KR20180088301A - Positive electrode active material for secondary battery and method for preparing the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a secondary battery, and to a manufacturing method thereof, wherein the positive electrode active material comprises: a core containing a lithium composite metal oxide; and a surface treatment layer located on the surface of the core and containing an amorphous oxide containing at least one kind of metallic element, which is selected from a group consisting of phosphorus (P), group 2A elements and group 3A elements. An object of the present invention is to provide the positive electrode active material for the secondary battery which can exhibit excellent life characteristics and high voltage stability by providing the positive electrode active material having the surface treatment layer excellent in flexibility and chemical resistance, and to provide the manufacturing method thereof.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material for a secondary battery, and a method for manufacturing the same. BACKGROUND OF THE INVENTION [0002]

The present invention relates to a cathode active material for a secondary battery, which can exhibit excellent lifetime characteristics and high voltage stability, and a method for producing the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

However, there is a problem that the lifetime of the lithium secondary battery rapidly decreases as the charge and discharge are repeated. In particular, such problems are more serious in long-life or high-voltage cells. This is due to the phenomenon that electrolytic decomposition or deterioration of the active material occurs due to moisture or other influences inside the battery, and also the internal resistance of the battery is increased. Particularly, in the case of the cathode material, if the degradation of the cathode material itself is intensified, the elution of the constituent elements of the cathode active material increases, and as a result, the battery life is rapidly degraded or the battery can not be used at high voltage.

In order to solve such a problem, methods of forming a surface treatment layer on the surface of a cathode active material have been proposed. In the case of an aluminum-based surface treatment layer, which has high double voltage and stability in electrolytic solution, it is difficult to uniformly coat the active material because it is coated on the surface of the particles in a crystalline state. In addition, there is a problem of increased resistance due to crystallinity of the aluminum-based compound itself. In addition, the boron (B) -based coating is uniformly coated in an amorphous state, so that it does not hinder the movement of lithium ions moving from the cathode material to the electrolyte. However, since the boron (B) -based coating reacts with water, the coating layer can not function as a coating layer if the reaction with the electrolyte is prolonged.

Accordingly, there is an urgent need to develop a cathode active material capable of improving the performance of a lithium secondary battery while solving the above problems.

Korean Patent Publication No. 2003-0083476

An object of the present invention is to provide a cathode active material for a secondary battery which can exhibit excellent life characteristics and high voltage stability by providing a cathode active material having a surface treatment layer excellent in flexibility and chemical resistance and a method for producing the same.

In order to solve the above problems, the present invention provides a lithium secondary battery comprising: a core comprising a lithium composite metal oxide; And a surface treatment layer which is located on the surface of the core and comprises an amorphous oxide containing phosphorus (P) and at least one metal element selected from the group consisting of Group 2A elements and Group 3A elements, Thereby providing an active material.

In addition, the present invention provides a method for producing phosphorus (P) and phosphorus (P) by using a first raw material containing phosphorus and a second raw material containing at least one metallic element selected from the group consisting of Group 2A element and Group 3A element, And an amorphous oxide containing at least one metal element selected from the group consisting of Group 3A; And a second step of mixing the amorphous oxide and the lithium composite metal oxide and then performing a heat treatment to form a surface treatment layer containing the amorphous oxide on the lithium composite metal oxide. do.

The present invention also provides a positive electrode for a secondary battery comprising the positive electrode active material for the secondary battery.

The present invention also provides a secondary battery comprising the positive electrode for the secondary battery.

The cathode active material for a secondary battery according to the present invention includes a surface treatment layer containing an amorphous oxide including at least one of phosphorus, 2A group element and 3A group element, thereby improving flexibility and chemical resistance, The structural stability is improved. As a result, the secondary battery, which is a final product, can realize excellent life characteristics and high voltage stability.

FIG. 1 is a graph showing the discharge capacity retention ratios of the lithium secondary batteries manufactured in Example 1 and Comparative Examples 2 and 3 according to the number of cycles. FIG.
2 is a graph showing the capacity retention rate of the lithium secondary batteries manufactured in Examples 2 to 3 and Comparative Example 1 according to high temperature storage.
3 is a graph showing resistance characteristics of the lithium secondary batteries manufactured in Examples 2 to 3 and Comparative Example 1 according to high-temperature storage.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The cathode active material for a secondary battery according to an embodiment of the present invention may include a core and a surface treatment layer.

The surface treatment layer included in the cathode active material for a secondary battery according to an embodiment of the present invention is disposed on the surface of the core and includes at least one metal selected from the group consisting of phosphorus (P), group 2A element and group 3A element An amorphous oxide containing an element. Particularly, since the surface treatment layer contains phosphorus (P), it is possible to form a surface treatment layer with high binding force with at least one metal element selected from the group consisting of Group 2A elements and Group 3A elements, This improved surface treatment layer can be formed. In addition, the surface-treated layer contains at least one metal element selected from the group consisting of Group 2A element and Group 3A element, thereby ensuring acid resistance to the electrolytic solution. Preferably, the metal element may be at least one element selected from the group consisting of Mg, Ca, Al, B, Sr, Ba, Ra, Be, Ga, In and Tl, Al, and the like.

In addition, the amorphous oxide is excellent in flexibility by including both phosphorus and the above-mentioned metal element, and is capable of flexibly coping with volume change of the core due to insertion and desorption of lithium. Therefore, the amorphous oxide can stably protect the core. Since the amorphous oxide has excellent chemical resistance, it is not damaged even after long contact with the electrolytic solution and the hydrogen fluoride derived from the electrolytic solution. Accordingly, the amorphous oxide prevents direct contact between the core and the electrolytic solution and hydrogen fluoride from the electrolyte during operation of the secondary cell, thereby preventing the core from being damaged. Thus, the cathode active material with improved stability can be manufactured . In addition, since the amorphous oxide has excellent fracture toughness, the rolling density of the cathode active material can be increased as a result.

Due to the effect of the amorphous oxide, the life characteristics, output characteristics, and cycle characteristics of the secondary battery as a final product are improved, and the amount of gas generated in the battery can be reduced.

On the other hand, when the amorphous oxide contains only phosphorus (P) or contains only one or more metal elements selected from the group consisting of Group 2A elements and Group 3A elements, or includes other metal elements not described above, It is difficult to achieve the effect of preventing contact between the core and the electrolyte due to the formation of the surface treatment layer having excellent flexibility and chemical resistance as described above. Specifically, when the amorphous oxide contains Si, the flexibility of the surface treatment layer is lowered, and accordingly, the surface treatment layer may be damaged due to the expansion and contraction of the core during charging and discharging. When the amorphous oxide contains Li It may be advantageous in the initial capacity. However, since Li has good reactivity with the electrolytic solution, there is a fear that an additional layer is formed on the surface of the positive electrode.

The molar ratio of the phosphorus and metal elements in the amorphous oxide may be 1: 0.1 to 1: 2, specifically 1: 0.2 to 1: 1.5. When the above-mentioned range is satisfied, an amorphous oxide excellent in both flexibility, chemical resistance and fracture toughness can be provided. When the molar ratio of phosphorus and metal element satisfies the above range, excellent chemical resistance and flexibility are exhibited.

Further, the surface treatment layer may be formed on the whole surface of the core, or may be partially formed. Specifically, when the surface treatment layer is partially formed, it can be formed for a surface area of 25% or more and less than 100% of the total surface area of the core. When the surface treatment layer formation area is less than 25%, the effect of improving the surface treatment layer is insignificant.

On the other hand, when the surface treatment layer is partially formed, a plurality of surface treatment layers formed locally on the core surface may exist.

The surface treatment layer is preferably formed to have an appropriate thickness in consideration of the particle diameter of the core for determining the capacity of the cathode active material. The surface treatment layer may have an average thickness of 0.001 to 1 times, more preferably 0.001 to 0.2 times, the average radius of the core. More specifically, the surface treatment layer may have an average thickness of 10 to 500 nm, And may be 10 to 100 nm. If it is less than the above-mentioned range, the effect of improving the surface treatment layer formation may be insignificant. Exceeding the above range can increase the resistance to lithium ions passing through the surface treatment layer.

In the present invention, the thickness of the surface treatment layer can be measured through particle section analysis using a forced ion beam (fib).

The surface treatment layer may be contained in an amount of 0.05 wt% to 1 wt%, specifically 0.1 wt% to 0.7 wt%, more specifically 0.2 wt% to 0.6 wt% based on the total weight of the cathode active material have. When the above-described range is satisfied, the effect due to the surface treatment layer can be realized without deteriorating the capacity characteristics of the cathode active material as compared with the cathode active material having the same size.

Meanwhile, the core included in the cathode active material for a secondary battery according to an embodiment of the present invention may include a lithium composite metal oxide.

The lithium composite metal oxide is a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound). The lithium composite metal compound may be a layered lithium composite metal oxide which can be used at a high capacity and a high voltage.

The lithium composite metal compound may be represented by the following general formula (1).

≪ Formula 1 >

Li _a Ni _x Co _y M1 _z M2 _w O ₂

Wherein M 1 is Mn or Al and M 2 is at least one element selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Fe, V, Cr, Ba, Ca, 0? Z? 0.35, 0? W? 0.02 and x + y + z + w = 1.

In the lithium composite metal oxide represented by the general formula (1), Li may be contained in an amount corresponding to a, that is, 0.8? A? 1.2. When the above-described range is satisfied, it is possible to balance the improvement of the capacity characteristics of the cathode active material and the sintering property at the time of manufacturing the active material according to the Li content control. If the amount is less than the above-mentioned range, the capacity of the cathode active material may be lowered, and if it exceeds the above-mentioned range, the lithium composite metal oxide particles are sintered in the firing step, so that the production of the cathode active material may be difficult.

In the lithium composite metal oxide represented by Formula 1, Ni may be contained in an amount corresponding to x, that is, 0.3? X <1, specifically, 0.6? X <1. When the above-described range is satisfied, better capacity characteristics and high-temperature stability can be realized. Particularly, when Ni is contained in a high content of 0.6 or more, capacity characteristics of the battery can be improved when the battery is applied to the battery.

In the lithium composite metal oxide represented by Formula 1, Co may be included in an amount corresponding to y, that is, 0 <y? 0.35, specifically 0? Y? 0.2. When the above-described range is satisfied, the capacity characteristics of the positive electrode active material can be improved. When y is 0, the capacity characteristics may be degraded. If the amount exceeds the above range, the effect due to the increase of the content of Co may be insignificant.

In the lithium composite metal oxide of Formula 1, M 1 may be at least one selected from the group consisting of Mn and Al. In the case of the Mn of M1, since the capacity characteristics and the structural stability of the cathode active material are improved, a secondary battery which is the final product can realize a high capacity and the output characteristics can be improved. When M1 is Al, the output characteristics of the active material can be improved.

M1 may be included in the content corresponding to z, 0 < z < = 0.35, specifically 0 &lt; z = 0.2. If z is 0, an improvement effect according to the inclusion of M1 can not be obtained. If the value exceeds the above range, the output characteristics and the capacity characteristics of the secondary battery may be deteriorated.

The elements of Ni, Co, and M 1 in the lithium composite metal oxide of Formula 1 or the lithium composite metal oxide may be further modified by another element, that is, by M2, to improve battery characteristics by controlling the distribution of metal elements in the active material Some of which may be substituted or doped. M2 may be specifically at least one element selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Fe, V, Cr, Ba, Ca, Al and Nb, In the case of Mn, W, Ti, Mg or Al may be used, and when M1 is Al, W, Ti or Mg may be used. By the M2, the structural stability of the positive electrode active material is improved, and as a result, the output characteristics of the secondary battery can be improved.

The element of M2 may be contained in an amount corresponding to w, that is, an amount of 0? W? 0.02 within a range that does not deteriorate the properties of the cathode active material.

The core may be a primary particle or a secondary particle with aggregated primary particles. Where the primary particles can be uniform or non-uniform.

In addition, the core may have an average particle diameter (D ₅₀ ) of 1 탆 to 20 탆, specifically, 3 to 18 탆, in consideration of the specific surface area of the cathode active material and the density of the positive electrode mixture. When the core is a secondary particle, the average particle diameter (D ₅₀ ) may be from 50 nm to 1,000 nm. When the above-described range is satisfied, the rate characteristic and the initial capacity characteristic of the battery can be improved. If the amount is less than the above-mentioned range, the dispersibility in the positive electrode mixture may deteriorate due to agglomeration between the positive electrode active materials. Exceeding the above-mentioned range may lower the mechanical strength of the cathode active material and reduce the specific surface area.

In the present invention, the average particle diameter of the core can be measured through particle section analysis using a forced ion beam (fib).

The average particle diameter (D ₅₀ ) of the cathode active material according to an embodiment of the present invention can be defined as a particle diameter at a standard of 50% of the particle diameter distribution. The average particle diameter (D ₅₀ ) of the cathode active material can be measured using, for example, a laser diffraction method. Specifically, the average particle diameter (D ₅₀ ) of the cathode active material is measured by dispersing the particles of the cathode active material in a dispersion medium and then introducing the particles into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000) to output an ultrasonic wave of about 28 kHz 60 W, and the average particle diameter (D ₅₀ ) of 50% of the particle diameter distribution in the measuring apparatus can be calculated.

The cathode active material according to one embodiment of the present invention has the above-described structure and composition, and has an average particle diameter (D ₅₀ ) of 1 탆 to 20 탆 and a BET specific surface area of 0.1 m 2 / g to 0.7 m 2 / g . If the average particle diameter (D ₅₀ ) of the cathode active material is less than 1 탆 or the BET specific surface area exceeds 0.7 m 2 / g, there is a concern that the dispersion of the cathode active material in the active material layer due to agglomeration between the cathode active materials may decrease, . When the average particle diameter (D ₅₀ ) is more than 20 μm or the BET specific surface area is less than 0.1 m 2 / g, the dispersibility of the positive electrode active material per se and the capacity may decrease. In addition, the cathode active material according to one embodiment of the present invention can exhibit excellent capacity and charge / discharge characteristics by simultaneously satisfying the above-described average particle diameter and BET specific surface area condition. More specifically, the cathode active material may have an average particle diameter (D ₅₀ ) of 3 탆 to 18 탆 and a BET specific surface area of 0.2 m 2 / g to 0.5 m 2 / g.

The average particle diameter (D ₅₀ ) of the cathode active material according to an embodiment of the present invention can be defined and measured in the same manner as in the measurement of the average particle diameter of the core. In the present invention, the specific surface area of the positive electrode active material is measured by the BET (Brunauer-Emmett-Teller) method. Specifically, the specific surface area of the positive electrode active material is measured by using BEL Japan's BELSORP- Can be calculated from the nitrogen gas adsorption amount.

Also, the cathode active material according to one embodiment of the present invention may have a tap density of 1.5 g / cc or more, or 1.5 g / cc to 4 g / cc. By having a high tap density in the above-mentioned range, high capacity characteristics can be exhibited. More specifically, the cathode active material may have a tap density of 2.0 g / cc to 3.0 g / cc.

Also, the tap density of the cathode active material according to one embodiment of the present invention can be measured using a conventional tap density measuring instrument, specifically, TAP-2S manufactured by LOGAN.

According to another embodiment of the present invention, there is provided a method of manufacturing a cathode active material, which comprises the steps of: forming a first raw material containing phosphorus and a second raw material containing at least one metal element selected from the group consisting of Group 2A and Group 3A; A first step of forming an amorphous oxide containing phosphorus (P) and at least one metal element selected from the group consisting of Group 2A and Group 3A; And a second step of mixing the amorphous oxide and the lithium composite metal oxide and then performing a heat treatment to form a surface treatment layer containing the amorphous oxide on the lithium composite metal oxide.

The first raw material may be at least one selected from the group consisting of PO ₄ , P ₂ O ₄ and P ₂ O ₅ , and may be specifically P ₂ O ₅ . The first raw material has a glass property and has a ring structure or a layered structure since it has non-bridging oxygen (NBO) having double bonds. Due to this structure, excellent flexibility can be imparted to the amorphous oxide as compared with the silicate-based glass. Accordingly, the amorphous oxide made of the first raw material can be coated uniformly on the core, and the amorphous oxide can flexibly cope with the volume change of the core.

The second raw material may include one or more metal elements selected from the group consisting of Group 2A and Group 3AA and oxygen, and preferably, one selected from the group consisting of magnesium oxide, calcium oxide, and aluminum oxide It can be more than a species. The second raw material can impart excellent chemical resistance, hardness and fracture toughness to an amorphous oxide and an electrolytic solution and hydrogen fluoride derived from an electrolyte solution.

Meanwhile, in the first step, the first and second raw materials are mixed and melted at 600 ° C to 1,500 ° C, specifically 800 ° C to 1,100 ° C, and then cooled to form an amorphous oxide. The above-mentioned melting temperature can be controlled according to the kind and mixing ratio of the first and second raw materials.

The mixing ratio of the first raw material and the second raw material may be appropriately determined in consideration of the content of phosphorus and metal elements in the amorphous oxide forming the surface treatment layer. Specifically, the first raw material and the second raw material may be mixed in a molar ratio of 1: 0.1 to 1: 2, specifically 1: 0.2 to 1: 1.5. The reason for the numerical limitation is as described in the description of the molar ratio of phosphorus and metal element in the amorphous oxide.

After the first step, the amorphous oxide may be pulverized to have an average particle diameter of 10 nm to 500 nm, specifically, 100 nm to 300 nm. In order for the amorphous oxide to be well coated on the core, it is preferable to have the above-mentioned particle size. If it is less than the above-mentioned range, there is a fear that coating property on the surface of the positive electrode active material is lowered due to aggregation of the raw material particles. Exceeding the above range may lower the compactness of the surface treatment layer formed on the core.

The pulverization may be carried out by a conventional pulverizing process such as a ball mill.

In the second step, the mixing may be solid phase mixing. Solid-phase mixing is free from the formation of byproducts by a solvent or the like used in the liquid phase mixing, and a more uniform surface treatment layer can be formed.

In the second step, the heat treatment may be performed at 300 ° C to 600 ° C, specifically 300 ° C to 500 ° C. When the above-mentioned temperature is satisfied, the surface treatment layer forming property is excellent and the positive electrode active material is not denatured. In addition, no side reactions are formed between the amorphous oxide and the lithium composite metal oxide.

The atmosphere at the time of the heat treatment is not particularly limited and may be carried out under a vacuum, inert atmosphere or atmospheric environment. The heat treatment may be performed under the above conditions for 5 hours to 48 hours, or for 10 hours to 20 hours.

In addition, the heat treatment process may be performed in multiple stages within the temperature range described above, and may be performed by varying the temperature according to the progress of each step.

According to another embodiment of the present invention, it is possible to provide a positive electrode comprising the positive electrode active material.

Specifically, the anode includes a cathode current collector and a cathode active material layer formed on the cathode current collector and including the cathode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium, , Silver or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the cathode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

In addition, the cathode active material layer may include a conductive material and a binder together with the cathode active material described above.

At this time, the conductive material is used for imparting conductivity to the electrode. The conductive material can be used without particular limitation as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or a conductive polymer such as a polyphenylene derivative, and mixtures of at least one of these may be used. The conductive material may be typically contained in an amount of 1 to 30% by weight based on the total weight of the cathode active material layer.

In addition, the binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose ), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and mixtures of at least one of them may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the cathode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the composition for forming a cathode active material layer containing the above-mentioned cathode active material and optionally a binder and a conductive material may be coated on the cathode current collector, followed by drying and rolling. At this time, the types and contents of the cathode active material, the binder, and the conductive material are as described above.

Examples of the solvent include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and the like. Water, etc., and mixtures of at least one of them may be used. The amount of the solvent to be used is sufficient to dissolve or disperse the cathode active material, the conductive material and the binder in consideration of the coating thickness of the slurry and the yield of the slurry, and then to have a viscosity capable of exhibiting excellent thickness uniformity Do.

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

According to another embodiment of the present invention, there is provided an electrochemical device including the anode. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, it may be a lithium secondary battery.

Specifically, the lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. In addition, the lithium secondary battery may further include a battery container for storing the positive electrode, the negative electrode, and an electrode assembly of the separator, and a sealing member for sealing the battery container.

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

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

The anode active material layer optionally includes a binder and a conductive material together with the anode active material. The negative electrode active material layer may be formed by applying and drying a composition for forming a negative electrode including a negative electrode active material on the negative electrode collector and, optionally, a binder and a conductive material, or by casting the composition for forming a negative electrode on a separate support , And a film obtained by peeling from the support may be laminated on the negative electrode collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and dedoping lithium such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a composite containing the above-mentioned metallic compound and a carbonaceous material such as Si-C composite or Sn-C composite, and mixtures of at least one of them may be used. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar coke derived cokes).

In addition, the binder and the conductive material may be the same as those described above for the anode.

Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions. The separator can be used without any particular limitation as long as it is used as a separator in a lithium secondary battery. Particularly, It is preferable to have a low resistance and an excellent ability to impregnate the electrolyte. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a multilayer structure.

Examples of the electrolyte used in the present invention include an organic-based liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. It is not.

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

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is a straight, branched or cyclic hydrocarbon group of C2 to C20, which may contain a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

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

In addition to the electrolyte components, the electrolyte may contain, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate or the like, pyridine, triethanolamine, or the like for the purpose of improving lifetime characteristics of the battery, Ethyl phosphite, triethanol amine, cyclic ether, ethylenediamine, glyme, hexametriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, At least one additive such as benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, The additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention ratio, it can be used in portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles hybrid electric vehicle (HEV)).

In particular, the lithium secondary battery according to the present invention can be usefully used as a high voltage battery having a voltage of 4.3 V or higher. Concretely, the capacity retention ratio after charging and discharging 400 times under the condition that the charging end voltage of the lithium battery is 4.3 V or more, specifically 4.3 V to 4.35 V, specifically 80% or more, preferably 85 % &Lt; / RTI &gt;

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example  One

( Cathode active material  Produce)

P ₂ O ₅ and Al ₂ O ₃ were mixed at the molar ratios shown in Table 1 below. The resultant was melted at the melting temperature shown in Table 1 below. Thereafter, the resultant was cooled at room temperature to prepare an amorphous oxide. Thereafter, the amorphous oxide was pulverized to have an average particle size (D ₅₀ ) of 300 nm.

Subsequently, 0.5 part by weight of the amorphous oxide was mixed in a solid phase with 100 parts by weight of the lithium composite metal oxide described in Table 1 below and then heated at the heat treatment temperature described in Table 1 below. Thus, a cathode active material having a surface-treated layer containing an amorphous oxide formed on a core containing a lithium composite metal oxide was produced.

(Preparation of positive electrode)

The cathode active material, carbon black, and PVdF prepared above were mixed in a weight ratio of 95: 2.5: 2.5 and mixed with N-methylpyrrolidone to prepare a composition for forming an anode (viscosity: 5000 mPa.s) , Dried at 130 캜, and rolled to prepare a positive electrode.

(Preparation of negative electrode)

A mixture of natural graphite, a carbon black conductive material and a PVDF binder as a negative electrode active material in a weight ratio of 85: 10: 5 was mixed with N-methyl pyrrolidone as a solvent to prepare a composition for forming a negative electrode, To prepare a negative electrode.

(Production of lithium secondary battery)

An electrode assembly was made between the positive electrode and the negative electrode through a separator made of porous polyethylene. After the electrode assembly was positioned inside the case, an electrolyte solution was injected into the case to manufacture a lithium secondary battery. The electrolyte solution was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent composed of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3/4/3) Respectively.

Example  2

P ₂ O ₅ and MgO were mixed in the molar ratios shown in Table 1 below. The resultant was melted at the melting temperature shown in Table 1 below. Thereafter, the amorphous oxide was prepared by cooling at room temperature, and the amorphous oxide was pulverized to have an average particle size (D ₅₀ ) of 300 nm. Subsequently, 0.5 part by weight of the amorphous oxide was mixed in a solid phase with 100 parts by weight of the lithium composite metal oxide, and the mixture was heated at the heat treatment temperature shown in Table 1 to form a surface treatment layer containing an amorphous oxide Thereby preparing a cathode active material.

A positive electrode, a negative electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that the above-prepared positive electrode active material was used.

Example  3

P ₂ O ₅ and CaO were mixed in the molar ratios shown in Table 1 below. The resultant was melted at the melting temperature shown in Table 1 below. Thereafter, the amorphous oxide was prepared by cooling at room temperature, and the amorphous oxide was pulverized to have an average particle size (D ₅₀ ) of 300 nm. Subsequently, 0.5 part by weight of the amorphous oxide was mixed in a solid phase with 100 parts by weight of the lithium composite metal oxide, and the mixture was heated at the heat treatment temperature shown in Table 1 to form a surface treatment layer containing an amorphous oxide Thereby preparing a cathode active material.

A positive electrode, a negative electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that the above-prepared positive electrode active material was used.

division Metal oxide P ₂ O ₅ : metal oxide mole ratio Melting temperature
(° C) Heat treatment temperature (캜) Furtherance Example 1 Al ₂ O ₃ 1: 1 1,100 500 LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ Example 2 MgO 1: 0.5 950 400 LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ Example 3 CaO 1: 0.5 800 400 LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂

Comparative Example 1

A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1 except that no separate surface treatment layer was formed.

Comparative Example  2

A positive electrode active material and a positive electrode and a lithium secondary battery comprising the positive electrode active material were prepared in the same manner as in Example 1 except that only PO _{4 was} used as the surface treatment layer.

Comparative Example  3

A positive electrode active material and a positive electrode and a lithium secondary battery comprising the same were prepared in the same manner as in Example 1 except that only Al ₂ O _{3 was} used as the surface treatment layer.

Experimental Example  One: The lithium secondary battery  Character rating

The lithium secondary batteries of Example 1, Comparative Example 2, and Comparative Example 3 were charged at a constant current (CC) of 0.33 C at 45 캜 until the voltage shown in Table 2 was obtained, and a constant voltage (CV) of 4.3 V was applied. And charged once until the charge current became 0.05%. Subsequently, discharge was performed until the voltage reached 2.5 V at a constant current of 0.33 C, and the discharge capacity of one cycle was measured. This was repeated up to 400 cycles, and the discharge capacity retention ratio, which is the ratio of the discharge capacity according to the number of cycles versus the discharge capacity in one cycle, was measured. The results are shown in Fig.

division Charging end voltage Example 1 4.35V Comparative Example 2 4.35V Comparative Example 3 4.20V

Referring to FIG. 1, in the case of the lithium secondary battery of Example 1, since the cycle number is elapsed, the discharge capacity retention rate is gradually lowered, thereby exhibiting a stable life characteristic. However, in the case of the lithium secondary battery of Comparative Example 2, the durability of the positive electrode active material was not excellent, and the discharge capacity retention ratio rapidly decreased. It was confirmed that the lithium secondary battery of Comparative Example 3 can be driven at a voltage lower than that of the lithium secondary battery of Example 1 and the rate of decrease of the discharge capacity retention rate is faster than that of the lithium secondary battery of Example 1. [

Experimental Example  2: Capacity retention rate after high temperature storage

The capacity retention ratios of the lithium secondary batteries prepared in Examples 2 to 3 and Comparative Example 1 after storage at high temperature were measured. At this time, four samples were prepared for each of Examples 2 to 3 and Comparative Example 1, and the capacity retention ratio after storage at high temperature was measured.

Specifically, the lithium secondary batteries prepared in Examples 2 to 3 and Comparative Example 1 were fully charged at a constant current of 0.33 C at a room temperature (25 캜) to 4.35 V, and then charged at a constant current of 0.33 C at a SOC of 100% And discharged. The discharge capacity was calculated to be the capacity immediately after the production. Thereafter, the lithium secondary batteries prepared in Examples 2 to 3 and Comparative Example 1 were fully charged to 4.35 V, and then the capacity retention ratio was measured while being stored at 60 ° C for 4 weeks.

After preparation, the capacities after 1, 2, 3 and 4 weeks after storage and after storage at high temperature, respectively, were calculated and are shown in FIG.

As shown in FIG. 2, it was confirmed that the lithium secondary batteries prepared in Examples 2 and 3 exhibited a capacity retention ratio of 80% or more during storage for 4 weeks at a high temperature. However, when the lithium secondary battery of Comparative Example 1 was stored at a high temperature for 2 weeks or longer, it was confirmed that the capacity of the lithium secondary battery was deteriorated by the damage of the lithium composite metal oxide due to contact between the lithium composite metal oxide and the electrolyte .

Experimental Example  3: Resistance characteristic after high temperature storage

The resistance of the lithium secondary batteries prepared in Examples 2 to 3 and Comparative Example 1 after storage at high temperature was measured. At this time, four samples were prepared for each of Examples 2 to 3 and Comparative Example 1, and the capacity retention ratio after storage at high temperature was measured.

Specifically, the lithium secondary batteries prepared in Examples 2 to 3 and Comparative Example 1 were charged to 4.35 V at a constant current of 0.33 C at 25 캜, discharged at 2.5 V with a constant current of 0.33 C at an SOC of 100% Respectively. Then, the lithium secondary batteries prepared in Examples 2 to 3 and Comparative Example 1 were fully charged to 4.35 V and then stored at 60 ° C. for 4 weeks. The resistance characteristics of the lithium secondary batteries were measured as shown in FIG.

As shown in FIG. 3, it was confirmed that the resistance of the lithium secondary battery manufactured in Examples 2 and 3 hardly increased during storage for 4 weeks at a high temperature. However, the resistance of the lithium secondary battery prepared in Comparative Example 1 was rapidly increased when stored for 1 week or more at high temperature, and the resistance increased more than twice as much as the initial resistance when stored for 2 weeks or more.

Claims (15)

A core comprising a lithium composite metal oxide; And
And a surface treatment layer which is located on the surface of the core and comprises an amorphous oxide containing phosphorus (P) and at least one metal element selected from the group consisting of Group 2A elements and Group 3A elements, Active material.
The method according to claim 1,
Wherein the mole ratio of phosphorus: metal element in the amorphous oxide is 1: 0.1 to 1: 2.
The method according to claim 1,
Wherein the surface treatment layer has an average thickness of 0.001 to 1 times the average radius of the core.
The method according to claim 1,
Wherein the surface treatment layer is 0.05 wt% to 1 wt% with respect to the total weight of the cathode active material.
The method according to claim 1,
Wherein the lithium composite metal oxide is represented by the following Formula 1:
&Lt; Formula 1 >
Li _a Ni _x Co _y M1 _z M2 _w O ₂
In Formula 1,
M1 is Mn or Al,
M2 is at least one element selected from the group consisting of W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca,
0? Z? 0.35, 0? W? 0.02 and x + y + z + w = 1.
(P), the group 2A element, and the group 3A element, by using a first raw material containing phosphorus and a second raw material containing at least one metal element selected from the group consisting of Group 2A elements and Group 3A elements, A first step of forming an amorphous oxide containing at least one metal element selected from the group consisting of Group III elements; And
And a second step of mixing the amorphous oxide and the lithium composite metal oxide and then performing a heat treatment to form a surface treatment layer containing the amorphous oxide on the lithium composite metal oxide.
The method of claim 6,
Wherein the first raw material is at least one selected from the group consisting of PO ₄ , P ₂ O _4, and P ₂ O ₅ .
The method of claim 6,
Wherein the second raw material is at least one selected from the group consisting of magnesium oxide, calcium oxide, and aluminum oxide.
The method of claim 6,
Wherein the first step comprises mixing the first and second raw materials, melting the first and second raw materials at 600 ° C to 1,500 ° C, and then cooling to form an amorphous oxide.
The method of claim 9,
Wherein the mixing is performed by mixing the first raw material and the second raw material at a molar ratio of 1: 0.1 to 1: 2.
The method of claim 6,
Further comprising the step of grinding the amorphous oxide to have an average particle diameter of 10 nm to 500 nm after the first step.
The method of claim 6,
Wherein the heat treatment is performed at a temperature of 300 ° C to 600 ° C in the second step.
A positive electrode for a secondary battery comprising the positive electrode active material for a secondary battery according to claim 1.
A secondary battery comprising a positive electrode for a secondary battery according to claim 13.
15. The method of claim 14,
Wherein the secondary battery has a discharge capacity retention rate of 80% or more after 400 charge / discharge cycles with a charge end voltage of 4.3 V or higher.

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