KR20100007236A - Positive active material for a lithium secondary battery, method of preparing thereof, and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: A method for preparing a positive active material is provided to reduce interfacial resistance between the surface of positive active materials and electrolyte while stabilizing the surface of a positive active material by forming a surface treatment layer on the surface near the positive active material. CONSTITUTION: A method for preparing a positive active material for a lithium secondary battery comprises the steps of: vacuum-drying an ammonium metal fluoride compound at 100-150 °C for 1-24 hours to remove moisture within the ammonium metal fluoride compound; and mixing the ammonium metal fluoride compound and a core capable of reversible intercalation/deintercalation of a lithium, and then coating the ammonium metal fluoride compound on the positive active material surface layer using a dry coating device such as ball mill or mechano fusion.

Description

A positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same {POSITIVE ACTIVE MATERIAL FOR A LITHIUM SECONDARY BATTERY, METHOD OF PREPARING THEREOF, AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same. More specifically, the lithium secondary battery improves charge / discharge characteristics, lifetime characteristics, high voltage characteristics, high modulus, and thermal stability. The present invention relates to a cathode active material for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

Power sources for portable electronic devices such as PDAs, mobile phones, and notebook computers, hybrid electric vehicles, plug-in hybrid electric vehicles, and even electric vehicles. As a result, the demand for secondary batteries that are being used while charging and discharging is increasing rapidly. More recently, there is an increasing demand for aerospace power supplies such as satellites and spacecraft.

Small rechargeable lithium battery on the market today uses the carbon to LiCoO _2, a negative electrode to the positive electrode. More recently, demand for Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ is replaced by LiCoO ₂ or composite electrodes mixed with LiCoO ₂ . Recently, the _{Li [Ni 1/2 Mn 1} /2] O 2 that is _{Li [Ni x Co 1 -2 x} Mn x] O ₂ is not into Co in the system, due to its high thermal stability, excellent life span and low cost LiMPO ₄ (M = Fe, Mn, Co, Ni), which has an olivine structure, has been commercialized or has been researched for some materials due to its low cost and excellent thermal stability.

However, the materials are poor in high rate and low temperature characteristics due to lower electronic conductivity than LiCoO ₂ , and the energy density of the battery is not improved despite the high capacity due to the low tap density. In order to solve this problem, a method of treating conductive carbon black on the surface (Japanese Patent Laid-Open No. 2003-059491) or a surface treatment method using a silane coupling agent (Japanese Patent Laid-Open No. 2002-367610, 2007-280830) has been proposed, but many improvements have been made. Is not reported yet.

More recently, the trend toward higher capacities for electronics and plug-in hybrid automotive power supplies is accelerating. In order to meet the demand for high capacity, high energy materials are being developed, but higher capacity materials are not being developed than currently commercialized materials. Another way to achieve this is to increase the charge potential of current commercially available materials, allowing more lithium ions to participate in electrochemical reactions to achieve higher capacity. However, this method is known to collapse the crystal structure and increase the capacity drastically as the charge potential is raised by more than 4.3 V (T. Ohzuku and A. Ueda, J. Electrochem. Soc., 141, 2972 (1994)). . For example, in the case of Li _{1 - x} CoO ₂ having the most stable crystal structure of the positive electrode active material, that is, α-NaFeO ₂ structure, the life characteristics during charge and discharge in the range of 0 <x <0.5 are almost unchanged, but when x> 0.5 or more The capacity is drastically reduced due to the instability of the structure due to the phase transition from the O3 phase to the monoclinic phase. The formation of this phase leads to a drastic decrease in the c-axis of the hexagonal phase resulting in uneven stress on the positive electrode active material particles, resulting in fracture in the particles. Other factors of capacity reduction at stratified high potentials are 1) dissolution of transition metals such as Co, Ni, Mn (GG Amatucci avbJ, .M. Tarascon asc, L.C.Klein, Solid State lonics, 83, 167 (1996) ), 2) it is known to increase surface resistance (Zhaohui Chen, JR Dahn, Electrochimica Acta, 49, 1079 (2004)) according to transition metal dissolution and surface structure transition of cathode active material.

In order to solve this sudden capacity reduction at high potential, a method of modifying the surface of the positive electrode active material has been proposed. Japanese Laid-Open Patent Publication No. 9-55210 describes a positive electrode active material prepared by coating a lithium nickel-based positive electrode active material with an alkoxide precursor of Co, Al, and Mn, followed by heat treatment, and Japanese Laid-Open Patent Publication No. 11-16566. Lithium oxide based cathode active materials coated with metals and / or oxides thereof, such as, Bi, Cu, Si, Ga, W, Zr, B, or Mo, are described. However, these methods did not sufficiently increase the initial temperature at which the surface of the positive electrode active material reacts with the electrolyte, and did not sufficiently reduce the amount of oxygen to be decomposed. Korean Patent Publication No. 10-277796 discloses a technique of coating a metal oxide by coating a metal such as Mg, Al, Co, K, Na, Ca on the surface of the positive electrode active material and heat-treating in an oxidizing atmosphere.

In addition, Korean Patent Laid-Open Publication No. 2003-32363 also includes metals of Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, and Zr on the surface of a positive electrode active material. It is known to coat hydroxide, oxyhydroxide, oxycarbonate, hydroxycarbonate salts. However, these technologies also do not solve the problem of high voltage life reduction of the positive electrode active material. More recently, Korean Patent Publication No. 10-0043652 discloses that an electrode active material having an acid point (Bronstead acid point and Lewis acid point) in part or all of an electrode active material such as a complex of inorganic or organic (quasi) metal and inorganic material is substantially acidic. Because it acts as a substance, it is known that the reactivity with strong acids such as hydrofluoric acid (HF) generated in the electrolyte is lowered, thereby ensuring structural stability of the electrode active material and improving battery performance.

However, the inorganic acid compound having such an acid point may act as an acid catalyst to accelerate the decomposition reaction of the electrolyte, causing swelling, and the like, and cause various side reaction products due to various acid points. Electrode active materials such as inorganic or organic (quasi) metals having such a scattering point and composites of inorganic materials do not significantly prevent the structure transition of the surface of the electrode active material by hydrofluoric acid generated in the electrolyte and thus do not significantly improve the life characteristics at high potentials. have.

An object of the present invention for solving the above problems is a metal fluoride (MF _x (1 <x <5)), ammonium metal fluoride ((NH ₄ ) _x MF having a Lewis acid catalyst characteristic on the surface near the positive electrode active material _y , x and y are determined by stoichiometry) and mixtures thereof to form a surface treatment layer comprising a fluoride compound and a carbon material selected from the group consisting of not only stabilize the surface of the positive electrode active material, The present invention provides a cathode active material having excellent battery capacity and high rate characteristics and a method of manufacturing the same.

In order to achieve the above object, the present invention

A core comprising a compound capable of reversible intercalation / deintercalation of lithium; And

A group consisting of metal fluoride (MF _x (1 <x <5)), ammonium metal fluoride ((NH ₄ ) _x MF _y , x and y are determined by stoichiometry) and mixtures thereof on the surface of the core It provides a positive electrode active material of a core-shell structure comprising a surface treatment layer comprising a fluoride compound and a carbon material selected from.

In addition, the present invention

Preparing a precursor solution by mixing a raw material solution including a metal surface treatment element and a core of a compound capable of reversible intercalation / deintercalation of lithium;

Obtaining a coprecipitation compound by adding a solution containing a fluoride compound selected from the group consisting of metal fluoride, ammonium metal fluoride, and mixtures thereof to the precursor solution; And

It provides a method for producing a positive electrode active material comprising the step of filtering, drying, and heat treating the co-precipitation compound.

In addition, the present invention

Vacuum drying the ammonium metal fluoride compound at 100-150 ° C. for 1 to 24 hours to remove moisture in the ammonium metal fluoride compound;

By mixing the ammonium metal fluoride compound and a core of a compound capable of reversible intercalation / deintercalation of lithium, an ammonium metal fluoride compound is prepared by using a dry coating device such as a ball mill or Mechano Fusion. It provides a method for producing a positive electrode active material comprising coating the surface layer of the positive electrode active material.

In another aspect, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte including the positive electrode active material.

A cathode active material including a surface treatment layer including a fluoride compound and a carbon material selected from the group consisting of metal fluoride, ammonium metal fluoride, and mixtures thereof according to an embodiment of the present invention is a life of a lithium secondary battery Characteristics and high voltage characteristics can be improved.

The positive electrode active material according to the present invention improves charge and discharge characteristics, life characteristics, high voltage characteristics, high rate characteristics, and thermal safety at high potentials as well as 4.5 V or less of a lithium secondary battery.

The cathode active material uses a compound capable of reversible intercalation / deintercalation of lithium (hereinafter referred to as a 'core') as a core, and a metal fluoride compound having a Lewis acid point or an ammonium having a Lewis acid point on its surface. The metal fluoride compound is coated in the form of a fine powder, and has a structure in which a layer of carbonaceous material is present between or on the fine powder.

The carbon material layer may be formed by a catalysis of a metal fluoride compound or an ammonium metal fluoride having a Lewis acid point by performing charging and discharging 1-2 times. Alternatively, the carbon material layer may be formed by coating with a carbon material precursor solution and then carbonizing.

The core may be a compound capable of reversible intercalation / deintercalation of lithium used as a cathode active material known in the art, and is not particularly limited in the present invention.

Preferably, the core may be a compound having a structure of Formulas 1 to 6 below.

Li _a Co _1-x M _x O _2-δ X _δ

(In Formula 1, M is Ni, Mn, Mg, Ca, Sr, B, Al, Ga, Si, Ge, Sn, Sb, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, and one of the elements selected from the group consisting of W, X is halogen or sulfur, 0.9≤a≤1.2, 0≤x≤0.2 and 0≤δ≤0.2)

Li _a Ni _1-xyz Co _x Mn _y M _z O _2-δ X _δ

(In Formula 2, M is in the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, and W) One element selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0.02 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.2, and 0 ≦ δ ≦ 0.2)

Li _a Ni _x Co _{1 -2 x} Mn _{x - y} M _y O _{2 -δ} X _δ

(In Formula 3, M is in the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, and W) One element selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.2, and 0 ≦ δ ≦ 0.2).

Li [M _{x / 2} N _{x / 2} Li _{(1 / 3-x / 2)} Mn _{(2 / 3-x / 2)} ] O _{2 -δ} X _δ

(In Formula 4, M is a divalent metal, N is a trivalent metal ion selected from the group consisting of Ni, Mg, Ca, B, Al, Co, Ga, Cr, Zn, Cu, Sc, V, and Y) At least one or more elements, X is halogen or sulfur, 0 ≦ x ≦ 2/3, 0 ≦ δ ≦ 0.2).

Li _a Mn _{2 - x} M _x O _{4 -δ} X _δ

(In Formula 5, M is M is B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Co, Ni, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, And W is one kind selected from the group consisting of, X is halogen or sulfur, 0.9≤a≤1.2, 0≤x≤0.5, and 0≤δ≤0.2)

Li _a M _x Fe _{1 - x} PO _{4 -δ} X _δ

(In Formula 6, M is in the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, Bi, and V One element selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 1 and 0 ≦ δ ≦ 0.2)

Li ₄ Ti ₅ O _{12 -δ} X _δ

(In Formula 7, X is halogen or sulfur, and 0 ≦ δ ≦ 0.2)

In this case, the compounds of Formulas 1 to 4 have a layered crystal rock salt structure, the compounds of Formulas 5 and 7 are spinel compounds having a cubic crystal structure, the compound of Formula 5 has an olivine (olivine) crystal structure.

The metal fluoride compound having a Lewis acid point or the ammonium metal fluoride compound having a Lewis acid point and a carbon material coated on the surface of the core may solve the problem of dissolving the positive electrode active material by hydrofluoric acid generated during the charge / discharge process of a conventional battery. In addition, by suppressing the reaction between the electrolyte and the positive electrode active material to suppress the increase in the interfacial resistance according to the charge and discharge cycle. For example, aluminum fluoride (AlF ₃ ) is a chemical industry, for example Friedel-Crafts type reaction or halogen exchange reaction or addition of hydrogen halide on multiple carbon-carbon bonds due to its high Lewis acidity. It is well known that inorganic solids are widely used as heterogeneous catalysts in the reaction. For example, in patent FR 1,383,927 aluminum fluoride (AlF ₃ ) is used to catalyze the addition of hydrofluoric acid (HF) to acetylene. AlF ₃ is also used as a support on other catalysts. In addition, the catalyst AlF ₃ is known to cause parasitic reactions which lead to the formation of unwanted byproducts or to form carbon residues which are attached to the catalyst and reduce its activity (e.g. See patent FR 1,383,927). The phenomenon mentioned last here is known to the person skilled in the art of fouling, or more specifically as coking, when the impurities are composed of carbonaceous material. Formation and "fouling" by-products adversely affect industrial processes due to the downtime required to further increase raw material consumption and regenerate the catalyst.

The resulting carbon coating layer is presumed to come from a carbon element present in ethylene carbonate or diethylene carbonate in the electrolyte in the presence of a catalyst such as a metal fluoride compound having a Lewis acid point or an ammonium metal fluoride having a Lewis acid point. Compounds with a Lewis acid point have a low LUMO energy and thus are easily reacted with a compound having a high HOMO energy, and are known to accept covalent pairs and produce covalent compounds well (http://en.wikipedia.org/wiki). / Lewis_acid). In the carbonate-based electrolyte solvent, carbon having a relatively positive charge on the dipole moment and oxygen having a negative charge are present. At this time, the compound having a Lewis acid point present on the surface of the positive electrode active material reacts with the carbonate-based electrolyte solution having a non-covalent electron pair to generate a carbon coating layer.

In addition, the ammonium cation (NH ₄ ⁺ ) present in the ammonium metal fluoride compound is easily decomposed due to the weak bonding force between the ammonium metal fluoride compounds. For example, ammonium hexanefluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) compounds are known to decompose into ammonium cations and ammonium tetrafluoroaluminate (NH ₄ AlF ₄ ) at around 150 ° C. (Chem. Mater., 12, 1148 2000). The ammonium cations (NH ₄ ⁺ ) thus decomposed (F ⁻ ) react with the fluorine anion decomposed from the electrolyte salt LiPF ₆ to form ammonium fluoride (NH ₄ F). Therefore, ammonium metal fluoride compounds with ammonium cation not only suppress the generation of hydrofluoric acid in the battery but also form a carbon coating layer on the surface of the positive electrode active material to suppress the reaction between the electrolyte and the surface of the positive electrode active material to maintain a constant resistance value of the battery. It improves lifespan characteristics, high rate characteristics and thermal stability.

The metal fluoride compound having Lewis acid catalyst property of the surface coating layer is a metal fluoride is aluminum fluoride (AlF ₃ ), titanium fluoride (TiF ₄ ), zirconium fluoride (ZrF ₄ ), chromium fluoride (CrF ₃ ) , Iron fluoride (FeF ₃ ), gallium fluoride (GaF ₃ ), indium fluoride (InF ₃ ), vanadium fluoride (VF ₃ ), and antimony fluoride (SbF ₅ ) The above is possible. Ammonium metal fluoride compounds with Lewis acid catalytic properties include ammonium hexafluoroaluminate (NH ₄ ) ₃ AlF ₆ ), ammonium hexafluoro titanate (NH ₄ ) ₂ TiF ₆ ), ammonium hexafluorozirconate (NH ₄₎ ) ₂ ZrF ₆ ), ammonium tetrafluoroaluminate (NH ₄ AlF ₄ ) and the like can be selected.

It is preferable that the metal fluoride compound or the ammonium metal fluoride compound having Lewis acid catalyst characteristics located on the surface of the positive electrode active material on the surface of the present invention is present in nano size. At this time, the size of the metal fluoride compound or the ammonium metal fluoride compound is preferably 3nm to 900nm, more preferably 3nm to 500nm. If the particle size of the metal fluoride compound or the ammonium metal fluoride compound is smaller than 3 nm, the nano-sized metal fluoride compound or the ammonium metal fluoride compound particles may aggregate together to form large particles larger than 900 nm, If it exceeds, the positive electrode active material surface resistance increases, rather it lowers the characteristic of a battery, and it is unpreferable.

In the positive electrode active material of the present invention, the metal fluoride compound or ammonium metal fluoride compound having the Lewis acid catalyst property may be present in the form of a coating layer on the surface of the positive electrode active material, or may be present in a sparse island type (island type). . When present in the form of a coating layer, the coating layer preferably has a thickness of 3 to 500 nm, more preferably a thickness of 5 to 500 nm, and most preferably a thickness of 5 to 300 nm. When the thickness of the coating layer is less than 3nm, it is difficult to obtain an effect of forming the coating layer, and when the thickness of the coating layer exceeds 500nm, it is not preferable because it inhibits the electrochemical properties of the anode splitting material. In addition, when present in an island shape, the metal fluoride compound or the ammonium metal fluoride compound having the Lewis acid catalyst property is preferably present in an area of 1 to 100% with respect to 100% of the surface area of the cathode active material. More preferably, it is present in an area of from 100% to 100%, most preferably in an area of 10 to 100%. When the metal fluoride compound or ammonium metal fluoride compound having Lewis acid catalyst property is present in an area of less than 1%, the effect of the presence of the metal fluoride compound or ammonium metal fluoride compound having Lewis acid catalyst property is obtained. it's difficult. When present in an island shape, present in an area of 100% means present as a coating layer.

In this case, the metal fluoride compound or the ammonium metal fluoride compound having Lewis acid catalyst characteristics surface-treated is 0.005 to 10 mol, preferably 0.01 to 5 mol, and more preferably 0.02 to 2 mol, based on 100 mol of the cathode active material core. It is contained in the content of. If the content of the metal fluoride compound or ammonium metal fluoride compound is less than 0.005 mol, the effect of including the metal fluoride compound or ammonium metal fluoride compound having Lewis acid catalytic properties is insignificant, on the contrary, exceeds 10 mol In this case, the initial discharge capacity of the lithium secondary battery is reduced, and the high rate characteristic is deteriorated.

In the positive electrode active material of the present invention, the carbon material may be present in the form of a coating layer on the surface of the positive electrode active material, or may be present in a sparse island type (island type). When present in the form of a coating layer, the coating layer preferably has a thickness of 2 to 1000 nm, more preferably 4 to 800 nm, most preferably 5 to 500 nm. When the thickness of the coating layer is less than 2nm, it is difficult to obtain an effect of forming the coating layer, and when the thickness of the coating layer exceeds 1000 nm, it is not preferable because it inhibits the electrochemical properties of the anode splitting material. In addition, when present in an island shape, the carbon material is preferably present in an area of 5 to 100% with respect to 100% of the surface area of the cathode active material, more preferably in an area of 10 to 100%. Most preferably present in an area of from 100% to 100%. If the carbon material is present in an area of less than 5%, the effect of the carbon material is difficult to obtain. When present in an island shape, present in an area of 100% means present as a coating layer.

The carbon material of the present invention may be amorphous carbon or crystalline carbon. The crystalline carbon may be low crystalline carbon or high crystalline graphite. In the initial charging and discharging state, an amorphous carbon layer is formed, and as the cycle of charging and discharging increases, crystallinity increases to form a graphite layer.

The metal fluoride compound or ammonium metal fluoride compound having a Lewis acid catalyst characteristic present on the surface of the compound core capable of reversible intercalation / deintercalation of lithium reacts with the carbonate solvent in the electrolyte during charge and discharge. This carbon material is used to protect the surface of the formed positive electrode active material from hydrofluoric acid, thereby solving the problem of dissolving the positive electrode active material, inhibiting side reactions between the electrolyte solution and the positive electrode active material, and greatly increasing the life characteristics. In addition, since the carbon layer formed on the surface of the positive electrode active material improves the electronic conductivity, it is possible to greatly improve the load characteristics at a high rate.

A core as described above; And a surface treatment layer comprising a fluoride compound and a carbon material selected from the group consisting of metal fluoride, ammonium metal fluoride, and mixtures thereof having Lewis acid catalytic properties on the surface of the core. It can be prepared using a wet method.

Hereinafter, an example of a method of manufacturing the cathode active material of the present invention will be described in detail, but the following production method is just an example of preparing the cathode active material of the present invention, and a metal fluoride having Lewis acid catalyst characteristics on the surface of the cathode active material, Any method may be used as long as the surface treatment layer containing a fluoride compound and a carbon material selected from the group consisting of ammonium metal fluoride and mixtures thereof can be located.

One example of a wet method is a core; And a surface treatment layer containing an ammonium metal fluoride compound on the surface of the core is performed by using co-precipitation properties between a salt containing a surface treatment element and a fluoride compound. First, the wet method includes adding a metal compound precursor to a solvent, preparing a mixed solution by adding a positive electrode core material capable of inserting and detaching lithium ions to the solvent, and adding a fluorine compound precursor to the mixed solution to add ammonium metal fluorine. Adhering a lide compound to the positive electrode core material; and drying or filtering the mixed solution to remove the solvent.

The metal compound precursor may be selected from the group consisting of oxides, nitrides, sulfides, fluorides, amine compounds, lactic acid compounds, acetate compounds, organometallic compounds, and mixtures thereof. In the present production method, the positive electrode active core material may be first added to the solvent, and then an ammonium metal fluoride compound precursor may be generated. The solvent may be a solvent in which a metal compound precursor may be dissolved. As representative examples thereof, a solvent selected from the group consisting of water, alcohols and ethers may be used alone or in combination. As the alcohol, C1 to C4 lower alcohols may be used, and specific examples thereof may be selected from the group consisting of methanol, ethanol, isopropanol, and combinations thereof, and the ether may be ethylene glycol or butylene. Glycol and the like can be used. Regardless of the order of adding the positive electrode active material core, the metal compound precursor, and the fluorine compound, the addition step and the step of preparing the mixed solution are all preferably performed at 10 to 100 ° C, more preferably at 20 to 90 ° C. Do. If the process of adding the metal compound precursor is carried out at a temperature of less than 0 ℃, there is a problem that the reaction does not occur quickly to generate a lot of impurities due to the unreacted material, when carried out at a process over 100 ℃, the reaction rate is too fast nano Particles of size are difficult to synthesize and the solvent is difficult to evaporate to match the reaction concentration, which is undesirable. The prepared precursor solution is adjusted so that the concentration of the precursor is 0.0005 M to 0.1 M. If the concentration of the precursor is less than 0.0005 M, the reaction with the fluoride compound is insufficient in the subsequent process, making it difficult to form the surface treatment layer on a sufficient amount of the core. On the contrary, if the content exceeds 0.1 M, it is difficult to coat the surface of the core due to the excessive reaction with the fluoride compound in the subsequent process of coating, which makes the coating layer selected appropriately within the above range. In addition, the stirring is performed using a conventional stirring device, typically in a reactor to which an impeller is attached.

The fluoride compound may be one containing fluorine (F) such as NH ₄ F, NH ₄ HF ₂ , CF ₃ COOH, HF, and AHF (Anhydrous hydrogen fluoride) including fluoride (F), and a combination thereof. Provided is a method for producing a fine powdered ammonium metal fluoride compound, which is at least one compound selected from the group consisting of: At this time, the solvent used is the same as the solvent of the precursor solution, or a solvent having excellent miscibility. The amount of the fluorine compound precursor used is preferably 2 to 12 mol based on 1 mol of the metal compound precursor. When the amount of the fluorine compound precursor is less than 2 moles with respect to 1 mole of the positive electrode active material core, there is almost no effect of using the chelating agent. Generated and not preferred.

The ammonium metal fluoride coprecipitation compound may be obtained in the form of large particles due to the strong agglomeration phenomenon due to the characteristics of the fine powder of high dispersion, wherein the larger the particle size, the lower the properties of the cathode active material. Therefore, to obtain co-precipitation compounds in the form of highly dispersed fine powders, it is necessary to control the concentration of the reactants, the dropping rate, the stirring speed and the reaction temperature. This coprecipitation reaction is carried out for 3 to 48 hours by dropping the fluoride compound solution at a constant rate by stirring at a rate of 50 to 1000 rpm at a temperature of 20 to 100 ℃. Further, the addition of the fluoride compound solution is slowly added after adding the fluoride compound solution at a constant rate while mixing the core alone in the precursor solution without causing precipitation in the reactor alone.

The drying step may be performed using a device conventionally used in the art. At this time, the drying step is performed for 5 to 30 hours at 110 to 200 ℃, it is preferable to dry in a vacuum to reduce the deformation of the compound.

The heat treatment step is preferably carried out at 200 to 800 ℃ for 2 to 10 hours. In this case, when the temperature of the heat treatment is less than 200 ° C., impurities are not properly removed and purity thereof is lowered. On the contrary, when the temperature exceeds 800 ° C., the metal fluoride compound or the ammonium metal fluoride compound loses the Lewis acid point and the positive electrode active material core. The reaction produces impurities on the surface, which degrades the electrochemical properties.

In one embodiment of the dry method, an ammonium metal fluoride compound, an ammonium metal fluoride compound, and a carbon mixture are mixed in the particles of the positive electrode active material core portion, followed by dry mixing. As the mixing method, any known method or apparatus such as hybridization, mechno fusion, speed mill, or ball mill can be used. In one embodiment of the present invention, the positive electrode active material may include one step of mixing a lithium metal oxide or a lithium metal phosphate, which is a core forming a core layer, with an ammonium metal fluoride compound, an ammonium metal fluoride compound, and a carbon mixture; And a second step of physically attaching the ammonium metal fluoride compound to the oxide surface in a ball mill apparatus in the presence of a ball. The mixture of the oxide, the ammonium metal fluoride compound, or the ammonium metal fluoride compound, and the carbon mixture, which is the core of the first step, is made from 99.99 to 90 moles of 0.01 to 90 moles of lithium metal oxide or lithium metal phosphate to the ammonium metal fluoride compound. It can be mixed in 10 mol parts. The ball and the mixture of the second step may be a ratio of the ball to the mixture of the first step 10 to 60 parts by weight to 90 to 40 parts by weight. If the mixture of the first stage is greater than 90 parts by weight, it is impossible to transfer the compressive stress to the mixture. In addition, the ball of the second step may be used a stainless ball or zirconia ball of 0.1 to 10mm in diameter.

The cathode material according to the present invention, prepared by the method described above, is preferably applied as an anode material of an electrochemical device, in particular, a lithium secondary battery.

The lithium secondary battery may include a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material capable of intercalating and deintercalating lithium ions; And an electrolyte between the positive electrode and the negative electrode, wherein the core comprises a compound capable of reversible intercalation / deintercalation of lithium according to the present invention as the positive electrode active material; And a surface treatment layer of an ammonium metal fluoride compound on the surface of the core.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, and the like, Depending on the size, it can be divided into bulk type and thin film type. Since the structure and manufacturing method of these batteries are well known in the art, detailed description thereof will be omitted.

In this case, the positive electrode is manufactured using the positive electrode active material according to the present invention. The positive electrode may be prepared by mixing the positive electrode active material, the conductive material, and the binder to prepare a composition for forming a positive electrode active material layer, and then rolling the composition after applying the composition to a positive electrode current collector such as aluminum foil.

As the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or polypropylene may be used. It may be, but is not limited thereto.

In addition, in the battery constituted as the conductive material, any electronic conductive material can be used without causing chemical change. For example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, copper, nickel , Metal powders such as aluminum and silver, metal fibers, and the like can be used, and conductive materials such as polyphenylene derivatives can be mixed and used.

The negative electrode includes a 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 of the negative electrode active material may be a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, or the like. In addition to the carbonaceous material, a metallic compound capable of alloying with lithium, or a composite containing a metallic compound and a carbonaceous material may also be used as the negative electrode active material. As a metal which can be alloyed with lithium, Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, Al alloy, etc. can be illustrated. Moreover, a metal lithium thin film can also be used as a negative electrode active material.

Like the positive electrode, the negative electrode may be prepared by mixing the negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then coating the negative electrode current collector such as copper foil.

As the electrolyte charged in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based or ketone-based solvent can be used. As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used. Examples of the ester solvent include n-methyl acetate, n-ethyl acetate, n-propyl acetate, and the like. Can be used.

The separator may exist between the positive electrode and the negative electrode according to the type of the lithium secondary battery. As the separator, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / poly It goes without saying that a mixed multilayer film such as a propylene three-layer separator can be used.

At this time, by using the positive electrode active material according to the present invention as a positive electrode not only solves the problem of dissolving the positive electrode active material by the acid generated by the oxidation of the electrolyte during the charging process of the conventional battery, but also suppresses the reaction between the electrolyte solution and the positive electrode active material. As a result, the charge and discharge characteristics, lifespan characteristics, high voltage characteristics, high rate characteristics, and thermal stability of the lithium secondary battery are improved. Especially when used at high voltage, the effect is increased.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1) LiCoO ₂ positive active material containing aluminum fluoride and a carbon material

An aqueous 0.013 M Al (NO ₃ ) ₃ .H ₂ O solution was injected into the reactor, and then 4 kg of LiCoO ₂ , a positive electrode active material, was added. At this time, the reactor was stirred at an impeller speed of 600 rpm while maintaining the temperature at 80 ° C for 2 hours. Subsequently, 0.2 L of 6 M NH ₄ F aqueous solution was slowly added to the reactor at a flow rate of 1 ml / min, and stirred for 24 hours to precipitate all unreacted materials to obtain a coprecipitation compound.

The coprecipitation compound was collected by filtration and dried in a 110 ° C. warm air thermostat for 12 hours. Subsequently, heat treatment was performed at 400 ° C. under a nitrogen atmosphere to prepare AlF ₃ coated LiCoO ₂ positive electrode active material powder. The prepared cathode active material powder was coated with 0.2 mol of AlF _{3 based} on 100 mol of LiCoO ₂ .

The AlF ₃ coated LiCoO ₂ positive electrode active material, acetylene black, graphite (KS6, manufactured by Lonza) as a conductive material, polyvinylidene fluoride (PVdF) as a binder is mixed in a weight ratio of 85: 3.75: 3.75: 7.5 To prepare a slurry. The slurry was uniformly coated on an aluminum foil having a thickness of 20 μm, dried at 110 ° C., and pressed by a roll press to prepare a positive electrode plate. Electrolyte solution in which 1 mol LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate: dimethyl carbonate = 1: 1 (volume ratio) and a porous polyethylene membrane (thickness: 25 μm) is used as a counter electrode using the prepared positive electrode and lithium metal as a counter electrode. According to the conventional manufacturing process of a lithium battery, a coin cell of 2032 standard was prepared.

In order to evaluate the characteristics of the coin battery, 0.5 cycles after charging and discharging at 0.2 C-rate in a potential region of 3.0 to 4.5 V at room temperature (25 ° C.) using a charger / discharger (manufactured by Toyo, Toscat3000U, Japan) 50 cycle charge and discharge experiments were performed with C-rate, and the results are shown in Table 1.

After 50 cycle charge / discharge experiments, the positive electrode active material obtained after disassembling the coin cell from the dry box was recovered and subjected to TEM analysis. Figure 1 shows a scanning electron microscope (Scanning Electron Microscopy: SEM) photograph of the positive electrode active material powder before and after performing the charge and discharge. As shown in FIG. 1 (a), AlF ₃ before charge and discharge was present in the form of 10-20 nm fine powder on the core, which is a cathode active material. The surface of the positive electrode active material after charge and discharge is AlF ₃ It could be observed that a thick coating layer was formed in addition to the fine powder.

2 shows a transmission electron microscope (TEM) photograph of the positive electrode active material powder after charge and discharge are performed. As can be seen in Figure 2 it was observed that the graphite layer of 12-15 nm size is well coated on the surface of the positive electrode active material core. This is because AlF ₃ having a strong Lewis acid point acts as a catalyst on ethylene carbonate or diethylene carbonate in the electrolyte to form a graphite carbon layer.

(Example ₂₎ LiCoO 2 positive active material containing aluminum fluoride and a carbon material

A carbon coating layer was produced in the same manner as in Example 1 except for two charge and discharge experiments instead of 50 charge and discharge experiments. 3 shows a transmission electron microscopy (TEM) photograph of the cathode active material obtained in Example 2. FIG. It can be seen from FIG. 3 that a carbon material layer of 30-100 nm size was formed on the surface of the LiCoO ₂ cathode active material. This was found to be the catalytic action of AlF ₃ with Lewis acid point as described in Example 1 above. It is estimated that this carbon material layer is converted to a high crystalline graphite carbon layer as the charge and discharge cycle proceeds in the low crystalline carbon layer at the initial stage of charge and discharge.

(Comparative Example 1) LiCoO ₂ positive active material

The charging and discharging experiments were carried out in the same manner as in Example 1 using LiCoO ₂ not coated as a cathode active material (made by Nippon Chemical Co., Ltd.), and the results are shown in Table 1 and a transmission electron microscope photograph in FIG. 4. As shown in FIG. 4, the surface of the LiCoO ₂ positive electrode active material was dissolved in Co due to the reaction between the hydrofluoric acid and the carbonate solvent in the electrolyte, and thus, the crystal structure of the surface was transferred to the impurity phase in which the surface crystal was not collapsed. Therefore, it can be seen that capacity decrease occurs due to an increase in the interfacial resistance between the surface of the positive electrode active material and the electrolyte according to the charge / discharge cycle.

(Example 3), ammonium aluminum fluoride and LiCoO ₂ positive electrode active material comprising a carbon material

0.5 g of ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ) from which moisture was removed by vacuum drying at 120 ° C. for 15 hours was added to a ball mill and 100 g of LiCoO ₂ (Japan Chemicals) was added and ball milled at room temperature for 1 hour. Hexafluoroaluminate was coated onto the LiCoO ₂ active material powder. The coating amount of (NH ₄ ) ₃ AlF ₆ in the prepared cathode active material was 0.25 mol%. The carbon coating layer was generated using a coin battery in the same manner as in Example 1.

Table 1 and Fig. 5 shows the transmission characteristics of the positive electrode active material powder according to the charge and discharge after the charge and discharge after 50 times, the transmission electron microscopy (TEM) of the positive electrode active material powder, respectively. As can be seen in Figure 5 it was observed that the 30-40 nm graphite layer is well coated on the surface of the positive electrode active material core.

(Example 4) LiCoO ₂ positive electrode active material containing the ammonium aluminum fluoride and a carbon material

In Example 3, surface modification was performed in the same manner as in Example 1, except that 0.25 mol% of ammonium aluminum fluoride and 0.3 mol% of 100 nm acetylene black having excellent conductivity were coated instead of the ammonium aluminum profluoride coating. . In Table 2, a transmission electron microscope (TEM) photograph of the positive electrode active material powder is shown in Table 2 for the life characteristics according to the charge and discharge after the 50th charge and discharge of the positive electrode active material using a coin battery in the same manner as in Example 1. Represented in each. As observed in Figure 6 LiCoO ₂ It was also observed that a 30-40 nm carbon layer was well coated on the surface of the positive electrode active material core.

The lifetime characteristics were obtained from the following equations and the results are shown in Table 1.

Life time characteristic (%) = (discharge capacity at 50 cycles / 1 discharge capacity at cycles) x 100

TABLE 1

sample Initial capacity (mAh / g) Life characteristic (%) Example 1 LiCoO ₂ Coated with 0.2mol% AlF ₃ 182 98 Example 3 LiCoO ₂ coated with 0.25 mol% (NH ₄ ) ₃ AlF ₆ 181 96.5 Example 4 LiCoO ₂ coated with 0.25 mol% (NH ₄ ) ₃ AlF ₆ and 0.3 mol% acetylene black 180 82.5 Comparative Example 1 LiCoO ₂ 179 62.4

As can be clearly seen in Table 1, the life characteristics of the samples coated with aluminum fluoride and the samples coated with ammonium hexafluoro aluminate were excellent compared to the uncoated samples. The best capacity retention rate was 98%. In addition, the positive electrode active material coated with ammonium hexafluoroaluminate and acetylene black showed a slightly lower lifespan than those of Examples 1 and 3, but showed much better life behavior than the sample without surface treatment. This is because the ammonium aluminum fluoride is wrapped in acetylene black when coated, resulting in poor catalytic activity.

(Comparative Example _{2) Li [Ni 1/2} Mn 1/2] O 2 positive active material

The results are coatings that do not handle _{Li [Ni 1/2 Mn 1} /2] O 2 by the performing 50 times of charge and discharge test in the same manner as in Example 1 by using as a cathode active material are shown in Table 2, the transmission electron microphotograph 6 is shown respectively. As shown in FIG. 6, the surface of the Li [Ni _1/2 Mn _1/2 ] O ₂ positive electrode active material is dissolved in Ni and Mn elements due to the reaction between hydrofluoric acid and a carbonate solvent present in the electrolyte, resulting in a crystal structure of the surface. It can be seen that the transition to the impurity phase failed to collapse. Therefore, it can be seen that capacity decrease occurs due to an increase in the interfacial resistance between the surface of the positive electrode active material and the electrolyte according to the charge / discharge cycle.

(Example _{5) Li [Ni 1/2} Mn 1/2] O 2 positive active material containing aluminum fluoride and a carbon material

Except for changing the positive electrode active material core in _{Li [Ni 1/2 Mn 1} /2] O 2 was carried out the surface modification in the same manner as in Example 1. In Table 2, a transmission electron microscope (TEM) photograph of the positive electrode active material powder is shown in Table 2 for the life characteristics according to the charge and discharge after the 50th charge and discharge of the positive electrode active material using a coin battery in the same manner as in Example 1. Represented in each. Just as it is observed in 7 do this _{Li [Ni 1/2 Mn 1} /2] O 2 addition, the graphite layer of 30-40 nm in size that are well coated with the positive electrode active material core surface was observed.

Life time characteristic (%) = (discharge capacity at 50 cycles / 1 discharge capacity at cycles) x 100

TABLE 2

sample Initial capacity (mAh / g) Life characteristic (%) Example 4 0.2mol% of _{Li [Ni 1/2 Mn 1} /2] coated with AlF ₃ O ₂ 182 98 Comparative Example 2 _{Li [Ni 1/2 Mn 1} /2] O 2 179 62.4

As can be clearly seen in Table 2, it was found that the life characteristics of the samples coated with aluminum fluoride were very superior to those without the coating, and the capacity retention rate was 98%.

1 is a scanning electron micrograph after (a) charge and discharge and (b) charge and discharge of the positive electrode active material prepared in Example 1 of the present invention.

Figure 2 is a transmission electron micrograph of the positive electrode active material prepared in Example 1 of the present invention.

Figure 3 is a transmission electron micrograph of the positive electrode active material prepared in Example 2 of the present invention.

Figure 4 is a transmission electron micrograph of the positive electrode active material prepared in Comparative Example 1 of the present invention.

5 is a transmission electron micrograph of the positive electrode active material prepared in Example 3 of the present invention.

6 is a transmission electron micrograph of the positive electrode active material prepared in Example 4 of the present invention.

7 is a transmission electron micrograph of the positive electrode active material prepared in Comparative Example 2 of the present invention.

8 is a transmission electron micrograph of the positive electrode active material prepared in Example 5 of the present invention.

Claims (13)

A core comprising a compound capable of reversible intercalation / deintercalation of lithium; And A cathode active material for a lithium secondary battery comprising a surface treatment layer including a fluoride compound and a carbon material selected from the group consisting of metal fluoride, ammonium metal fluoride, and mixtures thereof on the surface of the core. The method of claim 1, The core is a cathode active material for a lithium secondary battery containing one selected from the group consisting of compounds represented by the following formulas 1 to 7: [Formula 1] Li _a Co _{1 - x} M _x O _{2 -δ} X _δ (In Formula 1, M is Ni, Mn, Mg, Ca, Sr, B, Al, Ga, Si, Ge, Sn, Sb, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, and one of the elements selected from the group consisting of W, X is halogen or sulfur, 0.9≤a≤1.2, 0≤x≤0.2 and 0≤δ≤0.2) [Formula 2] Li _a Ni _1-xyz Co _x Mn _y M _z O _2-δ X _δ (In Formula 2, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0.02 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.2, and 0 ≦ δ ≦ 0.2) [Formula 3] Li _a Ni _x Co _1-2x Mn _xy M _y O _2-δ X _δ (In Formula 3, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.2, and 0 ≦ δ ≦ 0.2) [Formula 4] Li [M _{x / 2} N _{x / 2} Li _{(1 / 3-x / 2)} Mn _{(2 / 3-x / 2)} ] O _{2 -δ} X _δ (In Formula 4, M is a divalent metal, N is a trivalent metal ion selected from the group consisting of Ni, Mg, Ca, B, Al, Co, Ga, Cr, Zn, Cu, Sc, V, and Y) At least one element, X is halogen or sulfur, 0 ≦ x ≦ 2/3, 0 ≦ δ ≦ 0.2) [Formula 5] Li _a Mn _{2 - x} M _x O _{4 -δ} X _δ (In Formula 5, M is M is B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and W in the group consisting of 1 species selected, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 0.5, and 0 ≦ δ ≦ 0.2) [Formula 6] Li _a M _x Fe _{1 - x} PO _{4 -δ} X _δ (In Chemical Formula 6, M is 1 selected from the group consisting of B, Al, Ga, Mg, Ca, Ti, V, Cr, Fe, Zn, Si, Y, Zr, Nb, In, Sn, Mo, and V) Element of species, X is halogen or sulfur, 0.9 ≦ a ≦ 1.2, 0 ≦ x ≦ 1 and 0 ≦ δ ≦ 0.2) [Formula 7] Li ₄ Ti ₅ O _{12 -δ} X _δ (In Formula 7, X is halogen or sulfur, and 0 ≦ δ ≦ 0.2) The metal fluoride of the surface treatment layer is aluminum fluoride (AlF ₃ ), titanium fluoride (TiF ₄ ), zirconium fluoride (ZrF ₄ ), chromium fluoride (CrF ₃ ), iron fluoride (FeF ₃ ), gallium fluoride (GaF ₃ ), indium fluoride (InF ₃ ), vanadium fluoride (VF ₃ ), and antimony fluoride (SbF ₅ ) for at least one kind of lithium secondary battery Positive electrode active material. The method of claim 1, The ammonium metal fluoride compound of the surface treatment layer is ammonium hexafluoroaluminate (NH ₄ ) ₃ AlF ₆ ), ammonium hexafluoro titanate (NH ₄ ) ₂ TiF ₆ ), ammonium hexafluorozirconate (NH ₄ ) ₂ ZrF ₆ ), ammonium tetrafluoroaluminate (NH ₄ AlF ₄ ) One or more types of positive electrode active material for a lithium secondary battery. The method of claim 1, The cathode active material is a cathode active material for a lithium secondary battery containing 0.005 to 10 mol of a metal fluoride or an ammonium metal fluoride compound with respect to 100 mol of the core. The method of claim 1, The cathode active material is a cathode active material for a lithium secondary battery containing 0.02 to 2 moles of a metal fluoride or an ammonium metal fluoride compound with respect to 100 mol of the core. Vacuum drying the ammonium metal fluoride compound at 100 to 150 ° C. for 1 to 24 hours to remove moisture in the ammonium metal fluoride compound; The ammonium metal fluoride compound is mixed with a core of a reversible intercalation / deintercalation compound of lithium and the dry coating device such as ball mill or Mechano Fusion. A method of manufacturing a cathode active material for a lithium secondary battery according to claim 1, comprising coating on a surface layer of a cathode active material. Preparing a precursor solution by mixing a salt solution including a surface treatment element and a core of a compound capable of reversible intercalation / deintercalation of lithium; Obtaining a coprecipitation compound by adding a fluoride compound solution selected from the group consisting of metal fluoride, ammonium metal fluoride, and mixtures thereof to the precursor solution; And The coprecipitation compound is dried after filtration and a heat treatment under an inert atmosphere. The method of claim 8, The precursor solution is a method for producing a cathode active material for a lithium secondary battery that is used at a concentration of 0.005 M to 0.2 M. The method of claim 8, The fluoride compound is a method for producing a positive electrode active material for a lithium secondary battery using one compound selected from the group consisting of NH ₄ F, NH ₄ HF ₂ , HF, AHF (Anhydrous hydrogen fluoride) and combinations thereof. The method of claim 8, The fluoride compound solution is a method of producing a positive electrode active material for a lithium secondary battery using one selected from the group consisting of water, alcohol, ether and combinations thereof as a solvent. The cathode active material for a lithium secondary battery manufactured by any one of claims 1 to 11. A positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte present between them, The lithium secondary battery comprising the positive electrode active material is a positive electrode active material prepared by any one of claims 1 to 11.

Images