KR101406673B1 - Positive electrode active material for lithium ion secondary battery and lithium ion secondary battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium ion secondary battery which contains lithium metal oxide and a cerium compound, and is represented by chemical formula 1: (1-x)LiaNibMncCodO2-xCe2O3. (In the chemical formula described above, 0.001<x<0.01, 1<a<2, 0<b+c+d<1, and a+b+c+d=2, and a=(c-b)/2+1).

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery comprising the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a positive active material for a lithium ion secondary battery,

The present invention relates to a cathode active material for a lithium ion secondary battery and a lithium ion secondary battery containing the same, and more particularly, to a lithium ion secondary battery comprising a lithium metal oxide and a cerium compound as a cathode active material capable of inserting and desorbing lithium ions, And a lithium ion secondary battery comprising the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a positive active material for a lithium ion secondary battery.

Lithium ion secondary batteries are increasingly used in IT applications and are increasingly used in electric vehicles and the need for high-capacity materials is emerging. In the case where the capacity of the anode material and the anode material is increased at the same weight, continuous research is being conducted so that the capacity can be expressed in a small amount. In particular, a lithium ion secondary battery is used while lithium ions are transferred from an anode to a cathode when charged and from a cathode to an anode when discharged. Therefore, the relationship between the amount of lithium and the capacity of the lithium ion secondary battery is very close.

The conventional electrode material contains one equivalent of Li such as LiMn ₂ O ₄ , LiNi _x Co _y Mn _z O ₂ (x + y + z = 1), and LiCoO _{2. In} recent years, The Li ₂ MnO ₃ Research on materials is underway. However, when Li ₂ MnO ₃ alone is used, it is considered that Mn ^{4 +} is very stable and high voltage is required for oxidation-reduction reaction, and it is not suitable for battery material because Li ion is not inserted smoothly. Further, Li ₂ MnO ₃ It is difficult to use the battery as an actual battery because O ₂ is generated in use to increase the pressure inside the battery.

In order to solve the above problems, an object of the present invention is to provide a positive active material containing lithium in an excess amount which can insert and desorb lithium ions, effectively removing oxygen generated by the lithium metal oxide and the cerium compound, And to provide a positive electrode active material for a lithium ion secondary battery having improved safety.

Another object of the present invention is to provide a lithium ion secondary battery using the above-mentioned cathode active material.

The present invention relates to a cathode active material for a lithium ion secondary battery, which comprises lithium metal oxide and a cerium compound and is represented by the following chemical formula (1).

(1-x) Li _a Ni _b Mn _c Co _d O ₂ -xCe ₂ O ₃ (1)

A + b + c + d = 2 where a = (c-b) / 2 + 1 where 0 <

The present invention also provides a lithium ion secondary battery comprising a cathode including the cathode active material, an electrolyte, and a cathode.

According to the present invention, it is possible to manufacture a lithium ion secondary battery having improved stability and improved capacity by suppressing generation of oxygen in a battery by containing a cerium compound in a positive electrode active material containing lithium in an excessive amount.

1 schematically shows a pouch type lithium ion secondary battery according to an embodiment of the present invention.

The present invention relates to a cathode active material for a lithium ion secondary battery, which comprises a lithium metal oxide and a cerium compound and is represented by the following chemical formula (1).

(1-x) Li _a Ni _b Mn _c Co _d O ₂ -xCe ₂ O ₃ (1)

A + b + c + d = 2 where a = (c-b) / 2 + 1 where 0 <

The lithium metal oxide of the positive electrode active material represented by the above formula (1) contains an excess amount of lithium, and in particular, Mn is bound 1: 1 around Ni to form LiNixCoyMnzO ₂ (x + y + z = 1) After the excess Mn is combined with excess Li to form Li ₂ MnO ₃ , Li is dissolved in the transition metal layer in addition to the lithium layer. That is, the positive electrode active material represented by the above formula (1) is composed of LiMO ₂ , Li ₂ MnO ₃ And Ce ₂ O ₃ .

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. The Li ₂ MnO ₃ When an applied voltage of 4.5 V or more is applied to an inactive region having Mn ^{4 +} at 4.5 V or less, an electrochemical reaction occurs. In this case, MnO ₂ is converted into an active material.

Therefore, a low voltage (4.5V or less) in the LiMO _2, the high-voltage using a capacitor in the Li ₂ MnO _3, wherein Li ₂ MnO ₃ is contributing to the structural stability of the battery and the high voltage can be expressed by a high capacity serves to provide a Li have.

Charged when the Li ₂ MnO ₃ is 2Li + In + 1 / 2O ₂ + As digested with MnO ₂ the O ₂ is generated and there is increasing the battery's internal pressure, since the positive electrode active material of the present invention contains a cerium compound Li ₂ MnO ₃ Li + The oxygen at the time of desorption is combined with the cerium compound having excellent chemical activation, so that oxygen is not contained in the cell as a gas, so that the stability of the cell can be ensured.

The content of the cerium compound is preferably 0.005 mol to 0.01 mol of the entire positive electrode active material. When the content is less than 0.005 mol, the oxygen generation inhibiting effect may not be exhibited, and when it exceeds 0.01 mol, the capacity of the battery may be decreased.

The cathode active material of the present invention can be prepared by mixing a lithium compound, a transition metal precursor, and a cerium precursor, followed by heat treatment at a temperature of 700 ° C to 900 ° C.

As the lithium compound, at least one selected from the group consisting of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate may be used, and the transition metal precursor may be a compound containing nickel, manganese, and cobalt. The cerium precursor may be at least one selected from the group consisting of Ce ₂ (CO ₃ ) ₃ , CeCl ₄ , Ce (OH) ₄ , Ce (NO ₃ ) ₃ and hydrates thereof.

The present invention provides a lithium ion secondary battery comprising a cathode, an electrolyte and a cathode including the cathode active material of the present invention.

As the shape of the lithium ion secondary battery according to the present invention, those used in lithium ion secondary batteries such as pouch type, coin type, button type, sheet type, cylindrical type, flat type and square type can be used.

The lithium ion secondary battery of the present invention can be manufactured by a conventional method known in the art including a positive electrode prepared using the positive electrode 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.

The positive electrode may be formed by mixing and dispersing a positive electrode active material, a conductive material and a binder in a solvent, applying a slurry on the positive electrode collector, and drying the slurry.

The cathode current collector functions to collect electrons generated by the electrochemical reaction of the cathode active material or to supply electrons necessary for the electrochemical reaction and has conductivity. As the positive electrode collector, aluminum, stainless steel, nickel, titanium, sintered carbon, or the like can be used.

In the present invention, fine unevenness may be formed on the surface of the positive electrode collector to enhance the bonding force of the positive electrode active material layer, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, .

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 commonly used in lithium ion 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. Examples of the conductive material include artificial graphite, natural graphite, acetylene black, denka 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.

In the lithium ion secondary battery of the present invention, those commonly used in the related 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 have. As the negative electrode current collector, stainless steel, nickel, copper, titanium, an alloy thereof, or the like can be used.

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 source of lithium ions and can be used as a lithium ion secondary battery electrolyte.

The lithium ion secondary battery according to the present invention may further include a separator between the positive electrode and the negative electrode to prevent a short circuit between the two electrodes. As the separation membrane, conventionally used materials 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 with reference to Examples, but the present invention is not limited by these Examples.

Example

Example 1

Li ₂ CO ₃ 31g and _{Ni 0 .2 Co 0 .2 Mn 0} .6 (OH) 2 51g, Ce (NO 3) 3 · 6 hours at 850 ℃ in a nitrogen atmosphere and then uniformly mixing the H ₂ O 1.5g The cathode active material was synthesized by heat treatment.

Example 2

Li ₂ CO ₃ 31g and _{Ni 0 .2 Co 0 .2 Mn 0} .6 (OH) 2 51g, Ce (NO 3) 3 · 6 hours at 850 ℃ in a nitrogen atmosphere and then uniformly mixing the H ₂ O 3.0g The cathode active material was synthesized by heat treatment.

Example 3

Li ₂ CO ₃ 31g and _{Ni 0 .2 Co 0 .2 Mn 0} .6 (OH) 2 51g, Ce (NO 3) 3 · 6 hours at 850 ℃ in a nitrogen atmosphere and then uniformly mixing the H ₂ O 0.3g The cathode active material was synthesized by heat treatment.

Example 4

Li ₂ CO ₃ 31g and _{Ni 0 .2 Co 0 .2 Mn 0} .6 (OH) 2 20g, Ce (NO 3) 3 · 6 hours at 850 ℃ in a nitrogen atmosphere and then uniformly mixing the H ₂ O 152g heat treatment To synthesize a cathode active material.

Example 5

Li ₂ CO ₃ 31g and _{Ni 0 .2 Co 0 .2 Mn 0} .6 (OH) 2 20g, Ce (CO 3) 3 3.2g uniformly mixed and then the positive electrode to 6 hours heat treatment at 850 ℃ active material in a nitrogen atmosphere Were synthesized.

Example 6

The Li ₂ CO ₃ 31g and _{Ni 0 .2 Co 0 .2 Mn 0} .6 (OH) 2 20g, Ce (OH) 4 1.5g of a uniformly mixed and then the positive electrode to 6 hours heat treatment at 850 ℃ active material in a nitrogen atmosphere Were synthesized.

Example 7

Li ₂ CO _{3 .2} 31g and _{Ni 0 Co 0 .2 Mn 0 .6} (OH) 2 20g, CeCl 4 After uniformly mixing the positive electrode active material was synthesized from 2.0g to 6 hours heat treatment at 850 ℃ in a nitrogen atmosphere.

Comparative Example 1

The cathode active material was synthesized in the same manner as in Example 1, except that Ce (NO ₃ ) ₃ .H ₂ O was not mixed.

The powder synthesized in the above example was measured by XRD and the peak of Ce ₂ O ₃ was confirmed to confirm that the cerium compound was synthesized.

The cathode active material obtained in the above Examples and Comparative Examples was mixed with a Denka Black and a PVDF binder as a conductive material in a ratio of 94: 3: 3 and coated on an Al foil to prepare an electrode plate. 100 mm * 100 mm pouch cells were fabricated by using lithium metal as a cathode and 1.3 M LiPF ₆ EC / EMC / DMC = 5: 3: 2 electrolyte as an electrolyte and then subjected to 50 charge / The battery capacity was measured. The results are shown in Table 1.

- Capacity measurement

The capacity per g obtained by discharging at 2 V to 4.7 V at 0.1 C is measured.

Measurement of cell swelling after 50 charge / discharge cycles

After 50 cycles of charging and discharging at 2V to 4.7V voltage range at 1C, measure the thickness of the thickest part of the cell to measure the difference in thickness before and after charging and discharging.

Content of cerium compounds
(mol) Change in cell thickness
(mm) Battery capacity
(mAh / g) Example 1 0.005 mol 2.2 245 Example 2 0.01 mol 1.4 230 Example 3 0.001 mol 2.7 251 Example 4 0.5 mol 1.0 206 Example 5 0.01 mol 1.7 234 Example 6 0.01 mol 1.8 232 Example 7 0.01 mol 1.7 229 Comparative Example 1 - 5.4 243

As shown in Table 1, the battery including the cathode active material of the present invention has a high capacity, and since the change in the thickness of the battery is small, the stability of the battery is improved because oxygen is less generated. Therefore, by using the positive electrode active material of the present invention, a lithium ion secondary battery of high capacity can be manufactured with improved stability.

Claims (5)

A lithium metal oxide, and a cerium compound, and is represented by the following chemical formula (1).
(1-x) Li _a Ni _b Mn _c Co _d O ₂ -xCe ₂ O ₃ (1)
B + c + d < 1, a + b + c + d = 2 where a = (cb) / 2 + 1 ) The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the content of the cerium compound is 0.005 mol to 0.01 mol based on the total amount of the positive electrode active material. The cathode active material for a lithium ion secondary battery according to claim 1, wherein the cathode active material is obtained by mixing lithium compound, transition metal precursor and cerium precursor, followed by heat treatment at a temperature of 700 to 900 ° C. The lithium _secondary battery according to claim 3, wherein the cerium precursor is at least one selected from the group consisting of Ce ₂ (CO ₃ ) ₃ , CeCl ₄ , Ce (OH) _4, Ce (NO ₃ ) ₃ and hydrates thereof. Cathode active material for ion secondary battery. A lithium ion 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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