Electrode for lithium secondary battery and lithium secondary battery

Abstract

The present invention relates to an electrode for a lithium secondary battery, which comprises: a binder resin formed on an electrode substrate and containing a (co)polymer having a predetermined structure; and a porous layer containing inorganic fine particles; and a lithium secondary battery comprising the electrode.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0105065, filed August 22, 2022, and Korean Patent Application No. 10-2023-0109223, filed August 21, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an electrode for a lithium secondary battery that has high high-temperature stability, solid structural stability, and high interfacial adhesion with a counter electrode, and that can improve the life characteristics, charge capacity, and discharge capacity of the lithium secondary battery and has high flex resistance, and to a lithium secondary battery including the same. [Background technology]

[0003] Recently, with the increasing technological development and demand for mobile devices, the demand for rechargeable secondary batteries as an energy source has been increasing rapidly, and as a result, much research is being conducted on secondary batteries that can meet various requirements. Secondary batteries are also attracting attention as a power source for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (Plug-in HEVs), which are being proposed as a solution to air pollution caused by existing gasoline and diesel vehicles that use fossil fuels.

[0004] When a short circuit occurs in a lithium secondary battery due to contact between the positive and negative electrodes, it can generate significant heat and explode. The porous separator of a secondary battery exhibits significant thermal shrinkage at temperatures above 100°C due to its material properties and manufacturing process characteristics, including stretching, which can cause a short circuit between the positive and negative electrodes.

[0005] Accordingly, various researches have been conducted on methods for ensuring the morphological stability and high temperature stability of lithium secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides an electrode for a lithium secondary battery that has high high-temperature stability, solid structural stability, and high interfacial adhesion to a counter electrode, and that can improve the life characteristics, charge capacity, and discharge capacity of the lithium secondary battery, and has high flex resistance.

[0007] The present invention also provides a lithium secondary battery including the electrode for a lithium secondary battery. [Means for solving the problem]

[0008] The present invention provides an electrode for a lithium secondary battery, comprising: an electrode substrate; and a porous layer formed on the electrode substrate, the porous layer comprising: a binder resin containing a (co)polymer including a repeating unit derived from a urethane (meth)acrylate monomer or oligomer; and inorganic fine particles.

[0009] The present invention also provides a lithium secondary battery including the electrode for a lithium secondary battery.

[0010] Hereinafter, an electrode for a lithium secondary battery and a lithium secondary battery according to embodiments of the present invention will be described in detail.

[0011] In this specification, a photopolymerizable compound is a general term for a compound that undergoes a polymerization reaction when irradiated with light, for example, visible light or ultraviolet light.

[0012] Also, (meth)acryl is meant to include both acryl and methacryl.

[0013] Furthermore, the term "(co)polymer" is intended to include both copolymers and homopolymers.

[0014] The electrode substrate refers to a current collector.

[0015] An electrode refers to an electrode substrate on which an electrode layer is coated, and an electrode layer coated on one side or both sides is called a single-side electrode or a double-side electrode, respectively.

[0016] According to one embodiment of the present invention, there is provided an electrode for a lithium secondary battery, comprising: an electrode substrate; and a porous layer formed on the electrode substrate, the porous layer comprising: a binder resin including a (co)polymer including a repeating unit derived from a urethane (meth)acrylate-based monomer or oligomer; and inorganic fine particles.

[0017] The present inventors have developed an electrode for a lithium secondary battery having the porous layer, and have confirmed through experiments that such an electrode for a lithium secondary battery has high high-temperature stability, solid structural stability, and high interfacial adhesion with a counter electrode, and can improve the life characteristics, charge capacity, and discharge capacity of a lithium secondary battery, thereby completing the invention.

[0018] In particular, the porous layer can connect, bond, or fix inorganic fine particles via the binder resin described above. Since the binder resin contains a (co)polymer including a repeating unit derived from a urethane (meth)acrylate-based monomer or oligomer, the porous layer can have flexibility or bending resistance that is difficult to achieve in a secondary battery having a separator with a known electrode coating layer or coating layer.

[0019] Specifically, the porous layer or the electrode for a lithium secondary battery including the porous layer can have bending resistance such that no cracks occur when wound around a cylindrical mandrel having a diameter of 2 mm or more according to the ISO1519:2011 standard method.

[0020] The porous layer or a lithium secondary battery electrode including the porous layer is subjected to a cylindrical mandrel test in order of diameter from largest to smallest according to the ISO 1519:2011 standard method to determine its bending resistance. The measurement sample may be a lithium secondary battery electrode including the porous layer, and the electrode may be a single-sided electrode or a double-sided electrode. In the case of a single-sided electrode, the porous layer is formed on the side opposite the current collector in contact with the electrode layer. In the case of a double-sided electrode, the porous layer is formed on the side opposite the current collector in contact with only one electrode layer.

[0021] The porous layer can be formed on the electrode substrate and adhered to the cylindrical mandrel so that the porous layer faces outward and does not come into contact with the mandrel, and the bending resistance can be evaluated.

[0022] The flex resistance value can be determined as the largest diameter of a first mandrel at which, when an electrode coated with the porous layer is tightly attached to a cylindrical mandrel, the coating layer cracks, the coating layer is separated from the electrode layer, or both the coating layer and the electrode layer are separated from the current collector. When this method is applied, the porous layer or a lithium secondary battery electrode including the porous layer may have a flex resistance that does not cause cracks when wound around a cylindrical mandrel having a diameter of 2 mm or more, 3 mm or more, or 4 mm or more according to the ISO 1519:2011 standard method, and may have a flex resistance of 2 mm to 40 mm, 3 mm to 30 mm, or 4 mm to 20 mm.

[0023] On the other hand, conventional lithium secondary batteries have a problem that the polymer separator between the positive and negative electrodes has weak interfacial adhesion with the counter electrode, making the battery assembly process difficult. Also, the expansion and contraction of the electrodes causes interfacial peeling due to insufficient adhesion, resulting in reduced battery life characteristics. In particular, they exhibit severe thermal shrinkage at temperatures above approximately 100°C, causing short circuits between the positive and negative electrodes.

[0024] In contrast, in the lithium secondary battery electrode of this embodiment, the porous layer formed on the electrode substrate replaces the function of the existing polymer separator, and has high interfacial adhesion with the counter electrode and a robust internal structure, preventing a decrease in structural stability or battery performance even at high temperatures of 100°C or higher.

[0025] More specifically, the binder resin containing a (co)polymer containing a repeating unit derived from a urethane (meth)acrylate monomer or oligomer contains flexible functional groups inside that can absorb external impacts, and can serve to fix the positions of the alumina particles distributed among the binder resins by forming a crosslinked structure by bonding with adjacent binder resins through a photopolymerization reaction.

[0026] The inorganic fine particles are the main component of the porous layer, and serve to form micropores by providing empty spaces between the inorganic fine particles, while also serving as a kind of spacer that can maintain the physical shape of the porous layer.

[0027] Furthermore, the crosslinked structure of the porous layer has higher thermal stability and dimensional stability than existing polyolefin-based separators, which can improve the lifespan, charge capacity, and discharge capacity of lithium secondary batteries.

[0028] The porous layer can form micropores by adjusting the size of the inorganic fine particles, the content of the inorganic fine particles, and the content of the binder resin, and the pore size and porosity can also be adjusted. For example, the porosity of the porous layer may be 40% to 80%, 45% to 75%, or 50% to 70%.

[0029] The porosity of the porous layer can be achieved by adjusting the composition of the porous layer. The porosity of the porous layer can be achieved by satisfying the above-described contents of inorganic fine particles and binder resin. When the porous layer has a porosity within the above-described range, a technical effect of improving battery performance due to electrochemical reasons, such as smooth movement of lithium ions in the electrolyte through the pores, can be achieved.

[0030] If the porosity of the porous layer is less than 40%, the movement of lithium ions is restricted, resulting in increased resistance, which may cause technical problems such as poor charge / discharge characteristics of the battery. If the porosity of the porous layer is more than 80%, the mechanical properties of the porous layer may be weakened, which may cause technical problems such as poor durability of the battery element.

[0031] The porosity can be calculated by the following Equation 1 using the ratio of the density obtained by measuring the volume and mass of a porous layer of a sample coated with the composition on an electrode substrate of a certain area to the theoretical density of the solid content of the coating composition.

[0032] [Formula 1] Porosity (%) = {1 (actual density) / (theoretical density)} x 100

[0033] The size of the pores formed in the porous layer can be controlled by adjusting the size of the inorganic fine particles, the content of the inorganic fine particles, and the content of the binder resin. Specifically, the porous layer may have micropores having a cross-sectional diameter of 20 to 2000 nm, 30 to 1000 nm, 100 to 1000 nm, or 100 to 500 nm.

[0034] In particular, since the porous layer contains inorganic fine particles, it is possible to form fine pores having a cross-sectional diameter within the aforementioned range. As a result, the electrode for a lithium secondary battery has high high-temperature stability, solid structural stability, and high interfacial adhesion with a counter electrode, and the life characteristics, charge capacity, and discharge capacity of the lithium secondary battery can be improved.

[0035] Meanwhile, the porous layer may include 1 to 50 parts by weight, 3 to 45 parts by weight, 5 to 40 parts by weight, or 20 to 38 parts by weight of the binder resin per 100 parts by weight of the inorganic fine particles. As described above, the porous layer can form micropores and adjust the pore size and porosity by adjusting the size of the inorganic fine particles, the content of the inorganic fine particles, and the content of the binder resin.

[0036] That is, the porous layer may include 1 to 50 parts by weight, 3 to 45 parts by weight, 5 to 40 parts by weight, or 20 to 38 parts by weight of the binder resin per 100 parts by weight of the inorganic microparticles, so that the porosity of the porous layer may be 40% to 80%, 45% to 75%, or 50% to 70%, and micropores having a cross-sectional diameter of 20 to 2,000 nm, 30 to 1,000 nm, or 30 to 500 nm may be formed in the porous layer.

[0037] In addition, the porous layer may contain 1 to 50 parts by weight, 3 to 45 parts by weight, 5 to 40 parts by weight, or 20 to 38 parts by weight of the binder resin per 100 parts by weight of the inorganic fine particles, thereby preventing the ion conductivity from being inhibited and achieving the effect of the porous layer maintaining stable adhesion to the electrode substrate.

[0038] If the porous layer contains an excessive or insufficient amount of binder resin relative to the inorganic fine particles, the void space formed between the inorganic fine particles may be reduced, resulting in a decrease in pore size and porosity, which may result in a decrease in final battery performance, or the mechanical properties of the porous layer may be reduced, resulting in a decrease in peel resistance due to a decrease in adhesive strength between the inorganic fine particles.

[0039] The inorganic fine particles may each have a diameter in the nanometer or micrometer range, for example, 1 nm to 500 μm. Furthermore, the inorganic fine particles may be formed by agglomeration of individual particles (primary particles) to form a single particle (secondary particle), and the formed secondary particle may behave as a single independent particle.

[0040] More specifically, the inorganic fine particles may include boehmite containing primary particles having an average particle size of 10 nm to 500 nm, 20 nm to 400 nm, or 30 nm to 300 nm.

[0041] The average particle size can be measured using commonly known methods and devices, for example, by taking a scanning electron microscope (SEM) photograph at 50,000x magnification using a Jeol JSM-7400F and then calculating the average particle size using an image analysis program (Image Pro Plus ver. 4.5).

[0042] Meanwhile, the inorganic fine particles have a D of 10 to 2000 nm, 20 nm to 1000 nm, or 50 nm to 800 nm. 50 The secondary particles may have the following structure:

[0043] The inorganic fine particles may include boehmite containing primary particles having an average particle size of 10 to 500 nm, 20 to 400 nm, or 30 to 300 nm, and the boehmite may have a D of 10 to 2000 nm, 20 to 1000 nm, or 50 to 800 nm. 50 The secondary particles may have the following structure:

[0044] The above D 50 means the particle size of particles that make up 50% of the total number of particles when the measured particles are sorted in order from smallest to largest. 50The measurement can be performed using a commonly known method and device, for example, a particle size analyzer (PSA) or a dynamic light scattering (DLS) can be used to measure D 50 For example, D using PSA can be measured. 50 The particle size distribution of the solution containing dispersed particles can be measured using Malvern's Mastersizer 3000, and DLS can be used to measure the D 50 The particle size distribution of a solution in which particles are dispersed can be measured using an ELSZ-2000 DLS manufactured by Otsuka Electronics.

[0045] If the diameter of the inorganic fine particles is too small, dispersibility may decrease, making it difficult to control the physical properties of the porous layer. If the diameter of the inorganic fine particles is too large, the thickness of the porous layer may increase, resulting in decreased mechanical properties. Furthermore, excessively large pore sizes may increase the likelihood of internal short circuits occurring during battery charge and discharge.

[0046] The inorganic fine particles are not particularly limited as long as they are electrochemically stable. Specifically, the inorganic fine particles are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the battery to which they are applied. In particular, inorganic fine particles with ion transfer ability can improve the ionic conductivity in a lithium secondary battery, thereby improving its performance. Furthermore, inorganic fine particles with a high dielectric constant can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in a liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

[0047] For example, the inorganic fine particles may include one or more inorganic fine particles selected from the group consisting of alumina (Al2O3), boehmite (AlOOH), aluminum hydroxide (Al(OH)3), silicon dioxide (SiO2), titanium dioxide (TiO2), and magnesium hydroxide (Mg(OH)2).

[0048] The inorganic fine particles may not have a separate functional group or compound substituted on their surfaces, or may include inorganic fine particles whose surfaces have been modified with one or more compounds selected from the group consisting of (meth)acrylates, thiol groups, and organic silane compounds. The functional groups or compounds substituted on the surfaces of the inorganic particles may be selected in consideration of the physical properties and type of binder resin of the porous layer.

[0049] Meanwhile, as described above, in one embodiment, the binder resin may function to connect, bond, or fix the inorganic fine particles, and the binder resin may include a (co)polymer including repeating units derived from a urethane (meth)acrylate-based monomer or oligomer.

[0050] Examples of the urethane (meth)acrylate monomer or oligomer include one or more selected from the group consisting of polyester (meth)urethane acrylate, polyester urethane di(meth)acrylate, polyether (meth)urethane acrylate, and polyether urethane di(meth)acrylate.

[0051] The specific molecular weight of the urethane (meth)acrylate oligomer is not limited, but may be, for example, 50,000 g / mol or less, 40,000 g / mol or less, or 30,000 g / mol or less, and 300 g / mol or more, 1,000 g / mol or more, or 3,000 g / mol or more. The weight average molecular weight (weight average molecular weight in terms of polystyrene measured by GPC) may be 300 to 50,000 g / mol, 1,000 to 50,000 g / mol, 3,000 to 50,000 g / mol, or 3,000 to 30,000 g / mol.

[0052] Meanwhile, the (co)polymer may further contain a repeating unit derived from a polyfunctional acrylate in addition to the repeating unit derived from the urethane (meth)acrylate monomer or oligomer.

[0053] The polyfunctional acrylate may be a polyfunctional (meth)acrylate monomer or oligomer, and in this case, the number of (meth)acrylate functional groups may be 2 to 10, preferably 2 to 8, and more preferably 2 to 7.

[0054] Examples of the polyfunctional acrylate may be one or more selected from the group consisting of pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol hepta(meth)acrylate, tripentaerythritol hepta(meth)acrylate, tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, trimethylolpropane tri(meth)acrylate, and trimethylolpropane polyethoxytri(meth)acrylate, but specific examples are not limited to these.

[0055] The (co)polymer may contain an appropriate content of repeating units derived from the urethane (meth)acrylate monomer or oligomer and repeating units derived from the polyfunctional acrylate, taking into consideration the specific physical properties of the porous layer.

[0056] Meanwhile, the porous layer is formed by curing (thermal curing or photocuring) the binder resin and the inorganic particles together, and the components contained in the binder resin and the inorganic particles form cross-linked or covalent bonds, thereby improving the heat resistance and mechanical strength of the porous layer and the electrode for a lithium secondary battery.

[0057] The content of the repeating units derived from the urethane (meth)acrylate monomer or oligomer in the (co)polymer is not particularly limited, and for example, the (co)polymer may contain 1 to 99 wt %, or 10 to 90 wt %, of the repeating units derived from the urethane (meth)acrylate monomer or oligomer.

[0058] Meanwhile, in this embodiment, the thickness of the porous layer is not particularly limited and may be adjusted to, for example, 0.01 to 100 μm in consideration of the performance of the battery.

[0059] For example, the porous layer may have a thickness of 0.1 μm or more and 30 μm or less.

[0060] More specifically, the thickness of the porous layer may be 0.1 μm or more, 1 μm or more, 5 μm or more, 10 μm or more, and 30 μm or less, or may be 0.1 μm or more and 30 μm or less, 1 μm or more and 30 μm or less, 5 μm or more and 30 μm or less, or 10 μm or more and 30 μm or less.

[0061] If the thickness of the porous layer is less than 0.1 μm, the coating uniformity may be poor, which may cause a short circuit in the lithium secondary battery. If the thickness exceeds 30 μm, the ionic conductivity of lithium ions may be low, which may result in poor battery performance. When multiple cells are stacked, the volume increases, which may result in poor energy density of the lithium secondary battery.

[0062] Meanwhile, the electrode for a lithium secondary battery may be a negative electrode for a lithium secondary battery or a positive electrode for a lithium secondary battery. As described above, when the electrode for a lithium secondary battery provided above is used, a separate porous polymer separator is not required, and sufficient interfacial adhesion with the positive electrode can be ensured, thereby relatively increasing the battery life.

[0063] Meanwhile, the electrode for a lithium secondary battery can be obtained by coating a porous layer-forming composition, which includes a binder containing a urethane (meth)acrylate-based monomer or oligomer and inorganic fine particles, on an electrode substrate, and then thermally curing or photocuring the coated resultant.

[0064] The step of applying the composition for forming the porous layer may be performed using a conventional coating method known in the art, such as spin coating, dip coating, die coating, roll coating, comma coating, gravure coating, bar coating, curtain coating, extrusion, casting, screen printing, inkjet printing, doctor blade, or a combination thereof.

[0065] In the step of photocuring the porous layer-forming composition, ultraviolet rays or visible light having a wavelength of 200 to 400 nm can be irradiated, and the exposure dose during irradiation is 100 to 4,000 mJ / cm . 2 The exposure time is also not particularly limited, and can be appropriately changed depending on the exposure device used, the wavelength of the irradiating light, or the exposure dose.

[0066] In addition, in the step of photocuring the photocurable coating composition, nitrogen purging or the like may be performed to apply nitrogen atmosphere conditions.

[0067] The porous layer-forming composition may be dried after being applied and cured. The drying method for the drying step is not particularly limited, and known methods may be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. For example, the drying may be performed in a drying chamber under atmospheric or pressurized conditions by applying heat or hot air to the substrate as needed.

[0068] The temperature applied during the drying is not particularly limited, and may be determined depending on the components used and the type of solvent or non-solvent. For example, the drying may be performed at a temperature of 60°C or higher, 80°C or higher, 90°C or higher, 150°C or lower, 120°C or lower, 110°C or lower, 80°C or higher and 140°C or lower, 90°C or higher and 120°C or lower, 80°C or higher and 110°C or lower, or 90°C or higher and 110°C or lower.

[0069] When the porous layer-forming composition is photocured, the composition may contain a photopolymerization initiator. The photopolymerization initiator may be any compound known to be used in photocurable resin compositions without significant limitations, and specifically, benzophenone-based compounds, acetophenone-based compounds, non-imidazole-based compounds, triazine-based compounds, oxime-based compounds, or a mixture of two or more thereof may be used.

[0070] The porous layer-forming composition may further contain an organic solvent. Non-limiting examples of the organic solvent include ketones, alcohols, acetates, and ethers, or mixtures of two or more thereof. Specific examples of such organic solvents include ketones such as methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and isobutyl ketone; alcohols such as methanol, ethanol, diacetone alcohol, n-propanol, i-propanol, n-butanol, i-butanol, and t-butanol; acetates such as ethyl acetate, i-propyl acetate, and polyethylene glycol monomethyl ether acetate; ethers such as tetrahydrofuran and propylene glycol monomethyl ether; and mixtures of two or more thereof.

[0071] Meanwhile, the composition for forming a porous layer may optionally further include a dispersant.

[0072] The dispersant can increase the dispersibility of inorganic fine particles or prevent particle aggregation during the formation of the porous layer, thereby improving the surface properties of the porous layer, and thereby improving the mechanical properties and resistance properties of the porous layer.

[0073] A particle dispersion containing the inorganic fine particles, a dispersant, and an organic solvent may be separately prepared, and then mixed with a photocurable composition containing a binder containing a urethane (meth)acrylate monomer or oligomer and a photopolymerization initiator to form a composition for forming the porous layer. The porous layer may be formed by thermally or photocuring the coated resultant.

[0074] The type of the dispersant is not particularly limited, but specific examples of the dispersant include monoesters or diesters of phosphoric acid or monoesters of acidic dicarboxylic acids having an acid value of 90 to 110 KOH / g.

[0075] More specifically, the dispersant uses (a) a mono- or diester of phosphoric acid, such as a mono- or diester of phosphoric acid containing alkyl, aryl, aralkyl, or alkylaryl alkoxylate (e.g., nonylphenol ethoxylate, isotridecyl alcohol ethoxylate, alkylene oxide polyethers made from butanol), a mono- or diester of phosphoric acid containing polyester (e.g., lactone polyester, e.g., caprolactone polyester, or mixed caprolactone / valerolactone polyester), or (b) Acidic dicarboxylic acid monoesters, exemplified by acidic dicarboxylic acid monoesters (more specifically, succinic acid, maleic acid, or phthalic acid), containing alkyl, aryl, aralkyl, or alkylaryl alkoxylates (e.g., nonylphenol ethoxylate, isotridecyl alcohol ethoxylate, or alkylene oxide polyethers produced from butanol), can be used.

[0076] The content or amount of the dispersant used is not particularly limited, and for example, the dispersant may be used in an amount of 0.01 to 30 parts by weight, 0.1 to 20 parts by weight, 0.5 to 15 parts by weight, or 1 to 10 parts by weight per 100 parts by weight of the inorganic fine particles.

[0077] Meanwhile, according to another embodiment of the present invention, there is provided a lithium secondary battery including the lithium secondary battery electrode. Specifically, the lithium secondary battery may include the lithium secondary battery electrode of the embodiment, a counter electrode, and an electrolyte interposed therebetween.

[0078] The electrode for a lithium secondary battery may be a positive electrode for a lithium secondary battery or a negative electrode for a lithium secondary battery.

[0079] The electrode for a lithium secondary battery includes all of the above-mentioned features.

[0080] As described above, the lithium secondary battery of the embodiment includes a lithium secondary battery electrode including a porous layer as a separator, instead of a porous polymer separator including a porous substrate and a porous layer formed on the porous substrate. This allows the electrode to maintain adhesion even when the electrode expands and contracts, thereby achieving excellent battery life characteristics.

[0081] The negative electrode may include a negative electrode material including a negative electrode active material, a conductive material, and a binder, and a current collector that supports the negative electrode material.

[0082] The negative electrode active material may include a material capable of reversibly intercalating and deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, and a transition metal oxide.

[0083] Examples of substances that can reversibly intercalate and deintercalate lithium ions include crystalline carbon, amorphous carbon, or a mixture thereof as carbonaceous substances. Specifically, the carbonaceous substance may be natural graphite, artificial graphite, kish graphite, pyrolytic carbon, mesophase pitches, mesophase pitch-based carbon fibers, meso-carbon microbeads, petroleum or coal tar pitch-derived cokes, soft carbon, hard carbon, and the like.

[0084] The alloy of the lithium metal may be an alloy of lithium and one or more metals selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn, Bi, Ga, and Cd.

[0085] Examples of substances that can be doped and undoped with lithium include Si, Si-C composites, SiOx (0 < x < 2), Si-Q alloys (where Q is an element containing one or more selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof; excluding Si), Sn, SnO2, Sn-R alloys (where R is an element containing one or more selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof; excluding Sn), and the like.

[0086] The material capable of doping and dedoping lithium can be a mixture of at least one of the above examples and SiO2. Q and R may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, or the like.

[0087] The transition metal oxide may be vanadium oxide, lithium vanadium oxide, lithium titanium oxide, or the like.

[0088] The negative electrode current collector may be formed to a thickness of typically 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys.

[0089] In addition, similar to the positive electrode current collector, the bonding strength of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and the positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0090] Preferably, the negative electrode may include a negative electrode active material containing one or more selected from the group consisting of carbonaceous materials and silicon compounds.

[0091] Here, the carbonaceous material is a substance containing one or more selected from the group consisting of natural graphite, artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch, mesophase pitch-based carbon fiber, carbon microspheres, petroleum or coal-based coke, softened carbon, and hardened carbon, as exemplified above. And the silicon compound may be a compound containing Si exemplified above, that is, Si, Si-C composite, SiOx (0 < x < 2), the Si-Q alloy, a mixture thereof, or a mixture of at least one of these and SiO2.

[0092] Also, the negative electrode may contain micro-silicon. When the negative electrode contains micro-silicon, it can exhibit superior capacity compared to the case where a carbonaceous material is used as the negative electrode active material. Specifically, when a specific micro-silicon is used in the silicon compound, it can maintain a residual capacity of 80% or more even after 500 or more charge and discharge cycles, and can exhibit significantly superior energy density compared to conventional lithium secondary batteries. Further, when the negative electrode contains micro-silicon, the charge and discharge life of a solid battery using a solid electrolyte can be greatly increased, and the charging rate can also be significantly improved at room temperature.

[0093] The size of the micro-silicon is not greatly limited. For example, the micro-silicon can have a diameter of 100 μm or less, or a diameter of 1 to 100 μm, or a diameter of 1 to 20 μm.

[0094] On the other hand, the negative electrode active material may be contained at 85% to 98% by weight based on the total weight of the negative electrode material.

[0095] Specifically, the content of the negative electrode active material may be 85% by weight or more, or 87% by weight or more, or 90% by weight or more and 98% by weight or less, or 97% by weight or less, or 96% by weight or less, based on the total weight of the negative electrode material. Preferably, the content of the negative electrode active material may be 85% by weight or more and 98% by weight or less, 85% by weight or more and 97% by weight or less, 85% by weight or more and 96% by weight or less, 87% by weight or more and 98% by weight or less, 87% by weight or more and 97% by weight or less, 87% by weight or more and 96% by weight or less, 90% by weight or more and 98% by weight or less, 90% by weight or more and 97% by weight or less, or 90% by weight or more and 96% by weight or less, based on the total weight of the negative electrode material.

[0096] The conductive material is used to impart conductivity to the electrode.

[0097] The conductive material can be any material that has electronic conductivity and does not cause chemical changes in the battery. Non-limiting examples of the conductive material include carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; graphite, such as natural graphite and artificial graphite; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. The conductive material can be one or a mixture of two or more of the above-mentioned materials.

[0098] The content of the conductive material may be adjusted within a range that provides an appropriate level of conductivity without causing a decrease in battery capacity, and may be preferably 0.5 wt % to 10 wt %, or 1 wt % to 10 wt %, or 1 wt % to 5 wt %, based on the total weight of the negative electrode material.

[0099] The binder is used to facilitate adhesion of the negative electrode material to the current collector. Non-limiting examples of the binder include polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber. The binder may be one or a mixture of two or more of the above-mentioned examples.

[0100] The content of the binder may be adjusted to a range that provides an appropriate level of adhesiveness without causing a decrease in battery capacity, and may be 0.5 wt % to 10 wt %, or 1 wt % to 10 wt %, or 1 wt % to 5 wt %, based on the total weight of the negative electrode material.

[0101] The lithium secondary battery of this embodiment may optionally further include a porous polymer substrate.

[0102] The type of the porous polymer substrate is not particularly limited, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenyleneoxide, and cyclic olefin copolymers. Polymer substrates formed of one or more polymers selected from the group consisting of polyphenylene sulfide, polyethylene naphthalene copolymer, polyphenylene sulfide, and polyethylene naphthalene, or a mixture of two or more of these, or multilayers thereof, woven fabrics, and nonwoven fabrics thereof can be used.

[0103] The porous polymer substrate may be adjusted in terms of the type and thickness of the substrate, the size and number of pores, and, in the case of a nonwoven fabric, the thickness of the ultrafine threads, taking into consideration the melting temperature, ease of manufacture, porosity, ion migration, insulating properties, etc.

[0104] The thickness of the porous polymer substrate is not particularly limited and can be adjusted to, for example, 0.01 to 100 μm in consideration of the performance of the battery.

[0105] The positive electrode for a lithium secondary battery may include a positive electrode active material, a binder, a conductive material, and a positive electrode additive.

[0106] The positive electrode additive for a lithium secondary battery has a property of irreversibly releasing lithium during charge and discharge of the lithium secondary battery, and therefore, when included in the positive electrode of the lithium secondary battery, the positive electrode additive for a lithium secondary battery can serve as a sacrificial positive electrode material for prelithiation.

[0107] Specifically, the positive electrode can be manufactured by applying a positive electrode mixture to a positive electrode current collector and then drying the mixture, and if necessary, a filler can be further added to the mixture.

[0108] Preferably, the positive electrode for a lithium secondary battery includes a positive electrode material including a positive electrode active material, a conductive material, the sacrificial positive electrode material, and a binder, and a current collector supporting the positive electrode material.

[0109] As the capacity of a battery increases, the ratio of anode active material in the anode must be increased, which also increases the amount of lithium consumed in the SEI layer. Therefore, after calculating the amount of lithium consumed in the SEI layer of the anode, the amount of sacrificial cathode material that must be applied to the cathode side can be calculated to determine the design capacity of the battery.

[0110] According to one embodiment, the sacrificial cathode material may be included in an amount greater than 0 wt % and less than or equal to 15 wt % of the total weight of the cathode material. To compensate for irreversible lithium consumed in forming the SEI layer, the amount of the sacrificial cathode material is preferably greater than 0 wt % of the total weight of the cathode material. However, if the sacrificial cathode material is included in excess, the amount of the cathode active material exhibiting reversible charge / discharge capacity may be reduced, resulting in a decrease in battery capacity. Furthermore, residual lithium within the battery may be plated onto the anode, causing a short circuit or compromising safety. Therefore, the amount of the sacrificial cathode material is preferably less than or equal to 15 wt % of the total weight of the cathode material.

[0111] Specifically, the content of the sacrificial positive electrode material may be more than 0% by weight, or 0.5% by weight or more, or 1% by weight or more, or 2% by weight or more, or 3% by weight or more, and 15% by weight or less, or 12% by weight or less, or 10% by weight or less, based on the total weight of the positive electrode material.

[0112] As the positive electrode active material, compounds known to be applicable to lithium secondary batteries in the technical field to which the present invention belongs can be used without particular limitation.

[0113] As non-limiting examples, the positive electrode active material is NCM (Li[Ni, Co, Mn]O2), NCMA (Li[Ni, Co, Mn, Al]O2), LiCoO2, LiNiO2, LiMnO2, LiMn2O2, LiNi 1-d Co d O2, LiCo 1-d Mn d O2, LiNi 1-d Mn d O2 (where 0 ≦ d < 1), Li(Ni a Co b Mn c )O4 (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-e Ni e O4, LiMn 2-e Co​​​​​​​​​The positive electrode for the lithium secondary battery may be formed by stacking a positive electrode material including the positive electrode active material, the conductive material, the sacrificial positive electrode material, and a binder on the current collector. The filler is selectively used as a component to suppress expansion of the positive electrode, and is not particularly limited as long as it does not induce chemical changes in the battery and is a fibrous material, for example, olefin polymers such as polyethylene and polypropylene; glass fiber, carbon fiber, or other fibrous materials. The conductive material and binder contained in the positive electrode material, and the current collector, all include the same as those described above.

[0116] Meanwhile, the electrolyte may be any electrolyte known in the art to which the present invention pertains that is applicable to lithium secondary batteries, without any particular limitation, and may be, for example, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or an aqueous electrolyte.

[0117] The aqueous electrolyte is a salt dissolved in an aqueous solvent such as water or alcohol, and lithium secondary batteries using such an aqueous electrolyte are advantageous in terms of high ionic conductivity and safety, as well as low manufacturing costs and process costs. Furthermore, batteries using aqueous electrolytes are more environmentally friendly than non-aqueous organic electrolytes.

[0118] Specifically, the aqueous electrolyte may contain an aqueous solvent and a lithium salt. The aqueous solvent is a solvent containing water, and although not particularly limited, may contain 1 wt % or more of water based on the total weight of the aqueous solvent constituting the electrolyte. Water may be used alone as the aqueous solvent, or a solvent miscible with water may be used in combination.

[0119] The water-miscible solvent may be a polar solvent, and may include, for example, one or more selected from the group consisting of C1 to C5 alcohols and C1 to C10 glycol ethers.

[0120] For example, the C1 to C5 alcohol may be one or more selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, glycerol, and 1,2,4-butanetriol, but is not limited thereto.

[0121] Furthermore, the C1 to C10 glycol ether may be one or more selected from the group consisting of ethylene glycol monomethyl ether (MG), diethylene glycol monomethyl ether (MDG), triethylene glycol monomethyl ether (MTG), polyethylene glycol monomethyl ether (MPG), ethylene glycol monoethyl ether (EG), diethylene glycol monoethyl ether (EDG), ethylene glycol monobutyl ether (BG), diethylene glycol monobutyl ether (BDG), triethylene glycol monobutyl ether (BTG), propylene glycol monomethyl ether (MFG) and dipropylene glycol monomethyl ether (MFDG), but is not limited thereto.

[0122] The lithium salt contained in the electrolyte dissolves in the aqueous solvent and acts as a source of lithium ions within the battery, enabling basic operation of the lithium secondary battery and promoting the movement of lithium ions between the positive electrode and the negative electrode.

[0123] Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCFSO, LiC4F9SO, LiN(C2F5SO3), LiN(C2F5SO2), LiN(CF3SO2), LiN(SO2F)2 (LiFSI, lithium bis(fluorosulfonyl)imide), LiCl, LiI, LiB(C2O4), etc. Preferably, the lithium salt may be LiPF, LiFSI, or a mixture thereof.

[0124] The lithium salt may be contained in the electrolyte at a concentration of 0.1 M to 2.0 M. The lithium salt contained in this concentration range provides the electrolyte with suitable conductivity and viscosity, thereby enabling the electrolyte to exhibit excellent electrolyte performance.

[0125] Alternatively, the electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0126] The non-aqueous organic solvent may be any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0127] Specifically, the non-aqueous organic solvent may be an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether-based solvent such as dibutylether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). The solvent may be a carbonate solvent such as propylene carbonate (PC); an alcohol solvent such as ethyl alcohol and isopropyl alcohol; a nitrile such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group which may contain a double bond aromatic ring or an ether bond); an amide such as dimethylformamide; a dioxolane such as 1,3-dioxolane; or sulfolane.

[0128] Among the above examples, carbonate-based solvents are preferably used as the non-aqueous organic solvent. In particular, taking into consideration the charge / discharge performance of the battery and compatibility with the sacrificial cathode material, a mixture of a cyclic carbonate (e.g., ethylene carbonate, propylene carbonate) having high ionic conductivity and a high dielectric constant and a low-viscosity linear carbonate (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate) can be preferably used as the non-aqueous organic solvent. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of 1:1 to 1:9 is advantageous for achieving the above-mentioned performance.

[0129] Furthermore, as the non-aqueous organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2 to 1:10, or a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 1-3:1-9:1 can be preferably used.

[0130] The lithium salt contained in the electrolyte dissolves in the non-aqueous organic solvent and acts as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive electrode and the negative electrode.

[0131] Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCFSO, LiC4F9SO, LiN(C2F5SO3), LiN(C2F5SO2), LiN(CF3SO2), LiN(SO2F)2 (LiFSI, lithium bis(fluorosulfonyl)imide), LiCl, LiI, LiB(C2O4), etc. Preferably, the lithium salt may be LiPF, LiFSI, or a mixture thereof.

[0132] The lithium salt may be contained in the electrolyte at a concentration of 0.1 M to 2.0 M. The lithium salt contained in this concentration range provides the electrolyte with suitable conductivity and viscosity, thereby enabling the electrolyte to exhibit excellent electrolyte performance.

[0133] Optionally, the electrolyte may contain an additive for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, and the like.

[0134] For example, the additive may be a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. The additive may be included in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0135] The lithium secondary battery of the embodiment may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery depending on the type of electrolyte.

[0136] The liquid electrolyte may be a lithium salt-containing nonaqueous electrolyte, which is composed of a nonaqueous electrolyte and lithium, and the nonaqueous electrolyte may be, but is not limited to, a nonaqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte.

[0137] Examples of organic solid electrolytes that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymerizing agents containing ionic dissociative groups.

[0138] Examples of inorganic solid electrolytes that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0139] Furthermore, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the lithium salt-containing nonaqueous electrolyte may contain, for example, pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further added to impart nonflammability, and carbon dioxide, FEC (fluoro-ethylene carbonate), PRS (propene sultone), etc. may be further added to improve high-temperature storage properties.

[0140] In one specific example, a lithium salt such as LiPF, LiClO, LiBF, or LiN(SOCF) can be added to a mixed solvent of a high dielectric constant solvent, such as cyclic carbonate EC or PC, and a low dielectric constant solvent, such as linear carbonate DEC, DMC, or EMC, to prepare a lithium salt-containing non-aqueous electrolyte.

[0141] The lithium secondary battery can be used as an energy supply source with improved performance and safety in the fields of portable electronic devices such as mobile phones, laptops, tablet computers, mobile batteries, and digital cameras; and in the field of transportation means such as electric cars, electric motorcycles, and personal mobility devices.

[0142] The lithium secondary battery may have various shapes such as a prismatic shape, a cylindrical shape, a pouch shape, and the like.

[0143] The lithium secondary battery of the above-described other embodiments may be embodied as a battery module including the battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source.

[0144] In this case, specific examples of the device may be, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

[0145] In this embodiment, after the porous layer is coated, the porous layer may be assembled through a process such as winding or stacking, and then an electrolyte solution may be injected to manufacture a lithium secondary battery.

[0146] Meanwhile, in the lithium secondary battery according to the embodiment, the electrode for the lithium secondary battery may have a peel strength of 10 gf / 20 mm or more when peeled from a counter electrode at a 90-degree angle. The peel strength can be achieved by the composition of the porous layer.

[0147] Specifically, in the lithium secondary battery of the embodiment, when the lithium secondary battery electrode is peeled from a counter electrode at a 90-degree angle, the peel strength may be 10 gf / 20 mm or more, 20 gf / 20 mm or more, 30 gf / 20 mm or more, 200 gf / 20 mm or less, 180 gf / 20 mm or less, or 150 gf / 20 mm or less, or 10 gf / 20 mm or more, 20 gf / 20 mm or more, 20 gf / 20 mm or more, 30 gf / 20 mm or more, 180 gf / 20 mm or less, or 30 gf / 20 mm or more, 150 gf / 20 mm or less.

[0148] The electrode for a lithium secondary battery may have a peel strength of 10 gf / 20 mm or more when peeled from a counter electrode at an angle of 90 degrees. The peel strength can be measured by a texture analyzer according to ASTM D6862.

[0149] In addition, the lithium secondary battery of the embodiment may have a coulombic efficiency of 75% to 99%, 75% to 90%, or 75% to 83%. The coulombic efficiency can be calculated as the ratio of discharge capacity to charge capacity. [Effects of the Invention]

[0150] According to the present invention, it is possible to provide an electrode for a lithium secondary battery and a lithium secondary battery which have high high-temperature stability, solid structural stability, and high interfacial adhesion with a counter electrode, and which can improve the life characteristics, charge capacity, and discharge capacity of a lithium secondary battery and have high flex resistance. [Brief explanation of the drawings]

[0151] [Figure 1] FIG. 1 is a schematic diagram showing the method for measuring the flex resistance in Experimental Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0152] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, but these are presented as examples of the present invention and do not limit the scope of the invention in any way.

[0153] <Preparation Examples 1 to 6: Preparation of particle dispersion and coating composition for forming porous layer> 1) Production of particle dispersion liquid The components of the particle dispersion listed in Table 1 below were mixed and mixed on an orbital shaker using a 1 mm bead at 200 rpm for 24 hours to form a particle dispersion.

[0154] 2) Preparation of coating composition for forming porous layer The components of the photocurable composition shown in Table 1 below were mixed together, and then mixed with the obtained particle dispersion to prepare a coating composition for forming a porous layer.

[0155] [Table 1]

[0156] MIBK: Methyl isobutyl ketone cyH: Cyclohexanone Boehmite: The average particle size of the primary particles is about 50-60 nm, and the D of the secondary particles is 50 Aluminum hydroxide particles with a diameter of approximately 130 nm Dispersant (BYK-102): Poly(oxy-1,2-ethanediyl) α-isotridecyl-w-hydroxy-phosphate copolymer with acidic groups (acid value: 101 mg KOH / g) UA5216 (Miwon product): Polyester urethane diacrylate (weight average molecular weight: 30,000 g / mol) contains approximately 40% (diluted with isobornyl acrylate) BR-345: difunctional polyether urethane acrylate (trade name, product of Bomar, solid content approximately 100% by weight) Linc-3A: Fluorine-based (meth)acrylate compound (manufacturer: Kyoeisha, solid content: approximately 100% by weight) DPHA: Dipentaerythritol hexaacrylate PETA: Pentaerythritol triacrylate IBOA: Isobornyl Acrylate HEA: 2-Hydroxyethyl acrylate

[0157] <Examples and Comparative Examples: Manufacture of Lithium Secondary Battery Electrodes and Lithium Secondary Battery> Examples 1 to 4 1) Manufacturing of single-sided negative electrodes A slurry for the electrode layer was prepared by adding 91.5%, 4%, 1.5%, 2%, and 1% by weight of carbon-based and silicon-based powders as negative electrode active materials, carbon black as a conductive material, and styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders to distilled water (DI Water) as a solvent. The slurry for the electrode layer was applied to one side of a 10 μm-thick copper (Cu) thin film current collector, dried, and roll-pressed to prepare an electrode.

[0158] 2)Battery (Half-cell) manufacturing (single side) The composition for forming a porous layer obtained above was coated onto the prepared single-sided electrode using a #30 Mayer bar to a uniform thickness of 15 to 20 μm, and dried at 110° C. for 2 minutes to prepare a negative electrode having a porous layer formed thereon.

[0159] A 0.3 mm thick lithium metal was stacked on the negative electrode on which the porous layer was formed, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), lithium hexafluorophosphate (LiPF6) 1 mol) was injected into the assembled battery to manufacture a lithium secondary battery.

[0160] Comparative Examples 1 and 2 An electrode for a lithium secondary battery and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the particle dispersion and the coating composition for forming a porous layer of Preparation Examples 5 and 7 were used, respectively.

[0161] <Experimental Example> Experimental Example 1: Measurement of bending resistance As shown in FIG. 1, the single-sided negative electrodes including the porous layer prepared in each of the Examples and Comparative Examples were subjected to a cylindrical mandrel test in order of diameter from largest to smallest according to the ISO 1519:2011 standard method to determine their bending resistance.

[0162] The sample was prepared by cutting it to a length of 12 cm and a width of 2.5 cm. The copper current collector surface of the negative single-sided electrode was placed in contact with a part of the cylindrical mandrel, and the negative single-sided electrode sample was slowly wrapped around the cylindrical mandrel so that the coating layer could bend 180 degrees.

[0163] The flex resistance value was determined as the largest diameter of the first mandrel at which the porous coating layer cracked, the coating layer separated from the electrode layer, or both the coating layer and the electrode layer separated from the current collector.

[0164] Experimental Example 2: Porous Layer Analysis The thickness and porosity of the porous layer of each of the lithium secondary batteries fabricated in the Examples and Comparative Examples were analyzed and are shown in Table 1 below.

[0165] The porosity of the porous layer was calculated as follows: The thickness of the porous layer was measured to calculate the volume of the porous layer per a certain area, and the weight of the porous layer alone, excluding the weight of the electrode substrate and current collector, was calculated from the sample weight. The weight was then divided by the volume to calculate the actual density of the porous layer. The theoretical density when the solid composition of the porous layer is 100% dense was calculated, and the porosity was calculated using the following Equation 1.

[0166] [Formula 1] Porosity (%) = {1-(actual density) / (theoretical density)} x 100

[0167] Experimental Example 3: Adhesion The single-sided negative electrodes including the porous layer prepared in the examples and comparative examples were cut into specimens measuring 2 cm wide and 10 cm long. The specimens were fixed onto a 0.1T glass plate using 3M double-sided tape so that the porous layer was in contact with the double-sided tape. The specimen was positioned so that the short edge of the sample was aligned with the short edge of the glass slide. The other end not attached to the double-sided tape was peeled off at a 90-degree angle, and the peel strength values ​​were measured according to ASTM D6862 using a Texture Analyzer (Model: TA.XT plus100, Stable Micro Systems). The values ​​are shown in Table 2 below.

[0168] Experimental Example 4: Electrochemical properties The negative electrodes having the porous layers prepared in the examples and comparative examples were dried in a vacuum at 80° C. for 10 hours, and then fabricated into coin cells to measure the ionic conduction resistance.

[0169] To fabricate a coin cell, the negative electrode with the porous layer was punched into a circle with a diameter of 16 mm and placed in a coin cell can with the porous layer visible. 0.1 ml of electrolyte (EC / EMC = 3 / 7 vol%, VC 2%) was then poured into the coin cell. A spacer was placed on the porous layer, and a 15 mm diameter lithium metal positive electrode was inserted into the coin cell. The can was then closed to fabricate a coin cell. The battery was left at room temperature for 2 hours and at 45°C for 10 hours to allow the electrolyte to soak in thoroughly. After three charge / discharge cycles at 0.1C discharge and 0.1C charge, the first discharge capacity was measured. st The coulombic efficiency is calculated through the following formula:

[0170] 1 st Coulomb efficiency = 1st cycle discharge capacity) / 1 st discharge capacity of the cycle) × 100 (%)

[0171] Using coin cells that underwent three charge / discharge cycles, the charge capacity retention and discharge capacity retention were measured through c-rate analysis. Specifically, after three cycles of charge / discharge were performed in the order of 0.33C, 1C, 2C, 3C, and 0.33C, the charge capacity retention was calculated by calculating the ratio of the average charge capacity at the last 0.33C to the average charge capacity at the first 0.33C. The discharge capacity retention was also calculated by calculating the ratio of the average discharge capacity at the last 0.33C to the average discharge capacity at the first 0.33C.

[0172] [Table 2]

[0173] As shown in Table 2, the lithium secondary battery of the example exhibited a peel strength between the porous layer and the counter electrode of 49 gf / 20 mm or more, demonstrating excellent electrode adhesion.

[0174] Furthermore, the lithium secondary batteries of Examples 1 to 4 exhibited a discharge capacity of 8000 mAh / g or more, a coulombic efficiency of 85% or more, an ionic conduction resistance of 0.37 Ω or more and 0.4 Ω or less, a discharge capacity retention rate of 85% or more, and a charge capacity retention rate of 75% or more, and it was confirmed that sufficient battery efficiency and operating performance could be ensured.

[0175] On the other hand, the lithium secondary batteries of Comparative Examples 1 and 2 remained at low levels in discharge capacity, coulomb efficiency, discharge capacity retention rate, and charge capacity retention rate. In particular, the lithium ion battery of Comparative Example 2 is expected to suffer from poor adhesion due to expansion and contraction of the electrodes, resulting in interfacial peeling and a decrease in battery life characteristics.

Claims

1. an electrode substrate; a porous layer formed on the electrode substrate, the porous layer comprising: a binder resin containing a (co)polymer containing a repeating unit derived from a urethane (meth)acrylate monomer or oligomer; and inorganic fine particles; The urethane (meth)acrylate monomer or oligomer includes at least one selected from the group consisting of polyester (meth)urethane acrylate, polyester urethane di(meth)acrylate, polyether (meth)urethane acrylate, and polyether urethane di(meth)acrylate.

2. 2. The electrode for a lithium secondary battery according to claim 1, wherein the porosity of the porous layer is 40% or more and 80% or less.

3. 2. The electrode for a lithium secondary battery according to claim 1, wherein the porous layer has micropores having a cross-sectional diameter of 20 nm to 2000 nm.

4. 2. The electrode for a lithium secondary battery according to claim 1, wherein the porous layer comprises 1 to 50 parts by weight of the binder resin with respect to 100 parts by weight of the inorganic fine particles.

5. 2. The electrode for a lithium secondary battery according to claim 1, wherein the urethane (meth)acrylate oligomer has a weight average molecular weight of 3,000 to 50,000 g / mol.

6. The electrode for a lithium secondary battery according to claim 1 , wherein the (co)polymer further contains a repeating unit derived from a polyfunctional acrylate.

7. The inorganic fine particles are alumina (Al ２ O ３ ), boehmite (AlOOH), aluminum hydroxide (Al(OH) ３ ), silicon dioxide (SiO ２ ), titanium dioxide (TiO ２ ), and magnesium hydroxide (Mg(OH) ２ 2. The electrode for a lithium secondary battery according to claim 1, comprising one or more inorganic fine particles selected from the group consisting of:

8. 2. The electrode for a lithium secondary battery according to claim 1, wherein the inorganic fine particles comprise boehmite having primary particles with an average particle size of 10 nm to 500 nm.

9. 2. The electrode for a lithium secondary battery according to claim 1, wherein the inorganic fine particles comprise inorganic fine particles whose surfaces have been modified with one or more compounds selected from the group consisting of (meth)acrylate, thiol, and organic silane compounds.

10. The electrode for a lithium secondary battery according to claim 1 , wherein the porous layer has a thickness of 0.1 μm or more and 30 μm or less.

11. the electrode substrate is a negative electrode substrate, 2. The electrode for a lithium secondary battery according to claim 1, wherein the electrode for a lithium secondary battery is a negative electrode for a lithium secondary battery.

12. 2. The electrode for a lithium secondary battery according to claim 1, wherein no cracks occur when the electrode for a lithium secondary battery is wound around a cylindrical mandrel having a diameter of 2 mm or more according to the ISO 1519:2011 standard method.

13. A lithium secondary battery comprising the electrode for a lithium secondary battery according to any one of claims 1 to 12.

14. The lithium secondary battery electrode; The lithium secondary battery of claim 13 , further comprising a counter electrode in contact with the porous layer included in the electrode for the lithium secondary battery.

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