Electrode for lithium secondary battery and lithium secondary battery comprising same

Abstract

The present disclosure relates to an electrode for a lithium secondary battery, which can improve output characteristics, low-temperature characteristics and the like of the lithium secondary battery, and a lithium secondary battery including the same. The electrode for a lithium secondary battery includes: a metal current collector; and an active material layer formed on the metal current collector and including an electrode active material, a conductive material, and an oxide-based solid electrolyte having a lithium ion source, wherein the electrode active material and the oxide-based solid electrolyte are dispersed in the active material layer in the form of particles and have a particle size distribution that spans 1 or less.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2023-0113515, filed with the Korean Intellectual Property Office on August 29, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This disclosure relates to an electrode for a lithium secondary battery that can improve the output characteristics and low-temperature characteristics of a lithium secondary battery, and a lithium secondary battery including the electrode. Background Technology

[0004] Recently, as the application of lithium secondary batteries has rapidly expanded to energy storage power supplies for large-area devices (such as automobiles and energy storage devices), as well as power, electronics, communication and power supplies for electronic devices (such as computers), the demand for high-capacity, high-output, long-life and high-stability lithium secondary batteries is increasing.

[0005] Lithium-ion batteries are typically configured to include a positive electrode, a negative electrode, a separator, and an electrolyte containing lithium salts and organic solvents, wherein lithium ions move through the electrolyte during charging and discharging.

[0006] Lithium ions in the electrolyte exist in a solvated state, surrounded by organic solvents. Therefore, in order for these lithium ions to move and insert into the electrode active material, they undergo a desolvation process, in which they separate from or desorb from the organic solvent molecules. Consequently, the success of this desolvation process can affect the output, resistance, and stability of the lithium-ion secondary battery.

[0007] On the other hand, in recent years, with the need for higher capacity and higher output of lithium secondary batteries, new electrolytes are being actively developed. In particular, in order to accelerate the desolvation of lithium ions and improve the output of lithium secondary batteries, new electrolyte compositions (such as those containing high concentrations of lithium salts or changing the composition of organic solvents) are being proposed to form localized high-concentration regions of lithium salts around the electrodes.

[0008] However, when using new electrolyte compositions containing high concentrations of lithium salts, the increased viscosity of the electrolyte can lead to reduced flowability. In particular, there is a drawback: the ionic conductivity of the electrolyte decreases at low temperatures, resulting in deterioration of the low-temperature characteristics of the lithium secondary battery, such as increased resistance or reduced battery output.

[0009] Therefore, there is a continued need to develop technologies that can accelerate the desolvation of lithium ions in the electrolyte, thereby improving the output characteristics of lithium secondary batteries and maintaining excellent low-temperature characteristics. Summary of the Invention

[0010] Technical issues

[0011] Therefore, one object of this disclosure is to provide an electrode for lithium secondary batteries that can accelerate the desolvation of lithium ions in the electrolyte, thereby improving the output characteristics of lithium secondary batteries and maintaining excellent low-temperature characteristics, such as high output at low temperatures.

[0012] Another object of this disclosure is to provide a lithium secondary battery including electrodes for lithium secondary batteries, which exhibits improved output characteristics and low-temperature characteristics.

[0013] Technical solution

[0014] In the following, electrodes for lithium secondary batteries according to specific embodiments of this disclosure will be described.

[0015] The terms or words used in the specification and appended claims should not be construed as limited to their ordinary or dictionary meanings, and this disclosure should be interpreted in a meaning and concept consistent with the technical concept of this disclosure, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their own inventions.

[0016] The terminology used herein is provided to describe exemplary embodiments and not to limit the inventive concept. Unless the context clearly indicates otherwise, the singular forms include the plural forms.

[0017] It should be understood that the terms “comprising,” “including,” “having,” etc., are used herein to specify the presence of the said feature, integer, step, component, or combination thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0018] Electrodes for lithium secondary batteries

[0019] According to one embodiment of this disclosure, an electrode for a lithium secondary battery is provided, comprising: a metal current collector; and an active material layer formed on the metal current collector and comprising an electrode active material, a conductive material, and an oxide-based solid electrolyte having a lithium-ion source, wherein the electrode active material and the oxide-based solid electrolyte are dispersed in the active material layer in particulate form and have a particle size distribution with a span of 1 or less.

[0020] Specifically, oxide-based solid electrolytes can have a uniform particle size distribution spanning 1 or less. As a result of experiments conducted by the inventors, since the active material layer contains oxide-based solid electrolyte particles satisfying a specific particle size distribution, such oxide-based solid electrolyte particles can be uniformly distributed around the active material particles within the active material layer. Figure 2Furthermore, they can be abundantly distributed near the interface between the active material layer and the electrolyte. This distinguishes them from cases where, in conventional active material layers, oxide-based solid electrolyte particles aggregate and cannot be uniformly distributed. Figure 1 Therefore, oxide-based solid electrolyte particles can reduce the activation energy associated with the desolvation process of lithium ions in the electrolyte at the interface where the active material layer and the electrolyte come into contact, and accelerate the desolvation of lithium ions. Furthermore, this can improve the lithium-ion conductivity around the electrode active material particles.

[0021] Therefore, even without using electrolyte compositions containing high concentrations of lithium salts, lithium secondary batteries including electrodes according to one embodiment of this disclosure can accelerate lithium-ion desolvation and improve the lithium-ion conductivity of the active material layer, thereby reducing the resistance of the lithium secondary battery and improving its output characteristics. Thus, not only can problems such as increased electrolyte viscosity, reduced fluidity, and decreased electrolyte ion conductivity and battery output at low temperatures caused by the application of high-concentration lithium salts be solved, but also excellent low-temperature characteristics of lithium secondary batteries can be achieved.

[0022] Meanwhile, in the embodiments disclosed herein, one embodiment in which the electrode for a lithium secondary battery is the positive electrode is mainly described, but the scope of this disclosure is not limited thereto, and therefore, the electrode according to one embodiment may be the negative electrode.

[0023] In one exemplary embodiment, the positive electrode for a lithium secondary battery may include a metal current collector. There are no particular limitations on the metal current collector, as long as it is conductive and does not cause chemical changes within the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., can be used.

[0024] Furthermore, the active material layer on the metal current collector may comprise a positive electrode active material, a conductive material, and an oxide-based solid electrolyte with a lithium-ion source, and may also optionally comprise a binder.

[0025] At this point, the positive electrode active material can be a compound capable of reversibly inserting and de-inserting lithium, and specifically, it can include a lithium metal oxide containing lithium and at least one metal (e.g., iron, cobalt, manganese, nickel, or aluminum).

[0026] Specifically, lithium metal oxides can include lithium-manganese based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt based oxides (e.g., LiCoO2, etc.), lithium-nickel based oxides (e.g., LiNiO2, etc.), and lithium-nickel-manganese based oxides (e.g., LiNi... 1-Y Mn YO2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc., lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc., lithium-manganese-cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc., lithium-nickel-manganese-cobalt-based oxides (such as Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2), etc., or lithium-nickel-cobalt-transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc., lithium iron phosphate (such as, Li 1+a Fe 1-x M x (PO 4-b )X b (where M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1)), and so on, and any one of them or a mixture of two or more of them can be used.

[0027] Among them, the positive electrode active material includes a lithium metal oxide, the lithium metal oxide contains lithium and two or more metals selected from nickel, manganese, cobalt, and aluminum, and based on the total metal content excluding lithium, the lithium metal oxide can contain 60 mol% or more, or 60 mol% to 99 mol%, or 70 mol% to 95 mol% of nickel. Such a lithium metal oxide can be represented, for example, by the following Chemical Formula 1:

[0028] [Chemical Formula 1]

[0029] Li x Ni a Co b M 1 c M 2 d O2

[0030] In chemical formula 1, M 1 It can be one or more of Mn and Al, or a combination thereof, M 2 It can be one or more of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, 0.90≤x≤1.1, or 0.95≤x≤1.08, or 1.0≤x≤1.08, and 0.60≤a≤1.0, or 0.70≤a≤0.99, or 0.80≤a≤0.95.

[0031] By using lithium metal oxides with such a high nickel content as the positive electrode active material and combining them with oxide-based solid electrolytes, the output and capacity characteristics of lithium secondary batteries can be further improved.

[0032] Based on the total weight of the active material layer, the aforementioned positive electrode active material may be included in an amount of 60% to 99% by weight, or 70% to 99% by weight, or 80% to 98% by weight.

[0033] In one exemplary embodiment, any solid electrolyte having a lithium-ion source containing lithium in its structure and having the form of lithium metal oxide or lithium metal phosphate can be used as an oxide-based solid electrolyte.

[0034] Specific examples include at least one lithium metal oxide or lithium metal phosphate selected from: Nasicon-type solid electrolytes, Lisicon-type solid electrolytes, garnet-type solid electrolytes, perovskite-type solid electrolytes, and LiPON-type solid electrolytes. More specific examples include at least one of the following: compounds based on LAGP (lithium aluminum germanium phosphate), compounds based on LLZO (lithium lanthanum zirconium oxide), compounds based on LATP (lithium aluminum titanium phosphate), compounds based on LLZTO (lithium lanthanum zirconium tantalum oxide), compounds based on LLTO (lithium lanthanum titanium oxide), compounds based on LSTP (lithium silicon titanium phosphate), and compounds based on LGPO (lithium germanium phosphate).

[0035] From the perspective of accelerating the desolvation of lithium ions at the interface between the active material layer and the electrolyte and improving the ion conductivity and output of lithium secondary batteries, Nasicon-type solid electrolytes, such as LAGP-based compounds or LATP-based compounds, can be appropriately used.

[0036] In one exemplary embodiment, the oxide-based solid electrolyte can have one or more particle size distributions, such as a D50 of 100 nm to 1 μm and a D90 of 400 nm to 1.5 μm. For example, the oxide-based solid electrolyte can have a particle size distribution with a D50 of 300 nm to 700 nm and / or a D90 of 400 nm to 900 nm. When the oxide-based solid electrolyte particles are uniformly distributed within the above ranges, they can exhibit excellent output characteristics and low-temperature characteristics.

[0037] In one exemplary embodiment, the sample variance of the oxide-based solid electrolyte, as represented by the following mathematical equation 1, can be 0.04 or less, according to EDS analysis.

[0038] [Mathematical Equation 1]

[0039]

[0040] Among them, s 2 Let y be the sample variance, and y be the variable. denoted as the sample mean, n as the sample size, SS as the sum of squared deviations, and df as the degrees of freedom.

[0041] For example, the sample variance can be 0.04 or less, or 0.03 or less, and if the sample variance exceeds 0.04, it may not be possible to ensure a uniform distribution of oxide-based solid electrolytes, and therefore may not be possible to ensure output characteristics and low-temperature characteristics.

[0042] Specifically, by extracting pixel information from the EDS Ti and / or P element mapping image, dividing it into n uniform grids, and setting each grid as a sample, the sample variance can be calculated using mathematical equation 1. The sample variance value represents the distribution of Ti and P relative to the grid, meaning that the smaller the sample variance value, the more uniformly Ti and P elements are distributed across the entire grid. Therefore, it indicates that the smaller the sample variance value, the more uniformly the oxide-based solid electrolyte (LATP) is distributed in the positive electrode.

[0043] In one exemplary embodiment, from the perspective of accelerating the desolvation of lithium ions at the interface between the active material layer and the electrolyte and improving lithium ion conductivity, without inhibiting the lithium ion insertion and desorption process of the positive electrode active material, the oxide-based solid electrolyte may be included in an amount of 0.3 to 5 parts by weight based on 100 parts by weight of the electrode active material. For example, the oxide-based solid electrolyte may be included in an amount of 0.5 to 5 parts by weight, or 1 to 4 parts by weight, or 2 to 3.5 parts by weight based on 100 parts by weight of the positive electrode active material.

[0044] In one exemplary embodiment, the conductive material included in the active material layer is a component used to further improve the conductivity of the positive electrode active material. Such conductive materials are not particularly limited, as long as they are conductive and do not cause chemical changes in the battery. For example, conductive materials such as: carbon powder, such as carbon black, acetylene black, Ketjen black, celluloidic black, furnace black, lampblack, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-formed crystal structure; conductive nanomaterials, such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives. The conductive material, including conductive nanomaterials such as carbon nanotubes or carbon nanofibers, can further reduce the resistance of the lithium secondary battery including the positive electrode according to one embodiment and further improve output characteristics, etc.

[0045] Typically, based on the total weight of the positive electrode active material layer, the conductive material may be included in an amount of 1% to 20% by weight, or 1% to 15% by weight, or 1% to 10% by weight.

[0046] The binder selectively included in the active material layer is a component that facilitates bonding between the positive electrode active material and the conductive material, as well as bonding with the current collector. Examples of binders may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, nitrile rubber, styrene-butadiene rubber, fluororubber, etc. Mixtures or copolymers selected from two or more of these may also be used.

[0047] Typically, the binder may be included in an amount of 1% to 20% by weight, or 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0048] In addition, fillers may optionally be added to the positive electrode as a component to suppress its expansion. There are no particular limitations on such fillers, as long as they suppress electrode expansion without causing chemical changes in the battery, and examples may include: olefinic polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.

[0049] In another embodiment of this disclosure, a method for manufacturing an electrode for a lithium secondary battery is provided, the method comprising the steps of: mixing and dispersing an oxide-based solid electrolyte and a solvent to prepare a solid electrolyte dispersion; mixing the solid electrolyte dispersion, an electrode active material, and a conductive material to prepare an electrode active material slurry; and applying the electrode active material slurry to an electrode current collector.

[0050] In one exemplary embodiment, the step of preparing the solid electrolyte dispersion can be performed using a bead milling method. Prior to manufacturing the electrode active material slurry, the oxide-based solid electrolyte and solvent are pre-dispersed such that the oxide-based solid electrolyte particles are uniformly distributed around the electrode active material particles within the active material layer.

[0051] Meanwhile, the positive electrode for a lithium secondary battery according to an exemplary embodiment can be manufactured, for example, by dispersing and mixing a positive electrode active material, an oxide-based solid electrolyte, a binder, a conductive material, etc., in a dispersion medium (solvent) to form a slurry, coating the slurry onto a metal current collector, and then drying and rolling it. In this case, the dispersion medium can be NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof, but is not necessarily limited to these.

[0052] Lithium secondary batteries

[0053] In another embodiment of this disclosure, a lithium secondary battery is provided, comprising: a positive electrode; a negative electrode; and an electrolyte containing a lithium salt and a non-aqueous organic solvent, wherein the electrode used in the lithium secondary battery is included as the positive electrode. Because the lithium secondary battery according to another embodiment of this disclosure includes the electrode (e.g., the positive electrode) according to the above embodiment, it can exhibit excellent output characteristics and low-temperature characteristics.

[0054] In another embodiment of the lithium secondary battery, the negative electrode can have a conventional configuration known in the art. For example, the negative electrode may include a negative electrode current collector and a layer of negative electrode active material formed on the negative electrode current collector, wherein the negative electrode active material layer may contain, for example, a negative electrode active material, and, if necessary, may contain additives such as conductive materials, binders, and fillers. Furthermore, such a negative electrode can be formed by a general method: dispersing and mixing the components of the negative electrode active material layer in a dispersion medium (solvent) to form a slurry, coating the slurry onto the negative electrode current collector, and then drying and rolling it.

[0055] At this time, the negative electrode current collector can be platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In-doped SnO2), FTO (F-doped SnO2), or alloys thereof, or copper (Cu) or stainless steel whose surface has been treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not necessarily limited to these. The shape of the negative electrode current collector can be foil, film, sheet, stamped form, porous body, foam, etc.

[0056] Furthermore, compounds capable of reversibly inserting and deintercalating lithium can be used as negative electrode active materials. Specific examples include: carbon-containing materials such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, or lithium vanadium oxide; or composite materials containing metal compounds and carbon-containing materials, such as Si-C composites or Sn-C composites, and mixtures of any one or more of these can be used. Additionally, thin films of metallic lithium can be used as negative electrode active materials.

[0057] Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon-containing materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, sheet-like, flake-like, spherical, or fibrous natural or artificial graphite, crystalline graphite (Kish graphite), pyrolytic carbon, carbon fibers based on meso-phase pitch, meso-carbon microbeads, meso-phase pitch, and high-temperature calcined carbon such as coke derived from petroleum or coal tar pitch.

[0058] Based on the total weight of the negative electrode active material layer, the aforementioned negative electrode active material may be included in an amount of 60% to 99% by weight, or 70% to 99% by weight, or 80% to 98% by weight.

[0059] In other embodiments, the negative electrode may not include a negative electrode active material layer, but may only include a negative electrode current collector. In such a negative electrode, lithium ions that migrate from the positive electrode during charging and discharging are electrodeposited on the negative electrode current collector to form a lithium metal layer, and this lithium metal layer can be used as the negative electrode active material.

[0060] In one exemplary embodiment, the binder and conductive materials included in the negative electrode active material layer may be the same as those previously described for the positive electrode, and therefore further description thereof will be omitted. Furthermore, when the electrode for a lithium secondary battery of the above embodiment serves as the negative electrode, the negative electrode active material layer may also include the aforementioned oxide-based solid electrolyte with a lithium-ion source. In this case, the oxide-based solid electrolyte can satisfy the above-described D... 50 D 90 And the particle size distribution within the span range.

[0061] Another embodiment of the lithium secondary battery described above includes an electrolyte containing a lithium salt and a non-aqueous organic solvent. Such an electrolyte serves as a lithium-ion transfer medium between the positive and negative electrodes, wherein the lithium ions exist in a solvated state within the electrolyte, and can be inserted into the electrode active material through desolvation at the interface between the electrolyte and the electrodes. The secondary battery of another embodiment can accelerate this desolvation and exhibit even better output characteristics as described above.

[0062] The lithium salt contained in the electrolyte serves as a medium for transferring ions within the lithium secondary battery. For example, the lithium salt may contain Li. + It can be a cation and may contain anions selected from the following: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6- SbF6 - CH3SO3 - (CF3CF2SO2)2N - (CF3SO2)2N - (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - and SCN - For example, lithium salts may include at least one of the following: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2).

[0063] The concentration of lithium salts can be appropriately varied within the normal usable range and can be included in the electrolyte at a concentration of 0.5 M to 6 M or 1 M to 5 M.

[0064] In a more specific example, the electrolyte may contain lithium salt at a relatively low concentration of 0.5 M or greater but less than 2 M, or 0.7 M to 1.5 M. Even in such cases, lithium secondary batteries of other embodiments can exhibit improved output characteristics due to the accelerated desolvation of lithium ions caused by the action of the electrode in one embodiment described above. Therefore, not only can problems such as increased electrolyte viscosity, reduced fluidity, and decreased electrolyte ion conductivity and battery output at low temperatures caused by the use of electrolyte compositions containing high concentrations of lithium salts be solved, but also excellent low-temperature characteristics of lithium secondary batteries can be achieved.

[0065] On the other hand, by applying an electrode for lithium-ion batteries according to one embodiment, lithium-ion conductivity can be improved and resistance can be reduced even at low temperatures. This reduces the degradation of low-temperature output characteristics caused by high concentrations of lithium salts, etc.

[0066] Furthermore, there are no particular limitations on the types of non-aqueous organic solvents that can be included in the electrolyte, and any organic solvent known to be suitable for electrolytes of lithium-ion batteries can be used. Examples of such organic solvents include those selected from at least one of the following: carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents.

[0067] More specifically, carbonate-based solvents may include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butyl carbonate, fluoroethylene carbonate, methyl propyl carbonate, methyl ethyl carbonate, ethyl propyl carbonate, methyl (2,2,2-trifluoroethyl) carbonate, etc., and phosphate-based solvents may include trimethyl phosphate, triethyl phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphine 2-oxide, etc.

[0068] Furthermore, ether-based solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, or tetrahydrofuran derivatives such as 2-methyltetrahydrofuran, and nitrile-based solvents may include succinate, adiponitrile, sebaconitrile, acetonitrile, propionitrile, etc. Additionally, sulfone-based solvents may include dimethyl sulfone, ethylmethyl sulfone, sulfolane, etc.

[0069] In addition to lithium salts and non-aqueous organic solvents, the electrolyte may also contain a diluent that exhibits lithium salt solubility at least 10 times lower than that of lithium salts in non-aqueous organic solvents. Such a diluent is an organic solvent miscible with non-aqueous organic solvents but substantially insoluble in lithium salts. For example, it may be an ether-based solvent having fluorinated alkyl groups, and more specifically, it may include one or more of the following: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonfluorobutane (MOFB), and ethoxynonfluorobutane (EOFB).

[0070] When such a diluent is also included, locally high concentrations of lithium salt can exist in the non-aqueous organic solvent of the electrolyte, while lithium salt can be essentially absent in the diluent. Since the locally high concentration of lithium salt exists in the electrolyte in a solvated form in this way, the output characteristics of the lithium secondary battery can be further improved, and the increase in electrolyte viscosity and decrease in fluidity can also be reduced. Furthermore, if the electrode of one embodiment is used with this locally high concentration of salt electrolyte, lithium-ion conductivity can be improved and resistance can be reduced even at low temperatures, thereby reducing the degradation of low-temperature output characteristics caused by high concentrations of lithium salt.

[0071] The amount of diluent used can be adjusted according to the type of non-aqueous organic solvent and lithium salt, or the total concentration of lithium salt. For example, the diluent:non-aqueous organic solvent can be included in the electrolyte at a molar ratio of 1:0.2 to 1:5, or 1:0.5 to 1:2.

[0072] Meanwhile, the lithium secondary battery in some of the above embodiments may also include a porous separator membrane inserted between the positive and negative electrodes.

[0073] Such porous separators can be made from olefinic polymers (e.g., polyethylene and polypropylene), glass fibers, etc., in the form of sheets, multilayer membranes, microporous membranes, woven fabrics, and nonwoven fabrics, but are not necessarily limited to these. However, porous polyethylene or porous glass fiber nonwoven fabrics (glass filters) are preferred as separators, and porous polyethylene is even more preferred. The separator can be an insulating film with high ion permeability and mechanical strength, and the pore size of the separator is typically in the range of 0.01 μm to 10 μm, and the thickness is typically in the range of 5 μm to 300 μm, but is not limited to these.

[0074] Furthermore, in another embodiment of the lithium secondary battery, a separator membrane may not be inserted, but the electrolyte can be inserted between the positive and negative electrodes in the form of an electrolyte film or electrolyte membrane. In this case, the electrolyte film or electrolyte membrane may be in the form of a polymer matrix containing the aforementioned lithium salt and a non-aqueous organic solvent. Known polymer-based solid electrolytes can be used as the polymer matrix. In this case, other embodiments of the lithium secondary battery may be semi-solid batteries that combine liquid and solid electrolytes.

[0075] Meanwhile, another embodiment of the lithium secondary battery can be prepared according to conventional methods in the art. For example, the lithium secondary battery can be prepared by accommodating an electrode assembly including a positive electrode, a negative electrode, and a separator membrane (or electrolyte membrane) in a housing, and injecting and impregnating the aforementioned electrolyte into the housing.

[0076] Such lithium secondary batteries can be used not only as battery cells for powering small devices, but also as cell batteries in battery modules for powering medium and large devices.

[0077] Beneficial effects

[0078] The electrode for lithium secondary batteries disclosed herein comprises oxide-based solid electrolyte particles dispersed in an active material layer, wherein the oxide-based solid electrolyte particles may have a specific range of D0. 50 D 90 And the particle size distribution with span values. Such oxide-based solid electrolyte particles can be uniformly distributed around the electrode active material particles in the active material layer, and can be abundantly distributed near the interface between the active material layer and the electrolyte.

[0079] Such oxide-based solid electrolyte particles can reduce the activation energy associated with the desolvation process of lithium ions in the electrolyte at the interface where the electrode active material and the electrolyte come into contact with each other, and can accelerate the desolvation of lithium ions, thereby improving the output characteristics of lithium secondary batteries.

[0080] Furthermore, since the output characteristics of lithium secondary batteries can be improved even without the application of new electrolyte compositions such as those containing high concentrations of lithium salts, problems such as increased electrolyte viscosity, reduced fluidity, and decreased electrolyte ion conductivity and battery output caused by the application of new electrolyte compositions can be solved, and excellent low-temperature characteristics of lithium secondary batteries can be achieved.

[0081] Furthermore, even when using an electrolyte composition containing a high concentration of lithium salts, the electrode disclosed herein allows for smooth desolvation of lithium ions, thereby improving lithium-ion conductivity, reducing resistance, and enhancing efficiency and rate performance. Therefore, by using a high concentration of lithium salts, not only can the output characteristics of lithium-ion secondary batteries be further improved, but the degradation of low-temperature characteristics can also be reduced.

[0082] Therefore, this disclosure can greatly facilitate the development of next-generation lithium secondary batteries that exhibit improved output and low-temperature characteristics. Attached Figure Description

[0083] Figure 1 The illustrations schematically depict an active material with a non-uniform distribution of a conventional solid electrolyte without the application of a pre-dispersion of an oxide-based solid electrolyte and an active material with a uniform distribution of a solid electrolyte using a dispersion of a solid electrolyte according to one embodiment of the present disclosure.

[0084] Figure 2 The particle size distributions of the pre-dispersion of the oxide-based solid electrolyte according to Example 1 and the oxide-based solid electrolyte particle powders of Comparative Examples 2-2 are shown.

[0085] Figure 3 Cross-sectional SEM images of the positive electrode using the solid electrolyte distribution active material according to Comparative Example 2-2 and Example 2-2 are shown, along with mapping images of Ti and P elements obtained by EDS analysis. Furthermore, the sample variance values ​​of the particle size of the oxide-based solid electrolyte in the positive electrode are shown.

[0086] Figure 4 A graph showing a comparison of the results of measuring the resistance of each state of charge (SOC) of lithium secondary batteries using the positive electrodes of Comparative Example 1, Comparative Example 2-2, Comparative Example 2-3 and Example 2-2.

[0087] Figure 5 A graph is shown to illustrate the capacity ratio of lithium secondary batteries using the positive electrodes of Comparative Examples 1, 2-2, 2-3, and 2-2 at each C-rate of 0.2 C, 0.33 C, 0.5 C, 1 C, 2 C, and 3 C during three charge / discharge cycles, relative to the 0.2 C discharge capacity at each C-rate.

[0088] Figure 6 A graph comparing the voltage drop at each discharge time while discharging the lithium secondary batteries with the positive electrodes of Comparative Example 1 and Examples 2-2 from 50% state of charge (SOC) at -10°C for 30 seconds. Detailed Implementation

[0089] The embodiments of this disclosure will be described below so that those skilled in the art can readily implement them. However, this disclosure can be modified in a variety of ways and is not limited to the embodiments set forth herein.

[0090] Example 1: Preparation of solid electrolyte nanoparticle dispersion

[0091] 50 g of LiAl, an oxide-based solid electrolyte with an average primary particle size of 300 nm, was used. 0.3 Ti 1.7 (PO4)3 (LATP) and 50 g of NMP were mixed, and the mixture was added to the mixture using a bead mill. The mixture was then subjected to dispersion treatment for 40 minutes using a pointed mill to prepare a solid electrolyte nanoparticle dispersion.

[0092] Example 2-1: Manufacturing of Lithium Secondary Batteries

[0093] A lithium nickel cobalt manganese composite oxide (NCM 811; D50: 10 μm) containing 80 mol% nickel in all transition metals was used as the positive electrode active material, carbon nanotubes were used as the conductive material, and polyvinylidene fluoride (PVDF) was used as the binder.

[0094] A positive electrode active material slurry was prepared by mixing 96.5 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, 1.5 parts by weight of binder, and 0.5 parts by weight of oxide-based solid electrolyte (LATP) from Example 1. The prepared slurry was coated onto an aluminum current collector and dried to prepare the positive electrode. Graphite was used as the negative electrode active material, and the negative electrode active material: conductive material: binder was mixed in a weight ratio of 96.5:1.5:2 without using oxide-based solid electrolyte, and the same process as for the positive electrode was performed to manufacture the negative electrode.

[0095] The prepared positive and negative electrodes were positioned facing each other, a 15 μm thick polyethylene (PE) separator was inserted between them, and an electrolyte was filled to fabricate a bi-cell type lithium secondary battery. The electrolyte was prepared by dissolving LiFSI at a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixed volume ratio of 3 / 7).

[0096] Example 2-2: Manufacturing of Lithium Secondary Batteries

[0097] The lithium secondary battery was manufactured in the same manner as in Example 2-1, except that 96 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, 1.5 parts by weight of binder and 1 part by weight of oxide-based solid electrolyte (LATP) of Example 1 were mixed to prepare a positive electrode active material slurry.

[0098] Examples 2-3: Manufacturing of Lithium Secondary Batteries

[0099] The lithium secondary battery was manufactured in the same manner as in Example 2-1, except that 94 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, 1.5 parts by weight of binder and 3 parts by weight of oxide-based solid electrolyte (LATP) of Example 1 were mixed to prepare a positive electrode active material slurry.

[0100] Comparative Example 1: Manufacturing of Lithium-ion Secondary Batteries

[0101] A positive electrode active material slurry was prepared by mixing 97 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, and 1.5 parts by weight of binder. The prepared slurry was coated onto an aluminum current collector and dried to prepare the positive electrode. The positive electrode active material, conductive material, binder, and negative electrode were the same as those used in Examples 2-1.

[0102] The prepared positive and negative electrodes were positioned facing each other, a 20 μm thick polyethylene (PE) separator was inserted between them, and an electrolyte was filled to fabricate a bi-cell type lithium secondary battery. The electrolyte was prepared by dissolving LiFSI at a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixed volume ratio of 3 / 7).

[0103] Comparative Example 2-1: Manufacturing of Lithium-ion Secondary Batteries

[0104] The lithium secondary battery was manufactured in the same manner as in Example 2-1, except that 96.5 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, 1.5 parts by weight of binder, and 0.5 parts by weight of oxide-based solid electrolyte LiAl with an average primary particle size of 300 nm were used. 0.3 Ti 1.7 (PO4)3 (LATP) is mixed to prepare a slurry for positive electrode active material.

[0105] Comparative Example 2-2: Manufacturing of Lithium-ion Secondary Batteries

[0106] The lithium secondary battery was manufactured in the same manner as in Example 2-1, except that 96 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, 1.5 parts by weight of binder, and 1 part by weight of oxide-based solid electrolyte LiAl with an average primary particle size of 300 nm were used. 0.3 Ti 1.7 (PO4)3 (LATP) is mixed to prepare a slurry for positive electrode active material.

[0107] Comparative Examples 2-3: Manufacturing of Lithium-ion Secondary Batteries

[0108] The lithium secondary battery was manufactured in the same manner as in Example 2-1, except that 94 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, 1.5 parts by weight of binder, and 3 parts by weight of oxide-based solid electrolyte LiAl with an average primary particle size of 300 nm were used. 0.3 Ti 1.7 (PO4)3 (LATP) is mixed to prepare a slurry for positive electrode active material.

[0109] Comparative Examples 2-4: Manufacturing of Lithium-ion Secondary Batteries

[0110] The lithium secondary battery was manufactured in the same manner as in Example 2-1, except that 93 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, 1.5 parts by weight of binder, and 4 parts by weight of oxide-based solid electrolyte LiAl with an average primary particle size of 300 nm were used. 0.3 Ti 1.7 (PO4)3 (LATP) is mixed to prepare a slurry for positive electrode active material.

[0111] Experimental Example 1: Particle Size Analysis

[0112] The Z-mean particle size of the LATP dispersion of Example 1 was measured using a laser diffraction particle size analyzer (Malvern Mastersizer 3000). Specifically, 3 ml of the pre-dispersion of Example 1 was collected and diluted 1000-fold with NMP solvent to measure the particle size. Furthermore, the LATP particle powders of Comparative Examples 2-2 were diluted in the same manner to measure the particle size. The results are shown in Table 1 below. Figure 2 middle.

[0113] [Table 1]

[0114]

[0115] As a result, it was determined that the oxide-based solid electrolyte nanoparticle pre-dispersion of Example 1 had a relatively small average particle size of D50 and D90 compared to Comparative Example 2-2, which was an undispersed LATP sample, and was uniformly dispersed while the span value was significantly reduced to 1 or less. Furthermore, the sample variance value determined that the uniform dispersion, when mixed with the positive electrode active material, formed a uniform distribution of the oxide-based solid electrolyte nanoparticles in the positive electrode.

[0116] Experimental Example 2: Analysis of Nanoparticle Distribution in Electrodes Based on EDS

[0117] Based on the SEM and EDS analysis results of the positive electrode cross section, the distribution of oxide-based solid electrolyte (LATP) in the electrode was analyzed using the mapping images of Ti and P elements of oxide-based solid electrolyte LATP as a benchmark.

[0118] First, based on the pixel information of the EDS Ti and P element-mapped images, the data is converted and extracted into an Excel file format. The extracted data is divided into 1,150 grids (50×23) and set as samples, and the sample variances of Ti and P elements are calculated. The specific sample variances are obtained through the following mathematical equation 1.

[0119] [Mathematical Equation 1]

[0120]

[0121] Among them, s 2 Let y be the sample variance, and y be the variable. denoted as the sample mean, n as the sample size, SS as the sum of squared deviations, and df as the degrees of freedom.

[0122] As a result, Figure 3 The elemental images of Ti and P from the EDS analysis of Comparative Example 2-2 are shown, with a sample variance of 0.045. Furthermore, the elemental images of Ti and P from the EDS analysis of Example 2-2 are shown, with a sample variance of 0.034, confirming a relatively more uniform distribution of LATP within the cathode.

[0123] Experiment Example 3: Evaluation of Charge / Discharge Characteristics

[0124] For the lithium secondary batteries of Examples 2-2 and Comparative Examples 1, 2-2 and 2-3, the resistance of each state of charge (SOC) was measured while repeatedly performing charge / discharge tests at room temperature (about 25°C) under the following conditions: 1) charging from 0.2 C to 0.33 C (cutoff: 4.2 V, 0.05 C) and 2) discharging from 0.2 C to 0.33 C (cutoff: 2.5 V).

[0125] Specifically, the above charge / discharge tests were repeated at SOC settings of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, and 10%, and the DC resistance was measured after each charge / discharge (2.5 C discharge (cutoff: 10 seconds or 2 V)). Figure 4 The resistance measurement results for each state of charge are shown in the figure.

[0126] As a result, refer to Figure 4 It was determined that, compared with Comparative Example 1, Examples 2-2 exhibited lower resistance and higher ionic conductivity for each state of charge.

[0127] Experiment Example 4: Evaluation of C-rate characteristics

[0128] For the lithium secondary batteries of Examples 2-1, 2-2, and 2-3, and Comparative Examples 1, 2-1, 2-2, and 2-3, the capacity ratio at each C rate was measured while repeatedly performing charge / discharge tests at room temperature (approximately 25°C) under the following conditions: 1) 0.2 C charging (cutoff: 4.2 V, 0.05 C) and 2) 0.2 C, 0.33 C, 0.5 C, 1 C, 2 C, and 3 C discharging (cutoff: 2.5 V). The results are shown in Table 2 below. Figure 5 middle.

[0129] [Table 2]

[0130]

[0131] As shown in Table 2, the lithium secondary battery of Example 2-2, which uses a uniform oxide-based solid electrolyte LATP predispersant, was found to have superior characteristics in terms of resistance and C-rate efficiency compared to Comparative Example 2-2.

[0132] Experimental Example 5: Evaluation of Low-Temperature Properties

[0133] For the lithium secondary batteries of Examples 2-2 and Comparative Example 1, a discharge test was performed for 30 seconds starting from SOC 50% at a temperature of -10°C.

[0134] Specifically, firstly, the lithium secondary battery was charged at 25°C at 0.1 C to 0.33 C until it reached 50% SOC. Then, the lithium secondary battery with 50% SOC was stored in a -10°C room for 3 to 5 hours, and the temperature of the lithium secondary battery was cooled to -10°C. Next, it was discharged at 1 C for 30 seconds or until a 2.5 V cutoff was achieved, while simultaneously measuring the voltage drop at each discharge time.

[0135] Then, after charging again at -10°C and 0.1 C, the discharge test was repeated while changing the discharge rate from 1 C to 2 C, 3 C, 3.5 C, and 4.5 C. Through this process, the voltage drop at each discharge rate for 30 seconds was measured and displayed. Figure 6 b in.

[0136] Reference Figure 6 It was determined that at a low temperature of -10°C, compared with Comparative Example 1, Example 2-2 exhibited a lower voltage drop in the early stage of discharge and showed superior output characteristics.

Claims

1. An electrode for a lithium secondary battery, comprising: Metal current collector; and An active material layer is formed on the metal current collector and includes an electrode active material, a conductive material, and an oxide-based solid electrolyte having a lithium-ion source. The electrode active material and the oxide-based solid electrolyte are dispersed in the active material layer in the form of particles and have a particle size distribution with a span of 1 or less.

2. The electrode for a lithium secondary battery according to claim 1, wherein: The electrode active material comprises a lithium metal oxide, wherein the lithium metal oxide contains lithium and two or more metals selected from nickel, manganese, cobalt, and aluminum. Based on the total metal content excluding lithium, the lithium metal oxide contains 60 mol% or more nickel.

3. The electrode for a lithium secondary battery according to claim 1, wherein: The oxide-based solid electrolyte includes at least one lithium metal oxide or lithium metal phosphate selected from the following: Nasicon type solid electrolyte, Lisicon type solid electrolyte, garnet type solid electrolyte, perovskite type solid electrolyte and LiPON type solid electrolyte.

4. The electrode for a lithium secondary battery according to claim 1, wherein: The oxide-based solid electrolyte includes at least one of the following: LAGP (lithium aluminum germanium phosphate), LLZO (lithium lanthanum zirconium oxide), LATP (lithium aluminum titanium phosphate), LLZTO (lithium lanthanum zirconium tantalum oxide), LLTO (lithium lanthanum titanium oxide), LSTP (lithium silicon titanium phosphate), and LGPO (lithium germanium phosphate).

5. The electrode for a lithium secondary battery according to claim 1, wherein: The oxide-based solid electrolyte has one or more particle size distributions, including D50 of 100 nm to 1 μm and D90 of 400 nm to 1.5 μm.

6. The electrode for a lithium secondary battery according to claim 1, wherein: The oxide-based solid electrolyte has a particle size distribution with a D50 of 300 nm to 700 nm and a D90 of 400 nm to 900 nm.

7. The electrode for a lithium secondary battery according to claim 1, wherein: The sample variance of the oxide-based solid electrolyte, as expressed by EDS analysis in the following mathematical equation 1, is 0.04 or less. [Mathematical Equation 1] Among them, s 2 Let y be the sample variance, and y be the variable. denoted as the sample mean, n as the sample size, SS as the sum of squared deviations, and df as the degrees of freedom.

8. The electrode for a lithium secondary battery according to claim 1, wherein: Based on 100 parts by weight of the electrode active material, the oxide-based solid electrolyte is included in an amount of 0.3 to 5 parts by weight.

9. The electrode for a lithium secondary battery according to claim 1, wherein: The conductive material includes carbon nanotubes or carbon nanofibers, and the active material layer also includes a binder.

10. A lithium secondary battery, comprising: Positive electrode; negative electrode; and electrolyte containing lithium salt and non-aqueous organic solvent. The lithium secondary battery electrode according to any one of claims 1 to 9 is included as the positive electrode.

11. The lithium secondary battery according to claim 10, wherein: The lithium salt includes at least one of the following: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2 and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2).

12. The lithium secondary battery according to claim 10, wherein: The lithium salt is contained in the electrolyte at a concentration of 0.5 M to 6 M.

13. The lithium secondary battery according to claim 10, wherein: The lithium secondary battery also includes a separator membrane inserted between the positive electrode and the negative electrode, or The electrolyte has the form of an electrolyte film or electrolyte membrane containing the lithium salt and the non-aqueous organic solvent in a polymer matrix, which is inserted between the positive electrode and the negative electrode.

14. A method for manufacturing an electrode for a lithium secondary battery according to any one of claims 1 to 9, the method comprising the following steps: An oxide-based solid electrolyte and a solvent are mixed and dispersed to prepare a solid electrolyte dispersion; The solid electrolyte dispersion, electrode active material, and conductive material are mixed to prepare an electrode active material slurry; and The electrode active material slurry is applied to the electrode current collector.

15. The method for manufacturing an electrode for a lithium secondary battery according to claim 14, wherein: The step of preparing the solid electrolyte dispersion was performed using a bead milling method.

Images