Method for treating positive electrode active material particles, positive electrode active material, and non-aqueous electrolyte secondary battery using the same

Abstract

The present invention relates to a method for treating positive electrode active material particles, which reduces excess lithium remaining in the surface layers of lithium-nickel composite compound particles and achieves a balance between lowering resistance due to reduced resistance components and improving battery capacity.The present invention also relates to such positive electrode active material particles and a nonaqueous electrolyte secondary battery including a positive electrode containing such positive electrode active material.

Description

[Technical Field]

[0001] The present invention relates to a method for treating positive electrode active material particles, a positive electrode active material, and a non-aqueous electrolyte secondary battery using the same. [Background technology]

[0002] Small, lightweight, and high-energy-density non-aqueous secondary batteries are well known as power sources for mobile phones, laptops, etc. Among these, lithium-ion secondary batteries, which have large charge / discharge capacities and use high-nickel materials such as lithium cobalt oxide or lithium nickel oxide for the positive electrode, are widely used.

[0003] Examples of positive electrode active materials used in lithium-ion secondary batteries include high-nickel positive electrode active materials, such as nickel-cobalt-manganese (NCM)-based positive electrode active materials in which nickel is partially replaced with cobalt and manganese is incorporated, and nickel-cobalt-aluminum (NCA)-based positive electrode active materials in which nickel is partially replaced with cobalt and aluminum is incorporated. Currently, high-capacity batteries can be obtained by using positive electrode active materials formed from high-nickel layered compounds with nickel contents exceeding 80 mol%. However, repeated use of lithium-ion secondary batteries using such positive electrode active materials over long periods of time can result in problems such as gas generation from the lithium-ion secondary battery and increased reaction resistance, resulting in reduced output and cycle characteristics.

[0004] One of the causes of this problem is thought to be the influence of lithium components remaining on the surface of positive electrode active material particles. To obtain positive electrode active material particles with a good crystalline state in such high-nickel-content positive electrode active materials, the lithium compound and precursor composite compound must be mixed together in a molar amount slightly greater than the metal components in the precursor composite compound, i.e., the Li / (metal components in the precursor composite compound) ratio must be slightly greater than 1.0. As a result, excess lithium remains on the surface of the lithium-nickel composite compound particles obtained through the calcination process. Attempts have been made to reduce the amount of residual lithium by washing the lithium-nickel composite compound after the calcination process with water and heat treating it. While using a temperature of approximately 100°C in the drying step of the heat treatment can reduce the excess lithium, washing with water does not eliminate proton exchange to Li sites in the particle surface layer, resulting in the formation of resistance components. Furthermore, using temperatures above 450°C causes lithium to separate from the crystal lattice within the particles and dissolve into the particle surface layer during the heat treatment, ultimately resulting in the formation of excess lithium in the particle surface layer. For this reason, attempts have been made to reduce the resistance component resulting from proton exchange into the Li site while reducing the excess lithium remaining on the particle surface.

[0005] For example, Patent Document 1 discloses that in a lithium-ion secondary battery, the surface layer of a high-nickel positive electrode active material is coated with an oxide containing lithium and niobium in order to prevent gas generation and improve the battery output characteristics. Specifically, Patent Document 1 discloses a method for producing an active material composite powder, which includes a spray-drying step in which a solution containing a niobium peroxo complex and lithium is sprayed onto an active material such as lithium-nickel-manganese-cobalt (NMC) while drying the material in parallel; and a heat-treatment step in which the material is heat-treated after the spray-drying step, where the heat-treatment temperature is above 123°C and not more than 350°C.

[0006] Furthermore, Patent Document 2 discloses that the surfaces of positive electrode active material particles are coated with lithium niobate, and for this purpose, a slurry obtained by dispersing Nb2O5 in pure water is added to an aqueous solution of nickel-cobalt-manganese hydroxide, followed by drying and calcination.

[0007] Furthermore, Patent Document 3 discloses that the surfaces of positive electrode active material particles are coated with lithium niobate, and for this purpose, the positive electrode active material and niobium oxide are mixed and stirred while being sprayed with 10 mass % pure water, and then heat-treated.

[0008] Furthermore, Patent Document 4 describes a positive electrode active material containing calcium on the surface of primary particles and niobium on the surface of secondary particles. To obtain such a positive electrode active material, calcium-containing positive electrode active material particles are washed with water, then mixed with niobium hydroxide, and the mixture is heat-treated. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2015-056307 A [Patent Document 2] JP 2019-139862 A [Patent Document 3] WO 2021 / 054468 A1 [Patent Document 4] WO 2021 / 241078 A1 [Non-patent literature]

[0010] [Non-Patent Document 1] Analele Universitatii din Bucuresti-Chimie, Anul XIV(serie noua), vol.I-II, pp.65-72 Summary of the Invention [Problem to be solved by the invention]

[0011] As mentioned above, Patent Document 1 describes the production of active material particles in which a solution containing a niobium peroxo complex and lithium is sprayed onto an active material, and the solution is dried in parallel to the spraying, thereby forming a lithium niobate (LiNbO) coating layer on the surface layer of the active material. This lithium niobate coating layer allows a lithium ion conductive oxide layer to be interposed at the interface between the sulfide-based solid electrolyte and the positive electrode active material, which is expected to improve battery characteristics. Furthermore, Patent Document 1 shows that the lithium niobate coating layer formed in this manner has few voids and therefore high lithium ion conductivity, making it possible to produce active material particles for lithium batteries with reduced resistance components.

[0012] However, since no special operation was performed to reduce the amount of lithium contained in the active material particles produced in this manner, it is believed that excess lithium remains in the surface layer of the active material particles. Therefore, when these active material particles are actually used as a positive electrode active material, there are problems in that gas is generated by the residual lithium in the lithium secondary battery and the reduction of the resistance component is insufficient.

[0013] Furthermore, in Patent Documents 2 to 4, it is believed that the effect of excess lithium on the particle surfaces can be suppressed to some extent by washing the particles with water (forming a slurry) or coating the surfaces of the positive electrode active material particles with lithium niobate.

[0014] However, none of the treatment methods described in the above documents are suitable for reducing excess lithium present on the particle surface of the positive electrode active material, and there is a risk that the excess lithium may not be sufficiently reduced. Furthermore, the excess lithium may cause gelation of the slurry during battery production and gas generation after battery production. Furthermore, as a result of water washing (slurrying), there is a possibility that resistance components, mainly due to proton exchange with Li in the particle surface layer, may increase. Even if an attempt is made to increase the capacity of the battery by performing heat treatment to remove excess lithium, the resistance components may cause problems with the long-term life of the battery.

[0015] For these reasons, there is a demand for materials that can achieve both low resistance and high capacity while suppressing excess residual lithium.

[0016] The present invention has been made in view of the above-mentioned problems of the conventional art, and an object of the present invention is to provide a method for treating positive electrode active material particles that reduces the amount of lithium remaining in excess on the surface layers of lithium-nickel composite compound particles, thereby achieving both lower resistance due to a reduction in the resistance component and improved battery capacity, and also to provide a positive electrode active material and a nonaqueous electrolyte secondary battery using the same. [Means for solving the problem]

[0017] To achieve this object, the present invention provides a method for treating positive electrode active material particles, which reduces excess lithium in the surface layer of the positive electrode active material particles by suitably carrying out slurry formation of a lithium-nickel composite compound, including a water-washing step, and mixing with a transition metal compound, thereby achieving both low resistance and high battery capacity of the positive electrode active material particles after heat treatment. Furthermore, this treatment method achieves the above object by ensuring that compounds containing lithium and a transition metal element, and compounds containing a transition metal element, are present on the surfaces of the secondary particles of the positive electrode active material and at least in part of the grain boundaries (interfaces of the primary particles) formed by adjacent primary particles located on the surfaces of multiple primary particles that make up the secondary particles.

[0018] Specifically, the present invention provides a method for treating positive electrode active material particles containing a lithium-nickel composite compound that contains lithium, nickel, and oxygen and may contain other elements in addition to lithium, nickel, and oxygen, the method comprising the following steps: (1) a slurry formation step of introducing a lithium-nickel composite compound into an aqueous solvent and stirring the mixture to prepare a slurry; (2) a filtration / separation step of filtering the slurry to obtain a cake-like compound after the slurry-forming step; and (3) a heat treatment step of heat treating the cake-like compound obtained in the filtration separation step to obtain a dried lithium-nickel composite compound; Including, wherein the method further comprises, in at least one of steps (1), (2) and / or (3), a step of mixing the aqueous solvent (used in step (1)), the slurry (in step (1)), the cake-like compound (in step (2)) and / or the dried lithium nickel composite compound (in step (3)) with (i) a compound containing at least one transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta, and (ii) optionally with a lithium compound; when the compound containing at least one transition metal element is mixed with the dried lithium nickel composite compound (in step (3)), the mixing is carried out in the presence of an aqueous solvent; and The resulting products include compounds containing lithium and transition metal elements, and compounds containing transition metal elements: (a) The surface of secondary particles of a dried lithium-nickel composite compound, and (b) at least a portion of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surfaces of multiple primary particles constituting a secondary particle; exists in.

[0019] The method of the present invention can alternatively be described as a method for preparing positive electrode active material particles comprising a lithium-nickel composite compound that includes lithium, nickel, and oxygen, and may include other elements other than lithium, nickel, and oxygen, and this method includes the same steps as outlined above, i.e., (1) a slurry formation step of introducing a lithium-nickel composite compound into an aqueous solvent and stirring the mixture to prepare a slurry; (2) a filtration / separation step of filtering the slurry to obtain a cake-like compound after the slurry-forming step; and (3) a heat treatment step of heat treating the cake-like compound obtained in the filtration separation step to obtain a dried lithium-nickel composite compound; Including, wherein the method further comprises, in at least one of steps (1), (2) and / or (3), a step of mixing the aqueous solvent (used in step (1)), the slurry (in step (1)), the cake-like compound (in step (2)), or the dried lithium nickel composite compound (in step (3)) with (i) a compound containing at least one transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta, and (ii) optionally with a lithium compound; when the compound containing at least one transition metal element is mixed with the dried lithium nickel composite compound, the mixing is carried out in the presence of an aqueous solvent; and The resulting products include compounds containing lithium and transition metal elements, and compounds containing transition metal elements: (a) The surface of secondary particles of a dried lithium-nickel composite compound, and (b) at least a portion of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surfaces of multiple primary particles constituting a secondary particle; exists in.

[0020] Hereinafter, what has been said about the "processing method" of the present invention also applies mutatis mutandis to the expression "preparation method."

[0021] The present invention also relates to a positive electrode active material obtainable by the method according to the present invention; Similarly, the present invention also relates to a positive electrode active material containing a lithium-nickel composite compound that contains lithium, nickel, and oxygen and may contain other elements in addition to lithium, nickel, and oxygen, Compounds containing lithium and transition metal elements, and compounds containing transition metal elements: (a) the surface of secondary particles of the lithium nickel composite compound, and (b) at least a portion of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surfaces of multiple primary particles constituting a secondary particle; present in; The transition metal element is at least one selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta; and The amount of residual lithium determined by neutralization titration is preferably 0.15% by mass or less.

[0022] Furthermore, the present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material of the present invention.

[0023] According to the present invention, by controlling the excess amount of lithium generated in the slurry formation step and introducing a transition metal element that reacts with this excess amount of lithium, not only is it possible to reduce the excess amount of lithium that ultimately remains, but it is also possible to effectively control the location and amount of the compound of lithium and the transition metal element, thereby achieving both high battery capacity and low resistance. [Effects of the Invention]

[0024] According to the present invention, by suitably carrying out the formation of a slurry of a lithium-nickel composite compound, including a water-washing step, and the mixing of a transition metal compound, it is possible to provide a method for treating positive electrode active material particles that reduces excess lithium in the surface layer of the positive electrode active material particles and achieves both low resistance of the positive electrode active material particles and high battery capacity after heat treatment, and also to provide a positive electrode active material and a nonaqueous electrolyte secondary battery using the same. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic vertical cross-sectional view of the surface layer of a secondary particle of a lithium-nickel composite compound when a coating layer of a compound containing lithium and a transition metal element and a compound containing a transition metal element is formed by a method for treating positive electrode active material particles according to an embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of a secondary particle of a lithium-nickel composite compound when a coating layer of a compound containing lithium and a transition metal element and a compound containing a transition metal element is formed by a method for treating positive electrode active material particles according to an embodiment. [Figure 3] FIG. 3 is a photograph of a cross section of the positive electrode active material produced by the treatment method according to Examples 1 to 4, taken with a scanning electron microscope using energy dispersive X-ray spectroscopy (SEM-EDX). DETAILED DESCRIPTION OF THE INVENTION

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description of preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its application, or its uses.

[0027] To the extent applicable, the preferred embodiments also apply to the method of the present invention, the positive electrode active material of the present invention, and the nonaqueous electrolyte secondary battery of the present invention.

[0028] <Method for treating positive electrode active material particles> As described above, Patent Document 1 describes a method for producing active material particles having a lithium niobate (LiNbO) coating layer on the surface by spraying a solution containing a niobium peroxo complex and lithium onto the active material and drying the solution in parallel. However, the production method described in Patent Document 1 does not actively involve a treatment to reduce the amount of lithium, so it is believed that excess Li remains in the surface layer of the active material particles. Furthermore, the production method described in Patent Document 1 forms a coating layer on the surface layer of the active material simply by spraying a solution containing a niobium compound. When such active material particles are actually used as a positive electrode active material, problems arise, such as paste gelation during coating formation due to the excess lithium, gas generation after battery production, and insufficient reduction of resistance components.

[0029] Therefore, the present invention has clarified a method for reducing the amount of lithium present in excess in the surface layer of a lithium-nickel composite compound, thereby achieving lower resistance and improved battery capacity by reducing the resistance component, by further mixing a compound containing at least one transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta in at least one of the slurry formation step, filtration separation step, and heating step in addition to washing the lithium-nickel composite compound with water (slurry formation) to remove the excess lithium.

[0030] A method for treating positive electrode active material particles according to one embodiment of the present invention preferably constitutes a method for treating positive electrode active material particles whose main component is a lithium-nickel composite compound that contains lithium (Li), nickel (Ni), and oxygen (O) and may contain other elements in addition to Li, Ni, and O. Therefore, this treatment method includes the following steps (1) to (3), and further includes a step of mixing a compound containing a transition metal element in at least one of step (1), step (2), and / or step (3): (1) a slurry formation step of introducing a lithium-nickel composite compound into an aqueous solvent and stirring the mixture to prepare a slurry; (2) a filtration / separation step of filtering the slurry to obtain a cake-like compound after the slurry-forming step; and (3) A heat treatment step in which the cake-like compound obtained in the filtration separation step is heat treated to obtain a dried lithium-nickel composite compound.

[0031] In a treatment method comprising the above steps (1) to (3) and further comprising a step of mixing a compound containing a transition metal element in at least one of steps (1), (2) and / or (3), the amount of lithium eluted from the lithium-nickel composite compound into the aqueous solvent as a result of slurry formation, and the amount of the compound containing a transition metal element mixed therein, are so small that it is difficult to identify the primary particle size, and it is believed that very fine compounds containing lithium and a transition metal element, and very fine compounds containing a transition metal element, are precipitated on the lithium-nickel composite compound.

[0032] In particular, when the aqueous solvent or slurry is mixed with a compound containing a transition metal element in the slurry formation step (1), the resulting slurry of the lithium-nickel composite compound exhibits an alkaline pH of approximately 11 to 13. Therefore, it is believed that a portion of the mixed transition metal element compound dissolves and penetrates into the secondary particles of the lithium-nickel composite compound as transition metal element ions from the grain boundaries between the primary particles that make up the secondary particles, and ultimately reacts with excess lithium present on the surfaces of the primary particles. As a result, through the filtration separation step (2) and the heat treatment step (3), the compound containing lithium and a transition metal element and the transition metal element compound can be precipitated on the surface layers of the secondary particles and on the grain boundaries between the primary particles of the ultrafine particle lithium-nickel composite compound.

[0033] That is, a compound containing lithium and a transition metal element, and a compound containing a transition metal element are present on the surfaces of the secondary particles of the lithium-nickel composite compound and in the grain boundary portions (surfaces between the primary particles) between the primary particles that make up the secondary particles. As a result, excess lithium remaining on the particle surface layers of the lithium-nickel composite compound can be effectively reduced. Furthermore, due to the effect of improving lithium ion conductivity by the compound containing lithium and a transition metal element synthesized by mixing the transition metal element compound, it is possible to achieve an effect of achieving a balanced combination of lower resistance due to a reduction in reaction resistance components and an improvement in battery capacity.

[0034] However, this also works when a compound containing a transition metal element is added to the cake-like compound obtained in step (2) or the dried lithium nickel composite compound obtained in step (3), as long as some moisture is present (the content of moisture (aqueous solvent) is preferably at least 1% by mass) (relative to the mixture obtained by mixing the lithium nickel composite compound, in the form in which it is present (e.g., in the form of a slurry in step (1) or in the form of a cake-like compound in step (2) or in the form of a dry compound in step (3)), with the compound containing a transition metal element and, optionally, the Li compound), and wherein, in the slurry in step (1) and the cake-like compound obtained in step (2), the moisture content is more preferably at least 3% by mass relative to the total mass of the lithium nickel composite compound and the compound containing a transition metal element (i.e., relative to the mixture obtained by mixing the lithium nickel composite compound, in the form in which it is present (e.g., in the form of a slurry in step (1) or in the form of a cake-like compound in step (2)), with the compound containing a transition metal element and, optionally, the Li compound). When adding the compound containing a transition metal element to the cake-like compound obtained in step (2), the addition of additional water (i.e., aqueous solvent) is possible, but is not necessary because the filter cake after filtration is generally still sufficiently moist. When adding the compound containing a transition metal element to the dried lithium-nickel composite compound obtained in step (3), unless the drying is not complete (which is generally not the case), some water must be introduced to obtain the desired water content and to enable the desired reaction between lithium and the compound containing a transition metal element. This can be done, for example, by rewetting the dried filter cake, or more simply, and therefore preferably, by providing the compound containing a transition metal element in the form of an aqueous solution, or by simultaneously mixing the dried filter cake, the compound containing a transition metal element, and the aqueous solvent.

[0035] "Solution" in the present invention is not limited to a solution in the proper sense (a solution in the proper sense is a single-phase homogeneous mixture of two or more substances in which particles of the solute are invisible to the naked eye; a solution does not cause scattering of light rays), but also includes suspensions and emulsions. Similarly, the term "solvent" means a liquid medium in which solid particles can be dispersed, without the need for a solution in the proper sense to be formed, and therefore also refers to the form of a suspension.

[0036] The steps will be explained below in order.

[0037] (1) Slurry formation process In the slurry formation step (1), a lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry of the lithium-nickel composite compound. In the treatment method of the present invention, the purpose of this step is to remove excess lithium remaining in the lithium-nickel composite compound, but it also aims to minimize damage to the particles caused by washing the lithium-nickel composite compound with water and to precipitate a compound containing lithium and a transition metal element on the particle surface of the lithium-nickel composite compound by reacting with an added transition metal element compound. Therefore, it is necessary to control the amount of Li eluted into the slurry. Therefore, this step is not solely intended to reduce the amount of excess lithium remaining.

[0038] This slurry formation step (1) is a particularly important step in view of the fact that, as described above, it has a sufficient effect of reducing excess lithium in the lithium-nickel composite compound; it controls to suppress proton exchange on the particle surface layer that would be caused by excessive water washing; and it also causes the lithium eluted in the slurry to react with the transition metal element, thereby precipitating a compound containing lithium and a transition metal element on the particle surface of the lithium-nickel composite compound.

[0039] Furthermore, in one option for introducing the compound containing a transition metal element, it is preferable to mix the compound containing a transition metal element with stirring before and / or after introducing the lithium nickel composite compound into the aqueous solvent to prepare a slurry, which will be described in detail later.

[0040] The lithium nickel composite compound used in the present invention contains Li, Ni, and O, and may contain elements other than Li, Ni, and O. There are no particular limitations on the lithium nickel composite compound, and it can be changed as appropriate. Furthermore, the lithium nickel composite compound preferably has a composition having a layered rock salt structure, and is represented by the following formula (I): Li a Ni 1-b-c Mn b M c O2(I) (In the formula, M is one or more different elements other than Li, Ni, Mn, or O, 0.95≦a≦1.15, 0≦b≦0.20, 0≦c≦0.20, and Ni is 0.80 to 0.98 (more precisely, (1−bc) is 0.80 to 0.98)).

[0041] When the Ni content in the lithium-nickel composite compound is high, a high battery capacity is realized, but a problem occurs in that a large amount of excess lithium is present when synthesizing the lithium-nickel composite compound. However, this problem can be solved by using the processing method according to this embodiment.

[0042] Examples of elements M other than Li, Ni, Mn, and O include Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P, and B, and M can be two or more different elements. In specific embodiments, M is one or both of Al and / or Co.

[0043] In a preferred embodiment, b is 0.05 to 0.2 and c is 0; therefore, compound (I) is a compound of formula (I.1): Lia Ni 1-b Mn b O2 (I.1) (where b is 0.05 to 0.2, and Ni is 0.80 to 0.95 (more precisely, (1 - b) is 0.80 to 0.95).

[0044] In another preferred embodiment, the lithium nickel composite compound is represented by the following formula (I.2): Li a Ni 1-c1-c2 Co c1 Al c2 O2 (I.2) (where 0.95 ≤ a ≤ 1.15, 0 < c1 ≤ 0.20, 0 < c2 ≤ 0.20, Ni is 0.80 to 0.98 (more precisely, (1 - c1 - c2) is 0.80 to 0.98), preferably 0.95 ≤ a ≤ 1.15, 0 < c1 < 0.20, 0 < c2 < 0.20, Ni is 0.80 to 0.98 (more precisely, (1 - c1 - c2) is 0.80 to 0.98), more preferably 0.01 ≤ c1 ≤ 0.09, 0.01 ≤ c2 ≤ 0.09).

[0045] The preparation of the slurry can be carried out, for example, by introducing an aqueous solvent containing a predetermined amount of pure water or the like into a reaction tank, introducing the lithium nickel composite compound into the aqueous solvent, and then stirring. The aqueous solvent is not particularly limited and may similarly contain an organic solvent. Suitable organic solvents are water - miscible (preferably miscible with water at 25 °C in any mixing ratio), and examples thereof include C1 - C3 - alkanols (i.e., methanol, ethanol, n - propanol, isopropanol), diols, particularly ethylene glycol and propylene glycol, and cyclic ethers, particularly tetrahydrofuran and 1,4 - dioxane. Preferably, the aqueous solvent is water, and more preferably deionized water. Here, the ratio of the introduction amount of the lithium nickel composite compound to the amount of the aqueous solvent (hereinafter also referred to as the "solid - liquid ratio") can be adjusted within an appropriate range.

[0046] The amount of lithium eluted from the lithium-nickel composite compound is determined by controlling the solid-liquid ratio, and this lithium reacts with the transition metal element in the compound containing the transition metal element that has been mixed at an appropriate time to form a compound containing lithium and the transition metal element, thereby making it possible to appropriately control the amount of remaining lithium in the positive electrode active material, which is the final target product.

[0047] That is, in the slurry formation step (1), the ratio of the amount of the lithium nickel composite compound to the amount of the aqueous solvent (solid-liquid ratio) is preferably adjusted to 750 g / L to 2000 g / L, more preferably 800 g / L to 1800 g / L, and the volume refers to the volume of the solvent used (not the volume of the solution formed; that is, the solid-liquid ratio is preferably adjusted to 750 to 2000 g of the lithium nickel composite compound per 1 liter of aqueous solvent, more preferably 800 to 1800 g of the lithium nickel composite compound per 1 liter of aqueous solvent). The volume refers to the volume of the solvent at room temperature (25°C). If the solid-liquid ratio is below the lower limit, the amount of aqueous solvent becomes excessive, causing excessive elution of Li from the inside of the lithium nickel composite compound particles, which may lead to a deterioration in the quality of the final target positive electrode active material. Furthermore, if the solid-liquid ratio exceeds the upper limit, the amount of aqueous solvent may be insufficient, and the amount of lithium remaining in the surface layer of the secondary particles may become excessively large, making it difficult to appropriately control the amount of residual lithium in the final target positive electrode active material. In this embodiment, by controlling the solid-liquid ratio within the above range, the amount of lithium eluted into the slurry is controlled, and therefore, it is preferable to control the pH of the slurry to 11 to 13 (see also Reaction α below).

[0048] Furthermore, a slurry is prepared by introducing a lithium nickel composite compound into an aqueous solvent and stirring the mixture. By adjusting the stirring time, a sufficiently large amount of Li can be eluted from the secondary particles of the lithium nickel composite compound into the slurry, thereby further improving stability.

[0049] That is, in the slurry formation step (1), the stirring time is preferably adjusted to 3 to 30 minutes, more preferably 5 to 25 minutes, to prepare the slurry. If the stirring time is less than the lower limit, the amount of Li expected to be eluted from the secondary particles of the lithium nickel composite compound may decrease, and the amount of residual lithium may increase. Furthermore, if the stirring time exceeds the upper limit, the effect of preparing the slurry will not be improved, and productivity will decrease.

[0050] The temperature of the aqueous solvent into which the lithium nickel composite compound is introduced is not particularly limited, but in order to prepare an appropriate slurry as described above, it is preferable to adjust the temperature of the aqueous solvent to, for example, about 15°C to 35°C.

[0051] In the slurry formation step (1), for example, a lithium nickel composite compound represented by the formula: Li x When expressed as NiO2, the following reaction α occurs:

[0052] [Reaction α]Li x NiO2Li x-y NiO2+yLiOHaq

[0053] (2) Filtration separation process In the filtration separation step (2), after the completion of the slurry formation step (1), the slurry is filtered using a filtering device such as a Büchner funnel or a filter press to obtain a cake-like compound.

[0054] The filtration / separation step (2) allows the moisture content of the cake-like compound to be adjusted appropriately, thereby further improving the quality of the finally obtained positive electrode active material particles. The moisture content of the cake-like compound after filtration / separation is not particularly limited, but is 20% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less. However, the moisture content of the cake-like compound after filtration / separation is preferably 3% by mass or more. Therefore, the moisture content of the cake-like compound after filtration / separation is preferably 3 to 20% by mass, more preferably 3 to 10% by mass, particularly preferably 3 to 8% by mass, and specifically 5 to 8% by mass, based on the total mass of the cake-like compound.

[0055] The water content of the slurry in the present invention is 65% by mass or less, preferably 60% by mass or less, taking into consideration that the solid-liquid ratio of the slurry is controlled to 750 g / L to 2000 g / L.

[0056] "Water" means an aqueous solvent.

[0057] (3) Heat treatment process In the heat treatment step (3), the cake-like compound obtained in the filtration / separation step (2) is heat-treated and dried to obtain a dried lithium-nickel composite compound. When performing the heat treatment, Non-Patent Document 1 can be referenced, for example. In the present invention, the temperature is preferably set to 100°C to 400°C, e.g., 140°C to 400°C, and more preferably 200°C to 350°C. If the temperature is lower than the lower limit, sufficient drying cannot be easily achieved (generally, it can be achieved only under high vacuum and / or after an excessively long drying time). Unless such measures are taken, a large amount of moisture remains in the finally obtained lithium-nickel composite compound. Furthermore, the added transition metal element does not sufficiently react with the Li fraction, and sufficient effects cannot be obtained. On the other hand, if the temperature is higher than the upper limit, Li separates from the crystal lattice of the lithium-nickel composite compound and dissolves into the particle surface layer, which may increase the amount of residual lithium in the finally obtained lithium-nickel composite compound. Therefore, the heat treatment can also be useful for annealing the composite compound.

[0058] Furthermore, the drying method is not particularly limited, and for example, treatment using a roller hearth kiln or a rotary kiln, vacuum drying treatment, etc. can be suitably employed. Furthermore, the atmosphere during the heat treatment needs to take into consideration the nickel content of the lithium nickel composite compound to be dried, and the drying treatment is preferably carried out, for example, in an oxygen atmosphere, a vacuum atmosphere, an inert gas atmosphere, or decarbonated air with a carbon dioxide concentration of 100 ppm or less.

[0059] In a preferred embodiment of the heat treatment step (3), the cake-like compound obtained in the filtration / separation step (2) is heat-treated in a first step at 100 to 195° C. and an optional second step at 200 to 400° C., more preferably 200 to 350° C. Preferably, the second step is carried out.

[0060] Preferably, the first heat treatment is carried out under reduced pressure, for example under a pressure of 0.1 to 100 mbar. For this purpose, a conventional heatable vacuum drying apparatus can be used.

[0061] Preferably, the second heat treatment is carried out in an oxygen-enriched atmosphere (oxygen-enriched air, an oxygen-nitrogen mixture containing more than 20% oxygen by weight, an oxygen mixture containing oxygen, preferably at least 90% oxygen by weight based on the total weight of the mixture, or pure oxygen); and / or the second heat treatment is carried out in an atmosphere with a reduced CO content, preferably an atmosphere with a CO content of at most 100 ppm by volume (0.01% by volume), more preferably at most 50 ppm by volume (0.005% by volume). More preferably, the second heat treatment is carried out in an oxygen-enriched atmosphere with a simultaneous reduced CO content, preferably a CO content of at most 100 ppm by volume, more preferably at most 50 ppm by volume.

[0062] Preferably, a second heat treatment is performed. Dividing the process into two heating steps is particularly useful when a compound containing a transition metal element is added in step (3). In this case, it is convenient to carry out a first heating step to dry the cake-like compound obtained in step (2), then add a compound containing a transition metal element (and a small amount of water to enable reaction, and optionally the lithium compound) to the dried product, and then carry out a second heating step to dry the resulting mixture and, depending on the temperature, also anneal it.

[0063] <Step of mixing a compound containing a transition metal element> This embodiment further includes a step of mixing a compound containing a transition metal element in at least one of steps (1), (2), and / or (3). Specifically, the compound containing a transition metal element is mixed with an aqueous solvent or a slurry (formed from an aqueous solvent and a lithium-nickel composite compound) in step (1), or mixed with a cake-like compound in step (2), or mixed with a dried cake-like compound in step (3). This allows the lithium in the lithium-nickel composite compound to react with the mixed compound containing a transition metal element, and the surface layer of the particle can be coated with the compound containing lithium and a transition metal element and the compound containing a transition metal element.

[0064] The step of mixing the compound containing a transition metal element can be carried out in one, two, or all three of steps (1), (2), and (3). Specifically, the step of mixing the compound containing a transition metal element is preferably carried out before and / or after introducing the lithium nickel composite compound into the aqueous solvent in step (1), or is carried out using a cake-like compound obtained by filtering and separating the slurry in step (2). In another preferred embodiment, the mixing of the compound containing a transition metal element is carried out in step (3). As already explained, in this case, the mixing is carried out in the presence of an aqueous solvent. Preferably, this is carried out by using the compound containing a transition metal element in the form of an aqueous solution or suspension containing the compound containing the transition metal element and optionally the lithium compound. Therefore, in this alternative, preferably, the aqueous solution or suspension containing the compound containing the transition metal element and optionally the lithium compound is mixed with the lithium nickel composite compound dried in step (3). In this alternative, it is preferable to use an aqueous solution or suspension containing the lithium compound and the compound containing the transition metal element. When mixing with the cake-like compound obtained in step (2), the compound containing a transition metal element is preferably used in the form of an aqueous solution or suspension containing the compound containing the transition metal element and, optionally, the lithium compound.

[0065] Furthermore, as described above, after mixing a compound containing a transition metal element in step (1), a compound containing a transition metal element may be further mixed in step (2). Furthermore, different transition metal element compounds may be added in steps (1) and (2).

[0066] That is, when a step of mixing a compound containing a transition metal element is carried out in step (1) and / or step (2), the pH of the slurry is about 11 to 13, and the cake-like compound also has a pH of about 11 to 13, so that at least a small amount of the compound containing the transition metal element can be dissolved. As a result, it is presumed that lithium and the dissolved transition metal element can penetrate into grain boundary portions formed by adjacent primary particles located on the surfaces of multiple primary particles that make up the secondary particles of the lithium nickel composite compound, and these grain boundary portions can be coated with lithium and the compound containing the transition metal element and the compound containing the transition metal element.

[0067] When the heat treatment step (3) is carried out in this state, the reaction between the excess lithium remaining on the surfaces of the primary particles of the lithium nickel composite compound and the transition metal element is further promoted, and the formation of a compound containing lithium and a transition metal element can be promoted. As described above, the compound containing lithium and a transition metal element is thought to be able to suppress the generation of a resistance component without deteriorating the battery characteristics.

[0068] Alternatively, after mixing a compound containing a transition metal element in step (1) and / or step (2), a compound containing a transition metal element may be further mixed in step (3). Furthermore, different transition metal element compounds may be added in step (1) / step (2) and step (3).

[0069] The transition metal elements are preferably used in the form of transition metal oxides, hydroxides, mixed oxide-hydroxides, sulfates, oxalates or hydrates of the above forms, with oxides and oxide hydrates being preferred.

[0070] The transition metal element is not particularly limited, but is preferably at least one transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta. More preferably, the transition metal element is at least one element selected from the group consisting of V and Nb, specifically Nb. Furthermore, when the transition metal element is Nb, for example, the compound containing the transition metal element is preferably niobium pentoxide (Nb2O5) or niobium pentoxide hydrate (Nb2O5·nH2O). Furthermore, when the transition metal element is V, the compound containing the transition metal element is preferably vanadium pentoxide (VO5).

[0071] Furthermore, by suitably adjusting the amount of the compound containing a transition metal element to be mixed, at least a portion of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surfaces of the secondary particles and the multiple primary particles that make up the secondary particles can be coated with the compound containing lithium and a transition metal element and the compound containing a transition metal element.

[0072] That is, in the step of mixing the compound containing a transition metal element, the amount of the compound containing a transition metal element to be mixed is preferably set to an amount of compound such that the transition metal element accounts for 0.01 mol % to 1.5 mol % of the total amount of all elements in the lithium-nickel composite compound excluding lithium and oxygen. If the amount of the compound containing a transition metal element to be mixed is less than the lower limit, the amount of compound containing lithium and transition metal element that cannot coat the secondary particles of the lithium-nickel composite compound may increase. Furthermore, if the amount of the compound containing a transition metal element to be mixed exceeds the upper limit, the compound may be present in excess in the surface layer of the secondary particles, resulting in an excessively large resistance component. Furthermore, if the amount of excess lithium required for the reaction is insufficient, Li may be extracted from the lithium-nickel composite compound, resulting in an excessively large resistance component. The amount of the compound containing a transition metal element to be mixed is more preferably an amount such that the transition metal element accounts for 0.1 mol % to 1.2 mol % of the transition metal element.

[0073] When the step of mixing a compound containing a transition metal element is carried out in step (1), the slurry into which the compound containing a transition metal element is mixed is preferably alkaline so that the compound containing the transition metal element does not precipitate in a certain amount or more in the aqueous solvent or the slurry, specifically, has a pH of 11 to 13. By dissolving at least a portion of the compound containing a transition metal element in this way, the transition metal element and the compound containing a transition metal element also permeate the secondary particles and react with excess lithium not only in the surface layer of the secondary particles of the lithium-nickel composite compound but also in the surface layer of the primary particles, thereby reducing the amount of excess lithium remaining in the finally obtained lithium-nickel composite compound.

[0074] As described above, the treatment method of the present invention includes steps (1) to (3), and further includes a step of mixing a compound containing a transition metal element in at least one of steps (1), (2), and (3), thereby making it possible for the compound containing lithium and a transition metal element and the compound containing a transition metal element to be present in the surface layer of the secondary particles of the lithium nickel composite compound.

[0075] Furthermore, in steps (1) to (3), an A element compound can be optionally mixed. By mixing the A element compound in this way, the A element compound can be present on the particle surface of the lithium nickel composite compound in the form of a compound of lithium and the A element or in the form of the A element compound, and effects based on the A element compound can be obtained. The A element is not particularly limited, but examples include the following: aluminum (Al), manganese (Mn), titanium (Ti), cobalt (Co), magnesium (Mg), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), antimony (Sb), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr), boron (B), etc.

[0076] In the treatment method of the present invention, the portion where the compound containing lithium and a transition metal element and the compound containing a transition metal element are present on the surface of the lithium-nickel composite compound are present on the surface of particles of the lithium-nickel composite compound that constitute the lithium-nickel composite compound, and the compounds may be present in the following portions (a) and (b): (a) at least a portion of the surface of a secondary particle of a lithium nickel composite compound; and (b) At least a portion of the grain boundary (interface between primary particles) formed by adjacent primary particles located on the surfaces of multiple primary particles that make up the secondary particle.

[0077] Furthermore, when an A element compound is optionally added in the steps (1) to (3), the A element compound can be present on the surface of the lithium nickel composite compound. For example, the A element compound is a compound of lithium and the A element, or an oxide of the A element. Furthermore, the type of the A element is as described above.

[0078] The type of lithium compound (ii) to be mixed with the aqueous solvent (used in step (1)), the slurry (in step (1)), the cake-like compound (in step (2)), or the dried lithium-nickel composite compound (in step (3)) is not particularly limited, but is preferably LiOH.

[0079] FIG. 1 is a schematic vertical cross-sectional view of the surface layer of a secondary particle of a lithium nickel composite compound when a coating layer of a compound containing lithium and a transition metal element and a compound containing a transition metal element is formed by the treatment method of the present invention.

[0080] As shown in the vertical cross section of Figure 1, not only is a coating layer 3 of a compound containing lithium and a transition metal element and a compound containing a transition metal element formed on the surface 2 of a secondary particle 1 formed by a plurality of primary particles 11, 12, 13, 14..., but also a coating layer 3 of a compound containing lithium and a transition metal element and a compound containing a transition metal element is formed in a grain boundary portion 4 formed by adjacent primary particles 11, 12; 12, 13; 13, 14... located on the uppermost surface. In the example of Figure 1, a case has been described in which a coating layer is formed by a compound containing lithium and a transition metal element and a compound containing a transition metal element, but the formation of a layer is not necessarily required, and as will be described later, the compound may be present in the form of particles.

[0081] Fig. 2 is a schematic cross-sectional view of the surface layer of a secondary particle of a lithium-nickel composite compound when a coating layer formed of a compound containing lithium and a transition metal element and a compound containing a transition metal element is formed by the treatment method of the present invention. Specifically, Fig. 2 is a schematic cross-sectional view cut near the height of the grain boundary portion 4 of the secondary particle 1.

[0082] As described above, the cross section of Figure 2 shows a state in which a coating layer 3 of a compound containing lithium and a transition metal element and a compound containing a transition metal element is formed also on a portion of the grain boundary portion 4 formed by the multiple primary particles 11, 12, 13, 14... that make up the secondary particle 1. In Figure 2, the thick lines indicate the grain boundary portion 4 where no coating layer 3 is formed. Furthermore, Figure 2 shows a partial cross section of the secondary particle 1, and although many primary particles are present at the edge of the secondary particle 1 in Figure 2, these are not depicted.

[0083] <Cathode active material> The positive electrode active material according to the present invention preferably contains, as a main component, a lithium-nickel composite compound containing Li, Ni, and O, and may contain elements other than Li, Ni, and O. As described above, the compound containing lithium and a transition metal element and the compound containing a transition metal element are present in predetermined portions of this nickel-lithium composite compound, i.e., the following (a) and (b): (a) the surface of secondary particles of the lithium nickel composite compound, and (b) At least a portion of the grain boundary (interface between primary particles) formed by adjacent primary particles located on the surfaces of multiple primary particles that make up the secondary particle.

[0084] As the term suggests, "a part of the grain boundary portion" does not mean the entire grain boundary portion, but a part of the grain boundary portion. The entire length of the grain boundary portion varies depending on the size of the primary particles that make up the secondary particle, and is not particularly limited, but is, for example, about 80 nm to 800 nm, taking into account the minor axis portion of the shape of the primary particles that make up the secondary particle.

[0085] In this specification, the average particle size is a value measured using a scanning electron microscope SEM-EDS (field emission scanning electron microscope JS-7100F: manufactured by JEOL Corporation) at an acceleration voltage of 10 kV, and is based on a scanning electron microscope photograph (SEM photograph) of primary particles or secondary particles of the lithium nickel composite compound taken so that the grain boundaries of the primary particles can be confirmed.

[0086] The compound containing lithium and a transition metal element is formed by combining the excess lithium contained in the primary particles and secondary particles of the lithium-nickel composite compound with the compound containing the transition metal element, and thus has the effect of reducing the excess lithium by forming the compound containing lithium and a transition metal element. For example, when the compound containing the transition metal element is niobium pentoxide (Nb2O5) or niobium pentoxide hydrate (Nb2O5·nH2O), the compound containing lithium and a transition metal element is considered to be formed from LiNbO3 or Li3NbO4, etc. Furthermore, the ratio of Li to the transition metal element in the compound containing lithium and a transition metal element is not particularly limited and may be, for example, Li / transition metal element = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0087] The compound containing a transition metal element is preferably an oxide containing the transition metal element. For example, when Nb is selected as the transition metal element, the compound containing the transition metal element is preferably an oxide such as Nb2O5 or Nb2O5·nH2O.

[0088] The compound containing lithium and a transition metal element and the compound containing a transition metal element present on the surface or grain boundary of the lithium nickel composite compound may be present in the form of particles and do not necessarily need to form a (coating) layer. However, the compound may form a layer, and there is no particular limitation. Furthermore, there is no particular limitation on the thickness of the layer when a layer is formed, and it may have any thickness.

[0089] In this specification, the coating state and coating layer thickness obtained by the compound containing lithium and a transition metal element, and the compound containing a transition metal element, can be examined using, for example, Auger electron spectroscopy (hereinafter also referred to as "AES"), scanning electron microscopy using energy dispersive X-ray spectroscopy (hereinafter also referred to as "SEM-EDX"), or transmission electron microscopy using energy dispersive X-ray spectroscopy (hereinafter also referred to as "TEM-EDX"), etc.

[0090] The coefficient of variation of the amount of the transition metal element present in the coating layer of the compound containing lithium and a transition metal element and the compound containing a transition metal element is not particularly limited and may have any value.

[0091] In this specification, the coefficient of variation of the amount of transition metal element present on the particle surface can be determined using, for example, the above-mentioned AES, SEM-EDX, or TEM-EDX.

[0092] For example, when using the above-mentioned SEM-EDX, the coefficient of variation can be determined by point analysis of SEM-EDX from the results of five randomly selected locations (N=5) in the coating layer, using the standard deviation and average value of the values ​​obtained after confirming the presence of transition metal elements, based on the following formula:

[0093] Coefficient of variation (%) = (standard deviation / average value) x 100 In this specification, the coating rate of the coating layer can be determined by, for example, image analysis.

[0094] The positive electrode active material according to the present invention is formed from a lithium-nickel composite compound that contains Li, Ni, and O and may contain elements other than Li, Ni, and O. The composition of the lithium-nickel composite compound is not particularly limited, but preferably has a composition represented by the following formula (I): Li a Ni 1-b-c Mn b M c O2(I) (In the formula, M is an element other than Li, Ni, Mn, or O, 0.95≦a≦1.15, 0≦b≦0.20, 0≦c≦0.20, and Ni is 0.80 to 0.98 (more precisely, (1−bc) is 0.80 to 0.98)).

[0095] In the above formula (I), the element M other than Li, Ni, and O is not particularly limited, and examples thereof include: aluminum (Al), titanium (Ti), cobalt (Co), magnesium (Mg), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), antimony (Sb), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr), silicon (Si), phosphorus (P), and boron (B), etc. In a specific embodiment, M is one or both of Al and / or Co.

[0096] In a preferred embodiment, b is 0.05 to 0.2 and c is 0; therefore, the compound (I) is a compound of formula (I.1): Li a Ni 1-b Mn b O2(I.1) (where b is 0.05 to 0.2 and Ni is 0.80 to 0.95 (more precisely, (1 - b) is 0.80 to 0.95).

[0097] In another preferred embodiment, the lithium nickel composite compound is represented by the following formula (I.2): Li a Ni 1-c1-c2 Co c1 Al c2 O2(I.2) (where 0.95 ≤ a ≤ 1.15, 0 < c1 ≤ 0.20, 0 < c2 ≤ 0.20, Ni is 0.80 to 0.98 (more precisely, (1 - c1 - c2) is 0.80 to 0.98), preferably 0.95 ≤ a ≤ 1.15, 0 < c1 < 0.20, 0 < c2 < 0.20, Ni is 0.80 to 0.98 (more precisely, (1 - c1 - c2) is 0.80 to 0.98), more preferably 0.01 ≤ c1 ≤ 0.09, 0.01 ≤ c2 ≤ 0.09).

[0098] Furthermore, the positive electrode active material according to the present invention contains a lithium-nickel composite compound, but an A element compound may also be present on the particle surface of the lithium-nickel composite compound, and the A element compound may be present in the form of a compound of lithium and the A element, or in the form of an A element oxide. Therefore, in the present invention, there are differences in the effects. For example, when an Al compound and an Nb compound are present on the particle surface, the effect of improving the long-term cycle characteristics when a battery is fabricated can be imparted. The element A is not particularly limited, but examples thereof include aluminum (Al), manganese (Mn), titanium (Ti), cobalt (Co), magnesium (Mg), zinc (Zn), niobium (Nb), tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), calcium (Ca), iron (Fe), gallium (Ga), strontium (Sr), yttrium (Y), antimony (Sb), ruthenium (Ru), indium (In), tin (Sn), tantalum (Ta), bismuth (Bi), zirconium (Zr), and boron (B).

[0099] Furthermore, the amount of residual lithium in the positive electrode active material according to the present invention, as determined by neutralization titration, is preferably 0.15% by mass or less, more preferably 0.12% by mass or less. If the amount of residual lithium exceeds the upper limit, gas generation may occur and the reaction resistance of the lithium battery may increase. The amount of residual lithium refers to, for example, the amount of Li derived from LiOH or Li2CO3 that is not contained in the lithium-nickel composite compound or coating layer (a compound containing lithium and a transition metal element).

[0100] In this specification, the amount of residual lithium was calculated based on the Warder method. Specifically, 20 g of lithium-nickel composite compound particles, which would become the positive electrode active material particles, was added to 100 mL of water, stirred at room temperature for 20 minutes, and then the solids were filtered off to obtain a supernatant. The amount of residual lithium was determined by titration with 0.2 N hydrochloric acid. In a pH curve plotted with titer (mL) on the horizontal axis and the pH of the supernatant on the vertical axis, the two points where the gradient is greatest from the point where the titer becomes small were designated the first titer point and the second titer point. The amount of residual lithium was calculated using a formula based on the titer at these points.

[0101] <Method of manufacturing positive electrode active material> The method for producing the positive electrode active material according to the present invention is not particularly limited as long as it is a method for treating positive electrode active material particles in accordance with the contents described in the above section "<Method for treating positive electrode active material particles>", and the lithium-nickel composite compound that constitutes the positive electrode active material particles can be produced by a conventional method.

[0102] That is, for example, a method can be employed in which a precursor composite compound containing at least Ni is synthesized, this precursor composite compound is mixed with a lithium compound to obtain a mixture, and then this mixture is calcined, or other methods can also be employed.

[0103] The method for synthesizing the precursor composite compound is not particularly limited, and examples include a method in which aqueous solutions containing a nickel compound aqueous solution and various aqueous solutions of compounds containing elements other than Ni are added dropwise to a reaction tank while stirring, depending on the desired composition of the positive electrode active material, and an alkaline aqueous solution such as a sodium hydroxide aqueous solution or an ammonia aqueous solution is used as the mother liquor, and sodium hydroxide or the like is also added dropwise while monitoring and controlling the pH to an appropriate range, thereby obtaining a precursor composite compound by a coprecipitation method using a wet reaction. Examples of precursor composite compounds include hydroxides, oxides obtained by calcining the hydroxides, carbonates, etc.

[0104] After the alkaline aqueous solution that will become the mother liquor has been prepared for the synthesis reaction, it should be noted that the reaction tank should be filled with nitrogen, preferably using an inert gas or industrially preferred nitrogen gas, so that the oxygen concentration in the reaction tank system and in the solution is kept as low as possible.

[0105] The nickel compound is not particularly limited, but examples thereof include nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel.

[0106] The elements other than Ni that constitute the positive electrode active material are not particularly limited, but examples thereof include Mn, and also include Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P, B, etc., which are given as examples of the element M other than Li, Ni, Mn, and O in the above formula (I).

[0107] Compounds containing elements other than Ni are not particularly limited, but examples thereof include cobalt compounds, aluminum compounds, manganese compounds, titanium compounds, magnesium compounds, zinc compounds, niobium compounds, and tungsten compounds.

[0108] The cobalt compound is not particularly limited, but examples thereof include cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt.

[0109] The aluminum compound is not particularly limited, but examples thereof include aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum.

[0110] The manganese compound is not particularly limited, but examples thereof include manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and manganese metal.

[0111] The titanium compound is not particularly limited, but examples thereof include titanyl sulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium.

[0112] The magnesium compound is not particularly limited, but examples thereof include magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium.

[0113] The zinc compound is not particularly limited, but examples thereof include zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and metallic zinc.

[0114] The niobium compound is not particularly limited, but examples thereof include niobium oxide, niobium chloride, lithium niobate, and niobium iodide.

[0115] The tungsten compound is not particularly limited, and examples thereof include tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, and tungsten sulfide.

[0116] The compounding ratio of the nickel compound to the various compounds containing elements other than Ni is adjusted appropriately while taking into consideration the composition of the target positive electrode active material so that the amount of Ni and the amount of the various elements other than Ni are in the desired ratio.

[0117] The appropriate range for controlling the pH when synthesizing the precursor complex compound can be determined so as to achieve the desired secondary particle size and coarseness / fineness, and the pH is generally in the range of about 10 to about 13.

[0118] The precursor complex compound obtained by the above-mentioned wet reaction is preferably subjected to a washing treatment, and after dehydration, is subjected to a drying treatment.

[0119] By carrying out the washing treatment, impurities incorporated into the aggregated particles during the reaction, such as sulfate radicals and carbonate radicals attached to the surface layer, and sodium fractions, can be washed away. Usable washing treatments include the Nutsche washing process using a Büchner funnel if the amount of impurities is small, and a process in which the suspension is fed to a press filter after the reaction, washed with water, and dehydrated. For the washing treatment, pure water, an aqueous sodium hydroxide solution, an aqueous sodium carbonate solution, or the like can be used, but from an industrial perspective, pure water is preferred. However, if a large amount of sulfate radicals remains, washing can also be carried out using an aqueous sodium hydroxide solution whose pH is controlled according to the amount of residue.

[0120] The precursor composite compound thus synthesized and a lithium compound are mixed in a predetermined ratio to prepare a mixture. The mixing may be a solvent-based mixing in which the precursor composite compound and the lithium compound are each in the form of a solution such as an aqueous solution and these solutions are mixed in a predetermined ratio, or a non-solvent-based mixing in which a powder of the precursor composite compound and a powder of the lithium compound are weighed in a predetermined ratio and mixed by a dry method.

[0121] The lithium compound is not particularly limited, and various lithium salts can be used. Examples of the lithium compound include anhydrous lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, and lithium oxide. Among these, lithium carbonate, anhydrous lithium hydroxide, and lithium hydroxide hydrate are preferred.

[0122] The blending ratio of the lithium compound and the precursor composite compound is appropriately adjusted so that the total amount of Li, Ni, and other various elements is in the desired ratio, taking into consideration the intended composition of the positive electrode active material.

[0123] The firing temperature when firing the mixture of the precursor composite compound and the lithium compound is not particularly limited, but is, for example, preferably about 700°C to 950°C, more preferably about 720°C to 930°C. If the firing temperature is below the lower limit, it may be difficult to obtain the desired crystals. On the other hand, if the firing temperature exceeds the upper limit, crystal growth may proceed excessively, resulting in a decrease in energy density.

[0124] The atmosphere during firing is not particularly limited, and any atmosphere may be used as long as it has an oxygen partial pressure such that the lithium production reaction of the precursor composite compound is sufficiently carried out, crystal growth is sufficiently carried out, and Ni contained in the mixture to be fired is not reduced. For example, an oxidizing gas atmosphere or an oxygen atmosphere is preferably used.

[0125] The calcination time is not particularly limited, and similarly, it is sufficient that the lithium production reaction of the precursor composite compound is sufficiently carried out and crystal growth is sufficiently carried out, and for example, it is preferably 1 hour to 15 hours, more preferably 2 hours to 10 hours.

[0126] The thus obtained positive electrode active material particles containing a lithium-nickel composite compound are subjected to a processing method according to an embodiment of the present invention, which includes steps (1) to (3) and further includes, as described above, a step of mixing a compound containing a transition metal element in at least one of steps (1), (2), and (3). As a result, it is possible to obtain a positive electrode active material according to the present invention, in which the compound containing lithium and a transition metal element and the compound containing a transition metal element are present: (a) on the surfaces of secondary particles of the lithium-nickel composite compound, and (b) in at least a portion of the grain boundary formed by adjacent primary particles located on the surfaces of a plurality of primary particles that make up the secondary particles.

[0127] <Nonaqueous electrolyte secondary battery> The nonaqueous electrolyte secondary battery according to the present invention includes, for example, a positive electrode containing the positive electrode active material of the present invention produced as described above, and the nonaqueous electrolyte secondary battery includes the positive electrode, a negative electrode, and an electrolytic solution containing an electrolyte.

[0128] When manufacturing the positive electrode, a conductive agent and a binder are mixed with the positive electrode active material of the present invention by a conventional method. As the conductive agent, for example, acetylene black, carbon black, graphite, etc. are preferable. As the binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, etc. are preferable.

[0129] For the negative electrode, for example, not only a negative electrode active material such as lithium metal, graphite, and a low-crystalline carbon material, but also at least one non-metal or metal element selected from the group consisting of Si, Al, Sn, Pb, Zn, Bi, and Cd, or an alloy containing these, or a chalcogen compound containing these can also be used.

[0130] Examples of solvents for the electrolytic solution that can be used include an organic solvent containing at least one carbonate such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, or at least one ether such as dimethoxyethane.

[0131] In addition to lithium hexafluorophosphate (LiPF6), for example, at least one lithium salt such as lithium perchlorate or lithium tetrafluoroborate may be dissolved in a solvent and used as an electrolyte.

[0132] <Effect> By the method for treating the positive electrode active material particles of the present invention, the amount of excessive lithium remaining in the positive electrode active material is sufficiently reduced, and the resistance component is also reduced. Therefore, in a non-aqueous electrolyte secondary battery using this positive electrode active material for its positive electrode, it is possible to provide a positive electrode active material that suppresses gas generation in a lithium battery while achieving low resistance and high battery capacity.

Examples

[0133] Hereinafter, the present invention will be specifically described by giving representative examples and comparative examples of the present invention, but the present invention is not limited to these examples. The methods for obtaining physical properties and characteristics are as shown below.

[0134] <XRD Diffraction> XRD diffraction data of the positive electrode active material was obtained using an X-ray diffractometer [SmartLab, manufactured by Rigaku Corp.] under the following X-ray diffraction conditions, and then this XRD diffraction data was used to perform Rietveld analysis with reference to "R.A. Young (ed.), The Rietveld Method, Oxford University Press (1992)."

[0135] (X-ray diffraction conditions) Radiation source: Cu-Kα Accelerating voltage and current: 45 kV and 200 mA Sampling width: 0.02 degrees Scanning width: 15 degrees to 122 degrees Scan speed: 1.0 steps / second Divergence slit: 2 / 3 degrees Receiving slit width: 0.15 mm Scattering slit: 2 / 3 degrees.

[0136] <Composition of precursor composite compound and positive electrode active material> 0.2 g of the precursor composite compound and the cathode active material sample were each dissolved in 25 mL of 20% aqueous hydrochloric acid solution by heating. After cooling, the solution was transferred to a 100 mL measuring flask and purified water was added to prepare a liquid. The elements in the liquid were quantitatively determined using ICP-AES (Optima 8300, manufactured by PerkinElmer, Inc.).

[0137] <Coin cell using positive electrode active material> A 2032-type coin cell using a positive electrode active material was fabricated using a positive electrode, a negative electrode, and an electrolyte prepared by the following methods.

[0138] (positive electrode) Acetylene black and graphite were used as conductive agents in a mass ratio of 1:1, and polyvinylidene fluoride was used as a binder. The positive electrode active material, conductive agent, and binder were blended in a mass ratio of 90:6:4, and these materials were mixed with N-methylpyrrolidone to obtain a slurry, which was then coated onto aluminum foil. The coated aluminum foil was dried at 110°C to prepare a sheet, which was then punched out into a 15 mm diameter sheet. The density of the composite material was 3.0 g / cm. 3 This was used as a positive electrode.

[0139] (Negative electrode) A lithium foil with a thickness of 500 μm and punched to a diameter of 16 mm was used as the negative electrode.

[0140] (electrolyte) A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was prepared at a volume ratio of EC:DMC=1:2, and the solution obtained by mixing this with 1M LiPF6 electrolyte was used as the electrolyte.

[0141] <Characteristics of non-aqueous electrolyte secondary batteries> (1) Initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency The coin cell prepared by the above method was charged at a constant current of 20 mA / g up to 4.30 V (maximum voltage) at 25°C, and then charged at a constant voltage until the current reached 2 mA / g. The capacity at this time was defined as the initial charge capacity (mAh / g).

[0142] After a 5-minute rest, constant current discharge was carried out at a current density of 20 mA / g up to 3.00 V under the same environment, and the initial discharge capacity (mAh / g) after the 5-minute rest was measured.

[0143] The initial charge / discharge efficiency was calculated based on the following formula using the measured values ​​of the initial charge capacity and the initial discharge capacity.

[0144] Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) x 100

[0145] (2) Initial reaction resistance The measurements were carried out using the coin cell manufactured by the above method in an environment of 25°C under the following conditions:

[0146] 1st Cycle 0.1C charging (4.3V cc-cv) 5 minute pause 0.1C charging (2.5V cc) 5 minute pause 2nd Cycle 0.1C charging (4.3V cc-cv).

[0147] Using the cell after the second cycle charging, the impedance was measured under the following conditions in an environment of 25°C. The result was used as the second cycle impedance measurement result (second cycle reaction resistance (initial reaction resistance)).

[0148] Frequency range: 300k-0.01Hz (76 points) Amplitude: 10mV.

[0149] <Production Example 1: Production of Positive Electrode Active Material Particles 1> A mixed aqueous solution was obtained by mixing an aqueous nickel sulfate solution and an aqueous manganese sulfate solution so that the molar ratio of Ni to Mn was Ni:Mn = 88:12. 300 g of aqueous sodium hydroxide solution and 500 g of aqueous ammonia were added to 10 L of pure water to prepare a mother liquor in a reaction tank. A nitrogen atmosphere was created in the reaction tank by adding nitrogen gas at a flow rate of 0.7 L / min, and the reaction was then carried out under the nitrogen atmosphere.

[0150] After this, while rotating the stirring blade at 1000 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously added dropwise at a predetermined rate, and the amount of alkaline aqueous solution added was adjusted so that the pH became 11.7. Through a crystallization reaction, Ni and Mn crystallized and co-precipitated to form agglomerated particles, and a coprecipitate was obtained.

[0151] After this, the slurry in the reactor was subjected to solid-liquid separation and further washed with pure water to reduce residual impurities, and then the coprecipitate cake was dried in air at 110°C for 12 hours to obtain precursor composite compound 1.

[0152] Precursor composite compound 1 and anhydrous lithium hydroxide were weighed out so that the ratio (molar ratio) of the total amounts of Li, Ni, and Mn was Li / (Ni+Mn)=1.040, and mixed using a mixer to prepare a mixture.

[0153] Next, this mixture was fired in an electric furnace in an oxygen atmosphere (oxygen concentration: 97% by volume) at a maximum temperature of 750°C for 5 hours to obtain positive electrode active material particles 1 (lithium nickel composite compound) (hereinafter also referred to as "NM"). The average particle size of the primary particles in the positive electrode active material particles 1 was approximately 500 nm, and the average particle size of the secondary particles was approximately 12.8 μm.

[0154] <Production Example 2: Production of Positive Electrode Active Material Particles 2> A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and an aluminum sulfate aqueous solution were mixed so that the molar ratio of Ni, Co, and Al was Ni:Co:Al = 90:5:5 to obtain a mixed aqueous solution. 300 g of sodium hydroxide aqueous solution and 500 g of ammonia water were added to 10 L of pure water to prepare a mother liquor in a reaction tank. A nitrogen atmosphere was created in the reaction tank by adding nitrogen gas at a flow rate of 0.7 L / min, and the reaction was then carried out under the nitrogen atmosphere.

[0155] After this, while rotating the stirring blade at 1000 rpm, the mixed aqueous solution, sodium hydroxide aqueous solution, and ammonia water were simultaneously added dropwise at a predetermined rate, and the amount of alkaline aqueous solution added was adjusted so that the pH became 11. Through a crystallization reaction, Ni, Co, and Al crystallized and coprecipitated to form aggregated particles, and a coprecipitate was obtained.

[0156] After this, the slurry in the reactor was subjected to solid-liquid separation and further washed with pure water to reduce remaining impurities, and then the cake-like coprecipitate was dried at 110°C in air for 12 hours to obtain precursor complex compound 2.

[0157] Precursor composite compound 2 and anhydrous lithium hydroxide were weighed out so that the total ratio (molar ratio) of Li, Ni, and Al was Li / (Ni+Co+Al) = 1.020, and mixed using a mixer to prepare a mixture. Note that coarse anhydrous lithium hydroxide particles with a particle size exceeding 500 μm were crushed before use to prevent such coarse particles from being included in the mixture.

[0158] Next, this mixture was fired in an electric furnace in an oxygen atmosphere (oxygen concentration: 97% by volume) at a maximum temperature of 740°C for 5 hours to obtain positive electrode active material particles 2 (lithium nickel composite compound) (hereinafter also referred to as "NCA"). The average particle size of the primary particles in the positive electrode active material particles 2 was approximately 280 nm, and the average particle size of the secondary particles was approximately 11.3 μm.

[0159] <Example 1-1: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)> (1) Slurry formation step and step of mixing a compound containing a transition metal element Cathode active material particles 1 (NM) were added to pure water (25°C) in a reaction tank (10 L capacity) and stirred for 10 minutes to prepare a slurry. The ratio of the amount of cathode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g / L. Niobium pentoxide hydrate (Nb2O5·nH2O) powder, a transition metal element-containing compound, was then added to the slurry while stirring for 10 minutes. The amount of niobium in the niobium pentoxide hydrate (Nb2O5·nH2O) powder was 0.5 mol% relative to the amount of metal element in the cathode active material particles 1. The pH of the slurry was 12.2.

[0160] (2) Filtration separation process Thereafter, the mixed slurry was separated by filtration using a Büchner funnel to obtain a cake-like compound.

[0161] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 155°C for 19 hours using a vacuum dryer to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0162] The amount of residual Li (the total amount of Li derived from LiOH and Li2CO3) was determined for the obtained positive electrode active material. Furthermore, the treatment steps, added components, added amounts, and final heat treatment temperature (hereinafter collectively referred to as "conditions for each step") are shown in Table 1 below.

[0163] <Example 1-2: Treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation step and step of mixing a compound containing a transition metal element A slurry was prepared in the same manner as in Example 1, and niobium pentoxide hydrate (Nb2O5·nH2O) powder was mixed in.

[0164] (2) Filtration separation process In the same manner as in Example 1, the slurry was separated by filtration to obtain a cake-like compound.

[0165] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried cake-like compound, from which a positive electrode active material was produced.

[0166] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0167] <Example 1-3: Treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation step and step of mixing a compound containing a transition metal element A slurry was prepared in the same manner as in Example 1, and 0.2 mol % of niobium pentoxide hydrate (Nb2O5·nH2O) powder was mixed in.

[0168] (2) Filtration separation process In the same manner as in Example 1, the slurry was separated by filtration to obtain a cake-like compound.

[0169] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0170] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0171] <Example 1-4: Treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation step and step of mixing a compound containing a transition metal element A slurry was prepared in the same manner as in Example 1, and 1.0 mol% of niobium pentoxide hydrate (Nb2O5·nH2O) powder was mixed in.

[0172] (2) Filtration separation process In the same manner as in Example 1, the slurry was separated by filtration to obtain a cake-like compound.

[0173] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0174] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0175] <Example 1-5: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)> (1) Slurry formation process Positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25°C) in a reaction tank (volume 10 L) and stirred for 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g / L. The pH of the slurry at this time was 12.1.

[0176] (2) Filtration separation step and step of mixing compounds containing transition metal elements 0.1 mol% niobium pentoxide hydrate (Nb2O5·nH2O) powder was added, and the slurry obtained in the slurry formation step (1) was filtered to obtain a cake-like compound. The water content of the cake-like compound was 6.1 mass%. The obtained cake-like compound was mixed with 0.1 mol% niobium pentoxide hydrate (Nb2O5·nH2O) powder.

[0177] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 250°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0178] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0179] <Example 1-6: Treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation step and step of mixing a compound containing a transition metal element A slurry was prepared in the same manner as in Example 1, except that the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1500 g / L. Next, 0.2 mol % of niobium pentoxide hydrate (NbO·nHO) powder was mixed in.

[0180] (2) Filtration separation process In the same manner as in Example 1, the slurry was separated by filtration to obtain a cake-like compound.

[0181] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 300°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0182] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0183] <Example 1-7: Treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation process Positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25°C) in a reaction tank (volume 10 L) and stirred for 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1500 g / L. The pH of the slurry at this time was 12.3.

[0184] (2) Filtration separation step and step of mixing compounds containing transition metal elements The slurry obtained in the slurry formation step (1) was filtered to obtain a cake-like compound. The water content of the cake-like compound was 6% by mass. The obtained cake-like compound was mixed with niobium pentoxide hydrate (Nb2O5·nH2O) dissolved in an aqueous LiOH solution (Nb2O5·nH2O was present in an amount of 0.2 mol% relative to the amount of all elements other than Li and O in the lithium nickel composite compound). The water content of the cake-like compound after mixing was 14.4% by mass.

[0185] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 300°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0186] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0187] <Example 1-8: Treatment of positive electrode active material particles 1 (production of positive electrode active material)> (1) Slurry formation process Positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25°C) in a reaction tank (volume 10 L) and stirred for 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) was adjusted to 1500 g / L. The pH of the slurry at this time was 12.3.

[0188] (2) Filtration separation step and step of mixing compounds containing transition metal elements The slurry obtained in the slurry formation step (1) was filtered to obtain a cake-like compound, which had a water content of 6.2% by mass.

[0189] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer. Niobium pentoxide hydrate (Nb2O5·nH2O) dissolved in an aqueous LiOH solution (Nb2O5·nH2O is present in an amount of 0.2 mol% relative to the total amount of elements other than Li and O in the lithium-nickel composite compound) was mixed with the dried cake-like compound to increase the water content to 8.2 mass%. Then, another heat treatment was performed in an electric furnace under an oxygen atmosphere (oxygen concentration 97% by volume) at 300°C for 120 minutes.

[0190] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0191] <Example 1-9: Treatment of positive electrode active material particles 1 (production of positive electrode active material)> The procedure was the same as in Examples 1-8, except that the moisture content after treating the dried cake-like compound with niobium pentoxide hydrate (Nb2O5·nH2O) dissolved in LiOH aqueous solution was lower (only 1.2%) than in Examples 1-8. The characteristics of the positive electrode active material and the conditions for each step are shown in Table 1.

[0192] <Comparative Example 1-1: Production of Positive Electrode Active Material> The amount of residual Li in the positive electrode active material particles 1 (positive electrode active material) was measured without undergoing any of the steps of slurry formation (1) to heat treatment (3) or the step of mixing a compound containing a transition metal element. The results are shown in Table 1.

[0193] <Comparative Example 1-2: Production of Positive Electrode Active Material> (1) Slurry formation process A slurry was prepared as in Example 1.

[0194] (2) Filtration separation process The slurry obtained in the slurry formation step (1) was filtered using a Büchner funnel to obtain a cake-like compound, which had a water content of 5.7% by mass.

[0195] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer. A dried cake-like compound was obtained by the heat treatment step, and a positive electrode active material was produced.

[0196] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0197] <Comparative Example 1-3: Production of Positive Electrode Active Material> Niobium pentoxide hydrate (Nb2O5·nH2O) powder, a compound containing a transition metal element, was mixed with positive electrode active material particles 1 and heat-treated in an electric furnace in an oxygen atmosphere (oxygen concentration: 97% by volume) at 350°C for 120 minutes to produce a positive electrode active material. The properties of the resulting positive electrode active material were measured. The properties of the positive electrode active material and the conditions for each process are shown in Table 1.

[0198] <Comparative Example 1-4: Production of Positive Electrode Active Material> Powdered lithium niobate (LiNbO3), a compound containing a transition metal element, was mixed with positive electrode active material particles 1 and heat-treated in an electric furnace in an oxygen atmosphere (oxygen concentration: 97% by volume) at 350°C for 120 minutes to produce a positive electrode active material. The properties of the resulting positive electrode active material were measured. The properties of the positive electrode active material and the conditions for each process are shown in Table 1.

[0199] <Comparative Example 1-5: Production of Positive Electrode Active Material> (1) Slurry formation process A slurry was prepared as in Example 1.

[0200] (2) Filtration separation process The slurry obtained in the slurry formation step (1) was filtered using a Büchner funnel to obtain a cake-like compound, which had a water content of 5.9% by mass.

[0201] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0202] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each process are shown in Table 1.

[0203] <Test example: Non-aqueous electrolyte secondary battery characteristic test> The properties of the nonaqueous electrolyte secondary batteries using the positive electrode active materials obtained in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5 as positive electrodes were determined, including initial charge capacity, initial discharge capacity, initial charge / discharge efficiency, initial reaction resistance, and resistance ratio (compared with Comparative Example 1-2). The results are shown in Table 1.

[0204] [Table 1]

[0205] Drying is a (first) heating step carried out at temperatures below 200° C. to remove moisture.

[0206] Annealing is a (second) heating step carried out at a higher temperature to promote reaction of excess lithium with the transition metal element and to promote the formation of compounds containing lithium and the transition metal element.

[0207] As shown in the columns for Examples 1-1 and 1-2 and Comparative Examples 1-2 and 1-5 in Table 1, it was confirmed that when the slurry formation step (1) was performed in the production of the positive electrode active material, the amount of residual Li in the positive electrode active material was reduced. On the other hand, as shown in the columns for Comparative Examples 1-3 and 1-4 in Table 1, it was confirmed that when the slurry formation step (1) was not performed in the production of the positive electrode active material, no reduction in the amount of residual Li in the positive electrode active material was observed, even compared to Comparative Example 1-1 in which no treatment was performed at all.

[0208] As shown in the columns for Example 1-1 and Comparative Example 1-2 in Table 1, the battery using the positive electrode active material of Example 1-1, in which the step of mixing Nb2O5·nH2O powder with the slurry, the filtration separation step (2), and the heat treatment step (3) were performed, showed an initial reaction resistance of 59 Ω, while the battery using the positive electrode active material of Comparative Example 1-2, in which the addition of the slurry was not performed and the filtration separation step (2) and the heat treatment step (3) were performed, showed an initial reaction resistance of 220 Ω.

[0209] From the above, it is believed that the processing method involves mixing Nb2O5·nH2O powder with the slurry, filtering and separating (2), and heat-treating (3). As a result of the heat treatment of the eluted lithium and the added element Nb, compounds containing Li and Nb are formed on the particle surface as shown in Figure 1. Therefore, it is believed that the initial reaction resistance is reduced by the effect of improving lithium ion conductivity. Furthermore, it is believed that the amount of residual Li is reduced because the amount of excess lithium is reduced by the formation of compounds containing Li and Nb.

[0210] Furthermore, as in Example 1-2 and Comparative Example 1-5, when the temperature of the heat treatment step was 350°C, the same effect was confirmed and the initial battery capacity increased. From this, it is presumed that during the synthesis of the positive electrode active material, Mn, which replaced Ni in the positive electrode active material, reacted with Li, resulting in the formation of Li2MnO3, an unstable resistance component that inhibits the movement of Li within the crystal structure, as a domain in the crystal lattice due to the excess Li content. Therefore, when the heat treatment step in Example 1-2 was performed at 350°C, the added Nb not only reacted with the eluted lithium but also extracted lithium from the Li2MnO3 domain. As a result, for example, Li 1-x Ni y MnO2 or Li x MnO 4-y It is presumed that the phase change to a crystal structure like this removes the Li2MnO3 in the resistance component, increasing the amount of Li that can move within the crystal structure and increasing the battery capacity.

[0211] Furthermore, it is presumed that the above-mentioned phenomenon occurs in a positive electrode active material in which Mn is replaced with Ni, and that this phenomenon can be resolved by carrying out the treatment method according to the present invention.

[0212] On the other hand, as shown in the column for Comparative Example 1-3 in Table 1, when Nb2O5·nH2O powder was directly added to the powdered positive electrode active material, and as shown in the column for Comparative Example 1-4 in Table 1, when lithium niobate (LiNbO3) powder was added to the positive electrode active material, it was confirmed that the residual Li did not decrease and there was no increase in battery capacity, such as initial charge capacity and initial discharge capacity, even though the heat treatment step (3) was performed at a final heat treatment temperature of 350°C.

[0213] These results suggest that simply performing the heat treatment step (3) is insufficient to achieve high battery capacity. It is important to perform the slurry formation step (1) and the filtration / separation step (2) or the heat treatment step (3) while the moisture content of the cathode active material is 3% by mass or higher. The dried cake-like compound is treated with a transition metal compound in the presence of a small amount of moisture during the slurry formation step (1) and the filtration / separation step (2) or the heat treatment step (3), and then the step of mixing the transition metal compound is performed. This step can reduce the moisture content to approximately 1% by mass. This is because the added transition metal compound partially dissolves in the cathode active material with a moisture content of 3% by mass or higher, making it prone to depositing in very fine form on the secondary particle surfaces and grain boundaries. Furthermore, the lithium fraction also has a high moisture content, making it prone to partial dissolution and mobility. As a result, the transition metal element reacts with the dissolved Li and excess Li on the particle surfaces, resulting in the morphology shown in Figures 1 and 2.

[0214] As can be seen from the above results, the method for treating positive electrode active material particles according to the embodiment, which includes the steps of slurry formation (1) to heat treatment (3) and further includes a step of mixing a compound containing a transition metal element in at least one of steps (1), (2), and (3), can achieve low resistance by reducing the resistance component and higher battery capacity, and can provide positive electrode active material particles that reduce excess Li on the surfaces of the primary particles and secondary particles of the lithium-nickel composite compound.

[0215] <Confirmation of the site where the compound containing lithium and Nb and the compound containing Nb exist in the positive electrode active material> The cathode active materials obtained in Examples 1-4 were subjected to SEM-EDX analysis as described in the above embodiment, and cross-sectional photographs of the cathode active materials were obtained, as shown in Figure 3. Detection positions (detection sites) were selected, and Nb / (NiMnNb) (mol%) was calculated. The results are shown in Table 2 below. The Nb detection results were represented by O and X, with values ​​of Nb / (NiMnNb) of 0.10 mol% or greater being evaluated as O, and values ​​less than 0.10 mol% being evaluated as X. Furthermore, the Nb content in Nb / (NiMnNb) indicates the total amount of Nb in the Nb-containing compound, including both the lithium-Nb-containing compound and the Nb-containing compound. The numerical values ​​"039," "040," "041," "042," "043," "044," "045," "046," "047," "048," "049," "050," and "051" in Figure 3 indicate detection positions in the cathode active material and correspond to the detection positions in Table 2 below.

[0216] [Table 2]

[0217] As shown in FIG. 3 and Table 2, it was first confirmed that in the positive electrode active material obtained in Example 1-4, a compound containing lithium and Nb and a compound containing Nb were present on the surfaces of the secondary particles of the positive electrode active material particles (detection positions 045 to 047). Furthermore, it was confirmed that a compound containing lithium and Nb and a compound containing Nb were also present in the grain boundary formed by adjacent primary particles located on the surfaces of multiple positive electrode active material particles constituting the secondary particles (detection positions 039 to 044 and 051). On the other hand, it was confirmed that a compound containing lithium and Nb and a compound containing Nb were almost absent within the primary particles of the positive electrode active material (detection positions 048 to 050).

[0218] From these results, it was confirmed that in the positive electrode active material according to the present invention, a compound containing lithium and Nb, and a compound containing Nb are present on the surface of the secondary particle of the lithium nickel composite compound, and at least in part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface of a plurality of primary particles constituting the secondary particle.

[0219] Example 2-1: Treatment of positive electrode active material particles 2 (production of positive electrode active material).

[0220] (1) A step of mixing a compound containing a transition metal element to form a slurry. Niobium pentoxide hydrate (Nb2O5·nH2O) powder, a transition metal compound, was added to pure water (25°C) in a reaction vessel (10 L capacity) and stirred. The amount of niobium in the niobium pentoxide hydrate (Nb2O5·nH2O) powder was 0.5 mol% relative to the total amount of elements other than Li and O in the positive electrode active material particles 2 (NCA). The positive electrode active material particles 2 (NCA) were then added and stirred for over 10 minutes to prepare a slurry. The ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g / L. The pH of the slurry was 12.2.

[0221] (2) Filtration separation process The slurry obtained in the slurry formation step (1) was filtered using a Büchner funnel to obtain a cake-like compound.

[0222] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0223] The amount of residual Li (the total amount of Li derived from LiOH and Li2CO3) was determined for the obtained positive electrode active material. Furthermore, the treatment steps, added components, added amounts, and final heat treatment temperatures (hereinafter collectively referred to as "conditions for each step") are shown in Table 3 below.

[0224] <Example 2-2: Treatment of positive electrode active material particles 2 (production of positive electrode active material)>.

[0225] A slurry was prepared in the same manner as in Example 2-1.

[0226] (2) Filtration separation process In the same manner as in Example 1, the slurry was separated by filtration to obtain a cake-like compound.

[0227] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0228] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each step are shown in Table 3.

[0229] <Example 2-3: Treatment of positive electrode active material particles 2 (production of positive electrode active material)>.

[0230] (1) A step of mixing a compound containing a transition metal element to form a slurry. Cathode active material particles 2 (NCA) were introduced into pure water (water temperature 25°C) in a reaction vessel (volume 10 L) and stirred for 10 minutes to prepare a slurry. The ratio of the amount of cathode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g / L. Subsequently, vanadium pentoxide (VO) powder was added as a compound containing a transition metal element while stirring, and the mixture was stirred for 10 minutes. The amount of vanadium added in the vanadium pentoxide (VO) powder was 0.2 mol% relative to the amount of all elements other than Li and O in the cathode active material particles 2 (NCA). Furthermore, the pH of the slurry at this time was 12.2.

[0231] (2) Filtration separation process Thereafter, the mixed slurry was filtered using a Buchner funnel to obtain a cake-like compound.

[0232] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0233] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each step are shown in Table 3.

[0234] <Example 2-4: Treatment of positive electrode active material particles 2 (production of positive electrode active material)>.

[0235] (1) A step of mixing a compound containing a transition metal element to form a slurry. Niobium pentoxide (Nb2O5) was added as a compound containing a transition metal element to pure water (water temperature 25°C) in a reaction tank (volume 10 L) and stirred. The amount of niobium added in the niobium pentoxide (Nb2O5) powder was 0.5 mol% relative to the total amount of elements other than Li and O in the positive electrode active material particles 2 (NCA). Then, the positive electrode active material particles 2 (NCA) were introduced and stirred for 10 minutes to prepare a slurry. Here, the ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 800 g / L.

[0236] (2) Filtration separation process The slurry obtained in the slurry formation step (1) was filtered using a Büchner funnel to obtain a cake-like compound.

[0237] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0238] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each step are shown in Table 3.

[0239] <Example 2-5: Treatment of positive electrode active material particles 2 (production of positive electrode active material)>.

[0240] (1) A step of mixing a compound containing a transition metal element to form a slurry. Niobium pentoxide (Nb2O5) was added as a compound containing a transition metal element to pure water (water temperature 25°C) in a reaction tank (volume 10 L) and stirred. The amount of niobium added in the niobium pentoxide (Nb2O5) powder was 0.5 mol% relative to the total amount of elements other than Li and O in the positive electrode active material particles 2 (NCA). Then, the positive electrode active material particles 2 (NCA) were introduced and stirred for 10 minutes to prepare a slurry. The ratio of the amount of positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1800 g / L. The pH of the slurry at this time was 12.5.

[0241] (2) Filtration separation process The slurry obtained in the slurry formation step (1) was filtered using a Büchner funnel to obtain a cake-like compound.

[0242] (3) Heat treatment process The cake-like compound obtained in the filtration separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0243] <Comparative Example 2-1: Production of Positive Electrode Active Material> The amount of residual Li was measured for the cathode active material particles 2 (cathode active material) that did not contain the cathode active material particles 2 (NCA) and that had undergone any of the slurry formation step (1) to the heat treatment step (3) and the step of mixing a compound containing a transition metal element. The results are shown in Table 3.

[0244] <Comparative Example 2-2: Production of Positive Electrode Active Material> (1) Slurry formation process The positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25°C) in a reaction tank (volume 10 L) and stirred for 10 minutes to prepare a slurry. Here, the ratio of the amount of the positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g / L.

[0245] (2) Filtration separation process The slurry obtained in the slurry formation step (1) was filtered using a Büchner funnel to obtain a cake-like compound, which had a water content of 5.5% by mass.

[0246] (3) Heat treatment process The cake-like compound obtained in the filter separation step (2) was heat-treated using a vacuum dryer at 185°C for 19 hours. This heat treatment step resulted in a dried cake-like compound, from which a positive electrode active material was produced.

[0247] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each step are shown in Table 3.

[0248] <Comparative Example 2-3: Production of Positive Electrode Active Material> (1) Slurry formation process The positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25°C) in a reaction tank (volume 10 L) and stirred for 10 minutes to prepare a slurry. Here, the ratio of the amount of the positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g / L.

[0249] (2) Filter separation process The slurry obtained in the slurry formation step (1) was filtered using a Büchner funnel to obtain a cake-like compound, which had a water content of 5.9% by mass.

[0250] (3) Heat treatment process The cake-like compound obtained in the filter separation step (2) was heat-treated at 185°C for 19 hours using a vacuum dryer, and then heat-treated at 350°C for 120 minutes in an oxygen atmosphere (oxygen concentration 97% by volume) using an electric furnace to obtain a dried lithium-nickel composite compound, from which a positive electrode active material was produced.

[0251] The properties of the obtained positive electrode active material were measured. The properties of the positive electrode active material and the conditions of each step are shown in Table 3.

[0252] [Table 3]

[0253] As shown in the columns for Examples 2-1 and 2-2 and Comparative Examples 2-2 and 2-3 in Table 3, similar to Table 1, it was confirmed that the amount of residual Li in the positive electrode active material was reduced when the slurry formation step (1) was performed in the production of the positive electrode active material. Furthermore, from these results, it was confirmed that the positive electrode active material particles are not limited to NM, and that the effects of the present invention can also be achieved with NCA. Furthermore, a similar effect was obtained in Example 2-3, in which the transition metal element was V.

[0254] Furthermore, from the results of Examples 2-1 and 2-2, it was confirmed that the effects of the present invention were also achieved when a transition metal element compound was added before forming the slurry.

[0255] In addition, the columns for Example 2-4 and Example 2-5 show cases where the solid-liquid ratio during slurry formation was different, but the results for the amount of residual Li and the battery characteristics were different. These results demonstrate the importance of adjusting the amount of eluted lithium by adjusting the solid-liquid ratio during slurry formation, as described above, and of controlling the reaction with transition metal elements, and it was confirmed that it is necessary to consider the influence of the finally obtained positive electrode active material on the residual Li and battery characteristics.

[0256] [Industrial Applicability] The positive electrode active material according to the present invention can provide positive electrode active material particles that reduce excess Li on the surfaces of the primary particles and secondary particles of the lithium-nickel composite compound, reduce the resistance component to achieve low resistance, and improve battery capacity, and is therefore suitable for the positive electrode of a non-aqueous electrolyte secondary battery. [Explanation of symbols]

[0257] 1...Secondary particles 2...Surface 3...Compound containing lithium and transition metal element and coating layer of compound containing transition metal element 4...grain boundary area 11, 12, 13, 14...primary particles

Claims

1. 1. A method for treating positive electrode active material particles comprising a lithium-nickel composite compound that includes lithium, nickel, and oxygen, and may include another element other than lithium, nickel, and oxygen, the method comprising the steps of: (1) a slurry formation step of introducing the lithium nickel composite compound into an aqueous solvent and stirring the mixture to prepare a slurry; (2) a filtration / separation step of filtering the slurry obtained in the slurry formation step (1) to obtain a cake-like compound; and (3) a heat treatment step of heat treating the cake-like compound obtained in the filtration separation step (2) to obtain a dried lithium-nickel composite compound; Including, In at least one of steps (1), (2) and / or (3), the method further comprises the step of mixing the aqueous solvent used in step (1), the slurry in step (1), the cake-like compound in step (2) and / or the dried lithium nickel composite compound in step (3) with (i) a compound containing at least one transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta, and (ii) optionally with a lithium compound; when the compound containing at least one transition metal element is mixed with the dried lithium nickel composite compound in step (3), the mixing is carried out in the presence of an aqueous solvent; and The resulting product includes a compound containing lithium and a transition metal element, and a compound containing a transition metal element: (a) the surface of the secondary particles of the dried lithium nickel composite compound, and (b) at least a part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surfaces of a plurality of primary particles constituting the secondary particle; A method that exists in.

2. 2. The method of claim 1, wherein the step of mixing the compound containing a transition metal element is performed before and / or after introducing the lithium nickel composite compound into the aqueous solvent in step (1).

3. The method according to claim 1, wherein the compound containing a transition metal element and optionally the lithium compound are mixed with the cake-like compound of step (2), and the compound containing a transition metal element and optionally the lithium compound are preferably used as an aqueous solution or suspension containing the compound containing a transition metal element and optionally the lithium compound.

4. 2. The method of claim 1, wherein the aqueous solution or suspension containing the compound containing a transition metal element and optionally the lithium compound is mixed with the dried lithium nickel composite compound of step (3).

5. 3. The method according to claim 1 or 2, wherein the transition metal element is used in the form of a transition metal oxide, hydroxide, mixed oxide-hydroxide, sulfate, oxalate, or hydrate of the aforementioned forms.

6. The method according to claim 1 or 2, wherein the transition metal element is at least one selected from the group consisting of Ti, V, Zr, Nb and Mo.

7. The method according to claim 6, wherein the transition metal element is at least one selected from the group consisting of V and Nb.

8. The transition metal element is Nb, and the compound containing Nb is preferably Nb ２ O ５ or a hydrate thereof.

9. 3. The method according to claim 1, wherein the lithium compound mixed with the aqueous solvent used in step (1), the slurry in step (1), the cake-like compound in step (2), or the dried lithium nickel composite compound in step (3) is LiOH.

10. 3. The method according to claim 1, wherein in the slurry formation step (1), the lithium nickel composite compound is introduced at a ratio (solid-liquid ratio) of the amount of the lithium nickel composite compound to the amount of the aqueous solvent adjusted to 750 g to 2000 g per liter of the aqueous solvent.

11. 3. The method according to claim 1, wherein the amount of the transition metal element added is 0.01 mol % to 1.5 mol % based on the total amount of all elements excluding lithium and oxygen in the lithium nickel composite compound.

12. 3. The method according to claim 1 or 2, wherein the content of the aqueous solvent, preferably water, of the lithium nickel composite compound is 1% by mass or more, preferably 3% by mass or more, when the compound containing a transition metal element is mixed.

13. When the cake-like compound in step (2) is mixed with the compound containing a transition metal element and optionally the lithium compound, the total content of the aqueous solvent, preferably water, in the mixture obtained by mixing the cake-like compound, the compound containing a transition metal element and optionally the lithium compound is 3 mass% or more based on the total mass of the obtained mixture; and / or When the dried lithium nickel composite compound in step (3) is mixed with the compound containing a transition metal element and optionally the lithium compound, the total content of an aqueous solvent, preferably water, in a mixture obtained by mixing the dried lithium nickel composite compound with the compound containing a transition metal element and optionally the lithium compound is 1 mass % or more based on the total mass of the obtained mixture; In the latter case, the desired content of aqueous solvent is preferably obtained by mixing the dried lithium nickel composite compound of step (3) with an aqueous solution or suspension comprising the compound containing a transition metal element and optionally the lithium compound.

14. The method according to claim 1 or 2, wherein the heat treatment in the heat treatment step (3) is carried out at a temperature of 100°C to 400°C.

15. The method according to claim 14, wherein in the heat treatment step (3), the cake-like compound obtained in the filtration and separation step (2) is heat-treated at a first step temperature of 100 to 195°C and an optional second step temperature of 200 to 400°C.

16. 16. The method of claim 15, wherein a second heat treatment is performed, preferably the second heat treatment is performed at 200°C to 350°C.

17. The following conditions (a), (b) and / or (c): (a) the first heat treatment is carried out under reduced pressure; and / or (b) the second heat treatment is carried out under an oxygen-enriched atmosphere, such as oxygen-enriched air, oxygen-nitrogen mixtures with more than 20% oxygen by volume, and oxygen; and / or (c) The second heat treatment is ２ In an atmosphere with a reduced content of CO ２ The process is carried out in an atmosphere with a maximum content of 100 ppm by volume, more preferably 50 ppm by volume.

16. The method of claim 15, wherein one or two or all three of the following are applied:

18. The lithium nickel composite compound has a composition having a layered rock salt structure and is represented by the following formula (I): Li ａ Ni １－ｂ－ｃ Mn ｂ M ｃ O ２ (I) (wherein M is one or more elements other than Li, Ni, Mn, or O, 0.95≦a≦1.15, 0≦b≦0.20, 0≦c≦0.20, and Ni is 0.80 to 0.98), the method of claim 1.

19. 19. The method of claim 18, wherein M is one or more elements selected from the group consisting of Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P and B, in particular M is Al and / or Co.

20. 19. The method of claim 18, wherein b is 0.05 to 0.2 and c is 0.

21. The lithium nickel composite compound is represented by the following formula (I.2): Li ａ Ni １－ｃ１－ｃ２ Co ｃ１ Al ｃ２ O ２ (-.2) (wherein 0.95≦a≦1.15, 0<c1≦0.20, 0<c2≦0.20, and Ni is 0.80 to 0.98, preferably 0.95≦a≦1.15, 0<c1<0.20, 0<c2<0.20, and Ni is 0.80 to 0.98, and more preferably 0.01≦c1≦0.09, 0.01≦c2≦0.09).

22. A positive electrode active material obtainable by the method according to claim 1 or 2.

23. A positive electrode active material comprising a lithium-nickel composite compound that contains lithium, nickel, and oxygen and can contain another element in addition to lithium, nickel, and oxygen, A compound containing lithium and a transition metal element, and a compound containing a transition metal element: (a) the surface of the secondary particles of the lithium nickel composite compound, and (b) at least a part of a grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surfaces of a plurality of primary particles constituting the secondary particle; present in; The transition metal element is at least one selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta; and A positive electrode active material in which the amount of residual lithium as determined by neutralization titration is preferably 0.15% by mass or less.

24. 24. The positive electrode active material according to claim 23, wherein the transition metal element is at least one selected from the group consisting of Ti, V, Zr, Nb and Mo, preferably V and Nb, and particularly Nb.

25. The lithium nickel composite compound has a composition having a layered rock salt structure and is represented by the following formula (I): Li ａ Ni １－ｂ－ｃ Mn ｂ M ｃ O ２ (I) (In the formula, M is one or more elements other than Li, Ni, Mn, or O, 0.95≦a≦1.15, 0≦b≦0.20, and 0≦c≦0.20; Ni is 0.80 to 0.98; 24. The cathode active material of claim 23, wherein M is one or more elements selected from the group consisting of: preferably Al, Ti, Co, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, Si, P, and B; more preferably Ti, Mg, Zn, Nb, W, Mo, V, Cr, Ca, Fe, Ga, Sr, Y, Sb, Ru, In, Sn, Ta, Bi, Zr, Si, P, and B; in particular Al and / or Co.

26. In the lithium nickel composite compound, b is 0.05 to 0.2 and c is 0; or The lithium nickel composite compound is represented by the following formula (I.2): Li ａ Ni １－ｃ１－ｃ２ Co ｃ１ Al ｃ２ O ２ (-.2) (wherein, 0.95≦a≦1.15, 0<c1≦0.20, 0<c2≦0.20, and Ni is 0.80 to 0.98, preferably, 0.95≦a≦1.15, 0<c1<0.20, 0<c2<0.20, and Ni is 0.80 to 0.98, and more preferably, 0.01≦c1≦0.09, 0.01≦c2≦0.09).

27. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material according to any one of claims 23 to 26.

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