Electrode for lithium secondary battery and lithium secondary battery

Abstract

The present invention relates to an electrode for a lithium secondary battery capable of improving output characteristics and low-temperature characteristics of the lithium secondary battery, and a lithium secondary battery comprising same. The electrode for a lithium secondary battery comprises: a metal current collector; and an active material layer formed on the metal current collector and containing 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 may be dispersed in a particle form within the active material layer, with a particle size distribution having a span of 1 or less.

Description

Electrodes for lithium secondary batteries and lithium secondary batteries

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0113515, filed August 29, 2023, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery including the same, which can improve the output characteristics and low-temperature characteristics of a lithium secondary battery.

[0004] Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computer devices, but also power storage for large-area devices such as automobiles and power storage devices, the demand for lithium secondary batteries with high capacity, high output, long life, and high stability is increasing.

[0005] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte including a lithium salt and an organic solvent, and lithium ions move through the electrolyte during the charging and discharging process.

[0006] Within the electrolyte, lithium ions exist in a solvated state, surrounded by an organic solvent. Therefore, for the lithium ions within the electrolyte to migrate and be inserted into the electrode active material, they must undergo a desolvation process, in which the lithium ions are separated or desorbed from the organic solvent molecules. Therefore, the smooth progress of this desolvation process can affect the output, resistance, or stability of the lithium secondary battery.

[0007] Meanwhile, with the recent demand for higher capacity and higher output in lithium secondary batteries, the development of novel electrolytes is actively underway. In particular, novel electrolyte compositions have been proposed, such as those that include high concentrations of lithium salts or that change the composition of the organic solvent to form localized, high-concentration regions of lithium salts around the electrode, to accelerate the desolvation of lithium ions and thereby increase the output of lithium secondary batteries.

[0008] However, when applying the above novel electrolyte composition including a high concentration of lithium salt, there is a disadvantage in that the problem of reduced fluidity due to increased viscosity of the electrolyte may occur, and in particular, the ion conductivity of the electrolyte may decrease at low temperatures, resulting in increased resistance or reduced battery output, thereby deteriorating the low-temperature characteristics of the lithium secondary battery.

[0009] Accordingly, there is a continuous demand for the development of technology that can improve the output characteristics of lithium secondary batteries by accelerating the desolvation of lithium ions within the electrolyte while maintaining excellent low-temperature characteristics.

[0010] Accordingly, the present invention provides an electrode for a lithium secondary battery that can improve the output characteristics of a lithium secondary battery by accelerating the desolvation of lithium ions in an electrolyte, while maintaining excellent low-temperature characteristics such as high output at low temperatures.

[0011] The present invention also provides a lithium secondary battery including the electrode, which exhibits improved output characteristics and low-temperature characteristics.

[0012] Hereinafter, an electrolyte composition for a lithium metal battery according to a specific embodiment of the invention will be described.

[0013] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0014] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0015] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0016]

[0017] Electrodes for lithium secondary batteries

[0018] According to one embodiment of the present invention, 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 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 of span 1 or less.

[0019] In particular, the oxide-based solid electrolyte can have a uniform particle size distribution of span 1 or less. As a result of the experiments of the inventors of the present invention, since oxide-based solid electrolyte particles satisfying a specific particle size distribution are included in the active material layer, these oxide-based solid electrolyte particles can be uniformly distributed around the electrode active material particles within the active material layer (Fig. 2), and in particular, can be distributed in large numbers near the interface between the active material layer and the electrolyte. This can be distinguished from the conventional active material layer in which oxide-based solid electrolyte particles aggregate with each other and are not evenly distributed (Fig. 1). Accordingly, the oxide-based solid electrolyte particles can accelerate the desolvation process of lithium ions within the electrolyte by reducing the activation energy involved in the desolvation process of lithium ions at the interface where the active material layer and the electrolyte come into contact. In addition, this can improve lithium ion conductivity around the electrode active material particles.

[0020] Therefore, a lithium secondary battery including an electrode for a lithium secondary battery according to one embodiment of the present invention can accelerate the desolvation of lithium ions and improve the lithium ion conductivity of an active material layer, thereby lowering the resistance of the lithium secondary battery and improving the output characteristics, even without applying an electrolyte composition including a high-concentration lithium salt, etc. As a result, problems such as increased electrolyte viscosity, decreased fluidity, and decreased ion conductivity of the electrolyte and output of the battery at low temperatures due to the application of the high-concentration lithium salt, etc., can be solved, and excellent low-temperature characteristics of the lithium secondary battery can be achieved at the same time.

[0021] Meanwhile, in the embodiments of the present invention, the description focuses on an embodiment in which the electrode for the lithium secondary battery is used as a positive electrode, but the scope of the invention is not limited thereto, and the electrode according to one embodiment may be used as a negative electrode.

[0022] In an exemplary embodiment, the positive electrode for the lithium secondary battery may include a metal current collector. The metal current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0023] Additionally, the active material layer on the metal current collector may include an oxide-based solid electrolyte having a positive electrode active material, a conductive material, and a lithium ion source, and may optionally further include a binder.

[0024] At this time, the positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium metal oxide containing lithium and one or more metals such as iron, cobalt, manganese, nickel, or aluminum.

[0025] Specifically, the lithium metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Coq Mn r )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2) etc.), lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, 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 any one or two or more compounds thereof may be included.

[0026] Among these, the positive electrode active material includes a lithium metal oxide including lithium and two or more metals selected from the group consisting of nickel, manganese, cobalt, and aluminum, and the lithium metal oxide may include nickel in an amount of 60 mol% or more, or 60 to 99 mol%, or 70 to 95 mol%, based on the total metal content excluding lithium. Such a lithium metal oxide may be represented by, for example, the following chemical formula 1:

[0027] [Chemical Formula 1]

[0028] Li x Ni a Cob M 1 c M 2 d O2

[0029] In the above chemical formula 1, the M 1 Mn and Al may be one or more selected from or a combination thereof, and M 2 may be at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and may be 0.90≤x≤1.1, or 0.95≤x≤1.08, or 1.0≤x≤1.08, and may be 0.60≤a<1.0, or 0.70≤a≤0.99, or 0.80≤a≤0.95.

[0030] By using lithium metal oxide containing such a high nickel content as a cathode active material and combining it with an oxide-based solid electrolyte, the output and capacity characteristics of a lithium secondary battery can be further improved.

[0031] The above-described positive electrode active material may be included in an amount of 60 to 99 wt%, or 70 to 99 wt%, or 80 to 98 wt% based on the total weight of the active material layer.

[0032] In an exemplary embodiment, the oxide-based solid electrolyte may be any solid electrolyte having a lithium ion source including lithium in its structure and having the form of a lithium metal oxide or lithium metal phosphate.

[0033] Specific examples thereof include at least one lithium metal oxide or lithium metal phosphate selected from a Nasicon-type solid electrolyte, a Lisicon-type solid electrolyte, a Garnet-type solid electrolyte, a Perovskite-type solid electrolyte, and a LiPON-type solid electrolyte, and more specific examples thereof include at least one selected from the group consisting of a LAGP (lithium aluminum germanium phosphate) compound, an LLZO (lithium lanthanum zirconium oxide) compound, a LATP (lithium aluminum titanium phosphate) compound, an LLZTO (lithium lanthanum zirconium tantalum oxide) compound, an LLTO (lithium lanthanum titanium oxide) compound, a LSTP (lithium silicon titanium phosphate) compound, and a LGPO (lithium germanium phosphate) compound.

[0034] Among these, a NASICON-type solid electrolyte such as the LAGP-type compound or LATP-type compound can be appropriately used in terms 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 a lithium secondary battery.

[0035] In an exemplary embodiment, the oxide-based solid electrolyte may have a particle size distribution of at least one of D50 of 100 nm to 1 μm and D90 of 400 nm to 1.5 μm. For example, the oxide-based solid electrolyte may have a particle size distribution of D50 of 300 to 700 nm and / or D90 of 400 to 900 nm. When the oxide-based solid electrolyte particles are uniformly distributed within the above ranges, excellent output characteristics and low-temperature characteristics may be achieved.

[0036] In an exemplary embodiment, the oxide-based solid electrolyte may have a sample dispersion of 0.04 or less, as expressed by the following mathematical formula 1, as determined through EDS analysis.

[0037] [Mathematical Formula 1]

[0038]

[0039] Here, S 2 is the sample variance, y is the variable, is the sample mean, n is the sample size, SS is the sum of squared deviations, and df is the degrees of freedom.

[0040] For example, the sample dispersion may be 0.04 or less, or 0.03 or less, and if the sample dispersion exceeds 0.04, uniform dispersion of the oxide-based solid electrolyte may not be ensured, and thus output characteristics and low-temperature characteristics may not be ensured.

[0041] Specifically, the sample variance can be calculated by extracting pixel information of an EDS Ti and / or P element mapping image, dividing it into n uniform grids, and setting each of them as a sample using the above mathematical formula 1. The sample variance value represents the distribution of the dispersion of Ti and P between each grid, and a smaller sample variance value means that the Ti and P elements are distributed uniformly throughout the entire grid. Therefore, a smaller sample variance value indicates that the oxide-based solid electrolyte (LATP) within the anode is distributed more uniformly.

[0042] In an exemplary embodiment, 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, in order to accelerate the desolvation of lithium ions at the interface between the active material layer and the electrolyte and improve lithium ion conductivity without inhibiting the insertion and desorption process of lithium ions by the positive electrode active material, and for example, 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.

[0043] In an exemplary embodiment, the conductive material included in the active material layer is a component for further improving the conductivity of the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used. Among these, the conductive material can further lower the resistance of a lithium secondary battery including the positive electrode of one embodiment and improve output characteristics, etc. by including a conductive nanomaterial such as carbon nanotubes or carbon nanofibers.

[0044] Typically, the conductive material may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the active material layer.

[0045] The binder optionally included in the above active material layer is a component that assists in the bonding of the positive electrode active material and the conductive material, and the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0046] Typically, the binder may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0047] Additionally, a filler may be optionally added to the positive electrode as a component that suppresses its expansion. Such filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes in the battery. Examples of fillers that can be used include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0048] A method for manufacturing an electrode for a lithium secondary battery as described above is provided, comprising: a step of preparing a solid electrolyte dispersion by mixing and dispersing an oxide-based solid electrolyte and a solvent; a step of preparing an electrode active material slurry by mixing the solid electrolyte dispersion, an electrode active material, and a conductive material; and a step of applying the electrode active material slurry to an electrode current collector.

[0049] In an exemplary embodiment, the solid electrolyte dispersion preparation step may be performed using a bead-milling method. By pre-dispersing the oxide-based solid electrolyte and the solvent prior to preparing the electrode active material slurry, the oxide-based solid electrolyte particles can be uniformly distributed around the electrode active material particles within the active material layer.

[0050] Meanwhile, a positive electrode for a lithium secondary battery according to an exemplary embodiment can be manufactured by, for example, mixing and dispersing the positive electrode active material, oxide-based solid electrolyte, binder, and conductive agent in a dispersion medium (solvent) to make a slurry, applying the slurry on a metal current collector, and then drying and rolling. At this time, the dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.

[0051]

[0052] lithium secondary battery

[0053] In another embodiment according to the present invention, a lithium secondary battery is provided, which comprises a positive electrode; a negative electrode; and an electrolyte including a lithium salt and a non-aqueous organic solvent, and which comprises the aforementioned electrode for a lithium secondary battery as a positive electrode. The lithium secondary battery according to another embodiment of the present invention can exhibit low-temperature characteristics along with excellent output characteristics by including the electrode (e.g., positive electrode) according to one embodiment described above.

[0054] In the lithium secondary battery of these other embodiments, the negative electrode may have a conventional configuration known in the art. For example, the negative electrode may include an negative electrode current collector and an negative electrode active material layer formed on the negative electrode current collector, and the negative electrode active material layer may include, for example, an negative electrode active material and, if necessary, additives such as a conductive material, a binder, and a filler. In addition, the negative electrode may be formed by a conventional method of dispersing and mixing each component of the negative electrode active material layer in a dispersion medium (solvent) to make a slurry, applying the slurry on the negative electrode current collector, and then drying and rolling the slurry.

[0055] At this time, the negative electrode current collector may be, but is not limited to, 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), and alloys thereof, as well as copper (Cu) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The negative electrode current collector may have a form such as a foil, a film, a sheet, a punched form, a porous body, or a foam.

[0056] In addition, a compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metallic oxides capable of doping and dedoping lithium such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may also be used as the negative electrode active material.

[0057] In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0058] The above-described negative electrode active material may be included in an amount of 60 to 99 wt%, or 70 to 99 wt%, or 80 to 98 wt% based on the total weight of the negative electrode active material layer.

[0059] In another embodiment, 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 moved from the positive electrode during the charge and discharge process may be deposited on the negative electrode current collector to form a lithium metal layer, and this lithium metal layer may function as a negative electrode active material.

[0060] In an exemplary embodiment, the binder and conductive material included in the negative electrode active material layer may be the same as those described above for the positive electrode, so further description thereof will be omitted. In addition, when the lithium secondary battery electrode of the embodiment already described above becomes the negative electrode, the negative electrode active material layer may further include an oxide-based solid electrolyte having the lithium ion source already described above, and in this case, the oxide-based solid electrolyte is the D described above. 50 , D 90, and can satisfy the particle size distribution of the span value range.

[0061] The lithium secondary battery of another embodiment described above comprises an electrolyte comprising a lithium salt and a non-aqueous organic solvent. This electrolyte acts as a transport medium for lithium ions between the positive and negative electrodes. These lithium ions exist in the electrolyte in a solvated state, while at the interface between the electrolyte and the electrode, they can be desolvated and inserted into the electrode active material. As described above, in the secondary battery of another embodiment, this desolvation is accelerated, thereby exhibiting improved output characteristics, etc.

[0062] The lithium salt included in the above electrolyte is used as a medium for transferring ions within a lithium secondary battery. The lithium salt is, for example, Li as a cation. + Including, 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 - It may contain an anion selected from the group consisting of. For example, the lithium salt may be 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 the above lithium salt can be appropriately changed within a commonly usable range, and can be included in the electrolyte at a concentration of 0.5 M to 6 M, or a concentration of 1 M to 5 M.

[0064] In a more specific embodiment, the electrolyte may include a lithium salt in a relatively low concentration of 0.5 M or more and less than 2 M, or 0.7 M to 1.5 M. Even in this case, since the desolvation of lithium ions is accelerated by the action of the electrode of the above-described embodiment, the lithium secondary battery of another embodiment may exhibit improved output characteristics. As a result, problems such as increased electrolyte viscosity, decreased fluidity, and decreased ion conductivity of the electrolyte and battery output at low temperatures due to the application of an electrolyte composition including a high concentration of lithium salt can be solved, and excellent low-temperature characteristics of the lithium secondary battery can be achieved at the same time.

[0065] Meanwhile, by applying a lithium-ion battery electrode according to one embodiment, lithium ion conductivity can be improved and resistance can be reduced even at low temperatures. This can reduce the deterioration of low-temperature output characteristics due to high-concentration lithium salts, etc.

[0066] Meanwhile, the type of non-aqueous organic solvent that can be included in the electrolyte is not particularly limited, and any organic solvent previously known to be applicable to electrolytes of lithium ion batteries, etc., can be used. Examples of such organic solvents include at least one selected from the group consisting of carbonate solvents, ether solvents, nitrile solvents, phosphate solvents, and sulfone solvents.

[0067] More specifically, as the carbonate solvent, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate or methyl (2,2,2-trifluoroethyl) carbonate can be used, and as the phosphate solvent, trimethyl phosphate, triethyl phosphate or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide can be used.

[0068] In addition, as the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxy ethane, or tetrahydrofuran derivatives such as 2-methyl tetrahydrofuran can be used, and as the nitrile solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. In addition, as the sulfone solvent, dimethyl sulfone, ethylmethyl sulfone, or sulforane can be used.

[0069] Meanwhile, the electrolyte may further include, in addition to the lithium salt and the non-aqueous organic solvent described above, a diluent that exhibits a solubility in the lithium salt that is at least 10 times lower than that of the non-aqueous organic solvent. The diluent may be an organic solvent that is miscible with the non-aqueous organic solvent while exhibiting substantially no solubility in the lithium salt, for example, an ether solvent having a fluorine-substituted alkyl group, and more specifically, may include at least one selected from the group consisting of 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), methoxynonafluorobutane (MOFB), and ethoxynonafluorobutane (EOFB).

[0070] When such a diluent is further included, a high-concentration lithium salt may be locally present in the non-aqueous organic solvent within the electrolyte, and substantially no lithium salt may be present within the diluent. In this way, since a high-concentration lithium salt is locally present in a solvated form within the electrolyte, the output characteristics of the lithium secondary battery can be further improved, while the increase in viscosity and decrease in fluidity of the electrolyte can be reduced. In addition, when the electrode of one embodiment is applied together with such a high-concentration salt electrolyte, lithium ion conductivity can be improved and resistance can be reduced even at low temperatures, thereby reducing the deterioration of low-temperature output characteristics due to high-concentration lithium salt, etc.

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

[0072] Meanwhile, the lithium secondary battery of another embodiment described above may further include a porous separator interposed between the positive electrode and the negative electrode.

[0073] These porous membranes can be made of olefin polymers such as polyethylene and polypropylene, glass fibers, etc. in the form of sheets, multi-membranes, microporous films, woven fabrics, and non-woven fabrics, but are not necessarily limited thereto. However, it may be preferable to use porous polyethylene or porous glass fiber non-woven fabric (glass filter) as the membrane, and it may be more preferable to use porous polyethylene as the membrane. The membrane may be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the membrane may generally be in the range of 0.01 to 10 ㎛, and the thickness may generally be in the range of 5 to 300 ㎛, but is not limited thereto.

[0074] In addition, in another example of the lithium secondary battery, the separator may not be interposed, and the electrolyte described above may be interposed between the positive and negative electrodes in the form of an electrolyte membrane or electrolyte film. In this case, the electrolyte membrane or electrolyte film may be in the form of a polymer matrix containing the lithium salt and a non-aqueous organic solvent described above, and a well-known polymer-based solid electrolyte or the like may be used as the polymer matrix. In this case, the lithium secondary battery of the other embodiment may be a semi-solid battery that uses a liquid electrolyte and a solid electrolyte in combination.

[0075] Meanwhile, the lithium secondary battery of the above-described other embodiment can be manufactured according to a conventional method in the art. For example, the electrode assembly including the positive electrode, negative electrode, and separator (or electrolyte membrane) can be manufactured by housing it in a case and injecting and impregnating the electrolyte described above.

[0076] These lithium secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit cells in battery modules that serve as power sources for medium- to large-sized devices.

[0077] The electrode for a lithium secondary battery of the present invention comprises oxide-based solid electrolyte particles dispersed within an active material layer, and these oxide-based solid electrolyte particles have a specific range of D 50 , D 90 And may have a particle size distribution having a span value. These oxide-based solid electrolyte particles may be uniformly distributed around the electrode active material particles within the active material layer, and may be distributed in large numbers near the interface between the active material layer and the electrolyte.

[0078] These oxide-based solid electrolyte particles can reduce the activation energy involved in the desolvation process of lithium ions in the electrolyte at the interface where the active material layer and the electrolyte come into contact, and can accelerate the desolvation of lithium ions, thereby improving the output characteristics of a lithium secondary battery.

[0079] Furthermore, since the output characteristics of a lithium secondary battery can be improved without applying a new electrolyte composition including a high concentration of lithium salt, problems such as increased electrolyte viscosity, decreased fluidity, and decreased ion conductivity of the electrolyte and output of the battery at low temperatures due to the application of the new electrolyte composition can be solved, and excellent low-temperature characteristics of a lithium secondary battery can be achieved.

[0080] In addition, even when applying an electrolyte composition including the high-concentration lithium salt, etc., the electrode application of the present invention can facilitate the desolvation of lithium ions, thereby improving lithium ion conductivity, reducing resistance, and enhancing efficiency and rate characteristics. Accordingly, the output characteristics of a lithium secondary battery can be further improved by using the high-concentration lithium salt, etc., while reducing the deterioration of low-temperature characteristics.

[0081] Accordingly, the present invention can greatly contribute to the development of next-generation lithium secondary batteries exhibiting improved output characteristics and low-temperature characteristics.

[0082] Figure 1 schematically illustrates a conventional solid electrolyte non-uniform distribution active material to which the pre-dispersion of an oxide-based solid electrolyte is not applied and a solid electrolyte uniform distribution active material to which the solid electrolyte dispersion according to an embodiment of the present invention is applied.

[0083] Figure 2 shows the particle size distribution of the pre-dispersed oxide-based solid electrolyte according to Example 1 and the oxide-based solid electrolyte particle powder of Comparative Example 2-2.

[0084] Figure 3 shows a cross-sectional SEM image of a positive electrode with a solid electrolyte distribution active material applied according to Comparative Example 2-2 and Example 2-2, and an EDS-analyzed Ti and P element mapping image. In addition, it shows the particle size distribution value of the oxide-based solid electrolyte in the positive electrode.

[0085] Figure 4 is a graph comparing the results of resistance measurements by state of charge (SOC) for lithium secondary batteries using the positive electrodes of Comparative Example 1, Comparative Example 2-2, Comparative Example 2-3, and Example 2-2.

[0086] Figure 5 is a graph showing the capacity ratio at each C-rate compared to the 0.2C discharge capacity by performing charge and discharge three times at each C-rate of 0.2C, 0.33C, 0.5C, 1C, 2C, and 3C for 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 6 is a graph comparing the degree of voltage drop according to the discharge time while discharging from a state of charge (SOC) of 50% at -10°C for 30 seconds for a lithium secondary battery using the positive electrodes of Comparative Example 1 and Example 2-2.

[0088] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0089]

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

[0091] LiAl with an average primary particle size of 300 nm 0.3 Ti 1.750 g of (PO4)3 oxide-based solid electrolyte (LATP) and 50 g of NMP were mixed, a bead mill was added to the mixture, and dispersion treatment was performed for 40 minutes using a spike mill to prepare a solid electrolyte nanoparticle dispersion.

[0092]

[0093] Example 2-1: Manufacturing of lithium secondary batteries

[0094] As the cathode active material, lithium nickel cobalt manganese composite oxide (NCM 811; D50: 10㎛) containing 80 mol% of nickel among the total transition metals was used, carbon nanotubes were used as the conductive material, and polyvinylidene fluoride (PVDF) was used as the binder.

[0095] A slurry of positive electrode active material was prepared by mixing 96.5 parts by weight of positive electrode active material, 1.5 parts by weight of conductive agent, 1.5 parts by weight of binder, and 0.5 parts by weight of the oxide-based solid electrolyte (LATP) of Example 1. The prepared slurry was coated on an aluminum current collector and dried to prepare a positive electrode. Graphite was used as the negative electrode active material, and the negative electrode active material: conductive agent: binder was mixed in a weight ratio of 96.5:1.5:2 without using the oxide-based solid electrolyte, and the same process as for the positive electrode was performed to prepare the negative electrode.

[0096] The prepared positive and negative electrodes were positioned so that they face each other, a 15 μm thick polyethylene (PE) separator was interposed between them, and an electrolyte was filled to manufacture a bi-cell type lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M LiFSI in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixing volume ratio of 3 / 7).

[0097]

[0098] Example 2-2: Manufacturing of lithium secondary batteries

[0099] A lithium secondary battery was manufactured in the same manner as in Example 2-1, except that a positive electrode active material slurry was manufactured by mixing 96 parts by weight of a positive electrode active material, 1.5 parts by weight of a conductive material, 1.5 parts by weight of a binder, and 1 part by weight of an oxide-based solid electrolyte (LATP) of Example 1.

[0100]

[0101] Example 2-3: Manufacturing of lithium secondary batteries

[0102] A lithium secondary battery was manufactured in the same manner as in Example 2-1, except that a positive electrode active material slurry was manufactured by mixing 94 parts by weight of a positive electrode active material, 1.5 parts by weight of a conductive material, 1.5 parts by weight of a binder, and 3 parts by weight of an oxide-based solid electrolyte (LATP) of Example 1.

[0103]

[0104] Comparative Example 1: Manufacturing of Lithium Secondary Battery

[0105] A slurry of positive electrode active material was prepared by mixing 97 parts by weight of positive electrode active material, 1.5 parts by weight of conductive agent, and 1.5 parts by weight of binder. The prepared slurry was coated on an aluminum current collector and dried to prepare a positive electrode. The positive electrode active material, conductive agent, binder, and negative electrode were the same as those used in Example 2-1.

[0106] The prepared positive and negative electrodes were positioned so that they face each other, a 20 μm thick polyethylene (PE) separator was interposed between them, and an electrolyte was filled to manufacture a bi-cell type lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M LiFSI in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixing volume ratio of 3 / 7).

[0107]

[0108] Comparative Example 2-1: Manufacturing of Lithium Secondary Battery

[0109] 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 LiAl having an average primary particle size of 300 nm0.3 Ti 1.7 A lithium secondary battery was manufactured in the same manner as in Example 2-1, except that a positive electrode active material slurry was manufactured by mixing 0.5 parts by weight of a (PO4)3 oxide-based solid electrolyte (LATP).

[0110]

[0111] Comparative Example 2-2: Manufacturing of Lithium Secondary Battery

[0112] 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 LiAl having an average primary particle size of 300 nm 0.3 Ti 1.7 A lithium secondary battery was manufactured in the same manner as in Example 2-1, except that a positive electrode active material slurry was manufactured by mixing 1 part by weight of a (PO4)3 oxide-based solid electrolyte (LATP).

[0113]

[0114] Comparative Example 2-3: Manufacturing of Lithium Secondary Battery

[0115] 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 LiAl having an average primary particle size of 300 nm 0.3 Ti 1.7 A lithium secondary battery was manufactured in the same manner as in Example 2-1, except that a positive electrode active material slurry was manufactured by mixing 3 parts by weight of a (PO4)3 oxide-based solid electrolyte (LATP).

[0116]

[0117] Comparative Example 2-4: Manufacturing of Lithium Secondary Battery

[0118] 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 LiAl having an average primary particle size of 300 nm 0.3 Ti 1.7 A lithium secondary battery was manufactured in the same manner as in Example 2-1, except that a positive electrode active material slurry was manufactured by mixing 4 parts by weight of a (PO4)3 oxide-based solid electrolyte (LATP).

[0119]

[0120] Experimental Example 1: Particle Size Analysis

[0121] The Z-average particle size of LATP in the dispersion of Example 1 was measured using a laser diffraction particle size measuring device (Malvern Mastersizer 3000). Specifically, 3 ml of the pre-dispersed solution of Example 1 was collected, diluted 1000-fold with NMP solvent, and the particle size was measured. In addition, the LATP particle powder of Comparative Example 2-2 was diluted in the same manner and the particle size was measured. The results are shown in Table 1 and Fig. 2 below.

[0122] Sample Dx(10)(㎛) Dx(50)(㎛) Dx(90)(㎛) span Comparative Example 2-2 (LATP undispersed) 0.30 2 0.5 1 2 3.3 5 76 6 Example 1 (LATP dispersed) 0.23 4 0.34 5 0.49 5 0.757

[0123] As a result, it was confirmed that, compared to Comparative Example 2-2, which is a LATP undispersed sample, Example 1 had a relatively small average particle size in terms of D50 and D90 of the oxide-based solid electrolyte nanoparticle pre-dispersion, and was uniformly dispersed with a significantly reduced span value of less than 1. In addition, it was confirmed by the sample dispersion value that a uniform distribution of oxide-based solid electrolyte nanoparticles in the positive electrode was formed by mixing this uniform dispersion with the positive electrode active material.

[0124]

[0125] Experimental Example 2: EDS-based analysis of nanoparticle distribution within an electrode

[0126] Based on the mapping images of Ti and P elements of the oxide-based solid electrolyte LATP among the SEM and EDS analysis results of the anode cross-section, the distribution of the oxide-based solid electrolyte (LATP) within the electrode was analyzed.

[0127] First, based on the pixel information of the EDS Ti, P element mapping image, it was converted into an Excel file and extracted. The extracted data was divided into 1150 grids (50 X 23) and set as samples, and the sample variance of Ti and P elements was calculated. The specific sample variance was obtained using the following mathematical equation 1.

[0128] [Mathematical Formula 1]

[0129]

[0130] Here, S2 is the sample variance, y is the variable, is the sample mean, n is the sample size, SS is the sum of squared deviations, and df is the degrees of freedom.

[0131] As a result, Fig. 3 shows the Ti and P element images from the EDS analysis of Comparative Example 2-2, and the sample dispersion at this time was 0.045. In addition, the Ti and P element images from the EDS analysis of Example 2-2 are shown, and the sample dispersion at this time was 0.034, confirming that LATP is relatively more uniformly distributed within the anode.

[0132]

[0133] Experimental Example 3: Evaluation of Charge-Discharge Characteristics

[0134] For the lithium secondary batteries of Example 2-2 and Comparative Examples 1, 2-2, and 2-3, charge and discharge tests were repeatedly performed at room temperature (approximately 25°C) under the conditions of 1) 0.2C - 0.33C charge (cut-off: 4.2V, 0.05C) and 2) 0.2C - 0.33C discharge (cut-off: 2.5V), and resistance was measured according to the state of charge (SOC).

[0135] Specifically, the above charge-discharge test was repeatedly performed under SOC settings of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, and 10%, and the DC resistance was measured (2.5C discharge (cut-off: 10 s or 2 V)) after each charge-discharge. The resistance measurement results for each charge state are shown in Fig. 4.

[0136] As a result, referring to FIG. 4, it was confirmed that Example 2-2 exhibited lower resistance and higher ionic conductivity according to the state of charge compared to Comparative Example 1.

[0137]

[0138] Experimental Example 4: Evaluation of C-rate Characteristics

[0139] 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, experiments were repeated three times at each C-rate at room temperature (approximately 25°C) under the conditions of 1) 0.2C charge (cut-off: 4.2 V, 0.05 C) and 2) 0.2C, 0.33C, 0.5C, 1C, 2C, and 3C (cut-off: 2.5 V), and the capacity ratio at each C-rate was measured. The results are shown in Table 2 and Fig. 5 below.

[0140] Active material (parts by weight) LATP (parts by weight) LATP Line dispersion DC-IR@SOC 50% (mΩ) Capacity retention (%, 2C) Capacity retention (%, 3C) Comparative example 197.50-0.72777.553.2 Comparative example 2-197.00.5×0.71779.753.4 Comparative example 2-296.51×0.67180.455.7 Comparative example 2-394.53×0.63982.761.4 Comparative example 2-493.54×0.66577.847.2 Example 2-197.00.5○0.67680.654.8 Example 2-296.51○0.65980.360.2 Example 2-394.53○0.70878.051.3

[0141] As shown in Table 2 above, it can be seen that the resistance and C-rate efficiency of the lithium secondary battery of Example 2-2, which applied a uniform oxide-based solid electrolyte LATP line dispersion, are superior to those of Comparative Example 2-2.

[0142]

[0143] Experimental Example 5: Low-Temperature Characteristics Evaluation

[0144] For the lithium secondary batteries of Example 2-2 and Comparative Example 1, a discharge test was conducted for 30 seconds starting from an SOC of 50% at a temperature of -10°C.

[0145] Specifically, first, charging was performed up to 50% SOC under the conditions of 0.1C - 0.33C at a temperature of 25℃. Then, the lithium secondary battery with 50% SOC was stored in a chamber at -10℃ for 3 to 5 hours to cool the temperature of the lithium secondary battery to -10℃. Then, discharge was performed under the condition of 1C with a cut-off of 30 s or 2.5 V, and the degree of voltage drop according to the discharge time was measured.

[0146] Next, the battery was recharged to the same amount of discharge as above under the conditions of -10℃ and 0.1C, and the discharge test was repeated while changing the discharge rate condition from 1C to 2C, 3C, 3.5C, and 4.5C. Through the above process, the voltage drop for each discharge time was measured while the discharge was performed for 30 seconds at each discharge rate, and the result is shown in Fig. 6b.

[0147] Referring to Fig. 6, it was confirmed that Example 2-2 exhibited a lower voltage drop at the beginning of discharge and superior output characteristics compared to Comparative Example 1 at a low temperature of -10°C.

Claims

1. Metal current collector; and It comprises an active material layer formed on the above metal current collector and including an oxide-based solid electrolyte having an electrode active material, a conductive material, and a lithium ion source, An electrode for a lithium secondary battery, 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 of span 1 or less.

2. In paragraph 1, The above electrode active material comprises a lithium metal oxide including lithium and two or more metals selected from the group consisting of nickel, manganese, cobalt and aluminum, An electrode for a lithium secondary battery, wherein the lithium metal oxide contains nickel in an amount of 60 mol% or more based on the total metal content excluding lithium.

3. In paragraph 1, An electrode for a lithium secondary battery, wherein the oxide-based solid electrolyte comprises at least one lithium metal oxide or lithium metal phosphate selected from a Nasicon-type solid electrolyte, a Lisicon-type solid electrolyte, a Garnet-type solid electrolyte, a Perovskite-type solid electrolyte, and a LiPON-type solid electrolyte.

4. In paragraph 1, An electrode for a lithium secondary battery, wherein the oxide-based solid electrolyte comprises at least one selected from the group consisting of a LAGP (lithium aluminum germanium phosphate)-based compound, an LLZO (lithium lanthanum zirconium oxide)-based compound, a LATP (lithium aluminum titanium phosphate)-based compound, an LLZTO (lithium lanthanum zirconium tantalum oxide)-based compound, an LLTO (lithium lanthanum titanium oxide)-based compound, a LSTP (lithium silicon titanium phosphate)-based compound, and a LGPO (lithium germanium phosphate)-based compound.

5. In paragraph 1, An electrode for a lithium secondary battery, wherein the above oxide-based solid electrolyte has a particle size distribution of at least one of D50 of 100 nm to 1 ㎛ and D90 of 400 nm to 1.5 ㎛.

6. In paragraph 1, The above oxide-based solid electrolyte is an electrode for a lithium secondary battery, wherein D50 has a particle size distribution of 300 to 700 nm and D90 has a particle size distribution of 400 to 900 nm.

7. In paragraph 1, The above oxide-based solid electrolyte is an electrode for a lithium secondary battery, having a sample dispersion of 0.04 or less, as expressed by the following mathematical formula 1, as determined through EDS analysis. [Mathematical Formula 1] Here, S 2 is the sample variance, y is the variable, is the mean of the sample, n is the sample size, SS is the sum of squares of deviations, and df is the degrees of freedom.

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

9. In paragraph 1, An electrode for a lithium secondary battery, wherein the conductive material comprises carbon nanotubes or carbon nanofibers, and the active material layer further comprises a binder.

10. Containing a positive electrode; a negative electrode; and an electrolyte including a lithium salt and a non-aqueous organic solvent; A lithium secondary battery comprising an electrode for a lithium secondary battery according to any one of claims 1 to 9 as a positive electrode.

11. In paragraph 10, The above lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 A lithium secondary battery comprising at least one selected from the group consisting of 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. In paragraph 10, A lithium secondary battery, wherein the lithium salt is contained in the electrolyte at a concentration of 0.5 M to 6 M.

13. In paragraph 10, or further comprising a separator interposed between the positive and negative electrodes, A lithium secondary battery, wherein the electrolyte has the form of an electrolyte membrane or electrolyte film containing the lithium salt and a non-aqueous organic solvent within a polymer matrix, and is interposed 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, A step of preparing a solid electrolyte dispersion by mixing and dispersing an oxide-based solid electrolyte and a solvent; A step of preparing an electrode active material slurry by mixing the solid electrolyte dispersion, electrode active material, and conductive material; and A method for manufacturing an electrode for a lithium secondary battery, comprising the step of applying the electrode active material slurry to an electrode current collector.

15. In paragraph 14, A method for manufacturing an electrode for a lithium secondary battery, wherein the above solid electrolyte dispersion preparation step is performed using a bead-milling method.

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