condensation of the cracked precursor, electric heating is used in the pipe connecting the sublimator and the tube furnace. The nitrogen flowmeter in the figure is the flowmeter for carrier gas 2. The other flowmeter for carrier gas 1 is not shown and is directly connected to carrier gas 1 entering the main furnace.

[0079] The above is only a further embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solutions and concepts of the present invention within the scope disclosed by the present invention, which fall within the scope of protection of the present invention.

Claims

1. A method for preparing a porous carbon structure containing a sub-nanometer ion conduction improvement layer, characterized by: The steps include: Step 1: Place the porous carbon substrate into a CVD tube furnace, evacuate the tube, and heat to 650-850°C using nitrogen as carrier gas 1; Step 2: heating aluminum chloride to 180-300° C. in a sublimator to form a vapor precursor, introducing nitrogen as carrier gas 2 into the CVD tube furnace, and controlling the mass ratio of aluminum chloride to porous carbon substrate to be 1:1-20; Step 3: Pyrolysis deposition at 650-850°C for 30-180 min; Step 4: After cooling, the porous carbon substrate is exposed to dry air with a humidity of 10%-20% RH for 2-8 hours to form a sub-nanometer-scale aluminum oxide ion conduction improvement layer.

2. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: The carrier gas 1 and the carrier gas 2 are two independent nitrogen gases, and the sum of the flow rates of the carrier gas 1 and the carrier gas 2 is 0.8-1.2 L / min.

3. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: The heating temperature is 680-750°C.

4. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: The mass ratio of the aluminum chloride to the porous carbon substrate is 1:2-10.

5. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: The heating temperature of the aluminum chloride is 180-250°C.

6. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: The cracking and sedimentation time is 60-150 minutes.

7. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: Before being loaded into the CVD tube furnace, the porous carbon substrate was soaked in a 1 mol / L sodium hydroxide solution for 2 hours, and then washed and dried before use.

8. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: Before the temperature is raised to 650° C., the flow rate of the carrier gas is controlled at 5-15 mL / min; in the temperature range from 650° C. to the target temperature, the flow rate of the carrier gas is controlled at 10-50 mL / min.

9. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: The sub-nanometer-scale aluminum oxide ion conduction improvement layer has a thickness of 0.5-2 nm and is α-aluminum oxide.

10. The method for preparing a porous carbon structure containing a sub-nanometer ion conduction improving layer according to claim 1, characterized in that: The CVD tube furnace is equipped with a precursor aluminum source sublimation device, and the connecting pipe between the sublimator and the CVD tube furnace adopts electric heating to prevent the precursor from condensing.

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