Patent Application
20250087674
The present disclosure relates to a negative electrode active material, a negative electrode including the same, a secondary battery including the negative electrode, and a method for manufacturing a negative electrode active material.
Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, laptop computers and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries is rapidly increasing. In particular, lithium secondary batteries are in the limelight as a driving power source for portable devices because they lightweight and have a high energy density.
Accordingly, research and development efforts to improve the performance of lithium secondary batteries are being actively conducted.
In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte solution, an organic solvent, and the like. In addition, the positive electrode and the negative electrode may be formed on current collectors with active material layers each including a positive electrode active material and a negative electrode active material. In general, for the positive electrode, a lithium-containing metal oxide such as LiCoO2 and LiMn2O4 is used as the positive electrode active material, and for the negative electrode, a carbon-based active material or a silicon-based active material that does not contain lithium is used as the negative electrode active material.
Among the negative electrode active materials, silicon-based active materials have attracted attention in that they typically have higher capacity than carbon-based active materials and excellent high-speed charge characteristics. However, silicon-based active materials have disadvantages in that a degree of volume expansion/contraction during charging and discharging is high, an irreversible capacity is high, and therefore, the initial efficiency is low.
On the other hand, among the silicon-based active materials, a silicon-based oxide, specifically, a silicon-based oxide represented by SiOx (0<x<2) has an advantage in that the degree of volume expansion/contraction during the charging and discharging is lower as compared with other silicon-based active materials such as silicon (Si). However, the silicon-based oxide still has a disadvantage in that the initial efficiency is lowered due to the presence of irreversible capacity.
In this regard, studies have been conducted to reduce the irreversible capacity and to improve the initial efficiency by doping or intercalating metals such as Li, Al, and Mg into silicon-based oxides. However, a negative electrode slurry including a metal-doped silicon-based oxide as a negative electrode active material can exhibit a problem in that the metal oxide formed by doping metal reacts with moisture to increase pH of the negative electrode slurry and to change the viscosity. As a result, the state of the manufactured negative electrode is poor and the charging and discharging efficiency of the negative electrode is lowered.
Accordingly, there is a need to develop a negative electrode active material that is capable of improving phase stability of a negative electrode slurry including a silicon-based oxide, and improving charging and discharging efficiency of a negative electrode manufactured from the slurry.
The background description provided herein is for the purpose of generally presenting context of the disclosure. Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art, or suggestions of the prior art, by inclusion in this section.
The present disclosure relates to a negative electrode active material, a negative electrode including the same, a secondary battery including the negative electrode, and a method for manufacturing a negative electrode active material.
An exemplary embodiment of the present disclosure provides a negative electrode active material including a silicon-based particle including SiOx (0<x<2) and a Li compound; a carbon layer provided on at least a portion of a surface of the silicon-based particle; and a surface layer provided on at least a portion of a surface of the carbon layer and including Li, Al and P, wherein an oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W and Ti is provided at an interface between the silicon-based particle and the carbon layer.
Another exemplary embodiment of the present disclosure provides a negative electrode including the negative electrode active material.
Still another exemplary embodiment of the present disclosure provides a secondary battery including the negative electrode.
Yet another exemplary embodiment of the present disclosure provides a method for manufacturing a negative electrode active material according to an exemplary embodiment of the present disclosure, the method including: manufacturing a preliminary silicon-based particle including SiOx (0<x<2); mixing the preliminary silicon-based particle and an oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W and Ti, or depositing the oxide on the preliminary silicon-based particle, to provide a surface of the preliminary silicon-based particle with the oxide; providing at least a portion of the surface of the preliminary silicon-based particle with a carbon layer; mixing the preliminary silicon-based particle provided with the carbon layer with a Li precursor to provide a mixture, and heat-treating the mixture to manufacture a silicon-based particle; and mixing the silicon-based particle with one or more selected from the group consisting of an Al precursor, a P precursor, and a precursor including Al and P, to provide at least a portion of a surface of the carbon layer with a surface layer.
The negative electrode active material according to an exemplary embodiment of the present disclosure includes the surface layer including Li, Al, and P, and the oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W and Ti is provided at the interface between the silicon-based particle and the carbon layer. The negative electrode active material includes both the surface layer and the oxide at the same time. Thereby, it is possible to lower the reactivity of silicates that are highly reactive with water or basicity and to easily block contact with the outside, thereby improving the aqueous processability of the slurry.
Specifically, during a process of forming the surface layer, lithium by-products included in the silicon-based particles can be effectively removed, and the formed surface layer effectively covers unreacted lithium by-products. Thereby, it is possible to prevent a phenomenon that lithium by-products or silicates in the silicon-based particles react with moisture of the slurry to deteriorate physical properties of the slurry. In addition, since the surface layer includes Li, the lithium diffusion resistance on the surface of the negative electrode active material is lowered, which has the effect of improving discharge rate capability.
Further, the oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W, and Ti is included at the interface between the silicon-based particle and the carbon layer, so that the reactivity of the highly reactive silicate in the silicon-based particle can be lowered and the contact with the outside can be blocked, which has the effect of significantly improving the aqueous processability.
Accordingly, the negative electrode including the negative electrode active material according to an exemplary embodiment of the present disclosure, and the secondary battery including the negative electrode have effects of improving the discharge capacity, initial efficiency, resistance performance and/or life characteristics of the battery.
Hereinafter, the present disclosure will be described in more detail.
In the present specification, when a part is referred to as “including” a certain component, it means that the part can further include another component, not excluding another component, unless explicitly described to the contrary.
Throughout the present specification, when a member is referred to as being “on” another member, the member can be in direct contact with another member or an intervening member may also be present.
It should be understood that the terms or words used throughout the specification should not be construed as being limited to their ordinary or dictionary meanings, but construed as having meanings and concepts consistent with the technical idea of the present disclosure, based on the principle that an inventor may properly define the concepts of the words or terms to best explain the disclosure.
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
In the present specification, the crystallinity of the structure included in the negative electrode active material can be confirmed through X-ray diffraction analysis, and the X-ray diffraction analysis may be performed by using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: Bruker), or by appropriately adopting devices that are used in the art, in addition to the above device.
In the present specification, the presence or absence of elements and the contents of elements in the negative electrode active material can be confirmed through ICP analysis, and the ICP analysis may be performed using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300).
In the present specification, the average particle diameter (D50) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles (graph curve of the particle size distribution). The average particle diameter (D50) may be measured using, for example, a laser diffraction method. In the laser diffraction method, in general, particle diameters ranging from a submicron range to several millimeters can be measured, and results with high reproducibility and high resolvability can be obtained.
Hereinafter, preferred embodiments of the present disclosure will be described in detail. However, it should be understood that the embodiments of the present disclosure may be modified in various forms and the scope of the present disclosure is not limited to the embodiments described below.
An exemplary embodiment of the present disclosure provides a negative electrode active material including a silicon-based particle including SiOx (0<x<2) and a Li compound; a carbon layer provided on at least a portion of a surface of the silicon-based particle; and a surface layer including Li, Al and P provided on at least a portion of a surface of the carbon layer, wherein an oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W and Ti is provided at an interface between the silicon-based particle and the carbon layer.
The negative electrode active material according to an exemplary embodiment of the present disclosure includes a silicon-based particle. The silicon-based particle includes SiOx (0<x<2) and a Li compound.
The SiOx (0<x<2) may correspond to a matrix in the silicon-based particle. The SiOx (0<x<2) may be in a form including Si and/or SiO2, and the Si may form a phase. That is, x corresponds to a ratio of the number of O to Si included in the SiOx (0<x<2). When the silicon-based particle includes the SiOx (0<x<2), a discharge capacity of a secondary battery can be improved.
The Li compound may correspond to a matrix in the silicon-based particle. The Li compound may be present in a form of at least one of a lithium atom, lithium silicate, lithium silicide or a lithium oxide in the silicon-based particle. When the silicon-based particle includes a Li compound, the initial efficiency is improved.
The Li compound may be distributed on the surface and/or in the inside of the silicon-based particle in the form of being doped into the silicon-based particle. The Li compound may be distributed on the surface and/or in the inside of the silicon-based particle to serve to control volume expansion/contraction of the silicon-based particle to an appropriate level and to prevent damage to the active material. In addition, the Li compound may be contained, in terms of lowering a ratio of an irreversible phase (for example, SiO2) of silicon-based oxide particle to increase the efficiency of the active material.
In an exemplary embodiment of the present disclosure, the Li compound may be present in a form of lithium silicate. The lithium silicate is represented by LiaSibOc (2≤a≤4, 0<b≤2, 2≤c≤5) and may be divided into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may be present in the silicon-based particles in a form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4 and Li2Si2O5, and the amorphous lithium silicate may have a complex form of LiaSibOc (2≤a≤4, 0<b≤2, 2≤c≤5). However, the present disclosure is not limited thereto.
In an exemplary embodiment of the present disclosure, Li may be included in an amount of 0.1 part by weight to 40 parts by weight, or 0.1 part by weight to 25 parts by weight, on the basis of 100 parts by weight of the total of the negative electrode active material. Specifically, Li may be included in an amount of 1 part by weight to 25 parts by weight, and more specifically, 2 parts by weight to 20 parts by weight. As the Li content increases, the initial efficiency increases, but the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be implemented.
The content of Li in the negative electrode active material can be confirmed through ICP analysis. Specifically, a predetermined amount (about 0.01 g) of a negative electrode active material is precisely aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid and sulfuric acid thereto. Then, by using an inductively coupled plasma atomic emission spectrometer (ICP-AES, Perkin-Elmer 7300), a reference calibration curve is obtained by measuring the intensity of a standard liquid, which has been prepared using a standard solution (5 mg/kg), at an intrinsic wavelength of an element to be analyzed. Subsequently, a pre-treated sample solution and a blank sample are introduced into the spectrometer, and by measuring the intensity of each component to calculate an actual intensity, calculating the concentration of each component based on the obtained calibration curve, and performing a conversion such that the sum of the calculated concentrations of the components is equal to a theoretical value, the element content of the prepared negative electrode active material can be analyzed.
In an exemplary embodiment of the present disclosure, the silicon-based particle may include a further metal-containing moiety. The metal-containing moiety may be present in the form of at least one of a metal atom, a metal silicate, a metal silicide and a metal oxide in the silicon-based particle. The metal atom may include at least one selected from the group consisting of Mg, Li, Al and Ca. Accordingly, initial efficiency of the negative electrode active material may be improved.
In an exemplary embodiment of the present disclosure, the silicon-based particle is provided with a carbon layer on at least a portion of a surface thereof. In this case, the carbon layer may be partially coated on at least a portion of the surface, i.e., the surface of the particle, or may be coated on the entire surface of the particle. Conductivity is imparted to the negative electrode active material by the carbon layer, so that the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery can be improved.
In an exemplary embodiment of the present disclosure, the carbon layer includes amorphous carbon. Further, the carbon layer may further include crystalline carbon.
The crystalline carbon may further improve conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fluorene, carbon nanotubes, and graphene.
The amorphous carbon may appropriately maintain the strength of the carbon layer to suppress expansion of the silicon-based particle. The amorphous carbon may be a carbon-based material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic materials, or a hydrocarbon as a source of chemical vapor deposition.
The carbide of other organic materials may be an organic carbide selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose carbide, and combinations 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. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or the like.
In an exemplary embodiment of the present disclosure, the carbon layer may be an amorphous carbon layer.
In an exemplary embodiment of the present disclosure, the carbon layer may be included in an amount of 0.1 part by weight to 50 parts by weight, 0.1 part by weight to 30 parts by weight, or 0.1 part by weight to 20 parts by weight based on 100 parts by weight of the total of the negative electrode active material. More specifically, the carbon layer may be included in an amount of 0.5 part by weight to 15 parts by weight, 1 part by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight. When the above range is satisfied, reduction in capacity and efficiency of the negative electrode active material can be prevented.
In an exemplary embodiment of the present disclosure, a thickness of the carbon layer may be 1 nm to 500 nm, and specifically 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative electrode active material is improved, the change in volume of the negative electrode active material is easily suppressed, and the side reaction between the electrolyte solution and the negative electrode active material is suppressed, thereby improving the initial efficiency and/or life of the battery.
Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane and acetylene.
In the present disclosure, the crystallinity of the carbon layer can be confirmed by calculating the D/G band ratio according to Raman spectroscopy. Specifically, measurements can be made using a Renishaw 2000 Raman microscope system and 532 nm laser excitation, and using a 100× optical lens with a low laser power density and an exposure time of 30 seconds in order to avoid a laser heat effect. In order to reduce a deviation depending on position, a total of 25 points can be determined for a region of 5 μm×5 μm, and fitted using the Lorentzian function. Thereafter, average values of the D band and G band can be calculated.
The negative electrode active material according to an exemplary embodiment of the present disclosure includes a surface layer provided on at least a portion of a surface of the carbon layer and including Li, Al, and P.
Specifically, the surface layer may be present in a form that covers at least a portion of the surface of the silicon-based particle having the carbon layer. That is, the surface layer may be partially coated on a surface of the particle, or may be coated on the entire surface of the particle. A shape of the surface layer may include an island type or a thin film type, but the shape of the surface layer is not limited thereto.
The surface layer may be provided on at least a portion on the carbon layer. That is, the surface layer may be coated on the particle adjacent to the carbon layer, and may be provided in the form of the surface layer-the carbon layer-the particle including SiOx (0<x<2) and a Li compound. The surface layer may substantially or completely cover the carbon layer or may partially cover the carbon layer.
Additionally, the surface layer may be further provided on a region, in which the carbon layer is not provided, of the surface of the silicon-based particle. That is, the surface layer may be coated adjacent to a surface of the silicon-based particle that is not coated with the carbon layer, and may be provided in the form of the surface layer-the silicon-based particle.
In an exemplary embodiment of the present disclosure, the surface layer includes Li, Al and P.
In an exemplary embodiment of the present disclosure, the surface layer may include Li, Al, P and O.
In an exemplary embodiment of the present disclosure, the Al included in the negative electrode active material may be included in an amount of 0.05 part by weight or more and 0.5 part by weight or less based on 100 parts by weight of a total of the negative electrode active material. Specifically, Al may be included in an amount of 0.1 part by weight or more and 0.4 part by weight or less, 0.12 part by weight or more and 0.35 part by weight or less, or 0.15 part by weight or more and 0.3 part by weight or less. The lower limit of the content of Al is 0.05 part by weight, 0.1 part by weight, 0.12 part by weight, or 0.15 part by weight, and the upper limit thereof is 0.5 part by weight, 0.4 part by weight, 0.35 part by weight or 0.3 part by weight.
In an exemplary embodiment of the present disclosure, the P element included in the negative electrode active material may be included in an amount of 0.05 part by weight or more and 2 parts by weight or less based on 100 parts by weight of the total of the negative electrode active material. Specifically, P may be included in an amount of 0.1 part by weight or more and 1.5 parts by weight or less, 0.15 part by weight or more and 1.2 parts by weight or less, or 0.3 part by weight or more and 1.2 parts by weight or less. The lower limit of the content of P is 0.05 part by weight, 0.1 part by weight, 0.15 part by weight, 0.2 part by weight, 0.25 part by weight, 0.3 part by weight, 0.35 part by weight, 0.4 part by weight, 0.45 part by weight or 0.5 part by weight, and the upper limit thereof is 2 parts by weight, 1.5 parts by weight, 1.2 parts by weight or 1 part by weight.
In an exemplary embodiment of the present disclosure, the Li element included in the negative electrode active material may be included in an amount of 0.05 part by weight or more and 2 parts by weight or less based on 100 parts by weight of the total of the negative electrode active material. Specifically, Li may be included in an amount of 0.1 part by weight or more and 1.5 parts by weight or less, or 0.15 part by weight or more and 1 part by weight or less. The lower limit of the content of Li included in the surface layer is 0.05 part by weight, 0.1 part by weight, 0.15 part by weight, 0.2 part by weight, 0.25 part by weight, 0.3 part by weight, 0.35 part by weight, 0.4 part by weight, 0.45 part by weight or 0.5 part by weight, and the upper limit thereof is 2 parts by weight, 1.5 parts by weight, 1.2 parts by weight or 1 part by weight.
In an exemplary embodiment of the present disclosure, the surface layer may include a phase of LiyAlzPwOy (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10). The y, z, w and v each represent a ratio of the number of each atom.
In an exemplary embodiment of the present disclosure, the surface layer may include one or more selected from the group consisting of aluminum oxide, phosphorus oxide, lithium oxide, aluminum phosphate, lithium salt, lithium phosphate, and lithium aluminate. In one example, the phase of LiyAlzPwOv may include a mixture or a compound formed from Li3PO4, AlPO4, Al(PO3)3, LiAlO2 or the like, but is not limited thereto.
When the surface layer including the components as described above is provided, it is possible to prevent a phenomenon that the Li compound included in the silicon-based particle reacts with moisture of slurry to lower viscosity of the slurry, which has the effect of improving the stability of the electrode state and/or charging and discharging capacity.
In an exemplary embodiment of the present disclosure, the surface layer may include an amorphous phase. In one example, the surface layer may be an amorphous phase. In one example, when performing an X-ray diffraction analysis on the negative electrode active material according to an exemplary embodiment of the present disclosure, a crystalline peak originating from the surface layer may not appear.
In an exemplary embodiment of the present disclosure, the surface layer may further include one or more selected from the group consisting of Li2O, LiOH and Li2CO3. In general, during the process of doping lithium into silicon-based particles, the remaining materials may be exposed to moisture or air to form lithium by-products such as Li2O, LiOH and Li2CO3. Therefore, the surface layer may be in a form including one or more selected from the group consisting of Li2O, LiOH and Li2CO3.
In an exemplary embodiment of the present disclosure, the y may satisfy 0<y≤3.
In an exemplary embodiment of the present disclosure, the z may satisfy 0<z≤1.
In an exemplary embodiment of the present disclosure, the w may satisfy 0.5<w≤3.
In an exemplary embodiment of the present disclosure, the v may satisfy 4<v≤12.
The surface layer may be formed by dry-mixing 1) silicon-based particles and aluminum phosphate, 2) silicon-based particles, an aluminum precursor and a phosphorus precursor or 3) silicon-based particles and a Li—Al—P—O-based precursor and heat-treating the mixture, or mixing 1), 2) or 3) with a solvent, and then reacting the mixture while vaporizing the solvent.
In an exemplary embodiment of the present disclosure, the surface layer may be included in an amount of more than 0 part by weight and 10 parts by weight or less based on 100 parts by weight of the total of the negative electrode active material. Specifically, the surface layer may be included in an amount of 0.1 part by weight or more and 10 parts by weight or less, 0.3 part by weight or more and 8 parts by weight or less, or 0.5 part by weight or more and 5 parts by weight or less. More specifically, the surface layer may be included in an amount of 1 part by weight or more and 3.5 parts by weight or less or 1.5 parts by weight or more and 3 parts by weight or less. If the content of the surface layer is less than the above range, it is difficult to prevent gas generation on the slurry, and if the content is more than the above range, it is difficult to implement the capacity or efficiency.
The upper limit of the content of the surface layer may be 10 parts by weight, 8 parts by weight, 6 parts by weight, 5 parts by weight, 4 parts by weight, 3.5 parts by weight, or 3 parts by weight, and the lower limit thereof may be 0.1 part by weight, 0.3 part by weight, 0.5 part by weight, 0.8 part by weight, 1 part by weight, 1.2 parts by weight, 1.4 parts by weight, or 1.5 parts by weight.
In an exemplary embodiment of the present disclosure, a weight ratio of the surface layer and the carbon layer may be 1:0.1 to 1:30. Specifically, the weight ratio may be 1:0.5 to 1:5, 1:1 to 1:4, or 1:1 to 1:3. By satisfying the above range, the carbon layer and the surface layer can effectively cover the silicon-based particles, effectively suppressing side reactions on the slurry, and stably implementing capacity and/or efficiency. On the other hand, if the content of the surface layer is excessively higher than that of the carbon layer, it is difficult to implement capacity or efficiency, and if the content of the carbon layer is excessively higher than that of the surface layer, it is difficult to prevent gas generation on the slurry.
In an exemplary embodiment of the present disclosure, the surface layer may be included in an amount of 90 parts by weight or less based on 100 parts by weight of the carbon layer. Specifically, the surface layer may be included in an amount of 80 parts by weight or less, 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less based on 100 parts by weight of the carbon layer. In addition, the surface layer may be included in an amount of 0.1 part by weight or more, 1 part by weight or more, 5 parts by weight or more, or 10 parts by weight or more based on 100 parts by weight of the carbon layer. By satisfying the above range, the carbon layer and the surface layer can effectively cover the silicon-based particles, effectively suppressing side reactions on the slurry, and stably implementing the capacity and/or efficiency.
In an exemplary embodiment of the present disclosure, an oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W, and Ti is provided at an interface between the silicon-based particle and the carbon layer.
The oxide including Zr, B, Al, Zn, W or Ti is provided at the interface between the silicon-based particle and the carbon layer as described above, so that the reactivity of silicate, which is highly reactive with water or basicity, can be lowered and contact with the outside can be easily blocked.
Additionally, the oxide has low reactivity with the binder component of the slurry, which can further improve aqueous processability.
The oxide may include Zr, and specifically, may be in the form of ZrO2.
The oxide may include B, and specifically, may be in the form of B2O3.
The oxide may include Al, and specifically, may be in the form of Al2O3.
The oxide may include Zn, and specifically, may be in the form of ZnO.
The oxide may include W, and specifically, may be in the form of WO3.
The oxide may include Ti, and specifically, may be in the form of TiO2.
The oxide may include one or more selected from the group consisting of ZrO2, B2O3, Al2O3, ZnO, WO3 and TiO2.
The oxide is not limited to the types described above, and oxides known in the art can be appropriately selected and adopted.
The configuration ‘the oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W and Ti is provided at the interface between the silicon-based particle and the carbon layer’ means that the oxide is provided adjacent to the surface of the silicon-based particle and the carbon layer is provided adjacent to the oxide. That is, the configuration may be such a form that the carbon layer covers the silicon-based particle provided with the oxide on the surface of the silicon-based particle.
In addition, the oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W, and Ti may be additionally provided adjacent to a surface of the silicon-based particle without a carbon layer.
In an exemplary embodiment of the present disclosure, the oxide may be included in an amount of 0.01 part by weight or more and 0.5 part by weight or less based on 100 parts by weight of the total of the negative electrode active material. Specifically, the oxide may be included in an amount of 0.01 part by weight or more and 0.3 part by weight or less, 0.02 part by weight or more and 0.25 part by weight or less, 0.03 part by weight or more and 0.2 part by weight or less, 0.05 part by weight or more and 0.2 part by weight or less, 0.01 part by weight or more and 0.2 part by weight or less, or 0.07 part by weight or more and 0.16 part by weight or less. When the above content is satisfied, the reactivity of silicate, which is highly reactive with water or basicity, can be effectively lowered, preventing the negative electrode active material from reacting with moisture in the aqueous slurry or lithium by-products from eluting, which has an effect of improving aqueous processability. On the other hand, if the content of the oxide exceeds the above range, the conductivity of the surface of the silicon-based particle decreases, resulting in a problem in which charging and discharging capacity/efficiency is not properly implemented, and if the content of the oxide is less than the above range, the reactivity of silicate near the surface of the silicon-based particle cannot be sufficiently lowered, resulting in a problem in that the effect of improving processability of the aqueous slurry is not sufficiently exhibited.
The lower limit of the content of the oxide may be 0.01 part by weight, 0.02 part by weight, 0.03 part by weight, 0.04 part by weight, 0.05 part by weight, 0.06 part by weight, or 0.07 part by weight, and the upper limit thereof may be 0.5 part by weight, 0.4 part by weight, 0.3 part by weight, 0.25 part by weight, 0.2 part by weight, 0.18 part by weight, 0.15 part by weight, or 0.12 part by weight.
In an exemplary embodiment of the present disclosure, any of Zr, B, Zn, W and Ti included in the oxide may be each included in an amount of 0.003 part by weight or more and 0.2 part by weight or less based on 100 parts by weight of the total of the negative electrode active material. Specifically, each of the metals may be included in an amount of 0.003 part by weight or more and 0.18 part by weight or less, 0.004 part by weight or more and 0.17 part by weight or less, 0.005 part by weight or more and 0.16 part by weight or less, 0.01 part by weight or more and 0.15 part by weight or less, 0.03 part by weight or more and 0.15 part by weight or less, or 0.05 part by weight or more and 0.12 part by weight or less. When the above content is satisfied, the reactivity of silicate, which is highly reactive with water, or basicity, is lowered, preventing the negative electrode active material from reacting with moisture in the aqueous slurry or lithium by-products from eluting, which has an effect of improving aqueous processability. On the other hand, if the content of each metal exceeds the above range, the conductivity of the surface of the silicon-based particle is lowered, so the charging and discharging capacity/efficiency is not properly implemented, and the metal is highly likely to be also present as a simple metal at the interface between the silicon-based particle and the carbon layer, not in the form of metal oxide, and thus, acts as a metal impurity, thereby having a negative effect on the charging and discharging of the battery, causing lithium dendrite to grow inside, and further causing an internal short. If the content of each metal is less than the above range, the reactivity of silicate near the surface of the silicon-based particle cannot be sufficiently lowered, resulting in a problem in that the effect of improving processability of the aqueous slurry is not sufficiently exhibited.
In an exemplary embodiment of the present disclosure, Al included in the oxide may be included in an amount of 0.003 part by weight or more and 0.2 part by weight or less based on 100 parts by weight of the total of the negative electrode active material. Specifically, Al may be included in an amount of 0.003 part by weight or more and 0.18 part by weight or less, 0.004 part by weight or more and 0.17 part by weight or less, 0.005 part by weight or more and 0.16 part by weight or less, 0.01 part by weight or more and 0.15 part by weight or less, 0.03 part by weight or more and 0.15 part by weight or less, or 0.05 part by weight or more and 0.12 part by weight or less. When the above content is satisfied, the reactivity of silicate, which is highly reactive with water, or basicity, is lowered, preventing the negative electrode active material from reacting with moisture in the aqueous slurry or lithium by-products from eluting, which has an effect of improving aqueous processability.
The oxide may be included in an amount of 1 part by weight or more and 12 parts by weight or less, specifically, 2 parts by weight or more and 12 parts by weight or less, 2 parts by weight or more and 10 parts by weight or less, 2 parts by weight or more and 8 parts by weight or less, or 3 parts by weight or more and 7 parts by weight or less based on 100 parts by weight of a total of the surface layer. When the above range is satisfied, the reactivity of silicate, which is highly reactive with water, or basicity, is lowered, preventing the negative electrode active material from reacting with moisture in the aqueous slurry or lithium by-products from eluting, which has an effect of improving aqueous processability. On the other hand, if the content of the oxide exceeds the above range, the conductivity of the surface of the silicon-based particle is lowered, so the charging and discharging capacity/efficiency is not properly implemented, and the metal is highly likely to be also present as a simple metal at the interface between the silicon-based particle and the carbon layer, not in the form of metal oxide, and thus, acts as a metal impurity, thereby having a negative effect on the charging and discharging of the battery, causing lithium dendrite to grow inside, and further causing an internal short. If the content of the oxide is less than the above range, the reactivity of silicate near the surface of the silicon-based particle cannot be sufficiently lowered, resulting in a problem in that the effect of improving processability of the aqueous slurry is not sufficiently exhibited.
In an exemplary embodiment of the present disclosure, a lithium by-product may be present on the silicon-based particle. Specifically, the lithium by-product may be present on the surface of the silicon-based particle or on the surface of the carbon layer. In addition, the lithium by-product may be present between the surface layer and the silicon-based particle.
Specifically, the lithium by-product may refer to a lithium compound remaining near the surface of the silicon-based particle or the carbon layer after the silicon-based particle is manufactured. As described above, even after the acid treatment process, unreacted lithium by-products with the acid may remain.
The lithium by-product may include one or more selected from the group consisting of Li2O, LiOH and Li2CO3.
Whether or not the lithium by-product exists can be confirmed through X-ray diffraction analysis (XRD) or X-ray photoelectron analysis (XPS).
The lithium by-product may be included in an amount of 5 parts by weight or less based on 100 parts by weight of the total of the negative electrode active material. Specifically, the lithium by-product may be included in an amount of 0.01 part by weight to 5 parts by weight, 0.05 part by weight to 2 parts by weight, or 0.1 part by weight to 1 part by weight. More specifically, the lithium by-product may be included in an amount of 0.1 part by weight to 0.8 part by weight or 0.1 part by weight to 0.5 part by weight. When the content of the lithium by-product satisfies the above range, the side reaction in the slurry can be reduced and the change in viscosity can be reduced, thereby improving the aqueous processability characteristics. On the other hand, when the content of the lithium by-product is higher than the above range, the slurry becomes basic when formed, which causes a side reaction or a change in viscosity and problems in the aqueous processability.
The content of the lithium by-product can be calculated by measuring an amount of a HCl solution in a specific section where pH changes in a process of titrating an aqueous solution including the negative electrode active material with the HCl solution using a titrator, and then calculating an amount of the lithium by-product.
An average particle diameter (D50) of the negative electrode active material may be 0.1 μm to 30 μm, specifically 1 μm to 20 μm, and more specifically 1 μm to 10 μm. When the above range is satisfied, the structural stability of the active material is ensured during charging and discharging, a problem that the level of volume expansion/contraction increases as the particle diameter becomes excessively large can be prevented, and a problem that the initial efficiency is reduced when the particle diameter is excessively small can also be prevented.
An exemplary embodiment of the present disclosure provides a method for manufacturing the negative electrode active material including manufacturing a preliminary silicon-based particle including SiOx (0<x<2); mixing the preliminary silicon-based particle and an oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W and Ti, or depositing the oxide on the preliminary silicon-based particle, to provide a surface of the preliminary silicon-based particle with the oxide; providing at least a portion of a surface of the preliminary silicon-based particle with a carbon layer; mixing the preliminary silicon-based particle provided with the carbon layer with a Li precursor to form a mixture, and heat-treating the mixture to manufacture a silicon-based particle; and mixing the silicon-based particle and one or more selected from the group consisting of an Al precursor, a P precursor, and a precursor including Al and P to provide at least a portion of a surface of the carbon layer with a surface layer.
The preliminary silicon-based particle may be manufactured by heating Si powder and SiO2 powder in a vacuum to vaporize the same and then depositing the vaporized mixed gas.
The Si powder and the SiO2 powder may be included at a weight ratio of 2:8 to 8:2, and specifically, may be included at a weight ratio of 4:6 to 6:4 or 5:5.
Specifically, the mixed powder of the Si powder and SiO2 powder may be heat-treated at 1300° C. to 1800° C., 1400° C. to 1800° C. or 1400° C. to 1600° C. under vacuum.
The mixed gas vaporized through the heat treatment can be cooled under vacuum and deposited into a solid phase.
Additionally, the preliminary silicon-based particle can be manufactured by heat-treating the deposited solid phase in an inert atmosphere. The heat treatment may be performed at 500° C. to 1000° C. or 700° C. to 900° C.
The formed preliminary silicon-based particle may be present in the form of SiOx (x=1).
Thereafter, the preliminary silicon-based particle and an oxide including one or more selected from the group consisting of Zr, B, Al, Zn, W and Ti may be mixed, or the oxide may be deposited on the preliminary silicon-based particle, to provide a surface of the preliminary silicon-based particle with the oxide.
The step of providing a surface of the preliminary silicon-based particle with the oxide may further include mixing the oxide and then pulverizing the mixture.
The oxide may be included in an amount of 0.01 part by weight to 0.5 part by weight based on 100 parts by weight of a total of the mixture. Specifically, the oxide may be included in an amount of 0.05 part by weight to 0.3 part by weight, or 0.1 part by weight to 0.2 part by weight.
The pulverizing may be performed using a method such as a ball mill process, a jet mill process, or an air classification process, and is preferably performed through a ball mill process. The pulverizing method is not limited thereto, and pulverizing methods known in the art may be appropriately adopted. Through the pulverizing step, the particle size of the preliminary silicon-based particle can be adjusted, and at the same time, the oxide can be provided on the surface of the preliminary silicon-based particle.
For example, when adjusting the particle size of the preliminary silicon-based particles using a ball mill, 5 to 20 sus ball media can be input, and specifically, 10 to 15 sus ball media can be input, but the present disclosure is not limited thereto.
In the step of adjusting the particle size, a pulverizing time of the preliminary silicon-based negative electrode active material may be 2 to 5 hours, specifically 2 to 4 hours, and more specifically 3 hours, but is not limited thereto.
In the step of depositing the oxide on the preliminary silicon-based particle to provide the oxide on the surface of the preliminary silicon-based particle, the deposition step may be performed through physical vapor deposition (PVD) using a source including an oxide. The deposition method is not limited thereto, and any deposition method known in the art may be appropriately adopted. Through the deposition step, the oxide can be provided on the surface of the preliminary silicon-based particle.
Thereafter, a carbon layer may be provided on the surface of the preliminary silicon-based particle.
The carbon layer may be formed, for example, by using chemical vapor deposition (CVD) in which a carbon-based material, for example, hydrocarbon gas is used or by carbonizing a material serving as a carbon source.
Specifically, the carbon layer may be formed by putting the formed preliminary particle into a reactor, and then depositing hydrocarbon gas at 600° C. to 1200° C. by chemical vapor deposition (CVD). 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° C. to 1000° C.
Thereafter, the preliminary silicon-based particle provided with the carbon layer may be mixed with a Li precursor and then heat-treated to produce a silicon-based particle.
The step of mixing the preliminary particle formed with the carbon layer and Li powder and performing heat treatment may be performed at 700° C. to 900° C. for 4 hours to 6 hours, and specifically at 800° C. for 5 hours.
The silicon-based particle formed through the heat treatment includes SiOx (0<x<2) and a Li compound.
The silicon-based particle may include, as the Li compound described above, a Li silicate, a Li silicide, a Li oxide, or the like.
The particle size of the silicon-based particle may be further adjusted through a method such as a ball mill, a jet mill, or an air classification, but the present disclosure is not limited thereto.
A lithium compound (lithium by-product) is provided on at least a portion of the surface of the silicon-based particle having the carbon layer as described above. Specifically, in the processes of forming a preliminary particle including the SiOx (0<x<2), forming a carbon layer on the preliminary particle, and then doping Li to manufacture the silicon-based particle described above, a lithium compound, i.e., a lithium by-product formed due to unreacted lithium remains near the surface of the silicon-based particle.
Thereafter, a surface layer may be provided on at least a portion of a surface of the carbon layer.
The step of providing the surface layer on at least a portion of the surface of the carbon layer may include mixing and reacting the silicon-based particle with one or more selected from the group consisting of an Al precursor, a P precursor, and a precursor including Al and P.
In an exemplary embodiment, the step of providing a surface layer on at least a portion of the surface of the carbon layer may include mixing and reacting the silicon-based particle with a precursor including Al and a precursor including P.
The precursor including Al and P may be included in an amount of 0.1 part by weight to 5 parts by weight on the basis of 100 parts by weight of a total of the mixture. Specifically, the precursor may be included in an amount of 0.5 part by weight to 4 parts by weight, or 1 part by weight to 3 parts by weight.
The precursor including Al and P may be aluminum phosphate.
Specifically, the surface layer may be formed on at least a portion of the surface of the carbon layer by 1) dry-mixing the silicon-based particle and aluminum phosphate and heat-treating the mixture, or 2) mixing the silicon-based particle and aluminum phosphate with a solvent, and then reacting the silicon-based particle and aluminum phosphate while vaporizing the solvent through heat treatment. When forming a surface layer using the above method, the surface layer can be easily formed by reacting aluminum phosphate with lithium by-products formed or remaining during the manufacturing process of silicon-based particle.
The aluminum phosphate may be in a form of AlbPcOa (0<b≤10, 0<c≤10, 0<d≤10). Specifically, the aluminum phosphate may be Al(PO3)3 or AlPO4, but is not limited thereto, and salts used in the art may be appropriately adopted to form the surface layer.
In another exemplary embodiment, the step of providing a surface layer on at least a portion of the surface of the carbon layer may include mixing and reacting the silicon-based particle with a precursor including Al (aluminum precursor) and a precursor including P (phosphorus precursor).
Specifically, the surface layer may be formed on at least a portion of the surface of the carbon layer by 3) dry-mixing the silicon-based particle, the aluminum precursor, and the phosphorus precursor and heat treating the mixture, or 4) mixing the silicon-based particle, the aluminum precursor, and the phosphorus precursor with a solvent, and then reacting the silicon-based particle, the aluminum precursor, and the phosphorus precursor while vaporizing the solvent through heat treatment. When forming the surface layer by the above method, the surface layer can be easily formed by reacting the lithium by-products formed during the manufacturing process of silicon-based particle, the aluminum precursor, and the phosphorus precursor.
The aluminum precursor may be aluminum oxide in the form of AlaOb (0<a≤10, 0<b≤10), and specifically, may be Al2O3.
Alternatively, the aluminum precursor may be aluminum hydroxide, aluminum nitrate, aluminum sulfate, or the like, and specifically, may be Al(OH)3, Al(NO3)3·9H2O or Al2(SO4)3, but is not limited thereto, and an aluminum precursor used in the art may be appropriately adopted to form the surface layer.
The phosphorus precursor may be phosphorous oxide in the form of PcOa (0<c≤10, 0<d≤10).
Alternatively, the phosphorus precursor may be ammonium phosphate, diammonium phosphate, phosphoric acid, or the like, and specifically, may be (NH4)3PO4, (NH4)2HPO4, H3PO4 or NH4H2PO4, but is not limited thereto, and a phosphorus precursor used in the art may be appropriately adopted to form the surface layer.
The precursor including Al and P may be a precursor including Li, Al, P, and O (Li—Al—P—O-based precursor).
In another exemplary embodiment, the step of providing a surface layer on at least a portion of the surface of the carbon layer may include mixing and reacting the silicon-based particle with a precursor including Li, Al, P, and O (Li—Al—P—O-based precursor).
Specifically, the surface layer may be formed on at least a portion of the surface of the carbon layer by 5) dry-mixing the silicon-based particle and the Li—Al—P—O-based precursor and heat-treating the mixture, or 6) mixing the silicon-based particle and the Li—Al—P—O-based precursor with a solvent, and then reacting the silicon-based particle and the Li—Al—P—O-based precursor while vaporizing the solvent through heat treatment. When forming the surface layer using the above method, the surface layer can be formed by directly adding the Li—Al—P—O-based precursor.
The Li—Al—P—O-based precursor may be in a form of LiyAlzPwOv (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10). Specifically, the Li—Al—P—O-based precursor may be a mixture or compound formed complexly from Li3PO4, AlPO4, Al(PO3)3, LiAlO2 or the like, but is not limited thereto, and a configuration used in the art may be appropriately adopted to form the surface layer.
The precursor may be aluminum phosphate.
In the step of providing a surface layer on at least a portion of the surface of the carbon layer, the heat treatment may be performed at 500° C. to 700° C., and specifically 550° C. to 650° C. However, the heat treatment is not limited thereto, and may differ depending on the salt or precursor used. When the heat treatment temperature is higher than the above range, the surface layer is formed in a crystalline form, making it difficult for Li ions to enter and exit through the surface layer, thereby reducing resistance and life characteristics and lowering capacity and/or efficiency. When the heat treatment temperature satisfies the above range, the reaction between the salt or precursor and the Li by-product occurs well and the surface layer contains Li, so the durability of the formed negative electrode active material against moisture increases, and a lithium diffusion resistance on the surface of the negative electrode active material is lowered, which has an effect of improving discharge rate capability.
The solvent may be water or ethanol, but is not limited thereto, and a solvent used in the art may be appropriately adopted.
The surface layer formed on at least a portion of the surface of the carbon layer preferably includes a phase of LiyAlzPwOv (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10), and the phase of LiyAlzPwOv may be an amorphous phase.
Details of the surface layer are the same as described above.
A negative electrode according to an exemplary embodiment of the present disclosure may include the negative electrode active material described above.
Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder a thickener and/or a conductive material.
The negative electrode active material layer may be formed by applying a negative electrode slurry including a negative electrode active material, a binder, a thickener, and/or a conductive material to at least one surface of a current collector, and drying and roll-pressing the same.
The negative electrode slurry may further include an additional negative electrode active material.
As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; a metallic compound capable of being alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metallic oxides capable of doping and undoping lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or a composite including the metallic compound and the carbonaceous material, such as a Si—C composite or a Sn—C composite, and any one thereof or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of the low-crystalline carbon include soft carbon and hard carbon, and representative examples of the high-crystalline carbon include amorphous, platy, scaly, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum- or coal tar pitch-derived cokes.
The additional negative electrode active material may be a carbon-based negative electrode active material.
In an exemplary embodiment of the present disclosure, a weight ratio of the negative electrode active material and the additional negative electrode active material included in the negative electrode slurry may be 10:90 to 90:10, and specifically 10:90 to 50:50.
The negative electrode slurry may include a solvent for negative electrode slurry formation. Specifically, the solvent for negative electrode slurry formation may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, and specifically, distilled water, in terms of facilitating dispersion of components.
The negative electrode slurry including the negative electrode active material according to an exemplary embodiment of the present disclosure may have pH of 7 to 11 at 25° C. When pH of the negative electrode slurry satisfies the above range, the rheological properties of the slurry are stabilized. On the other hand, when pH of the negative electrode slurry is less than 7 or pH of the negative electrode slurry exceeds 11, carboxymethylcellulose (CMC) used as a thickener is decomposed, resulting in lowering in viscosity of the slurry and a decrease in dispersion degree of the active material included in the slurry.
The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, for the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel each surface treated with carbon, nickel, titanium, silver, or the like, or the like may be used. Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used for the current collector. A thickness of the current collector may be 6 μm to 20 μm. However, the thickness of the current collector is not limited thereto.
The binder may include at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, poly acrylic acid, and the above-mentioned materials in which a hydrogen is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.
The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; a conductive fiber such as a carbon fiber and a metal fiber; a conductive tube such as a carbon nanotube; metal powders such as fluorocarbon, aluminum, and nickel powder; a conductive whisker such as zinc oxide and potassium titanate; a conductive metal oxide such as titanium oxide; a conductive material such as polyphenylene derivative, and the like may be used.
The thickener may be carboxymethylcellulose (CMC), but is not limited thereto, and thickeners used in the art may be appropriately adopted.
In an exemplary embodiment of the present disclosure, a weight ratio of the negative electrode active material and the additional negative electrode active material included in the negative electrode slurry may be 1:99 to 30:70, and specifically 5:95 to 30:70 or 10:90 to 20:80.
In an exemplary embodiment of the present disclosure, the entire negative electrode active materials included in the negative electrode slurry may be included in an amount of 60 parts by weight to 99 parts by weight, and specifically 70 parts by weight to 98 parts by weight on the basis of 100 parts by weight of a total of solid content of the negative electrode slurry.
In an exemplary embodiment of the present disclosure, the binder may be included in an amount of 0.5 part by weight to 30 parts by weight, and specifically 1 part by weight to 20 parts by weight, on the basis of 100 parts by weight of the total of the solid content of the negative electrode slurry.
In an exemplary embodiment of the present disclosure, the conductive material may be included in an amount of 0.5 part by weight to 25 parts by weight, specifically 1 part by weight to 20 parts by weight on the basis of 100 parts by weight of the total of the solid content of the negative electrode slurry.
In an exemplary embodiment of the present disclosure, the thickener may be included in an amount of 0.5 part by weight to 25 parts by weight, specifically 0.5 part by weight to 20 parts by weight, and more specifically 1 part by weight to 20 parts by weight on the basis of 100 parts by weight of the total of the solid content of the negative electrode slurry.
The negative electrode slurry according to an exemplary embodiment of the present disclosure may further include a solvent for negative electrode slurry formation. Specifically, the solvent for negative electrode slurry formation may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, and specifically, distilled water, in terms of facilitating dispersion of components.
In an exemplary embodiment of the present disclosure, a weight of the solid content of the negative electrode slurry may be 20 parts by weight to 75 parts by weight, and specifically 30 parts by weight to 70 parts by weight based on 100 parts by weight of the total of the negative electrode slurry.
A secondary battery according to an exemplary embodiment of the present disclosure may include the negative electrode according to an exemplary embodiment of the present disclosure described above. 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 solution, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof is 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 it has conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel each surface treated with carbon, nickel, titanium, silver, or the like, or the like may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and a surface of the current collector may be formed with microscopic irregularities to enhance adhesive force of the positive electrode active material. 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 foamed body, and a non-woven fabric body.
The positive electrode active material may be a positive electrode active material that is typically used. Specifically, the positive electrode active material may be a layered compound such as a lithium cobalt oxide (LiCoO2) and a lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; a lithium manganese oxide such as chemical formula Li1+c1Mn2-c1O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; a lithium copper oxide (Li2CuO2); a vanadium oxide such as LiV3O8, V2O5 and Cu2V2O7; a Ni-site type lithium nickel oxide represented by chemical formula LiNi1-c2Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.5); a lithium manganese composite oxide represented by chemical formula LiMn2-c3Mc3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); LiMn2O4 in which a part of Li of the chemical formula is substituted with 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 described above.
In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as the positive electrode conductive material has electronic conductivity without causing a chemical change in a battery. Specific examples may include graphite such as natural graphite and artificial graphite; a carbon-based material 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; a conductive whisker such as zinc oxide and potassium titanate; a conductive metal oxide such as titanium oxide; or a conductive polymer such as polyphenylene derivative, or the like, and any one thereof or a mixture of two or more thereof may be used.
In addition, the positive electrode binder serves to improve bonding between particles of the positive electrode active material and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidenefluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoro rubber, or various copolymers thereof, and the like, and any one thereof or a mixture two or more thereof may be used.
The separator serves to separate the negative electrode and the positive electrode and to provide a movement path of lithium ions, in which any separator may be used as the separator without particular limitation as long as it is typically used in a secondary battery, and particularly, a separator having high moisture-retention ability for an electrolyte solution as well as a low resistance to the movement of electrolyte solution ions may be preferably used. Specifically, a porous polymer film, for example, a porous polymer film manufactured from 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 having two or more layers thereof may be used. In addition, a typical porous non-woven fabric, for example, a non-woven fabric formed of high melting point glass fibers, polyethylene terephthalate fibers, or the like may be used. Furthermore, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and the separator having a single layer or multilayer structure may be selectively used.
Examples of the electrolyte solution may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten-type inorganic electrolyte and the like that may be used in the manufacturing of the lithium secondary battery, but are not limited thereto.
Specifically, the electrolyte solution may include a non-aqueous organic solvent and a metal salt.
As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimetoxy ethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, or ethyl propionate may be used.
In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and can be preferably used because they have high permittivity to dissociate a lithium salt well. When the cyclic carbonate is mixed with a linear carbonate with low viscosity and low permittivity, such as dimethyl carbonate or diethyl carbonate, in a suitable ratio and used, an electrolyte solution with high electric conductivity may be prepared, and therefore, may be more preferably used.
A lithium salt may be used as the metal salt, and the lithium salt is a material that is readily soluble in the non-aqueous electrolyte solution, in which, for example, one or more species selected from the group consisting of F−, Cl−, I−, NO3, N(CN)2, BF4, ClO4−, PF6−, (CF3)2PF4−, (CF3)3PF3, (CF3)4PF2−, (CF3)5PF−, (CF3)6P−, CF3SO3, CF3CF2SO3−, (CF3SO2)2N−, (FSO2)2N−, CF3CF2(CF3)2CO−, (CF3SO2)2CH−, (SF5)3C−, (CF3SO2)3C−, CF3(CF2)7SO3, CF3CO2−, CH3CO2−, SCN− and (CF3CF2SO2)2N− may be used as an anion of the lithium salt.
One or more additives, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride, may be further included in the electrolyte solution for the purpose of improving life characteristics of the battery, suppressing a decrease in battery capacity, improving discharge capacity of the battery, and the like, in addition to the above-described electrolyte solution components.
Another embodiment of the present disclosure provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high-rate capability, and high cycle characteristics, the battery module and the battery pack may be used as a power source of a medium to large sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.
100 g of powder of Si and SiO2 mixed in a molar ratio of 1:1 was vacuum-heated to a sublimation temperature of 1,400° C. in a reactor. Then, a mixed gas of vaporized Si and SiO2 was reacted in a cooling zone in a vacuum state where a cooling temperature was 800° C., and condensed into a solid phase. Thereafter, heat treatment was performed in an inert atmosphere and at a temperature of 800° C. to prepare preliminary silicon-based particles. Thereafter, the preliminary silicon-based particles and ZrO2 were added at a weight ratio of 99.9:0.1, and pulverized for 3 hours to prepare silicon-based particles having a size of 6 μm (D50) by using 15 sus ball media added for ball mill. Thereafter, the silicon-based particles were positioned in a hot zone of a CVD apparatus while maintaining the inert atmosphere by causing Ar gas to flow, and a reaction was carried out at 10−1 torr for 20 minutes while blowing methane into the hot zone of 900° C. using Ar as a carrier gas, thereby forming a carbon layer on the surface of the silicon-based particles.
10 g of Li metal powder was added to 90 g of the silicon-based particles, which were then subjected to heat treatment in an inert atmosphere and at the temperature of 800° C., resulting in Li-doped silicon-based particles. 98.5 g of the silicon-based particles were mixed with 1.5 g of Al(PO3)3, and the mixture was subjected to heat treatment at 600° C. to prepare a negative electrode active material including a surface layer including Li, Al, and P and formed on surfaces of the silicon-based particles.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included ZrO2 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Zr were 9.5 wt %, 0.15 wt %, 0.5 wt %, and 0.06 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that the preliminary silicon-based particles and ZrO2 were added at a weight ratio of 99.8:0.2 and then a ball mill was used for the preparation.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included ZrO2 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Zr were 9.5 wt %, 0.15 wt %, 0.5 wt %, and 0.12 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that 97.0 g of the silicon-based particles were mixed with 3.0 g of Al(PO3)3.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included ZrO2 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Zr were 9.5 wt %, 0.3 wt %, 1.1 wt %, and 0.06 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that the preliminary silicon-based particles and B2O3 were added at a weight ratio of 99.9:0.1 and then a ball mill was used for the preparation.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included B2O3 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and B were 9.5 wt %, 0.15 wt %, 0.5 wt %, and 0.03 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that the preliminary silicon-based particles and Al2O3 were added at a weight ratio of 99.9:0.1 and then a ball mill was used for the preparation.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included Al2O3 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, and P were 9.5 wt %, 0.19 wt %, and 0.5 wt %, respectively, based on 100 wt % of a total of the negative electrode active material. (Al content in the interface was 0.04 wt %)
A negative electrode active material was prepared in the same process as in Example 1, except that the preliminary silicon-based particles and ZnO were added at a weight ratio of 99.9:0.1 and then a ball mill was used for the preparation.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included ZnO present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Zn were 9.5 wt %, 0.15 wt %, 0.5 wt % and 0.07 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that the preliminary silicon-based particles and WO3 were added at a weight ratio of 99.9:0.1 and then a ball mill was used for the preparation.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included WO3 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and W were 9.5 wt %, 0.15 wt %, 0.5 wt %, and 0.07 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that the preliminary silicon-based particles and TiO2 were added at a weight ratio of 99.9:0.1 and then a ball mill was used for the preparation.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included TiO2 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Ti were 9.5 wt %, 0.15 wt %, 0.5 wt %, and 0.05 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that the preliminary silicon-based particles and Zr were added at a weight ratio of 99.9:0.1 and then a ball mill was used for the preparation.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included Zr present in the interface between the silicon-based particles and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Zr were 9.5 wt %, 0.15 wt %, 0.5 wt % and 0.08 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that only the preliminary silicon-based particles were added (ZrO2 was not added), silicon-based particles were prepared using a ball mill, and then 98.5 g of Li-doped silicon-based particles were mixed with 1.5 g of Al(PO3)3 and 0.1 g of ZrO2.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included ZrO2 in the surface layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Zr were 9.5 wt %, 0.15 wt %, 0.5 wt %, and 0.07 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that only the preliminary silicon-based particles were added (ZrO2 was not added), and then silicon-based particles were prepared using a ball mill.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
As a result of ICP analysis on the negative electrode active material, the contents of Li, Al, and P were 9.5 wt %, 0.15 wt %, and 0.5 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
A negative electrode active material was prepared in the same process as in Example 1, except that a surface layer including Li, Al, and P was not formed by not adding Al(PO3)3 to the Li-doped silicon-based particles.
The D50 of the negative electrode active material was 6 μm, and the BET specific surface area was 2.5 m2/g.
The negative electrode active material included ZrO2 present in the interface between the silicon-based particle and the carbon layer, and as a result of ICP analysis on the negative electrode active material, the contents of Li, Al, P, and Zr were 9.8 wt %, 0.0 wt %, 0.0 wt %, and 0.06 wt %, respectively, based on 100 wt % of a total of the negative electrode active material.
The configurations of the negative electrode active materials prepared in the Examples and the Comparative Examples are shown in Table 1 below.
The contents of elements were confirmed by ICP analysis using an inductively coupled plasma atomic emission spectrometer (ICP-OES, AVIO 500 of Perkin-Elmer 7300).
The location of the oxide included in the negative electrode active material (interface between silicon-based particle and carbon layer) was analyzed by XPS.
The content of the carbon layer was confirmed under oxygen conditions by an elemental analysis method through combustion (G4 ICARUS of Bruker).
The D50 of the negative electrode active material was analyzed by a PSD measurement method using a Microtac apparatus.
The specific surface area was measured by degassing gas at 200° C. for 8 hours using a BET measuring apparatus (BEL-SORP-MAX, Nippon Bell), and performing N2 adsorption/desorption at 77 K.
A negative electrode and a battery were manufactured using the negative electrode active materials of Examples and Comparative Examples, respectively.
A mixture was manufactured by mixing the negative electrode active material, carbon black as a conductive material, and polyacrylic acid (PAA) as a binder in a weight ratio of 80:10:10. Thereafter, 7.8 g of distilled water was added to 5 g of the mixture, which was then stirred to manufacture a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film as a negative electrode current collector having a thickness of 20 μm, and dried. In this case, the temperature of the circulating air was 60° C. Subsequently, the thin film was roll-pressed and dried 130° C. for 12 hours in a vacuum oven to prepare a negative electrode.
A lithium (Li) metal thin film obtained by cutting the prepared negative electrode into a circular shape of 1.7671 cm2 was used as a positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and an electrolyte solution obtained by dissolving vinylene carbonate to 0.5 part by weight in a mixed solution in which ethyl methyl carbonate (EMC) and ethylene carbonate (EC) were mixed in a volume ratio of 7:3, and dissolving LiPF6 to a concentration of 1M was injected to manufacture a lithium coin half-cell.
The prepared batteries were charged and discharged to evaluate discharge capacity, initial efficiency, and capacity retention rate, which are shown in Table 2 below.
The charging and discharging were performed at 0.1 C for the first cycle and the second cycle, and the charging and discharging were performed at 0.5 C from the third cycle to the 49th cycle. At the 50th cycle, the charging and discharging were terminated in a charge state (with lithium contained in the negative electrode).
The discharge capacity (mAh/g) and the initial efficiency (%) were derived from the result after charging and discharging once. Specifically, the initial efficiency (%) was derived by the following calculation.
The capacity retention rate was derived by the following calculation.
As part of the evaluation of processability, the change in shear viscosity at shear rate (=1 Hz) of the slurry prepared by mixing graphite, negative electrode active material, carbon black, CMC and SBR at a weight ratio of 77:20:1:1:1 was measured and shown in Table 2 below. Specifically, the change (%) in shear viscosity was derived by the following calculation formula.
In Table 2, it could be confirmed that the negative electrode active materials used in Examples 1 to 8 included the oxide in the interface between the silicon-based particle and the carbon layer and the surface layer including Li, Al, and P, so that the reactivity of silicate, which is highly reactive with water or basicity, could be lowered and the contact with the outside could be easily blocked, resulting in improvements in the capacity retention rate and processability of the battery.
On the other hand, it could be confirmed that in Comparative Example 1 in which the negative electrode active material including Zr rather than an oxide was used, Zr acted as a metal impurity, so the discharge capacity, initial efficiency, and processability of the battery were lowered, and in particular, lithium precipitation occurred due to Zr during the cycles of the battery, and accordingly, the capacity retention rate was hardly secured.
It could be confirmed that in Comparative Examples 2 and 3 in which the negative electrode active material including an oxide in the surface layer or not including an oxide was used, it was difficult to lower the reactivity of the silicate in the silicon-based particles, resulting in a side reaction of the slurry, which lowered the capacity retention rate and processability of the battery.
It could be confirmed that in Comparative Example 4 relating to a negative electrode active material without a surface layer, not only the discharge capacity and the initial efficiency were low, but also, in particular, the capacity retention rate and the processability were significantly lowered. In other words, it can be confirmed that, as in Comparative Example 4, even when an oxide such as ZrO2 is present between the silicon-based particle and the carbon layer, if the surface layer is not included, the capacity retention rate and the processability cannot be improved, and rather, the capacity retention rate and the processability are further lowered, as compared with Comparative Example 3 in which an oxide is not included.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0111916 | Sep 2022 | KR | national |
| 10-2023-0115379 | Aug 2023 | KR | national |
The present application is a National Phase entry pursuant to 35 U.S.C. § 371 of International Application No. PCT/KR2023/013057, filed on Sep. 1, 2023, and claims the benefit of and priority to Korean Patent Application No. 10-2022-0111916, filed on Sep. 5, 2022 with the Korean Intellectual Property Office, and Korean Patent Application No. 10-2023-0115379, filed on Aug. 31, 2023 with the Korean Intellectual Property Office, the disclosures of both of which are incorporated herein by reference in their entireties for all purposes as if fully set forth herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2023/013057 | 9/1/2023 | WO |
