CN113666354B - Preparation method of silicon-carbon composite material, silicon negative electrode piece and battery - Google Patents
Preparation method of silicon-carbon composite material, silicon negative electrode piece and battery Download PDFInfo
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- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- C01B33/025—Preparation by reduction of silica or free silica-containing material with carbon or a solid carbonaceous material, i.e. carbo-thermal process
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- H01M10/00—Secondary cells; Manufacture thereof
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- H—ELECTRICITY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H—ELECTRICITY
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- H01M4/02—Electrodes composed of, or comprising, active material
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
The invention discloses a preparation method of a silicon-carbon composite material, a silicon cathode pole piece and a battery, relates to the technical field of preparation of functional composite materials and batteries, and aims to overcome the defects of the conventional silicon cathode lithium ion battery at the same time, the preparation method of the silicon-carbon composite material provided by the invention comprises the following steps: uniformly mixing a silicon source and carbon black to obtain a silicon source mixture; mixing a silicon source mixture and porous carbon powder, performing ultrasonic dispersion, performing ball milling, and heating; introducing a reducing agent, and carrying out constant-temperature reduction reaction; removing impurities with hydrochloric acid solution, and drying to obtain the silicon-carbon composite material; the invention also provides a silicon negative pole piece and a battery prepared by using the material, and solves the problems that material particles are easy to break, particles and granules in the silicon negative pole piece and particles and current collectors are easy to fall off, and the overall cycle performance and energy density of the battery are further influenced, and the like, caused by the volume expansion of silicon materials in the traditional silicon negative pole battery.
Description
Technical Field
The invention relates to the technical field of functional composite materials and battery preparation, in particular to a preparation method of a silicon-carbon composite material, a silicon negative electrode plate and a battery.
Background
With the rapid development of electric vehicles and other electric consumer product industries, the demand of people on the long endurance of batteries is more and more urgent, wherein the application range of lithium ion batteries is the widest, and the endurance of lithium ion batteries is influenced by the energy density to a certain extent, so how to further improve the energy density of lithium ion batteries to meet the development demand of the electric China industry becomes an important technical direction for the development of lithium ion batteries.
Under the technical progress demand, the silicon cathode lithium ion battery replaces the traditional graphite cathode, has obvious advantage in energy density improvement, and the advantage is mainly derived from the material characteristics of silicon materials, namely, compared with the current commercialized graphite cathode, the theoretical gram capacity of silicon is 4200mAh/g, which is much higher than 372mAh/g of the graphite cathode; the silicon material has a relatively low discharge potential plateau and generates a high operating voltage when paired with a cathode. Meanwhile, the silicon material has rich reserves, and has the advantages of good environmental compatibility, low toxicity, relatively stable chemical properties and the like. Therefore, the silicon anode material will become a key technical route for the development of the next generation of high energy density batteries.
However, the existing silicon negative electrode lithium ion battery has technical defects, in the process of fully pre-lithium, the volume expansion of silicon materials in the silicon negative electrode is about three times of the original volume, a silicon negative electrode plate is influenced by the volume effect in the charging and discharging process, material particles are easy to break, and meanwhile, particles in the silicon negative electrode plate and particles are easy to fall off from a current collector, so that the cycle performance of the lithium ion battery is sharply reduced, and the application prospect of the silicon negative electrode lithium ion battery is seriously influenced.
A porous silicon-carbon mixed anode pole piece and a lithium ion secondary battery (CN 201410348929.3) containing the same disclosed in the Chinese patent application disclose a porous silicon-carbon mixed anode pole piece, which solves the problem of large volume expansion in the cycle process of a silicon negative battery by a negative porous current collector method, and simultaneously can improve the cycle capacity retention rate of the silicon-carbon mixed anode lithium ion secondary battery and reduce the thickness expansion rate of the lithium ion battery in the cycle process. However, the method provided by the patent can only play a certain buffering role on the contact surface of the silicon negative electrode pole piece and the current collector, the problem of expansion among silicon particles is difficult to solve, and meanwhile, the problem of material particle breakage caused by charging and discharging cannot be solved, so that the technical scheme has certain limitation.
Disclosure of Invention
In order to overcome the problems that material particles are easy to break, particles and granules in a silicon negative pole piece and particles and current collectors are easy to fall off due to volume expansion of silicon materials in the conventional silicon negative pole lithium ion battery, and the overall cycle performance and energy density of the battery are further influenced, the invention provides a silicon-carbon composite material, and the silicon-carbon composite material is applied to the silicon negative pole piece and the corresponding silicon negative pole battery to solve the problems.
In some embodiments of the invention, the porous carbon spheres can have the following technical characteristics: with macropores > 10um, pore volume distribution > 70%; mesopores with the diameter of 2-50 nm and the pore volume distribution is more than 10 percent; s BET ＜800m 2 (iv) g. The porous carbon source can be porous carbon balls, phenolic resin-based porous carbon and other porous carbon materials.
In some embodiments of the present invention, the preparation method of the silicon-carbon composite material and the application of the silicon-carbon composite material in preparing a silicon negative electrode plate can be integrally embodied as follows:
using a magnesiothermic reduction method to prepare SiO 2 Mixing the silicon source and the porous carbon powder according to a mass ratio (20-50 percent by weight) to (50-80 percent by weight) for 2-8h, heating to 600-1000 ℃ in a ball mill at a speed of 10 ℃/min in an argon atmosphere, introducing a reducing agent Mg steam, carrying out a constant-temperature reduction reaction for 0.5-8h, carrying out impurity removal treatment on the obtained mixture and 0.1-10mol/l hydrochloric acid for 0.5-2h, filtering after the reaction to obtain a solid silicon-carbon composite material, and drying the composite material at a low temperature of 80-200 ℃ to obtain the final silicon-carbon composite material.
Mixing the multi-composite material with commercial graphite according to the mass ratio of (10% -50% by weight) to (50% -90% by weight) to prepare a composite negative electrode material, and mixing the composite negative electrode material: the conductive agent (CNT, superP and the like), the binder (SBR), the thickening agent (CMC) = (92% -97%), the (1% -3%) and the (1% -2%) are mixed in a mass ratio to prepare a mixed material required by the coating of the negative pole piece.
In order to achieve the purpose of the invention, the complete technical scheme provided by the invention is as follows:
firstly, the invention provides a preparation method of a silicon-carbon composite material, which comprises the following steps:
(1) Preparing a silicon source mixture: uniformly mixing a silicon source mixture material, wherein the silicon source mixture material in the step comprises a silicon source and carbon black; (2) mixing the materials, performing ultrasonic dispersion, performing ball milling, and heating; introducing a reducing agent, and carrying out constant-temperature reduction reaction, wherein the materials in the step comprise a silicon source mixture and porous carbon powder; (3) And (3) removing impurities from the mixture obtained in the step (2) by using a hydrochloric acid solution, and drying to obtain the silicon-carbon composite material.
Preferably, step (1) is specifically: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethyl alcohol dispersion liquid, dropwise adding the silicon source ethyl alcohol dispersion liquid into a carbon black powder ethyl alcohol dispersion liquid, carrying out ultrasonic dispersion, carrying out solid-liquid separation, and drying a solid part; the silicon source is nano silicon dioxide, and the content of the silicon source in the final ethanol dispersion liquid of the silicon source is 0.3-0.9g/mL; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is (0.06-0.09): 1; the ultrasonic dispersion time is 4-12h; the solid-liquid separation method comprises centrifugation and supernatant removal; the drying can be drying or freeze-drying, and the drying temperature is not higher than 60 ℃. The carbon black is conductive carbon black.
Preferably, the mass ratio of the silicon source mixture to the porous carbon powder in the step (2) is (2-7): (2-20), preferably (2-5): (5-8); the ultrasonic dispersion time is 2-8h; the ball milling time is 1-5h; heating to 600-1000 ℃ under the argon atmosphere at the heating rate of 10-15 ℃/min; the reducing agent is Mg steam, the constant temperature reduction reaction temperature is 600-1000 ℃, and the constant temperature reduction reaction time is 0.5-8h.
The porous carbon powder has macropores with a pore diameter of more than 10 μm and a pore volume distribution of more than 70%, and also has mesopores with a pore diameter of 20-50nm and a pore volume distribution of more than 10%, S BET Is 600-1500m 2 (ii)/g; the particle size of the silicon particles after the silicon source is reduced is 3-15nm.
Preferably, the concentration of the hydrochloric acid solution in the step (3) is 0.1-10mol/L; the hybridization removal treatment time is 0.5-2h; the hydrochloric acid solution is preferably used in such an amount that the mixture obtained in step (2) is completely immersed in the solution. The drying temperature is 80-200 ℃.
In some embodiments of the present invention, the silicon source mixture material in step (1) further includes high-substituted hydroxypropyl cellulose and polyethylene glycol, and step (1) specifically includes: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethanol dispersion liquid, dropwise adding the silicon source ethanol dispersion liquid into a carbon black powder ethanol dispersion liquid, dropwise adding a high-substituted hydroxypropyl cellulose ethanol dispersion liquid and polyethylene glycol into the mixture, and ultrasonically dispersing; wherein the silicon source is nano silicon dioxide, and the content of the silicon source in the final ethanol dispersion liquid is 0.3-0.9g/mL; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is (0.06-0.09): 1; the mass ratio of the silicon source to the high-substituted hydroxypropyl cellulose is (0.02-0.2) to 1; the mass/volume ratio of the silicon source to the polyethylene glycol is 0.05-0.1g/mL; the ultrasonic dispersion time is 8-12h; the carbon black is conductive carbon black. Correspondingly, preferably, step (2) is specifically: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is (3-7) to (8-15); the ultrasonic dispersion time is 4-8h; the ball milling time is 2-5h; heating in argon atmosphere at a heating rate of 10-15 deg.C/min to 100-120 deg.C, maintaining for 4-6 hr, removing solvent, and curing; heating to 500-850 deg.C at 10-15 deg.C/min, maintaining the temperature for 2-5h, and carbonizing; the reducing agent is Mg steam, the constant temperature reduction reaction temperature is 600-1000 ℃, and the constant temperature reduction reaction time is 0.5-8h.
In some embodiments of the present invention, the silicon source mixture material in step (1) further comprises polyacrylamide, and the polyacrylamide is low molecular weight polyacrylamide. The step (1) is specifically as follows: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethyl alcohol dispersion liquid, dropwise adding the silicon source ethyl alcohol dispersion liquid into a carbon black powder ethyl alcohol dispersion liquid, adding polyacrylamide into the mixture, and performing ultrasonic dispersion; wherein the silicon source is nano silicon dioxide, and the content of the silicon source in the final ethanol dispersion liquid is 0.3-0.9g/mL; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is (0.06-0.09): 1; the mass ratio of the silicon source to the polyacrylamide is (0.02-0.2): 1; the ultrasonic dispersion time is 8-12h; the carbon black is conductive carbon black. Correspondingly preferably, step (2) is specifically: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is (3-7) to (8-15); the ultrasonic dispersion time is 4-8h; the ball milling time is 3-5h; heating under argon atmosphere at a heating rate of 10-15 deg.C/min to 100-120 deg.C for 4-6 hr, removing solvent, and curing; heating to 500-850 deg.C at 10-15 deg.C/min, maintaining the temperature for 2-5 hr, and carbonizing; the reducing agent is Mg steam, the constant temperature reduction reaction temperature is 600-1000 ℃, and the constant temperature reduction reaction time is 0.5-8h.
In some embodiments of the present invention, the silicon source mixture material in step (1) further comprises polyacrylamide, high-substituted hydroxypropyl cellulose and polyethylene glycol. The step (1) is specifically as follows: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethanol dispersion liquid, dropwise adding the silicon source ethanol dispersion liquid into a carbon black powder ethanol dispersion liquid, adding polyacrylamide into the mixture, dropwise adding a high-substituted hydroxypropyl cellulose ethanol dispersion liquid and polyethylene glycol into the mixture, and ultrasonically dispersing; wherein the silicon source is nano silicon dioxide, and the content of the silicon source in the final ethanol dispersion liquid is 0.3-0.9g/mL; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is (0.06-0.09): 1; the mass ratio of the silicon source to the polyacrylamide is (0.02-0.2) to 1; the mass ratio of the silicon source to the high-substituted hydroxypropyl cellulose is (0.02-0.2): 1; the mass/volume ratio of the silicon source to the polyethylene glycol is 0.05-0.1g/mL; the ultrasonic dispersion time is 10-12h; the carbon black is conductive carbon black. Correspondingly, preferably, step (2) is specifically: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is (5-7) to (8-12); the ultrasonic dispersion time is 6-8h; the ball milling time is 4-5h; heating under argon atmosphere at a heating rate of 10-15 deg.C/min to 100-120 deg.C for 4-6 hr, removing solvent, and curing; heating to 500-850 deg.C at 10-15 deg.C/min, maintaining the temperature for 2-5h, and carbonizing; the reducing agent is Mg steam, the constant temperature reduction reaction temperature is 600-1000 ℃, and the constant temperature reduction reaction time is 0.5-8h.
In some embodiments of the invention, the material in the step (2) further comprises polyacrylonitrile, the mass ratio of the polyacrylonitrile to the porous carbon powder is (1-3) to (8-20), and the average degree of polymerization of the polyacrylonitrile is 200-800. Correspondingly, preferably, step (2) is specifically: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion and ball milling, adding DMF (dimethyl formamide) dispersion liquid of polyacrylonitrile, performing ball milling again, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is (2-7) to (8-20), preferably (2-3) to (15-20); the ultrasonic dispersion time is 6-8h; the ball milling time is 4-5h; the polyacrylonitrile content in the DMF dispersion is 1-12% by weight; the ball milling time is 6-8h again; heating under argon atmosphere at a heating rate of 10-15 deg.C/min to 100-120 deg.C for 4-6 hr, removing solvent, and curing; heating to 650-850 deg.C at 10-15 deg.C/min, maintaining the temperature for 4-5h, and carbonizing; the reducing agent is Mg steam, the constant temperature reduction reaction temperature is 600-1000 ℃, and the constant temperature reduction reaction time is 0.5-8h.
Secondly, the invention provides a silicon negative electrode plate of the silicon-carbon composite material prepared by the preparation method.
The silicon negative pole piece comprises a current collector and a silicon-carbon composite material layer, wherein the carbon-silicon composite material layer is a thin film coated on the surface of the current collector.
The silicon-carbon composite material layer comprises an upper layer and a lower layer, the lower layer is positioned between the upper layer and the current collector, the lower layer comprises a silicon-carbon composite material, a conductive agent, a binder and a thickening agent, and the upper layer comprises graphite, the silicon-carbon composite material, the conductive agent, the binder and the thickening agent.
Preferably, the conductive agent is one or two of carbon nano tube or conductive carbon black; the binder is Styrene Butadiene Rubber (SBR); the thickener is sodium carboxymethylcellulose (CMC).
Preferably, in the lower layer, the mass part ratio of the silicon-carbon composite material, the conductive agent, the binder and the thickening agent is (85-90): (5-7): (10-15): (3-9); in the upper layer, the mass part ratio of the graphite and the silicon-carbon composite material is (1-5) to (5-9), and the mass part ratio of the total mass part of the graphite and the silicon-carbon composite material to the mass part ratio of the conductive agent, the binder and the thickening agent is (92-97) to (1-3) to (1-2).
In some embodiments of the present invention, the preparation method of the silicon negative electrode sheet based on the silicon-carbon composite material comprises: respectively mixing the materials of the upper layer and the lower layer according to the required proportion, uniformly mixing for 10-20min under high stirring (300 rpm), and performing ultrasonic treatment for 5-30min to respectively obtain the mixed membrane materials of the upper layer and the lower layer; coating a lower layer mixed membrane material on the surface of the current collector, and immediately coating an upper layer mixed membrane material on the surface of the lower layer after surface drying; and (5) drying. The ratio of the coating mass per unit area of the upper layer to the lower layer is (1.5-15): 1, wherein the coating mass per unit area of the lower layer is 0.0002-0.0030g/m 2 . The coating method is a spin coating method or a spray coating method, preferably a spray coating method. The drying is natural drying at room temperature or drying below 60 ℃. The current collector is a copper foil.
The invention provides a battery, which is a silicon negative electrode battery and comprises the silicon negative electrode pole piece, a positive electrode pole piece, electrolyte, a diaphragm between the positive electrode and the negative electrode and a shell. The diaphragm is a polyethylene microporous film or a polypropylene microporous film.
Advantageous effects
The invention has the beneficial effects that:
the silicon negative lithium ion battery is constructed by using the negative pole piece prepared from the silicon-carbon composite material, the special structure of the porous carbon base provides a buffer space for the volume expansion of the silicon material in the charging and discharging processes, the risk of particle crushing is reduced, the cycle performance of the battery is improved, meanwhile, the macropores in the material can be used as a liquid storage tank, the transmission distance of lithium ions under high-rate charging is reduced, the transmission of ions is facilitated, and the quick charging performance of the battery is improved.
The beneficial effects are specifically discussed as follows:
firstly, the silicon source is coated and isolated by the carbon black, so that the silicon source is prevented from being agglomerated or adhered before or after entering the pore channel of the porous carbon, the silicon source is prevented from being adhered too early before being uniformly dispersed, and finally, the silicon particles are uniformly dispersed on the pore wall of the porous carbon, so that the inter-particle acting force caused by the volume expansion of the silicon particles is reduced, the particle crushing and the particle extrusion falling off are avoided, meanwhile, the carbon black is uniformly distributed among the silicon particles and the porous carbon pore channel and is positioned among the silicon particles, the porous carbon and the electrolyte, the conductivity is increased, and the energy density is increased on the basis of improving the cycle performance of the battery.
Secondly, on the basis of adding high-substituted hydroxypropyl cellulose and polyethylene glycol into a silicon source mixture and further uniformly dispersing the silicon source, adding a plurality of heating steps for heating and temperature rise after the silicon source mixture enters porous carbon pore channels, respectively carrying out desolventizing, curing and carbonizing, so that after the mixture is processed, a finer and uniform porous (or net-shaped) structure is further formed in the porous carbon pore channels, the main effect component of the net-shaped structure is the high-substituted hydroxypropyl cellulose, the main effect component of pore forming is the polyethylene glycol, most of the silicon source is attached to the porous carbon pore walls, and the rest of the silicon source is combined on the porous (or net-shaped) structures, which is also a reason for adopting the larger-pore porous carbon.
Thirdly, polyacrylamide is added into a silicon source mixture, on the basis of the technical scheme, the polyacrylamide still has the effect of enabling the silicon source to be more uniformly dispersed, and meanwhile, a fine and stable pore-shaped (or net-shaped) structure is formed in a porous carbon pore channel; in addition, the pores (or meshes) are uniformly distributed in porous carbon pore channels, so that the contact between silicon particles and electrolyte is more sufficient, uniform and free from obstruction, and the electronic structure after the polyacrylamide carbonization also enables the battery to be more easily charged and discharged, so that the quick charging performance and the energy density of the battery are improved.
Fourthly, the dropping problem between silicon particles and between particles and the current collector is further improved by adding polyacrylonitrile in the step (2) of the present invention, probably because the N on the polyacrylonitrile and the silicon can be more tightly combined, and in addition, the polyacrylonitrile still retains partial toughness (elasticity) after carbonization, so that the stress generated by the volume change of the silicon particles during charging and discharging is transferred/dispersed, however, we found that if polyacrylonitrile is added to the silicon source mixture in the step (1) in the same manner, such an effect cannot be achieved.
Based on the explanations of the above beneficial effects one to four, it can be seen that although the factors added in the present invention all play a positive role in the cycle performance, energy density, and fast charge performance of the battery, they act separately and are not related to each other, but through the analysis of the research data, the factors do not act in complete isolation but are related to each other: it is known that when two factors act on a system in similar ways, if the two factors act on the system simultaneously, competition effects can occur between the factors, and both of the two factors can not fully exert their respective effects, even in most cases, when two factors of the relationship act on the system simultaneously, the result is that the effect of 1+1 > 1 is not achieved, but when a plurality of factors are combined, the improvement of the battery performance is very obvious additive, and is greatly improved on the basis of the effect of a single factor.
Fifth, the silicon negative electrode plate prepared by the invention adopts a two-layer structure, and a special process is adopted, no obvious limit exists between the two layers, no layering exists, the transition is gentle, the conductivity is good, the interlayer bonding strength is high, and the specific structure is not easy to fall off from a current collector (the lower layer has less silicon particle content, the influence of deformation on bonding to a certain degree is small, the upper layer has more silicon particle content, and the energy density is ensured).
The discussion of the beneficial effects is the presumption that the analysis is obtained according to experimental data and experimental facts, some factors are not determined, and particularly the action mechanism of mutual addition among the factors is not determined, but the invention really adopts the specific silicon-carbon composite material to prepare the silicon negative pole piece, thereby greatly improving the problems of poor battery cycle performance, low battery energy density and the like of the silicon negative pole battery caused by the volume expansion of the silicon material.
Drawings
FIG. 1 SEM image of the surface of a pole piece prepared in example 15;
FIG. 2 is a graph comparing the high temperature cycle capacity retention rate curves of example 15 and comparative example 4 for a high temperature cycle test of a battery, wherein the experimental group is example 15 and the comparative group is comparative example 4;
FIG. 3 is a graph comparing the cell thickness expansion rate curves of high temperature cycling of the battery corresponding to example 15 and comparative example 4, where the experimental group is example 15 and the comparative group is comparative example 4.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Unless otherwise indicated, the following examples and comparative examples are parallel runs, omitting the same processing steps and parameters.
Example 1 preparation of silicon carbon composite a:
(1) Preparing a silicon source mixture: uniformly mixing a silicon source mixture material, wherein the silicon source mixture material in the step comprises a silicon source and carbon black; (2) mixing the materials, performing ultrasonic dispersion, performing ball milling, and heating; introducing a reducing agent, and carrying out constant-temperature reduction reaction, wherein the materials in the step comprise a silicon source mixture and porous carbon powder; (3) And (3) removing impurities from the mixture obtained in the step (2) by using a hydrochloric acid solution, and drying to obtain the silicon-carbon composite material.
The step (1) is specifically as follows: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethanol dispersion liquid, dropwise adding the silicon source ethanol dispersion liquid into the carbon black powder ethanol dispersion liquid, performing ultrasonic dispersion, performing solid-liquid separation, and drying a solid part; the silicon source is nano silicon dioxide, and the content of the silicon source in the final ethanol dispersion liquid of the silicon source is 0.6g/mL; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is 0.06; the ultrasonic dispersion time is 4h; the solid-liquid separation method comprises centrifugation and supernatant removal; the drying is drying at the temperature of 45 ℃. The carbon black is conductive carbon black.
The mass ratio of the silicon source mixture to the porous carbon powder in the step (2) is 1; the ultrasonic dispersion time is 2h; the ball milling time is 2h; heating is carried out under the argon atmosphere, the heating rate is 15 ℃/min, and the temperature is raised to 800 ℃; the reducing agent is Mg steam, the constant-temperature reduction reaction temperature is 800 ℃, and the constant-temperature reduction reaction time is 4 hours.
The porous carbon powder has macropores with a pore diameter of more than 10 μm and a pore volume distribution of more than 70%, and also has mesopores with a pore diameter of 20-50nm and a pore volume distribution of more than 10%, S BET Is 600-1500m 2 (iv) g; the particle size of the silicon particles after the silicon source reduction is 3-15nm.
The concentration of the hydrochloric acid solution in the step (3) is 0.8mol/L; the hybridization removal treatment time is 1h; the amount of the hydrochloric acid solution is such that the mixture obtained in the step (2) is completely immersed in the solution. The drying temperature was 80 ℃.
Example 2 preparation of silicon carbon composite b:
the same procedure parameters as in example 1 were used with the following exceptions:
the silicon source mixture material in the step (1) also comprises high-substituted hydroxypropyl cellulose and polyethylene glycol, and the step (1) specifically comprises the following steps: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethanol dispersion liquid, dropwise adding the silicon source ethanol dispersion liquid into the carbon black powder ethanol dispersion liquid, dropwise adding a high-substituted hydroxypropyl cellulose ethanol dispersion liquid and polyethylene glycol into the mixture, and performing ultrasonic dispersion; the mass ratio of the silicon source to the high-substituted hydroxypropyl cellulose is 0.1; the mass/volume ratio of the silicon source to the polyethylene glycol is 0.08g/mL; the ultrasonic dispersion time is 8h; correspondingly, the step (2) is specifically as follows: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is 1:5; the ultrasonic dispersion time is 4h; the ball milling time is 2.5h; heating is carried out under the argon atmosphere, the heating rate is 15 ℃/min, the temperature is firstly increased to 100-120 ℃, the temperature is kept constant for 4h, and solvent removal and solidification are carried out; heating to 500 ℃ at a speed of 15 ℃/min, keeping the temperature for 3 hours, and carbonizing; the reducing agent is Mg steam, the constant-temperature reduction reaction temperature is 800 ℃, and the constant-temperature reduction reaction time is 4 hours.
Example 3 preparation of silicon carbon composite material c:
the same procedure parameters as in example 1 were used with the following exceptions:
the silicon source mixture material in the step (1) also comprises polyacrylamide, and the polyacrylamide is low molecular weight polyacrylamide. The step (1) is specifically as follows: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethanol dispersion liquid, dropwise adding the silicon source ethanol dispersion liquid into the carbon black powder ethanol dispersion liquid, adding polyacrylamide into the mixture, and performing ultrasonic dispersion; the mass ratio of the silicon source to the polyacrylamide is 0.1; the ultrasonic dispersion time is 8h; correspondingly, the step (2) is specifically as follows: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is 1:5; the ultrasonic dispersion time is 4h; the ball milling time is 3h; heating is carried out under the argon atmosphere, the heating rate is 15 ℃/min, the temperature is firstly increased to 100-120 ℃, the temperature is kept constant for 4h, and solvent removal and solidification are carried out; heating to 500 ℃ at a speed of 15 ℃/min, keeping the temperature for 3 hours, and carbonizing; the reducing agent is Mg steam, the constant-temperature reduction reaction temperature is 800 ℃, and the constant-temperature reduction reaction time is 4 hours.
Example 4 silicon carbon composite d preparation:
the same procedure parameters as in example 1 were used with the following exceptions:
the silicon source mixture in the step (1) also comprises polyacrylamide, high-substituted hydroxypropyl cellulose and polyethylene glycol. The step (1) is specifically as follows: dispersing a silicon source in absolute ethyl alcohol to obtain a silicon source ethanol dispersion liquid, dropwise adding the silicon source ethanol dispersion liquid into a carbon black powder ethanol dispersion liquid, adding polyacrylamide into the mixture, dropwise adding a high-substituted hydroxypropyl cellulose ethanol dispersion liquid and polyethylene glycol into the mixture, and ultrasonically dispersing; the mass ratio of the silicon source to the polyacrylamide is 0.1; the mass ratio of the silicon source to the high-substituted hydroxypropyl cellulose is 0.1; the mass/volume ratio of the silicon source to the polyethylene glycol is 0.08g/mL; the ultrasonic dispersion time is 10h; correspondingly, the step (2) is specifically as follows: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is 5; the ultrasonic dispersion time is 6h; the ball milling time is 4h; heating is carried out under the argon atmosphere, the heating rate is 15 ℃/min, the temperature is firstly increased to 100-120 ℃, the temperature is kept constant for 6 hours, and solvent removal and solidification are carried out; heating to 500 ℃ at a speed of 15 ℃/min, keeping the temperature for 3 hours, and carbonizing; the reducing agent is Mg steam, the constant-temperature reduction reaction temperature is 800 ℃, and the constant-temperature reduction reaction time is 4 hours.
Example 5 preparation of silicon carbon composite e:
the same procedure parameters as in example 2 were used with the following exceptions:
the material in the step (2) also comprises polyacrylonitrile, the mass ratio of the polyacrylonitrile to the porous carbon powder is 1. Correspondingly, the step (2) is specifically as follows: the step (2) is specifically as follows: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion and ball milling, adding DMF (dimethyl formamide) dispersion liquid of polyacrylonitrile, performing ball milling again, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is 1:8; the ultrasonic dispersion time is 8h; the ball milling time is 5h; the content of polyacrylonitrile in the DMF dispersion was 12% by weight; the ball milling time is 8h again; heating is carried out under the argon atmosphere, the heating rate is 15 ℃/min, the temperature is firstly increased to 100-120 ℃, the temperature is kept constant for 6 hours, and solvent removal and solidification are carried out; then heating to 650 ℃ at a speed of 15 ℃/min, keeping the temperature for 3 hours, and carbonizing; the reducing agent is Mg steam, the constant-temperature reduction reaction temperature is 800 ℃, and the constant-temperature reduction reaction time is 4 hours.
Example 6 preparation of silicon carbon composite material f:
the same procedure as in example 3 was followed with the following exceptions:
the material in the step (2) also comprises polyacrylonitrile, the mass ratio of the polyacrylonitrile to the porous carbon powder is 1. Correspondingly, the step (2) is specifically as follows: the step (2) is specifically as follows: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion and ball milling, adding DMF (dimethyl formamide) dispersion liquid of polyacrylonitrile, performing ball milling again, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is 1:8; the ultrasonic dispersion time is 8h; the ball milling time is 5h; the content of polyacrylonitrile in the DMF dispersion was 12% by weight; the ball milling time is 8h again; heating is carried out under the argon atmosphere, the heating rate is 15 ℃/min, the temperature is firstly increased to 100-120 ℃, the temperature is kept constant for 6 hours, and solvent removal and solidification are carried out; heating to 650 ℃ at a speed of 15 ℃/min, keeping the temperature for 3 hours, and carbonizing; the reducing agent is Mg steam, the constant-temperature reduction reaction temperature is 800 ℃, and the constant-temperature reduction reaction time is 4 hours.
Example 7 silicon carbon composite g preparation:
the same parameters as in example 4 were used except for the following differences:
the material in the step (2) also comprises polyacrylonitrile, the mass ratio of the polyacrylonitrile to the porous carbon powder is 1. Correspondingly, the step (2) is specifically as follows: the step (2) is specifically as follows: mixing the silicon source mixture obtained in the step (1) with porous carbon powder, performing ultrasonic dispersion and ball milling, adding DMF (dimethyl formamide) dispersion liquid of polyacrylonitrile, performing ball milling again, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is 1:8; the ultrasonic dispersion time is 8h; the ball milling time is 5h; the content of polyacrylonitrile in the DMF dispersion was 12% by weight; the ball milling time is 8h again; heating is carried out under the argon atmosphere, the heating rate is 15 ℃/min, the temperature is firstly increased to 100-120 ℃, the temperature is kept constant for 6 hours, and solvent removal and solidification are carried out; then heating to 650 ℃ at a speed of 15 ℃/min, keeping the temperature for 3 hours, and carbonizing; the reducing agent is Mg steam, the constant-temperature reduction reaction temperature is 800 ℃, and the constant-temperature reduction reaction time is 4 hours.
Examples 8-19 preparation of silicon negative electrode sheets:
the silicon negative electrode plate was prepared according to the following formulation and procedure with the ratio of the coating mass per unit area of the lower layer and the coating mass per unit area of the upper and lower layers shown in table 1, respectively:
the formula is as follows: the lower layer comprises a silicon-carbon composite material, a conductive agent, a binder and a thickening agent, and the upper layer comprises graphite, a silicon-carbon composite material, a conductive agent, a binder and a thickening agent; the conductive agent is conductive carbon black; the binder is Styrene Butadiene Rubber (SBR); the thickener is sodium carboxymethylcellulose (CMC); the silicon-carbon composite material is the silicon-carbon composite material a prepared in the embodiment 1; in the lower layer, the mass part ratio of the silicon-carbon composite material, the conductive agent, the binder and the thickening agent is 90; in the upper layer, the mass part ratio of the graphite and the silicon-carbon composite material is 3:7, and the mass part ratio of the total mass part of the graphite and the silicon-carbon composite material to the conductive agent, the binder and the thickener is 96.
The method comprises the following steps: respectively mixing the materials of the upper layer and the lower layer according to the required proportion, uniformly mixing for 15min under high stirring (300 rpm), and performing ultrasonic treatment for 20min to respectively obtain the mixed membrane materials of the upper layer and the lower layer; a lower layerCoating the mixed membrane material on the surface of the current collector, and immediately coating the upper layer mixed membrane material on the surface of the lower layer after surface drying; and (5) drying. The ratio of the coating mass per unit area of the upper layer to the lower layer is (1.5-15): 1, wherein the coating mass per unit area of the lower layer is 0.0002-0.0030g/m 2 . The coating method is a spray coating method. The drying is drying at 80 ℃. The current collector is a copper foil.
TABLE 1 examples 8-19 parameter design Table (coating Density in Table indicates coating quality per unit area)
Examples 20-25 silicon negative electrode pieces were prepared using different silicon carbon composites:
the procedure and parameters used in example 15 were followed except that in examples 20-25, silicon carbon composite material a from example 15 was replaced with silicon carbon composite materials b-g prepared in examples 2-7, respectively.
Comparative examples 1-3 silicon carbon composite materials were prepared by changing the order of polyacrylonitrile addition, and then silicon negative electrode sheets were prepared as follows:
the preparation method of the silicon-carbon composite material is based on the examples 5-7 respectively, and the differences are that:
the silicon source mixture material in the step (1) also comprises polyacrylonitrile, and in the step (1), DMF dispersion liquid of the polyacrylonitrile is added into the mixture before ultrasonic dispersion; the mass ratio of the polyacrylonitrile to the porous carbon powder added in the step (2) is 1; in the step (2), polyacrylonitrile or a DMF dispersion liquid of polyacrylonitrile is not added; the other process parameters were the same as in examples 5 to 7, respectively.
According to the method and parameters adopted in the example 15, the silicon-carbon composite material a in the example 15 is replaced by the silicon-carbon composite materials prepared in the comparative examples 1 to 3 respectively, and the silicon negative pole piece is prepared.
Comparative example 4 a pure silicon carbon mixed material was prepared, and then a silicon negative electrode sheet was prepared therefrom:
the silicon-carbon mixed material is used to replace the silicon-carbon composite material a in example 15 to prepare the silicon negative electrode piece, wherein the silicon-carbon mixed material is a mixture of carbon nanotubes and nano silicon particles, and the nano silicon particles account for 15% by mass.
Constructing a battery:
electrolyte: mixing ethylene carbonate, propylene carbonate, diethyl carbonate, fluoroethylene carbonate, and vinylene carbonate in a mass ratio of 30 6 Thus obtaining the electrolyte.
A diaphragm: polyethylene microporous membrane.
Silicon negative pole piece: pole pieces prepared in examples 8-24 and comparative examples 1-4.
Positive pole piece: uniformly mixing lithium cobaltate, a conductive agent carbon nanotube and a binder styrene butadiene rubber according to the mass percentage of 90 2 And drying at 85 ℃.
And the positive pole piece and the silicon negative pole piece are subjected to cold pressing, cutting, vacuum drying, welding and the like according to requirements.
The battery is constructed: through lamination, the positive pole piece, the diaphragm and the silicon negative pole piece are assembled into the lithium ion battery with the thickness of 4.2mm, and the positive pole piece and the silicon negative pole piece are not adjacent to each other. And after the assembly is finished, drying for 12h in vacuum at 100 ℃, and packaging in a shell. The battery is 82mm long and 34mm wide. Injecting the electrolyte into the shell, standing for 48h, charging to 4.2V at constant current of 0.1C (160 mA), and charging to 0.05C (80 mA) at constant voltage of 4.2V; discharging to 3.0V at constant current of 0.1C (160 mA), repeating the above steps twice, and charging to 3.8V at constant current of 0.1C (160 mA).
And (3) performance detection:
1. SEM characterization is carried out on the surfaces of the pole pieces prepared in the examples 8-25 and the comparative examples 1-4 respectively, and the results are as follows: in the pole pieces of the embodiments 8 to 25, silicon elements are distributed on the surface of the pole pieces very uniformly, wherein, in the pole piece of the embodiment 15, the SEM image of the surface of the pole piece is shown in figure 1; in the pole pieces of comparative examples 1 to 3, the distribution of silicon element in the pole pieces is also very uniform, but the silicon element in comparative example 4 is obviously agglomerated, and a large amount of blank areas of silicon element are formed on the pole pieces. Therefore, the method provided by the invention can ensure that the silicon element is not agglomerated and is uniformly dispersed in the pole piece.
2. The high-temperature cycle test is carried out on the battery constructed above, and the high-temperature cycle capacity retention rate of each group of batteries is compared, so that the result is as follows: the data of example 11 is best in examples 8-13, and the data of examples 15 and 18 is best in examples 14-19; the capacity retention rate of example 25 is the least reduced, the capacity retention rate of 400 cycles is still more than 98% (98.3%), next, examples 22-24, the capacity retention rate of 400 cycles is 96.2% -97.0%, next, examples 20-21, the capacity retention rate of 400 cycles is 94.3% and 94.9%, next, examples 15 and 18 are 92.5% and 92.6%, respectively, and examples 14, 16, 17 and 19, the capacity retention rate of 400 cycles is 90.1% -91.8%; the capacity retention rate of the comparative examples 1-3 after circulating 400 times is 87.4% -88.9%; comparative example 4 capacity retention rate of 85.0% after 400 cycles; from the results, it can be seen that the capacity retention rates of examples 14-19 after 400 cycles are not clearly regular, wherein examples 15 and 18 have the best effect, but the upper layer coating density of example 15 is one fourth of that of example 18, and the effect is still stable after repeated tests, which is unexpected and not analyzed, but the optimal upper layer coating density provided by the invention adopts the parameters of example 15 for cost; wherein, the high temperature cycle capacity retention rate curve of the battery corresponding to the example 15 and the battery corresponding to the comparative example 4 are compared and shown in figure 2, and the capacity retention capacity of the comparative example 4 is poor in the high temperature cycle test; the curves of the capacity retention rates of the comparative examples 1 to 3 all have step-like changes, the capacity retention capacity is good before 180 to 200 cycles and is similar to the data of the examples 23 to 25, and the capacity retention rate is rapidly reduced after 180 to 200 cycles, which may be caused by the fact that the polyacrylonitrile cannot play a role in design in a system due to the fact that the adding step sequence of the polyacrylonitrile is not suitable for the technical scheme of the invention, but the reason is unclear.
3. And (3) performing high-temperature cycle test on the constructed batteries, and comparing the high-temperature cycle battery core thickness expansion rate of each battery group, wherein the result is as follows: the data of example 11 is best in examples 8-13, and the data of examples 15 and 18 is best in examples 14-19; example 25, the thickness expansion rate increases slowest, the cell thickness expansion rate is still below 3.0% (2.1%) after 400 cycles, then examples 23-24, the thickness expansion rate is between 2.8% -3.0% after 400 cycles, again examples 20-22, the thickness expansion rate is between 3.4% -3.8% after 400 cycles, then examples 15 and 18, which are both 9.2%, and the thickness expansion rate is between 9.7% -10.9% after 400 cycles for examples 14, 16, 17 and 19; comparative examples 1-3 the thickness expansion rate of 400 cycles is 11.8% -12.4%; comparative example 4 the thickness swell ratio after 400 cycles was 13.9%; from the results, it can be seen that the thickness expansion ratios of examples 14-19, which are 400 cycles, are not clearly defined, with examples 15 and 18 being the most effective, as discussed above; wherein, the cell thickness expansion rate curve of the battery corresponding to the example 15 and the cell corresponding to the comparative example 4 are compared and shown in figure 3, and the cell thickness expansion rate of the comparative example 4 is increased rapidly in a high-temperature cycle test; the thickness expansion rate curves of comparative examples 1 to 3 were different from the battery retention rate curves, and no stepwise-like change occurred, and the increase rates of the thickness expansion rates before 180 to 200 cycles and after 180 to 200 cycles were relatively uniform, but the slope of the curves was significantly larger than that of all the examples.
In conclusion, the battery prepared from the carbon-silicon composite material and the silicon negative electrode plate provided by the invention has the characteristics of low battery cell expansion rate and high battery capacity retention rate, and the overall cycle performance of the battery is excellent.
While the preferred embodiments and examples of the present invention have been described in detail, the present invention is not limited to the embodiments and examples, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (9)
1. The preparation method of the silicon-carbon composite material is characterized by comprising the following steps:
(1) Preparing a silicon source mixture: uniformly mixing a silicon source mixture material, wherein the silicon source mixture material in the step comprises a silicon source and carbon black;
(2) Mixing a silicon source mixture with porous carbon powder, performing ultrasonic dispersion and ball milling, adding DMF (dimethyl formamide) dispersion liquid of polyacrylonitrile, performing ball milling again, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction;
(3) Removing impurities from the mixture obtained in the step (2) by using a hydrochloric acid solution, and drying to obtain a silicon-carbon composite material;
the silicon source mixture material in the step (1) also comprises high-substituted hydroxypropyl cellulose and polyethylene glycol and/or polyacrylamide.
2. The method of claim 1, wherein: the silicon source mixture material in the step (1) also comprises high-substituted hydroxypropyl cellulose and polyethylene glycol, and the step (1) specifically comprises the following steps: mixing the silicon source ethanol dispersion liquid, the carbon black powder ethanol dispersion liquid, the high-substituted hydroxypropyl cellulose ethanol dispersion liquid and polyethylene glycol; the silicon source is nano silicon dioxide; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is (0.06-0.09) 1; the mass ratio of the silicon source to the high-substituted hydroxypropyl cellulose (0.02-0.2) is 1; the mass/volume ratio of the silicon source to the polyethylene glycol is 0.05-0.1g/mL; the step (2) is specifically as follows: mixing the silicon source mixture with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating for carbonization; introducing a reducing agent, and reducing at constant temperature: removing the solvent, and curing at 100-120 deg.C; the carbonization temperature is 500-850 ℃; the constant temperature reduction temperature is 600-1000 ℃.
3. The method of claim 1, wherein: the silicon source mixture material in the step (1) also comprises polyacrylamide, wherein the polyacrylamide is low molecular weight polyacrylamide; the step (1) is specifically as follows: mixing the silicon source ethanol dispersion liquid, the carbon black powder ethanol dispersion liquid and polyacrylamide; the silicon source is nano silicon dioxide; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is (0.06-0.09) 1; the mass ratio of the silicon source to the polyacrylamide (0.02-0.2) is 1; the step (2) is specifically as follows: mixing the silicon source mixture with porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating for carbonization; introducing a reducing agent, and reducing at constant temperature: removing the solvent, and curing at 100-120 deg.C; the carbonization temperature is 500-850 ℃; the constant temperature reduction temperature is 600-1000 ℃.
4. The production method according to claim 1, characterized in that: the silicon source mixture material in the step (1) also comprises polyacrylamide, high-substituted hydroxypropyl cellulose and polyethylene glycol; the step (1) is specifically as follows: mixing the silicon source ethanol dispersion liquid, the carbon black powder ethanol dispersion liquid, polyacrylamide, high-substituted hydroxypropyl cellulose ethanol dispersion liquid and polyethylene glycol; the silicon source is nano silicon dioxide; the particle size of the carbon black powder is 8-30nm; the mass ratio of the silicon source to the carbon black powder is (0.06-0.09) 1; the mass ratio of the silicon source to the polyacrylamide (0.02-0.2) is 1; the mass ratio of the silicon source to the high-substituted hydroxypropyl cellulose (0.02-0.2) is 1; the mass/volume ratio of the silicon source to the polyethylene glycol is 0.05-0.1g/mL; step (2) comprises mixing a silicon source mixture and porous carbon powder, performing ultrasonic dispersion, performing ball milling, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is (5-7) to (8-12); removing the solvent, and curing at 100-120 deg.C; the carbonization temperature is 500-850 ℃; the constant temperature reduction temperature is 600-1000 ℃.
5. The production method according to any one of claims 2 to 4, characterized in that: the material in the step (2) also comprises polyacrylonitrile, and the mass ratio of the polyacrylonitrile to the porous carbon powder is (1-3) to (8-20); step (2): mixing a silicon source mixture and porous carbon powder, performing ultrasonic dispersion and ball milling, adding DMF (dimethyl formamide) dispersion liquid of polyacrylonitrile, performing ball milling again, heating to remove a solvent, curing, and heating to carbonize; introducing a reducing agent, and carrying out constant-temperature reduction reaction: the mass ratio of the silicon source mixture to the porous carbon powder is (2-7) to (8-20); the polyacrylonitrile content in the DMF dispersion is 1-12% by weight; firstly, heating to 100-120 ℃, keeping the temperature for 4-6h, removing the solvent and curing; then heating to 650-850 ℃, keeping the temperature for 4-5h, and carbonizing; the reducing agent is Mg steam, the constant temperature reduction reaction temperature is 600-1000 ℃, and the constant temperature reduction reaction time is 0.5-8h.
6. The method of claim 5, wherein: the mass ratio of the silicon source mixture to the porous carbon powder is (2-3) to (15-20).
7. A silicon negative pole piece is characterized in that: the silicon negative pole piece comprises a current collector and a silicon-carbon composite material layer, wherein the carbon-silicon composite material layer is a thin film coated on the surface of the current collector; the silicon-carbon composite material layer comprises an upper layer and a lower layer, the lower layer is positioned between the upper layer and the current collector, the lower layer comprises a silicon-carbon composite material, a conductive agent, a binder and a thickening agent, and the upper layer comprises graphite, the silicon-carbon composite material, the conductive agent, the binder and the thickening agent; in the lower layer, the mass parts of the silicon-carbon composite material, the conductive agent, the binder and the thickening agent are (85-90): (5-7): (10-15): (3-9); in the upper layer, the mass part ratio of the graphite and the silicon-carbon composite material is (1-5): 5-9), the mass part ratio of the total mass part of the graphite and the silicon-carbon composite material to the respective mass part ratios of the conductive agent, the binder and the thickening agent is (92-97): 1-3: (1-2), wherein the silicon-carbon composite material is prepared by the preparation method of any one of claims 1-6.
8. The silicon negative electrode tab of claim 7, wherein: the conductive agent is one or two of carbon nano tube or conductive carbon black; the binder is styrene butadiene rubber; the thickening agent is sodium carboxymethyl cellulose; the preparation method of the silicon negative pole piece comprises the following steps: respectively mixing the materials of the upper layer and the lower layer according to the required proportion, stirring uniformly for 10-20min, and performing ultrasonic treatment for 5-30min to respectively obtain the mixed membrane materials of the upper layer and the lower layer; coating the lower layer mixed membrane material on the surface of the current collector, immediately coating the upper layer mixed membrane material on the surface of the lower layer after surface drying, and drying; the ratio of the coating mass per unit area of the upper layer to the lower layer is (1.5-15): 1, wherein the coating mass per unit area of the lower layer is 0.0002-0.0030g/m 2 。
9. A battery, characterized by: the silicon negative electrode plate comprises the silicon negative electrode plate of claim 7 or 8, and further comprises a positive electrode plate, an electrolyte, a diaphragm between the positive electrode plate and the negative electrode plate, and a shell; the diaphragm is a polyethylene microporous film or a polypropylene microporous film.
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| CN113666354A (en) | 2021-11-19 |
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