Positive electrode active material for lithium secondary battery, method for manufacturing the same, and lithium secondary battery including the same

Abstract

To provide a positive electrode active material for a lithium secondary battery that has an excellent effect of improving high-temperature life and provides an effect of suppressing ignition during overcharging by increasing the amount of gas generated during overcharging at 4.8 V or more.SOLUTION: A positive electrode active material for a lithium secondary battery includes a nickel-based active material, a cobalt-containing coating layer on a surface of the nickel-based active material, and a boron-containing coating layer on a surface of the cobalt-containing coating layer, the positive electrode active material has a specific surface area of 0.45 m2 / g to 0.60 m2 / g.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

Background Art

[0002] In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. As a result, research and development for improving the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolytic solution, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted and desorbed at the positive electrode and the negative electrode.

[0004] As the positive electrode active material of a lithium secondary battery, a nickel-based active material may be used. Since the performance of the nickel-based active material may deteriorate due to growth between particles and side reactions with the electrolytic solution during the charge and discharge process, improvement thereof is required.

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to one embodiment, there is provided a positive electrode active material for a lithium secondary battery, which has an excellent high-temperature life improvement effect and provides an ignition suppression effect during overcharge by increasing the gas generation amount during overcharge of 4.8 V or more.

[0006] According to another embodiment, there is provided a positive electrode active material for a lithium secondary battery, which provides an increase in charge and discharge efficiency, an improvement in capacity, suppression of side reactions such as gas generation, and a reduction in resistance.

[0007] According to still other embodiments, there is provided a method for manufacturing a positive electrode active material for a lithium secondary battery as described above.

[0008] According to still other embodiments, there is provided a lithium secondary battery including the positive electrode active material for a lithium secondary battery as described above.

Means for Solving the Problems

[0009] According to one embodiment, the positive electrode active material for a lithium secondary battery includes a nickel-based active material; a cobalt-containing coating layer on the surface of the nickel-based active material; and a boron-containing coating layer on the surface of the cobalt-containing coating layer, and the positive electrode active material for a lithium secondary battery has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g.

[0010] According to another embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery includes manufacturing a first positive electrode active material in which a cobalt compound is wet-coated on the surface of a nickel-based active material from a mixture including the nickel-based active material, a cobalt compound, and a solvent; manufacturing a second positive electrode active material by dry-coating a boron compound on the surface of the first positive electrode active material; and manufacturing a positive electrode active material for a lithium secondary battery by heat-treating the second positive electrode active material at 700°C to 750°C, and the boron compound is dry-coated so as to provide 0.25 mol% to 0.5 mol% of boron with respect to the total content of transition metal elements excluding lithium in the nickel-based active material.

[0011] According to still another embodiment, a lithium secondary battery contains a positive electrode including the positive electrode active material for a lithium secondary battery; a negative electrode; and an electrolytic solution disposed between them.

Effects of the Invention

[0012] The positive electrode active material for a lithium secondary battery according to one embodiment is excellent in the effect of improving high-temperature life, and when overcharged at 4.8 V or higher, the amount of gas generated increases to operate an overcharge prevention component, thereby providing an overcharge ignition suppression effect. Further, the positive electrode active material for a lithium secondary battery according to one embodiment can provide an increase in charge-discharge efficiency, an improvement in capacity, suppression of side reactions such as gas generation, and a reduction in resistance.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

[0014] In FIGS. 7 to 12, the solid line represents Example 1, the dotted line represents Example 2, the one-dot chain line represents Comparative Example 1, and the two-dot chain line represents Comparative Example 2.

Mode for Carrying Out the Invention

[0015] Hereinafter, specific embodiments will be described in detail so that those having ordinary knowledge in this technical field can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0016] The terms used herein are merely for explaining exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly has a different meaning.

[0017] Here, "these combinations" can mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, etc.

[0018] Here, terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude in advance the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0019] In the drawings, the thickness is enlarged to clearly show many layers and regions, and the same drawing reference numerals are given to similar parts throughout the specification. When a part such as a layer, film, region, plate, etc. is "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there are further other parts in between. Conversely, when one part is "directly on" another part, it means that there are no other parts in between.

[0020] Also, here, the "layer" includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a part of the surface.

[0021] In this specification, the "specific surface area" may be a value measured by the BET measurement method.

[0022] In this specification, "X to Y" may mean "X ≤ and ≤ Y".

[0023] As the high-capacity positive electrode material, a nickel-based active material with a high nickel content, for example, a nickel-based active material with a nickel content of 50 mol% or more, 70 mol% or more, 80 mol% or more is used.

[0024] The nickel-based active material may be produced, for example, by the co-precipitation method. According to this production method, doping elements such as transition metal elements, for example, cobalt (Co) and / or aluminum (Al), manganese (Mn), zirconium (Zr), titanium (Ti), magnesium (Mg), etc. can be uniformly distributed in the main component nickel. The nickel-based active material obtained by such a production method is obtained in the form of secondary particles.

[0025] In the form of secondary particles, cracks can grow in the secondary particles during the repeated charge and discharge process, and side reactions with the electrolyte can occur. Therefore, the life of the lithium secondary battery equipped with the positive electrode containing the nickel-based active material may be reduced. In particular, the nickel-based active material can also reduce the life at high temperatures. Therefore, a nickel-based active material that can improve the life at high temperatures may be preferred.

[0026] On the other hand, even if it operates stably at a general driving voltage, for example, 2.8V or more and less than 4.8V, at a high voltage of 4.8V or more, for example, 5.0V or more, gas is generated by a chemical reaction during overcharging, and it is necessary to operate the fire prevention component during overcharging. As the fire prevention component during overcharging, there may be those that operate by internal pressure such as a current interrupt device (CID) and a vent assembly. The fire prevention component during overcharging is one of the safety devices of the lithium secondary battery and can significantly reduce the possibility of ignition of the lithium secondary battery.

[0027] Therefore, the inventors of the present invention formed a cobalt-containing coating layer and a boron-containing coating layer on the surface of the nickel-based active material to provide a positive electrode active material that can improve the life characteristics at high temperatures, generate gas during overcharging at 4.8V or more, and operate the fire prevention component. The specific surface area of the outermost surface of the positive electrode active material is 0.45 m 2 / g to 0.60 m 2By controlling it to / g, the life characteristics at high temperatures described above can be improved, gas can be generated during overcharging at 4.8 V or higher, and the ignition prevention component can be operated, so the safety of the lithium secondary battery can be enhanced.

[0028] According to one embodiment, the positive electrode active material for a lithium secondary battery includes a nickel-based active material; a cobalt-containing coating layer on the surface of the nickel-based active material; and a boron-containing coating layer on the surface of the cobalt-containing coating layer. The outermost surface of the positive electrode active material has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g.

[0029] The positive electrode active material having a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g can include a coating layer that is an optimal combination of boron and cobalt. When the specific surface area exceeds 0.60 m 2 / g, while the cobalt-containing coating layer is formed more on the surface of the secondary particles than on the grain boundaries of the primary particles, side reaction products are formed during the life, and it may become vulnerable to life improvement. When the specific surface area is less than 0.45 m 2 / g, there is almost no boron-containing coating layer, which may be disadvantageous for gas generation in the overcharge voltage range (4.8 V or higher). The inventor has confirmed that the positive electrode active material having both the effect of improving the life characteristics at high temperatures and the effect of operating the ignition prevention component during overcharging has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g.

[0030] Also, when the specific surface area of the outermost surface of the positive electrode active material is less than 0.45 m 2 / g, the increase in charge-discharge efficiency and the effect of improving the life at high temperatures become negligible, and since the gas generation amount during overcharging is low, the ignition prevention suppression component may not operate reliably in some cases. When the specific surface area of the outermost surface of the positive electrode active material exceeds 0.60 m 2 / g, the charge-discharge capacity and efficiency may become low. When the specific surface area of the outermost surface of the positive electrode active material is 0.60 m 2The effect of improving the lifespan at high temperatures may be negligible compared to the case of / g.

[0031] According to one embodiment, the nickel-based active material may be secondary particles formed by aggregating primary particles by physical and / or chemical methods.

[0032] According to one embodiment, the nickel-based active material may be, for example, a nickel-based active material represented by the following Chemical Formula 1: [Chemical Formula 1] Li a (Ni 1-x-y-z Co x M y M’ z )O 2-δ (In Chemical Formula 1, M is one or more elements selected from Mn and Al, M’ is one or two or more elements selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), 0.95 ≦ a ≦ 1.3, x ≦ (1 - x - y - z), y ≦ (1 - x - y - z), z ≦ (1 - x - y - z), 0 < x < 1, 0 ≦ y < 1, 0 ≦ z < 1, and 1.98 ≦ 2 - δ ≦ 2).

[0033] In the nickel-based active material of Chemical Formula 1, the content of nickel is larger than the contents of cobalt, M, and M’.

[0034] According to one embodiment, in Chemical Formula 1, 0.3 ≦ 1 - x - y - z ≦ 0.99, 0.5 < 1 - x - y - z ≦ 0.99, 0.6 < 1 - x - y - z ≦ 0.99, 0.8 ≦ 1 - x - y - z ≦ 0.99, or 0.8 ≦ 1 - x - y - z ≦ 0.95.

[0035] The nickel-based active material of Chemical Formula 1 may be the nickel-based active material of the following Chemical Formula 1-1. In Chemical Formula 1-1, 0.001 ≦ x ≦ 0.5, for example, 0.001 ≦ x ≦ 0.334, 0.001 ≦ y ≦ 0.5, for example, 0.001 ≦ y ≦ 0.334, 0 ≦ z < 1, for example, z is 0. [Chemical Formula 1-1] Li a (Ni 1-x-y-z Co x Al y M z )O 2-δ (In Chemical Formula 1-1, M is one or more elements selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and manganese (Mn), 0.95 ≦ a ≦ 1.3, x ≦ (1 - x - y - z), y ≦ (1 - x - y - z), z ≦ (1 - x - y - z), 0 < x < 1, 0 ≦ y < 1, 0 ≦ z < 1, and 1.98 ≦ 2 - δ ≦ 2.) In Chemical Formula 1-1, 0.3 ≦ 1 - x - y - z ≦ 0.99, 0.5 < 1 - x - y - z ≦ 0.99, 0.6 < 1 - x - y - z ≦ 0.99, 0.8 ≦ 1 - x - y - z ≦ 0.99, or 0.8 ≦ 1 - x - y - z ≦ 0.95. And in Chemical Formula 2-1, 0.001 ≦ x ≦ 0.5, for example, 0.001 ≦ x ≦ 0.334, 0.001 ≦ y ≦ 0.5, for example, 0.001 ≦ y ≦ 0.334, 0 ≦ z < 1, for example, z is 0.)

[0036] According to one embodiment, the nickel-based active material is Li 1.01 Ni 0.8 Co 0.1 Al 0.1 O2, Li 1.01 Ni 0.8 Co 0.05 Al 0.15 O2, Li 1.01 Ni 0.8 Co 0.15 Al 0.05 O2, LiNi 0.95 Co 0.04 Al0.01 It may be O2 or a combination thereof.

[0037] According to one embodiment, the nickel-based active material can include one or more of (i) first secondary particles, (ii) single particles, and (iii) particles having a single crystal structure. Here, (i) the first secondary particles are larger than the particles (iii) having a single crystal structure.

[0038] For example, the nickel-based active material may be a mixture of (i) first secondary particles and (iii) particles having a single crystal structure. According to one embodiment, among 100 parts by weight of the mixture, (i) the first secondary particles may be included in an amount of 60 to 90 parts by weight, for example, 60 to 80 parts by weight, and (iii) the particles having a single crystal structure may be included in an amount of 10 to 40 parts by weight, for example, 20 to 40 parts by weight.

[0039] The first secondary particles may be secondary particles formed by aggregation of primary particles having a size of 1 μm or less physically and / or chemically, and having a size of 13 to 20 μm. In the above size range, there may be an effect of maximizing the electrode density. For example, the size of the first secondary particles may be 14 to 18 μm, or 14 to 17 μm.

[0040] In the first secondary particles, the primary particles have an average particle size of 0.01 to 1 μm, 0.02 to 0.8 μm, 0.03 to 0.5 μm, 0.04 to 0.1 μm, or 0.05 to 0.07 μm (50 nm to 70 nm). According to one embodiment, the first secondary particles may be secondary particles having a polycrystalline structure. As used herein, "polycrystalline" means a form in which a large number of crystal particles are aggregated.

[0041] As used herein, "size" refers to the average diameter when the nickel-based active material particles are spherical. When the nickel-based active material particles are not spherical, "size" refers to the maximum value among the lengths of the major axes obtained from the cross-section of the particles.

[0042] The average particle size can be measured using a PSD (Particle Size Distribution) measuring instrument or through SEM or the like. Unless otherwise defined, the average particle size means the diameter (D50) of the particles at which the cumulative volume is 50% by volume in the particle size distribution. And the length of the major axis can be measured through SEM or the like.

[0043] In this specification, "single particle" means a structure in which each particle exists as an independent phase that is not mutually aggregated morphologically. Examples of particle structures contrasted with single particles include structures in which small particles (primary particles) are physically and / or chemically aggregated to form a relatively large particle form (secondary particles).

[0044] In this specification, "single crystal" is a form in which a number of crystal particles are not aggregated, but are separated and / or dispersed from each other so as to form independent and / or distinct phases for each particle, and forms in which less than 10 particles are attached to each other may also be included.

[0045] (ii) Single particles or (iii) particles having a single crystal structure can each have a size of 1 μm to 7 μm. According to one embodiment, the nickel-based active material can include single particles containing primary particles having a size of 1 μm to 7 μm. According to other embodiments, the nickel-based active material can include second secondary particles of single crystals having a size of 1 μm to 7 μm.

[0046] According to one embodiment, the nickel-based active material can have a size of 10 μm to 20 μm.

[0047] The positive electrode active material according to one embodiment includes: a cobalt-containing coating layer formed on the surface of the secondary particles; and a boron-containing coating layer formed on the cobalt-containing coating layer.

[0048] The cobalt-containing coating layer can improve the thermal stability at high temperatures by protecting the nickel-based active material.

[0049] According to one embodiment, the cobalt-containing coating layer may also be present on the surface of the secondary particles and at the grain boundaries (surfaces) of the primary particles constituting the secondary particles. This cobalt-containing coating layer can prevent the generation of cracks in the secondary particles at high temperatures, and even if cracks occur, it can suppress side reactions caused by the cracks and improve the lifespan.

[0050] According to one embodiment, the cobalt-containing coating layer may be composed of a lithium-cobalt compound.

[0051] According to one embodiment, the cobalt-containing coating layer may have a thickness of 100 nm or less, for example, 1 nm to 100 nm, for example, 1 nm to 50 nm, for example, 5 nm to 50 nm. When within the said range, the effect of improving the stability of the positive electrode active material becomes excellent.

[0052] The boron-containing coating layer can reduce the resistance and increase the charge-discharge efficiency by improving the conductivity of the nickel-based active material.

[0053] According to one embodiment, the boron-containing coating layer may be formed integrally with the cobalt-containing coating layer. Here, "formed integrally" means that a cobalt compound is wet-coated on the surface of the nickel-based active material, and then a boron compound is dry-coated, and after that, heat treatment is performed at 700°C to 750°C, whereby the cobalt-containing coating layer and the boron-containing coating layer are formed simultaneously.

[0054] According to one embodiment, the boron-containing coating layer may be a separate layer from the cobalt-containing coating layer.

[0055] According to one embodiment, the boron-containing coating layer may be composed of a lithium-boron compound.

[0056] According to one embodiment, the boron-containing coating layer may have a thickness of 100 nm or less, for example, 1 nm to 100 nm, for example, 1 nm to 50 nm, for example, 5 nm to 50 nm. When it is within the above range, the effect of improving the stability of the positive electrode active material is excellent.

[0057] The nickel content in the positive electrode active material may be, for example, 70 mol% or more, for example, 70 mol% to 95 mol%, for example, 80 mol% to 95 mol%.

[0058] According to one embodiment, 0.45 m 2 / g to 0.60 m 2 The positive electrode active material having a specific surface area of / g may be manufactured by the method for manufacturing a positive electrode active material described below.

[0059] Method for manufacturing a positive electrode active material for a lithium secondary battery

[0060] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery will be described.

[0061] The manufacturing method includes a step of manufacturing a first positive electrode active material in which a cobalt compound is wet-coated on the surface of the nickel-based active material from a mixture containing the nickel-based active material, the cobalt compound, and a solvent; a step of manufacturing a second positive electrode active material by dry-coating a boron compound on the surface of the first positive electrode active material; and a step of manufacturing a positive electrode active material for a lithium secondary battery by heat-treating the second positive electrode active material at 700°C to 750°C, and the boron compound is dry-coated so as to provide 0.25 mol% to 0.5 mol% of boron with respect to the total content of transition metal elements excluding lithium in the nickel-based active material.

[0062] (1) First, a mixture is prepared by mixing a nickel-based active material, a cobalt compound, and a solvent. The nickel-based active material may be a compound represented by the above Chemical Formula 1.

[0063] The cobalt compound may be, for example, cobalt hydroxide, cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt carbonate, cobalt citrate, cobalt acetate, or a combination thereof.

[0064] The cobalt compound may be included in the mixture so as to provide 1 mol% to 3 mol% of cobalt with respect to the total content of transition metals excluding lithium among the nickel-based active materials. The content of 1 mol% to 3 mol% of cobalt can facilitate the production of the positive electrode active material having the above-described specific surface area range at the coating amount of the boron compound described below and the heat treatment temperature described below.

[0065] Any solvent that can dissolve or disperse the nickel-based active material and the cobalt compound can be used. For example, it may be distilled water, ethanol, methanol, isopropanol, butanol, pentanol, or a combination thereof, or may be an aqueous solvent such as distilled water.

[0066] (2) Next, a first positive electrode active material in which a cobalt compound is wet-coated on the surface of the nickel-based active material is produced. The wet coating can be performed by mixing a composition containing the nickel-based active material, the cobalt compound, and the solvent with each other.

[0067] (3) Next, a second positive electrode active material is produced by dry-coating a boron compound on the surface of the first positive electrode active material. The dry coating can be performed by a step of mixing the first positive electrode active material and the boron compound.

[0068] The boron compound may be boron trioxide (B2O3), sodium borohydride (NaBH4), sodium cyanoborohydride (NaCNBH3), sodium acetate cyanoborohydride (NaBH3OAc), or a mixture thereof.

[0069] The boron compound is added so as to provide 0.25 mol% to 0.5 mol% of boron based on the total content of transition metal elements excluding lithium in the nickel-based active material, and is dry-coated.

[0070] When the boron content is less than 0.25 mol%, the effect of improving the life characteristics at high temperature becomes negligible, and the amount of gas generated during overcharge is extremely low, so that the ignition prevention component cannot operate reliably. When the boron content exceeds 0.5 mol%, the effect of improving the life characteristics at high temperature becomes negligible, and the resistance increases due to the excessive boron content in the boron-containing coating layer, and the charge-discharge capacity and efficiency may be low.

[0071] (4) A positive electrode active material for a lithium secondary battery is manufactured by heat-treating the second positive electrode active material at 700°C to 750°C. In this temperature range, the manufacture of the positive electrode active material having the specific surface area may be facilitated.

[0072] Lithium secondary battery

[0073] A lithium secondary battery according to an embodiment includes a positive electrode including the positive electrode active material for a lithium secondary battery; a negative electrode; and an electrolytic solution.

[0074] The positive electrode may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material and may further include a binder and / or a conductive material.

[0075] As an example, the positive electrode may further include an additive that can serve as a sacrificial positive electrode.

[0076] The content of the positive electrode active material may be 90 wt% to 99.5 wt% based on 100 wt% of the positive electrode active material layer, and the contents of the binder and the conductive material may be 0.5 wt% to 5 wt% respectively based on 100 wt% of the positive electrode active material layer.

[0077] The positive electrode active material layer contains a positive electrode active material for a lithium secondary battery according to one embodiment.

[0078] The positive electrode active material layer may further contain a positive electrode active material different from the positive electrode active material for a lithium secondary battery according to one embodiment.

[0079] As the different positive electrode active materials according to one embodiment, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof and lithium can be used.

[0080] The composite oxide may be a lithium transition metal composite oxide. Specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0081] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni b Co cL 1 d G e O2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0 ≤ e ≤ 0.1); Li a NiG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4(0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); Li a FePO4(0.90 ≤ a ≤ 1.8).

[0082] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al, or a combination thereof.

[0083] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the content of nickel with respect to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. Since the high-nickel positive electrode active material can achieve a high capacity, it can be applied to high-capacity and high-density lithium secondary batteries.

[0084] The binder serves to well adhere the positive electrode active materials to each other and also to well adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0085] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material that does not cause a chemical change and is an electron conductive material can be used. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0086] Al can be used as the current collector, but it is not limited thereto.

[0087] The negative electrode includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or a conductive material.

[0088] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0089] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0090] The material capable of reversibly intercalating / deintercalating the lithium ions can include, as a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon can include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon can include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0091] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0092] As the material capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), an Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, an Sn-based alloy, or a combination thereof.

[0093] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface thereof. For example, it may include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0094] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0095] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used by being mixed with a carbon-based negative electrode active material.

[0096] The binder serves to well adhere each negative electrode active material particle to each other and also well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0097] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0098] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0099] When using an aqueous binder as the negative electrode binder, it may further contain a cellulose-based compound capable of imparting viscosity. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used.

[0100] The dry binder is a polymer substance capable of being fibrillated, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0101] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any material that does not cause a chemical change and is an electron conductive material can be used. Specific examples include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0102] As the negative electrode current collector, it is possible to use one selected from a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0103] The electrolytic solution contains a non-aqueous organic solvent and a lithium salt.

[0104] The non-aqueous organic solvent serves as a medium through which each ion involved in the electrochemical reaction of the battery can move.

[0105] The non-aqueous organic solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, or a combination thereof.

[0106] As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used.

[0107] As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. may be used.

[0108] As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Also, as the ketone-based solvent, cyclohexanone, etc. may be used. As the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolane-based solvents, etc. may be used.

[0109] The non-aqueous organic solvent can be used alone or in a mixture of two or more.

[0110] Also, when using a carbonate-based solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed at a volume ratio of 1:1 to 1:9.

[0111] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery, enables the basic operation of a lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts are LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1(where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB), and may contain one or more selected therefrom.

[0112] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0113] The separator may include a porous substrate and a coating layer located on one or both surfaces of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0114] The porous substrate may be a polymer selected from any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a polymer film formed of a copolymer or mixture of two or more of these.

[0115] The organic substance can include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer. The inorganic substance can include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0116] The organic substance and the inorganic substance can be present as being mixed in one coating layer, or can be present in a form in which a coating layer containing the organic substance and a coating layer containing the inorganic substance are laminated.

[0117] The lithium secondary battery may be classified into a cylindrical type, a prismatic type, a pouch type, a coin type, etc. according to its form. FIGS. 1 to 4 are schematic views showing a lithium secondary battery according to an embodiment. It can be said that FIG. 1 is a cylindrical type, FIG. 2 is a prismatic type, and FIGS. 3 and 4 are pouch type battery forms. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolytic solution (not shown). The lithium secondary battery 100 can include a sealing member 60 for sealing the case 50 as shown in FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 can include electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for guiding the current formed by the electrode assembly 40 to the outside.

[0118] The lithium secondary battery according to an embodiment of the present invention is applicable to automobiles, mobile phones, and / or various forms of electrical devices, etc., but the present invention is not limited thereto.

Examples

[0119] The following will be described in more detail through examples and comparative examples. However, the examples are merely for illustration purposes, and the present invention is not limited thereto.

[0120] Example 1: Manufacture of a positive electrode active material for a lithium secondary battery (1) Al2(SO4)3(H2O), which is an aluminum precursor 18 was mixed with NaOH, NH4OH, and water to produce an aqueous solution of the aluminum precursor.

[0121] Separately, NiSO4(H2O)6, which is a nickel precursor, and CoSO4(H2O)7, which is a cobalt precursor, were each mixed with water to obtain an aqueous solution of the nickel precursor and an aqueous solution of the cobalt precursor.

[0122] The aqueous solution of the aluminum precursor was placed in a reactor, and the aqueous solutions of the nickel precursor and the cobalt precursor were dropped into the reactor to obtain a reaction mixture, and stirring of the reaction mixture was carried out for 10 to 20 hours. In the reaction mixture, the contents of the nickel precursor, the cobalt precursor, and the aluminum precursor were stoichiometrically controlled so that the mixing ratio of nickel, cobalt, and aluminum was 95:4:1 in molar ratio.

[0123] An aqueous solution of sodium hydroxide was dropped into the reaction mixture to adjust the pH of the reaction mixture to 10 to 12. The obtained precipitate was filtered, washed with water, and the resulting product was vacuum dried at 100 °C to produce Ni 0.95 Co 0.04 Al 0.01 O2(OH)2 powder.

[0124] The nickel cobalt aluminum hydroxide and lithium hydroxide (LiOH), which is a lithium precursor, were mixed in a mortar and then placed in a furnace, and primary heat treatment was carried out at 750 °C for 20 hours while flowing O2 to produce a nickel-based active material. The contents of the nickel cobalt aluminum hydroxide and the lithium precursor were controlled so that the mixing ratio of the transition metal and lithium was 1:1.03.

[0125] The manufactured nickel-based active material is NCA (LiNi 0.95 Co 0.04 Al 0.01 O2) having a first secondary particle state, and the average particle diameter of the first secondary particles is 14 μm.

[0126] (2) While converting the stirring time of the reaction mixture for obtaining nickel cobalt aluminum hydroxide to 30 hours, the size of the precursor was controlled. Except that the primary heat treatment was carried out by converting to 850 °C instead of 750 °C and then heat treated at 750 °C through a pulverization process, it was carried out in the same manner as above to produce single crystal particle NCA (LiNi 0.95 Co 0.04 Al 0.01 O2), and the average particle diameter of the single crystal particles is 3 μm to 4 μm.

[0127] (3) A nickel-based active material was produced by mixing 70 parts by weight of the first secondary particles and 30 parts by weight of the single crystal particles out of a total of 100 parts by weight of the first secondary particles and the single crystal particles.

[0128] (4) The obtained nickel-based active material was mixed with cobalt hydroxide (Co(OH)2) as a cobalt compound and water as a solvent to obtain a composition for a positive electrode active material containing a nickel-based active material in which the cobalt compound was wet-coated on the surface of the nickel-based active material. The content of cobalt hydroxide was added so that the content of cobalt was 3 mol% with respect to the total content of transition metal elements excluding lithium in the nickel-based active material produced in (3).

[0129] (5) Subsequently, B2O3 was added to the composition as a boron compound under a nitrogen gas atmosphere, and then mixed at 25°C for 2 hours. The boron compound was dry-coated on the surface of the cobalt compound-wet-coated nickel-based active material, and then subjected to a secondary heat treatment at 725°C for 12 hours to obtain the target positive electrode active material. The content of the boron compound was added such that the boron content was 0.25 mol% with respect to the total content of the transition metal elements excluding lithium in the nickel-based active material produced in (3).

[0130] Example 2: Manufacture of a positive electrode active material The positive electrode active material was produced in the same manner as in Example 1, except that the content of the boron compound in (5) of Example 1 was added such that the boron content was 0.5 mol% with respect to the total content of the transition metal elements excluding lithium in the nickel-based active material produced in (3).

[0131] Comparative Example 1: Manufacture of a positive electrode active material (1) to (4) of Example 1 were carried out in the same manner. Thereafter, a positive electrode active material was obtained by performing a secondary heat treatment at 725°C for 12 hours.

[0132] Comparative Example 2: Manufacture of a positive electrode active material The positive electrode active material was produced in the same manner as in Example 1, except that the content of the boron compound in Example 1 was added such that the boron content was 0.75 mol% with respect to the total content of the transition metal elements excluding lithium in the nickel-based active material produced in (3).

[0133] (Manufacture of Lithium Secondary Battery) A lithium secondary battery was manufactured as follows using the positive electrode active material obtained in the example or comparative example as the positive electrode active material.

[0134] Using a mixer, air bubbles were removed from a mixture of a positive electrode active material, carbon black as a conductive material, polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a solvent to produce a slurry for forming a uniformly dispersed positive electrode active material layer. The mixing weight ratio of the positive electrode active material, carbon black, and polyvinylidene fluoride is 97.7:1.0:1.3 based on a total of 100 parts by weight, and the content of the solvent is about 50 parts by weight with respect to 90 parts by weight of the positive electrode active material.

[0135] The slurry produced by the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, and after drying this at 135 °C for 3 hours or more, a positive electrode was produced through a rolling and vacuum drying process.

[0136] Graphite powder (japan carbon), which is a negative electrode active material, was mixed with a mixture of SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) in a weight ratio of 1:1 in a weight ratio of 98:2 to prepare a slurry for a negative electrode active material layer.

[0137] The prepared slurry for the negative electrode active material layer was coated on a copper foil current collector with a thickness of 8 μm at a level of 19.5 mg / cm 2 After the coated electrode plate was dried at 100 °C for 1 hour or more, it was rolled to produce a negative electrode with a combined agent density of 1.60 g / cm 3

[0138] Using the above positive and negative electrodes, a polyethylene separator (separator, STAR 20, Asahi) was used as the separator, and as the electrolyte, a mixture of EC (ethylene carbonate):EMC (ethyl methyl carbonate):DMC (dimethyl carbonate) (volume ratio 2:4:4) in which 1.15 M LiPF6 was dissolved was used to produce a lithium secondary battery having a capacity of 30 mAh.

[0139] Evaluation Example 1: Scanning electron microscope (FE-SEM) The cross-section of the positive electrode manufactured using the positive electrode active material produced in Example 1 was measured by the SEM method, and the results are shown in FIG. 5. Then, FIG. 6 shows the results of magnifying the edge portion (the portion surrounded by the square) of the positive electrode active material in FIG. 5 by SEM.

[0140] As shown in FIG. 5, it can be confirmed that the positive electrode active material produced in Example 1 has a coating material uniformly coated on the nickel-based active material.

[0141] As shown in FIG. 6, the bright-colored portion indicates cobalt, and it can be confirmed that cobalt is uniformly coated on the grain boundaries of the primary particles of the nickel-based active material.

[0142] Evaluation Example 2: Specific surface area of the positive electrode active material The specific surface area of the positive electrode active materials produced in the examples and comparative examples was measured by the BET measurement method, and the results are shown in Table 1 below. As shown in Table 1 below, the positive electrode active materials of the examples coated with 0.25 mol% and 0.5 mol% of boron with respect to 3 mol% of cobalt have a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g. However, in the comparative examples where boron is not coated or boron is coated at 0.75 mol% with respect to 3 mol% of cobalt, it can be confirmed that the specific surface area deviates from 0.45 m 2 / g to 0.60 m 2 / g.

[0143] Evaluation Example 3: Charge capacity, discharge capacity and efficiency For the lithium secondary batteries produced in the examples and comparative examples, charging was performed at a constant current of 25 °C and 0.2C from 2.8V to the upper limit voltage of 4.2V, and charging was continued until it dropped to 0.05C, which is the end condition, under constant voltage conditions. Then, discharging was performed at 0.2C until the discharge cut-off voltage of 2.8V, and the initial discharge capacity was measured. At this time, the ratio of the discharge capacity to the charge capacity was calculated as the efficiency, and the results are shown in Table 1 below.

[0144] As shown in Table 1 below, in the examples where the positive electrode active material has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g, it can be confirmed that the efficiency is significantly improved compared to the comparative examples.

[0145] Evaluation Example 4: High temperature life For the lithium secondary batteries of the examples and comparative examples, charging was performed at a constant current of 45 °C and 0.2 C from 2.8 V to the upper limit voltage of 4.2 V, and then charging was continued at a constant voltage until the current dropped to 0.05 C, which is the end condition, while maintaining 4.2 V under the constant voltage condition. Subsequently, during discharge, discharge was performed at a constant current of 0.2 C until the voltage reached 2.8 V. (Formation stage)

[0146] For the lithium secondary battery that has undergone the above formation stage, charging was performed at a constant current of 45 °C and 1 C from 2.8 V until the voltage reached 4.2 V, and then charging was continued at a constant voltage until the current became 0.05 C while maintaining 4.2 V. Subsequently, during discharge, a cycle of discharging at a constant current of 1 C until the voltage reached 2.8 V was repeated 50 times.

[0147] The results are shown in FIG. 7. As shown in FIG. 7, in the examples where the positive electrode active material has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g, it can be confirmed that the high-temperature life is significantly improved compared to the comparative examples. In particular, the positive electrode active material of the examples with a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g shows a significantly improved high-temperature life compared to Comparative Example 1 with a specific surface area of 0.41 m 2 / g and Comparative Example 2 with a specific surface area of 0.76 m 2 / g.

[0148] Evaluation Example 5: Gas generation amount after standing at 80°C While the lithium secondary batteries of the examples and comparative examples were left in a constant-temperature chamber at 80 °C for a predetermined period, the gas generation amount in the battery per unit weight of the positive electrode active material was evaluated. The gas generation amount was evaluated by the Archimedes measurement method. The results are shown in FIG. 8.

[0149] As shown in FIG. 8, it can be confirmed that the positive electrode active material of the example has a significantly lower gas generation amount after being left at a high temperature compared to Comparative Example 1 without any boron coating layer.

[0150] Evaluation Example 6: Gas generation amount in an overcharged state from 2.8 V to 5 V For the lithium secondary batteries of the examples and comparative examples, after charging from 2.8 V to 5 V at a constant current of 25° C. and 0.2 C, they were cut off at 0.1 C in the constant voltage mode. At this time, the gas emission amount in the battery per unit weight of the positive electrode active material was measured, and the results are shown in FIG. 9.

[0151] As shown in FIG. 9, it can be confirmed that the positive electrode active material of the example has a higher gas emission amount in the battery per unit weight of the positive electrode active material in the overcharged state compared to Comparative Example 1. Thus, it is considered that the positive electrode active material of the example can ensure safety by quickly operating the safety device during overcharging.

[0152] Evaluation Example 7: Content of glass lithium The glass lithium (residual lithium) of the positive electrode active materials of the examples and comparative examples was evaluated. 100 g of deionized water was added to 10 g of the positive electrode active material sample, and this was stirred at about 250 rpm for 30 minutes. After filtering the resulting product, titration was carried out using a 0.1 M hydrochloric acid aqueous solution. After titration, as shown in FIG. 12, two inflection points occurred. At this time, the amount of the hydrochloric acid aqueous solution added at the part where the inflection point occurred was confirmed, and the content of glass lithium was calculated. The results are shown in Table 1 below. As shown in Table 1, it can be confirmed that the higher the content of the boron compound, the higher the measured amount of glass lithium.

[0153] Evaluation Example 8: Profile analysis evaluation during overcharging from 2.8 V to 5 V For the lithium secondary batteries of the examples and comparative examples, after charging from 2.8 V to 5 V at a constant current of 25° C. and 0.5 C, they were cut off at 0.1 C in the constant voltage mode.

[0154] In FIG. 10, the relationship between time and voltage during charging up to 5V was compared in profiles. As the boron coating content on the surface of the positive electrode active material increases, it can be considered that phase transformation and chemical reactions occur while the profile extends in the range of 4.8V or higher. The expected chemical reaction is the generation of O2 gas and other gases due to the chemical reaction decomposition of the lithium-boron coating layer at high voltage. As the amount of chemical reaction increases and more gas is generated, the graph shows a general shape of flattening while further extending.

[0155] FIGS. 11 and 12 show the relationship between voltage (X-axis) and dQ / dV in profiles during 5V charging. Generally, for a High Ni (Ni 80 or higher) positive electrode active material, when charging in the range of 4.1V to 4.2V, elongation occurs while showing a flattening section, and a peak occurs in the dQ / dV graph. When the peak in this section (4.1V - 4.2V) is set as I1 and the peak in the range of 4.7V to 4.9V that occurs during overcharging is set as I2, I1 / I2 satisfies the optimal cobalt and boron coating conditions when it is 20 or more.

[0156] [Table 1]

[0157] Above, one embodiment has been described with reference to the drawings and examples, but this is merely illustrative, and those with ordinary knowledge in the relevant technical field will understand that various modifications and equivalent other embodiments are possible from now on. Therefore, the protection scope of the present invention should be determined by the appended claims.

Explanation of Reference Numerals

[0158] 10 Positive electrode 20 Negative electrode 30 Separator 40 Electrode assembly 50 Case 60 Sealing member 100 Lithium secondary battery

Claims

1. A positive electrode active material for a lithium secondary battery, comprising: a nickel-based active material; a cobalt-containing coating layer on a surface of the nickel-based active material; and a boron-containing coating layer on a surface of the cobalt-containing coating layer, The positive electrode active material has a specific surface area of ​​0.45 m 2 / g~0.60m 2 / g.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the nickel-based active material is a nickel-based active material represented by the following Chemical Formula 1: [Chemical formula 1] Li a (N 1-x-y-z Co x M y M' z )O 2-δ (In Chemical Formula 1, M is one or more elements selected from Mn and Al; M' is one or more elements selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); 0.95≦a≦1.3, x≦(1-x-y-z), y≦(1-x-y-z), z≦(1-x-y-z), 0<x<1, 0≦y<1, 0≦z<1, and 1.98≦2-δ≦2.

3. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the boron-containing coating layer is integrally formed with the cobalt-containing coating layer.

4. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material has a nickel content of 70 mol % or more.

5. 2 . The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the nickel-based active material includes secondary particles formed by agglomeration of primary particles by a physical and / or chemical method.

6. The positive electrode active material for a lithium secondary battery according to claim 5 , wherein the cobalt-containing coating layer is present on the surfaces of the secondary particles and on the grain boundaries of the primary particles.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the nickel-based active material includes at least one of (i) first secondary particles, (ii) single particles, (ii) single particles, and (iii) particles having a single crystal structure.

8. 8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein the nickel-based active material is a mixture of: (i) first secondary particles; and (ii) particles having a single crystal structure.

9. 9. The positive electrode active material for a lithium secondary battery according to claim 8, wherein, of 100 parts by weight of the mixture, (i) the first secondary particles are contained in an amount of 60 to 90 parts by weight, and (iii) the particles having a single crystal structure are contained in an amount of 10 to 40 parts by weight.

10. 8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein (i) the size of the first secondary particles is 14 to 18 μm, and (iii) the size of the particles having a single crystal structure is 1 to 7 μm.

11. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein in a voltage and dQ / dV profile when charging from 2.8 V to 5 V, when a peak in the 4.1 V to 4.2 V section is defined as I1 and a peak in the 4.7 V to 4.9 V section is defined as I2, the ratio of I1 / I2 is 20 or more.

12. The nickel-based active material is Li 1.01 Ni 0.8 Co 0.1 A 0.1 O 2 , Li 1.01 Ni 0.8 Co 0.05 A 0.15 O 2 , Li 1.01 Ni 0.8 Co 0.15 A 0.05 O 2 , LiNi 0.95 Co 0.04 A 0.01 O 2 The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the positive electrode active material is a cation exchange material or a combination thereof.

13. preparing a first positive electrode active material in which a cobalt compound is wet-coated on a surface of the nickel-based active material from a mixture including a nickel-based active material, a cobalt compound, and a solvent; preparing a second positive electrode active material by dry coating a boron compound on a surface of the first positive electrode active material; and heat-treating the second positive electrode active material at 700° C. to 750° C. to prepare a positive electrode active material for a lithium secondary battery; The boron compound is dry-coated to provide 0.25 mol % to 0.5 mol % of boron based on the total content of transition metal elements excluding lithium in the nickel-based active material.

14. A positive electrode comprising the positive electrode active material for a lithium secondary battery according to claim 1.

15. A lithium secondary battery comprising: a positive electrode containing the positive electrode active material for lithium secondary batteries according to claim 1; a negative electrode; and an electrolyte disposed therebetween.

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