CN111418096A - Silicon-graphite composite electrode active material for lithium secondary battery, electrode comprising same, lithium secondary battery, and method for producing silicon-graphite composite electrode active material - Google Patents

Silicon-graphite composite electrode active material for lithium secondary battery, electrode comprising same, lithium secondary battery, and method for producing silicon-graphite composite electrode active material Download PDF

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CN111418096A
CN111418096A CN201980000097.7A CN201980000097A CN111418096A CN 111418096 A CN111418096 A CN 111418096A CN 201980000097 A CN201980000097 A CN 201980000097A CN 111418096 A CN111418096 A CN 111418096A
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silicon
graphite
electrode active
graphite composite
active material
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秦洪秀
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/02—Pretreatment of the material to be coated
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/04—Coating on selected surface areas, e.g. using masks
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/24—Deposition of silicon only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • 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
    • 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
    • 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
    • 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
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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

An embodiment of the present invention provides a silicon-graphite composite electrode active material that can be used for a secondary battery. The silicon-graphite composite electrode active material for a secondary battery according to an embodiment of the present invention may include a silicon-graphite composite as a unit powder, in which silicon is mixed with a graphite material, the silicon-graphite composite may include a graphite material and silicon located inside the graphite material, silicon may not be present outside the graphite material, or silicon may be located only on a portion of an outer surface of the graphite material.

Description

Silicon-graphite composite electrode active material for lithium secondary battery, electrode comprising same, lithium secondary battery, and method for producing silicon-graphite composite electrode active material
Technical Field
The present invention relates to an electrode active material for a lithium secondary battery, an electrode and a secondary battery including the same, and a method for preparing the silicon-graphite composite electrode active material, and more particularly, to an electrode active material capable of providing high-capacity, high-efficiency charge and discharge characteristics by compounding graphite and silicon, an electrode and a secondary battery including the same, and a method for preparing the electrode active material.
Background
Recently, lithium secondary batteries are receiving attention as power sources for driving electronic devices, and such lithium secondary batteries are being developed for various purposes from IT devices such as mobile phones and the like to electric vehicles and energy storage devices, and the demand for them is also on a large trend.
With the increase in the application fields and demands of lithium secondary batteries, various lithium ion battery structures have been developed, and characteristics more excellent than ever in terms of capacity, life, safety, and the like are required.
In response to such a demand, various research and development are also being conducted on electrode active materials for secondary batteries. Conventionally, graphite-based materials have been mainly used as electrode active materials for lithium secondary batteries, but since the capacity per unit mass of graphite is only 372mAh/g, there is a limitation in increasing the capacity, and it is difficult to sufficiently improve the performance of secondary batteries.
As a method for overcoming the capacity limit of graphite, a method has been proposed in which a graphite material is replaced with a material that forms an electrochemical alloy with lithium, such as silicon (Si), tin (Sn), antimony (Sb), or aluminum (Al). However, these materials have characteristics of volume expansion and contraction during charge and discharge by forming an electrochemical alloy with lithium, and volume change due to such charge and discharge causes volume expansion of an electrode, so that cycle characteristics of a secondary battery are deteriorated.
For example, silicon is attracting attention as an electrode active material for a secondary battery that can substitute for a graphite material, and can provide a high capacity because each silicon can absorb a maximum of 4.4 lithium, however, the volume of silicon expands about four times during the process of absorbing lithium ions (for reference, graphite, which has been conventionally used as an electrode active material, exhibits an expansion ratio of about 1.2 times at the time of charge and discharge), and therefore, if the secondary battery continues to be charged and discharged, the expansion of the electrode progresses, resulting in rapid deterioration of the cycle characteristics of the secondary battery.
As a method for solving such problems, a technique of forming an electrode active material by mixing silicon nanoparticles or a silicon coating with a graphite-based material that has been used in the past has recently been proposed. For example, refer to patent documents 1 and 2, which disclose techniques for improving the performance of a secondary battery by forming a silicon layer on a carbon-based material such as graphite.
Specifically, patent document 1 discloses an attempt to form a silicon coating layer on the surface of a carbon-based material such as graphite to ensure a higher capacity than a conventional electrode active material formed of a graphite material, while reducing deterioration in cycle performance of a secondary battery due to expansion and contraction of silicon. However, as shown in fig. 1, since the electrode active material disclosed in patent document 1 has a structure in which the silicon layer entirely surrounds the outer surface of the carbon-based material, the outer silicon layer surrounding the carbon-based material greatly expands and contracts during charge and discharge, and thus, the volume of the electrode excessively expands, so that the electrode active material is electrically short-circuited with the electrode or the surface of the electrode active material is not differentiated to accelerate a side reaction with an electrolyte solution, etc., and the problem of deterioration of the secondary battery performance is still unavoidable.
On the other hand, patent document 2 discloses a technique of forming a silicon coating layer inside a carbon-based material such as graphite to improve the performance of an electrode active material. Specifically, patent document 2 discloses a technique of depositing a silicon coating layer in a cavity inside a carbon-based material by depositing the silicon coating layer by Chemical Vapor Deposition (CVD) after spheroidizing the carbon-based material to form a cavity inside thereof. However, the technique disclosed in patent document 2 also deposits a silicon coating layer by placing a carbon-based material, which is subjected to a spheroidizing treatment to form a cavity inside thereof, into a reaction chamber and injecting a raw material gas from the outside, so that the silicon coating layer is naturally formed outside the carbon-based material in the process of forming the silicon coating layer in the cavity inside the carbon-based material, and the silicon coating layer thus formed outside repeats expansion and contraction during charge and discharge, thereby becoming a cause of reducing the cycle characteristics of the secondary battery similarly to patent document 1.
Accordingly, there is still a need in the field of electrode active materials for secondary batteries to develop an electrode active material capable of improving battery capacity and ensuring good cycle characteristics, and a method for preparing the same.
(patent document 1) Korean granted patent No. 10-1628873 (granted date: 2016.06.02.)
(patent document 2) Korean granted patent No. 10-1866004 (granted date: 2018.06.01.)
Disclosure of Invention
Technical problem
The present invention has been made to solve the above-mentioned problems of the conventional electrode active material for secondary batteries, and an object thereof is to provide an electrode active material for secondary batteries, an electrode and a secondary battery including the same, and a method for producing the electrode active material, which can improve the capacity of the secondary battery and provide good cycle characteristics.
Means for solving the problems
To achieve the above object, a representative structure of the present invention is as follows.
An embodiment of the present invention provides a silicon-graphite composite electrode active material that can be used for a secondary battery. The silicon-graphite composite electrode active material for a secondary battery according to an embodiment of the present invention may include a silicon-graphite composite in which silicon is mixed with a graphite material as a unit powder, the silicon-graphite composite may include a graphite material and silicon located inside the graphite material, silicon may not be present outside the graphite material, or silicon may be located only on a portion of an outer surface of the graphite material.
According to an embodiment of the present invention, in the silicon-graphite composite comprising the silicon-graphite composite electrode active material, the average of the area ratio of silicon occupying the entire outer surface with respect to silicon located at the outside of the graphite material may be 50% or less.
According to an embodiment of the present invention, in the silicon-graphite composite comprising the silicon-graphite composite electrode active material, the average of the area ratio of silicon occupying the entire outer surface with respect to silicon located at the outside of the graphite material may be 25% or less.
According to an embodiment of the present invention, in the silicon-graphite composite contained in the silicon-graphite composite electrode active material, the weight ratio between silicon located at the outside of the graphite material and the entire silicon contained in the silicon-graphite composite may be 20% or less on average.
According to an embodiment of the present invention, in the silicon-graphite composite contained in the silicon-graphite composite electrode active material, the weight ratio between silicon located at the outside of the graphite material and the entire silicon contained in the silicon-graphite composite may be 15% or less on average.
According to an embodiment of the present invention, in the silicon-graphite composite contained in the silicon-graphite composite electrode active material, the weight ratio between silicon located at the outside of the graphite material and the entire silicon contained in the silicon-graphite composite may be 10% or less on average.
According to an embodiment of the present invention, the silicon contained in the silicon-graphite composite may be formed by depositing a thin film layer on the graphite material by a chemical vapor deposition method.
According to an embodiment of the present invention, the silicon may be included in the silicon-graphite composite in an amount of more than 10 wt% with respect to the total weight of the silicon-graphite composite.
According to an embodiment of the present invention, the silicon contained in the silicon-graphite composite may be contained in an amount of more than 15 wt% with respect to the total weight of the silicon-graphite composite.
According to an embodiment of the present invention, silicon may be formed by using SiH-containing silicon4、Si2H6、Si3H8、SiCl4、SiHCl3、Si2Cl6、SiH2Cl2And SiH3More than one of the Cl source gases is deposited on the graphite material.
According to an embodiment of the invention, silicon may be deposited on the graphite material in the form of a thin film layer having a thickness of 20nm to 500 nm.
According to an embodiment of the present invention, silicon may be obtained by simultaneously supplying SiH4、Si2H6、Si3H8、SiCl4、SiHCl3、Si2Cl6、SiH2Cl2And SiH3One or more source gases of Cl and an assist gas comprising one or more of carbon, nitrogen and germanium are deposited on the graphite material.
According to an embodiment of the present invention, the silicon deposited on the graphite material may further include one or more elements of carbon, nitrogen and germanium.
According to an embodiment of the present invention, the silicon thin film layer formed on the silicon-graphite composite may be formed of amorphous or quasi-crystalline silicon particles.
According to an embodiment of the present invention, a surface coating of a carbon material may be further formed on the outer surface of the silicon-graphite composite.
According to an embodiment of the present invention, the surface coating layer may be formed of a carbon material of a type different from the graphite material described above.
According to an embodiment of the present invention, the carbon material forming the surface coating layer may include one or more of coal tar pitch, petroleum pitch, epoxy resin, phenolic resin, polyvinyl alcohol, polyvinyl chloride, ethylene, and acetylene.
According to an embodiment of the present invention, the weight ratio of the surface coating of the carbon material to the total weight of the silicon-graphite composite may be 15 wt% or less.
An embodiment of the present invention may provide a negative electrode for a lithium secondary battery. The negative electrode for a lithium secondary battery according to an embodiment of the present invention may include an electrode active material, the electrode active material may include a silicon-graphite composite as a unit powder, the silicon-graphite composite may include a graphite material and silicon located inside the graphite material, the silicon may not be present outside the graphite material, or the silicon may be located only on a portion of an outer surface of the graphite material.
According to an embodiment of the present invention, in the silicon-graphite composite comprising the silicon-graphite composite electrode active material, the average of the area ratio of silicon occupying the entire outer surface with respect to silicon located at the outside of the graphite material may be 50% or less.
According to an embodiment of the present invention, in the silicon-graphite composite comprising the silicon-graphite composite electrode active material, the average of the area ratio of silicon occupying the entire outer surface with respect to silicon located at the outside of the graphite material may be 25% or less.
According to an embodiment of the present invention, in the silicon-graphite composite contained in the silicon-graphite composite electrode active material, the weight ratio between silicon located at the outside of the graphite material and the entire silicon contained in the silicon-graphite composite may be 20% or less on average.
According to an embodiment of the present invention, in the silicon-graphite composite contained in the silicon-graphite composite electrode active material, the weight ratio between silicon located at the outside of the graphite material and the entire silicon contained in the silicon-graphite composite may be 15% or less on average.
According to an embodiment of the present invention, in the silicon-graphite composite contained in the silicon-graphite composite electrode active material, the weight ratio between silicon located at the outside of the graphite material and the entire silicon contained in the silicon-graphite composite may be 10% or less on average.
An embodiment of the present invention provides a lithium secondary battery, including: a positive electrode; the above-described negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode.
An embodiment of the present invention provides a method of preparing a silicon-graphite composite electrode active material that can be used for a secondary battery. The method of preparing a silicon-graphite composite electrode active material according to an embodiment of the present invention may include: a base material preparation step of preparing a plate-like graphite material; a silicon coating layer forming step of forming a silicon layer on the prepared plate-like graphite material; and a spheroidizing step of pulverizing or polishing the plate-shaped graphite having the silicon layer formed thereon by a mechanical device and reassembling the same.
According to an embodiment of the present invention, in the silicon coating layer forming step, the silicon layer may be formed by depositing a thin film layer on the plate-shaped graphite by a chemical vapor deposition method.
According to an embodiment of the present invention, SiH may be used as a raw material gas in the silicon coating layer forming step4、Si2H6、Si3H8、SiCl4、SiHCl3、Si2Cl6、SiH2Cl2And SiH3Cl to form a silicon layer.
According to an embodiment of the present invention, in the silicon coating layer forming step, a silicon thin film layer having a thickness of 2nm to 500nm may be formed on the plate-shaped graphite.
According to an embodiment of the present invention, in the silicon coating layer forming step, the silicon coating layer may be deposited on the graphite material by simultaneously supplying the above-described raw material gas and auxiliary gas.
According to an embodiment of the present invention, the auxiliary gas may include one or more of carbon, nitrogen and germanium.
According to an embodiment of the present invention, after the spheroidizing step, a surface coating step of coating the carbon material on the outer surface is further included.
According to an embodiment of the present invention, in the surface coating step, the carbon material coated on the outer surface may be a different type of carbon material from the plate-like graphite.
According to an embodiment of the present invention, in the surface coating step, a weight ratio of the carbon material coated on the outer surface to the total weight of the electrode active material may be 15 wt% or less.
According to an embodiment of the present invention, in the surface coating step, the carbon material coated on the outer surface may include one or more of coal tar pitch, petroleum pitch, epoxy resin, phenolic resin, polyvinyl alcohol, polyvinyl chloride, ethylene, and acetylene.
According to an embodiment of the present invention, a surface modification step of modifying the surface of the plate-shaped graphite base material may be further included between the base material preparation step and the silicon coating layer formation step.
According to an embodiment of the present invention, the surface modification step may be performed by coating the precursor on the surface of the plate-shaped graphite.
According to an embodiment of the present invention, the precursor used in the surface modification step may be one or more of petroleum asphalt, coal asphalt, resin, asphalt, methane, ethylene, and acetylene.
According to an embodiment of the present invention, the plate-shaped graphite prepared in the parent material preparation step may be natural or artificial plate-shaped graphite having a thickness of 2 to 20 μm.
In addition to this, the electrode active material, the electrode (negative electrode) and the secondary battery including the same, and the method for preparing the electrode active material according to the present invention may include other additional structures within the scope not departing from the technical idea of the present invention.
ADVANTAGEOUS EFFECTS OF INVENTION
An electrode active material prepared according to an embodiment of the present invention is formed of a graphite material and a silicon-graphite composite combined with silicon so as to be able to improve the capacity and efficiency of a secondary battery, the silicon portion combined with the graphite material is located on a portion of the outer and outer surfaces of the graphite material, and the remaining silicon is located in a cavity (cavity) formed inside the graphite material, and thus, the capacity is improved by the silicon material, the volume expansion of an electrode due to the expansion and contraction of silicon is reduced, the risk of electrical short between the electrode active material and the electrode is remarkably suppressed, and moreover, a phenomenon of accelerating a side reaction between silicon present on the surface of the electrode active material and an electrolyte solution can be reduced, thereby improving the life and cycle characteristics of the secondary battery.
Drawings
Fig. 1 schematically shows a Scanning Electron Microscope (SEM) photograph of a conventional electrode active material for a secondary battery (electrode active material disclosed in patent document 1).
Fig. 2 schematically shows a scanning electron micrograph of an electrode active material for a secondary battery according to an embodiment of the present invention.
Fig. 3 schematically shows a state where silicon is deposited on a graphite material according to an embodiment of the present invention (part (a) of fig. 3) and a state where silicon is removed therefrom ((b) part shows that only exposed silicon on the surface is removed, (c) part shows that all silicon inside and outside is removed).
Fig. 4 schematically shows a scanning electron microscope photograph of plate-shaped graphite that can be used to prepare an electrode active material for a secondary battery according to an embodiment of the present invention.
Fig. 5 schematically shows a state where a silicon coating is formed on the plate-shaped graphite shown in fig. 4.
Fig. 6 schematically shows a state in which plate-shaped graphite having a silicon coating layer formed thereon is spheroidized.
Fig. 7 schematically shows the change in specific surface area characteristics of graphite before and after the surface modification process.
Fig. 8 schematically shows a state where different types of carbon materials are coated on the surface of the spheroidized silicon-graphite composite material shown in fig. 6, in which (a) part shows spray drying, (b) part shows a rotation-revolution agitator, (c) part shows a planetary dispersion agitator, and (d) part shows mechanical coating.
Fig. 9 schematically shows a comparative table of electrochemical characteristics between an electrode active material according to an embodiment of the present invention and a conventional electrode active material in which silicon is coated on the surface of graphite.
Detailed Description
Best mode for carrying out the invention
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings to the extent that they can be easily implemented by those skilled in the art to which the present invention pertains.
The same or similar components are denoted by the same reference numerals throughout the specification. In addition, since the sizes and the like of the respective structures shown in the drawings are arbitrarily shown for convenience of explanation, the present invention is not limited to the shown drawings. That is, it is to be understood that the specific shapes, structures, and characteristics described in the specification may be changed from one embodiment to another without departing from the spirit and scope of the present invention, and the positions or arrangements of individual components may be changed without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention includes the appended claims and all equivalents thereof.
Electrode active material according to the present invention, negative electrode including the same, and secondary battery
One embodiment of the present invention provides a silicon-graphite composite electrode active material (negative electrode active material) obtained by mixing a graphite material and silicon.
As described above, the graphite material, which has been conventionally used as an electrode active material for a secondary battery, has a capacity limitation and has a problem of deterioration of output characteristics at the time of rapid charging, etc., whereas the silicon material has a problem in that significant volume expansion occurs at the time of charge and discharge, and thus the electrode active material and an electrode plate are seriously damaged, resulting in a great reduction in cycle characteristics of the secondary battery.
In contrast, the electrode active material according to an embodiment of the present invention has a composite structure in which a graphite material and silicon are mixed, and thus can significantly improve battery capacity as compared to a conventional electrode active material made of graphite, and as will be described below, a silicon part included in the electrode active material is located on a portion of an outer surface in the outside of the graphite material, and the remaining silicon is located in a cavity inside the graphite material, and thus, it is possible to prevent the problem of the reduction in the life and performance of a secondary battery due to the expansion and contraction of silicon occurring at the time of charge and discharge.
Specifically, the electrode active material of an embodiment of the present invention may be formed of a silicon-graphite composite (powder lump shown in fig. 2 and 3 in an enlarged manner) mixed with a graphite material and a silicon material.
The above-described silicon-graphite composite is used as a unit powder for forming an electrode active material of a secondary battery, and may be formed in a form in which a graphite material and silicon are mixed. For example, the silicon-graphite composite constituting the electrode active material of an embodiment of the present invention may be formed by mixing a graphite material and silicon by vapor deposition or the like. A plurality of the above-described silicon-graphite composites are aggregated to form an electrode active material according to the capacity of a secondary battery.
According to an embodiment of the present invention, silicon may be formed by depositing silicon on a graphite material in the form of a thin film layer by a Chemical Vapor Deposition (CVD) method or the like, and preferably, silicon may not be present on the outer portion of the graphite material, or silicon may be only partially located on a portion of the outer surface of the graphite material (a minimum amount of silicon may be formed on the outer surface of the graphite material), and the remaining silicon may be located inside the graphite material.
According to an embodiment of the present invention, in the silicon-graphite composite constituting the electrode active material, the average value of the area ratio occupied by silicon located at the outer portion of the graphite material with respect to the entire outer surface is preferably 50% or less, more preferably 25% or less.
According to an embodiment of the present invention, in the silicon-graphite composite constituting the electrode active material, the weight ratio between silicon located at the outside of the graphite material and the entire silicon mixed in the silicon-graphite composite may be 20% or less on average, preferably 15% or less on average, more preferably 10% or less on average. As described above, when only a small amount of silicon is located outside the graphite material and the remaining silicon is located inside the graphite material, it is possible to suppress the volume expansion rate of the electrode from being greatly increased to damage the electrode due to the volume expansion of the externally exposed silicon, and to effectively prevent the externally exposed silicon from being in contact with the electrolyte to cause side reactions, so that the life of the secondary battery can be remarkably improved.
As described above, when the electrode active material (silicon-graphite composite) is formed such that silicon is not present outside the graphite material as the base material or silicon is located only at a part of the outer surface, it is possible to suppress an excessive increase in the volume expansion rate of the electrode due to volume expansion and contraction of silicon at the time of charge and discharge of the secondary battery, and to significantly reduce side reactions caused by contact between the electrolyte and silicon, so that the life of the secondary battery can be improved.
The inventors of the present application analyzed the composition of the silicon-graphite composite of the electrode active material of an embodiment of the present invention, and as a result, it could be confirmed that in the case of the silicon-graphite composite containing 15 wt% of silicon with respect to the total weight of the silicon-graphite composite (the composition of the silicon-graphite composite was analyzed by ICP measurement), only 2.2 wt% of silicon was present on the outer surface of the graphite material with respect to the total weight of the silicon-graphite composite, so that only 15% or less of the silicon in the entire silicon was exposed to the outside (the graphite material was immersed in a NaOH solution for 5 minutes to remove the externally present silicon as shown in part (b) of fig. 3 and then the composition was analyzed by ICP measurement), while the remaining silicon was located inside the graphite material. Therefore, the electrode active material according to an embodiment of the present invention can effectively prevent the electrode of the secondary battery from being damaged and the cycle characteristics and the lifespan of the secondary battery from being reduced due to the expansion of silicon exposed to the outside of the graphite material and the contact with the electrolyte.
According to an embodiment of the present invention, the content of silicon contained in the silicon-graphite composite constituting the electrode active material may be greater than 10 wt%, preferably, may be greater than 15 wt%, with respect to the total weight of the silicon-graphite composite. Since silicon can provide a larger capacity than graphite, the larger the content of silicon in the electrode active material, the higher the capacity of the secondary battery, but silicon contained in the electrode active material may significantly reduce the cycle characteristics of the secondary battery due to expansion occurring during charge and discharge, and thus there may be a limitation in increasing the amount of silicon added to the electrode active material. For example, in the silicon-graphite composite electrode active material known in the prior art, the electrode active material actually contains about 10 wt% or less of silicon due to the problem of deterioration of the cycle characteristics of the secondary battery caused by the expansion and contraction of silicon. However, in the electrode active material according to an embodiment of the present invention, silicon is only partially located on a portion of the outer surface of the exterior of the graphite material, and the remaining silicon is located in the cavity formed in the graphite material, and thus, even if more than 10 wt% of silicon is included, surface cracking due to expansion and contraction of silicon can be suppressed, so that more silicon and the silicon-graphite composite can be mixed to further improve the capacity of the secondary battery.
According to an embodiment of the present invention, silicon contained in the silicon-graphite composite constituting the electrode active material may have amorphous or quasi-crystalline silicon particles. Unlike crystalline silicon, amorphous or quasi-crystalline silicon does not have the absorption directionality of lithium, so that the volume can be uniformly expanded, and the movement speed of lithium is high, and stress or strain required for absorption or desorption of lithium is low compared to crystalline silicon, thus having an advantage of being able to stably maintain the structure. Therefore, when silicon is formed of amorphous or quasicrystalline particles, even if a greater amount of silicon is contained in the electrode active material, the problem that the secondary battery is damaged due to the expansion of silicon can be prevented.
On the other hand, according to an embodiment of the present invention, the outer circumferential surface of the silicon-graphite composite constituting the electrode active material may further include a surface coating layer. The surface coating layer formed on the outer circumferential surface of the silicon-graphite composite may perform the functions of stabilizing the interface between graphite and silicon, providing an electron transport path to improve conductivity, suppressing a volume change of silicon at the time of charge and discharge, and thus improving the stability of the electrode plate.
According to an embodiment of the present invention, the surface coating layer formed on the outer circumferential surface of the silicon-graphite composite may be formed of a coating layer of a carbon material, and the carbon material forming the surface coating layer is preferably a carbon material of a type different from graphite, which is a base material of the electrode active material. For example, the surface coating layer may be formed of one or more carbon materials selected from coal tar pitch, petroleum pitch, epoxy resin, phenol resin, polyvinyl alcohol, polyvinyl chloride, ethylene, and acetylene.
However, the surface coating layer is not essential, and the surface coating layer may be omitted to form the electrode active material, or an additional coating layer may be further formed on the surface coating layer of the carbon material described above.
On the other hand, an embodiment of the present invention may provide an electrode (negative electrode) including the electrode active material described above. That is, the electrode for a secondary battery (negative electrode) according to an embodiment of the present invention may include the electrode active material formed of the silicon-graphite composite described above.
Specifically, the electrode for a secondary battery (negative electrode) according to an embodiment of the present invention may include an electrode active material formed of a silicon-graphite composite. The silicon-graphite composite forming the electrode active material includes a graphite material and silicon located inside the graphite material, and the silicon may not be present outside the graphite material or may be located on only a portion of the outer surface of the graphite material.
For example, according to an embodiment of the present invention, in the silicon-graphite composite contained in the electrode active material of the secondary battery electrode (negative electrode), the average value of the area ratio of silicon occupying the outer portion of the graphite material of the silicon-graphite composite with respect to the entire outer surface may be 50% or less, and preferably, may be 25% or less.
Also, according to an embodiment of the present invention, in the silicon-graphite composite contained in the electrode active material of the secondary battery electrode (negative electrode), the weight ratio between silicon located outside the graphite material of the silicon-graphite composite and the entire silicon contained in the silicon-graphite composite may be 20% or less on average, preferably 15% or less, more preferably 10% or less.
According to the structure as described above, silicon mixed in the graphite material is only partially exposed to the outside, and a considerable portion of the silicon is located inside the graphite material, so that it is possible to prevent the electrode from being damaged due to the volume expansion of silicon and the contact with the electrolyte when the secondary battery is charged and discharged, and to improve the cycle performance and the lifespan of the secondary battery.
On the other hand, the electrode active material according to an embodiment of the present invention may be used not only alone to form a secondary battery, but also mixed together with an existing electrode active material (for example, an electrode active material formed of a graphite-based material) to form an electrode active material for a secondary battery. The electrode active material according to an embodiment of the present invention can stably control problems such as damage to an electrode due to volume expansion of silicon, and therefore, a larger amount of silicon is contained in the electrode active material than ever to enable sufficient capacity enlargement, and therefore, even if used in combination with a conventional electrode active material, it is possible to provide a capacity sufficiently improved than ever, and instead, the problem of volume expansion due to silicon is more effectively controlled by a conventional electrode active material such as an electrode active material formed of a graphite-based material.
In addition, an embodiment of the present invention may provide a lithium secondary battery including the electrode (negative electrode) described above.
The method for preparing the electrode active material according to the present invention
An embodiment of the present invention provides a method for preparing a silicon-graphite composite electrode active material (specifically, a silicon-graphite composite constituting an electrode active material) in which silicon is added to a graphite material.
According to an embodiment of the present invention, a method of preparing an electrode active material (a silicon-graphite composite constituting the electrode active material) may include: (i) a base material preparation step of preparing a plate-like graphite material; (ii) a silicon coating layer forming step of forming a silicon layer on the prepared plate-like graphite material; and (iii) a spheroidizing step of pulverizing or polishing the plate-shaped graphite formed with the silicon layer by a mechanical device and reassembling.
The base material preparation step is a step of preparing a base material serving as a base material of the silicon-graphite composite according to an embodiment of the present invention, wherein the base material may be natural or artificial graphite having a plate-like structure, and may be formed of a material having a particle size of 2 μm to 20 μm, for example.
The silicon coating layer forming step is a step of coating a silicon material on the plate-shaped graphite base material for the purpose of increasing the capacity of the electrode active material, and the silicon coating layer may be formed by chemical vapor deposition or the like.
Specifically, the silicon coating layer may be formed by injecting a silicon-containing raw material gas into a high-temperature reaction chamber and depositing on plate-shaped graphite. For example, by reacting e.g. SiH4、Si2H6、Si3H8、SiCl4、SiHCl3、Si2Cl6、SiH2Cl2、SiH3Raw material gas of Cl or the likeA reaction chamber heated to a temperature of 450 to 700 ℃ is injected to deposit a silicon coating on the graphite plate material.
As described above, in the silicon-graphite composite electrode active material according to an embodiment of the present invention, since the silicon coating layer is formed at a relatively low temperature (temperature range of 450 to 700 ℃), the silicon coating layer may be formed of amorphous or quasi-crystalline silicon particles rather than crystalline silicon particles.
On the other hand, the silicon coating layer can be formed by simultaneously injecting the above-described source gas and an assist gas containing carbon, nitrogen, germanium, or the like. As described above, when silicon deposition is performed in such a manner that auxiliary gases containing substances of carbon, nitrogen, germanium, and the like are simultaneously supplied, substances of carbon, nitrogen, germanium, and the like are contained in the silicon deposition layer formed on the graphite material, and these materials contained in the silicon deposition layer can suppress the expansion of silicon to further reduce the electrode damage and the life shortening of the secondary battery.
According to an embodiment of the present invention, the content of silicon contained in the silicon-graphite composite forming the electrode active material may be greater than 10 wt%, preferably, greater than 15 wt%, with respect to the total weight of the silicon-graphite composite, and may be formed in the form of a thin film layer having a thickness ranging from 20nm to 500 nm.
The spheroidizing step performs a function of pulverizing or polishing and reassembling the plate-shaped graphite formed with the silicon layer. By the above-described spheroidization step, the silicon-graphite composite is reassembled so that the silicon coating layer deposited on the outside of the plate-like graphite in the silicon coating layer forming step moves to the inside of the graphite and is positioned.
According to an embodiment of the present invention, in the spheroidization step, the plate-shaped graphite deposited with the silicon coating is injected into a machine equipped with a rotating rotor and blades, the surface of the plate-shaped graphite deposited with the silicon coating is polished while rotating at a high speed, and the spheroidization is achieved by reassembling chips falling down by polishing, or the spheroidization is achieved by crushing (crush) and reassembling flake graphite deposited with the silicon coating by pressing.
According to an embodiment of the present invention, in the spheroidizing step, in order to prevent graphite or silicon from being included in the powderThe graphite plate formed with the silicon coating layer is oxidized by strong frictional heat generated during crushing or grinding, and the inside atmosphere can be treated with N, for example2Or an inert gas such as AR. In order to improve the binding force between graphite and silicon, it may be performed in a state in which coal tar pitch, petroleum pitch, epoxy resin, phenol resin, polyvinyl alcohol, polyvinyl chloride, or the like is added as a binder.
On the other hand, according to an embodiment of the present invention, after preparing the plate-shaped graphite, before forming the silicon coating layer on the plate-shaped graphite, a surface modification step of modifying the surface of the plate-shaped graphite material may be further included. The surface modification performs a function of preventing silicon from flowing into micropores, in which it is difficult to secure an expansion space, by filling the micropores formed in the plate-like graphite. Specifically, when the surface modification process is performed, the micropores of 50nm or less formed on the plate-shaped graphite are filled with different kinds of amorphous or crystalline carbon, and thus the specific surface area of the plate-shaped graphite material is reduced (when the surface modification process is performed, the micropores inside the plate-shaped graphite are filled with different kinds of amorphous or crystalline carbon, and thus, as shown in fig. 7, the specific surface area is reduced to 2 to 10m2A/g of 1 to 5m2G), whereby the silicon coating can be formed only in the large cavities present inside the plate-like graphite and outside the plate-like graphite. The silicon coating layer formed in the micro-pores may cause cracks when expanding because it does not have a sufficient space required for silicon to expand, but if it is subjected to a surface modification process, the silicon coating layer is prevented from being formed in the micro-pores, so that damage as described above can be suppressed.
According to an embodiment of the present invention, the surface modification process may be performed by coating a precursor of coal tar pitch, coal pitch, resin, pitch, methane, ethylene, acetylene, and the like on the surface of the plate-shaped graphite. For example, a precursor of coal tar pitch, coal pitch, resin, pitch, or the like may be coated on the plate-like graphite by using a rotary furnace, an atmosphere furnace, or the like, and may be coated on the plate-like graphite by using a coating solution of N2The coating is performed by holding the material in a temperature range of 600 to 1,000 c for 2 hours or more in an inert gas atmosphere of Ar, or the like. On the other hand, it is possible to use, for example, methane, ethylene and ethyleneA precursor of an alkyne or the like is coated on the plate-like graphite by using a vapor deposition apparatus or a rotary furnace or the like, and the precursor is coated on the surface by supplying the precursor at a flow rate of 3L to 8L per minute for the plate-like graphite at a temperature of 800 ℃ to 1,000 ℃.
On the other hand, according to an embodiment of the present invention, after spheroidizing the plate-shaped graphite, surface coating for forming a coating layer on the outside of the silicon-graphite composite may be further performed. The surface coating functions to stabilize the interface between the silicon-graphite composite and improve the electrical conductivity.
According to an embodiment of the present invention, the surface coating may be performed by coating a carbon material having a weight ratio of 15 wt% or less with respect to the total weight of the silicon-graphite composite forming the electrode active material on the surface of the silicon-graphite composite, and the surface coating may have a thickness of 150nm or less.
According to an embodiment of the present invention, the carbon material for surface coating may be a different type of carbon material from the plate-like graphite used as a base material of the silicon-graphite composite, and for example, may be coal tar pitch, petroleum pitch, epoxy resin, phenol resin, polyvinyl alcohol, polyvinyl chloride, ethylene, acetylene, or the like.
According to an embodiment of the present invention, after forming a precursor using a combination material of the different types of carbon materials and at least two of tetrahydrofuran, methylpyrrolidone, ethanol, acetone, isopropyl alcohol, and methyl butyl ketone as an organic solvent, the precursor is subjected to spray drying, a rotation and revolution stirrer, a planetary dispersion stirrer, mechanical coating, and the like (see fig. 8).
After forming the surface coating on the silicon-graphite composite, the surface coating may be on, for example, N2And Ar or the like in an inert gas atmosphere, and then subjected to carbonization treatment in a high-temperature environment. The carbonization treatment may be performed by maintaining the silicon-graphite composite formed with the surface coating at a temperature of 700 ℃ or more and 1100 ℃ or less.
Modes for carrying out the invention
Electrode active Material (Siliconite) according to the present inventionInk composites) embodiments
① example 1
First, a plate-like graphite material having an average particle diameter of 4 μm was prepared. Next, 10g of graphite was charged into the rotary kiln, the inside of the rotary kiln was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 580 ℃. After reaching 580 deg.C, 99.999% pure SiH is added4The silicon coating was coated on the plate-shaped graphite by air-cooling by flowing nitrogen gas having a purity of 99.999% for about 30 minutes. Thereafter, the plate-shaped graphite deposited with the silicon coating layer was put into a spheroidizing apparatus and mechanically polished at a rotation speed of 16,000RPM for 10 minutes to achieve spheroidization. After the spheronization, petroleum pitch was supplied for coating the surface with petroleum pitch, the pitch-coated material was put into a tube, and the inside of the tube was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 850 ℃ at a rate of 5 ℃ per minute while flowing nitrogen gas having a purity of 99.999%, and then maintained at 850 ℃ for two hours to carbonize the surface-coated petroleum pitch.
② example 2
First, a plate-like graphite material having an average particle diameter of 4 μm was prepared. Next, 10g of graphite was charged into the rotary kiln, the inside of the rotary kiln was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 580 ℃. After reaching 580 deg.C, 99.999% pure SiH is added4The flow was for about 45 minutes, and nitrogen gas having a purity of 99.999% was also flowed to perform air cooling, thereby coating the silicon coating on the plate-shaped graphite. Thereafter, the plate-shaped graphite deposited with the silicon coating layer was put into a spheroidizing apparatus and mechanically polished at a rotation speed of 16,000RPM for 10 minutes to achieve spheroidization. After the spheronization, petroleum pitch was supplied for coating the surface with petroleum pitch, the pitch-coated material was put into a tube furnace, and the inside of the tube was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 850 ℃ at a rate of 5 ℃ per minute while flowing nitrogen gas having a purity of 99.999%, and then maintained at 850 ℃ for two hours to carbonize the surface-coated petroleum pitch.
③ example 3
First, a plate-like graphite material having an average particle diameter of 4 μm was prepared. Next, 10g of graphite was charged into the rotary kiln, the inside of the rotary kiln was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 580 ℃. After reaching 580 deg.C, 99.999% pure SiH is added4The silicon coating was coated on the plate-shaped graphite by air-cooling by flowing nitrogen gas having a purity of 99.999% for about 60 minutes. Thereafter, the plate-shaped graphite deposited with the silicon coating layer was put into a spheroidizing apparatus and mechanically polished at a rotation speed of 16,000RPM for 10 minutes to achieve spheroidization. After the spheronization, petroleum pitch was supplied for coating the surface with petroleum pitch, the pitch-coated material was put into a tube furnace, and the inside of the tube was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 850 ℃ at a rate of 5 ℃ per minute while flowing nitrogen gas having a purity of 99.999%, and then maintained at 850 ℃ for two hours to carbonize the surface-coated petroleum pitch.
④ example 4
First, a plate-like graphite material having an average particle diameter of 4 μm was prepared. Next, 10g of graphite was charged into the rotary kiln, the inside of the rotary kiln was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 580 ℃. After reaching 580 deg.C, 99.999% pure SiH is added4The silicon coating was coated on the plate-shaped graphite by air-cooling by flowing nitrogen gas having a purity of 99.999% for about 100 minutes. Thereafter, the plate-shaped graphite deposited with the silicon coating layer was put into a spheroidizing apparatus and mechanically polished at a rotation speed of 16,000RPM for 10 minutes to achieve spheroidization. After the spheronization, petroleum pitch was supplied for coating the surface with petroleum pitch, the pitch-coated material was put into a tube furnace, and the inside of the tube was vacuum-replaced with a nitrogen atmosphere, and then the temperature was raised to 850 ℃ at a rate of 5 ℃ per minute while flowing nitrogen gas having a purity of 99.999%, and then maintained at 850 ℃ for two hours to carbonize the surface-coated petroleum pitch.
⑤ comparative example
In comparative example, according to the process conditions of the example disclosed in patent document 1, a silicon-graphite composite is formed by coating a silicon material on the surface of a graphite material.
Referring to fig. 9, the performance of the electrode active material (silicon-graphite composite; examples 1 to 4) prepared according to an example of the present invention and the performance of the comparative example are compared and summarized. As shown in the table of fig. 9, it can be confirmed that the silicon-graphite composite of an embodiment of the present invention ensures high capacity and provides good cycle characteristics. For example, as shown in the table of fig. 9, it was confirmed that the silicon-graphite composite according to an embodiment of the present invention provides a high capacity of 600mAh/g, and the life of the battery is not greatly reduced (the 50-cycle retention rate of 90% or more is exhibited) even though the charge and discharge are repeated.
The present invention has been described above with reference to specific details such as specific structural elements and limited embodiments and drawings, but this is provided only to facilitate a more complete understanding of the present invention, and the present invention is not limited to the above-described embodiments, and various modifications and changes can be made by those skilled in the art to which the present invention pertains based on the description.
Therefore, the idea of the present invention is not limited to the above-described embodiments, and not only the scope of the claims described below but also all the scope equivalent to or modified equivalently from the scope of the claims also belong to the scope of the idea of the present invention.

Claims (39)

1. A silicon-graphite composite electrode active material for a secondary battery, as a silicon-graphite composite electrode active material for a secondary battery, characterized by comprising a silicon-graphite composite as a unit powder, which is obtained by mixing silicon with a graphite material,
the silicon-graphite composite includes a graphite material and silicon located within the graphite material,
there is no silicon on the outside of the graphite material or silicon is only on a portion of the outer surface of the graphite material.
2. The silicon-graphite composite electrode active material for a secondary battery according to claim 1, wherein the average value of the area ratio of silicon located outside the graphite material to the entire outer surface in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 50% or less.
3. The silicon-graphite composite electrode active material for a secondary battery according to claim 2, wherein the average value of the area ratio of silicon located outside the graphite material to the entire outer surface in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 25% or less.
4. The silicon-graphite composite electrode active material for secondary batteries according to claim 1, wherein the weight ratio of silicon located outside the graphite material to the entire silicon contained in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 20% or less on average.
5. The silicon-graphite composite electrode active material for secondary batteries according to claim 4, wherein the weight ratio of silicon located outside the graphite material to the entire silicon contained in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 15% or less on average.
6. The silicon-graphite composite electrode active material for secondary batteries according to claim 5, wherein the weight ratio of silicon located outside the graphite material to the entire silicon contained in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 10% or less on average.
7. The silicon-graphite composite electrode active material for secondary batteries according to any one of claims 1 to 6, wherein the silicon contained in the silicon-graphite composite is formed by depositing a thin film layer on a graphite material by a chemical vapor deposition method.
8. The silicon-graphite composite electrode active material for a secondary battery according to claim 7, wherein the content of silicon contained in the silicon-graphite composite is greater than 10 wt% with respect to the total weight of the silicon-graphite composite.
9. The silicon-graphite composite electrode active material for a secondary battery according to claim 8, wherein the content of silicon contained in the silicon-graphite composite is more than 15 wt% with respect to the total weight of the silicon-graphite composite.
10. The silicon-graphite composite electrode active material for secondary batteries according to claim 7, wherein the silicon is obtained by using a material containing SiH4、Si2H6、Si3H8、SiCl4、SiHCl3、Si2Cl6、SiH2Cl2And SiH3More than one of the Cl source gases is deposited on the graphite material.
11. The silicon-graphite composite electrode active material for secondary batteries according to claim 10, wherein the silicon is deposited on the graphite material in the form of a thin film having a thickness of 20nm to 500 nm.
12. The silicon-graphite composite electrode active material for secondary batteries according to claim 10, wherein the silicon is prepared by supplying SiH4、Si2H6、Si3H8、SiCl4、SiHCl3、Si2Cl6、SiH2Cl2And SiH3One or more source gases of Cl and an assist gas comprising one or more of carbon, nitrogen and germanium are deposited on the graphite material.
13. The silicon-graphite composite electrode active material for a secondary battery as claimed in claim 12, wherein the silicon deposited on the graphite material further comprises one or more elements selected from carbon, nitrogen and germanium.
14. The silicon-graphite composite electrode active material for a secondary battery as claimed in claim 7, wherein the silicon thin film layer formed on the silicon-graphite composite is formed of amorphous or quasi-crystalline silicon particles.
15. The silicon-graphite composite electrode active material for a secondary battery according to claim 7, wherein a surface coating film of a carbon material is further formed on an outer surface of the silicon-graphite composite.
16. The silicon-graphite composite electrode active material for a secondary battery according to claim 15, wherein the surface coating film is formed of a carbon material of a type different from that of the graphite material.
17. The silicon-graphite composite electrode active material for a secondary battery according to claim 16, wherein the carbon material forming the surface coating film includes one or more of coal tar pitch, petroleum pitch, epoxy resin, phenol resin, polyvinyl alcohol, polyvinyl chloride, ethylene, and acetylene.
18. The silicon-graphite composite electrode active material for a secondary battery according to claim 17, wherein the weight ratio of the surface coating of the carbon material to the total weight of the silicon-graphite composite is 15 wt% or less.
19. A negative electrode for a lithium secondary battery, which is used for a negative electrode for a lithium secondary battery, is characterized by comprising an electrode active material containing a silicon-graphite composite obtained by mixing a silicon and a graphite material as a unit powder,
the silicon-graphite composite includes a graphite material and silicon located within the graphite material,
there is no silicon on the outside of the graphite material or silicon is only on a portion of the outer surface of the graphite material.
20. The negative electrode for a lithium secondary battery according to claim 19, wherein the silicon-graphite composite electrode active material contains a silicon-graphite composite in which the average value of the area ratio of silicon located outside the graphite material to the entire outer surface is 50% or less.
21. The negative electrode for a lithium secondary battery according to claim 20, wherein the silicon-graphite composite electrode active material contains a silicon-graphite composite in which the average value of the area ratio of silicon located outside the graphite material to the entire outer surface is 25% or less.
22. The negative electrode for a lithium secondary battery according to claim 19, wherein the weight ratio of silicon located outside the graphite material to the entire silicon contained in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 20% or less on average.
23. The negative electrode for a lithium secondary battery according to claim 22, wherein the weight ratio of silicon located outside the graphite material to the entire silicon contained in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 15% or less on average.
24. The negative electrode for a lithium secondary battery according to claim 23, wherein the weight ratio of silicon located outside the graphite material to the entire silicon contained in the silicon-graphite composite contained in the silicon-graphite composite electrode active material is 10% or less on average.
25. A lithium secondary battery, characterized by comprising:
a positive electrode;
the negative electrode of any one of claims 19 to 24; and
and an electrolyte disposed between the positive electrode and the negative electrode.
26. A method for preparing a silicon-graphite composite electrode active material as a method for preparing a silicon-graphite composite electrode active material for a secondary battery, comprising:
a base material preparation step of preparing a plate-like graphite material;
a silicon coating layer forming step of forming a silicon layer on the prepared plate-like graphite material; and
and a spheroidizing step of pulverizing or polishing the plate-shaped graphite formed with the silicon layer by a mechanical device and reassembling the same.
27. The method for preparing a silicon-graphite composite electrode active material according to claim 26, wherein, in the silicon coating layer forming step, the silicon layer is formed by depositing a thin film layer on the plate-shaped graphite by a chemical vapor deposition method.
28. The method for producing a silicon-graphite composite electrode active material as claimed in claim 27, wherein SiH is used as a raw material gas in the silicon coating layer forming step4、Si2H6、Si3H8、SiCl4、SiHCl3、Si2Cl6、SiH2Cl2And SiH3Cl to form a silicon layer.
29. The method of producing a silicon-graphite composite electrode active material according to claim 28, wherein in the silicon coating layer forming step, a silicon thin film layer having a thickness of 2nm to 500nm is formed on the plate-shaped graphite.
30. The method of producing a silicon-graphite composite electrode active material according to claim 29, wherein in the silicon coating layer forming step, a silicon coating layer is deposited on the graphite material by simultaneously supplying the raw material gas and the assist gas.
31. The method of claim 30, wherein the assist gas comprises at least one of carbon, nitrogen, and germanium.
32. The method of preparing a silicon-graphite composite electrode active material according to claim 27, further comprising a surface coating step of coating a carbon material on the outer surface after the spheroidization step.
33. The method of preparing a silicon-graphite composite electrode active material according to claim 32, wherein, in the surface coating step, the carbon material coated on the outer surface is a type of carbon material different from the plate-shaped graphite.
34. The method of preparing a silicon-graphite composite electrode active material according to claim 33, wherein, in the surface coating step, a weight ratio of the carbon material coated on the outer surface to the total weight of the electrode active material is 15 wt% or less.
35. The method of preparing a silicon-graphite composite electrode active material according to claim 34, wherein, in the surface coating step, the carbon material coated on the outer surface includes one or more of coal tar pitch, petroleum pitch, epoxy resin, phenol resin, polyvinyl alcohol, polyvinyl chloride, ethylene, and acetylene.
36. The method of producing a silicon-graphite composite electrode active material according to claim 32, further comprising a surface modification step of modifying a surface of the plate-like graphite base material between the base material preparation step and the silicon coating layer formation step.
37. The method of preparing a silicon-graphite composite electrode active material according to claim 36, wherein the surface modification step is performed by coating a precursor on the surface of the plate-shaped graphite.
38. The method of preparing a silicon-graphite composite electrode active material according to claim 37, wherein the precursor used in the surface modification step is one or more of petroleum pitch, coal pitch, resin, pitch, methane, ethylene, and acetylene.
39. The method of producing a silicon-graphite composite electrode active material according to claim 32, wherein the plate-shaped graphite prepared in the base material preparation step is natural or artificial plate-shaped graphite having a thickness of 2 μm to 20 μm.
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