KR102585297B1 - Lithium secondary battery - Google Patents

Abstract

Embodiments of the present invention provide a lithium secondary battery that includes first positive electrode active material particles having a concentration gradient and second positive electrode active material particles having a polymorphic structure as a positive electrode active material, and has improved both electrical performance and mechanical safety.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

The present invention relates to lithium secondary batteries. More specifically, it relates to a lithium secondary battery containing lithium metal oxide.

Secondary batteries are batteries that can be repeatedly charged and discharged, and with the development of the information and communication and display industries, they are widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, and laptop PCs. Additionally, recently, battery packs including secondary batteries have been developed and applied as a power source for eco-friendly vehicles such as hybrid vehicles.

Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and weight reduction. It is being actively developed and applied.

For example, a lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an exterior material, for example in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

Lithium metal oxide is used as a positive electrode active material for the lithium secondary electricity, and it is desirable to have high capacity, high output, and long lifespan characteristics. However, as the application range of the lithium secondary battery expands, securing stability in harsher environments such as high or low temperature environments needs to be considered. In addition, the lithium secondary battery or the positive electrode active material needs to be safe against defects such as short circuit and ignition when penetration by an external object occurs.

However, it is not easy for the positive electrode active material to satisfy all of the above-described characteristics. For example, Korean Patent Publication No. 10-2017-0093085 discloses a positive electrode active material containing a transition metal compound and an ion adsorption binder, but there are limitations in ensuring sufficient lifespan characteristics and safety.

Korean Patent Publication No. 10-2017-0093085

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

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 disposed between the anode and the cathode. The first positive electrode active material particles include lithium metal oxide in which at least one metal forms a concentration gradient, and the second positive active material particles include primary particles of different shapes or crystal structures.

In some embodiments, the second positive electrode active material particles include first particles arranged in a central region and second particles arranged in an outer region, and the first particles and the second particles have different shapes or crystals. It can have a structure.

In some embodiments, the first particle may have a granular or spherical structure, and the second particle may have a rod-shaped or needle-shaped structure.

In some embodiments, the central area of the second positive active material particle may encompass an area corresponding to a radius of 20 to 80% from the center of the particle.

In some embodiments, the first positive electrode active material particles include a core portion, a shell portion, and a concentration gradient region interposed between the core portion and the shell portion, and the concentration gradient may be formed in the concentration gradient region.

In some embodiments, the core portion and the shell portion may each include lithium metal oxide with a fixed composition.

In some embodiments, the first positive electrode active material particles may include a continuous concentration gradient formed from the center to the surface.

In some embodiments, the first positive electrode active material particles may be represented by Formula 1 below.

[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 , 0<x≤1.1, 1.98≤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 (M1) may be nickel (Ni), the second metal (M2) may be manganese (Mn), and the third metal (M3) may be cobalt (Co). .

In some embodiments, the second positive electrode active material particles may be represented by Formula 2 below.

[Formula 2]

Li _x Ni _a Co _b Mn _c M4 _d M5 _e O _y

(In Formula 2, M4 includes one or more elements selected from the group consisting of Ti, Zr, Al, Mg, and Cr, and M5 includes one or more elements selected from the group consisting of Sr, Y, W, and Mo, 0<x<1.5, 1.98≤y≤2.02, 0.313≤a≤0.353, 0.313≤b≤0.353, 0.313≤c≤0.353, 0≤d≤0.03, 0≤e≤0.03, 0.98≤a+b+c≤ is 1.02).

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

In some embodiments, the second positive electrode active material particles may exhibit an exothermic peak of 40 J/g or less at a temperature of 200°C or higher when measured by differential scanning calorimetry (DSC).

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

Therefore, a lithium secondary battery with improved both electrical performance and mechanical safety can be implemented.

1 is a schematic cross-sectional view showing a lithium secondary battery according to example embodiments.
Figure 2 is a cross-sectional SEM photograph of a second positive electrode active material particle of an example.
Figure 3 is a cross-sectional SEM photograph of a second positive electrode active material particle of a comparative example.
Figure 4 is a differential scanning calorimetry (DSC) graph for second positive electrode active material particles of Examples and Comparative Examples.

Embodiments of the present invention provide a lithium secondary battery that includes first positive electrode active material particles having a concentration gradient and second positive electrode active material particles having a polymorphic structure as a positive electrode active material, and has improved both electrical performance and mechanical safety.

Hereinafter, embodiments of the present invention will be described in detail. However, this is only illustrative and the present invention is not limited to the specific embodiments described as examples. The meaning of the terms “first” and “second” used in this specification does not limit the number or order of objects modified by “first” and “second”, but refers to different objects being modified. It is nothing more than a distinction.

1 is a schematic cross-sectional view showing a lithium secondary battery according to example 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 exemplary embodiments, the positive electrode active material may include first positive electrode active material particles and second positive electrode active material particles, and may be formed by mixing the first positive electrode active material particles and the second positive active material particles.

The first positive electrode active material particles may include a concentration gradient. For example, at least one metal inside the particle may include lithium metal oxide that forms a concentration gradient. The lithium metal oxide may include nickel and other transition metals, and nickel may be included in excess among metals other than lithium. The term “excess” used in this application refers to inclusion in the largest content or molar ratio among metals other than lithium.

In some embodiments, the first positive electrode active material particle may include a concentration gradient region between the center and the surface. For example, the concentration gradient region may be formed in a specific area between the center and the surface.

In one embodiment, the first positive electrode active material particles may include a core portion and a shell portion, and the concentration gradient region may be included between the core portion and the shell portion. For example, the core portion may include the central portion, and the shell portion may include the surface.

A concentration gradient for some metal elements in lithium metal oxide may be formed in the concentration gradient region. The concentration may be uniform or fixed in the core portion and the shell portion. For example, the lithium metal oxide of the core portion and the shell portion may have a substantially fixed composition.

In one embodiment, the concentration gradient area may be formed in the center. In one embodiment, the concentration gradient region may be formed on the surface.

According to some embodiments, in the first positive electrode active material particle, the concentration of lithium and oxygen is substantially fixed in the entire particle region, and at least one element other than lithium and oxygen is continuous in the concentration gradient region. There may be a concentration gradient.

The term “continuous concentration gradient” as used in this application means having a concentration distribution that changes continuously with a certain trend or trend in the concentration gradient region. The constant trend includes a decrease or increase in the concentration change trend.

In some embodiments, the first positive electrode active material particles may include lithium metal oxide having a continuous concentration gradient from the center of the particle to the surface. For example, the concentration gradient region may be formed over the entire diameter or radius from the center of the first positive active material particle to the surface. For example, the first positive electrode active material particle may have a full concentration gradient (FCG) structure in which a concentration gradient is formed substantially completely throughout the particle.

The term “center” used in this application includes the exact center point of the active material particle, and may also include an area within a predetermined radius from the center point. For example, the “center” may encompass an area within a radius of about 0.1 μm from the exact center point of the active material particle.

The term “surface” used in this 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 an area within a thickness of about 0.1 μm from the outermost surface of the active material particle.

In some embodiments, the continuous concentration gradient includes a case where 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 one embodiment, the concentration of at least one metal other than lithium contained in the first positive electrode active material particle may continuously increase, and the concentration of at least one metal may continuously decrease.

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

In one embodiment, metals other than lithium contained 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 in the concentration gradient region. The concentration of the second metal M2 may continuously increase in the concentration gradient region.

In one embodiment, metals other than lithium contained in the first positive electrode 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 through the concentration gradient region.

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

For example, the first positive electrode active material particles may be represented by Formula 1 below.

[Formula 1]

Li _x M1 _a M2 _b M3 _c O _y

In Formula 1 above, 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 , 0<x≤1.1, 1.98≤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 lithium secondary batteries. The higher the nickel content, the better the capacity and output of the lithium secondary battery. However, if the nickel content is excessively increased, the lifespan may decrease and it may be disadvantageous in terms of mechanical and electrical stability. For example, if the nickel content is excessively increased, defects such as ignition or 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, the capacity and output characteristics of the lithium secondary battery are secured by securing a high nickel content in the center, and the nickel concentration is reduced toward the surface. Penetration instability and reduced lifespan can be suppressed.

For example, manganese (Mn) can be provided as a metal related to the mechanical and electrical stability of lithium secondary batteries. According to exemplary embodiments, by increasing the content of manganese toward the surface, defects such as ignition and short circuit caused by penetration through the surface of the first positive electrode active material particles can be suppressed or reduced, and lithium secondary It can increase the lifespan of electricity.

For example, cobalt (Co) may be a metal associated with the conductivity or resistance of lithium secondary batteries. According to exemplary embodiments, the concentration of cobalt may be fixed or maintained constant over substantially the entire area of the first positive electrode active material. Accordingly, improved conductivity and low-resistance characteristics can be secured 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 is nickel, and for example, 0.6≤a≤0.95 and 0.05≤b+c≤0.4. For example, the concentration (or mole ratio) of nickel may be reduced from about 0.95 to about 0.6 from the core to the surface.

If the lower limit of nickel concentration (eg, surface concentration) is less than about 0.6, the capacity and output on the surface of the active material particle may be excessively reduced. If the upper limit of nickel concentration (for example, center concentration) exceeds about 0.95, lifespan reduction and mechanical instability may occur in the center.

Preferably, it can be adjusted to 0.7≤a≤0.9 and 0.1≤b+c≤0.3, considering the above-mentioned capacity and stability together.

In some embodiments, the first positive electrode active material particle may include a concentration gradient region where at least one metal forms a concentration gradient between the center and the surface. For example, the concentration gradient may include a specific region between the center and the surface. The first positive electrode active material particles may have a fixed concentration profile in areas excluding the concentration gradient area.

In one embodiment, the first metal (M1), the second metal (M2), and the third metal (M3) in the concentration gradient region may have the above-described concentration profile. In one embodiment, the concentration gradient area may be formed in the center. In one embodiment, the concentration gradient region may be formed on the surface.

In some example embodiments, the first positive electrode 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, alloys thereof, or oxides thereof. These may be used alone or in combination of two or more. The first positive electrode active material particles are passivated by the coating layer, and penetration safety and lifespan can be further improved.

In one embodiment, the elements, alloys, or oxides of the coating layer described above may be inserted as dopants into the first positive electrode active material particles.

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

As described above, high capacity/high output characteristics can be realized by using, for example, lithium metal oxide containing an excessive amount of nickel as the first positive electrode active material particles. Additionally, by including a concentration gradient in the first positive electrode active material, it is possible to suppress deterioration in lifespan and operational stability due to excessive use of nickel.

According to exemplary embodiments, as the first positive electrode active material particles are blended with the second positive electrode active material particles having a polymorphic structure, the penetration safety or resistance characteristics of the lithium secondary battery may be significantly improved.

For example, when a positive electrode active material containing an excessive amount of nickel is used alone, if the secondary battery is penetrated by an external object, a large amount of heat energy is generated in a short moment due to overcurrent, which may cause ignition or explosion.

However, according to embodiments of the present invention, when the second cathode active material with a polymorphic structure is used in combination with the above-described first cathode active material, the heat generation phenomenon due to overcurrent during penetration is suppressed, thereby preventing ignition or explosion of the secondary battery. there is.

For example, as the second positive electrode active material particles include primary particles of different particle shapes, the internal structure of the positive electrode active material particles ensures irregularity, and the particles of different particle shapes act as resistors to each other, resulting in rapid heat propagation, Heat progression may be inhibited.

According to exemplary embodiments, the second positive electrode active material particles may have a multi-shape structure. As used in this application, the term “polymorphic” is used to distinguish it from “single-shape,” and may mean an agglomerated structure of particles of different shapes.

For example, the second positive electrode active material particles may have a secondary particle structure formed by agglomerating primary particles. The second positive electrode active material particles may include primary particles having a plurality of different shapes or crystal structures.

In some embodiments, the second positive electrode active material particles (e.g., primary particles included in the second positive active material particles) include first particles and second particles having different shapes or crystal structures. can do.

For example, the first particles and the second particles may have various shapes such as granule, spherical shape, oval shape, rod shape, needle shape, etc., and may have different shapes or crystal structures.

The first particles may be arranged in a central area of the second positive electrode active material particles, and the second particles may be arranged in an outer area of the second positive electrode active material particles.

For example, the central area may encompass an area corresponding to about 20 to 80% of the radius of the second positive active material particle from the center of the particle. The outer area may correspond to the remaining area outside the central area. In one embodiment, the central area may encompass an area corresponding to about 40 to 70% of the radius of the second positive active material particle from the center of the particle, and the outer area corresponds to the remaining area outside the central area. It can be.

In some embodiments, the first particle in the central region may have a granular or spherical structure, and the second particle in the outer region may have a rod-shaped or needle-shaped structure. In this case, electrical conductivity and capacity characteristics can be secured in the outer region through the second particles, and rapid heat propagation in the central region can be effectively blocked through the first particles.

According to some exemplary embodiments, the second positive electrode active material is lithium nickel-cobalt-manganese oxide and may be represented by the following formula (2).

[Formula 2]

Li _x Ni _a Co _b Mn _c M3 _d M4 _e O _y

In Formula 2, M4 contains one or more elements selected from the group consisting of Ti, Zr, Al, Mg and Cr, M5 contains one or more elements selected from the group consisting of Sr, Y, W and Mo, 0 <x<1.5, 1.98≤y≤2.02, 0.313≤a≤0.353, 0.313≤b≤0.353, 0.313≤c≤0.353, 0≤d≤0.03, 0≤e≤0.03, 0.98≤a+b+c≤1.02 am.

For example, the second positive electrode active material particles maintain a relatively lower nickel concentration or molar ratio than that of the first positive electrode active material particles throughout the entire particle area, and manganese may be evenly distributed. In one embodiment, the content or molar ratio of nickel, cobalt, and manganese of the second positive electrode active material is adjusted to be substantially the same, so that thermal and mechanical properties such as life stability and penetration safety are relatively improved through the second positive electrode active material. It can be improved.

According to some exemplary embodiments, the second positive electrode active material particles may exhibit an exothermic peak of 40 J/g or less at a temperature of 200° C. or higher when measured using differential scanning calorimetry (DSC). According to some embodiments, the second positive electrode active material particles may exhibit an exothermic peak of 15 J/g or less at a temperature of 320°C or higher when measured by DSC method.

In some embodiments, the second positive electrode active material particles may further include a coating layer. The coating layer may include a metal or a metal oxide, for example, Al, Ti, Ba, Zr, Si, B, Mg, P and alloys thereof, or an oxide, phosphide or fluoride of the metal. It can be included. The second positive electrode active material particles are passivated by the coating layer, and penetration safety and lifespan can be further improved. Additionally, by including the coating layer, the capacity and output characteristics of the positive electrode active material can be improved. In one embodiment, the elements, alloys, or oxides of the coating layer described above may be inserted as dopants into the second positive electrode active material particles.

In some embodiments, the positive electrode active material may be manufactured by separately manufacturing the first positive electrode active material particles and the second positive electrode active material particles and then blending them.

In exemplary embodiments, the mixing weight ratio of the first positive electrode active material particles and the second positive electrode active material particles may be, for example, 9:1 to 1:9. Within the above mixing weight ratio range, the high energy density characteristics of the secondary battery can be secured while improving lifespan and thermal stability, and preventing ignition due to penetration can be more easily implemented. More preferably, the mixing weight ratio may be 6:4 to 9:1.

The positive electrode active material may be manufactured by separately manufacturing the first positive electrode active material particles and the second positive electrode active material particles and then blending them.

In forming the first positive electrode active material particles, metal precursor solutions with different concentrations can 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, acid salt, etc.

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 (e.g., concentration of nickel, manganese, and cobalt in the center) of the center of the first positive electrode active material particle and a target composition of the surface (e.g., 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, mixing may be performed by continuously changing the mixing ratio so that a concentration gradient is continuously formed from the target composition at the center to the target composition at the surface. Accordingly, the concentration of metals inside the precipitate may form a concentration gradient within the particle.

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

The second positive electrode active material particles are formed by forming a precipitate while stirring using a single metal precursor solution having a target composition, and changing the composition, input flow rate, temperature, and stirring speed of the precursor solution during the formation of the precipitate to form a plurality of shapes or A polymorphic structure with a crystal structure can be created.

According to exemplary embodiments, a positive electrode active material formed by blending the first positive electrode active material particles and the second positive electrode active material particles may be obtained. A slurry can be prepared by mixing and stirring the positive electrode active material with a binder, a conductive material, and/or a dispersant in a solvent. After coating the slurry on the positive electrode current collector 110, the positive electrode 130 can be manufactured by compressing and drying.

The positive electrode current collector 110 is a metal with high conductivity and to which a mixture of active materials can easily adhere, and a metal that is not reactive within the voltage range of the battery may be used. For example, it may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably includes aluminum or an aluminum alloy.

The binder is, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethyl methacryl. It may include an organic binder such as polymethylmethacrylate or an aqueous binder such as styrene-butadiene rubber (SBR), and may be used with a thickener such as carboxymethyl cellulose (CMC).

For example, a PVDF-based binder can be used as a binder for forming an anode. In this case, the amount of binder for forming the positive electrode active material layer can be reduced and the amount of the first and second positive active material particles can be relatively increased, thereby improving the output and capacity of the secondary battery.

The conductive material may be included to promote electron transfer between active material particles. 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 , or LaSrMnO ₃ It may include a metal-based conductive material including the like.

According to 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 a negative electrode active material.

As the anode active material, any material known in the art that can occlude and desorb lithium ions may be used without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composite, and carbon fiber; lithium alloy; Silicon or tin, etc. may be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500°C or lower, and mesophase pitch-based carbon fibers (MPCF). Examples of the crystalline carbon include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium.

The negative electrode current collector 120 is a metal with high conductivity and to which a mixture of active materials can easily adhere, and a metal that is not reactive within the voltage range of the battery may be used. For example, it may include gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably includes copper or a copper alloy.

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

Materials that are substantially the same as or similar to the materials described above may be used as the binder and 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, and carboxymethyl cellulose (CMC). 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 polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. The separator may include a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc.

In some embodiments, the area (eg, contact area with the separator 150) and/or volume of the cathode 140 may be larger than that of the anode 130. Accordingly, lithium ions generated from the anode 130 can be smoothly moved to the cathode 140 without precipitating, for example. Therefore, the effect of simultaneously improving output and safety through the combination of the above-described first and second positive electrode active material particles can be more easily implemented.

According to exemplary embodiments, the electrode cell 160 is defined by the anode 130, the cathode 140, and the separator 150, and a plurality of electrode cells 160 are stacked to form, for example, a jelly roll ( An electrode assembly in the form of a jelly roll may be formed. For example, the electrode assembly can be formed through winding, lamination, folding, etc. of the separator.

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

The non- ^aqueous electrolyte solution contains a lithium ^salt as an electrolyte and ^an organic solvent ^{. The} lithium salt is ^, for example, expressed as Li ⁺ 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 ^- , Examples include SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC). ), methylpropyl carbonate, dipropyl carbonate, dimethylsulperoxide, 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.

Electrode tabs may be formed from the positive electrode current collector 110 and the negative electrode current collector 120 belonging to each electrode cell, respectively, and extend to one side of the exterior case 170. The electrode tabs may be fused together with the one side of the exterior case 170 to form an electrode lead that extends or is exposed to the outside of the exterior case 170.

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

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but these examples are only illustrative of the present invention and do not limit the scope of the appended claims, and are examples within the scope and technical idea 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 changes and modifications fall within the scope of the appended patent claims.

Experimental Example 1

1. Examples 1 to 8: Preparation of secondary batteries

(1) Anode

The first positive electrode active material particles (hereinafter referred to as positive electrode 1) have an overall composition of LiNi _0.8 Co _0.11 Mn _0.09 O ₂ , and the compositions of the core and shell parts are LiNi _0.84 Co _0.11 Mn _0.05 O ₂ and LiNi _0.78 Co _0.1 0Mn _0.12 O _{2 ,} respectively. The first positive electrode active material particles having a concentration gradient section were manufactured by forming a precipitate by continuously changing the precursor mixing ratio to form a concentration gradient zone (decreased Ni concentration, increased Mn concentration) between the core portion and the shell portion.

The second positive electrode active material particle (hereinafter referred to as polymorph NCM111) has a composition of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and contains granular primary particles in the central area up to 60% of the radius from the center of the particle. , the outer region was manufactured to contain rod-shaped primary particles.

Specifically, the second positive electrode active material particles include a metal oxide precursor containing the following elements of Ni, Co, and Mn in a molar ratio of about 1:1:1; And a precursor solution containing a chelating agent containing ammonia and NaOH was coprecipitated under first conditions and then continuously coprecipitated under second conditions. The first and second conditions are shown in Table 1 below.

division Raw material input speed Metal oxide precursor flow rate Chelating agent
flux Stirring speed temperature reaction time unit Hz L/min L/min rpm ℃ h 1st condition 10 8 4 200 50 50 2nd condition 5 4 2 300 50 30

A positive electrode mixture was prepared by mixing the positive electrode active material particles in the weight ratio shown in Table 2 below, Denka Black conductive material, and PVDF binder in a mass ratio of 92:5:3, respectively, and then coated on an aluminum current collector and dried. and pressing to prepare a positive electrode. The electrode density of the positive electrode after the press was 3.5 g/cc or more.

(2) cathode

93% by weight of natural graphite as a negative electrode active material, 5% by weight of KS6, 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 cathode slurry containing The cathode slurry was coated on a copper substrate, dried, and pressed to prepare a cathode.

(3) Manufacturing of lithium secondary batteries

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

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

Afterwards, pre-charging was performed for 36 minutes at a current (5A) equivalent to 0.25C. After 1 hour, degassing was performed and aging was performed for more than 24 hours, followed by chemical charging and discharging (charging conditions CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharge conditions CC 0.2C 2.5V CUT). -OFF). Afterwards, standard charging and discharging was performed (charging conditions CC-CV 0.5C 4.2V 0.05C CUT-OFF, discharging conditions CC 0.5C 2.5V CUT-OFF).

2. Comparative Examples 1 to 6

Comparative Examples 1 to 6 were secondary cathode active material particles in the same manner as the above example, except that a cathode active material having the composition of NCM111 and having the same particle shape in the central region and outer region of the particle (hereinafter referred to as short-type NCM111) was used as the second cathode active material particle. A battery was manufactured.

Experimental Example 1

(1) Room temperature lifespan characteristics

After repeating charging (CC-CV 1.0C 4.2V 0.05C CUT-OFF) and discharging (CC 1.0C 2.7V CUT-OFF) 500 times with the cells manufactured in the examples and comparative examples, the discharge capacity at 500 times was Room temperature lifespan characteristics were measured by calculating % of one-time discharge capacity. The results are shown in Table 2 below.

(2) Penetration safety evaluation

After charging (1C 4.2V 0.1C CUT-OFF) with the cells manufactured in Examples and Comparative Examples, a test was performed by penetrating the battery from the outside with a 3mm diameter nail at a speed of 80mm/sec to observe whether it ignited or exploded. The results are shown in Table 2 below.

<Evaluation criteria, EUCAR Hazard Level>

L1: No problem with battery performance

L2: Irreversible damage to battery performance.

L3: Battery electrolyte weight reduced by less than 50%

L4: The weight of the battery's electrolyte is reduced by more than 50%

L5: Ignition or explosion occurs

division First positive electrode active material Second positive active material mixed weight ratio life span(%)
(500cycle) Penetration results Example 1 anode 1 Polymorphic NCM111 80:20 93.2% L3 Example 2 anode 1 Polymorphic NCM111 70:30 94.1% L3 Example 3 anode 1 Polymorphic NCM111 60:40 96.2% L3 Example 4 anode 1 Polymorphic NCM111 50:50 96.9% L3 Example 5 anode 1 Polymorphic NCM111 40:60 98.0% L3 Example 6 anode 1 Polymorphic NCM111 30:70 98.5% L3 Example 7 anode 1 Polymorphic NCM111 20:80 99.3% L3 Example 8 anode 1 Polymorphic NCM111 10:90 99.9% L3 Comparative Example 1 anode 1 Short type NCM111 90:10 85.1% L5 Comparative Example 2 anode 1 Short type NCM111 80:20 86.4% L5 Comparative Example 3 anode 1 Short type NCM111 70:30 87.6% L5 Comparative Example 4 anode 1 Short type NCM111 60:40 89.3% L4 Comparative Example 5 anode 1 Short type NCM111 50:50 91.5% L4 Comparative Example 6 anode 1 Short type NCM111 40:60 92.9% L4

Referring to Table 2, it was confirmed that compared to the comparative examples in which monomorphic NCM 111 was mixed with the positive electrode 1 material, the lifespan and penetration safety of examples in which polymorphic NCM111 was mixed were improved.

Experimental Example 2: Surface/cross-section observation

The surfaces and cross-sections of polymorphic NCM111 and monomorphic NCM 111 used in the examples of the present invention were observed using a scanning electron microscope (SEM) to obtain the photographs in FIGS. 2 and 3.

Referring to Figures 2 and 3, while NCM111 of the conventional monomorphic structure has substantially the same particle shape in the center region and outer region, in the case of the second positive electrode active material (polymorphic NCM111) according to some exemplary embodiments of the present invention, the particle shape in the center region and the outer region is substantially the same. It was confirmed that the particle shapes in the area and the outer area were different. For example, in the case of polymorph NCM111 shown in Figure 2, the central region occupied a space corresponding to approximately 60% of the particle radius, and the particle shape in the central region was observed to be granular. The outer area occupied the space excluding the central area, and the particle shape appeared as needles.

Experimental Example 3: DSC measurement

Polymorphic NCM111 ('C1') and monomorphic NCM 111 ('C2') used in the examples of the present invention were analyzed by differential scanning calorimetry (DSC) to evaluate thermal properties. As a result, the graph in Figure 4 was obtained.

Referring to FIG. 4, it was found that the positive electrode active material of the polymorphic NCM111 (C1) according to some exemplary embodiments of the present invention had improved thermal properties compared to the monomorphic NCM111 (C2). In particular, in the case of C2, a narrow peak of 61 J/g was observed around a temperature of 320°C, while in the case of C1, a broad peak corresponding to about 13 J/g was observed around a temperature of about 335°C. Therefore, it was found that high-temperature safety and reliability of the secondary battery could be secured by using polymorphic NCM111.

3. Examples 9 to 14

Secondary batteries of Examples 9 to 14 were manufactured in the same manner as Example 3, except that the central area of the second positive electrode active material was changed from the particle center to the radius shown in Table 3 below.

The lifespan and penetration characteristics of the secondary batteries of Examples 9 to 14 were evaluated by the method described above and are shown in Table 3 below.

Anode 1:weight ratio of polymorphic NCM 111 Radius of the central region of polymorph NCM111 life span(%) Penetration results Example 3 60:40 60% 96.2 L3 Example 9 60:40 10% 96.0 L4 Example 10 60:40 20% 95.5 L3 Example 11 60:40 40% 98.1 L3 Example 12 60:40 70% 97.5 L3 Example 13 60:40 80% 95.2 L3 Example 14 60:40 90% 94.5 L4

Referring to Table 3 above, when the central area is 20 to 80% of the radius of the second positive electrode active material particle, penetration safety is improved, and when the radius of the second positive electrode active material particle is 40 to 70%, penetration safety and lifespan are further improved. I was able to confirm.

Claims (12)

Comprising first positive electrode active material particles and second positive electrode active material particles each containing lithium metal oxide containing nickel, cobalt, and manganese,
The first positive electrode active material particles include a concentration gradient of at least one metal among nickel, cobalt, and manganese,
The second positive electrode active material particles include primary particles of different shapes or crystal structures, and nickel, cobalt, and manganese do not contain a concentration gradient across the entire area of the second positive electrode active material particles. The method according to claim 1, wherein the second positive electrode active material particles include first particles arranged in a central region and second particles arranged in an outer region, and the first particles and the second particles have different shapes or crystal structures. A positive electrode active material for a lithium secondary battery. The cathode active material for a lithium secondary battery according to claim 2, wherein the first particles have a granular or spherical structure, and the second particles have a rod-shaped or needle-shaped structure. The cathode active material for a lithium secondary battery according to claim 2, wherein the central region of the second cathode active material particle encompasses an area corresponding to a radius of 20 to 80% from the center of the particle. The method according to claim 1, wherein the first positive electrode active material particles include a core portion, a shell portion, and a concentration gradient region interposed between the core portion and the shell portion,
The concentration gradient is a positive electrode active material for a lithium secondary battery formed in the concentration gradient region. The cathode active material for a lithium secondary battery according to claim 5, wherein the core portion and the shell portion each include lithium metal oxide with a fixed composition. The cathode active material for a lithium secondary battery according to claim 1, wherein the first cathode active material particles include a continuous concentration gradient formed from the center to the surface. The method according to claim 1, wherein the first positive electrode active material particles are represented by the following formula (1), a positive electrode active material for a lithium secondary battery:
[Formula 1]
Li _x Ni _a Mn _b Co _c O _y
(In Formula 1, 0<x≤1.1, 1.98≤y≤2.02, 0.7≤a≤0.9 and 0.1≤b+c≤0.3). delete The method according to claim 1, wherein the second positive electrode active material particles are represented by the following formula (2), a positive electrode active material for a lithium secondary battery:
[Formula 2]
Li _x Ni _a Co _b Mn _c M4 _d M5 _e O _y
(In Formula 2, M4 includes one or more elements selected from the group consisting of Ti, Zr, Al, Mg, and Cr, and M5 includes one or more elements selected from the group consisting of Sr, Y, W, and Mo, 0<x<1.5, 1.98≤y≤2.02, 0.313≤a≤0.353, 0.313≤b≤0.353, 0.313≤c≤0.353, 0≤d≤0.03, 0≤e≤0.03, 0.98≤a+b+c≤ is 1.02). The cathode active material for a lithium secondary battery according to claim 1, wherein the mixing weight ratio of the first cathode active material particles and the second cathode active material particles is 9:1 to 1:9. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the second positive electrode active material particles exhibit an exothermic peak of 40 J/g or less at a temperature of 200° C. or higher when measured by differential scanning calorimetry (DSC).