Composition for manufacturing cathode, cathode for secondary battery, and secondary battery

Abstract

A cathode for a secondary battery, according to an embodiment of the present disclosure, comprises: a cathode current collector; and a cathode mixture layer, which is formed on at least one surface of the cathode current collector and includes a cathode active material and a polymer, wherein the polymer comprises a vinylidene-based polymer including a halogen element, and the crystallinity of the polymer is 10-60%.

Description

Composition for manufacturing anode, anode for secondary battery and secondary battery

[0001] Embodiments of the present disclosure relate to a composition for manufacturing a positive electrode, a positive electrode for a secondary battery, and a secondary battery.

[0002] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, are being commercialized and widely used.

[0003] Furthermore, with growing concern for environmental issues, research is being conducted on electric vehicles (EVs) and hybrid electric vehicles (HEVs) as alternatives to fossil fuel-powered vehicles, such as gasoline and diesel vehicles, a major source of air pollution. Lithium secondary batteries, which boast high energy density, high discharge voltage, and stable output, are primarily being studied and used as power sources for these EVs and HEVs.

[0004] These lithium secondary batteries are generally manufactured by stacking or winding positive and negative electrodes with a separator between them, and then embedding them in a secondary battery case together with an electrolyte.

[0005] At this time, the electrode is manufactured by applying an electrode active material slurry, which is manufactured by mixing an electrode mixture composed of an electrode active material, a conductive material, and a binder for adhering the electrode active material to the metal current collector, in an organic solvent, and then drying and rolling the electrode.

[0006] Afterwards, the electrode is rolled into a roll shape and vacuum dried using hot air supplied into the chamber. The temperature of the hot air used is considered for the purpose of removing residual solvent and moisture, and is generally performed under various temperature conditions considering the composition of the active material of the electrode and the thickness of the electrode mixture layer.

[0007] Meanwhile, the binder included in the electrode mixture layer may mainly be a crystalline polymer, particularly polyvinylidene fluoride (PVDF) as a binder for the positive electrode. This binder plays a role in binding active material particles to each other and maintaining adhesiveness at the interface between the electrode mixture layer including the active material particles and the current collector. However, the crystalline polymer has a problem in that the physical properties of the electrode mixture layer change depending on the temperature conditions in the vacuum drying process, which may also result in a deterioration in secondary battery performance.

[0008] Therefore, research on new cathodes that can prevent performance degradation of secondary batteries is required.

[0009] Embodiments of the present disclosure provide a composition for manufacturing a positive electrode capable of preventing expansion of the positive electrode, a positive electrode for a secondary battery, and a secondary battery.

[0010] A secondary battery according to an embodiment of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and solar and wind power generation using batteries.

[0011] A positive electrode for a secondary battery according to an embodiment of the present disclosure comprises: a positive electrode current collector; and a positive electrode composite layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material and a polymer; wherein the polymer includes a vinylidene polymer including a halogen element, and the crystallinity of the polymer is 10 to 60%.

[0012] In one embodiment, the polymer may comprise a polyvinylidene fluoride (PVDF) polymer.

[0013] In one embodiment, the anode may include a plasticizer.

[0014] In one embodiment, the molecular weight of the plasticizer may be from 200 g / mol to 500 g / mol.

[0015] In one embodiment, the plasticizer may include at least one selected from the group consisting of acetyltributyl citrate, dibutyl sebacate, diisooctyl azelate, triethyl citrate, glyceryl triacetate, dioctyl adipate, and polyethylene glycol.

[0016] A composition for manufacturing a positive electrode according to an embodiment of the present disclosure comprises a positive electrode active material, a polymer and a plasticizer, wherein the polymer comprises a vinylidene polymer containing a halogen element, and the plasticizer has a molecular weight of 200 g / mol to 500 g / mol.

[0017] In one embodiment, the polymer may include a polyvinylidene fluoride (PVDF) polymer.

[0018] In one embodiment, the plasticizer may be included in an amount of 0.1 wt% to 1 wt% based on the total solid content of the composition for manufacturing the anode.

[0019] In one embodiment, the composition for manufacturing the anode may further comprise an organic solvent.

[0020] In one embodiment, the plasticizer may be soluble in the organic solvent.

[0021] In one embodiment, the plasticizer may include at least one selected from the group consisting of acetyltributyl citrate, dibutyl sebacate, diisooctyl azelate, triethyl citrate, glyceryl triacetate, dioctyl adipate, and polyethylene glycol.

[0022] A secondary battery according to an embodiment of the present disclosure comprises a positive electrode; and a negative electrode; wherein the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material and a polymer, wherein the polymer comprises a vinylidene polymer containing a halogen element, and the crystallinity of the polymer is 10 to 60%.

[0023] In one embodiment, the polymer may comprise a polyvinylidene fluoride (PVDF) polymer.

[0024] In one embodiment, the anode may include a plasticizer.

[0025] In one embodiment, the plasticizer may include at least one selected from the group consisting of acetyltributyl citrate, dibutyl sebacate, diisooctyl azelate, triethyl citrate, glyceryl triacetate, dioctyl adipate, and polyethylene glycol.

[0026] In one embodiment, the secondary battery may further include a separator interposed between the positive electrode and the negative electrode.

[0027] According to the present disclosure, a composition for manufacturing a positive electrode capable of preventing expansion of the positive electrode, a positive electrode for a secondary battery, and a secondary battery are provided.

[0028] In addition, according to the present disclosure, a composition for manufacturing a positive electrode capable of improving the adhesive strength of a positive electrode mixture layer, a positive electrode for a secondary battery, and a secondary battery are provided.

[0029] FIG. 1 is a drawing for explaining the structure of a polyvinylidene fluoride (PVDF) polymer included in a positive electrode for a secondary battery according to an embodiment of the present disclosure.

[0030] The structural or functional descriptions of the embodiments disclosed in this specification or application are merely illustrative for the purpose of explaining embodiments according to the technical idea of ​​the present invention, and the embodiments according to the technical idea of ​​the present invention may be implemented in various forms other than the embodiments disclosed in this specification or application, and the technical idea of ​​the present invention is not construed as being limited to the embodiments described in this specification or application.

[0031] Cathode for secondary batteries

[0032] In one aspect of the present disclosure, a positive electrode for a secondary battery is provided, comprising: a positive electrode current collector; and a positive electrode composite layer formed on at least one surface of the positive electrode current collector and including a positive electrode active material and a polymer; wherein the polymer includes a vinylidene polymer including a halogen element, and the crystallinity of the polymer is 10 to 60%.

[0033] Hereinafter, each component of the positive electrode for a secondary battery provided in one aspect of the present disclosure will be described in detail.

[0034] First, the positive electrode for a secondary battery provided in one aspect of the present disclosure includes a positive electrode current collector.

[0035] The positive electrode current collector may comprise stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also comprise aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector may have a thickness of, but is not limited to, 10 μm to 50 μm, for example.

[0036] Next, the cathode for a secondary battery provided in one aspect of the present disclosure includes a cathode composite layer.

[0037] The positive electrode composite layer is formed on at least one surface of the positive electrode current collector.

[0038] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0039] According to exemplary embodiments, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0040] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1.

[0041] [Chemical Formula 1]

[0042] Li x Ni a M b O 2+z

[0043] In Chemical Formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0044] The chemical structure represented by Chemical Formula 1 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn can serve as the main active element of the positive electrode active material together with Ni. Chemical Formula 1 is provided to express the bonding relationship of the above main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0045] In one embodiment, in addition to the main active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered structure / crystal structure. The auxiliary elements may be incorporated into the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0046] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, for example, Al.

[0047] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1-1.

[0048] [Chemical Formula 1-1]

[0049] Li x Ni a M1 b1 M2 b2 O 2+z

[0050] In Chemical Formula 1, M1 may include Co, Mn, and / or Al. M2 may include the auxiliary elements described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, -0.5≤z≤0.1 may be satisfied.

[0051] The above-described positive electrode active material may further include a coating element or doping element. For example, elements substantially identical to or similar to the above-described auxiliary elements may be used as the coating element or doping element. For example, the above-described elements may be used singly or in combination of two or more.

[0052] The above coating element or doping element may be present on the surface of the lithium-nickel metal oxide particle, or may penetrate through the surface of the lithium-nickel metal composite oxide particle and be included in the bonding structure represented by the above chemical formula 1 or chemical formula 1-1.

[0053] The above positive electrode active material may include a nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0054] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by employing a high-content (High-Ni) composition as described above in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0055] However, as the Ni content increases, the long-term storage stability and lifespan stability of the cathode or secondary battery may relatively deteriorate, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, the inclusion of Co can maintain electrical conductivity, while the inclusion of Mn can improve lifespan stability and capacity retention characteristics.

[0056] The content of Ni (e.g., the mole fraction of nickel among the total moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0057] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0058] In some embodiments, the positive electrode active material may include, for example, a Mn-rich active material, a Li-rich layered oxide (LLO) / over lithiated oxide (OLO) active material, or a Co-less active material having a chemical structure or crystal structure represented by Chemical Formula 2.

[0059] [Chemical Formula 2]

[0060] p[Li2MnO3]·(1-p)[Li q JO2]

[0061] In chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0062] Additionally, the positive electrode composite layer comprises a polymer (which can be used as a binder). In an embodiment, the polymer may be a vinylidene polymer comprising a halogen element, wherein the halogen element may be a fluorine element, a chlorine element, a bromine element, an iodine element, and specifically, a fluorine element.

[0063] In one embodiment, the polymer may be a polyvinylidene fluoride (PVDF)-based polymer. The polyvinylidene fluoride (PVDF)-based polymer may include, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), polyvinylidene fluoride-tetrafluoroethylene (PVDF-TFE), and polyvinylidene fluoride-chlorofluoroethylene (PVDF-CTFE).

[0064] In an embodiment, the crystallinity of the polymer may be 60% or less, specifically 55% or less, more specifically 50% or less, and most specifically 40% or less. When the crystallinity of the polymer is within the above-described range, expansion of the positive electrode can be effectively suppressed, and adhesive performance within the electrode can be improved. In addition, the crystallinity of the polymer may be 10% or more, specifically 20% or more, more specifically 30% or more, more specifically 40% or more, and most specifically 45% or more. When the crystallinity of the polymer is within the above-described range, expansion of the positive electrode can be effectively suppressed, and adhesive performance within the electrode can be improved. In addition, the resistance of the electrode can be controlled within an appropriate level.

[0065] In an embodiment, the anode may include a plasticizer, and specifically, the polymer described above may include a plasticizer. In an embodiment, a vinylidene polymer (specifically, a PVDF polymer) including a halogen element may include a plurality of PVDF polymer chains, and a plasticizer may penetrate between the vinylidene polymer chains including a halogen element, as shown in FIG. 1. As the plasticizer penetrates between the vinylidene polymer chains including a halogen element, the attractive force between the chains becomes weaker, and at the same time, the free volume increases, so that a space in which the polymer chains can move can be secured. The vinylidene polymer including a halogen element may have a crystallinity controlled within the above-described range by including a plasticizer.

[0066] In an embodiment, the molecular weight of the plasticizer may be from 200 g / mol to 500 g / mol. When the molecular weight of the plasticizer is within the above-described range, the plasticizer can easily penetrate between polymer chains.

[0067] For example, the plasticizer may include, but is not limited to, one or more selected from the group consisting of Acetyltributyl citrate (ATBC), Dibutyl sebacate (DBS), Diisooctyl azelate (DOZ), Triethyl citrate (TEC), Glyceryl triacetate (GTA), Dioctyl adipate (DOA), and Polyethylene glycol (PEG).

[0068] In an embodiment, the degree of expansion of the positive electrode for a secondary battery provided in one aspect of the present disclosure may be 0.48% or less, more specifically 0.42% or less, even more specifically 0.37% or less, and most specifically 0.32% or less.

[0069] In addition, in the embodiment, as the crystallinity of the vinylidene polymer including a halogen element that can be used as a binder is controlled to an appropriate level, the adhesion of the positive electrode mixture layer to the positive electrode current collector can also be improved. For example, the adhesion of the positive electrode mixture layer to the positive electrode current collector can be 0.42 N or more, specifically 0.45 N or more, more specifically 0.5 N or more, and most specifically 0.55 N or more.

[0070] That is, by controlling the crystallinity of a vinylidene polymer containing a halogen element, which is a binder included in a positive electrode for a secondary battery, using a plasticizer, not only can expansion of the positive electrode for a secondary battery be suppressed, but also the adhesive strength between the positive electrode current collector and the positive electrode composite layer can be improved.

[0071] In an embodiment, the cathode for a secondary battery provided in one aspect of the present disclosure may further include a conductive material. The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the cathode mixture layer. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0072] Composition for manufacturing anode

[0073] In another aspect of the present disclosure, a composition for manufacturing a positive electrode is provided, which comprises a positive electrode active material, a polymer, and a plasticizer, wherein the polymer comprises a vinylidene polymer containing a halogen element, and the plasticizer has a molecular weight of 200 g / mol to 500 g / mol.

[0074] Hereinafter, each component of the composition for manufacturing anode provided in another aspect of the present disclosure will be described in detail.

[0075] First, the composition for manufacturing a positive electrode provided in another aspect of the present disclosure includes a positive electrode active material. As described above, the positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions. Specific details regarding the positive electrode active material will not be described in detail.

[0076] Next, in another aspect of the present disclosure, a composition for manufacturing a positive electrode is provided, which comprises a polymer that can be used as a binder, wherein the polymer is as described above.

[0077] Specifically, the polymer may include a vinylidene polymer containing a halogen element, and more specifically, a polyvinylidene fluoride (PVDF) polymer may be included as a binder in the composition for manufacturing an anode. The polyvinylidene fluoride (PVDF) polymer may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), polyvinylidene fluoride-tetrafluoroethylene (PVDF-TFE), and polyvinylidene fluoride-chlorofluoroethylene (PVDF-CTFE), as described above.

[0078] Next, a composition for manufacturing a cathode provided in another aspect of the present disclosure includes a plasticizer. The plasticizer may have a molecular weight of 200 g / mol to 500 g / mol. When the molecular weight of the plasticizer is within the above-described range, the plasticizer can easily penetrate between polymer chains.

[0079] As described above, the plasticizer may include, but is not limited to, one or more selected from the group consisting of Acetyltributyl citrate (ATBC), Dibutyl sebacate (DBS), Diisooctyl azelate (DOZ), Triethyl citrate (TEC), Glyceryl triacetate (GTA), Dioctyl adipate (DOA), and Polyethylene glycol (PEG).

[0080] In an embodiment, the plasticizer may be included in an amount of 0.1 wt% to 1 wt% based on the total solid content of the composition for manufacturing the positive electrode, more specifically 0.15 wt% to 0.7 wt%, even more specifically 0.25 wt% to 0.55 wt%, and most specifically 0.35 wt% to 0.45 wt%. When the content of the plasticizer is within the above-described range, expansion of the positive electrode can be effectively suppressed.

[0081] In addition, the composition for manufacturing a cathode provided in another aspect of the present disclosure may further include an organic solvent. In an embodiment, the plasticizer may be soluble in the organic solvent. For example, the organic solvent may be, but is not limited to, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like.

[0082] In addition, the composition for manufacturing a positive electrode provided in another aspect of the present disclosure may further include a conductive material. The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the positive electrode mixture layer. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0083] In an embodiment, the conductive material may be included in an amount of 0.01 to 10 wt% based on the total solid content of the composition for manufacturing the anode, and specifically, may be included in an amount of 0.1 wt% or more or 0.3 wt% or more, and may be included in an amount of 5 wt% or less, 3 wt% or less, or 1 wt% or less.

[0084] In addition, the composition for manufacturing an anode provided in another aspect of the present disclosure may further include a thickener and / or a dispersant, etc., as needed. In one embodiment, the composition for manufacturing an anode may include a thickener such as carboxymethyl cellulose (CMC).

[0085] In an embodiment, the above-described secondary battery positive electrode can be manufactured by coating the positive electrode manufacturing composition provided in another aspect of the present disclosure on a positive electrode current collector. More specifically, the positive electrode manufacturing composition provided in another aspect of the present disclosure can be coated on a positive electrode current collector, and then dried and rolled to form a positive electrode mixture layer on the positive electrode current collector, thereby manufacturing a secondary battery positive electrode. The coating process can be performed by a method such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., but is not limited thereto.

[0086] The crystallinity of a vinylidene polymer (specifically, a PVDF polymer) containing a halogen element used as a binder in the above-described positive electrode manufacturing process and the secondary battery manufacturing process described below can be increased. However, according to the present disclosure, by including an appropriate plasticizer in the composition for positive electrode manufacturing or the positive electrode for a secondary battery, the increase in the crystallinity of the vinylidene polymer (specifically, a PVDF polymer) containing a halogen element can be controlled, and thus, a positive electrode for a secondary battery having a crystallinity within an appropriate range can be ultimately obtained.

[0087] secondary batteries

[0088] In another aspect of the present disclosure, a secondary battery is provided, comprising: a positive electrode; a negative electrode; and a separator interposed between the positive electrode and the negative electrode; wherein the positive electrode comprises: a positive electrode current collector; and a positive electrode composite layer formed on at least one surface of the positive electrode current collector and including a positive electrode active material and a polyvinylidene fluoride (PVDF) polymer having a crystallinity of 60% or less.

[0089] Hereinafter, the secondary battery provided in another aspect of the present disclosure will be described in detail for each configuration.

[0090] First, a secondary battery provided in another aspect of the present disclosure includes a positive electrode. As described above, the positive electrode includes a positive electrode current collector and a positive electrode composite layer. The positive electrode composite layer includes an active material and a polymer, wherein the polymer may include a vinylidene polymer containing a halogen element, and the polymer has a crystallinity of 10 to 60% or less.

[0091] In another aspect of the present disclosure, the positive electrode included in the secondary battery is applicable to all of the contents of the positive electrode for the secondary battery described above, and thus will not be described again.

[0092] Next, in another aspect of the present disclosure, a secondary battery is provided that includes a negative electrode.

[0093] The negative electrode may include a negative electrode current collector and a negative electrode composite layer disposed on at least one surface of the negative electrode current collector.

[0094] Non-limiting examples of the negative electrode current collector include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and a polymer substrate coated with a conductive metal. The negative electrode current collector may have a thickness of, but is not limited to, 10 μm to 50 μm.

[0095] The negative electrode composite layer may include a negative electrode active material. A material capable of adsorbing and desorbing lithium ions may be used as the negative electrode active material. For example, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber; lithium metal; lithium alloy; a silicon (Si)-containing material, or a tin (Sn)-containing material.

[0096] Examples of the above amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0097] Examples of the above crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0098] The lithium metal may be pure lithium metal or lithium metal with a protective layer formed thereon to suppress dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector may be used as the negative electrode active material layer. In one embodiment, a lithium thin film layer may also be used as the negative electrode active material layer.

[0099] Elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0100] The above silicon-containing material can provide increased capacity characteristics. The above silicon-containing material is Si, SiO x (0 <x<2), 금속 도핑된 SiO x (0 <x<2), 실리콘-탄소 복합체 등을 포함할 수 있다. 상기 금속은 리튬 및 / 또는 마그네슘을 포함할 수 있으며, 금속 도핑된 SiO x (0 <x<2)는 금속 실리케이트를 포함할 수 있다.

[0101] The cathode composite layer may include the aforementioned materials that can be used as a binder, a conductive agent, and a thickener in the manufacture of the cathode. In some embodiments, a styrene-butadiene rubber (SBR)-based binder, a carboxymethyl cellulose (CMC)-based binder, a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene, PEDOT)-based binder, or the like may be used as the cathode binder.

[0102] Next, in another aspect of the present disclosure, a secondary battery is provided that includes a separator.

[0103] A separator may be interposed between the anode and cathode. The separator may be configured to prevent electrical short-circuiting between the anode and cathode and to allow ion flow. Depending on the embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0104] For example, the separator may include a porous polymer film or a porous nonwoven fabric. The porous polymer film may include a polyolefin polymer, such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. The porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, or the like. The separator may also include a ceramic material. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0105] The separator may have a single-layer or multi-layer structure including the above-described polymer film and / or non-woven fabric.

[0106] According to exemplary embodiments, an electrode assembly may be formed by repeatedly arranging a positive electrode, a negative electrode, and a separator. In some embodiments, the electrode assembly may be of a winding type, a stacking type, a z-folding type, or a stack-folding type.

[0107] Additionally, a secondary battery provided in another aspect of the present disclosure may further include an electrolyte. In an embodiment, a secondary battery provided in another aspect of the present disclosure may be defined as having the electrode assembly described above housed within an outer case and an electrolyte therein. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0108] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - is expressed as and the anion of the lithium salt (X - ) as F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2- , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples include:

[0109] The organic solvent may include an organic compound that has sufficient solubility for the lithium salt and additive and does not exhibit reactivity within the battery. For example, the organic solvent may include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, and an aprotic solvent.Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methylacetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, Tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite can be used. These can be used alone or in combination of two or more.

[0110] The above non-aqueous electrolyte may further include an additive. The additive may include, for example, a cyclic carbonate compound, a fluorine-substituted carbonate compound, a sultone compound, a cyclic sulfate compound, a cyclic sulfite compound, a phosphate compound, and a borate compound.

[0111] The above cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0112] The above fluorine-substituted cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0113] The above sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0114] The above cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0115] The above cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc.

[0116] The above phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0117] The above borate compound may include lithium bis(oxalate) borate, etc.

[0118] In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte described above. In this case, the lithium secondary battery may be manufactured in the form of an all-solid-state battery. Furthermore, a solid electrolyte layer may be disposed between the positive and negative electrodes instead of the separator described above. Here, the solid electrolyte may include a polymer electrolyte, a sulfide-based electrolyte, an oxide-based electrolyte, or a gel polymer electrolyte.

[0119] The above solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte is Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (m, n are positive numbers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , (p, q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), Li 7-x PS 6-x I x (0≤x≤2) etc. These can be used alone or in combination of two or more.

[0120] In one embodiment, the solid electrolyte may include an oxide-based amorphous solid electrolyte, such as, for example, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0121] Hereinafter, embodiments of the present invention will be further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and technical idea of ​​the present invention, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0122] <Example 1> - Manufacturing of anode 1

[0123] LiNi 0.8 Co 0.1 Mn 0.1 A composition for manufacturing a cathode was prepared by adding 0297.9 wt%, carbon nanotubes 0.5 wt%, PVDF 1.5 wt%, and acetyltributyl citrate 0.1 wt% to NMP (N-methyl-2-pyrrolidone), a solvent.

[0124] The composition for manufacturing the anode described above was applied to an aluminum (Al) thin film, which is a cathode current collector, with a thickness of about 20 μm, dried to manufacture the cathode, and then roll pressed to manufacture the cathode.

[0125] The width of the manufactured positive electrode was cut to a small width, and the positive electrode plate cut to a small width was notched into the shape of the battery to be actually used.

[0126] Afterwards, the temperature was gradually increased to 140°C, which is a temperature between the Tc and Tm of PVDF, in a vacuum drying furnace for about 60 minutes, maintained at a temperature of 150°C for 120 minutes, and then gradually decreased to room temperature for 20 minutes to dry, thereby manufacturing a cathode for a secondary battery.

[0127] <Example 2> - Manufacturing of the anode 2

[0128] LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode was manufactured in the same manner as in Example 1, except that a composition for manufacturing a positive electrode was manufactured by adding 0297.8 wt%, carbon nanotubes 0.5 wt%, PVDF 1.5 wt%, and acetyltributyl citrate 0.2 wt% to NMP (N-methyl-2-pyrrolidone), a solvent.

[0129] <Example 3> - Manufacturing of the anode 3

[0130] LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode was manufactured in the same manner as in Example 1, except that a composition for manufacturing a positive electrode was manufactured by adding 0297.7 wt%, 0.5 wt% of carbon nanotubes, 1.5 wt% of PVDF, and 0.3 wt% of acetyltributyl citrate to NMP (N-methyl-2-pyrrolidone), a solvent.

[0131] <Example 4> - Manufacturing of the anode 4

[0132] LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode was manufactured in the same manner as in Example 1, except that a composition for manufacturing a positive electrode was manufactured by adding 0297.6 wt%, carbon nanotubes 0.5 wt%, PVDF 1.5 wt%, and acetyltributyl citrate 0.4 wt% to NMP (N-methyl-2-pyrrolidone), a solvent.

[0133] <Example 5> - Manufacturing of the anode 5

[0134] LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode was manufactured in the same manner as in Example 1, except that a composition for manufacturing a positive electrode was manufactured by adding 0297.5 wt%, carbon nanotubes 0.5 wt%, PVDF 1.5 wt%, and acetyltributyl citrate 0.5 wt% to NMP (N-methyl-2-pyrrolidone), a solvent.

[0135] <Example 6> - Manufacturing of the anode 6

[0136] LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode was manufactured in the same manner as in Example 1, except that a composition for manufacturing a positive electrode was manufactured by adding 0297.4 wt%, carbon nanotubes 0.5 wt%, PVDF 1.5 wt%, and acetyltributyl citrate 0.6 wt% to NMP (N-methyl-2-pyrrolidone), a solvent.

[0137] <Comparison Example 1>

[0138] LiNi 0.8 Co 0.1 Mn 0.1 An anode was manufactured in the same manner as in Example 1, except that a composition for manufacturing an anode was manufactured by adding 0298.0 wt%, carbon nanotubes 0.5 wt%, and PVDF 1.5 wt% to NMP (N-methyl-2-pyrrolidone), a solvent.

[0139] <Comparison Example 2>

[0140] LiNi 0.8 Co 0.1 Mn 0.1A positive electrode was manufactured in the same manner as in Example 1, except that a composition for manufacturing a positive electrode was manufactured by adding 0296.5 wt%, carbon nanotubes 0.5 wt%, PVDF 1.5 wt%, and acetyltributyl citrate 1.5 wt% to NMP (N-methyl-2-pyrrolidone), a solvent.

[0141] <Experimental Example 1> - Confirming the crystallinity of PVDF

[0142] The crystallinity of PVDF, the binder of Examples 1 to 6 and Comparative Examples 1 and 2, was measured using the DSC method. Specifically, the crystallinity was calculated by dividing the area value of the Heat of fusion that appears due to crystallization after the DSC measurement of the sample by the Heat of fusion value of 100% crystallinity of PVDF theoretically (6.70 kJ / mol). Additionally, the crystallinity can be calculated and cross-validated using XRD and WAXS methods. The measured crystallinity of PVDF of Examples 1 to 6 and Comparative Examples 1 and 2 is shown in Table 1.

[0143] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 2 Plasticizer addition ratio (%) 0 0.1 0.2 0.3 0.4 0.5 0.6 1.5 PVDF crystallinity (%) 6 0.2 4 5 6.5 2 5 3.0 4 4 9 0 8 4 6.2 4 2.3 6 38 4 1 0.0

[0144] As can be seen in Table 1, as the content of plasticizer in the composition for manufacturing the anode increased, the crystallinity of PVDF decreased. In other words, Experimental Example 1 confirms that the crystallinity of the PVDF polymer used as a binder can be controlled by adjusting the content of plasticizer.

[0145] <Experimental Example 2> - Bipolar Performance Experiment

[0146] First, the degree of expansion of the anodes of Examples 1 to 6 and Comparative Examples 1 and 2 was measured through an automatic method using a microscope (taking a picture of one vertex of the electrode, moving the microscope from there to the other vertex, and measuring the distance moved), and a length measurement method using a loupe and a ruler as a gauge. Specifically, the width and length of the anode before and after vacuum drying were measured to calculate the amount of change, and since the measurement results showed that the amount of change in the length of the anode was greater, the degree of expansion was compared based on the length of the anode.

[0147] In addition, the electrodes were cut into an area of ​​25㎠ and the adhesive strength of Examples 1 to 6, Comparative Examples 1 and 2 was measured using the method of ASTM D4541.

[0148] In addition, the cells produced with each electrode of Examples 1 to 6 and Comparative Examples 1 and 2 were set to SOC50, and after applying 1 C discharge current for 10 seconds, d(Voltage) / current was calculated to measure the direct current internal resistance (DCIR).

[0149] The measured anode expansion, adhesion, and DC internal resistance are shown in Table 2 below.

[0150] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 2 Degree of anode expansion (%) 0.1 0.08 0.06 0.04 0.02 0.04 0.05 0.1 Adhesive force (N) 0.4 0.44 0.48 0.51 0.59 0.52 0.43 0.3 DCIR (mohm) 1.2 1.21 1.22 1.23 1.24 1.26 1.28 1.4

[0151] As shown in Table 2, it can be confirmed that the degree of anode expansion was reduced in Examples 1 to 6, in which the crystallinity of PVDF was controlled to 10 to 60% by adding a plasticizer, compared to Comparative Examples 1 and 2. In addition, it can be confirmed through Table 2 that the adhesion of the anode was improved in Examples 1 to 6, in which the crystallinity of PVDF was controlled to 10 to 60% by adding a plasticizer, compared to Comparative Examples 1 and 2. In addition, looking at Table 2, it can be seen that as the amount of plasticizer added increased, the DC internal resistance of the anode increased.

[0152] In summary, by controlling the crystallinity of a vinylidene polymer (specifically PVDF) containing a halogen element to 10 to 60% through the addition of a plasticizer, a secondary battery positive electrode can be provided that suppresses positive electrode expansion, improves the adhesive strength of the positive electrode, and has low DC internal resistance of the positive electrode.

[0153] According to the present disclosure, a composition for manufacturing a positive electrode capable of preventing expansion of a positive electrode, a positive electrode for a secondary battery, and a secondary battery are provided, and a composition for manufacturing a positive electrode capable of improving the adhesiveness of a positive electrode mixture layer, a positive electrode for a secondary battery, and a secondary battery are provided.

Claims

1. Anode current collector; and A positive electrode composite layer is disposed on at least one surface of the positive electrode current collector and includes a positive electrode active material and a polymer; The above polymer comprises a vinylidene polymer containing a halogen element, A cathode for a secondary battery, wherein the crystallinity of the polymer is 10 to 60%.

2. In paragraph 1, the polymer, A cathode for a secondary battery comprising a polyvinylidene fluoride (PVDF) polymer.

3. In paragraph 1, the anode, A cathode for a secondary battery containing a plasticizer.

4. In the third paragraph, the molecular weight of the plasticizer is A cathode for a secondary battery having a density of 200 g / mol to 500 g / mol.

5. In paragraph 4, the plasticizer is, A cathode for a secondary battery comprising at least one selected from the group consisting of acetyltributyl citrate, dibutyl sebacate, diisooctyl azelate, triethyl citrate, glyceryl triacetate, dioctyl adipate, and polyethylene glycol.

6. Containing a positive electrode active material, a polymer and a plasticizer; The above polymer comprises a vinylidene polymer containing a halogen element, A composition for manufacturing an anode, wherein the molecular weight of the plasticizer is 200 g / mol to 500 g / mol.

7. In paragraph 6, the polymer, A composition for manufacturing an anode comprising a polyvinylidene fluoride (PVDF) polymer.

8. In paragraph 6, the plasticizer is, A composition for manufacturing an anode, comprising 0.1 wt% to 1 wt% of the total solid content of the composition for manufacturing an anode.

9. In paragraph 6, A composition for manufacturing an anode further comprising an organic solvent.

10. In paragraph 9, the plasticizer is, A composition for manufacturing an anode that is soluble in the above organic solvent.

11. In paragraph 6, the plasticizer is, A composition for manufacturing an anode, comprising at least one selected from the group consisting of acetyltributyl citrate, dibutyl sebacate, diisooctyl azelate, triethyl citrate, glyceryl triacetate, dioctyl adipate, and polyethylene glycol.

12. Bipolar; and Containing a cathode; The above anode is, Bipolar collector and A positive electrode composite layer is disposed on at least one surface of the positive electrode current collector and includes a positive electrode active material and a polymer, The above polymer comprises a vinylidene polymer containing a halogen element, A secondary battery wherein the crystallinity of the polymer is 10 to 60%.

13. In paragraph 12, the polymer, A secondary battery containing a polyvinylidene fluoride (PVDF) polymer.

14. In paragraph 12, The above positive electrode is a secondary battery containing a plasticizer.

15. In paragraph 14, the plasticizer is, A secondary battery comprising at least one selected from the group consisting of acetyltributyl citrate, dibutyl sebacate, diisooctyl azelate, triethyl citrate, glyceryl triacetate, dioctyl adipate, and polyethylene glycol.

16. In paragraph 12, A secondary battery further comprising a separator interposed between the positive and negative electrodes.

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