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

Abstract

The present invention relates to a composite electrolyte that exhibits improved mechanical properties and ionic conductivity while preventing liquid leakage, a method for manufacturing the same, and a lithium secondary battery including the same. The composite electrolyte may include a liquid electrolyte, a crosslinked polymer of a monomer having a curable functional group, and oxide-based solid electrolyte particles dispersed on the crosslinked polymer and having a particle size exceeding 300 nm.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2022 - 0132212 filed on October 14, 2022 and Korean Patent Application No. 10 - 2023 - 0125560 filed on September 20, 2023, and all the contents disclosed in the documents of the Korean patent applications are included as part of this specification.

[0002] The present invention relates to a composite electrolyte that exhibits improved mechanical properties and ionic conductivity while preventing liquid leakage, a method for manufacturing the same, and a lithium secondary battery including the same.

Background Art

[0003] Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small, light, and relatively high - capacity secondary batteries has been increasing rapidly. In particular, lithium secondary batteries are lightweight and have a high energy density, so they are in the spotlight as a driving power source for portable devices. As a result, research and development efforts for improving the performance of lithium secondary batteries are actively underway.

[0004] Such lithium secondary batteries, for example, lithium - ion batteries, generally have a structure in which a separator is interposed between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions, and a liquid - state electrolyte is charged. However, in the case of lithium - ion batteries, due to the inclusion of a liquid - state electrolyte, there is a high possibility of liquid leakage during charging / discharging or use, and there is a high risk of ignition or explosion, which has become a major problem.

[0005] Therefore, recently, development of solid electrolytes for improving the safety of lithium secondary batteries has been actively carried out, and among these, research on polymer solid electrolytes has been conducted. However, such polymer solid electrolytes themselves exhibit lower ionic conductivity compared to electrolytes in a liquid state, so the use of composite electrolytes in a form that includes a liquid electrolyte, for example, a lithium salt and an organic solvent, within the polymer has been more widely studied.

[0006] However, even in the case of such existing composite electrolytes, there are still drawbacks such as the possibility of liquid leakage occurring during the manufacturing or battery usage process, or insufficient mechanical properties. In addition, there is the problem that a separator membrane for supporting the composite electrolyte is inevitably required, and such existing composite electrolytes also cannot exhibit sufficient ionic conductivity, and improvements in this regard are both required.

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, the present invention provides a composite electrolyte that exhibits improved mechanical properties and ionic conductivity while preventing liquid leakage, and a method for manufacturing the same.

[0008] The present invention also provides a lithium secondary battery that includes the composite electrolyte and exhibits further improved electrical characteristics and safety.

Means for Solving the Problems

[0009] The present invention provides a composite electrolyte including a liquid electrolyte, a crosslinked polymer of a monomer having a curable functional group, and oxide-based solid electrolyte particles dispersed on the crosslinked polymer and having a particle size exceeding 300 nm.

[0010] The present invention also provides a method for producing a composite electrolyte, comprising the steps of forming a composition on a substrate that includes a liquid electrolyte, monomers having curable functional groups, and oxide-based solid electrolyte particles having a particle size greater than 300 nm, and thermal curing the monomers contained in the composition at 60°C or higher in the presence of an initiator.

[0011] Furthermore, the present invention provides a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the composite electrolyte interposed between the positive electrode and the negative electrode.

[0012] The following describes a composite electrolyte, its manufacturing method, and a lithium secondary battery, which are specific examples of the invention.

[0013] A composite electrolyte according to one embodiment of the invention comprises a liquid electrolyte, a monomer crosslinked polymer having a curable functional group, and oxide-based solid electrolyte particles dispersed on the crosslinked polymer and having a particle size exceeding 300 nm.

[0014] The composite electrolyte according to the above embodiment includes a crosslinked polymer obtained by curing monomers having curable functional groups (such as ethylene-based unsaturated bonds) by a method such as thermosetting, and includes a liquid electrolyte contained within such a crosslinked polymer and oxide-based solid electrolyte particles dispersed on the crosslinked polymer having a particle size greater than 300 nm, or 310 to 800 nm, or 350 to 600 nm.

[0015] In this embodiment of the composite electrolyte, the crosslinked structure of the crosslinked polymer contains a liquid electrolyte, such as a non-aqueous organic solvent and a lithium salt, which allows the electrolyte to exhibit excellent mechanical properties without the need for a separate separation membrane. This minimizes the risk of leakage of the liquid electrolyte and subsequent ignition.

[0016] Furthermore, it was confirmed that by further including oxide-based solid electrolyte particles, particularly oxide-based solid electrolyte particles with optimized particle size and / or content range, within the crosslinked polymer, an improved ionic conductivity can be achieved. This is predicted to be because the particle size and content of the oxide-based solid electrolyte particles are optimized, allowing these particles to be dispersed more uniformly within the crosslinked polymer and liquid electrolyte. As a result, the ionic conductivity of the liquid electrolyte and oxide-based solid electrolyte particles is maximized, further improving the ionic conductivity of the composite electrolyte of the embodiment described above.

[0017] On the other hand, the liquid electrolyte contained within the crosslinked polymer may also contain a non-aqueous organic solvent and a lithium salt. Such a non-aqueous organic solvent may maintain a liquid state within the crosslinked structure of the crosslinked polymer, or a portion of it may harden together with the crosslinked polymer to further improve the mechanical properties of the composite electrolyte. Such a non-aqueous organic solvent can dissociate the lithium salt within the crosslinked polymer and act as an ion transfer medium. As a result, the crosslinked polymer contains such a liquid electrolyte, and the composite electrolyte can exhibit superior ionic conductivity compared to a solid polymer solid electrolyte in a solid state.

[0018] In this case, the type of non-aqueous organic solvent that can be used is not particularly limited, and any organic solvent known to be applicable to the electrolyte of conventional lithium-ion batteries can be used. Examples of such organic solvents include one or more selected from the group consisting of carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents.

[0019] More specifically, the carbonate-based solvent may be 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, and the phosphate-based solvent may be trimethyl phosphate, triethyl phosphate, or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide.

[0020] Furthermore, as the ether-based solvent, dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, or tetrahydrofuran derivatives such as 2-methyltetrahydrofuran may be used, and as the nitrile-based solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile may be used. Furthermore, as the sulfone-based solvent, dimethyl sulfone, ethyl methyl sulfone, or sulforane may be used.

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

[0022] On the other hand, the lithium salt to be dissolved or dispersed in the organic solvent is any lithium salt known to be applicable to the electrolyte of conventional lithium secondary batteries, for example, LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiCl, LiBr, LiI, LiClO4, LiBF4, LiPF6, LiB 10 Cl 10 You may also use one or more selected from the group consisting of LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (C2F5SO2)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylates with 4 or fewer carbon atoms, lithium 4-phenylborate, and lithium imide.

[0023] Such lithium salts 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 of one embodiment to exhibit excellent thermal stability and ionic conductivity.

[0024] On the other hand, the composite electrolyte of one embodiment includes a crosslinked polymer containing the liquid electrolyte and oxide-based solid electrolyte particles, described later, within its crosslinked structure. Such a crosslinked polymer may be a crosslinked polymer obtained by thermosetting a polyfunctional monomer having multiple curable unsaturated bonds, such as (meth)acrylate groups, alkoxylate groups, hydroxyl groups, cyano groups, or carboxylic acid groups.

[0025] By including the liquid electrolyte within the crosslinked structure of such a crosslinked polymer, the composite electrolyte exhibits excellent mechanical properties without the need for a separate separation membrane, and also suppresses leakage, thereby further improving the safety of the lithium secondary battery.

[0026] More specific examples of curable monomers for forming the crosslinked polymer include one or more 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 cyanoethoxyacrylate, cyanoacrylic acid, hydroxyethyl methacrylate, and hydroxypropyl acrylate. It goes without saying that the crosslinked polymer may be a single polymer formed by curing one of these selected monomers, or a copolymer formed by curing two or more of these monomers.

[0027] Such crosslinked polymers may be included in an amount of 3 to 20% by weight, or 5 to 15% by weight, based on the total weight of the composite electrolyte. This allows the composite electrolyte of the above embodiment to exhibit superior mechanical properties, thereby more effectively suppressing leakage, while also allowing the liquid electrolyte and oxide-based solid electrolyte particles to be uniformly contained and dispersed on such crosslinked polymers, resulting in even greater ionic conductivity.

[0028] On the other hand, the composite electrolyte of one embodiment further includes oxide-based solid electrolyte particles dispersed on the crosslinked polymer, having a particle size of over 300 nm, or 310 to 800 nm, or 350 to 600 nm, so that it can exhibit even more improved ionic conductivity.

[0029] In particular, as supported by the following examples, it has been confirmed that optimizing the particle size range and / or content range of such oxide-based solid electrolyte particles can result in improved ionic conductivity for the composite electrolyte of one embodiment. In contrast, it has been confirmed that when the particle size range of the oxide-based solid electrolyte particles becomes smaller than 300 nm, the ionic conductivity of the composite electrolyte is inferior. Furthermore, if the particle size range becomes excessively large, the oxide-based solid electrolyte particles may not be uniformly dispersed, and the properties of the composite electrolyte may deteriorate.

[0030] Such oxide-based solid electrolyte particles may include, for example, one or more lithium-containing oxide particles selected from the group consisting of 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 oxide (e.g., Li2O). Among these, the cation transport coefficient can be further improved by using particles of the LATP (lithium aluminum titanium phosphate) compound, and the composite electrolyte of one embodiment can exhibit even higher ionic conductivity.

[0031] Furthermore, the oxide-based solid electrolyte particles may be included in an amount of 0.1 to 15 parts by weight, or 0.3 to 12 parts by weight, based on a total of 100 parts by weight of the liquid electrolyte and crosslinked polymer mentioned above. It has been confirmed that if the content of the oxide-based solid electrolyte particles is excessively small, the ionic conductivity of the composite electrolyte is insufficient, and if the content is excessively large, the ionic conductivity of the composite electrolyte actually decreases.

[0032] The composite electrolyte of the above-described embodiment can be manufactured by a method comprising the steps of forming a composition on a substrate that includes each component of the composite electrolyte described above, namely a liquid electrolyte, monomers having curable functional groups, and oxide-based solid electrolyte particles having a particle size greater than 300 nm, and thermal curing the monomers contained in the composition at 60°C or higher, or 60 to 80°C, in the presence of an initiator.

[0033] According to this manufacturing method, a composite electrolyte of one embodiment exhibiting excellent mechanical properties and ionic conductivity can be produced by simply mixing the components of the composite electrolyte of one embodiment and thermosetting the monomers in the presence of a thermal initiator. Furthermore, by producing the composite electrolyte by thermosetting at a temperature of about 60 to 80°C using this manufacturing method, the phenomenon of evaporation of organic solvents contained in the liquid electrolyte during the manufacturing process can be reduced, and a composite electrolyte with better properties can be produced.

[0034] On the other hand, according to one example of the method for producing the composite electrolyte, a liquid electrolyte is first formed by mixing the aforementioned organic solvent and lithium salt. A monomer having a curable functional group, oxide-based solid electrolyte particles having a particle size exceeding 300 nm, and a thermal initiator are added to this liquid electrolyte simultaneously or sequentially and mixed. After that, the composition is coated onto the substrate and heat-treated and cured to produce the composite electrolyte.

[0035] In this case, the curing process may be carried out on a separate porous separation membrane or on the positive or negative electrode, or on a separate substrate prepared in advance, such as a resin substrate such as PET or polyester. Depending on the type of substrate on which such a curing process is carried out, the composite electrolyte may be manufactured in a form coated on the separation membrane, in a form coated and attached to each electrode, or it may be manufactured as a free-standing film and applied as an electrolyte membrane to replace the porous separation membrane of a lithium secondary battery.

[0036] Furthermore, the composition may be coated onto the substrate by a general liquid composition coating method, and the curing step may vary depending on the specific composition of the composition, but may be performed by heat treatment for 1 to 24 hours or 2 to 12 hours, for example.

[0037] On the other hand, for proper thermal curing of the monomers mentioned above, conventional thermal initiators known to be usable for curing or crosslinking polymerization of polyfunctional monomers having (meth)acrylate groups, alkoxylate groups, hydroxyl groups, cyano groups, or carboxylic acid groups can be used as initiators. Specific examples of such initiators include peroxide initiators such as benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butylperoxy-2-ethyl-hexanoate, cumylhydroperoxide, or hydrogen peroxide, as well as 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), or 2,2'-azobisdimethylvaleronitrile (AMVN). Two or more of these may be used together, or a variety of other thermal initiators may be used.

[0038] On the other hand, according to another embodiment of the invention, a lithium secondary battery comprising the composite electrolyte described above is provided. Such a lithium secondary battery may include, for example, a positive electrode comprising a positive electrode active material, a negative electrode comprising a negative electrode active material, and the composite electrolyte of the first embodiment interposed between the positive electrode and the negative electrode.

[0039] More specifically, the composite electrolyte may be included in the form of a topcoat film coated and attached to the positive or negative electrode (see, for example, Battery Example 2 below), or in the form of an electrolyte membrane manufactured in the form of a freestanding film or the like, which does not adhere to the positive and negative electrodes but is separated and interposed between them (see, for example, Battery Example 1 below). Such an electrolyte membrane may be included alone, but a porous separation membrane may be further included interposed with the electrolyte membrane between the positive and negative electrodes to impart additional mechanical properties and insulation to the lithium secondary battery, and the electrolyte membrane may be laminated on such a porous separation membrane.

[0040] On the other hand, 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 extraction of lithium ions. For example, it may contain a lithium metal composite oxide containing 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.

[0041] 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); Li a 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 Dα (In the above equation, 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 equation, 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 (wherein the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni b E c G d O2(In the above equation, 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 G e O2(In the above equation, 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 equation, 0.90≦a≦1.8 and 0.001≦b≦0.1.);Li a CoG b O2(In the above equation, 0.90≦a≦1.8 and 0.001≦b≦0.1.);Li a MnG b O2(In the above equation, 0.90≦a≦1.8 and 0.001≦b≦0.1.);Li a Mn2G b O4 (In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2).

[0042] 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; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0043] Furthermore, the positive electrode may also contain a binder and a conductive material in addition to the positive electrode active material described above. The binder is a component that assists in the bonding of the positive electrode active material to a conductive material and to the current collector, and may be, but is not limited to, one or more selected from the group consisting of, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, 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, hydroxypropylcellulose, regenerated cellulose, and mixtures thereof.

[0044] The binder may be used in an amount of 1 to 50 parts by weight, or 3 to 15 parts by weight, per 100 parts by weight of the total weight of the positive electrode. As a result, excellent adhesion between the positive electrode active material and the current collector, as well as the capacity characteristics of the secondary battery, can be maintained.

[0045] Furthermore, the conductive material contained 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. Typically, graphite or conductive carbon may be used, for example, 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, and lamp black; carbon-based materials whose crystalline structure is graphene or graphite; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskey such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives may be used individually or in combination of two or more, but are not necessarily limited to these.

[0046] The conductive material may be used in an amount of 0.5 to 50 parts by weight, or 1 to 30 parts by weight, per 100 parts by weight of the total weight of the positive electrode. This makes it possible to maintain excellent electrochemical properties such as conductivity and capacity of the positive electrode and lithium secondary battery.

[0047] Furthermore, a filler may be selectively added to the positive electrode as a component to suppress its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and may be, for example, an olefin polymer such as polyethylene or polypropylene; a fibrous material such as glass fiber or carbon fiber; etc.

[0048] The aforementioned positive electrode can be manufactured, for example, by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to create a slurry, applying this slurry to a positive electrode current collector, and then drying and rolling it. In this case, the dispersion medium may be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof.

[0049] Furthermore, the positive electrode current collector may be made of 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 with a surface treatment of carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not necessarily limited to these. The positive electrode current collector may take the form of foil, film, sheet, punched material, porous material, foam, etc.

[0050] Furthermore, in the lithium secondary batteries of the other embodiments mentioned above, the negative electrode can be manufactured by conventional methods known in the art. For example, a slurry can be made by dispersing and mixing a negative electrode active material, a conductive material, a binder, and optionally a filler in a dispersion medium (solvent), applying this slurry onto a negative electrode current collector, and then drying and rolling it to manufacture the negative electrode.

[0051] In this case, the negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples 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 alloys, Sn alloys, or Al alloys; metallic oxides capable of doping and dedoping with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. Furthermore, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystallinity carbon and high-crystallinity carbon may be used as the carbonaceous material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flake-like, 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.

[0052] Furthermore, the binder and conductive material used are the same as those described for the positive electrode, so no further explanation regarding them will be provided.

[0053] Furthermore, the negative electrode current collector may be made of 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 with a surface treatment of carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not necessarily limited to these. The negative electrode current collector may take the form of foil, film, sheet, punched material, porous material, foam, etc.

[0054] On the other hand, in the lithium secondary battery of the other embodiment described above, a composite electrolyte of one embodiment may be interposed between the positive electrode and the negative electrode, for example, in the form of a layered membrane or film, as already described above. In this case, the composite electrolyte membrane can also serve as a separation membrane (i.e., electrically insulating the negative electrode and the positive electrode while simultaneously allowing lithium ions to pass through). In this case, the composite electrolyte membrane may be included in the secondary battery as a thin film coating and attached to one surface of the positive or negative electrode. Alternatively, the composite electrolyte membrane may be interposed independently between the positive electrode and the negative electrode. Furthermore, the lithium secondary battery of the other embodiment described above may be a semi-solid-state battery that uses both a liquid electrolyte and a solid electrolyte.

[0055] At the same time, when a porous separation membrane is added to the lithium secondary battery, such a separation membrane may be made of polyethylene, olefin polymers such as polypropylene, glass fibers, etc., in the form of a sheet, multilayer membrane, fine porous film, woven fabric, or nonwoven fabric, but is not necessarily limited thereto. However, it is preferable to use porous polyethylene or porous glass fiber nonwoven fabric (glass filter) as the separation membrane, and it is even more preferable to use porous glass fiber nonwoven fabric (glass filter) as the separation membrane. The separation membrane may be a thin insulating film having high ion permeability and mechanical strength, and the pore diameter of the separation membrane may generally be in the range of 0.01 to 10 μm, and the thickness may generally be in the range of 5 to 300 μm, but is not limited thereto.

[0056] On the other hand, the lithium secondary batteries of the other embodiments described above can be manufactured by conventional methods in this field. For example, they can be manufactured by forming a composite electrolyte membrane between the positive and negative electrodes and selectively adding a porous separation membrane.

[0057] Such lithium-ion secondary batteries are not only suitable for use as battery cells in power supplies for small devices, but are also particularly suitable for use as unit batteries in battery modules that power medium to large devices. [Effects of the Invention]

[0058] According to the present invention, by including a liquid electrolyte within the crosslinked structure of the crosslinked polymer, a composite electrolyte is provided that exhibits excellent mechanical properties without the need for a separate separation membrane, thereby minimizing the risk of leakage of the liquid electrolyte and subsequent ignition.

[0059] Furthermore, such composite electrolytes can exhibit improved ionic conductivity, which can significantly contribute to improving the safety and electrical characteristics of lithium-ion batteries. [Brief explanation of the drawing]

[0060] [Figure 1a] Figure 1a is a photograph comparing the surface state of the positive electrode before the composite electrolyte of Example 2 is applied to the positive electrode (Figure 1a) and the surface state after the application (Figure 1b), as part of the manufacturing process of Battery Example 2. [Figure 1b] Figure 1b is a photograph comparing the surface state of the positive electrode before the composite electrolyte of Example 2 is applied to the positive electrode (Figure 1a) and the surface state after the application (Figure 1b), as part of the manufacturing process of Battery Example 2. [Modes for carrying out the invention]

[0061] The following examples illustrate the invention, but these examples are merely illustrative. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the invention and the technical concept, and that such changes and modifications will naturally fall within the scope of the claims.

[0062] Comparative Example 1: Manufacturing of Composite Electrolytes First, a mixed solvent of ethylene carbonate and propylene carbonate in a 1:1 volume ratio was used as a non-aqueous organic solvent, and lithium salt LiPF6 was dissolved in it at a concentration of 1 M to form a liquid electrolyte. This liquid electrolyte was mixed with ethoxylate trimethylolpropane triacrylate (ETPTA), a monomer having a curable functional group, in a weight ratio of 90:10, and then 0.1 parts by weight of AIBN, a thermal initiator, was added to 100 parts by weight of the mixture to produce a composite electrolyte-forming composition.

[0063] Such a composition was coated onto a PET substrate using a bar coater and then heat-treated at 60°C for 360 minutes to induce thermocuring. Through this process, the composite electrolyte of Comparative Example 1 was produced on the substrate.

[0064] Example 1: Manufacturing of a composite electrolyte The manufacturing method of Comparative Example 1 was carried out similarly up to the mixing step of the liquid electrolyte and the monomer having a curable functional group. Furthermore, 0.1 parts by weight of AIBN as a thermal initiator and LiAl having a particle size of 400 nm were added to 100 parts by weight of the mixture. 0.3 Ti 1.7 A composite electrolyte-forming composition was prepared by mixing 4 parts by weight of (PO4)3 (LATP-based) oxide-based solid electrolyte particles (weight ratio of liquid electrolyte + monomer to oxide-based particles = 25:1).

[0065] The subsequent thermosetting steps were carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Example 1.

[0066] Example 2: Manufacturing of a composite electrolyte The manufacturing method of Comparative Example 1 was carried out similarly up to the mixing step of the liquid electrolyte and the monomer having a curable functional group. Furthermore, 0.1 parts by weight of AIBN as a thermal initiator and LiAl having a particle size of 400 nm were added to 100 parts by weight of the mixture. 0.3 Ti 1.7 A composite electrolyte-forming composition was prepared by mixing 11.1 parts by weight of (PO4)3 (LATP-based) oxide-based solid electrolyte particles (weight ratio of liquid electrolyte + monomer:oxide-based particles = 9:1).

[0067] The subsequent thermosetting steps were carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Example 2.

[0068] Example 3: Manufacturing of a composite electrolyte The manufacturing method for Comparative Example 1 was carried out similarly up to the mixing step of the liquid electrolyte and the monomer having a curable functional group. Furthermore, a composite electrolyte-forming composition was produced by mixing 0.1 parts by weight of AIBN, a thermal initiator, and 4 parts by weight of lithium oxide (Li2O) oxide-based solid electrolyte particles having a particle size of 310 nm (weight ratio of liquid electrolyte + monomer:oxide-based particles = 25:1) with 100 parts by weight of the mixture.

[0069] The subsequent thermosetting steps were carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Example 3.

[0070] Example 4: Manufacturing of a complex electrolyte The manufacturing method for Comparative Example 1 was carried out similarly up to the mixing step of the liquid electrolyte and the monomer having a curable functional group. Furthermore, a composite electrolyte-forming composition was produced by mixing 0.1 parts by weight of AIBN, a thermal initiator, and 11.1 parts by weight of lithium oxide (Li2O) oxide-based solid electrolyte particles having a particle size of 310 nm (weight ratio of liquid electrolyte + monomer:oxide-based particles = 9:1) with 100 parts by weight of the mixture.

[0071] The subsequent thermosetting steps were carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Example 4.

[0072] Comparative Example 2: Manufacturing of Composite Electrolytes In the manufacturing method of Example 2, LiAl having a particle size of 400 nm 0.3 Ti 1.7 The composite electrolyte of Comparative Example 2 was prepared in the same manner as in Example 2, except that oxide-based solid electrolyte particles with the same chemical formula but a particle size of 200 nm were used instead of oxide-based solid electrolyte particles of (PO4)3 (LATP-based).

[0073] Comparative Example 3: Manufacturing of Composite Electrolytes The manufacturing method of Comparative Example 1 was carried out similarly up to the mixing step of the liquid electrolyte and the monomer having a curable functional group. Furthermore, 0.1 parts by weight of AIBN as a thermal initiator and LiAl having a particle size of 200 nm were added to 100 parts by weight of the mixture. 0.3 Ti 1.7 A composite electrolyte-forming composition was prepared by mixing 25 parts by weight of (PO4)3 (LATP-based) oxide-based solid electrolyte particles (weight ratio of liquid electrolyte + monomer:oxide-based particles = 8:2).

[0074] The subsequent thermosetting process was carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Comparative Example 3.

[0075] Comparative Example 4: Manufacturing of Composite Electrolytes The manufacturing method of Comparative Example 1 was carried out similarly up to the mixing step of the liquid electrolyte and the monomer having a curable functional group. Furthermore, 0.1 parts by weight of AIBN as a thermal initiator and LiAl having a particle size of 200 nm were added to 100 parts by weight of the mixture. 0.3 Ti 1.7 A composite electrolyte-forming composition was prepared by mixing 42.86 parts by weight of (PO4)3 (LATP-based) oxide-based solid electrolyte particles (weight ratio of liquid electrolyte + monomer to oxide-based particles = 7:3).

[0076] The subsequent thermosetting process was carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Comparative Example 4.

[0077] Battery Example 1: Manufacturing of Lithium-ion Rechargeable Batteries First, as the positive electrode active material, lithium nickel cobalt manganese composite oxide (NCM 811), which contains 80 mol% nickel among the total transition metals, was used. As the positive electrode active material, carbon black and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 96.5:1.5:2, and dispersed in NMP solvent to produce a slurry. This slurry was then coated onto 25 μm thick aluminum foil (Al foil) to a uniform thickness using a blade-type coating machine called a Metis coater (Labdryer / coater type LTE, Werner Mathis AG), and dried in a vacuum oven at 120°C for 13 hours to produce a positive electrode for a lithium secondary battery.

[0078] A negative electrode for a lithium secondary battery was manufactured using graphite as the negative electrode active material, in the same manner as the positive electrode described above.

[0079] After positioning the positive and negative electrodes facing each other, an electrode assembly was manufactured by interposing the composite electrolyte membrane produced in the above example or comparative example between them, and the electrode assembly was placed inside a case to manufacture a lithium secondary battery.

[0080] Battery Example 2: Manufacturing of Lithium-ion Rechargeable Batteries First, as the positive electrode active material, lithium nickel cobalt manganese composite oxide (NCM 811), which contains 80 mol% nickel among the total transition metals, was used. As the positive electrode active material, carbon black and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 96.5:1.5:2, and dispersed in NMP solvent to produce a slurry. This slurry was then coated onto 25 μm thick aluminum foil (Al foil) to a uniform thickness using a blade-type coating machine called a Metis coater (Labdryer / coater type LTE, Werner Mathis AG), and dried in a vacuum oven at 120°C for 13 hours to produce a positive electrode for a lithium secondary battery.

[0081] A negative electrode for a lithium secondary battery was manufactured using graphite as the negative electrode active material, in the same manner as the positive electrode described above.

[0082] After applying the composite electrolyte-forming composition of Example 2 onto the positive electrode, a thermosetting process was carried out on the positive electrode under the same conditions as in Comparative Example 1. As a result, the composite electrolyte of Example 2 was produced with the composite electrolyte coated onto the positive electrode. For reference, surface photographs of the positive electrode before application of the composite electrolyte-forming composition and the positive electrode with the composite electrolyte of Example 2 coated are shown in Figures 1a and 1b, respectively.

[0083] Next, after positioning the positive and negative electrodes facing each other, an electrode assembly was manufactured by interposing a composite electrolyte membrane or a porous polyethylene-based separation membrane, which was produced in the above example or comparative example, between them. The electrode assembly was then positioned inside a case to manufacture a lithium secondary battery.

[0084] Experimental example: Measurement of ionic conductivity The ionic conductivity of the composite electrolytes for lithium secondary batteries produced in Examples 1 to 4 and Comparative Examples 1 to 4 was measured, and the results are shown in Table 1 below. An AC impedance (AC impedance) meter, the SP-300 Potentiostat / Galvanostat (Bio-Logic SAS, France), was used to measure the ionic conductivity.

[0085] [Table 1]

[0086] Referring to Table 1 above, it was confirmed that the composite electrolytes of Examples 1 to 4 exhibited superior electrical conductivity not only compared to Comparative Example 1, which does not contain oxide-based solid electrolyte particles, but also compared to Comparative Examples 2 to 4, in which the particle size of the oxide-based solid electrolyte particles deviates from a certain standard.

Claims

1. Liquid electrolytes, A monomer crosslinked polymer having a curable functional group, The crosslinked polymer contains oxide-based solid electrolyte particles having a particle size between 300 nm and 800 nm, A composite electrolyte comprising oxide-based solid electrolyte particles in an amount of 0.1 to 11.1 parts by weight per 100 parts by weight of the liquid electrolyte and crosslinked polymer.

2. The composite electrolyte according to claim 1, wherein the liquid electrolyte comprises an organic solvent and a lithium salt.

3. The composite electrolyte according to claim 2, wherein the organic solvent comprises one or more selected from the group consisting of carbonate solvents, ether solvents, nitrile solvents, sulfone solvents, and phosphate solvents.

4. The composite electrolyte according to claim 1, wherein the monomer having a curable functional group comprises one or more 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 cyanoethoxyacrylate, cyanoacrylic acid, hydroxyethyl methacrylate, and hydroxypropyl acrylate.

5. The composite electrolyte according to claim 1, wherein the crosslinked polymer is included in an amount of 3 to 20% by weight based on the total weight of the composite electrolyte.

6. The composite electrolyte according to claim 1, wherein the oxide-based solid electrolyte particles have a particle size of 310 to 800 nm.

7. The composite electrolyte according to claim 1, wherein the oxide-based solid electrolyte particles include one or more particles selected from the group consisting of 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.

8. The composite electrolyte according to claim 1, wherein the oxide-based solid electrolyte particles are contained in an amount of 0.1 to 4 parts by weight per 100 parts by weight of the liquid electrolyte and the crosslinked polymer.

9. The process involves forming a composition on a substrate that includes a liquid electrolyte, a monomer having a curable functional group, and oxide-based solid electrolyte particles having a particle size exceeding 300 nm. A method for producing a composite electrolyte according to any one of claims 1 to 8, comprising the step of thermally curing the monomer contained in the composition at 60°C or higher in the presence of an initiator.

10. The method for producing a composite electrolyte according to claim 9, wherein the initiator is selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butylperoxy-2-ethyl-hexanoate, cumylhydroperoxide, hydrogen peroxide, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), and 2,2'-azobisdimethylvaleronitrile (AMVN).

11. A lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a composite electrolyte according to any one of claims 1 to 8 interposed between the positive electrode and the negative electrode.

12. The lithium secondary battery according to claim 11, wherein the composite electrolyte is coated on the positive electrode or the negative electrode.

13. The lithium secondary battery according to claim 11, wherein the electrolyte layer containing the composite electrolyte is separated and interposed between the positive electrode and the negative electrode.

14. The lithium secondary battery according to claim 11, further comprising a porous separation membrane interposed between the positive electrode and the negative electrode.

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