KR102323190B1 - Lithium composite oxide, positive electrode active material and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium composite oxide, a positive electrode active material for a lithium secondary battery including the lithium composite oxide, and a lithium secondary battery using a positive electrode including the positive electrode active material.

Description

Lithium composite oxide, a cathode active material for a lithium secondary battery, and a lithium secondary battery comprising the same

The present invention relates to a lithium composite oxide, a positive electrode active material for a lithium secondary battery including the lithium composite oxide, and a lithium secondary battery using a positive electrode including the positive electrode active material.

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 lithium composite oxide with improved structural stability in order to solve the problems of the conventional lithium composite oxide for a cathode active material for a lithium secondary battery.

Another object of the present invention is to provide a positive electrode active material having improved high-temperature storage stability and lifespan characteristics by simultaneously including the lithium composite oxide and the coating oxide as defined herein.

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, there may be provided a lithium composite oxide including primary particles represented by the following Chemical Formula 1 and secondary particles formed by aggregation of the primary particles.

[Formula 1]

Li _a Ni _1-(b+c+d+e) Co _b M1 _c M2 _d W _e O ₂

(here,

M1 is at least one selected from Mn and Al,

M2 comprises at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd,

0.5≤a≤1.5, 0.01≤b≤0.50, 0.01≤c≤0.20, 0≤d≤0.20, 0.001≤e≤0.20)

In one embodiment, the sum of the content (at%) of the M2 element and W contained in the primary particles present in the surface portion of the secondary particles may be greater than the content (at%) of Ni.

According to another aspect of the present invention, there is provided a cathode active material comprising a lithium composite oxide as defined herein and a coating oxide present on at least a portion of an interface between the primary particles forming the lithium composite oxide and a surface of the secondary particles can be

In one embodiment, the coating oxide may exhibit a concentration gradient that decreases from the surface portion of the secondary particles toward the center of the secondary particles. Accordingly, it is possible to prevent the overall structural collapse of the cathode active material during the electrochemical reaction by the coating oxide.

According to another aspect of the present invention, a lithium secondary battery using a positive electrode including the positive electrode active material as defined herein may be provided.

In the lithium composite oxide according to various embodiments of the present invention, the sum of the content of the doping metal contained in the primary particles present in the surface portion of the secondary particles constituting the same is greater than the content of Ni, thereby improving the structural stability of the coating oxide can do it

In addition, the positive active material according to various embodiments of the present invention includes a coating oxide present on 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 the aggregation of the primary particles. By doing so, structural stability can be improved, and thus, when the positive electrode including the positive electrode active material according to various embodiments of 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 5 show transmission electron microscopy (TEM) analysis and TEM/EDS mapping results for a cathode active material prepared according to an embodiment of the present invention.
6 is a graph (line sum spectrum) showing the content of metal elements (Ni, Co, Al, W) measured according to the TEM / EDS mapping result of the positive electrode active material prepared according to an embodiment of the present invention.
7 shows the results of electron transmission microscopy (TEM) analysis of the positive active material prepared according to an embodiment of the present invention.
8 is a schematic diagram illustrating a crystal structure in which some of Ni inserted into Li 3a sites among the positive active material manufactured according to an embodiment of the present invention is substituted with W. Referring to FIG.
9 and 10 show TEM/EDS mapping results for a doped metal among positive active materials prepared according to another embodiment of the present invention.
11 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 another embodiment of the present invention.
12 to 15 show transmission electron microscope (TEM) analysis and TEM/EDS mapping results for the positive active material prepared according to Comparative Example.
16 to 18 are graphs showing XRD analysis results of positive active materials prepared according to various embodiments of the present invention.

In order to better understand the present invention, certain terms are defined herein for convenience. Unless defined otherwise herein, scientific and technical terms used herein shall have the meanings commonly understood by one of ordinary skill in the art. Also, unless the context specifically dictates otherwise, it is to be understood that a term in the singular includes its plural form as well, and a term in the plural form also includes its singular form.

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

lithium composite oxide

According to an aspect of the present invention, there may be provided a lithium composite oxide including primary particles represented by the following Chemical Formula 1 and secondary particles formed by aggregation of the primary particles.

[Formula 1]

Li _a Ni _1-(b+c+d+e) Co _b M1 _c M2 _d W _e O ₂

(Here, M1 is at least one selected from Mn and Al, and M2 is Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, Nd And at least one selected from Gd, 0.5≤a≤1.5, 0.01≤b≤0.50, 0.01≤c≤0.20, 0≤d≤0.20, 0.001≤e≤0.20)

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.

Here, the average diameter of the primary particles may be 0.1 μm to 6.0 μm, and the average diameter of the secondary particles may be 6.0 μm to 20.0 μm. A surface present inside the secondary particles may be formed by contacting the internal voids without forming a grain boundary in contact with each other. 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 addition, at least one selected from the M2 element and W included in the primary particles present in the surface portion of the secondary particles may represent a concentration gradient that decreases toward the center of the secondary particles. That is, the direction of the concentration gradient of the M2 element and W formed in the primary particle may be a direction from the surface portion of the secondary particle toward the center of the secondary particle.

Accordingly, a movement path of lithium ions (a diffusion path of lithium ions) arranged toward the center of the secondary particles may be formed in the primary particles (refer to FIG. 7 ), through which lithium composite oxide and positive electrode active material It is possible to improve lithium ion conductivity by

More specifically, the concentration gradient of the M2 element and W included in the primary particles may be greater at the surface of the secondary particle than at the central portion of the secondary particle based on the central portion of the primary particle.

In this case, the secondary particles may include a first region and a second region having different concentrations of the M2 element. In this case, the first region and the second region may be defined as regions having different concentrations of the W element.

Here, the region in which at least one selected from the M2 element and W included in the primary particle exhibits a concentration gradient in which the concentration gradient decreases toward the center of the secondary particle may be the first region. That is, the concentration gradient of M2 element and/or W as defined herein means a concentration gradient that appears based on a single primary particle.

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 When the region of 0.02R to 0.02R is defined as the first region, the M2 element and/or W present in the first region may represent a concentration gradient that decreases toward the center of the secondary particle in the primary particle.

On the other hand, Ni present in the first region may exhibit a concentration gradient that increases toward the center of the secondary particle in the primary particle as opposed to M2 element and/or W. Here, the center of the secondary particles may refer to the center of the secondary particles.

In this case, the content (at%) of W contained in the primary particles present in the first region of the secondary particles may be greater than the content (at%) of Ni. In addition, when the M2 element is included in the primary particle, the sum of the content (at%) of the M2 element and W included in the primary particle present in the first region of the secondary particle is the Ni content (at %) can be greater.

Here, M2 element and/or W may exist in a substituted state with Ni inserted into at least one of Li 3a site and 3b site among the primary particles by Rietveld analysis of an X-ray diffraction pattern.

_{In this case, the ratio of W inserted into the Li 3a site (W occ} ) of the primary particles present in the first region of the secondary particles by Rietveld analysis of an X-ray diffraction pattern is the amount of W inserted into the Li 3a site. It may be larger than the ratio of Ni (Ni _{occ ).} In addition, when the M2 element is included in the primary particles, the primary particles present in the first region of the secondary particles have a ratio of W inserted into the Li 3a site by Rietveld analysis of an X-ray diffraction pattern ( W _occ ) and the ratio of the M2 element (M2 _occ ) may be greater than the ratio of Ni inserted into the Li 3a site (Ni _{occ ).}

As described above, the content (or the sum of the contents) of the M2 element and/or W present in the first region of the secondary particles is not simply greater than the content of Ni, but rather in the Rietveld analysis of the X-ray diffraction pattern. Because the ratio of insertion into the Li 3a site by have.

The above-described M2 element and/or the opposite concentration gradient of W and Ni indicates that the M2 element and/or W included in the primary particles present in the first region is at least one of Li 3a sites and 3b sites in the lithium composite oxide. It may appear as Ni inserted into one and substituted.

In this case, the concentration change rate of the M2 element and/or W contained in the primary particles present in the first region may be 50% or more, preferably 60% or more, but is not necessarily limited thereto.

In addition, regions other than the first region may be defined as a second region, and when a region in which the distance (R′) from the outermost surface of the secondary particles is 0 to 0.02R is defined as the first region, the A region in which the distance (R′) from the outermost surface of the secondary particles is greater than 0.02R and 1.0R may be defined as the second region. Here, the M2 element and/or W included in the primary particles present in the second region may not have a concentration gradient in which the concentration increases or decreases in a predetermined direction in the primary particles.

In another embodiment, the concentration change rate of the M2 element and/or W in the primary particles present in the second region may be 49% or less, preferably 30% or less, and more preferably 15% or less.

In addition, in this case, the concentration change rate of the M1 element and Co contained in the primary particles present in the first region and the second region is 49% or less, preferably 30% or less, more preferably 15% or less can

As described above, the secondary particles constituting the lithium composite oxide are partitioned into first and second regions having different concentrations of M2 element and/or W, and M2 element and/or W is the first region. and by exhibiting a concentration gradient of another aspect in the second region, the structural stability of the lithium composite oxide may be improved.

Cathode Active Material for Lithium Secondary Battery

According to another aspect of the present invention, there is provided a cathode active material comprising a lithium composite oxide as defined herein and a coating oxide present on at least a portion of an interface between the primary particles forming the lithium composite oxide and a surface of the secondary particles can be Here, since the lithium composite oxide 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 coating oxide may be physically and/or chemically bonded to the primary particles and/or the secondary particles forming the lithium composite oxide.

At this time, the coating 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 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 coating 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 coating oxide may affect the improvement of the efficiency characteristics of the lithium secondary battery by acting as a movement path (pathway) of lithium ions in the positive electrode active material.

In addition, in some cases, the coating 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.

Here, the coating oxide may be represented by the following formula (2).

[Formula 2]

Li _f M3 _g O _h

(Wherein, M3 includes at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd, and , 0≤f≤6, 0<g≤6, 0≤h≤10)

As shown in Formula 2 above, the coating oxide is an oxide in which lithium and a metal element represented by M3 are complexed, and the coating oxide is, for example, Li(W)O, Li(Zr)O, Li( Ti)O, Li(B)O, WO _x , ZrO _x , TiO _{x and the} like may be used, but the above-described examples are merely described for convenience in order to facilitate understanding, and the coating oxide defined herein is not limited to the above-described examples. does not Therefore, in Experimental Examples to be described later, for convenience, experimental results for some examples of representative coating oxides that may be represented by Chemical Formula 1 will be described.

In another embodiment, the coating oxide may further include an oxide in which lithium and at least two elements represented by M3 are complexed, or an oxide in which lithium and at least two elements represented by M3 are complexed. The coating oxide in which lithium and at least two elements represented by M3 are complexed is, for example, Li(W/Ti)O, Li(W/Zr)O, Li(W/Ti/Zr)O, Li(W It may be /Ti/B)O, but is not necessarily limited thereto.

In addition, in this case, at least one metal element in the tungsten oxide may have a doped lattice structure. That is, the coating oxide is tungsten in the lattice structure formed by _{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 them have a lattice structure substituted with metal elements. Here, the metal element substituting for tungsten in the lattice structure is selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd. At least one of which may be used.

In one embodiment, the coating 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 coating oxide may decrease from the outermost surface of the secondary particle toward the center of the secondary particle.

As described above, the coating oxide exhibits 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, thereby removing residual lithium present on the surface of the positive electrode active material. By effectively reducing it, side reactions caused by unreacted residual lithium can be prevented in advance, and crystallinity in the inner surface region of the positive electrode active material due to the coating oxide can be prevented from being lowered. In addition, it is possible to prevent the overall structural collapse of the cathode active material during the electrochemical reaction by the coating oxide.

In another embodiment, the coating oxide may include a first coating oxide represented by Formula 3 below and a second coating oxide represented by Formula 4 below.

[Formula 3]

Li _i W _j O _k

(Here, 0≤i≤6, 0<j≤6, 0<k≤10)

[Formula 4]

Li _l M4 _m O _n

(Where M4 includes at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd, 0 ≤l≤6, 0<m≤6, 0<n≤10)

In this case, the first coating oxide and the second coating 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 coating oxide may decrease from the outermost surface of the secondary particle toward the center of the secondary particle.

At this time, it is preferable that the concentration reduction rate of the second coating oxide is greater than the concentration reduction rate of the first coating oxide, and the concentration reduction rate of the second coating oxide is greater than the concentration reduction rate of the first coating oxide, including the coating oxide Structural stability of the positive electrode active material may be maintained. In addition, by forming an efficient lithium ion movement path in the positive electrode active material, it may positively act to improve the efficiency characteristics of the lithium secondary battery.

Accordingly, when the positive electrode including the positive electrode active material according to various embodiments of 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 an additional embodiment, the second coating oxide may include a zirconium oxide represented by the following Chemical Formula 5 and a titanium oxide represented by the following Chemical Formula 6.

[Formula 5]

Li _o Zr _p O _q

(Here, 0≤o≤6, 0<p≤6, 0<q≤10)

[Formula 6]

Li _r Ti _s O _t

(Here, 0≤r≤6, 0<s≤6, 0<t≤10)

The zirconium oxide represented by Chemical Formula 5 and the titanium oxide represented by Chemical Formula 6 may contribute to increasing the structural stability of the positive electrode active material together with the tungsten oxide represented by Chemical Formula 3, and efficient in the positive active material A pathway for lithium ions may be formed.

In this case, the zirconium oxide and the titanium oxide may exhibit a concentration gradient decreasing toward the center of the secondary particle from the surface portion of the secondary particle forming the lithium composite oxide, like the tungsten oxide. Accordingly, the concentrations of the zirconium oxide and the titanium oxide may decrease from the outermost surface of the secondary particle toward the center of the secondary particle.

At this time, in order to maintain structural stability and crystallinity of the positive active material including the zirconium oxide and the titanium oxide together with the tungsten oxide, the concentration reduction rate of the zirconium oxide is preferably greater than the concentration reduction rate of the titanium oxide.

lithium secondary battery

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.

In addition, in another embodiment, the negative electrode 　 active material layer is a negative electrode 　 active material layer on the negative electrode current collector, and optionally by dissolving or dispersing a binder and a conductive material in a solvent to form a negative electrode 　 active material layer formed by coating and drying, or It may 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 off 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 ) 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. Then, heat treatment and cooling were additionally performed once under the same conditions as above. The positive active material prepared in Example 1 was found to have a composition formula of _{Li 1.05} Ni _0.9060 Co _0.0790 Al _0.0140 W _0.0010 O _{2 .}

Example 2

A cathode active material was prepared in the same manner as in Example 1, except that the cathode active material was mixed with a _{W-containing raw material (WO 3} ) so that the prepared cathode active material had a composition formula of _{Li 1.04} Ni _0.9020 Co _0.0790 Al _0.0140 W _0.0050 O _{2 .} .

Example 3

A cathode active material was prepared in the same manner as in Example 1, except that the cathode active material was mixed with a _{W-containing raw material (WO 3} ) so that the prepared cathode active material had a composition formula of _{Li 1.03} Ni _0.8970 Co _0.0790 Al _0.0140 W _0.010 O _{2 .} .

Example 4

The prepared anode active material, except that a mixture of the _{Li 1.04 Ni 0.9037 Co 0.0786 Al 0.0138} W 0.0029 B 0.001 O a positive electrode active material to have a _second composition formula W-containing raw materials (WO ₃₎ and a B-containing raw material (B ₂ O ₃₎ , A positive electrode active material was prepared in the same manner as in Example 1.

Example 5

The prepared cathode active material 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 6

The prepared positive electrode active material, _{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 7

_{Example 1 Except} that the prepared cathode active material 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 , Ti-containing raw material (TiO ₂ ) is used instead of B-containing raw material (B ₂ O _{3 )} A positive electrode active material was prepared in the same manner as described above.

Example 8

Example 1 Except for using the Zr-containing raw material (ZrO ₂ ) instead of the B-containing raw material (B ₂ O ₃ ) so that the prepared cathode active material 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 described above.

Example 9

The prepared cathode active material 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.}

Example 10

A cathode active material was prepared in the same manner as in Example 1, except that the cathode active material was mixed with the W-containing raw material (WO _{3 ) in Example 1 and then heat-treated at 600° C. only once.}

Comparative Example 1

In Example 1, a cathode active material was prepared in the same manner as in Example 1, except that the cathode active material and the W-containing raw material (WO _{3 ) were mixed and then heat-treated at 700 °C.}

Comparative Example 2

In Example 1, a cathode active material was prepared in the same manner as in Example 1, except that after mixing the cathode active material and the W-containing raw material (WO _{3 ), heat treatment was performed only once at 700° C.}

Comparative Example 3

A cathode active material was prepared in the same manner as in Example 7, except that in Example 7, the cathode active material was mixed with W-containing raw material (WO ₃ ) and Ti-containing raw material (TiO _{2 ) and then heat-treated only once at 700 ° C.} .

Comparative Example 4

A cathode active material was prepared in the same manner as in Example 8, except that in Example 8, the cathode active material and the W-containing raw material (WO ₃ ) and the Zr-containing raw material (ZrO _{2 ) were mixed and then heat-treated only once at 700 ° C.} .

(2) SEM and TEM analysis of cathode active material

1 to 5 show transmission electron microscope (TEM) analysis and TEM/EDS mapping results of primary particles constituting the positive electrode active material prepared according to Example 1, and FIG. 6 is a TEM/EDS mapping result according to the results. It is a graph (line sum spectrum) showing the contents of the measured metal elements (Ni, Co, Al, W).

1 shows a portion from the outermost surface of the primary particles constituting the positive active material prepared in Example 1, and FIGS. 2 to 5 are Ni, Co, Al and W present in the primary particles shown in FIG. 1, respectively. shows the distribution of

2 to 6 , W contained in the primary particles positioned on the surface of the positive active material prepared in Example 1 is the center (left) of the secondary particles from the surface (right) of the secondary particles. On the other hand, it can be confirmed that Ni exhibits a concentration gradient that increases from the surface portion of the secondary particles toward the center of the secondary particles, while showing a concentration gradient that decreases toward the On the other hand, it can be confirmed that Co and Al among the positive active materials prepared in Example 1 do not show a large variation in concentration change or a concentration gradient in the secondary particles, unlike Ni and W.

7 shows the results of electron transmission microscopy (TEM) analysis of the positive active material prepared according to Example 1, and FIG. 8 shows the crystal structure in which some of Ni inserted into the Li 3a site of the positive active material is substituted with W It is a schematic diagram

Referring to FIG. 7 , it can be confirmed that a Ni—O layer (cation mixing layer) is formed on the surface of the primary particles of the positive electrode active material prepared according to Example 1, which is, as schematically shown in FIG. 8, Ni ²⁺ It means occupying the 3a site of ^{Li + .}

Also, referring to FIG. 7 , it can be confirmed that all lithium ion diffusion paths formed in the positive active material prepared according to Example 1 are isotropic in the long axis direction. That is, since lithium ions in the positive active material do not diffuse in multiple directions but are concentrated and diffused in one direction, it is possible to improve the conductivity of lithium ions by the positive electrode active material.

In addition, as will be described later along with specific experimental results, as shown in FIG. 8 , in the primary particles constituting the positive active material prepared according to Examples 1 to 9, some of the Ni inserted into the Li 3a site is W and It may have a crystal structure substituted with a doping metal other than W. In some cases, the sum of the ratios of W and doping metals other than W inserted into the Li 3a sites of the primary particles positioned on the surface of the positive electrode active material may be greater than the ratio of Ni.

9 shows the TEM/EDS mapping results for Ti, which is a doping metal, among primary particles constituting the positive electrode active material prepared according to Example 7, and FIG. TEM/EDS mapping results for Zr, which is a doping metal, among tea particles are shown.

9 and 10, Ti and Zr contained in the primary particles located on the surface portion of the positive electrode active material are also the center (left) of the secondary particles from the surface portion (left) of the secondary particles, like W shown in FIG. It can be seen that the concentration gradient decreases toward the right).

11 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 primary particles constituting the positive electrode active material prepared according to Example 9. .

Referring to FIG. 11 , Zr, Ti, and W contained in the primary particles positioned on the surface of the positive active material prepared in Example 9 have a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles. In this case, in the case of Ti and Zr, the concentration reduction rate in the primary particles located on the surface of the secondary particles is greater than W, and the concentration of Zr in the primary particles located on the surface of the secondary particles is greater than W. It can be seen that the reduction rate is larger than the reduction rate of the Ti concentration.

The results shown in FIG. 11 show not only the concentration gradient of W, Ti and Zr in the primary 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 the coating oxide present on at least a part of the surface of the secondary particles.

12 to 15 show transmission electron microscopy (TEM) analysis and TEM/EDS mapping results for the positive active material prepared according to Comparative Example 1. FIG.

12 shows a portion from the outermost surface of the primary particles constituting the positive active material prepared in Comparative Example 1, and FIG. 13 shows the distribution of W present in the primary particles shown in FIG. 12 .

13, unlike the positive electrode active material according to various embodiments of the present invention, W among the primary particles shows a concentration gradient that decreases from the surface portion (lower right) of the secondary particles toward the center (upper left) of the secondary particles. It can be seen that it is not shown.

14 shows TEM/EDS mapping results for Ti, which is a doped metal included in primary particles located on the surface of the positive electrode active material prepared according to Comparative Example 2, and FIG. 15 is a positive electrode prepared according to Comparative Example 3 TEM/EDS mapping results for Zr, a heavy doped metal included in primary particles located on the surface of the active material, are shown.

14 and 15, Ti and Zr also, like W shown in FIG. 11, does not show a decreasing concentration gradient from the surface portion (lower right) of the secondary particles toward the center (upper left) of the secondary particles. can

In addition, in addition, TEM / EDS Mapping result measurement for the surface portion (region from the outermost surface of the secondary particles to 0.05 μm) of the positive active material prepared according to Examples 1 to 10 and Comparative Examples 1 to 4 The average content of Ni and doped metal is shown in Table 1 below.

division Ni
(at%) dopant W
(at%) B
(at%) Nb
(at%) Ce
(at%) Ti
(at%) Zr
(at%) Sum
(at%) Example 1 29.5 41.4 - - - - - 41.4 Example 2 28.8 43.6 - - - - - 43.6 Example 3 26.7 46.8 - - - - - 46.8 Example 4 30.1 42.5 10.3 - - - - 52.8 Example 5 27.4 43.1 - 10.2 - - - 53.1 Example 6 29.6 42.1 - - 9.7 - - 51.8 Example 7 28.7 42.8 - - - 18.5 - 61.3 Example 8 29.3 41.9 - - - - 19.2 61.1 Example 9 29.6 42.2 - - - 17.3 18.5 78.0 Example 10 30.3 39.3 - - - - - 39.3 Comparative Example 1 32.4 25.3 - - - - - 25.3 Comparative Example 2 33.5 24.9 - - - - - 24.9 Comparative Example 3 33.9 24.1 - - - 7.1 - 31.2 Comparative Example 4 34.6 25.3 - - - - 7.9 33.2

Referring to the results of Table 1, in the case of the positive active materials prepared according to Examples 1 to 10, the primary present in the surface portion (region from the outermost surface of the secondary particles to 0.05 μm) of the positive active material. It can be seen that the sum of the average contents of doping metals included in the particles is greater than the average content of Ni.

On the other hand, in the case of the positive electrode active material prepared according to Comparative Examples 1 to 4, the doping metal contained in the primary particles present in the surface portion (the region from the outermost surface of the secondary particles to 0.05 μm) of the positive electrode active material. It can be seen that the sum of the average content is lower than the average content of Ni.

(3) XRD analysis of positive electrode active material

Occupancy (or content; occupancy) of Ni metal inserted into Li 3a sites of positive active materials prepared according to Examples 1 to 10 and Comparative Examples 1 to 4 was measured through Rietveld analysis of the X-ray diffraction pattern. did. The measurement results are shown in Table 2 below. Rietveld analysis of the X-ray diffraction pattern was performed on the surface portion (region from the outermost surface of the secondary particles to 0.05 μm) of the positive active materials prepared according to Examples 1 to 9 and Comparative Examples 1 to 4 became

division W content
(mol%) Ni _occ
in 3a site (%) d(003) (Å) Example 1 0.1 1.34 4.7293 Example 2 0.5 1.31 4.7300 Example 3 1.0 1.28 4.7302 Example 4 0.29 1.32 4.7296 Example 5 0.31 1.31 4.7296 Example 6 0.3 1.32 4.7298 Example 7 0.28 1.33 4.7297 Example 8 0.3 1.32 4.7301 Example 9 0.3 1.31 4.7299 Example 10 0.1 1.35 4.7294 Comparative Example 1 0.1 1.38 4.7292 Comparative Example 2 0.1 1.40 4.7291 Comparative Example 3 0.28 1.39 4.7291 Comparative Example 4 0.3 1.38 4.7292

Referring to the results of Table 2, in the case of the positive active materials prepared according to Examples 1 to 10, the primary present in the surface portion (the region from the outermost surface of the secondary particles to 0.05 μm) of the positive active material. The occupancy of Ni inserted into the Li 3a site of the particles is that of the primary particles present in the surface portion (region from the outermost surface of the secondary particles to 0.05 μm) of the positive active material prepared according to Comparative Examples 1 to 4 It can be seen that the occupancy of Ni inserted into the Li 3a site is lower than that of Ni.

That is, comparing Example 1 and Comparative Example 1 through the results of Table 2, it can be confirmed that even though the W content in the positive active material is the same or similar, the region in which W is present in the positive active material is different. Some of the W present in the surface portion of the positive active material may exist in a state substituted with Ni inserted into the Li 3a site, which can be confirmed by a decrease in the occupancy of the Ni inserted into the Li 3a site. As schematically shown in FIG. 8 , in particular, a portion of W present in the surface portion of the positive electrode active material may be a result of being substituted with Ni inserted into the Li 3a site. In addition, in view of the results of Table 2, it can be expected that the positive active material according to the Examples has a greater W content inserted into the Li 3a site and/or 3b site than the positive active material according to the Comparative Examples.

Additionally, X-ray diffraction (XRD) analysis was performed on the cathode active materials prepared according to Examples 7 to 9 to determine whether a coating oxide and an alloy oxide were present in the cathode active material. XRD analysis was performed using a Bruker D8 Advance diffractometer using Cu Kαradiation (1.540598 Å).

16 to 18 are graphs showing XRD analysis results of the positive active materials prepared according to Examples 7 to 9;

_{Referring to FIG. 16 , a characteristic peak corresponding to Li 4} WO ₅ , which is a coating oxide in the cathode active material, is confirmed. In particular, the (220) peak is not shifted, but the (111) and (200) peaks are specific. It was confirmed that a heterogeneous coating oxide in which a part of tungsten was substituted with Ti in the lattice structure formed by _{Li 4} WO ₅ was present as the low-angle side shifted.

_{In addition, referring to FIG. 17 , characteristic peaks corresponding to Li 4} WO ₅ , which are coating oxides in the positive electrode active material, are confirmed, and in particular, (111), (200) and (220) peaks are specifically low angle (low angle) peaks. It was confirmed that a heterogeneous coating oxide in which some of the tungsten was substituted with Zr in the lattice structure formed by _{Li 4} WO ₅ as the side shifted existed.

Referring to FIG. 18 , 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 in the positive active material.} was confirmed to exist.

(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 10 and Comparative Examples 1 to 4 was measured in the amount of 0.1M HCl used until pH 4 by pH titration. measured. 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 Х Solution Weight) / Water Weight

LiOH (wt%) = [(Q1-Q2)ХCХM1Х100]/(SPL Size Х1000)

Li ₂ CO ₃ (wt%) = [2ХQ2ХCХM2/2Х100]/(SPL SizeХ1000)

The measurement results of unreacted lithium measured through the above formula are shown in Table 3 below.

division LiOH (ppm) Li ₂ CO ₃ (ppm) Example 1 3,943 6,257 Example 2 3,011 5,829 Example 3 2011 5,624 Example 4 5,306 6,982 Example 5 5,137 7,050 Example 6 4,985 7,438 Example 7 5,573 6,781 Example 8 4,635 6,411 Example 9 2,762 5,309 Example 10 3,718 6.129 Comparative Example 1 6,758 6,428 Comparative Example 2 7,100 6,324 Comparative Example 3 10,590 6,894 Comparative Example 4 9,892 6,357

Referring to the results of Table 3, it can be seen that the positive active materials prepared according to Examples 1 to 10 significantly reduced the amount of residual lithium compared to the positive electrode active materials prepared according to Comparative Examples 1 to 4.

Experimental Example 2.

(1) Preparation of lithium secondary battery

N-methyl-2 pyrrolidone in each of 94 wt%, 3 wt% of carbon black, and 3 wt% of PVDF binder prepared according to Examples 1 to 10 and Comparative Examples 1 to 4 (NMP) was dispersed in 30 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 4 below.

division Charging capacity (mAh/g) Discharge capacity (mAh/g) Charging/discharging efficiency (%) Example 1 234.2 208.9 89.2% Example 2 233.1 210.3 90.2% Example 3 230.1 205.0 89.1% Example 4 233.9 211.4 90.4% Example 5 233.5 207.5 88.9% Example 6 233.9 211.6 90.5% Example 7 233.8 211.1 90.3% Example 8 233.8 211.0 90.3% Example 9 233.7 211.5 90.5% Example 10 233.8 211.2 90.4% Comparative Example 1 233.5 204.2 87.4% Comparative Example 2 233.6 204.5 87.5% Comparative Example 3 233.9 203.9 87.2% Comparative Example 4 233.2 204.1 87.5%

Referring to the results of Table 4, the lithium secondary battery using the positive active material prepared according to Examples 1 to 10 was compared to the lithium secondary battery using the positive electrode active material prepared according to Comparative Examples 1 to 4, compared to the charging and discharging efficiency. And it can be confirmed that the improvement in terms of capacity characteristics.

(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 the battery at 25 ° C based on SOC 100%, and then storing the battery at 60 ° C for 7 days. was confirmed.

The measurement results are shown in Table 5 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 92.1% 4.0 14.1 Example 3 92.7% 4.3 13.9 Example 4 87.8% 4.3 27.5 Example 5 88.6% 4.2 33.8 Example 6 90.0% 2.9 19.9 Example 7 90.1% 3.0 16.8 Example 8 91.8% 3.0 11.7 Example 9 92.1% 2.8 10.3 Example 10 87.3% 4.9 25.0 Comparative Example 1 81.5% 3.1 88.8 Comparative Example 2 81.8% 2.2 90.0 Comparative Example 3 82.7% 2.5 87.4 Comparative Example 4 82.4% 2.8 88.9

Referring to the results of Table 5, the lithium secondary battery using the positive active material prepared according to Examples 1 to 10 has a capacity retention rate compared to the lithium secondary battery using the positive active material prepared according to Comparative Examples 1 to 4 It can be seen that not only is excellent, but also the range of resistance change before and after high-temperature storage is small.

In the above, although the embodiments of the present invention have been described, those of ordinary skill in the art may add, change, delete or add components within the scope that does not depart from the spirit of the present invention described in the claims. It will be possible to variously modify and change the present invention by this, which will also be included within the scope of the present invention.

Claims (9)

A lithium composite oxide represented by the following formula (1) primary particles and secondary particles formed by agglomeration of the primary particles; and
[Formula 1]
Li _a Ni _1-(b+c+d+e) Co _b M1 _c M2 _d W _e O ₂
(here,
M1 is at least one selected from Mn and Al,
M2 comprises at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd,
0.5≤a≤1.5, 0.01≤b≤0.50, 0.01≤c≤0.20, 0≤d≤0.20, 0.001≤e≤0.20)
a coating oxide present on at least a portion of a surface of the primary particle and the secondary particle;
As a positive active material comprising a,
The sum of the content (at%) of the M2 element and the content of W (at%) relative to the content of all elements present in the surface portion of the positive active material is 39 at% or more,
positive electrode active material.
According to claim 1,
The content (at%) of W present in the surface portion of the positive active material is 39 at% or more,
positive electrode active material.
According to claim 1,
The content (at%) of W present in the surface portion of the positive active material is greater than the content (at%) of Ni,
positive electrode active material.
According to claim 1,
The occupancy of Ni inserted into the Li 3a site of the primary particles present on the surface of the positive active material is 1.35% or less,
positive electrode active material.
According to claim 1,
The interplanar distance of the (003) crystal plane of the primary particles present on the surface of the positive electrode active material is 4.7293 Å or more,
positive electrode active material.
According to claim 1,
At least one selected from the M2 element and W contained in the primary particles present in the surface portion of the secondary particles represents a concentration gradient that decreases toward the center of the secondary particles,
positive electrode active material.
According to claim 1,
The coating oxide exhibits a decreasing concentration gradient from the surface portion of the secondary particle toward the central portion of the secondary particle,
positive electrode active material.
According to claim 1,
The coating oxide is represented by the following formula (2),
Cathode active material:
[Formula 2]
Li _f M3 _g O _h
(here,
M3 comprises at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd,
0≤f≤6, 0<g≤6, 0<h≤10)
A lithium secondary battery using a positive electrode comprising the positive electrode active material according to any one of claims 1 to 8.

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