KR20230086235A - Positive electrode active material, method for manufacturing the same, positive electrode and secondary battery comprising the same - Google Patents

Abstract

The present invention is a lithium cobalt-based oxide; and a metal element M ¹ doped into or coated on the surface of the lithium cobalt-based oxide, wherein the metal element M ¹ includes yttrium (Y), and the metal element M ¹ is the positive active material It provides a positive electrode active material contained in 500ppm to 900ppm.

Description

Cathode active material, manufacturing method thereof, cathode and secondary battery including the same

The present invention relates to a cathode active material, a manufacturing method thereof, and a cathode and a secondary battery including the same.

Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight and relatively high-capacity secondary batteries is rapidly increasing. In particular, lithium secondary batteries are in the limelight as a driving power source for portable electronic devices because they are lightweight and have high energy density. Small-sized lithium secondary batteries used in such portable electronic devices are required to have excellent battery performance under conditions of high energy density, high temperature, and high voltage. Accordingly, research and development efforts to improve the performance of lithium secondary batteries are being actively conducted.

In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. In addition, an active material layer including a positive electrode active material or a negative electrode active material may be formed on the current collector for the positive electrode and the negative electrode. In general, a lithium transition metal oxide is used as a cathode active material in the cathode, and accordingly, a carbon-based active material or a silicon-based active material that does not contain lithium is used as an anode active material in the anode.

In particular, among lithium transition metal oxides used as cathode active materials, lithium cobalt-based oxide is in the spotlight due to its high operating voltage and excellent capacity characteristics. There is a problem with the cancellation. In addition, as the oxidation value of Co is oxidized to ⁴⁺ during charging, there is a problem of surface stability deterioration and lifespan deterioration due to a side reaction with the electrolyte.

On the other hand, the demand for high-capacity lithium secondary batteries is gradually increasing. In the case of lithium cobalt-based oxide, unlike ternary cathode active materials, the capacity can be increased only by raising the voltage, so the voltage of 4.5V is higher than the existing 4.45V or less. It is necessary to secure structural stability even at or above V, and at the same time, it is necessary to develop a lithium cobalt-based oxide capable of improving surface stability by preventing side reactions with the electrolyte and improving lifetime characteristics and high temperature / high voltage stability.

Chinese Patent Publication No. 103500827

One object of the present invention is to provide a cathode active material having low resistance and high lifetime characteristics at high voltage and high temperature.

In addition, another object of the present invention is to provide a method for producing the above-described cathode active material.

In addition, another object of the present invention is to provide a positive electrode including the positive electrode active material described above.

In addition, another object of the present invention is to provide a secondary battery including the positive electrode described above.

The present invention is a lithium cobalt-based oxide; and a metal element M ¹ doped into or coated on the surface of the lithium cobalt-based oxide, wherein the metal element M ¹ includes yttrium (Y), and the metal element M ¹ is the positive active material It provides a positive electrode active material contained in 500ppm to 900ppm.

In addition, the present invention comprises the steps of mixing a lithium raw material and a cobalt precursor and performing a primary heat treatment to form a lithium cobalt-based oxide; and mixing the lithium cobalt-based oxide and the precursor including the metal element M ¹ and performing secondary heat treatment to form a lithium cobalt-based oxide doped or coated with the metal element M ¹ therein. A method for manufacturing a positive electrode active material is provided.

In addition, the present invention is a positive electrode current collector; and a cathode active material layer disposed on at least one surface of the cathode current collector, wherein the cathode active material layer provides a cathode including the cathode active material described above.

In addition, the present invention is the anode described above; a cathode facing the anode; a separator interposed between the anode and the cathode; And an electrolyte; it provides a secondary battery comprising a.

The cathode active material of the present invention is characterized in that it includes a lithium cobalt-based oxide doped or coated with a metal element M ¹ including yttrium (Y) in a specific amount. Since the metal element M ¹ may stabilize the surface structure of the lithium cobalt-based oxide, low resistance may be achieved even under high voltage and high temperature conditions, and excellent life characteristics may be exhibited.

Therefore, the positive electrode and the secondary battery including the positive electrode active material exhibit excellent life characteristics and improved output characteristics even under high temperature and high voltage conditions.

1 is a graph showing changes in capacity retention rates according to cycle charging and discharging in Example 1 and Comparative Examples 1 to 4.

The terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, number, step, component, or combination thereof, but one or more other features or It should be understood that the presence or addition of numbers, steps, components, or combinations thereof is not precluded.

In the present specification, the average particle diameter (D ₅₀ ) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle diameter distribution curve of the particles. The average particle diameter (D ₅₀ ) may be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle diameters of several millimeters in the submicron region, and can obtain results with high reproducibility and high resolution.

Hereinafter, the present invention will be specifically described.

<Cathode active material>

The present invention relates to a cathode active material, specifically a cathode active material for a lithium secondary battery.

The cathode active material of the present invention is a lithium cobalt-based oxide; and a metal element M ¹ doped into or coated on the surface of the lithium cobalt-based oxide, wherein the metal element M ¹ includes yttrium (Y), and the metal element M ¹ is the positive active material It is characterized in that contained in 500ppm to 900ppm in.

In general, when lithium cobalt-based oxide is used at a high voltage, a large amount of lithium ions are released from the lithium cobalt-based oxide, resulting in a loss of crystal structure, which causes the unstable crystal structure to collapse, resulting in a decrease in reversibility. In addition, when Co ³⁺ or Co ⁴⁺ ions present on the surface of the lithium cobalt-based oxide are reduced by the electrolyte solution in a state in which lithium ions are released, oxygen is desorbed from the crystal structure and the above-described structural collapse can be further promoted. .

In order to solve this problem, the cathode active material of the present invention is characterized by including a lithium cobalt-based oxide doped or coated with a metal element M ¹ including yttrium (Y) in a specific amount. The metal element M ¹ stabilizes the surface structure of the lithium cobalt-based oxide and protects the surface of the active material to reduce side reactions, thereby preventing structural collapse of the lithium cobalt-based oxide and reducing the resistance of the positive electrode active material even under high voltage and high temperature conditions. , can contribute to improving life characteristics.

The cathode active material of the present invention is a lithium cobalt-based oxide; and a metal element M ¹ doped into or coated on the surface of the lithium cobalt-based oxide.

The cathode active material includes lithium cobalt-based oxide. The lithium cobalt-based oxide exhibits stability in a higher voltage range, for example, a charging voltage of 4.4V or higher, compared to other cathode active materials such as lithium-nickel-cobalt-manganese oxide, but there is still a risk of deterioration in structural stability when used at high voltage. . However, structural stability and durability of the cathode active material according to the present invention may be improved as yttrium (Y) described later is doped or coated on the surface thereof.

The lithium cobalt-based oxide may include a compound represented by the chemical formula LiCoO ₂ .

The metal element M ¹ includes yttrium (Y). The yttrium (Y) may be doped or coated on the lithium cobalt-based oxide to stabilize the surface structure of the lithium cobalt-based oxide and reduce side reactions by protecting the surface of the active material. In particular, when yttrium (Y) is doped into a lithium cobalt-based oxide, it exhibits excellent structural stability even under a high voltage condition, for example, 4.5 V or higher, is advantageous in reducing resistance, and may have high lifespan characteristics.

The metal element M ¹ is included in the cathode active material in an amount of 500 ppm to 900 ppm. If the metal element M ¹ is included in the cathode active material in an amount of less than 500 ppm, the aforementioned effects of improving resistance, preventing structural collapse of lithium cobalt-based oxide, and stabilizing the surface structure cannot be obtained. If the metal element M ¹ is included in the positive electrode active material in an amount exceeding 900 ppm, the metal element M ¹ acts as a resistance and hinders the intercalation and deintercalation of lithium ions, so output characteristics and lifespan characteristics may deteriorate.

Specifically, the metal element M ¹ may be included in the positive electrode active material in an amount of 600 ppm to 800 ppm, and more specifically, 650 ppm to 750 ppm, and when the amount is within the above range, the above-described structural stability improvement and surface structure stabilization effect of the lithium cobalt-based oxide are preferably achieved. In particular, life characteristics under high voltage and high temperature conditions can be remarkably improved.

The cathode active material may further include an additional metal element. Specifically, the cathode active material is a metal doped into or coated on the surface of the lithium cobalt-based oxide in terms of improving structural stability of the active material, suppressing phase transition, and improving conductivity and rate characteristics. Element M ² may be further included.

The metal element M ² may include at least one selected from the group consisting of aluminum (Al), titanium (Ti), and magnesium (Mg), and may specifically improve the structural stability of the active material and cause phase transition In terms of suppressing and further improving conductivity and rate characteristics, aluminum (Al), titanium (Ti), and magnesium (Mg) may be included.

Specifically, the aluminum (Al) may improve the structural stability of the active material and contribute to improving high-temperature lifespan characteristics. When the magnesium (Mg) is doped inside or on the surface of the active material, it has an effect of improving structural stability of the active material through a wide band gap and facilitating lithium movement and electron movement on the surface of the active material. The titanium (Ti) can contribute to controlling the particle size of the active material, and can further contribute to improving structural stability and rate characteristics of the active material when used together with magnesium.

The metal element M ² may be included in the cathode active material in an amount of 10,500 ppm or less, specifically 1,500 ppm to 10,500 ppm, and more specifically, 4,400 ppm to 9,000 ppm. More specifically, the metal element M ² may include aluminum (Al), titanium (Ti), and magnesium (Mg), and the amount of aluminum (Al) in the cathode active material is 500 ppm to 8,000 ppm, specifically 3,000 ppm to 3,000 ppm. 6,500 ppm, the titanium (Ti) is included in the positive electrode active material at 500 ppm to 1,000 ppm, specifically 600 ppm to 800 ppm, and the magnesium (Mg) is included at 500 ppm to 1,500 ppm, specifically 800 ppm to 1,200 ppm in the positive electrode active material may be included in ppm. When the metal element M ² is included in the cathode active material within the above range, structural stability, conductivity, and rate characteristics of the above-described active material may be improved, and thus lifespan characteristics may be further improved.

The content of the metal elements M ¹ and/or M ² included in the cathode active material may be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES).

In the cathode active material, the molar ratio of lithium and metal elements other than lithium included in the cathode active material may be 0.95:1 to 1.05:1, specifically 0.98:1 to 1.03:1.

Specifically, the cathode active material may include a compound represented by Chemical Formula 1 below.

[Formula 1]

Li _a Co _(1-xy) M ¹ _x M ² _y O ₂

In Formula 1, M ¹ is yttrium (Y), M ² is at least one selected from the group consisting of aluminum (Al), titanium (Ti), and magnesium (Mg), 0.95 ≤ a ≤ 1.05, and 0.004 ≤ x ≤ 0.012, and 0 ≤ y ≤ 0.05.

In Formula 1, a may be 0.95 to 1.05, specifically 0.98:1 to 1.03:1.

In Formula 1, x may be 0.004 to 0.012, specifically 0.006 to 0.010, and more specifically 0.007 to 0.009, and when it is in the above range, the above-described structural stability improvement and surface structure stabilization effect of the lithium cobalt-based oxide are preferably implemented. In particular, life characteristics under high voltage and high temperature conditions can be remarkably improved.

In Formula 1, y may be 0 to 0.05, specifically 0.01 to 0.04, and more specifically 0.015 to 0.035.

Implementation of the compound represented by Chemical Formula 1 may be implemented by adjusting the content of the metal element M ¹ or M ² doped or coated on the lithium cobalt-based oxide.

The positive electrode active material according to the present invention may have an average particle diameter (D ₅₀ ) of 3 μm to 30 μm, preferably 10 μm to 20 μm. When the average particle diameter (D ₅₀ ) of the positive electrode active material satisfies the above range, an appropriate ratio Surface area and anode density can be realized.

<Method of manufacturing cathode active material>

In addition, the present invention provides a method for manufacturing a cathode active material. More specifically, the manufacturing method of the cathode active material may be the manufacturing method of the cathode active material described above.

The manufacturing method of the cathode active material includes forming a lithium cobalt-based oxide by mixing a lithium source material and a cobalt precursor and performing a primary heat treatment; and forming a lithium cobalt-based oxide doped with the metal element M ¹ by mixing the lithium cobalt-based oxide and a precursor including the metal element M ¹ and performing secondary heat treatment. The cathode active material prepared by the above manufacturing method may include 500 ppm to 900 ppm of the metal element M ¹ .

In the manufacturing method of the cathode active material, a metal element M ¹ may be doped or coated on the lithium cobalt-based oxide by heat-treating the lithium cobalt-based oxide and the metal element M ¹ . In particular, when doping or coating the lithium cobalt-based oxide with the metal element M ¹ in an appropriate amount, the structural stability of the lithium cobalt-based oxide can be improved, in particular, the surface structure can be stabilized, and the structure of the lithium cobalt-based oxide can be collapsed under high voltage conditions. It is possible to implement a cathode active material with improved low resistance characteristics and lifespan characteristics.

Hereinafter, a method for manufacturing a cathode active material according to the present invention will be described in detail.

First, a lithium source material and a cobalt precursor are mixed and subjected to primary heat treatment to form a lithium cobalt-based oxide.

The lithium raw material may be a lithium-containing oxide, hydroxide, oxyhydroxide, halogenated salt, nitrate, carbonate, acetate, oxalate, citrate, or sulfate. More specifically, the lithium source material is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH H ₂ O, LiH, LiF, LiCl, LiBr, LiI, Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi, Or Li ₃ C ₆ H ₆ O ₇ and the like, any one or a mixture of two or more of them may be used.

The cobalt precursor may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate or sulfate containing cobalt, and more specifically, Co(OH) ₂ , Co ₃ O ₄ , CoOOH, Co(OCOCH ₃ ) ₂ 4H ₂ O, Co(NO ₃ ) ₂ 6H ₂ O or Co(SO ₄ ) ₂ 7H ₂ O, and the like, any one or a mixture of two or more of these may be used. there is.

The lithium source material and the cobalt precursor may include lithium included in the lithium source material; And it may be mixed so that the atomic ratio of cobalt and the metal element M ¹ included in the cobalt precursor is 0.95:1 to 1.05:1, specifically 0.98:1 to 1.03:1. If the above-mentioned metal element M ² is further included in the cathode active material, lithium included in the lithium source material; And cobalt contained in the cobalt precursor, the metal element M ¹ and metal element M ² ; may be mixed so that the atomic ratio is 0.95:1 to 1.05:1, specifically 0.98:1 to 1.03:1.

The first heat treatment may be performed at 950 °C to 1,200 °C, specifically 1,000 °C to 1,100 °C. When the primary heat treatment is performed in the above temperature range, it is possible to minimize the residual of unreacted raw materials and the generation of side reactants, to realize an active material having a desirable size, discharge capacity, cycle characteristics, and operating voltage. It is preferable from the viewpoint of preventing deterioration or the like.

The primary heat treatment may be performed for 7 hours to 15 hours, specifically 9 hours to 11 hours, and when the above range is satisfied, a diffusion reaction between raw materials may be sufficiently performed.

The first heat treatment may be performed in an air atmosphere or an oxygen atmosphere.

Next, the lithium cobalt-based oxide and the precursor including the metal element M ¹ are mixed and subjected to secondary heat treatment to form a lithium cobalt-based oxide doped or coated with the metal element M ¹ .

Through the second heat treatment process, the metal element M ¹ is doped or coated on the lithium cobalt-based oxide. As described above, yttrium (Y) included in the metal element M ¹ may be concentrated and doped or coated on the surface of the lithium cobalt-based oxide by a secondary heat treatment process, thereby stabilizing the surface structure of the lithium cobalt-based oxide. can contribute favorably to improvement.

The secondary heat treatment may be performed at 800 °C to 900 °C. When the secondary heat treatment is performed in the above temperature range, it is preferable in that a metal element can be sufficiently diffused into the active material and a desired size and structure of the active material can be realized.

The secondary heat treatment may be performed for 3 hours to 8 hours, specifically 4 hours to 6 hours.

The secondary heat treatment may be performed in an air atmosphere or an oxygen atmosphere.

According to the manufacturing method of the cathode active material, the metal element M ¹ may be included in the cathode active material in an amount of 500 ppm to 900 ppm, specifically 600 ppm to 800 ppm, and more specifically 650 ppm to 750 ppm. When within the above range, the above-described structural stability improvement and surface structure stabilization effect of the lithium cobalt-based oxide are preferably implemented, and in particular, life characteristics under high voltage and high temperature conditions can be remarkably improved.

According to the manufacturing method of the cathode active material, the cathode active material may further include a metal element M ² doped in a lithium cobalt-based oxide. The metal element M ² may include at least one selected from aluminum (Al), titanium (Ti), and magnesium (Mg), and specifically include aluminum (Al), titanium (Ti), and magnesium (Mg). can

The additional doping or coating of the metal element M ² is (1) implemented by using a cobalt precursor doped with the metal element M ² as the cobalt precursor in the mixing step of the lithium raw material and the cobalt precursor, or (2) When mixing the lithium cobalt-based oxide and the precursor including the metal element M ¹ , it may be implemented by further mixing the precursor including the metal element M ² . Alternatively, the additional doping or coating of the metal element M ² may be implemented by performing both methods (1) and (2).

The precursor containing the metal element M ² contains the metal element M ² containing oxides, hydroxides, oxyhydroxides, halides, nitrates, carbonates, acetates, oxalates, citrates or sulfates.

When additionally doping with the metal element M ² , the type and amount of the metal element M ² may be adjusted in consideration of the type and amount of the metal element M ² included in the cathode active material.

<Anode>

In addition, the present invention provides a positive electrode including the positive electrode active material described above.

Specifically, the positive electrode is a positive electrode current collector; and a cathode active material layer disposed on at least one surface of the cathode current collector, wherein the cathode active material layer includes the cathode active material described above.

The positive current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. Specifically, the cathode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy, and may specifically include aluminum.

The cathode current collector may typically have a thickness of 3 to 500 μm.

The positive electrode current collector may form fine irregularities on the surface to enhance bonding strength of the negative electrode active material. For example, the cathode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or non-woven fabric.

The positive electrode active material layer may be disposed on at least one surface of the positive electrode current collector, and may be specifically disposed on one surface or both surfaces of the positive electrode current collector.

The positive electrode active material layer includes the positive electrode active material described above.

The positive electrode active material may be included in an amount of 80% to 99% by weight, preferably 90% to 98% by weight in the positive electrode active material layer in consideration of exhibiting sufficient capacity of the positive electrode active material.

The positive electrode active material layer may further include a positive electrode binder and a positive electrode conductive material together with the positive electrode active material.

The positive electrode binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, specifically polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose The group consisting of rose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber and fluororubber It may include at least one selected from, preferably polyvinylidene fluoride.

The positive electrode binder is 0.1% to 10% by weight, preferably 0.1% to 3% by weight, more specifically 0.5% to 2.5% by weight in the positive electrode active material layer in order to sufficiently secure binding force between components such as the positive electrode active material. can be included

The positive electrode conductive material may be used to assist and improve the conductivity of a secondary battery, and is not particularly limited as long as it has conductivity without causing chemical change. Specifically, the conductive material is graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, farnes black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon nanotubes such as single-walled carbon nanotubes and multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; And it may include at least one selected from the group consisting of polyphenylene derivatives, and specifically, carbon black may be included in terms of improving conductivity.

The positive electrode conductive material may be included in an amount of 0.1% to 10% by weight in the positive electrode active material layer in order to sufficiently secure electrical conductivity.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material according to the present invention. For example, the positive electrode is prepared by dissolving or dispersing components constituting the positive electrode active material layer, that is, a positive electrode active material, a positive electrode conductive material, and/or a positive electrode binder in a solvent to prepare a positive electrode slurry, and It may be prepared by coating at least one surface of the whole, then drying and rolling, or by casting the positive electrode slurry on a separate support and then laminating a film obtained by peeling from the support on the positive electrode current collector. there is.

<Secondary Battery>

In addition, the present invention provides a secondary battery including the positive electrode described above.

Specifically, the secondary battery according to the present invention includes the aforementioned positive electrode; a cathode facing the anode; a separator interposed between the anode and the cathode; and an electrolyte.

A description of the anode has been given above.

The cathode faces the anode.

The negative electrode may include a negative electrode current collector; and an anode active material layer disposed on at least one surface of the anode current collector.

The anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. Specifically, the anode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy, and may specifically include copper.

The negative current collector may typically have a thickness of 3 to 500 μm.

The negative electrode current collector may form fine irregularities on the surface to enhance bonding strength of the negative electrode active material. For example, the negative current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or non-woven fabric.

The anode active material layer is disposed on at least one surface of the anode current collector. Specifically, the negative electrode active material layer may be disposed on one side or both sides of the negative electrode current collector.

The anode active material layer may include an anode active material.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the anode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and undoping lithium, such as SiO _v (0<v<2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; or a composite including the metallic compound and the carbonaceous material, such as a Si—C composite or a Sn—C composite, and any one or a mixture of two or more of these may be used. In addition, a metal lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low crystalline carbon, and high crystalline carbon includes amorphous, platy, scaly, spherical or fibrous natural graphite, artificial graphite, or kish graphite. graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is representative.

The anode active material layer may further include an anode binder, an anode conductive material, and/or a thickener in addition to the anode active material described above.

The anode binder is a component that assists in bonding between the active material and/or the current collector, and may be typically included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 10 wt%, in the anode active material layer.

The anode binder is polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene At least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber and fluororubber, preferably polyvinylidene fluoride and styrene-butadiene rubber It may include at least one selected from among.

As the thickener, all thickeners conventionally used in lithium secondary batteries may be used, and one example is carboxymethyl cellulose (CMC) and the like.

The anode conductive material is a component for further improving conductivity of the anode active material, and may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 10 wt%, in the anode active material layer.

The negative electrode conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; 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 may be used. Specific examples of commercially available conductive materials include Chevron Chemical Company, which is an acetylene black series, Denka Singapore Private Limited, Gulf Oil Company products, etc.), Ketjenblack, EC family (made by Armak Company), Vulcan XC-72 (made by Cabot Company) and Super P (made by Timcal).

The negative electrode may be manufactured according to a conventional negative electrode manufacturing method generally known in the art. For example, the negative electrode slurry is prepared by dissolving or dispersing components constituting the negative electrode active material layer, that is, the negative electrode active material, the negative electrode conductive material, and/or the negative electrode binder in a solvent, and the negative electrode slurry is used as a negative electrode collector. It can be prepared by coating at least one surface of the whole, then drying and rolling, or by casting the negative electrode slurry on a separate support and then laminating the film obtained by peeling from the support on the negative electrode current collector. there is.

On the other hand, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions. If it is normally used as a separator in a secondary battery, it can be used without particular limitation. It is preferable to have an excellent ability to absorb the electrolyte while being resistant. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

Meanwhile, as the electrolyte, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of secondary batteries may be used, but are not limited thereto.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, PC) and other carbonate-based solvents; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as Ra-CN (Ra is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane or the like may be used. Among them, carbonate-based solvents are preferred, and cyclic carbonates (eg, ethylene carbonate or propylene carbonate, etc.) having high ion conductivity and high dielectric constant capable of increasing the charge and discharge performance of batteries, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to 9, the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO _{4 , LiAlCl 4 ,} LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the components of the electrolyte, the electrolyte may include, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate for the purpose of improving life characteristics of a battery, suppressing a decrease in battery capacity, and improving a discharge capacity of a battery; or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N - One or more additives such as substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

As described above, the secondary battery including the positive electrode active material according to the present invention has excellent electrical characteristics and high temperature storage properties, so that it can be used in portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (HEV). It can be usefully applied to the field of electric vehicles and the like. In particular, the secondary battery according to the present invention can be usefully used as a high voltage battery higher than 4.45V.

In addition, the secondary battery according to the present invention can be used as a unit cell of a battery module, and the battery module can be applied to a battery pack. The battery module or battery pack may include a power tool; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for one or more medium or large-sized devices among power storage systems.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Example

Example 1: Preparation of cathode active material

Li ₂ CO ₃ as a lithium source material and Al-doped Co ₃ O ₄ as a cobalt precursor were prepared. Al doped into the cobalt precursor is doped in an amount of 3,000 ppm of the weight of the cathode active material to be manufactured.

A lithium cobalt-based oxide doped with Al and Mg was prepared by mixing the lithium raw material, the cobalt precursor, Al ₂ O ₃ as an Al precursor, and MgO as a Mg precursor, and performing a primary heat treatment at 1,050 ° C. for 10 hours. The Al precursor and Mg precursor used in the first heat treatment were mixed with the lithium raw material and the cobalt precursor in an amount of 2,000 ppm and 1,000 ppm of the weight of the cathode active material to be produced, respectively.

Next, a mixture of Al and Mg-doped lithium cobalt-based oxide, Al ₂ O ₃ as an Al precursor, TiO ₂ as a Ti precursor, and Y ₂ O ₃ as a Y precursor, followed by secondary heat treatment at 850° C. for 5 hours , a positive electrode active material was prepared. The Al precursor, Ti precursor, and Y precursor used in the secondary heat treatment are 1,000 ppm, 700 ppm, and 700 ppm of the weight of the positive electrode active material in which doped Al, Ti, and Y are prepared, respectively, and the Al and Mg are It is mixed with doped lithium cobalt-based oxide.

As a result, in the case of the cathode active material, 700 ppm of Y, 6,000 ppm of Al, 700 ppm of Ti, and 1,000 ppm of Mg were doped or coated on the lithium cobalt-based oxide. The average particle diameter (D ₅₀ ) of the cathode active material was 15 μm.

The contents of Y, Al, Ti, and Mg included in the cathode active material were measured using an inductively coupled plasma emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer Co.).

Comparative Example 1: Preparation of cathode active material

In the second heat treatment step, a positive electrode active material was prepared in the same manner as in Example 1, except that the Y precursor was not mixed with the Al and Mg-doped lithium cobalt-based oxide, the Al precursor, and the Ti precursor.

As a result, in the case of the cathode active material, 6,000 ppm of Al, 700 ppm of Ti, and 1,000 ppm of Mg were doped or coated on the lithium cobalt-based oxide.

Comparative Example 2: Preparation of cathode active material

In the second heat treatment step, the positive electrode was prepared in the same manner as in Example 1, except that the Y precursor was mixed with Al and Mg-doped lithium cobalt-based oxide, an Al precursor, and a Ti precursor so that Y was 300 ppm of the weight of the positive electrode active material. Active material was prepared.

As a result, in the case of the cathode active material, 300 ppm of Y, 6,000 ppm of Al, 700 ppm of Ti, and 1,000 ppm of Mg were doped or coated on the lithium cobalt-based oxide. The average particle diameter (D ₅₀ ) of the cathode active material was 15 μm.

Comparative Example 3: Preparation of cathode active material

In the second heat treatment step, the same method as in Example 1 except that the Y precursor was mixed with Al and Mg-doped lithium cobalt-based oxide, an Al precursor, and a Ti precursor so that Y was 1,000 ppm of the weight of the positive electrode active material. A positive electrode active material was prepared.

As a result, in the case of the cathode active material, 1,000 ppm of Y, 6,000 ppm of Al, 700 ppm of Ti, and 1,000 ppm of Mg were doped or coated on the lithium cobalt-based oxide. The average particle diameter (D ₅₀ ) of the cathode active material was 15 μm.

Comparative Example 4: Preparation of cathode active material

(1) in the second heat treatment step, the Y precursor is not mixed with the Al and Mg-doped lithium cobalt-based oxide, the Al precursor, and the Ti precursor, (2) in the second heat treatment step, the Al precursor is A positive electrode active material was prepared in the same manner as in Example 1, except that the lithium cobalt-based oxide doped with Al and Mg was mixed with the Ti precursor so that the weight of the positive electrode active material was 4,000 ppm.

As a result, the cathode active material was doped or coated with 10,000 ppm of Al, 700 ppm of Ti, and 1,000 ppm of Mg.

Experimental example

<Manufacture of lithium secondary battery>

1. Preparation of anode

A positive electrode slurry was prepared by mixing the positive electrode active material prepared in Example 1 and Comparative Examples 1 to 4, the carbon black conductive material, and the PVdF binder in a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent, which After coating on an aluminum current collector, drying and rolling were performed to prepare positive electrodes of Example 1 and Comparative Examples 1 to 4.

2. Manufacturing of lithium secondary battery

Lithium metal was used as the negative electrode.

An electrode assembly was prepared by interposing a porous polyethylene separator between the positive electrode and the negative electrode prepared above, the electrode assembly was placed inside the battery case, and an electrolyte was injected into the battery case to prepare a half-cell lithium secondary battery. . At this time, the electrolyte is ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) 3: 4: 3 in an organic solvent mixed with a volume ratio of 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) prepared by dissolution.

Experimental Example 1: Evaluation of initial charge capacity and initial efficiency

The lithium secondary batteries of Example 1 and Comparative Examples 1 to 4 prepared as described above were charged at 25° C. in CC/CV mode at 0.2C until 4.55V, and discharged at 0.2C CC mode to 3.0V.

When the charge and discharge experiments were performed, the initial charge capacity and initial efficiency of the lithium secondary batteries of Example 1 and Comparative Examples 1 to 4 were measured and calculated, and the results are shown in Table 1 below.

The initial efficiency was obtained by the following equation.

Initial Efficiency (%) = (Initial Discharge Capacity/Initial Charge Capacity) × 100%

Experimental Example 2: Evaluation of rate characteristics

First, the lithium secondary batteries of Example 1 and Comparative Examples 1 to 4 prepared as described above were charged at 25° C. in CC/CV mode at 0.1C until 4.55V, and discharged at 0.1C CC mode to 3.0V. and the discharge capacity at 0.1 C discharge was obtained.

Next, preparing a separate lithium secondary battery of Example 1 and Comparative Examples 1 to 4, charging the lithium secondary battery at 25 ℃ CC / CV mode at 0.1C until 4.55V, 0.1C CC It was discharged to 3.0V in mode, and the discharge capacity at the time of 2.0C discharge was calculated|required.

Then, the rate characteristics were evaluated by calculating with the formula below. At this time, excellent rate characteristics mean that the rate of decrease in normalized capacity (ie, capacity retention rate) according to the increase in the discharge rate (C-rate) is small.

Rate characteristics (%) = (discharge capacity at 2.0C discharge / discharge capacity at 0.1C discharge) × 100%

Experimental Example 3: Evaluation of life characteristics at high temperatures

Conditions in which the lithium secondary batteries of Example 1 and Comparative Examples 1 to 4 prepared as described above are charged at 45° C. in CC/CV mode at 0.5C until 4.55V, and discharged at 1.0C CC mode to 3.0V. The capacity retention rate when charging and discharging for 50 cycles was measured.

The capacity retention rate was calculated by the formula below, the change in capacity retention rate according to the cycle is shown in FIG. 1, and the capacity retention rate in the 50th cycle charge/discharge is shown in Table 1 below.

Capacity retention rate (%) = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%

Experimental Example 1 Experimental Example 2 Experimental Example 3 Initial charge capacity (mAh/g) Initial Efficiency (%) Rate characteristic (%) Capacity retention rate (%) (@ 50 ^th cycle) Example 1 206.8 92.5 92.3 93.3 Comparative Example 1 208.6 93.7 93.3 86.5 Comparative Example 2 208.1 93.4 93.0 89.2 Comparative Example 3 207.0 92.0 90.8 91.4 Comparative Example 4 207.1 90.7 88.9 87.6

Referring to Table 1, it can be seen that the lithium secondary battery of Example 1 using the positive electrode active material doped with the metal element M ¹ in a preferred amount has overall excellent initial efficiency, rate characteristics, and lifespan performance compared to Comparative Examples. .

Claims (15)

lithium cobalt-based oxide; and
As a positive electrode active material containing a metal element M ¹ doped inside or coated on the surface of the lithium cobalt-based oxide,
The metal element M ¹ includes yttrium (Y),
The metal element M ¹ is included in the positive electrode active material in an amount of 500 ppm to 900 ppm.
The method of claim 1,
The cathode active material further includes a metal element M ² doped into or coated on the surface of the lithium cobalt-based oxide,
The metal element M ² is a cathode active material including at least one member selected from the group consisting of aluminum (Al), titanium (Ti), and magnesium (Mg).
The method of claim 2,
The metal element M ² is a cathode active material including aluminum (Al), titanium (Ti), and magnesium (Mg).
The method of claim 3,
The aluminum (Al) is included in the cathode active material in an amount of 500 ppm to 8,000 ppm,
The titanium (Ti) is included in the cathode active material in an amount of 500 ppm to 1,000 ppm,
The positive electrode active material includes magnesium (Mg) in an amount of 500 ppm to 1,500 ppm in the positive electrode active material.
The method of claim 1,
A positive electrode active material having a molar ratio of lithium and metal elements other than lithium included in the positive electrode active material of 0.95:1 to 1.05:1.
The method of claim 1,
The positive electrode active material has an average particle diameter (D ₅₀ ) of 3 μm to 30 μm.
Forming a lithium cobalt-based oxide by mixing a lithium source material and a cobalt precursor and performing a primary heat treatment; and
mixing the lithium cobalt-based oxide and the precursor including the metal element M ¹ and performing secondary heat treatment to form a lithium cobalt-based oxide doped or coated on the surface with the metal element M ¹ ; claim 1 including Method for producing a cathode active material according to.
The method of claim 7,
The first heat treatment is a method for producing a cathode active material performed at 950 ° C to 1,200 ° C.
The method of claim 7,
The primary heat treatment is a method for producing a positive electrode active material performed for 7 hours to 15 hours.
The method of claim 7,
The secondary heat treatment is a method for producing a positive electrode active material performed at 800 ° C to 900 ° C.
The method of claim 7,
The secondary heat treatment is a method for producing a positive electrode active material performed for 3 hours to 8 hours.
The method of claim 7,
The cobalt precursor is doped with a metal element M ² ,
The metal element M ² is a method for producing a cathode active material comprising at least one selected from aluminum (Al), titanium (Ti), and magnesium (Mg).
The method of claim 7,
When mixing the lithium cobalt-based oxide and the precursor containing the metal element M ¹ , further mixing the precursor containing the metal element M ² ,
The metal element M ² is a method for producing a cathode active material comprising at least one selected from aluminum (Al), titanium (Ti), and magnesium (Mg).
positive current collector; and
A cathode active material layer disposed on at least one surface of the cathode current collector,
The positive electrode active material layer is a positive electrode including the positive electrode active material according to claim 1.
an anode according to claim 14;
a cathode facing the anode;
a separator interposed between the anode and the cathode; and
A secondary battery including an electrolyte.

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