Positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery

Abstract

The present invention provides a positive electrode active material which is capable of achieving high thermal stability at low cost.　A positive electrode active material for lithium ion secondary batteries, said positive electrode active material containing a lithium-nickel composite oxide that has a hexagonal lamellar structure and is composed of secondary particles, in each of which a plurality of primary particles aggregate. The lithium-nickel composite oxide contains lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and optionally element M1; and the amount of substance ratio among those elements is expressed as Li:Ni:Mn:M:Ti:Nb = a:(1 – x1 – y1 – b – c):x1:y1:b:c (wherein 0.95 ≤ a ≤ 1.25, (1 – x1 – y1 – b – c) < 0.80, 0.03 ≤ x1 ≤ 0.35, 0 ≤ y1 ≤ 0.35, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03), while satisfying (b + c) ≤ 0.06 and b > c. If this positive electrode active material for lithium ion secondary batteries is immersed in water, the amount of lithium dissolved in water is 0.07% by mass or less relative to the entirety of the positive electrode active material.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium ion secondary battery and a lithium ion secondary battery.

Background Art

[0002] In recent years, with the spread of portable electronic devices such as mobile phone terminals and notebook personal computers, the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density and durability has been strongly desired. In addition, the development of high-output secondary batteries has been strongly desired as batteries for electric vehicles including power tools and hybrid automobiles.

[0003] As a secondary battery satisfying such requirements, there is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. As a positive electrode active material, a lithium ion secondary battery using a lithium metal composite oxide having a layered or spinel crystal structure has been put into practical use as a battery having a high energy density because a high voltage of 4V class can be obtained.

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

[0005] By the way, when a non-aqueous electrolyte is used as a battery material in a lithium ion secondary battery, high thermal stability is required. For example, when a short circuit occurs inside a lithium ion secondary battery, heat generation due to a rapid current occurs, so higher thermal stability is required.

[0006] Therefore, lithium nickel cobalt manganese composite oxides and lithium nickel composite oxides, which have excellent thermal stability, have attracted attention. Lithium nickel cobalt manganese composite oxides are layered compounds like lithium cobalt composite oxides and lithium nickel composite oxides, and those with a composition ratio of nickel, cobalt, and manganese in the transition metal site of 1:1:1 are called ternary cathode active materials.

[0007] In particular, in recent years, ternary cathode active materials and cathode active materials with a high nickel ratio (Hi-Ni cathode materials) in which the nickel ratio of lithium nickel composite oxides has been increased in order to achieve high capacity have attracted attention. However, since an increase in battery capacity due to the nickel ratio results in a trade-off with a decrease in thermal stability, a cathode active material that combines high performance (high cycle characteristics, high capacity, high output) and short-circuit resistance and thermal stability as a lithium-ion secondary battery is required.

[0008] For the purpose of improving thermal stability, several techniques for adding niobium to lithium metal composite oxides have been proposed. For example, Patent Document 1 discloses a general formula: Li a Ni 1-x-y-z Co x M y Nb z O b (where M is one or more elements selected from the group consisting of Mn, Fe, and Al, 1 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.05, 2 ≦ b ≦ 2.2), and a non-aqueous secondary battery cathode active material composed of a composition comprising at least one compound composed of lithium, nickel, cobalt, element M, niobium, and oxygen has been proposed. According to Patent Document 1, since the Li-Nb-O-based compound present near the surface or inside the particles has high thermal stability, a cathode active material having high thermal stability and a large discharge capacity is obtained.

[0009] Further, Patent Document 2 discloses a general formula (1): Li d Ni 1-a-b-c Mn a M b Nb c O2+γ (In the general formula (1), M is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, and Ta, and 0.05 ≦ a ≦ 0.60, 0 ≦ b ≦ 0.60, 0.0003 ≦ c ≦ 0.03, 0.95 ≦ d ≦ 1.20, and 0 ≦ γ ≦ 0.5.) It is composed of a lithium nickel manganese composite oxide represented by, and at least a part of niobium in the lithium nickel manganese composite oxide is dissolved in primary particles, and a positive electrode active material for a non-aqueous electrolyte secondary battery has been proposed. According to Patent Document 2, it is said that a non-aqueous secondary battery can be obtained that achieves both high energy density and excellent output characteristics and thermal stability at the time of short circuit due to a decrease in conductivity in a high dimension.)

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0011] The positive electrode active materials described in Patent Documents 1 and 2 are described as improving thermal stability by containing niobium in a specific form. However, in lithium nickel composite oxides, further improvement in thermal stability is required. In addition, since niobium is expensive, there is a demand for a positive electrode active material that can achieve high thermal stability at a lower cost.

[0012] The present invention has been made in view of these circumstances, and an object thereof is to provide a positive electrode active material capable of realizing higher thermal stability at a lower cost in a positive electrode active material containing a lithium nickel composite oxide.

[0013] By the way, for the purpose of obtaining a positive electrode active material having high battery characteristics, several techniques for adding titanium to a lithium metal composite oxide, for example, have been proposed. According to Patent Documents 3 to 7, a positive electrode active material composed of a lithium nickel cobalt titanium composite oxide is said to have good thermal stability and a high battery capacity.

[0014] In addition, when a short circuit occurs inside a lithium ion secondary battery, as one method for suppressing a rapid current due to the short circuit, for example, as described in Patent Document 2 above, it is considered effective to lower the conductivity of the positive electrode active material in a state where it is compressed and present in the positive electrode, or to increase the volume resistivity.

[0015] However, Patent Documents 1 to 7 do not describe at all the effect of containing a combination of niobium and titanium as different elements in a lithium nickel composite oxide.

Means for Solving the Problems

[0016] In a first aspect of the present invention, there is provided a positive electrode active material for a lithium-ion secondary battery, which includes a lithium nickel composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated. The lithium nickel composite oxide contains lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and an element M1 which is at least one element arbitrarily selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The molar ratio of each element is Li:Ni:Mn:M1:Ti:Nb = a:(1 - x1 - y1 - b - c):x1:y1:b:c (where 0.95 ≤ a ≤ 1.25, (1 - x1 - y1 - b - c) < 0.80, 0.03 ≤ x1 ≤ 0.35, 0 ≤ y1 ≤ 0.35, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03). In the molar ratio, (b + c) ≤ 0.06 and b > c are satisfied, and the amount of lithium eluted into water when immersed in water is 0.07% by mass or less based on the total amount of the positive electrode active material.

[0017] In a second aspect of the present invention, there is provided a positive electrode active material for a lithium-ion secondary battery, which includes a lithium nickel composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated. The lithium nickel composite oxide contains lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and an element M2 which is at least one element arbitrarily selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The molar ratio of each element is Li:Ni:Mn:M2:Ti:Nb = a:(1 - x2 - y2 - b - c):x2:y2:b:c (where 0.95 ≤ a ≤ 1.25, 0.880 < (1 - x2 - y2 - b - c), 0.01 ≤ x2 ≤ 0.113, 0 ≤ y2 ≤ 0.103, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03). In the molar ratio, (b + c) ≤ 0.06 and b > c are satisfied, and the amount of lithium eluted into water when immersed in water is 0.20% by mass or less based on the total amount of the positive electrode active material.

[0018] In a third aspect of the present invention, there is provided a positive electrode active material for a lithium-ion secondary battery, which includes a lithium nickel composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated. The lithium nickel composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), aluminum (Al), titanium (Ti), niobium (Nb), and an element M3 which is at least one element arbitrarily selected from Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, and Zr. The molar ratio of each element is Li:Ni:Co:Al:M3:Ti:Nb = a:(1 - x3 - y3 - z3 - b - c):x3:y3:z3:b:c (where 0.95 ≤ a ≤ 1.25, 0.01 ≤ x3 ≤ 0.25, 0.005 ≤ y3 ≤ 0.15, 0 ≤ z3 ≤ 0.15, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03). In the molar ratio, (b + c) ≤ 0.06 and b > c are satisfied, and the amount of lithium eluted in water when immersed in water is 0.25% by mass or less based on the total amount of the positive electrode active material.

[0019] Further, it is preferable that the niobium concentration at the grain boundaries between the primary particles is 1.3 times or more the niobium concentration inside the primary particles of the lithium nickel composite oxide, as determined by point analysis using STEM-EDX. Further, it is preferable that the titanium concentration at the grain boundaries between the primary particles is less than 1.3 times the titanium concentration inside the primary particles of the lithium nickel composite oxide, as determined by point analysis using STEM-EDX. Further, it is preferable that the particle size variation index [(D90 - D10) / Mv], calculated by D90 and D10 in the particle size distribution by the laser diffraction scattering method and the volume average particle size (Mv), is 0.80 or more and 1.20 or less. Further, it is preferable that the volume average particle size Mv is 8 μm or more and 20 μm or less. Further, in the ratio of the amounts of substances, c indicating the ratio of the amount of substance of Nb may be 0.002 ≦ c ≦ 0.03. Further, the positive electrode active material of the third aspect may have a lithium elution amount of 0.09 mass% or less with respect to the entire positive electrode active material when immersed in water.

[0020] In a fourth aspect of the present invention, a lithium ion secondary battery is provided, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode contains the positive electrode active material for a lithium ion secondary battery described above.

Advantages of the Invention

[0021] According to the present invention, it is possible to provide a positive electrode active material that has a high battery capacity and can achieve high thermal stability at low cost. Further, the positive electrode active material of the present invention can be easily manufactured in industrial-scale production, and it can be said that its industrial value is extremely large.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0023] Hereinafter, a positive electrode active material for a lithium ion secondary battery obtained by the manufacturing method according to this embodiment, its manufacturing method, and further, a lithium ion secondary battery using this positive electrode active material will be described.

[0024] 1. Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for a lithium ion secondary battery according to this embodiment (hereinafter also referred to as "positive electrode active material") has a hexagonal layered structure and contains a lithium nickel composite oxide composed of secondary particles in which a plurality of primary particles are aggregated. The lithium nickel composite oxide contains at least lithium (Li), nickel (Ni), titanium (Ti), and niobium (Nb) as elements other than oxygen.

[0025] In particular, for a lithium ion secondary battery using a flammable non-aqueous electrolyte as a constituent material of the lithium ion secondary battery, high thermal stability is required. Also, in a lithium ion secondary battery, when the positive electrode and the negative electrode are short-circuited in a charged state, a large current flows suddenly and a large amount of heat is generated, which may cause a chain reaction in which the positive electrode active material decomposes and further generates heat. Therefore, by using a positive electrode active material having a high volume resistivity under the compressed conditions in the positive electrode, the sudden increase in current caused by a short circuit can be suppressed, and the thermal stability during a short circuit can be further improved.

[0026] As a result of intensive studies, the present inventors have found that in the lithium nickel composite oxide used for the positive electrode active material, i) by containing a specific amount of titanium (Ti) and niobium (Nb) in a specific distribution, the positive electrode active material can achieve high thermal stability by suppressing oxygen release during overcharging at low cost, and ii) by washing and drying the lithium nickel composite oxide, the battery capacity can be improved, and thus the present invention has been completed. Hereinafter, the configuration of the positive electrode active material according to this embodiment will be described in detail.

[0027] [Elements constituting the lithium nickel composite oxide] The lithium nickel composite oxide according to the present embodiment includes a lithium nickel composite oxide containing at least lithium (Li), nickel (Ni), titanium (Ti), and niobium (Nb) as elements other than oxygen. Further, as a preferred example of the positive electrode active material according to the present embodiment, each element constituting the lithium nickel composite oxide may be represented by any of the following molar ratios A to C.

[0028] [Molar ratio A] The lithium nickel composite oxide may contain, for example, as elements other than oxygen, lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and optionally at least one element M1 selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al.

[0029] From the viewpoint of high battery capacity and thermal stability, the molar ratio of the above elements is preferably Li:Ni:Mn:M1:Ti:Nb = a:(1 - x1 - y1 - b - c):x1:y1:a:b (where 0.95 ≤ a ≤ 1.25, (1 - x1 - y1 - b - c) < 0.80, 0.03 ≤ x1 ≤ 0.35, 0 ≤ y1 ≤ 0.35, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03). Hereinafter, the molar ratio of the above elements is referred to as molar ratio A. Further, in molar ratio A, b indicating the molar ratio of titanium (Ti) and c indicating the molar ratio of niobium (Nb) satisfy the relationship (b + c) ≤ 0.06 and b > c. Hereinafter, the preferred compositions of the elements other than titanium and niobium will be described. The molar ratios of titanium and niobium will be described later.

[0030] (Lithium) In the above-described molar ratio A, since the total molar ratio of the above elements other than Li is 1, a indicating the molar ratio of Li corresponds to the molar ratio of lithium to the above elements (Me) other than lithium (hereinafter also referred to as "Li / Me"). Further, the range of a is 0.95 ≦ a ≦ 1.25, preferably 0.95 ≦ a ≦ 1.15. When the value of a is within the above range, the reaction resistance of the positive electrode decreases, and the output of the battery can be improved. Also, the range of a may be 1.00 ≦ a ≦ 1.15, or may be 1.00 ≦ a ≦ 1.05. Further, the range of a may be less than 1.00.

[0031] (Manganese) In the above-described molar ratio A, the range of x1 indicating the molar ratio of Mn is 0.03 ≦ x1 ≦ 0.35, preferably 0.05 ≦ x1 ≦ 0.35, more preferably 0.10 ≦ x1 ≦ 0.35. When the value of x1 is within the above range, it can have high battery capacity and high thermal stability. On the other hand, when the value of x1 is less than 0.03, the effect of improving thermal stability cannot be obtained. Also, when the value of x1 exceeds 0.35, the battery capacity decreases. Further, by including manganese within the above range, in the firing step (S20) described later, the firing temperature can be increased, and the dispersion of titanium or the like can be promoted.

[0032] (Element M1) In the above-mentioned molar ratio A, the element M1 is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. Also, the range of y1 indicating the molar ratio of the element M1 is 0 ≦ y1 ≦ 0.35, preferably 0 < y1 ≦ 0.35. When y is 0 or more, the thermal stability, storage characteristics, and battery characteristics can be improved. On the other hand, when y1 exceeds 0.35, the battery capacity may decrease due to the relatively decreased ratio of Ni. For example, when M1 contains Co, the battery capacity and output characteristics are more excellent. In the above-mentioned molar ratio A, when the molar ratio of cobalt contained in M1 is y2, the range of y2 is preferably 0 < y2 ≦ 0.35, more preferably 0.02 ≦ y2 ≦ 0.35, and even more preferably 0.05 ≦ y2 ≦ 0.35.

[0033] (Nickel) In the above-mentioned molar ratio A, (1 - x1 - y1 - b - c) indicating the molar ratio of Ni is (1 - x1 - y1 - b - c) < 0.80. When the molar ratio of nickel is within the above range, a secondary battery having extremely high thermal stability can be obtained. When the molar ratio of nickel is low, the thermal stability tends to be high. However, the lithium nickel composite oxide according to this embodiment has the above-described composition, so that the thermal stability is further improved, and a secondary battery having extremely high thermal stability can be obtained.

[0034] [Molar ratio B] The lithium nickel composite oxide may contain, for example, as elements other than oxygen, lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and optionally at least one element M2 selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al.

[0035] From the perspective of high battery capacity, the molar ratio of the above elements is preferably Li:Ni:Mn:M2:Ti:Nb = a:(1 - x2 - y2 - b - c):x2:y2:b:c (where 0.95 ≤ a ≤ 1.25, 0.880 < (1 - x2 - y2 - b - c), 0.01 ≤ x2 ≤ 0.113, 0 ≤ y2 ≤ 0.103, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03). Hereinafter, the molar ratio of each of the above elements is referred to as molar ratio B. Also, in the above molar ratio B, z indicating the molar ratio of titanium (Ti) and w indicating the molar ratio of niobium (Nb) satisfy the relationship (b + c) ≤ 0.06 and b > c. Hereinafter, the preferred compositions of each element except titanium and niobium will be described. The molar ratios of titanium and niobium will be described later.

[0036] (Lithium) In the above molar ratio, since the sum of the molar ratios of the above elements other than Li is 1, a indicating the molar ratio of Li corresponds to the molar ratio of lithium to the above elements other than lithium (hereinafter also referred to as "Li / Me"). Also, the range of a is 0.95 ≤ a ≤ 1.25, preferably 0.95 ≤ a ≤ 1.15. When the value of a is within the above range, the reaction resistance of the positive electrode decreases and the output of the battery can be improved. Also, the range of a may be 1.00 ≤ a ≤ 1.15, or may be 1.00 ≤ a ≤ 1.05. Also, the range of a may be less than 1.00.

[0037] (Manganese) In the above molar ratio B, the range of x2 indicating the molar ratio of Mn is 0.01 ≤ x2 ≤ 0.113, preferably 0.02 ≤ x2 ≤ 0.10, more preferably 0.03 ≤ x2 ≤ 0.10. When the value of x2 is within the above range, high battery capacity and high thermal stability can be achieved. On the other hand, when the value of x2 is less than 0.01, the effect of improving thermal stability cannot be obtained. Also, when the value of x2 exceeds 0.113, the battery capacity decreases. Also, by including manganese within the above range, in the firing step (S20) described later, the firing temperature can be increased and the dispersion of titanium etc. can be promoted.

[0038] (Element M2) In the above-mentioned molar ratio B, element M2 is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The range of x2 indicating the molar ratio of element M2 is 0 ≦ y2 ≦ 0.103, preferably 0 < y2 ≦ 0.103. When y2 is 0 or more, the thermal stability, storage characteristics, and battery characteristics can be improved. On the other hand, when y2 exceeds 0.103, the battery capacity may decrease due to a relatively lower ratio of Ni. For example, when M2 contains Co, the battery capacity and output characteristics are more excellent. When M is Co, preferably 0 < y2 ≦ 0.10. Also, when the molar ratio of Co contained in element M2 is y2', preferably 0 < y2' ≦ 0.10, more preferably 0.01 ≦ y2' ≦ 0.10. Also, M may contain Al. When the molar ratio of Al contained in element M2 is y2", preferably 0 < y2" ≦ 0.10, more preferably 0.01 ≦ y2" ≦ 0.10.

[0039] (Nickel) In the above-mentioned molar ratio B, (1 - x2 - y2 - b - c) indicating the molar ratio of Ni is 0.880 < (1 - x2 - y2 - b - c), preferably 0.880 < (1 - x2 - y2 - b - c) ≦ 0.950. When the molar ratio of nickel is within the above range, a secondary battery having a high battery capacity can be obtained. When the molar ratio of nickel is high, although the battery capacity improves, the thermal stability may decrease. However, the lithium nickel composite oxide according to the present embodiment can have high thermal stability regardless of the high nickel ratio by having the composition as described above.

[0040] [Molar ratio C] The lithium nickel composite oxide may contain, for example, as elements other than oxygen, lithium (Li), nickel (Ni), cobalt (Co), aluminum (Al), titanium (Ti), niobium (Nb), and optionally at least one element M3 selected from Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, and Zr.

[0041] From the perspective of high battery capacity, the molar ratio of the above elements is preferably Li:Ni:Co:Al:M3:Ti:Nb = a:(1 - x3 - y3 - z3 - b - c):x3:y3:z3:b:c (where 0.95 ≤ a ≤ 1.25, 0.01 ≤ x3 ≤ 0.25, 0.005 ≤ y3 ≤ 0.15, 0 ≤ z3 ≤ 0.15, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03). Hereinafter, the molar ratio of each of the above elements is referred to as the molar ratio C. Also, in the above molar ratio C, b representing the molar ratio of titanium (Ti) and c representing the molar ratio of niobium (Nb) satisfy the relationship (b + c) ≤ 0.06 and b > c. Hereinafter, the preferred compositions of the elements excluding titanium and niobium will be described. The molar ratios of titanium and niobium will be described later.

[0042] (Lithium) In the above molar ratio C, since the sum of the molar ratios of the above elements other than Li is 1, a representing the molar ratio of the amount of lithium corresponds to the molar ratio of lithium to the above elements other than lithium (hereinafter also referred to as "Li / Me"). Also, the range of a is 0.95 ≤ a ≤ 1.25, preferably 0.95 ≤ a ≤ 1.15. When the value of a is within the above range, the reaction resistance of the positive electrode decreases and the output of the battery can be improved. Also, the range of a may be 1.00 ≤ a ≤ 1.15, or may be 1.00 ≤ a ≤ 1.05. Also, the range of a may be less than 1.00.

[0043] (Cobalt) In the above-mentioned molar ratio C, the range of x3 indicating the molar ratio of Co is 0.01 ≤ x3 ≤ 0.25, preferably 0.03 ≤ x3 ≤ 0.20, and more preferably 0.05 ≤ x1 ≤ 0.20. On the other hand, when the value of x3 exceeds 0.25, the battery capacity decreases due to the relatively decreased ratio of Ni.

[0044] (Aluminum) In the above-mentioned molar ratio C, the range of y3 indicating the molar ratio of Al is 0.005 ≤ y3 ≤ 0.15, preferably 0.01 ≤ y3 ≤ 0.13, and more preferably 0.01 ≤ y3 ≤ 0.10. When the value of y3 is within the above range, the cycle characteristics and output characteristics can be improved. On the other hand, when the value of y3 exceeds 0.15, the battery capacity decreases due to the relatively decreased ratio of Ni.

[0045] (Element M3) In the above-mentioned molar ratio C, element M3 is at least one element selected from Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, and Zr. Also, the range of z3 indicating the molar ratio of element M3 is 0 ≤ z3 ≤ 0.15, preferably 0 < x ≤ 0.10. When z3 is 0 or more, the thermal stability, storage characteristics improvement, battery characteristics, etc. can be improved. On the other hand, when z3 exceeds 0.15, the battery capacity may decrease due to the relatively decreased ratio of Ni.

[0046] (Nickel) At the above-described molar ratio C, (1 - x3 - y3 - z3 - b - c), which represents the molar ratio of Ni, satisfies 0.39 ≤ (1 - x3 - y3 - z3 - b - c), preferably 0.50 ≤ (1 - x3 - y3 - z3 - b - c), and more preferably 0.70 ≤ (1 - x3 - y3 - z3 - b - c) ≤ 0.950. When the molar ratio of nickel is within the above range, a secondary battery having a high battery capacity can be obtained. When the molar ratio of nickel is high, although the battery capacity improves, the thermal stability may decrease. However, the lithium nickel composite oxide according to the present embodiment can have high thermal stability regardless of the high nickel ratio by having the above-described composition.

[0047] Hereinafter, the molar ratios of titanium (Ti) and niobium (Nb) and the distributions of titanium (Ti) and niobium (Nb) at the above-described molar ratios A to C will be described. (Titanium) At the above-described molar ratios A to C, the range of b, which represents the molar ratio of Ti, is 0.005 ≤ b ≤ 0.05. As described above, when titanium is included in the above range together with niobium, the volume resistivity of the lithium nickel composite oxide during compression can be significantly increased, and oxygen evolution can be suppressed when used as the positive electrode of a secondary battery, thereby obtaining high thermal stability. On the other hand, when the value of b is less than 0.005, the effect of improving thermal stability is not sufficient. Further, when the value of b exceeds 0.05, the ratios of Ni and Mn relatively decrease, the crystal structure is not stable, and cation mixing is likely to occur, so the battery capacity may significantly decrease.

[0048] (Niobium) In the above substance quantity ratios A to C, the range of c indicating the ratio of the substance quantity of Nb is 0.001 < c ≤ 0.03, preferably 0.002 ≤ c ≤ 0.03, more preferably 0.002 ≤ c ≤ 0.02, and even more preferably 0.002 ≤ c ≤ 0.01. As described above, by including niobium within the above range in combination with titanium, even with a small content of niobium, the volume resistivity during compression of the lithium nickel composite oxide can be significantly increased, and when used as the positive electrode of a secondary battery, oxygen release can be suppressed and high thermal stability can be achieved.

[0049] Also, in the above substance quantity ratios A to C, the sum (b + c) of the ratio of the substance quantity of titanium (b) and the ratio of the substance quantity of niobium (c) is 0.06 or less, preferably 0.05 or less, and more preferably 0.03 or less. When b + c is within the above range, it is possible to obtain a higher battery capacity while having high thermal stability.

[0050] Also, in the above substance quantity ratios A to C, the ratio of the substance quantity of niobium (c) is smaller than the ratio of the substance quantity of titanium (b) (b > c), preferably b ≥ 2c, more preferably b ≥ 3c, and even more preferably b ≥ 4c. Since niobium is a more expensive element than titanium, the manufacturing cost can be reduced by reducing the content of niobium compared to titanium, and high thermal stability can be achieved by combining it with titanium.

[0051] The composition of the lithium nickel composite oxide can be measured by quantitative analysis using inductively coupled plasma (ICP) optical emission spectrometry.

[0052] (Distribution of Niobium) At least a part of niobium (Nb) contained in the lithium nickel composite oxide according to this embodiment preferably segregates at the grain boundaries between primary particles. The segregation of niobium can be confirmed, for example, by performing surface analysis / line analysis on the composition of the cross-section of primary particles using energy-dispersive X-ray spectroscopy (EDX) of a scanning transmission electron microscope (S-TEM) to detect the enrichment of niobium in at least a part of the grain boundaries between primary particles. Note that at least a part of niobium may be present inside the primary particles.

[0053] Moreover, the niobium concentration at the grain boundaries between primary particles with respect to the niobium concentration inside the primary particles determined by STEM-EDX is preferably 1.3 times or more, more preferably 1.4 times or more, and even more preferably 1.5 times or more. Note that the upper limit of the niobium concentration is not particularly limited and is, for example, 5 times or less.

[0054] Note that the concentration of niobium inside the primary particles or at the grain boundaries can be confirmed by performing surface analysis / line analysis / point analysis on the composition of the cross-sections of a plurality of secondary particles by EDX measurement of a scanning transmission electron microscope (S-TEM).

[0055] For example, the niobium concentration at the grain boundaries between primary particles can be obtained by randomly selecting 20 regions (for example, a region of 130 nm × 130 nm that includes the grain boundaries between primary particles such that the grain boundaries cross the inside of the region) from the cross-sections of a plurality of secondary particles, confirming the composition of each region by point analysis, and calculating the average value. Similarly, the niobium concentration inside the primary particles can be obtained by randomly selecting 20 regions (for example, a region of 130 nm × 130 nm that does not include the grain boundaries) inside the primary particles, analyzing the composition of each region, and calculating the average value.

[0056] (Distribution of Titanium) The distribution of titanium (Ti) contained in the lithium nickel composite oxide according to this embodiment is not particularly limited, and it may be present in at least one of the surface and grain boundaries of the primary particles, or may be solid-solved in the primary particles. However, from the viewpoint of improving the battery capacity in a secondary battery, it is preferable that titanium is solid-solved. Here, the solid solution of titanium means, for example, a state in which titanium is detected inside the primary particles by surface analysis of the cross section of the secondary particles using EDX in S-TEM, and the concentration of titanium at the interface of the primary particles is not confirmed. It is preferable that titanium is detected over the entire surface inside the primary particles.

[0057] For example, the titanium concentration at the grain boundaries between primary particles with respect to the titanium concentration inside the primary particles determined by STEM-EDX is preferably less than 1.3 times, preferably 1.2 times or less, preferably 1.1 times or less, and may be 1.0 times or less. Also, the lower limit of the titanium concentration at the grain boundaries between primary particles with respect to the titanium concentration inside the primary particles may be 0.6 times or more, may be 0.7 times or more. For example, it may be 0.8 times or more and 1.2 times or less, or 0.9 times or more and 1.1 times or less. The titanium concentration can be measured by surface analysis of EDX of S-TEM in the same manner as the niobium concentration described above.

[0058] In the lithium nickel composite oxide according to this embodiment, the distribution of each element other than the above niobium (Nb) and titanium (Ti) is not particularly limited. For example, when Ni, Mn, and Co are included as element M1 or element M2, these metal elements are preferably detected over the entire surface inside the plurality of primary particles constituting the secondary particles.

[0059] [Volume average particle size (Mv)] The volume average particle size (Mv) of the positive electrode active material according to this embodiment is preferably 8 μm or more and 20 μm or less, and more preferably 10 μm or more and 18 μm or less. When the volume average particle size (Mv) is within the above range, when the positive electrode active material is used for the positive electrode of a secondary battery, high output characteristics and battery capacity can be achieved while achieving high fillability to the positive electrode.

[0060] On the one hand, when the volume average particle diameter (Mv) is less than 8 μm, high fillability into the positive electrode may not be obtained. Further, when the volume average particle diameter (Mv) exceeds 20 μm, high output characteristics and battery capacity may not be obtained. The volume average particle diameter (Mv) can be obtained, for example, from the volume integration value measured by a laser light diffraction / scattering particle size distribution analyzer.

[0061] [(D90 - D10) / Mv] (dispersion index) For the positive electrode active material according to this embodiment, it is preferable that [(D90 - D10) / Mv] is 0.80 or more and 1.20 or less. Note that [(D90 - D10) / Mv] represents the dispersion index of the particle diameters of the particles constituting the positive electrode active material, which is calculated from D90 and D10 (the particle diameter at 90% and 10% in the volume integration of the particle amount in the particle size distribution curve) and the volume average particle diameter (Mv) in the particle size distribution by the laser light diffraction / scattering method.

[0062] When the particle size distribution of the particles constituting the positive electrode active material is wide, there are many fine particles with a particle diameter smaller than the volume average particle diameter (Mv) and coarse particles with a particle diameter larger than the average particle diameter. When the dispersion index is within the above range, the fine particles and the coarse particles are appropriately mixed, the packing density increases, and the energy density per volume can be increased. Further, from the viewpoint of improving the energy density per volume, [(D90 - D10) / Mv] may be 0.90 or more, or may be 0.95 or more.

[0063] On the other hand, when the dispersion index of the positive electrode active material is less than 0.80, the volume energy density may decrease. Further, when the manufacturing method of the positive electrode active material according to this embodiment is used, the upper limit is about 1.20. In the firing step (S20) described later, when the firing temperature exceeds 1000°C, the dispersion index of the particle diameters may exceed 1.20. In this case, when the positive electrode active material is formed, the specific surface area may decrease, the resistance of the positive electrode may increase, and the battery capacity may decrease.

[0064] [Amount of eluted lithium] The cathode active material according to this embodiment preferably has an amount of lithium eluted in water (eluted lithium amount) smaller than that of a cathode active material produced under the same conditions except that the subsequent water washing step (S30) and drying step (S40) are not performed when immersed in water. By reducing the eluted lithium amount to a specific amount, the crystallinity of the cathode active material is improved, the discharge capacity is improved, and gelation of the cathode composite paste during production of the electrode plate of the secondary battery can be suppressed.

[0065] For example, in the case of a cathode active material containing a lithium nickel composite oxide having the above substance mass ratio A, the eluted lithium amount is preferably 0.07% by mass or less, may be 0.05% by mass or less, or may be less than 0.04% by mass with respect to the entire cathode active material. Also, the lower limit of the eluted lithium amount is not particularly limited, but is, for example, 0.005% by mass or more. When the eluted lithium amount is within the above range, excess lithium in the lithium nickel composite oxide can be extracted, and gelation of the cathode binder paste and the like can be suppressed. Note that when the eluted lithium amount is less than 0.005% by mass, lithium may be excessively extracted from the lithium nickel composite oxide during water washing, and in that case, the battery characteristics deteriorate.

[0066] For example, in the case of a cathode active material containing a lithium nickel composite oxide having the above substance mass ratio B, the eluted lithium amount is preferably 0.20% by mass or less, may be 0.09% by mass or less, may be 0.05% by mass or less, or may be less than 0.03% by mass with respect to the entire cathode active material. Also, the lower limit of the eluted lithium amount is not particularly limited, but is, for example, 0.005% by mass or more. When the eluted lithium amount is within the above range, excess lithium in the lithium nickel composite oxide can be extracted, and gelation of the cathode binder paste and the like can be suppressed. Note that when the eluted lithium amount is less than 0.005% by mass, lithium may be excessively extracted from the lithium nickel composite oxide during water washing, and in that case, the battery characteristics deteriorate.

[0067] For example, in the case of a positive electrode active material containing a lithium nickel composite oxide having the above-described substance amount ratio C, the amount of eluted lithium is preferably 0.25% by mass or less, and may be 0.15% by mass or less, with respect to the entire positive electrode active material. Further, the lower limit of the amount of eluted lithium is not particularly limited, but is, for example, 0.005% by mass or more. When the amount of eluted lithium is within the above range, excess lithium in the lithium nickel composite oxide can be extracted, and gelation of the positive electrode binder paste or the like can be suppressed. Note that when the amount of eluted lithium is less than 0.005% by mass, lithium may be excessively extracted from the lithium nickel composite oxide during water washing. In that case, battery characteristics deteriorate.

[0068] Note that the amount of eluted lithium can be measured by taking 2 g of the positive electrode active material, putting it into 125 ml of pure water at room temperature stirred by a stirrer, and immediately performing neutralization titration using an HCl aqueous solution after the positive electrode active material is added. The neutralization titration was evaluated by the Warder method, the amount of lithium hydroxide (LiOH) and the amount of lithium carbonate (Li2CO3) were calculated, and the sum of these lithium amounts was calculated as the eluted lithium.

[0069] [Specific surface area] Furthermore, the positive electrode active material according to the present embodiment preferably has a specific surface area measured by the BET method of 1.5 m 2 / g or less. In the case of a positive electrode active material with a high nickel ratio, when the specific surface area exceeds 1.5 m 2 / g, even if the water washing step (S30) described later is performed to once remove the eluted alkali component on the surface of the particles, it may react with moisture in the air and the alkali component derived from lithium eluted from the surface of the particles may increase. When a positive electrode binder paste is produced using such a positive electrode active material, the positive electrode binder paste may gel and it may become difficult to produce a positive electrode. On the other hand, the lower limit of the specific surface area of the positive electrode active material is, for example, 0.4 m 2 / g or more. For example, by performing the water washing step (S30) and the drying step (S40) described later, the specific surface area can be made larger than that of the lithium nickel manganese composite oxide before water washing.

[0070] [Maximum oxygen generation peak intensity] The cathode active material according to the present embodiment preferably has a maximum oxygen generation peak intensity obtained by measuring the amount of oxygen when the temperature is raised from 200°C to 300°C in an overcharged state, which is smaller than the peak intensity of the cathode active material manufactured under the same conditions except that titanium and niobium are not added.

[0071] For example, in the case of a cathode active material containing a lithium nickel composite oxide having the above substance mass ratio A, the maximum oxygen generation peak intensity ratio obtained by measuring the amount of oxygen when the temperature is raised from 200°C to 300°C in an overcharged state is preferably 0.25 or less, and more preferably 0.20 or less. The maximum oxygen generation peak intensity ratio refers to the ratio of the peak intensity when the maximum oxygen generation peak intensity of the cathode active material manufactured under the same conditions except that titanium and niobium are not added is set to 1.

[0072] Also, for example, in the case of a cathode active material containing a lithium nickel composite oxide having the above substance mass ratio B, the maximum oxygen generation peak intensity ratio obtained by measuring the amount of oxygen when the temperature is raised from 200°C to 300°C in an overcharged state is preferably 0.70 or less, and more preferably 0.65 or less.

[0073] Also, for example, in the case of a cathode active material containing a lithium nickel composite oxide having the above substance mass ratio C, the maximum oxygen generation peak intensity ratio obtained by measuring the amount of oxygen when the temperature is raised from 200°C to 300°C in an overcharged state is preferably 0.50 or less.

[0074] The lower limit of the maximum oxygen generation peak intensity ratio during temperature rise is not particularly limited, but is about 0.01 or more. The maximum oxygen generation peak intensity ratio can be measured by the method described in the examples. The maximum oxygen generation peak intensity refers to the intensity of the peak where the oxygen generated during the temperature rise from 200°C to 300°C is the maximum and the largest.

[0075] In addition, the lithium nickel composite oxide according to the present embodiment may contain a small amount of elements other than the above-described elements (Li, Ni, Mn, Co, Al, elements M1 to M3, Ti, Nb) and oxygen, as long as the effects of the present invention are not inhibited. Further, as the lithium nickel composite oxide contained in the positive electrode active material, a small amount of single primary particles may be contained in addition to secondary particles. Further, the positive electrode active material may contain a compound other than the above-described lithium nickel composite oxide.

[0076] 2. Method for manufacturing positive electrode active material for lithium ion secondary battery FIG. 1 is a diagram showing an example of a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to the present embodiment (hereinafter also referred to as "method for manufacturing a positive electrode active material"). By the manufacturing method according to the present embodiment, a positive electrode active material containing the above-described lithium nickel composite oxide can be easily obtained on an industrial scale.

[0077] As shown in FIG. 1, the manufacturing method according to the present embodiment includes at least a mixing step (S10) of mixing a nickel composite compound, a titanium compound, a niobium compound, and a lithium compound to obtain a mixture, a firing step (S20) of firing the mixture to obtain the lithium nickel composite oxide, a water washing step (S30) of mixing water with the lithium nickel composite oxide obtained after the firing step (S20), stirring, and then performing solid-liquid separation, and a drying step (S40) of drying the obtained lithium nickel composite oxide (precipitate).

[0078] Hereinafter, each step will be described in detail. Note that the following description is an example of the manufacturing method according to the present embodiment and does not limit the manufacturing method.

[0079] [Crystallization step (S1)] The nickel composite compound used in the mixing step (S10) is preferably obtained, for example, by a method including a crystallization step (S1) and / or a heat treatment step (S2) as shown in FIGS. 2(A) and 2(B).

[0080] The nickel composite hydroxide obtained in the crystallization step (S1) may contain, as elements other than the hydroxyl group (OH), nickel (Ni) and at least one element M (a general term for elements M1, M2, M3) selected arbitrarily from Co, Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. Note that at least a part of the element M may be added in a solid phase in the mixing step (S10).

[0081] For example, when producing a positive electrode active material containing a lithium nickel composite oxide having the above substance amount ratio A, the nickel composite hydroxide obtained in the crystallization step (S1) contains, as elements other than the hydroxyl group (OH), nickel (Ni), manganese (Mn), and at least one element M1 selected arbitrarily from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The molar ratio of each element is preferably represented by Ni:Mn:M1 = (1 - x1 - y1):x1:y1 (where (1 - x1 - y1) < 0.80, 0.03 ≤ x1 ≤ 0.35, 0 ≤ y1 ≤ 0.35). Note that at least a part of the element M1 may be added in a solid phase in the mixing step (S10). Also, for example, when producing a positive electrode active material containing a lithium nickel composite oxide having the above substance amount ratio B, the nickel composite hydroxide obtained in the crystallization step (S1) contains, as elements other than the hydroxyl group (OH), nickel (Ni), manganese (Mn), and at least one element M2 selected arbitrarily from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The molar ratio of each element is preferably represented by Ni:Mn:M2 = (1 - x2 - y2):x2:y2 (where 0.88 < (1 - x2 - y2), 0.01 < x2 ≤ 0.12, 0 ≤ y2 ≤ 0.11). Note that at least a part of the element M2 may be added in a solid phase in the mixing step (S10). Further, for example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-described molar ratio C, the nickel composite hydroxide obtained in the crystallization step (S1) contains, as elements other than the hydroxyl group (OH), nickel (Ni), cobalt (Co), aluminum (Al), and optionally at least one element M3 selected from Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, and Zr, and the molar ratio of each element is preferably represented as Ni:Co:Al:M3 = (1 - x3 - y3 - z3):x3:y3:z3 (where 0.01 ≤ x3 ≤ 0.25, 0.005 ≤ y3 ≤ 0.15, 0 ≤ z3 ≤ 0.15). Note that at least a part of the element M3 may be added in a solid phase in the mixing step (S10).

[0082] The crystallization step (S1) can be carried out by a known crystallization method as long as a nickel composite hydroxide having the above-described molar ratio (molar ratio) can be obtained. Hereinafter, an example of the crystallization step (S1) for obtaining a nickel composite hydroxide by crystallization will be described.

[0083] For example, in a reaction vessel, while stirring a mixed aqueous solution containing at least nickel and element M at a constant rate, a neutralizing agent is added to form a reaction aqueous solution, and the pH of the reaction aqueous solution is controlled by neutralization to generate a nickel composite hydroxide by coprecipitation.

[0084] As the mixed aqueous solution containing nickel and element M, for example, a sulfate solution, a nitrate solution, a chloride solution, etc. of nickel and element M can be used. Note that after separately preparing an aqueous solution containing nickel and an aqueous solution containing element M, they may be respectively supplied into the reaction vessel to form a mixed aqueous solution containing nickel and element M.

[0085] The composition of the metal elements contained in the mixed aqueous solution substantially coincides with the composition of the metal elements contained in the obtained nickel composite hydroxide. Therefore, the composition of the metal elements in the mixed aqueous solution can be adjusted to be the same as the composition of the metal elements of the target nickel composite hydroxide.

[0086] As the neutralizing agent, an alkaline aqueous solution can be used. For example, sodium hydroxide, potassium hydroxide, etc. can be used.

[0087] In addition, it is preferable to add a complexing agent to the reaction aqueous solution together with the neutralizing agent. The complexing agent is not particularly limited as long as it can form a complex by binding to nickel ions and other metal ions in the reaction aqueous solution in the reaction tank, and known ones can be used. For example, an ammonium ion donor can be used. The ammonium ion donor is not particularly limited, but 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.

[0088] In the crystallization step (S1), when the complexing agent is not used, the temperature of the reaction aqueous solution (liquid temperature) is preferably in the range exceeding 60°C and not exceeding 80°C, and the pH of the reaction aqueous solution at the above temperature is preferably 10 or more and 12 or less (based on 25°C). When the pH of the reaction aqueous solution exceeds 12, the obtained nickel composite hydroxide becomes fine particles, and the filterability deteriorates, and spherical particles may not be obtained. On the other hand, when the pH of the reaction aqueous solution is less than 10, the production rate of the nickel composite hydroxide becomes extremely slow, Ni remains in the filtrate, the precipitation amount of Ni deviates from the target composition, and a nickel composite hydroxide with the target ratio may not be obtained.

[0089] In addition, when the temperature of the reaction aqueous solution exceeds 60°C, the solubility of Ni increases, the precipitation amount of Ni deviates from the target composition, and the phenomenon of non-coprecipitation can be avoided. On the other hand, when 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, crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration increases, etc., and the charge-discharge capacity of the positive electrode active material may decrease.

[0090] In the crystallization process (S1), when using a complexing agent such as an ammonium ion donor, the temperature of the reaction aqueous solution is preferably 30°C or higher and 60°C or lower because the solubility of Ni in the reaction aqueous solution increases. Also, the pH of the reaction aqueous solution is preferably 10 or higher and 13 or lower (based on 25°C), more preferably 12 or higher and 13 or lower.

[0091] In addition, the ammonia concentration in the reaction aqueous solution is preferably maintained at a constant value within the range of 3 g / L or higher and 25 g / L or lower. When the ammonia concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, so primary particles of a composite hydroxide with a regular shape and particle size may not be formed. Also, since gel-like nuclei are likely to be generated, the particle size distribution of the obtained nickel composite hydroxide is likely to broaden. 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 nickel composite hydroxide are likely to occur. Note that when the ammonia concentration fluctuates, the solubility of metal ions fluctuates and uniform hydroxide particles are not formed, so it is preferable to maintain it at a constant value. For example, the ammonia concentration is preferably maintained at a desired concentration with a width between the upper and lower limits of about 5 g / L.

[0092] When the nickel composite hydroxide obtained by crystallization contains at least one element M selected from Co, Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, the method of incorporating element M into the nickel composite hydroxide is not particularly limited, and known methods can be used. For example, from the perspective of improving productivity, a mixed solution containing nickel and element M may be prepared in advance and then added to the reaction tank, or an aqueous solution containing element M may be added to the aqueous solution containing nickel in the reaction tank to coprecipitate a nickel composite hydroxide containing element M.

[0093] Examples of the aqueous solution containing element M include aqueous solutions containing cobalt sulfate, manganese sulfate, vanadium oxychloride, vanadium oxy 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, aluminum sulfate, sodium aluminate, and the like.

[0094] Also, from the viewpoint of optimizing the crystallization conditions to facilitate the control of the composition ratio, after obtaining the nickel composite hydroxide by the crystallization step (S1), a step of coating the obtained nickel composite hydroxide with element M may be provided. The method for coating element M is not particularly limited, and known methods can be used.

[0095] An example of the method for coating element M will be described below. First, the nickel composite hydroxide obtained by crystallization is dispersed in pure water to form a slurry. Next, an aqueous solution containing element M corresponding to the target coating amount is mixed with this slurry, and a neutralizing agent (acid or alkali) is added dropwise and adjusted to a predetermined pH. Examples of the acid include sulfuric acid, hydrochloric acid, nitric acid, etc. Examples of the alkali include sodium hydroxide, potassium hydroxide, etc. Then, after mixing the slurry for a predetermined time, the slurry is filtered and dried to obtain a nickel composite hydroxide coated with element M. In addition, other coating methods include a spray drying method in which a solution containing a compound containing element M is sprayed onto the nickel composite hydroxide and then dried, and a method in which a solution containing a compound containing element M is impregnated into the nickel composite hydroxide.

[0096] In addition, the method of incorporating element M into the nickel composite hydroxide may include one or both of mixing element M into the above mixed aqueous solution and coating the nickel composite hydroxide with element M. For example, 1) the nickel composite hydroxide crystallized by adding an alkaline aqueous solution to a mixed aqueous solution containing nickel (excluding element M) may be coated with element M, or 2) a mixed aqueous solution containing nickel and a part of element M may be prepared, the nickel composite hydroxide (containing element M) may be co-precipitated, and the co-precipitate may be further coated with element M to adjust the content of M.

[0097] In addition, the crystallization step (S1) may use 1) a production method by batch crystallization (batch crystallization method) or 2) a production method by 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 steady state, filtered, and washed with water to obtain the nickel composite hydroxide. In the case of the continuous crystallization method, a mixed aqueous solution, an alkaline aqueous solution, and in some cases, an aqueous solution containing an ammonium ion donor can be continuously supplied, overflowed from the reaction tank to collect the precipitate, filtered, and washed with water to obtain the nickel composite hydroxide.

[0098] In the method for producing a positive electrode active material according to the present embodiment, from the viewpoint of obtaining a positive electrode active material that exhibits a high volume energy density when used in a secondary battery, it is preferable to use the continuous crystallization method. In the production by continuous crystallization, a positive electrode active material with a high variation index, a broad particle size distribution, and high fillability can be easily obtained. In addition, the continuous crystallization method has higher productivity than the batch crystallization method and is suitable for industrial-scale production.

[0099] [Heat treatment step (S2)] The nickel composite compound may be obtained by a method further comprising a heat treatment step (S2) after the crystallization step (S1). The heat treatment step (S2) is a step of removing at least a part of the moisture contained in the nickel composite hydroxide by heat treatment. When the heat treatment step (S2) is provided, by removing at least a part of the moisture remaining in the nickel composite hydroxide, it is possible to prevent variations in Li / Me of the positive electrode active material obtained in the firing step (step S20) described later.

[0100] In the heat treatment step (S2), it is sufficient to remove the moisture in the nickel composite hydroxide to such an extent that no variation occurs in Li / Me of the positive electrode active material. However, from the viewpoint of further reducing the variation in Li / Me, it is preferable to sufficiently oxidize the nickel composite hydroxide to convert it to a nickel composite oxide. Note that it is not necessary to convert all of the nickel composite hydroxide to a nickel composite oxide.

[0101] Further, when the heat treatment step (S2) is provided, at least one of the nickel composite hydroxide and the nickel composite oxide obtained by the heat treatment step (S2) can be used as the nickel composite compound in the mixing step (S10). Further, when the nickel composite hydroxide contains element M, a compound containing element M may be coated on the nickel composite hydroxide and then the heat treatment step (S2) may be performed, or a compound containing element M may be coated on at least one of the nickel composite hydroxide and the nickel composite oxide obtained by the heat treatment step (S2).

[0102] The heat treatment may be carried out by heating under conditions where the residual moisture in the nickel composite hydroxide is removed. For example, the temperature of the heat treatment is preferably 105°C or higher and 700°C or lower. When the nickel composite hydroxide is heated at 105°C or higher, at least a part of the residual moisture can be easily removed. If the temperature of the heat treatment is less than 105°C, it takes a long time to remove the residual moisture, which is not industrially appropriate. On the other hand, when the temperature of the heat treatment exceeds 700°C, the particles converted to nickel composite oxide may sinter and aggregate. For example, when most of the nickel composite hydroxide is converted to nickel composite oxide, the temperature of the heat treatment is preferably 350°C or higher and 700°C or lower.

[0103] The atmosphere of the heat treatment is not particularly limited. For example, from the viewpoint of easy operation, the air flow is preferable. Also, the time of the heat treatment is not particularly limited and can be, for example, 1 hour or longer. When the time of the heat treatment is less than 1 hour, the removal of the residual moisture in the particles of the nickel composite hydroxide may not be sufficient. Also, the time of the heat treatment is preferably 5 hours or longer and 15 hours or shorter. Also, the equipment used for the heat treatment is not particularly limited as long as it can heat the nickel composite hydroxide in an air flow. For example, a blow dryer, an electric furnace without gas generation, etc. can be preferably used.

[0104] In addition, in FIG. 2(B), the nickel composite hydroxide after the crystallization step (S1) is heat-treated, but the nickel composite hydroxide obtained in steps other than the crystallization step (S1) may also be heat-treated. Even in this case, by removing at least a part of the moisture in the nickel composite hydroxide, the above-described effects can be obtained.

[0105] [Mixing step (S10)] As shown in FIG. 1, the mixing step (S10) is a step of mixing at least a nickel composite compound, a titanium compound, a niobium compound, and a lithium compound to obtain a mixture. In the mixing step (S10), in addition to the above compounds, a compound containing element M may be mixed. In the mixing step (S10), each compound can be added and mixed, for example, in powder (solid phase). Each material will be described below.

[0106] (Nickel composite compound) The nickel composite compound used in the mixing step (S10) contains, as elements other than hydrogen (H) and oxygen (O), nickel (Ni) and at least one element M selected arbitrarily from Co, Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The nickel composite compound may be at least one of a hydroxide and an oxide.

[0107] For example, when producing a positive electrode active material containing a lithium nickel composite oxide having the above substance amount ratio A, the nickel composite compound contains, as elements other than hydrogen (H) and oxygen (O), nickel (Ni), manganese (Mn), and at least one element M1 selected arbitrarily from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. It is preferable that the ratio of the amount of substances of each element is represented by Ni:Mn:M1 = (1 - x1 - y1):x1:y1 (where (1 - x1 - y1) < 0.80, 0.03 ≤ x1 ≤ 0.35, 0 ≤ y1 ≤ 0.35).

[0108] Further, for example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-described molar ratio B, the nickel composite compound contains, as elements other than hydrogen (H) and oxygen (O), nickel (Ni), manganese (Mn), and optionally at least one element M2 selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, and the molar ratio of each element is preferably represented as Ni:Mn:M2 = (1 - x2 - y2):x2:y2 (where 0.88 < (1 - x2 - y2), 0.01 < x2 ≤ 0.12, 0 ≤ y2 ≤ 0.11). Note that at least a part of the element M2 may be added in a solid phase in the mixing step (S10).

[0109] Further, for example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-described molar ratio C, the nickel composite compound contains, as elements other than hydrogen (H) and oxygen (O), nickel (Ni), cobalt (Co), aluminum (Al), and optionally at least one element M3 selected from Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, and Zr, and the molar ratio of each element is preferably represented as Ni:Co:Al:M3 = (1 - x3 - y3 - z3):x3:y3:z3 (where 0.01 ≤ x3 ≤ 0.25, 0.005 ≤ y3 ≤ 0.15, 0 ≤ z3 ≤ 0.15).

[0110] Since the content (composition) of each element (Ni, M) in the nickel composite compound is substantially maintained even in the particles of the lithium nickel composite oxide, the content of each element (Ni, M) is preferably in the same range as the content in the above-described lithium nickel composite oxide. Note that the nickel composite compound used in the present embodiment may contain a small amount of elements other than the above-described elements (Ni, M), hydrogen, and oxygen as long as the effects of the present invention are not inhibited.

[0111] As the nickel composite compound, as described above, the nickel composite hydroxide obtained by the crystallization step (S1) may be used, or at least one of the nickel composite hydroxide obtained by the heat treatment step (S2) and the nickel composite oxide may be used. Note that the nickel composite compound can be obtained by the crystallization step (S1) and / or the heat treatment step (S2), but it may also be obtained by other methods.

[0112] Further, when the nickel composite compound contains manganese as the element M, it is preferable that nickel and manganese are uniformly contained in the particles. For example, when a mixture obtained by separately mixing nickel hydroxide particles and a manganese compound, nickel hydroxide particles coated with a manganese compound, etc. are used as raw materials, the distribution of manganese in the obtained positive electrode active material becomes non-uniform, and the effect obtained by containing manganese may not be sufficiently obtained.

[0113] (Titanium compound) As the titanium compound, known compounds containing titanium can be used. For example, titanium oxide, titanium sulfate, titanium tetrabromide, titanium tetrachloride, titanium silicide, etc. can be used. Note that one type of titanium compound may be used, or two or more types may be used.

[0114] Among these, titanium oxide is preferable from the viewpoints of easy availability and avoiding contamination of impurities into the lithium nickel composite oxide. Note that when impurities are mixed into the lithium nickel composite oxide, it may cause a decrease in the thermal stability, battery capacity, and cycle characteristics of the obtained secondary battery.

[0115] The titanium compound is preferably mixed in the form of particles (solid phase). When adding titanium in the solid phase, since the reactivity in the firing step (S20) changes depending on the particle size of the titanium compound, the particle size of the titanium compound used is one of the important factors. 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 even more preferably 0.08 μm or more and 1 μm or less. When the average particle size is less than 0.01 μm, problems such as very difficult handling of the powder may occur, and in the mixing step (S10) and the firing step (S20), the titanium compound may scatter, and it may not be possible to add the desired composition to the active material. On the other hand, when the average particle size is greater than 5 μm, titanium may not be uniformly distributed in the lithium nickel composite oxide after firing, and the battery capacity may decrease. The average particle size is the volume average particle size (Mv), and can be obtained, for example, from the volume integration value measured by a laser light diffraction scattering type particle size distribution analyzer.

[0116] The titanium compound may be pulverized in advance using various pulverizers such as a ball mill, a planetary ball mill, a jet mill / nano jet mill, a bead mill, and a pin mill so as to have a particle size within the above range. Further, the titanium compound may be classified by a dry classifier or sieving as necessary. For example, particles close to 1 μm can be obtained using a dry classifier.

[0117] (Niobium compound) As the niobium compound, known compounds containing niobium can be used. For example, niobic acid, niobium oxide, niobium nitrate, niobium pentachloride, niobium nitrate, etc. can be used. Among these, from the viewpoints of easy availability and avoiding contamination of impurities into the lithium nickel composite oxide, niobium oxide, niobic acid, or a mixture thereof is preferable. When impurities are mixed into the lithium nickel composite oxide, it may cause a decrease in the thermal stability, battery capacity, and cycle characteristics of the resulting secondary battery.

[0118] The niobium compound is preferably mixed in the form of particles (solid phase). When adding niobium in the solid phase, due to the change in reactivity during the subsequent firing process (step S20) depending on the particle size of the niobium compound, the particle size of the niobium compound used becomes one of the important factors. The average particle size of the niobium compound is preferably 0.01 μm or more and 20 μm or less, more preferably 0.08 μm or more and 5 μm or less, and even more preferably 0.10 μm or more and 3 μm or less. When the average particle size is less than 0.01 μm, there are problems such as very difficult handling of the powder, and in the mixing process (S10) and the firing process (S20), the niobium compound may scatter, and the problem may occur that the desired composition cannot be added to the active material. On the other hand, when the average particle size is greater than 10 μm, Nb may not be uniformly distributed in the lithium nickel composite oxide after firing, and the thermal stability may not be ensured. The average particle size is the volume average particle size (Mv), and can be obtained, for example, from the volume integration value measured by a laser light diffraction scattering type particle size distribution meter.

[0119] The niobium compound may be preliminarily pulverized using various pulverizers such as a ball mill, a planetary ball mill, a jet mill - nano jet mill, a bead mill, a pin mill, etc. so as to have a particle size within the above range. Further, the niobium compound may be classified using a dry classifier or sieving as necessary. For example, particles with an average particle size close to 0.05 μm can be obtained using a dry classifier.

[0120] (Compound containing element M) As the compound containing element M, known compounds containing element M can be used. For example, cobalt oxide, manganese oxide, vanadium pentoxide, magnesium oxide, molybdenum oxide, calcium oxide, calcium carbonate, chromium oxide, tantalum pentoxide, sodium carbonate, tungsten trioxide, iron oxide, zinc oxide, boric acid, boron oxide, silicon oxide, phosphoric acid, zirconium oxide, etc. can be used. When impurities are mixed into the lithium nickel composite oxide, it may cause a decrease in the thermal stability, battery capacity, and cycle characteristics of the resulting secondary battery.

[0121] Note that the element M may be mixed in the form of particles (solid phase) using a compound containing the element M, or may be incorporated into the nickel composite compound in the crystallization step (S1) described above. When adding the compound containing the element M in the solid phase, since the reactivity in the subsequent firing step (step S20) changes depending on the particle size of the compound containing the element M, it is preferable to appropriately adjust the particle size of the compound containing the element M to be used. Further, when mixing the compound containing the element M in the mixing step (S10), it is preferable to mix the compound containing the element M so that the total amount of the nickel composite compound and the element M contained in the compound containing the element M falls within the range of the molar ratio of the element M in the above-described lithium nickel composite compound.

[0122] The compound containing the element M may be pulverized in advance using various pulverizers such as a ball mill, a planetary ball mill, a jet mill / nano jet mill, a bead mill, or a pin mill so as to have a particle size within the above range. Further, the compound containing the element M may be classified as necessary by a dry classifier or sieving.

[0123] (Lithium compound) 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 these, lithium carbonate, lithium hydroxide, or a mixture thereof is preferable from the viewpoint of having less influence of residual impurities and dissolving at the firing temperature.

[0124] (Mixing method) The mixing method of the above compounds is not particularly limited, as long as these particles are sufficiently mixed to the extent that the skeletons of these particles are not destroyed. As the mixing method, for example, it can be mixed using a general mixer, for example, it can be mixed using a shaker mixer, a Lodige mixer, a Julia mixer, a V blender, or the like. It should be noted that it is preferable to mix the titanium mixture sufficiently before the firing step described later. If the mixing is not sufficient, problems such as variations in the molar ratio of Li to elements other than Li (Me: in this embodiment, Me = Ni + element M + Ti + Nb) among the individual particles of the positive electrode active material and failure to obtain sufficient battery characteristics may occur.

[0125] The lithium compound is mixed so that Li / Me in the mixture is 0.95 or more and 1.25 or less. That is, it is mixed so that Li / Me in the mixture is the same as Li / Me in the obtained lithium nickel composite oxide. This is because the molar ratio of Li / Me and each element does not change before and after the firing step (S20), so Li / Me of the mixture in this mixing step (S10) is the same as Li / Me of the lithium nickel composite oxide before water washing. When the subsequent water washing step (S30) is carried out, since a part of the excess lithium component present on the surface of the lithium nickel composite oxide dissolves in water, the Li / Me ratio may decrease compared to the lithium nickel composite oxide after the firing step (S20). The decrease width of this Li / Me ratio varies depending on the composition and physical properties of the lithium nickel composite oxide and the water washing conditions, but in an example of the manufacturing method according to this embodiment, it decreases by approximately 0.02 due to the water washing step (S30).

[0126] In addition, the mixing amounts of the titanium compound and the niobium compound are adjusted so that the ratio (b) of the amount of titanium to the total amount of the above elements excluding lithium and the ratio (c) of the amount of niobium satisfy 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03, (b + c) ≤ 0.06, and b > c. Also, in the mixture, the ratio (c) of the amount of niobium may be 0.002 ≤ c ≤ 0.03.

[0127] In addition, since the contents (ratios) of niobium (Nb) and titanium (Ti) in the mixture are almost maintained even in the lithium nickel composite oxide, the mixing amounts of the niobium compound and the titanium compound are preferably in the same range as the contents of niobium and titanium in the above-described lithium nickel composite oxide.

[0128] [Firing Step (S20)] The firing step (S20) is a step of firing the mixture obtained in the mixing step (S10) to obtain a lithium nickel composite oxide.

[0129] When the mixture is fired, lithium in the lithium compound diffuses into the nickel composite compound, so that a lithium nickel composite oxide composed of particles having a polycrystalline structure is formed. The lithium compound melts at the temperature during firing and penetrates into the nickel composite compound to form a lithium nickel composite oxide. The lithium compound melts at the temperature during firing and penetrates into the nickel composite compound to form a lithium nickel composite oxide. At this time, niobium and titanium contained in the lithium mixture are considered to penetrate into the secondary particles together with the melted lithium compound and also penetrate into the primary particles if there are grain boundaries or the like.

[0130] The firing atmosphere is preferably an oxidizing atmosphere, more preferably an oxygen concentration of 80% by volume or more and 100% by volume or less, and even more preferably an oxygen concentration of 90% by volume or more and 100% by volume or less. In a lithium nickel composite oxide with a high nickel ratio, so-called cation mixing occurs in which transition metal elements such as Ni are arranged at Li sites in the layered compound. In addition, the crystallinity of the layered compound decreases, and disorder in the atomic distribution easily occurs. Due to these structural disorders, titanium or the like cannot be uniformly dissolved in the Me site (transition metal element site), and it is considered that the battery capacity decreases. On the other hand, when firing is performed in the above oxygen concentration range, it is possible to obtain a positive electrode active material that improves thermal stability while maintaining a high battery capacity and achieves both a high battery capacity and thermal stability. The oxidizing atmosphere means an atmosphere containing oxygen equal to or more than the atmospheric atmosphere.

[0131] For example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-mentioned molar ratio A, the firing temperature is preferably 750°C or higher and 1100°C or lower in an oxidizing atmosphere, more preferably 800°C or higher and 1000°C or lower. When firing at the above temperature, melting of the lithium compound occurs, promoting the penetration and diffusion of titanium. Further, the lithium mixture can have a higher firing temperature by containing manganese. Also, the crystallinity of the lithium nickel composite oxide increases, enabling further improvement of the battery capacity.

[0132] Also, for example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-mentioned molar ratio B and molar ratio C, the firing temperature is preferably 750°C or higher and 1000°C or lower in an oxidizing atmosphere, more preferably 750°C or higher and 950°C or lower. When firing at the above temperature, melting of the lithium compound occurs, promoting the penetration and diffusion of titanium. Also, the crystallinity of the lithium nickel composite oxide increases, enabling further improvement of the battery capacity.

[0133] The firing temperature can be appropriately adjusted within the above range. By increasing the firing temperature, the diffusion of titanium and niobium is promoted. Also, when the lithium mixture contains manganese, the firing temperature can be increased.

[0134] On the other hand, when the firing temperature is lower than the above range, the diffusion of lithium, titanium, and niobium into the nickel composite compound is insufficient, and problems such as remaining excess lithium or unreacted particles, or an insufficiently ordered crystal structure, result in failure to obtain sufficient battery characteristics. Also, when the firing temperature exceeds the above range, intense sintering occurs between the particles of the formed lithium nickel composite oxide, and abnormal grain growth may occur. When abnormal grain growth occurs, the particles after firing become coarse, resulting in reduced packing density when forming the positive electrode active material, as well as increased reaction resistance due to disorder of the crystal structure and decreased discharge capacity.

[0135] The firing time is preferably 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 production of the lithium nickel composite oxide may not be sufficiently carried out. Further, the furnace used for firing is not particularly limited, and any furnace that can fire the titanium mixture in an oxygen stream may be used, but it is preferable to use an electric furnace without gas generation, and either a batch type or a continuous type furnace can be used.

[0136] The lithium nickel composite oxide obtained after firing has a volume resistivity when compressed to 3.5 g / cm 3 higher than that of the positive electrode active material produced under the same conditions except that titanium and niobium are not added, as determined by the measurement of the compacted powder resistance. Usually, the higher the conductivity of the positive electrode active material, the better the active material with lower resistance in the electrochemical reaction is considered. However, considering the thermal stability during short circuit, an appropriately high volume resistivity can suppress the sudden generation of current during short circuit. Further, the lithium nickel composite oxide obtained after firing may have a volume resistivity, for example, 5 times or more higher than that of the positive electrode active material produced under the same conditions except that niobium is not added. Note that since the volume resistivity is a value that varies depending on the composition of the lithium nickel composite oxide, the suitable range may differ depending on the composition.

[0137] For example, in the lithium nickel composite oxide having the above substance amount ratio A, the volume resistivity when compressed to 3.5 g / cm 3 is preferably 1.0×10 3 Ω·cm or more and 1.0×10 5 Ω·cm or less, more preferably 1.0×10 3 Ω·cm or more and 1.0×10 4 Ω·cm or less, and more preferably 1.0×10 3 Ω·cm or more and 5.0×10 3 Ω·cm or less. When the volume resistivity of the above positive electrode active material is within the above range, high thermal stability during short circuit can be obtained.

[0138] Further, for example, in the lithium nickel composite oxide having the above substance quantity ratio B, the volume resistivity when compressed to 3.5 g / cm 3 is preferably 1.0×10 2 Ω·cm or more and 1.0×10 5 Ω·cm or less, more preferably 1.0×10 2 Ω·cm or more and 1.0×10 4 Ω·cm or less, and even more preferably 1.0×10 2 Ω·cm or more and 5.0×10 3 Ω·cm or less. When the volume resistivity of the above positive electrode active material is within the above range, high thermal stability during short circuit can be obtained.

[0139] Further, for example, in the lithium nickel composite oxide having the above substance quantity ratio C, the volume resistivity when compressed to 3.5 g / cm 3 is preferably 5.0×10 2 Ω·cm or more and 1.0×10 5 Ω·cm or less. When the volume resistivity of the above positive electrode active material is within the above range, high thermal stability during short circuit can be obtained.

[0140] Note that the volume resistivity can be obtained, for example, by weighing the positive electrode active material within the range of 4.5 g or more and 5.5 g or less, pressure molding it into a cylindrical shape with a diameter of 20 mm so as to be 3.5 g / cm 3 , and then measuring it by a resistivity test method using a four-probe method conforming to JIS K 7194:1994 in the pressurized state.

[0141] [Calcination] Note that the firing step (S20) may further include a pre-firing step at a temperature lower than the firing temperature before firing at the temperature within the above range. The pre-firing is preferably performed at a temperature at which the lithium compound in the mixture can melt and react with the nickel composite compound. The pre-firing temperature can be, for example, 350°C or higher and lower than the firing temperature. Also, the lower limit of the pre-firing temperature is preferably 400°C or higher. By holding (pre-firing) the mixture within the above temperature range, the lithium compound penetrates into the nickel composite compound, sufficient diffusion of lithium occurs, and a uniform lithium nickel composite oxide can be obtained. For example, when using lithium hydroxide as the lithium compound, the pre-firing is preferably performed by holding at a temperature of 400°C or higher and 550°C or lower for about 1 hour or more and 10 hours or less.

[0142] [Crushing] Note that the lithium nickel composite oxide obtained after the firing step (S20) has suppressed sintering between particles, but may form coarse particles due to weak sintering or aggregation. In such a case, the sintering and aggregation can be eliminated by crushing to adjust the particle size distribution.

[0143] [Washing step (S30)] The washing step (S30) is a step of mixing the lithium nickel composite oxide obtained in the firing step (S20) with water, stirring (hereinafter referred to as "water stirring"), and then performing solid-liquid separation.

[0144] The manufacturing method according to the present embodiment includes the washing step (S30) and the drying step (S40) described later, thereby improving the crystallinity of the positive electrode active material and the discharge capacity. Although the details are not clear, for example, when lithium in the positive electrode active material is extracted by water stirring, it is considered that the disorder of the atomic arrangement is relaxed, improving the crystallinity of the positive electrode active material and showing a high discharge capacity. Also, by the washing step (S30), the excess lithium component on the surface is dissolved and removed by water, so that the gelation of the positive electrode composite paste during the production of the positive electrode plate of the secondary battery can be suppressed.

[0145] In the water washing step (S30), the amount of water to be mixed is preferably 50 parts by mass or more and 200 parts by mass or less with respect to 150 parts by mass of the lithium nickel composite oxide. When the mixing ratio of water is 200 parts by mass or more, an excessive amount of lithium may be extracted 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 excess lithium components become insufficient, which may cause a decrease in battery capacity and gelation of the positive electrode composite paste. Further, the amount of water to be mixed may be 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the lithium nickel composite oxide.

[0146] The time for water washing is not particularly limited, but for example, it is about 1 minute or more and 2 hours or less, and may be 5 minutes or more and 50 minutes or less.

[0147] After stirring the lithium nickel composite oxide with water, solid-liquid separation is performed to obtain a lithium nickel composite oxide (precipitate). The method of solid-liquid separation is not particularly limited, and a known method can be used. For example, solid-liquid separation can be performed using one or more selected from suction filters such as Nutsche (Buchner funnel), filter presses, centrifuges, etc.

[0148] [Drying step (S40)] The drying step (S40) is a step of drying the lithium nickel composite oxide (precipitate) obtained by the above water washing step (S30) to obtain a powder of the lithium metal composite hydroxide (dry powder).

[0149] The drying conditions are preferably heat treatment at a temperature of 100°C or more and 250°C or less in an oxidizing atmosphere or a vacuum atmosphere. When the drying temperature is 100°C or more, the moisture in the precipitate can be sufficiently evaporated. Also, when the drying temperature is 250°C or less, a compact drying device can be used, which is suitable for industrial-scale implementation.

[0150] In order to avoid the reaction between the moisture and carbon dioxide in the atmosphere and the resulting positive electrode active material during drying, 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 preferably used. Further, from the viewpoint of quickly discharging the water vapor generated by drying, it is preferable to add an exhaust mechanism to the drying device.

[0151] The drying time is not particularly limited, but in order to sufficiently evaporate the moisture in the raw material mixture, it is preferably 0.5 hours or more at the maximum temperature reached during drying. Also, the upper limit of the drying time is preferably 48 hours or less from the viewpoint of productivity.

[0152] 3. Lithium Ion Secondary Battery The lithium ion secondary battery (hereinafter also referred to as "secondary battery") according to the present embodiment includes a positive electrode containing the above-described positive electrode active material, a negative electrode, and a non-aqueous electrolyte. The secondary battery includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. Further, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. Also, the secondary battery may be a secondary battery that performs charge and discharge by the desorption and insertion of lithium ions. For example, it may be a non-aqueous electrolyte secondary battery or an all-solid-state lithium secondary battery. Note that the embodiments described below are merely examples, and the secondary battery according to the present embodiment may be applied to various modified and improved forms based on the embodiments described in this specification.

[0153] [Positive Electrode] Using the above-described positive electrode active material, the positive electrode of the secondary battery is manufactured. An example of the manufacturing method of the positive electrode will be described below.

[0154] First, the above positive electrode active material, conductive material, and binder are mixed, and further, if necessary, activated carbon or a solvent for purposes such as viscosity adjustment is added, and this is kneaded to prepare a positive electrode composite paste. At this time, according to the performance of the target secondary battery, the mixing ratio of each in the positive electrode composite paste can be appropriately adjusted. For example, when the solid content of the positive electrode composite excluding the solvent is 100 parts by mass, the content of the positive electrode active material may be 60 parts by mass or more and 95 parts by mass or less, the content of the conductive material may be 1 part by mass or more and 20 parts by mass or less, and the content of the binder may be 1 part by mass or more and 20 parts by mass or less.

[0155] The obtained positive electrode composite paste is applied, for example, to the surface of a current collector made of aluminum foil, dried to disperse the solvent, and a sheet-shaped positive electrode is produced. If necessary, it may be pressed by a roll press or the like to increase the electrode density. The sheet-shaped positive electrode obtained in this way can be cut to an appropriate size according to the target battery and used for the production of the battery. However, the method for producing the positive electrode is not limited to the above-exemplified one and may rely on other methods.

[0156] As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black-based materials such as acetylene black and ketjen black can be used.

[0157] As the binder, it plays a 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.

[0158] If necessary, the positive electrode active material, conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode composite. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Further, activated carbon can be added to the positive electrode composite to increase the electric double layer capacitance.

[0159] [Negative Electrode] As the negative electrode, metallic lithium, a lithium alloy, or the like may be used. Alternatively, a negative electrode composite material may be used, which is obtained by mixing a negative electrode active material capable of occluding and desorbing lithium ions with a binder, adding an appropriate solvent to form a paste, applying the paste onto the surface of a metal foil current collector such as copper, drying the paste, and compressing it as necessary to increase the electrode density.

[0160] As the negative electrode active material, for example, powders of carbonaceous materials such as natural graphite, artificial graphite, fired products of organic compounds such as phenolic resins, and coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used, similar to the positive electrode. As the solvent for dispersing these active materials and binders, an organic solvent such as N-methyl-2-pyrrolidone can be used.

[0161] [Separator] A separator is disposed between the positive electrode and the negative electrode, sandwiching the separator. 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 having a large number of minute pores can be used.

[0162] [Non-aqueous electrolyte] As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used. The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Alternatively, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an ionic liquid may be used. Note that an ionic liquid refers to a salt composed of cations and anions other than lithium ions and is in a liquid state even at room temperature.

[0163] Examples of the organic solvent include one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, which can be used alone or in combination of two or more.

[0164] Examples of the supporting salt include LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts. Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

[0165] Also, a solid electrolyte may be used as the non-aqueous electrolyte. The solid electrolyte has a property of withstanding a high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

[0166] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0167] The oxide-based solid electrolyte is not particularly limited, and for example, those containing oxygen (O) and having lithium ion conductivity and electron insulation can be preferably used. Examples of the oxide-based solid electrolyte include 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 Ge2-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 One or more selected from the group consisting of O4 and the like can be used.

[0168] The sulfide-based solid electrolyte is not particularly limited. For example, those containing sulfur (S) and having lithium ion conductivity and electron insulation can be preferably used. As the sulfide-based solid electrolyte, for example, one or more selected from the group consisting of 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.

[0169] In addition, as the inorganic solid electrolyte, those other than the above may be used. For example, Li3N, LiI, Li3N-LiI-LiOH, etc. may be used. As the organic solid electrolyte, there is no particular limitation as long as it is a polymer compound exhibiting ion conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt).

[0170] In addition, it is also possible to configure a secondary battery using a solid electrolyte instead of the non-aqueous electrolyte. Since the solid electrolyte does not decompose even at a high potential, there is no gas generation or thermal runaway due to the decomposition of the electrolyte during charging as seen in the non-aqueous electrolyte, and thus it has high thermal stability. Therefore, when used in a lithium ion secondary battery using the positive electrode active material according to the present invention, a secondary battery with higher thermal stability can be obtained.

[0171] [Shape and Configuration of Secondary Battery] The configuration of the secondary battery is not particularly limited, and as described above, it may be composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, etc., or may be composed of a positive electrode, a negative electrode, a solid electrolyte, etc. Further, the shape of the secondary battery is not particularly limited, and it can be made into various shapes such as cylindrical and laminated shapes.

[0172] For example, when the secondary battery is a non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte solution. Connect between the positive electrode current collector and the positive electrode terminal leading to the outside, and between the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead or the like, and seal it in a battery case to complete the secondary battery.

[0173] Note that the secondary battery according to this embodiment is not limited to the form using a non-aqueous electrolyte solution as the non-aqueous electrolyte. For example, a secondary battery using a solid non-aqueous electrolyte, that is, an all-solid-state battery can also be used. In the case of an all-solid-state battery, the configuration other than the positive electrode active material can be changed as necessary.

[0174] The secondary battery according to this embodiment can achieve high thermal stability at low cost. Further, the positive electrode active material used in the secondary battery can be obtained by the above-described industrial production method. In addition, the secondary battery is suitable as a power source for small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity. Further, the secondary battery is excellent not only in capacity but also in durability and thermal stability during overcharging compared with a battery using a conventional positive electrode active material such as lithium cobalt-based oxide or lithium nickel-based oxide. Therefore, since it can be miniaturized and have a high capacity, it is suitable as a power source for electric vehicles that are restricted in mounting space. Note that the secondary battery can be used not only as a power source for electric vehicles that are purely driven by electrical energy, but also as a power source for so-called hybrid vehicles that are used in combination with combustion engines such as gasoline engines and diesel engines.

Examples

[0175] The following further details the present invention by way of examples and comparative examples of the present invention. However, the present invention is not limited in any way by these examples. The various evaluation methods used in the examples and comparative examples are as follows.

[0176] (1) Composition analysis: Measured by ICP emission spectrometry.

[0177] (2) Volume average particle size (Mv) and particle size dispersion index [(D90 - D10) / average volume particle size]: Measured on a volume basis using a laser diffraction scattering particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0178] (3) Concentration of each element The positive electrode active material was processed so that cross-sectional analysis of primary particles by S-TEM was possible. Twenty primary particles were arbitrarily selected from a plurality of secondary particles contained in the positive electrode active material, and the composition of the region (130 nm × 130 nm) including the inside and grain boundaries of each primary particle cross-section was analyzed by point analysis using EDX of S-TEM.

[0179] (4) Amount of eluted lithium: 2 g of the positive electrode active material was taken and put into 125 ml of pure water at room temperature stirred by a stirrer. Immediately after the positive electrode active material was added, neutralization titration was performed using an HCl aqueous solution with a concentration of 1 mol / L. The titration was carried out under the following conditions using an automatic titrator COM-1750 (manufactured by Hiranuma Sangyo Co., Ltd.). Endpoint detection method: Inflection point detection Detection sensitivity: 2500 Burette type number: H-1700 Burette speed: 2 Minimum drop volume: 0.013 mL The titration results were evaluated by the Warder method, lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) were calculated, and the sum of these lithium amounts was calculated as the eluted lithium.

[0180] (5) Specific surface area: Measured by the BET method using nitrogen adsorption with a specific surface area and pore size distribution measuring apparatus (manufactured by Mountech Co., Ltd., model: Macsorb HM1200 series).

[0181] (6) Initial discharge capacity: The initial charge capacity and the initial discharge capacity were measured as follows. After fabricating the coin-type battery CBA shown in Fig. 3 and leaving it standing for about 24 hours, after the open circuit voltage OCV (open circuit voltage) became stable, the current density with respect to the positive electrode was set to 0.1 mA / cm 2 and it was charged up to a cut-off voltage of 4.3 V as the initial charge capacity. After a 1-hour rest, the capacity when discharging to a cut-off voltage of 3.0 V was taken as the initial discharge capacity. For the measurement of the discharge capacity, a multi-channel voltage / current generator (manufactured by Advantest Corporation, R6741A) was used.

[0182] (Fabrication of coin-type battery CBA) 52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm to fabricate a positive electrode PE (evaluation electrode). After drying the fabricated positive electrode PE in a vacuum dryer at 120°C for 12 hours, the 2032-type coin-type battery CBA was fabricated using this positive electrode PE in a glove box with an Ar atmosphere where the dew point was controlled to -80°C. For the negative electrode NE, lithium (Li) metal with a diameter of 17 mm and a thickness of 1 mm was used, and for the electrolyte, an equal-volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Chemical Co., Ltd.) with 1 M LiClO4 as the supporting electrolyte was used. For the separator SE, a polyethylene porous membrane with a film thickness of 25 μm was used. Also, for the coin-type battery CBA, a gasket GA and a wave washer WW were arranged and assembled into a coin-type battery using a positive electrode can PC and a negative electrode can NC.

[0183] (7) Maximum oxygen generation peak intensity The thermal stability of the positive electrode was evaluated by quantifying the amount of oxygen released by heating the positive electrode active material in an overcharged state. A coin-type battery was fabricated in the same manner as in (6) and charged at a 0.05C rate up to a cut-off voltage of 4.3V (constant current-constant voltage charging). Subsequently, the coin-type battery was disassembled, and only the positive electrode was carefully taken out without short-circuiting, washed with DMC (dimethyl carbonate), and dried. Approximately 2 mg of the dried positive electrode was weighed, and using a gas chromatograph mass spectrometer (GCMS, Shimadzu Corporation, QP-2010plus), the temperature was raised from room temperature to 450°C at a heating rate of 10°C / min. Helium was used as the carrier gas. The generation behavior of oxygen (m / z = 32) generated during heating was measured to obtain the maximum oxygen generation peak intensity. The maximum oxygen peak intensity ratios in Tables 2 and 4 are relative values with the peak intensities of Comparative Example 1A and Comparative Example 1B set to 1 (reference) in the oxygen generation behavior when heated from 200°C to 300°C, respectively.

[0184] [Example 1A, Reference Example 1A, Comparative Example 1A] Hereinafter, the characteristics of the positive electrode active material containing the lithium nickel composite oxide satisfying the above substance mass ratio A will be described with reference to Example 1A, Reference Example 1A, and Comparative Example 1A. (Reference Example 1A) [Crystallization step] A predetermined amount of pure water was placed in a reaction tank (60 L), and the temperature inside the tank was set to 45°C while stirring. At this time, N2 gas was flowed into the reaction tank so that the dissolved oxygen concentration in the reaction tank liquid became 0.8 mg / L. Into this reaction tank, a 2.0M mixed aqueous solution of nickel sulfate, manganese sulfate, and cobalt sulfate with a molar ratio of nickel:manganese:cobalt of 55:25:20, a 25 mass% sodium hydroxide solution as an alkaline solution, and 25 mass% aqueous ammonia as a complexing agent were continuously added to the reaction tank simultaneously, and crystallization was performed by the continuous crystallization method.

[0185] At this time, the flow rate was controlled so that the residence time of the mixed aqueous solution was 8 hours, and the pH in the reaction tank was adjusted to 11.2 - 12.0, and the ammonia concentration was adjusted to 10 - 14 g / L. After the reaction tank was stabilized, the slurry containing nickel-manganese-cobalt composite hydroxide was recovered from the overflow port, and then filtration was performed to obtain a cake of nickel-manganese-cobalt composite hydroxide. By passing 1 L of pure water through 140 g of nickel-manganese-cobalt composite hydroxide in the filter, the impurities were washed. The filtered powder was dried to obtain particles of nickel-manganese-cobalt composite hydroxide with the molar ratio of nickel:manganese:cobalt being Ni:Mn:Co = 0.55:0.25:0.20.

[0186] [Mixing step] The obtained particles of nickel-manganese-cobalt composite hydroxide, lithium hydroxide, titanium oxide (TiO2), and niobium acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):titanium:niobium was 1.02:0.973:0.022:0.005, and then thoroughly mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy E. Bachofen (WAB)) to obtain a lithium mixture.

[0187] [Firing step] The obtained lithium mixture was held at 930 °C for 5 hours in an oxygen (oxygen concentration: 90 vol%) stream for firing, and then crushed to obtain particles of lithium nickel manganese cobalt composite oxide.

[0188] [Evaluation] The production conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results of the obtained positive electrode active material are shown in Table 2. Also, the volume resistivity during compression of Reference Example 1 was 1.9×10 3 (Ω·cm). 3 (Ω·cm).

[0189] (Example 1A) 150 parts by mass of a lithium nickel manganese cobalt composite oxide obtained under the same conditions as in Reference Example 1A was mixed with 100 parts by mass of water, and after stirring the water, suction filtration was performed using a Nutsche filter to obtain a precipitate (water washing step). The obtained precipitate was placed in a SUS container and heated to 100 °C for 12 hours and then to 190 °C for 10 hours using a vacuum dryer, and allowed to stand and dry to obtain a positive electrode active material (drying step). Table 1 shows the production conditions of the positive electrode active material, and Tables 2 and 3 show the evaluation results of the obtained positive electrode active material.

[0190] (Comparative Example 1A) In the mixing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A, except that the titanium compound and the niobium compound were not mixed, and the particles of the obtained nickel manganese cobalt composite hydroxide, lithium hydroxide, were weighed so that the molar ratio of lithium:nickel:manganese:cobalt was 1.02:0.554:0.247:0.199.

[0191] [Table 1]

[0192] [Table 2]

[0193] [Table 3]

[0194] [Evaluation Result 1] The positive electrode active material obtained in Example 1A was confirmed to have high thermal stability as compared with the positive electrode active material obtained in Comparative Example 1A. Further, the amount of eluted lithium in the positive electrode active material obtained in Example 1A was 0.07% by mass or less. Furthermore, the positive electrode active material obtained in Example 1A showed a high discharge capacity as compared with Reference Example 1A in which the water washing step and the drying step were not carried out. The titanium concentration at the grain boundary between the primary particles with respect to the titanium concentration inside the primary particles of the positive electrode active materials obtained in Example 1A and Reference Example 1A was 0.8 times or more and 1.1 times or less.

[0195] [Example 1B, Reference Example 1B, Comparative Example 1B] Hereinafter, the characteristics of the positive electrode active material containing the lithium nickel composite oxide satisfying the above substance amount ratio B will be described with reference to Example 1B, Reference Example 1B, and Comparative Example 1B.

[0196] (Reference Example 1B) [Crystallization step] A predetermined amount of pure water was placed in a reaction tank (60 L), and the temperature inside the tank was set to 49 °C while stirring. At this time, N2 gas was flowed into the reaction tank so that the dissolved oxygen concentration in the reaction tank liquid was 0.8 mg / L. A 2.0 M mixed aqueous solution of nickel sulfate, manganese sulfate, and cobalt sulfate, a 25% by mass sodium hydroxide solution as an alkaline solution, and 25% by mass aqueous ammonia as a complexing agent were continuously added to the reaction tank simultaneously so that the molar ratio of nickel:manganese:cobalt was 90:5:5, and crystallization by a continuous crystallization method was carried out.

[0197] At this time, the flow rate was controlled so that the residence time of the mixed aqueous solution was 8 hours, and the pH in the reaction tank was adjusted to 11.6 - 12.4, and the ammonia concentration was adjusted to 10 - 14 g / L. After the reaction tank was stabilized, the slurry containing nickel manganese cobalt composite hydroxide was recovered from the overflow port, and then filtration was performed to obtain a cake of nickel manganese cobalt composite hydroxide. 1 L of pure water was passed through 140 g of nickel manganese cobalt composite hydroxide in the filter to wash the impurities. The filtered powder was dried to obtain particles of nickel manganese cobalt composite hydroxide in which the molar ratio of nickel, manganese, and cobalt was represented as Ni:Mn:Co = 0.90:0.05:0.05.

[0198] [Mixing process] The obtained particles of nickel manganese cobalt composite hydroxide, lithium hydroxide, titanium oxide (TiO2), niobic acid (Nb2O5·4H2O), and zirconium oxide (ZrO2) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):titanium:niobium:zirconium was 1.02:0.982:0.010:0.005:0.003, and then thoroughly mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy E. Bachofen (WAB)) to obtain a lithium mixture.

[0199] [Firing process] The obtained lithium mixture was fired by holding it at 840 °C for 10 hours in an oxygen (oxygen concentration: 90 vol%) stream, and then crushed to obtain particles of lithium nickel manganese cobalt composite oxide (cathode active material).

[0200] [Evaluation] The production conditions of the obtained cathode active material are shown in Table 1, and the evaluation results of the obtained cathode active material are shown in Table 5. Also, for 3.5 g / cm of Reference Example 1 3 The volume resistivity during compression was 2.6×10 2 (Ω·cm).

[0201] (Example 1B) 100 parts by mass of the lithium nickel manganese cobalt composite oxide obtained under the same conditions as in Reference Example 1B was mixed with 150 parts by mass of water, and after stirring the water, suction filtration was carried out using a Nutsche filter to obtain a precipitate (water washing step). The obtained precipitate was placed in a SUS container, heated to 100 °C using a vacuum dryer for 12 hours, heated to 190 °C for 10 hours, and allowed to stand and dry to obtain a positive electrode active material (drying step). The production conditions of the positive electrode active material are shown in Table 4, and the evaluation results of the obtained positive electrode active material are shown in Tables 5 and 6.

[0202] (Comparative Example 1B) In the mixing step, the titanium compound and the niobium compound were not mixed, and the particles of the obtained nickel manganese cobalt composite hydroxide, lithium hydroxide, and zirconium oxide (ZrO2) were weighed so that the molar ratio of lithium:nickel:manganese:cobalt:zirconium was 1.02:0.895:0.050:0.052:0.003. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example B except that the firing temperature was 780 °C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 4 to 7.

[0203]

Table 4

[0204]

Table 5

[0205]

Table 6

[0206] [Evaluation Results 2] The cathode active material obtained in Example 1B was confirmed to have high thermal stability compared with the cathode active material obtained in Comparative Example 1B. Further, the amount of eluted lithium in the cathode active material obtained in Example 1B was 0.20 mass% or less, which was a smaller value than that in Comparative Example 1B and Reference Example 1B. Furthermore, the cathode active material obtained in Example 1B showed a higher discharge capacity compared with Reference Example 1B in which the water washing step and the drying step were not carried out. In addition, the titanium concentration at the grain boundary between primary particles with respect to the titanium concentration inside the primary particles of the cathode active materials obtained in Example 1B and Reference Example 1B was 0.8 times or more and 1.1 times or less.

[0207] [Example 1C, Reference Example 1C, Comparative Example 1C] Hereinafter, the characteristics of the cathode active material containing the lithium nickel composite oxide satisfying the above substance amount ratio C will be described with reference to Example 1C, Reference Example 1C, and Comparative Example 1C.

[0208] (Reference Example 1C) [Crystallization step] A predetermined amount of pure water was placed in a reaction tank (60 L), and the temperature inside the tank was set to 49 °C while stirring. At this time, N2 gas was flowed into the reaction tank so that the dissolved oxygen concentration in the reaction tank liquid became sufficiently low. Into this reaction tank, a 2.0 M mixed aqueous solution of nickel sulfate and cobalt sulfate, an aqueous sodium aluminate solution with a concentration of 10 g / L, a 25 mass% sodium hydroxide solution which is an alkaline solution, and 25 mass% aqueous ammonia as a complexing agent were continuously added simultaneously to the reaction tank, and crystallization by a continuous crystallization method was carried out.

[0209] At this time, the flow rate was controlled so that the residence time of the mixed aqueous solution was 8 hours, and the pH in the reaction tank was adjusted to 11.6 - 12.4 and the ammonia concentration was adjusted to 10 - 14 g / L. After the reaction tank was stabilized, the slurry containing nickel cobalt aluminum composite hydroxide was recovered from the overflow port, and then filtration was performed to obtain a cake of nickel cobalt aluminum composite hydroxide. 1 L of pure water was passed through 140 g of nickel cobalt aluminum composite hydroxide in the filter to wash the impurities. The powder after filtration was dried to obtain particles of nickel cobalt aluminum composite hydroxide in which the molar ratio of nickel, cobalt, and aluminum was represented as Ni:Co:Al = 0.82:0.15:0.03.

[0210] [Mixing step] The obtained particles of nickel cobalt aluminum composite hydroxide, lithium hydroxide, titanium oxide (TiO2), and niobic acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + cobalt + aluminum):titanium:niobium was 1.01:0.973:0.022:0.005, and then sufficiently mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy E. Bachofen (WAB)) to obtain a lithium mixture.

[0211] [Firing step] The obtained lithium mixture was held at 810 °C for 10 hours in an oxygen (oxygen concentration: 90 vol%) stream for firing, and then crushed to obtain particles of lithium nickel cobalt aluminum composite oxide (cathode active material). The manufacturing conditions and evaluation results of the cathode active material are shown in Tables 4 - 6.

[0212] (Example 1C) 100 parts by mass of the lithium nickel cobalt aluminum composite oxide obtained under the same conditions as in Reference Example 1C was mixed with 150 parts by mass of water, and after stirring with water, suction filtration was performed using a Nutsche to obtain a precipitate (water washing step). The obtained precipitate was placed in a SUS container, heated to 100 °C using a vacuum dryer for 12 hours, heated to 190 °C for 10 hours, and allowed to stand and dry to obtain a positive electrode active material (drying step). The production conditions and evaluation results of the positive electrode active material are shown in Tables 7 to 9.

[0213] (Comparative Example 1C) In the mixing step, the titanium compound and the niobium compound were not prepared, and the particles of the obtained nickel cobalt aluminum composite hydroxide and lithium hydroxide were weighed so that the molar ratio of lithium:nickel:cobalt:aluminum was 1.02:0.817:0.147:0.036. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example C except that the firing temperature was 760 °C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 7 to 9.

[0214] [Table 7]

[0215] [Table 8]

[0216] [Table 9]

[0217] [Evaluation Result 3] The positive electrode active material obtained in Example 1C was confirmed to have high thermal stability as compared with the positive electrode active material obtained in Comparative Example 1C. Further, the amount of eluted lithium in the positive electrode active material obtained in Example 1C was 0.25 mass% or less, which was a smaller value than that in Comparative Example 1C and Reference Example 1C. Furthermore, the positive electrode active material obtained in Example 1C exhibited a higher discharge capacity as compared with Reference Example 1C in which the water washing step and the drying step were not carried out. The titanium concentration at the grain boundary between primary particles with respect to the titanium concentration inside the primary particles of the positive electrode active materials obtained in Example 1C and Reference Example 1C was 0.8 times or more and 1.1 times or less.

Industrial Applicability

[0218] In the present embodiment, a positive electrode active material for a lithium ion secondary battery having high thermal stability and excellent battery characteristics can be obtained by an industrial production method. This lithium ion secondary battery is suitable as a power source for small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity.

[0219] In addition, the secondary battery using the positive electrode active material according to the present embodiment is excellent in thermal stability and also excellent in terms of capacity even in comparison with a battery using a positive electrode active material of a conventional lithium nickel-based oxide. Therefore, since it can be miniaturized, it is suitable as a power source for electric vehicles that are restricted in mounting space.

[0220] In addition, the secondary battery using the positive electrode active material according to the present embodiment can be used not only as a power source for electric vehicles that are purely driven by electric energy, but also as a power source for so-called hybrid vehicles that are used in combination with combustion engines such as gasoline engines and diesel engines, or as a stationary battery.

[0221] Note that the technical scope of the present invention is not limited to the aspects described in the above embodiments and the like. One or more of the requirements described in the above embodiments and the like may be omitted. Also, the requirements described in the above embodiments and the like can be combined as appropriate. Further, to the extent permitted by law, the contents of Japanese Patent Application Nos. 2019-127260 and 2020-100828, which are Japanese patent applications, and all the documents cited in this specification are incorporated by reference and made part of the description of the present text.

Explanation of Reference Numerals

[0222] CBA... Coin-type battery (for evaluation) PE... Positive electrode (electrode for evaluation) NE... Negative electrode SE... Separator GA... Gasket WW... Wave washer PC... Positive electrode can NC... Negative electrode can G... Gap

Claims

1. A positive electrode active material for a lithium-ion secondary battery, comprising a lithium nickel composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated, wherein the lithium nickel composite oxide contains lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and optionally at least one element M1 selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, the molar ratio of each of the elements is represented by Li:Ni:Mn:M1:Ti:Nb = a:(1 - x1 - y1 - b - c):x1:y1:b:c (where 0.95 ≤ a ≤ 1.25, (1 - x1 - y1 - b - c) < 0.80, 0.03 ≤ x1 ≤ 0.35, 0 ≤ y1 ≤ 0.35, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03), in the molar ratio, (b + c) ≤ 0.06 and b > c are satisfied, the amount of lithium eluted in water when immersed in water is 0.07% by mass or less based on the total positive electrode active material, the niobium concentration at the grain boundaries between the primary particles is 1.3 times or more the niobium concentration inside the primary particles of the lithium nickel composite oxide determined by point analysis using STEM-EDX, the titanium concentration at the grain boundaries between the primary particles is less than 1.3 times the titanium concentration inside the primary particles of the lithium nickel composite oxide determined by point analysis using STEM-EDX, a positive electrode active material for a lithium-ion secondary battery.

2. A positive electrode active material for a lithium-ion secondary battery, comprising a lithium nickel composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated, wherein the lithium nickel composite oxide contains lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and optionally at least one element M2 selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, The molar ratio of each of the above elements is Li:Ni:Mn:M2:Ti:Nb = a:(1 - x2 - y2 - b - c):x2:y2:b:c (where 0.95 ≤ a ≤ 1.25, 0.880 < (1 - x2 - y2 - b - c), 0.01 ≤ x2 ≤ 0.113, 0 ≤ y2 ≤ 0.103, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03), in the molar ratio, (b + c) ≤ 0.06 and b > c are satisfied, when immersed in water, the amount of lithium eluted into water is 0.20% by mass or less based on the entire positive electrode active material, the niobium concentration at the grain boundaries between the primary particles is 1.3 times or more the niobium concentration inside the primary particles of the lithium nickel composite oxide determined by point analysis using STEM-EDX, the titanium concentration at the grain boundaries between the primary particles is less than 1.3 times the titanium concentration inside the primary particles of the lithium nickel composite oxide determined by point analysis using STEM-EDX, A positive electrode active material for a lithium ion secondary battery.

3. A positive electrode active material for a lithium ion secondary battery, comprising a lithium nickel composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated, the lithium nickel composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), aluminum (Al), titanium (Ti), niobium (Nb), and optionally at least one element M3 selected from Mn, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, and Zr, the molar ratio of each of the above elements is Li:Ni:Co:Al:M3:Ti:Nb = a:(1 - x3 - y3 - z3 - b - c):x3:y3:z3:b:c (where 0.95 ≤ a ≤ 1.25, 0.01 ≤ x3 ≤ 0.25, 0.005 ≤ y3 ≤ 0.15, 0 ≤ z3 ≤ 0.15, 0.005 ≤ b ≤ 0.05, 0.001 < c ≤ 0.03), in the molar ratio, (b + c) ≤ 0.06 and b > c are satisfied, when immersed in water, the amount of lithium eluted into water is 0.25% by mass or less based on the entire positive electrode active material, the niobium concentration at the grain boundaries between the primary particles is 1.3 times or more the niobium concentration inside the primary particles of the lithium nickel composite oxide determined by point analysis using STEM-EDX, The titanium concentration at the grain boundaries between the primary particles is less than 1.3 times the titanium concentration inside the primary particles of the lithium nickel composite oxide, as determined by point analysis using STEM-EDX. A positive electrode active material for a lithium-ion secondary battery. **Claim 4** The lithium-ion secondary battery positive electrode active material according to any one of claims 1 to 3, wherein the particle size variation index [(D90 - D10) / Mv] calculated by D90 and D10 in the particle size distribution by the laser diffraction scattering method and the volume average particle size (Mv) is 0.80 or more and 1.20 or less. **Claim 5** The lithium-ion secondary battery positive electrode active material according to any one of claims 1 to 4, wherein the volume average particle size Mv is 8 μm or more and 20 μm or less. **Claim 6** The lithium-ion secondary battery positive electrode active material according to any one of claims 1 to 3, wherein c, which represents the molar ratio of Nb, satisfies 0.002 ≤ c ≤ 0.03 in the molar ratio of the substances. **Claim 7** The lithium-ion secondary battery positive electrode active material according to claim 2, wherein the amount of lithium eluted into water when immersed in water is 0.09% by mass or less based on the entire positive electrode active material. **Claim 8** A lithium-ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains the lithium-ion secondary battery positive electrode active material according to any one of claims 1 to 7.

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