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 0.97 ≤ 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.

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 vehicles.

[0003] As a secondary battery that satisfies 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-type 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) that is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2) using nickel that 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 for 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 sites 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 causes 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 said to be 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 that achieves high energy density, excellent output characteristics, and thermal stability during short circuit due to a decrease in conductivity in a high dimension can be obtained.

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] Although it is described in Patent Documents 1 and 2 that the cathode active material contains niobium in a specific form to improve thermal stability, in lithium nickel composite oxides, further improvement in thermal stability is required. In addition, since niobium is expensive, a cathode active material that can achieve high thermal stability at a lower cost is required.

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

[0013] By the way, for the purpose of obtaining a cathode active material having high battery characteristics, for example, several techniques of adding titanium to a lithium metal composite oxide have been proposed. According to Patent Documents 3 to 7, a cathode 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 of 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 cathode active material in a state of being compressed in the cathode or to increase the volume resistivity.

[0015] However, Patent Documents 1 to 7 do not describe any effects of combining and containing 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 represented as Li:Ni:Mn:M:Ti:Nb = a:(1 - x1 - y1 - b - c):x1:y1:b:c (where 0.97 ≤ 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.

[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 represented as Li:Ni:Mn:M2:Ti:Nb = a:(1 - x2 - y2 - b - c):x2:y2:b:c (where 0.97 ≤ 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.

[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 0.97 ≤ 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), and in the molar ratio, (b + c) ≤ 0.06 and b > c are satisfied.

[0019] Further, in the first aspect, the positive electrode active material has a volume resistivity of 1.0×10 3 Ω·cm or more and 1.0×10 3 Ω·cm or less when compressed to 3.5 g / cm 5 as determined by pressure powder resistance measurement. In the second aspect, the positive electrode active material has a volume resistivity of 1.0×10 3 Ω·cm or more and 1.0×10 2 Ω·cm or less when compressed to 3.5 g / cm 5 as determined by pressure powder resistance measurement. In the third aspect, the positive electrode active material has a volume resistivity of 5.0×10 3 Ω·cm or more and 1.0×10 2 Ω·cm or less when compressed to 3.5 g / cm 5 as determined by pressure powder resistance measurement.

[0020] Further, it is preferable that the concentration of niobium 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 concentration of titanium 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 [(D90 - D10) / Mv], which indicates the particle size variation index 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 the substances, it is preferable that 0.002 ≦ c ≦ 0.03, where c represents the ratio of the amount of substance of Nb.

[0021] 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

[0022] According to the present invention, it is possible to provide a positive electrode active material that 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

[0023]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0024] Hereinafter, a positive electrode active material for a lithium-ion secondary battery obtained by the manufacturing method according to the present embodiment, its manufacturing method, and further, a lithium-ion secondary battery using this positive electrode active material will be described.

[0025] 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.

[0026] In particular, for a lithium ion secondary battery, when a flammable non-aqueous electrolyte is used as a constituent material of the lithium ion secondary battery, high thermal stability is required. Further, 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, it is possible to suppress a sudden increase in current caused by a short circuit and further improve the thermal stability during a short circuit.

[0027] As a result of intensive studies, the inventors of the present invention have found that by containing a specific amount of titanium (Ti) and niobium (Nb) in a specific distribution in the lithium nickel composite oxide used as the positive electrode active material, the positive electrode active material has a high volume resistivity and high thermal stability can be realized at low cost by suppressing oxygen release during overcharge, and thus the present invention has been completed.

[0028] Hereinafter, the effects of containing titanium (Ti) and niobium (Nb) in the lithium nickel composite oxide according to this embodiment will be described with reference to FIGS. 1 to 3. FIGS. 1 to 3 are created based on the evaluation results of the positive electrode active materials and secondary batteries obtained in Examples 1A, 4A and Comparative Examples 1A to 3A described later.

[0029] FIG. 1 is a graph showing the maximum oxygen generation peak intensity ratio (with the peak intensity of Comparative Example 1 taken as 1) obtained by measuring the amount of oxygen when the lithium nickel composite oxide (positive electrode active material) is in an overcharged state and the temperature is raised from 200°C to 300°C.

[0030] The graph in Fig. 1 shows the maximum oxygen generation peak intensity ratios of Comparative Example 1A which does not contain titanium and niobium, Comparative Example 2A which contains titanium alone (Ti: 2.2 atomic %), Comparative Example 3A which contains niobium alone (Nb: 0.5 atomic %), and Example 1A which contains both titanium and niobium (Ti: 2.2 atomic %, Nb: 0.5 atomic %) from left to right.

[0031] As shown in Fig. 1, compared with Comparative Example 1A which does not contain titanium and niobium, in Comparative Example 2A which contains only titanium (Ti: 2.2 atomic %) and Comparative Example 3A which contains only niobium (Nb: 0.5 atomic %), the maximum oxygen generation peak intensity ratio decreases. Also, in Example 1A which contains both titanium and niobium (Ti: 2.2 atomic %, Nb: 0.5 atomic %), the maximum oxygen generation peak intensity ratio further decreases compared with Comparative Examples 2A and 3A.

[0032] Also, in Example 1A, by containing 0.5 atomic % of Nb together with Ti, it shows a lower maximum oxygen generation peak intensity ratio than Comparative Example 3A which contains only Nb (Nb: 0.5 atomic %). Therefore, in the positive electrode active material according to this embodiment, by combining and containing Ti and Nb, the amount of use of expensive niobium necessary for suppressing oxygen generation during overcharge can be reduced.

[0033] The graph in Fig. 2 shows the volume resistivity (Ω·cm) when the lithium nickel composite oxide (positive electrode active material) is compressed to 3.5 g / cm 3 The volume resistivity (Ω·cm) when the lithium nickel composite oxide (positive electrode active material) is compressed to 3.5 g / cm

[0034] As shown in Fig. 2, compared with Comparative Example 1A that does not contain titanium and niobium, in Comparative Example 2A that contains only titanium (Ti: 2.2 atomic %) and Comparative Example 3A that contains only niobium (Nb: 0.5 atomic %), the volume resistivity increases to a certain extent. However, in Example 1A that contains both titanium and niobium (Ti: 2.2 atomic %, Nb: 0.5 atomic %), it is clear that the volume resistivity increases significantly even compared with Comparative Examples 2A and 3A. Therefore, in the positive electrode active material according to the present embodiment, by containing titanium and niobium, the volume resistivity during compression increases significantly, indicating excellent thermal stability during short circuit.

[0035] Also, the graph in Fig. 3 shows the discharge capacities (mAh / g) of Example 1A and Example 4A (Ti: 2.2 atomic %, Nb: 0.5 atomic %) manufactured under the same conditions except that the oxygen concentration in the atmosphere during the firing process was changed. As shown in Fig. 3, in Example 1A where the oxygen concentration during firing was 80% by volume or more (oxygen concentration: 90% by volume), the discharge capacity is improved compared with Example 4A where the oxygen concentration during firing was 20% by volume.

[0036] In addition, the present inventors have confirmed that the same results can be obtained even when the composition of the lithium nickel composite oxide is different (see Examples 1B, 3B and Comparative Examples 1B to 3B, Figs. 4 to 6, Examples 1C, 4C and Comparative Examples 1C to 3C, Figs. 7 to 9).

[0037] Therefore, although it is generally considered difficult to achieve both a high volume resistivity and a high battery capacity, the positive electrode active material according to the present embodiment can have a high battery capacity despite having a very high volume resistivity (3.5 g / cm 3 during compression) by adjusting the manufacturing conditions (for example, the oxygen concentration during the firing process, etc.), and can achieve both high thermal stability and high battery capacity at low cost.

[0038] From the above, the positive electrode active material according to the present embodiment can achieve high thermal stability during overcharging and very high volume resistivity during compression at low cost by containing a lithium nickel composite oxide in combination with titanium and niobium, and is excellent in thermal stability during short circuit. Also, it is clear that by adjusting the manufacturing conditions, both high battery capacity and thermal stability during short circuit can be achieved. Hereinafter, the configuration of the positive electrode active material according to the present embodiment will be described in detail.

[0039] [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.

[0040] [Molar ratio A] The lithium nickel composite oxide may contain, for example, 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 as elements other than oxygen.

[0041] From the perspective of high battery capacity and thermal stability, the molar ratio of the amounts of substances of each of the above elements is preferably Li:Ni:Mn:M1:Ti:Nb = a:(1 - x1 - y1 - b - c):x1:y1:a:b (where 0.97 ≤ 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 amounts of substances of each of the above elements is referred to as the molar ratio A. Further, in the 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.

[0042] (Lithium) In the above molar ratio A, since the sum of the molar ratios of the above elements other than Li is 1, a indicating the molar ratio of the amount of lithium corresponds to the molar ratio of lithium to the above elements other than lithium (Me) (hereinafter also referred to as "Li / Me"). Further, the range of a is 0.97 ≤ a ≤ 1.25, preferably 1.00 ≤ 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. Further, the range of a may be 1.00 ≤ a ≤ 1.05.

[0043] (Manganese) In the above molar ratio A, the range of x1 indicating the molar ratio of the amount 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, high battery capacity and high thermal stability can be achieved. On the other hand, when the value of x1 is less than 0.03, the effect of improving thermal stability cannot be obtained. Further, 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.

[0044] (Element M1) In the above-described 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. 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, battery characteristics, etc. 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-described 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.

[0045] (Nickel) In the above-described molar ratio A, (1 - x1 - 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 the present 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.

[0046] [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.

[0047] From the perspective of high battery capacity, the molar ratio of the above substances of the 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 the 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 of (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.

[0048] (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 (Me) other than lithium (hereinafter also referred to as "Li / Me"). Also, the range of a is 0.97 ≤ a ≤ 1.25, preferably 1.00 ≤ 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 ≤ 1.05.

[0049] (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, it can have high battery capacity and high thermal stability. 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 and the like can be promoted.

[0050] (Element M2) In the above molar ratio B, the 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 the 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 the element M2 is y2', preferably 0 < y2' ≦ 0.10, more preferably 0.01 ≦ y2' ≦ 0.10. Further, M may contain Al. When the molar ratio of Al contained in the element M2 is y2", preferably 0 < y2" ≦ 0.10, more preferably 0.01 ≦ y2" ≦ 0.10.

[0051] (Nickel) In the above 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 due to having the composition as described above.

[0052] [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.

[0053] From the perspective of high battery capacity, the molar ratio of the amounts of substances 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 0.97 ≤ 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 the amounts of substances of each of the above elements is referred to as the molar ratio C. Further, in the molar ratio C, 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.

[0054] (Lithium) In the above molar ratio C, since the sum of the molar ratios of the elements other than Li is 1, a indicating the molar ratio of the amount of Li corresponds to the molar ratio of lithium to the amount of substances of the elements other than lithium (Me) (hereinafter also referred to as "Li / Me"). Further, the range of a is 0.97 ≤ a ≤ 1.25, preferably 1.00 ≤ 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 ≤ 1.05.

[0055] (Cobalt) In the above molar ratio C, the range of x3 indicating the molar ratio of the amount of Co is 0.01 ≤ x3 ≤ 0.25, preferably 0.03 ≤ x3 ≤ 0.20, 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.

[0056] (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.

[0057] (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 < z3 ≦ 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.

[0058] (Nickel) In the above-mentioned molar ratio C, (1 - x3 - y3 - z3 - b - c) indicating the molar ratio of Ni is 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 due to having the above-described composition.

[0059] Hereinafter, the molar ratios of titanium (Ti) and niobium (Nb) in the above-mentioned molar ratios A to C, and the distributions of titanium (Ti) and niobium (Nb) will be described. (Titanium) In the above-mentioned molar ratios A to C, the range of b indicating 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 increased significantly, and when used as the positive electrode of a secondary battery, oxygen evolution can be suppressed and high thermal stability can be obtained. On the other hand, when the value of b is less than 0.005, the effect of improving thermal stability is not sufficient. Also, when the value of b exceeds 0.05, the ratios of Ni and Mn relatively decrease, the crystal structure is unstable, and cation mixing is likely to occur, which may cause a significant decrease in battery capacity.

[0060] (niobium) In the above-mentioned molar ratios A to C, the range of c indicating the molar ratio of Nb is 0.001 < c ≤ 0.03, preferably 0.002 ≤ c ≤ 0.03, more preferably 0.002 ≤ c ≤ 0.02, and still more preferably 0.002 ≤ w ≤ 0.01. As described above, by including niobium in the above range together with titanium, even with a small content of niobium, the volume resistivity of the lithium nickel composite oxide during compression can be increased significantly, and when used as the positive electrode of a secondary battery, oxygen evolution can be suppressed and high thermal stability can be achieved.

[0061] Also, in the above-mentioned molar ratios A to C, the sum (b + c) of the molar ratio of titanium (b) and the molar ratio 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.

[0062] Also, in the above substance quantity ratios A to C, the ratio (c) of the amount of niobium is smaller than the ratio (b) of the amount of titanium (b > c), preferably b ≥ 2c, more preferably b ≥ 3c, and even more preferably b ≥ 4c. Since niobium is a more expensive element than titanium, reducing the content compared to titanium can reduce the manufacturing cost, and by combining with titanium, high thermal stability can be achieved.

[0063] The composition of the lithium nickel composite oxide can be measured by quantitative analysis using inductively coupled plasma (ICP) optical emission spectrometry.

[0064] (Distribution of niobium) At least a part of the niobium (Nb) contained in the lithium nickel composite oxide according to this embodiment preferably segregates at the grain boundaries between the 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 the primary particles by 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 the primary particles. Note that at least a part of the niobium may be present inside the primary particles.

[0065] Also, the niobium concentration at the grain boundaries between the 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. The upper limit of the niobium concentration is not particularly limited, for example, it is 5 times or less.

[0066] 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).

[0067] 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 so that the grain boundaries cross 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 within the primary particles can be obtained by randomly selecting 20 regions (for example, a region of 130 nm × 130 nm that does not include grain boundaries) inside the primary grains, analyzing the composition of each region, and calculating the average value.

[0068] (Distribution of titanium) The distribution of titanium (Ti) contained in the lithium nickel composite oxide according to this embodiment is not particularly limited and may be present in at least one of the surface and grain boundaries of the primary particles or may be dissolved in the interior of the primary particles. However, from the perspective of improving the battery capacity in a secondary battery, it is preferable that titanium is dissolved. Here, the dissolution 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 no enrichment of titanium at the interface of the primary particles is confirmed, and it is preferable that titanium is detected over the entire interior of the primary particles.

[0069] For example, the titanium concentration at the grain boundaries between primary particles relative to the titanium concentration inside the primary particles determined by STEM-EDX is preferably less than 1.3 times, more preferably 1.2 times or less, still more preferably 1.1 times or less, and may be 1.0 times or less. Also, the titanium concentration at the grain boundaries between primary particles relative to the titanium concentration inside the primary particles may have a lower limit of 0.6 times or more, 0.7 times or more, for example, may be from 0.8 times to 1.2 times, or from 0.9 times to 1.1 times. The titanium concentration can be measured by surface analysis of EDX in S-TEM in the same manner as the niobium concentration described above.

[0070] In the lithium nickel composite oxide according to the present embodiment, the distribution of each element other than niobium (Nb) and titanium (Ti) described above is not particularly limited. For example, when Ni, Mn, and Co are included as element M1 or element M2, it is preferable that these metal elements are detected over the entire inside of the plurality of primary particles constituting the secondary particles.

[0071] [Volume average particle size (Mv)] The volume average particle size (Mv) of the positive electrode active material according to the present 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, it is possible to achieve both high output characteristics and battery capacity and high fillability into the positive electrode.

[0072] On the other hand, when the volume average particle size (Mv) is less than 8 μm, high fillability into the positive electrode may not be obtained. Further, when the volume average particle size (Mv) exceeds 20 μm, high output characteristics and battery capacity may not be obtained. The volume average particle size (Mv) can be obtained, for example, from the volume integration value measured by a laser light diffraction scattering type particle size distribution analyzer.

[0073] [(D90 - D10) / Mv] (variation index) The positive electrode active material according to the present embodiment preferably has [(D90 - D10) / Mv] of 0.80 or more and 1.20 or less. Note that [(D90 - D10) / Mv] indicates the variation index of the particle size of the particles constituting the positive electrode active material, which is calculated from D90 and D10 (the particle size at 90% and 10% in the volume integration of the particle amount in the particle size distribution curve) and the volume average particle size (Mv) in the particle size distribution by the laser light diffraction scattering method.

[0074] When the particle size distribution of the particles constituting the positive electrode active material is wide, there are many fine particles with a small particle size relative to the volume average particle diameter (Mv) and many coarse particles with a large particle size relative to the average particle diameter. When the variation index is within the above range, the fine particles and the coarse particles are appropriately mixed, the packing density becomes high, 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, and may be 0.95 or more.

[0075] On the other hand, when the variation 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 the present 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 variation index of the particle size 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.

[0076] [3.5 g / cm 3 Volume resistivity at compression The positive electrode active material according to the present embodiment has a volume resistivity when compressed to 3.5 g / cm 3 which is higher than that of a positive electrode active material manufactured under the same conditions except that titanium and niobium are not added. 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, the appropriate increase in the volume resistivity can suppress the generation of a sudden current during short circuit. Further, the positive electrode active material according to the present embodiment may have a volume resistivity, for example, 5 times or more higher than that of a positive electrode active material manufactured under the same conditions except that niobium is not added. Note that the volume resistivity is a value that varies depending on the composition of the lithium nickel composite oxide, and the suitable range may differ depending on the composition.

[0077] For example, in the positive electrode active material containing the lithium nickel composite oxide having the above substance amount ratio A, the volume resistivity obtained by the compacted powder resistance measurement at 3.5 g / cm 3When compressed, the volume resistivity 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, 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.

[0078] Also, for example, in the positive electrode active material containing a lithium nickel composite oxide having the above substance mass 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, 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.

[0079] Also, for example, in the positive electrode active material containing a lithium nickel composite oxide having the above substance mass 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, more preferably 5.0×10 2 Ω·cm or more and 1.0×10 4 Ω·cm or less, more preferably 5.0×10 2 Ω·cm or more and 8.0×10 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.

[0080] The volume resistivity can be obtained, for example, by weighing the positive electrode active material in the range of 4.5 g or more and 5.5 g or less, and pressure molding it into a cylindrical shape with a diameter of 20 mm so that it becomes 3.5 g / cm 3 After that, in the pressurized state, it can be measured and obtained by a resistivity test method using a four-probe method conforming to JIS K 7194:1994.

[0081] [Maximum oxygen generation peak intensity] The positive electrode active material according to the present embodiment 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 a positive electrode active material manufactured under the same conditions except that titanium and niobium are not added.

[0082] For example, in the positive electrode 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 a positive electrode active material manufactured under the same conditions except that titanium and niobium are not added is set to 1.

[0083] Further, for example, in the positive electrode 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.

[0084] Further, for example, in the positive electrode 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, and more preferably 0.40 or less.

[0085] The lower limit of the maximum oxygen generation peak intensity ratio during temperature increase 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 increase from 200°C to 300°C is at its maximum and peak value.

[0086] In addition, the lithium nickel composite oxide according to this 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 the secondary particles. Further, the positive electrode active material may contain a compound other than the above-described lithium nickel composite oxide.

[0087] 2. Method for manufacturing a positive electrode active material for a lithium ion secondary battery FIG. 10 is a diagram showing an example of a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to this embodiment (hereinafter, also referred to as "method for manufacturing a positive electrode active material"). By the manufacturing method according to this embodiment, a positive electrode active material containing the above-described lithium nickel composite oxide can be easily obtained on an industrial scale.

[0088] As shown in FIG. 10, the manufacturing method according to this 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, and a firing step (S20) of firing the mixture to obtain the lithium nickel composite oxide.

[0089] Hereinafter, each step will be described in detail. The following description is an example of the manufacturing method according to this embodiment and does not limit the manufacturing method.

[0090] [Crystallization step (S1)] The nickel composite compound used in the mixing step (S10) is preferably obtained by a method including, for example, a crystallization step (S1) and / or a heat treatment step (S2) as shown in FIGS. 11(A) and 11(B).

[0091] 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 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).

[0092] 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 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 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).

[0093] Further, for example, when producing a positive electrode active material containing a lithium nickel composite oxide having the above-described molar 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 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).

[0094] Further, for example, when producing 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).

[0095] 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.

[0096] For example, in a reaction tank, 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.

[0097] The mixed aqueous solution containing nickel and element M can use, for example, sulfate solutions, nitrate solutions, chloride solutions, etc. of nickel and element M. Additionally, after separately preparing an aqueous solution containing nickel and an aqueous solution containing element M, they may be respectively supplied into the reaction tank to form a mixed aqueous solution containing nickel and element M.

[0098] The composition of the metal elements contained in the mixed aqueous solution is substantially the same as 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.

[0099] As the neutralizing agent, an aqueous alkali solution can be used, for example, sodium hydroxide, potassium hydroxide, etc. can be used.

[0100] Also, 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 with 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 the metal ions in the reaction aqueous solution can be adjusted.

[0101] In the crystallization process (S1), when no complexing agent is used, the temperature of the reaction aqueous solution is preferably in the range of exceeding 60°C and not exceeding 80°C for the temperature (liquid temperature), 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, 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.

[0102] Also, 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, since the evaporation amount of water is large, the slurry concentration (reaction aqueous solution concentration) becomes high, the solubility of Ni decreases, crystals such as sodium sulfate are generated in the filtrate, the impurity concentration increases, etc., and the charge-discharge capacity of the positive electrode active material may decrease.

[0103] In the crystallization process (S1), when a complexing agent such as an ammonium ion donor is used, the temperature of the reaction aqueous solution is preferably 30°C or more and 60°C or less because the solubility of Ni in the reaction aqueous solution increases, and the pH of the reaction aqueous solution is preferably 10 or more and 13 or less (based on 25°C), more preferably 12 or more and 13 or less.

[0104] 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 more and 25 g / L or less. When the ammonia concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, so primary particles of composite hydroxide with 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 tends 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 preferably maintained at a constant value. For example, the ammonia concentration is preferably maintained at a desired concentration with the width between the upper limit and the lower limit being about 5 g / L.

[0105] Moreover, 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 viewpoint of enhancing productivity, a mixed solution containing nickel and element M may be prepared in advance and then added into 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 the nickel composite hydroxide containing element M.

[0106] As the aqueous solution containing element M, for example, 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, etc. can be used.

[0107] Further, 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.

[0108] 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. Next, 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, as other coating methods, there are mentioned the spray drying method in which a solution containing a compound containing element M is sprayed onto the nickel composite hydroxide and then dried, and the method in which a solution containing a compound containing element M is impregnated into the nickel composite hydroxide.

[0109] Note that the method for blending 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 aqueous alkali 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 further the co-precipitate may be coated with element M to adjust the content of M.

[0110] Note that, for the crystallization step (S1), 1) a production method by batch crystallization (batch crystallization method) may be used, or 2) a production method by continuous crystallization (continuous crystallization method) may also be used. For example, in the case of the batch crystallization method, after the reaction aqueous solution in the reaction tank reaches a steady state, a precipitate is collected, filtered, and washed with water to obtain a nickel composite hydroxide. Further, 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 are continuously supplied, overflowed from the reaction tank to collect a precipitate, and filtered and washed with water to obtain a nickel composite hydroxide.

[0111] 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 volumetric 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 having a high variation index, a broad particle size distribution, and high fillability can be easily obtained. Further, the continuous crystallization method has higher productivity than the batch crystallization method and is suitable for industrial-scale production.

[0112] [Heat treatment step (S2)] The nickel composite compound may be obtained by a method further including 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 subsequent firing step (step S20).

[0113] 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 and 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.

[0114] In addition, when a 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. 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).

[0115] The heat treatment may be performed by heating under conditions where the residual moisture in the nickel composite hydroxide is removed. For example, the heat treatment temperature 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. When the heat treatment temperature is less than 105°C, a long time is required to remove the residual moisture, which is not industrially suitable. On the other hand, when the heat treatment temperature exceeds 700°C, the particles converted into the nickel composite oxide may sinter and aggregate. For example, when most of the nickel composite hydroxide is converted to the nickel composite oxide, the heat treatment temperature is preferably 350°C or higher and 700°C or lower.

[0116] The atmosphere for the heat treatment is not particularly limited. For example, from the viewpoint of easy operation, the air stream is preferred. Also, the heat treatment time is not particularly limited and can be, for example, 1 hour or more. When the heat treatment time 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 heat treatment time is preferably 5 hours or more and 15 hours or less. 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 stream. For example, a blow dryer, an electric furnace without gas generation, etc. can be preferably used.

[0117] In FIG. 3(B), the nickel composite hydroxide after the crystallization step (S1) is heat-treated, but the nickel composite hydroxide obtained in a step 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.

[0118] [Mixing step (S10)] As shown in FIG. 7, 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. Further, in the mixing step (S10), a compound containing element M may be mixed in addition to the above compounds. In the mixing step (S10), each compound can be added and mixed, for example, in powder (solid phase). Hereinafter, each material will be described.

[0119] (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. Further, the nickel composite compound may be at least one of a hydroxide and an oxide.

[0120] For example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-described molar ratio A, the nickel composite compound contains, as elements other than hydrogen (H) and oxygen (O), nickel (Ni) and 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, and the molar ratio of each element is preferably represented as Ni:Mn:M1 = (1 - x1 - y1):x1:y1 (where (1 - x1 - y1) < 0.80, 0.03 ≤ x1 ≤ 0.35, 0 ≤ y1 ≤ 0.35).

[0121] Also, for example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-mentioned 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 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).

[0122] Also, for example, when manufacturing a positive electrode active material containing a lithium nickel composite oxide having the above-mentioned 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 by 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).

[0123] 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-mentioned 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-mentioned elements (Ni, M), hydrogen, and oxygen as long as the effects of the present invention are not inhibited.

[0124] 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 be obtained by other methods.

[0125] 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.

[0126] (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.

[0127] 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.

[0128] The titanium compound is preferably mixed in the form of particles (solid phase). When adding titanium in the solid phase, the reactivity in the firing step (S20) changes depending on the particle size of the titanium compound. Therefore, the particle size of the titanium compound to be 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 into 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.

[0129] 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.

[0130] (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.

[0131] 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 in 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 extremely difficult handling of the powder, and in the mixing process (S10) and the firing process (S20), the niobium compound may scatter and it may not be possible to add the desired composition into 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 it may not be possible to ensure thermal stability. 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.

[0132] The niobium compound may be pre-crushed using various crushers such as a ball mill, a planetary ball mill, a jet mill - nano jet mill, a bead mill, a pin mill, etc. so as to have a particle size within the above range. Also, 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.

[0133] (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. 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 resulting secondary battery.

[0134] 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 above-described crystallization step (S1). 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 substance of the element M contained in the nickel composite compound and the compound containing the element M falls within the range of the ratio of the amount of the element M in the above-described lithium nickel composite compound.

[0135] The compound containing the element M 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, 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 by a dry classifier or sieving as necessary.

[0136] (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 is used. Among these, lithium carbonate, lithium hydroxide, or a mixture thereof is preferable from the viewpoint of less influence of residual impurities and dissolution at the firing temperature.

[0137] (Mixing method) The mixing method of the above-mentioned 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, etc. Incidentally, it is preferable to sufficiently mix the titanium mixture before the firing step described later. If the mixing is insufficient, 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.

[0138] The lithium compound is mixed so that Li / Me in the mixture is 0.97 or more and 1.25 or less. That is, Li / Me in the mixture is mixed to be the same as Li / Me in the obtained positive electrode active material. 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) becomes Li / Me of the positive electrode active material.

[0139] In addition, the mixture adjusts the mixing amounts of the titanium compound and the niobium compound 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.

[0140] Incidentally, 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-mentioned lithium nickel composite oxide.

[0141] [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.

[0142] 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 molten lithium compound and also penetrate into the primary particles if there are grain boundaries or the like in the primary particles.

[0143] 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 still 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 is likely to occur. 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 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. Note that the oxidizing atmosphere means an atmosphere containing oxygen more than the atmospheric atmosphere.

[0144] 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, since the lithium mixture contains manganese, the firing temperature can be increased. Also, the crystallinity of the lithium nickel composite oxide is increased, and the battery capacity can be further improved.

[0145] 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 is increased, and the battery capacity can be further improved.

[0146] 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.

[0147] 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 not sufficiently carried out, and problems such as remaining excess lithium or unreacted particles, or an insufficiently ordered crystal structure, resulting in insufficient battery characteristics, occur. 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 a decrease in the packing density when forming the positive electrode active material, and an increase in the reaction resistance due to the disorder of the crystal structure, leading to a decrease in the discharge capacity.

[0148] The firing time is preferably at least 3 hours or more, more preferably 6 hours or more and 24 hours or less. If the firing time is less than 3 hours, the formation of the lithium nickel composite oxide may not be sufficiently carried out. Also, 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 continuous-type furnace can be used.

[0149] [Pre-firing] In addition, the firing step (S20) may further include a pre-firing step at a temperature lower than the firing temperature before firing at the temperature in the above range. The pre-firing is preferably carried out 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 in the above temperature range, the lithium compound penetrates into the nickel composite compound, and the diffusion of lithium is sufficiently carried out, 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 carried out by holding at a temperature of 400°C or higher and 550°C or lower for about 1 hour or more and 10 hours.

[0150] [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.

[0151] 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. Further, the secondary battery may be any secondary battery that performs charge and discharge by 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.

[0152] [Positive Electrode] The positive electrode of the secondary battery is manufactured using the above-described positive electrode active material. An example of the manufacturing method of the positive electrode will be described below.

[0153] First, the above positive electrode active material, conductive material, and binder are mixed, and further, if necessary, activated carbon or a solvent for the purpose of viscosity adjustment is added, and this is kneaded to produce a positive electrode composite paste. At that time, according to the performance of the target secondary battery, the mixing ratio of each component 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.

[0154] The obtained positive electrode composite paste is applied, for example, to the surface of a current collector made of aluminum foil and dried to disperse the solvent, thereby producing a sheet-shaped positive electrode. If necessary, it may be pressed by a roll press or the like to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut to an appropriate size according to the target battery and used for manufacturing the battery. However, the manufacturing method of the positive electrode is not limited to the above example and may depend on other methods.

[0155] As the conductive material, for example, graphite (such as natural graphite, artificial graphite, and expanded graphite), carbon black-based materials such as acetylene black and ketjen black can be used.

[0156] As the binder, it plays a role in connecting the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, etc. can be used.

[0157] If necessary, the positive electrode active material, conductive material, and activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode composite material. Specifically, organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent. In addition, activated carbon can be added to the positive electrode composite material to increase the electric double layer capacitance.

[0158] [Negative electrode] As the negative electrode, metallic lithium, lithium alloy, etc. may be used. Also, as the negative electrode, a negative electrode composite material in which a binder is mixed with a negative electrode active material capable of occluding and desorbing lithium ions, an appropriate solvent is added to make it into a paste form, and it is applied to the surface of a metal foil current collector such as copper, dried, and compressed as necessary to increase the electrode density may be used.

[0159] As the negative electrode active material, for example, organic compound fired bodies such as natural graphite, artificial graphite, and phenolic resin, and powder bodies of carbon materials such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the case of the positive electrode, and organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders.

[0160] [Separator] A separator is disposed by sandwiching it between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and known ones can be used. For example, a thin film such as polyethylene or polypropylene and a film having a large number of minute pores can be used.

[0161] [Non-aqueous electrolyte] As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used. The non-aqueous electrolyte solution is a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent. Further, as the non-aqueous electrolyte solution, a 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 being in a liquid state even at normal temperature.

[0162] As the organic solvent, 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, further, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. can be used alone or in combination of two or more.

[0163] As the supporting salt, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts, etc. can be used. Further, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, etc.

[0164] Also, as the non-aqueous electrolyte, a solid electrolyte may be used. The solid electrolyte has the property of withstanding a high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

[0165] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0166] 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 Ge 2-X (PO4)3 (0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3 (0≦X≦2 / 3), Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, etc., and one or more selected therefrom can be used.

[0167] The sulfide-based solid electrolyte is not particularly limited, and for example, those containing sulfur (S) and having lithium ion conductivity and electron insulation can be preferably used. Examples of the sulfide-based solid electrolyte include 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., and one or more selected therefrom can be used.

[0168] 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, as long as it is a polymer compound showing ion conductivity, it is not particularly limited. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt).

[0169] 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, so 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.

[0170] [Shape and Configuration of Secondary Battery] The configuration of the secondary battery is not particularly limited. As described above, it may be composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, etc., or may also 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 can be various shapes such as cylindrical and laminated.

[0171] 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. Between the positive electrode current collector and the positive electrode terminal communicating with the outside, and between the negative electrode current collector and the negative electrode terminal communicating with the outside, they are connected using a current collecting lead, etc., and sealed in a battery case to complete the secondary battery.

[0172] Note that the secondary battery according to the present embodiment is not limited to the form using a non-aqueous electrolyte 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.

[0173] 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 manufacturing method. Further, 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 overcharge, even in comparison with a battery using a positive electrode active material of a conventional 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 an electric vehicle that is restricted in mounting space. Note that the secondary battery can be used not only as a power source for an electric vehicle that is purely driven by electric energy, but also as a power source for a so-called hybrid vehicle that is used in combination with a combustion engine such as a gasoline engine or a diesel engine.

Example

[0174] Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. Note that the various evaluation methods used in the examples and comparative examples are as follows.

[0175] (1) Analysis of composition: Measured by ICP emission spectrometry.

[0176] (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 measuring device (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0177] (3) Concentration of each element The positive electrode active material was processed so that cross-sectional analysis of primary particles by S-TEM became possible. Twenty primary particles were arbitrarily selected from a plurality of secondary particles contained in the positive electrode active material, and the composition of a region (130 nm × 130 nm) including the inside and grain boundaries of each primary particle cross-section was subjected to point analysis by EDX of S-TEM.

[0178] (4) Volume resistivity: After 5 g of the positive electrode active material was pressure-molded into a cylindrical shape with a diameter of 20 mm to a density of 3.5 g / cm 3 and then measured and obtained by the resistivity test method using the four-probe method in accordance with JIS K 7194:1994 under the pressurized state.

[0179] (5) 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. 12 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 charged up to a cut-off voltage of 4.3 V to obtain the initial charge capacity. After a 1-hour rest, the capacity when discharging to a cut-off voltage of 3.0 V was defined 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.

[0180] (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 into 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.

[0181] (6) Maximum oxygen generation peak intensity The thermal stability evaluation of the positive electrode was performed 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 (5) 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. Note that the maximum oxygen peak intensity ratios in Tables 2 and 4 are relative values with the peak intensities of Comparative Example 1A, Comparative Example 1B, and Comparative Example 1C set to 1 (reference) in the oxygen generation behavior when heated from 200°C to 300°C.

[0182] [Examples 1A to 4A, Comparative Examples 1A to 3A] 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 Examples 1A to 4A and Comparative Examples 1A to 3A. (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. A 2.0M mixed aqueous solution of nickel sulfate, manganese sulfate, and cobalt sulfate, 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 so that the molar ratio of nickel:manganese:cobalt was 55:25:20, and crystallization by the continuous crystallization method was performed.

[0183] 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, a 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 powder after filtration 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 = 0.55:0.25:0.20.

[0184] [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.

[0185] [Firing step] The obtained lithium mixture was held in an oxygen (oxygen concentration: 90% by volume) stream at 980 °C for 8 hours for firing, and then crushed to obtain particles of lithium nickel manganese cobalt composite oxide (cathode active material).

[0186] [Evaluation] The manufacturing conditions of the cathode active material are shown in Table 1, and the evaluation results of the obtained cathode active material are shown in Table 2.

[0187] (Example 2A) In the mixing step, the particles of the obtained nickel manganese cobalt composite hydroxide, lithium hydroxide, titanium oxide (TiO₂), niobium acid (Nb₂O₅·4H₂O), and magnesium oxide (MgO) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):titanium:niobium:magnesium was 1.02:0.970:0.022:0.005:0.003. Then, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A except for this. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0188] (Example 3A) In the mixing step, the particles of the obtained nickel manganese cobalt composite hydroxide, lithium hydroxide, titanium oxide (TiO₂), niobium acid (Nb₂O₅·4H₂O), and zirconium oxide (ZrO₂) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):titanium:niobium:zirconium was 1.02:0.970:0.022:0.005:0.003. Then, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A except for this. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0189] (Example 4A) In the firing step, firing was carried out in an oxygen stream (oxygen concentration: 20% by volume). Then, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A except for this. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0190] (Comparative Example 1A) In the mixing step, the particles of the obtained nickel manganese cobalt composite hydroxide and lithium hydroxide were weighed so that the molar ratio of lithium:nickel:manganese:cobalt was 1.02:0.554:0.247:0.199 without mixing a titanium compound and a niobium compound. Then, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A except that the firing temperature was 930°C and the holding time was 5 hours in the firing step. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0191] (Comparative Example 2A) In the mixing step, without mixing a niobium compound, the obtained particles of nickel manganese cobalt composite hydroxide, lithium hydroxide, and titanium oxide (TiO₂) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):titanium was 1.02:0.978:0.022. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A, except that the firing temperature was 960 °C and the holding time was 5 hours. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0192] (Comparative Example 3A) In the mixing step, without mixing a titanium compound, the obtained particles of nickel manganese cobalt composite hydroxide, lithium hydroxide, and niobic acid (Nb₂O₅·4H₂O) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):niobium was 1.02:0.995:0.005. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A, except that the firing temperature was 980 °C and the holding time was 5 hours. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0193]

Table 1

[0194]

Table 2

[0195] [Evaluation Result 1] As shown in Tables 1 to 2 and Figures 1 and 2, the positive electrode active material obtained in the examples had a volume resistivity of 1.0×10 3 Ω·cm or more and a maximum oxygen generation peak intensity ratio of 0.25 or less during compression. Therefore, it is clear that the positive electrode active material obtained in the examples has high thermal stability and suppresses oxygen evolution during overcharging.

[0196] Also, as shown in Tables 1 to 2 and FIG. 3, in Examples 1A to 3A fired in an atmosphere with an oxygen concentration of 90% by volume, a cathode active material having a high discharge capacity of 160 mAh / g or more, high thermal stability, and a high battery capacity was obtained.

[0197] Also, as shown in Table 2, for the cathode active material obtained in the examples, the niobium concentration at the grain boundaries between primary particles with respect to the niobium concentration inside the primary particles (niobium concentration at the grain boundaries / grain interior niobium concentration) was 1.3 times or more, and niobium was segregated at the grain boundaries between primary particles. Regarding titanium, segregation at the grain boundaries between primary particles was not confirmed, and the titanium concentration at the grain boundaries between primary particles with respect to the titanium concentration inside the primary particles (titanium concentration at the grain boundaries / grain interior titanium concentration) was 0.8 times or more and 1.1 times or less.

[0198] On the other hand, since the cathode active material of Comparative Example 1A does not contain titanium and niobium, the volume resistivity during compression and the maximum oxygen generation peak intensity ratio were high, and the thermal stability was insufficient.

[0199] Also, for the cathode active materials of Comparative Examples 2A and 3A, since they contain only one of titanium or niobium, the volume resistivity during compression is slightly higher compared to Comparative Example 1, but lower compared to the examples, and the thermal stability during short circuit cannot be said to be sufficient. Also, for the cathode active material of Comparative Example 3 containing only niobium (Nb: 0.005), the maximum oxygen generation peak intensity ratio was higher than that of the cathode active material of Example 1 (Nb: 0.005). Therefore, in order to obtain an effect comparable to that of the examples by containing niobium alone, a large amount of niobium is required, which poses a problem in terms of cost.

[0200] [Examples 1B to 3B, Comparative Examples 1B to 3B] Hereinafter, the characteristics of the cathode active material containing the lithium nickel composite oxide satisfying the above substance quantity ratio B will be described with reference to Examples 1B to 3B and Comparative Examples 1B to 3B. (Example 1B) [Crystallization step] A predetermined amount of pure water was placed in a reaction tank (60 L), and while stirring, the temperature inside the tank was set to 49 °C. 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 2.0 M mixed aqueous solution of nickel sulfate, manganese sulfate, and cobalt sulfate, 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 so that the molar ratio of nickel:manganese:cobalt was 90:5:5, and crystallization was carried out by the continuous crystallization method.

[0201] At this time, the flow rate was controlled so that the residence time of the mixed aqueous solution was 8 hours, and the pH inside 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, a slurry containing nickel manganese cobalt composite hydroxide was recovered from the overflow port, and then filtration was carried out to obtain a cake of nickel manganese cobalt composite hydroxide. Washing of impurities was carried out by passing 1 L of pure water through 140 g of nickel manganese cobalt composite hydroxide in the filter. The powder after filtration was dried to obtain particles of nickel manganese cobalt composite hydroxide in which the molar ratio of the amounts of substances of nickel, manganese, and cobalt was represented as Ni:Mn:Co = 0.90:0.05:0.05.

[0202] [Mixing step] 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 sufficiently mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy E. Bachofen (WAB)) to obtain a lithium mixture.

[0203] [Firing step] The obtained lithium mixture was held at 840 °C for 10 hours in an oxygen stream (oxygen concentration: 90% by volume) for firing, and then crushed to obtain particles of lithium nickel manganese cobalt composite oxide (positive electrode active material).

[0204] [Evaluation] The production conditions of the 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.

[0205] (Example 2B) In the mixing step, particles of the obtained nickel manganese cobalt composite hydroxide, lithium hydroxide, titanium oxide (TiO2), niobium acid (Nb2O5·4H2O), and magnesium oxide (MgO) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):titanium:niobium:magnesium was 1.02:0.982:0.010:0.005:0.003. Then, a positive electrode active material was obtained and evaluated in the same manner as in Example 1B. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0206] (Example 3B) In the firing step, firing was carried out in an oxygen stream (oxygen concentration: 60% by volume). Then, a positive electrode active material was obtained and evaluated in the same manner as in Example 1B. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0207] (Comparative Example 1B) In the mixing step, a titanium compound and a niobium compound were not mixed. 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. Then, 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 in the firing step. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0208] (Comparative Example 2B) In the mixing step, without mixing the niobium compound, the obtained particles of nickel manganese cobalt composite hydroxide, lithium hydroxide, titanium oxide (TiO2), and zirconium oxide (ZrO2) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):titanium:zirconium was 1.01:0.987:0.010:0.003. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1B except that the firing temperature was 790 °C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0209] (Comparative Example 3B) In the mixing step, without mixing the titanium compound, the obtained particles of nickel manganese cobalt composite hydroxide, lithium hydroxide, niobic acid (Nb2O5·4H2O), and zirconium oxide (ZrO2) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt):niobium:zirconium was 1.02:0.992:0.005:0.003. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1B except that the firing temperature was 830 °C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0210] [Table 3]

[0211] [Table 4]

[0212] (Evaluation Results 2) As shown in Tables 3 - 4 and Figure 6, in Examples 1 and 2 fired in an atmosphere with an oxygen concentration of 90% by volume, a positive electrode active material with an extremely high discharge capacity of 210 mAh / g or more, high thermal stability, and an extremely high battery capacity was obtained.

[0213] As shown in Tables 3 - 4 and Figures 4 and 5, the positive electrode active material obtained in the examples had a volume resistivity of 1.0×10 2Above Ω·cm and with a maximum oxygen generation peak intensity ratio of 0.70 or less, it is clear that it has high thermal stability and oxygen release during overcharge is suppressed. Hereinafter, with reference to FIGS. 4 to 6, the results of these examples will be described.

[0214] In the graph of FIG. 4, from the left, Comparative Example 1B that does not contain titanium and niobium, Comparative Example 2B that contains titanium alone (Ti: 1.0 atomic %), Comparative Example 3B that contains niobium alone (Nb: 0.5 atomic %), and Example 1B that contains both titanium and niobium (Ti: 1.0 atomic %, Nb: 0.5 atomic %) are shown for the maximum oxygen generation peak intensity ratio.

[0215] As shown in FIG. 4, compared with Comparative Example 1B that does not add titanium and niobium, in Comparative Example 2B that contains only titanium (Ti: 1.0 atomic %) and Comparative Example 3B that contains only niobium (Nb: 0.5 atomic %), the maximum oxygen generation peak intensity ratio decreases. Further, in Example 1B that contains both titanium and niobium (Ti: 1.0 atomic %, Nb: 0.5 atomic %), the maximum oxygen generation peak intensity ratio further decreases compared with Comparative Examples 2B and 3B.

[0216] In addition, in Example 1B, by containing 0.5 atomic % of Nb in addition to Ti, it shows a lower maximum oxygen generation peak intensity ratio than Comparative Example 3B that contains only Nb (Nb: 0.5 atomic %). Therefore, in the positive electrode active material according to this embodiment, by combining and containing Ti and Nb, the amount of expensive niobium used, which is necessary to suppress oxygen generation during overcharge, can be reduced.

[0217] FIG. 5 is a graph showing the volume resistivity (Ω·cm) when a lithium nickel composite oxide (positive electrode active material) is compressed to 3.5 g / cm 3 It is a graph showing the volume resistivity (Ω·cm) when compressed to 3.5 g / cm.

[0218] As shown in FIG. 5, the volume resistivity increases to some extent in Comparative Example 2B containing only titanium (Ti: 1.0 atomic %) and Comparative Example 3B containing only niobium (Nb: 0.5 atomic %) as compared with Comparative Example 1B without adding titanium and niobium. However, in Example 1B containing both titanium and niobium (Ti: 1.0 atomic %, Nb: 0.5 atomic %), it is clear that the volume resistivity increases very much even when compared with Comparative Examples 2B and 3B. Therefore, in the positive electrode active material according to the present embodiment, by containing titanium and niobium, the volume resistivity during compression increases remarkably, and it has been shown that the thermal stability during short circuit is excellent.

[0219] Further, FIG. 6 is a graph showing the discharge capacity (mAh / g) of Example 1B and Example 3B (Ti: 1.0 atomic %, Nb: 0.5 atomic %) manufactured under the same conditions except that the oxygen concentration in the atmosphere in the firing process was changed. As shown in FIG. 6, in Example 1B where the oxygen concentration during firing was 80% by volume or more (oxygen concentration: 90% by volume), the discharge capacity is improved as compared with Example 3B where the oxygen concentration during firing was 60% by volume.

[0220] Further, as shown in Table 4, in the positive electrode active material obtained in the examples, the niobium concentration at the grain boundary between primary particles with respect to the niobium concentration inside the primary particles (niobium concentration at the grain boundary / niobium concentration inside the grain) was 1.3 times or more, and niobium was segregated at the grain boundary between primary particles. Regarding titanium, segregation at the grain boundary between primary particles was not confirmed, and the titanium concentration at the grain boundary between primary particles with respect to the titanium concentration inside the primary particles (titanium concentration at the grain boundary / titanium concentration inside the grain) was 0.8 times or more and 1.1 times or less.

[0221] On the other hand, in the positive electrode active material of Comparative Example 1B, since it does not contain titanium and niobium, the volume resistivity during compression and the maximum oxygen generation peak intensity ratio are high, and the thermal stability is not sufficient.

[0222] In addition, in the cathode active materials of Comparative Examples 2B and 3B, since they contain only one of titanium or niobium, the volume resistivity during compression is slightly higher compared to Comparative Example 1B, but lower compared to the Examples, and it cannot be said that the thermal stability during short circuit is sufficient. Also, in the cathode active material (Nb: 0.005) of Comparative Example 3B which contains only niobium, the maximum oxygen generation peak intensity ratio was higher than that of the cathode active material (Nb: 0.005) of Example 1B. Therefore, in order to obtain an effect comparable to that of the Examples by containing niobium alone, a large amount of niobium is required, which poses a problem in terms of cost.

[0223] [Examples 1C to 4C, Comparative Examples 1C to 3C] Hereinafter, the characteristics of the cathode active material containing the lithium nickel composite oxide satisfying the above substance ratio C will be described with reference to Examples 1C to 4C and Comparative Examples 1C to 3C. (Example 1C) [Crystallization step] A predetermined amount of pure water was put into 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 to the reaction tank simultaneously, and crystallization was carried out by the continuous crystallization method.

[0224] 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 filtered 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 filtered powder 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.

[0225] [Mixing step] The obtained particles of nickel cobalt aluminum composite hydroxide, lithium hydroxide, titanium oxide (TiO2), and niobium 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.

[0226] [Firing step] The obtained lithium mixture was fired by holding it at 810 °C for 10 hours in an oxygen (oxygen concentration: 90% by volume) stream, and then crushed to obtain particles of lithium nickel cobalt aluminum composite oxide (cathode active material).

[0227] [Evaluation] The manufacturing conditions of the cathode active material are shown in Table 5, and the evaluation results of the obtained cathode active material are shown in Table 6.

[0228] (Example 2C) In the mixing step, the particles of the obtained nickel cobalt aluminum composite hydroxide, lithium hydroxide, titanium oxide (TiO₂), niobium acid (Nb₂O₅·4H₂O), and magnesium oxide (MgO) were weighed so that the molar ratio of lithium:(nickel + cobalt + aluminum):titanium:niobium:magnesium was 1.01:0.970:0.022:0.005:0.003, and then a positive electrode active material was obtained and evaluated in the same manner as in Example 1C except for this. The production conditions and evaluation results of the positive electrode active material are shown in Tables 5 and 6.

[0229] (Example 3C) In the mixing step, the particles of the obtained nickel cobalt aluminum composite hydroxide, lithium hydroxide, titanium oxide (TiO₂), niobium acid (Nb₂O₅·4H₂O), and zirconium oxide (ZrO₂) were weighed so that the molar ratio of lithium:(nickel + cobalt + aluminum):titanium:niobium:zirconium was 1.01:0.970:0.022:0.005:0.003, and then a positive electrode active material was obtained and evaluated in the same manner as in Example 1C except for this. The production conditions and evaluation results of the positive electrode active material are shown in Tables 5 and 6.

[0230] (Example 4C) In the firing step, firing was carried out in an oxygen (oxygen concentration: 60% by volume) stream, and then a positive electrode active material was obtained and evaluated in the same manner as in Example 1C except for this. The production conditions and evaluation results of the positive electrode active material are shown in Tables 5 and 6.

[0231] (Comparative Example 1C) In the mixing step, 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 without mixing a titanium compound and a niobium compound. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1C except that the firing temperature was 760°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 5 and 6.

[0232] (Comparative Example 2C) In the mixing step, without mixing a niobium compound, the obtained particles of nickel cobalt aluminum composite hydroxide, lithium hydroxide, and titanium oxide (TiO2) were weighed so that the molar ratio of lithium:(nickel + cobalt + aluminum):titanium was 1.01:0.990:0.010. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1C except that the firing temperature was 790°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 5 and 6.

[0233] (Comparative Example 3C) In the mixing step, without mixing a titanium compound, the obtained particles of nickel cobalt aluminum composite hydroxide, lithium hydroxide, and niobic acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + cobalt + aluminum):niobium was 1.02:0.995:0.005. In the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1C except that the firing temperature was 810°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 5 and 6.

[0234]

Table 5

[0235]

Table 6

[0236] (Evaluation Results 3) As shown in Tables 5 to 6 and Figures 7 and 8, the positive electrode active material obtained in the examples has a volume resistivity of 5.0×10 2 Ω·cm or more and a maximum oxygen generation peak intensity ratio of 0.50 or less, has high thermal stability, and it is clear that oxygen release during overcharge is suppressed.

[0237] Also, as shown in Tables 5 to 6 and Figure 9, in Examples 1C to 3C fired in an atmosphere with an oxygen concentration of 90% by volume, a positive electrode active material having a high discharge capacity of 165 mAh / g or more, high thermal stability, and a high battery capacity was obtained.

[0238] Also, as shown in Table 6, in the positive electrode active material obtained in the examples, the niobium concentration at the grain boundaries between primary particles with respect to the niobium concentration inside the primary particles (grain boundary niobium concentration / intragranular niobium concentration) was 1.3 times or more, and niobium was segregated at the grain boundaries between primary particles. Regarding titanium, segregation at the grain boundaries between primary particles was not confirmed, and the titanium concentration at the grain boundaries between primary particles with respect to the titanium concentration inside the primary particles (grain boundary titanium concentration / intragranular titanium concentration) was 0.8 times or more and 1.1 times or less.

[0239] On the other hand, since the positive electrode active material of Comparative Example 1C does not contain titanium and niobium, the volume resistivity during compression and the maximum oxygen generation peak intensity ratio are high, and the thermal stability is not sufficient.

[0240] Also, in the positive electrode active materials of Comparative Examples 2C and 3C, since they contain only one of titanium or niobium, the volume resistivity during compression is slightly higher compared to Comparative Example 1C, but lower compared to the examples, and the thermal stability during short circuit cannot be said to be sufficient. Also, in the positive electrode active material of Comparative Example 3C containing only niobium (Nb: 0.005), the maximum oxygen generation peak intensity ratio was higher than that of the positive electrode active material of Example 1C (Nb: 0.005). Therefore, in order to obtain the same level of effect as in the examples by containing niobium alone, a large amount of niobium is required, which poses a problem in terms of cost.

Industrial Applicability

[0241] In this 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.

[0242] 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 conventional positive electrode active material of a lithium nickel-based oxide. Therefore, since it can be miniaturized, it is suitable as a power source for an electric vehicle that is restricted in mounting space.

[0243] 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 an electric vehicle that is purely driven by electric energy, but also as a power source for a so-called hybrid vehicle that is used in combination with a combustion engine such as a gasoline engine or a diesel engine, or as a stationary battery.

[0244] 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. In addition, the requirements described in the above embodiments and the like can be combined as appropriate. Also, to the extent permitted by law, the content of Japanese Patent Application No. 2019-127261, which is a Japanese patent application, 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

[0245] CBA…Coin-type battery (for evaluation) PE…Positive electrode (evaluation electrode) NE…Negative electrode SE…Separator GA…Gasket WW…Wave washer PC…Positive electrode can NC…Negative electrode can G…Void

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 0.97 ≤ 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 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, 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.

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 elements is represented by Li:Ni:Mn:M2:Ti:Nb = a:(1 - x2 - y2 - b - c):x2:y2:b:c (where 0.97 ≤ 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 ratio of the amounts of substances, (b + c) ≦ 0.06 and b > c are satisfied, 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 ratio of the amounts of substances of the respective elements is Li:Ni:Co:Al:M3:Ti:Nb = a:(1 - x3 - y3 - z3 - b - c):x3:y3:z3:b:c (where 0.97 ≦ 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 ratio of the amounts of substances, (b + c) ≦ 0.06 and b > c are satisfied, 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.

4. The volume resistivity when compressed to 3.5 g / cm ３ obtained by powder pressure resistance measurement is 1.0 × 10 ３ Ω·cm or more and 1.0 × 10 ５ Ω·cm or less. The positive electrode active material for a lithium ion secondary battery according to claim 1.

5. The volume resistivity when compressed to 3.5 g / cm ３ obtained by powder pressure resistance measurement is 1.0×10 ２ Ω·cm or more and 1.0×10 ５ Ω·cm or less, the positive electrode active material for a lithium ion secondary battery according to claim 2.

6. The volume resistivity when compressed to 3.5 g / cm ３ obtained by powder pressure resistance measurement is 5.0×10 ２ Ω·cm or more and 1.0×10 ５ Ω·cm or less, the positive electrode active material for a lithium ion secondary battery according to claim 3.

7. The lithium ion secondary battery positive electrode active material according to any one of claims 1 to 6, wherein the particle size variation index [(D90 - D10) / Mv] calculated by D90 and D10 in the particle size distribution by laser diffraction scattering method and the volume average particle size (Mv) is 0.80 or more and 1.20 or less.

8. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 7, wherein the volume average particle diameter Mv is 8 µm or more and 20 µm or less.

9. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein, in the ratio of the amounts of the substances, c indicating the ratio of the amount of Nb is 0.002 ≦ c ≦ 0.

03.

10. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 9.

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