KR20230083792A - Positive electrode for rechargeable lithium battery and rechargeable lithium battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. The positive electrode for a rechargeable lithium battery comprises: a current collector; a first active material layer located on the current collector and including a first active material; and a second active material layer located on the first active material layer and including a second active material. The second active material includes: a core containing lithium nickel-based composite oxide; and a shell disposed along the surface of the core. The shell comprises a composite in which a first metal oxide represented by M_aO_b (where M is at least one metal selected from groups 2 to 13, 15, and 16 of the periodic table of elements, 0 < a <= 3, 0 < b < 4, and if a is 1, 2, or 3, b is not an integer) is disposed in a carbon-based matrix. According to the present invention, high-temperature lifespan characteristics are excellent.

Description

Positive electrode for lithium secondary battery and lithium secondary battery including the same

It relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same.

Lithium secondary batteries, which have high energy density and are easy to carry, are mainly used as driving power sources for mobile information terminals such as mobile phones, laptop computers, and smart phones. Recently, research into using a lithium secondary battery with high energy density as a driving power source or power storage power source for a hybrid vehicle or an electric vehicle has been actively conducted.

Such a lithium secondary battery requires a high-capacity electrode, but there is a limit to increasing the capacity of the active material itself for this purpose, so it is necessary to increase the amount of the active material to make the electrode thick. A problem caused by the thick film of the electrode is non-uniform reaction between the upper and lower parts of the electrode.

In addition, attempts have been made to improve the performance of lithium secondary batteries by modifying the surface of the cathode active material or using a mixture of various types of cathode active materials. In this case, some performance can be improved, but specific capacity, energy density, There is a problem that is disadvantageous in terms of .

Provided are a positive electrode for a lithium secondary battery having excellent high-temperature lifespan characteristics and at the same time improved output characteristics and rate performance, and a lithium secondary battery including the same.

In one embodiment, the current collector; a first active material layer disposed on the current collector and including a first active material; and a second active material layer disposed on the first active material layer and including a second active material, wherein the second active material includes a core including a lithium nickel-based composite oxide, and a surface of the core. Includes a shell disposed along, wherein the shell is M _a O _b (M is one or more metals selected from groups 2 to 13, 15 and 16 of the periodic table of the elements, 0 <a ≤ 3, 0<b<4, if a is 1, 2, or 3, b is not an integer).

Another embodiment provides a lithium secondary battery including the positive electrode, the negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte.

A positive electrode according to an embodiment and a lithium secondary battery including the same have excellent high-temperature lifespan characteristics, and at the same time, have low initial resistance, so they have excellent output characteristics and excellent rate performance.

1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment.
2 is a Raman spectrum analysis graph of the composite of Example 1 and the second active material.
3 is a graph showing rate-rate charging characteristics of the batteries of Example 1 and Comparative Examples 1 to 3;
4 is a graph showing rate-rate discharge characteristics of the batteries of Example 1 and Comparative Examples 1 to 3;
5 is a graph showing the high-temperature lifespan characteristics of the batteries of Example 1 and Comparative Example 1 and the change in DC-IR according to the cycle progress.

Hereinafter, specific embodiments will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

Terms used herein are merely used to describe exemplary implementations and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

As used herein, “combination thereof” means a mixture of constituents, laminates, composites, copolymers, alloys, blends, reaction products, and the like.

The terms “comprise,” “comprise,” or “have” are intended to indicate that there is an embodied feature, number, step, component, or combination thereof, but that one or more other features, numbers, or steps are present. It should be understood that it does not preclude the possibility of existence or addition of components, components, or combinations thereof.

In the drawings, the thickness is enlarged in order to clearly express various layers and regions, and the same reference numerals are attached to similar parts throughout the specification. When a part such as a layer, film, region, plate, etc. is said to be "on" or "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a part is said to be "directly on" another part, it means that there is no other part in between.

In addition, the term "layer" includes not only shapes formed on the entire surface when observed in plan view, but also shapes formed on some surfaces.

Also, the average particle diameter can be measured by a method well known to those skilled in the art, for example, it can be measured with a particle size analyzer, or it can be measured with a transmission electron micrograph or a scanning electron micrograph. Alternatively, the average particle diameter value can be obtained by measuring using the dynamic light scattering method, performing data analysis, counting the number of particles for each particle size range, and then calculating from this. Unless otherwise defined, the average particle diameter may mean the diameter (D50) of particles whose cumulative volume is 50% by volume in the particle size distribution.

anode

In one embodiment, the current collector; a first active material layer disposed on the current collector and including a first active material; and a second active material layer disposed on the first active material layer and including a second active material. The second active material includes a core including a lithium nickel-based composite oxide, and a shell disposed along a surface of the core. The shell includes a composite, and the composite is M _a O _b (M is one or more metals selected from groups 2 to 13, 15, and 16 of the periodic table, 0<a≤3, 0<b<4 , if a is 1, 2, or 3, b is not an integer) is disposed in the carbon-based matrix.

A positive electrode according to one embodiment is a double-layered or multi-layered positive electrode having two or more active material layers. Such a multi-layer structured anode can realize high capacity. One embodiment seeks to improve battery performance while maximizing capacity by adjusting the characteristics of a positive electrode active material in each layer.

In the positive electrode for a lithium secondary battery according to an embodiment, the second active material layer, which is an upper layer, includes a second active material having a core-shell structure, and the shell includes a composite containing carbon and a metal oxide. Such a second active material may be referred to as an active material surface-modified into a composite. The surface-modified cathode active material as described above is evaluated to have excellent stability and lifespan characteristics at high temperatures. However, when the positive electrode active material surface-modified with the composite is applied alone to the positive electrode, problems arise in that capacity is not maximized, energy density is lowered, the electrode is excessively thick, or output characteristics and rate characteristics are deteriorated. Accordingly, in one embodiment, by applying the active material surface-modified as a composite only to the second active material layer, which is the upper layer where the reaction occurs first in the multilayer structure of the positive electrode, while improving the high-temperature lifespan characteristics, the capacity is maximized and the output characteristics and rate characteristics are improved. A positive electrode and a lithium secondary battery are provided.

A positive electrode for a lithium secondary battery according to an embodiment is a positive electrode in which an active material surface-modified as a composite is applied to the entirety of the first active material layer and the second active material layer, or a positive electrode in which an active material surface-modified as a composite and an unmodified active material are simply mixed. Compared to the case, output characteristics and rate characteristics can be improved while maintaining high high-temperature life characteristics, and problems of energy density decrease or excessive thickness of the electrode can be suppressed. In addition, the positive electrode for a lithium secondary battery according to an embodiment can remarkably improve high-temperature lifespan characteristics even when a very small amount of the composite is used.

Second active material layer

Hereinafter, the second active material will be described in detail.

In general, carbon-based materials such as graphene are difficult to uniformly coat on cores due to their agglomeration characteristics. On the other hand, the composite according to one embodiment can be uniformly coated on the core without aggregation and can exist in the form of a shell. Accordingly, the shell containing the composite effectively blocks the contact between the core and the electrolyte, effectively preventing a side reaction caused by the contact between the core and the electrolyte. In addition, the reduction of nickel ions (Ni ³⁺ → Ni ²⁺ ) and cation mixing by the electrolyte can be suppressed, and the formation of a resistive layer such as a NiO phase can be suppressed, and the elution of nickel ions from the core is also suppressed. can be suppressed The shell including the composite has high flexibility and can easily accommodate the change in volume of the lithium nickel-based composite oxide of the core during charging and discharging, thereby suppressing the occurrence of cracks inside the positive electrode active material. In addition, since the composite has high electron conductivity, interface resistance between the second active material and the electrolyte may be reduced. Accordingly, internal resistance of the lithium secondary battery may be maintained or reduced despite the introduction of the shell. In addition, since the metal oxide in the composite has voltage resistance, deterioration of the lithium nickel-based composite oxide of the core during charging and discharging at a high voltage can be prevented.

complex

The composite is one in which the first metal oxide is disposed in a carbon-based mattress, for example, the first metal oxide may be embedded in the carbon-based mattress, and the first metal oxide in particulate form is a carbon-based mattress. It may be evenly dispersed within the matrix, and/or the first metal oxide fine particles may be chemically bonded to the carbon element of the carbon-based mattress. The composite may be expressed as a carbon-metal oxide composite or a carbon-based metal oxide composite.

The metal M included in the first metal oxide is selected from, for example, Al, Ag, Co, Cu, Fe, Mg, Mn, Pd, Sb, Sc, Se, Si, Ti, V, W, Zn, and Zr can be at least one.

The first metal oxide is, for example, Al ₂ O _z (0<z<3), AgO _x (0<x<1), Co ₃ O _w (0<w<4), CuO _x (0<x<1 ), Fe ₂ O _z (0<z<3), MgO _x (0<x<1), MnO _y (0<y<2), PdO _x (0<x<1), Sb ₂ O _z (0 <z<3), Sc ₂ O _z (0<z<3), SeO _y (0<y<2), SiO _y (0<y<2), TiO _y (0<y<2), V ₂ It may be at least one selected from O _z (0<z<3), WO _y (0<y<2), ZnO _x (0<x<1), and ZrO _y (0<y<2). The composite containing the first metal oxide may be uniformly coated on the surface of the core to form a shell and may improve withstand voltage of the second active material. For example, the first metal oxide may include Al ₂ O _x (0<x<3).

The composite may further include a second metal oxide represented by the formula M _a O _c (0<a≤3, 0<c≤4, when a is 1, 2, or 3, c is an integer). Here, the definition of M is as defined in the first metal oxide.

The second metal oxide may include the same metal as the first metal oxide. Also, c/a, which is the ratio of c to a in the second metal oxide, may have a greater value than b/a, which is the ratio of b to a in the first metal oxide. That is, (c/a)>(b/a) may be satisfied.

The second metal oxide is, for example, Al ₂ O ₃ , AgO, Co ₃ O ₄ , CuO, Fe ₂ O ₃ , MgO, MnO ₂ , PdO, Sb ₂ O ₃ , Sc ₂ O ₃ , SeO ₂ , SiO ₂ , It may be at least one selected from TiO ₂ , V ₂ O ₃ , WO ₂ , ZnO, and ZrO ₂ .

Here, the first metal oxide may be a reduction product of the second metal oxide. Part or all of the second metal oxide may be reduced to obtain the first metal oxide. Accordingly, the first metal oxide has a lower oxygen content and a higher metal oxidation number than the second metal oxide. For example, the composite may include Al ₂ O _x (0<x<3) as a first metal oxide and Al ₂ O ₃ as a second metal oxide.

The first metal oxide and the second metal oxide may be in the form of particulates, and each independently have an average particle diameter of 1 nm to 50 nm, such as 1 nm to 40 nm, 1 nm to 35 nm, and 1 nm to 30 nm. nm, 3 nm to 25 nm, 5 nm to 25 nm, 5 nm to 20 nm, 7 nm to 20 nm, or 7 nm to 15 nm. The first metal oxide and the second metal oxide can be more uniformly distributed in the carbon-based matrix by having a particle size in the range of several to several tens of nanometers, and the composite containing them can be uniformly coated on the core without aggregation, forming a shell. can form Accordingly, withstand voltage characteristics of the second active material may be further improved.

The average particle diameters of the first metal oxide and the second metal oxide may be measured using, for example, a laser diffraction method or a dynamic light scattering method. For example, the average particle diameter is measured using a laser scattering particle size distribution analyzer (eg, Horiba LA-920), and the value of the median particle diameter (D50) when accumulated by 50% from the small particle side in terms of volume may mean

The first metal oxide and/or the second metal oxide may be very uniformly distributed in the carbon-based matrix, and for example, a uniformity deviation in the carbon-based matrix may be 1% or less. The uniformity can be obtained by, for example, XPS.

The carbon-based matrix may include, for example, graphene, carbon nanotubes, carbon nanosheets, graphite sheets, or combinations thereof. The carbon-based matrix may have, for example, a branched structure. The branched carbon-based matrix may include, for example, a plurality of carbon-based particles in contact with each other, for example, graphene particles. A carbon-based matrix with a branched structure can provide more diverse conductive pathways.

As another example, the carbon-based matrix may have a spherical structure. The spherical carbon-based matrix may have a size of about 50 nm to about 300 nm. A composite containing a spherical structure of a carbon-based matrix may exhibit more robust properties.

As another example, the carbon-based matrix may have a faceted-ball structure. In this case, the composite can be easily coated on the irregular surface irregularities of the core.

The carbon-based matrix may include a plurality of carbon layers, for example, a plurality of graphene layers, and may include, for example, 1 to 20 graphene layers. The carbon-based matrix may have a thickness of, for example, 0.6 nm to 12 nm.

The content of the composite may be 1% by weight or less based on the total weight of the second active material. As such, even if a very small amount of the composite is contained, the positive electrode for a lithium secondary battery according to an embodiment can realize excellent high-temperature performance.

The content of the composite is, for example, 0.01 wt% to 1 wt%, 0.1 wt% to 1 wt%, 0.01 wt% to 0.7 wt%, 0.01 wt% to 0.6 wt%, or 0.01 wt% to 0.01 wt% based on the second active material. It may be 0.5% by weight. When the above range is satisfied, the positive electrode for a lithium secondary battery including the same may exhibit excellent high-temperature performance, maximize capacity, and improve output characteristics and rate characteristics.

Meanwhile, the manufacturing method of the composite may include supplying a carbon source in a gaseous state to the metal oxide represented by Chemical Formula 2 and subjecting the metal oxide to heat treatment. According to this method, a carbon-based matrix such as graphene can be grown on the surface of the metal oxide particles.

The carbon source may be, for example, methane, ethylene, propylene, methanol, ethanol, propanol, carbon dioxide, carbon monoxide, or a combination thereof. The carbon source may additionally include inert gas and/or water vapor. The carbon source is, for example, methane; mixed gas of methane and inert gas; mixed gas of methane and carbon dioxide; mixed gas of methane and water vapor; Alternatively, it may be a mixed gas of methane, carbon dioxide, and water vapor.

The heat treatment may be performed in a temperature range of 700 ° C to 1100 ° C, for example, 800 ° C to 1100 ° C, or 900 ° C to 1100 ° C, for 10 minutes to 48 hours, for example, 1 hour to 24 hours, or 4 It can run from 1 hour to 10 hours. In addition, the pressure during the heat treatment may be, for example, 0.5 atm or more, 1 atm or more, 2 atm or more, 3 atm or more, 4 atm or more, or 5 atm or less.

The manufacturing method of the composite may further include cooling after the heat treatment, which may mean adjusting the reaction temperature to room temperature of 20 °C to 25 °C. The cooling process may be performed in air or in an inert gas atmosphere such as nitrogen, helium, or argon. The cooling process may be carried out over, for example, 1 hour to 5 hours.

Second active material

In the second active material, the composite of the shell may be chemically bonded to the lithium nickel-based composite oxide of the core. For example, the carbon atom (C) of the composite and the metal (Me) in the lithium nickel-based composite oxide of the core are bonded through an oxygen atom to form a C-O-Me bond (eg, a C-O-Ni bond). . Here, the chemical bond may be a covalent bond. Accordingly, the shell and the core may be chemically bonded to form a composite. This is distinct from simple physical mixing of the composite with the lithium nickel-based composite oxide.

The lithium nickel-based composite oxide included in the core of the second active material may be, for example, represented by Chemical Formula 1 below.

[Formula 1]

Li _a1 Ni _x1 M ¹ _y1 M ² _1-x1-y1 O ₂

In Formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M ¹ and M ² are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F , Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

In Formula 1, 0.4≤x1≤1 and 0≤y1≤0.6, 0.5≤x1≤1 and 0≤y1≤0.5, 0.6≤x1≤1 and 0≤y1≤0.4, or 0.7≤x1≤ 1 and 0≤y1≤0.3, or 0.8≤x1≤1 and 0≤y1≤0.2, or 0.9≤x1≤1 and 0≤y1≤0.1.

The lithium nickel-based composite oxide may be represented by Formula 2 below, for example.

[Formula 2]

Li _a2 Ni _x2 Co _y2 M ³ _1-x2-y2 O ₂

In Formula 2, 0.9≤a2≤1.8, 0.3≤x2<1, 0<y2≤0.7 and M ³ is Al, B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

In Formula 2, 0.3≤x2≤0.99 and 0.01≤y2≤0.7, 0.4≤x2≤0.99 and 0.01≤y2≤0.6, 0.5≤x2≤0.99 and 0.01≤y2≤0.5, or 0.6≤x2≤0.99 and 0.01≤y2≤0.4, 0.7≤x2≤0.99 and 0.01≤y2≤0.3, 0.8≤x2≤0.99 and 0.01≤y2≤0.2, or 0.9≤x2≤0.99 and 0.01≤y2≤0.1.

The lithium nickel-based composite oxide may be represented by Formula 3 below, for example.

[Formula 3]

Li _a3 Ni _x3 Co _y3 M ⁴ _z3 M ⁵ _1-x3-y3-z3 O ₂

In Formula 3, 0.9≤a3≤1.8, 0.3≤x3≤0.98, 0.01≤y3≤0.69, 0.01≤z3≤0.69, M ⁴ is selected from Al, Mn and combinations thereof, M ⁵ is B, Ba , Ca, Ce, Cr, Cu, F, Fe, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

In Formula 3, 0.4≤x3≤0.98, 0.01≤y3≤0.59, and 0.01≤z3≤0.59, 0.5≤x3≤0.98, 0.01≤y3≤0.49, and 0.01≤z3≤0.49, or 0.6≤x3≤ 0.98, 0.01≤y3≤0.39, and 0.01≤z3≤0.39, or 0.7≤x3≤0.98, 0.01≤y3≤0.29, and 0.01≤z3≤0.29; ≤z3≤0.19, or 0.9≤x3≤0.98, 0.01≤y3≤0.09, and 0.01≤z3≤0.09.

In general, as the nickel content in the cathode active material increases, the mixing of cations in which Ni ²⁺ ions occupy lithium sites increases, and rather, the capacity decreases, or the diffusion of lithium ions is hindered by impurities such as NiO, which can reduce battery life. , Structural collapse or cracking of the cathode active material due to charging and discharging increases side reactions with the electrolyte, which reduces battery life and may cause safety problems. On the other hand, according to one embodiment, by disposing a shell containing a specific composite on a core containing the lithium nickel-based composite oxide, it is possible to improve high-temperature performance while solving the problem of high nickel. In addition, by applying the second active material of this structure only to the second active material layer, which is the upper layer of the multi-layered anode, it is possible to solve the problem of lowering capacity and energy density and improve output characteristics and rate performance characteristics.

In the second active material, the thickness of the shell may be, for example, 1 nm to 100 nm, specifically 1 nm to 90 nm, 1 nm to 80 nm, 1 nm to 70 nm, 1 nm to 60 nm, 1 nm to 50 nm, 1 nm to 40 nm, 1 nm to 30 nm, 1 nm to 20 nm, or 1 nm to 10 nm. When the thickness of the shell is the same, an increase in internal resistance of the lithium secondary battery can be suppressed, and the effect of shell formation, that is, modification by the composite, can be maximized.

The aforementioned second active material may be included in an amount of 90 wt% to 99.5 wt% or 95 wt% to 99 wt% based on the total weight of the second active material layer.

Meanwhile, the method of preparing the second active material may include mixing and mechanically milling the lithium nickel-based composite oxide and the composite.

Here, the mixing amount of the composite may be 3 wt% or less, 2 wt% or less, 1 wt% or less, or 0.01 wt% or more based on the total weight of the lithium nickel-based composite oxide and the composite. The mechanical milling may be performed using, for example, a Novilta mixer or the like. The rotational speed of the mixer during milling may be, for example, 1000 rpm to 3000 rpm, 1000 rpm to 2500 rpm, or 1000 rpm to 2200 rpm. If the milling speed is less than 1000 rpm, since the shear force applied to the lithium nickel-based composite oxide and the composite is weak, it may be difficult to form a chemical bond between them. If the milling speed is too high, the composite may not be uniformly coated on the lithium nickel-based composite oxide, and it may be difficult to form a continuous shell. The milling time is, for example, 5 to 100 minutes, 5 to 60 minutes, 5 to 30 minutes, 5 to 20 minutes, or 5 to 15 minutes. If the milling time is too short, the composite may not be uniformly coated on the lithium nickel-based composite oxide and it may be difficult to form a continuous shell. If the milling time is too long, production efficiency may decrease.

Meanwhile, the second active material layer may further include a binder and/or a conductive material in addition to the second active material described above.

The binder serves to well attach the cathode active material particles to each other and to well attach the cathode active material to the current collector, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and polyvinyl Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but are not limited thereto.

The content of the binder in the second active material layer may be about 0.5% to about 5% by weight based on the total weight of the second active material layer.

The conductive material is used to impart conductivity to the electrode, and in the battery, any material that does not cause chemical change and conducts electrons can be used, such as natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. carbon-based materials such as black, carbon fibers, and carbon nanotubes; metal-based materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof.

The content of the conductive material in the second active material layer may be 0.5 wt % to 5 wt % based on the total weight of the second active material layer.

first active material layer

The first active material layer may include the first active material and optionally further include a binder and/or a conductive material.

The first active material may include, for example, a lithium nickel-based composite oxide. The lithium nickel-based composite oxide of the first active material may be the same as or different from the lithium nickel-based oxide in the core of the second active material. Unlike the second active material, the first active material is characterized in that it does not contain the aforementioned complex.

The lithium nickel-based composite oxide of the first active material may be represented by Formula 1 below as an example.

[Formula 1]

Li _a1 Ni _x1 M ¹ _y1 M ² _1-x1-y1 O ₂

In Formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M ¹ and M ² are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F , Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

In Formula 1, 0.4≤x1≤1 and 0≤y1≤0.6, 0.5≤x1≤1 and 0≤y1≤0.5, 0.6≤x1≤1 and 0≤y1≤0.4, or 0.7≤x1≤ 1 and 0≤y1≤0.3, or 0.8≤x1≤1 and 0≤y1≤0.2, or 0.9≤x1≤1 and 0≤y1≤0.1.

The lithium nickel-based composite oxide of the first active material may be represented by Formula 2 below, for example.

[Formula 2]

Li _a2 Ni _x2 Co _y2 M ³ _1-x2-y2 O ₂

In Formula 2, 0.9≤a2≤1.8, 0.3≤x2<1, 0<y2≤0.7 and M ³ is Al, B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

In Formula 2, 0.3≤x2≤0.99 and 0.01≤y2≤0.7, 0.4≤x2≤0.99 and 0.01≤y2≤0.6, 0.5≤x2≤0.99 and 0.01≤y2≤0.5, or 0.6≤x2≤0.99 and 0.01≤y2≤0.4, 0.7≤x2≤0.99 and 0.01≤y2≤0.3, 0.8≤x2≤0.99 and 0.01≤y2≤0.2, or 0.9≤x2≤0.99 and 0.01≤y2≤0.1.

The lithium nickel-based composite oxide of the first active material may be represented by Formula 3 below, for example.

[Formula 3]

Li _a3 Ni _x3 Co _y3 M ⁴ _z3 M ⁵ _1-x3-y3-z3 O ₂

In Formula 3, 0.9≤a3≤1.8, 0.3≤x3≤0.98, 0.01≤y3≤0.69, 0.01≤z3≤0.69, M ⁴ is selected from Al, Mn and combinations thereof, M ⁵ is B, Ba , Ca, Ce, Cr, Cu, F, Fe, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

In Formula 3, 0.4≤x3≤0.98, 0.01≤y3≤0.59, and 0.01≤z3≤0.59, 0.5≤x3≤0.98, 0.01≤y3≤0.49, and 0.01≤z3≤0.49, or 0.6≤x3≤ 0.98, 0.01≤y3≤0.39, and 0.01≤z3≤0.39, or 0.7≤x3≤0.98, 0.01≤y3≤0.29, and 0.01≤z3≤0.29; ≤z3≤0.19, or 0.9≤x3≤0.98, 0.01≤y3≤0.09, and 0.01≤z3≤0.09.

The first active material may be included in, for example, 90 wt% to 99.5 wt%, or 95 wt% to 99 wt% based on the total weight of the first active material layer.

The binder and the conductive material in the first active material layer may be the same as or different from those in the second active material layer.

In the first active material layer, the binder serves to well attach the cathode active material particles to each other and to well attach the cathode active material to the current collector, representative examples of which are polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, Diacetylcellulose, polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene , polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

The amount of the binder in the first active material layer may be about 0.5% to about 5% by weight based on the total weight of the first active material layer.

In the first active material layer, the conductive material is used to impart conductivity to the electrode, and in the configured battery, any material that does not cause chemical change and conducts electrons can be used, such as natural graphite, artificial graphite, and carbon. carbon-based materials such as black, acetylene black, ketjen black, carbon fibers, and carbon nanotubes; metal-based materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof.

The content of the conductive material in the first active material layer may be 0.5 wt% to 5 wt% based on the total weight of the first active material layer.

Meanwhile, the entire thickness of the positive electrode active material layer including the first active material layer and the second active material layer may be about 20 μm to 300 μm, for example, 30 μm to 300 μm, 40 μm to 300 μm, 50 μm to 300 μm. 300 μm, 60 μm to 300 μm, 20 μm to 250 μm, 20 μm to 200 μm, or 20 μm to 150 μm. The entire thickness of the positive electrode active material layer can be said to be thicker than that of existing electrode plates, and thus is within a range capable of realizing high capacity. In the positive electrode according to an embodiment, when the total thickness of the positive electrode active material layer satisfies the above range, high temperature lifespan characteristics, output characteristics, and rate performance characteristics may be simultaneously improved while achieving high capacity.

The thickness of the first active material layer may be 10 μm to 150 μm, for example, 20 μm to 120 μm, 20 μm to 100 μm, 20 μm to 80 μm, 30 μm to 150 μm, 30 μm to 100 μm, It may be 30 μm to 80 μm. When the thickness of the first active material layer satisfies the above range, high-temperature lifespan characteristics, output characteristics, and rate characteristics may be simultaneously improved while achieving high capacity.

The second active material layer may have a thickness of 10 μm to 150 μm, for example, 20 μm to 120 μm, 20 μm to 100 μm, 20 μm to 80 μm, 30 μm to 150 μm, or 40 μm to 150 μm. can be When the thickness of the second active material layer satisfies the above range, high-temperature lifetime characteristics, output characteristics, and rate characteristics may be simultaneously improved while achieving high capacity.

An aluminum foil may be used as the current collector of the positive electrode, but is not limited thereto.

lithium secondary battery

Another embodiment provides a lithium secondary battery including a positive electrode, a negative electrode, a separator positioned between the positive electrode and the positive electrode, and an electrolyte.

1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment of the present invention includes a positive electrode 114, a negative electrode 112 opposite to the positive electrode 114, and a space between the positive electrode 114 and the negative electrode 112. A battery cell including an electrolyte for a lithium secondary battery impregnating the separator 113 and the positive electrode 114, the negative electrode 112, and the separator 113 disposed in the battery container 120 containing the battery cell and the A sealing member 140 for sealing the battery container 120 is included.

cathode

A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer positioned on the current collector. The anode active material layer may include an anode active material, and may further include a binder and/or a conductive material.

The anode active material includes a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

The material capable of reversibly intercalating/deintercalating the lithium ions is a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide , calcined coke, and the like.

The alloy of lithium metal is from the group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. Alloys of selected metals may be used.

A Si-based negative active material or a Sn-based negative active material may be used as the material capable of doping and undoping the lithium, and the Si-based negative active material may include silicon, silicon-carbon composite, SiO _x (0 < x < 2), Si -Q alloy (Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and Si is not ), the Sn-based negative electrode active material is Sn, SnO ₂ , Sn-R alloy (wherein R is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and It is an element selected from the group consisting of combinations thereof, but not Sn), and the like, and at least one of these and SiO ₂ may be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, What is selected from the group consisting of S, Se, Te, Po, and combinations thereof may be used.

The silicon-carbon composite may be, for example, a silicon-carbon composite including a core including crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on a surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. As the amorphous carbon precursor, coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin such as a phenol resin, a furan resin, or a polyimide resin may be used. In this case, the content of silicon may be 10% to 50% by weight based on the total weight of the silicon-carbon composite. In addition, the content of the crystalline carbon may be 10% to 70% by weight based on the total weight of the silicon-carbon composite, and the content of the amorphous carbon may be 20% to 40% by weight based on the total weight of the silicon-carbon composite. there is. In addition, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. An average particle diameter (D50) of the silicon particles may be 10 nm to 20 μm. The average particle diameter (D50) of the silicon particles may be preferably 10 nm to 200 nm. The silicon particles may exist in an oxidized form, and at this time, the atomic content ratio of Si:O in the silicon particles indicating the degree of oxidation may be 99:1 to 33:66 by weight. The silicon particles may be SiO _x particles, and in this case, the range of x in SiO _x may be greater than 0 and less than 2. In this specification, unless otherwise defined, the average particle diameter (D50) means the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution.

The Si-based negative active material or the Sn-based negative active material may be used in combination with a carbon-based negative active material. When the Si-based negative active material or the Sn-based negative active material and the carbon-based negative active material are mixed and used, the mixing ratio may be 1:99 to 90:10 by weight.

The content of the negative active material in the negative active material layer may be 95% to 99% by weight based on the total weight of the negative active material layer.

In one embodiment, the negative active material layer may further include a binder and optionally further include a conductive material. The content of the binder in the negative active material layer may be 1% to 5% by weight based on the total weight of the negative active material layer. In addition, when the conductive material is further included, the negative electrode active material layer may include 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material.

The binder serves to well attach the anode active material particles to each other and also to well attach the anode active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoro ethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

The water-soluble binder may include a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymeric resin binder is polyethylene oxide, polyvinylpyrrolidone, polyepicrohydrin, polyphosphazene, polyacrylonitrile, ethylenepropylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, poly It may be selected from ester resins, acrylic resins, phenol resins, epoxy resins, polyvinyl alcohol, and combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, at least one of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof may be used in combination. As the alkali metal, Na, K or Li may be used. The content of the thickener may be 0.1 part by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

The conductive material is used to impart conductivity to the electrode, and in the battery, any material that does not cause chemical change and conducts electrons can be used, such as natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. carbon-based materials such as black, carbon fibers, and carbon nanotubes; metal-based materials including copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

As the current collector, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a conductive metal-coated polymer substrate, and combinations thereof may be used.

electrolyte

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used. As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC) and the like may be used. Examples of the ester-based solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalono Lactone (mevalonolactone), caprolactone (caprolactone) and the like can be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether-based solvent, and cyclohexanone or the like may be used as the ketone-based solvent. there is. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and R-CN as the aprotic solvent (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group) , double bonded aromatic rings or ether linkages), nitriles such as dimethylformamide, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like may be used.

The above non-aqueous organic solvents may be used alone or in combination with one or more of them, and when used in combination with one or more, the mixing ratio may be appropriately adjusted according to the desired battery performance, which is widely understood by those skilled in the art. It can be.

In addition, in the case of the carbonate-based solvent, a mixture of cyclic carbonate and chain carbonate may be used. 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 non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

As the aromatic hydrocarbon-based solvent, an aromatic hydrocarbon-based compound of Formula I below may be used.

[Formula I]

In Formula I, R ⁴ to R ⁹ are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

Specific examples of the aromatic hydrocarbon-based solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluoro Low benzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1, 2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2 ,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Toluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3 ,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3, It is selected from the group consisting of 5-triiodotoluene, xylene, and combinations thereof.

The electrolyte solution may further include vinylene carbonate or an ethylene-based carbonate-based compound represented by Formula II below as a life-enhancing additive in order to improve battery life.

[Formula II]

In Formula II, R ¹⁰ and R ¹¹ are the same as or different from each other, and are selected from the group consisting of hydrogen, a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms, and among R ¹⁰ and R ¹¹ At least one is selected from the group consisting of a halogen group, a cyano group, a nitro group, and a fluorinated C1-C5 alkyl group, provided that neither R ¹⁰ nor R ¹¹ is hydrogen.

Representative examples of the ethylene-based carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. can be heard When such a life-enhancing additive is further used, its amount may be appropriately adjusted.

The lithium salt is a substance that dissolves in a non-aqueous organic solvent, acts as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and promotes the movement of lithium ions between the positive electrode and the negative electrode. .

Representative examples of lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , Li (FSO ₂ ) ₂ N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiPO ₂ F ₂ , LiN ( C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers, eg integers from 1 to 20), lithium difluorobisoxalato phosphate (lithium difluoro (bisoxolato) phosphate), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate: LiBOB), and lithium difluoro(oxalato)borate (LiDFOB) ) and one or more selected from the group consisting of.

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.

separator

The separator 113, also called a separator, separates the positive electrode 114 and the negative electrode 112 and provides a passage for lithium ions to move, and any one commonly used in a lithium ion battery may be used. That is, an electrolyte having low resistance to ion movement of the electrolyte and excellent ability to absorb the electrolyte may be used. For example, it is selected from glass fibers, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof, and may be in the form of non-woven fabric or woven fabric. For example, in lithium ion batteries, polyolefin-based polymer separators such as polyethylene and polypropylene are mainly used, and coated separators containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and optionally single- or multi-layer separators. structure can be used.

Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries according to the type of separator and electrolyte used, and can be classified into cylindrical, prismatic, coin, pouch, etc. depending on the shape, Depending on the size, it can be divided into a bulk type and a thin film type. Structures and manufacturing methods of these batteries are well known in the art, so detailed descriptions thereof will be omitted.

A lithium secondary battery according to an embodiment implements high capacity and has excellent storage stability at high temperatures, lifespan characteristics, high rate characteristics, etc., so that it can be used for electric vehicles (EVs) and plug-in hybrid electric vehicles (plug-in hybrid electric vehicles). vehicle, PHEV) and the like.

Examples and comparative examples of the present invention are described below. The following examples are only examples of the present invention, but the present invention is not limited to the following examples.

Example 1

(1) Manufacture of anode

first active material layer

A first active material slurry was prepared by mixing 97.7 wt% of LiNi _0.92 Co _0.07 Al _0.01 O ₂ cathode active material, 1.3 wt% of PVDF binder, and 1.0 wt% of carbon nanotube and ketjen black conductive material in an NMP solvent. The prepared first active material slurry is coated on one surface of an aluminum current collector having a thickness of 12 μm and dried to prepare a first active material layer on the current collector. The thickness of the prepared first positive electrode active material layer is about 40 μm.

Second active material layer

After Al ₂ O ₃ particles having an average particle diameter of about 15 nm were placed in the reactor, the temperature inside the reactor was raised to 1000 ° C. under the condition that CH ₄ was supplied into the reactor at a rate of about 300 sccm at 1 atm for about 30 minutes , heat treatment is performed at the above temperature for 7 hours. Thereafter, by adjusting the internal temperature of the reactor to room temperature (20-25° C.), a composite in which Al ₂ O ₃ particles and their reduction product Al ₂ O _z (0<z<3) particles are embedded in a graphene matrix is prepared. The content of graphene in the obtained composite is about 30.9% by weight.

LiNi _0.92 Co _0.07 Al _0.01 O ₂ and the obtained composite were mixed in a weight ratio of 99.6:0.4 and milled in a Novilta mixer at a rotational speed of about 2000 rpm for about 10 minutes to obtain a second active material.

A second active material slurry is prepared by mixing 97.7% by weight of the second positive electrode active material, 1.3% by weight of a PVDF binder, and 1.0% by weight of carbon nanotubes and Ketjen Black conductive material in an NMP solvent. The second active material slurry is applied on the first active material layer, then dried and rolled to prepare a positive electrode in which a current collector, a first active material layer, and a second active material layer are sequentially stacked. The thickness of the prepared second active material layer is about 40 μm.

(2) Manufacture of cathode

A negative active material slurry was prepared by mixing 97.3% by weight of graphite, 0.5% by weight of Denka Black, 0.9% by weight of carboxymethyl cellulose, and 1.3% by weight of styrene-butadiene rubber in an aqueous solvent. The prepared anode active material slurry is coated on copper foil, dried, and then rolled to prepare a cathode.

(3) Manufacture of batteries

A pouch-type cell was prepared by sequentially stacking the prepared positive electrode, the polyethylene/polypropylene multilayer separator, and the prepared negative electrode in order, and then 1.0 M LiPF in a solvent mixed with ethylene carbonate and diethyl carbonate at a volume ratio of 50:50 ₆ A lithium secondary battery is fabricated by injecting an electrolyte with lithium salt added thereto.

Comparative Example 1

In the manufacture of the positive electrode of Example 1, only the first active material layer was coated on the current collector, then dried and rolled to obtain a thickness of 80 μm. A positive electrode, a negative electrode, and a battery were prepared in the same manner as in Example 1, except that a positive electrode having a single layer thickness was prepared.

Comparative Example 2

In the preparation of the positive electrode of Example 1, only the second active material layer was coated on the current collector, then dried and rolled to obtain a thickness of 80 μm. A positive electrode, a negative electrode, and a battery were prepared in the same manner as in Example 1, except that a positive electrode having a single layer thickness was prepared.

Comparative Example 3

A mixture of the first active material and the second active material in Example 1 at a weight ratio of 50:50 was used as the active material of Comparative Example 2, 97.7 wt% of the active material, 1.3 wt% of the PVDF binder, and 1.0 wt% of the CNT and ECP conductive material. A slurry obtained by mixing wt% in an NMP solvent was coated on a current collector, dried and rolled to obtain a thickness of 80 μm. Fabricate an anode of a single layer of thickness. Otherwise, a negative electrode and a battery were prepared in the same manner as in Example 1.

Evaluation Example 1: Analysis of complexes in the second active material - XPS

In the process of preparing the composite during the preparation of the second active material layer of Example 1, XPS spectra (Qunatum 2000; Physical Electronics) over time are measured. Before, after 1 minute, after 5 minutes, after 30 minutes, after 1 hour, and after 4 hours, XPS spectra of C 1s orbital and Al 2p orbital of the composite sample were measured.

As a result of the measurement, only the Al 2p orbital peak appeared at the initial stage of temperature rise, and the C 1s orbital peak did not appear. After 30 minutes, the peak for the C 1s orbital appeared clearly, and the size of the peak for the Al 2p orbital significantly decreased. After 30 minutes, peaks for C 1s orbitals due to C-C bonding and C=C bonding due to the growth of graphene appeared near 284.5 eV. As the reaction time elapsed, the peak position of the Al 2p orbital shifted toward a lower binding energy (eV) as the oxidation number of aluminum decreased. Accordingly, it can be seen that as the reaction progresses, graphene grows on the Al ₂ O ₃ particles, and _{Al 2 O x} (0<x<3), which is a reduction product of Al 2 O ₃ , is produced.

In addition, the average contents of carbon and aluminum are measured through XPS analysis results in 10 regions of the prepared composite. Calculate the deviation of the aluminum content for each area with respect to the measurement result. The variation in aluminum content is expressed as a percentage of the average value and is called uniformity.

As a result of the analysis, the percentage of the average value of the variation of the aluminum content, that is, the uniformity of the aluminum content was about 1%. Accordingly, it can be confirmed that aluminum oxide is uniformly distributed in the prepared composite.

Evaluation Example 2: Analysis of complexes in the second active material - SEM-EDAX

SEM-EDAX (FEI Titan 80-300 from Philips) analysis was performed on the composite prepared during the fabrication of the second active material layer of Example 1.

As a result of the analysis, the prepared composite had a structure in which Al ₂ O ₃ particles and their reduction product Al ₂ O _z (0<z<3) particles were embedded in the graphene matrix. That is, it was confirmed that a graphene layer was grown on the outside of the Al ₂ O ₃ particle and/or the Al ₂ O _z (0<z<3) particle. One or more particles selected from Al ₂ O ₃ particles and Al ₂ O _z (0<z<3) were uniformly dispersed in the graphene matrix. The average particle diameter of one or more of the Al ₂ O ₃ particles and the Al ₂ O _z (0<z<3) particles was about 15 nm, and the size of the composite was about 100 nm to 200 nm.

In addition, SEM-DEAX analysis is performed on the second active material prepared in Example 1. As a result of the analysis, it was confirmed that a shell formed by the composite was disposed on the lithium nickel-based composite oxide core.

Evaluation Example 3: Analysis of the second active material - XPS

For the second active material of Example 1, the XPS spectrum for the O 1s orbital was measured using Qunatum 2000 (Physical Electronics).

As a result of the measurement, a peak due to C-O-Ni bonding was observed near 530.2 eV. This peak is determined to be a peak due to a bond formed between the NiO phase present on the surface of the lithium nickel-based composite oxide and the carbon of the composite. Accordingly, it can be confirmed that the carbon of the composite of the shell forms a covalent bond with the nickel of the core through oxygen.

Evaluation Example 4: Analysis of Second Active Material - Raman Spectrum

Raman spectra were measured for the composite of Example 1 and the second active material, and the results are shown in FIG. 2 . Referring to FIG. 2, the composite exhibited a D band peak at 1338.7 cm ^-1 and a G band peak at 1575.0 cm ^-1 due to graphene. On the other hand, in the second active material, the D band peak shifted to 1351.3 cm ^-1 by about 12 cm ^-1 and the G band peak shifted to 1593.6 cm ^-1 by about 18 cm ^-1 . Here, it is determined that the shift of the D-band peak is due to the strain of graphene coupled to the core by milling to form a shell. It is understood that the shift of the G band peak is due to the fact that the lithium nickel-based composite oxide of the core and the graphene of the shell form a composite by CO-Ni bonding, and charge transfer between the core and the shell occurs in this composite. Accordingly, it can be confirmed that the composite of the shell forms a chemical bond (covalent bond) with the lithium nickel-based composite oxide of the core.

Evaluation Example 5: Evaluation of Battery Output Characteristics

For the lithium secondary batteries prepared in Example 1 and Comparative Examples 1 to 3, initial resistance, that is, DC-IR, was measured, and the results are shown in Table 1 below. Specifically, after charging SOC 50% of the rated capacity of the battery, charging and discharging are performed for 10 seconds at a rate of 1 C to obtain a charging voltage and a discharging voltage, through which DC-IR is calculated. Then, the rated output value is calculated by multiplying the rated capacity and the voltage, and the result is shown in Table 1 below.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Resistance (mΩ) 9.59 9.7 9.4 9.25 Rated power (Wh) 544 538.7 544.7 547

Referring to Table 1, it can be seen that the initial resistance decreased and the rated output value increased in Example 1 compared to Comparative Examples 1 to 3, and thus the output characteristics were improved.

Evaluation Example 6: Evaluation of rate-rate charging characteristics of battery

The lithium secondary batteries prepared in Example 1 and Comparative Examples 1 to 3 were charged with a constant current at 25 ° C to an upper limit voltage of 4.25V, and then discharged with a constant current to a discharge end voltage of 2.8V. The charging rate at each C rate of 0.5C, 0.7C, 1C, 1.5C, and 2C was evaluated, and the results are shown in FIG. 3.

Referring to FIG. 3, Example 1 shows a high charging rate at all C rates. On the other hand, in the case of Comparative Example 2, it can be seen that the filling rate drops at a high rate of 1.5C or more.

Evaluation Example 7: Evaluation of rate-rate discharge characteristics of battery

The lithium secondary batteries prepared in Example 1 and Comparative Examples 1 to 3 were charged with a constant current of 0.33 C at 25 ° C to an upper limit voltage of 4.25V, and then discharged with a constant current to a discharge end voltage of 2.8V. The discharge rate was evaluated in each case where the discharge current was changed to 0.33C, 0.5C, 0.7C, 1C, 1.5C, and 2C, and the results are shown in FIG. 4 .

Referring to FIG. 4, it can be seen that Example 1 shows a high discharge rate at all C rates, and in particular, shows a better discharge rate than Comparative Examples 1 to 3 at high rates of 1.5C and 2C.

Evaluation Example 8: High Temperature Life Characteristics

With respect to the lithium secondary battery of Example 1 and Comparative Example 1, at 45 ° C., after charging to 4.25V at a constant current of 0.5 C rate, cut-off at 0.2 C rate in constant voltage mode, and discharging to 2.8V at a constant current at 0.5 C rate Repeat the cycle 200 times. The capacity retention rate and DC-IR according to the number of cycles were measured, and the results are shown in FIG. 5 . DC-IR is obtained by calculating the charging voltage and discharging voltage by performing charging and discharging at 1 C rate for 10 seconds after charging 50% of the SOC, and calculating the DC-IR value through this.

Referring to FIG. 5 , it can be seen that the battery of Example 1 has significantly improved high-temperature lifespan characteristics compared to the battery of Comparative Example 1 without an increase in resistance.

Although the preferred embodiments have been described in detail, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts defined in the following claims are also within the scope of the present invention. it belongs

100: lithium secondary battery 112: negative electrode
113: Separator 114: Anode
120: battery container 140: sealing member

Claims (16)

current collector;
a first active material layer disposed on the current collector and including a first active material; and
a second active material layer disposed on the first active material layer and including a second active material;
As a positive electrode for a lithium secondary battery comprising a,
The second active material includes a core including a lithium nickel-based composite oxide, and a shell disposed along a surface of the core,
The shell is M _a O _b (M is one or more metals selected from groups 2 to 13, 15 and 16 of the periodic table of elements, 0<a≤3, and 0<b<4, a is 1, A positive electrode for a lithium secondary battery comprising a composite in which a first metal oxide represented by 2 or 3, b is not an integer) disposed in a carbon-based matrix. In paragraph 1,
A cathode for a lithium secondary battery in which the first active material does not contain the composite. In paragraph 1,
In the composite of the second active material, the metal M included in the first metal oxide is Al, Ag, Co, Cu, Fe, Mg, Mn, Pd, Sb, Sc, Se, Si, Ti, V, W, Zn, And a positive electrode for a lithium secondary battery, which is a metal selected from Zr. In paragraph 1,
In the composite of the second active material, the first metal oxide is Al ₂ O _z (0<z<3), AgO _x (0<x<1), Co ₃ O _w (0<w<4), CuO _x ( 0<x<1), Fe ₂ O _z (0<z<3), MgO _x (0<x<1), MnO _y (0<y<2), PdO _x (0<x<1), Sb ₂ O _z (0<z<3), Sc ₂ O _z (0<z<3), SeO _y (0<y<2), SiO _y (0<y<2), TiO _y (0<y< 2), V ₂ O _z (0<z<3), WO _y (0<y<2), ZnO _x (0<x<1), and ZrO _y (0<y<2). A cathode for a lithium secondary battery. In paragraph 1,
The complex of the second active material has the formula M _a O _c (M is one or more metals selected from Groups 2 to 13, 15 and 16 of the Periodic Table of Elements, 0<a≤3, and 0<c≤4, , if a is 1, 2, or 3, c is an integer) further comprising a second metal oxide represented by,
the second metal oxide contains the same metal as the first metal oxide;
A positive electrode for a lithium secondary battery, wherein c/a, the ratio of c to a in the second metal oxide, has a larger value than b/a, the ratio of b to a in the first metal oxide. In paragraph 5,
The second metal oxide is Al ₂ O ₃ , AgO, Co ₃ O ₄ , CuO, Fe ₂ O ₃ , MgO, MnO ₂ , PdO, Sb ₂ O 3 , Sc ₂ O ₃ , SeO ₂ , SiO _{2 ,} TiO ₂ , A cathode for a lithium secondary battery selected from V ₂ O ₃ , WO ₂ , ZnO, and ZrO ₂ . In paragraph 5,
A positive electrode for a lithium secondary battery, wherein the first metal oxide is a reduction product of the second metal oxide. In paragraph 5,
The positive electrode for a lithium secondary battery, wherein the first metal oxide and the second metal oxide are in the form of particles, and each has an average particle diameter of 1 nm to 50 nm. In paragraph 1,
In the composite of the second active material, the first metal oxide is chemically bonded to the carbon-based matrix. In paragraph 1,
In the composite of the second active material, the carbon-based matrix includes 1 to 20 carbon layers and has a thickness of 0.6 nm to 12 nm. In paragraph 1,
In the second active material, the content of the composite is 1% by weight or less based on the total weight of the second active material. In paragraph 1,
In the second active material, the composite is a positive electrode for a lithium secondary battery that is chemically bonded to the lithium nickel-based composite oxide of the core. In paragraph 1,
In the second active material, the lithium nickel-based composite oxide of the core is a positive electrode for a lithium secondary battery represented by the following formula (1):
[Formula 1]
Li _a1 Ni _x1 M ¹ _y1 M ² _1-x1-y1 O ₂
In Formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M ¹ and M ² are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F , Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof. In paragraph 1,
In the second active material, the shell has a thickness of 1 nm to 100 nm. In paragraph 1,
The first active material includes a lithium nickel-based composite oxide,
The lithium nickel-based composite oxide of the first active material is the same as or different from the lithium nickel-based composite oxide contained in the core of the second active material. The anode according to any one of claims 1 to 15;
cathode;
a separator positioned between the anode and the anode; and
A lithium secondary battery containing an electrolyte.

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