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

Abstract

A composite film for an electrolyte according to one embodiment of the present invention contains an ion-conducting polymer and inorganic particles, the ion-conducting polymer containing a polyurethane-based compound, and the elongation at break of the composite film for an electrolyte is 50% or more.

Description

Technical Field

[0001] This invention relates to a composite membrane for electrolytes, a composite electrolyte, a method for manufacturing the same, and a lithium secondary battery including the same. Background Technology

[0002] In recent years, with increasing concern about environmental issues, lithium-ion batteries, characterized by high discharge voltage and power stability, have been primarily used as power sources for electric vehicles (EVs) and other fuel-powered vehicles, replacing fossil fuel-based vehicles. However, existing lithium-ion batteries using liquid electrolytes such as organic solvents suffer from problems such as fire risks due to electrolyte leakage, electrolyte decomposition due to electrode reactions, and resulting battery swelling. Therefore, to address these issues, research is actively underway on lithium-ion batteries using solid-state electrolytes. Summary of the Invention

[0003] (a) Technical problems to be solved One aspect of the present invention aims to provide a composite electrolyte with excellent ionic conductivity.

[0004] Another aspect of the present invention aims to provide a composite electrolyte with improved mechanical and physical properties.

[0005] Another aspect of the present invention aims to provide a lithium secondary battery with excellent performance.

[0006] (II) Technical Solution An electrolyte composite membrane according to one embodiment comprises an ion-conducting polymer and inorganic particles, wherein the ion-conducting polymer comprises a polyurethane-based compound, and the electrolyte composite membrane has an elongation at break of 50% or more.

[0007] The number of functional groups capable of forming hydrogen bonds in each structural unit of the polyurethane-based compound can be from 2 to 18.

[0008] The polyurethane-based compound may include soft-segment and hard-segment.

[0009] The soft segment may contain structural units represented by the following chemical formula 1.

[0010] [Chemical Formula 1] -OR 1 -O- In the chemical formula 1, R 1 It is a divalent aliphatic organic group.

[0011] The hard segment may contain structural units represented by the following chemical formula 2.

[0012] [Chemical Formula 2] -C(=O)(NR 3 )-R 2 -(NR 4 )C(=O)- In the chemical formula 2, R 2 R is an organic group containing an aromatic ring. 3 and R 4 Each is independently hydrogen or an alkyl group having 1 to 5 carbon atoms, either substituted or unsubstituted.

[0013] The ion-conducting polymer may further comprise any one selected from polyethylene oxide (PEO)-based compounds, polyvinylidene fluoride (PVDF)-based compounds, polymethyl methacrylate (PMMA)-based compounds, and combinations thereof.

[0014] The inorganic particles may include any one selected from garnet compounds, sodium superionic conductor compounds, perovskite compounds, and combinations thereof.

[0015] The composite electrolyte according to one embodiment comprises: an electrolyte composite membrane according to any of the above embodiments; an acrylic compound; and a liquid electrolyte.

[0016] The acrylic compound may comprise a compound having 3 to 8 (meth)acryloyl groups per molecule.

[0017] The acrylate compound may include any one selected from ethoxylated trimethylolpropane triacrylate (TMPETA), trimethylolpropane trimethacrylate (TMPTMA), trimethylolpropane triacrylate (TMPTA), tetramethylolmethane tetraacrylate (TMMTA), and combinations thereof.

[0018] The liquid electrolyte may contain lithium salts and carbonate-based solvents.

[0019] The content of the ion-conducting polymer in the composite electrolyte can be from 10% to 70% by weight.

[0020] The content of inorganic particles in the composite electrolyte can be from 1% to 20% by weight.

[0021] The weight ratio of ion-conducting polymer to inorganic particles in the composite electrolyte can be from 1:1 to 30:1.

[0022] The content of acrylic acid compounds in the composite electrolyte can be from 1% to 10% by weight.

[0023] The composite electrolyte can be a free-standing membrane.

[0024] The thickness of the composite electrolyte can be from 10 μm to 200 μm.

[0025] A method for manufacturing a composite electrolyte according to one specific embodiment includes the following steps: preparing a slurry comprising an ion-conducting polymer, inorganic particles, and an organic solvent; coating the slurry onto a substrate and drying it to form a composite membrane for electrolyte; and mixing the composite membrane for electrolyte with an acrylic-based compound and a liquid electrolyte and then curing it to form a composite electrolyte, wherein the ion-conducting polymer comprises a polyurethane-based compound.

[0026] A lithium secondary battery according to one embodiment includes a composite electrolyte according to any of the above embodiments.

[0027] The lithium secondary battery may include a lithium metal anode (LMA).

[0028] (III) Beneficial Effects According to one specific embodiment of the present invention, a composite electrolyte with improved ionic conductivity can be manufactured with excellent processability.

[0029] According to another specific embodiment of the present invention, a composite electrolyte with improved mechanical and physical properties can be manufactured with excellent processability.

[0030] According to another specific embodiment of the present invention, the risk of fire caused by leakage of electrolyte inside a lithium secondary battery can be mitigated.

[0031] According to another specific embodiment of the present invention, a lithium secondary battery with excellent performance can be provided. Attached Figure Description

[0032] Figure 1 This is a diagram showing the morphology of the electrolyte composite membrane according to Example 1 and Comparative Examples 1 to 3.

[0033] Figure 2 This is a graph showing the stress-strain curves measured for the electrolyte composite membranes according to Example 1 and Comparative Examples 1 to 3.

[0034] Figure 3 This is a graph showing the stress-strain curves measured for the electrolyte composite membrane according to Example 1.

[0035] Figure 4 This is a graph showing the results of measuring the voltage over time during the charging / discharging process of a lithium secondary battery comprising the composite electrolytes according to Example 1 and Comparative Examples 1 to 3.

[0036] Figure 5 This is a diagram showing the morphology of the electrolyte composite membrane according to Comparative Example 1 before and after impregnation with liquid electrolyte.

[0037] Figure 6 This is a graph showing the results of lithium surface analysis and electrolyte layer confirmation after charging / discharging a lithium secondary battery including the composite electrolytes according to Example 1 and Comparative Examples 1 to 3. Best practice

[0038] In this specification, "polymer" may include oligomers and may also include copolymers with homopolymers. The copolymers may be alternating copolymers, block copolymers, random copolymers, graft copolymers, crosslinked copolymers, or substances comprising all of these.

[0039] In this specification, "alkyl" can refer to an organic radical derived from an aliphatic hydrocarbon by removing a hydrogen atom, and can include straight-chain or branched forms. The alkyl group can have 1 to 10 carbon atoms, specifically 1 to 7 carbon atoms, 1 to 5 carbon atoms, or 1 to 3 carbon atoms. The alkyl group can include, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, ethylhexyl, etc., but is not limited thereto.

[0040] In this specification, aromatic rings may include monocyclic or fused-ring groups, each ring suitably comprising four to seven, specifically five or six, ring atoms, and may also include multiple aromatic rings bonded by single or alkyl bonds. As an example, aromatic rings may include benzene, naphthalene, biphenyl, terphenyl, etc., but are not limited thereto.

[0041] Unless otherwise defined in this specification, “(meth)acrylic acid” may be used to mean both “methacrylic acid” and “acrylic acid”.

[0042] In this specification, "polymer electrolyte" can refer not only to all-solid-state electrolytes, but also to "gel polymer electrolytes" that contain an electrolyte in a polymer-based electrolyte. For example, depending on the manufacturing method, the gel polymer electrolyte can be in the form of a polymer matrix that is swollen with electrolyte (physical gel), or it can be in the form of a composition that is cured by curing a mixture of electrolyte and monomer (chemical gel).

[0043] Solid electrolytes can be classified into oxide-based electrolytes, sulfide-based electrolytes, and polymer-based electrolytes. Among these, polymer-based solid electrolytes offer relatively excellent economic benefits, but their ionic conductivity and mechanophysical properties may be insufficient. To address these issues, a composite electrolyte combining polymer and inorganic particles can be used in one specific implementation. However, the ionic conductivity and mechanophysical properties of polymer-based solid electrolytes may be in a trade-off relationship, making it difficult to improve both simultaneously.

[0044] Specifically, in manufacturing composite electrolytes that combine polymers and inorganic particles, polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF) can be used as polymer materials. However, composite electrolytes using PEO have relatively insufficient mechanical and physical properties and formability, making them potentially unsuitable for high voltage applications. Furthermore, composite electrolytes using PMMA exhibit brittleness, and their ionic conductivity and processability are insufficient, potentially hindering practical use. Additionally, composite electrolytes using PVDF may present difficulties in practical applications due to their low ionic conductivity and interfacial side reactions caused by defluorination.

[0045] As mentioned above, polymers used in composite electrolytes not only need to have excellent ionic conductivity, but also appropriate dissociation ability for lithium salts, excellent moldability / processability, etc., and have no side reactions with inorganic particles and excellent contact with electrodes.

[0046] According to one specific embodiment of the present invention, a composite electrolyte can be manufactured, comprising inorganic particles with excellent conductivity to lithium ions and an ion-conducting polymer. The ion-conducting polymer is composed of a polyurethane (PU)-based compound with excellent extensibility, resilience, mechanical / chemical stability, and processability, thus exhibiting superior performance. (See reference...) Figures 1 to 6 The specific details are as follows.

[0047] Figure 1 This is a diagram showing the morphology of the electrolyte composite membrane according to Example 1 and Comparative Examples 1 to 3.

[0048] Figure 2 This is a graph showing the stress-strain curves measured for the electrolyte composite membranes according to Example 1 and Comparative Examples 1 to 3.

[0049] Figure 3 This is a graph showing the stress-strain curves measured for the electrolyte composite membrane according to Example 1.

[0050] Figure 4 This is a graph showing the results of measuring the voltage over time during the charging / discharging process of a lithium secondary battery comprising the composite electrolytes according to Example 1 and Comparative Examples 1 to 3.

[0051] Figure 5 This is a diagram showing the morphology of the electrolyte composite membrane according to Comparative Example 1 before and after impregnation with liquid electrolyte.

[0052] Figure 6 This is a graph showing the results of lithium surface analysis and electrolyte layer confirmation after charging / discharging a lithium secondary battery including the composite electrolytes according to Example 1 and Comparative Examples 1 to 3.

[0053] Electrolyte composite membrane An electrolyte composite membrane according to one embodiment comprises an ion-conducting polymer and inorganic particles, wherein the ion-conducting polymer comprises a polyurethane-based compound, and the electrolyte composite membrane has an elongation at break of 50% or more.

[0054] The electrolyte composite membrane is a composite membrane that can be used to manufacture composite electrolytes, comprising an ion-conducting polymer and inorganic particles. Specifically, the ion-conducting polymer comprises a polyurethane-based compound, which can be a polymer containing urethane bonds (-NHCOO-), i.e., polyurethane, or a copolymer thereof with other polymers. As mentioned above, polyurethane has excellent chemical / mechanical stability, ionic conductivity, etc., and high elongation / resilience, thus exhibiting excellent formability. It can appropriately dissociate lithium salts, thereby allowing the liquid electrolyte to swell internally. Compared with existing composite electrolytes, it also has higher adhesion to the electrode, thus making it highly practical as a composite electrolyte. The polyurethane-based compound will be described in more detail below.

[0055] <Polyurethane-based compounds> The number of functional groups capable of forming hydrogen bonds in each structural unit of the polyurethane-based compound can be from 2 to 18. Specifically, the number of functional groups capable of forming hydrogen bonds in each structural unit of the polyurethane-based compound can be more than 4 and less than 16. When the number of functional groups capable of forming hydrogen bonds in each structural unit of the polyurethane-based compound is within the above range, it can exhibit excellent elasticity, resilience, and elongation. The number of functional groups capable of forming hydrogen bonds in each structural unit of the polyurethane-based compound can be calculated by analyzing the repeating unit structure and measuring the amount of oxygen and nitrogen contained therein using nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FT-IR).

[0056] The polyurethane-based compound may include soft segments and hard segments. The soft segments may contain aliphatic organic groups, specifically, structural units represented by Chemical Formula 1 below, and more specifically, may be derived from polyol compounds containing aliphatic organic groups. The hard segments may contain aromatic rings, specifically, structural units represented by Chemical Formula 2 below, and more specifically, may be derived from diisocyanate compounds containing aromatic rings.

[0057] [Chemical Formula 1] -OR 1 -O- In the chemical formula 1, R 1 It is a divalent aliphatic organic group.

[0058] [Chemical Formula 2] -C(=O)(NR 3 )-R 2 -(NR 4 )C(=O)- In the chemical formula 2, R 2 R is an organic group containing an aromatic ring. 3 and R 4 Each is independently hydrogen or an alkyl group having 1 to 5 carbon atoms, either substituted or unsubstituted. In the chemical formula 1, R 1 It can be a residue containing a branched or linear acyclic aliphatic divalent organic group with 2 to 40 carbon atoms. In this case, the divalent aliphatic organic group can have a substituted or unsubstituted structure. Specifically, the R... 1 It can be an alkyl group with 2 to 40 carbon atoms, either substituted or unsubstituted, and the alkyl group may contain ester groups, ether groups, carbonate groups, etc. at both ends.

[0059] In the chemical formula 2, R 2 It can be an organic group containing an aromatic ring with 6 to 15 carbon atoms. In this case, the organic group containing the aromatic ring can have a substituted or unsubstituted structure. Specifically, the R... 2 It can be an organic group containing only an aromatic ring, such as phenylene, tolyl, xylene, or naphthyl, or it can be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms as an organic group containing aromatic rings at both ends, such as diphenylmethane.

[0060] Furthermore, the soft segment can be derived from a polyol compound having hydroxyl groups (-OH) at both ends, and can be a low-polarity moiety. Conversely, the hard segment can be derived from a diisocyanate compound having isocyanate groups (-N=C=O) at both ends, and can be a moiety containing reactive groups (-NH-) capable of forming hydrogen bonds.

[0061] The polyol compound can be represented by the following chemical formula 1-1.

[0062] [Chemical Formula 1-1] HO-R 1 -OH In the chemical formula 1-1, R 1 These are residues containing divalent aliphatic organic groups.

[0063] The R 1 Represents R in chemical formula 1 1 The same meaning is repeated in the detailed explanation above, so it is omitted here.

[0064] For example, the polyol compound may include, but is not limited to, any one selected from polyester polyols, polyether polyols, polycarbonate polyols, polycaprolactone polyols, and combinations thereof.

[0065] The diisocyanate compound can be represented by the following chemical formula 2-1.

[0066] [Chemical Formula 2-1] OCN-R 2 -NCO In the chemical formula 2-1, R 2 It is an aromatic ring.

[0067] The R 2 Represents R in chemical formula 2 2 The same meaning is repeated in the detailed explanation above, so it is omitted here.

[0068] For example, the diisocyanate compound may be selected from diphenylmethane diisocyanate (MDI), phenyl diisocyanate (PDI), toluene diisocyanate (TDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI), and combinations thereof, but is not limited thereto.

[0069] The ion-conducting polymer may further comprise any one selected from polyethylene oxide (PEO)-based compounds, polyvinylidene fluoride (PVDF)-based compounds, polymethyl methacrylate (PMMA)-based compounds, and combinations thereof. According to one specific embodiment, the ion-conducting polymer, while comprising a polyurethane-based compound, may further comprise any one selected from polyethylene oxide (PEO)-based compounds, polyvinylidene fluoride (PVDF)-based compounds, polymethyl methacrylate (PMMA)-based compounds, and combinations thereof. The term "-based compound" in the polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), and polymethyl methacrylate (PMMA)-based compounds, similar to the above description regarding polyurethane-based compounds, refers to any one selected from polymers containing "-", copolymers thereof, or combinations thereof. The inorganic particles are described in more detail below.

[0070] <Inorganic particles> The inorganic particles are oxide particles containing lithium, specifically, lithium conductive oxide-based particles. These lithium conductive oxide-based particles are compound particles containing oxygen and conductive to lithium ions. They can be in powder form and can contain at least one or more other metallic elements besides lithium, such as zirconium (Zr), phosphate (PO4), and titanium (Ti). They can also contain two or more oxide particles.

[0071] According to one specific embodiment, the inorganic particles may include any one selected from garnet compounds, sodium superionic conductor compounds, perovskite compounds, and combinations thereof. The inorganic particles are particulate inorganic materials that are conductive to lithium ions, which can help improve both the ionic conductivity and mechanophysical properties of the composite electrolyte.

[0072] The garnet compound may be a compound having a garnet crystal structure or a garnet-like crystal structure, may be a compound containing lithium, lanthanum, zirconium, and oxygen, and may be composed of Li. 7-3x+y-z A x La 3-y B y Zr 2-z M z O 12The garnet-type oxide is represented by the chemical formula. In the chemical formula, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, A can be a substituted dopant element of Li, B can be a substituted dopant element of La, and M can be a substituted dopant element of Zr. A and B can each independently be at least one selected from aluminum (Al), gallium (Ga), barium (Ba), magnesium (Mg), calcium (Ca), strontium (Sr), potassium (K), cerium (Ce), and rubidium (Rb). Furthermore, M can be at least one selected from molybdenum (Mo), tungsten (W), antimony (Sb), yttrium (Y), niobium (Nb), and tantalum (Ta). The garnet-type oxide is not limited to this, but can be exemplarily Li7La3Zr2O. 12 Li5La3Nb2O 12 Li5La3Ta2O 12 or Li6La2BaTa2O 12 .

[0073] It can be made of Li7La3Zr2O 12 Lithium lanthanum zirconium oxide (LLZO)-based compounds, represented by chemical formulas. These garnet compounds, such as lithium lanthanum zirconium oxide (LLZO)-based compounds, can be compounds doped with metals such as aluminum (Al) and tantalum (Ta).

[0074] The sodium superionic conductor compound is a compound having a sodium superionic conductor crystal structure or a sodium-like superionic conductor crystal structure, and L can be exemplarily selected from AGP (Li 1+x Al x Ge 2-x (PO4)3(0≤x≤1)), LATP(Li 1+ x Al x Ti 2-x (PO4)3(0≤x≤1)) and LZP(Li 1+4x Zr 2―x At least one of (PO4)3 (0≤x≤0.4)).

[0075] The perovskite compound is a compound having a perovskite crystal structure or a perovskite-like crystal structure. For example, it can be a compound derived from Li. 0.31 La 0.56 Lithium lanthanum titanium oxide (LLTO) based compounds represented by the chemical formula TiO3 or lithium lanthanum niobate (Li x La (1-x) / 3 NbO3)(0≤x≤1).

[0076] The inorganic particles may contain one or more compounds selected from zirconium (Zr), phosphate (PO4), and titanium (Ti). Specifically, the lithium conductive oxide-based particles 21 may be one or more compounds selected from lithium lanthanum zirconium oxide (LLZO)-based compounds, lithium lanthanum titanium oxide (LLTO)-based compounds, lithium aluminum germanium phosphate (LAGP)-based compounds, and lithium aluminum titanium phosphate (LATP)-based compounds. More specifically, the lithium conductive oxide-based particles 21 may be composed of Li7La3Zr2O 12 The chemical formula is represented by [chemical formula], and it can be a lithium lanthanum zirconium oxide (LLZO)-based compound with a garnet structure. When the above-mentioned compounds, specifically LLZO-based compounds, are used as the inorganic particles, composite electrolytes with excellent ionic conductivity, stability with lithium metal, and a wide potential window range can be manufactured.

[0077] The composite membrane for the electrolyte exhibits an elongation at break of 50% or more, demonstrating excellent extensibility, resilience, and elasticity. Specifically, the elongation at break of the composite membrane for the electrolyte can be 100% or more, 300% or more, or 500% or more, and can be less than 2000% or less than 1000%. The elongation at break can be the elongation at the point where necking occurs in the stress-strain curve measured using a UTM device (tensile strain). The point where necking occurs can be the point where the stress decreases in the stress-strain curve. When the elongation at break of the composite membrane for the electrolyte is within the above range, the resulting composite electrolyte exhibits excellent extensibility, resilience, and elasticity, resulting in excellent reversibility of lithium dendrites formed during battery charging / discharging to their original state, and effectively suppressing the formation of lithium dendrites. Therefore, it also possesses excellent battery safety characteristics.

[0078] Composite electrolyte The composite electrolyte according to one specific embodiment comprises: an electrolyte composite membrane according to any of the above specific embodiments; an acrylic compound; and a liquid electrolyte. Specifically, the composite electrolyte has a structure in which a liquid electrolyte used in gel-polymer electrolytes is impregnated in the above-mentioned electrolyte composite membrane, and contains an acrylic compound as a crosslinking polymer, thereby achieving excellent electrochemical performance, mechanical and physical properties, processability, etc.

[0079] The acrylic compound may comprise a compound containing a (meth)acryloyl group as a polymeric group, and the acrylic compound may comprise a compound having 3 to 8 (meth)acryloyl groups per molecule, specifically 3 to 6 per molecule, more specifically 3 or 4 per molecule.

[0080] The acrylic compound may include any one selected from ethoxylated trimethylolpropane triacrylate (TMPETA), trimethylolpropane trimethacrylate (TMPTMA), trimethylolpropane triacrylate (TMPTA), tetramethylolmethane tetraacrylate (TMMTA), and combinations thereof. When the composite electrolyte contains the above-mentioned acrylic compound, it can exhibit excellent chemical stability, temperature stability, and heat resistance, and the functional groups with excellent copolymerization properties facilitate control over the characteristics of the components. Furthermore, free radical polymerization can be easily carried out without byproducts during the impregnation and gelation process of the liquid electrolyte applied to the gel-polymer electrolyte.

[0081] The liquid electrolyte may contain lithium salts and carbonate-based solvents. The lithium salts may suitably use one or more of the following: lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluoride (LiF), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), and lithium difluoro(oxalate)borate (LiDFOB).

[0082] The carbonate-based solvent may suitably use one or more linear and non-linear (or cyclic) carbonates. For example, the linear carbonate may be at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), etc., and the non-linear carbonate may be at least one selected from ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), etc. When the liquid electrolyte contains lithium salts and carbonate-based solvents of the above types, these salts and solvents can form a stable SEI at the negative electrode (Li) interface of the lithium metal anode (LMA), thereby enabling the lithium metal battery to exhibit excellent battery characteristics.

[0083] According to one specific embodiment, the carbonate-based solvent may comprise three non-linear carbonates. Specifically, the carbonate-based solvent may comprise ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC). Ethylene carbonate (EC) has high polarity and a significant ability to dissociate lithium salts, enabling it to form a stable negative electrode SEI layer. However, it is solid at room temperature, resulting in relatively low ionic conductivity when used alone. On the other hand, although propylene carbonate (PC) has relatively lower polarity than ethylene carbonate (EC), it exists as a liquid at room temperature. Therefore, mixing propylene carbonate (PC) and ethylene carbonate (EC) can produce an electrolyte with high ionic conductivity in a liquid state. Furthermore, fluoroethylene carbonate (FEC), due to its fluorine (F)-containing structure, can form a Li-F-rich negative electrode SEI with excellent ionic conductivity and durability, thereby contributing to a stable negative electrode lifespan. However, its structure will deform when left at room temperature for a long time, making it difficult to use as a primary solvent.

[0084] Therefore, when the carbonate-based solvent is mixed with ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC), the disadvantages of the carbonate-based solvent can be compensated for while maximizing the advantages, thereby enabling the manufacture of an electrolyte that can ensure high ionic conductivity and form a stable negative electrode SEI.

[0085] The content of the ion-conducting polymer in the composite electrolyte can be from 10% to 70% by weight. Specifically, the content of the ion-conducting polymer in the composite electrolyte can be more than 20% by weight or more than 40% by weight, and can be less than 50% by weight.

[0086] The content of inorganic particles in the composite electrolyte can be from 1% to 20% by weight. Specifically, the content of inorganic particles in the composite electrolyte can be more than 2.5% by weight or more than 4% by weight, and can be less than 10% by weight or less than 5% by weight.

[0087] The weight ratio of ion-conducting polymer to inorganic particles in the composite electrolyte can be from 1:1 to 30:1. Specifically, the weight ratio of ion-conducting polymer to inorganic particles in the composite electrolyte can be from 3:1 to 25:1 or from 10:1 to 20:1.

[0088] When the content of the ion-conducting polymer is too low and the content of inorganic particles is too high, the elongation of the electrolyte may be reduced, and it may be difficult to maintain the self-supporting film morphology. The ionic conductivity may be low, and due to the brittle nature of inorganic materials, electrolyte breakage may occur. Furthermore, when the content of the ion-conducting polymer is too high and the content of inorganic particles is too low, it is practically difficult to achieve the effect of improving mechanical and physical properties by adding inorganic particles.

[0089] Therefore, when the content and ratio of the ion-conducting polymer and inorganic particles are appropriately adjusted to the above range, the electrolyte can have excellent extensibility, shear coefficient, etc.

[0090] The content of acrylic acid compounds in the composite electrolyte can be from 1% to 10% by weight. Specifically, the content of acrylic acid compounds in the composite electrolyte can be more than 2% by weight or more than 3% by weight, and can be less than 7% by weight or less than 5% by weight.

[0091] The content of liquid electrolyte in the composite electrolyte can be from 10% to 70% by weight. Specifically, the content of liquid electrolyte in the composite electrolyte can be more than 20% by weight or more than 40% by weight, and can be less than 50% by weight.

[0092] When the contents of the acrylic compound and the liquid electrolyte are within the above range, the battery's capacity and lifespan characteristics can be excellent.

[0093] The composite electrolyte may further include an initiator. When the composite electrolyte further includes an initiator, gelation of the electrolyte is easier, and a polymer network can be fully formed without early polymerization or overpolymerization, thereby further improving mechanical strength. The type of initiator is not particularly limited, but exemplary examples include tert-butylperoxy pivalate (T-bpp), benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), etc. When the composite electrolyte further includes an initiator, the initiator content in the composite electrolyte can be from 0.01% by weight to 5% by weight. Specifically, the initiator content in the composite electrolyte can be more than 0.1% and less than 1% by weight. Excessive initiator content may actually reduce the mechanical strength of the electrolyte. Therefore, when the initiator content is within the above range, excellent mechanical strength can be ensured while gelation of the electrolyte is easier.

[0094] The composite electrolyte can be a self-supporting membrane. According to one specific embodiment, the composite electrolyte is a free-standing (or self-supporting) membrane, which can have sufficient mechanical strength and excellent processability even without separate external supporting elements such as current collectors or support webs, and can further improve the energy density of the battery including it.

[0095] The thickness of the composite electrolyte can be from 10 μm to 200 μm. Specifically, the thickness of the composite electrolyte can be greater than 20 μm, and can be less than 150 μm, less than 100 μm, less than 50 μm, or less than 40 μm.

[0096] The ionic conductivity of the composite electrolyte can be 1.0 × 10⁻⁶. -4 (S·cm -1 ) to 5.0×10 -4 (S·cm -1 Specifically, the ionic conductivity of the composite electrolyte can be 1.5 × 10⁻⁶. -4 (S·cm -1 ) or above, 2.4×10 -4 (S·cm -1 ) or above or 3.0×10 -4 (S·cm -1 (and above, and can be 4.0 × 10) -4 (S·cm -1 The ionic conductivity value can be a value measured at room temperature (25°C). When the ionic conductivity of the composite electrolyte is within the above range, it can have relatively excellent ionic conductivity characteristics.

[0097] A method for manufacturing a composite electrolyte according to one specific embodiment includes the following steps: preparing a slurry comprising an ion-conducting polymer, inorganic particles, and an organic solvent; coating the slurry onto a substrate and drying it to form a composite membrane for electrolyte; and mixing the composite membrane for electrolyte with an acrylic-based compound and a liquid electrolyte and then curing it to form a composite electrolyte, wherein the ion-conducting polymer comprises a polyurethane-based compound.

[0098] The type of organic solvent is not particularly limited, and tetrahydrofuran (THF), dimethylformamide (DMF), etc. can be used appropriately.

[0099] The substrate is not particularly limited and can be an electrode such as a negative electrode or a positive electrode, or a release film. Furthermore, the method of coating the slurry onto the substrate is not particularly limited, and processes such as blade coating or dip coating can be appropriately applied.

[0100] The heat treatment temperature for drying the slurry coated on the substrate can be from 20°C to 150°C, and the treatment time can be from 1 hour to 24 hours.

[0101] The heat treatment temperature for curing the electrolyte composite membrane after mixing it with an acrylic compound and a liquid electrolyte can be from 50°C to 100°C, and the treatment time can be from 0.5 hours to 3 hours.

[0102] The detailed descriptions of the ion-conducting polymers, inorganic particles, composite membranes for electrolytes, acrylic compounds, liquid electrolytes, and composite electrolytes are repeated above, and therefore are omitted.

[0103] Lithium secondary batteries A lithium secondary battery according to one embodiment includes a composite electrolyte according to any of the above embodiments. Specifically, the lithium secondary battery may include a positive electrode, a negative electrode, and an electrolyte disposed therebetween, the electrolyte being a composite electrolyte according to any of the above embodiments.

[0104] The positive electrode is not particularly limited. Exemplarily, the positive electrode may have a structure including a positive electrode current collector and a positive electrode mixture layer formed on at least one side of the positive electrode current collector, the positive electrode mixture layer containing a positive electrode active material.

[0105] The positive electrode active material is not particularly limited and may include lithium-transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4) or lithium nickel oxide (LiNiO2), or lithium-transition metal composite oxides in which a portion of these transition metals is replaced by other transition metals.

[0106] Specifically, the positive electrode active material can be an NCM-based positive electrode active material represented by the following chemical formula 3; or a lithium-rich layered oxide (LLO), OverLithiated Oxides, Over-lithiated layered oxide, OLO, LLOs)-based positive electrode active material represented by the following chemical formula 4.

[0107] [Chemical Formula 3] Li a Ni b M 1-b O2 In the chemical formula 3, 0.9 ≤ a ≤ 1.2, b ≥ 0.5, and M is at least one of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0108] Specifically, in the chemical formula 1, a can be 0.95≤a≤1.08, and b can be 0.6 or more, 0.8 or more, greater than 0.8, 0.9 or more, or 0.98 or more.

[0109] Specifically, in the chemical formula 3, M may include Co, Mn or Al, more specifically, M may include Co and Mn, and may further include Al if chosen.

[0110] [Chemical Formula 4] Li 1+x M 1-x O2 In the chemical formula 4, 0 ≤ x ≤ 0.4, and M is at least one of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ni, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0111] Specifically, in the chemical formula 4, M may include Ni, Co, Mn or Al, more specifically, it may include Ni, Co and Mn, and may further include Al by choice.

[0112] In addition, the positive electrode active material may also include lithium iron phosphate (LFP) based positive electrode active material represented by the chemical formula LiFePO4.

[0113] Furthermore, the lithium-transition metal oxide can be a secondary particle formed by the assembly or aggregation of multiple primary particles into a single particle, or it can be in the form of a single particle. The single particle form, for example, can mean excluding the assembly or aggregation of multiple primary particles (e.g., more than 10) into a single secondary particle. However, the single particle form does not exclude the form of two to ten individual particles attached or adhered to each other. In some embodiments, the positive electrode active material may simultaneously comprise both secondary particle and single particle forms.

[0114] The composition of the positive electrode current collector is not particularly limited, and a sheet (plate) or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or their alloys can be used, etc.

[0115] The positive electrode mixture layer may further contain an adhesive. Exemplarily, the adhesive may include one or more of polyvinylidene fluoride, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidenefluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc.

[0116] The positive electrode mixture layer may further contain a conductive material. Exemplarily, the conductive material may include: graphites such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber, carbon nanotube (CNT), etc.; metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide, etc.; or conductive polymers such as polyphenylene derivatives, etc., one or more of them.

[0117] The negative electrode is not particularly limited. Exemplarily, the negative electrode may have a structure including a negative electrode current collector and a negative electrode mixture layer formed on at least one surface of the negative electrode current collector.

[0118] The composition of the negative electrode current collector is not particularly limited, and a plate or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or their alloys can be used, etc.

[0119] The negative electrode mixture layer may contain: carbon-based active substances such as artificial graphite and natural graphite; silicon-based active substances such as silicon oxide (SiOx; 0 < x < 2), Si-C composite, etc.; and metals such as lithium metal as negative electrode active substances. According to a specific embodiment, the negative electrode mixture layer may have a pure silicon structure substantially containing only silicon-based active substances as negative electrode active substances.

[0120] The negative electrode mixture layer may further contain an adhesive. Exemplarily, the adhesive may include one or more of styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc.

[0121] The negative electrode mixture layer may further comprise a conductive material. Exemplarily, the conductive material may include: graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, carbon fiber, and carbon nanotubes (CNTs); metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, etc., one or more of the following.

[0122] The lithium secondary battery may further include a lithium metal anode (LMA). Specifically, the lithium metal anode (LMA) may have a non-anode structure comprising a lithium metal layer containing lithium metal or an alloy thereof. In this case, the lithium metal anode (LMA) may have a structure further comprising a separate negative electrode current collector, or it may have a structure without a separate negative electrode current collector. Furthermore, the lithium metal layer may have a structure in which a separate protective layer is formed on at least one side.

[0123] When a lithium secondary battery including the above-mentioned composite electrolyte has a structure in which the negative electrode includes a lithium metal negative electrode (LMA), dendrite growth can be effectively suppressed due to its excellent extensibility and resilience. Detailed Implementation

[0124] Example 1. Manufacturing of composite electrolytes 1) Example 1 (1) Composite membrane for electrolyte Organic solvents (tetrahydrofuran; THF), ion-conducting polymers (polyurethane; PU), and inorganic particles (Li7La3Zr2O) were used. 12 The organic solvent and ion-conducting polymer were mixed and stirred for 12 hours to prepare a slurry. At this time, the weight ratio of organic solvent to ion-conducting polymer in the slurry was 80:20, and the weight ratio of ion-conducting polymer to ion-conducting inorganic material was 10:1.

[0125] The slurry prepared as described above was cast onto a glass substrate using a doctor blade coating method, and then dried at room temperature to 70°C for 24 hours to manufacture an electrolyte composite membrane. The morphology of the electrolyte composite membrane of Example 1 is as follows. Figure 1 As shown.

[0126] (2) Composite electrolyte The electrolyte composite membrane prepared as described above is mixed with a liquid electrolyte, an acrylic compound, and an initiator, and then cured at 70°C for 1 hour to produce the composite electrolyte. At this time, the liquid electrolyte used is one with the composition 0.8M LiFSI + 0.2M LiDFOB + EC / PC / FEC (v / v 1 / 1 / 1), the acrylic compound used is trimethylolpropane ethoxylated triacrylate (TMPETA), and the initiator used is a tert-butyl peroxytert-butyl initiator (T-bpp).

[0127] The contents of each component in the final composite electrolyte are shown in Table 1 below. In Table 1, THF represents tetrahydrofuran, DMF represents dimethylformamide, PU represents polyurethane, PEO represents polyethylene oxide, PMMA represents polymethyl methacrylate, and PVDF represents polyvinylidene fluoride.

[0128] 2) Comparative Examples 1 to 3 The composite electrolytes of Comparative Examples 1 to 3 were manufactured using the same method as in Example 1, except that different types of organic solvents and ion-conducting polymers were used. The types of organic solvents and ion-conducting polymers used in Comparative Examples 1 to 3, as well as the content of each component, are shown in Table 1 below. Furthermore, the morphology of the composite membrane of the electrolyte of Comparative Example 1 before and after immersion in the liquid electrolyte is shown below. Figure 5 As shown.

[0129] [Table 1] 2. Performance Evaluation 1) Composite membrane for electrolytes (1) Dispersibility / Chemical resistance / Film-forming properties / Extensibility A. Dispersion The electrolyte composite membrane slurry prepared as described above was stored overnight with stirring. The dispersibility was then visually evaluated. Proper dispersion was marked with ○, and otherwise marked with ×. The results are shown in Table 2 below.

[0130] B. Chemical resistance The chemical resistance of the electrolyte composite membrane manufactured as described above was evaluated by visual inspection based on whether it changed color, and the results are shown in Table 2 below. In this case, if the electrolyte composite membrane reacts chemically with the oxide and turns colored, it is marked with ×; otherwise, it is marked with ○.

[0131] C. Film-forming properties During the process of drying the slurry prepared as described above to manufacture a composite membrane for electrolytes, the film-forming properties were evaluated, and the results are shown in Table 2 below. At this time, if the composite membrane for electrolytes exhibits cracks or agglomeration, it is marked with ×; otherwise, it is marked with ○.

[0132] D. Extensibility The electrolyte composite membrane manufactured as described above was stretched by hand, and its elongation was then visually evaluated. The results are shown in Table 2 below. In this case, a properly stretched composite membrane is marked with ○, and otherwise marked with ×.

[0133] [Table 2] (2) Elongation at break and fracture stress The stress-strain curves of the electrolyte composite membrane manufactured as described above were measured using a UTM device (see reference). Figure 2 and Figure 3 The elongation and stress values ​​at the point where necking occurs are determined as the elongation at break and the stress at break, respectively, and the measurement results are shown in Table 3 below.

[0134] 2) Composite electrolyte (1) Manufacturing of symmetrical battery cells To evaluate the electrochemical performance of the composite electrolyte manufactured as described above, a symmetrical cell comprising the composite electrolyte was fabricated. Specifically, using lithium metal as the working electrode and the counter electrode, a symmetrical cell was fabricated with these electrodes positioned on both sides, i.e., a lithium metal battery sample comprising the composite electrolyte manufactured as described above as the electrolyte between the two electrodes.

[0135] (2) Electrodeposition / Deposition characteristics The charge / discharge characteristics of Examples 1 and Comparative Examples 1 to 3, which were manufactured as described above, were evaluated. Specifically, the lithium metal battery samples were charged / discharge cycled at 25°C with a capacity of 2 mAh per area and a current density of 1 mA per area. The battery voltage was measured over time. If the battery voltage remained at 0V after 60 hours, it was determined that the battery had experienced a short circuit within 60 hours and was marked with ×; otherwise, it was marked with ○. The results are shown in Table 3 below.

[0136] (3) Ionic conductivity The ionic conductivity of Examples 1 and Comparative Examples 1 to 3, which were manufactured as described above, was evaluated using EIS analysis. Specifically, the ionic conductivity of the lithium metal battery samples was measured at room temperature (25°C), and the results are shown in Table 3 below.

[0137] [Table 3] Referring to Tables 1 to 3 above, the electrolyte composite films of Comparative Examples 1 to 3, which respectively contain polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF) as ion-conducting polymers, exhibited relatively poor elongation and elongation at break. In particular, Comparative Example 3, which contains polyvinylidene fluoride (PVDF) as an ion-conducting polymer, also showed poor dispersibility and chemical resistance. On the other hand, the electrolyte composite film of Example 1, which contains polyurethane (PU) as an ion-conducting polymer, showed excellent dispersibility, chemical resistance, film-forming properties, elongation, and elongation at break. Furthermore, the composite electrolyte of Example 1, which contains polyurethane (PU) as an ion-conducting polymer, showed excellent electrodeposition / deposition characteristics and ion conductivity. On the other hand, the composite electrolytes of Comparative Examples 1 to 3 exhibited poor electrodeposition / deposition characteristics, resulting in a short circuit within 60 hours of battery charging / discharging.

[0138] On the other hand, in the cases of Comparative Examples 1 to 3, the morphology, color, etc., of the electrolyte composite membrane differed from those in Example 1, and the membrane was not properly formed (see [reference]). Figure 1 In Comparative Example 1, during the impregnation of the liquid electrolyte, the electrolyte dissolved in the composite membrane and failed to maintain its shape, indicating inadequate gelation (see [reference]). Figure 5 Furthermore, unlike Example 1, the morphology of the electrolyte layer on the lithium metal surface in Comparative Examples 1 to 3 was not properly maintained after charging / discharging (see Example 3). Figure 6 ).

[0139] Taking these results into account, when manufacturing composite electrolytes containing inorganic particles and ion-conducting polymers, using polyurethane-based compounds as ion-conducting polymers can produce composite electrolytes with improved ion conductivity, processability, and mechanical and physical properties with excellent processability.

[0140] The specific embodiments of the present invention have been described in detail above, but their scope is not limited thereto. Various modifications and variations can be made without departing from the technical concept of the present invention as described in the claims, which will be obvious to those skilled in the art.

[0141] Industrial applicability As described above, the features of the present invention can be applied in whole or in part to composite membranes for electrolytes, composite electrolytes, methods for manufacturing the same, and lithium secondary batteries including the same.

Claims

1. An electrolyte composite membrane, comprising an ion-conducting polymer and inorganic particles, wherein, The ion-conducting polymer comprises a polyurethane-based compound, and the elongation at break of the composite membrane for the electrolyte is 50% or more.

2. The composite membrane for electrolytes according to claim 1, wherein, The number of functional groups capable of forming hydrogen bonds in each structural unit of the polyurethane-based compound is from 2 to 18.

3. The composite membrane for electrolytes according to claim 1, wherein, The polyurethane-based compound includes soft segments and hard segments.

4. The composite membrane for electrolytes according to claim 3, wherein, The soft segment comprises structural units represented by the following chemical formula 1. [Chemical Formula 1] -O-R 1 -O- In the chemical formula 1, R 1 It is a divalent aliphatic organic group.

5. The composite membrane for electrolytes according to claim 3, wherein, The hard segment comprises structural units represented by the following chemical formula 2. [Chemical Formula 2] -C(=O)(NR 3 )-R 2 -(NR 4 )C(=O)- In the chemical formula 2, R 2 R is an organic group containing an aromatic ring. 3 and R 4 Each is independently hydrogen or an alkyl group having 1 to 5 carbon atoms, either substituted or unsubstituted.

6. The composite membrane for electrolytes according to claim 1, wherein, The ion-conducting polymer further comprises any one selected from polyethylene oxide (PEO)-based compounds, polyvinylidene fluoride (PVDF)-based compounds, polymethyl methacrylate (PMMA)-based compounds, and combinations thereof.

7. The composite membrane for electrolytes according to claim 1, wherein, The inorganic particles include any one selected from garnet compounds, sodium superionic conductor compounds, perovskite compounds, and combinations thereof.

8. A composite electrolyte comprising: an electrolyte composite membrane according to any one of claims 1 to 7; an acrylic compound; and a liquid electrolyte.

9. The composite electrolyte according to claim 8, wherein, The acrylic compounds comprise compounds having 3 to 8 (meth)acryloyl groups per molecule.

10. The composite electrolyte according to claim 8, wherein, The acrylate compound includes any one selected from ethoxylated trimethylolpropane triacrylate (TMPETA), trimethylolpropane trimethacrylate (TMPTMA), trimethylolpropane triacrylate (TMPTA), tetramethylolmethane tetraacrylate (TMMTA), and combinations thereof.

11. The composite electrolyte according to claim 8, wherein, The liquid electrolyte contains lithium salt and carbonate-based solvent.

12. The composite electrolyte according to claim 8, wherein, The content of the ion-conducting polymer in the composite electrolyte is 10% to 70% by weight.

13. The composite electrolyte according to claim 8, wherein, The content of inorganic particles in the composite electrolyte is 1% to 20% by weight.

14. The composite electrolyte according to claim 8, wherein, The weight ratio of ion-conducting polymer to inorganic particles in the composite electrolyte is from 1:1 to 30:

1.

15. The composite electrolyte according to claim 8, wherein, The content of acrylic acid compounds in the composite electrolyte is from 1% to 10% by weight.

16. The composite electrolyte according to claim 8, wherein, The composite electrolyte is a self-supporting membrane.

17. The composite electrolyte according to claim 8, wherein, The thickness of the composite electrolyte is 10 μm to 200 μm.

18. A method for manufacturing a composite electrolyte, comprising the following steps: Prepare a slurry containing ion-conducting polymers, inorganic particles, and organic solvents; The slurry is coated onto a substrate and then dried to form a composite membrane for electrolytes. as well as The electrolyte is formed by mixing the composite membrane with an acrylic compound and a liquid electrolyte and then curing the mixture. The ion-conducting polymer comprises a polyurethane-based compound.

19. A lithium secondary battery comprising the composite electrolyte of claim 8.

20. The lithium secondary battery according to claim 19, wherein, The lithium secondary battery includes a lithium metal anode (LMA).

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