KR20200022904A - Method for manufacturing positive electrode active material for lithium rechargeable battery, and lithium rechargeable battery including the positive electrode active material manufactured by the method - Google Patents

Abstract

According to an embodiment of the present invention, provided is a method for modifying a surface of lithium cobalt-based oxide particles with a specific material and a specific method. Specifically, according to an embodiment of the present invention, provided is a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the following steps: dry-mixing core particles containing lithium cobalt-based oxide, nickel cobalt manganese-based hydroxide particles, and lithium raw material; and firing the dry mixture to form a coating layer comprising lithium nickel cobalt manganese-based oxide on the surface of the core particle containing the lithium cobalt oxide.

Description

METHOD FOR MANUFACTURING POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM RECHARGEABLE BATTERY INCLUDING THE POSITIVE ELECTRODE ACTIVE MATERIAL MANUFACTURE

The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the positive electrode active material according to the production method.

Recently, the demand for large-capacity power storage devices, as well as small electronic devices, has increased significantly. In response to these demands, there is a growing interest in electrochemical devices that exhibit high capacity and high power characteristics.

In this regard, the charge / discharge region of a commercial lithium secondary battery is generally in the range of 3.0 to 4.2V, and attempts to expand the capacity by increasing the charge voltage thereof have continued.

Specifically, a component that implements the capacity of the lithium secondary battery is a positive electrode active material, and lithium cobalt oxide (LiCoO ₂ , so-called LCO) is used as a positive electrode active material in commercial lithium secondary batteries.

LiCoO ₂ is a compound having a crystal structure of a layered structure, and has a high rolling density and relatively excellent electrochemical properties such as cycle characteristics. However, since LiCoO ₂ is a compound having a low charge / discharge current of about 150 mAh / g, when a charging voltage exceeding 4.2 V is applied to a battery to which it is applied, the crystal structure of LiCoO ₂ becomes unstable, and Co in ³⁺ ions are eluted, and thus the Co ³⁺ ions eluted cause side reactions with the electrolyte on the surface of LiCoO ₂ , resulting in deterioration of battery life characteristics.

Therefore, in order to implement a lithium secondary battery having high stability and stability while expressing high capacity and high output characteristics, improvement of a positive electrode active material should be made in advance.

In an embodiment of the present invention, in order to solve the above-mentioned problem, a method of modifying the surface of lithium cobalt-based oxide particles with a specific material and a specific material is provided.

Specifically, in one embodiment of the present invention, dry mixing the core particles, nickel cobalt manganese hydroxide particles and lithium raw material containing a lithium cobalt-based oxide; And calcining the dry mixture to form a coating layer including lithium nickel cobalt manganese oxide on a surface of the core particle including the lithium cobalt oxide.

In addition, other embodiments of the present invention provides various examples of applying the positive electrode active material prepared by the method of the embodiment (anode, lithium secondary battery, battery module, battery pack, etc.).

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

In addition, the particle size D0.9 in the present specification, 0.1, 0.2, 0.3 .... 3, 5, 7 .... 10, 20, 30㎛ 0.9 by volume ratio of the active material particles having various particle sizes are distributed D10 means particle size when particles are accumulated up to%, D10 is particle size when particles are accumulated up to 10% by volume, D50 particle size is particle size when particles are accumulated up to 50% by volume, D6 is Particle size when particles are accumulated up to 6% by volume ratio, D95 means particle size when particles are accumulated up to 95% by volume ratio.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

Manufacturing method of the positive electrode active material

In one embodiment of the present invention, a method of modifying the surface of lithium cobalt-based oxide particles with a specific material and a specific material is provided.

Commercial LiCoO ₂ Inherent in

As pointed out above, LiCoO ₂ is a compound having a low charge / discharge current of about 150 mAh / g. Therefore, when a charging voltage exceeding 4.2V is applied to a battery to which it is applied, the inner metal (Co) is ionized and eluted. As a result, the eluted metal ions cause side reactions with the electrolyte solution to generate gas in the battery, thereby reducing the life of the battery.

To solve this problem, the small particle size (D50 particle size, about 5 to 10 μm) LiCoO _{2 used} in commercial lithium secondary batteries is replaced with a large particle size (D50 particle size, about 12 to 25 μm) LiCoO ₂ , or particle form by mixing LiCoO ₂ and LiCoO ₂ is substituted path can be applied to the positive electrode active material with (a so-called bimodal, bi-modal) form.

However, the assignment If LiCoO ₂ is a small particle size in case of LiCoO _2, the mechanical (kinetic) characteristic is inferior, so, substituting light LiCoO order to increase the mechanical (kinetic) properties of the _two as small particle size LiCoO ₂ level, the surface of the assignment If LiCoO ₂ part It is possible to artificially form a Li deficient layer in the region.

Herein, although the crystal structure of general LiCoO ₂ is a layered structure regardless of particle size, in the case of lithium deficient layer, the spinel structure having a crystal structure similar to that of LiMn ₂ O ₄ depends on the change in the molar ratio of Li / Co. spinel) structure.

The lithium depleted region may be formed uniformly from the surface of the large particle size LiCoO ₂ to a constant depth and formed of a layered structure; And a shell formed of a spinel structure. On the contrary, a core made of a layered structure is formed such that the layered structure and the spinel structure are mixed from the surface of the large-size particle LiCoO ₂ to a constant depth; And a shell in which a layered structure and a spinel structure are mixed.

Any form, artificially lithium depletion region in the surface portion of assignment If LiCoO ₂ the case of forming a (Li deficient layer), it is possible to increase the mechanical (kinetic) properties to particles of small particle size LiCoO ₂ level, with respect to the cell applied it Even if the charging voltage is applied up to 4.4 V, problems such as internal metal (Co) elution may not occur.

However, when the charging voltage is further increased to about 4.45 V or more, elution of the internal metal (Co) occurs even in a state in which a lithium deficient layer is artificially formed in a portion of the surface of the large particle size LiCoO ₂ . That is, the charging voltage of not less than about 4.45 V, spinel (spinel) existing on the surface portion of substituting LiCoO ₂ light structure also unstable and, in the end results in a small particle size conventional LiCoO ₂ and a similar problem.

Surface Modification by NCM

Therefore, in one embodiment of the present invention, core particles including lithium cobalt oxide; And dry mixing the lithium nickel cobalt manganese hydroxide particles and firing to provide lithium cobalt oxide particles surface-modified with lithium nickel cobalt manganese oxide (so-called NCM) as a cathode active material.

The crystal structure of the NCM, even if the crystal structure is applied to a charging voltage exceeding 4.2V, 4.4V or more, and 4.45V or more, the stability of the structure can be maintained. In addition, the NCM is a material that can implement the capacity of the battery as the core itself.

Therefore, the positive electrode active material prepared according to the embodiment, even if a charging voltage of 4.2V, 4.4V or more, and even 4.45V or more is applied to the lithium secondary battery to which the same is applied, a problem such as internal metal (Co) elution occurs. And may contribute to improving the capacity of the battery.

Advantages of the surface modification method according to the embodiment

For reference, a lithium nickel cobalt manganese system on a surface of a core-shell structure precursor (ie, cobalt raw material material) is co-precipitated with lithium nickel cobalt manganese hydroxide on the surface of a cobalt raw material of lithium cobalt oxide (eg, Co ₃ O ₄ ). When the hydroxide-coated structure is obtained, the precursor of the core-shell structure and the lithium raw material (for example, LiOH, Li ₂ CO ₃ , hydrates thereof, mixtures thereof, etc.) are mixed and fired (hereinafter, In some cases, also in the "precursor surface modification method"), a positive electrode active material having the same structure as the above embodiment (hereinafter, referred to as "active material surface modification method of the above embodiment)) can be obtained.

However, the active material surface modification method of the embodiment has the following advantages over the precursor surface modification method.

1) First, according to the active material surface modification method of the embodiment, compared to the precursor surface modification method, raw material costs, process operating costs, time, etc. can be reduced. That is, in terms of process efficiency, there is an advantage of the active material surface modification of the embodiment.

2) In particular, the structure of the product actually obtained according to the precursor surface modification method may be different from the structure of the product actually obtained according to the surface modification of the active material of the embodiment.

Specifically, cobalt raw material may inevitably be mixed in the core particles of the product according to the precursor surface modification method, but according to the active material surface modification method of the embodiment, the cobalt raw material may not be included in the core particles at all.

More specifically, according to the precursor surface modification method, in the firing process, the lithium raw material is difficult to diffuse to the core inside the core material of the core-shell structure, and remains in the cobalt raw material state without being converted into lithium cobalt-based oxide. That part can happen.

On the other hand, according to the active material surface modification method of the embodiment, since the core particles, which have already been completely converted from the cobalt raw material to the lithium cobalt oxide, are dry mixed with lithium nickel cobalt manganese hydroxide particles and calcined, the core particles of the product Cobalt raw material may not be included at all. Here, the cobalt raw material is a material that can not implement the capacity of the battery. Therefore, when the cobalt raw material is inevitably mixed in the core particles (the two-step synthesis method), the cobalt raw material is more disadvantageous than the case in which no cobalt raw material is included in the core particles (one step synthesis method of the above embodiment). There is this.

Hereinafter, the active material surface modification method of the embodiment will be described in more detail.

Mixing process of raw materials

In the mixing step, the lithium nickel cobalt manganese hydroxide particles may be included in an amount of 500 to 50000 ppm based on the total amount of the mixture of the core particles including the lithium cobalt oxide and the nickel cobalt manganese hydroxide particles.

On the contrary, when the coating amount is less than 500 ppm, the surface coating uniformity may not be low and the coating may not be coated. Co dissolution may increase rapidly due to the reaction between the surface of the core particle including the lithium cobalt oxide and the electrolyte solution. On the contrary, when a coating amount of more than 50000 ppm is applied, the content of the coating layer is relatively higher than that of the core, thereby reducing the capacity of the positive electrode active material, and the excessively thick coating layer is formed, resulting in a problem of increasing surface resistance. Can be.

Meanwhile, the mixing time, speed, temperature, equipment, and the like conditions of the mixing step are not particularly limited, but in the art, conditions for mixing the core and the coating material to modify the surface of the positive electrode active material, for example, mixing The cobalt raw material and the core particles are added to the apparatus, and stirred at 800 to 1200 rpm at room temperature for 5 to 30 minutes.

Here, as a mixing device, a paste mixer (pastemixer) can be used as in the following embodiment, but is not limited thereto, and an apparatus generally used in solid state mixing in the art may be used.

However, this is merely an example, whereby the present invention is not limited.

Coating process

In the coating step, converting the nickel cobalt manganese hydroxide particles into lithium nickel cobalt manganese oxide particles; And coating the core particles with the lithium nickel cobalt manganese oxide particles.

Specifically, after the nickel cobalt manganese hydroxide particles react with the lithium raw material to be converted to lithium nickel cobalt manganese oxide particles, the converted lithium nickel cobalt manganese oxide particles may be coated on the surface of the core particles. .

Alternatively, in the state in which the nickel cobalt manganese hydroxide particles are coated on the surface of the core particle, the nickel cobalt manganese hydroxide particles may be converted into lithium nickel cobalt manganese oxide particles by reacting with a lithium raw material.

Thus, in the coating step, converting the nickel cobalt manganese hydroxide particles into lithium nickel cobalt manganese oxide particles without changing the crystal structure of the core particles; And coating the core particles with the lithium nickel cobalt manganese oxide particles. Conditions may be applied at the same time.

For example, for this purpose, the mixture of the cobalt raw material and the core particles may be fired at a firing temperature of 800 to 1200 ° C. for 2 to 10 hours. More specifically, starting at a temperature of 900 to 1000 ℃ can be raised to a temperature increase rate of 3 to 5 ℃ / hr for 2 to 6 hours, and then maintained at the temperature reached for 3 to 5 hours. However, this is merely an example, whereby the present invention is not limited.

Selection and / or Preparation of Core Particles

As described above, the core particle may be one in which a lithium deficient layer is artificially formed in a portion of the surface of the large particle size LiCoO ₂ .

In this case, the core particle, the lithium cobalt oxide crystal structure of the first region having a layered (layered) structure; And a second structure in which the crystal structure of the lithium cobalt oxide is a spinel structure, or a spinel structure and a layered structure are mixed, from the interface with the first region to the surface of the core particle. Region; may be to include.

Here, the first region may be represented by the following Chemical Formula 1, and the second region may be represented by the following Chemical Formula 2.

[Formula 1] Li _a Co _(1-xyz) M1 _x M2 _y M3 _z O ₂

[Formula 2] Li _am Co _(1-xyz) M1 _x M2 _y M3 _z O ₂

(M1, M2, and M3 are each independently one selected from the group containing Ti, Mg, Al, Zr, Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo; a, x , y, z, and m are values satisfying 0.95 ≦ a ≦ 1.05, 0 ≦ x ≦ 0.02, 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02, and 0 <m <0.25, respectively)

The difference between the formulas 1 and 2 is in the molar ratio of Li / Co, wherein the molar ratio of Li / Co is a / (1-xyz), (am) / (1-xyz) in the formula (2) . That is, the difference in molar ratio of Li / Co represented by Formulas 1 and 2 reveals that the second region is a lithium deficient region.

Meanwhile, in Chemical Formulas 1 and 2, M1, M2, and M3 correspond to dopants, which replace cobalt sites in the crystal (lattice) structure of lithium cobalt oxide, respectively. In addition, in the case of x, y, and z, the doping amount of M1, M2, and M3 is meant. Molar fractions of 0 ≦ x ≦ 0.02, 0 ≦ y ≦ 0.02, and 0 ≦ z ≦ 0.02 represented by Formulas 1 and 2 based on ppm (reference: 1 g of the core particles in total) In some cases, depending on the atomic weight of M1, M2, and M3 may vary, for example, Al may be 2000-4000 ppm, Ti and Mg may be 500-1500 ppm, respectively.

When the one, whether the introduction of whether the dopant to form the artificially lithium depletion region (Li deficient layer) on the surface of a part of the assigned path LiCoO ₂ as the core particles, small that the mechanical (kinetic) characteristic diameter LiCoO ₂ Even if the charging voltage is increased to 4.4 V and the charging voltage is applied to the battery to which the battery is applied, the problem such as internal metal (Co) dissolution may not occur.

However, the introduction of the dopant may stabilize the crystal (lattice) structure of the lithium cobalt oxide, and may help to further suppress problems such as internal metal (Co) elution.

Furthermore, when the core particle is formed by artificially forming a lithium deficient layer on a part of the surface of the large particle size LiCoO ₂ , and a dopant is introduced into the core particle, the surface of the core particle is modified. Even greater synergistic effects are developed and problems such as internal metal (Co) elution are further suppressed even when applying a charging voltage exceeding 4.2 V, 4.4 V or more, and 4.45 V or more, thereby ensuring stability while expressing high capacity and high power characteristics. The lithium secondary battery can be implemented.

The core particles may be purchased by using a commercially available material, but may be prepared and used directly.

In the latter case, the mixing step; The method may further include preparing core particles including the lithium cobalt-based oxide before.

Specifically, preparing a core particle including the lithium cobalt-based oxide; the heat treatment of the first mixture of the lithium raw material and the cobalt raw material mixed in a molar ratio of 0.95: 1 to 1.05: 1, lithium cobalt oxide Forming particles in which the crystal structure is a layered structure; And mixing the second mixture of the lithium raw material and the cobalt raw material in a molar ratio of 0.65: 1 to 0.85: 1 with heat treatment by mixing the lithium cobalt oxide crystal structure with particles having a layered structure. Can be.

The first region may be formed in the heat treatment of the first mixture, and then the second region may be formed in the heat treatment process by mixing with the second mixture.

Selection and / or Manufacturing Process of Coating Precursors

In the case of the nickel cobalt manganese hydroxide particles, the nickel content may be used in the range of 30 to 50 mol%, so-called commercially available in the composition of NCM 111 to 523 may be purchased, or may be prepared and used directly.

In the latter case, the nickel cobalt manganese hydroxide particles may be prepared using coprecipitation methods generally known in the art. For example, in a reactor in which the pH is kept constant and the chelating agent is introduced, an aqueous solution mixed with nickel raw material, cobalt raw material, manganese raw material, and sometimes doping raw material may be introduced at a constant rate and coprecipitated. . The coprecipitation product thus obtained is obtained through a washing and drying step generally known in the art, and can be added to the mixing step of the raw materials. However, this is merely an example, whereby the embodiment is not limited.

Co Elution Suppression Characteristics (Parameters)

On the other hand, the positive electrode active material is actually stored for 1 week at a temperature in the range of 50 to 80 ℃, when discharged at a voltage of 4.4 V to 4.5 V, Co dissolution amount per 100 g of the positive electrode active material 100 to 3000 ppm / g For example, it may be 300 to 2700 ppm / g.

This is a significant decrease in Co elution compared to the core particle itself (bare) not modified with the NCM, which is supported by the experimental example described later.

Here, the Co leaching amount may be measured, for example, as follows: In order to reduce the measurement error, the loading amount of the positive electrode mixture per area of one side of the electrode is increased to 60 to 80 mg / cm ^{2 by} increasing the loading amount in general during manufacturing of the electrode. The electrodes charged within the range of 4.4 V to 4.5 V were prepared, respectively, and placed in a raw bottle with 4 ml of electrolyte. Seal completely with parafilm and aluminum pouch to prevent the electrolyte from evaporating. The fully sealed bottle is stored for one week in a 60 ° C chamber. After one week, to extract only the electrolyte, a sealing filter is used to completely remove the cathode active material that may be present as a suspended solid in the electrolyte. The electrolyte is evaporated to quantify the amount of Co present in the electrolyte, that is, eluted out through the ICP. Co elution is calculated by dividing Co, which has been confirmed for quantification, by the weight of LiCoO ₂ cathode splitter of the charging electrode that was initially put in the electrolyte. However, this is merely an example, whereby the present invention is not limited.

Lithium Secondary Battery, Battery Module, Battery

In other embodiments of the present invention, various examples of applying a cathode active material according to the embodiment (anode, lithium secondary battery, battery module, battery pack, etc.) are provided.

The lithium secondary battery according to the embodiment includes an electrode assembly including a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte solution impregnated with the positive electrode, the negative electrode and the separator, and the electrode assembly And a sealing member for sealing the battery container.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material described above. Accordingly, the electrochemical device can express excellent thermal stability and lifespan while expressing high capacity and high power characteristics.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative active material generally used in a lithium ion secondary battery may be used, and a representative example thereof is crystalline carbon. , Amorphous carbon or a combination thereof can be used. Examples of the crystalline carbon may include graphite such as amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon may include soft carbon (soft carbon). Or hard carbon, mesophase pitch carbide, calcined coke, or the like.

Examples of the alloy of the lithium metal include lithium and metals of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or Sn. Alloys can be used.

Examples of materials capable of doping and undoping lithium include Si, SiO _x (0 <x <2), Si-C composites, and Si-Q alloys (wherein Q is an alkali metal, an alkaline earth metal, and a group 13 to 16 element). , A transition metal, a rare earth element or a combination thereof, not Si), Sn, SnO ₂ , Sn-C composite, Sn-R (wherein R is an alkali metal, an alkaline earth metal, an element of Group 13-16, a transition metal, Rare earth elements or a combination thereof, and not Sn). Specific elements of Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof is mentioned.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

The negative electrode active material layer also includes a binder, and optionally may further include a conductive material.

The binder adheres the anode active material particles to each other well, and also serves to adhere the anode active material to the current collector well, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, and carboxylation. Polyvinylchloride, polyvinylfluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic ray Tied styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and may be used as long as it is an electronic conductive material without causing chemical change in the battery to be constructed. Examples thereof include natural graphite, artificial graphite, carbon black, acetylene black, and ketjen black. Carbon-based materials such as carbon fibers; Metal materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive polymers such as polyphenylene derivatives; Or a conductive material containing a mixture thereof.

The current collector may be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam (foam), copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

The electrolyte solution contains a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol or aprotic solvent. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used, and the ester solvent may be methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methylpropionate. , Ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone may be used as the ketone solvent. have. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol solvent, and as the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, Amides such as nitriles such as dimethyl formamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like, may be used.

The non-aqueous organic solvent may be used alone or in combination of one or more, the mixing ratio in the case of using one or more mixed can be appropriately adjusted according to the desired battery performance, which is widely understood by those skilled in the art Can be.

In the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolyte may be excellent.

The non-aqueous organic solvent may further include the aromatic hydrocarbon organic solvent in the carbonate solvent. In this case, the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of about 1: 1 to about 30: 1.

The non-aqueous electrolyte may further include a vinylene carbonate or ethylene carbonate-based compound to improve battery life.

Representative examples of the ethylene carbonate compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, vinylene Ethylene carbonate etc. are mentioned. When the vinylene carbonate or the ethylene carbonate-based compound is further used, the amount thereof may be appropriately adjusted to improve life.

The lithium salt is dissolved in the non-aqueous organic solvent, acts as a source of lithium ions in the battery to enable the operation of the basic lithium secondary battery, and serves to promote the movement of lithium ions between the positive electrode and the negative electrode to be. Representative examples of the lithium salt are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y +1} SO ₂ ), where x and y are natural numbers, LiCl, LiI, LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate (LiBOB) or combinations thereof The lithium salt may be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is included in the above range, the electrolyte has an appropriate conductivity and viscosity. It can exhibit excellent electrolyte performance, and lithium ions can move effectively.

The separator may be used as long as it is commonly used in lithium batteries by separating the negative electrode from the positive electrode and providing a passage for moving lithium ions. In other words, a low resistance to the ion migration of the electrolyte and excellent in the ability to hydrate the electrolyte can be used. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in a nonwoven or woven form. For example, a polyolefin-based polymer separator such as polyethylene or polypropylene is mainly used for a lithium ion battery, and a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and optionally, a single layer or a multilayer. Can be used as a structure.

The lithium metal battery of the above embodiment can be used not only in a unit cell used as a power source of a small device, but also can be used as a unit battery in a medium-large battery module including a plurality of battery cells. Furthermore, a battery pack including the battery module may be configured.

According to the embodiments of the present invention, it is possible to implement a lithium secondary battery that ensures stability while expressing high capacity and high output characteristics.

In Examples 1 and 2 and Comparative Examples 1 to 3, after performing two charge / discharge cycles under specific conditions, the amount of Co elution generated in each battery was measured and recorded.
In Examples 1 and 2 and Comparative Examples 1 to 3, after performing two charge / discharge cycles under specific conditions, the amount of gas generated in each battery was measured and recorded.
For Examples 1 and 2 and Comparative Examples 1 to 3, the electrochemical characteristics of the battery were evaluated and recorded.

Hereinafter, preferred examples of the present invention, comparative examples, and experimental examples for evaluating them are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

Example 1 (LCO core @ NCN 111 coating; active material surface modification method of the above embodiment)

(1) Preparation of Positive Electrode Active Material

1) Preparation of Core Particles

The dry mixture of Co ₃ O ₄ and Li ₂ CO ₃ was calcined for 8 hours at 1050 ° C. in a furnace to form Al-doped lithium cobalt oxide (LiCoO ₂ ) particles. In the dry mixture, the molar ratio of Li: Co in Co ₃ O ₄ and Li ₂ CO ₃ was set to 1: 1.

Subsequently, in order to form lithium cobalt oxide (LiCoO ₂ ) particles as a first region and to form a lithium deficient region on its outer surface, Co ₃ O ₄ and Li ₂ CO ₃ are further added to the furnace to dry. The mixture was calcined at 800 ° C. for 6 hours. In the materials added during the formation of the second region, the molar ratio of Li: Co in Co ₃ O ₄ and Li ₂ CO ₃ was set to 0.3: 1.

As a result, a core particle having a 20 nm thick second region (Li _0.3 CoO ₂ ) formed on the surface of the first region (LiCoO ₂ ) was obtained (D50 of all core particles: 18 μm).

2) Formation of Coating Layer

For the core particles, an NCM precursor and a Li raw material were mixed and calcined at 900 ° C. for 6 hours to obtain a cathode active material having a 30 nm thick NCM 111 coating layer formed on the surface of the core particles.

In consideration of the coating layer composition, (NiCoMn) OOH having a molar ratio of Ni: Co: Mn of 1: 1: 1 is used as the NCM precursor, and the Li raw material is Li ₂ CO ₃ , The stoichiometric molar ratio of the NCM precursor and the Li raw material was controlled so that the molar ratio was 1.02 (where the total moles of Me = Ni, Co, and Mn).

(2) fabrication of a lithium secondary battery

A positive electrode was prepared using the positive electrode active material of Example 1, a negative electrode was prepared separately, and assembled into a battery according to a method commonly known in the art.

1) Preparation of Anode

Specifically, the positive electrode active material of Example 1 was used, carbon black was used as the conductive material, and polyvinylidene fluoride (PVdF) was used as the binder, and these were weight ratios of 96: 2: 2. , Positive electrode active material: conductive material: binder), and a positive electrode slurry was prepared using N-methyl pyrrolidone (NMP) solvent.

On the surface of 20 μm thick aluminum foil, the prepared positive electrode slurry was applied at a loading amount of 15 g / cm ² , dried at 130 ° C. for 2 hours to prepare a positive electrode, and then roll-pressed to obtain a positive electrode.

2-1) Preparation of negative electrode (applied to CFC, Coin Full Cell)

Natural graphite is used as the negative electrode active material, carbon black is used as the conductive material, and styrene-butadiene rubber (SBR) is used as the binder, and these are weight ratios of 96: 2: 2 (the order of the negative electrode active material is : Conductive material: binder) to prepare a negative electrode slurry.

The prepared negative electrode slurry was applied to a copper foil, vacuum dried at 60 ° C. for 12 hours to prepare a negative electrode, and then roll press was performed.

2-2) Reference Electrode (applied to CHC, Coin Half Cell)

Li metal foil of 300 μm thickness was used as a reference electrode.

3-1) Assembly of Battery (CFC, Coin Full Cell)

The positive electrode and the negative electrode were used, and as a separator, a polyethylene separator (manufacturer: Celgard, thickness = 12 μm) was used, and an electrolyte (1 mol of lithium hexafluorophosphate (LiPF ₆ ) and ethylene carbonate (EC)) was used. / Dimethyl carbonate (DMC = 1/1 volume ratio) was injected to finally produce a lithium full battery in the form of a coin full cell.

3-2) Battery Assembly (CHC, Coin Half Cell)

A coin half cell type lithium interest battery was manufactured by the same method as 3-1), except that the prepared anode was used as a working electrode, and the 300 μm-thick lithium foil was used as a reference electrode. It was.

However, the descriptions omitted in the production of the positive electrode, the production of the negative electrode, and the assembly of the battery are in accordance with methods commonly known in the art.

Example 2 (LCO Core @ NCN 523 Coating; Active Material Surface Modification of One Embodiment)

(1) Preparation of Positive Electrode Active Material

Unlike Example 1, in consideration of the coating layer composition, (Ni _0.5 Co _0.2 Mn _0.3 ) OOH having a molar ratio of 5: 2: 3 of Ni: Co: Mn is used as the NCM precursor, and the Li raw material is Li ₂ CO ₃ was used to control the stoichiometric molar ratio of the NCM precursor and the Li raw material such that the molar ratio of Li / Me was 1.02 (where Me = Ni, Co, and Mn total moles). Except for this point, a positive electrode active material of Example 2 was prepared in the same manner as in Example 1.

(2) fabrication of a lithium secondary battery

Using the positive electrode active material of Example 2, a positive electrode was produced in the same manner as in Example 1 to fabricate a battery.

Comparative Example 1 (Bare)

(1) Selection of the positive electrode active material

Commercially available LCO (D50: 18 μm) was used as the positive electrode active material of Comparative Example 1.

(2) fabrication of a lithium secondary battery

Using the positive electrode active material of Comparative Example 1, a positive electrode was produced in the same manner as in Example 1 to prepare a battery.

Comparative Example 2 (LCO Core @ NCN 111 Coating; Precursor surface modification )

(1) Preparation of Positive Electrode Active Material

The nickel sulphate to a mole ratio of 1 (NiSO ₄₎ and cobalt sulfate (CoSO ₄₎ and manganese sulfate (MnSO ₄₎ are mixed a mixed aqueous solution 500ml: Co ₃ O ₄ particles, 50g of Ni: Co: Mn = 1: 1 Dispersed and co-precipitated Ni-Co-Mn based hydroxides to the Co ₃ O ₄ particles using sodium hydroxide. This dispersion system was filtered and washed at 120 ° C. A precursor sample was obtained in which a Ni-Co-Mn-based hydroxide was formed on the surfaces of Co ₃ O ₄ particles.

After adding 26.4 g of LiOH.H ₂ O to a molar ratio of total elements in the particles to a molar ratio of Li: M (Ni, Co, Mn) = 1: 1 to 50 g of the precursor, and mixing with a zirconia ball using a ball mill, The mixture was calcined at 1050 ° C. for 15 hours at high temperature in an air atmosphere to carry out to synthesize a core-shell structured active material.

(2) fabrication of a lithium secondary battery

Using the positive electrode active material of Comparative Example 2, a positive electrode was produced in the same manner as in Example 1 to prepare a battery.

Comparative Example 3 (LCO Core @ NCN 523 Coating; Precursor surface modification )

(1) Preparation of Positive Electrode Active Material

The third nickel sulfate so that the molar ratio of (NiSO ₄₎ and cobalt sulfate (CoSO ₄₎ and manganese sulfate (MnSO ₄₎ are mixed a mixed aqueous solution 500ml: Co ₃ O ₄ particles, 50g of Ni: Co: Mn = 5: 2 Dispersed and co-precipitated Ni-Co-Mn based hydroxides to the Co ₃ O ₄ particles using sodium hydroxide. This dispersion system was filtered and washed at 120 ° C. A precursor sample was obtained in which a Ni-Co-Mn-based hydroxide was formed on the surfaces of Co ₃ O ₄ particles.

After adding 26.4 g of LiOH.H ₂ O to a molar ratio of the total elements in the particles to a molar ratio of Li: M (Ni, Co, Mn) = 1: 1, the mixture was mixed with a zirconia ball by using a ball mill. The mixture was calcined at 1050 ° C. for 15 hours at high temperature in an air atmosphere to carry out to synthesize a core-shell structured active material.

(2) fabrication of a lithium secondary battery

Using the positive electrode active material of Comparative Example 3, a positive electrode was produced in the same manner as in Example 1 to prepare a battery.

Experimental Example 1: Evaluation of Co Elution and Gas Generation After High Temperature Storage

For Examples 1 and 2 and Comparative Examples 1 to 3, the high temperature storage characteristics were evaluated, respectively. There are two items for evaluating high temperature storage characteristics, Co leaching amount and gas generation amount, and the evaluation method of each item is as follows.

Co elution : measured as described above. Specifically, a positive electrode mixture loading amount of 80 mg / cm ² per area of one side of the electrode was prepared, and a positive electrode charged at 4.55 V was prepared, respectively, and 4 ml electrolyte [EC: DMC = 3: 7, VC 2 wt%] was added to the raw bottle. Put in. In order to prevent the electrolyte from evaporating, the raw Jen bottle was completely sealed with parafilm and aluminum pouch. This fully sealed bottle was stored for one week in a 60 ° C. chamber. After one week, the cathode active material, which may be present as a suspended solid in the electrolyte, was completely removed using a sealing paper filter to extract only the electrolyte solution. Thereafter, the electrolyte was evaporated to quantify the amount of Co that was present in the electrolyte through the ICP. As a result, Co was eluted by dividing Co, which was confirmed to be quantified, by the weight of the anode splitting material of the charged anode that was first put into the electrolyte.

The Co leaching amount evaluation results are shown in FIG. 1 and Table 1.

Gas generation amount : For each of the lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3, two charge / discharge cycles were carried out under a driving voltage range of 4.4 to 4.5 V and 0.2 C / 0.2 C. Thereafter, the amount of gas generated in each battery was measured.

The gas generation amount evaluation results are shown in FIG. 2 and Table 1. FIG.

Voltage 4.55 V Sample Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Co leaching amount (ppm / g) 2355 2555 3509 3043 2875 Gas generation amount (μl / g) 4358 5020 7512 6110 6672

Looking at Table 1, Figures 1 and 2, compared to Comparative Examples 1 to 3 it can be seen that the Co leaching amount and the gas generation amount of Examples 1 and 2 is significantly lower.

(1) Advantages of Examples 1 and 2 over Comparative Example 1

In particular, in contrast to Comparative Example 1 (Bare), the Co elution amount of Examples 1 and 2 is low, the effect of the NCM surface modification. As described above, the crystal structure of the NCM, even if the crystal structure is applied to a charging voltage exceeding 4.2V, 4.4V or more, and 4.45V or more, the stability of the structure can be maintained. In addition, the NCM is a material that can implement the capacity of the battery as the core itself.

Accordingly, even if a charging voltage of 4.2 V or more, 4.4 V or more, or even 4.45 V or more as in the above experimental example is applied, problems of internal metal (Co) elution and consequent gas generation can be prevented from occurring.

(2) Advantages of Examples 1 and 2 over Comparative Examples 2 and 3

In Comparative Examples 2 and 3, however, the surface was modified by NCM. However, the Co-eluted amount and the gas generation amount were higher than those of Examples 1 and 2 because the surface was modified using the "precursor surface modification method" described above.

In particular, the structure of the product actually obtained by the precursor surface modification method is different from the structure of the product actually obtained by the active material surface modification method of the above embodiment. More specifically, according to the precursor surface modification method, in the firing process, the lithium raw material is difficult to diffuse to the core inside the core material of the core-shell structure, and remains in the cobalt raw material state without being converted into lithium cobalt-based oxide. That part can happen.

On the other hand, according to the active material surface modification method of the embodiment, since the core particles, which have already been completely converted from the cobalt raw material to the lithium cobalt oxide, are dry mixed with lithium nickel cobalt manganese hydroxide particles and calcined, the core particles of the product Cobalt raw material may not be included at all. Here, since the cobalt raw material is a material that can not realize the capacity of the battery, if the cobalt raw material is inevitably mixed in the core particles (the two-step synthesis method, that is, Comparative Examples 2 and 3), the cobalt raw material is not in the core particles at all When not included (one step synthesis method of the embodiment, that is, Examples 1 and 2), it is demonstrated from the above experimental example that there is a disadvantage in implementing the battery capacity.

In terms of process efficiency, of course, there is an advantage of the active material surface modification of the embodiment.

(3) Comparing Example 1 and 2

On the other hand, compared with Example 1 and 2, compared with Example 1, it can be confirmed that the amount of Co elution and gas generated in Example 2 is low.

Although Examples 1 and 2 were prepared in the same manner, the difference in the mutual effects was due to the difference in the coating layer (ie, NCM) composition.

Specifically, the NCM 111 composition has a greater effect of suppressing Co dissolution and gas generation compared to the NCM523 composition, which is excellent in high voltage stability of the NCM 111 composition having an excessive Ni content compared to the NCM523 composition, It is because the effect which suppresses side reaction with electrolyte solution is larger.

Of course, of the above embodiment According to the active material surface modification method, both the surface modification of the NCM 111 composition and the surface modification of the NCM523 composition are excellent in suppressing side reactions with the electrolyte on the surface of the active material.

Experimental Example 2: Evaluation of Electrochemical Characteristics of Battery

For Examples 1 and 2 and Comparative Examples 1 to 3, the electrochemical properties of the battery were confirmed. Specifically, 50 cycles of each battery were performed, and the evaluation results were recorded in FIG. 3.

Charge: 0.5C, CC / CV, 4.55 V, 1 / 20C cut-off

Discharge: 1.0C, CC, 3.0 V, cut-off

Referring to Figure 3, compared to Comparative Examples 1 to 3, it can be seen that the capacity retention rate is significantly higher after 50 cycles of Examples 1 and 2. This may be associated with the Co leaching amount and the gas generation amount, which was confirmed in Experimental Example 1 above. Specifically, in comparison with Comparative Examples 1 to 3, the electrochemical characteristics of the Examples 1 and 2 batteries with low Co elution amount and gas generation amount may be improved.

That is, the first and second positive electrode active materials are surface-modified by structurally stable NCM, and co-dissolution and gas generation are suppressed even at a high voltage of 4.45 V or higher, thereby improving the electrochemical characteristics of the battery.

In particular, the electrochemical properties of the Examples 1 and 2 batteries are significantly improved compared to Comparative Example 1, because NCM itself contained in each of the cathode active materials of Examples 1 and 2 also contributes to improving the capacity of the batteries. .

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (14)

Dry mixing the core particles comprising lithium cobalt oxide, the nickel cobalt manganese hydroxide particles, and the lithium raw material; And
Firing the dry mixture to form a coating layer including lithium nickel cobalt manganese oxide on a surface of the core particle including the lithium cobalt oxide;
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 1,
In the mixing step;
Regarding the total amount of the mixture of the core particles including the lithium cobalt oxide and the nickel cobalt manganese hydroxide particles, the nickel cobalt manganese hydroxide particles are included in an amount of 500 to 50000 ppm,
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 1,
In the total amount of nickel cobalt manganese hydroxide 100 mol%, the nickel content is 30 to 50 mol%,
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 1,
In the coating step;
The firing temperature is 700 to 1100 ℃,
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 1,
In the coating step;
The firing time is 5 to 10 hours,
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 1,
Mixing; Before,
Producing the core particles; further comprising,
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 6,
D50 particle diameter of the core particles,
12 to 25 μm,
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 7, wherein
Mixing; Further comprising; preparing a core particle comprising the lithium cobalt-based oxide;
Preparing a core particle including the lithium cobalt oxide;
Heat treating a first mixture of a lithium raw material and a cobalt raw material in a molar ratio of 0.95: 1 to 1.05: 1 to form particles in which the lithium cobalt oxide crystal structure is a layered structure; And
And mixing the second mixture of the lithium raw material and the cobalt raw material in a molar ratio of 0.65: 1 to 0.85: 1 with heat treatment by mixing the lithium cobalt oxide crystal structure with particles having a layered structure. ,
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 8,
The core particle is,
A first region in which the lithium cobalt oxide crystal structure is a layered structure; And
From the interface with the first region to the surface of the core particle, the crystal structure of the lithium cobalt oxide is a spinel structure, or a second region in which a spinel structure and a layered structure are mixed. Containing;
The manufacturing method of the positive electrode active material for lithium secondary batteries.
The method of claim 9,
The first region is represented by the following formula (1),
Method for producing a positive electrode active material for a lithium secondary battery:
[Formula 1]
Li _a1 Co _(1-x1-y1-z1) M1 _x1 M2 _y1 M3 _z1 O ₂
In Chemical Formula 1,
M1, M2, and M3 are each independently one selected from the group containing Ti, Mg, Al, Zr, Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo,
a1, x1, y1, and z1 are values satisfying 0.95 ≦ a2 ≦ 1.05, 0 ≦ x2 ≦ 0.02, 0 ≦ y2 ≦ 0.02, and 0 ≦ z2 ≦ 0.02, respectively.
The method of claim 9,
The second region is represented by the following formula (2),
Method for producing a positive electrode active material for a lithium secondary battery:
[Formula 2]
Li _a1-m1 Co _(1-x1-y1-z1) M1 _x1 M2 _y1 M3 _z1 O ₂
In Chemical Formula 2,
M1, M2, and M3 are each independently one selected from the group containing Ti, Mg, Al, Zr, Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo,
a1, x1, y1, z1, and m1 are values satisfying 0.95 ≦ a1 ≦ 1.05, 0 ≦ x1 ≦ 0.02, 0 ≦ y1 ≦ 0.02, 0 ≦ z1 ≦ 0.02, and 0 <m1 <0.25, respectively.
A cathode active material for a lithium secondary battery prepared according to claim 1.
The method of claim 12,
The positive electrode active material,
When stored at a temperature in the range of 50 to 80 ° C. for 1 week, then discharged at a voltage of 4.4 V to 4.5 V,
Co leaching amount per 1 g of the positive electrode active material is 100 to 3000 ppm / g,
Cathode active material for lithium secondary battery.
A positive electrode comprising the positive electrode active material of claim 12;
Electrolyte; And
Including, the cathode;
Lithium secondary battery.

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