KR102499796B1 - Positive electrode slurry composition for secondary battery, and positive electrode for secondary battery and lithium secondary battery including the same - Google Patents

Abstract

The present invention is a lithium transition metal oxide containing nickel; and a copolymer binder comprising a polyvinylidene fluoride moiety and a polychlorotrifluoroethylene moiety, wherein the polychlorotrifluoroethylene fraction is present in the copolymer binder in an amount of 1.4 mol % to 1.4 mol%. It relates to a positive electrode slurry composition containing 4.7 mol%, and a positive electrode and a lithium secondary battery including the same.

Description

Positive electrode slurry composition for secondary battery, positive electrode for secondary battery and lithium secondary battery comprising the same

The present invention relates to a positive electrode slurry composition for a secondary battery, a positive electrode for a secondary battery and a lithium secondary battery comprising the positive electrode slurry composition.

As the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Batteries have been commercialized and are widely used.

An electrode of a lithium secondary battery is manufactured by mixing a positive electrode active material or negative electrode active material and a binder resin component, dispersing them in a solvent to form a slurry, applying the slurry to the surface of an electrode current collector, and forming a mixture layer after drying.

As the cathode active material, a lithium-containing cobalt oxide such as LiCoO ₂ of a layered structure, a lithium-containing nickel oxide such as LiNiO ₂ of a layered structure, and a lithium-containing manganese oxide such as LiMn ₂ O ₄ of a spinel crystal structure etc. are being used.

Among them, LiCoO ₂ is widely used due to its excellent physical properties such as excellent cycle characteristics, but has low safety, is expensive due to resource limitations of cobalt as a raw material, and has limitations in mass use as a power source in fields such as electric vehicles. In addition, LiNiO ₂ exhibits battery characteristics of relatively low cost and high discharge capacity, but a rapid phase transition of the crystal structure appears according to the volume change accompanying the charge and discharge cycle, and stability is rapidly deteriorated when exposed to air and moisture. There is a problem. On the other hand, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have the advantage of using resource-rich and environmentally friendly manganese as a raw material, but have a small capacity and poor high-temperature characteristics and cycle characteristics.

In order to solve these problems, attempts and studies have been conducted to use a lithium transition metal oxide mixed with nickel-cobalt-manganese as a positive electrode active material. A cathode active material prepared by mixing nickel, cobalt, and manganese has an advantage in that various physical properties are improved compared to a battery manufactured using each transition metal separately.

However, in the case of the lithium transition metal oxide in which the nickel-cobalt-manganese is mixed, stability is deteriorated when exposed to moisture in the air due to nickel. Specifically, moisture in the air and nickel in nickel-cobalt-manganese react to generate a hydroxyl group. In addition, the generated hydroxy group reacts with a binder typically included in a positive electrode slurry composition to cause gelation. When the binder is gelated, the viscosity of the positive electrode slurry composition also rises rapidly, thereby reducing the uniformity of the positive electrode active material layer, resulting in a decrease in the electrode and the adhesion between the electrodes, and causing problems such as non-expression of cell capacity and reduced output.

Therefore, when using a lithium transition metal oxide containing a ternary transition metal of nickel-cobalt-manganese, it is required to improve resistance to moisture. To this end, a cathode slurry containing a binder that is not affected by the reaction between nickel and moisture Development of the composition is required.

Korean Patent Publication No. 2016-0039835

In order to solve the above problems, a first technical problem of the present invention is to provide a positive electrode slurry composition capable of preventing deterioration in the electrochemical performance of a battery by suppressing gelation of a binder due to moisture in the air.

A second technical problem of the present invention is to provide a cathode for a lithium secondary battery comprising the cathode slurry composition.

A third technical problem of the present invention is to provide a lithium secondary battery including the cathode for the lithium secondary battery.

The present invention is a lithium transition metal oxide containing nickel; and a copolymer binder comprising a polyvinylidene fluoride moiety and a polychlorotrifluoroethylene moiety, wherein the polychlorotrifluoroethylene fraction is present in the copolymer binder in an amount of 1.4 mol % to 1.4 mol%. It provides a positive electrode slurry composition containing 4.7 mol%.

In addition, the present invention provides a positive electrode for a lithium secondary battery including a positive electrode current collector and the positive electrode slurry composition applied to at least one surface of the positive electrode current collector.

In addition, the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

The cathode active material composition according to the present invention includes a copolymer binder containing a polyvinylidene fluoride (PVDF) moiety and a polychlorotrifluoroethylene (PCTFE) moiety, thereby forming lithium containing nickel. Gelation of the copolymer binder may be prevented even when the transition metal oxide is included. Accordingly, when an electrode is manufactured with the cathode slurry containing the copolymer binder, it is possible to exhibit more stable electrochemical performance by maintaining adhesion by suppressing the decrease in electrode uniformity, and thus it can be usefully used in the manufacture of a lithium secondary battery. .

1 is a graph showing changes in viscosity over time in a 100% humidity environment of positive electrode slurry compositions prepared by Examples 1-1 and 2-1 of the present invention and Comparative Example 1-1.
2 is a graph showing the discharge capacity according to the C-rate of the secondary batteries manufactured by Examples 1-2 and 2-2 and Comparative Examples 1-2 and 2-2 of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Anode Slurry Composition

A cathode slurry composition according to an embodiment of the present invention includes a lithium transition metal oxide containing nickel; and a copolymer binder comprising a polyvinylidene fluoride (PVDF) moiety and a poly chlorotrifluoroethylene (PCTFE) moiety.

The positive electrode slurry composition includes a copolymer binder including a polyvinylidene fluoride (PVDF) moiety and a polychlorotrifluoroethylene (PCTFE) moiety, so that conventional polyvinylidene fluoride (PVDF) It is possible to prevent gelation of the binder that occurs when using alone. That is, even when nickel included in the lithium transition metal oxide containing nickel reacts with moisture in the air to form a hydroxyl group and increases the pH of the positive electrode slurry composition, polychlorotrifluoroethylene included in the copolymer binder (PCTFE) fraction prevents interaction with the hydroxy groups so that gelation of the copolymer binder does not occur. In addition, gelation of the positive electrode slurry composition including the copolymer binder does not occur, and when the electrode is manufactured using this, the uniformity of the electrode is improved, so that the electrochemical performance of the secondary battery can be improved.

For example, the copolymer binder may be one in which the polychlorotrifluoroethylene (PCTFE) block is bonded to a main chain made of polyvinylidene fluoride (PVDF), but is not limited thereto.

For example, when a copolymer binder containing a PVDF fraction and a PCTFE fraction is used alone, as described above, when heterogeneous binders of different types are simply mixed and used, the binder partially aggregates due to the binding properties of the binder. this can happen When applied to the positive electrode current collector, the uniformity of the electrode may be deteriorated due to aggregation of the binder.

A polychlorotrifluoroethylene (PCTFE) fraction may be included in the copolymer binder in an amount of 1.4 mol% to 4.7 mol%.

For example, 95.3 to 98.6 mol% of the polyvinylidene fluoride (PVDF) fraction: polychlorotrifluoroethylene (PCTFE) fraction in the copolymer binder: 1.4 to 4.7 mol%, preferably 95.5 to 97.5 mol% : It may be included in a molar ratio of 2.5 to 4.5 mol%. For example, when the molar ratio of the polyvinylidene fluoride (PVDF) fraction to the polychlorotrifluoroethylene (PCTFE) fraction satisfies the above range, a copolymer binder including the polyvinylidene fluoride (PVDF) fraction may exhibit appropriate adhesive strength, and thus When a positive electrode for a lithium secondary battery and a lithium secondary battery are prepared using the positive electrode slurry composition comprising the above, more stable electrochemical performance can be exhibited.

On the other hand, since the molar ratio of the polyvinylidene fluoride (PVDF) fraction to the polychlorotrifluoroethylene (PCTFE) fraction is outside the above range, the polychlorotrifluoroethylene (PCTFE) fraction in the copolymer binder is 4.7 mol%. When included in an excessive amount, the resistance of the anode manufactured using the same may excessively increase, and output characteristics and rate characteristics may be deteriorated. In addition, when the polychlorotrifluoroethylene (PCTFE) fraction is included in less than 1.4 mol% in the copolymer binder, it may be impossible to manufacture a positive electrode using the same due to insufficient adhesive strength, and deterioration is accelerated during cycling at high temperatures, resulting in high temperature Cycle life characteristics may deteriorate.

The copolymer binder according to the present invention may have a weight average molecular weight of 100,000 to 1,000,000, more preferably 400,000 to 900,000. When the weight average molecular weight of the copolymer-based binder is 100,000 or less, the adhesive effect between the electrode layer and the current collector is lowered, and the electrode layer may be separated from the current collector during charge and discharge cycles, and there is a risk of lifespan reduction due to this, and the weight of the copolymer-based binder When the average molecular weight is 1,000,000 or more, the resistance of the electrode layer increases, resulting in inferior output characteristics and shifting the phase stability of the slurry to a high elastic region, thereby degrading the uniformity of electrode quality. At this time, the weight average molecular weight can be measured using gel permeation chromatography (GPC). For example, after preparing a sample sample of a certain concentration, the GPC measuring instrument is stabilized. When the instrument is stabilized, a standard sample and a sample sample are injected into the instrument to obtain a chromatogram, and then the molecular weight is calculated according to the analysis method.

The method for preparing the copolymer binder is not particularly limited as long as it is a method conventionally used for preparing the copolymer binder, but may be prepared according to, for example, a suspension polymerization method, an emulsion polymerization method, or a seed polymerization method.

The copolymer binder may be prepared by polymerizing a binder composition including a PVDF fraction and a PCTFE fraction and, if necessary, one or more other components such as a polymerization initiator, a crosslinking agent, a buffer, a molecular weight modifier, and an emulsifier.

The polymerization temperature and polymerization time may be appropriately determined depending on the polymerization method or the type of polymerization initiator. For example, the polymerization temperature may be 50 to 300° C., and the polymerization time may be 1 to 20 hours, but is not particularly limited.

Inorganic or organic peroxides may be used as the polymerization initiator, and examples thereof include water-soluble initiators including potassium persulfate, sodium persulfate and ammonium persulfate, and oil-soluble initiators including cumene hydroperoxide and benzoyl peroxide. can On the other hand, an activator may be used together to accelerate the initiation reaction of the polymerization initiator, and the activator is selected from the group consisting of sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate and dextrose 1 or more types are mentioned.

The crosslinking agent may be used to promote crosslinking of the copolymer binder, for example, amines such as diethylenetriamine, triethylenetetramine, diethylaminopropylamine, xylene diamine, isophorone diamine, and dodecyl succinic acid. Acid anhydrides such as dodecyl succinic anhydride and phthalic anhydride, polyamide resin, polysulfide resin, phenolic resin, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate Latex, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, trimethylol propane trimethacrylate, trimethylol methane triacrylate, glycy Dill methacrylate etc. are mentioned. Meanwhile, a grafting agent may be used together, and examples thereof include aryl methacrylate (AMA), triaryl isocyanurate (TAIC), triaryl amine (TAA), and diaryl amine (DAA).

Examples of the buffer include NaHCO ₃ , NaOH, or NH ₄ OH.

Examples of the molecular weight modifier include mercaptans or terpins such as terbinolene, dipentene, and t-terpiene, and halogenated hydrocarbons such as chloroform and carbon tetrachloride.

The emulsifier may be an anionic emulsifier, a nonionic emulsifier, or both, and when the nonionic emulsifier is used together with the anionic emulsifier, in addition to the electrostatic stabilization of the anionic emulsifier, additional colloidal form through van der Waals force of the polymer particles stabilization can be provided.

Examples of the anionic emulsifier include phosphate, carboxylate, sulfate, succinate, sulfosuccinate, sulfonate, or disulfonate emulsifiers, but are not particularly limited. Sodium alkyl sulfate, sodium polyoxyethylene sulfate, sodium lauryl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium lauryl sulfate, sodium alkyl sulfonate, sodium alkyl ether sulfonate, sodium alkylbenzene sulfonate, Sodium linear alkylbenzene sulfonate, sodium alpha-olefin sulfonate, sodium alcohol polyoxyethylene ether sulfonate, sodium dioctylsulfosuccinate, sodium perfluorooctanesulfonate, sodium perfluorobutanesulfonate, alkyldiphenyloxide disulfonate, sodium dioctyl sulfosuccinate, sodium alkyl-aryl phosphate, sodium alkyl ether phosphate, or sodium lauroyl sarcosinate.

Examples of the nonionic emulsifier include ester-type, ether-type, and ester-ether type emulsifiers, which are not particularly limited, but are specifically polyoxyethylene glycol, polyoxyethylene glycol methyl ether, polyoxyethylene monoallyl ether, and polyoxyethylene glycol. Oxyethylene bisphenol-A ether, polypropylene glycol, polyoxyethylene neopentyl ether, polyoxyethylene cetyl ether, polyoxyethylene lauryl ether, polyoxyethyl oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene decyl Ether and polyoxyethylene octyl ether are mentioned.

In addition, the lithium transition metal oxide containing nickel included in the positive electrode slurry composition according to the present invention is lithium-nickel-based oxide, lithium-nickel-manganese-based oxide, lithium-nickel-cobalt-based oxide, and lithium-nickel-manganese -It may be selected from the group consisting of cobalt-based oxides, specifically Li _{1 +x} (Ni _a Co _b Mn _c ) _{1- x} O ₂ (0<a<1, 0<b<1, 0<c<1 , -0.3≤x≤0.3, and a+b+c=1), Li(Ni _d Co _e Mn _f )O ₄ (0<d<2, 0<e<2, 0<f<2, d+ e+f=2), Li _g NiO ₂ (0.5<g<1.3), LiNi _{1 - h} M _h O ₂ (M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, and 0≤h <1), LiMn _{2 - y} Ni _y O ₄ (0 < y < 2), and LiMn _{2 - z} Co _z O ₄ (0 < Z < 2).

Preferably, the lithium transition metal oxide is represented by Formula 1 below, and may include a lithium transition metal oxide having a nickel content of 50% or more, 60% or more, and preferably 80% or more. [Formula 1]

Li _1+x (Ni _a Co _b Mn _c ) _1-x O ₂

In Formula 1,

-0.3≤x≤0.3, 0.5≤a<1, 0<b≤0.3, 0<c≤0.3, and a+b+c=1.

As described above, when the lithium transition metal oxide having a nickel content of 50% or more is used as the lithium transition metal oxide, it exhibits high capacity characteristics, while as the nickel content of the lithium transition metal oxide increases, the reaction of nickel with moisture in the air The production of hydroxyl groups may also be increased. Accordingly, as the content of nickel in the lithium transition metal oxide increases, gelation of the composition for forming a cathode including the nickel may be accelerated.

Therefore, as a binder, a polyvinylidene fluoride (PVDF) moiety and a polychlorotrifluoroethylene (PCTFE) moiety capable of suppressing the reaction of nickel included in the lithium transition metal oxide with moisture in the air ) By adding a copolymer binder containing hydroxy groups, it is possible to prevent gelation of the composition for forming a cathode due to generation of hydroxyl groups.

The positive electrode slurry composition may be prepared by a conventional method known in the art. For example, it may be prepared by mixing and stirring the lithium transition metal oxide containing nickel as a cathode active material, the copolymer binder according to the present invention, a solvent, and optionally a conductive material and/or a dispersant.

For example, the positive electrode slurry composition may include 85% to 99.6% by weight of lithium transition metal oxide, 0.1% to 10% by weight of a conductive material, and 0.1% to 5% by weight of a copolymer binder, based on the total weight of the total solid content. Preferably, 70 to 99.7% by weight of lithium transition metal oxide, specifically 84 to 99% by weight, 0.01 to 10% by weight of conductive material, specifically 0.1 to 5% by weight, and 1 to 4% by weight of copolymer binder may be included. .

Solvents included in the positive electrode slurry composition include organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, and dimethyl acetamide, or water, and these solvents are used alone or at least one The above may be mixed and used. The amount of solvent used is sufficient to dissolve and disperse the positive electrode active material, the copolymer binder, and the conductive material in consideration of the coating thickness and manufacturing yield of the slurry.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and includes, for example, a material having point-shaped, linear, or plate-shaped conductivity. For example, graphite, such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

The dispersant may optionally be used as an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone, if necessary.

The positive electrode slurry composition according to the present invention has a solid content of 50% to 80% by weight, preferably 60% to 70% by weight, more preferably 65% to 70% by weight based on the total weight of the positive electrode slurry composition can For example, when the positive electrode slurry composition has a solid content of 50% to 80% by weight based on the total weight of the positive electrode slurry composition, when the solid content of the positive electrode slurry composition is less than 50% by weight based on the total weight of the positive electrode slurry composition , It is not possible to manufacture a thick electrode having a predetermined thickness or more, and when manufacturing a thick electrode, the number of current collectors must be increased, so there is a concern about cost increase during cell manufacturing. Conversely, when the solid content of the positive electrode slurry composition exceeds 80% by weight based on the total weight of the positive electrode slurry composition, it is difficult to uniformly coat the slurry composition on the current collector, so separate equipment is used to disperse it on the current collector, Alternatively, since it must be transferred to a current collector after coating on another support, this also has a risk of cost increase.

The positive electrode slurry composition according to the present invention may be prepared in the air, and the lithium transition metal oxide containing nickel contained in the positive electrode slurry composition reacts with moisture contained in the air to form a hydroxyl group and increase the pH Even if the above-described copolymer binder is included, gelation of the positive electrode slurry composition may be suppressed, and accordingly, the viscosity of the positive electrode slurry composition may not increase.

Specifically, the viscosity of the cathode slurry composition immediately after preparing the cathode slurry by mixing the lithium transition metal oxide, the copolymer binder, and the conductive material is 1,500 to 20,000 cP, preferably 3,000 cP to 10,000 cP, more preferably 3,000 cP to 4,000 cP.

In addition, the positive electrode slurry composition has a viscosity of 1,500 to 20,000 cP, preferably 3,000 cP to 10,000 after being left for 24 hours in a harsh environment with a relative humidity of 30% or more, 50% or more, specifically, a relative humidity of 80% to 100%. cP, more preferably 3,000 cP to 4,000 cP. At this time, the viscosity is measured at 12 rpm at 25 ° C using a Brookfield B-type viscometer.

That is, even when the positive electrode slurry composition according to the present invention is prepared and left in a harsh environment with a relative humidity of 80% or more, specifically, a relative humidity of 80% to 100% for 24 hours or more, compared with immediately after preparation of the positive electrode slurry composition Therefore, since the viscosity hardly increases, the positive electrode layer can maintain a more uniform state when manufacturing the positive electrode using this, so that problems such as decrease in positive electrode capacity and output can be prevented.

The environment with a relative humidity of 80% or more means an environment in which the relative humidity is 80% or more regardless of a specific temperature, as long as the temperature is generally allowed in the process of preparing the positive electrode slurry composition. For example, the relative humidity may be a relative humidity measured at a typical cathode slurry composition manufacturing temperature, and the temperature may be room temperature, specifically 25°C.

Anode for secondary battery

Meanwhile, the present invention provides a positive electrode for a lithium secondary battery including a positive electrode current collector and the positive electrode slurry composition coated on at least one surface of the positive electrode current collector.

The positive current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, conductive polymer, carbon coated paper, and fired carbon. Alternatively, aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, conductive polymer, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, nonwoven fabrics, wires, and pins.

The positive electrode may be prepared according to a conventional positive electrode manufacturing method except for using the positive electrode active material slurry composition. Specifically, it may be prepared by applying (coating) the above-described positive electrode slurry composition on a positive electrode current collector, followed by drying and rolling. For example, drying of the electrode may be performed in a temperature range of 60 °C to 130 °C.

Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, and then laminating a film obtained by peeling from the support on a positive electrode current collector.

lithium secondary battery

In addition, the present invention can manufacture an electrochemical device including the anode. The electrochemical device may be specifically a battery, a capacitor, and the like, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, it is formed on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the anode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and undoping lithium, such as SiO _β (0 < β < 2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; or a composite including the metallic compound and the carbonaceous material, such as a Si—C composite or a Sn—C composite, and any one or a mixture of two or more of these may be used. In addition, a metal lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low crystalline carbon, and high crystalline carbon includes amorphous, platy, scaly, spherical or fibrous natural graphite, artificial graphite, or kish graphite. graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is representative.

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

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

As an example, the negative electrode active material layer may be formed by applying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, a binder, and a conductive material in a solvent on a negative electrode current collector and drying the composition, or by separately applying the composition for forming the negative electrode active material layer. It may also be produced by casting on a support, and then laminating a film obtained by peeling from the support on a negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ion movement, and any separator used as a separator in a lithium secondary battery can be used without particular limitation, especially for the movement of ions in the electrolyte. It is preferable to have low resistance to the electrolyte and excellent ability to absorb the electrolyte. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single layer or multilayer structure.

In addition, the electrolyte used in the present invention includes organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, and are limited to these. it is not going to be

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, PC) and other carbonate-based solvents; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane or the like may be used. Among them, carbonate-based solvents are preferred, and cyclic carbonates (eg, ethylene carbonate or propylene carbonate, etc.) having high ion conductivity and high dielectric constant capable of increasing the charge and discharge performance of batteries, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO _{4 , LiAlCl 4 ,} LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) _{2 .} LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the above electrolyte components, the electrolyte may include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and triglycerides for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicles such as hybrid electric vehicles (HEVs).

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

The battery module or battery pack may include a power tool; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for one or more medium or large-sized devices among power storage systems.

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

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

Hereinafter, examples will be described in detail to explain the present invention in detail. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Example 1-1: Preparation of positive electrode slurry composition

A cathode slurry composition was prepared by adding 97 g of Li(Ni _0.8 Co _0.1 Mn _0.1 )O ₂ , 2 g of a PVDF-PCTFE copolymer containing a CTFE fraction of 2.5 mol%, and 1 g of carbon black as a conductive material to NMP as a solvent.

Example 2-1: Preparation of positive electrode slurry composition

A binder and a positive electrode slurry composition including the same were prepared in the same manner as in Example 1, except that the PVDF-PCTFE copolymer containing a CTFE fraction of 4.5 mol% was used.

Comparative Example 1-1: Preparation of positive electrode slurry composition

A positive electrode slurry composition was prepared in the same manner as in Example 1, except that only 2 g of PVDF was included as a binder.

Comparative Example 2-1: Preparation of cathode slurry composition

A binder and a positive electrode slurry composition including the same were prepared in the same manner as in Example 1, except that a PVDF-PCTFE copolymer containing a CTFE fraction of 15 mol% was used.

Comparative Example 3-1: Preparation of positive electrode slurry composition

A positive electrode slurry composition was prepared in the same manner as in Example 1, except that PVDF and a PVDF-CTFE copolymer containing a CTFE fraction of 15 mol% were included as a binder in a weight ratio of 1:1.

Comparative Example 4-1: Preparation of positive electrode slurry composition

A binder and a positive electrode slurry composition including the same were prepared in the same manner as in Example 1, except that the PVDF-PCTFE copolymer containing a CTFE fraction of 0.1 mol% was used.

Comparative Example 5-1: Preparation of positive electrode slurry composition

A binder and a positive electrode slurry composition including the same were prepared in the same manner as in Example 1, except that the PVDF-PCTFE copolymer containing a CTFE fraction of 5 mol% was used.

Example 1-2: Preparation of secondary battery

The positive electrode slurry composition prepared in Example 1-1 was applied to a positive electrode current collector (Al thin film) having a thickness of 15 μm, dried, and then roll pressed to prepare a positive electrode.

Meanwhile, a negative electrode slurry composition was prepared by mixing natural graphite as an anode active material, sodium carboxylmethylcellulose as a binder, and carbon black as a conductive material in an amount of 96.25 : 2.75 : 1% by weight, respectively, together with water as a solvent. The negative electrode slurry composition was applied to a negative electrode current collector (Cu thin film) having a thickness of 20 μm, dried, and then roll pressed to prepare a negative electrode.

An electrode assembly was prepared by laminating the positive and negative electrodes prepared above together with a polyethylene separator, and then putting them into a battery case, mixing EC:DMC in a ratio of 1:3, and injecting an electrolyte solution containing 1M LiPF ₆ to form a lithium secondary battery. was manufactured.

Example 2-2: Manufacturing of Secondary Battery

A positive electrode and a secondary battery including the same were prepared in the same manner as in Example 1-2, except that the positive electrode slurry composition prepared in Example 2-1 was used.

Comparative Example 1-2: Preparation of secondary battery

A positive electrode and a secondary battery including the same were prepared in the same manner as in Example 1-2, except that the positive electrode slurry composition prepared in Comparative Example 1-1 was used.

Comparative Example 2-2: Preparation of secondary battery

A positive electrode and a secondary battery including the same were prepared in the same manner as in Example 1-2, except that the positive electrode slurry composition prepared in Comparative Example 2-1 was used.

Comparative Example 3-2: Preparation of secondary battery

A positive electrode and a secondary battery including the same were prepared in the same manner as in Example 1-2, except that the positive electrode slurry composition prepared in Comparative Example 3-1 was used.

Comparative Example 4-2: Preparation of secondary battery

A positive electrode and a secondary battery including the same were prepared in the same manner as in Example 1-2, except that the positive electrode slurry composition prepared in Comparative Example 4-1 was used.

Comparative Example 5-2: Preparation of secondary battery

A positive electrode and a secondary battery including the same were prepared in the same manner as in Example 1-2, except that the positive electrode slurry composition prepared in Comparative Example 5-1 was used.

Experimental Example 1: Viscosity measurement of cathode slurry composition

Immediately after preparation of the positive electrode slurry compositions prepared in Examples 1-1 and 2-1 and Comparative Examples 1-1 to 5-1, the change in viscosity over time in an environment of 100% relative humidity was measured by Brookfield's type B After each measurement at 25 ° C. and 12 rpm using a viscometer, they are shown in Table 1 and FIG. 1 below.

Initial Viscosity (cP) 24 hours elapsed (cP) Point of 100% increase in viscosity Example 1-1 3,500 3,500 50+ hours Example 2-1 3,850 3,550 50+ hours Comparative Example 1-1 3,700 not measurable 5 hours Comparative Example 2-1 3,600 3,700 50+ hours Comparative Example 3-1 3,550 4,450 50+ hours Comparative Example 4-1 3,700 7,000 26 hours Comparative Example 5-1 3,400 3,500 50+ hours

Referring to Table 1 and FIG. 1, the positive electrode slurry composition of Example 1-1 had an initial viscosity of 3,500 cP immediately after preparation, and 3,500 cP when 24 hours elapsed after preparation in a harsh environment of 100% relative humidity. , The positive electrode slurry composition of Example 2-1 had an initial viscosity of 3,850 cP immediately after preparation, and 3,550 cP when 24 hours elapsed after preparation in a harsh environment of 100% relative humidity. Therefore, Examples 1-1 and 2 It was confirmed that all of the positive electrode slurry compositions of -1 did not cause a rapid increase in viscosity or gelation problem for 24 hours even in a humid environment. In addition, it was confirmed that the viscosity of the positive electrode slurry compositions of Examples 1-1 and 2-1 did not change even after 50 hours had elapsed.

However, the positive electrode slurry composition of Comparative Example 1-1 had an initial viscosity of 3,700 cP immediately after preparation, but the viscosity increased by 100% 5 hours after preparation in a harsh environment of 100% relative humidity, and after preparation of the positive electrode slurry composition When 24 hours elapsed, it gelled and the viscosity could not be measured. Therefore, it was confirmed that if the positive electrode slurry composition of Comparative Example 1-1 using PVDF as a binder is not used immediately after preparation, humidity control is essential, otherwise it loses its function as a positive electrode slurry composition.

On the other hand, the positive electrode slurry compositions of Comparative Examples 2-1 and 5-1 were able to maintain viscosity at a level similar to that of Examples 1-1 and 2-1 as the content of the CTFE fraction exceeded 4.7 mol%.

However, in the case of the positive electrode active material slurry composition prepared in Comparative Example 4-1, as the content of the CTFE fraction was relatively small, it was confirmed that the viscosity maintaining effect of the positive electrode active material slurry due to the inclusion of CTFE was insignificant.

In addition, in the case of the positive electrode active material slurry composition including heterogeneous binders of Comparative Example 3-1, the content of PVDF in the slurry was relatively high and the content of the CTFE fraction was relatively low compared to Examples 1-2 and 2-2. Since a relatively small amount of the CTFE fraction was included in the entire positive electrode active material slurry composition, it was confirmed that the viscosity improvement effect of the positive electrode active material slurry due to the inclusion of CTFE was insignificant.

Experimental example 2: Measurement of discharge capacity

For each of the lithium secondary batteries prepared in Examples 1-2 and 2-2 and Comparative Examples 1-2 to 5-2, first, the charge/discharge current density was set to 0.2C, and the charge end voltage was set to 4.2V (Li/Li ⁺ ), and the discharge end voltage was set to 2.5V (Li/Li ⁺ ), and the charge/discharge test was performed twice. Then, after measuring the discharge capacity by setting the charging current density to 0.2C and the discharging current density to 0.4C, the capacity ratio was obtained by dividing by the second discharging capacity, and then regarded as 0.4C discharging capacity (%), and the results are shown in Table 2 below. and shown in FIG. 2 .

In addition, 0.8C discharge capacity and 1.2C discharge capacity were measured in the same manner as in the above method except that the discharge current density was changed to 0.8C and 1.2C, respectively, and are shown in Table 2 below.

0.4C discharge capacity (%) 0.8C discharge capacity (%) 1.2C discharge capacity (%) Example 1-2 100 96.34 93.99 Example 2-2 100 96.39 93.95 Comparative Example 1-2 100 96.54 94.22 Comparative Example 2-2 100 94.43 90.78 Comparative Example 3-2 100 89.22 83.78 Comparative Example 4-2 100 96.71 93.91 Comparative Example 5-2 100 94.84 91.63

As shown in Table 2 and FIG. 2, in the case of the secondary batteries of Examples 1-2 and 2-2 according to the present invention, excellent discharge capacity equivalent to that of the conventionally used lithium secondary battery of Comparative Example 1-2. It could be confirmed that the However, in the case of Comparative Examples 2-2 and 5-2, compared to Comparative Example 1-2 and Examples 1-2 and 2-2, it was confirmed that the performance was inferior by about 2 to 3%, which is It was determined that the resistance of the anode increased as the content of CTFE increased, and thus the output characteristics deteriorated.

On the other hand, in the case of Comparative Example 3-1, partial gelation of the positive electrode active material slurry composition may occur due to a relatively lower content of the CTFE fraction in the positive electrode active material slurry. In addition, since heterogeneous binders are included, aggregation of the binder may occur during the electrode manufacturing process, and when manufacturing the electrode using this, the uniformity of the electrode quality after coating is lowered, and it is judged that the output characteristics are deteriorated accordingly. It became.

In the case of Comparative Example 4-2, since the content of PVDF in the positive electrode slurry was relatively high, it was confirmed that excellent discharge capacity was exhibited.

In the case of Comparative Examples 1-2 and 4-2, as shown in Experimental Example 2, excellent discharge capacity and / or rate characteristics are exhibited, but this is when a lithium secondary battery is used immediately after preparing the positive electrode slurry composition, As judged in Experimental Example 1, gelation of the cathode slurry compositions prepared in Comparative Examples 1-1, 3-1, and 4-1 occurred in an environment where time elapsed after preparation or relative humidity was excessively high, resulting in lithium using the same. It was determined that the production of secondary batteries (Comparative Examples 1-2, 3-2 and 4-2) would be impossible.

Claims (10)

lithium transition metal oxides containing nickel; and
A copolymer binder comprising a polyvinylidene fluoride moiety and a polychlorotrifluoroethylene moiety;
A cathode slurry composition comprising 2.5 mol% to 4.5 mol% of a polychlorotrifluoroethylene fraction in the copolymer binder.
According to claim 1,
The copolymer binder has a weight average molecular weight of 100,000 to 1,000,000, a positive electrode slurry composition.
According to claim 1,
The positive electrode slurry composition further comprises a conductive material.
According to claim 3,
The positive electrode slurry composition includes 85% to 99.6% by weight of the lithium transition metal oxide, 0.1% to 10% by weight of the conductive material, and 0.1% to 5% by weight of the copolymer binder, based on the total weight of the total solid content , the positive electrode slurry composition.
According to claim 1,
The lithium transition metal oxide is a positive electrode slurry composition represented by Formula 1 below:
[Formula 1]
Li _1+x (Ni _a Co _b Mn _c ) _1-x O ₂
In Formula 1,
-0.3≤x≤0.3, 0.5≤a<1, 0<b≤0.3, 0<c≤0.3, and a+b+c=1.
According to claim 1,
The positive electrode slurry composition has a solid content of 50% to 80% by weight based on the total weight of the positive electrode slurry composition.
According to claim 1,
The positive electrode slurry composition has a viscosity of 1,500 to 20,000 cP.
According to claim 1,
The positive electrode slurry composition having a viscosity of 1,500 to 20,000 cP after leaving the positive electrode slurry composition for 24 hours in an environment of 30% or more relative humidity.
positive current collector, and
A positive electrode for a lithium secondary battery comprising the positive electrode slurry composition according to any one of claims 1 to 8 applied to at least one surface of the positive electrode current collector.
A lithium secondary battery comprising the cathode for a lithium secondary battery according to claim 9.

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