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

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same, the positive electrode active material for the lithium secondary battery including a core including a lithium nickel-based compound having a Ni content of 80 mol % or more, and a coating material located on at least a portion of the core surface, the coating material including a first coating material including one or more of a Group 5 element and a Group 6 element, and S, and a second coating material including B, LiOH, Li2CO3, and Li2SO4, the second coating material being an acicular material.

Description

[Technical field]

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

[0002] Recently, in response to the explosive increase in demand for IT mobile devices and small power-driven devices (e-bikes, small EVs, etc.), as well as the demand for electric vehicles with driving distances of over 400 km, the development of high-capacity, high-energy density secondary batteries to power these devices is being actively pursued around the world.

[0003] In order to manufacture such high-capacity batteries, a high-capacity positive electrode active material is required. In particular, LiNiO, which is a layered high-capacity positive electrode active material with the highest capacity, is used. 2 (275mAh / g) was proposed, but this active material is prone to structural collapse during charging and discharging, and has low thermal stability due to oxidation number issues, making it difficult to commercialize.

[0004] Therefore, research into high-capacity positive electrode active materials is being continued. Summary of the Invention [Problem to be solved by the invention]

[0005] One embodiment is intended to provide a positive electrode active material for a lithium secondary battery having excellent electrochemical stability.

[0006] Another embodiment provides a lithium secondary battery including the positive electrode active material. [Means for solving the problem]

[0007] According to one embodiment, the present invention includes a core including a lithium nickel-based compound having a Ni content of 80 mol % or more; and a coating material located on at least a portion of the surface of the core, the coating material including a first coating material including at least one of a group 5 element and a group 6 element, and S, and a second coating material including at least one of B, LiOH, Li, 2 CO 3 and Li 2 SO 4 wherein the second coating is an acicular material.

[0008] The needle-shaped material has a long axis and a short axis, and the length ratio of the long axis (L1) to the short axis (L2) can satisfy the relationship of the following formula 1. [Formula 1] 0.1<(L2 / L1)<1.00

[0009] The core may include secondary particles formed by granulating at least one of primary particles including a lithium nickel-based compound.

[0010] The lithium nickel-based compound may be represented by the following formula 1: [Chemical formula 1] Li(Ni) 1-(x+y) Co x Mn y X z )O 2 (In the above chemical formula 1, 0<(x+y)<0.2, 0≦x≦0.2, 0≦y≦0.2, and 0≦z≦0.2, X contains at least one of Zr, Al, Ti, B, Mg, Ce, Si, Na, and Zn.

[0011] The first coating may be disposed on at least a portion of the surface of the primary particles and at least a portion of the surface of the secondary particles, and the second coating may be disposed on at least a portion of the surface of the secondary particles.

[0012] Any one or more of the Group 5 and Group 6 elements may be V, Nb, W, or a combination thereof.

[0013] The content of the Group 5 element and the Group 6 element may be 10 ppm to 10,000 ppm based on the total amount of the positive electrode active material.

[0014] The content of LiOH may be 100 ppm to 10,000 ppm based on the total amount of the positive electrode active material.

[0015] Li 2 SO 4 The content of may be 10 ppm to 3000 ppm based on the total amount of the positive electrode active material.

[0016] According to another embodiment, there is provided a lithium secondary battery including a positive electrode including the positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte. Effect of the Invention

[0017] The positive electrode active material for a lithium secondary battery according to an embodiment may exhibit excellent cycle life characteristics and a low resistance increase rate. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram illustrating a schematic structure of a lithium secondary battery according to an embodiment; [Diagram 2] 2 is a SEM photograph of the positive electrode active material prepared in Example 1. [Diagram 3] 3 is a photograph showing the major and minor axes of the SEM photograph shown in FIG. 2. [Figure 4] 1 is a SEM photograph of a positive electrode active material prepared in Comparative Example 1. [Diagram 5] 1 is a SEM photograph of a positive electrode active material prepared in Comparative Example 2. [Figure 6] 1 is a SEM photograph of a positive electrode active material prepared in Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail, but they are given by way of example only and are not intended to limit the present invention, which is defined only by the scope of the following claims.

[0020] In this specification, unless otherwise specified, % means % by weight, and 1 ppm means 0.0001% by weight.

[0021] According to one embodiment, a positive electrode active material for a lithium secondary battery includes a core including a lithium nickel-based compound having a Ni content of 80 mol % or more, and a coating material located on at least a portion of a surface of the core. The coating material includes a first coating material including at least one of a group 5 element and a group 6 element, and S, and a second coating material including at least one of B, LiOH, Li, 2 CO 3 and Li 2 SO 4 The second coating comprises:

[0022] In particular, the second coating material may be a needle-like material having a long axis and a short axis, and the length ratio of the long axis (L1) to the short axis (L2) may satisfy the relationship of the following formula 1:

[0023] [Formula 1] 0.1<(L2 / L1)<1.00

[0024] When the length ratio (L2 / L1) of the long axis (L1) to the short axis (L2) of the needle-shaped material satisfies the above formula 1, it is possible to exhibit better cycle life characteristics and a low resistance increase rate. According to one embodiment, the length ratio (L2 / L1) of the long axis (L1) to the short axis (L2) may be more than 0.2 and 0.5 or less.

[0025] If the length ratio (L2 / L1) of the major axis (L1) to the minor axis (L2) is small, such as 0.1 or less, the length of the major axis is too large compared to the minor axis, which may cause problems such as impurities being included and increased resistance. If the length ratio (L2 / L1) of the major axis (L1) to the minor axis (L2) is 1.0 or more, it is not appropriate because the lengths of the major axis and the minor axis are the same or the minor axis is longer than the major axis.

[0026] In addition, the positive electrode active material according to an embodiment includes a first coating material and a second coating material as coating materials, thereby ensuring high capacity of the positive electrode active material, obtaining excellent high-temperature cycle characteristics, and reducing initial resistance and resistance increase rate. The effect of including such coating materials is that the first coating material includes at least one of Group 5 elements and Group 6 elements, and S, and the first coating material includes B, LiOH, Li 2 CO 3 and Li 2 SO 4 This can be achieved, in particular, when the second coating is an acicular material, including all second coatings comprising:

[0027] In addition, the effect of using such a coating material can be more excellent when a high-nickel (High-Ni) lithium nickel-based compound having a Ni content of 80 mol % or more is used as the core, for example, a compound represented by the following Chemical Formula 1. Even if a coating material including a first coating material and a second coating material according to an embodiment is used, when a lithium nickel-based compound having a Ni content of less than 80 mol % or a compound not containing nickel is used as the core, the resistance and the resistance increase rate are sufficiently small, so that the effect of including the first coating material and the second coating material cannot be obtained.

[0028] [Chemical formula 1] Li(Ni) 1-(x+y) Co x Mn y X z )O 2

[0029] In the above chemical formula 1, 0<(x+y)<0.2, 0≦x≦0.2, 0≦y≦0.2, and 0≦z≦0.2;

[0030] X contains at least one of Zr, Al, Ti, B, Mg, Ce, Si, Na, and Zn.

[0031] According to an embodiment, X may be Zr or Al. Zr ions occupy Li sites, and thus act as a kind of pillar, which can further stabilize the layered structure by alleviating the contraction of the lithium ion path during charging and discharging. In addition, Al can further stabilize the layered structure of the positive electrode active material. Therefore, the life characteristics of the lithium secondary battery can be further improved.

[0032] The core may include secondary particles formed by granulating at least one of the primary particles containing the lithium nickel-based compound. In this case, the first coating may be disposed on at least a portion of the surface of the primary particles and at least a portion of the surface of the secondary particles, and the second coating may be disposed only on at least a portion of the surface of the secondary particles. In this manner, the first coating is disposed on all the surfaces of the primary particles and the secondary particles, and the second coating is disposed only on the surfaces of the secondary particles, thereby obtaining an effect of suppressing the rate of increase in resistance and improving the lifespan. This effect cannot be obtained when the first coating and the second coating are disposed only on the surfaces of the secondary particles, because the surfaces of the primary particles deteriorate. Alternatively, when the first coating and the second coating are disposed on all the surfaces of the primary particles and the secondary particles, the effect of suppressing the rate of increase in resistance and improving the lifespan according to one embodiment cannot be obtained, because the resistance increases. In addition, when the first coating is disposed only on the surfaces of the secondary particles and the second coating is disposed on all the surfaces of the primary particles and the secondary particles, the resistance increases, and the desired effect cannot be obtained.

[0033] In the first coating, any one or more of the group 5 and group 6 elements may be V, Nb, W, or a combination thereof.

[0034] The content of the Group 5 element and the Group 6 element in the positive electrode active material may be 10 ppm to 10,000 ppm, 30 ppm to 5,000 ppm, 80 ppm to 2,000 ppm, or 300 ppm to 800 ppm based on the entire positive electrode active material. When the content of the Group 5 element and the Group 6 element in the positive electrode active material is within the above range, excellent cycle life characteristics can be exhibited without an increase in the resistance increase rate.

[0035] The content of LiOH may be in the range of 100 ppm to 10,000 ppm, more specifically 500 ppm to 7,000 ppm, and even more specifically 1,200 ppm to 3,000 ppm, based on the total amount of the positive electrode active material. When the content of LiOH in the positive electrode active material satisfies the above range, excellent initial charge / discharge efficiency and cycle life characteristics can be further improved.

[0036] Li 2 CO 3 The content of Li may be in the range of 1000 ppm to 5000 ppm, more specifically 1500 ppm to 4000 ppm, and even more specifically 2000 ppm to 3500 ppm based on the entire positive electrode active material. 2 CO 3 When the content satisfies the above range, the excellent room temperature and high temperature life characteristics can be further improved and the resistance increase rate can be further reduced.

[0037] Li 2 SO 4 The content of Li may be in the range of 10 ppm to 10,000 ppm, more specifically 80 ppm to 3,000 ppm, further specifically 100 ppm to 2,000 ppm, further specifically 100 ppm to 800 ppm, and further specifically 100 ppm to 400 ppm, based on the entire positive electrode active material. 2 SO4 When the content of satisfies the above range, excellent capacity characteristics can be well ensured, and the cycle life characteristics can be further improved and the initial resistance value can be further reduced.

[0038] The content of B may be 300 ppm to 2000 ppm, or 300 ppm to 1000 ppm, based on the total amount of the positive electrode active material. When the content of B satisfies the above range, excellent capacity characteristics can be well ensured, and cycle life characteristics can be further improved and initial resistance can be further reduced.

[0039] Another embodiment provides a method for producing the positive electrode active material, the method including the steps of: mixing a precursor compound containing nickel, cobalt, and manganese with an X-containing compound (X being at least one of Zr, Al, Ti, B, Mg, Ce, Si, Na, and Zn) to produce a first mixture; performing a first heat treatment on the first mixture and cooling it to produce a cooled product; washing the cooled product with a solution containing a compound containing at least one of Group 5 elements and Group 6 elements and a S source to produce a washed product; washing the washed product with LiOH, a boron compound, and Li 2 SO 4 to form a second mixture; and subjecting the second mixture to a second heat treatment.

[0040] The manufacturing method will now be described in more detail.

[0041] First, a precursor compound containing nickel, cobalt, and manganese, a lithium-containing compound, and an X-containing compound (X is at least one of Zr, Al, Ti, B, Mg, Ce, Si, Na, and Zn) are mixed together to produce a first mixture.

[0042] The precursor compound containing nickel, cobalt and manganese may be prepared by mixing a nickel source material, a cobalt source material and a manganese source material in water to prepare a metal salt aqueous solution, followed by coprecipitation, filtration and drying. At this time, the amounts of the nickel source material, the cobalt source material and the manganese source material used may be appropriately adjusted so as to obtain the final core composition of Formula 1.

[0043] The coprecipitation reaction may be carried out by purging with an inert gas to prevent oxidation of metal ions, and may be carried out at a temperature of 10°C to 70°C.

[0044] The inert gas is N 2 , argon gas, or a combination thereof.

[0045] The coprecipitation reaction can be carried out by adding a chelating agent and a pH adjusting agent to the aqueous metal salt solution. 4 (OH), and the pH adjusting agent may be, but is not limited to, NaOH.

[0046] The drying step can be carried out at 80° C. to 200° C. for 1 hour to 48 hours.

[0047] The average particle diameter (D50) of the precursor compound may be, but is not limited to, 10 μm to 20 μm. Unless otherwise defined in the present specification, the average particle diameter (D50) refers to the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution, and can be measured by a PSA (particle size analyzer).

[0048] The lithium compound may be lithium hydroxide, lithium carbonate, lithium nitrate, hydrates thereof, or a combination thereof.

[0049] The X-containing raw material may be an X-containing oxide, an X-containing nitrate, an X-containing hydroxide, or a combination thereof.

[0050] The mixing ratio of the precursor compound, the lithium compound, and the X-containing source material may be appropriately adjusted to obtain the core of Formula 1.

[0051] Next, the first mixture is subjected to a primary heat treatment and cooled to produce a cooled product. The primary heat treatment process may be performed by, for example, performing a pre-heat treatment at a temperature range of 300°C to 500°C, then heating the mixture to a temperature range of 700°C to 900°C at a heating rate of 1°C / min to 10°C / min, and maintaining the mixture at this temperature for 1 hour to 48 hours. The primary heat treatment process may be performed while flowing oxygen at a rate of 100ml / min to 100,000ml / min.

[0052] When the first heat treatment process is performed under the above temperature conditions, particularly while oxygen is being introduced, the lifetime may be improved. Through the first heat treatment process, the core primary particles of Formula 1 are granulated to form secondary particles.

[0053] The cooling step can be carried out by a conventional method, for example, by natural cooling to room temperature.

[0054] The cooled product is washed with a first solution containing at least one element-containing compound of Group 5 and Group 6 elements and a second solution containing a S source to produce a washed product. In this process, residual lithium on the product surface can be removed, and the cooled product can be coated with a solution containing at least one element-containing compound of Group 5 and Group 6 elements and a S source. At this time, the first solution and the second solution are present in a state of being impregnated into the primary particles.

[0055] The compound containing at least one of the Group 5 elements and the Group 6 elements may be ammonium meta-tungstate, ammonium para-tungstate, tungsten oxide, tungsten halide (halide may be F, Cl, I or a combination thereof), tungsten hexaethoxide, tungsten isopropoxide, tungsten boride, tungsten nitride, tungsten carbonyl or a combination thereof, and the S source may be ammonium sulfate, Li 2 SO 4 , S, or a combination thereof.

[0056] In the solution, the solvent may be water, ethanol, propanol, or a combination thereof.

[0057] The solution may contain at least one element-containing compound of Group 5 elements and Group 6 elements at 0.0001 M to 0.1 M, or at 0.001 M to 0.005 M. The solution may also contain an S source at 0.01 M to 0.5 M, or at 0.01 M to 0.2 M. When the solution contains the element-containing compound and the S source in the above ranges, a positive electrode active material having improved cycle life characteristics and a low resistance increase rate while maintaining excellent initial efficiency and initial resistance can be effectively manufactured.

[0058] The cleaning product is then mixed with a second coating source material to form a second mixture. The mixing process can be performed in a dry process without using a solvent. The second coating source material can be a boron compound, LiOH, and Li 2SO 4 That is, the Li contained in the second coating of the finally obtained positive electrode active material can be 2 CO 3 is formed by the internal reaction of the raw materials added during the manufacturing process, and is not formed by adding a separate raw material.

[0059] The boron compound is H 3 BO 3 , boron oxide, boron nitride, B 4 C, B 2 H 6 , B 2 F 4 , B 2 Cl 4 , B 2 Br 4 , B 2 I 4 The boron compound may be used in an amount of 300 ppm to 2000 ppm, more specifically 300 ppm to 1000 ppm, of boron based on the entire second coating source material.

[0060] The amount of LiOH used may be in the range of 100 ppm to 1000 ppm, more specifically 50 ppm to 700 ppm, and even more specifically 120 ppm to 300 ppm based on the entire second coating raw material. When the content of LiOH added as the second coating raw material satisfies the above range, it is possible to prepare a slurry that can be applied to an electrode during the manufacture of a positive electrode by suppressing the gelation phenomenon of the slurry caused by the residual lithium.

[0061] Li 2 SO 4 The content may be in the range of 10 ppm to 500 ppm, more specifically 10 ppm to 200 ppm, even more specifically 10 ppm to 100 ppm, and even more specifically 20 ppm to 5 ppm based on the entire second coating raw material. 2 SO 4 When the content of satisfies the above range, Li-BC-SO 4Since the ionic conductor of the system is formed, the mobility of lithium ions on the surface of the positive electrode active material is improved, and a lithium secondary battery having excellent life characteristics can be realized.

[0062] That is, in one embodiment, LiOH and Li 2 SO 4 The amount of LiOH and Li present as the second coating of the final positive electrode active material is 2 SO 4 This is believed to be due to the reaction of the lithium and metal raw materials present in the lithium metal oxide during the second heat treatment process after mixing with the second coating raw material.

[0063] Next, the second mixture may be subjected to a second heat treatment, which may be carried out at a temperature in the range of 200° C. to 450° C., and the heat treatment time may be in the range of 1 hour to 12 hours.

[0064] By carrying out the second heat treatment process, the compound containing at least one of group 5 elements and group 6 elements and the S raw material source contained in the first and second solutions are decomposed, and at least one of group 5 elements and group 6 elements and the first coating material of S are present in the positive electrode active material. In addition, the boron compound is also decomposed and exists as boron (B) in the positive electrode active material, and LiOH and Li 2 SO 4 The added state is maintained, and LiOH and Li are added to the positive electrode active material. 2 SO 4 At the same time, some of the LiOH is converted to CO in the atmosphere by the second heat treatment process. 2 Reacts with Li 2 CO 3 This Li 2 CO 3 is present in the positive electrode active material.

[0065] The compound containing at least one of the group 5 and group 6 elements and the S raw material source are used in the form of a solution, and as described above, they are impregnated between the primary particles and are also present on the surfaces of the secondary particles, so that they are present on at least a part of the surfaces of the primary particles and at least a part of the surfaces of the secondary particles in the final active material, thereby more effectively reducing the resistance increase rate.

[0066] Also, LiOH, boron compounds, and Li 2 SO 4 The mixing of LiOH, B, and Li is carried out in a dry process. 2 SO 4 is present only on the surface of the secondary particles, and at the same time, Li 2 CO 3 are present only on the surface of the secondary particles.

[0067] According to yet another embodiment, a lithium secondary battery is provided that includes a positive electrode, a negative electrode, and an electrolyte.

[0068] The positive electrode includes a current collector and a positive electrode active material layer including a positive electrode active material formed on the current collector. The positive electrode active material includes a positive electrode active material according to an embodiment.

[0069] In the positive electrode, the content of the positive electrode active material may be 90 wt % to 98 wt % based on the total weight of the positive electrode active material layer.

[0070] In an embodiment, the positive electrode active material layer may further include a binder and a conductive material, each of which may be in an amount of 1 wt % to 5 wt % based on the total weight of the positive electrode active material layer.

[0071] The binder serves to adhere the positive electrode active material particles to each other and to 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, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc.

[0072] The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause chemical changes in the battery that is constructed and is electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures thereof.

[0073] The current collector may be, but is not limited to, aluminum foil, nickel foil, or a combination thereof.

[0074] The positive electrode active material layer is formed by mixing a positive electrode active material, a binder, and an optional conductive material in a solvent to prepare an active material composition, and then coating the active material composition on a current collector. Since the method for forming the active material layer is well known in the art, detailed description thereof will be omitted in this specification. The solvent may be, but is not limited to, N-methylpyrrolidone.

[0075] The negative electrode may include a current collector and a negative electrode active material layer formed on the current collector and including the negative electrode active material according to an embodiment.

[0076] In the negative electrode active material layer, the content of the negative electrode active material in the negative electrode active material layer may be 80% to 98% by weight based on the total weight of the negative electrode active material layer.

[0077] The negative electrode active material layer contains a binder and may further selectively contain a conductive material. In the negative electrode active material layer, the content of the binder may be 1% to 5% by weight based on the total weight of the negative electrode active material layer. When further containing a conductive material, 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material can be used.

[0078] 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 dedoping lithium, or a transition metal oxide as the negative electrode active material.

[0079] The material capable of reversibly intercalating / deintercalating lithium ions is a carbon material, and any carbon-based negative electrode active material generally used in a lithium ion secondary battery can be used. Typical examples thereof include crystalline carbon, amorphous carbon, or a combination thereof.

[0080] As the alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0081] Examples of the material capable of doping and dedoping lithium include Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof and is not Si), Sn, SnO 2, Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn).

[0082] The transition metal oxide may include vanadium oxide, lithium vanadium oxide, etc. The negative electrode active material layer may also include a binder, and may optionally further include a conductive material.

[0083] The binder serves to adhere the negative active material particles to each other and to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0084] The non-water-soluble binder may be an ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0085] The water-soluble binder may be styrene butadiene rubber, acrylated styrene butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0086] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal may be Na, K, or Li. The amount of the thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0087] The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause chemical changes in the battery that is constructed and is electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures thereof.

[0088] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0089] The negative electrode is formed by mixing a negative active material, a binder, and optionally a conductive material in a solvent to prepare an active material composition, and then coating the active material composition on a current collector. The solvent may be water.

[0090] Since the method for forming the negative electrode is well known in the art, a detailed description thereof will be omitted here.

[0091] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0092] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0093] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0094] Examples of the carbonate solvent include 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. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. The ketone solvent may be cyclohexanone, etc. The alcohol solvent may be ethyl alcohol, isopropyl alcohol, etc., and the aprotic solvent may be nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0095] The non-aqueous organic solvents may be used alone or in combination. When using in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which should be widely understood by those skilled in the art.

[0096] In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate, in which the performance of the electrolyte can be excellent when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9.

[0097] When the non-aqueous organic solvents are used in combination, a mixed solvent of a cyclic carbonate and a chain carbonate, a mixed solvent of a cyclic carbonate and a propionate-based solvent, or a mixed solvent of a cyclic carbonate, a chain carbonate, and a propionate-based solvent may be used. As the propionate-based solvent, methyl propionate, ethyl propionate, propyl propionate, or a combination thereof may be used.

[0098] In this case, when a cyclic carbonate and a chain carbonate or a cyclic carbonate and a propionate-based solvent are mixed and used in a volume ratio of 1:1 to 1:9, the performance of the electrolyte may be excellent. In addition, when a cyclic carbonate, a chain carbonate and a propionate-based solvent are mixed and used in a volume ratio of 1:1:1 to 3:3:4, the electrolyte may be mixed and used in a volume ratio of 1:1:1 to 3:3:4. Of course, the mixing ratio of the solvents may be appropriately adjusted according to the desired physical properties.

[0099] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent, and the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0100] As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound represented by the following formula 2 can be used.

[0101] [Chemical formula 2] [ka]

[0102] (In the above chemical formula 2, R 1 ~R 6 are the same or different and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

[0103] Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, It is selected from the group consisting of fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0104] The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by the following Formula 3 as a life-improving additive in order to improve the battery life.

[0105] [Chemical formula 3] [ka]

[0106] (In the above chemical formula 3, R 7 and R 8 are the same or different and represent hydrogen, halogen, cyano (CN), nitro (NO 2 ), and a fluorinated alkyl group having 1 to 5 carbon atoms, 7 and R 8 At least one of the following is a halogen group, a cyano group (CN), a nitro group (NO 2 ), and fluorinated alkyl groups having 1 to 5 carbon atoms, with the proviso that R 7 and R 8 But not all of them are hydrogen.)

[0107] Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life-improving additive is further used, the amount of the additive used can be appropriately adjusted.

[0108] The electrolyte may further include vinyl ethylene carbonate, propane sultone, succinonitrile, or a combination thereof, and the amount used may be appropriately adjusted.

[0109] The lithium salt is dissolved in an organic solvent and serves as a source of lithium ions in the battery to enable basic operation of a lithium secondary battery and promote the movement of lithium ions between the positive and negative electrodes. A representative example of such a lithium salt is LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6, LiN(SO 2 C 2 F 5 ) 2 , Li(CF 3 SO 2 ) 2 N, LiN(SO 3 C 2 F 5 ) 2 , LiC 4 F 9 SO 3 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ) (where x and y are natural numbers, for example integers from 1 to 20), LiCl, LiI, and LiB(C 2 O 4 ) 2 (lithium bis(oxalato)borate (LiBOB)) as a supporting electrolyte salt. The concentration of the lithium salt is preferably within a range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, and therefore excellent electrolyte performance can be exhibited, and lithium ions can be effectively transferred.

[0110] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multi-layer film of two or more layers of these may be used, and of course, a mixed multi-layer 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 be used.

[0111] An exploded perspective view of a lithium secondary battery according to an embodiment of the present invention is shown in Fig. 1. Although the lithium secondary battery according to the embodiment is described as being prismatic, the present invention is not limited thereto and may be applied to batteries of various shapes such as cylindrical and pouch types.

[0112] 1, a lithium secondary battery 100 according to an embodiment may include an electrode assembly 40 in which a separator 30 is interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown).

[0113] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples. EXAMPLES

[0114] (Production Example 1 - Production of Positive Electrode Active Material Precursor) The nickel source material is NiSO 4 6H 2 O, CoSO as a cobalt source material 4 7H 2 O, MnSO as manganese source material 4 H 2 These raw materials were dissolved in distilled water using O to prepare aqueous metal salt solutions.

[0115] The metal salt aqueous solution was co-precipitated with N 2 While maintaining the reactor temperature at 50° C., NH was added as a chelating agent to the coprecipitation reactor. 4 A co-precipitation step was carried out by dosing (OH) and using NaOH for pH adjustment.

[0116] The precipitate obtained by the coprecipitation process was filtered, washed with distilled water, and then dried in an oven at 100°C for 24 hours to obtain a 14.8μm average particle diameter (Ni 0.88 Co 0.05 Mn0.07 )(OH) 2 A positive electrode active material precursor was produced.

[0117] (Comparative example 1-Ni 85% positive electrode active material production) Based on 1 mole of the positive electrode active material precursor prepared in Preparation Example 1, LiOH·H 2 The first mixture was prepared by uniformly mixing 1.05 mol of O (Morita Chemical, battery grade) and the X-containing compound. At this time, the X-containing compound was ZrO 2 (Aldrich, 3N) and Al(OH) 3 (Aldrich, 4N) was used, and the amount of the X-containing compound used was such that the desired compound composition was obtained.

[0118] The first mixture was charged into a tube furnace and subjected to a first heat treatment while oxygen was flowed in at 200 mL / min. The first heat treatment process was performed by pre-heating at 480°C for 5 hours, then heating to 760°C at a heating rate of 5°C / min and maintaining this temperature for 16 hours. The product of the first heat treatment was then naturally cooled to 25°C to obtain LiNi 0.85 Co 0.09 Mn 0.06 Zr 0.0037 Al 0.0001 O 2 The cooled product was formed of secondary particles formed by granulating the primary particles.

[0119] (Comparative Example 2 - LiOH 2500ppm and Li 2 CO 3 (Contains 2000ppm Ni (85% positive electrode active material) The cooled product prepared in Comparative Example 1 was washed with distilled water, filtered and dried. The resulting dried product was subjected to a secondary heat treatment at 280°C for 5 hours to obtain LiNi 0.85 Co 0.09 Mn 0.06 Zr 0.0037 Al 0.0001 O 2The core contains secondary particles formed by granulating the primary particles represented by the formula: 2 CO 3 A positive electrode active material having a coating layer containing the above was prepared.

[0120] (Comparative Example 3 - W 200 ppm, LiOH 2500 ppm and Li 2 CO 3 (85% positive electrode active material containing 2000ppm Ni) The cooled product prepared in Comparative Example 1 was washed with an aqueous solution of 0.0004M ammonium meta-tungstate (AMT) in distilled water, filtered, and dried.

[0121] The resulting dried product was subjected to a secondary heat treatment at 280°C for 5 hours to obtain LiNi 0.85 Co 0.09 Mn 0.06 Zr 0.0037 Al 0.0001 O 2 The core contains secondary particles formed by granulating the primary particles represented by the formula: 2 CO 3 , 200ppm W and 300ppm Li 2 SO 4 A positive electrode active material having a coating layer containing the above was prepared.

[0122] (Example 1 - W 200 ppm, LiOH 2500 ppm, Li 2 CO 3 2000ppm, B 500ppm, and Li 2 SO 4 (85% positive electrode active material containing 500ppm Ni) The cooled product prepared in Comparative Example 1 was washed with an aqueous solution of 0.0004M ammonium meta-tungstate (AMT) and 0.04M ammonium sulfate (AS) in distilled water, filtered, and dried.

[0123] The resulting dried product was dissolved in 500 ppm LiOH, H 3 BO 3 500 ppm, and Li 2 SO 4 The mixture was then subjected to a secondary heat treatment at 280°C for 5 hours to prepare a positive electrode active material. 0.85 Co 0.09 Mn 0.06 Zr 0.0037 Al 0.0001 O 2 and a coating material located on the surface of the core. W and S are located on the surface of the primary particles, and W, S, LiOH, Li are located on the surface of the secondary particles. 2 CO 3 , B, and Li 2 SO 4 In this case, the W content is 200 ppm, the LiOH content is 2500 ppm, and the Li 2 CO 3 The content is 2000ppm, the B content is 500ppm, and the Li 2 SO 4 The content was 500 ppm.

[0124] The AMT content and AS content used in Example 1 and Comparative Examples 1 to 3, and the W, S and Li contained in the active material 2 SO 4 The contents are summarized in Table 1 below.

[0125] [Table 1]

[0126] (Production example 2) Half cell production The positive electrode active materials prepared in Example 1 and Comparative Examples 1 to 3, a denka black conductive material, and a polyvinylidene fluoride binder (product name: KF1100) were mixed in a weight ratio of 92.5:3.5:4, and the mixture was added to an N-methyl-2-pyrrolidone solvent so that the solid content was about 30% by weight, to prepare a positive electrode active material slurry.

[0127] The slurry was coated on an aluminum foil (thickness: 15 μm) as a positive electrode current collector using a doctor blade, dried, and then rolled to prepare a positive electrode. The loading amount of the positive electrode was 14.6 mg / cm 2 and the rolling density is 3.1 g / cm 3 It was.

[0128] A 2032 coin-type half cell was fabricated in a conventional manner using the positive electrode, a lithium metal negative electrode (200 μm, Honzo metal), an electrolyte, and a polypropylene separator. The electrolyte was 1M LiPF 6 The above was dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (mixing ratio EC:DMC:EMC = 3:4:3 by volume), and 1.5 wt% vinylene carbonate was added to the resulting product (100 wt%) to prepare a mixed solution.

[0129] (Experimental example 1: SEM evaluation) SEM photographs of the positive electrodes prepared using the positive electrode active materials prepared in Example 1 and Comparative Examples 1 to 3 were taken, and the results are shown in FIGS. 2 to 5 (FIGS. 2 and 3: Example 1, FIG. 4: Comparative Example 1, FIG. 5: Comparative Example 2, and FIG. 5: Comparative Example 3).

[0130] As shown in Figure 4, the positive electrode active material of Comparative Example 1, which was not subjected to a water washing process, has an uneven surface, whereas the positive electrode active material of Comparative Example 2, which was subjected to a water washing process, has a smooth surface, as shown in Figure 5. In addition, as shown in Figure 6, the positive electrode active material of Comparative Example 3, which includes only the first coating material, does not have a needle-shaped coating on the surface.

[0131] On the other hand, it is clear that the positive electrode active material of Example 1 including the first coating and the second coating has needle-shaped materials on the surface as shown in Figure 2. In addition, the major axis / minor axis length ratio (average ratio) was calculated from Figure 3 showing the major axis and minor axis of the SEM photograph of Figure 2, and was found to be 0.27.

[0132] (Experimental Example 2: Evaluation of charge / discharge capacity, initial efficiency, and initial resistance at room temperature (25°C)) The manufactured coin-type half cell was aged at room temperature (25° C.) for 10 hours, and then charged and discharged.

[0133] Charge and discharge were performed once at a constant current / constant voltage of 2.5V to 4.25V with a 1 / 20C cut-off condition, charging at 0.1C and discharging at 0.1C, and the charge capacity and discharge capacity were determined, and the results are shown in Table 2 below. The ratio of the discharge capacity to the charge capacity was also determined, and the result is shown in Table 2 below as the single cycle efficiency. When evaluating the capacity, the reference capacity was set to 215mAh / g.

[0134] The initial resistance was calculated by fully charging the battery to 4.25V at 0.2C (charging rate: 100%) and discharging it at 0.2C, measuring the voltage value after 60 seconds and the change in the voltage value relative to the applied current, i.e., the voltage change over 60 seconds. The results are shown in Table 2 below.

[0135] (Experimental Example 3: High temperature (45℃) cycle life and resistance increase rate evaluation) The manufactured coin-type half cell was charged and discharged 30 times at 0.3 C with a constant current / constant voltage of 2.5 V to 4.25 V and a 1 / 20 C cut-off condition at 45° C. The ratio of the single discharge capacity to the discharge capacity after 30 cycles was calculated, and the results are shown in Table 3 below as cycle life characteristics.

[0136] In addition, the resistance increase rate was determined by fully charging to 4.25 V at 0.2 C at high temperature (45°C) (charging rate: 100%), discharging at 0.2 C, measuring the voltage fluctuation for 60 seconds, and determining the 1-cycle resistance. After fully charging and discharging 30 times, the 30-cycle resistance was measured with a voltage fluctuation for 60 seconds, and the results are shown in Table 3 below. In addition, the ratio of the 30-cycle resistance to the 1-cycle resistance was determined, and the results are shown in Table 3 below.

[0137] [Table 2]

[0138] [Table 3]

[0139] As shown in Tables 2 and 3, the half cell using the positive electrode active material of Example 1 exhibits a low high-temperature resistance increase rate while maintaining a low initial resistance, excellent single-cycle efficiency, and high-temperature cycle life. In contrast, the positive electrode active materials of Comparative Examples 1 to 3 exhibited a somewhat low single-cycle efficiency and a very large resistance increase rate.

[0140] The present invention is not limited to the above-mentioned embodiments, and can be manufactured in various different forms, and a person having ordinary skill in the art to which the present invention pertains can understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting.

Claims

1. A core including a lithium nickel-based compound having a Ni content of 80 mol% or more; and a coating material located on at least a portion of a surface of the core; The coating material is a first coating material containing at least one of Group 5 elements and Group 6 elements and S, and B, LiOH, Li ２ CO ３ and Li ２ SO ４ a second coating comprising The second coating is a needle-shaped material, The needle-shaped material has a major axis and a minor axis, and the length ratio of the major axis (L1) to the minor axis (L2) satisfies the relationship of the following formula 1. [Formula 1] 0.1<(L2 / L1)<1.00

2. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the core of the positive electrode active material includes secondary particles formed by granulating at least one of the primary particles including the lithium nickel-based compound.

3. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the lithium nickel-based compound is represented by the following Chemical Formula 1: [Chemical formula 1] L) １－（ｘ＋ｙ） Co ｘ Mn ｙ X ｚ )O ２ (In the above chemical formula 1, 0<(x+y)<0.2, 0≦x≦0.2, 0≦y≦0.2, and 0≦z≦0.2, X includes at least one of Zr, Al, Ti, B, Mg, Ce, Si, Na, and Zn.

4. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the first coating is located on at least a portion of a surface of the primary particles and at least a portion of a surface of the secondary particles.

5. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the second coating is located on at least a portion of a surface of the secondary particle.

6. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein at least one of the Group 5 elements and the Group 6 elements is V, Nb, W, or a combination thereof.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of the Group 5 element and the Group 6 element is 10 ppm to 10,000 ppm based on the total amount of the positive electrode active material.

8. 2. The positive active material for lithium secondary transfer according to claim 1, wherein the content of LiOH is 100 ppm to 10,000 ppm based on the total amount of the positive active material.

9. The Li ２ SO ４ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of is 10 ppm to 3000 ppm based on the total amount of the positive electrode active material.

10. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 9; A negative electrode; and Nonaqueous electrolyte A lithium secondary battery comprising:

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