Composite electrolyte membrane, manufacturing method thereof, and lithium secondary battery comprising same

Abstract

Disclosed in the present specification is a composite electrolyte membrane comprising: a liquid electrolyte; a cross-linked polymer of a monomer having a curable functional group; and oxide nanoparticles dispersed in the crosslinked polymer and having a particle diameter of 300 nm or less, wherein the oxide nanoparticles include particles of a lithium-containing oxide or a lithium-containing phosphate.

Description

Composite electrolyte membrane, method for manufacturing the same, and lithium secondary battery including the same

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0104172, filed August 9, 2023, and Korean Patent Application No. 10-2024-0105886, filed August 8, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present specification discloses a composite electrolyte membrane, a method for manufacturing the same, and a lithium secondary battery including the same.

[0004] With the recent rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, demand for small, lightweight, and relatively high-capacity secondary batteries is rapidly increasing. In particular, lithium secondary batteries, due to their lightweight design and high energy density, are attracting attention as power sources for portable devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0005] These lithium secondary batteries, such as lithium ion batteries (LIBs) and lithium metal batteries (LMBs), currently use liquid electrolytes or polymer electrolytes. In particular, most of the lithium secondary batteries currently commercialized use liquid electrolytes, and these liquid electrolytes It has an ionic conductivity of about 0.3. However, the ionic conductivity value is not the ionic conductivity of pure cations alone, but a measurement of the ionic conductivity including anions. For this reason, the cation transport coefficient, which can calculate the contribution of pure cations to the ionic conductivity, is another important performance indicator of the electrolyte. Meanwhile, it is theoretically known that concentration polarization does not occur even if the ionic conductivity is low when the cation transport coefficient is 1, and the cation transport coefficient of the currently widely used liquid electrolyte is known in many documents to be around 0.3. The task of increasing the cation transport coefficient to improve the performance of lithium secondary batteries is a topic that is continuously challenging from the perspective of the electrolyte.

[0006] Accordingly, the inventors of the present invention intend to apply various oxide nanoparticles to an electrolyte membrane to achieve a high cation transport coefficient and to contribute to improving the performance of a lithium secondary battery to which the same is applied.

[0007] Hereinafter, an electrolyte composition for a lithium metal battery according to a specific embodiment of the invention will be described.

[0008] 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.

[0009] 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.

[0010] 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.

[0011]

[0012] composite electrolyte membrane

[0013] According to one embodiment of the present invention, a composite electrolyte membrane is provided, comprising: a liquid electrolyte; a crosslinked polymer of a monomer having a curable functional group; and oxide nanoparticles dispersed on the crosslinked polymer and having a particle size of 300 nm or less, wherein the oxide nanoparticles include particles of at least one compound selected from the group consisting of lithium-containing oxides and lithium-containing phosphates.

[0014] Such a composite electrolyte membrane may include a crosslinked polymer obtained by curing a monomer having a curable functional group (e.g., an ethylenically unsaturated bond, etc.) by a method such as thermal curing, and may include a liquid electrolyte contained in the crosslinked polymer and oxide nanoparticles having a particle size of 300 nm or less dispersed on the crosslinked polymer.

[0015] The above composite electrolyte can exhibit excellent mechanical properties without a separate separator because it includes a liquid electrolyte, for example, an electrolyte solution including a non-aqueous organic solvent and a lithium salt, within the crosslinked structure of the crosslinked polymer, and can minimize leakage of the liquid electrolyte, etc., resulting in ignition, etc.

[0016] In addition, by further including the oxide nanoparticles, particularly oxide nanoparticles having an optimized particle size and / or content range, in the crosslinked polymer, more improved cation transport coefficient characteristics can be exhibited. This can be predicted because the particle size and content of the oxide nanoparticles are optimized, so that these particles can be more uniformly dispersed in the crosslinked polymer and the liquid electrolyte, and as a result, the cation transport coefficient characteristics according to the liquid electrolyte and oxide nanoparticles are maximized, and further, the performance of a lithium secondary battery to which this is applied can also be further improved.

[0017] Meanwhile, the liquid electrolyte contained within the cross-linked polymer may include a non-aqueous organic solvent and a lithium salt. This non-aqueous organic solvent may maintain a liquid state within the cross-linked structure of the cross-linked polymer, or a portion thereof may be cured together with the cross-linked polymer to further improve the mechanical properties of the composite electrolyte. This non-aqueous organic solvent may dissociate the lithium salt within the cross-linked polymer and act as an ion transfer medium. Therefore, by including this liquid electrolyte within the cross-linked polymer, the composite electrolyte may exhibit superior ion conductivity compared to a solid polymer solid electrolyte in a solid state.

[0018] The type of non-aqueous organic solvent that can be used at this time is not particularly limited, and any organic solvent that has been 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.

[0019] 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.

[0020] 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.

[0021] However, in terms of superior mechanical properties and safety of the composite electrolyte membrane, it is preferable to use a carbonate-based solvent, a sulfone-based solvent, or a phosphate-based solvent, which can be cured at least in part together with the crosslinked polymer and exhibit flame retardancy, as the organic solvent. In addition, it is more preferable to use a solvent that exhibits low volatility under curing conditions for forming the crosslinked polymer, for example, under thermal curing conditions of 60 to 80°C.

[0022] Meanwhile, the lithium salt dissolved or dispersed in the organic solvent may be any lithium salt that has been previously known to be applicable to the electrolyte of a lithium secondary battery, for example, LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiCl, LiBr, LiI, LiClO4, LiBF4, LiPF6, LiB 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (C2F5SO2)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylic acid having 4 or less carbon atoms, lithium 4-phenylborate, and lithium imide, and one or more selected from the group consisting of these can be used.

[0023] Such lithium salt may be included in the organic solvent of the liquid electrolyte at a concentration of 0.8 M to 4.0 M, or 1.0 M to 2.0 M, thereby enabling the composite electrolyte membrane of one embodiment to exhibit excellent thermal stability and ionic conductivity.

[0024] In an exemplary embodiment, the composite electrolyte membrane may include a crosslinked polymer comprising the liquid electrolyte and oxide nanoparticles described below within a crosslinked structure. This crosslinked polymer may be a crosslinked polymer formed by thermally curing a multifunctional monomer having multiple curable unsaturated bonds, such as (meth)acrylate groups, alkoxylate groups, hydroxyl groups, cyano groups, or carboxylic acid groups.

[0025] As the liquid electrolyte is included within the crosslinked structure of the crosslinked polymer, the composite electrolyte membrane exhibits excellent mechanical properties without a separate separator, while suppressing leakage to further improve the safety of the lithium secondary battery.

[0026] More specific examples of curable monomers for forming the above crosslinked polymer include at least one selected from the group consisting of ethylene glycol diacrylate, triethylene glycol diacrylate, ethoxylate trimethylolpropane triacrylate, bisphenol A ethoxylate dimethacrylate, acrylic acid, carboxyethyl acrylate, methyl cyanoacrylate, ethyl cyanoacrylate, ethyl cyano ethoxyacrylate, cyanoacrylic acid, hydroxyethyl methacrylate, and hydroxypropyl acrylate, and the above crosslinked polymer may be a single polymer in which one selected from these is cured, or a copolymer in which two or more are cured.

[0027] The crosslinked polymer may be included in an amount of 3 to 20, or 5 to 15 wt%, based on the total weight of the composite electrolyte membrane. As a result, the composite electrolyte membrane of the above embodiment can exhibit better mechanical properties, and thereby leakage and the like can be more effectively suppressed, while the liquid electrolyte and oxide nanoparticles can be uniformly included and dispersed on the crosslinked polymer to exhibit further improved ionic conductivity.

[0028]

[0029] oxide nanoparticles

[0030] Meanwhile, the composite electrolyte membrane according to the exemplary embodiment may further include oxide nanoparticles having a particle size of 300 nm or less, for example, 100 to 300 nm, and dispersed on the crosslinked polymer so as to exhibit a further improved cation transport coefficient.

[0031] In addition, as confirmed through the following examples and the like, as the particle size range and / or content range of the oxide nanoparticles are optimized, the composite electrolyte membrane of one embodiment can exhibit more improved cation transport coefficient characteristics. On the other hand, if the particle size range of the oxide nanoparticles is excessively large, exceeding 300 nm, or excessively small, less than 100 nm, the oxide nanoparticles may not be uniformly dispersed, which may deteriorate the characteristics of the composite electrolyte membrane and deteriorate the ionic conductivity of the composite electrolyte.

[0032] In an exemplary embodiment, the oxide nanoparticles may include particles of one or more compounds selected from the group consisting of lithium-containing oxides and lithium-containing phosphates. For example, the lithium-containing oxide or lithium-containing phosphate may be one or more lithium-containing oxide particles selected from the group consisting of Li2O, LAGP (lithium aluminum germanium phosphate) compounds, LLZO (lithium lanthanum zirconium oxide) compounds, LATP (lithium aluminum titanium phosphate) compounds, LLZTO (lithium lanthanum zirconium tantalum oxide) compounds, LSTP (lithium silicon titanium phosphate) compounds, and lithium oxides (e.g., Li2O).

[0033] For example, by using particles of the above LATP (lithium aluminum titanium phosphate) compound or Li2O-based particles, the cation transport coefficient can be further improved, and thus the performance of a lithium secondary battery to which this is applied can also be further improved.

[0034] In addition, the oxide nanoparticles may be included in an amount of 5 to 50 wt% based on the total weight of the composite electrolyte membrane. Preferably, the oxide nanoparticles are included in an amount of 10 to 30 wt% based on the total weight of the composite electrolyte membrane. If the content of the oxide nanoparticles is too small, the effect of increasing the cation transport coefficient in the composite electrolyte membrane may not be exerted, and if the content is too large, the physical properties of the composite electrolyte membrane itself may be greatly affected.

[0035]

[0036] Method for manufacturing composite electrolyte membrane

[0037] In another embodiment according to the present invention, a method for manufacturing the composite electrolyte membrane described above may be produced by a method including: forming a composition comprising a liquid electrolyte, a lithium salt, a monomer having a curable functional group, and particles of a lithium-containing oxide or particles of a lithium-containing phosphate having a particle size of 300 nm or less on a substrate; and, in the presence of an initiator, thermally curing the monomer of the composition at 60° C. or higher or photocuring it under ultraviolet irradiation.

[0038] According to the above manufacturing method, a composite electrolyte exhibiting excellent mechanical properties and a cation transport coefficient can be manufactured by a simple method of mixing each component of the composite electrolyte membrane of one embodiment and thermally curing the monomer in the presence of a thermal initiator or the like. In addition, in this manufacturing method, since the composite electrolyte membrane is manufactured by thermal curing at a temperature of about 60 to 80°C, the phenomenon of organic solvents, etc. contained in the liquid electrolyte evaporating during the manufacturing process can be reduced, and a composite electrolyte membrane having better characteristics can be manufactured.

[0039] Meanwhile, according to an example of a method for manufacturing the above-described composite electrolyte membrane, the above-described organic solvent and lithium salt are mixed to first form a liquid electrolyte, and then a monomer having a curable functional group, an oxide nanoparticle having a particle size of 300 nm or less, and a thermal initiator are simultaneously or sequentially added to the liquid electrolyte and mixed, and then this composition is coated on the substrate and heat-treated and cured to manufacture the above-described composite electrolyte membrane.

[0040] At this time, the above curing process, etc. may be carried out on a separate porous separator or an electrode of the positive or negative electrode, or may be carried out on a separate substrate prepared in advance, for example, a resin substrate such as polyester such as PET. Depending on the type of each substrate on which the curing process is carried out, the composite electrolyte membrane may be manufactured in the form of being coated on a separator, in the form of being overcoated and attached to each electrode, or in the form of a free-standing film itself, and may be applied as an electrolyte membrane replacing a porous separator of a lithium secondary battery.

[0041] In addition, the composition can be coated on the substrate according to a general liquid composition coating method, and the curing process can vary depending on the specific composition of the composition, but can be performed by heat treatment for, for example, 1 to 24 hours, or 2 to 12 hours.

[0042] In an exemplary embodiment, for proper thermal curing of the above-described monomer, the initiator may be a thermal initiator known to be usable for curing or crosslinking polymerization of a multifunctional monomer having a (meth)acrylate group, an alkoxylate group, a hydroxy group, a cyano group or a carboxylic acid group. Specific examples of such initiators include peroxide initiators such as benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide or hydrogen peroxide; Examples thereof include 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), or 2,2'-azobisdimethyl-valeronitrile (AMVN), and two or more selected from these may be used together, or various other thermal initiators may be used.

[0043]

[0044] lithium secondary battery

[0045] In another embodiment according to the present invention, a lithium secondary battery comprising the above-described composite electrolyte is provided, wherein the lithium secondary battery comprises: a positive electrode; a negative electrode; and the above-described composite electrolyte membrane interposed between the positive electrode and the negative electrode; wherein the composite electrolyte membrane may be coated on the negative electrode or may be removably interposed between the positive electrode and the negative electrode.

[0046] According to more specific examples, the composite electrolyte membrane may be included in the form of an overcoating membrane coated and attached to the positive or negative electrode, or may be manufactured in the form of a freestanding film or the like and may be included in the form of an electrolyte membrane that is not attached to the positive and negative electrodes but is releasably interposed between the positive and negative electrodes. In addition, the electrolyte membrane may be included alone, but in order to provide additional mechanical properties and insulating properties of the lithium secondary battery, a porous separator may be further included interposed between the positive and negative electrodes together with the electrolyte membrane, and the electrolyte membrane may have a form in which it is laminated on the porous separator.

[0047] Meanwhile, in the lithium secondary battery of the other embodiment, the positive electrode active material is not particularly limited as long as it is a material capable of reversible insertion and de-insertion of lithium ions, and may include, for example, a lithium metal composite oxide including one or more metal elements selected from the group consisting of Co, Mn, Ni, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, and Mo.

[0048] More specifically, as the positive electrode active material, a compound represented by any one of the following chemical formulas may be used: Li a A 1-b R b D2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Lia Ni 1-b-c Co b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Co b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Co b R c O 2-α Z2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Mn b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Mn b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Mn b R c O 2-α Z2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni b E c G dO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; and Li (3-f) J2(PO4)3(0 ≤ f ≤ 2).

[0049] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, V or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0050] In addition, the positive electrode may further include a binder and a conductive material in addition to the positive electrode active material described above. The above binder 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, and includes, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinylacetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethylcellulose (CMC), starch, One or more selected from the group consisting of hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof may be used, but is not necessarily limited thereto.

[0051] The above binder may be used in an amount of 1 to 50 parts by weight, or 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. As a result, the adhesive strength between the positive electrode active material and the current collector and the capacity characteristics of the secondary battery can be excellently maintained.

[0052] In addition, the conductive material included in the positive electrode is not particularly limited as long as it does not cause side reactions in the internal environment of the lithium secondary battery, does not cause chemical changes in the battery, and has excellent electrical conductivity. Representative examples thereof include graphite or conductive carbon, and examples thereof include, but are not limited to, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and the like; carbon-based materials having a crystal structure of graphene or graphite; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powders such as aluminum powder or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more, but are not necessarily limited thereto.

[0053] The above-mentioned conductive material may be used in an amount of 0.5 to 50 parts by weight, or 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. As a result, the electrochemical properties, such as conductivity and capacity, of the positive electrode and lithium secondary battery can be maintained excellently.

[0054] 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.

[0055] The above-described positive electrode can be manufactured, for example, by dispersing and mixing the positive electrode active material, binder, and conductive agent in a dispersion medium (solvent) to make a slurry, applying the slurry on a positive electrode 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.

[0056] In addition, the positive electrode current collector may be formed of, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, as well as aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The positive electrode current collector may be formed in the form of a foil, a film, a sheet, a punched body, a porous body, a foam, or the like.

[0057] In addition, in the lithium secondary battery of the other embodiment described above, the negative electrode can be manufactured according to a conventional method known in the art. For example, a slurry can be prepared by dispersing and mixing a negative electrode active material, a conductive material, a binder, and, if necessary, a filler in a dispersion medium (solvent), and then applying the slurry onto a negative electrode current collector, followed by drying and rolling, to manufacture the negative electrode.

[0058] At this time, 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 be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may 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 natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fibers, 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.

[0059] In addition, since the binder and conductive material described above can be used as the same as those described above for the positive electrode, further description thereof will be omitted.

[0060] In addition, as the negative electrode current collector, 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), but is not necessarily limited thereto. 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 body.

[0061] Meanwhile, in the lithium secondary battery of the other embodiment, as already described above, the composite electrolyte of one embodiment may be interposed between the positive and negative electrodes, for example, in the form of a layered membrane or film. In this case, the composite electrolyte membrane may also function as a separator (i.e., electrically insulating the negative and positive electrodes while simultaneously allowing lithium ions to pass through). At this time, the composite electrolyte membrane may be included in the secondary battery by being coated and attached in the form of a thin film on one surface of the positive or negative electrode. In addition, the composite electrolyte membrane may be independently interposed between the positive and negative electrodes. In addition, the lithium secondary battery of the other embodiment may be a semi-solid battery that uses a liquid electrolyte and a solid electrolyte together.

[0062] In addition, when a porous separator is added to the lithium secondary battery, the separator may be made of an olefin polymer such as polyethylene or polypropylene, glass fiber, etc. in the form of a sheet, a multi-film, a microporous film, a woven fabric, a non-woven fabric, etc., but is not necessarily limited thereto. However, it may be preferable to apply porous polyethylene or porous glass fiber non-woven fabric (glass filter) as the separator, and it may be more preferable to apply a porous glass filter (glass fiber non-woven fabric) as the separator. The separator may be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the separator 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.

[0063] Meanwhile, the lithium secondary battery of the above-described other embodiment can be manufactured according to conventional methods in the art. For example, it can be manufactured by forming a composite electrolyte membrane or the like between the positive and negative electrodes, and optionally adding a porous separator or the like.

[0064] 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.

[0065] As described above, the composite electrolyte membrane according to the embodiment of the present invention can exhibit improved cation transport coefficient characteristics as the particle size range and / or content range of the oxide nanoparticles are optimized.

[0066] In addition, since the liquid electrolyte is included within the crosslinked structure of the crosslinked polymer, excellent mechanical properties can be exhibited without a separate separator, and leakage of the liquid electrolyte, etc., resulting in ignition, etc. can be minimized.

[0067] Figure 1 compares and illustrates the measured cation transport coefficients in composite electrolyte membranes according to comparative examples and embodiments of the present invention.

[0068] 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.

[0069]

[0070] Comparative Example 1: Preparation of composite electrolyte membrane (Li2O 0 wt%)

[0071] First, a mixed solvent containing ethylene carbonate and propylene carbonate in a volume ratio of 1:1 as a non-aqueous organic solvent was used, and lithium salt LiPF6 was dissolved in the mixed solvent at a concentration of 1 M to form a liquid electrolyte. This liquid electrolyte and ethoxylated trimethylolpropane triacrylate (ETPTA), a monomer having a curable functional group, were mixed in a weight ratio of 90:10, and further, 0.1 part by weight of AIBN, a thermal initiator, was mixed with respect to 100 parts by weight of the mixture to prepare a composition for forming a composite electrolyte.

[0072] This composition was coated on a PET substrate using a bar coater and heat-cured at a temperature of 60°C for 360 minutes. Through this, a composite electrolyte membrane of Comparative Example 1 formed on the substrate was manufactured.

[0073]

[0074] Example 1: Preparation of composite electrolyte membrane (Li2O 10 wt%)

[0075] In the manufacturing method of Comparative Example 1 described above, the same process was followed up to the mixing process of the liquid electrolyte and the monomer having a curable functional group. In addition, for 100 parts by weight of the mixture, 0.1 part by weight of AIBN as a thermal initiator, 10% by weight of Li2O oxide-based solid electrolyte particles having a particle size of 100 nm (Example 1-1) and 5% by weight of Li2O oxide-based solid electrolyte particles having a particle size of 300 nm (Example 1-2) (weight ratio of liquid electrolyte + monomer: oxide-based particles = 25:1) were mixed to prepare a composition for forming a composite electrolyte.

[0076] The subsequent thermal curing process was carried out in the same manner as in Comparative Example 1 to manufacture the composite electrolyte of Example 1.

[0077]

[0078] Example 2: Preparation of composite electrolyte membrane (Li2O 20 wt%)

[0079] A composite electrolyte membrane was manufactured in the same manner as in Example 1, except that 20 wt% (Example 2-1) of Li2O oxide-based solid electrolyte particles having a particle size of 100 nm and 20 wt% (Example 2-2) of Li2O oxide-based solid electrolyte particles having a particle size of 300 nm were used, respectively.

[0080]

[0081] Example 3: Preparation of composite electrolyte membrane (Li2O 30 wt%)

[0082] A composite electrolyte membrane was manufactured in the same manner as in Example 1, except that 30 wt% (Example 3-1) of Li2O oxide-based solid electrolyte particles having a particle size of 100 nm and 30 wt% (Example 3-2) of Li2O oxide-based solid electrolyte particles having a particle size of 300 nm were used, respectively.

[0083]

[0084] Comparative Example 2: Preparation of composite electrolyte membrane (Li2O 5 wt%)

[0085] A composite electrolyte membrane was manufactured in the same manner as in Example 1, except that 5 wt% (Comparative Example 2-1) of Li2O oxide-based solid electrolyte particles having a particle size of 100 nm, 5 wt% (Comparative Example 2-2) of Li2O oxide-based solid electrolyte particles having a particle size of 300 nm, and 5 wt% (Comparative Example 2-3) of Li2O oxide-based solid electrolyte particles having a particle size of 400 nm were used.

[0086]

[0087] Comparative Example 3-5: Preparation of composite electrolyte membrane (Li2O 10-30 wt%)

[0088] A composite electrolyte membrane was manufactured in the same manner as in Example 1, except that 10 wt% (Comparative Example 3-3) of Li2O oxide-based solid electrolyte particles having a particle size of 400 nm, 20 wt% (Comparative Example 4-3) of Li2O oxide-based solid electrolyte particles having a particle size of 400 nm, and 30 wt% (Comparative Example 5-3) of Li2O oxide-based solid electrolyte particles having a particle size of 400 nm were used, respectively.

[0089]

[0090] Comparative Example 6: Preparation of composite electrolyte membrane (Li2O 40 wt%)

[0091] A composite electrolyte membrane was manufactured in the same manner as in Example 1, except that 40 wt% (Comparative Example 6-1) of Li2O oxide-based solid electrolyte particles having a particle size of 100 nm, 40 wt% (Comparative Example 6-2) of Li2O oxide-based solid electrolyte particles having a particle size of 300 nm, and 40 wt% (Comparative Example 6-3) of Li2O oxide-based solid electrolyte particles having a particle size of 400 nm were used, respectively.

[0092]

[0093] Comparative Example 7: Preparation of composite electrolyte membrane (Li2O 50 wt%)

[0094] A composite electrolyte membrane was manufactured in the same manner as in Example 1, except that 50 wt% (Comparative Example 7-1) of Li2O oxide-based solid electrolyte particles having a particle size of 100 nm, 50 wt% (Comparative Example 7-2) of Li2O oxide-based solid electrolyte particles having a particle size of 300 nm, and 50 wt% (Comparative Example 7-3) of Li2O oxide-based solid electrolyte particles having a particle size of 400 nm were used.

[0095]

[0096] Battery Example: Manufacturing of Lithium Secondary Batteries

[0097] First, a lithium nickel cobalt manganese composite oxide (NCM 811) containing 80 mol% nickel among the total transition metals was used as a cathode active material. This cathode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 96.5:1.5:2, and dispersed in an NMP solvent to prepare a slurry, which was then coated to a uniform thickness on a 25 ㎛ thick aluminum foil (Al foil) using a blade-type coating machine, a Labdryer / coater type LTE, Werner Mathis AG, and dried in a vacuum oven at 120°C for 13 hours to prepare a cathode for a lithium secondary battery.

[0098] A negative electrode for a lithium secondary battery was manufactured using the same method as the positive electrode above, using graphite as the negative electrode active material.

[0099] After positioning the positive and negative electrodes so that they face each other, an electrode assembly was manufactured by interposing the composite electrolyte membrane manufactured in Comparative Example 1-7 or Example 1-3 therebetween, and the electrode assembly was positioned inside a case to manufacture a lithium secondary battery.

[0100]

[0101] Experimental Example: Measurement of Cation Transport Coefficient

[0102] The cation transport coefficient of the manufactured lithium secondary battery was measured using the following method. First, a voltage was applied to the manufactured lithium secondary battery to induce polarization in the electrodes, and the current in the polarized state was measured. Based on the measured current value, the cation transport coefficient (t+) was measured using the following mathematical equation 1 according to the Bruce-Vincent method.

[0103] [Mathematical Formula 1]

[0104]

[0105] In the above mathematical expression 1, I ss is the current value flowing in the steady state, I0 is the current value flowing in the polarized state, △V is the potential difference applied across the cell, R0 is the interface resistance in the polarized state, R ss is the interfacial resistance in the normal state.

[0106] The cation transport coefficients of the composite electrolyte membranes for lithium secondary batteries manufactured in Comparative Example 1-7 and Example 1-3 were measured, and the results are shown in Table 1 and Figure 1 below.

[0107] Sample transport coefficient (Li2O 100 nm) Sample transport coefficient (Li2O 300 nm) Sample transport coefficient (Li2O 400 nm) Comparative example 1 (Li2O 0 wt%) 0.32 Comparative example 1 (Li2O 0 wt%) 0.32 Comparative example 1 (Li2O 0 wt%) 0.32 Comparative example 2-1 (Li2O 5 wt%) 0.84 Comparative example 2-2 (Li2O 5 wt%) 0.61 Comparative example 2-3 (Li2O 5 wt%) 0.62 Example 1-1 (Li2O 10 wt%) 0.90 Example 1-2 (Li2O 10 wt%) 0.72 Comparative example 3-3 (Li2O 10 wt%) 0.70 Example 2-1 (Li2O 20 wt%) 0.87 Example 2-2 (Li2O 20 wt%) 0.70 Comparative Example 4-3 (Li2O 20 wt%) 0.67 Example 3-1 (Li2O 30 wt%) 0.92 Example 3-2 (Li2O 30 wt%) 0.65 Comparative Example 5-3 (Li2O 30 wt%) 0.61 Comparative Example 6-1 (Li2O 40 wt%) 0.81 Comparative Example 6-2 (Li2O 40 wt%) 0.60 Comparative Example 6-3 (Li2O 40 wt%) 0.54 Comparative Example 7-1 (Li2O 50 wt%) 0.72 Comparative Example 7-2 (Li2O 50 wt%) 0.52 Comparative Example 7-3 (Li2O 50 wt%) 0.51

[0108] FIG. 1 compares the measured values ​​of cation transport coefficients in composite electrolyte membranes according to comparative examples and embodiments of the present invention. Referring to Table 1 and FIG. 1, in particular, the particle size of the oxide nanoparticles is 300 nm or less, preferably 100 nm to 300 nm, and the oxide nanoparticles are contained in an amount of 10 to 30 wt% based on the total weight of the composite electrolyte membrane, thereby confirming the effect of improving the cation transport coefficient by applying oxide particles to the composite electrolyte membrane for lithium secondary batteries.

[0109] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings.

Claims

1. Liquid electrolyte; A crosslinked polymer of a monomer having a curable functional group; and It comprises oxide nanoparticles dispersed on the crosslinked polymer and having a particle size of 300 nm or less; A composite electrolyte membrane, wherein the oxide nanoparticles comprise one or more compound particles selected from the group consisting of lithium-containing oxides and lithium-containing phosphates.

2. In paragraph 1, A composite electrolyte membrane, wherein the lithium-containing oxide or lithium-containing phosphate comprises at least one selected from the group consisting of Li2O, LAGP (lithium aluminum germanium phosphate) compounds, LLZO (lithium lanthanum zirconium oxide) compounds, LATP (lithium aluminum titanium phosphate) compounds, LLZTO (lithium lanthanum zirconium tantalum oxide) compounds, and LSTP (lithium silicon titanium phosphate) compounds.

3. In paragraph 1, A composite electrolyte membrane, wherein the oxide nanoparticles are contained in an amount of 5 to 50 wt% based on the total weight of the composite electrolyte membrane.

4. In paragraph 3, A composite electrolyte membrane, wherein the oxide nanoparticles are contained in an amount of 10 to 30 wt% based on the total weight of the composite electrolyte membrane.

5. In paragraph 1, A composite electrolyte membrane wherein the oxide nanoparticles have a particle size of 100 to 300 nm.

6. In paragraph 1, A composite electrolyte membrane comprising at least one monomer having the above curable functional group selected from the group consisting of ethylene glycol diacrylate, triethylene glycol diacrylate, ethoxylate trimethylolpropane triacrylate, bisphenol A ethoxylate dimethacrylate, acrylic acid, carboxyethyl acrylate, methyl cyanoacrylate, ethyl cyanoacrylate, ethyl cyano ethoxyacrylate, cyanoacrylic acid, hydroxyethyl methacrylate, and hydroxypropyl acrylate.

7. In paragraph 1, A composite electrolyte membrane, wherein the crosslinked polymer is included in an amount of 3 to 20 wt% based on the total weight of the composite electrolyte membrane.

8. A positive electrode; a negative electrode; and a composite electrolyte membrane of claim 1 interposed between the positive electrode and the negative electrode; A lithium secondary battery, wherein the composite electrolyte membrane is coated on the negative electrode or is releasably interposed between the positive electrode and the negative electrode.

9. A method for manufacturing a composite electrolyte membrane according to Article 1, A step of forming a composition comprising a liquid electrolyte, a lithium salt, a monomer having a curable functional group, and particles of a lithium-containing oxide or particles of a lithium-containing phosphate having a particle size of 300 nm or less on a substrate; and A method for producing a composite electrolyte membrane, comprising the step of thermally curing the monomer of the composition at 60°C or higher or photocuring it under ultraviolet irradiation in the presence of an initiator.

10. In paragraph 9, A method for producing a composite electrolyte, wherein the above initiator is selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, hydrogen peroxide, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), and 2,2'-azobisdimethyl-valeronitrile (AMVN).

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