KR101469436B1 - Cathode Active Material and Lithium Secondary Battery For Controlling Impurity or Swelling Comprising the Same and Method For Manufacturing Cathode Active Material Of Improved Productivity - Google Patents

Abstract

The present invention relates to a metal cation represented by the following formula (1) and having a larger ionic radius than Ni cation so as to prevent mixing of Ni cation in the Li layer, in the void space in the Li cation spot or crystal lattice And a lithium secondary battery including the same, and a method for producing a positive electrode active material having improved productivity.
Li _a Ni _x Mn _y Co _z M _w O _{2 - te t} (1)
(Wherein a, x, y, w, M, A, z, t are as defined in the specification)

Description

TECHNICAL FIELD [0001] The present invention relates to a cathode active material, a lithium secondary battery for controlling impurities or swelling thereof, and a method for manufacturing a cathode active material having improved productivity. [0002] Productivity}

The present invention relates to a positive electrode active material represented by a specific chemical formula and containing a metal cation having an ionic radius larger than Ni cation in a void space in a Li cation spot or a crystal lattice to prevent Ni cation mixing in the Li layer and a lithium secondary And a method of manufacturing a positive electrode active material having improved battery and productivity.

As the technology development and demand for mobile devices have increased, the demand for secondary batteries has increased sharply as an energy source. Among such secondary batteries, lithium secondary batteries having high energy density and operating potential, long cycle life, Have been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of the lithium secondary battery. In addition, a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, (LiNiO ₂ ) is also being considered.

Of the above cathode active materials, LiCoO ₂ is most widely used because it has excellent lifetime characteristics and charge / discharge efficiency. However, since it has low safety at high temperature and cobalt used as a raw material is an expensive material due to its resource limit, Have.

Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have an advantage that they are excellent in thermal stability, inexpensive and easy to synthesize, but have a problem of low capacity, poor high temperature characteristics, and low conductivity.

The LiNiO ₂ cathode active material is relatively inexpensive and exhibits a high discharge capacity of the battery. However, the Ni cation has swelling due to cation mixing to replace a portion of the Li cation site, deterioration of high-rate discharge characteristics, A rapid phase transition of the crystal structure occurs depending on the volume change accompanied with the charge-discharge cycle, and the stability is drastically lowered when exposed to air and moisture.

In order to solve these problems, many studies and studies have been conducted to use lithium oxide mixed with 1: 1 or 1: 1: 1 of nickel-manganese and nickel-cobalt-manganese in the cathode active material.

The positive electrode active material prepared by mixing nickel, cobalt or manganese has an advantage in that the cycle characteristics and the capacity characteristics are superior to those of the batteries prepared using the respective transition metals separately. However, in this case, And problems such as swelling caused by generation of gas due to cationic mixing and deterioration of high-rate discharge characteristics are not sufficiently solved.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that when a predetermined alkaline earth metal is doped into a LiNiO ₂ based cathode active material having a specific composition, the incorporation of Ni cations into the Li layer is prevented, Respectively.

In addition, the inventors of the present application have confirmed that when the cathode active material is synthesized by adding a predetermined alkaline earth metal, the sintering temperature can be lowered. The present invention has been completed based on this.

Accordingly, the cathode active material according to the present invention is represented by the following Chemical Formula 1, and the metal cation represented by the following M, which has an ion radius larger than that of the Ni cation to prevent mixing of the Ni cation in the Li layer, And is included in an empty space.

Li _a Ni _x Mn _y Co _z M _w O _{2 - te t} (1)

In this formula,

0? X? 0.9, 0? Y? 0.9, 0? Z? 0.9, 0? W? 0.3, 2? A + x + y + z + w? 2.3, x> y, x> z, 0? t <0.2;

M is one or more metal cations of +2 oxidation;

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

Since the metal cation is mainly located in the Li cation site or the void space in the crystal lattice in the crystal structure of the cathode active material, the charge balance can be minimized so that the cation mixing in which the Ni cation is incorporated into the Li cation site can be minimized. At this time, the Ni cations are Ni ^{2 +} having an oxidation number of +2 valence.

The metal cations function as a kind of filler in the crystal lattice, thereby achieving structural stability of the cathode active material and minimizing the natural loss of Li cations. As a result, the lithium secondary battery including the positive electrode active material has an effect of minimizing swelling caused by impurities Li ₂ CO ₃ and LiOH generated due to the natural loss of Li cations, thereby improving safety.

The metal cation is a cation of an alkaline earth metal having an ionic radius larger than that of the Ni cation (Ni ^{2 +} ) and having an oxidation number of +2 valency. According to experiments conducted by the inventors of the present application, as the ion radius of the metal cation increases, It is more preferable that the metal cation is Sr ⁺² or Ba &lt; ^{2 + &} gt ;.

In the above formula (1), the oxygen ion may be substituted by an anion (A) having an oxidation number of -1 or a valence of 2 in a predetermined range. The A is preferably independently selected from the group consisting of F, Cl, Br and I Halogen, S, and N, which may be the same or different.

By substituting these anions, the binding force with the transition metal is improved and the structural transition of the compound is prevented, so that the lifetime of the battery can be improved. On the other hand, if the substitution amount of the anion A is too large (t? 0.2), the life characteristic is deteriorated due to the incomplete crystal structure, which is not preferable.

The positive electrode active material is not particularly limited as long as it is a material satisfying the above formula (1) and is included in the present invention. Preferably, y + z? 0.5, more preferably y + z? It is a cathode active material.

On the other hand, the cathode active material may further contain a Li-containing compound due to natural loss of Li cations or the like, and the Li-containing compound may be contained in an amount of less than 0.5% by weight based on the total weight of the cathode active material. Containing compound may be LiCO ₃ and / or LiOH.

The present invention also provides a positive electrode mixture for a secondary battery comprising the above-mentioned positive electrode active material, and a positive electrode for a secondary battery comprising the positive electrode mixture.

In addition to the positive electrode active material, the positive electrode mixture may optionally contain a conductive material, a binder, a filler, and the like.

The conductive material is usually added in an amount of 1 to 30% 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 whiskey 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 added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. 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, and various copolymers.

The filler is optionally used as a component for suppressing 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-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The positive electrode according to the present invention can be prepared by applying a slurry prepared by mixing a positive electrode mixture containing the above-described compounds to a solvent such as NMP, coating the positive electrode collector, followed by drying and rolling.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel 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 present invention also provides a lithium secondary battery comprising the positive electrode, the negative electrode, the separator, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode is prepared, for example, by coating a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the mixture. The negative electrode mixture may contain the above-described components as required.

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 < 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 and the like can be used.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, 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 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 lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

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.

Examples of the inorganic solid electrolyte include 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can 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 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

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), FPC (fluoro-propylene carbonate), and the like.

The secondary battery according to the present invention can be used not only in a battery cell used as a power source for a small device but also as a unit cell in a middle or large battery module including a plurality of battery cells.

Also, the present invention provides a battery pack including the battery module as a power source of a middle- or large-sized device, wherein the middle- or large-sized device is an electric vehicle (EV), a hybrid electric vehicle (HEV) An electric vehicle including a plug-in hybrid electric vehicle (PHEV), a power storage device, and the like, but the present invention is not limited thereto.

The present invention also provides a method for producing a cathode active material having improved productivity by lowering the synthesis temperature.

The cathode active material according to the above production method is prepared by adding a source of an alkaline earth metal having an oxidation number of +2 to a mixture obtained by mixing a transition metal source and a lithium source, and sintering the mixture in the air.

The inventors of the present application have confirmed that when the cathode active material is sintered by adding the alkaline earth metal, the sintering temperature is lowered. Therefore, the above-described method for producing a cathode active material exhibits an effect of improving the productivity by lowering the sintering temperature.

The transition metal source is not particularly limited, but when it is composed of two or more transition metals, it is preferably a transition metal hydroxide prepared by coprecipitation and represented by the following formula (2).

M (OH) ₂ (M = Ni _x Mn _y Co _z , x + y + z = 1 ) (2)

Further, the alkaline earth metal source may be SrCO ₃ Or BaCO ₃ may be, as the case may be a mixture thereof.

Since the positive electrode active material according to the present invention contains metal cations in the Li cation sites or hollow spaces in the crystal lattice in the crystal structure, the structural stability can be improved and the natural loss of Li cations can be minimized.

Therefore, the lithium secondary battery including the cathode active material has an effect of minimizing swelling caused by impurities Li ₂ CO ₃ and LiOH generated due to the natural loss of Li cations, thereby improving safety.

Further, in the method for producing a cathode active material according to the present invention, the synthesis temperature of the cathode active material can be lowered by adding an alkaline earth metal, so that the productivity is improved.

FIG. 1 is a graph showing XRD analysis results of specific examples of the present invention and comparative examples 1 and 2 sintered at 890 ° C., 900 ° C. and 910 ° C., respectively.

Hereinafter, the present invention will be described in further detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

&Lt; Example 1 >

As a transition metal precursor metal hydroxide _{M (OH) 2 (M =} Ni 0 .6 Mn 0 .2 Co 0 .2) (0.5 wt%) was prepared and, MgCO ₃ (0.5% by weight as the metal hydroxide and the doping metal source ), Li ₂ CO ₃ as a lithium source was mixed at a stoichiometric ratio, and the mixture was sintered in the air at a temperature of 890 to 930 ° C for 10 hours to prepare a Mg-doped cathode active material.

&Lt; Example 2 >

A Sr-doped cathode active material was prepared in the same manner as in Example 1 except that SrCO ₃ (0.5 wt%) was used as a doping metal source.

&Lt; Example 3 >

A Ba-doped cathode active material was prepared in the same manner as in Example 1 except that BaCO ₃ (0.5 wt%) was used as the doping metal source.

&Lt; Comparative Example 1 &

Transition metal hydroxide _{M (OH) 2 (M =} Ni 0 .6 Mn 0 .2 Co 0 .2) and 10 hours of mixing, and the mixture of Li ₂ CO ₃ in a stoichiometric ratio at a temperature of 910 in air ℃ To prepare a cathode active material.

&Lt; Comparative Example 2 &

A cathode active material was prepared in the same manner as in Comparative Example 1, except that the sintered body was sintered in a temperature range of 850 to 900 캜 for 10 hours.

<Experimental Example 1>

The amounts of impurities Li ₂ CO ₃ and LiOH were measured using the cathode active materials of Examples 1, 2 and 3 and Comparative Example 1, and the results are shown in Table 1 below. The amount of impurities was determined by titration with HCl.

<Table 1>

As can be seen from the above Table 1, the cathode active materials of Examples 1, 2 and 3 doped with Mg ^{2 +} , Sr ^{2 +} and Ba ^{2 +} were comparative examples in which no metal cation having +2 valence was added the amount of impurities Li ₂ CO _3, LiOH was reduced as compared to cathode active materials of FIG. That is, by doping Mg ²⁺ , Sr ²⁺ , and Ba ²⁺ , cation mixing of Ni ²⁺ is suppressed, minimizing the natural loss of Li ⁺ .

Further, when comparing Examples 1, 2 and 3, it can be seen that the Mg ^{+ 2,} the large ionic radius as compared with the case Sr doped ^2+, Ba ^{+ 2} is the amount of impurities reduced further when doped. Ion radius is greater Sr ^2+, Ba ²⁺ is predicted to be due to block the path taken by Ni ²⁺ mainly located in the empty space in the crystal lattice than the Li cation place more efficiently than Mg ^{+ 2.}

<Experimental Example 2>

X-ray diffraction analysis was performed using the cathode active material of Example 2 and the cathode active materials of Comparative Examples 1 and 2 sintered at 890 ° C, 900 ° C and 910 ° C, respectively. The results are shown in Table 2 and FIG. 1 .

<Table 2>

As can be seen from the above Table 2, the (003) / (014) value of the cathode active material of Example 2 sintered at 910 ° C is larger than that of the cathode active material of Comparative Example 1, (003) / (014) value is smaller than that of the cathode active material of Comparative Example 1. [

This is a second embodiment the positive electrode active material is a cathode active material of the comparative example relative to the positive electrode active material of the 1-ordered (ordering) it means jyeoteum is made stronger, and Comparative Example 2 sintered at 910 ℃ has α-NaFeO ₂ type (space group R3m) But it means that ordering is not done.

On the other hand, the (003) / (014) value of the cathode active material of Example 2 sintered at 890 캜 is similar to that of the cathode active material of Comparative Example 1.

It can be seen from the above results that the sintering is performed at a lower temperature than that of Comparative Example 1 in Example 2 in which Sr is added and sintered.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (16)

Characterized in that a metal cation represented by the following formula (M) having an ionic radius larger than that of the Ni cation is contained in the Li cation spot or the void space in the crystal lattice, which is represented by the following formula (1) and prevents the mixing of the Ni cation in the Li layer Cathode active material.
Li _a Ni _x Mn _y Co _z M _w O _{2 - te t} (1)
In this formula,
0? X? 0.9, 0? Y? 0.9, 0? Z? 0.9, 0? W? 0.3, 2? A + x + y + z + w? 2.3, x> y, x> z, 0? t <0.2;
M is one or more metal cations of +2 oxidation;
A is one or more of an anion of -1 or -2. The positive electrode active material according to claim 1, wherein y + z? 0.4 in the formula (1) is satisfied. The positive electrode active material according to claim 1, wherein M is Sr ⁺² . 2. The method of claim 1, wherein M is a positive electrode active material, characterized in that Ba ^{+ 2.} The positive electrode active material according to claim 1, wherein the Ni cation is Ni ^{2 +} . The positive electrode active material according to claim 1, wherein the positive electrode active material further comprises a Li-containing compound, and the Li-containing compound is contained in an amount of less than 0.5% by weight based on the total weight of the positive electrode active material. The cathode active material according to claim 6, wherein the Li-containing compound is LiCO ₃ or LiOH, or LiCO ₃ and LiOH. A positive electrode material mixture for a secondary battery, comprising the positive electrode active material according to any one of claims 1 to 7. A positive electrode for a secondary battery according to claim 8, wherein the positive electrode mixture for a secondary battery is applied on the current collector. A lithium secondary battery comprising a positive electrode for a secondary battery according to claim 9. A battery module comprising the lithium secondary battery according to claim 10 as a unit cell. A battery pack comprising the battery module according to claim 11. A device according to claim 12, wherein the battery pack is used as a power source. delete delete delete

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