KR102006173B1 - A Cathode Active Material, Anode and A Lithium Ion Secondary Battery Having The Same and A Fabricating Method Thereof - Google Patents

Abstract

The present invention relates to a positive electrode active material having a coating layer formed on a surface thereof in order to suppress the occurrence of swelling in a lithium ion secondary battery, a positive electrode comprising the same, a lithium ion secondary battery comprising the positive electrode, and a method for manufacturing the lithium ion secondary battery. The present invention is characterized in that a passivation layer formed by stabilizing residual lithium on the surface of the positive electrode active material is continuously formed on the surface. According to the present invention, by suppressing a side reaction with an electrolyte generated on the surface of the positive electrode active material, the swelling phenomenon caused by gas generation can be prevented, and a positive electrode active material, a positive electrode, and a lithium ion secondary battery with excellent performances such as capacity, rate characteristics, and cycle life can be implemented.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode containing the same, a lithium ion secondary battery including the positive electrode active material,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium ion secondary battery, a positive electrode containing the same, a lithium ion secondary battery including the same, and a method of manufacturing the same. More particularly, A positive electrode comprising the same, a lithium ion secondary battery comprising the same, and a method of manufacturing the same.

Lithium ion battery has been actively applied not only as an energy storage medium for mobile devices but also in medium and large fields such as electric vehicles and electric power storage. The main component of the lithium ion secondary battery can be classified into a cathode material, an anode material, a separator, and an electrolyte. The commercial lithium ion secondary battery includes a layered structure of a cathode material, a carbon anode material, a polymer separator, and an electrolyte of a liquid component .

BACKGROUND ART It is known that, when a lithium ion secondary battery is driven, particularly in a charged state, the surface of a cathode material and a liquid electrolyte cause various types of side reactions as well as movement of lithium ions for driving a battery. The side reaction is accompanied by decomposition of the electrolyte, elution of the metal component of the cathode material, formation of a film (SEI layer), and swelling phenomenon of the swelling of the lithium ion secondary battery due to gas generated as a by- .

Attempts to solve the above problems and improve the performance by modifying the electrode surface of the lithium ion secondary battery have been made in various ways and have been reported in many papers and patents. And there is a high demand for solving these problems.

Accordingly, the present inventors have conducted intensive studies to prevent a side reaction with an electrolyte generated on the surface of a cathode active material, thereby preventing the generation of gas to prevent the phenomenon of swelling and to provide a positive electrode active material having excellent performance such as capacity, Ion invented a secondary battery.

1. Published Japanese Patent Application No. 10-2013-0084361 (Feb. 2. Published Japanese Patent Application No. 10-2017-0078892 (July 10, 2017).

The present invention relates to a positive electrode active material which prevents a swelling phenomenon due to generation of a gas by suppressing a side reaction with an electrolyte generated on the surface of a positive electrode active material and provides a positive electrode active material having excellent performance such as capacity, I want to.

The present invention provides a method for producing a cathode active material for a lithium ion secondary battery which is simple in manufacturing process and can be mass-produced at low cost.

The first aspect of the present invention may be a positive electrode active material for a lithium ion secondary battery in which a passivation layer formed by stabilizing residual lithium on the surface of the positive electrode active material is continuously formed on the surface.

In this aspect, a lithium channel through which lithium ions can pass may be further formed in an island shape discontinuously through a passivation layer.

In this aspect, the passivation layer may comprise an organolithium compound. Specifically, the organolithium compound may be selected from the group consisting of lithium methyl carbonate, lithium ethyl carbonate, lithium methoxide, lithium ethoxide, methyllithium, and ethyllithium. One or more selected from the group.

In this aspect, the lithium channel may comprise lithium fluoride.

The second aspect of the present invention is a process for producing a lithium ion secondary battery, comprising the steps of: (a) mixing a cathode active material for a lithium ion secondary battery and an electrolyte solvent for a lithium ion secondary battery; and (b) heating the mixture to react the lithium component present on the surface of the cathode active material with an electrolyte solvent Forming a passivation layer on the surface of the cathode active material by stabilizing residual lithium on the surface of the cathode active material, but without performing a sintering process.

In this aspect, examples of the positive electrode active material for a lithium ion secondary battery include a lithium cobalt oxide series, a lithium nickel cobalt oxide series, a lithium nickel cobalt manganese oxide series, a lithium manganese oxide series, a lithium iron oxide series and a lithium nickel cobalt aluminum oxide series May be used.

In this aspect, as the electrolyte solvent for a lithium ion secondary battery, at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate and propylene carbonate can be used.

In this aspect, the lithium source providing lithium may be further mixed in step (a). As the lithium source, one or more selected from the group consisting of lithium carbonate, lithium hydroxide and lithium acetate may be used.

In this aspect, heating of the mixture in step (b) may be performed at 25 ° C to 150 ° C.

In this aspect, in the step (a), a fluorine source for providing fluorine is further mixed, and in the step (b), a lithium channel through which lithium ions can pass is discontinuously formed in the form of an island, layer.

In this aspect, as the fluorine source, at least one selected from the group consisting of hydrofluoric acid, ammonium fluoride, and ammonium hydrogen fluoride may be used.

A third aspect of the present invention is a cathode active material for a lithium ion secondary battery produced according to the method of the second aspect.

A fourth aspect of the present invention may be a positive electrode for a lithium ion secondary battery comprising the positive electrode active material of the third aspect.

A fifth aspect of the present invention may be a lithium ion secondary battery comprising the positive electrode of the fourth aspect.

According to the present invention, it is possible to prevent a swelling phenomenon due to generation of a gas by suppressing a side reaction with an electrolyte generated on the surface of a positive electrode active material, and to provide a positive electrode active material having excellent performance such as capacity, Can be implemented.

Further, according to the present invention, the production process is simple and mass production is possible at low cost.

FIG. 1 is a schematic view schematically showing a cross section of a cathode active material for a lithium ion secondary battery according to an aspect of the present invention. FIG.
2 is a scanning electron microscope image (left: Example 1, right: Example 2) of the surface of a cathode material prepared according to Example 1 (p-SEI1) and Example 2 (p-SEI2).
3 is a TEM image of a cathode material prepared according to Example 1 (p-SEI1) and Example 2 (p-SEI2) (left: Example 1, right: Example 2).
4 is a graph showing the results of analyzing EDS components for Example 2 (p-SEI2).
5 is a graph showing the capacities of a lithium ion battery coin cell manufactured according to Example 1 (p-SEI1), Example 2 (p-SEI2) and Comparative Example (LNCA).
6 is a graph showing the rate characteristics of a lithium ion battery coin cell manufactured according to Example 1 (p-SEI1), Example 2 (p-SEI2), and Comparative Example (LNCA).
7 is a graph showing cycle life characteristics of a lithium ion battery coin cell manufactured according to Example 1 (p-SEI1), Example 2 (p-SEI2) and Comparative Example (LNCA).
8 is a graph showing the results of measurement of the amount of gas generated in the cathode material produced according to Example 1 (p-SEI1), Example 2 (p-SEI2) and Comparative Example (LNCA).

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

The present invention relates to a positive electrode active material having a coating layer formed on a surface thereof to suppress swelling in a lithium ion secondary battery, a positive electrode containing the positive electrode active material, a lithium ion secondary battery comprising the same, and a manufacturing method thereof.

1 is a cross-sectional view of a cathode active material for a lithium ion secondary battery according to an aspect of the present invention. Referring to FIG. 1, the first aspect of the present invention may be a cathode active material for a lithium ion secondary battery, wherein a passivation layer formed by stabilizing residual lithium on the surface of the cathode active material is continuously formed on the surface. This aspect can be said to be a structure in which the particle surface of the cathode active material is coated with a passivation layer.

When the lithium ion secondary battery is driven, the electrolyte and the surface of the cathode active material are brought into contact with each other to cause a chemical reaction and a side reaction such as generation of gas may occur, which may cause swelling. In order to prevent side reactions on the surface of the positive electrode active material, a surface of the positive electrode active material is stabilized by chemically reacting the surface of the electrolyte with the surface of the positive electrode active material in advance to form a passivation layer, The chemical reaction on the surface can be suppressed and the swelling phenomenon due to gas generation can be prevented. Lithium present on the surface of the cathode active material is allowed to react with the electrolyte in advance, thereby stabilizing the state of the surface of the cathode active material.

The mechanism of the side reaction occurring on the surface of the cathode material of the battery in the charged state is as follows: i) decomposition of the electrolyte through contact and reaction between the cathode material and the electrolyte and ii) lithium compound (lithium carbonate or lithium hydroxide) remaining on the surface of the cathode material Electrolyte reaction. In the present invention, the former is solved by forming a coating layer in the form of a thin film on the surface of the cathode material, and the latter is solved by consuming or stabilizing the surface residual lithium in the surface modification.

The passivation layer may be formed by chemically reacting the electrolyte of the lithium ion secondary battery with lithium present on the surface of the cathode active material. The greater the amount of lithium present on the surface of the cathode active material, the thicker the passivation layer can be formed. In order to form a thicker passivation layer, a lithium source may be further supplied from the outside in addition to lithium existing on the surface of the cathode active material itself. For example, when lithium carbonate, lithium hydroxide, lithium acetate, or the like is added and mixed with the electrolyte, the passivation layer may be formed thicker.

The passivation layer can continuously cover the surface of the cathode active material particles. The entire surface of the cathode active material particles may be covered with a passivation layer. If some of the surfaces of the cathode active material particles are not covered with a passivation layer, a chemical side reaction as described above may occur during the operation of the lithium ion secondary battery in the exposed portion.

The thickness of the passivation layer may be from several to several tens of nanometers. If the passivation layer is thinner than the lower limit, the function of the passivation layer can not be properly performed and swelling may occur in the operation of the battery in the future. If the passivation layer is thicker than the upper limit, The movement of ions may be disturbed and the rate characteristics, cycle characteristics, etc. of the battery may be deteriorated.

The passivation layer is formed on the surface of the cathode active material before assembling the battery to prevent the reaction between the electrolyte and the cathode active material while the lithium ion is used, but does not completely block the passage of lithium.

The passivation layer may comprise an organic lithium compound. Specifically, the organic lithium compound may be selected from the group consisting of lithium methyl carbonate, lithium ethyl carbonate, lithium methoxide, lithium ethoxide, methyl lithium and ethyl lithium. Or more species. When the organolithium compound contains two or more kinds, a complex can be formed.

In this aspect, a lithium channel may be further formed in the passivation layer. The lithium channel refers to a channel through which lithium ions can pass. The lithium channel may be discontinuously formed in the form of an island through a passivation layer. The lithium channel is formed through the middle of the passivation layer, and may have an island shape. The passivation layer may be formed in a continuous phase, and the lithium channel may be discontinuously formed in the form of an island.

The passivation layer is a stable formed by the reaction of the electrolyte and lithium, and the ion conductivity to lithium ion may be relatively small. Battery performance can be improved by stabilizing the surface of the cathode active material. However, the migration of lithium ions through the passivation layer is limited. A lithium channel can be formed to compensate the movement limitation of the lithium ion.

The lithium channel may comprise lithium fluoride. In particular, lithium fluoride has a high ionic conductivity with respect to lithium ions, so that the lithium channel can provide a smooth passage of lithium ions when the lithium ion battery is driven.

The second aspect of the present invention is a process for producing a lithium ion secondary battery, comprising the steps of: (a) mixing a cathode active material for a lithium ion secondary battery and an electrolyte solvent for a lithium ion secondary battery; and (b) heating the mixture to react the lithium component present on the surface of the cathode active material with an electrolyte solvent Forming a passivation layer on the surface of the cathode active material by stabilizing residual lithium on the surface of the cathode active material, but without performing a sintering process.

In this aspect, a process of treating a surface of a cathode active material by simulating a process of forming a SEI layer on a surface of a cathode through a side reaction occurring between a cathode and an electrolyte in a lithium ion secondary battery is employed. However, it is characterized in that it does not undergo a firing process.

First, a cathode active material for a lithium ion secondary battery and an electrolyte solvent for a lithium ion secondary battery can be mixed (a). When the battery is assembled and used, there is a possibility that the cathode active material and the electrolyte come into contact with each other, causing a chemical reaction on the surface of the cathode active material and generating gas. In a situation It is possible to coat the surface of the cathode active material particle itself with a material which is formed in advance during use of the battery.

As the cathode active material, a cathode active material having lithium on its surface can be used. Specific examples include, but are not limited to, lithium cobalt oxide, lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron oxide, and lithium nickel cobalt aluminum oxide. More than species can be used.

As the electrolyte solvent, an electrolyte solvent used in a lithium ion secondary battery can be used. Specifically, at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate and propylene carbonate can be used.

In step (a), a lithium source may be further mixed. That is, in the step (a), the electrolyte, the cathode active material, and the lithium source may be simultaneously mixed. The lithium source may be dissolved in the electrolyte to provide lithium. By increasing the content of lithium, it is possible to form a thicker passivation layer. The thickness of the passivation layer can be controlled by adjusting the content of lithium appropriately. As the lithium source, a substance which is dissolved in an electrolyte solution and can provide lithium can be used. Although not limited thereto, at least one selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium acetate may be used as a lithium source.

Next, the mixture of the cathode active material and the electrolyte solvent can be heated while stirring (b). Through this process, a passivation layer formed by stabilizing the residual lithium on the surface of the cathode active material by reacting the lithium component present on the surface of the cathode active material with the electrolyte solvent can be continuously formed on the surface of the cathode active material.

A coating film called a passivation layer can be formed on the surface of the cathode active material by simply passing through a wet process. It is possible to form a thin film on the surface of the positive electrode active material particles which is expected to be formed on the surface of the positive electrode active material by the reaction of lithium on the surface of the positive electrode active material and the electrolyte.

This aspect is characterized in that it does not go through the firing step. That is, a passivation layer can be formed even at a low temperature without being subjected to high temperature firing. The heating temperature may be 25 占 폚 (normal temperature) to 150 占 폚. Preferably 40 [deg.] C to 80 [deg.] C. At temperatures below 25 ° C, the reaction is too slow to allow for a long process time, or the reaction itself may not be activated. At temperatures above 150 ° C, some solvents have a boiling point above that which is difficult to react and may be disadvantageous in terms of process cost.

For example, a carbonate or hydroxide-based lithium compound remaining on the surface of the cathode active material may be reacted with dimethyl carbonate through heating at an appropriate temperature, thereby forming an organolithium thin film layer of several nanometers on the surface of the cathode active material.

In the step (a), a fluorine source providing fluorine may be further mixed. In this case, in step (b), a lithium channel through which lithium ions can pass may be discontinuously formed in an island shape through a passivation layer. The lithium channel refers to a channel through which lithium ions can pass. The lithium channels formed can be randomly distributed on a continuous passivation layer. The lithium channel may be formed through a passivation layer. For example, in the step (a), it is also possible to incorporate lithium fluoride nanoparticles in the middle of the passivation layer by further adding a raw material containing fluorine.

As the fluorine source, at least one selected from the group consisting of hydrofluoric acid, ammonium fluoric acid and ammonium hydrofluoric acid can be used. Considering the hazards in process and ease of storage, it is preferable to use ammonium fluoride or ammonium hydrogen fluoride.

For example, through the present process, residual lithium on the surface of the cathode active material can be converted into a coating layer in which the organic lithium compound thin film or the organic lithium compound thin film is combined with lithium fluoride.

For example, it is possible to realize a simple low-cost process in which a small amount of dimethyl carbonate, which is a relatively inexpensive solvent, is mixed with the cathode active material and reacted through a single wet process, and a further heat treatment process is not required, And it is suitable for mass production.

A third aspect of the present invention is a cathode active material for a lithium ion secondary battery produced according to the method of the second aspect. A passivation layer (and a lithium channel) may be formed on the surface of the cathode active material according to this aspect (see FIG. 1). The matters relating to the cathode active material according to the present invention are the same as those described in the first aspect.

A fourth aspect of the present invention may be a positive electrode for a lithium ion secondary battery comprising the positive electrode active material of the third aspect. The anode may be prepared by applying a slurry prepared by mixing a cathode mixture to a solvent such as NMP, and then drying and rolling the cathode slurry.

In addition to the positive electrode active material of the third aspect, the positive electrode mixture may optionally contain a conductive material, a binder, a filler, and the like.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers 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.

The binder is a component which assists in bonding of the positive electrode active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery and is optionally used as a component for suppressing the expansion of the anode. Examples of the filler include olefin based additives such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like can be used.

The positive electrode collector may generally be made to have a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery. For example, surfaces of stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like may be used. It is possible to form fine irregularities on the surface of the current collector to increase the adhesive force of the cathode active material and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

A fifth aspect of the present invention may be a lithium ion secondary battery comprising the positive electrode of the fourth aspect. This aspect can be composed of the positive electrode, the negative electrode, the separator, and a nonaqueous electrolyte solution containing a lithium salt.

The negative electrode is prepared, for example, by applying a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the negative electrode mixture. The negative electrode mixture may contain the above-described components as required. Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength can be used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. As the separation membrane, for example, an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene, or the like can be used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, Ethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyl, triethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, pyrophosphoric acid Methyl propionate, and ethyl propionate may be used.

The organic solid electrolyte includes, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an acid dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include 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 can be used.

The lithium salt is a substance which is easily dissolved in the non-aqueous electrolyte. For example, 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, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenylborate, .

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the electrolytic solution includes, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, , Sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol and aluminum trichloride. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

&Lt; Example 1 >

1. Preparation of a cathode active material having an organic lithium compound coating layer in a continuous thin film form (p-SEI1)

First, LiNi _0.85 Co _0.12 Al _0.03 O ₂ (LNCA) commercially available as a cathode active material for a lithium ion secondary battery was prepared and prepared.

Next, a mixed solution (coating solution) was prepared by mixing 10 g of ethyl alcohol and 1 g of dimethyl carbonate (DiMethyl Carbonate).

Next, 10 g of LNCA was added to the mixed solution, and the mixture was stirred for 2 hours while being maintained at 60 占 폚.

Next, the positive electrode active material powder was separated from the solution by washing with ethanol and centrifugation.

Next, the separated cathode active material powder was dried at 80 캜 using a convection oven to obtain an LNCA cathode active material (p-SEI1) having an organic lithium compound thin film formed on its surface.

&Lt; Example 2 >

A cathode active material having a coating layer in which a continuous thin film organic lithium compound and a discontinuous lithium fluoride nanoparticle are present in combination is prepared (p-SEI2).

A cathode active material was prepared according to the same procedure as in Example 1, except that 0.04 g of NH ₄ FHF capable of providing fluorine was further added to the mixed solution (coating solution).

<Comparative Example>

As a comparative example, commercially available LiNi _0.85 Co _0.12 Al _0.03 O ₂ (LNCA) cathode active material (LNCA) was used.

<Evaluation>

1. Surface observation and component analysis

The surface was observed using a scanning electron microscope and a transmission electron microscope, and the components were analyzed through EDS. The results are shown in FIGS. 2 to 4.

2, a scanning electron microscope image (left: Example 1, right: Example 2) was applied to the surface of the cathode active material prepared according to Example 1 (p-SEI1) and Example 2 (p- 3 shows a transmission electron microscope image (left: Example 1, right: Example 2) of the cross section. FIG. 4 shows the result of analyzing the EDS component of the elliptical part of Example 2 (p-SEI2).

Referring to FIG. 2, it can be seen that the coating layer of rough texture was formed on the surface of Example 1, and that the particle-shaped LiF was added to the surface treatment layer from the image of Example 2.

Referring to FIG. 3, it can be seen that a stabilizing layer in the form of a continuous thin film is formed on the surface through Example 1, and LiF particles are formed in the middle of the stabilizing layer in the form of a thin film through Example 2.

Referring to FIG. 4, when the F component is detected as a result of the EDS analysis, it can be confirmed that these particles are LiF.

2. Fabrication of anode and coin cell

In order to evaluate the characteristics, an anode and a coin cell were fabricated using the cathode active materials of Examples and Comparative Examples.

First, a slurry composed of 90 wt% of the positive electrode active material, 5 wt% of acetylene black, and 5 wt% of PVDF (polyvinylidene fluoride) was coated on the Al current collector, and the resultant was rolled to produce a positive electrode plate.

Next, a coin-type CR2032 coin cell was assembled in a glove box filled with argon gas. The prepared positive electrode plate was dried in a 110 ° C vacuum dryer for one day before cell assembly. A lithium-metal chip (Li-metal chip) was used as a cathode. A PP (polypropylene) membrane was used as a separator. A solution of 1.3 M LiPF ₆ salt dissolved in a mixed solvent of 3: 4: 3 (volumetric ratio) of EC (Ethyl Carbonate), EMC (Ethyl Methyl Carbonate) and DEC (Diethyl Carbonate) was used as the electrolyte.

3. Capacity assessment

The electrochemical performance of the fabricated cell was evaluated by galvanostatic charging and discharging. Charging and discharging are between 3.0V and 4.3V vs.. Li ^&lt; ^{+ &gt;} / Li. The constant current / constant voltage method was used for charging, and the constant current method was used for discharging.

The test results are shown in Figs. 5 to 7. FIG. 5 shows the capacity, FIG. 6 shows the rate characteristics, and FIG. 7 (b) shows the charge / discharge characteristics of the lithium ion battery coin cell manufactured according to Example 1 (p-SEI1) Cycle life characteristics.

Referring to FIG. 5, as a result of the charge-discharge test, it can be confirmed that the treatment shown in Example 1 and Example 2 did not lower the charge-discharge capacity of the cathode material.

Referring to FIG. 6, as a result of the rate characteristic test, it can be confirmed that the treatment of Example 2 does not lower the rate characteristic of the cathode material.

Referring to FIG. 7, as a result of the cycle test, it can be confirmed that the treatment through Example 2 is effective for improving the cycle life. It can be confirmed that the effect of the first embodiment is slightly improved.

4. Evaluation of gas generation

In order to measure the gas emission amount due to the side reaction between the cathode active material and the electrolyte, each of the coin cells manufactured in accordance with the examples and the comparative examples in the charged state was disassembled to separate the positive electrode, the separated positive electrode and the electrolyte into the polypropylene pouch, Respectively. Cell assembling and disassembling, pouch manufacturing and other processes were carried out in a glove box filled with argon gas. The volume change of the pouch was measured at 60 캜 over time and converted into the amount of gas generated by the side reaction.

The test results are shown in Fig. Referring to FIG. 8, it can be seen that the amount of gas generated in the embodiment is greatly reduced as compared with the comparative example. From this, it can be predicted that swelling phenomenon will be greatly improved when the battery is driven.

The terms used in the present invention are intended to illustrate specific embodiments and are not intended to limit the invention. The singular presentation should be understood to include plural meanings, unless the context clearly indicates otherwise. The word &quot; comprises &quot; or &quot; having &quot; means that there is a feature, a number, a step, an operation, an element, or a combination thereof described in the specification. The present invention is not limited to the above-described embodiments and the accompanying drawings, but is intended to be limited only by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. something to do.

10: cathode active material
20: Stabilization layer (passivation layer)
30: Lithium channel

Claims (16)

A positive electrode active material for a lithium ion secondary battery, wherein a passivation layer formed by stabilizing residual lithium on the surface of the positive electrode active material is continuously formed on the surface, and the passivation layer comprises an organic lithium compound.
The method according to claim 1,
A cathode active material for a lithium ion secondary battery, wherein a lithium channel through which lithium ions can pass is further formed in an island shape discontinuously through the passivation layer.
delete The method according to claim 1,
Wherein the organic lithium compound comprises at least one member selected from the group consisting of lithium methyl carbonate, lithium ethyl carbonate, lithium methoxide, lithium ethoxide, methyl lithium and ethyl lithium.
3. The method of claim 2,
Wherein the lithium channel comprises lithium fluoride.
(a) mixing a cathode active material for a lithium ion secondary battery and an electrolyte solvent for a lithium ion secondary battery; And
(b) heating the mixture to cause a lithium component present on the surface of the cathode active material to react with the electrolyte solvent to stabilize residual lithium on the surface of the cathode active material, thereby forming a passivation layer continuously on the surface of the cathode active material , &Lt; / RTI &gt;
A method for producing a cathode active material for a lithium ion secondary battery, which is not subjected to a firing step.
The method according to claim 6,
Examples of the positive electrode active material for the lithium ion secondary battery include one selected from the group consisting of lithium cobalt oxide series, lithium nickel cobalt oxide series, lithium nickel cobalt manganese oxide series, lithium manganese oxide series, lithium iron oxide series and lithium nickel cobalt aluminum oxide series. Wherein the positive electrode active material is a negative active material.
The method according to claim 6,
As the electrolyte solvent for the lithium ion secondary battery, at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate and propylene carbonate is used.
The method according to claim 6,
wherein the lithium source for providing lithium is further mixed in the step (a).
10. The method of claim 9,
Wherein the lithium source is at least one selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium acetate.
The method according to claim 6,
(b), the mixture is heated at 25 ° C to 150 ° C. The method for producing a cathode active material for a lithium ion secondary battery according to claim 1,
The method according to claim 6,
In the step (a), the fluorine source providing the fluorine is further mixed,
In the step (b), a lithium channel through which lithium ions can pass is discontinuously formed in an island shape through the passivation layer.
A method for producing a cathode active material for a lithium ion secondary battery.
13. The method of claim 12,
Wherein the fluorine source is at least one selected from the group consisting of hydrofluoric acid, ammonium fluoride, and ammonium hydrogen fluoride.
7. A cathode active material for a lithium ion secondary battery produced according to claim 6.
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