Binder for cathode of lithium secondary battery, and cathode and lithium secondary battery including same

Abstract

The present invention provides a binder for a cathode of a lithium secondary battery, the binder comprising an ammonium cation-substituted cationic polyvinylidene fluoride-based polymer.

Description

Binder for a lithium secondary battery cathode, a cathode including the same, and a lithium secondary battery

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0138982 filed on October 11, 2024, and all contents disclosed in said Korean Patent Application are incorporated herein as part of this specification.

[0002] The present invention relates to a binder for a positive electrode of a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery.

[0003]

[0004] As industries utilizing secondary batteries, such as mobile phones, laptop computers, and electric vehicles, grow rapidly, active research and development efforts are underway to improve their performance. Among these, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

[0005] Here, the electrode for a lithium-ion secondary battery typically comprises a current collector and an electrode active material layer formed as a functional layer on the current collector. The electrode active material layer is formed by applying a slurry-like composition, for example, comprising an electrode active material and a binder composition including a polymer that acts as a binder, onto the current collector and drying it.

[0006] Conventionally, binders for active material layers have been developed to improve battery performance, such as enhancing the dispersibility of the cathode active material, improving the mechanical strength of the cathode, and enhancing cathode stability. In particular, polyvinylidene fluoride (PVdF) binders, which have excellent electrochemical performance and thermal stability, are frequently used as binders for cathode active material layers, but there is a need for performance improvement.

[0007]

[0008] The present invention provides a binder for a lithium secondary battery positive electrode with improved mechanical strength and lithium ion conductivity.

[0009] In addition, the anode of the present invention includes the above-mentioned binder for a lithium secondary battery anode, thereby providing an anode with improved electrode stability.

[0010] In addition, the lithium secondary battery of the present invention includes a binder for the positive electrode of the lithium secondary battery, thereby providing a lithium secondary battery with improved cycle characteristics, particularly high-temperature life characteristics.

[0011]

[0012] The present invention provides a binder for a lithium secondary battery positive electrode comprising a cationic polyvinylidene fluoride-based polymer substituted with an ammonium cation.

[0013] The present invention provides an anode comprising: an anode current collector; and an anode active material layer comprising an anode active material, an anode conductive material, and an anode binder, wherein the anode binder comprises an anode binder.

[0014] The present invention provides a lithium secondary battery comprising the anode; the cathode; and a non-aqueous electrolyte.

[0015]

[0016] The binder for the positive electrode of a lithium secondary battery according to the present invention has ammonium cations present in its structure and has high affinity for the relative anions of lithium ions supplied from the lithium salt in the non-aqueous electrolyte included in the lithium secondary battery. As a result, lithium ions are well dissociated, and the mobility of lithium ions within the electrode is improved, thereby enhancing electrode stability during charging and discharging of the lithium secondary battery. In addition, the mechanical stability and chemical stability are improved as the ammonium cations are substituted with aliphatic or aromatic functional groups.

[0017] In addition, since the electrode stability of the anode of the present invention is improved during charging and discharging, electrode collapse during charging and discharging is suppressed, and the lifespan characteristics of a lithium secondary battery including the anode of the present invention are improved.

[0018]

[0019] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0020] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0021] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0022] In addition, in the description of "a to b carbon atoms" within this specification, "a" and "b" refer to the number of carbon atoms included in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, "alkylene group having 1 to 5 carbon atoms" refers to an alkylene group containing 1 to 5 carbon atoms, namely -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH(CH3)CH2-, or -CH(CH3)CH2CH2-, etc.

[0023] In addition, all alkyl groups in this specification may be substituted or unsubstituted. Unless otherwise defined, "substituted" means that at least one hydrogen bonded to a carbon is substituted with an element other than hydrogen, for example, a halogen atom, a nitro group, a nitrile group, etc.

[0024]

[0025] In this specification, "weight-average molecular weight" can be measured using a gel permeation chromatography (GPC) device. Specifically, in this invention, the measurement is performed using an Agilent 1200 series under GPC conditions, and the column used may be an Agilent PL mixed B column, and the solvent may be tetrahydrofuran (THF) or dimethylformamide (DMF). Meanwhile, unless otherwise specifically defined in this specification, molecular weight may refer to weight-average molecular weight.

[0026]

[0027] In addition, "viscosity" in this specification may be measured using a commercially available viscometer. Specifically, in this invention, "viscosity" was measured using an Anton Paar Rheometer MCR 302, and the slurry viscosity could be measured at a temperature of 25 degrees and a shear rate of 2.5 (1 / s).

[0028]

[0029] The present invention will be described in more detail below.

[0030] A binder for a lithium secondary battery positive electrode, a positive electrode, and / or a lithium secondary battery according to the present invention comprises at least one of the configurations disclosed below, and may comprise any combination of technically feasible configurations among the configurations below.

[0031]

[0032] Binder for lithium secondary battery cathode

[0033] The present invention provides a binder for a lithium secondary battery positive electrode comprising a cationic polyvinylidene fluoride-based polymer substituted with an ammonium cation. Specifically, the ammonium cation may be a quaternary ammonium cation. The quaternary ammonium cation has a high affinity for the relative anion of the lithium ion supplied from the lithium salt in the non-aqueous electrolyte. As a result, the lithium ion dissociates well, thereby improving the mobility of the lithium ion within the electrode.

[0034]

[0035] The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer may include repeating units of the following chemical formula 1.

[0036] [Chemical Formula 1]

[0037]

[0038] In the above chemical formula 1, R1 may be a divalent organic group. The divalent organic group may be, for example, an alkylene group having 1 to 10 carbon atoms, an alkenylene group having 2 to 10 carbon atoms, an alkynylene group having 2 to 10 carbon atoms, or an arylalkylene group having 7 to 20 carbon atoms.

[0039] In the above chemical formula 1, R1 may have the structure of the following chemical formula 1-1.

[0040] [Chemical Formula 1-1]

[0041]

[0042] In the above chemical formula 1-1, A1 and A2 may each independently be a direct bond or an alkylene group having 1 to 5 carbon atoms, and preferably a direct bond.

[0043] In the above chemical formula 1-1, * may be a binding site.

[0044] In the above-mentioned cationic polyvinylidene fluoride-based polymer substituted with ammonium cations, when the ammonium cation includes a functional group comprising an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylaryl group, or a benzene ring as in [Formula 1-1], the main chain-side chain interaction is stabilized, which can improve the mechanical strength of the polymer and improve resistance to oxidation / reduction and thermal decomposition, thereby improving chemical stability.

[0045] In the above formula 1, R2, R3, and R4 may each independently be any one selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, an aryl group having 6 to 8 carbon atoms, and an alkylaryl group having 8 to 10 carbon atoms. Preferably, R2, R3, and R4 may each independently be an alkyl group having 1 to 5 carbon atoms.

[0046]

[0047] The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer may contain the repeating unit of Formula 1 in a mole fraction of 0.01 to 20 mol% relative to the total number of repeating units of the polymer, preferably 0.05 to 15 mol%, and more preferably 0.1 to 10 mol%. When the mole fraction of the polymer containing the repeating unit of Formula 1 satisfies the above range, the positively charged portion of the polymer attracts anions in the electrolyte during battery manufacturing, thereby sufficiently improving the mobility of lithium ions, which has the effect of improving electrode stability during charging and discharging and improving cycle characteristics.

[0048]

[0049] The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer may include repeating units of the following chemical formula 2.

[0050] [Chemical Formula 2]

[0051]

[0052]

[0053] The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer may contain the repeating unit of Formula 2 in a mole fraction of 80.00 to 99.99 mol% relative to the total number of repeating units of the polymer, preferably 85.00 to 99.95 mol%, and more preferably 90.0 to 99.9 mol%. When the mole fraction of the polymer containing the repeating unit of Formula 2 satisfies the above range, it has the effect of maintaining electrochemical and thermal stability as an anode binder.

[0054]

[0055] The cationic polyvinylidene fluoride-based polymer of the present invention may have a weight-average molecular weight of 300,000 g / mol to 1,500,000 g / mol, preferably 500,000 g / mol to 1,400,000 g / mol, and more preferably 700,000 g / mol to 1,300,000 g / mol. When the molecular weight satisfies the above range, phase separation of the slurry composition does not occur, the positive active material is sufficiently dispersed, and uniform stirring is possible. In addition, when manufacturing a positive active material layer using the positive slurry composition, there is an effect of excellent adhesion to the electrode current collector.

[0056]

[0057] anode

[0058] The anode slurry composition of the present invention can be prepared by dissolving or dispersing an anode active material, a conductive material, and a binder, etc., in a solvent.

[0059] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used may be 20% by weight or more and 50% by weight or less, 21% by weight or more and 45% by weight or less, or 25% by weight or more and 42% by weight or less, based on the total weight of the anode slurry composition.

[0060]

[0061] The solid content of the entire anode slurry composition of the present invention may be 50% by weight or more and 80% by weight or less, 55% by weight or more and 79% by weight or less, or 58% by weight or more and 75% by weight or less. Since the anode slurry composition of the present invention maintains low viscosity despite having a high solid content, the motor of the stirrer or the transfer pump is not subjected to a heavy load during the preparation of the slurry composition, thereby improving the processability of the anode manufacturing process. In addition, when manufacturing an anode using the anode slurry composition of the present invention, the anode active material layer is uniformly coated.

[0062]

[0063] The anode of the present invention comprises an anode current collector; an anode active material; an anode conductive material; and an anode active material layer comprising an anode binder.

[0064] The anode of the present invention can be manufactured by applying the anode slurry composition described above, followed by drying and rolling. Alternatively, the anode may be manufactured by casting the anode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0065]

[0066] The positive current collector of the present invention may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the positive current collector may typically have a thickness of 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0067]

[0068] The above-mentioned cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 Examples include )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, such that 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc., and any one or more of these compounds may be included.

[0069] Among these, the lithium metal oxides mentioned above include LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al0.05 It may be O2, etc., and any one or more of these may be used.

[0070]

[0071] Among these, the positive electrode active material of the present invention may be a lithium transition metal oxide having a composition represented by the following chemical formula 3. As the nickel content increases, lithium by-products such as LiOH and Li2CO3 are leached from the positive electrode active material, causing changes in the positive electrode slurry composition over time to occur easily; however, the positive electrode slurry composition of the present invention can suppress such changes over time by controlling the mole fraction of aromatic repeating units and aliphatic repeating units in the aramid-based polyamide polymer binder.

[0072] [Chemical Formula 3]

[0073] Li a Ni 1-x-y Co x M 1 y M 2 z O2

[0074] In the above chemical formula 3, M 1 It may be one or more selected from Mn and Al, and preferably may be Mn or a combination of Mn and Al.

[0075] In the above chemical formula 3, M 2 may be any one or more elements selected from the group consisting of Zr, Ti, Mg, Ta, Nb, W, Mo and Cr.

[0076] The above a represents the molar ratio of lithium in the lithium transition metal oxide, and may be 1.0≤a≤1.3, 1.0≤a≤1.2, or 1.0≤a≤1.1.

[0077] The above 1-xy represents the molar ratio of nickel among metal elements excluding lithium in the lithium transition metal oxide, and may be 0.80≤1-xy<1.0, 0.80≤1-xy≤0.98, 0.80≤1-xy≤0.95, 0.83≤1-xy≤0.95, or 0.90≤1-xy≤0.95. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0078] The above x represents the molar ratio of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, where 0 <x<0.4, 0<x≤0.2, 또는 0.01≤x≤0.10일 수 있다.

[0079] The above y represents the molar ratio of M1 among metal elements excluding lithium in the lithium transition metal oxide, where 0 <y<0.4, 0<y≤0.2, 또는 0.01≤y≤0.10일 수 있다.

[0080] The above z represents the molar ratio of M2 among metal elements excluding lithium in the lithium transition metal oxide, and may be 0≤z≤0.1 or 0≤z≤0.05.

[0081]

[0082] The positive active material included in the positive active material layer of the present invention may be included in an amount of 95% to 100% by weight, preferably 98% to 100% by weight, and more preferably 99% to 100% by weight, based on the weight of the total positive active material included in the positive active material layer.

[0083]

[0084] The above-mentioned positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above-mentioned conductive material may be included in an amount of 0.1 to 15 weight% based on the total weight of the positive electrode slurry composition.

[0085]

[0086] The anode binder of the present invention may include a cationic polyvinylidene fluoride-based polymer substituted with ammonium cations. The cationic polyvinylidene fluoride-based polymer substituted with ammonium cations may be included in an amount of 0.1 wt% or more and 5 wt% or less, 0.2 wt% or more and 4.0 wt% or less, 0.3 wt% or more and 3.8 wt% or less, or 0.5 wt% or more and 3.5 wt% or less with respect to the entire anode active material layer.

[0087]

[0088] The anode binder of the present invention may additionally include a conventional binder in addition to a cationic polyvinylidene fluoride-based polymer substituted with ammonium cations. Examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above additional binder may be included in an amount of 0.1 to 5 weight percent based on the total weight of the anode slurry composition.

[0089]

[0090] electrochemical device

[0091] Next, an electrochemical device according to the present invention will be described. The electrochemical device according to the present invention comprises the positive electrode of the present invention described above. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0092] Specifically, the above lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is identical to the one described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0093] Additionally, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0094]

[0095] In the lithium secondary battery of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0096] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0097]

[0098] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0099] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0100] The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0101]

[0102] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0103] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0104]

[0105] The above-mentioned negative electrode active material layer may be manufactured by applying and drying a composition for forming a negative electrode active material layer, prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent, or by casting the composition for forming a negative electrode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto a negative electrode current collector.

[0106]

[0107] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0108]

[0109] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0110]

[0111] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0112] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0113]

[0114] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may be at least one selected from the group consisting of, and the lithium salt is, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc., may be used. It is preferable to use the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0115]

[0116] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0117]

[0118] As described above, since the lithium secondary battery including the positive electrode according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0119] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0120] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0121] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0122] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0123] Examples of the above-mentioned medium-to-large devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, but are not limited to these.

[0124]

[0125] Examples

[0126] Preparation Example 1

[0127] 1 g of polyvinylidene fluoride (Solvay product, weight-average molecular weight: 1,000,000 g / mol) was dissolved in 100 mL of dimethylacetamide (Sigma-Aldrich product, NN dimethyl acetamide), and a 0.1 M polymer solution was synthesized by dissolving sodium hydroxide (Sigma-Aldrich product, NaOH·H2O) in 2-methyl-1-propanol (Sigma-Aldrich product, 2-methyl-1-propanol). The NaOH solution and the dissolved polymer solution were added to a stirrer and high-speed stirred for 4 hours at a temperature of 40°C. Subsequently, 10 wt% of an initiator (Sigma-Aldrich product, 2,2'-azobis (2-methylpropionitrile) (AIBN), purity 98%) was added relative to the polymer, followed by the addition of 3.5 wt% of benzyl trimethylammonium chloride (Sigma-Aldrich product, Benzyl trimethylammonium chloride) relative to the polymer, and the reaction was carried out for 24 hours at a temperature of 60°C. Afterward, DI-Water (Deionized Water) was added to form a precipitate, which was then washed several times. This precipitate was dried to obtain a cationic polyvinylidene fluoride-based polymer.

[0128]

[0129] Preparation Example 2

[0130] 1 g of polyvinylidene fluoride (Solvay product, weight-average molecular weight: 1,000,000 g / mol) was dissolved in 100 mL of dimethylacetamide (Sigma-Aldrich product, NN dimethyl acetamide), and a 0.1 M polymer solution was synthesized by dissolving sodium hydroxide (Sigma-Aldrich product, NaOH·H2O) in 2-methyl-1-propanol (Sigma-Aldrich product, 2-methyl-1-propanol). The alkaline (NaOH) solution and the dissolved polymer solution were added to a stirrer and stirred at high speed for 4 hours under conditions of 40°C. Subsequently, 10 wt% of an initiator (Sigma-Aldrich product, 2,2'-azobis (2-methylpropionitrile) (AIBN), purity 98%) was added relative to the polymer, followed by the addition of 8 wt% of benzyl trimethylammonium chloride (Sigma-Aldrich product, Benzyl trimethylammonium chloride) relative to the polymer, and the reaction was carried out for 24 hours at a temperature of 60°C. Afterward, DI-Water (Deionized Water) was added to form a precipitate, which was then washed several times. This precipitate was dried to obtain a cationic polyvinylidene fluoride-based polymer.

[0131]

[0132] Example 1

[0133] Cathode active material (LiNi 0.84 Co 0.08 Mn 0.08 O2), a conductive material (carbon black), and the ammonium cation-substituted cationic polyvinylidene fluoride-based polymer of Preparation Example 1 were mixed in N-methyl-2-pyrrolidone in a weight ratio of 90:5:5, and an anode slurry composition was prepared by stirring with a high-speed stirrer (Homodisper) at 3000 rpm for 90 minutes. At this time, the solid content of the anode slurry composition was 70% by weight based on the total weight of the anode slurry composition.

[0134] After applying the above anode slurry composition to one side of an aluminum current collector, drying it for 10 minutes under atmospheric pressure conditions at 110°C, drying it for 10 hours under vacuum conditions at 130°C, and rolling it to manufacture an anode.

[0135] In addition, a cathode slurry was prepared by mixing graphite as the cathode active material, super C as the conductive material, and a styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) composite as the binder in a weight ratio of 95.6:1.0:3.4, and the slurry was applied to one side of a copper current collector, dried at 130°C, and then rolled to manufacture a cathode.

[0136] An electrode assembly was manufactured by interposing a separator between the anode and the cathode, and then the assembly was placed inside a battery case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. The electrolyte was prepared by dissolving LiPF6 at a concentration of 1 M in a mixed organic solvent in which ethylene carbonate / dimethyl carbonate / diethyl carbonate were mixed in a volume ratio of 1:2:1, and adding 2 wt% of vinylene carbonate (VC).

[0137]

[0138] Example 2

[0139] Cathode active material (LiNi 0.84 Co 0.08 Mn 0.08 O2), a conductive material (carbon black), and the ammonium cation-substituted cationic polyvinylidene fluoride-based polymer of Preparation Example 2 were mixed in N-methyl-2-pyrrolidone in a weight ratio of 90:5:5, and an anode slurry composition was prepared by stirring with a high-speed stirrer (Homodisper) at 3000 rpm for 90 minutes. At this time, the solid content of the anode slurry composition was 70% by weight based on the total weight of the anode slurry composition.

[0140] After applying the above anode slurry composition to one side of an aluminum current collector, drying it for 10 minutes under atmospheric pressure conditions at 110°C, drying it for 10 hours under vacuum conditions at 130°C, and rolling it to manufacture an anode.

[0141] In addition, a cathode slurry was prepared by mixing graphite as the cathode active material, super C as the conductive material, and a styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) composite as the binder in a weight ratio of 95.6:1.0:3.4, and the slurry was applied to one side of a copper current collector, dried at 130°C, and then rolled to manufacture a cathode.

[0142] An electrode assembly was manufactured by interposing a separator between the anode and the cathode, and then the assembly was placed inside a battery case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. The electrolyte was prepared by dissolving LiPF6 at a concentration of 1 M in a mixed organic solvent in which ethylene carbonate / dimethyl carbonate / diethyl carbonate were mixed in a volume ratio of 1:2:1, and adding 2 wt% of vinylene carbonate (VC).

[0143]

[0144] Comparative Example 1

[0145] Cathode active material (LiNi 0.84 Co 0.08 Mn 0.08 O2), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVdF) were mixed in N-methyl-2-pyrrolidone in a weight ratio of 90:5:5, and an anode slurry composition was prepared by stirring with a high-speed stirrer (Homodisper) at 1500 rpm for 2 hours. At this time, the solid content of the anode slurry composition was 70% by weight based on the total weight of the anode slurry composition.

[0146] After applying the above anode slurry composition to one side of an aluminum current collector, drying it for 10 minutes under atmospheric pressure conditions at 110°C, drying it for 10 hours under vacuum conditions at 130°C, and rolling it to manufacture an anode.

[0147] In addition, a cathode slurry was prepared by mixing graphite as the cathode active material, super C as the conductive material, and a styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) composite as the binder in a weight ratio of 95.6:1.0:3.4, and the slurry was applied to one side of a copper current collector, dried at 130°C, and then rolled to manufacture a cathode.

[0148] An electrode assembly was manufactured by interposing a separator between the anode and the cathode, and then the assembly was placed inside a battery case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. The electrolyte was prepared by dissolving LiPF6 at a concentration of 1 M in a mixed organic solvent in which ethylene carbonate / dimethyl carbonate / diethyl carbonate were mixed in a volume ratio of 1:2:1, and adding 2 wt% of vinylene carbonate (VC).

[0149]

[0150] Experimental Example - High-temperature life evaluation

[0151] The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 were each charged to 4.2V and 1 / 20C at 45°C under CC / CV and 1.0C conditions using an electrochemical charge / discharger, and then discharged to 3.0V under CC and 0.5C conditions, with this being one cycle, and the capacity retention rate was measured. The capacity retention rate was calculated using the formula below, and the number of cycles at which the capacity retention rate reached 80% is shown in Table 1 below.

[0152] Capacity Retention Rate (%) = {(Discharge Capacity after N cycles / Discharge Capacity after 1 cycle)} × 100

[0153] (In the above formula, N is an integer greater than or equal to 1)

[0154] Number of cycles when the capacity retention rate reaches 80% Example 1753 Example 2932 Comparative Example 1507

[0155] As shown in Table 1, the lithium secondary batteries of Examples 1 and 2, which include an ammonium cation-substituted cationic polyvinylidene fluoride-based polymer as a positive electrode binder, had superior high-temperature cycle characteristics compared to the lithium secondary battery of Comparative Example 1.

Claims

1. A binder for a lithium secondary battery positive electrode comprising a cationic polyvinylidene fluoride-based polymer substituted with ammonium cations.

2. In Paragraph 1, The above ammonium cation is a quaternary ammonium cation, a binder for a lithium secondary battery positive electrode.

3. In Paragraph 1, The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer is a binder for a lithium secondary battery positive electrode comprising a repeating unit of the following chemical formula 1. [Chemical Formula 1] In the above Chemical Formula 1, R1 is a divalent organic group, and The above R2, R3, and R4 are each independently selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, an aryl group having 6 to 8 carbon atoms, and an alkylaryl group having 8 to 10 carbon atoms.

4. In Paragraph 2, The above R1 is a binder for a lithium secondary battery positive electrode having the structure of the following chemical formula 1-1. [Chemical Formula 1-1] In the above chemical formula 1-1, The above A1 and A2 are each independently directly bonded or are alkylene groups having 1 to 5 carbon atoms, and * is the connection site.

5. In Paragraph 3, The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer is a binder for a lithium secondary battery positive electrode containing the repeating unit of Formula 1 in an amount of 0.01 to 20 mol% relative to the total number of repeating units of the polymer.

6. In Paragraph 1, The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer is a binder for a lithium secondary battery positive electrode comprising a repeating unit of the following chemical formula 2. [Chemical Formula 2] 7. In Paragraph 6, The above ammonium cation-substituted cationic polyvinylidene fluoride-based polymer is a binder for a lithium secondary battery positive electrode containing the repeating unit of Formula 2 in an amount of 80.00 to 99.99 mol% relative to the total number of repeating units of the polymer.

8. In Paragraph 1, A binder for a lithium secondary battery positive electrode, wherein the weight-average molecular weight of the above-mentioned cationic polyvinylidene fluoride-based polymer is 300,000 to 1,500,000 g / mol.

9. A positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer comprising a positive electrode active material, a positive electrode conductive material, and a positive electrode binder; wherein The above-mentioned positive electrode binder is a positive electrode comprising the lithium secondary battery positive electrode binder of claim 1.

10. In Paragraph 9, The above-mentioned anode binder is included in the anode active material layer at a concentration of 0.1 to 15 weight percent relative to the total.

11. A lithium secondary battery comprising the positive electrode of claim 9; a negative electrode; and a non-aqueous electrolyte.

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