KR20200022320A - 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 comprising the lithium composite oxide, and a lithium secondary battery using a positive electrode comprising the positive electrode active material. To this end, the lithium composite oxide comprises primary particles and secondary particles formed by aggregation of the primary particles, and the structural stability of a lithium alloy oxide can be improved.

Description

Lithium composite oxide, positive electrode active material for lithium secondary battery, and lithium secondary battery including the same {LITHIUM COMPOSITE OXIDE, POSITIVE ELECTRODE ACTIVE MATERIAL AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

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

A battery stores power by using a material capable of electrochemical reactions at the positive and negative electrodes. A typical example of such a battery is a lithium secondary battery that stores electrical energy due to a difference in chemical potential when lithium ions are intercalated / deintercalated at 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 or a polymer electrolyte between the positive electrode and the negative electrode.

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

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

Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have the advantages of excellent thermal safety and low price, but have a problem of small capacity and poor high temperature characteristics. In addition, the LiNiO ₂ -based positive electrode active material exhibits high discharge capacity of battery characteristics, but is difficult to synthesize due to cation mixing problem between Li and the 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 depth of the cation mixing, and most of these Li by-products are composed of a compound of LiOH and Li ₂ CO ₃ , which causes gelation and production of an anode paste. After manufacture, it causes gas generation due to charging / discharging progress. Residual Li ₂ CO ₃ not only reduces the cycle by increasing the swelling of the cell, 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 problem of the conventional lithium composite oxide for a cathode active material for lithium secondary batteries.

In addition, another object of the present invention is to provide a cathode active material having improved high temperature storage stability and lifespan by simultaneously including the lithium composite oxide and lithium alloy oxide defined herein.

In addition, another object of the present invention to provide a lithium secondary battery using a positive electrode comprising a positive electrode active material 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 which are not mentioned above may be understood by the following description and more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may 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 represented by Formula 1 below and secondary particles formed by aggregation of the primary particles may be provided.

[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 elements 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, a positive electrode active material including a lithium composite oxide as defined herein and a lithium alloy oxide present on at least some of the interface between the primary particles forming the lithium composite oxide and the surface of the secondary particles Can be provided.

In one embodiment, the lithium alloy oxide may exhibit a concentration gradient decreasing 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 positive electrode active material during the electrochemical reaction by the lithium alloy oxide.

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

Lithium composite oxide according to various embodiments of the present invention is the sum of the content of the doping metal contained in the primary particles present in the surface portion of the secondary particles constituting it is greater than the content of Ni to improve the structural stability of the lithium alloy oxide Can be improved.

In addition, the cathode active material according to various embodiments of the present disclosure may include a lithium alloy oxide present on at least part of an interface between primary particles constituting the lithium composite oxide and a surface of the secondary particles formed by aggregation of the primary particles. By including the structural stability can be improved, accordingly, when using a positive electrode including a positive electrode active material according to various embodiments of the present invention as a positive electrode of a lithium secondary battery it can further improve the high temperature storage stability and life characteristics.

In addition to the effects described above, the specific effects of the present invention will be described together with the following description of specifics for carrying out the invention.

1 to 5 show transmission electron microscope (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 showing the content of metal elements (Ni, Co, Al, W) measured according to the TEM / EDS Mapping results for the positive electrode active material prepared according to the embodiment of the present invention.
Figure 7 shows the results of the electron transmission microscope (TEM) analysis for the positive electrode active material prepared according to an embodiment of the present invention.
FIG. 8 is a schematic diagram showing a crystal structure in which a part of Ni inserted into a Li 3a site of a cathode active material prepared according to an embodiment of the present invention is substituted with W. FIG.
9 and 10 illustrate TEM / EDS mapping results of the doped metal in the cathode active material prepared according to another embodiment of the present invention.
FIG. 11 is a line sum spectrum showing the content of the doped metal elements (Zr, Ti, W) measured according to the TEM / EDS Mapping results for the cathode 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 a cathode active material prepared according to a comparative example.
16 to 18 are graphs showing the results of XRD analysis on the cathode active material prepared according to various embodiments of the present disclosure.

Certain terms are defined herein for convenience of understanding the invention. Unless defined otherwise herein, scientific and technical terms used herein have the meanings that are commonly understood by one of ordinary skill in the art. Also, unless specifically indicated in the context, the singular forms "a", "an", and "the" are intended to include their plural forms as well.

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

Lithium composite oxide

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

[Formula 1]

Li _a Ni _{1- (b + c + d + e)} Co _b M1 _c M2 _d W _e O ₂

(Wherein 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, wherein 0.5 ≦ a ≦ 1.5, 0.01 ≦ b ≦ 0.50, 0.01 ≦ c ≦ 0.20, 0 ≦ d ≦ 0.20, and 0.001 ≦ e ≦ 0.20).

Herein, the lithium composite oxide may be defined as particles including aggregates in which the primary particles and the plurality of primary particles are aggregated (physically bonded) to each other. The primary particles may have a rod shape, ellipse shape and / or indefinite shape.

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

Herein, 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. The surfaces present inside the secondary particles can be formed by contacting the internal pores without forming grain boundaries in contact with each other. On the other hand, the surface of the primary particles existing on the outermost surface of the secondary particles exposed to the outside air forms the surface of the secondary particles.

In addition, at least one selected from the elements M2 and W contained in the primary particles present in the surface portion of the secondary particles may exhibit a concentration gradient decreasing 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 particles may be a direction from the surface portion of the secondary particles toward the center of the secondary particles.

Accordingly, a movement path of lithium ions (diffusion path of lithium ions) formed in the primary particles toward the center of the secondary particles may be formed (see FIG. 7), thereby forming a lithium composite oxide and a cathode active material. It is possible to improve the lithium ion conductivity by.

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

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

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

For example, when the distance from the outermost surface of the secondary particles forming the lithium composite oxide to the center of the secondary particles is R, the distance R 'from the outermost surface of the secondary particles is 0. If the region of about 0.02R is defined as the first region, the M2 element and / or W present in the first region may exhibit a concentration gradient decreasing 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 increasing toward the center of the secondary particles in the primary particles as opposed to the M2 element and / or W. Here, the center of the secondary particles may refer to the center of gravity of the secondary particles.

At this time, 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 in the primary particle is included, 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 content of Ni (at May be greater than%).

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

At this time, the primary particles present in the first region of the secondary particles, the ratio (W _occ ) of the W inserted in the Li 3a site by Rietveld analysis of the X-ray diffraction pattern is inserted in 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 may have a ratio of W inserted into Li 3a sites 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 in the Li 3a site (Ni _occ ).

As described above, the content (or sum of the contents) of the M2 elements and / or W present in the first region of the secondary particles is not simply greater than the content of Ni, but is used for Rietveld analysis of the X-ray diffraction pattern. Due to the large insertion rate at the Li 3a site, the structural stability of the primary particles, and the secondary particles formed by the aggregation of the primary particles can be improved, thereby increasing the electrical properties and reliability of the prepared cathode active material. have.

The above-described contrast concentration gradient between M2 element and / or W and Ni is such that M2 element and / or W contained in the primary particles present in the first region is at least one of Li 3a site and 3b site in the lithium composite oxide. It may appear as it is substituted with Ni inserted in one.

At this time, 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, the remaining region except the first region may be defined as the second region, and if the region R 'from the outermost surface of the secondary particle is 0 to 0.02R, the region is defined as the first region. The area | region whose distance R 'from the outermost surface of a secondary particle is more than 0.02R and 1.0R can be defined as a 2nd area | region. Here, the M2 element and / or W contained in the primary particles present in the second region may not have a concentration gradient in the form of increasing or decreasing concentration in a predetermined direction in the primary particles.

In another embodiment, the rate of change of the concentration of 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 this case, the concentration change rate of M 1 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, and more preferably 15% or less. Can be.

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 are the first region. And showing a concentration gradient of another embodiment in the second region, thereby improving structural stability of the lithium composite oxide.

Cathode Active Material for Lithium Secondary Battery

According to another aspect of the present invention, a positive electrode active material including a lithium composite oxide as defined herein and a lithium alloy oxide present on at least some of the interface between the primary particles forming the lithium composite oxide and the surface of the secondary particles Can be provided. Here, since the lithium composite oxide is the same as described above, a detailed description thereof will be omitted for convenience, and only the rest of the configuration which has not been described above will be described below.

The lithium alloy oxide may be in a state physically and / or chemically bonded to the primary particles and / or the secondary particles forming the lithium composite oxide.

In this case, the lithium alloy oxide is the interface between the primary particles forming the lithium composite oxide and the interface between the primary particles forming the lithium composite oxide or coating the surface of the secondary particles as a whole and the second At least a portion of the surface of the primary particles may be coated, and in some cases, the interface between the primary particles forming the lithium composite oxide and the entire surface or at least a portion of the surface of the secondary particles may be distributed in a particulate form.

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

In some cases, the lithium alloy oxide may be present in not only at least a portion of the interface between the primary particles forming the lithium composite oxide and the surface of the secondary particles, but also in internal voids formed inside the secondary particles. Can be.

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

[Formula 2]

Li _f M3 _g O _h

Wherein M 3 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)

As shown in Formula 2, the lithium alloy oxide is an oxide in which a metal element represented by lithium and M 3 is complexed, and the lithium alloy oxide is, for example, Li (W) O, Li (Zr) O, Li (Ti) O, Li (B) O, WO _x , ZrO _x , TiO _x, etc., but the above examples are merely described for convenience of understanding, and the lithium alloy oxides defined herein are examples described above. It is not limited to. Therefore, in the experimental examples to be described later, the experimental results for some examples of the representative lithium alloy oxide, which may be represented by Chemical Formula 1, will be described.

In another embodiment, the lithium alloy oxide may further include an oxide in which at least two metal elements represented by lithium and M 3 are combined, or an oxide in which at least two metal elements represented by lithium and M 3 are combined. have. Lithium alloy oxides in which at least two metal elements represented by lithium and M3 are combined include, for example, Li (W / Ti) O, Li (W / Zr) O, Li (W / Ti / Zr) O, Li (W / Ti / B) O and the like, but is not necessarily limited thereto.

In this case, the lithium tungsten oxide may have a lattice structure doped with at least one metal element. That is, the lithium alloy oxide is a lattice structure formed by lithium tungsten oxide (for example, 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 the tungsten in the structure will have a lattice structure substituted with a metal element. Here, the metal element to substitute 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 lithium alloy oxide may exhibit a concentration gradient that decreases toward the center of the secondary particles from the surface portion of the secondary particles forming the lithium composite oxide. Accordingly, the concentration of the lithium alloy oxide may decrease from the outermost surface of the secondary particles toward the center of the secondary particles.

As described above, the residual lithium present on the surface of the positive electrode active material by exhibiting a concentration gradient decreasing from the surface portion of the secondary particles forming the lithium composite oxide toward the center of the secondary particles. In addition, it is possible to effectively reduce the side reaction by the unreacted residual lithium in advance, as well as to prevent the crystallinity in the inner region of the surface of the positive electrode active material is lowered by the lithium alloy oxide. In addition, it is possible to prevent the overall structural collapse of the positive electrode active material during the electrochemical reaction by the lithium alloy oxide.

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

[Formula 3]

Li _i W _j O _k

(Where 0 ≦ i ≦ 6, 0 <j ≦ 6, 0 <k ≦ 10)

[Formula 4]

Li _l M4 _m O _n

(Wherein 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 lithium alloy oxide and the second lithium alloy oxide may exhibit a concentration gradient that decreases toward the center of the secondary particles from the surface portion of the secondary particles forming the lithium composite oxide. Accordingly, the concentration of the lithium alloy oxide may decrease from the outermost surface of the secondary particles toward the center of the secondary particles.

In this case, the concentration reduction rate of the second lithium alloy oxide is preferably greater than the concentration reduction rate of the first lithium alloy oxide, and the concentration reduction rate of the second lithium alloy oxide is greater than the concentration reduction rate of the first lithium alloy oxide. Structural stability of the positive electrode active material including the lithium alloy oxide may be maintained. In addition, by forming an efficient path of lithium ions in the positive electrode active material may act positively to improve the efficiency characteristics of the lithium secondary battery.

Accordingly, when the cathode including the cathode active material according to various embodiments of the present disclosure is used as a cathode of a lithium secondary battery, high temperature storage stability and lifespan characteristics may be further improved.

In a further embodiment, the second lithium alloy oxide may include lithium zirconium oxide represented by the following Formula 5 and lithium titanium oxide represented by the following Formula 6.

[Formula 5]

Li _o Zr _p O _q

(Where 0 ≦ o ≦ 6, 0 <p ≦ 6, 0 <q ≦ 10)

[Formula 6]

Li _r Ti _s O _t

(Where 0 ≦ r ≦ 6, 0 <s ≦ 6, 0 <t ≦ 10)

The lithium zirconium oxide represented by Chemical Formula 5 and the lithium titanium oxide represented by Chemical Formula 6 may contribute to enhancing the structural stability of the positive electrode active material together with the lithium tungsten oxide represented by Chemical Formula 3, and the positive electrode It is possible to form an efficient route of lithium ions in the active material.

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

At this time, in order to maintain structural stability and crystallinity of the positive electrode active material including the lithium zirconium oxide and the lithium titanium oxide simultaneously with the lithium tungsten oxide, the concentration reduction rate of the lithium zirconium oxide is less than the concentration reduction rate of the lithium titanium oxide. It is desirable to be large.

Lithium secondary battery

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

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The positive electrode active material layer may optionally include a conductive material and optionally a binder together with the positive electrode active material.

In this case, the cathode 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 cathode active material layer. When included in the above content range may exhibit excellent capacity characteristics, but is not necessarily limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any conductive material may be used as long as it has electronic conductivity without causing chemical change. Specific examples thereof 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 powder 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, or a mixture of two or more kinds 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 cathode active material layer.

The binder serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode 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), fluororubbers, or various copolymers thereof, and the like, and one or more of these may be used. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the cathode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material described above. Specifically, the positive electrode active material and optionally, a 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 applied onto a positive electrode current collector, followed by drying and rolling.

The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the coating thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during application for the production of the positive electrode. Do.

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

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

The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned to face the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, the positive electrode is the same as described above, and for convenience, a detailed description thereof will be omitted, and hereinafter, only the remaining components which are not described above will be described in detail.

The lithium secondary battery may 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 a negative electrode 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. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of about 3 μm to 500 μm, and like the positive electrode current collector, minute unevenness may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

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

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium, such as SiO _β (0 <β <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, 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 anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.

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

The binder is a component that assists in the 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 active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluor Low ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber, various copolymers thereof, and the like.

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 anode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks 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 powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

In one embodiment, the negative electrode active material layer is prepared by applying and drying the negative electrode active material layer and the composition for forming a negative electrode active material layer prepared by dissolving or dispersing a binder and a conductive material in a solvent selectively on a negative electrode current collector, or The composition for forming the negative electrode active material layer may be cast on a separate support, and then the film obtained by peeling from the support may be laminated on a negative electrode current collector.

In another embodiment, the negative electrode active material layer may be coated with a negative electrode active material, and optionally a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a binder and a conductive material in a solvent, or drying, or The negative electrode active material layer-forming composition may be cast on a separate support, and then the film obtained by peeling from the support may be manufactured by laminating on a negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular in the ion transfer of the electrolyte It is desirable to have a low resistance against the electrolyte solution and excellent in electrolytic solution moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, or the like Laminate structures of two or more layers may be used. In addition, a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting glass fibers, polyethylene terephthalate fibers, or the like 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 be optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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

The organic solvent may be used without 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, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles, such as R-CN (R is a C2-C20 linear, branched or cyclic hydrocarbon group, and may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge / discharge performance of a battery, and low viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolyte may be excellent.

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, LiB (C ₂ O ₄ ) _2, or the like 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, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

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

As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics. It is useful for electric vehicle fields 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 cylindrical, square, pouch type or coin type using a can. In addition, the lithium secondary battery may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium-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 can 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); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, these examples are only for illustrating the present invention, the scope of the present invention will not be construed as 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 90 M reactor, 25 wt% NaOH and 30 wt% NH ₄ OH were added to a 1.5 M aqueous solution of a complex transition metal sulfuric acid containing NiSO ₄ · 7H ₂ O and CoSO ₄ · 7H ₂ O at a molar ratio of 92: 8. Input. The pH in the reactor was maintained at 11.5 and the reactor temperature was maintained at 60 ° C., and an inert gas, N ₂ , was added to the reactor to prevent the prepared precursor from being oxidized. 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 ℃ After natural cooling. The obtained positive electrode active material was mixed with the W-containing raw material (WO ₃ ) using a mixer. The O ₂ atmosphere was maintained in the same kiln, and the temperature was raised to 2 ° C. per minute and maintained at 600 ° C. for 5 hours, followed by natural cooling. Subsequently, heat treatment and cooling were further performed once under the same conditions as above. It was confirmed that the cathode active material prepared in Example 1 had a Li _1.05 Ni _0.9060 Co _0.0790 Al _0.0140 W _0.0010 O ₂ compositional formula.

(Example 2)

The positive electrode active material was mixed in the same manner as in Example 1 except that the positive electrode active material was mixed with the W-containing raw material (WO ₃ ) so that the positive electrode active material obtained in Example 2 had a Li _1.04 Ni _0.9020 Co _0.0790 Al _0.0140 W _0.0050 O ₂ composition formula. Was prepared.

(Example 3)

The positive electrode active material was mixed in the same manner as in Example 1 except that the positive electrode active material was mixed with the W-containing raw material (WO ₃ ) so that the positive electrode active material obtained in Example 3 had a Li _1.03 Ni _0.8970 Co _0.0790 Al _0.0140 W _0.010 O ₂ composition formula. Was prepared.

(Example 4)

Embodiment in this example four positive electrode active material obtained in 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₎ and mixed Except that, a positive electrode active material was prepared in the same manner as in Example 1.

(Example 5)

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

(Example 6)

The exemplary cathode active material prepared in Example 6 _{Li 1.04 Ni 0.9034 Co 0.0787 Al 0.0138} W 0.003 Ce 0.0011 O 2 A positive electrode active material was manufactured in the same manner as in Example 1, except that Ce-containing raw material (CeO ₂ ) was used instead of B-containing raw material (B ₂ O ₃ ) to have a composition formula.

(Example 7)

Except for using the Ti-containing raw material (TiO ₂ ) instead of B-containing raw material (B ₂ O ₃ ) so that the positive electrode active material prepared in Example 7 has a Li _1.03 Ni _0.9030 Co _0.0789 Al _0.0143 W _0.0028 Ti _0.001 O ₂ composition formula , The positive electrode active material was prepared in the same manner as in Example 1.

(Example 8)

Except for using the Zr-containing raw material (ZrO ₂ ) instead of the B-containing raw material (B ₂ O ₃ ) so that the positive electrode active material prepared in Example 8 has a Li _1.06 Ni _0.9032 Co _0.0787 Al _0.0141 W _0.003 Zr _0.001 O ₂ composition formula , The positive electrode active material was prepared in the same manner as in Example 1.

(Example 9)

The positive electrode active material prepared in Example 9 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 manufactured 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 the B-containing raw material (B ₂ O ₃ ) to have a composition formula.

(Example 10)

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

(Comparative Example 1)

A positive electrode active material was prepared in the same manner as in Example 1 except that the positive electrode active material and the W-containing raw material (WO ₃ ) were mixed in Example 1 and then heat-treated at 700 ° C.

(Comparative Example 2)

A positive electrode active material was prepared in the same manner as in Example 1 except that the positive electrode active material and the W-containing raw material (WO ₃ ) were mixed in Example 1 and then heat treated only once at 700 ° C.

(Comparative Example 3)

A positive electrode active material was manufactured in the same manner as in Example 7, except that the positive electrode active material, the W-containing raw material (WO ₃ ), and the Ti-containing raw material (TiO ₂ ) were mixed in Example 7 and then heat treated only once at 700 ° C. .

(Comparative Example 4)

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

(2) SEM and TEM analysis of the positive electrode active material

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

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

2 to 6, W contained in the primary particles positioned in the surface portion of the positive electrode active material prepared in Example 1 is determined from the surface portion (right side) of the secondary particles to the center portion (left side) of the secondary particles. While showing a decreasing concentration gradient toward the Ni, it can be seen that Ni shows a concentration gradient increasing toward the center of the secondary particles from the surface portion of the secondary particles. On the other hand, Co and Al of the positive electrode active material prepared in Example 1, unlike Ni and W it can be seen that the variation of the concentration change in the secondary particles is not large or the concentration gradient does not appear.

FIG. 7 illustrates an electron transmission microscope (TEM) analysis result of the cathode active material prepared according to Example 1, and FIG. 8 illustrates a crystal structure in which a part of Ni inserted at a Li 3a site in the cathode active material is replaced with W. FIG. It is a schematic diagram.

Referring to FIG. 7, it can be seen that a Ni-O layer (cation mixing layer) is formed on the surface of the primary particles of the cathode active material prepared according to Example 1, which is represented by Ni ²⁺ as schematically shown in FIG. 8. Occupies 3a site of Li ⁺ .

In addition, referring to FIG. 7, it can be seen that all of the lithium ion diffusion paths formed in the cathode active material prepared according to Example 1 are equilateral in the long axis direction. That is, since the lithium ions in the positive electrode active material can be concentrated and diffused in one direction without being diffused in multiple directions, it is possible to improve the conductivity of lithium ions by the positive electrode active material.

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

FIG. 9 illustrates TEM / EDS mapping results of Ti, which is a doping metal, of primary particles constituting the positive electrode active material prepared according to Example 7. FIG. 10 illustrates 1 of the positive electrode active material prepared according to Example 8. TEM / EDS Mapping results for Zr, a doping metal, is shown in the primary particles.

9 and 10, Ti and Zr contained in the primary particles positioned on the surface portion of the positive electrode active material are also similar to W shown in FIG. 5, and the center portion of the secondary particles from the surface portion (left side) of the secondary particles (left). It can be seen that the concentration gradient decreases toward the right).

FIG. 11 is a line sum spectrum showing the content of doped metal elements (Zr, Ti, W) measured according to the TEM / EDS Mapping results for the primary particles constituting the cathode active material prepared in Example 9. FIG. .

Referring to FIG. 11, Zr, Ti, and W contained in the primary particles located in the surface portion of the cathode active material prepared in Example 9 decrease in concentration from the surface portion 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 at the surface portion of the secondary particles is greater than W, and the concentration of Zr in the primary particles located at the surface portion of the secondary particles is shown. It can be seen that the reduction rate is greater than the Ti concentration decrease rate.

The results shown in FIG. 11 indicate that the concentration gradients of W, Ti and Zr in the primary particles forming the lithium composite oxide, as well as the interface between the primary particles forming the lithium composite oxide and the primary particles are aggregated It can be expected that the effect is due to the concentration gradient of the lithium alloy oxide present on at least part of the surface of the secondary particles.

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

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

Referring to FIG. 13, unlike the cathode active material according to various embodiments of the present disclosure, a concentration gradient in which W decreases from the surface portion (lower end) of the secondary particles toward the center portion (upper left) of the secondary particles is shown. It can confirm that it is not shown.

FIG. 14 illustrates TEM / EDS Mapping results for Ti, a doping metal included in primary particles positioned on a surface of a cathode active material prepared according to Comparative Example 2. FIG. 15 illustrates a cathode prepared according to Comparative Example 3. TEM / EDS mapping results for Zr, which is a heavy doping metal contained in the primary particles located on the surface of the active material, are shown.

Referring to FIGS. 14 and 15, it is confirmed that Ti and Zr also do not show a decreasing concentration gradient from the surface portion (lower end) of the secondary particles toward the center portion (upper left) of the secondary particles, as in W shown in FIG. 11. Can be.

Further, additionally, TEM / EDS mapping results were measured for the surface portions (regions from the outermost surface of the secondary particles to 0.05 μm) of the positive electrode active materials prepared according to Examples 1 to 10 and Comparative Examples 1 to 4. The average content of Ni and doped metals 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 electrode active material 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) region of the positive electrode active material It can be seen that the sum of the average contents of the doped metals included in the particles is greater than the average contents 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 (region from the outermost surface of the secondary particles to 0.05 μm) region of the positive electrode active material It can be seen that the sum of the average contents is lower than the average contents of Ni.

(3) XRD analysis of the positive electrode active material

The occupancy (or content; occupancy) of the Ni metal inserted in the Li 3a site of the positive electrode active materials prepared according to Examples 1 to 10 and Comparative Examples 1 to 4 was determined by Rietvelt analysis of the X-ray diffraction pattern. It was. The measurement results are shown in Table 2 below. Rietveld analysis of the X-ray diffraction pattern was performed on the surface portions (regions from the outermost surface of the secondary particles to 0.05 μm) of the positive electrode active materials prepared according to Examples 1 to 9 and Comparative Examples 1 to 4. It 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 electrode active material 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) region of the positive electrode active material The occupancy ratio of Ni inserted into the Li 3a site of the particles is determined by the presence of the primary particles in the region of the surface portion (region from the outermost surface of the secondary particles to 0.05 μm) of the positive electrode active material prepared according to Comparative Examples 1 to 4. It can be seen that the occupancy of the Ni inserted in the Li 3a site is lower.

That is, when comparing Example 1 and Comparative Example 1 through the results of Table 2, even if the W content in the positive electrode active material is the same or similar, it can be confirmed that the W region of the positive electrode active material is different. Some of the W present in the surface portion of the positive electrode active material may exist in a substituted state with Ni inserted in the Li 3a site, which can be confirmed that the occupancy rate of Ni inserted in the Li 3a site decreases. This may be a result, as schematically shown in Figure 8, in particular a portion of the W present in the surface portion of the positive electrode active material is substituted with Ni inserted in the Li 3a site. In addition, in view of the results of Table 2, it can be expected that the positive electrode active material according to the embodiments has a higher W content inserted into the Li 3a site and / or 3b site than the positive electrode active material according to the comparative examples.

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

16 to 18 are graphs showing the results of XRD analysis on the positive electrode active material prepared according to Examples 7 to 9.

Referring to FIG. 16, a characteristic peak corresponding to Li ₄ WO ₅ , which is a lithium alloy oxide of the positive electrode active material, is identified. In particular, the (220) peak is not shifted, but the (111) and (200) peaks are specific. As a result of shifting to the low angle side, it was confirmed that a heterogeneous lithium alloy oxide in which some of tungsten was substituted with Ti in the lattice structure formed by Li ₄ WO ₅ was formed.

In addition, referring to FIG. 17, a characteristic peak corresponding to Li ₄ WO ₅ , which is a lithium alloy oxide of the positive electrode active material, is identified, and in particular, the (111), (200), and (220) peaks specifically have a low angle. As a result of shifting), it was confirmed that a heterogeneous lithium alloy oxide in which some of tungsten was substituted with Zr in the lattice structure formed by Li ₄ WO ₅ was formed.

Referring to FIG. 18, it can be seen that a positive electrode 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 electrode active material are formed. It was confirmed to exist.

(4) Unreacted lithium measurement of the positive electrode active material

Unreacted lithium measurements on the positive electrode active materials prepared according to Examples 1-10 and Comparative Examples 1-4 were carried out in an amount of 0.1M HCl used until pH 4 by pH titration. Measured. First, 5 g of each of the cathode active materials prepared according to Examples 1 to 6 and Comparative Example 1 was put into 100 ml of DIW, stirred for 15 minutes, filtered, and 50 ml of the filtered solution was taken, and 0.1 M HCl was added thereto. To determine the Q1 and Q2 by measuring the HCl consumption according to the pH change, through which the unreacted LiOH and Li ₂ CO ₃ was calculated.

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)

Measurement results of the 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 2,011 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 electrode active material prepared according to Examples 1 to 10 significantly reduced the amount of residual lithium compared to the positive electrode active material prepared according to Comparative Examples 1 to 4.

Experimental Example 2.

(1) Manufacture of Lithium Secondary Battery

N-methyl-2 pyrrolidone was added to 94 wt% of the cathode active materials prepared according to Examples 1 to 10 and Comparative Examples 1 to 4, 3 wt% of carbon black, and 3 wt% of PVDF binder, respectively. Dispersion was carried out in 30 g (NMP) to prepare a positive electrode slurry. The positive electrode slurry was coated on a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of 15 μm, 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 .

Metal lithium was used as a counter electrode for the positive electrode, and as an electrolyte, 1.15 in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 2: 4: 4. Prepared by the addition of M LiPF ₆ .

A battery assembly was formed between the positive electrode and the negative electrode through a separator made of a porous polyethylene (PE) film, 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 4.25 V, and then charged with a constant voltage (CV) of 4.25 V to charge current of 0.05 mAh. The first charge was performed until Thereafter, the sample was left for 20 minutes, and then discharged until a constant current of 0.1 C reached 3.0 V, and the discharge capacity of the first cycle was measured. The charge capacity, discharge capacity and charge / discharge efficiency at the time of the first charge and discharge are shown in Table 4 below.

division Charge capacity (mAh / g) Discharge Capacity (mAh / g) Charge / discharge 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 charge and discharge efficiency of the lithium secondary battery using the positive electrode active material prepared according to Examples 1 to 10 compared to the lithium secondary battery using the positive electrode active material prepared according to Comparative Examples 1 to 4 And it can be seen that improved 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 range of 3.0 to 4.25 V driving voltage. Accordingly, the cycle capacity retention, which is the ratio of the discharge capacity at the 100th cycle to the initial capacity after 100 charge / discharge cycles at room temperature, was measured.

In addition, in order to confirm the high temperature storage characteristics of the lithium secondary battery, the battery charged and discharged at 25 ° C. was charged based on 100% SOC, and the resistance thereof was measured. It was confirmed.

The measurement results are shown in Table 5 below.

division Capacity retention rate (%) Resistance before high temperature storage Resistance after high temperature storage 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 capacity retention ratio of the lithium secondary battery using the positive electrode active material prepared according to Examples 1 to 10 compared to the lithium secondary battery using the positive electrode active material prepared according to Comparative Examples 1 to 4 Not only is it excellent, it can be seen that the change in resistance before and after high temperature storage is small.

As mentioned above, although embodiment of this invention was described, those of ordinary skill in the art should add, change, delete, add, etc. the component within the range which does not deviate from the idea of this invention described in the claim. The present invention may be modified and changed in various ways, which will also be included within the scope of the present invention.

Claims (13)

A lithium composite oxide comprising 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)
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 is greater than the content of Ni (at%),
Lithium composite oxide.
The method of claim 1,
The content (at%) of W contained in the primary particles present in the surface portion of the secondary particles is greater than the content (at%) of Ni,
Lithium composite oxide.
The method of claim 1,
Ni in the primary particles present in the surface portion of the secondary particles exhibit a concentration gradient increasing toward the center of the secondary particles,
Lithium composite oxide.
The method of claim 1,
At least one selected from M2 elements and W contained in the primary particles present in the surface portion of the secondary particles exhibit a concentration gradient decreasing toward the center of the secondary particles,
Lithium composite oxide.
The method of claim 1,
At least one selected from the element M2 and W among the primary particles represented by Chemical Formula 1 is substituted with Ni inserted in at least one of Li 3a site and 3b site in the lithium composite oxide by Rietveld analysis of the X-ray diffraction pattern. Done,
Lithium composite oxide.
The method of claim 1,
The secondary particles include a first region and a second region having different concentrations of M2 elements,
At least one selected from the elements M2 and W contained in the primary particles present in the first region exhibits a concentration gradient decreasing towards the center of the secondary particles,
Lithium composite oxide.
The method of claim 6,
At least one concentration change rate selected from the M2 elements and W contained in the primary particles present in the first region is 50% or more,
Lithium composite oxide.
The method of claim 6,
At least one concentration change rate selected from the M2 elements and W contained in the primary particles present in the second region is 49% or less,
Lithium composite oxide.
The method of claim 1,
The concentration gradient of the M2 element contained in the primary particles is greater at the surface side of the secondary particles than the central side of the secondary particles based on the longitudinal direction of the primary particles.
Lithium composite oxide.
A lithium composite oxide according to any one of claims 1 to 9; And
Lithium alloy oxides present on at least some of the interface between the primary particles forming the lithium composite oxide and the surface of the secondary particles;
Including;
The lithium alloy oxide exhibits a concentration gradient decreasing from the surface portion of the secondary particles toward the center of the secondary particles,
Cathode active material for lithium secondary battery.
The method of claim 10,
The lithium alloy oxide is represented by the following formula (2),
Cathode active material for lithium secondary battery:
[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)
The method of claim 10,
The lithium alloy oxide,
A first lithium alloy oxide represented by Formula 3 below; And
A second lithium alloy oxide represented by Formula 4 below;
Including,
Cathode active material for lithium secondary battery:
[Formula 3]
Li _i W _j O _k
(Where 0 ≦ i ≦ 6, 0 <j ≦ 6, 0 <k ≦ 10)
[Formula 4]
Li _l M4 _m O _n
(here,
M4 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≤l≤6, 0 <m≤6, 0 <n≤10)
A lithium secondary battery using a positive electrode comprising the positive electrode active material according to claim 10.

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