Electrochemical element including porous separator

Abstract

To provide an electrochemical element including a positive electrode, a negative electrode, a separator, and an electrolyte.SOLUTION: The separator is a porous polymer membrane including a mixture of one or more hydrophilic inorganic particles and hydrophilic polymers. The electrolyte contains a nitrile compound. The electrochemical element can achieve high ionic conductivity by including a porous separator exhibiting wettability toward the electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electrochemical device that includes a porous separator. [Background technology]

[0002] A typical electrochemical device is manufactured by rolling or stacking a cell consisting of a negative electrode, a positive electrode, and a separator between the negative and positive electrodes into a cylindrical shape and inserting the cell into a pouch. A liquid electrolyte is then injected into the pouch to manufacture the battery. The electrolyte facilitates the smooth transfer of charge between the electrodes and generally contains a solvent and a salt.

[0003] In recent years, electrochemical devices have been required to have larger capacities so that they can be applied to electric vehicles and energy storage devices, etc. However, the larger the capacity of the electrochemical device, the higher the risk of fire and explosion, so the heat resistance and safety of the electrochemical device are required. In addition, it is necessary to realize high-capacity, high-power electrode active materials and ensure the wettability of the separator with the electrolyte for the electrochemical properties of the device. Summary of the Invention [Problem to be solved by the invention]

[0004] One embodiment aims to provide an electrochemical device including an electrolyte containing a nitrile compound and a porous separator having wettability with respect to the electrolyte. [Means for solving the problem]

[0005] One embodiment provides an electrochemical device including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is a porous polymer membrane in which one or more of hydrophilic inorganic particles and a hydrophilic polymer are mixed in a porous substrate, and the electrolyte includes a nitrile-based compound.

[0006] In one embodiment, the electrolyte may further include a lithium salt. When the electrolyte further includes a lithium salt, the weight ratio of the nitrile compound to the lithium salt may be 1:10 to 10:1.

[0007] In one embodiment, the nitrile compound may include succinonitrile, (3,4-dimethoxyphenyl)acetonitrile, 2-(4-bromo-2-methoxyphenyl)acetonitrile, 2-fluorophenylacetonitrile, 2-chloro-4-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonanedinitrile, sebaconitrile, undecanedinitrile, and / or dodecanedinitrile.

[0008] In one embodiment, the lithium salt is selected from the group consisting of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide), LiBOB (lithium bis(oxalato)borate), (C2F5SO2)2NLi, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)3CLi, LiBF2(C2O4), LiAlO2, and / or LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) where x and y are natural numbers.

[0009] In one embodiment, the porous substrate (polymer base material) included in the separator may include polyolefin, which may include polyethylene and / or polypropylene.

[0010] In one embodiment, the hydrophilic inorganic particles can include Al2O3, boehmite (AlOOH), SiO2, SnO2, ZrO2, TiO2, SiC, Si3N4, CaO, MgO, ZnO, BaTiO3, LiAlO2, BaSO4, CaCO3, Y2O3, and / or CeO2.

[0011] In one embodiment, the hydrophilic inorganic particles may have an average particle size of 50 nm to 3 μm.

[0012] In one embodiment, the hydrophilic polymer may include polyethylene oxide (PEO), polyimide (PI), polysulfone (PS), polyethersulfone (PES), cellulose acetate (CA), polyacrylonitrile (PAN), polyethylene glycol (PEG), polypropylene glycol (PPG), polymethyl methacrylate (PMMA), polyacrylic acid (PAA), and / or polyvinyl alcohol (PVA).

[0013] In one embodiment, the weight ratio of at least one of the hydrophilic inorganic particles and the hydrophilic polymer to the porous substrate may be 0.1:9.9 to 5.0:5.0.

[0014] In one embodiment, the electrolyte may exist in a liquid phase or a gel phase at room temperature. The liquid and gel phases may have a haze of 50% or less, and the gel phase may have a haze of more than 50% but less than 90%, when the electrolyte is placed in a 10×40×50 mm quartz cell, left at room temperature for 12 hours, and then the haze is measured using a colorimeter (COH400, Nippon Denshoku Co., Ltd.) at a distance of 100 mm perpendicular to a halogen lamp with a rated voltage of 12 V and a power consumption of 50 W.

[0015] In one embodiment, a portion of the electrolyte may be contained in a form filled in the pores of the separator.

[0016] In one embodiment, the electrolyte may include 0.1 wt % to 10 wt % of a carbonate-based additive based on the total weight of the electrolyte.

[0017] In one embodiment, the separator may have a thickness of 1 μm to 100 μm.

[0018] In one embodiment, the separator may have a contact angle of 5° to 50° with respect to the electrolyte. In one embodiment, the separator has an ionic conductivity of 0.1×10 -4 It may be S / cm or more.

[0019] In one embodiment, the porosity of the separator may be 30% or greater.

[0020] In one embodiment, the electrochemical device may be a lithium secondary battery. [Effects of the Invention]

[0021] The present disclosure relates to an electrochemical device including a porous separator. The electrochemical device according to one embodiment includes an electrolyte containing a nitrile compound and a porous separator having wettability with respect to the electrolyte, thereby achieving high ionic conductivity. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic plan view of a lithium secondary battery according to an embodiment; [Figure 2] 1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] The embodiments described herein may be modified into various other forms, and therefore the technology according to one embodiment is not limited to the embodiments described below. Furthermore, throughout the specification, unless specifically stated to the contrary, the words "comprising," "including," "containing," "having," "comprise," "include," or "have" mean that other elements may be included, but do not exclude other elements, materials, or steps not further recited.

[0024] Numerical ranges used herein include lower and upper limits, all values ​​within the range, increments logically derived from the form and width of the defined range, all values ​​limited therein, and all possible combinations of upper and lower limits of numerical ranges limited in different forms. For example, if the content of a composition is limited to 10% to 80% or 20% to 50%, numerical ranges of 10% to 50% or 50% to 80% should also be interpreted as being within the scope of this specification. Unless otherwise specified in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0025] Hereinafter, unless otherwise defined in this specification, "about" can be considered as a value within 30%, 25%, 20%, 15%, 10%, 5%, 3%, 2%, 1% or 0.5% of the specified value.

[0026] Unless otherwise defined herein, the particle diameter is D 50 It may be a value.

[0027] In this specification, unless otherwise defined, when a layer, film, thin film, region, plate, or other part is said to be "on" or "on top of" another part, this includes not only the case where it is "directly on top of" the other part, but also the case where there is another part in between.

[0028] Numerical ranges used herein include lower and upper limits, all values ​​within the range, increments logically derived from the form and width of the defined range, all values ​​limited therein, and all possible combinations of upper and lower limits of numerical ranges limited in different forms. For example, if the content of a composition is limited to 10% to 80% or 20% to 50%, numerical ranges of 10% to 50% or 50% to 80% should also be interpreted as being within the scope of this specification. Unless otherwise specified in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0029] Unless otherwise defined herein, "polymer" refers to a molecule of relatively high molecular weight, whose structure may comprise multiple repeating units derived from lower molecular weight molecules. In one aspect, the polymer may be an alternating copolymer, block copolymer, random copolymer, graft copolymer, gradient copolymer, branched copolymer, crosslinked copolymer, or a copolymer containing all of these (e.g., a polymer containing more than one type of monomer). In another aspect, the polymer may be a homopolymer (e.g., a polymer containing one type of monomer).

[0030] One embodiment provides an electrochemical device including a separator having wettability with an electrolyte containing a nitrile-based compound. Specifically, one embodiment provides an electrochemical device including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is a porous polymer membrane in which one or more of hydrophilic inorganic particles and hydrophilic polymers are mixed in a porous substrate, and the electrolyte contains a nitrile-based compound.

[0031] According to one embodiment, the separator is manufactured by blending a polymer substrate (porous substrate) with hydrophilic inorganic particles and / or hydrophilic polymers, thereby comprising a structure in which hydrophilic inorganic particles and / or polymers are intentionally / randomly blended within a porous polymer membrane (porous substrate). The separator blended with hydrophilic inorganic particles and / or hydrophilic polymers according to one embodiment exhibits wettability with the electrolyte according to one embodiment, and in particular, exhibits significantly higher wettability than a hydrophobic polymer separator without blended hydrophilic inorganic particles and / or hydrophilic polymers. Furthermore, the separator has significantly higher ionic conductivity than a separator formed by coating hydrophilic inorganic particles and / or hydrophilic polymers on a hydrophobic polymer separator.

[0032] In one embodiment, the hydrophilic inorganic particles are not particularly limited as long as they are recognizable to those of ordinary skill in the art of the present disclosure as hydrophilic inorganic particles, and may include, for example, one or more of Al2O3, boehmite (AlOOH), SiO2, SnO2, ZrO2, TiO2, SiC, Si3N4, CaO, MgO, ZnO, BaTiO3, LiAlO2, BaSO4, CaCO3, YO3, and / or CeO2.

[0033] In one embodiment, the average particle size (D 50 ) is not particularly limited, and may be, for example, 50 nm to 3 μm, 50 nm to 1 μm, 50 nm to 500 nm, 50 nm to 300 nm, 50 nm to 200 nm, 100 nm to 200 nm, 120 nm to 180 nm, 150 nm to 200 nm, or about 170 nm.

[0034] In one embodiment, the specific surface area of ​​the hydrophilic inorganic particles is, for example, 1 m 2 / g~1000m 2 / g, 10m 2 / g~500m 2 / g, 10m 2 / g~100m 2 / g.

[0035] In one embodiment, the hydrophilic polymer is not particularly limited as long as it is recognizable as a hydrophilic polymer by those of ordinary skill in the art disclosed herein. For example, the hydrophilic polymer may be a polymer containing 3 to 10, 3 to 8, or 3 to 6 carbon atoms, or may contain a hydrophilic group (a substituent containing an oxygen atom). Specifically, the hydrophilic polymer may include one or more of polyethylene oxide (PEO), polyimide (PI), polysulfone (PS), polyethersulfone (PES), cellulose acetate (CA), polyacrylonitrile (PAN), polyethylene glycol (PEG), polypropylene glycol (PPG), polymethyl methacrylate (PMMA), polyacrylic acid (PAA), and / or polyvinyl alcohol (PVA). In one embodiment, the hydrophilic polymer may be a block copolymer containing one or more of the hydrophilic polymers and a hydrophobic polymer.

[0036] In one embodiment, the weight ratio of the hydrophilic inorganic particles and / or hydrophilic polymer to the porous substrate is not particularly limited, and may be, for example, 0.1:9.9 to 5.0:5.0, 0.1:9.9 to 3.0:7.0, 0.1:9.9 to 2.0:8.0, 0.5:9.5 to 3.0:7.0, 0.5:9.5 to 2.0:8.0, or approximately 1.0:9.0.

[0037] In one embodiment, the nitrile-based compound contained in the electrolyte is not particularly limited as long as it is a compound containing one or more nitrile groups (—CN). For example, the nitrile-based compound may include one or more of succinonitrile (SN), (3,4-dimethoxyphenyl)acetonitrile, 2-(4-bromo-2-methoxyphenyl)acetonitrile, 2-fluorophenylacetonitrile, 2-chloro-4-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonanedinitrile, sebaconitrile, undecanedinitrile, and / or dodecanedinitrile.

[0038] In one embodiment, the electrolyte may further include a lithium salt. The lithium salt is not particularly limited as long as it is an ionizable lithium salt clearly known to those of ordinary skill in the art disclosed herein. For example, the lithium salt may be LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, (CFSO)NLi), LiFSI (lithium bis(fluorosulfonyl)imide, (SOF)NLi), LiBOB (lithium bis(oxalato)borate, LiB(C0)), (C5SO)NLi, LiCl, LiBr, LiI, LiClO, LiBF, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)3CLi, LiBF2(C2O4), LiAlO2, and / or LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are natural numbers). In one embodiment, the electrolyte contains an imide-based lithium salt such as LiFSI, which allows a strong and thin SEI film to be formed on the negative electrode.

[0039] In one embodiment, the electrolyte may not contain an additional solvent, in which case it may consist of only a nitrile-based compound, or only a nitrile-based compound and a lithium salt, or only a nitrile-based compound, a lithium salt, and a predetermined additive.

[0040] In one embodiment, when the electrolyte further includes a lithium salt, the weight ratio of the nitrile compound to the lithium salt may be 1:10 to 10:1, 2:8 to 8:2, 4:6 to 6:4, or about 3:1, although the weight ranges are merely examples and are not necessarily limited to these ranges.

[0041] In one embodiment, the electrolyte may further include a carbonate-based additive. The carbonate-based additive may improve the coating properties of the electrolyte and may be used to more effectively form a solid electrolyte interphase (SEI) layer. According to one embodiment, the carbonate-based additive may be used in a content smaller than that used as a solvent in a typical liquid electrolyte. For example, the carbonate-based additive may be included in an amount of 0.1 wt % to 10 wt % based on the total weight of the electrolyte, or may be included in an amount of 10 wt % or less, 8 wt % or less, or 5 wt % or less, where the lower limit may be 0.1 wt % or more, 0.5 wt % or more, or 1.0 wt % or more. Specifically, the carbonate-based additive may be included in an amount of 1.0 wt % to 5.0 wt %.

[0042] The carbonate-based additive may include, for example, one or more of FEC (Fluoroethylene Carbonate), VC (Vinylene Carbonate), VEC (Vinyl enthylene Carbonate), EC (Ethylene Carbonate), PC (Propylene Carbonate), and / or DiFEC (Di-fluoroethylene carbonate).

[0043] Furthermore, the electrolyte may further contain additives commonly used in the technical field disclosed herein, if necessary, and the content thereof may be 5 wt % or less based on the total weight of the electrolyte, but the content is not limited as long as the effects of the present disclosure are achieved. The additives are not particularly limited as long as they are known additives that can be contained in electrolytes, and further explanation will be omitted here.

[0044] According to one embodiment, the electrolyte may be in a liquid or gel phase at room temperature.

[0045] Here, the liquid phase and gel phase may be visually evaluated or measured as follows: The electrolyte is placed in a 10 x 40 x 50 mm quartz cell and left at room temperature for 12 hours. After that, the haze is measured using a colorimeter (COH400, Nippon Denshoku Co., Ltd.) at a distance of 100 mm perpendicular to a halogen lamp with a rated voltage of 12 V and a power consumption of 50 W. When the haze is measured, the liquid phase refers to a haze of 50% or less, and the gel phase refers to a haze of more than 50% but less than 90%.

[0046] According to one embodiment, the electrolyte may be present between the electrode and the separator in a liquid or gel phase, and a portion of the electrolyte may be present in a form filled in the pores of the porous separator.

[0047] In one embodiment, the electrolyte may be a liquid or gel electrolyte, or may be two or more solid functional layers heated to a predetermined temperature or higher to mix with each other and eventually undergo phase conversion to a liquid or gel phase at room temperature. Specifically, a first functional layer (solid phase) containing a nitrile compound and a second functional layer (solid phase) containing a nitrile compound may be formed by coating and / or filling both surfaces of a separator and / or the pores of the separator, respectively, and then heated to a predetermined temperature or higher to mix with each other.

[0048] As described above, the first and second functional layers may further contain a lithium salt in addition to the nitrile-based compound, and may optionally further contain a carbonate-based additive.

[0049] In one embodiment, the functional layer may be formed over a range of 50% or more, 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, or approximately 100% of the total surface area of ​​the separator. The functional layer may also have an area between these values, for example, 80% to 100% of the total surface area of ​​the separator. However, the above ranges are merely examples and are not necessarily limited to these ranges.

[0050] In one embodiment, the functional layers are in a solid phase at room temperature, for example, 20°C to 35°C, but when heated to a temperature of 40°C or higher, 50°C or higher, or 60°C or higher, the solid-phase functional layers melt and mix with each other, changing the composition of the components of each layer, so that even at low room temperature, the functional layers may maintain a liquid or gel phase without changing to a solid phase. Here, the heating temperature is not limited as long as it does not affect the pores of the separator according to one embodiment and is a temperature at which the coating layers coated on both sides melt and can mix with each other, and may be, for example, 40°C to 80°C or 60°C to 80°C.

[0051] Among the various examples of the above-mentioned nitrile compounds, succinonitrile (SN), (3,4-dimethoxyphenyl)acetonitrile, 2-(4-bromo-2-methoxyphenyl)acetonitrile, 2-fluorophenylacetonitrile, 2-chloro-4-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile are compounds having a melting point of 40°C or higher and exist as a solid at room temperature, and glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonanedinitrile, sebaconitrile, undecanedinitrile, and dodecanedinitrile are compounds that can exist as a solid at room temperature when mixed with a lithium salt.

[0052] The nitrile compound may be present in an amount of 50% by weight or more, 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, 99.9% by weight or less, 95% by weight or less, 90% by weight or less, or any value between the above values, for example, 50% by weight to 99.9% by weight, 55% by weight to 99.9% by weight, 60% by weight to 90% by weight, or 60% by weight to 80% by weight.

[0053] In one embodiment, when the electrolyte further comprises a lithium salt, the content of the lithium salt is mixed with the nitrile compound and exists as a solid phase at 10°C to 35°C. However, when the separator is heated and the functional layers are melted and mixed with each other, the content of the lithium salt is not limited as long as it no longer maintains a solid state at room temperature (e.g., 10°C to 35°C) and exists as a liquid or gel phase.

[0054] In one embodiment, the content of the lithium salt may be, for example, less than 50 wt %, 49 wt % or less, 45 wt % or less, 40 wt % or less, 35 wt % or less, 30 wt % or less, 25 wt % or less, 20 wt % or less, 15 wt % or less, 10 wt % or more, 20 wt % or more, or any value between the above values, for example, 10 wt % to 49 wt %, 10 wt % to 30 wt %, or 20 wt % to 30 wt %, based on the total weight of the electrolyte.

[0055] In one embodiment, the first functional layer may be composed solely of a nitrile-based compound, and the second functional layer may be composed of a mixture of a nitrile-based compound and a lithium salt in a weight ratio of 1:1 to 1.5:1, or about 10:1. In one embodiment, the total weight of the first and second functional layers may be adjusted so that the total weight of the nitrile-based compound contained in the functional layers is 2 to 7 times that of the lithium salt. By adjusting the weight within this range, each functional layer may maintain a solid phase and be easily transported.

[0056] In one embodiment, the first functional layer may be formed by impregnating the surface of the porous substrate and some or all of the pores therein. For example, the first functional layer may be formed at a concentration of 0.5 g / m 2 ~10g / m 2 The second functional layer may be formed by impregnating the surface of the porous substrate and some or all of the pores therein, and may be formed at a concentration of, for example, 0.5 g / m 2 ~10g / m 2 Here, the first functional layer and the second functional layer may have the same or different coating amounts.

[0057] In one embodiment, succinonitrile and a lithium salt undergo a phase transformation from a solid phase to a liquid or gel phase when mixed together. Succinonitrile exhibits ionic conduction behavior due to the existence of a trans-gauche isomer around the central C-C bond below its melting point. Therefore, it can function as an electrolyte. The trans isomer can enhance ion mobility by reducing lattice defects and lowering the activation energy for ionic conduction. Therefore, an electrolyte according to one embodiment can provide a wider electrochemical window than conventional liquid electrolytes containing organic solvents and ionic liquids.

[0058] According to an embodiment, the electrolyte may consist of only a nitrile-based compound, or only a nitrile-based compound and a lithium salt, or only a nitrile-based compound, a lithium salt, and a carbonate-based additive.

[0059] In one embodiment, the separator's porous polymer membrane may be a porous film in the form of a polymer containing polyolefin. For example, the polyolefin may include polyethylene (PE) and / or polypropylene (PP). Specifically, the polymer membrane may be polypropylene or polyethylene, or may be laminated in the order of polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, or polypropylene / polyethylene / polypropylene.

[0060] The separator according to one embodiment may be surface-treated to improve the coating and / or impregnation of the electrolyte, for example, but not limited to, by plasma or arc discharge in the presence of oxygen or air to make it hydrophilic.

[0061] While liquid or gel phase electrolytes require a porous support, commonly used wet or dry separators made from polyolefin-based polymers have problems with consistently high electrolyte wettability due to various variables (porosity, pore size, polarity), which can result in low electrolyte uptake and reduced battery performance. In contrast, a porous separator incorporating hydrophilic inorganic fibers and / or a hydrophilic polymer according to one embodiment has sufficient wettability with an electrolyte containing a nitrile-based compound, thereby achieving excellent battery life and performance while also achieving the fire stability benefits of a nitrile-based compound.

[0062] In one embodiment, the thickness of the separator may be 1 μm to 100 μm, 10 μm to 80 μm, 10 μm to 50 μm, 10 μm to 30 μm, or 15 μm to 25 μm. However, the thickness ranges are merely examples and are not necessarily limited to these ranges.

[0063] According to an embodiment, the separator may have a contact angle with the electrolyte of 5° to 50°, 5° to 30°, 10° to 30°, 10° to 20°, 7° to 20°, 12° to 18°, or 10° to 18°. The contact angle may be measured 10 seconds after dropping 3 μL of electrolyte onto the separator using a drop shape analyzer (Mobile Surface Analyzer, Kruss GmbH, Germany) in a dry room environment at a temperature of 24° C. and a relative humidity of 0.5 RH% or less.

[0064] The separator according to one embodiment has an ionic conductivity of 0.1×10 -4 S / cm or more, 1.0×10 -4 S / cm or more, 3.0×10 -4 S / cm or more, 5.0×10 -4 S / cm or more, or 6.0 x 10 -4 S / cm or more, 7.0×10 -4 S / cm or more, 7.5×10 -4 S / cm or more, 7.6×10 -4 S / cm or more, 7.8×10 -4 S / cm or more, or 7.9 x 10 -4 Here, the upper limit may be, for example, 0.01 S / cm or less, 0.005 S / cm or less, 0.003 S / cm or less, 0.001 S / cm or less, 9.0×10 -4 It may be S / cm or less.

[0065] The separator according to one embodiment may have a porosity of 30% or more, 40% or more, 45% or more, 46% or more, 48% or more, or 50% or more, and the upper limit may be, for example, 70% or less, 60% or less, or 55% or less. The porosity can be measured using the following formula:

[0066] Porosity = [1-{(W / T)÷ρ}]×100

[0067] W = separator weight per unit area (g / m 2 ) T = sample thickness (m) ρ = True density of the entire separator calculated from the resin and coating layer materials (g / m 3 )

[0068] In one embodiment, the electrochemical device may be a lithium secondary battery, which may be prismatic, cylindrical, or pouch-shaped.

[0069] In one embodiment, the lithium secondary battery may be, for example, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0070] The positive electrode included in the lithium secondary battery according to one embodiment includes a positive electrode active material capable of absorbing and desorbing lithium ions. The positive electrode active material may be a composite metal oxide of lithium and at least one selected from cobalt, manganese, and nickel. The solid solubility between the metals may vary, and in addition to these metals, an element selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V, and rare earth elements may be further included. Specific examples of the positive electrode active material include compounds represented by any one of the following chemical formulas:

[0071] Li a A 1-b B b D2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b B b O 2-c D c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B b O 4-c D c (wherein 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co bB c D α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Co b B c O 2-α F α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Co b B c O 2-α F2 (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b B c D α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Mn b B c O 2-α F α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b B c O 2-α F2 (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Ni b Co c Mn d GeO2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li aCoG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Fe2(PO4)3(0≦f≦2); and LiFePO4.

[0072] In the above chemical formula, A can be Ni, Co, Mn, or a combination thereof; B can be Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D can be O, F, S, P, or a combination thereof; E can be Co, Mn, or a combination thereof; F can be F, S, P, or a combination thereof; G can be Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q can be Ti, Mo, Mn, or a combination thereof; I can be Cr, V, Fe, Sc, Y, or a combination thereof; and J can be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0073] The negative electrode includes a negative electrode active material capable of absorbing and desorbing lithium ions. Examples of such a negative electrode active material include carbon materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, as well as lithium metal and alloys of lithium with other elements. Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500°C or less, and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based materials, such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbon material may have an interplanar distance of 3.35 Å to 3.38 Å and a crystallite size (Lc) of at least 20 nm as determined by X-ray diffraction. Other elements that can be used to alloy with lithium include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0074] The positive electrode or negative electrode can be manufactured by dispersing an electrode active material, a binder, a conductive material, and, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and then coating the slurry composition on an electrode current collector. The positive electrode current collector can typically be made of aluminum or an aluminum alloy, and the negative electrode current collector can typically be made of copper or a copper alloy. The positive electrode current collector and the negative electrode current collector can be in the form of a foil or a mesh.

[0075] In one embodiment, the binder is a substance that functions to form a paste of the active material, to adhere the active material to each other, to adhere the active material to the current collector, and to buffer the expansion and contraction of the active material, and examples of the binder include polyvinylidene fluoride (PVdF), polyhexafluoropropylene-polyvinylidene fluoride copolymer (PVdF / HFP), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, and acrylonitrile-butadiene rubber. The binder content may be 0.1 wt% to 30 wt%, or 1 wt% to 10 wt%, of the electrode active material. If the content of the binder is too low, the adhesive strength between the electrode active material and the current collector will be insufficient, and if the content of the binder is too high, the adhesive strength will be good, but the content of the electrode active material will be reduced accordingly, which may be disadvantageous in increasing the battery capacity.

[0076] In one embodiment, the conductive material is used to impart conductivity to the electrode. Any material that does not undergo chemical change and is electronically conductive can be used, including at least one selected from the group consisting of graphite-based conductive materials, carbon black-based conductive materials, and metal or metal compound-based conductive materials. Examples of graphite-based conductive materials include artificial graphite and natural graphite. Examples of carbon black-based conductive materials include acetylene black, ketjen black, denka black, thermal black, and channel black. Examples of metal or metal compound-based conductive materials include tin, tin oxide, tin phosphate (SnPO), titanium oxide, potassium titanate, and perovskite materials such as LaSrCoO and LaSrMnO. However, the conductive material is not limited to these examples. The content of the conductive material may be 0.1 wt % to 10 wt % of the electrode active material.

[0077] The thickener is not particularly limited as long as it can adjust the viscosity of the active material slurry. For example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc. can be used.

[0078] A non-aqueous or aqueous solvent can be used as the solvent for dispersing the electrode active material, binder, conductive material, etc. Examples of non-aqueous solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

[0079] 1 and 2 are a schematic plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to an exemplary embodiment, for example, FIG. 2 is a cross-sectional view taken along line II' in FIG.

[0080] Referring to Figures 1 and 2, a lithium secondary battery may include an electrode assembly including a positive electrode 100, a negative electrode 130, and a separator 140 interposed between the positive electrode and the negative electrode. The electrode assembly may be housed and impregnated in a case 160 together with an electrolyte.

[0081] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 on the positive electrode current collector 105. The positive electrode active material layer 110 may include a positive electrode active material, and optionally a positive electrode binder, a conductive material, and / or a dispersion medium. The positive electrode 100 may be manufactured, for example, by mixing and stirring the positive electrode active material, the positive electrode binder, the conductive material, the dispersion medium, etc. to prepare a positive electrode slurry, which is then coated on the positive electrode current collector 105, dried, and compressed.

[0082] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 on the negative electrode current collector 125. The negative electrode active material layer 120 may include a negative electrode active material, and optionally a negative electrode binder, a conductive material, and / or a dispersion medium. The negative electrode 130 may be manufactured, for example, by mixing and stirring the negative electrode active material, the negative electrode binder, the conductive material, the dispersion medium, etc. to prepare a negative electrode slurry, which is then coated on the negative electrode current collector 125, dried, and compressed.

[0083] Electrode tabs (positive electrode tab and negative electrode tab) may protrude from the positive electrode current collector 105 and the negative electrode current collector 125 of each electrode cell, respectively, and may extend to one side of the case 160. The electrode tabs may be fused to the one side of the case 160 to form electrode leads (positive electrode lead 107 and negative electrode lead 127) that extend or are exposed to the outside of the case 160.

[0084] Examples and experimental examples are described below in detail, but the examples and experimental examples are merely illustrative of a portion of one embodiment and should not be construed as limiting the technology described herein.

[0085] <Test Method> 1. Analysis of separator properties The thickness of the separator was calculated by measuring the thickness of 10 layers of separator using a contact type micrometer (Mitutoyo, Japan) and dividing the measured value by 10 to obtain the average value.

[0086] The weight per area of ​​the separator was measured by measuring the weight of a 10 cm x 10 cm area using an electronic balance capable of measuring to four decimal places, and then converting it into a unit area.

[0087] The porosity of the separator was calculated using the following formula based on the thickness and weight per area of ​​the separator measured previously.

[0088] Porosity = [1-{(W / T)÷ρ}]×100 (W = separator weight per unit area (unit: g / m 2 ), T = sample thickness (unit: m), ρ = true density of the entire separator calculated from the materials of the resin and coating layer (unit: g / m 3 ))

[0089] 2. Contact angle analysis The contact angles of the liquid electrolyte were measured immediately after the preparation of the separators prepared in the examples and comparative examples using a drop shape analyzer (Mobile Surface Analyzer, Kruss GmbH, Germany). The contact angles were measured 10 seconds after 3 μL of the liquid electrolyte was dropped onto the separator. The measurements were performed in a dry room environment at a temperature of 24°C and a relative humidity of 0.5% or less.

[0090] 3. Analysis of spreading rate 10 mg of liquid electrolyte was dropped onto a separator with an area of ​​10 cm x 10 cm using a pipette, and the longest radius of the circularly diffusing electrolyte was measured after 10 seconds.

[0091] 4. Analysis of ionic conductivity The ionic conductivity of the separator of each example and comparative example was calculated using the following formula.

[0092] Ionic conductivity = L ÷ (R × A)

[0093] (L = thickness of separator impregnated with liquid electrolyte (unit: cm), R = impedance value of separator impregnated with liquid electrolyte (unit: Ω = 1 / S) (value of real part when imaginary part of impedance is 0), A = overlapping area between two electrodes during impedance measurement (unit: cm) 2 ))

[0094] To determine the R value, the separator was punched out into concentric circles with a diameter of 18 mm and then immersed in liquid electrolyte. The L value was measured with a micrometer, and the A value was 2.5447 cm. 2 Next, a 2032 standard coin cell (SUS material) was assembled as a separator impregnated with liquid electrolyte, and constant voltage impedance measurements were performed using Zahner GmbH's IM6 equipment at an initial voltage of 0V and an amplitude of 5mV in the range of 100MHz to 100mHz. The real part of the impedance, R, was determined by fitting the measured impedance equivalent circuit when the imaginary part was 0.

[0095] 5. Capacity realization rate analysis A single-plate cell manufactured to have a theoretical design capacity of 80mAh was charged / discharged at 2.7V (constant current) to 4.3V (constant current constant voltage) at 0.1C for the first cycle, 0.2C for the second cycle, and 0.5C for the third cycle, and the capacity was measured. The capacity realization rate was calculated as the ratio of the measured capacity to the theoretical design capacity in percentage.

[0096] 6. Measurement of weight-average molecular weight The weight-average molecular weight was measured using GPC (EcoSEC HLC-8320 GPC Reflectance Detector, manufactured by Tosoh Corporation) with two columns (7.8 × 300 mm) of TSKgel guard PWx, i.e., TSKgel GMPWxl and TSKgel G2500PWxl, as the GPC columns, 0.1 M aqueous NaNO3 solution as the developing solvent, and polyethylene glycol as the standard substance, at a flow rate of 1 mL / min at 40 °C.

[0097] 7. Melting Point Measurement The melting points of the polymers were measured according to the standard (ASTM e794) using a differential scanning calorimeter (DSC) (Mettler Toledo, DSC1) with a temperature range of −100° C. to 200° C. and a heating rate of 20° C. / min. 8. Particle size measurement The particle size was measured using a particle size analyzer (Microtrac S3500, manufactured by Microtrac) in accordance with the ISO standard (ISO13320-1). 9. Measurement of specific surface area The specific surface area was measured using a surface area analyzer (TriStar II, manufactured by Micromeritics) according to the standard (KS A 0094).

[0098] Example 1 Separator manufacturing Weight average molecular weight is 3.0 x 10 5 Polyethylene with a melting point of 135°C and a kinematic viscosity of 95 cSt at 40°C was mixed in a weight ratio of 3:7, and then hydrophilic inorganic particles of Al2O3 (average particle diameter (D 50 10% by weight of ethylene glycol stearate (150 nm) was further mixed with 100% by weight of polyethylene. The mixture was compounded in a twin-screw compounder at a compounding temperature of 225°C. The mixture was then fed into an extruder, extruded through a T-shaped die, and molded using a casting roll at 30°C to produce a polyethylene sheet. The thickness of the produced sheet was 1050 μm. The sheet was sequentially stretched 6.5 times in the machine direction at 120°C and 6.0 times in the transverse direction at 125°C. The diluent was extracted from the stretched film using methylene chloride at 25-30°C. Heat setting was performed at 130°C. In the stretching step, the film was elongated to 140% of its initial width in the transverse direction, and in the shrinking step, it was shrunk by 20% of its final width in the stretching step.

[0099] Electrolyte production 60 g of succinonitrile (SN) was heated to 60° C. to melt it, and then 20 g of LiFSI and 4 g of FEC were added to prepare an electrolyte.

[0100] The phases and measured haze at room temperature for different electrolyte compositions are shown in Table 1 below.

[0101] [Table 1]

[0102] Battery manufacturing Fabrication of cathode: 92 wt% of lithium cobalt composite oxide (LiCoO2) as a cathode active material, 4 wt% of carbon black as a conductive agent, and 4 wt% of polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to fabricate a cathode mixture slurry. The slurry was applied to a 30 μm-thick aluminum (Al) thin film, dried at 120°C, and then roll-pressed to fabricate a 140 μm-thick cathode.

[0103] Fabrication of negative electrode: Graphite carbon, PVdF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt%, and 1 wt%, respectively, and added to NMP as a solvent to fabricate a negative electrode mixture slurry. The slurry was applied to a 20 μm-thick copper (Cu) thin film, dried at 120°C, and roll-pressed to fabricate a 150 μm-thick negative electrode.

[0104] The separator was applied between the positive and negative electrodes to assemble pouch-type batteries, and 2 g of the liquid electrolyte was injected into each assembled battery to manufacture a lithium secondary battery. This resulted in the manufacture of a pouch-type lithium-ion secondary battery with a capacity of 80 mAh.

[0105] <Example 2> A battery was manufactured with reference to Example 1, but hydrophilic inorganic particles SiO2 (average particle diameter (D 50):170 nm) was used, where the weight ratio of SiO2 to polyethylene was 1:10.

[0106] Example 3 A battery was manufactured by referring to Example 1, but when manufacturing the separator, hydrophilic inorganic particles of boehmite (Al(OOH)) (average particle diameter (D 50 ):175 nm) was used, where the weight ratio of boehmite to polyethylene was 1:10.

[0107] Example 4 A battery was manufactured by referring to Example 1, except that the hydrophilic polymer PE-b-PEG (polyethylene-block-poly(ethylene glycol)) (Sigma Aldrich Inc., number average molecular weight (Mw): 2250 g / mol) was used instead of Al2O3 when manufacturing the separator. The weight ratio of PE-b-PEG to polyethylene was 1:10.

[0108] <Comparative Example 1> A battery was manufactured by referring to Example 1, except that a 9.0 μm thick polyethylene (PE) microporous membrane (SK Innovation Co., Ltd., average pore diameter: 40 nm) was used as the separator. The weight per unit area and porosity of the polyethylene separator were 5.1 g / m 2 , 40.35%.

[0109] <Comparative Example 2> A battery was fabricated by referring to Example 1, except that a 9.1 μm thick polypropylene (PP) microporous membrane (SK Innovation Co., Ltd., average pore diameter: 40 nm) was used as the separator. The weight per unit area and porosity of the polypropylene separator were 5.2 g / m. 2 , 42.92%.

[0110] <Comparative Example 3> A homogeneous aqueous slurry with a solids content of 30 wt% was prepared by adding 100 wt parts of boehmite (γ-AlO(OH)) with an average particle size of 300 nm to 3 wt parts of polyacrylamide (MW 150,000 g / mol, Sigma Aldrich Inc.) and adding 0.7 wt parts of a dispersant (BYK-2018) based on the boehmite. The mixture was stirred to prepare a homogeneous aqueous slurry with a solids content of 30 wt%. The resulting slurry composition was applied to the surface of a 9 μm-thick polyethylene microporous membrane (ENPASS, SK Innovation Co., Ltd., average pore size: 40 nm) using a bar coating method at a speed of 10 m / min. The aqueous slurry was then coated on both sides of the substrate using hot air at 45°C until no further weight loss occurred and the membrane was wound up. After drying, the thickness of the coating layer on both sides was 2.0 μm. The resulting porous separator had a thickness of 13 μm and an area weight of 9.3 g / m. 2 The porosity was 46.83%. Next, a battery was manufactured in the same manner as in Example 1 using the manufactured separator.

[0111] Table 2 below shows the components and properties of the separators manufactured in accordance with the examples and comparative examples.

[0112] [Table 2]

[0113] <Experimental Example> The properties of the separators and batteries prepared in the examples and comparative examples were analyzed using the above test methods, and the results are shown in Table 3 below.

[0114] [Table 3]

[0115] As can be seen from Table 3, the separators of the examples, which were prepared by mixing hydrophilic inorganic particles or hydrophilic polymers with polyolefin polymers, all had contact angles of approximately 20° or less and diffusion rates of 0.7 cm / 10 s or more, demonstrating excellent wettability with respect to electrolytes containing nitrile compounds, enabling higher ionic conductivity than the comparative examples. Furthermore, the batteries prepared in the examples all had capacity realization rates of approximately 98% or more, enabling higher battery capacity than the comparative examples.

[0116] Although one embodiment has been described in detail above with reference to examples and experimental examples, the scope of one embodiment should not be limited to a specific example, but should be interpreted by the scope of the appended claims. [Explanation of symbols]

[0117] 100 positive electrode 105 Positive electrode current collector 107 Positive lead 110 Cathode active material layer 120 Negative electrode active material layer 125 Negative electrode current collector 127 Negative lead 130 negative electrode 140 Separator 150 Electrode assembly 160 cases

Claims

1. a positive electrode, a negative electrode, a separator, and an electrolyte; The separator is a porous polymer membrane in which at least one of hydrophilic inorganic particles and hydrophilic polymers is mixed in a porous substrate, The electrochemical element, wherein the electrolyte contains a nitrile compound.

2. 2. The electrochemical device of claim 1, wherein the nitrile-based compound comprises at least one selected from the group consisting of succinonitrile, (3,4-dimethoxyphenyl)acetonitrile, 2-(4-bromo-2-methoxyphenyl)acetonitrile, 2-fluorophenylacetonitrile, 2-chloro-4-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonanedinitrile, sebaconitrile, undecanedinitrile, and dodecanedinitrile.

3. 10. The electrochemical device of claim 1, wherein the electrolyte further comprises a lithium salt.

4. The lithium salts include LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide), LiBOB (lithium bis(oxalato)borate), (C ２ F ５ SO ２ ) ２ NLi, LiCl, LiBr, LiI, LiClO ４ , LiBF ４ , LiB １０ Cl １０ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiC ４ BO ８ , LiAsF ６ , LiSbF ６ , LiAlCl ４ , C.H. ３ SO ３ Li, (CF ３ SO ２ ) ３ CLi, LiBF ２ (C ２ O ４ ), LiAlO ２ , and LiN(C ｘ F ２ｘ＋１ SO ２ ) (C ｙ F ２ｙ＋１ SO ２ 4. The electrochemical device according to claim 3, wherein x and y are natural numbers.

5. The electrochemical device according to claim 1 , wherein the porous substrate comprises a polyolefin.

6. 6. The electrochemical device according to claim 5, wherein the polyolefin comprises at least one of polyethylene and polypropylene.

7. The hydrophilic inorganic particles are Al ２ O ３ , boehmite (AlOOH), SiO ２ , SnO ２ , ZrO ２ , TiO ２ , SiC, Si ３ N ４ , CaO, MgO, ZnO, BaTiO ３ , LiAlO ２ , BaSO ４ , CaCO ３ , Y ２ O ３ and CeO ２ The electrochemical device according to claim 1 , comprising at least one selected from the group consisting of:

8. 2. The electrochemical device according to claim 1, wherein the hydrophilic inorganic particles have an average particle size of 50 nm to 3 μm.

9. 2. The electrochemical element of claim 1, wherein the hydrophilic polymer comprises at least one selected from the group consisting of polyethylene oxide (PEO), polysulfone (PS), polyimide (PI), polyethersulfone (PES), cellulose acetate (CA), polyacrylonitrile (PAN), polyethylene glycol (PEG), polypropylene glycol (PPG), polymethyl methacrylic acid (PMMA), polyacrylic acid (PAA), and polyvinyl alcohol (PVA).

10. 2. The electrochemical device according to claim 1, wherein a weight ratio of the hydrophilic inorganic particles and / or the hydrophilic polymer to the porous substrate is 0.1:9.9 to 5.0:5.

0.

11. 2. The electrochemical device according to claim 1, wherein the electrolyte is in a liquid phase or a gel phase at room temperature.

12. The electrolyte was placed in a 10x40x50mm quartz cell and left at room temperature for 12 hours. Then, the haze was measured using a colorimeter (COH400, Nippon Denshoku Co., Ltd.) at a distance of 100mm perpendicular to a halogen lamp with a rated voltage of 12V and a power consumption of 50W.

12. The electrochemical device according to claim 11, wherein the liquid phase electrolyte has a haze of 50% or less, and the gel phase electrolyte has a haze of more than 50% and less than 90%.

13. 2. The electrochemical element according to claim 1, wherein a portion of the electrolyte is contained in a form filled in pores of the separator.

14. 4. The electrochemical device according to claim 3, wherein the weight ratio of the nitrile compound to the lithium salt is 1:10 to 10:

1.

15. 2. The electrochemical device according to claim 1, wherein the electrolyte further comprises a carbonate-based additive in an amount of 0.1% by weight to 10% by weight based on the total weight of the electrolyte.

16. 2. The electrochemical device according to claim 1, wherein the separator has a thickness of 1 μm to 100 μm.

17. 2. The electrochemical device according to claim 1, wherein the separator has a contact angle with the electrolyte of 5° to 50°.

18. The separator has an ionic conductivity of 0.1×10 －４ 2. The electrochemical device according to claim 1, wherein the electrical conductivity is 1.5 S / cm or more.

19. 2. The electrochemical device according to claim 1, wherein the separator has a porosity of 30% or more.

20. 2. The electrochemical device according to claim 1, wherein the electrochemical device is a lithium secondary battery.

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