CN114613955A - Graphene modified silicon negative electrode material and preparation method and application thereof - Google Patents

Graphene modified silicon negative electrode material and preparation method and application thereof Download PDF

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CN114613955A
CN114613955A CN202210220183.2A CN202210220183A CN114613955A CN 114613955 A CN114613955 A CN 114613955A CN 202210220183 A CN202210220183 A CN 202210220183A CN 114613955 A CN114613955 A CN 114613955A
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CN114613955B (en
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谢英朋
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Eve Energy Co Ltd
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    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H—ELECTRICITY
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Abstract

The invention provides a graphene modified silicon negative electrode material and a preparation method and application thereof, wherein the preparation method comprises the following steps: and mixing the aminated nano silicon source with the sulfonated graphene, and performing spray drying to obtain the graphene modified silicon anode material. According to the preparation method, the aminated nano silicon source and the sulfonated graphene are mixed, the graphene modified silicon negative electrode material is prepared in a spray drying mode, amino contained in the nano silicon source reacts with sulfonic acid groups of the graphene to generate sulfonamide, so that the graphene and the nano silicon are connected through covalent bonds, the compactness and uniformity of graphene coating are improved, the volume expansion of silicon is effectively reduced, and the rate capability and the cycle performance of the battery are improved.

Description

Graphene modified silicon negative electrode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of batteries, and relates to a graphene modified silicon negative electrode material, and a preparation method and application thereof.
Background
Lithium ion batteries are considered to be a green power source suitable for portable electronic products and electric vehicles, and therefore, it is important to develop advanced lithium ion batteries with high energy density, high cycle performance, and low cost to meet the increasing demand of next-generation energy storage devices. Silicon has an ultra-high theoretical specific capacity (corresponding to Li)4.44200mAh/g of Si), which is generally considered as one of the most promising anode materials, however, the silicon anode has low ion diffusion and poor conductivity, and particularly has large volume expansion (about 400%) during delithiation and lithium intercalation, eventually leading to a drastic drop in the capacity of the material, hindering its application. Meanwhile, volume expansion inevitably causes cracking of an unstable Solid Electrolyte Interphase (SEI) layer, resulting in rapid capacity fading and poor rate capability of the material. In recent years, attempts have been made to solve these problemsMany efforts have been made to complex graphene with silicon in a more efficient manner.
Graphene (Graphene) is sp2The hybridized and connected carbon atoms are tightly stacked to form a new material with a single-layer two-dimensional honeycomb lattice structure, and the new material has excellent optical, electrical and mechanical properties. Graphene is used as a novel conductive agent, and due to the unique sheet structure (two-dimensional structure), the contact with an active substance is a point-surface contact rather than a conventional point-point contact form, so that the using amount of the conductive agent can be reduced, and the capacity of a lithium battery is improved. The preparation method comprises the steps of adding silicon powder and graphite micropowder into graphene oxide dispersion liquid, adding a dispersing agent, performing ultrasonic dispersion treatment to form suspension, performing spray drying and pelletizing on the obtained suspension, and performing heat treatment at 500-800 ℃ in a reducing atmosphere to obtain the silicon powder and graphite micropowder composite negative electrode material coated by graphene, so that the cycle performance of a single silicon material is improved. CN107910513A discloses a graphene/silicon composite lithium ion battery cathode and a preparation method thereof, wherein a current collector is provided with a multilayer structure in which a graphene layer and a silicon/carbon nanotube layer are matched, graphene and a carbon tube are used to successfully wrap silicon nanoparticles, and a special layered structure is used to improve the volume effect of a silicon material in the charge and discharge processes and improve the conductivity and cycle performance of the material. CN111403723A provides a preparation method of a silicon-carbon negative electrode composite material, which comprises the steps of adding silicon powder into a graphene oxide suspension, mixing, drying, and roasting at 600-1200 ℃ for 1-5 h in an inert atmosphere to obtain the silicon-carbon negative electrode composite material, wherein the stability of the material is improved.
In the prior art, graphene and silicon materials are combined in various ways to improve the electrochemical performance of silicon, but in the technical scheme, the coating compactness and the uniformity of graphene are poor, so that an electrolyte solution is contacted with silicon to form an SEI (solid electrolyte interface) film due to poor coating compactness, and the rate performance of a battery can be reduced due to poor uniformity; in addition, in the circulation process, the graphene is easily spread due to huge volume expansion of silicon, so that exposed silicon is in contact with electrolyte, more SEI films are formed, active lithium is consumed, and the circulation performance is poor.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a graphene modified silicon negative electrode material and a preparation method and application thereof. According to the preparation method, the aminated nano silicon source and the sulfonated graphene are mixed, the graphene modified silicon negative electrode material is prepared in a spray drying mode, amino contained in the nano silicon source reacts with sulfonic acid groups of the graphene to generate sulfonamide, so that the graphene and the nano silicon are connected through covalent bonds, the compactness and uniformity of graphene coating are improved, the volume expansion of silicon is effectively reduced, and the rate capability and the cycle performance of the battery are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a preparation method of a graphene modified silicon negative electrode material, which comprises the following steps:
and mixing the aminated nano silicon source with sulfonated graphene, and performing spray drying to obtain the graphene modified silicon negative electrode material.
According to the invention, the aminated nano silicon source and the sulfonated graphene are mixed, and the graphene modified silicon negative electrode material is prepared in a spray drying manner, so that the prepared material has good rate capability and cycle performance.
The technical principle of the invention is as follows: firstly, amino groups on a nano silicon source react with sulfonic groups on sulfonated graphene to form sulfonamide, so that the graphene can uniformly coat nano silicon, compared with the traditional coating means, the coating layer prepared by the chemical reaction coating method is more compact and uniform, the phenomenon that an electrolyte Solution (SEI) film is formed by direct contact of the electrolyte solution and silicon can be reduced, and the rate capability of a battery can be improved; secondly, the graphene and the nano-silicon are connected through covalent bonds by the chemical reaction coating method, and when the silicon undergoes huge volume expansion, the graphene is tightly adhered to the surface of the silicon cathode, so that the volume expansion rate of the silicon cathode is reduced, and the cycle performance of the battery is improved; thirdly, the aminated nano silicon source is adopted to react with the sulfonated graphene, the aminated nano silicon source has higher reactivity, is more favorable for the reaction with the sulfonated graphene, has better matching effect with the sulfonated graphene, and has better rate capability and cycle performance, meanwhile, the addition of the graphene reduces the using amount of a conductive agent, and the energy density of the battery is improved.
Preferably, the molar ratio of the aminated nano silicon source to the sulfonated graphene is (1-30): 1, and may be, for example, 1:1, 2:1, 4:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, 22:1, 24:1, 26:1, 28:1 or 30:1, and preferably (20-30): 1.
The aminated nano silicon source and the sulfonated graphene have the most appropriate proportion, the proportion is too low, the aminated nano silicon content is low, the energy density of the battery can be reduced, the proportion is too high, the sulfonated graphene content is low, the thickness of a coating layer is small, the buffer layer is difficult to play a buffering role, and the buffer layer is easy to be propped open by silicon expansion.
Preferably, the aminated nano silicon source is aminated nano silicon.
As a preferable technical scheme of the preparation method, the aminated nano silicon is prepared in the following way:
stirring the nano silicon in an acid solution, drying, mixing with a first solvent and a second solvent, and heating to obtain the aminated nano silicon.
Preferably, the particle size D50 of the nano-silicon is 5-80 nm, for example, 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm or 80nm, preferably 28-32 nm.
In the invention, the nano silicon with a specific particle size is preferably adopted to prepare the aminated nano silicon to participate in the reaction with the sulfonated graphene, the nano silicon with the particle size of 5-80 nm has higher activity and is easier to aminate, the aminated product has higher activity, and the aminated product has good bonding performance with the sulfonated graphene and good dispersibility. Preferably, the acid solution comprises a HCl solution.
Illustratively, the content of the solute in the acid solution is 20 to 30%, for example, 20%, 22%, 24%, 26%, 28%, 30%, or the like, based on 100% by mass of the acid solution.
The drying temperature is, for example, 60 to 80 ℃ and may be, for example, 60 ℃, 62 ℃, 64 ℃, 66 ℃, 68 ℃, 70 ℃, 72 ℃, 74 ℃, 76 ℃, 78 ℃ or 80 ℃.
Preferably, the first solvent comprises toluene, which acts as a dispersing solvent for the nano-silicon, and the amount of the first solvent is 1 (1-10) by mass of the nano-silicon to toluene, and may be, for example, 1:1, 1:2, 1:4, 1:6, 1:8, or 1: 10.
Preferably, the second solvent includes 3-Aminopropyltriethoxysilane (APTES) as a reactant for amination of the nanosilicon.
Preferably, the molar ratio of the nano-silicon to the second solvent is 1 (0.2-5), and may be, for example, 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, or the like.
Preferably, the heating temperature is 80-120 ℃, for example, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃ or 120 ℃, and the time is 6-24 h, for example, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24 h.
Preferably, the gas in the heated atmosphere comprises nitrogen.
The aminated nano-silicon prepared by the preparation method is more suitable for being combined with sulfonated graphene, and the aminated nano-silicon and the sulfonated graphene have better electrochemical properties under the synergistic effect.
In a preferred embodiment of the preparation method of the present invention, the particle size D50 of the sulfonated graphene is 1.2 to 4 μm, and may be, for example, 1.2 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, or 4 μm.
Preferably, the number of sulfonated graphene layers is less than 5, for example, the number of sulfonated graphene layers may be 1, 2, 3 or 4, preferably 2 to 4.
In the invention, sulfonated graphene with a specific size is preferred, when the particle size D50 of the sulfonated graphene is smaller, the sulfonated graphene is not beneficial to the dispersion and easy agglomeration with the aminated nano-silicon, and the size of the sulfonated graphene is not suitable to be changed in a larger range, otherwise, the sulfonated graphene is not beneficial to being matched with the aminated nano-silicon; meanwhile, the number of the sulfonated graphene layers is preferably 2 or more and 4 or less, the volume expansion cannot be inhibited when the sulfonated graphene is thin, and the sulfonated graphene is not beneficial to the transmission of lithium ions when the sulfonated graphene is thick.
Preferably, a third solvent and a catalyst are further added during the mixing of the aminated silicon source and the sulfonated graphene.
Preferably, the third solvent comprises thionyl chloride.
Preferably, the catalyst comprises N, N-Dimethylformamide (DMF).
Illustratively, the amount of catalyst added may be 0.5 to 2mL, for example, 0.5mL, 0.8mL, 1mL, 1.2mL, 1.5mL, 1.8mL, or 2mL, and the like.
Preferably, the temperature for mixing the aminated silicon source and the sulfonated graphene is 60-100 ℃, for example, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃ or 100 ℃.
Preferably, the mixing time of the aminated silicon source and the sulfonated graphene is 12-36 h, for example, 12h, 15h, 20h, 25h, 30h, 35h or 36 h.
Preferably, the mixing of the aminated silicon source and the sulfonated graphene is performed in a nitrogen atmosphere.
In a preferred embodiment of the preparation method of the present invention, the inlet temperature of the spray drying is 150 to 300 ℃, and may be, for example, 150 ℃, 180 ℃, 200 ℃, 220 ℃, 240 ℃, 260 ℃, 280 ℃, or 300 ℃.
Preferably, the outlet temperature of the spray drying is 110 to 190 ℃, and may be, for example, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃ or the like.
As a preferable technical scheme of the preparation method of the invention, the preparation method comprises the following steps:
(1) stirring nano silicon with the particle size D50 of 5-80 nm in an acid solution, drying at 60-80 ℃, mixing with a first solvent and a second solvent, and heating at 80-120 ℃ for 6-24 hours to obtain aminated nano silicon;
(2) performing ultrasonic dispersion on the aminated nano silicon and a third solvent in the step (1), adding 0.5-2 mL of catalyst, dropwise adding sulfonated graphene with the particle size D50 of 1.2-4 mu m at the temperature of 60-100 ℃ in a nitrogen atmosphere, wherein the molar ratio of the aminated nano silicon to the sulfonated graphene is (20-30): 1, and mixing for 12-36 h to obtain a mixed solution;
(3) and (3) carrying out spray drying on the mixed solution obtained in the step (2), wherein the inlet temperature of the spray drying is 150-300 ℃, and the outlet temperature of the spray drying is 110-190 ℃, so as to obtain the graphene modified silicon negative electrode material.
In a second aspect, the invention provides a graphene modified silicon negative electrode material, which is prepared by the preparation method according to the first aspect, and comprises graphene and silicon loaded on the surface of the graphene.
In the graphene modified silicon negative electrode material prepared by the invention, graphene and silicon are connected through a covalent bond, and the graphene is coated more uniformly and compactly, so that the volume expansion of a silicon negative electrode can be reduced, and the graphene modified silicon negative electrode material has better stability.
In a third aspect, the invention provides a lithium ion battery, wherein a negative electrode of the lithium ion battery comprises the graphene modified silicon negative electrode material according to the first aspect.
The lithium ion battery prepared by the invention has higher energy density and better cycle performance.
Compared with the prior art, the invention has the following beneficial effects:
according to the preparation method, the aminated nano silicon source and the sulfonated graphene are mixed, the graphene modified silicon negative electrode material is prepared in a spray drying mode, amino contained in the nano silicon source reacts with sulfonic acid groups of the graphene to generate sulfonamide, so that the graphene and the nano silicon are connected through covalent bonds, the compactness and uniformity of graphene coating are improved, the volume expansion of silicon is effectively reduced, and the rate capability and the cycle performance of the battery are improved.
Drawings
Fig. 1 is a flow chart of a preparation method of a graphene-modified silicon negative electrode material according to an embodiment of the present invention.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The embodiment of the invention provides a preparation method of a graphene modified silicon negative electrode material, which comprises the following steps:
and mixing the aminated nano silicon source with sulfonated graphene, and performing spray drying to obtain the graphene modified silicon negative electrode material.
In some embodiments, the molar ratio of the aminated nano-silicon source to the sulfonated graphene is (1-30): 1, preferably (20-30): 1.
In some embodiments, the aminated nano-silicon source is aminated nano-silicon.
In some embodiments, the aminated nano-silicon is prepared as follows:
stirring the nano silicon in an acid solution, drying, mixing with a first solvent and a second solvent, and heating to obtain the aminated nano silicon.
In some embodiments, the nano silicon has a particle size D50 of 5 to 80nm, preferably 28 to 32 nm.
In some embodiments, the acid solution comprises a HCl solution.
In some embodiments, the first solvent comprises toluene.
In some embodiments, the second solvent comprises 3-aminopropyltriethoxysilane.
In some embodiments, the molar ratio of the nano-silicon to the second solvent is 1 (0.2-5).
In some embodiments, the heating temperature is 80-120 ℃ and the heating time is 6-24 h.
In some embodiments, the gas in the heated atmosphere comprises nitrogen.
In some embodiments, the sulfonated graphene has a particle size D50 of 1.2 to 4 μm.
In some embodiments, the number of layers of sulfonated graphene is less than 5.
In some embodiments, the number of layers of sulfonated graphene is 2 to 4.
In some embodiments, a third solvent and a catalyst are also added during the mixing of the aminated silicon source with the sulfonated graphene.
In some embodiments, the third solvent comprises thionyl chloride.
In some embodiments, the catalyst comprises N, N-Dimethylformamide (DMF).
In some embodiments, the temperature at which the aminated silicon source is mixed with the sulfonated graphene is 60-100 ℃.
In some embodiments, the aminated silicon source is mixed with the sulfonated graphene for a time period ranging from 12 to 36 hours.
In some embodiments, the mixing of the aminated silicon source with the sulfonated graphene is performed in a nitrogen atmosphere.
In some embodiments, the inlet temperature of the spray drying is 150 to 300 ℃.
In some embodiments, the spray-dried outlet temperature is 110 to 190 ℃.
In some embodiments, a flow diagram of the method of making is shown in fig. 1, comprising:
(1) stirring nano silicon with the particle size D50 of 5-80 nm in an acid solution, drying at 60-80 ℃, mixing with a first solvent and a second solvent, and heating at 80-120 ℃ for 6-24 hours to obtain aminated nano silicon;
(2) carrying out ultrasonic dispersion on the aminated nano silicon and a third solvent in the step (1), adding 0.5-2 mL of catalyst, dropwise adding sulfonated graphene with the particle size D50 of 1.2-4 mu m at the temperature of 60-100 ℃ in a nitrogen atmosphere, wherein the molar ratio of the aminated nano silicon to the sulfonated graphene is (20-30): 1, and mixing for 12-36 h to obtain a mixed solution;
(3) and (3) carrying out spray drying on the mixed solution obtained in the step (2), wherein the inlet temperature of the spray drying is 150-300 ℃, and the outlet temperature of the spray drying is 110-190 ℃, so as to obtain the graphene modified silicon negative electrode material.
Example 1
The embodiment provides a graphene modified silicon negative electrode material and a preparation method thereof, the graphene modified silicon negative electrode material comprises graphene and silicon loaded on the surface of the graphene, and the preparation method comprises the following steps:
(1) stirring nano silicon with the particle size D50 of 30nm in 25% HCl solution at room temperature for 1h, then drying in vacuum at 70 ℃ for 5h, placing the dried product in anhydrous toluene for ultrasonic treatment for 1h, adding APTES, reacting in 100 ℃ nitrogen atmosphere for 15h, centrifuging and washing with anhydrous toluene to obtain aminated nano silicon (marked as nano Si-NH)2)；
(2) Subjecting the nano Si-NH in the step (1)2Performing ultrasonic dispersion with thionyl chloride, adding 1.5mL of N, N-Dimethylformamide (DMF) catalyst, and dropwise adding sulfonated graphene and nano Si-NH with 2-4 layers and a particle size D50 of 2.5 mu m at 80 ℃ in a nitrogen atmosphere2Reacting for 20 hours to obtain a mixed solution, wherein the molar ratio of the sulfonated graphene to the sulfonated graphene is 25: 1;
(3) and (3) carrying out spray drying on the mixed solution obtained in the step (2), wherein the inlet temperature of the spray drying is 250 ℃, and the outlet temperature of the spray drying is 150 ℃, so as to obtain the graphene modified silicon negative electrode material.
Example 2
The embodiment provides a graphene modified silicon negative electrode material and a preparation method thereof, the graphene modified silicon negative electrode material comprises graphene and silicon loaded on the surface of the graphene, and the preparation method comprises the following steps:
(1) stirring nano silicon with the particle size D50 of 60nm in 30% HCl solution at room temperature for 1h, then drying in vacuum at 70 ℃ for 5h, placing the dried product in anhydrous toluene for ultrasonic treatment for 1h, adding APTES, reacting in nitrogen atmosphere at 120 ℃ for 10h, centrifuging and washing with anhydrous toluene to obtain nano Si-NH2；
(2) Subjecting the nano Si-NH in the step (1)2Performing ultrasonic dispersion with thionyl chloride, adding 2mL of DMF catalyst, and dropwise adding sulfonated graphene with 2-4 layers and 4 mu m of particle size D50 and nano Si-NH at 120 ℃ in a nitrogen atmosphere2And sulfonated graphene in a molar ratio of 20:1, reacting for 10 hours to obtain a mixed solution;
(3) and (3) carrying out spray drying on the mixed solution obtained in the step (2), wherein the inlet temperature of the spray drying is 150 ℃, and the outlet temperature of the spray drying is 190 ℃, so as to obtain the graphene modified silicon negative electrode material.
Example 3
The embodiment provides a graphene modified silicon negative electrode material and a preparation method thereof, the graphene modified silicon negative electrode material comprises graphene and silicon loaded on the surface of the graphene, and the preparation method comprises the following steps:
(1) stirring nano silicon with the particle size D50 of 10nm in 20% HCl solution at room temperature for 1h, then drying in vacuum at 70 ℃ for 5h, placing the dried product in anhydrous toluene for ultrasonic treatment for 1h, adding APTES, reacting in nitrogen atmosphere at 80 ℃ for 24h, centrifuging and washing with anhydrous toluene to obtain nano Si-NH2；
(2) Subjecting the nano Si-NH in the step (1)2Performing ultrasonic dispersion with thionyl chloride, adding 0.5mL of DMF catalyst, and dropwise adding sulfonated graphene with 2-4 layers and a particle size D50 of 1.2 mu m and nano Si-NH at the temperature of 60 ℃ in a nitrogen atmosphere2Reacting for 20 hours to obtain a mixed solution, wherein the molar ratio of the sulfonated graphene to the sulfonated graphene is 30: 1;
(3) and (3) carrying out spray drying on the mixed solution obtained in the step (2), wherein the inlet temperature of the spray drying is 300 ℃, and the outlet temperature of the spray drying is 110 ℃, so as to obtain the graphene modified silicon negative electrode material.
Example 4
Removing the nano Si-NH in the step (2)2And sulfonated graphene in a molar ratio of 10:1, the remainder being identical to example 1.
Example 5
Removing the nano Si-NH in the step (2)2And sulfonated graphene in a molar ratio of 32:1, the remainder being identical to example 1.
Example 6
The procedure of example 1 was repeated, except that the particle diameter D50 of the nano-silicon in step (1) was 5 nm.
Example 7
The procedure of example 1 was repeated, except that the particle diameter D50 of the nano-silicon in step (1) was 80 nm.
Example 8
The procedure of example 1 was repeated, except that the particle size D50 of the sulfonated graphene in step (2) was 0.5. mu.m.
Example 9
The procedure of example 1 was repeated except that the particle size D50 of the sulfonated graphene in step (2) was 5 μm.
Example 10
The method is the same as that in the embodiment 1 except that the number of the sulfonated graphene layers in the step (2) is 8-10.
Example 11
The procedure of example 1 was repeated, except that the inlet temperature of the spray-drying in step (3) was 120 ℃.
Example 12
The procedure of example 1 was repeated, except that the inlet temperature of the spray-drying in step (3) was 350 ℃.
Comparative example 1
The process is the same as example 1 except that the step (1) is not performed, that is, the nano silicon and the sulfonated graphene are directly used for reaction in the step (2).
Comparative example 2
The procedure of example 1 was repeated except that the sulfonated graphene in step (2) was replaced with graphene.
Comparative example 3
Except that the operation of step (1) will not be performed, and the nano Si-NH in step (2) will be performed2The procedure of example 1 was repeated except that the amino group-containing silicone oil was used instead.
Preparation of pole piece and lithium ion battery
(1) Preparing a negative pole piece: dissolving the graphene modified silicon negative electrode material, graphite, a conductive agent SP and a binder PAA which are prepared in the examples and the comparative examples in a solvent according to the mass percentage of 8:88.5:0.5:3, mixing to obtain slurry, controlling the solid content of the slurry to be 55%, coating the slurry on a copper foil current collector, and drying in vacuum to obtain a negative electrode plate.
(2) Preparing a lithium ion battery: mixing the negative pole piece, the positive pole piece and 1mol/L LiPF6/EC+The soft package lithium ion battery is assembled by DMC + EMC (v/v is 1:1:1) electrolyte and Celgard2400 diaphragm, the active substance in the positive pole piece is NCM523, and the content of the active substance is 94 wt%.
Second, performance test
(1) And (3) testing the expansion rate of the full-electric negative pole piece: the negative pole pieces prepared by the materials in the examples and the comparative examples are subjected to expansion rate test, the battery is charged to 0.5C CC CV to 4.2V, the cut-off is 0.05C, then the thickness of the negative pole piece is measured by disassembling a caliper, the thickness of the negative pole piece is compared with the thickness of the negative pole piece before the battery is assembled, the full-electricity expansion rate of the negative pole is calculated, and the test results are shown in Table 1.
(2) Capacity retention rate test: the lithium ion batteries prepared by using the materials in the examples and the comparative examples are tested on a LAND battery test system of Wuhanjinnuo electronic Co., Ltd, and the charging and discharging voltage is limited to 2.5V-4.2V.
The cycle test procedure is as follows: charging to 0.5C CC CV to 4.2V at 45 deg.C, stopping at 0.05C, and standing for 10 min; discharging 1C DC to 2.5V, recording the initial discharge capacity of the battery and the discharge capacity of 900 weeks after cycling for 900 weeks, and obtaining the capacity retention rate of 900 weeks by dividing the discharge capacity of 900 weeks by the initial discharge capacity, wherein the test results are shown in Table 1.
The multiplying power discharge process comprises the following steps: charging to 1C CC CV to 4.2V at 25 deg.C, stopping at 0.05C, and standing for 10 min; the discharge capacity was divided by the charge capacity to obtain capacity retention rates of 1C/1C, 1C/3C and 1C/5C, respectively, at 1C, 3C and 5C DC to 2.5V, respectively, and the test results are shown in Table 1.
TABLE 1
Figure BDA0003536790970000131
Figure BDA0003536790970000141
To sum up, the embodiments 1 to 12 show that the method prepares the graphene modified silicon negative electrode material by mixing the aminated nano silicon source with the sulfonated graphene and matching with a spray drying mode, and the amino group contained in the nano silicon source reacts with the sulfonic group of the graphene to generate sulfonamide, so that the graphene and the nano silicon are connected by a covalent bond, the compactness and the uniformity of graphene coating are improved, the volume expansion of silicon is effectively reduced, and the rate capability and the cycle performance of the battery are improved.
From the comparison between example 1 and examples 4 to 5, it can be seen that the nano Si-NH in the present invention2The proportion of the sulfonated graphene to the graphene can influence the comprehensive performance of the graphene modified silicon negative electrode material; when nano Si-NH2When the content is lower, the energy density of the battery can be reduced, and simultaneously, the graphene mostly causes steric hindrance effect, so that the rate capability and the cycle performance are poor, and when the content is lower, the nano Si-NH is used as the material2When the content is higher, the sulfonated graphene is difficult to have a good coating effect on the silicon cathode, and the expansion of the silicon cathode causes the graphene of the surface coating layer to be spread, so the rate performance and the cycle performance of the embodiments 4-5 are slightly inferior to those of the embodiment 1.
By comparing the embodiment 1 with the embodiments 6 to 10, it can be known that the size and the number of layers of the nano silicon and the sulfonated graphene can affect the comprehensive performance of the graphene modified silicon negative electrode material; when the size of the nano silicon is larger, the silicon expansion is too large, and when the size of the nano silicon is smaller, the nano silicon is not dispersed; when the size of the graphene is too large, the lithium ion transmission path is enlarged, when the size of the graphene is too small, the specific surface area is large, the dispersion is difficult, and more active lithium is easily consumed, and when the number of graphene layers is too large, the lithium ion transmission path is enlarged, so that the rate performance and the cycle performance of example 1 are optimal.
As can be seen from the comparison between example 1 and examples 11 to 12, the temperature of the spray drying in the present invention affects the overall performance of the graphene-modified silicon negative electrode material; too low a spraying temperature leads to poor dispersibility of the material, and too high a spraying temperature leads to decomposition of the material.
As can be seen from the comparison between example 1 and comparative examples 1-2, in the present invention, when the nano silicon source does not have an amino group or the graphene does not have a sulfonic group, the graphene and the nano silicon cannot be covalently connected, and cannot be combined with a carboxyl group and/or a hydroxyl group on the nano silicon to generate a hydrogen bond, so that the coating uniformity and the compactness are poor, and therefore, the expansion rate of the electrode sheet of comparative examples 1-2 is too high, and the capacity retention rate is also significantly lower than that of example 1.
It can be seen from the comparison between example 1 and comparative example 3 that the graphene modified silicon negative electrode material prepared by reacting the specific aminated nano silicon source with the sulfonated graphene in the present invention has the best performance, and when the amino silicone oil is used, the amino silicone oil has a high oxygen content, which reduces the energy density of the battery, and the amino silicone oil has a poorer conductivity, so the rate capability and cycle performance of comparative example 3 are inferior to those of example 1.
The above description is only for the specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the protection scope and the disclosure of the present invention.

Claims (10)

1. A preparation method of a graphene modified silicon negative electrode material is characterized by comprising the following steps:
and mixing the aminated nano silicon source with the sulfonated graphene, and performing spray drying to obtain the graphene modified silicon anode material.
2. The preparation method according to claim 1, wherein the molar ratio of the aminated nano silicon source to the sulfonated graphene is (1-30): 1, preferably (20-30): 1.
3. The method according to claim 1 or 2, wherein the aminated nano-silicon source is aminated nano-silicon.
4. The preparation method according to claim 3, wherein the aminated nano-silicon is prepared as follows:
stirring the nano silicon in an acid solution, drying, mixing with a first solvent and a second solvent, and heating to obtain aminated nano silicon;
preferably, the particle size D50 of the nano silicon is 5-80 nm, preferably 28-32 nm;
preferably, the acid solution comprises a HCl solution;
preferably, the first solvent comprises toluene;
preferably, the second solvent comprises 3-aminopropyltriethoxysilane;
preferably, the molar ratio of the nano silicon to the second solvent is 1 (0.2-5);
preferably, the heating temperature is 80-120 ℃, and the time is 6-24 h;
preferably, the gas in the heated atmosphere comprises nitrogen.
5. The preparation method according to any one of claims 1 to 4, wherein the particle size D50 of the sulfonated graphene is 1.2 to 4 μm;
preferably, the number of sulfonated graphene layers is less than 5, and preferably 2-4.
6. The preparation method according to any one of claims 1 to 5, wherein a third solvent and a catalyst are further added during the mixing of the aminated silicon source and the sulfonated graphene;
preferably, the third solvent comprises thionyl chloride;
preferably, the catalyst comprises N, N-dimethylformamide;
preferably, the mixing temperature of the aminated silicon source and the sulfonated graphene is 60-100 ℃;
preferably, the mixing time of the aminated silicon source and the sulfonated graphene is 12-36 h;
preferably, the mixing of the aminated silicon source and the sulfonated graphene is performed in a nitrogen atmosphere.
7. The method according to any one of claims 1 to 6, wherein the inlet temperature of the spray drying is 150 to 300 ℃;
preferably, the outlet temperature of the spray drying is 110-190 ℃.
8. The production method according to any one of claims 1 to 7, characterized by comprising:
(1) stirring nano silicon with the particle size D50 of 5-80 nm in an acid solution, drying at 60-80 ℃, mixing with a first solvent and a second solvent, and heating at 80-120 ℃ for 6-24 hours to obtain aminated nano silicon;
(2) carrying out ultrasonic dispersion on the aminated nano silicon and a third solvent in the step (1), adding 0.5-2 mL of catalyst, dropwise adding sulfonated graphene with the particle size D50 of 1.2-4 mu m at the temperature of 60-100 ℃ in a nitrogen atmosphere, wherein the molar ratio of the aminated nano silicon to the sulfonated graphene is (20-30): 1, and mixing for 12-36 h to obtain a mixed solution;
(3) and (3) carrying out spray drying on the mixed solution obtained in the step (2), wherein the inlet temperature of the spray drying is 150-300 ℃, and the outlet temperature of the spray drying is 110-190 ℃, so as to obtain the graphene modified silicon negative electrode material.
9. The graphene-modified silicon negative electrode material is prepared by the preparation method according to any one of claims 1 to 8, and comprises graphene and silicon loaded on the surface of the graphene.
10. A lithium ion battery, wherein the graphene-modified silicon negative electrode material according to claim 9 is included in a negative electrode of the lithium ion battery.
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