Preparation method of anti-blowout porous carbon material for silicon-carbon negative electrode

Abstract

The present invention provides a preparation method for a blowout-proof porous carbon material for a silicon-carbon negative electrode, comprising the following steps: (S1) preparing a mixed solution of a solvent, an emulsifier, and a nucleating agent, adding a resin oligomer and a curing agent, and polymerizing into spherical resins under stirring conditions at 40-80 °C, and drying and agglomerating into blocks; the emulsifier includes a small molecule anionic surfactant and a polymer emulsifier; (S2) crushing and screening to obtain spherical agglomerates with a suitable particle size, and pyrolyzing and carbonizing the spherical agglomerates under an inert atmosphere to obtain pyrolytic carbon; (S3) activating and creating pores in the pyrolytic carbon under an activation atmosphere to obtain an activated carbon aggregate; (S4) depolymerizing and separating the activated carbon aggregate to obtain a porous carbon material. The present invention enables larger agglomerations of spherical particles to solve the pain point of gas blowout during the industrial activation process, improves the activation yield, and can simultaneously adjust the mechanical properties of the material by controlling the crosslinking degree.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials for lithium-ion batteries, and is mainly used for the preparation of silicon-carbon anode materials. Specifically, it relates to a preparation method of a blowout-preventing porous carbon material for silicon-carbon anodes. Background Art

[0002] Currently, secondary batteries have become the focus in the new energy field due to their advantage of being reusable. Especially in the field of power batteries, relatively high requirements are put forward for battery capacity. Silicon-based anode materials are currently promising anode materials for lithium-ion batteries. However, silicon-based anode materials are prone to volume expansion during use, ultimately leading to a decrease in battery capacity. Carbon materials have a relatively small volume expansion effect. In silicon-carbon composite materials, the carbon matrix can form a good buffer layer to mitigate volume expansion. However, under high pressure, carbon-based materials with irregular morphologies will cut the current collector, resulting in internal short circuits in the battery. To solve the drawbacks of irregularly shaped carbon, researchers have proposed the idea of spherical porous carbon.

[0003] However, there are currently spherical porous carbon precursors on the market, which have the drawback of material being blown away during the gas activation process. Currently, rotary furnaces are used for activation in the field of porous carbon activation. During the activation process, activation gas is continuously introduced, and the metal filter element is an important part of the activation furnace. Currently, the minimum limit of the pore diameter of the metal filter element in the industry is 10 μm, which causes a large amount of carbon powder to be carried away by the activation gas during the activation process, resulting in raw material blowout. After the material is blown away, the gas-solid ratio of the activation gas to the raw material changes, ultimately affecting the stability of the activation process and leading to a sharp increase in the cost of porous carbon materials.

[0004] The resin ball preparation method provided by the present invention uses the method of emulsifier compounding to form balls by emulsification. During the drying process, the resin balls are agglomerated into aggregates within a certain particle size range by the weak connection effect of the emulsifier, preventing sample blowout during the activation process, increasing the activation yield, and providing a good idea for industrial production. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that existing spherical resins are severely blown away during the gas activation process, resulting in low activated carbon yield and high manufacturing cost. To achieve the purpose of the present invention, spherical resin aggregates are prepared using resin oligomers as raw materials and an emulsification system containing a high-molecular binder. The present invention solves the above technical problems through the following technical solutions.

[0006] A preparation method of a blowout-preventing porous carbon material for silicon-carbon anodes includes the following steps:

[0007] (S1) Prepare a mixed solution of a solvent, an emulsifier, and a nucleating agent, add a resin oligomer and a curing agent, and polymerize into spherical resin under stirring conditions at 40-80 °C, and dry and agglomerate into blocks; the emulsifier includes a small molecule anionic surfactant and a polymer emulsifier;

[0008] (S2) Crush and screen to obtain spherical aggregates with appropriate particle sizes. Under an inert atmosphere, pyrolyze and carbonize the spherical aggregates to obtain pyrolytic carbon;

[0009] (S3) Under an activation atmosphere, activate and pore-form the pyrolytic carbon to obtain an activated carbon aggregate;

[0010] (S4) Depolymerize and separate the activated carbon aggregate to obtain a porous carbon material.

[0011] Further, in step (S1), the resin oligomer is selected from at least one of a phenolic resin oligomer and an acrylonitrile oligomer, and the weight average molecular weight of the resin oligomer is 1000-3000.

[0012] Further, in step (S1), the mass ratio of the solvent, the emulsifier, the nucleating agent, the polymer precursor, and the curing agent is 100:1-5:1-5:30-50:1-10.

[0013] Further, in step (S1), the solvent is a mixed solvent of water and C1-3 alcohol, and the C1-3 alcohol is selected from methanol, ethanol, and propanol; the alcohol in the solvent accounts for 1-5 wt%; further, the solvent is a mixed solvent of water, C1-3 alcohol, and an organic solvent miscible with water; the organic solvent is selected from dimethylformamide, sulfolane, and dimethyl sulfoxide, and the organic solvent accounts for 1-5 wt%. The addition of alcohol and / or organic solvent can change the surface tension of the system, increase the water solubility of the oligomer, and facilitate the rapid dispersion of the oligomer precursor and the solvent at the initial stage of the polymerization reaction. If alcohol and organic solvent are not added, it will be difficult for the polymerization system to quickly form an emulsion. When the weight average molecular weight of the resin oligomer is below 1500, a mixed solvent of water and C1-3 alcohol is used; when the weight average molecular weight of the resin oligomer > 1500, an organic solvent is also added.

[0014] Further, in step (S1), the anionic surfactant is selected from at least one of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate; the polymer emulsifier is selected from at least one of gum arabic powder, polyvinyl alcohol, polyethylene glycol, F127, PVP, and P123, and the molecular weight of the polymer emulsifier is 1000-5000, preferably 2000-3000.

[0015] Further, the mass ratio of the anionic surfactant to the polymer emulsifier is 6-10:1.

[0016] Further, in step (S1), the nucleating agent is selected from at least one of sodium chloride, anhydrous sodium sulfate, ammonium carbonate, ammonium acetate, and ammonium bicarbonate; the curing agent is selected from at least one of hexamethylenetetramine, N,N'-methylenebisacrylamide, p-toluenesulfonic acid, phenolsulfonic acid, and oxalic acid. Further, in step (S1), there is no particular limitation on drying, which is well-known in the art, such as drying by baking or vacuum drying.

[0017] Further, in step (S2), the appropriate particle size is controlled by screening to make the particle size of the material 30 - 100 mesh. The unqualified numerical particles can be put into the emulsion waste liquid and dried into blocks again to achieve the purpose of recycling. The inert atmosphere includes but is not limited to at least one of nitrogen, helium, and argon.

[0018] Further, in step (S2), the process conditions for pyrolysis carbonization are 600 - 800 °C and the pyrolysis time is 1 - 10 h.

[0019] Further, in step (S3), the activation atmosphere includes but is not limited to at least one of carbon dioxide and water vapor, the activation temperature is 800 - 1200 °C, and the activation time is 5 - 20 h.

[0020] Further, in step (S4), a powder depolymerization and dispersion machine is used for depolymerization separation, and the purpose is to depolymerize the agglomerated activated carbon aggregates to obtain porous carbon with an appropriate particle size.

[0021] The porous carbon product obtained by the preparation method provided by the present invention has a sphericity ≥ 90%, no rough particles on the surface morphology, and a uniform particle size distribution. It has good fluidity in powder compaction and can fill the void parts. At the same time, the resin microspheres in this technical solution have a controllable particle size, can be matched with silicon materials, and reduce the volume expansion effect of silicon materials.

[0022] Compared with the prior art, the preparation method provided by the present invention is an emulsification method for resin spheroidization, drying and agglomeration into blocks, carbonization, pulverization, and gas activation. Among them, a high-molecular emulsifier is selected to be compounded with a low-molecular surfactant, which simultaneously acts as a dispersant and an adhesive, causing the spherical particles to form larger agglomerations, and the agglomerations are due to weak bonding forces. The depolymerization treatment after activation will not cause morphological damage, and it can solve the problem of gas blowing loss during industrial activation and maintain a good spherical morphology at the same time. Description of the Drawings

[0023] Figure 1 It is the SEM image of the activated carbon obtained in step (S3) of Example 1.

[0024] Figure 2 It is the SEM image of the porous carbon material of the product obtained in Example 1.

[0025] Figure 3SEM image of the porous carbon product obtained in Comparative Example 2.

[0026] Figure 4 Particle size distribution diagram of the porous carbon product obtained in Example 1. Detailed implementation manners

[0027] To more clearly illustrate the technical solutions in the present invention, the following will describe the technical solutions of the present invention completely. Obviously, the described embodiments are partial cases of the present invention, and the present invention is not limited to the following embodiments.

[0028] Example 1

[0029] (S1) Add 6.80 g of polyethylene glycol (PEG 2000, number average molecular weight 2000), 0.76 g of sodium dodecyl sulfate (the dosage of the emulsifier is 3.78 wt% of water), and 2.00 g of ethanol into 200.00 g of water, stir evenly at 500 r / min under the condition of 30 °C, then add 10 g of NaCl as a nucleating agent to prepare a solution. After that, add 60 g of low molecular weight phenolic resin (weight average molecular weight about 1500) and 2.5 g of oxalic acid as a curing agent (the dosage of the curing agent is 1.25 wt% of water), disperse at 30 °C for 4 h, react at 95 °C for 24 h. After the reaction, an emulsion is obtained. The emulsion is subjected to solid-liquid separation, and the separated solid is dried in a forced-air oven for 24 h at a drying temperature of 80 °C to obtain a block-shaped spherical resin aggregate; in Example 1, the weight average molecular weight of the oligomer precursor is about 1500, which can be well dispersed in the solution, so no additional organic solvent needs to be added;

[0030] (S2) Crush and screen the dried and agglomerated block resin into 100-mesh particles by a pair of roller screens; the unqualified small-particle-size resin is dispersed into the emulsion waste liquid and dried into blocks again to achieve the purpose of recycling; the screened spherical resin particles are pyrolytically carbonized in an argon atmosphere at a pyrolysis temperature of 700 °C and a pyrolysis time of 2 h to obtain pyrolytic carbon;

[0031] (S3) The pyrolytic carbon is activated, and the activation gas is CO 2 , the activation temperature is 900 °C, and the activation time is 12 h to obtain an activated carbon aggregate;

[0032] (S4) The activated carbon aggregate is depolymerized in a powder depolymerizer and disperser to obtain monodisperse spherical particles, that is, the product is a porous carbon material for preventing blow-off of silicon-carbon anodes.

[0033] Figure 1 SEM image of the activated carbon obtained in step (S3) of Example 1; Figure 2 SEM image of the porous carbon material for preventing blow-off of the silicon-carbon anode product obtained in Example 1. Figure 4 Particle size distribution diagram of the porous carbon product obtained in Example 1.

[0034] Example 2

[0035] Other conditions are the same as those in Example 1, except that in step (S1), the amount of polyethylene glycol is 3.4 g and the amount of sodium dodecyl sulfate is 0.38 g, that is, the amount of emulsifier is 1.89% of water.

[0036] Example 3

[0037] Other conditions are the same as those in Example 1, except that in step (S1), the amount of polyethylene glycol is 1.7 g and the amount of sodium dodecyl sulfate is 0.19 g, that is, the amount of emulsifier is 0.945% of water.

[0038] Example 4

[0039] Other conditions are the same as those in Example 1, except that in step (S1), the amount of oxalic acid added is 5 g and the amount of curing agent is 2.5 wt% of water.

[0040] Example 5

[0041] Other conditions are the same as those in Example 1, except that in step (S1), the amount of oxalic acid added is 10 g and the amount of curing agent is 5 wt% of water.

[0042] Example 6

[0043] Other conditions are the same as those in Example 1, except that in step (S1), the amount of oxalic acid added is 20 g and the amount of curing agent is 10 wt% of water.

[0044] Example 7

[0045] (S1) Add 9.2 g of polyethylene glycol (PEG 2000, number average molecular weight 2000), 1.0 g of sodium dodecyl sulfate (the amount of emulsifier is 3.78 wt% of water), 5.0 g of ethanol, and 8.0 g of sulfolane to 200.00 g of water, stir evenly at 500 r / min under the condition of 30 °C, and then add 10 g of Na 2 SO 4 nucleating agent to prepare a solution, and then add 60 g of acrylonitrile oligomer (weight average molecular weight about 3000) and 5 g of N,N'-methylenebisacrylamide as a curing agent (the amount of curing agent is 2 wt% of water), disperse at 30 °C for 4 h, react at 95 °C for 24 h, after the reaction, an emulsion is obtained, the emulsion is subjected to solid-liquid separation, and the separated solid is dried in a blast drying oven for 24 h, and the drying temperature is 80 °C to obtain a block-shaped spherical resin aggregate; in Example 1, the weight average molecular weight of the oligomer precursor is about 3000, and an additional organic solvent sulfolane needs to be added;

[0046] Subsequent steps (S2) to (S4) are the same as those in Example 1.

[0047] Comparative Example 1

[0048] Other conditions were the same as those in Example 1, except that in step (S1), the emulsifier was 7.56 g of polyethylene glycol, that is, sodium dodecyl sulfate was not added. In Comparative Example 1, step (S5) could not depolymerize smoothly, indicating that the anionic surfactant was missing in the emulsifier and could not depolymerize smoothly.

[0049] Comparative Example 2

[0050] Other conditions were the same as those in Example 1, except that in step (S1), the emulsifier was 7.56 g of sodium dodecyl sulfate, that is, polyethylene glycol was not added.

[0051] Figure 3 The SEM image of the porous carbon obtained in Comparative Example 2 is shown in [Figure number]. The obtained porous carbon in Comparative Example 2 had a lower sphericity, and polyethylene glycol was missing in the emulsifier, so the resin could not form spheres; it shows that a suitable emulsifier for the reaction system needs to be selected in the polymerization reaction to smoothly obtain spherical resin. If it cannot become spherical, under high-pressure conditions, the irregular carbon-based material has a risk of cutting the current collector, resulting in a short circuit inside the battery. From the design level, reducing the edges and corners of the irregular carbon and preparing it into a spherical morphology. In the present invention, the compounding of a small molecule anionic surfactant and a certain amount of polyethylene glycol, etc. as the emulsifier can smoothly make the resin spherical.

[0052] The Dv50 of the emulsion obtained in step (S1) of Example 1 was 10.16 μm, and the particle size of the spherical resin aggregate in block shape after solid-liquid separation and drying was 50.26 μm. The corresponding Dv50 of the emulsion in Comparative Example 2 was 9.52 μm, and the particle size of the spherical resin aggregate in block shape after solid-liquid separation and drying was 15.63 μm. It can be seen that when in the emulsion state, the average particle size difference was not significant. After drying, in Example 1, the agglomeration of the spheres was more obvious, resulting in an increase in particle size.

[0053] Example 1

[0054] The particle size of the pyrolytic carbon obtained in step (S2) of the above examples and comparative examples was tested, and the results are shown in Table 1 below.

[0055] Table 1 Product Particle Size Analysis

[0056]

[0057] As can be seen from Table 1, the particle size can be regulated by controlling the content of the emulsifier. The hydroxyl groups in the polymer emulsifier interact with water and extend towards the water end; the hydrophobic groups are adsorbed together with the resin molecules due to electrostatic forces, protecting the resin droplets. The polymer emulsifier can significantly reduce the interfacial tension between the resin and water phases, thereby reducing the surface free energy between the two phases and maintaining the thermodynamic stability of the polymerization system. Then, under the action of stirring, the resin is dispersed into oil droplets of corresponding sizes. When the concentration of the polymer emulsifier is low, the number of emulsifier molecules attached to the surface of a single droplet decreases, the protection ability for the droplet weakens, and the coalescence between resins is likely to occur, resulting in a large particle size of the finally formed resin balls. When the concentration of the polymer emulsifier is high, the protection ability for the droplets is enhanced, and the particle size of the formed resin balls is smaller. After adding the polymer emulsifier, the proportion of fine powder is relatively low, indicating that agglomeration has occurred; without adding the polymer emulsifier, the proportion of fine powder is relatively high, indicating that good agglomeration has not been formed. In Comparative Example 2, the proportion of fine powder with a particle size greater than 800 mesh in the recovered pyrolytic carbon is very high, indicating that good agglomeration has not been formed.

[0058] The pore structure, yield, and maximum bearing pressure of the porous carbon materials obtained in the above examples and comparative examples were tested, and the results are shown in Table 2 below. The yield is obtained by dividing the output after the reaction in the industrial activation furnace by the amount of pyrolytic carbon powder added before activation. The lower the yield, the more serious the blow-off, resulting in an increase in production costs.

[0059] Table 2 Performance Test of Porous Carbon Materials

[0060]

[0061] As can be seen from Table 2, the porous carbon prepared in the present invention is a porous carbon with a micropore proportion of more than 90%, and has a certain mesopore proportion. The yields are all above 40%, and have good mechanical properties.

[0062] Application Example

[0063] The porous carbon materials and silane gas obtained in the above examples and comparative examples were subjected to silicon deposition under the condition of nitrogen as the carrier gas. The silicon deposition process conditions were: 500 - 600 °C, deposition time: 4 - 9 h, so that the silicon content in the obtained composite silicon-carbon material was about 50 wt%, and the electrochemical performance was tested. The battery composition was: the positive electrode was a lithium sheet; the negative electrode was the silicon-carbon composite material coated on copper foil and then trimmed. The rest were a double-layer PP / PE diaphragm and an electrolyte of 1 mol / L LiPF 6 (The solvent was a mixed solution of diethyl carbonate, dimethyl carbonate, and ethylene carbonate with a volume ratio of 1:1:1), and the test conditions were: a blue electrochemical test system, and charge-discharge tests were carried out between 0.005 - 1.5 V. The results are shown in Table 3 below.

[0064] Table 3 Electrochemical Performance Test

[0065]

[0066] As can be seen from Table 3, the silicon-carbon composite anode material supported by silicon deposition of the porous carbon prepared by the present invention has excellent electrochemical performance. For the finished product prepared by pressing the porous carbon, although the electrochemical performance is reduced, the reduction amplitude is very small and within an acceptable range. However, the preparation method of the present invention significantly improves the loss caused by blowing loss during the preparation of porous carbon, saves costs, and has more industrial advantages.

Claims

1. A method for preparing a blow-off-proof porous carbon material for a silicon-carbon negative electrode, characterized in that: The following steps are involved: (S1) preparing a mixed solution of a solvent, an emulsifier and a nucleating agent, adding a resin oligomer and a curing agent, polymerizing under stirring at 40-80°C to form a spherical resin, and drying and agglomerating into blocks; the emulsifier comprises a small molecule anionic surfactant and a polymer emulsifier; the resin oligomer is selected from at least one of a phenolic resin oligomer and an acrylonitrile oligomer; the weight average molecular weight of the resin oligomer is 1000-3000; the mass ratio of the solvent, the emulsifier, the nucleating agent, the polymer precursor and the curing agent is 100:1-5:1-5:30-50:1-10; the anionic surfactant is selected from at least one of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate; the polymer emulsifier is polyethylene glycol, and the molecular weight of the polymer emulsifier is 2000-3000; the mass ratio of the anionic surfactant to the polymer emulsifier is 6-10:1; the nucleating agent is selected from at least one of sodium chloride and anhydrous sodium sulfate; (S2) crushing and screening to obtain spherical agglomerates of suitable particle size, and pyrolyzing and carbonizing the spherical agglomerates under an inert atmosphere to obtain pyrolytic carbon; the suitable particle size is controlled by screening to a particle size of 30-100 mesh; (S3) activating and pore-forming the pyrolytic carbon in an activation atmosphere to obtain activated carbon aggregates; (S4) Activating the carbon aggregates for depolymerization and separation to obtain a porous carbon material with a sphericity ratio of ≥ 90%.

2. The preparation method according to claim 1, characterized in that: In step (S1), when the weight average molecular weight of the resin oligomer is below 1500, the solvent is a mixed solvent of water and C1-3 alcohol, and the C1-3 alcohol is selected from methanol, ethanol, and propanol; the alcohol accounts for 1-5wt% in the solvent.

3. The preparation method according to claim 1, characterized in that: In step (S1), when the weight average molecular weight of the resin oligomer is greater than 1500, the solvent is a mixed solvent of water, C1-3 alcohol, and an organic solvent miscible with water; the organic solvent is selected from dimethylformamide, cyclopentane, and dimethyl sulfoxide, and the organic solvent accounts for 1-5wt%.

4. The preparation method according to claim 1, characterized in that: In step (S1), the curing agent is selected from at least one of urotropine, N,N'-methylenebisacrylamide, p-toluenesulfonic acid, phenolsulfonic acid, and oxalic acid.

5. The preparation method according to claim 1, characterized in that: In step (S2), the inert atmosphere includes but is not limited to at least one of nitrogen, helium, and argon.

6. The preparation method according to claim 5, characterized in that: In step (S2), the process conditions of pyrolysis carbonization are 600-800°C and pyrolysis time is 1-10h.

7. The preparation method according to claim 1, characterized in that: In step (S3), the activation atmosphere includes but is not limited to at least one of carbon dioxide and water vapor, the activation temperature is 800-1200° C., and the activation time is 5-20 hours.

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