KR102559194B1 - Lithium composite oxide and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium composite oxide having improved stability and electrical properties as a positive electrode active material by suppressing interfacial side reactions in lithium composite oxide and improving stability and ion conductivity of a crystal structure, and a lithium secondary battery including the same.

Description

Lithium composite oxide and lithium secondary battery containing the same

The present invention relates to a lithium composite oxide having improved stability and electrical properties as a positive electrode active material by suppressing interfacial side reactions in lithium composite oxide and improving stability and ion conductivity of a crystal structure, and a lithium secondary battery including the same.

A battery stores electric power by using materials capable of electrochemical reactions in its anode and 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 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 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 of a lithium secondary battery, and for example, composite oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiMnO ₂ are being studied.

Among the cathode active materials, LiCoO ₂ is the most widely used because of its excellent lifespan characteristics and charge/discharge efficiency.

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

In addition, a large amount of Li by-products are generated according to the degree of intensification 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 a problem of gelation during cathode paste preparation and gas generation during charging and discharging after electrode preparation. Residual Li ₂ CO ₃ increases swelling of the cell, reducing cycle time and causing the battery to swell.

In order to compensate for these disadvantages, demand for Ni-rich cathode active materials having a Ni content of 60% or more as a cathode active material for secondary batteries has begun to increase. In particular, such a Ni-rich cathode active material is proposed as a composite oxide in which a portion of Ni is substituted with Co, Mn, and/or Al. However, while these Ni-rich cathode active materials exhibit high-capacity characteristics, there is a problem in that structural instability is caused by Li/Nication mixing as the Ni content in the cathode active material increases. Due to the structural instability of the cathode active material, the lithium secondary battery may be rapidly deteriorated not only at high temperature but also at room temperature.

Recently, as higher capacity characteristics and output characteristics of batteries used in electric vehicles are required to improve driving distance after full charge of electric vehicles, various methods such as changing the composition of lithium composite oxide used as a cathode active material, controlling particle shape and size, doping, or surface treatment have been studied. However, the stability of the positive electrode active material and the electrical characteristics of the secondary battery, which are in a trade-off relationship, have not yet been achieved to a sufficiently satisfactory level.

Korean Patent Publication No. 10-2015-0069334

In the lithium secondary battery market, while the growth of lithium secondary batteries for electric vehicles is driving the market, the demand for cathode active materials used in lithium secondary batteries is also constantly changing.

For example, in the past, lithium secondary batteries using LFP have been mainly used from the viewpoint of securing safety, etc., but recently, the use of nickel-based lithium composite oxide having a higher energy capacity per weight than that of LFP is increasing.

Accordingly, an object of the present invention is to provide a lithium composite oxide for a cathode active material capable of simultaneously improving stability and electrical properties as a cathode active material for a lithium secondary battery.

In addition, another object of the present invention is to provide a lithium secondary battery using a positive electrode including the lithium composite oxide defined herein.

The objects of the present invention are not limited to the above-mentioned objects (for example, for electric vehicles), and other objects and advantages of the present invention not mentioned above can be understood by the following description and will be more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the present invention may be realized by means of the instrumentalities and combinations indicated in the claims.

According to one aspect of the present invention, there is provided a lithium composite oxide including primary particles capable of occluding and releasing lithium and secondary particles in which the primary particles are aggregated, wherein a niobium (Nb)-containing oxide exists in at least a part of a region selected from interfaces between the primary particles and surfaces of the secondary particles.

Here, the interplanar distance d1 of the (003) plane in the crystal structure of the primary particles and the interplanar distance d2 of the (400) plane in the crystal structure in the interface between the primary particles may satisfy the following relational expression 1.

<Relationship 1>

d1 > d2

At this time, the interplanar distance (d1) of the (003) plane of the crystal structure in the primary particles is 0.40 nm or more, and the interplanar distance (d2) of the (400) plane of the crystal structure in the interface between the primary particles may be 0.30 nm or less.

In one embodiment, niobium (Nb) in the primary particles may be doped, and in this case, niobium (Nb) in the primary particles may exist in a solid solution state with the primary particles. In addition, niobium (Nb) doped in the primary particle may exhibit a concentration gradient that decreases from the surface portion of the primary particle toward the center portion of the primary particle.

In the above embodiment, the primary particle may be represented by Formula 1 below.

[Formula 1]

Li _w Ni _1-(x+y+z+z') Co _x M1 _y M2 _z Nbz'O ₂

(Where M1 is at least one selected from Mn and Al,

M2 is at least one selected from P, Sr, Ba, B, Ti, Zr, Mn, Al, W, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd, and Cu;

M1 and M2 are different elements,

0.5≤w≤1.5, 0≤x≤0.50, 0≤y≤0.20, 0≤z≤0.20, 0≤z'≤0.20)

In one embodiment, there is a first coating layer covering at least a portion of the surface of the primary particle, but the first coating layer may include a niobium (Nb)-containing oxide.

In this case, the first coating layer may further include an oxide represented by Chemical Formula 2 below.

[Formula 2]

Li _a M3 _b O _c

(Wherein, M3 is at least one selected from Ni, Mn, Co, P, Sr, Ba, B, Ti, Zr, Mn, Al, W, Nb, Fe, Cu, Mo, Cr, Zn, Na, K, Ca, Mg, Pt, Au, Eu, Sm, Ce, V, Ta, Sn, Hf, Ce, Gd, and Nd, and 0≤a≤10, 0≤b≤8, and 2≤c≤13)

In a further embodiment, the lithium composite oxide may include a second coating layer covering at least a part of the surface of the secondary particle. In this case, the second coating layer may include an oxide represented by Chemical Formula 3 below.

[Formula 3]

Li _a M4 _b O _c

(here,

M4 is at least one selected from Ni, Mn, Co, P, Sr, Ba, B, Ti, Zr, Mn, Al, W, Nb, Fe, Cu, Mo, Cr, Zn, Na, K, Ca, Mg, Pt, Au, Eu, Sm, Ce, V, Ta, Sn, Hf, Ce, Gd and Nd, and 0≤a≤10, 0≤b≤8, 2≤c≤13)

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

As a cathode active material, a region exposed to the electrolyte solution, such as an interface between primary particles included in lithium composite oxide and a surface of secondary particles, is a region in which a side reaction between the cathode active material and the electrolyte may occur. If a side reaction between the cathode active material and the electrolyte solution occurs, not only electrical characteristics of the lithium secondary battery may deteriorate due to gas generated by the cathode active material, but stability may also rapidly deteriorate.

In the lithium composite oxide according to the present invention, a niobium (Nb)-containing oxide is present in at least a part of an interface between primary particles and a region selected from the surface of the secondary particles, and in this case, the interplanar distance (d1) of the (003) plane in the crystal structure of the primary particles is formed to be larger than the interplanar distance (d2) of the (400) plane in the crystal structure in the interface between the primary particles, thereby stabilizing the crystal structure of the lithium composite oxide. In addition, through this, it is possible to suppress side reactions between primary particles included in the lithium composite oxide.

By using the lithium composite oxide according to the present invention as a cathode active material for a lithium secondary battery, stability of the cathode active material may be improved and electrical characteristics may be improved.

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

1 is a schematic diagram of a lithium composite oxide according to an embodiment of the present invention.
FIG. 2 shows a transmission electron microscope (TEM) image of primary particles constituting the lithium composite oxide according to Example 1 and a diffraction pattern for a labeled region.
3 and 4 show results of measuring interplanar distances in regions corresponding to the hexagonal and cubic crystal structures shown in FIG. 2, respectively.
5 to 8 show the distribution of metal elements measured by TEM/EDX Mapping for several lithium composite oxides prepared according to preparation examples of the present invention.
9 to 11 show XRD analysis results for some lithium composite oxides prepared according to the preparation example of the present invention.

Certain terms are defined herein for convenience in order to more readily understand the present invention. Unless otherwise defined herein, scientific and technical terms used herein shall have meanings commonly understood by one of ordinary skill in the art. In addition, it should be understood that terms in the singular form also include their plural forms, and terms in the plural form also include their singular forms, unless otherwise specified in context.

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

lithium complex oxide

According to one aspect of the present invention, there is provided a lithium composite oxide including primary particles capable of intercalating and releasing lithium and secondary particles in which the primary particles are aggregated. The lithium composite oxide may serve as a cathode active material of a lithium secondary battery.

Here, the primary particle means one grain or crystallite, and the secondary particle means an aggregate formed by aggregating a plurality of primary particles. The primary particles may have a rod shape, an elliptical shape and/or an irregular shape. Gaps and/or grain boundaries may exist between the primary particles constituting the secondary particles.

For example, the primary particle may be spaced apart from neighboring primary particles inside the secondary particle to form internal voids. In addition, the primary particle may form a surface existing inside the secondary particle by contacting an internal void without forming a crystal grain boundary by contacting the primary particle adjacent to each other. On the other hand, the surface of the primary particles exposed to the outside air existing on the outermost surface of the secondary particles forms the surface of the secondary particles.

Here, the average major axis length of the primary particles is in the range of 0.1 μm to 5 μm, preferably 0.1 μm to 2 μm, so that the optimum density of the positive electrode manufactured using the positive electrode active material according to various embodiments of the present invention can be implemented. In addition, the average particle diameter of the secondary particles may vary depending on the number of agglomerated primary particles, but may be 1 μm to 30 μm.

Referring to FIG. 1 showing a schematic view of a lithium composite oxide according to an embodiment of the present invention, the lithium composite oxide according to an embodiment of the present invention may include a niobium (Nb)-containing oxide present in at least a part of a region selected from the interface between the primary particles and the surface of the secondary particle.

Here, the interface between the primary particles may mean an interspace defined by two adjacent primary particles, that is, a surface where two adjacent primary particles contact each other. Also, the interface between the primary particles may refer to an independent surface of the primary particles.

The surface of the secondary particle means the outermost surface of the secondary particle in which at least one of the primary particles is aggregated, and the outermost surface of the secondary particle is the exposed surface of the primary particle located at the outermost part of the secondary particle. It may mean.

The niobium (Nb)-containing oxide is a lithium ion conductive material, and is present in at least a part of a region selected from the interface between the primary particles defined above and the surface of the secondary particle, thereby forming a lithium ion diffusion pathway.

The niobium (Nb)-containing oxide may include not only a single oxide of niobium (Nb), such as NbO or Nb ₂ O ₅ , but also a composite oxide of lithium and niobium (Nb), such as LiNbO ₃ , LiNb ₃ O ₈ or Li ₃ NbO ₄ . In addition, the type of the niobium (Nb)-containing oxide is not limited to the above-described examples, and may be present in the form of a single oxide of various niobium (Nb) represented by Formula 2, a composite oxide of lithium and niobium (Nb), or a composite oxide of lithium, niobium (Nb), and other metal elements.

As described above, the lithium composite oxide according to an embodiment of the present invention is characterized by the presence of niobium (Nb)-containing oxide present in at least a part of a region selected from the interface between the primary particles and the surface of the secondary particle.

At this time, the interplanar distance (d1) of the (003) plane in the crystal structure of the primary particles and the interplanar distance (d2) of the (400) plane in the crystal structure in the interface between the primary particles preferably satisfy the following relational expression 1.

<Relationship 1>

d1 > d2

The interplanar distances d1 and d2 refer to average values of interplanar distances measured from analysis results of crystal structures such as TEM analysis of the lithium composite oxide.

The niobium (Nb)-containing oxide is present at the interface between the primary particles, and thus the interplanar distance (d2) of the (400) plane in the crystal structure of the interface between the primary particles is smaller than the interplanar distance (d1) of the (003) plane in the crystal structure of the primary particles, thereby stabilizing the crystal structure of the lithium composite oxide.

In addition, when the lithium composite oxide is used as a cathode active material for a lithium secondary battery by suppressing a side reaction between primary particles included in the lithium composite oxide through this, stability and electrical properties of the cathode active material can be simultaneously improved.

At this time, the interplanar distance (d1) of the (003) plane in the crystal structure in the primary particles is 0.40 nm or more, preferably 0.45 nm or more, and the (400) plane in the crystal structure in the interface between the primary particles. The interplanar distance (d2) may be 0.30 nm or less, preferably 0.25 nm or less.

Accordingly, the interplanar distance d1 of the (003) plane in the crystal structure of the primary particles and the interplanar distance d2 of the (400) plane in the crystal structure in the interface between the primary particles can additionally satisfy the following relational expression 2.

<Relationship 2>

d1 - d2 ≥ 0.10

In the case where the interplanar distance d1 of the (003) plane of the crystal structure in the primary particle of the lithium composite oxide and the interplanar distance d2 of the (400) plane of the crystal structure in the interface between the primary particles do not satisfy at least one selected from the relational expressions 1 and 2, the stabilizing effect of the crystal structure of the lithium composite oxide may be insignificant or rather deteriorated.

In addition, the lithium composite oxide may be a High-Ni type lithium composite oxide containing a high nickel content. In the case of the High-Ni type lithium composite oxide, as the content of nickel in the lithium composite oxide increases, crystal structure stability and thermal stability tend to decrease.

However, according to the present invention, when the interplanar distance (d1) of the (003) plane of the crystal structure in the primary particle of the lithium composite oxide and the interplanar distance (d2) of the (400) plane of the crystal structure of the interface between the primary particles satisfy the above relational expressions 1 and 2, even if the content of nickel in the lithium composite oxide increases, the stability of the crystal structure and the thermal stability can be prevented from deterioration.

In another embodiment of the present invention, niobium (Nb) is not only present in the form of a niobium (Nb)-containing oxide on at least a part of a region selected from the interface between the primary particles and the surface of the secondary particle, but also niobium (Nb) in the primary particle may exist in a doped state. In this case, the niobium (Nb) may exist in a solid solution state with the primary particles.

In the above embodiment, the primary particle may be represented by Formula 1 below.

[Formula 1]

Li _w Ni _1-(x+y+z+z') Co _x M1 _y M2 _z Nbz'O ₂

(here,

M1 is at least one selected from Mn and Al,

M2 is at least one selected from P, Sr, Ba, B, Ti, Zr, Mn, Al, W, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd, and Cu;

M1 and M2 are different elements,

0.5≤w≤1.5, 0≤x≤0.50, 0≤y≤0.20, 0≤z≤0.20, 0≤z'≤0.20)

In the primary particle represented by Formula 1, the dopant represented by M2 is uniformly distributed inside the primary particle, or decreases from the surface portion of the primary particle toward the center of the primary particle. It may exhibit a concentration gradient.

In addition, in the primary particles represented by Formula 1, niobium (Nb) may also be uniformly distributed inside the primary particles, or may exhibit a concentration gradient that decreases from the surface portion of the primary particles toward the center of the primary particles.

Niobium (Nb) present in a concentration gradient that decreases from the surface of the primary particle toward the center of the primary particle in the primary particle may form a lithium ion diffusion path in the primary particle. The niobium (Nb) may exist in a state in which a solid solution is formed with the primary particles.

In addition, niobium (Nb) in the primary particles may exhibit a concentration gradient that decreases along a direction from the surface portion of the secondary particle toward the center of the secondary particle.

For example, the concentration of niobium (Nb) in the primary particles present in the region adjacent to the center of the secondary particle compared to niobium (Nb) in the region adjacent to the surface portion of the secondary particle may be low. However, the concentration of niobium (Nb) in the primary particles present in the region adjacent to the surface portion of the secondary particle and the concentration of niobium (Nb) in the primary particle present in the region adjacent to the center portion of the secondary particle may both exhibit a decreasing gradient along a direction from the surface portion of the secondary particle toward the center of the secondary particle.

According to the above-described embodiment, the lithium composite oxide is not only doped with niobium (Nb) in the primary particles, but also contains niobium (Nb)-containing oxides in at least some of the regions selected from the interface between the primary particles and the surface of the secondary particles, thereby satisfying the crystal structure-related properties according to the relational expressions 1 and 2, and through this, it is possible to improve the stability and electrical properties of the crystal structure of the lithium composite oxide.

Additionally, the lithium composite oxide may include a coating layer covering at least a portion of the surface of the primary particles (eg, interfaces between the primary particles) and/or secondary particles formed by aggregation of the primary particles.

Specifically, the lithium composite oxide includes a first coating layer covering at least a portion of the surface of the primary particle, and the above-described niobium (Nb)-containing oxide may be present in the first coating layer.

That is, when a niobium (Nb)-containing oxide is present at the interface between the primary particles, the niobium (Nb)-containing oxide may be provided as a first coating layer including the niobium (Nb)-containing oxide.

In addition, the first coating layer may additionally include an oxide represented by Chemical Formula 2 below.

[Formula 2]

Li _a M3 _b O _c

(here,

M3 is at least one selected from Ni, Mn, Co, P, Sr, Ba, B, Ti, Zr, Mn, Al, W, Nb, Fe, Cu, Mo, Cr, Zn, Na, K, Ca, Mg, Pt, Au, Eu, Sm, Ce, V, Ta, Sn, Hf, Ce, Gd and Nd, and 0≤a≤10, 0≤b≤8, 2≤c≤13)

When the oxide represented by Formula 2 is additionally present in the first coating layer, the metal element M3 in Formula 2 is uniformly distributed inside the primary particles, like niobium (Nb), or the surface portion of the primary particle. It may exhibit a decreasing concentration gradient toward the center of the primary particle.

Additionally, the lithium composite oxide includes a second coating layer covering at least a portion of the surface of the secondary particle, and an oxide represented by Formula 3 below may be present in the second coating layer.

[Formula 3]

Li _a M4 _b O _c

(here,

M4 is at least one selected from Ni, Mn, Co, P, Sr, Ba, B, Ti, Zr, Mn, Al, W, Nb, Fe, Cu, Mo, Cr, Zn, Na, K, Ca, Mg, Pt, Au, Eu, Sm, Ce, V, Ta, Sn, Hf, Ce, Gd and Nd, and 0≤a≤10, 0≤b≤8, 2≤c≤13)

The second coating layer may exist as a layer that continuously or discontinuously coats the surface of the secondary particles. When the coating layer is discontinuously present, it may be present in the form of an island.

In addition, in some cases, the oxide present in the first coating layer and / or the second coating layer may be present in the interface between the primary particles and at least a part of the surface of the secondary particle, as well as in the internal void formed inside the secondary particle.

The first coating layer and the second coating layer present as described above can improve the lithium ion conductivity of the lithium composite oxide and at the same time improve the stability of the lithium composite oxide as a positive electrode active material by reducing a side reaction between the primary particles included in the lithium composite oxide (eg, an interface between the primary particles) and/or an electrolyte solution occurring on the surface of secondary particles formed by aggregation of the primary particles.

The first coating layer and/or the second coating layer may exist in the form of a solid solution that does not form a boundary with the primary particles and/or the secondary particles formed by aggregation of the primary particles, but this is not necessarily the case.

In addition, the first coating layer and / or the second coating layer reduces the residual lithium in the lithium composite oxide and at the same time serves as a diffusion path of lithium ions, thereby improving the efficiency characteristics of the lithium secondary battery. Can have an effect.

Additionally, the c-axis length obtained from Rietveld analysis of X-ray diffraction of lithium composite oxide (primary particles) according to various embodiments of the present invention may be greater than 14.177 Å and less than 14.218 Å, preferably 14.189 Å to 14.211 Å. In addition, the length of the a-axis obtained from Rietveld analysis of X-ray diffraction of lithium composite oxide (primary particle) according to various embodiments of the present invention may be 2.8730 Å to 2.8797 Å. The ratio (c/a) of the c-axis length to the a-axis length of the primary particle calculated therefrom may be 4.934 to 4.939.

When the doping amount of the lithium composite oxide niobium (Nb) is insufficient, a c-axis length obtained from Rietveld analysis of X-ray diffraction of the lithium composite oxide may be 14.177 Å or less. In this case, the stabilizing effect of the crystal structure of the lithium composite oxide may be insufficient, and furthermore, the effect of increasing the lithium ion conductivity of the cathode active material may be insignificant.

On the other hand, when only the niobium (Nb) doping amount in the lithium composite oxide is increased instead of niobium present on at least a part of the interface between the primary particles and the surface of the secondary particles, the length of the c-axis obtained from Rietveld analysis of X-ray diffraction may exceed 14.218 Å. In this case, the effect of suppressing a side reaction by niobium oxide or lithium niobium oxide present on at least a part of the interface between the primary particles and the surface of the secondary particles may be insufficient.

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 cathode active material layer may include the lithium composite oxide according to various embodiments of the present invention described above as a cathode active material.

Therefore, a detailed description of the lithium composite oxide will be omitted, and only the remaining components not described above will be described below. In addition, hereinafter, for convenience, the above-described lithium composite oxide will be referred to as a positive electrode active material.

The positive current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 μm to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The positive electrode active material layer may be prepared by applying a positive electrode slurry composition including the positive electrode active material, a conductive material, and optionally a binder to the positive electrode current collector.

In this case, the cathode active material may be included in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, based on the total weight of the cathode active material layer. When included in the above content range, it 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, any material that does not cause chemical change and has electronic conductivity can be used without particular limitation. Specific examples include graphite such as natural graphite or 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 of them alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the cathode active material layer.

The binder serves to improve adhesion between particles of the positive electrode active material and 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EP DM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like may be used alone or a mixture of two or more of them. The binder may be included in an amount of 0.1 wt % 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 positive electrode active material. Specifically, it may be prepared by coating a positive electrode slurry composition prepared by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent on a positive electrode current collector, followed by drying and rolling.

The solvent may be a solvent commonly used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of them alone or a mixture of two or more may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity capable of exhibiting excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

Also, in another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support and then laminating a film obtained by peeling from the support on a positive electrode current collector.

In addition, according to another aspect of the present invention, an electrochemical device including the anode described above may be provided. The electrochemical device may be specifically a battery, a capacitor, and the like, and more specifically, may be 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 thereof is 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 accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member 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 anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, the anode current collector may typically have a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The negative electrode active material layer may be prepared by applying a negative electrode slurry composition including the negative electrode active material, a conductive material, and optionally a binder to the negative electrode current collector.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the anode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed 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 of these may be used. In addition, a metal lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low-crystalline carbon. High-crystalline carbon includes amorphous, plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum and coal-based carbon. High-temperature calcined carbon such as coke (petroleum or coal tar pitch derived cokes) is representative.

The negative active material may be included in an amount of 80wt% to 99wt% based on the total weight of the negative electrode 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 wt% 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, various of these A copolymer etc. are mentioned.

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. The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include 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; Conductive materials such as polyphenylene derivatives may be used.

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

In another embodiment, the negative electrode active material layer is formed by applying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent and drying the negative electrode active material layer, or casting the negative electrode slurry composition on a separate support and then peeling the support from the support and laminating a film obtained on the negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and can be used without particular limitation as long as it is normally used as a separator in a lithium secondary battery. In particular, it is preferable that the separator has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption ability. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

In addition, the electrolyte used in the present invention includes an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in manufacturing a lithium secondary battery, but is not limited thereto.

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 includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane or the like may be used. Of these, a carbonate-based solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high permittivity capable of enhancing the charge/discharge performance of a battery and a linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) with low viscosity 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 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 , LiAlO 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 may be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, a haloalkylene carbonate-based compound such as difluoro ethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N One or more additives such as -substituted imidazolidine, 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 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the "cathode" active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, it is useful for portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

The appearance 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 shape, or a coin shape. In addition, the lithium secondary battery can be used not only as a battery cell used as a power source for small-sized devices, 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 may be provided.

The battery module or the battery pack may include a 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 one or more medium or large-sized devices among power storage systems.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only intended to illustrate the present invention, and the scope of the present invention will not be construed as being limited by these examples.

manufacturing example. Preparation of lithium complex oxide

1) Example 1

A spherical Ni _0.91 Co _0.08 Mn _0.01 (OH) ₂ hydroxide precursor was synthesized by a co-precipitation method. In a 90L reactor, 25wt% of NaOH and 30wt% of NH ₄ OH were added to a 1.5M aqueous solution of complex transition metal sulfuric acid in which nickel sulfate, cobalt sulfate, and manganese sulfate were mixed at a molar ratio of 91:8:1. The pH in the reactor was maintained at 11.5, the reactor temperature at this time was maintained at 60°C, and N ₂ , an inert gas, was introduced into the reactor to prevent oxidation of the prepared precursor. After completion of synthetic stirring, washing and dehydration were performed using a filter press (F/P) equipment to obtain a Ni _0.91 Co _0.08 Mn _0.01 (OH) ₂ hydroxide precursor.

Subsequently, LiOH and a Nb-containing raw material (Nb ₂ O ₅ ) were added to the synthesized precursor and then calcined to prepare a lithium composite oxide. Specifically, after mixing LiOH and Nb-containing raw materials (Nb ₂ O ₅ ) with the precursor, the temperature was raised to 700 ° C. at 1 ° C. per minute while maintaining an O ₂ atmosphere in a sintering furnace, followed by heat treatment for 10 hours, followed by natural cooling to obtain lithium composite oxide. The Nb-containing raw material (Nb ₂ O ₅ ) was mixed to 3 mol% of the total composition before firing, and LiOH was mixed to a molar ratio of 1.03 with the total metal.

Then, the obtained lithium composite oxide was heat-treated for 4 hours by raising the temperature to 700 °C at 1 °C per minute while maintaining an O ₂ atmosphere in a sintering furnace, followed by natural cooling.

(2) Example 2

A lithium composite oxide was prepared in the same manner as in Example 1, except that the B-containing raw material (H ₃ BO ₃ ) was mixed with the Nb-containing raw material (Nb ₂ O ₅ ) during firing. B-containing raw material (H ₃ BO ₃ ) was mixed so as to be 1.0 mol% of the total composition.

(3) Example 3

A lithium composite oxide was prepared in the same manner as in Example 1, except that the Al-containing raw material (Al(OH) ₃ ) was mixed with the Nb-containing raw material (Nb ₂ O ₅ ) during firing. The Al-containing raw material (Al(OH) ₃ ) was mixed so as to be 1.0 mol% of the total composition.

(4) Example 4

After mixing LiOH with the precursor synthesized by the method of Example 1, while maintaining an O ₂ atmosphere in a sintering furnace, the temperature was raised to 700 ° C. at 1 ° C. per minute, followed by heat treatment for 10 hours, followed by natural cooling to obtain lithium composite oxide.

Then, after mixing the obtained cathode active material with the Nb-containing raw material (Nb ₂ O ₅ ), the temperature was raised to 700 ° C. at 1 ° C. per minute while maintaining the O ₂ atmosphere in a sintering furnace, heat-treated for 4 hours, and then cooled naturally to obtain lithium composite oxide. The Nb-containing raw material (Nb ₂ O ₅ ) is Before heat treatment, it was mixed so as to be 3 mol% of the total composition.

(5) Example 5

LiOH and a B-containing raw material (H ₃ BO ₃ ) were mixed with the precursor synthesized by the method of Example 1 and then fired to prepare a lithium composite oxide. Specifically, after mixing LiOH and H ₃ BO ₃ with the precursor, the temperature was raised to 700 °C at 1 °C per minute while maintaining an O ₂ atmosphere in a sintering furnace, followed by heat treatment for 10 hours, followed by natural cooling to obtain lithium composite oxide. The B-containing raw material (H ₃ BO ₃ ) was mixed to 1 mol% of the total composition before firing.

Then, after mixing the obtained cathode active material with the Nb-containing raw material (Nb ₂ O ₅ ), the temperature was raised to 700 ° C. at 1 ° C. per minute while maintaining the O ₂ atmosphere in a sintering furnace, heat-treated for 4 hours, and then cooled naturally to obtain lithium composite oxide. The Nb-containing raw material (Nb ₂ O ₅ ) was mixed so as to be 3 mol% of the lithium composite oxide.

(6) Example 6

A cathode lithium composite oxide was prepared in the same manner as in Example 5, except that an Al-containing raw material (Al(OH) ₃ ) was mixed instead of the B-containing raw material (H ₃ BO ₃ ) during firing.

(7) Comparative Example 1

A lithium composite oxide was prepared in the same manner as in Example 1, except that the Nb-containing raw material (Nb ₂ O ₅ ) was mixed to 1 mol% of the total composition before firing.

(8) Comparative Example 2

A lithium composite oxide was prepared in the same manner as in Example 1, except that LiOH and Nb-containing raw materials (Nb ₂ O ₅ ) were mixed and calcined at 750 °C.

(9) Comparative Example 3

A lithium composite oxide was prepared in the same manner as in Example 1, except that LiOH was mixed with all metals in a molar ratio of 1.05 before firing.

(10) Comparative Example 4

A lithium composite oxide was prepared in the same manner as in Example 3, except that the Nb-containing raw material (Nb ₂ O ₅ ) was mixed to 1 mol% of the lithium composite oxide.

Experimental Example 1. TEM-EDX analysis of lithium composite oxide

FIG. 2 shows a transmission electron microscope (TEM) image of primary particles constituting the lithium composite oxide according to Example 1 and a diffraction pattern for a labeled region.

Referring to the diffraction pattern shown in FIG. 2, it can be seen that the core region of the primary particle has a hexagonal crystal structure (hexagonal α-NaFeO ₂ ) structure having an R-3m space group, and the surface of the primary particle (interface between adjacent primary particles) region has a cubic crystal structure.

3 and 4 show the results of measuring the interplanar distance in the region corresponding to the hexagonal crystal structure and cubic crystal structure shown in FIG.

3 and 4, the interplanar distance (d1) of the (003) plane in the crystal structure of the primary particle of the lithium composite oxide is 0.480 nm, while the interplanar distance (d2) of the (400) plane in the crystal structure in the interface of the primary particle of the lithium composite oxide is measured to be 0.205 nm. Referring to the above results, it can be confirmed that the interplanar distance (d1) of the (003) plane in the crystal structure in the primary particles and the interplanar distance (d2) in the (400) plane in the crystal structure in the interface between the primary particles satisfy the following relational expressions 1 and 2.

<Relationship 1>

d1 > d2

<Relationship 2>

d1 - d2 ≥ 0.10

In addition, the interplanar distance (d1) of the (003) plane of the crystal structure in the primary particle of the lithium composite oxide according to other Examples and Comparative Examples and the (400) plane of the crystal structure in the interface between the primary particles The interplanar distance (d2) is shown in Table 1 below.

division d1 d2 d1-d2 Example 1 0.4804 0.2051 0.2753 Example 2 0.4807 0.2051 0.2756 Example 3 0.4804 0.2050 0.2754 Example 4 0.4806 0.2049 0.2757 Example 5 0.4807 0.2050 0.2757 Example 6 0.4805 0.2050 0.2755 Comparative Example 1 0.4755 0.4785 -0.0030 Comparative Example 2 0.4810 0.4805 0.0005 Comparative Example 3 0.4749 0.4780 -0.0031 Comparative Example 4 0.4799 0.4804 -0.0005

5 to 8 show TEM/EDX Mapping results of lithium composite oxides according to Examples 1, 3, 6, and Comparative Example 1, respectively.

5 to 7, it can be confirmed that Nb is present on at least some of the grain boundaries of primary particles and the surface of secondary particles in all of the lithium composite oxides according to Examples 1, 3, and 6, and in particular, it can be confirmed that Nb is partially doped inside the primary particles.

On the other hand, referring to FIG. 8 , in the lithium composite oxide according to Comparative Example 1, Nb is only partially doped inside the primary particles, and Nb does not exist at the grain boundary of the primary particles and the surface of the secondary particles.

As such, in a lithium composite oxide in which Nb is doped only inside the primary particles and Nb (or Nb-containing oxides) does not exist on at least some of the grain boundaries of the primary particles and the surface of the secondary particles, it may be difficult to expect an improvement effect on the stability and thermal stability of the crystal structure intended herein.

In addition, as shown in Table 2 below, it was observed that the c-axis length of the primary particles significantly changed according to the addition amount of the niobium (Nb)-containing raw material when preparing the lithium composite oxide.

division a c c/a Example 1 2.8797 14.211 4.934 Example 2 2.8786 14.206 4.934 Example 3 2.8775 14.209 4.938 Example 4 2.8746 14.196 4.938 Example 5 2.8731 14.189 4.939 Example 6 2.8730 14.190 4.939 Comparative Example 1 2.8684 14.176 4.936 Comparative Example 2 2.8799 14.218 4.942 Comparative Example 3 2.8782 14.218 4.940 Comparative Example 4 2.8681 14.177 4.937

Referring to the results of Table 2, in the case of Comparative Example 1 and Comparative Example 4, it can be seen that the c-axis length of the primary particle is shorter than that of Example 1. This difference in c-axis length indicates that the doping amount of niobium (Nb) in the primary particles of the lithium composite oxide according to Comparative Example 1 and Comparative Example 4 is less than that of the primary particle of the lithium composite oxide according to Example 1.

In addition, in the case of Comparative Example 2 and Comparative Example 3, it can be confirmed that the c-axis length is longer than that of Example 1. These results show that in the lithium composite oxides according to Comparative Examples 2 and 3, Nb (or Nb-containing oxide) does not exist on at least some of the grain boundaries of the primary particles and the surface of the secondary particles, and only the inside of the primary particles. As Nb is doped, the c-axis length is longer than that of the lithium composite oxide according to Example 1.

Experimental Example 2. XRD analysis of lithium composite oxide

X-ray diffraction (XRD) analysis was performed on the lithium composite oxide prepared according to the above Preparation Example to confirm whether a niobium (Nb)-containing oxide was present in the lithium composite oxide. XRD analysis was performed using a Bruker D8 Advance diffractometer using Cu Kα radiation (1.540598Å).

9 and 10 show XRD analysis results of the lithium composite oxide according to Example 1. Referring to FIGS. 9 and 10 , it can be confirmed that (111), (211), and (400) peaks specific to Li ₃ NbO ₄ in the lithium composite oxide are detected.

Combining the TEM/EDX analysis results of FIG. 5 and the XRD analysis results of FIG. 9 , Nb in the lithium composite oxide according to Example 1 exists in a doped state inside the primary particles, and at the same time, the grain boundaries of the primary particles and the surface of the secondary particles. It can be confirmed that it exists in the form of lithium composite oxide.

11 shows XRD analysis results for lithium composite oxides according to Comparative Example 1. Referring to FIG. 11 , peaks specific to the lithium composite oxide Nb-containing oxide, in particular, Nb-containing lithium composite oxide are not observed.

Combining the TEM/EDX analysis results of FIG. 8 and the XRD analysis results of FIG. 11 , it can be confirmed that Nb in the lithium composite oxide according to Comparative Example 1 exists only in a doped state inside the primary particles.

Experimental Example 3. Characteristic evaluation result of lithium secondary battery

(1) Manufacture of lithium secondary battery

A positive electrode slurry was prepared by dispersing 94 wt% of each of the lithium composite oxide, 3 wt% of carbon black, and 3 wt% of a PVDF binder prepared according to the preparation example in 30 g of N-methyl-2 pyrrolidone (NMP). The positive electrode slurry was applied to a 15 μm thick aluminum (Al) thin film as a positive electrode current collector, dried, and roll pressed 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 anode, and the electrolyte was prepared by adding 1.15M LiPF ₆ to a solvent in which ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 2:4:4.

A lithium secondary battery (coin cell) was manufactured by forming a battery assembly with a separator made of a porous polyethylene (PE) film interposed between the positive electrode and the negative electrode, and injecting the electrolyte solution.

(2) Evaluation of lithium secondary battery capacity characteristics

The manufactured lithium secondary battery (coin cell) was charged at 25° C. with a constant current (CC) of 0.15C until it reached 4.25V, and then charged at a constant voltage (CV) of 4.25V until the charging current reached 0.05mAh. The first charge was performed. Then, after leaving it for 20 minutes, it was discharged at a constant current of 0.1C until it became 3.0V, and the discharge capacity of the first cycle was measured. The charge capacity, discharge capacity, and charge/discharge efficiency during the first charge/discharge are shown in Table 3 below.

division Charge capacity (mAh/g) Discharge capacity (mAh/g) Charge/discharge efficiency (%) Example 1 238.2 213.3 89.5 Example 2 237.1 212.7 89.7 Example 3 236.4 212.2 89.7 Example 4 237.2 213.3 89.9 Example 5 235.7 212.5 90.1 Example 6 235.1 211.8 90.1 Comparative Example 1 240.1 210.1 87.5 Comparative Example 2 238.2 210.3 88.2 Comparative Example 3 237.9 209.0 87.8 Comparative Example 4 239.4 209.0 87.3

Referring to the results of Table 3, the lithium secondary battery using the lithium composite oxide according to Examples 1 to 6 was compared to the lithium secondary battery using the lithium composite oxide according to Comparative Examples 1 to 4. It can be seen that the improvement in terms of efficiency and capacity characteristics.

(3) Lithium secondary battery thermal stability evaluation

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

In addition, to check the high-temperature storage characteristics of the lithium secondary battery, the battery charged and discharged at 25 ° C. was charged based on SOC 100%, the resistance was measured, and then the resistance was measured after storage at 60 ° C. for 7 days to confirm the change in resistance.

The measurement results are shown in Table 4 below.

division Capacity retention rate (%) Resistance before life (Ω) Resistance after life (Ω) Example 1 93.1 5.1 13.7 Example 2 93.3% 4.0 17.1 Example 3 94.3% 4.0 20.1 Example 4 91.3% 4.3 11.5 Example 5 93.5% 6.0 15.8 Example 6 92.1% 9.0 19.1 Comparative Example 1 79.5% 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 3, the lithium secondary battery using the lithium composite oxide according to Examples 1 to 6 has an excellent capacity retention rate compared to the lithium secondary battery using the lithium composite oxide according to Comparative Examples 1 to 4. In addition, it can be seen that the resistance change width before and after high temperature storage is small.

Although the embodiments of the present invention have been described above, those skilled in the art will be able to variously modify and change the present invention by adding, changing, deleting, or adding components within the scope not departing from the spirit of the present invention described in the claims, and this will also be said to be included within the scope of the present invention.

Claims (13)

A lithium composite oxide comprising primary particles capable of occluding and releasing lithium and secondary particles in which the primary particles are aggregated,
A niobium (Nb)-containing oxide is present in at least a part of a region selected from the interface between the primary particles and the surface of the secondary particles,
The c-axis length of the primary particles obtained from Rietveld analysis of X-ray diffraction is greater than 14.177 Å and less than 14.218 Å,
The ratio (c / a) of the c-axis length to the a-axis length of the primary particle is 4.934 to 4.939,
lithium complex oxide.
According to claim 1,
The a-axis length of the primary particles obtained from Rietveld analysis of X-ray diffraction is 2.8730 Å to 2.8797 Å,
lithium complex oxide.
According to claim 1,
The lithium composite oxide is (1) nickel; (2) containing at least one selected from cobalt, manganese and aluminum;
lithium complex oxide.
According to claim 3,
The mole fraction of nickel in the lithium composite oxide is 0.6 or more,
lithium complex oxide.
According to claim 1,
Niobium (Nb) in the primary particles is doped,
lithium complex oxide.
According to claim 1,
Niobium (Nb) in the primary particles exhibits a concentration gradient that decreases from the surface portion of the primary particle toward the center of the primary particle,
lithium complex oxide.
According to claim 1,
The primary particle is represented by Formula 1 below,
lithium complex oxide.
[Formula 1]
Li _w Ni _1-(x+y+z+z') Co _x M1 _y M2 _z Nb _z' O ₂
(here,
M1 is at least one selected from Mn and Al,
M2 is at least one selected from P, Sr, Ba, B, Ti, Zr, Mn, Al, W, Ce, Hf, Ta, Cr, F, Mg, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd, and Cu;
M1 and M2 are different elements,
0.5≤w≤1.5, 0≤x≤0.50, 0≤y≤0.20, 0≤z≤0.20, 0<z'≤0.20)
According to claim 1,
There is a gradient in which the concentration of niobium (Nb) decreases along the direction from the surface of the secondary particle to the center of the secondary particle,
lithium complex oxide.
According to claim 1,
Further comprising an oxide represented by Formula 2 below on at least a part of the interface between the primary particles and the surface of the secondary particles,
lithium complex oxide.
[Formula 2]
Li _a M3 _b O _c
(here,
M3 is at least one selected from Ni, Mn, Co, P, Sr, Ba, B, Ti, Zr, Al, W, Nb, Fe, Cu, Mo, Cr, Zn, Na, K, Ca, Mg, Pt, Au, Eu, Sm, Ce, V, Ta, Sn, Hf, Gd and Nd, and 0<a≤10, 0<b≤8, 2≤c≤13)
According to claim 9,
The oxide represented by Formula 2 is additionally present in the internal voids formed inside the secondary particles,
lithium complex oxide.
According to claim 1,
Further comprising an oxide represented by Formula 3 below on at least a part of the surface of the secondary particle,
lithium complex oxide.
[Formula 3]
Li _a M4 _b O _c
(here,
M4 is at least one selected from Ni, Mn, Co, P, Sr, Ba, B, Ti, Zr, Al, W, Nb, Fe, Cu, Mo, Cr, Zn, Na, K, Ca, Mg, Pt, Au, Eu, Sm, Ce, V, Ta, Sn, Hf, Gd and Nd, and 0<a≤10, 0<b≤8, 2≤c≤13)
According to claim 11,
The oxide represented by Formula 3 is additionally present in the internal void formed inside the secondary particle,
lithium complex oxide.
A lithium secondary battery using a positive electrode comprising the lithium composite oxide according to any one of claims 1 to 12.