Cathode active material composite, and electrode for secondary battery and lithium secondary battery containing same

Abstract

The present invention relates to a cathode active material composite, and an electrode for a secondary battery and a lithium secondary battery containing same. The cathode active material composite according to the present invention contains: cathode active material particles having the properties of adsorbing and releasing lithium ions; and ionic materials, and satisfies equation 1. [Equation 1] 3.0≤|ζ| / D50≤7.0 (where |ζ| denotes the absolute value of a zeta potential in an aqueous solution of the cathode active material composite, and D50 denotes the particle size corresponding to a cumulative volume of 50% in a particle size distribution)

Description

A composite of positive active materials, an electrode for a secondary battery containing the composite, and a lithium secondary battery

[0001] The present invention relates to a composite of positive active materials, an electrode for a secondary battery including the composite, and a lithium secondary battery including the composite.

[0002] Recently, as the energy density requirements for batteries have rapidly increased, the development of high-capacity lithium secondary batteries has become increasingly urgent. To this end, active research is underway to replace existing anode materials, such as graphite or silicon, with lithium metal, or to incorporate high-energy-density cathode materials into the electrodes.

[0003] However, as the anode becomes thicker to achieve high energy density, it is difficult to secure stable battery performance and lifespan characteristics, so there is a practical limit to increasing its thickness.

[0004] For example, these thick-film anodes have a fundamental problem: the cathode material is unevenly distributed. This leads to uneven lithium ion flow, resulting in uneven charge / discharge characteristics and polarization along the thickness. Furthermore, increased anode thickness increases the distance lithium ions travel, leading to decreased battery performance.

[0005] In addition, since the positive electrode active material comes into contact with the electrolyte in the battery environment, there is a disadvantage in that the life of the battery is shortened as the interface structure is destroyed due to heat and corrosion generated during charging and discharging of the battery.

[0006] Furthermore, as the anode becomes thicker, physical cracks and unevenness of the components (anode material) that make up the anode can occur during the coating, drying, and rolling processes, making it difficult to ensure stable battery performance and lifespan characteristics. Furthermore, the high defect rate in the process significantly reduces productivity.

[0007] Therefore, there is an urgent need for research and development of new cathode active materials that have uniform distribution of components in thick-film positive electrodes to induce uniform flow characteristics of lithium ions, and that increase the lifespan of the battery by preventing the interface structure from being easily destroyed even during frequent charging and discharging, and further have excellent rate characteristics even during high-speed charging.

[0008] An object of the present invention is to provide a composite of positive electrode active materials that enables uniform distribution of components constituting the positive electrode.

[0009] Another object of the present invention is to provide an electrode for a secondary battery with excellent performance, in which the components constituting the positive electrode are uniformly distributed in a thick-film type positive electrode, thereby enabling a uniform flux of lithium ions.

[0010] Another object of the present invention is to provide a lithium secondary battery in which the components constituting the positive electrode are uniformly distributed to maintain excellent battery performance even during frequent charging and discharging, and the deviation in positive electrode performance according to process conditions is significantly reduced to maintain consistent quality.

[0011] The positive electrode active material composite according to the present invention comprises positive electrode active material particles and an ionic material having lithium ion absorption and release properties, and the positive electrode active material composite is characterized in that it satisfies the following equation 1.

[0012] [Formula 1]

[0013] 3.0 ≤ |ζ| / D 50 < 7.0

[0014] The above |ζ| means the absolute value of the zeta potential of the positive electrode active material complex in the aqueous medium, and D 50 It means the particle size corresponding to 50% of the volume accumulation of the particle size distribution.

[0015] In a positive electrode active material composite according to one embodiment of the present invention, D of the positive electrode active material particles 50 can be 1 to 20 μm.

[0016] In the positive electrode active material composite according to one embodiment of the present invention, the positive electrode active material particles may be a single crystal active material, a polycrystalline active material, or a mixture of a single crystal and a polycrystalline active material.

[0017] In the positive electrode active material composite according to one embodiment of the present invention, the ionic material may be an ionic organic compound or an ion-dissociable metal salt.

[0018] In the positive electrode active material composite according to one embodiment of the present invention, the ionic material may contain fluorine.

[0019] In the positive electrode active material composite according to one embodiment of the present invention, the ionic material may be any one or a combination of two or more selected from the group consisting of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm TFSI), poly(1-ethyl-3-methylimidazolium)bis(trifluoromethanesulfonyl)imide (PVIm[TFSI]), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0020] In the positive electrode active material composite according to one embodiment of the present invention, the ion-dissociable metal salt may be a sulfonyl group-containing metal salt selected from the following chemical formula 1 or chemical formula 2.

[0021] [Chemical Formula 1]

[0022]

[0023] [Chemical Formula 2]

[0024]

[0025] In the above chemical formulas 1 and 2, n is 1 or 2; A is an n-valent cation; and R1 to R3 are each independently fluoro(C1-C7)alkyl or a fluoro group.

[0026] In the positive electrode active material composite according to one embodiment of the present invention, A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium.

[0027] In a positive electrode active material composite according to one embodiment of the present invention, a nonionic compound may be further included.

[0028] The electrode for a secondary battery according to the present invention comprises the above-described positive electrode active material composite, a binder, and optionally a conductive material.

[0029] In an electrode for a secondary battery according to one embodiment of the present invention, the electrode may have a tortuosity of 7 or less.

[0030] In the electrode for a secondary battery according to the present invention, the wetting time, which is the time from the time when 3 μL of propylene carbonate (PC) is applied to the surface of the electrode until the electrolyte is no longer observed with the naked eye, may be 690 seconds or less.

[0031] A lithium secondary battery according to the present invention includes the electrode described above.

[0032] The positive electrode active material composite according to the present invention enables uniform distribution of components constituting the positive electrode as the positive electrode active material particles and ionic material are combined, and when used as a positive electrode material in an electrode for a lithium secondary battery, the electrode can have low curvature and fast electrolyte wettability.

[0033] In addition, since the lithium secondary battery according to the present invention has a secondary battery electrode including a positive electrode active material composite, lithium ions can maintain a smooth flow even during high-speed charging and discharging, thereby having excellent rate characteristics.

[0034] In addition, the lithium secondary battery according to the present invention maintains excellent battery performance even during frequent charging and discharging, and the deviation in cathode performance according to process conditions is significantly reduced, so that the quality of the lithium secondary battery can be maintained consistently.

[0035] The present invention is described in more detail below through specific examples or examples. However, the following specific examples or examples are merely references for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

[0036] Unless otherwise defined herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0037] Additionally, the singular forms used herein may be intended to include the plural forms as well, unless the context specifically indicates otherwise.

[0038] In addition, units used in this specification without special mention are based on mass, and for example, units of % or ratio mean mass% or mass ratio, and mass% means the mass% that any one component of the entire composition occupies in the composition unless otherwise defined.

[0039] In addition, in the present specification and the appended claims, when a part such as a film (layer), region, component, etc. is said to be on or above another part, it includes not only a case where it is directly above and in contact with another part, but also a case where another film (layer), another region, another component, etc. is interposed therebetween.

[0040] Additionally, the numerical ranges used herein include lower and upper limits and all values ​​within that range, increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of upper and lower limits of numerical ranges defined in different shapes. Unless otherwise specified herein, values ​​outside the defined numerical range that may arise due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0041] The term "comprises" in this specification is an open-ended description equivalent to expressions such as "includes," "contains," "has," or "characterized by," and does not exclude additional elements, materials, or processes not listed herein.

[0042] The term "porous binder scaffold" as used herein refers to a structure in which a mesh structure is uniformly formed in three dimensions by a binder, in which the binder forms a framework and pores are abundantly developed within the framework. The pores preferably have an open pore structure, and the porous mesh structure formed by the binder can serve as a support in which a positive electrode active material and a conductive material can be evenly distributed. The pores may have a diameter of 0.1 μm to 50 μm, and specifically, may have a diameter of 0.5 μm to 10 μm, but is not limited thereto.

[0043] The positive electrode active material composite according to the present invention comprises positive electrode active material particles and an ionic material having lithium ion absorption and release properties, and the positive electrode active material composite is characterized in that it satisfies the following equation 1.

[0044] [Formula 1]

[0045] 3.0 ≤ |ζ| / D 50 ≤ 7.0

[0046] The above |ζ| means the absolute value of the zeta potential of the positive electrode active material complex in the aqueous medium, and D50 means the particle size corresponding to 50% of the volume accumulation of the particle size distribution. Advantageously, |ζ| / D 50 may be 3.5 to 7.0, more advantageously 3.5 to 6.0, or even more advantageously 3.5 to 5.5.

[0047] Zeta potential is an indicator of the degree of surface charge of colloidal particles suspended or dispersed in a medium (water and / or organic solvent). When an external electric field is applied to a colloid, the colloidal particles will migrate (move) in the opposite direction to the sign of their surface potential. This value is calculated by considering the strength of the electric field that applied the particle movement speed and hydrodynamic effects (viscosity and permittivity of the solvent). The dispersion stability of colloidal particles suspended in a liquid is judged by the size of the absolute value of the zeta potential. The larger the absolute value of the zeta potential, the stronger the repulsion between particles, which increases the degree of dispersion and dispersion maintenance. When the absolute value of the zeta potential approaches 0, the electrostatic attraction between particles becomes stronger, causing aggregation and sedimentation, resulting in an unstable dispersion state.

[0048] The positive electrode active material composite according to the present invention enables uniform distribution of components constituting the positive electrode by complexing positive electrode active material particles and ionic materials and satisfying the above-described formula 1, and when used as a positive electrode material in an electrode for a lithium secondary battery, the electrode can have low curvature and fast electrolyte wettability.

[0049] In addition, the lithium secondary battery according to the present invention has an electrode for a secondary battery including a positive electrode active material composite satisfying the above-described formula 1, so that lithium ions can maintain a smooth flow even during high-speed charging and discharging, thereby having excellent rate characteristics.

[0050] In addition, the lithium secondary battery according to the present invention maintains excellent battery performance even during frequent charging and discharging, and the deviation in cathode performance according to process conditions is significantly reduced, so that the quality of the lithium secondary battery can be maintained consistently.

[0051] In one embodiment, D of the positive electrode active material particles 50 The size may be 1 to 20 μm, specifically 4 to 20 μm or 1 to 5 μm, more specifically 6 to 15 μm, or even more specifically 7 to 13 μm. In the above range, it is possible to manufacture an electrode in which the components are more homogeneously distributed, and thus the defect rate can be reduced during the electrode manufacturing process, thereby increasing productivity.

[0052] The cathode active material composite is not particularly limited as long as it is a composite of cathode active material particles and an ionic substance. The content of the cathode active material particles and the ionic substance in the cathode active material composite is also not particularly limited. However, the cathode active material composite may have an SA ratio (%) satisfying the following Equation 2 of 0.5 to 2.0, specifically 0.6 to 1.7.

[0053] [Formula 2]

[0054] SA ratio (%) = A / B * 100

[0055] In the above equation 2, A is the mass (g) of the ionic material, and B is the surface area of ​​the positive electrode active material particles. The surface area of ​​the positive electrode active material particles satisfies the following equation 3.

[0056] [Formula 3]

[0057] B = specific surface area of ​​positive electrode active material particles (m 2 / g) * Mass of positive electrode active material particles (g)

[0058] In the above range, the curvature of the positive electrode active material can be minimized, thereby achieving a better charge / discharge effect.

[0059] The cathode active material particles are not particularly limited as long as they are known as conventional cathode active materials.

[0060] Specifically, the positive electrode active material particles may be a single crystal active material, a polycrystalline active material, or a mixture of a single crystal active material and a polycrystalline active material.

[0061] Specifically, the cathode active material is LiMO2 (M is a transition metal selected from one or more of Co and Ni); LiMO2 substituted with one or more of a heterogeneous element selected from Mg, Al, Fe, Ni, Cr, Zr, Ce, Ti, B and Mn, or coated with an oxide of such a heterogeneous element; Li x Ni α Co β M γ O2 (a real number with 0.8≤x≤1.5, a real number with 0.7≤α≤0.9, a real number with 0.05≤β≤0.35, a real number with 0.01≤γ≤0.1, α + β + γ =1, M is one or more elements selected from the group consisting of Mg, Sr, Ti, Zr, V, Nb, Ta, Mo, W, B, Al, Fe, Cr, Mn, and Ce); or Li x Ni a Mn b Co c M d Oxides with a layered structure represented by O2 (real numbers with 0.9≤x≤1.1, real numbers with 0.3≤a≤0.6, real numbers with 0.3≤b≤0.4, real numbers with 0.1≤c≤0.4, real numbers with 0≤d≤0.4, a+b+c+d=1, M is one or more elements selected from the group consisting of Mg, Sr, Ti, Zr, V, Nb, Ta, Mo, W, B, Al, Fe, Cr, and Ce); Li a Mn 2-x M x O4 (M = one or more elements selected from Al, Co, Ni, Cr, Fe, Zn, Mg, B, and Ti, real numbers 1≤a≤1.1, real numbers 0≤x≤0.2) or Li4Mn5O 12 It may be, but is not limited to, a spinel structure oxide represented by LiMPO4 (M is Fe, Co, Mn), or an olivine structure phosphate material represented by LiMPO4 (M is Fe, Co, Mn), or a mixture thereof.

[0062] In one embodiment, the positive electrode active material particles may be a nickel-cobalt-manganese positive electrode active material represented by the following chemical formula 1.

[0063] [Chemical Formula 1]

[0064] LiNi a Co b Mn c O2

[0065] In the above chemical formula 1, a+b+c=1, and 0.5≤a≤1.0, 0 <b≤0.5, 0<c≤0.5이다.

[0066] When such positive electrode active material particles are combined with an ionic material, an electrode having excellent electrolyte wettability can be manufactured. Specifically, the positive electrode active material particles may have an average particle diameter of 1 to 20 μm, specifically 4 to 20 μm, more specifically 6 to 15 μm, and even more specifically 7 to 13 μm. In the above range, an electrode having not only excellent electrolyte wettability but also excellent curvature can be manufactured. At this time, the average particle diameter of the positive electrode active material particles is the cumulative volume median diameter (D) of the positive electrode active material particles. 50 ) may be, and experimentally, the average particle diameter may correspond to the diameter at the point where the cumulative volume is 50% after obtaining the cumulative volume diameter distribution using a conventional laser diffraction particle size distribution measuring device. At this time, the average particle diameter of the positive electrode active material composite may correspond to (substantially be identical to) the average particle diameter of the positive electrode active material particles.

[0067] The above-described positive electrode active material particles may include, as another specific example, lithium iron phosphate (LiFePO4). In this case, the positive electrode active material particles may have an average particle diameter of 10 μm or less, specifically 1 to 5 μm, and within the above range, it may be possible to manufacture an electrode having excellent electrolyte wettability and excellent bendability.

[0068] According to one embodiment, the ionic substance may be an ionic organic compound or an ion-dissociating metal salt. The ionic organic compound may be an ionic liquid or an ionic polymer. The ionic organic compound may refer to a hydrocarbon ligand in which the cation and the anion include a hydrocarbon or heteroatom, and is not limited to a cyclic or acyclic type. An example of such a hydrocarbon ligand or a hydrocarbon ligand including a heteroatom may include a ligand (cation group) including a linear or branched substituted imidazolium, ammonium, pyrrolidinium, or piperidinium cation, such as PF6. - , BF4 - , CF3SO3 - , (CF3SO2)2N - , (C2F5SO2)2N - , (C6F5SO2)2N - or (CN)2N - Ligands (anionic groups) including the following can be mentioned.

[0069] According to one embodiment, the ionic material may contain fluorine. The fluorine may be located in an anionic group of the ionic material. The anionic group containing fluorine is, for example, PF6. - , BF4 - , CF3SO3 - , (CF3SO2)2N - , (C2F5SO2)2N - , (C6F5SO2)2N - or ((SO2)2C p F 2p )N - (where p is a natural number from 1 to 10).

[0070] According to one embodiment, the ionic material may be one or a combination of two or more selected from the group consisting of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm TFSI), poly(1-ethyl-3-methylimidazolium)bis(trifluoromethanesulfonyl)imide (PVIm[TFSI]), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0071] The above ion-dissociable metal salt may be an ion-dissociable lithium salt, and specifically, may be an ion-dissociable fluorine-containing lithium salt. The term "ion-dissociable" means dissociating into metal cations and anions in a solvent used in the electrolyte of a lithium secondary battery.

[0072] According to one embodiment, the ion-dissociable metal salt may be a sulfonyl group-containing metal salt selected from the following chemical formula 1 or chemical formula 2.

[0073] [Chemical Formula 1]

[0074]

[0075] [Chemical Formula 2]

[0076]

[0077] In the above chemical formulas 1 and 2, n is independently 1 or 2; A is independently an n-valent cation; and R1 to R3 are each independently a fluoro(C1-C7)alkyl or a fluoro group.

[0078] According to one embodiment, A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium, and may be specifically lithium.

[0079] As the above-described positive electrode active material composite is included in the electrode slurry, it can form a porous binder scaffold within the electrode through interaction with the binder, and the binder can form a skeleton but have an open pore structure with abundantly developed pores. The porous scaffold structure of the binder is induced by the positive electrode active material composite, and the positive electrode active material composite and conductive material can be uniformly distributed throughout this porous scaffold structure, so that the electrochemical characteristics of the electrode can be significantly improved.

[0080] The above-described positive electrode active material composite can function as a precursor that induces the formation of a porous binder scaffold within the electrode, and in particular, when manufacturing a thick film electrode, it can reduce the defect rate of the electrode and maintain the quality of the electrode at a constant level by preventing the occurrence of deviations in the electrochemical properties of the electrode in each individual manufacturing process.

[0081] In order to more significantly enhance the interaction between the positive electrode active material composite and the conductive agent and binder in the slurry, particularly the induction of a porous binder scaffold by the positive electrode active material composite, the positive electrode active material composite may be a positive electrode active material composite for use with a positive electrode binder comprising a fluorinated polymer, a hydrocarbon polymer, or a copolymer of a fluorinated polymer and a hydrocarbon polymer. Specifically, the positive electrode active material composite may be a positive electrode active material composite for use with a positive electrode binder comprising one or a combination of two or more selected from the group consisting of polyvinylidene fluoride (PVdF), a vinylidene fluoride copolymer, a butadiene rubber, a nitrile rubber, a nitrile-butadiene rubber, and a hydrogenated nitrile-butadiene rubber. Representative examples of vinylidene fluoride copolymers include, but are not limited to, one or a combination of two or more selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polyvinylidene fluoride-tetrafluoroethylene copolymer (PVdF-TrFE), polyvinylidene fluoride-polymethyl methacrylate (PVdF-PMMA), and polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE). Representative examples of organic polymers belonging to the butadiene rubber, nitrile rubber, nitrile-butadiene rubber, and hydrogenated nitrile-butadiene rubber include, but are not limited to, one or a combination of two or more selected from the group consisting of butadiene rubber, styrene-butadiene rubber, acrylate-styrene-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylonitrile-butadiene rubber, carboxylated styrene-butadiene rubber, nitrile rubber, nitrile-butadiene rubber, carboxylated nitrile-butadiene rubber, and hydrogenated nitrile-butadiene rubber. The positive electrode binder may have a weight average molecular weight of 10,000 g / mol or more, and may be, but is not limited to, 5,000,000 g / mol or less.For example, the weight average molecular weight of the positive electrode binder may be, but is not limited to, 10,000 to 5,000,000 g / mol or 20,000 to 1,000,000 g / mol.

[0082] In a positive electrode active material composite according to one embodiment of the present invention, a nonionic compound may be further included.

[0083] The nonionic compound may be a nonionic polymer or a nonionic polymerizable compound. Specifically, the nonionic polymer may be a water-soluble nonionic polymer, and the water-soluble nonionic polymer may be a polymer including a polymerizable group at a terminal or side chain, or a water-soluble nonionic polymer not including a polymerizable group. Representative examples of the polymerizable group include, but are not limited to, a cyanomethyl group, a cyanoethyl group, or a nitrile group including a methoxycyanate group, an ester group including a methacryloyl group, an acryloyl group, or a vinyl group. Representative examples of the water-soluble nonionic polymer include, but are not limited to, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, hydroxyethyl cellulose, and molar acrylamide.

[0084] The nonionic polymerizable compound may be a nonionic acrylic monomer, and the number of polymerizable groups of the monomer may be two or more, but may not be limited to ten, and in a practical example, may be two to six, and in a more practical example, may be two to four. Specific examples of nonionic acrylic monomers having two polymerizable groups include, but are not limited to, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,2-propylene glycol diacrylate, 1,2-propylene glycol dimethacrylate, butylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, or combinations thereof. Specific examples of nonionic acrylic monomers having three polymerizable groups include, but are not limited to, trimethylolpropane triacrylate, triethylene glycol triacrylate, glyceryl triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, tripropylene glycol triacrylate, trimethylene glycol triacrylate, or combinations thereof. Specific examples of nonionic acrylic monomers having four polymerizable groups include, but are not limited to, pentaerythritol tetraacrylate, ethoxylated pentaerythritol tetraacrylate, tetraethylene glycol tetraacrylate, trimethylolpropane tetraacrylate, dipeptylene glycol tetraacrylate, tetramethylene glycol tetraacrylate, or combinations thereof.

[0085] When the positive electrode active material composite further contains a non-ionic compound, the weight ratio of the ionic material contained in the positive electrode active material composite to the non-ionic compound may be 100:50 to 150, but is not necessarily limited thereto.

[0086] The electrode for a secondary battery according to the present invention comprises the above-described positive electrode active material composite, a binder, and optionally a conductive material. The binder and the conductive material are not particularly limited as long as they are binders and conductive materials used in conventional secondary battery electrodes, specifically positive electrodes. However, in terms of forming a stronger interaction with the positive electrode active material composite, the binder may include one or a combination of two or more selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride copolymers, butadiene rubbers, nitrile rubbers, nitrile-butadiene rubbers, and hydrogenated nitrile-butadiene rubbers, as described above.

[0087] In one embodiment, the electrode for a secondary battery may have a tortuosity of 7.0 or less, specifically 2.0 to 7.0, and more specifically 4.0 to 6.5. The tortuosity may be measured under the following tortuosity measurement conditions. That is, the ionic conductivity is measured through impedance analysis of a measurement cell manufactured by arranging the same electrodes as the positive and negative electrodes and injecting a liquid electrolyte, and then the tortuosity is calculated using the following calculation formula using the measured ionic conductivity value.

[0088] [Calculation formula]

[0089] Nm = K electrolyte / K electrode = Tortuosity / Porosity

[0090] In the above calculation formula, Nm is the MacMullin number, K electrolyte Is Ionic conductivity of liquid electrolyte , K electrode is the ionic conductivity of the electrode.

[0091] In one embodiment, the electrode for a secondary battery may have a wetting time of 690 seconds or less, which is the time from the time 3 μL of propylene carbonate (PC) is applied to the surface until the electrolyte is no longer visible to the naked eye. The wetting time may be specifically 100 to 600 seconds, more specifically 300 to 550 seconds, even more specifically 300 to 520 seconds, and even more specifically 300 to 480 seconds.

[0092] The secondary battery electrode according to the present invention can have the low curvature and short wetting time (excellent electrolyte wettability) described above by including the above-described positive electrode active material composite. Furthermore, such a secondary battery electrode can have the positive electrode active material composite uniformly distributed. Accordingly, the secondary battery electrode according to the present invention can have smooth ion flow not only during frequent charging and discharging but also during high-speed charging and discharging.

[0093] The present invention includes a method for manufacturing the electrode for a secondary battery described above.

[0094] Specifically, the method for manufacturing an electrode according to the present invention may include a step of manufacturing an electrode slurry including a positive electrode active material composite, a binder, and optionally a conductive material; and a step of coating the electrode slurry on a current collector. The method of coating the electrode slurry may be manufactured through a conventional manufacturing method known in the art, such as applying and drying the electrode slurry on a current collector and rolling it.

[0095] In a method for manufacturing an electrode according to one embodiment, a positive electrode active material composite can be manufactured through a step of complexing a positive electrode active material and an ionic material.

[0096] The above complexing step can be performed by injecting an ionic substance into the positive electrode active material particles and then applying energy. The applied energy can be thermal energy, light energy, or both thermal and light energy, and the application of thermal and light energy can include sequential or simultaneous application.

[0097] Specifically, the energy application may be thermal energy application. When thermal energy is applied, the positive electrode active material and the ionic material may be mixed, and then the positive electrode active material and the ionic material may be composited through a single heat treatment process or a multi-stage heat treatment process. In one embodiment, the ionic material may be added to the positive electrode active material particles and then mixed, and the second heat treatment may be performed at the final temperature that has been heated after the first heat treatment at a constant heating rate. As a practical example, the heating rate in the temperature raising step of the first heat treatment may be 1 to 10 °C / min, specifically 3 to 8 °C / min, and the final temperature reached by the heating (the second heat treatment temperature) may be a temperature of 150 to 250 °C, specifically 180 to 230 °C, and the heat treatment time at the final temperature (the second heat treatment time) may be 0.5 to 2 hours.

[0098] A lithium secondary battery according to the present invention comprises the electrode described above. The secondary battery according to the present invention exhibits smooth rate characteristics even during high-speed charging, thereby achieving excellent battery performance and lifespan.

[0099] The present invention will be described in more detail based on the following examples and comparative examples. However, the following examples and comparative examples are merely illustrative examples for further explaining the present invention, and the present invention is not limited by the following examples and comparative examples.

[0100] [Physical property evaluation]

[0101] (1) Evaluation of particle zeta potential

[0102] Zeta potential of the particulate cathode active material complexes of Examples and Comparative Examples was measured using a zeta potential meter (Equipment name: Litesizer 500, Manufacturer: Anton Paar). Specifically, water (deionized water) was used as a medium, and the cathode active material complex was dispersed in the medium to be 0.1 wt%. Then, the absolute value (|ζ|) of the zeta potential of the particles measured through the zeta potential meter was divided into the particle size (D) corresponding to 50% of the volume accumulation of the particle size distribution of the active material. 50 ) are summarized in Table 1.

[0103] (2) Evaluation of ionic conductivity within the electrode

[0104] A symmetrical cell was made by overlapping two electrodes manufactured using the composite of the positive active materials of the examples and comparative examples, and finally, a liquid electrolyte was injected to manufacture an ionic conductivity measurement cell. The ionic resistance was measured through impedance analysis of the ionic conductivity measurement cell, and the ionic conductivity value within the electrode was calculated. The liquid electrolyte was manufactured to be 1 M LiPF6 in a co-solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) in a volume ratio of 1:1.

[0105] (3) Evaluation of tortuosity within the electrode

[0106] The measured ionic conductivity values ​​within the electrode were used to calculate the tortuosity within the electrode using the MacMullin number (Nm) formula. Nm can be defined as follows.

[0107] Nm = K electrolyte / K electrode = Tortuosity / Porosity

[0108] K electrolyte is the ionic conductivity of the liquid electrolyte, K electroderefers to the ionic conductivity of the electrode according to the examples and comparative examples. The liquid electrolyte was prepared to be 1 M LiPF6 in a co-solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) mixed in a volume ratio of 1:1. The ionic conductivity of the electrode was calculated by measuring the conductivity in the thickness direction of the electrode after filling the electrode with an EC / DEC solution of 1 M LiPF6.

[0109] Porosity was measured from the pore volume based on the adsorption amount according to the change in partial pressure of nitrogen gas at 77 K. The tortuosity was finally calculated from the measured porosity and McMullin number.

[0110] (4) Electrolyte wettability evaluation

[0111] 3 μl of Propylene Carbonate (PC) was dropped onto the electrode manufactured using the positive electrode active material composite of the examples and comparative examples, and the time until the solvent completely penetrated into the electrode and no solvent was observed with the naked eye was measured.

[0112] [Example 1]

[0113] 1) Manufacturing of anode active material composite

[0114] As a positive electrode active material particle, the average particle diameter is 11.5 ㎛ and the specific surface area is 0.6 m 2 / g lithium-nickel-manganese-cobalt composite oxide (LiNi 0.8 Co 0.1 Mn 0.1O2) was injected, and lithium trifluorometal sulfonate was injected as an ionic substance to manufacture a cathode active material composite. Specifically, the cathode active material particles and the ionic substance were injected so that the SA ratio (%) satisfying the above equation 2 was 1.66. The mixture of the cathode active material particles and the ionic substance was mixed using a rotating mixer at 2000 rpm for 3 minutes, then placed in a furnace and heated to 200°C at a heating rate of 5°C / min, maintained at this temperature for 1 hour, and the product subjected to the firing process was naturally cooled to 25°C to manufacture a cathode active material composite.

[0115] 2) Anode manufacturing

[0116] A cathode material was manufactured by mixing 94 g of the cathode active material composite manufactured in 1), 3 g of Super-P having an average particle size of 40 nm as a conductive material, and 3 g of polyvinylidene fluoride as a binder. Using N-methyl-2-pyrrolidone as a solvent, the cathode material was added to the solvent so that the cathode material content was 55 mass% to manufacture a cathode material slurry. The cathode material slurry was applied to a 20 ㎛ thick aluminum thin film using a doctor blade, dried with hot air at 100°C, vacuum-dried at 130°C for 24 hours, and rolled with a roll press so that the composite density was 3.6 g / cc to form a cathode active material layer having a thickness of 60 ㎛, thereby manufacturing a cathode of Example 1 in which cathode active material particles were evenly distributed within a porous binder scaffold structure.

[0117] 3) Cathode manufacturing

[0118] A negative electrode slurry was prepared by adding 96 g of natural graphite powder as a negative active material, 2 g of carbon black with an average particle size of 40 nm as a conductive material, 1 g of styrene-butadiene rubber as a binder, and 1 g of carboxymethyl cellulose to water. The negative electrode slurry was applied to a copper thin film with a thickness of 20 μm using a doctor blade, dried at 120°C, and then rolled using a roll press so that the mixture density became 1.5 g / cc, thereby preparing a negative electrode coated with a 40 μm thick active material layer.

[0119] 4) Lithium secondary battery manufacturing

[0120] Using the positive and negative electrodes manufactured above, a separator (thickness 13 ㎛, SC13-D4-BP, Gellec) was laminated to manufacture a battery assembly, and an aluminum battery tab (0.1T x 7 mm) was ultrasonically welded to the non-coated portion of the positive electrode assembly, and a nickel battery tab (0.1T x 7 mm) was welded to the non-coated portion of the negative electrode assembly, respectively, and then placed in a battery pouch film (153 ㎛, DNP) formed to fit the battery assembly and sealed. Thereafter, a liquid electrolyte in which 1 mol of LiPF6 was dissolved in a solvent in which ethylene carbonate and dimethyl carbonate were mixed in a volume ratio of 1:1 was injected to manufacture a lithium secondary battery of Example 1.

[0121] [Example 2]

[0122] In the above Example 1, a positive electrode and a lithium secondary battery were manufactured in the same manner as described above, except that the SA ratio (%) was added to 0.83 when manufacturing the positive electrode active material composite.

[0123] [Example 3]

[0124] In the above Example 1, a positive electrode and a lithium secondary battery were manufactured by heat treatment in the same manner as in Example 1, except that the SA ratio (%) was added to be 1 when manufacturing the positive electrode active material composite, and a mixed solvent of 50:50 mass% of N-methyl-2-pyrrolidone and propylene carbonate was added and mixed in an amount of 10 mass%.

[0125] [Example 4]

[0126] In the above Example 1, a positive electrode and a lithium secondary battery were manufactured in the same manner as described above, except that poly(1-ethyl-3-methylimidazolium)bis(trifluoromethanesulfonyl)imide (PVIm[TFSI]) was added so that the SA ratio (%) was 1 when manufacturing the positive electrode active material composite.

[0127] [Example 5]

[0128] In the above Example 1, a positive electrode and a lithium secondary battery were manufactured in the same manner as described above, except that trimethylolpropane ethoxylate triacrylate and lithium trifluorometal sulfonate were mixed in a mass ratio of 50:50 and added so that the SA ratio (%) was 1 when manufacturing the positive electrode active material composite.

[0129] [Example 6]

[0130] In the above Example 1, a positive electrode and a lithium secondary battery were manufactured in the same manner as described above, except that cyanoethyl polyvinyl alcohol (PVA-CN) and lithium trifluorometal sulfonate were mixed in a mass ratio of 50:50 and added so that the SA ratio (%) was 1 when manufacturing a positive electrode active material composite.

[0131] [Example 7]

[0132] In the above Example 1, a positive electrode and a lithium secondary battery were manufactured in the same manner as described above, except that cesium bis(trifluoromethanesulfonyl)imide was added so that the SA ratio (%) was 0.83 when manufacturing the positive electrode active material composite.

[0133] [Example 8]

[0134] In the above Example 1, when manufacturing the positive electrode active material composite, the positive electrode active material has an average particle diameter of 8.2 ㎛ and a specific surface area of ​​0.52 m 2 / g, lithium-nickel-manganese-cobalt composite oxide (LiNi 0.9 Co 0.05 Mn 0.05A cathode and a lithium secondary battery were manufactured in the same manner except that O2 was used.

[0135] [Example 9]

[0136] In the above Example 1, when manufacturing the positive electrode active material composite, the positive electrode active material has an average particle diameter of 11.6 ㎛ and a specific surface area of ​​0.87 m 2 / g, lithium-nickel-cobalt-aluminum composite oxide (LiNi 0.83 Co 0.14 Al 0.02 A cathode and a lithium secondary battery were manufactured in the same manner except that O2 was used.

[0137] [Example 10]

[0138] In the above Example 1, when manufacturing the positive electrode active material composite, the positive electrode active material has an average particle diameter of 2 ㎛ and a specific surface area of ​​9.5 m 2 / g, a cathode and a lithium secondary battery were manufactured in the same manner except that lithium iron phosphate (LiFePO4) was used.

[0139] [Example 11]

[0140] In the above Example 1, when manufacturing the positive electrode active material composite, the positive electrode active material has an average particle diameter of 4 ㎛ and a specific surface area of ​​0.65 m 2 / g, single crystal lithium-nickel-manganese-cobalt composite oxide (LiNi 0. 8Co 0.1 Mn 0.1 A cathode and a lithium secondary battery were manufactured in the same manner except that O2 was used.

[0141] [Comparative Example 1]

[0142] In the above Example 1, a lithium-nickel-manganese-cobalt composite oxide (LiNi) was used as the positive electrode active material during the positive electrode manufacturing process. 0.8 Co 0.1 Mn 0.1O2) 94 g, Super-P 3 g as a conductive agent, and polyvinylidene fluoride 3 g as a binder were used to manufacture a cathode slurry, and a cathode and a lithium secondary battery were manufactured in the same manner.

[0143] [Comparative Example 2]

[0144] In the above comparative example 1, a lithium-nickel-manganese-cobalt composite oxide (LiNi) was used as the positive electrode active material. 0.9 Co 0.05 Mn 0.05 A cathode and a lithium secondary battery were manufactured in the same manner except that O2 was used.

[0145] [Comparative Example 3]

[0146] In the above comparative example 1, a lithium-nickel-cobalt-aluminum composite oxide (LiNi) was used as the positive electrode active material. 0.83 Co 0.14 Al 0.02 A cathode and a lithium secondary battery were manufactured in the same manner except that O2 was used.

[0147] [Comparative Example 4]

[0148] In the above comparative example 1, a positive electrode and a lithium secondary battery were manufactured in the same manner as in the above comparative example 1, except that lithium iron phosphate (LiFePO4) was used as the positive electrode active material.

[0149] [Comparative Example 5]

[0150] In the above comparative example 1, a single crystal lithium-nickel-manganese-cobalt composite oxide (LiNi) was used as the cathode material. 0.8 Co 0.1 Mn 0.1 A cathode and a lithium secondary battery were manufactured in the same manner except that O2 was used.

[0151] [Comparative Example 6]

[0152] Lithium-nickel-manganese-cobalt composite oxide (LiNi) as the cathode active material 0.8 Co 0.1 Mn 0.1O2), lithium trifluorometal sulfonate was added as an ionic substance so that the SA ratio (%) was 1, and a complex mixture was prepared by mixing for 3 minutes at 1000 rpm using a magnetic stirrer.

[0153] A cathode and a lithium secondary battery were manufactured in the same manner as described above, except that 94 g of the above composite mixture, 3 g of Super-P as a conductive agent, and 3 g of polyvinylidene fluoride as a binder were used to manufacture a cathode slurry.

[0154] <Evaluation of the characteristics of the positive electrode active material composite electrode>

[0155] The particle specific energy, electrode curvature, and electrolyte wetting time of the positive electrodes manufactured in the above examples and comparative examples were evaluated and are listed in Table 1 below.

[0156] (Table 1)

[0157]

[0158] As shown in Table 1 above, the positive electrode active material composites according to Examples 1 to 11 have a particle size (D) corresponding to 50% of the volume accumulation of the particle size distribution of the positive electrode active material particles, whereby the interaction between the particles is controlled as the positive electrode active material particles and the ionic material are complexed. 50 ) is measured in the range of 3 to 7. On the other hand, in the comparative example, the interaction between particles is not controlled, and the attractive or repulsive force between particles is dominant, so the absolute value of the zeta potential (|ζ|) is the particle size (D ) corresponding to 50% of the volume accumulation of the particle size distribution of the active material. 50) was measured to be 3 or less or 7 or more. Through this, when manufacturing a slurry using a positive electrode active material complex, the unbalanced movement of the conductive material and binder that occur during electrode drying can be suppressed by forming a network through the interaction between the conductive material, binder and positive electrode active material complex that constitute the electrode, and thus, a positive electrode in which the positive electrode active material is evenly distributed within a uniform porous binder scaffold structure can be manufactured. It can be confirmed that the electrode manufactured according to Examples 1 to 11 in which such a structure is formed has a reduced degree of curvature within the electrode and the electrolyte is quickly absorbed. Through this, the electrode manufactured according to Examples 1 to 11 can provide improved ionic conductivity and electronic conductivity characteristics.

[0159] Battery Performance Evaluation

[0160] The capacity of the lithium secondary batteries manufactured in the above examples and comparative examples was measured under charge / discharge conditions of 0.1 C / 0.1 C, 0.1 C / 0.3 C, and 0.1 C / 3.0 C, respectively, and the discharge capacity retention rate according to the rate (C-rate) was evaluated and recorded in Table 2 below.

[0161] The above lithium secondary battery was charged at 0.1 C-rate to 4.3 V under constant current / constant voltage (CC / CV) conditions at 25°C and then cut-off. Thereafter, it was discharged at 0.1 C-rate to 3.0 V (CC conditions) and the capacity under 0.1 C / 0.1 C charge / discharge conditions was measured. Then, the C-rate was changed to 0.3 C and 3.0 C, respectively, and the capacities under 0.1 C / 0.3 C and 0.1 C / 3.0 C charge / discharge conditions were measured, respectively.

[0162] Here, the relative discharge capacity means the value obtained by dividing the discharge capacity at 0.3 C and 3.0 C based on the discharge capacity at 0.1 C, and the discharge capacity maintenance rate means the value obtained by multiplying the relative discharge capacity at 0.3 C and 3.0 C by 100.

[0163] (Table 2)

[0164]

[0165] As shown in Table 2 above, it can be seen that the lithium secondary battery of the positive electrode active material composite according to the embodiment effectively maintains the discharge capacity even when the rate is increased. In other words, it can be seen that the positive electrode according to one embodiment effectively controls the structure within the electrode, so that lithium ions have uniform flow characteristics and excellent output characteristics.

[0166] Battery Performance Uniformity Evaluation

[0167] After manufacturing 30 positive electrodes for each example and comparative example, 10 of the manufactured positive electrodes were randomly selected to manufacture 100 lithium secondary batteries, and the capacities were measured under 0.1 C / 0.1 C and 0.1 C / 0.2 C charge / discharge conditions, respectively, and the standard deviation of the 0.1 C / 0.2 C capacity was evaluated and recorded in Table 3 below.

[0168] (Table 3)

[0169]

[0170] As shown in Table 3 above, it can be seen that the lithium secondary battery of the positive electrode active material composite according to the example exhibits uniform battery performance. That is, it can be seen that the positive electrode according to the example significantly improves the uniformity of electrode performance by using a positive electrode active material composite in which an ionic substance and a positive electrode active material are combined through a homogeneous mixing and sintering process as the positive electrode material. On the other hand, it can be seen that the positive electrode according to Comparative Example 6, which uses a composite mixture manufactured through only a simple mixing process, shows a significant increase in the standard deviation of electrode performance.

[0171] As described above, the present invention has been described by limited embodiments, but these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains can make various modifications and variations based on this description.

[0172] Therefore, the idea of ​​the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. In the bipolar active material complex, The above cathode active material complex comprises cathode active material particles and ionic materials having lithium ion absorption and release properties, The above positive electrode active material complex is a positive electrode active material complex characterized by satisfying the following equation 1. [Formula 1] 3 < |ζ| / D 50 < 7 (The above |ζ| means the absolute value of the zeta potential in the aqueous solution of the positive electrode active material complex, and D 50 (means the particle size corresponding to 50% of the volume accumulation of the particle size distribution) 2. In paragraph 1, D of the above positive electrode active material particles 50 A composite of positive electrode active materials having a size of 1 to 20 μm.

3. In paragraph 1, The above cathode active material particles are cathode active material composites, which are single crystal active materials, polycrystalline active materials, or a mixture of single crystal and polycrystalline active materials.

4. In paragraph 1, The above ionic substance is a composite of a cathode active material, which is an ionic organic compound or an ion-dissociable metal salt.

5. In paragraph 4, A composite of a cathode active material, wherein the ionic substance contains fluorine.

6. In paragraph 1, A cathode active material composite, wherein the ionic substance is one or a combination of two or more selected from the group consisting of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm TFSI), poly(1-ethyl-3-methylimidazolium)bis(trifluoromethanesulfonyl)imide (PVIm[TFSI]), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

7. In paragraph 3, A composite of a cathode active material, wherein the ion-dissociable metal salt is a sulfonyl group-containing metal salt selected from the following chemical formula 1 or chemical formula 2. [Chemical Formula 1] [Chemical formula 2] (In the above chemical formulas 1 and 2, n is 1 or 2; A is a cation of valence n; R 1 Inland R 3 are each independently a fluoro(C1-C7) alkyl or fluoro group) 8. In paragraph 7, The above A is a composite of a positive electrode active material selected from lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium.

9. In paragraph 1, A composite of a cathode active material further comprising a nonionic compound.

10. An electrode for a secondary battery, comprising a composite of a positive electrode active material according to any one of claims 1 to 9, a binder, and optionally a conductive material.

11. In paragraph 10, The above electrode is an electrode for a secondary battery having a tortuosity of 7.0 or less.

12. In paragraph 10, The above electrode is an electrode for a secondary battery, having a wetting time of 690 seconds or less, which is the time from the time 3 ㎕ of propylene carbonate (PC) is applied to the surface until the electrolyte is no longer observed with the naked eye.

13. A lithium secondary battery comprising an electrode according to Article 10.

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