CN108511719B

CN108511719B - Double-shell-layer-structure composite material, preparation method thereof and lithium ion battery comprising composite material

Info

Publication number: CN108511719B
Application number: CN201810272638.9A
Authority: CN
Inventors: 何鹏; 车宗洲; 任建国; 黄友元; 岳敏
Original assignee: BTR New Material Group Co Ltd
Current assignee: BTR New Material Group Co Ltd
Priority date: 2018-03-29
Filing date: 2018-03-29
Publication date: 2021-01-19
Anticipated expiration: 2038-03-29
Also published as: CN108511719A

Abstract

The invention discloses a double-shell structure composite material, a preparation method thereof and a lithium ion battery containing the composite material. The double-shell structure composite material comprises a nano-silicon core, wherein a first coating layer and a second coating layer are sequentially arranged on the surface of the core, the first coating layer is nano-metal particles embedded on the surface of the core, and pores are formed among the nano-metal particles; the second coating layer is a carbon coating layer on the outermost side of the composite material. According to the invention, a layer of metal hydroxide is coated on the surface of the nano-silicon particles in situ, then the surface of the nano-silicon particles is coated with organic carbon, the organic carbon of the coating layer is carbonized at a high temperature, the metal hydroxide of the first coating layer is firstly decomposed into metal oxide, and then the metal oxide is reduced into nano-metal simple substance particles by the carbon coating layer of the second coating layer, a large number of pores are left, and the composite material with the double-shell structure is obtained. The invention has simple process, and the composite material has very high specific capacity and excellent cycle performance when being used for the cathode of the lithium ion battery.

Description

Double-shell-layer-structure composite material, preparation method thereof and lithium ion battery comprising composite material

Technical Field

The invention belongs to the field of lithium ion battery cathode materials, and relates to a double-shell structure composite material, a preparation method thereof and a lithium ion battery containing the composite material, in particular to a double-shell structure silicon/nano copper/carbon composite cathode material, a preparation method thereof and a lithium ion battery containing the composite cathode material.

Background

At present, most of the commercialized negative electrode materials of lithium ion secondary batteries are various graphite materials such as natural graphite, artificial graphite and the like, although the graphite materials have many advantages, such as rich raw materials, low lithium intercalation potential, good cycle performance and the like. However, the theoretical capacity of the graphite material is only 372mA h/g, which cannot meet the increasing demand of the current market for high energy density lithium ion batteries, and in order to adapt to the market change, a novel high energy density negative electrode material needs to be developed to replace the graphite material. The silicon material as the negative electrode material has high theoretical specific capacity (4200mA h/g) and a low lithium removal potential platform, and is an ideal choice for replacing graphite to become a new generation of negative electrode material of lithium batteries. However, the silicon negative electrode is accompanied by large volume expansion (up to 300%) in the process of lithium removal/insertion, so that silicon particles are crushed and pulverized, the material loses activity, and finally, the cycle performance is seriously attenuated; in addition, silicon has low conductivity and poor rate capability. These factors together limit the application of silicon in the negative electrode material of lithium battery.

In order to solve the above-mentioned problems of the silicon negative electrode, researchers have conducted a lot of research in recent years. On one hand: silicon is subjected to nanoscale treatment, such as silicon nanowires, silicon nanoparticles and nano-microstructure porous silicon, so that the volume effect of the silicon nanowires, the silicon nanoparticles and the nano-microstructure porous silicon can be relieved to a certain extent, and the circulation stability of the material is improved; on the other hand: silicon is compounded with carbon-based materials with stable mechanical properties and good conductivity to prepare silicon/graphite, silicon/carbon nanotubes, silicon/mesoporous carbon, silicon/graphene and other composite materials, so that the overall conductivity of the composite material is increased, and the stress caused by volume expansion of the silicon in the charging and discharging processes can be effectively relieved. In addition, the silicon-based composite material with the porous structure is designed, an expansion space is reserved, the volume expansion of the silicon cathode material in the charging and discharging process can be further relieved, and the material cycling stability is improved.

Although a large number of documents report methods for improving the electrochemical properties of silicon-based materials, compared with commercial graphite materials, the volume expansion of the materials prepared by the methods is still large, and the cycle retention rate is poor, so that the requirements of commercial negative electrode materials are far from being met.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a composite material with a double-shell structure, a preparation method thereof and a lithium ion battery containing the composite material, in particular to a silicon/nano-copper/carbon composite cathode material with a double-shell structure, a preparation method thereof and a lithium ion battery containing the composite cathode material.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a composite material with a double-shell structure, which comprises a nano-silicon core, wherein a first coating layer and a second coating layer are sequentially arranged on the surface of the core, the first coating layer is a nano-metal particle embedded on the surface of the core, and the second coating layer is a carbon coating layer on the outermost side of the composite material; wherein pores exist among the nano metal particles of the first coating layer.

The double-shell structure composite material can be referred to as a double-shell structure silicon/nano metal/carbon composite material for short. The inner core is made of nano silicon, a large number of nano metal particles (such as copper particles) are inlaid on the surface of the inner core, the outer layer is a compact carbon coating layer, and pores are formed among the nano metal particles of the first coating layer. In the structure, metal particles such as copper are in close contact with the core nano-silicon and the outer carbon coating layer, so that a bridge effect is achieved, the expansion of nano-silicon can be relieved, and the conductivity of the material can be improved. The pores between the nano-metal particles of the first coating further reserve expansion space for the expansion of the nano-silicon. Therefore, the material has excellent electrochemical performance when being used for the negative electrode of the lithium ion battery.

The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.

Preferably, the nano silicon is crystalline silicon.

Preferably, the nano-silicon has a median particle size of 50nm to 120nm, such as 50nm, 65nm, 80nm, 90nm, 100nm, 105nm, 110nm, 120nm, or the like.

Preferably, the nano metal particles are any one or a combination of at least two of copper nanoparticles, nano zinc particles or nano iron particles, and are preferably nano copper particles.

Preferably, the particle size of the nano-metal particles is in the range of 10nm to 30nm, such as 10nm, 15nm, 18nm, 20nm, 22nm, 25nm, or 30nm, and the like.

Preferably, the carbon coating layer is amorphous carbon, and preferably includes any one or a combination of at least two of resin carbon, coke, mesocarbon microbeads, pitch cracked carbon, polymer cracked carbon, or carbon fibers.

Preferably, the carbon coating has a thickness of 50nm to 300nm, such as 50nm, 70nm, 80nm, 100nm, 125nm, 150nm, 170nm, 180nm, 200nm, 220nm, 240nm, 260nm, 300nm, or the like.

As a preferable embodiment of the composite material of the present invention, the width of the pores between the nano metal particles of the first coating layer is 10nm to 30nm, for example, 10nm, 15nm, 20nm, 22nm, 24nm, 28nm, or 30 nm.

Preferably, the pores have a pore volume of 0.2cc/g to 0.4cc/g, such as 0.2cc/g, 0.22cc/g, 0.25cc/g, 0.28cc/g, 0.3cc/g, 0.35cc/g, or 0.4cc/g, and the like.

In a second aspect, the present invention provides a process for the preparation of a double shell structured composite material as described in the first aspect, said process comprising the steps of:

(1) preparing a solution of nano-silicon particles;

(2) coating metal hydroxide on the surface of the nano silicon particles by using the solution of the nano silicon particles obtained in the step (1), and drying to obtain a precursor I;

(3) and (3) coating the precursor I obtained in the step (2) with organic carbon, and then calcining to obtain the composite material with the double-shell structure.

According to the method, a layer of metal hydroxide is coated on the surface of the nano silicon particles, then organic carbon coating is carried out on the surface of the nano silicon particles, the organic matter of the coating layer is carbonized at high temperature, the metal hydroxide in the middle layer is decomposed into copper oxide firstly, and then the copper oxide is reduced into metal simple substance nano particles (such as copper nano particles) by the carbon coating layer, and a large number of pores are left, so that the double-shell structure composite material, namely the double-layer core-shell structure silicon/nano metal/carbon composite material, is obtained.

As a preferred technical solution of the method of the present invention, the solution for preparing nano silicon particles in step (1) is prepared by any one of a first method or a second method, wherein the first method comprises: dispersing the nano silicon particles in a solvent, and carrying out ultrasonic stirring to obtain a solution of the nano silicon particles.

The second method comprises the following steps: dispersing the nano silicon particles into the solvent under the condition of ultrasonic stirring, and continuously stirring for 0.5-3 h to obtain a solution of the nano silicon particles.

The solution of the nano silicon particles prepared by the invention is in a uniform or uniformly dispersed state.

Preferably, the solvent in the first and second methods is independently any one or a mixed solvent of at least two of water, ethanol, propanol, isopropanol, butanol, acetone, ethyl acetate or N-methyl pyrrolidone (NMP).

Preferably, the solvent in the first and second methods is independently a mixed solvent of water and alcohol, and the mass percentage of the alcohol is 50% to 80%, for example, 50%, 60%, 65%, 70%, 75%, or 80%, etc., based on 100% of the total mass of the mixed solvent.

As a preferred technical scheme of the method, the coating in the step (2) is in-situ coating, and the specific operation of preparing the precursor I in the step (2) comprises the following steps: mixing the water-soluble metal salt and the solution of the nano silicon particles, adjusting the pH value to 2-5, ultrasonically stirring, adding an alkali solution, enabling the metal hydroxide to be embedded on the surface of the nano silicon particles, and stopping adding the alkali solution when the pH value of the solution is 7 to obtain a precursor I.

In the preferable technical scheme, after the water-soluble metal salt and the nano silicon particle solution are mixed, the pH is adjusted to 2-5, such as 2, 3, 4 or 5, and the like, and is preferably 3. The regulator used for adjusting the pH is an acid, for example 0.5mol/L hydrochloric acid.

Preferably, in the process of preparing the first precursor in the step (2), the water-soluble metal salt includes any one of or a combination of at least two of water-soluble copper salt, zinc salt or iron salt.

Preferably, in the preparation of the first precursor in the step (2), the molar ratio of the water-soluble metal salt to the nano-silicon particles in the solution of the nano-silicon particles is 2-12, for example, 2, 2.3, 2.5, 3, 4, 5, 6, 7, 8, 10, 11 or 12, and the like, and is preferably 10: 3.

Preferably, in the process of preparing the first precursor in the step (2), the time of ultrasonic stirring after the pH is adjusted is 0.5h to 1h, and preferably 0.5 h.

Preferably, in the process of preparing the first precursor in the step (2), the alkali solution is a sodium hydroxide solution, and the concentration of the alkali solution is preferably 0.5 mol/L.

Preferably, in the process of preparing the first precursor in the step (2), the method further comprises the steps of continuing stirring for 0.5h and filtering after the addition of the alkali solution is stopped.

As a preferable technical scheme of the method of the present invention, the organic carbon coating method in step (3) comprises: any one of in-situ polymerization coating, in-situ solvent thermal carbon coating or liquid phase coating.

Preferably, in the method for in-situ polymerization coating, the polymer obtained by in-situ polymerization coating comprises any one or a combination of at least two of polyacrylic acid, polymeric phenolic resin or polymeric dopamine.

Preferably, the specific operations of the in-situ polymerization coating comprise: dispersing the precursor I into a solvent, adding a reaction monomer, and polymerizing in the presence of an oxidative initiator to enable the reaction monomer to perform a polymerization reaction on one surface of the precursor I. For different kinds of reaction monomers, in order to obtain better polymerization effect, the pH value of the slurry needs to be properly adjusted, which is prior art and will not be described herein.

Preferably, in the in-situ polymerization coating method, the oxidative initiator is any one or a combination of at least two of ammonium persulfate, sodium persulfate and hydrogen peroxide.

Preferably, the reactive monomer in the in situ polymerization coating method comprises any one of acrylic acid, aniline or dopamine monomer or a combination of at least two of the acrylic acid, aniline or dopamine monomer.

Preferably, the specific operations of in-situ solvent thermal carbon coating comprise: dispersing the precursor I into a solvent, then adding a carbon source to form slurry, and placing the obtained slurry into a solvothermal reaction kettle for reaction for a period of time.

Preferably, in the in-situ solvent thermal carbon coating method, the carbon source is any one or a combination of at least two of glucose, sucrose or pitch.

Preferably, in the in-situ solvent thermal carbon coating method, the mass ratio of the precursor I to the carbon source is 1 (0.5-2), for example, 1:0.5, 1:0.8, 1:1, 1:1.5, 1:1.7 or 1:2, and preferably 1:2.

Preferably, in the in-situ solvent thermal carbon coating method, the carbon source is added and then stirred to form a uniform slurry.

Preferably, in the in-situ solvent hot carbon coating method, the reaction temperature is 100 ℃ to 180 ℃, for example, 100 ℃, 120 ℃, 125 ℃, 135 ℃, 150 ℃, 160 ℃, 180 ℃ or the like.

Preferably, in the in-situ solvent thermal carbon coating method, the reaction time is 2h to 10h, such as 2h, 3h, 5h, 6h, 7h, 8h, 9h or 10 h.

Preferably, the liquid phase coating comprises the following specific operations: dispersing the precursor I into a solvent, adding a carbon source to form slurry, and then carrying out spray drying;

preferably, in the liquid phase coating method, the solvent is any one of deionized water, ethanol or isopropanol or a combination of at least two of the deionized water, the ethanol and the isopropanol.

Preferably, in the liquid phase coating method, the carbon source is any one or a combination of at least two of glucose, sucrose or pitch.

Preferably, in the liquid phase coating method, the mass ratio of the precursor I to the carbon source is 1 (0.5-2), for example, 1:0.5, 1:0.8, 1:1, 1:1.5, 1:1.7 or 1:2, preferably 1: 2;

preferably, in the liquid phase coating method, the carbon source is added and then stirred to form a uniform slurry.

Preferably, the calcination of step (3) is carried out under the protection of protective gas.

Preferably, the protective gas comprises any one of nitrogen, helium, neon, argon or xenon, or a combination of at least two thereof.

Preferably, the temperature of the calcination in step (3) is 600 ℃ to 1000 ℃, such as 600 ℃, 650 ℃, 700 ℃, 800 ℃, 850 ℃, 900 ℃, or 1000 ℃, etc.

Preferably, the calcination time in step (3) is 1h to 6h, such as 1h, 2h, 3h, 3.5h, 4h, 5h or 6 h.

As a further preferred technical solution of the method of the present invention, the method comprises the steps of:

(1) dispersing nano silicon particles with the median particle size of 50 nm-120 nm in a mixed solvent of water and alcohol, and ultrasonically stirring to obtain a uniformly dispersed nano silicon particle solution;

(2) adjusting the pH value of a copper salt aqueous solution and a nano-silicon particle solution to 3, ultrasonically stirring for 0.5h, then adding a 0.5mol/L sodium hydroxide solution to coat the copper hydroxide on the surface of the nano-silicon particle, stopping adding the sodium hydroxide solution when the pH value of the solution is 7, continuously stirring for 0.5h, filtering, and drying to obtain a precursor I;

(3) carrying out in-situ polymerization coating on the precursor I obtained in the step (2), and calcining for 1-6 h at 600-1000 ℃ under the protection of protective gas to obtain a composite material with a double-shell structure;

wherein the polymer obtained by in-situ polymerization coating is any one or the combination of at least two of polyacrylic acid, polymeric phenolic resin or polymeric dopamine.

In a third aspect, the invention provides a lithium ion battery electrode material, which is the composite material with the double-shell structure of the first aspect.

Preferably, the electrode material is an anode material.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the method, firstly, a layer of metal hydroxide is coated on the surface of the nano silicon particles, then, the surface of the nano silicon particles is coated with organic carbon, the organic carbon of the coating layer is carbonized at a high temperature, simultaneously, the metal hydroxide of the first coating layer is firstly decomposed into metal oxide, and then the metal oxide is reduced into nano metal simple substance particles (such as nano copper particles) by the carbon coating layer of the second coating layer, and a large number of pores are left, so that the double-shell structure composite material, namely the double-layer core-shell structure silicon/nano metal/carbon composite material, is obtained.

(2) The method has simple process and easy operation, and is suitable for industrial production.

(3) The double-shell structure composite material has a novel structure, the inner core is made of nano silicon, the first coating layer is a large number of nano metal particles (such as copper particles) embedded on the surface of the inner core, the second coating layer is a compact carbon coating layer, and pores are formed among the nano metal particles of the first coating layer. In the structure, metal particles such as copper are in close contact with the core nano-silicon and the second coating layer carbon coating layer, so that the bridge effect is achieved, the expansion of nano-silicon can be relieved, and the conductivity of the material can be improved. The pores between the nano-metal particles of the first coating further reserve expansion space for the expansion of the nano-silicon. Therefore, the material has high specific capacity and excellent cycle performance: the 0.1C discharge capacity is larger than 1600mA h/g, the first charge-discharge efficiency is larger than 89%, and the capacity is kept above 95% after 50 cycles.

Drawings

FIG. 1a is a schematic structural diagram of a sample prepared in example 1 of the present invention, wherein 1-nano-copper, 2-nano-silicon, 3-pore, 4-carbon coating layer.

FIG. 1b is an SEM image of a sample prepared in example 1 of the present invention.

Figure 2 is an XRD pattern of a sample prepared in example 1 of the present invention.

Fig. 3 is a first-cycle charge and discharge curve of a battery fabricated using a sample prepared in example 1 of the present invention for a negative electrode.

Fig. 4 is a cycle curve of a battery fabricated using a sample prepared in example 1 of the present invention for a negative electrode.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

The anode materials of the respective examples and comparative examples were tested by the following methods:

the particle size range of the material and the average particle size of the raw material particles are tested by a Malvern laser particle size tester MS 2000.

② adopting X' Pert Pro, PANALYTICAL to test the structure of the material.

Thirdly, observing the surface appearance, the particle size and the particle section of the sample by adopting a scanning electron microscope of the Hitachi S4800.

Fourthly, testing the first charge-discharge performance by adopting the following method:

dissolving the negative electrode material, the conductive agent and the binder of each embodiment and the comparative example in a solvent according to the mass percentage of 80:10:10, mixing, coating the obtained mixed slurry on a copper foil current collector, and drying in vacuum to obtain a negative electrode piece; then 1mol/L LiPF6/EC + DMC + EMC (v/v ═ 1:1:1) electrolyte, SK (12 μm) diaphragm and shell were used to assemble CR2016 button cell by conventional process, electrochemical performance test current density 1C equals 1000mA h/g.

Example 1

(1) Dispersing nano-silicon with the median particle size of 100nm in a mixed solvent of ethanol and deionized water, wherein the mass ratio of the ethanol to the deionized water is 8:2, and ultrasonically stirring for 1h to obtain a precursor suspension A.

(2) Adding copper sulfate solid with a molar ratio of 10:3 to nano-silicon into the precursor suspension A under the condition of stirring, then dropwise adding 0.5mol/L hydrochloric acid solution into the solution to adjust the pH of the solution to be 3, continuously dropwise adding 0.5mol/L sodium hydroxide solution into the solution after ultrasonic stirring for 0.5h to convert copper particles into copper hydroxide and uniformly coat the copper hydroxide on the surfaces of the nano-silicon particles, stopping dropwise adding the sodium hydroxide solution when the pH of the solution is 7, continuously stirring for 0.5h, filtering, and drying to obtain a precursor I.

(3) Dispersing the precursor I obtained in the step (2) in deionized water, adding glucose with the mass ratio of 1:2 to the precursor I, stirring for 0.5h, then carrying out spray drying on the mixture, firing the spray-dried product at 850 ℃ for 2h under inert gas, screening the fired sample to obtain the double-layer core-shell structure silicon/nano-copper/carbon composite material, and detecting the negative electrode material sample, wherein the result is shown in table 1.

FIG. 1a is a schematic structural diagram of a sample prepared in example 1, wherein the sample comprises 1-nano-copper, 2-nano-silicon, 3-pore, and 4-carbon coating.

FIG. 1b is an SEM image of the sample prepared in example 1, and it can be seen that the sample surface is coated with a dense carbon layer.

Fig. 2 is an XRD pattern of the sample prepared in this example 1, from which diffraction peaks of silicon, copper and carbon are clearly observed.

Fig. 3 is a first cycle charge and discharge curve of a battery using the sample prepared in this example 1 for a negative electrode, from which it can be seen that the material has a first charge capacity of 1605mA h/g and a first coulombic efficiency of 89%.

Fig. 4 is a cycle curve of a battery using the sample prepared in this example 1 for a negative electrode, the capacity retention ratio of the sample material is 95.6% after 50 cycles at a current density of 1C, and the material has excellent cycle stability.

Example 2

(1) Dispersing nano-silicon with the median particle size of 100nm in a mixed solvent of ethanol and deionized water, wherein the mass ratio of the ethanol to the deionized water is 8:3, and ultrasonically stirring for 1h to obtain a precursor suspension A.

(2) Adding a copper chloride solid with a molar ratio of 10:3 to nano-silicon into the precursor suspension A under the condition of stirring, then dropwise adding 0.5mol/L hydrochloric acid solution into the solution to adjust the pH of the solution to be 3, continuously dropwise adding 0.5mol/L sodium hydroxide solution into the solution after ultrasonic stirring for 0.5h to convert copper particles into copper hydroxide and uniformly coat the copper hydroxide on the surfaces of the nano-silicon particles, stopping dropwise adding the sodium hydroxide solution when the pH of the solution is 7, continuously stirring for 0.5h, filtering, and drying to obtain a precursor I.

(3) Dispersing the precursor I obtained in the step (2) in deionized water, adding aniline monomer with the mass ratio of 1:2.5, dropwise adding hydrochloric acid solution with the concentration of 0.5Mol/L to adjust the pH value to about 5, then adding ammonium persulfate powder with the mass ratio of 5:3 to aniline, stirring for 8 hours, filtering and drying, heating the dried precursor to 900 ℃, preserving the temperature for 2 hours, naturally cooling to room temperature, screening to obtain the double-layer core-shell structure silicon/nano copper/carbon composite material, and detecting a negative electrode material sample, wherein the result is shown in table 1.

Example 3

(1) Dispersing nano-silicon with the median particle size of 100nm in an ethanol/deionized water mixed solvent, wherein the mass ratio of ethanol to deionized water is 1:1, and ultrasonically stirring for 1h to obtain a precursor suspension A.

(3) And (3) dispersing the precursor I obtained in the step (2) and asphalt in a n-butanol solution according to the mass ratio of 55:45, stirring for 30min, and then carrying out spray drying to obtain a precursor II with the median particle size of 10 microns. And then placing the obtained precursor II in a box-type furnace, introducing nitrogen, heating to 850.0 ℃ at the heating rate of 3.0 ℃/min, preserving the heat for 2.0h, naturally cooling to room temperature, screening to obtain the double-layer core-shell structure silicon/nano copper/carbon composite material, and detecting a negative electrode material sample, wherein the result is shown in table 1.

Example 4

The preparation method and conditions were the same as in example 1, except that:

the median particle size of the nano silicon in the step (1) is 50nm, and the ultrasonic stirring time is 0.5 h;

dropwise adding hydrochloric acid to adjust the pH value of the solution to 4;

and (3) firing for 6h at 650 ℃ under inert gas.

Example 5

The preparation method and conditions were the same as in example 1 except for the step (3):

the specific operation of the step (3) is as follows: and (3) dispersing the precursor I obtained in the step (2) and glucose in a deionized water solution according to the mass ratio of 50:100, stirring for 30min, placing the mixture in a hydrothermal reaction kettle for reaction at 180 ℃ for 6h, naturally cooling, filtering and drying to obtain a precursor II with the median particle size of 8 microns. And then placing the obtained precursor II in a box-type furnace, introducing nitrogen, heating to 750.0 ℃ at the heating rate of 3.0 ℃/min, preserving the heat for 2.0h, naturally cooling to room temperature, and screening to obtain the double-layer core-shell structure silicon/nano copper/carbon composite material.

Example 6

The preparation method and conditions were the same as in example 1 except that copper chloride was replaced with zinc chloride.

Comparative example 1

(1) Dispersing nano silicon with the median particle size of 100nm in an ethanol/deionized water (mass ratio of 1:1) mixed solvent, and ultrasonically stirring for 1h to obtain a precursor suspension A.

(2) And (2) adding glucose with the mass ratio of 1:2 to the nano-silicon into the precursor suspension A obtained in the step (1) under the stirring condition, stirring for 0.5h, then carrying out spray drying on the precursor suspension A, firing the spray-dried product at 850 ℃ under inert gas for 2h, screening the fired sample to obtain the core-shell structure silicon/carbon composite material, and detecting the negative electrode material sample, wherein the result is shown in table 1.

TABLE 1

It can be seen from the examples and the comparative examples that the double-layer core-shell structure silicon/nano metal/carbon composite material prepared in the examples of the invention has excellent electrochemical performance, and in the negative electrode material of the comparative example, no nano metal particles exist on the surface of the inner core, no gap exists between the core and the shell, and the first coulombic efficiency and the cycle performance are poor.

The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. The composite material with the double-shell structure is characterized by comprising a nano-silicon core, wherein a first coating layer and a second coating layer are sequentially arranged on the surface of the core, the first coating layer is a nano-metal particle embedded on the surface of the core, and the second coating layer is a carbon coating layer on the outermost side of the composite material;

wherein pores exist among the nano metal particles of the first coating layer;

the double-shell structure composite material is prepared by the following method, and the method comprises the following steps:

(1) preparing a solution of nano-silicon particles;

(2) mixing a water-soluble metal salt and a nano silicon particle solution, adjusting the pH value to 2-5, ultrasonically stirring, and then adding an alkali solution to enable a metal hydroxide to be embedded on the surface of the nano silicon particle to obtain a precursor I;

2. The composite material of claim 1, wherein the nano-silicon is crystalline silicon.

3. The composite material of claim 1, wherein the nano-silicon has a median particle size of 50nm to 120 nm.

4. The composite material of claim 1, wherein the nano-metal particles are any one of nano-copper particles, nano-zinc particles or nano-iron particles or a combination of at least two of the nano-copper particles, the nano-zinc particles or the nano-iron particles.

5. The composite material of claim 1, wherein the nano-metal particles are nano-copper particles.

6. The composite material of claim 1, wherein the nano-metal particles have a particle size of 10nm to 30 nm.

7. The composite of claim 1, wherein the carbon coating is amorphous carbon.

8. The composite of claim 7, wherein the carbon coating comprises any one or a combination of at least two of resinous carbon, coke, mesocarbon microbeads, pitch cracked carbon, polymer cracked carbon, or carbon fibers.

9. The composite material of claim 1, wherein the carbon coating layer has a thickness of 50nm to 300 nm.

10. The composite material of claim 1, wherein the width of the pores is 10nm to 30 nm.

11. The composite of claim 1, wherein the pores have a pore volume of 0.2cc/g to 0.4 cc/g.

12. A method of making a double shell structured composite material as claimed in claim 1, comprising the steps of:

(1) preparing a solution of nano-silicon particles;

13. The method of claim 12, wherein the step (1) of preparing the solution of nano-silicon particles is performed by any one of a first method or a second method, wherein the first method comprises: dispersing the nano silicon particles in a solvent, and ultrasonically stirring to obtain a solution of the nano silicon particles;

14. The method according to claim 13, wherein the solvent in the first and second methods is independently any one or a mixed solvent of at least two of water, ethanol, propanol, isopropanol, butanol, acetone, ethyl acetate or N-methylpyrrolidone.

15. The method according to claim 13, wherein the solvent in the first and second methods is independently a mixed solvent of water and alcohol, and the mass percent of the alcohol is 50-80% based on 100% of the total mass of the mixed solvent.

16. The method of claim 12, wherein in the step (2) of preparing the first precursor, the water-soluble metal salt comprises any one of or a combination of at least two of water-soluble copper salt, zinc salt or iron salt.

17. The method according to claim 12, wherein the molar ratio of the water-soluble metal salt to the nano-silicon particles in the solution of the nano-silicon particles in the step (2) of preparing the first precursor is 2-12.

18. The method of claim 17, wherein during the step (2) of preparing the first precursor, the molar ratio of the water-soluble metal salt to the nano-silicon particles in the solution of nano-silicon particles is 10: 3.

19. The method of claim 12, wherein during the step (2) of preparing the first precursor, the pH is adjusted by using an acid.

20. The method of claim 12, wherein during the step (2) of preparing precursor one, the pH is adjusted to 3.

21. The method according to claim 12, wherein in the process of preparing the first precursor in the step (2), the time of ultrasonic stirring after the pH is adjusted is 0.5h to 1 h.

22. The method of claim 21, wherein during the preparation of the first precursor in the step (2), the time for ultrasonic stirring after the pH is adjusted is 0.5 h.

23. The method of claim 12, wherein during the step (2) of preparing the first precursor, the alkali solution is a sodium hydroxide solution.

24. The method according to claim 12, wherein the concentration of the alkali solution is 0.5 mol/L.

25. The method according to claim 12, wherein during the preparation of the first precursor in the step (2), the addition of the alkali solution is stopped when the pH of the solution is 7, and after the addition of the alkali solution is stopped, the stirring is continued for 0.5h and the filtering is performed.

26. The method of claim 12, wherein the organic carbon coating method of step (3) is: any one of in-situ polymerization coating, in-situ solvent thermal carbon coating or liquid phase coating.

27. The method of claim 26, wherein in the method of in situ polymerization coating, the polymer obtained by in situ polymerization coating comprises any one or a combination of at least two of polyacrylic acid, polyaniline, polymeric phenolic resin or polymeric dopamine.

28. The method of claim 26, wherein the in situ polymerization coating comprises: dispersing the precursor I into a solvent, adding a reaction monomer, and polymerizing in the presence of an oxidative initiator to enable the reaction monomer to perform a polymerization reaction on one surface of the precursor I.

29. The method of claim 28, wherein in the in-situ polymerization coating method, the oxidative initiator is any one or a combination of at least two of ammonium persulfate, sodium persulfate and hydrogen peroxide.

30. The method of claim 28, wherein in the in situ polymerization coating method, the reactive monomer comprises any one or a combination of at least two of acrylic acid, aniline, or dopamine monomers.

31. The method of claim 26, wherein the in-situ solvothermal carbon coating comprises: dispersing the precursor I into a solvent, then adding a carbon source to form slurry, and placing the obtained slurry into a solvothermal reaction kettle for reaction.

32. The method of claim 31, wherein in the in situ solvent thermal carbon coating method, the carbon source is any one or a combination of at least two of glucose, sucrose or pitch.

33. The method of claim 31, wherein in the in-situ solvent thermal carbon coating method, the mass ratio of the precursor I to the carbon source is 1 (0.5-2).

34. The method of claim 33, wherein the mass ratio of the precursor one to the carbon source in the in-situ solvothermal carbon coating method is 1:2.

35. The method of claim 31, wherein the in-situ solvothermal carbon coating method comprises stirring after adding the carbon source to form a uniform slurry.

36. The method of claim 31, wherein the in situ solvent thermal carbon coating method comprises a reaction temperature of 100 ℃ to 180 ℃.

37. The method of claim 31, wherein the in situ solvent thermal carbon coating method comprises a reaction time of 2 to 10 hours.

38. The method according to claim 26, wherein the liquid phase coating comprises: dispersing the precursor I into a solvent, then adding a carbon source to form slurry, and then carrying out spray drying.

39. The method of claim 38, wherein in the liquid phase coating method, the solvent is any one of deionized water, ethanol or isopropanol or a combination of at least two of the deionized water, the ethanol and the isopropanol.

40. The method of claim 38, wherein in the liquid phase coating method, the carbon source is any one or a combination of at least two of glucose, sucrose or pitch.

41. The method of claim 38, wherein the mass ratio of the precursor I to the carbon source in the liquid phase coating method is 1 (0.5-2).

42. The method of claim 41, wherein in the liquid phase coating method, the mass ratio of the precursor I to the carbon source is 1:2.

43. The method of claim 38, wherein the liquid phase coating method comprises stirring after adding the carbon source to form a uniform slurry.

44. The method of claim 12, wherein the calcining of step (3) is performed under a protective gas.

45. The method of claim 44, wherein the protective gas comprises any one of nitrogen, helium, neon, argon, or xenon, or a combination of at least two thereof.

46. The method according to claim 12, wherein the temperature of the calcination in the step (3) is 600 ℃ to 1000 ℃.

47. The method of claim 12, wherein the calcination time in step (3) is 1-6 hours.

48. A method according to any of claims 12-47, characterized in that the method comprises the steps of:

49. A lithium ion battery electrode material, characterized in that the lithium ion battery electrode material is the double-shell structure composite material of any one of claims 1 to 11.

50. The lithium ion battery electrode material of claim 49, wherein the electrode material is an anode material.