KR102335313B1 - Method for preparing positive electrode active material for lithium secondary battery, positive electrode active material prepared by the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a precursor forming solution comprising a cobalt-containing starting material and a first doping element source; and co-precipitating the precursor-forming solution, and forming a Co ₃ O ₄ or CoOOH precursor doped with a first doping element. In addition, the first doping element-doped Co ₃ O ₄ or CoOOH precursor, a lithium raw material and a second doping element source are mixed and subjected to primary heat treatment to prepare lithium cobalt oxide doped with a second doping element additionally step; and mixing the lithium cobalt oxide and a third doping element source and performing secondary heat treatment to prepare a lithium cobalt oxide surface doped with a third doping element additionally; may further include.

Description

A method of manufacturing a cathode active material for a lithium secondary battery, a cathode active material manufactured as described above, and a lithium secondary battery comprising the same }

The present invention relates to a method for manufacturing a positive electrode active material for a lithium secondary battery, a positive electrode active material prepared as described above, and a lithium 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, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.

A lithium secondary battery includes a positive electrode including a positive electrode active material capable of insertion/desorption of lithium ions, a negative electrode including a negative electrode active material capable of insertion/deintercalation of lithium ions, and an electrode having a microporous separator interposed between the positive electrode and the negative electrode It means a battery in which an electrolyte containing lithium ions is included in the assembly.

Lithium transition metal oxide is used as a cathode active material of a lithium secondary battery, and lithium metal, a lithium alloy, crystalline or amorphous carbon, or a carbon composite material is used as an anode active material. The active material is applied to the electrode current collector with an appropriate thickness and length, or the active material itself is coated in a film shape and wound or laminated together with a separator, which is an insulator, to make an electrode group, then put in a can or similar container, and then inject the electrolyte to manufacture a secondary battery.

As a cathode active material of a lithium secondary battery that has been actively researched and developed at present, there is a layered lithium cobalt oxide (LiCoO ₂ ). Lithium cobalt oxide (LiCoO ₂ ) has advantages of high operating voltage and excellent capacity characteristics, but has poor thermal characteristics due to destabilization of the crystal structure due to lithium removal and the structure is unstable under high voltage.

Recently, the demand for high-capacity lithium secondary batteries is gradually increasing. In the case of lithium cobalt oxide (LiCoO ₂ ), unlike the ternary positive electrode active material, the capacity can be increased only by raising the voltage. There is a need to develop _{lithium cobalt oxide (LiCoO 2} ) capable of securing structural stability even at phosphorus 4.5V or higher.

Chinese Laid-Open Patent No. 103500827

The present invention is a cathode active material of lithium cobalt oxide (LiCoO ₂ ) having excellent structural stability, in particular, a method of manufacturing a cathode active material for a lithium secondary battery that can secure structural stability even under a high voltage of 4.5V or more, and has high capacity and improved lifespan characteristics and to provide a positive electrode active material prepared as described above.

The present invention provides a precursor forming solution comprising a cobalt-containing starting material and a first doping element source; and co-precipitating the precursor-forming solution, and forming a precursor of Co ₃ O ₄ or CoOOH doped with a first doping element.

In one embodiment of the present invention, _{a precursor of Co 3} O ₄ or CoOOH doped with the first doping element, a lithium raw material, and a second doping element source are mixed and subjected to primary heat treatment, the second doping element is additionally doped preparing lithium cobalt oxide; and mixing the lithium cobalt oxide and a third doping element source and performing secondary heat treatment to prepare a lithium cobalt oxide surface doped with a third doping element additionally; may further include.

In addition, the present invention provides a positive electrode active material prepared as described above, a positive electrode comprising the same, and a lithium secondary battery.

According to the present invention, it is possible to secure excellent structural stability, particularly structural stability even under a high voltage of 4.5V or more, and to manufacture a positive active material for a lithium secondary battery having improved high capacity and lifespan characteristics.

1 is a graph showing the capacity retention rate according to the progress of 50 cycles of a lithium secondary battery cell including a positive active material prepared according to Examples and Comparative Examples.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to describe his invention in the best way. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

A method of manufacturing a cathode active material for a lithium secondary battery of the present invention comprises: preparing a precursor forming solution including a cobalt-containing starting material and a first doping element source; and co-precipitating the precursor-forming solution to form a Co ₃ O ₄ or CoOOH precursor doped with a first doping element.

In addition, an embodiment of the present invention _{mixes the Co 3} O ₄ or CoOOH precursor doped with the first doping element, the lithium raw material and the second doping element source, and performs primary heat treatment, so that the second doping element is additionally doped preparing lithium cobalt oxide; and mixing the lithium cobalt oxide and a third doping element source and performing secondary heat treatment to prepare a lithium cobalt oxide surface doped with a third doping element additionally; may further include.

The manufacturing method of the positive electrode active material for a lithium secondary battery of the present invention will be described in detail step by step below.

<Precursor doping>

The cathode active material for a lithium secondary battery of the present invention is doped with the precursor by co-precipitating the doping element source together when forming the precursor. By doping the precursor by adding a doping element source together in the precursor co-precipitation step, it is possible to dope with a uniform concentration, and since the particle size of the doped precursor prepared in the precursor doping step can be adjusted, the particle size control is easy, and the high content of doping is possible.

In the precursor doping, first, a precursor forming solution including a cobalt-containing starting material and a first doping element source is prepared.

The cobalt-containing starting material may be a sulfate, halide, acetate, sulfide, hydroxide, oxide or oxyhydroxide containing cobalt, and is not particularly limited as long as it can be dissolved in water. For example, the cobalt-containing starting material is Co(SO ₄ ) ₂ ㆍ7H ₂ O, CoCl ₂ , Co(OH) ₂ , Co(OCOCH ₃ ) ₂ ㆍ4H ₂ O or Co(NO ₃ ) ₂ ㆍ6H ₂ O and the like, and any one or a mixture of two or more thereof may be used.

The source of the first doping element may include sulfate, nitrate, acetate, halide, hydroxide, or oxyhydroxide containing the first doping element, and any one or a mixture of two or more thereof may be used. The first doping element may be at least one selected from the group consisting of Al, Mg, Ti, Zr, Ca, F and Nb, and more preferably, may include Al as the first doping element.

The precursor forming solution may be prepared by adding the cobalt-containing starting material and the first doping element source to a solvent, specifically water, or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) and water, , or a solution including each cobalt-containing starting material and a solution including the first doping element source may be prepared and then mixed and used.

Next, the precursor forming solution is subjected to a co-precipitation reaction to form a Co ₃ O ₄ or CoOOH precursor doped with a first doping element.

The precursor-forming solution may be introduced into a reactor, and a chelating agent and a basic aqueous solution may be added through a co-precipitation reaction _{to prepare a Co 3} O ₄ or CoOOH precursor doped with a first doping element. In the case of Co ₃ O _{4 , first, CoCO 3} doped with a first doping element is formed through a co-precipitation reaction, and heat treatment is performed at 650° C. to 800° C. for 3 to 7 hours to convert _{to Co 3} O _{4 .} Since CoCO ₃ has low productivity, it can be used by converting _{CoCO 3} into Co ₃ O ₄ as described above to improve productivity.

The chelating agent may include NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , or NH ₄ CO ₃ , and one or two of them. A mixture of the above may be used. In addition, the chelating agent may be used in the form of an aqueous solution, and as the solvent, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) and water may be used.

The basic compound is NaOH, KOH, Ca(OH) ₂ or Na ₂ CO ₃ It may be a hydroxide of an alkali metal or alkaline earth metal, such as, or a hydrate thereof, and one type alone or a mixture of two or more types thereof may be used. The basic compound may also be used in the form of an aqueous solution, and as the solvent, water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) and water may be used. In this case, the concentration of the basic aqueous solution may be 2M to 10M.

The co-precipitation reaction for preparing the cathode active material precursor may be carried out under a condition in which the pH is in the range of pH 10 to pH 12. When the pH is out of the above range, there is a risk of changing the size of the prepared cathode active material precursor or causing particle splitting. More specifically, it may be carried out under conditions of pH 11 to pH 12. The pH adjustment as described above can be controlled through the addition of a basic aqueous solution.

The co-precipitation reaction for preparing the cathode active material precursor may be performed in a temperature range of 30° C. to 80° C. under an inert atmosphere such as nitrogen. In order to increase the reaction rate during the reaction, a stirring process may be optionally performed, and in this case, the stirring rate may be 100 rpm to 2000 rpm.

_{Prepared as described above to form a Co 3} O ₄ or CoOOH precursor doped with the first doping element. The content of the first doping element is finally prepared lithium cobalt oxide Compared to 1,000 to 5,000 ppm, more preferably 2,500 to 4,500 ppm may be. By doping the precursor as described above, the first doping element may be doped with a high content. In addition, since it is easy to control the particle size when preparing the precursor, it may be easy to control the size of the cathode active material particles. In addition, in the precursor prepared as described above, the first doping element may be uniformly doped without a concentration gradient from the center to the surface of the positive electrode active material precursor particle. In addition, the positive active material prepared using the precursor doped with the precursor as described above exhibits a composition in which the first doping element doped with the precursor is doped without a concentration gradient from the center of the positive electrode active material particle to the surface.

For the precipitated precursor, after separation according to a conventional method, a drying process may be optionally performed, and in this case, the drying process may be performed at 110° C. to 400° C. for 15 to 30 hours.

<Primary Heat Treatment - Doping in Lithium Cobalt Oxide Production >

_{Next, after mixing the Co 3} O ₄ or CoOOH precursor and the lithium raw material doped with the first doping element, the first heat treatment is performed to prepare lithium cobalt oxide.

In this case, the lithium cobalt oxide additionally doped with the second doping element may be prepared by further mixing the source of the second doping element together with the precursor and the lithium raw material and performing the first heat treatment.

The lithium raw material may include lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH·H ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi, or Li ₃ C ₆ H ₅ O ₇ and the like, and any one or a mixture of two or more thereof may be used.

The source of the second doping element may include sulfate, nitrate, acetate, halide, hydroxide, oxyhydroxide, or oxide containing the second doping element, and any one or a mixture of two or more thereof may be used. The second doping element may be at least one selected from the group consisting of Al, Mg, Ti, Zr, Ca, F, and Nb, and more preferably, may include Mg and/or Ti as the second doping element. .

Meanwhile, when mixing the precursor, the lithium raw material, and the source of the second doping element, a sintering agent may be optionally further added. Examples of the sintering agent include compounds containing ammonium ions, such _{as NH 4} F, NH ₄ NO ₃ , or (NH ₄ ) ₂ SO _{4 ;} metal oxides such as B ₂ O ₃ or Bi ₂ O _{3 ;} or a _{metal halide such as NiCl 2} or CaCl _{2 ,} and any one or a mixture of two or more thereof may be used. The sintering agent may be used in an amount of 0.01 to 0.2 moles based on 1 mole of the precursor. If the content of the sintering agent is too low, less than 0.01 mol, the effect of improving the sintering properties of the positive electrode active material precursor may be insignificant, and if the content of the sintering agent is too high, exceeding 0.2 mol, the performance as a positive electrode active material is reduced due to excessive sintering agent And there is a possibility that the initial capacity of the battery may decrease during charging and discharging.

In addition, when mixing the precursor, the lithium raw material, and the source of the second doping element, a moisture scavenger may be optionally further added. Specifically, the water removing agent may include citric acid, tartaric acid, glycolic acid or maleic acid, and any one or a mixture of two or more thereof may be used. The moisture removing agent may be used in an amount of 0.01 to 0.2 moles based on 1 mole of the precursor.

The primary heat treatment may be performed at 900 °C to 1,100 °C, more preferably at 1,000 to 1,050 °C. If the primary heat treatment temperature is less than 900°C, there is a risk of a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage due to residual unreacted raw materials, and when it exceeds 1,100°C, due to the generation of side reactants There is a risk of a decrease in the discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in the operating voltage.

The primary heat treatment may be performed in an oxidizing atmosphere such as air or oxygen, or in a reducing atmosphere containing nitrogen or hydrogen for 5 to 30 hours.

The content of the second doping element is finally prepared lithium cobalt oxide Compared to 500 to 4,000 ppm, more preferably, it may be 1,000 to 3,000 ppm. This may be the total doping content of the plurality of second doping elements doped during the first heat treatment process.

As described above, the second doping element added when the precursor and the lithium raw material are mixed is diffused from the surface side to the center of the lithium cobalt oxide particles to be doped, and thus, the second doping element is the surface of the lithium cobalt oxide particles. It can show a decreasing concentration gradient from to the center.

<Secondary Heat Treatment - Surface Doping>

Next, the lithium cobalt oxide and the source of the third doping element are mixed and subjected to secondary heat treatment to prepare lithium cobalt oxide in which the surface of the third doping element is additionally doped.

The third doping element source may include sulfate, nitrate, acetate, halide, hydroxide, oxyhydroxide or oxide containing the third doping element, and any one or a mixture of two or more thereof may be used. The third doping element may be at least one selected from the group consisting of Al, Mg, Ti, Zr, Ca, F and Nb, and more preferably include Al and/or Mg as the third doping element. .

In this case, the second doping element and the third doping element may include at least one doping element identical to each other. For example, the second doping elements are Mg and Ti, and the third doping elements are Al and Mg, and thus Mg may be overlapped. As described above, by making the second doping element and the third doping element include at least one of the same doping element, structural stability may be improved, and resistance and lifespan characteristics may be improved through surface structure stabilization. More specifically, the doping element equally included as the second doping element and the third doping element may be at least one selected from the group consisting of Mg and Al.

The secondary heat treatment may be performed at 800 °C to 950 °C, more preferably at 850 to 900 °C. If the secondary heat treatment temperature is less than 800 ℃, there is a risk of resistance increase due to the doping material remaining on the surface of the lithium cobalt oxide particles, and when it exceeds 950 ℃, additional grain growth occurs, there is a risk of causing an increase in resistance and a decrease in capacity.

The secondary heat treatment may be performed in an oxidizing atmosphere such as air or oxygen for 3 to 7 hours.

The content of the third doping element doped as described above is the final prepared lithium cobalt oxide. Compared to 500 to 5,000 ppm, more preferably 1,000 to 3,000 ppm, and most preferably 1,000 to 2,000 ppm. This may be the total doping content of the plurality of third doping elements doped during the secondary heat treatment process.

As described above, the third doping element introduced during the secondary heat treatment of lithium cobalt oxide may be doped on the surface of the lithium cobalt oxide particle, or a part of the lithium cobalt oxide particle may be doped by being diffused into the particle from the surface side.

The content ratio of the first doping element, the second doping element, and the third doping element of the lithium cobalt oxide prepared as described above can be adjusted in consideration of battery performance and manufacturing process, etc., and is not particularly limited, but more preferably Doping may be performed in a weight ratio of 0.5 to 5:1:0.5 to 3, and more preferably in a weight ratio of 1 to 5:1:1 to 2.

The positive electrode active material of lithium cobalt oxide prepared by the above manufacturing method has excellent structural stability, and in particular, it can secure excellent structural stability even under a high voltage of 4.5V or more, so it can be used in high voltage secondary batteries of 4.5V or more, and has a high capacity. At the same time, it is possible to significantly improve the lifespan characteristics.

According to another embodiment of the present invention, there is provided a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode active material.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the positive electrode current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.

In addition, the positive active material layer may include a conductive material and a binder together with the above-described positive active material.

In this case, the conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the binder serves to improve adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above positive electrode active material. Specifically, it may be prepared by applying the above-described positive active material and, optionally, a composition for forming a positive electrode active material layer including a binder and a conductive material on a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water, and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for the production of the positive electrode thereafter. do.

Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling it from the support on the positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the positive electrode is provided. The electrochemical device may specifically be a battery or a capacitor, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material. The anode active material layer may be formed by applying a composition for forming an anode including an anode active material, and optionally a binder and a conductive material on an anode current collector and drying, or casting the composition for forming a cathode on a separate support, and then , may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiOx (0 < x < 2), SnO2, vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

In addition, the binder and the conductive material may be the same as those described above for the positive electrode.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is usually used as a separator in a lithium secondary battery, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to respect and an excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. 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 optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, and the like, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it is not going to be

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

The organic solvent may be used without any 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, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, 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, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane (sulfolane) may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( 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 in a volume ratio of about 1:1 to about 1:9, 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 , LiAl0 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 ,} etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, 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 lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, so portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle and HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (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 any one or more medium-to-large devices in a system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Example One

In a batch-type 5L reactor set at 60° C., CoSO ₄ was mixed in water, and Al ₂ (SO ₄ ) ₃ was further mixed as an Al source to prepare a 2M concentration of a precursor forming solution. The container containing the precursor forming solution was connected to enter the reactor, and an _{aqueous solution of Na 2} CO _{3 having a} concentration of 25% and an aqueous solution of NH ₄ OH having a concentration of 15% were prepared and connected to the reactor, respectively. After putting 1 liter of deionized water into the co-precipitation reactor (capacity 5L), nitrogen gas was purged into the reactor at a rate of 2 liters/min to remove dissolved oxygen in the water, and a non-oxidizing atmosphere was created in the reactor. Thereafter, 10 ml of 25% Na ₂ CO ₃ aqueous solution was added, followed by stirring at a stirring speed of 1200 rpm at a temperature of 60° C. to maintain a pH of 12.0. Then, the precursor forming solution was added at a rate of 4ml/min, Na ₂ CO ₃ aqueous solution 1ml/min, and NH ₄ OH aqueous solution at a rate of 1ml/min, respectively, and the co-precipitation reaction was performed for 1440 minutes to grow _{Al-doped CoCO 3 .} The resulting Al-doped CoCO ₃ particles were separated, washed with water, and then dried in an oven at 120° C. Dry Al-doped CoCO ₃ was heat-treated at 750° C. for 5 hours to prepare a cathode active material precursor of _{Al-doped Co 3} O _{4 .} The Al doping content of the prepared Co ₃ O ₄ was 3,000 ppm compared to the final prepared lithium cobalt oxide.

The positive electrode active material precursor (finally prepared lithium cobalt oxide) prepared in this way Compared to 3,000ppm Al-doped Co ₃ O ₄ ) 80.27 g and Li ₂ CO ₃ 36.95 g as a lithium raw material were mixed, MgO as a Mg source, and TiO ₂ as a Ti source were mixed together, and mixed together at 1,050 ° C. for about 5 hours. Lithium cobalt oxide finally prepared by primary heat treatment _{Lithium cobalt oxide (LiCoO 2} ) additionally doped with 1,500 ppm Mg and 1,000 ppm Ti was prepared.

Thereafter, the lithium cobalt oxide prepared in this way, Al ₂ O ₃ as an Al source, and MgO as a Mg source were mixed, and secondary heat treatment was performed at 850° C. for about 5 hours. A positive electrode active material of lithium cobalt oxide (LiCoO _{2 ) in which ppm Mg was additionally doped was prepared.}

Example 2

Lithium cobalt oxide finally produced during precursor doping A cathode active material was prepared in the same manner as in Example 1, except that a precursor of 1,000 ppm Al-doped Co ₃ O _{4 was prepared.}

Example 3

Lithium cobalt oxide finally produced during precursor doping A cathode active material was prepared in the same manner as in Example 1, except that a precursor _{of Co 3} O ₄ doped with 5,000 ppm Al was prepared.

Example 4

Example 1 except that 2,500 ppm of Mg alone was doped instead of 1,500 ppm Mg and 1,000 ppm Ti in the first heat treatment, and only 1,000 ppm of Al was doped instead of 1,000 ppm Al and 1,000 ppm Mg in the second heat treatment A positive electrode active material was prepared in the same manner as described above.

comparative example One

_{A cathode active material was prepared in the same manner as in Example 1, except that a Co 3} O ₄ precursor not doped with the precursor was used, and 1,500 ppm Mg and 1,000 ppm Ti and 3,000 ppm of Al were doped together during the first heat treatment. .

[ Experimental example One: charging and discharging Capacity and Efficiency Evaluation]

A composition for forming a positive electrode was prepared by using the positive electrode active material prepared in Examples 1 to 4 and Comparative Example 1, and mixing carbon black and a PVDF binder in an N-methylpyrrolidone solvent in a weight ratio of 90:5:5. and applied to one surface of an aluminum current collector, dried at 130° C., and then rolled to prepare positive electrodes, respectively.

In addition, as an anode active material, natural graphite, a carbon black conductive material, and a PVdF binder are mixed in an N-methylpyrrolidone solvent in a weight ratio of 85:10:5 to prepare a composition for forming an anode, and this is used to form a copper current collector. was applied to prepare a negative electrode.

An electrode assembly was prepared by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, the electrode assembly was placed inside the case, and the electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving _{lithium hexafluorophosphate (LiPF 6} ) at a concentration of 1.0 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3 / 4 / 3). did

A charge/discharge experiment was performed on each lithium secondary battery cell (half cell) prepared as described above to measure 0.2C capacity and efficiency, 1.0C, and 2.0C efficiency, and the results are shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Charging capacity (mAh/g) 0.2C 210.5 215.4 208.1 220.7 210.3 Discharge capacity (mAh/g) 0.2C 202.3 207.9 197.9 214.3 200.8 efficiency(%) 0.2C 96.1 96.5 95.1 97.1 95.5 efficiency(%) 1.0C 95.0 95.5 94.9 96.5 94.0 efficiency(%) 2.0C 91.2 92.0 90.7 93.5 90.5

* Temperature 25℃, loading ^{380mg/25cm 2} , voltage 4.55V

Referring to Table 1, compared to Comparative Example 1 without precursor doping, Example 1 doped through three steps during the first heat treatment/second heat treatment after precursor doping showed equivalent or somewhat superior capacity and efficiency.

[ Experimental example 2: Cycle characteristic evaluation]

Each lithium secondary battery cell (half cell) prepared as described above was charged at 45°C in CCCV mode until it became 0.5C and 4.55V, cut off at 0.55C condition, 3.0V at a constant current of 1.0C The capacity retention rate (Capacity Retention [%]) was measured while charging and discharging 50 times. The results are shown in FIG. 1 .

Referring to FIG. 1 , compared to Comparative Example 1 without precursor doping, it can be seen that Examples 1 to 4 doped over three steps during the first heat treatment / second heat treatment after precursor doping show a high capacity retention rate up to 30 charge/discharge cycles. can

On the other hand, in the case of Example 4, which did not contain the same doping elements by doping with Mg during the first heat treatment doping and with Al during the second heat treatment doping, a high capacity retention rate was exhibited until 30 times of charge and discharge, but 35 times of charge and discharge were observed. After discharging, the capacity retention rate decreased sharply. On the other hand, in Examples 1 to 3 in which the second doping element and the third doping element include at least one or more identical doping elements, lifespan characteristics were further improved through structural stability and surface structure stabilization.

Claims (17)

preparing a precursor forming solution comprising a cobalt-containing starting material and a first doping element source;
co-precipitating the precursor-forming solution to form a Co ₃ O ₄ or CoOOH precursor doped with a first doping element;
_{preparing a lithium cobalt oxide doped with a second doping element by mixing the Co 3} O ₄ or CoOOH precursor doped with the first doping element, a lithium raw material, and a second doping element source and performing primary heat treatment; and
mixing the lithium cobalt oxide and a third doping element source and performing secondary heat treatment to prepare a lithium cobalt oxide surface doped with a third doping element additionally;
including,
The first doping element includes Al, and the second doping element and the third doping element include at least one doping element identical to each other.
delete delete delete According to claim 1,
The second doping element and the third doping element are each at least one selected from the group consisting of Al, Mg, Ti, Zr, Ca, F and Nb. A method of manufacturing a cathode active material for a lithium secondary battery.
delete According to claim 1,
The method of manufacturing a cathode active material for a lithium secondary battery, wherein the second doping element and the third doping element equally include at least one selected from the group consisting of Mg and Al.
According to claim 1,
The first doping element is finally prepared lithium cobalt oxide A method of preparing a cathode active material for a lithium secondary battery doped at 1,000 to 5,000 ppm.
According to claim 1,
The second doping element is finally prepared lithium cobalt oxide A method of preparing a positive active material for a lithium secondary battery doped with 500 to 4,000 ppm compared to the present invention.
According to claim 1,
The third doping element is lithium cobalt oxide finally prepared A method of preparing a positive active material for a lithium secondary battery doped with 500 to 5,000 ppm compared to the present invention.
According to claim 1,
The first heat treatment is a method of manufacturing a cathode active material for a lithium secondary battery that is performed at a heat treatment temperature of 900 to 1,100 ℃.
According to claim 1,
The secondary heat treatment is a method of manufacturing a cathode active material for a lithium secondary battery is performed at a heat treatment temperature of 800 to 950 ℃.
According to claim 1,
The doping content of the first doping element, the second doping element, and the third doping element is in a weight ratio of 0.5 to 5:1:0.5 to 3, a method of manufacturing a positive electrode active material for a lithium secondary battery.
The cathode active material for a lithium secondary battery prepared according to claim 1, wherein the first doping element is doped without a concentration gradient from the center to the surface of the cathode active material particles.
A cathode active material for a lithium secondary battery prepared according to claim 1 .
A positive electrode for a secondary battery comprising the positive active material according to any one of claims 14 to 15.
A lithium secondary battery comprising the positive electrode according to claim 16 .

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