KR20180077081A - Positive electrode active material for lithium secondary battery, method for preparing the same, and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery having improved structural stability and thermal stability; a manufacturing method thereof; and a lithium secondary battery including the same. The positive electrode active material of the present invention comprises: a central part including a first lithium composite metal oxide in which an average composition is represented by chemical formula 1, Li_(1+x1)(Ni_a1Mn_b1Co_(1-a1-b1-c1)Me_c1)O_(2-y1)A_y1; and a surface part including a second lithium composite metal oxide in which an average composition is represented by chemical formula 2, Li_(1+x2)(Ni_a2Mn_b2Co_(1-a2-b2-c2)Me_c2)O_(2-y2)A_y2.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the lithium secondary battery. BACKGROUND ART [0002]

The present invention relates to a cathode active material for a lithium secondary battery, a method for producing the cathode active material, and a lithium secondary battery including the cathode active material.

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.

Lithium transition metal complex oxides are used as the positive electrode active material of lithium secondary batteries, and lithium cobalt composite metal oxides such as LiCoO ₂ having a high operating voltage and excellent capacity characteristics are mainly used. However, LiCoO ₂ has very poor thermal properties due to the destabilization of the crystal structure due to the depolymerization. In addition, since LiCoO ₂ is expensive, it can not be used in large quantities as a power source for fields such as electric vehicles and the like.

A variety of lithium transition metal oxides such as LiNiO ₂ , LiMnO ₂ , LiMn ₂ O _4, or LiFePO ₄ have been developed as cathode active materials to replace them. LiNiO ₂ has the advantage of exhibiting a high discharge capacity of a battery, but it is difficult to synthesize a simple solid phase reaction, and has a low thermal stability and low cycle characteristics. Lithium manganese type oxides such as LiMnO ₂ or LiMn ₂ O ₄ have the advantages of excellent thermal stability and low cost, but have a problem of low capacity and low temperature characteristics. In particular, in the case of LiMn ₂ O ₄ but a part commercialized in low-end products, there is a problem that occurs structure modification (Jahn-Teller distortion) due to the Mn ^{+ 3} during the charge and discharge whereby the life characteristics deteriorate. In addition, LiFePO ₄ has been studied for hybrid electric vehicle (HEV) due to its low cost and excellent safety, but it is difficult to apply LiFePO ₄ to other fields due to its low conductivity.

As a result, LiCoO ₂ has been widely used as an alternative cathode active material because it is a lithium nickel manganese cobalt oxide, Li (Ni _a Co _b Mn _c ) O ₂ (At this time, 1, 0 <b <1, 0 <c <1, and a + b + c = 1), where a, b, and c are atomic fractions of independent oxide elements. This material is advantageous in that it can be used at a high capacity and a high voltage at a lower cost than LiCoO ₂ , but has a disadvantage of poor rate capability and high lifetime at high temperature.

The lithium secondary battery using the above-mentioned positive electrode active material has a problem in that, as the charging and discharging are repeated, the interfacial resistance between the electrode including the active material and the electrolyte increases, the electrolyte decomposes due to moisture or other influences inside the battery, There is a problem that the safety and lifespan characteristics of the battery are drastically deteriorated due to an exothermic reaction accompanied by a sudden structural collapse, and this problem is particularly serious at high temperature and high voltage conditions.

To solve these problems, there have been proposed methods of improving the structural stability and surface stability of the active material itself and enhancing the interfacial stability between the electrolyte and the active material by doping or surface-treating the positive electrode active material. However, It is not satisfactory.

Moreover, with the recent increase in demand for high-capacity batteries, there is a growing need to develop a cathode active material capable of securing internal structure and surface stability of active material particles and improving battery safety and life characteristics.

Japanese Patent Application Laid-Open No. 2009-140787 (published on Jun. 25, 2009)

In order to solve the above problems, a first technical object of the present invention is to provide a cathode active material for a lithium secondary battery which can improve output characteristics, lifetime characteristics and thermal stability.

A second object of the present invention is to provide a method for producing the cathode active material having improved output characteristics, lifetime characteristics and thermal stability.

A third object of the present invention is to provide a positive electrode and a lithium secondary battery including the positive electrode active material.

In one aspect, the present invention is a cathode active material having a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface, wherein the cathode active material has a first lithium composite metal oxide having an average composition represented by the following Formula 1 A center containing; And a surface portion comprising a second lithium composite metal oxide having an average composition represented by the following Formula 2, wherein the cathode active material has a peak at 235 ° C or higher when measured by a differential scanning calorimetry method, A cathode active material is provided:

[Chemical Formula 1]

Li _{1 + x 1} (Ni _a1 Mn _b1 Co1 _-a1-b1-c1 Me _c1 ) O2 _-y1 A _y1

(2)

_{Li 1 + x2 (Ni a2 Mn} b2 Co 1-a2-b2-c2 Me c2) O 2-y2 A y2

In the above Formulas 1 and 2, Me is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, , Mg, B and Mo, A is at least one doping element selected from the group consisting of PO ₄ ^3- , NO ₄ ^- , CO ₃ ^2- , BO ₃ ^- , Cl ^- , Br ^- , I ^- and F ^- B1 + c1 < 1, 0? X1? 0.1 and 0.0001 < y1 < 0.2, 0.1? A2 <0.8, 0.1 <b2? 0.9, 0 <c2? 0.1, 0.2 <a2 + b2 + c2 <1, 0? X2? 0.1 and 0.0001 <y2?

In another aspect, the present invention is directed to a method of forming a thin film of nickel, cobalt, manganese and doping element Me, wherein Me is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Wherein the first metal-containing solution contains at least one selected from the group consisting of Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo; Preparing a second metal containing solution comprising nickel, cobalt, manganese and doping element Me; Containing solution and the second metal-containing solution so that the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100 vol%: 0 vol% to 0 vol%: 100 vol% Adding an ammonium cationic complexing agent and an anion-containing basic compound to prepare a cathode active material precursor exhibiting a concentration gradient in which the nickel and manganese gradually change from the center of the particle to the surface independently from each other; Mixing and baking the cathode active material precursor and the lithium-containing raw material to synthesize a cathode active material; And performing the heat treatment of the cathode active material at 600 ° C to 800 ° C under an oxygen atmosphere.

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

The cathode active material according to the present invention has a concentration gradient in which nickel and manganese gradually change from the center to the surface of the particles, thereby making it possible to produce a cathode active material having increased structural stability and thermal stability. In particular, by providing a cathode active material including a nickel portion having a high nickel content and a nickel portion having a low nickel content, it is possible to manufacture a secondary battery exhibiting excellent capacity and improved output characteristics when applied to a secondary battery.

Further, the cathode active material of the present invention can further improve the output characteristics of a battery using the doping element (Me) by doping the metal position of the lithium composite metal oxide with the doping element (Me). In addition, partial replacement of the anion at the oxygen position of the lithium composite metal oxide can prevent the desorption of oxygen during charging and discharging of the lithium secondary battery, thereby providing a lithium secondary battery having a high capacity and excellent lifetime characteristics.

1 is a graph showing the heat flow rate of the cathode active material prepared in Examples 1 and 2 and Comparative Examples 2 and 3 according to the present invention.
2A and 2B are scanning electron microscope (SEM) photographs of the cathode active material prepared in Example 2 and Comparative Example 2 of the present invention, respectively.
3 is a graph showing lifetime characteristics of the lithium secondary battery manufactured in Example 2 and Comparative Example 1 according to the cycle at 4.25 V according to the present invention.
4 is a comparative graph showing lifetime characteristics and resistance increase rate of the lithium secondary battery according to the cycle of Example 1 and Comparative Example 3 according to the present invention.
5 is a graph showing resistance characteristics according to the state of charge (SOC) according to Example 2 and Comparative Example 2 of the present invention.
6 is a graph showing lifetime characteristics of the lithium secondary battery manufactured in Example 1 and Comparative Example 2 according to the cycle at 4.5 V according to the present invention.

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

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.

In the case of the cathode active material, cracks and collapse of the active material particles are liable to occur in the coating and rolling process during the production of the battery, and the active material particles are cracked during the charging / discharging process of the battery, thereby deteriorating the life characteristics. When the nickel content of the cathode active material having a constant internal / external composition is increased, the anode degeneration occurs at the surface due to the side reaction at the surface. On the other hand, in the case of the cathode active material having a concentration gradient in which the content of the metallic element in the active material gradually changes, since the nickel content in the central portion is higher than the surface or the average composition, cracking in the cathode active material causes internal stability There is a problem that it is greatly weakened.

In order to solve such a problem, in the present invention, in the cathode active material of the concentration gradient type in which the content of the metal in the cathode active material gradually changes to have excellent structural stability, nickel having a high capacity characteristic at the center portion of the cathode active material And a portion of the metal in the cathode active material is partially doped with a highly stable doping element to improve the output characteristics. In addition, A positive electrode active material capable of preventing the desorption of oxygen during charging and discharging by substituting anions is provided.

Specifically, the cathode active material according to an embodiment of the present invention is a cathode active material having a concentration gradient in which nickel and manganese gradually change from the center to the surface of the particles, and the cathode active material has an average composition represented by the following formula A first lithium composite metal oxide; And a surface portion comprising a second lithium composite metal oxide having an average composition represented by the following Formula 2, wherein the cathode active material has a peak at 235 ° C or higher when measured by a differential scanning calorimetry method, A cathode active material is provided:

[Chemical Formula 1]

Li _{1 + x 1} (Ni _a1 Mn _b1 Co1 _-a1-b1-c1 Me _c1 ) O2 _-y1 A _y1

(2)

_{Li 1 + x2 (Ni a2 Mn} b2 Co 1-a2-b2-c2 Me c2) O 2-y2 A y2

In the above Formulas 1 and 2, Me is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, , Mg, B and Mo, A is at least one doping element selected from the group consisting of PO ₄ ^3- , NO ₄ ^- , CO ₃ ^2- , BO ₃ ^- , Cl ^- , Br ^- , I ^- and F ^- B1 + c1 <1, 0? X1? 0.1, 0.0001 <y1? 0.1 where 0 <b1 <0.2, 0 <c1? 0.1 and 0.8 <a1 + b1 + c1 < 0.2? A2 + b2 + c2? 1, 0? X2? 0.1 and 0.0001 <y2? 0.1, 0.1? A2 <0.8, 0.1 <b2? 0.9, 0 <c2? 0.1.

Nickel and manganese contained in the cathode active material may independently increase or decrease while exhibiting a concentration gradient gradually changing from the center of the cathode active material particle to the particle surface. At this time, the concentration gradient slope of the metal element may be constant.

The nickel, cobalt, and manganese contained in the cathode active material may each independently have a concentration gradient slope value.

Specifically, the concentration of nickel contained in the cathode active material may decrease with a concentration gradient gradually changing from the center of the cathode active material particle to the particle surface, wherein the concentration gradient slope of the nickel is the center of the cathode active material particle From surface to surface. As described above, when the concentration of nickel is maintained at a high concentration at the center of the particles in the active material particle and the concentration gradient is decreased toward the particle surface side, reduction of the capacity can be prevented while exhibiting thermal stability.

Also, the concentration of manganese contained in the cathode active material may increase with a concentration gradient gradually changing from the center of the active material particle to the particle surface, wherein the concentration gradient slope of the manganese is from the center of the cathode active material particle to the surface It can be constant. As described above, when the concentration of manganese in the active material particle maintains a low concentration in the center of the particle and the concentration gradient increases in concentration toward the surface side, excellent thermal stability can be obtained without decreasing the capacity.

Also, the concentration of cobalt contained in the cathode active material may be kept constant from the center of the active material particles to the particle surface due to the diffusion of cobalt during synthesis of the cathode active material.

In the present invention, the metal indicates a gradual gradient of concentration, which means that the concentration of the metal is present in a concentration distribution in which the concentration of the metal continuously changes stepwise in the whole or a specific region. Specifically, the concentration distribution is such that the change in the metal concentration per 1 탆 toward the surface in the particle is 0.1 atom% to 30 atom%, more specifically 0.1 atom%, more preferably 0.1 atom%, based on the total atomic weight of the metal contained in the active material particle. And may be a difference of at% to 20 atomic%.

As described above, the cathode active material according to the embodiment of the present invention has a concentration gradient in which the concentration of the metal gradually changes according to the position in the cathode active material particles, so that there is no abrupt phase boundary region from the center to the surface The crystal structure is stabilized and the thermal stability is increased. In addition, when the gradient of the concentration gradient of the metal is constant, the effect of improving the structural stability can be further improved. By varying the concentration of each metal in the active material particle through the concentration gradient, The battery performance improvement effect of the active material can be further improved.

As described above, the cathode active material for a secondary battery according to an embodiment of the present invention includes lithium composite metal oxide particles having a concentration gradient in which nickel and manganese gradually change from the center to the surface of the particle, , High durability and thermal stability, and at the same time, performance degradation at high voltage can be minimized.

Specifically, the central portion includes a first lithium composite metal oxide having an average composition represented by Formula 1.

The central portion may contain nickel in an amount of 80 mol% or more and less than 100 mol%, preferably 90 mol% or more and less than 100 mol%, based on the total moles of metal elements excluding lithium contained in the entire central portion. At this time, when the nickel content is less than 80 mol%, the capacity of the cathode active material is decreased, and thus there is a problem that it can not be applied to an electrochemical device requiring a high capacity.

The center portion may contain manganese in an amount of more than 0 mol% and less than 20 mol%, preferably more than 0 mol% and 5 mol% or less, based on the total moles of metal elements excluding lithium contained in the entire central portion. At this time, when the content of manganese is 20 mol% or more, a problem may arise in expressing a high capacity.

In addition, the content of cobalt contained in the central portion may vary depending on the contents of nickel, manganese, and Me. When the content of cobalt is excessively high, the cost of the raw material increases due to the high content of cobalt, And there is a problem that it is difficult to achieve sufficient rate characteristics and high powder density of the battery at the same time when the content of cobalt is too low. The cobalt contained in the central portion may be contained in an amount of more than 0 mol% and less than 20 mol%, preferably 5 mol% or more and 10 mol% or less, based on the total moles of metal elements contained in the entire central portion.

On the other hand, the surface portion includes a second lithium composite metal oxide having an average composition represented by Formula 2.

The surface portion may contain nickel in an amount of 10 mol% or more and less than 80 mol%, preferably 60 mol% or more and less than 80 mol%, based on the total molar amount of metal elements excluding lithium contained in the entire surface portion. If the nickel content is less than 10 mol%, the average capacity of the cathode active material may decrease. If the nickel content exceeds 80 mol%, the stability required for the surface portion is not satisfied, Can be degraded.

The surface portion may have a manganese content of more than 10 mol% and less than 90 mol%, preferably 10 mol% or more and 20 mol% or less, based on the total moles of metal elements excluding lithium contained in the entire surface portion. At this time, when the manganese content exceeds 90 mol%, a problem may arise in expressing a high capacity.

In addition, the content of cobalt contained in the surface portion may vary depending on the contents of nickel, manganese, and Me, and may be uniformly maintained throughout the center portion and the surface portion. The cobalt contained in the surface portion may be contained in an amount of more than 0 mol% and less than 20 mol%, preferably 5 mol% or more and 15 mol% or less, based on the total moles of the metal elements contained in the entire surface portion.

When a second lithium composite metal oxide having a large amount of nickel having a high capacity characteristic as described above is formed into a center portion and a nickel content is low on the surface of the center portion and a second lithium composite metal oxide having excellent thermal stability is formed as a surface portion, It is possible to provide a positive electrode active material excellent in output characteristics, life characteristics and thermal stability.

Meanwhile, the nickel, cobalt, or manganese contained in the central portion and the surface portion may be doped with one or more doping elements Me. In the case of the cathode active material doped with such a doping element, the doping element may be uniformly contained on the surface and inside of the cathode active material, thereby improving the structural stability of the cathode active material and improving lifetime characteristics and thermal stability.

For example, the doping element Me may be any one of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, and Ta, as long as it can contribute to improvement of the structural stability of the cathode active material. And at least one doping element selected from the group consisting of La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, .

The Me may be independently 0 mol% or more and 10 mol% or less, preferably 0.05 mol% or more and 5 mol% or less, based on the total moles of metal elements excluding lithium contained in the entire central portion and the surface portion. For example, when the Me and the Me in the central portion and the surface portion independently are greater than 10 mol%, the lithium byproduct may increase.

The oxygen (O ₂ ) contained in the central portion and the surface portion may be substituted with one or more anions A. In the case of such a positive electrode active material substituted with an anion, since the negative electrode can be uniformly contained on the surface and inside of the positive electrode active material, the secondary battery manufactured based thereon exhibits excellent output characteristics and lifetime characteristics and exhibits high charging / discharging efficiency .

That is, a specific anion uniformly contained on the surface and inside of the positive electrode active material contributes to improvement of ion conductivity between the grains and induces a small amount of crystal or crystal growth, thereby reducing the structural change during oxygen generation in the activation step, And it is possible to improve the performance of the battery such as the rate characteristic.

And A is as long as they can contribute to increase the ionic conductivity between crystals can be used without particular limitation, for _{^{example, PO 4 3-, NO 4 -}} , CO 3 2-, BO 3 -, Cl -, Br -, I ^- and F ^- , preferably at least one selected from the group consisting of PO ₄ ^3- , NO ₄ ^- , CO ₃ ^2- , BO ₃ ^- and F ^- .

The above A may be substituted independently with 0.01 mol% or more and 10 mol% or less, preferably 0.05 mol% or more and 5 mol% or less, relative to the total moles of oxygen contained in the entire central portion and the surface portion have. For example, each of the A and the A contained in the central part and the surface part independently includes less than 0.01 mol%, the effect of preventing the desorption of oxygen may be insignificant, and if it exceeds 10 mol%, the crystallization of the cathode active material is disturbed, It may be difficult to improve the performance of the active material.

The average particle diameter (D ₅₀ ) of the cathode active material may be 4 탆 to 20 탆, and preferably 6 탆 to 15 탆. For example, when the average particle diameter of the cathode active material is less than 4 탆, the rolling density is low and a high energy density can not be realized. When the average particle diameter is more than 20 탆, the cathode active material can not be rolled down to a certain thickness.

In the present specification, the average particle diameter (D ₅₀ ) can be defined as a particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve of the particles. The average particle diameter (D ₅₀ ) can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of a particle diameter of several millimeters from a submicron region, resulting in high reproducibility and high degradability.

The cathode active material may further include a coating layer formed on the surface thereof. The coating layer may include at least one selected from the group consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr. have.

The coating layer prevents contact between the cathode active material and the electrolyte contained in the lithium secondary battery to suppress the occurrence of side reactions, thereby improving lifetime characteristics and increasing the packing density of the cathode active material.

The coating layer may be formed on the entire surface of the cathode active material, or may be partially formed. Specifically, when the coating layer is partially formed on the surface of the cathode active material, the coating layer may be formed from 20% or more to less than 100% of the total area of the cathode active material. If the area of the coating layer is less than 20%, the lifetime characteristics and the packing density improvement effect due to the formation of the coating layer may be insignificant.

The coating layer may have a thickness ratio of 0.001 to 1 based on the average particle diameter of the cathode active material particles. If the ratio of the thickness of the coating layer to the particles of the cathode active material is less than 0.001, the lifetime characteristics and the filling density improvement effect of the formation of the coating layer is insignificant, and if the thickness ratio exceeds 1, .

When the heat flow rate is measured by differential scanning calorimetry, the cathode active material may exhibit a peak at a temperature of 235 ° C or higher, preferably 235 ° C to 250 ° C, and more preferably 235 ° C to 240 ° C. For example, the heat flow rate is a measure of the amount of heat that is emitted while the temperature of the cathode active material is raised to 10 ° C / min using a differential scanning calorimeter (DSC). When the heat flow rate measured by the differential scanning calorimetry of the cathode active material satisfies the above range, the thermal stability of the cathode active material can be improved.

Further, the crystal grains of the cathode active material may further have crystal orientation in a direction perpendicular to the C axis. When the crystal grains of the cathode active material have crystal orientation in a direction perpendicular to the C axis, the mobility of lithium ions contained in the cathode active material is improved and the structural stability of the active material is increased. Thus, , The resistance characteristic and the long-term life characteristic can be improved.

For example, the particles of the cathode active material have a structure in which one or more oxygen layers and metal layers are layered, and lithium ions are interposed between the oxygen layer and the metal layer, wherein the C- Means a direction perpendicular to the metal layer and the oxygen layer in the stacked structure of the active material particles.

In addition, when the cathode active material has a crystalline orientation in one direction, intercalation and deintercalation of lithium ions can be facilitated during charging and discharging in the laminated cathode active material, thereby improving the output characteristics of the lithium secondary battery .

The cathode active material may include, but is not limited to, less than 1% by weight lithium byproduct. Specifically, the cathode active material may include less than 1% by weight of lithium by-products including LiOH and Li ₂ CO ₃ . When the lithium byproduct is contained in the positive electrode active material in an amount of 1 wt% or more, the output characteristics of the lithium secondary battery may be deteriorated.

The method of manufacturing a positive electrode active material according to an embodiment of the present invention includes the steps of preparing nickel, cobalt, manganese and doping element Me (where Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, A first metal containing solution containing at least one selected from the group consisting of Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo; 1) preparing a second metal-containing solution containing nickel, cobalt, manganese and a doping element Me at a concentration different from that of the first metal-containing solution; Containing solution and the second metal-containing solution so that the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100 vol%: 0 vol% to 0 vol%: 100 vol% Adding an ammonium cationic complexing agent and an anion-containing basic compound to produce a cathode active material precursor exhibiting a concentration gradient in which the nickel and manganese gradually change from the center of the particle to the surface independently of each other 2); Synthesizing the cathode active material by mixing and firing the cathode active material precursor and the lithium-containing raw material (Step 3); And performing the heat treatment of the cathode active material at 600 ° C to 800 ° C under an oxygen atmosphere (Step 4).

As for the method for producing the positive electrode active material, all of the contents described in the above-mentioned positive electrode active material may be applied.

First, nickel, cobalt, manganese and doping element Me (where Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, , At least one selected from the group consisting of Ca, Ce, Nb, Mg, B and Mo) and a first metal-containing solution containing nickel, cobalt, manganese and A second metal-containing solution containing the doping element Me is prepared (step 1).

The first metal-containing solution is prepared by adding a nickel raw material, a cobalt raw material, a manganese raw material, and a raw material of Me to a solvent, specifically, a mixture of water and an organic solvent (such as alcohol) Or an aqueous solution containing each of the metal-containing raw materials may be prepared and then mixed and used. At this time, the respective metal raw materials are mixed so as to include the nickel in an amount of 80 mol% or more and less than 100 mol% based on the total molar amount of nickel, cobalt, manganese and doping element Me in the production of the first metal-containing solution.

The second metal-containing solution contains a raw material of a nickel raw material, a cobalt raw material, a manganese raw material and a doping element Me, and can be produced in the same manner as the first metal containing solution. At this time, the respective metal raw materials are mixed so as to include the nickel in an amount of 10 mol% or more and less than 80 mol% based on the total molar amount of nickel, cobalt, manganese and doping element Me in the production of the second metal-containing solution.

As the raw materials of the nickel, cobalt, manganese and doping element Me, sulfates, nitrates, acetates, halides, hydroxides or oxyhydroxides containing the respective metal elements may be used. It can be used without particular limitation.

Specifically, the cobalt raw material may be Co (OH) ₂ , CoOOH, CoSO ₄ , Co (OCOCH ₃ ) ₂揃 4H ₂ O, Co (NO ₃ ) ₂揃 6H ₂ O, or Co (SO ₄ ) ₂揃 7H ₂ O, etc., and mixtures of at least one of them may be used.

In addition, the nickel raw material is _{Ni (OH) 2, NiO,} NiOOH, NiCO 3 2Ni (OH) 2 4H 2 O, NiC 2 O 2 2H 2 O, Ni (NO 3) 2 6H 2 O, NiSO 4, NiSO ₄ 6H ₂ O, fatty acid nickel salt or nickel halide, and mixtures of at least one of these may be used.

The raw materials for the manganese include manganese oxides such as Mn ₂ O ₃ , MnO ₂ and Mn ₃ O ₄ ; Manganese salts such as MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganous dicarboxylate, manganese citrate and manganese fatty acid; Oxyhydroxide, and manganese chloride, and mixtures of at least one of these may be used.

Next, the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100 vol%: 0 vol% to 0 vol%: 100 vol% Containing solution and an ammonium cation complexing agent and an anion-containing basic compound are added to cause a coprecipitation reaction, whereby a precursor of the cathode active material exhibiting a concentration gradient in which the nickel and manganese gradually change from the center of the particle to the surface gradually (Step 2).

Since the reaction (particle nucleation and particle growth) is performed in the state where only the first metal-containing solution is present at the beginning of the production process of the cathode active material precursor, the precursor particles initially prepared have a composition of the first metal-containing solution, Since the second metal-containing solution is gradually mixed with the first metal-containing solution, the composition of the precursor particles also gradually changes from the center of the precursor particle to the composition of the second metal-containing solution. For example, the first metal-containing solution has a high nickel content and a low manganese content, and the second metal-containing solution has a nickel content lower than that of the first metal-containing solution and a higher manganese content The concentration of nickel decreases with a continuous concentration gradient from the center of the active material particle to the direction of the particle surface while the concentration of manganese has a continuous concentration gradient from the center of the particle to the particle surface direction And cobalt can be produced as a precursor particle in the form of a constant concentration from the center of the particle to the surface of the particle.

Therefore, by adjusting the composition of the first metal-containing solution and the second metal-containing solution, and controlling the mixing rate and the ratio thereof, the metal element in the precursor so that the desired position in the direction from the center of the precursor particle toward the surface has a desired composition And the slope of the gradient can be controlled.

Further, the mixing of the first metal-containing solution and the second metal-containing solution is continuously performed, and by successively supplying and reacting the second metal-containing solution, as one proceeds from the center of the particle to the surface in one coprecipitation reaction process It is possible to obtain a precipitate having a continuous concentration gradient of the metal, wherein the gradient of the concentration of the metal in the active precursor and the gradient of the concentration of the metal in the precursor of the active material is such that the composition of the first metal- As shown in FIG.

Further, the concentration gradient of the metal element in the particle can be formed by controlling the reaction rate or the reaction time. In order to obtain a high-density state in which a specific metal concentration is high, it is preferable to lengthen the reaction time and decrease the reaction rate. In order to obtain a low-density state in which the specific metal concentration is low, it is preferable to shorten the reaction time and increase the reaction rate .

The size of the cathode active material particle and the thickness of the surface of the cathode active material particle can be controlled by adjusting the amount of the second metal containing solution supplied to the first metal containing solution and the reaction time. Specifically, it may be desirable to appropriately adjust the supply amount of the second metal-containing solution and the reaction time so as to have the particle size of the cathode active material as described above.

On the other hand, the ammonium cation complexing agent may be NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , or NH ₄ CO ₃ , Can be used. The ammonium cation-containing complex-forming agent may be used in the form of an aqueous solution. As the solvent, water or a mixture of water and an organic solvent which can be uniformly mixed with water (specifically, alcohol or the like) and water may be used.

The ammonium cation-containing complex-forming agent may be added in an amount such that the molar ratio is 0.5 to 1 based on 1 mol of the mixed solution of the first metal-containing solution and the second metal-containing solution. Generally, the ammonium cation-containing complex-forming agent reacts with the metal at a molar ratio of 1: 1 to form an complex. However, the basic aqueous solution in the complex formed and the unreacted complex which has not reacted are converted into intermediate products and recovered as an ammonium cation- , The amount of the ammonium cation-containing complex-forming agent to be used can be lowered in the present invention than usual. As a result, the crystallinity of the cathode active material can be increased and stabilized.

The anion-containing basic compound is _{^{PO 4 3-, NO 4 -,}} CO 3 2-, BO 3 -, Cl -, Br -, I - and F ^- at least one anion selected from the group consisting of, preferably PO ₄ ^{3 -} , NO ₄ ^- , CO ₃ ^2- , BO ₃ ^- and F ^- , and the anion may include a state dissolved in a basic substance.

The basic substance contained in the anion-containing basic compound may be a hydroxide of an alkali metal or an alkaline earth metal such as NaOH, KOH or Ca (OH) ₂ , or a hydrate thereof, and a mixture of at least one of them may be used. The anion-containing basic compound may also be used in the form of an aqueous solution. As the solvent, water or a mixture of water and an organic solvent (specifically, alcohol or the like) which can be mixed with water and water may be used. At this time, the concentration of the anion-containing basic aqueous solution may be 2 M to 10 M, preferably 2 M to 8 M. If the concentration of the anion-containing basic aqueous solution is less than 2 M, the particle formation time becomes longer, the tap density decreases, and the yield of the coprecipitation reaction may be lowered. When the concentration exceeds 10 M, Therefore, it is difficult to form uniform particles and the tap density may also decrease.

The anion-containing basic compound is added to a mixed solution obtained by mixing the first metal-containing solution and the second metal-containing solution, so that the anion contained in the anion-containing basic compound is converted into the oxygen position . &Lt; / RTI &gt; By substituting the anion at the oxygen position, it is possible to prevent desorption of oxygen during charging and discharging of the lithium secondary battery including the cathode active material.

Further, the coprecipitation reaction can be carried out under the conditions that the pH of the mixed first metal-containing solution and the second metal-containing solution is from pH 10 to pH 13, specifically from pH 10 to pH 12. When the coprecipitation reaction is carried out in the above-mentioned pH range, the precursor particles can be produced without the generation of various oxides by the size change of the precursor to be produced, generation of particle cleavage, or side reaction accompanying elution of metal ions on the surface of the precursor. Accordingly, the ammonium cation-containing complexing agent and the anion-containing basic compound may be used in a molar ratio of 1: 10 to 1: 2 so as to satisfy the above-mentioned pH range.

In addition, the coprecipitation reaction may be carried out under an inert atmosphere such as nitrogen or argon at a temperature of 40 ° C to 70 ° C. Also, in order to increase the reaction rate during the reaction, an agitation process may be selectively performed, wherein the agitation speed may be 100 rpm to 2,000 rpm.

Subsequently, the cathode active material precursor and the lithium-containing raw material are mixed and fired to synthesize a cathode active material (Step 3).

The lithium-containing raw material may be a commonly used one without any particular limitation, for example, a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, And is not particularly limited as long as it can be dissolved in water. Specifically, the lithium-containing raw material is at least one selected from the group consisting of Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH.H ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi, or Li ₃ C ₆ H ₅ O ₇ may be used.

The amount of the lithium-containing raw material to be used may be determined according to the content of lithium and metal in the cathode active material to be finally produced. Specifically, the amount of the lithium-containing raw material to be contained in the lithium- Ni, Co, Mn and Me) (molar ratio of lithium / metal element) is 1.0 or more, preferably 1.03 to 1.20.

The cathode active material precursor and the lithium-containing raw material may be sintered by one-stage or two-stage sintering.

For example, when the firing is carried out using a one-step firing, the one-step firing is performed at a temperature of 700 ° C to 1,000 ° C, preferably 750 ° C to 850 ° C for 5 hours to 30 hours, more preferably 20 hours 30 hours. &Lt; / RTI &gt; When the cathode active material precursor and the lithium-containing raw material are performed at 700 ° C to 1,000 ° C as described above, the molecules in the active material are rearranged, thereby stabilizing the molecules and improving the thermal stability of the cathode active material. On the other hand, when the firing temperature is less than 700 ° C. and the firing time is less than 5 hours, there is a fear that the discharge capacity per unit weight, the cycle characteristics and the operating voltage are lowered due to the residual unreacted raw material, If the calcination time exceeds 30 hours, the generation of byproducts may lower the discharge capacity per unit weight, lower the cycle characteristics, and lower the operating voltage.

For example, when the firing is carried out using two-step firing, the two-step firing is carried out by raising the temperature from 25 DEG C to 400 DEG C at a temperature raising rate of 2 DEG C / min to 5 DEG C / min And a second firing in which the temperature is raised from 400 ° C to 800 ° C at a heating rate of 7 ° C / min to 10 ° C / min and held for 10 hours to 15 hours. More preferably, the first firing includes heating from 350 DEG C to 400 DEG C at a heating rate of 4 DEG C / min to 5 DEG C / min and then for 9 to 10 hours, and the second firing includes heating at 9 DEG C / min to 10 &lt; RTI ID = 0.0 &gt; C / min. &lt; / RTI &gt; When the cathode active material precursor and the lithium-containing raw material are sintered in two steps as described above, the crystal growth of the cathode active material can have a crystal orientation in a direction perpendicular to the C axis by slowing the rate of temperature increase, The mobility of lithium ions to be added is improved, and the structural stability of the active material is increased, so that the initial capacity characteristics, the output characteristics, the resistance characteristics, and the long-term life characteristics can be improved when the battery is applied. On the other hand, when the firing temperature and the heating rate of the first firing and the second firing of the second firing are out of the above range, the discharge capacity per unit weight, the cycle characteristics, and the drop in operating voltage There is a concern.

The firing step may be performed in an oxidizing atmosphere such as air or oxygen or a reducing atmosphere containing nitrogen or hydrogen. Through the firing process under these conditions, the diffusion reaction between the particles can be sufficiently performed, and diffusion of the metal occurs even in a portion where the internal metal concentration is constant. As a result, the cathode active material having a continuous metal concentration distribution from the center to the surface .

On the other hand, when mixing the cathode active material precursor and the lithium-containing raw material, a sintering agent may be optionally added. The above-mentioned sintering is specifically a compound containing an ammonium ion such as NH ₄ F, NH ₄ NO ₃ , or (NH ₄ ) ₂ SO ₄ ; Metal oxides such as B ₂ O ₃ or Bi ₂ O ₃ ; Or metal halides such as NiCl ₂ or CaCl _2, and mixtures of at least one of them may be used. The sintering may be used in an amount of 0.01 to 0.2 mol based on 1 mol of the positive electrode active material precursor. If the content of the sintering agent is less than 0.01 mol, the effect of improving the sintering property of the cathode active material precursor may be insignificant. If the content of the sintering agent is excessively high, the excessive sintering agent may deteriorate the performance of the cathode active material And there is a possibility that the initial capacity of the battery is lowered during the charge / discharge process.

In mixing the cathode active material precursor and the lithium-containing raw material, a moisture removing agent may be optionally added. Specifically, examples of the moisture removing agent include citric acid, tartaric acid, glycolic acid, and maleic acid, and mixtures of at least one of them may be used. The moisture removing agent may be used in an amount of 0.01 to 0.2 mol based on 1 mol of the positive electrode active material precursor.

In addition, the method may further include washing the synthesized cathode active material at a temperature of 15 ° C or lower.

The washing step is carried out at a temperature of 15 DEG C or lower, preferably 5 DEG C to 15 DEG C, more preferably 5 DEG C to 10 DEG C or lower. By washing the positive electrode active material in the temperature range, the lithium by-product and unreacted anions present on the surface of the positive electrode active material can be effectively removed, and the life characteristics of the battery can be improved when the negative active material is applied to the secondary battery. On the other hand, when the water washing temperature is higher than 15 ° C, the lithium secondary battery may be excessively aged, and in this case, life and capacity characteristics may deteriorate.

The positive electrode active material may include lithium by-products containing LiOH and Li ₂ CO ₃ in an amount of more than 1.0 wt% and less than 3.0 wt% immediately after synthesis. At this time, by washing the cathode active material in a temperature range of 15 DEG C or less, the lithium by-product present in the cathode active material can be effectively removed. After the water washing step, the cathode active material may contain less than 1% by weight of lithium by-products including LiOH and Li ₂ CO ₃ , but is not limited thereto.

Finally, the cathode active material is subjected to a heat treatment at 600 ° C to 800 ° C under an oxygen atmosphere (Step 5). The thermal stability of the cathode active material can be improved by performing the heat treatment of the washed cathode active material at 600 ° C to 800 ° C, more preferably 650 ° C to 750 ° C, for 5 hours to 10 hours, The rearrangement of the metal elements takes place and the lithium diffusion in the cathode active material progresses, recrystallization of the cathode active material occurs, and the life characteristic can be further improved.

Further, after washing the cathode active material, the cathode active material may be selectively washed with water, which is composed of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr The coating layer may be formed by coating at least one selected from the group consisting of the above materials.

Specifically, the method for forming the coating layer on the cathode active material is not particularly limited as long as it is a method for forming a coating layer on the surface of the active material. For example, the composition prepared by dispersing the metal in a solvent, It is possible to form the coating layer on the surface of the cathode active material by surface-treating the cathode active material using a conventional slurry coating method such as dipping, spraying, and the like.

Examples of the solvent capable of dispersing the metal to form the coating layer include water, at least one selected from the group consisting of alcohols having 1 to 8 carbon atoms, dimethyl sulfoxide (DMSO), N-methyl pyrrolidone, acetone, One or more mixtures may be used.

In addition, the solvent may exhibit an appropriate coating property and may be contained in an amount that can be easily removed in a subsequent heat treatment.

Then, the heat treatment for forming the coating layer may be performed at a temperature range in which the solvent contained in the composition can be removed, specifically, at 200 ° C to 700 ° C, preferably at 250 ° C to 400 ° C Lt; / RTI &gt; If the heat treatment temperature is less than 200 ° C, side reactions may occur due to the residual solvent and the battery characteristics may be deteriorated. If the heat treatment temperature exceeds 700 ° C, side reactions may occur due to high temperature heat.

According to another embodiment of the present invention, there is provided an anode comprising the cathode active material.

The positive electrode may be formed by coating a positive electrode current collector with a positive electrode active material, a binder, a conductive material, and a solvent.

Since the positive electrode active material is the same as that described above, a detailed description thereof will be omitted, and only remaining structures will be specifically described below.

The positive electrode collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery. For example, the positive electrode collector may be formed of a metal such as carbon, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver, or the like may be used.

The cathode active material may include 80 wt% to 99 wt% based on the total weight of each cathode mix.

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

The conductive material is usually added in an amount of 1 wt% to 30 wt% based on the total weight of the cathode mix.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and includes, for example, graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that provides a preferable viscosity when the positive electrode active material and optionally a binder and a conductive material are included. For example, the concentration of the solid material including the cathode active material and optionally the binder and the conductive material may be 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

According to another embodiment of the present invention, there is provided a lithium secondary battery comprising the positive electrode.

The lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The lithium secondary battery may further include a battery container for storing the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

Since the anode is the same as that described above, a detailed description thereof will be omitted, and only the remaining constitution will be specifically described below.

The negative electrode may be prepared, for example, by coating a negative electrode current collector with a negative electrode mixture including a negative electrode active material, a binder, a conductive material, and a solvent.

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, an aluminum-cadmium alloy, or the like can 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, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Examples of the negative electrode active material include natural graphite, artificial graphite, carbonaceous material; A metal (Me) having a lithium-containing titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; An alloy composed of the metal (Me); An oxide of the metal (Me); And at least one negative electrode active material selected from the group consisting of a combination of the metal (Me) and carbon.

The negative electrode active material may include 80% by weight to 99% by weight based on the total weight of the negative electrode material mixture.

The binder is a component for assisting the bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 1 to 30 wt% based on the total weight of the negative electrode material mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the negative electrode material mixture. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount which is preferred to contain the negative electrode active material and, optionally, a binder and a conductive material. For example, the concentration of the solid material including the anode active material and optionally the binder and the conductive material may be 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

At this time, an organic / inorganic composite membrane having an additional inorganic coating may be used for securing heat resistance or mechanical strength, and may be selectively used as a single layer or a multi-layer structure.

The inorganic material is not particularly limited as long as it can control the pores of the organic / inorganic composite separation membrane uniformly and improve the heat resistance. For example, the inorganic material is a non-limiting example is _{SiO 2, Al 2 O 3,} TiO 2, BaTiO 3, Li 2 O, LiF, LiOH, Li 3 N, BaO, Na 2 O, Li 2 CO 3, CaCO 3, At least one selected from the group consisting of LiAlO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO 2, SiC and derivatives thereof and mixtures thereof.

The average diameter of the inorganic material may be 0.001 탆 to 10 탆, and more specifically 0.001 탆 to 1 탆. If the average diameter of the inorganic materials is within the above range, the dispersibility in the coating solution is improved and the occurrence of problems in the coating process can be minimized. In addition, the physical properties of the final separation membrane can be made uniform, the inorganic particles can be uniformly distributed in the pores of the nonwoven fabric to improve the mechanical properties of the nonwoven fabric, and the advantage of easily controlling the pore size of the organic- .

The average diameter of the pores of the organic / inorganic hybrid separator may be in the range of 0.001 to 10 mu m, more specifically 0.001 to 1 mu m. When the average diameter of the pores of the organic / inorganic hybrid separator is within the above range, gas permeability and ion conductivity can be controlled within a desired range. In addition, when the battery is manufactured using the organic / inorganic hybrid separator, It is possible to eliminate the possibility of an internal short circuit of the battery by the battery.

The porosity of the organic / inorganic hybrid membrane may range from 30% by volume to 90% by volume. When the porosity is within the above range, the ion conductivity can be increased and the mechanical strength can be enhanced.

Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel 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 linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, 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 electric vehicle (HEV), and the like.

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 same.

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.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail by way of examples with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example  One

[ Cathode active material  Produce]

In batch batch (batch) type 5L reactor is set to _{60 ℃, NiSO 4, CoSO 4} , MnSO 4 and Na ₂ WO ₄ the nickel: cobalt: manganese: The mole ratio of tungsten 98.77: 0.63: 0.57: in an amount such that 0.03 Water To prepare a first metal-containing solution having a concentration of 2M, and to add NiSO ₄ , CoSO ₄ , MnSO ₄ and Na ₂ WO ₄ to a molar ratio of nickel: cobalt: manganese: tungsten of 69.16: 25.97: 4.84: 0.03 To prepare a second metal-containing solution having a concentration of 2M.

The vessel containing the first metal-containing solution and the vessel containing the second metal-containing solution were connected to an in-line static static mixer, and the reactor was connected to the outlet side of the static mixer. A 4 M NaOH solution containing 1 mol% Na ₃ PO ₄ and a 7% NH ₄ OH aqueous solution were further added to the reactor. 3 liters of deionized water was added to the coprecipitation reactor (capacity: 5 L), and nitrogen gas was purged into the reactor at a rate of 2 L / min to remove dissolved oxygen in the water, thereby forming a non-oxidizing atmosphere in the reactor. Then, 100 mL of 4 M NaOH containing 1 mol% of Na ₃ PO ₄ was added, and the mixture was stirred at a temperature of 60 ° C at a stirring speed of 1,100 rpm to maintain a pH of 11.2.

Then, the first metal-containing solution and the second metal-containing solution were mixed at a ratio of 100 vol%: 0 vol% to 0 vol%: 100 vol%. A mixed metal and the resulting solution so that a continuous input into the reactor at a rate of 5m / s through a pipe for the mixed solution, and the NaOH aqueous solution containing a _{1 mol% Na 3 PO 4 180} mL / hr, NH 4 an OH aqueous solution 10 mL / hr, respectively, followed by a coprecipitation reaction for 24 hours to precipitate particles of nickel-manganese-cobalt-tungsten-based composite metal hydroxide. The precipitated nickel manganese cobalt tungsten composite metal-containing hydroxide particles were separated, washed with water and then dried in an oven at 120 ° C for 24 hours to prepare a precursor for a cathode active material.

The precursor thus obtained was dry-mixed with Li ₂ CO ₃ (1.07 mol of lithium carbonate per mole of the precursor), and then heat-treated at 750 ° C for 27 hours in an oxygen atmosphere to obtain a concentration gradient of the metal element in the active material particle Thereby preparing a cathode active material.

Specifically, the average by the above method a composition of _{Li 1.03 Ni 0.9124 Co 0.0722 Mn 0.0104} W 0.005 O 1.9955 (PO 4) is center, and an average composition represented by _{0.0045 Li 1.03 Ni 0.7626 Co 0.1046 Mn} 0.1278 W 0.005 (O 2) _0.99775 (PO ₄ ) _0.0045 .

Then, the cathode active material prepared above was washed with water at 9 占 폚, washed with water and then dried at 130 占 폚 for 10 hours.

The surface of the washed cathode active material was coated with boron using boric acid at 300 ° C for 5 hours, and then the cathode active material was heat-treated at 700 ° C for 5 hours under oxygen atmosphere.

[Manufacture of positive electrode]

A carbon black conductive material and a polyvinylidene fluoride (PVDF) binder were mixed at a ratio of 96.5: 1.5: 2.0 (wt%) based on 100 parts by weight of N-methyl-2-pyrrolidone (NMP) (Viscosity: 5,000 mPas) was prepared, applied to a positive electrode current collector (Al thin film) having a thickness of 100 占 퐉, dried, and roll pressed to prepare a positive electrode.

[Manufacture of Secondary Battery]

A polyethylene porous film was interposed between the positive electrode prepared as described above and Li metal as a counter electrode, and then an organic solvent consisting of ethylene carbonate / dimethyl carbonate (1: 1 by volume) was added with 1 M lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the electrolyte solution to prepare a coin type half-cell.

Example  2

The cathode active material precursor prepared in Example 1 was dry-mixed with Li ₂ CO ₃ (1.07 mol of lithium carbonate in terms of 1 mol of the precursor), and then the temperature was raised to 400 ° C. at a rate of 5 ° C./min in an oxygen atmosphere, Except that the first firing was carried out while maintaining the temperature at a heating rate of 10 ° C / min to 780 ° C and the temperature was maintained for 12 hours to carry out a second firing to prepare a cathode active material. A positive electrode active material, a positive electrode and a secondary battery comprising the same were prepared.

Comparative Example

Comparative Example  One

A positive electrode and a secondary battery including the positive electrode active material were prepared using the positive electrode active material represented by Li (Ni _0.88 Mn _0.09 Co _0.03 ) (O ₂ ) as the positive electrode active material. At this time, the method of manufacturing the positive electrode and the secondary battery is the same as that described in the first embodiment.

Comparative Example  2

In batch batch (batch) type 5L reactor is set to _{60 ℃, NiSO 4, CoSO 4} , MnSO 4 and Na ₂ WO ₄ the nickel: cobalt: manganese: The mole ratio of tungsten 98.77: 0.63: 0.57: in an amount such that 0.03 Water To prepare a first metal-containing solution having a concentration of 2M, and to add NiSO ₄ , CoSO ₄ , MnSO ₄ and Na ₂ WO ₄ to a molar ratio of nickel: cobalt: manganese: tungsten of 69.16: 25.97: 4.84: 0.03 To prepare a second metal-containing solution having a concentration of 2M.

The vessel containing the first metal-containing solution and the vessel containing the second metal-containing solution were connected to a coprecipitation reactor, respectively. A 4 M NaOH solution containing 1 mol% Na ₃ PO ₄ and a 7% NH ₄ OH aqueous solution were further added to the reactor. After adding 3 L of deionized water to the coprecipitation reactor (capacity 5 L), nitrogen gas was purged into the reactor at a rate of 2 L / min to remove dissolved oxygen in the water, and the reactor was set up in a non-oxidizing atmosphere. Then, 100 mL of 4 M NaOH containing 1 mol% of Na ₃ PO ₄ was added, and the mixture was stirred at a temperature of 60 ° C at a stirring speed of 1,100 rpm to maintain a pH of 11.2.

The first metal-containing solution, NaOH solution and NH ₄ OH aqueous solution were added to the coprecipitation reactor at 5 m / s, 180 mL / hr, and 10 mL / hr, respectively, and reacted for 12 hours to form the center of the cathode active material.

Then, the second metal-containing solution, the NaOH solution and the NH ₄ OH aqueous solution were charged into the reactor at the same rate and reacted for 12 hours to prepare a cathode active material precursor having a surface portion formed on the surface of the center portion. A positive electrode and a secondary battery including the positive electrode were prepared in the same manner as in Example 1, except that the precursor was used.

Comparative Example  3

A cathode active material, a cathode and a secondary battery including the cathode active material were prepared in the same manner as in Example 1, except that the produced cathode active material was not heat-treated in an oxygen atmosphere.

Experimental Example

Experimental Example  1: Evaluation of thermal stability

The cathode active materials prepared in Examples 1 and 2 and Comparative Examples 2 and 3 were evaluated for thermal stability.

Specifically, the cathode active materials prepared in Examples 1 and 2 and Comparative Examples 2 and 3 were heated at a rate of 10 ° C / min using a differential scanning calorimeter (DSC) Respectively.

As shown in FIG. 1, the cathode active materials of Examples 1 and 2 showed a higher heat flow peak at a higher temperature and a lower heat flow peak height than the cathode active material prepared in Comparative Example 3. As a result, the thermal stability of the cathode active material prepared by synthesizing the cathode active material as in Examples 1 and 2 and further heat-treated at a higher temperature was higher than that of the cathode active material prepared without the additional heat treatment in the oxygen atmosphere after synthesis as in Comparative Example 3 And it was confirmed that it was even better. In addition, since the cathode active materials prepared in Examples 1 and 2 of the present invention have a concentration gradient from the center to the surface of the particles, the crystal structure is stabilized because there is no abrupt phase boundary region throughout the particles, The thermal stability was further increased as compared with Comparative Example 2 having no gradient.

Experimental Example  2: Synthesized Cathode active material  analysis

The crystal orientations of the cathode active materials prepared in Example 2 and Comparative Example 2 were confirmed using a scanning electron microscope.

As a result, as shown in FIG. 2A, the crystal grains of the cathode active material prepared in Example 2 exhibited crystal orientation in the direction perpendicular to the C axis, while the cathode active material produced by the one- It was confirmed that it did not show a specific orientation as shown in Fig.

That is, it was confirmed that when the cathode active material precursor and Li ₂ CO ₃ were fired in two stages as in Example 2, a cathode active material having crystal orientation in a specific direction could be realized.

Experimental Example  3: Evaluation of cycle life

The cycle life of the lithium secondary batteries prepared in Example 2 and Comparative Example 1 was evaluated, and the results are shown in FIG.

Specifically, a lithium secondary battery having a battery capacity of 5 mAh prepared in Example 2 and Comparative Example 1 was charged at a constant current of 0.3 C at 4.2 캜 at a temperature of 25 캜 until charging to 4.25 V and then charged at a constant voltage of 4.25 V, The charging was terminated. Thereafter, the film was allowed to stand for 10 minutes, and then discharged at a constant current of 0.3 C until it reached 2.5 V. The charge-discharge behavior was set as one cycle, and the capacity retention rate after repeating this cycle 30 times was measured.

As shown in FIG. 3, the lithium secondary battery of Example 2 exhibited a capacity retention rate of about 95% during a cycle of 30 cycles. On the other hand, the positive electrode active material showed the same composition throughout the particles, The lithium secondary battery of Comparative Example 1 to which Li (Ni _0.88 Mn _0.09 Co _0.03 ) O ₂ not subjected to anion substitution was applied exhibited a capacity retention ratio of less than 80%, and the lithium secondary battery of Example 2 was a lithium secondary battery of Comparative Example 1 Cycle characteristics.

Experimental Example  4: Evaluation of resistance characteristics

The resistance characteristics and life characteristics of the lithium secondary batteries prepared in Example 1 and Comparative Example 3 were evaluated, and the results are shown in FIG.

Specifically, a lithium secondary battery having a cell capacity of 5 mAh prepared in Example 1 and Comparative Example 3 was charged at 25 ° C at a constant current of 0.3 C until it reached 4.25 V, then left to stand for 10 minutes, Lt; RTI ID = 0.0 &gt; 2.5 &lt; / RTI &gt;

First, the charge / discharge behavior was set as one cycle, and the capacity retention rate after repeating this cycle 30 times was measured. As shown in FIG. 4, the lithium secondary battery manufactured in Example 1 showed a capacity retention ratio of 95% or more during a cycle of 30 cycles. However, the lithium secondary battery of Comparative Example 3, which was manufactured in the same manner as Example 1 but was not subjected to the additional heat treatment with oxygen after the production of the active material, showed a capacity retention rate of less than 95% during 30 cycles of the cycle.

Then, after the battery was charged and discharged in the same manner as the capacity retention rate measurement, the charging and discharging behavior was set as one cycle. After repeating this cycle 30 times, the resistance increase rate was measured based on the resistance measured at the time of one discharging .

As shown in FIG. 4, in the case of the lithium secondary battery of Example 1, the resistance increase rate was improved as compared with the lithium secondary battery of Comparative Example 3 while the cycle was repeated 30 times.

The resistances of the lithium secondary batteries prepared in Example 2 and Comparative Example 2 were measured at SOC of 20%, 40%, 60%, 80%, and 100%, respectively. Specifically, a lithium secondary battery having a cell capacity of 5 mAh prepared in Example 2 and Comparative Example 2 was charged at 25 ° C until the voltage reached 4.25 V at a constant current of 0.3 C, and then at a constant current of 0.3 C and 2.5 V And the resistance was measured by SOC. The resistance measurement results by the SOC are shown in FIG.

Referring to FIG. 5, the resistance of the lithium secondary battery manufactured in Example 2 was the lowest among all the SOCs. The positive electrode active material of Example 2 not only has a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface but also has a crystal orientation and thus has excellent structural stability of the active material and the lithium ion mobility Resistance is lower than that of the lithium secondary battery to which the active material of Comparative Example 2, which does not exhibit a concentration gradient and crystal orientation, is applied.

Experimental Example 5: at 4.5V  Life cycle assessment by cycle

The cycle life of the lithium secondary batteries prepared in Example 1 and Comparative Example 2 was evaluated at high voltage (4.5 V) according to cycles. The results are shown in FIG.

Specifically, a lithium secondary battery having a cell capacity of 5 mAh prepared in Example 1 and Comparative Example 2 was charged at a constant current of 0.5 C at a temperature of 25 캜 until the voltage reached 4.5 V, then left for 10 minutes, Lt; RTI ID = 0.0 &gt; 2.5V. &Lt; / RTI &gt; The charging / discharging behavior was set as one cycle. After repeating this cycle 50 times, the capacity retention ratio of the battery after 50 cycles was measured.

As shown in FIG. 6, it was confirmed that the lithium secondary battery manufactured in Example 1 exhibited an excellent capacity retention ratio of 95% or more even after 50 cycles of charging / discharging of the battery at 4.5V. On the other hand, it was confirmed that the capacity retention ratio of the lithium secondary battery manufactured in Comparative Example 2 was lower than that in Example 1 after the battery was charged and discharged 50 times at 4.5 V.

Claims (14)

A cathode active material having a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface,
Wherein the cathode active material comprises: a center portion comprising a first lithium composite metal oxide having an average composition represented by Formula 1; And a surface portion comprising a second lithium composite metal oxide having an average composition represented by the following Formula 2,
Wherein the cathode active material has a peak at 235 DEG C or higher when a heat flow rate is measured by differential scanning calorimetry,
[Chemical Formula 1]
Li _{1 + x 1} (Ni _a1 Mn _b1 Co1 _-a1-b1-c1 Me _c1 ) O2 _-y1 A _y1
(2)
_{Li 1 + x2 (Ni a2 Mn} b2 Co 1-a2-b2-c2 Me c2) O 2-y2 A y2
In the above Formulas 1 and 2,
Me is a rare earth element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, At least one doping element selected from the group consisting of
A is at least one anion selected from the group consisting of PO ₄ ^3- , NO ₄ ^- , CO ₃ ^2- , BO ₃ ^- , Cl ^- , Br ^- , I ^- and F ^-
B1 + c1 < 1, 0? X1? 0.1, 0.0001 < y1? 0.1 and 0 < a1 &
0.2? A2 + b2 + c2? 1, 0? X2? 0.1 and 0.0001 <y2? 0.1, 0.1? A2 <0.8, 0.1 <b2 <0.9 and 0 <c2? 0.1.
The method according to claim 1,
Wherein A is at least one anion selected from the group consisting of PO ₄ ^3- , NO ₄ ^- , CO ₃ ^2- , BO ₃ ^- and F ^- .
The method according to claim 1,
Wherein the crystal grains of the cathode active material have crystal orientation in a direction perpendicular to the C axis.
The method according to claim 1,
Wherein the cathode active material comprises less than 1% by weight lithium by-product.
The method according to claim 1,
Further comprising a coating layer on the positive electrode active material, the coating layer comprising at least one selected from the group consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr.
The method according to claim 1,
Wherein the average particle diameter (D ₅₀ ) of the cathode active material is 4 탆 to 20 탆.
Ni, cobalt, manganese and doping element Me (where Me is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, , Ce, Nb, Mg, B, and Mo), and a second metal-containing solution containing nickel, cobalt, manganese, and doping at a different concentration than the first metal- Preparing a second metal containing solution comprising the element Me;
Containing solution and the second metal-containing solution so that the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100 vol%: 0 vol% to 0 vol%: 100 vol% Adding an ammonium cationic complexing agent and an anion-containing basic compound to prepare a cathode active material precursor exhibiting a concentration gradient in which the nickel and manganese gradually change from the center of the particle to the surface independently from each other;
Mixing the cathode active material precursor and the lithium-containing raw material and firing to synthesize the cathode active material; And
And performing heat treatment of the cathode active material at 600 ° C to 800 ° C under an oxygen atmosphere.
The method of claim 7,
Wherein the sintering of the cathode active material precursor and the lithium-containing source material is performed by one-stage or two-stage sintering.
The method of claim 8,
Wherein the one-stage firing is performed at 700 ° C to 800 ° C.
The method of claim 8,
The first firing in which the two-step firing is performed by raising and maintaining the temperature from 25 DEG C to 400 DEG C at a temperature raising rate of 2 DEG C / min to 5 DEG C / min; And a second firing in which the temperature is raised and maintained from 400 DEG C to 800 DEG C at a temperature raising rate of 7 DEG C / min to 10 DEG C / min.
The method of claim 7,
Further comprising washing the synthesized positive electrode active material at a temperature of 15 캜 or less.
The method of claim 7,
Further comprising the step of forming a coating layer on the cathode active material, the coating layer including at least one selected from the group consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr.
A positive electrode for a lithium secondary battery, comprising the positive electrode active material according to claim 1.
A lithium secondary battery comprising a positive electrode according to claim 13.

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