KR102449152B1 - Lithium secondary battery and method of fabricating the same - Google Patents

Abstract

A lithium secondary battery includes a positive electrode formed of a positive electrode active material including first positive electrode active material particles and a second positive electrode active material particle, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The first positive active material particles include lithium metal oxide having a continuous concentration gradient formed from the center to the surface, and the second positive active material particles include lithium metal oxide having a constant concentration composition. Capacity and stability may be simultaneously improved by mixing the first and second positive electrode active materials.

Description

Lithium secondary battery and manufacturing method thereof

The present invention relates to a lithium secondary battery and a method for manufacturing the same. More particularly, it relates to a lithium secondary battery including a lithium metal oxide and a method for manufacturing the same.

A secondary battery is a battery that can be repeatedly charged and discharged, and is widely applied as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook PCs with the development of information communication and display industries. Also, recently, a battery pack including a secondary battery has been developed and applied as a power source for an eco-friendly vehicle such as a hybrid vehicle.

Examples of the secondary battery include a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, and the like, and among them, the lithium secondary battery has high operating voltage and energy density per unit weight, and is advantageous for charging speed and weight reduction. It is being actively developed and applied in this respect.

For example, a lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator (separator), and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include, for example, a pouch-type casing accommodating the electrode assembly and the electrolyte.

Lithium metal oxide is used as the positive electrode active material of the lithium secondary electricity, and it is preferable to have high capacity, high output, and long life characteristics. However, as the application range of the lithium secondary battery is expanded, it is necessary to consider securing stability in a harsher environment such as a high temperature or low temperature environment. In addition, the lithium secondary battery or the positive electrode active material needs to have stability against defects such as short circuit and ignition when penetration by an external object occurs.

However, it is not easy for the positive active material to satisfy all of the above-described characteristics. For example, Korean Patent Application Laid-Open No. 10-2017-0093085 discloses a cathode active material including a transition metal compound and an ion adsorption binder, but there is a limit in securing sufficient lifespan characteristics and stability.

Korean Patent Publication No. 10-2017-0093085

One object of the present invention is to provide a lithium secondary battery having excellent electrical and mechanical reliability and stability.

One object of the present invention is to provide a method for manufacturing a lithium secondary battery having excellent electrical and mechanical reliability and stability.

A lithium secondary battery according to exemplary embodiments includes a positive electrode formed of a positive electrode active material including first positive electrode active material particles and second positive electrode active material particles; cathode; and a separator interposed between the positive electrode and the negative electrode. The first positive active material particles include lithium metal oxide having a continuous concentration gradient formed from the center to the surface, and the second positive active material particles include lithium metal oxide having a constant concentration composition.

In some embodiments, the first positive active material particles may include a first metal whose concentration is continuously decreased from the center to the surface and a second metal whose concentration is continuously increased from the center to the surface. .

In some embodiments, the first positive active material particles may further include a third metal having a constant concentration from the center to the surface.

In some embodiments, the first positive active material particle may be represented by the following Chemical Formula 1.

[Formula 1]

Li _x M1 _a M2 _b M3 _c O _y

(Formula 1, M1, M2 and M3 represent the first metal, the second metal and the third metal, respectively, and are Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, selected from the group consisting of Ba, Zr, Nb, Mo, Al, Ga and B, 0<x≤1.1, 2≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, 0<a+b+c≤1).

In some embodiments, in Formula 1, 0.6≤a≤0.95 and 0.05≤b+c≤0.4.

In some embodiments, in Formula 1, 0.7≤a≤0.9 and 0.1≤b+c≤0.3.

In some embodiments, the first metal may be nickel (Ni), the second metal may be manganese (Mn), and the third metal may be cobalt (Co).

In some embodiments, the second cathode active material particle may include at least one metal element having a uniform concentration composition from the center to the surface.

In some embodiments, the second cathode active material particle may include at least two kinds of metal elements, and a concentration ratio of the metal elements may be the same.

In some embodiments, the second positive electrode active material particles may be represented by the following Chemical Formula (2).

[Formula 2]

Li _x M1' _a M2' _b M3' _c O _y

(in formula 2, M1', M2' and M3' are Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W and B is selected from the group consisting of 0<x≤1.1, 2≤y≤2.02 and 0<a+b+c≤1).

In some embodiments, in Formula 2, 0.313≤a≤0.353, 0.313≤b≤0.353, and 0.313≤c≤0.353.

In some embodiments, in Formula 2, 0.323≤a≤0.343, 0.323≤b≤0.343, and 0.323≤c≤0.343.

In some embodiments, M1', M2' and M3' may be nickel (Ni), manganese (Mn) and cobalt (Co), respectively.

In some embodiments, a mixing weight ratio of the first positive active material particles and the second positive active material particles may be 8:2 to 1:9.

In some embodiments, a mixing weight ratio of the first positive active material particles and the second positive active material particles may be 6:4 to 1:9.

In some embodiments, the average particle diameter (D ₅₀ ) of the particles of the second positive electrode active material may be 3 to 15 μm.

In some embodiments, the average particle diameter (D ₅₀ ) of the particles of the second positive active material may be 4.5 to 15 μm.

In the method of manufacturing a lithium secondary battery according to exemplary embodiments, the positive active material is prepared by blending the first positive active material particles having a continuous concentration gradient from the center to the surface, and the second positive active material particles having a constant concentration composition . A positive electrode is formed by coating the positive electrode active material on a positive electrode current collector. A negative electrode is formed to face the positive electrode with a separator interposed therebetween.

In some embodiments, the first cathode active material particles may be formed by precipitating a first metal precursor having a target composition at the center and a second metal precursor having a target composition at the surface while continuously changing a mixing ratio. The second cathode active material particles may be formed using a metal precursor having a single composition.

According to the above-described exemplary embodiments, the positive active material of the lithium secondary battery may include the first positive active material particles having a concentration gradient and the second positive active material particles having a fixed concentration profile. High capacity and high output characteristics of the lithium secondary battery may be secured through the first positive active material particles, and penetration stability and thermal stability of the lithium secondary battery may be secured through the second positive active material particles.

Accordingly, it is possible to implement a lithium secondary battery having improved both electrical performance and mechanical stability.

In some embodiments, lifespan characteristics and penetration stability may be further improved by adjusting the size of the particles of the second positive active material or by forming a coating layer on the particles of the first positive active material.

1 is a schematic cross-sectional view illustrating a lithium secondary battery according to exemplary embodiments.
2 is a cross-sectional view schematically illustrating a concentration gradient measurement position of particles of a first positive electrode active material prepared according to example embodiments.
3 is a cross-sectional photograph of particles of a first positive electrode active material prepared according to example embodiments.
4 is a cross-sectional photograph of lithium-metal oxide particles used in Comparative Examples.

Embodiments of the present invention provide a lithium secondary battery with improved both electrical performance and mechanical stability, including first positive active material particles having a concentration gradient as a positive electrode active material, and second positive active material particles having a fixed concentration profile. In addition, embodiments of the present invention provide a method of manufacturing the lithium secondary battery or the positive electrode active material.

Hereinafter, embodiments of the present invention will be described in detail. However, this is merely exemplary and the present invention is not limited to the specific embodiments described by way of example. The terms "first" and "second" used herein do not limit the number or order of the objects modified by "first" and "second", but refer to different modified objects. only to distinguish

1 is a schematic cross-sectional view illustrating a lithium secondary battery according to exemplary embodiments.

Referring to FIG. 1 , the lithium secondary battery of the present invention may include a positive electrode 130 , a negative electrode 140 , and a separator 150 interposed between the positive electrode and the negative electrode.

The positive electrode 130 may include a positive electrode current collector 110 and a positive electrode active material layer 115 formed by applying a positive electrode active material to the positive electrode current collector 110 . According to example embodiments, the positive active material may include first positive active material particles and second positive active material particles.

The first positive active material particles may include lithium metal oxide having a continuous concentration gradient from the particle center to the surface. In some embodiments, the first positive active material particle may have a full concentration gradient (FCG) structure in which a concentration gradient is formed substantially completely throughout the particle.

According to some embodiments, in the first positive active material particle, the concentrations of lithium and oxygen are substantially fixed in the entire region of the particle, and at least one of the elements other than lithium and oxygen is continuous from the center of the particle to the surface. It can have a negative concentration gradient.

As used herein, the term "continuous concentration gradient" means having a concentration distribution that continuously changes with a constant trend or trend between the surfaces at the center. The constant trend includes a decrease or an increase in a concentration change trend.

As used herein, the term “central portion” includes a central point of the active material particle, and may include an area within a predetermined radius from the central point. For example, the “center” may encompass a radius of about 0.1 μm from the central point of the active material particle.

The term "surface" used in the present application includes, for example, the outermost surface of the active material particle, and may include a predetermined thickness from the outermost surface. For example, the “surface portion” may encompass a region within about 0.1 μm in thickness from the outermost surface of the active material particle.

In some embodiments, the continuous concentration gradient includes a case in which the concentration profile according to the particle area is a straight line or a curve, and in the case of the curve, it may include a change in a constant trend without a concentration inflection point.

In an embodiment, the concentration of at least one metal among metals other than lithium included in the first positive electrode active material particles may continuously increase, and the concentration of the at least one metal may decrease continuously.

In an embodiment, at least one of the metals other than lithium included in the first positive electrode active material particle may have a substantially constant concentration from the center to the surface.

In an embodiment, metals other than lithium included in the first positive electrode active material particles may include a first metal M1 and a second metal M2. The concentration of the first metal M1 may continuously decrease from the center to the surface. The concentration of the second metal M2 may continuously increase from the center to the surface.

In an embodiment, metals other than lithium included in the first positive active material particles may further include a third metal M3. The third metal M3 may have a substantially constant concentration from the center to the surface.

As used herein, the term “concentration” may mean, for example, a molar ratio of the first to third metals.

For example, the first positive active material particle may be represented by the following Chemical Formula 1.

[Formula 1]

Li _x M1 _a M2 _b M3 _c O _y

In Formula 1, M1, M2 and M3 are selected from the group consisting of Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B and 0<x≤1.1, 2≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, 0<a+b+c≤1.

In some embodiments, M1, M2, and M3 in Formula 1 may be nickel (Ni), manganese (Mn), and cobalt (Co), respectively.

For example, nickel may be provided as a metal associated with the capacity of a lithium secondary battery. As the content of nickel increases, the capacity and output of the lithium secondary battery may be improved. However, if the content of nickel is excessively increased, the lifespan may decrease and may be disadvantageous in terms of mechanical and electrical stability. For example, when the content of nickel is excessively increased, defects such as ignition and short circuit may not be sufficiently suppressed when penetration by an external object occurs.

However, according to exemplary embodiments, the first metal M1 is set to nickel and the content of nickel is high in the center to secure the capacity and output characteristics of the lithium secondary battery, and the nickel concentration is decreased toward the surface. Penetration instability and deterioration of life can be suppressed.

For example, manganese (Mn) may be provided as a metal related to mechanical and electrical stability of a lithium secondary battery. According to exemplary embodiments, by increasing the content of manganese toward the surface portion, it is possible to suppress or reduce defects such as ignition and short circuit due to penetration occurring through the surface of the first positive electrode active material particle, and lithium secondary It can increase the life of electricity.

For example, cobalt (Co) may be a metal associated with conductivity or resistance of a lithium secondary battery. In example embodiments, the concentration of cobalt over substantially the entire area of the first positive electrode active material may be fixed or maintained constant. Accordingly, it is possible to secure improved conductivity and low resistance characteristics while maintaining a constant flow of current and charge through the first positive electrode active material.

In some embodiments, the first metal M1 in Formula 1 may be nickel, for example, 0.6≤a≤0.95 and 0.05≤b+c≤0.4. For example, the concentration (or molar ratio) of nickel may decrease continuously from about 0.95 to about 0.6 from the center to the surface.

When the lower limit of the nickel concentration (eg, the surface concentration) is less than about 0.6, the capacity and output at the surface of the active material particles may be excessively reduced. When the upper limit of the nickel concentration (eg, the concentration of the core) exceeds about 0.95, the lifespan and mechanical instability may be caused in the core.

Preferably, it may be adjusted to 0.7≤a≤0.9 and 0.1≤b+c≤0.3 in consideration of the above-described capacity and stability together.

In some example embodiments, the first positive active material particles may further include a coating layer on the surface. For example, the coating layer may include Al, Ti, Ba, Zr, Si, B, Mg, P, or an alloy thereof or an oxide thereof. These may be used alone or in combination of two or more. The first positive active material particles are passivated by the coating layer, so that penetration stability and lifespan may be further improved.

In an embodiment, the elements, alloys, or oxides of the above-described coating layer may be inserted as a dopant in the particles of the first positive electrode active material.

In some embodiments, the first positive active material particles may have a rod-type primary particle shape. In addition, the average particle diameter of the first positive active material particles may be about 3 to about 25㎛.

The positive active material may include second positive active material particles blended with the first positive active material particles. In example embodiments, the second positive active material particles may have a uniform or fixed concentration over the entire region of the particles.

In some embodiments, the second positive active material particles may include lithium metal oxide, for example, at least two or more metals other than lithium. Concentrations of metals other than lithium may be maintained the same from the center to the surface, for example.

In some embodiments, the second cathode active material particles may also include a first metal M1 ′, a second metal M2 ′, and a third metal M3 ′. For example, the first metal M1', the second metal M2', and the third metal M3' may be nickel (Ni), manganese (Mn), and cobalt (Co), respectively.

As described above, the concentration or molar ratio of nickel, manganese, and cobalt may be uniformly maintained over the entire area of the second positive active material particle. In some embodiments, the molar ratio of nickel, manganese, and cobalt over the entire region of the second positive active material particle may be the same (eg, substantially 1:1:1).

For example, the second positive electrode active material particles may be represented by the following Chemical Formula 2.

[Formula 2]

Li _x M1' _a M2' _b M3' _c O _y

In Formula 2, M1', M2' and M3' are Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W and B It is selected from the group consisting of, and may be 0<x≤1.1, 2≤y≤2.02, and 0<a+b+c≤1.

In some embodiments, in Formula 2, 0.313≤a≤0.353, 0.313≤b≤0.353, and 0.313≤c≤0.353, preferably 0.323≤a≤0.343, 0.323≤b≤0.343, and 0.323≤c≤0.343 can be

In some embodiments, as described above, the first metal (M1'), the second metal (M2'), and the third metal (M3') are nickel (Ni), manganese (Mn), and cobalt (Co), respectively. ) can be

According to example embodiments, as the second positive active material particles are blended with the first positive active material particles, thermal stability of a lithium secondary battery or a positive electrode may be improved. In the second positive active material particles, a relatively lower nickel concentration or molar ratio than in the first positive active material particles is maintained over the entire particle area, and manganese may be uniformly distributed.

Accordingly, the possibility of ignition caused when penetrating an external object is remarkably reduced, and heat resistance is improved during repeated high-temperature charging and discharging, so that the operation uniformity and lifespan of the lithium secondary battery can be improved.

In addition, for example, the concentration of cobalt may be uniformly maintained over the entire region of the second positive active material particle, so that uniform conductivity or resistance may be realized throughout the positive electrode.

In some embodiments, the average particle diameter (D ₅₀ ) of the particles of the second positive electrode active material may be about 3 to 15 μm. In the above range, the lifespan and stability of the lithium secondary battery or the positive electrode may be improved without interfering with the electrical activity of the first positive electrode active material particles by the second positive electrode active material particles. In a preferred embodiment, the average particle diameter (D ₅₀ ) of the particles of the second positive active material may be about 4.5 to 15 μm.

When the average particle diameter (D ₅₀ ) of the particles of the second positive electrode active material is less than about 3 μm, the particle size is excessively reduced, making it difficult to implement a desired composition and difficult to control to have desired activity and stability. When the average particle diameter (D ₅₀ ) of the particles of the second cathode active material exceeds about 15 μm, too much heat is consumed to generate the particles, thereby increasing process inefficiency.

In example embodiments, the mixing weight ratio of the first positive active material particles and the second positive active material particles may be, for example, 8:2 to 1:9, preferably 6:4 to 1:9. . Within the above range, improvement of thermal stability through the particles of the second cathode active material and prevention of ignition due to penetration may be more easily realized.

The positive active material may be prepared by blending the first positive active material particles and the second positive active material particles, respectively.

In forming the first positive electrode active material, metal precursor solutions having different concentrations may be prepared. The metal precursor solution may include metal precursors to be included in the positive electrode active material. For example, the metal precursor may be a metal halide, hydroxide, or acid salt.

For example, the metal precursor may include a lithium precursor (eg, lithium oxide), a nickel precursor, a manganese precursor, and a cobalt precursor.

According to exemplary embodiments, a first precursor solution having a target composition (eg, concentrations of nickel, manganese, and cobalt in the central portion) of the central portion of the first positive active material particle and a target composition of the surface (eg, A second precursor solution having a concentration of nickel, manganese and cobalt on the surface) may be prepared, respectively.

after. A precipitate may be formed while mixing the first and second precursor solutions. During the mixing, the mixing ratio may be continuously changed so that a concentration gradient is continuously formed from the target composition in the center to the target composition in the surface. Accordingly, in the precipitate, the concentration of metals therein may form a concentration gradient in the particle.

In some embodiments, the precipitate may be performed by adding a chelating agent and a basic agent during the mixing. In some embodiments, after heat-treating the precipitate, it may be mixed with a lithium salt and heat-treated again.

The second cathode active material particles may be formed by forming a precipitate while stirring using a single metal precursor solution having a target composition.

According to example embodiments, a cathode active material formed by blending the particles of the first cathode active material and the particles of the second cathode active material may be obtained. A slurry may be prepared by mixing and stirring the positive active material with a binder, a conductive material and/or a dispersing material in a solvent. After the slurry is coated on the positive electrode current collector 110 , the positive electrode 130 may be manufactured by compression and drying.

The positive electrode current collector 110 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, preferably aluminum or an aluminum alloy.

The binder, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride, PVDF), polyacrylonitrile (polyacrylonitrile), polymethylmethacrylic An organic binder such as polymethylmethacrylate or an aqueous binder such as styrene-butadiene rubber (SBR) may be included, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

For example, a PVDF-based binder may be used as a binder for forming a positive electrode. In this case, the amount of the binder for forming the positive electrode active material layer may be decreased and the amount of the first and second positive electrode active material particles may be relatively increased, and thus the output and capacity of the secondary battery may be improved.

The conductive material may be included to promote electron movement between the particles of the active material. For example, the conductive material may be a carbon-based conductive material such as graphite, carbon black, graphene, or carbon nanotubes and/or a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO ₃ , and LaSrMnO ₃ . It may include a metal-based conductive material including the like.

In example embodiments, the negative electrode 140 may include a negative electrode current collector 120 and a negative electrode active material layer 125 formed by coating the negative electrode current collector 120 with an anode active material.

As the anode active material, any one known in the art capable of intercalating and deintercalating lithium ions may be used without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composite material, and carbon fiber; lithium alloy; Silicon or tin may be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500° C. or lower, mesophase pitch-based carbon fiber (MPCF), and the like. Examples of the crystalline carbon include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Examples of the element contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

The negative electrode current collector 120 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, preferably copper or a copper alloy.

In some embodiments, a slurry may be prepared by mixing and stirring the negative active material with a binder, a conductive material, and/or a dispersing material in a solvent. After coating the slurry on the negative electrode current collector 120 , the negative electrode 140 may be manufactured by compression and drying.

Materials substantially the same as or similar to those described above may be used as the binder and the conductive material. In some embodiments, the binder for forming the negative electrode may include, for example, an aqueous binder such as styrene-butadiene rubber (SBR) for compatibility with the carbon-based active material, such as carboxymethyl cellulose (CMC). It can be used with thickeners.

A separator 150 may be interposed between the anode 130 and the cathode 140 . The separator 150 may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, or an ethylene/methacrylate copolymer. The separator may include a nonwoven fabric formed of high melting point glass fiber, polyethylene terephthalate fiber, or the like.

In some embodiments, an area (eg, a contact area with the separator 150 ) and/or a volume of the negative electrode 140 may be larger than that of the positive electrode 130 . Accordingly, lithium ions generated from the positive electrode 130 may be smoothly moved to the negative electrode 140 without being precipitated in the middle, for example. Accordingly, the effect of simultaneously improving output and stability through the combination of the above-described first and second positive active material particles can be more easily realized.

According to exemplary embodiments, the electrode cell 160 is defined by the positive electrode 130 , the negative electrode 140 , and the separator 150 , and a plurality of electrode cells 160 are stacked, for example, a jelly roll ( A jelly roll type electrode assembly may be formed. For example, the electrode assembly may be formed by winding, lamination, or folding of the separator.

The electrode assembly may be accommodated together with the electrolyte in the outer case 170 to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

The non-aqueous electrolyte includes a lithium salt serving as an electrolyte and an organic solvent, and the lithium salt is, for example, represented by Li ⁺ X ⁻ and F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , NO as an anion (X ⁻ ) of the lithium salt. ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , ( CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- _, CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ⁻ and (CF ₃ CF ₂ SO ₂ ) ₂ N ⁻ and the like can be exemplified.

As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) ), methylpropyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran can be used. . These may be used alone or in combination of two or more.

An electrode tab may be formed from each of the positive electrode current collector 110 and the negative current collector path 120 belonging to each electrode cell to extend to one side of the outer case 170 . The electrode tabs may be fused together with the one side of the outer case 170 to form an electrode lead extending or exposed to the outside of the outer case 170 .

The lithium secondary battery may be manufactured, for example, in a cylindrical shape, a square shape, a pouch type, or a coin type using a can.

Hereinafter, preferred embodiments are presented to help the understanding of the present invention, but these examples are merely illustrative of the present invention and do not limit the appended claims, and are within the scope and spirit of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible, and it is natural that such variations and modifications fall within the scope of the appended claims.

Manufacturing of secondary batteries

(1) Anode

The overall composition is LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ , and the central composition LiNi _{0 . 84} Co _{0 . 11} Mn _{0 . 05} O ₂ surface composition LiNi _{0 . 78} Co _{0 . 10} Mn _{0 .} By continuously changing the precursor mixing ratio to have a concentration gradient up to ₁₂ O ₂ to form a precipitate, first positive active material particles having a continuous concentration gradient were prepared (hereinafter referred to as CAM10, see FIG. 3 ). In addition, a second positive electrode active material particle (hereinafter referred to as NCM111) having substantially the same concentration (or molar ratio) of nickel, manganese, and cobalt from the center to the surface was prepared.

The positive active material particles were prepared by adjusting the blending ratio of the first and second positive active material particles as described in the following tables. The positive electrode active material particles, Denka Black as a conductive material, and PVDF as a binder were prepared in a mass ratio composition of 92: 5: 3, and then a positive electrode mixture was prepared, coated on an aluminum current collector, and dried and pressed to prepare a positive electrode. . After the press, the electrode density of the positive electrode was adjusted to 3.3 g/cc.

2 is a cross-sectional view schematically illustrating a concentration gradient measurement position of particles of a first positive electrode active material prepared according to exemplary embodiments. Referring to FIG. 2 , for lithium-metal oxide particles having a distance of 5 μm from the center of the particle to the surface, the concentration was measured at intervals of 5/7 μm from the surface, and the results are as shown in Table 1 below.

location (number) Molar ratio of Ni Co molar ratio Molar ratio of Mn One 77.97 10.07 11.96 2 80.98 9.73 9.29 3 82.68 10.32 7 4 82.6 10 7.4 5 82.55 10.37 7.07 6 83.24 10.86 5.9 7 84.33 10.83 4.84

(2) cathode

93% by weight of natural graphite as an anode active material, 5% by weight of KS6 as a flake type conductive material as a conductive material, 1% by weight of styrene-butadiene rubber (SBR) as a binder, and 1% by weight of carboxymethyl cellulose (CMC) as a thickener A negative electrode slurry containing The negative electrode slurry was coated on a copper substrate, dried and pressed to prepare a negative electrode.

(3) lithium secondary battery

The positive electrode and the negative electrode prepared as described above are laminated by predetermined notching, respectively, and a separator (polyethylene, thickness 25 μm) is interposed between the positive electrode and the negative electrode to form an electrode cell, and then tab portions of the positive electrode and the negative electrode, respectively welded. The welded anode/separator/cathode combination was placed in a pouch and sealed on three sides except for the electrolyte injection side. At this time, the part with the electrode tab was included in the sealing part. Electrolyte was injected through the remaining surface except for the sealing part, and the remaining surface was sealed and then impregnated for more than 12 hours.

The electrolyte solution was prepared by dissolving 1M LiPF ₆ in a mixed solvent of EC/EMC/DEC (25/45/30; volume ratio), then vinylene carbonate (VC) 1wt%, 1,3-propensultone (PRS) 0.5wt% and 0.5 wt% of lithium bis(oxalato)borate (LiBOB) was used.

Thereafter, pre-charging was performed for 36 minutes at a current (2.5A) corresponding to 0.25C. After 1 hour, degassing and aging for 24 hours or more, chemical charge and discharge were performed (charge condition CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharge condition CC 0.2C 2.5V CUT- OFF). After that, standard charge/discharge was performed (charge condition CC-CV 0.5 C 4.2V 0.05C CUT-OFF, discharge condition CC 0.5C 2.5V CUT-OFF).

Example and comparative example

In Examples, as described above, a blend of CAM10 and NCM111 was used as the cathode active material particles. Comparative Examples are LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ (hereinafter referred to as CAM20. See FIG. 4) particles were used.

In Examples and Comparative Examples, the above-described positive electrode, negative electrode and lithium secondary battery manufacturing methods were performed in the same manner except for the positive electrode active material particles.

Experimental example

(One) Experimental example 1: D50 is 3 μm NCM111 blending Life and penetration stability evaluation according to the ratio

Charging (1C 4.2V 0.1C CUT-OFF) and discharging (1C 3.0V CUT-OFF) were repeated 500 times for the electrode cells according to the Examples and Comparative Examples prepared as described in Table 2 below 500 times The lifetime maintenance rate was evaluated as a percentage of the value obtained by dividing the discharge capacity by the discharge capacity at one time.

In addition, after charging (1C 4.2V 0.1C CUT-OFF) the electrode cells according to Examples and Comparative Examples, they were penetrated with a 3mm diameter nail at a speed of 80mm/sec to evaluate whether or not to ignite. The evaluation results are also described in Table 2 below.

division first positive active material particles Particles of the second positive active material
D50 (3㎛) NCM111
Blending ratio (wt%) life span
retention rate
(%) Penetrate
evaluation Example 1 CAM10 10 83.6 utterance Example 2 CAM10 20 84.8 utterance Example 3 CAM10 30 86.5 utterance Example 4 CAM10 40 87.5 not ignited Example 5 CAM10 50 89.3 not ignited Example 6 CAM10 60 90.5 not ignited Example 7 CAM10 70 92 not ignited Example 8 CAM10 80 93.5 not ignited Example 9 CAM10 90 94.9 not ignited Comparative Example 1 CAM10 0 82.0 utterance Comparative Example 2 CAM20 0 70.0 utterance Comparative Example 3 CAM20 10 70.5 utterance Comparative Example 4 CAM20 20 71.3 utterance Comparative Example 5 CAM20 30 71.6 utterance Comparative Example 6 CAM20 40 72.6 utterance Comparative Example 7 CAM20 50 73.1 utterance Comparative Example 8 CAM20 60 73.6 utterance Comparative Example 9 CAM20 70 74.3 utterance Comparative Example 10 CAM20 80 74.9 not ignited Comparative Example 11 CAM20 90 75.5 not ignited

(2) Experimental example 2: D50 of 4.5 μm NCM111 blending Life and penetration stability evaluation according to the ratio

Life retention and penetration stability were evaluated in the same manner as in Experimental Example 1 for the electrode cells of Examples and Comparative Examples prepared according to the composition of the positive active material shown in Table 3 below.

division first positive active material particles Particles of the second positive active material
D50 (4.5㎛) NCM111
Blending ratio (wt%) life span
retention rate
(%) Penetrate
evaluation Example 10 CAM10 10 83.7 utterance Example 11 CAM10 20 85 not ignited Example 12 CAM10 30 86.4 not ignited Example 13 CAM10 40 87.8 not ignited Example 14 CAM10 50 89.3 not ignited Example 15 CAM10 60 90.9 not ignited Example 16 CAM10 70 92.4 not ignited Example 17 CAM10 80 94 not ignited Example 18 CAM10 90 95.2 not ignited Comparative Example 1 CAM10 0 82.0 utterance Comparative Example 2 CAM20 0 70.0 utterance Comparative Example 12 CAM20 10 70.8 utterance Comparative Example 13 CAM20 20 71.2 utterance Comparative Example 14 CAM20 30 72.1 utterance Comparative Example 15 CAM20 40 72.5 utterance Comparative Example 16 CAM20 50 73.3 utterance Comparative Example 17 CAM20 60 73.8 utterance Comparative Example 18 CAM20 70 74.8 not ignited Comparative Example 19 CAM20 80 75.3 not ignited Comparative Example 20 CAM20 90 76 not ignited

(3) Experimental example 3: D50 of 7 μm NCM111 blending Life and penetration stability evaluation according to the ratio

Life retention and penetration stability were evaluated in the same manner as in Experimental Example 1 for the electrode cells of Examples and Comparative Examples prepared according to the composition of the positive active material shown in Table 4 below.

division first positive active material particles Particles of the second positive active material
D50 (7㎛) NCM111
Blending ratio (wt%) life span
retention rate
(%) Penetrate
evaluation Example 19 CAM10 10 83.5 utterance Example 20 CAM10 20 84.9 not ignited Example 21 CAM10 30 86.6 not ignited Example 22 CAM10 40 88.2 not ignited Example 23 CAM10 50 89.9 not ignited Example 24 CAM10 60 91.2 not ignited Example 25 CAM10 70 92.5 not ignited Example 26 CAM10 80 94.2 not ignited Example 27 CAM10 90 95.8 not ignited Comparative Example 1 CAM10 0 82.0 utterance Comparative Example 2 CAM20 0 70.0 utterance Comparative Example 21 CAM20 10 70.8 utterance Comparative Example 22 CAM20 20 71.5 utterance Comparative Example 23 CAM20 30 72 utterance Comparative Example 24 CAM20 40 72.9 utterance Comparative Example 25 CAM20 50 73.6 utterance Comparative Example 26 CAM20 60 74.4 not ignited Comparative Example 27 CAM20 70 75 not ignited Comparative Example 28 CAM20 80 75.8 not ignited Comparative Example 29 CAM20 90 76.3 not ignited

(4) Experimental example 4: D50 is 10 μm NCM111 blending Life and penetration stability evaluation according to the ratio

Life retention and penetration stability were evaluated in the same manner as in Experimental Example 1 for the electrode cells of Examples and Comparative Examples prepared according to the composition of the positive active material shown in Table 5 below.

division first positive active material particles Particles of the second positive active material
D50 (10㎛) NCM111
Blending ratio (wt%) life span
retention rate
(%) Penetrate
evaluation Example 28 CAM10 10 83.8 utterance Example 29 CAM10 20 85.5 not ignited Example 30 CAM10 30 86.7 not ignited Example 31 CAM10 40 88.6 not ignited Example 32 CAM10 50 90.2 not ignited Example 33 CAM10 60 92 not ignited Example 34 CAM10 70 93.5 not ignited Example 35 CAM10 80 95.1 not ignited Example 36 CAM10 90 96.5 not ignited Comparative Example 1 CAM10 0 82.0 utterance Comparative Example 2 CAM20 0 70.0 utterance Comparative Example 30 CAM20 10 70.9 utterance Comparative Example 31 CAM20 20 71.5 utterance Comparative Example 32 CAM20 30 72.4 utterance Comparative Example 33 CAM20 40 73.2 utterance Comparative Example 34 CAM20 50 73.9 utterance Comparative Example 35 CAM20 60 74.6 not ignited Comparative Example 36 CAM20 70 75.4 not ignited Comparative Example 37 CAM20 80 76.2 not ignited Comparative Example 38 CAM20 90 77 not ignited

(5) Experimental example 5: D50 of 15 μm NCM111 blending Life and penetration stability evaluation according to the ratio

Life retention and penetration stability were evaluated in the same manner as in Experimental Example 1 for the electrode cells of Examples and Comparative Examples prepared according to the composition of the positive active material shown in Table 6 below.

division first positive active material particles Particles of the second positive active material
D50 (15㎛) NCM111
Blending ratio (wt%) life span
retention rate
(%) Penetrate
evaluation Example 37 CAM10 10 83.8 utterance Example 38 CAM10 20 85.6 not ignited Example 39 CAM10 30 87 not ignited Example 40 CAM10 40 89 not ignited Example 41 CAM10 50 90.5 not ignited Example 42 CAM10 60 92.1 not ignited Example 43 CAM10 70 93.8 not ignited Example 44 CAM10 80 95.8 not ignited Example 45 CAM10 90 97.1 not ignited Comparative Example 1 CAM10 0 82.0 utterance Comparative Example 2 CAM20 0 70.0 utterance Comparative Example 39 CAM20 10 70.9 utterance Comparative Example 40 CAM20 20 71.6 utterance Comparative Example 41 CAM20 30 72.5 utterance Comparative Example 42 CAM20 40 73.2 utterance Comparative Example 43 CAM20 50 74.2 utterance Comparative Example 44 CAM20 60 75 not ignited Comparative Example 45 CAM20 70 75.6 not ignited Comparative Example 46 CAM20 80 76.5 not ignited Comparative Example 47 CAM20 90 77.4 not ignited

Referring to Tables 2 to 6, in the examples in which the first positive active material particles CAM10 having a concentration gradient and the second positive active material particles NCM111 having a fixed concentration are blended, life retention rate and penetration stability It was significantly improved compared to these comparative examples.

In the case of Comparative Examples, overall lifespan and penetration stability were reduced, and only when NCM111 was included in excess, ignition did not occur.

In Experimental Examples 1 to 5, when the mixing weight ratio of the first positive active material particles and the second positive active material particles in Examples was 60:40 to 10:90, ignition due to penetration did not occur.

In addition, when the average particle size (D50) of the second positive electrode active material particles (NCM111) is 4.5 to 15 μm, the mixed weight ratio of the first positive active material particles and the second positive active material particles that are not ignited during penetration was more widely distributed.

110: positive electrode current collector 115: positive electrode active material layer
120: negative electrode current collector 125: negative electrode active material layer
130: positive electrode 140: negative electrode
150: separator 160: electrode cell
170: external case

Claims (19)

a positive electrode including a positive active material including first lithium metal oxide particles and second lithium metal oxide particles;
cathode; and
A separator interposed between the positive electrode and the negative electrode,
The first lithium metal oxide particles contain Ni, and Ni has a continuous concentration gradient from the center to the surface of the first lithium metal oxide particles,
The second lithium metal oxide particles contain Ni, and Ni has a uniform concentration from the center to the surface of the second lithium metal oxide particles,
The first lithium metal oxide particles have a higher Ni concentration than the second lithium metal oxide particles over the entire region of the particles,
The average particle diameter (D ₅₀ ) of the second lithium metal oxide particles is 4.5 to 15 μm,
A mixing weight ratio of the first lithium metal oxide particles and the second lithium metal oxide particles is 8:2 to 1:9, a lithium secondary battery.
The method according to claim 1, wherein the first lithium metal oxide particles contain a first metal that continuously decreases in concentration from the center to the surface and a second metal that continuously increases in concentration from the center to the surface,
The first metal is Ni, a lithium secondary battery.
The lithium secondary battery of claim 2, wherein the first lithium metal oxide particles further contain a third metal having a constant concentration from the center to the surface.
The lithium secondary battery according to claim 3, wherein the first lithium metal oxide particles are represented by the following Chemical Formula 1:
[Formula 1]
Li _x M1 _a M2 _b M3 _c O _y
(Formula 1, M1, M2 and M3 represent the first metal, the second metal and the third metal, respectively, M1 is Ni, M2 and M3 are each Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, selected from the group consisting of Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B, 0<x≤1.1, 2≤y≤2.02, 0<a<1, 0<b< 1, 0<c<1, 0<a+b+c≤1).
The lithium secondary battery according to claim 4, wherein in Formula 1, 0.6≤a≤0.95 and 0.05≤b+c≤0.4.
The lithium secondary battery according to claim 4, wherein in Formula 1, 0.7≤a≤0.9 and 0.1≤b+c≤0.3.
The lithium secondary battery of claim 4, wherein the second metal is manganese (Mn), and the third metal is cobalt (Co).
delete The lithium secondary battery of claim 1 , wherein the second lithium metal oxide particles include at least two kinds of metal elements, and a concentration ratio of the metal elements is the same.
The lithium secondary battery according to claim 9, wherein the second lithium metal oxide particles are represented by the following Chemical Formula 2:
[Formula 2]
Li _x M1' _a M2' _b M3' _c O _y
(in Formula 2, M1' is Ni, M2' and M3' are Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W and B is selected from the group consisting of 0<x≤1.1, 2≤y≤2.02 and 0<a+b+c≤1).
The lithium secondary battery according to claim 10, wherein in Formula 2, 0.313≤a≤0.353, 0.313≤b≤0.353, and 0.313≤c≤0.353.
The lithium secondary battery according to claim 10, wherein in Formula 2, 0.323≤a≤0.343, 0.323≤b≤0.343, and 0.323≤c≤0.343.
The lithium secondary battery according to claim 10, wherein M2' and M3' are manganese (Mn) and cobalt (Co), respectively.
delete a positive electrode including a positive active material including first lithium metal oxide particles and second lithium metal oxide particles;
cathode; and
A separator interposed between the positive electrode and the negative electrode,
The first lithium metal oxide particles contain Ni, and Ni has a continuous concentration gradient from the center to the surface of the first lithium metal oxide particles,
The second lithium metal oxide particles contain Ni, and Ni has a uniform concentration from the center to the surface of the second lithium metal oxide particles,
The first lithium metal oxide particles have a higher Ni concentration than the second lithium metal oxide particles over the entire region of the particles,
A mixing weight ratio of the first lithium metal oxide particles and the second lithium metal oxide particles is 6:4 to 1:9, a lithium secondary battery.
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