KR20230166448A - Positive electrode active material for lithium secondary battery, preparing method of the same, positive electrode and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for lithium secondary batteries, a manufacturing method thereof, and a lithium secondary battery containing the same. The high-nickel-based positive electrode active material according to an embodiment of the present invention includes a core portion containing a nickel-containing compound; and a coating portion formed on the surface of the core portion and containing a phosphorus-based compound. The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention effectively suppresses the release of active oxygen generated within the active material and prevents reaction with the electrolyte, thereby providing a positive electrode active material with excellent thermal stability and a lithium secondary battery containing the same. You can.

Description

Positive electrode active material for lithium secondary batteries, manufacturing method thereof, positive electrode for lithium secondary batteries containing the same, and lithium secondary batteries

The present invention relates to a positive electrode active material for a lithium secondary battery, a method of manufacturing the positive electrode active material, a positive electrode for a lithium secondary battery containing the positive electrode active material, and a lithium secondary battery containing the same.

Recently, with the rapid spread of electronic devices that use batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high capacity secondary batteries is rapidly increasing. In particular, lithium secondary batteries are lightweight and have high energy density, so they are attracting attention as a driving power source for portable devices. Accordingly, research and development efforts to improve the performance of lithium secondary batteries are actively underway.

As cathode active materials for lithium secondary batteries, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O ₄ , etc.), and lithium iron phosphate compounds (LiFePO ₄ ) were used. . In addition, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO ₂ , a lithium composite metal oxide ( Hereinafter simply referred to as ‘NCM-based lithium composite transition metal oxide’ or ‘NCA-based lithium composite transition metal oxide’) was developed. However, the conventionally developed NCM-based/NCA-based lithium composite transition metal oxide had insufficient capacity characteristics and had limitations in application.

To overcome the shortcomings of LiCoO ₂ , lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O ₄ , etc.), lithium iron phosphate compound (LiFePO ₄ ), etc. have been used, and recently, the excellent reversibility of LiNiO ₂ has been used. As a method to improve low thermal stability while maintaining capacity, a lithium composite metal oxide (hereinafter simply referred to as 'NCM-based lithium composite') in which a portion of nickel (Ni) is replaced with cobalt (Co) or manganese (Mn)/aluminum (Al) ‘Transition metal oxide’ or ‘NCA-based lithium composite transition metal oxide’) has been developed. However, the conventionally developed NCM-based/NCA-based lithium composite transition metal oxide had insufficient capacity characteristics and had limitations in application.

To improve this problem, research has recently been conducted to increase the Ni content in NCM-based/NCA-based lithium composite transition metal oxide. However, in the case of a high-concentration nickel positive electrode active material with a high nickel content, there is a problem in that the structural and chemical stability of the active material is poor, and the thermal stability is rapidly reduced. In particular, during the oxidation/reduction reaction of a lithium secondary battery, when lithium is released from the positive electrode active material and the crystal structure becomes unstable, active oxygen (oxygen radicals) may be generated, and the active oxygen (oxygen radicals) released at this time may cause electrolyte. It decomposes and generates gases such as carbon dioxide, which can worsen the lifespan and stability of lithium secondary batteries.

Therefore, there is a need for the development of a high-concentration nickel (High Ni) positive electrode active material that is suitable for high capacity and has excellent structural and chemical stability and excellent thermal stability.

Korean Patent Publication No. 2014-0130063

The object of the present invention is to provide a positive electrode active material of a high-content nickel (High-Ni)-based lithium composite transition metal oxide with a high concentration of nickel (Ni), and to provide lithium with high capacity, improved structural and chemical stability, and improved thermal stability. The goal is to provide a positive electrode active material for secondary batteries.

Specifically, the present invention seeks to provide a positive electrode active material for a lithium secondary battery that can effectively capture oxygen radicals that may be generated from the positive electrode active material during charging and discharging of the lithium secondary battery.

In addition, the present invention seeks to provide a positive electrode active material for a lithium secondary battery having a coating portion that effectively captures the above-described oxygen radicals.

The present invention seeks to provide a method for manufacturing a positive electrode active material for a lithium secondary battery having a coating portion that effectively captures the above-described oxygen radicals.

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

In order to solve the above problems, the present invention

A core portion containing a nickel-containing compound; and a coating portion formed on the surface of the core portion and containing a phosphorus compound. It provides a positive electrode active material for a lithium secondary battery including a.

In one embodiment of the present invention, the nickel-containing compound may be a lithium complex transition metal oxide represented by the following formula (1).

[Formula 1]

Li _p Ni _1-(x1+y1+z1) Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ²

In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and is at least one element selected from the group consisting of Cr, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0< x1≤0.4, 0<y1≤0.4, 0≤z1≤0.1, 0≤q1≤0.1, and 0<x1+y1+z1≤0.4.

In one embodiment of the present invention, the phosphorus-based compound may be a phosphorus-based compound containing a functional group capable of bonding to at least one hydroxy group or a phosphorus-based compound containing an aromatic ring. Specifically, the phosphorus-based compound may be phosphono benzoic acid.

In one embodiment of the present invention, the coating portion may be formed in a weight range of 0.5% by weight to 5% by weight based on the total weight of the core portion.

In one embodiment of the present invention, the thickness of the coating portion may be 30 to 100 nm.

In one embodiment of the present invention, the positive electrode active material for a lithium secondary battery may have an average particle diameter (D ₅₀ ) of 0.1 ㎛ to 20 ㎛.

Meanwhile, the present invention

(a) preparing a nickel-containing compound; and

(b) mixing and reacting the nickel-containing compound with a phosphorus-based compound, wherein the phosphorus-based compound forms a coating on the surface of the nickel-containing compound.

In one embodiment of the present invention, the nickel-containing compound may be a lithium complex transition metal oxide represented by the following formula (1).

Method for manufacturing positive electrode active material for lithium secondary battery.

[Formula 1]

Li _p Ni _1-(x1+y1+z1) Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ²

In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and is at least one element selected from the group consisting of Cr, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0< x1≤0.4, 0<y1≤0.4, 0≤z1≤0.1, 0≤q1≤0.1, and 0<x1+y1+z1≤0.4.

In one embodiment of the present invention, the phosphorus-based compound may be mixed in an amount of 0.5% by weight to 5% by weight based on the total weight of the nickel-containing compound.

In one embodiment of the present invention, step (b) reaction between the nickel-containing compound and the phosphorus-based compound may be performed by adding an acid additive.

In one embodiment of the present invention, the acid additive may be a weak acid with a pka of 2 to 6, and specifically includes at least one selected from the group consisting of citric acid, acetic acid, malic acid, and formic acid. You can.

In one embodiment of the present invention, the acid additive may be added in an amount of 0.05% to 0.5% by weight based on the total weight of the nickel-containing compound.

In one embodiment of the present invention, it further includes the step of (c) heat-treating the reaction product produced by mixing and reacting the nickel-containing compound with the phosphorus-based compound, and the heat treatment step may be performed at a temperature of 100 ^o C or higher. there is.

The present invention can provide a positive electrode containing the positive electrode active material of the present invention and a lithium secondary battery containing the positive electrode.

The means for solving the above problems do not enumerate all the features of the present invention. The various features of the present invention and its advantages and effects can be understood in more detail by referring to the specific examples below.

According to the cathode active material for lithium secondary batteries of the present invention, high capacity is realized by further increasing the nickel (Ni) content in the lithium composite transition metal oxide, and structural stability and stability of the high-content nickel (High-Ni)-based lithium composite transition metal oxide are achieved. Chemical stability can be improved and thermal stability can be improved.

According to the positive electrode active material for lithium secondary batteries of the present invention, it is possible to provide a positive electrode active material that can effectively capture oxygen radicals that can be released from the positive electrode active material during charging and discharging of a lithium secondary battery.

In addition to the above-described effects, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

1 is a TGA analysis graph of a positive electrode active material according to an embodiment of the present invention.
Figure 2 is a FT-IR analysis graph of a positive electrode active material according to an embodiment of the present invention.
Figure 3 shows (a) a STEM image, (b) an EDS mapping image of Ni, and (c) an EDS mapping image of P of a positive electrode active material according to an embodiment of the present invention.
Figure 4 is a DSC analysis graph of an anode according to an embodiment of the present invention.
Figure 5 is a DEMS analysis graph of a positive electrode active material according to an embodiment of the present invention.
Figure 6 is an ESR analysis graph of a positive electrode active material according to an embodiment of the present invention.
Figure 7 is a voltage-capacitance graph of a positive electrode active material according to an embodiment of the present invention.

Hereinafter, the principles of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings and description. However, the drawings shown below and the description below are for preferred implementation methods among various methods for effectively explaining the characteristics of the present invention, and the present invention is not limited to the drawings and description below.

Meanwhile, terms such as first or second may be used to describe various components, but these terms should be interpreted only for the purpose of distinguishing one component from other components. For example, a first component may be named a second component, and similarly, the second component may also be named a first component.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise” or “have” are intended to designate the presence of the described features, numbers, steps, operations, components, parts, or combinations thereof, and are intended to indicate the presence of one or more other features or numbers, It should be understood that this does not exclude in advance the possibility of the presence or addition of steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art. Terms as defined in commonly used dictionaries should be interpreted as having meanings consistent with the meanings they have in the context of the related technology, and unless clearly defined in this specification, should not be interpreted in an idealized or overly formal sense. No.

Hereinafter, the present invention will be described in more detail.

Cathode active material for lithium secondary batteries

In the case of a positive electrode containing a high-nickel (High-Ni)-based positive electrode active material, the energy density of a lithium secondary battery can be increased, but structural stability may be reduced at high temperatures. If the crystal structure of the positive electrode active material becomes unstable, active oxygen (oxygen radicals) may be generated. The oxygen radicals react with the electrolyte to decompose the electrolyte and generate gases such as hydrogen and carbon dioxide, thereby improving battery life, stability, etc. It may deteriorate overall performance. In particular, the reaction between the positive electrode and the electrolyte is an exo-thermic reaction, which can lead to a fire accident such as an explosion of a lithium secondary battery.

Meanwhile, a method of doping a high-content nickel-based positive electrode active material with a transition metal has been designed to increase thermal stability. Through transition metal doping, the positive electrode active material has the advantage of reducing cation mixing, maintaining a stable structure, and suppressing the release of active oxygen by strengthening the transition metal oxide bond. However, doping a high-content nickel-based positive electrode active material with a transition metal has the problem of hindering the diffusion of lithium ions in the active material or irreversibly reducing capacity.

Accordingly, the inventors of the present invention attempted to solve the above problem by developing a positive electrode active material for a lithium secondary battery including a core portion containing a nickel-containing compound and a coating portion formed on the surface of the core portion.

Specifically, the positive electrode active material for a lithium secondary battery of the present invention consists of a core portion containing a nickel-containing compound and a coating portion formed on the surface of the core portion, and the nickel-containing compound includes nickel (Ni) and cobalt (Co). , it may be a lithium complex transition metal containing at least one selected from the group consisting of manganese (Mn) and aluminum (Al).

The nickel-containing compound contained in the core portion of the positive electrode active material of the present invention may be a high-nickel (High-Ni)-based lithium composite transition metal oxide having a nickel (Ni) content of 60 mol% or more among all metal elements. More preferably, the nickel-containing compound may be a high-Ni-based lithium composite transition metal oxide in which the nickel (Ni) content of all metal elements is 70 mol% or 80 mol% or more. As the nickel-containing compound includes a high-content nickel (High-Ni)-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more, it may be possible to secure high capacity of a lithium secondary battery.

Specifically, the nickel-containing compound may be an NCM-based lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn), or nickel (Ni), cobalt (Co), and aluminum (Al). ) It may be an NCA-based lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). It may be possible. Since the core part includes manganese (Mn) and/or aluminum (Al) along with nickel (Ni) and cobalt (Co), structural stability can be greatly improved and lifespan characteristics can be significantly improved. In general, when manganese (Mn) and/or aluminum (Al) is included, it is effective in terms of stability, but may be disadvantageous in terms of capacity characteristics and output characteristics. However, if the positive electrode active material structure of the present invention is satisfied, sufficient capacity characteristics are secured. However, stability and lifespan characteristics can be significantly improved.

More specifically, the nickel-containing compound included in the core portion may be represented by the following formula (1).

[Formula 1]

Li _p Ni _1-(x1+y1+z1) Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ²

In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and is at least one element selected from the group consisting of Cr, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0< x1≤0.4, 0<y1≤0.4, 0≤z1≤0.1, 0≤q1≤0.1, and 0<x1+y1+z1≤0.4.

In the nickel-containing compound of Formula 1, Li may be included in an amount corresponding to p, that is, 0.9≤p≤1.5. If p is less than 0.9, there is a risk that the capacity may decrease, and if it exceeds 1.5, the particles may be sintered during the firing process, making it difficult to manufacture the positive electrode active material. Considering the significant effect of improving the capacity characteristics of the positive electrode active material by controlling the Li content and the balance of sinterability during manufacturing the active material, Li may be more preferably included in an amount of 1.0≤p≤1.15.

In the nickel-containing compound of Formula 1, Ni may be included in an amount corresponding to 1-(x1+y1+z1), for example, 0.6≤1-(x1+y1+z1)<1. When the Ni content in the nickel-containing compound of Formula 1 is 0.6 or more, a sufficient amount of Ni is secured to contribute to charging and discharging, thereby achieving high capacity. More preferably, Ni may be included as 0.8≤1-(x1+y1+z1)≤0.99. More specifically, the Ni content of the core portion may be 0.8≤1-(x1+y1+z1)≤0.99, and the average Ni content of the shell portion may be 0.6≤1-(x1+y1+z1)≤0.9. You can.

In the nickel-containing compound of Formula 1, Co may be included in an amount corresponding to x1, that is, 0<x1≤0.4. If the Co content in the nickel-containing compound of Formula 1 exceeds 0.4, there is a risk of increased cost. Considering the significant effect of improving capacity characteristics due to the inclusion of Co, Co may be included in an amount of 0.05≤x1≤0.2 more specifically.

In the nickel-containing compound of Formula 1, M ^a may be Mn or Al, or Mn and Al, and these metal elements can improve the stability of the active material and, as a result, improve the stability of the battery. Considering the effect of improving lifespan characteristics, M ^a may be included in an amount corresponding to y1, that is, 0<y1≤0.4. If y1 in the nickel-containing compound of Formula 1 exceeds 0.4, there is a risk that the output characteristics and capacity characteristics of the battery may deteriorate. More specifically, M ^a may be included in an amount of 0.05≤y1≤0.2.

In the nickel-containing compound of Formula 1, M ^b may be a doping element included in the crystal structure of the lithium composite transition metal oxide, and M ^b may be included in a content corresponding to z1, that is, 0≤z1≤0.1.

In the nickel-containing compound of Formula 1, the metal element of M ^c may not be included in the lithium composite transition metal oxide structure, and when mixing and sintering the precursor and the lithium source, the M ^c source may be mixed and sintered, or the lithium source may be mixed and sintered. After forming the composite transition metal oxide, a M ^c source is separately added and fired to produce a lithium composite transition metal oxide in which M ^c is doped on the surface of the lithium composite transition metal oxide. The M ^c may be included in an amount corresponding to q1, that is, in an amount that does not deteriorate the characteristics of the positive electrode active material within the range of 0≤q1≤0.1.

Meanwhile, the coating portion of the positive electrode active material of the present invention may include a phosphorus compound. By forming a coating containing a phosphorus compound on the surface of a nickel-containing compound containing nickel (Ni), cobalt (Co), and at least one selected from the group consisting of manganese (Mn) and aluminum (Al). The coating part can easily capture oxygen radicals released from the core part, thereby suppressing the emission of oxygen radicals, reducing gas production, and improving thermal stability by delaying thermal decomposition of the positive electrode active material at high temperatures.

The phosphorus-based compound of the coating portion may be a phosphorus-based compound containing a functional group capable of bonding to at least one hydroxy group or a phosphorus-based compound containing an aromatic ring. Specifically, the phosphorus-based compound may be phosphono benzoic acid.

The phosphorus-based compound may form a coating on the surface of the core portion, and the coating may capture active oxygen generated from the positive electrode active material.

According to one embodiment, the coating portion may be formed in a weight range of 0.5% by weight to 5% by weight based on the total weight of the core portion. If the coating portion is formed in a weight range of less than 0.5% by weight based on the total weight of the core portion, the coating portion may not be formed to sufficiently surround the core, and if the coating portion is formed in a weight range exceeding 5% by weight, the coating portion may be formed too thick. This may hinder the diffusion of lithium ions.

The positive electrode active material for a lithium secondary battery of the present invention may have an average particle diameter (D ₅₀ ) of 0.1 ㎛ to 20 ㎛. Specifically, the average particle diameter (D ₅₀ ) of the positive electrode active material for lithium secondary batteries of the present invention is 0.1 ㎛ to 15 ㎛, 0.1 ㎛ to 10 ㎛, 1 ㎛ to 20 ㎛, 5 ㎛ to 20 ㎛, 1 ㎛ to 15 ㎛, 1 It may be ㎛ to 10 ㎛, 5 ㎛ to 15 ㎛, or 5 ㎛ to 10 ㎛. When the average particle diameter of the positive electrode active material of the present invention falls within the above range, the target energy density per volume can be achieved. Specifically, if the average particle diameter of the positive electrode active material of the present invention exceeds 20 ㎛, it may lead to a rapid decrease in charge and discharge capacity, and if it is 0.1 ㎛ or less, it may be difficult to obtain the desired energy density per volume.

Meanwhile, according to the present invention, the thickness of the coating portion coated on the core portion of the present invention may be 30 to 100 nm.

Manufacturing method of positive electrode active material for lithium secondary battery

Next, a method for manufacturing the positive electrode active material for a lithium secondary battery of the present invention will be described.

The method for producing a positive electrode active material for lithium secondary batteries according to the present invention is,

(a) preparing a nickel-containing compound and

(b) may include mixing and reacting the nickel-containing compound with the phosphorus-based compound.

At this time, the nickel-containing compound may be a high-nickel (High-Ni)-based lithium composite transition metal oxide with a nickel (Ni) content of 60 mol% or more among all metal elements. More preferably, the nickel-containing compound may be a high-Ni-based lithium composite transition metal oxide in which the nickel (Ni) content of all metal elements is 70 mol% or 80 mol% or more. As the nickel-containing compound includes a high-content nickel (High-Ni)-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more, it may be possible to secure high capacity of a lithium secondary battery.

Specifically, the nickel-containing compound may be an NCM-based lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn), or nickel (Ni), cobalt (Co), and aluminum (Al). ) It may be an NCA-based lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). It may be possible. Since the core part includes manganese (Mn) and/or aluminum (Al) along with nickel (Ni) and cobalt (Co), structural stability can be greatly improved and lifespan characteristics can be significantly improved. In general, when manganese (Mn) and/or aluminum (Al) is included, it is effective in terms of stability, but may be disadvantageous in terms of capacity characteristics and output characteristics. However, if the positive electrode active material structure of the present invention is satisfied, sufficient capacity characteristics are secured. However, stability and lifespan characteristics can be significantly improved.

More specifically, the nickel-containing compound may be represented by the following formula (1).

[Formula 1]

Li _p Ni _1-(x1+y1+z1) Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ²

In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and is at least one element selected from the group consisting of Cr, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0< x1≤0.4, 0<y1≤0.4, 0≤z1≤0.1, 0≤q1≤0.1, and 0<x1+y1+z1≤0.4.

According to one embodiment of the present invention, in the step of mixing and reacting the nickel-containing compound and the phosphorus-based compound, the phosphorus-based compound may be mixed in an amount of 0.5% to 5% by weight based on the total weight of the nickel-containing compound. If the phosphorus-based compound is mixed in an amount of less than 0.5% by weight based on the total weight of the nickel-containing compound, the phosphorus-based compound may not be sufficiently coated to surround the nickel-containing compound, and if the phosphorus-based compound is mixed in more than 5% by weight, the phosphorus-based compound may not be coated sufficiently to surround the nickel-containing compound. If the coating made of the compound is formed too thick, diffusion of lithium ions may be hindered during battery charging and discharging.

The method for producing a cathode active material for a lithium secondary battery of the present invention may include the step of further mixing an acid additive in the reaction of a nickel-containing compound and a phosphorus-based compound. At this time, the acid additive may be a weak acid with a pka of 2 to 6, and may specifically include at least one selected from the group consisting of citric acid, acetic acid, malic acid, and formic acid.

The acid additive may be added in an amount of 0.05% to 0.5% by weight based on the total weight of the nickel-containing compound.

Meanwhile, the method for producing a positive electrode active material for a lithium secondary battery of the present invention may further include the step of (c) heat-treating the reaction product produced by mixing and reacting a nickel-containing compound with a phosphorus-based compound.

At this time, the step of heat treating the reaction product (c) may be performed at a temperature of 100 ^o C or higher.

Anode and lithium secondary battery for lithium secondary battery

According to another embodiment of the present invention, a positive electrode for a lithium secondary battery and a lithium secondary battery containing the positive electrode active material prepared as described above are provided.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or an aluminum or stainless steel surface. Surface treatment with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500㎛, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

Additionally, the positive electrode active material layer may include a conductive material and a binder along with the positive electrode active material described above.

At this time, the conductive material is used to provide conductivity to the electrode, and can be used without particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, etc., of which one type alone or a mixture of two or more types may be used. The conductive material may typically be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

Additionally, the binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, and carboxymethyl cellulose ( CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene. Examples include butadiene rubber (SBR), fluorine rubber, and various copolymers thereof, and one type of these may be used alone or a mixture of two or more types may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode can be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material described above. Specifically, it can be manufactured by applying a composition for forming a positive electrode active material layer containing the above-described positive electrode active material and, optionally, a binder and a conductive material onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are the same as described above.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may specifically be a battery or capacitor, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, it can be used on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector may typically have a thickness of 3 to 500㎛, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, net porous materials, foams, and non-woven materials.

The negative electrode active material layer optionally includes a binder and a conductive material along with the negative electrode active material. As an example, the negative electrode active material layer is formed by applying and drying a negative electrode forming composition containing a negative electrode active material and optionally a binder and a conductive material on a negative electrode current collector, or casting the negative electrode forming composition on a separate support. Next, it may be manufactured by laminating the film obtained by peeling from this support onto the negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Metallic compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; Metal oxides that can dope and undope lithium, such as SiOβ (0 <β<2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite containing the above-described metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, may be used, and any one or a mixture of two or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Additionally, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and high-crystalline carbon includes amorphous, plate-shaped, flaky, spherical, or fibrous natural graphite, artificial graphite, and Kish graphite. graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch. Representative examples include high-temperature calcined carbon such as derived cokes.

In addition, electrolytes used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries. It is not limited.

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-based solvents such as dibutyl ether or tetrahydrofuran; Ketone-based solvents such as cyclohexanone; Aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (propylene) Carbonate-based solvents such as carbonate (PC); Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or ring-structured hydrocarbon group and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane, etc. may be used.

The lithium salt can be used without particular restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl4, 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 0.1 to 2.0M. When the concentration of lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be achieved and lithium ions can move effectively.

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

As described above, the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity maintenance rate, and is therefore widely used in portable devices such as mobile phones, laptop computers, digital cameras, and hybrid electric vehicles ( It is useful in electric vehicle fields such as hybrid electric vehicle (HEV).

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, this is only an example, and the scope of rights of the present invention is determined by the following contents. Not limited.

Manufacturing example

Example 1

에서 교반하며 2시간 동안 반응시켜 혼합물 파우더를 제조하였다. 이후 혼합물 파우더를 회수하여 진공 오븐에 넣고 120

에서 12시간 동안 열처리하여 용매를 기화시켜 본 발명의 고함량 니켈의 양극 활물질을 제조하였다.Add 100 mL of acetonitrile, 0.995 g of LiNi _0.945 Co _0.04 Al _0.015 O ₂ active material, 0.005 g of Phosphonobenzoic acid (PBA), and 0.0005 g of citric acid as an acid additive into the container and add 80 g.

The mixture powder was prepared by reacting for 2 hours while stirring. Afterwards, the mixture powder was recovered and placed in a vacuum oven at 120 °C.

The high-nickel positive electrode active material of the present invention was prepared by heat treatment for 12 hours to vaporize the solvent.

Example 2

In Example 1, a high-content nickel-based positive electrode active material was prepared in the same manner as in Example 1, except that 0.990 g of NCA active material and 0.01 g of phosphonobenzoic acid were added.

Comparative Example 1

In Example 1, a high-content nickel-based positive electrode active material containing pure NCA active material without adding phosphonobenzoic acid or citric acid was prepared as a comparative example.

Experimental Example 1

In order to quantitatively measure the amount of PBA coated on the positive electrode active material, TGA (thermogravimetric analysis) analysis was performed on the positive electrode active material according to Example 1 and Comparative Example. 1 is a TGA analysis graph of a positive electrode active material according to an embodiment of the present invention.

근처에서 급격한 질량 감소를 보이는 반면, 비교예 1에 따른 양극 활물질은 온도 증가에 따라 질량 변화가 거의 없다. 이는 PBA가 열분해되기 때문에 나타나는 현상으로 실시예 1의 양극 활물질의 경우 약 0.5 중량%가 감소하는 것을 확인할 수 있다.Referring to Figure 1, the quantitative amount of PBA reacting with the surface of the positive electrode active material prepared in Example 1 and forming a chemical bond can be confirmed. 200 for the positive electrode active material according to Example 1

While it shows a rapid decrease in mass nearby, the positive electrode active material according to Comparative Example 1 shows little change in mass as the temperature increases. This phenomenon occurs because PBA is thermally decomposed. In the case of the positive electrode active material of Example 1, it can be confirmed that the amount decreases by about 0.5% by weight.

Experimental Example 2

FT-IR analysis was performed on the positive electrode active materials according to Example 2 and Comparative Example 1. Figure 2 is a FT-IR analysis graph of a positive electrode active material according to an embodiment of the present invention.

Referring to Figure 2, in the case of the positive electrode active material according to Example 2, peaks were observed at 984 cm ^-1 (P-OH bond) and 1072 cm ^-1 (P=O bond) corresponding to the functional group of PBA, which It can be confirmed that PBA is chemically bonded to the surface of the NCA positive electrode active material. On the other hand, it can be seen that no peaks are observed in the positive electrode active material according to Comparative Example 1.

Experimental Example 3

Scanning Transmission Electron Microscope (STEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyzes were performed to confirm whether PBA reacted and bonded evenly to the entire surface. Figure 3 shows (a) a STEM image, (b) an EDS mapping image of Ni, and (c) an EDS mapping image of P of the positive electrode active material according to Example 1 of the present invention.

Referring to Figure 3, it can be seen that PBA is evenly coated over the entire surface of the positive electrode active material according to Example 1.

Example 3

에서 건조하여 양극을 준비하였다.The positive electrode active material according to Example 1, Super-P (Timcal) as a conductive material, and PVdF (polyvinylidene fluoride) as a binder were mixed in a ratio of 8:1:1, respectively. Afterwards, NMP (N-methylpyrrolidone) was added to prepare a positive electrode active material slurry and then applied on an aluminum current collector. The current collector on which the slurry is applied is 100%

The anode was prepared by drying.

The positive electrode and the lithium metal negative electrode were used as electrodes, and 1.3 M LiPF ₆ was used as an electrolyte (solvent: EC (ethyl carbonate): EMC (ethyl methyl carbonate): DMC (dimethyl carbonate) = 3: 4: 3). A secondary battery (2032-type coin cell) was produced.

Example 4

In Example 3, a Li lithium secondary battery (2032-type coin cell) was manufactured under the same conditions, except that the positive electrode active material of Example 2 was used instead of the positive active material of Example 1.

Comparative Example 2

In Example 3, a lithium secondary battery (2032-type coin cell) was manufactured under the same conditions, except that the positive electrode active material of Comparative Example 1 was used instead of the positive electrode active material of Example 1.

Experimental Example 4

A charging and discharging current of 0.1 C-rate was applied to the batteries according to Example 3, Example 4, and Comparative Example 2, charging them to 4.3 V compared to lithium metal, discharging them to 2.7 V, and then 0.1 C again to 4.3 V. It was charged with -rate current. Then, the charged battery was disassembled to recover the positive electrode, and the recovered positive electrode was washed with DMC (Dimethyl carbonate) for 30 seconds to remove the electrolyte remaining on the electrode surface and dried.

에서 300

까지 분당 5

씩 승온하면서 발열량을 측정하였다.2 mg of each anode was added to the pan of a DSC (differential scanning calorimeter) device (TA's DSC25), 2.5 ㎕ of electrolyte was added, and the pan was sealed. 30 degrees ceiling fan

From 300

Up to 5 per minute

The calorific value was measured while increasing the temperature step by step.

Figure 4 is a DSC analysis graph of an anode according to an embodiment of the present invention.

Referring to FIG. 4, the positive electrode recovered from the battery of Comparative Example 2 had an exothermic peak temperature of 207 ^o C. The positive electrode recovered from the battery of Example 3 had an exothermic peak temperature of 224 ^o C. The anode has an exothermic peak temperature of 231 ^o C, and it can be seen that the exothermic peak temperature increases as the amount of the phosphorus coating increases.

In the process of increasing the temperature, the electrolyte is burned by active oxygen generated from the anode. The positive electrode recovered from the batteries of Examples 3 and 4 effectively suppresses the release of active oxygen, increasing the temperature at which heat generation begins and the heat generation peak. It can be confirmed that the calorific value is reduced. Through this, it can be seen that the thermal stability of the positive electrode active material, positive electrode, and battery increases depending on the PBA coating.

Experimental Example 5

Differential electrochemical mass spectrometry (DEMS) analysis was performed to confirm whether radicals were captured in the coating part of the positive electrode active material of the present invention. In the batteries produced in Example 4 and Comparative Example 2, only the electrolyte was replaced with 1M LiPF ₆ (solvent EC:DEC=1:1) to produce a DEMS battery (Example 4-1, Comparative Example 2-1 battery). did. The DEMS battery was charged at a current density of 0.1 C-rate in the range of 3.6 - 4.8 V compared to lithium metal, and the amount of gas generated was confirmed. Figure 5 is a DEMS analysis graph that can confirm the amount of gas generated from the positive electrode active material.

Referring to Figure 5, (a) a DEMS analysis graph of the battery according to Comparative Example 2-1 and (b) a DEMS analysis graph of the battery according to Example 4-1 can be seen. From the above graph, it can be seen that oxygen gas is hardly generated in both batteries. However, it can be seen that the battery of Comparative Example 2-1 generated a large amount of carbon dioxide as charging progressed to the high voltage region, and that the battery of Example 4-1 did not generate a large amount of carbon dioxide even when charging progressed to the high voltage region.

From these results, it can be confirmed that the PBA coating can capture released active oxygen (oxygen radicals), reduce the amount of gas generated during battery operation, and improve battery stability.

Experimental Example 6

Electron spin resonance (ESR) analysis was performed to observe radical intermediates generated through the oxidation reaction of the coated positive electrode active material and the electrolyte. A current of 0.1 C-rate was applied to the battery according to Example 4 and Comparative Example 2 and charged to 4.3 V compared to lithium metal, discharged to 2.7 V, and then charged again to 4.3 V with a current of 0.1 C-rate. . Afterwards, the charged battery was disassembled to recover the positive electrode, and the recovered positive electrode was washed with DMC for 30 seconds to remove the electrolyte remaining on the electrode surface and dried.

Then, 6 mg of the dried electrode was added to 600 ㎕ of electrolyte, stored for 1 hour, and ESR analysis was performed. Figure 6 is an ESR analysis graph of a positive electrode active material according to an embodiment of the present invention.

Referring to FIG. 6, it can be seen that in the case of the electrolyte stored together with the positive electrode active material extracted from the battery of Comparative Example 2, a peak occurs due to the generation of radicals. However, the positive electrode active material extracted from the battery of Example 4 and the stored electrolyte almost did not show the corresponding peak, confirming that in the case of the positive electrode active material coated with PBA, the coating captured oxygen radicals and suppressed the release of oxygen radicals into the electrolyte.

Experimental Example 7

In order to measure the effect of the PBA coating of the positive electrode active material of Example 3 and Comparative Example 2 on the initial capacity of the battery, charging and discharging of the lithium secondary battery was performed by applying a 0.1 C-rate current density, and the resulting voltage-capacity was measured. The curve is shown in Figure 7.

The battery manufactured in Comparative Example 2 developed an initial discharge capacity of 208 mAh/g, while the battery manufactured in Example 3 developed an initial discharge capacity of 204 mAh/g. It is thought that the expression capacity was partially reduced due to the increased resistance caused by the coating. However, it was observed that this corresponded to a capacity reduction of about 1.9% and that the change in reversible capacity due to coating was very small.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements can be made by those skilled in the art using the basic concept of the present invention defined in the following claims. It falls within the scope of invention rights.

Claims (15)

A core portion containing a nickel-containing compound; and
A coating portion formed on the surface of the core portion and containing a phosphorus-based compound,
Cathode active material for lithium secondary batteries.
According to paragraph 1,
The nickel-containing compound is a lithium complex transition metal oxide represented by the following formula (1):
Cathode active material for lithium secondary batteries.
[Formula 1]
Li _p Ni _1-(x1+y1+z1) Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ²
In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and is at least one element selected from the group consisting of Cr, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0< x1≤0.4, 0<y1≤0.4, 0≤z1≤0.1, 0≤q1≤0.1, and 0<x1+y1+z1≤0.4.
According to paragraph 1,
The phosphorus-based compound is a phosphorus-based compound containing a functional group capable of bonding to at least one hydroxy group or a phosphorus-based compound containing an aromatic ring,
Cathode active material for lithium secondary batteries.
According to paragraph 1,
The coating portion is formed in a weight range of 0.5% by weight to 5% by weight based on the total weight of the core portion,
Cathode active material for lithium secondary batteries.
According to paragraph 1,
The thickness of the coating portion is 30 to 100 nm,
Cathode active material for lithium secondary batteries.
According to paragraph 1,
The positive electrode active material for a lithium secondary battery has an average particle diameter (D ₅₀ ) of 0.1 ㎛ to 20 ㎛.
(a) preparing a nickel-containing compound; and
(b) mixing and reacting the nickel-containing compound with the phosphorus-based compound;
The phosphorus-based compound forms a coating on the surface of the nickel-containing compound,
Method for manufacturing positive electrode active material for lithium secondary battery.
In clause 7,
The nickel-containing compound is a lithium complex transition metal oxide represented by the following formula (1):
Method for manufacturing positive electrode active material for lithium secondary battery.
[Formula 1]
Li _p Ni _1-(x1+y1+z1) Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ²
In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and is at least one element selected from the group consisting of Cr, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0< x1≤0.4, 0<y1≤0.4, 0≤z1≤0.1, 0≤q1≤0.1, and 0<x1+y1+z1≤0.4.
In clause 7,
The phosphorus-based compound is mixed in an amount of 0.5% to 5% by weight based on the total weight of the nickel-containing compound,
Method for manufacturing positive electrode active material for lithium secondary battery.
In clause 7,
(b) the reaction step of the nickel-containing compound and the phosphorus-based compound is performed by adding an acid additive,
Method for manufacturing positive electrode active material for lithium secondary battery.
According to clause 10,
The acid additive is a weak acid of pka 2 to 6,
Method for manufacturing positive electrode active material for lithium secondary battery.
According to clause 11,
The acid additive is added to be 0.05% by weight to 0.5% by weight based on the total weight of the nickel-containing compound.
Method for manufacturing positive electrode active material for lithium secondary battery.
In clause 7,
(c) mixing and reacting the nickel-containing compound with the phosphorus-based compound and heat-treating the resulting reaction product,
The heat treatment step is performed at a temperature of 100 ^o C or higher,
Method for manufacturing positive electrode active material for lithium secondary battery.
A positive electrode comprising the positive electrode active material according to any one of claims 1 to 6.
A lithium secondary battery comprising the positive electrode of claim 14.