KR20190089385A - Negative electrode for rechargeable lithium battery and rechargeable lithium battery including the same - Google Patents

Abstract

A negative electrode for a lithium secondary battery and a lithium secondary battery comprising the same are provided. The negative electrode comprises: a current collector; a negative electrode active material layer positioned on the current collector; and a coating layer positioned on the negative electrode active material layer and comprising an inorganic material and a binder polymer. The binder polymer comprises a first polymer represented by chemical formula 1 and a second polymer which is a polyvinylidene fluoride copolymer. In the chemical formula 1, Ar is a substituted or unsubstituted C6 to C30 aryl group, and n is an integer of 4 to 200. A lithium secondary battery having excellent penetration safety, thermal stability, and cycle life characteristics of the battery can be implemented.

Description

TECHNICAL FIELD The present invention relates to a negative electrode for a lithium secondary battery, and a lithium secondary battery including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a negative electrode for a lithium secondary battery,

A negative electrode for a lithium secondary battery, and a lithium secondary battery comprising the negative electrode.

[0002] Lithium secondary batteries, which have been popular as power sources for portable electronic devices in recent years, exhibit a high energy density by using an organic electrolytic solution and exhibiting discharge voltages two times higher than those of conventional batteries using an aqueous alkaline solution.

As a cathode active material of a lithium secondary battery is _{LiCoO 2, LiMn 2 O 4,} LiNi 1 - x Co x O 2 (0 <x <1) oxide consisting of lithium and a transition metal having a structure capable of intercalation of lithium, such as . As the negative electrode active material, various types of carbon-based materials such as artificial graphite, natural graphite, and hard carbon capable of inserting and removing lithium are being applied.

In such a lithium secondary battery, the anode and the cathode are thermally unstable depending on the charged state at a temperature of 25 ° C or higher, and the electrolyte salt, the organic solvent, the cathode active material and the anode active material are decomposed to cause problems in battery stability and safety.

In addition, batteries are becoming increasingly more demanding as customers demand, and it is becoming increasingly difficult to satisfy high durability with high levels of stability and safety requirements.

In one embodiment, the insulating property of the electrode is improved by applying a material having excellent heat resistance and durability, and by improving the adhesion of the material having excellent heat resistance and durability to the electrode, it is possible to provide a battery having superior safety performance, thermal stability and cycle life And a cathode for a lithium secondary battery.

Another embodiment is to provide a lithium secondary battery including the negative electrode for the lithium secondary battery.

One embodiment includes a current collector, a negative active material layer disposed on the current collector, and a coating layer disposed on the negative active material layer and including an inorganic material and a binder polymer, wherein the binder polymer includes a first polymer represented by Formula 1 And a second polymer which is a polyvinylidene fluoride copolymer. The present invention also provides a negative electrode for a lithium secondary battery comprising the same.

[Chemical Formula 1]

In Formula 1,

Ar is a substituted or unsubstituted C6 to C30 aryl group,

n is an integer of 4 to 200;

The weight ratio of the first polymer and the second polymer may be 40:60 to 80:20.

The second polymer may be a polyvinylidene fluoride-hexafluoropropylene copolymer.

The repeating unit derived from hexafluoropropylene in the polyvinylidene fluoride-hexafluoropropylene copolymer may be 3% by weight or more and 20% by weight or less based on the weight of the polyvinylidene fluoride-hexafluoropropylene copolymer.

The weight ratio of the inorganic material and the binder polymer may be 99: 1 to 60:40.

The mineral boehmite, zeolite, apatite, kaoline, mullite, spinel, olivine, _{mica, SiO 2, Al 2 O 3} , Al (OH) 3, AlO (OH), TiO 2, BaTiO 2, ZnO 2, At least one selected from the group consisting of Mg (OH) ₂ , MgO, Ti (OH) ₄ , aluminum nitride (AIN), silicon carbide (SiC), boron nitride (BoN)

The thickness of the coating layer may be from 1 탆 to 10 탆.

Another embodiment provides a lithium secondary battery comprising the negative electrode, the positive electrode, the electrolyte, and the separator.

Other details of the embodiments of the present invention are included in the following detailed description.

Heat resistance and durability to improve the insulation characteristics of the electrode and improve the adhesion of the material having excellent heat resistance and durability to the electrode to thereby provide a lithium rechargeable battery excellent in penetration safety, Can be implemented.

1 is a schematic view illustrating a structure of a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

It is to be understood that where a layer, film, region, plate, or the like is referred to as being "on" another portion, unless stated otherwise in this specification, .

As used herein, unless specified otherwise, at least one of the substituents or at least one hydrogen in the compound is substituted with one or more substituents selected from the group consisting of deuterium, a halogen group, a hydroxyl group, an amino group, a C1 to C30 amine group, a nitro group, a silyl group, A C1 to C10 alkylsilyl group, a C6 to C30 arylsilyl group, a C3 to C30 cycloalkyl group, a C3 to C30 heterocycloalkyl group, a C6 to C30 aryl group, a C2 to C30 heteroaryl group, a C1 to C20 alkoxy group, A fluoroalkyl group, a cyano group, or a combination thereof.

The negative electrode according to an embodiment includes a current collector, a negative electrode active material layer disposed on the current collector, and a coating layer disposed on the negative electrode active material layer and including an inorganic material and a binder polymer, And a second polymer that is a polyvinylidene fluoride copolymer.

[Chemical Formula 1]

In Formula 1,

Ar is a substituted or unsubstituted C6 to C30 aryl group,

n is an integer of 4 to 200;

By including the coating layer containing the first polymer, it is possible to suppress the heat generation of the battery and prevent a short circuit between the positive electrode and the negative electrode, thereby improving the safety, thermal stability, and cycle life characteristics of the lithium secondary battery.

In particular, since the first polymer represented by Formula 1 has heat resistance at a high temperature of 200 ° C or higher, unlike the conventional polyimide, the polymer is dissolved in a solvent in a state where polymerization is almost completed. Therefore, The stability of the secondary battery can be secured against penetration and heat exposure.

That is, in the case of conventional polyimide, polyamic acid (PAA) is synthesized through primary polymerization, and the polyamic acid is converted to polyimide by heating at a high temperature (over 300 ° C.) do or; A monomer or an oligomer is diluted in a solvent and then circulated and polymerized at a high temperature to synthesize the monomer. At this time, water is produced because the dehydration process is performed. Any method is subject to dehydration and high temperature process conditions are required.

As a result, the conversion efficiency to polyimide is low at a process temperature of 150 ° C or less, which is the general process drying temperature of the secondary battery, and battery performance is deteriorated due to moisture generation.

This can be improved by using the first polymer represented by the above formula (1) having high heat resistance so that the inorganic material is densified in the coating layer and the insulation of the electrode plate can be maintained even at a high temperature of 200 ° C or more.

The method of synthesizing the first polymer represented by Formula 1 is not particularly limited. However, when synthesized by a direct synthesis method diisocyanate method, since the imidization is almost completed, unreacted imide residues are small, Is relatively small.

The weight average molecular weight of the first polymer may be 1,000 to 50,000, and may be 10,000 to 20,000.

When the weight average molecular weight of the first polymer is within the above range, the migration resistance of lithium ions can be minimized and the performance of the battery can be secured.

The polyvinylidene fluoride copolymer as the second polymer means a polymer prepared by using a monomer other than vinylidene fluoride in combination. Specifically, the polymer includes a repeating unit derived from hexafluoropropylene, a vinylidene fluoride repeating unit And a repeating unit derived from hexafluoropropylene in addition to 5% by weight or more of other kinds of repeating units. Wherein the polyvinylidene fluoride copolymer is a polyvinylidene fluoride-hexafluoropropylene (PVdF) copolymer comprising a repeating unit derived from vinylidene fluoride and a repeating unit derived from hexafluoropropylene, HFP) based copolymers. The polyvinylidene fluoride-hexapropylene-based copolymer may be a polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) binary copolymer or a vinylidene fluoride-derived repeating unit and hexafluoro And a copolymer of three or more members including additional repeating units other than propylene-derived repeating units.

Specifically, a polyvinylidene fluoride-hexafluoropropylene copolymer having a repeating unit derived from hexafluoropropylene of 3% by weight to 20% by weight and a weight average molecular weight of 600,000 or more may be used as the second polymer. In the case of using the polyvinylidene fluoride-hexafluoropropylene copolymer satisfying the content range and the weight average molecular weight range, the adhesion between the coating layer and the negative electrode active material layer is strengthened, The negative electrode can be manufactured without causing the coating layer to separate from the negative electrode active material layer. In addition, stable characteristics can be maintained even after the cell is expanded in thickness.

The first polymer and the second polymer may be mixed at a ratio of 40:60 to 80:20 to form a binder polymer. When the ratio of the second polymer is lower than 80:20 due to a shortage of the amount of the second polymer in the mixing ratio, deterioration of the adhesive force occurs and the amount of the first polymer is insufficient, The adhesive strength is deteriorated, which is undesirable.

The thickness of the coating layer may be 1 탆 to 10 탆, specifically 1 탆 to 5 탆, 1 탆 to 4 탆, and most specifically 1 탆 to 3 탆.

When the thickness of the coating layer is within the above range, an electrical insulating layer may be formed on the surface of the negative electrode to prevent a short circuit between the positive electrode and the negative electrode.

The porosity of the coating layer may be 30% to 70%, specifically 40% to 60%, and most specifically 50% to 55%.

When the porosity of the coating layer is within the above range, the movement resistance of lithium ions can be minimized by improving the mobility of lithium ions, thereby ensuring battery performance.

The inorganic material and the binder polymer may be contained in a weight ratio of 99: 1 to 60:40, and specifically 99: 1 to 70:30, 99: 1 to 80:20, and most specifically 96: 4 to 90: : 10. &Lt; / RTI &gt;

The binder polymer may be included in an amount of 0.5 wt% to 10 wt% with respect to the total amount of the anode active material layer and the coating layer, and may be 3 wt% to 7 wt%.

When the binder polymer is contained in the above content range, heat generation of the battery can be suppressed and the thermal stability can be improved.

The inorganic material may be included in an amount of 1 wt% to 20 wt%, and more specifically 5 wt% to 12 wt% with respect to the total amount of the anode active material layer and the coating layer. When the inorganic material is contained in the above content range, it is possible to prevent a short circuit between the positive electrode and the negative electrode due to the excellent electrical insulation property.

Packing density of the inorganic material may be a 1.0 g / cm ³ to 4.0 g / cm ^3, Specifically, it may be 1.5 g / cm ³ to 3.0 g / cm ³ days.

The packing density represents the density of the powder before compression molding and drying of the inorganic material, and when the packing density is within the above range, the heat resistance is greatly improved.

The mineral boehmite, zeolite, apatite, kaoline, mullite, spinel, olivine, _{mica, SiO 2, Al 2 O 3} , Al (OH) 3, AlO (OH), TiO 2, BaTiO 2, ZnO 2, Mg (OH) ₂ , MgO, Ti (OH) ₄ , aluminum nitride (AIN), silicon carbide (SiC), boron nitride (BoN) or a combination thereof.

The inorganic material may have an average particle size of 0.1 to 5 占 퐉, more specifically 0.3 to 1 占 퐉. When the average particle diameter of the inorganic particles is within the above range, the anode active material layer can be uniformly coated on the anode active material layer. Thus, the anode active material layer can be prevented from shorting between the anode and the cathode. In addition, the migration resistance of lithium ions can be minimized to ensure performance.

The first polymer and the second polymer included in the binder polymer may further include a binder different from the first polymer and the second polymer. Specific examples of the binder include styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), ethylene vinyl acetate (EVA), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral ), An ethylene-acrylic acid copolymer, acrylonitrile, a vinyl acetate derivative, a polyethylene glycol, an acrylic rubber or a combination thereof. Among these, the styrene-butadiene rubber (SBR), the styrene-butadiene rubber (EVA), the polyvinyl alcohol (PVA), the ethylene-acrylic acid copolymer, or the acrylic rubber may be used as the mixture of the carboxymethyl cellulose (CMC) and the carboxymethyl cellulose (CMC).

When the binder is further included in the coating layer, adhesion between the organic particles, between the inorganic particles, or between the organic particles and the inorganic particles can be improved as well as the adhesive strength with the negative electrode active material layer.

The collector of the negative electrode may be selected from the group consisting of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, .

The negative electrode active material layer may further include a negative electrode active material, a binder, and optionally a conductive material.

As the negative electrode active material, a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide may be used.

Examples of the material capable of reversibly intercalating / deintercalating lithium ions include a carbonaceous material, that is, a carbonaceous anode active material generally used in a lithium secondary battery. Representative examples of the carbon-based negative electrode active material include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type. Examples of the amorphous carbon include soft carbon or hard carbon hard carbon, mesophase pitch carbide, fired coke, and the like.

Examples of the lithium metal alloy include lithium and a group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, May be used.

As the material capable of being doped and dedoped into lithium, Si, SiO _x (0 <x <2) and Si-Q alloy (Q is an alkali metal, an alkali earth metal, a Group 13 element, a Group 14 element, a Group 15 element, group elements, transition metals, rare earth elements and an element selected from the group consisting of, but not Si), Si- carbon composite, Sn, SnO _2, Sn-R (where R is an alkali metal, alkaline earth metal, 13 An element selected from the group consisting of Group IV elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Sn), and Sn-carbon composites. May be mixed with SiO ₂ . The element Q and the element R may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

As the transition metal oxide, lithium titanium oxide may be used.

According to one embodiment, the negative electrode active material may be a Si-carbon composite, and the Si-carbon composite may include silicon particles and crystalline carbon. The average particle diameter (D50) of the silicon particles may be 10 nm to 200 nm. The Si-C composite may further include an amorphous carbon layer formed on at least a portion thereof. Unless defined otherwise herein, the mean particle diameter (D50) means the diameter of a particle having a cumulative volume of 50 vol% in the particle size distribution.

According to another embodiment, the negative electrode active material may be a mixture of two or more kinds of negative electrode active materials. For example, the negative active material may include a Si-carbon composite material as a first negative active material, . &Lt; / RTI &gt; When two or more kinds of negative electrode active materials are mixed and used as the negative electrode active material, mixing ratio thereof can be appropriately adjusted, but it may be appropriate to adjust the content of Si to 3 wt% to 50 wt% with respect to the total weight of the negative electrode active material .

The content of the negative electrode active material in the negative electrode active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative electrode active material layer. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% with respect to the total weight of the negative electrode active material layer. When the conductive material is further included, the negative electrode active material may be used in an amount of 90 to 98 wt%, the binder may be used in an amount of 1 to 5 wt%, and the conductive material may be used in an amount of 1 to 5 wt%.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and olefin copolymers having 2 to 8 carbon atoms, (meth) acrylic acid and (meth) Copolymers or combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further contained as a thickener. As the cellulose-based compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, alkali metal salts thereof or the like may be used in combination. As the alkali metal, Na, K or Li can be used. The content of the thickener may be 0.1 part by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

The conductive material is used for imparting conductivity to the electrode. Any conductive material may be used for the battery without causing any chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, denka black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof.

The negative electrode active material composition, the binder and the conductive material are mixed in a solvent to prepare a negative electrode active material composition, and the negative electrode active material composition is applied to the negative electrode collector to form the negative electrode active material layer. At this time, N-methylpyrrolidone or the like may be used as the solvent, but it is not limited thereto. The negative electrode may be manufactured by coating the coating composition on the negative active material layer to form a coating layer.

Another embodiment provides a lithium secondary battery comprising the negative electrode, the positive electrode, and the nonaqueous electrolyte.

The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector and including a positive electrode active material.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (ritied intercalation compound) can be used. Specifically, cobalt, manganese, nickel, and combinations thereof At least one of composite oxides of metal and lithium may be used. As a more specific example, a compound represented by any one of the following formulas may be used. Li _a A _{1 - b} X _b D ₂ (0.90? A? 1.8, 0? B? 0.5); Li _a A _{1 - b} X _b O _{2 - c} D _c (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05); Li _a E _1-b X _b O _{2 -c} D _c (0? B? 0.5, 0? C? 0.05); Li _a E _{2 - b} X _b O _{4 - c} D _c (0? B? 0.5, 0? C? 0.05); Li _a Ni _{1 -b- c} Co _b X _c D _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.5, 0 <?? 2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 - ?} T _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Co _b X _c O _{2 - ?} T ₂ (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? <2); Li _a Ni _{1 -b- c} Mn _b X _c D _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <?? 2); Li _a Ni _{1 -b- c} Mn _b X _c O _{2 - ?} T _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? <2); Li _a Ni _{1 -b- c} Mn _b X _c O _{2 - ?} T ₂ (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? <2); Li _a Ni _b E _c G _d O ₂ (0.90? A? 1.8, 0? B? 0.9, 0? C? 0.5, 0.001? D? 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90? A? 1.8, 0? B? 0.9, 0? C? 0.5, 0? D? 0.5, 0.001? E? 0.1); Li _a NiG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a CoG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn _{1 -b} G _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ (0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn _{1 - g} G _g PO ₄ (0.90? A? 1.8, 0? G? 0.5); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); Li _a FePO ₄ (0.90? A? 1.8)

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer comprises at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element and a hydroxycarbonate of the coating element . The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be any coating method as long as it can coat the above compound by a method that does not adversely affect physical properties of the cathode active material (for example, spray coating, dipping, etc.) by using these elements, It will be understood by those skilled in the art that a detailed description will be omitted.

According to one embodiment, Li _a Ni _{1 -b - c} Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 ≤ α ≤ 2) as the cathode active material; Li _a Ni _{1 -b- c} Co _b X _c O _{2 - ?} T _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0?? <2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 - ?} T ₂ (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0??? 2); Li _a Ni _{1 -b- c} Mn _b X _c D _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0??? 2); Li _a Ni _{1 -b- c} Mn _b X _c O _{2 - ?} T _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0??? 2); Li _a Ni _{1 -bc} Mn _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α ≤ 2); Li _a Ni _b E _c G _d O ₂ (0.90? A? 1.8, 0? B? 0.9, 0? C? 0.5, 0.001? D? 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1), or a mixture of the nickel-based positive electrode active material and the positive electrode active material, Other active materials other than the nickel-based positive electrode active material may be mixed and used.

In particular, as the nickel-based cathode active material, Li _a Ni _b1 Co _c1 X _d1 G _z1 O ₂ (0.90 ≤ a ≤ 1.8, 0.5 ≤ b1 ≤ 0.98, 0 <c1 ≤ 0.3, 0 <d1 ≤ 0.3, 0 ≤ z1 ≤ 0.1 , b1 + c1 + d1 + z1 = 1, X is Mn, Al or a combination thereof, and G is Cr, Fe, Mg, La, Ce, Sr, V or a combination thereof.

When these are mixed and used, these mixing ratios can be suitably mixed and used depending on the desired physical properties. For example, when the nickel-based cathode active material is mixed with other active materials, the content of the nickel-based cathode active material may be 30 wt% to 97 wt% with respect to the total weight of the cathode active material.

In the anode, the content of the cathode active material may be 90 wt% to 98 wt% with respect to the total weight of the cathode active material layer.

In one embodiment of the present invention, the cathode active material layer may further include a binder and a conductive material. At this time, the content of the binder and the conductive material may be 1 wt% to 5 wt% with respect to the total weight of the cathode active material layer.

The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl Polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-acrylonitrile, styrene-butadiene rubber, Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material may be used for the battery without causing any chemical change. Examples of the conductive material include conductive materials such as natural graphite, synthetic graphite, carbon black, carbon-based materials such as acetylene black, ketjen black and carbon fiber, metal powders such as nickel, aluminum and silver, Polymer or a mixture thereof.

The current collector may be an aluminum foil, a nickel foil or a combination thereof, but is not limited thereto.

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol, or aprotic solvent.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, caprolactone, Etc. may be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. As the ketone-based solvent, cyclohexanone and the like can be used. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, , A double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used .

The organic solvent may be used singly or in a mixture of one or more. If one or more of the organic solvents are used in combination, the mixing ratio may be appropriately adjusted according to the performance of the desired battery, and this may be widely understood by those skilled in the art have.

In the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1: 1 to 1: 9, the performance of the electrolytic solution may be excellent.

In the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1: 1 to 1: 9, the performance of the electrolytic solution may be excellent.

When the non-aqueous organic solvent is mixed, a mixed solvent of a cyclic carbonate and a chain carbonate; A mixed solvent of a cyclic carbonate and a propionate-based solvent; Or a mixed solvent of cyclic carbonate, chain carbonate and propionate solvent can be used. As the propionate solvent, methyl propionate, ethyl propionate, propyl propionate or a combination thereof may be used.

In this case, when the cyclic carbonate and the chain carbonate or the cyclic carbonate and the propionate solvent are used in a mixed manner, mixing in a volume ratio of 1: 1 to 1: 9 may be used to improve the performance of the electrolytic solution. When cyclic carbonate, chain carbonate and propionate solvent are mixed and used, they may be mixed at a ratio of 1: 1: 1 to 3: 3: 4. Of course, the mixing ratio of the solvents may be appropriately adjusted depending on the desired physical properties.

The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1: 1 to 30: 1.

The aromatic hydrocarbon-based organic solvent may be an aromatic hydrocarbon-based compound represented by the following formula (1).

[Chemical Formula 1]

Wherein R ₁ to R ₆ are the same or different from each other and selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 , 2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, Examples of the solvent include 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4- Dichlorotoluene, 2,3-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3-trifluorotoluene, 3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2 , 5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

The electrolyte may further include vinylene carbonate or an ethylene carbonate compound of the following formula (2) as a life improving additive in order to improve battery life.

(2)

(Wherein R ₇ and R ₈ are the same or different and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and an alkyl group having 1 to 5 fluorinated carbon atoms , At least one of R ⁷ and R ⁸ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and an alkyl group having 1 to 5 fluorinated carbon atoms, provided that R ₇ and R ₈ both It is not hydrogen.)

Representative examples of the ethylene carbonate-based compound include diethylene carbonate, diethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and the like, such as difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, . When such a life improving additive is further used, its amount can be appropriately adjusted.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the cell to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the anode and the cathode. The lithium salt Representative examples are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 2 C 2 F 5) 2, Li (CF 3 SO 2) 2 N, LiN (SO 3 C 2 F 5) 2, _{LiC 4 F 9 SO 3, LiClO} 4, LiAlO 2, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y + 1 SO 2) ( where, x and y are natural numbers, e.g. 1 to 20), LiCl, LiI and LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate: LiBOB) The concentration of the lithium salt is preferably in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, Lithium ions can move effectively.

Depending on the type of the lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. The separator may be a polyethylene / polypropylene double layer separator, a polyethylene / polypropylene / polyethylene triple layer separator, a polypropylene / polyethylene / poly It is needless to say that a mixed multilayer film such as a propylene three-layer separator and the like can be used.

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. The lithium secondary battery according to one embodiment is explained as an example, but the present invention is not limited thereto, and can be applied to various types of batteries such as a cylindrical type, a pouch type, and the like.

1, a lithium secondary battery 100 according to an embodiment includes an electrode assembly 40 wound between a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, And a case 50 having a built- The anode 10, the cathode 20 and the separator 30 may be impregnated with an electrolyte solution (not shown).

Hereinafter, examples and comparative examples of the present invention will be described. However, the following embodiments are only examples of the present invention, and the present invention is not limited to the following embodiments.

Example  One

(Preparation of negative electrode)

2 weight% of a polyamideimide having a weight average molecular weight of 300,000 (Kudo Chemical Co., Ltd., KDPI-1103D) and 2 weight% of a polyvinylidene fluoride-hexafluoropropylene copolymer (Arkema, LBG) having a weight average molecular weight of 600,000 , And 96 wt% of boehmite (BH-611, Anhui Estone Co.) having a size of 0.8 mu m were mixed with N-methylpyrrolidone solvent to prepare a coating composition. 97.5% by weight of graphite, 1.5% by weight of styrene-butadiene rubber (SBR) and 1% by weight of carboxymethylcellulose (CMC) were added to a water solvent to prepare a slurry for forming a negative electrode active material layer.

The slurry was coated on a copper foil, dried, and rolled to produce a negative electrode active material layer. Subsequently, the coating composition was applied to the anode active material layer to form a coating layer, wherein the thickness of the coating insulating layer was 3 占 퐉.

(Preparation of positive electrode)

LiNi _{0 . 33} Co _{0 . 33} Mn _{0 . 33} O ₂ 80 wt% and LiNi _{0 . 8} Co _{0 . 15} Al _{0 . 05} O ₂ 20% mixture of 94% by weight, of the weight by the addition of carbon black, 3% by weight and 3% by weight of polyvinylidene fluoride in N- methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was applied to an aluminum (Al) thin film, dried, and roll pressed to produce a positive electrode.

(Preparation of electrolytic solution)

1.15 M of LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate mixed at a volume ratio of 2: 4: 4 to prepare an electrolytic solution.

(Production of lithium secondary battery)

A lithium secondary battery was fabricated using the positive electrode, the negative electrode, the electrolyte, and a separator made of polyethylene.

Example  2

In the same manner as in Example 1 except that the weight ratio of the polyamide-imide and the polyvinylidene fluoride-hexafluoropropylene-based copolymer was changed to 2.4 wt% and 1.6 wt%, respectively, , An anode, an electrolytic solution and a lithium secondary battery using the same.

Example  3

In the same manner as in Example 1 except that the weight ratio of polyamide imide in the preparation of the coating composition was changed to 3 wt% and the weight ratio of polyvinylidene fluoride-hexafluoropropylene copolymer was changed to 1 wt% , An anode, an electrolytic solution and a lithium secondary battery using the same.

Comparative Example  One

A lithium secondary battery was fabricated in the same manner as in Example 1 except that 4 wt% of polyamide imide (KUDO-1103D) as a binder polymer of the coating composition was used in Example 1.

Comparative Example  2

A lithium secondary battery was produced in the same manner as in Example 1, except that 4 wt% of a polyvinylidene fluoride-hexafluoropropylene copolymer (Arkema, LBG) as a binder polymer of the coating composition was used in Example 1 Respectively.

Evaluation: Coating layer and cathode Active material layer  Evaluation of adhesive strength

In order to compare the adhesive strength between the coating layer and the negative electrode active material layer in the negative electrode according to Examples 1 to 3 and Comparative Examples 1 and 2, the adhesive strength was measured four times each and the average value thereof was determined. The results are shown in Table 1 below.

Adhesion was measured using a tensile tester, Instron 3343 (product name).

Adhesion (N / mm) 1 time Episode 2 3rd time 4 times Average Example 1 3.304 3.898 4.282 4.545 4.01 Example 2 4.453 4.378 4.718 4.807 4.59 Example 3 3.278 3.189 3.589 3.419 3.37 Comparative Example 1 3.499 2.244 3.069 2.633 2.86 Comparative Example 2 1.069 0.61 0.896 0.836 0.85

Referring to Table 1, it can be seen that Examples 1 to 3, in which the first polymer and the second polymer were mixed to form a binder polymer, exhibited excellent adhesion between the coating layer and the negative electrode active material layer. On the other hand, in the case of Comparative Example 1 using only the first polymer or Comparative Example 2 using only the second polymer, the adhesive strength is very weak.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

Claims (8)

Collecting house;
A negative electrode active material layer disposed on the current collector; And
And a coating layer disposed on the anode active material layer and including an inorganic material and a binder polymer,
Wherein the binder polymer comprises a first polymer represented by the following Chemical Formula 1 and a second polymer that is a polyvinylidene fluoride copolymer.
[Chemical Formula 1]

In Formula 1,
Ar is a substituted or unsubstituted C6 to C30 aryl group,
n is an integer of 4 to 200; The method according to claim 1,
Wherein the weight ratio of the first polymer and the second polymer is 40:60 to 80:20. The method according to claim 1,
Wherein the second polymer is a polyvinylidene fluoride-hexafluoropropylene copolymer. The method of claim 3,
Wherein the repeating unit derived from hexafluoropropylene in the polyvinylidene fluoride-hexafluoropropylene copolymer is 3% by weight or more and 20% by weight or less based on the weight of the polyvinylidene fluoride-hexafluoropropylene copolymer, cathode. The method according to claim 1,
Wherein the weight ratio of the inorganic material and the binder polymer is from 99: 1 to 60:40. The method according to claim 1,
The mineral boehmite, zeolite, apatite, kaoline, mullite, spinel, olivine, _{mica, SiO 2, Al 2 O 3} , Al (OH) 3, AlO (OH), TiO 2, BaTiO 2, ZnO 2, Wherein the negative electrode is at least one selected from the group consisting of Mg (OH) ₂ , MgO, Ti (OH) ₄ , aluminum nitride (AIN), silicon carbide (SiC), boron nitride (BoN) The method according to claim 1,
Wherein the thickness of the coating layer is 1 占 퐉 to 10 占 퐉. A cathode according to any one of claims 1 to 7;
anode;
Electrolytic solution; And
Separator
And a lithium secondary battery.

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