Electrochemical device including porous separator

Abstract

The invention relates to an electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte. Specifically, the diaphragm comprises a porous hydrophilic polymeric membrane, and the electrolyte comprises a nitrile-based compound. An electrochemical device according to one particular embodiment may achieve high ionic conductivity by including a porous separator having wettability to an electrolyte.

Description

Technical Field

[0001] The present invention relates to an electrochemical device comprising a porous separator. Background Art

[0002] In conventional electrochemical devices, batteries are manufactured by winding or stacking a battery cell consisting of a negative electrode, a positive electrode, and a separator between them into a cylinder, inserting the cylinder into a pouch, and injecting a liquid electrolyte into the pouch. The electrolyte facilitates the transfer of charge between the electrodes and typically consists of a solvent and a salt.

[0003] In recent years, electrochemical devices have required larger capacities for applications such as electric vehicles and energy storage devices. This increase in capacity also increases the risk of fire and explosion, placing greater demands on their heat resistance and safety. Furthermore, while achieving high-capacity, high-power electrode active materials, the wettability of the separator with the electrolyte must be ensured to maintain the device's electrochemical properties. Summary of the Invention

[0004] (1) Technical issues to be resolved

[0005] An object of one embodiment is to provide an electrochemical device including an electrolyte containing a nitrile-based compound and a porous separator having wettability with the electrolyte.

[0006] (2) Technical solution

[0007] One embodiment provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator comprises a porous hydrophilic polymer film, and the electrolyte comprises a nitrile-based compound.

[0008] 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.

[0009] In one embodiment, the nitrile compound may comprise succinonitrile, (3,4-dimethoxyphenyl)acetonitrile, 2-(4-bromo-2-methoxyphenyl)acetonitrile, 2-fluorophenylacetonitrile, 2-chloro-4-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid, sebacononitrile, undecane dicarbonitrile and / or dodecane dicarbonitrile.

[0010] In one embodiment, the lithium salt may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), (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) (wherein x and y are natural numbers).

[0011] In one embodiment, the hydrophilic polymer membrane may comprise a hydrophilic polymer, wherein the hydrophilic polymer may comprise one or more selected from polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), 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).

[0012] In one embodiment, the hydrophilic polymer membrane may include hydrophilic polymers in the form of fibers. In this case, the average length of the hydrophilic polymers in the form of fibers may be about 500 nm or more.

[0013] In one embodiment, the electrolyte may exist in a liquid phase or a gel phase at room temperature. For the liquid phase and gel phase, after the electrolyte is placed in a 10×40×50 mm quartz cell and left at room temperature for 12 hours, a colorimeter (COH400, Nippon Denshoku Co., Ltd.) is used to measure the haze at a vertical distance of 100 mm from a halogen lamp with a rated voltage of 12 V and a power consumption of 50 W. The haze of the liquid phase may be less than 50%, and the haze of the gel phase may be greater than 50% and less than 90%.

[0014] In one embodiment, a portion of the electrolyte may be included in the form of filling the pores of the separator.

[0015] In one embodiment, the electrolyte may include 0.1 wt % to 10 wt % of the carbonate-based additive relative to the total weight of the electrolyte.

[0016] In one embodiment, the separator may have a thickness of 1 μm to 100 μm.

[0017] In one embodiment, the contact angle of the separator relative to the electrolyte may be 5° to 50°. In one embodiment, the ionic conductivity of the separator may be 0.1×10 -4 In one embodiment, the porosity of the separator may be 20% to 80%.

[0018] In one embodiment, the electrochemical device may be a lithium secondary battery.

[0019] (3) Beneficial effects

[0020] The present invention relates to an electrochemical device including a porous separator. An electrochemical device according to a specific embodiment can achieve high ion conductivity by including an electrolyte including a nitrile-based compound and a porous separator having wettability with the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic plan view of a lithium secondary battery according to one embodiment.

[0022] Figure 2 is a schematic cross-sectional view of a lithium secondary battery according to one embodiment.

[0023] [Explanation of Reference Signs]

[0024] 100: positive electrode; 105: positive electrode current collector

[0025] 107: positive electrode lead; 110: positive electrode active material layer

[0026] 120: negative electrode active material layer; 125: negative electrode current collector

[0027] 127: negative lead; 130: negative electrode

[0028] 140: diaphragm; 150: electrode assembly

[0029] 160: Shell DETAILED DESCRIPTION

[0030] The embodiments described in this specification can be modified into various other embodiments, and therefore, the technology according to a specific embodiment is not limited to the embodiment described below. In addition, throughout the specification, unless otherwise specifically stated to the contrary, the description of "comprising, including, containing," "having," "containing," or "having" a component means that other components may also be included, rather than excluding other components, and does not exclude elements, materials, or processes not further listed.

[0031] The numerical ranges used in this specification include the lower limit and the upper limit, as well as all values ​​within the range, increments logically derived from the form and width of the defined range, all values ​​defined therein, and all possible combinations of upper and lower limits of the numerical range defined in different forms. As an example, when the content of a composition is defined as 10% to 80% or 20% to 50%, it should be interpreted that the numerical range of 10% to 50% or 50% to 80% is also recorded in this specification. In this specification, unless otherwise specifically defined, values ​​outside the numerical range that may appear due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0032] Hereinafter, in this specification, unless specifically defined otherwise, “about” may be considered to be a value within 30%, 25%, 20%, 15%, 10%, 5%, 3%, 2%, 1% or 0.5% of the explicitly stated value.

[0033] In this specification, unless otherwise defined, when describing a part such as a layer, a membrane, a film, a region, a plate, etc. as being "on" or "over" another part, this includes not only the case of being "directly" "on" another part, but also the case of having other parts in between.

[0034] In this specification, unless otherwise defined, "polymer (macromolecule)" refers to a molecule of relatively high molecular weight, the structure of which may include multiple repetitions of units derived from molecules of low molecular weight. In one embodiment, the polymer may be an alternating copolymer, a block copolymer, a random copolymer, a graft copolymer, a gradient copolymer, a branched copolymer, a crosslinked copolymer, or a copolymer comprising all of these copolymers (e.g., a polymer comprising more than one monomer). In another embodiment, the polymer may be a homopolymer (e.g., a polymer comprising one monomer).

[0035] One embodiment provides an electrochemical device comprising a separator having wettability for an electrolyte comprising a nitrile-based compound. Specifically, one embodiment provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator comprises a porous hydrophilic polymer membrane, and the electrolyte comprises a nitrile-based compound.

[0036] A separator according to one embodiment uses a hydrophilic polymer as its polymer material, thereby exhibiting wettability with respect to the electrolyte according to one embodiment. In particular, the separator has significantly higher wettability than a hydrophobic polyolefin polymer separator. Furthermore, the separator has significantly higher ionic conductivity than a separator obtained by coating a hydrophobic polyolefin polymer membrane with inorganic particles.

[0037] In one embodiment, the hydrophilic polymer can be identified as the macromolecule of hydrophilic polymer as long as the technical personnel of the technical field disclosed in this specification sheets can be, then there is no particular limit.For example, the hydrophilic polymer can be the macromolecule comprising 3 to 10, 3 to 8 or 3 to 6 carbons, or can include hydrophilic group (substituent comprising oxygen atom).Specifically, for example, the hydrophilic polymer can include polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyimide (PI), polysulfone (PS), polyether sulfone (PES), cellulose acetate (CA), polyacrylonitrile (PAN), polyethylene glycol (PEG), polypropylene glycol (PPG), polymethyl methacrylate (PMMA), polyacrylic acid (PAA) and / or polyvinyl alcohol (PVA) in any one or more.

[0038] In one embodiment, the hydrophilic polymer can be in fiber form. At this time, the average length of the hydrophilic polymer in the fiber form can be about 500nm or more, wherein the upper limit can be not particularly limited. For example, the hydrophilic polymer in the fiber form according to an embodiment can also be a fiber bundle entangled to form a structure of a porous membrane. In addition, the average diameter of the hydrophilic polymer in the fiber form according to an embodiment can be about 50nm to 5000nm, 100nm to 5000nm, 100nm to 3000nm or 1000nm to 2000nm, but this is merely an example, and the average diameter of the hydrophilic polymer is not particularly limited.

[0039] In one embodiment, the nitrile compound included 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 compound may include succinonitrile (SN), (3,4-dimethoxyphenyl)acetonitrile, 2-(4-bromo-2-methoxyphenyl)acetonitrile, 2-fluorophenylacetonitrile, 2-chloro-4-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid, sebacononitrile, undecane dinitrile and / or dodecane dinitrile.

[0040] 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 known to those skilled in the art of the present invention. For example, the lithium salt may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, (CF3SO2)2NLi), lithium bis(fluorosulfonyl)imide (LiFSI, (SO2F)2NLi), lithium bis(oxalate)borate (LiBOB, LiB(C2O4)2), (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) (wherein, x and y are natural numbers). In one embodiment, the electrolyte contains an imide lithium salt such as LiFSI, so that a strong and thin SEI film can be formed on the negative electrode.

[0041] In one embodiment, the electrolyte may not contain an additional solvent, in which case the electrolyte may consist solely of the nitrile compound, or the electrolyte may consist solely of the nitrile compound and a lithium salt, or the electrolyte may consist solely of a nitrile compound, a lithium salt, and specified additives.

[0042] In one embodiment, when the electrolyte further comprises 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. However, the above weight range is merely an example and is not necessarily limited to the above range.

[0043] In one embodiment, the electrolyte can further include a carbonate-based additive. The carbonate-based additive can improve the coating property of the electrolyte, and can use the carbonate-based additive in terms of the viewpoint of forming a more effective solid electrolyte interface (Solid Electrolyte Interphase, SEI) layer. Compared with the content of the solvent as a conventional liquid electrolyte, the carbonate-based additive according to an embodiment can be used with a smaller amount of content. For example, based on the gross weight of the electrolyte, the content of the carbonate-based additive can be 0.1 % by weight to 10 % by weight, or the content of the carbonate-based additive can be for example below 10 % by weight, below 8 % by weight, below 5 % by weight or below 3 % by weight, wherein, the lower limit of the content of the carbonate-based additive can be more than 0.1 % by weight, more than 0.5 % by weight or more than 1.0 % by weight.

[0044] The carbonate-based additive may include, for example, any one or more of fluoroethylene carbonate (Fluoroethylene Carbonate, FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene carbonate (EC), propylene carbonate (PC) and / or difluoroethylene carbonate (DiFEC).

[0045] In addition, the electrolyte may further include additives commonly used in the technical field disclosed in this specification as needed, and the content of the additives may be 5% by weight or less relative to the total weight of the electrolyte, but as long as the effect of the present invention is achieved, the content of the additives is not limited. As long as the additives are known additives that can be included in the electrolyte, there is no particular limitation, so further description is omitted here.

[0046] The electrolyte according to one embodiment may be in a liquid phase or a gel phase at normal temperature.

[0047] At this time, the liquid phase and the gel phase can be evaluated visually or measured as follows. After the electrolyte is placed in a quartz cell of 10×40×50 mm and left at room temperature for 12 hours, the haze is measured using a colorimeter (COH400, Nippon Denshoku Industries Co., Ltd.) at a vertical distance of 100 mm from a halogen lamp with a rated voltage of 12 V and a power consumption of 50 W. The liquid phase may refer to a haze of 50% or less, and the gel phase may refer to a haze of more than 50% and less than 90%.

[0048] The electrolyte according to one embodiment may exist between the electrode and the separator in a liquid phase or a gel phase. In this case, a portion of the electrolyte may also exist in the form of filling the pores of the porous separator.

[0049] In one embodiment, the electrolyte may be a liquid electrolyte or a gel electrolyte, or may be a solid functional layer of two or more layers that are heated to a specified temperature or above and mixed with each other, and finally phase-transformed into a liquid phase or a gel phase at room temperature. Specifically, the first functional layer (solid phase) containing a nitrile compound and the second functional layer (solid phase) containing a nitrile compound may be formed by coating and / or filling the two sides of the diaphragm and / or the pores of the diaphragm, respectively, and then heated to a specified temperature or above and mixed with each other.

[0050] At this time, as described above, the first functional layer and the second functional layer may further include a lithium salt in addition to the nitrile-based compound, and may optionally further include a carbonate-based additive.

[0051] In one embodiment, the functional layer may be formed to occupy 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. Furthermore, the functional layer may have an area between the aforementioned values. For example, the functional layer may be formed to occupy an area of ​​80% to 100% of the total surface area of ​​the separator. However, the aforementioned ranges are merely examples and are not necessarily limited to the aforementioned ranges.

[0052] In one embodiment, the functional layer is in a solid phase at room temperature, for example, 20°C to 35°C. However, when heated to a temperature above 40°C, 50°C, or 60°C, the solid-phase functional layer melts and intermixes, changing the composition of the components of each layer. Therefore, even at relatively low room temperatures, the functional layer does not undergo a phase transition to a solid phase, but remains in a liquid or gel phase. The heating temperature is not limited, as long as it allows the coatings applied to both surfaces to melt and intermix without affecting the pores of the separator according to one embodiment. For example, the heating temperature may be 40°C to 80°C or 60°C to 80°C.

[0053] 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 existing as a solid at room temperature, and glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dicarbonitrile, sebacononitrile, undecane dicarbonitrile and dodecane dicarbonitrile are compounds that can exist as a solid at room temperature when mixed with a lithium salt.

[0054] With the gross weight of electrolyte as benchmark, the content of described itrile group compound can be more than 50 % by weight, more than 55 % by weight, more than 60 % by weight, more than 65 % by weight, more than 70 % by weight, more than 75 % by weight, more than 80 % by weight, more than 85 % by weight, more than 90 % by weight, below 99.9 % by weight, below 95 % by weight, below 90 % by weight or any value between the numerical value of above-mentioned record.For example, the content of described itrile group compound can be 50 % by weight to 99.9 % by weight, 55 % by weight to 99.9 % by weight, 60 % by weight to 90 % by weight.

[0055] In one embodiment, when the electrolyte further includes a lithium salt, the content of the lithium salt is not limited as long as the lithium salt is mixed with the nitrile compound and exists in a solid phase at 10°C to 35°C, but when the separator is heated to melt the functional layers and mix with each other, it no longer remains in a solid state at room temperature (for example, the above-mentioned 10°C to 35°C) but exists in a liquid phase or a gel phase.

[0056] As an embodiment, for example, based on the total weight of the electrolyte, the content of the lithium salt can be less than 50% by weight, less than 49% by weight, less than 45% by weight, less than 40% by weight, less than 35% by weight, less than 30% by weight, less than 25% by weight, less than 20% by weight, less than 15% by weight, or greater than 10% by weight, or any value in between. For example, the content of the lithium salt can be from 10% to 49% by weight, or from 10% to 45% by weight.

[0057] In one embodiment, the first functional layer may be formed solely of a nitrile compound, and the second functional layer may be formed by mixing a nitrile compound and a lithium salt in a weight ratio of 1:1 to 1.5:1 or approximately 10:1. In one embodiment, the total weight of the first and second functional layers may be adjusted such that the total weight of the nitrile compound contained in the functional layers is 2 to 7 times that of the lithium salt. By adjusting the total weight of the first and second functional layers to the above range, each functional layer remains in a solid phase, thereby facilitating transportation.

[0058] In one embodiment, the first functional layer can be formed by impregnating the surface of the porous substrate and part or all of the pores therein. For example, the first functional layer can be formed to 0.5 g / m 2 Up to 10g / m 2 The second functional layer can be formed by impregnating the surface of the porous substrate and part or all of the pores inside the porous substrate. For example, the second functional layer can be formed to 0.5 g / m 2 Up to 10g / m 2At this time, the coating amounts of the first functional layer and the second functional layer may be the same as or different from each other.

[0059] In one embodiment, succinonitrile and a lithium salt are mixed with each other and transformed from a solid phase into a liquid phase or a gel phase. At the same time, succinonitrile has a para-cross isomer (para-cross-ortho-cross isomerism) relative to the central C-C bond below the melting point, and thus has ion-conducting behavior. Therefore, it can act as an electrolyte. In this case, the para-cross isomer contributes to the aggravation of lattice defects and the reduction of activation energy for ion conduction, thereby improving ion mobility. Therefore, compared with existing liquid electrolytes containing organic solvents and ionic liquids, the electrolyte according to one embodiment can provide a wider potential window (electrochemical window).

[0060] The electrolyte according to one embodiment may consist of only the nitrile-based compound, or the electrolyte may consist of only the nitrile-based compound and a lithium salt, or the electrolyte may consist of only the nitrile-based compound, the lithium salt, and a carbonate-based additive.

[0061] Liquid-phase or gel-phase electrolytes require a porous support. On the other hand, wet-type or dry-type separators made from commonly used polyolefin polymers have difficulty consistently ensuring high wettability with the electrolyte due to various variables (porosity, pore size, and polarity). This can result in reduced electrolyte uptake and ultimately lower battery performance. In contrast, a porous separator made from a hydrophilic polymer according to one embodiment exhibits sufficient wettability with an electrolyte containing a nitrile compound, resulting in excellent battery life and performance while also achieving the fire stability benefits of the nitrile compound.

[0062] In one embodiment, the thickness of the separator or the porous hydrophilic polymer film may be 1 μm to 100 μm, 10 μm to 80 μm, 10 μm to 50 μm, 10 μm to 30 μm, or 20 μm to 30 μm. The above thickness ranges are merely examples and are not necessarily limited to the above ranges.

[0063] In one embodiment, the separator may be in the form of a woven or non-woven fabric.

[0064] The contact angle of the separator according to one embodiment with respect to the electrolyte may be 5° to 50°, 5° to 30°, 5° to 20°, 5° to 15°, or 10° to 15°. The contact angle is measured 10 seconds after 3 μL of electrolyte is dropped onto the separator using a drop shape analyzer device (Mobile Surface Analyzer, Kruss GmbH, Germany), and the contact angle may be a value measured in a dry room environment at a temperature of 24° C. and a relative humidity of 0.5 RH% or less.

[0065] The ionic conductivity of the separator according to one embodiment may be 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, 6.0×10 -4 S / cm or more, 7.0×10 -4 S / cm or more, 8.0×10 -4 S / cm or above or 9.0×10 -4 In this case, the upper limit of the ion conductivity of the separator 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 S / cm or less.

[0066] The porosity of the separator according to one embodiment may be 20% to 80%, 30% to 60%, 35% to 60%, 35% to 55%, or 40% to 55%. The porosity can be measured using the following formula.

[0067] Porosity = [1-{(W / T)÷ρ}]×100

[0068] W = weight of the diaphragm per unit area (g / m 2 )

[0069] T = sample thickness (m)

[0070] ρ = True density of the entire diaphragm calculated based on the resin and coating materials (g / m 3 )

[0071] In one embodiment, the electrochemical device may be a lithium secondary battery, which may be formed in a prismatic, cylindrical, or pouch shape.

[0072] 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.

[0073] The positive electrode included in the lithium secondary battery according to one embodiment may include a positive electrode active material that can intercalate and deintercalate lithium ions, and as such a positive electrode active material, a composite metal oxide of at least one selected from cobalt, manganese, and nickel and lithium may be used. The solid solubility ratio between the metals may vary, and in addition to these metals, an element selected from 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. As a specific example of the positive electrode active material, a compound represented by any one of the following chemical formulas may be used:

[0074] Li a A 1-b B b D2 (in the formula, 0.90≤a≤1.8, 0≤b≤0.5); Li a E 1-b B b O 2-c D c (In the formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b B b O 4-c D c (In the formula, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b B c D α (In the formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Co b B c O 2-α F α (In the formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 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, 0<α<2); Li a Ni 1-b-c Mn b Bc D α (In the formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b- c Mn b B c O 2-α F α (In the formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 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, 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 G e O2 (wherein, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li a NiG b O2 (in the formula, 0.90≤a≤1.8, 0.001≤b≤0.1.); Li a CoG b O2 (in the formula, 0.90≤a≤1.8, 0.001≤b≤0.1.); Li a MnG b O2 (in the formula, 0.90≤a≤1.8, 0.001≤b≤0.1.); Li a Mn2G b O4 (where 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.

[0075] 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; J can be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0076] The negative electrode may contain a negative electrode active material that can embed and deintercalate lithium ions, and as such a negative electrode active material, carbon materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, lithium metal, alloys of lithium and other elements, etc. may be used. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) calcined below 1500°C, mesophase pitch-based carbon fiber (MPCF), etc. Crystalline carbon includes graphite-based materials, specifically, crystalline carbon includes natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. The carbon material may be a material having an interplanar distance of 3.35Å to 3.38Å and a crystallite size (Lc) of at least 20nm according to X-ray diffraction. As other elements forming an alloy with lithium, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium can be used.

[0077] The positive electrode or negative electrode can be manufactured by the following method: an electrode active material, a binder, a conductive material, and a thickener as needed are dispersed in a solvent to prepare an electrode slurry composition, and the slurry composition is coated on an electrode current collector to manufacture the positive electrode or negative electrode. The positive electrode current collector can generally be made of aluminum or an aluminum alloy, and the negative electrode current collector can generally 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 foil or mesh.

[0078] In one embodiment, the binder is a material that plays a role in the paste formation of the active material, the mutual adhesion of the active material, the adhesion to the current collector, the buffering effect on the expansion and contraction of the active material, etc. For example, the binder can use polyvinylidene fluoride (PVDF), polyhexafluoropropylene-polyvinylidene fluoride copolymer (PVDF / HFP), poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), poly (ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, etc. The content of the binder can be 0.1% to 30% by weight or 1% to 10% by weight relative to the electrode active material. When the content of the binder is too little, the adhesion between the electrode active material and the current collector is insufficient. When the content of the binder is too much, although the adhesion is improved, the content of the electrode active material is correspondingly reduced, and therefore it may be unfavorable to achieve a high capacity of the battery capacity.

[0079] In one embodiment, the conductive material is used in order to impart conductivity to the electrode, as long as it is a conductive material that does not cause chemical changes, any conductive material can be used, and the conductive material can be selected from at least one of graphite-based conductive materials, carbon black-based conductive materials, metal-based conductive materials or metal compound-based conductive materials. The example of the graphite-based conductive material includes artificial graphite, natural graphite, etc., and the example of the carbon black-based conductive material includes acetylene black, Ketjen black (ketjen black), acetylene carbon black (denka black), thermal black (thermal black), channel black (channel black), etc. The example of the metal-based conductive material or metal compound-based conductive material includes tin, tin oxide, tin phosphate (SnPO4), titanium oxide, potassium titanate, LaSrCoO3, LaSrMnO3 and other perovskite (perovskite) materials. However, it is not limited to the above-mentioned conductive materials listed. The content of conductive material can be 0.1 weight % to 10 weight % relative to electrode active material.

[0080] The thickener is not particularly limited as long as it can adjust the viscosity of the active material slurry, and examples thereof include carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0081] As a solvent for dispersing the electrode active material, binder, conductive material, etc., a non-aqueous solvent or a water-based solvent can be used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0082] Figure 1 and Figure 2 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Figure 2 It is along Figure 1 A cross-sectional view taken along line II'.

[0083] Reference Figure 1 and Figure 2 The 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 and negative electrodes. The electrode assembly may be housed in a case 160 together with an electrolyte and impregnated in the electrolyte.

[0084] 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 contain a positive electrode active material and may contain a positive electrode binder, a conductive material, and / or a dispersion medium as needed. The positive electrode 100 may be manufactured by the following method: for example, the positive electrode active material, the positive electrode binder, the conductive material, the dispersion medium, etc. are mixed and stirred to prepare a positive electrode slurry, and then the positive electrode slurry is coated (applied) on the positive electrode current collector 105 and dried and rolled (compressed) to manufacture the positive electrode.

[0085] 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 contain a negative electrode active material and may contain a negative electrode binder, a conductive material, and / or a dispersion medium as needed. The negative electrode 130 may be manufactured by, for example, 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, and then applying (coating) the negative electrode slurry on the negative electrode current collector 125 and drying and rolling (compressing) to manufacture the negative electrode.

[0086] The tabs (positive tabs and negative tabs) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell and extend to one side of the case 160. The tabs may be fused to the one side of the case 160 to form electrode leads (positive lead 107 and negative lead 127) extending to the outside of the case 160 or exposed to the outside of the case 160.

[0087] The following examples and experimental examples are specifically illustrated and described. However, the following examples and experimental examples are only used to illustrate a part of a specific embodiment, and the technology described in this specification should not be interpreted as being limited thereto.

[0088] <Test method>

[0089] 1. Analysis of the physical properties of the diaphragm

[0090] The thickness of the separator was calculated as the average value of the thickness of 10 separator layers measured using a contact micrometer (Mitutoyo, Japan) and divided by 10.

[0091] The weight per unit area of ​​the separator was measured by measuring the weight of a separator having an area of ​​10 cm×10 cm using an electronic scale capable of measuring to four decimal places and converting the weight into the weight per unit area.

[0092] The porosity of the separator was calculated using the following formula based on the previously measured thickness and weight per unit area of ​​the separator.

[0093] Porosity = [1-{(W / T)÷ρ}]×100

[0094] (W = weight of the diaphragm per unit area (unit: g / m 2 ), T = sample thickness (unit: m), ρ = true density of the entire diaphragm calculated based on the materials of the resin and coating (unit: g / m 3 ))

[0095] 2. Contact angle analysis

[0096] The contact angles of the separators produced in Examples and Comparative Examples with respect to the liquid electrolyte immediately after production were measured using a droplet shape analyzer (Mobile Surface Analyzer, Krues, Germany). The contact angles were measured 10 seconds after 3 μL of liquid electrolyte was dropped onto the separator. The contact angles were measured in a dry room environment at a temperature of 24°C and a relative humidity of 0.5 RH% or less.

[0097] 3. Analysis of spreading rate

[0098] Using a pipette, a 10 mg drop of liquid electrolyte was dropped onto a separator having an area of ​​10 cm×10 cm, and then 10 seconds later, the longest portion of the radius of the electrolyte spread in a circle was measured.

[0099] 4. Analysis of ionic conductivity

[0100] The ion conductivity of the separators of each example and comparative example was calculated using the following formula.

[0101] Ionic conductivity = L ÷ (R × A)

[0102] (L = thickness of the membrane impregnated with liquid electrolyte (unit: cm), R = impedance value of the membrane impregnated with liquid electrolyte (unit: Ω = 1 / S) (real value when the imaginary part of the impedance value is 0), A = the area of ​​overlap between the two electrodes when measuring the impedance value (unit: cm) 2 ))

[0103] To determine the R value, the separator was punched into concentric circles with a diameter of 18 mm and then immersed in liquid electrolyte. At this time, the L value was measured with a micrometer and the A value was determined to be 2.5447 cm 2 A 2032-standard coin cell (made of stainless steel (SUS)) was then assembled using a separator impregnated with a liquid electrolyte. Constant-voltage impedance measurements were performed using a Zahner GmbH IM6 instrument within a frequency range of 100 MHz to 100 mHz, with an initial voltage of 0 V and an amplitude of 5 mV. The real impedance value, R, was calculated when the imaginary part was 0 by equivalent circuit fitting of the measured impedance values.

[0104] 5. Analysis of Capacity Achievement Rate

[0105] For a single cell with a theoretical design capacity of 80 mAh, the first cycle is charged / discharged at 0.1C, the second cycle is charged / discharged at 0.2C, and the third cycle is charged / discharged at 0.5C within the range of 2.7V (constant current) to 4.3V (constant current constant voltage), and the capacity is measured. The capacity realization rate is calculated as the percentage of the measured capacity to the theoretical design capacity.

[0106] 6. Scanning Electron Microscopy (SEM) Analysis

[0107] The samples were platinum coated using a Quorum technologies Q150V S Plus model at 20 mA / 30 seconds, and then subjected to scanning electron microscopy (SEM) analysis using a Hitachi s4800 model at 5 kV and 10 μA.

[0108] 7. Measurement of weight average molecular weight (Mw)

[0109] The weight-average molecular weight was measured using GPC (EcoSECHLC-8320 GPC reflection index detector from Tosoh Corporation) using two TSKgel guard PWx columns, namely TSKgel GMPWxl and TSKgelG2500PWxl (7.8×300 mm) as GPC columns, a 0.1 M NaNO3 aqueous solution as a developing solvent, polyethylene glycol as a standard, and analysis was performed at 40°C at a flow rate of 1 mL / min.

[0110] <Example 1>

[0111] Diaphragm manufacturing

[0112] 20 wt% of polyimide (PI, weight average molecular weight (Mw): 60000 g / mol) powder was added to dimethylsulfoxide (DMSO) and dissolved to prepare a uniform solution, and then electrospinning was used to manufacture a porous membrane with a thickness of 80 μm. The size of the needle used at this time was 23G (outer diameter of 0.64 mm, inner diameter of 0.34 mm), the distance between the needle and the grounded SUS plate was 22 cm, and the applied voltage was 20 kV. The prepared porous membrane was pressed into a thickness of 20 μm, thereby producing a weight per unit area of ​​16.3 g / m 2 And the porosity of the diaphragm is 42.49%.

[0113] Preparation of electrolyte

[0114] 60 g of succinonitrile (SN) was heated to 60° C. to be melted, and then 20 g of LiFSI and 4 g of FEC were added to prepare an electrolyte.

[0115] Table 1 below shows the phases and measured haze of different electrolyte compositions at room temperature.

[0116] [Table 1]

[0117]

[0118] Battery manufacturing

[0119] Positive electrode production: 92% by weight of lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, 4% by weight of carbon black as the conductive material, and 4% by weight of polyvinylidene fluoride (PVDF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry. The prepared slurry was coated on a 30μm thick aluminum (Al) film and dried at 120°C. It was then roll-pressed to produce a 140μm thick positive electrode.

[0120] Negative electrode preparation: 96 wt% graphite carbon, 3 wt% PVDF as a binder, and 1 wt% carbon black as a conductive agent were added to NMP as a solvent to prepare a negative electrode mixture slurry. The prepared slurry was coated on a 20 μm thick copper (Cu) film, dried at 120°C, and roll-pressed to produce a 150 μm thick negative electrode.

[0121] A pouch-type battery was assembled with the prepared separator between the positive electrode and the negative electrode, and 2 g of the liquid electrolyte prepared above was injected into each assembled battery to produce a lithium secondary battery. Thus, a pouch-type lithium ion secondary battery with a capacity of 80 mAh was produced.

[0122] <Example 2>

[0123] A battery was manufactured with reference to Example 1, except that the diaphragm was manufactured as follows. 10 wt % of polyvinyl alcohol (PVA, weight average molecular weight (Mw): 180,000 g / mol) powder was added to distilled water and heated at 80°C to dissolve it, thereby preparing a uniform aqueous solution, and then electrospinning was used to manufacture a porous membrane with a thickness of 90 μm. The size of the needle used at this time was 23G (outer diameter of 0.64 mm, inner diameter of 0.34 mm), the distance between the needle and the grounded SUS plate was 15 cm, and the applied voltage was 12 kV. The obtained porous diaphragm was pressed into a thickness of 25 μm, thereby manufacturing a porous membrane with a weight per unit area of ​​14.2 g / m 2 And the porosity of the diaphragm is 52.30%.

[0124] <Example 3>

[0125] The battery was manufactured with reference to the embodiment 1, except that the diaphragm was manufactured as follows. Using the vacuum filtration method, a dispersion of 0.5 wt% 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (20 nm in diameter and 1 μm in length) was uniformly dispersed in distilled water to form a cellulose film with a thickness of 20 μm, and then freeze drying was used to remove the moisture. The thickness of the obtained porous cellulose diaphragm was 20 μm, and the weight per unit area was 14.5 g / m 2 , the porosity is 51.70%.

[0126] <Example 4>

[0127] A battery was manufactured with reference to Example 1, except that the diaphragm was manufactured as follows. 6 wt% of polyethylene oxide (PEO, weight average molecular weight (Mw): 400,000 g / mol) powder was added to distilled water and methanol (8:2 (v / v)) and heated at 80°C to dissolve it, thereby preparing a uniform solution, and then electrospinning was used to manufacture a porous membrane with a thickness of 80 μm. The needle size used at this time was 23G (outer diameter of 0.64 mm, inner diameter of 0.34 mm), the distance between the needle and the grounded SUS plate was 16 cm, and the applied voltage was 9.5 kV. The obtained porous diaphragm was pressed into a thickness of 25 μm, thereby producing a weight per unit area of ​​15.6 g / m 2 And the porosity of the diaphragm is 44.80%.

[0128] <Comparative Examples 1 and 2>

[0129] Batteries were manufactured with reference to Example 1, except that the separators used microporous membranes (SK New Technology Co., Ltd., average pore size: 40 nm) of polyethylene (PE) with a thickness of 9.0 μm and polypropylene (PP) with a thickness of 9.1 μm. The weight and porosity of the separators were 5.1 g / m 2 , 40.35%, 5.2g / m 2 , 42.92%.

[0130] <Comparative Example 3>

[0131] A battery was manufactured with reference to Example 1, except that the diaphragm was manufactured as follows. 3 wt% of polyacrylamide (weight average molecular weight (Mw) of 150,000 g / mol, Sigma Aldrich) relative to 100 wt% of boehmite (AlO(OH)) with an average particle size of 300 nm was added to water, and 0.7 wt% of a dispersant (BYK-2018) was added and stirred relative to the boehmite to prepare a uniform water-based slurry with a solid content of 30 wt%. The obtained water-based slurry was coated on both sides of a polyethylene microporous membrane (ENPASS, SK New Technology Co., Ltd., average pore size: 40 nm) having a thickness of 9 μm at a speed of 10 m / min using bar coating, and then dried with hot air at 45 ° C until the weight no longer decreased and wound. After drying, the thickness of the coating on both sides was 2.0 μm. The thickness of the porous membrane was 13 μm and the weight per unit area was 9.3 g / m 2 , the porosity is 46.83%.

[0132] The compositions and physical properties of the separators manufactured by the examples and comparative examples are summarized and shown in Table 2 below.

[0133] [Table 2]

[0134]

[0135] <Experimental Example>

[0136] The physical properties of the separators and batteries produced in Examples and Comparative Examples were analyzed according to the above test methods. The results are shown in Table 3 below.

[0137] [Table 3]

[0138]

[0139] It can be confirmed from Table 3 that in the case of the separators of the embodiments manufactured using hydrophilic polymers in the form of nanofibers, the contact angles are all below about 15°, and they have excellent wettability to the electrolyte, and the diffusion rates are all as high as 1.0 cm / 10 seconds or more, thereby ensuring high ionic conductivity. Specifically, the results of analyzing the ionic conductivity show that the separators of the embodiments have significantly higher ionic conductivity than the separators of the comparative examples. In addition, the capacity realization rates of the batteries manufactured in the embodiments are all above about 98%, which is different from the comparative examples, and the high capacity of the batteries can be achieved.

[0140] A specific embodiment has been described in detail above through examples and experimental examples. However, the scope of a specific embodiment is not limited to the specific examples but should be interpreted according to the claims.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, The separator comprises a porous hydrophilic polymer membrane, The electrolyte includes a nitrile-based compound.

2. The electrochemical device according to claim 1, wherein The nitrile compound comprises at least one selected from succinonitrile, (3,4-dimethoxyphenyl)acetonitrile, 2-(4-bromo-2-methoxyphenyl)acetonitrile, 2-fluorophenylacetonitrile, 2-chloro-4-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid, sebacononitrile, undecane dicarbonitrile and dodecane dicarbonitrile.

3. The electrochemical device according to claim 1, wherein The electrolyte further comprises a lithium salt.

4. The electrochemical device according to claim 3, wherein The lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalate)borate (LiBOB), (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 LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) in any one or more, wherein x and y are natural numbers.

5. The electrochemical device according to claim 1, wherein The hydrophilic polymer membrane comprises one or more selected from polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyimide (PI), polysulfone (PS), polyethersulfone (PES), cellulose acetate (CA), polyacrylonitrile (PAN), polyethylene glycol (PEG), polypropylene glycol (PPG), polymethyl methacrylate (PMMA), polyacrylic acid (PAA) and polyvinyl alcohol (PVA).

6. The electrochemical device according to claim 1, wherein The hydrophilic polymer membrane includes a hydrophilic polymer in the form of fibers.

7. The electrochemical device according to claim 6, wherein The average length of the hydrophilic polymer in the form of fibers is 500 nm or longer.

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

9. The electrochemical device according to claim 8, wherein After the electrolyte is placed in a quartz cell of 10×40×50 mm and left at room temperature for 12 hours, the haze is measured using a colorimeter at a vertical distance of 100 mm from a halogen lamp with a rated voltage of 12 V and a power consumption of 50 W. The haze of the liquid phase electrolyte is less than 50%, and the haze of the gel phase electrolyte is more than 50% and less than 90%.

10. The electrochemical device according to claim 1, wherein A portion of the electrolyte is contained in the form of filling the pores of the separator.

11. 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.

12. The electrochemical device according to claim 1, wherein The electrolyte further comprises 0.1 wt % to 10 wt % of a carbonate-based additive relative to the total weight of the electrolyte.

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

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

15. The electrochemical device according to claim 1, wherein The ionic conductivity of the membrane is 0.1×10 -4 S / cm or more.

16. The electrochemical device according to claim 1, wherein The porosity of the separator is 20% to 80%.

17. The electrochemical device according to claim 1, wherein The electrochemical device is a lithium secondary battery.

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