CN115050950B - Silicon-based negative electrode material, preparation method thereof and lithium ion battery comprising silicon-based negative electrode material - Google Patents

Silicon-based negative electrode material, preparation method thereof and lithium ion battery comprising silicon-based negative electrode material Download PDF

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CN115050950B
CN115050950B CN202210965996.4A CN202210965996A CN115050950B CN 115050950 B CN115050950 B CN 115050950B CN 202210965996 A CN202210965996 A CN 202210965996A CN 115050950 B CN115050950 B CN 115050950B
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silicon
coating layer
negative electrode
based core
electrode material
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CN115050950A (en
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单旭意
李康
张�浩
金新凯
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China Lithium Battery Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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

Disclosed are a silicon-based negative electrode material, a preparation method thereof and a lithium ion battery comprising the same, wherein the silicon-based negative electrode material comprises: a silicon-based core; a first cladding layer coated outside the silicon-based core; and a second coating layer coated outside the first coating layer, wherein the first coating layer and the second coating layer are both made of carbon-based materials, the distance between the lattice layers of the first coating layer is 0.344 to 0.352nm, the distance between the lattice layers of the second coating layer is 0.345 to 0.354nm, and the distance between the lattice layers of the first coating layer is smaller than the distance between the lattice layers of the second coating layer. The crystal face layer intervals of different coating layers are different, the crystallinity is different, and when the silicon material is embedded with lithium and expands, relative slippage is generated between the coating layers, so that the whole structure of the coating layer is kept stable, the integrity and the stability of a silicon material interface are further improved, the consumption of active lithium is reduced, and the cycle performance and the storage performance of the battery are further improved.

Description

Silicon-based negative electrode material, preparation method thereof and lithium ion battery comprising silicon-based negative electrode material
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a silicon-based negative electrode material with a slipping coating layer structure, a preparation method thereof and a lithium ion battery containing the silicon-based negative electrode material.
Background
The cruising ability of the battery-powered new energy automobile depends on the energy density of the battery, and with the increasing requirements of consumers on the cruising mileage of the automobile, the realization of high energy density becomes the development direction of the power battery in recent years. Under the condition that the potential of the energy density of the traditional graphite cathode is fully exploited, the development of a novel cathode material becomes a key for improving the battery capacity, solving the problem of energy density and promoting the further development of the power battery.
Recent studies have found that the introduction of Silica (SiO) into the negative electrodex) Silicon (Si) and other silicon-containing materials can obviously improve the gram capacity of the cathode of the lithium ion secondary batteryAnd the silicon-based negative electrode material is expected to replace the traditional graphite negative electrode to realize the breakthrough of energy density. However, the silicon-based negative electrode material is easy to expand and deform in the lithium desorption process, and after the lithium desorption process is repeated, material phase pulverization occurs, so that the structure of an initial SEI film is damaged, a new interface is generated, the SEI film is repeatedly generated, active lithium is consumed, and the cycle performance is degraded. In addition, the silicon-based negative electrode material has the problems of loose and porous film formation at the initial stage of the interface and poor compactness, and can also cause continuous consumption of active lithium during storage and circulation. Interface stability is one of the key issues limiting silicon-based anode applications.
Therefore, the interface of the silicon-based negative electrode material needs to be further improved, so that the integrity and stability of the interface are improved, and the cycle and storage performance of the silicon-based negative electrode material are further improved, so that the advantage of high energy density of the silicon-based negative electrode material is really exerted in practical application.
Disclosure of Invention
The invention aims to solve the technical problems that a fresh interface is exposed to electrolyte and the like caused by interface stability of a silicon-based negative electrode material and volume expansion of the silicon material in a lithium embedding process, so that the problems of poor cycle performance and poor storage performance of the silicon-based negative electrode material are solved. Therefore, the inventors of the present invention have conducted extensive studies to find that, when lithium is inserted into and expands in a silicon-based core, two or more carbon material coating layers with different graphitization degrees are coated outside the silicon-based core, and expansion displacement is generated between the coating layers with different graphitization degrees between the coating layers, so that relative slip can be generated, thereby greatly reducing the probability that the silicon-based core is directly exposed to an electrolyte due to the cracking of the coating layers, and have completed the present invention.
Thus, in one aspect, the present invention provides a silicon-based anode material comprising: a silicon-based core; a first cladding layer coated outside the silicon-based core; and a second coating layer coated outside the first coating layer, wherein the first coating layer and the second coating layer are made of graphitized carbon-based materials, the distance between the lattice planes of the first coating layer is 0.344 to 0.352nm, the distance between the lattice planes of the second coating layer is 0.345 to 0.354nm, and the distance between the lattice planes of the first coating layer is smaller than the distance between the lattice planes of the second coating layer.
In another aspect, the present invention provides a method of preparing a silicon-based anode material, comprising: step (1): introducing a gas-phase carbon source into the silicon-based core to coat the silicon-based core, and treating at the temperature T1 to form a first coating layer on the surface of the silicon-based core; and a step (2): and introducing a gas-phase carbon source into the silicon-based core coated with the first coating layer to coat the silicon-based core coated with the first coating layer, and treating at the temperature of T2 to form a second coating layer on the first coating layer to obtain the silicon-based cathode material, wherein T1 is greater than T2.
In another aspect, the invention provides a lithium ion battery, wherein the negative electrode of the lithium ion battery is the silicon-based negative electrode material or the silicon-based negative electrode material obtained by the method.
Alternatively, the silicon-based anode material according to the present invention may be further coated with a third coating layer having a different graphitization degree from the second coating layer, in addition to the second coating layer.
As mentioned above, because two or more carbon material coating layers with different interplanar spacings are coated outside the silicon-based core, when the silicon-based core is embedded with lithium and expands, relative slippage can be generated between the coating layers due to different interplanar spacings and different crystallinities, so that the probability that the silicon-based core is directly exposed to the electrolyte because of the cracking of the coating layers is greatly reduced, the probability that the initial SEI film structure is damaged and a new SEI interface is formed is further reduced, the consumption of active lithium and the electrolyte is reduced, and the cycle performance of the battery is remarkably improved.
In addition, silicon crystal grains in the silicon-based core are easy to grow into grains with larger sizes at high temperature, and then the larger grains show larger volume expansion effect in the lithium intercalation process. The silicon-based negative electrode material has lower temperature when a coating layer is formed, and has smaller influence on the growth of silicon crystal grains in a silicon-based core into grains with larger size, so that the volume expansion effect of the silicon-based negative electrode material is further reduced, and the cycle performance is further improved.
In addition, because the silicon-based negative electrode material provided by the invention has the silicon-based inner core and the two or more coating layers with different crystal plane layer distances, the interface integrity and the stability are improved, so that the storage performance is improved while the cycle performance is improved, and the advantage of high energy density of the silicon-based material can be really exerted in practical application.
Drawings
Fig. 1 is a schematic structural diagram of a silicon-based anode material with a slip cladding structure according to the invention;
FIG. 2 is a schematic structural diagram of a conventional single-clad silicon-based negative electrode material before and after lithium intercalation;
FIG. 3 is a schematic structural diagram of a silicon-based negative electrode material with a double coating layer before and after lithium intercalation;
fig. 4A, 4B and 4C are electron micrographs of SEI films at the beginning of battery life (BOL) and at the end of battery life (EOL) of a conventional single-clad silicon-based negative electrode material;
fig. 5A and 5B are electron micrographs of an initial SEI film at the beginning of battery life (BOL) and an SEI film at the end of battery life (EOL) of the silicon-based anode material with a double coating layer according to the present invention.
Detailed Description
The present application is described in further detail below with reference to the figures and examples. The features and advantages of the present application will become more apparent from the description.
In addition, the technical features described below in the different embodiments of the present application may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the silicon-based negative electrode material with a slip cladding layer structure provided by the invention comprises: a silicon-based core; a first cladding layer coated outside the silicon-based core; and the second coating layer is coated outside the first coating layer, wherein the first coating layer and the second coating layer are both made of carbon-based materials, the distance between the crystal planes of the first coating layer is 0.344 to 0.352nm, the distance between the crystal planes of the second coating layer is 0.345 to 0.354nm, and the distance between the crystal planes of the first coating layer is smaller than that of the second coating layer.
It should be noted that, unlike the silicon-based material with a single cladding layer, as shown in fig. 2, the silicon-based negative electrode material of the present invention has two cladding layers, and the spacing between the crystal planes of the first cladding layer and the second cladding layer is different, which reflects the difference in crystallinity between the two cladding layers, so that a relative slip is generated between the two cladding layers when the silicon-based core is embedded with lithium to expand, which is suitable for the larger volume expansion of the silicon-based negative electrode material, as shown in fig. 3, the probability that the silicon-based core is directly exposed to the electrolyte is greatly reduced.
FIGS. 4A, 4B and 4C are electron micrographs of conventional single coated silicon-based material cathodes, showing that the initial film formation (shown in FIG. 4B) is loose and porous and has poor compactness, so that active lithium is continuously consumed during storage and cycling, and the cycling performance is reduced; at the end of the battery life, the negative electrode material exhibited bulk pulverization (shown in fig. 4C); in between, the thickening phenomenon of the SEI film occurs (shown in fig. 4A).
Fig. 5A and 5B are electron micrographs of a negative electrode using the silicon-based negative electrode material of the present invention, respectively, showing that a dense SEI film (shown in fig. 5A) can be formed at the initial stage of the battery life; the SEI film remained intact at the end of the battery life (shown in fig. 5B). Therefore, the problems of loose and porous SEI film, poor compactness, thickening SEI film, bulk phase pulverization and the like which are formed initially can be solved, the situation that the battery continuously consumes active lithium in the storage and circulation processes is improved, and the storage stability and the circulation performance of the battery are obviously improved.
In one embodiment of the silicon-based anode material, the size d of the silicon crystal grains in the silicon-based core is less than 10nm, the thickness ratio of the first coating layer to the second coating layer is 0.5 to 1.2, the total thickness H of the first coating layer and the second coating layer is 5 to 200nm, and the ratio H/d of the total thickness H to the size d of the silicon crystal grains is more than 0.5.
Tests show that most of the consumption of active lithium by the silicon-based negative electrode material is caused by the expansion of a silicon-based core; the expansion of the silicon-based core is mainly caused by the alloying reaction of silicon grains and lithium ions; the degree of expansion of the silicon-based core is highly correlated with the silicon grain size. Therefore, in the present invention, the size d of the silicon grains in the silicon-based core is less than 10nm, so as to minimize the volume expansion of the silicon-based core during lithium intercalation. It is noted that the silicon crystal described hereinThe particles being nano-silicon particles present in a silicon-based core, e.g. the silica as the silicon-based core being formed from SiOxAnd nano silicon crystal grains; the silicon carbon used as the silicon-based inner core consists of a carbon-based framework and silicon nano-crystal grains.
In addition, the total thickness H of each coating layer is 5-200nm, and if the total thickness H is less than the range, the coating integrity is poor, a silicon-based core is exposed, active lithium is consumed, and the performance is deteriorated; above this range, the gram capacity of the silicon-based anode material is caused, resulting in an increase in the amount used in the battery, thereby deteriorating the battery performance. Experiments show that when the ratio H/d of the total thickness H of the coating layer to the size d of silicon crystal grains is more than 0.5, a better slip effect can be achieved between the first coating layer and the second coating layer, and the direct exposure of the silicon-based core to the electrolyte during lithium intercalation expansion can be prevented to a greater extent.
In another embodiment of the silicon-based anode material according to the present invention, the silicon-based core is selected from the group consisting of silica SiOx(0 < x < 2), one or more of nano silicon, silicon carbon and silicon alloy, preferably SiOx(0＜x＜2)。
In another embodiment of the silicon-based anode material according to the present invention, the carbon-based material content of the first coating layer and the second coating layer is 1 to 10 wt% based on the total weight of the silicon-based anode material. If the content is less than 1wt%, the coating effect is poor; if the content is higher than 10 wt%, the specific capacity of the silicon-based anode material is reduced.
Alternatively, in another embodiment of the silicon-based anode material according to the present invention, a third coating layer coated outside the second coating layer may be further included.
In another aspect, the present invention provides a method for preparing a silicon-based anode material, comprising: step (1): introducing a gas-phase carbon source into the silicon-based core to coat the silicon-based core, and treating at the temperature T1 to form a first coating layer on the surface of the silicon-based core; step (2): and introducing a gas-phase carbon source into the silicon-based core coated with the first coating layer to coat the silicon-based core coated with the first coating layer, and treating at the temperature of T2 to form a second coating layer on the first coating layer to obtain the silicon-based cathode material, wherein T1 is greater than T2.
The silicon-based core is coated with a carbon layer, and a gas carbon source, a liquid carbon source or a solid carbon source can be used. In order to realize that the first coating layer and the second coating layer have different crystal plane layer distances, the method can be realized by controlling different graphitization temperatures under the condition of using the same carbon source generally, and can also be realized by directly selecting solid carbon sources with different graphitization degrees. In the present invention, it is preferable that the carbon coating layer of low graphitization degree is realized by in-situ growth by CVD at a lower temperature or low-temperature carbonization, and the carbon coating layer of high crystallinity is realized by in-situ growth by CVD at a slightly higher temperature or high-temperature carbonization or a carbon source of high graphitization degree. More preferably, the present invention employs vapor phase cladding such that the interplanar spacing of the first cladding layer is smaller than the interplanar spacing of the second cladding layer by controlling the temperature T1 at which the first cladding layer is formed to be higher than the temperature T2 at which the second cladding layer is formed.
In one embodiment of the process according to the invention, T1 in step (1) is 730 to 1200 ℃ and the treatment time is 0.1 to 100h; in the step (2), the T2 is 700 to 1100 ℃, and the processing time is 0.1 to 100h.
In another embodiment of the method according to the invention, T1 in step (1) is 1000 to 1100 ℃, and the treatment time is 2 to 30h; in the step (2), the T2 is 950 to 1050 ℃, and the processing time is 2 to 30h.
In another embodiment of the process according to the invention, the silicon-based core is selected from the group consisting of silica SiOx(0 < x < 2), one or more of nano silicon, silicon carbon and silicon alloy, preferably SiOx(x is more than 0 and less than 2); the gas-phase carbon source is one or more selected from alkane, alkene, alkyne or benzene-ring-containing gas-phase carbon source; the liquid-phase carbon source is one or more selected from polysilane coupling agent, lignin, acrylic acid, polyvinyl alcohol, polyimide, polyaniline and polyvinylpyrrolidone; the solid-phase carbon source is selected from one or more of graphene and carbon nanotubes.
In another embodiment of the method according to the present invention, the first coating layer has an interplanar distance of 0.344 to 0.352nm, the second coating layer has an interplanar distance of 0.345 to 0.354nm, and the interplanar distance of the first coating layer is smaller than the interplanar distance of the second coating layer.
In another embodiment of the method according to the invention, the size d of the silicon grains in the silicon-based core is less than 10nm, the thickness H of the coating layer is 5 to 2000 nm, and the ratio H/d of the thickness H of the coating layer to the size d of the silicon grains is greater than 0.5.
In another embodiment of the method according to the present invention, the carbon-based material content of the first coating layer and the second coating layer is 1 to 10 wt% based on the total weight of the silicon-based anode material.
The silicon-based anode material with a plurality of cladding layers with different interplanar spacings can be formed by alternately preparing the cladding layers with high interplanar spacings and the cladding layers with low interplanar spacings by adopting the method.
In yet another aspect, the present invention also provides a lithium ion battery, wherein the negative electrode comprises the silicon-based negative electrode material according to the embodiment of the silicon-based negative electrode material or obtained according to the embodiment of the preparation method.
The present invention will be described more specifically with reference to examples. It is to be noted that the starting materials used in the respective examples and comparative examples are commercially available.
Example 1
The method comprises the following steps: preparation of silica
Uniformly mixing silicon dioxide powder and silicon powder with a molar ratio of 1.02 in a VC mixer, placing the mixed powder in a vacuum atmosphere furnace sample chamber, carrying out high-temperature vacuum treatment at 1650 ℃, reacting the silicon dioxide and the silicon to generate silicon monoxide, depositing the sublimed silicon monoxide in a deposition chamber to obtain blocky silicon monoxide, and crushing, ball-milling and airflow crushing the blocky silicon monoxide to obtain micron-sized silicon monoxide.
Step two: coating of
Placing 500g of silicon monoxide powder in a CVD (chemical vapor deposition) tubular furnace, introducing a mixed gas of argon and acetylene into one end of the tubular furnace, introducing the mixed gas of argon and acetylene at a flow ratio of 7:3, introducing air for 20min, discharging air in the furnace tube, heating to 730 ℃ at a heating rate of 5 ℃/min, and preserving heat for 1h to form a first coating layer. Then, under the same atmosphere condition, the temperature of the CVD tube furnace is reduced to 700 ℃ at the speed of 2 ℃/min, and the temperature is kept for 2h under the condition of 700 ℃ to form a second coating layer. And continuously maintaining the ventilation of the CVD tube furnace, and taking out the sample after the temperature of the tube furnace is reduced to the room temperature to obtain the carbon-coated silicon-based negative electrode material with two different crystal face layer intervals arranged on the surface of the silicon-based inner core.
Step three: physical and chemical property test
And (3) coating the carbon content, burning the carbon-coated silicon oxide material in an oxygen atmosphere, calculating the content of the carbon element by measuring the concentration of carbon dioxide, and taking 5g of the coated silicon-based negative electrode material to perform carbon content test by adopting a carbon-sulfur tester to obtain the content of a coated carbon layer of 1wt%.
< test of coating layer thickness >
The thickness of the coating layer is tested, and the coating layer on the surface of the silicon-based inner core is an amorphous carbon layer, so that the boundary between the carbon coating layer and the silicon monoxide can be obviously distinguished under a high-power transmission electron microscope; therefore, the thickness of the carbon coating layer can be tested by adopting a high-power transmission electron microscope, a proper amount of samples are taken to carry out a high-power transmission electron microscope (HRTEM) scanning test, and the total thickness of the carbon coating layer is tested to be 5nm by testing software. Measuring the interplanar spacing close to the silicon-based core cladding by (HRTEM) scanning and software analysis as the interplanar spacing of the first cladding; and simultaneously, measuring the crystal plane interlayer spacing close to the surface of the silicon-based negative electrode material as the crystal plane interlayer spacing of the second coating layer.
< silicon grain size test >
The silicon grain size of the coated silica material can be measured by a size measuring tool of HRTEM, and since the processing temperature in this experiment is low, the silicon grains in the silica are not developed and are in an amorphous structure.
Step four: evaluation of electrochemical Properties
(1) Preparation of negative pole piece
Mixing the silicon-based negative electrode material prepared in the step two with graphite, a conductive agent acetylene black, a thickening agent CMC and a binder SBR according to the mass ratio of 1.2.
(2) Preparation of positive pole piece
Mixing an NCM523 positive electrode active material, a conductive agent acetylene black and a binder PVDF (polyvinylidene fluoride) according to a mass ratio of 96; and uniformly coating the positive electrode slurry on two surfaces of the positive electrode current collector aluminum foil, airing at room temperature, transferring to an oven for continuous drying, and then performing cold pressing and slitting to obtain the positive electrode piece.
(3) Preparation of the electrolyte
Ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 16Dissolving the mixture in the mixed organic solvent to prepare electrolyte with the concentration of 1 mol/L.
(4) Preparation of the separator
Selected from polyethylene films as barrier films.
(5) Preparation of lithium ion battery
The positive pole piece, the isolating membrane and the negative pole piece are sequentially stacked, the isolating membrane is positioned between the positive pole piece and the negative pole piece to play an isolating role, then the bare cell is obtained by winding, the bare cell is placed in an outer packaging shell, electrolyte is injected after drying, and the lithium ion battery is obtained through the procedures of vacuum packaging, standing, formation, shaping and the like.
< test on cycle Property >
The lithium ion batteries prepared in examples and comparative examples were charged at a rate of 2C and discharged at a rate of 1C at 25C, and subjected to a full charge discharge cycle test, and the battery capacity retention rate was 84% after 800 cycles of battery cycling.
< storage test >
And (3) placing the fully charged battery in a 70 ℃ thermostat for standing for 30 days, carrying out a capacity recovery test on the battery, and dividing the capacity exerted by the battery after storage by the capacity before storage of the battery to obtain the recovery rate of the storage capacity of the battery, wherein the recovery rate of the storage capacity of the battery is 90%.
Example 2
The method comprises the following steps: preparation of silica
The silica powder was prepared according to the same procedure as in step one of example 1.
Step two: coating of
And (3) placing the 500g of the silicon monoxide powder prepared in the step (II) into a CVD (chemical vapor deposition) tubular furnace, and introducing a mixed gas of argon and acetylene into one end of the tubular furnace, wherein the flow ratio of the argon to the acetylene is 6:4. Ventilating for 20min, discharging air in a furnace pipe, heating to 780 ℃ at the heating rate of 5 ℃/min, preserving heat for 10h, cooling to 750 ℃, and preserving heat for 15h at 750 ℃; and after the temperature is reduced to room temperature, taking out the sample to obtain the coated silicon-based negative electrode material.
The coated silicon-based negative electrode material prepared in example 1 was tested in the same manner, and the test results are shown in table 1.
Batteries were prepared in the same manner as in example 1, and were subjected to cycle and high-temperature storage property tests, the results of which are shown in table 1.
Example 3
The method comprises the following steps: preparation of silica
The silica powder was prepared according to the same procedure as in step one of example 1.
Step two: coating of
And (3) placing the 500g of the silicon monoxide powder prepared in the step (II) into a CVD (chemical vapor deposition) tubular furnace, and introducing a mixed gas of argon and acetylene into one end of the tubular furnace, wherein the flow ratio of the argon to the acetylene is 6:4. Ventilating for 20min, discharging air in a furnace pipe, heating to 1120 ℃ at a heating rate of 5 ℃/min, preserving heat for 30h, cooling to 1080 ℃, and preserving heat for 24h at 1080 ℃; and after the temperature is reduced to the room temperature, taking out the sample to obtain the coated silicon-based negative electrode material.
The coated silicon-based negative electrode material prepared in the same manner as in example 1 was tested, and the test results are shown in table 1.
A battery was prepared in the same manner as in example 1, and subjected to cycle and high-temperature storage property tests, the results of which are shown in table 1.
Example 4
The method comprises the following steps: preparation of silica
The silica powder was prepared according to the same procedure as in step one of example 1.
Step two: coating of
And (3) placing the 500g of the silicon monoxide powder prepared in the step (II) into a CVD (chemical vapor deposition) tubular furnace, and introducing a mixed gas of argon and acetylene into one end of the tubular furnace, wherein the flow ratio of the argon to the acetylene is 7:3. Ventilating for 20min, discharging air in a furnace pipe, heating to 1000 ℃ at the heating rate of 5 ℃/min, preserving heat for 6h, cooling to 980 ℃, and preserving heat for 8h at the temperature of 980 ℃; and after the temperature is reduced to the room temperature, taking out the sample to obtain the coated silicon-based negative electrode material.
The coated silicon-based negative electrode material prepared in the same manner as in example 1 was tested, and the test results are shown in table 1.
A battery was prepared in the same manner as in example 1, and subjected to cycle and high-temperature storage property tests, the results of which are shown in table 1.
Example 5
The method comprises the following steps: preparation of silica
The silica powder was prepared according to the same procedure as in step one of example 1.
Step two: coating of
And (3) placing the 500g of the silicon monoxide powder prepared in the step (II) into a CVD (chemical vapor deposition) tubular furnace, and introducing a mixed gas of argon and acetylene into one end of the tubular furnace, wherein the flow ratio of the argon to the acetylene is 7:3. Introducing gas for 20min, discharging air in a furnace tube, heating to 1060 ℃ at the heating rate of 5 ℃/min, preserving heat for 5h, then cooling to 1040 ℃, and preserving heat for 6h at 1040 ℃; and after the temperature is reduced to the room temperature, taking out the sample to obtain the coated silicon-based negative electrode material.
The coated silicon-based negative electrode material prepared in the same manner as in example 1 was tested, and the test results are shown in table 1.
A battery was prepared in the same manner as in example 1, and subjected to cycle and high-temperature storage property tests, the results of which are shown in table 1.
Comparative example 1
The method comprises the following steps: preparation of silica
The silica powder was prepared according to the same procedure as in step one of example 1.
Step two: coating of
And (3) placing the 500g of the silicon monoxide powder prepared in the step (II) into a CVD (chemical vapor deposition) tubular furnace, and introducing a mixed gas of argon and acetylene into one end of the tubular furnace, wherein the flow ratio of the argon to the acetylene is 7:3. Introducing gas for 20min, discharging air in a furnace tube, heating to 1060 ℃ at the heating rate of 5 ℃/min, preserving heat for 0.6h, then cooling to 1040 ℃, and preserving heat for 2h at 1040 ℃; and after the temperature is reduced to room temperature, taking out the sample to obtain the coated silicon-based negative electrode material.
The coated silicon-based negative electrode material prepared in the same manner as in example 1 was tested, and the test results are shown in table 1.
A battery was prepared in the same manner as in example 1, and subjected to cycle and high-temperature storage property tests, the results of which are shown in table 1.
Comparative example 2
The method comprises the following steps: preparation of silica
The silica powder was prepared according to the same procedure as in step one of example 1.
Step two: coating of
And (3) placing the 500g of the silica powder prepared in the second step into a CVD (chemical vapor deposition) tubular furnace, and introducing a mixed gas of argon and acetylene into one end of the tubular furnace, wherein the flow ratio of the argon to the acetylene is 7:3. Ventilating for 20min, discharging air in a furnace pipe, heating to 700 ℃ at a heating rate of 5 ℃/min, preserving heat for 40h, cooling to 680 ℃, and preserving heat for 32h at 680 ℃; and after the temperature is reduced to the room temperature, taking out the sample to obtain the coated silicon-based negative electrode material.
The coated silicon-based negative electrode material prepared in the same manner as in example 1 was tested, and the test results are shown in table 1.
A battery was prepared in the same manner as in example 1, and subjected to cycle and high-temperature storage property tests, the results of which are shown in table 1.
TABLE 1
First layer of carbon bag Between the crystal faces of the cladding layer Distance/nm Second layer carbon bag Between the crystal faces of the cladding layer Distance/nm First coating layer Thickness/second package Thickness of coating Total carbon of coating layer Content% Total thickness of coating layer Degree H/nm Silicon grain size d/nm H/d Capacity of 800 weeks Retention rate Storage capacity recovery Recovery rate
Example 1 0.344 0.346 0.5 1 5 Amorphous form / 84% 90%
Example 2 0.348 0.35 0.8 5 55 5 4 89% 94%
Example 3 0.352 0.354 1.2 10 200 10 200 82% 91%
Example 4 0.346 0.348 0.7 2.5 20 4.5 4 92% 93%
Example 5 0.350 0.353 1.0 7.5 80 7.5 4 94% 95%
Comparative example 1 0.346 0.342 0.4 0.05 2.5 7.5 0.33 80% 88%
Comparative example 2 0.356 0.351 1.3 15 125 2.5 30 81% 87%
As can be seen from examples 1 to 5 and comparative examples 1 and 2, the distance between the crystal planes of the first coating layer is set to be smaller than that between the crystal planes of the second coating layer, and by using the characteristic that the distances between the crystal planes of the first coating layer and the second coating layer are different, the silicon-based core material is relatively deformed due to expansion close to the outer surface of the silicon-based negative electrode material in the lithium embedding expansion process, and by using the larger distance between the crystal planes of the second coating layer, the second coating layer has better ductility, so that relative slippage can be generated between the first coating layer and the second coating layer, the integrity of the coating state is maintained, and the leakage of a fresh interface is avoided.
Meanwhile, the distance between the crystal faces of the first coating layer is smaller than that of the second coating layer, so that the better bonding force between the first coating layer and the surface of the silicon-based core can be kept, and the electronic conduction between the first coating layer and the silicon-based core can be improved, so that the completeness of a coating structure of a silicon-based cathode material can be kept in the battery cycle process, the good electronic conduction of the material in the life cycle of the battery can be kept, and the cycle performance and the storage performance of the battery can be improved.
As shown in examples 1-5 and comparative examples 1-2, the total thickness of the coating layer of the silicon-based core material is set to be 0.5-200nm, so that the silicon-based core material not only has better structural strength, but also can keep higher gram capacity; if the thickness of the coating layer is too low and is less than 0.5nm, the coating structure is incomplete, and if the thickness of the coating layer is too thick, the gram capacity of the silicon-based negative electrode material is low.
Controlling the size of silicon crystal grains to be less than 10nm, preventing the silicon-based core material from generating larger volume expansion, and if the size of the silicon crystal grains is too large, the larger the relative volume expansion is, the larger the load brought to the coating layer structure is; in the invention, the thickness H of the coating layer and the size d of the silicon crystal grains are controlled within a proper proportion range, namely H/d is controlled to be more than 0.5, so that the coating layer can better adapt to the volume expansion of the silicon-based negative electrode material, and the damage of the coating layer caused by the volume expansion is avoided.
The present application has been described above in connection with preferred embodiments, which are, however, merely exemplary and illustrative. On the basis of the above, the present application can be subjected to various substitutions and modifications, and the present application is within the protection scope of the present application.

Claims (13)

1. A silicon-based anode material comprising:
a silicon-based core;
a first cladding layer coated outside the silicon-based core; and
a second cladding layer coated outside the first cladding layer,
the first coating layer and the second coating layer are made of graphitized carbon-based materials, the distance between the lattice planes of the first coating layer is 0.344-0.352nm, the distance between the lattice planes of the second coating layer is 0.345-0.354nm, and the distance between the lattice planes of the first coating layer is smaller than that of the lattice planes of the second coating layer.
2. The silicon-based anode material of claim 1, wherein the size d of the silicon grains in the silicon-based core is less than 10nm, the thickness ratio of the first coating layer to the second coating layer is 0.5 to 1.2, the total thickness H of the first coating layer and the second coating layer is 5 to 200nm, and the ratio H/d of the total thickness H to the size d of the silicon grains is more than 0.5.
3. The silicon-based anode material of claim 1, wherein the silicon-based core is selected from the group consisting of silica SiOxOne or more of nano silicon, silicon carbon and silicon alloy, wherein x is more than 0 and less than 2.
4. The silicon-based anode material of claim 3, wherein the silicon-based core is SiOx，0＜x＜2。
5. The silicon-based anode material according to claim 1, wherein the graphitized carbon-based material content of the first coating layer and the second coating layer is 1 to 10 wt% based on the total weight of the silicon-based anode material.
6. A method of preparing a silicon-based anode material, comprising:
step (1): introducing a gas-phase carbon source into the silicon-based core to coat the silicon-based core, and treating at the temperature T1 to form a first coating layer on the surface of the silicon-based core;
step (2): introducing a gas-phase carbon source into the silicon-based core coated with the first coating layer to coat the silicon-based core coated with the first coating layer, processing at the temperature of T2 to form a second coating layer on the first coating layer to obtain the silicon-based cathode material,
wherein T1> T2;
the distance between the crystal planes of the first coating layer is 0.344-0.352nm, the distance between the crystal planes of the second coating layer is 0.345-0.354 nm, and the distance between the crystal planes of the first coating layer is smaller than that of the second coating layer.
7. The method according to claim 6, wherein T1 in step (1) is 730 to 1200 ℃, and the treatment time is 0.1 to 100h; in the step (2), the T2 is 700 to 1100 ℃, and the processing time is 0.1 to 100h.
8. The method of claim 7, wherein in step (1), T1 is 1000 to 1100 ℃, and the treatment time is 2 to 30 hours; in the step (2), the T2 is 950 to 1050 ℃, and the processing time is 2 to 30 hours.
9. The method of claim 6, wherein the silicon-based core is selected from the group consisting of silica SiOxOne or more of nano silicon, silicon carbon and silicon alloy, wherein x is more than 0 and less than 2; the gas-phase carbon source is one or more selected from alkane, alkene, alkyne or aromatic hydrocarbon-containing gas-phase carbon sources.
10. The method of claim 9, wherein the silicon-based core is silica SiOx，0＜x＜2。
11. The method according to any one of claims 6 to 10, wherein the size d of the silicon crystal grains in the silicon-based core is less than 10nm, the thickness H of the coating layer is 5 to 2000 nm, and the ratio H/d of the thickness H of the coating layer to the size d of the silicon crystal grains is more than 0.5.
12. The method according to claim 11, wherein the carbon-based material content of the first coating layer and the second coating layer is 1 to 10 wt% based on the total weight of the silicon-based anode material.
13. A lithium ion battery, wherein the negative electrode comprises the silicon-based negative electrode material of 1~5 or obtained by the method of any one of claims 6 to 12.
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