CN116762188A - Negative electrode active material, method for producing negative electrode active material, negative electrode comprising negative electrode active material, and secondary battery comprising same - Google Patents
Negative electrode active material, method for producing negative electrode active material, negative electrode comprising negative electrode active material, and secondary battery comprising same Download PDFInfo
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- CN116762188A CN116762188A CN202280011241.9A CN202280011241A CN116762188A CN 116762188 A CN116762188 A CN 116762188A CN 202280011241 A CN202280011241 A CN 202280011241A CN 116762188 A CN116762188 A CN 116762188A
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- active material
- silicon
- sio
- based composite
- negative electrode
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Abstract
The present application relates to a negative electrode active material, a method for preparing the same, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode, wherein the negative electrode active material includes: comprising SiO x (0<x<2) And silicon-based composite particles of a Li compound; a carbon layer; siO y (1<y.ltoreq.2), wherein the carbon layer covers at least a part of the surface of the silicon-based composite particles, and the SiO y (1<y.ltoreq.2) covering at least a part of the surface of the silicon-based composite particles orAt least a portion of the surface of the carbon layer.
Description
Technical Field
The present application claims priority and equity from korean patent applications No. 10-2021-0107522 and No. 10-2022-0014132, filed to the korean intellectual property office on day 13 of 2021 and day 3 of 2022, respectively, the entire contents of which are incorporated herein by reference.
The present application relates to a negative electrode active material, a method of preparing the negative electrode active material, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode active material.
Background
Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small and lightweight secondary batteries having a relatively high capacity is rapidly increasing. In particular, lithium secondary batteries are light in weight and high in energy density, and thus are attracting attention as driving power sources for mobile devices. Accordingly, research and development efforts have been actively conducted for improving the performance of the lithium secondary battery.
Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. Further, for the positive electrode and the negative electrode, a living body each containing a positive electrode active material and a negative electrode active material may be formed on a current collectorA layer of a sexual material. Typically, lithium-containing metal oxides such as LiCoO have been used for the positive electrode 2 And LiMn 2 O 4 As the positive electrode active material, and as the negative electrode active material, a carbon-based active material and a silicon-based active material that do not contain lithium have been used for the negative electrode.
Among the negative electrode active materials, silicon-based active materials have been attracting attention because of their high capacity and excellent high-rate charging characteristics as compared with carbon-based active materials. However, the silicon-based active material has a large degree of volume expansion/contraction due to charge/discharge and a large irreversible capacity, and thus has a disadvantage of low initial efficiency.
On the other hand, among silicon-based active materials, silicon-based oxides, specifically, silicon oxide is composed of SiO x (0<x<2) The silicon-based oxide shown has an advantage that the degree of volume expansion/contraction due to charge/discharge is small compared to other silicon-based active materials such as silicon (Si). However, silicon-based oxides still have the disadvantage of reduced initial efficiency due to the presence of irreversible capacity.
In this regard, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or embedding metals such as Li, al, and Mg in silicon-based oxides. However, in the case where the anode slurry contains a metal-doped silicon-based oxide as an anode active material, there is a problem in that a metal oxide formed by doping a metal reacts with moisture to raise the pH of the anode slurry and change its viscosity, and thus, there is a problem in that the state of the prepared anode is deteriorated and the charge/discharge efficiency of the anode is lowered.
Therefore, there is a need to develop an anode active material capable of improving the phase stability of an anode slurry containing a silicon-based oxide and improving the charge/discharge efficiency of an anode prepared therefrom.
Korean patent No. 10-0794192 relates to a method for preparing a carbon-coated silicon-graphite composite negative electrode material for a lithium secondary battery, and a method for preparing a secondary battery comprising the same, but has limitations in solving the above-described problems.
Prior art literature
(patent document 1) Korean patent No. 10-0794192
Disclosure of Invention
Technical problem
The present invention relates to a negative electrode active material, a method of preparing the negative electrode active material, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode active material.
Technical proposal
An exemplary embodiment of the present invention provides a negative active material including: comprising SiO x (0<x<2) And silicon-based composite particles of a Li compound; a carbon layer; and SiO y (1<y.ltoreq.2), wherein the carbon layer is provided in a form of coating at least a part of the surface of the silicon-based composite particles, and SiO y (1<y.ltoreq.2) is provided in the form of coating at least a portion of the surface of the silicon-based composite particles or coating at least a portion of the surface of the carbon layer.
An exemplary embodiment of the present invention provides a method of preparing a negative active material, the method including: preparation of a composition comprising SiO x (0<x<2) And silicon-based composite particles of a Li compound; and subjecting the silicon-based composite particles to an acid treatment to thereby obtain SiO y (1<y.ltoreq.2) coating at least a part of the surface of the silicon-based composite particles.
An exemplary embodiment of the present invention provides a negative electrode including the negative electrode active material.
An exemplary embodiment of the present invention provides a secondary battery including the negative electrode.
Advantageous effects
In the present invention, by acid-treating the Li-doped silicon-based composite particles, lithium by-products generated during the step of doping the Li-doped silicon-based composite particles can be effectively removed, and in the acid-treating step, siO y (1<y.ltoreq.2) are formed on the silicon-based composite particles, thereby functioning to passivate the particles. SiO formed in this case y (1<y.ltoreq.2) may be provided in the form of coating at least a part of the surface of the carbon layer, or coating the surface of the silicon-based composite particlesIn the form of at least a portion of (a). Specifically, the SiO y (1<y.ltoreq.2) may be provided in the form of coating at least a part of the surface of the silicon-based composite particle between the surface of the silicon-based composite particle and the carbon layer, in the form of coating at least a part of the region on the surface of the silicon-based composite particle where the carbon layer is not provided, or in the form of coating at least a part of the surface of the carbon layer.
In addition, the silicon-based composite particles may include the carbon layer, thereby preventing elution of unreacted lithium by-products in the acid treatment process and minimizing reaction between the anode active material and water in the aqueous slurry.
Accordingly, the anode including the anode active material and the secondary battery including the anode have the effect of improving the discharge capacity, initial efficiency, resistance performance, and/or service life characteristics of the battery.
Drawings
Fig. 1 and 2 schematically illustrate the structure of a negative active material according to an exemplary embodiment of the present invention, respectively.
Fig. 3 and 4 relate to XPS analysis results of the anode active materials of example 1 and comparative example 1, respectively.
Symbol description
1: silicon composite particle
2: carbon layer
3：SiO y
4: lithium by-product
Detailed Description
Hereinafter, the present specification will be described in more detail.
In this specification, when a portion "includes" one constituent element, unless otherwise specified, this does not mean to exclude other constituent elements, but means that other constituent elements may be further included.
In this specification, when one member is arranged "on" another member, this includes not only the case where one member is in contact with the other member but also the case where the other member exists between the two members.
The terms or words used in the present specification should not be construed as limited to conventional or dictionary meanings, but interpreted based on the principle that the inventor can properly define the concept of terms so as to describe his/her own invention in the best way, with the meanings and concepts conforming to the technical spirit of the present invention.
As used in this specification, the singular reference of a term includes the plural reference unless the context clearly indicates to the contrary.
In this specification, the crystal form of the structure contained in the anode active material can be confirmed by X-ray diffraction analysis which can be performed using an X-ray diffraction (XRD) analyzer (trade name: D4-endavor, manufacturer: bruker corporation), and in addition to this, an apparatus used in the art can be appropriately employed.
In this specification, the presence or absence of an element and the content of the element in the anode active material can be confirmed by ICP analysis, which can be performed using an inductively coupled plasma atomic emission spectrometer (ICPAES, perkin Elmer 7300).
In the present specification, the specific surface area can be measured by degassing an object to be measured at 130℃for 2 hours by using BET measuring equipment (BEL-SORP-MAX, bell corporation, japan), and N at 77K 2 Adsorption/desorption.
In the present specification, the average particle diameter (D 50 ) Can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (curve of the particle size distribution curve) of the particles. Average particle diameter (D) 50 ) Can be measured using, for example, laser diffraction. The laser diffraction method is generally capable of measuring particle diameters ranging from a submicron region to several millimeters, and can obtain results of high reproducibility and high resolution.
Hereinafter, preferred exemplary embodiments of the present invention will be described in detail. However, the exemplary embodiment of the present invention may be changed to various other forms, and the scope of the present invention is not limited to the exemplary embodiment to be described below.
< negative electrode active Material >
One of the present inventionExemplary embodiments provide a negative active material including: comprising SiO x (0<x<2) And silicon-based composite particles of a Li compound; a carbon layer; and SiO y (1<y.ltoreq.2), wherein the carbon layer is provided in a form of coating at least a part of the surface of the silicon-based composite particles, and the SiO y (1<y.ltoreq.2) is provided in the form of coating at least a part of the surface of the silicon-based composite particles or coating at least a part of the surface of the carbon layer.
In general, lithium by-products formed from unreacted lithium exist on the particles in the step of doping the silicon-based particles with Li, and thus become alkaline when forming a slurry. Therefore, there is a problem that the rheological properties of the slurry change and Si of the silicon particles reacts with alkali to generate gas.
Therefore, in the present invention, by subjecting the Li-doped silicon-based composite particles to an acid treatment, lithium by-products formed during the step of doping the Li-doped silicon-based composite particles can be effectively removed, and in the acid treatment step, siO y (1<y.ltoreq.2) are formed on the surface of the silicon-based composite particles, thereby serving to passivate the particles. SiO formed in such a case y (1<y.ltoreq.2) may be provided in the form of coating at least a part of the surface of the silicon-based composite particle between the surface of the silicon-based composite particle and the carbon layer, in the form of coating at least a part of the region on the surface of the silicon-based composite particle where the carbon layer is not provided, or in the form of coating at least a part of the surface of the carbon layer.
In addition, the silicon-based composite particles may include the carbon layer, thereby preventing elution of unreacted lithium by-products in the acid treatment process and minimizing reaction between the anode active material and water in the aqueous slurry.
The anode active material according to an exemplary embodiment of the present invention includes silicon-based composite particles. The silicon-based composite particles comprise SiO x (0<x<2) And a Li compound.
The SiO is x (0<x<2) May correspond to the matrix in the silicon-based composite particles. The SiO is x (0<x<2) Can be Si and SiO containing 2 And Si may also form a phase. That is, x corresponds to SiO x (0<x<2) The number ratio of O to Si contained in the alloy. When the silicon-based composite particles contain the SiO x (0<x<2) When this is done, the discharge capacity of the secondary battery can be improved.
In one exemplary embodiment of the present invention, the silicon-based composite particles may include a Li compound. The Li compound may correspond to a matrix in the silicon-based composite particle. The Li compound may be present in the silicon-based composite particles in the form of at least one of a lithium atom, a lithium silicate, a lithium silicide, and a lithium oxide. When the silicon-based composite particles contain Li compounds, there is an effect that initial efficiency is improved.
The Li compound is in a form in which silicon-based composite particles are doped with the compound, and may be distributed on the surface and/or inside the silicon-based composite particles. The Li compound is distributed on the surface and/or inside of the silicon-based composite particle, so that the volume expansion/contraction of the silicon-based composite particle can be controlled to an appropriate level, and can be used to prevent the damage of the active material. In addition, the irreversible phase of the silicon-based oxide particles (for example, siO 2 ) The Li compound may be contained in an amount to thereby increase the efficiency of the active material.
In one exemplary embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is composed of Li a Si b O c (2≤a≤4，0<b.ltoreq.2, 2.ltoreq.c.ltoreq.5), and may be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may be selected from the group consisting of Li 2 SiO 3 、Li 4 SiO 4 And Li (lithium) 2 Si 2 O 5 At least one form of lithium silicate in the group consisting of is present in the silicon-based particles, and the amorphous lithium silicate may be composed of Li a Si b O c (2≤a≤4，0<b.ltoreq.2, 2.ltoreq.c.ltoreq.5), and is not limited to this form.
In one exemplary embodiment of the present invention, the content of Li may be 0.1 to 40 parts by weight or 0.1 to 25 parts by weight with respect to 100 parts by weight of the total negative electrode active material. Specifically, the content of Li may be 1 to 25 parts by weight, more specifically 2 to 20 parts by weight. There is a problem in that as the content of Li increases, the initial efficiency increases, but the discharge capacity decreases, so that when the content satisfies the above range, an appropriate discharge capacity and initial efficiency can be achieved.
The content of Li element can be confirmed by ICP analysis. Specifically, after a predetermined amount (about 0.01 g) of the anode active material was weighed, the anode active material was completely decomposed on a hot plate by transferring the sample to a platinum crucible and adding nitric acid, hydrofluoric acid, or sulfuric acid thereto. Thereafter, a reference calibration curve was prepared by measuring the intensity of a standard solution prepared using a standard solution (5 mg/kg) at the inherent wavelength of the element to be analyzed using an inductively coupled plasma atomic emission spectrometer (ICPAES, perkin-Elmer 7300). Thereafter, the pretreated sample solution and the blank sample are each introduced into the apparatus, the actual intensity is calculated by measuring each intensity, the concentration of each component is calculated with respect to the prepared calibration curve, and then the element content of the prepared anode active material can be analyzed by converting the sum into a theoretical value.
In one exemplary embodiment of the present invention, the silicon-based composite particles may include additional metal atoms. The metal atom may be present in the silicon-based composite particle in the form of at least one of a metal atom, a metal silicate, a metal silicide, and a metal oxide. The metal atom may include at least one selected from the group consisting of Mg, li, al, and Ca. Thereby, the initial efficiency of the anode active material can be improved.
In one exemplary embodiment of the present invention, the anode active material includes a carbon layer. Specifically, the carbon layer is provided in a form of coating at least a part of the surface of the silicon-based composite particle.
Specifically, the negative electrode active material is given conductivity by the carbon layer, and the initial efficiency, service life characteristics, and battery capacity characteristics of the secondary battery can be improved.
In one exemplary embodiment of the present invention, the carbon layer may include at least one of amorphous carbon and crystalline carbon.
In one exemplary embodiment of the present invention, the carbon layer may be an amorphous carbon layer. The amorphous carbon can suppress expansion of the silicon-based composite particles by appropriately maintaining the strength of the carbon layer.
Furthermore, the carbon layer may or may not contain additional crystalline carbon.
The crystalline carbon may further improve the conductivity of the anode active material. The crystalline carbon may include at least one selected from the group consisting of fullerenes, carbon nanotubes, and graphene.
The amorphous carbon can suppress expansion of the silicon-based composite particles by appropriately maintaining the strength of the carbon layer. The amorphous carbon may be a carbide of at least one selected from the group consisting of tar, pitch, and other organic materials, or may be a carbon-based material formed using hydrocarbon as a source of a chemical vapor deposition method.
The carbide of the other organic material may be a carbide of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or aldohexose, and a carbide of an organic material selected from a combination thereof.
The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane or the like. Examples of the aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, benzofuran, pyridine, anthracene, phenanthrene, and the like.
In one exemplary embodiment of the present invention, the carbon layer may be contained in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, with respect to 100 parts by weight of the total negative electrode active material. More specifically, the carbon layer may be contained in an amount of 0.5 to 15 parts by weight or 1 to 10 parts by weight. When the above range is satisfied, the capacity and efficiency of the anode active material can be prevented from decreasing while improving the conductivity.
In an exemplary embodiment of the present invention, the thickness of the carbon layer may be 1nm to 500nm, specifically 5nm to 300nm, and more specifically 5nm to 100nm. When the above range is satisfied, the conductivity of the anode active material is improved, the volume change of the anode active material is easily suppressed, and the side reaction between the electrolyte and the anode active material is suppressed, so that there is an effect of improving the initial efficiency and/or the service life of the battery.
Specifically, the carbon layer may be formed by a Chemical Vapor Deposition (CVD) method using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.
The carbon layer may be formed before doping the silicon-based particles with lithium or after doping the silicon-based particles with lithium.
In one exemplary embodiment of the present invention, the anode active material includes SiO y (1<y.ltoreq.2). Specifically, the SiO y (1<y.ltoreq.2) is provided in the form of coating at least a part of the surface of the silicon-based composite particles or coating at least a part of the surface of the carbon layer.
Specifically, in the present invention, by subjecting the Li-doped silicon-based composite particles to an acid treatment, lithium by-products formed during the process of doping the Li-doped silicon-based composite particles can be effectively removed, and in the acid treatment process, siO y (1<y.ltoreq.2) are formed on the silicon-based composite particles, thereby serving to passivate the particles.
In addition, the silicon-based composite particles may include the carbon layer, thereby preventing elution of unreacted lithium by-products in the acid treatment process and minimizing reaction between the anode active material and water in the aqueous slurry.
SiO y (1<y.ltoreq.2) y corresponds to SiO y (1<y.ltoreq.2) O pairs contained inSi number ratio.
The SiO is y (1<y.ltoreq.2) is formed during the process of preparing the silicon-based composite particles and then acid-treating lithium compounds, i.e., lithium by-products, remaining near the surface of the silicon-based composite particles or the carbon layer. Specifically, lithium by-product is removed by acid treatment, lithium is deintercalated from lithium silicate near the surface of the silicon-based composite particles, and materials having various oxidation numbers are mixed to form SiO y (1<y.ltoreq.2) phase.
The SiO is y (1<y.ltoreq.2) may exist as a layer formed in an island type or a thin film type, and may exist in various forms without being limited thereto.
In this case, siO generated in the step of acid-treating the silicon-based particles y (1<y.ltoreq.2) may be present in each part on the silicon-based composite particles. Specifically, the SiO y (1<y.ltoreq.2) may be provided in the form of coating at least a part of the surface of the silicon-based composite particle between the surface of the silicon-based composite particle and the carbon layer, in the form of coating at least a part of the region on the surface of the silicon-based composite particle where the carbon layer is not provided, or in the form of coating at least a part of the surface of the carbon layer.
In one example, the SiO y (1<y.ltoreq.2) may be provided in the form of coating at least a part of the surface of the silicon-based composite particle between the surface of the silicon-based composite particle and the carbon layer. Namely, the SiO y (1<y.ltoreq.2) may be at least a part of the surface of the coated silicon-based composite particles, and is formed on the SiO y In the form of a carbon layer further coated thereon. Namely, the SiO y (1<y.ltoreq.2) may be disposed adjacent to the surface of the silicon-based composite particles, and the carbon layer may be disposed adjacent to the SiO y (1<y.ltoreq.2) are adjacent. The SiO is y (1<y.ltoreq.2) may be in the form of partially coating the surface of the silicon-based composite particles, or coating the entire surface. SiO (SiO) y (1<Examples of the shape of y.ltoreq.2) include island type, film type, etc., but are not limited thereto.
In one example, the carbon layer may be partially coated with SiO y (1<y.ltoreq.2), or coatingCovering the entire surface. Examples of the shape of the carbon layer include, but are not limited to, island type, thin film type, and the like.
In one example, the SiO y (1<y.ltoreq.2) may be provided in the form of coating at least a part of the region on the surface of the silicon-based composite particle where the carbon layer is not provided. Namely, the SiO y (1<y.ltoreq.2) may be disposed adjacent to the surface of the silicon-based composite particle. The SiO is y (1<y.ltoreq.2) may be in the form of partially coating the surface of the silicon-based composite particles, or coating the entire surface. SiO (SiO) y (1<Examples of the shape of y.ltoreq.2) include island type, film type, etc., but are not limited thereto.
Specifically, while the silicon-based composite particles are doped with lithium, the particles generally expand so that there may be regions where the carbon layer cannot completely coat the silicon-based composite particles. In this case, siO formed during the acid treatment step of the silicon composite particles y (1<y.ltoreq.2) is formed on the region, and thus may be disposed adjacent to the surface of the silicon-based composite particle, so that passivation of the silicon-based composite particle may be more easily achieved.
In one example, the SiO y (1<y.ltoreq.2) may be provided in the form of coating at least a portion of the surface of the carbon layer. Namely, the SiO y (1<y.ltoreq.2) may be disposed adjacent to the surface of the carbon layer. The SiO is y (1<y.ltoreq.2) may be in the form of a surface coated partially with the carbon layer or an entire surface coated with the carbon layer. SiO (SiO) y (1<Examples of the shape of y.ltoreq.2) include island type, film type, etc., but are not limited thereto.
That is, the anode active material may have a silicon-based composite particle/carbon layer/SiO therein y (1<y.ltoreq.2) a composition coated in succession, or wherein the silicon-based composite particles/SiO y (1<Y.ltoreq.2)/carbon layer, or wherein silicon composite particles/SiO y (1<y.ltoreq.2) is coated in this order, but the order is not limited thereto.
As described above, when the lithium by-product remaining near the surface of the silicon-based composite particles or the carbon layer is subjected to the acid treatment, the slurry can be prevented from being by-produced due to the lithium by-productThe substance becomes alkaline and SiO due to the formation of by-products from lithium is present y (1<y.ltoreq.2) to prevent elution of the Li compound contained in the silicon composite particles, thereby improving the aqueous workability of the slurry.
In one exemplary embodiment of the present invention, the anode active material has a peak existing between 101eV and 104eV when analyzed by X-ray photoelectron spectroscopy. Which may be referred to as a first peak. Specifically, the first peak occurs around 102eV to 103eV, and may be formed of SiO y (1<y.ltoreq.2).
In one exemplary embodiment of the present invention, the anode active material has a second peak existing between 99eV and 101eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the second peak may occur in the vicinity of 99eV to 100eV, and may be a peak caused by Si.
In one exemplary embodiment of the present invention, the anode active material has a third peak existing between 102eV and 105eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the third peak may occur around 103eV to 104eV, and may be formed of SiO 2 A peak caused.
In an exemplary embodiment of the invention, the first peak is present between the second peak and the third peak. That is, the first peak exists in the second peak caused by Si (oxidation number=0) and in the second peak caused by SiO 2 (oxidation number = +4), and the anode active material of the present invention contains Si having an oxidation number between 0 and +4 on the surface.
In one exemplary embodiment of the present invention, the anode active material has a fourth peak existing between 282eV and 286eV when analyzed by X-ray photoelectron spectroscopy. Specifically, the peak appears in the vicinity of 283eV to 285eV, and may be a peak caused by carbon (C) of the carbon layer.
In the present invention, the X-ray photoelectron spectroscopy of the negative electrode active material can be performed by the Nexsa ESCA system, siemens technologies (Thermo Fisher Scientific) (ESCA-02).
Specifically, after the full scan spectrum (survey scan spectrum) and the narrow scan spectrum (narrow scan spectrum) are acquired for each sample, the full scan spectrum and the narrow scan spectrum may be acquired while depth profile (depth profile) is performed. Depth profiles of up to 3000 seconds can be made using monoatomic Ar ions, with the measurement and data processing conditions as follows.
-an X-ray source: monochromatic Al K alpha (1486.6 eV)
X-ray spot size: 400 μm
-a sputter gun: monoatomic Ar (energy: 1000eV, flow: low, grating width: 2 mm)
Etch rate: for Ta 2 O 5 0.09nm/s
-an operating mode: CAE (constant analyzer energy) mode
-full scan: with an energy of 200eV and an energy level of 1eV
Narrow scan: scanning mode, energy of 50eV, energy level of 0.1eV
-charge compensation: flood gun closing
-SF：Al THERMO1
-ECF：TPP-2M
Background subtraction: shirley
In one exemplary embodiment of the present invention, the depth profile of X-ray photoelectron spectroscopy (XPS) may be measured spectroscopically at 0.09nm/s for up to 3000 seconds under an X-ray source of monochromatic alkα.
Fig. 1 and 2 schematically illustrate the structure of a negative active material according to an exemplary embodiment of the present invention, respectively. Specifically, at least a part of the silicon-based composite particles 1 is coated with SiO y (1<y≤2)3，SiO y (1<y.ltoreq.2) 3 may be coated with the carbon layer 2. Alternatively, at least a part of the silicon-based composite particles 1 is coated with the carbon layer 2, and at least a part of the carbon layer 2 may be coated with SiO y (1<y.ltoreq.2) 3. Furthermore, although not shown in fig. 1 and 2, the region on the silicon-based composite particle where the carbon layer is not formed may be coated with SiO y (1<y≤2)。
In fig. 1 and 2, siO y (1<y.ltoreq.2) is shown as particlesThe surface of the sub-is partially coated in an island shape, but other shapes may be displayed without being limited thereto.
The anode active material according to an exemplary embodiment of the present invention may include: a first surface layer provided on at least a part of the silicon-based composite particles; and a second surface layer disposed on at least a portion of the first surface layer.
The first surface layer may be in a form of coating at least a part of the silicon-based composite particles, i.e. partially coating the surface of the particles, or completely coating the surface of the particles. Examples of the shape of the first surface layer include, but are not limited to, island type, thin film type, and the like.
The second surface layer may be in a form of coating at least a part of the first surface layer, i.e. partially coating the surface of the first surface layer, or completely coating the surface of the first surface layer. Examples of the shape of the second surface layer include, but are not limited to, island type, thin film type, and the like.
The second surface layer may be additionally provided on at least a part of the silicon-based composite particles. That is, the second surface layer may be present in the form of a portion where the first surface layer is not provided of the silicon-based composite particles, in addition to the first surface layer. For example, when the first surface layer is a carbon layer and the second surface layer is a carbon layer containing SiO y (1<y.ltoreq.2) a layer comprising SiO y (1<y.ltoreq.2) may be formed on the region where the carbon layer fails to entirely coat the silicon-based composite particles.
In one exemplary embodiment of the present invention, the first surface layer is a carbon layer, and the second surface layer may be a layer containing SiO y (1<y.ltoreq.2). Specifically, the anode active material includes a carbon layer disposed on at least a portion of the silicon-based composite particles, and may include a silicon oxide layer disposed on at least a portion of the carbon layer y (1<y.ltoreq.2).
In an exemplary embodiment of the present invention, the first surface layer is a material comprising SiO y (1<y.ltoreq.2), and the second surface layer may be a carbon layer. In particular, the method comprises the steps of,the negative electrode active material comprises SiO-containing particles disposed on at least a part of the silicon-based composite particles y (1<y.ltoreq.2), and may comprise a layer provided on said SiO-comprising layer y (1<y.ltoreq.2) a carbon layer on at least a portion of the layer.
Namely, siO formed by acid treatment y (1<y.ltoreq.2) may be provided on the surface of the carbon layer in the form of a second surface layer or between the carbon layer and the surface of the silicon-based composite particles.
Furthermore, while the silicon-based composite particles are doped with lithium, the particles generally expand so that there may be a region in which the carbon layer cannot completely coat the silicon-based composite particles, and the SiO y (1<y.ltoreq.2) is formed on the region, and thus may be disposed adjacent to the surface of the silicon-based composite particles.
In an exemplary embodiment of the invention, the carbon layer and SiO y (1<y.ltoreq.2) may be disposed adjacent to each other.
In one exemplary embodiment of the present invention, the first surface layer and the second surface layer may be disposed adjacent to each other. That is, no additional layer may be provided between the first surface layer and the second surface layer.
In one exemplary embodiment of the present invention, the SiO is based on 100 parts by weight of the total negative electrode active material y (1<y.ltoreq.2) may be set in an amount of 0.01 parts by weight to 50 parts by weight. Preferably, the SiO y (1<y.ltoreq.2) may be set in an amount of 0.1 to 30 parts by weight or 1 to 20 parts by weight. When the above range is satisfied, the aqueous workability is improved, and thus the capacity and efficiency of the anode active material can be prevented from being lowered. When the content is below the above range, there are problems in that passivation cannot be properly performed, and when the content is above the above range, there are problems in that conductivity is deteriorated and capacity and efficiency are lowered.
The anode active material according to an exemplary embodiment of the present invention includes SiO y (1<y.ltoreq.2), and the SiO y (1<y.ltoreq.2) may comprise SiO 2 。
In an exemplary embodiment of the invention, the SiO y (1<y.ltoreq.2) may comprise an amorphous phase. In one example, during X-ray diffraction analysis of the anode active material, no SiO-derived source was detected y (1<y.ltoreq.2).
In one exemplary embodiment of the present invention, si in the anode active material: (SiO) x (0<x<2)+SiO y (1<y.ltoreq.2)) may be 88:12 to 60:40. the weight ratio may specifically be 85:15 to 65:35, more specifically 80:20 to 70:30. when the above range is satisfied, siO of the silicon-based composite particles coated in the anode active material y The particles can be coated more effectively to prevent side reactions during slurry formation.
In one exemplary embodiment of the present invention, a ratio (p 1: p 2) of a peak intensity of Si (p 1) to a peak intensity of si—o bond representing (p 2) may be 88:12 to 60:40. the ratio may be specifically 85:15 to 65:35, more specifically 80:20 to 70:30. when the above range is satisfied, siO of the silicon-based composite particles coated in the anode active material y The particles can be coated more effectively to prevent side reactions during the formation of the slurry.
Si and silicon-based oxide (SiO x And SiO y ) The NMR peak intensity or weight ratio of (a) can be confirmed by nuclear magnetic resonance spectroscopy (advanced III HD 600MHz NMR Spectrometer from Bruker corporation) at MAS ratio=10 kHz.
In this case, the peak of Si may be measured in the chemical shift value range of-80 ppm to-90 ppm, and the peak of Si-O bond may be measured in the chemical shift value range of-100 ppm to-120 ppm.
In one exemplary embodiment of the invention, the carbon layer and SiO y (1<y.ltoreq.2) by weight (carbon layer: siO (SiO) y (1<y.ltoreq.2)) may be 1:10 to 1:2. when the above range is satisfied, there is a passivation effect while maintaining appropriate conductivity, and when the above range is not satisfied, there is a problem in that conductivity is deteriorated.
In an exemplary embodiment of the invention, theThe anode active material may further include lithium by-products disposed on at least a portion of the silicon-based composite particles. The lithium by-product may comprise a material selected from the group consisting of Li 2 O, liOH and Li 2 CO 3 At least one of the group consisting of.
Specifically, the lithium by-product may refer to a lithium compound remaining near the surface of the silicon-based composite particle or the carbon layer after the preparation of the silicon-based composite particle. As described above, lithium by-products that have not reacted with the acid may remain even after the acid treatment process.
Fig. 1 and 2 each schematically show the structure of a negative electrode active material according to an exemplary embodiment of the present invention, and the negative electrode active material according to an exemplary embodiment of the present invention may be in a form in which lithium by-products 4 are disposed on at least a portion of silicon-based composite particles 1, and a carbon layer 2 coats the lithium by-products 4. However, although fig. 1 and 2 show the presence of lithium by-products, lithium by-products may also be absent.
The content of the lithium by-product may be 5 parts by weight or less with respect to 100 parts by weight of the total negative electrode active material. Specifically, the content of the lithium by-product may be 0 to less than 5 parts by weight, more than 0 to 5 parts by weight, 0.01 to 5 parts by weight, 0.05 to 2 parts by weight, or 0.1 to 1 part by weight. More specifically, the content of the lithium by-product may be 0.1 parts by weight or more and 0.8 parts by weight or less or 0.1 parts by weight or more and 0.5 parts by weight or less. The lower limit of the content of the lithium by-product may be 0 parts by weight (excluding), 0.01 parts by weight or 0.1 parts by weight, and the upper limit thereof may be 5 parts by weight, 1 part by weight, 0.8 parts by weight or 0.5 parts by weight. When the content of the lithium by-product satisfies the above range, side reactions in the slurry can be reduced, and the aqueous workability can be improved by reducing the viscosity change. In contrast, when the content of the lithium by-product is higher than the above range, there is a problem in that the slurry becomes alkaline during formation of the slurry, which causes side reactions or viscosity changes, and problems of aqueous workability.
The content of the lithium by-product may be calculated by measuring the amount of HCl solution in a specific interval of pH change during the titration of the aqueous solution containing the anode active material with HCl solution using a titrator, and then calculating the amount of lithium by-product.
A carbon layer may be additionally provided on at least a portion of the surface of the lithium byproduct. The carbon layer may be provided in a form to coat the lithium by-product. In particular, the carbon layer may be formed during the preparation of the silicon-based composite particles, and lithium by-products that are not reacted with the acid may be present in a lower portion of the carbon layer or in an upper portion of the carbon layer.
In one exemplary embodiment of the present invention, the silicon-based composite particles and SiO in relation to the negative electrode active material y (1<y.ltoreq.2) and the ratio of the amorphous phase may be 32% or more. In particular, the ratio may be 32% to 70%, 35% to 60% or 35% to 55%.
As described above, siO is produced by acid-treating lithium by-products remaining near the surface of the silicon-based composite particles or the carbon layer y (1<y.ltoreq.2) contains an amorphous phase, so that the ratio of the amorphous phase in the anode active material after the acid treatment increases. Therefore, when the silicon-based composite particles and SiO are contained in the negative electrode active material y (1<y.ltoreq.2) in the above-mentioned range, the phase-containing SiO is suitably formed y (1<y.ltoreq.2) has the effect of improving the passivation properties.
The ratio of the amorphous phase in the anode active material can be measured by an X-ray diffraction analysis method (D4 Endeavor from Bruker corporation) using quantitative analysis.
The BET specific surface area of the anode active material may be 1m 2 Above/g and 20m 2 Per gram of less than 1m 2 Above/g and 15m 2 Less than/g and greater than 2m 2 /g and less than 10m 2 /g and 2.5m 2 Above/g and 8m 2 And/g or less. The BET specific surface area may have an upper limit of 20m 2 /g、18m 2 /g、15m 2 /g、10m 2 /g、8m 2 /g、5m 2 /g or 4m 2 /g, andand its lower limit may be 1m 2 /g、1.5m 2 /g、2m 2 /g or 2.5m 2 /g。
The average particle diameter (D) 50 ) May be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, more specifically 1 μm to 10 μm. When the above range is satisfied, structural stability of the active material during charge and discharge is ensured, and it is possible to prevent the problem that the volume expansion/contraction level also becomes large with an excessive increase in particle size, and the problem that the initial efficiency is lowered because the particle size is excessively small.
< preparation method of negative electrode active Material >
An exemplary embodiment of the present invention provides a method of preparing a negative active material, the method including: preparation of a composition comprising SiO x (0<x<2) And silicon-based composite particles of a Li compound; and forming SiO by acid treatment of the silicon-based composite particles y (1<y≤2)。
The silicon-based composite particles may be formed by: si powder and SiO under vacuum 2 Heating and gasifying the powder, and then depositing the gasified mixed gas to form preliminary particles; the preliminary particles are mixed with Li powder, and then the resultant mixture is heat-treated.
In this case, the step may include forming a carbon layer. The formation of the carbon layer may be performed after the formation of the preliminary particles and before the mixing of the preliminary particles with the Li powder, or may be performed after the mixing of the preliminary particles with the Li powder and then heat treatment of the resultant mixture.
Alternatively, the silicon-based composite particles may be formed by: si powder and SiO under vacuum 2 Heating and gasifying the powder, and then depositing the gasified mixed gas to form preliminary particles; the preliminary particles are mixed with Li powder, and then the resultant mixture is heat-treated.
Specifically, si powder and SiO 2 The mixed powder of powders may be heat treated under vacuum at 1400 ℃ to 1800 ℃ or 1400 ℃ to 1600 ℃.
The prepared particles can be formed by SiO x (x=1).
The silicon-based composite particles may contain the above-mentioned Li silicate, li silicide, li oxide, or the like.
The particle size of the silicon-based composite particles may be adjusted by a method such as ball milling, jet milling, or jet classification, and the method is not limited thereto.
In the formation of the carbon layer, the carbon layer may be prepared by a Chemical Vapor Deposition (CVD) method using a hydrocarbon gas, or by carbonizing a material used as a carbon source.
Specifically, the carbon layer may be formed by introducing the formed preliminary particles into a reaction furnace and then performing Chemical Vapor Deposition (CVD) on a hydrocarbon gas at 600 to 1200 ℃. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900 to 1000 ℃.
In this case, when the preparation of the silicon-based composite particles does not include forming the carbon layer, it may further include forming the carbon layer on the acid-treated particles after the acid treatment step.
In order to remove lithium by-products remaining in the step of forming the silicon composite particles, the silicon composite particles may be subjected to an acid treatment.
In the acid treatment step, the silicon-based composite particles and the acid may be mixed in an amount of 80:20 to 99.9:0.01 weight ratio. Specifically, the silicon-based composite particles and the acid may be mixed in an amount of 85:15 to 99.5:0.5, 90:10 to 99.5:0.5 or 95:5 to 99:1 by weight ratio.
As the acid during the acid treatment, phosphoric acid (H 3 PO 4 ) Sulfuric acid (H) 2 SO 4 ) Boric acid (H) 3 BO 3 ) Citric acid, protonated aniline, etc., in particular phosphoric acid (H 3 PO 4 ). However, the acid is not limited thereto, and any constitution known in the art may be suitably employed.
As the solvent during the acid treatment, distilled water, alcohol, N-methylpyrrolidone (NMP), or the like can be used, and for example, ethanol can be used. However, the solvent is not limited thereto, and any constitution known in the art may be suitably employed according to the type of acid.
The acid treatment may be performed in a range of 50 to 200 ℃, but the temperature is not limited thereto, and the acid treatment temperature may vary according to the types of acid and solvent. For example, when ethanol is used as a solvent, the acid treatment may be performed at 60 ℃ to 100 ℃ or below or 70 ℃ to 90 ℃ or below.
Unreacted lithium compounds, i.e., lithium byproducts, remain during the preparation of the silicon-based composite particles and remain near the surface of the silicon-based composite particles or the carbon layer. Therefore, when the silicon-based composite particles are acid-treated, the remaining lithium by-product reacts with the acid and is removed, and Li is deintercalated from the lithium silicate near the surface of the silicon-based composite particles, thereby forming SiO y (1<y≤2)。
SiO formed y (1<y.ltoreq.2) may be provided in the form of coating at least a part of the surface of the silicon-based composite particles, in the form of coating at least a part of the region on the surface of the silicon-based composite particles where the carbon layer is not provided, or in the form of coating at least a part of the surface of the carbon layer.
As described above, lithium by-products formed during the Li doping process can be effectively removed by acid-treating the silicon-based composite particles, and in the acid-treating process, siO y (1<y.ltoreq.2) are formed on the silicon composite particles, thereby serving as passivation of the particles.
SiO formed by the acid treatment process y (1<y.ltoreq.2) may be present to form an island type or film type layer, and may be present in various forms without being limited thereto. In addition to the SiO formed y (1<y.ltoreq.2) may be present in each part on the silicon-based composite particles.
That is, the anode active material formed by the above-described preparation method may have a structure in which silicon-based composite particles/carbon layer/SiO y (1<y.ltoreq.2) a composition coated in succession, or wherein the silicon-based composite particles/SiO y (1<y.ltoreq.2)/carbon layer, or wherein the silicon-based composite particles/SiO y (1<y.ltoreq.2) in succession, butThe order is not limited thereto.
Due to the inclusion of SiO by formation as described above y (1<y.ltoreq.2) is effective in removing lithium by-products remaining in the silicon composite particles and in passivating the particles, and therefore has an effect of improving the aqueous workability by preventing elution of the Li compound contained in the silicon composite particles.
In addition, the silicon-based composite particles may include a carbon layer to prevent elution of unreacted lithium by-products in the acid treatment process and minimize reaction between the anode active material and water in the aqueous slurry.
< cathode >
The anode according to an exemplary embodiment of the present invention may include the anode active material described above.
Specifically, the anode may include an anode current collector and an anode active material layer disposed on the anode current collector. The anode active material layer may contain the anode active material. In addition, the anode active material layer may further include a binder and/or a conductive material.
The anode active material layer may be formed by applying an anode slurry containing an anode active material, a binder, and/or a conductive material to at least one surface of an anode current collector, and drying and calendaring the anode current collector.
The negative electrode slurry contains the negative electrode active material, a binder, and/or a conductive material.
The anode slurry may further contain an additional anode active material.
As the additional anode active material, a compound capable of reversibly intercalating and deintercalating lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers and amorphous carbon; a metal compound that can be alloyed with lithium, such as Si, al, sn, pb, zn, bi, in, mg, ga, cd, si alloy, sn alloy, or Al alloy; metal oxides which can be doped and undoped with lithium, such as SiO β (0<β<2)、SnO 2 Vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or (b)The metal compound and carbonaceous material may be used in combination with one or more of them, for example, a Si-C compound or a Sn-C compound. In addition, a metallic lithium thin film may be used as the anode active material. Alternatively, as the carbon material, both low crystalline carbon and high crystalline carbon, or the like may be used. Typical examples of the low crystalline carbon include soft carbon and hard carbon, and typical examples of the high crystalline carbon include irregular, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite, floating graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch and high-temperature fired carbon such as coke derived from petroleum or coal tar pitch.
The additional anode active material may be a carbon-based anode active material.
In one exemplary embodiment of the present invention, the weight ratio of the anode active material and the additional anode active material included in the anode slurry may be 10:90 to 90:10, specifically 10:90 to 50:50.
the anode current collector is sufficient as long as it has conductivity without causing chemical changes to the battery, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel material whose surface is treated with carbon, nickel, titanium, silver, or the like may be used. In particular, a transition metal such as copper or nickel, which well adsorbs carbon, may be used as the current collector. Although the thickness of the current collector may be 6 μm to 20 μm, the thickness of the current collector is not limited thereto.
The adhesive may comprise at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene Propylene Diene Monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and a material whose hydrogen is substituted with Li, na, ca, or the like, and may also include various copolymers thereof.
The conductive material is not particularly limited as long as the conductive material has conductivity without causing chemical changes to the battery, for example, graphite such as natural graphite or artificial graphite may be used; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; the conductive material is, for example, a polyphenylene derivative or the like.
The negative electrode slurry may further contain a solvent for forming a negative electrode slurry. Specifically, in terms of promoting the dispersion of the components, the negative electrode slurry-forming solvent may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropanol, specifically distilled water.
< Secondary Battery >
The secondary battery according to an exemplary embodiment of the present invention may include the above-described negative electrode according to an exemplary embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is identical to the above-described negative electrode. Since the anode has been previously described, a detailed description thereof will be omitted.
The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.
In the positive electrode, the positive electrode current collector is not particularly limited as long as the positive electrode current collector has conductivity without causing chemical changes to the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel material whose surface is treated with carbon, nickel, titanium, silver, or the like may be used. Further, the thickness of the positive electrode current collector may be generally 3 μm to 500 μm, and the adhesion of the positive electrode active material may also be enhanced by forming fine irregularities on the surface of the current collector. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric body.
The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material includes: layered compounds such as lithium cobalt oxide (LiCoO) 2 ) And lithium nickel oxide (LiNiO) 2 ) Or a compound substituted with more than one transition metal; lithium iron oxides such as LiFe 3 O 4 The method comprises the steps of carrying out a first treatment on the surface of the Lithium manganese oxides, e.g. of formula Li 1+c1 Mn 2-c1 O 4 (0≤c1≤0.33)、LiMnO 3 、LiMn 2 O 3 And LiMnO 2 The method comprises the steps of carrying out a first treatment on the surface of the Lithium copper oxide (Li) 2 CuO 2 ) The method comprises the steps of carrying out a first treatment on the surface of the Vanadium oxides such as LiV 3 O 8 、V 2 O 5 And Cu 2 V 2 O 7 The method comprises the steps of carrying out a first treatment on the surface of the Ni-site lithium nickel oxide, which is composed of LiNi 1-c2 M c2 O 2 (here, M is at least one selected from the group consisting of Co, mn, al, cu, fe, mg, B and Ga, and c2 satisfies 0.01.ltoreq.c2.ltoreq.0.3); lithium manganese composite oxide consisting of LiMn 2-c3 M c3 O 2 (here, M is at least any one selected from the group consisting of Co, ni, fe, cr, zn and Ta, and c3 satisfies 0.01.ltoreq.c3.ltoreq.0.1) or Li 2 Mn 3 MO 8 (here, M is at least any one selected from the group consisting of Fe, co, ni, cu and Zn); liMn 2 O 4 Wherein Li in the chemical formula is partially replaced by an alkaline earth metal ion or the like, but is not limited thereto. The positive electrode may be Li metal.
The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material.
In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and may be used without particular limitation as long as the positive electrode conductive material has electron conductivity without causing chemical changes in the constituent battery. Specific examples thereof include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and any one or a mixture of two or more thereof may be used.
Alternatively, the positive electrode binder is used to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene Propylene Diene Monomer (EPDM), sulfonated EPDM, styrene Butadiene Rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used.
The separator separates the negative electrode and the positive electrode and provides a passage for movement of lithium ions, and may be used without particular limitation as long as the separator is a separator generally used in a secondary battery, and in particular, a separator having excellent electrolyte moisturizing ability and low resistance to movement of ions in the electrolyte is preferable. Specifically, a porous polymer film, for example, a porous polymer film formed of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, or the like may also be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used as a single-layer or multi-layer structure.
Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, and the like, which can be used in the preparation of lithium secondary batteries.
In particular, the electrolyte may comprise a non-aqueous organic solvent and a metal salt.
As the nonaqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate can be used.
In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates may be preferably used because the cyclic carbonates have a high dielectric constant as a high-viscosity organic solvent and thus dissociate lithium salts well, and when the cyclic carbonates are mixed with a low-viscosity and low-dielectric constant linear carbonate such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte of high conductivity can be prepared, so that such a combined use is more preferable.
As the metal salt, a lithium salt, which is a material easily dissolved in a nonaqueous electrolytic solution, may be used, and for example, as an anion of the lithium salt, one or more selected from the group consisting of: f (F) - 、Cl - 、I - 、NO 3 - 、N(CN) 2 - 、BF 4 - 、ClO 4 - 、PF 6 - 、(CF 3 ) 2 PF 4 - 、(CF 3 ) 3 PF 3 - 、(CF 3 ) 4 PF 2 - 、(CF 3 ) 5 PF - 、(CF 3 ) 6 P - 、CF 3 SO 3 - 、CF 3 CF 2 SO 3 - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、(SF 5 ) 3 C - 、(CF 3 SO 2 ) 3 C - 、CF 3 (CF 2 ) 7 SO 3 - 、CF 3 CO 2 - 、CH 3 CO 2 - 、SCN - Sum (CF) 3 CF 2 SO 2 ) 2 N - 。
In the electrolyte, for the purpose of improving the service life characteristics of the battery, suppressing the decrease in the battery capacity and improving the discharge capacity of the battery, in addition to the above electrolyte constituent components, one or more additives, for example, halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substitutedOxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.
According to still another exemplary embodiment of the present invention, there are provided a battery module including a secondary battery as a unit cell and a battery pack including the same. The battery module and the battery pack include secondary batteries having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.
Modes for carrying out the application
Hereinafter, the present specification will be described in detail with reference to examples for specifically describing the present specification. However, the embodiments according to the present specification may be changed in various forms and should not be construed as limiting the scope of the present application to the embodiments described in detail below. Embodiments of the present application are provided so as to more fully explain the present description to those skilled in the art.
< examples and comparative examples >
Example 1
In which Si and SiO 2 1, the method comprises the following steps: 1, 94g of the powder obtained by mixing them in a molar ratio was mixed in a reaction furnace, and the resulting mixture was heated under vacuum at a sublimation temperature of 1400 ℃. Thereafter, gasified Si and SiO 2 Is reacted in a cooling zone in a vacuum state having a cooling temperature of 800 ℃ and condensed into a solid phase. Next, silicon-based particles having a size of 6 μm were prepared by pulverizing the aggregated particles for 3 hours using a ball mill. Thereafter, silicon-based particles were placed in the hot zone of the CVD apparatus while maintaining an inert atmosphere by flowing Ar gas, and methane was blown into the hot zone of 900 ℃ at 10 using Ar as a carrier gas -1 The reaction was carried out for 20 minutes under the support to form a carbon layer on the surface. Thereafter, 6g of Li metal powder was added, and further heat treatment was performed at a temperature of 800 ℃ under an inert atmosphere, and then silicon-based particles were prepared at a temperature of 80 ℃ using ethanol as a solvent: phosphoric acid = 99:1 to prepare SiO therein y (1<y.ltoreq.2) a negative electrode active material formed on the surface of the particles.
As a result of XPS analysis of the anode active material, as shown in fig. 3, a first peak around 102eV to 103eV, a second peak around 99eV to 100eV, a third peak around 103eV to 104eV, and a fourth peak around 283eV to 285eV were obtained.
Example 2
A negative electrode active material was prepared in the same manner as in example 1, except that the process of heat treatment by introducing methane was performed for 1 hour.
As a result of XPS analysis of the anode active material, a first peak around 102eV to 103eV, a second peak around 99eV to 100eV, a third peak around 103eV to 104eV, and a fourth peak around 283eV to 285eV were obtained.
Example 3
A negative electrode active material was prepared in the same manner as in example 1, except that the process of heat treatment by introducing methane was changed to that after the acid treatment.
As a result of XPS analysis of the anode active material, a first peak around 102eV to 103eV, a second peak around 99eV to 100eV, a third peak around 103eV to 104eV, and a fourth peak around 283eV to 285eV were obtained.
Example 4
A negative electrode active material was prepared in the same manner as in example 1, except that the temperature of the heat treatment by introducing methane was changed to 1100 ℃.
As a result of XPS analysis of the anode active material, a first peak around 102eV to 103eV, a second peak around 99eV to 100eV, a third peak around 103eV to 104eV, and a fourth peak around 283eV to 285eV were obtained.
Example 5
Except for the silicon composite particles: phosphoric acid = 90:10 weight ratio a negative electrode active material was prepared in the same manner as in example 1, except that the acid treatment was performed.
As a result of XPS analysis of the anode active material, a first peak around 102eV to 103eV, a second peak around 99eV to 100eV, a third peak around 103eV to 104eV, and a fourth peak around 283eV to 285eV were obtained.
Comparative example 1
A negative electrode active material was prepared in the same manner as in example 1, except for the acid treatment process. The negative electrode active material formed does not contain SiO y (1<y≤2)。
As a result of XPS analysis of the anode active material, as shown in fig. 4, a second peak around 99eV to 100eV, a third peak around 103eV to 104eV, and a fourth peak around 283eV to 285eV were obtained.
Comparative example 2
A negative electrode active material was prepared in the same manner as in example 1, except for the procedure of introducing methane and performing heat treatment.
As a result of XPS analysis of the anode active material, a first peak around 102eV to 103eV, a second peak around 99eV to 100eV, and a third peak around 103eV to 104eV were obtained.
The constitution of the anode active materials prepared in examples and comparative examples is shown in table 1 below.
TABLE 1
X-ray photoelectron spectroscopy of the negative electrode active material was performed by the Nexsa ESCA system, siemens technologies (ESCA-02). Specifically, after the full-scan spectrum and the narrow-scan spectrum are acquired for each sample, the full-scan spectrum and the narrow-scan spectrum may be acquired while the depth distribution is performed. Depth distribution was performed for up to 3000 seconds using monoatomic Ar ions, and measurement and data processing conditions were as follows.
-an X-ray source: monochromatic Al K alpha (1486.6 eV)
X-ray spot size: 400 μm
-a sputter gun: monoatomic Ar (energy: 1000eV, flow: low, grating width: 2 mm)
Etch rate: for Ta 2 O 5 0.09nm/s
-an operating mode: CAE (constant analyzer energy) mode
-full scan: with an energy of 200eV and an energy level of 1eV
Narrow scan: scanning mode, energy of 50eV, energy level of 0.1eV
-charge compensation: flood gun closing
-SF：Al THERMO1
-ECF：TPP-2M
Background subtraction: shirley
The particle size of the negative electrode active material was analyzed by a laser diffraction particle size analysis method using a Microtrac S3500 apparatus.
The content of Li atoms was confirmed by ICP analysis using an inductively coupled plasma atomic emission spectrometer (ICP-OES, AVIO 500 from Perkin-Elmer 7300 Co.).
The presence and amount of the carbon layer was confirmed by combustion under oxygen conditions using elemental analysis (G4 ICARUS from Bruker).
Si and silicon-based oxide (SiO x And SiO y ) The NMR peak intensity or weight ratio of (a) was confirmed by nuclear magnetic resonance spectroscopy (advanced III HD 600MHz NMR Spectrometer from Bruker corporation) at MAS rate=10 kHz.
The content of lithium by-products was measured by karl fischer titration (Titrator Excellence T5 from Mettler Toledo company) by adding the sample to distilled water and then filtering the resulting product, and titrating the dissolved components with HCl solution.
The ratio of the total amorphous phase in the anode active material was measured by quantitative analysis using an X-ray diffraction analysis method (D4 Endeavor from Bruker corporation).
< experimental example: evaluation of discharge capacity, initial efficiency and service life (Capacity Retention Rate) characteristics ]
The negative electrode active materials in examples and comparative examples were used to prepare a negative electrode and a battery, respectively.
By mixing the negative electrode active material, conductive material carbon black, and binder polyacrylic acid (PAA) in an amount of 80:10:10 weight ratio to prepare a mixture. Thereafter, 7.8g of distilled water was added to 5g of the mixture, and the resultant mixture was stirred to prepare a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film having a thickness of 20 μm as a negative electrode current collector and dried. In this case, the temperature of the circulated air was 60 ℃. Subsequently, the anode was prepared by rolling an anode current collector and drying the anode current collector in a vacuum oven at 130 ℃ for 12 hours.
Cutting the prepared negative electrode into 1.7671cm 2 And a lithium (Li) metal thin film is used as a positive electrode. A porous polyethylene separator is interposed between the positive electrode and the negative electrode, wherein carbon is containedThe mixing volume ratio of ethylene carbonate (EMC) and Ethylene Carbonate (EC) in which 0.5 parts by weight of vinylene acid was dissolved was 7:3, and LiPF 6 An electrolyte dissolved at a concentration of 1M was injected thereto to prepare a lithium coin half cell.
The discharge capacity, initial efficiency and capacity retention rate were evaluated by charging and discharging the prepared battery, and are shown in table 2 below.
For cycles 1 and 2, the battery was charged and discharged at 0.1C, from cycle 3 to cycle 49, and at 0.5C. The 50 th cycle is completed in the charged state (in which lithium is contained in the negative electrode).
Charging conditions: CC (constant current)/CV (constant voltage) (5 mV/0.005C current cut-off)
Discharge conditions: CC (constant current) Condition 1.5V
The discharge capacity (mAh/g) and initial efficiency (%) were derived from the results during the primary charge/discharge. Specifically, the initial efficiency (%) is derived from the following calculation formula.
Initial efficiency (%) = (1 discharge capacity/1 charge capacity) ×100
The capacity retention rates are each derived from the following calculation formula.
Capacity retention (%) = (49 discharge capacities/1 discharge capacity) ×100
< experimental example: evaluation of Process (shear viscosity) Properties
As part of the procedural evaluation, the measurement was performed by the method described in 77:20:1:1:1 weight ratio of graphite: negative electrode active material: carbon black: CMC: the amount of change in shear viscosity at shear rate=1 Hz for the slurries prepared by PAA mixing is shown in table 2 below. Specifically, the shear viscosity change (%) is derived from the following formula.
Shear viscosity change (%) = ((shear viscosity of slurry after 48 hours-shear viscosity of slurry immediately after mixing)/shear viscosity of slurry immediately after mixing) ×100
TABLE 2
The negative electrode active material according to the present invention is characterized by comprising a carbon layer and SiO on silicon composite particles y (1<y.ltoreq.2), the content of lithium by-products in the anode active material is low, and since the carbon layer and the SiO-containing layer are y (1<y.ltoreq.2) with excellent passivation.
In Table 2, in examples 1 to 5, the content of lithium by-product in the acid-treated anode active material was low, and SiO y (1<y.ltoreq.2) increases the ratio of amorphous phases in the anode active material. It was confirmed that in examples 1 to 5, the content of lithium by-product in the anode active material was low, and that since SiO y (1<y.ltoreq.2), the discharge capacity, initial efficiency and capacity retention ratio are better as a whole than those of the comparative example. In addition, it was confirmed that SiO was used to prepare the alloy y (1<y.ltoreq.2) minimizes the influence of the lithium compound eluted from the lithium by-product or the silicon-based composite particles, and the change amount of the shear viscosity of the slurry is significantly reduced as compared with comparative examples 1 and 2.
In contrast, in comparative example 1, no acid treatment was performed, and no SiO was formed from lithium by-products y (1<y.ltoreq.2). It was confirmed that, in the case of comparative example 1, since the lithium content was higher than that of the example, the initial efficiency was slightly higher than that of the example, but the discharge capacity and the capacity retention rate were significantly reduced, and the shear viscosity change amount was significantly larger than that in the example, because the side reaction of the slurry occurred due to the lithium by-product and the viscosity of the slurry was changed.
Since the carbon layer is not included in the case of comparative example 2, the expansion of the silicon-based composite particles cannot be prevented, the conductivity is low, and the silicon-based composite particles cannot be effectively coated. It was thus confirmed that the negative electrode active material failed to exhibit an appropriate capacity due to the volume expansion during charge/discharge, and that lithium by-products not coated with the carbon layer caused side reactions of the slurry, and that the viscosity of the slurry was changed, and thus the discharge capacity and capacity maintenance rate were significantly reduced and the shear viscosity change amount was significantly greater as compared with the examples.
Thus, the present invention is achieved by providing a carbon layer and SiO therein y (1<y.ltoreq.2) the negative electrode active material provided on the silicon-based composite particles, can effectively remove lithium by-products, and easily improve the overall aqueous workability, discharge capacity, efficiency, and capacity retention rate by utilizing the passivation effect.
Claims (14)
1. A negative electrode active material comprising:
silicon composite particles comprising 0 of<x<SiO 2 of 2 x And a Li compound; a carbon layer; and wherein 1<SiO with y less than or equal to 2 y ，
Wherein the carbon layer is provided in a form of coating at least a part of the surface of the silicon-based composite particles, and
wherein 1 is described in<SiO with y less than or equal to 2 y Is provided in the form of coating at least a portion of the surface of the silicon-based composite particles or coating at least a portion of the surface of the carbon layer.
2. The anode active material according to claim 1, wherein the anode active material has a peak present at 101eV to 104eV when analyzed by X-ray photoelectron spectroscopy.
3. The anode active material according to claim 1, wherein 1 of the materials<SiO with y less than or equal to 2 y Is provided in a form of coating at least a part of the surface of the silicon-based composite particle between the surface of the silicon-based composite particle and the carbon layer, is provided in a form of coating at least a part of a region on the surface of the silicon-based composite particle where the carbon layer is not provided, or is provided in a form of coating at least a part of the surface of the carbon layer.
4. The anode active material according to claim 1, wherein the SiO is contained in an amount of 100 parts by weight in total of the anode active material y (1<y.ltoreq.2) is 0.1 to 50 parts by weight.
5. The anode active material according to claim 1, further comprising a lithium by-product disposed on at least a portion of the silicon-based composite particles.
6. The anode active material according to claim 5, wherein the content of the lithium by-product is 5 parts by weight or less with respect to 100 parts by weight of the total anode active material.
7. The anode active material of claim 5, further comprising a carbon layer disposed on at least a portion of the lithium byproduct.
8. The anode active material according to claim 1, wherein a ratio (p 1: p 2) of peak intensity of Si (p 1) to peak intensity of Si-O bond representing (p 2) during NMR measurement of the anode active material is 88:12 to 60:40.
9. the anode active material according to claim 1, wherein the silicon-based composite particles and the SiO are opposed to each other y (1<y.ltoreq.2) and the ratio of amorphous phase is 32% or more.
10. The anode active material according to claim 1, wherein a content of Li contained in the silicon-based composite particles is 0.1 to 40 parts by weight with respect to 100 parts by weight of the total anode active material.
11. The anode active material according to claim 1, wherein the content of the carbon layer is 0.1 to 20 parts by weight with respect to 100 parts by weight of the total anode active material.
12. A method of producing the anode active material according to any one of claims 1 to 11, the method comprising:
preparing a silicon-based composite particle comprising 0 of<x<SiO 2 of 2 x And a Li compound; and
by combiningThe silicon-based composite particles are subjected to an acid treatment to form 1 of them<SiO with y less than or equal to 2 y 。
13. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 11.
14. A secondary battery comprising the negative electrode according to claim 13.
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| KR10-2021-0107522 | 2021-08-13 | ||
| KR1020220014132A KR20230025319A (en) | 2021-08-13 | 2022-02-03 | Negative electrode active material, manufacturing method of negative electrode active material, negative electrode comprising negative electrode active material and secondary battery comprising same |
| KR10-2022-0014132 | 2022-02-03 | ||
| PCT/KR2022/011577 WO2023018108A1 (en) | 2021-08-13 | 2022-08-04 | Negative electrode active material, method for manufacturing negative electrode active material, negative electrode comprising negative electrode active material, and secondary battery comprising same |
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