Composite electrolyte, method for producing the same, and lithium secondary battery including 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 rapidly increasing. In particular, lithium secondary batteries have attracted attention as a driving power source for portable devices because they are lightweight and have a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively promoted.

[0004] Such lithium secondary batteries, for example, lithium - ion batteries, generally have a configuration in which a separator is interposed between a positive electrode and a negative electrode made of active materials capable of intercalation and deintercalation of lithium ions, and a liquid - state electrolyte is charged. However, in the case of lithium - ion batteries, since a liquid - state electrolyte is included, there is a high possibility of liquid leakage occurring 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 them, research on polymer solid electrolytes has been conducted. However, such polymer solid electrolytes themselves exhibit lower ionic conductivity compared to liquid electrolytes, so the use of composite electrolytes in a form containing a liquid electrolyte, for example, a lithium salt and an organic solvent, in the polymer has been more widely studied.

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

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to provide 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 manufacturing the composite electrolyte, including forming a composition containing a liquid electrolyte, a monomer having a curable functional group, and oxide-based solid electrolyte particles having a particle size exceeding 300 nm on a substrate, and thermally curing the monomer contained in the composition at 60°C or higher in the presence of an initiator.

[0011] The present invention also provides a lithium secondary battery including 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] Hereinafter, the composite electrolyte, its manufacturing method, the lithium secondary battery, etc. according to specific embodiments of the invention will be described.

[0013] The composite electrolyte according to an embodiment of the invention includes 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.

[0014] The composite electrolyte according to the above embodiment includes a crosslinked polymer obtained by curing a monomer having a curable functional group (such as an ethylenic unsaturated bond) by a method such as thermal curing, and a liquid electrolyte contained in such a crosslinked polymer and oxide-based solid electrolyte particles having a particle size exceeding 300 nm, or 310 to 800 nm, or 350 to 600 nm, dispersed on the crosslinked polymer.

[0015] The composite electrolyte of such an embodiment contains a liquid electrolyte, for example, an electrolytic solution containing a non-aqueous organic solvent and a lithium salt, in the crosslinked structure of the crosslinked polymer, and thus can exhibit excellent mechanical physical properties without a separate separator, and can minimize the occurrence of liquid leakage of the liquid electrolyte and ignition.

[0016] Furthermore, it has been confirmed that by further including the oxide-based solid electrolyte particles in the crosslinked polymer, particularly oxide-based solid electrolyte particles with optimized particle size and / or content range, it is possible to exhibit more improved ionic conductivity. This is presumably because the particle size and content of the oxide-based solid electrolyte particles are optimized, and these particles can be more uniformly dispersed in the crosslinked polymer and the liquid electrolyte. As a result, the ionic conductivity related to the liquid electrolyte and the oxide-based solid electrolyte particles is maximized, and the ionic conductivity of the composite electrolyte of the one embodiment can be further improved.

[0017] On the other hand, the liquid electrolyte contained in the crosslinked polymer may contain a non-aqueous organic solvent and a lithium salt. Such a non-aqueous organic solvent can maintain a liquid state within the crosslinked structure of the crosslinked polymer, or a part of it can be cured 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. Thereby, such a liquid electrolyte is contained in the crosslinked polymer, and the composite electrolyte can exhibit excellent ionic conductivity compared to a solid-state polymer solid electrolyte.

[0018] At this time, the type of non-aqueous organic solvent that can be used is not particularly limited, and any organic solvent known to be applicable to electrolytes of conventional lithium-ion batteries and the like can be used. Examples of such organic solvents include one or more 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, methyl (2,2,2-trifluoroethyl) carbonate, etc. may be used. As the phosphate solvent, trimethyl phosphate, triethyl phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide, etc. may be used.

[0020] Further, as the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, or tetrahydrofuran derivatives such as 2-methyltetrahydrofuran may be used. As the nitrile solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, propionitrile, etc. may be used. Also, as the sulfone solvent, dimethyl sulfone, ethyl methyl sulfone, sulforane, etc. may be used.

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

[0022] On the one hand, as the lithium salt dissolved or dispersed in the organic solvent, any lithium salt known to be applicable to the electrolyte of a conventional lithium secondary battery may be used. For example, LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiCl, LiBr, LiI, LiClO 4 4 4 6 6 10 10 4 10 3 3 3 3 3 3 3 2 3 4 3 8 6 6 6 6 4 4 3 3 3 3 3 3 3 3 3 2 3 5 3 2 ) 2 2 3 3 2 ) 3 2

[0023] Such a lithium salt may be contained 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, whereby the composite electrolyte of one embodiment can 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 below in a crosslinked structure. Such a crosslinked polymer may be a crosslinked polymer obtained by thermosetting a polyfunctional monomer having a plurality of curable unsaturated bonds, such as a (meth)acrylate group, an alkoxylate group, a hydroxy group, a cyano group, or a carboxylic acid group.

[0025] When the liquid electrolyte is contained within the crosslinked structure of such a crosslinked polymer, the composite electrolyte exhibits excellent mechanical properties even without a separate separator, and can suppress liquid leakage to further improve the safety of the lithium secondary battery.

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

[0027] Such a crosslinked polymer may be contained in a content of 3 to 20% by weight, or 5 to 15% by weight, based on the total weight of the composite electrolyte. Thereby, the composite electrolyte of the above-described embodiment can exhibit more excellent mechanical properties, and while liquid leakage and the like are more effectively suppressed, the liquid electrolyte and the oxide-based solid electrolyte particles are uniformly contained and dispersed on such a crosslinked polymer, and can exhibit further improved ionic conductivity.

[0028] On the other hand, in order for the composite electrolyte of one embodiment to exhibit further improved ionic conductivity, it further includes oxide-based solid electrolyte particles having a particle size exceeding 300 nm, or 310 to 800 nm, or 350 to 600 nm and dispersed on the crosslinked polymer.

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

[0030] Examples of such oxide-based solid electrolyte particles include, for example, LAGP (lithium aluminum germanium phosphate)-based compounds, LLZO (lithium lanthanum zirconium oxide)-based compounds, LATP (lithium aluminum titanium phosphate)-based compounds, LLZTO (lithium lanthanum zirconium tantalum oxide)-based compounds, LSTP (lithium silicon titanium phosphate)-based compounds, and one or more lithium-containing oxide-based particles selected from the group consisting of lithium oxides (e.g., Li 2 O). Among these, using particles of the LATP (lithium aluminum titanium phosphate)-based compound can further improve the cation transport coefficient, and the composite electrolyte of one embodiment can exhibit further improved ionic conductivity.

[0031] Further, the oxide-based solid electrolyte particles may be contained in an amount of 0.1 to 15 parts by weight, or 0.3 to 12 parts by weight, based on 100 parts by weight in total of the aforementioned liquid electrolyte and crosslinked polymer. When the content of the oxide-based solid electrolyte particles becomes excessively small, the ionic conductivity of the composite electrolyte is not sufficient, and it has been confirmed that when the content becomes excessively large, the ionic conductivity of the composite electrolyte rather decreases.

[0032] The composite electrolyte of the above-described embodiment can be produced by a method including the steps of forming, on a substrate, a composition containing each component of the above-described composite electrolyte, that is, a liquid electrolyte, a monomer having a curable functional group, and oxide-based solid electrolyte particles having a particle size exceeding 300 nm; and thermally curing the monomer contained in the composition at 60°C or higher, or at 60 to 80°C, in the presence of an initiator.

[0033] According to such a production method, a composite electrolyte of an embodiment having excellent mechanical physical properties and ionic conductivity can be produced by a simple method of mixing each component of the composite electrolyte of an embodiment and thermally curing the monomer in the presence of a thermal initiator or the like. Further, by producing the composite electrolyte by thermal curing at a temperature of about 60 to 80°C by such a production method, it is possible to reduce the phenomenon that an organic solvent or the like contained in the liquid electrolyte evaporates during the production process, and a composite electrolyte having better characteristics can be produced.

[0034] On the other hand, according to an example of the production method of the composite electrolyte, the above-described organic solvent and lithium salt are first mixed to form a liquid electrolyte, and a monomer having a curable functional group, oxide-based solid electrolyte particles having a particle size exceeding 300 nm, a thermal initiator, and the like are simultaneously or sequentially added and mixed to such a liquid electrolyte, and then such a composition is coated on the substrate and heat-treated and cured to produce the above-described composite electrolyte.

[0035] At this time, the curing step or the like may be performed on a separate porous separation membrane, or on the electrodes of the positive electrode or the negative electrode, or on a separately prepared substrate, for example, a resin substrate such as polyester like PET. Depending on the type of each substrate on which such a curing step is performed, the composite electrolyte may be produced in a form coated on a separation membrane, in a form coated and adhered on each electrode, or in a free-standing film form by itself, and may be applied as an electrolyte membrane replacing the porous separation membrane of a lithium secondary battery.

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

[0037] On the other hand, for the appropriate thermal curing of the above-described monomer, as the initiator, a thermal initiator known to be usable for the curing or crosslinking polymerization of a polyfunctional monomer having a conventional (meth) acrylate group, alkoxylate group, hydroxy group, cyano group or carboxylic acid group can be used. 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, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN) or 2,2'-azobisdimethyl-valeronitrile (AMVN), etc. Two or more selected from these may be used together, or other various thermal initiators may be used.

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

[0039] More specifically, according to an example, the composite electrolyte may be included in the form of an overcoating film coated and adhered on the positive electrode or the negative electrode (for example, refer to Battery Example 2 below), or may be manufactured in the form of a free-standing film, etc., and is not adhered on the positive electrode and the negative electrode, and may be included in the form of an electrolyte film that is separably interposed between these positive electrode and negative electrode (for example, refer to Battery Example 1 below). Further, such an electrolyte film may be included alone, but for imparting additional mechanical physical properties and insulation properties of the lithium secondary battery, etc., it may further include a porous separator interposed between the positive electrode and the negative electrode together with the electrolyte film, and may have a form in which the electrolyte film is laminated on such a porous separator.

[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 desorption of lithium ions. For example, it may include 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 D 2 (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 Z 2 (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 Z 2 (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 d O 2 (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 G e O 2 (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 NiGb O 2 (In the above formula, 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li a CoG b O 2 (In the above formula, 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li a MnG b O 2 (In the above formula, 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li a Mn 2 G b O 4 (In the above formula, 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); QO 2 ; QS 2 ; LiQS 2 ; V 2 O 5 ; LiV 2 O 5 ; LiTO 2 ; LiNiVO 4 ; Li (3-f) J 2 (PO 4 ) 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] Further, the positive electrode may further contain a binder, a conductive material, etc. in addition to the positive electrode active material described above. The binder is a component that assists in the binding between the positive electrode active material and the conductive material, etc. and the binding to the current collector. For example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride - hexafluoropropylene 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, polyvinyl pyridine, polyvinyl pyrrolidone, styrene - butadiene rubber, acrylonitrile - butadiene rubber, ethylene - propylene - diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene - butylene rubber, fluorine rubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and one or more selected from the group consisting of mixtures thereof may be used, but it is not necessarily limited thereto.

[0044] The binder may be used in a content 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, excellent adhesion between the positive electrode active material and the current collector and capacity characteristics of the secondary battery, etc. can be maintained.

[0045] In addition, 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 and 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 substances whose crystal 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 whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives may be used alone or in combination of two or more, but are not necessarily limited thereto.

[0046] The conductive material may be used in a content 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. Thereby, electrochemical properties such as conductivity and capacity of the excellent positive electrode and lithium secondary battery can be maintained.

[0047] In addition, a filler may be selectively added to the positive electrode as a component for suppressing its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous substances such as glass fibers and carbon fibers may be used.

[0048] The above-described positive electrode can be manufactured, for example, by dispersing and mixing the positive electrode active material, binder, conductive material, etc. in a dispersion medium (solvent) to form a slurry, applying this slurry onto a positive electrode current collector, and then drying and rolling. At this time, as the dispersion medium, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof may be used, but it is not necessarily limited thereto.

[0049] Also, as the positive electrode current collector, 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 SnO 2 )、FTO (F doped SnO 2 ), and alloys thereof, and those obtained by surface-treating the surface of aluminum (Al) or stainless steel with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) may be used, but it is not necessarily limited thereto. The form of the positive electrode current collector may be in the form of foil, film, sheet, punched material, porous body, foam, etc.

[0050] Also, in the lithium secondary battery of the other embodiments described above, the negative electrode can be manufactured by a conventional method 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, if necessary, a filler, etc. in a dispersion medium (solvent), applying this slurry onto a negative electrode current collector, and then drying and rolling to manufacture the negative electrode.

[0051] At this time, as the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. 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 alloy, Sn alloy, or Al alloy; metal oxides capable of doping and undoping lithium such as SiOβ(0 < β < 2), SnO 2 , vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, and any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. In addition, as the carbonaceous material, both low-crystalline carbon and high-crystalline carbon may be used. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural graphite 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] Also, as the binder and the conductive material, the same materials as those described for the positive electrode above are used, so additional explanation regarding this is omitted.

[0053] 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 SnO 2 )), FTO (F doped SnO 2 ))), and alloys thereof, and those obtained by surface-treating the surface of copper (Cu) or stainless steel with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) may be used, but are not necessarily limited thereto. The form of the negative electrode current collector may be in the form of a foil, film, sheet, punched material, porous body, foam, or the like.

[0054] On the other hand, in the lithium secondary battery of the other embodiment, as already described above, a composite electrolyte of one embodiment may be interposed, for example, in the form of a film or a film having a layered structure between the positive electrode and the negative electrode. In this case, the composite electrolyte membrane can also serve as a separator (that is, a role of electrically insulating the negative electrode and the positive electrode and at the same time allowing lithium ions to pass through). At this time, the composite electrolyte membrane may be coated and adhered to one surface of the positive electrode or the negative electrode in the form of a thin film and included in the secondary battery. Further, the composite electrolyte membrane may be independently interposed between the positive electrode and the negative electrode. And the lithium secondary battery of the other embodiment may be a semi-solid battery that uses a liquid electrolyte and a solid electrolyte in combination.

[0055] Meanwhile, when a porous separator is added to the lithium secondary battery, such a separator may be used in the form of a sheet, a multilayer film, a microporous film, a woven fabric, a non-woven fabric, etc. made of an olefin polymer such as polyethylene or polypropylene, glass fiber, etc., but is not necessarily limited thereto. However, it is preferable to apply a porous polyethylene or a porous glass fiber non-woven fabric (glass filter) as the separator, and it is more preferable to apply a porous glass fiber non-woven fabric (glass filter) 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 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 battery of the other embodiment can be manufactured by a conventional method in the art. For example, a composite electrolyte membrane or the like can be formed between the positive electrode and the negative electrode, and a porous separator or the like can be selectively added for manufacturing.

[0057] Such a lithium secondary battery is particularly suitable for being used as a unit cell of a battery module which is a power source for medium and large-sized devices, as well as being applied to a battery cell used as a power source for small-sized devices.

Advantages of the Invention

[0058] According to the present invention, since the liquid electrolyte is contained in the cross-linked structure of the cross-linked polymer, a composite electrolyte can be provided which can exhibit excellent mechanical physical properties even without a separate separator, and from which leakage of a liquid such as the liquid electrolyte and ignition can be minimized.

[0059] In addition, such a composite electrolyte can exhibit improved ion conductivity, and can greatly contribute to the improvement of the safety and electrical characteristics of the lithium secondary battery.

Brief Description of the Drawings

[0060]

Fig. 1a

Fig. 1b

[0061] Hereinafter, preferred embodiments are presented for the understanding of the invention. However, the following embodiments are only illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the invention and the scope of the technical idea. It is natural that such changes and modifications belong to the scope of the appended claims.

[0062] Comparative Example 1: Production of Composite Electrolyte First, as a non-aqueous organic solvent, a mixed solvent obtained by mixing ethylene carbonate and propylene carbonate at a volume ratio of 1:1 was used. To this, lithium salt LiPF 6 was dissolved at a concentration of 1 M to form a liquid electrolyte. Such a liquid electrolyte was mixed with ethoxylated trimethylolpropane triacrylate (ETPTA), a monomer having a curable functional group, at a weight ratio of 90:10. Further, 0.1 part by weight of AIBN, a thermal initiator, was mixed with 100 parts by weight of the mixture to produce a composition for forming a composite electrolyte.

[0063] Such a composition was coated on a PET substrate with a bar coater and heat-treated at a temperature of 60°C for 360 minutes to perform thermosetting. Through this, the composite electrolyte of Comparative Example 1 formed on the substrate was produced.

[0064] Example 1: Production of Composite Electrolyte Using the manufacturing method of Comparative Example 1, the process was carried out in the same manner up to the mixing process of the liquid electrolyte and the monomer having a curable functional group. Further, with respect to 100 parts by weight of the mixture, 0.1 part by weight of AIBN as a thermal initiator and LiAl 0.3 Ti 1.7 (PO 4 ) 3 (LATP-based) oxide-based solid electrolyte particles were mixed at 4 parts by weight (weight ratio of liquid electrolyte + monomer: oxide-based particles = 25:1) to produce a composition for forming a composite electrolyte.

[0065] The subsequent heat curing process was carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Example 1.

[0066] Example 2: Production of Composite Electrolyte Using the manufacturing method of Comparative Example 1, the process was carried out in the same manner up to the mixing process of the liquid electrolyte and the monomer having a curable functional group. Further, with respect to 100 parts by weight of the mixture, 0.1 part by weight of AIBN as a thermal initiator and LiAl 0.3 Ti 1.7 (PO 4 ) 3 (LATP-based) oxide-based solid electrolyte particles were mixed at 11.1 parts by weight (weight ratio of liquid electrolyte + monomer: oxide-based particles = 9:1) to produce a composition for forming a composite electrolyte.

[0067] The subsequent heat curing process was carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Example 2.

[0068] Example 3: Production of Composite Electrolyte Using the manufacturing method of Comparative Example 1, the process was carried out in the same manner up to the mixing process of the liquid electrolyte and the monomer having a curable functional group. Further, with respect to 100 parts by weight of the mixture, 0.1 part by weight of AIBN as a thermal initiator and lithium oxide (Li 2 O) oxide-based solid electrolyte particles having a particle size of 310 nm were mixed at 4 parts by weight (weight ratio of liquid electrolyte + monomer: oxide-based particles = 25:1) to produce a composition for forming a composite electrolyte.

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

[0070] Example 4: Production of Composite Electrolyte The production method of Comparative Example 1 was carried out in the same manner up to the mixing process of the liquid electrolyte and the monomer having a curable functional group. Further, with respect to 100 parts by weight of the mixture, 0.1 part by weight of AIBN as a thermal initiator and lithium oxide (Li 2 O) oxide-based solid electrolyte particles having a particle size of 310 nm were mixed at 11.1 parts by weight (weight ratio of liquid electrolyte + monomer: oxide-based particles = 9:1) to produce a composition for forming a composite electrolyte.

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

[0072] Comparative Example 2: Production of Composite Electrolyte The composite electrolyte of Comparative Example 2 was produced in the same manner as in Example 2, except that oxide-based solid electrolyte particles having the same chemical formula with a particle size of 200 nm were used instead of the oxide-based solid electrolyte particles of LiAl 0.3 Ti 1.7 (PO 4 ) 3 (LATP-based) having a particle size of 400 nm.

[0073] Comparative Example 3: Production of Composite Electrolyte The production method of Comparative Example 1 was carried out in the same manner up to the mixing process of the liquid electrolyte and the monomer having a curable functional group. Further, with respect to 100 parts by weight of the mixture, 0.1 part by weight of AIBN as a thermal initiator and LiAl having a particle size of 200 nm 0.3 Ti 1.7 (PO 4 ) 3 (LATP-based) oxide-based solid electrolyte particles were mixed at 25 parts by weight (weight ratio of liquid electrolyte + monomer: oxide-based particles = 8:2) to produce a composition for forming a composite electrolyte.

[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: Production of Composite Electrolyte Using the production method of Comparative Example 1, the process up to the mixing process of the liquid electrolyte and the monomer having a curable functional group was carried out in the same manner. Further, with respect to 100 parts by weight of the mixture, 0.1 part by weight of AIBN which is a thermal initiator and LiAl having a particle size of 200 nm 0.3 Ti 1.7 (PO 4 ) 3 (LATP-based) oxide-based solid electrolyte particles were mixed at 42.86 parts by weight (weight ratio of liquid electrolyte + monomer: oxide-based particles = 7:3) to produce a composition for forming a composite electrolyte.

[0076] Subsequent heat curing steps were carried out in the same manner as in Comparative Example 1 to produce the composite electrolyte of Comparative Example 4.

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

[0078] Using graphite as the negative electrode active material, a negative electrode for a lithium secondary battery was produced in the same manner as the above positive electrode.

[0079] After positioning the positive electrode and the negative electrode to face each other, an electrode assembly was produced with the composite electrolyte film produced in the above Example or Comparative Example interposed therebetween, and the electrode assembly was positioned inside a case to produce a lithium secondary battery.

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

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

[0082] After applying the composition for forming the composite electrolyte of Example 2 on the positive electrode, a thermosetting process was performed on the positive electrode under the same conditions as in Comparative Example 1. As a result, the composite electrolyte of Example 2 was manufactured in a state where the composite electrolyte was overcoated on the positive electrode. For reference, surface photographs of the positive electrode before applying the composition for forming the composite electrolyte and the positive electrode overcoated with the composite electrolyte of Example 2 are shown in FIGS. 1a and 1b, respectively.

[0083] Next, after positioning the positive electrode and the negative electrode to face each other, an electrode assembly was manufactured with the composite electrolyte membrane or porous polyethylene-based separator manufactured in the above Example or Comparative Example interposed therebetween, and the electrode assembly was positioned inside a case to manufacture a lithium secondary battery.

[0084] Experimental Example: Measurement of Ionic Conductivity The ionic conductivities of the composite electrolytes for lithium secondary batteries respectively produced in Examples 1 to 4 and Comparative Examples 1 to 4 were measured, and the results are shown in Table 1 below. For the measurement of the ionic conductivity, an SP-300 Potentiostat / Galvanostat (Bio-Logic SAS, France), which is an alternating current impedance (AC impedance) measuring device, was used.

[0085]

Table 1

[0086] Referring to Table 1 above, it was confirmed that the composite electrolytes of Examples 1 to 4 exhibit excellent electrical conductivity not only as compared with Comparative Example 1 in which no oxide-based solid electrolyte particles are contained, but also as compared with Comparative Examples 2 to 4 in which the particle size and the like of the oxide-based solid electrolyte particles deviate from a certain level.

Claims

1. 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, a composite electrolyte.

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

3. The composite electrolyte according to claim 2, wherein the organic solvent contains 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 contains one or more selected from the group consisting of ethylene glycol diacrylate, triethylene glycol diacrylate, ethoxylated 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 contained in a content 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 contain one or more particles selected from the group consisting of LAGP (lithium aluminum germanium phosphate) - based compounds, LLZO (lithium lanthanum zirconium oxide) - based compounds, LATP (lithium aluminum titanium phosphate) - based compounds, LLZTO (lithium lanthanum zirconium tantalum oxide) - based compounds, LSTP (lithium silicon titanium phosphate) - based compounds, and lithium oxides.

8. The composite electrolyte according to claim 1, wherein the oxide-based solid electrolyte particles are contained in a content of 0.1 to 15 parts by weight with respect to a total of 100 parts by weight of the liquid electrolyte and the crosslinked polymer.

9. Forming a composition containing a liquid electrolyte, a monomer having a curable functional group, and oxide-based solid electrolyte particles having a particle size exceeding 300 nm on a substrate, A method for manufacturing the composite electrolyte according to any one of claims 1 to 8, comprising the step of thermosetting the monomer contained in the composition at 60°C or higher in the presence of an initiator.

10. The method for manufacturing the 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-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).

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 the 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 an electrolyte layer containing the composite electrolyte is separably interposed between the positive electrode and the negative electrode.

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

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