KR102081858B1 - Positive electrode active material precursor for secondary battery and positive electrode active material for secondary battery prepared by using the same - Google Patents

Abstract

In the present invention, a cathode active material precursor for a secondary battery capable of stabilizing a surface and an internal structure of an active material having an optimized composition and structure according to a position in the precursor particles, and a cathode active material for a secondary battery prepared using the same are provided.

Description

Positive electrode active material precursor for secondary battery and positive electrode active material for secondary battery manufactured using same

The present invention relates to a cathode active material precursor for a secondary battery capable of stabilizing the surface and internal structure of an active material and having a composition and structure optimized according to the position in the precursor particles, and a cathode active material for a secondary battery prepared using the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.

A lithium transition metal composite oxide is used as a cathode active material of a lithium secondary battery, and among these, lithium cobalt composite metal oxide of LiCoO ₂ having a high operating voltage and excellent capacity characteristics is mainly used. However, since LiCoO ₂ has very poor thermal characteristics due to destabilization of the crystal structure due to de-lithography and is expensive, there is a limit to using LiCoO ₂ as a power source in fields such as electric vehicles.

As a material for replacing LiCoO ₂ , lithium manganese composite metal oxides (such as LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron phosphate compounds (such as LiFePO ₄ ), or lithium nickel composite metal oxides (such as LiNiO ₂ ) have been developed. Among them, research and development of lithium nickel composite metal oxides having a high reversible capacity of about 200 mAh / g, which is easy to implement a large-capacity battery, are being actively studied. However, LiNiO ₂ has a poor thermal stability compared to LiCoO _2, and when an internal short circuit occurs due to pressure from the outside in a charged state, the positive electrode active material itself is decomposed to cause the battery to rupture and ignite.

Accordingly, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a method of replacing a portion of nickel (Ni) with cobalt (Co) or manganese (Mn) has been proposed. However, LiNi _{1 - α} Co _α O ₂ (α = 0.1 ~ 0.3) in which a part of nickel is substituted with cobalt shows excellent charge / discharge characteristics and life characteristics, but there is a problem of low thermal stability. In the case of nickel manganese-based lithium composite metal oxide in which a part of Ni is replaced with Mn having excellent thermal stability, and nickel cobalt manganese-based lithium composite metal oxide substituted with Mn and Co (hereinafter simply referred to as 'NCM-based lithium oxide') The output characteristics are low, and there is a fear of dissolution of metal elements and deterioration of battery characteristics.

In order to solve this problem, a lithium transition metal oxide having a different metal composition in a core and a shell has been proposed. The lithium transition metal oxide as described above is prepared by coating a material having a different composition on the outside after synthesizing the core material to prepare a double layer, and then mixing the lithium salt with a heat treatment. However, the lithium transition metal oxide prepared by the above method is not satisfactory in the improvement of the output characteristics, and there is a problem of low reproducibility.

As another method, researches are being made to increase the Ni content in NCM-based lithium oxide for high energy density in small automotive and power storage batteries. In general, in the positive electrode active material, capacity, life, or stability have a trade-off in which the life and stability of a battery decrease rapidly as the capacity increases. Accordingly, a method of using only within a limited composition and voltage range, a method of stabilizing a structure by restricting a partial composition of NCM oxide with a heterogeneous element, and a method of reducing surface side reactions through coating have been proposed. However, in all these methods, there is a limit to fundamentally improve the electrochemical and thermal stability of the active material, and the high energy density of the battery is also difficult because the deterioration of performance is accelerated at the time of high voltage.

Korean Patent Publication No. 2005-0083869 (published Aug. 26, 2005)

The first technical problem to be solved by the present invention is to provide a cathode active material precursor having a composition and structure optimized according to the position in the precursor particles, which can stabilize the surface and the internal structure of the active material and a method of manufacturing the same.

The second technical problem to be solved by the present invention is to provide a cathode active material for a secondary battery prepared using the precursor.

In addition, a third technical problem to be solved by the present invention is to provide a lithium secondary battery, a battery module and a battery pack including a cathode active material prepared using the precursor.

According to one embodiment of the present invention for solving the above problems, a plurality of primary particles of a composite metal hydroxide including nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) Secondary particles formed by agglomeration of at least one of the nickel, cobalt, and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al), wherein the metal is gradually added from the center to the surface of the secondary particles; Varying concentration gradient, wherein the concentration gradient comprises at least one inflection point, the amount of nickel at the center of the secondary particle is X1, the amount of nickel at the inflection point is X2, and at the secondary particle surface When the nickel content is X3, nickel provides a cathode active material precursor for a secondary battery, which is present under any one of the following conditions (a1) or (a2). .

(a1) X1 = X3 <X2

(a2) X1 ≠ X3 <X2

In addition, according to another embodiment of the present invention, the first metal-containing solution containing nickel, cobalt and metal elements M, and nickel, cobalt and metal elements M at different concentrations from the first metal-containing solution Preparing a second metal-containing solution; The mixing ratio of the first metal-containing solution and the second metal-containing solution in the first metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume to 0% by volume and 100% by volume. At the same time as mixing, adding an ammonium cation-containing complex forming agent and a basic compound to first coprecipitation to form a core in which primary particles of the composite metal hydroxide are aggregated; And for the core, the mixing ratio of the first metal-containing solution and the second metal-containing solution to the first metal-containing solution and the second metal-containing solution is from 0% by volume to 100% by volume: 0% by volume. Continuously mixing to gradually change, and simultaneously adding a ammonium cation-containing complex former and a basic compound to form a shell on the core, wherein the shell contains a first metal. A method of preparing a cathode active material precursor having a pH of 10.5 to 11.5 when the amount of the solution is 100 vol% and a pH of 11 to 12 when the amount of the second metal-containing solution is 100 vol% in the second coprecipitation reaction is described. to provide.

According to another embodiment of the present invention, there is provided a method of manufacturing a cathode active material for a secondary battery comprising the step of heat treatment after mixing the cathode active material precursor with a lithium raw material.

In addition, according to another embodiment of the present invention, a plurality of primary particles of lithium composite metal oxide including nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) A secondary particle formed by agglomeration, wherein the primary particle includes at least one metal of nickel, cobalt, and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) from the center to the surface of the primary particle. The present invention provides a cathode active material for a secondary battery, wherein the concentration gradient is present in a gradually changing concentration gradient, and the concentration gradient has at least one inflection point.

Furthermore, according to another embodiment of the present invention, a cathode, a lithium secondary battery, a battery module, and a battery pack including the cathode active material are provided.

The cathode active material precursor for a secondary battery according to the present invention has an optimized composition and structure according to the position in the precursor particles, thereby stabilizing the surface and the internal structure of the active material. As a result, a battery including a cathode active material prepared using the precursor may exhibit more improved battery characteristics, specifically, life characteristics and output characteristics.

1 is an SEM image of the cathode active material precursor prepared in Example 1. FIG.

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

The terms or words used in this specification and claims are not to be construed as being limited to the common or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meanings and concepts corresponding to the technical idea of the present invention based on the principle that the present invention.

In general, when the nickel content in the positive electrode active material is increased to achieve high capacity characteristics, the deterioration of the positive electrode is intensified due to an increase in side reaction between nickel and the electrolyte on the surface. A concentration gradient type cathode active material having a concentration gradient in which the content of metal elements in the active material particles gradually changes is proposed to solve such a problem, and the inside of the active material particles has a high content of nickel to realize high capacity. In order to stabilize the surface structure by increasing the content of manganese to improve the capacity characteristics and life characteristics of the active material.

However, in order to increase the energy density during the production of the positive electrode, cracking and disintegrating of the active material particles are likely to occur during the rolling process of the positive electrode active material after application, and also, the lifetime characteristics of the active material particles may be deteriorated during the battery charging and discharging process. In particular, in the case of the concentration-graded cathode active material, when the cracks and collapses of the particles occur, a large portion of nickel inside reacts directly with the electrolyte, which makes the safety and life characteristics more vulnerable.

On the other hand, the dose expression of the concentration-graded positive electrode active material is known to occur in a large portion of nickel inside, but in reality, a portion of the composition having a certain depth at the surface contributes to the capacity expression, and the capacity characteristic is internal nickel. It is more affected by the average composition of the entire active material than the composition.

Accordingly, in the present invention, by having a concentration gradient composition in both directions of the center and the surface of the positive electrode active material, it is possible to maintain a stable structure even if cracks and collapses occur due to electrode rolling, etc. The characteristic can be further improved.

That is, the cathode active material precursor for a secondary battery according to an embodiment of the present invention is a primary particle of a composite metal hydroxide containing nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al). A secondary particle composed of a plurality of aggregates, wherein at least one metal of the nickel, cobalt, and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) gradually increases from the center to the surface of the secondary particles. The concentration gradient includes at least one inflection point, the amount of nickel at the center of the secondary particle is X1, the amount of nickel at the inflection point is X2, and the surface of the secondary particle. When the content of nickel in X is X3, nickel is present under any one of the following conditions (a1) or (a2).

(a1) X1 = X3 <X2

(a2) X1 ≠ X3 <X2

Specifically, the cathode active material precursor for a secondary battery according to an embodiment of the present invention is a primary particle of a composite metal hydroxide containing nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al). Is secondary particles formed by agglomeration of plural pieces.

In the present invention, 'primary particles' means a primary structure of a single particle, 'secondary particles' means the intentional aggregation or assembly process for the primary particles (or primary structure) constituting the secondary particles Without agglomerates means aggregates, ie secondary structures, aggregated between primary particles by physical or chemical bonding between the primary particles.

In addition, the cathode active material precursor for secondary battery-shaped secondary battery is located in the core of the aggregated primary particles and the outer surface of the core, the primary particles shell having a radial orientation from the center of the particle to the surface It may have a core-shell structure of. For example, on the surface of the active material particles, primary particles are given radial orientation to the surface side to facilitate insertion and desorption of lithium, thereby increasing lithium ion mobility and structural stability of the active material, thereby increasing initial capacity characteristics and output characteristics of the battery. It can improve long-term life characteristics and safety.

The 'core-shell structure' is distinguished by the orientation of the primary particles, such a core-shell structure can be implemented by controlling the pH in the coprecipitation reaction is carried out in two steps in the preparation of the precursor described below have.

Specifically, the core may occupy 60% by volume to 80% by volume with respect to the total volume of the precursor particles. When the core portion occupies the above-mentioned range in the precursor particles, the initial capacity characteristics, output characteristics and long-term characteristics of the battery are applied due to the mobility of lithium ions and the structural stability of the active material according to the orientation control of the primary particles on the surface side without deterioration of the capacity characteristics. Lifespan characteristics can be improved.

In the present invention, the volume of the core in the precursor may be calculated by using an electron probe micro analysis (EPMA).

In addition, the shell is located on the outer surface of the core, and may include primary particles having a radial orientation from the center of the precursor particles to the surface. As described above, since the primary particles forming the shell have a crystal orientation in a direction in which lithium is easily inserted and removed, high output characteristics may be realized as compared with particles having no crystal orientation of the same composition.

On the other hand, the primary particles constituting the core and shell may have a rod (rod) shape. In the present invention, the 'rod form' refers to a shape of a rod, rod or pole shape in which a circular or oval cross section extends in one direction. Specifically, the rod-shaped primary particles have a length ratio of the major axis passing through the center of the primary particle and perpendicular to the minor axis with respect to the length of the minor axis passing through the center of the primary particle, that is, the aspect ratio is greater than one. It may be 5 or less, and more specifically, may be 1.2 to 3. When the aspect ratio of the primary particles meets the above range, the particle growth is uniform, which can further improve the electrochemical properties.

In addition, the primary particles include a composite metal hydroxide containing nickel, cobalt and metal element M (wherein M is at least one selected from the group consisting of Mn and Al), the composite metal hydroxide is W, Cu, Fe , V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo It may be doped by any one or more doping elements.

Specifically, the primary particles may include a composite metal hydroxide of Formula 1 below:

[Formula 1]

Ni _x Co _y M _z M ' _w (OH) ₂

In Chemical Formula 1,

M is at least one element selected from the group consisting of Mn and Al,

M 'is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B Any one or two or more doping elements selected from the group consisting of

x, y, and z are atomic fractions of independent elements, respectively, 0 <x <1, 0 <y <1, 0 <z <1, 0 ≦ w ≦ 0.05, x + y + z = 1, and Specifically, 0.5 <x <1, 0 <y≤0.5, 0 <z≤0.5, and 0≤w≤0.05, x + y + z = 1, more specifically 0.5 <x≤0.98, 0 <y ≦ 0.4, 0 <z ≦ 0.4, and 0 ≦ z ≦ 0.05, x + y + z = 1.

The composition of the compound of Formula 1 is the average composition of the composite metal hydroxide in the primary particles.

In addition, at least one metal of the nickel, cobalt and metal element M (wherein M is at least one selected from the group consisting of Mn and Al) is a concentration gradient that gradually changes from the center of the cathode active material precursor on the secondary particles to the surface. May exist.

In this case, since the precursor does not have a sharp phase boundary region throughout the particle, the crystal structure is stabilized and thermal stability is increased, and as a result, when the precursor is applied to a secondary battery, the precursor exhibits high capacity, long life and thermal stability, and deteriorates performance at high voltage. Can be minimized.

In the present invention, the metal 'shows a gradually changing concentration gradient' means that the concentration of the metal is present in a concentration distribution that continuously changes in stages throughout the particle. Specifically, the concentration distribution is 0.1 atomic% to 30 atomic%, more specifically 0.1 atomic%, based on the total atomic weight of the corresponding metal contained in the particles, wherein the change in metal concentration per micrometer in the particle is directed to the surface. % To 20 atomic%, more specifically may be a difference of 1 atomic% to 10 atomic%.

In addition, in the present invention, the concentration gradient structure and concentration of the metal in the precursor particles are determined by using an Electron Probe Micro Analyzer (EPMA), Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-). AES) or Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and the like, and specifically, the precursor particles are milled with argon ions to prepare a cross section. After that, it can be measured by analyzing the elemental detection amount through EPMA.

In addition, the concentration gradient of at least one of the nickel, cobalt and metal element M (wherein M is at least one selected from the group consisting of Mn and Al) may include an inflection point.

In the present invention, the inflection point means that the concentration gradient slope changes from a negative value to a positive value or from a positive value to a negative value.

Specifically, in the precursor of the cathode active material for a secondary battery according to an embodiment of the present invention, the nickel is present in a concentration gradient that gradually changes in the secondary particles, the concentration gradient of nickel includes one inflection point X1 is the content of nickel at the center of the secondary particle, X2 is the content of nickel at the inflection point located in the inner region excluding the center and the surface of the secondary particle, and When the content is each referred to as X 3, nickel may be present under one of (a1) or (a2).

(a1) X1 = X3 <X2

(a2) X1 ≠ X3 <X2

Particularly, the nickel content (X2) at the inflection point located inside the precursor on the secondary particles such as (a1) or (a2) is higher than the nickel content (X3) on the surface, thereby maintaining excellent capacity characteristics, Stability at the surface can be improved and side reaction with electrolyte solution can be suppressed. In addition, the structural stability inside the precursor can be improved by lowering the nickel content (X1) at the particle center at the particle center side where the primary particles are agglomerated, and since the nickel content is not high, cracking and collapse occurs due to electrode rolling. Even so, the nickel composition at the particle center side can maintain a more stable structure than the surface. The composition change of the above (a1) and (a2) can change the composition of cobalt and / or manganese in addition to nickel using the same method.

In addition, in the precursor of the cathode active material for a secondary battery according to an embodiment of the present invention, the metal element M is present in a concentration gradient that gradually changes from the center of the secondary particles to the surface, the concentration gradient of the metal element M It includes one inflection point, the content of the metal element M in the center of the secondary particles Z1, the content of the metal element M at the inflection point located in the inner region excluding the center and the surface of the secondary particles Z2, And when the content of the metal element M on the surface of the secondary particle is Z3, the metal element M may be present under at least one condition of (b1) to (b4), more preferably (b1) or may exist under the condition of one of (b3).

(b1) Z1 = Z3> Z2

(b2) Z1 = Z3 <Z2

(b3) Z1 ≠ Z3> Z2

(b4) Z1 ≠ Z3 <Z2

The metal element M serves to improve the structural stability of the active material. In the present invention, the metal element M content (Z3) on the surface of the secondary particles is higher than the content (Z2) inside the particle, The surface stabilization effect according to the inclusion of M can be further enhanced. The metal element M may be preferably Mn in consideration of the improvement effect of the concentration gradient as described above and the effect of improving the thermal stability of the active material.

The precursor having the above structure and composition may have an average particle diameter (D ₅₀ ) of 4 μm to 30 μm. When having an average particle diameter within the above range, there is no fear of lowering the dispersibility in the active material layer due to agglomeration between the active materials during the production of the active material, and lowering the mechanical strength of the positive electrode active material and lowering the specific surface area. In addition, when considering the effect of improving the battery characteristics due to the characteristic distribution according to the position in the precursor particles, the precursor may have an average particle diameter (D ₅₀ ) of 4 ㎛ to 25 ㎛.

In the present invention, the average particle diameter (D ₅₀ ) of the precursor may be defined as the particle size at 50% of the particle size distribution. The average particle diameter (D ₅₀ ) of the precursor particles can be measured using, for example, a laser diffraction method. Specifically, the average particle diameter (D ₅₀ ) of the precursor is dispersed in the precursor particles in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac MT 3000) to output ultrasonic waves of about 28 kHz. was irradiated with 60 W, it is possible to calculate the mean particle size (D ₅₀₎ of from 50% based on the particle size distribution of the measuring device.

In addition, the cathode active material precursor for a secondary battery according to an embodiment of the present invention may be prepared by a two-step coprecipitation reaction, specifically, a first metal-containing solution containing nickel, cobalt, and metal element M, and the first Preparing a second metal containing solution containing nickel, cobalt, and metal element M at different concentrations from the metal containing solution (step 1); The mixing ratio of the first metal-containing solution and the second metal-containing solution in the first metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume to 0% by volume and 100% by volume. Simultaneously mixing with the ammonium cation-containing complex forming agent and the basic compound to first coprecipitation to form a core in which the primary particles of the composite metal hydroxide are aggregated (step 2); And for the core, the mixing ratio of the first metal-containing solution and the second metal-containing solution to the first metal-containing solution and the second metal-containing solution is from 0% by volume to 100% by volume: 0% by volume. It can be prepared by a manufacturing method comprising the step of forming a shell on the core (step 3) by continuously co-reacting by adding a basic compound and an ammonium cation-containing complex forming agent while continuously mixing to change gradually. have. In this case, the pH of the first metal-containing solution in the first coprecipitation reaction when the amount of the first metal-containing solution is 100% by volume and the pH of the second metal-containing solution in the second coprecipitation reaction is 100% by volume May be 11 to 12.

Hereinafter, each step will be described in detail.

In the method of manufacturing a cathode active material precursor for a secondary battery according to an embodiment of the present invention, step 1 is a first containing nickel, cobalt, and a metal element M (wherein M is at least one selected from the group consisting of Mn and Al). Preparing a metal containing solution, and a second metal containing solution.

The first and second metal-containing solutions may be prepared in the same manner, except that they contain nickel, cobalt and metal element M in different concentrations. Specifically, the first metal-containing solution and the second metal-containing solution are organic materials capable of uniformly mixing a nickel raw material, a cobalt raw material, and a raw material of metal element M with a solvent, specifically, water or water, respectively. It may be prepared by adding to a mixture of a solvent (specifically, alcohol, etc.) and water, or may be used after mixing a solution containing each metal-containing raw material, specifically, an aqueous solution.

The raw materials of nickel, cobalt and M, which can be used in the preparation of the first and second metal-containing solutions, include respective metal element-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides. It does not specifically limit as long as it can melt | dissolve in said solvent, such as water.

For example, the cobalt raw material may be Co (OH) ₂ , CoOOH, Co (OCOCH ₃ ) ₂ ㆍ 4H ₂ O, Co (NO ₃ ) ₂ ㆍ 6H ₂ O or Co (SO ₄ ) ₂ ㆍ 7H ₂ O And any one or a mixture of two or more thereof may be used.

In addition, as the nickel raw material, 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 salts or nickel halides, and the like, and any one or a mixture of two or more thereof may be used.

As the raw material of the metal element M, for example, when M is manganese, manganese oxides such as Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ as raw materials; Manganese salts such as MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylic acid, manganese citrate and fatty acid manganese; Oxy hydroxide, manganese chloride, and the like, and any one or a mixture of two or more thereof may be used. In addition, when M is aluminum, AlSO ₄ , AlCl ₃ , Al-isopropoxide or AlNO ₃ may be used as a raw material, and any one or a mixture of two or more thereof may be used.

The amount of the raw materials of nickel, cobalt, and metal element M in the preparation of the first and second metal-containing solutions may be appropriately determined according to the composition of the composite metal hydroxide in the final precursor.

Next, in the manufacturing method for producing the positive electrode active material, step 2, using the first and the second metal-containing solution prepared in step 1 to form a core agglomerated primary particles of the composite metal hydroxide to be.

Specifically, in the step 2, the mixing ratio of the first metal-containing solution and the second metal-containing solution is 100% by volume: 0% by volume and 0% by volume: 100% by volume. It may be carried out by adding and mixing to gradually change up to%, and coprecipitation reaction (hereinafter referred to as 'first coprecipitation reaction') by adding an ammonium cation-containing complex former and a basic compound. At this time, the first coprecipitation reaction is carried out under the condition that the pH of 10.5 to 11.5 when the dose of the first metal-containing solution is 100% by volume.

In step 2, adjusting the mixing ratio of the first metal-containing solution and the second metal-containing solution may be controlled by controlling the input flow rate of the first metal-containing solution and the input flow rate of the second metal-containing solution. . For example, the input flow rate of the first metal-containing solution and the input flow rate of the second metal-containing solution may be controlled by using a pump connected to each of the first and second metal-containing solutions.

In addition, in step 2, the mixing process of the first metal-containing solution and the second metal-containing solution may be performed using a static mixer (static mixer) to be carried out continuously. Specifically, the first metal-containing solution and the second metal-containing solution are introduced into the static mixer through separate pipes, respectively, and the mixing process is performed while gradually changing the mixing ratio.

In the present invention, the static mixer is the same as commonly used as a component used when mixing a substance such as a fluid, and is also called a mixing nozzle. The static mixer can improve the problem that the mixing is not well performed at the insufficient flow rate when the fluid is mixed by a continuous process.

The shape of the static mixer is not particularly limited as long as it has a shape suitable for dispersion in the mixer, in consideration of the degree of mixing may be specifically screw or spiral. More specifically, the static mixing may be performed by intra-tube mixing using an in-line static mixer.

The mixed metal solution mixed through the mixer is continuously introduced into the reactor, and coprecipitation occurs by adding a cation-containing complex former and a basic compound to form seeds of the composite metal hydroxide particles. Thereafter, as the first metal-containing solution and the second metal-containing solution are continuously introduced into the mixer, subsequent static mixing, subsequent injection of the mixed metal solution into the reactor, and first coprecipitation reaction are continuously performed. As a result, the growth of the composite metal hydroxide particles is achieved.

The first coprecipitation reaction may be performed under the condition that the pH of the mixed metal-containing solution is 10 to 12, provided that the pH of the first metal-containing solution is 100% by volume may be 10.5 to 11.5. When the first coprecipitation reaction is performed at the above pH condition, a plurality of composite metals are not produced by various changes in the size of the prepared precursor or particle splitting and side reactions caused by elution of metal ions on the precursor surface. The precursor particles in which the primary particles of the hydroxide are aggregated can be produced. The pH condition may be controlled according to the amount of the ammonium cation-containing complex forming agent and the basic compound.

Specifically, the ammonium cation-containing complexing agent may specifically 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 , and the like. Species alone or mixtures of two or more may be used. In addition, the ammonium cation-containing complex forming agent may be used in the form of an aqueous solution, in which case a mixture of water or an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

In addition, the ammonium cation-containing complex forming agent may be added in an amount such that 5 wt% to 150 wt% with respect to the total weight of the mixed solution of the first and second metal-containing solutions. In general, the ammonium cation-containing complex forming agent reacts with the metal in a molar ratio of at least 1: 1 to form a complex, but the unreacted complex which has not reacted with the basic aqueous solution turns into an intermediate product and is recovered as an ammonium cation-containing complex forming agent for reuse. In the present invention, the amount of the ammonium cation-containing complex forming agent can be lowered than that in the present invention. As a result, the crystallinity of the positive electrode active material can be increased and stabilized.

In addition, the 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 one or more of these may be used. The basic compound may also be used in the form of an aqueous solution, in which case a mixture of water or an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

The basic compound may be added in an amount that satisfies the pH conditions of the first coprecipitation reaction, specifically, it may be added in a molar ratio of basic compounds 1 to 10 per mole of the ammonium cation-containing complex forming agent. have.

In addition, the addition amount of the ammonium cation-containing complex forming agent and the basic compound in the coprecipitation reaction may be appropriately determined according to the concentration gradient of the metal element in the precursor to be prepared and the input amount of the mixed metal solution. Specifically, the amount of the ammonium cation-containing complex forming agent added may be 4% by weight to 100% by weight, preferably 4% by weight to 30% by weight, based on the total weight of the first and second metal-containing solutions.

In addition, the first coprecipitation reaction may be performed at 40 to 80 ° C. under an inert atmosphere such as nitrogen or argon. In addition, the stirring process may be selectively performed to increase the reaction rate during the reaction, wherein the stirring speed may be 100rpm to 1000rpm based on the 20L reactor, when the length of the stirrer relative to the reactor radius is about 40%. However, when the stirrer is larger than that described above, the stirring speed may be sufficient, so that the stirring speed may be lower than the above range.

As a result of the first coprecipitation reaction under the above conditions, primary particles of the composite metal hydroxide aggregate, and nickel, cobalt, and metal elements M constituting the composite metal hydroxide, wherein M is Mn and Al At least one of the metals selected) forms a core of the precursor that is present in a concentration gradient that changes gradually from the particle center to the surface.

Next, step 3 is a step of forming a shell on the outer surface of the core of the composite metal hydroxide prepared in step 2.

Specifically, step 3 is a mixing ratio of the first metal-containing solution and the second metal-containing solution to the core of the composite metal hydroxide in the opposite direction to that in step 2, specifically, the first metal-containing solution and the second metal. Continuous mixing was carried out so that the mixing ratio of the solution contained was gradually changed from 0% to 100% by volume to 100% by volume to 0% by volume, and co-precipitation reaction was performed by adding an ammonium cation-containing complex former and a basic compound (hereinafter, 'secondary' By coprecipitation reaction).

At this time, the pH when the amount of the second metal-containing solution is 100% by volume during the second coprecipitation reaction may be performed at a higher pH condition, specifically pH 11.0 to 12 during the first coprecipitation reaction in step 2.

When carried out at pH conditions in the above range, the composite metal hydroxide on the core grows radially oriented from the core center to the surface. When the precursor particles have an orientation as described above, a secondary battery having improved capacity and output characteristics among electrochemical characteristics may be manufactured.

Step 3 may be performed in the same manner as in Step 2 except for changing the mixing ratio and pH conditions of the first metal-containing solution and the second metal-containing solution.

As a result of the above manufacturing process, secondary particles are formed by agglomeration of a plurality of primary particles of a composite metal hydroxide including nickel, cobalt and a metal element M (wherein M is at least one selected from the group consisting of Mn and Al). At least one metal of the nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) is present in a concentration gradient that gradually changes from the center of the secondary particle to the surface. The concentration gradient includes at least one inflection point, the content of nickel at the center of the secondary particle is X1, the content of nickel at the inflection point is X2, and the content of nickel at the surface of the secondary particle is X3. When the nickel is present, the cathode active material precursor for a secondary battery, wherein the nickel is present under any one of the following conditions (a1) or (a2) is produced.

(a1) X1 = X3 <X2

(a2) X1 ≠ X3 <X2

The prepared cathode active material precursor may be selectively separated after the separation according to a conventional method, and the drying process may be optionally performed at 110 ° C. to 400 ° C. for 15 to 30 hours.

Meanwhile, in the cathode active material precursor according to an embodiment of the present invention, a concentration gradient of at least one metal of nickel, cobalt, and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) is 2 or more. In the case of including the inflection point, the mixing ratio of the first metal-containing solution and the second metal-containing solution in step 2 or 3 may be implemented by changing the method such as increasing after decreasing or increasing after decreasing.

In addition, when the cathode active material precursor is doped, at the time of preparing the first and second metal-containing solutions in step 1, at least one metal-containing solution of the first and second metal-containing solutions is a raw material of the doping element. Is further added; Or in the mixing of the first and second metal-containing solutions in step 2, through a separate pipe from the first and second metal-containing solutions, nickel, cobalt, and metal elements M (where M is Mn and Al). Metal containing solution comprising at least one selected from the group consisting of) and the doping element may be further added into the mixer.

At this time, the doping element is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, It may be selected from the group consisting of Mg, B, and Mo, sulfates, nitrates, acetates, halides, hydroxides or oxyhydroxides including any one or two or more of the above doping elements may be used as a raw material. have. For example, when the doping element is tungsten, tungsten sulfate (W (SO ₄ ) ₂ ) may be used as a raw material.

The raw material of the doping element may be appropriately determined according to the content of the doping element in the precursor to be finally prepared.

In addition, the distribution of the doping element in the precursor to be prepared may be determined according to the dosing time of the doping element, the mixing ratio control when mixing the metal-containing solutions.

For example, when the raw material of the doping element is added immediately before the mixer as a separate metal-containing solution and maintained with the same mixing ratio from the beginning to the end of the mixing process, the doping element may be uniformly distributed throughout the precursor to be produced. Can be. In another example, a doping element raw material is contained in the second metal-containing solution, and the mixing ratio of the first metal-containing solution and the second metal-containing solution is from 100% by volume to 0% by volume: 100% by volume. When gradually changed, the concentration gradient of the doping element may gradually increase from the center of the precursor particles to the surface to be prepared.

As such, when the doping element has a concentration gradient uniformly distributed or gradually changes in the precursor, there is no crystal boundary phase in the particle, thereby further improving the structural stability of the precursor and the active material prepared using the same.

According to another embodiment of the present invention, a method of manufacturing a cathode active material for a secondary battery using the precursor prepared by the above-described manufacturing method is provided.

Specifically, the manufacturing method includes the step of heat treatment after mixing the precursor of the cathode active material prepared above with a lithium raw material.

Examples of the lithium raw material include lithium-containing carbonates (for example, lithium carbonate), hydrates (for example, lithium hydroxide I hydrate (LiOH · H ₂ O), etc.), hydroxides (for example, lithium hydroxide, etc.), nitrates ( For example, lithium nitrate (LiNO ₃ ), etc.), chlorides (for example, lithium chloride (LiCl), etc.), and the like may be used alone, or a mixture of two or more thereof may be used. In addition, the amount of the lithium raw material used may be determined according to the amount of lithium and metal elements other than lithium in the final lithium composite metal oxide to be manufactured. Specifically, the metal included in the lithium and the precursor included in the lithium raw material It may be used in an amount such that the molar ratio of the elements (Me = Ni + Co + M) (molar ratio of lithium / metal element (Me)) is 1.0 or more, more specifically 1.0 to 1.07.

In addition, although the precursor prepared according to the method for preparing the precursor is not doped, when the positive electrode active material is finally prepared, the raw material of the doping element may be selectively added when the positive electrode active material precursor and the lithium raw material are mixed. have.

As a raw material of the doping element, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce , Nb, Mg, B, and an oxide or a hydrate including one or more doping elements (M ') selected from the group consisting of, and any one or a mixture of two or more of these may be used. . For example, when the doping element is tungsten, tungsten oxide (WO ₃ ) or the like may be used as a raw material. The raw material of the doping element may be determined according to the content of the doping element in the lithium composite metal oxide in the final active material.

When the raw material of the doping element is added in the mixing step of the precursor and the lithium raw material, the doping element may be present in a concentration gradient decreasing from the surface of the precursor particle toward the center in the final active material. The surface stability of the active material can be improved to suppress the occurrence of side reactions with the electrolyte.

In addition, when the precursor and the lithium raw material is mixed when the cathode active material is manufactured, a sintering agent may be optionally added. Specific examples of the sintering agent include compounds containing ammonium ions 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 any one or a mixture of two or more thereof may be used. The sintering agent may be used in an amount of 0.01 mol to 0.2 mol with respect to 1 mol of the cathode active material precursor.

In addition, when the cathode active material precursor and the lithium raw material is mixed, a moisture removing agent may be optionally further added. Specifically, the water removing agent may include citric acid, tartaric acid, glycolic acid or maleic acid, and any one or a mixture of two or more thereof may be used. The moisture remover may be used in an amount of 0.01 to 0.2 mole based on 1 mole of the positive electrode active material precursor.

In addition, the mixing process of the precursor and the lithium raw material of the positive electrode active material, and if necessary the raw material and other additives of the doping element may be carried out by a dry mixing method, more specifically in a mechanical mixing method such as a ball mill Can be performed by

In addition, the heat treatment process may be performed at 720 ℃ to 950 ℃. When the temperature during the heat treatment is within the above range, there is no fear of lowering the discharge capacity per unit weight, lowering of cycle characteristics, and lowering of operating voltage due to the residual and unreacted materials of the unreacted raw materials. More specifically, it may be performed at 750 ℃ to 900 ℃. For example, when the firing temperature exceeds the above range, there may be no concentration gradient of the positive electrode active material.

In addition, the heat treatment process may be performed for 5 to 30 hours in an oxidizing atmosphere such as air or oxygen, a non-oxidizing atmosphere containing nitrogen. Through the heat treatment process under such conditions, the diffusion reaction between the particles can be sufficiently performed, and the diffusion of the metal occurs even in the portion where the internal metal concentration is constant. As a result, a metal oxide having a continuous metal concentration distribution from the center to the surface is obtained. Can be prepared.

Meanwhile, preliminary firing may be optionally performed at 250 ° C. to 750 ° C. for 5 to 20 hours before the heat treatment process. In addition, the annealing process for 10 to 20 hours at 700 ℃ to 900 ℃ may be optionally performed after the heat treatment process.

The positive electrode active material produced by the above-described manufacturing method, a plurality of primary particles of a lithium composite metal oxide containing nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al). Wherein the primary particles are progressively formed of at least one metal of nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) from the center to the surface of the primary particles. It may be present in a concentration gradient to change, the concentration gradient may have at least one inflection point.

Specifically, in the cathode active material for a secondary battery according to an embodiment of the present invention, the nickel is present in a concentration gradient gradually changing in the secondary particles, the concentration gradient of nickel includes one inflection point, The content of nickel at the center of the secondary particle is X1, the content of nickel at the inflection point located at the inner region excluding the center and the surface of the secondary particle is X2, and the content of nickel at the surface of the secondary particle. When each referred to as X 3, nickel may be present under one of (a1) or (a2).

(a1) X1 = X3 <X2

(a2) X1 ≠ X3 <X2

Particularly, the nickel content (X2) at the inflection point located inside the active material on the secondary particles such as (a1) or (a2) is higher than the nickel content (X3) on the surface, thereby maintaining excellent capacity characteristics. Stability at the surface can be improved, and side reaction with electrolyte solution can be suppressed. In addition, the structural stability inside the active material can be improved by lowering the nickel content (X1) at the particle center at the particle center side where the primary particles are agglomerated, and since the nickel content is not high, cracking and collapse occurs due to electrode rolling. Even so, the nickel composition at the particle center side can maintain a more stable structure than the surface. The composition change of the above (a1) and (a2) can change the composition of cobalt and / or manganese in addition to nickel using the same method.

In addition, in the cathode active material for a secondary battery according to an embodiment of the present invention, the metal element M is present in a concentration gradient that gradually changes from the center of the secondary particles to the surface, and the concentration gradient of the metal element M is one. A content of the metal element M at the center of the secondary particles, including an inflection point, Z 1, a content of the metal element M at the inflection point located at an internal region excluding the center and the surface of the secondary particles, and Z 2; When the content of the metal element M on the surface of the secondary particle is Z3, the metal element M may be present under at least one of the following (b1) to (b4), more preferably (b1) or (b3). May exist as one of the following conditions.

(b1) Z1 = Z3> Z2

(b2) Z1 = Z3 <Z2

(b3) Z1 ≠ Z3> Z2

(b4) Z1 ≠ Z3 <Z2

The metal element M serves to improve the structural stability of the active material. In the present invention, the metal element M content (Z3) on the surface of the secondary particles is higher than the content (Z2) inside the particle, The surface stabilization effect according to the inclusion of M can be further enhanced. The metal element M may be preferably Mn in consideration of the improvement effect of the concentration gradient as described above and the effect of improving the thermal stability of the active material.

The secondary particles of the positive electrode active material are core-shell structure in which the primary particles are agglomerated and the outer surface of the core, the primary particles including a shell having a radial orientation from the center of the particles to the surface It can have

The positive electrode active material may control the distribution of metal elements throughout the active material particles by controlling the pH, concentration and rate of the reactant, thereby exhibiting high capacity characteristics and excellent thermal stability. As a result, it can exhibit high capacity, long life and thermal stability when the battery is applied, while minimizing performance degradation at high voltage.

According to another embodiment of the present invention, a cathode including the cathode active material is provided.

Specifically, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer containing the positive electrode 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 on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of typically 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive 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, a nonwoven body.

In addition, at least one surface of the current collector includes a positive electrode active material, and optionally a positive electrode active material layer further includes at least one of a conductive material and a binder.

At this time, the positive electrode active material may be included in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight based on the total weight of the positive electrode active material layer. When included in the above content range may exhibit excellent capacity characteristics.

In addition, the conductive material is used to impart conductivity to the electrode, and in the battery constituted, any conductive material can be used without particular limitation as long as it has electronic 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, thermal black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used. The conductive material may be included in an amount of 0.5% to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the binder serves to improve adhesion between the cathode active material particles and adhesion between the cathode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof, and the like, and one or more of these may be used. The binder may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except using the positive electrode active material described above. Specifically, the positive electrode active material and optionally, a composition for forming a positive electrode active material layer prepared by dissolving or dispersing at least one of a binder and a conductive material in a solvent is applied to at least one surface of the positive electrode current collector, and then dried and rolled. It can be prepared by. In this case, the type and content of the cathode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the coating thickness of the slurry, the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during the coating for the positive electrode production. Do.

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

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

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and 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 positioned on at least one surface of the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of 3 μm to 500 μm, and similarly to the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding 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, foam, a nonwoven body.

The negative electrode active material layer includes a negative electrode active material, and optionally further includes at least one of a binder and a conductive material.

For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It can also be produced by laminating a film obtained by peeling from this support onto a negative electrode current 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 fibers, and amorphous carbon; Metallic 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 undoping lithium, such as SiO _v (0 <v <2), SnO ₂ , vanadium oxide, lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular for ion transfer of the electrolyte It is desirable to have a low resistance against the electrolyte solution and excellent in electrolytic solution moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting glass fibers, polyethylene terephthalate fibers, or the like may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

In addition, 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, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles, such as Ra-CN (Ra is a C2-C20 linear, branched or ring-shaped hydrocarbon group, and may contain a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge / discharge performance of a battery, and low viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to 1: 9, so that the performance of the electrolyte may be excellent.

The lithium salt may 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 is 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 and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

The electrolyte includes, in addition to the electrolyte components, haloalkylene carbonate-based compounds such as difluoroethylene carbonate and the like for the purpose of improving battery life characteristics, reducing battery capacity, and improving battery discharge capacity; Or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N One or more additives such as -substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be included. In this case, 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, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and therefore, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

[ Example  One]

(Production of precursor)

In a batch 20L reactor set at 60 ° C., nickel sulfate, cobalt sulfate and manganese sulfate were mixed in water in an amount such that the molar ratio of nickel: cobalt: manganese was 60:20:20 in water at a 2 M concentration. A first metal-containing solution was prepared, and nickel sulfate, cobalt sulfate and manganese sulfate were mixed in water in an amount such that the molar ratio of nickel: cobalt: manganese was 90: 5: 5, and containing a second metal at 2M concentration. The solution was prepared.

The vessel containing the first metal containing solution and the vessel containing the second metal containing solution were respectively connected to an in-line static mixer in the tube, and a reactor was connected to the outlet side of the static mixer. In addition, a 25% NaOH solution and a 15% NH ₄ OH aqueous solution were prepared and connected to the reactor, respectively. 4 liters of deionized water was added to the coprecipitation reactor (capacity 20L), and nitrogen gas was purged at 2 L / min in the reactor to remove dissolved oxygen in water and to form a non-oxidizing atmosphere in the reactor. Thereafter, 10 ml of 25% NaOH and 300 ml of 15% ammonia water were added to the reactor, followed by stirring at a stirring speed of 500 rpm at a temperature of 60 ° C., while the first metal-containing solution was used at a flow rate of 6 ml / min using a first pump. The second metal-containing solution was changed to 0 ml / min, using a second pump at a rate of 100 vol%: 0 vol% to 0 vol%: 100 vol% at a flow rate of 0 ml / min at 6 ml / min. It was gradually changed and put into the static mixer to perform continuous mixing.

Subsequently, NH ₄ OH aqueous solution was added to the reactor at a rate of 2 mL / min, and NaOH aqueous solution was added to maintain a pH of 10.8 to 11.2 in the reactor. A seed having an average particle diameter of 4 μm was formed while reacting for 30 minutes, followed by primary coprecipitation for 360 minutes in succession to form a core made of nickel manganese cobalt composite metal hydroxide. During the reaction time, the pH gradually rose from 10.8 to finally bring the pH to 11.7.

Thereafter, the first metal-containing solution was used at 6 mL / min at a flow rate of 0 mL / min using a first pump, and the second metal-containing solution was used at 0 mL / min at 6 mL / min using a second pump. Gradually adding a volume ratio of 100% by volume to 100% by volume to 0% by volume into the static mixer to perform continuous mixing, while introducing NH ₄ OH aqueous solution into the reactor at a rate of 2 mL / min, When the content of the second metal-containing solution is 100% by volume, the pH in the reactor is 11.7, and when the content of the second metal-containing solution is 0% by volume, a NaOH aqueous solution was added so that the pH in the reactor was 10.8. . The second co-precipitation reaction for 18 hours induced the growth of nickel cobalt manganese-based composite metal hydroxide particles and at the same time induced a concentration gradient inside the particles. In this case, the pH of the first metal-containing solution in the first coprecipitation reaction is set to 10.8 when the volume of the first metal-containing solution is 100% by volume, and until the volume of the second metal-containing solution is 100% by volume as the reaction proceeds. The pH was increased so that the pH in the reactor was 11.7 upon completion of the first coprecipitation reaction. Meanwhile, the flow rates of the first metal-containing solution and the second metal-containing solution according to the reaction time are shown in Table 1 below.

The resulting nickel manganese cobalt-based composite metal-containing hydroxide particles were separated and washed with water and dried in an oven at 120 ℃ to prepare a precursor having an average particle diameter of 15㎛. The resulting composition of the positive electrode active material precursor was LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ .

Reaction time (minutes) Flow rate of the first metal-containing solution (mL / min) Flow rate of the second metal-containing solution (mL / min) 0 6 0 120 5.9 0.1 240 One 5 360 0 6 660 One 5 960 2.5 3.5 1200 4.5 1.5 1470 6 0

(Production of active substance)

The precursor prepared above was dry mixed with lithium hydroxide (1.03 mol of lithium hydroxide per 1 mol of precursor) as a lithium raw material, and then heat-treated at 650 ° C. for 3 hours in an oxygen atmosphere and then at 750 ° C. for 15 hours to form active material particles. Particles of a lithium composite metal oxide including a concentration gradient of a metal element were prepared.

(Manufacture of Lithium Secondary Battery)

The positive electrode active material, the denka black conductive material, and the polyvinylidene fluoride precursor binder prepared above were mixed at a weight ratio of 95: 2.5: 2.5 to prepare a composition for forming a positive electrode using an N-methylpyrrolidone solvent. The prepared positive electrode forming composition was coated on aluminum foil, roll pressed, and dried at 120 ° C. for 12 hours to prepare a positive electrode. Further, as a negative electrode active material, natural graphite, carbon black conductive material, and styrene-butadiene rubber (SBR) were used. ) Was mixed in a weight ratio of 96: 2: 2 to prepare a composition for forming a negative electrode. The prepared negative electrode composition was applied to a copper foil, and vacuum dried at 110 ° C. for 2 hours to prepare a negative electrode.

After the polyethylene separator is interposed between the positive electrode and the negative electrode prepared above, 1M LiPF ₆ mixed electrolyte is injected into a mixed solvent in which ethylene carbonate: dimethylcarbonate is mixed at a volume ratio of 1: 1, thereby injecting a coin-type battery. Was prepared.

[ Comparative example  One]

In Example 1, instead of the first and second metal-containing solutions, nickel sulfate, cobalt sulfate: manganese sulfate is mixed in water in an amount such that the molar ratio of nickel: cobalt: manganese is a molar ratio of 80:10:10, 2M A precursor and a cathode active material were prepared in the same manner as in Example 1, except for using a metal-containing solution prepared at a concentration and maintaining a pH of 11.5 during the reaction.

[ Comparative example  2]

Nickel sulphate, cobalt sulphate and manganese sulphate are mixed at a concentration of 2M in water in an amount such that the molar ratio of nickel: cobalt: manganese is 90: 5: 5 and used as a first metal containing solution, nickel sulphate, cobalt Example 1 except that the sulfate and manganese sulfate were mixed at a concentration of 2M in water in an amount such that the molar ratio of nickel: cobalt: manganese was 60:20:20 and used as a second metal-containing solution. Using the same method as the precursor and the cathode active material was prepared.

[ Experimental Example  1: Particle Characteristics of Cathode Active Material Precursor]

The change in Ni composition according to the growth of the cathode active material precursor particles prepared in Example 1 was confirmed through high frequency inductively coupled plasma (ICP) analysis. Specifically, 1 mL of hydrochloric acid was added to 0.1 g of the positive electrode active material precursor prepared in Example 1, and then heated to 100 ° C. to dissolve. When the sample was completely decomposed, ultrapure water was added and diluted to 10 mL. The diluted solution was analyzed by ICP and the results are shown in Table 2 below.

Reaction time (minutes) Particle Size (μm) Ni content (mol%) 30 4.5 60 120 6.2 74.9 240 6.8 93.5 360 9 92.8 390 11.3 92.5 660 12.5 91.7 960 13.3 84.8 1200 14.5 74.6 1440 14.9 64.4 1470 15.4 60

[ Experimental Example  2: in positive electrode active material precursor Concentration gradient  analysis]

In order to confirm the structure of the cathode active material precursor particles prepared in Example 1, the internal composition of the cathode active material precursor particles was confirmed while moving in 500 nm units using an electron probe micro analyzer (EPMA). It is shown in Table 3 below.

Distance (nm) Ni Mn Co 0 (center) 60.5 20.0 19.5 500 61.4 20.1 18.5 1000 64.7 18.3 17.0 1500 71.5 13.9 14.6 2000 80.4 9.1 10.5 2500 88.7 5.3 6.0 3000 89.1 5.2 5.7 3500 89.8 5.6 4.6 4000 89.5 4.3 6.2 4500 81.1 9.5 9.4 5000 73.0 13.7 13.3 5500 71.8 18.2 10.0 6000 65.4 16.2 18.4 6500 63.5 17.9 18.6 7000 61.2 19.9 18.9 7500 (surface) 60.5 23.9 15.6

As shown in Table 3, in the positive electrode active material precursor particles prepared in Example 1, all of nickel, cobalt, and manganese exist in a concentration gradient that gradually changes from the center of the secondary particles to the surface, wherein the concentration gradient is one or more inflection points. It could be confirmed to include.

[ Experimental Example  3: in positive electrode active material Concentration gradient  analysis]

In order to confirm the structure of the positive electrode active material particles prepared in Example 1, the internal composition of the positive electrode active material particles was confirmed while moving in 500 nm units using an electron probe micro analyzer (EPMA), and the results are as follows. Table 4 shows.

Distance (nm) Ni Mn Co 0 (center) 74.2 13.5 12.3 500 73.9 14.1 12.0 1000 75.4 12.6 12.0 1500 78.3 9.2 12.5 2000 77.6 8.85 13.55 2500 79.6 9.9 10.5 3000 81.5 9.0 9.5 3500 83.0 9.0 8.0 4000 83.9 8.9 7.2 4500 83.8 9.1 7.1 5000 83.5 9.6 6.9 5500 81.2 9.2 9.6 6000 78.9 9.3 11.8 6500 75.7 10.3 14.0 7000 75.3 11.6 13.1 7500 (surface) 73.5 12.7 12.8

As shown in Table 4, in the positive electrode active material particles prepared in Example 1, nickel, cobalt, and manganese are all present in a concentration gradient that gradually changes from the center of the secondary particles to the surface, wherein the concentration gradient is one or more inflection points. It was confirmed to include.

[ Experimental Example  4: Battery Characteristic Evaluation of Lithium Secondary Battery]

Battery characteristics of the lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 2 were evaluated using the following method.

Specifically, the battery was charged at 25 ° C until it became 4.25V with 0.2C constant current and discharged until it became 2.5V with 0.2C constant current. With the charge and discharge behavior as one cycle, the cycle capacity retention and the resistance increase rate, which are ratios of the discharge capacity at the 30th cycle with respect to the initial capacity after 30 cycles, were measured, respectively, and are shown in Table 5 below.

Charge capacity
(mAh / g) Discharge capacity
(mAh / g) Capacity retention rate (%) % Increase in resistance Example 1 225.3 201.4 98.2 35.1 Comparative Example 1 223.5 198.1 95.8 61.3 Comparative Example 2 225.5 200.3 97.5 37.8

As shown in Table 5, the lithium secondary battery prepared in Example 1 was confirmed to exhibit excellent efficiency compared to the batteries of Comparative Examples 1 and 2 when charging and discharging at 0.2C rate.

In addition, it was confirmed that the lithium secondary battery of Example 1 was superior to the lithium secondary batteries manufactured in Comparative Examples 1 and 2 after the charge and discharge for 30 cycles.

Claims (14)

As secondary particles formed by agglomeration of a plurality of primary particles of a composite metal hydroxide including nickel, cobalt and a metal element M (wherein M is at least one selected from the group consisting of Mn and Al),
At least one metal of the nickel, cobalt and metal element M (wherein M is at least one selected from the group consisting of Mn and Al) is present in a concentration gradient that gradually changes from the center of the secondary particle to the surface. The concentration gradient includes at least one inflection point at which the concentration gradient slope changes from a negative value to a positive value or a positive value to a negative value,
When the content of nickel at the center of the secondary particles is X1, the content of nickel at the inflection point is X2, and the content of nickel at the surface of the secondary particles is X3, nickel is the following (a1) or (a2) A cathode active material precursor for a secondary battery that is present under any one condition.
(a1) X1 = X3 <X2
(a2) X1 ≠ X3 <X2
The method of claim 1,
The secondary particles are located on the core and the outer surface of the core agglomerated the primary particles, the primary particles have a core-shell structure of the shell having a radial orientation from the center of the particle to the surface Cathode active material precursor.
The method of claim 1,
The metal element M is present in a concentration gradient gradually changing from the center of the secondary particle to the surface, the concentration gradient of the metal element M includes one inflection point,
When the content of the metal element M at the center of the secondary particles is X1, the content of the metal element M at the inflection point is X2, and the content of the metal element M at the surface of the secondary particles is Z3, the metal element M is A cathode active material precursor for a secondary battery, which is present under any one of the following conditions (b1) to (b4).
(b1) Z1 = Z3> Z2
(b2) Z1 = Z3 <Z2
(b3) Z1 ≠ Z3> Z2
(b4) Z1 ≠ Z3 <Z2
The method of claim 3,
The metal element M is manganese positive electrode active material precursor.
The method of claim 2,
The core is a positive electrode active material precursor for a secondary battery, which occupies 60% by volume to 80% by volume with respect to the total volume of secondary particles.
The method of claim 1,
The primary particles have a rod (rod) having a cathode active material precursor for a secondary battery.
The method of claim 1,
The primary particle, the positive electrode active material precursor for a secondary battery is a ratio of the length of the long axis passing through the center of the primary particle and perpendicular to the short axis with respect to the length of the short axis passing through the center of the primary particle.
The method of claim 1,
W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo A cathode active material precursor for a secondary battery further comprising being doped with one or more doping elements selected from the group consisting of.
Preparing a first metal containing solution containing nickel, cobalt and metal element M, and a second metal containing solution containing nickel, cobalt and metal element M at different concentrations from the first metal containing solution;
The mixing ratio of the first metal-containing solution and the second metal-containing solution in the first metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume to 0% by volume and 100% by volume. At the same time as mixing, adding an ammonium cation-containing complex forming agent and a basic compound to first coprecipitation to form a core in which primary particles of the composite metal hydroxide are aggregated; And
With respect to the core, the mixing ratio of the first metal-containing solution and the second metal-containing solution to the first metal-containing solution and the second metal-containing solution is 0 vol%: 100 vol% to 100 vol%: 0 vol% Continuously mixing so as to change into the second compound, and adding a basic compound with an ammonium cation-containing complex forming agent to form a shell on the core,
The pH when the dose of the first metal-containing solution in the first coprecipitation reaction is 100 vol% is 10.5 to 11.5, and the pH when the dose of the second metal-containing solution in the second coprecipitation reaction is 100 vol% is 11 Method for producing a positive electrode active material precursor of 12 to 12.
A method of manufacturing a cathode active material for a secondary battery comprising the step of heat treatment after mixing the cathode active material precursor according to claim 1 with a lithium raw material.
As secondary particles formed by agglomeration of a plurality of primary particles of a lithium composite metal oxide including nickel, cobalt and a metal element M (wherein M is at least one selected from the group consisting of Mn and Al),
The primary particles are present in a concentration gradient in which at least one metal of nickel, cobalt and metal elements M (wherein M is at least one selected from the group consisting of Mn and Al) is gradually changed from the center to the surface of the primary particles. The concentration gradient is a positive electrode active material for a secondary battery having at least one inflection point in which the concentration gradient is changed from a negative value to a positive value or a positive value to a negative value.
The method of claim 11,
The secondary particles having a core-shell structure comprising a core in which the primary particles are aggregated and an outer surface of the core, wherein the primary particles comprise a shell having a radial orientation from the center of the particles to the surface Cathode active material for phosphorus secondary batteries.
A lithium secondary battery positive electrode comprising the positive electrode active material according to claim 12.
A lithium secondary battery comprising the positive electrode according to claim 13.

Images