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

Abstract

A composite membrane for an electrolyte according to an embodiment disclosed herein comprises an ionic conductive polymer and inorganic particles, wherein the ionic conductive polymer includes a polyurethane-based compound, and the composite membrane for an electrolyte has an elongation at break of 50% or more.

Description

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

[0001] The present disclosure relates to a composite membrane for electrolyte, a composite electrolyte, a method for producing the same, and a lithium secondary battery including the same.

[0002] With growing concern about environmental issues, lithium secondary batteries, with their high discharge voltage and stable output, are increasingly being used as power sources for electric vehicles (EVs) and other vehicles that can replace fossil fuel-based vehicles. However, conventional lithium secondary batteries, which utilize liquid electrolytes such as organic solvents, pose problems such as the risk of fire due to electrolyte leakage, electrolyte decomposition due to electrode reactions, and consequent battery swelling. Consequently, active research is being conducted on lithium secondary batteries utilizing solid-state electrolytes to address these issues.

[0003] One aspect of the present disclosure is to provide a composite electrolyte having excellent ion conducting properties.

[0004] Another aspect of the present disclosure is to provide a composite electrolyte having improved mechanical properties.

[0005] Another aspect of the present disclosure is to provide a lithium secondary battery having excellent performance.

[0006] According to one embodiment, a composite membrane for electrolyte comprises an ion-conducting polymer and inorganic particles, wherein the ion-conducting polymer comprises a polyurethane-based compound, and the composite membrane for electrolyte has an elongation at break of 50% or more.

[0007] The number of hydrogen-bondable functional groups per structural unit of the above polyurethane compound may be 2 to 18.

[0008] The above polyurethane compound may include a soft segment and a hard segment.

[0009] The above soft segment may include a structural unit represented by the following chemical formula 1.

[0010] [Chemical Formula 1]

[0011] *-OR 1 -O-*

[0012] In the above chemical formula 1, R 1 is a divalent aliphatic organic group.

[0013] The above-mentioned hard segment may include a structural unit represented by the following chemical formula 2.

[0014] [Chemical Formula 2]

[0015] *-C(=O)(NR 3 )-R 2 -(NR 4 )C(=O)-*

[0016] In the above chemical formula 2, R 2 is an organic group containing an aromatic ring,

[0017] R 3 and R 4 are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

[0018] The above ion conductive polymer may further include any one selected from a polyethylene oxide (PEO) compound, a polyvinylidene fluoride (PVDF) compound, a polymethyl methacrylate (PMMA) compound, and a combination thereof.

[0019] The above inorganic particles may include any one selected from a garnet compound, a NASICON compound, a perovskite compound, and a combination thereof.

[0020] A composite electrolyte according to one embodiment comprises a composite membrane for electrolyte according to any one of the above-described embodiments; an acrylic compound and a liquid electrolyte.

[0021] The above acrylic compound may include a compound having 3 to 8 (meth)acryloyl groups per molecule.

[0022] The above acrylic compound may include any one selected from trimethylol propane ethoxylate triacrylate (TMPETA), trimethylol propane trimethacrylate (TMPTMA), trimethylol propane triacrylate (TMPTA), tetramethylol methane tetraacrylate (TMMTA), and combinations thereof.

[0023] The above liquid electrolyte may include a lithium salt and a carbonate-based solvent.

[0024] The content of the ion-conducting polymer in the above composite electrolyte may be 10 to 70 wt%.

[0025] The content of inorganic particles in the above composite electrolyte may be 1 to 20 wt%.

[0026] The weight ratio of the ion-conducting polymer and inorganic particles in the above composite electrolyte may be 1:1 to 30:1.

[0027] The content of the acrylic compound in the above composite electrolyte may be 1 to 10 wt%.

[0028] The above composite electrolyte may be a free-standing film.

[0029] The above composite electrolyte may have a thickness of 10 to 200 μm.

[0030] A method for manufacturing a composite electrolyte according to one embodiment includes the steps of: manufacturing a slurry including an ion-conducting polymer, inorganic particles, and an organic solvent; applying the slurry onto a substrate and then drying it to form a composite membrane for an electrolyte; and mixing the composite membrane for an electrolyte with an acrylic compound and a liquid electrolyte and then curing it to form a composite electrolyte, wherein the ion-conducting polymer includes a polyurethane compound.

[0031] A lithium secondary battery according to one embodiment includes a composite electrolyte according to any one of the above-described embodiments.

[0032] The above lithium secondary battery may include a lithium metal negative electrode (LMA).

[0033] According to one embodiment of the present disclosure, a composite electrolyte with improved ion conductivity characteristics can be manufactured with excellent processability.

[0034] According to another embodiment of the present disclosure, a composite electrolyte with improved mechanical properties can be manufactured with excellent processability.

[0035] According to another embodiment of the present disclosure, the risk of fire due to leakage of electrolyte inside a lithium secondary battery can be mitigated.

[0036] According to another embodiment of the present disclosure, a lithium secondary battery having excellent performance can be provided.

[0037] Figure 1 is a drawing showing the form of a composite membrane for electrolyte according to Example 1 and Comparative Examples 1 to 3.

[0038] FIG. 2 is a diagram showing a stress-strain curve measured for a composite membrane for electrolyte according to Example 1 and Comparative Examples 1 to 3.

[0039] Figure 3 is a diagram showing a stress-strain curve measured for a composite membrane for electrolyte according to Example 1.

[0040] FIG. 4 is a diagram showing the results of measuring voltage over time during a charge / discharge process for a lithium secondary battery including a composite electrolyte according to Example 1 and Comparative Examples 1 to 3.

[0041] Figure 5 is a drawing showing the shape of a composite membrane for electrolyte according to Comparative Example 1 before and after liquid electrolyte impregnation.

[0042] FIG. 6 is a drawing showing the results of post-charge / discharge lithium surface analysis and electrolyte layer confirmation for lithium secondary batteries including composite electrolytes according to Example 1 and Comparative Examples 1 to 3.

[0043] In this specification, "polymer" may include oligomers, and may also include copolymers with homopolymers, which may be alternating polymers, block copolymers, random copolymers, branched copolymers, crosslinked copolymers, or all of these.

[0044] As used herein, "alkyl" refers to an organic radical derived from an aliphatic hydrocarbon by the removal of one hydrogen, and may include both straight-chain and branched forms. The alkyl may have 1 to 10 carbon atoms, specifically 1 to 7 carbon atoms, specifically 1 to 5 carbon atoms, specifically 1 to 3 carbon atoms. Examples of the alkyl include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl, ethylhexyl, and the like.

[0045] In the present specification, the aromatic ring may include a single or fused ring system, each ring suitably containing 4 to 7 ring atoms, specifically 5 or 6 ring atoms, and may include a form in which multiple aromatic rings are connected by single bonds or alkyl groups. As an example, the aromatic ring may include, but is not limited to, benzene, naphthalene, biphenyl, terphenyl, and the like.

[0046] Unless otherwise specifically defined herein, “(meth)acryl” may be used to mean both “methacryl” and “acryl.”

[0047] In this specification, "polymer electrolyte" may refer not only to an all-solid-state electrolyte, but also to a "gel polymer electrolyte" in which an electrolyte is included in a polymer-based electrolyte. For example, the gel polymer electrolyte may be manufactured by swelling an electrolyte after manufacturing a polymer matrix (physical gel), or by curing a composition in which an electrolyte and a monomer are mixed (chemical gel), depending on the manufacturing method.

[0048] Solid electrolytes can be categorized into oxide-based electrolytes, sulfide-based electrolytes, and polymer-based electrolytes. Among these, polymer-based solid electrolytes offer relatively good economic efficiency, but may lack ionic conductivity and mechanical properties. To address these issues, one embodiment suggests the use of a composite electrolyte that mixes polymers and inorganic particles. However, the ionic conductivity and mechanical properties of polymer-based solid electrolytes may be in a trade-off relationship, making it difficult to improve both.

[0049] Specifically, when manufacturing a composite electrolyte that mixes polymers and inorganic particles, polymer materials such as polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF) can be used. However, composite electrolytes using polyethylene oxide (PEO) have relatively poor mechanical properties and moldability, and may not be suitable for high voltage. In addition, composite electrolytes using polymethyl methacrylate (PMMA) have brittle characteristics, which may make them unsuitable for practical use due to poor ionic conductivity and processability. In addition, composite electrolytes using polyvinylidene fluoride (PVDF) may have difficulties in practical use due to low ionic conductivity and interfacial side reactions caused by defluorination.

[0050] Thus, the polymer used in the composite electrolyte must have not only excellent ion conductivity but also appropriate dissociation ability for lithium salts, excellent formability / processability, no side reactions with inorganic particles, and excellent contact with the electrode.

[0051] According to one embodiment of the present disclosure, a composite electrolyte comprising inorganic particles having excellent conductivity for lithium ions and an ion-conductive polymer can be manufactured, wherein the ion-conductive polymer includes a polyurethane (PU) compound having excellent stretchability, resilience, mechanical / chemical stability, processability, etc., thereby producing a composite electrolyte having excellent performance. With reference to FIGS. 1 to 6, specific details are disclosed below.

[0052] Figure 1 is a drawing showing the form of a composite membrane for electrolyte according to Example 1 and Comparative Examples 1 to 3.

[0053] FIG. 2 is a diagram showing a stress-strain curve measured for a composite membrane for electrolyte according to Example 1 and Comparative Examples 1 to 3.

[0054] Figure 3 is a diagram showing a stress-strain curve measured for a composite membrane for electrolyte according to Example 1.

[0055] FIG. 4 is a diagram showing the results of measuring voltage over time during a charge / discharge process for a lithium secondary battery including a composite electrolyte according to Example 1 and Comparative Examples 1 to 3.

[0056] Figure 5 is a drawing showing the shape of a composite membrane for electrolyte according to Comparative Example 1 before and after liquid electrolyte impregnation.

[0057] FIG. 6 is a drawing showing the results of post-charge / discharge lithium surface analysis and electrolyte layer confirmation for lithium secondary batteries including composite electrolytes according to Example 1 and Comparative Examples 1 to 3.

[0058] Composite membrane for electrolyte

[0059] According to one embodiment, a composite membrane for electrolyte comprises an ion-conducting polymer and inorganic particles, wherein the ion-conducting polymer comprises a polyurethane-based compound, and the composite membrane for electrolyte has an elongation at break of 50% or more.

[0060] The above-described composite membrane for electrolyte is a film-shaped composite membrane that can be used in the manufacture of a composite electrolyte, and includes an ion-conducting polymer and inorganic particles. Specifically, the ion-conducting polymer includes a polyurethane-based compound, and the polyurethane-based compound may be a polyurethane, a polymer containing a urethane bond (-NHCOO-); or a copolymer obtained by copolymerizing the polyurethane with another polymer. As described above, polyurethane has excellent chemical / mechanical stability, ion conductivity, etc., has high ductility / resilience, and thus has excellent moldability, etc., can appropriately dissociate lithium salts, allowing a liquid electrolyte to swell inside, and has higher adhesion to electrodes than existing composite electrolytes, making it highly useful as a composite electrolyte. Hereinafter, the polyurethane-based compound will be described in more detail.

[0061] Polyurethane compounds

[0062] The number of hydrogen-bondable functional groups per structural unit of the polyurethane-based compound may be 2 to 18. Specifically, the number of hydrogen-bondable functional groups per structural unit of the polyurethane-based compound may be 4 or more and 16 or less. When the number of hydrogen-bondable functional groups per structural unit of the polyurethane-based compound is within the above-described range, elasticity, resilience, and stretchability may be excellent. The number of hydrogen-bondable functional groups per structural unit of the polyurethane-based compound may be calculated by analyzing the repeating unit structure of the polyurethane-based compound by performing nuclear magnetic resonance spectroscopy (NMR) and four-dimensional infrared spectroscopy (FT-IR) and measuring the number of oxygen and nitrogen it contains.

[0063] The polyurethane compound may include a soft segment and a hard segment. At this time, the soft segment may include an aliphatic organic group, and specifically, may include a structural unit represented by the following chemical formula 1, and more specifically, may be derived from a polyol compound including an aliphatic organic group. The hard segment may include an aromatic ring, may include a structural unit represented by the following chemical formula 2, and more specifically, may be derived from a diisocyanate compound including an aromatic ring.

[0064] [Chemical Formula 1]

[0065] *-OR 1 -O-*

[0066] In the above chemical formula 1, R 1 is a divalent aliphatic organic group.

[0067] [Chemical Formula 2]

[0068] *-C(=O)(NR 3 )-R 2 -(NR 4 )C(=O)-*

[0069] In the above chemical formula 2, R 2 is an organic group containing an aromatic ring,

[0070] R 3 and R 4 are each independently hydrogen, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. In the above chemical formula 1, R 1 It may be a residue containing a branched or linear acyclic aliphatic divalent organic group having 2 to 40 carbon atoms. At this time, the divalent aliphatic organic group may have a substituted or unsubstituted structure. Specifically, R 1 It may be a substituted or unsubstituted alkyl group having 2 to 40 carbon atoms, and the alkyl group may include an ester group, an ether group, a carbonate group, etc. at both terminals.

[0071] In the above chemical formula 2, R 2 may be an organic group containing an aromatic ring having 6 to 15 carbon atoms. At this time, the organic group containing the aromatic ring may have a substituted or unsubstituted structure. Specifically, R 2 An organic group containing only an aromatic ring may be, for example, a phenylene group, a toluene group, a xylene group, or a naphthalene group, or an organic group containing aromatic rings at both terminals as a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, for example, diphenylmethane.

[0072] In addition, the soft segment may be a portion derived from a polyol compound having hydroxyl groups (-OH) at both terminals and having low polarity. In addition, the hard segment may be a portion derived from a diisocyanate compound having isocyanate groups (-N=C=O) at both terminals and including a reactive group (-NH-) capable of hydrogen bonding.

[0073] The above polyol compound can be represented by the following chemical formula 1-1.

[0074] [Chemical Formula 1-1]

[0075] HO-R 1 -OH

[0076] In the above chemical formula 1-1, R 1 is a residue containing a divalent aliphatic organic group.

[0077] The above R 1 R of chemical formula 1 1 It has the same meaning as , and a detailed explanation of it is omitted as it overlaps with the above content.

[0078] By way of example, the polyol compound may include, but is not limited to, any one selected from polyester polyol, polyether polyol, polycarbonate polyol, polycaprolactone polyol, and combinations thereof.

[0079] The above diisocyanate compound can be represented by the following chemical formula 2-1.

[0080] [Chemical Formula 2-1]

[0081] OCN-R 2 -NCO

[0082] In the above chemical formula 2-1, R 2 is an aromatic ring.

[0083] The above R 2 is R of chemical formula 2 2 It has the same meaning as , and a detailed explanation of it is omitted as it overlaps with the above content.

[0084] By way of example, the diisocyanate compound may be any one selected from, but is not limited to, methylene diphenyl diisocyanate (MDI), phenylene diisocyanate (PDI), toluene diisocyanate (TDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI), and combinations thereof.

[0085] The ion conductive polymer may further include any one selected from a polyethylene oxide (PEO)-based compound, a polyvinylidene fluoride (PVDF)-based compound, a polymethyl methacrylate (PMMA)-based compound, and a combination thereof. The ion conductive polymer according to one embodiment may further include, in addition to a polyurethane-based compound, any one selected from a polyethylene oxide (PEO)-based compound, a polyvinylidene fluoride (PVDF)-based compound, a polymethyl methacrylate (PMMA)-based compound, and a combination thereof. In the polyethylene oxide (PEO)-based compound, the polyvinylidene fluoride (PVDF)-based compound, and the polymethyl methacrylate (PMMA)-based compound, the '~-based compound' means any one selected from a polymer including '~', a copolymer thereof, or a combination thereof, as described above with respect to the polyurethane-based compound. Hereinafter, the inorganic particles will be described in more detail.

[0086] <Inorganic particles>

[0087] The above-mentioned inorganic particles may be oxide particles containing lithium element, and specifically, lithium conductive oxide particles. The lithium conductive oxide particles may be compound particles containing oxygen element and having conductivity toward lithium ions, and may be in powdered form. In addition to the lithium element, the lithium conductive oxide particles may contain at least one or more other metal elements such as zirconium (Zr), phosphate (PO4), and titanium (Ti), and may also contain two or more types of oxide particles.

[0088] According to one embodiment, the inorganic particles may include any one selected from a garnet compound, a NASICON compound, a perovskite compound, and a combination thereof. The inorganic particles are particles of an inorganic material that are conductive to lithium ions, and can contribute to improving both the ionic conductivity and mechanical properties of the composite electrolyte.

[0089] The above garnet compound is a compound having a garnet crystal structure or a garnet-like crystal structure, and contains lithium, lanthanum, zirconium and oxygen, Li 7-3x+y-z A x La 3-y B y Zr 2-z M z O 12 It may be an oxide represented by the chemical formula. In the chemical formula, 0≤x≤1, 0≤y≤1, 0≤z≤1, A is a substitutional doping element of Li, B is a substitutional doping element of La, M is a substitutional doping element of Zr, and A and B may each independently be at least one selected from the group consisting of aluminum (Al), gallium (Ga), barium (Ba), magnesium (Mg), calcium (Ca), strontium (Sr), potassium (K), cerium (Ce), and rubidium (Rb). In addition, M may be at least one selected from the group consisting of molybdenum (Mo), tungsten (W), antimony (Sb), yttrium (Y), niobium (Nb), and tantalum (Ta). The garnet-type oxide is not limited thereto, but is exemplified by Li7La3Zr2O 12 , Li5La3Nb2O 12 , Li5La3Ta2O 12 or Li6La2BaTa2O 12 It could be.

[0090] Li7La3Zr2O 12 It may be a lithium lanthanum zirconium oxide (LLZO) compound expressed by the chemical formula, etc. The garnet compound such as the lithium lanthanum zirconium oxide (LLZO) compound may be a compound doped with a metal such as aluminum (Al) or tantalum (Ta).

[0091] The above NASICON compound is a compound having a NASICON crystal structure or a NASICON-like crystal structure, for example, AGP(Li 1+xAl 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+4 xZr 2―x It may be at least one selected from the group consisting of (PO4)3(0≤x≤0.4).

[0092] The above perovskite compound is a compound having a perovskite crystal structure or a perovskite-like crystal structure, and for example, Li 0.31 La 0.56 Lithium lanthanum titanate oxide (LLTO) compounds represented by chemical formulas such as TiO3; or lithium lanthanum niobate (Li x La (1-x) / 3 NbO3)(0≤x≤1).

[0093] The above-mentioned inorganic particles may include at least one selected from zirconium (Zr), phosphate (PO4), and titanium (Ti). Specifically, the lithium conductive oxide particles (21) may be at least one compound selected from a lithium lanthanum zirconium oxide (LLZO) compound, a lithium lanthanum titanate oxide (LLTO) compound, a lithium aluminum germanium phosphate (LAGP) compound, and a lithium aluminum titanium phosphate (LATP) compound. More specifically, the lithium conductive oxide particles (21) may be Li7La3Zr2O 12 It can be a lithium lanthanum zirconium oxide (LLZO) compound having a garnet structure and is expressed by the chemical formula of . When the above-described type of compound, specifically the LLZO compound, is applied as the inorganic particle, a composite electrolyte having properties such as excellent ionic conductivity, stability with lithium metal, and a wide potential window range can be manufactured.

[0094] The above-described composite membrane for electrolyte has an elongation at break of 50% or more, and has excellent elongation, resilience, elasticity, etc. Specifically, the composite membrane for electrolyte may have an elongation at break of 100% or more, 300% or more, or 500% or more, and may be 2000% or less or 1000% or less. The elongation at break may be the tensile strain at the point of necking when a stress-strain curve is measured using a UTM device for the composite membrane for electrolyte. The point of necking may be the point at which stress decreases in the stress-strain curve. When the elongation at break of the composite membrane for the electrolyte is within the above-described range, the elongation, resilience, elasticity, etc. of the final manufactured composite electrolyte are excellent, so that the reversibility of lithium dendrites formed during the charge / discharge process of the battery returning to their original state is excellent, and the formation of lithium dendrites is effectively suppressed, so that the characteristics such as battery safety can also be excellent.

[0095] composite electrolyte

[0096] A composite electrolyte according to one embodiment comprises a composite membrane for electrolyte according to any one of the above-described embodiments; an acrylic compound; and a liquid electrolyte. Specifically, the composite electrolyte has a structure in which a liquid electrolyte applicable to a gel-polymer electrolyte is impregnated into the composite membrane for electrolyte described above, and may include an acrylic compound as a crosslinked polymer, thereby exhibiting excellent electrochemical performance, mechanical properties, processability, etc.

[0097] The acrylic compound may include a compound containing a (meth)acryloyl group as a polymerizable group, and the acrylic compound may include a compound having 3 to 8 (meth)acryloyl groups per molecule, specifically, 3 to 6 per molecule, and more specifically, 3 or 4 (meth)acryloyl groups per molecule.

[0098] The above acrylic compound may include any one selected from trimethylol propane ethoxylated triacrylate (TMPETA), trimethylol propane trimethacrylate (TMPTMA), trimethylol propane triacrylate (TMPTA), tetramethylol methane tetraacrylate (TMMTA), and combinations thereof. When the composite electrolyte includes the above-described acrylic compound, it may have excellent chemical stability, temperature stability, and heat resistance, and the control of the properties of the constituent components may be advantageous through a functional group having excellent copolymerization characteristics. In addition, radical polymerization may easily proceed without byproducts in the process of impregnating and gelling the liquid electrolyte applied to the gel-polymer electrolyte.

[0099] The above liquid electrolyte may include a lithium salt and a carbonate-based solvent. The lithium salt may be one or more of 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), lithium difluoro(oxalato)borate (LiDFOB), and the like.

[0100] The above carbonate-based solvent may appropriately use one or more types of linear carbonates 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 includes the above-described types of lithium salts and carbonate-based solvents, the salts and solvents may form a stable SEI at the negative electrode (Li) interface of the lithium metal negative electrode (LMA), so that the cell characteristics of the lithium metal battery may be excellent.

[0101] According to one embodiment, the carbonate solvent may include three types of nonlinear carbonates. Specifically, the carbonate solvent may include three types of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC). Ethylene carbonate (EC) has a high polarity and thus has an excellent ability to dissociate lithium salts, and can form a stable negative electrode SEI layer, but has relatively low ionic conductivity when used alone in a solid state at room temperature. On the other hand, propylene carbonate (PC) has relatively low polarity compared to ethylene carbonate (EC), but exists in a liquid state at room temperature. Therefore, when propylene carbonate (PC) and ethylene carbonate (EC) are mixed, an electrolyte having high ionic conductivity in a liquid state can be prepared. Furthermore, due to its fluorine (F)-containing structure, fluoroethylene carbonate (FEC) can form a Li-F-rich cathode SEI with excellent ion conductivity and durability, contributing to the stable life of the cathode. However, its structure deforms when left at room temperature for extended periods, making it difficult to use as a primary solvent.

[0102] Therefore, when the carbonate solvent comprises a mixture of three types of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC), the disadvantages of the above-described carbonate solvents are complemented while the advantages are maximized, thereby producing an electrolyte capable of securing high ionic conductivity and forming a stable negative electrode SEI.

[0103] The content of the ion-conducting polymer in the composite electrolyte may be 10 to 70 wt%. Specifically, the content of the ion-conducting polymer in the composite electrolyte may be 20 wt% or more, or 40 wt% or more, and 50 wt% or less.

[0104] The content of inorganic particles in the composite electrolyte may be 1 to 20 wt%. Specifically, the content of inorganic particles in the composite electrolyte may be 2.5 wt% or more or 4 wt% or more, and 10 wt% or less or 5 wt% or less.

[0105] The weight ratio of the ion-conducting polymer and the inorganic particles in the composite electrolyte may be 1:1 to 30:1. Specifically, the weight ratio of the ion-conducting polymer and the inorganic particles in the composite electrolyte may be 3:1 to 25:1 or 10:1 to 20:1.

[0106] If the content of the ion-conducting polymer is too low and the content of the inorganic particles is too high, the elongation of the electrolyte may be reduced, it may be difficult to maintain a free-standing film form, the ionic conductivity may be low, and the brittle nature of the inorganic particles may cause the electrolyte to break. In addition, if the content of the ion-conducting polymer is too high and the content of the inorganic particles is too low, it may be practically difficult to achieve the effect of improving the mechanical properties through the addition of the inorganic particles.

[0107] Therefore, when the content and ratio of the ion-conducting polymer and inorganic particles are appropriately adjusted within the above-described range, the stretchability and shear coefficient of the electrolyte can all be excellent.

[0108] The content of the acrylic compound in the composite electrolyte may be 1 to 10 wt%. Specifically, the content of the acrylic compound in the composite electrolyte may be 2 wt% or more or 3 wt% or more, and 7 wt% or less or 5 wt% or less.

[0109] The content of the liquid electrolyte in the composite electrolyte may be 10 to 70 wt%. Specifically, the content of the liquid electrolyte in the composite electrolyte may be 20 wt% or more, or 40 wt% or more, and 50 wt% or less.

[0110] When the content of the acrylic compound and the liquid electrolyte is within the above-described range, both the capacity and life characteristics of the battery can be excellent.

[0111] The composite electrolyte may further comprise an initiator. When the composite electrolyte further comprises an initiator, gelation of the electrolyte can proceed more easily, and a polymer network can be sufficiently formed without premature polymerization or overpolymerization, thereby further improving mechanical strength. The type of the initiator is not particularly limited, and examples thereof may include Tert-butylperoxy pivalate (T-bpp), benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), etc. When the composite electrolyte further comprises an initiator, the content of the initiator in the composite electrolyte may be 0.01 to 5 wt%. Specifically, the content of the initiator in the composite electrolyte may be 0.1 wt% or more and 1 wt% or less. If the content of the initiator is excessively high, the mechanical strength of the electrolyte may actually be reduced. Therefore, when the content of the initiator is within the above-described range, gelation of the electrolyte can proceed more easily, while also ensuring excellent mechanical strength.

[0112] The composite electrolyte may be a free-standing film. According to one embodiment, the composite electrolyte is a free-standing film or a self-supporting film, which has sufficient mechanical strength and excellent processability without a separate external support element such as a current collector or a support web, and can further improve the energy density of a battery including the same.

[0113] The composite electrolyte may have a thickness of 10 to 200 μm. Specifically, the composite electrolyte may have a thickness of 20 μm or more, 150 μm or less, 100 μm or less, 50 μm or less, or 40 μm or less.

[0114] The above composite electrolyte has an ionic conductivity of 1.0 x 10 -4 5.0 x 10 -4(S·cm -1 ) may be. Specifically, the composite electrolyte has an ionic conductivity of 1.5 x 10 -4 (S·cm -1 ) or more, 2.4 x 10 -4 (S·cm -1 ) or 3.0 x 10 -4 (S·cm -1 ) may be greater than or equal to 4.0 x 10 -4 (S·cm -1 ) may be less than or equal to. The above ionic conductivity value may be a value measured at room temperature (25°C). When the ionic conductivity of the composite electrolyte is within the above-described range, the ionic conductivity characteristics of the electrolyte may be relatively excellent.

[0115] A method for manufacturing a composite electrolyte according to one embodiment includes the steps of: manufacturing a slurry including an ion-conducting polymer, inorganic particles, and an organic solvent; applying the slurry onto a substrate and then drying it to form a composite membrane for an electrolyte; and mixing the composite membrane for an electrolyte with an acrylic compound and a liquid electrolyte and then curing it to form a composite electrolyte, wherein the ion-conducting polymer includes a polyurethane compound.

[0116] The type of the above organic solvent is not particularly limited, and tetrahydrofuran (THF), dimethylformamide (DMF), etc. can be appropriately used.

[0117] The substrate is not particularly limited, and may be an electrode such as a cathode or anode, or a release film. In addition, the method for applying the slurry onto the substrate is not particularly limited, and a method such as a doctor blade or dip coating may be appropriately applied.

[0118] The heat treatment temperature during drying of the slurry applied on the above substrate may be 20 to 150°C, and the treatment may be performed for 1 to 24 hours.

[0119] When the above-mentioned composite membrane for electrolyte is mixed with an acrylic compound and a liquid electrolyte and then cured, the heat treatment temperature may be 50 to 100°C, and the treatment may be performed for 0.5 to 3 hours.

[0120] Detailed descriptions of the above ion-conducting polymer, inorganic particles, composite membrane for electrolyte, acrylic compound, liquid electrolyte, composite electrolyte, etc. are omitted as they overlap with the above-described contents.

[0121] lithium secondary battery

[0122] A lithium secondary battery according to one embodiment includes a composite electrolyte according to any one of the above-described embodiments. Specifically, the lithium secondary battery may include a positive electrode, a negative electrode, and an electrolyte disposed therebetween, and the electrolyte may be a composite electrolyte according to any one of the above-described embodiments.

[0123] The above positive electrode is not particularly limited. For example, the positive electrode may have a structure including a positive electrode current collector; and a positive electrode mixture layer formed on at least one surface of the positive electrode current collector, and the positive electrode mixture layer may include a positive electrode active material.

[0124] The above positive electrode active material is not particularly limited, and may include a lithium-transition metal oxide such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), or lithium nickel oxide (LiNiO2), or a lithium-transition metal composite oxide in which some of these transition metals are substituted with other transition metals.

[0125] Specifically, the positive electrode active material may be an NCM-based positive electrode active material represented by the following chemical formula 3; or an LLO (Li rich layered oxides, Over Lithiated Oxides, Over-lithiated layered oxide, OLO, LLOs)-based positive electrode active material represented by the following chemical formula 4.

[0126] [Chemical Formula 3]

[0127] Li a Ni b M 1-b O2

[0128] In the above 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.

[0129] Specifically, in the above chemical formula 1, 0.95≤a≤1.08 may be satisfied, and b may be 0.6 or more, 0.8 or more, greater than 0.8, 0.9 or more, or 0.98 or more.

[0130] Specifically, in the above chemical formula 3, M may include Co, Mn or Al, and more specifically, M may include Co and Mn and optionally further include Al.

[0131] [Chemical Formula 4]

[0132] Li 1+x M 1-x O2

[0133] In the above 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.

[0134] Specifically, in the above chemical formula 4, M may include Ni, Co, Mn, or Al, and more specifically, may include Ni, Co, and Mn, and optionally further include Al.

[0135] Additionally, the cathode active material may include a lithium iron phosphate (LFP)-based cathode active material represented by the chemical formula LiFePO4.

[0136] In addition, the lithium-transition metal oxide may be a secondary particle formed by assembling or agglomerating a plurality of primary particles to form a substantially single particle, or may be in the form of a single particle. The single particle form may mean, for example, excluding a secondary particle formed by assembling or agglomerating a plurality of primary particles (for example, more than 10) to form a substantially single particle. However, the single particle form does not exclude a case where 2 to 10 single particles are attached or adhered to each other to form a single body. In some embodiments, the positive electrode active material may include both a secondary particle form and a single particle form.

[0137] The components of the above-mentioned positive electrode collector are 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 an alloy thereof may be used.

[0138] The above-mentioned positive electrode mixture layer may further include a binder. The binder may include, for example, one or two or more kinds of polyvinylidene fluoride, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate.

[0139] The above-described positive electrode mixture layer may further include a conductive material. Examples of the conductive material include one or more types of graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes (CNT); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0140] The above negative electrode is not particularly limited. For example, the negative electrode may have a structure including a negative electrode current collector; and a negative electrode composite layer formed on at least one surface of the negative electrode current collector.

[0141] The components of the above negative electrode collector are 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 an alloy thereof may be used.

[0142] The above negative electrode composite layer is a negative electrode active material, including carbon-based active materials such as artificial graphite and natural graphite, and silicon oxide (SiOx; 0 <x<2), Si-C 복합체 등의 규소계 활물질, 리튬 메탈 등의 금속을 포함할 수 있다. 일 구현예에 따르면, 상기 음극합제층은 음극활물질로 실질적으로 규소계 활물질만을 포함하는 퓨어 실리콘(Pure Silicon) 구조일 수 있다.

[0143] The above-mentioned negative electrode composite layer may further include a binder. The binder may include, for example, one or two or more types of styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc.

[0144] The above-described negative electrode composite layer may further include a conductive material. Examples of the conductive material include one or more types of graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes (CNT); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0145] The lithium secondary battery may further include a lithium metal anode (LMA). Specifically, the lithium metal anode (LMA) may have a non-anode structure including a lithium metal layer containing lithium metal or an alloy thereof. In this case, the lithium metal anode (LMA) may have a structure further including a separate anode current collector, or may not have a structure including one. In addition, the lithium metal layer may have a structure in which a separate protective layer is formed on at least one surface.

[0146] When a lithium secondary battery including the composite electrolyte described above has a structure including a lithium metal anode (LMA) as a negative electrode, the growth of dendrites can be effectively suppressed due to excellent stretchability and recoverability.

[0147] Example

[0148] 1. Preparation of composite electrolyte

[0149] 1) Example 1

[0150] (1) Composite membrane for electrolyte

[0151] Organic solvent (tetrahydrofuran; THF), ion-conducting polymer (polyurethane; PU), and inorganic particles (Li7La3Zr2O 12 ); LLZO) was mixed and stirred for 12 hours to prepare a slurry. At this time, the weight ratio of the organic solvent and the ion-conducting polymer in the slurry was 80:20, and the weight ratio of the ion-conducting polymer and the ion-conducting inorganic material was 10:1.

[0152] The slurry prepared as described above was cast onto a glass substrate using the doctor blade method and then dried at room temperature to 70°C for 24 hours to prepare a composite membrane for electrolyte. The shape of the composite membrane for electrolyte of Example 1 prepared as described above is as shown in Fig. 1.

[0153] (2) Composite electrolyte

[0154] A composite electrolyte was prepared by mixing a liquid electrolyte, an acrylic compound, and an initiator into the composite membrane for electrolyte manufactured as described above, and curing at 70°C for 1 hour. At this time, a liquid electrolyte having a composition of 0.8 M LiFSI + 0.2 M LiDFOB + EC / PC / FEC (v / v 1 / 1 / 1) was applied as the liquid electrolyte, trimethylolpropane ethoxylated triacrylate (TMPETA) was applied as the acrylic compound, and tert-butylperoxy pivalate (T-bpp) was applied as the initiator.

[0155] The contents of each component included in the final manufactured composite electrolyte are as shown in Table 1 below. In Table 1 below, THF means tetrahydrofuran, DMF means dimethylformamide, PU means polyurethane, PEO means polyethylene oxide, PMMA means polymethyl methacrylate, and PVDF means polyvinylidene difluoride.

[0156] 2) Comparative examples 1 to 3

[0157] Composite electrolytes of Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the types of organic solvents and ion-conducting polymers were applied differently. The types of organic solvents and ion-conducting polymers applied in Comparative Examples 1 to 3 and the contents of each component are as shown in Table 1 below. In addition, the shape of the electrolyte composite membrane of Comparative Example 1 before and after impregnation with the liquid electrolyte is as shown in Fig. 5.

[0158] Classification Organic solvent type Polymer type Composite electrolyte Component content (weight %) Ion conductive polymer (A) Inorganic particle (B) A:B Liquid electrolyte Acrylic polymer Initiator Example 1 THFPU 44.364.44 10:147.32 3.84 0.04 Comparative example 1 THF PEO 44.364.44 10:147.32 3.84 0.04 Comparative example 2 THF PMMA 44.364.44 10:147.32 3.84 0.04 Comparative example 3 DMFP VDF 44.364.44 10:147.32 3.84 0.04

[0159] 2. Performance Evaluation

[0160] 1) Composite membrane for electrolyte

[0161] (1) Dispersibility / chemical resistance / film forming / elasticity

[0162] A. Dispersibility

[0163] The composite membrane slurry for electrolyte prepared as described above was stirred and stored overnight. The dispersibility was evaluated visually. If it was appropriately dispersed, it was marked as ○, and if not, it was marked as Ⅹ. The results are shown in Table 2 below.

[0164] B. Chemical resistance

[0165] The composite membrane for electrolyte manufactured as described above was visually observed to evaluate chemical resistance according to coloration, and the results are shown in Table 2 below. In this case, if the composite membrane for electrolyte changed color by chemically reacting with an oxide, it was marked with Ⅹ, and if not, it was marked with ○.

[0166] C. The unveiling

[0167] The membrane forming properties were evaluated in the process of manufacturing a composite membrane for electrolyte by casting and drying the slurry manufactured as described above, and the results are shown in Table 2 below. At this time, if cracks or condensation occurred in the composite membrane for electrolyte, it was marked as Ⅹ, and if not, it was marked as ○.

[0168] D. Flexibility

[0169] The composite membrane for electrolyte manufactured as described above was pulled by hand and the stretchability was visually evaluated, and the results are shown in Table 2 below. At this time, if the pulled composite membrane was appropriately stretched, it was marked with ○, and if not, it was marked with Ⅹ.

[0170] DispersibilityChemical resistanceFilm forming propertyExtensibilityExample 1○○○○Comparative example 1○○○ⅩComparative example 2○○○ⅩComparative example 3ⅩⅩ○Ⅹ

[0171] (2) Breaking elongation and breaking stress

[0172] The stress-strain curve of the composite membrane for electrolyte manufactured as described above was measured using UTM equipment (see Figs. 2 and 3), and the tensile strain and stress values ​​at the necking point were determined as the breaking elongation and breaking stress, respectively, and the measured results are shown in Table 3 below.

[0173] 2) Composite electrolyte

[0174] (1) Manufacturing of symmetrical cells

[0175] To evaluate the electrochemical performance of the composite electrolyte manufactured as described above, a symmetric cell containing the composite electrolyte was manufactured. Specifically, a lithium metal battery sample was manufactured as a symmetric cell using lithium metal as a working electrode and a counter electrode, with these electrodes positioned on both sides, and containing the composite electrolyte manufactured as described above as an electrolyte between the two electrodes.

[0176] (2) Pre-deposition characteristics

[0177] Among the samples manufactured as described above, the charge / discharge characteristics of Example 1 and Comparative Examples 1 to 3 were evaluated. Specifically, the lithium metal battery samples were subjected to charge / discharge cycles at 25°C under the conditions of a capacity per area of ​​2 mAh and a current density per area of ​​1 mA, and the voltage of the battery over time was measured. If the voltage of the battery was maintained at 0 V after 60 hours, it was determined that a short circuit of the battery occurred within 60 hours and was marked as X, otherwise it was marked as O, and the results are shown in Table 3 below.

[0178] (3) Ionic conductivity

[0179] Among the samples manufactured as described above, the ionic conductivity of Example 1 and Comparative Examples 1 to 3 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.

[0180] Composite membrane for electrolyte composite membrane Composite electrolyte Elongation at break (%) Stress at break (MPa) Pre-deposition / deposition characteristics Ionic conductivity (S cm) -1 ) Example 170015○3.2 x 10 -4 Comparative Example 168Ⅹ(paragraph)2.0 x 10 -4 Comparative Example 2212Ⅹ(paragraph)1.9 x 10 -4 Comparative Example 341Ⅹ(Paragraph)2.3 x 10 -4

[0181] Referring to Tables 1 to 3 above, Comparative Examples 1 to 3, which each included polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyvinylidene difluoride (PVDF) as ion-conducting polymers, showed relatively inferior stretchability and elongation at break of the composite membrane for electrolyte. In particular, Comparative Example 3, which included polyvinylidene difluoride (PVDF) as the ion-conducting polymer, also showed inferior dispersibility and chemical resistance. On the other hand, the composite membrane for electrolyte according to Example 1 containing polyurethane (PU) as an ion-conducting polymer was found to have excellent dispersibility, chemical resistance, membrane-forming properties, stretchability, and elongation at break. In addition, the composite electrolyte according to Example 1 containing polyurethane (PU) as an ion-conducting polymer was found to have excellent both charge / deposition characteristics and ion conductivity characteristics, whereas the composite electrolytes according to Comparative Examples 1 to 3 were found to have inferior charge / deposition characteristics, with a short circuit occurring in the battery within 60 hours of battery charge / discharge.

[0182] Meanwhile, in Comparative Examples 1 to 3, the shape, color, etc. of the composite membrane for electrolyte were found to be improperly formed, unlike in Example 1 (see Fig. 1), and in Comparative Example 1, the composite membrane for electrolyte was found to dissolve when impregnated with liquid electrolyte, so that the shape was not maintained and gelation did not proceed properly (see Fig. 5). In addition, in Comparative Examples 1 to 3, unlike in Example 1, the shape of the electrolyte layer on the lithium metal surface after charge / discharge was found to not be properly maintained (see Fig. 6).

[0183] Considering these results, it is believed that when a polyurethane-based compound is included as an ion-conducting polymer in the manufacture of a composite electrolyte containing inorganic particles and an ion-conducting polymer, a composite electrolyte with improved ion-conducting characteristics, processability, and mechanical properties can be manufactured with excellent processability.

[0184] Although the embodiments of the present disclosure have been described in detail above, the scope is not limited thereto, and it will be apparent to those skilled in the art that various modifications and variations are possible within a scope that does not depart from the technical spirit of the present disclosure described in the claims.

[0185] As described above, the features of the present invention can be applied in whole or in part to a composite membrane for electrolyte, a composite electrolyte, a method for manufacturing the same, and a lithium secondary battery including the same.

Claims

1. A composite membrane for electrolyte comprising an ion-conducting polymer and inorganic particles, The above ion-conducting polymer comprises a polyurethane compound, The above composite membrane for electrolyte has a breaking elongation of 50% or more. Composite membrane for electrolyte.

2. In paragraph 1, The number of hydrogen bondable functional groups per structural unit of the above polyurethane compound is 2 to 18. Composite membrane for electrolyte.

3. In paragraph 1, The above polyurethane compound comprises a soft segment and a hard segment. Composite membrane for electrolyte.

4. In paragraph 3, The above soft segment comprises a structural unit represented by the following chemical formula 1: Composite membrane for electrolyte; [Chemical Formula 1] *-O-R 1 -O-* In the above chemical formula 1, R 1 is a divalent aliphatic organic group.

5. In paragraph 3, The above hard segment comprises a structural unit represented by the following chemical formula 2: Composite membrane for electrolyte; [Chemical Formula 2] *-C(=O)(NR 3 )-R 2 -(NR 4 )C(=O)-* In the above chemical formula 2, R 2 is an organic group containing an aromatic ring, R 3 and R 4 are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

6. In paragraph 1, The above ion conductive polymer further comprises one selected from among a polyethylene oxide (PEO) compound, a polyvinylidene fluoride (PVDF) compound, a polymethyl methacrylate (PMMA) compound, and a combination thereof. Composite membrane for electrolyte.

7. In paragraph 1, The above inorganic particles include any one selected from among a Garnet compound, a NASICON compound, a Perovskite compound, and a combination thereof. Composite membrane for electrolyte.

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

9. In paragraph 8, The above acrylic compound includes a compound having 3 to 8 (meth)acryloyl groups per molecule. Composite electrolyte.

10. In paragraph 8, The above acrylic compound A composition comprising any one selected from trimethylol propane ethoxylate triacrylate (TMPETA), trimethylol propane trimethacrylate (TMPTMA), trimethylol propane triacrylate (TMPTA), tetramethylol methane tetraacrylate (TMMTA), and combinations thereof. Composite electrolyte.

11. In paragraph 8, The liquid electrolyte comprises a lithium salt and a carbonate solvent. Composite electrolyte.

12. In paragraph 8, The content of the ion-conducting polymer in the above composite electrolyte is 10 to 70 wt%, Composite electrolyte.

13. In paragraph 8, The content of inorganic particles in the above composite electrolyte is 1 to 20 wt%, Composite electrolyte.

14. In paragraph 8, The weight ratio of the ion-conducting polymer and the inorganic particles in the above composite electrolyte is 1:1 to 30:

1. Composite electrolyte.

15. In paragraph 8, The content of the acrylic compound in the above composite electrolyte is 1 to 10 wt%, Composite electrolyte.

16. In paragraph 8, The above composite electrolyte is a free-standing film, Composite electrolyte.

17. In paragraph 8, The above composite electrolyte has a thickness of 10 to 200 μm, Composite electrolyte.

18. A step of preparing a slurry containing an ion-conducting polymer, inorganic particles, and an organic solvent; A step of forming a composite membrane for electrolyte by applying the slurry on a substrate and then drying it; and A method for manufacturing a composite electrolyte, comprising the step of forming a composite electrolyte by mixing the composite membrane for the electrolyte with an acrylic compound and a liquid electrolyte and then curing the mixture, The above ion conductive polymer comprises a polyurethane compound. Method for manufacturing a composite electrolyte.

19. Containing a composite electrolyte according to Article 8, Lithium secondary battery.

20. In paragraph 19, Containing a lithium metal anode (LMA), Lithium secondary battery.

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