Positive electrode for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

Disclosed are a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. The positive electrode includes a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, in which the positive electrode mixture layer includes a positive electrode active material and a first binder, and the first binder is a hydrogenated nitrile rubber (HNBR) derivative.

Description

Technical Field

[0001] Disclosed are a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the positive electrode. Background Art

[0002] Recently, with the rapid popularization of electronic devices using batteries (such as mobile phones, laptop computers and electric vehicles), interest in rechargeable batteries with high energy density and high capacity has increased rapidly. Therefore, research and development to improve the performance of rechargeable lithium batteries is being actively carried out.

[0003] The rechargeable lithium battery includes positive and negative electrodes including an active material capable of intercalating and deintercalating lithium ions and an electrolyte, and generates electric energy through oxidation and reduction reactions if lithium ions are intercalated / deintercalated from the positive and negative electrodes.

[0004] The positive electrode for a rechargeable lithium battery includes a positive electrode current collector and a positive electrode mixture layer thereon. The positive electrode mixture layer substantially includes a positive electrode active material, and optionally further includes a positive electrode binder and / or a conductive material (eg, an electrically conductive material).

[0005] A polyvinylidene fluoride-based binder is widely used as a positive electrode binder, which is also used as a resistor (eg, a resistor).

[0006] Therefore, to increase the cycle life of rechargeable lithium batteries while increasing the adhesion of the positive electrode and reducing the resistance (eg, electrical resistance), it is useful to use the polyvinylidene fluoride-based positive electrode binder in a minimal or reduced amount or to replace it entirely with another binder. Summary of the invention

[0007] Some embodiments of the present disclosure provide positive electrodes for rechargeable lithium batteries in which a polyvinylidene fluoride-based positive electrode binder is used in a reduced amount, minimally used, or completely replaced by another binder.

[0008] Some embodiments provide a rechargeable lithium battery including the positive electrode.

[0009] Some embodiments provide a positive electrode for a rechargeable lithium battery, the positive electrode comprising a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, wherein the positive electrode mixture layer comprises a positive electrode active material and a first binder, and the first binder comprises a hydrogenated nitrile rubber (HNBR) derivative.

[0010] Some embodiments provide a rechargeable lithium battery including the positive electrode.

[0011] The positive electrode according to some embodiments can use a polyvinylidene fluoride positive electrode binder in a reduced or minimal amount, or can completely replace the polyvinylidene fluoride positive electrode binder with a hydrogenated nitrile rubber derivative. As a result, the cycle life of the rechargeable lithium battery can be increased while increasing the adhesion of the positive electrode and reducing the resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings, together with the specification, illustrate embodiments of the presently disclosed subject matter, and, together with the description, serve to explain principles of the embodiments of the presently disclosed subject matter.

[0013] Figure 1 is a cross-sectional perspective view of a rechargeable lithium battery according to some embodiments. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments of the present disclosure will be described in more detail. However, these embodiments are examples, the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the appended claims and their equivalents.

[0015] As used herein, if no specific definition is provided otherwise, it will be understood that if an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present.

[0016] As used herein, if no specific definition is provided otherwise, the singular may also include the plural. In addition, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B".

[0017] As used herein, "combinations thereof" may mean mixtures, stacks, composites, copolymers, alloys, blends, and / or reaction products of the components.

[0018] As used herein, if a specific definition is not otherwise provided, “alkyl” refers to C1 to C20 alkyl, “alkenyl” refers to C2 to C20 alkenyl, “cycloalkenyl” refers to C3 to C20 cycloalkenyl, “heterocycloalkenyl” refers to C3 to C20 heterocycloalkenyl, “aryl” refers to C6 to C20 aryl, “arylalkyl” refers to C6 to C20 arylalkyl, the term “alkylene” refers to C1 to C20 alkylene, “arylene” refers to C6 to C20 arylene, “alkylenearyl” refers to C6 to C20 alkylenearyl, “heteroarylene” refers to C3 to C20 heteroarylene, and “alkyleneoxy” refers to C1 to C20 alkyleneoxy.

[0019] As used herein, if no specific definition is provided otherwise, "substituted" means that at least one hydrogen atom is replaced by a halogen atom (F, Cl, Br or I), a hydroxyl group, a C1 to C20 alkoxy group, a nitro group, a cyano group, an amino group, an imino group, an azido group, an amidino group, a hydrazine group, a hydrazone group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, an ether group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphate group or a salt thereof, a C1 to C20 alkyl group, a C2 to C20 alkenyl group, a C2 to C20 alkynyl group, a C6 to C20 aryl group, a C3 to C20 cycloalkyl group, a C3 to C20 cycloalkenyl group, a C3 to C20 cycloalkynyl group, a C2 to C20 heterocycloalkyl group, a C2 to C20 heterocycloalkenyl group, a C2 to C20 heterocycloalkynyl group, a C3 to C20 heteroaryl group or a combination thereof.

[0020] Furthermore, as used herein, if a specific definition is not otherwise provided, “hetero” means that at least one hetero atom of N, O, S and P is included in a chemical formula.

[0021] As used herein, if no specific definition is otherwise provided, the term "combination" means mixing and / or copolymerizing.

[0022] As used herein, if no definition is otherwise provided, in a chemical formula, if a chemical bond is not drawn at a position where it should be given, a hydrogen is bonded at that position.

[0023] As used herein, the weight average molecular weight (Mw) may be a value measured using gel permeation chromatography (GPC).

[0024] Positive electrode

[0025] Some embodiments provide a positive electrode for a rechargeable lithium battery, the positive electrode comprising a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, wherein the positive electrode mixture layer comprises a positive electrode active material and a first binder, and the first binder comprises a hydrogenated nitrile rubber (HNBR) derivative.

[0026] The hydrogenated nitrile rubber derivative as the first binder has low electrical resistance (eg, resistance to electrical resistance) while exhibiting an equal level or higher level of adhesive strength compared to the polyvinylidene fluoride-based positive electrode binder.

[0027] Therefore, the positive electrode according to some embodiments can use a reduced or minimal amount of polyvinylidene fluoride positive electrode binder, or can completely replace the polyvinylidene fluoride positive electrode binder with a hydrogenated nitrile rubber derivative. As a result, the cycle life of the rechargeable lithium battery can be increased while increasing the adhesion of the positive electrode and reducing the resistance (e.g., resistance to electrical resistance).

[0028] Hereinafter, the positive electrode of some embodiments will be described in more detail.

[0029] First binder (hydrogenated nitrile rubber derivative)

[0030] The positive electrode mixture layer generally includes a first binder, and the first binder includes a hydrogenated nitrile rubber (HNBR) derivative.

[0031] The first binder may include: a repeating unit having an acrylonitrile-derived structure represented by Chemical Formula 1; a repeating unit including at least one selected from repeating units having a hydrogenated butadiene-derived structure represented by Chemical Formula 2 and Chemical Formula 3; and a repeating unit represented by Chemical Formula 4:

[0032] Chemical formula 1

[0033]

[0034] Chemical formula 2

[0035]

[0036] Chemical formula 3

[0037]

[0038] Chemical formula 4

[0039]

[0040] In chemical formula 4, R 1 and R 2 are independently substituted or unsubstituted C1 to C20 alkyl, ester group (-COOR, wherein R is substituted or unsubstituted C1 to C20 alkyl), cyano group (-CN), pyrrolidone group (-C3H5NHCO), carboxyl group (-COOH), caprolactam group (-NCOC5H 10 ), morpholinyl (-NC4H8O), hydroxyl (-OH), amino (-NH2), vinyl (-CH=CH2), epoxy (-COCH2) or thiol (-SH).

[0041] The first adhesive including the hydrogenated nitrile rubber derivative may have higher adhesive strength than the hydrogenated nitrile rubber itself because it further includes the repeating unit including Chemical Formula 4.

[0042] The first binder may be represented by Chemical Formula I.

[0043] Chemical formula I

[0044]

[0045] In Formula I, R 1 and R 2The definition of is the same as described above. For example, R 1 It can be methyl, R 2 It may be a carboxyl group (-COOH).

[0046] In some embodiments, in Formula I, a to d are each independently an integer from 1 to 20.

[0047] The first binder may be represented by Chemical Formula I-1.

[0048] Chemical formula I-1

[0049]

[0050] In Chemical Formula I-1, a to d are the same as defined above.

[0051] The first binder may have a weight average molecular weight (Mw) measured according to a GPC method of about 100,000 g / mol to about 1,000,000 g / mol (or Dalton), about 100,000 g / mol to about 500,000 g / mol (or Dalton), or about 100,000 g / mol to about 200,000 g / mol (or Dalton).

[0052] The first binder may be included in an amount greater than or equal to about 0.1 wt % and less than or equal to about 5 wt %, greater than or equal to about 0.3 wt % and less than or equal to about 3 wt %, greater than or equal to about 0.5 wt % and less than or equal to about 2 wt %, or greater than or equal to about 0.55 wt % and less than or equal to about 1.1 wt %, based on the total amount (100 wt %) of the positive electrode mixture layer.

[0053] Second binder (hydrogenated nitrile rubber)

[0054] The positive electrode mixture layer may further optionally include a second binder, and the second binder may include hydrogenated nitrile rubber (HNBR).

[0055] The second binder may include: a repeating unit having an acrylonitrile-derived structure represented by Chemical Formula 5; a repeating unit including at least one selected from the group consisting of an alkylene repeating unit represented by Chemical Formula 6 and a repeating unit having a hydrogenated butadiene-derived structure represented by Chemical Formula 7; and a repeating unit represented by Chemical Formula 8:

[0056] Chemical formula 5

[0057]

[0058] Chemical formula 6

[0059]

[0060] Chemical formula 7

[0061]

[0062] Chemical formula 8

[0063]

[0064] In Chemical Formula 8,

[0065] R 3 is a substituted or unsubstituted C1 to C20 alkyl group, an ester group (-COOR, wherein R is a substituted or unsubstituted C1 to C20 alkyl group), a cyano group (-CN), a pyrrolidone group (-C3H5NHCO), a carboxyl group (-COOH), a caprolactam group (-NCOC5H 10 ), morpholinyl (-NC4H8O), hydroxyl (-OH), amino (-NH2), vinyl (-CH=CH2), epoxy (-COCH2) or thiol (-SH).

[0066] The second binder may be represented by Chemical Formula II or Chemical Formula III.

[0067] Chemical formula II

[0068]

[0069] Chemical formula III

[0070]

[0071] In Formula II and Formula III, R 3 The definition of is the same as described above. As an example, R 3 It may be an ethyl group or an ester group (—COOR), wherein R may be a substituted or unsubstituted C1 to C20 alkyl group.

[0072] In addition, in Chemical Formula II and Chemical Formula III, e to j and n may each independently be an integer of 1 to 20.

[0073] Examples of the second binder are as follows.

[0074] Chemical formula II-1

[0075]

[0076] Chemical formula III-1

[0077]

[0078] In Chemical Formula II-1 and Chemical Formula III-1, the definitions of R, e to j and n are the same as described above.

[0079] The second binder may have a weight average molecular weight (Mw) measured according to a GPC method of about 100,000 to about 1,000,000 g / mol (or Dalton), about 100,000 to about 500,000 g / mol (or Dalton), or about 100,000 to about 200,000 g / mol (or Dalton).

[0080] The second binder may be included in an amount greater than about 0 wt % and less than about 5 wt %, greater than or equal to about 0.1 wt % and less than or equal to about 3 wt %, greater than or equal to about 0.1 wt % and less than or equal to about 2 wt %, or greater than or equal to about 0.2 wt % and less than or equal to about 0.3 wt %, based on the total amount (100 wt %) of the positive electrode mixture layer.

[0081] Third binder (polyvinylidene fluoride, derivatives of polyvinylidene fluoride, copolymers of polyvinylidene fluoride)

[0082] The positive electrode mixture layer may further optionally include a third binder, and the third binder may include polyvinylidene fluoride, a derivative of polyvinylidene fluoride, a copolymer including polyvinylidene fluoride, or a combination thereof.

[0083] It may be suitable or desirable to completely replace the third binder with the first binder; or to replace the third binder with a mixture of the first binder and the second binder, but the third binder may be provided to ensure adhesion strength and / or compatibility, etc.

[0084] The third binder may include a repeating unit having a vinylidene fluoride-derived structure represented by Chemical Formula 9:

[0085] Chemical formula 9

[0086]

[0087] In some embodiments, the third binder may further optionally include a repeating unit including at least one selected from a repeating unit having a vinylidene fluoride derivative-derived structure represented by Chemical Formula 10 and a repeating unit having a hexafluoropropylene-derived structure represented by Chemical Formula 11:

[0088] Chemical formula 10

[0089]

[0090] Chemical formula 11

[0091]

[0092] Examples of the third binder are as follows.

[0093] Chemical formula IV

[0094]

[0095] Chemical formula V

[0096]

[0097] Chemical formula VI

[0098]

[0099] In Chemical Formulae IV to VI, m, o to q, x, and y may each independently be an integer of 1 to 20.

[0100] The third binder may have a weight average molecular weight (Mw) measured according to a GPC method of about 500,000 g / mol to about 5,000,000 g / mol (or Dalton), about 500,000 g / mol to about 3,000,000 g / mol (or Dalton), or about 500,000 g / mol to about 1,500,000 g / mol (or Dalton).

[0101] The third binder may be included in an amount greater than about 0 wt % and less than or equal to about 3 wt %, greater than about 0 wt % and less than or equal to about 2.5 wt %, greater than about 0 wt % and less than or equal to about 2 wt %, greater than about 0 wt % and less than or equal to about 1 wt %, or greater than about 0 wt % and less than or equal to about 0.1 wt %, based on the total amount (100 wt %) of the positive electrode mixture layer.

[0102] Fourth binder

[0103] The positive electrode mixture layer may further optionally include a fourth binder, and the fourth binder may include an acrylic binder, a derivative of an acrylic binder, a copolymer including an acrylic binder, or a combination thereof.

[0104] The fourth binder may include poly(meth)acrylic acid, poly(meth)acrylate, polymethyl(meth)acrylate, polyacrylonitrile, acrylonitrile-styrene-butadiene copolymer, or a combination thereof.

[0105] The fourth binder may be included in an amount greater than about 0 wt % and less than or equal to about 3 wt %, greater than about 0 wt % and less than or equal to about 2.5 wt %, greater than about 0 wt % and less than or equal to about 2 wt %, greater than about 0 wt % and less than or equal to about 1 wt %, or greater than about 0 wt % and less than or equal to about 0.1 wt %, based on the total amount (100 wt %) of the positive electrode mixture layer.

[0106] Crosslinking agent

[0107] The positive electrode mixture layer may further include a cross-linking agent in addition to the binder to ensure that the positive electrode active material particles adhere to each other and the positive electrode active material adheres to the current collector.

[0108] In some embodiments, the crosslinking agent may be a carbodiimide compound series crosslinking agent. The carbodiimide compound series crosslinking agent may increase adhesion strength by crosslinking the first binder including the repeating unit of Chemical Formula 4.

[0109] In some embodiments, the cross-linking agent may be represented by Chemical Formula 12:

[0110] Chemical formula 12

[0111]

[0112] In chemical formula 12,

[0113] R 4 and R 5 are independently substituted or unsubstituted C1 to C20 alkyl, substituted or unsubstituted C3 to C20 cycloalkyl, substituted or unsubstituted C6 to C20 aryl, or substituted or unsubstituted C2 to C20 heteroaryl including at least one selected from N, O, S and P,

[0114] L 1 and L 2 are independently substituted or unsubstituted C1 to C20 alkylene, substituted or unsubstituted C3 to C20 cycloalkylene, substituted or unsubstituted C6 to C20 arylene, or substituted or unsubstituted C2 to C20 heteroarylene including at least one selected from N, O, S and P, and

[0115] z is an integer of 1-20.

[0116] Examples of cross-linking agents are as follows:

[0117]

[0118] The crosslinking agent may be included in an amount greater than about 0 wt % and less than or equal to about 3 wt %, greater than about 0 wt % and less than or equal to about 2.5 wt %, greater than about 0 wt % and less than or equal to about 2 wt %, greater than about 0 wt % and less than or equal to about 1 wt %, or greater than about 0 wt % and less than or equal to about 0.1 wt %, based on the total amount (100 wt %) of the positive electrode mixture layer.

[0119] Conductive Materials

[0120] The positive electrode mixture layer may further include an electrically conductive material (eg, an electronically conductive material).

[0121] The conductive material is included to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material may be used as the conductive material unless it causes chemical changes (e.g., undesirable chemical changes in a rechargeable lithium battery). Examples of the conductive material may be: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials in the form of metal powder and / or metal fiber, such as copper, nickel, aluminum, silver, etc.; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0122] The conductive material may be included in an amount of greater than or equal to about 0.1 wt % and less than or equal to about 5 wt %, greater than or equal to about 0.5 wt % and less than or equal to about 3 wt %, or greater than or equal to about 1 wt % and less than or equal to about 2 wt %, based on the total amount (100 wt %) of the positive electrode mixture layer.

[0123] Positive electrode active material

[0124] The positive electrode active material may be a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). In some embodiments, a composite oxide of lithium and one or more types (or species) of metals selected from cobalt, manganese, nickel, aluminum, and combinations thereof may be used.

[0125] The composite oxide may be a lithium transition metal composite oxide, and examples thereof may include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, or combinations thereof.

[0126] As an example, a compound represented by any one of the following chemical formulas may be used: Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NeG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); and Li a FePO4(0.90≤a≤1.8).

[0127] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; and L 1 It is Mn, Al or a combination thereof.

[0128] As an example, the positive electrode active material may be a high nickel-based positive electrode active material having a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%, based on 100 mol% of metals other than lithium in the lithium transition metal composite oxide. The high nickel-based positive electrode active material may achieve high capacity and may be applied to high capacity, high density rechargeable lithium batteries.

[0129] The amount of the positive electrode active material may be about 90 wt % to about 99.5 wt % based on 100 wt % of the positive electrode mixture layer.

[0130] Positive electrode

[0131] A positive electrode for a rechargeable lithium battery may include a current collector and a positive electrode active material layer on the current collector. The positive electrode active material layer may include a positive electrode active material, and may further include a binder and / or a conductive material (eg, an electrically conductive material).

[0132] In some embodiments, the positive electrode may also include an additive that may function as a sacrificial positive electrode.

[0133] The amount of the positive electrode active material may be about 90 wt % to about 99.5 wt % based on 100 wt % of the positive electrode active material layer, and the amount of the binder and the conductive material may be about 0.5 wt % to about 5 wt % based on 100 wt % of the positive electrode active material layer.

[0134] The current collector may include Al, but is not limited thereto.

[0135] Rechargeable lithium battery

[0136] Some embodiments provide a rechargeable lithium battery including a positive electrode.

[0137] This can improve cycle life by including a positive electrode.

[0138] Hereinafter, at least some elements other than the positive electrode constituting the rechargeable lithium battery will be described in more detail.

[0139] Negative electrode active material

[0140] The negative electrode active material may be a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, and / or a transition metal oxide.

[0141] Materials capable of reversibly inserting / extracting lithium ions may include carbonaceous negative electrode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. Crystalline carbon may be graphite, such as natural graphite and / or artificial graphite in irregular shapes, sheet shapes, flake shapes, spherical shapes, and / or fiber shapes. Amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, and / or calcined coke, etc.

[0142] The lithium metal alloy may include lithium and metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0143] Materials capable of doping / dedoping lithium may be Si-based negative electrode active materials and / or Sn-based negative electrode active materials. Si-based negative electrode active materials may include silicon, silicon-carbon composites, SiO x (0 < x < 2), Si-Q alloys (where Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof). Sn-based negative electrode active materials may include Sn, SnO2, Sn-based alloys, or combinations thereof.

[0144] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to some embodiments, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are assembled and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon may also be between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be present dispersed in an amorphous carbon matrix.

[0145] The silicon-carbon composite may also include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core.

[0146] Si-based negative electrode active materials and / or Sn-based negative electrode active materials may be used in combination with carbonaceous negative electrode active materials.

[0147] Negative electrode

[0148] The negative electrode for a rechargeable lithium battery includes a current collector and a negative electrode mixture layer on the current collector. The negative electrode mixture layer includes negative electrode active materials and may also include a binder and / or a conductive material (e.g., an electrically conductive material).

[0149] For example, the negative electrode mixture layer may include about 90 wt % to about 99 wt % of a negative electrode active material, about 0.5 wt % to about 5 wt % of a binder, and about 0 wt % to about 5 wt % of a conductive material based on 100 wt % of the negative electrode mixture layer.

[0150] The binder may be used to well attach the negative electrode active material particles to each other and also to well attach the negative electrode active material to the current collector. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0151] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0152] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and combinations thereof.

[0153] If an aqueous binder is used as the negative electrode binder, it may also include a cellulose compound that can impart or increase viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and / or their alkali metal salts. The alkali metal may be Na, K and / or Li.

[0154] The dry binder may be a polymer material capable of fiberization (or fibrillation), and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0155] The conductive material is included to provide electrode conductivity (e.g., electrical conductivity), and any suitable electrically conductive material may be used as the conductive material unless it causes chemical changes (e.g., undesirable chemical changes in a rechargeable lithium battery). Examples of the conductive material may be: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials in the form of metal powder and / or metal fiber such as copper, nickel, aluminum, silver, etc.; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0156] The negative electrode current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal (eg, an electrically conductive material), and combinations thereof, but is not limited thereto.

[0157] Electrolyte

[0158] The electrolyte for a rechargeable lithium battery includes a non-aqueous organic solvent and a lithium salt.

[0159] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0160] The non-aqueous organic solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent or a combination thereof.

[0161] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC) and / or butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, valerolactone and / or caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran and / or tetrahydrofuran, etc. Ketone solvents may include cyclohexanone. Alcohol solvents may include ethanol and / or isopropanol, etc., and aprotic solvents may include: nitriles, such as R-CN (wherein R is a C2 to C20 linear, branched or cyclic hydrocarbon group, and may include a double bond, an aromatic ring or an ether group); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane and / or 1,4-dioxolane; and / or cyclopentane sulfone; etc.

[0162] The nonaqueous organic solvent may be used alone or as a mixture of two or more.

[0163] In some embodiments, if a carbonate-based solvent is used, a cyclic carbonate and a linear carbonate may be mixed together and used, and the cyclic carbonate and the linear carbonate may be mixed together in a volume ratio of about 1:1 to about 1:9.

[0164] The lithium salt dissolved in the organic solvent supplies lithium ions in the battery, enables the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts may include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are integers from 1 to 20), one or more of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(bisoxalato)phosphate (LiDFOB) and lithium bis(oxalato)borate (LiBOB).

[0165] Diaphragm

[0166] Depending on the type of battery, the rechargeable lithium battery may further include a separator between the negative electrode and the positive electrode. Examples of suitable separator materials include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof, such as polyethylene / polypropylene double-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators.

[0167] The separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof on one or both surfaces (eg, two opposing surfaces) of the porous substrate.

[0168] The porous substrate can be a polymer film formed from any one selected from the following: polyolefins (such as polyethylene and / or polypropylene), polyesters (such as polyethylene terephthalate or polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, polymers of Teflon (tetrafluoroethylene) and polytetrafluoroethylene, or copolymers or mixtures of two or more thereof.

[0169] The organic material may include a polyvinylidene fluoride-based polymer and / or a (meth)acrylic-based polymer.

[0170] The inorganic material may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but is not limited thereto.

[0171] An organic material and an inorganic material may be mixed together in one coating layer, or a coating layer including an organic material and a coating layer including an inorganic material may be stacked.

[0172] Rechargeable lithium battery

[0173] The accompanying drawings show cross-sectional perspective views of rechargeable lithium batteries according to some embodiments of the present invention. Referring to the accompanying drawings, the rechargeable lithium battery 100 includes an electrode assembly having a separator 30 between a positive electrode 10 and a negative electrode 20 and a housing 50 in which the electrode assembly is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. As shown in the accompanying drawings, the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50.

[0174] The rechargeable lithium battery according to some embodiments may be applied to various suitable types (or kinds) of batteries, such as a cylindrical battery, a prismatic battery, and a pouch-type battery, and the present disclosure is not limited thereto.

[0175] Hereinafter, aspects of embodiments of the present disclosure are illustrated in more detail with reference to examples. However, these examples are not restrictive, and therefore, the present disclosure is not limited thereto.

[0176] Examples and comparative examples

[0177] Examples 1 to 5 and Comparative Examples 1 to 3

[0178] (1) Fabrication of positive electrode

[0179] Positive electrode slurry was prepared by dispersing a positive electrode active material, a binder, a crosslinking agent and a conductive material in N-methyl-2-pyrrolidone according to the composition in Table 1. The positive electrode slurry was coated on an aluminum foil having a thickness of 12 μm, and then dried and pressed to manufacture a positive electrode.

[0180] (2) Manufacturing of rechargeable lithium battery cells

[0181] A coin half-cell was fabricated using a positive electrode and a lithium metal counter electrode as a counter electrode. A separator made of a porous polyethylene film (thickness: about 16 μm) was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected. The electrolyte was a solution including 1.1 M LiPF6 dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed together in a volume ratio of 3:5.

[0182] Table 1 (Unit: wt%)

[0183]

[0184] The materials used in Table 1 are as follows.

[0185] (A) Positive electrode active material

[0186] A-1: LiNi 0.94 Co 0.045 Al 0.015 O2(D50:13μm)

[0187] (B) Adhesive

[0188] B-1: A hydrogenated nitrile rubber derivative including a structural unit represented by Chemical Formula I-1 (Mw: 160,000 g / mol)

[0189] Chemical formula I-1

[0190]

[0191] In Chemical Formula I-1, a to d are each independently an integer of 1 to 20.

[0192] B-2: Hydrogenated nitrile rubber including a structural unit represented by Chemical Formula II-1 (Mw: 131,770 g / mol to 151,677 g / mol)

[0193] Chemical formula II-1

[0194]

[0195] In Chemical Formula II-1, R is CH3; e, f and g are each independently an integer of 1 to 20.

[0196] B-3: polyvinylidene fluoride including a structural unit represented by Chemical Formula IV (Mw: 685,000 g / mol to 1,100,000 g / mol)

[0197] Chemical formula IV

[0198]

[0199] (C) Cross-linking agent

[0200] C-1: A mixture of the following three carbodiimide compounds

[0201]

[0202]

[0203] (D) Conductive materials

[0204] D-1: Carbon black

[0205] Evaluation example

[0206] The evaluation results of the examples and comparative examples are shown in Table 2.

[0207] Evaluation Example 1: Adhesion Strength (Peel Strength) of Positive Electrode

[0208] The positive electrode was cut into a size of 25 mm × 120 mm to prepare 20 samples. A double-sided tape was adhered to a glass substrate at room temperature, the positive electrode plate was attached to the double-sided tape, and after rolling it, one end of the positive electrode plate was folded 180° and then stretched at 1.5 mm / sec in the opposite direction of the one end to measure the force applied thereto.

[0209] The evaluation results are shown in Table 2. The force measurements of 20 samples were averaged to obtain the peel strength.

[0210] Evaluation Example 2: Resistance of positive electrode mixture layer

[0211] A 46-pin electrode resistance meter is placed on the positive electrode, and a constant current is generated by selecting the output current and selecting the voltage range. Then, the 46-pin voltage is measured, the composite layer, interface, and current collector of the positive electrode are regarded as three-layer resistors, and the composite layer resistance and interface resistance are calculated by dual parameter fitting calculation.

[0212] Evaluation Example 3: Cycle life (capacity retention rate) of rechargeable lithium battery cells

[0213] Compared with lithium metal, the rechargeable lithium battery cell was charged and discharged 100 times at a constant current of 0.5C in a voltage range of 2.8V to 4.25V at 25°C. Room temperature charge / discharge measurement was used to evaluate the capacity and charge / discharge efficiency, and the results are shown in Table 2. On the other hand, the capacity retention rate was calculated according to Equation 1.

[0214] Equation 1

[0215] Capacity retention rate [%] = [discharge capacity at the 100th cycle / discharge capacity at the 1st cycle] × 100

[0216] Table 2

[0217]

[0218] Summarize

[0219] The positive electrodes of Examples 1 to 5 use a minimum amount of polyvinylidene fluoride-based positive electrode binder or completely replace the polyvinylidene fluoride-based positive electrode binder with the first binder to reduce resistance while increasing the adhesion strength of the positive electrode, thereby increasing the cycle life of the rechargeable lithium battery.

[0220] While the disclosure has been described in connection with what are presently considered to be practical example embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and equivalents thereof.

[0221] Description of the symbol

[0222] 100: Rechargeable lithium battery

[0223] 10: Positive electrode

[0224] 20: Negative electrode

[0225] 30: Diaphragm

[0226] 50: Shell

[0227] 60: Sealing component.

Claims

1. A positive electrode for a rechargeable lithium battery, the positive electrode include: a positive electrode current collector and a positive electrode mixture layer, the positive electrode mixture layer being on the positive electrode current collector, wherein the positive electrode mixture layer comprises a positive electrode active material and a first binder, and The first binder includes a hydrogenated nitrile rubber derivative.

2. The positive electrode according to claim 1, in: The first binder comprises: A repeating unit having an acrylonitrile-derived structure represented by Chemical Formula 1; A repeating unit including at least one of the repeating units having a hydrogenated butadiene-derived structure represented by one of Chemical Formula 2 and Chemical Formula 3; and The repeating unit represented by chemical formula 4: Chemical formula 1 Chemical formula 2 Chemical formula 3 Chemical formula 4 Among them, in chemical formula 4, R 1 and R 2 are independently substituted or unsubstituted C1 to C20 alkyl, ester, cyano, pyrrolidone, carboxyl, caprolactam, morpholine, hydroxyl, amino, vinyl, epoxy or thiol, wherein the ester is -COOR, wherein R is a substituted or unsubstituted C1 to C20 alkyl, cyano is -CN, and the pyrrolidone is -C 3 H 5 NHCO, carboxyl is -COOH, caprolactam is -NCOC 5 H 10 , morpholinyl is -NC 4 H 8 O, hydroxyl is -OH, amino is -NH 2 , vinyl is -CH=CH 2 , the epoxy group is -COCH 2 , the thiol group is -SH.

3. The positive electrode according to claim 1, in: The first binder is included in an amount of greater than or equal to 0.1 wt % and less than or equal to 5 wt % based on the total amount of the positive electrode mixture layer.

4. The positive electrode according to claim 1, in: The positive electrode mixture layer further includes a second binder, and The second binder includes hydrogenated nitrile rubber.

5. The positive electrode according to claim 4, in: The second binder comprises: a repeating unit having an acrylonitrile-derived structure represented by Chemical Formula 5; a repeating unit including at least one of an alkylene repeating unit represented by Chemical Formula 6 and a repeating unit having a hydrogenated butadiene-derived structure represented by Chemical Formula 7; and The repeating unit represented by Chemical Formula 8: Chemical formula 5 Chemical formula 6 Chemical formula 7 Chemical formula 8 Among them, in chemical formula 8, R 3 is a substituted or unsubstituted C1 to C20 alkyl, ester, cyano, pyrrolidone, carboxyl, caprolactam, morpholine, hydroxyl, amino, vinyl, epoxy or thiol group, wherein the ester group is -COOR, wherein R is a substituted or unsubstituted C1 to C20 alkyl, cyano is -CN, and the pyrrolidone is -C 3 H 5 NHCO, carboxyl is -COOH, caprolactam is -NCOC 5 H 10 , morpholinyl is -NC 4 H 8 O, hydroxyl is -OH, amino is -NH 2 , vinyl is -CH=CH 2 , the epoxy group is -COCH 2 , the thiol group is -SH.

6. The positive electrode according to claim 4, in: The second binder is included in an amount greater than 0 wt % and less than or equal to 5 wt % based on the total amount of the positive electrode mixture layer.

7. The positive electrode according to claim 1, in: The positive electrode mixture layer further includes a third binder, and The third binder includes polyvinylidene fluoride, a derivative of polyvinylidene fluoride, a copolymer including polyvinylidene fluoride, or a combination thereof.

8. The positive electrode according to claim 7, in: The third binder includes a repeating unit having a vinylidene fluoride-derived structure represented by Chemical Formula 9: Chemical formula 9 9. The positive electrode according to claim 8, in: The third binder further includes a repeating unit including at least one of a repeating unit having a vinylidene fluoride derivative-derived structure represented by Chemical Formula 10 and a repeating unit having a hexafluoropropylene-derived structure represented by Chemical Formula 11: Chemical formula 10 Chemical formula 11 10. The positive electrode according to claim 7, in: The third binder is included in an amount greater than 0 wt % and less than or equal to 3 wt % based on the total amount of the positive electrode mixture layer.

11. The positive electrode according to claim 1, in: The positive electrode mixture layer further includes a fourth binder, and The fourth binder includes poly(meth)acrylic acid, poly(meth)acrylate, polyacrylonitrile, acrylonitrile-styrene-butadiene copolymer or a combination thereof.

12. The positive electrode according to claim 11, in: The fourth binder is included in an amount of greater than 0 wt % and less than or equal to 3 wt % based on the total amount of the positive electrode mixture layer.

13. The positive electrode according to claim 1, in: The positive electrode mixture layer further includes a cross-linking agent.

14. The positive electrode according to claim 13, in: The cross-linking agent is a cross-linking agent of carbodiimide compound series.

15. The positive electrode according to claim 14, in: The cross-linking agent is represented by Chemical Formula 12: Chemical formula 12 Among them, in chemical formula 12, R 4 and R 5 are independently substituted or unsubstituted C1 to C20 alkyl, substituted or unsubstituted C3 to C20 cycloalkyl, substituted or unsubstituted C6 to C20 aryl, or substituted or unsubstituted C2 to C20 heteroaryl including at least one selected from N, O, S and P; L 1 and L 2 are each independently a substituted or unsubstituted C1 to C20 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C2 to C20 heteroarylene group including at least one selected from N, O, S and P; and z is an integer of 1-20.

16. The positive electrode according to claim 13, in: The cross-linking agent is included in an amount of greater than 0 wt % and less than or equal to 3 wt % based on the total amount of the positive electrode mixture layer.

17. The positive electrode according to claim 1, in: The positive electrode mixture layer further includes a conductive material.

18. The positive electrode according to claim 17, in: The conductive material is included in an amount of greater than 0 wt % and less than or equal to 5 wt % based on the total amount of the positive electrode mixture layer.

19. A rechargeable lithium battery comprising the positive electrode according to claim 1.

Images