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

Abstract

The present invention provides a positive electrode active material capable of achieving a high-level balance between high battery capacity and high thermal stability in a lithium-ion secondary battery. A positive electrode active material for a lithium-ion secondary battery, which comprises a lithium nickel manganese composite oxide composed of secondary particles aggregated from a plurality of primary particles, the lithium nickel manganese composite oxide having a hexagonal layered structure and containing lithium (Li), nickel (Ni), manganese (Mn), element M (M), and titanium (Ti), the molar ratio of the elements being represented by Li:Ni:Mn:M:Ti = a:(1-x-y-z):x:y:z (where 0.97 ≤ a ≤ 1.25, 0.03 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15, 0.01 ≤ z ≤ 0.05), the ratio of the total peak intensity of the strongest spectral lines of the titanium compound to the (003) diffraction peak intensity of the strongest spectral line of the hexagonal layered structure being 0.2 or less, the crystallite diameter of the (003) plane being 80 nm or more and less than 160 nm, and the specific surface area being 0.7 m² / g or more and 4.0 m² / g or less.

Description

Technical Field

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

[0002] In recent years, with the popularization of portable electronic devices such as mobile terminals and laptop computers, there has been a strong expectation for the development of small and lightweight non-aqueous electrolyte secondary batteries having a high energy density and durability. In addition, as a battery for electric vehicles typified by power tools and hybrid vehicles, there has been a strong expectation for the development of a secondary battery with high output.

[0003] As a secondary battery that meets such requirements, there are non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. A lithium ion secondary battery using a layered or spinel-type lithium metal composite oxide as a positive electrode material can obtain a high voltage of 4V class, and thus is being promoted to practical use as a battery having a high energy density.

[0004] As the lithium metal composite oxide, a lithium cobalt composite oxide (LiCoO2) that is relatively easy to synthesize, a lithium nickel composite oxide (LiNiO2) using nickel that is cheaper than cobalt, a lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), a lithium manganese composite oxide (LiMn2O4) using manganese, a lithium nickel manganese composite oxide (LiNi 0.5 Mn 0.5 O2), etc. have been proposed.

[0005] However, when a lithium ion secondary battery uses a non-aqueous electrolyte as a battery material, high thermal stability is required. For example, when a short circuit occurs inside the lithium ion secondary battery, heat generation due to a rapid current is generated, and thus higher thermal stability is required.

[0006] Therefore, a lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) and a lithium nickel manganese composite oxide that are excellent in thermal stability have attracted attention. The lithium nickel cobalt manganese composite oxide is the same as the lithium cobalt composite oxide, the lithium nickel composite oxide, etc., and is a layered compound. A substance having a composition ratio of nickel, cobalt, and manganese at a ratio of 1:1:1 in the transition metal site is called a ternary positive electrode active material.

[0007] Furthermore, in recent years, a cathode active material with a high nickel ratio (Hi-Ni cathode material), which aims for high capacity and has an increased nickel ratio of a ternary cathode active material and a lithium nickel manganese composite oxide, has attracted attention. However, there is a trade-off between the increase in battery capacity caused by the nickel ratio and the decrease in thermal stability. Therefore, as a lithium-ion secondary battery, a cathode active material that combines high performance (high capacity, high cycle characteristics, high output, etc.) with short-circuit resistance and thermal stability is required.

[0008] For the purpose of improving battery characteristics such as thermal stability, several techniques for adding foreign elements such as niobium to lithium metal composite oxides have been proposed. For example, Patent Document 1 proposes a cathode active material for a non-aqueous secondary battery, which includes a composition composed of a compound containing at least one of lithium, nickel, cobalt, element M, niobium, and oxygen. In this proposal, since the Li-Nb-O-based compound present near the surface or inside the particles has high thermal stability, a cathode active material with high thermal stability and a large discharge capacity can be obtained.

[0009] In addition, Patent Document 2 proposes a cathode active material for a non-aqueous electrolyte secondary battery, which is composed of a lithium transition metal composite oxide obtained by a manufacturing method including a niobium coating process and a firing process, has a porous structure, and a specific surface area of 2.0 to 7.0 m 2 / g. By using this cathode active material, a non-aqueous electrolyte secondary battery with high safety, battery capacity, and excellent cycle characteristics can be obtained.

[0010] In addition, Patent Document 3 proposes a cathode active material for a non-aqueous electrolyte secondary battery, which is a cathode active material for a non-aqueous electrolyte secondary battery of a lithium transition metal composite oxide having at least a layered structure. The lithium transition metal composite oxide exists in a particle form including one or both of primary particles and secondary particles as aggregates thereof, and at least the surface of the particles has a compound containing at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron, and fluorine. By having the above compound on the surface of the particles, the conductivity is improved.

[0011] In addition, Patent Document 4 proposes a lithium transition metal-based compound powder for a lithium secondary battery cathode material, which has a lithium transition metal-based compound capable of realizing the insertion / extraction of lithium ions as a main component. After adding a compound containing at least one element selected from B and Bi and a compound containing at least one element selected from Mo, W, Ti, Ta, and Re to the main component raw material and firing them together. By firing after adding the additive elements together, a lithium transition metal-based compound powder with improved rate and output characteristics and easy handling and electrode preparation can be obtained.

[0012] In addition, Patent Document 5 proposes a positive electrode composition for a non-aqueous electrolyte secondary battery, which contains a lithium transition metal composite oxide and a boron compound containing at least boron element and oxygen element. By using a positive electrode composition containing a lithium transition metal composite oxide having nickel and tungsten as essential components and a specific boron compound, the output characteristics and cycle characteristics can be improved in the positive electrode composition using the lithium transition metal composite oxide.

[0013] In addition, Patent Document 6 proposes a positive electrode active material for a non-aqueous electrolyte secondary battery, which is characterized in that it is a positive electrode active material composed of a lithium nickel manganese composite oxide. The lithium nickel manganese composite oxide is composed of a hexagonal lithium-containing composite oxide having a layered structure. The average particle size of the positive electrode active material is 2 to 8 μm, [(d90 - d10) / average particle size], which is an index representing the particle size distribution width, is 0.60 or less, and it has a hollow structure. The hollow structure is composed of a shell portion sintered from aggregated primary particles and a hollow portion existing inside thereof. When this positive electrode active material is used in a non-aqueous secondary battery, it has a high capacity and good cycle characteristics, and can achieve high output.

[0014] In addition, in Patent Document 7, by adding 1 to 10% of zirconium to a lithium cobalt composite oxide in terms of the molar ratio to cobalt, the surface of the lithium cobalt composite oxide particles is covered with zirconium oxide or a composite oxide of lithium and zirconium. When this lithium cobalt composite oxide is used for the positive electrode of a secondary battery, the decomposition reaction and crystal destruction of the electrolyte at a high potential are suppressed, and excellent cycle characteristics and storage characteristics are exhibited.

[0015] Prior Art Documents

[0016] Patent Documents

[0017] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-151071

[0018] Patent Document 2: International Publication No. 2014 / 034430

[0019] Patent Document 3: Japanese Patent Application Laid-Open No. 2005-251716

[0020] Patent Document 4: Japanese Patent Application Laid-Open No. 2011-108554

[0021] Patent Document 5: Japanese Patent Application Laid-Open No. 2013-239434

[0022] Patent Document 6: International Publication No. 2012 / 131881

[0023] Patent Document 7: Japanese Patent Application Laid-Open No. 4-319260 Summary of the Invention

[0024] Problems to be Solved by the Invention

[0025] However, although improvements in battery capacity, output characteristics, and durability can be observed in the above-mentioned proposals, the improvement in thermal stability is insufficient, and further improvement in thermal stability is required.

[0026] As a method for improving thermal stability during overcharging, a method of coating the surface of the positive electrode active material with oxides such as SiO2, Al2O3, and ZrO2 has been proposed. However, in this method, the initial capacity decreases significantly, or the coating layer becomes resistive, resulting in a decrease in output characteristics. In addition, due to the complicated process, it is difficult to scale up, so it is often difficult to carry out industrial-scale production.

[0027] In addition, a method of adding a foreign element to the positive electrode active material to improve thermal stability during overcharging, as in the above-mentioned proposal, has also been proposed. However, in a positive electrode active material with a high nickel ratio, cation mixing in which metal elements such as nickel are easily transferred to the lithium ion sites is likely to occur. Therefore, compared with a positive electrode active material with a low nickel ratio, the firing temperature needs to be lowered, and it is difficult for foreign elements to dissolve in the active material.

[0028] The present invention has been completed in view of these circumstances, and an object thereof is to provide a positive electrode active material for a lithium ion secondary battery that can achieve a high level of both excellent battery capacity and high thermal stability. Another object of the present invention is to provide a method for easily manufacturing such a positive electrode active material in industrial-scale production.

[0029] Means for Solving the Problems

[0030] In a first aspect of the present invention, there is provided a positive electrode active material for a lithium ion secondary battery, which is a positive electrode active material for a lithium ion secondary battery containing a lithium nickel manganese composite oxide composed of secondary particles aggregated from a plurality of primary particles.

[0031] The lithium nickel manganese composite oxide has a layered structure of hexagonal crystal system and contains lithium (Li), nickel (Ni), manganese (Mn), element M (M) and titanium (Ti). The element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb and Al. The molar ratio of each element is represented by Li:Ni:Mn:M:Ti = a:(1 - x - y - z):x:y:z (where 0.97 ≤ a ≤ 1.25, 0.03 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15, 0.01 ≤ z ≤ 0.05). In the XRD measurement of the positive electrode active material, the ratio of the total peak intensity of the strongest spectral lines of the titanium compound to the (003) diffraction peak intensity of the strongest spectral line of the layered structure of the hexagonal crystal system is 0.2 or less. The crystallite diameter of the (003) plane obtained by XRD measurement is 80 nm or more and less than 160 nm, and the specific surface area measured by the BET method is 0.7 m 2 / g or more and 4.0 m 2 / g or less.

[0032] In addition, [(D90 - D10) / Mv], which represents the deviation index of particle size calculated from D90 and D10 based on volume basis in the particle size distribution by laser diffraction scattering method and the volume average particle size (Mv), is preferably 0.80 or more and 1.20 or less. In addition, the volume average particle size Mv is preferably 8 μm or more and 20 μm or less. In addition, the amount of lithium dissolved in water when immersed in water is preferably 0.2 mass% or less relative to the whole positive electrode active material.

[0033] In a second aspect of the present invention, there is provided a method for manufacturing a positive electrode active material for a lithium ion secondary battery, the positive electrode active material for a lithium ion secondary battery comprising a lithium nickel manganese composite oxide composed of secondary particles aggregated from a plurality of primary particles, the method for manufacturing the positive electrode active material for a lithium ion secondary battery comprising: a mixing step of adding a mixture containing at least a nickel manganese composite compound, a titanium compound, and a lithium compound; a firing step of firing the mixture in an oxidizing atmosphere having an oxygen concentration of 80% by volume or more and 100% by volume or less at 700°C or more and 950°C or less to obtain a lithium nickel manganese composite oxide; a water washing step of mixing and stirring at a ratio of 50 parts by mass or more and 200 parts by mass or less of water with respect to 100 parts by mass of the lithium nickel manganese composite oxide, and then performing solid-liquid separation; and a drying step of drying the water-washed lithium nickel manganese composite oxide. The nickel manganese composite compound contains nickel (Ni), manganese (Mn), and an element M (M), and the element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al. The molar ratio of each element is Ni:Mn:M = (1 - x - y):x:y (where 0 ≤ x ≤ 0.15 and 0 ≤ y ≤ 0.15). In the mixture obtained in the mixing step, the molar ratio of lithium (Li) to the total molar amount of nickel, manganese, element M, and titanium contained (Me) (Li / Me) is 0.97 or more and 1.25 or less, and the molar ratio of titanium (Ti) (Ti / Me) is 0.01 or more and 0.05 or less. In the XRD measurement of the positive electrode active material, the total peak intensity of the strongest spectral lines of the titanium compound is 0.2 or less than the (003) diffraction peak intensity of the strongest spectral line of the hexagonal layered structure, and the crystallite diameter of the (003) plane obtained by XRD measurement is 80 nm or more and less than 160 nm.

[0034] In addition, the volume average particle diameter Mv of the titanium compound is preferably 0.01 μm or more and 5 μm or less. In addition, the titanium compound is preferably a titanic acid compound or titanium oxide.

[0035] In a third aspect of the present invention, there is provided a lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains the above positive electrode active material.

[0036] Advantages of the Invention

[0037] According to the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery that can achieve a high level of balance between high battery capacity and high thermal stability. In addition, the present invention can easily manufacture such a positive electrode active material in industrial-scale production, and it can be said that the industrial value is extremely high. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] ​Figure 1 Figure 1 The upper part of [] shows a graph of the maximum oxygen generation peak intensity of the positive electrode active materials obtained in Comparative Examples 1 to 4 and Example 1. Figure 1 The lower part of [] shows a graph of the initial discharge capacity of the positive electrode active materials obtained in Comparative Examples 1 to 4 and Example 1, and a table showing the respective titanium contents, peak intensity ratios, and presence or absence of water washing.

[0039] Figure 2 Figure 2 is a graph showing the initial discharge capacity of the positive electrode active materials obtained in Comparative Example 1 and Comparative Example 2.

[0040] Figure 3 Figure 3 is a graph showing the initial discharge capacity of the positive electrode active materials obtained in Comparative Example 3 and Example 1.

[0041] Figure 4 Figure 4 is a diagram showing an example of the manufacturing method of the positive electrode active material for a lithium ion secondary battery of the present embodiment.

[0042] Figure 5 Figure 5 (A) and Figure 5 (B) are diagrams showing an example of the manufacturing method of the nickel-manganese composite compound of the present embodiment.

[0043] Figure 6 Figure 6 is a schematic cross-sectional view of a coin-type battery used in battery evaluation. Detailed Embodiments

[0044] Hereinafter, for the present embodiment, a positive electrode active material for a lithium ion secondary battery, a manufacturing method thereof, and a lithium ion secondary battery will be described. In addition, the present embodiment described below does not unduly limit the content of the present invention described in the claims, and can be changed without departing from the gist of the present invention. In addition, not all the configurations described in the present embodiment are essential as a solution to the present invention.

[0045] 1. Positive Electrode Active Material for Lithium Ion Secondary Battery

[0046] The positive electrode active material for a lithium ion secondary battery of the present embodiment (hereinafter, also referred to as "positive electrode active material") contains a lithium nickel manganese composite oxide composed of secondary particles aggregated from a plurality of primary particles. That is, the lithium nickel manganese composite oxide is composed of particles having a polycrystalline structure.

[0047] ​​​​​​​​​​​The lithium nickel manganese composite oxide has a layered structure of a hexagonal crystal system and contains lithium (Li), nickel (Ni), manganese (Mn), element M (M), and titanium (Ti) within specific ranges, and the element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al.

[0048] When a lithium ion secondary battery uses a flammable non-aqueous electrolyte as a constituent material, high thermal stability is particularly required. For example, it is known that in a charged state, when a short circuit occurs between the positive electrode and the negative electrode due to the mixing of metal foreign matters or the like, a short-circuit current is generated, and the positive electrode active material decomposes due to the heat generated by the short-circuit current, oxygen is released from the crystal, and reacts with the electrolyte, thereby causing thermal runaway.

[0049] As a method for improving the thermal stability during charging of a secondary battery, as described above, a method of coating the surface of the positive electrode active material with oxides such as SiO2, Al2O3, and ZrO2 has been proposed. However, in this method, the initial capacity decreases significantly, or the coating layer becomes a resistance and the output characteristics are reduced. In addition, a method of adding a foreign element to the positive electrode active material to improve the thermal stability during overcharging has also been proposed, but in a positive electrode active material with a high nickel ratio, cation mixing in which metal elements such as nickel transfer to the sites of lithium ions easily occurs. Therefore, compared with a positive electrode active material with a low nickel ratio, the firing temperature needs to be lowered, and it is difficult for the foreign element to be solid-solved in the positive electrode active material. When a foreign element is added, it is difficult to improve the thermal stability during overcharging while maintaining a high battery capacity.

[0050] The present inventors have conducted in-depth research and obtained the following insights: in a lithium nickel manganese composite oxide having a high nickel ratio and containing a specific amount of manganese, i) by adding a specific amount of titanium and controlling the atmosphere to a high oxygen concentration for firing, high battery characteristics (such as battery capacity) can be maintained, and by suppressing oxygen release during overcharging, it is possible to achieve both thermal stability, and ii) further, by washing the fired lithium nickel manganese composite oxide with water, the battery capacity is further increased, and thus the present invention is completed.

[0051] Hereinafter, with reference to Figures 1 to 3 An example of the effect brought about by the inclusion of titanium (Ti) in the lithium nickel manganese composite oxide of the present embodiment will be described. It should be noted that Figures 1 to 3 is made based on the evaluation results of the positive electrode active material and the secondary battery obtained in the examples and comparative examples described later.

[0052] Figure 1It is a graph showing the evaluation results of the maximum oxygen generation peak intensity and the initial discharge capacity of lithium nickel manganese composite oxides (positive electrode active materials) with different titanium contents, distributions, and presence or absence of post-firing water washing and drying.

[0053] It should be noted that the maximum oxygen generation peak intensity is the relative intensity of the oxygen generation amount when the lithium nickel manganese composite oxide (positive electrode active material) is set to an overcharged state and the amount of oxygen is measured when heating from room temperature to 450°C (comparative example 1 is set to 100). The lower this value, the less the oxygen generation amount and the higher the thermal stability during overcharging.

[0054] As Figure 1 shown in the upper graph of [], the positive electrode active materials of comparative example 3, comparative example 4, and example 1 containing titanium have a lower maximum oxygen generation peak intensity and higher thermal stability compared to the positive electrode active materials of comparative examples 1 and 2 without titanium.

[0055] Furthermore, as Figure 1 shown in the lower graph of [], in the positive electrode active material of example 1 containing titanium, with a peak intensity ratio of 0.2 or less and having undergone water washing and drying, the initial discharge capacity is significantly improved compared to the positive electrode active materials of comparative example 3 containing titanium but not having undergone water washing and drying and comparative example 4 with a peak intensity ratio exceeding 0.2.

[0056] It should be noted that, as described later, the peak intensity ratio is the ratio of the total peak intensity of the strongest spectral lines of the diffraction peaks derived from each titanium compound (titanium oxide, lithium titanate, etc.) to the peak intensity of the (003) diffraction peak, which is the strongest spectral line of the hexagonal layered structure. For example, as Figure 1 shown in comparative example 3 and example 1 of [], when the peak intensity ratio is 0.2 or less, it indicates that titanium is basically dissolved in the primary particles of the lithium nickel manganese composite oxide. Additionally, for example, as Figure 1 shown in comparative example 4 of [], when the peak intensity ratio exceeds 0.2, it indicates that titanium compounds are formed on the particle surface of the lithium nickel manganese composite oxide.

[0057] From the above results, it can be seen that the positive electrode active material containing lithium nickel manganese composite oxide of the present embodiment, i) has high thermal stability despite a high nickel ratio; ii) by performing water washing and drying after firing, the battery capacity is further improved, and it is possible to achieve a higher level of both high battery capacity and high thermal stability.

[0058] In addition, Figure 2 is a graph showing the evaluation results of the initial discharge capacity using the positive electrode active materials of comparative example 1 and comparative example 2 without titanium and obtained under the same manufacturing conditions except for the presence or absence of water washing and drying. Figure 3The figure shows the evaluation results of the initial discharge capacity using the cathode active materials of Comparative Example 3 and Example 1, which contain titanium and are obtained under the same manufacturing conditions except for water washing and drying.

[0059] As Figure 2 shown, in the case of a lithium nickel manganese composite oxide with a high nickel ratio and containing a specific amount of manganese and no titanium, by performing water washing and drying after firing, a reduction in battery capacity (initial discharge capacity) is shown. The detailed reason is not yet clear, but it is considered that through water washing, lithium dissolution occurs on the particle surface and grain boundaries of the lithium nickel manganese composite oxide, increasing the reaction resistance, and thus reducing the battery capacity.

[0060] On the other hand, as Figure 3 shown, in the case of containing titanium, compared with Comparative Example 3 without water washing and drying, in the cathode active material of Example 1 with water washing, the battery capacity (initial discharge capacity) is significantly improved. The detailed reason is not yet clear, but it is speculated that titanium dissolved in the primary particles has the effect of suppressing the deterioration of the particle surface and grain boundaries caused by lithium dissolution and suppressing the increase in reaction resistance.

[0061] It should be noted that, as described later, by containing a specific amount of manganese and controlling the firing atmosphere in the firing process (S20) to a high oxygen concentration, or appropriately adjusting the manufacturing conditions, titanium can be dissolved in the primary particles. Therefore, the cathode active material of the present embodiment contains a specific amount of titanium and manganese in the cathode active material with a high nickel ratio, and titanium is basically dissolved in the primary particles. Furthermore, by performing water washing and drying, high battery capacity and high thermal stability can be balanced at a higher level. Hereinafter, the composition of the cathode active material of the present embodiment will be described in detail.

[0062] [Lithium nickel manganese composite oxide]

[0063] The lithium nickel manganese composite oxide contained in the cathode active material of the present embodiment is composed of secondary particles aggregated from a plurality of primary particles.

[0064] The lithium nickel manganese composite oxide has a hexagonal layered structure and contains lithium (Li), nickel (Ni), manganese (Mn), element M (M), and titanium (Ti), where the element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al. In addition, the molar ratio of each element is represented by Li:Ni:Mn:M:Ti = a:(1 - x - y - z):x:y:z (where 0.97 ≤ a ≤ 1.25, 0.03 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15, 0.01 ≤ z ≤ 0.05).

[0065] In addition, in the X-ray diffraction (XRD) measurement of the positive electrode active material of the present embodiment, diffraction peaks other than the hexagonal layered structure are hardly detected. Therefore, it can be said that titanium is almost entirely dissolved in the primary particles. In addition, the crystallite diameter of the (003) plane obtained by XRD measurement is 80 nm or more and less than 160 nm, and the specific surface area measured by the BET method is 0.7 m 2 / g or more and 4.0 m 2 / g or less.

[0066] Such a positive electrode active material can be produced, for example, by appropriately adjusting the conditions of each process in the manufacturing method described below. For example, in the mixing step (S10), it is also effective to use a titanium compound having an average particle diameter within a specific range. Furthermore, the crystallite diameter of the (003) plane and the amount of lithium dissolved in water can be adjusted by performing the water washing step (S30) and the drying step (S40) described below. Hereinafter, each metal element contained in the lithium nickel manganese composite oxide will be described.

[0067] (Lithium)

[0068] In the above molar ratio of the amounts of substances, the range of a representing the molar ratio of the amount of Li is 0.97 ≤ a ≤ 1.25, preferably 1.00 ≤ a ≤ 1.15. When the range of a is within the above range, the reaction resistance of the positive electrode decreases and the output of the battery increases. When the value of a is less than 0.97 or exceeds 1.25, the reaction resistance sometimes increases and the output of the battery decreases.

[0069] (Manganese)

[0070] In the above molar ratio of the amounts of substances, the range of x representing the molar ratio of the amount of Mn to the amount of the contained metal elements is 0.03 ≤ x ≤ 0.15, preferably 0.03 ≤ x ≤ 0.10. When the value of x is within the above range, high capacity and high thermal stability can be achieved. On the other hand, when the value of x is less than 0.03, the improvement effect of thermal stability cannot be obtained. In addition, when the value of x exceeds 0.15, the battery capacity decreases. In addition, in the firing step (S20) described below, by containing manganese, the firing temperature can be made higher, and the dispersion of titanium and the like can be promoted. It should be noted that in the manufacturing method described below, even when the firing temperature is lowered, by appropriately adjusting other manufacturing conditions, titanium can be dispersed and dissolved in the entire positive electrode active material.

[0071] (Element M)

[0072] Among the above-mentioned mass ratios, element M is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al. The range of y representing the mass ratio of element M is 0 ≤ y ≤ 0.15. When y is 0 or more, thermal stability, storage characteristics, and battery characteristics can be improved. When y exceeds 0.15, the structure becomes unstable, and sometimes a compound with a layered crystal structure cannot be formed, and sometimes the battery capacity decreases due to the relatively reduced ratios of Ni and Mn. For example, when M contains Co, the battery capacity and output characteristics are more excellent. When M is Co, it is preferably 0 ≤ y ≤ 0.10. In addition, among the above-mentioned mass ratios, when the mass ratio of Co contained in element M is set as y1, it is preferably 0 ≤ y1 ≤ 0.10, and more preferably 0.01 ≤ y1 ≤ 0.10.

[0073] (Titanium)

[0074] Among the above-mentioned mass ratios, the range of z representing the amount of Ti is 0.01 ≤ z ≤ 0.05, and preferably 0.01 ≤ z ≤ 0.03. When the range of z is within the above range, oxygen evolution can be suppressed when used as the positive electrode of a secondary battery, and high thermal stability can be obtained. On the other hand, when the value of z is less than 0.01, the solid solution amount of titanium is insufficient, so the effect of improving thermal stability is insufficient. In addition, when the value of z exceeds 0.05, in addition to the relatively reduced ratios of Ni and Mn, the crystal structure is also unstable, and cation mixing is likely to occur, so the battery capacity is greatly reduced.

[0075] (Nickel)

[0076] Among the above-mentioned mass ratios, the lower limit of (1 - x - y - z) representing the mass ratio of Ni is 0.65 or more, preferably 0.70 or more, and more preferably 0.80 or more. When the mass ratio of nickel is within the above range, a secondary battery with a high battery capacity can be obtained. When the mass ratio of nickel is high, although the battery capacity increases, sometimes the thermal stability decreases. However, the positive electrode active material of the present embodiment has a specific distribution of a specific amount of Ti and includes a water washing step (S30) and a drying step (S40), so that regardless of whether it is a high nickel ratio, it can have very high thermal stability.

[0077] It should be noted that the composition of the lithium nickel manganese composite oxide can be determined by quantitative analysis based on inductively coupled plasma (ICP) emission spectrometry.

[0078] (Distribution of titanium)

[0079] In the positive electrode active material of this embodiment, no diffraction peak derived from the compound containing titanium is detected or it is extremely weak in XRD measurement, and a strong diffraction peak of the hexagonal layered structure is detected. That is, in the lithium nickel manganese composite oxide, it is preferred that titanium is almost entirely dissolved in the primary particles.

[0080] For example, when a lithium nickel manganese composite oxide containing titanium is produced without using appropriate production conditions as described later, titanium is sometimes not dissolved in the primary particles, but precipitated on the surface of the primary particles or the grain boundaries between the primary particles. As the form of titanium precipitated on the surface of the primary particles, for example, TiO2 remaining as an unreacted product in the firing process of the titanium compound used as a raw material, and lithium titanate such as LiTiO2 generated by the reaction of the titanium compound with the lithium compound can be cited.

[0081] Here, titanium solid solution in the particles of lithium nickel manganese composite oxide refers to the following state: for example, in XRD measurement, no peak originating from titanium compounds including the above-mentioned TiO2, LiTiO2, etc. can be detected, or even if the peak is detected, it is weak and has substantially no effect on the battery characteristics of the obtained positive electrode active material.

[0082] Specifically, when using CuK α In the XRD measurement of the line, the total peak intensity of the strongest line of the titanium compound (I Ti化合物 ) and the (003) diffraction peak intensity (I (003) ) ratio (I Ti化合物 / I (003) : hereinafter referred to as "peak intensity ratio") is preferably less than 0.2, more preferably greater than 0 and less than 0.1, and may also be 0. When the peak intensity ratio exceeds 0.2, the titanium compound will precipitate more than a certain amount, and the battery capacity may be reduced. It should be noted that when each diffraction peak is below the detection limit, the diffraction peak intensity is set to 0 (zero).

[0083] For example, when TiO2 and LiTiO2 are detected as titanium compounds, the peak intensity ratio becomes the diffraction peak intensity (I TiO2 ) and the diffraction peak intensity of the strongest spectral line of LiTiO2 (I LiTiO2 ) and the (003) diffraction peak intensity (I 003) ) of the ratio [(I TiO2 +I LiTiO2 ) / I (003) ].

[0084] In addition, TiO2 has a rutile type and anatase type. Therefore, the intensity of the diffraction peak of TiO2 refers to the sum of the intensity (I TiO2 Rutile(110) ) of the (110) diffraction peak, which is the strongest spectral line of rutile TiO2, and the integrated intensity (I TiO2 Anatase(101) ) of the (101) diffraction peak, which is the strongest spectral line of anatase TiO2. Here, the position of the (110) diffraction peak, which is the strongest spectral line of rutile TiO2, is 2θ = 27.9° (from JCPDS No.: 01-088-1175), and the position of the (101) diffraction peak, which is the strongest spectral line of anatase TiO2, is 2θ = 25.3° (from JCPDS No.: 01-084-1286).

[0085] In addition, when multiple lithium titanates with different compositions are detected simultaneously, the peak intensity of the strongest spectral line of lithium titanate is calculated as the sum of the peak intensities of the strongest spectral lines of the detected lithium titanates. Examples of lithium titanate include LiTiO2, Li2TiO3, Li4TiO4, Li4Ti5O 12 and so on.

[0086] In addition, in XRD measurement, when diffraction peaks of other titanium compounds (such as TiO, Ti2O3, TiC, etc.) are detected, the peak intensity ratio becomes the sum of the diffraction peak intensities of the strongest spectral lines of all these detected titanium compounds relative to I (003) . For example, when TiO2, LiTiO2, and another titanium compound A are detected as titanium compounds, if the peak intensity of the strongest spectral line of titanium compound A is set as I 钛化合物A , then the peak intensity ratio becomes [(I TiO2 +I LiTiO2 +I 钛化合物A ) / I (003) .[[]]

[0087] [(003) plane crystallite diameter]

[0088] The crystallite diameter (hereinafter referred to as the "(003) plane crystallite diameter") of the positive electrode active material of the present embodiment, which is measured from the diffraction peak of the (003) plane of the hexagonal layered structure obtained by XRD measurement, is preferably 80 nm or more and less than 160 nm, may be 100 nm or more and less than 160 nm, may be 100 nm or more and 150 nm or less, or may be 100 nm or more and 140 nm or less. When the (003) plane crystallite diameter is in the above range, it has a high charge-discharge capacity, and can suppress the breakage of the positive electrode active material particles during repeated charge and discharge, improving durability.

[0089] On the other hand, when the (003) microcrystal diameter is 160 nm or more, the crystallinity is high and the discharge capacity is increased. However, the expansion and contraction of each primary particle during charge and discharge become larger, so particle breakage is likely to occur during repeated charge and discharge. In addition, when the (003) microcrystal diameter is less than 80 nm, the discharge capacity decreases due to low crystallinity. It should be noted that the (003) plane microcrystal diameter can be set within the above range by appropriately adjusting the manufacturing conditions using the manufacturing method described later. The details will be described later. For example, by washing and drying the particles of the lithium nickel manganese composite oxide obtained by firing, the crystallinity is improved and a higher discharge capacity can be obtained. Therefore, by setting the (003) plane microcrystal diameter within the above range, the battery capacity and thermal stability can be balanced at a high level, and higher durability can be achieved. It should be noted that the (003) plane microcrystal diameter is calculated by the Scherrer equation using the half-value width in the diffraction peak of the (003) plane of the hexagonal layered structure obtained by XRD measurement.

[0090] [Specific surface area]

[0091] The positive electrode active material of the present embodiment preferably has a specific surface area measured by the BET method of 0.7 m 2 / g or more and 4.0 m 2 / g or less. When the specific surface area is set to 0.7 m 2 / g or more, the reaction sites where lithium ions can enter and exit increase, and the overvoltage at the end of discharge decreases, thereby increasing the discharge capacity. In addition, the upper limit of the specific surface area can be 0.8 m 2 / g or more, or can be 0.9 m 2 / g or more. Even when the positive electrode active material of the present embodiment has a large specific surface area, by combining a specific titanium distribution and a specific microcrystal diameter, high thermal stability and high battery capacity can be achieved.

[0092] The details will be described in the washing process described later. By washing and drying the particles of the lithium nickel manganese composite oxide obtained by firing, the remaining lithium components on the particle surface and grain boundaries are dissolved out, forming voids and irregularities, thereby increasing the specific surface area. In addition, in addition to this, for example, in the pulverization process of the fired product (aggregate) after the firing process, by sufficiently dissociating sintering and aggregation, the specific surface area is adjusted to the above range, thereby improving durability and obtaining a higher discharge capacity.

[0093] On the other hand, in the positive electrode active material with a high nickel ratio, if the specific surface area exceeds 4.0 m 2 / g, even when the eluted alkali component on the surface is removed once in the water washing step (S30), the alkali component derived from lithium eluted from the particle surface due to reaction with moisture in the air increases, and when the positive electrode active material is pasted, the paste sometimes gels and it becomes difficult to produce a plate electrode.

[0094] [Deviation index: [(D90 - D10) / Mv]]

[0095] The deviation index [(D90 - D10) / Mv] representing the particle size calculated from D90 and D10 (the particle size at 90% and 10% in terms of volume accumulation of the particle amount in the particle size distribution curve) and the volume average particle size (Mv) in the particle size distribution of the positive electrode active material of the present embodiment is preferably 0.80 or more and 1.20 or less.

[0096] When the particle size distribution of the positive electrode active material has a wide range, there are a large number of fine particles with a particle size smaller than the average particle size and coarse particles with a particle size larger than the average particle size. If these fine particles and coarse particles are mixed, the packing density becomes high and the energy density per unit volume can be increased. Therefore, when the deviation index of the particle size is less than 0.80, the volume energy density sometimes decreases. If the manufacturing method described later is used, the upper limit is 1.20. If the firing temperature described later exceeds 950 °C, the deviation index of the particle size sometimes exceeds 1.20, but when forming the positive electrode active material, the specific surface area decreases, the resistance of the positive electrode increases, and the battery capacity sometimes decreases.

[0097] [Volume average particle size (Mv)]

[0098] The volume average particle size (Mv) of the positive electrode active material of one embodiment of the present invention is preferably 8 μm or more and 20 μm or less, more preferably 10 μm or more and 20 μm or less. When the volume average particle size (Mv) is in the above range, when the positive electrode active material is used for the positive electrode of a secondary battery, high output characteristics, battery capacity, and high fillability of the positive electrode can be balanced. If the average particle size of the secondary particles is less than 8 μm, high fillability of the positive electrode may not be obtained, and if the average particle size exceeds 20 μm, high output characteristics and battery capacity may not be obtained. It should be noted that the average particle size can be obtained, for example, from the volume accumulation value measured by a laser diffraction scattering type particle size distribution meter.

[0099] [Amount of eluted lithium]

[0100] In the positive electrode active material of the present embodiment, the amount of lithium dissolved in water when the positive electrode active material is immersed in water, that is, the dissolved lithium amount, is preferably 0.20% by mass or less, may be 0.17% by mass or less, or may be 0.15% by mass or less, relative to the entire positive electrode active material. By removing lithium by stirring with water, the amount of dissolved lithium is reduced. In the case of being in the above range, gelation during paste preparation is not likely to occur, and defects caused by gelation during the production of battery plates can be reduced. It should be noted that there is no particular limitation on the lower limit of the dissolved lithium amount. In the positive electrode active material obtained by the manufacturing method described later, the lower limit of the dissolved lithium amount is, for example, 0.01% by mass or more, may be 0.05% by mass or more, or may be 0.08% by mass or more.

[0101] 2. Manufacturing method of positive electrode active material for lithium ion secondary battery

[0102] Next, a manufacturing method of a positive electrode active material for a lithium ion secondary battery (hereinafter also referred to as "positive electrode active material") according to an embodiment of the present invention will be described with reference to the accompanying drawings. It should be noted that the following description is an example of the manufacturing method and does not limit the manufacturing method.

[0103] Figure 4 、 Figure 5 (A) and (B) are schematic process diagrams showing an example of the manufacturing method of the positive electrode active material of the present embodiment. As Figure 4 shown, the manufacturing method of the positive electrode active material includes: a mixing step (S10) of obtaining a mixture by mixing at least a nickel-manganese composite compound, a titanium compound, and a lithium compound, a firing step (S20), a water washing step (S30), and a drying step (S40). In addition, for example, as Figure 5 (A) and (B) shown, the nickel-manganese composite compound used in the mixing step (S10) can be obtained by a method including a crystallization step (S1) and / or a heat treatment step (S2).

[0104] The positive electrode active material obtained by the manufacturing method of the present embodiment has a high nickel ratio, contains a specific amount of manganese and titanium, can obtain a high capacity by dissolving titanium without precipitating an impurity phase, and can improve short-circuit resistance and thermal stability by containing manganese and titanium. Furthermore, as described later, by including the water washing step (S30), the disorder of the atomic arrangement of the lithium nickel manganese composite oxide is alleviated, and the specific surface area is increased due to the dissolution of the residual lithium present on the particle surface and grain boundaries, thereby enabling a higher battery capacity to be obtained. Hereinafter, each step will be described in detail.

[0105] [Crystallization step (S1)]

[0106] As Figure 5As shown in (A), the crystallization step (S1) is a step of obtaining a nickel-manganese composite hydroxide (nickel-manganese composite compound) by crystallization.

[0107] Preferably, the nickel-manganese composite hydroxide (hereinafter sometimes referred to as "composite hydroxide") obtained in the crystallization step (S1) contains nickel (Ni), manganese (Mn), and element M (M), and the element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al. The molar ratio of the amounts of the respective elements is represented by Ni:Mn:M = 1 - x - y:x:y (where 0.03 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15). In addition, the content (composition) of each element (Ni, Mn, M) in the nickel-manganese composite hydroxide is almost maintained in the lithium nickel-manganese composite oxide. Therefore, the content of each element (Ni, Mn, M) is preferably in the same range as the content in the finally obtained lithium nickel-manganese composite oxide.

[0108] The crystallization step (S1) can be carried out by a known method as long as a composite hydroxide having the above molar ratio can be obtained. For example, in a reaction tank, while stirring a mixed aqueous solution containing at least nickel and manganese at a constant speed, a neutralizing agent is added for neutralization, thereby controlling the pH, and a nickel-manganese composite hydroxide is formed by coprecipitation.

[0109] The mixed aqueous solution containing nickel and manganese can be, for example, a sulfate solution, a nitrate solution, or a chloride solution of nickel and manganese. In addition, as described later, the mixed aqueous solution may also contain element M. The composition of each element contained in the mixed aqueous solution is substantially the same as the composition of each element contained in the obtained composite hydroxide. Therefore, the composition of each element of the mixed aqueous solution can be prepared in the same manner as the composition of each element of the target composite hydroxide. As the neutralizing agent, an aqueous alkali solution can be used. For example, sodium hydroxide, potassium hydroxide, etc. can be used.

[0110] In addition, it is preferable to add a complexing agent to the mixed aqueous solution together with the neutralizing agent. The complexing agent is not particularly limited as long as it can bind to nickel ions and other metal ions in the aqueous solution (hereinafter referred to as "reaction aqueous solution") in the reaction tank to form a complex, and known substances can be used. For example, an ammonium ion donor can be used. The ammonium ion donor is not particularly limited. For example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc. can be used. By adding the complexing agent, the solubility of metal ions in the reaction aqueous solution can be adjusted.

[0111] In the crystallization step (S1), without using a complexing agent, regarding the temperature of the reaction aqueous solution, it is preferable to set the temperature (liquid temperature) in the range of exceeding 60°C and 80°C or lower, and the pH of the reaction aqueous solution at the above temperature is preferably 10 or higher and 12 or lower (25°C reference). When the pH of the reaction aqueous solution exceeds 12, the obtained composite hydroxide becomes fine particles, and the filterability also deteriorates, and sometimes spherical particles cannot be obtained. On the other hand, when the pH of the reaction aqueous solution is less than 10, the formation rate of the composite hydroxide significantly slows down, Ni remains in the filtrate, and the precipitation amount of Ni deviates from the target composition, and sometimes a composite hydroxide with a target ratio cannot be obtained.

[0112] In addition, when the temperature of the reaction aqueous solution exceeds 60°C, the solubility of Ni increases, and it is possible to avoid the phenomenon that the precipitation amount of Ni deviates from the target composition and coprecipitation does not occur. On the other hand, if the temperature of the reaction aqueous solution exceeds 80°C, the evaporation amount of water is large, so the slurry concentration (reaction aqueous solution concentration) becomes high, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration increases, etc., and there is a possibility that the charge-discharge capacity of the positive electrode active material decreases.

[0113] In the crystallization step, when using an ammonium ion donor (complexing agent), since the solubility of Ni in the reaction aqueous solution increases, the temperature of the reaction aqueous solution is preferably 30°C or higher and 60°C or lower, and the pH of the reaction aqueous solution is preferably 10 or higher and 13 or lower (25°C reference), more preferably 12 or higher and 13 or lower.

[0114] In addition, the ammonia concentration in the reaction aqueous solution is preferably maintained at a constant value in the range of 3 g / L or higher and 25 g / L or lower. When the ammonia concentration is lower than 3 g / L, the solubility of metal ions cannot be kept constant, so sometimes primary particles of a composite hydroxide with a regular shape and particle size cannot be formed. In addition, since a gel-like nucleus is easily formed, the particle size distribution of the obtained composite hydroxide also tends to widen. On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of metal ions becomes too large, the amount of metal ions remaining in the reaction aqueous solution increases, and deviations in the composition of the obtained composite hydroxide are likely to occur. It should be noted that if the ammonia concentration changes, the solubility of metal ions changes, and uniform hydroxide particles cannot be formed, so it is preferably kept constant. For example, the ammonia concentration is preferably maintained at a desired concentration by setting the amplitude of the upper and lower limits to about 5 g / L.

[0115] In addition, as shown by the following formula, the nickel-manganese composite hydroxide may contain element M, which is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al. As a method for incorporating element M into the composite hydroxide, there is no particular limitation, and known methods can be used. For example, from the viewpoint of improving productivity, it is preferable to add an aqueous solution containing element M to a mixed aqueous solution containing nickel and manganese to coprecipitate the composite hydroxide containing element M.

[0116] As the aqueous solution containing element M, for example, an aqueous solution containing cobalt sulfate, vanadyl chloride, vanadyl sulfate, magnesium sulfate, magnesium chloride, molybdenum chloride, calcium chloride, chromium chloride, sodium tantalate, sodium hydroxide, sodium tungstate, tungsten oxide, iron sulfate, zinc chloride, zinc sulfate, boric acid, ammonium borate, silicon bromide, phosphoric acid, zirconium sulfate, zirconium nitrate, niobium hydroxide, niobium pentachloride, niobic acid, aluminum sulfate, sodium aluminate, etc. can be used.

[0117] In addition, from the viewpoint of optimizing the crystallization conditions and facilitating the control of the composition ratio, a step of coating element M on the obtained composite hydroxide can be provided after obtaining the particles of the composite hydroxide by crystallization. The method for coating element M is not particularly limited, and known methods can be used.

[0118] Hereinafter, an example of the method for coating element M will be described. First, the nickel-manganese composite hydroxide obtained by crystallization is dispersed in pure water to prepare a slurry. Then, a solution containing element M corresponding to the target coating amount is mixed into the slurry, and an acid or a base is added dropwise to adjust the pH to a specified value. As the acid, for example, sulfuric acid, hydrochloric acid, nitric acid, etc. can be used. As the base, for example, sodium hydroxide, potassium hydroxide, etc. can be used. Then, after mixing the slurry for a specified time, the slurry is filtered and dried to obtain a nickel-manganese composite hydroxide coated with element M. It should be noted that as other coating methods, there are a spray drying method in which a solution containing a compound containing element M is sprayed onto the nickel-manganese composite hydroxide and then dried, a method in which a solution containing a compound containing element M is impregnated into the nickel-manganese composite hydroxide, etc.

[0119] It should be noted that the method of incorporating element M into the nickel-manganese composite hydroxide may include mixing element M in the above mixed aqueous solution and / or coating element M on the composite hydroxide. For example, 1) element M can be coated on the nickel-manganese composite hydroxide obtained by crystallizing a mixed aqueous solution containing nickel and manganese (excluding element M therein) by adding an aqueous alkali solution, or 2) a mixed aqueous solution containing nickel, manganese, and a part of element M can be prepared, and nickel-manganese composite hydroxide (containing element M) can be co-precipitated, and then element M can be coated on the co-precipitate to adjust the content of M.

[0120] It should be noted that the crystallization step (S1) can use 1) a production method based on batch crystallization (batch crystallization method) or 2) a production method based on continuous crystallization (continuous crystallization method). For example, in the case of the batch crystallization method, the precipitate can be collected after the reaction aqueous solution in the reaction tank reaches a stable state, and then filtered and washed with water to obtain the composite hydroxide. In addition, in the case of the continuous crystallization method, the mixed aqueous solution, the aqueous alkali solution, and optionally the aqueous solution containing an ammonium ion donor can be continuously supplied, and the precipitate can be collected by overflowing from the reaction tank, and then filtered and washed with water to obtain the composite hydroxide.

[0121] In the method for manufacturing the positive electrode active material of the present embodiment, from the viewpoint of obtaining a positive electrode active material that exhibits a high volumetric energy density when used in a secondary battery, it is preferable to use the continuous crystallization method. In the production based on continuous crystallization, it is possible to easily obtain a positive electrode active material with a high deviation index, a wide particle size distribution width, and high packing properties. In addition, the continuous crystallization method has a higher productivity than the batch crystallization method and is suitable for industrial-scale production.

[0122] [Heat treatment step (S2)]

[0123] As Figure 5 shown in (B), for the composite hydroxide obtained by the crystallization step (S1), the crystallization step (S1) may further include a heat treatment step (S2). The heat treatment step (S2) is a step of removing at least a part of the water contained in the composite hydroxide by heat treatment. By having the heat treatment step (S2), at least a part of the remaining water in the composite hydroxide is removed, thereby preventing the deviation of Li / Me of the positive electrode active material obtained in the subsequent firing step (S20).

[0124] From the viewpoint of further reducing the deviation of Li / Me, the heat treatment in the heat treatment step (S2) preferably fully oxidizes the composite hydroxide and converts it into composite oxide particles. It should be noted that as long as the moisture can be removed to the extent that the Li / Me of the positive electrode active material does not deviate, it is not necessarily required to convert all the hydroxides (composite hydroxides) in the composite hydroxide into composite oxides. That is, by heat-treating the composite hydroxide, a nickel-manganese composite compound containing at least one of nickel-manganese composite hydroxide and nickel-manganese composite oxide can be obtained.

[0125] In addition, when performing the heat treatment step (S2), as Figure 5 (B) shows, the nickel-manganese composite compound obtained by the heat treatment step (S2) can be used in the mixing step (S10). In addition, when the composite hydroxide contains element M, the heat treatment step (S2) can be performed after coating the composite hydroxide with a compound containing element M, or the compound containing element M can be coated on the particles of the composite hydroxide and / or composite oxide after the heat treatment step (S2).

[0126] The heat treatment in the heat treatment step (S2) only needs to be heated to a temperature at which the residual moisture in the composite hydroxide can be removed. For example, the heat treatment temperature is preferably set to 105 °C or higher and 700 °C or lower. When the composite hydroxide is heated at 105 °C or higher, at least a part of the residual moisture can be removed. It should be noted that when the heat treatment temperature is lower than 105 °C, a long time is required to remove the residual moisture, so it is not suitable industrially. On the other hand, when the heat treatment temperature exceeds 700 °C, the particles converted into composite oxide particles sometimes sinter and aggregate. For example, when most of the composite hydroxide is converted into composite oxide particles, the heat treatment temperature is preferably set to 350 °C or higher and 700 °C or lower.

[0127] The atmosphere for heat treatment is not particularly limited. For example, from the viewpoint of easy operation, it is preferably performed in an air stream. In addition, the heat treatment time is not particularly limited. For example, it can be set to 1 hour or more. When the heat treatment time is less than 1 hour, the residual moisture in the composite hydroxide may not be sufficiently removed. In addition, the heat treatment time is preferably 5 hours or more and 15 hours or less. In addition, the equipment used for heat treatment is not particularly limited as long as it can heat the composite hydroxide in an air stream. For example, a blast dryer, an electric furnace that does not generate gas, etc. can be suitably used.

[0128] It should be noted that Figure 5(B), the nickel-manganese composite hydroxide after the crystallization step (S1) is heat-treated, but the nickel-manganese composite hydroxide obtained in a step other than the crystallization step (S1) can also be heat-treated and used in the mixing step (S10) as the nickel-manganese composite compound. In this case, by removing at least a part of the moisture in the nickel-manganese composite hydroxide, the above-mentioned effect can also be obtained.

[0129] [Mixing step (S10)]

[0130] The nickel-manganese composite compound used in the mixing step (S10) contains nickel (Ni), manganese (Mn), and an optional element M (M) as metal elements. The above-mentioned element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al. The molar ratio of these metal elements is represented by Ni:Mn:M = 1 - x - y:x:y (where 0.03 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15).

[0131] The content (composition) of each element (Ni, Mn, M) in the nickel-manganese composite compound is also almost maintained in the lithium nickel manganese composite oxide particles. Therefore, the content of each element (Ni, Mn, element M) is preferably in the same range as that in the above-mentioned lithium nickel manganese composite oxide. It should be noted that the nickel-manganese composite compound used in this embodiment may contain elements other than the above-mentioned elements (Ni, Mn, element M), hydrogen, and oxygen in a small amount within a range that does not hinder the effects of the present invention.

[0132] By containing manganese in the nickel-manganese composite compound within the above range, manganese can be uniformly distributed within a plurality of primary particles of the obtained positive electrode active material. The positive electrode active material containing (solid-solved) manganese and titanium in a plurality of primary particles has high thermal stability, an increased volume resistivity, and improved short-circuit resistance.

[0133] In addition, by containing manganese in the primary particles, the lithium titanium mixture can be fired at a higher temperature. Moreover, by firing at a higher temperature, titanium in the titanium compound can be more uniformly solid-solved in the primary particles.

[0134] The manufacturing method of the nickel-manganese composite compound is not particularly limited. As shown in Figure 5 (A) and Figure 5 (B), it is preferable to use the composite hydroxide and / or composite oxide obtained through the crystallization step (S1) and / or the heat treatment step (S2), and more preferably to use the nickel-manganese composite hydroxide obtained through the crystallization step (S1). Thereby, in the subsequent firing step (S20), it is possible to easily obtain a lithium nickel manganese composite oxide in which titanium is solid-solved in the primary particles.

[0135] In addition, the nickel-manganese composite compound preferably contains nickel and manganese uniformly within the particles. For example, when using a mixture of nickel hydroxide particles and a manganese compound, nickel hydroxide particles coated with a manganese compound, etc. as raw materials, the distribution of manganese in the obtained positive electrode active material sometimes becomes uneven, and the effects obtained by containing manganese cannot be fully achieved.

[0136] (titanium compound)

[0137] As the titanium compound used in the mixing step (S10), known compounds containing titanium can be used. For example, titanium oxide, titanium sulfate, titanium tetrabromide, titanium tetrachloride, titanium silicide, etc. can be used. It should be noted that one type of titanium compound can be used, or two or more types can be used.

[0138] Among them, from the viewpoints of ease of acquisition and avoiding impurity mixing into the lithium nickel manganese composite oxide, titanium oxide is preferred. It should be noted that when impurities are mixed into the lithium nickel manganese composite oxide, the thermal stability, battery capacity, and cycle characteristics of the obtained secondary battery sometimes decrease.

[0139] The titanium compound is preferably mixed in particles (solid phase). When adding titanium in the solid phase, the reactivity in the subsequent firing step (S20) changes according to the particle size of the titanium compound. Therefore, the particle size of the titanium compound used becomes one of the important factors.

[0140] The average particle size of the titanium compound is preferably 0.01 μm or more and 5 μm or less, more preferably 0.05 μm or more and 3 μm or less, and further preferably 0.08 μm or more and 3 μm or less. When the average particle size is less than 0.01 μm, problems such as very difficult powder handling and scattering of the titanium compound in the mixing step (S10) and the firing step (S20) may occur, resulting in the inability to add the target composition to the active material. On the other hand, when the average particle size is greater than 5 μm, the titanium may be unevenly distributed in the fired lithium nickel manganese composite oxide, resulting in a decrease in battery capacity. It should be noted that the average particle size is the volume average particle size Mv, and can be obtained from the volume cumulative value measured by a laser diffraction scattering particle size distribution analyzer, for example.

[0141] The titanium compound can be pre-crushed using various crushers such as a ball mill, a planetary ball mill, a jet mill / nano jet mill, a bead mill, a needle mill, etc. to have a particle size within the above range. In addition, the titanium compound can also be classified by a dry classifier or sieving as needed. For example, particles close to 1 μm can be obtained using a dry classifier.

[0142] (lithium compound)

[0143] The lithium compound is not particularly limited, and known compounds containing lithium can be used. For example, lithium carbonate, lithium hydroxide, lithium nitrate, or a mixture thereof can be used. Among them, from the viewpoint of less influence of residual impurities and dissolution at the firing temperature, lithium carbonate, lithium hydroxide, or a mixture thereof is preferred.

[0144] (Mixing method)

[0145] The mixing method of the nickel-manganese composite compound, the lithium compound, and the titanium compound is not particularly limited, as long as the composite hydroxide, the lithium compound, and the titanium compound are sufficiently mixed to the extent that the skeleton such as the composite hydroxide is not damaged. As the mixing method, for example, a general mixer can be used for mixing, such as a vibration mixer, a Loedige mixer, a Julia mixer, a V-type blender, etc. It should be noted that the lithium-titanium mixture is preferably pre-mixed sufficiently before the firing process described below. In the case of insufficient mixing, the ratio of the amount of substance of Li to the element Me other than Li (i.e., Ni + Mn + element M + Ti) (Li / Me, corresponding to a in the amount-of-substance ratio described below, atomic% ratio) deviates between the respective particles of the positive electrode active material, and problems such as insufficient battery characteristics may occur.

[0146] The lithium compound is mixed in such a way that Li / Me in the lithium-titanium mixture is 0.97 or more and 1.25 or less. That is, it is mixed in such a way that Li / Me in the lithium-titanium mixture is the same as Li / Me in the obtained positive electrode active material. This is because the Li / Me and the molar ratio of each metal element do not change before and after the firing process (S20) described below, so Li / Me of the lithium-titanium mixture during the above mixing becomes Li / Me of the positive electrode active material. In addition, for example, by adjusting the value of Li / Me in the mixture, the microcrystalline diameter of the lithium nickel manganese composite oxide obtained after firing can be adjusted.

[0147] The titanium compound is mixed in such a way that the ratio of the amount of substance of titanium (Ti) in the lithium-titanium mixture to the total amount of metal elements (Ni, Mn, element M, Ti) other than Li in the lithium-titanium mixture (Ti / Me) is 0.01 or more and 0.05 or less.

[0148] [Firing process (S20)]

[0149] The firing process (S20) is a process of firing the above-mentioned lithium-titanium mixture obtained in the mixing process (S10) in an oxidation atmosphere with an oxygen concentration of 80% by volume or more and 100% by volume or less at a temperature of 700°C or more and 950°C or less to obtain a lithium nickel manganese composite oxide.

[0150] When firing a lithium-titanium mixture, lithium in the lithium compound diffuses into the particles of the nickel-manganese composite compound, and thus particles (secondary particles) of a lithium nickel manganese composite oxide composed of particles having a polycrystalline structure are formed. The lithium compound melts at the firing temperature and penetrates into the particles of the nickel-manganese composite compound to form a lithium nickel manganese composite oxide. At this time, the titanium compound penetrates into the interior of the secondary particles together with the molten lithium compound. In addition, if there are grain boundaries or the like in the primary particles, penetration also occurs. By the penetration of the lithium compound and the titanium compound, diffusion inside the primary particles is promoted, and titanium is uniformly solid-solved inside the primary particles. The inventors of the present invention conducted research and found that, for example, by controlling the oxygen concentration and the firing temperature in the firing atmosphere, titanium can be uniformly solid-solved inside the primary particles, and precipitation of a titanium compound phase and segregation to the interface between the primary particles can be suppressed.

[0151] The firing atmosphere has an oxygen concentration of 80% by volume or more and 100% by volume or less, preferably 90% by volume or more and 100% by volume or less. In a lithium nickel manganese composite oxide with a high nickel ratio, so-called cation mixing in which transition metal elements such as Ni are arranged at the Li site in the layered compound easily occurs. In addition, the crystallinity of the layered compound is likely to decrease, and the atomic distribution is likely to be disordered. Due to these structural disorders, it is possible that titanium cannot be solid-solved in the Me site (transition metal site), and impurities such as a titanium compound phase (heterogeneous phase) precipitate, resulting in a decrease in battery capacity. On the other hand, when firing is performed within the above oxygen concentration range, the phase transition of the lithium nickel manganese composite oxide to a layered compound is promoted, and titanium is easily solid-solved in the transition metal site in the layered compound. Therefore, even within the above titanium content range, titanium can be uniformly solid-solved into the primary particles without precipitating an impurity phase. Thus, a positive electrode active material can be obtained that maintains high thermal stability while increasing battery capacity, reducing volume resistivity, and achieving both battery characteristics and short-circuit resistance and thermal stability.

[0152] The firing temperature is 700°C or higher and 950°C or lower in an oxidizing atmosphere, preferably 700°C or higher and 900°C or lower, and may also be 750°C or higher and 850°C or lower. When firing is performed at the above temperature, melting of the lithium compound occurs, and the penetration and diffusion of titanium are promoted. In addition, the lithium-titanium mixture can increase the firing temperature by containing manganese. By increasing the firing temperature, the diffusion of titanium is promoted, and titanium is easily solid-solved in the particles of the lithium nickel manganese composite oxide, and high thermal stability and high battery capacity can be achieved. In addition, in the subsequent water washing and drying steps (S30, S40), considering the part where the microcrystalline diameter of the (003) plane increases, by appropriately adjusting the firing temperature within the above range, the microcrystalline diameter of the finally obtained lithium nickel manganese composite oxide can be adjusted.

[0153] On the other hand, when the firing temperature is lower than 700 °C, the diffusion of lithium and titanium into the composite hydroxide cannot proceed sufficiently, and the remaining lithium and unreacted particles remain, or the crystal structure cannot become sufficiently regular, resulting in the problem that sufficient battery characteristics cannot be obtained. In addition, the solid solution of titanium into the primary particles becomes insufficient, and sometimes sufficient short-circuit resistance and thermal stability cannot be obtained. Furthermore, if the firing temperature exceeds 950 °C, sintering may occur violently between the particles of the formed lithium nickel manganese composite oxide, and abnormal grain growth may occur. If abnormal grain growth occurs, the fired particles become coarse, and the filling property decreases when forming the positive electrode active material. In addition, problems such as an increase in reaction resistance and a decrease in discharge capacity due to the disorder of the crystal structure also occur.

[0154] The firing time is preferably set to at least 3 hours or more, more preferably 6 hours or more and 24 hours or less. When the firing time is less than 3 hours, the formation of the lithium nickel manganese composite oxide may not proceed sufficiently. In addition, the furnace used for firing is not particularly limited, as long as it is a furnace capable of firing the lithium titanium mixture in an oxygen stream, but an electric furnace that does not generate gas is preferably used, and both batch-type and continuous-type furnaces can be used.

[0155] [Pre-firing]

[0156] The firing process may further include a pre-firing process at a temperature lower than the firing temperature before firing at a temperature of 700 °C or higher and 950 °C or lower. The pre-firing is preferably carried out at a temperature at which the lithium compound in the lithium titanium mixture melts and can react with the composite hydroxide. The pre-firing temperature can be set, for example, to 350 °C or higher and a temperature lower than the firing temperature. In addition, the lower limit of the pre-firing temperature is preferably 400 °C or higher. By holding (pre-firing) the lithium titanium mixture within the above temperature range, the lithium compound and / or titanium compound can penetrate into the particles of the nickel manganese composite compound, and the diffusion of lithium and titanium can proceed sufficiently to obtain a uniform lithium nickel manganese composite oxide. For example, when using lithium hydroxide as the lithium compound, the pre-firing is preferably carried out by holding at a temperature of 400 °C or higher and 550 °C or lower for 1 hour or more and about 10 hours.

[0157] [Crushing]

[0158] Although the sintering between particles of the lithium nickel manganese composite oxide obtained after the firing process (S20) is suppressed, sometimes coarse particles are formed due to weak sintering and aggregation. In such a case, the above sintering and aggregation can be eliminated by crushing to adjust the particle size distribution. The method of crushing is not particularly limited, and by sufficiently dissociating the above sintering and aggregation by crushing, the specific surface area of the lithium nickel manganese composite oxide can be increased.

[0159] [Washing process (S30)]

[0160] The water washing step (S30) is a step of mixing the lithium nickel manganese composite oxide obtained in the firing step (S20) with water, stirring (hereinafter referred to as "water stirring"), and then performing solid-liquid separation.

[0161] By including the water washing step (S30) and the drying step (S40) described later, the manufacturing method of the present embodiment alleviates the disorder of the atomic arrangement of the positive electrode active material and improves the crystallinity. Furthermore, the residual lithium present on the particle surface and grain boundary of the lithium nickel manganese composite oxide dissolves into water, thereby increasing the specific surface area. Although the detailed situation is unknown, it is considered that through these effects, the overvoltage during discharge is reduced, thereby increasing the discharge capacity.

[0162] It should be noted that as described above, when the positive electrode active material does not contain titanium, in addition to the non-improvement of crystallinity, although the specific surface area increases, the reaction resistance increases. Therefore, even if water washing is performed, the discharge capacity does not increase. Regarding the reason, although the detailed situation is unknown, in the positive electrode active material of the present embodiment, titanium solid-dissolved inside the primary particles may have the effect of suppressing the deterioration of the particle surface and grain boundary caused by the dissolution of lithium. In addition, through the water washing step (S30), the residual lithium component on the surface dissolves in water and is removed, thereby enabling the suppression of the gelation of the positive electrode mixture paste when manufacturing the electrode plate of the secondary battery.

[0163] The amount of water mixed in the water washing step (S30) is preferably 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the lithium nickel manganese composite oxide. When the mixing ratio of water is 200 parts by mass or more, excessive lithium is removed from the positive electrode active material, which may cause a decrease in battery capacity and an increase in reaction resistance. On the other hand, when the mixing ratio of water is less than 50 parts by mass, the effect of improving crystallinity and the removal of the residual lithium component become insufficient, which may cause a decrease in battery capacity and the gelation of the positive electrode mixture paste.

[0164] The time for water washing is not particularly limited. For example, it is about 1 minute or more and 2 hours or less, and it can also be 5 minutes or more and 50 minutes or less.

[0165] After the lithium nickel manganese composite oxide is subjected to water stirring, solid-liquid separation is performed to obtain the lithium nickel manganese composite oxide (precipitate). The method of solid-liquid separation is not particularly limited, and a known method can be used. For example, one or more selected from suction filters (Buchner funnels) and other suction filters, filter presses, centrifuges, etc. can be used for solid-liquid separation.

[0166] [Drying step (S40)]

[0167] The drying step (S40) is a step of drying the lithium nickel manganese composite oxide (precipitate) obtained through the above water washing step (S30) to obtain a powder of the lithium metal composite oxide (dry powder).

[0168] The drying conditions are preferably heat-treated at a temperature of 100 °C or higher and 250 °C or lower in an oxidizing atmosphere or a vacuum atmosphere. When the drying temperature is 100 °C or higher, the moisture in the precipitate can be sufficiently evaporated. In addition, when the drying temperature is 250 °C or lower, a compact drying device can be used, which is suitable for industrial-scale implementation.

[0169] Regarding the atmosphere during drying, in order to avoid the reaction of moisture and carbonic acid in the atmosphere with the obtained positive electrode active material, an atmosphere free of water vapor and carbon dioxide is preferred. Specifically, an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is preferred. In addition, from the viewpoint of being able to quickly discharge the water vapor generated by drying, it is preferable to attach an exhaust mechanism to the drying device.

[0170] The drying time is not particularly limited. In order to sufficiently evaporate the moisture in the raw material mixture, it is preferably set to 0.5 hours or more at the maximum temperature reached during drying. In addition, from the viewpoint of productivity, the upper limit of the drying time is preferably set to 48 hours or less.

[0171] [Positive electrode active material]

[0172] According to the positive electrode active material obtained by the manufacturing method of this embodiment, when used as the positive electrode of a lithium ion secondary battery, high battery characteristics and high thermal stability can be achieved at a high level. In addition, the manufacturing method of this embodiment can easily manufacture such a positive electrode active material in industrial-scale production, and it can be said that the industrial value is extremely high.

[0173] In addition, the crystallite diameter of the (003) plane of the lithium nickel manganese composite oxide (positive electrode active material) obtained after the drying process (S40) increases compared to the crystallite diameter of the (003) plane of the lithium nickel manganese composite oxide obtained after the firing process (S20) and before the water washing process (S30). The crystallite diameter of the (003) plane of the obtained positive electrode active material can increase by, for example, 15 nm or more, or 20 nm or more compared to before the water washing process (S30). When the crystallite diameter of the (003) plane increases after the water washing process (S30), the battery capacity when the obtained positive electrode active material is used in a secondary battery can be improved. The detailed reason is not yet clear, but it is considered that, for example, when lithium in the lithium nickel manganese composite oxide is removed through the water washing process (S30), the disorder of the atomic arrangement is alleviated, so that the diffraction peak measured by XRD becomes sharp and the crystallite diameter increases apparently. In addition, the increase in the crystallite diameter of the (003) plane is particularly significant in the lithium nickel manganese composite oxide containing a specific amount of titanium.

[0174] 3. Lithium ion secondary battery

[0175] The lithium ion secondary battery of the present embodiment (hereinafter also referred to as "secondary battery") includes a positive electrode, a negative electrode, and a non-aqueous electrolyte containing the above positive electrode active material. The secondary battery includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. In addition, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. In addition, the secondary battery only needs to be a secondary battery that performs charge and discharge through the insertion and extraction of lithium ions. For example, it may be a non-aqueous electrolyte secondary battery or an all-solid-state lithium secondary battery. It should be noted that the embodiments described below are merely examples, and the lithium ion secondary battery may be represented by the following embodiments and implemented in various modified and improved ways based on the knowledge of those skilled in the art. In addition, the use of the secondary battery is not particularly limited.

[0176] [Positive Electrode]

[0177] Using the above positive electrode active material, a positive electrode of a secondary battery is fabricated. Hereinafter, an example of the manufacturing method of the positive electrode will be described.

[0178] First, the above positive electrode active material (powder form), a conductive material, and a binder (adhesive) are mixed, and then a solvent for purposes such as adding activated carbon and viscosity adjustment is added as needed, and they are kneaded to produce a positive electrode mixture paste.

[0179] The mixing ratio of each material in the positive electrode mixture becomes a factor determining the performance of the lithium ion secondary battery, so it can be adjusted according to the use. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium secondary battery. For example, when the total mass of the solid components of the positive electrode mixture excluding the solvent is set to 100% by mass, it may contain 60 to 95% by mass of the positive electrode active material, 1 to 20% by mass of the conductive material, and 1 to 20% by mass of the binder.

[0180] The obtained positive electrode mixture paste is coated on the surface of a current collector made of, for example, aluminum foil, and dried to disperse the solvent, thereby producing a sheet-like positive electrode. If necessary, in order to increase the electrode density, it is sometimes pressed by a roll press or the like. The sheet-like positive electrode thus obtained can be cut into an appropriate size according to the target battery and used for battery production. However, the manufacturing method of the positive electrode is not limited to the method exemplified above, and other methods may also be used.

[0181] As the conductive material, for example, carbon black-based materials such as graphite (natural graphite, artificial graphite, and expanded graphite), acetylene black, and Ketjen black can be used.

[0182] As the binder (adhesive), which plays the role of connecting the active material particles, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, and polyacrylic acid can be used.

[0183] As needed, the positive electrode active material, conductive material, and activated carbon are dispersed, and a solvent in which a binder is dissolved is added to the positive electrode mixture. Specifically, as the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, in order to increase the electric double layer capacitance, activated carbon can be added to the positive electrode mixture.

[0184] [Negative electrode]

[0185] As the negative electrode, metallic lithium, a lithium alloy, etc. can be used. In addition, as the negative electrode, a negative electrode formed as follows can also be used, that is, a negative electrode mixture made by mixing a binder in a negative electrode active material capable of occluding / delithiating lithium ions and adding an appropriate solvent to make it into a paste is coated on the surface of a metal foil current collector such as copper, dried, and compressed as needed to increase the electrode density, thereby forming.

[0186] As the negative electrode active material, for example, natural graphite, artificial graphite, fired bodies of organic compounds such as phenolic resin, and powdery substances of carbon materials such as coke can be used. In this case, as the negative electrode binder, similar to the positive electrode, a fluororesin such as PVDF can be used, and as the solvent for dispersing these active materials and the binder, an organic solvent such as N-methyl-2-pyrrolidone can be used.

[0187] [Separator]

[0188] It is disposed with a separator sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and a known separator can be used. For example, a thin film such as polyethylene or polypropylene and a film having a plurality of micropores can be used.

[0189] [Non-aqueous electrolyte]

[0190] As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

[0191] The non-aqueous electrolyte solution is made by dissolving a lithium salt as a supporting salt in an organic solvent. In addition, as the non-aqueous electrolyte solution, an electrolyte solution in which a lithium salt is dissolved in an ionic liquid can also be used. It should be noted that an ionic liquid refers to a salt composed of a cation and an anion other than a lithium ion and being in a liquid state at room temperature.

[0192] As the organic solvent, one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and propyl trifluorocarbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, further ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. can be used alone, or two or more of them can be mixed and used.

[0193] As the supporting salt, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts, etc. can be used. Furthermore, the non-aqueous electrolyte can contain radical scavengers, surfactants, flame retardants, etc.

[0194] In addition, as the non-aqueous electrolyte, a solid electrolyte can be used. The solid electrolyte has the property of being able to withstand high voltages. As the solid electrolyte, inorganic solid electrolytes and organic solid electrolytes can be cited.

[0195] As the inorganic solid electrolyte, oxide-based solid electrolytes, sulfide-based solid electrolytes, etc. can be cited.

[0196] As the oxide-based solid electrolyte, there is no particular limitation, and substances containing oxygen (O) and having lithium ion conductivity and electron insulation can be suitably used. As the oxide-based solid electrolyte, for example, those selected from lithium phosphate (Li3PO4), Li3PO4N X , LiBO2N X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3 (0 ≤ X ≤ 1), Li 1+X Al X Ge 2-X (PO4)3 (0 ≤ X ≤ 1), LiTi2(PO4)3, Li 3x La 2 / 3-X TiO3 (0 ≤ X ≤ 2 / 3), Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, etc. can be cited.

[0197] As the sulfide-based solid electrolyte, there is no particular limitation, and a substance containing sulfur (S) and having lithium ion conductivity and electron insulation can be suitably used. As the sulfide-based solid electrolyte, for example, one or more selected from Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, etc. can be used.

[0198] It should be noted that as the inorganic solid electrolyte, substances other than those described above can be used. For example, Li3N, LiI, Li3N-LiI-LiOH, etc. can be used.

[0199] As the organic solid electrolyte, as long as it is a polymer compound showing ion conductivity, there is no particular limitation. For example, polyethylene oxide, polypropylene oxide, their copolymers, etc. can be used. In addition, the organic solid electrolyte can contain a supporting salt (lithium salt).

[0200] It should be noted that a solid electrolyte can also be used to form a secondary battery instead of the non-aqueous electrolyte. Since the solid electrolyte does not decompose even at high potentials, gas generation and thermal runaway caused by electrolyte decomposition during charging, which are visible in non-aqueous electrolytes, do not occur, so it has high thermal stability. Therefore, in the case of a lithium ion secondary battery using the positive electrode active material of the present invention, a secondary battery with higher thermal stability can be obtained.

[0201] [Shape and structure of secondary battery]

[0202] The structure of the secondary battery is not particularly limited. As described above, it can be composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, etc., or can also be composed of a positive electrode, a negative electrode, a solid electrolyte, etc. In addition, the shape of the secondary battery is not particularly limited and can be various shapes such as cylindrical and laminated.

[0203] For example, in the case of a non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode are laminated with a separator in between to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte. The positive electrode current collector is connected to the positive terminal leading to the outside and the negative electrode current collector is connected to the negative terminal leading to the outside using current collecting leads, etc., and then sealed in a battery case to complete the secondary battery.

[0204] It should be noted that the secondary battery of this embodiment is not limited to the method of using a non-aqueous electrolyte as the non-aqueous electrolyte. For example, it can also be a secondary battery using a solid non-aqueous electrolyte, that is, an all-solid battery. In the case of manufacturing an all-solid battery, the configuration other than the positive electrode active material can be changed as needed.

[0205] The secondary battery of this embodiment can achieve high thermal stability at low cost. In addition, the positive electrode active material used in the secondary battery can be obtained by the above industrial manufacturing method. In addition, the secondary battery is suitable as a power source for small portable electronic devices (such as notebook personal computers, portable phone terminals, etc.) that always require high capacity. In addition, compared with conventional batteries using positive electrode active materials of lithium cobalt oxide or lithium nickel oxide, the secondary battery not only has excellent capacity, but also has excellent durability and thermal stability during overcharging. Therefore, miniaturization and high capacity can be achieved, so it is suitable as a power source for electric vehicles where the mounting space is restricted. It should be noted that the secondary battery can be used not only as a power source for purely electrically driven electric vehicles, but also as a power source for so-called hybrid vehicles used in combination with internal combustion engines such as gasoline engines and diesel engines.

[0206] Examples

[0207] Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited by any of these examples. It should be noted that the various evaluation methods of the positive electrode active material in the examples and comparative examples are as follows.

[0208] (A) Analysis of composition: Measured by ICP emission spectrometry.

[0209] (B) Qualitative evaluation of crystal structure and presence or absence of impurity phases and calculation of the crystallite diameter of the (003) plane:

[0210] Using an XRD diffractometer (manufactured by PANalytical, X’Pert PRO), evaluation is performed with an XRD diffraction pattern using Cu-Kα rays. The measurement conditions are set with an output of 45 kV, 40 mA, step size: 0.0168°, and scanning speed: 0.0508° / sec.

[0211] The presence or absence of heterogeneous phases other than the layered structure of the hexagonal system and the peak intensity ratio (I Ti化合物 / I (003) ) are obtained from the diffraction pattern. It should be noted that for peaks below the detection limit, their peak intensity = 0 is used for calculation. Specifically, in the comparative example described later, when LiTiO2 is detected as a Ti compound, the diffraction peak intensity I LiTiO2 of the (200) diffraction peak, which is the strongest spectral line of LiTiO2, is used to obtain the peak intensity ratio as (I LiTiO2 / I(003) )。Here, the position of the (200) diffraction peak, which is the strongest spectral line of LiTiO2, is around 2θ = 43.7°, and the position of the (003) diffraction peak, which is the strongest spectral line of the layered structure of the hexagonal crystal system, is around 2θ = 18.7°.

[0212] In addition, the crystallite diameter of (003) is obtained by the Scherrer's calculation formula from the half-value width of the (003) of the obtained layered structure of the hexagonal crystal system.

[0213] (C) Dissolved lithium amount: Take 20 g of the positive electrode active material, put it into 100 ml of pure water at 25 °C, soak and stir for 30 minutes, and titrate the supernatant after standing for 10 minutes with an HCl aqueous solution. The titration is evaluated by the Warder method, lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) are calculated, and the sum of their lithium amounts is calculated as the dissolved lithium.

[0214] (D) Volume average particle size Mv and particle size deviation index [(D90 - D10) / volume average particle size Mv]:

[0215] It is carried out on a volume basis using a laser diffraction / scattering particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Microtrac HRA).

[0216] (E) Specific surface area: It is measured by the BET method based on nitrogen adsorption using a specific surface area / pore size distribution measuring device (manufactured by Mountech Co., Ltd., model: MACSORB HM1200 series).

[0217] (F) Initial charge capacity and initial discharge capacity:

[0218] Regarding the initial charge capacity and initial discharge capacity, after fabricating the 2032-type coin-shaped battery CBA shown Figure 6 and leaving it for about 24 hours, after the open circuit voltage OCV (open circuit voltage) stabilizes, the current density relative to the positive electrode is set to 0.1 mA / cm 2 , charged to the cut-off voltage of 4.3 V, and after stopping for 1 hour, discharged to the cut-off voltage of 3.0 V, and the capacity at this time is taken as the initial discharge capacity. The measurement of the discharge capacity uses a multi-channel voltage / current generator (manufactured by Advantest Corporation, R6741A).

[0219] The coin-type battery CBA is prepared by mixing 52.5 mg of a positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE), and pressing and forming them at a pressure of 100 MPa into a shape with a diameter of 11 mm and a thickness of 100 μm to produce the positive electrode (evaluation electrode) PE. After drying the produced positive electrode PE in a vacuum dryer at 120°C for 12 hours, the coin-type battery CBA is produced in a glove box with an Ar atmosphere where the dew point is controlled at -80°C using this positive electrode PE.

[0220] The negative electrode NE uses a lithium (Li) metal with a diameter of 17 mm and a thickness of 1 mm, and the electrolyte uses an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Chemical Co., Ltd.) with 1 M LiClO4 as the supporting electrolyte. The separator SE uses a polyethylene porous membrane with a film thickness of 25 μm. In addition, the coin-type battery has a gasket GA and a wave washer WW, and is assembled into a coin-type battery from a positive electrode can PC and a negative electrode can NC.

[0221] (G) Thermal stability evaluation

[0222] The thermal stability evaluation of the positive electrode is carried out by quantifying the amount of oxygen released by heating the positive electrode active material in an overcharged state. The coin-type battery CBA is produced in the same manner as in (E), and CC charging (constant current - constant voltage charging) is performed at a rate of 0.05C to a cut-off voltage of 4.3V. Then, the coin-type battery CBA is disassembled, and only the positive electrode is carefully taken out without short-circuiting, washed with DMC (dimethyl carbonate), and dried. Approximately 2 mg of the dried positive electrode is weighed, and using a gas chromatography-mass spectrometer (GCMS, Shimadzu Corporation, QP-2010plus), it is heated from room temperature to 450°C at a heating rate of 10°C / min. Helium is used as the carrier gas. The generation behavior of oxygen (m / z = 32) generated during heating is measured, and the semi-quantification of the oxygen generation amount is performed from the maximum oxygen generation peak height and peak area obtained, and they are used as evaluation indices for thermal stability. It should be noted that the semi-quantification value of the oxygen generation amount is calculated by injecting pure oxygen as a standard sample into the GCMS and extrapolating the standard curve obtained from its measurement results.

[0223] (Example 1)

[0224] [Crystallization process]

[0225] A predetermined amount of pure water was added to a reaction tank (60 L), and the temperature in the tank was set to 49° C. while stirring. At this time, N2 gas was circulated in the reaction tank so that the dissolved oxygen concentration in the reaction tank liquid became 0.8 mg / L. In the reaction tank, a 2.0 M mixed aqueous solution of nickel sulfate, manganese sulfate, and cobalt sulfate, a 25 mass % sodium hydroxide solution as an alkaline solution, and a 25 mass % ammonia water as a complexing agent were simultaneously and continuously added to the reaction tank so that the molar ratio of nickel: manganese: cobalt was 85:10:5.

[0226] At this time, the flow rate is controlled in such a way that the residence time of the mixed aqueous solution is 8 hours, the pH in the reaction tank is adjusted to 12.0-12.6, and the ammonia concentration is adjusted to 10-14 g / L. After the reaction tank is stabilized, the slurry containing the nickel-manganese-cobalt composite hydroxide is recovered from the overflow port and filtered to obtain a filter cake of the nickel-manganese-cobalt composite hydroxide (crystallization process). 140 g of the nickel-manganese-cobalt composite hydroxide in the filtered Denver is passed through 1 L of pure water to clean the impurities. The filtered powder is dried to obtain nickel-manganese-cobalt composite hydroxide particles in which the mass ratio of nickel, manganese and cobalt is represented by Ni:Mn:Co=0.85:0.10:0.05.

[0227] [Mixing process]

[0228] The obtained nickel-manganese-cobalt composite hydroxide particles, lithium hydroxide and titanium oxide (TiO2) with an average particle size of 2.5 μm were weighed in a manner such that the molar ratio of lithium: nickel: manganese: cobalt: titanium became 1.05:0.81:0.10:0.05:0.04, and then fully mixed using a vibration mixer device (TURBULA Type T2C manufactured by WAB) to obtain a lithium mixture.

[0229] [Firing process]

[0230] The obtained lithium mixture was calcined in an oxygen (oxygen concentration: 90 volume %) gas flow at 800° C. for 10 hours, and then pulverized to obtain lithium nickel manganese cobalt titanium composite oxide particles.

[0231] [Water washing process]

[0232] 150 parts by mass of water was added to 100 parts by mass of the obtained lithium nickel manganese cobalt titanium composite oxide particles, and the mixture was stirred for 15 minutes and then suction filtered using a suction filter to obtain a precipitate.

[0233] [Drying process]

[0234] The obtained precipitate was placed in a SUS container, heated to 100° C. using a vacuum dryer and allowed to stand for 12 hours, and then heated to 190° C. and allowed to stand for 10 hours to obtain a positive electrode active material.

[0235] [Evaluation]

[0236] The (003) microcrystal diameter, dissolved lithium amount, volume average particle size Mv, particle size deviation index, and specific surface area of the obtained positive electrode active material are shown in Table 1. As a result of XRD measurement, no heterogeneous phase (impurity phase) other than the hexagonal layered structure was particularly confirmed. In addition, the coin-type battery CBA shown in Figure 6 was fabricated, and the initial charge-discharge capacity and thermal stability were evaluated. It should be noted that the maximum oxygen generation peak intensity is a relative value with respect to Comparative Example 1 without titanium (a relative value with Comparative Example 1 set to 100). The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0237] (Example 2)

[0238] In the firing process, the firing temperature was set to 760 °C. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 1. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0239] (Example 3)

[0240] In the mixing process, the obtained nickel-manganese-cobalt composite hydroxide particles, lithium hydroxide, and titanium oxide (TiO2) with an average particle size of 2.5 μm were weighed so that the molar ratio of lithium: nickel: manganese: cobalt: titanium was 1.05: 0.82: 0.10: 0.05: 0.03. In the firing process, the firing temperature was set to 780 °C. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 1. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0241] (Example 4)

[0242] In the firing process, the firing temperature was set to 790 °C. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 3. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0243] (Example 5)

[0244] In the mixing process, the obtained nickel-manganese-cobalt composite hydroxide particles, lithium hydroxide, and titanium oxide (TiO2) with an average particle size of 2.5 μm were weighed so that the molar ratio of lithium: nickel: manganese: cobalt: titanium was 1.05: 0.83: 0.10: 0.05: 0.02. In the firing process, the firing temperature was set to 760 °C. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 1. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0245] (Comparative Example 1)

[0246] In the mixing step, titanium oxide was not prepared, and the obtained nickel-manganese-cobalt composite hydroxide particles were weighed so that the molar ratio of lithium:nickel:manganese:cobalt was 1.02:0.85:0.10:0.05. In the firing step, the firing temperature was set at 800°C, and the washing step and the drying step were not carried out. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 1. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0247] (Comparative Example 2)

[0248] For the lithium nickel manganese cobalt composite oxide particles obtained in the firing step of Comparative Example 1, the washing step and the drying step were carried out in the same manner as in Example 1, and a positive electrode active material was obtained and evaluated. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0249] (Comparative Example 3)

[0250] Except for not carrying out the washing step and the drying step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0251] (Comparative Example 4)

[0252] In the firing step, the lithium mixture was fired in a stream of oxygen (oxygen concentration: 60% by volume), and the washing step and the drying step were not carried out. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 2. In addition, as a result of XRD measurement, a peak attributable to LiTiO2 was confirmed. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0253] (Comparative Example 5)

[0254] In the mixing step, the obtained nickel-manganese-cobalt composite hydroxide particles, lithium hydroxide, and titanium oxide (TiO2) with an average particle diameter of 2.5 μm were weighed so that the molar ratio of lithium:nickel:manganese:cobalt:titanium was 1.01:0.79:0.08:0.05:0.08, and the washing step and the drying step were not carried out. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 1. In addition, as a result of XRD measurement, a peak attributable to LiTiO2 was confirmed. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0255] (Comparative Example 6)

[0256] In the crystallization step, an aqueous mixed solution of nickel sulfate, manganese sulfate, and cobalt sulfate at 2.0 M was added to the reaction tank such that the molar ratio of nickel:manganese:cobalt was 60:20:20, to obtain nickel-manganese-cobalt composite hydroxide particles with a molar ratio of nickel, manganese, and cobalt represented by Ni:Mn:Co = 0.60:0.20:0.20. In the mixing step, the obtained nickel-manganese-cobalt composite hydroxide particles, lithium hydroxide, and titanium oxide (TiO2) with an average particle size of 2.5 μm were weighed such that the molar ratio of lithium:nickel:manganese:cobalt:titanium was 1.03:0.58:0.20:0.20:0.02. In the firing step, the firing temperature was set at 900 °C, and the water washing step and the drying step were not carried out. Except for this, a positive electrode active material was obtained and evaluated in the same manner as in Example 1. The manufacturing conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results are shown in Tables 2 and 3.

[0257] [Table 1]

[0258]

[0259] [Table 2]

[0260]

[0261] [Table 3]

[0262]

[0263] (Evaluation results)

[0264] As shown in Tables 1 to 3, the positive electrode active material obtained in the examples had extremely good thermal stability and high initial charge-discharge capacity. In the positive electrode active materials obtained in the examples, titanium was solid-dissolved in the crystal phase, and no impurity phase (heterogeneous phase) was precipitated.

[0265] On the other hand, in the positive electrode active material of Comparative Example 1, since titanium was not added, the thermal stability was low. In addition, since the water washing step and the drying step were not carried out, the specific surface area was low.

[0266] In the positive electrode active material of Comparative Example 2, although the water washing step and the drying step were carried out, compared with the positive electrode active material of Comparative Example 1, the initial charge-discharge capacity slightly decreased, and the maximum oxygen generation peak intensity and the oxygen generation amount also slightly increased, and neither the battery capacity nor the thermal stability was improved.

[0267] In the positive electrode active material of Comparative Example 3, since the water washing step and the drying step were not carried out, the specific surface area was low and the initial discharge capacity was low. In addition, the amount of dissolved lithium was also large.

[0268] In the positive electrode active material of Comparative Example 4, since the oxygen concentration during firing was low, a part of titanium could not be dissolved in the positive electrode active material and an impurity phase was formed. Therefore, although the thermal stability was good, due to the lack of lithium and cation mixing disorder in the positive electrode active material, the initial charge-discharge capacity was significantly reduced. In addition, since the water washing process and the drying process were not carried out, the specific surface area was low and the amount of dissolved lithium was large.

[0269] In the positive electrode active material of Comparative Example 5, the addition amount of titanium was large. Therefore, for example, the thermal stability was as good as that of the positive electrode active materials of Examples 1 and 2. However, due to the excessive addition of titanium, a large amount of Ti compounds precipitated, and the initial charge-discharge capacity deteriorated significantly. In addition, due to the increase in the amount of titanium, the amount of Ni contributing to redox decreased, which also affected the capacity reduction. It is speculated that due to the low electrochemical characteristics, the thermal stability was apparently optimized. In addition, since the water washing process and the drying process were not carried out, the specific surface area was low and the amount of dissolved lithium was large.

[0270] In the positive electrode active material of Comparative Example 6, the nickel ratio of the positive electrode active material was lower than that of the Example, so the thermal stability was good, but the initial charge-discharge capacity deteriorated significantly.

[0271] From the above, for the positive electrode active material for a lithium ion secondary battery, the manufacturing method of the positive electrode active material for a lithium ion secondary battery, and the lithium ion secondary battery according to an embodiment of the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery that can achieve a high level of both high thermal stability and excellent battery characteristics. In addition, the present invention can easily manufacture such a positive electrode active material in industrial-scale production, and it can be said that the industrial value is extremely large.

[0272] Industrial Applicability

[0273] In the present embodiment, it is possible to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery that achieves a high level of both high thermal stability and excellent battery characteristics through an industrial manufacturing method. The non-aqueous electrolyte secondary battery is suitable as a power source for small portable electronic devices (such as notebook personal computers, portable phone terminals, etc.) that always require high capacity and long life.

[0274] In addition, compared with a conventional battery using a positive electrode active material of a lithium nickel-based oxide, the secondary battery according to an embodiment of the present invention is also excellent in safety, and further excellent in capacity and durability. Therefore, miniaturization and long life can be achieved, and thus it is suitable as a power source for electric vehicles where the mounting space is restricted.

[0275] In addition, the positive electrode active material of one embodiment of the present invention and the secondary battery using the positive electrode active material can be used not only as a power source for an electric vehicle driven purely by electric energy, but also as a power source for a so-called hybrid vehicle used in combination with an internal combustion engine such as a gasoline engine or a diesel engine, and a stationary battery.

[0276] It should be noted that although the embodiments and examples of the present invention have been described in detail as above, those skilled in the art can easily understand that various modifications can be made without substantially departing from the new matters and effects of the present invention. Therefore, all such modified examples are included within the scope of the present invention.

[0277] For example, in the specification or the drawings, a term that is described at least once together with a different term that is more general or synonymous can be replaced with that different term at any position in the specification or the drawings. In addition, the constitution and operation of the positive electrode active material for a lithium ion secondary battery, the lithium ion secondary battery, and the manufacturing method of the positive electrode active material for a lithium ion secondary battery are not limited to the contents described in the embodiments and examples of the present invention, and various modifications can be made.

[0278] One or more of the elements described in the above embodiments and the like may sometimes be omitted. In addition, the elements described in the above embodiments and the like can be appropriately combined. In addition, as long as the law permits, the contents of Japanese Patent Application No. 2020-161397 and all the documents cited in this specification are cited as part of the content described herein.

[0279] Symbol Explanation

[0280] CBA... Coin-type battery

[0281] PE... Positive electrode (evaluation electrode)

[0282] NE... Negative electrode (lithium metal)

[0283] SE... Separator

[0284] GA... Gasket

[0285] WW... Wave washer

[0286] PC... Positive electrode can

[0287] NC... Negative electrode can.

Claims

1. A positive electrode active material for a lithium-ion secondary battery, which comprises a lithium nickel manganese composite oxide composed of secondary particles aggregated from a plurality of primary particles, The lithium nickel manganese composite oxide has a hexagonal layered structure and contains lithium (Li), nickel (Ni), manganese (Mn), element M (M), and titanium (Ti), and the element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al, The molar ratio of the elements is represented by Li:Ni:Mn:M:Ti = a:(1 - x - y - z):x:y:z, where, 0.97 ≤ a ≤ 1.25, 0.03 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15, 0.01 ≤ z ≤ 0.05, In the XRD measurement of the positive electrode active material, the ratio of the total integrated intensity of the strongest spectral lines of the titanium compound to the intensity of the (003) diffraction peak, which is the strongest spectral line of the hexagonal layered structure, is 0.2 or less, The crystallite diameter of the (003) plane obtained by XRD measurement is 80 nm or more and less than 160 nm, The specific surface area measured by the BET method is 0.7 m 2 / g or more and 4.0 m 2 / g or less.

2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein, [(D90 - D10) / Mv], which represents the deviation index of particle size calculated from D90 and D10 based on volume basis in the particle size distribution by laser diffraction scattering method and the volume average particle size Mv, is 0.80 or more and 1.20 or less.

3. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein, The volume average particle size Mv is 8 μm or more and 20 μm or less.

4. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein, When immersed in water, the amount of lithium dissolved in water is 0.2 mass% or less relative to the whole positive electrode active material.

5. A method for manufacturing a positive electrode active material for a lithium-ion secondary battery, the positive electrode active material for a lithium-ion secondary battery comprising a lithium nickel manganese composite oxide composed of secondary particles aggregated from a plurality of primary particles, The method for manufacturing the positive electrode active material for a lithium-ion secondary battery includes: A mixing step of adding a mixture containing at least a nickel manganese composite compound, a titanium compound, and a lithium compound; A firing step of firing the mixture in an oxidizing atmosphere with an oxygen concentration of 80 vol% or more and 100 vol% or less at 700 °C or more and 950 °C or less to obtain the lithium nickel manganese composite oxide; A water washing step of mixing and stirring at a ratio of 50 parts by mass or more and 200 parts by mass or less of water with respect to 100 parts by mass of the lithium nickel manganese composite oxide, and then performing solid-liquid separation; and A drying step of drying the water-washed lithium nickel manganese composite oxide, The nickel-manganese composite compound contains nickel (Ni), manganese (Mn), and element M (M), where the element M (M) is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, Nb, and Al, and the molar ratio of the elements is Ni:Mn:M = (1 - x - y):x:y, where, 0.03 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15, In the mixture, the ratio of the amount of substance of lithium Li to the total amount of substance of nickel, manganese, element M, and titanium Me contained, that is, Li / Me, is 0.97 or more and 1.25 or less, and the ratio of the amount of substance of titanium Ti to the total amount of substance of nickel, manganese, element M, and titanium Me contained, that is, Ti / Me, is 0.01 or more and 0.05 or less, In the XRD measurement of the positive electrode active material, the ratio of the total integrated intensity of the diffraction peaks of the strongest spectral lines of the titanium compound to the intensity of the (003) diffraction peak, which is the strongest spectral line of the hexagonal layered structure, is 0.2 or less, The crystallite diameter of the (003) plane obtained by XRD measurement is 80 nm or more and less than 160 nm.

6. The manufacturing method of the positive electrode active material for a lithium ion secondary battery according to claim 5, wherein, The volume average particle diameter Mv of the titanium compound is 0.01 μm or more and 5 μm or less.

7. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 5 or 6, wherein, The titanium compound is titanium oxide.

8. A lithium ion secondary battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains the positive electrode active material according to any one of claims 1 to 4.

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