KR20130117717A - Cathode active material of high voltage and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: A positive active material maximizes the lifetime performance of a secondary battery and the energy performance of a secondary battery by setting the ratio of elements forming a lithium nickel manganese complex oxide within a specific range. CONSTITUTION: A positive active material includes a lithium nickel manganese complex oxide represented by chemical formula 1: Li_xNi_yMn_(2-y)O_(4-z). In chemical formula 1, 0.9<=x<=1.2, 0.1<=y<0.4, and -0.1<=z<=0.1. A positive electrode for a secondary battery includes the positive active material. The secondary battery includes the positive electrode. The secondary battery is a lithium secondary battery. The battery module includes the secondary battery as a unit battery. A battery pack includes the battery module. A device includes the battery pack.

Description

High voltage positive electrode active material and lithium secondary battery comprising same {Cathode Active Material of High Voltage and Lithium Secondary Battery Comprising the Same}

The present invention relates to a high voltage positive electrode active material, and more particularly, to a positive electrode active material including a lithium nickel manganese complex oxide (LNMO) having a specific range of element ratios.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on a current collector. The positive electrode active material is mainly composed of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide and the like, and the negative electrode active material is mainly composed of a carbon-based material.

However, in a lithium secondary battery using a carbon-based material as a negative electrode active material, irreversible capacity occurs in some lithium ions inserted into the layered structure of the carbon-based material during initial charge and discharge, resulting in a decrease in discharge capacity. Also, the carbon material has a low oxidation / reduction potential of about 0.1 V relative to the potential of Li / Li +, which causes decomposition of the nonaqueous electrolyte on the surface of the negative electrode. The carbon material reacts with lithium to form a passivating layer or a solid electrolyte interface (SEI film) is formed. Such SEI membranes have different thickness and interface states depending on the electrolyte system used, and thus affect the charge and discharge characteristics. Moreover, in a secondary battery such as a power tool, which is used in a field where high output characteristics are required, even with such a thin SEI film, the resistance can be increased to become a rate determining step (RDS). In addition, since the lithium compound is generated on the surface of the negative electrode, the reversible capacity of lithium gradually decreases as the charge and discharge are repeated, thereby causing a problem that the discharge capacity decreases and cycle degradation occurs.

On the other hand, lithium titanium oxide (LTO) has been studied as a structurally stable anode material having good cycle characteristics. Lithium secondary batteries including LTO as a negative electrode active material have a relatively high oxidation / reduction potential of about 1.5V relative to the potential of Li / Li +, and thus do not cause electrolyte decomposition. Do.

LiCoO ₂ was mainly used as a positive electrode active material, but currently, other layered positive electrode active materials include Ni-based (Li (Ni-Co-Al) O ₂ ) and Ni-Co-Mn-based (Li (Ni-Co-Mn) O ₂ ) and the like highly stable spinel type Mn (LiMn ₂ O ₄ ) and the like are used. Especially, although spinel type manganese batteries were once applied to mobile phones, they have not been able to take advantage of the advantages of low price because of the aging of energy density in the face of the high-priority mobile phone market. Accordingly, a lot of research has been conducted on a method of increasing the energy density of the spinel-type manganese-based cathode active material.

On the other hand, several methods are considered as a method of increasing the energy density of a lithium secondary battery, but among them, increasing the operating potential of the battery is an effective method. Lithium secondary batteries using LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ as conventional cathode active materials have an operating potential of 4 V class and an average operating potential of 3.6 to 3.8 V. This is because the potential is determined by oxidation and reduction of Co ion, Ni ion or Mn ion. On the other hand, when a compound having a spinel structure in which a part of Mn of LiMn ₂ O ₄ is substituted with Ni or the like is used as the positive electrode active material, it is possible to obtain a lithium secondary battery having a 5V class operating potential. Therefore, lithium nickel manganese composite oxide (LNMO) has recently been considered as a corresponding cathode material of LTO anode material.

However, lithium nickel manganese composite oxide shows different performance according to the ratio of each element, and the total energy and lifetime stability are affected by the ratio of nickel to manganese, so the ratio of nickel to appropriate manganese is important.

Therefore, there is a very high need for a technology that can fundamentally solve this demand.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application can achieve a desired effect when manufacturing a lithium nickel manganese composite oxide by setting the ratio of each element to a specific range, as will be described later. It was confirmed that the present invention was completed.

Accordingly, the present invention provides a cathode active material including a lithium nickel manganese composite oxide represented by Formula 1 as a high voltage cathode active material.

Li _x Ni _y Mn _2-y O _4-z (1)

Wherein 0.9 ≦ x ≦ 1.2, 0.1 ≦ y <0.4, and −0.1 ≦ z ≦ 0.1.

The lithium nickel manganese composite oxide (LNMO) is a composite oxide of a spinel structure having a relatively high potential due to the high potential of LTO, and has a high voltage of 4.7V when compared with a conventional anode having a voltage characteristic of 3.5 to 4.3V. It is a substance with properties. In this high voltage spinel type cathode active material, Mn is present in a Mn ⁴⁺ state, and an operating voltage is determined by a Ni ²⁺ / Ni ⁴⁺ redox reaction instead of a redox reaction of Mn ³⁺ / Mn ⁴⁺ .

That is, Ni ²⁺ substitution not only reduces the capacity reduction factor due to Mn ³⁺ ions, but also enables insertion and desorption of lithium ions stabilized to Ni ²⁺ / Ni ⁴⁺ by redox reaction at 4.7V voltage range. do.

Lithium nickel manganese composite oxide shows different performance according to the ratio of each element. For example, when the ratio of nickel to manganese decreases, the potential flat plane appears at about 4.0 V as Mn participates in the reaction, reducing the overall energy. On the other hand, lifespan stability is increased, and vice versa, total energy is increased but lifespan stability is low. In view of this point, the lithium nickel manganese composite oxide of the present invention represented by Chemical Formula 1 satisfies an optimal range of content of the ratio of nickel to the amount of manganese.

In one specific example, the nickel content y may be in the range of 0.2 ≦ y <0.4, specifically, in the range of 0.3 ≦ y <0.4, and more specifically in the range of 0.35 <y <0.4. Can be.

At this time, the range of the content x of lithium may be 0.97 <x <1.0.

The present invention also provides a cathode for a secondary battery comprising the cathode active material.

The anode is prepared by applying a mixture of a cathode active material, a conductive material and a binder on a cathode current collector, followed by drying and pressing. If necessary, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention also provides a secondary battery including the positive electrode, and in detail, a lithium secondary battery having a structure in which a lithium salt-containing electrolyte is impregnated in an electrode assembly having a structure in which a separator is interposed between the positive electrode and the negative electrode.

The negative electrode is manufactured by coating, drying, and pressing a negative electrode active material on a negative electrode current collector, and optionally, the conductive material, binder, filler, etc. may be further included as necessary.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide and the like can be used.

In one specific example, in response to the positive electrode active material including the lithium nickel manganese composite oxide, the negative electrode active material may be a lithium metal oxide represented by the following Chemical Formula 2.

Li _a M ' _b O _4-c A _c (2)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;

c is determined according to the oxidation number in the range of 0? c <0.2;

A is one or more of an anion of -1 or -2.

In detail, the lithium metal oxide of Chemical Formula 2 may be lithium titanium oxide (LTO) represented by Chemical Formula 3, specifically, Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, etc., but if the lithium ions can be occluded / released there is no restriction in the composition and type, and more specifically, the crystal structure of the charge and discharge It may be Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ of the spinel structure with little change and excellent reversibility.

Li _a Ti _b O ₄ (3)

In the above formula, 0.5? A? 3, 1? B? 2.5.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one specific example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) _2, and the like, may be prepared by cyclic carbonate of EC or PC, which is a highly dielectric solvent, and DEC, DMC, or EMC, which are low viscosity solvents. Lithium salt-containing non-aqueous electrolyte can be prepared by adding to a mixed solvent of linear carbonate.

The present invention also provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module.

The battery pack may be used as a power source for devices requiring high temperature stability, long cycle characteristics, high rate characteristics, and the like.

Specific examples of the device include a power tool moving by being driven by an electric motor; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

The positive electrode active material according to the present invention has an effect of maximizing life performance and energy performance by setting the ratio of each element constituting the lithium nickel manganese composite oxide to a specific range.

Hereinafter, although described in more detail with reference to embodiments according to the present invention, the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Preparation of cathode active material

Metal Oxyhydroxide MOOH (M = Ni _0.38 Mn _1.62 ) (0.5% by weight) was prepared as a transition metal precursor, dry mixed Li ₂ CO ₃ as a lithium source, and the mixture was heated at 800 ° C. to air. By sintering for 10 hours at a temperature range of 1,000 ℃, a positive electrode active material of Li _0.98 Ni _0.38 Mn _1.62 O _3.9 was prepared.

Manufacture of batteries

A cathode mixture was prepared by mixing the cathode active material (Li _0.98 Ni _0.38 Mn _1.62 O _3.9 ), the conductive material (Denka black), and the binder (PVdF) in NMP at a weight ratio of 90: 5: 5 to mix. The positive electrode mixture was coated on a 200 μm thick aluminum foil having a thickness of 200 μm, followed by rolling and drying.

Lithium metal was used as a negative electrode, and the positive electrode was punched into a coin shape, and a coin-type battery was manufactured using a carbonate electrolyte in which 1 mol of LiPF ₆ was dissolved as the negative electrode and electrolyte.

<Example 2>

In Example 1, except that a positive electrode active material of Li _0.98 Ni _0.36 Mn _1.64 O _3.9 was prepared using a metal oxyhydroxide MOOH (M = Ni _0.36 Mn _1.64 ) (0.5 wt%) as the transition metal precursor. A positive electrode active material and a battery were prepared in the same manner as in Example 1.

<Example 3>

In Example 1, except that a positive electrode active material of Li _0.98 Ni _0.2 Mn _1.8 O _3.9 was prepared using a metal oxyhydroxide MOOH (M = Ni _0.2 Mn _1.8 ) (0.5 wt%) as the transition metal precursor. A positive electrode active material and a battery were prepared in the same manner as in Example 1.

&Lt; Comparative Example 1 &

Prepare a metal oxyhydroxide MOOH (M = Ni _0.5 Mn _1.5 ) (0.5 wt%) as the transition metal precursor, dry mix Li ₂ CO ₃ as a lithium source, and mix the mixture in air at a temperature of 800 ° C. to 1,000 ° C. By sintering for 10 hours in the range, a positive electrode active material of LiNi _0.5 Mn _1.5 O ₄ was prepared, and a battery was prepared in the same manner as in Example 1.

Comparative Example 2

In Comparative Example 1, a cathode active material and a battery were manufactured in the same manner as in Comparative Example 1, except that a cathode active material of LiMn ₂ O ₄ was prepared using metal oxyhydroxide MnOOH (0.5 wt%) as the transition metal precursor. It was.

<Experimental Example 1>

Charge and discharge of the secondary batteries according to Examples 1 to 3 and Comparative Example 1 at 3.5 V ~ 4.9 V section, the secondary battery according to Comparative Example 2 at 1 C in 3.0 V ~ 4.2 V section capacity and its efficiency Was measured and the capacity retention rate was measured while repeating charging and discharging 100 times under the same conditions, and the results are shown in Table 1 below.

1 ^st discharge Cycle characteristics 1C capacity (mAh) Capacity efficiency
(%) At 100 cycles
Capacity retention rate (%) Example 1 130.8 93.7 90 Example 2 129.5 93.9 88 Example 3 110 94.5 92 Comparative Example 1 139 92.4 70 Comparative Example 2 104 98 98

Referring to Table 1, the battery according to Comparative Example 1 has a high capacity, but the cycle characteristics are not very good as the content of Ni increases, and the battery according to Comparative Example 2 does not contain Ni, and thus the cycle characteristics are good. This is very low. On the other hand, the battery according to Examples 1 to 3 has a somewhat lower capacity than the battery according to Comparative Example 1, but the cycle characteristics are superior, and the cycle characteristics are slightly lower than the battery according to Comparative Example 2, but the capacity is high, either characteristic It can be seen that the capacity and cycle characteristics are both excellent without this remarkable drop.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (12)

A high voltage positive electrode active material, the positive electrode active material comprising a lithium nickel manganese composite oxide represented by the following formula (1).
Li _x Ni _y Mn _2-y O _4-z (1)
Wherein 0.9 ≦ x ≦ 1.2, 0.1 ≦ y <0.4, and −0.1 ≦ z ≦ 0.1. The cathode active material according to claim 1, wherein the content y of nickel is in a range of 0.2 ≦ y <0.4. The cathode active material according to claim 1, wherein the content y of nickel is in a range of 0.3 ≦ y <0.4. The cathode active material according to claim 1, wherein the content y of nickel is in a range of 0.35 <y <0.4. The cathode active material according to claim 1, wherein the content x of lithium is in the range of 0.97 <x <1.0. A secondary battery positive electrode comprising the positive electrode active material according to claim 1. A secondary battery comprising the positive electrode according to claim 6. The secondary battery according to claim 7, wherein the secondary battery is a lithium secondary battery. A battery module comprising the secondary battery according to claim 8 as a unit cell. A battery pack comprising the battery module according to claim 9. A device comprising a battery pack according to claim 10. The device of claim 11, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.