CN113130870B - Composite silicon material and lithium ion battery - Google Patents
Composite silicon material and lithium ion battery Download PDFInfo
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- CN113130870B CN113130870B CN202110387372.4A CN202110387372A CN113130870B CN 113130870 B CN113130870 B CN 113130870B CN 202110387372 A CN202110387372 A CN 202110387372A CN 113130870 B CN113130870 B CN 113130870B
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- 239000002210 silicon-based material Substances 0.000 title claims abstract description 118
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- 239000002131 composite material Substances 0.000 title claims abstract description 64
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- 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
- H01M4/362—Composites
- H01M4/364—Composites as mixtures
-
- 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
-
- 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
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- Chemical & Material Sciences (AREA)
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- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Composite Materials (AREA)
- Manufacturing & Machinery (AREA)
- Inorganic Chemistry (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a composite silicon material and a lithium ion battery. The invention provides a composite silicon material in a first aspect, which comprises a plurality of base particles and a first conductive material dispersed among the base particles, wherein the base particles comprise a silicon material and a coating layer coated on the outer surface of the silicon material part, and the coating layer comprises Al 2 O 3 And a carbon material; the first conductive material includes graphene and/or conductive carbon tubes. The composite silicon material provided by the application improves the cycle performance and the safety of the lithium ion battery on the basis of improving the energy density of the lithium ion battery. In a second aspect of the present invention, a negative electrode sheet includes a double-layer negative electrode active layer, and the negative electrode active layer including the composite silicon material is disposed inside the negative electrode sheet, so as to further improve cycle performance of the lithium ion battery.
Description
Technical Field
The invention relates to a composite silicon material and a lithium ion battery, and relates to the technical field of lithium ion batteries.
Background
In recent years, the sales volume of portable consumer electronic products has increased explosively, and lithium ion batteries are increasingly demanded as power supply sources of portable consumer electronic products, wherein the demand for energy density of the lithium ion batteries is also increasing in order to solve the problem of "endurance and charging anxiety" of the products. The specific capacity of graphite serving as the most mature carbon-based negative electrode active material at present is basically and fully exerted, while the specific capacity of silicon material serving as a novel negative electrode active material is up to 4200mAh/g, so that the energy density of the lithium ion battery is improved.
However, the potential and polarization degree of the carbon-based negative electrode active material and the silicon material are different in the charging process, so that the concentration distribution of lithium ions in the negative electrode sheet is uneven, and the problem of lithium precipitation is easily caused; meanwhile, the volume expansion of the silicon material is severe in the charging and discharging processes, so that the electrode material is structurally collapsed and particles are differentiated in the circulating process, the electronic conductivity between active materials and between the active materials and a current collector is lost, and the silicon material is poor in conductivity, so that the irreversible capacity loss is finally caused, and the circulating performance of the lithium ion battery is influenced.
Disclosure of Invention
The invention provides a composite silicon material which is used for relieving the problems of volume expansion of the silicon material and lithium precipitation of a negative plate and improving the cycle performance and safety of a lithium ion battery.
The invention also provides a lithium ion battery which comprises the composite silicon material and has higher energy density, cycle performance and safety.
The invention provides a composite silicon material in a first aspect, which comprises a plurality of base particles and a first conductive material dispersed among the base particles;
wherein, the substrate particles comprise a silicon material and a coating layer coated on the outer surface of the silicon material part, and the coating layer comprises Al 2 O 3 And a carbon material;
the first conductive material includes graphene and/or conductive carbon tubes.
The application provides a compound silicon material, this compound silicon material includes a plurality of base particles and the first conducting material of dispersion between the base particle, and the base particle is as granular solid, exists the space between base particle and the base particle, and first conducting material dispersion forms the conductive network in the space to improve the electric conductivity of silicon material, simultaneously, first conducting materialThe formed conductive network also helps to restrain the expansion of the silicon material and prevent the electrode material structure from collapsing; the substrate particles comprise silicon materials and coating layers coated on the outer surfaces of the silicon materials, namely the silicon materials are arranged in the substrate particles, the coating layers are arranged on the outer surfaces of the substrate particles, and Al in the coating layers 2 O 3 Not only helps to improve the rigidity of the surface of the silicon material and inhibit the volume expansion of the silicon material, but also helps to inhibit the decomposition of electrolyte on the surface of the silicon material, inhibits the growth of SEI film and relieves the loss of the capacity of the lithium ion battery, and in addition, al 2 O 3 But also can improve the wettability of the silicon cathode in the electrolyte and reduce the interface polarization and the particle transfer impedance, and Al 2 O 3 Can be used as LiPF in electrolyte 6 Reaction to LiPO 2 F 2 And LiPO 2 F 2 The electrolyte additive is an excellent low-impedance and negative-electrode film-forming electrolyte additive, is beneficial to forming an interface film with high conductivity, low impedance and high stability on the surface of the composite silicon material, inhibits the oxidation of the electrolyte, the damage of an electrode structure and the increase of electrode polarization, is beneficial to improving the dynamic performance of the surface of a negative electrode, improves the rate capability of a lithium ion battery, and is beneficial to improving the conductivity of a coating layer and the silicon material. According to the invention, through the improvement of the silicon material, the conductivity of the silicon material is improved, the potential and polarization degree difference between the silicon material and the carbon-based negative electrode active material is reduced, and the problem of lithium precipitation is avoided; meanwhile, the volume expansion of the silicon material is inhibited, the loss of the capacity of the lithium ion battery is avoided, and the cycle performance of the lithium ion battery is improved; therefore, the composite silicon material provided by the application can further improve the cycle performance and the safety of the lithium ion battery on the basis of improving the energy density of the lithium ion battery.
In one embodiment, to further reduce the difference in potential and polarization degree between the silicon material and the carbon-based negative electrode active material, and to further increase the Al on the surface of the matrix particles 2 O 3 The invention provides a double-layer coating mode, and carbon and Al are coated 2 O 3 Sequentially coated on the outer surface of the silicon material and coated on Al 2 O 3 In which a conductive material is added, in particular, the coating layerThe silicon material comprises a first coating layer and a second coating layer, wherein the first coating layer and the second coating layer are sequentially coated on the outer surface of part of the silicon material, the first coating layer comprises carbon, and the second coating layer comprises Al 2 O 3 And a second conductive material.
It should be noted that, in order to distinguish from the first conductive material dispersed between the matrix particles, the conductive material added in the coating layer is the second conductive material, and the present invention is not limited to the second conductive material, which may be a material having a conductive capability conventionally used in the art, such as graphene, conductive carbon tubes, conductive carbon black, graphite, etc., and the second conductive material may be the same as or different from the first conductive material.
In order to further explain the structure of the composite silicon material, the application also provides a preparation method of the composite silicon material, and specifically, the composite silicon material is prepared by the following preparation method:
coating the outer surface of the silicon material with asphalt, and calcining to obtain the silicon material coated with a first coating layer on the surface;
dispersing the silicon material coated with the first coating layer on the surface in a second coating layer slurry, adjusting the pH to 4.5-11.3, volatilizing a solvent in the second coating layer slurry until the mass fraction of solid matters is 40-55%, then transferring the second coating layer slurry into a reaction kettle, continuously heating to 100-200 ℃, and stirring for 1-10 hours to obtain a matrix particle precursor, wherein the second coating layer slurry comprises an aluminum salt and a second conductive material;
calcining the matrix particle precursor at 800-1350 ℃ for 1-10h, raising the temperature to 1300-1550 ℃ and continuing calcining for 1-10h to obtain the matrix particles;
and dispersing the base particles in first conductive slurry, and granulating to obtain the silicon composite material, wherein the first conductive slurry comprises a first conductive material.
The preparation method of the composite silicon material is described in detail as follows:
step 1, coating asphalt on the outer surface of the silicon material, and calcining to obtain the silicon material coated with a first coating layer on the surface:
selecting silicon materials common in the field, such as one or more of simple silicon, silicon oxide, silicon carbide and silicon nitride;
then, putting the silicon material into a reaction kettle, taking asphalt as a coating agent, and coating the asphalt on the outer surface of the silicon material, wherein the asphalt can be coal-series high-temperature asphalt or petroleum high-temperature asphalt, the mass ratio of the silicon material to the asphalt is (95-85): 5-15, and further the mass ratio of the silicon material to the asphalt is 90:10, after the silicon material and the asphalt are mixed evenly, adding N 2 Calcining under protection, and removing moisture and volatile substances in the asphalt to obtain a silicon material with a first coating layer coated on the surface;
in addition, in order to facilitate the mixing of the asphalt and the silicon material, a surfactant can be added into the silicon material firstly, the temperature is increased to 270-580 ℃ after the uniform mixing, and then the asphalt is atomized and sprayed into the reaction kettle to enable the asphalt to be coated on the outer surface of the silicon material.
In particular, the surfactant may be PVP, the mass being 1% of the mass of the silicone material.
Step 2, dispersing the silicon material coated with the first coating layer on the surface in a second coating layer slurry, adjusting the pH to 4.5-11.3, volatilizing a solvent in the second coating layer slurry until the mass fraction of solid matters is 40-55%, transferring the solution to a reaction kettle, continuously heating to 100-200 ℃, and stirring for 1-10 hours to obtain a matrix particle precursor:
dispersing aluminum salt and a second conductive material in a solvent to obtain a second coating layer slurry, wherein the aluminum salt may be Al (NO) 3 ) 3 ·9H 2 O、AlCl 3 ·6H 2 O、Al 2 (SO 4 ) 3 ·18H 2 One or more of O; the second conductive material is graphene and/or a conductive carbon tube, and the solvent can be deionized water;
the mass fraction of the aluminum salt in the second coating layer slurry is 0.5% -45%, the mass fraction of the second conductive material is 1.5% -10%, and when the second conductive material comprises graphene and conductive carbon tubes, the mass ratio of the graphene to the conductive carbon tubes is 1: (1.25-9); further, the mass ratio of the graphene to the conductive carbon tubes is 1:4;
dispersing the silicon material coated with the first coating layer in the second coating layer slurry, adjusting pH to 4.5-11.3, further adjusting pH to 6.5-9, and heating Al in the second coating layer slurry 3+ Slowly generating precipitation and coating on the surface of the first coating, and specifically comprising: volatilizing the solvent in the second coating layer slurry until the mass fraction of solid matters is 40-55%, then transferring the second coating layer slurry into a reaction kettle, continuously heating to 100-200 ℃, and stirring for 1-10h to obtain a matrix particle precursor;
step 3, calcining the matrix particle precursor at 800-1350 ℃ for 1-10h, raising the temperature to 1300-1550 ℃ and continuing calcining for 1-10h to obtain the matrix particle;
to obtain Al by sufficient calcination 2 O 3 The matrix particle precursor is required to be calcined for the second time, specifically, the matrix particle precursor is calcined for 1 to 10 hours at 800 to 1350 ℃, and the temperature is raised to 1300 to 1550 ℃ for further calcination for 1 to 10 hours; further, the matrix particle precursor is calcined at 900-1050 ℃ for 3-7h, the temperature is raised to 1300-1450 ℃, and the calcination is continued for 2-4h, and two calcination processes are performed, so that the preparation method is not only helpful for obtaining the matrix particle precursor with Al-coated surface 2 O 3 The matrix particles of (2) also contribute to further carbonizing the pitch.
And 4, dispersing the matrix particles in first conductive slurry, and granulating to obtain the composite silicon material:
the first conductive material is dispersed in the solvent to prepare first conductive slurry, the first conductive material comprises graphene and/or conductive carbon tubes, in order to further improve the conductivity of the composite silicon material, the graphene and the conductive carbon tubes can be simultaneously dispersed in the solvent to prepare the first conductive slurry, the conductive carbon tubes are favorable for preventing the graphene from clustering, the dispersibility of the graphene is improved, and the mass ratio of the graphene to the conductive carbon tubes is 1: (1.25-9); further, the mass ratio of the graphene to the conductive carbon tubes is 1:4; the solvent may be deionized water.
And (4) dispersing the matrix particles prepared in the step (3) in the first conductive slurry, and uniformly stirring to obtain the composite silicon material through granulation.
In summary, the present application provides a method for preparing a composite silicon material, the composite silicon material prepared by the method includes substrate particles and conductive materials dispersed among the substrate particles, the substrate particles include a silicon material and a coating layer coated on an outer surface of the silicon material, and by improving the silicon material, the conductivity of the silicon material is improved, and the volume expansion of the silicon material is relieved, so that the composite silicon material provided by the present application can further improve the cycle performance and the safety of a lithium ion battery on the basis of improving the energy density of the lithium ion battery.
Because the composite silicon material needs to be mixed with a carbon-based negative electrode active material to be used as a negative electrode active material, in order to further reduce the difference between the composite silicon material and the carbon-based negative electrode active material and alleviate the problem of lithium precipitation of a negative electrode sheet, the D50 of the composite silicon material and the D50 of the carbon-based negative electrode active material can be kept close to each other, and specifically, the difference between the D50 of the carbon-based negative electrode active material and the D50 of the composite silicon material is 0-3.5 μm.
In combination with the particle size range of the existing carbon-based negative electrode active material, the D50 of the composite silicon material is 12-18 μm, and in the preparation process of the composite silicon material, a person skilled in the art can grind and sieve the product obtained in step 1 and/or step 3 according to actual needs to ensure the particle size of the final composite silicon material, specifically, the D50 of the silicon material coated with the first coating layer on the surface is 5-10 μm.
In addition, the particle size distribution range of the composite silicon material is not suitable to be too large, specifically, the difference value between D90 and D50 of the composite silicon material is 3-6 μm, and when the composite silicon material and the carbon-based negative electrode active material are mixed to be used as a negative electrode active material to be added into a negative electrode active layer, the uniformity of the porosity of the negative electrode active layer is improved, and the cycle performance of the lithium ion battery is further improved.
In conclusion, the composite silicon material provided by the application can further improve the cycle performance and the safety of the lithium ion battery on the basis of improving the energy density of the lithium ion battery.
The invention provides a lithium ion battery, which comprises a negative plate, wherein the negative plate comprises a negative current collector and a first negative active layer arranged on the surface of the negative current collector, and the first negative active layer comprises a carbon-based negative active material and any one of the silicon composite materials.
The present invention provides a lithium ion battery, and a person skilled in the art may mix the above-mentioned composite silicon material with a carbon-based negative electrode active material as a negative electrode active material to be added to a negative electrode active layer according to conventional technical means, for example, the lithium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer, the negative electrode active layer includes a carbon-based negative electrode active material and the above-mentioned composite silicon material, fig. 1 is a schematic structural diagram of the negative electrode sheet provided in an embodiment of the present invention, as shown in fig. 1, the negative electrode sheet includes a negative electrode current collector 101 and a first negative electrode active layer 102, the first negative electrode active layer 102 is disposed on a surface of the negative electrode current collector 101, the first negative electrode active layer 102 includes a composite silicon material and a negative electrode active material, the negative electrode active material is a material commonly used in the art, for example, the negative electrode active material may be one or more of artificial graphite, natural carbon-based carbon, intermediate carbon microspheres, soft carbon, hard carbon, and organic polymer carbon (i.e., a product after carbonization of an organic polymer).
With the increasing content of the silicon material in the first active layer, the energy density of the lithium ion battery is gradually increased, but the defects of the silicon material are also gradually highlighted, so in order to balance the relationship between the two, the mass ratio of the carbon-based negative electrode active material to the composite silicon material is (75-99.9): (25-0.1); further, the mass ratio of the carbon-based negative electrode active material to the silicon composite material is (85-97): (15-3).
In order to further alleviate the problem of lithium precipitation of the negative electrode sheet, a second negative electrode active layer may be disposed on the surface of the first negative electrode active layer away from the current collector, where the second negative electrode active layer includes a carbon-based negative electrode active material.
Fig. 2 is a schematic structural diagram of a negative electrode sheet according to still another embodiment of the present invention, as shown in fig. 2, the negative electrode sheet includes a negative electrode current collector 101, and a first negative electrode active layer 102 and a second negative electrode active layer 103 sequentially stacked on a surface of the negative electrode current collector 101, where the second negative electrode active layer 103 includes a carbon-based negative electrode active material and does not include a silicon material. In the charging process, lithium ions pass through the second negative electrode active layer and then enter the first negative electrode active layer, so that the potential difference of the surface of the first negative electrode active layer is favorably further reduced, the problem of lithium precipitation is solved, and the cycle life and the safety of the lithium ion battery are further improved.
The thicknesses of the first negative electrode active layer and the second negative electrode active layer can be set according to actual production needs, and specifically, the ratio of the thicknesses of the first negative electrode active layer to the second negative electrode active layer is (1-9): (9-1); further, the ratio of the thickness of the first negative electrode active layer to the second negative electrode active layer is (4-6): (6-4).
When the negative electrode sheet includes the second negative electrode active layer, in order to improve the dynamic performance of the lithium ion battery, the D50 of the carbon-based negative electrode active material in the second negative electrode active layer located on the surface of the negative electrode sheet should be smaller than the D50 of the carbon-based negative electrode active material in the first negative electrode active layer. Further, in order to facilitate adhesion of the first and second anode active layers and reduce the degree of polarization of the anode active material, the difference in particle size of the carbon-based anode active material in the first and second anode active layers is not preferably made excessively large, and specifically, the difference between D50 of the carbon-based anode active material in the first anode active layer and D50 of the carbon-based anode active material in the second anode active layer is 3 to 9 μm, that is (D50 of the carbon-based anode active material in the first anode active layer) - (D50 of the carbon-based anode active material in the second anode active layer) =3 to 9 μm;
further, the difference between D90 and D50 of the carbon-based anode active material in the second anode active layer is 4-10 μm, and the difference between D50 and D10 is 4-8 μm; the difference value between D90 and D50 of the carbon-based negative electrode active material in the first negative electrode active material is 6-12 mu m.
In the preparation process of the negative plate, first, a first negative active layer slurry is prepared, and is uniformly coated on the surface of a negative current collector to obtain a first negative active layer, and then the negative plate is obtained, wherein the preparation of the first negative active layer can be performed according to conventional technical means in the field, for example, first, a carbon-based negative active material and a composite silicon material are mixed and ball-milled to obtain a negative active material, the negative active material, a conductive agent, a binder and a thickening agent are added into a stirring tank, and deionized water is added to prepare a first negative active layer slurry, wherein the solid content of the first negative active layer slurry is 40-45%, and the mass ratio of the negative active material, the conductive agent, the binder and the thickening agent is (75-99): (0.1-5): (0.5-5): (0.5-5); further, the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickening agent is (80-98): (0.1-3): (0.3-4): (0.3-4).
When the negative plate comprises the second negative active layer, the second negative active layer slurry can be prepared and coated on the surface of the first negative active layer far away from the negative current collector, and the second negative active layer can be obtained, wherein the first negative active layer slurry can be referred to for the preparation of the second negative active layer slurry, and the difference is that the negative active material is only a carbon-based negative active material and does not comprise a silicon material.
On the basis of the negative electrode plate, a person skilled in the art can combine the positive electrode plate, the diaphragm and the electrolyte to prepare the lithium ion battery according to a conventional technical means. The lithium ion battery provided by the application has higher energy density, and better cycle performance and safety.
The implementation of the invention has at least the following advantages:
1. the composite silicon material provided by the application can further improve the cycle performance and the safety of the lithium ion battery on the basis of improving the energy density of the lithium ion battery.
2. The lithium ion battery provided by the application has the advantages of higher energy density, better cycle performance and better safety.
Drawings
Fig. 1 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a negative electrode sheet according to still another embodiment of the present invention.
Description of the reference numerals:
101-a negative current collector;
102 — a first negative active layer;
103-second negative active layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Example 1
The composite silicon material provided by the embodiment is prepared by the following preparation method:
1. putting silica particles with the D50 of 6 mu m into a reaction kettle, adding 1% of PVP (polyvinyl pyrrolidone), stirring at the speed of 45rmp, heating to 320 ℃, keeping the temperature, atomizing and spraying coal-series high-temperature asphalt solution to the surface of the silica, wherein the mass ratio of the silica to the asphalt is 90:10, continuously stirring in the process to ensure that the asphalt is uniformly coated on the surface of the silicon monoxide particles;
in N 2 Calcining under protection, and uniformly grinding and sieving after the calcining to obtain the silicon material with the surface coated with the first coating layer.
2. Mixing Al (NO) 3 ) 3 ·9H 2 Dispersing O, graphene and conductive carbon tubes in deionized water to obtain a second coating layer slurry, wherein Al (NO) 3 ) 3 ·9H 2 The mass fraction of O is 5%, the mass fraction of graphene is 0.8%, and the mass fraction of the conductive carbon tube is 3.2%;
dispersing the silicon material coated with the first coating layer on the surface, which is prepared in the step 1, in second coating layer slurry, adjusting the pH to 8.3 by using 2mol/L ammonia water, continuously stirring in 80 ℃ water bath, evaporating water, stopping heating when the mass fraction of solid reaches 45%, transferring to a reaction kettle, heating to 150 ℃, andstirring is continued for 8h, then under N 2 Calcining at 1000 deg.C for 4h under protection, increasing temperature to 1350 deg.C, and calcining for 3h to obtain matrix particles.
3. Dissolving graphene and a conductive carbon tube in deionized water to prepare a first conductive slurry, wherein the mass ratio of the graphene to the conductive carbon tube is 1:4;
and dispersing the matrix particles in the first conductive slurry, uniformly mixing, granulating, uniformly grinding and sieving to obtain the composite silicon material with the D50 of 12 microns and the D90 of 17 microns.
Example 2
The preparation method of the composite silicon material provided by the embodiment can refer to embodiment 1, and is different from embodiment 1 in that D50 of the silicon monoxide particles is 7 μm; the D50 of the composite silicon material is 14 μm, and the D90 is 18 μm.
Example 3
The embodiment provides a lithium ion battery, which comprises a positive plate, a negative plate and a diaphragm, wherein:
the positive plate comprises a positive current collector aluminum foil and a positive active layer, wherein the positive active layer comprises 97.2 parts by mass of positive active material lithium cobaltate, 1.5 parts by mass of conductive carbon black and 1.3 parts by mass of polyvinylidene fluoride;
the negative plate includes negative current collector copper foil and range upon range of first negative pole active layer and the second negative pole active layer of setting on the copper foil surface in proper order, wherein:
the first negative electrode active layer comprises 96.9 parts by mass of a negative electrode active material, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethyl cellulose, and the negative electrode active material comprises 97 parts by mass of graphite and 3 parts by mass of the composite silicon material provided in example 1; the D10 of the graphite is 8 μm, the D50 is 14 μm and the D90 is 23 μm;
the second negative active layer comprises 96.9 parts by mass of graphite, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethylcellulose; the graphite had a D10 of 6 μm, a D50 of 11 μm and a D90 of 20 μm.
The thickness of the first negative electrode active layer was 50 μm, and the thickness of the second negative electrode active layer was 50 μm.
The preparation method of the lithium ion battery provided by the embodiment comprises the following steps:
the preparation method of the positive plate comprises the following steps:
dispersing 97.2 parts by mass of a positive electrode active material lithium cobaltate, 1.5 parts by mass of conductive carbon black and 1.3 parts by mass of polyvinylidene fluoride in NMP, fully stirring, filtering by using a 200-mesh screen to obtain positive electrode active layer slurry, then coating the positive electrode active layer slurry on the surface of an aluminum foil by using a coating machine, and drying at 120 ℃ to obtain a positive electrode sheet;
the preparation method of the negative plate comprises the following steps:
1. mixing 97 parts by mass of graphite and 3 parts by mass of the composite silicon material provided in example 1, performing ball milling for 2-5min to obtain a negative electrode active material, and dissolving 96.9 parts by mass of the negative electrode active material, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethylcellulose in deionized water to prepare a first negative electrode active layer slurry with a solid content of 45.3%;
2. dissolving 96.9 parts by mass of graphite, 0.5 part by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex and 1.3 parts by mass of sodium carboxymethylcellulose in deionized water to prepare second negative electrode active layer slurry, wherein the solid content is 45.3%;
3. coating the first negative active layer slurry on the surface of a negative current collector copper foil to obtain a first negative active layer, coating the second negative active layer slurry on the surface of the first negative active layer, which is far away from the negative current collector copper foil, to obtain a second negative active layer, and finally drying to obtain a negative plate.
The preparation method of the electrolyte comprises the following steps:
propylene Carbonate (PC), ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) were mixed in a weight ratio of 1 6 Obtaining an electrolyte solution in which LiPF 6 The concentration of (1 mol/L).
And (3) preparing the positive plate and the negative plate by matching with commercial diaphragms to obtain a battery core, and packaging and injecting according to a conventional preparation method in the field to obtain the lithium ion battery.
Example 4
The lithium ion battery provided by the present embodiment can refer to embodiment 3, and the difference is that:
the negative electrode active material in the first negative electrode active layer included 97 parts by mass of graphite and 3 parts by mass of the silicon composite material provided in example 2, in which D10 of graphite was 9 μm, D50 was 16 μm, and D90 was 29 μm;
the negative electrode active material in the second negative electrode active layer was graphite, and the graphite had a D10 of 7 μm, a D50 of 13 μm, and a D90 of 23 μm.
Example 5
The lithium ion battery provided in this example can be referred to example 3, except that the negative electrode active material in the first negative electrode active layer includes 95 parts by mass of graphite and 5 parts by mass of the composite silicon material provided in example 1.
Example 6
The lithium ion battery provided in this example can be referred to example 3, except that the negative electrode active material in the first negative electrode active layer includes 92 parts by mass of graphite and 8 parts by mass of the silicon composite material provided in example 1.
Example 7
The lithium ion battery provided in this example can be referred to example 3, except that the negative electrode active material in the first negative electrode active layer includes 90 parts by mass of graphite and 10 parts by mass of the silicon composite material provided in example 1.
Example 8
The lithium ion battery provided in this example can be referred to example 5, except that the thickness of the first negative electrode active layer is 60 μm and the thickness of the second negative electrode active layer is 40 μm.
Example 9
The lithium ion battery provided in this example can be referred to example 5, except that the thickness of the first negative electrode active layer was 40 μm and the thickness of the second negative electrode active layer was 60 μm.
Comparative example 1
The lithium ion battery provided by the present comparative example can refer to example 3, except that the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer, and the negative electrode active layer includes 96.9 parts by mass of graphite, 0.5 parts by mass of conductive carbon black, 1.3 parts by mass of styrene-butadiene latex, and 1.3 parts by mass of sodium carboxymethyl cellulose, that is, the same as the second negative electrode active layer in example 3, and the thickness of the negative electrode active layer is 100 μm.
Comparative example 2
The lithium ion battery provided by this comparative example can be referred to example 3, except that the silicon material in the first negative electrode active layer is silicon monoxide.
Comparative example 3
A lithium ion battery provided by this comparative example can be referred to as example 5, except that the silicon material in the first negative electrode active layer is a silica.
Comparative example 4
A lithium ion battery provided by this comparative example can be referred to as example 7, except that the silicon material in the first negative electrode active layer is a silica.
The lithium ion batteries provided in examples 3 to 9 and comparative examples 1 to 4 were tested for energy density, lithium deposition, capacity retention rate, expansion rate and safety performance, and the test results are shown in table 1:
testing of energy density: carrying out 0.2C/0.2C charge and discharge on the lithium ion battery at 25 ℃ to test the discharge energy of the lithium ion battery, and further testing to obtain the length, height and thickness of the lithium ion battery; calculating to obtain the volume energy density of the lithium ion battery according to the volume energy density = discharge energy/length/height/thickness;
lithium separation condition test: 1.0C charging/0.7C discharging is carried out on the lithium ion battery at 25 ℃, the lithium ion battery is disassembled after different cycle tests, the lithium separation condition on the surface of a negative electrode is observed, the lithium ion battery is divided into five grades according to the lithium separation condition of the lithium ion battery, and the grades are represented by 0, 1, 2, 3, 4 and 5, wherein 0 represents no lithium separation, 5 represents serious lithium separation, 1, 2, 3 and 4 represent different lithium separation degrees, and the larger the number is, the more serious the lithium separation degree is;
testing of capacity retention: testing initial capacity Q of lithium ion battery 1 And charging at 1.0C/discharging at 0.7C, and testing the capacity of the lithium ion battery after 700T of circulation to obtain Q 2 Capacity retention (%) = Q 2 /Q 1 *100％；
Testing of expansion ratio: testing the thickness P of the lithium ion battery 1 And the lithium ion battery is charged at 25 ℃ by 1.0 charge/0.7 discharge, and the thickness P of the lithium ion battery is tested after 700T circulation 2 Cycle expansion ratio (%) = (P) 2 -P 1 )/P 1 *100％。
Table 1 results of performance testing of lithium ion batteries provided in examples 3-9 and comparative examples 1-4
According to the data provided by the comparative examples 1 to 4, the energy density of the lithium ion battery is continuously improved along with the continuous improvement of the mass fraction of the silicon monoxide, but the lithium separation condition of the negative plate is continuously worsened, the expansion rate of the lithium ion battery is continuously improved, and the capacity retention rate is continuously reduced, and according to the comparison of the data provided by the examples 3 to 9 and the comparative examples 2 to 4, the composite silicon material provided by the application further relieves the problem of lithium separation of the negative plate on the basis of ensuring the energy density of the lithium ion battery, reduces the expansion rate of the lithium ion battery, and improves the capacity retention rate of the lithium ion battery; according to the data provided by the embodiments 3 to 4, the particle size of the carbon-based negative electrode active material in the surface layer of the negative electrode sheet is smaller, which is beneficial to improving the capacity retention rate of the lithium ion battery; according to the data provided in examples 3 and 5-7, the energy density is continuously improved with the increasing of the mass fraction of the composite silicon material in the first negative active layer, but the lithium ion battery has a gradually serious lithium precipitation condition, a capacity retention rate is reduced, and an expansion rate is continuously improved, that is, the defects of the silicon material are gradually highlighted; as can be seen from the data provided in examples 5 and 8-9, as the thickness of the first negative active layer increases, the energy density of the lithium ion battery increases, but the capacity retention rate decreases, so that a person skilled in the art can set the mass fraction of the silicon composite material and the thickness of the negative active layer including the silicon composite material according to actual production needs.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.
Claims (5)
1. The lithium ion battery is characterized by comprising a negative plate, wherein the negative plate comprises a negative current collector, a first negative active layer arranged on the surface of the negative current collector and a second negative active layer arranged on the surface of the first negative active layer far away from the negative current collector, the first negative active layer comprises a carbon-based negative active substance and a composite silicon material, and the second negative active layer comprises a carbon-based negative active substance;
the composite silicon material comprises a plurality of base particles and a first conductive material dispersed among the base particles;
the substrate particles comprise a silicon material and coating layers coated on partial outer surfaces of the silicon material, the coating layers comprise a first coating layer and a second coating layer, the first coating layer and the second coating layer are sequentially coated on partial outer surfaces of the silicon material, the first coating layer comprises carbon, and the second coating layer comprises Al 2 O 3 And a second conductive material comprising graphene and conductive carbon tubes;
the first conductive material comprises graphene and/or conductive carbon tubes;
the difference value of D50 of the carbon-based negative electrode active material in the first negative electrode active layer and the composite silicon material is 0-3.5 mu m;
the D50 of the carbon-based negative electrode active material in the second negative electrode active layer is smaller than the D50 of the carbon-based negative electrode active material in the first negative electrode active layer, and the difference between the D50 of the carbon-based negative electrode active material in the first negative electrode active layer and the D50 of the carbon-based negative electrode active material in the second negative electrode active layer is 3-9 μm.
2. The lithium ion battery of claim 1, wherein the silicon composite material is prepared by the following preparation method:
coating the outer surface of the silicon material with asphalt, and calcining to obtain the silicon material coated with the first coating layer on the surface;
dispersing the silicon material coated with the first coating layer on the surface in a second coating layer slurry, adjusting the pH to 4.5-11.3, volatilizing a solvent in the second coating layer slurry until the mass fraction of solid matters is 40-55%, then transferring the second coating layer slurry into a reaction kettle, continuously heating to 100-200 ℃, and stirring for 1-10 hours to obtain a matrix particle precursor, wherein the second coating layer slurry comprises an aluminum salt and a second conductive material;
calcining the matrix particle precursor at 800-1350 ℃ for 1-10h, raising the temperature to 1300-1550 ℃ and continuing calcining for 1-10h to obtain the matrix particles;
and dispersing the base particles in a first conductive slurry, and granulating to obtain the silicon composite material, wherein the first conductive slurry comprises a first conductive material.
3. The lithium ion battery of any one of claims 1-2, wherein the first conductive material comprises graphene and conductive carbon tubes, and the mass ratio of graphene to conductive carbon tubes is 1: (1.25-9).
4. The lithium ion battery of claim 1, wherein the D50 of the silicon composite material is 12-18 μ ι η, and the difference between the D90 and the D50 of the silicon composite material is 3-6 μ ι η.
5. The lithium ion battery according to claim 1, wherein the mass ratio of the carbon-based negative electrode active material to the silicon composite material in the first negative electrode active layer is (75-99.9): (25-0.1).
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| CN114784237A (en) * | 2022-04-02 | 2022-07-22 | 合肥工业大学 | Silicon-based negative electrode, preparation method and application thereof |
| CN114649505B (en) * | 2022-04-07 | 2024-07-16 | 珠海冠宇电池股份有限公司 | Negative plate and lithium ion battery |
| CN114975966B (en) * | 2022-06-29 | 2024-05-31 | 宜春瑞富特新能源材料技术有限公司 | Aluminum-carbon coated graphite negative electrode material for lithium ion battery and preparation method thereof |
| CN115394973B (en) * | 2022-07-20 | 2023-05-16 | 晖阳(贵州)新能源材料有限公司 | High-first-efficiency high-energy-density negative electrode material and preparation method thereof |
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