KR100797099B1 - Positive active material for a lithium secondary battery, method of preparing thereof, and lithium secondary battery comprising the same - Google Patents

Abstract

 The present invention relates to a cathode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same, and more particularly, a core including a compound capable of reversible intercalation / deintercalation of lithium; And a positive electrode active material formed on the surface of the core and including a surface treatment layer of an oxyfluoride compound containing a surface treatment element, and a method for manufacturing the same, and a lithium secondary battery provided with a positive electrode including the positive electrode active material. .

The oxyfluoride compound including the surface treatment element of the surface treatment layer protects the positive electrode active material by reducing the resistance to acid generated near the positive electrode active material, or suppresses the reaction between the positive electrode active material and the electrolyte, thereby increasing the capacity of the battery. As the shrinkage phenomenon is improved, the charge / discharge characteristics, lifetime characteristics, high voltage characteristics, high rate characteristics, and thermal stability of the lithium secondary battery are improved.

Cathode active material, oxyfluoride compound, high capacity, high rate characteristic, high voltage characteristic

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}

1 is a flow chart showing a manufacturing process of the positive electrode active material according to the present invention.

2 is a perspective view of a lithium secondary battery according to one embodiment of the present invention.

Figure 3 is a scanning electron micrograph of the positive electrode active material AlOF prepared in Example 1 of the present invention coated on the LiCoO ₂ surface.

4 is a graph showing cycle life characteristics of a battery using AlOF-coated LiCoO ₂ of Example 3 as a cathode active material and a battery using LiCoO ₂ of Comparative Example 1 alone as a cathode active material.

Figure 5 embodiment the 4 AlOF a coating of _{Li [Ni 1/3 Co 1} /3 Mn 1/3] of the battery and Comparative Example 2 with O ₂ as a positive electrode active material _{Li [Ni 1/3 Co 1} /3 Mn _1/3] O ₂ a graph showing the cycle life characteristics of the battery using the positive electrode active material alone.

FIG. 6 is a graph showing discharge capacity according to C-rate of a battery using AlOF-coated LiCoO ₂ of Example 3 as a positive electrode active material and a battery using AlF ₃ coated LiCoO ₂ of the positive electrode active material of Reference Example 1. FIG. .

FIG. 7 is a graph showing charge and discharge cycle life characteristics of a battery using AlOF-coated LiCoO ₂ of Example 5 as a positive electrode active material and a battery using AlF ₃ coated LiCoO ₂ of reference example ₂ as a positive electrode active material.

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 particularly, the lithium secondary battery improves charge / discharge characteristics, lifetime characteristics, high voltage characteristics, high rate characteristics, 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.

The demand for secondary batteries, which are used for charging and discharging with portable electronic devices such as PDAs, mobile phones, notebook computers, and electric bicycles and electric vehicles, is rapidly increasing. In particular, since their product performance depends on secondary batteries, which are key components, the demand for high performance batteries is very large.

The characteristics required for the battery have various aspects such as charge and discharge characteristics, lifespan, high rate characteristics, and stability at high temperatures. Among them, lithium secondary batteries have the highest voltage and high energy density and are the most attracting attention.

Lithium secondary batteries are divided into lithium batteries using a negative electrode as a lithium metal and lithium ion batteries using an interlayer compound such as carbon that lithium ions can insert and desorb. Alternatively, depending on the electrolyte used, it may be classified into a liquid battery using a liquid, a gel polymer battery using a mixture of a liquid and a polymer, and a solid polymer battery using purely a polymer.

Commercially available small lithium secondary batteries use LiCoO ₂ for the positive electrode and carbon for the negative electrode. Japan's Molly Energy Company uses LiMn ₂ O ₄ as its anode, but its use is negligible compared to LiCoO ₂ . LiNiO ₂ , LiCo _x Ni _{1 - x} O ₂ and LiMn ₂ O ₄ are the positive electrode materials currently being actively researched and developed.

Among them, LiCoO ₂ is an excellent material having stable charge and discharge characteristics, excellent electronic conductivity, high thermal stability, and flat discharge voltage characteristics, but Co has low reserves, is expensive, and toxic to humans, and thus requires development of other anode materials. In addition, LiNiO ₂ is not commercialized because of difficulty in material synthesis and thermal stability, and part of LiMn ₂ O ₄ is commercialized in low-cost products. However, LiMn ₂ O ₄ with spinel structure has a theoretical capacity of 148 ㎃h / g, which is smaller than other materials, and has a three-dimensional tunnel structure. It is lower than LiCoO ₂ and LiNiO ₂ and has poor cycle characteristics due to the Jahn-Teller effect. In particular, the high temperature characteristics at 55 ° C or higher are inferior to LiCoO ₂ and are not widely used in actual batteries.

Therefore, much research has been conducted on materials having a layered crystal structure as a material capable of overcoming the above problems. A material having a layered crystal structure, recently, the most popular in the double nickel-manganese and nickel-cobalt-manganese are respectively 1: _{Li [Ni 1/2 Mn 1/2] O} 2 and Li [Ni _1/3 to 1 mixture and the like _{Co 1/3 Mn 1/3} ] O 2. These materials exhibit lower cost, higher capacity and better thermal stability than LiCoO ₂ .

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 particular, electronic conductivity for _{Li [Ni 1/2 Mn 1} /2] O 2 is difficult to put to practical use and has a very low (J. Power Sources , 112 (2002) 41-48). In particular, the high power characteristics of these materials are less than that of LiCoO ₂ or LiMn ₂ O ₄ for use as hybrid power sources for electric vehicles. In order to solve this problem, a method of treating conductive carbon black on a surface (Japanese Patent Laid-Open No. 2003-59491) has been proposed, but many improvements have not been reported yet.

Lithium secondary batteries have a problem in that their lifespan drops rapidly as they are repeatedly charged and discharged. This problem is particularly acute at high temperatures. This is due to a phenomenon in which the electrolyte is decomposed or the active material is deteriorated due to moisture or other effects in the battery, and the internal resistance of the battery is increased. Many efforts have been made to solve this problem.

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.

There is also, a technique TiO ₂ was added to improve the energy density and high-rate characteristics have been studied in LiCoO ₂ active material (Electrochemical and Solid - State Letters , 4 (6) A65-A67 2001). There is also known a technique of improving the lifespan by surface treatment of natural graphite with aluminum ( Electrochemical and Solid - State Letters , 4 (8) A109-A112 2001).

However, it is not yet completely solved the problem of deterioration of life or the generation of gas due to decomposition of the electrolyte during charging and discharging.

Further, the phenomenon in which the active material is dissolved by the acid, which is a cause of the reduction in capacity of the battery generated during charging, the electrolyte is oxidized is introduced bar (Journal of Electrochemical Society , 143 (1996) P2204).

Recently, Korean Patent Publication No. 2003-32363 discloses a hydride containing a metal 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. Techniques for coating the hydroxide, oxyhydroxide, oxycarbonate, hydroxycarbonate salts are known. However, this technique also does not solve the problem of reducing the lifetime of the cathode active material, especially LiCoO ₂ at high voltage.

More recently, it has been reported that AlF ₃ is coated on the surface of the LiCoO ₂ active material so that the capacity is not reduced even at 4.5 V Li / Li ⁺ , and the high rate characteristic is greatly improved ( Electrochem. Commun ., 8 (5), 821-826 2006 ). However, it is known that in the oxyfluoride compound having semiconductor properties than the non-conductive fluoride compound increases electron conductivity improves the electrochemical characteristics (Journal of The Electrochemical Society , 153 1A159-A170 2006).

An object of the present invention for solving the above problems is to reduce the resistance to the acid generated near the positive electrode active material to protect the positive electrode active material, suppress the reaction of the positive electrode active material and the electrolyte, thereby reducing the capacity of the battery It is to provide a positive electrode active material and a method for manufacturing the same that can be improved.

In addition, another object of the present invention is to provide a lithium secondary battery having a positive electrode including the positive electrode active material and having improved charge / discharge characteristics, lifetime characteristics, high voltage characteristics, high rate characteristics, and thermal stability.

In order to achieve the above object, the present invention

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

It provides a cathode active material formed on the surface of the core and including a surface treatment layer of the oxyfluoride compound containing a surface treatment element.

In addition, the present invention

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;

Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound; And

It provides a method for producing a positive electrode active material comprising the step of filtering the coprecipitation compound and drying, and heat treatment in an oxidizing atmosphere.

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.

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

The positive electrode active material according to the present invention improves the charge and discharge characteristics, life characteristics, high voltage characteristics, high rate characteristics, and thermal stability of the 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 an oxyfluoride compound containing a surface treatment element on its surface is a surface treatment layer. It has a structure formed as.

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 5 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 -xy- z} 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)

Li _a Ni _x Co _{1 -2 x} Mn _{x - y} 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)

Li _a Mn _{2 - x} M _x O _{4 -δ} X _δ

(In Formula 4, 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)

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

(In Chemical Formula 5, 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)

In this case, the compounds of Formulas 1 to 3 have a layered crystal rock salt structure, the compound of Formula 4 is a spinel compound having a cubic crystal structure, the compound of Formula 5 has an olivine (olivine) crystal structure.

Oxyfluoride compound containing a surface treatment element on the surface of the core to form a surface treatment layer to solve the problem that the positive electrode active material is dissolved by the acid generated by the oxidation of the electrolyte during the charging process of the conventional battery as well as the electrolyte solution And reaction between the positive electrode active material and the positive electrode active material.

The surface treatment element of the surface treatment layer is a Group 3 transition metal, Group 4 transition metal, Group 5 transition metal, Group 6 transition metal, Group 7 transition metal, Group 8 transition metal, Group 9 transition metal, Group 13 element, Group 14 One kind selected from the group consisting of an element, a group 15 element, a lanthanide element, and a combination thereof is possible.

Preferably, the Group 3 transition metal is Sc and Y, the Group 4 transition metal is Ti and Zr, the Group 5 transition metal is V, Nb, Group 6 transition metal is Cr, Mo, and W, Group 7 The transition metal is Mn, the Group 8 transition metal is Fe, the Group 9 transition metal is Co, the Group 13 elements are B, Al, Ga, and In, and the Group 14 elements are C, Si, Ge, and Sn, Group 15 elements may be P, As, and Sb, and lanthanide elements may be La, Ce, Sm, and Gd.

More preferably, the surface treatment element is a Sc, Y, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, Ga, In, As, La, having a trivalent oxidation value One selected from the group consisting of Ce, Sm, Gd, and combinations thereof is possible.

At this time, the oxyfluoride compound containing the surface treatment element to be surface-treated is contained in an amount of 0.1 to 20 mol, preferably 0.5 to 10 mol, more preferably 0.5 to 4 mol with respect to 100 mol of the core. If the content of the oxyfluoride compound is less than 0.1 mole does not exhibit a coating effect, on the contrary, if it exceeds 20 moles, the initial discharge capacity of the lithium secondary battery decreases and the high rate characteristic is deteriorated.

The positive electrode active material in which an oxyfluoride compound containing a surface treatment element is formed on the surface of a compound core capable of reversible intercalation / deintercalation of lithium has a surface treatment layer formed by oxidation of an electrolyte during a charging process of a conventional battery. Not only does it solve the problem of dissolving the positive electrode active material by the generated acid, but also suppresses the reaction between the electrolyte solution and the positive electrode active material.

At this time, the surface treatment layer has an amorphous, crystalline, or a mixture of crystalline and amorphous depending on the heat treatment temperature.

As mentioned above, the core; And a surface treatment layer including an oxyfluoride compound containing a surface treatment element on the surface of the core is performed using co-precipitation properties between a salt containing a surface treatment element and a fluoride compound. In this case, the preparation of the cathode active material may be performed by the following method.

1 is a flowchart showing a method of manufacturing a cathode active material of the present invention.

1, the cathode active material according to the present invention,

Preparing a precursor solution by mixing a salt containing a surface treatment element with a solvent and a core which is a compound capable of reversible intercalation / deintercalation of lithium (S1);

Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound (S2); And

The coprecipitation compound is manufactured after filtration, drying, and heat treatment under an oxidizing atmosphere (S3).

First, a solvent is injected into the reactor, a salt containing the surface treatment element is added, and then uniformly mixed to prepare a salt solution including the surface treatment element (S1).

The salt containing the surface treatment element M is a Group 3 transition metal, Group 4 transition metal, Group 5 transition metal, Group 6 transition metal, Group 7 transition metal, Group 8 transition metal, Group 9 transition metal, Group 13 element, One compound selected from the group consisting of alkoxides, sulfates, nitrates, acetates, chlorides, and phosphates comprising one element selected from the group consisting of group 14 elements, group 15 elements, lanthanide elements, and combinations thereof Do.

The solvent used is preferably a solvent in which the salt can be dissolved, and a solvent having good miscibility with a fluoride compound solution to be added later is possible. Typically, single or mixed solvents thereof selected from the group consisting of water, alcohols and ethers are used. At this time, the alcohol is preferably C1 to C4 lower alcohols selected from the group consisting of methanol, ethanol, isopropanol and combinations thereof. In addition, the ether is preferably ethylene glycol or butylene glycol.

Subsequently, a precursor solution is prepared by adding a compound capable of reversible intercalation / deintercalation of lithium as a core to be surface treated to a salt solution including the prepared surface treatment element and uniformly mixing the same.

In this case, the salt containing the surface treatment element is 0.1 to 20 mol with respect to 100 mol of the core oxyfluoride compound containing the surface treatment element to be prepared is a compound capable of reversible intercalation / deintercalation of lithium, Preferably the content is adjusted to be 0.5 to 10 moles, more preferably 0.5 to 4 moles.

The prepared precursor solution is adjusted so that the concentration of the precursor is 0.005 M to 0.1 M. If the concentration of the precursor is less than 0.005 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.

At this time, the preparation of the precursor is carried out by stirring at 50 to 1000 rpm for 2 to 48 hours at a temperature of 50 to 100 ℃. In this case, when the reaction temperature is less than 50 ° C., it is difficult to prepare a uniform precursor solution. On the contrary, when the reaction temperature is 100 ° C. or more, the solvent evaporates. In addition, the stirring is performed using a conventional stirring device, typically in a reactor to which an impeller is attached.

Next, after the fluoride compound solution is added to the precursor solution prepared above, a coprecipitation compound is obtained through reaction with the surface treatment element (S2).

The fluoride compound may be one containing fluorine (F) such as NH ₄ F, HF, AHF (Anhydrous hydrogen fluoride) including fluoride (F), and at least one compound selected from the group consisting of A method for producing a fine powder fluorine compound is provided. At this time, the solvent used is the same as the solvent of the precursor solution, or a solvent having excellent miscibility.

This fluoride compound reacts with the surface treatment elements present around the core in the precursor solution to form a complex compound, and together with the core to form a fine powder of high dispersion. The high dispersion fine powder is not dissolved in a solvent to obtain a coprecipitation compound and precipitates as it is to the bottom of the reactor.

The coprecipitation compound may be obtained in the form of large particles due to the strong pulverization phenomenon due to the characteristics of the fine powder of high dispersion, wherein the larger the particle size, the lower the properties of the positive electrode 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.

Preferably, the fluoride compound is used at a concentration of 0.1M to 18M. At this time, the content of the fluoride compound is adjusted to the stoichiometric ratio to be co-precipitated with the surface treatment element. That is, the content is within the range that the oxyfluoride compound containing the surface-treated element to be produced is 0.1 to 20 moles, preferably 0.5 to 10 moles, more preferably 0.5 to 4 moles with respect to 100 moles of the core. Adjust

The coprecipitation reaction of this step 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 50 to 100 ℃. If the reaction temperature is less than 50 ℃ co-precipitation does not occur well, if the reaction temperature is more than 100 ℃ to increase the particles of the material forming the surface treatment layer is greatly grown coating effect.

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.

Next, the coprecipitation compound obtained above is filtered, and then dried and heat-treated under an oxidizing atmosphere to convert the fluoride compound containing the surface treatment element present on the surface of the coprecipitation compound into the oxyfluoride compound containing the surface treatment element. (S3). Through this step, a cathode active material having a surface treatment layer of an oxyfluoride compound containing a surface treatment element on the surface of the core is prepared.

The filtration and drying may be carried out using a device commonly used in this field. At this time, the drying is carried out at 110 to 200 ℃ for 15 to 30 hours.

At this time, the heat treatment is performed for 2 to 10 hours at 300 to 1000 ℃ under an oxidizing atmosphere. This heat treatment not only converts the fluoride compound containing the surface treatment element formed in the surface treatment layer into the oxyfluoride compound containing the surface treatment element, but also removes impurities that have not been removed during drying, and the core and surface treatment. The binding force between the layers and the surface treatment layer material is further increased. If the temperature of the heat treatment is less than 300 ℃ cyclic fluoride is not properly removed when including the oxyfluoride on the surface, the cycle characteristics are reduced, on the contrary, if the temperature exceeds 1000 ℃ it becomes difficult to form oxyfluoride after heat treatment The cycle characteristics of are reduced.

At this time, the oxidizing atmosphere is performed by introducing oxygen or air containing oxygen into the heat treatment apparatus.

The positive electrode active material according to the present invention, prepared by the method described above, is preferably applied as a positive electrode active material of a positive electrode of 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 oxyfluoride compound containing a surface treatment element 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 widely known in the art, detailed description thereof will be omitted.

2 is a perspective view of a lithium secondary battery according to an embodiment of the present invention. FIG. 2 shows the preparation of the electrode assembly 9 by placing the separator 7 between the cathode 3, the anode 5, the cathode 3, and the anode 5 and placing it in the case 15. Injection is performed so that the cathode 3, the anode 5, and the separator 7 are impregnated with the electrolyte. The negative electrode 3 and the positive electrode 5 serve to collect current generated during battery operation, and conductive lead members are respectively attached to each other, and the lead members respectively induce positive and negative currents generated from the positive and negative terminals. Done. Although the pouch type secondary battery is illustrated in the drawings, the lithium secondary battery of the present invention is not limited to this shape, and any shape capable of operating as a battery is possible.

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, ester, ether or ketone solvent may be used. Examples of the carbonate solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and 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.

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

Positive electrode active material

( Example  One) AlOF  coating- LiCoO ₂ Manufacture of positive electrode active material

An aqueous 0.013 M Al (NO ₃ ) ₃ .9H 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, 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, an AlOF-coated LiCoO ₂ positive electrode active material powder was prepared by heat treatment at 400 ° C. under an air atmosphere. In this case, the prepared cathode active material powder was coated with 2 mol of AlOF based on 100 mol of LiCoO ₂ .

( Example  2) AlOF  coating- Li [ Ni _{One / 3} Co _{One / 3} Mn _{One / 3} ] O ₂  Manufacture of positive electrode active material

In place of LiCoO ₂ as a positive electrode active material _{Li [Ni 1/3 Co 1} /3 Mn 1/3] O used by changing the _second to the content, and Example 1 and using the same procedure Li [Ni _1-cost AlOF the coating _{/ 3} Co _1/3 Mn _1/3 ] O ₂ positive electrode active material powder was prepared. At this time, the prepared cathode active material powder was _{Li [Ni 1/3 Co 1} /3 Mn 1/3] O 2 was coated AlOF 0.5 moles per 100 moles.

( Experimental Example  1) Surface Characterization

The surface of the AlOF-coated LiCoO ₂ positive electrode active material prepared in Example 1 was observed with a scanning electron microscope (SEM, trade name: JSM 6400, company name: JEOL, Japan), and the results obtained are shown in FIG. 3.

3 is a scanning electron micrograph of the positive electrode active material prepared in Example 1, it can be seen that AlOF of the fine powder is uniformly coated on the LiCoO ₂ surface.

Half battery ( Half cell )

( Example  3) AlOF  coating- LiCoO ₂ Inclusion Battery Manufacturing

AlOF-coated LiCoO ₂ positive electrode active material prepared in Example 1, acetylene black, graphite (KS6, manufactured by Lonza) as a conductive material, polyvinylidene fluoride (PVdF) as a binder is 85: 3.75: 3.75: A slurry was prepared by mixing at a weight ratio of 7.5. 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 using a prepared positive electrode plate and a lithium metal as a counter electrode, a porous polyethylene membrane (thickness: 25 μm) as a separator, and ethylene carbonate: dimethyl carbonate = 1: 1 (volume ratio) mixed solvent. According to the conventional manufacturing process of a lithium battery, a coin cell of 2032 standard was prepared.

( Comparative example  One) LiCoO ₂  Single cell manufacture

As a cathode active material was prepared in a coin cell in the same way as in Example 3, except that the LiCoO ₂ powder AlOF is uncoated.

( Comparative example  2) Li [ Ni _{One / 3} Co _{One / 3} Mn _{One / 3} ] O ₂  Single cell manufacture

As a cathode active material was prepared in a coin cell in the same way as in Example 3, except that the _{Li [Ni 1/3 Co 1} /3 Mn 1/3] O 2 powder AlOF is uncoated.

( Reference Example  One) AlF ₃  coating- LiCoO ₂  Inclusion Battery Manufacturing

A coin battery was manufactured in the same manner as in Example 3, except that LiCoO ₂ powder coated with AlF ₃ was used as the cathode active material. At this time, AlF ₃ coated LiCoO ₂ positive electrode active material powder was carried out in the same manner as in Example 1, the final heat treatment was prepared by heat treatment at 400 ℃ under an inert atmosphere.

( Experimental Example  2) AlOF  surface Treatment layer  Formed LiCoO ₂ Life characteristics of a battery containing

In order to evaluate the characteristics of the battery manufactured in Example 3 and Comparative Example 1 using a charger and discharger (Toyo, Toscat3000U, Japan) 0.5 C-rate in the potential region of 3.0 to 4.5 V at room temperature (30 ℃) Charge and discharge experiments were carried out as shown in FIG. 4.

4 is a graph showing cycle life characteristics of a battery using AlOF-coated LiCoO ₂ of Example 3 as a cathode active material and a battery using LiCoO ₂ of Comparative Example 1 alone as a cathode active material.

Referring to FIG. 4, in the case of a battery using LiCoO ₂ not coated with AlOF of Comparative Example 1 as a cathode active material, a sudden decrease in capacity occurred due to charge and discharge. On the other hand, the battery of Example 3 using AlOF-coated LiCoO ₂ as the positive electrode active material according to the present invention showed an initial discharge capacity of 180 mAh / g, which is the same as that of uncoated LiCoO _2, and an excellent capacity of 90% until the 20th cycle. Retention rate was shown. As a result, it can be seen that the battery including the AlOF-coated positive electrode active material according to the present invention has excellent cycle life even in a high voltage region of 4.5 V or more.

( Experimental Example  3) AlOF  surface Treatment layer  Formed Li [ Ni _{One / 3} Co _{One / 3} Mn _{One / 3} ] O ₂ Containing Battery Life Characteristics

In order to evaluate the characteristics of the batteries manufactured in Examples 4 and 2, 0.5 C-rate in a potential region of 3.0 to 4.5 V at room temperature (30 ° C.) using a charger / discharger (manufactured by Toyo, Toscat3000U, Japan). Charge and discharge experiments were carried out as shown in FIG. 5.

Figure 5 embodiment the 4 AlOF a coating of _{Li [Ni 1/3 Co 1} /3 Mn 1/3] of the battery and Comparative Example 2 with O ₂ as a positive electrode active material _{Li [Ni 1/3 Co 1} /3 Mn _1/3] O ₂ is a graph showing the cycle life characteristics of the battery using the positive electrode active material alone.

Referring to FIG. 5, both batteries had the same initial capacity as 173 mAh / g, but after 50 cycles, the battery using the AlOF-coated positive electrode active material of Comparative Example 2 had a capacity of 75% of the initial capacity. While the retention rate was shown, the battery using the AlOF-coated positive electrode active material of Example 4 according to the present invention showed a capacity retention rate of 92%.

( Experimental Example  4) surface With processing layer AlOF  or AlF ₃ Characteristics of the battery according to the active material

In order to evaluate the characteristics of the batteries manufactured in Example 3 and Reference Example 1, the current density was 0.2 in a potential region of 3.0 to 4.5 V at room temperature (30 ° C.) using a charger / discharger (manufactured by Toyo, Toscat3000U, Japan). The experiment was carried out with C to 5.0 C-rate, and the obtained results are shown in FIG. 6.

6 is a discharge capacity graph according to C-rate of a battery using AlOF-coated LiCoO ₂ of Example 3 as a cathode active material and a battery using AlCo ₃ coated LiCoO ₂ of the reference example 1 as a cathode active material.

Referring to FIG. 6, both electrodes showed a similar discharge capacity at 175 mAh / g at a low current of 0.2 C-rate, but as C-rate increased (meaning that the current density increased), AlOF was increased according to the present invention. Coated LiCoO ₂ The battery of Example 3 using the positive electrode active material showed better C-rate characteristics compared to that of Reference Example 1.

Full battery Full cell )

( Example  5) AlOF  coating- LiCoO ₂ Inclusion Battery Manufacturing

The positive electrode plate prepared in Example 3 was used as a positive electrode, and a coin-type complete cell was prepared. In this case, the negative active material was MCMB 2528 having high crystallinity, and was uniformly applied to copper foil. As a negative electrode, mesocarbon microbeads (MCMB) and PVdF were mixed in a weight ratio of 96: 4 to prepare a slurry for the negative electrode, and the negative electrode slurry was uniformly coated on a copper foil.

Using the positive electrode and the negative electrode as the counter electrode, the porous polyethylene membrane (thickness: 25㎛) as a separator, ethylene carbonate: dimethyl carbonate = 1: 1 (volume ratio) by using an electrolyte solution in which 1 mol LiPF ₆ dissolved in a mixed solvent A battery of the 2032 standard was manufactured according to a conventional manufacturing process of a lithium secondary battery.

( Reference Example  2) AlF ₃  coating- LiCoO ₂ Inclusion Battery Manufacturing

A coin-type full cell was prepared in the same manner as in Example 5 except that the cathode was manufactured using AlCo ₃ coated LiCoO ₂ powder as the cathode active material. In this case, the preparation of AlCo ₃ coated LiCoO ₂ powder, which is a cathode active material, was prepared as shown in Reference Example 1.

( Experimental Example  5) surface With processing layer AlOF  or AlF ₃ Life Characteristics of Batteries According to the Active Materials Formed

In order to evaluate the characteristics of the complete battery manufactured in Example 5 and Reference Example 2, 1 C- in a potential region of 3.0 to 4.4 V at room temperature (30 ° C.) using a charge / discharger (manufactured by Toyo, Toscat3000U, Japan). The experiment was performed at a rate, and the obtained results are shown in FIG. 7.

FIG. 7 is a graph showing cycle life characteristics of a battery using AlOF-coated LiCoO ₂ of Example 5 as a positive electrode active material and a battery using AlF ₃ coated LiCoO ₂ of reference example ₂ as a positive electrode active material.

7, the eoteuna indicate the Reference Example 2 The initial capacity of 173 mAh / g for the cell with the AlF ₃ is coated with LiCoO ₂ as a cathode active material of 300 exhibited a capacity holding ratio of over 88% of initial capacity after cycles . In comparison, the battery of Example 5 using AlOF-coated LiCoO ₂ as a cathode active material according to the present invention showed a capacity retention rate of 92% even after 300 cycles.

As described above, by including the positive electrode active material coated with the oxyfluoride compound containing a surface treatment element on the surface according to the present invention, the charge and discharge characteristics, life characteristics, high voltage characteristics, high rate characteristics and thermal stability of the lithium secondary battery Improve.

Claims (17)

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 of an oxyfluoride compound (except for VOF ₃ ) containing a surface treatment element on the surface of the core. The method of claim 1, The core is a cathode active material for a lithium secondary battery comprising one selected from the group consisting of compounds represented by the following formulas 1 to 5: [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 -xy- z} 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 -2 x} Mn _{x - y} 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 _a Mn _{2 - x} M _x O _{4 -δ} X _δ (In Formula 4, 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 5] Li _a M _x Fe _{1 - x} PO _{4 -δ} X _δ (In Chemical Formula 5, 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) The method of claim 1, The surface treatment element is a Group 3 transition metal, Group 4 transition metal, Group 5 transition metal (except V), Group 6 transition metal, Group 7 transition metal, Group 8 transition metal, Group 9 transition metal, Group 13 element, A cathode active material for a lithium secondary battery, which is one selected from the group consisting of Group 14 elements, Group 15 elements, lanthanide elements, and combinations thereof. The method of claim 1, The surface treatment elements are Sc, Y, Ti, Zr, Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, La , Ce, Sm, Gd, and a positive electrode active material for a lithium secondary battery that is one selected from the group consisting of these. The method of claim 1, The cathode active material is a cathode active material for a lithium secondary battery containing 0.1 to 20 moles of an oxyfluoride compound containing a surface treatment element relative to 100 moles of the core. The method of claim 1, The cathode active material is a cathode active material for a lithium secondary battery containing 0.5 to 10 moles of an oxyfluoride compound containing a surface treatment element with respect to 100 moles of the core. 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; Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound; And The method of manufacturing a cathode active material for a lithium secondary battery according to claim 1, wherein the coprecipitation compound is dried after filtration and heat-treated under an oxidizing atmosphere. The method of claim 7, wherein The salt containing the surface treatment element is a Group 3 transition metal, Group 4 transition metal, Group 5 transition metal (excluding V), Group 6 transition metal, Group 7 transition metal, Group 8 transition metal, Group 9 transition metal, Selected from the group consisting of alkoxides, sulfates, nitrates, acetates, chlorides, and phosphates comprising one surface treatment element selected from the group consisting of Group 13 elements, Group 14 elements, Group 15 elements, lanthanide elements, and combinations thereof The manufacturing method of the positive electrode active material for lithium secondary batteries which uses 1 type of compound. The method of claim 7, wherein The salt solution of the surface treatment element is a method for 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 method of claim 7, wherein 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 0.1 M. The method of claim 7, wherein Preparation of the precursor solution is to be carried out at 50 to 100 ℃ a method for producing a positive electrode active material for a lithium secondary battery. The method of claim 7, wherein The fluoride compound is a method of producing a positive electrode active material for a lithium secondary battery using one compound selected from the group consisting of NH ₄ F, HF, AHF (Anhydrous hydrogen fluoride) and combinations thereof. The method of claim 7, wherein 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 method of claim 7, wherein The drying is a method for producing a positive electrode active material for a lithium secondary battery that is carried out at 110 to 200 ℃. The method of claim 7, wherein The oxidizing atmosphere is a method for producing a positive active material for a lithium secondary battery that is performed by introducing oxygen or air containing oxygen. The method of claim 7, wherein The heat treatment is carried out at 300 to 1000 ° C a method for producing a cathode active material for a lithium secondary battery. 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 cathode secondary battery is the cathode active material according to any one of claims 1 to 6.

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