Positive electrode material, positive electrode, and secondary battery

Abstract

The present invention relates to a first positive electrode active material having a single particle shape and having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface; and a second positive electrode active material having a larger particle size than the first positive electrode active material, having a single particle shape, and having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface, a positive electrode material containing the same, a positive electrode containing the same, and a secondary battery.

Description

Technical Field

[0001] The present invention relates to a positive electrode material, a positive electrode, and a secondary battery.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0125334, filed with the Korean Intellectual Property Office on September 30, 2022, and all of its contents are incorporated herein by reference.

Background Art

[0003] Secondary batteries are widely applied not only to portable devices but also to electric vehicles (EVs), hybrid electric vehicles (HEVs), etc., which are driven by an electric drive source.

[0004] Such secondary batteries have not only the primary advantage of significantly reducing the use of fossil fuels but also the advantage of generating no by-products associated with energy use, so they are environmentally friendly and are attracting attention as a new energy source for improving energy efficiency.

[0005] Generally, a secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Further, an electrode such as a positive electrode or a negative electrode can have an electrode active material layer provided on a current collector.

[0006] As the utilization rate of secondary batteries increases, various battery performances are required. For example, in order to develop a high-capacity battery, the application of a silicon-based active material to the negative electrode has been attempted, but in the case of a silicon-based active material, there is a problem of large initial irreversibility. Attempts have been made to adjust the components of the positive electrode or the negative electrode or to add an additive to improve the battery performance, but the selection or combination of wrong materials may conversely have an adverse effect on the performance of the final battery. Therefore, research on improving battery performance by the selection or combination of positive electrode or negative electrode materials is necessary.

Summary of the Invention

Problems to be Solved by the Invention

[0007] When used together with a negative electrode using a silicon-based active material, the present invention can not only provide an irreversible capacity of the negative electrode, but also reduce the resistance difference from the negative electrode to prevent the problem of deterioration of cycle performance, and can realize a high-density electrode. An object of the present invention is to provide a positive electrode material, a positive electrode, and a secondary battery including the same.

Means for Solving the Problems

[0008] One embodiment of the present invention includes a first positive electrode active material having a single particle shape and having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface; and a particle size larger than that of the first positive electrode active material. A positive electrode material is provided, which has a single particle shape and includes a second positive electrode active material having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface.

[0009] Another embodiment of the present invention provides a positive electrode for a secondary battery, which includes a current collector; and a positive electrode active material layer provided on the current collector and including the positive electrode material according to the above-described embodiment.

[0010] Another embodiment of the present invention provides a secondary battery including the positive electrode, the negative electrode, and a separator according to the above-described embodiment.

[0011] According to another embodiment of the present invention, the negative electrode includes a silicon-based active material.

Advantages of the Invention

[0012] According to the embodiments described in this specification, by using both the first cathode active material and the second cathode active material with different particle sizes as single particles as the cathode active material, not only can a high-density electrode be realized, but also since it has low-efficiency characteristics, it can provide the irreversible capacity of the anode when used with an anode using a silicon-based active material. Further, by applying a boron coating layer to both the first cathode active material and the second cathode active material with different particle sizes, the interfacial resistance of the cathode is increased, the sharp decrease in the discharge end resistance is improved, the depth of use (usable voltage range) of the silicon-based active material of the anode is reduced, and the normal-temperature life can be significantly improved. Furthermore, when a cobalt coating layer is formed on the first cathode active material and the second cathode active material before forming the boron coating layer, since cobalt and boron coexist in the coating layer, it is possible to simultaneously achieve the improvement of the cathode resistance by cobalt and the improvement of the sharp resistance decrease of the discharge end resistance by boron.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. At this time, the terms and words used in this specification and the claims are not to be construed as limited to their ordinary or dictionary meanings, but in accordance with the principle that the inventors can appropriately define the concept of the terms in order to explain their invention in the best way, and are to be construed as meanings and concepts consistent with the technical idea of the present invention.

[0014] In this specification, terms such as "including", "providing", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and it should be understood that they do not preclude the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof in advance.

[0015] Also, when a certain part such as a layer is present "above" or "on top of" another part, this includes not only the case where it is present "directly above" the other part, but also the case where other parts are present in between. Conversely, when a certain part is present "directly above" another part, it means that no other part is present in between. Also, being present "above" or "on top of" a reference part means being located above or below the reference part, and does not necessarily mean being located "above" or "on top of" in the opposite direction of gravity.

[0016] In this specification, the particle size means the average particle size represented by D50. D50 means the particle size at the 50% reference of the volume cumulative particle size distribution of the positive electrode active material powder. The average particle size D50 can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and after obtaining a volume cumulative particle size distribution graph, it can be measured by obtaining the particle size corresponding to 50% of the volume cumulative amount.

[0017] In this specification, "primary particle" means a particle that, when observed at a magnification of 5000 to 20000 times using a scanning electron microscope, has no grain boundaries visible in appearance. "Average particle size of primary particles" means the arithmetic mean value calculated after measuring the particle sizes of the primary particles observed from a scanning electron microscope image.

[0018] In this specification, "secondary particle" is a particle formed by the aggregation of a plurality of primary particles.

[0019] In this specification, "single particle" is a term used to distinguish from the secondary particle-like positive electrode active material particles formed by the aggregation of several tens to several hundreds of primary particles that are generally used conventionally, and is a concept including a single particle composed of 1 primary particle and an aggregate particle of 10 or fewer primary particles.

[0020] In this specification, when referring to "particles", it may mean including any or all of single particles, secondary particles, and primary particles.

[0021] In this specification, the "specific surface area" is measured by the BET method. Specifically, it can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan, Inc.

[0022] In this specification, the content of each component of the positive electrode active material can be measured by inductively coupled plasma mass spectrometry (ICP). Specifically, after pretreating the sample to be measured with an acid, it is measured using an ICP-OES (PerkinElmer, Optima7300DV) device.

[0023] The positive electrode material according to an embodiment of this specification has single-particle form and includes a first positive electrode active material having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface; and a second positive electrode active material having a larger average particle diameter (D50) than the first positive electrode active material, having single-particle form, and having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface. According to this embodiment, by using two types of single particles with different average particle diameters (D50) as the positive electrode active material, the voids between the large-particle positive electrode active material particles are filled with small-particle positive electrode active material particles, the electrode density is enhanced, the contact area between the positive electrode active material particles is increased, and the effect of improving the energy density can be obtained. Also, it can have low-efficiency characteristics due to the single-particle form, and thereby, when used together with a negative electrode using a silicon-based active material, it can provide the irreversible capacity of the negative electrode. Further, by applying a coating layer containing boron and cobalt to both the first positive electrode active material and the second positive electrode active material, the interfacial resistance of the positive electrode can be increased and the rapid decrease in the discharge end resistance can be improved.

[0024] According to one embodiment, the discharge end resistance of the battery including the aforementioned positive electrode material is 2.6 Ω or more, for example, it may be 2.65 Ω or more, and may be 4 Ω or less, for example, 3.5 Ω or less. The normal temperature life measured by the method described in the embodiments to be described later is preferably 90% or more respectively, for example, it may be 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 97% or more, or 98% or more. The high temperature life measured by the method described in the embodiments to be described later is preferably 87% or more respectively, for example, it may be 88% or more, 90% or more, 92% or more, 93% or more, 94% or more, 95% or more, or 97% or more.

[0025] According to one embodiment, the D50 of the first positive electrode active material is 1 μm or more and 7 μm or less, and the D50 of the second positive electrode active material may be 3 μm or more and 12 μm or less. Specifically, the D50 of the first positive electrode active material may be 1 μm or more, 2 μm or more, or 3 μm or more, and may be 7 μm or less, 6 μm or less, 5 μm or less, or 4 μm or less. The D50 of the second positive electrode active material may be 3 μm or more, 4 μm or more, or 5 μm or more, and may be 12 μm or less, 11 μm or less, 10 μm or less, 9 μm or less, 8 μm or less, or 7 μm or less.

[0026] The average particle size of the second positive electrode active material may be 0.5 μm to 7 μm, for example, 0.8 μm to 5 μm, or 1 μm to 4 μm larger than that of the first positive electrode active material. When the difference in average particle size is less than 0.5 μm, the thickness of the coated electrode increases due to the decrease in the tap density (g / cc) of the positive electrode active material, and the rolling characteristics during electrode rolling are inferior. When it exceeds 7 μm, the imbalance between two particles during the electrochemical reaction may increase due to the increase in the difference in specific surface area.

[0027] According to one embodiment, the weight ratio of the first positive electrode active material to the second positive electrode active material is 1:9 to 9:1, for example, 3:7 to 7:3, specifically 4:6 to 6:4, or 5:5. The closer the weight ratio of the first positive electrode active material to the second positive electrode active material is, the better the electrode density.

[0028] According to one embodiment, the first positive electrode active material and the second positive electrode active material may each contain a lithium nickel-based oxide in which the molar fraction of nickel among the metal elements excluding lithium is 50 mol% or more. The first positive electrode active material and the second positive electrode active material may have the same composition and differ only in average particle size, or may differ in both composition and average particle size.

[0029] The lithium nickel-based oxide may be a lithium nickel cobalt manganese-based oxide in which the molar fraction of nickel among the metal elements excluding lithium is 50 to 99 mol%, for example 60 to 99 mol%, specifically 80 to 98 mol%.

[0030] According to one embodiment, the lithium nickel-based oxide may have a composition represented by the following [Chemical Formula 1].

[0031] [Chemical Formula 1] Li 1+x (Ni a Co b Mn c M d )O 2 In the Chemical Formula 1, M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, x, a, b, c, and d are respectively 0 ≦ x ≦ 0.2, 0.50 ≦ a < 1, 0 < b ≦ 0.25, 0 < c ≦ 0.25, 0 ≦ d ≦ 0.1, and a + b + c + d = 1.

[0032] In the above [Chemical Formula 1], M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, preferably one or more selected from the group consisting of Al, Zr, Y, Mg, and Ti, and more preferably Al or Zr. The M element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting particle growth during firing or improving the stability of the crystal structure.

[0033] The above a represents the molar ratio of nickel among the metals excluding lithium in the lithium nickel-based oxide, and may be 0.5 ≦ a ≦ 0.99, 0.6 ≦ a ≦ 0.99, 0.7 ≦ a ≦ 0.98, or 0.8 ≦ a ≦ 0.98.

[0034] The above b represents the molar ratio of cobalt among the metals excluding lithium in the lithium nickel-based oxide, and may be 0 < b ≦ 0.25, 0.01 ≦ b ≦ 0.2.

[0035] The above c represents the molar ratio of manganese among the metals excluding lithium in the lithium nickel-based oxide, and may be 0 < c ≦ 0.25, 0.01 ≦ c ≦ 0.2.

[0036] The above d represents the molar ratio of the M element among the metals excluding lithium in the lithium nickel-based oxide, and may be 0 ≦ d ≦ 0.1 or 0 ≦ d ≦ 0.08.

[0037] Preferably, the lithium nickel-based oxide may be a lithium nickel cobalt manganese oxide doped with Zr. In the case of Zr doping, the effect of suppressing particle cracking during electrode rolling is even more excellent. At this time, the Zr may be contained in an amount of 3,000 ppm to 6,000 ppm, preferably 3,500 ppm to 5,500 ppm, more preferably 4,000 ppm to 5,000 ppm based on the total weight of the positive electrode material. When the content of Zr satisfies the above range, it has excellent structural stability and can improve the life characteristics.

[0038] According to one embodiment, each of the coating layers of the first positive electrode active material and the second positive electrode active material includes a coating layer containing boron (B) and a coating layer containing cobalt (Co). The coating layer containing cobalt (Co) is provided on at least a part of the surface of the first positive electrode active material or the second positive electrode active material, or between the coating layer containing boron (B) and at least a part of the surface of the first positive electrode active material or the second positive electrode active material.

[0039] The aforementioned coating layer containing boron is formed on the surface of the lithium nickel-based oxide. At this time, the coating layer containing boron may cover the entire surface of the lithium nickel-based oxide, but is not limited thereto, and may cover only a part thereof. The coating layers containing boron may be continuously arranged with each other on the surface of the lithium nickel-based oxide, but two or more portions may be arranged separately, and at least a part thereof may be arranged in an island shape.

[0040] When a coating layer containing boron (B) is formed on the surface of a lithium nickel-based oxide, by increasing the interfacial resistance of the positive electrode, a rapid decrease in resistance at the end of discharge can be improved. As a result, the difference in resistance from the negative electrode can be reduced, so the depth of use of the silicon-based active material of the negative electrode can be reduced, thereby preventing deterioration of the cycle performance of the battery and improving the normal temperature life. Further, the contact between the electrolyte and the lithium nickel-based oxide is minimized by the coating layer containing boron, and the occurrence of side reactions between the electrolyte and the lithium nickel-based oxide and the elution of transition metals are suppressed, thereby obtaining the effect of improving the life characteristics and reducing particle cracking during rolling.

[0041] At this time, the boron (B) may be contained in an amount of 200 ppm to 3,000 ppm, for example, 300 ppm to 2,000 ppm, 300 ppm to 1,800 ppm, 400 ppm to 1,500 ppm, or 500 ppm to 1,300 ppm based on the weight of each of the first positive electrode active material and the second positive electrode active material. When the content of boron (B) is less than 200 ppm based on the weight of each of the first positive electrode active material and the second positive electrode active material, a coating layer cannot be sufficiently formed on the surface of the positive electrode active material, so the interfacial resistance of the positive electrode cannot be increased. When it exceeds 3,000 ppm, the surface of the positive electrode active material is completely covered by the coating layer, and an electrochemical reaction cannot occur appropriately.

[0042] According to one embodiment, the content of boron in the first positive electrode active material may be more than the content of boron in the second positive electrode active material. Since the first positive electrode active material having a relatively smaller particle size has a larger specific surface area than the second positive electrode active material, the content of boron is made larger than that of the second positive electrode active material, and side reactions with the electrolyte can be effectively controlled. By suppressing side reactions with the electrolyte in this way, resistance characteristics and high-temperature life can be improved.

[0043] According to one embodiment, the weight ratio (A / B) of the boron content A in the first positive electrode active material to the boron content B in the second positive electrode active material may be 1 to 3, for example, 1.5 to 3, or 1 to 2.5, specifically 1.5 to 2.5, or 1.5 to 2. For example, based on the weight of the first positive electrode active material, the boron (B) content in the first positive electrode active material may be 600 ppm to 3,000 ppm, for example, 700 ppm to 1,500 ppm, and based on the weight of the second positive electrode active material, the boron (B) content in the second positive electrode active material may be 200 ppm to 1,000 ppm, for example, 300 ppm to 700 ppm, or 400 ppm to 650 ppm.

[0044] According to a further embodiment, the first positive electrode active material and the second positive electrode active material may further include a coating layer containing cobalt (Co) provided on at least a part of the surface or between the coating layer containing boron (B) and at least a part of the single particle surface. At this time, the coating layer containing cobalt may cover the entire surface of the lithium nickel-based oxide, but is not limited thereto, and may cover only a part thereof. The coating layers containing cobalt may be continuously arranged with each other on the surface of the lithium nickel-based oxide, but two or more portions may be arranged separately, and at least a part thereof may be arranged in an island shape. When applying a coating layer containing cobalt, the coating layer containing boron may be provided on the coating layer containing cobalt, or may be provided in direct contact with the surface of the lithium nickel-based oxide where the coating layer containing cobalt does not exist. According to an example, there is no additional layer between the boron coating layer and the lithium nickel-based oxide other than the cobalt coating layer. By applying a coating layer containing cobalt, the positive electrode resistance can be improved. However, when applying a coating layer containing cobalt, the discharge end resistance is significantly improved, and the depth of use of the silicon-based active material contained in the negative electrode increases, and the cycle characteristics may deteriorate. However, in the embodiments described in this specification, by increasing the interfacial resistance of the positive electrode due to the presence of the coating layer containing boron, a sharp decrease in the discharge end resistance can be improved.

[0045] The cobalt contained in the coating layer containing cobalt (Co) may be contained in an amount of 5,000 ppm to 50,000 ppm, for example, 5,000 ppm to 30,000 ppm, 10,000 ppm to 30,000 ppm, 15,000 ppm to 25,000 ppm, or 17,000 ppm to 23,000 ppm, based on the weight of each of the first cathode active material and the second cathode active material. When the content of cobalt (Co) satisfies the above range, it is advantageous for improving the cathode resistance.

[0046] According to one embodiment, in each of the first cathode active material and the second cathode active material, the content of boron in the coating layer may be 0.001 to 1, preferably 0.02 to 0.8, 0.02 to 0.7, 0.03 to 0.6, 0.04 to 0.5, 0.05 to 0.4, or 0.06 to 0.3, more preferably 0.005 to 0.175, 0.02 to 0.15, or 0.025 to 0.1, relative to the content of cobalt. The above content ratio is calculated based on the content in ppm units. When the above ratio is less than 0.001, the effect due to the presence of boron in the coating layer is negligible, and when the above ratio exceeds 0.2, boron is excessively contained relative to cobalt, which may have a negative impact on battery performance.

[0047] According to one embodiment, the ratio (Co / B) of the content of cobalt to the content of boron contained in the entire first cathode active material and second cathode active material may be 5 to 70, for example, 7 to 60, 20 to 55, or 25 to 50. Here, the cobalt includes cobalt contained in single particles in addition to cobalt in the coating layer.

[0048] According to one embodiment, the BET specific surface area of the first cathode active material and the second cathode active material or the 0.2 to 1 m 2 / g, preferably 0.25 to 0.85 m 2It may also be / g. When the specific surface area of the lithium nickel-based oxide is large, there are many side reactions with the electrolyte, which can deteriorate the life characteristics. When the specific surface area of the positive electrode active material is decreased, the effect of improving the life characteristics can be obtained by reducing the side reactions with the electrolyte.

[0049] One embodiment provides a method for manufacturing a positive electrode active material, which includes: a step of mixing a transition metal precursor and a lithium raw material substance and then firing to produce a single-particle positive electrode active material; a step of washing the positive electrode active material with water; and a step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material.

[0050] According to one embodiment, the step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material may further include a step of forming a coating layer containing cobalt (Co) before forming a coating layer containing boron (B); and a step of manufacturing a coating layer containing boron (B).

[0051] Another embodiment provides a method for manufacturing a positive electrode material according to the foregoing embodiment, which includes: a step of mixing a transition metal precursor and a lithium raw material substance and then firing to form a single-particle first positive electrode active material; a step of washing the positive electrode active material with water; and a step of manufacturing a first positive electrode active material including a step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material; a step of mixing a transition metal precursor and a lithium raw material substance and then firing to form a single-particle second positive electrode active material having a particle size larger than that of the single particles of the first positive electrode active material; a step of washing the positive electrode active material with water; and a step of manufacturing a second positive electrode active material including a step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material; and a step of mixing the first positive electrode active material and the second positive electrode active material.

[0052] According to one embodiment, in the step of manufacturing at least one of the first positive electrode active material and the second positive electrode active material, the step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material may further include the step of forming a coating layer containing cobalt (Co) before forming the coating layer containing boron (B); and the step of manufacturing the coating layer containing boron (B).

[0053] The control of the particle sizes of the first positive electrode active material and the second positive electrode active material can be achieved by changing process conditions such as the firing temperature, firing time, and precursor synthesis time.

[0054] An exemplary manufacturing method of the aforementioned first positive electrode active material and second positive electrode active material will be described.

[0055] The aforementioned lithium nickel-based oxide can be manufactured by mixing a transition metal precursor and a lithium raw material and then firing. The precursor can be purchased and used from commercially available precursors, or can be manufactured by introducing a transition metal aqueous solution, an ammonium cation complexing agent, and a basic compound into a reactor, stirring, and performing a coprecipitation reaction.

[0056] For example, when a transition metal aqueous solution, an ammonium cation complexing agent, and a basic compound are introduced into a reactor and stirred, the transition metal in the transition metal aqueous solution coprecipitates, and precursor particles in the form of transition metal hydroxides are generated.

[0057] At this time, the transition metal aqueous solution, the ammonium cation complexing agent, and the basic compound are introduced in amounts such that the pH of the reaction solution is within a desired range.

[0058] When precursor particles are formed by the method as described above, the precursor is obtained by separating it from the reaction solution.

[0059] The transition metal aqueous solution is produced by dissolving a transition metal-containing raw material substance in a solvent such as water. For example, it can be produced by dissolving a nickel-containing raw material substance, a cobalt-containing raw material substance, a manganese-containing raw material substance, and / or an aluminum-containing raw material substance in water.

[0060] On the other hand, the transition metal-containing raw material substance may be a transition metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, etc.

[0061] The nickel-containing raw material substance is Ni(OH) 2 , NiO, NiOOH, NiCO 3 ·2Ni(OH) 2 ·4H 2 O, NiC 2 O 2 ·2H 2 O, Ni(NO 3 ) 2 ·6H 2 O, NiSO 4 , NiSO 4 ·6H 2 O, nickel fatty acid salt, or nickel halide, etc. may be used, and any one or a mixture of two or more of these may be used.

[0062] The cobalt-containing raw material substance is Co(OH) 2 , CoOOH, Co(OCOCH 3 ) 2 ·4H 2 O, Co(NO 3 ) 2 ·6H 2 O, or Co(SO 4 ) 2 ·7H 2 O, etc. may be used, and any one or a mixture of two or more of these may be used.

[0063] The manganese-containing raw material substance is manganese oxides such as Mn 2 O 3 , MnO 2 , and Mn 3 O 4 ; MnCO3 , Mn(NO 3 ) 2 , MnSO 4 , manganese salts such as manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; it may also be oxyhydroxide, or manganese chloride, etc., and a mixture of any one or two or more of these may be used.

[0064] Optionally, the transition metal aqueous solution may further contain a doping element (M) in addition to nickel, cobalt, and manganese. At this time, the M may contain at least one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. When the positive electrode active material further contains a doping element, the effects of improving life characteristics, discharge characteristics, and / or stability, etc. can be achieved.

[0065] When the transition metal aqueous solution further contains the doping element M, the doping element M-containing raw material substance may be selectively further added during the production of the transition metal precursor.

[0066] As the doping element M-containing raw material substance, at least one or more selected from the group consisting of acetate, sulfate, sulfide, hydroxide, oxide, or oxyhydroxide containing the doping element M may be used.

[0067] On the other hand, the ammonium cation complexing agent is NH 4 OH, (NH 4 ) 2 SO 4 , NH 4 NO 3 , NH 4 Cl, CH 3 COONH 4 , and (NH 4 ) 2 CO 3It may be at least one or more selected from the group consisting of, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. As the solvent, water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

[0068] Next, the basic compound may be at least one or more selected from the group consisting of NaOH, KOH, and Ca(OH) 2 It may be at least one or more selected from the group consisting of, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, as the solvent, water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

[0069] As the lithium raw material substance, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, etc. may be used. For example, Li 2 CO 3 , LiNO 3 , LiNO 2 , LiOH, LiOH·H 2 O, LiH, LiF, LiCl, LiBr, LiI, CH 3 COOLi, Li 2 O, Li 2 SO 4 , CH 3 COOLi, Li 3 C 6 H 5 O 7 , or a mixture thereof may be used.

[0070] The precursor and the lithium raw material substance may be mixed so that the molar ratio of the transition metal (Me) contained in the precursor to lithium (Li) is 1:1 to 1:1.2, preferably 1:1 to 1:1.1. When the lithium raw material substance is mixed less than the above range, the capacity of the produced positive electrode active material may decrease. When the lithium raw material substance is mixed exceeding the above range, the particles are sintered during the firing process, making it difficult to manufacture the positive electrode active material, and capacity reduction and separation of the positive electrode active material particles after firing may occur.

[0071] Also, if necessary, an M-containing substance may be further mixed during the firing. The doping element M may be, for example, at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. The raw material substance containing the doping element M may be at least one selected from the group consisting of acetate, sulfate, sulfide, hydroxide, oxide, or oxyhydroxide containing the doping element M.

[0072] The firing may be carried out at 700 °C to 1,000 °C for 10 hours to 35 hours, preferably at 750 °C to 900 °C for 15 hours to 30 hours, but is not limited thereto.

[0073] Next, a step of washing the fired and uncoated cathode active material with water is performed. The water washing is preferably carried out so that the content of residual lithium by-products in the cathode active material can be removed by about 30 wt% or more, 40 wt% or more, 50 wt% or more. For example, if the content of residual lithium by-products in the cathode active material before water washing is 1 wt%, the content of residual lithium by-products in the water-washed cathode active material may be 0.5 wt%. Here, the residual lithium by-products refer to compounds containing lithium, such as LiOH, Li 2 CO 3 and so on. The water washing may be carried out under conditions that can reach the content of the residual lithium by-products as described above. For example, the water washing may be carried out by mixing the fired cathode active material with water and stirring. At this time, the weight ratio of the cathode active material to water may be 7:3 to 3:7, for example, 5:5. The water washing time may be determined as necessary, for example, it may be 3 minutes or more, or 5 minutes. The water washing conditions such as time, temperature, and the weight ratio of the active material to water can be carefully selected so as to achieve an appropriate reduction in the content of residual lithium by-products.

[0074] Next, after mixing the lithium nickel-based oxide and the boron-containing coating raw material substance, heat treatment is performed to form a coating layer.

[0075] The boron-containing coating raw material substance is, for example, H 2 BO 3 , HBO 2 , H 3 BO 3 , H 2 B 4 O 7 , B 2 O 3 , C 6 H 5 B(OH) 2 , (C 6 H 5 O) 3 , B, (CH 3 (CH 2 ) 3 O) 3 , C 3 H 9 B 3 O 6 , (C 3 H 7 O 3 )B, etc. may be used. The coating raw material substance is mixed in an amount such that the content of boron (B) is 200 ppm to 3,000 ppm based on the total weight of each positive electrode active material.

[0076] On the other hand, the mixing of the lithium nickel-based oxide and the coating raw material substance may be performed by solid-phase mixing, and the heat treatment may be performed at a temperature of 200°C to 500°C, or 250°C to 400°C, but is not limited thereto.

[0077] If necessary, before forming the boron-containing coating layer, a cobalt-containing coating layer may be formed. Except for using the aforementioned cobalt-containing coating raw material substance, a method similar to the method for forming the boron-containing coating layer may be used. The cobalt-containing raw material is Co 3 O 4 , Co(OH) 2 , Co 2 O 3 , Co3 (PO 4 ) 2 、CoF 3 、Co(OCOCH 3 ) 2 ·4H 2 O、Co(NO 3 ) 2 ·6H 2 O、Co(SO 4 ) 2 ·7H 2 O, and CoC 2 O 4 It may be one or more selected from the group consisting of. At this time, the cobalt-containing coating raw material substance is preferably mixed in an amount such that the cobalt content is 5,000 ppm to 50,000 ppm based on the weight of each cathode active material.

[0078] On the other hand, after manufacturing the first cathode active material and the second cathode active material respectively, these are mixed to form a mixture, and after mixing the mixture with a cobalt-containing coating raw material substance or a boron-containing coating raw material substance, heat treatment is performed to form a coating layer on the surfaces of the first cathode active material and the second cathode active material, whereby the cathode material of the present invention can be manufactured.

[0079] According to one embodiment, the cathode active material having the boron-containing coating layer and / or the cobalt-containing coating layer, by performing the above-described water washing step, the content of residual lithium by-products is 1% by weight or less, preferably 0.8% by weight or less, 0.7% by weight or less, 0.6% by weight or less, 0.55% by weight or less, or 0.5% by weight based on 100% by weight of the cathode active material. The residual lithium by-products can be measured by the following method. 10 g of the cathode active material is poured into distilled water, and after dissolving the lithium by-products remaining on the surface of the cathode active material, only the solution is filtered, and titration is performed while injecting 0.1M HCl at a rate of 0.3 to 0.5 mL / min. At this time, the content of residual lithium by-products is calculated by the amount of HCl injected until pH 5. The apparatus used for pH titration is an apparatus manufactured by Metrohm. The above measurement can be performed on the cathode active material after the coating layer described above is formed.

[0080] A further embodiment of the present specification provides a positive electrode for a secondary battery, including a current collector; and a positive electrode active material layer provided on the current collector and including a positive electrode material according to the foregoing embodiment.

[0081] The positive electrode active material layer may further include a binder and a conductive material.

[0082] According to one embodiment, the positive electrode binder can serve to improve the adhesion between positive electrode active material particles and the adhesive force between the positive electrode active material particles and the positive electrode current collector. As the positive electrode binder, any material well-known in the art can be used. Non-limiting examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0083] The positive electrode binder may be included in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the positive electrode active material layer. For example, preferably, it may be included in an amount of 0.3 part by weight or more and 35 parts by weight or less, and more preferably 0.5 part by weight or more and 20 parts by weight or less.

[0084] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electron conductivity without causing chemical changes in the battery. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0085] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). The conductive material may be contained in an amount of 0.1 part by weight or more and 2 parts by weight or less based on 100 parts by weight of the composition for the positive electrode active material layer. For example, it may preferably be contained in an amount of 0.3 part by weight or more and 1.5 parts by weight or less, more preferably 0.5 part by weight or more and 1.2 parts by weight or less.

[0086] According to a further embodiment of the present specification, a positive electrode for a secondary battery is provided, which includes a current collector and a positive electrode active material layer provided on the current collector and containing the aforementioned positive electrode composition. The thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less.

[0087] With respect to 100 parts by weight of the positive electrode active material layer, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and still more preferably 96 parts by weight or more and 99.9 parts by weight or less.

[0088] The positive current collector is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive current collector may usually have a thickness of 1 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies, etc.

[0089] A further embodiment of the present specification provides a secondary battery including a positive electrode, a negative electrode, and a separator according to the foregoing embodiments.

[0090] The negative electrode may include a current collector and a negative electrode active material layer provided on the current collector.

[0091] According to one embodiment, the negative electrode includes a silicon-based active material.

[0092] As the silicon-based active material, an active material containing SiO x (0 ≦ x < 2) may be silicon-based composite particles containing SiO x (0 < x < 2) and pores.

[0093] The SiO x (0 < x < 2) corresponds to a matrix in the silicon-based composite particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO 2 , and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based composite particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0094] The silicon-based composite particles may further contain at least one of an Mg compound and an Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon-based composite particles.

[0095] The Mg compound and / or the Li compound may be present inside and / or on the surface of the SiO x (where 0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0096] The Mg compound may contain at least any one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may contain at least any one of Mg 2 SiO 4 and MgSiO 3 . The Mg silicide may contain Mg 2 Si. The Mg oxide may contain MgO.

[0097] In one embodiment of this specification, the Mg element may be contained in an amount of 0.1 wt% to 20 wt%, or may be contained in an amount of 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon-based active material. Specifically, the Mg element may be contained in an amount of 0.5 wt% to 8 wt%, or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be contained in a suitable content in the silicon-based active material, so that the volume change of the silicon-based active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0098] The Li compound may contain at least any one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may contain Li 2 SiO 3 , Li 4 SiO 4 , and Li 2 Si 2 O 5It may contain at least any one of them. The Li silicide may contain Li 7 Si 2 The Li oxide may contain Li 2 O.

[0099] In one embodiment of the present invention, the Li compound may contain a lithium silicate form. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li 2 SiO 3 , Li 4 SiO 4 , and Li 2 Si 2 O 5 in the silicon-based composite particles, and the amorphous lithium silicate may be in the form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to the above form.

[0100] In one embodiment of the present specification, the Li element may be contained in an amount of 0.1% by weight to 20% by weight, or may be contained in an amount of 0.1% by weight to 10% by weight, based on 100% by weight of the total silicon-based active material. Specifically, the Li element may be contained in an amount of 0.5% by weight to 8% by weight, and more specifically, may be contained in an amount of 0.5% by weight to 4% by weight. When the above range is satisfied, the Li compound can be contained in an appropriate content in the silicon-based active material, so that the volume change of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0101] The content of the Mg element or Li element can be confirmed by ICP analysis. For the ICP analysis, after accurately separating a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, and nitric acid, hydrofluoric acid, and sulfuric acid are added and completely decomposed on a hot plate. Then, using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300), at the wavelength specific to the Mg element or Li element, the intensity of the standard solution prepared using a standard solution (5 mg / kg) is measured to create a reference calibration curve. Then, the pretreated sample solution and blank sample are introduced into the instrument, the intensity of each is measured to calculate the actual intensity, and after calculating the concentration of each component with respect to the created calibration curve, it is converted so that the overall total becomes the theoretical value, and the content of the Mg element or Li element in the manufactured silicon-based active material can be analyzed.

[0102] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon-based composite particles. The carbon layer imparts conductivity to the silicon-based composite particles, and the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery including the negative electrode active material containing the silicon-based composite particles can be improved. The total weight of the carbon layer may be included at 5 wt% to 40 wt% based on 100 wt% of the total of the silicon-based composite particles.

[0103] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0104] The average particle size (D50) of the silicon-based active material may be 2 μm to 15 μm, specifically may be 3 μm to 12 μm, and more specifically may be 4 μm to 10 μm. When the above range is satisfied, the side reaction between the silicon-based composite particles and the electrolyte can be controlled, and the discharge capacity and initial efficiency of the battery can be effectively realized.

[0105] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve of the particles. The average particle size (D50) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes in the range from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolved results.

[0106] According to one embodiment of this specification, the negative electrode active material layer may further contain an additional negative electrode active material in addition to the aforementioned silicon-based active material.

[0107] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO β (0 < β < 2), SnO 2 , metal oxides capable of doping and undoping lithium such as vanadium oxides, lithium titanate oxides, and lithium vanadate oxides; composites containing the metallic compound and a carbonaceous material such as Si-C composites or Sn-C composites; or carbon-based active materials, etc., and a mixture of any one or two or more of these may be used. Also, a thin film of metallic lithium may be used as the negative electrode active material.

[0108] In one embodiment of the present invention, the weight ratio of the silicon-based active material and the additional negative electrode active material contained in the negative electrode active material layer may be 1:99 to 90:10, and specifically may be 1:99 to 50:50.

[0109] In one embodiment of the present specification, the carbonaceous active material can be used without particular limitation, and typical examples thereof include crystalline carbon, amorphous carbon, or both of them may be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite and artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke. The graphite may be natural graphite, artificial graphite, or a mixture thereof. Based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer, the carbonaceous active material may be contained in an amount of 60 parts by weight or more and 99 parts by weight or less.

[0110] In one embodiment of the present specification, based on 100 parts by weight of the negative electrode active material layer, the negative electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and still more preferably 96 parts by weight or more and 99.9 parts by weight or less.

[0111] According to a further embodiment of the present specification, the negative electrode active material layer may further contain a negative electrode binder in addition to the silicon-based active material and the carbon-based active material.

[0112] The negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive force between the negative electrode active material particles and the negative electrode current collector. As the negative electrode binder, any well-known material in the technical field can be used. Non-limiting examples include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and at least any one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and various copolymers thereof may also be included.

[0113] The negative electrode binder may be included in an amount of 0.1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode active material layer. For example, preferably, it may be included in an amount of 0.3 part by weight or more and 20 parts by weight or less, and more preferably 0.5 part by weight or more and 10 parts by weight or less.

[0114] The negative electrode active material layer may not contain a conductive material, but may further contain a conductive material as needed. The conductive material contained in the negative electrode active material layer is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used. The content of the conductive material in the negative electrode active material layer may be 0.01 to 20 parts by weight, preferably 0.03 to 18 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0115] In one embodiment of the present specification, the thickness of the negative electrode active material layer may be 10 μm or more and 500 μm or less.

[0116] In one embodiment, the negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a surface-treated product with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0117] The positive electrode and the negative electrode can be manufactured by the usual manufacturing methods of positive and negative electrodes, except for using the aforementioned positive and negative electrode active materials. Specifically, after applying a composition for forming an active material layer, which contains the aforementioned active material and optionally a binder and a conductive material, onto a current collector, it can be manufactured by drying and rolling. At this time, the types and contents of the aforementioned positive and negative electrode active materials, binder, and conductive material are as described above. As the solvent, a solvent generally used in the technical field may be used, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the solvent used is such that, considering the coating thickness of the composition and the manufacturing yield, it can dissolve or disperse the active material, conductive material, and binder, and then has a viscosity that can exhibit excellent thickness uniformity during the coating for the manufacture of the positive and negative electrodes. Also, as another method, the positive electrode and the negative electrode can also be manufactured by casting the composition for forming the active material layer onto another support, and then laminating the film obtained by peeling it from the support onto the current collector.

[0118] In a secondary battery according to an embodiment, the efficiency Ec of the positive electrode may be smaller than the efficiency Ea of the negative electrode. According to an example, the ratio (Ec / Ea) of the efficiency Ec of the positive electrode to the efficiency Ea of the negative electrode is 0.5 to 0.8. As described above, when using a lithium nickel-based oxide having a coating layer containing a specific material as the positive electrode active material and a silicon-based active material as the negative electrode active material, by having the above relationship between the efficiency of the positive electrode and the efficiency of the negative electrode, the irreversible capacity of the negative electrode can be complemented.

[0119] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Generally, any separator that can be used in a secondary battery can be used without particular limitation, and it is particularly preferably low in resistance to the ion migration of the electrolyte and excellent in electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multilayer structure.

[0120] Examples of the electrolyte include, but are not limited to, 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 manufacture of lithium secondary batteries.

[0121] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0122] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0123] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can well dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate at an appropriate ratio and used, an electrolyte having high electrical conductivity can be produced, so they can be more preferably used.

[0124] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 )3 PF 3 - ,(CF 3 ) 4 PF 2 - ,(CF 3 ) 5 PF - ,(CF 3 ) 6 P - ,CF 3 SO 3 - ,CF 3 CF 2 SO 3 - ,(CF 3 SO 2 ) 2 N - ,(FSO 2 ) 2 N - ,CF 3 CF 2 (CF 3 ) 2 CO - ,(CF 3 SO 2 ) 2 CH - ,(SF 5 ) 3 C - ,(CF 3 SO 2 ) 3 C - ,CF 3 (CF 2 ) 7 SO 3 - ,CF 3 CO 2 - ,CH 3 CO 2 - ,SCN - ,and (CF 3 CF 2 SO 2 ) 2 N - selected from the group consisting of one or more of these may be used.

[0125] In addition to the constituent components of the electrolyte, 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, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc.

[0126] The secondary battery according to an embodiment of the present invention includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte, and this may be a lithium secondary battery.

[0127] A further embodiment of the present invention provides a battery module including the aforementioned secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0128] The secondary battery according to an embodiment of the present invention can be used as a power source for not only portable devices such as mobile phones, notebook computers, and digital cameras, but also medium- and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems in order to stably exhibit excellent discharge capacity, output characteristics, and cycle performance. For example, the battery module or battery pack can be used as a power source for any one or more of medium- and large-sized devices including power tools; electric vehicles including electric vehicles (Electric Vehicle, EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (Plug-in Hybrid Electric Vehicle, PHEV); or power storage systems.

[0129] Hereinafter, preferred examples are presented to assist in understanding the present invention. However, it should be apparent to those skilled in the art that the examples are merely illustrative of the description and that various changes and modifications are possible within the scope of the description and the scope of the technical idea. Needless to say, such variations and modifications belong to the scope of the appended claims.

[0130] Example 1 Ni 0.84 Co 0.08 Mn 0.08 (OH) 2 The precursor of the composition and LiOH were put into a Henschel mixer (700 L) so that the molar ratio of (Ni + Co + Mn):Li was 1:1.06, and mixed at a speed of 400 rpm at the center for 20 minutes. The mixed powder was put into an alumina crucible with a size of 330 mm × 330 mm, and heat-treated at 760 °C for 12 hours in an oxygen (O 2 ) atmosphere to obtain Li 1.0 Ni 0.84 Co 0.08 Mn 0.08 O 2A composite lithium transition metal oxide was produced. Subsequently, the produced composite lithium transition metal oxide was mixed with water at a ratio of 1:1 and stirred for 5 minutes, and then dried in a vacuum oven at 130 °C for 12 hours to produce single-particle composite lithium transition metal oxide. Next, 20,000 ppm of Co(OH) was dry-mixed with respect to the total weight of the single-particle composite lithium transition metal oxide. 2 and dry-mixed. The mixture was heat-treated at 600 °C for 6 hours in an air atmosphere to produce single-particle composite lithium transition metal oxide with a cobalt coating layer formed thereon. Then, 1200 ppm of H was dry-mixed with respect to the total weight of the composite lithium transition metal oxide with the cobalt coating layer formed thereon. 3 BO 3 and dry-mixed, and then heat-treated at 400 °C for 5 hours to produce a first positive electrode active material with a boron coating layer formed thereon. Under the production conditions of the first positive electrode active material, a second positive electrode active material was produced in the same manner except that the firing temperature was 800 °C and the boron coating content was 600 ppm.

[0131] A first positive electrode active material and a second positive electrode active material, which are single-particle composite lithium transition metal oxides provided with a cobalt coating layer and a boron coating layer on a part of the particle surface, a conductive material (CNT), and a binder (PVDF) were put into a N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1:2 to produce a positive electrode slurry (the solid content of the positive electrode slurry is included in 70 parts by weight of the total positive electrode slurry).

[0132] Here, the first positive electrode active material and the second positive electrode active material are single particles with D50 values of 3 μm and 7 μm, respectively, and the amounts of cobalt and boron are as shown in Table 1 below. The first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 5:5.

[0133] The positive electrode slurry produced above was coated on an Al current collector and dried at 130 °C and then cold-rolled at room temperature to produce a positive electrode.

[0134] A negative electrode active material containing a SiO-based active material and graphite (the SiO-based active material is contained in 5 parts by weight of the total negative electrode active material), a conductive material (carbon black), a binder (SBR), and a thickener (CMC) were put into a distilled water solvent at a weight ratio of 96:1:2:1 to produce a negative electrode slurry (the solid content of the negative electrode slurry is contained in 50 parts by weight of the total negative electrode slurry).

[0135] The negative electrode slurry produced above was applied onto a Cu current collector, dried at a high temperature, and then cold-rolled at room temperature to fabricate a negative electrode.

[0136] A separator was interposed between the positive electrode and the negative electrode fabricated above, assembled, and after injecting an electrolytic solution, it was activated to fabricate a cell.

[0137] - Composition of the electrolytic solution: 1M LiPF 6 , ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 3 / 7), vinylene carbonate (VC) / propane sultone (PS, propane sultone) (each contained in 3 parts by weight and 1.5 parts by weight based on 100 parts by weight of the electrolyte) - Activation: After charging at 0.1C for 3 hours, degassing after high temperature / room temperature aging

[0138] The electrode density, discharge end resistance, room temperature life, and high temperature life of the positive electrode are shown in Table 2 below.

[0139] The meanings or measurement methods of the electrode density, discharge end resistance, room temperature life, and high temperature life are as follows.

[0140] * Electrode density: (weight of the electrode / (thickness of the electrode * area of the electrode)) - Weight of the electrode: Weight of the slurry excluding the weight of the aluminum foil - Thickness of the electrode: Thickness of the slurry layer excluding the thickness of the aluminum foil *Discharge terminal resistance: The fabricated cell was charged at a constant current / constant voltage (CC / CV) up to 4.2 V at 0.33C (0.05C cut-off), and discharged at a constant current (CC) of 0.33C (2.5V cut-off) three times. The discharge capacity of the third time was measured (initial capacity). After that, after charging as described above, the SOC was set to 5% by discharging at 0.33C, and the resistance was measured by discharging with a 2C pulse for 10 seconds (initial resistance). *Normal temperature life: Cycles were performed by charging at a constant current / constant voltage (CC / CV) up to 4.2 V at 0.5C at normal temperature (25°C) (0.05C cut-off) and discharging at a constant current (CC) of 0.5C (2.5V cut-off). After repeating 100 times, the capacity and resistance were measured in the same manner as in Experimental Example 1, and the capacity retention rate (capacity after 100 times / initial capacity × 100%) was measured. *High temperature life: Cycles were performed by charging at a constant current / constant voltage (CC / CV) up to 4.2 V at 1C at high temperature (45°C) (0.05C cut-off) and discharging at a constant current (CC) of 1C (2.5V cut-off). After repeating 400 times, the capacity and resistance were measured in the same manner as when measuring the discharge terminal resistance, and the capacity retention rate (capacity after 100 times / initial capacity × 100%) was measured.

[0141] Examples 2 to 10 It was carried out in the same manner as in Example 1, except that the content or average particle size (D50) of cobalt and boron coating in the first positive electrode active material and the second positive electrode active material was changed as shown in Tables 1 to 3 below.

[0142] Comparative Example 1 It was carried out in the same manner as in Example 1, except that the first positive electrode active material and the second positive electrode active material were not washed with water before forming the coating layer and no boron-containing coating layer was formed.

[0143] Comparative Example 2 It was carried out in the same manner as in Example 1, except that the first positive electrode active material and the second positive electrode active material did not form a boron-containing coating layer.

[0144]

Table 1

[0145]

Table 2

[0146]

Table 3

[0147] As shown in Tables 1 to 3 above, in the case of the examples, it was confirmed that the discharge terminal resistance was high and the normal temperature life and high temperature life were excellent compared to Comparative Examples 1 and 2. In particular, in the case of Example 1, compared with Examples 2, 8, and 9, since the boron content in the first positive electrode active material was higher, the discharge terminal resistance was high and higher normal temperature and high temperature life characteristics were shown. In the case of Examples 1, 2, and 8, compared with Examples 3, 5, and 6, since the average particle size was larger, the discharge terminal resistance was relatively larger, and thus, more excellent normal temperature and high temperature life characteristics were shown. Examples 1, 2, and 8 showed more excellent normal temperature and high temperature life characteristics due to the appropriate B content compared to Examples 9 and 10. In the case of Examples 1 to 10, compared with Examples 11 and 12, excellent normal temperature and high temperature life were shown due to the appropriate Co content.

[0148] The content of the residual lithium by-product was measured by pH titration. The pH region where the residual lithium by-product and LBO (lithium borate oxide oxide) are titrated is similar. In the examples, the amount of LBO by B coating is included in the LiOH value, while in Comparative Examples 1 and 2, no B coating layer was formed and no LBO phase exists, so the content of the residual lithium by-product was measured to be relatively small.

Claims

1. A first positive electrode active material having a single particle shape and having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface, and A second positive electrode active material having a larger average particle diameter (D50) than the first positive electrode active material, having a single particle shape, and having a coating layer containing boron (B) and cobalt (Co) provided on at least a part of the surface, and a positive electrode material containing the same.

2. The positive electrode material according to claim 1, wherein the average particle diameter (D50) of the first positive electrode active material is 1 μm or more and 7 μm or less, and the average particle diameter (D50) of the second positive electrode active material is 3 μm or more and 12 μm or less.

3. The positive electrode material according to claim 1, wherein the average particle diameter (D50) of the second positive electrode active material is 0.5 μm to 7 μm larger than the average particle diameter (D50) of the first positive electrode active material.

4. The positive electrode material according to claim 1, wherein in each of the first positive electrode active material and the second positive electrode active material, the ratio (B / Co) of the content of boron to the content of cobalt in the coating layer is 0.001 to 0.

2.

5. The positive electrode material according to claim 1, wherein the ratio (Co / B) of the content of cobalt to the content of boron contained in the whole of the first positive electrode active material and the second positive electrode active material is 5 to 70.

6. The coating layer of each of the first positive electrode active material and the second positive electrode active material includes a coating layer containing boron (B) and a coating layer containing cobalt (Co), and the coating layer containing cobalt (Co) is provided on at least a part of the surface of the first positive electrode active material or the second positive electrode active material, or is provided between the coating layer containing boron (B) and at least a part of the single particle surface. The positive electrode material according to claim 1.

7. The positive electrode material according to claim 1, wherein each of the first positive electrode active material and the second positive electrode active material contains cobalt in an amount of 5,000 ppm to 50,000 ppm.

8. The positive electrode material according to claim 1, wherein the content of boron in the first positive electrode active material is larger than the content of boron in the second positive electrode active material.

9. The positive electrode material according to claim 1, wherein the weight ratio (A / B) of the content A of boron in the first positive electrode active material to the content B of boron in the second positive electrode active material is 1 to 3.

10. The positive electrode material according to claim 1, wherein each of the first positive electrode active material and the second positive electrode active material contains boron in an amount of 200 ppm to 3,000 ppm.

11. The positive electrode material according to claim 1, wherein the first positive electrode active material and the second positive electrode active material are lithium nickel-based oxides in which the molar fraction of nickel among metal elements excluding lithium is 50 mol% or more.

12. The lithium nickel-based oxide has a composition represented by the following [Chemical Formula 1], [Chemical Formula 1] Li １＋ｘ (Ni ａ Co ｂ Mn ｃ M ｄ )O ２ In the Chemical Formula 1, M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, x, a, b, c, and d are 0 ≦ x ≦ 0.2, 0.50 ≦ a < 1, 0 < b ≦ 0.25, 0 < c ≦ 0.25, 0 ≦ d ≦ 0.1, and a + b + c + d = 1, respectively, for the positive electrode material of claim 11.

13. The positive electrode material according to claim 1, wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is 9:1 to 1:

9.

14. The positive electrode material according to claim 1, wherein the first positive electrode active material and the second positive electrode active material each have a residual lithium by-product content of 1 wt% or less based on 100 wt% of the positive electrode active material.

15. A positive electrode for a secondary battery, comprising a current collector and a positive electrode active material layer provided on the current collector and containing the positive electrode material according to any one of claims 1 to 14.

16. A secondary battery comprising the positive electrode for a secondary battery according to claim 15, a negative electrode, and a separator.

17. The secondary battery according to claim 16, wherein the negative electrode contains a silicon-based active material.

18. The secondary battery according to claim 17, wherein the negative electrode further contains a carbon-based active material.

19. The secondary battery according to claim 16, wherein the efficiency Ec of the positive electrode for the secondary battery is smaller than the efficiency Ea of the negative electrode.

20. A step of manufacturing a single-particle positive electrode active material by mixing a transition metal precursor and a lithium raw material and then firing, A step of washing the positive electrode active material with water, A method for manufacturing a positive electrode active material, comprising a step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material.

21. The step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material includes a step of forming a coating layer containing cobalt (Co) before forming a coating layer containing boron (B), and a step of manufacturing a coating layer containing boron (B), for the method for manufacturing a positive electrode active material according to claim 20.

22. A method for manufacturing a positive electrode material according to any one of claims 1 to 14, comprising: forming a single-particle first positive electrode active material by firing after mixing a transition metal precursor and a lithium raw material substance; washing the first positive electrode active material with water; and forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the first positive electrode active material, a step of manufacturing a first positive electrode active material; forming a single-particle second positive electrode active material having a particle size larger than that of the single particles of the first positive electrode active material by firing after mixing a transition metal precursor and a lithium raw material substance; washing the second positive electrode active material with water; and forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the second positive electrode active material, a step of manufacturing a second positive electrode active material; mixing the first positive electrode active material and the second positive electrode active material, a method for manufacturing a positive electrode material.

23. In at least one of the step of manufacturing the first positive electrode active material and the step of manufacturing the second positive electrode active material, the step of forming a coating layer containing boron (B) and cobalt (Co) on at least a part of the surface of the positive electrode active material includes forming a coating layer containing cobalt (Co) before forming a coating layer containing boron (B), and a step of manufacturing a coating layer containing boron (B), the method for manufacturing a positive electrode material according to claim 22.

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