CN115282890B - Preparation method of silicon-graphene reinforced composite aerogel and preparation method of electrode - Google Patents
Preparation method of silicon-graphene reinforced composite aerogel and preparation method of electrode Download PDFInfo
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- CN115282890B CN115282890B CN202210914328.9A CN202210914328A CN115282890B CN 115282890 B CN115282890 B CN 115282890B CN 202210914328 A CN202210914328 A CN 202210914328A CN 115282890 B CN115282890 B CN 115282890B
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- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 115
- 239000004964 aerogel Substances 0.000 title claims abstract description 97
- 239000002131 composite material Substances 0.000 title claims abstract description 91
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 69
- 239000010703 silicon Substances 0.000 claims abstract description 69
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 67
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 59
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- 238000000034 method Methods 0.000 claims abstract description 23
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- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 claims description 3
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 9
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- UFVKGYZPFZQRLF-UHFFFAOYSA-N hydroxypropyl methyl cellulose Chemical compound OC1C(O)C(OC)OC(CO)C1OC1C(O)C(O)C(OC2C(C(O)C(OC3C(C(O)C(O)C(CO)O3)O)C(CO)O2)O)C(CO)O1 UFVKGYZPFZQRLF-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
- B01J13/0091—Preparation of aerogels, e.g. xerogels
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
-
- 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The application provides a silicon-graphene reinforced composite aerogel and a preparation method thereof, an electrode and a preparation method thereof, wherein the silicon-graphene reinforced composite aerogel comprises the steps of uniformly mixing a dispersion liquid C of graphene oxide, a silicon nanomaterial and a water-soluble reducing agent with a conductive polymer, a lithium-conducting polymer, a reinforcing agent and a doping agent, adding the mixture into a closed reactor, heating the mixture, and reducing and self-assembling the graphene oxide to obtain silicon-graphene reinforced composite hydrogel; freeze-drying the silicon-graphene reinforced composite hydrogel to obtain silicon-graphene reinforced composite aerogel; grinding the silicon-graphene reinforced composite aerogel into powder, mixing the powder with a binder, preparing slurry, and directly coating the slurry on release paper to form the negative electrode. The negative electrode aerogel frame structure can relieve the expansion of the silicon volume, prevent the negative electrode from losing efficacy in the circulation process, fully exert the advantage of high specific capacity of nano silicon, and simultaneously can further improve the specific capacity of the electrode without the existence of a current collector.
Description
Technical Field
The application belongs to the field of new energy materials, and particularly relates to silicon-graphene reinforced composite aerogel and a preparation method thereof, an electrode and a preparation method thereof.
Background
Lithium ion batteries have been widely used in the fields of portable electronic devices, electric vehicles, power grid energy storage and the like because of their advantages of high energy density, high open circuit voltage, long cycle life, no memory effect and the like. However, the current commercial lithium ion battery mainly adopts carbon negative electrode materials such as graphite, has low theoretical specific capacity (372 mAh/g), and a lithium intercalation potential platform is close to metal lithium, so that potential safety hazards are easily caused by 'lithium precipitation' during rapid charging, and the requirement of the lithium ion battery on high energy density in the future cannot be met.
Silicon is the lithium battery anode material with highest specific capacity, the theoretical specific capacity is up to 4200mAh/g, but the most fatal defect is that the volume expansion change in the reaction reaches 320%, the SEI film grows and lithium ions are consumed when the silicon reacts with electrolyte, the conductivity of the silicon is poor, and the factors severely restrict the application of the silicon as the anode material. To solve the two problems, a method of compounding with a conductive material is necessary.
In recent years, graphene and silicon composite materials are frequently reported as negative electrode materials of lithium ion batteries. However, the existing graphene/silicon anode material production method only adopts a mode of coating graphene on the surface of silicon particles, so that the problems of expansion and poor conductivity of the silicon electrode are partially solved. The pulverization of the silicon electrode and the continuous growth of the SEI film are not well solved. Moreover, as the stability of graphene and silicon is good and the melting point is high, the graphene and silicon are difficult to combine together, the constructed three-dimensional graphene grid is not firm, and the graphene network collapses along with the expansion and contraction of the silicon electrode, so that the performance is greatly reduced. Therefore, developing a silicon-graphene composite negative electrode material with high mechanical strength and long cycle life is a technical problem in the field of lithium ion batteries.
In order to solve the problems, the silicon nano material is embedded into the graphene aerogel, and when the composite condition and the proportion of silicon and graphene are controlled, the graphene aerogel can be used as a better conductive framework supporting material, and the silicon-graphene reinforced composite aerogel anode with long service life and high specific capacity is developed.
Disclosure of Invention
In order to overcome the defects and the shortcomings of the prior art, the application aims to provide silicon-graphene reinforced composite aerogel and a preparation method thereof, a current collector-free electrode and a preparation method thereof, so as to solve the problem of short service life of a silicon-carbon negative electrode of an existing lithium ion battery.
In a first aspect of the present application, there is provided a silicon-graphene reinforced composite aerogel, the silicon-graphene reinforced composite aerogel comprising at least a carbon element and a silicon element;
the carbon element mainly exists in the form of silicon-graphene reinforced composite aerogel;
the carbon element existing in the form of the silicon-graphene reinforced composite aerogel accounts for more than 96% of the total mass of the carbon element of the silicon-graphene reinforced composite aerogel;
the silicon element exists in the form of silicon nano particles, the silicon element exists at least partially in the form of being wrapped in a graphene, conductive polymer and lithium-conducting polymer aerogel network, and the wrapped silicon element accounts for more than 96% of the total mass of the silicon element;
the mass ratio of the silicon element to the carbon element is 2:1-1:2.
In a second aspect of the present application, there is provided a method for preparing a silicon-graphene reinforced composite aerogel, comprising the steps of:
s1, uniformly mixing a graphene oxide solution, a silicon nano material dispersion liquid and a dispersion liquid C of a water-soluble reducing agent which are uniformly mixed with a lithium-conducting polymer and a reinforcing agent, and adding the mixture into a closed reactor;
s2, heating the closed reactor, and reducing and self-assembling graphene oxide to obtain silicon-graphene reinforced composite hydrogel;
s3, performing low-temperature freezing treatment on the silicon-graphene reinforced composite hydrogel, and then drying by a freeze dryer to obtain the silicon-graphene reinforced composite aerogel.
Further, the water-soluble reducing agent is one or more of ascorbic acid, sodium ascorbate, sodium citrate, hydroiodic acid, hydrobromic acid, sodium bisulphite, sodium sulfide and ethylenediamine.
Further, the lithium-conducting polymer is at least one of lithium carboxymethyl cellulose (CMC-Li), lithium polyacrylate (PAA-Li), lithium alginate (SA-Li), a compound of an organic polymer matrix and lithium salt, lithium polyvinyl alcohol (PVA-Li), lithium polyimide (PI-Li) and lithium polymethyl methacrylate (PMMA-Li); the reinforcing agent is carbon fiber.
Further, step S1 also comprises mixing graphite oxide slurry prepared by Hummers method with solvent a, and performing ultrasonic dispersion to obtain dispersion A; mixing the silicon nano material and the anti-agglomeration material with the solvent B to obtain a dispersion liquid B; and then mixing the dispersion liquid A and the dispersion liquid B with a water-soluble reducing agent, and magnetically stirring uniformly to obtain a dispersion liquid C.
Further, the heating temperature in the step S2 is 60-96 ℃;
further, the temperature of freeze drying in the step S3 is-80 to-60 ℃;
further, the silicon nanoparticles have a particle size in the range of 10-100nm.
In a third aspect of the application, there is provided an electrode comprising the aforementioned silicon-graphene reinforced composite aerogel;
further, the electrode further comprises a conductive agent and a binder, and the mass ratio of the silicon-graphene reinforced composite aerogel to the binder is a to b, wherein a is more than or equal to 90 and less than or equal to 95,5 and less than or equal to 10, and a+b=100.
In a fourth aspect of the present application, there is provided an electrode preparation method comprising the steps of:
s4, grinding the silicon-graphene reinforced composite aerogel prepared in the step S3 into silicon-graphene reinforced composite aerogel powder, and weighing the silicon-graphene reinforced composite aerogel powder and the silicon-graphene reinforced composite aerogel powder according to the mass ratio of a to b of the silicon-graphene reinforced composite aerogel powder to the binder, wherein a is more than or equal to 90 and less than or equal to 95,5 and less than or equal to 10, and a+b=100;
s5, uniformly mixing the silicon-graphene reinforced composite aerogel powder, a binder and a solvent to prepare slurry, coating the slurry on continuous release paper, and then drying and rolling to obtain a negative electrode roll;
s6, cutting the negative electrode roll according to the required size;
s7, packaging, spot inspection and shipment.
Further, the mixing mode in the step S5 is magnetic stirring after the temperature is raised, and the temperature range is as follows: the magnetic stirring speed is 38-46 ℃, and the magnetic stirring speed is as follows: 80-200 rpm, and stirring time is as follows: 20-80 min.
Advantageous technical effects
1. According to the application, the anti-agglomeration material is added in the dispersion stage of the silicon nano material, so that the silicon nano material is uniformly dispersed and has low agglomeration rate, when the silicon nano material is mixed with graphene oxide and a lithium-conducting polymer to form hydrogel in a self-assembly way, the silicon nano material is basically dispersed in a frame formed by the graphene and the lithium-conducting polymer hydrogel, and the ratio of the silicon nano material overflowed from the frame structure of the graphene and the lithium-conducting polymer aerogel after freeze drying is extremely low, so that the mass ratio of silicon element to carbon element is ensured to be in the range of 1:2-2:1, namely a large amount of silicon nano material is dispersed in the frame structure formed by the aerogel, the high theoretical specific capacity of silicon is utilized, and the volume change of silicon in the circulation process is prevented by utilizing the frame structure of the graphene, the conductive polymer and the lithium-conducting polymer aerogel, and the failure of the anode material is prevented.
2. According to the application, the size range of the powder ground by the silicon-graphene reinforced composite aerogel is limited to 1-100 mu m, so that the double-interwoven aerogel formed by the graphene-lithium-conducting polymer can be ensured to be reserved in the anode material relative to the framework structure of the silicon nano material, and the mixing and contact of the anode active material silicon-graphene reinforced composite aerogel and the caking agent can be considered.
3. The lithium ion battery cathode does not contain a current collector, and the silicon-graphene reinforced composite aerogel has good conductivity, and meanwhile, the content of the binder in the cathode slurry is improved, so that the electrode slurry can directly form an electrode membrane material, the preparation process is simplified, the current collector of a conventional cathode is removed, and the energy density is improved.
Drawings
FIG. 1 is a schematic illustration of a process for preparing a silicon-graphene reinforced composite aerogel according to the present application;
FIG. 2 is a flow chart of the electrode preparation process of the application.
Reference numerals
1. A dispersion of silicon nanomaterial/graphene oxide/lithium conducting polymer/enhancer; 2. silicon-graphene reinforced composite hydrogel; 3. silicon-graphene reinforced composite aerogel.
Detailed Description
In order that those skilled in the art will better understand the present application, a technical solution of the embodiments of the present application will be clearly and completely described below, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments.
As used herein, "about" or "approximately" includes the stated values and is meant to be within an acceptable range of deviation from the particular values as determined by one of ordinary skill in the art in view of the measurements in question and the errors associated with the measurement of the particular quantities (i.e., limitations of the measurement system). For example, "about" may mean that the deviation from the stated value is within one or more deviation ranges, or within + -30%, 20%, 10%, or 5%.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the present disclosure and relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Silicon-graphene reinforced composite aerogel
The application firstly provides a silicon-graphene reinforced composite aerogel, which at least comprises a carbon element and a silicon element;
the carbon element existing in the form of the silicon-graphene reinforced composite aerogel accounts for more than 96% of the total mass of the carbon element of the silicon-graphene reinforced composite aerogel;
the silicon element exists in the form of silicon nano particles, the silicon element exists at least partially in the form of being wrapped in a graphene, conductive polymer and lithium-conducting polymer aerogel network, and the wrapped silicon element accounts for more than 96% of the total mass of the silicon element;
the mass ratio of the silicon element to the carbon element is 2:1-1:2, specifically, the mass ratio of the silicon element to the carbon element can be 1:2, 1:1.9, 1:1.8, 1:1.7, 1:1.6, 1:1.5, 1:1.4, 1:1.3, 1:1.2, 1:1.1, 1:1.9, 2:1.8, 2:1.7, 2:1.6, 2:1.5, 2:1.4, 2:1.3, 2:1.2, 2:1.1, 2:1, 1.9:1, 1.8:1, 1.97:1, 1.6:1, 1.5:1, 1.4:1, 1.3:1, 1.2:1, 1.1:1.
Preferably, the silicon nanoparticles may be replaced with other silicon nanomaterials including, but not limited to, at least one of silicon nanowires, silicon nanotubes, silicon nanoplatelets; the dimensions of the other silicon nanomaterial in at least one dimension are 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 96nm, 100nm.
In order to further show how the coated silicon element accounts for more than 96% of the total mass of the silicon element, a method for preparing the silicon-graphene reinforced composite aerogel will be described in detail below.
Preparation method of silicon-graphene reinforced composite aerogel
The method comprises the following steps:
s1, firstly mixing graphite oxide slurry prepared by adopting a Hummers method with a solvent a, and performing ultrasonic dispersion to obtain a dispersion liquid A; mixing the silicon nano material and the anti-agglomeration material with the solvent B to obtain a dispersion liquid B; then mixing the dispersion liquid A, the dispersion liquid B and the water-soluble reducing agent, and uniformly magnetically stirring to obtain a dispersion liquid C; and uniformly mixing the uniformly mixed graphene oxide solution, the silicon nano material dispersion liquid and the dispersion liquid C of the water-soluble reducing agent with the lithium-conducting polymer and the reinforcing agent, and adding the uniformly mixed mixture into a closed reactor.
S2, heating the closed reactor, and reducing and self-assembling graphene oxide to obtain silicon-graphene reinforced composite hydrogel; the heating temperature is 60-96 ℃, and the specific optional temperature is as follows: 60 ℃, 62 ℃, 64 ℃, 66 ℃, 68 ℃, 70 ℃, 72 ℃, 74 ℃, 76 ℃, 78 ℃, 80 ℃, 82 ℃, 84 ℃, 86 ℃, 88 ℃, 90 ℃, 92 ℃, 94 ℃, 96 ℃.
S3, performing low-temperature freezing treatment on the silicon-graphene reinforced composite hydrogel, and then drying by a freeze dryer to obtain the silicon-graphene reinforced composite aerogel.
Further, the anti-agglomerating material includes, but is not limited to, povidone, hydroxypropyl methylcellulose, hydroxypropyl cellulose, polyoxyethylene, carbomer, acacia, gelatin, polyvinyl alcohol, methylcellulose, or hydroxyethyl cellulose.
Further, the water-soluble reducing agent is one or more of ascorbic acid, sodium ascorbate, sodium citrate, hydroiodic acid, hydrobromic acid, sodium bisulphite, sodium sulfide and ethylenediamine.
Further, the lithium-conducting polymer is at least one of lithium carboxymethyl cellulose (CMC-Li), lithium polyacrylate (PAA-Li), lithium alginate (SA-Li), a compound of an organic polymer matrix and lithium salt, lithium polyvinyl alcohol (PVA-Li), lithium polyimide (PI-Li) and lithium polymethyl methacrylate (PMMA-Li); the reinforcing agent is carbon fiber.
S3, freeze-drying the graphene-silicon nano material composite hydrogel to obtain silicon-graphene reinforced composite aerogel; the freezing temperature is-170 to-20 ℃, and the specific optional temperature is as follows: -170 ℃, -165 ℃, -160 ℃, -155 ℃, -150 ℃, -145 ℃, -140 ℃, -135 ℃, -130 ℃, -125 ℃, -120 ℃, -115 ℃, -110 ℃, -105 ℃, -100 ℃, -95 ℃, -90 ℃, -85 ℃, -80 ℃, -75 ℃, -70 ℃, -65 ℃, -60 ℃, -55 ℃, -40 ℃, -45 ℃, -40 ℃, -35 ℃, -30 ℃, -25 ℃, -20 ℃.
Wherein the pressure of freeze drying is 5-20 Pa.
The specific process steps of the Hummers method for preparing graphite oxide adopted by the application are as follows:
(1) Low Wen Jiashi agent: fixing the dry three-neck flask on an iron stand table, ensuring half of the flask body to be immersed in ice water, and sequentially adding weighed graphite and NaNO 3 And (3) powder. Turning on the stirrer, and measuring concentrated H in batches 2 SO 4 Slowly adding into a flask, and then weighing KMnO in batches 4 The powder was slowly added to the flask, and after each addition was completed, additional additions were made at 12 minutes intervals and the temperature in the flask was maintained below 10 ℃.
(2) Heating and adding water: after the reagent is added, the flask is transferred into a constant temperature oil bath device for constant temperature heating reaction. The temperature is slowly raised to 35 ℃, the reaction is continued for 6 hours after the stabilization, 400ml of deionized water is added in batches, and the temperature is raised to 95 ℃ for half an hour.
(3) Cooling and removing oxidant: after cooling to room temperature, all the solutions were transferred to a 2000ml beaker, and 100ml hydrogen peroxide was added to a bright yellow color without bubbles, and finally 700ml deionized water was added.
(4) Acid washing twice: concentrated HCl is added into a 500ml volumetric flask to prepare 15% HCl solution, and then added into a 2000ml beaker of the previous step, and then water is added into the beaker to 2000ml. Standing for layering, pouring out the upper liquid, and pickling again by the same method.
(5) And (3) washing twice: after the previous step is finished, pouring out the upper liquid, adding deionized water to 2000ml, standing and layering, pouring out the upper liquid, and washing again by the same method.
(6) And (3) centrifuging: and adding deionized water in batches for centrifugation to obtain graphite oxide slurry with PH=7.
Electrode
According to another aspect of the present application, there is provided a current collector-free electrode comprising an active material coating disposed on a release paper, the active material coating encasing the aforementioned silicon-graphene reinforced composite aerogel.
Preferably, the current collector-free electrode further comprises a binder, and the mass ratio of the silicon-graphene reinforced composite aerogel to the binder is a to b, wherein a is more than or equal to 90 and less than or equal to 95,5 and less than or equal to 10, and a+b=100.
Wherein a is preferably 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95; b 5,5.5,6,6.5,7,7.5,8,8.5,9,9.5, 10.
Electrode preparation method
According to a fourth aspect of the present application, there is provided an electrode preparation method comprising the steps of:
s4, grinding the silicon-graphene reinforced composite aerogel into silicon-graphene reinforced composite aerogel powder, and weighing the silicon-graphene reinforced composite aerogel powder and the silicon-graphene reinforced composite aerogel powder according to the mass ratio of the silicon-graphene reinforced composite aerogel powder to the binder of a to b, wherein a is more than or equal to 90 and less than or equal to 95,5 and less than or equal to 10, and a+b=100.
Wherein a is preferably 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95; b 5,5.5,6,6.5,7,7.5,8,8.5,9,9.5, 10.
The silicon-graphene reinforced composite aerogel has the advantages that the graphene and lithium-conducting polymer framework structure is good in conductivity, so that excessive conductive agents are not needed to be added when the negative electrode slurry is manufactured, the size of silicon is smaller than 100nm, preferably, the D50 of silicon nano particles is 40-60nm, the size of silicon one-dimensional and two-dimensional materials in at least one dimension is 40-60nm, the range of the hole size L of the graphene framework is 20-80 mu m, when the composite aerogel is ground into particles, the D50 of the particles is 100-200 mu m, the particles can keep relatively complete and lithium-conducting polymer framework structure, and the framework structures can ensure that the silicon nano materials have sufficient expansion space during charge and discharge cycles, and have a good buffering effect on the volume expansion of silicon during the cycle; it is also noted that if the aerogel particles are larger, the frame structure remains more complete, however, while the frame remains more complete, the overall negative density is lower when the frame is larger, thus providing more room for expansion of the silicon, but the energy density is reduced dramatically due to the excessive volume; in summary, when the silicon-graphene reinforced composite aerogel is ground into particles, the frame structure cannot be well maintained due to too small particle size, and the volume of the mixed binder is large and the energy density is reduced due to too large particle size. Preferably, the D50 of the silicon-graphene reinforced composite aerogel particles can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm.
S5, uniformly mixing the silicon-graphene reinforced composite aerogel particles, the binder and the solvent to prepare slurry, coating the slurry on continuous release paper, and then drying and rolling to obtain an electrode coil;
wherein the mixing mode is magnetic stirring after the temperature is increased, and the temperature range is as follows: the magnetic stirring speed is 38-46 ℃, and the magnetic stirring speed is as follows: 80-200 rpm, and stirring time is as follows: 20-80 min.
S6, cutting the electrode roll according to the required size.
S7, packaging, spot inspection and shipment.
The electrode can be applied to a lithium ion battery or a sodium ion battery, and when the electrode is applied to the sodium ion battery, the lithium-conducting polymer is replaced by a common sodium-conducting polymer, so long as the electrode can play a role in better cation transmission capacity in the reinforced composite aerogel.
In the silicon-graphene reinforced composite aerogel prepared by the method, the graphene-lithium-conductive polymer aerogel forms a double-interwoven main body frame, so that a buffer space can be formed, a good electron transmission medium effect can be achieved, and the strength of the electrode can be improved due to the introduction of the reinforcing agent carbon fiber, so that the electrode without a current collector also has certain strength.
Preferably, after the electrode slurry is coated on the release paper and dried, the electrode is further subjected to a low-pressure treatment using a low-pressure flexible press roll, which can further improve the density of the electrode. The low pressure of 1.2-2atm is adopted, and the void structure in the electrode is destroyed by the excessive pressure, and the porosity of the finally prepared electrode is 50-65% by measurement.
The present application is described in detail below with reference to specific examples, and in examples 1 to 12 and comparative examples 1 to 12, the low pressure treatment was performed using a pressure of 1.5atm after the electrodes were fabricated.
Example 1
S1, firstly, mixing 42g of graphite oxide slurry prepared by graphite with deionized water, and performing ultrasonic dispersion on the mixture and the deionized water to obtain graphene dispersion liquid A, wherein the volume V=7L of the deionized water mixed with the graphite; mixing silicon nano powder with the mass of m=21 g with 1L of deionized water to obtain a dispersion liquid B; mixing the dispersion liquid A and the dispersion liquid B with 100g of sodium ascorbate, and magnetically stirring uniformly to obtain a dispersion liquid C; the dispersion C was charged into a closed reactor with 6g of lithium conducting polymer SA-Li and 1g of carbon fiber reinforcement.
S2, heating the closed reactor to 68 ℃ and keeping the temperature constant, and assembling and self-reducing graphene oxide to obtain graphene-silicon nano material composite hydrogel; the reaction time was 3 hours.
S3, performing low-temperature freezing treatment at-170 ℃ on the graphene-silicon nano material composite hydrogel, and then drying by a freeze dryer to obtain silicon-graphene reinforced composite aerogel; wherein the pressure of freeze drying is 5-20 Pa.
S4, grinding the silicon-graphene reinforced composite aerogel into silicon-graphene reinforced composite aerogel particles by a ball milling method, wherein the ball milling time is T=3 hours, d50=100 μm of the silicon-graphene reinforced composite aerogel particles after ball milling,
the silicon-graphene reinforced composite aerogel particles and the binder are weighed according to the mass ratio of a to b, wherein a=91 and b=9.
In the process of preparing the negative electrode, the binder plays a vital role, and because the aerogel is loose and porous, a relatively large amount of binder is selected, so that aerogel powder can be well bonded, firm bonding is provided between powder particles, and the conductivity is not excessively lost.
S5, uniformly mixing silicon-graphene reinforced composite aerogel particles (91 wt%), a binder (7 wt%CMC and 3 wt%SBR) and deionized water through magnetic stirring to form slurry, wherein 'wt%' represents the percentage of each component in the total weight of the core-shell structure composite material, the conductive agent and the binder.
The magnetic stirring is specifically carried out by heating a magnetic stirrer to 40 ℃, stirring at 100rpm for 45min to prepare slurry, coating the slurry on a continuous current collector, drying and rolling to obtain an electrode coil;
s6, cutting the electrode roll according to the required size;
s7, packaging, spot inspection and shipment.
Examples 2 to 12
The process steps of examples 2-12 are the same as example 1, except for the specific compounding parameters, which are shown in Table 1.
The process steps of comparative examples 1-12 were the same as in example 1, except for the specific compounding parameters, as shown in Table 2.
Test example 1 lithium battery preparation and Performance test
The electrode sheets obtained in examples 1 to 12 and comparative examples 1 to 12 were cut into a wafer matching with the button half cell to be tested, and assembled with a counter electrode lithium sheet and a conventional electrolyte into a button half cell, and charge and discharge tests were performed under the following conditions: the cycle was performed at 0.1C/0.1C for 2 cycles and 0.3C/0.3C in the voltage range of 5 mV-0.8V. The electrochemical performance parameters of the cells fabricated with the electrodes of examples 1-12 and comparative examples 1-12 were tested as shown in tables 1-2 below.
Table 1: example related proportioning parameter and test data
As can be seen from comparative examples 1-12, as the volume of deionized water in which graphene oxide is dispersed increases, the density of the aerogel formed decreases, the volume becomes larger, and the porosity increases, and the capacity after being made into a negative electrode is greater because a larger intra-frame space is provided. As the density decreases, the proportion of silicon that adheres to the aerogel pores also increases, which allows a greater expandable space to be obtained in the frame, and thus a relatively higher cycle retention rate.
The capacity is lower than the theoretical capacity because during processing into an electrode, the aerogel is crushed resulting in loss of material and a small amount of silicon is pulled out of the aerogel frame.
Table 2: comparative examples related formulation parameters and test data
As can be seen from comparative examples 1 to 12 and comparative examples 1 to 6, the silicon nanoparticles were too small (comparative examples 1 to 3), and although the cycle retention was improved, the capacity was relatively low due to the too small Si content; with increasing silicon addition, the capacity increases exponentially, but when the silicon nanoparticles are too much (comparative examples 4-6), the cycle retention is low, especially the retention after 100 cycles is lower than 50%, although the capacity is very high, wherein the main reason is that too much Si results in aerogel not being retained much, si is not completely in the frame structure, and expansion causes a lot of Si failure when cycling; and thus the mass ratio of the silicon element to the carbon element is finally selected to be 2:1-1:2.
Comparative examples 5 and comparative examples 7 to 9, it is seen that the smaller the powder particles of the silicon-graphene-enhanced aerogel are milled, the lower the cycle retention rate is, because the smaller the milled powder particles are, the more severely the frame thereof is broken, resulting in a reduction in the buffering effect against Si expansion, which is one of the most critical consideration parameters in the electrode preparation method proposed by the present application, when the powder particles are controlled to 100 to 200 μm, both the buffering structure of the frame and the density of the electrode are maintained not to be too low, and the fabricated negative electrode density is within a usable range within the range of these dimensions.
Comparative examples 5 and comparative examples 10 to 12, it can be seen that when the silicon-graphene-reinforced aerogel milled powder particles were then bonded with an appropriate amount of binder, the aerogel particles were not well bonded due to the too low content of binder, resulting in serious electrode shedding in the electrolyte, and thus, the cycle retention rate was low, which is not suitable as an electrode material of a battery.
The above embodiments are only for illustrating the technical solution of the present application and not for limiting the scope of the present application, and although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solution of the present application, but these modifications or substitutions are all within the scope of the present application.
Claims (5)
1. A preparation method of a silicon-graphene reinforced composite aerogel, wherein the silicon-graphene reinforced composite aerogel at least comprises a carbon element and a silicon element;
the method is characterized in that the carbon element mainly exists in the form of silicon-graphene reinforced composite aerogel;
the carbon element existing in the form of the silicon-graphene reinforced composite aerogel accounts for more than 96% of the total mass of the carbon element of the silicon-graphene reinforced composite aerogel;
the silicon element exists in the form of silicon nano particles, the silicon element exists at least partially in the form of being wrapped in the graphene, conductive polymer and lithium-conducting polymer aerogel network, and the wrapped silicon element accounts for more than 96% of the total mass of the silicon element;
the mass ratio of the silicon element to the carbon element is 2:1-1:2;
the granularity of the silicon nano particles ranges from 10nm to 100nm;
and the D50 of the silicon-graphene reinforced composite aerogel particles is 100-200 mu m;
specifically, the preparation method of the silicon-graphene reinforced composite aerogel comprises the following steps:
s1, mixing graphite oxide slurry prepared by adopting a Hummers method with a solvent a, and performing ultrasonic dispersion to obtain a dispersion liquid A; mixing the silicon nano material and the anti-agglomeration material with the solvent B to obtain a dispersion liquid B; mixing the dispersion liquid A and the dispersion liquid B with a water-soluble reducing agent, magnetically stirring uniformly to obtain a dispersion liquid C, mixing uniformly the graphene oxide solution, the silicon nanomaterial dispersion liquid and the dispersion liquid C of the water-soluble reducing agent, a lithium-conducting polymer and a reinforcing agent uniformly, and adding the mixture into a closed reactor;
s2, heating the closed reactor, and carrying out reduction and self-assembly of graphene oxide to obtain silicon-graphene reinforced composite hydrogel;
s3, performing low-temperature freezing treatment on the silicon-graphene reinforced composite hydrogel, and then drying by a freeze dryer to obtain the silicon-graphene reinforced composite aerogel.
2. The method for preparing the silicon-graphene reinforced composite aerogel according to claim 1, wherein the water-soluble reducing agent is one or more of ascorbic acid, sodium ascorbate, sodium citrate, hydroiodic acid, hydrobromic acid, sodium bisulphite, sodium sulfide and ethylenediamine.
3. The method for preparing the silicon-graphene reinforced composite aerogel according to claim 1, wherein the lithium conducting polymer is at least one of lithium carboxymethyl cellulose (CMC-Li), lithium polyacrylate (PAA-Li), lithium alginate (SA-Li), a complex of an organic polymer matrix and a lithium salt, lithium polyvinyl alcohol (PVA-Li), lithium polyimide (PI-Li), and lithium polymethyl methacrylate (PMMA-Li); the reinforcing agent is carbon fiber.
4. The method for preparing the silicon-graphene reinforced composite aerogel according to any one of claims 1 to 3, wherein the heating temperature in the step S2 is 60 to 96 ℃, and the freeze-drying temperature in the step S3 is-80 to-60 ℃.
5. A method of preparing an electrode comprising the steps of:
s4, grinding the silicon-graphene reinforced composite aerogel prepared by the preparation method of the silicon-graphene reinforced composite aerogel claimed in any one of claims 1-4 into silicon-graphene reinforced composite aerogel powder, and weighing the silicon-graphene reinforced composite aerogel powder and the silicon-graphene reinforced composite aerogel powder according to the mass ratio of the silicon-graphene reinforced composite aerogel powder to the binder of a to b, wherein a is more than or equal to 90 and less than or equal to 95,5, b is more than or equal to 10, and a+b=100;
s5, uniformly mixing the silicon-graphene reinforced composite aerogel powder, a binder and a solvent to prepare slurry, coating the slurry on continuous release paper, and then drying and rolling to obtain a negative electrode roll;
the mixing mode is magnetic stirring after the temperature is increased, and the temperature range is as follows: 38-46 ℃, the speed of magnetic stirring is as follows: 80-200 rpm, stirring time is: 20-80 min;
s6, cutting the negative electrode roll according to the required size;
s7, packaging, spot inspection and shipment.
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