KR20210100526A - Positive electrode active material for lithium secondary battery, positive electrode including same, and lithium secondary battery including same - Google Patents

Abstract

A cathode active material for a lithium secondary battery including a lithium composite metal oxide represented by Formula 1, and a surface layer formed on the surface of the lithium composite metal oxide and including an airgel, and a cathode and a lithium secondary battery including the same are provided. Formula 1 is described in the detailed description.

Description

Positive electrode active material for lithium secondary battery, positive electrode including same, and lithium secondary battery including same

A cathode active material for a lithium secondary battery, and a cathode and a lithium secondary battery including the same.

With the development of portable electronic devices and communication devices, there is a high need for the development of a lithium secondary battery having a high energy density.

As a cathode active material of a lithium secondary battery, lithium cobalt oxide, lithium nickel cobalt aluminum composite oxide, lithium nickel manganese cobalt composite oxide, and the like are used.

However, as the positive electrode active material comes into contact with external substances such as electrolyte, moisture, and carbon dioxide at a high temperature, there is a risk of generating a gas such as oxygen or a side reaction material such as lithium hydroxide and lithium salt, which are electrochemically inactive materials. Since the side reaction material reduces the lifespan characteristics and thermal stability of the positive electrode active material, it is necessary to block direct contact of the electrolyte or external materials with the positive electrode active material during charging and discharging.

An object of the present invention is to provide a positive electrode active material for a lithium secondary battery having excellent lifespan characteristics and cell resistance characteristics, and a positive electrode including the same.

In addition, an object of the present invention is to provide a lithium secondary battery excellent in both lifespan characteristics and cell resistance characteristics by having a positive electrode including the above-described positive electrode active material.

According to one embodiment, there is provided a cathode active material for a lithium secondary battery comprising a lithium composite metal oxide represented by Chemical Formula 1, and a surface layer formed on the surface of the lithium composite metal oxide and including an airgel.

[Formula 1]

Li _a (Ni _x M' _y M" _z )O ₂

In Formula 1, M' is at least one element selected from the group consisting of Co, Mn, Ni, Al, Mg and Ti, and M" is Ca, Mg, Al, Ti, Sr, Fe, Co, Mn , Ni, Cu, Zn, Y, Zr, Nb, and at least one element selected from the group consisting of B, 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4 and x+y+z=1.

According to another embodiment, there is provided a method of manufacturing a cathode active material for a lithium secondary battery comprising drying the airgel particles, and forming a surface layer including the dried airgel particles on the surface of the lithium composite metal oxide.

According to another embodiment, a positive electrode including the above-described positive electrode active material for a lithium secondary battery, and a lithium secondary battery including the same are provided.

It is possible to provide a positive electrode active material for a lithium secondary battery having excellent lifespan characteristics and cell resistance characteristics, and a positive electrode including the same.

In addition, it is possible to provide a lithium secondary battery excellent in both lifespan characteristics and cell resistance characteristics by providing a positive electrode including the above-described positive electrode active material.

1 schematically shows a cathode active material for a lithium secondary battery according to an embodiment.
2 schematically shows the structure of a lithium secondary battery having a positive electrode including a positive electrode active material according to an exemplary embodiment.
3 shows a transmission election microscope (TEM) image of a cathode active material for a lithium secondary battery according to an exemplary embodiment.
4 shows the results of X-ray diffraction analysis of the positive active material for a lithium secondary battery according to Example 1 and Comparative Example.
5 is a graph showing the lifespan characteristics of a coin half cell including a positive active material for a lithium secondary battery according to Example 1 (solid line) and Comparative Example (dotted line), respectively.
6 is a graph showing the cell resistance characteristics of the coin half cell including the positive active material for a lithium secondary battery according to Example 1 and Comparative Example.

Hereinafter, with reference to the accompanying drawings, the embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

In various embodiments, components having the same configuration will be typically described in one embodiment using the same reference numerals, and only configurations different from the one embodiment will be described in other embodiments.

In one embodiment, with respect to the size and particle diameter of various particles, there is a method of expressing the average size of a group by quantifying it by a metrology method, but it is universally used and the mode diameter indicating the maximum value of the distribution, the median value of the integral distribution curve There are median diameters and various average diameters (number average, length average, area average, mass average, volume average, etc.) corresponding to , means that D50 (particle diameter at the point where the distribution rate is 50%) was measured.

Hereinafter, a positive active material for a lithium secondary battery according to an embodiment will be described.

1 schematically shows a cathode active material for a lithium secondary battery according to an embodiment. Referring to FIG. 1 , a positive active material 11 for a lithium secondary battery according to an exemplary embodiment may include a lithium composite metal oxide 12 and a surface layer 13 formed on the lithium composite metal oxide 12 .

The lithium composite metal oxide 12 may include a lithium nickel-based oxide. Specifically, the lithium composite metal oxide 12 may be represented by Formula 1 below.

[Formula 1]

Li _a (Ni _x M' _y M" _z )O ₂

In Formula 1, M' is at least one element selected from the group consisting of Co, Mn, Ni, Al, Mg and Ti, and M" is Ca, Mg, Ba, Al, Ti, Sr, Fe, Co , Mn, Ni, Cu, Zn, Y, Zr, Nb, and at least one element selected from the group consisting of B, 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ It may have a range of z ≤ 0.4 and x + y + z = 1. The lithium composite metal oxide 12 represented by Formula 1, specifically, a lithium nickel-based oxide having a nickel content of 60 mol% or more is used as a positive electrode active material ( 11), it is possible to realize a lithium secondary battery having a high capacity and excellent electrochemical properties such as rate characteristics.

For example, the lithium composite metal oxide 12 may be a lithium nickel-based oxide represented by Formula 2 below.

[Formula 2]

Li _a (Ni _x Co _y M" _z )O ₂

In Formula 2, M" is at least one element selected from the group consisting of Al, Mg, Ba, Ti, Zr, Y, and Mn, and 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, and x+y+z = 1. Meanwhile, in Formula 2, M″ may be Al, 0.8 < a ≤ 1.3, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2 and x+y+z=1.

The three-component lithium nickel cobalt aluminum oxide or lithium nickel cobalt manganese oxide represented by Formula 2 has high capacity of lithium nickel oxide, thermal stability and economy of lithium aluminum (manganese) oxide, and stable electrochemical properties of lithium cobalt oxide By combining the above advantages, excellent battery characteristics can be exhibited.

The surface layer 13 may include an airgel. Since the positive electrode active material 11 according to this embodiment forms the surface layer 13 with airgel, the damage applied to the active material when the surface layer 13 is formed is small, and the side reaction with the electrolyte is suppressed and the cell resistance is improved. Life characteristics can be improved.

In one embodiment, the airgel included in the surface layer 13 may be a hydrophobic airgel. For example, in one embodiment, the airgel may include a hydrophobic airgel. The surface layer 13 may contain, for example, 0.05 wt% to 3 wt%, for example 0.1 wt% to 3 wt%, based on 100 wt% of the lithium composite metal oxide 12. When the surface layer 13 in the positive electrode active material 11 is contained within the above range, the lithium composite metal oxide 12 is treated with an electrolyte solution, moisture, carbon dioxide, etc. without interfering with the charge/discharge reaction of the lithium composite metal oxide 12 . can be effectively protected from

The proportion of airgel in the surface layer 13 may be, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, and even 100% by weight. When the ratio of the airgel in the surface layer 13 is the same as above, it is possible to effectively protect the lithium composite metal oxide from external substances such as electrolyte, moisture, and carbon dioxide without interfering with the charge/discharge reaction of the lithium composite metal oxide.

In one embodiment, the surface layer 13 may be hydrophobic. The hydrophobicity of the surface layer 13 may be due to hydrophobic airgel. In one embodiment, the hydrophobicity of the surface layer 13 may be due to the hydrophobic airgel. Due to the hydrophobic surface, it is possible to suppress structural collapse of the positive electrode active material due to moisture.

In one embodiment, the surface layer 13 may cover at least a part of the surface of the lithium composite metal oxide 12, or may cover the entire surface. When the surface layer 13 covers the entire surface of the lithium composite metal oxide 12 , the lithium composite metal oxide 12 can be effectively protected from external substances such as electrolyte, moisture, and carbon dioxide. In addition, the surface layer 13 may be formed in the form of a film or an island covering all or a part of the lithium composite metal oxide 12 .

In one embodiment, the thickness of the surface layer 13 may vary depending on the size, material, material of the airgel, the degree of hydrophobicity of the airgel, etc. of the lithium composite metal oxide 12, for example, from 20 nm to 70 nm, for example 30 nm to 70 nm, for example about 50 nm. When the thickness of the surface layer 13 is within the above range, the lithium composite metal oxide 12 can be effectively protected from external substances such as electrolyte, moisture, and carbon dioxide without interfering with the charge/discharge reaction of the lithium composite metal oxide 12. there is.

In one embodiment, the specific surface area of the airgel may vary depending on the material of the airgel, the size of the airgel particles used, etc., but for example, 80 m ² /g to 300 m ² /g, for example 100 m ² /g to 300 m ² /g, for example 150 m ² /g to 250 m ² /g, for example about 200 m ² /g. When the specific surface area of the airgel satisfies the aforementioned range, the positive active material 11 for a lithium secondary battery according to an embodiment may exhibit excellent lithium ion conductivity. The specific surface area of the airgel may be measured using a known Brunauer-Emmett-Teller (BET) specific surface area measuring device.

In one embodiment, the average particle diameter of the airgel particles may vary depending on the thickness of the surface layer 13, the material of the airgel, the degree of hydrophobicity of the airgel, etc., but for example, 5 nm to 50 nm, for example 20 nm to 40 nm , for example about 30 nm.

In one embodiment, the airgel may include silica (SiO ₂ ) airgel. For example, the airgel may be a silica airgel. When the surface layer 13 is formed using silica airgel, the lifespan characteristics and cell resistance of the battery can be improved. Silica airgel can be prepared using a method such as washing/drying silica wet gel. Alternatively, a silica airgel having a high degree of hydrophobization may be prepared by hydrophobizing the silica airgel. Silica airgel is a relatively easily available material, and if the silica airgel treated to have hydrophobicity is used, the surface layer 13 having high hydrophobicity can be formed at a relatively low cost. However, the scope of the present invention is not limited thereto , and the hydrophobic airgel according to an embodiment may include an airgel made of various materials processed to have hydrophobicity, for example, hydrophobicized carbon airgel, and the like.

As described above, the positive electrode active material 11 according to the exemplary embodiment forms a hydrophobic surface layer 13 on the surface of the lithium composite metal oxide 12, thereby preventing the lithium composite metal oxide 12 from external materials such as electrolyte, moisture, and carbon dioxide. can protect As a result, the occurrence of side reactions from the lithium composite metal oxide 12 is minimized, so that the positive electrode active material 11 having excellent lifespan characteristics and cell resistance characteristics can be manufactured.

Hereinafter, a method of manufacturing a cathode active material according to an exemplary embodiment will be described.

The method of manufacturing the positive active material according to the present embodiment includes drying the airgel particles, and forming a surface layer 13 including the dried airgel particles on the surface of the lithium composite metal oxide 12 .

First, the airgel particles are prepared by the method as described above, or are commercially available. Examples of usable airgel particles include, but are not limited to, silica airgel particles. In addition, the airgel particles may be subjected to a separate hydrophobization treatment or airgel particles subjected to hydrophobization treatment may be used. The hydrophobization treatment may be performed by a conventional method known in the art, and may be performed prior to the drying.

First, drying is performed on the prepared airgel particles. Residual moisture inside the airgel particles can be removed through drying, and direct contact of the residual moisture inside the airgel particles with the lithium composite metal oxide 12 in a subsequent coating process can be prevented.

In one embodiment, the drying temperature may vary depending on the material, size, residual moisture, etc. of the airgel particles, but may be performed at, for example, 50 ℃ or more, 60 ℃ or more, 70 ℃ or more, for example, 120 ℃ or less, It may be carried out at 110 °C or less, 100 °C or less, 90 °C or less, for example, at 50 °C to 120 °C, for example at 60 °C to 120 °C, for example at 80 °C.

In one embodiment, the drying time may vary depending on the material, size, residual moisture content, drying temperature, etc. of the airgel particles, but may be performed for, for example, 1 hour or more, 2 hours or more, 3 hours or more, for example, 8 hours or less , can be carried out for less than 7 hours, for example, 1 hour to 8 hours, for example, 3 hours to 7 hours, for example, it can be carried out for about 5 hours.

Thereafter, a surface layer 13 including dried airgel particles is formed on the lithium composite metal oxide 12 . Specifically, the dried airgel particles and the lithium composite metal oxide 12 are mixed in a predetermined ratio so that the dried airgel particles can be located on all or at least a part of the surface of the lithium composite metal oxide 12 . As the lithium composite metal oxide 12, the lithium nickel-based oxide as described above may be used, and specifically, the compound represented by Formula 1 may be used, for example, the compound represented by Formula 2 may be used. The lithium nickel-based oxide 12 may be synthesized by a method known in the art, and accordingly, a description of the synthesis method will be omitted. Meanwhile, in the mixing process, the mixing ratio of the airgel particles and the lithium composite metal oxide 12 may be 0.001:1 to 0.02:1 based on the weight ratio. Through this, the surface layer 13 covering at least a portion of the surface of the lithium composite metal oxide 12 may be formed using the airgel particles. In the mixing process, the mixing speed may be adjusted, for example, from 1000 rpm to 5000 rpm, for example, about 3000 rpm.

When the mixing speed is less than 1000 rpm, there is a risk that the airgel particles are not uniformly attached to the surface of the lithium composite metal oxide 12, so that the surface layer may not be formed uniformly, and when it exceeds 5000 rpm, the lithium composite metal oxide 12 There is a risk of cracking during this mixing.

In one embodiment, the mixing process of the airgel particles and the lithium composite metal oxide 12 is performed in a dry atmosphere. Through this, it is possible to prevent direct contact of moisture with the lithium composite metal oxide 12 during the mixing process, and since it proceeds in a non-aqueous condition, the post-heat treatment process can be omitted. In one embodiment, the mixing process of the airgel particles and the lithium composite metal oxide 12 may be performed at room temperature. Accordingly, the overall mixing process can be easily controlled.

On the other hand, in the mixing process of the airgel particles and the lithium composite metal oxide 12, it is possible to form the surface layer 13 even by mixing only the airgel particles and the lithium composite metal oxide 12 without other additives. Through this, the overall mixing process can be maintained in a non-aqueous condition, and there is no need to remove unreacted substances and side-reacted substances after the mixing process. Therefore, the cleaning process can be omitted.

As described above, in the method for manufacturing the positive active material according to one embodiment, the positive active material 11 can be manufactured even by a process of mixing airgel particles and lithium metal oxide 12 at room temperature without a separate additive, so the overall process control is relatively simple and the process reproducibility is excellent.

On the other hand, in the positive active material manufacturing method according to the exemplary embodiment, since the entire process maintains the non-aqueous process at room temperature, it is possible to prevent deterioration of the performance of the lithium composite metal oxide 12 due to moisture during the process. In addition, since a post-heat treatment process is not required, side reactions that may occur on the surface of the completed positive electrode active material 11 can be prevented.

In addition, the positive active material 11 manufactured by using the method for manufacturing the positive active material according to the exemplary embodiment may exhibit excellent lifespan characteristics and cell resistance characteristics as described above.

Hereinafter, the structure and manufacturing method of a lithium secondary battery having a positive electrode including a positive electrode active material according to an embodiment will be described.

2 schematically shows the structure of a lithium secondary battery having a positive electrode including a positive electrode active material according to an exemplary embodiment.

The lithium secondary battery 21 of FIG. 2 includes a positive electrode 23 , a negative electrode 22 , and a separator 24 containing a positive electrode active material according to an exemplary embodiment.

The positive electrode 23 and the negative electrode 22 are manufactured by respectively coating and drying a composition for forming a positive electrode active material layer and a composition for forming a negative electrode active material layer on a current collector.

The composition for forming a cathode active material layer is prepared by mixing a cathode active material, a conductive agent, a binder, and a solvent, and the cathode active material 11 according to the above-described embodiment is used as the cathode active material.

The binder is a component that assists in bonding of the active material and the conductive agent and bonding to the current collector, and is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. Non-limiting examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro ethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers, and the like. The content is used in an amount of 2 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the binder is within the above range, the binding force of the active material layer to the current collector is good.

The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

The amount of the conductive agent is used in an amount of 2 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the conductive agent is within the above range, the conductivity characteristics of the finally obtained electrode are excellent.

As a non-limiting example of the solvent, N-methylpyrrolidone and the like are used.

The amount of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the solvent is within the above range, the operation for forming the active material layer is easy.

The positive electrode current collector has a thickness of 3 μm to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, heat-treated carbon , or a surface treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven body are possible.

Separately, a composition for forming an anode active material layer is prepared by mixing the anode active material, a binder, a conductive agent, and a solvent.

As the negative active material, a material capable of occluding and releasing lithium ions is used. Non-limiting examples of the negative active material include graphite, carbon-based materials such as carbon, lithium metal, alloys thereof, silicon oxide-based materials, and the like. According to an embodiment of the present invention, silicon oxide is used.

The binder is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the negative active material. As a non-limiting example of such a binder, the same type as the positive electrode may be used.

The conductive agent is used in an amount of 1 to 5 parts by weight based on 100 parts by weight of the total weight of the negative active material. When the content of the conductive agent is within the above range, the conductivity characteristics of the finally obtained electrode are excellent.

The content of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the total weight of the negative active material. When the content of the solvent is within the above range, the operation for forming the anode active material layer is easy.

* The conductive agent and the solvent may be the same type of material as those used in manufacturing the positive electrode.

As the negative electrode current collector, it is generally made to have a thickness of 3 μm to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or a surface of copper or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

A separator is interposed between the positive electrode and the negative electrode manufactured according to the above process.

The separator has a pore diameter of 0.01 μm to 10 μm and a thickness of generally 5 μm to 300 μm. Specific examples include olefinic polymers such as polypropylene and polyethylene; Alternatively, a sheet or non-woven fabric made of glass fiber is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a non-aqueous electrolyte solution and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous electrolyte include, but are not limited to, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2- Dimethoxyethane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, Phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, An aprotic organic solvent such as ethyl propionate may be used.

Examples of the organic solid electrolyte include, but are not limited to, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and the like.

Examples of the inorganic solid electrolyte include, but are not limited to, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like may be used.

The lithium salt is a material easily soluble in the non-aqueous electrolyte, and includes, but is not limited to, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO _{2, LiAsF 6, LiSbF 6,} LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) ₂ NLi, lithium chloroborate, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, imide and the like can be used.

As described above, the positive electrode 23 , the negative electrode 22 , and the separator 24 are wound or folded and accommodated in the battery case 25 . Next, an organic electrolyte is injected into the battery case 25 and sealed with a cap assembly 26 , thereby completing the lithium secondary battery 21 as shown in FIG. 2 .

The battery case 25 may have a cylindrical shape, a square shape, a thin film shape, or the like. For example, the lithium secondary battery 20 may be a large-sized thin film type battery. The lithium secondary battery may be a lithium ion battery. A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, impregnated with an organic electrolyte, and the obtained result is accommodated in a pouch and sealed, a lithium ion polymer battery is completed. In addition, a plurality of the battery structure is stacked to form a battery pack, and the battery pack can be used in any device requiring high capacity and high output. For example, it can be used in a laptop, a smart phone, an electric vehicle, and the like.

In addition, since the lithium secondary battery has excellent storage stability, lifespan characteristics, and high rate characteristics at high temperatures, it can be used in electric vehicles (EVs). For example, it may be used in a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV).

Since the lithium secondary battery according to an embodiment uses the above-described positive electrode active material for a lithium secondary battery as a positive electrode active material, it may exhibit excellent lifespan characteristics and cell resistance characteristics.

In addition, the lithium secondary battery according to an embodiment reacts with moisture in the air, carbon dioxide, etc. when using lithium nickel cobalt aluminum oxide as a lithium composite metal oxide, for example, to generate NiO and oxygen, or to generate an inert material such as _{LiOH and LiCO 3} cases can be minimized. Accordingly, it is possible to form a positive electrode having both excellent electrochemical properties and stability with respect to a positive electrode active material having various compositions and a lithium secondary battery including the same.

Hereinafter, specific embodiments of the present invention are presented. However, the examples described below are only for specifically illustrating or explaining the present invention, and the present invention is not limited thereto. In addition, since the content not described here can be sufficiently technically inferred by a person skilled in the art, the description thereof will be omitted.

(Production of positive electrode active material)

Example One

Prepare hydrophobic silica airgel particles (Aladin Corporation, specific surface area 150 m ² /g to 200 m ² /g) having an average particle diameter of 30 nm. The prepared hydrophobic silica airgel particles were placed in an oven at 80 °C and -0.1 MPa and dried in a vacuum for about 5 hours.

Meanwhile, nickel cobalt aluminum metal composite hydroxide and lithium hydroxide (LiOH) in which Ni, Co, and Al have a molar ratio of 0.915:0.075:0.01 are mixed so as to have a molar ratio of Li/(Ni+Co+Al)=1.03 to 1.05. . The mixed material is placed in a crucible and then _{calcined in an oxygen (O 2} ) atmosphere at a temperature of 680 ° C. to 730 ° C., for example, 710 ° C. for 10 to 20 hours to obtain a calcined NCA material. The NCA material is LiNi _{0 . 915} Co _{0 . 075} Al _{0 . It} has a composition of 01 O _{2 .}

Thereafter, the vacuum-dried hydrophobic silica airgel particles and the NCA material are put into a glove box, and the weight ratio of the vacuum-dried hydrophobic silica airgel particles and the NCA material in the mixture satisfies 0.002:1. The weighed mixture was put into a ball-mill in a dry atmosphere at room temperature (25° C.), and then mixed at a speed of 3000 rpm for about 2 hours to prepare a cathode active material.

Example 2

A positive active material was prepared through the same process as in Example 1, except that a mixture in which the vacuum-dried hydrophobic silica airgel particles and the NCA material had a weight ratio of 0.001:1 was used.

Example 3

A positive electrode active material was prepared in the same manner as in Example 1, except that a mixture in which the vacuum-dried hydrophobic silica airgel particles and the NCA material had a weight ratio of 0.005:1 was used.

Example 4

A positive electrode active material was prepared in the same manner as in Example 1, except that a mixture in which the vacuum-dried hydrophobic silica airgel particles and the NCA material had a weight ratio of 0.01:1 was used.

comparative example

_{LiNi 0} , which is an NCA material synthesized in Example 1 above _{. 915} Co _{0 . 075} Al _{0 . 01} O ₂ was used as a positive electrode active material.

(Lithium secondary battery production)

The positive active materials obtained in Examples 1 to 4 and Comparative Examples were mixed with polyvinylidene fluoride (PVDF) and Denka black dissolved in N-methyl-2-pyrrolidone, respectively, in a mass ratio of 92:4:4. After that, it ^{was put in a centrifugal mixer (Thinky tm} mixer) and dispersed at a speed of 2000 r/min for about 15 minutes to obtain a slurry. The obtained slurry was applied to an Al thin film substrate in a uniform thickness, and then dried in a vacuum drying chamber at a temperature of 110° C. for 10 hours, and a positive electrode ^{having a loading weight of 8 mg/cm 2} to 10 mg/cm ² to obtain an electrode plate substrate. After the obtained positive electrode plate substrate was punched with a punching machine and processed into a circular positive electrode plate substrate having a diameter of 10 mm, it was rolled again at a pressure of 4 MPa, dried at a temperature of 110 ° C. get a pole

A coin-type half battery was manufactured using the obtained positive electrode plate as a positive electrode, and metallic lithium as a counter electrode of the positive electrode (CR2032 type). At this time, an electrolyte solution in which 1.15 M LiPF6 was dissolved in a solvent of ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) (EC:EMC:DMC=1:2:2 volume ratio) was used, and polyethylene (PE) was used. ) was used as a separator.

Evaluation 1: of the cathode active material TEM analysis

A transmission election microscope (TEM) image of Example 1 was observed and shown in FIG. 3 . Referring to FIG. 3 , it can be seen that a surface layer made of silica airgel is formed on the NCA material.

Although not all shown, in the positive active materials according to Examples 1 to 4 prepared, a surface layer including hydrophobic silica airgel covered the surface of the NCA material as shown in FIG. 1 .

Evaluation 2: X-ray diffraction analysis of the positive active material

The results of X-ray diffraction analysis of the positive active materials prepared in Example 1 and Comparative Example are shown in FIG. 4 .

Referring to FIG. 4 , it can be confirmed that Example 1 exhibits the same peak positions and peak intensity as those of Comparative Example despite further comprising a surface layer made of hydrophobic silica airgel compared to Comparative Example. Through this, even if the hydrophobic silica airgel according to the embodiment is coated, it can be confirmed that the structural change of the NCA material does not occur.

Also, referring to FIGS. 3 and 4 together, in Example 1, it can be confirmed that a surface layer made of hydrophobic silica airgel is formed on the surface of the NCA material without changing the structure of the NCA material.

Evaluation 3: Lifespan characteristics of lithium secondary batteries

The lithium secondary battery prepared in Example 1 and Comparative Example was charged with a constant current at 60 ° C. at a constant current of 1 C rate until the voltage reached 4.3 V, and the current was 0.005 C (1/200 C) while maintaining 4.3 V was charged at a constant voltage until Then, a cycle of discharging at a constant current of 1 C until the voltage reached 3.0 V during discharging was repeated up to 50 times. Life characteristics were evaluated under the following conditions, and the results are shown in FIG. 5 . In FIG. 5 , the lifespan characteristics of the lithium secondary battery according to Example 1 are indicated by solid lines, and the lifespan characteristics of the lithium secondary battery according to Comparative Example are indicated by dotted lines, respectively.

Referring to FIG. 5 , it can be seen that Example 1 in which an NCA material having a surface layer made of hydrophobic silica airgel formed on the surface thereof is used as a positive electrode active material exhibits superior lifespan characteristics compared to the comparative example.

Evaluation 4: Cell resistance characteristics of lithium secondary batteries

For the lithium secondary batteries prepared in Example 1 and Comparative Example, using an electrochemical impedance spectroscopy (EIS) under a frequency of 0.1 Hz to 100 kHz at 60 ° C. Assessing the complex impedance of each cell Thus, the results are shown in FIG. 6 . In FIG. 6 , the x-axis denotes a "real part (Z)" of the complex impedance, and the y-axis denotes a "negative imaginary part (-Z')" of the complex impedance.

Referring to FIG. 6 , it can be seen that the case of Example 1, in which an NCA material having a surface layer made of hydrophobic silica airgel formed on the surface thereof, as a positive electrode active material, exhibits improved cell resistance compared to the comparative example. This is considered to be because the side reaction of the NCA material is suppressed due to the formation of the surface layer, and thus the interfacial resistance is reduced.

In the above, the present invention has been described through preferred embodiments as described above, but the present invention is not limited thereto, and various modifications and variations are possible without departing from the concept and scope of the following claims. Those of ordinary skill in the art to which the invention pertains will readily understand.

11: cathode active material 12: lithium composite metal oxide
13: surface layer 21: lithium secondary battery
22: negative electrode 23: positive electrode
24: separator 25: battery case
26: cap assembly

Claims (10)

A lithium composite metal oxide represented by the following formula (1), and
A surface layer comprising an airgel formed on the lithium composite metal oxide
A cathode active material for a lithium secondary battery comprising:
[Formula 1]
Li _a (Ni _x M' _y M" _z )O ₂
In Formula 1, M' is at least one element selected from the group consisting of Co, Mn, Ni, Al, Mg and Ti, and M" is Ca, Mg, Ba, Al, Ti, Sr, Fe, Co , Mn, Ni, Cu, Zn, Y, Zr, Nb, and at least one element selected from the group consisting of B, 0.8 < a ≤ 1.3, 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4 and x+y+z = 1. In claim 1,
The thickness of the surface layer is 30 nm to 100 nm of a cathode active material for a lithium secondary battery. In claim 1,
The airgel has a specific surface area of 100 m ² /g to 300 m ² /g of a cathode active material for a lithium secondary battery. In claim 1,
The airgel is a positive active material for a lithium secondary battery, which is a hydrophobic airgel. In claim 1,
The airgel includes hydrophobic airgel particles,
The average particle diameter of the hydrophobic airgel particles is a positive active material for a lithium secondary battery of 10 nm to 50 nm. In claim 1,
The airgel is a cathode active material for a lithium secondary battery comprising a silica airgel. drying the airgel particles;
A method of manufacturing a cathode active material for a lithium secondary battery, comprising forming a surface layer comprising the dried airgel particles on the surface of the lithium composite metal oxide. In claim 7,
The airgel particles are a method of manufacturing a cathode active material for a lithium secondary battery comprising hydrophobic airgel particles. A positive electrode comprising the positive active material for a lithium secondary battery of any one of claims 1 to 6. The positive electrode according to claim 9;
cathode; and
A lithium secondary battery comprising an electrolyte interposed between the positive electrode and the negative electrode.

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