Preparation method of double-layer coated silicon-carbon composite material

Abstract

The application discloses a preparation method of a double-layer coated silicon-carbon composite material, which comprises the following steps: uniformly mixing acid-based resin and organic alkali-based pore-forming agent, then adding the mixture into lithium carboxymethyl cellulose, uniformly dispersing, spray drying, transferring the obtained material into a tube furnace for carbonization, naturally cooling to room temperature, and obtaining lithium-doped porous carbon; adding niobium salt and titanium salt into liquid silane to prepare a 1-10wt% solution in an organic solvent, uniformly dispersing, then adding the lithium-doped porous carbon, uniformly dispersing, spray drying, transferring into a tube furnace for sintering, obtaining titanium niobate coated silicon-carbon composite material, transferring into a tube furnace, and depositing amorphous carbon on the surface of the titanium niobate coated silicon-carbon composite material, thereby obtaining the titanium niobate coated silicon-carbon composite material. The material obtained by the application can improve the initial efficiency, fast charging performance and reduce the expansion.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery materials, specifically a method for preparing a double-layer coated silicon-carbon composite material. Background Technology

[0002] Novel silicon-carbon anode materials have become the preferred material for high-energy-density lithium-ion batteries due to their advantages such as high specific capacity (1800-2000 mAh / g), high initial efficiency (90-92%), low full-charge expansion, excellent cycle performance, and low cost. However, because novel silicon-carbon materials are composed of porous carbon and nano-silicon deposited in the pores, the powder resistivity of the material is relatively high, which reduces its fast-charging performance. At the same time, the electrode expansion is high during charging and discharging, resulting in large expansion of the battery module and posing safety hazards. Therefore, it is necessary to dope, coat, and modify the interface of silicon-carbon materials to reduce the material impedance and reduce expansion. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a method for preparing a double-layer coated silicon-carbon composite material that can improve initial efficiency, fast charging performance and reduce expansion.

[0004] The present invention discloses a method for preparing a double-layer coated silicon-carbon composite material, comprising the following steps:

[0005] Step S1: Mix the acid-based resin and organic-based pore-forming agent evenly according to the mass ratio of acid-based resin: organic-based pore-forming agent: lithium carboxymethyl cellulose = 100:1-10:1-5, and then add it to the lithium carboxymethyl cellulose solution. Disperse evenly and spray dry for 0.5 h at an inlet temperature of 220℃, an outlet temperature of 80℃, and a flow rate of 1 kg / h. Transfer the obtained material to a tube furnace and carbonize it at a temperature of 700-900℃ for 1-6 h. Then raise the temperature to 1100℃ and pass water vapor through it at a flow rate of 500-1000 ml / min for 2-12 h. After that, let it cool naturally to room temperature to obtain lithium-doped porous carbon.

[0006] Step S2: According to the mass ratio (niobium salt + titanium salt): liquid silane: lithium-doped porous carbon = 5-20: 100-300: 100, niobium salt, titanium salt and liquid silane are added to an organic solvent to prepare a 1-10 wt% solution and dispersed evenly. Then lithium-doped porous carbon is added and dispersed evenly. Spray drying is carried out for 0.5 h at an inlet temperature of 220℃, an outlet temperature of 80℃ and a flow rate of 1 kg / h. The obtained material is transferred to a tube furnace, inert gas is introduced to purge the air in the tube, and the temperature is raised to 300-500℃ for sintering for 1-6 h to obtain titanium niobate coated silicon carbon composite material.

[0007] The niobium salt is one of niobium oxalate, niobium n-propoxide, niobium isopropoxide, niobium pentanol, or niobium phenolate.

[0008] The titanium salt is one of ethyl titanate, tetraethyl titanate, propyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraisopropoxy titanium, or tetraisopropoxide titanium.

[0009] The organic solvent is one of methyl ether, diethyl ether, dipropyl ether, ethyl butyl ether, dibutyl ether, or dipentyl ether;

[0010] The molar ratio of niobium salt to titanium salt is 1:1-2.

[0011] Step S3: Transfer the titanium niobate-coated silicon-carbon composite material to a tube furnace. First, introduce an inert gas to purge the air from the tube. Then, heat the furnace to 500-800℃ and introduce a carbon source gas at a flow rate of 50-500 ml / min for 1-6 hours to deposit amorphous carbon on the surface, thus obtaining a double-layer coated silicon-carbon composite material.

[0012] The above-mentioned method for preparing a double-layer coated silicon-carbon composite material, wherein the acidic resin in step S1 is one of diallyl isophthalate resin, acrylic resin, alkyd resin, fumaric acid resin or malic acid resin.

[0013] The above-mentioned method for preparing a double-layer coated silicon-carbon composite material, wherein the organic base pore-forming agent in step S1 is one of dimethylisopropylamine, 1-methylpyrrolidine, triethylamine, 1-methylpiperidine, or 4-methylmorpholine.

[0014] In the above-mentioned method for preparing a double-layer coated silicon-carbon composite material, the liquid silane mentioned in step S2 is one of tetraethoxysilane, tetramethyldivinyldisiloxane, triethylsilane, trimethylchlorosilane, triphenylchlorosilane, or hexamethyldisiloxane.

[0015] In the above-mentioned method for preparing a double-layer coated silicon-carbon composite material, the carbon source gas in step S3 is one of methane, ethane, ethylene, acetylene, or propyne.

[0016] Compared with existing technologies, this invention has significant advantages. As can be seen from the above technical solutions: This invention uses acid-based resins and organic base pore-forming agents to prepare hard carbon materials through curing, carbonization, and activation. Then, it performs lithium doping of carboxymethyl cellulose to obtain lithium-doped porous carbon materials, reducing core defects and improving initial efficiency. Simultaneously, the acid-based resin undergoes a dehydration reaction during carbonization, forming more pores, increasing the silicon storage capacity and specific capacity of the novel silicon-carbon composite material. By using a liquid-phase method to mix niobium salts, titanium salts, liquid silanes, and lithium-doped porous carbon in the liquid phase, followed by carbonization, titanium niobate is coated onto the surface of the silicon-carbon composite material, reducing expansion and improving initial efficiency. Furthermore, by coating amorphous carbon in the outer shell using vapor deposition, the electronic conductivity of the material is improved, and gas generation is reduced. Attached Figure Description

[0017] Figure 1 The image shows a SEM image of the silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0018] Example 1

[0019] A method for preparing a double-layer coated silicon-carbon composite material includes the following steps:

[0020] Step S1: Mix 100g diallyl isophthalate resin and 5g dimethyl isopropylamine evenly, then add 300g of 1wt% lithium carboxymethyl cellulose aqueous solution, disperse evenly, and spray dry (inlet temperature 220℃, outlet temperature 80℃, flow rate 1kg / h, 0.5h). Then transfer the obtained material to a tube furnace and carbonize at 800℃ for 3h. Then raise the temperature to 1100℃ and pass water vapor at a flow rate of 800ml / min for 6h. Then cool naturally to room temperature to obtain lithium-doped porous carbon.

[0021] Step S2: 5.38 g (0.01 mol) of niobate oxalate, 3.42 g (0.015 mol) of ethyl titanate and 200 g of tetraethoxysilane were added to 4176 g of diethyl ether organic solvent to prepare a solution with a mass concentration of 5 wt%. The solution was dispersed evenly. Then, 100 g of lithium-doped porous carbon was added and dispersed evenly. The solution was spray-dried (inlet temperature 220℃, outlet temperature 80℃, flow rate 1 kg / h, 0.5 h). The resulting material was then transferred to a tube furnace, and argon inert gas was introduced to purge the air from the tube. The furnace was heated to 400℃ and sintered for 3 h to obtain titanium niobate-coated silicon-carbon composite material.

[0022] Step S3: Transfer the titanium niobate-coated silicon-carbon composite material to a tube furnace. First, argon inert gas is introduced to purge the air from the tube. Then, the temperature is raised to 600°C, and ethylene gas (flow rate 100 ml / min) is introduced and kept at this temperature for 360 min. Amorphous carbon is deposited on its surface to obtain a double-layer coated silicon-carbon composite material.

[0023] Example 2

[0024] A method for preparing a double-layer coated silicon-carbon composite material includes the following steps:

[0025] Step S1: Mix 100g of acrylic resin and 1g of 1-methylpyrrolidine evenly, then add it to 100g of an aqueous solution of 1wt% lithium carboxymethyl cellulose, disperse evenly, and spray dry (inlet temperature 220℃, outlet temperature 80℃, flow rate 1kg / h, 0.5h). Then transfer the obtained material to a tube furnace and carbonize it at 700℃ for 6h. Then raise the temperature to 1100℃ and pass water vapor through it at a flow rate of 500ml / min for 12h. Then let it cool naturally to room temperature to obtain lithium-doped porous carbon.

[0026] Step S2: 3.15g (0.0082mol) of niobium n-propoxide, 1.85g (0.0082mol) of tetraethyl titanate and 100g of tetramethyldivinyldisiloxane were added to 10500g of dipropyl ether organic solvent to prepare a solution with a mass concentration of 1wt%. The solution was dispersed evenly. Then, 100g of lithium-doped porous carbon was added and dispersed evenly. The solution was spray-dried (inlet temperature 220℃, outlet temperature 80℃, flow rate 1kg / h, 0.5h). The resulting material was then transferred to a tube furnace, and argon inert gas was introduced to purge the air from the tube. The furnace was heated to 300℃ and sintered for 6h to obtain titanium niobate-coated silicon-carbon composite material.

[0027] Step S3: Transfer the titanium niobate-coated silicon-carbon composite material to a tube furnace. First, argon inert gas is introduced to purge the air inside the tube. Then, the temperature is raised to 500°C, and acetylene carbon source gas is introduced. The temperature is maintained at 500 ml / min for 1 hour to deposit amorphous carbon on its surface, thus obtaining a double-layer coated silicon-carbon composite material.

[0028] Example 3

[0029] A method for preparing a double-layer coated silicon-carbon composite material includes the following steps:

[0030] Step S1: Mix 100g of fumaric acid resin and 10g of 1-methylpiperidine evenly, then add it to 500g of 1wt% carboxymethyl cellulose lithium aqueous solution, disperse evenly, spray dry (inlet temperature 220℃, outlet temperature 80℃, flow rate 1kg / h, 0.5h), then transfer the obtained material to a tube furnace and carbonize at 900℃ for 1h, then raise the temperature to 1100℃ and pass water vapor at a flow rate of 1000ml / min for 2h, then let it cool naturally to room temperature to obtain lithium-doped porous carbon;

[0031] Step S2: 12.84 g (0.033 mol) of niobium isopropoxide, 7.16 g (0.066 mol) of propyl titanate and 200 g of triethylsilane were added to 2200 g of dibutyl ether organic solvent to prepare a solution with a mass concentration of 10 wt%. The solution was dispersed evenly. Then, 100 g of lithium-doped porous carbon was added and dispersed evenly. The solution was spray-dried (inlet temperature 220℃, outlet temperature 80℃, flow rate 1 kg / h, 0.5 h). The resulting material was then transferred to a tube furnace, and argon inert gas was introduced to purge the air from the tube. The furnace was heated to 500℃ and sintered for 1 h to obtain titanium niobate-coated silicon-carbon composite material.

[0032] Step S3: Transfer the titanium niobate-coated silicon-carbon composite material to a tube furnace. First, argon inert gas is introduced to purge the air inside the tube. Then, the temperature is raised to 800°C, and propyne carbon source gas is introduced. The temperature is maintained at 50 ml / min for 6 hours to deposit amorphous carbon on its surface, thus obtaining a double-layer coated silicon-carbon composite material.

[0033] Comparative Example 1:

[0034] A method for preparing a silicon-carbon composite material, comprising:

[0035] Unlike Example 1, dimethylisopropylamine and lithium carboxymethyl cellulose are not added in step S1, but otherwise the same as in Example 1.

[0036] Comparative Example 2:

[0037] A method for preparing a silicon-carbon composite material, comprising:

[0038] Unlike Example 1, niobium oxalate and ethyl titanate are not added in step S2, but everything else is the same as in Example 1.

[0039] Experimental example:

[0040] (1) Physicochemical performance testing:

[0041] To verify the effectiveness of the above embodiments and comparative examples, the present invention conducted physicochemical property tests and coin cell tests on the silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-2. The specific surface area and tap density of the corresponding silicon-carbon composite materials were tested according to the national standard GB / T38823-2020 "Silicon-Carbon". The powder resistivity of the corresponding silicon-carbon composite materials was tested using a four-probe tester, and the grain size of the corresponding silicon-carbon composite materials was tested using XRD. The gas production of the powder material was also tested (45℃, 48h). The test results are shown in Table 1 below.

[0042] Simultaneously, the morphology of the powder material was tested using scanning electron microscopy. Figure 1It can be seen that the material has a granular structure, a smooth surface, a uniform particle size distribution, and a particle size D50 between 5 and 10 μm.

[0043] (2) Button cell battery test:

[0044] In the silicon-carbon composite materials corresponding to Examples 1-3 and Comparative Examples 1-2, binders, conductive agents, and solvents were added, stirred to form a slurry, coated onto copper foil, and dried and rolled to obtain negative electrode sheets. The binder used was LA136D binder (specifically including: a crosslinked product of acrylonitrile and polyacrylic acid, molecular weight 200,000), the conductive agent was conductive carbon black (SP), and the solvent was double-distilled water. The silicon-carbon composite material ratio was SP:LA136D:double-distilled water = 90g:4g:6g:250mL. A lithium metal sheet was used as the counter electrode, a polyethylene (PE) membrane was used as the separator, and LiPF6 / EC+DEC (1:1) was used as the electrolyte. The button cell was assembled in an argon-filled glove box. The electrochemical performance tests were conducted on a 5V / 10mA battery tester from Wuhan Landian Xinwei. The charge / discharge conditions used were: a charge / discharge voltage range of 0.005V-2.0V and a charge / discharge rate of 0.1C. The rate performance (1C / 0.1C) was calculated. The test results are shown in Table 1 below.

[0045] Table 1

[0046]

[0047] As can be seen from Table 1 above, the coin cells and their physicochemical properties prepared using the silicon-carbon composite materials obtained in Examples 1-3 of this invention are significantly better than those of Comparative Examples 1-2 in terms of initial efficiency, powder resistivity, rate capability, and full-charge expansion. This confirms the superiority of the composite materials. The reason may be that the silicon-carbon composite materials provided in Examples 1-3 are doped with lithium compounds in their core. During charging and discharging, lithium ions are released, reducing the irreversible capacity and improving the initial efficiency. Furthermore, the lithium ion diffusion rate is increased, improving the rate capability. Simultaneously, the niobium titanate doping in these examples exhibits low expansion and structural stability, further reducing expansion.

[0048] (3) Soft package performance test:

[0049] The silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-3, respectively, and doped with 95% artificial graphite, were used as the negative electrode materials, and the ternary material LiNi was used. 1 / 3 Co 1 / 3 Mn 1 / 3Using O2 as the positive electrode material, a LiPF6 solution (solvent: EC+DEC, volume ratio: 1:1, LiPF6 concentration: 1.3 mol / L) as the electrolyte, and a Celgard 2400 membrane as the separator, 5Ah pouch cells C1, C2, C3, D1, and D2, along with their corresponding negative electrode sheets, were fabricated. The cycle performance, rate performance, and expansion performance under different conditions of the pouch cells were then tested. The specific test conditions are as follows:

[0050] 3.1 Cyclic performance test conditions: charge / discharge current 1C / 1C, voltage range 2.5-4.2V, number of cycles 500.

[0051] 3.2. Rate performance test conditions: charging rate 1C / 3C / 5C / 8C, discharging rate 1C; voltage range 2.5-4.2V.

[0052] 3.3. Expansion performance test conditions: 25℃, 1C / 1C, initial state of full charge expansion of the negative electrode, 500 cycles of full charge expansion of the negative electrode.

[0053] The test results for cycle performance are shown in Table 2; the test results for rate performance are shown in Table 3; and the test results for expansion performance are shown in Table 4.

[0054] Table 2

[0055]

[0056] As shown in Table 2 above, under the condition of charge / discharge current of 1C / 1C, after 500 cycles, the pouch battery prepared by the silicon-carbon composite material provided in Examples 1-3 of this application has significantly better cycle performance than Comparative Examples 1-3. This indicates that by doping lithium compounds into silicon-carbon materials, lithium ions are released during charge and discharge to reduce the irreversible capacity of the material and improve cycle performance. At the same time, the materials in the examples have low expansion, which also improves cycle performance.

[0057] Table 3

[0058]

[0059] As can be seen from Table 3 above, under different charging rates, the soft-pack battery prepared using the silicon-carbon composite material provided in Examples 1-3 of the present invention has better constant current ratio performance. This further confirms that the lithium polymer material in the core of the silicon-based material of the present invention can effectively reduce impedance when lithium ions are released during charging and discharging. Moreover, the silicon-carbon composite material provided has a low powder resistivity, which is beneficial to improving the fast charging performance of the battery.

[0060] Table 4

[0061]

[0062]

[0063] As shown in Table 4 above, under the test conditions of 25℃ and 1C / 1C, the pouch battery prepared using the composite material provided in Examples 1-3 of this invention exhibits significantly lower negative electrode expansion under full charge in the initial state compared to Comparative Examples 1-3. Furthermore, after 500 cycles, the negative electrode expansion under full charge is still significantly lower than that of Comparative Examples 1-3. This is because niobium salt, titanium salt, liquid silane, and lithium-doped porous carbon are mixed and carbonized in a liquid phase using a liquid phase method, resulting in titanium niobate coating of silicon-carbon composite material on its surface, thus reducing expansion.

[0064] The above descriptions are merely some embodiments of the present invention. It should be noted that those skilled in the art can make other modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a double-layer coated silicon-carbon composite material, comprising the following steps: Step S1: Mix the resin and organic base pore-forming agent evenly according to the mass ratio of resin: organic base pore-forming agent: lithium carboxymethyl cellulose = 100:1-10:1-5, then add it to the lithium carboxymethyl cellulose solution and disperse it evenly. Spray dry it for 0.5 h at an inlet temperature of 220℃, an outlet temperature of 80℃, and a flow rate of 1 kg / h. Transfer the obtained material to a tube furnace and carbonize it at a temperature of 700-900℃ for 1-6 h. Then raise the temperature to 1100℃ and pass water vapor through it at a flow rate of 500-1000 ml / min for 2-12 h. Then let it cool naturally to room temperature to obtain lithium-doped porous carbon. Step S2: Niobium salt + titanium salt : liquid silane : lithium-doped porous carbon = 5-20 : 100-300 : 100, add niobium salt, titanium salt and liquid silane to an organic solvent to prepare a 1-10 wt% solution, disperse evenly, then add lithium-doped porous carbon, disperse evenly, spray dry for 0.5 h at an inlet temperature of 220℃, an outlet temperature of 80℃ and a flow rate of 1 kg / h, transfer the obtained material to a tube furnace, introduce inert gas to purge the air in the tube, and sinter at 300-500℃ for 1-6 h to obtain titanium niobate coated silicon carbon composite material; in, The niobium salt is one of niobium oxalate, niobium n-propoxide, niobium isopropoxide, niobium pentanol, or niobium phenolate; The titanium salt is one of ethyl titanate, tetraethyl titanate, propyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraisopropoxy titanium, or tetraisopropoxide titanium. The organic solvent is one of methyl ether, diethyl ether, dipropyl ether, ethyl butyl ether, dibutyl ether, or dipentyl ether; The molar ratio of niobium salt to titanium salt is 1:1-2. Step S3: Transfer the titanium niobate-coated silicon-carbon composite material to a tube furnace. First, introduce an inert gas to purge the air from the tube. Then, heat the furnace to 500-800℃ and introduce a carbon source gas at a flow rate of 50-500 ml / min for 1-6 hours to deposit amorphous carbon on the surface, thus obtaining a double-layer coated silicon-carbon composite material. Wherein: the resin mentioned in step S1 is one of diallyl isophthalate resin, acrylic resin, alkyd resin, fumaric resin or malic acid resin.

2. The method for preparing a double-layer coated silicon-carbon composite material as described in claim 1, wherein: The organic base pore-forming agent mentioned in step S1 is one of dimethylisopropylamine, 1-methylpyrrolidine, triethylamine, 1-methylpiperidine, or 4-methylmorpholine.

3. The method for preparing a double-layer coated silicon-carbon composite material as described in claim 1, wherein: The liquid silane mentioned in step S2 is one of tetraethoxysilane, tetramethyldivinyldisiloxane, triethylsilane, trimethylchlorosilane, triphenylchlorosilane, or hexamethyldisiloxane.

4. The method for preparing a double-layer coated silicon-carbon composite material as described in claim 1, wherein: In step S3, the carbon source gas is one of methane, ethane, ethylene, acetylene, or propyne.

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