CN110649236B - Porous silicon-carbon composite material and preparation method thereof - Google Patents

Porous silicon-carbon composite material and preparation method thereof Download PDF

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CN110649236B
CN110649236B CN201910907214.XA CN201910907214A CN110649236B CN 110649236 B CN110649236 B CN 110649236B CN 201910907214 A CN201910907214 A CN 201910907214A CN 110649236 B CN110649236 B CN 110649236B
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silicon
carbon
composite material
carbon composite
porous silicon
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CN110649236A (en
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郭玉国
李阁
黄林波
殷雅侠
岳风树
姚钧
赵岸光
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Beijing One Gold Amperex Technology Ltd
Shanxi Fuji New Energy Material Technology Co ltd
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Beijing One Gold Amperex Technology Ltd
Institute of Chemistry CAS
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    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • H01M4/625—Carbon or graphite
    • 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
    • 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 invention discloses a porous silicon-carbon composite material and a preparation method thereof, wherein the porous silicon-carbon composite material is formed by bonding a silicon-based material and a carbon-based material, wherein the silicon-based material comprises silicon, silicon oxide and silicate, the silicate is dispersed in a silicon oxide substrate, the carbon-based material comprises a carbon material and an amorphous carbon coating material, the carbon material and the silicon-based material are mutually contacted and bonded together to form a porous structure, and the amorphous carbon coating material is coated on the surface of the porous structure; the condition is that the total mass of the porous silicon-carbon composite material is 100 percent, wherein the mass percentage of the silicate is 5 to 30 percent. The porous silicon-carbon composite material provided by the invention shows extremely low expansion rate when being used as a lithium ion battery cathode material, and has high specific capacity, first coulombic efficiency, excellent cycle performance and rate capability. In addition, the preparation method is simple, and is a method suitable for industrial large-scale production of the silicon-carbon composite material for the lithium ion battery.

Description

Porous silicon-carbon composite material and preparation method thereof
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a porous silicon-carbon composite material, a preparation method thereof, a battery cathode containing the porous silicon-carbon composite material and a lithium ion battery.
Background art:
the high dependence of people on non-renewable energy has caused more and more environmental problems, and the development of research and development on clean energy has become one of the most interesting issues worldwide. On the one hand, clean energy sources from solar and wind energy are gradually occupying a larger market scale, and in order to realize wider application thereof, more efficient energy conversion and storage devices need to be developed; on the other hand, research into electric vehicles to get rid of our reliance on traditional energy sources such as oil also requires energy storage devices of higher energy density. By virtue of the characteristics of high energy density, safety and environmental friendliness, the lithium ion battery has been widely applied in various industries and is the most important power source of portable electronic equipment at present. However, due to the problems of driving range and charging time, the current electric vehicles still cannot replace vehicles using traditional energy sources, and it is still urgent to develop lithium ion batteries with higher energy density and power density, lower cost, and higher safety and stability.
In the aspect of novel lithium ion battery cathode materials, the silicon-based cathode material has ultrahigh lithium storage capacity (complete lithiation state Li)22Si54200mAh/g), relatively low voltage plateau (-0.4V vs Li+Li), extremely abundant reserves in the earth crust, environmental protection, chemical stability and the like, and is considered to be an ideal next-generation lithium ion battery cathode material. However, there is a huge volume expansion of the silicon-based anode material during alloying: (>300%), which causes pulverization and exfoliation of the active material on the electrode sheet and rapid capacity decay, thus hindering the industrial application thereof. The continuous growth of SEI on the surface of the active material can be promoted by the particle breakage caused by huge volume expansion, so that the silicon-based material has lower coulombic efficiency, and the cycling stability of the battery is seriously influenced. In addition, since silicon is a semiconductor material, the conductivity of electrons is poor, which is not favorable for the rapid transmission of electrons on the electrode plate to influence the normal performance of the capacity of the silicon-based material, so that the silicon-based negative electrode material has poor rate performance.
In order to solve the problem of volume expansion, patent CN 106129411 a discloses a hollow silicon-based composite material, in the invention, silicon oxide and/or silicon are uniformly adhered on the surface of graphite, then the graphite is removed by oxidation heat treatment to obtain a hollow structure, nano-silicon is obtained by reduction with a reducing agent to obtain hollow particles consisting of hollow cavities and secondary particle silicon layers, then in-situ coating is carried out on the surface of the secondary particle silicon layers, and finally coating of a coating carbon layer is carried out to obtain the hollow silicon-based composite material. The hollow composite material effectively relieves the volume expansion in the circulation process, has excellent circulation performance, but the hollow structure can not keep the existing morphology in the electrode plate preparation process, and a new interface can be exposed through rolling of the electrode plate to continuously grow SEI, so that the performance of the battery is attenuated.
In order to solve the problem of low coulombic efficiency, patent CN 109075330 a discloses a prelithiation method for inserting lithium into a silicon-based negative electrode material by wet impregnation, in which metal lithium is inserted into silicon monoxide in the impregnation process to consume oxygen which can generate irreversible capacity in the silicon monoxide in advance, thereby achieving the purpose of improving the coulombic efficiency of the silicon-based negative electrode material. However, the material needs to go through a multi-step long-time impregnation process, and finally needs to be sintered to achieve the purpose of prelithiation, the preparation process is complicated, and various organic solvents are used, so that the industrial application of the material is difficult.
According to the invention, the silicon oxide with silicate dispersed inside is used as the silicon-based material, so that the irreversible capacity in the first charge-discharge process can be effectively reduced, the coulombic efficiency of the composite material is improved, the silicon-based material and the carbon material are contacted with each other to form a porous structure, on one hand, the electronic conductivity of the composite material can be effectively improved, on the other hand, the volume expansion of the silicon-based material can be effectively buffered, and the cycle stability of the composite material is improved. The preparation method of the porous silicon-carbon composite material is simple and efficient, is beneficial to industrial implementation, and has wide application prospect.
Disclosure of Invention
The invention aims to solve the problems of poor cycle performance, poor rate performance and low coulombic efficiency of the conventional silicon-based composite material, provides a porous silicon-carbon composite material containing silicon oxide, silicate, a carbon material and a carbon coating layer, and effectively prolongs the cycle life and energy density of the current lithium ion battery cathode material.
The purpose of the invention is realized by the following technical scheme:
a porous silicon-carbon composite material is formed by bonding a silicon-based material and a carbon-based material, wherein the silicon-based material comprises silicon, silicon oxide and silicate, the silicate is dispersed in a silicon oxide substrate, the carbon-based material comprises a carbon material and an amorphous carbon coating material, the carbon material and the silicon-based material are mutually contacted and bonded together to form a porous structure, and the amorphous carbon coating material is coated on the surface of the porous structure; the condition is that the total mass of the porous silicon-carbon composite material is 100 percent, wherein the mass percentage of the silicate is 5 to 30 percent.
The chemical formula of the silicon oxide is SiOxWherein 0 is<x is less than or equal to 2; and/or the cation element of the silicate is alkali metal, alkaline earth metal, third main group element and transition metal element, preferably one or more combination of lithium, sodium, magnesium, calcium, aluminum, nickel, cobalt, iron and manganese.
The carbon material is one or a combination of more of crystalline graphite, mesocarbon microbeads, hard carbon, soft carbon, graphene, carbon nanotubes, carbon nanowires and carbon fibers; more preferably, the carbon material is one or a combination of several of crystalline flake graphite, graphene, carbon nanotubes and carbon nanowires.
The carbon coating layer is a uniform coating layer formed by liquid phase coating, solid phase coating or vapor deposition coating; preferably, the thickness of the carbon coating layer is 1-100 nm; more preferably, the coating has a thickness of 5 to 50 nm.
The total mass of the porous silicon-carbon composite material is 100%, wherein the mass percentage of silicate is 5% -30%, and the preferable mass percentage is 10% -20%; less than 5% gives poor effect of buffering volume expansion and poor cycle stability, and more than 30% gives a significant decrease in capacity. Preferably, the silicate content accounts for 10-20% of the total mass of the porous silicon-carbon composite material, and the circulation stability and the capacity are well balanced.
The pores are formed by non-dense accumulation of silicon-based materials and carbon-based materials, and can be adjusted by the state of the slurry in the preparation process. In a preferred technical scheme of the invention, the median particle size of the porous silicon-carbon composite material is 1-50 μm, and preferably the median particle size is 2-30 μm; a porosity of 1-50%, preferably a porosity of 5-30%; the pore size is not more than 5 μm, typically not more than 2 μm.
The invention also provides a preparation method of the porous silicon-carbon composite material, which comprises the following steps:
(1) crushing the silicon-based material to a proper particle size, dispersing the silicon-based material into a solvent to prepare slurry A, gradually adding hydrofluoric acid in the dispersing process, and etching the surface of the silicon-based material;
(2) uniformly mixing a carbon material, a water-soluble inorganic salt and a binder, and dispersing into a proper solvent to prepare slurry B;
(3) uniformly mixing the slurry A and the slurry B, drying to obtain a composite material, and then washing the composite material after high-temperature treatment to remove water-soluble salts to obtain a porous silicon-carbon composite material;
(4) the composite material is coated with amorphous carbon.
The silicon-based material in the step (1) is silicon and/or silicon oxide, and is prepared by respectively forming steam to react with reducing substances under the high-temperature vacuum condition and carrying out in-situ doping, wherein the reducing substances are one or the combination of more than two of simple substances of alkali metals, alkaline earth metals, third main group elements and transition metal elements, oxides thereof and alloys thereof; provided that the alloy accounts for 20 wt% or more of the reduced matter.
Specifically, the in-situ doping is to evaporate silicon and/or silicon oxide, and at least one or more of simple substances of alkali metal, alkaline earth metal, third main group element and transition metal element, oxides thereof and alloys thereof into gas state under high temperature and high vacuum condition, then react and condense and deposit into bulk material.
The alkali metal, alkaline earth metal, third main group element and transition metal element are selected from lithium, sodium, magnesium, calcium, aluminum, nickel, cobalt, iron and manganese.
The alloy is an alloy of magnesium and other metals, and the magnesium accounts for more than 30wt% of the alloy; the alloy is preferably magnesium lithium alloy, magnesium sodium alloy, magnesium calcium alloy, magnesium aluminum alloy and magnesium manganese alloy.
More preferably, the alloy accounts for 30wt% or more of the reduced matter, still more preferably, the alloy accounts for 40wt% or more of the reduced matter, and most preferably, the alloy accounts for 50wt% or more of the reduced matter.
The inventors have unexpectedly found that when carrying out a reaction of a vapor of silicon and/or an oxide of silicon in a silicon-based material with a vapor of a reducing substance in which there is a certain amount of an alloy, particularly a magnesium alloy, the silicon-based material formed by condensation after the reaction of the two vapors has a small proportion of silicon crystal domains. More crystalline regions indicate more agglomeration of silicon. The silicon in the crystalline region undergoes significantly greater volume expansion during charge and discharge than does uniformly dispersed silicon monoxide, resulting in a decrease in the cycle stability of the battery. Therefore, when the silicon-based material is prepared, the reducing substance contains a certain amount of alloy, so that the proportion of a silicon crystal area of the silicon-based material obtained by condensation is reduced, and further, the expansion rate of the porous silicon-carbon composite material prepared by the method is small in the charge and discharge processes, and the improvement of the cycle performance is facilitated.
The vacuum heating is performed in a vacuum furnace with a deposition system, having one or two or more heating chambers. Preferably, the vacuum furnace has two or more heating chambers, and the silicon and/or the silicon oxide are heated to SiO in one heating chamberx(0<x is less than or equal to 2), and the reducing substance is placed in another heating cavity to be heated into steam. Wherein the heating temperature of the heating cavity for placing the silicon and/or the silicon oxide is 1200-1600 ℃, and the heating temperature of the heating cavity for placing the reducing substance is 1000-1200 ℃.
The caliber of a gas path of the gas entering the deposition system of the heating cavity is adjustable, preferably, the gas SiO entering the deposition systemx(0<x is less than or equal to 2) the volume flow ratio of the steam to the steam of the reducing substance is 100:1-20, preferablySelecting 100: 5-15. The two kinds of steam are controlled within the numerical range, so that the inactive components in the silicon monoxide can be consumed more, the first coulombic efficiency of the material is improved, and meanwhile, the higher capacity of the silicon monoxide material is ensured.
In the preparation method of the porous silicon-carbon composite material provided by the invention, the steps are explained and illustrated in more detail, and it should be understood by those skilled in the art that the following further limitations are only for clearly illustrating the implementation manner of the invention, and do not necessarily depend on the following specific steps, reagents, equipment, proportions, process conditions and the like to complete the invention, i.e. the following limitations should not be understood as a limitation to the scope of the invention.
According to the preparation method of the porous silicon-carbon composite material provided by the invention, the crushing in the step (1) is carried out by one or more crushing modes of ball milling, sand milling, roller crushing, jaw crushing, air flow crushing, mechanical crushing and the like; for example, the silicon oxide bulk material doped with silicate can be further ground after ball milling or further ground after air flow pulverization to achieve a nanometer level of material particle size; the preparation method of the porous silicon-carbon composite material is characterized by comprising the following steps: the suitable particle size in step (1) is micron-scale or nanometer-scale, and is not particularly limited, and it is generally considered that less than 50nm reaches the processing limit and is difficult to process; whereas more than 5 μm, the cycle performance in the battery is affected, and thus a suitable particle size is 50nm to 5 μm, preferably 200nm to 4.5. mu.m.
In the step (1), the solvent is one or more of water, ethanol and methanol, and the solid content of the slurry A is 10-50 wt%, preferably 15-40 wt%;
the amount of the hydrofluoric acid used in the step (1) is 0.1-1 wt%, preferably 0.1-0.3 wt% of the silicon-based material, and the concentration of the hydrofluoric acid is 0.1-1mol/L, preferably 0.2-0.5 mol/L. And etching the surface of the silicon-based material by adopting hydrofluoric acid to realize roughening treatment, so that the silicon-based material is easier to compound with the carbon-based material.
According to the preparation method of the porous silicon-carbon composite material provided by the invention, the water-soluble salts in the step (2) include, but are not limited to, metal sodium or potassium carbonate, bicarbonate and sulfate, such as sodium carbonate, sodium bicarbonate, sodium chloride, sodium sulfate and the like. The water-soluble salt is uniformly mixed with the silicon-based material and the carbon-based material before drying, the water-soluble salt is uniformly dispersed in a spherical particle after drying, the water-soluble salt can be washed away by subsequent water washing to form a porous structure, a certain gap is formed in the porous structure, the volume expansion of the material during charging and discharging can be buffered, the stress generated by expansion is reduced, and therefore the particles are kept complete and stable in the circulating process.
The binder in the step (2) is one or more of methylcellulose, hydroxypropyl methylcellulose, sodium carboxymethylcellulose, hydroxyethyl cellulose, starch, gelatin, sodium alginate, casein, guar gum, chitosan, gum arabic, xanthan gum, soybean protein gum, natural rubber, lanolin, agar, polyacrylamide, polyvinyl alcohol, polyvinylpyrrolidone, modified paraffin resin, carbomer resin, polyacrylic acid, butadiene rubber, styrene butadiene rubber and polyurethane;
the mass ratio of the carbon material, the water-soluble inorganic salt and the binder in the step (2) is 100-150: 12-25: 1-10, preferably 100-120: 17-22: 5-8.
In the step (2), the solvent is one or more of water, ethanol and methanol, and the solid content of the slurry B is 10-50 wt%, preferably 15-40 wt%.
According to the preparation method of the porous silicon-carbon composite material provided by the invention, the uniform mixing in the step (3) can be realized by one or more mixing modes of a high-speed mixer, a ribbon mixer, a mechanical stirrer, a ball mill, a sand mill and the like; for example, the slurry a and the slurry B may be added into a ball mill at the same time in a certain proportion and milled for 3 hours at a high speed, so that the two slurries are mixed uniformly;
the solvent removal in the step (3) can be realized by methods such as spray drying, vacuum drying, freeze drying, flash evaporation drying and the like; for example, the uniformly mixed slurry of slurry a and slurry B can be prepared by spray drying technology, wherein the temperature of the feed inlet is 200 ℃ and the temperature of the discharge outlet is 90 ℃, so that the solvent in the slurry is rapidly volatilized to obtain the composite microspheres.
The high-temperature treatment in the step (3) is to sinter the obtained composite microspheres, carbonize the binder in the composite microspheres to bond the silicon-based material and the carbon-based material together, wherein the treatment temperature is 400-800 ℃, and preferably 500-700 ℃; the high-temperature treatment can be realized by dynamic sintering or static sintering and the like, and the used equipment can be a rotary furnace, a pushed slab kiln, a roller kiln, a tubular furnace and a muffle furnace.
According to the preparation method of the porous silicon-carbon composite material provided by the invention, in the step (4), the carbon coating is liquid phase coating, solid phase coating or chemical vapor deposition coating; for example, the equipment used for liquid phase coating is a ball mill; the coating agent is one or more of coal pitch, petroleum pitch, needle coke or petroleum coke, preferably one or the combination of the coal pitch and the needle coke; uniformly mixing the obtained material and a coating agent in a solvent, removing the solvent by vacuum drying, and sintering at a high temperature; the sintering temperature is 400-800 ℃, preferably 500-700 ℃; the sintering time is 1-3h, preferably 1.5-2.5 h;
for another example, the equipment used for solid phase coating is a solid phase coating machine; the coating agent is one or more of coal pitch, petroleum pitch, needle coke or petroleum coke, preferably one or the combination of the coal pitch and the needle coke; the temperature of the solid phase coating is 400-800 ℃, preferably 500-700 ℃; the solid phase coating time is 1-3h, preferably 1.5-2.5 h;
for another example, the chemical vapor deposition coating gas source is one or two of acetylene, methane, propane, butane, benzene and toluene; the coating temperature is 600-1100 ℃, preferably 700-1000 ℃; the coating time is 1-6h, preferably 2-5 h.
The invention also provides application of the porous silicon-carbon composite material as a lithium ion battery cathode material.
The invention also provides a lithium ion battery, and the lithium ion battery contains the porous silicon-carbon composite material provided by the invention or the porous silicon-carbon composite material prepared by the preparation method provided by the invention.
Compared with the prior art, the porous silicon-carbon composite material provided by the invention has the advantages that:
the silicon-based material is a silicon oxide composite structure containing silicate, a reducing substance is used for consuming an inactive component (oxygen in the silicon oxide) in the silicon-based material, and the doped silicate formed by an alkali metal element, an alkaline earth metal element and a transition metal element can buffer volume expansion generated in a lithium intercalation process, so that the cycle performance of the composite material is effectively improved.
And secondly, the silicon-based material and the carbon material are contacted with each other to form a porous structure, so that the electronic conductivity of the composite material can be effectively improved, the volume expansion of the silicon-based material can be effectively buffered, and the circulation stability of the composite material is improved.
Thirdly, the inventors have also unexpectedly found thatx(0<x is less than or equal to 2), when the steam reaction is carried out, a certain amount of alloy is contained in the reducing substance, the proportion of a silicon crystal region in the silicon-based composite material obtained by condensation and sedimentation can be greatly reduced, and therefore the first-turn coulomb efficiency of the composite cathode material is greatly improved.
And fourthly, optimizing and screening various process conditions for preparing the silicon-based material, particularly respectively heating silicon and/or silicon oxide and reducing substances in different heating cavities in a vacuum furnace, and regulating and controlling the flow ratio of two kinds of steam in a deposition area, so that the obtained silicon-based composite material is used as the lithium battery cathode material, and the performance is further improved.
Fifthly, the uniform carbon coating on the surface is beneficial to improving the conductivity of the material and the multiplying power performance of the composite material.
And sixthly, the preparation method provided by the invention also has the advantages of simple method, cheap and easily available raw materials, suitability for large-scale production, high practicability and the like.
Drawings
Fig. 1 is a transmission electron microscope photograph of a silicon-based material in the porous silicon carbon composite material prepared in preparation example 1.
FIG. 2 is a TEM photograph of Si-based material in porous Si-C composite material prepared in comparative preparation example 1.
FIG. 3 is a SEM photograph of the porous Si-C composite material prepared in example 1 of the present invention.
FIG. 4 is an X-ray diffraction spectrum of the porous Si-C composite material obtained in example 1 of the present invention.
Fig. 5 is a charge-discharge curve of the porous silicon-carbon composite material prepared in example 1 of the present invention as a negative electrode of a lithium ion battery.
Fig. 6 is a cycle performance curve of the porous silicon-carbon composite material prepared in example 1 of the present invention as a negative electrode of a lithium ion battery.
Fig. 7 is a rate performance curve of the porous silicon-carbon composite material prepared in example 1 of the present invention as a negative electrode of a lithium ion battery.
Fig. 8 is an electrochemical impedance curve of the porous silicon-carbon composite material prepared in example 1 of the present invention after 200 cycles of the negative electrode of the lithium ion battery.
Detailed Description
The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.
The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.
In the examples, the silicate content of the porous Si-C composite material was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) (HK-8100) to determine the content of the metal element, and then the corresponding silicate content was calculated.
Scanning Electron Microscope (SEM) Japanese Electron scanning Electron microscope JEOL-6701F was used.
Preparation examplePreparation of silicon-based materials
Preparation example 1
(1) 3Kg of Si powder with 6Kg of SiO2Adding the powder into a high-speed mixer, and cooling with circulating water under the protection of inert atmosphere for 1000rStirring and mixing for 30min to obtain uniformly mixed raw material A, and then, preserving the temperature of the raw material A for 2h under the protection of argon gas at 50 ℃ to fully remove moisture; simultaneously, 0.5Kg of metal magnesium powder and 0.5Kg of magnesium-aluminum alloy (the magnesium content is 36.2 wt%) are kept at 50 ℃ under the protection of argon for 2 hours to fully remove the water, thus obtaining the raw material B.
(2) Adding the dried raw material A into a heating cavity 1 of a vacuum furnace with a condensation collection system, vacuumizing to below 1Pa, starting heating, heating to 1300 ℃, and preserving heat for 20 hours; and simultaneously adding the dried raw material B into the heating cavity 2, vacuumizing to below 1Pa, starting heating, heating to 1000 ℃, and keeping the temperature for 20 h. During the period, the caliber of a gas path of the heating cavity 1 and the heating cavity 2 entering the deposition system is regulated, the volume flow ratio of raw material A steam and raw material B steam entering the deposition system is 100:15, meanwhile, the temperature of a deposition area is controlled to be maintained at about 600 ℃, and after the deposition area is naturally cooled to the room temperature, a blocky deposition material, namely a silicon-based material, namely the silicon-based material 1, is obtained.
FIG. 1 is a TEM photograph of the Si-based material in the porous Si-C composite material obtained in example 1, and it can be seen that the Si-based material obtained has no distinct crystalline regions, indicating that the SiO in the whole material is amorphous. The silicon oxide is uniformly distributed with silicon atoms and oxygen atoms, but due to the problem of treatment temperature, the silicon atoms are aggregated together to form a silicon crystal region, the more crystal regions are, the more serious the aggregation of the silicon is, and the volume expansion of the silicon in the crystal region is obviously larger than that of the amorphous silicon oxide during charging and discharging, so that the cycling stability of the battery is not good as the amorphous state, and therefore, the material is made into the amorphous state with the low crystal region proportion as much as possible.
Preparation example 2
The same operation was carried out as in preparation example 1 except that in step (1), 0.3Kg of metallic magnesium powder and 0.7Kg of magnesium-aluminum alloy were used as the raw material B. The resulting bulk deposited material is a silicon-based material, referred to as silicon-based material 2
Preparation example 3
The same operation was carried out as in preparation example 1 except that in step (1), 0.7Kg of metallic magnesium powder and 0.3Kg of magnesium-aluminum alloy were used as the raw material B. The resulting bulk deposited material is a silicon-based material, referred to as silicon-based material 3.
Preparation example 4
The same operation as in preparation example 1 was carried out except that in step (2), the magnesium-aluminum alloy was replaced with a magnesium-lithium alloy (in which the magnesium content was 32.5 wt%). The resulting bulk deposited material is a silicon-based material, referred to as silicon-based material 4.
Comparative preparation example 1
The operation was carried out in the same manner as in preparation example 1, except that in step (1), the raw material B was a mixture of 0.681kg of magnesium powder and 0.319kg of aluminum powder. The resulting bulk deposited material is a silicon-based material, referred to as silicon-based material 5.
FIG. 2 is a TEM photograph of a silicon-based material prepared in comparative preparation example 1, and compared with FIG. 1, it can be seen from FIG. 2 that there are many lattice fringes, and the regions of the lattice fringes correspond to the crystalline silicon, and the proportion of the crystalline regions is large, and the volume expansion rate of the crystalline silicon is much larger than that of amorphous silicon oxide, so that the material with a crystalline structure is more likely to crack during the charge and discharge processes, resulting in rapid decay of the material capacity and poor cycle performance.
ExamplesPreparation of porous silicon-carbon composite material
Example 1
Adding 7Kg of the silicon-based material 1 obtained in preparation example 1 into a ball mill, ball-milling at a rotating speed of 600r/min for 3h until the particle size is 4.5 μm, dispersing in 35L of water, and adding 1000mL of 0.5mol/L hydrofluoric acid to obtain slurry A with a solid content of about 20%; simultaneously adding 3Kg of crystalline flake graphite with the granularity of 20 mu m, 150g of sodium carboxymethylcellulose, 500g of sodium bicarbonate and 15L of water into a pulping machine for pulping for 30min to obtain slurry B with the solid content of about 20 percent; adding the slurry B into the slurry A, continuously performing ball milling for 3h at the rotating speed of 300r/min to obtain uniformly mixed slurry, performing spray drying, carbonizing at 600 ℃, and washing with water to obtain a porous silicon-carbon composite material precursor; adding the precursor powder into a CVD vapor deposition furnace for carbon coating treatment, introducing acetylene gas at the mass flow of 600sccm, depositing for 3h at 760 ℃, placing the coated material under the protection of nitrogen, heating to 900 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1h, and naturally cooling to obtain the porous silicon-carbon composite material, wherein the silicate content is 14.5 wt%.
The morphology of the composite material was analyzed by scanning electron microscopy (SEM, Japanese Electron scanning Electron microscopy JEOL-6701F), and FIG. 3 is a scanning electron micrograph of the porous silicon carbon composite material prepared in example 1, which is spheroidal, has a porous surface and a coating layer, and has a particle size of about 20 μm.
When the X-ray diffraction peak of the composite material was analyzed by an X-ray diffraction analyzer (XRD, Rigaku D/max 2500, Cu K α), and FIG. 4 is an XRD diffraction pattern of the porous silicon-carbon composite material obtained in example 1, the diffraction peak of mainly graphite was observed, and no significant silicon diffraction peak was observed, thus confirming that the silicon-based material was amorphous.
The particle size of the composite material was measured with a Malvern laser particle sizer (Malvern, Mastersizer 3000) to obtain a median particle size of 23 μm, consistent with the results obtained for electron microscopy photographs.
Example 2
The other procedure was the same as in example 1 except that the silicon-based material 2 obtained in preparation example 2 was used in place of the silicon-based material 1 to prepare a porous silicon-carbon composite material having a silicate content of 16.7 wt%.
Example 3
The other procedure was the same as in example 1 except that the silicon-based material 3 obtained in preparation example 3 was used in place of the silicon-based material 1 to prepare a porous silicon-carbon composite material having a silicate content of 12.4 wt%. .
Example 4
The other procedure was the same as in example 1 except that the silicon-based material 4 obtained in preparation example 4 was used in place of the silicon-based material 1 to prepare a porous silicon-carbon composite material having a silicate content of 13.6 wt%.
Example 5
The other steps are the same as example 1, except that in the preparation of slurry A in example 1, the amount of the silicon-based material 1 was changed to 5kg, and in the preparation of slurry B, the amount of the flake graphite was changed to 5kg, to prepare a porous silicon-carbon composite material having a silicate content of 11.2 wt%.
Example 6
The other steps are the same as example 1, except that in the preparation of slurry A in preparation example 1, the amount of the silicon-based material 1 was changed to 3kg, and in the preparation of slurry B, the amount of the flake graphite was changed to 7kg, to prepare a porous silicon-carbon composite material having a silicate content of 7.8 wt%.
Example 7
The other steps are the same as example 1, except that in the preparation of the slurry B, a composite of crystalline flake graphite and graphene in a mass ratio of 50:1 is used as a carbon source to prepare a porous silicon-carbon composite material, wherein the silicate content is 15.3 wt%.
Example 8
The other steps are the same as example 1, except that the slurry A is prepared by adding the silicon-based material 1 into a ball mill, and ball-milling for 6h at the rotating speed of 900r/min until the particle size is 500nm, so as to prepare the porous silicon-carbon composite material, wherein the silicate content is 14.1 wt%.
Comparative example 1
The other procedure was the same as in example 1 except that the silicon-based material 5 obtained in comparative preparation example 1 was used in place of the silicon-based material 1 to prepare a porous silicon-carbon composite material having a silicate content of 13.7 wt%.
Comparative example 2
The other steps are the same as those in example 1, except that hydrofluoric acid is not added in the preparation of the slurry A, and the porous silicon-carbon composite material is prepared.
Comparative example 3
The other steps are the same as example 1, except that in the preparation of slurry B, no sodium bicarbonate is added, and the prepared silicon-carbon composite material has no porous structure.
Comparative example 4
The other steps are the same as those in the embodiment 1, except that the step of carbon coating is not performed after the porous silicon-carbon composite material precursor is obtained.
Application example
The porous silicon-carbon composite materials prepared in the examples and the comparative examples are assembled into a lithium battery, and the electrochemical performance of the lithium battery is tested as follows: compounding the prepared porous composite negative electrode material, carbon black, carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR)Mixing the binder at a mass ratio of 80:10:10 to prepare slurry (wherein the mass ratio of CMC to SBR is 1:1), uniformly coating the slurry on a copper foil current collector, and carrying out vacuum drying for 12h to prepare a working electrode; lithium foil as counter electrode, glass fiber membrane (from Whatman, UK) as separator, 1mol/L LiPF6(the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with the volume ratio of 1:1) is used as electrolyte, VC with the volume fraction of 1% and FEC with the volume fraction of 5% are added into the electrolyte, and the button cell is assembled in a German Braun inert gas glove box in an argon atmosphere. And (3) carrying out charge and discharge tests on the assembled battery on a LAND charge and discharge tester.
Electrochemical analysis tests were performed on the porous silicon carbon composite material prepared in example 1, and the results are shown in fig. 5. The material capacity can reach 1085.6mAh/g, the first turn coulombic efficiency is 87.8%, the capacity retention rate after 200 cycles is 89.3% (as shown in figure 6), and the composite material still has the specific charge capacity of 945.6mAh/g under the high current density of 5C (as shown in figure 7, five sections from left to right respectively correspond to the multiplying power of 0.2C,1C,2C,5C and 0.2C), and is 87.1% under 0.2C in a multiplying power test, so that the composite material obtained by the invention has higher capacity and excellent cycle performance, and the electrochemical impedance spectrum test of a battery after 200 cycles is carried out, and the charge transfer resistance is only 59.1 omega (as shown in figure 8), which indicates that the material has longer cycle life.
The porous silicon-carbon composites prepared in the examples of the present invention and the comparative examples were assembled into batteries according to the same method, and the performance of the batteries was tested, with the results shown in table 1:
table 1 electrochemical performance test results of porous composite anode material
Figure BDA0002213629240000131
As can be seen from the data in Table 1, the porous silicon-carbon composite material provided by the invention is used as a lithium battery cathode material, and a lithium battery assembled by the porous silicon-carbon composite material has excellent comprehensive performance, high first coulombic efficiency, good rate capability and good cycle performance.
The invention adopts specific process conditions, controls the silicate of the porous silicon-carbon composite material in a proper proportion, and the obtained material is used as the cathode of the lithium ion battery, so that the battery capacity and the cycling stability are balanced. The inventor unexpectedly finds that when the silicon-based material of the porous silicon-carbon composite material is prepared, a certain amount of alloy is used as the reducing substance to replace a metal simple substance or an oxide, the proportion of a crystal region in the obtained silicon-based material can be reduced, and the first coulombic efficiency and the cycling stability of the negative electrode material are improved.
The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (12)

1. A porous silicon-carbon composite material is formed by bonding a silicon-based material and a carbon-based material, wherein the silicon-based material comprises silicon, silicon oxide and silicate, the silicate is dispersed in a silicon oxide substrate, the carbon-based material comprises a carbon material and an amorphous carbon coating material, the carbon material and the silicon-based material are mutually contacted and bonded together to form a porous structure, and the amorphous carbon coating material is coated on the surface of the porous structure; the condition is that the total mass of the porous silicon-carbon composite material is 100 percent, wherein the mass percentage of the silicate is 5 to 30 percent;
the preparation method of the porous silicon-carbon composite material comprises the following steps:
(1) crushing a silicon-based material, dispersing the crushed silicon-based material into a solvent to prepare slurry A, gradually adding hydrofluoric acid in the dispersing process, and etching the surface of the silicon-based material;
(2) uniformly mixing a carbon material, a water-soluble inorganic salt and a binder, and dispersing into a proper solvent to prepare slurry B;
(3) uniformly mixing the slurry A and the slurry B, drying to obtain a composite material, and then performing high-temperature treatment on the composite material, and washing to remove water-soluble inorganic salt to obtain a porous silicon-carbon composite material precursor;
(4) coating amorphous carbon on the porous silicon-carbon composite material precursor;
the silicon-based material in the step (1) is prepared by respectively forming steam from silicon and/or silicon oxide and reducing substances under the conditions of high temperature and vacuum for reaction and carrying out in-situ doping; the reducing substance is one or the combination of more than two of simple substances of alkali metal, alkaline earth metal, third main group element and transition metal element, oxides thereof and alloys thereof, wherein at least one is alloy and the alloy accounts for more than 30wt% of the reducing substance;
the alloy is an alloy of magnesium and other metals, and the magnesium accounts for more than 30wt% of the alloy.
2. The porous silicon carbon composite material according to claim 1, wherein the alloy accounts for 40wt% or more of the reduced matter.
3. The porous silicon carbon composite material according to claim 1, wherein the alloy accounts for 50wt% or more of the reduced matter.
4. The porous silicon carbon composite material of claim 1, wherein the oxide of silicon has the chemical formula SiOxWherein 0 is<x is less than or equal to 2; the cation element of the silicate is one or more of lithium, sodium, magnesium, calcium, aluminum, nickel, cobalt, iron and manganese.
5. The porous silicon-carbon composite material of claim 1, wherein the carbon material is one or more of flake graphite, crystalline graphite, mesocarbon microbeads, hard carbon, soft carbon, graphene, carbon nanotubes, carbon nanowires, carbon fibers.
6. The porous silicon carbon composite material of claim 1, wherein the silicate is present in an amount of 10% to 20% by mass based on 100% by mass of the porous silicon carbon composite material.
7. The porous silicon-carbon composite material of claim 1, wherein the mass ratio of the silicon-based material to the carbon material is 3-10: 2-7.
8. The porous silicon-carbon composite material of claim 7, wherein the mass ratio of the silicon-based material to the carbon material is 5-7: 3-5.
9. The porous silicon carbon composite of claim 1, wherein the alloy is selected from the group consisting of magnesium lithium alloys, magnesium sodium alloys, magnesium calcium alloys, magnesium aluminum alloys, magnesium manganese alloys.
10. The porous silicon carbon composite material of claim 1, wherein the high temperature vacuum is performed in a vacuum furnace with a deposition system having one or more heating chambers; the caliber of the gas path for the gas of the heating cavity to enter the deposition system is adjustable, and the SiO gas enters the deposition systemxWherein 0 is<x≤2，SiOxThe steam and the steam of the reducing substance have a volume ratio of 100: 1-20.
11. The porous silicon carbon composite of claim 10, wherein the SiO entering the deposition systemxThe volume ratio of the steam to the steam of the reducing substance is 100: 5-15.
12. The porous silicon-carbon composite material of claim 1, wherein the water-soluble inorganic salt comprises a carbonate, bicarbonate, and sulfate salt of sodium or potassium metal.
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