CN112366306B - Nano silicon composite negative electrode material and manufacturing method thereof - Google Patents

Nano silicon composite negative electrode material and manufacturing method thereof Download PDF

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CN112366306B
CN112366306B CN202110033033.6A CN202110033033A CN112366306B CN 112366306 B CN112366306 B CN 112366306B CN 202110033033 A CN202110033033 A CN 202110033033A CN 112366306 B CN112366306 B CN 112366306B
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nano
silicon
anode material
silicon composite
composite anode
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CN112366306A (en
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喻维杰
李福生
张锡强
赵常
代学志
詹勇军
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Tuomi Chengdu Applied Technology Research Institute 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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 relates to a nano silicon composite negative electrode material and a manufacturing method thereof. The nano-silicon composite negative electrode material comprises multi-coating nano-silicon powder and in-situ grown carbon nanotubes, wherein the multi-coating nano-silicon powder comprises a core part of nano-silicon particles and a composite coating layer arranged on the core part, and the composite coating layer comprises conductive carbon, polyacene and inorganic metal oxide.

Description

Nano silicon composite negative electrode material and manufacturing method thereof
Technical Field
The invention relates to the technical field of battery materials, in particular to a nano silicon composite anode material and a manufacturing method thereof.
Background
The development of human society is severely restricted by the excessive consumption of fossil fuels and the consequent environmental problems in the world today. The construction of a novel society with high efficiency, energy conservation, low carbon and environmental protection becomes the target of the global efforts of all countries. Mankind has formally stepped into the era of electric vehicles in the 21 st century. The electric automobile industry in China has explosive growth from 2015, and the production capacity of Chinese pure electric automobiles and plug-in hybrid electric automobiles reaches 200 thousands in 2020. On the premise of ensuring safety, the energy density of the battery needs to be improved if the endurance mileage of the electric automobile needs to be improved. According to the development planning, the energy density of the battery cell of the power lithium battery for the vehicle reaches 300 Wh/kg by 2020. In order to achieve such an energy density, the positive electrode material must be a high-capacity nickel-cobalt-manganese 811 type positive electrode material or a nickel-cobalt-aluminum NCA type positive electrode material; on the other hand, the use of high-capacity silicon carbon cathode materials is required, which is a technical route adopted by the united states tesla company of the benchmarking enterprise in the field of global electric vehicles to obtain success.
The graphite cathode applied in the traditional commercialization has the advantages of long cycle life, low cost, rich resources and the like, but the theoretical gram capacity of the graphite cathode is only 372 mAh/g, and the high energy density requirement of the lithium ion battery cannot be realized. In addition, the lithium intercalation potential of the graphite negative electrode is very close to the deposition potential of metallic lithium, and when the battery is overcharged, lithium dendrite is easily generated on the surface of the electrode, so that the battery is ignited and even explodes, and huge potential safety hazards exist.
The silicon negative electrode material has the ultrahigh theoretical capacity of up to 4200 mAh/g, and also has the advantages of abundant reserves, low cost, environmental friendliness and the like. In addition, the silicon anode material has a low lithium insertion/extraction potential (0.4V vs. Li/Li)+) And lithium dendrite is not easily formed on the surface of the silicon negative electrode material when the full battery is charged. Therefore, the safety performance of the silicon cathode material is superior to that of the graphite cathode material. Based on the above advantages, silicon is recognized as the most promising negative electrode material for new high-capacity lithium ion batteries.
As a negative electrode material, after lithium is inserted into crystalline silicon, the volume of the crystalline silicon expands by 3-4 times, and after lithium is removed, the volume of the crystalline silicon shrinks violently, so that after the battery is cycled, the silicon particles are seriously pulverized, a new interface is generated, and an SEI film is continuously broken and regenerated to quickly consume lithium in an electrolyte. This results in a rapid decay of the battery capacity. In addition, the conductivity of the silicon material is only 6.7 multiplied by 10-4S/cm, poor conductivity, which also seriously affectsElectrochemical performance of the cell. The practical application of the silicon negative electrode material in the field of lithium ion batteries is greatly hindered by the defects.
Silicon negative electrode materials have significant drawbacks: during the lithium insertion process, the silicon particles expand by up to 300% in volume, and during the lithium removal process, the silicon particles shrink by a large amount in volume. The maximum elastic deformation of the commonly used binder polyvinylidene fluoride (PVDF) is only 9.3%, which is not sufficient to withstand a volume expansion of 300% of the silicon particles. Under the condition, great stress is generated inside the electrode, so that the pole piece is seriously cracked, the active silicon particles are pulverized, and the pulverized silicon particles lose the electric contact with the copper foil of the current collector, thereby causing the severe attenuation of the capacity. Cracking of the silicon particles, an increase in the contact surface with the electrolyte, leads to: 1) a new SEI film is formed, consuming more lithium; 2) the side reactions are exacerbated. These factors result in poor cycling performance of the cell, which has a dramatic decline in cell discharge capacity of 20-50% after several cycles, and also has a low coulombic efficiency (often less than 80%). In addition, the electrical conductivity of silicon material is only 6.7 × 10-4 S/cm, the conductivity is poor, which also severely affects the electrochemical performance of the cell.
In addition, when the silicon negative electrode material is used for manufacturing the negative electrode plate, the pole plate can be seriously cracked after being coated and dried; and when the battery is circulated for many times, the pole piece cracking phenomenon is more and more serious. The pole piece cracking can cause the phenomenon of 'island', so that the electrical contact between the negative electrode material coating and the current collector is degraded, and further the polarization phenomenon of the battery occurs and the capacity of the battery is obviously attenuated. When the silicon cathode material is used for preparing cathode slurry, a certain amount of one-dimensional conductive carbon nanotubes can be added. Because the carbon nanotube has very big draw ratio, can partially alleviate the fracture of pole piece: even if the pole piece is cracked, the criss-cross carbon nanotubes can form a conductive path crossing the crack, so that the phenomenon of island is avoided, and a good conductive state is maintained between the silicon negative material coating and the current collector. However, the carbon nanotube dry powder is particularly difficult to disperse, and it is difficult for all existing dispersing apparatuses to uniformly disperse the carbon nanotube dry powder into the anode slurry. At present, the nano-carbon tube conductive slurry is prepared by adopting a wet grinding method of a nano-sand mill in industry. However, after wet grinding, a large number of carbon nanotubes are broken, and the aspect ratio is greatly reduced, so that the broken carbon nanotubes cannot avoid the "island" phenomenon in the pole piece. Therefore, in order to achieve the effect of improving cycle performance, the amount of carbon nanotubes added is usually 10wt% or more. The addition of a large amount of carbon nanotubes further causes serious problems of great reduction of the first coulombic efficiency of the battery, reduction of the energy density of the battery and the like.
Disclosure of Invention
The invention aims to solve the technical problems of avoiding active silicon particle pulverization of the silicon-based negative electrode material during charging and discharging and avoiding the phenomenon of 'island' during the preparation of a pole piece of the silicon-based negative electrode material. The technical problem to be solved by the invention is how to make a silicon-based negative electrode for a lithium ion battery show excellent cycle performance while having high first coulombic efficiency and discharge capacity.
In a first aspect, the present invention provides a nano-silicon composite anode material, characterized in that the nano-silicon composite anode material comprises a multi-coated nano-silicon powder and in-situ grown carbon nanotubes, the multi-coated nano-silicon powder has a core of nano-silicon particles and a composite coating layer disposed on the core, the composite coating layer comprises conductive carbon, polyacene and an inorganic metal oxide.
In an exemplary embodiment, the inorganic oxide is selected from titanium oxide, zirconium oxide, or mixtures thereof.
In an exemplary embodiment, the content of carbon nanotubes in the nano-silicon composite anode material is 0.1 to 8 wt%, preferably 1 to 5 wt%, more preferably 1 to 2 wt%.
In a second aspect, the present invention provides a method of preparing a nano-silicon composite anode material as described in the first aspect, the method comprising the steps of:
(1) dissolving an organic metal compound, phenolic resin and an organic carbon source in an organic solvent, and uniformly mixing;
(2) adding nano silicon powder into the mixture obtained in the step (1), and grinding to form slurry;
(3) after the slurry obtained in the step (2) is dried in vacuum, adding ferrocene powder and uniformly mixing;
(4) putting the mixture obtained in the step (3) into a pressure-resistant closed reactor for high-temperature reaction, and decomposing the organic metal compound, the phenolic resin and the carbohydrate at high temperature to form a composite coating layer on the surface of the nano silicon particles, wherein the organic metal compound is decomposed to form inorganic metal oxide, the phenolic resin is decomposed to polyacene, and the organic carbon source is decomposed to conductive carbon; and wherein the ferrocene is decomposed to form in situ grown carbon nanotubes; and
(5) and (3) removing the reaction product from the reactor, and cooling to obtain the nano silicon composite negative electrode material.
In an exemplary embodiment, the organic solvent is xylene, cyclohexane, N-methylpyrrolidone, N-dimethylacetamide, or a mixture thereof.
In an exemplary embodiment, the organometallic compound is one or more of butyl titanate, propyl titanate, butyl zirconate, propyl zirconate.
In an exemplary embodiment, the organic carbon source is an organic saccharide, and preferably, the organic carbon source is one or more of carboxymethyl cellulose, starch, glucose, and sucrose.
In an exemplary embodiment, the high temperature reaction in step (4) is carried out at 600-750 ℃.
In an exemplary embodiment, the high temperature reaction in step (4) is carried out for 20 to 36 hours.
In an exemplary embodiment, the pressure in the pressure-resistant sealed reactor during the high-temperature reaction in step (4) is 25 to 60 atmospheres.
In an exemplary embodiment, the phenolic resin is added in an amount of 10 to 30 parts by weight based on 100 parts by weight of the nano-silicon powder.
In an exemplary embodiment, the organometallic compound is added in an amount of 20 to 30 parts by weight based on 100 parts by weight of the nano-silicon powder.
In an exemplary embodiment, the organic carbon source is added in an amount of 6.7 to 10 parts by weight based on 100 parts by weight of the nano silicon powder.
In an exemplary embodiment, the ferrocene is added in an amount of 10 to 20 parts by weight based on 100 parts by weight of the nano silicon powder.
In an exemplary embodiment, the primary particles of the nano-silicon powder have a particle size of 80 to 150 nm.
Advantageous effects
The nano silicon composite negative electrode material has the following beneficial effects:
(1) the composite coating layer formed by the inorganic metal oxide, the polyacene and the conductive carbon can effectively inhibit the volume expansion and contraction of the nano silicon particles in charging and discharging, thereby preventing the pulverization of the active silicon particles and further avoiding the violent attenuation of the capacity of the electrode material;
(2) organometallic compounds such as organotitanium and/or organozirconium sources decompose at elevated temperatures to form TiO2And/or ZrO2(ii) a The inorganic metal oxides are very stable in the electrolyte, and the inorganic metal oxides are directly and/or indirectly coated on the surface of the nano silicon core particles, so that the direct contact of the nano silicon particles and the electrolyte is reduced, and the chance of side reaction between the nano silicon and the electrolyte is reduced;
(3) the polyacene and the conductive carbon in the composite coating layer are good conductive materials, and can provide a good internal conductive path in the multiple-coated nano silicon powder particles, so that the internal resistance of the battery is reduced, and the cycle and rate performance of the battery are improved; in addition, polyacene has good cohesiveness, which helps to bond powdered coating materials to each other to form a strong coating layer, thereby more effectively inhibiting volume expansion and contraction of the core nano-silicon particles during charge and discharge;
(4) the carbon nanotubes grown in situ are dispersed among the silicon powder particles like numerous earthworms, so that good conductive channels are formed among the silicon particles; the carbon nano-tube formed by in-situ growth is not damaged by grinding, so that the carbon nano-tube has larger length-diameter ratio, and even the content of the carbon nano-tube (such as 1-2 wt%) is lower, good conductive channels can be formed between silicon nano-particles and between the silicon nano-particles and a current collector, thereby avoiding the phenomenon of 'isolated island' on a pole piece and further improving the cycle and rate capability of the battery;
(5) when the button cell is manufactured by using the nano silicon composite negative electrode material and tested, the first discharge gram capacity of the button cell is more than 3500 mAh/g, the first coulombic efficiency reaches more than 92 percent, and the capacity and the cycle performance of the button cell are both excellent.
Drawings
For a better understanding of the present invention and to show how the same may be carried into effect, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:
fig. 1 is a scanning electron micrograph of in-situ grown carbon nanotubes/multi-coated nano-silicon composite anode material prepared in example 1;
fig. 2 is a first charge-discharge curve of the button cell prepared in example 1;
fig. 3 is a cycling curve for the button cell prepared in example 1;
fig. 4 is a first charge-discharge curve of the button cell prepared in example 2;
fig. 5 is a first charge-discharge curve of the button cell prepared in example 3;
fig. 6 is a first charge-discharge curve of the button cell prepared in example 4;
fig. 7 is a first charge-discharge curve of the button cell prepared in comparative example 1;
fig. 8 is a cycling curve for the button cell prepared in comparative example 1;
fig. 9 is a first charge-discharge curve of the button cell prepared in comparative example 2;
fig. 10 is a cycling curve for the button cell prepared in comparative example 2.
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 present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.
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. All percentages, ratios, proportions, or parts are by weight unless otherwise specified. 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. 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 embodiments and materials described herein are intended to be exemplary only.
All numbers expressing dimensions, physical characteristics, processing parameters, quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as being modified in all instances by the term "about".
It is to be understood that all ranges disclosed herein encompass the beginning and ending range values and any and all subranges subsumed therein. For example, a stated range of "1 to 10" should be considered to include any and all subranges between (and including) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, e.g., 1 to 2, 3 to 5, 8 to 10, etc.
The discussion of the invention herein may describe certain features as being "particularly" or "preferably" within certain limits (e.g., "preferably," "more preferably," or "even more preferably" within certain limits). It is to be understood that the invention is not limited to these specific or preferred limits but is to be accorded the full scope of the disclosure.
Example 1
200g of N-methyl pyrrolidone is taken, and 45g of phenolic resin, 37.5g of butyl titanate, 12 g of carboxymethyl cellulose and 150 g of nano silicon powder are added, wherein the primary particle size of the silicon powder is 110 nm. And stirring and grinding the zirconium oxide balls with the phi 5 weight percent for 10 minutes by a wet method, performing vacuum rotary drying, adding 30 grams of ferrocene, and performing dry vibration grinding for 15 minutes by a phi 10 vibration ball mill. Then, the powder is added into a 310S stainless steel sealed container, and the container is strictly sealed by a brass sealing ring after being vacuumized. Placing in a muffle furnace, heating to 600 deg.C for 3 hr from room temperature, holding at 600 deg.C for 36 hr, cooling to 300 deg.C, taking out, and rapidly cooling to room temperature with water. The sealing cap was opened and the composite sample was removed. The scanning electron micrograph of the in-situ grown carbon nanotube/multi-coated nano-silicon composite anode material prepared in example 1 is shown in fig. 1. It can be seen in figure 1 that there are a number of serpentine-grown carbon nanotubes between the particles, grown in situ at high temperature from the thermal decomposition of ferrocene, which form good conductive paths between the silicon particles.
Taking 1.8 g of conductive carbon black SuperP, adding 40 g of N-methyl pyrrolidone, grinding, adding 15g of self-made polyamic acid binder, and grinding. And then 15g of the prepared silicon-based composite powder material is added and uniformly stirred, and the viscosity of the obtained slurry is 3800 mPa.s. Coating on 10um purple copper foil, coating wet thickness 150um, vacuum drying at 100 deg.C, rolling, imidizing at 290 deg.C/30 min in argon atmosphere. Then, metal lithium is taken as a counter electrode, Celgard 2400 is taken as a diaphragm, and the electrolyte is 1M LiPF6The electrochemical performance of a CR2032 button cell was tested as per EC + DEC. Fig. 2 is a first charge-discharge curve of the button cell prepared in example 1; fig. 3 is a cycling curve for the button cell prepared in example 1. The first discharge gram capacity of the nano-silicon composite negative electrode material prepared in example 1 is 3673 mAh/g, and the first coulombic efficiency is 92.15%. The battery was further cycled at 0.1C without a decay in the charge capacity of the battery during the first 11 cycles.
Example 2
Taking 300g of cyclohexane, adding 30g of phenolic resin, 30g of propyl titanate, 10 g of starch, 150 g of nano silicon powder and phi 5 zirconia balls, stirring and grinding for 10 minutes by a wet method, carrying out vacuum rotary drying, then adding 25g of ferrocene, and carrying out dry vibration grinding for 15 minutes by a phi 10 vibration ball mill. Then, the powder is added into a 310S stainless steel sealed container, and the container is strictly sealed by a brass sealing ring after being vacuumized. Placing in a muffle furnace, heating from room temperature for 3 hours to 650 ℃, keeping the temperature at 650 ℃ for 30 hours,then cooling to 300 ℃ along with the furnace, taking out and then spraying water to rapidly cool to room temperature. The sealing cap was opened and the composite sample was removed. Taking 1.7 g of conductive carbon black SuperP, adding 40 g of N-methyl pyrrolidone, grinding, adding 15g of self-made polyamic acid binder, and grinding. And then 15g of the prepared silicon-based composite powder material is added and uniformly stirred, and the viscosity of the obtained slurry is 3850 mPa.s. Coating on 10um purple copper foil, drying at 100 deg.C under vacuum with wet thickness of 150um, rolling, and imidizing at 280 deg.C/40 min in argon atmosphere. Then, metal lithium is taken as a counter electrode, Celgard 2400 is taken as a diaphragm, and the electrolyte is 1M LiPF6The electrochemical performance of a CR2032 button cell was tested as per EC + DEC. Fig. 4 shows the first charge-discharge curve of the button cell prepared in example 2. The first discharge gram capacity of the nano-silicon composite negative electrode material prepared in example 2 is 3736.2mAh/g, and the first coulombic efficiency is 90.73%. The battery was further cycled at 0.1C without a decay in the charge capacity of the battery during the first 11 cycles.
Example 3
250g of dimethylbenzene is taken, 25g of phenolic resin, 45g of butyl zirconate, 15g of glucose, 150 g of nano silicon powder and phi 5 zirconia balls are added, stirred, milled and wet-ground for 10 minutes, and after vacuum rotary drying, 20 g of ferrocene and phi 10 vibrating ball mill are added, and dry-process vibrating and grinding is carried out for 15 minutes. Then, the powder is added into a 310S stainless steel sealed container, and the container is strictly sealed by a brass sealing ring after being vacuumized. Placing in a muffle furnace, heating to 700 deg.C for 3 hr from room temperature, holding at 700 deg.C for 25 hr, cooling to 300 deg.C, taking out, and rapidly cooling to room temperature with water. The sealing cap was opened and the composite sample was removed. Taking 1.8 g of conductive carbon black SuperP, adding 40 g of N-methyl pyrrolidone, grinding, adding 15g of self-made polyamide acid binder, and grinding. And then 15g of the prepared silicon-based composite powder material is added and uniformly stirred, and the viscosity of the obtained slurry is 3700 mPa.s. Coating on 10um purple copper foil, drying at 100 deg.C under vacuum with wet thickness of 150um, rolling, and imidizing at 285 deg.C/35 min in argon atmosphere. Then, metal lithium is taken as a counter electrode, Celgard 2400 is taken as a diaphragm, and the electrolyte is 1M LiPF6EC + DEC, manufacture of CR2032 button cell, testing of its electrochemical propertiesChemical properties. Fig. 5 shows the first charge-discharge curve of the button cell prepared in example 3. The first discharge gram capacity of the nano-silicon composite negative electrode material prepared in example 3 is 3543.9mAh/g, and the first coulombic efficiency is 90.46%. The battery was further cycled at 0.1C without a decay in the charge capacity of the battery during the first 11 cycles.
Example 4
Taking 200g of N, N-dimethylacetamide, adding 15g of phenolic resin, 31g of propyl zirconate, 12 g of sucrose, 150 g of nano silicon powder and phi 5 zirconia balls, stirring, grinding for 10 minutes by a wet method, drying in a vacuum rotary manner, adding 15g of ferrocene and phi 10 vibration ball mill, and carrying out dry vibration grinding for 15 minutes. Then, the powder is added into a 310S stainless steel sealed container, and the container is strictly sealed by a brass sealing ring after being vacuumized. Placing in a muffle furnace, heating to 750 deg.C for 3 hr from room temperature, holding at 750 deg.C for 20 hr, cooling to 300 deg.C, taking out, and rapidly cooling to room temperature with water. The sealing cap was opened and the composite sample was removed. Taking 1.7 g of conductive carbon black SuperP, adding 40 g of N-methyl pyrrolidone, grinding, adding 15g of self-made polyamic acid binder, and grinding. And then 15g of the prepared silicon-based composite powder material is added and uniformly stirred, and the viscosity of the obtained slurry is 3700 mPa.s. Coating on 10um purple copper foil, drying at 100 deg.C under vacuum with wet thickness of 150um, rolling, and imidizing at 290 deg.C/35 min in argon atmosphere. Then, metal lithium is taken as a counter electrode, Celgard 2400 is taken as a diaphragm, and the electrolyte is 1M LiPF6The electrochemical performance of a CR2032 button cell was tested as per EC + DEC. Fig. 6 shows the first charge-discharge curve of the button cell prepared in example 4. The first discharge gram capacity of the nano-silicon composite anode material prepared in example 4 is 3502.0mAh/g, and the first coulombic efficiency is 90.82%. The battery was further cycled at 0.1C without a decay in the charge capacity of the battery during the first 11 cycles.
Comparative example 1
To verify the effect of in-situ grown carbon nanotubes, comparative example 1 was prepared as follows.
Taking 200g of N-methyl pyrrolidone, adding 45g of phenolic resin, 37.5g of butyl titanate, 12 g of carboxymethyl cellulose and 1g of nano silicon powder50g, stirring and grinding a phi 5 zirconia ball for 10 minutes by a wet method, and carrying out dry vibration and grinding for 15 minutes by a phi 10 vibration ball mill after vacuum rotary drying. Then, the powder is added into a 310S stainless steel sealed container, and the container is strictly sealed by a brass sealing ring after being vacuumized. Placing in a muffle furnace, heating to 600 deg.C for 3 hr from room temperature, holding at 600 deg.C for 36 hr, cooling to 300 deg.C, taking out, and rapidly cooling to room temperature with water. The sealing cap was opened and the composite sample was removed. The material sample did not have carbon nanotubes. Taking 1.8 g of conductive carbon black SuperP, adding 40 g of N-methyl pyrrolidone, grinding, adding 15g of self-made polyamide acid binder, and grinding. And then 15g of the prepared silicon-based composite powder material is added and uniformly stirred, and the viscosity of the obtained slurry is 3800 mPa.s. Coating on 10um purple copper foil, coating wet thickness 150um, vacuum drying at 100 deg.C, rolling, imidizing at 290 deg.C/30 min in argon atmosphere. Then, metal lithium is taken as a counter electrode, Celgard 2400 is taken as a diaphragm, and the electrolyte is 1M LiPF6The electrochemical performance of a CR2032 button cell was tested as per EC + DEC. Fig. 7 shows the initial charge-discharge curve of the button cell of comparative example 1, and fig. 8 shows the cycle curve of the button cell of comparative example 1. The composite material prepared in comparative example 1 had a first discharge gram capacity of 3162.45mAh/g and a first coulombic efficiency of 86.79%. The battery was further cycled at a rate of 0.1C, and the capacity retention rate of the battery was 97.5% after the first 11 cycles.
The silicon-based composite powder material in comparative example 1 has no carbon nanotubes, and the capacity of the battery has 2.5% of attenuation after 11 cycles; in example 1, however, the capacity hardly decayed after the battery was cycled 11 times. This proves that the cycle performance of the battery can be improved by introducing the carbon nanotubes grown in situ into the silicon-based composite powder material.
Comparative example 2
To compare the scheme of in-situ grown carbon nanotubes with the scheme of physical mixing and addition of carbon nanotubes, comparative example 2 was made as follows.
200g of N-methyl pyrrolidone is taken and added with 45g of phenolic resin, 37.5g of butyl titanate, 12 g of carboxymethyl cellulose, 150 g of nano silicon powder and 19.35 g of carbon nano tube powder and phi 5 zirconia balls for stirring and wet grindingGrinding for 10 minutes, performing vacuum rotary drying, and performing dry vibration grinding for 15 minutes by using a phi 10 vibration ball mill. Then, the powder is added into a 310S stainless steel sealed container, and the container is strictly sealed by a brass sealing ring after being vacuumized. Placing in a muffle furnace, heating to 600 deg.C for 3 hr from room temperature, holding at 600 deg.C for 36 hr, cooling to 300 deg.C, taking out, and rapidly cooling to room temperature with water. The sealing cap was opened and the composite sample was removed. The material sample did not have carbon nanotubes. Taking 1.8 g of conductive carbon black SuperP, adding 40 g of N-methyl pyrrolidone, grinding, adding 15g of self-made polyamic acid binder, and grinding. And then 15g of the prepared silicon-based composite powder material is added and uniformly stirred, and the viscosity of the obtained slurry is 3800 mPa.s. Coating on 10um purple copper foil, coating wet thickness 150um, vacuum drying at 100 deg.C, rolling, imidizing at 290 deg.C/30 min in argon atmosphere. Then, metal lithium is taken as a counter electrode, Celgard 2400 is taken as a diaphragm, and the electrolyte is 1M LiPF6The electrochemical performance of a CR2032 button cell was tested as per EC + DEC. Fig. 9 shows the initial charge-discharge curve of the button cell of comparative example 1, and fig. 10 shows the cycle curve of the button cell of comparative example 1. The composite prepared in comparative example 2 had a first discharge gram capacity of 2415.6mAh/g and a first coulombic efficiency of only 84.59%. The battery was further cycled at a rate of 0.1C, and the capacity retention rate of the battery was 99.2% after the first 11 cycles.
In comparative example 2, carbon nanotube powder in an amount of 12.9% relative to silicon powder was added during the preparation of the silicon-based negative electrode material, so that the decrease in the gram discharge capacity after the compounding was significant, and the decrease in the first coulombic efficiency was significant. Compared with comparative example 1 of silicon-based composite powder material without carbon nanotubes, the cycle performance of the nano-silicon composite anode material in comparative example 2 is improved. However, the cycle performance of comparative example 2 was still inferior to that of example 1. This is because although the carbon nanotubes were added in the preparation process of comparative example 2, since the subsequent mixing process by ball milling resulted in the breaking of a large number of carbon nanotubes, these broken carbon nanotubes could not form sufficient conductive paths between silicon particles and could not completely eliminate the "islanding" phenomenon in the pole piece. Although the carbon nanotube powder was added in an amount of up to 12.9% in comparative example 2, the cycle performance was not as good as that in example 1. This demonstrates that in-situ grown carbon nanotubes are more effective than physically mixed with carbon nanotubes in improving the cycling performance of the cell.
While the present invention has been described with respect to specific exemplary embodiments, it will be appreciated that various modifications, alterations, and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims.

Claims (8)

1. A nano-silicon composite anode material, characterized in that the nano-silicon composite anode material comprises a multi-coated nano-silicon powder and in-situ grown carbon nanotubes, the multi-coated nano-silicon powder has a core of nano-silicon particles and a composite coating layer disposed on the core, the composite coating layer comprises conductive carbon, polyacene, and an inorganic metal oxide, and in that the nano-silicon composite anode material is prepared by a method comprising the steps of:
(1) dissolving an organic metal compound, phenolic resin and organic saccharides in an organic solvent, and uniformly mixing;
(2) adding nano silicon powder into the mixture obtained in the step (1), and grinding to form slurry;
(3) after the slurry obtained in the step (2) is dried in vacuum, adding ferrocene powder and uniformly mixing;
(4) placing the mixture obtained in the step (3) in a pressure-resistant closed reactor for high-temperature reaction, and decomposing the organic metal compound, the phenolic resin and the organic saccharide at high temperature to form a composite coating layer on the surface of the nano silicon particles, wherein the organic metal compound is decomposed to form inorganic metal oxide, the phenolic resin is decomposed to polyacene, and the organic saccharide is decomposed to conductive carbon; and wherein the ferrocene is decomposed to form in situ grown carbon nanotubes;
(5) and (3) removing the reaction product from the reactor, and cooling to obtain the nano silicon composite negative electrode material.
2. The nano-silicon composite anode material according to claim 1, wherein the inorganic metal oxide is titanium oxide, zirconium oxide or a mixture thereof.
3. The nano-silicon composite anode material according to claim 1, wherein the content of the carbon nanotubes in the nano-silicon composite anode material is 0.1 to 8 wt%.
4. The nano-silicon composite anode material according to claim 1, wherein the organic solvent is xylene, cyclohexane, N-methylpyrrolidone, N-dimethylacetamide, or a mixture thereof.
5. The nano-silicon composite anode material according to claim 1, wherein the organic metal compound is one or more of butyl titanate, propyl titanate, butyl zirconate, and propyl zirconate.
6. The nano-silicon composite anode material as claimed in claim 1, wherein the high temperature reaction in step (4) is carried out at 600-750 ℃.
7. The nano-silicon composite anode material according to claim 1, wherein the high temperature reaction in the step (4) is performed for 20 to 36 hours.
8. The nano-silicon composite anode material according to claim 1, characterized in that during the high-temperature reaction in step (4), the pressure in the pressure-resistant closed reactor is 25 to 60 atmospheres.
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