CN116072872B - Silicon-carbon negative electrode material, preparation method thereof and lithium ion battery - Google Patents

Silicon-carbon negative electrode material, preparation method thereof and lithium ion battery Download PDF

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CN116072872B
CN116072872B CN202310084811.3A CN202310084811A CN116072872B CN 116072872 B CN116072872 B CN 116072872B CN 202310084811 A CN202310084811 A CN 202310084811A CN 116072872 B CN116072872 B CN 116072872B
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silicon
carbon
negative electrode
mofs
carbon composite
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CN116072872A (en
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闫泽
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Chongqing Talent New Energy Co Ltd
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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
    • H01M4/62—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
    • 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
    • H01M4/36—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
    • H01M4/36—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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • 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 relates to a silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery. The silicon-carbon negative electrode material comprises a silicon-carbon composite material and MOFs (metal oxide semiconductor field effect transistors) material; the MOFs material coats the silicon carbon composite and a portion of the silicon carbon composite is embedded in pores of the MOFs material; the silicon-carbon composite material is a mixture of a carbon-containing material and nano silicon. According to the invention, the MOFs material coats the silicon-carbon composite material, and part of the silicon-carbon composite material is embedded into the pores of the MOFs material, so that the volume expansion of silicon can be restrained without damaging the effective structure of the material, and the high specific capacity and long cycle performance are achieved. The preparation method of the negative electrode material is simple and convenient, high energy consumption is not needed, and the preparation of the high specific capacity material can be completed by using conventional equipment and conventional preparation environment.

Description

Silicon-carbon negative electrode material, preparation method thereof and lithium ion battery
Technical Field
The invention relates to the field of lithium batteries, in particular to a silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery.
Background
The current main current lithium battery cathode material is graphite, but the theoretical specific capacity of the graphite is lower and is 372mAh/g, and the current graphite material is basically developed to the limit capacity. The main research direction of the current lithium battery cathode is to replace a base material or add other high-capacity materials on the basis of a carbon-based material to improve the performance of the lithium battery.
The following methods for preparing a negative electrode material exist in the prior art. Graphite and nano silicon are fully ball-milled and mixed, asphalt and ball-milled composite material are calcined for 2 hours at 850 ℃ in nitrogen atmosphere, and high-temperature carbonized asphalt is coated on the carbon-silicon composite material to prepare a core-shell structure to inhibit the volume expansion of silicon, so that the material has high specific capacity and stable cycle performance. In the method, graphite and nano silicon are fully ground for 2 hours in a planetary ball mill, the ground carbon-silicon composite material is mixed with asphalt, and nitrogen is introduced into a tube furnace for fully burning for 2 hours. Asphalt is fully carbonized at the temperature, and the silicon-carbon material prepared in the first step is wrapped to form a core-shell structure, so that the anode material is successfully prepared.
However, in the preparation method, asphalt is carbonized by firing to cover the surface of the silicon-carbon material, so that the energy consumption is high in the preparation process, and the production cost is high for enterprise production. In addition, the silicon-carbon material is limited in the inner core through the asphalt hard structure, so that the problem of silicon volume expansion is solved to a certain extent, but the silicon cannot provide more effective capacity for the negative electrode due to the fact that the silicon is relatively not expanded. Further, although the hard carbon structure can buffer the problem of silicon volume expansion in a certain sense, if too much silicon is added, the expansion of the silicon cannot be completely inhibited due to the low hardness of the asphalt material, and the problem of damaging the material such as structural collapse and the like due to the silicon volume expansion still can be caused, so that the extremely rapid attenuation of reversible capacity can be caused, and the cycle performance of the material is reduced.
Disclosure of Invention
Problems to be solved by the invention
In view of the above, there is a need to provide a negative electrode material capable of suppressing the volume expansion of silicon even when a large amount of silicon is added, and a method for producing a negative electrode material which is low in energy consumption, easy in production process, and industrially producible.
Solution for solving the problem
The present inventors have conducted intensive studies to solve the above-mentioned problems and found that by coating a silicon-carbon composite material comprising a mixture of a carbonaceous material and nano-silicon with a MOFs material and embedding a part of the silicon-carbon composite material in pores of the MOFs material, volume expansion of silicon can be suppressed without damaging the effective structure of the material by the synergistic effect of the carbonaceous material and the MOFs material, thereby achieving a high specific capacity and long cycle performance. In addition, the preparation method of the negative electrode material is simple and convenient, high energy consumption is not needed, and the preparation of the material with high specific capacity can be completed by using conventional equipment and conventional preparation environment.
Specifically, the invention provides a silicon-carbon negative electrode material, which comprises a silicon-carbon composite material and MOFs (metal oxide semiconductor field effect transistors) material; the MOFs material coats the silicon carbon composite and a portion of the silicon carbon composite is embedded in pores of the MOFs material; the silicon-carbon composite material is a mixture of a carbon-containing material and nano silicon.
The silicon-carbon negative electrode material according to the above, wherein the mass ratio of the silicon-carbon composite material to the MOFs material is (1 to 10): 1, preferably (2 to 8): 1.
the silicon carbon negative electrode material according to the above, wherein the nano silicon has a particle size of 20 to 2000nm, preferably 20 to 60nm.
The silicon carbon negative electrode material according to the above, wherein the carbonaceous material is selected from graphite and/or a porous carbon material; the nano silicon is embedded in the pores of the porous carbon material;
preferably, the mass ratio of the graphite and/or porous carbon material to the nano-silicon is 5:1-20:1.
The silicon-carbon anode material according to the above, wherein the MOFs material has a three-dimensional structure, a pore size of 1-1000nm and a porosity of 1-80%.
The silicon-carbon negative electrode material according to the above, wherein the metal ions in the MOFs material are selected from at least one of Cu, zn and Co, and the organic ligand is selected from at least one of trimesic acid, terephthalic acid and dimethyl imidazole.
The silicon-carbon negative electrode material according to the above, wherein the porous carbon material has a pore diameter of 1-1000nm and a porosity of 1-80%.
The invention also provides a preparation method of the silicon-carbon anode material, which comprises the following steps:
step S1: mixing and grinding a carbon-containing material and nano silicon to obtain a silicon-carbon composite material;
step S2: mixing and grinding the silicon-carbon composite material and MOFs material, so as to obtain the silicon-carbon negative electrode material which is formed by coating the silicon-carbon composite material by the MOFs material and embedding part of the silicon-carbon composite material into holes of the MOFs material.
The preparation method according to the above, wherein in the step S1 and the step S2, the grinding comprises ball milling.
The preparation method is characterized in that in the step S1, the ball-material ratio is 10:1, the ball milling time is 2-8h, and the ball milling rotating speed is 200-600r/min;
in the step S2, the ball-material ratio is 10:1, the ball milling time is 2-4h, and the ball milling rotating speed is 100-500r/min.
The preparation method according to the above, wherein said step S1 and said step S2 are performed at room temperature.
The method of preparation according to the above, wherein the carbonaceous material is selected from graphite and/or porous carbon materials; the porous carbon material is obtained by burning a carbon source precursor at 600-1000 ℃.
The preparation method according to the above, wherein the carbon source precursor is selected from one or more of citric acid, cellulose, glucose, sucrose, xylan, lignin, starch, pectin.
The present invention further provides a lithium ion battery comprising a silicon carbon negative electrode material according to the above or a silicon carbon negative electrode material obtained by the preparation method according to the above.
ADVANTAGEOUS EFFECTS OF INVENTION
The technical scheme of the invention has the following beneficial effects:
(1) By coating the silicon-carbon composite material by MOFs and embedding a part of the silicon-carbon composite material into the pores of the MOFs material, the nano-silicon not only fully exerts the capacity advantage, but also can inhibit the collapse of the structure caused by the excessive expansion of the volume of the silicon, so that the capacity of the battery is extremely attenuated.
(2) Compared with the conventional graphite-based negative electrode material, the silicon-carbon negative electrode material provided by the invention has the advantages that the capacity is obviously improved, and the cycle times are obviously improved.
(3) The silicon-carbon negative electrode material can form a more stable SEI film, reduce repeated generation of the SEI film and seriously consume electrolyte, and improve the coulomb efficiency of a battery.
(4) The preparation method of the silicon-carbon anode material is simple, convenient, efficient and environment-friendly, and is a pollution-free environment-friendly production mode which can be industrialized.
Drawings
FIG. 1 shows that example 1 was conducted at 0.5 A.g -1 Cycling diagram at current density.
FIG. 2 shows that example 2 was conducted at 0.5 A.g -1 Cycling diagram at current density.
Fig. 3 shows a graph of the rate performance of example 1 at different current densities.
Fig. 4 shows a plot of the rate performance of example 2 at different current densities.
FIG. 5 shows that comparative example 1 was at 0.5 A.g -1 Cycling diagram at current density.
FIG. 6 shows that comparative example 2 was at 0.5 A.g -1 Cycling diagram at current density.
Fig. 7 shows a graph of the rate performance of comparative example 1 at different current densities.
Fig. 8 shows a graph of the rate performance of comparative example 2 at different current densities.
Fig. 9 shows a scanning electron microscope image of embodiment 1.
Fig. 10 shows a scanning electron microscope image of embodiment 1.
Detailed Description
The following describes embodiments of the present invention, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the invention as claimed, and embodiments obtained by appropriately combining the technical means disclosed in the different embodiments and the appropriate combination examples are also included in the technical scope of the present invention. All documents described in the present specification are incorporated by reference in the present specification.
Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
In the present specification, the numerical range indicated by the term "numerical value a to numerical value B" means a range including the end point numerical value A, B.
In the present specification, unless specifically stated otherwise, "a plurality" of "a plurality of" etc. means a numerical value of 2 or more.
In this specification, the terms "substantially", "substantially" or "substantially" mean that the error is less than 5%, or less than 3%, or less than 1% as compared to the relevant perfect or theoretical standard.
In the present specification, "%" means mass% unless otherwise specified.
In the present specification, if "room temperature", "normal temperature" or the like occurs, the temperature thereof may be generally 10 to 37℃or 15 to 35 ℃.
In the present specification, the meaning of "can" or "can" includes both the meaning of the presence or absence of both, and the meaning of both the treatment and the absence of both.
In this specification, "optional" and "optionally" mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
The term "comprising" in the description of the invention and the claims and in the above figures and any variants thereof is intended to cover a non-exclusive inclusion. For example, a process, method, or system, article, or apparatus that comprises a list of steps or elements is not limited to only those listed but may optionally include additional steps or elements not listed or inherent to such process, method, article, or apparatus.
Reference throughout this specification to "some/preferred embodiments," "an embodiment," etc., means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the elements may be combined in any suitable manner in the various embodiments.
< silicon carbon negative electrode Material >
In the invention, the MOFs structure locks the silicon-carbon composite material to provide a certain stress so as to improve the cycle performance and capacity of the battery. Specifically, by making a silicon-carbon composite material including a mixture of a carbonaceous material and nano-silicon coated with MOFs and embedding a portion of the silicon-carbon composite material into the pores of the MOFs material, it is possible to suppress the volume expansion of silicon without damaging the effective structure of the material, thereby achieving a high specific capacity and long cycle performance.
The silicon-carbon negative electrode material comprises a silicon-carbon composite material and MOFs (metal oxide semiconductor) materials, wherein the MOFs materials cover the silicon-carbon composite material and part of the silicon-carbon composite material is embedded into holes of the MOFs materials; the silicon-carbon composite material is a mixture of a carbon-containing material and nano silicon.
In the present invention, the silicon volume expansion is suppressed by coating the silicon carbon composite material with the MOFs material. In addition, the MOFs material has a three-dimensional structure and a certain macropores, so that an active site can be provided for subsequent preparation, and the silicon-carbon composite material occupies the pore space of the MOFs material, so that stress is further provided for inhibiting the volume expansion of silicon. In some embodiments of the invention, the MOFs material has a pore size of about 1-5nm and a porosity of 30%.
In the present invention, some, but not all, of the silicon carbon composite is embedded in the pores of the MOFs material. In some embodiments, 5 to 50 mass% of the silicon carbon composite is embedded in the pores of the MOFs material. In some preferred embodiments, 8 to 40 mass%, preferably 10 to 30 mass%, more preferably 10 to 20 mass% of the silicon carbon composite is embedded in the pores of the MOFs material.
In the silicon-carbon anode material, nano silicon is mixed with the carbon-containing material, the carbon-containing material plays a certain role in inhibiting the volume expansion of silicon, and the silicon-carbon composite material is coated by the MOFs material, so that the expansion of silicon is inhibited. Therefore, the volume expansion of silicon can be sufficiently restrained by the synergistic effect of MOFs material and carbon-containing material, and the cycle performance and capacity of the battery are improved.
In the present invention, the kind of MOFs material is not particularly limited as long as it satisfies the above-described structure. For example, the MOFs material may be selected from HKUST, ZIF-8, ZIF-67, etc., wherein the metal ion may be selected from Cu, co, zn, and the organic ligand may be selected from one or more of trimesic acid, terephthalic acid, and dimethyl imidazole.
In the invention, the mass ratio of the silicon-carbon composite material to the MOFs material is (1-10): 1, preferably (2-8): 1. the mass ratio of the two affects the coating of the silicon carbon composite material by the MOFs material and the amount of silicon carbon composite material embedded in the MOFs material. If the amount of MOFs material is too large, this results in an excessively thick coating layer that affects the capacity of the silicon-carbon composite, and in addition, the silicon-carbon composite may not fully occupy the pore space of the MOFs material, resulting in an inability to maximize the capacity. If the amount of the MOFs material is too small, the MOFs material cannot well coat the silicon-carbon composite, the effect of suppressing silicon expansion may be insufficient, and in addition, the silicon-carbon composite may not be moderately embedded in the pores of the MOFs material. In some preferred embodiments of the invention, the mass ratio of the silicon carbon composite material to the MOFs material may be (2-4): 1.
in the present invention, the selection of the particle size of the nano-silicon is very important. If the particle size of the nano-silicon is too large, the nano-silicon cannot be embedded into the three-dimensional structure of the MOF material, and the particle size of the nano-silicon needs to be matched with the pore size or the phase of the MOF material. If the particle size of the nano-silicon is too small, the cost is too high. In an embodiment of the invention, the nanosilicon has a particle size of 20-2000nm, preferably 20-60nm.
In the silicon carbon composite material of the present invention, the carbonaceous material is selected from graphite and/or a porous carbon material. Graphite is different from nano silicon in a mixed state due to a structural difference between the graphite and the porous carbon material. If the silicon-carbon composite material contains graphite, the nano silicon and the graphite are physically mixed; if the silicon-carbon composite material contains a porous carbon material, nano-silicon is embedded in the porous carbon material. In some preferred embodiments of the present invention, the silicon carbon composite comprises both graphite and a porous carbon material.
In the silicon-carbon composite material, the mass ratio of graphite and/or porous carbon material to nano silicon can be 5:1-20:1, preferably 8:1-12:1. if the nano-silicon content is too low, the negative electrode capacity may be low, and if the nano-silicon content is too high, the silicon volume may be excessively expanded.
In the invention, the pore diameter of the porous carbon material can be 1-1000nm, and the porosity is 1-80%.
According to the invention, the silicon-carbon composite material is coated by the MOFs material, and a part of the silicon-carbon composite material is embedded into the holes of the MOFs material, so that the capacity advantage of nano silicon is fully exerted, and the capacity of the battery is extremely attenuated due to structural collapse caused by excessive expansion of the volume of silicon. Compared with the conventional graphite-based negative electrode material, the silicon-carbon negative electrode material provided by the invention has the advantages that the capacity is obviously improved, and the cycle times are obviously improved. According to the invention, as the silicon has the effects of volume expansion and the like in the charge and discharge process, if the structure collapses, a new surface can be exposed, and then the structure contacts with electrolyte, so that a new SEI film can be correspondingly formed to consume the electrolyte, and the coulomb efficiency of the material is reduced. The MOFs material used in the present application forms a framework that is a framework that addresses the collapse of the silicon lattice, delaying or limiting the occurrence of this phenomenon to some extent. Therefore, the silicon-carbon negative electrode material can form a more stable SEI film, the repeated generation of the SEI film is reduced, the electrolyte is seriously consumed, and the coulomb efficiency of the battery is improved.
< preparation method of silicon carbon negative electrode Material >
The preparation method of the silicon-carbon anode material comprises the following steps:
step S1: mixing and grinding a carbon-containing material and nano silicon to obtain a silicon-carbon composite material;
step S2: mixing and grinding the silicon-carbon composite material and MOFs material, so as to obtain the silicon-carbon negative electrode material which is formed by coating the silicon-carbon composite material by the MOFs material and embedding part of the silicon-carbon composite material into holes of the MOFs material.
In the present invention, the step S1 and the step S2 may be performed at room temperature. Therefore, the preparation method of the silicon-carbon anode material does not need high energy consumption of heating to more than 700 ℃, and can finish the preparation of the material with high specific capacity only by using conventional equipment and conventional preparation environment.
According to the invention, the carbon-containing material and the nano silicon are mixed and ball-milled, so that the nano silicon is embedded into the holes of the porous carbon material, and then the obtained silicon-carbon composite material is mixed and ground with the MOFs material, so that the MOFs material coats the silicon-carbon composite material and a part of the silicon-carbon composite material can be embedded into the holes of the MOFs material.
In the step S1 and the step S2, the grinding includes ball milling. In the step S1, ball milling can be performed under the conditions that the ball-material ratio is 10:1, the ball milling time is 2-8h, and the rotating speed is 200-600r/min. In the step S2, ball milling can be performed under the conditions that the ball-material ratio is 10:1, the ball milling time is 2-4h, and the rotating speed is 100-500r/min.
In the present invention, the carbonaceous material is selected from graphite and/or porous carbon materials. The porous carbon material can be obtained by burning a carbon source precursor at 600-1000 ℃ and removing an impurity portion. The carbon source precursor is not particularly limited as long as a porous carbon material can be obtained. However, from the viewpoint of environmental friendliness, a material which is not liable to generate pollutants or a biomass material is preferably used. For example, the carbon source precursor may be selected from one or more of citric acid, cellulose, lignin, starch, vegetable proteins, pectin, xylan.
In the present invention, MOFs materials can be obtained by mixing trimesic acid with an organic salt and ball milling. Wherein the organic salt comprises one or more of copper acetate, zinc acetate, copper nitrate and zinc nitrate. The ball milling can be carried out under the conditions that the ball-material ratio is 10:1, the milling time is 1-2h and the rotating speed is 100-400 r/min. The product obtained by ball milling can be obtained by washing with ethanol and water and then vacuum drying.
< lithium ion Battery >
The invention also provides a lithium ion battery, which comprises the silicon-carbon anode material or the silicon-carbon anode material obtained by the preparation method.
Examples
The present invention will be described in detail by examples. The examples of embodiments are intended to illustrate the invention and are not to be construed as limiting the invention. The specific techniques or conditions are not identified in the examples and are performed according to techniques or conditions described in the literature in this field or according to the product specifications. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
Example 1
Preparation of silicon-carbon negative electrode material
1g of graphite and 0.1g of nano silicon powder (particle size is 20-60 nm) are weighed, put into a ball mill, the ball-material ratio is 10:1, the ball milling time is 1-2h, and the rotating speed is 100-400r/min, so that the silicon-carbon composite material is obtained.
Weighing 3g of copper acetate monohydrate, adding 2g of trimesic acid, putting into a ball mill, wherein the ball-material ratio is 10:1, the grinding time is 1-2h, and the rotating speed is 100-400r/min, thus obtaining HKUST-1.
The silicon-carbon composite material and MOFs material prepared by the method are mixed according to the mass ratio of 2:1, the silicon-carbon anode material is prepared by putting the silicon-carbon anode material into a ball mill according to the proportion of 1, wherein the ball-material ratio is 10:1, the grinding time is 1-2h, and the rotating speed is 100-400 r/min.
Preparation of negative plate and assembly of half battery
Weighing the following components in percentage by mass: 5:5, the silicon-carbon anode material, the conductive agent SP and the adhesive PAA are mixed with deionized water (the solid content of the slurry is 45%) which is 1.2 times of the weight of the materials, and the mixture is mechanically stirred on a magnetic stirrer for 12 hours, and the stirred slurry is slowly and uniformly coated on a copper foil.
And (3) putting the coated copper foil into a vacuum drying oven to be dried for 12 hours at 80 ℃, taking out the copper foil the next day, and cutting the copper foil into 12mm wafers for later use by using a Shenzherake crystal cutting machine.
The negative electrode sheet was transferred into a glove box in preparation for assembly of half cells. The 2032 battery shell, the PP diaphragm and the commercial LB315 electrolyte are used, the prepared electrode sheet is used as a negative electrode, the lithium sheet is used as a counter electrode to assemble a half battery, the assembled battery still needs to stand for 12 hours, and then an electrochemical test is carried out.
Electrochemical performance test
Different technical tests were performed by a new wilt electrical tester: the method comprises the steps of charge-discharge cycle and rate performance test. The test conditions were: constant temperature and humidity at 25 ℃ and voltage range of 0.01-1.5V;
0.5 A.g of example 1 -1 The results of capacity retention after 100 cycles are shown in Table 1 below, at 0.5 A.g -1 A cycle chart at current density is shown in fig. 1, and a ratio performance chart at different current densities is shown in fig. 3.
Example 2
In this example, the mass ratio of the silicon-carbon composite material to the MOFs material was changed to 4:1, and the other steps and conditions were the same as in example 1, and the negative electrode tab was prepared and the half cell composition and electrochemical performance test were performed by the same steps and conditions as in example 1.
0.5 A.g of example 2 -1 The results of capacity retention after 100 cycles are shown in Table 1 below, at 0.5 A.g -1 A cycle chart at current density is shown in fig. 2, and a ratio performance chart at different current densities is shown in fig. 4.
Example 3
In this example, the mass ratio of the silicon-carbon composite material to the MOFs material was changed to 8:1, and the other steps and conditions were the same as in example 1, and the negative electrode tab was prepared and the half cell composition and electrochemical performance test were performed by the same steps and conditions as in example 1.
The battery prepared in this example has higher cycle performance and rate performance similar to those of example 1.
Example 4
The nano-silicon used in this example had a particle size of 1000-2000nm, and other steps and conditions were the same as in example 1, and a negative electrode tab was prepared and a half cell composition and electrochemical performance test were performed by the same steps and conditions as in example 1.
The battery prepared in this example has higher cycle performance and rate performance similar to those of example 1.
Example 5
In this example a porous carbon material was used instead of graphite, wherein the porous carbon material was obtained by burning citric acid at 700 ℃ for 2 hours. Other steps and conditions were the same as in example 1, and a negative electrode tab was prepared, and the composition of a half cell and electrochemical performance test were performed by the same steps and conditions as in example 1.
The battery prepared in this example has higher cycle performance and rate performance similar to those of example 1.
Example 6
In this example, the amount of graphite added was 2g, and other steps and conditions were the same as in example 1, and a negative electrode sheet was prepared, and the composition of a half cell and electrochemical performance test were performed by the same steps and conditions as in example 1.
The battery prepared in this example has higher cycle performance and rate performance similar to those of example 1.
Example 7
In this example, the amount of graphite added was 0.5g, and the other steps and conditions were the same as in example 1, and a negative electrode sheet was prepared, and the composition of a half cell and electrochemical performance test were performed by the same steps and conditions as in example 1.
The battery prepared in this example has higher cycle performance and rate performance similar to those of example 1.
Comparative example 1
The graphite was directly used as a negative electrode, and a negative electrode tab was prepared, and the assembly of half cells and electrochemical performance test were performed by the same procedure and conditions as in example 1.
0.5 A.g of comparative example 1 -1 The results of capacity retention after 100 cycles are shown in Table 1 below, at 0.5 A.g -1 A cycle chart at current density is shown in fig. 5, and a ratio performance chart at different current densities is shown in fig. 7.
Comparative example 2
The negative electrode tab was prepared directly using nano silicon as a negative electrode by the same procedure and conditions as in example 1, and the assembly of half cells and electrochemical performance test were performed.
0.5 A.g of comparative example 2 -1 The results of capacity retention after 100 cycles are shown in Table 1 below, at 0.5 A.g -1 A cycle chart at current density is shown in fig. 6, and a ratio performance chart at different current densities is shown in fig. 8.
Table 1.0.5A g -1 Capacity retention after 100 cycles
The capacity retention rates of the respective examples can be seen from table 1, wherein the capacity retention rates in examples 1 and 2 are 78.62% and 74.45%. As can be seen from FIG. 1, the anode material prepared in example 1 has a higher specific capacity and cycle retention, wherein at 0.5 A.g -1 The specific capacity of the second discharge at the current density of (2) is 830.6 mAh.g -1 Specific capacity after 100 cycles is 653 mAh.g -1 The capacity retention was 78.62%. The capacity performance was far higher than that of the graphite of comparative example 1 in terms of cycle performance and specific capacity performance, as shown in FIG. 5 (the specific capacity after 100 cycles was 270.76mAh g -1 ) The cycling performance was also superior to that of the pure nano-silicon of comparative example 2, as shown in fig. 6 (100 cycles of the incomplete cycle).
As can be seen from FIG. 2, example 2 was madeThe prepared cathode material has higher specific capacity and cycle retention rate, wherein the specific capacity is 0.5Ag -1 The specific capacity of the second discharge at the current density of (2) is 781.7mAh g -1 The specific capacity after 100 times of circulation is 582mAh g -1 The capacity retention was 74.45%. The capacity performance was far higher than that of the graphite of comparative example 1 in terms of cycle performance and specific capacity performance, as shown in FIG. 5 (the specific capacity after 100 cycles was 270.76mAh g -1 ) The cycling performance was superior to that of the pure nano-silicon of comparative example 2, as shown in fig. 6 (100 cycles of the incomplete cycle).
As can be seen from FIG. 3, the anode material prepared in example 1 has a higher specific capacity and cycle retention, wherein at 0.1Ag -1 The specific capacity of the second discharge at the current density of (2) is 921.4mAh g -1 After experiencing 2Ag -1 High current density cycling and return to 0.1Ag -1 At a current density of (2), the 30 th-turn discharge capacity was 907.2mAh g -1 The capacity retention was 98.46%, and the specific capacity was higher than that of the graphite of comparative example 1 and the nano-silicon of comparative example 2, as shown in fig. 7 and 8, respectively. This demonstrates that the anode material of example 1 can maintain good electrochemical performance under high rate charge and discharge of the battery, and can meet the current fast charge and fast discharge requirements.
As can be seen from FIG. 4, the anode material prepared in example 2 has higher specific capacity and cycle retention, wherein the anode material has a specific capacity of 0.1Ag -1 The specific capacity of the second discharge at the current density of (2) is 855.2mAh g -1 After experiencing 2Ag -1 High current density cycling and return to 0.1Ag -1 At a current density of (2), the 30 th-turn discharge capacity was 98.12mAh g -1 The capacity retention was 98.46%, and the specific capacity was higher than that of the graphite of comparative example 1 and the nano-silicon of comparative example 2, as shown in fig. 7 and 8, respectively. This demonstrates that the anode material of example 2 can maintain good electrochemical performance under high rate charge and discharge of the battery, and can meet the current fast charge and fast discharge requirements.
Fig. 9 and 10 are sem images of the composite material prepared in example 1 at different magnifications. The outermost coating layer is shown to have a particle size of about 100nm and to be uniformly adhered to the surface of the inner layer. This demonstrates the reason that examples 1, 2 have a very high capacity retention during cycling, with more buffering than nano-silicon, providing some protection.
The foregoing description of embodiments of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described. The terminology used herein was chosen in order to best explain the principles of the embodiments, the practical application, or the technical improvements in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
Industrial applicability
According to the invention, the MOFs material coats the silicon-carbon composite material, and a part of the silicon-carbon composite material is embedded into the pores of the MOFs material, so that the volume expansion of silicon is restrained without damaging the effective structure of the material, and the high specific capacity and long cycle performance of the battery are realized. The preparation method of the negative electrode material is simple and convenient, high energy consumption is not needed, and the preparation of the material with high specific capacity can be finished by using conventional equipment and conventional preparation environment, so that the preparation method is an industrialized pollution-free environment-friendly production mode.

Claims (16)

1. A silicon-carbon negative electrode material, which is characterized by comprising a silicon-carbon composite material and MOFs material; wherein the MOFs material coats the silicon carbon composite and a portion of the silicon carbon composite is embedded in pores of the MOFs material; the silicon-carbon composite material is a mixture of a carbon-containing material and nano silicon, the carbon-containing material is a porous carbon material, the nano silicon is embedded into the pores of the porous carbon material,
wherein the mass ratio of the silicon-carbon composite material to the MOFs material is (1-10): 1,
wherein the silicon carbon anode material is prepared by a method comprising the steps of:
step S1: mixing and grinding the carbon-containing material and the nano silicon to obtain the silicon-carbon composite material;
step S2: and mixing and grinding the silicon-carbon composite material and the MOFs material to obtain the silicon-carbon negative electrode material which is formed by coating the silicon-carbon composite material by the MOFs material and embedding part of the silicon-carbon composite material into holes of the MOFs material.
2. The silicon-carbon negative electrode material according to claim 1, wherein a mass ratio of the silicon-carbon composite material to the MOFs material is (2-8): 1.
3. the silicon-carbon negative electrode material of claim 1, wherein the nano-silicon has a particle size of 20-2000nm.
4. A silicon-carbon negative electrode material as claimed in any one of claims 1 to 3 wherein the nanosilicon has a particle size of 20 to 60nm.
5. A silicon-carbon negative electrode material as claimed in any one of claims 1 to 3 wherein the mass ratio of porous carbon material to nano-silicon is from 5:1 to 20:1.
6. A silicon carbon negative electrode material as claimed in any one of claims 1 to 3 wherein the MOFs material has a three dimensional structure with a pore size of 1 to 1000nm and a porosity of 1 to 80%.
7. A silicon carbon negative electrode material as claimed in any one of claims 1 to 3 wherein the metal ions in the MOFs material are selected from at least one of Cu, zn, co and the organic ligands are selected from at least one of trimesic acid, terephthalic acid, dimethyl imidazole.
8. A silicon-carbon anode material as claimed in any one of claims 1 to 3 wherein the porous carbon material has a pore size of 1 to 1000nm and a porosity of 1 to 80%.
9. A method of preparing the silicon carbon anode material of claim 1.
10. The method of claim 9, wherein in step S1 and step S2, the milling comprises ball milling.
11. The method according to claim 10, wherein in the step S1, the ball-milling ratio is 10:1, the ball-milling time is 2-8 hours, and the ball-milling rotation speed is 200-600r/min.
12. The method according to claim 10, wherein in the step S2, the ball-milling ratio is 10:1, the ball-milling time is 2-4 hours, and the ball-milling rotation speed is 100-500r/min.
13. The production method according to any one of claims 9 to 12, wherein the step S1 and the step S2 are performed at room temperature.
14. The production method according to any one of claims 9 to 12, wherein the porous carbon material is obtained by firing a carbon source precursor at 600 to 1000 ℃.
15. The method of claim 14, wherein the carbon source precursor is selected from one or more of citric acid, cellulose, glucose, sucrose, xylan, lignin, starch, pectin.
16. A lithium ion battery comprising the silicon-carbon negative electrode material according to any one of claims 1 to 8 or obtained by the production method according to any one of claims 9 to 15.
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