KR101478880B1 - Positive electrode for lithium ion secondary battery and lithium ion secondary battery including the same - Google Patents

Abstract

The present invention relates to a cathode active material comprising lithium and having primary particles grained to form secondary particles, the cathode active material having an average primary particle size of 0.1 to 1.5 占 퐉, an average secondary particle size of 1 to 10 占 퐉, 1 to 6 m < ² > / g, for the positive electrode active material for a lithium secondary battery.

Description

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

The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same. More particularly, the present invention relates to a lithium secondary battery, A cathode active material, a method for producing the same, and a lithium secondary battery comprising the same.

Lithium secondary batteries have been increasingly used in small electronic devices for electric vehicles and electric power storage, and there is a growing demand for cathode materials for secondary batteries having high safety, long life, high energy density and high output characteristics.

The lithium secondary battery generally comprises a positive electrode and a negative electrode capable of inserting and separating lithium ions, a separator for preventing physical contact between the positive and negative electrodes, and an electrolyte for transferring lithium ions. The lithium secondary battery generates electrical energy by electrochemical oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.

The performance of the lithium secondary battery is largely determined by the cathode active material. LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1 -x- y} Co _x Mn _y O ₂ (0 <x + y <1), and LiMnO 2 _2, and so on.

Recently, many studies have been made to improve the capacity characteristics, energy density, output characteristics, lifetime characteristics, and the like of the cathode active material for a lithium secondary battery.

It is an object of the present invention to provide a positive electrode active material for a lithium secondary battery which can improve life characteristics and high-rate characteristics of a lithium secondary battery.

The present invention also provides a method for producing the cathode active material and a lithium secondary battery comprising the cathode active material.

In order to solve the above problems, the present invention provides a cathode active material comprising lithium and having primary particles aggregated to form secondary particles, the cathode active material having an average primary particle size of 0.1 to 1.5 占 퐉, And a specific surface area of 1 to 6 m &lt; ² &gt; / g. The present invention also provides a positive electrode active material for a lithium secondary battery.

The present invention also provides a method for preparing a lithium-containing compound, comprising: mixing a lithium-containing compound and a transition metal compound to obtain a mixture; Pre-heat-treating the mixture; And firing the preliminarily heat-treated mixture to produce a cathode active material for a lithium secondary battery according to the present invention.

The present invention provides a lithium secondary battery comprising a positive electrode containing the positive electrode active material, an electrolyte and a negative electrode.

By using the positive electrode active material of the present invention, deterioration in lifetime characteristics due to side reactions with the electrolyte can be reduced, and output characteristics of a battery having a reduced capacity at a high rate can be improved.

Also, according to the method for producing a cathode active material of the present invention, the particle size and specific surface area of the cathode active material can be controlled within a certain range, thereby improving the specific capacity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows particles of a cathode active material obtained in an embodiment of the present invention. FIG.
2 is a SEM photograph showing the primary particles obtained in the example of the present invention.
3 is a SEM photograph of the cathode active material according to the present invention.
4 is a graph showing the high-rate characteristics measured in the embodiment of the present invention.
5 is a graph showing life characteristics measured in an embodiment of the present invention.
6 is a cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. In the following detailed description, embodiments of the invention are presented and described for purposes of illustration. It will be appreciated by those skilled in the art that the present invention may be illustrated in various forms and that the embodiments described below can not be construed as limiting the present invention.

The present invention relates to a cathode active material comprising lithium and having primary particles grained to form secondary particles, the cathode active material having an average primary particle size of 0.1 to 1.5 占 퐉, an average secondary particle size of 1 to 10 占 퐉, 1 to 6 m &lt; ² &gt; / g, for the positive electrode active material for a lithium secondary battery.

The lithium-containing positive electrode active material may be represented by formula (1) as a positive electrode active material containing lithium in an excessive amount.

Li _{1 + x} M _{1 - x} O ₂ (1)

Wherein M is at least one selected from the group consisting of Co, Ni, Mn, Zr, Cr, V, Ti, Fe and Cu.

The cathode active material represented by the formula (1) is preferably a cathode active material represented by the formula (2).

Li [Li _y (Ni _a Co _b Mn _c ) _z ] O ₂ (2)

(0 <a <1, 0 <b <1, 0 <c <1, 0 <y <1, 0 <z <1, y + z = 1 in the above formula).

The lithium metal oxide represented by the above formula (2) is excessively liable to form LiNi _a Co _b Mn _c O ₂ (LiMO ₂ ) phase and Li ₂ MnO ₃ Lt; / RTI &gt; The LiMO ₂ phase is an active region in which two MO ₂ layers are present in one crystal structure and lithium ions are present between the MO ₂ layers and reversible charge and discharge proceed. Li ₂ MnO ₃ When an applied voltage of 4.4 V or higher is applied to an inactive region having Mn ^{4 +} at 4.4 V or less, an electrochemical reaction takes place. In this case, MnO ₂ is converted into an active material.

The positive electrode active material of the present invention has a primary particle size of 0.1 to 1.5 占 퐉, an average secondary particle size of 1 to 10 占 퐉, a specific surface area of 1 to 10 占 퐉, 6 m ² / g.

The lithium secondary battery to which the cathode active material is applied is less likely to experience deterioration in lifetime characteristics due to side reactions with the electrolyte and the output characteristics of the battery having a reduced capacity at a high rate can be improved. If the particle size and the specific surface area of the positive electrode active material exceed the above range, the reactivity deteriorates and the capacity rapidly decreases at a high rate. If the particle size and the specific surface area of the positive electrode active material are less than the above range, the side reaction with the electrolyte increases, .

In the present invention, the measurement of the particle size can be performed using a laser light scattering method. The particle size can be measured by converting the wavelength value of scattered light by transmitting light to each particle. The specific surface area can be measured by the BET method. The N ₂ monolayer can be adsorbed on the surface of the powder, and the mass value of the adsorbed gas can be measured in terms of area.

The positive electrode active material preferably has a press density of 2.3 to 2.7 g / cc. The press density within the above range can improve the battery capacity per unit volume.

The present invention provides a method for preparing a lithium-containing compound, comprising: mixing a lithium-containing compound and a transition metal compound to obtain a mixture; Pre-heat-treating the mixture; And firing the preliminarily heat-treated mixture to produce a cathode active material for a lithium secondary battery.

In the mixing step, the chemical equivalent ratio of lithium to the transition metal is preferably 1.3 to 1.7: 1. By mixing the lithium-containing compound and the transition metal compound in such a range as described above, a lithium-excessive amount of the cathode active material can be produced to improve battery capacity and battery life.

The preheating step may be performed at 200 to 600 ° C for 1 to 15 hours, preferably 300 to 500 ° C for 3 to 10 hours. The firing step may be performed at 700 to 1000 ° C for 5 to 30 hours, preferably at 800 to 950 ° C for 5 to 24 hours. The cathode active material having the particle size and specific surface area of the present invention can be produced through the preliminary heat treatment and the firing step in the temperature and time range of the above range. By applying the preliminary heat treatment step and the baking step, it is possible to reduce the primary and secondary particle sizes, thereby increasing the specific surface area.

In the method for producing a cathode active material of the present invention, after the firing step, the cathode active material may be further ground and / or the powder phase may be controlled to control the particle size or to remove impurities.

The present invention provides a lithium secondary battery comprising a positive electrode comprising the positive electrode active material, a negative electrode and an electrolyte.

The lithium secondary battery of the present invention can be produced by a conventional method known in the art including a cathode prepared using the cathode active material of the present invention. For example, a porous separator may be placed between an anode and a cathode, and an electrolyte may be added.

6 is a partial cross-sectional view of a lithium secondary battery according to an embodiment of the present invention. The method of manufacturing a secondary battery described below is intended to facilitate understanding of the present invention and may be appropriately modified and used by using the technical contents known in the art.

Referring to FIG. 6, a lithium secondary battery includes a can 10, an electrode assembly 20, a cap assembly 30, and an electrolyte. The lithium secondary battery is formed by housing the electrode assembly 20 and the electrolyte inside the can 10 and the cap assembly 30 sealing the upper end of the can 10.

The electrode assembly 20 includes a positive electrode plate 21, a negative electrode plate 23, and a separator 22. The electrode assembly 20 may be formed by winding a positive electrode plate 21, a separation membrane 22, a negative electrode plate 23, and a separation membrane 22 in this order.

The cap assembly 30 may include a cap plate 40, an insulation plate 50, a terminal plate 60, and an electrode terminal 80. The cap assembly 30 is coupled with the insulating case 70 to seal the can 10.

The electrode terminal 80 is inserted into a terminal through-hole 41 formed at the center of the cap plate 40. When the electrode terminal 80 is inserted into the terminal through-hole 41, a tubular gasket 46 is coupled to the outer surface of the electrode terminal 80 and inserted together. Therefore, the electrode terminal 80 is electrically insulated from the cap plate 40.

The electrolyte is injected into the can 10 through the electrolyte injection hole 42 after the cap assembly 30 is assembled to the upper end of the can 10. The electrolyte injection hole 42 is sealed by a separate plug 43. The electrode terminal 80 is connected to the negative electrode tab 17 of the negative electrode plate 23 or the positive electrode tab 16 of the positive electrode plate 21 to function as a negative electrode terminal or a negative electrode terminal.

The electrode used in the lithium secondary battery is usually prepared by coating a slurry obtained by mixing and dispersing an active material, a binder and a conductive material in a solvent, and then drying and pressing the electrode collector.

In the lithium secondary battery of the present invention, those commonly used in the art such as natural graphite, artificial graphite, carbon fiber, coke, carbon black, carbon nanotube, fullerene, activated carbon, lithium metal or lithium alloy can be used as the negative electrode active material .

The current collector of the lithium secondary battery functions to collect electrons by an electrochemical reaction of the active material or to supply electrons necessary for an electrochemical reaction. The anode current collector may be aluminum or an aluminum alloy, and the anode current collector may be stainless steel, nickel, copper, titanium, or an alloy thereof.

The binder serves to bind the active material and the conductive material to bind to the current collector. The binder may be a binder such as polyvinylidene fluoride, polypropylene, carboxymethyl cellulose, starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, Those conventionally used in lithium secondary batteries such as polyethylene, ethylene-propylene-diene polymer (EPDM), polyvinyl alcohol, styrene-butadiene rubber and fluorine rubber can be used.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include synthetic graphite, natural graphite, denka black, acetylene black, ketjen black, channel black, lamp black, Conductive fibers such as metal fibers, conductive metal oxides such as titanium oxide, and metal powders such as aluminum and nickel.

The electrolyte may be an organic electrolyte in which a lithium salt is dissolved in a non-aqueous organic solvent. Non-aqueous organic solvents serve as mediators through which ions involved in the electrochemical reactions of the cell can migrate. Examples of the non-aqueous organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, and acetonitrile. These solvents may be used alone or in combination. The lithium salt acts as a supply source of lithium ions and may be one commonly used for a lithium secondary battery electrolyte. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) _{2, LiN (CF 3 SO 2} ) 2, CF 3 SO 3 Li and the like, and _{LiC (CF 3 SO 2) 3} , may be used either alone or in combination thereof.

The lithium secondary battery according to the present invention may further include a separator disposed between the anode and the cathode to prevent a short circuit between the two electrodes. As the separation membrane, those conventionally used such as a polymer membrane such as polyolefin, polypropylene, and polyethylene, a microporous film, a woven fabric and a nonwoven fabric may be used.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited by these examples.

Example

[Examples 1 to 5]

NiSO ₄ : CoSO ₄ : MnSO ₄ = 2: 2: 6 molar ratio, 0.1 ~ 2M ammonia solution was added, NaOH solution was mixed and Ni _{0 .2} Co _{0 .2} Mn _{0 .6} (OH) ₂ to prepare a transition metal compound. Li ₂ CO ₃ and _{Ni 0 .2 Co 0 .2 Mn 0} .6 (OH) 2 the other transition metal and the chemical equivalent ratio of 1.4 Li: After uniformly mixed to 1 400 ℃ ~ 500 ℃ for 6 hours pre-heat treatment And then calcined at 800 ° C to 900 ° C for 10 hours to obtain a layered Li [Li _{0 .17} (Ni _{0 .17} Co _{0 .17} Mn _{0 .5} ) _0.83 ] O ₂ cathode active material was synthesized.

Denka Black and a PVDF binder were mixed at a ratio of 94: 3: 3 and coated on Al foil to prepare an electrode. A coin cell was fabricated using lithium metal as the cathode and 1.3M LiPF ₆ EC / DMC / EC = 5: 3: 2 solution as the electrolyte.

 [Examples 6 to 10]

Except that the preliminary heat treatment in Example 1 was carried out at 400 ° C to 500 ° C for 20 hours and then calcined at 800 ° C to 950 ° C for 24 hours to prepare a cathode active material having a particle size and specific surface area shown in the following Table 1 , The same experiment was carried out.

 [Examples 11 to 15]

Except that the preliminary heat treatment was carried out at 400 ° C to 500 ° C for 10 hours and then calcined at 900 ° C to 1000 ° C for 30 hours to prepare a cathode active material having particle sizes and specific surface areas shown in Table 1 below , The same experiment was carried out.

 [Comparative Examples 1 to 6]

The same experiment was carried out except that the cathode active material having the particle size and specific surface area shown in Table 1 was produced by firing at 950 ° C to 1000 ° C for 30 hours without performing the preliminary heat treatment step in Example 1.

The high-rate characteristics and the life characteristics of the coin cells prepared in the above-described Examples and Comparative Examples were measured. The results are shown in Table 1.

[Method for measuring high rate property]

To confirm the rapid charge / discharge characteristics, capacity was measured at 0.2C, 0.33C, 1C, 2C, 3C charge / discharge conditions.

[Method for measuring lifetime characteristics]

The life span was measured by checking the capacity after 50 charge / discharge cycles of the coin cell and confirming the capacity of the initial capacity and the last cycle.

The average secondary particle Size (D ₅₀ ) Average first
Particle Size Specific surface area High rate characteristic Life characteristics μm μm m ² / g % % Example 1 3.27 0.2 4.87 85 92 Example 2 3.27 0.8 4.23 83 90 Example 3 3.27 One 4.04 82 91 Example 4 3.27 1.3 3.85 81 89 Example 5 3.27 1.5 3.54 81 89 Example 6 3.89 0.4 4.69 80 88 Example 7 5.7 0.4 3.89 78 88 Example 8 7.84 0.4 3.22 77 89 Example 9 9.45 0.4 3.14 77 86 Example 10 10 0.4 2.32 77 87 Example 11 5.19 0.5 2.82 77 91 Example 12 5.19 0.5 3.95 76 88 Example 13 5.19 0.5 4.15 75 87 Example 14 5.19 0.5 5.77 74 86 Example 15 5.19 0.5 6 72 84 Comparative Example 1 14.76 1.3 0.92 70 81 Comparative Example 2 5.45 0.05 8 79 64 Comparative Example 3 6 3 5 69 79 Comparative Example 4 8.45 0.9 0.8 70 78 Comparative Example 5 8.95 1.35 7.15 72 76 Comparative Example 6 0.8 0.05 9.4 79 52

Claims (10)

A positive electrode active material comprising lithium and having primary particles aggregated to form secondary particles, the positive electrode active material having an average primary particle size of 0.1 to 1.5 占 퐉, an average secondary particle size of 3.27 to 10 占 퐉, a specific surface area of 2.32 to 4.87 m &lt; ² &gt; / g of the positive electrode active material for a lithium secondary battery. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material is represented by Formula (1).
Li _{1 + x} M _{1 - x} O ₂ (1)
Wherein M is at least one selected from the group consisting of Co, Ni, Mn, Zr, Cr, V, Ti, Fe and Cu. The positive electrode active material for a lithium secondary battery according to claim 2, wherein the positive electrode active material represented by the formula (1) is a positive electrode active material represented by the formula (2).
Li [Li _y (Ni _a Co _b Mn _c ) _z ] O ₂ (2)
(0 <a <1, 0 <b <1, 0 <c <1, 0 <y <1, 0 <z <1, y + z = 1 in the above formula). The positive electrode active material for a lithium secondary battery according to claim 1, wherein the press density is 2.3 to 2.7 g / cc. A method for producing a cathode active material according to any one of claims 1 to 4,
Mixing a lithium-containing compound and a transition metal compound to obtain a mixture;
Pre-heat-treating the mixture; And
The method of manufacturing a cathode active material for a lithium secondary battery according to any one of claims 1 to 4, comprising firing the preheated mixture. 6. The method of claim 5, wherein in the mixing step, the lithium-containing compound and the transition metal compound are mixed such that the chemical equivalent ratio of lithium to the transition metal is 1.3 to 1.7: 1. The method of claim 5, wherein the preliminary heat treatment is performed at 200 to 600 ° C for 1 to 15 hours. 6. The method of claim 5, wherein the calcining step is performed at 700 to 1000 DEG C for 5 to 30 hours. 6. The method of claim 5, further comprising a grinding and powdering step after the firing step. A lithium secondary battery comprising a positive electrode, an electrolyte, and a negative electrode comprising the positive electrode active material of any one of claims 1 to 4.

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