CN111816857A

CN111816857A - Nano-silicon composite material with core-shell structure and preparation method and application thereof

Info

Publication number: CN111816857A
Application number: CN202010706618.5A
Authority: CN
Inventors: 黄杰
Original assignee: Individual
Current assignee: Sichuan Wuke Golden Silicon New Material Technology Co ltd
Priority date: 2020-07-21
Filing date: 2020-07-21
Publication date: 2020-10-23
Anticipated expiration: 2040-07-21
Also published as: CN111816857B

Abstract

The invention relates to the technical field of battery cathode materials, in particular to a core-shell nano-silicon composite material and a preparation method and application thereof. The composite material comprises an inner core and an outer shell coated on the surface of the inner core, wherein the inner core is in a porous structure formed by bonding nano silicon and an electronic conductor material together by using a bonding agent, and the outer shell is a conductive polymer layer or a composite layer formed by a conductive polymer and a carbon material. The nano silicon composite material prepared by the invention not only has a core-shell structure, but also has a porous structure as an inner core, wherein the inner core consisting of nano silicon and a conductive material ensures the conductivity of silicon particles, and a polymer layer or a shell formed by a polymer and conductive agent composite layer can effectively solve the side reaction of silicon and the outside in the material mixing process, and the direct contact of silicon and electrolyte is kept, so that the cycling stability of the battery is improved. In addition, the outermost conductive polymer can improve the conductivity of the whole particles, and the cycle efficiency of the battery is greatly improved.

Description

Nano-silicon composite material with core-shell structure and preparation method and application thereof

Technical Field

The invention relates to the technical field of battery cathode materials, in particular to a nano-silicon composite material with a core-shell structure and a preparation method and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The silicon negative electrode material has large volume change in the charging and discharging process, so that the silicon negative electrode material is easy to pulverize and fall off from a current collector, a stable SEI film is difficult to form, a fresh silicon interface embedded with lithium is reduced by contacting with an electrolyte, active lithium is consumed, and the cycle performance of the battery is poor due to the factors. The current methods for solving the problems mainly comprise the following methods: (1) space for silicon expansion is reserved. (2) Reducing the silicon particle size reduces the effect of volume effects. (3) And (5) surface coating treatment.

For example, patent document CN 110556519 a discloses a method for preparing a composite silicon anode material by mechanically mixing silicon particles, porous carbon and polyacrylonitrile, and then forming an anode sheet and heating to carbonize the polyacrylonitrile. The method is simple mechanical mixing, the uniformity and the integrity of the polyacrylonitrile coating on the surface of the silicon particles in the porous carbon are difficult to ensure, and most of the silicon particles can not enter the porous carbon. And the subsequent heat treatment carbonizes polyacrylonitrile, and can also carbonize a binder in the negative electrode material and lose the binding effect, so that an active substance falls off in the circulation process, and the battery circulation is seriously influenced.

For another example, patent document CN 105958023B discloses a method for producing an alumina-coated silicon negative electrode material, in which nano silicon particles are heat-treated in an oxygen-containing atmosphere to obtain an oxide layer, and then mixed with aluminum powder and tin powder for heat treatment, and finally unreacted metal is removed by an acid or an oxidizing agent to obtain an alumina-coated silicon negative electrode material. According to the method, an oxide layer is reduced by using metal aluminum and tin to generate a metal oxide coating layer, but the method is difficult to ensure that a silicon oxide layer is completely reduced to be simple substance silicon, and then the silicon oxide layer and metal are reacted in an acid washing process to enable the surfaces of particles to generate holes, so that the simple substance silicon is exposed, and the use of the particles in a battery is influenced.

Disclosure of Invention

The invention provides a core-shell nano-silicon composite material and a preparation method and application thereof, aiming at the problems of falling and low cycle efficiency caused by product expansion/contraction of a silicon cathode in the charging and discharging processes, the composite material reserves a space required by silicon expansion, can effectively eliminate the negative influence of volume effect on battery cycle, uses polymer to wrap nano-silicon to avoid direct contact of silicon and water, effectively reduces the occurrence of side reaction, and can also prevent the peeling of an active material caused by the volume expansion of silicon, thereby effectively improving the cycle stability of a battery, and the inner-doped and outer-layer-wrapped carbon materials can improve the conductivity of the cathode material and greatly improve the cycle efficiency of the battery.

Specifically, to achieve the above object, the technical solution of the present invention is as follows:

in a first aspect of the invention, a nano-silicon composite material with a core-shell structure is disclosed, which comprises an inner core and an outer shell coated on the surface of the inner core, wherein the inner core is a porous structure formed by bonding nano-silicon and an electronic conductor material together by an adhesive, and the outer shell is a polymer layer or a composite layer formed by a polymer and the electronic conductor material.

Further, the nano-silicon comprises any one or combination of more of crystalline nano-silicon, amorphous nano-silicon, crystalline porous nano-silicon, amorphous porous nano-silicon, crystalline carbon coated nano-silicon, amorphous carbon coated nano-silicon, crystalline carbon coated porous nano-silicon and amorphous carbon coated porous nano-silicon; preferably, the nano silicon particle diameter D50 is between 10nm and 150 nm.

Further, the electronic conductor material is one or a combination of more of carbon nanotubes, super carbon, ketjen carbon, acetylene black, artificial graphite, graphene, multilayer graphite, expanded graphite and vapor-grown carbon fiber.

Further, the adhesive includes any one of polyacrylonitrile, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyvinylidene fluoride, and the like.

Further, the conductive polymer is polymerized by the following polymer monomers: hexafluoropropylene, vinylidene fluoride, acrylonitrile, acrylic acid, polyethylene glycol dimethacrylate, ethylene glycol methyl ether methacrylate, vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tripropoxy silane, hydrogen polysiloxane, trimethyl carbonate, vinyl tri-t-butyl peroxy silane, butadiene, styrene, acrylic acid, maleic acid, lithium maleate, sodium acrylate, lithium acrylate, methacrylic acid, sodium methacrylate, lithium methacrylate, acrylonitrile.

Further, the polymer is prepared from hexafluoropropylene, vinylidene fluoride, acrylonitrile, acrylic acid, polyethylene glycol dimethacrylate, ethylene glycol methyl ether methacrylate, vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tripropoxy silane, hydrogen polysiloxane, trimethyl carbonate, vinyl tri-t-butyl peroxy silane, butadiene, styrene, acrylic acid, maleic acid, lithium maleate, sodium acrylate, lithium acrylate, methacrylic acid, sodium methacrylate, lithium methacrylate, acrylonitrile, one or more of ethylene carbonate, propylene carbonate, methyl methacrylate, acrylic ester, ethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, trifluoroethyl methacrylate, 2- (trifluoromethyl) methyl acrylate, methyl methacrylate, ethyl methacrylate, methyl methacrylate, ethyl methacrylate, one or more of hydroxypropyl methacrylate.

Further, the diameter of the nano silicon composite material with the core-shell structure is between 200nm and 30 μm, and preferably between 300nm and 5 μm.

Further, the thickness of the polymer layer or the composite layer of the polymer and the sub-conductor material is between 10nm and 10 μm, preferably between 10nm and 4 μm.

The second aspect of the invention discloses a preparation method of the core-shell nano-silicon composite material, which comprises the following steps:

(1) dissolving nano silicon, electronic conductor material, solid soluble substance and adhesive in solvent, and granulating to obtain spherical core.

(2) And (2) coating a conductive polymer layer or a composite layer of a polymer and an electronic conductor material on the surface of the inner core obtained in the step (1) to obtain a precursor.

(3) And adding the precursor into a solvent capable of dissolving the solid soluble substances, and dissolving out the solid soluble substances in the inner core to ensure that the inner core has a porous structure.

Further, in the step (1), the mass ratio of the nano silicon, the electronic conductor material, the solid soluble substance and the adhesive is 7.4-9.4: 0.2-0.6: 0.4-1.3: 0 to 0.7.

Further, in the step (1), the solid soluble substance includes any one of water-soluble chloride salt, ethylene carbonate, water-soluble bicarbonate, water-soluble sulfate, urea, water-soluble vitamin, paraffin, and the like.

Further, in the step (1), the solvent includes any one of isopropanol, dimethyl carbonate, N-methyl pyrrolidone solvent, toluene, acetone, ethanol, isopropanol, diethyl ether, and the like, and preferably, a dispersant is added to the solvent.

Further, in the step (1), the granulation method comprises spray drying or ball milling.

Further, in the step (2), the preparation method of the precursor comprises: and uniformly mixing the kernel, the conductive polymer monomer, the electronic conductor material, the initiator and the solvent of the conductive polymer monomer, then heating for polymerization reaction, and drying and crushing the product after the polymerization reaction is finished to obtain the precursor.

Alternatively, the initiator includes azo type initiators, organic peroxide initiators, and the like, and the solvent includes N-methylpyrrolidone, dimethyl carbonate, and the like.

Or, in the step (2), the preparation method of the precursor comprises the following steps: and mixing the inner core, the electronic conductor material and the solution for dissolving the polymer, and then drying to remove the solvent, so as to crush the obtained product.

Further, in the step (2), the mass ratio of the core to the electronic conductor material to the polymer is 85-96%: 0-4: 4 to 11 percent.

Further, in the step (3), the solvent includes any one of water, dimethyl carbonate, cyclohexane, and octane.

In a first aspect of the invention, the use of the core-shell nano-silicon composite material in energy storage components, such as lithium batteries, as a negative electrode material is disclosed.

Compared with the prior art, the invention has the following beneficial effects: the nano silicon composite material prepared by the invention not only has a core-shell structure, but also has a porous structure as an inner core, wherein the inner core consisting of nano silicon and a conductive material ensures the conductivity of silicon particles, and a polymer layer or a shell formed by a polymer and conductive agent composite layer can effectively solve the side reaction of silicon and the outside in the material mixing process, and continuously keeps the direct contact of silicon and electrolyte, thereby improving the cycling stability of the battery. In addition, the outermost conductive polymer can improve the conductivity of the whole particles, and the cycle efficiency of the battery is greatly improved.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

fig. 1 is a schematic structural diagram of a core-shell nano-silicon composite material prepared according to an embodiment of the present invention.

Fig. 2 is a charge-discharge curve of a button cell made of the core-shell nano-silicon composite material of example 1 and the untreated nano-silicon of comparative example 1 as a negative electrode material.

Fig. 3 shows the capacity retention rate of button cell prepared by using the polymer porous nano-silicon negative electrode material of example 1 and the untreated nano-silicon of comparative example 1 as negative electrode materials for 20 weeks.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The reagents or starting materials used in the present invention can be purchased from conventional sources, and unless otherwise specified, the reagents or starting materials used in the present invention can be used in a conventional manner in the art or in accordance with the product specifications. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred methods and materials described in this invention are exemplary only. The invention will now be further illustrated with reference to specific examples.

As described above, the silicon negative electrode material has a large volume change during charging and discharging processes, so that it is easily pulverized, falls off from a current collector, and is difficult to form a stable SEI film, and the lithium-embedded silicon material directly contacts with an electrolyte to consume active lithium, thereby causing capacity fading, which all cause deterioration of battery cycle performance. Therefore, the invention provides a core-shell nano-silicon composite material, which is further explained by combining the attached drawings and the detailed description of the specification.

The method comprises the following steps: the preparation method of the core-shell nano-silicon composite material comprises the following steps:

(1) mixing the nano silicon powder, the electronic conductor material and the solid soluble substance according to a ratio, adding a solvent and a dispersing agent, uniformly mixing, and then granulating to prepare the spherical core.

(2) And (2) mixing the core obtained in the step (1) with a polymer monomer, adding a solvent and an initiator, uniformly stirring, fully polymerizing, drying and crushing a product, namely preparing a shell on the surface of the core by initiating polymerization of the monomer, thereby obtaining the precursor.

(3) Dispersing the precursor in a solvent capable of dissolving the solid soluble substance, removing the solid soluble substance in the inner core, and drying to obtain the product.

The method 2 comprises the following steps: the preparation method of the core-shell nano-silicon composite material comprises the following steps:

(2) And (2) mixing the core obtained in the step (1) with the solution dissolved with the polymer, drying to remove the solvent, and crushing the obtained product, namely preparing a shell on the surface of the core by dissolving, evaporating and coating, so as to obtain the precursor.

The core-shell nano-silicon composite materials A1-A14 are prepared according to the method 1 or the method 2, and the process parameters such as the components, the proportion and the like are shown in the table 1, wherein the products A2 and A4 are prepared by the method 2, and other products are prepared by the method 1.

TABLE 1

The samples A1-A14 in Table 1 were selected for battery assembly and performance testing: in the application of the battery, the above sample (i.e. the composite nano-silicon negative electrode material prepared in each example) is: SP: SBR (styrene butadiene rubber): sizing a CMC (sodium carboxymethylcellulose) with the mass ratio of 95:2:1.5:1.5, coating the sizing agent on a copper foil with the thickness of 8um, drying the sizing agent for 2h at the temperature of 60 ℃ in a blast oven, cutting a plurality of pole pieces with the diameter of 12mm, putting the pole pieces into a vacuum oven for 110 ℃ and drying the pole pieces for 7h, quickly transferring the pole pieces into a glove box after baking is finished, taking a metal lithium piece with the diameter of 14 as a counter electrode, a single-sided ceramic diaphragm and 1mol of LiPF6/(PC + DMC) (1: 1) as electrolyte, assembling the button cell in the glove box, and controlling the water content of the glove box to be less than 0.1 ppm.

Control group: untreated crystalline nano-silicon was directly taken as the negative electrode material of the lithium ion battery (comparative example 1).

The assembled cells were discharged to 5mV at 0.5C, 0.1C, 0.05C step, and constant current charged to 1.5V at 0.1C, and cycled for 50 weeks, with the results shown in Table 2.

TABLE 2

	First effect (%)	Specific capacity of first cycle charge (mAh/g)	Capacity retention ratio (% at 20 weeks)
				Product A1	74.5	2664.9	93.6
Product A2	74.2	2784.6	93.9
				Product A3	74.6	2601.9	93.2
Product A4	74.9	2542	93.5
				Product A5	75.1	2841.3	93.1
Product A6	74.2	2696.4	93.7
				Product A7	74.2	2542.1	93.6
Product A8	74.6	2762.5	93.8
				Product A9	74.3	2789.2	93.2
Product A10	74.8	2551.6	93.4
				Product A11	74.6	2674.4	93.2
Product A12	74.1	2683.8	93.8
				Product A13	74.9	2806.7	93.5
Product A14	74.5	2809.8	93.7
				Comparative example 1	67.4	3189	85.6

From the test results in table 2, it can be seen that the first effect of the core-shell nano-silicon composite product a1-a14 is higher than that of pure silicon, and the minimum is 74.1% which is much higher than 67.4% of comparative example 1. Specifically, as can be seen from the first-cycle charge and discharge curves of the battery in example 1 and the battery in comparative example 1 in fig. 2 and by combining with table 2, the first efficiency of the battery in example 1 is 74.5%, while the first efficiency of the battery in comparative example 1 is only 67.4%, which is 7.1% lower than that of the battery in example 1, because the shell formed by the polymer layer or the polymer and conductive agent composite layer in the nano silicon composite material prepared by the invention can effectively solve the side reaction between silicon and the outside during the material mixing process, and the degree of oxidation of nano silicon is reduced, so that the oxidized nano silicon absorbs active lithium, the loss of active lithium is reduced, and the first-cycle efficiency of the battery is improved. It should be noted that, according to the mass ratio of the nano-silicon to the product a1 of the present invention, the first charge specific capacity of the nano-silicon in the product a1 is 3150mAh/g, which is calculated by using the first charge specific capacity of the battery in example 1, and is not much different from the first charge specific capacity 3189mAh/g of the battery in comparative example 1, which means that the electrochemical performance of the nano-silicon is not affected by the related treatment of the present invention, but rather is greatly improved.

As can be seen from the 20-cycle capacity retention rate graphs of battery example 1 and battery comparative example 1 in fig. 3, the capacity retention rate of battery example 1 is significantly higher than that of battery comparative example 1 because the porous structure of the core-shell nano silicon composite core of the present invention gives enough room for nano silicon to expand during the cycle (refer to fig. 1); the conductive material and the nano-silicon are always kept in good contact, so that the capacity of the nano-silicon can be well exerted; the polymer layer or the polymer and conductive material blending layer continuously keeps direct contact of silicon and electrolyte, and the cycling stability of the battery is improved. In addition, the outermost conductive polymer can improve the conductivity of the whole particles, and the cycle efficiency of the battery is greatly improved.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The nano-silicon composite material with the core-shell structure is characterized by comprising an inner core and a shell layer coated on the surface of the inner core, wherein the inner core is of a porous structure formed by bonding nano-silicon and an electronic conductor material together by using an adhesive, and the shell is a polymer layer or a conductive composite layer formed by mixing the polymer and the electronic conductor material.

2. The core-shell nano-silicon composite material of claim 1, wherein the nano-silicon comprises any one or more of crystalline nano-silicon, amorphous nano-silicon, crystalline porous nano-silicon, amorphous porous nano-silicon, crystalline carbon coated nano-silicon, amorphous carbon coated nano-silicon, crystalline carbon coated porous nano-silicon, and amorphous carbon coated porous nano-silicon; preferably, the nano silicon particle diameter D50 is between 10nm and 150 nm.

3. The core-shell nano-silicon composite material of claim 1, wherein the electron conductor material is a combination of one or more of carbon nanotubes, super carbon, ketjen carbon, acetylene black, artificial graphite, graphene, multi-layered graphite, expanded graphite, and vapor grown carbon fiber.

Or the adhesive comprises any one of polyacrylonitrile, sodium carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, polypropylene salt and polyvinylidene fluoride.

4. The shell layer of the core-shell structured nano-silicon composite material according to claim 1, wherein the polymer is polymerized from one or more of the following polymer monomers: hexafluoropropylene, vinylidene fluoride, acrylonitrile, acrylic acid, polyethylene glycol dimethacrylate, ethylene glycol monomethyl ether methacrylate, vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tripropoxysilane, hydrogen polysiloxane, trimethyl carbonate, vinyl tri-t-butylperoxysilane, butadiene, styrene, acrylic acid, maleic acid, lithium maleate, sodium acrylate, lithium acrylate, methacrylic acid, sodium methacrylate, lithium methacrylate, acrylonitrile;

or the polymer is prepared from hexafluoropropylene, vinylidene fluoride, acrylonitrile, acrylic acid, polyethylene glycol dimethacrylate, ethylene glycol monomethyl ether methacrylate, vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tripropoxy silane, hydrogen polysiloxane, trimethyl carbonate, vinyl tri-t-butyl peroxy silane, butadiene, styrene, acrylic acid, maleic acid, lithium maleate, sodium acrylate, lithium acrylate, methacrylic acid, sodium methacrylate, lithium methacrylate, acrylonitrile, one or more of ethylene carbonate, propylene carbonate, methyl methacrylate, acrylic ester, ethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, trifluoroethyl methacrylate, 2- (trifluoromethyl) methyl acrylate, methyl methacrylate, ethyl methacrylate, One or more of hydroxypropyl methacrylate.

5. The core-shell structured nano-silicon composite according to any of claims 1 to 4, wherein the particle size of the core-shell structured nano-silicon composite is between 200nm and 30 μm, preferably 300nm to 5 μm;

alternatively, the thickness of the shell layer is between 10nm and 10 μm, preferably between 10nm and 4 μm.

6. The preparation method of the core-shell nano-silicon composite material according to any one of claims 1 to 5, characterized by comprising the following steps:

(1) dissolving nano silicon, an electronic conductor material, a solid soluble substance and an adhesive in a solvent, and then granulating to prepare a spherical core for later use;

(2) coating a polymer layer or a composite layer of a polymer and an electronic conductor material on the surface of the inner core obtained in the step (1) to obtain a precursor;

(3) and adding the precursor into a solvent capable of dissolving the solid soluble substances, and dissolving the solid soluble substances in the inner core out to ensure that the inner core has a porous structure.

7. The preparation method of the core-shell nano-silicon composite material according to claim 6, wherein in the step (1), the mass ratio of the nano-silicon to the electronic conductor material to the solid soluble substance to the adhesive is 7.4-9.4: 0.2-0.6: 0.4-1.3: 0 to 0.7.

Alternatively, in the step (1), the solid solubles include any one of water-soluble chloride salt, ethylene carbonate, water-soluble bicarbonate, water-soluble sulfate, urea, water-soluble vitamin and paraffin.

Alternatively, in the step (1), the solvent includes any one of isopropanol, dimethyl carbonate, N-methylpyrrolidone solvent, toluene, acetone, ethanol, isopropanol, heptane and diethyl ether, and preferably, a dispersant is added into the solvent.

Alternatively, in the step (1), the granulation method comprises spray drying or ball milling.

8. The preparation method of the core-shell nano-silicon composite material according to claim 6 or 7, wherein in the step (2), the preparation method of the precursor comprises the following steps: uniformly mixing the inner core, the polymer monomer, the initiator, the electronic conductor material and a solvent of the polymer monomer, then heating for polymerization reaction, and drying and crushing a product after the polymerization reaction is finished to obtain a precursor; preferably, the initiator includes azo-type initiator, organic peroxide initiator, etc., and the solvent includes N-methylpyrrolidone, dimethyl carbonate, ethanol;

or, in the step (2), the preparation method of the precursor comprises the following steps: mixing the core, the electronic conductor material and the solution for dissolving the polymer, then drying to remove the solvent, and crushing the obtained product to obtain a precursor;

or in the step (2), the mass ratio of the core to the electronic conductor material to the polymer is 85-96%: 0-4%: 4 to 11 percent.

9. The method for preparing the core-shell nano-silicon composite material according to claim 8, wherein in the step (3), the solvent comprises any one of water, dimethyl carbonate, ethylene glycol dimethyl ether and octane cyclohexane.

10. Use of the core-shell nano-silicon composite material according to any of claims 1 to 5 or the core-shell nano-silicon composite material prepared by the method according to any of claims 6 to 9 in an energy storage component, preferably as a negative electrode material in a lithium battery.