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

Abstract

The present invention relates to a method for processing particles of a positive electrode active material, in which excess residual lithium in a particle surface layer of a lithium-nickel composite compound is reduced and a balance between lower resistance and higher battery capacity due to the reduction of resistance components is achieved. The present invention also relates to such positive electrode active material particles and a non-aqueous electrolyte secondary battery comprising a positive electrode containing such a positive electrode active material.

Description

[Technical Field]

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

[0002] Non-aqueous secondary batteries are compact, lightweight, and have a high energy density, and are known as power sources for driving cellular phones, notebook personal computers, and the like. Among these, lithium ion secondary batteries having a large charge / discharge capacity and using lithium cobaltate or a high-nickel material (such as lithium nickelate) in the positive electrode are widely used.

[0003] Examples of positive electrode active materials for lithium ion secondary batteries include high-nickel positive electrode active materials, such as positive electrode active materials based on nickel-cobalt-manganese (NCM), in which a part of nickel is replaced by cobalt and manganese is introduced; and positive electrode active materials based on nickel-cobalt-aluminum (NCA), in which a part of nickel is replaced by cobalt and aluminum is introduced. In particular, at present, it is possible to obtain a high-capacity battery by using a positive electrode active material formed of a high-nickel layered compound having a nickel content of more than 80 mol%. However, when a lithium ion secondary battery using such a positive electrode active material is repeatedly used over a long period of time, the lithium ion secondary battery generates gas, and there is also an increase in reaction resistance, which results in a decrease in battery output characteristics and cycle characteristics.

[0004] The influence of the lithium component remaining on the surface of the positive electrode active material particles is considered to be one of the causes of the above problems. In order to obtain positive electrode active material particles having a favorable crystal state in the high-nickel content positive electrode active material as described above, when a lithium compound and a precursor composite compound are mixed, it is necessary to set the molar amount of lithium to be slightly larger than the metal component in the precursor composite compound, that is, the ratio Li / (metal component in the precursor composite compound) needs to be slightly larger than 1.0, and thus, excessive lithium remains on the surface of the particles of the lithium-nickel composite compound obtained via a firing step. Attempts are being made to reduce the amount of residual lithium by washing with water and heat-treating the lithium-nickel composite compound after the firing step, and although excessive lithium can be reduced when a temperature of about 100 °C is used in the drying step of the heat treatment, proton exchange into the Li sites in the particle surface layer portion cannot be eliminated due to washing with water, and a resistance component is formed. In addition, when a temperature of 450 °C or higher is used, lithium separates from the lattice inside the particles and dissolves into the particle surface layer during the heat treatment, and ultimately excessive lithium is formed on the particle surface layer. For this reason, attempts are being made to reduce the resistance component generated due to proton exchange into the Li sites while reducing the excessive lithium remaining on the particle surface.

[0005] For example, in Patent Document 1, the surface layer of the high-nickel cathode active material is coated with an oxide containing lithium and niobium, aiming to prevent gas generation in a lithium-ion secondary battery and improve the battery output characteristics. Specifically, Patent Document 1 discloses a method for producing a composite powder of an active material, which includes: a spray drying step, in which an active material such as lithium-nickel-manganese-cobalt (NMC) is sprayed with a solution containing a niobium peroxo complex and lithium, and at the same time, parallel to this spraying, the solution is dried; and a heat treatment step, in which the material is heat-treated after the spray drying step, where the heat treatment temperature is higher than 123 °C and lower than 350 °C.

[0006] In addition, Patent Document 2 indicates that the surface of the cathode active material particles is 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, and then dried and fired.

[0007] In addition, Patent Document 3 also indicates that the surface of the cathode active material particles is coated with lithium niobate, and for this purpose, the cathode active material and niobium oxide are sprayed with 10% by mass of pure water while mixing and stirring, and then the material is heat-treated.

[0008] In addition, Patent Document 4 describes a cathode active material in which the primary particle surface contains calcium and the secondary particle surface contains niobium, and to obtain such a cathode active material, the calcium-containing cathode active material particles are washed with water, then niobium hydroxide is mixed, and the mixture is heat-treated.

[0009] [Prior Art Documents]

[0010] [Patent Documents]

[0011] [Patent Document 1]JP 2015-056307 A

[0012] [Patent Document 2]JP 2019-139862 A

[0013] [Patent Document 3]WO 2021 / 054468 A1

[0014] [Patent Document 4]WO 2021 / 241078 A1

[0015] [Non-Patent Documents]

[0016] [Non-Patent Document 1]Analele Universitatii din Bucuresti - Chimie [Annals of the University of Bucharest - Chemistry], Volume XIV (New Series), Issues I-II, pp. 65-72 [Summary of the Invention]

[0017] [Problems to be Solved by the Invention]

[0018] As indicated above, Patent Document 1 describes the production of active material particles, in which when the active material is sprayed with a solution containing a niobium peroxo complex and lithium and the solution is dried in parallel with the spraying, a lithium niobate (LiNbO3) coating is formed on the surface layer of the active material. This lithium niobate coating enables the insertion of a lithium ion conductive oxide layer at the interface between a sulfide-based solid electrolyte and a positive electrode active material, and thus improved battery characteristics are expected. Patent Document 1 also indicates that the lithium niobate coating formed in this way has a small number of voids and thus has a high lithium ion conductivity, enabling the production of active material particles for lithium batteries with a reduced resistance component.

[0019] However, no special operation was performed to reduce the amount of lithium in the active material particles produced in this way, and it was considered that excessive lithium remained on the surface layer of the active material particles. When these active material particles are actually used as a positive electrode active material, there is a problem of gas generation due to residual lithium in a lithium secondary battery, and the reduction of the resistance component is also insufficient.

[0020] In addition, in Patent Documents 2 - 4, the particles are washed with water (to form a slurry) or the surface of the positive electrode active material particles is coated with lithium niobate, and thus it is considered that the influence of excessive lithium on the particle surface can be restricted to a certain extent.

[0021] However, the treatment methods in the above documents are not suitable for reducing excessive lithium on the surface of the positive electrode active material particles, and there is a risk that excessive lithium cannot be sufficiently reduced. In addition, excessive lithium may cause the slurry to gel during battery production and generate gas after battery production. In addition, due to the water washing step (to form a slurry), the resistance component mainly generated by the exchange of protons with Li in the particle surface layer may increase, and even if the intention is to achieve a higher battery capacity by performing heat treatment to remove excessive lithium, there may still be problems with the long-term life of the battery due to the resistance component.

[0022] In view of these problems, there is a need for a material that can achieve a balance between a lower resistance and a higher battery capacity while also reducing excessive residual lithium.

[0023] The present invention has been designed in view of the problems of the prior art as described above, and an object thereof is to provide a method for treating positive electrode active material particles in which excessive residual lithium in the particle surface layer of a lithium-nickel composite compound is reduced, and a balance is achieved between a lower resistance due to the reduction of the resistance component and a higher battery capacity, and also to provide a positive electrode active material and a non-aqueous electrolyte secondary battery using the same.

[0024] [Means for Solving the Problems]

[0025] To achieve this object, the present invention provides a method for treating positive electrode active material particles, in which the formation of a lithium-nickel composite compound slurry (which also constitutes a water washing step) and the mixing of a transition metal compound are appropriately carried out to reduce the excessive lithium in the surface layer of the positive electrode active material particles, and to achieve a balance between a lower resistance and a higher battery capacity in the positive electrode active material particles after heat treatment. In addition, the treatment method achieves the above object by virtue of the fact that compounds containing lithium and transition metal elements and compounds containing transition metal elements are also present on the surface of the secondary particles of the positive electrode active material and on at least a part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles.

[0026] Specifically, the present invention provides a method for treating positive electrode active material particles containing a lithium-nickel composite compound, the lithium-nickel composite compound containing lithium, nickel and oxygen and optionally containing another element other than lithium, nickel and oxygen, the method being characterized by comprising:

[0027] (1) A slurry forming step, in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;

[0028] (2) A filtration separation step after the slurry forming step, in which the slurry is filtered and separated to obtain a cake-like compound; and

[0029] (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,

[0030] wherein the method further comprises mixing the aqueous solvent (used in step (1)), the slurry (step (1)), the cake-like compound (step (2)) and / or the dried lithium-nickel composite compound (step (3)) with (i) a compound containing at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta and (ii) optionally a lithium compound in at least one of step (1), step (2) and / or step (3); wherein when the compound containing at least one type of transition metal element is mixed with the dried lithium-nickel composite compound (step (3)), the mixing is carried out in the presence of an aqueous solvent; and

[0031] wherein in the obtained product, compounds containing lithium and transition metal elements and compounds containing transition metal elements are present on:

[0032] (a) The surface of the secondary particles of the dried lithium-nickel composite compound, and

[0033] (b) At least a part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particle.

[0034] The method of the present invention can alternatively be described as a method for preparing positive electrode active material particles containing a lithium-nickel composite compound, the lithium-nickel composite compound containing lithium, nickel, and oxygen and optionally containing another element other than lithium, nickel, and oxygen, the method being characterized by the same steps as outlined above, that is, characterized by including:

[0035] (1) A slurry formation step in which a lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;

[0036] (2) A filtration separation step after the slurry formation step in which the slurry is filtered and separated to obtain a cake-like compound; and

[0037] (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,

[0038] wherein the method further includes, in at least one of step (1), step (2), and / or step (3), mixing the aqueous solvent (used in step (1)), the slurry (step (1)), or the cake-like compound (step (2)) or the dried lithium-nickel composite compound (step (3)) with (i) a compound containing at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta and (ii) optionally a lithium compound; wherein when the compound containing at least one type of 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

[0039] wherein in the obtained product, the compound containing lithium and the transition metal element and the compound containing the transition metal element are present on:

[0040] (a) The surface of the secondary particles of the dried lithium-nickel composite compound, and

[0041] (b) At least a part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particle.

[0042] The following description of the "treatment method" of the present invention applies, with necessary modifications, to the wording of the "preparation method".

[0043] The present invention also relates to a positive electrode active material obtainable by the method according to the present invention;

[0044] and a positive electrode active material containing a lithium-nickel composite compound, the lithium-nickel composite compound containing lithium, nickel and oxygen, and optionally containing another element other than lithium, nickel and oxygen,

[0045] wherein a compound containing lithium and a transition metal element and a compound containing a transition metal element are present on the following:

[0046] (a) the surface of the secondary particles of the lithium-nickel composite compound, and

[0047] (b) at least a part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles;

[0048] wherein the transition metal element is at least one selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta; and

[0049] wherein the amount of residual lithium determined by neutralization titration is preferably 0.15 wt% or less.

[0050] Furthermore, the present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode containing the positive electrode active material of the present invention.

[0051] According to the present invention, by controlling the excessive lithium generated in the slurry forming step and by introducing a transition metal element that reacts with the excessive lithium, not only the excessive lithium finally remaining is reduced, but also the position and amount of the compound of lithium and the transition metal element present are effectively controlled, thus achieving a balance between high battery capacity and low resistance.

[0052] [Advantages of the Present Invention]

[0053] The present invention enables the provision of a method for treating positive electrode active material particles in which the formation of a lithium-nickel composite compound slurry (which also constitutes a water washing step) and the mixing of a transition metal compound are appropriately carried out to reduce the excessive lithium in the surface layer of the positive electrode active material particles, and to achieve a balance between lower resistance and higher battery capacity in the positive electrode active material particles after heat treatment, and also enables the provision of a positive electrode active material and a non-aqueous electrolyte secondary battery using the same. [Description of the Drawings]

[0054] Figure 1 is a longitudinal sectional view of the surface layer of secondary particles of a lithium-nickel composite compound when a coating containing a compound of lithium and a transition metal element and a compound containing the transition metal element is formed by the method for treating positive electrode active material particles according to an embodiment.

[0055] Figure 2 ​​It is a schematic cross-sectional view of secondary particles of a lithium-nickel composite compound when a coating containing a compound of lithium and a transition metal element and a compound containing the transition metal element is formed by a method for treating positive electrode active material particles according to an embodiment.

[0056] Figure 3 is a photograph of a cross-section of a positive electrode active material produced by a treatment method according to Examples 1-4 obtained by scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX). [Detailed Description]

[0057] Embodiments of the present invention will be described below with reference to the accompanying drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its application methods, or its uses.

[0058] As applicable, the preferred embodiments are applicable to both the method of the present invention and the positive electrode active material and the non-aqueous electrolyte secondary battery of the present invention.

[0059] <Method for Treating Positive Electrode Active Material Particles>

[0060] As indicated above, Patent Document 1 describes a method for producing active material particles having a lithium niobate (LiNbO3) coating on the surface layer, wherein the active material particles are produced by spraying an active material with a solution containing a niobium peroxo complex and lithium and drying the solution in parallel with the spraying. However, in the production method of Patent Document 1, no treatment for reducing the amount of lithium is actively carried out, and thus it is considered that excessive Li remains on the surface layer of the active material particles. In addition, in the production method of Patent Document 1, the coating is formed by simply spraying a solution of a niobium-containing compound on the surface layer of the active material, and when such active material particles are actually used as a positive electrode active material, the lithium secondary battery has the following problems: when the coating is formed, gelling of the paste occurs due to excessive lithium, gas is generated after battery production, and reduction of the resistance component is insufficient.

[0061] As a method for reducing excessive lithium on the surface layer of the lithium-nickel composite compound and achieving lower resistance and higher battery capacity by reducing the resistance component, the present invention thus elucidates that in addition to washing (slurry formation) the lithium-nickel composite compound to remove excessive lithium, in at least one of the slurry formation step, the filtration separation step, and the heating step, a step of further mixing a compound containing at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta.

[0062] ​A method for treating positive electrode active material particles according to an embodiment of the present invention constitutes a method for treating positive electrode active material particles, which preferably contain a lithium-nickel composite compound as a main component. The lithium-nickel composite compound contains lithium (Li), nickel (Ni), and oxygen (O) and may contain another element in addition to Li, Ni, and O. The treatment method thus includes the following steps (1)-(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).

[0063] (1) A slurry formation step, in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry;

[0064] (2) A filtration separation step after the slurry formation step, in which the slurry is filtered and separated to obtain a cake-like compound; and

[0065] (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.

[0066] In the treatment method including the above steps (1)-(3) and further including a step of mixing a compound containing a transition metal element in at least one of step (1), (2), and / or (3), the amount of lithium dissolved from the lithium-nickel composite compound into the aqueous solvent due to slurry formation and the compound containing the transition metal element mixed therewith are so minute that it is difficult to identify the primary particle size, and it is considered that a very fine compound containing lithium and the transition metal element and a very fine compound containing the transition metal element are deposited on the lithium-nickel composite compound.

[0067] Particularly in the slurry formation step (1), when the aqueous solvent or the slurry is mixed with the compound containing the transition metal element, the slurry of the lithium-nickel composite compound exhibits an alkalinity with a pH of about 11-13. Therefore, it is considered that some of the mixed transition metal element compounds dissolve and penetrate into the secondary particles of the lithium-nickel composite compound as transition metal element ions from the grain boundary portion between the primary particles constituting the secondary particles, and react with the excess lithium finally present on the surface portion of the primary particles. Therefore, the compound containing lithium and the transition metal element and the transition metal element compound can be deposited on the surface layer of the secondary particles of the very fine lithium-nickel composite compound and on the grain boundary portion between the primary particles through the filtration separation step (2) and the heat treatment step (3).

[0068] That is to say, a compound containing lithium and a transition metal element and a compound containing a transition metal element are present on the surface of the secondary particles of the lithium-nickel composite compound and at the grain boundary part (primary particle surface) between the primary particles constituting the secondary particles. Therefore, the excess lithium remaining on the particle surface layer of the lithium-nickel composite compound can be effectively reduced, and by means of the effect of improving the lithium ion conductivity by further mixing the compound containing a transition metal element, the balance effect between the lower resistance and the higher battery capacity generated by reducing the reaction resistance component can be achieved.

[0069] However, if a compound containing a transition metal element is added to the cake-like compound obtained in step (2) or to the dried lithium-nickel composite compound obtained in step (3), the method is equally applicable as long as there is some moisture (the moisture (aqueous solvent) content is preferably at least 1% by weight (relative to the mixture obtained by mixing the lithium-nickel composite compound in its respective existing form (e.g., the slurry form of step (1) or the cake-like compound form of step (2) or the dried compound form of step (3)) with the compound containing a transition metal element and optionally the Li compound)), where in the slurry of step (1) and in the cake-like compound obtained in step (2), the moisture content is more preferably at least 3% by weight relative to the total weight 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 its respective existing form (e.g., the slurry form of step (1) or the cake-like compound form of step (2)) with the compound containing a transition metal element and optionally the Li compound)). If a compound containing a transition metal element is added to the cake-like compound obtained in step (2), additional moisture (i.e., aqueous solvent) can be added, but it is not necessary because after filtration, the filter cake is usually still moist enough. If a compound containing a transition metal element is added to the dried lithium-nickel composite compound obtained in step (3), unless the drying is incomplete (which is not usually the case), some moisture must be introduced to obtain the desired moisture content and allow the desired reaction between lithium and the compound containing a transition metal element. This can be done, for example, by re-wetting 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 also by simultaneously mixing the dried filter cake, the compound containing a transition metal element, and the aqueous solvent.

[0070] For the present invention, "solution" is not limited to a solution in the true sense (a true solution is a single-phase, homogeneous mixture of two or more substances in which the solute particles cannot be seen by the naked eye; the solution does not cause light beam scattering), but also encompasses suspensions and emulsions. Similarly, the term "solvent" does not require the formation of a true solution, but means any liquid medium in which solid particles can be distributed and thus also in the form of a suspension.

[0071] The steps will be described in order below.

[0072] (1) Slurry formation step

[0073] 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, one purpose of this step is also to remove the excess lithium remaining in the lithium-nickel composite compound, but in addition to minimizing the damage to the particles caused by the water washing of the lithium-nickel composite compound, the simultaneous purpose is also to deposit a compound containing lithium and a transition metal element on the particle surface of the lithium-nickel composite compound by causing a reaction with the added transition metal element compound, and therefore it is necessary to control the amount of Li eluted into the slurry. Therefore, this step is not only aimed at reducing the amount of residual excess lithium.

[0074] Considering the following, the slurry formation step (1) is an especially important step: it achieves the effect of sufficiently reducing the excess lithium in the lithium-nickel composite compound, as described above; it is controlled to limit the proton exchange in the particle surface layer caused by excessive water washing; and it also deposits a compound containing lithium and a transition metal element on the particle surface of the lithium-nickel composite compound by causing a reaction between the transition metal element and the lithium eluted into the slurry.

[0075] Furthermore, in one alternative of introducing a compound containing a transition metal element, the compound containing a transition metal element is preferably mixed with stirring before and / or after introducing the lithium-nickel composite compound into the aqueous solvent to prepare the slurry, but this will be described in detail later.

[0076] The lithium-nickel composite compound used in the present invention contains Li, Ni, and O, and may contain another element in addition to Li, Ni, and O. There is no particular limitation on the lithium-nickel composite compound, and it can be appropriately modified. Furthermore, the lithium-nickel composite compound preferably has a composition with a layered rock salt structure and is represented by the following formula (I):

[0077] Li a Ni 1-b-c Mn b M c O2 (I)

[0078] (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 - 0.98 (more precisely, (1 - b - c) is 0.80 - 0.98)).

[0079] When a high content of Ni is present in the lithium-nickel composite compound, this achieves a high battery capacity, but also causes a problem of a large excess of lithium during the synthesis of the lithium-nickel composite compound, which can be solved by using the treatment method according to this embodiment.

[0080] Examples of the element M other than Li, Ni, Mn and O are 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, etc., and M can also be two or more different elements. In a specific embodiment, M is one or two of Al and / or Co.

[0081] In a preferred embodiment, b is 0.05 to 0.2 and c is 0; thus, the compound (I) is a compound having the formula (I.1):

[0082] Li a Ni 1-b Mn b O2 (I.1),

[0083] where b is 0.05 to 0.2 and Ni is 0.80 - 0.95 (more precisely, (1 - b) is 0.80 - 0.95).

[0084] In another preferred embodiment, the lithium-nickel composite compound is represented by the following formula (I.2):

[0085] Li a Ni 1-c1-c2 Co c1 Al c2 O2 (I.2)

[0086] (In this formula, 0.95 ≤ a ≤ 1.15, 0 < c1 ≤ 0.20, 0 < c2 ≤ 0.20, and Ni is 0.80 - 0.98 (more precisely, (1 - c1 - c2) is 0.80 - 0.98), where preferably 0.95 ≤ a ≤ 1.15, 0 < c1 < 0.20, 0 < c2 < 0.20, and Ni is 0.80 - 0.98 (more precisely, (1 - c1 - c2) is 0.80 - 0.98), and where more preferably 0.01 ≤ c1 ≤ 0.09 and 0.01 ≤ c2 ≤ 0.09).

[0087] The slurry is prepared, for example, by introducing an aqueous solvent containing a predetermined amount of pure water or the like into a reaction vessel, introducing a lithium-nickel composite compound into the aqueous solvent, and then stirring these materials. It should be noted that there is no particular limitation on the aqueous solvent, and it may also include an organic solvent. Suitable organic solvents are water-miscible (preferably having miscibility with water at any mixing ratio at 25 °C), and examples are C1-C3-alkanols (i.e., methanol, ethanol, n-propanol, isopropanol), diols, especially ethylene glycol and propylene glycol, and cyclic ethers, especially tetrahydrofuran and 1,4-dioxane. Preferably, the aqueous solvent is water; more preferably deionized water. Here, the ratio of the amount of the introduced lithium-nickel composite compound to the amount of the aqueous solvent (hereinafter also referred to as "solid-liquid ratio") can be adjusted to a suitable range.

[0088] 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 a transition metal element mixed at an appropriate time to form a compound containing lithium and a transition metal element, whereby the amount of residual lithium in the positive electrode active material as the final target product can be appropriately controlled.

[0089] 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 - 2000 g / L, and more preferably 800 g / L - 1800 g / L. The volume refers to the volume of the solvent used (not the volume of the formed solution; that is, the solid-liquid ratio is preferably adjusted to 750 - 2000 g of lithium-nickel composite compound per liter of aqueous solvent, and more preferably adjusted to 800 - 1800 g of lithium-nickel composite compound per liter of aqueous solvent). The volume refers to the volume of the solvent at room temperature (25 °C). If the solid-liquid ratio is lower than the lower limit value, there may be an excessive amount of aqueous solvent, which may cause an excessive amount of Li to elute from within the particles of the lithium-nickel composite compound, and there is a risk of deterioration in the quality of the positive electrode active material as the final target product. In addition, if the solid-liquid ratio is higher than the upper limit value, the amount of the aqueous solvent may be insufficient and the amount of residual lithium in the surface layer of the secondary particles may be greater than necessary, making it difficult to appropriately control the amount of residual lithium in the positive electrode active material as the final target product. In this example, the amount of lithium eluted into the slurry is controlled by controlling the solid-liquid ratio within the above range, and therefore the pH of the slurry is preferably controlled at 11 - 13 (see also the following reaction α).

[0090] Furthermore, the slurry is prepared by introducing a lithium-nickel composite compound into an aqueous solvent and stirring the materials, but a sufficient amount of Li can be eluted from the secondary particles of the lithium-nickel composite compound into the slurry by adjusting the stirring time, and this can achieve greater stability.

[0091] That is, in the slurry formation step (1), the slurry is prepared by stirring, wherein the stirring time is preferably adjusted to 3 minutes to 30 minutes, and more preferably 5 minutes to 25 minutes. If the stirring time is lower than the lower limit value, the amount of Li dissolved from the secondary particles of the lithium-nickel composite compound is expected to decrease, and there is a risk of a larger amount of residual lithium. Further, if the stirring time is higher than the upper limit value, the effects related to the preparation of the slurry are not further improved, and thus the productivity decreases.

[0092] It should be noted that there is no particular limitation on the temperature of the aqueous solvent into which the lithium-nickel composite compound is introduced, but as described above, it is preferable to adjust the temperature of the aqueous solvent to, for example, about 15°C to 35°C in order to prepare an appropriate slurry.

[0093] In the slurry formation step (1), when the lithium-nickel composite compound is represented, for example, by the following formula: Li x NiO2, the following [Reaction α] is carried out.

[0094] [Reaction α] Li x NiO2 → Li x-y NiO2 + yLiOHaq

[0095] (2) Filtration separation step

[0096] In the filtration separation step (2), after the slurry formation step (1) is completed, the slurry is filtered and separated using a filtration device such as a Buchner funnel or a filter press to obtain a cake-like compound.

[0097] This filtration separation step (2) enables the water content of the cake-like compound to be adjusted to an appropriate amount, which further improves the quality of the finally obtained positive electrode active material particles. There is no particular limitation on the water content of the cake-like compound after filtration separation, but it is 20 wt% or less, preferably 10 wt% or less, and more preferably 8 wt% or less. However, the water content of the cake-like compound after filtration separation is preferably 3 wt% or more. Therefore, preferably, based on the total weight of the cake-like compound, the water content of the cake-like compound after filtration separation is preferably 3 wt% to 20 wt%, more preferably 3 wt% to 10 wt%, and particularly 3 wt% to 8 wt%, and specifically 5% to 8% by weight.

[0098] It should be noted that considering the control of the solid-liquid ratio of the slurry within 750 g / L - 2000 g / L, the water content of the slurry in the present invention is 65 wt% or less, and preferably 60 wt% or less.

[0099] "Water content" means an aqueous solvent.

[0100] (3) Heat treatment step

[0101] In the heat treatment step (3), the cake-like compound obtained in the filtration and separation step (2) is heat treated and dried to obtain a dried lithium-nickel composite compound. When performing the heat treatment, for example, Non-Patent Document 1 can be referred to, but the temperature in the present invention is preferably set at 100°C to 400°C, for example, 140°C to 400°C, and more preferably 200°C to 350°C. When the temperature is lower than the lower limit value, sufficient drying is not easily achieved (usually only achieved under high vacuum and / or after an overly long drying time), and unless such measures are taken, a large amount of water remains in the finally obtained lithium-nickel composite compound. In addition, the added transition metal element does not react sufficiently with the Li part, so sufficient effects cannot be achieved. On the other hand, when the temperature is higher than the upper limit value, Li may separate from the lattice of the lithium-nickel composite compound and dissolve into the particle surface layer, so there is a risk of an increase in the amount of residual lithium in the finally obtained lithium-nickel composite compound. Therefore, the heat treatment can also be used for annealing the composite compound.

[0102] Furthermore, there is no particular limitation on the drying method, and for example, treatment using a roller hearth kiln or a rotary kiln, or vacuum drying treatment, etc. can be appropriately adopted. In addition, the atmosphere during the heat treatment needs to consider the nickel content of the dried lithium-nickel composite compound, and the drying treatment is preferably carried out, for example, in an oxygen atmosphere, a vacuum atmosphere, an inert gas atmosphere, or decarbonized air with a carbon dioxide concentration of 100 ppm or less.

[0103] In a preferred embodiment of the heat treatment step (3), the cake-like compound obtained in the filtration and separation step (2) is heat treated in a first step at 100°C to 195°C and in an optional second step at 200°C to 400°C, and more preferably 200°C to 350°C. Preferably, the second step is carried out.

[0104] Preferably, the first heat treatment is carried out under reduced pressure, for example, at a pressure of 0.1 to 100 mbar. For this purpose, a conventional heatable vacuum drying device can be used.

[0105] Preferably, the second heat treatment is carried out in an oxygen-rich atmosphere (such as oxygen-rich air, an oxygen-nitrogen mixture having more than 20% oxygen by weight, and oxygen, preferably an oxygen mixture containing 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 having a reduced CO2 content, preferably 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-rich atmosphere which simultaneously has a reduced CO2 content, preferably at most 100 ppm by volume, more preferably at most 50 ppm by volume.

[0106] Preferably, the second heat treatment is carried out. If a compound containing a transition metal element is added in step (3), it is particularly useful to divide it into two heating steps. In this case, it is advantageous to carry out a first heating step in which the cake-like compound obtained in the drying step (2) is dried, then the compound containing the transition metal element (and some moisture to allow reaction, and optionally the lithium compound) is added to the dried material, and then a second heating step is carried out in which the obtained mixture is dried and, depending on the temperature, annealing is also carried out.

[0107] <Step of mixing a compound containing a transition metal element>

[0108] This embodiment 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). Specifically, the compound containing the transition metal element is mixed with an aqueous solvent or a slurry (formed by an aqueous solvent and a lithium-nickel composite compound) in step (1), or with the cake-like compound in step (2), or with the dried cake-like compound in step (3). In this way, lithium in the lithium-nickel composite compound reacts with the mixed compound containing the transition metal element, and the surface layer of the particles can be coated with a compound containing lithium and a transition metal element and the compound containing the transition metal element.

[0109] The step of mixing the compound containing a transition metal element can be carried out in one or two or all three of step (1), step (2) and step (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 with the cake 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 a compound containing a transition metal element in the form of an aqueous solution or suspension, which aqueous solution or suspension contains the compound containing the transition metal element and optionally the lithium compound. Thus, in this alternative, preferably an aqueous solution or suspension containing the compound containing the transition metal element and optionally the lithium compound is mixed with the dried lithium-nickel composite compound in step (3). In this alternative, an aqueous solution or suspension containing the compound containing the transition metal element and the lithium compound is preferably used.

[0110] Furthermore, when mixing with the cake 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.

[0111] In addition, as described above, the compound containing a transition metal element can also be further mixed in step (2) after the compound containing a transition metal element has been mixed in step (1). Additionally, different transition metal element compounds can be added in step (1) and step (2).

[0112] That is, when the step of mixing the compound containing a transition metal element is carried out in step (1) and / or step (2), since the pH of the slurry is about 11 - 13 and the cake compound also has a pH of about 11 - 13, at least a small amount of the compound containing a transition metal element can dissolve, and it is assumed that lithium and the dissolved transition metal element also penetrate into the grain boundary portion formed by adjacent primary particles located on the surface of the plurality of primary particles constituting the secondary particles of the lithium-nickel composite compound, and thus these grain boundary portions can be coated with a compound containing lithium and a transition metal element and the compound containing a transition metal element.

[0113] When the heat treatment step (3) is carried out in this state, the reaction between the excess lithium remaining on the surface of the primary particles of the lithium-nickel composite compound and the transition metal element is further promoted, and the formation of the compound containing lithium and the transition metal element can be promoted. The compound containing lithium and the transition metal element is as described above, but it is considered to be able to limit the formation of the resistance component without degrading the battery characteristics.

[0114] Alternatively, after the compound containing the transition metal element has been mixed in step (1) and / or step (2), the compound containing the transition metal element can be further mixed in step (3). Additionally, different transition metal element compounds can be added in step (1) / step (2) and step (3).

[0115] The transition metal element is preferably used in the form of a transition metal oxide, hydroxide, mixed oxide-hydroxide, sulfate, oxalate, or hydrate of the forms listed above. Oxides and oxide hydrates are preferred.

[0116] There is no particular limitation on the transition metal element, but it is preferably at least one type of 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 selected from the group consisting of V and Nb, and specifically Nb. Further, when the transition metal element is, for example, Nb, the compound containing the transition metal element is preferably niobium pentoxide (Nb2O5) or niobium pentoxide hydrate (Nb2O5·nH2O). Additionally, when the transition metal element is V, the compound containing the transition metal element is preferably vanadium pentoxide (V2O5).

[0117] Furthermore, by appropriately adjusting the amount of the compound containing the transition metal element mixed, at least a part of the surface of the secondary particles and the grain boundary portion (interface between the primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles can be coated with the compound containing lithium and the transition metal element and the compound containing the transition metal element.

[0118] That is to say, in the step of mixing a compound containing a transition metal element, the amount of the compound containing a transition metal element to be mixed is preferably set such that the amount of the transition metal element is 0.01 mol% - 1.5 mol% with respect to the total amount of all elements other than lithium and oxygen in the lithium-nickel composite compound. If the amount of the compound containing a transition metal element to be mixed is lower than the lower limit value, there is a risk that the amount of the compound containing lithium and a transition metal element that cannot coat the secondary particles of the lithium-nickel composite compound increases. Further, if the amount of the compound containing a transition metal element to be mixed is higher than the upper limit value, the compound exists in an excessive amount on the surface layer of the secondary particles, and there is a risk that the resistance component becomes excessive. There is an additional risk that the amount of excess lithium used for the reaction will be insufficient, Li will be extracted from the lithium-nickel composite compound, and the resistance component will become even larger in any case. The amount of the compound containing a transition metal element to be mixed is more preferably such that the transition metal element is 0.1 mol% - 1.2 mol%.

[0119] When the step of mixing a compound containing a transition metal element is carried out in step (1), the slurry mixed with the compound containing a transition metal element is preferably alkaline so that an excessive amount of the compound containing a transition metal element does not precipitate in the aqueous solvent or slurry, and specifically, the pH is preferably 11 - 13. Therefore, at least some of the compound containing a transition metal element dissolves, and thus the transition metal element and the compound containing a transition metal element can also penetrate into the secondary particles and react not only with the excessive lithium on the surface layer of the secondary particles of the lithium-nickel composite compound but also with the excessive lithium on the surface layer of the primary particles, so that the amount of excessive lithium remaining in the finally obtained lithium-nickel composite compound can be reduced.

[0120] As indicated above, the treatment method includes step (1) - step (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 step (3), and in this way, the compound containing lithium and a transition metal element and the compound containing a transition metal element can exist on the surface layer of the secondary particles of the lithium-nickel composite compound.

[0121] In addition, an A element compound can be optionally mixed in steps (1) to (3). By mixing an A element compound like this, the A element compound can exist on the surface of the particles 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 the effect based on the A element compound can be achieved. There is no particular limitation on the A element, 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), etc.

[0122] In the treatment method of the present invention, a part containing a compound of lithium and a transition metal element and a compound containing a transition metal element on the surface of the lithium-nickel composite compound constitutes the surface of the particles of the lithium-nickel composite compound, and the compound can exist on the following parts (a) and (b):

[0123] (a) At least a part of the surface of the secondary particles of the lithium-nickel composite compound, and

[0124] (b) At least a part of the grain boundary part (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles.

[0125] In addition, when an A element compound has been optionally added in the above steps (1) to (3), the A element compound can exist 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 A element oxide, etc. In addition, the type of the A element is as described above.

[0126] There is no particular limitation on the type of the lithium compound (ii) optionally mixed with the aqueous solvent (used in step (1)), the slurry (step (1)), the cake-like compound (step (2)), or the dried lithium-nickel composite compound (step (3)), but LiOH is preferably used.

[0127] Figure 1 It is a schematic longitudinal sectional view of the surface layer of the secondary particles of the lithium-nickel composite compound when a coating containing a compound of lithium and a transition metal element and a compound containing a transition metal element is formed by the treatment method of the present invention.

[0128] As Figure 1As shown in the longitudinal section, the coating 3 of the compound containing lithium and transition metal elements and the compound containing transition metal elements is formed not only on the surface 2 of the secondary particle 1 formed by a plurality of primary particles 11, 12, 13, 14... but also on a part of the grain boundary portion 4 formed by the adjacent primary particles 11, 12; 12, 13; 13, 14... located on the uppermost surface. For Figure 1 In the examples of , the cases where the compound containing lithium and transition metal elements and the compound containing transition metal elements form a coating have been described, but it is not necessarily required to form a layer, and the compound can exist in the form of particles, as will be described later.

[0129] Figure 2 FIG. is a schematic cross-sectional view of the surface layer of the secondary particle of the lithium-nickel composite compound when a coating formed of the compound containing lithium and transition metal elements and the compound containing transition metal elements is formed by the treatment method of the present invention. Specifically, Figure 2 FIG. is a schematic cross-sectional view of the cross-section cut at a height close to the grain boundary portion 4 of the secondary particle 1.

[0130] Figure 2 The cross-section of shows such a state where the coating 3 of the compound containing lithium and transition metal elements and the compound containing transition metal elements is also formed on a part of the grain boundary portion 4 formed by a plurality of primary particles 11, 12, 13, 14... constituting the secondary particle 1, as described above. It should be noted that in Figure 2 FIG., the thick line represents the grain boundary portion 4 on which the coating 3 is not formed. In addition, in Figure 2 FIG., a partial cross-section of the secondary particle 1 is shown, and there are a large number of primary particles at the end of the secondary particle 1 in Figure 2 FIG., although these are not depicted.

[0131] <Positive electrode active material>

[0132] The positive electrode active material according to the present invention preferably contains a lithium-nickel composite compound as a main component, and the lithium-nickel composite compound contains Li, Ni, and O and may contain another element other than Li, Ni, and O. As indicated above, the compound containing lithium and transition metal elements and the compound containing transition metal elements are present on a predetermined part of the nickel-lithium composite compound, that is, on the following (a) and (b):

[0133] (a) the surface of the secondary particle of the lithium-nickel composite compound, and

[0134] (b) at least a part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particle.

[0135] "A part of the grain boundary portion", as indicated by this phrase, means a part of the grain boundary portion rather than its entire surface. The length of the entire surface of the grain boundary portion varies depending on the size of the primary particles constituting the secondary particles and is not particularly limited. However, considering the short axis portion in the shape of the primary particles constituting the secondary particles, this length is about 80 nm - 800 nm.

[0136] In this specification, the average particle size is a value obtained by using a scanning electron microscope SEM-EDS (field emission scanning electron microscope JS-7100F: manufactured by JEOL Ltd.) at an acceleration voltage of 10 kV, and is based on a scanning electron microscope photograph (SEM photograph) of the primary particles or secondary particles of the imaged lithium-nickel composite compound, such that the grain boundaries of the primary particles can be confirmed.

[0137] The compound containing lithium and a transition metal element is formed by compounding the excess lithium in the primary particles and secondary particles of the lithium-nickel composite compound with a compound containing a transition metal element, and thus has the effect of reducing the excess lithium by forming a compound containing lithium and a transition metal element. For example, when the compound containing a transition metal element is niobium pentoxide (Nb2O5) or niobium pentoxide hydrate (Nb2O5·nH2O), it is considered that the compound containing lithium and a transition metal element is formed of LiNbO3 or Li3NbO4, etc. In addition, there is no particular limitation on the ratio of Li and the transition metal element in the compound containing lithium and a transition metal element, and it can be such that, for example, Li / transition metal element = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0138] The compound containing a transition metal element is preferably an oxide containing a transition metal element. For example, when Nb is selected as the transition metal element, the compound containing a transition metal element is preferably an oxide such as Nb2O5 or Nb2O5·nH2O.

[0139] The compound containing lithium and a transition metal element and the compound containing a transition metal element present on the surface or grain boundary portion of the lithium-nickel composite compound may exist in the form of particles and do not necessarily need to form a (coating) layer. However, these compounds can form a layer and there is no particular limitation. When forming a layer, there is also no particular limitation on the thickness of the layer, and it can have any thickness.

[0140] In the present specification, the coating condition and coating thickness provided by a compound containing a lithium and a transition metal element and a compound containing a transition metal element can be studied by using, for example, Auger electron spectroscopy (hereinafter also referred to as "AES"), scanning electron microscopy combined with energy dispersive X-ray spectroscopy (hereinafter also referred to as "SEM-EDX"), or transmission electron microscopy combined with energy dispersive X-ray spectroscopy (hereinafter also referred to as "TEM-EDX").

[0141] There is no particular limitation on the coefficient of variation of the amount of the transition metal element present in the coating of the compound containing a lithium and a transition metal element and the compound containing a transition metal element, and it can have any value.

[0142] In the present specification, the coefficient of variation of the amount of the transition metal element present on the particle surface can be determined, for example, by using the above AES, SEM-EDX or TEM-EDX.

[0143] For example, when using the above SEM-EDX, the coefficient of variation can be determined based on the following formula by performing SEM-EDX point analysis on the results at five randomly selected positions (N = 5) in the coating and using the standard deviation and average value of the numerical values obtained after confirming the presence of the transition metal element.

[0144] Coefficient of variation (%) = (standard deviation / average value) × 100

[0145] In the present specification, the coating ratio of the coating can be obtained, for example, by image analysis.

[0146] The positive electrode active material according to the present invention should be formed of a lithium-nickel composite compound which contains Li, Ni and O and may contain another element other than Li, Ni and O, and there is no particular limitation on its composition, but the lithium-nickel composite compound preferably has a composition represented by the following formula (I):

[0147] Li a Ni 1-b-c Mn b M c O2 (I)

[0148] (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 - 0.98 (more precisely, (1 - b - c) is 0.80 - 0.98)).

[0149] In the above formula (I), there is no particular limitation on the element M other than Li, Ni, and O, but 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.

[0150] In a preferred embodiment, b is 0.05 to 0.2 and c is 0; thus, the compound (I) is a compound having the formula (I.1):

[0151] Li a Ni 1-b Mn b O2(I.1),

[0152] where b is 0.05 to 0.2 and Ni is 0.80 - 0.95 (more precisely, (1 - b) is 0.80 - 0.95).

[0153] In another preferred embodiment, the lithium-nickel composite compound is represented by the following formula (I.2):

[0154] Li a Ni 1-c1-c2 Co c1 Al c2 O2(I.2)

[0155] (In this formula, 0.95 ≤ a ≤ 1.15, 0 < c1 ≤ 0.20, 0 < c2 ≤ 0.20, and Ni is 0.80 - 0.98 (more precisely, (1 - c1 - c2) is 0.80 - 0.98), where preferably 0.95 ≤ a ≤ 1.15, 0 < c1 < 0.20, 0 < c2 < 0.20, and Ni is 0.80 - 0.98 (more precisely, (1 - c1 - c2) is 0.80 - 0.98), and where more preferably 0.01 ≤ c1 ≤ 0.09 and 0.01 ≤ c2 ≤ 0.09).)

[0156] In addition, the positive electrode active material according to the present invention should contain a lithium-nickel composite compound, and the A element compound may also be present on the surface of the particles of the lithium-nickel composite compound, and the A element compound may exist in the form of a compound of lithium and the A element or in the form of an A element oxide, and its effects may vary in some aspects of the present invention. For example, when an Al compound is present on the particle surface while an Nb compound is also present, an effect of improving long-term cycle characteristics can be imparted when the battery has been produced. There is no particular limitation on the A element, 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), etc.

[0157] In addition, as determined by neutralization titration, the amount of residual lithium in the positive electrode active material according to the present invention is preferably 0.15 wt% or less, and more preferably 0.12 wt% or less. If the amount of residual lithium is higher than the upper limit value, this results in gas generation, and there is also a risk of an increase in the reaction resistance in the lithium battery. It should be noted that the amount of residual lithium is the amount of Li derived from, for example, LiOH or Li2CO3, which is not included in the lithium-nickel composite compound or the coating (compound containing lithium and transition metal elements).

[0158] In this specification, the amount of residual lithium is calculated based on the Warder method. Specifically, 20 g of the powder of the lithium-nickel composite compound particles as the positive electrode active material particles is added to 100 mL of water, and stirred at room temperature for 20 minutes, and then the solid is separated by filtration and removed to obtain a supernatant, and the amount of residual lithium in it is determined by titration with 0.2N hydrochloric acid. Starting from the point with a smaller titration amount, two points with the largest gradient on the pH curve drawn by plotting the titration amount (mL) on the horizontal axis and the pH of the supernatant on the vertical axis are taken as the first titration point and the second titration point, and the amount of residual lithium is the value obtained by using the calculation formula from the titration amounts at these points.

[0159] <Method for producing a positive electrode active material>

[0160] There is no particular limitation on the method for producing the positive electrode active material according to the present invention, provided that the positive electrode active material particles are treated as described above in the "<Method for treating positive electrode active material particles>" section, and the lithium-nickel composite compound constituting the positive electrode active material particles can be produced by a usual method.

[0161] That is to say, for example, a method can be adopted in which a precursor composite compound containing at least Ni is synthesized, and the precursor composite compound is mixed with a lithium compound to obtain a mixture, and then the mixture is fired, or other methods can be adopted.

[0162] There is no particular limitation on the method for synthesizing the precursor composite compound. For example, an alkaline aqueous solution such as an aqueous sodium hydroxide solution or an aqueous ammonia solution is used as a mother liquor, and according to the expected composition of the positive electrode active material, an aqueous solution containing an aqueous nickel compound solution and various types of aqueous solutions containing compounds of elements other than Ni are dropped into a reaction tank under stirring, while dropping sodium hydroxide or the like, the pH is monitored and controlled within an appropriate range, and coprecipitation is carried out by means of a wet reaction to obtain the precursor composite compound. Examples of the precursor composite compound that can be cited include hydroxides, oxides obtained by calcining the hydroxides, carbonates, and the like.

[0163] It should be noted that once an alkaline aqueous solution used as a mother liquor is prepared for the reaction related to synthesis, it is preferable to set a nitrogen atmosphere in the reaction tank using an inert gas or industrially preferred nitrogen so that the oxygen concentration in the reaction tank system and the solution is as low as possible.

[0164] There is no particular limitation on the nickel compound, but examples that can be cited include nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, and metallic nickel, etc.

[0165] There is no particular limitation on the elements other than Ni that constitute the positive electrode active material, but in the above formula (I), examples thereof include Mn, and also 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, etc., which are given as examples of the element M other than Li, Ni, Mn, and O.

[0166] There is no particular limitation on the compound containing an element other than Ni, but examples thereof include cobalt compounds, aluminum compounds, manganese compounds, titanium compounds, magnesium compounds, zinc compounds, niobium compounds, and tungsten compounds, etc.

[0167] There is no particular limitation on the cobalt compound, but examples that can be cited include cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, and metallic cobalt, etc.

[0168] There is no particular limitation on the aluminum compound, but examples that can be cited include aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, and metallic aluminum, etc.

[0169] There is no particular limitation on the manganese compound, but examples thereof include: manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, and metallic manganese, etc.

[0170] There is no particular limitation on the titanium compound, but examples thereof include: titanium oxysulfate, titanium oxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, and metallic titanium, etc.

[0171] There is no particular limitation on the magnesium compound, but examples thereof include: magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, and metallic magnesium, etc.

[0172] There is no particular limitation on the zinc compound, but examples thereof include: zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, and metallic zinc, etc.

[0173] There is no particular limitation on the niobium compound, but examples thereof include: niobium oxide, niobium chloride, lithium niobate, and niobium iodide, etc.

[0174] There is no particular limitation on the tungsten compound, but examples thereof include: tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, and tungsten sulfide, etc.

[0175] The blending ratio of the nickel compound and various types of compounds containing elements other than Ni should be appropriately adjusted while considering the expected composition of the positive electrode active material, so that the amounts of Ni and various elements other than Ni reach a desired ratio.

[0176] When synthesizing the precursor composite compound, an appropriate range for pH control can be determined in order to obtain a desired secondary particle size and coarseness / fineness, and the pH is generally in the range of about 10 to about 13.

[0177] Preferably, the precursor composite compound obtained by the wet reaction as described above is subjected to a washing treatment, and then a drying treatment is carried out after dehydration.

[0178] By performing the washing treatment, it is possible to wash away impurities such as sulfate and carbonate ions adhering to the surface layer and sodium moieties that are incorporated into the agglomerated particles during the reaction. Washing treatments that can be used include the Nutsche washing method using a Buchner funnel provided that there are only a small amount of impurities, and a method of feeding the reaction suspension into a filter press, washing with water and dehydrating. It should be noted that the washing treatment can be carried out using pure water, an aqueous sodium hydroxide solution, an aqueous sodium carbonate solution, etc., but pure water is preferably used from an industrial perspective. However, when there is a large amount of residual sulfate, an aqueous sodium hydroxide solution with pH control can also be used for the washing treatment according to the residual amount.

[0179] Then, the precursor composite compound synthesized in this manner and the lithium compound are mixed at a predetermined ratio to prepare a mixture. This mixing can be solvent-based mixing, where 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 at a predetermined ratio, or it can be non-solvent-based mixing, where the powders of the precursor composite compound and the lithium compound are weighed out in a predetermined proportion and mixed by dry mixing.

[0180] There is no particular limitation on the lithium compound, and various types of lithium salts can be used. Examples of the lithium compound that can be cited 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, etc. Among them, lithium carbonate, anhydrous lithium hydroxide, and lithium hydroxide hydrate are preferred.

[0181] While considering the expected composition of the positive electrode active material, the blending ratio of the lithium compound and the precursor composite compound should be appropriately adjusted so that the total amount of the Li amount, Ni amount, and the amounts of any various other elements reaches the desired ratio.

[0182] There is no particular limitation on the firing temperature when firing the mixture of the precursor composite compound and the lithium compound. However, for example, it is preferably about 700 °C - 950 °C, and more preferably about 720 °C - 930 °C. If the firing temperature is lower than the lower limit value, there is a risk of difficulty in obtaining the desired crystal. In addition, if the firing temperature is higher than the upper limit value, crystal growth proceeds excessively, and there is a risk of a decrease in energy density.

[0183] The atmosphere during firing is also not particularly limited, and it should be an atmosphere that can cause a sufficient lithium formation reaction and sufficient crystal growth of the precursor composite compound, and in addition, has an oxygen partial pressure such that the Ni contained in the mixture to be fired is not reduced, and preferably an oxidation gas atmosphere or an oxygen atmosphere is used, for example.

[0184] The firing time during firing is also not particularly limited, and it should be a time that can also cause a sufficient lithium formation reaction and sufficient crystal growth of the precursor composite compound. For example, it is preferably a time of 1 hour - 15 hours, and more preferably 2 hours - 10 hours.

[0185] The positive electrode active material particles containing a lithium-nickel composite compound obtained in this way are subjected to the treatment method according to an embodiment of the present invention. The treatment method includes steps (1)-(3), and further includes a step of mixing the compound containing a transition metal element as described above in at least one of step (1), step (2), and step (3). Therefore, a positive electrode active material according to the present invention can be obtained, in which the compound containing lithium and a transition metal element and the compound containing a transition metal element are present on the following: (a) the surface of the secondary particles of the lithium-nickel composite compound, and (b) at least a part of the grain boundary portion formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles.

[0186] <Non-aqueous electrolyte secondary battery>

[0187] The non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode containing the positive electrode active material of the present invention produced in the above-described manner, and the non-aqueous electrolyte secondary battery includes the above positive electrode, a negative electrode, and an electrolytic solution containing an electrolyte.

[0188] When producing the positive electrode, a conductive agent and a binder are mixed with the positive electrode active material of the present invention by a usual method. For example, acetylene black, carbon black, graphite, etc. are preferred as the conductive agent. For example, polytetrafluoroethylene and polyvinylidene fluoride, etc. are preferred as the binder.

[0189] For the negative electrode, not only negative electrode active materials such as lithium metal, graphite, and low-crystallinity carbon materials can be used, 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 them, or a chalcogenide containing them can be used.

[0190] Examples of solvents of the electrolytic solution that can be used include organic solvents, which include at least one type of carbonate such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, or at least one type of ether such as dimethoxyethane.

[0191] In addition to lithium hexafluorophosphate (LiPF6), at least one type of lithium salt, such as lithium perchlorate or lithium tetrafluoroborate, can be dissolved in the solvent and used as the electrolyte.

[0192] <Function>

[0193] By means of the method for treating the positive electrode active material particles, the amount of excessive lithium remaining in the positive electrode active material is sufficiently reduced, and the resistance component is also reduced. Therefore, a positive electrode active material can be provided, which suppresses gas generation in a lithium battery, and at the same time enables a non-aqueous electrolyte secondary battery using the positive electrode active material in the positive electrode to achieve lower resistance and higher battery capacity.

[0194] [Examples]

[0195] Representative examples and comparative examples of the present invention will be given below to describe the present invention in specific terms, but the present invention is not limited to these examples. It should be noted that the physical properties and the methods for obtaining the characteristics are given as follows.

[0196] <XRD Diffraction>

[0197] 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 Rietveld analysis was performed using this XRD diffraction data with reference to "edited by R.A. Young, 'The Rietveld Method', Oxford University Press (1992)".

[0198] (X-ray Diffraction Conditions)

[0199] Radiation source: Cu-Kα

[0200] Acceleration voltage and current: 45 kV and 200 mA

[0201] Sampling width: 0.02 degrees

[0202] Scanning width: 15 degrees - 122 degrees

[0203] Scanning speed: 1.0 step / second

[0204] Divergence slit: 2 / 3 degrees

[0205] Receiving slit width: 0.15 mm

[0206] Scattering slit: 2 / 3 degrees

[0207] <Composition of the Precursor Composite Compound and the Positive Electrode Active Material>

[0208] 0.2 g samples of the precursor composite compound and the positive electrode active material were each heated and dissolved in 25 mL of 20% hydrochloric acid solution, and the materials were cooled and then transferred to a 100 mL volumetric flask, and pure water was introduced to prepare a conditioned liquid. The elements in the conditioned liquid were quantitatively determined using ICP-AES (Optima 8300, manufactured by PerkinElmer, Inc.).

[0209] <Button Battery Using the Positive Electrode Active Material>

[0210] The 2032 type button battery using the positive electrode active material is produced by using the positive electrode, negative electrode and electrolyte generated by the following corresponding methods.

[0211] (Positive electrode)

[0212] Using acetylene black and graphite as conductive agents, the weight ratio of acetylene black:graphite = 1:1, and using polyvinylidene fluoride as a binder, the positive electrode active material, conductive agent and binder are blended to achieve a weight ratio of positive electrode active material:conductive agent:binder = 90:6:4, and the slurry obtained by mixing these materials with N-methylpyrrolidone is coated on aluminum foil. The coated aluminum foil is dried at 110 °C to prepare a sheet, and the sheet is stamped to a diameter of 15 mm and then wound so that the density of the composite material is 3.0 g / cm 3 , and it is used as the positive electrode.

[0213] (Negative electrode)

[0214] A lithium foil with a diameter of 16 mm and a thickness of 500 μm, which is stamped, is used as the negative electrode.

[0215] (Electrolyte)

[0216] A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) is prepared at a volume ratio of EC:DMC = 1:2, and the solution obtained by mixing 1 M LiPF6 electrolyte with this mixed solvent is used as the electrolyte.

[0217] (Non-aqueous electrolyte secondary battery characteristics)

[0218] (1) Initial charge capacity, initial discharge capacity and initial charge / discharge efficiency

[0219] Using the button battery produced by the above method, after constant current charging at a current density of 20 mA / g to 4.30 V (upper limit voltage) in a 25 °C environment, constant voltage charging is carried out until the current reaches 2 mA / g. The capacity at this time is used as the initial charge capacity (mAh / g).

[0220] After a 5-minute pause, constant current discharge is carried out at a current density of 20 mA / g to 3.00 V in the same environment, and the initial discharge capacity (mAh / g) is measured after a 5-minute pause.

[0221] Based on the following formula, the initial charge / discharge efficiency is calculated using the measured value of the initial charge capacity and the measured value of the initial discharge capacity.

[0222] Initial charge / discharge efficiency (%) = (Initial discharge capacity / Initial charge capacity) × 100

[0223] (2) Initial reaction resistance

[0224] Measurements were carried out using button cells produced by the above method under the conditions of 25 °C environment and those indicated below.

[0225] First cycle:

[0226] Charge at 0.1C (4.3V cc-cv)

[0227] 5-minute pause

[0228] Charge at 0.1C (2.5V cc)

[0229] 5-minute pause

[0230] Second cycle:

[0231] Charge at 0.1C (4.3V cc-cv)

[0232] Measure the impedance using the battery that has completed the second charge cycle under the conditions of 25 °C environment and those indicated below. Use the result as the impedance measurement result for the second cycle (reaction resistance in the second cycle (initial reaction resistance)).

[0233] Frequency range: 300k - 0.01Hz (76 points)

[0234] Amplitude: 10 mV

[0235] <Production Example 1: Production of Cathode Active Material Particles 1>

[0236] Mix an aqueous nickel sulfate solution and an aqueous manganese sulfate solution so that the ratio of Ni and Mn (molar ratio) is Ni:Mn = 88:12, and obtain a mixed aqueous solution. Prepare 10 L of pure water to which 300 g of an aqueous sodium hydroxide solution and 500 g of ammonia water have been added in a reaction tank in advance as the mother liquor, set a nitrogen atmosphere in the reaction tank with nitrogen at a flow rate of 0.7 L / min, and the reaction is also carried out under the nitrogen atmosphere.

[0237] Thereafter, simultaneously drip the mixed aqueous solution, the aqueous sodium hydroxide solution, and ammonia water at a predetermined rate while the stirring blade rotates at 1000 rpm, and through a crystallization reaction, where the dropping amount of the alkaline solution is adjusted to reach pH 11.7, Ni and Mn crystallize and co-precipitate, forming agglomerated particles, and obtain a co-precipitate.

[0238] Thereafter, subject the slurry in the reactor to solid-liquid separation, and further wash with pure water to reduce residual impurities, and then dry the co-precipitate in a lump state at 110 °C under the atmosphere for 12 hours to obtain a precursor composite compound 1.

[0239] Weigh out the precursor composite compound 1 and anhydrous lithium hydroxide such that the ratio (molar ratio) of the total amount of Li, Ni, and Mn is Li / (Ni + Mn) = 1.040, and mix these materials using a mixer to prepare a mixture.

[0240] Then, the mixture is fired in an electric furnace at a maximum temperature of 750 °C for 5 hours in an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain the 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 is approximately 500 nm, and the average particle size of the secondary particles is approximately 12.8 μm.

[0241] <Production Example 2: Production of Positive Electrode Active Material Particles 2>

[0242] Mix an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of aluminum sulfate such that the ratio (molar ratio) of Ni, Co, and Al is Ni:Co:Al = 90:5:5, and obtain a mixed aqueous solution. Prepare 10 L of pure water with 300 g of an aqueous sodium hydroxide solution and 500 g of ammonia water added thereto in a reaction tank in advance as the mother liquor, set a nitrogen atmosphere in the reaction tank by nitrogen with a flow rate of 0.7 L / min, and the reaction is also carried out in the nitrogen atmosphere.

[0243] Thereafter, while the stirring blade rotates at 1000 rpm, the mixed aqueous solution, the aqueous sodium hydroxide solution, and the ammonia water are simultaneously added dropwise at a predetermined rate, and through a crystallization reaction, where the amount of the added alkaline solution is adjusted to reach pH 11, Ni, Co, and Al crystallize and co-precipitate, forming aggregated particles, and a co-precipitate is obtained.

[0244] Thereafter, the slurry in the reactor is subjected to solid-liquid separation and further washed with pure water to reduce residual impurities, and then the co-precipitate in the agglomerated state is dried at 110 °C in the atmosphere for 12 hours to obtain the precursor composite compound 2.

[0245] Weigh out the precursor composite compound 2 and anhydrous lithium hydroxide such that the ratio (molar ratio) of the total amount of Li, Ni, and Al is Li / (Ni + Co + Al) = 1.020, and mix these materials using a mixer to prepare a mixture. Note that the coarse anhydrous lithium hydroxide particles with a particle size greater than 500 μm are pulverized before use so that the mixture does not contain such coarse particles.

[0246] Then, the mixture was fired using an electric furnace at a maximum temperature of 740 °C for 5 hours in an oxygen atmosphere (oxygen concentration: 97 vol%), and positive electrode active material particles 2 (lithium-nickel composite compound) (hereinafter also referred to as "NCA") were obtained. The average particle size of the primary particles in the positive electrode active material particles 2 was about 280 nm, and the average particle size of the secondary particles was about 11.3 μm.

[0247] <Example 1-1: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)>

[0248] (1) Slurry formation step and step of mixing a compound containing a transition metal element

[0249] Positive electrode active material particles 1 (NM) were introduced into pure water (water temperature 25 °C) in a reaction tank (10 L capacity) 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. Thereafter, niobium pentoxide hydrate (Nb2O5·nH2O) powder as a compound containing a transition metal element was mixed while further stirring the slurry, and stirred for 10 minutes. It should be noted that the addition amount of niobium in the niobium pentoxide hydrate (Nb2O5·nH2O) powder was 0.5 mol% relative to the amount of metal elements in the positive electrode active material particles 1. In addition, the pH of the slurry at this time was 12.2.

[0250] (2) Filtration and separation step

[0251] Then, the mixed slurry was filtered and separated using a Buchner funnel to obtain a cake-like compound.

[0252] (3) Heat treatment step

[0253] The cake-like compound obtained in the filtration and separation step (2) was heat-treated at 155 °C for 19 hours using a vacuum drying device, and a dried lithium-nickel composite compound was obtained to produce a positive electrode active material.

[0254] The amount of residual Li in the obtained positive electrode active material (total amount of Li derived from LiOH and Li2CO3) was determined. In addition, the treatment steps, added components, added amounts, and final heat treatment temperature (hereinafter also collectively referred to as "conditions in the steps") are also shown in Table 1 below.

[0255] <Example 1-2: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)>

[0256] (1) Slurry formation step and step of mixing a compound containing a transition metal element

[0257] Prepare the slurry in the same manner as in Example 1, and mix niobium pentoxide hydrate (Nb2O5·nH2O) powder.

[0258] (2) Filtration and separation step

[0259] Filter and separate the slurry in the same manner as in Example 1 to obtain a cake-like compound.

[0260] (3) Heat treatment step

[0261] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then, heat-treat it at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and obtain a dried cake-like compound to produce a positive electrode active material.

[0262] Determine the properties of the obtained positive electrode active material. The properties of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0263] <Example 1-3: Treatment of positive electrode active material particles 1 (production of positive electrode active material)>

[0264] (1) Slurry formation step and step of mixing a compound containing a transition metal element

[0265] Prepare the slurry in the same manner as in Example 1, and mix 0.2 mol% niobium pentoxide hydrate (Nb2O5·nH2O) powder.

[0266] (2) Filtration and separation step

[0267] Filter and separate the slurry in the same manner as in Example 1 to obtain a cake-like compound.

[0268] (3) Heat treatment step

[0269] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then, heat-treat it at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and obtain a dried lithium-nickel composite compound to produce a positive electrode active material.

[0270] Determine the properties of the obtained positive electrode active material. The properties of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0271] <Example 1-4: Treatment of positive electrode active material particles 1 (production of positive electrode active material)>

[0272] (1) Slurry formation step and step of mixing a compound containing a transition metal element

[0273] Prepare the slurry in the same manner as in Example 1, and mix 1.0 mol% niobium pentoxide hydrate (Nb2O5·nH2O) powder.

[0274] (2) Filtration and separation step

[0275] Filter and separate the slurry in the same manner as in Example 1 to obtain a cake-like compound.

[0276] (3) Heat treatment step

[0277] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then, heat-treat it at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and obtain a dried lithium-nickel composite compound to produce a positive electrode active material.

[0278] Determine the properties of the obtained positive electrode active material. The properties of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0279] <Examples 1-5: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)>

[0280] (1) Slurry formation step

[0281] Introduce positive electrode active material particles 1 (NM) into pure water (water temperature 25 °C) in a reaction tank (10 L capacity), and stir for 10 minutes to prepare a slurry. Here, adjust the ratio of the amount of positive electrode active material particles 1 to the amount of pure water (solid-liquid ratio) to 1250 g / L. The pH of the slurry at this time is 12.1.

[0282] (2) Filtration and separation step and step of mixing a compound containing a transition metal element

[0283] Add 0.1 mol% niobium pentoxide hydrate (Nb2O5·nH2O) powder, and filter and separate the slurry obtained in the slurry formation step (1) to obtain a cake-like compound. The moisture content of the cake-like compound is 6.1 wt%. Mix 0.1 mol% niobium pentoxide hydrate (Nb2O5·nH2O) powder with the obtained cake-like compound.

[0284] (3) Heat treatment step

[0285] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then, heat-treat it at 250 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and obtain a dried lithium-nickel composite compound to produce a positive electrode active material.

[0286] Determine the properties of the resulting positive electrode active material. The properties of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0287] <Examples 1 - 6: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)>

[0288] (1) Slurry formation step and step of mixing a compound containing a transition metal element

[0289] Prepare a slurry 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) is adjusted to 1500 g / L. Then mix 0.2 mol% niobium pentoxide hydrate (Nb2O5·nH2O) powder.

[0290] (2) Filtration and separation step

[0291] Filter and separate the slurry in the same manner as in Example 1 to obtain a cake - shaped compound.

[0292] (3) Heat treatment step

[0293] Heat - treat the cake - shaped compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then heat - treat it at 300 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and obtain a dried lithium - nickel composite compound to produce a positive electrode active material.

[0294] Determine the properties of the resulting positive electrode active material. The properties of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0295] <Examples 1 - 7: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)>

[0296] (1) Slurry formation step

[0297] Introduce positive electrode active material particles 1 (NM) into pure water (water temperature 25 °C) in a reaction tank (10 L capacity), and stir 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) is adjusted to 1500 g / L. The pH of the slurry at this time is 12.3.

[0298] (2) Filtration and separation step and step of mixing a compound containing a transition metal element

[0299] The slurry obtained in the slurry formation step (1) is filtered and separated to obtain a cake-like compound. The moisture content of the cake-like compound is 6 wt%. The niobium pentoxide hydrate (Nb2O5·nH2O) dissolved in an aqueous LiOH solution (Nb2O5·nH2O is present in an amount of 0.2 mol% based on the amount of all elements other than Li and O in the lithium-nickel composite compound) is mixed with the obtained cake-like compound. The moisture content of the cake-like compound after mixing is 14.4 wt%.

[0300] (3) Heat treatment step

[0301] The cake-like compound obtained in the filtration and separation step (2) is heat-treated at 185 °C for 19 hours using a vacuum drying device. Then, it is heat-treated at 300 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound is obtained to produce a positive electrode active material.

[0302] The properties of the obtained positive electrode active material are determined. The properties of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0303] <Examples 1-8: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)>

[0304] (1) Slurry formation step

[0305] Positive electrode active material particles 1 (NM) are introduced into pure water (water temperature 25 °C) in a reaction tank (10 L capacity) 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) is adjusted to 1500 g / L. The pH of the slurry at this time is 12.3.

[0306] (2) Filtration and separation step and step of mixing a compound containing a transition metal element

[0307] The slurry obtained in the slurry formation step (1) is filtered and separated to obtain a cake-like compound. The moisture content of the cake-like compound is 6.2 wt%.

[0308] (3) Heat treatment step

[0309] The cake-like compound obtained in the filtration and separation step (2) is heat-treated at 185 °C for 19 hours using a vacuum drying device. The dried cake-like compound is mixed with the niobium pentoxide hydrate (Nb2O5·nH2O) dissolved in an aqueous LiOH solution (Nb2O5·nH2O is present in an amount of 0.2 mol% based on the amount of all elements other than Li and O in the lithium-nickel composite compound), which increases the moisture content to 8.2 wt%. Then, another heat treatment is carried out at 300 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace.

[0310] Determine the characteristics of the resulting positive electrode active material. The characteristics of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0311] <Examples 1-9: Treatment of Positive Electrode Active Material Particles 1 (Production of Positive Electrode Active Material)>

[0312] The procedure is similar to that of Examples 1-8, except that the water content after treating the dried cake-like compound with niobium pentoxide hydrate (Nb2O5·nH2O) dissolved in an aqueous LiOH solution is lower than that in Examples 1-8 (only 1.2%). The characteristics of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0313] <Comparative Example 1-1: Production of Positive Electrode Active Material>

[0314] Determine the amount of residual Li in the positive electrode active material particles 1 (positive electrode active material) without subjecting the positive electrode active material particles 1 to any of the slurry formation step (1) - heat treatment step (3) or the step of mixing a compound containing a transition metal element. The results are shown in Table 1.

[0315] <Comparative Example 1-2: Production of Positive Electrode Active Material>

[0316] (1) Slurry formation step

[0317] Prepare the slurry in the same manner as in Example 1.

[0318] (2) Filtration and separation step

[0319] Filter the slurry obtained in the slurry formation step (1) using a Buchner funnel to obtain a cake-like compound. The water content of the cake-like compound is 5.7 wt%.

[0320] (3) Heat treatment step

[0321] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Perform the heat treatment step and obtain a dried cake-like compound to produce the positive electrode active material.

[0322] Determine the characteristics of the resulting positive electrode active material. The characteristics of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0323] <Comparative Example 1-3: Production of Positive Electrode Active Material>

[0324] Mix the niobium pentoxide hydrate (Nb2O5·nH2O) powder with the positive electrode active material particles 1 which are a compound containing a transition metal element. Heat-treat the mixture in an oxygen atmosphere (oxygen concentration: 97 vol%) at 350 °C for 120 minutes using an electric furnace to produce the positive electrode active material. Determine the characteristics of the obtained positive electrode active material. The characteristics of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0325] <Comparative Example 1-4: Production of Positive Electrode Active Material>

[0326] Mix the powdered lithium niobate (LiNbO3) powder with the positive electrode active material particles 1 which are a compound containing a transition metal element. Heat-treat the mixture in an oxygen atmosphere (oxygen concentration: 97 vol%) at 350 °C for 120 minutes using an electric furnace to produce the positive electrode active material. Determine the characteristics of the obtained positive electrode active material. The characteristics of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0327] <Comparative Example 1-5: Production of Positive Electrode Active Material>

[0328] (1) Slurry formation step

[0329] Prepare the slurry in the same manner as in Example 1.

[0330] (2) Filtration and separation step

[0331] Filter the slurry obtained in the slurry formation step (1) using a Buchner funnel to obtain a cake-like compound. The moisture content of the cake-like compound is 5.9 wt%.

[0332] (3) Heat treatment step

[0333] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then heat-treat it in an oxygen atmosphere (oxygen concentration: 97 vol%) at 350 °C for 120 minutes using an electric furnace and obtain a dried lithium-nickel composite compound to produce the positive electrode active material.

[0334] Determine the characteristics of the obtained positive electrode active material. The characteristics of the positive electrode active material and the conditions in the steps are shown in Table 1.

[0335] <Test Example: Non-aqueous Electrolyte Secondary Battery Characteristic Test>

[0336] Obtain the initial charge capacity, initial discharge capacity, initial charge / discharge efficiency, initial reaction resistance, and resistance ratio (compared with Comparative Example 1-2) as the characteristics of non-aqueous 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 the positive electrode. The results are shown in Table 1.

[0337]

[0338]

[0339] As shown in the columns of Examples 1-1 and 1-2 and Comparative Examples 1-2 and 1-5 in Table 1, it was first confirmed that when the slurry forming 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 smaller. At the same time, as shown in the columns of Comparative Examples 1-3 and 1-4 in Table 1, it was confirmed that when the slurry forming step (1) was not performed in the production of the positive electrode active material, the amount of residual Li in the positive electrode active material was not reduced even compared with Comparative Example 1-1 in which no treatment was performed at all.

[0340] As shown in the columns of Example 1-1 and Comparative Example 1-2 in Table 1, in the battery using the positive electrode active material according to Example 1-1 in which the steps of mixing Nb2O5·nH2O powder with the slurry, the filtering separation step (2) and the heat treatment step (3) were performed, the initial reaction resistance was 59Ω, while in the battery using the positive electrode active material according to Comparative Example 1-2 in which the filtering separation step (2) and the heat treatment step (3) were performed without adding any substance to the slurry, the initial reaction resistance was 220Ω.

[0341] Based on the above situation, if Figure 1 As shown, since the treatment method undergoes the step of mixing Nb2O5·nH2O powder with slurry, the filtration separation step (2) and the heat treatment step (3), as a result of heat treatment of the dissolved lithium and the added element Nb, it is considered that a compound containing Li and Nb is formed on the surface of the particles, and thus the initial reaction resistance is reduced due to the effect of improving lithium ion conductivity. In addition, it is considered that the amount of residual Li is reduced because the amount of excess lithium is reduced due to the formation of the compound containing Li and Nb.

[0342] In addition, when the temperature of the heat treatment step for the above-mentioned substances was 350°C (as in Examples 1-2 and Comparative Examples 1-5), the same effect was also confirmed, and the initial battery capacity increased. It is inferred that Li2MnO3 (which is considered to be an unstable resistance component that hinders the migration of Li within the crystal structure) is formed as a domain in the lattice due to the excessive Li portion contained. This is because when the positive electrode active material is synthesized, Mn replaced by Ni in the positive electrode active material reacts with Li, and therefore during the heat treatment at 350°C in the heat treatment step in Example 1-2, the added Nb not only reacts with the dissolved lithium, but it is also considered to extract Li from the Li2MnO3 domain. It is believed that due to, for example, a phase transition to a crystal structure such as Li 1-x Ni y MnO2 or Li xMn2O 4-y , Li2MnO3 in the resistance component is eliminated, which is thus inferred to result in an increase in Li that can migrate within the crystal structure, and thus an increase in battery capacity.

[0343] In addition, it is speculated that the phenomenon described above is manifested in the positive electrode active material in which Mn is replaced by Ni, and it is considered that this phenomenon can be solved by implementing the treatment method according to the present invention.

[0344] Meanwhile, when Nb2O5·nH2O powder is directly added to the powdered positive electrode active material, as shown in the columns of Comparative Examples 1-3 in Table 1, and when powdered lithium niobium oxide (LiNbO3) powder is added to the positive electrode active material, as shown in the columns of Comparative Examples 1-4 in Table 1, although the heat treatment step (3) is carried out at a final heat treatment temperature of 350 °C, the residual Li does not decrease, and it is confirmed that the battery capacity (such as the initial charge capacity and the initial discharge capacity) does not increase.

[0345] These results show that in order to achieve a higher battery capacity, simply carrying out the heat treatment step (3) is not enough. It is also important to implement the step of mixing a compound containing a transition metal element through the slurry formation step (1) and the filtration separation step (2) in a state where the moisture content of the positive electrode active material is 3 wt% or more, or to treat the dried cake-like compound with a compound containing a transition metal element in the presence of some moisture during the heat treatment step (3), where the moisture content can even be as low as 1 wt%. It is inferred that this is because the added compound containing a transition metal element is partially dissolved in the positive electrode active material with a moisture content of 3 wt% or more and is easily deposited in a very fine state on the surface of the secondary particles and their grain boundary parts, and also because the lithium part also has a state of high moisture content, so it is partially dissolved and easily migrates. Therefore, the transition metal element and the Li dissolved out on the particle surface and the excess Li can react, and it is considered that the form as in Figure 1 and 2 can be achieved.

[0346] From the above results, it can be understood that by means of the method for treating positive electrode active material particles according to the examples (which includes the slurry formation step (1) - the heat treatment step (3), and further includes the step of mixing a compound containing a transition metal element in at least one of step (1), step (2), and step (3)), positive electrode active material particles can be provided, which achieve lower resistance and higher battery capacity by reducing the resistance component, while also reducing the excess Li on the surface of the primary particles and secondary particles of the lithium-nickel composite compound.

[0347] <Confirmation of Sites in the Positive Electrode Active Material Wherein Compounds Containing Lithium and Nb and Compounds Containing Nb Exist>

[0348] The positive electrode active materials obtained in Examples 1-4 were subjected to SEM-EDX described in the above examples, and cross-sectional photographs of the positive electrode active materials as shown in Figure 3 were obtained. Detection positions (detection sites) were selected, Nb / (NiMnNb) (mol%) was calculated, and these are shown in Table 2 below together with the detection results. The Nb detection results are indicated by O and X: an evaluation of O is given when the value of Nb / (NiMnNb) is 0.10 mol% or more, and an evaluation of X is given when the value is less than 0.10 mol%. In addition, the amount of Nb in Nb / (NiMnNb) represents the total amount of substances in the compounds containing Nb, and includes both compounds containing lithium and Nb and compounds containing Nb. It should be noted that Figure 3 "039", "040", "041", "042", "043", "044", "045", "046", "047", "048", "049", "050", and "051" in

[0349] [Table 2]

[0350]

[0351] As shown in Figure 3 and Table 2, first, it was confirmed that compounds containing lithium and Nb and compounds containing Nb exist on the surface of the secondary particles of the positive electrode active material particles (detection positions 045-047) obtained in Examples 1-4. In addition, it was confirmed that compounds containing lithium and Nb and compounds containing Nb also exist at the grain boundary portions (detection positions 039-044 and 051) formed by adjacent primary particles located on the surface of the plurality of positive electrode active material particles constituting the secondary particles. At the same time, it was confirmed that compounds containing lithium and Nb and compounds containing Nb are largely absent inside the primary particles of the positive electrode active material (detection positions 048-050).

[0352] These results confirm that compounds containing lithium and Nb and compounds containing Nb exist in the positive electrode active material according to the present invention, on the surface of the secondary particles of the lithium-nickel composite compound, and on at least a part of the grain boundary portions (interfaces between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles.

[0353] <Example 2-1: Treatment of Positive Electrode Active Material Particles 2 (Production of Positive Electrode Active Material)>

[0354] (1) Step of mixing a compound containing a transition metal element and slurry formation step

[0355] Powder of niobium pentoxide hydrate (Nb2O5·nH2O) as a compound containing a transition metal element was added to pure water (water temperature 25 °C) in a reaction tank (10 L capacity) and stirred. It should be noted that the addition amount of niobium in the powder of niobium pentoxide hydrate (Nb2O5·nH2O) was 0.5 mol% relative to the amount of all elements other than Li and O in the positive electrode active material particles 2 (NCA). Thereafter, 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 the positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) was adjusted to 1250 g / L. In addition, the pH of the slurry at this time was 12.2.

[0356] (2) Filtration and separation step

[0357] The slurry obtained in the slurry formation step (1) was filtered using a Buchner funnel to obtain a cake-like compound.

[0358] (3) Heat treatment step

[0359] The cake-like compound obtained in the filtration and separation step (2) was heat-treated at 185 °C for 19 hours using a vacuum drying device, and a dried lithium-nickel composite compound was obtained to produce a positive electrode active material.

[0360] The amount of residual Li in the obtained positive electrode active material (total amount of Li derived from LiOH and Li2CO3) was determined. In addition, the treatment steps, added components, added amounts, and final heat treatment temperature (hereinafter also collectively referred to as "conditions in the steps") are also shown in Table 3 below.

[0361] <Example 2-2: Treatment of positive electrode active material particles 2 (production of positive electrode active material)>

[0362] (1) Step of mixing a compound containing a transition metal element and slurry formation step

[0363] A slurry was prepared in the same manner as in Example 2-1.

[0364] (2) Filtration and separation step

[0365] The slurry was filtered and separated in the same manner as in Example 1 to obtain a cake-like compound.

[0366] (3) Heat treatment step

[0367] The cake-like compound obtained in the filtration and separation step (2) was heat-treated at 185 °C for 19 hours using a vacuum drying device. Then, it was heat-treated at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce a positive electrode active material.

[0368] The properties of the obtained positive electrode active material were determined. The properties of the positive electrode active material and the conditions in the steps are shown in Table 3.

[0369] <Example 2-3: Treatment of Positive Electrode Active Material Particles 2 (Production of Positive Electrode Active Material)>

[0370] (1) Slurry formation step and step of mixing a compound containing a transition metal element

[0371] Positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25 °C) in a reaction tank (10 L capacity) 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 1250 g / L. Thereafter, vanadium pentoxide (V2O5) powder as a compound containing a transition metal element was mixed under further stirring and stirred for 10 minutes. It should be noted that the addition amount of vanadium in the vanadium pentoxide (V2O5) powder was 0.2 mol% relative to the amount of all elements other than Li and O in the positive electrode active material particles 2 (NCA). In addition, the pH of the slurry at this time was 12.2.

[0372] (2) Filtration and separation step

[0373] Then, the mixed slurry was filtered and separated using a Buchner funnel to obtain a cake-like compound.

[0374] (3) Heat treatment step

[0375] The cake-like compound obtained in the filtration and separation step (2) was heat-treated at 185 °C for 19 hours using a vacuum drying device. Then, it was heat-treated at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce a positive electrode active material.

[0376] The properties of the obtained positive electrode active material were determined. The properties of the positive electrode active material and the conditions in the steps are shown in Table 3.

[0377] <Example 2-4: Treatment of Positive Electrode Active Material Particles 2 (Production of Positive Electrode Active Material)>

[0378] (1) Step of mixing a compound containing a transition metal element and slurry formation step

[0379] Add niobium pentoxide (Nb2O5) powder as a compound containing a transition metal element to pure water (water temperature 25 °C) in a reaction tank (10 L capacity) and stir. Note that the addition amount of niobium in the niobium pentoxide (Nb2O5) powder is 0.5 mol% relative to the amount of all elements other than Li and O in the positive electrode active material particles 2 (NCA). Thereafter, introduce the positive electrode active material particles 2 (NCA) and stir for 10 minutes to prepare a slurry. Here, adjust the ratio of the amount of the positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) to 800 g / L.

[0380] (2) Filtration and separation step

[0381] Filter the slurry obtained in the slurry formation step (1) using a Buchner funnel to obtain a cake-like compound.

[0382] (3) Heat treatment step

[0383] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then heat-treat it at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and obtain a dried lithium-nickel composite compound to produce a positive electrode active material.

[0384] Determine the properties of the obtained positive electrode active material. The properties of the positive electrode active material and the conditions in the steps are shown in Table 3.

[0385] <Example 2-5: Treatment of Positive Electrode Active Material Particles 2 (Production of Positive Electrode Active Material)>

[0386] (1) Step of mixing a compound containing a transition metal element and slurry formation step

[0387] Add niobium pentoxide (Nb2O5) powder as a compound containing a transition metal element to pure water (water temperature 25 °C) in a reaction tank (10 L capacity) and stir. Note that the addition amount of niobium in the niobium pentoxide (Nb2O5) powder is 0.5 mol% relative to the amount of all elements other than Li and O in the positive electrode active material particles 2 (NCA). Thereafter, introduce the positive electrode active material particles 2 (NCA) and stir for 10 minutes to prepare a slurry. Here, adjust the ratio of the amount of the positive electrode active material particles 2 to the amount of pure water (solid-liquid ratio) to 1800 g / L. At this time, the pH of the slurry is 12.5.

[0388] (2) Filtration and separation step

[0389] Filter the slurry obtained in the slurry formation step (1) using a Buchner funnel to obtain a cake-like compound.

[0390] (3) Heat treatment step

[0391] The cake-like compound obtained in the filtration and separation step (2) was heat-treated at 185 °C for 19 hours using a vacuum drying device. Then, it was heat-treated at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace, and a dried lithium-nickel composite compound was obtained to produce a positive electrode active material.

[0392] <Comparative Example 2-1: Production of Positive Electrode Active Material>

[0393] The amount of residual Li in the positive electrode active material particles 2 (positive electrode active material) was determined without subjecting the positive electrode active material particles 2 (NCA) to any of the slurry formation step (1) - heat treatment step (3) or the step of mixing a compound containing a transition metal element. The results are shown in Table 3.

[0394] <Comparative Example 2-2: Production of Positive Electrode Active Material>

[0395] (1) Slurry formation step

[0396] The positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25 °C) in a reaction tank (10 L capacity) 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.

[0397] (2) Filtration and separation step

[0398] The slurry obtained in the slurry formation step (1) was filtered using a Buchner funnel to obtain a cake-like compound. The moisture content of the cake-like compound was 5.5 wt%.

[0399] (3) Heat treatment step

[0400] The cake-like compound obtained in the filtration and separation step (2) was heat-treated at 185 °C for 19 hours using a vacuum drying device. The heat treatment step was carried out and a dried cake-like compound was obtained to produce a positive electrode active material.

[0401] The characteristics of the obtained positive electrode active material were determined. The characteristics of the positive electrode active material and the conditions in the steps are shown in Table 3.

[0402] <Comparative Example 2-3: Production of Positive Electrode Active Material>

[0403] (1) Slurry formation step

[0404] The positive electrode active material particles 2 (NCA) were introduced into pure water (water temperature 25 °C) in a reaction tank (10 L capacity) 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.

[0405] (2) Filtration and separation step

[0406] Filter the slurry obtained in step (1) using a Buchner funnel to obtain a cake-like compound. The moisture content of the cake-like compound is 5.9 wt%.

[0407] (3) Heat treatment step

[0408] Heat-treat the cake-like compound obtained in the filtration and separation step (2) at 185 °C for 19 hours using a vacuum drying device. Then, heat-treat it at 350 °C for 120 minutes in an oxygen atmosphere (oxygen concentration: 97 vol%) using an electric furnace to obtain a dried lithium-nickel composite compound for producing a positive electrode active material.

[0409] Determine the properties of the obtained positive electrode active material. The properties of the positive electrode active material and the conditions in the steps are shown in Table 3.

[0410]

[0411] As shown in the columns of Examples 2-1 and 2-2 and Comparative Examples 2-2 and 2-3 in Table 3, first, it was confirmed in the same manner as in Table 1 that when the slurry formation step (1) is carried out in the production of the positive electrode active material, the amount of residual Li in the positive electrode active material is smaller. In addition, it was confirmed from the results that the positive electrode active material particles are not limited to NM, and the effects such as those seen in the present invention are also obvious for NCA. Additionally, the same effect was also achieved in Example 2-3 in which the transition metal element is V.

[0412] Furthermore, it was confirmed from the results of Examples 2-1 and 2-2 that when a transition metal element compound is added before forming the slurry, the effects such as those seen in the present invention are also obvious.

[0413] The columns of Examples 2-4 and 2-5 are cases where the solid-liquid ratio during slurry formation is different, but the results of residual Li and battery characteristics are different. As described above, these results show the importance of adjusting the amount of dissolved lithium and controlling the reaction with the transition metal element by adjusting the solid-liquid ratio during slurry formation in the present invention, and it can be confirmed that the influence of the finally obtained positive electrode active material on residual Li and battery characteristics must be considered.

[0414] [Industrial applicability]

[0415] The positive electrode active material according to the present invention enables the provision of positive electrode active material particles that achieve lower resistance and higher battery capacity by reducing the resistance components, while also reducing the excess Li on the surfaces of the primary and secondary particles of the lithium-nickel composite compound, and is thus suitable for the positive electrode of a non-aqueous electrolyte secondary battery.

[0416] [Symbol Explanation]

[0417] 1…Secondary particle

[0418] 2…Surface

[0419] 3…Coating of a compound containing lithium and a transition metal element and a compound containing a transition metal element

[0420] 4…Grain boundary part

[0421] 11, 12, 13, 14…Primary particle

Claims

1. A method for treating positive electrode active material particles containing a lithium-nickel composite compound, the lithium-nickel composite compound containing lithium, nickel and oxygen and optionally containing another element other than lithium, nickel and oxygen, the method being characterized by comprising: (1) A slurry formation step in which the lithium-nickel composite compound is introduced into an aqueous solvent and stirred to prepare a slurry; (2) A filtration separation step after the slurry formation step (1) in which the slurry is filtered and separated to obtain a cake-like compound; And (3) A heat treatment step in which the cake-like compound obtained in the filtration separation step (2) is heat-treated to obtain a dried lithium-nickel composite compound, wherein the method further comprises, in at least one of step (1), step (2) and / or step (3), mixing the aqueous solvent (used in step (1)), the slurry (step (1)), the cake-like compound (step (2)) and / or the dried lithium-nickel composite compound (step (3)) with (i) a compound containing at least one type of transition metal element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf and Ta and (ii) optionally a lithium compound; wherein when the compound containing at least one type of transition metal element is mixed with the dried lithium-nickel composite compound (step (3)), the mixing is carried out in the presence of an aqueous solvent; and wherein in the obtained product, a compound containing lithium and the transition metal element, and the compound containing the transition metal element are present on: (a) the surface of the secondary particles of the dried lithium-nickel composite compound, and (b) at least a part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles.

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

4. The method according to claim 1, wherein, Mixing an aqueous solution or suspension containing the compound containing the transition metal element and optionally the lithium compound with the dried lithium-nickel composite compound of step (3).

5. The method according to any one of the preceding claims, 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 above form.

6. The method according to any one of the preceding claims, 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 method according to claim 7, wherein, The transition metal element is Nb, and the compound containing Nb is preferably Nb2O5 or its hydrate.

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

10. The method according to any one of the preceding claims, wherein, The lithium-nickel composite compound is introduced into the slurry formation step (1), where the ratio of the amount of the lithium-nickel composite compound to the amount of the aqueous solvent (solid-liquid ratio) is adjusted to 750 g - 2000 g per liter of the aqueous solvent.

11. The method according to any one of the preceding claims, wherein, The addition amount of the transition metal element is 0.01 mol% - 1.5 mol% relative to the total amount of all elements other than lithium and oxygen in the lithium-nickel composite compound.

12. The processing method according to any one of the preceding claims, wherein, When mixing the compound containing the transition metal element, the content of the aqueous solvent, preferably water, in the lithium-nickel composite compound is 1 wt% or more, preferably 3 wt% or more.

13. The method according to claim 12, wherein in the case where the cake compound in step (2) is mixed with the compound containing the transition metal element and optionally with the lithium compound, the total content of the aqueous solvent, preferably water, in the mixture obtained by mixing the cake compound, the compound containing the transition metal element, and optionally the lithium compound is 3 wt% or more based on the total weight of the obtained mixture; and / or wherein in the case where the dried lithium-nickel composite compound in step (3) is mixed with the compound containing the transition metal element and optionally with the lithium compound, the total content of the aqueous solvent, preferably water, in the mixture obtained by mixing the dried lithium-nickel composite compound with the compound containing the transition metal element and optionally the lithium compound is 1 wt% or more based on the total weight of the obtained mixture; wherein in the latter case, the desired content of the aqueous solvent is preferably obtained by mixing the dried lithium-nickel composite compound in step (3) with an aqueous solution or suspension containing the compound containing the transition metal element and optionally the lithium compound.

14. The method according to any one of the preceding claims, wherein, In the heat treatment step (3), the heat treatment is carried out at 100°C - 400°C.

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

16. The method according to claim 15, wherein, The second heat treatment is carried out, and the second heat treatment is preferably carried out at 200°C - 350°C.

17. The method according to any one of claims 15 or 16, wherein One or two or all three of the following conditions (a), (b), and / or (c) apply: (a) The first heat treatment is carried out under reduced pressure; and / or (b) The second heat treatment is carried out in an oxygen-rich atmosphere (such as oxygen-rich air, an oxygen-nitrogen mixture having more than 20% oxygen by volume, and oxygen); and / or (c) The second heat treatment is carried out in an atmosphere having a reduced CO2 content, preferably having a CO2 content of at most 100 ppm by volume, more preferably at most 50 ppm by volume.

18. The method according to any one of the preceding claims, wherein The lithium-nickel composite compound has a layered rock salt structure and is represented by the following formula (I) Composition: Li a Ni 1-b-c Mn b M c O2(I) (In this formula, 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 - 0.98).

19. The method according to 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; wherein M is specifically Al and / or Co.

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

21. The method according to any one of claims 18 or 19, wherein The lithium-nickel composite material is represented by the following formula (I.2): Li a Ni 1-c1-c2 Co c1 Al c2 O2(I.2) (In this formula, 0.95 ≤ a ≤ 1.15, 0 < c1 ≤ 0.20, 0 < c2 ≤ 0.20, and Ni is 0.80 - 0.98; wherein preferably 0.95 ≤ a ≤ 1.15, 0 < c1 < 0.20, 0 < c2 < 0.20, and Ni is 0.80 - 0.98; wherein more preferably 0.01 ≤ c1 ≤ 0.09 and 0.01 ≤ c2 ≤ 0.09).

22. A positive electrode active material obtainable by the method according to any one of claims 1 to 21.

23. A positive electrode active material comprising a lithium-nickel composite compound containing lithium, nickel, and oxygen and optionally containing another element other than lithium, nickel, and oxygen, wherein: A compound containing lithium and a transition metal element and a compound containing the transition metal element are present on: (a) the surface of the secondary particles of the lithium-nickel composite compound, and (b) at least a part of the grain boundary portion (interface between primary particles) formed by adjacent primary particles located on the surface among the plurality of primary particles constituting the secondary particles; 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 wt% or less.

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 selected from V and Nb, and particularly Nb.

25. The positive electrode active material according to any one of claims 23 or 24, wherein The lithium-nickel composite compound has a layered rock salt structure and is represented by the following formula (I) Composition: Li a Ni 1-b-c Mn b M c O2(I) (In this formula, 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 - 0.98; wherein M is preferably 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; and more preferably an element selected from the group consisting of Ti, Mg, Zn, Nb, W, Mo, V, Cr, Ca, Fe, Ga, Sr, Y, Sb, Ru, In, Sn, Ta, Bi, Zr, Si, P, and B; and specifically Al and / or Co).

26. The positive electrode active material according to claim 25, wherein, In the lithium-nickel composite compound, b is from 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 O2(I.2) (In the formula, 0.95 ≤ a ≤ 1.15, 0 < c1 ≤ 0.20, 0 < c2 ≤ 0.20, and Ni is 0.80 - 0.98; preferably 0.95 ≤ a ≤ 1.15, 0 < c1 < 0.20, 0 < c2 < 0.20, and Ni is 0.80 - 0.98; more preferably 0.01 ≤ c1 ≤ 0.09 and 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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