Electrolyte for secondary battery and secondary battery comprising same

Abstract

According to an embodiment of the present invention, an electrolyte for a secondary battery includes a polymer matrix and inorganic particles containing boron and nitrogen and having a two-dimensional shape, in which a content of the inorganic particles is greater than or equal to a content of the polymer matrix on a weight basis. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte layer that is provided between the positive electrode and the negative electrode and contains the electrolyte for the secondary battery.

Description

Technical Field

[0001] The present invention relates to an electrolyte for a secondary battery and a secondary battery including the electrolyte for a secondary battery. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communications and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers. Furthermore, battery packs containing secondary batteries are being developed in recent years and used as power sources for environmentally friendly vehicles such as hybrid cars.

[0003] Secondary batteries include lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, calcium secondary batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and can be advantageous in charging speed and light weight.

[0004] Secondary batteries may include liquid electrolytes as electrolytes. When using liquid electrolytes, safety issues such as leakage, explosion, and fire may occur due to rapid environmental changes such as temperature changes and external impacts. Therefore, in order to enhance stability, secondary batteries comprising solid-phase electrolytes in gel form or solid form are being developed. For example, secondary batteries may include semi-solid batteries comprising electrolytes in a partially solid form or all-solid-state batteries comprising electrolytes in a completely solid form.

[0005] A solid-state battery may include an electrode assembly comprising a positive electrode, a negative electrode, and an electrolyte layer. The positive electrode, negative electrode, and / or electrolyte layer of the solid-state battery may comprise a solid electrolyte. As the application range of solid-state batteries expands, longer life, higher capacity, and higher energy density are required. Summary of the Invention

[0006] (1) Technical issues to be resolved

[0007] A technical problem of the present invention is to provide an electrode for a secondary battery having improved energy density and power characteristics.

[0008] A technical problem of the present invention is to provide a secondary battery with improved capacity and power characteristics.

[0009] (2) Technical solution

[0010] According to an embodiment of the present invention, an electrolyte for a secondary battery includes a polymer matrix and inorganic particles containing boron and nitrogen and having a two-dimensional shape, wherein the content of the inorganic particles is greater than or equal to the content of the polymer matrix on a weight basis.

[0011] In some embodiments, the inorganic particles may have a plate-like shape.

[0012] In some embodiments, the inorganic particles may include boron nitride.

[0013] In some embodiments, the boron nitride may have a hexagonal crystal structure.

[0014] In some embodiments, the inorganic particles may have a length of 50 nm to 400 nm.

[0015] In some embodiments, the content of the inorganic particles may be 50 wt % or more of the total weight of the electrolyte for a secondary battery.

[0016] In some embodiments, the inorganic particles may be present in an amount of 60 wt % to 80 wt % based on the total weight of the electrolyte for a secondary battery.

[0017] In some embodiments, the polymer matrix may include a fluorine-based resin or a sulfone-based resin.

[0018] In some embodiments, the polymer matrix may be present in an amount of 10 wt % to 50 wt % based on the total weight of the electrolyte for a secondary battery.

[0019] In some embodiments, the polymer matrix can have a porous structure.

[0020] In some embodiments, the secondary battery electrolyte may further include a liquid electrolyte impregnated into the polymer matrix.

[0021] In some embodiments, the liquid electrolyte may include a lithium salt and an organic solvent.

[0022] In some embodiments, the secondary battery electrolyte may further include a polymer of an acrylate-based monomer containing a phosphorus (P) atom or a fluorine (F) atom.

[0023] In some embodiments, the acrylate-based monomer may include a phosphazene moiety.

[0024] According to an embodiment of the present invention, the solid electrolyte layer may include the electrolyte for a secondary battery according to the above-described embodiment.

[0025] In some embodiments, the solid electrolyte layer may have a film shape or a sheet shape.

[0026] According to an embodiment of the present invention, a secondary battery may include: a positive electrode; a negative electrode disposed opposite to the positive electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, the electrolyte layer containing the electrolyte for the secondary battery according to the above embodiment.

[0027] (3) Beneficial effects

[0028] The secondary battery electrolyte may include a polymer matrix and inorganic particles containing boron and nitrogen and having a two-dimensional shape. The content of the inorganic particles in the secondary battery electrolyte may be greater than or equal to the content of the polymer matrix. The thermal stability, mechanical and physical properties, and ionic conductivity of the secondary battery electrolyte may be improved.

[0029] The electrolyte for secondary batteries may include a liquid electrolyte. A migration path for ions in the electrolyte for secondary batteries may be further provided, thereby further increasing ion conductivity.

[0030] A secondary battery may include the electrolyte for a secondary battery, and the fire resistance stability, lifespan characteristics, and durability of the secondary battery may be improved, and the driving characteristics under high voltage may be improved.

[0031] The secondary battery according to the embodiment of the present invention can be widely used in electric vehicles, battery charging stations, other green technology fields such as solar power generation and wind power generation using batteries. In addition, the secondary battery according to the embodiment of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic cross-sectional view illustrating a battery cell according to an exemplary embodiment.

[0033] Figure 2 This is a photographic image of the surface of the electrolyte membrane for a secondary battery according to Example 1.

[0034] Figure 3 This is a photographic image of the surface of the organic-inorganic film according to Comparative Example 7.

[0035] Description of reference numerals:

[0036] 100: Positive

[0037] 110: Positive electrode current collector

[0038] 120: Positive electrode active material layer

[0039] 200: negative electrode

[0040] 210: Negative electrode current collector

[0041] 220: Negative electrode active material layer

[0042] 300: electrolyte layer DETAILED DESCRIPTION

[0043] According to an embodiment of the present invention, there is provided an electrolyte for a secondary battery including a polymer resin and inorganic particles.

[0044] According to an embodiment of the present invention, there is provided a secondary battery including the electrolyte for a secondary battery.

[0045] The following describes embodiments of the present invention in more detail with reference to the accompanying drawings. However, the drawings in this specification are intended to illustrate some embodiments of the present invention and, together with the above-mentioned summary of the invention, are used to further understand the technical concept of the present invention. Therefore, the present invention should not be construed as being limited to the contents described in these drawings.

[0046] The terms "upper surface" and "bottom surface" used in the present invention indicate relative positions of various components and do not indicate an absolute upper-lower relationship.

[0047] Hereinafter, in the present invention, unless otherwise specifically defined, when describing a layer, membrane, film, region, plate or the like as being "above" or "on" another part, this may include not only the case where it is "directly" "above" another part, but also the case where there are other parts in between.

[0048] The present invention will be described in detail below, but this is merely exemplary, and the present invention is not limited to the specific embodiments described above.

[0049] The electrolyte for secondary batteries may include a polymer matrix and inorganic particles. For example, the inorganic particles may be dispersed in the polymer matrix or may be supported by the polymer matrix.

[0050] Inorganic particles can contain boron and nitrogen. Boron and nitrogen have different electron densities from each other, and therefore can increase the mobility of metal ions (e.g., lithium ions) on the surface of inorganic particles. For example, the repulsion caused by the asymmetry of lone pairs of electrons between boron and nitrogen can promote the migration of ions. Therefore, inorganic particles can have ionic conductivity, and the ionic conductivity of secondary battery electrolytes can be improved by inorganic particles.

[0051] The inorganic particles may have a two-dimensional shape. A two-dimensional shape may refer to a form in which atoms have a thickness of a single atomic layer and form a crystalline structure on a two-dimensional plane. For example, the inorganic particles may be a two-dimensional material having a thickness of less than 10 nm and a graphene-like form.

[0052] Because inorganic particles have a two-dimensional shape with a thickness at the atomic level, the ion transport path within the inorganic particles can be shortened, thereby improving the ion transport characteristics of the secondary battery electrolyte. In addition, the inorganic particles can have high thermal and physical stability, thereby improving the heat resistance and mechanical properties of the secondary battery electrolyte.

[0053] In some embodiments, the inorganic particles may have a flaky shape. For example, the inorganic particles may have a shape such as a nanoplate, nanoflake, or nanosheet. Since the inorganic particles have a flaky shape, the area within the inorganic particles where ions can migrate can be increased. Therefore, the migration path of ions on the surface of the inorganic particles can be increased, and the ionic conductivity can be further improved.

[0054] In some embodiments, the inorganic particles may include boron nitride. Boron nitride has a crystal structure composed of nitrogen and boron, and thus can further promote the migration of ions and can have thermal stability and physical stability. Therefore, the ionic conductivity, heat resistance and mechanical physical properties of the secondary battery electrolyte can be further improved.

[0055] In one embodiment, the boron nitride may include hexagonal boron nitride (hexagonal-BN). For example, the crystal structure of the boron nitride may be composed of a hexagonal arrangement of boron atoms and nitrogen atoms. Therefore, boron nitride may have electrical insulating properties due to a large band gap of about 5.9 eV, and may have more excellent physical and mechanical stability.

[0056] The content of the inorganic particles can be greater than or equal to the content of the polymer matrix on a weight basis. For example, the inorganic particles can be the main component or dominant component of the electrolyte for a secondary battery. The content can be expressed as a weight percentage relative to the sum of the weight of the inorganic particles and the weight of the polymer matrix.

[0057] When the content of inorganic particles is less than that of the polymer matrix, the ionic conductivity and thermal stability of the secondary battery electrolyte may decrease. For example, ionic bonds may be formed between the polymer matrix and the nitrogen and boron of the inorganic particles. Therefore, the electron density imbalance of the inorganic particles may decrease, or the stability of the crystal structure of the inorganic particles may decrease. Therefore, when the content of the polymer matrix is excessive relative to the content of the inorganic particles, the interaction between the inorganic particles and the polymer matrix may increase, thereby reducing the ionic conductivity and thermal stability of the inorganic particles.

[0058] In one embodiment, the ratio of the content of the inorganic particles to the content of the polymer matrix can be greater than 1 and less than 5, 1.2 to 4.5, 1.5 to 4, or 1.8 to 3.5, based on weight. Within the above range, the electrochemical stability, processability, and mechanical properties of the secondary battery electrolyte can be ensured, while heat resistance and ionic conductivity can be further improved.

[0059] According to an exemplary embodiment, the content of the inorganic particles may be 50 wt % or more of the total weight of the electrolyte for a secondary battery.

[0060] In one embodiment, the content of the inorganic particles can be about 50% to 90% by weight, 60% to 80% by weight, 65% to 80% by weight, or 65% to 75% by weight of the total weight of the secondary battery electrolyte. Within the above range, the ionic conductivity and flame retardancy of the secondary battery electrolyte can be improved, while the leakage and leaching of the components in the secondary battery electrolyte can be suppressed, and the processability and moldability can be improved.

[0061] According to some embodiments, the length of the inorganic particles may be 50 nm to 400 nm. The length may be calculated as the longest width of the plane of the inorganic particles. For example, when the length of the inorganic particles is 400 nm or less, the trapping of ions by the inorganic particles may be increased, and ionic conductivity may be improved. For example, when the length of the inorganic particles is 50 nm or more, the stability of the crystal structure may be further enhanced.

[0062] In one embodiment, the length of the inorganic particles may be about 50 nm to 300 nm, about 60 nm to 200 nm, or about 70 nm to 150 nm. Within the above range, the mechanical and physical properties, heat resistance, and ionic conductivity of the electrolyte for secondary batteries can be further improved.

[0063] According to an exemplary embodiment, the polymer matrix may include a fluorine-based resin, a sulfone-based resin, an imide-based resin, and / or a polyurethane-based resin. Thus, the flame retardancy of the electrolyte for a secondary battery may be improved.

[0064] For example, the polymer matrix may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polychlorotrifluoroethylene (PCTFE), polytetrafluoroethylene (PTFE), polysulfone (PS), polyethersulfone (PES), polyimide (PI), polyurethane (PU), etc. These may be used alone or in combination of two or more.

[0065] In one embodiment, the polymer matrix may include a fluorine-based resin or a sulfone-based resin. For example, the polymer matrix may include polyvinylidene fluoride, polysulfone, polyethersulfone, etc.

[0066] Fluorine-based resins and sulfone-based resins have high compatibility with inorganic particles, so the inorganic particles can be more evenly dispersed within the polymer matrix. In addition, the thermal stability of the polymer matrix can be further improved by the fluorine-based resin or sulfone-based resin.

[0067] In some embodiments, the content of the polymer matrix may be 10% to 50% by weight of the total weight of the secondary battery electrolyte. When the content of the polymer matrix exceeds 50% by weight, the heat resistance and ionic conductivity of the secondary battery electrolyte may be reduced. When the content of the polymer matrix is less than 10% by weight, the mechanical stability and moldability of the secondary battery electrolyte may be reduced.

[0068] In one embodiment, the content of the polymer matrix can be about 10 wt % to 45 wt %, about 10 wt % to 40 wt %, about 10 wt % to 35 wt %, 15 wt % to 35 wt %, or 25 wt % to 35 wt % of the total weight of the secondary battery electrolyte. Within the above range, the mechanical and physical properties of the secondary battery electrolyte can be improved, and the ionic conductivity and thermal stability can be further improved.

[0069] In some embodiments, the polymer matrix may have a porous structure. For example, the polymer matrix may include multiple pores formed on the surface and inside. The inorganic particles and / or liquid electrolyte may be impregnated and fixed or accommodated in the pores of the polymer matrix. Therefore, the stability of the secondary battery electrolyte can be improved, and the ionic conductivity can be further increased.

[0070] According to an exemplary embodiment, the secondary battery electrolyte may further include a liquid electrolyte. For example, the liquid electrolyte may be impregnated into a polymer matrix, and the secondary battery electrolyte may be a gel polymer electrolyte. Since the secondary battery electrolyte has a gel form, the electrochemical stability can be improved, and the adhesion to other substances (e.g., electrode active material layer) in the secondary battery can be increased.

[0071] According to an exemplary embodiment, the liquid electrolyte may include a lithium salt and an organic solvent. The lithium salt and the organic solvent may increase ion mobility.

[0072] The lithium salt can be represented by, for example, Li + X - As the anion of the lithium salt (X - ), we can exemplify F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - wait.

[0073] In some embodiments, the organic solvent may include carbonate-based solvents such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), and vinylene carbonate (VC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran, etc. These may be used alone or in combination of two or more.

[0074] In one embodiment, the organic solvent may include a carbonate-based solvent. Thus, the electrical stability and chemical stability of the electrolyte for a secondary battery may be further improved.

[0075] In one embodiment, the liquid electrolyte may further include additives, such as cyclic carbonate-based compounds, fluorine-substituted cyclic carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, cyclic sulfite-based compounds, phosphate-based compounds, borate-based compounds, and the like.

[0076] In some embodiments, the content of the liquid electrolyte may be 1 wt % to 10 wt % of the total weight of the secondary battery electrolyte. Within this range, the ionic conductivity of the secondary battery electrolyte may be increased, while the chemical stability and thermal stability may be further improved.

[0077] In some embodiments, the secondary battery electrolyte may further include a polymer of an acrylate-based monomer. For example, the liquid electrolyte may include an acrylate-based monomer. The polymer may be formed by impregnating the liquid electrolyte into a polymer matrix and curing the acrylate-based monomer. The polymerizable functional groups (e.g., acrylate groups) of the acrylate-based monomer may be cross-linked with each other by light irradiation or heat treatment.

[0078] The acrylate-based monomer may contain phosphorus (P) atoms or fluorine (F) atoms. Phosphorus and fluorine atoms can suppress chain reaction fires. For example, due to the phosphorus and fluorine atoms, the polymer can be self-extinguishing. Therefore, the flame retardancy of the secondary battery electrolyte can be further improved.

[0079] In one embodiment, the acrylate-based monomer may include a phosphazene moiety. The phosphazene moiety has a high phosphorus content and thus can further enhance the flame retardancy of the polymer.

[0080] In some embodiments, the liquid electrolyte may include a thermal initiator or a photoinitiator to initiate the polymerization reaction of the acrylate-based monomer.

[0081] For example, the thermal initiator may include an azo compound such as 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (AMVN), or a peroxide compound such as benzoyl peroxide, acetyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, cumyl peroxide, hydrogen peroxide, etc.

[0082] For example, the photoinitiator may include 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), benzoin ether, dialkyl acetophenone, hydroxylalkylketone, phenyl glyoxylate, Benzyl Dimethyl Ketal, (2,4,6-trimethylbenzoyl)trimethylphosphine oxide, and other acylphosphine and α-aminoketone.

[0083] In one embodiment, the content of the polymer may be about 1 wt % to 15 wt % or about 3 wt % to 10 wt % of the total weight of the secondary battery electrolyte. Within the above range, the secondary battery electrolyte can have high ionic conductivity while further improving flame retardancy and heat resistance.

[0084] In some embodiments, the secondary battery electrolyte may further include a solid electrolyte. The solid electrolyte may include an oxide-based electrolyte and / or a sulfide-based electrolyte.

[0085] In some embodiments, the sulfide-based electrolyte may be an LPS-based solid electrolyte comprising Li, P, and S, an LPSCl-based solid electrolyte comprising Li, P, S, and Cl, an LGPS-based solid electrolyte comprising Li, P, Ge, and S, or an LSiPSCl-based solid electrolyte comprising Li, Si, P, S, and Cl.

[0086] For example, the sulfide-based electrolyte can use Li2S-P2S5, Li 10 GeP2S 12 、Li 10 SnP2S 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li 10 (Si 0.5 Ge 0.5 )P2S 12 、Li 10 (Ge 0.5 Sn 0.5 )P2S 12 、Li 10 (Si 0.5 Sn 0.5 )P2S 12 、Li 10 GeP2S 11.7 O 0.3 、Li 9.6 P3S 12 、Li9P3S9O3、Li 10.35 Ge 1.35 P 1.65 S 12 、Li 10.35 Si 1.35 P 1.65 S 12 、Li 9.81 Sn 0.81 P 2.19 S 12 、Li 9.42 Si 1.02 P 2.1 S 9.96 O 2.04 , Li6PS5Cl, etc.

[0087] In one embodiment, the sulfide-based electrolyte may include a solid electrolyte having an argyrodite-type crystal structure.

[0088] In one embodiment, the oxide-based electrolyte may include a metal oxide and / or an ion-conductive compound containing oxygen.

[0089] Examples of the metal oxide include Al2O3, ZnO2, Ce2O3, TiO2, ZrO2, HfO2, MnO2, MgO, WO2, V2O5, etc.

[0090] Examples of the ion conductive compound include garnet-based compounds such as LLZO-based compounds; perovskite-based compounds such as LLTO-based compounds; Li 1+x Al x Ge 2-x (PO4)3 (0 < x < 2), Li 1+ x Al x Ti 2-x (PO4)3 (0 < x < 2), Li 1+x Ti 2-x-y Al x Si y (PO4) 3-y (0 ≤ x ≤ 1, 0 < y ≤ 1), LAGP-based compounds, LATP-based compounds, LiAl x Zr 2-x (PO4)3 (0 ≤ x ≤ 1), LiTi x Zr 2-x (PO4)3 (0 ≤ x ≤ 1), etc., NASICON-based compounds; LIPON-based compounds; Li6La2CaTa2O 12 ; Li6La2ANb2O 12 (A is Ca or Sr); Li2Nd3TeSbO 12 、Li3BO 2.5 N 0.5 ; Li9SiAlO8, etc.

[0091] In one embodiment, the content of the solid electrolyte may be 1 wt% to 10 wt% or 1 wt% to 5 wt% of the total weight of the electrolyte for the secondary battery.

[0092] According to an exemplary embodiment, an organic polymer, an inorganic particle, and / or a solid electrolyte contained in a polymer matrix may be mixed in a solvent to prepare a slurry for forming an electrolyte. The organic polymer may include the above-mentioned fluorine-based resin, sulfone-based resin, imide-based resin, polyurethane-based resin, etc.

[0093] The slurry for forming an electrolyte can be dried to prepare an electrolyte for a secondary battery comprising a polymer matrix, inorganic particles and / or a solid electrolyte. As the solvent dries and evaporates, the inorganic particles and / or the solid electrolyte can be uniformly dispersed in the polymer matrix.

[0094] For example, the solvent may include tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-Me-THF), N-methyl-2-pyrrolidone (NMP), 1,3-dioxolane, vinylene carbonate (VC), etc. These may be used alone or in combination of two or more.

[0095] In one embodiment, the solvent may comprise different types of solvents. By adjusting the drying conditions for the different types of solvents, a polymer matrix having a porous structure can be prepared. For example, by adjusting the solubility of the organic polymer in the different types of solvents, the boiling points of the different types of solvents, the order in which the solvents are removed, etc., pores can be formed within the polymer matrix.

[0096] For example, the solvent may include a first solvent and a second solvent that are different from each other. The solubility of the organic polymer in the first solvent may be greater than the solubility of the organic polymer in the second solvent. For example, the organic polymer is soluble in the first solvent and insoluble in the second solvent. Therefore, the organic polymer can selectively dissolve in the first solvent.

[0097] The first solvent can be removed from the slurry for forming the electrolyte to form a polymer matrix. The second solvent can be removed from the polymer matrix to form a porous structure. For example, pores can be formed in the area where the second solvent is removed. Inorganic particles can be distributed within the pores.

[0098] The boiling point of the first solvent may be lower than that of the second solvent. Therefore, the first solvent and the second solvent may be removed sequentially due to the difference in boiling points.

[0099] In one embodiment, the first solvent may include tetrahydrofuran, 2-methyltetrahydrofuran, N-methyl-2-pyrrolidone, 1,3-dioxolane, vinylene carbonate, etc. In one embodiment, the second solvent may include heptane, octane, nonane, decane, dodecane, 2,2,4-trimethylpentane, etc.

[0100] The liquid electrolyte may be impregnated into the polymer matrix having a porous structure. The liquid electrolyte may be impregnated into the pores of the polymer matrix.

[0101] In one embodiment, the liquid electrolyte may further include an acrylate-based monomer containing a phosphorus atom or a fluorine atom. The liquid electrolyte impregnated into the polymer matrix may be irradiated with light, or the liquid electrolyte may be heated. Thus, the acrylate-based monomer may be polymerized in the liquid electrolyte.

[0102] The electrolyte layer according to an embodiment of the present invention may include the secondary battery electrolyte according to the above embodiment. For example, the electrolyte layer may be a solid electrolyte layer. For example, the electrolyte layer may have a film shape or a sheet shape.

[0103] In some embodiments, the electrolyte layer can be disposed between the electrodes. The electrolyte layer can facilitate ion migration between the electrodes while preventing short circuits between the electrodes. For example, the electrolyte layer can essentially serve as a separator in a secondary battery.

[0104] A secondary battery according to an embodiment of the present invention may include the electrolyte for a secondary battery according to the above-described embodiment.

[0105] Figure 1 is a schematic cross-sectional view illustrating a battery cell according to an exemplary embodiment.

[0106] Reference Figure 1 The battery cell may include a positive electrode 100 and a negative electrode 200 arranged opposite to the positive electrode 100 .

[0107] The positive electrode 100 may include a positive current collector 110 and a positive active material layer 120 disposed on at least one side of the positive current collector 110. The positive active material layer 120 may also be formed on both sides (eg, upper and lower sides) of the positive current collector 110.

[0108] The positive electrode current collector 110 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. For example, the positive electrode current collector 110 may include aluminum or an aluminum alloy. In one embodiment, the positive electrode current collector 110 may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0109] The positive electrode active material layer 120 may include a positive electrode active material, a binder, and / or a conductive material. For example, a positive electrode slurry including a positive electrode active material, a binder, and / or a conductive material may be coated on the positive electrode current collector 110 and dried and rolled to form the positive electrode active material layer 120.

[0110] Examples of positive electrode active materials include lithium iron phosphate-based compounds, lithium cobalt-based oxides, lithium manganese-based oxides, lithium nickel-based oxides, and lithium composite oxides. For example, the secondary battery of the present invention can be provided as a lithium secondary battery.

[0111] For example, the positive electrode active material may include layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2) or lithium manganese oxides such as LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5 and Cu2VO7, lithium iron phosphate oxides such as LiFePO4, etc.

[0112] In one embodiment, the positive active material may include a compound represented by the following Chemical Formula 1.

[0113] [Chemical Formula 1]

[0114] Li a Ni b M 1-b O2

[0115] In Chemical Formula 1, 0.95≤a≤1.08, b≥0.5, and M may be at least one element selected from the group consisting 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 Sr.

[0116] In one embodiment, the positive electrode active material may further include at least one of cobalt (Co) or manganese (Mn). For example, nickel-cobalt-manganese (NCM)-based lithium oxide may be used as the positive electrode active material.

[0117] Nickel (Ni) can be provided as a metal related to the capacity of lithium secondary batteries. As the nickel content increases, the capacity and power of lithium secondary batteries can be improved, but when the nickel content increases excessively, it may be disadvantageous in terms of mechanical stability and electrical stability.

[0118] The use of cobalt (Co) may improve the conductivity or resistance of a lithium secondary battery, and the use of manganese (Mn) may improve the mechanical stability and electrical stability of a lithium secondary battery.

[0119] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained in the lattice structure or crystal structure of the positive active material, and does not exclude other additional elements. For example, M can be provided as the main active element (mainactive element) of the positive active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active elements, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0120] In one embodiment, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the crystal structure may be further included. The auxiliary element may be mixed into the crystal structure and form a bond, and it should be understood that this situation is also included in the chemical structure represented by Chemical Formula 1.

[0121] In some embodiments, the positive electrode active material may also be a sodium-based active material or a potassium-based active material. For example, the secondary battery of the present invention may be provided as a sodium secondary battery or a potassium secondary battery. The sodium-based active material and / or potassium-based active material may comprise a layered structure or a crystal structure in which the Li of the above chemical formula 1 is replaced by Na and / or K.

[0122] In some embodiments, the positive electrode active material may also be a calcium-based active material. For example, the secondary battery of the present invention may be provided as a calcium secondary battery. The calcium-based active material may include, for example, a calcium-cobalt active material and a calcium-phosphate active material.

[0123] The conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanofibers, and carbon nanotubes, and / or metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, etc. These materials may be included alone or in combination of two or more.

[0124] The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, the positive electrode binder may use a PVDF-based binder.

[0125] The negative electrode 200 may include a negative electrode collector 210 and a negative electrode active material layer 220 disposed on at least one side of the negative electrode collector 210. The negative electrode active material layer 220 may also be formed on both sides (eg, upper and lower sides) of the negative electrode collector 210.

[0126] The negative electrode current collector 210 may include gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. For example, the negative electrode current collector 210 may include copper or a copper alloy. In one embodiment, the negative electrode current collector 210 may also include copper surface-treated with carbon, nickel, titanium, or silver.

[0127] The negative active material layer 220 may include a negative active material, a binder, and / or a conductive material. For example, a negative electrode slurry including a negative active material, a binder, and / or a conductive material may be coated on the negative current collector 210 to form the negative active material layer 220 .

[0128] The negative electrode active material may include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.; lithium metal; lithium alloys; silicon-containing materials or tin-containing materials, etc.

[0129] Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined below 1500°C, and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Examples of elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium. The silicon-containing substance may include Si, SiOx (0 < x < 2), SiO doped with metal x (0 < x < 2), silicon-carbon composite, etc. SiO doped with metal x (0 < x < 2) may include metal silicate, and the metal may include lithium and / or magnesium, etc.

[0130] The binder and the conductive material may use the substances described in the positive electrode 100. In one embodiment, the binder for the negative electrode may use nitrile rubber, polybutadiene rubber, styrene-butadiene rubber, etc., and may further contain thickeners such as carboxymethyl cellulose (CMC), etc.

[0131] In some embodiments, the positive electrode active material layer 120 and / or the negative electrode active material layer 220 may further contain a solid electrolyte. Therefore, the ionic conductivity of the positive electrode 100 and the negative electrode 200 can be further improved.

[0132] The electrolyte layer 300 may be disposed between the positive electrode 100 and the negative electrode 200. The battery cell may be defined by the positive electrode 100, the electrolyte layer 300, and the negative electrode 200. The electrode assembly may be formed by sequentially stacking a plurality of the battery cells. For example, the secondary battery may be provided as a solid-state battery.

[0133] The electrolyte layer 300 may contain the electrolyte for the secondary battery according to the above embodiments. Therefore, the fire resistance stability of the secondary battery can be improved, and the ionic conductivity, mechanical stability, and durability can be enhanced.

[0134] In some embodiments, the electrolyte layer 300 may have a film shape or a sheet shape.

[0135] According to an exemplary embodiment, the electrolyte layer 300 can prevent the contact and short circuit between the positive electrode 100 and the negative electrode 200. Therefore, the electrolyte layer 300 can substantially serve as a separator, and the secondary battery may not include a separator such as a polymer film or a non-woven fabric.

[0136] In one embodiment, the secondary battery may further include a separator. For example, the separator may be disposed between the positive electrode 100 and the electrolyte layer 300 or between the negative electrode 200 and the electrolyte layer 300. For example, the electrode assembly may be formed by winding, stacking, folding, etc. of the separator.

[0137] The separator may include a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. The separator may also include a non-woven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0138] In one embodiment, the lithium secondary battery may further include a non-aqueous electrolyte impregnating the positive electrode and the negative electrode.

[0139] The non-aqueous electrolyte may include a lithium salt and an organic solvent. The organic solvent may be, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0140] The lithium salt can be selected from LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, LiB 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3 or a combination thereof.

[0141] Tabs (positive and negative) may protrude from the positive and negative current collectors 110 and 210, respectively, and extend to one side of the secondary battery housing. The tabs may be fused to the side of the housing to form electrode leads (positive and negative) that extend to or are exposed outside the housing.

[0142] The secondary battery may be manufactured in a cylindrical shape using a can, a prismatic shape, a pouch type, a coin type, or the like, for example.

[0143] Below, exemplary embodiments are proposed to help understand the present invention, but these embodiments are only used to illustrate the present invention and are not used to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope and technical concept of the present invention, which is obvious to those skilled in the art, and these variations and modifications also fall within the scope of the claims.

[0144] Experimental example

[0145] 1) Examples 1 to 8 and Comparative Examples 1 to 4

[0146] (1) Preparation of electrolyte for secondary batteries

[0147] Polyethersulfone (PES, Mw: 60000-100000 g·mol -1 ) and inorganic particles were added to N-methyl-2-pyrrolidone (NMP) in the amounts shown in Table 1 and stirred to prepare an electrolyte slurry. The inorganic particles used were hexagonal boron nitride (h-BN) with a two-dimensional shape and a length ranging from 50 nm to 400 nm.

[0148] In Table 1, the content of the organic polymer refers to the weight % of the organic polymer relative to the sum of the weight of the organic polymer contained in the electrolyte for secondary batteries and the weight of the inorganic particles, and the content of the inorganic particles refers to the weight % of the inorganic particles relative to the sum of the weight of the organic polymer contained in the electrolyte for secondary batteries and the weight of the inorganic particles.

[0149] The electrolyte slurry was applied on a substrate (aluminum foil) and dried at 80° C. to prepare secondary battery electrolytes of Examples 1 to 4 and Comparative Examples 1 to 4 in a film shape having a thickness of about 20 μm.

[0150] In Examples 5 to 8, electrolytes for secondary batteries were prepared by the same method as in Examples 1 to 4, except that two-dimensional hexagonal boron nitride (h-BN) with a length ranging from 0.5 μm to 2 μm was used as the inorganic particles.

[0151] (2) Evaluation of thermal stability

[0152] The thermal decomposition temperature of the secondary battery electrolyte was measured using a thermogravimetric analyzer (Q500, TA Instruments). Specifically, the secondary battery electrolyte was cut into 3 mm × 3 mm pieces and loaded into the thermogravimetric analyzer. The pieces were heated from room temperature to 700°C at a rate of 5°C / min, and the weight loss was measured. The thermal decomposition temperature was calculated as the temperature at which the weight of the secondary battery electrolyte decreased by 10% compared to the initial loaded weight.

[0153] The measurement results are shown in Table 1 below.

[0154] [Table 1]

[0155]

[0156] Referring to Table 1, in the case of Examples, the thermal stability of the electrolyte for a secondary battery is improved compared to that of Comparative Examples.

[0157] In the case of the comparative example, the content of the inorganic particles is less than 30% by weight or no inorganic particles are contained, so the thermal stability of the electrolyte for a secondary battery is reduced.

[0158] 2) Example, Comparative Example 5 and Comparative Example 6

[0159] (1) Preparation of electrolyte for secondary batteries

[0160] Polyethersulfone (PES, Mw: 60000-100000 g·mol -1 ) and inorganic particles were added to N-methyl-2-pyrrolidone (NMP) in the amounts shown in Table 2 below and stirred to prepare an electrolyte slurry. In Table 2 below, inorganic particles A are two-dimensional hexagonal boron nitride (h-BN) with a length ranging from 50 nm to 400 nm, and inorganic particles B are two-dimensional hexagonal boron nitride (h-BN) with a length ranging from 0.5 μm to 2 μm.

[0161] The electrolyte slurry was applied on a substrate (aluminum foil) and dried at 80° C., thereby forming a secondary battery electrolyte in a film shape having a thickness of about 20 μm.

[0162] (2) Evaluation of ionic conductivity

[0163] The ionic conductivity of the secondary battery electrolyte was measured using an electrochemical impedance spectroscopy instrument (EIS, VMP-300 potentiostat). Specifically, the secondary battery electrolyte was cut into a circular film with a diameter of about 10 mm and a thickness of about 3 mm, and the upper and lower surfaces were contacted with electrode terminals, respectively. The resistance was measured using an AC impedance method at 25°C, an amplitude of 10 mV, and a frequency range of 1 MHz to 100 MHz, and the ionic conductivity (S / cm) was calculated.

[0164] The measurement results are shown in Table 2 below. In Table 2, the content of the organic polymer refers to the weight % of the organic polymer relative to the sum of the weight of the organic polymer contained in the electrolyte for secondary batteries and the weight of the inorganic particles, and the content of the inorganic particles refers to the weight % of the inorganic particles relative to the sum of the weight of the organic polymer contained in the electrolyte for secondary batteries and the weight of the inorganic particles.

[0165] [Table 2]

[0166]

[0167] Referring to Table 2, the electrolyte for a secondary battery according to the embodiment has higher ion conductivity than the comparative example. In the embodiment, the electrolyte for a secondary battery including relatively small inorganic particles has higher ion conductivity.

[0168] In the comparative example, the content of the inorganic particles was less than 50% by weight, and the ion conductivity of the electrolyte for a secondary battery was reduced.

[0169] 3) Example 1 and Comparative Example 7

[0170] TiO2 particles with a particle size of 50nm to 400nm were coated on the surface of a circular polyethylene (PE) substrate with a diameter of about 10mm and a thickness of about 3mm to prepare an organic-inorganic film. Specifically, a composition containing TiO2 powder and PVDF was coated on the surface of the PE substrate and dried to form a coating with a thickness of about 20μm.

[0171] The film prepared in Example 1 and the organic-inorganic film prepared in Comparative Example 7 were placed in a convection oven at 120° C. for 20 minutes, respectively. The films were taken out of the convection oven, and the surfaces of the films were observed.

[0172] Figure 2 is a photographic image of the surface of the secondary battery electrolyte according to Example 1. Figure 3 This is a photographic image of the surface of the organic-inorganic film according to Comparative Example 7.

[0173] Reference Figure 2 and Figure 3 In Example 1, almost no wrinkles or deformation were observed on the surface of the secondary battery electrolyte membrane. In the secondary battery electrolyte membrane of Example 1, no high-temperature shrinkage occurred. However, in Comparative Example 7, the organic-inorganic membrane shrank at high temperatures, and wrinkles and deformation were observed on the surface of the organic-inorganic membrane.

Claims

1. An electrolyte for a secondary battery, comprising: a polymer matrix; and Inorganic particles containing boron and nitrogen and having a two-dimensional shape, in, Based on weight, the content of the inorganic particles is greater than or equal to the content of the polymer matrix.

2. The electrolyte for secondary batteries according to claim 1, wherein The inorganic particles have a flake shape.

3. The electrolyte for secondary batteries according to claim 1, wherein The inorganic particles include boron nitride.

4. The electrolyte for secondary batteries according to claim 3, wherein The boron nitride has a hexagonal crystal structure.

5. The electrolyte for secondary batteries according to claim 1, wherein The length of the inorganic particles is 50 nm to 400 nm.

6. The electrolyte for secondary batteries according to claim 1, wherein The content of the inorganic particles is 50 wt % or more of the total weight of the electrolyte for a secondary battery.

7. The electrolyte for secondary batteries according to claim 1, wherein The inorganic particles may be present in an amount of 60 to 80 wt % based on the total weight of the electrolyte for a secondary battery.

8. The electrolyte for secondary batteries according to claim 1, wherein The polymer matrix includes a fluorine-based resin or a sulfone-based resin.

9. The electrolyte for secondary batteries according to claim 1, wherein The polymer matrix may be present in an amount of 10 to 50 wt % based on the total weight of the electrolyte for a secondary battery.

10. The electrolyte for secondary batteries according to claim 1, wherein The polymer matrix has a porous structure.

11. The electrolyte for secondary batteries according to claim 1, wherein The secondary battery electrolyte further includes a liquid electrolyte impregnated into the polymer matrix.

12. The electrolyte for secondary batteries according to claim 11, wherein The liquid electrolyte includes a lithium salt and an organic solvent.

13. The electrolyte for secondary batteries according to claim 1, wherein The secondary battery electrolyte further includes a polymer of an acrylate-based monomer containing a phosphorus (P) atom or a fluorine (F) atom.

14. The electrolyte for secondary batteries according to claim 13, wherein The acrylate-based monomer comprises a phosphazene moiety. 15 . A solid electrolyte layer comprising the secondary battery electrolyte according to claim 1 .

16. The solid electrolyte layer according to claim 15, wherein The solid electrolyte layer has a film shape or a sheet shape.

17. A secondary battery comprising: positive electrode; a negative electrode, the negative electrode being arranged opposite to the positive electrode; and An electrolyte layer is provided between the positive electrode and the negative electrode, and contains the electrolyte for a secondary battery according to any one of claims 1 to 14.

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