KR102323189B1 - Positive electrode active material and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a cathode active material and a lithium secondary battery including the same.

Description

A cathode active material and a lithium secondary battery comprising the same

The present invention relates to a cathode active material and a lithium secondary battery including the same.

A battery stores electric power by using a material capable of electrochemical reaction on the anode and the cathode. A typical example of such a battery is a lithium secondary battery that stores electrical energy by a difference in chemical potential when lithium ions are intercalated/deintercalated in a positive electrode and a negative electrode.

The lithium secondary battery is manufactured by using a material capable of reversible intercalation/deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte solution or a polymer electrolyte solution between the positive electrode and the negative electrode.

A lithium composite oxide is used as a cathode active material for a lithium secondary battery, and for example, composite oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiMnO ₂ have been studied.

Among the cathode active materials, LiCoO ₂ is used the most because of its excellent lifespan characteristics and charge/discharge efficiency, but it is expensive due to the resource limitations of cobalt used as a raw material, so it has a limitation in price competitiveness.

LiMnO ₂ , LiMn ₂ O ₄ Lithium manganese oxide has advantages of excellent thermal stability and low price, but has problems in that it has a small capacity and poor high-temperature characteristics. In addition, the LiNiO ₂ -based positive electrode active material exhibits high discharge capacity battery characteristics, but is difficult to synthesize due to a cation mixing problem between Li and a transition metal, and thus has a large problem in rate characteristics.

In addition, a large amount of Li by-products are generated according to the degree of intensification of such cation mixing, and most of these Li by-products are composed _{of LiOH and Li 2} CO _{3 compounds.} It causes gas generation due to charging and discharging after manufacturing. Residual Li ₂ CO ₃ increases cell swelling, which not only reduces the cycle, but also causes the battery to swell.

Korean Patent Publication No. 10-2015-0069334

An object of the present invention is to provide a positive electrode active material capable of improving high-temperature storage stability and lifespan characteristics by increasing the structural stability of the positive electrode active material in order to solve the problems of the existing positive electrode active material for a lithium secondary battery.

In addition, another object of the present invention is to provide a lithium secondary battery using a positive electrode comprising a positive electrode active material as defined herein.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention not mentioned can be understood by the following description and will be more clearly understood by the examples of the present invention. It will also be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, a lithium composite oxide including primary particles and secondary particles formed by aggregation of the primary particles and represented by the following Chemical Formula 1, the interface between the primary particles and the secondary particles A positive electrode active material including a lithium metal oxide present on at least a portion of the surface of the may be provided.

[Formula 1]

Li _a (W _1-y M1 _y ) _b O _c

(Wherein, M1 includes at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd, and 0<a ≤6, 0<b≤6, 0<c≤10, 0<y≤0.50)

The positive active material according to an embodiment of the present invention has high temperature storage stability and lifespan characteristics as structural stability is increased by including lithium metal oxide present on at least a portion of the interface between the primary particles and the surface of the secondary particles. can be improved

In an embodiment, the lithium metal oxide may have a lattice structure doped with at least one M1 element in the lithium metal oxide represented by Chemical Formula 2 below.

[Formula 2]

Li _a W _b O _c

(Here, 0<a≤6, 0<b≤6, 0<c≤10)

In one embodiment, the lithium metal oxide may exhibit a concentration gradient that decreases from the surface portion of the secondary particle toward the center of the secondary particle, and thus the lithium metal oxide is used in the electrochemical reaction of the positive electrode active material. Overall structural collapse can be prevented.

In addition, according to another aspect of the present invention, a lithium secondary battery using a positive electrode including the above-described positive electrode active material may be provided.

The positive electrode active material according to the present invention includes lithium metal oxide present in at least a portion of the interface between the primary particles constituting the lithium composite oxide and the surface of the secondary particles formed by aggregation of the primary particles, thereby increasing structural stability. Accordingly, when the positive electrode including the positive electrode active material according to the present invention is used as a positive electrode of a lithium secondary battery, high temperature storage stability and lifespan characteristics can be further improved.

In addition to the above-described effects, the specific effects of the present invention will be described together while describing specific details for carrying out the invention below.

1 to 4 show transmission electron microscope (TEM) analysis and TEM/EDS mapping results for the positive active material prepared according to an embodiment of the present invention.
5 is a graph (line sum spectrum) showing the content of doping metal elements (Zr, Ti, W) measured according to the TEM/EDS mapping result of the positive electrode active material prepared according to an embodiment of the present invention.
6 and 7 show transmission electron microscopy (TEM) analysis and TEM/EDS mapping results for the positive active material prepared according to the comparative example.
8 to 10 are graphs showing XRD analysis results of positive active materials prepared according to various embodiments of the present invention.

The above-described objects, features and advantages will be described below in detail with reference to the accompanying drawings, and accordingly, those of ordinary skill in the art to which the present invention pertains will be able to easily implement the technical idea of the present invention. In describing the present invention, if it is determined that a detailed description of a known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

Hereinafter, the positive electrode active material according to the present invention and a lithium secondary battery including the same will be described in more detail.

According to an aspect of the present invention, a cathode active material including a lithium composite oxide and a lithium metal oxide including primary particles and secondary particles formed by aggregation of the primary particles may be provided.

Herein, the lithium composite oxide may be defined as a particle including the primary particle and an aggregate in which a plurality of the primary particles are aggregated (physically coupled) to each other. The primary particles may have a rod shape, an oval shape, and/or an irregular shape.

The primary particles may be in contact with neighboring primary particles to form an interface or a grain boundary between the primary particles. In addition, the primary particles may be spaced apart from the neighboring primary particles in the interior of the secondary particles to form internal voids.

In this case, the primary particles may form a surface existing inside the secondary particles by contacting the internal voids without forming a grain boundary by contacting the neighboring primary particles. On the other hand, the surface on which the primary particles present on the outermost surface of the secondary particles are exposed to external air forms the surface of the secondary particles.

In an embodiment, the positive active material may include the lithium metal oxide present in at least a portion of an interface between the primary particles forming the lithium composite oxide and a surface of the secondary particles.

The lithium metal oxide may be physically and/or chemically bonded to the primary particles and/or the secondary particles forming the lithium composite oxide.

In this case, the lithium metal oxide may coat the entire surface of the surface of the secondary particles and the interface between the primary particles forming the lithium composite oxide or the interface between the primary particles forming the lithium composite oxide and the 2 At least a portion of the surface of the primary particles may be coated, and in some cases, the lithium composite oxide may be distributed in the form of particles at the interface between the primary particles and all or at least part of the surface of the secondary particles.

Accordingly, the positive active material according to the present embodiment may increase structural stability by including the above-described lithium metal oxide. can In addition, the lithium metal oxide may affect the efficiency characteristics of the lithium secondary battery by acting as a movement path of lithium ions in the positive electrode active material.

In addition, in some cases, the lithium metal oxide may exist not only in at least a portion of an interface between the primary particles forming the lithium composite oxide and a surface of the secondary particles, but also in internal pores formed inside the secondary particles. can

Here, the lithium metal oxide may be represented by Formula 1 below.

[Formula 1]

Li _a (W _1-y M1 _y ) _b O _c

(Wherein, M1 includes at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd, and 0 < a ≤6, 0<b≤6, 0<c≤10, 0<y≤0.50)

As shown in Formula 1 above, the lithium metal oxide is an oxide in which lithium and at least one metal element are complexed, and the metal element complexed with lithium may include W and at least one metal element M1. .

Accordingly, the lithium metal oxide represented by Chemical Formula 1 is, for example, Li(W/Ti)O, Li(W/Zr)O, Li(W/Ti/Zr)O, Li(W/Ti)O It may be /B)O, and the like, but the above-described examples are merely described for convenience and the lithium metal oxide defined herein is not limited to the above-described examples. Therefore, in Experimental Examples to be described later, for convenience, experimental results for some examples of representative lithium metal oxides that may be represented by Chemical Formula 1 will be described.

In another embodiment, the lithium metal oxide represented by Formula 1 may have a lattice structure doped with at least one M1 element in the lithium metal oxide represented by Formula 2 below.

[Formula 2]

Li _a W _b O _c

(Here, 0<a≤6, 0<b≤6, 0<c≤10)

That is, the lithium metal oxide has a lattice structure formed by _{lithium tungsten oxide (eg, Li 2} WO ₄ , Li ₂ W ₂ O ₇ , Li ₄ WO ₅ , Li ₆ WO ₆ or Li ₆ W ₂ O _{9 ).} Some of my tungsten has a lattice structure substituted with M1 element.

In one embodiment, the lithium metal oxide may exhibit a concentration gradient that decreases from the surface portion of the secondary particles forming the lithium composite oxide toward the center of the secondary particles. Accordingly, the concentration of the lithium metal oxide may decrease from the outermost surface of the secondary particle toward the center of the secondary particle.

For example, when the distance from the outermost surface of the secondary particle forming the lithium metal oxide to the center of the secondary particle is R, the distance from the outermost surface of the secondary particle ( In a region where R′) is 0 to 0.02R, the concentration gradient may be decreased from the surface portion of the secondary particle toward the center of the secondary particle. In addition, the lithium metal oxide has a concentration of increasing or decreasing concentration in a certain direction within a region where the distance (R′) from the outermost surface of the secondary particles forming the lithium composite oxide is greater than 0.02R and 1.0R. It may not have a gradient.

As described above, the lithium metal oxide exhibits a concentration gradient that decreases from the surface portion of the secondary particles forming the lithium composite oxide toward the center of the secondary particles, thereby remaining lithium present on the surface of the positive electrode active material. can be effectively reduced to prevent side reactions caused by unreacted residual lithium in advance, and it is possible to prevent a decrease in crystallinity in a surface inner region of the positive electrode active material by the lithium metal oxide.

In another embodiment, the positive active material may include a metal oxide present in at least a portion of an interface between the primary particles forming the lithium composite oxide and a surface of the secondary particles.

Here, the metal oxide may be represented by Chemical Formula 3 below.

[Formula 3]

Li _d M2 _e O _f

(where M2 is selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd, 0≤d≤6, 0<e≤6, 0<f≤10)

As shown through Formula 3 above, the metal oxide is an oxide in which lithium and one metal element are complexed or an oxide of a metal element other than lithium, and the metal oxide represented by Formula 3 is, for example, Li(W)O, Li(Ti)O, Li(Zr)O, Li(B)O, WO _x , ZrO _x , TiO _x etc. The metal oxide as defined herein is not limited to the examples described above. Therefore, in Experimental Examples to be described later, for convenience, experimental results for some examples of representative metal oxides that may be represented by Chemical Formula 3 will be described.

Herein, in order to distinguish the lithium metal oxide from the metal oxide, an oxide in which lithium and at least two metals are complexed or an oxide in which lithium and tungsten are complexed with at least one metal in the oxide is referred to as a lithium metal oxide, , an oxide in which lithium and one type of metal are complexed or an oxide of a metal element other than lithium is referred to as a metal oxide.

Like the lithium metal oxide, the metal oxide may be physically and/or chemically bonded to the primary particles and/or the secondary particles forming the lithium composite oxide.

In this case, the metal oxide coats the entire surface of the surface of the secondary particles and the interface between the primary particles forming the lithium composite oxide or the interface between the primary particles forming the lithium composite oxide and the secondary At least a part of the surface of the particles may be coated, and in some cases, the particles may be distributed on the entire or at least part of the surface of the secondary particles and the interface between the primary particles forming the lithium composite oxide.

Accordingly, the positive active material according to the present embodiment may increase structural stability by including the above-described metal oxide, and when such a positive active material is used in a lithium secondary battery, the high temperature storage stability and lifespan characteristics of the positive active material may be improved. have. In addition, the metal oxide may affect the efficiency characteristics of the lithium secondary battery by acting as a movement path of lithium ions in the positive electrode active material.

In addition, in some cases, the metal oxide may exist not only in at least a part of the interface between the primary particles forming the lithium composite oxide and the surface of the secondary particles, but also in the internal pores formed inside the secondary particles. have.

In an embodiment, the metal oxide may exhibit a concentration gradient that decreases from a surface portion of the secondary particle forming the lithium composite oxide toward a central portion of the secondary particle. Accordingly, the concentration of the metal oxide may decrease from the outermost surface of the secondary particle toward the center of the secondary particle.

As described above, the metal oxide exhibits a concentration gradient that decreases from the surface portion of the secondary particles forming the lithium composite oxide together with the lithium metal oxide toward the center of the secondary particles, thereby forming the surface of the positive electrode active material. It is possible to effectively reduce the residual lithium present in the electrode to prevent side reactions caused by unreacted residual lithium in advance, and also to prevent the crystallinity in the inner surface region of the positive electrode active material from being lowered by the metal oxide. .

In another embodiment, the metal oxide may include a first metal oxide represented by Formula 4 below and a second metal oxide represented by Formula 5 below.

[Formula 4]

Li _g W _h O _i

(Here, 0≤g≤6, 0<h≤6, 0≤i≤10)

[Formula 5]

Li _j M3 _k O _l

(where M3 is selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd, 0≤j≤6, 0< k≤6, 0<l≤10)

In this case, the first metal oxide and the second metal oxide may exhibit a concentration gradient that decreases from the surface portion of the secondary particle forming the lithium composite oxide toward the center of the secondary particle. Accordingly, the concentration of the metal oxide may decrease from the outermost surface of the secondary particle toward the center of the secondary particle. In this case, the concentration reduction rate of the second metal oxide may be greater than the concentration reduction rate of the first metal oxide.

On the other hand, in the positive electrode active material according to an embodiment of the present invention, the primary particles forming the lithium composite oxide may be represented by the following formula (6).

[Formula 6]

Li _m Ni _1-(n+o+p) Co _n M4 _o M5 _p O ₂

(Wherein, M4 is Mn or Al, and M5 is selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. contains at least one, and is 0.5≤m≤1.2, 0≤n≤0.50, 0≤o≤0.20, 0≤p≤0.20)

In this case, the M5 element included in the primary particles present in the surface portion of the secondary particles may exhibit a concentration gradient that decreases toward the center of the secondary particles.

For example, when the distance from the outermost surface of the secondary particle forming the lithium composite oxide to the center of the secondary particle is R, the distance (R') from the outermost surface of the secondary particle is 0 The M5 element present in the region of to 0.02R may exhibit a concentration gradient that decreases toward the center of the secondary particle in the primary particle.

At this time, the concentration change rate of the M5 element contained in the primary particles present in the region where the distance (R′) from the outermost surface of the secondary particles forming the lithium composite oxide is 0 to 0.02R is 50% or more can

In addition, the M5 element contained in the primary particles present in the region where the distance (R′) from the outermost surface of the secondary particles forming the lithium composite oxide is greater than 0.02R and 1.0R is constant in the primary particles. It may not have a concentration gradient in the form of an increasing or decreasing concentration in the direction. In another embodiment, the concentration change rate of the M5 element in the primary particles present in the region where the distance (R′) from the outermost surface of the secondary particles forming the lithium composite oxide is greater than 0.02R and 1.0R is 49% or less, preferably 30% or less, and more preferably 15% or less.

According to another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector may be provided. Here, the positive active material layer may include the positive active material according to various embodiments of the present invention. Therefore, since the positive active material is the same as described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described below.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , silver or the like surface-treated may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, and the like.

The cathode active material layer may optionally include a binder together with the cathode active material and a conductive material as necessary.

In this case, the positive active material may be included in an amount of 80 to 99 wt%, more specifically, 85 to 98.5 wt%, based on the total weight of the positive active material layer. It may exhibit excellent capacity characteristics when included in the above content range, but is not necessarily limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive active material layer.

The binder serves to improve adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above positive electrode active material. Specifically, the positive electrode active material and optionally, the composition for forming a positive electrode active material layer prepared by dissolving or dispersing a binder and a conductive material in a solvent may be coated on a positive electrode current collector, and then dried and rolled.

The solvent may be a solvent commonly used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for the production of the positive electrode thereafter. do.

Also, in another embodiment, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling it from the support on the positive electrode current collector.

In addition, according to another aspect of the present invention, an electrochemical device including the above-described positive electrode may be provided. The electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

Specifically, the lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the 　 anode is the same as described above, a detailed description will be omitted for convenience, and only the remaining components not described above will be described in detail below.

The lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

The negative electrode may include a negative electrode current collector and an anode 　 active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

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

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0 < β < 2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the above-mentioned metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

The negative active material may be included in an amount of 80 to 99 wt% based on the total weight of the negative electrode and the active material layer.

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

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

In one embodiment, the anode 　 active material layer is prepared by applying and drying a composition for forming a negative electrode 　 active material layer prepared by dissolving or dispersing the negative electrode 　 active material, and optionally a binder and a conductive material in a solvent on the negative electrode current collector, or It can be prepared by casting the composition for forming the negative electrode 　 active material layer on a separate support, and then laminating a film obtained by peeling it from the support on the negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the anode and the anode and provides a passage for lithium ions to move, and as long as it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, 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, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

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

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

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

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) _2. LiCl, LiI, or LiB(C ₂ O ₄ ) _{2 ,} etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and lifespan characteristics, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle, HEV).

The external shape of the lithium secondary battery according to the present invention is not particularly limited, but may be a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin type. In addition, the lithium secondary battery may be used not only in a battery cell used as a power source for a small device, but may also be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells.

According to another aspect of the present invention, a battery module including the lithium secondary battery as a unit cell and/or a battery pack including the same may be provided.

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

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for illustrating the present invention, and it will not be construed that the scope of the present invention is limited by these examples.

Experimental Example 1.

(1) Preparation of positive electrode active material

(Example 1)

_{A spherical Ni 0.92} Co _0.08 (OH) ₂ hydroxide precursor was synthesized by a co-precipitation method. In a 90L reactor, _{25 wt% of NaOH and 30 wt% of NH 4} OH were added to a 1.5 M complex transition metal sulfuric acid aqueous solution _{in which NiSO 4 .7H 2} O and CoSO _{4 .7H 2 O were mixed in a molar ratio of 92:8.} was put in. The pH in the reactor was maintained at 11.5 and the reactor temperature at this time was maintained at 60 °C, and N ₂ as an inert gas was added to the reactor to prevent oxidation of the prepared precursor. After completion of the synthesis stirring, washing and dehydration were performed using a filter press (F/P) equipment to obtain a _{Ni 0.92} Co _0.08 (OH) _{2 hydroxide precursor.}

With a hydroxide precursor and the Li-containing raw material LiOH and Al-containing source material of Al ₂ O ₃ were mixed using a mixer keeping the O ₂ atmosphere in the firing furnace and the temperature was raised to per 1 ℃ kept 10 hours at the heat treatment temperature 650 ℃ Then, it was cooled naturally. The obtained cathode active material was mixed with a W-containing raw material (WO ₃ ) and a B-containing raw material (B ₂ O ₃ ) using a mixer. _{Maintaining the O 2} atmosphere in the same kiln, the temperature was raised to 2 ℃ per minute, the heat treatment temperature was maintained at 600 ℃ for 5 hours, and then cooled naturally.

(Example 2)

The positive active material prepared in Example 2 was Li _1.06 Ni _0.9029 Co _0.0788 Al _0.0142 W _0.0031 Nb _0.001 O ₂ A cathode active material was prepared in the same manner as in Example 1, except that an Nb-containing raw material (Nb ₂ O ₅ ) was used instead of a B-containing raw material (B ₂ O _{3 ) to have a compositional formula.}

(Example 3)

The exemplary cathode active material prepared in Example 3 _{Li 1.04 Ni 0.9034 Co 0.0787 Al 0.0138} W 0.003 Ce 0.0011 O 2 A cathode active material was prepared in the same manner as in Example 1, except that a Ce-containing raw material (CeO ₂ ) was used instead of a B-containing raw material (B ₂ O _{3 ) to have a compositional formula.}

(Example 4)

The cathode active material prepared in Example 4 has a _{composition formula of Li 1.03} Ni _0.9030 Co _0.0789 Al _0.0143 W _0.0028 Ti _0.001 O ₂ B-containing raw material (B ₂ O ₃ ) Instead of Ti-containing raw material (TiO ₂ ) Except for using , A positive electrode active material was prepared in the same manner as in Example 1.

(Example 5)

Zr-containing raw material (ZrO ₂ ) instead of B-containing raw material (B ₂ O ₃ ) so that the positive active material prepared in Example 5 has a _{composition formula of Li 1.06} Ni _0.9032 Co _0.0787 Al _0.0141 W _0.003 Zr _0.001 O ₂ , A positive electrode active material was prepared in the same manner as in Example 1.

(Example 6)

The positive active material prepared in Example 6 was Li _1.06 Ni _0.9027 Co _0.0787 Al _0.0141 W _0.0031 Ti _0.0009 Zr _0.0005 O ₂ A cathode active material was prepared in the same manner as in Example 1, except that Zr-containing raw material (ZrO ₂ ) and Ti-containing raw material (TiO ₂ ) were used instead of B-containing raw material (B ₂ O _{3 ) to have a compositional formula.}

(Comparative Example 1)

The cathode active material prepared in Comparative Example 1 had a _{composition of Li 1.05} Ni _0.9040 Co _0.0790 Al _0.0140 W _0.0030 O ₂ W-containing raw material (WO ₃ ) as a dopant alone, except that the cathode active material was used alone in the same manner as in Example 1 was prepared.

(2) SEM and TEM analysis of cathode active material

1 to 4 show transmission electron microscope (TEM) analysis and TEM/EDS mapping results for the positive active material prepared in Example 6, and FIG. 5 is a doped metal element (Zr) measured according to the TEM/EDS mapping results. , Ti, W) is a graph (line sum spectrum) showing the content.

FIG. 1 shows a portion from the outermost surface of the cathode active material prepared in Example 6, and FIGS. 2 to 4 show the distribution of W, Ti, and Zr present in the cathode active material shown in FIG. 1, respectively.

2 to 4 , it can be seen that W, Ti, and Zr of the positive active material prepared in Example 6 exhibit a decreasing concentration gradient from the surface portion of the secondary particle toward the center of the secondary particle.

Also, referring to FIG. 5 , in the case of Ti and Zr, it can be seen that the concentration reduction rate in the surface portion of the secondary particles is greater than W. The results shown in FIG. 5 show not only the concentration gradient of W, Ti and Zr in the secondary particles forming the lithium composite oxide, but also the interface between the primary particles forming the lithium composite oxide and the primary particles formed by aggregation. It can be predicted that the effect is due to the concentration gradient of lithium metal oxide and metal oxide present on at least a part of the surface of the secondary particles.

Although not separately attached as a drawing, all of the positive electrode active materials prepared according to Examples 1 to 6 showed a decrease from the surface portion of the secondary particles forming the positive electrode active material from the TEM/EDS Mapping results toward the center of the secondary particles. The concentration gradient of the oxide was confirmed.

6 and 7 show transmission electron microscopy (TEM) analysis and TEM/EDS mapping results for the positive active material prepared in Comparative Example 1. FIG.

6 shows a portion from the outermost surface of the cathode active material prepared in Comparative Example 1, and FIG. 7 shows the distribution of W present in the cathode active material shown in FIG. 6 .

Referring to FIG. 7 , unlike the positive active material according to Example 6 shown in FIGS. 2 to 4 , W among the positive active materials does not show a decreasing concentration gradient from the surface of the secondary particles toward the center of the secondary particles. can confirm.

(3) XRD analysis of positive electrode active material

X-ray diffraction (XRD) analysis was performed on the positive active materials prepared according to Examples 1 to 6 and Comparative Example 1 to determine whether lithium metal oxide and metal oxide were present in the positive active material. XRD analysis was performed using a Bruker D8 Advance diffractometer using Cu Kαradiation (1.540598 Å).

8 to 10 are graphs showing XRD analysis results of the positive active materials prepared according to Examples 4 to 6;

Referring to FIG. 8 , _{characteristic peaks corresponding to Li 4} WO ₅ in the positive active material are confirmed, and in particular, the (220) peak is not shifted, but the (111) and (200) peaks are specifically low-angle ( It was confirmed that a portion of tungsten in the lattice structure formed by _{Li 4} WO ₅ was substituted with Ti as the low angle side shifted.

Also, referring to FIG. 9 , _{characteristic peaks corresponding to Li 4} WO ₅ in the positive active material are confirmed, and in particular, (111), (200) and (220) peaks are specifically shifted to the low angle side ( shift), it was confirmed that some of the tungsten in the lattice structure formed by _{Li 4} WO _{5 was substituted with Zr.}

Referring to FIG. 10 , it can be seen that a positive active material having an NCA composition is formed, and at the same time, peaks corresponding to _{Li 4} WO ₅ , Li ₆ WO _{6 , LiTiO 2} , Li ₄ TiO ₄ and Li ₄ ZrO ₄ are observed in the positive active material. existence was confirmed.

(4) Measurement of unreacted lithium in positive electrode active material

The measurement of unreacted lithium for the positive active materials prepared according to Examples 1 to 6 and Comparative Example 1 was measured with the amount of 0.1M HCl used until the pH was 4 by pH titration. First, 5 g of each of the positive active materials prepared according to Examples 1 to 6 and Comparative Example 1 were put into 100 ml of DIW, stirred for 15 minutes, filtered, and after taking 50 ml of the filtered solution, 0.1 M HCl was added thereto. By measuring HCl consumption according to the pH change, Q1 and Q2 were determined, and unreacted LiOH and Li ₂ CO ₃ were calculated through this.

M1 = 23.95 (LiOH Molecular weight)

M2 = 73.89 (Li ₂ CO ₃ Molecular weight)

SPL Size = (Sample weight × Solution Weight)/ Water Weight

LiOH (wt%) = [(Q1-Q2) × C × M1 × 100]/(SPL Size × 1000)

Li ₂ CO ₃ (wt%) = [2 × Q2 × C × M2/2 × 100]/(SPL Size × 1000)

The measurement results of unreacted lithium measured through the above formula are shown in Table 1 below.

division LiOH (ppm) Li ₂ CO ₃ (ppm) Example 1 3,943 6,257 Example 2 5,306 6,982 Example 3 5,137 7,050 Example 4 4,985 7,438 Example 5 5,573 6,781 Example 6 4,635 6,411 Comparative Example 1 7,100 6,324

Referring to the results of Table 1, it can be seen that the positive active material prepared according to Examples 1 to 5 significantly reduced the amount of residual lithium compared to the positive active material prepared according to Comparative Example 1.

Experimental Example 2.

(1) Preparation of lithium secondary battery

94 wt%, 3 wt% of carbon black, and 3 wt% of PVDF binder each prepared according to Examples 1 to 6 and Comparative Example 1 were added to 30 N-methyl-2 pyrrolidone (NMP) g to prepare a positive electrode slurry. The positive electrode slurry was applied to a 15 μm-thick aluminum (Al) thin film, which is a positive electrode current collector, and dried, followed by roll press to prepare a positive electrode. The loading level of the positive electrode was 10 mg/cm ² , and the electrode density was 3.2 g/cm ³ .

For the positive electrode, metallic lithium was used as a counter electrode, and as an electrolyte, ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 2:4:4 in a solvent of 1.15. M LiPF ₆ was added.

A battery assembly was formed by interposing a separator made of a porous polyethylene (PE) film between the positive electrode and the negative electrode, and the electrolyte was injected to prepare a lithium secondary battery (coin cell).

(2) Lithium secondary battery capacity characteristics evaluation

The lithium secondary battery (coin cell) prepared above was charged at 25° C. with a constant current (CC) of 0.15 C until it became 4.25 V, and then charged at a constant voltage (CV) of 4.25 V so that the charging current was 0.05 mAh. The first charging was performed until the After leaving it for 20 minutes, it was discharged with a constant current of 0.1 C until it became 3.0 V, and the discharge capacity of the first cycle was measured. The charging capacity, the discharging capacity, and the charging/discharging efficiency during the first charging and discharging are shown in Table 2 below.

division Charging capacity (mAh/g) Discharge capacity (mAh/g) Charging/discharging efficiency (%) Example 1 233.6 207.0 88.6% Example 2 233.9 211.4 90.4% Example 3 233.5 207.5 88.9% Example 4 233.9 211.6 90.5% Example 5 233.8 211.1 90.3% Example 6 233.8 211.0 90.3% Comparative Example 1 233.6 204.5 87.5%

Referring to the results of Table 2, the lithium secondary battery using the positive active material prepared according to Examples 1 to 6 compared to the lithium secondary battery using the positive active material prepared according to Comparative Example 1 was charged and discharged in terms of efficiency and capacity characteristics. improvement can be seen.

(3) Lithium secondary battery stability evaluation

The lithium secondary battery (coin cell) prepared above was charged/discharged 100 times at a constant current (CC) of 1 C at 25° C. within a driving voltage range of 3.0 to 4.25 V. Accordingly, after 100 times of charging and discharging at room temperature, cycle capacity retention, which is the ratio of the discharge capacity at the 100th cycle to the initial capacity, was measured.

In addition, in order to check the high-temperature storage characteristics of lithium secondary batteries, the resistance was measured by charging and discharging batteries at 25°C based on SOC 100% and storing them at 60°C for 7 days, then measuring the resistance to change the resistance was confirmed.

The measurement results are shown in Table 3 below.

division Capacity retention rate (%) Resistance before high temperature storage (Ω) Resistance after high temperature storage (Ω) Example 1 87.4% 5.1 24.7 Example 2 87.8% 4.3 27.5 Example 3 88.6% 4.2 33.8 Example 4 90.0% 2.9 19.9 Example 5 90.1% 3.0 16.8 Example 6 91.8% 3.0 11.7 Comparative Example 1 81.8% 2.2 90.0

Referring to the results of Table 3, the lithium secondary battery using the positive active material prepared according to Examples 1 to 6 has excellent capacity retention compared to the lithium secondary battery using the positive active material prepared according to Comparative Example 1 as well as It can be seen that the resistance change range before and after high-temperature storage is small.

As described above, the present invention has been described with reference to the illustrated drawings, but the present invention is not limited by the embodiments and drawings disclosed in the present specification. It is obvious that variations can be made. In addition, although the effects according to the configuration of the present invention are not explicitly described and described while describing the embodiments of the present invention, it is natural that the effects predictable by the configuration should also be recognized.

Claims (10)

lithium composite oxide including primary particles and secondary particles formed by aggregation of the primary particles; and
a lithium metal oxide present in at least a portion of an interface between the primary particles and a surface of the secondary particles;
including,
The lithium metal oxide has a lattice structure in which at least a portion of tungsten in the lattice structure formed by the lithium tungsten oxide represented by the following Chemical Formula 2 is substituted with at least one dopant,
In the lithium metal oxide, at least one of the peaks specific to the lithium tungsten oxide in X-ray diffraction has a peak shifted to a low angle side,
[Formula 2]
Li _a W _b O _c
(here,
0<a≤6, 0<b≤6, 0<c≤10)
positive electrode active material.
According to claim 1,
The primary particles are represented by the following formula (6),
[Formula 6]
Li _m Ni _1-(n+o+p) Co _n M4 _o M5 _p O ₂
(here,
M4 is Mn or Al;
M5 comprises at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd,
0.5≤m≤1.2, 0≤n≤0.50, 0≤o≤0.20, 0≤p≤0.20)
positive electrode active material.
According to claim 1,
The lithium metal oxide has a peak in which at least one of the peaks corresponding to the (111), (200) and (220) planes of the lithium tungsten oxide is shifted to a low angle side in X-ray diffraction,
positive electrode active material.
According to claim 1,
The lithium metal oxide exhibits a concentration gradient that decreases from the surface portion of the secondary particle toward the center of the secondary particle,
positive electrode active material.
According to claim 1,
The lithium metal oxide is represented by the following formula (1),
[Formula 1]
Li _a (W _1-y M1 _y ) _b O _c
(here,
M1 comprises at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd,
0<a≤6, 0<b≤6, 0<c≤10, 0<y≤0.50)
positive electrode active material.
According to claim 1,
Represented by the following Chemical Formula 3, further comprising at least one metal oxide present in at least a portion of an interface between the primary particles and a surface of the secondary particles,
Cathode active material:
[Formula 3]
Li _d M2 _e O _f
(here,
M2 is selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd,
0≤d≤6, 0<e≤6, 0<f≤10)
7. The method of claim 6,
The metal oxide exhibits a concentration gradient that decreases from the surface portion of the secondary particle toward the center of the secondary particle,
positive electrode active material.
A lithium secondary battery using a positive electrode comprising the positive electrode active material according to any one of claims 1 to 7. delete delete

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