Method for manufacturing a positive electrode active material for a lithium secondary battery, a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery including the same, and a lithium secondary battery

Abstract

The present invention relates to a method for producing a positive electrode active material having a high ratio of charge / discharge capacity at an end-of-charge voltage of 4.1 V to 4.175 V to the charge / discharge capacity at an end-of-charge voltage of 4.2 V to 4.275 V, and excellent initial charge / discharge capacity.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0163379, filed November 24, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for producing a positive electrode active material for producing a secondary battery that exhibits excellent charge / discharge capacity over a wide range of end-of-charge voltages. [Background technology]

[0003] With the technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Lithium-transition metal composite oxides are used as the positive electrode active material for lithium secondary batteries, and among them, the lithium-cobalt composite metal oxide LiCoO2 is mainly used because of its high operating voltage and excellent capacity characteristics. However, LiCoO2 has very poor thermal properties due to the instability of its crystal structure caused by delithiation. In addition, the high cost of LiCoO2 limits its mass use as a power source in fields such as electric vehicles.

[0005] Materials being developed to replace LiCoO2 include lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate compounds (such as LiFePO4), and lithium nickel composite metal oxides (such as LiNiO2). Among these, research and development has been particularly active on lithium nickel composite metal oxides, which have a high reversible capacity of approximately 200 mAh / g and make it easier to create high-capacity batteries. However, LiNiO2 has inferior thermal stability compared to LiCoO2, and if an internal short circuit occurs due to external pressure while the battery is charged, the positive electrode active material itself decomposes, causing the battery to explode and catch fire.

[0006] Therefore, nickel-cobalt-manganese-based lithium composite metal oxides (hereinafter simply referred to as "NCM-based lithium oxides") have been developed in which part of the Ni is replaced with Mn and Co as a way to maintain the excellent reversible capacity of LiNiO2 while improving its low thermal stability. However, the NCM-based lithium oxides developed to date have not had sufficient capacity characteristics, limiting their application.

[0007] As described above, in the prior art, positive electrode active materials for lithium secondary batteries have been provided that include various coating layers to improve battery characteristics.

[0008] Meanwhile, when the same secondary battery is used for both an energy storage system (SS) and an electric vehicle (EV), it typically uses an end-of-charge voltage of 4.2 V or 4.1 V. Therefore, in order to be used for various purposes, the 4.2 V capacity and the 4.1 V capacity must be uniformly excellent. If the 4.2 V capacity is high but the 4.1 V capacity is low, it is difficult to use it for both an energy storage system and an electric vehicle. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2021-012807 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a method for producing a positive electrode active material that has a high ratio of charge / discharge capacity at an end-of-charge voltage of 4.1 V to 4.175 V to charge / discharge capacity at an end-of-charge voltage of 4.2 V to 4.275 V, and is excellent in initial charge / discharge capacity. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention provides a method for producing a positive electrode active material, comprising: (S1) preparing a positive electrode active material precursor containing nickel, cobalt, and manganese; (S2) mixing the positive electrode active material precursor and a lithium source and calcining the mixture to form a lithium transition metal oxide; and (S3) washing the lithium transition metal oxide with a washing solution, wherein the calcination is performed in an atmosphere having an oxygen concentration of 85% or more, the molar ratio (Li / M) of lithium (Li) in the lithium source to the total metal elements (M) in the positive electrode active material precursor is 1.03 to 1.05, and 50 to 110 parts by weight of the washing solution is used per 100 parts by weight of the lithium transition metal oxide.

[0012] The present invention also provides a positive electrode active material containing nickel, cobalt, and manganese, in which the nickel content of all metal elements is 60 mol % or more and the value calculated by the following formula 1 is 90% to 100%. [Formula 1] (1st discharge capacity) / (2nd discharge capacity)×100 In the formula 1, The first discharge capacity was measured by charging the battery in CC / CV mode at a constant current of 0.2C up to the first charge end voltage, and then discharging it in CC mode at a constant current of 0.2C down to 2.5V. The second discharge capacity was measured by charging the battery in CC / CV mode at a constant current of 0.2C up to the second charge cut-off voltage, and then discharging it in CC mode at a constant current of 0.2C down to 2.5V. Here, the first charge end voltage is 4.1V to 4.175V, and the second charge end voltage is 4.2V to 4.275V.

[0013] The present invention also provides a positive electrode for a lithium secondary battery, which contains the positive electrode active material. [Effects of the Invention]

[0014] The positive electrode active material prepared by the preparation method of the present invention has excellent charge / discharge capacity when the end-of-charge voltage is 4.2 V to 4.275 V and excellent charge / discharge capacity when the end-of-charge voltage is 4.1 V to 4.175 V, and can be used in a variety of applications such as energy storage devices and electric vehicles. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing the ratio of the charge capacity at the end-of-charge voltage of 4.175 V to the charge capacity at the end-of-charge voltage of 4.25 V in Examples 1 to 5 and Comparative Examples 1 and 2. FIG. [Figure 2] 1 is a diagram showing the ratio of the discharge capacity at the end of charge voltage of 4.175 V to the discharge capacity at the end of charge voltage of 4.25 V in Examples 1 to 5 and Comparative Examples 1 and 2. FIG. [Figure 3] FIG. 1 is a diagram showing the ratio of the charge capacity at the end-of-charge voltage of 4.175 V to the charge capacity at the end-of-charge voltage of 4.25 V in Examples 6 to 9 and Comparative Example 3. [Figure 4] FIG. 1 is a diagram showing the ratio of the discharge capacity at the end-of-charge voltage of 4.175 V to the discharge capacity at the end-of-charge voltage of 4.25 V in Examples 6 to 9 and Comparative Example 3. [Figure 5] 10 is a graph showing the change in dQ / dV depending on Li / M. [Figure 6] 1 is a graph showing DCIR for each SOC in Example 3 and Comparative Example 1. [Figure 7] 1 is a graph showing the capacity retention rates (%) at 20° C. in Example 3 and Comparative Example 1. [Figure 8] 1 is a graph showing the capacity retention rates (%) at 40° C. in Example 3 and Comparative Example 1. [Figure 9]FIG. 1 is a diagram showing the ratio of the charge capacity at the end-of-charge voltage of 4.175 V to the charge capacity at the end-of-charge voltage of 4.25 V in Examples 3, 10, and 11, and Comparative Examples 4 and 5. [Figure 10] FIG. 1 is a diagram showing the ratio of the discharge capacity at the end of charge voltage of 4.175 V to the discharge capacity at the end of charge voltage of 4.25 V in Examples 3, 10, and 11 and Comparative Examples 4 and 5. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0017] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0018] <Method of manufacturing positive electrode active material> The method for producing a positive electrode active material of the present invention includes: (S1) preparing a positive electrode active material precursor containing nickel, cobalt, and manganese; (S2) mixing the positive electrode active material precursor and a lithium source and calcining the mixture to form a lithium transition metal oxide; and (S3) rinsing the lithium transition metal oxide with a washing solution, wherein the calcination is performed in an atmosphere having an oxygen concentration of 85% or more, the molar ratio (Li / M) of lithium (Li) in the lithium source to the total metal elements (M) in the positive electrode active material precursor is 1.03 to 1.05, and 50 to 110 parts by weight of the washing solution is used per 100 parts by weight of the lithium transition metal oxide.

[0019] In the present invention, the oxygen concentration conditions of the atmospheric air during the step of mixing the cathode active material precursor with a lithium source and then calcining the mixture are limited, the molar ratio (Li / M) of lithium (Li) in the lithium source to the total metal elements (M) of the cathode active material precursor is limited to a range of 1.03 to 1.05, and the content of the rinsing solution during rinsing is adjusted within an appropriate range. This results in a cathode active material that, when used in a secondary battery, exhibits excellent charge / discharge capacity under both end-of-charge voltage conditions of 4.2V to 4.275V and 4.1V to 4.175V, and thus has a high ratio of charge / discharge capacity under end-of-charge voltage conditions of 4.1V to 4.175V.

[0020] Each step will be explained in detail below.

[0021] Step (S1) A positive electrode active material precursor containing nickel, cobalt, and manganese is prepared.

[0022] The positive electrode active material precursor may be a high-nickel (High-Ni) positive electrode active material precursor having a nickel (Ni) content of 60 mol% or more of the total metal elements, and the nickel (Ni) content of the total metal elements may be 80 mol% or more. A lithium transition metal oxide formed using the high-nickel (High-Ni) positive electrode active material precursor having a nickel (Ni) content of 60 mol% or more of the total metal elements can ensure high capacity.

[0023] The positive electrode active material precursor used in the present invention may be an NCM-based compound containing nickel (Ni), cobalt (Co), and manganese (Mn), or an NCA-based compound containing nickel (Ni), cobalt (Co), and aluminum (Al), or may be a four-component positive electrode active material precursor that necessarily contains the four components nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al).

[0024] In terms of capacity, efficiency, and lifespan, NCM-based compounds containing nickel (Ni), cobalt (Co), and manganese (Mn) or four-component cathode active material precursors containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) are more preferred. When a cathode active material is prepared using the four-component cathode active material precursor, the stability of the cathode active material can be improved, and the output and capacity characteristics can be prevented from deteriorating compared to NCM / NCA cathode active materials, while the lifespan can be improved.

[0025] Step (S2) The positive electrode active material precursor and a lithium source are mixed and calcined to form a lithium transition metal oxide.

[0026] Here, the molar ratio (Li / M) of lithium (Li) in the lithium source to the total metal elements (M) in the positive electrode active material precursor is 1.03 to 1.05, preferably 1.035 to 1.045, or 1.037 to 1.043.

[0027] Conventionally, the molar ratio (Li / M) of lithium (Li) in the lithium source to the total metal elements (M) in the positive electrode active material precursor has generally been set in the range of approximately 1.0 to 1.1. However, in this case, there is a problem that the capacity at the end-of-charge voltage of 4.1 V to 4.175 V is relatively low compared to the capacity at the end-of-charge voltage of 4.2 V to 4.275 V, making it difficult to apply to various uses.

[0028] To address this issue, the present invention controls the molar ratio (Li / M) of the lithium (Li) source to the total metal elements (M) of the cathode active material precursor to 1.03-1.05. This is achieved by adding a sufficient amount of lithium so that the hexagonal (H2) to hexagonal (H3) phase transition during charging begins at a low voltage. As a result, the ratio of charge / discharge capacity at end-of-charge voltages of 4.1V-4.175V to charge / discharge capacity at end-of-charge voltages of 4.2V-4.275V is increased. At the same time, the upper limit of Li / M is limited to 1.05, preventing a decrease in charge / discharge capacity and average voltage at 4.2V-4.275V due to an excessive amount of lithium (Figure 5).

[0029] If the Li / M is less than 1.03, the phase transition potential is high, resulting in a problem of low charge / discharge capacity at the end-of-charge voltage of 4.1V to 4.175V. If the Li / M is more than 1.05, the proportion of Li occupying the Ni site is excessive, resulting in a problem of low charge / discharge capacity at the end-of-charge voltage of 4.2V to 4.275V.

[0030] As described above, the range of Li / M used in the manufacturing method of the present invention is specified so as to exhibit uniformly excellent charge / discharge characteristics at various end-of-charge voltages and also to achieve a high quantitative capacity value.

[0031] In the present invention, the firing is carried out in an atmosphere with an oxygen concentration of 85% or more, specifically, in an atmosphere of 85% to 95%, or 87% to 93%.

[0032] In the present invention, as described above, the molar ratio (Li / M) of the lithium source (Li) to the total metal elements (M) of the cathode active material precursor is controlled, and the oxygen concentration during calcination is limited to 85% or more, thereby increasing the Li / M ratio and further maximizing the effect of lowering the phase transition potential, thereby more effectively achieving the object of the present invention.

[0033] If the oxygen concentration is less than 85%, the phase transition potential is high, resulting in a problem of reduced capacity at a relatively low end-of-charge voltage (4.1V to 4.175V).

[0034] The molar ratio (Li / M) of lithium (Li) in the lithium source to all metal elements (M) in the positive electrode active material precursor is 1.035 to 1.045, and the firing can be carried out in an atmosphere with an oxygen concentration of more than 85% and less than 95%.

[0035] Furthermore, firing can be carried out for 5 to 30 hours in an oxygen atmosphere within the above range.

[0036] In the present invention, the firing may be carried out at 700 to 900° C., more preferably 700 to 850° C., or 730 to 750° C. During the firing, the temperature may be increased to the firing temperature at a rate of 2 to 10° C. / min, more preferably 3 to 7° C. / min.

[0037] In the present invention, the lithium source may be a 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 source may be LI2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, or a mixture of two or more thereof.

[0038] In the present invention, the lithium transition metal oxide may be a compound represented by the following Chemical Formula 1.

[0039] [Chemical formula 1] Li a Ni 1-(b+c+d) Co b Mn c Q dO 2+e

[0040] In the above Chemical Formula 1, Q is one or more selected from the group consisting of Al, Mg, V, Ti, and Zr; 1.0≦a≦1.3, 0 <b≦0.5、0<c≦0.5、0≦d≦0.1、0<b+c+d≦0.4、-0.1≦e≦1.0である。

[0041] Step (S3) The lithium transition metal oxide is washed with a water washing solution.

[0042] In the case of high-nickel (High-Ni) lithium composite transition metal oxides, the amount of lithium by-products present on the surface of the positive electrode active material in the form of LiOH and Li2CO3 increases, which can lead to gas generation and swelling problems. Therefore, a water washing process is performed to remove the remaining lithium by-products.

[0043] In addition, in order to properly remove residual lithium by-products and improve the physical properties of the lithium secondary battery, the washing solution may be used in an amount of 50 to 110 parts by weight based on 100 parts by weight of the lithium transition metal oxide, more specifically, 60 to 110 parts by weight based on 100 parts by weight of the lithium transition metal oxide.

[0044] If the content of the washing solution is outside the above range, for example, if the content of the washing solution is less than 50 parts by weight per 100 parts by weight of the lithium transition metal oxide, the residual lithium cannot be sufficiently washed away with water, and the lithium remaining on the surface of the lithium transition metal oxide when used in a secondary battery will result in a decrease in the charge / discharge capacity at an end-of-charge voltage of 4.2V to 4.275V due to the lithium remaining on the surface of the lithium transition metal oxide. If the content of the washing solution is more than 110 parts by weight per 100 parts by weight of the lithium transition metal oxide, the lithium on the surface of the lithium transition metal oxide will be excessively washed away with water, causing the internal lithium to migrate to the surface, resulting in a decrease in the charge / discharge capacity of the secondary battery at an end-of-charge voltage of 4.2V to 4.275V.

[0045] The washing step may be performed by adding the lithium transition metal oxide to a washing solution and stirring the solution.

[0046] The solvent of the washing solution may be deionized water, distilled water, or a combination thereof. In this case, lithium is easily dissolved, and residual lithium on the surface of the lithium transition metal oxide can be effectively removed.

[0047] The temperature during the water washing may be 30° C. or lower, preferably −10 to 30° C. or 0 to 20° C., and the water washing time may be 10 minutes to 1 hour, preferably 20 to 40 minutes. When the water washing temperature and water washing time satisfy the above ranges, lithium by-products can be effectively removed.

[0048] <Cathode active material> The positive electrode active material according to the present invention contains nickel, cobalt, and manganese, and is characterized in that the content of nickel among all metal elements is 60 mol % or more, and the value calculated by the following formula 1 is 90% to 100%.

[0049] [Formula 1] (1st discharge capacity) / (2nd discharge capacity)×100

[0050] In the formula 1, The first discharge capacity was measured by charging the battery in CC / CV mode at a constant current of 0.2C up to the first charge end voltage, and then discharging it in CC mode at a constant current of 0.2C down to 2.5V. The second discharge capacity was measured by charging the battery in CC / CV mode at a constant current of 0.2C up to the second charge cut-off voltage, and then discharging it in CC mode at a constant current of 0.2C down to 2.5V. Here, the first charge end voltage is 4.1V to 4.175V, and the second charge end voltage is 4.2V to 4.275V.

[0051] Furthermore, the value calculated by the following formula 2 can be further satisfied to be 90% to 100%.

[0052] [Formula 2] (1st charging capacity) / (2nd charging capacity) x 100

[0053] In the formula 2, The first charge capacity was measured by charging the battery in CC / CV mode at a constant current of 0.2C up to the first charge end voltage, and then discharging it in CC mode at a constant current of 0.2C down to 2.5V. The second charge capacity is measured by charging the battery in CC / CV mode at a constant current of 0.2C up to the second charge end voltage, and then discharging it in CC mode at a constant current of 0.2C down to 2.5V. Here, the first charge end voltage is 4.1V to 4.175V, and the second charge end voltage is 4.2V to 4.275V.

[0054] Furthermore, before measuring the first discharge capacity and the second discharge capacity, or before measuring the first charge capacity and the second charge capacity, a step of activating the secondary battery by charging and discharging may be performed first, and the charge cut-off voltage for activation may be the same as or different from the first charge cut-off voltage or the second charge cut-off voltage.

[0055] For example, the battery can be charged in CC / CV mode at a constant current of 0.2 C to a voltage of 4.2 V to 4.275 V, and then discharged in CC mode at a constant current of 0.2 C to 2.5 V to activate it, after which the first charge capacity and the second charge capacity can be measured.

[0056] As described above, the positive electrode active material according to the present invention is characterized by excellent charge / discharge capacity both under the condition of an end-of-charge voltage of 4.2 V to 4.275 V and the condition of an end-of-charge voltage of 4.1 V to 4.175 V, and in particular, the charge / discharge capacity does not decrease significantly even when the end-of-charge voltage is lowered. Therefore, the ratio of the charge / discharge capacity at the first end-of-charge voltage (4.1 V to 4.175 V) to the charge / discharge capacity at the second end-of-charge voltage (4.2 V to 4.275 V) is calculated as a high value, and the discharge capacity ratio expressed by Equation 1 is 90% to 100%, and the charge capacity ratio expressed by Equation 2 is 90% to 100%.

[0057] The positive electrode active material may include a lithium transition metal oxide represented by the following Chemical Formula 1:

[0058] [Chemical formula 1] Li a Ni 1-(b+c+d) Co b Mn c Q d O 2+e

[0059] The definition of Chemical Formula 1 is as described above.

[0060] <Positive electrode for lithium secondary battery and lithium secondary battery> The present invention also provides a positive electrode for a lithium secondary battery, which contains the positive electrode active material produced by the above-described method.

[0061] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector and including the above-described positive electrode active material.

[0062] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0063] The positive electrode active material layer may contain a conductive material and a binder in addition to the positive electrode active material.

[0064] In this case, the positive electrode active material may be included in an amount of 80 wt % to 99 wt %, more specifically, 85 wt % to 98 wt %, based on the total weight of the positive electrode active material layer. When included in this range, excellent capacity characteristics can be exhibited.

[0065] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material can be present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0066] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0067] The positive electrode may be fabricated by a conventional method for fabricating a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be fabricated by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode composite, which is then coated on a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0068] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent application to fabricate a positive electrode, taking into consideration the coating thickness of the slurry and manufacturing yield.

[0069] Alternatively, the positive electrode can be produced by casting the positive electrode mixture on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0070] The present invention also provides an electrochemical device including the positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0071] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is as described above, detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0072] The lithium secondary battery may further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0073] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0074] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0075] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0076] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0077] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0078] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0079] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, specifically 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powder such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0080] For example, the negative electrode active material layer can be produced by applying a negative electrode composite, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, onto a negative electrode current collector and drying the applied material. Alternatively, the negative electrode composite can be produced by casting the negative electrode composite onto a separate support, peeling it off from the support, and laminating the resulting film onto the negative electrode current collector.

[0081] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to ion movement in the electrolyte and excellent humidification ability for the electrolyte solution is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0082] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0083] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0084] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, 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, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred, as they have high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries. In this case, the cyclic carbonate and linear carbonate should be mixed in a volume ratio of about 1:1 to about 1:9, which allows the electrolyte to exhibit excellent performance.

[0085] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used at a concentration in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0086] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be included in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the total weight of the electrolyte.

[0087] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0088] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0089] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0090] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0091] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium- to large-sized battery module including a large number of battery cells.

[0092] [Example] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0093] Manufacturing of positive electrode active materials Example 1 Positive electrode active material precursor Ni 0.86 Co 0.1 Mn 0.02 Al 0.02The mixture was placed in a Henschel mixer (700 L) and mixed at 300 rpm at the center for 20 minutes so that the molar ratio (Li / M) of lithium (Li) in the lithium source LiOH to the total metal elements (M) in (OH)2 was 1.030. The mixed powder was placed in an alumina crucible, heated at a rate of 5°C / min, and fired at 790°C for 10 hours in an atmosphere with a 90% oxygen concentration to produce lithium transition metal oxide.

[0094] 300 g of the prepared lithium transition metal oxide was added to 240 mL of 10°C pure water (equivalent to 80 parts by weight of water per 100 parts by weight of lithium transition metal oxide), stirred for 30 minutes, washed with water, and filtered for 20 minutes. The filtered lithium transition metal oxide was dried in a vacuum oven at 130°C for 10 hours to prepare a cathode active material.

[0095] Examples 2 to 11, Comparative Examples 1 to 5 A positive electrode active material was produced in the same manner as in Example 1, except that the reaction conditions were changed as shown in Table 1 below.

[0096] [Table 1]

[0097] Lithium secondary battery manufacturing The prepared positive electrode active materials, carbon black conductive material, and PVdF binder were mixed in a weight ratio of 95:2.5:2.5 in N-methylpyrrolidone solvent to prepare a positive electrode mixture (viscosity: 5000 mPa s). This mixture was applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode.

[0098] On the other hand, lithium metal was used as the negative electrode.

[0099] An electrode assembly was fabricated by interposing a porous polyethylene separator between the cathode and anode fabricated as described above, and the electrode assembly was placed inside a case. An electrolyte solution was then injected into the case to fabricate a coin half cell lithium secondary battery. The electrolyte solution was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (EC / DMC / EMC mixed in a volume ratio of 3 / 4 / 3).

[0100] Experimental Example 1: Evaluation of charge / discharge capacity ratio Each lithium secondary battery cell was charged in CC / CV mode at 25°C for the first cycle at 0.2 C (0.005 C) until the charge cut-off voltage reached 4.25 V, and then discharged at a constant current of 0.2 C until the charge cut-off voltage reached 2.5 V. The second cycle was performed under the same conditions, with the charge cut-off voltage set to 4.175 V and the discharge cut-off voltage set to 2.5 V. The third cycle was performed under the same conditions, with the charge cut-off voltage set to 4.25 V and the discharge cut-off voltage set to 2.5 V.

[0101] Table 2 below shows the charge capacities and charge capacity ratios for the second and third cycles, and Table 3 shows the discharge capacities and discharge capacity ratios for the second and third cycles.

[0102] [Table 2]

[0103] [Table 3]

[0104] As shown in Tables 2 and 3 and FIGS. 1 to 4, the lithium secondary batteries of Examples 1 to 9 manufactured by the manufacturing method of the present invention had excellent charge-discharge capacities at the end-of-charge voltages of 4.25 V and 4.175 V, respectively, and it was confirmed that the charge-discharge capacity ratio was significantly improved compared to Comparative Example 1 in which the Li / M value was less than 1.03 and Comparative Example 3 in which the oxygen concentration in the firing conditions was less than 85%.

[0105] On the other hand, in the case of Comparative Example 2, where the Li / M value was greater than 1.05, an excessive amount of Li was added, so the charge / discharge capacities were all lower than those of the Examples, and it was found that the output characteristics themselves were reduced.

[0106] Meanwhile, referring to Comparative Examples 4 and 5, in which water was used in an amount outside the range of 50 to 110 parts by weight per 100 parts by weight of the positive electrode active material during the water washing process, it was confirmed that in Comparative Example 4, an excessively small amount of water was used during water washing, resulting in a high amount of residual lithium on the surface of the positive electrode active material, which acted as resistance, and thus the charge / discharge capacity ratio was low and deviated from 90%. In Comparative Example 5, an excessive amount of water was used during water washing, resulting in excessive washing of the surface lithium, which caused the lithium inside the positive electrode active material to migrate to the outside, resulting in a low charge / discharge capacity ratio.

[0107] Experimental Example 2: Evaluation of initial capacity The charge capacity and discharge capacity of the first cycle measured in Experimental Example 1 are summarized in Table 4 below.

[0108] [Table 4]

[0109] As in Table 4, it was confirmed that the examples all had excellent initial charge / discharge capacities, while the comparative example 2, in which the Li / M value was greater than 1.05, generally had a reduced initial charge / discharge capacity.

[0110] As described above, when the positive electrode active material produced according to the present invention is used, the ratio of the charge / discharge capacity at the end-of-charge voltage of 4.1V to 4.175V to the charge / discharge capacity at the end-of-charge voltage of 4.2V to 4.275V of the lithium secondary battery is high, and the initial charge / discharge capacity is also excellent.

[0111] Experimental example 3: Evaluation of room temperature DCIR (mohm) of secondary batteries The lithium secondary batteries of Example 3 and Comparative Example 1 were evaluated for DCIR characteristics at different SOCs, and the results are shown in FIG.

[0112] Specifically, the lithium secondary battery was charged and discharged twice at 25°C under 0.5C CC-CV charging conditions (voltage driving range: 3.0 to 4.2V, SOC 100%), and then charged under 0.5C CC-CV conditions, followed by discharging at 0.5C until SOC reached 10%, and the DCIR was calculated using the following formula.

[0113] Here, measurements were taken in SOC10 units from SOC100 to SOC10 range.

[0114] DCIR=(V0-V1) / I (V0 = voltage before pulse, V1 = voltage after pulse 10 seconds, I = applied current)

[0115] [Table 5]

[0116] As a result, it was confirmed that the lithium secondary batteries using the cathode active materials of the Examples according to the present invention had better room temperature DCIR characteristics than the Comparative Examples. In particular, the excellent DCIR characteristics of the Examples were even more pronounced at SOC 10% and SOC 100%.

[0117] Experimental example 4: Evaluation of life characteristics The life characteristics of the lithium secondary batteries of Example 3 and Comparative Example 1 were evaluated.

[0118] Specifically, charge and discharge were performed under the following conditions at 20° C., which was defined as the first cycle, and the cycle was repeated up to the 70th cycle to evaluate the capacity retention rate (%). The results are shown in FIG.

[0119] -Charging conditions (CP / CV): Charge end voltage 4.1V, 0.5CP, end current 0.005C -Discharge conditions (CP / CV): 0.5CP, 3.0V cut-off

[0120] The same experiment was performed at a temperature of 40°C, and the results are shown in Figure 8.

[0121] As shown in Figures 7 and 8, in the case of the examples, it was found that the decrease in capacity due to repeated cycles was suppressed and the life characteristics were improved compared to the comparative examples, and it was confirmed that such effects were observed under various temperature conditions.

Claims

1. (S1) preparing a positive electrode active material precursor containing nickel, cobalt, and manganese; (S2) mixing the positive electrode active material precursor and a lithium source and calcining the mixture to form a lithium transition metal oxide; (S3) washing the lithium transition metal oxide with a water washing solution; The firing is carried out in an atmosphere having an oxygen concentration of 85% or more, a molar ratio (Li / M) of lithium (Li) of the lithium source to all metal elements (M) of the positive electrode active material precursor is 1.03 to 1.05; The method for producing a positive electrode active material, wherein the washing solution is used in an amount of 60 to 100 parts by weight per 100 parts by weight of the lithium transition metal oxide.

2. 2. The method for producing a positive electrode active material according to claim 1, wherein a molar ratio (Li / M) of lithium (Li) of the lithium source to all metal elements (M) of the positive electrode active material precursor is 1.035 to 1.

045.

3. The method for producing a positive electrode active material according to claim 1, wherein the firing is carried out at 700°C to 900°C.

4. The method for producing a positive electrode active material according to claim 1 , wherein the positive electrode active material precursor has a nickel content of 60 mol % or more of all metal elements.

5. The method for producing a positive electrode active material according to claim 1 , wherein the lithium transition metal oxide is a compound represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ni １－（ｂ＋ｃ＋ｄ） Co ｂ Mn ｃ Q ｄ O ２＋ｅ In the above Chemical Formula 1, Q is at least one element selected from the group consisting of Al, Mg, V, Ti, and Zr; 1.0≦a≦1.3, 0<b≦0.5, 0<c≦0.5, 0≦d≦0.1, 0<b+c+d≦0.4, −0.1≦e≦1.0.

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