KR20190133594A - Positive electrode for rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same. The positive electrode comprises a current collecting body and a positive electrode layer including a nickel-based positive electrode of chemical formula 1, Li_aNi_xCo_yA_zO_2, having 0.5-2.5 m^2/g of a BET specific surface area, metal fluoride, a conductive material, and a binder. The amount of the metal fluoride is 1-10 wt% for 100 wt% of the positive electrode layer. In chemical formula 1, a relation of individual elements is 0.9 <= a <= 1.1, 0.8 <= x <= 0.98, 0.1 <= y <= 0.3, 0.1 <= z <= 0.3, x + y + z = 1 and A is Mn or Al. The present invention can provide a lithium secondary battery with excellent high temperature storage properties.

Description

A positive electrode for a lithium secondary battery and a lithium secondary battery including the same {POSITIVE ELECTRODE FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY INCLUDING SAME}

It relates to a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the same.

Recently, lithium secondary batteries have been in the spotlight as power sources of portable small electronic devices.

The lithium secondary battery has a structure including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator located between the positive electrode and the negative electrode, and an electrolyte.

As the negative electrode active material, various types of carbon-based materials or Si-based active materials including artificial, natural graphite, and hard carbon capable of inserting / desorbing lithium are used.

LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1-x Co _x O ₂ (0 <x <1), LiNi _1-xy Co _x A _y O ₂ (0 <x + y <1, A is Oxides composed of lithium and a transition metal having a structure capable of intercalation of lithium ions, such as Mn or Al).

One embodiment of the present invention is to provide a positive electrode for a lithium secondary battery excellent in adhesion to the current collector, excellent cycle life characteristics and high temperature storage characteristics.

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

One embodiment of the present invention is formed on the current collector and the current collector, the BET specific surface area is 0.5 m 2 / g to 2.5 m 2 / g To include a positive electrode layer including a nickel-based positive electrode active material, a metal fluoride, a conductive material and a binder of the formula (1), the content of the metal fluoride is 1 weight based on 100% by weight of the total content of the positive electrode layer It provides a positive electrode for a lithium secondary battery that is% to 10% by weight.

[Formula 1]

Li _a Ni _x Co _y A _z O ₂

(In Formula 1, 0.9 ≦ a ≦ 1.1,0.8 ≦ x ≦ 0.98, 0.1 ≦ y ≦ 0.3, 0.1 ≦ z ≦ 0.3, x + y + z = 1, A is Mn or Al.)

Another embodiment is to prepare a positive electrode active material composition by mixing a nickel-based positive electrode active material, a metal fluoride, a binder and a conductive material of Formula 1 having a BET specific surface area of 0.5 m 2 / g to 2.5 m 2 / g in a solvent; A method of manufacturing a positive electrode for a lithium secondary battery comprising applying the positive electrode active material composition to a current collector, wherein the metal fluoride is 100% by weight of the nickel-based positive electrode active material, the metal fluoride, the binder, and the conductive material. It provides a method for producing a positive electrode for a lithium secondary battery that is used in an amount of 1% by weight to 10% by weight relative to%.

The metal fluoride may be Al fluoride, Mg fluoride, Zr fluoride, Bi fluoride or a combination thereof.

Another embodiment is the anode; A negative electrode including a negative electrode active material; And it provides a lithium secondary battery comprising an electrolyte.

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

The positive electrode for a lithium secondary battery according to an embodiment may provide a lithium secondary battery having excellent adhesion to a current collector, excellent cycle life characteristics, and high temperature storage characteristics.

1 is a view schematically showing the structure of a lithium secondary battery according to one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

Unless otherwise defined herein, the average particle diameter (D50) refers to the diameter of the particles having a cumulative volume of 50% by volume in the particle size distribution, and may be measured by a particle size analyzer (PSA).

In the present specification, "upper" and "lower" are defined based on the drawings, and according to a viewpoint, "upper" may be changed to "lower" and "lower" to "upper", and "on" or What is referred to as “on” may include not only the above but also intervening other structures in the middle. On the other hand, what is referred to as "directly on" or "directly on" means that there is no intervening structure in between.

One embodiment of the present invention includes a current collector and a positive electrode layer formed on the current collector, the positive electrode layer has a BET specific surface area of 0.5 m 2 / g or more nickel-based positive electrode active material of the following formula, metal fluoride, It may include a conductive material and a binder.

[Formula 1]

Li _a Ni _x Co _y A _z O ₂

(In Formula 1, 0.9 ≦ a ≦ 1.1, 0.8 ≦ x ≦ 0.98, 0.1 ≦ y ≦ 0.3, 0.1 ≦ z ≦ 0.3, x + y + z = 1, A is Mn or Al.)

The BET specific surface area may be at least 0.5 m 2 / g. For example, it may be 0.5 m 2 / g to 2.5 m 2 / g .

As shown in Chemical Formula 1, the positive electrode active material having a Ni content of 80 mol% or more is generally present in an excessive amount of residual Li, so that a large amount of gas may be generated by reaction with the electrolyte when exposed to high temperature, and thermal stability may be deteriorated. And the like, and the cathode active material may be treated with water, for example, to reduce the residual Li content. For example, in the case of washing with water, the specific surface area is greatly increased, the capacity is lowered, and the cycle life is sharply lowered. In order to prevent this, that is, to reduce the BET specific surface area, heat treatment or Additional processes, such as performing a polymer coating, are required, which results in a complicated process and an increase in manufacturing cost.

In the case of a low Ni positive electrode active material having a Ni content of less than 80 mol%, since residual Li is not present in excess, such a water washing process does not need to be performed, and thus the BET specific surface area due to water washing does not increase, and thus There is no associated problem, i.e. a decrease in cycle life. Therefore, it is not necessary to use additional metal fluoride, even if additional use, the effect of improving the cycle life characteristics according to the use of the metal fluoride does not occur.

The positive electrode according to the embodiment includes a metal fluoride, and as the metal fluoride serves to suppress electrolyte side reactions, a high Ni positive electrode having a BET specific surface area of 0.5 m 2 / g or more and a Ni content of 80 mol% or more The decrease in capacity and the decrease in cycle life of the active material can be suppressed. In addition, it is possible to stabilize side reactions between the surface of the positive electrode active material in which the metal fluoride is unstable and the electrolyte solution. Accordingly, the BET can be used in the positive electrode as it is at least 0.5 m 2 / g or more without performing an additional process such as heat treatment on the high Ni positive electrode active material having a BET specific surface area of 0.5 m 2 / g or more. That is, the nickel-based positive electrode active material according to one embodiment may be a process of washing the active material with water, for example, water to reduce residual lithium.

The metal fluoride may be Al fluoride, Mg fluoride, Zr fluoride, Bi fluoride or a combination thereof, and according to one embodiment, may be Al fluoride. Specifically, for example, it may be AlF ₃ , MgF ₂ , BiF ₃ , ZrF ₄ or a combination thereof. In the case of using Al fluoride, the capacity and cycle life improvement effect may be excellent as compared with the case of using fluoride such as, for example, Cs, K, Li.

The content of the metal fluoride may be 1 wt% to 10 wt% with respect to 100 wt% of the total content of the anode layer, and in one embodiment, may be 1 wt% to 5 wt%. When the content of the metal fluoride is included in the range, it is possible to further improve the capacity and cycle life, in particular room temperature cycle life characteristics, while minimizing the initial capacity and efficiency reduction.

The metal fluoride may be one having an average particle diameter (D50) of 3 μm or less, and specifically, may be used in the form of particles having a particle size of 0.1 μm to 3 μm or specifically, having a particle shape of 0.5 μm to 2.5 μm. Moreover, you may use the secondary particle form formed by the aggregation of the primary particle whose average particle diameter (D50) is 3 micrometers or less.

In one embodiment, the cathode active material may be a mixture of an allele and an active material. As such, when a mixture of the allele and the small active material is used as the cathode active material, the capacity can be further increased.

The average particle diameter (D50) of the alternative active material may be 15 μm to 20 μm, and the average particle diameter (D50) of the small active material may be 3 μm to 5 μm. When the average particle diameter of the allele and the small active material is included in the range, a particle size distribution having an appropriate density (g / cc) may be implemented. At this time, the mixing ratio of the allele and the small active material may be a weight ratio of 60: 40 to 80: 20. When the mixing ratio of the all active material and the small active material is included in the above range, a very high density (g / cc) may be realized when the positive electrode layer is formed.

The average particle diameter (D50) of the metal fluoride may be 0.5 μm to 2.5 μm. When the average particle diameter (D50) of the metal fluoride is included in the above range, the metal fluoride may be uniformly distributed among the positive electrode active material particles, thereby further improving the effect of using the metal fluoride.

In the positive electrode layer, the content of the positive electrode active material may be 86 wt% to 97 wt% based on the total weight of the positive electrode layer. The content of the metal fluoride may be 1 wt% to 10 wt% with respect to the total weight of the anode layer.

In the positive electrode layer, the content of the binder may be 0.5% by weight to 2% by weight based on the total weight of the positive electrode layer. The binder is polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene butadiene rubber, epoxy resin, nylon and the like can be used, but is not limited thereto.

In the anode layer, the content of the conductive material may be 0.5% by weight to 2% by weight based on the total weight of the anode layer. Examples of the conductive material include carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, metal powders such as copper, nickel, aluminum, and silver, and polyphenylene derivatives such as metallic fibers such as metal fibers. And conductive materials containing a conductive polymer or a mixture thereof.

The current collector supports the anode layer.

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

According to another exemplary embodiment, a method of manufacturing a cathode for a lithium secondary battery includes a cathode active material obtained by mixing a cathode active material, a metal fluoride, a binder, and a conductive material of Formula 1 having a BET specific surface area of 0.5 m 2 / g to 2.5 m 2 / g in a solvent. The process of manufacturing a composition and apply | coating this positive electrode active material composition to a current collector is included. The positive electrode active material composition may be in the form of a slurry.

[Formula 1]

Li _a Ni _x Co _y A _z O ₂

(In Formula 1, 0.9 ≦ a ≦ 1.1, 0.8 ≦ x ≦ 0.98, 0.1 ≦ y ≦ 0.3, 0.1 ≦ z ≦ 0.3, x + y + z = 1, A is Mn or Al.)

In this case, the metal fluoride is in a content of 1% by weight to 10% by weight with respect to the solid content of the positive electrode active material composition, that is, 100% by weight of the nickel-based positive electrode active material, the metal fluoride, the conductive material, and the total content of the binder. Can be used, and in one embodiment, can be from 1% to 5% by weight. When the metal fluoride is used in the above amount, it is possible to implement a positive electrode having improved capacity and cycle life, particularly room temperature cycle life, while minimizing initial capacity and efficiency reduction.

The content of the positive electrode active material, the conductive material, and the binder is 86% by weight to 97% by weight of the solid content of the positive electrode active material composition, that is, the total content of the nickel-based positive electrode active material, the metal fluoride, the conductive material, and the binder. Weight percent, 0.5 weight percent to 2 weight percent, and 0.5 weight percent to 2 weight percent.

The positive electrode active material, the metal fluoride, the conductive material, the binder, and the current collector may be the ones described above. The solvent may be an organic solvent such as N-methyl pyrrolidone. After applying the positive electrode active material composition to the current collector, and further performing a drying and rolling process, such a coating, drying and rolling process is a conventional process known in the art, so a detailed description thereof will be omitted. .

As such, the positive electrode according to the embodiment may be prepared by adding a metal fluoride during the production of a positive electrode active material composition in the form of a slurry in a general positive electrode manufacturing process, and thus, there is no need to add a separate process, and thus a conventional positive electrode process and The equipment can be used as it is.

Another embodiment is the anode; cathode; And it provides a lithium secondary battery comprising an electrolyte.

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

The anode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material doped and undoped with lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in a lithium ion secondary battery may be used, and representative examples thereof include crystalline carbon. , Amorphous carbon or these can be used together. Examples of the crystalline carbon include graphite such as amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon ( hard carbon), mesophase pitch carbide, calcined coke, and the like.

Examples of the alloy of the lithium metal include lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Alloys of the metals selected may be used.

Examples of materials that can be doped and undoped with lithium include Si, SiO _x (0 <x <2), and Si-Q alloys (wherein Q is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, and 16). An element selected from the group consisting of group elements, transition metals, rare earth elements, and combinations thereof, not Si), Sn, SnO ₂ , Sn-R alloys (wherein R is an alkali metal, an alkaline earth metal, a Group 13 element, 14 element, an element selected from group 15 elements, group 16 elements, transition metals, rare earth elements and combinations thereof, Sn may be mentioned not), and a mixture of at least one and SiO ₂ of which Can also be used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, One selected from the group consisting of S, Se, Te, Po, and a combination thereof can be used.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide or lithium titanium oxide.

The content of the negative electrode active material in the negative electrode layer may be 95% by weight to 99% by weight with respect to the total weight of the negative electrode layer.

In one embodiment of the present invention, the negative electrode layer includes a binder, and optionally may further include a conductive material. The content of the binder in the negative electrode layer may be 1% by weight to 5% by weight based on the total weight of the negative electrode layer. In addition, when the conductive material is further included, 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material may be used.

The binder adheres the anode active material particles to each other well, and also serves to adhere the anode active material to the current collector well. As the binder, a non-aqueous binder, an aqueous binder, or a combination thereof may be used.

The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

The aqueous binder may include styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluorine rubber, ethylene propylene copolymer, polyepichlorohydrin , Polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol or combinations thereof Can be.

When using an aqueous binder as the negative electrode binder, it may further include a cellulose-based compound that can impart viscosity as a thickener. As this cellulose type compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, these alkali metal salts, etc. can be used in mixture of 1 or more types. Na, K or Li may be used as the alkali metal. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

Examples of the conductive material include carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, metal powders such as copper, nickel, aluminum, and silver, and polyphenylene derivatives such as metallic fibers such as metal fibers. A conductive material containing a conductive polymer or a mixture thereof can be used.

The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

The negative electrode may be formed by mixing a negative electrode active material, a binder, and optionally a conductive material in a solvent to prepare a slurry type negative electrode active material composition, and applying the negative electrode active material composition to a current collector. After the coating step, the drying and rolling steps may be performed. Since the electrode forming method is well known in the art, detailed descriptions thereof will be omitted. N-methylpyrrolidone may be used as the solvent, but is not limited thereto. In the case of using a water-soluble binder as the binder, water may be used as the solvent.

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 is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalo Norlactone, caprolactone, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, cyclohexanone, ethyl alcohol, isopropyl alcohol, R Nitriles, such as -CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond aromatic ring or an ether bond); Amides such as methylformamide, dioxolanes such as 1,3-dioxolane, sulfolane and the like can be used.

The organic solvents may be used alone or in combination of one or more, and the mixing ratio in the case of mixing one or more may be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art. have.

In addition, the organic solvent may further include an aromatic hydrocarbon organic solvent. Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 , 2,4 trichlorobenzene, iodobenzene, 1,2-dioodobenzene, 1,3-dioodobenzene, 1,4-dioiobenzene, 1,2,3-triiodobenzene, 1,2 , 4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Toluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3 , 5-trichlorotoluene, iodotoluene, 2,3-dioodotoluene, 2,4-diaodotoluene, 2,5-diaodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

The electrolyte may further include vinylene carbonate or ethylene carbonate-based compound as a life improving additive.

Representative examples of the ethylene carbonate-based compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. Can be. In the case of further using such life improving additives, the amount thereof can be properly adjusted.

The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts 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, for example Supporting one or more selected from the group consisting of LiCl, LiI and LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate (LiBOB)); It is preferable to use the concentration of lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, Lithium ions can move effectively.

Depending on the type of lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. As the separator, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / poly It goes without saying that a mixed multilayer film such as a propylene three-layer separator can be used.

1 is an exploded perspective view of a rechargeable lithium battery according to one embodiment of the present invention. Although a lithium secondary battery according to an embodiment is described as an example of being rectangular, the present invention is not limited thereto, and may be applied to various types of batteries, such as a cylindrical shape and a pouch type.

Referring to FIG. 1, the lithium secondary battery 100 according to the exemplary embodiment includes an electrode assembly 40 and an electrode assembly 40 interposed between the positive electrode 10 and the negative electrode 20 with a separator 30 interposed therebetween. It may include a case 50 is built. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown).

Hereinafter, examples and comparative examples of the present invention are described. Such following examples are only examples of the present invention, and the present invention is not limited to the following examples.

(Example 1)

To 30% by weight: The mean particle diameter (D50) of the 18㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 and the alternative compound the average particle diameter (D50) of the 4㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 pellets compound 70 Mixing gave a mixture. The mixture was washed once with water at room temperature (25 ° C.) to prepare a positive electrode active material.

As a result of measuring the BET specific surface area of the positive electrode active material obtained by washing with water, 2.11 m 2 / g was obtained. Moreover, 0.12 weight% was obtained when the residual Li content of this positive electrode active material was measured.

95% by weight of the obtained positive electrode active material having a BET of 2.11 m 2 / g, 1% by weight of AlF ₃ having an average particle diameter (D50) of 1 μm, 2% by weight of polyvinylidene fluoride binder, and 2% by weight of carbon black conductive material were N-methyl. A positive electrode active material slurry was prepared by mixing in a pyrrolidone solvent.

The cathode active material slurry was coated, dried and rolled on an Al foil current collector to prepare a cathode including a cathode layer formed on the current collector.

(Example 2)

The AlF ₃ content was changed from 1% by weight to 2% by weight, except that 94% by weight of the positive electrode active material, 2% by weight of AlF _3, 2% by weight of the binder, and 2% by weight of the conductive material were used. It was carried out to prepare a positive electrode.

(Example 3)

The AlF ₃ content was changed from 1% by weight to 3% by weight, except that 93% by weight of the positive electrode active material, 3% by weight of AlF ₃ , 2% by weight of the binder, and 2% by weight of the conductive material were used. It was carried out to prepare a positive electrode.

(Example 4)

The AlF ₃ content was changed from 1% by weight to 5% by weight, except that 91% by weight of the positive electrode active material, 5% by weight of AlF ₃ , 2% by weight of the binder, and 2% by weight of the conductive material were used. It was carried out to prepare a positive electrode.

(Example 5)

The AlF ₃ content was changed from 1% by weight to 10% by weight, except that 86% by weight of the positive electrode active material, 10% by weight of AlF ₃ , 2% by weight of the binder, and 2% by weight of the conductive material were used. It was carried out to prepare a positive electrode.

(Example 6)

The same procedure as in Example 2 was carried out except that MgF ₂ was used instead of AlF ₃ .

(Example 7)

, Except that the BiF ₃ on AlF _3, instead was carried out in the same manner as in the second embodiment.

(Example 8)

The same procedure as in Example 2 was carried out except that ZrF ₄ was used instead of AlF ₃ .

(Comparative Example 1)

To 30% by weight: The mean particle diameter (D50) of the 18㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 and the alternative compound the average particle diameter (D50) of the 4㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 pellets compound 70 The positive electrode active material was prepared by mixing. It was 0.38 m <2> / g when the BET specific surface area of the produced positive electrode active material was measured. Moreover, 0.55 weight% was obtained when the residual Li content of this positive electrode active material was measured.

A cathode active material slurry was prepared by mixing 96% by weight of a positive electrode active material having a BET specific surface area of 0.38 m 2 / g, 2% by weight of polyvinylidene fluoride binder 2 and 2% by weight of a carbon black conductive material in an N-methyl pyrrolidone solvent.

The cathode active material slurry was coated, dried, and rolled on an Al foil current collector to prepare a cathode including a cathode layer formed on the current collector.

(Comparative Example 2)

To 30% by weight: The mean particle diameter (D50) of the 18㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 and the alternative compound the average particle diameter (D50) of the 4㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 pellets compound 70 Mixing gave a mixture. The mixture was washed once with water at room temperature (25 ° C.) to prepare a cathode active material. It was 2.11 m <2> / g when the BET specific surface area of the produced positive electrode active material was measured.

96 wt% of the positive electrode active material having a BET of 2.11 m 2 / g, polyvinylidene fluoride binder 2, and 2 wt% of the carbon black conductive material were mixed in an N-methyl pyrrolidone solvent to prepare a positive electrode active material slurry.

The cathode active material slurry was coated, dried, and rolled on an Al foil current collector to prepare a cathode including a cathode layer formed on the current collector.

(Comparative Example 3)

To 30% by weight: The mean particle diameter (D50) of the 18㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 and the alternative compound the average particle diameter (D50) of the 4㎛ _{Li 1 Ni 0.91 Co 0.07 Al 0.02} O 2 pellets compound 70 The positive electrode active material was prepared by mixing. It was 0.38 m <2> / g when the BET specific surface area of the produced positive electrode active material was measured. Moreover, 0.55 weight% was obtained when the residual Li content of this positive electrode active material was measured.

94 wt% of a positive electrode active material having a BET specific surface area of 0.38 m 2 / g, 2 wt% of AlF ₃ having an average particle diameter (D50) of 1 μm, polyvinylidene fluoride binder 2, and 2 wt% of carbon black conductive material were N-methylpi A positive electrode active material slurry was prepared by mixing in a rolidone solvent.

The cathode active material slurry was coated, dried, and rolled on an Al foil current collector to prepare a cathode including a cathode layer formed on a current collector.

(Comparative Example 4)

Average particle diameter (D50) instead of the Li ₁ Ni _0.91 Co _0.07 Al _0.02 O ₂ allele having an average particle diameter (D50) of 18 μm and the Li ₁ Ni _0.91 Co _0.07 Al _0.02 O ₂ small particle having an average particle diameter (D50) of 4 μm. ) Was performed in the same manner as in Comparative Example 1 except that a Li ₁ Ni _0.6 Co _0.2 Mn _0.3 O ₂ compound having a 10 μm was used as the positive electrode active material. As a result of measuring the residual Li content of the prepared cathode active material, 0.07 wt% was obtained.

(Comparative Example 5)

The same procedure as in Comparative Example 4 was carried out except that AlF ₃ was not used.

(Comparative Example 6)

Except for changing the AlF ₃ content from 1% by weight to 15% by weight was carried out in the same manner as in Example 1 to prepare a positive electrode.

(Comparative Example 7)

Except for changing the AlF ₃ content from 1% by weight to 20% by weight in the same manner as in Example 1 to prepare a positive electrode.

(Comparative Example 8)

An Li 1 Ni _0.6 Co _0.2 Mn _0.2 O ₂ positive electrode active material having an average particle diameter (D50) of 10 μm and a BET specific surface area of 0.38 m 2 / g was prepared.

94% by weight of the positive electrode active material, 2% by weight of AlF ₃ having an average particle diameter (D50) of 1 μm, 2% by weight of polyvinylidene fluoride binder, and 2% by weight of carbon black conductive material were mixed in an N-methyl pyrrolidone solvent. A positive electrode active material slurry was prepared.

The cathode active material slurry was coated, dried and rolled on an Al foil current collector to prepare a cathode including a cathode layer formed on the current collector.

(Comparative Example 9)

The same procedure as in Comparative Example 8 was carried out except that AlF ₃ was not used.

Evaluation Example 1 Residual Lithium and BET Specific Surface Area Measurement

Residual lithium content and BET specific surface area of the positive electrode active material prepared according to Examples 1 to 8 and Comparative Examples 1 to 9 were measured as follows and summarized in Table 1 below.

The residual lithium content was measured by an acidic acid titration method, and 50 g of the prepared active material was added to a beaker together with 100 ml of ultrapure water, and after stirring, the stirred solution was separated from the solution and powder using a filter paper, and then the obtained solution was PH titration was performed using 0.1 N hydrochloric acid, and the content was determined.

BET specific surface area was measured using the physical and chemical adsorption phenomena and Brunauer-Emmett-Teller (BET) method. That is, after measuring the weight of the prepared active material, nitrogen was adsorbed on the surface of the active material to measure the amount of adsorbed nitrogen gas, and then the BET specific surface area was calculated using the BET calculation formula. In Table 1 below, the positive electrode active materials of Comparative Examples 8 and 9 were Li 1 Ni _0.6 Co _0.2 Mn _0.2 O ₂ positive electrode active materials.

Cathode active material
(wt%) Metal fluoride
(wt%) bookbinder
(wt%) Conductive material
(wt%) Whether or not Residual lithium
(wt%) Specific surface area
(㎡ / g) Example 1 95 AlF ₃ , 1 2 2 ○ 0.12 2.11 Example 2 94 AlF ₃ , 2 2 2 ○ 0.12 2.11 Example 3 93 AlF ₃ , 3 2 2 ○ 0.12 2.11 Example 4 91 AlF ₃ , 5 2 2 ○ 0.12 2.11 Example 5 86 AlF ₃ , 10 2 2 ○ 0.12 2.11 Example 6 94 MgF ₂ , 2 2 2 ○ 0.12 2.11 Example 7 94 BiF ₃ , 2 2 2 ○ 0.12 2.11 Example 8 94 ZrF ₄ , 2 2 2 ○ 0.12 2.11 Comparative Example 1 96 X 2 2 X 0.55 0.38 Comparative Example 2 94 X 2 2 ○ 0.12 2.11 Comparative Example 3 94 AlF ₃ , 2 2 2 X 0.55 0.38 Comparative Example 4 94 AlF ₃ , 2 2 2 X 0.07 0.42 Comparative Example 5 96 X 2 2 X 0.07 0.42 Comparative Example 6 81 AlF ₃ , 15 2 2 ○ 0.12 2.11 Comparative Example 7 76 AlF ₃ , 20 2 2 ○ 0.12 2.11 Comparative Example 8 94 AlF ₃ , 2 2 2 X 0.07 0.38 Comparative Example 9 96 X 2 2 X 0.07 0.38

As shown in Table 1, as the washing process is carried out, as in Example 1 and Comparative Example 2, it can be seen that as the residual Li content decreases, the BET specific surface area increases.

Evaluation Example 2: Slurry Stability

After leaving the positive electrode active material slurry prepared according to Examples 1 to 5 and Comparative Examples 1 and 2 for 3 days at room temperature, the presence or absence of layer separation was measured. The results are shown in Table 2 below.

Slurry phase stability Example 1 Layered radish Example 2 Layered radish Example 3 Layered radish Example 4 Layered radish Example 5 Layered radish Comparative Example 1 Layered radish Comparative Example 2 Layer separation oil

As shown in Table 2, in Examples 1 to 5 in which AlF ₃ was added to the positive electrode active material having a BET specific surface area of 2.11 m 2 / g, since no layer separation occurred, it can be seen that the slurry phase stability was excellent. On the contrary, in Comparative Example 2 in which AlF ₃ was not added to the positive electrode active material having a BET specific surface area of 2.11 m 2 / g, since the layer separation occurred, it can be seen that the slurry phase stability was not good.

On the other hand, in the case of Comparative Example 1 using the positive electrode active material having a low BET specific surface area of 0.38 m 2 / g, it can be seen that layer separation does not occur even if AlF ₃ is not added. From this result, it can be seen that when a positive electrode active material having a BET specific surface area of 0.5 m 2 / g or more is used, layer separation occurs, which can be suppressed by adding AlF ₃ .

Evaluation Example 3 Adhesion to Current Collectors

In the positive electrode manufactured according to Examples 1 to 5 and Comparative Examples 1 to 2, the adhesive force of the current collector and the positive electrode layer was attached to the positive electrode by attaching a double-sided tape attached to the slide glass using a UTM tensile strength tester at 180 ° C. After the preparation, the sample was measured by a measuring method with a measuring instrument, and the results are shown in Table 3 below.

Adhesive force (gf / mm) Example 1 28.8 Example 2 28.3 Example 3 27.8 Example 4 27.1 Example 5 26.2 Comparative Example 1 26.5 Comparative Example 2 20.1

As shown in Table 3, in Examples 1 to 5 in which AlF ₃ was added to the positive electrode active material having a BET specific surface area of 2.11 m 2 / g, the adhesive strength was higher than that of Comparative Example 2 using the positive electrode active material having the same BET specific surface area. It can be seen that this is very excellent. In addition, in Examples 1 to 5, the adhesive strength was superior to that of Comparative Example 1 using a cathode active material having a low BET specific surface area of 0.38 m 2 / g.

From this result, it can be seen that when AlF ₃ is added to the positive electrode active material having a BET specific surface area of 0.5 m 2 / g or more, the adhesive force increases.

Evaluation Example 4: Initial Charge and Discharge Characteristics

A half cell was manufactured by a conventional method using the positive electrode, the lithium metal counter electrode, and the electrolyte prepared according to Examples 1 to 8, Comparative Examples 1 to 5, and Reference Examples 1 to 2, respectively. As the electrolyte, a mixed solvent (50:50 volume ratio) of ethylene carbonate and diethyl carbonate in which 1.0 M LiPF ₆ was dissolved was used.

After charging and discharging the prepared half cell at 0.1C once, and measuring the charge and discharge capacity, the results of the initial efficiency and initial discharge capacity of Examples 1 to 8 and Comparative Examples 1 to 7 are shown in Table 4 below. .

Evaluation Example 6: High Rate Characteristics

After charging and discharging the half battery prepared in Evaluation Example 5 once at 0.2C, charging and discharging was performed once at 1C. The 1C discharge capacity ratio to the 0.2C discharge capacity was obtained, and the results of Examples 1 to 8 and Comparative Examples 1 to 7 are shown in Table 4 below. In addition, the results of Comparative Examples 8 and 9 are shown in Table 5 below.

Evaluation Example 7: Cycle Life Characteristics

After charging and discharging the prepared half battery at room temperature (25 ° C.) at 50 ° C., 50 times, the discharge capacity ratio of 50 times to 1 time of discharge capacity was calculated. The results of Examples 1 to 8 and Comparative Examples 1 to 7 Table 4 shows each.

metal
Fluoride (wt%) Defensive
Whether Residue
lithium
(weight%) Specific surface area
(㎡ / g) Early
efficiency(%) Initial discharge capacity (mAh / g) High rate
characteristic(%) life span
characteristic(%) Example 1 AlF ₃ , 1 ○ 0.12 2.11 90.7 210.6 89.5 82 Example 2 AlF ₃ , 2 ○ 0.12 2.11 90.6 210.1 90.1 85 Example 3 AlF ₃ , 3 ○ 0.12 2.11 90.1 207.3 90.3 87 Example 4 AlF ₃ , 5 ○ 0.12 2.11 89.4 205.8 89.2 87 Example 5 AlF ₃ , 10 ○ 0.12 2.11 88.7 200.2 88.8 92 Example 6 MgF ₂ , 2 ○ 0.12 2.11 90.3 209.8 90.3 86 Example 7 BiF ₃ , 2 ○ 0.12 2.11 90.4 210.4 90.5 88 Example 8 ZrF ₄ , 2 ○ 0.12 2.11 90.3 210.0 90.5 86 Comparative Example 1 X X 0.55 0.38 89.5 219.3 89.9 83 Comparative Example 2 X ○ 0.12 2.11 89.1 211.7 88.4 73 Comparative Example 3 AlF ₃ , 2 X 0.55 0.38 89.3 218.8 89.6 84 Comparative Example 4 AlF ₃ , 2 X 0.07 0.42 90.7 174.3 92.4 91 Comparative Example 5 X X 0.07 0.42 91.1 175.8 92.9 90 Comparative Example 6 AlF ₃ , 15 ○ 0.12 2.11 85.1 188.7 87.1 91 Comparative Example 7 AlF ₃ , 20 ○ 0.12 2.11 81.4 176.1 85.3 92

Type of positive electrode active material AlF ₃ content
(weight%) Initial efficiency
(%) Initial discharge capacity
(mAh / g) High rate characteristics
(1C / 0.2C,%) Cycle characteristics
(50 times / 1 time,%) Comparative Example 8 NCM622 2 90.7 174.3 92.4 91 Comparative Example 9 NCM622 0 91.1 175.8 92.9 90

In Table 4, as shown in Examples 2 to 5 and MgF _2, BiF _3, and Examples 6 to 82 using weight% of ZrF _4, the AlF ₃ with 2 to 10% by weight, than Comparative Examples 1 and 2 It can be seen that excellent cycle characteristics.

In particular, Examples 2 and 3 and, MgF _2, BiF ₃ and carrying out 2 with% by weight of a ZrF ₄ In Examples 6 to 8, the initial efficiency, high-rate characteristics and cycle characteristics with AlF ₃ 2 wt% and 3 wt. All showed excellent results.

On the other hand, in Comparative Examples 1 and 3 that do not perform water washing, the residual lithium content is high, a large amount of gas can be generated, it can be predicted that the thermal stability will be poor.

In addition, looking at Example 1 and Comparative Example 2 subjected to water washing, it can be seen that the addition of AlF ₃ , the initial efficiency and high rate characteristics improved, in particular the cycle life characteristics significantly improved. A From the results, the positive electrode active material subjected to the washing water may be clear to an improved cell performance effect according to the addition of AlF _3.

In addition, in the case of Comparative Example 3 in which AlF ₃ was added to the positive electrode active material having a low BET specific surface area of 0.38 m 2 / g, compared to Comparative Example 1 in which AlF ₃ was not used while using the same positive electrode active material, the cycle life characteristics improved effect. Is insignificant, and it can be seen that the initial efficiency, initial discharge capacity and high rate characteristics are rather deteriorated. Thus, even if the Ni content is 80 mol% or more, it can be clearly seen that the effect of adding AlF ₃ to the cathode active material having a low BET specific surface area of 0.38 m 2 / g is not obtained, but can be deteriorated.

In addition, even in the case of using AlF ₃ , Comparative Examples 6 and 7, which have excessive amounts of 15% by weight and 20% by weight, have excellent cycle life characteristics, but have low high rate characteristics, and have a markedly lower initial efficiency and discharge capacity. It can be seen.

In addition, as shown in Table 4, when using a Ni content of 80 mol% or less as the positive electrode active material, even if the washing step is not performed, the amount of residual lithium is somewhat low, but the effect of using a metal fluoride You can see the insignificance.

In Table 5, NCM622 represents Li ₁ Ni _0.6 Co _0.2 Mn _0.1 O ₂ .

As shown in Table 5, in the case of using NCM622 having a Ni content of 60 mol% as the cathode active material, even if AlF ₃ is added as in Comparative Example 8, the cycle life compared to Comparative Example 9 without using AlF ₃ It can be seen that the effect of improving the characteristics is insignificant, and that the initial efficiency, initial discharge capacity and rate characteristics are rather deteriorated.

From this result, it can be seen that the effect of using a metal fluoride can not be obtained in the low Ni cathode active material having a Ni content of less than 80 mol%.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

Claims (11)

Current collectors; And
A positive electrode layer formed on the current collector and including a nickel-based positive electrode active material, a metal fluoride, a conductive material, and a binder having the BET specific surface area of 0.5 m 2 / g to 2.5 m 2 / g;
The content of the metal fluoride is 1% by weight to 10% by weight based on 100% by weight of the total content of the anode layer.
A positive electrode for a lithium secondary battery comprising a.
[Formula 1]
Li _a Ni _x Co _y A _z O ₂
(In Formula 1, 0.9 ≦ a ≦ 1.1, 0.8 ≦ x ≦ 0.98, 0.1 ≦ y ≦ 0.3, 0.1 ≦ z ≦ 0.3, x + y + z = 1, A is Mn or Al.) The method of claim 1,
The metal fluoride is Al fluoride, Mg fluoride, Zr fluoride, Bi fluoride or a combination thereof. The method of claim 1,
The positive electrode active material is a positive electrode for a lithium secondary battery which is a mixture of an active material and a small active material. The method of claim 1,
The positive electrode active material is a positive electrode for a lithium secondary battery which is a mixture of an active material having an average particle diameter (D50) of 15 μm to 20 μm and a small particle active material having an average particle diameter (D50) of 3 μm to 5 μm. The method of claim 1,
A mixing ratio of the allele and the small active material is 60:40 to 80:20 weight ratio of the positive electrode for a lithium secondary battery. The method of claim 1,
The average particle diameter (D50) of the metal fluoride is a lithium secondary battery positive electrode of 0.5㎛ to 2.5㎛. The method of claim 1,
The nickel-based positive electrode active material is a lithium secondary battery positive electrode that is subjected to a water washing step. Preparing a cathode active material composition by mixing a nickel-based cathode active material, a metal fluoride, a binder, and a conductive material having the BET specific surface area of 0.5 m 2 / g to 2.5 m 2 / g in a solvent;
Applying the positive electrode active material composition to a current collector
As a manufacturing method of the positive electrode for lithium secondary batteries containing a process,
Wherein the metal fluoride is used in the content of 1% by weight to 10% by weight relative to 100% by weight of the nickel-based positive electrode active material, the metal fluoride, the binder and the total content of the conductive material. .
[Formula 1]
Li _a Ni _x Co _y A _z O ₂
(In Formula 1, 0.9 ≦ a ≦ 1.1, 0.8 ≦ x ≦ 0.98, 0.1 ≦ y ≦ 0.3, 0.1 ≦ z ≦ 0.3, x + y + z = 1, A is Mn or Al.) The method of claim 8,
The metal fluoride is Al fluoride, Mg fluoride, Zr fluoride, Bi fluoride or a combination thereof. The method of claim 8,
The manufacturing method of the positive electrode for lithium secondary batteries which further performs the process of water-washing the said positive electrode active material before manufacturing the said positive electrode active material composition. An anode according to any one of claims 1 to 7;
A negative electrode including a negative electrode active material; And
Electrolyte
Lithium secondary battery comprising a.

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