CN113130849A - Composite silicon material and lithium ion battery - Google Patents

Composite silicon material and lithium ion battery Download PDF

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Publication number
CN113130849A
CN113130849A CN202110385326.0A CN202110385326A CN113130849A CN 113130849 A CN113130849 A CN 113130849A CN 202110385326 A CN202110385326 A CN 202110385326A CN 113130849 A CN113130849 A CN 113130849A
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negative electrode
silicon material
lithium ion
ion battery
electrode active
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CN113130849B (en
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张保海
彭冲
李俊义
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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 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 part of the silicon material, and the coating layer comprises Mg (OH)2MgO and carbon materials; the first conductive material includes graphene and/or conductive carbon tubes. The composite silicon material provided by the application can further improve the cycle performance and safety of the lithium ion battery on the basis of improving the energy density of the lithium ion batteryAnd (4) sex. 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 on a surface of the negative electrode sheet, so as to further improve safety of the lithium ion battery.

Description

Composite silicon material and lithium ion battery
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 conducting capacity among 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, the circulating life of the lithium ion battery is influenced, and the service life of the lithium ion battery is reduced.
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 better 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 matrix particles comprise a silicon material and a coating layer coated on the outer surface of the silicon material part, and the coating layer comprises Mg (OH)2MgO and carbon materials;
the first conductive material includes graphene and/or conductive carbon tubes.
The application provides a composite silicon material, which comprises a plurality of base particles and a first conductive material dispersed among the base particles, wherein the base particles are granular solids, gaps exist among the base particles, and the first conductive material is dispersed in the gaps to form a conductive network, so that the conductivity of the silicon material is improved, and the formed conductive network is also beneficial to restricting the expansion of the silicon material; the substrate particles comprise silicon material and a coating layer coated on the outer surface of the silicon material part, namely, the silicon material is arranged in the substrate particles, the coating layer comprises Mg (OH)2MgO and carbon material, Mg (OH) when the temperature of the lithium ion battery rises2The lithium ion battery can absorb heat, reduce the temperature inside the lithium ion battery and improve the safety performance of the lithium ion battery, MgO is beneficial to improving the rigidity of the surface of the silicon material and inhibiting the volume expansion of the silicon material, so that the decomposition of electrolyte on the surface of the silicon material is inhibited, the growth of an SEI film is inhibited, the loss of the capacity of the lithium ion battery is relieved, and the carbon material is beneficial to improving the conductivity of a coating layer and the silicon material. According to the invention, the silicon material is modified, so that 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 service life of the lithium ion battery is prolonged; in addition, the thermal runaway of the lithium ion battery is prevented, and the safety of the lithium ion battery is improved; therefore, the composite silicon material provided by the application can further improve the energy density of the lithium ion batteryThe cycle performance and the safety of the lithium ion battery are improved.
In one embodiment, to further reduce the difference in potential and polarization degree between the silicon material and the carbon-based negative active material, and to further increase the Mg (OH) on the surface of the matrix particles2The invention provides a double-layer coating mode, and carbon, Mg (OH)2And MgO coated on partial outer surface of the silicon material in sequence and in Mg (OH)2And MgO is added with a conductive material, specifically, the coating layer comprises a first coating layer and a second coating layer, the first coating layer and the second coating layer are sequentially coated on part of the outer surface of the silicon material, the first coating layer comprises carbon, and the second coating layer comprises Mg (OH)2MgO, 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, the invention does not limit the kind of the second conductive material, which may be a material having a conductive capability conventional 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 the first coating layer on the surface;
dispersing the silicon material coated with the first coating layer on the surface in 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 is 40-55%, then transferring the second coating layer slurry into a reaction kettle, heating to 100 ℃ and 200 ℃, and stirring for 1-10 hours to obtain a matrix particle precursor; the second coating layer slurry comprises a magnesium salt and a second conductive material;
calcining the precursor of the matrix particles at 800-1350 ℃ 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 the mixture into N2Calcining 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 order to facilitate the mixing of the asphalt and the silicon material, firstly, a surfactant is added into the silicon material, 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 silicon material.
Step 2, dispersing the silicon material coated with the first coating layer on the surface in second coating layer slurry, adjusting the pH to 4.5-11.3, volatilizing the solvent in the second coating layer slurry until the mass fraction of solid is 40-55%, transferring the mixture into a reaction kettle, heating to 100-:
dispersing magnesium salt and second conductive material in solvent to obtain second coating layer slurry, wherein the magnesium salt can be Mg (NO)3)2·9H2O、MgCl2·6H2O、MgSO4·7H2One or more of OA plurality of types; the second conductive material comprises graphene and/or conductive carbon tubes, and the solvent can be deionized water;
the mass fraction of the magnesium 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), and 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 to make Mg in the second coating layer slurry2+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 is 40-55%, transferring the second coating layer slurry into a reaction kettle, heating to 100-;
step 3, calcining the precursor of the matrix particles at 800-1350 ℃ for 1-10h to obtain the matrix particles;
on the basis of the preparation of the precursor of the matrix particles, by controlling the calcination temperature, part of Mg (OH) is made2MgO is formed to obtain Mg (OH)2And a coating layer of MgO for preventing Mg (OH) during calcination2Total conversion to MgO, or incomplete conversion, by controlling the calcination temperature and time such that Mg (OH)2And MgO exist at the same time, specifically, the calcining temperature is 800-1350 ℃ for 1-10h, and further the calcining temperature is 900-1050 ℃ for 3-7 h.
And 4, dispersing the matrix particles in the 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, 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 conductive slurry, the existence of the conductive carbon tubes is 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 conductive slurry, uniformly stirring, and granulating to obtain the composite silicon material.
In summary, the application provides a preparation method of a composite silicon material, the composite silicon material prepared by the method comprises substrate particles and first conductive materials dispersed among the substrate particles, the substrate particles comprise a silicon material and a coating layer coated on the 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 application can improve the cycle performance and the safety of a lithium ion battery.
Since the silicon composite 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 silicon composite material and the carbon-based negative electrode active material and alleviate the problem of lithium precipitation of the negative electrode sheet, D50 of the silicon composite material can be kept close to D50 of the carbon-based negative electrode active material, specifically, the difference between D50 of the carbon-based negative electrode active material and D50 of the silicon composite material is 0-3.5 μm, and it can be understood that D50 of the carbon-based negative electrode active material can be greater than or equal to or less than D50 of the silicon composite material, i.e., | D50 of the carbon-based negative electrode active material-D50 of the silicon composite 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 10-18 μm, and in the preparation process of the composite silicon material, the product obtained in step 1 and/or step 3 can be ground and sieved to ensure the particle size of the final composite silicon material, for example, 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 a 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, and the first negative active layer comprises a carbon-based negative active material and any one of the silicon composite materials.
The invention provides a lithium ion battery, and a person skilled in the art can mix the above-mentioned composite silicon material and carbon-based negative active material as a negative active material to be added to a negative active layer according to conventional technical means, for example, the lithium ion battery includes a positive plate, a negative plate and a separator, the negative plate includes a negative current collector and a negative active layer, the negative active layer includes a carbon-based negative active material and the above-mentioned composite silicon material, fig. 1 is a schematic structural diagram of the negative plate provided in an embodiment of the invention, as shown in fig. 1, the negative plate includes a negative current collector 101 and a first negative active layer 102, the first negative active layer 102 is disposed on the surface of the negative current collector 101, the first negative active layer 102 includes a composite silicon material and a carbon-based negative active material, wherein the carbon-based negative active material is a material commonly used in the art, for example, the carbon-based negative, One or more of natural graphite, mesocarbon microbeads, soft carbon, hard carbon, and organic polymer carbon (i.e., a carbonized product of an organic polymer).
With the increasing content of the composite silicon material in the first negative electrode active layer, the energy density of the lithium ion battery is gradually increased, but the defects of the silicon material are gradually highlighted, so that 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 (85-99): (15-1).
Because of Mg (OH) on the surface of the composite silicon material substrate particles2For facilitating absorption inside lithium-ion batteriesThe heat and the composite silicon material need to be arranged on the surface layer of the negative plate, and in order to further improve the safety of the lithium ion battery, the surface layer Mg (OH) of the negative plate can be further improved2The negative electrode sheet may include a second negative electrode active layer disposed between the negative electrode current collector and the first negative electrode active layer, the second negative electrode active layer including a carbon-based negative electrode active material.
Fig. 2 is a schematic structural diagram of a negative electrode sheet according to another embodiment of the present invention, as shown in fig. 2, the negative electrode sheet includes a negative electrode collector 101, a first negative electrode active layer 102, and a second negative electrode active layer 103, the second negative electrode active layer 103 is disposed between the negative electrode collector 101 and the first negative electrode active layer 102, that is, the second negative electrode active layer 103 is disposed on a surface of the negative electrode collector, and the first negative electrode active layer 102 is disposed on a surface of the second negative electrode active layer 103 away from the negative electrode collector 101, wherein the first negative electrode active layer 102 includes a carbon-based negative electrode active material and a silicon composite material, the second negative electrode active layer 103 includes a carbon-based negative electrode active material and does not include a silicon composite material, and when the temperature of the lithium ion battery increases, mg (oh) in the silicon composite material2The heat can be effectively absorbed, the temperature of the lithium ion battery is prevented from rising, and the safety of the lithium ion battery is improved.
Further, the thickness ratio of the first negative electrode active layer to the second negative electrode active layer is (2-5): (8-5).
When the negative electrode sheet comprises 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 first negative electrode active layer on the surface of the negative electrode sheet should be smaller than the D50 of the carbon-based negative electrode active material in the second negative electrode active layer, and simultaneously, in order to facilitate the adhesion of the first negative electrode active layer and the second negative electrode active layer and reduce the polarization degree of the negative electrode active material, the difference of the particle sizes of the carbon-based negative electrode active materials in the first negative electrode active layer and the second negative electrode active layer is not too large, specifically, the D50 of the carbon-based negative electrode active material in the first negative electrode active layer is smaller than the D50 of the carbon-based negative electrode active material in the second negative electrode active layer, and the difference is 3-9;
further, D90-D50 of the carbon-based anode active material in the second anode active layer is 3-8 μm.
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 negative current collector, and then the first negative active layer slurry is coated on the surface of the second negative active layer far away from the negative current collector, so that the negative plate can be obtained, wherein the preparation of the second negative active layer slurry can refer to the first 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 preparing the negative plate, a person skilled in the art can prepare the lithium ion battery by combining the positive plate, the diaphragm and the electrolyte according to the 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 higher energy density, and better cycle performance and 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 yet another embodiment of the present invention.
Description of 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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within 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 coal-series high-temperature asphalt solution and spraying the 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 N2And (4) calcining under protection, and uniformly grinding and sieving to obtain the silicon material with the surface coated with the first coating after the calcining is finished.
2. Mixing MgCl2·6H2Dispersing O, graphene and conductive carbon tubes in deionized water to obtain coating layer slurry, wherein MgCl2·6H2The mass fraction of O is 5%, the mass fraction of graphene is 0.8%, and the mass of the conductive carbon tubeThe fraction is 3.2%;
dispersing the silicon material coated with the first coating layer 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 matters reaches 45%, transferring to a reaction kettle, heating to 150 ℃, continuously stirring for 8 hours, and adding N2Calcining at 1000 ℃ for 4h under protection to obtain matrix particles.
3. Dispersing 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, wherein the D10 is 8 microns, the D50 is 12 microns, and the D90 is 18 microns.
Example 2
The preparation method of the composite silicon material provided by the embodiment can refer to the embodiment 1, and is different from the embodiment in that the D50 of the silicon monoxide is 7 μm, the D10 of the prepared composite silicon material is 9 μm, the D50 is 15 μm, and the D90 is 20 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 pole piece includes negative pole mass flow body copper foil and range upon range of second negative pole active layer and the first negative pole active layer that sets up on the copper foil surface in proper order, wherein:
the first negative active layer comprises 96.9 parts by mass of negative 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, the negative active material comprises 97 parts by mass of graphite and 3 parts by mass of the composite silicon material provided by the embodiment 1, and the D50 of the graphite is 13 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 carboxymethyl cellulose, and the D50 of the graphite is 17 mu m; d90 was 25 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 electrolyte comprises Propylene Carbonate (PC), Ethylene Carbonate (EC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC) and electrolyte LiPF6。
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, and 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, wherein the solid content is 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 second negative electrode active layer slurry on the surface of the negative electrode current collector copper foil to obtain a second negative electrode active layer, coating the first negative electrode active layer slurry on the surface of the second negative electrode active layer, which is far away from the negative electrode current collector copper foil, to obtain a first negative electrode 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 1:1:0.5:1, followed by the addition of LiPF6An electrolytic solution in which the concentration of LiPF6 was 1mol/L) was obtained.
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 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 2, in which D50 of the graphite in the first negative electrode active layer is 15 μm, D50 of the graphite in the second negative electrode active layer is 18 μm, and D90 is 26 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 silicon composite 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 was 40 μm and the thickness of the second negative electrode active layer was 60 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 30 μm and the thickness of the second negative electrode active layer was 70 μm.
Comparative example 1
The lithium ion battery provided by the present comparative example can be referred 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 silica.
Comparative example 4
A lithium ion battery provided by this comparative example can be referred to example 7 except that the silicon material in the first negative electrode active layer is 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 which is the 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 battery1And charging at 1.0C/discharging at 0.7C, and testing the capacity of the lithium ion battery after 700T of circulation to obtain Q2Capacity retention (%) ═ Q2/Q1*100％；
Testing of expansion ratio: testing the thickness P of the lithium ion battery1And 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 circulation2The percent of cyclic expansion (P) (%)2-P1)/P1*100％。
Thermal abuse test: the lithium ion batteries are placed in a 130 ℃ hot box in a full-charge state and stored for 60min, 10 lithium ion batteries are tested in each embodiment/comparative example, and the percent pass is calculated by taking the fact that the lithium ion batteries do not catch fire or explode as the pass.
Table 1 results of performance testing of lithium ion batteries provided in examples 3-9 and comparative examples 1-4
Figure BDA0003014515530000121
Figure BDA0003014515530000131
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 part 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 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 and the heat abuse pass rate; from the data provided in examples 3 and 5 to 7, as the mass fraction of the composite silicon material in the first negative active layer is increased,the energy density is continuously improved, but the lithium separation condition of the lithium ion battery is gradually serious, the capacity retention rate is continuously reduced, the expansion rate is continuously improved, namely the defects of the silicon material are gradually highlighted, but because of Mg (OH)2The content is increased, and the heat abuse passing rate is increased; according to the data provided in examples 5 and 8-9, it can be seen that the energy density of the lithium ion battery gradually decreases with the decrease of the thickness of the first negative electrode active layer, but the capacity retention rate of the lithium ion battery is continuously increased, and the expansion rate and the heat abuse throughput rate are also decreased to a certain extent, which may be related to the content of the composite silicon material.
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 the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (11)

1. The composite silicon material is characterized by comprising a plurality of base particles and a first conductive material dispersed among the base particles;
wherein, the matrix particles comprise a silicon material and a coating layer coated on the outer surface of the silicon material part, and the coating layer comprises Mg (OH)2MgO and carbon materials;
the first conductive material includes graphene and/or conductive carbon tubes.
2. The composite silicon material of claim 1 wherein the cladding layer comprises a first cladding layer and a second cladding layer, the first cladding layer and the second cladding layer in turn cladding portions of the outer surface of the silicon material, the first cladding layer comprising carbon and the second cladding layer comprising carbonComprising Mg (OH)2MgO, and a second conductive material.
3. The composite silicon material as claimed in claim 2, which 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 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 is 40-55%, then transferring the second coating layer slurry into a reaction kettle, heating to 100 ℃ and 200 ℃, and stirring for 1-10 hours to obtain a matrix particle precursor; the second coating layer slurry comprises a magnesium salt and a second conductive material;
calcining the precursor of the matrix particles at 800-1350 ℃ 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.
4. A composite silicon material according to any one of claims 1 to 3, wherein D50 of the composite silicon material is 10 to 18 μm.
5. The silicon composite material according to any one of claims 1 to 4, wherein the first conductive material comprises graphene and conductive carbon tubes, and the mass ratio of the graphene to the conductive carbon tubes is 1: (1.25-9).
6. A silicon composite material according to claim 2 or 3, wherein the second conductive material comprises graphene and/or conductive carbon tubes.
7. A lithium ion battery, characterized in that, the lithium ion battery comprises a negative plate, the negative plate comprises a negative current collector and a first negative active layer, the first negative active layer comprises a carbon-based negative active material and the silicon composite material of any one of claims 1 to 6.
8. The lithium ion battery of claim 7, wherein the mass ratio of the carbon-based negative electrode active material to the composite silicon material is (75-99.9): (25-0.1).
9. The lithium ion battery of claim 7 or 8, wherein the negative electrode sheet further comprises a second negative electrode active layer disposed between the negative electrode current collector and the first negative electrode active layer, the second negative electrode active layer comprising a carbon-based negative electrode active material.
10. The lithium ion battery of claim 9, wherein the ratio of the thicknesses of the first and second negative electrode active layers is (2-5): (8-5).
11. The lithium ion battery of claim 9, wherein the D50 of the carbon-based anode active material in the first anode active layer is less than the D50 of the carbon-based anode active material in the second anode active layer.
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