Active material composite, positive electrode active material layer, positive electrode for secondary battery, and secondary battery

Abstract

Provided are an active material composite capable of imparting good battery performance and high tensile strength, and a positive electrode active material layer, a positive electrode for a secondary battery, and a secondary battery formed using the active material composite. The active material composite is an active material-conductive material composite containing a particulate positive electrode active material, a conductive material, and a first binder for binding the positive electrode active material and the conductive material, wherein at least a portion of the conductive material may be bound to the surface of the positive electrode active material through the first binder so as to extend in the diametrical direction of the positive electrode active material.

Description

Active material composite, positive active material layer, positive and secondary battery for secondary battery

[0001] The present invention relates to an active material composite, a positive active material layer, a positive electrode for a secondary battery, and a secondary battery.

[0002] Rechargeable batteries, including lithium-ion batteries, are widely used as power sources for devices such as smartphones and laptop computers; however, as these electronic devices become smaller and lighter, there is a growing demand for higher energy densities in rechargeable batteries. Furthermore, with the recent increase in demand for rechargeable batteries as power sources for electric and hybrid vehicles, there is a need for higher energy densities to achieve performance equivalent to conventional gasoline engines.

[0003] To improve energy density, high-capacity electrodes containing, for example, carbon-based active materials are being developed. Conventionally, such electrodes are manufactured by a wet method in which an active material, a conductivity aid, a binder, etc., are dispersed in a solvent, stirred, and then coated onto a current collector foil and dried.

[0004] Meanwhile, recently, a method for manufacturing electrodes using a dry method that does not use a solvent has also been developed to reduce environmental burden by omitting the drying process in the wet method (Japanese Patent Publication No. 2022-003694).

[0005] In addition, polytetrafluoroethylene (PTFE) is widely used as a binder in electrodes of lithium-ion batteries containing a non-aqueous electrolyte. Japanese Patent Publication No. 2024-005891 discloses a method for manufacturing a self-standing electrode composite sheet by producing a binder containing PTFE and a conductivity aid, then adding a positive electrode active material to the binder, and further mixing and rolling.

[0006] However, when manufacturing a secondary battery using a dry method with self-supporting electrode composite sheets (self-supporting electrode sheets), a process of bonding these sheets to a positive current collector is required. Therefore, from the perspective of productivity and handling of self-supporting electrode sheets, it is desired that the self-supporting electrode sheets not only exhibit good battery performance but also high tensile strength.

[0007] The present invention is intended to provide an active material composite capable of imparting good battery performance and high tensile strength, a positive active material layer formed using the said active material composite, a positive electrode for a secondary battery, and a secondary battery.

[0008] An active material composite according to one embodiment comprises a particulate positive active material, a conductive agent, and a first binder that binds the positive active material and the conductive agent. At least a portion of the conductive agent is bound to the surface of the positive active material through the first binder so as to be extended in the diameter direction of the positive active material.

[0009] The above active material composite can provide good battery performance and high tensile strength, and the positive active material layer, the positive electrode for a secondary battery, and the secondary battery formed using the above active material composite can provide good battery performance.

[0010] FIG. 1 is a schematic cross-sectional diagram showing the schematic configuration of a secondary battery according to one embodiment.

[0011] FIG. 2 is a schematic diagram showing the schematic configuration of an active material complex according to one embodiment.

[0012] FIG. 3 is a schematic diagram showing a state in which a plurality of active material composites according to one embodiment are bound to each other through a second binder.

[0013] Hereinafter, an embodiment will be described in detail with reference to the drawings. In addition, common components in the following drawings are given the same reference numerals and are assumed to have the same function. Furthermore, for convenience, a positive electrode for a secondary battery may also be simply referred to as a “positive electrode.”

[0014] secondary battery

[0015] First, with reference to FIG. 1, an example of a secondary battery according to the present embodiment will be described. As shown in FIG. 1, the secondary battery (1) comprises a positive electrode (10), a negative electrode (20), and a separator (30). The positive electrode (10) includes a positive current collector (11), a positive active material layer (12), and a conductive adhesive layer (13) installed between the positive current collector (11) and the positive active material layer (12). The negative electrode (20) includes a negative current collector (21) and a negative active material layer (22). The separator (30) is formed between the positive electrode (10) and the negative electrode (20), and a non-aqueous electrolyte is contained in each pore within the separator (30) and in the gaps between the positive electrode (10) and the negative electrode (20). In addition, the positive electrode (10) corresponds to the positive electrode for a secondary battery described later. The secondary battery (1) is a lithium-ion secondary battery and corresponds to a non-aqueous electrolyte secondary battery formed using a non-aqueous electrolyte. The shape of the secondary battery (1) is not particularly limited, but can be any type such as a cylindrical, prismatic, laminated, or button type.

[0016] (anode)

[0017] As illustrated in FIG. 1, the anode (10) comprises an anode current collector (11), an anode active material layer (12), and a conductive adhesive layer (13) disposed between the anode current collector (11) and the anode active material layer (12). Additionally, the anode active material layer (12) may further include a non-aqueous electrolyte described later. In this embodiment, the anode (10) may be a self-supporting electrode sheet formed by a dry method.

[0018] The materials for the positive current collector (11) include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), and germanium (Ge). The positive current collector (11) may include any one of these metals or may be formed from an alloy of two or more metals. The shape of the positive current collector (11) may be, for example, plate-shaped or thin-shaped. An undercoating layer may be applied to the positive current collector (11). The thickness of the positive current collector is not particularly limited, but may be 1 μm or more and 20 μm or less.

[0019] The positive active material layer comprises a positive active material and a conductive agent combined in an active material complex. As illustrated in FIG. 2, the active material complex (12-1) comprises a particulate positive active material (12a), a conductive agent (12b), and a first binder (12c) that binds the positive active material (12a) and the conductive agent (12b). The active material complex (12-1) has a bimodal configuration in which two or more positive active materials (12a) having different particle diameters are mixed, and may exist in a form in which the small particle positive active material (12a) fills the gaps of the large particle positive active material (12a). At least a portion of the conductive agent (12b) is bound to the surface of the positive active material (12a) through the first binder (12c) so as to extend in the diameter direction of the particulate positive active material (12a). In this way, the active material composite (12-1) has a cluster-shaped form in which a conductive agent (12b) is arranged to extend outward from the surface of the positive active material (12a). Since the conductive agent (12b) is firmly fixed to the surface of the particulate positive active material (12a) through the first binder (12c), it is possible to stably express high conductivity in the positive active material (12a) and provide good battery performance. In FIG. 2, at least a portion of the conductive agent (12b) extends from the surface of the large particle positive active material (12a) through the first binder (12c), but this is not limited thereto, and at least a portion of the conductive agent (12b) may also extend from the surface of the small particle positive active material (12a) through the first binder (12c) (not shown).

[0020] Additionally, the positive active material layer may include an active material composite (12-2) to which a second binder (12d), which is a binder different from the first binder (12c), is further bonded, as shown in FIG. 3. The immobilized conductive agent (12b) is bonded to the surface of the positive active material (12a) so as to extend in the diameter direction of the positive active material (12a). Accordingly, due to the anchoring effect, the extending conductive agent (12b) can adhere more to the second binder (12d), and as a result, the self-supporting electrode sheet containing such an active material composite (12-2) exhibits high tensile strength.

[0021] The positive electrode active material may be a positive electrode active material capable of reversibly absorbing and releasing lithium ions. Such a positive electrode active material may be a lithium-containing metal oxide, for example, lithium cobaltate (hereinafter referred to as “LCO”), lithium nickelate, lithium nickel cobaltate, lithium nickel cobalt aluminum oxide (hereinafter referred to as “NCA”), lithium nickel cobalt manganese (hereinafter referred to as “NCM”), lithium manganese, lithium iron phosphate, lithium salts, nickel sulfide, copper sulfide, lithium sulfide, sulfur, iron oxide, or vanadium oxide. These positive electrode active materials may each be used individually or in combination of two or more types.

[0022] In addition, the positive electrode active material may include a lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium salts described above. Here, “layered rock salt type structure” refers to a cubic rock salt type structure. <111> It is a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in the direction, and as a result, each atomic layer forms a two-dimensional plane. In addition, the “cubic rock salt type structure” refers to a sodium chloride type structure, which is a type of crystal structure, and specifically, it refers to a structure in which the face-centered cubic lattices formed by each of the cations and anions are arranged offset from each other by half the corners of the unit cell.

[0023] As a lithium salt of a transition metal oxide having such a layered rock salt-type structure, for example, LiNi x Co y Al z O2(NCA), or LiNi x Co y Mn z O2(NCM)(however, 0 <x<1, 0<y<1, 0<z<1, 및 x+y+z=1) 등의 삼원계 전이금속 산화물의 리튬염이 있다.

[0024] When the positive active material includes a lithium salt of a ternary transition metal oxide having the layered rock salt type structure described above, the energy density and thermal stability of the secondary battery (1) can be improved.

[0025] The positive active material may be covered by a coating layer. Such a coating layer is not particularly limited as long as it is known as a coating layer for the positive active material of a solid-state secondary battery, and examples include Li2O-ZrO2.

[0026] In addition, when the positive electrode active material is formed from a lithium salt of a ternary transition metal oxide such as NCA or NCM and contains nickel (Ni) as the positive electrode active material, the capacity density of the solid-state secondary battery can be increased and the leaching of metal from the positive electrode active material during the charged state can be reduced. Accordingly, the solid-state secondary battery can improve long-term reliability and cycle characteristics during the charged state.

[0027] As for the positive active material, particles of various shapes such as spherical, polygonal, needle-shaped, scale-shaped, and irregular shapes can be examples, and as an example, a spherical positive active material may be used. Furthermore, "spherical" means that the overall shape of the particle is spherical or approximately spherical. The particle size of the positive active material is not particularly limited, and particles of various sizes may exist as the positive active material. In addition, the average particle diameter of the positive active material may be in the range of 0.1 μm or more and 50 μm or less, and may be 1 μm or more and 20 μm or less. In addition, the average particle diameter of the positive active material refers to the median diameter (D50), and can be measured, for example, by laser diffraction, a scattering particle size distribution measuring device, etc.

[0028] The conductive agent is not particularly limited as long as it can enhance the conductivity of the positive electrode active material layer, and examples include carbon materials such as carbon black, natural graphite, artificial graphite, carbon nanotubes, carbon fibers, carbon nanofibers, single-layer graphene, and multilayer graphene. Examples of carbon black include furnace black, channel black, thermal black, Kettjen black, and acetylene black. Meanwhile, the conductive agent may be a fibrous material in which at least a portion of the conductive agent extends in the diameter direction of the positive electrode active material through the first binder. Accordingly, the conductive agent may be a carbon material having a long, slender shape such as an ellipsoid, needle, or rod shape, and may be, for example, fibrous carbon, or for example, carbon nanotubes. The carbon nanotube can be any of single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT), or multi-walled carbon nanotubes (MWNT). The conductive agent may be used alone or in a mixture of two or more types.

[0029] The content of the conductive agent in the positive active material layer may be 0.01 weight% or more and 5 weight% or less when the entire positive active material layer is 100 weight%, for example, 0.01 weight% or more and 3 weight% or less, or 0.01 weight% or more and 1 weight% or less.

[0030] In the case where the conductive agent is a fibrous material, at least one end of the conductive agent may be bound to the surface of the positive active material by the first binder. The length of the conductive agent extending from the surface of the positive active material is not particularly limited, and it is sufficient if it can form a conductive path between the positive active materials and prevents excessive aggregation between adjacent extended conductive agents.

[0031] The first binder is not particularly limited and only needs to be capable of binding a conductive agent to the aforementioned positive active material. The first binder is supplied to the surface of the positive active material while dissolved or dispersed in a solvent, so that a part or all of the surface of the positive active material forms a layer composed of the predetermined binder. Accordingly, the first binder can be easily dissolved or dispersed in the solvent used, and from the perspective of eliminating environmental burden, it is more appropriate for the first binder to be water-soluble. It is even more appropriate for the first binder to be able to be dissolved or dispersed in a solvent, and furthermore, not to be dissolved in the electrolyte, and to possess charge-discharge resistance (a property of not degrading during charge-discharge).

[0032] The first binder is not particularly limited as long as it is a material capable of bonding the positive active material and the conductive agent. Examples include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), ethylene-containing resins such as styrene-butadiene rubber (SBR), ethylene-propylene-diene terpolymer (EPDM), acrylonitrile-butadiene rubber (NBR), fluororubber, polyvinyl acetate (PVAC), polymethyl methacrylate (PMMA), polyethylene (PE), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC) or carboxymethylcellulose derivatives (such as salts of carboxymethylcellulose), nitrocellulose, etc. Among these, the first binder may contain fluorine-containing resins such as PTFE and PVDF in order to increase the weight per unit area of ​​the positive active material layer. The first binder may be used alone or may be used in a mixture of two or more types.

[0033] The content of the first binder in the positive active material layer may be 0.001 weight% or more and 2 weight% or less, for example, 0.005 weight% or more and 1 weight% or less, or 0.01 weight% or more and 0.5 weight% or less, when the entire positive active material layer is 100 weight%.

[0034] The second binder is a fibrillary binder, and by the fibrillary binders forming a matrix, lattice, web, etc. with each other, mechanical strength required to manufacture a self-supporting electrode sheet can be imparted to the positive active material layer. As the second binder, a fibrillated binder generally included in a positive active material layer manufactured by a dry method can be widely used. Such a second binder may be, for example, a fluorine-containing polymer that is at least partially fibrillated. Examples of fluorine-containing polymers constituting the second binder include polytetrafluoroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE), and other suitable fibrillable fluorine-containing polymers. The second binder may be used alone or in a mixture of two or more types.

[0035] The content of the second binder in the positive active material layer may be 0.01 wt% or more and 5 wt% or less, for example, 0.05 wt% or more and 4 wt% or less, or 0.1 wt% or more and 3 wt% or less, when the entire positive active material layer is 100 wt%. In addition, it is appropriate for the content of the second binder to be greater than the content of the first binder mentioned above.

[0036] The thickness of the positive active material layer is not particularly limited, but may be 1 μm or more and 200 μm or less. If the thickness of the positive active material layer is 1 μm or more and 200 μm or less, the increase in the resistance value of the positive active material layer can be suppressed and the characteristics of the secondary battery can be maintained. The thickness of the positive active material layer can be estimated, for example, by observing the cross-section after assembling and pressure-molding the secondary battery using a scanning electron microscope (SEM).

[0037] A conductive adhesive layer (also referred to as a “base layer”) may be installed between the positive active material layer and the positive current collector. The conductive adhesive layer is an intermediate layer that prevents the positive active material layer from detaching or peeling off from the positive current collector, and contains a carbon material, a binder for the base layer, and a dispersant.

[0038] The carbon material included in the base layer is not particularly limited as long as it is intended to enhance the conductivity of the base layer. Specific examples of carbon materials include carbon black, natural graphite, artificial graphite, fibrous carbon, and nano carbon materials. Examples of carbon black include furnace black, channel black, thermal black, Kettjen black, and acetylene black. Examples of fibrous carbon include carbon fibers. Examples of nano carbon materials include carbon nanotubes, carbon nanofibers, single-layer graphene, and multi-layer graphene. Among these carbon materials, carbon black, which is easy to disperse, and acetylene black, which has high conductivity, may be used. Carbon materials may be used alone or in a mixture of two or more types.

[0039] The content of the carbon material in the base layer may be 1% by weight or more and 35% by weight or less, for example, 5% by weight or more and 30% by weight or less, based on the total base layer. If the content of the carbon material is 1% by weight or more, good conductivity can be imparted to the base layer, and if the content of the carbon material is 1% by weight or more, the conductivity of the base layer is further improved. On the other hand, if the content of the carbon material in the base layer is reduced, there is room to increase the content of the base layer binder, dispersant, etc. included in the base layer, which leads to the expression of good adhesion or improved dispersibility of the base layer. Accordingly, the content of the carbon material may be 35% by weight or less, for example, 30% by weight or less.

[0040] A binder for a base layer has the function of adhering each component, such as a carbon material included in the base layer, to one another, and also adhering the base layer to an anode current collector or an anode active material layer. Such a binder for a base layer includes, for example, a styrene-acrylic acid ester copolymer, and more specifically, is composed of a styrene-acrylic acid ester copolymer.

[0041] A styrene-acrylic acid ester copolymer is a copolymer whose main constituent unit is formed by polymerizing styrene and acrylic acid esters, and for example, is a copolymer containing styrene and acrylic acid ester constituent units in a range of 80% by weight or more and 99% by weight or less. As acrylic acid esters, methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, isobutyl acrylate, pentyl acrylate, n-hexyl acrylate, isoamyl acrylate, lauryl acrylate, stearyl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxy-2-hydroxyethyl-phthalic acid, ethoxy-diethyleneglycol acrylate, methoxy-triethyleneglycol acrylate, tetrahydrofurfuryl acrylate, phenoxy-polyethyleneglycol acrylate, phenoxydiethyleneglycol acrylate, phenoxyethyl acrylate, methoxyethyl acrylate, glycidyl acrylate, acrylonitrile, Examples include 2-acrylamide-2-methylpropanesulfonic acid and 2-acryloxyethyl acid phosphate, and may include butyl acrylate and 2-ethylhexyl acrylate.

[0042] The styrene-acrylic acid ester copolymer may comprise one or more constituent units other than styrene and acrylic acid ester in a range of 1% by weight or more and 20% by weight or less. Examples of such constituent units include, for example, constituent units polymerized from aromatic vinyl compounds such as p-methylstyrene, m-methylstyrene, o-methylstyrene, ot-butylstyrene, mt-butylstyrene, pt-butylstyrene, p-chlorostyrene, o-chlorostyrene; A constituent unit polymerized from unsaturated alkyl methacrylate compounds such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, isopropyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, isobutyl methacrylate, pentyl methacrylate, n-hexyl methacrylate, isoamyl methacrylate, lauryl methacrylate, stearyl methacrylate, and isobornyl methacrylate, and (meth)acrylic acid-based compounds such as methacrylic acid, acrylic acid, itaconic acid, fumaric acid, and maleic acid; A constituent unit polymerized from unsaturated carboxylic acid amide compounds such as (meth)acrylamide, (meth)N-methylacrylamide, (meth)N-dimethylacrylamide, (meth)N-hydroxymethylacrylamide, (meth)N-butoxymethylacrylamide, and (meth)isobutoxymethylacrylamide; There are constituent units polymerized from compounds such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 2-hydroxy-3-phenoxypropyl methacrylate, ethoxy-diethylene glycol methacrylate, methoxy-triethylene glycol methacrylate, tetrahydrofurfuryl methacrylate, phenoxy-polyethylene glycol methacrylate, phenoxydiethylene glycol methacrylate, phenoxyethyl methacrylate, methoxyethyl methacrylate, glycidyl methacrylate, methacrylonitrile, and 2-methacroyloxy acid phosphate.

[0043] The glass transition temperature of the styrene-acrylic acid ester copolymer may be -20°C or higher and 20°C or lower, for example, -15°C or higher and 15°C or lower, or -10°C or higher and 15°C or lower. If the glass transition temperature is -20°C or higher and 20°C or lower, good adhesion is imparted between the positive active material layer and the base layer when the positive active material layer is bonded to the base layer, even without setting the temperature of the heat roll press to an excessively high temperature exceeding, for example, 120°C.

[0044] The glass transition temperature of a styrene-acrylic acid ester copolymer can be appropriately adjusted depending on the type and content of the constituent units of the copolymer. Since the styrene-acrylic acid ester copolymer contains 80% by weight or more and 99% by weight or less of constituent units polymerized from styrene and acrylic acid ester, it can be adjusted by the content of styrene and acrylic acid ester. For example, since the glass transition temperature of a styrene homopolymer is about 100°C and the glass transition temperature of a 2-ethylhexyl acrylic acid homopolymer is about -55°C, a copolymer having a glass transition temperature between approximately -55°C and 100°C can be synthesized by adjusting the content of styrene and 2-ethylhexyl acrylic acid. In addition, if the glass transition temperature of the homopolymer of the monomer used is already known, the calculated glass transition temperature can be obtained using Fox's formula from the volume fraction of these monomer compounds. And, by synthesizing a copolymer while referring to this and performing differential scanning calorimetry (DSC), a styrene-acrylic acid ester copolymer having a glass transition temperature of -20°C or higher and 20°C or lower can be obtained.

[0045] In order to sufficiently prevent detachment or peeling of the positive active material layer by the base layer, the content of the base layer binder in the entire base layer may be 50 weight% or more. In addition, in order to sufficiently ensure the conductivity of the base layer, the content of the base layer binder in the entire base layer may be 90 weight% or less. The content of the base layer binder in the entire base layer may be 55 weight% or more and 85 weight% or less, for example, 60 weight% or more and 85 weight% or less, or 60 weight% or more and 80 weight% or less.

[0046] The dispersant is an additive that uniformly disperses the aforementioned carbon material and the binder for the base layer, and may be polyacrylic acid or polymethacrylic acid. Polyacrylic acid or polymethacrylic acid has multiple carboxyl groups within its molecule, and these carboxyl groups may be neutralized by alkali metal ions such as sodium ions. On the other hand, polyacrylic acid or polymethacrylic acid may not have these carboxyl groups neutralized. Specifically, among the carboxyl groups of polyacrylic acid or polymethacrylic acid, the proportion of neutralized carboxyl groups (neutralized carboxyl groups) may be 20% or less, 10% or less, or 0% (i.e., unneutralized).

[0047] The content of the dispersant in the base layer may be 1 wt% or more and 30 wt% or less, for example, 2 wt% or more and 25 wt% or less, or 3 wt% or more and 20 wt% or less. If the content of the dispersant is 1 wt% or more, the aforementioned carbon material and the binder for the base layer can be uniformly dispersed, and if it is 2 wt% or more, the carbon material and the binder for the base layer can be dispersed more uniformly. On the other hand, if the content of the dispersant is reduced, there is room to increase the content of the binder for the base layer and the conductive agent, leading to the expression of good adhesion of the base layer and improvement of battery performance due to low resistance. Accordingly, the content of the dispersant may be 30 wt% or less, for example, 25 wt% or less.

[0048] The thickness of the base layer is not particularly limited, but may be 1 μm or more and 20 μm or less. The thickness of the base layer can be estimated, for example, by observing the cross-section after assembling and pressure-molding a secondary battery using a scanning electron microscope (SEM).

[0049] (cathode)

[0050] As illustrated in FIG. 1, the cathode (20) comprises a cathode current collector (21) and a cathode active material layer (22). Additionally, the cathode active material layer (22) may further include a non-aqueous electrolyte described later. In this embodiment, the cathode (20) is a self-supporting electrode sheet formed by a dry method. The cathode active material layer (22) comprises a cathode active material and a conductive agent.

[0051] The negative current collector may comprise at least one selected from copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or a combination thereof, and may comprise at least one selected from copper (Cu), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or a combination thereof, and in one embodiment may comprise copper (Cu). The negative current collector may be composed of any one of these metals, or may be composed of an alloy or clad material of two or more metals. In addition, the surface of the negative current collector may be plated with Ni or Fe, etc. The shape of the negative current collector is, for example, plate-shaped or thin-walled.

[0052] Examples of negative electrode active materials include particles of various shapes such as spherical, polygonal, needle-shaped, scale-shaped, and irregular shapes, and as an example, a spherical negative electrode active material may be used. Meanwhile, "spherical" means that the overall shape of the particle is spherical or approximately spherical. The particle size of the negative electrode active material is not particularly limited, and particles of various sizes may exist as the negative electrode active material. In addition, the average particle diameter of the negative electrode active material may be in the range of 0.1 μm or more and 50 μm or less, for example, in the range of 1 μm or more and 20 μm or less.

[0053] The negative electrode active material is, for example, a graphite active material (synthetic graphite, natural graphite, a mixture of synthetic and natural graphite, natural graphite coated with synthetic graphite, etc.), a silicon-based active material (a mixture or complex of fine particles of silicon (Si) or its oxide and a graphite active material, fine particles of silicon, an alloy based on silicon), or a tin-based active material (for example, a mixture or complex of fine particles of tin (Sn) or its oxide and a graphite active material, fine particles of tin, an alloy based on tin), metallic lithium, and Li4Ti5O. 12It may include at least one selected from titanium oxide-based compounds, lithium nitride, or combinations thereof. The negative electrode active material may be used as a single type or in combination of two or more types. Among these, the negative electrode active material may contain a high-capacity active material exceeding 350 mAh / g, may have a capacity of 500 mAh / g or more, may have a capacity of 1000 mAh / g or more, and may have a capacity of 1500 mAh / g or more. Examples of such high-capacity active materials include silicon-based active materials. The silicon-based oxide is SiO₂ x It can be expressed as (0≤x≤2).

[0054] The content of the negative electrode active material in the negative electrode active material layer (total content in cases where two or more types of negative electrode active materials are used) may be 80% by weight or more and 99% by weight or less, for example, 85% by weight or more and 99% by weight or less, or 90% by weight or more and 99% by weight or less, with the entire negative electrode active material layer being 100% by weight.

[0055] The conductive agent is not particularly limited as long as it has the performance to improve the conductivity of the cathode active material layer. Specific examples of conductive agents include carbon materials such as carbon black, natural graphite, artificial graphite, fibrous carbon, and nano carbon materials. Examples of carbon black include furnace black, channel black, thermal black, Kettjen black, and acetylene black. Examples of fibrous carbon include carbon fibers. Examples of nano carbon materials include carbon nanotubes, carbon nanofibers, single-layer graphene, and multilayer graphene. Among these, the carbon material may have a slender, elongated shape such as an ellipsoid, needle, or rod shape, and may be, for example, fibrous carbon. The conductive agent may be used as a single type or in combination of two or more types. The content of the conductive agent in the negative electrode active material layer may be 0.01 wt% or more and 5 wt% or less, for example, 0.05 wt% or more and 3 wt% or less, or 0.1 wt% or more and 1 wt% or less, based on 100 wt% of the total negative electrode active material layer.

[0056] The thickness of the negative electrode active material layer is not particularly limited, but may be 1 μm or more and 200 μm or less. The thickness of the negative electrode active material layer can be estimated, for example, by observing a cross-section after assembling and press-molding a secondary battery using a scanning electron microscope (SEM).

[0057] (Separator)

[0058] The material of the separator is not particularly limited and may be a resin that can be used as a separator for a secondary battery, particularly a lithium-ion secondary battery. Such a separator may be a porous membrane, nonwoven fabric, etc., exhibiting excellent high-rate discharge performance, used alone, or two or more types may be used in combination. As for the resin constituting the separator, examples include polyolefin-based resins such as polyethylene and polypropylene; polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate;and, polyvinylidene difluoride, vinylidene difluoride-hexafluoropropylene copolymer, vinylidene difluoride-perfluorovinylether copolymer, vinylidene difluoride-tetrafluoroethylene copolymer, vinylidene difluoride-trifluoroethylene copolymer, vinylidene difluoride-fluoroethylene copolymer, vinylidene difluoride-fluoroethylene copolymer, vinylidene difluoride-hexafluoroacetone copolymer, vinylidene difluoride-ethylene copolymer, vinylidene difluoride-propylene copolymer, There are fluorine-based resins such as vinylidene difluoride-trifluoropropylene copolymer, vinylidene difluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene difluoride-ethylene-tetrafluoroethylene copolymer. Furthermore, the porosity of the separator is not particularly limited, and it is possible to arbitrarily apply the porosity of a known lithium-ion secondary battery separator.

[0059] On the surface of the separator, a heat-resistant layer containing inorganic particles to improve heat resistance, or a layer containing an adhesive to bond with the electrode to fix the battery element, may be installed. Examples of inorganic particles include Al2O3, AlO(OH), Mg(OH)2, SiO2, etc. Examples of adhesives include vinylidene fluoride-hexafluoropropylene copolymer, acid-modified vinylidene fluoride polymer, styrene-(meth)acrylic acid ester copolymer, etc.

[0060] (non-aqueous electrolyte)

[0061] The non-aqueous electrolyte may be used as a non-aqueous electrolyte for secondary batteries, particularly lithium-ion secondary batteries. The non-aqueous electrolyte has a composition comprising an electrolyte salt in a non-aqueous solvent, which is a solvent for the electrolyte.As non-aqueous solvents, for example, cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate; and chain esters such as methyl formate, methyl acetate, methyl butyrate, ethyl propionate, and propyl propionate. There are ethers such as tetrahydrofuran or its derivatives, 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, or methyldiglyme, ethylene glycol monopropyl ether, propylene glycol monopropyl ether; nitriles such as acetonitrile and benzonitrile; and heterocyclic compounds such as dioxolane or its derivatives, ethylene sulfide, sulfolane, sultone or its derivatives.These non-aqueous solvents may be used alone or in a mixture of two or more. When two or more non-aqueous solvents are mixed and used, the mixing ratio of each non-aqueous solvent may be the mixing ratio used in known secondary batteries.

[0062] As electrolytes, for example, LiClO4, LiBF4, LiAsF6, LiPF6, LiPF6 6-x (C n F 2n+1 ) x [However, 1 <x<6, n=1 또는 2], LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 Inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), such as NaClO4, NaI, NaSCN, NaBr, KClO4, KSCN, etc.; There are ionic compounds such as organic ionic salts including LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiC(C2F5SO2)3, (CH3)4NBF4, (CH3)4NBr, (C2H5)4NClO4, (C2H5)4NI, (C3H7)4NBr, (n-C4H9)4NClO4, (n-C4H9)4NI, (C2H5)4N-maleate, (C2H5)4N-benzoate, (C2H5)4N-phtalate, lithium stearylsulfonate, lithium octylsulfonate, and lithium dodecylbenzenesulfonate. These ionic compounds may be used alone or in a mixture of two or more types. In addition, the concentration of the electrolyte salt may be the same as that of a non-aqueous electrolyte used in known secondary batteries and is not particularly limited. In the present embodiment, a non-aqueous electrolyte containing such an electrolyte salt at a concentration of 0.8 mol / l or more and 1.5 mol / l or less may be used.

[0063] Various additives may be included in the non-aqueous electrolyte. Examples of such additives include cathodic additives, anode additives, ester-based additives, carbonate-based ester-based additives, sulfate-based ester-based additives, phosphoric acid-based ester-based additives, boric acid-based ester-based additives, anhydrous carbonate-based additives, and electrolyte-based additives. Among these, any one type may be added to the non-aqueous electrolyte, or multiple types of additives may be added to the non-aqueous electrolyte.

[0064] Method for manufacturing a secondary battery

[0065] Next, a method for manufacturing a lithium-ion secondary battery will be described.

[0066] (Method for manufacturing the anode)

[0067] A positive electrode active material is added to a dispersion in which a conductive agent and a first binder are dispersed, and the mixture is stirred. The mixture is then dried and subsequently ground to produce an active material composite in which the conductive agent is bound to the surface of the positive electrode active material by the first binder. When drying the mixture, the active material composite is dried while the conductive agent is arranged in a chestnut-like shape on the surface of the positive electrode active material due to capillary action, thereby fixing the conductive agent. The active material composite prepared in this manner and the second binder are mixed in a desired ratio to produce a mass of the active material composite. Furthermore, the mass is stretched into a sheet shape by a dry method manufacturing process involving rolling to produce a self-standing positive electrode sheet. Additionally, the positive electrode sheet produced in this manner may contain not only the active material composite combined with the conductive agent but also a positive electrode active material that is not combined with the conductive agent. A positive electrode is produced by a dry method in which this positive electrode sheet is laminated onto a positive electrode current collector with a base layer interposed therebetween using a hot roll press or the like. The apparatus used in the process of laminating an anode sheet onto a base layer by a dry method is not particularly limited and includes, for example, a roll press apparatus, a hot roll press apparatus, a dry laminator, a calendering apparatus, a heat press apparatus, etc. For example, when a hot roll press apparatus is used, the temperature of the press roll of the hot roll press apparatus can be appropriately changed depending on the material used for the anode active material, but may be 20°C or higher and 200°C or lower, for example, 40°C or higher and 170°C or lower, or 60°C or higher and 150°C or lower. In addition, the anode sheet may be laminated directly onto the anode current collector without interposing a base layer.

[0068] (Method for manufacturing the cathode)

[0069] First, the materials constituting the negative electrode active material layer are dispersed in a solvent for the negative electrode slurry to produce a negative electrode slurry. Next, the negative electrode slurry is applied onto a negative electrode current collector, dried, and then the negative electrode active material layer is pressed by a press machine to achieve a desired density. Accordingly, a negative electrode is produced. Furthermore, when producing a half cell (inverted battery) as a secondary battery, since the negative electrode functions as a counter electrode, a commercially available product in which a thin Li foil is adhered to a negative electrode current collector may be used as is.

[0070] (Method for manufacturing a non-aqueous electrolyte secondary battery)

[0071] An electrode structure is fabricated by inserting a separator between the fabricated positive and negative electrodes. Subsequently, the electrode structure is processed into a desired shape (e.g., cylindrical, prismatic, laminated, button-shaped, etc.) and inserted into a container of the same shape. Then, by injecting a non-aqueous electrolyte into the container, the electrolyte is impregnated into each pore within the separator or into the pores of the positive and negative electrodes. Accordingly, a non-aqueous electrolyte secondary battery is manufactured.

[0072] In the above-described embodiment, it may be applied as a cathode having the same base layer. Additionally, the positive or negative electrode may not have a base layer (adhesive layer), and the positive active material layer or the negative active material layer may be formed directly on the positive current collector or the negative current collector. Furthermore, the positive electrode according to the present invention is not limited to non-aqueous electrolyte secondary batteries but can be applied to secondary batteries in general, and, for example, can be applied to semi-solid secondary batteries or all-solid secondary batteries having a solid electrolyte layer.

[0073] Although embodiments of the present description have been described above, the present description is not limited to the above embodiments and includes all embodiments included in the concept and claims of the present description, and may be modified in various ways within the scope of the present description.

[0074] Based on the above embodiments, this description relates to [1] to [9] below.

[0075] [1] Particulate positive active material and,

[0076] Challenge system and,

[0077] A first binder that binds the positive active material and the conductive agent.

[0078] As an active material-conductive agent complex containing,

[0079] An active material complex in which at least a portion of the conductive agent is bonded to the surface of the positive active material so as to be extended in the diameter direction of the positive active material through the first binder.

[0080] [2] The active material complex described in [1], wherein the above-mentioned conductive agent is a fibrous material.

[0081] [3] The active material complex described in [1] or [2], wherein the positive active material is a lithium-containing metal oxide.

[0082] [4] A plurality of active material complexes described in any one of [1] to [3] above, and

[0083] A second binder that is different from the first binder mentioned above

[0084] As a positive electrode active material layer containing,

[0085] The above second binder is at least a partially fibrillated fluorine-based polymer, forming an anode active material layer.

[0086] [5] At least a portion of the plurality of active material complexes are bonded together through the second binder described above, in the positive active material layer described in [4].

[0087] [6] The positive active material layer described in [4] or [5] above, and

[0088] positive current collector and,

[0089] A conductive adhesive layer installed between the positive active material layer and the positive current collector

[0090] A positive electrode for a secondary battery comprising

[0091] [7] The conductive adhesive layer above contains a carbon material, a binder for the base layer, and a dispersant, and

[0092] The positive electrode for a secondary battery described in [6] comprises at least one of a styrene-butadiene copolymer and a styrene-acrylic acid ester copolymer.

[0093] [8] A secondary battery having a positive electrode and a negative electrode as described in [6] or [7] above.

[0094] [9] The secondary battery described in [8] is a secondary battery that is a non-aqueous electrolyte secondary battery.

[0095] Examples

[0096] Embodiments of the present invention will be described below, but the present invention is not limited to these examples without departing from the spirit thereof. Unless specifically stated otherwise, each operation is performed at room temperature, and the room temperature is within the range of 20℃±5℃.

[0097] [Example 1]

[0098] (Fabrication of chestnut-shaped positive electrode active material (K1))

[0099] NCA was prepared as the positive active material. Subsequently, the positive active material was added to an NMP dispersion containing dispersed PVDF and SWCNT such that the content of the conductive agent carbon nanotube (SWCNT) was 0.04 wt% and the content of the first binder PVDF was 0.2 wt%, and the mixture was stirred. Afterward, the resulting mixture was dried in air at 120°C and vacuum dried at 120°C for 6 hours to obtain a solidified material. The obtained solidified material was pulverized by grinding it with a mortar and pestle to produce a powdered active material composite (K1) (also referred to as a chestnut-shaped positive active material (K1)).

[0100] (Fabrication of dry anode sheet (P1))

[0101] A dry anode sheet (P1) was produced by mixing the obtained chestnut-shaped anode active material (K1) and the second binder, fibril-shaped PTFE, in a weight ratio of 98.5:1.5, stretching the resulting mixture into a sheet shape, and compressing it while it was placed in contact with a base layer formed on an anode current collector of 10 μm thick aluminum foil (a slurry mixture comprising acetylene black as a carbon material, styrene-acrylic acid 2-ethylhexyl copolymer as a binder for the base layer, and polyacrylic acid or polymethacrylic acid as a dispersant in a weight ratio of 28:60:12, applied to the surface of the anode current collector and dried).

[0102] (Preparation of a dry anode sheet (R1) for comparison)

[0103] An untreated (not made of chestnut-shaped active material) positive active material (S0), a conductive agent, and PTFE were mixed in a weight ratio of 98.0:1.0:1.5, and the resulting mixture was expanded into a sheet. Then, a dry positive sheet (R1) was produced by pressing the resulting sheet onto a positive current collector made of aluminum foil with a thickness of 10 μm.

[0104] (Polar sheet)

[0105] A lithium foil bonded to a copper foil was used.

[0106] (Fabrication of a test half cell)

[0107] A test half cell was fabricated by laminating the above dry positive sheet (P1) or dry positive sheet (R1) with a counter electrode sheet through a separator, clamping it with an aluminum laminate film, heat-sealing the edges of the aluminum laminate film except for a portion, and then sealing it in a vacuum after injecting the electrolyte with all edges heat-sealed. A portion of each of the positive sheet and the counter electrode sheet was pulled out to the outside of the laminate film so as not to break the vacuum of the battery, and the portions that were pulled out to the outside were made into the terminals of the positive and counter electrodes, respectively.

[0108] The charge-discharge characteristics of the half cell fabricated in this manner were evaluated under the following conditions. Measurements were performed by placing the half cell in a constant temperature bath at 25°C. Pressure was applied by sandwiching the half cell between two resin plates and clamping the plates together with a clip so that a predetermined pressure was applied to the electrode surface. 4.3V, 0.8mA / cm² 2 Charge for 15 hours with constant current and constant voltage, 0.8mA / cm² 2 Discharge was performed with a constant current until the battery voltage reached 1.5V. Afterwards, 4.3V, 0.8mA / cm² 2 Charge for 15 hours at constant current and constant voltage, 12mA / cm² 2 Discharge was performed with a constant current until the battery voltage reached 1.5V, and the discharge capacity was compared. With respect to the dry anode sheet (R1) for comparison, the capacity ratio of the half cell using the dry anode sheet (P1) was 1(R1):1.03(P1).

[0109] (Fabrication of self-supporting anode sheets for tensile strength measurement)

[0110] A dry anode sheet (P1) or a dry anode sheet (R1) was stamped into a dumbbell No. 6 shape in accordance with JIS K6251:2017, and the test specimen was pulled at a speed of 1 mm / min in a universal testing machine (manufactured by Shimadzu, “AGS-X”), and the first maximum stress observed during the test was measured as the tensile strength. With respect to the comparative dry anode sheet (R1), the ratio of the tensile strength of the self-supporting anode sheet using the dry anode sheet (P1) was 1 (R1):1.37 (P1).

[0111] From the above results, the dry anode sheet (P1) according to the present invention was able to achieve both good battery characteristics and high tensile strength with a small amount of conductive agent compared to the conventional dry anode sheet (R1). This compatibility is believed to be because the conductive agent is directly immobilized on the chestnut-shaped anode active material (K1), and furthermore, due to the anchoring effect of the immobilized conductive agent, the chestnut-shaped anode active material (K1) can be bonded more closely to the second binder, PTFE, and as a result, the tensile strength, which is the self-supporting strength, is improved.

[0112] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0113] [Explanation of the symbol]

[0114] 1: Secondary battery

[0115] 10: Anode

[0116] 11: Positive current collector

[0117] 12: Positive active material layer

[0118] 12a: Positive active material

[0119] 12b: Challenge

[0120] 12c: First binder

[0121] 12d: Second binder

[0122] 12-1, 12-2: Active substance complex

[0123] 13: Conductive adhesive layer

[0124] 20: Cathode

[0125] 21: Cathode current collector

[0126] 22: Cathode active material layer

[0127] 30: Separator

Claims

1. Particulate positive active material, Challenge system, and A first binder that binds the above positive active material and the conductive agent. As an active material-conductive agent complex containing, An active material complex in which at least a portion of the conductive agent is bonded to the surface of the positive active material so as to be extended in the diameter direction of the positive active material through the first binder.

2. In Paragraph 1, An active material complex in which the above-mentioned conductive agent is a fibrous material.

3. In Paragraph 1, An active material complex in which the positive active material is a lithium-containing metal oxide.

4. Multiple active material complexes according to paragraph 1, A second binder that is different from the first binder mentioned above As a positive electrode active material layer containing, The above second binder is at least a partially fibrillated fluorine-based polymer, forming an anode active material layer.

5. In Paragraph 4, A positive active material layer in which at least a portion of the plurality of active material complexes are bonded together through the second binder.

6. The positive active material layer described in Paragraph 4, positive current collector, and A conductive adhesive layer installed between the positive active material layer and the positive current collector A positive electrode for a secondary battery comprising 7. In Paragraph 6, The above conductive adhesive layer contains a carbon material, a binder for the base layer, and a dispersant, and A positive electrode for a secondary battery, wherein the binder for the base layer comprises one of a styrene-butadiene copolymer and a styrene-acrylic acid ester copolymer.

8. The anode for a secondary electrode described in paragraph 6 or 7, and A secondary battery including a negative electrode.

9. In Paragraph 8, The above secondary battery is a secondary battery that is a non-aqueous electrolyte secondary battery.

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