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CN115282891B - Preparation method of micron silicon-graphene composite aerogel, electrode and preparation method thereof - Google Patents

Preparation method of micron silicon-graphene composite aerogel, electrode and preparation method thereof Download PDF

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CN115282891B
CN115282891B CN202210914336.3A CN202210914336A CN115282891B CN 115282891 B CN115282891 B CN 115282891B CN 202210914336 A CN202210914336 A CN 202210914336A CN 115282891 B CN115282891 B CN 115282891B
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silicon
graphene composite
micron silicon
graphene
micron
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CN115282891A (en
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刘涛
刘静
陈鹏
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Dongguan Aozhongxin Material Technology Co ltd
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    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/36—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
    • 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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The application provides a preparation method of micron silicon-graphene composite aerogel, an electrode and a preparation method thereof, comprising the steps of adding graphene oxide, micron silicon material and dispersion liquid C of a water-soluble reducing agent into a closed reactor, heating, and carrying out reduction and self-assembly of the graphene oxide to obtain micron silicon-graphene composite hydrogel; performing low-temperature freezing treatment on the micron silicon-graphene composite hydrogel, and drying by a freeze dryer to obtain micron silicon-graphene composite aerogel; grinding the micron silicon-graphene composite aerogel into powder, preparing slurry according to the mass ratio of micron silicon-graphene composite aerogel particles, conductive agent and binder of a to b to c, and directly coating the slurry on a current collector to form a negative electrode. The negative electrode aerogel frame structure can better relieve the expansion of the silicon volume, prevent the negative electrode from losing efficacy in the circulation process, and can assist in realizing high-rate performance and circulation performance by the graphene and the conductive agent while fully playing the advantages of high specific capacity and low cost of micron silicon.

Description

Preparation method of micron silicon-graphene composite aerogel, electrode and preparation method thereof
Technical Field
The application belongs to the field of new energy materials, and particularly relates to a preparation method of micron silicon-graphene composite aerogel, a negative 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 above-mentioned problems, it is necessary to use a method of compounding with a conductive material.
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 is not well solved, and the graphene and silicon are very good in stability and very high in melting point, so that 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 preparation method of the micron silicon-graphene composite aerogel can be used for preparing the graphene aerogel serving as a better conductive framework supporting material by embedding the micron silicon material into the graphene aerogel and controlling the composite condition and the proportion of silicon and graphene, and meanwhile, the preparation process of the anode material is simplified by optimizing the proportion and the preparation method of the anode slurry, so that the micron silicon-graphene composite aerogel anode with long service life and high specific capacity is finally obtained.
Disclosure of Invention
In order to overcome the defects and the shortcomings of the prior art, the application aims to provide a preparation method of micron silicon-graphene composite aerogel, a lithium ion battery anode and a preparation method thereof, so as to solve the problems of short service life and complex preparation process of the traditional lithium ion battery silicon-carbon anode.
According to a first aspect of the present application, there is provided a method for preparing a micro silicon-graphene composite aerogel, the micro silicon-graphene composite aerogel comprising at least a carbon element and a silicon element; the carbon element mainly exists in the form of graphene aerogel; the carbon element existing in the graphene aerogel form accounts for more than 96% of the total mass of the carbon element of the micron silicon-graphene composite aerogel; the silicon element exists in the form of a micron silicon material, the silicon element exists at least partially in the form of being wrapped in the graphene aerogel network, and the wrapped silicon element accounts for more than 95% of the total mass of the silicon element; the molar ratio of the silicon element to the carbon element is 1:2-2:1.
The method comprises the following steps:
s1, adding a graphene oxide solution, a micron silicon material dispersion liquid and a dispersion liquid C of a water-soluble reducing agent which are uniformly mixed into a closed reactor;
s2, heating the closed reactor, and carrying out reduction and self-assembly of graphene oxide to obtain the micron silicon-graphene composite hydrogel;
s3, performing low-temperature freezing treatment on the micron silicon-graphene composite hydrogel, and then drying by a freeze dryer to obtain the micron silicon-graphene composite aerogel.
Preferably, the micrometer silicon comprises at least one of silicon micrometer powder, silicon micrometer wire, silicon micrometer tube and silicon micrometer sheet; wherein the effect is better as silicon micron powder.
Preferably, the water-soluble reducing agent is one of ascorbic acid, sodium ascorbate, sodium citrate, hydroiodic acid, hydrobromic acid, sodium bisulphite, sodium sulfide and ethylenediamine.
Preferably, the heating temperature in the step S2 is 60-75 ℃; the freezing temperature in the step S3 is-170 to-20 ℃, and the pressure of freeze drying is 5-20 Pa.
Preferably, the micrometer silicon material has a size in the range of 1-10 μm in at least one dimension.
Preferably, the step S1 is preceded by mixing graphite oxide slurry prepared by Hummers method with the solvent a, and obtaining the dispersion liquid a after ultrasonic dispersion; mixing the micron silicon 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.
Preferably, the micron silicon is subjected to surface treatment before being mixed and dispersed with the graphene oxide, wherein the surface treatment comprises, but is not limited to, coating the micron silicon material with a carbon-based material, and forming a uniform carbon coating layer on the surface of the micron silicon material after sintering; the carbon-based materials include, but are not limited to, phenolic resins, tannins, polypyrroles, polymeric dopamine, pitch; the sintering condition is 700-1000 ℃, inert atmosphere and 2-6 hours.
s
According to another aspect of the present application, there is provided an electrode comprising a current collector layer and an active material coating disposed on the current collector layer, the active material coating comprising the aforementioned micro-silicon-graphene composite aerogel.
According to a third aspect of the present application, there is provided a lithium ion battery anode preparation method, comprising the steps of:
s4, grinding the micron silicon-graphene composite aerogel prepared by the method into micron silicon-graphene composite aerogel particles, and weighing the micron silicon-graphene composite aerogel particles, wherein the mass ratio of the conducting agent to the binder is a to c, wherein a is more than or equal to 85 and less than or equal to 90, b is more than or equal to 5 and less than or equal to 7, c is more than or equal to 5 and less than or equal to 8, and a+b+c=100;
s5, uniformly mixing the micron silicon-graphene composite aerogel particles, the conductive agent, the binder and the solvent to prepare slurry, coating the slurry on a continuous current collector, and then drying and rolling to obtain an electrode coil;
s6, cutting the electrode roll according to the required size;
s7, packaging, spot inspection and shipment.
The mixing mode in the step S5 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.
The current collector is selected from copper foil, copper foam or nickel foam.
Advantageous technical effects
1. According to the application, the hydrogel is formed by self-assembly after the micron silicon material and the graphene oxide are mixed, the micron silicon material is basically dispersed in a frame formed by the graphene hydrogel, and the ratio of the micron silicon material overflowing the graphene aerogel frame structure after freeze-drying is extremely low, so that the mass ratio of the micron silicon material to the graphene aerogel is ensured to be in the range of 1:2-2:1, namely a large amount of micron silicon material is dispersed in the frame structure formed by the graphene 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 graphene aerogel frame structure, and the failure of the cathode material is prevented.
2. According to the application, the size distribution of particles ground by the micron silicon-graphene composite aerogel is limited to D50=100-200 mu m, so that the framework structure of the aerogel relative to the micron silicon material can be ensured to be reserved in the anode material, and the mixing and contact of the anode active material micron silicon-graphene composite aerogel, a conductive agent and a binder can be considered, and the conductive agent is introduced to reduce the problem of interfacial conductivity among micron silicon-graphene composite aerogel particles.
3. The micrometer silicon is used as the main material instead of the nanometer silicon, so that the cost of the product is reduced, and the problem caused by agglomeration of the silicon nanometer material is also reduced; meanwhile, in order to reduce the failure of the micrometer silicon, besides coating by using graphene aerogel, before the micrometer silicon is mixed with graphene, carbon-based material is used for coating the micrometer silicon, and then the micrometer silicon is further mixed with graphene oxide, so that the micrometer silicon is guaranteed in a double way, and the volume expansion effect of the micrometer silicon in the circulation process is further weakened.
Drawings
FIG. 1 is a schematic diagram of a preparation process of a micron silicon-graphene composite aerogel according to the application;
FIG. 2 is a flow chart of the electrode preparation process of the application.
Reference numerals
1. A dispersion of micron silicon/graphene oxide; 2. micron silicon-graphene composite hydrogel; 3. micron silicon-graphene 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 defined otherwise, 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.
Preparation method of micron silicon-graphene composite aerogel
The application firstly provides a preparation method of micron silicon-graphene composite aerogel, wherein the micron silicon-graphene composite aerogel at least comprises carbon element and silicon element;
the carbon element mainly exists in the form of graphene aerogel;
the carbon element existing in the form of the graphene aerogel accounts for more than 96% of the total mass of the carbon element of the micron silicon-graphene composite aerogel;
the silicon element exists in the form of a micron silicon material, the silicon element exists at least partially in the form of being wrapped in the graphene aerogel network, and the wrapped silicon element accounts for more than 95% of the total mass of the silicon element;
the mass ratio of the silicon element to the carbon element is 1:2-2:1, specifically, the mass ratio of the silicon element to the carbon element may 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, 2:1.9, 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 micrometer silicon comprises at least one of silicon micrometer powder, silicon micrometer wire, silicon micrometer tube and silicon micrometer sheet; wherein the effect is better as silicon micron powder;
the size of the microsilica material in at least one dimension (D50 of the micropowder in the case of micropowder) is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.
Before mixing and dispersing the micrometer silicon and the graphene oxide, carrying out surface treatment, wherein the surface treatment comprises, but is not limited to, coating the micrometer silicon material with a carbon-based material, and forming a uniform carbon coating layer on the surface of the micrometer silicon material after sintering; the carbon-based materials include, but are not limited to, phenolic resins, tannins, polypyrroles, polymeric dopamine, pitch; the sintering condition is 700-1000 ℃, inert atmosphere and 1-6 hours.
Specifically, the sintering temperature may be, for example, 700 ℃, 720 ℃, 740 ℃, 760 ℃, 780 ℃, 800 ℃, 820 ℃, 840 ℃, 860 ℃, 880 ℃, 900 ℃, 920 ℃, 940 ℃, 960 ℃, 980 ℃, 1000 ℃, etc., preferably 800 to 900 ℃; the inert atmosphere may be nitrogen or argon, and the sintering time is preferably 2-3 hours.
In order to further demonstrate how to achieve more than 95% of the total mass of the encapsulated silicon element, the method of preparing the micro silicon-graphene composite aerogel will be described in detail below.
The preparation method of the micron silicon-graphene composite aerogel comprises the following steps:
s1, carrying out surface treatment on micrometer silicon, wherein the surface treatment comprises, but is not limited to, coating a micrometer silicon material with a carbon-based material, and forming a uniform carbon coating layer on the surface of the micrometer silicon material after sintering; sintering at 700-1000 deg.c in inert atmosphere for 1-6 hr;
mixing graphite oxide slurry prepared by adopting a Hummers method with deionized water with the volume of V, and performing ultrasonic dispersion to obtain a dispersion liquid A; mixing the coated micron silicon material with the mass of m with a 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; the uniformly mixed graphene oxide solution, micron silicon material dispersion and water-soluble reducing agent dispersion C are added into a closed reactor.
Wherein the solvent b is deionized water.
The carbon-based materials include, but are not limited to, phenolic resins, tannins, polypyrroles, polymeric dopamine, pitch;
the water-soluble reducing agent is one of ascorbic acid, sodium ascorbate, sodium citrate, hydroiodic acid, hydrobromic acid, sodium bisulphite, sodium sulfide and ethylenediamine.
Preferably, the micrometer silicon comprises at least one of silicon micrometer powder, silicon micrometer wire, silicon micrometer tube and silicon micrometer sheet; wherein the effect is better as silicon micron powder;
the size of the microsilica material in at least one dimension (D50 of the micropowder in the case of micropowder) is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.
S2, heating the closed reactor, and carrying out reduction and self-assembly of graphene oxide to obtain the micron silicon-graphene composite hydrogel; the heating temperature is 60-75 ℃, and the specific optional temperature is as follows: 60 ℃, 61 ℃, 62 ℃, 63 ℃, 64 ℃, 65 ℃, 66 ℃, 67 ℃, 68 ℃, 69 ℃, 70 ℃, 71 ℃, 72 ℃, 73 ℃, 74 ℃, 75 ℃.
S3, performing low-temperature freezing treatment on the micron silicon-graphene composite hydrogel, and then drying by a freeze dryer to obtain micron silicon-graphene 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 graphite oxide of the application is prepared by adopting a Hummers method, and the specific process steps 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 a second aspect of the present application, there is provided an electrode comprising a current collector layer and an active material coating disposed on the current collector layer, the active material coating comprising the aforementioned micro-silicon-graphene composite aerogel and a binder. The mass ratio of the micron silicon-graphene composite aerogel to the conductive agent to the binder is a to b to c, wherein a is more than or equal to 85 and less than or equal to 90, b is more than or equal to 5 and less than or equal to 7, c is more than or equal to 5 and less than or equal to 8, and a+b+c=100.
Wherein a may be 85, 85.5, 86, 86.5, 87, 87.5, 88, 88.5, 89, 89.5, 90; b may be 5,5.2,5.3,5.4,5.6,5.7,5.8,5.9,6,6.1,6.2,6.3,6.4,6.5,6.6,6.7,6.8,6.9,7; c may be 5,5.1,5.2,5.3,5.4,5.6,5.7,5.8,5.9,6,6.1,6.2,6.3,6.4,6.5,6.6,6.7,6.8,6.9,7,7.1,7.2,7.3,7.4,7.5,7.6,7.7,7.8,7.9,8.
The electrode can be a negative electrode, and can be applied to batteries such as lithium ion batteries, sodium ion batteries and the like.
Electrode preparation method
According to a third aspect of the present application, there is provided an electrode preparation method comprising the steps of:
s4, grinding the micron silicon-graphene composite aerogel into micron silicon-graphene composite aerogel particles, and weighing the micron silicon-graphene composite aerogel particles, wherein a is more than or equal to 85 and less than or equal to 90, b is more than or equal to 5 and less than or equal to 7, c is more than or equal to 5 and less than or equal to 8, and a+b+c=100 according to the mass ratio of the micron silicon-graphene composite aerogel particles to the conductive agent to the adhesive of a to b to c.
Wherein a may be 85, 85.5, 86, 86.5, 87, 87.5, 88, 88.5, 89, 89.5, 90; b may be 5,5.2,5.3,5.4,5.6,5.7,5.8,5.9,6,6.1,6.2,6.3,6.4,6.5,6.6,6.7,6.8,6.9,7; c may be 5,5.1,5.2,5.3,5.4,5.6,5.7,5.8,5.9,6,6.1,6.2,6.3,6.4,6.5,6.6,6.7,6.8,6.9,7,7.1,7.2,7.3,7.4,7.5,7.6,7.7,7.8,7.9,8.
The micron silicon-graphene composite aerogel has a graphene frame structure and good conductivity, so that excessive conductive agents are not required to be added when the negative electrode slurry is manufactured, the size of silicon is smaller than 10 mu m, preferably, the D50 of micron particles is 3-9 mu m, the size of silicon one-dimensional and two-dimensional materials in at least one dimension is 3-9 mu m, the range of the hole size L of the graphene frame is 20-80 mu m, when the composite aerogel is ground into particles, the D50 of the particles is 100-200 mu m, and therefore, relatively complete graphene frame units in the particles can be kept, and the frame units can ensure that the micron silicon materials have sufficient expansion space during charge and discharge cycles, so that the volume expansion of the silicon during the cycle process can be well buffered; it is also noted that if the aerogel milled particles are larger, the frame structure remains more complete, however, while the frame remains more complete, the overall negative density is greater 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 conclusion, when the micron silicon-graphene composite aerogel is ground into particles, the frame structure cannot be well maintained due to the fact that the particle size is too small, the volume of the adhesive is large after the adhesive is mixed due to the fact that the particle size is too large, and the energy density is reduced. Preferably, the D50 of the micro silicon-graphene 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 micron silicon-graphene composite aerogel particles, the conductive agent, the binder and the solvent to prepare slurry, coating the slurry on a continuous current collector, 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.
Examples1
S1, carrying out surface treatment on micrometer silicon powder with the mass of m=21g, wherein the surface treatment comprises, but is not limited to, coating a micrometer silicon material with a carbon-based material, and forming a uniform carbon coating layer on the surface of the micrometer silicon material after sintering; sintering at 700-1000 deg.c in argon atmosphere for 1-6 hr; 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 the coated micron silicon with 1L deionized water to obtain a dispersion liquid B; then mixing the dispersion liquid A, the dispersion liquid B and 100g of sodium ascorbate, and magnetically stirring uniformly to obtain a dispersion liquid C; the dispersion C was added to the closed reactor.
S2, heating the closed reactor to 68 ℃ and keeping the temperature constant, and assembling and self-reducing graphene oxide to obtain graphene-micron silicon material composite hydrogel; the reaction time was 3 hours.
S3, carrying out low-temperature freezing treatment at-170 ℃ on the graphene-micrometer silicon material composite hydrogel, and then drying by a freeze dryer to obtain micrometer silicon-graphene composite aerogel; wherein the pressure of freeze drying is 5-20 Pa.
S4, grinding the micron silicon-graphene composite aerogel into micron silicon-graphene composite aerogel particles by a ball milling method, wherein the ball milling time is T=3 hours, d50=150 μm of the micron silicon-graphene composite aerogel particles after ball milling,
weighing the three according to the mass ratio of the micron silicon-graphene composite aerogel particles to the conductive agent to the binder as a to b to c, wherein a=85, b=7 and c=8.
Because of poor conductivity compared with micron silicon, the first aspect adopts carbon-based material to coat the silicon, and a first-order expansion limiting structure is formed while improving the conductivity of the silicon; the graphene aerogel formed next is micron silicon
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 micrometer silicon-graphene composite aerogel particles (85 wt%), a conductive agent (3 wt% of CNT and 4% of SP), a binder (5.6 wt% of CMC and 2.4wt% of SBR) and deionized water into slurry by magnetic stirring, 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
Table 2: comparative examples related proportioning parameters
As can be seen from comparative examples 1 to 12 and comparative examples 1 to 6, the micrometer silicon particles were too small (comparative examples 1 to 3), and although the cycle retention was improved, the capacity was relatively low because of the Si content being too small; with increasing silicon addition, the capacity increases exponentially, but when the micron silicon is too much (comparative examples 4-6), the cycle retention is low, especially below 50% after 100 cycles, although the capacity is very high, where the main reason is that too much Si results in aerogel not being held 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 micron silicon-graphene composite aerogel are milled, the lower the cycle retention rate is, because the smaller the milled powder particles are, the more serious the frame thereof is destroyed, resulting in a reduction of the buffering effect on 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 can be maintained and the density of the electrode can be made not too low, and the fabricated negative electrode density is within the range of the usable scale.
In comparative examples 5 and comparative examples 10 to 12, it was found that when the milled powder particles of the micro-silicon-graphene composite aerogel were then bonded with a proper amount of the conductive agent and the binder, the aerogel particles were not well bonded due to the excessively low content of the conductive agent and the binder, the conductive performance of the micro-silicon was not enhanced by the conductive agent, the electrode was severely peeled off in the electrolyte, the cycle retention rate was low, the electron transport performance of the electrode material was poor, and the first reversible capacity was greatly impaired, which was unsuitable 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 (4)

1. A preparation method of a micron silicon-graphene composite aerogel, wherein the micron silicon-graphene 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 graphene aerogel; the carbon element existing in the graphene aerogel form accounts for more than 96% of the total mass of the carbon element of the micron silicon-graphene composite aerogel; the silicon element exists in the form of a micron silicon material, the silicon element exists at least partially in the form of being wrapped in the graphene aerogel network, and the wrapped silicon element accounts for more than 95% of the total mass of the silicon element; the mol ratio of the silicon element to the carbon element is 1:2-2:1;
the micrometer silicon is silicon micrometer powder, and the D50 of the micrometer silicon is in the range of 1-10 mu m;
and the D50 of the micron silicon-graphene composite aerogel particles is 100-200 mu m;
the method is characterized by comprising the following steps of:
s0. the micron silicon is coated by carbon-based material, and a uniform carbon coating layer is formed on the surface of the micron silicon after sintering;
s1, adding a graphene oxide solution, a micron silicon material dispersion liquid and a dispersion liquid C of a water-soluble reducing agent which are uniformly mixed into a closed reactor;
s2, heating the closed reactor, and carrying out reduction and self-assembly of graphene oxide to obtain the micron silicon-graphene composite hydrogel;
s3, performing low-temperature freezing treatment on the micron silicon-graphene composite hydrogel, and then drying by a freeze dryer to obtain the micron silicon-graphene composite aerogel.
2. The method for preparing the micron silicon-graphene composite aerogel according to claim 1, wherein the water-soluble reducing agent is one of ascorbic acid, sodium ascorbate, sodium citrate, hydroiodic acid, hydrobromic acid, sodium bisulphite, sodium sulfide and ethylenediamine.
3. The method for preparing the micron silicon-graphene composite aerogel according to claim 1, wherein the heating temperature in the step S2 is 60-75 ℃; the freezing temperature in the step S3 is-170 to-20 ℃, and the pressure of freeze drying is 5-20 Pa.
4. The method for preparing the micron silicon-graphene composite aerogel according to any one of claims 1 to 3, wherein the step S1 further comprises mixing graphite oxide slurry prepared by a Hummers method with a solvent a, and performing ultrasonic dispersion to obtain a dispersion liquid a; mixing the micron silicon material with the solvent B to obtain a dispersion liquid B; and mixing the dispersion liquid A, the dispersion liquid B and the water-soluble reducing agent, and then magnetically stirring uniformly to obtain the dispersion liquid C.
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