Patent Application
20250183303
This application claims priority to Korean Patent Application No. 10-2023-0171126 filed on Nov. 30, 2023 in the Korean Intellectual Property Office (KIPO), the entire disclosure of which is incorporated by reference herein.
The disclosure of this patent application relates to an anode active material for a lithium secondary battery and a lithium secondary battery including the same.
A secondary battery which can be charged and discharged repeatedly has been widely employed as a power source of a mobile electronic device such as a camcorder, a mobile phone, a laptop computer, etc., according to developments of information and display technologies. Recently, a battery pack including the secondary battery is being developed and applied as a power source of an eco-friendly vehicle such as an electric automobile.
Examples of the secondary battery include a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, etc. The lithium secondary battery among the secondary batteries is being actively developed due to high operational voltage and energy density per unit weight, a high charging rate, a compact dimension, etc.
Recently, as an application range of the lithium secondary battery is expanded, the lithium secondary battery having higher capacity and power is being developed. For example, silicon having high capacity can be combined with carbon to be used as an anode active material.
However, a silicon-carbon composite anode active material has an increased volume expansion difference to result in cracks and an exposure to an electrolyte solution of the anode active material.
According to an aspect of the present disclosure, there is provided an anode active material for a lithium secondary battery having improved life-span properties.
According to an aspect of the present disclosure, there is provided a lithium secondary battery having improved life-span properties.
An anode active material for a lithium secondary battery includes a composite particle. The composite particle includes a carbon-based particle including pores, and a silicon-containing coating formed on a surface of the carbon-based particle. A peak distance of the composite particle defined by Equation 1 is 0.6 Å or less.
In Equation 1, p1 is a central peak value of a peak having a maximum height in a range from 3.4 Å to 4.1 Å of a pair distribution function (PDF) spectrum obtained by a PDF analysis for the composite particle, and p2 is a central peak value of a peak having a maximum height in a range of 4.1 Å to 4.9 Å of the PDF spectrum obtained by the PDF analysis for the composite particle.
In some embodiments, the peak distance may be in a range from 0.56 Å to 0.59 Å.
In some embodiments, the peak distance may be in a range from 0.57 Å to 0.59 Å.
In some embodiments, a peak intensity ratio of the composite particle defined by Equation 2 may be in a range from 0.1 to 0.35.
In Equation 2, Ip1 is a maximum height of a peak in a range of 3.4 Å to 4.1 Å of the PDF spectrum obtained by the PDF analysis of the composite particle, and Ip2 is a maximum height of a peak in a range of 4.1 Å to 4.9 Å of the PDF spectrum obtained by the PDF analysis of the composite particle.
In some embodiments, the peak intensity ratio may be in a range from 0.13 to 0.29.
In some embodiments, the peak intensity ratio may be in a range from 0.15 to 0.28.
In some embodiments, a pore size of the carbon-based particle may be in a range from 0.1 nm to 10 nm.
In some embodiments, the pore size of the carbon-based particle may be in a range from 1 nm to 5 nm.
In some embodiments, the composite particle may further include a carbon coating formed on the silicon-containing coating.
In some embodiments, the carbon coating may include an amorphous carbon and/or a conductive polymer.
In some embodiments, the pores of the carbon-based particle may have a shape indented from an outermost portion of the carbon-based particle into an inside of the carbon-based particle.
A lithium secondary battery includes an anode including the above-described anode active material for a lithium secondary battery, and a cathode facing the anode.
According to an embodiment of the present disclosure, physical and chemical stability of a composite particle may be improved.
According to an embodiment of the present disclosure, a capacity retention of a secondary battery may be improved.
According to an embodiment of the present disclosure, life-span properties of a secondary battery may be improved.
The anode active material and the lithium secondary battery according to the present disclosure may be widely applied in green technology fields such as an electric vehicle, a battery charging station, a solar power generation, a wind power generation, etc., using a battery, etc. The anode active material and the lithium secondary battery according to the present disclosure may be used for eco-friendly electric vehicles and hybrid vehicles to prevent a climate change by suppressing air pollution and greenhouse gas emissions, etc.
According to embodiments disclosed in the present application, an anode active material for a lithium secondary battery (hereinafter, that may be abbreviated as an anode active material) including a composite particle. According to embodiments of the present disclosure, a lithium secondary battery including the anode active material is also provided.
Hereinafter, the present disclosure will be described in detail with reference to the attached drawings and example embodiments. However, those are merely provided as examples and the present disclosure is not limited to the specific embodiments disclosed herein.
Referring to
According to embodiments of the present disclosure, the carbon-based particle 60 may include a pore 65. For example, the carbon-based particles 60 may be a porous particle including a plurality of pores.
In some embodiments, the carbon-based particle 60 may include an activated carbon, a carbon nanotube, a carbon nanowire, graphene, a carbon fiber, carbon black, graphite, a porous carbon, a pyrolyzed cryogel, a pyrolyzed xerogel, a pyrolyzed aerogel, etc. These may be used alone or in a combination of two or more therefrom.
In some embodiments, the carbon-based particle 60 may include an amorphous structure or a crystalline structure.
In an embodiment, the carbon-based particle 60 may include the amorphous structure. In this case, durability of the anode active material may be increased, so that cracks may be suppressed during charging and discharging or an external impact. Accordingly, the life-span properties of the secondary battery may be improved.
The silicon-containing coating 70 may be formed on a surface of the carbon-based particle 60 including the pores 65. For example, volume expansion of silicon contained in the silicon-containing coating 70 may be alleviated by the pores 65. Accordingly, cracks due to a difference between volume expansion ratios of carbon (e.g., about 150 volume % or less) and silicon (e.g., about 400 volume % or more) during charging and discharging of the battery may be prevented while employing the relatively high capacity properties of silicon. Accordingly, gas generation due to a side reaction between the anode active material and an electrolyte solution may be prevented, and the life-span properties of the secondary battery may be improved.
The pores 65 of the carbon-based particle 60 may have a shape indented into the carbon-based particle 60 from an outermost portion of the carbon-based particle 60 to an inside of the carbon-based particle 60. For example, the pores 65 may include open pores to an outside of the carbon-based particles 60.
As used herein, the term “a surface of the carbon-based particle” and/or “a surface of the carbon-based particle 60” may refer to an outer surface 62 of the carbon-based particle 60, an inner surface 67 of the pore 65, or the outer surface 62 of the carbon-based particle 60 and the inner surface 67 of the pore 65.
For example, the silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of the carbon-based particle 60.
For example, the silicon-containing coating 70 may be formed on at least a portion of the inner surface 67 of the pore 65 of the carbon-based particles 60.
For example, the silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of carbon-based particle 60 and at least a portion of the inner surface 67 of pore 65.
In some embodiments, the silicon-containing coating 70 may include an amorphous silicon. Accordingly, stability of the composite particle may be improved and the life-span properties of the secondary battery may be improved.
In an embodiment, the silicon-containing coating 70 may not include a crystalline silicon. Accordingly, stability of the composite particle may be further improved and the life-span properties of the secondary battery may be further improved.
According to embodiments of the present disclosure, a peak distance measured by a pair distribution function (PDF) analysis of the composite particle 50 and defined by Equation 1 below may be 0.6 Å or less, and, in some embodiments, may be in a range from 0.56 Å to 0.59 Å or from 0.57 Å to 0.59 Å.
In Equation 1, p1 is a central peak value of a peak having a maximum height in a range from 3.4 Å to 4.1 Å of a PDF spectrum obtained by the PDF analysis for the composite particle 50, and p2 is a central peak value of a peak having a maximum height in a range of 4.1 Å to 4.9 Å of the PDF spectrum obtained by the PDF analysis for the composite particle 50.
For example, the particle peak distance may correspond to a distance between silicon atoms included in the silicon-containing coating 70.
In the particle peak distance range above, the distance between the silicon atoms included in the silicon-containing coating 70 may be maintained at an appropriate level, so that stability and amorphousness of silicon may be enhanced. Accordingly, physical and chemical stability of the composite particle 50 may be improved, and the capacity retention during charging and discharging of the secondary battery may be improved.
Scattering data for the PDF analysis may be collected, e.g., from a beamline 1C of Pohang Light Source (PLS-II) of Pohang Accelerator Research Institute (PAL). In addition to the beamline 1C, another equipment capable of measuring the scattering data may also be used.
For example, a sample of the composite particles 50 may be introduced into a capillary, and the scattering data including 2D scattering images was measured at a step size of 0.017 degree in a range of 5 to 80 degrees (2θ) using a high energy X-ray (22.003 KeV) with a wavelength (A) of 0.56356 Å.
1D scattering intensity data may be obtained by integrating the 2D scattering image using a software (e.g., Dioptas). In the process of obtaining the 1D scattering intensity data, when the current collector and the composite particles 50 are adhered to each other, a diffraction peak of the current collector may be planarized.
For example, an X-ray scattered by the hollow capillary can be collected to obtain background data.
For example, the 1D scattering intensity data, the background data, the used wavelength and chemical composition may be applied to a software (e.g., PDFgetX3) to obtain a structural function S(Q). In this case, a relative intensity (background scale) of the background data relative to the 1D scattering intensity data may be set to 1.0, and a range of Q may be set to 0.1 to 12.0.
A G(r) function may be obtained by a Fourier transforming of S(Q). The PDF spectrum may be obtained by illustrating a change in G(r) according to an interatomic distance (r).
p1 and p2 of Equation 1 may be measured by drawing a baseline parallel to a horizontal axis (r) based on a vertical axis G(r) height when r of the PDF spectrum is 0 Å, and then deriving a central peak value of a peak having a maximum height based on the baseline.
In some embodiments, a peak intensity ratio measured by the PDF analysis of the composite particle 50 and defined by Equation 2 below may be in a range from 0.1 to 0.35, and in an embodiment, may be in a range from 0.13 to 0.29, or from 0.15 to 0.28.
In Equation 2, Ip1 is a maximum height of a peak in a range from 3.4 Å to 4.1 Å of the PDF spectrum obtained by the PDF analysis for the composite particle 50, and Ip2 is a maximum height of a peak in a range from 4.1 Å to 4.9 Å of the PDF spectrum obtained by the PDF analysis for the composite particle 50.
For example, the peak intensity ratio may correspond to a degree of dispersion of the PDF spectrum peak of silicon atoms included in the silicon-containing coating 70.
In the peak intensity ratio range, the silicon atoms may each have an appropriate amorphousness and may be uniformly coated on the surface of the carbon-based particle 60. Accordingly, the life-span properties of the secondary battery may be improved.
In some embodiments, a size of the pore 65 of the carbon-based particle 60 may be in a range from 0.1 nm to 10 nm, from 0.5 nm to 8 nm, or from 1 nm to 5 nm. In the above range, excessive deposition of silicon may be prevented, and cracks of the anode active material during charging and discharging of the secondary battery may be further suppressed. The size of the pore 65 may refer to a diameter of an entrance of the pore 65 formed on the surface of the carbon-based particle 60.
In some embodiments, the silicon-containing coating 70 may include silicon, and optionally may further include SiOx (0<x<2).
In an embodiment, the composite particle 50 may not include silicon carbide (SiC).
In this case, the capacity and life-span properties of the anode active material may be enhanced.
In some embodiments, the composite particle 50 may further include a carbon coating (not illustrated) formed on the silicon-containing coating 70. Accordingly, a contact between silicon and water in the anode active material may be prevented. Accordingly, a decrease in a discharge capacity and a capacity efficiency of the secondary battery may be prevented in a period from preparation of the anode active material and before formation of the anode.
In some embodiments, the carbon coating may be formed on a portion of the surface of the carbon-based particle 60 where the silicon-containing coating 70 is not formed. For example, the carbon coating may entirely cover the carbon-based particle 60 and the silicon-containing coating 70. Accordingly, mechanical and chemical stability of the anode active material may be improved.
In an embodiment, the carbon coating may include at least one of carbon and a conductive polymer. For example, the carbon may include an amorphous carbon. For example, the conductive polymer may include polyacetylene, polyaniline, polypyrrole, polythiophene, etc.
Hereinafter, a method of preparing the above-described anode active material for a lithium secondary battery according to example embodiments is provided.
In example embodiments, the carbon particle 60 including the pores 65 may be prepared.
In some embodiments, preliminary carbon particles and an additive may be mixed, and then a first firing and washing may be performed to form the carbon particles 60.
In an embodiment, the preliminary carbon particles may include at least one selected from the group consisting of glucose, sucrose, cellulose, a petroleum pitch, a coal pitch, a biomass and a resol oligomer.
In some embodiments, the additive may serve as a chemical etchant or a hard template.
In an embodiment, the chemical etchant may include a basic and/or acidic agent such as potassium hydroxide (KOH), potassium acetate, potassium carbonate (K2CO3), sodium hydroxide (NaOH), sodium carbonate (Na2CO3), ammonia water (NH4OH), sulfuric acid (H2SO4). These may be used alone or in a combination of two or more therefrom. For example, a reaction of the above-described preliminary carbon particles and the additive may be performed through a chemical activation method.
In an embodiment, the hard template may include silica, polystyrene, etc. These can be used alone or in a combination of two or more therefrom. The hard template may serve as, e.g., an additive for forming pores. For example, the size of the pores 65 may be controlled according to a particle size of the hard template.
In an embodiment, the first firing may be performed at a temperature in a range from 600° C. to 900° C. In this range, the size and/or volume of the pores 65 may be appropriately controlled.
In an embodiment, the washing may be performed by adding an acidic solution or an alkaline solution to the mixture. For example, the acidic solution may include a hydrochloric acid (HCl) solution, a sulfuric acid (H2SO4) solution, etc. For example, the alkaline solution may include a NaOH solution, etc.
In example embodiments, the carbon-based particle 60 and a silicon-containing gas may be co-fired (e.g., a second firing) to form the composite particles 50 including the silicon-containing coating 70 formed on the surface of the carbon-based particles 60. For example, the silicon-containing gas may include a silane gas and an inert gas. For example, the inert gas may include argon (Ar) gas.
In some embodiments, a volume of the silane gas based on a total volume of the silicon-containing gas may be in a range from 10 vol % (volume %) to 70 vol %, from 20 vol % to 70 vol %, from 20 vol % to 50 vol %, or from 30 vol % to 50 vol %. In the above range, a domain size of silicon included in the silicon-containing coating 70 before the heat treatment may be reduced. Accordingly, a crystallite size of silicon after the heat treatment may be reduced.
In some examples, the second firing may be performed at a temperature in a range from 400° C. to 600° C. In the above range, the crystallite size of silicon included in the silicon-containing coating 70 before the heat treatment may be reduced. Accordingly, mechanical stability of the anode active material may be improved during a pressing process or repeated charging and discharging of the secondary battery.
The peak distance defined by the above Equation 1 of the composite particle 50 formed by the above-described method may be 0.6 Å or less.
The lithium secondary battery may include an anode 130 including the above-described anode active material and the cathode 100 facing the anode 130.
The cathode 100 may include a cathode current collector 105 and a cathode active material layer 110 formed on at least one surface of the cathode current collector 105.
The cathode current collector 105 may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The cathode current collector 105 may include aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. For example, a thickness of the cathode current collector 105 may be 10 μm to 50 μm.
The cathode active material layer 110 may include a cathode active material. The cathode active material may include a compound capable of reversibly intercalating and de-intercalating lithium ions.
In example embodiments, the cathode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn) and aluminum (Al).
In some embodiments, the cathode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by Chemical Formula 1.
LixNiaMbO2+z [Chemical Formula 1]
In Chemical Formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and −0.5≤z≤0.1. As described above, M may include Co, Mn and/or Al.
The chemical structure represented by Chemical Formula 1 represents a bonding relationship included in the layered structure or the crystal structure of the cathode active material, and does not exclude other additional elements. For example, M includes Co and/or Mn, and Co and/or Mn may serve as a main active element of the cathode active material together with Ni. Chemical Formula 1 is provided to express the bonding relationship of the main active element and is to be understood as a formula encompassing introduction and substitution of the additional elements.
In an embodiment, an auxiliary element for enhancing chemical stability of the cathode active material or the layered structure/crystal structure in addition to the main active element may be further included. The auxiliary element may be incorporated into the layered structure/crystal structure to form a bond, and this case is to be understood as being included within the range of the chemical structure represented by Chemical Formula 1.
The auxiliary element may include at least one of, e.g., Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P and Zr. The auxiliary element may act as an auxiliary active element such as Al that contributes to capacity/power activity of the cathode active material together with Co or Mn.
For example, the cathode active material or the lithium-nickel metal oxide particle may include a layered structure or a crystal structure represented by Chemical Formula 1-1.
LixNiaM1b1M2b2O2+z [Chemical Formula 1-1]
In Chemical Formula 1-1, M1 may include Co, Mn and/or Al. M2 may include the above-described auxiliary element. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and −0.5≤z≤0.1.
The cathode active material may further include a coating element or a doping element. For example, elements substantially the same as or similar to the above-described auxiliary elements may be used as the coating element or the doping element. For example, the above-described elements may be used alone or in a combination of two or more therefrom as the coating element or the doping element.
The doping element of the coating element may be present on a surface of the lithium-nickel metal oxide particle, or may penetrate through the surface of the lithium-nickel metal oxide particle to be included in the bonding structure represented by Chemical Formula 1 or Chemical Formula 1-1.
The cathode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide having an increased nickel content may be used.
Ni may be provided as a transition metal related to the power and capacity of the lithium secondary battery. Thus, as described above, a high-capacity cathode and a high-capacity lithium secondary battery may be implemented using a high-Ni composition in the cathode active material.
However, as the content of Ni increases, long-term storage stability and life-span stability of the cathode or the secondary battery may be relatively lowered, and side reactions with an electrolyte may also be increased. However, according to example embodiments, life-span stability and capacity retention properties may be improved using Mn while maintaining an electrical conductivity by Co.
The content of Ni in the NCM-based lithium oxide (e.g., a mole fraction of nickel based on the total number of moles of nickel, cobalt and manganese) may be 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be in a range from 0.8 to 0.95, from 0.82 to 0.95, from 0.83 to 0.95, from 0.84 to 0.95, from 0.85 to 0.95, or from 0.88 to 0.95.
In some embodiments, the cathode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP) active material (e.g., LiFePO4).
In some embodiments, the cathode active material may include a Li-rich layered oxide (LLO)/OLO (Over-Lithiated Oxide)-based active material, a Mn-rich active material, a Co-less-based active material, etc., which may have a chemical structure or a crystal structure represented by Chemical Formula 2 below. These may be used alone or in a combination of two or more therefrom.
p[Li2MnO3]·(1−p)[LiqJO2] [Chemical Formula 2]
In Chemical Formula 2, 0<p<1, 0.9≤q≤1.2, and J may include at least one element from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg and B.
For example, the cathode slurry may be prepared by mixing the cathode active material in a solvent. The cathode slurry may be coated on the cathode current collector 105, and then dried and pressed to prepare the cathode active material layer 110. The coating may include, e.g., a gravure coating, a slot die coating, a multi-layered simultaneous die coating, an imprinting, a doctor blade coating, a dip coating, a bar coating, a casting, etc. The cathode active material layer 110 may further include a binder, may optionally further include a conductive material, a thickener, etc.
The solvent may include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.
The binder may include polyvinylidene fluoride (PVDF), vinylidene fluoride-co-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in a combination of two or more therefrom.
In an embodiment, a PVDF-based binder may be used as the cathode binder. In this case, an amount of the binder for forming the cathode active material layer 110 may be reduced and an amount of the cathode active material may be relatively increased. Accordingly, the power and capacity properties of the secondary battery may be improved.
The conductive material may be used to improve conductivity of the cathode active material layer 110 and/or mobility of lithium ions or electrons. For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, acetylene black, Ketjen black, graphene, a carbon nanotube, a vapor-grown carbon fiber (VGCF), a carbon fiber and/or a metal-based conductive material such as tin, tin oxide, titanium oxide, a perovskite material including LaSrCoO3 and LaSrMnO3, etc. These may be used alone or in a combination of two or more therefrom.
The cathode slurry may further include a thickener and/or a dispersive agent. In an embodiment, the cathode slurry may include the thickener such as carboxymethyl cellulose (CMC).
The anode 130 may include an anode current collector 125, and an anode active material layer 120 formed on at least one surface of the anode current collector 125.
For example, the anode current collector 125 may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, etc. These may be used alone or in a combination of two or more therefrom. For example, a thickness of the anode current collector 125 may be in a range from 10 μm to 50 μm.
The anode active material layer 120 may include the above-described anode active material including the composite particle 50. For example, the anode active material may include a plurality of the composite particles 50.
In some examples, the anode active material may include the composite particles and a graphite-based active material. For example, the graphite-based active material may include artificial graphite and/or natural graphite.
A content of the composite particles 50 based on a total weight of the anode active material (e.g., a total weight of the plurality of the composite particles 50 and a graphite-based active material) may be 3 wt % or more, 5 wt % or more, 10 wt % or more, 15 wt % or more, 20 wt % or more, 25 wt % or more, 30 wt % or more, 35 wt % or more, 40 wt % or more, or 45 wt % or more.
The content of the composite particles based on the total weight of the anode active material may be 90 wt % or less, 85 wt % or less, 80 wt % or less, 75 wt % or less, 70 wt % or less, 65 wt % or less, 60 wt % or less, 55 wt % or less, or 50 wt % or less.
In an embodiment, the anode active material may substantially consist of the composite particles 50 and the graphite-based active material. The anode active material may be mixed with a solvent to prepare an anode slurry.
The anode slurry may be coated or deposited on the anode current collector 125, and then dried and pressed to form the anode active material layer 120. The coating may include a gravure coating, a slot die coating, a multi-layered simultaneous die coating, an imprinting, a doctor blade coating, a dip coating, a bar coating, a casting, etc. The anode active material layer 120 may further include a binder, and may optionally further include a conductive material, a thickener, etc.
The solvent included in the anode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc. These may be used alone or in a combination of two or more therefrom.
The above-described materials used in the fabrication of the cathode 100 may also be used as the binder, the conductive material and thickener.
In some embodiments, a styrene-butadiene rubber (SBR)-based binder, carboxymethyl cellulose (CMC), a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene (PEDOT)-based binder, etc., may be used as the anode binder. These may be used alone or in a combination of two or more therefrom.
In example embodiments, a separator 140 may be interposed between the cathode 100 and the anode 130. The separator 140 may be included to prevent an electrical short-circuiting between the cathode 100 and the anode 130 while allowing an ion flow. For example, a thickness of the separator may be in a range from 10 μm to 20 μm.
For example, the separator 140 may include a porous polymer film or a porous non-woven fabric.
The porous polymer film may include a polyolefin-based polymer such as an ethylene polymer, a propylene polymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, an ethylene/methacrylate copolymer, etc. These may be used alone or in a combination of two or more therefrom.
The porous non-woven fabric may include a high melting point glass fiber, a polyethylene terephthalate fiber, etc.
The separator 140 may include a ceramic-based material. For example, inorganic particles may be coated on the polymer film or dispersed in the polymer film to improve a heat resistance.
The separator 140 may have a single-layered or a multi-layered structure including the polymer film and/or the non-woven fabric as described above.
In example embodiments, an electrode cell may be defined by the cathode 100, the anode 130 and the separator 140, and a plurality of the electrode cells may be stacked to form an electrode assembly 150 having, e.g., a jelly roll shape. For example, the electrode assembly 150 may be formed by winding, stacking, z-folding, stack-folding, etc., of the separator 140.
The electrode assembly 150 may be accommodated together with an electrolyte solution in a case 160 to define the lithium secondary battery. In example embodiments, a non-aqueous electrolyte solution may be used as the electrolyte solution.
The non-aqueous electrolyte solution may include a lithium salt serving as an electrolyte and an organic solvent. The lithium salt may be represented by, e.g., Li+X−, and examples of an anion X− may include F−, Cl−, Br−, 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−, (CF3CF2SO2)2N−, etc.
Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethylpropionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, propylene sulfite, etc. These may be used alone or in a combination of two or more therefrom.
The non-aqueous electrolyte solution may further include an additive. The additive may include, e.g., a cyclic carbonate-based compound, a fluorine-substituted carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, a cyclic sulfite-based compound, a phosphate-based compound, a borate-based compound, etc. These may be used alone or in a combination of two or more therefrom.
The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.
The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC).
The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.
The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.
The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, etc.
The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.
The borate-based compound may include lithium bis(oxalate) borate.
In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte solution. In this case, the lithium secondary battery may be manufactured in the form of an all-solid-state battery. Additionally, a solid electrolyte layer may be disposed between the cathode 100 and the anode 130 instead of the separator 140.
The solid electrolyte may include a sulfide-based electrolyte. Non-limiting examples of the sulfide-based electrolyte include Li2S—P2S5, Li2S—P2S5—LiCl, Li2S—P2S5—LiBr, Li2S—P2S5—LiCl—LiBr, Li2S—P2S5—Li2O, Li2S—P2S5—Li2O—LiI, Li2S—SiS2, Li2S—SiS2—LiI, Li2S—SiS2—LiBr, Li2S—SiS2—LiCl, Li2S—SiS2—B2S3—LiI, Li2S—SiS2—P2S5—LiI, Li2S—B2S3, Li2S—P2S5—ZmSn (m and n are positive numbers, and Z represents Ge, Zn or Ga), Li2S—GeS2, Li2S—SiS2—Li3PO4, Li2S—SiS2-LipMOq, (p and q positive numbers, and M represents P, Si, Ge, B, Al, Ga or In), Li7−xPS6-xClx (0≤x≤2), Li7-xPS6—XBrx (0≤x≤2), Li7-xPS6—XIx (0≤x≤2), etc. These may be used alone or in a combination of two or more therefrom.
In an embodiment, the solid electrolyte may include an oxide-based amorphous solid electrolyte such as Li2O—B203—P2O5, Li2O—SiO2, Li2O—B2O3, Li2O—B2O3—ZnO, etc.
As illustrated in
The lithium secondary battery may be manufactured in, e.g., a cylindrical shape using a can, a prismatic shape, a pouch shape or a coin shape.
Hereinafter, embodiments of the present disclosure are described in more detail with reference to experimental examples. However, the following examples are only given for illustrating the present invention and those skilled in the related art will obviously understand that various alterations and modifications are possible within the scope and spirit of the present invention. Such alterations and modifications are duly included in the appended claims.
Pitch and potassium acetate were dry-mixed in a weight ratio of 5:5, and a first firing was performed at 800° C. for 2 hours. The first fired mixture was washed with an excess of 0.5 M HCl aqueous solution to prepare carbon particles including pores. The carbon particles were prepared so that a specific volume of the pores of the carbon-based particles was 0.6 cm3/g.
A silicon-containing gas including a silane gas and an argon gas was injected into a CVD coater at a flow rate of 50 mL/min to 100 mL/min. A content of the silane gas based on a total volume of the silicon-containing gas was 50 vol %. A temperature was increased to 550° C. at a ramping rate of 5° C./min to 20° C./min, and then maintained for about 120 minutes to prepare composite particles including a silicon-containing coating.
The composite particles were prepared so that a silicon content based on a total weight of the composite particles was 45 wt % by weight.
95.5 wt % of an anode electrode active material mixed (a mixture of 15 wt % of the composite particles and 80.5 wt % of artificial graphite), 1 wt % of CNT as a conductive material, 2 wt % of styrene-butadiene rubber (SBR) as a binder and 1.5 wt % of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain an anode slurry.
The anode slurry was coated on a copper substrate, dried and pressed to obtain an anode.
A lithium half-cell including the anode and using a lithium metal as a counter electrode (cathode) was manufactured.
Specifically, a lithium coin half-cell of a CR2016 (diameter: 20 mm, thickness: 1.6 mm) standard was formed by interposing a separator (polyethylene, thickness: 20 μm) between the anode and the lithium metal (thickness: 1 mm).
The assembly of the lithium metal/separator/anode was placed in a coin cell plate, and a cap was covered and clamped after injecting an electrolyte solution. In the preparation of the electrolyte solution, a 1 M LiPF6 solution was formed using a mixed solvent of EC/EMC (3:7; volume ratio), and 2.0 vol % of fluoroethylene carbonate (FEC) was added based on a total volume of the electrolyte solution. After the clamping, impregnation was performed for 3 to 24 hours, and then 3 cycles of charge and discharge were performed at 0.1C (charge conditions: CC-CV 0.1C 0.01V 0.01C CUT-OFF, discharge conditions: CC 0.1C 1.5V CUT-OFF).
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a silica dispersion having an average particle size of 5 nm was added instead of potassium acetate, and the washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that the content of silane gas based on the total volume of silicon-containing gas was changed as shown in Table 1 below.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a silica dispersion having an average particle size of 5 nm was added instead of potassium acetate, the washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution, and the content of silane gas based on the total volume of silicon-containing gas was changed as shown in Table 1 below.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a silica dispersion having an average particle size of 6 nm was added instead of potassium acetate, and the washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution.
The carbon-based particles having the silicon-containing coating formed thereon were introduced into a thermal CVD chamber, and then a mixed gas of ethylene gas and argon was supplied and heat-treated at a temperature less than 600° C. to produce composite particles having a carbon coating formed on the silicon-containing coating.
Except for the above details, an anode and a lithium half-cell were manufactured by the same method as that in in Example 1.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a silica dispersion having an average particle size of 3 nm was added instead of potassium acetate, the washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution, and the content of silane gas based on the total volume of silicon-containing gas was changed as shown in Table 1 below.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a silica dispersion having an average particle size of 6 nm was added instead of potassium acetate, the washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution, and the content of silane gas based on the total volume of silicon-containing gas was changed as shown in Table 1 below.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a silica dispersion having an average particle size of 10 nm was added instead of potassium acetate, and the washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a silica dispersion having an average particle size of 50 nm was added instead of potassium acetate, and the washing was performed with a 0.5 M NaOH aqueous solution instead of the HCl aqueous solution.
An anode and a lithium half-cell were manufactured by the same method as that in Example 1, except that an equal amount of a dispersion of silica having an average particle size of 100 nm was added instead of potassium acetate, and washing was performed with a 0.5 M NaOH aqueous solution instead of an HCl aqueous solution.
Pore sizes of the carbon-based particles according to Examples and Comparative Examples were measured using a surface area analyzer (ASAP-2420) from Micromeritics. Specifically, the pore size of the carbon-based particles was measured by measuring a maximum peak position in a Barrett-Joyner-Halenda (BJH) pore size distribution curve obtained from a nitrogen gas sorption isotherm of each sample obtained from Examples and Comparative Examples.
Samples of the composite particles according to Examples and Comparative
Examples were placed in a polypropylene tube (PP tube). Nitric acid and a small amount of hydrofluoric acid were added to the polypropylene tube and left overnight at room temperature to be dissolved therein. After the sample was dissolved, the polypropylene tube was cooled, saturated boric acid water was added to neutralize hydrofluoric acid, and then diluted with ultrapure water. Carbon components were removed using a 0.45 μm syringe filter.
The sample was placed in an inductively coupled plasma spectroscopy analyzer (ICP-OES Optima 8300, Perkin Elmer Co.) and analyzed to measure a silicon content based on a total weight of the composite particles.
A PDF analysis was performed on the composite particles according to Examples and Comparative Examples to obtain a PDF spectrum graph in which a vertical axis was a PDF function G(r) and a horizontal axis was r (Å) corresponding to an interatomic distance.
Specifically, scattering data for the PDF analysis were collected from a beam line 1C of Pohang Light Source (PLS-II) of Pohang Accelerator Laboratory (PAL).
A sample of the composite particles was introduced into a capillary, and the scattering data including 2D scattering images was measured at a step size of 0.017 degree in a range of 5 to 80 degrees (2θ) using a high energy X-ray (22.003 KeV) with a wavelength (λ) of 0.56356 Å.
The 2D scattering images were integrated using a software (Dioptas) to obtain 1D scattering intensity data. In the process of obtaining the 1D scattering intensity data, a diffraction peak of the collector was planarized when the collector and the composite particles were adhered.
An X-ray scattered by the hollow capillary can be collected to obtain background data.
The 1D scattering intensity data, the background data, the used wavelength and the chemical composition were applied to a software (PDFgetX3) to obtain a structure function S(Q). In obtaining the S(Q), a relative intensity (background scale) of the background data compared to the 1D scattering intensity data was set to 1.0, and a range of Q was set to 0.1 to 12.0.
The S(Q) was Fourier transformed to obtain a G(r) function, and changes in G(r) according to the interatomic distance (r) was plotted to obtain the PDF spectrum.
A baseline was drawn to be parallel to the horizontal axis (r) based on a height of the vertical axis (G(r)) when r of the PDF spectrum was 0 Å, and then a central peak value of a peak having a maximum height in a range from 3.4 Å to 4.1 Å based on the baseline was derived as p1, and a central peak value of a peak having a maximum height in a range from 4.1 Å to 4.9 Å was derived as p2. A peak distance was calculated by substituting p1 and p2 into Equation 1.
The peak height of p1 was determined as Ip1, and the peak height of p2 was determined as Ip2. The Ip1 and Ip2 were substituted into Equation 2 to calculate the peak intensity ratio.
The lithium half-cell according to Examples and Comparative Examples was charged (CC/CV 0.5C 0.01V 0.01C CUT-OFF) and discharged (CC 0.1C 3.0V CUT-OFF) by 50 cycles, and a capacity retention was evaluated as a percentage of a discharge capacity at the 50th cycle relative to a discharge capacity at the 1st cycle.
The results of the measurement and evaluation are shown in Table 1 below.
Referring to Table 1, in Examples where the peak distance according to Equation 1 was 0.6 Å or less, the capacity retentions were generally improved compared to those from Comparative Examples.
In Examples and Comparative Examples, the silicon contents based on the total weight of the composite particles were substantially similar, but the physical and life-span properties of the composite particles were measured as being different according to the pore size and the silane gas concentration.
In Example 6 where the pore size of the carbon-based particles was greater than 10 nm, the capacity retention was lowered compared to those from other Examples.
In Examples 8 and 9 where the content of silane gas was not within a range of 10 vol % to 70 vol % based on the total volume of the silicon-containing gas, the capacity retentions were lowered compared to those from other Examples.
In Example 10 where the carbon coating was further formed on the silicon-containing coating, the capacity retention was improved compared to those from other Examples.
In Examples 11 and 12 where the peak intensity ratio according to Equation 2 was not within a range of 0.1 to 0.35, the capacity retentions were lowered compared to those from other Examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0171126 | Nov 2023 | KR | national |
