KR20190129614A - Preparing method of positive electrode active material for lithium secondary battery, positive electrode active material thereby, positive electrode and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to: a method for manufacturing positive electrode active materials comprising a step of preparing a lithium transition metal oxide containing at least 60 mol% of nickel based on a total number of moles of a transition metal oxide except lithium, and a step of mixing the lithium transition metal oxide and a coating source comprising lithium represented by chemical formula 1: Li_xP_yM^1_ wO_z, followed by heat treating the same at 500 to 900°C to form a coating layer containing phosphate on a surface of the lithium transition metal oxide; a positive electrode for a lithium secondary battery comprising the positive electrode active materials; and the lithium secondary battery. According to the present invention, it is possible to remove lithium by-products present on the surface of the lithium transition metal oxide by high temperature heat treatment.

Description

A method of manufacturing a positive electrode active material for a lithium secondary battery, a positive electrode active material manufactured thereby, a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the same SECONDARY BATTERY INCLUDING THE SAME}

The present invention relates to a method for producing a cathode active material for a lithium secondary battery, a cathode active material prepared by the method for producing a cathode active material, a cathode for a lithium secondary battery including the cathode active material, and a lithium secondary battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.

A lithium transition metal composite oxide is used as a cathode active material of a lithium secondary battery. Among them, a lithium cobalt composite metal oxide such as LiCoO ₂ having a high operating voltage and excellent capacity characteristics is mainly used. However, LiCoO ₂ has very poor thermal properties due to destabilization of the crystal structure due to thalithium. In addition, since the LiCoO ₂ is expensive, there is a limit to mass use as a power source in fields such as electric vehicles.

As a material for replacing LiCoO ₂ , lithium manganese composite metal oxides (such as LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron phosphate compounds (such as LiFePO ₄ ), or lithium nickel composite metal oxides (such as LiNiO ₂ ) have been developed. . Among them, research and development on lithium nickel composite metal oxides having a high reversible capacity of about 200 mAh / g, which is easy to implement a large-capacity battery, are being actively researched. However, LiNiO ₂ is inferior in thermal stability to LiCoO _2, and when an internal short circuit occurs due to pressure from the outside in a charged state, the positive electrode active material itself decomposes, causing a battery to rupture and ignite. Accordingly, as a method for improving low thermal stability while maintaining the excellent reversible capacity of LiNiO ₂ , lithium nickel cobalt metal oxides in which a part of Ni is substituted with Co and Mn or Al have been developed.

However, in the case of the lithium nickel cobalt metal oxide, as the charge and discharge are repeated, the interface resistance between the electrode and the electrolyte including the active material increases, electrolyte decomposition due to moisture or other effects inside the battery, deterioration of the surface structure of the active material, and There is a problem that the safety and lifespan characteristics of the battery are drastically lowered due to exothermic reactions accompanied by rapid structural collapse, and such a problem is particularly serious as the content of nickel is increased to manufacture a high capacity battery.

In order to solve this problem, a method of improving the stability between the electrolyte and the active material as well as improving the stability by coating the surface of the lithium nickel cobalt metal oxide has been proposed.

Conventionally, a method of forming a coating layer by using a wet coating method on a surface of a cathode active material is performed. However, in this case, there is a problem that the surface of the positive electrode active material is damaged depending on the pH of the coating solution.

Accordingly, the development of a positive electrode active material including lithium nickel cobalt metal oxide, wherein at this time without damaging the surface of the lithium nickel cobalt metal oxide to form a uniform coating layer to produce a battery with improved stability and life characteristics It is required.

Republic of Korea Patent Publication No. 2015-0042610

In order to solve the above problems, the first technical problem of the present invention is to form a coating layer containing a phosphate by heat-treating a specific coating source on the surface of the lithium transition metal oxide containing a high content of nickel, surface stability It is to provide a method for producing this improved cathode active material.

The second technical problem of the present invention is to provide a positive electrode active material manufactured by the above manufacturing method.

The third technical problem of the present invention is to provide a cathode for a lithium secondary battery including the cathode active material.

The fourth technical problem of the present invention is to provide a lithium secondary battery including the positive electrode for a lithium secondary battery.

The present invention comprises the steps of preparing a lithium transition metal oxide containing at least 60 mol% nickel based on the total number of moles of the transition metal oxide except lithium; And mixing the lithium transition metal oxide with a coating source including lithium represented by the following Chemical Formula 1 and performing a heat treatment at 500 ° C. to 900 ° C. to form a coating layer including a phosphate oxide on the surface of the lithium transition metal oxide. It provides a method for producing a positive electrode active material comprising;

[Formula 1]

Li _x P _y M ¹ _w O _z

In Formula 1, M ¹ is at least one selected from the group consisting of Al, Ti, La, Zr, V and Ge, 0 <x <4, 0 <y <4, 0≤w <8, 0 < z <13.

In addition, lithium transition metal oxide containing at least 60 mol% nickel with respect to the total moles of the transition metal except lithium; And a coating layer comprising a phosphate formed on the surface of the lithium transition metal oxide, wherein the coating layer does not include lithium as a metal element.

In addition, there is provided a cathode for a lithium secondary battery, including the cathode active material according to the present invention.

In addition, it provides a lithium secondary battery comprising a positive electrode according to the present invention.

According to the present invention, by mixing the surface of the lithium transition metal oxide with the coating raw material and heat treatment at a high temperature, it is possible to remove the lithium by-product present on the surface of the lithium transition metal oxide by high temperature heat treatment.

On the other hand, lithium ions present on the surface are also deficient by removing lithium by-products, and there is a problem that the initial capacity is lowered and the life characteristics are deteriorated by the lack of lithium ions. According to the present invention, by using a coating source containing lithium as a coating raw material during the high temperature heat treatment, the lithium ions in the raw material may fill the voids of the lithium ions removed from the surface of the lithium transition metal oxide. Accordingly, it is possible to provide a cathode active material having improved initial capacity and lifespan as well as improved structural stability.

1 is a graph showing the XPS spectrum of the positive electrode active material prepared in Example 1.
Figure 2 is a graph showing the capacity retention rate according to the cycle of the secondary battery prepared in Examples 1-2 and Comparative Examples 1-2.
Figure 3 shows the change of current with time under the high temperature and high voltage of the secondary battery prepared in Examples 1 and 2 and Comparative Examples 1 and 2.
Figure 4 is a measure of the amount of gas generation with time while storing the secondary batteries prepared in Examples 1 and 2 and Comparative Example 1 at a high temperature.

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

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Manufacturing method of the positive electrode active material

Conventionally, when using a cathode active material containing a high content of nickel in order to exhibit high capacity characteristics, excess lithium by-products present on the surface of lithium react with the electrolyte injected into the secondary battery, causing a swelling phenomenon of the lithium secondary battery. Therefore, there is a problem in that the life characteristics due to the deterioration of stability is lowered. Thus, in order to improve the stability and life characteristics there has been a study to form a coating layer on the surface of the positive electrode active material.

However, when the coating layer is formed on the surface, when the wet coating is used, there is a problem that damage occurs on the surface of the positive electrode active material, when dry coating, there is a problem that the composition of the coating layer is not uniform.

Accordingly, the present inventors, while manufacturing a cathode active material containing a high content of nickel, by using a coating source containing lithium to form a coating layer containing phosphate on the surface to suppress the damage of the lithium transition metal oxide surface structure stability It was found that this improved cathode active material could be prepared and completed the present invention.

In order to manufacture the positive electrode active material according to the present invention, preparing a lithium transition metal oxide containing at least 60 mol% nickel based on the total moles of the transition metal oxide except lithium; And mixing the lithium transition metal oxide with a coating source including lithium represented by the following Chemical Formula 1 and performing a heat treatment at 500 ° C. to 900 ° C. to form a coating layer including a phosphate oxide on the surface of the lithium transition metal oxide. It includes;

[Formula 1]

Li _x P _y M ¹ _w O _z

In Chemical Formula 1,

M ¹ is at least one selected from the group consisting of Al, Ti, La, Zr, V, and Ge, and 0 <x <4, 0 <y <4, 0 ≦ w <8, 0 <z <13)

Hereinafter, the manufacturing method of the positive electrode active material of this invention is demonstrated more concretely.

First, a lithium transition metal oxide including 60 mol% or more of nickel is prepared based on the total moles of transition metal oxides other than lithium.

Specifically, the lithium transition metal oxide may be included so that the content of nickel is 60 mol% to 100 mol% with respect to the total moles of transition metal elements excluding lithium. In this case, when the content of nickel in the lithium transition metal oxide is out of the above range, there is a problem that the capacity of the positive electrode active material is reduced and cannot be applied to an electrochemical device requiring a high capacity. The higher the nickel content within the above range, the battery containing the same may exhibit high capacity characteristics. However, as the content of nickel is higher, the content of cobalt and / or manganese is relatively decreased, and thus, charge and discharge efficiency may be lowered. Accordingly, the lithium transition metal oxide may include nickel in a content of preferably 60 mol% to 96 mol%, more preferably 60 mol% to 92 mol%, based on the total moles of transition metal elements other than lithium. Can be.

In addition, the lithium transition metal oxide may include cobalt in an amount of 0 mol% to 30 mol%, preferably 5 mol% to 20 mol%, based on the total number of moles of transition metal elements excluding lithium. In this case, when the cobalt content is out of the above range and the cobalt content exceeds 30 mol%, the cost of the raw material is increased as a result of the high content of cobalt, and the reversible capacity may be slightly reduced.

In addition, the lithium transition metal oxide may include a metal element X in an amount of 0 mol% to 30 mol%, preferably 5 mol% to 20 mol%, based on the total moles of transition metal elements excluding lithium. In this case, when the metal element X is manganese, the structural stability of the active material may be improved, and when the metal element X is Al, the surface properties of the active material may be improved, thereby improving thermal stability.

In addition, the lithium transition metal oxide may further include, optionally, doped with a doping element M ¹ . The doping element M ¹ may be used without particular limitation as long as it can contribute to improving the structural stability of the positive electrode active material. For example, Zr, B, W, Mg, Ta, Ti, Sr, Ba, Ce, Hf, F , P, S, La and Y may be at least one selected from the group consisting of. The doping element M ¹ may be included in an amount of 5 mol% or less, preferably 0.1 mol% to 1 mol%, based on the total number of moles of the transition metal excluding lithium. For example, when the doping element M ¹ is included in the content range, the doping element M ¹ may be uniformly included on the surface and the inside of the cathode active material, thereby improving the structural stability of the cathode active material, thereby improving output characteristics. Can be.

Preferably, the lithium transition metal oxide is Li _{1 + a} (Ni _b Co _c X _d M ¹ _e ) _{1- a} O ₂ (Wherein X is at least one of Mn or Al and M ¹ is Zr, B, W, Mg, Ta, Ti, Sr, Ba, Ce, Hf, F, P, S, La and Y) At least one selected, and 0 ≦ a ≦ 0.1, 0.6 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.3, 0 ≦ d ≦ 0.3, and 0 ≦ e ≦ 0.05).

Subsequently, the lithium transition metal oxide and a coating source containing lithium represented by the following Chemical Formula 1 are mixed and 1 hour to 10 hours at 500 ° C to 900 ° C, preferably 3 hours to 6 ° C at 650 ° C to 850 ° C. Heat treatment for a time to form a coating layer containing a phosphate represented by the formula (2) on the surface of the lithium transition metal oxide.

[Formula 1]

Li _x P _y M ¹ _w O _z

In Formula 1, M ¹ is at least one selected from the group consisting of Al, Ti, La, Zr, V and Ge, 0 <x <4, 0 <y <4, 0≤w <8, 0 < z <13.

[Formula 2]

P _y1 M ¹ _w1 O _z1

In Formula 2, M ¹ is at least one selected from the group consisting of Al, Ti, La, Zr, V, and Ge, and 0 <y1 <4, 0 ≦ w1 <8, 0 <z1 <13.

In this case, the mixing of the lithium transition metal oxide and the coating source including the lithium may be performed by a dry process.

For example, when a wet process is used to form the coating layer, when the coating solution is prepared using a coating source containing lithium represented by Formula 1, the pH of the coating solution is lowered to less than 7 by the coating source to reduce acidity. Will be displayed. Accordingly, when the coating solution exhibiting acidity and the lithium transition metal oxide are mixed, there is a problem of causing damage to the surface of the lithium transition metal oxide during the reaction. Dry mixing of the lithium transition metal oxide and the coating source including the lithium may suppress damage to the surface of the cathode active material that may occur during a wet process, thereby further improving surface stability of the cathode active material.

With respect to the total weight of the lithium transition metal oxide, the coating source including lithium may be mixed so as to be 0.05 parts by weight to 5 parts by weight, preferably 1 parts by weight to 3 parts by weight. For example, when the coating source is mixed in the above range, a coating layer having an appropriate thickness is formed on the surface of the lithium transition metal oxide, and when applied to the battery, there is no risk of initial capacity reduction due to coating layer formation.

The present invention, by dry mixing the lithium transition metal oxide and the coating source containing the lithium, and performing a heat treatment for 1 to 10 hours at 500 ℃ to 900 ℃, the lithium transition metal oxide by the high temperature heat treatment The recrystallization of can occur, thereby improving the firmness of the surface of the lithium transition metal oxide. For example, when the heat treatment temperature is less than 500 ° C., recrystallization of the lithium transition metal oxide does not occur, and decomposition of the coating source containing lithium does not occur completely, thereby improving initial capacity and surface stability. Cannot be achieved. In addition, when the heat treatment temperature exceeds 900 ℃, the lithium transition metal oxide is over-baked to change the shape and size of the primary particles, thereby increasing the average particle diameter of the lithium transition metal oxide. Accordingly, the initial capacity and efficiency can be reduced when applied to the battery.

In order to form a coating layer on the surface of the lithium transition metal oxide, when the high temperature heat treatment as described above, the structural stability of the lithium transition metal oxide can be improved, but lithium ions present on the surface of the lithium transition metal oxide There was a problem that volatilization occurs. When the lithium ions present on the surface of the lithium transition metal oxide are volatilized as described above, it may cause problems such as initial capacity reduction or deterioration of lifetime characteristics due to stoichiometric imbalance between lithium and the transition metal in the lithium transition metal oxide. have.

The coating source including lithium may be lithium phosphate, and preferably may be a coating source represented by Chemical Formula 1. In forming the coating layer, by using the coating source including the lithium, the lithium present in the coating source replaces the volatilized lithium on the surface of the lithium transition metal oxide, thereby preventing the initial capacity from being lowered. In addition, the surface stability of the positive electrode active material in which the coating layer is formed may be improved due to the P element present in the coating source. Accordingly, when applied to the battery, it is possible to provide a secondary battery with improved life characteristics. In addition to solving the problem of volatilization of lithium ions present on the surface of the lithium transition metal oxide by high temperature heat treatment, a coating layer having a uniform composition may be formed on the surface of the lithium transition metal oxide.

In more detail, the coating source containing lithium transition metal oxide and lithium, preferably, the coating source represented by the formula (1) by dry heat treatment at a high temperature, present on the surface of the lithium transition metal oxide The lithium ions are volatilized, and the coating source containing lithium decomposes into lithium ions and phosphates at high temperature.

In this case, of the lithium-containing coating source, lithium ions replace volatilized lithium on the surface of the lithium transition metal oxide, and phosphate forms a coating layer represented by Formula 2 on the surface of the lithium transition metal oxide. . In addition, since the phosphate does not react with other metal ions or the like and is formed on the surface of the lithium transition metal oxide by itself, the phosphate may exhibit a uniform composition throughout the coating layer. In addition, when the coating layer is formed on the surface of the lithium transition metal oxide by using a phosphate compound, the surface stability of the lithium transition metal oxide may be improved due to the P element. In addition, according to the improved surface stability it can be produced a secondary battery with further improved life characteristics when applied to the battery.

For example, the coating source including lithium may be decomposed at 450 ° C. to 800 ° C., preferably 600 ° C. to 800 ° C., and lithium ions and phosphates, specifically lithium ions and P _y M ¹ _w. It may be decomposed into O _z compound. The coating source including lithium is decomposed by the heat treatment, and in this case, lithium ions in the coating source including lithium may replace lithium volatilized on the surface of the lithium transition metal oxide. Accordingly, the lithium ion deficiency on the surface of the lithium transition metal oxide can be prevented. In addition, the P _y M ¹ _w O _z compound in the coating source decomposed by the heat treatment may form a coating layer on the surface of the lithium transition metal oxide, thereby preparing a cathode active material having improved structural stability and high temperature stability.

For example, when the heat treatment is performed below the range, the coating source including lithium may not be easily decomposed, so that the composition of the coating layer formed on the surface of the lithium transition metal oxide may not be uniformly formed. As a result, the amount of residual lithium present on the surface may increase, resulting in a decrease in lifetime or stability. In addition, when the heat treatment is performed over the above range, the lithium transition metal oxide is overfired to change the shape and size of the primary particles, thereby increasing the average particle diameter of the lithium transition metal oxide. Accordingly, the initial capacity and efficiency can be reduced when applied to the battery. can do.

The coating source containing lithium represented by the formula (1) according to the present invention is preferably Li ₃ PO ₄ , Li _x Zr _w (PO ₄ ) _{3 ,} Li _x V _w (PO ₄ ) ₃ (where 0 <x <4, 0 <w <8), Li _x Ge _w (PO ₄ ) ₃ (where 0 <x <4, 0 <w <8), Li _x Ti _w (PO ₄ ) ₃ (where 0 <x <4, 0 <w <8), Li _x Al _w1 Ti _w2 (PO ₄ ) ₃ (0 <x <4, 0 <w1 + w2 <8), Li _x Al _w1 Ge _w2 (PO ₄ ) ₃ (where 0 <x <4, 0 <w1 + w2 <8), (LiAlTiP) _x1 O _z (where 0 <x1 <4, 0 <z <13) and Li _x La _w TiO ₃ Wherein at least one selected from the group consisting of 0 <x <4 and 0 <w <8, more preferably Li ₃ PO ₄ , LiTi ₂ PO ₄ , LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiZr ₂ (PO ₄ ) ₃ , LiGe ₂ (PO ₄ ) ₃ and Li _{1 . 3} Al _{0 . 0 .7} Ti ₃ (PO ₄₎ may be one including at least one or more selected from the group consisting of _3. When using the above-described lithium-containing coating source as the coating source for forming the coating layer, not only does not damage the surface of the positive electrode active material, but also solves the problem of volatilization of lithium ions on the surface of the lithium transition metal oxide by high temperature heat treatment. In addition, a coating layer having a uniform composition may be easily formed on the surface of the lithium transition metal oxide.

For example, when using a coating source that does not contain lithium as the coating source for forming the coating layer, for example, phosphoric acid, the coating source that does not include lithium has high acidity and is unstable in air, When forming a coating layer on the surface of the lithium transition metal oxide, it may cause damage to the surface of the lithium transition metal oxide, it may be difficult to form a uniform coating layer.

Positive electrode active material

The present invention also provides a cathode active material prepared by the method for producing a cathode active material according to the present invention.

Specifically, the positive electrode active material according to the present invention is prepared by the method for producing a positive electrode active material described above, lithium transition metal oxide containing 60 mol% or more nickel based on the total number of moles of the transition metal except lithium; And a coating layer comprising a phosphate formed on the surface of the lithium transition metal oxide, wherein the coating layer shows a PO ₄ peak at 130 eV to 135 eV when analyzed by X-ray photoelectron spectroscopy.

The details described in the method of manufacturing the positive electrode active material described above will not be described in detail, and only the remaining configurations will be described below.

The cathode active material according to the present invention includes a coating layer containing a phosphate represented by the following Formula 2 formed on the surface of the lithium transition metal oxide.

The lithium transition metal oxide is Li _{1 + a} (Ni _b Co _c X _d M ¹ _e ) _{1- a} O ₂ (Wherein X is at least one of Mn or Al and M ¹ is Zr, B, W, Mg, Ta, Ti, Sr, Ba, Ce, Hf, F, P, S, La and Y) At least one selected, and 0 ≦ a ≦ 0.1, 0.6 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.3, 0 ≦ d ≦ 0.3, and 0 ≦ e ≦ 0.05). When the lithium transition metal oxide is the compound, while exhibiting high capacity characteristics, it may exhibit excellent rate characteristics, output characteristics and thermal stability.

The coating layer may be formed on the surface of the lithium transition metal oxide and include phosphoric acid represented by Formula 2 below.

[Formula 2]

P _y1 M ¹ _w1 O _z1

In Formula 2, M ¹ is at least one selected from the group consisting of Al, Ti, La, Zr, V, and Ge, and 0 <y1 <4, 0 ≦ w1 <8, 0 <z1 <13.

Preferably, the phosphate is PO ₄ , Ti ₂ PO ₄ , VOPO ₄ , V ₂ (PO ₄ ) ₃ , Zr ₂ (PO ₄ ) ₃ , Ge ₂ (PO ₄ ) ₃ and Al _{0 . 0 .7} Ti ₃ (PO _{4) 3} may be at least one phosphate compound selected from the group consisting of. Particularly, when the phosphorus oxide is PO ₄ , structural stability and thermal stability and chemical stability are excellent, and thus, when the phosphorus oxide is PO ₄ , structural stability may be improved.

In addition, the coating layer according to the present invention may be formed on the surface of the lithium transition metal oxide, and may exhibit a structurally stable PO ₄ phase. The coating layer does not form a PO ₄ phase and represents another PO phase or Li-M ¹ -PO phase (wherein M is at least one selected from the group consisting of Ti, V, Al, Z and Ge) When only the phase of, the surface and structural stability of the positive electrode active material may be inferior to that of the PO ₄ phase on the surface as shown in the present invention.

The phase present on the surface of the positive electrode active material is formed on the surface of the lithium transition metal oxide by X-ray photoelectron spectroscopy using an X-ray photoemission spectroscopy (ESCALAB250, ThermoFisher) device. The formed coating layer can be analyzed.

In addition, the thickness of the coating layer may be 3nm to 20nm, preferably 5nm to 10nm, may be formed by coating evenly on the surface of the lithium transition metal oxide. For example, when the thickness of the coating layer satisfies the above range, the contact area between the positive electrode active material and the electrolyte may be reduced, so that side reactions may be suppressed, and the stability thereof may be further increased when applied to the battery.

In the cathode active material according to the present invention, lithium by-products present on the surface of the cathode active material may be included in an amount of 0.33% by weight to 0.46% by weight, preferably 0.33% by weight to 0.40% by weight, based on the total weight of the cathode active material. have. When the lithium by-product content is included in the above range on the surface of the positive electrode active material as in the present invention, the stoichiometric imbalance between lithium and the transition metal due to the decrease in the lithium content present on the surface of the lithium transition metal oxide, and thus the initial capacity reduction The risk can be reduced.

anode

In addition, there is provided a cathode for a lithium secondary battery, which includes a cathode active material manufactured by the method for producing a cathode active material according to the present invention. Specifically, the positive electrode for a secondary battery includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material according to the present invention.

In this case, since the cathode active material is the same as described above, a detailed description thereof will be omitted, and only the remaining configurations will be described below.

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

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

In this case, the cathode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98.5 wt%, based on the total weight of the cathode active material layer. When included in the above content range may exhibit excellent capacity characteristics.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any conductive material can be used without particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used. The conductive material may be included in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

The binder serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, carboxymethyl cellulose Woods (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, Styrene butadiene rubber (SBR), fluorine rubber, various copolymers thereof, and the like, and one or a mixture of two or more of them may be used. The binder may be included in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material described above. Specifically, the positive electrode active material and optionally, a composition for forming a positive electrode active material layer prepared by dissolving or dispersing a binder and a conductive material in a solvent may be applied onto a positive electrode current collector, followed by drying and rolling.

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

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

Lithium secondary battery

In addition, the present invention can manufacture an electrochemical device comprising the positive electrode. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

Specifically, the lithium secondary battery includes a positive electrode, a negative electrode positioned to face the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is the same as described above, and thus, a detailed description thereof will be omitted. Hereinafter, only the remaining configurations will be described in detail.

In addition, the lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, the separator, and a sealing member for sealing the battery container.

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

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of 3 μm to 500 μm, and similarly to the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

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

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

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

The binder is a component that assists the bonding between the conductive material, the active material and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Low ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber, various copolymers thereof and the like.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

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

The negative electrode active material layer is, for example, coated with a negative electrode active material, and optionally a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a binder and a conductive material in a solvent and dried, or for forming the negative electrode active material layer The composition may be prepared by casting the composition on a separate support, and then laminating the film obtained by peeling from the support onto a negative electrode current collector.

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

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

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

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

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _{2 .} LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

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

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, portable devices such as mobile phones, laptop computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, square, pouch type, or coin type using a can.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Example  One

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 .} 270 g of ₂ O ₂ was mixed with 3 g of Li ₃ PO ₄ , followed by heat treatment at 800 ° C. for 3 hours to prepare a cathode active material having a 5 nm PO ₄ coating layer formed on the surface of the lithium transition metal oxide.

The positive electrode active material: carbon black conductive material: polyvinylidene fluoride binder prepared above was mixed in an N-methylpyrrolidone solvent at a weight ratio of 95: 2.5: 2.5 to prepare a composition for forming a positive electrode. This was applied onto an aluminum current collector having a thickness of 20 μm, dried, and roll pressed to prepare a positive electrode.

Electrode assembly was prepared by stacking the positive electrode and the lithium metal prepared above with a separator (Celgard Co., Ltd.), and then, put the same into a battery case and ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC). An electrolyte solution in which 1 M of LiPF ₆ was dissolved was mixed into a mixed solvent mixed at a volume ratio of 40:30:30 to prepare a lithium secondary battery.

Example  2

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 .} 270 g of ₂ O ₂ was mixed with 5.7 g of Li ₃ PO _4, and then heat-treated at 800 ° C. for 3 hours to prepare a cathode active material having a 12 nm PO ₄ coating layer formed on the surface of the lithium transition metal oxide, and using the same. Then, using the same method as in Example 1 to prepare a positive electrode and a lithium secondary battery comprising the same.

Comparative example  One

LiNi ₀ without a coating layer as a positive electrode active material _{. 6} Co _{0 . 2} Mn _{0 .} Except that ₂ O ₂ was used, a positive electrode and a lithium secondary battery including the same were prepared using the same method as Example 1 above.

Comparative example  2

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . A} positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that ₂ O ₂ was heat-treated at 800 ° C. for 3 hours and used as a cathode active material.

Comparative example  3

In forming the coating layer, LiNi _{0 . 6} Co _{0 . 2} Mn _{0 .} After mixing 270 g of ₂ O _{2 with} 1.5 g of H ₃ PO _4, and then heat-treating at 350 ° C. for 3 hours, a positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1. .

Comparative example  4

In forming the coating layer, LiNi _{0 . 6} Co _{0 . 2} Mn _{0 .} 270 g of ₂ O ₂ was mixed with 3 g of Li ₃ PO _4, and then a positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1 except for heat treatment at 350 ° C. for 3 hours.

Comparative example  5

1.5 g of LiH ₂ PO ₄ was dissolved in a H ₂ O solvent to prepare a coating solution having a pH of 5. 270 g of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ was mixed with the coating solution and dried to form a coating layer on the surface of the LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , except that the same as in Example 1 was used. Using the method, a positive electrode and a lithium secondary battery including the same were prepared.

Comparative example  6

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 .} After mixing 270 g of ₂ O ₂ with 1 g of LiOH, except for heat treatment at 800 ° C. for 3 hours, a positive electrode and a lithium secondary battery including the same were prepared in the same manner as in Example 1.

Experimental Example  1: of positive electrode active material Photoelectron spectroscopy ( XPS )

With respect to the positive electrode active material prepared in Example 1, the coating layer formed on the surface of the lithium transition metal oxide by X-ray photoelectron spectroscopy using an X-ray photoelectron spectroscopy apparatus (ESCALAB250, ThermoFisher), XPS analysis results Is shown in FIG.

As a result, in the case of the cathode active material prepared in Example 1, it was confirmed that the PO ₄ peak appears at 133.6 eV.

Through this, in the case of the positive electrode active material prepared in Example 1, Li of the Li ₃ PO ₄ source used to form the coating layer is introduced into the lithium transition metal oxide, it can be confirmed that only the PO _{4 on the} surface to form a coating layer. there was.

Experimental Example  2: Determination of lithium byproduct content of the positive electrode active material

In order to measure the amount of lithium byproducts present on the surfaces of the cathode active materials prepared in Examples 1 to 2 and Comparative Examples 1 to 6, pH titration was performed. Specifically, using a Metrohm pH meter, the pH was recorded by titration with 0.1 mL HCl 1mL each, it is shown in Table 1 below.

Li ₂ CO ₃ Content (wt%) Li ₂ CO ₃ content (%) compared to Comparative Example 1 LiOH content (wt%) LiOH content (%) compared to Comparative Example 1 Total Li content (wt%) Total Li content (%) compared to Comparative Example 1 Example 1 0.257 61.33 0.103 66.45 0.360 62.72 Example 2 0.271 64.68 0.116 74.84 0.387 67.42 Comparative Example 1 0.419 Ref. 0.155 Ref. 0.574 Ref. Comparative Example 2 0.190 45.35 0.097 62.58 0.287 50 Comparative Example 3 0.375 89.50 0.120 77.42 0.495 86.24 Comparative Example 4 0.347 82.82 0.123 79.35 0.470 81.88 Comparative Example 5 0.485 115.75 0.025 16.13 0.510 88.85

As shown in Table 1 above, when the same lithium transition metal oxide is subjected to high temperature heat treatment as in Comparative Example 2 as compared with the case where no separate coating layer is formed on the surface of the lithium transition metal oxide as in Comparative Example 1, the lithium transition metal It was confirmed that lithium by-products present on the surface of the oxide were volatilized, thereby reducing the content of lithium by-products present on the surface. On the contrary, when the lithium transition metal oxide and the lithium phosphate source are mixed and heat treated as in Examples 1 and 2 of the present application, lithium ions in the lithium phosphate source are added to the lithium transition metal oxide, thereby partially supplementing the amount of volatilized lithium. I could confirm that. In addition, in the case of the cathode active material prepared in Comparative Examples 3 to 4, since the coating layer was formed through low temperature heat treatment, it was not possible to achieve the effect of removing lithium by-products due to high temperature heat treatment. there was. In Comparative Example 5, a relatively high dissociation of lithium ions in the lithium transition metal oxide is caused by the high acidity of the coating source in the anode wet coating step, and the dissociated lithium ions react with CO or CO ₂ in the air during drying and heat treatment. Carbonized to form Li ₂ CO ₃ , so the lithium by-product content was high.

Experimental Example  3: Charge and discharge  Efficiency evaluation

The life characteristics of each of the lithium secondary batteries manufactured in Examples 1 to 2 and Comparative Examples 1 to 6 were measured.

Specifically, the lithium secondary batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 6 were charged to 4.4V at 0.2C constant current at 25 ° C., respectively, and discharged to 3V at 0.2C constant current. Charge and discharge characteristics were observed in the first cycle. Then, the charge and discharge capacity according to C-rate was measured by changing the discharge conditions, and the results are shown in Table 2 below.

First charge capacity
(mAh / g) First discharge capacity
(mAh / g) efficiency
(%) 1.0C
(mAh / g) 2.0C
(mAh / g) Example 1 213.46 190.38 89.19 180.19 173.37 Example 2 212.0 188.6 88.9 177.5 171.8 Comparative Example 1 211 185 87.5 173.7 167 Comparative Example 2 209.7 182.8 87.2 171.7 165.7 Comparative Example 3 210.88 184.80 87.63 174.30 168.16 Comparative Example 4 210.6 183.1 86.9 172.2 165.3 Comparative Example 5 207.67 181.36 87.33 168.93 161.45 Comparative Example 6 211.9 189.6 89.5 179.1 173.6

As shown in Table 2, in the case of the secondary batteries manufactured in Examples 1 and 2, it was confirmed that the initial capacity, 1C discharge capacity, 2C discharge capacity, etc. are superior to the secondary batteries manufactured in Comparative Examples 1-5. . This, the secondary battery prepared in Examples 1 to 2 by performing a heat treatment at a high temperature using a coating source containing lithium when forming a coating layer, by containing lithium volatilized on the surface of the lithium transition metal oxide, the coating source It was confirmed that the lithium is replaced by the initial capacity is not lowered, showing excellent charge and discharge efficiency and discharge capacity.

On the other hand, in the case of the secondary batteries manufactured in Comparative Examples 1 and 2, the excessive amount of lithium present on the surface of the lithium transition metal oxide is removed by high temperature heat treatment, resulting in damage to the surface, thereby increasing initial capacity and charge and discharge efficiency. Degraded. In addition, in the case of the secondary batteries manufactured in Comparative Examples 3 to 4, the effect of removing lithium by-products is inferior because the heat treatment is performed at a low temperature. The capacity was inferior to Examples 1 and 2 above. In addition, in the case of the secondary battery manufactured in Comparative Example 5, by forming a coating layer on the surface of the lithium transition metal oxide through a wet process, surface damage of the positive electrode active material occurred due to the pH (showing acidity) of the wet coating source. Due to this, the initial capacity and the charge / discharge efficiency of the battery were lower than those of Examples 1 to 2 above.

On the other hand, in the secondary battery manufactured in Comparative Example 6, by mixing the lithium transition metal oxide and lithium hydroxide and heat treatment at a high temperature, the lithium ions contained in the lithium hydroxide volatilized lithium present on the surface of the lithium transition metal oxide In place, the initial capacity was not lowered, indicating a charge and discharge efficiency equivalent to that of the present invention.

Experimental Example  4: Life characteristic evaluation

The life characteristics of each of the lithium secondary batteries manufactured in Examples 1 to 2 and Comparative Examples 1 to 6 were measured.

Specifically, the secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 6 were charged with 0.7 C cut off to 45 V at 0.2 C constant current at 45 ° C., respectively. Then, discharge was performed until it became 3.0V by 0.5C constant current. After repeating this cycle 100 times with the charge and discharge behavior as one cycle, the capacity retention ratios of the lithium secondary batteries according to Examples 1 and 2 and Comparative Examples 1 to 6 were measured. Shown in

life span (%) Example 1 95.9 Example 2 96.4 Comparative Example 1 92.4 Comparative Example 2 91.6 Comparative Example 3 86.1 Comparative Example 4 90.9 Comparative Example 5 91.6 Comparative Example 6 92.4

As shown in FIG. 2 and Table 3, in the case of the secondary batteries manufactured in Examples 1 and 2, the structural stability is improved by recrystallization of the lithium transition metal oxide due to high temperature heat treatment and the formation of a coating layer having excellent stability on the surface. As compared with the secondary batteries manufactured in Comparative Examples 1 to 6, it was confirmed that the capacity retention ratio was more excellent.

Experimental Example  5: stability evaluation

The stability of each of the lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 was evaluated. Specifically, the secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were continuously charged for 120 hours at 50 ° C. to 4.7 V at 0.2 C constant current, respectively, and observed changes in voltage and leakage current values. , And their average current is shown in FIG. 3 and Table 4 below. In addition, after continuous charging for 120 hours, the discharge was carried out until the 3.0V at a constant current of 0.2C, and charged again to 0.2C, and then evaluated its capacity recovery rate compared to the first discharge capacity, which is shown in Table 4 below. It was.

Average Current (mA = mAh / 120hr) Initial capacity
(mAh / g) Capacity after 120 hours of charging (mAh / g) Capacity recovery rate (%) Example 1 0.016 191.3 181.3 94.8 Example 2 0.009 188.6 186.5 98.9 Comparative Example 1 1.041 185.2 - 0 Comparative Example 2 0.358 181.9 153 84.1

As shown in Table 4 and FIG. 3, in the case of secondary batteries manufactured in Examples 1 and 2, when the charging was continuously performed for 120 hours with an average current value of 0.016 under high temperature and high voltage (that is, when overcharging), It was confirmed that it has a low current value. This is because there is no area in which the current rapidly changes during overcharging, and thus a short circuit does not occur when applied to an actual place. On the other hand, in the case of the secondary batteries manufactured in Comparative Examples 1 and 2, it was confirmed that the current rapidly changes after 40 hours. Therefore, in the case of the secondary batteries manufactured in Comparative Examples 1 and 2, since the structural stability of the positive electrode active material is inferior to those of Examples 1 and 2, when overcharging is performed for 120 hours, a short circuit of the battery due to a rapid current rise It was predicted that fires and explosions would occur.

On the other hand, after performing the overcharge, the battery was discharged to evaluate the recovery capacity of the battery.

As shown in Table 4, in the case of the secondary batteries manufactured in Examples 1 to 2, it was confirmed that exhibits a capacity recovery rate of 94% or more.

On the other hand, in the case of the secondary battery manufactured in Comparative Example 1, it could not be used due to the ignition or explosion of the battery during overcharging. In the case of the secondary battery manufactured in Comparative Example 2, the battery did not ignite or explode when overcharged, but the initial capacity was lowered due to inferior structural stability than the secondary batteries prepared in Examples 1 to 2, and the capacity recovery rate was also inferior. It was confirmed that.

Experimental Example  6: gas generation measurement

Gas generation amount was measured for each of the lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Example 1. Specifically, after charging the secondary batteries prepared in Examples 1 and 2 and Comparative Example 1 to 4.4V at 0.2C constant current, respectively, the cell was disassembled and a positive electrode and a predetermined amount of electrolyte were placed in a pouch. After sealing the pouch, while storing for 290 hours at 60 ℃ was measured the amount of gas generated every time. The high temperature storage characteristics were compared with each other by comparing the measured values, which are shown in FIG. 4.

As shown in FIG. 4, in the case of the secondary battery manufactured in Comparative Example 1, it was confirmed that a large amount of gas was generated in comparison with the secondary batteries manufactured in Examples 1 and 2 during high temperature storage. This, as confirmed through Experimental Example 2, in the case of the secondary battery prepared in Comparative Example 1, there were more lithium by-products remaining on the surface than the secondary battery prepared in Examples 1 to 2, and thus When charging and discharging, the area where side reactions occur with the electrolyte was widened, and the amount of gas generated was also increased.

Claims (10)

Preparing a lithium transition metal oxide including 60 mol% or more of nickel based on the total moles of transition metal oxides other than lithium; And
Mixing the lithium transition metal oxide and a coating source including lithium represented by Chemical Formula 1 and performing a heat treatment at 500 ° C. to 900 ° C. to form a coating layer including phosphate on the surface of the lithium transition metal oxide; Method for producing a positive electrode active material comprising:
[Formula 1]
Li _x P _y M ¹ _w O _z
In Chemical Formula 1,
M ¹ is at least one selected from the group consisting of Al, Ti, La, Zr, V, and Ge,
0 <x <4, 0 <y <4, 0≤w <8, 0 <z <13.
The method of claim 1,
The coating source containing lithium is Li ₃ PO ₄ , Li _x Zr _w (PO ₄ ) _{3 ,} Li _x V _w (PO ₄ ) ₃ , Li _x Ge _w (PO ₄ ) ₃ , Li _x Ti _w (PO ₄ ) ₃ , Li _x Al _w1 Ti _w2 (PO ₄ ) ₃ (where 0 <w1 + w2 <8), Li _x Al _w1 Ge _w2 (PO ₄ ) ₃ (where 0 <w1 + w2 <8) , (LiAlTiP) _x1 O _z (where 0 <x1 <4) and Li _x La _w TiO ₃ , at least one or more selected from the group consisting of methods for producing a positive electrode active material.
The method of claim 1,
The coating source comprising lithium has a lithium ion conductivity of 1 × 10 ⁻⁸ S / cm to 1 × 10 ⁻² S / cm.
The method of claim 1,
The lithium ion contained in the coating source containing lithium by the heat treatment is input to the lithium transition metal oxide, the method of producing a positive electrode active material.
The method of claim 1,
Regarding the total weight of the lithium transition metal oxide, the coating source including lithium is mixed in an amount of 1 part by weight to 20 parts by weight, and a method of manufacturing a positive electrode active material.
The method of claim 1,
The coating layer is a method of producing a positive electrode active material comprising a phosphate represented by the formula (2).
[Formula 2]
P _y1 M ¹ _w1 O _z1
In Chemical Formula 2,
M ¹ is at least one selected from the group consisting of Al, Ti, La, Zr, V, and Ge,
0 <y1 <4, 0 ≦ w1 <8, 0 <z1 <13.
Lithium transition metal oxides containing at least 60 mol% nickel based on the total moles of transition metals other than lithium; And
It includes; a coating layer comprising a phosphate formed on the surface of the lithium transition metal oxide,
The coating layer is a positive electrode active material, when the analysis by X-ray photoelectron spectroscopy, the PO ₄ peak appears at 130 eV to 135 eV.
The method of claim 7, wherein
The coating layer has a thickness of 1 nm to 20 nm.
A cathode for a lithium secondary battery, comprising the cathode active material according to claim 7.
A lithium secondary battery comprising the positive electrode according to claim 9.

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