Method for producing positive electrode active material for lithium ion secondary battery

Abstract

Provided is a manufacturing method for a positive electrode active material that can achieve extremely high thermal stability at a low cost.　A manufacturing method for a positive electrode active material for a lithium-ion secondary battery, said positive electrode active material including a lithium-nickel-manganese complex oxide that has a layered structure with a hexagonal crystal system and is structured from secondary particles in which a plurality of primary particles are aggregated, said manufacturing method comprising: a mixture preparation step in which a mixture is prepared, said mixture including at least a nickel-manganese complex compound, a lithium compound, and optionally one or both of a titanium compound and a niobium compound; and a firing step in which the mixture is fired at 750°C to 1000°C to obtain a lithium-nickel-manganese complex oxide, wherein the nickel-manganese complex compound includes at least nickel (Ni), manganese (Mn), and an element M, in the mixture the proportion (z) of the amount of substance of the titanium and the proportion (w) of the amount of substance of the niobium in relation to the total of the amounts of substances of the nickel, the manganese, the element M, the titanium, and the niobium satisfy the expressions 0.005≤z≤0.05, 0.001<w≤0.03, (z+w)≤0.06, and z>w, and at least a portion of the niobium in the lithium-nickel-manganese complex oxide is segregated to the particle boundaries between the primary particles.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a positive electrode active material for 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 is strongly desired as batteries for electric vehicles including power tools and hybrid automobiles.

[0003] As a secondary battery that satisfies such requirements, there is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. A lithium ion secondary battery using a lithium metal composite oxide having a layered or spinel-type crystal structure as a positive electrode active material 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, and thus higher thermal stability is required.

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

[0007] In particular, in recent years, ternary cathode active materials and cathode active materials with a high nickel ratio (Hi-Ni cathode materials) in which the nickel ratio of lithium nickel manganese composite oxides has been increased have attracted attention with the aim of increasing the capacity. However, since the increase in battery capacity due to the nickel ratio causes a trade-off with the decrease in thermal stability, a cathode active material that achieves 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 Nbc O 2+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.) The lithium composed of nickel manganese composite oxide, and at least a part of niobium in the lithium nickel manganese composite oxide is dissolved in primary particles, and a positive electrode active material for a non-aqueous electrolyte secondary battery has been proposed. According to Patent Document 2, it is said that a non-aqueous secondary battery can be obtained that achieves both high energy density and excellent output characteristics and thermal stability at the time of short circuit due to a decrease in conductivity in a high dimension.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0011] The positive electrode active materials described in Patent Documents 1 and 2 are described as improving thermal stability by containing niobium in a specific form. However, in lithium nickel manganese composite oxides having a high nickel ratio, further improvement in thermal stability is required. In addition, since niobium is expensive, a method for manufacturing a positive electrode active material capable of realizing 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 method capable of easily manufacturing, on an industrial scale, a positive electrode active material capable of realizing higher thermal stability at a lower cost in a positive electrode active material containing a lithium nickel manganese composite oxide having a high nickel ratio.

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

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

[0015] However, Patent Documents 1 to 7 do not describe at all the effect of containing a combination of niobium and titanium as different elements in a lithium nickel manganese composite oxide, and Patent Documents 1, 3 to 7 also do not describe at all the conductivity or volume resistivity of the positive electrode active material in a state of being compressed in the positive electrode.

Means for Solving the Problems

[0016] In a first aspect of the present invention, there is provided a method for producing a positive electrode active material for a lithium-ion secondary battery, comprising a lithium nickel manganese composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated, the method comprising at least: a mixture preparation step of preparing a mixture containing a nickel manganese composite compound, a lithium compound, and optionally one or both of a titanium compound and a niobium compound; and a firing step of firing the mixture at a temperature of 750° C. or higher and 1000° C. or lower to obtain a lithium nickel manganese composite oxide. The nickel manganese composite compound contains nickel (Ni), manganese (Mn), and optionally at least one element M (M) selected from the group consisting of Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, titanium (Ti), and niobium (Nb), and the molar ratio of each element is represented by Ni:Mn:M:Ti:Nb = (1−x−y):x:y:z′:w′ (where 0.03 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, 0 ≦ z′ ≦ 0.05, 0 ≦ w′ ≦ 0.03). The mixture satisfies the conditions that the molar ratio (z) of titanium and the molar ratio (w) of niobium to the total molar amount of nickel, manganese, element M, titanium, and niobium are 0.005 ≦ z ≦ 0.05, 0.001 < w ≦ 0.03, (z + w) ≦ 0.06, and z > w, and at least a part of the niobium in the lithium nickel manganese composite oxide segregates at the grain boundaries between the primary particles.

[0017] In a second aspect of the present invention, there is provided a method for producing a positive electrode active material for a lithium-ion secondary battery, which includes a lithium nickel manganese composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated. The method includes at least a mixture preparation step of mixing a nickel manganese composite compound, a titanium compound, a niobium compound, and a lithium compound to prepare a mixture, and a firing step of firing the mixture at 750 °C or higher and 1000 °C or lower to obtain a lithium nickel manganese composite oxide. The nickel manganese composite compound contains nickel (Ni), manganese (Mn), and an element M (M) 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, and the molar ratio of each element is represented by Ni:Mn:M = (1 - x - y):x:y (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30). In the mixture, the molar ratio (z) of titanium and the molar ratio (w) of niobium to the total molar amount of nickel, manganese, element M, titanium, and niobium satisfy 0.005 ≤ z ≤ 0.05, 0.001 < w ≤ 0.03, (z + w) ≤ 0.06, and z > w, and at least a part of niobium in the lithium nickel manganese composite oxide segregates at the grain boundaries between primary particles.

[0018] Further, in the first aspect or the second aspect described above, after firing, 50 to 200 parts by weight of water may be mixed with 150 parts by weight of the obtained lithium nickel manganese composite oxide at a ratio, and after stirring, a water washing step of performing solid-liquid separation and a drying step of drying the lithium nickel manganese composite oxide after water washing may be provided. Also, in the mixture, the molar ratio (z) of titanium and the molar ratio (w) of niobium to the total molar amount of nickel, manganese, element M, titanium, and niobium may satisfy 0.005 ≤ z ≤ 0.05, 0.002 ≤ w ≤ 0.03, (z + w) ≤ 0.06, and z > w.

[0019] In the mixture adjustment step, at least a nickel-manganese composite compound containing titanium, a niobium compound, and a lithium compound are mixed. The nickel-manganese composite compound contains nickel (Ni), manganese (Mn), titanium (Ti), and optionally at least one element M(M) 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 may be represented as Ni:Mn:M:Ti = (1 - x - y - z’):x:y:z’ (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.005 ≤ z’ ≤ 0.05).

[0020] The nickel-manganese composite compound containing titanium may be obtained by crystallization. Alternatively, the nickel-manganese composite compound containing titanium may be obtained by coating a nickel-manganese composite compound obtained by crystallization with a titanium-containing compound.

[0021] In the mixture adjustment step, at least a nickel-manganese composite compound containing niobium, a lithium compound, and a titanium compound are mixed. The nickel-manganese composite compound containing niobium contains nickel (Ni), manganese (Mn), niobium (Nb), and optionally at least one element M(M) selected from the group consisting of Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The molar ratio of each element may be represented as Ni:Mn:M:Nb = (1 - x - y):x:y:w’ (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.001 < w’ ≤ 0.03).

[0022] The nickel-manganese composite compound containing niobium may be obtained by coating a nickel-manganese composite compound obtained by crystallization with a niobium-containing compound. The molar ratio of the elements in the nickel-manganese composite compound containing niobium may also be represented as Ni:Mn:M:Nb = (1 - x - y):x:y:w’ (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.002 ≤ w’ ≤ 0.03).

[0023] Further, the firing process is preferably carried out in an atmosphere with an oxygen concentration of 80% by volume or more and 100% by volume or less. Further, it is preferable that titanium in the lithium nickel manganese composite oxide is present inside the primary particles. Further, it is preferable that the titanium compound is titanium oxide. Further, it is preferable that the niobium compound is niobium oxide, niobic acid, or a mixture thereof. Further, the lithium nickel manganese composite oxide obtained after firing has a volume resistivity of 5.0×10 3 when compressed to 4.0 g / cm 2 Ω·cm or more and 1.0×10 5 Ω·cm or less.

Advantages of the Invention

[0024] According to the present invention, it is possible to provide a method for manufacturing a cathode active material that can achieve extremely high thermal stability at low cost. Further, the present invention can easily manufacture such a cathode active material in industrial-scale production, and it can be said that the industrial value is extremely large.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0026] First, the positive electrode active material for a lithium ion secondary battery obtained by the manufacturing method according to the present embodiment will be described below. Next, the manufacturing method of the positive electrode active material for a lithium ion secondary battery according to the present embodiment, and further, the lithium ion secondary battery using this positive electrode active material will be described.

[0027] 1. Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for a lithium ion secondary battery according to the present embodiment (hereinafter, also referred to as "positive electrode active material") preferably contains a lithium nickel manganese composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated. The lithium nickel manganese composite oxide contains, as elements other than oxygen, lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and an element M (M) 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.

[0028] In particular, when a flammable non-aqueous electrolyte is used as a constituent material of a 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 amount of heat is generated due to a rapid flow of current, and a chain reaction may occur 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, an abrupt increase in current caused by a short circuit can be suppressed, and the thermal stability during a short circuit can be further improved.

[0029] As a result of intensive studies, the inventors of the present invention have found that, in a lithium nickel manganese composite oxide used as a positive electrode active material, by containing a specific amount of titanium (Ti) and niobium (Nb) in a specific distribution, the positive electrode active material has a very high volume resistivity and can achieve high thermal stability by suppressing oxygen release during overcharging, and thus completed the present invention.

[0030] Hereinafter, in the lithium nickel manganese composite oxide according to the present embodiment, the effects of containing titanium (Ti) and niobium (Nb) will be described with reference to FIGS. 1 to 5. FIGS. 1 to 5 are created based on the evaluation results of the positive electrode active materials and secondary batteries obtained in the examples and comparative examples described later.

[0031] FIG. 1 is a graph showing the maximum oxygen generation peak temperature (° C.) obtained by measuring the amount of oxygen when a lithium nickel manganese composite oxide (positive electrode active material) is in an overcharged state and the temperature is raised from room temperature to 450° C.

[0032] The graph of FIG. 1 shows, from the left, Comparative Example 1A that does not contain titanium and niobium, Comparative Example 2A that contains titanium alone (Ti: 2.6 atomic %), Comparative Example 3 that contains niobium alone (Nb: 1 atomic %), and Example 2 that contains both titanium and niobium (Ti: 2.2 atomic %, Nb: 0.5 atomic %) of the maximum oxygen generation peak temperature.

[0033] As shown in FIG. 1, compared with Comparative Example 1A that does not contain titanium and niobium, in Comparative Example 2A that contains only titanium (Ti: 2.6 atomic %) and Comparative Example 3 that contains only niobium (Nb: 1 atomic %), the maximum oxygen generation peak temperature increases. Further, in Example 2A that contains both titanium and niobium (Ti: 2.2 atomic %, Nb: 0.5 atomic %), the maximum oxygen generation peak temperature further increases compared with Comparative Examples 2A and 3A.

[0034] In Example 2A, only 0.5 atomic% of Nb is contained together with Ti, and it shows a maximum oxygen generation peak temperature higher than that of Comparative Example 3A (Nb: 1 atomic%). Therefore, in the positive electrode active material according to the present embodiment, it is possible to reduce the amount of expensive niobium used while suppressing oxygen generation during overcharge at a higher level.

[0035] Figure 2 is a graph showing the volume resistivity (Ω·cm) when a lithium nickel manganese composite oxide (positive electrode active material) is compressed to 4.0 g / cm 3 It is a graph showing the volume resistivity (Ω·cm) when compressed to 4.0 g / cm

[0036] As shown in Figure 2, compared with Comparative Example 1A that does not contain titanium and niobium, in Comparative Example 2A that contains only titanium (Ti: 2.6 atomic%) and Comparative Example 3 that contains only niobium (Nb: 1 atomic%), the volume resistivity increases to some extent. However, in Example 2 (Ti: 2.2 atomic%, Nb: 0.5 atomic%) that contains both titanium and niobium, it is clear that the volume resistivity increases very significantly compared with Comparative Examples 2 and 3. Therefore, in the positive electrode active material according to the present embodiment, by containing titanium and niobium, the volume resistivity during compression increases significantly, so it has excellent thermal stability during short circuit.

[0037] Figure 3 is a graph showing the discharge capacity (mAh / g) of Example 2A and Example 6A (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 is changed. As shown in Figure 3, in Example 2A where the oxygen concentration during firing is 80% by volume or more (oxygen concentration: 90% by volume), the discharge capacity is improved compared with Example 6A where the oxygen concentration during firing is 60% by volume.

[0038] Therefore, usually, it is considered difficult to achieve both a high volume resistivity and a high battery capacity. However, the positive electrode active material according to the present embodiment can achieve a very high volume resistivity (4.0 g / cm 3Despite having (during compression), it is possible to have a high battery capacity, and it is possible to achieve both high thermal stability and high battery capacity at low cost.

[0039] From the above, the positive electrode active material according to this embodiment can achieve high thermal stability during overcharge and extremely high volume resistivity during compression at low cost by containing a lithium nickel manganese composite oxide in combination with titanium and niobium, and is excellent in thermal stability during short circuit. Also, (ii) it is clear that by adjusting the manufacturing conditions, it is possible to achieve both high battery capacity and high thermal stability.

[0040] As a result of further intensive studies by the present inventors, it has been found that in the lithium nickel manganese composite oxide used as the positive electrode active material, (iii) by washing and drying the lithium nickel manganese composite oxide, it has high thermal stability and can further improve the battery capacity.

[0041] Hereinafter, with reference to FIGS. 4 and 5, the effects of washing and drying in the lithium nickel manganese composite oxide according to this embodiment will be described.

[0042] FIG. 4 is a graph showing the maximum oxygen generation peak temperature (° C.) obtained by measuring the amount of oxygen when the lithium nickel manganese composite oxide (positive electrode active material) is in an overcharged state and the temperature is raised from room temperature to 450° C.

[0043] The graph of FIG. 4 shows, from the left, Comparative Example 1A that does not contain titanium and niobium, Comparative Example 2A that contains titanium alone (Ti: 2.6 atomic %), Comparative Example 3A that contains niobium alone (Nb: 1 atomic %), and Example 2A that contains titanium and niobium (Ti: 2.2 atomic %, Nb: 0.5 atomic %), and the maximum oxygen generation peak temperature of Example 11A (Ti: 2.2 atomic %, Nb: 0.5 atomic %) obtained by washing and drying Example 2A.

[0044] As shown in Fig. 4, the maximum oxygen generation peak temperature increases in Comparative Example 2A containing only titanium (Ti: 2.6 atomic %) and Comparative Example 3 containing only niobium (Nb: 1 atomic %) as compared with Comparative Example 1A containing neither titanium nor niobium. Further, in Example 2A containing both titanium and niobium and Example 11A (Ti: 2.2 atomic %, Nb: 0.5 atomic %), the maximum oxygen generation peak temperature increases as compared with Comparative Example 2A and shows a maximum oxygen generation peak temperature equal to or higher than that of Comparative Example 3A.

[0045] Also, in Example 11A and Example 2A, by containing only 0.5 atomic % of Nb in addition to Ti, they show a maximum exothermic peak temperature higher than that of Comparative Example 2A (Ti: 2.6 atomic %) and Comparative Example 3A (Nb: 1 atomic %). Therefore, it is clear that the positive electrode active material according to the present embodiment can suppress oxygen generation during overcharge at a higher level while reducing the usage amount of expensive niobium.

[0046] Fig. 5 is a graph showing the battery capacity (initial discharge capacity) of Example 2A (Ti: 2.2 atomic %, Nb: 0.5 atomic %) containing titanium and niobium and Example 11 obtained by washing and drying Example 2A with water. As shown in Fig. 5, the battery capacity is improved in Example 11A washed with water as compared with Example 2A not washed with water.

[0047] Therefore, although the lithium nickel manganese composite oxide may have a slightly reduced battery capacity by containing titanium and niobium as different elements, the positive electrode active material according to the present embodiment can achieve both high thermal stability and a higher battery capacity by washing with water and drying after firing, as will be described later. Hereinafter, the preferred configuration of the positive electrode active material according to the present embodiment will be described in detail.

[0048] [Lithium Nickel Manganese Composite Oxide] The lithium nickel manganese composite oxide contained in the positive electrode active material is composed of secondary particles in which a plurality of primary particles are aggregated. Further, the lithium nickel manganese composite oxide preferably has a hexagonal layered structure.

[0049] The lithium nickel manganese composite oxide contains, as elements other than oxygen, lithium (Li), nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), and optionally at least one element M (M) selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al.

[0050] The molar ratio of the amounts of substances of the above elements contained in the lithium nickel manganese composite oxide is not particularly limited, but from the viewpoint of high battery capacity, it is preferably expressed as Li:Ni:Mn:M:Ti:Nb = a:(1 - x - y - z - w):x:y:z:w (where 0.97 ≤ a ≤ 1.25, 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.005 ≤ z ≤ 0.05, 0.001 < w ≤ 0.03). Also, in the above molar ratio of the amounts of substances, z representing the molar ratio of titanium (Ti) and w representing the molar ratio of niobium (Nb) satisfy the relationship (z + w) ≤ 0.06 and z > w. Hereinafter, the preferred compositions of each element will be described.

[0051] (Lithium) In the above molar ratio of the amounts of substances, since the sum of the molar ratios of the above elements other than Li is 1, a representing the molar ratio of the amount of 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.

[0052] (Manganese) In the above ratio of the amounts of substances, the range of x indicating the ratio of the amount of Mn is 0.03 ≤ x ≤ 0.30, preferably 0.05 ≤ x ≤ 0.15, more preferably 0.05 ≤ x ≤ 0.10. When the value of x is within the above range, high battery capacity and high thermal stability can be achieved. On the other hand, when the value of x is less than 0.03, the effect of improving thermal stability cannot be obtained. Also, when the value of x exceeds 0.30, 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 and the like can be promoted.

[0053] (Element M) In the above ratio of the amounts of substances, element M is at least one element selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. Also, the range of y indicating the ratio of the amount of element M is 0 ≤ y ≤ 0.30, preferably 0 ≤ y ≤ 0.15. When y is 0 or more, the thermal stability, the improvement of storage characteristics, and battery characteristics can be improved. On the other hand, when y exceeds 0.30, the crystal structure becomes unstable, the compound having a layered crystal structure may not be formed, and the battery capacity may decrease due to a relatively lower ratio of Ni or Mn. For example, when M contains Co, the battery capacity and output characteristics are more excellent. When M is Co, preferably 0 ≤ y ≤ 0.10. Also, when the ratio of the amount of Co contained in element M is y1, preferably 0 < y1 ≤ 0.10, more preferably 0.01 ≤ y1 ≤ 0.10.

[0054] (Titanium) In the above ratio of the amounts of substances, the range of z indicating the ratio of the amount of Ti is 0.005 ≦ z ≦ 0.05. As described above, when titanium is included in the above range together with niobium, the volume resistivity during compression of the lithium nickel manganese composite oxide can be increased very 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 z is less than 0.005, the effect of improving thermal stability is not sufficient. Also, when the value of z exceeds 0.05, the ratios of Ni and Mn relatively decrease, the crystal structure is not stable, and cation mixing is likely to occur, so the battery capacity may decrease significantly.

[0055] (niobium) In the above ratio of the amounts of substances, the range of w indicating the ratio of the amount of Nb is 0.001 < w ≦ 0.03, preferably 0.002 ≦ w ≦ 0.03, more preferably 0.002 ≦ w ≦ 0.02, and even 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 during compression of the lithium nickel manganese composite oxide can be increased very significantly, and when used as the positive electrode of a secondary battery, oxygen evolution can be suppressed and high thermal stability can be achieved.

[0056] Also, in the above ratio of the amounts of substances, the sum (z + w) of the ratio of the amount of Ti (z) and the ratio of the amount of Nb (w) is 0.06 or less, preferably 0.05 or less, and more preferably 0.03 or less. When z + w is in the above range, it is possible to obtain a higher battery capacity while having high thermal stability.

[0057] Also, in the above ratio of the amounts of substances, the ratio of the amount of Nb (w) is smaller than the ratio of the amount of Ti (z) (z > w), preferably z ≧ 2w, more preferably z ≧ 3w, and even more preferably z ≧ 4w. Since niobium is a more expensive element than titanium, the manufacturing cost can be reduced by reducing the content compared to titanium, and high thermal stability can be achieved by combining with titanium.

[0058] (Nickel) In the ratio of the above substance amounts, (1 - x - y - z - w) indicating the ratio of the substance amount of Ni is 0.34 or more, preferably 0.5 or more, more preferably 0.65 or more, still more preferably 0.70 or more, and even more preferably 0.80 or more, and may be 0.90 or more. When the substance amount ratio of nickel is within the above range, a secondary battery having a high battery capacity can be obtained. When the substance amount ratio of nickel is high, although the battery capacity is improved, the thermal stability may decrease. However, the lithium nickel manganese composite oxide according to the present embodiment can have high thermal stability regardless of the high nickel ratio by having the composition as described above.

[0059] Note that the composition of the lithium nickel manganese composite oxide can be measured by quantitative analysis using inductively coupled plasma (ICP) emission spectrometry.

[0060] (Distribution of Niobium) At least a part of the niobium (Nb) contained in the lithium nickel manganese composite oxide according to the present 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.

[0061] 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, and more preferably 1.5 times or more. Note that the upper limit of the niobium concentration is not particularly limited, and is, for example, 5 times or less.

[0062] Note that the concentration of niobium inside the primary particles or at the grain boundaries can be confirmed by performing surface analysis / line analysis / point analysis on the composition of the cross-sections of a plurality of secondary particles by EDX measurement using a scanning transmission electron microscope (S-TEM).

[0063] For example, the niobium concentration at the grain boundaries between primary particles can be obtained by randomly selecting 20 regions (for example, a measurement region of 130 nm × 130 nm as shown in FIG. 18, which includes a region where the grain boundary crosses the inside of the region) containing the grain boundaries between primary particles from the cross-sections of a plurality of secondary particles, confirming the composition of each region by point analysis, and calculating the average value. Similarly, the niobium concentration inside the primary particles can be obtained by randomly selecting 20 regions inside the primary grains (for example, a region of 130 nm × 130 nm that does not include grain boundaries; see FIG. 17), analyzing the composition of each region, and calculating the average value.

[0064] (Distribution of Titanium) The distribution of titanium (Ti) contained in the lithium nickel manganese 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 primary particles. However, from the viewpoint 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 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 inside of the primary particles.

[0065] For example, the titanium concentration at the grain boundaries between primary particles with respect to the titanium concentration inside the primary particles, as 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 even be 1.0 times or less. Further, the titanium concentration at the grain boundaries between primary particles with respect 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 0.8 times or more and 1.2 times or less, or 0.9 times or more and 1.1 times or less. The titanium concentration can be measured by, for example, surface analysis of EDX of S-TEM, in the same manner as the niobium concentration described above.

[0066] In the lithium nickel manganese composite oxide according to the present embodiment, the distribution of metal elements other than the above niobium (Nb) and titanium (Ti) is not particularly limited. For example, when Ni, Mn, and Co are included as element M, it is preferable that these metal elements are detected over the entire interior of a plurality of primary particles constituting the secondary particles.

[0067] [Volume average particle diameter (Mv)] The volume average particle diameter (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 17 μm or less. When the volume average particle diameter (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.

[0068] On the other hand, when the volume average particle diameter (Mv) is less than 8 μm, high fillability into the positive electrode may not be obtained. Further, when the volume average particle diameter (Mv) exceeds 20 μm, high output characteristics and battery capacity may not be obtained. The volume average particle diameter (Mv) can be determined, for example, from the volume integration value measured by a laser light diffraction scattering type particle size distribution analyzer.

[0069] [(D90 - D10) / Mv] (Dispersion index) The positive electrode active material according to this embodiment preferably has [(D90 - D10) / Mv] of 0.80 or more and 1.20 or less. Note that [(D90 - D10) / Mv] is an index of the particle size variation of the particles constituting the positive electrode active material, which is calculated by 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.

[0070] 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 size (Mv) and many coarse particles with a large particle size relative to the average particle size. When the variation index is within the above range, fine particles and coarse particles are moderately mixed, the packing density increases, and the energy density per volume can be increased. Also, from the viewpoint of improving the energy density per volume, [(D90 - D10) / Mv] may be 0.90 or more, or may be 0.95 or more.

[0071] 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. Also, when using the manufacturing method of the positive electrode active material according to this embodiment, the upper limit is about 1.20. Note that in the firing step (S20) described later, when the firing temperature exceeds 1000°C, the particle size variation index may exceed 1.20. In this case, when forming the positive electrode active material, the specific surface area may decrease, the resistance of the positive electrode may increase, and the battery capacity may decrease.

[0072] [4.0 g / cm 3 volume resistivity at compression The positive electrode active material obtained after the firing step (S20) 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 4.0 g / cm 5 Preferably, it is 1.0×10 3 Ω·cm or more and 1.0×10 4 Ω·cm or less, more preferably 2.0×10 3 Ω·cm or more and 1.0×10 4It is below Ω·cm. When the volume resistivity of the positive electrode active material is within the above range, high thermal stability during short circuit can be obtained. 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, by having an appropriately high volume resistivity, the generation of a sudden current during short circuit can be suppressed.

[0073] Note that the volume resistivity can be obtained, for example, by weighing the positive electrode active material within the range of 4.5 g or more and 5.5 g or less, and pressure-molding it into a cylindrical shape with a diameter of 20 mm to a density of 4.0 g / cm 3 and then measuring it by a resistivity test method using the four-probe method in accordance with JIS K 7194:1994 in the pressurized state.

[0074] [Maximum oxygen generation peak temperature] The positive electrode active material obtained after the firing step (S20) preferably has a maximum oxygen generation peak temperature during temperature rise in the overcharged state of 250 °C or higher, more preferably 260 °C or higher. The upper limit of the maximum oxygen generation peak temperature during temperature rise is not particularly limited, but is about 300 °C or lower.

[0075] Also, the positive electrode active material obtained after performing the water washing step (S30) and the drying step (S40) preferably has a maximum oxygen generation peak temperature during temperature rise in the overcharged state of 250 °C or higher.

[0076] The upper limit of the maximum oxygen generation peak temperature during temperature rise is not particularly limited, but is about 300 °C or lower. Note that the maximum oxygen generation peak temperature can be measured by the method described in the examples. Also, the maximum oxygen generation peak temperature refers to the temperature at which the oxygen generated during temperature rise reaches a maximum and peak.

[0077] [Amount of eluted lithium] The positive electrode active material according to this embodiment preferably has a lithium amount eluted in water (eluted lithium amount) when immersed in water that is smaller than the eluted lithium amount of a positive electrode active material produced under the same conditions except that the subsequent water washing step (S30) and drying step (S40) are not performed. By reducing the eluted lithium amount to a specific amount, the crystallinity of the positive electrode active material is improved, the discharge capacity is improved, and gelation of the positive electrode mixture paste during production of the electrode plate of the secondary battery can be suppressed.

[0078] The positive electrode active material obtained after performing the water washing step (S30) and the drying step (S40) preferably has a lithium amount eluted in water (eluted lithium amount) of 0.20% by mass or less, more preferably 0.10% by mass or less, may be 0.08% by mass or less, and may also be 0.06% by mass or less with respect to the entire positive electrode active material. Further, the lower limit of the eluted lithium amount is not particularly limited, but is, for example, 0.01% by mass or more. When the eluted lithium amount is within the above range, excess lithium in the lithium nickel manganese composite oxide is extracted, and the occurrence of gelation of the positive electrode mixture paste and the like can be suppressed. Note that when the eluted lithium amount is less than 0.01% by mass, lithium may be excessively extracted from the lithium nickel manganese composite oxide during water washing, and in that case, the battery characteristics deteriorate.

[0079] The eluted lithium amount can be measured by taking 2 g of the positive electrode active material, putting it into 125 ml of pure water at room temperature stirred with a stirrer, and immediately performing titration using an HCl aqueous solution after the active material is added. The titration was evaluated by the Warder method, the amounts of lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) were calculated, and the sum of these lithium amounts was calculated as the eluted lithium.

[0080] In addition, the lithium nickel manganese composite oxide according to this embodiment may contain a small amount of elements other than the above-described metal elements (Li, Ni, Mn, element M, Nb, Ti) and oxygen, as long as the effects of the present invention are not inhibited. Further, as the lithium nickel manganese composite oxide contained in the positive electrode active material, a small amount of single primary particles may be contained in addition to secondary particles. Further, the positive electrode active material may contain a compound other than the above-described lithium nickel manganese composite oxide.

[0081] 2. Method for manufacturing positive electrode active material for lithium ion secondary battery FIGS. 6 to 15 are diagrams 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 manganese composite oxide can be easily obtained on an industrial scale.

[0082] The method for manufacturing a positive electrode active material according to this embodiment includes at least a mixture preparation step (S10) of preparing a mixture containing a nickel manganese composite compound, a lithium compound, and optionally one or both of a titanium compound and a niobium compound, and a firing step (S20) of firing the mixture to obtain a lithium nickel manganese composite oxide. The nickel manganese composite compound contains nickel (Ni), manganese (Mn), and optionally at least one element M (M) selected from the group consisting of Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, titanium (Ti), and niobium (Nb), and the molar ratio of the respective elements is represented by Ni:Mn:M:Ti:Nb = (1 - x - y):x:y:z’:w’ (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0 ≤ z’ ≤ 0.05, 0 ≤ w’ ≤ 0.03). In the mixture prepared in the mixture preparation step, the molar ratio (z) of titanium and the molar ratio (w) of niobium to the total molar amount of nickel, manganese, element M, titanium, and niobium satisfy 0.005 ≤ z ≤ 0.05, 0.001 < w ≤ 0.03, (z + w) ≤ 0.06, and z > w.

[0083] The manufacturing method according to this embodiment may include, for example, as shown in FIG. 6, a mixture preparation step (S10A) of mixing a nickel-manganese composite compound, a titanium compound, a niobium compound, and a lithium compound to prepare a mixture, and a firing step (S20) of firing the mixture to obtain a lithium nickel-manganese composite oxide.

[0084] Further, the manufacturing method according to this embodiment may include, for example, as shown in FIG. 8, a mixture preparation step (S10B) of mixing at least a nickel-manganese composite compound containing titanium, a niobium compound, and a lithium compound to prepare a mixture, and a firing step (S20) of firing the mixture to obtain a lithium nickel-manganese composite oxide.

[0085] Further, the manufacturing method according to this embodiment may include, for example, as shown in FIG. 11, a mixture preparation step (S10C) of mixing at least a nickel-manganese composite compound containing niobium, a titanium compound, and a lithium compound to prepare a mixture, and a firing step (S20) of firing the mixture to obtain a lithium nickel-manganese composite oxide.

[0086] Further, in the mixture preparation step (S10D), the mixture may be prepared by mixing at least a nickel-manganese composite compound containing titanium and niobium and a lithium compound.

[0087] Further, the manufacturing method according to this embodiment may include, for example, as shown in FIG. 13, a mixture preparation step (S10A) of mixing at least a nickel-manganese composite compound, a titanium compound, a niobium compound, and a lithium compound to prepare a mixture, a firing step (S20) of firing the mixture to obtain the lithium nickel-manganese composite oxide, a water washing step (S30) of mixing water with the obtained lithium nickel-manganese composite oxide, stirring, and then performing solid-liquid separation, and a drying step (S40) of drying the lithium nickel-manganese composite oxide (precipitate) after water washing.

[0088] Further, as shown in FIG. 14, for example, the manufacturing method according to the present embodiment may include at least a mixture preparation step (S10B) of mixing a nickel-manganese composite compound containing titanium, a niobium compound, and a lithium compound to prepare a mixture, a firing step (S20) of firing the mixture to obtain a lithium nickel manganese composite oxide, a water washing step (S30) of mixing water with the obtained lithium nickel manganese composite oxide, stirring the mixture, and then performing solid-liquid separation, and a drying step (S40) of drying the lithium nickel manganese composite oxide (precipitate) after water washing.

[0089] Further, as shown in FIG. 15, for example, the manufacturing method according to the present embodiment may include at least a mixture preparation step (S10C) of mixing a nickel-manganese composite compound containing niobium, a titanium compound, and a lithium compound to prepare a mixture, a firing step (S20) of firing the mixture to obtain a lithium nickel manganese composite oxide, a water washing step (S30) of mixing water with the obtained lithium nickel manganese composite oxide, stirring the mixture, and then performing solid-liquid separation, and a drying step (S40) of drying the lithium nickel manganese composite oxide (precipitate) after water washing.

[0090] Hereinafter, the manufacturing method according to the present embodiment will be described in detail for each step. Note that the following description is an example of the manufacturing method according to the present embodiment and does not limit the manufacturing method.

[0091] [Crystallization Step (S1A, S1B)] The nickel-manganese composite compound used in the mixture preparation step (S10A) is preferably obtained by a method including a crystallization step (S1A) and / or a heat treatment step (S2) as shown in FIGS. 7(A) and 7(B).

[0092] Further, the nickel-manganese composite compound containing titanium used in the mixture preparation step (S10B) is preferably obtained by a method including a crystallization step (S1B) and / or a heat treatment step (S2) as shown in FIGS. 9(A) and 9(B).

[0093] In addition, the nickel-manganese composite compound containing niobium used in the mixture preparation step (S10C) can be obtained, for example, by changing the titanium salt shown in FIG. 9(A) to a niobium salt. Further, the nickel-manganese composite compound containing titanium and niobium used in the mixture preparation step (S10D) can be obtained, for example, by adding a niobium salt together with the titanium salt shown in FIG. 9(A).

[0094] The nickel-manganese composite hydroxide obtained in the crystallization step (S1A) contains nickel (Ni), manganese (Mn), and, as an element other than the hydroxyl group (OH), at least one element M selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The molar ratio (A) of each substance is preferably represented by Ni:Mn:M = (1 - x - y):x:y (where 0.03 ≤ x ≤ 0.30 and 0 ≤ y ≤ 0.30).

[0095] The nickel-manganese composite hydroxide obtained in the crystallization step (S1B) contains nickel (Ni), manganese (Mn), titanium (Ti), and, as an element other than the hydroxyl group (OH), at least one element M selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. The molar ratio (B) of each element is preferably represented by Ni:Mn:M:Ti = (1 - x - y - z'):x:y:z' (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, and 0.005 ≤ z' ≤ 0.05). The crystallization step (S1B) can be carried out under the same conditions as the crystallization step (S1A) except that a salt containing titanium (titanium salt) is added as a raw material to obtain a nickel-manganese composite hydroxide containing titanium.

[0096] In addition, the nickel-manganese composite hydroxide containing niobium contains nickel (Ni), manganese (Mn), niobium (Nb), and optionally at least one element M selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al as elements other than the hydroxyl group (OH). The molar ratio (C) of each element is preferably represented by Ni:Mn:M:Nb = (1 - x - y - w'):x:y:w' (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.001 < w' ≤ 0.03). The nickel-manganese composite hydroxide containing niobium can be carried out under the same conditions as the crystallization step (S1B), except that in the crystallization step (S1B), a salt containing niobium (niobium salt) is added as a raw material instead of the titanium salt to obtain the nickel-manganese composite hydroxide containing niobium.

[0097] The crystallization steps (S1A) and (S1B) can be carried out by a known crystallization method as long as a nickel-manganese composite hydroxide having the above molar ratio can be obtained. Hereinafter, an example of the crystallization step for obtaining a nickel-manganese composite hydroxide by crystallization will be described.

[0098] For example, in a reaction tank, a mixed aqueous solution containing at least nickel and manganese is stirred at a constant rate, and a neutralizing agent is added to form a reaction aqueous solution. By controlling the pH of the reaction aqueous solution by neutralization, a nickel-manganese composite hydroxide is produced by coprecipitation (crystallization).

[0099] The mixed aqueous solution containing nickel and manganese can be an aqueous solution containing a nickel salt and a manganese salt, for example, a sulfate solution, a nitrate solution, or a chloride solution of nickel and manganese. Alternatively, an aqueous solution containing nickel and an aqueous solution containing manganese may be separately prepared and then supplied into the reaction tank to form a mixed aqueous solution containing nickel and manganese.

[0100] Further, as will be described later, the mixed aqueous solution may contain element M. Further, when obtaining a nickel-manganese composite hydroxide containing titanium and / or niobium, the mixed aqueous solution may contain titanium and / or niobium. The composition of each metal element contained in the mixed aqueous solution substantially coincides with the composition of each metal element contained in the obtained nickel-manganese composite hydroxide. Therefore, the composition of the metal elements in the mixed aqueous solution can be adjusted so as to be the same as the composition of each metal element of the target nickel-manganese composite hydroxide.

[0101] As the neutralizing agent, an aqueous alkali solution can be used. For example, sodium hydroxide, potassium hydroxide, etc. can be used.

[0102] 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 to nickel ions and other metal ions in the reaction aqueous solution in the reaction tank, and known ones can be used. For example, an ammonium ion donor can be used. The ammonium ion donor is not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc. can be used. By adding the complexing agent, the solubility of metal ions in the reaction aqueous solution can be adjusted.

[0103] In the crystallization step (S1A) or (S1B), when the complexing agent is not used, the temperature of the reaction aqueous solution (liquid temperature) is preferably in the range exceeding 60°C and not exceeding 80°C, and the pH of the reaction aqueous solution at the above temperature is preferably 10 or more and 12 or less (based on 25°C). When the pH of the reaction aqueous solution exceeds 12, the obtained nickel-manganese composite hydroxide becomes fine particles, and the filterability deteriorates, and spherical particles may not be obtained. On the other hand, when the pH of the reaction aqueous solution is less than 10, the production rate of the nickel-manganese composite hydroxide becomes extremely slow, Ni remains in the filtrate, the precipitation amount of Ni deviates from the target composition, and a nickel-manganese composite hydroxide with the target ratio may not be obtained.

[0104] Moreover, 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, and the impurity concentration increases, etc., and there is a possibility that the charge-discharge capacity of the positive electrode active material decreases.

[0105] In the crystallization step (S1A) or (S1B), when using a complexing agent such as an ammonium ion donor, the temperature of the reaction aqueous solution is preferably 30°C or higher and 60°C or lower because the solubility of Ni in the reaction aqueous solution increases, and the pH of the reaction aqueous solution is preferably 10 or higher and 13 or lower (based on 25°C), more preferably 12 or higher and 13 or lower.

[0106] Moreover, 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 a composite hydroxide with a regular shape and particle size may not be formed. Also, since a gel-like nucleus is likely to be generated, the particle size distribution of the obtained nickel-manganese composite hydroxide is also likely to broaden. On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of metal ions becomes too large, the amount of metal ions remaining in the reaction aqueous solution increases, and deviations in the composition of the obtained nickel-manganese 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 a width between the upper limit and the lower limit of about 5 g / L.

[0107] In addition, when the nickel-manganese composite hydroxide obtained by crystallization contains at least one element M selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, the method for incorporating element M into the nickel-manganese composite hydroxide is not particularly limited, and known methods can be used. For example, from the perspective of enhancing productivity, an aqueous solution containing element M is added to the mixed aqueous solution containing nickel and manganese in the reaction tank, and a method of coprecipitating the nickel-manganese composite hydroxide containing element M is preferred.

[0108] In addition, when the nickel-manganese composite hydroxide obtained by crystallization contains titanium and / or niobium, the method for incorporating titanium and / or niobium into the nickel-manganese composite hydroxide is not particularly limited, and known methods can be used. For example, from the perspective of enhancing productivity, an aqueous solution containing titanium and / or niobium is added to the mixed aqueous solution containing nickel and manganese in the reaction tank, and a method of coprecipitating the nickel-manganese composite hydroxide containing titanium and / or niobium is preferred.

[0109] As the aqueous solution containing element M, for example, an aqueous solution containing cobalt 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. As the aqueous solution containing titanium, an aqueous solution containing a titanium salt, for example, an aqueous solution containing titanium sulfate, etc. can be used. As the aqueous solution containing niobium, an aqueous solution containing a niobium salt, for example, an aqueous solution obtained by dissolving niobium hydroxide, niobium pentachloride, niobic acid, etc. in potassium hydroxide or hydrochloric acid can be used.

[0110] Further, from the viewpoint of optimizing the crystallization conditions to facilitate the control of the composition ratio, after obtaining the nickel-manganese composite hydroxide by the crystallization step (S1A), a step of coating the obtained nickel-manganese composite hydroxide with element M may be provided. The coating method of element M is not particularly limited, and a known method can be used.

[0111] Also, when obtaining a nickel-manganese composite hydroxide containing titanium and / or niobium, as shown in FIGS. 10 and 12, after obtaining the nickel-manganese composite hydroxide by the crystallization step (S1A) or (S1B), a coating step (S3) of coating with a compound containing titanium and / or niobium may be provided. The coating method of titanium and / or niobium is not particularly limited, and a known method can be used. The coating method of titanium and / or niobium is also not particularly limited, and a known method can be used, similar to the coating method of element M.

[0112] An example of the coating method of at least one element among titanium, niobium, and element M (hereinafter also collectively referred to as "additive element") will be described below. First, the nickel-manganese composite hydroxide obtained by crystallization is dispersed in pure water to form a slurry. Next, an aqueous solution containing the additive element corresponding to the target coating amount is mixed with this slurry, and a neutralizing agent (acid or alkali) is dropped and adjusted to a predetermined pH. As the acid, for example, sulfuric acid, hydrochloric acid, nitric acid, etc. are used. As the alkali, for example, sodium hydroxide, potassium hydroxide, etc. are used. Then, after mixing the slurry for a predetermined time, filtration and drying of the slurry are performed to obtain a nickel-manganese composite hydroxide coated with the additive element. In addition, as other coating methods, a spray drying method in which a solution containing a compound containing the additive element is sprayed onto the nickel-manganese composite hydroxide and then dried, a method in which a solution containing a compound containing element M is impregnated into the nickel-manganese composite hydroxide, etc. can be mentioned.

[0113] In addition, the method of incorporating the additive element into the nickel-manganese composite hydroxide may include one or both of mixing the additive element into the above-described mixed aqueous solution and coating the additive element on the nickel-manganese composite hydroxide.

[0114] For example, 1) the additive element may be coated on the nickel-manganese composite hydroxide obtained by adding an alkaline aqueous solution to a mixed aqueous solution containing nickel and manganese (excluding the additive element) and subjecting it to crystallization, or 2) a mixed aqueous solution containing nickel, manganese, and a part of the additive element may be prepared, the nickel-manganese composite hydroxide (containing the additive element) may be co-precipitated, and the additive element may be further coated on the co-precipitate to adjust the content of the additive element.

[0115] For example, as a method for producing a nickel-manganese composite hydroxide containing titanium, as shown in FIG. 10, for example, 1) an alkaline aqueous solution may be added to a mixed aqueous solution containing nickel and manganese (excluding titanium) and subjected to crystallization to obtain a nickel-manganese composite hydroxide (S1A), and the obtained nickel-manganese composite hydroxide may be coated with titanium (S3), or 2) a mixed aqueous solution containing nickel, manganese, and titanium may be prepared, an alkaline aqueous solution may be added and subjected to crystallization to co-precipitate to obtain a nickel-manganese composite hydroxide containing titanium (S1B), and the obtained nickel-manganese composite hydroxide containing titanium (co-precipitate) may be coated with titanium (S3). When including the crystallization step (S1B) and the coating step (S3), the content of titanium may be adjusted so that the total amount of titanium added in these steps falls within the range of the above-described molar ratio (B).

[0116] In addition, as a method for producing a nickel-manganese composite hydroxide containing niobium, as shown in FIG. 12, a method similar to the above-described method for producing a nickel-manganese composite hydroxide containing titanium may be used, except that titanium shown in FIG. 10 is changed to niobium.

[0117] Note that the crystallization steps (S1A) and (S1B) may use 1) a production method by batch crystallization (batch crystallization method) or 2) a production method by continuous crystallization (continuous crystallization method). For example, in the case of the batch crystallization method, after the reaction aqueous solution in the reaction tank reaches a steady state, the precipitate is collected, filtered, and washed with water to obtain a nickel-manganese composite hydroxide. In the case of the continuous crystallization method, a mixed aqueous solution, an alkaline aqueous solution, and in some cases, an aqueous solution containing an ammonium ion donor are continuously supplied, overflowed from the reaction tank to collect the precipitate, and then filtered and washed with water to obtain a nickel-manganese composite hydroxide.

[0118] 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 with a high variation index, a broad particle size distribution, and high fillability can be easily obtained. In addition, the continuous crystallization method has higher productivity than the batch crystallization method and is suitable for industrial-scale production.

[0119] [Heat treatment step (S2)] The nickel-manganese composite compound may be obtained by a method including a heat treatment step (S2) after the crystallization step (S1A) or (S1B), as shown in FIGS. 7(B) and 9(B). Further, the nickel-manganese composite compound may be obtained by a method including the above-described heat treatment step (S2) after the coating step (S3) shown in FIGS. 10 and 12.

[0120] The heat treatment step (S2) is a step of removing at least a part of the moisture contained in the nickel-manganese 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-manganese 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).

[0121] In the heat treatment step (S2), it is sufficient to remove the moisture in the nickel-manganese composite hydroxide to such an extent that there is no variation 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-manganese composite hydroxide and convert it to a nickel-manganese composite oxide. Note that it is not necessary to convert all of the nickel-manganese composite hydroxide to a nickel-manganese composite oxide.

[0122] Further, when the heat treatment step (S2) is provided, at least one of the nickel-manganese composite hydroxide and the nickel-manganese composite oxide obtained by the heat treatment step (S2) can be used as a nickel-manganese composite compound in the mixture preparation step (S10). Further, when coating the nickel-manganese composite hydroxide with an additive element (at least one element among titanium, niobium, and element M), a compound containing the additive element may be coated on the nickel-manganese composite hydroxide and then the heat treatment step (S2) may be performed, or a compound containing the additive element may be coated on at least one of the nickel-manganese composite hydroxide and the nickel-manganese composite oxide obtained by the heat treatment step (S2).

[0123] The heat treatment may be performed by heating under conditions where the residual moisture in the nickel-manganese composite hydroxide is removed. For example, the temperature of the heat treatment is preferably 105°C or higher and 700°C or lower. When the nickel-manganese composite hydroxide is heated at 105°C or higher, at least a part of the residual moisture can be easily removed. Note that when the temperature of the heat treatment 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 temperature of the heat treatment exceeds 700°C, the particles converted to the nickel-manganese composite oxide may sinter and aggregate. For example, when most of the nickel-manganese composite hydroxide is converted to a nickel-manganese composite oxide, the temperature of the heat treatment is preferably 350°C or higher and 700°C or lower.

[0124] The atmosphere for the heat treatment is not particularly limited. For example, from the viewpoint of easy operation, the air flow is preferable. Also, the time for the heat treatment 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 residual moisture in the particles of the nickel-manganese 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, and any equipment that can heat the nickel-manganese composite hydroxide in an air flow may be used. For example, a blower dryer, an electric furnace without gas generation, etc. can be preferably used.

[0125] In addition, in Fig. 7(B), the nickel-manganese composite hydroxide after the crystallization step (S1) is heat-treated, but the nickel-manganese composite hydroxide obtained in steps other than the crystallization step (S1) may also be heat-treated. Even in this case, by removing at least a part of the moisture in the nickel-manganese composite hydroxide, the above-described effects can be obtained.

[0126] [Mixture preparation step (S10)] The mixture preparation step (S10) is a step of preparing a mixture containing at least a nickel-manganese composite compound, a lithium compound, and optionally one or both of a titanium compound and a niobium compound. Hereinafter, an example of the mixture preparation step (S10) will be described respectively. Note that the following description is an example of the mixture preparation step (S10), and the mixture preparation step (S10) may prepare the mixture by a method other than the method described below.

[0127] The mixture preparation step (S10A) is a step of mixing at least a nickel-manganese composite compound, a titanium compound, a niobium compound, and a lithium compound to prepare a mixture, as shown in Fig. 6. Also, in the mixture preparation step (S10), a compound other than the above compounds may be mixed. For example, a compound containing element M may be mixed.

[0128] Further, as shown in FIG. 8, the mixture preparation step (S10B) is a step of mixing at least a nickel manganese composite compound containing titanium, a niobium compound, and a lithium compound to prepare a mixture. In the mixture preparation step (S10B), compounds other than the above compounds may be mixed. For example, a titanium compound may be further mixed, or a compound containing element M may be mixed.

[0129] Further, as shown in FIG. 11, the mixture preparation step (S10C) is a step of mixing at least a nickel manganese composite compound containing niobium, a titanium compound, and a lithium compound to prepare a mixture. In the mixture preparation step (S10C), compounds other than the above compounds may be mixed. For example, a niobium compound may be further mixed, or a compound containing element M may be mixed.

[0130] In the mixture preparation step (S10), each compound can be added and mixed, for example, in powder (solid phase). Hereinafter, each material used in the mixture preparation step (S10) will be described.

[0131] (Nickel Manganese Composite Compound) The nickel manganese composite compound used in the mixture preparation step (S10A) contains, as elements other than hydrogen (H) and oxygen (O), nickel (Ni), manganese (Mn), and optionally at least one element M (M) selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. Further, it is preferable that the molar ratio of the above elements contained is represented by Ni:Mn:M = (1 - x - y):x:y (where 0 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30). The nickel manganese composite compound may be at least one of a hydroxide and an oxide.

[0132] The nickel-manganese composite compound containing titanium used in the mixture preparation step (S10B) contains, as elements other than hydrogen (H) and oxygen (O), nickel (Ni), manganese (Mn), titanium (Ti), and optionally at least one element M(M) selected from Co, V, Mg, Mo, Ca, Cr, Zr, Ta, Na, W, Fe, Zn, B, Si, P, and Al. Further, it is preferable that the molar ratio of the contained elements is represented as Ni:Mn:M:Ti = (1 - x - y - z'):x:y:z' (where 0 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.005 ≤ z' ≤ 0.05). The nickel-manganese composite compound containing titanium may be at least one of a hydroxide and an oxide.

[0133] The nickel-manganese composite hydroxide containing niobium used in the mixture preparation step (S10C) contains, as elements other than the hydroxyl group (OH), nickel (Ni), manganese (Mn), niobium (Nb), and optionally at least one element M(M) selected from Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al. Further, it is preferable that the molar ratio of the contained elements is represented as Ni:Mn:M:Nb = (1 - x - y - w'):x:y:w' (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.001 < w' ≤ 0.03). The nickel-manganese composite compound containing niobium may be at least one of a hydroxide and an oxide.

[0134] Since the content (composition) of each element (Ni, Mn, M) in the nickel-manganese composite compound is substantially maintained even in the particles of the lithium nickel-manganese composite oxide, the content of each element (Ni, Mn, M) is preferably in the same range as the content in the above-described lithium nickel-manganese composite oxide. Note that the nickel-manganese composite compound used in the present embodiment may contain a small amount of elements other than the above-described elements (Ni, Mn, M), hydrogen, and oxygen as long as the effects of the present invention are not inhibited.

[0135] As the nickel-manganese composite compound, as described above, the nickel-manganese composite hydroxide obtained by the crystallization step (S1A) or (S1B) may be used, or the nickel-manganese composite hydroxide obtained by the coating step (S3) may be used. Further, at least one of the nickel-manganese composite hydroxide obtained after the heat treatment step (S2) and the nickel-manganese composite oxide may be used. Note that the nickel-manganese composite compound can be obtained by the above-described crystallization steps (S1A, S1B) and / or heat treatment step (S2), etc., but it may be obtained by other methods.

[0136] Further, in the nickel-manganese composite compound, 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.

[0137] (Titanium compound) As the titanium compound, a known compound 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.

[0138] Among these, titanium oxide is preferable from the viewpoints of easy availability and avoiding the incorporation of impurities into the lithium nickel-manganese composite oxide. Note that when impurities are incorporated into the lithium nickel-manganese composite oxide, it may cause a decrease in the thermal stability, battery capacity, and cycle characteristics of the obtained secondary battery.

[0139] The titanium compound is preferably mixed in the form of particles (solid phase). When adding titanium in the solid phase, since the reactivity in the firing step (S20) changes depending on the particle size of the titanium compound, the particle size of the titanium compound used is one of the important factors. The average particle size of the titanium compound is preferably 0.01 μm or more and 5 μm or less, more preferably 0.05 μm or more and 3 μm or less, and still more preferably 0.08 μm or more and 1 μm or less. When the average particle size is less than 0.01 μm, there may be problems such as very difficult handling of the powder, and in the mixture preparation 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 manganese composite oxide after firing, and the battery capacity may decrease. Note that 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.

[0140] The titanium compound may be preliminarily pulverized using various pulverizers such as a ball mill, a planetary ball mill, a jet mill - nano jet mill, a bead mill, a pin mill, etc. so as to have a particle size within the above range. Also, the titanium compound may be classified using a dry classifier or sieving as necessary. For example, particles close to 1 μm can be obtained using a dry classifier.

[0141] (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 the mixing of impurities into the lithium nickel manganese composite oxide, niobium oxide, niobic acid, or a mixture thereof is preferable. Note that when impurities are mixed into the lithium nickel manganese composite oxide, it may cause a decrease in the thermal stability, battery capacity, and cycle characteristics of the resulting secondary battery.

[0142] The niobium compound is preferably mixed in the form of particles (solid phase). When adding niobium in the solid phase, the reactivity in the subsequent firing step (step S20) changes depending on the particle size of the niobium compound. Therefore, the particle size of the niobium compound used is one of the important factors. The average particle size of the niobium compound is preferably 0.01 μm or more and 20 μm or less, more preferably 0.08 μm or more and 5 μm or less, and even more preferably 0.10 μm or more and 3 μm or less. When the average particle size is less than 0.01 μm, there are problems such as very difficult handling of the powder, and in the mixture preparation step (S10) and the firing step (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 manganese 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 meter.

[0143] The niobium compound may be previously pulverized 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 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.

[0144] (Compound containing element M) As the compound containing element M, known compounds containing element M can be used. For example, cobalt 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 manganese composite oxide, it may cause a decrease in the thermal stability, battery capacity, and cycle characteristics of the resulting secondary battery.

[0145] Element M may be mixed in particles (solid phase) using a compound containing element M, or may be included in the nickel manganese composite hydroxide by the method described above. When adding the compound containing 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 element M, it is preferable to appropriately adjust the particle size of the compound containing element M to be used. Further, when mixing the compound containing element M in the mixture preparation step (S10), it is preferable to mix the compound containing element M such that the total amount of the nickel manganese composite compound and element M contained in the compound containing element M falls within the range of the molar ratio of element M in the above-described lithium nickel manganese composite compound.

[0146] The compound containing 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 element M may be classified by a dry classifier or sieving as necessary.

[0147] (Lithium compound) The lithium compound is not particularly limited, and known compounds containing lithium can be used. For example, lithium carbonate, lithium hydroxide, lithium nitrate, or a mixture thereof can be used. Among these, lithium carbonate, lithium hydroxide, or a mixture thereof is preferable from the viewpoint of having less influence of residual impurities and dissolving at the firing temperature.

[0148] (Mixing method) The mixing method of the above compounds is not particularly limited, as long as these particles are sufficiently mixed to the extent that the skeletons of these particles are not destroyed. As the mixing method, for example, it can be mixed using a general mixer, such as a shaker mixer, a Lodige mixer, a Julia mixer, a V blender, etc. Note that it is preferable to mix the titanium mixture sufficiently before the firing process described later. If the mixing is not sufficient, problems such as variations in the molar ratio of Li / Me (atomic % ratio) between individual particles of the positive electrode active material, where Li and metal elements other than Li (Me: in this embodiment, Me = Ni + Mn + element M + Ti + Nb), may occur, and sufficient battery characteristics may not be obtained.

[0149] When the water washing step (S30) described later is not performed, the lithium compound is mixed so that Li / Me in the mixture is 0.97 or more and 1.25 or less. That is, it is mixed so that Li / Me in the mixture is the same as Li / Me in the obtained positive electrode active material. This is because the molar ratios of Li / Me and each metal element do not change before and after the firing step (S20), so Li / Me of the mixture in the mixture preparation step (S10) becomes Li / Me of the positive electrode active material.

[0150] Also, when the water washing step (S30) is performed, since a part of the excess lithium component present on the surface of the lithium nickel composite oxide dissolves in water, the Li / Me ratio may decrease compared to the lithium nickel composite oxide after the firing step (S20). The decrease range of this Li / Me ratio varies depending on the composition and physical properties of the lithium nickel composite oxide and the water washing conditions. However, in an example of the manufacturing method according to this embodiment, it decreases by approximately 0.02 due to the water washing step (S30).

[0151] Further, the mixture is adjusted such that the ratio (z) of the amount of substance of titanium and the ratio (w) of the amount of substance of niobium to the total amount of substance of the above metal elements excluding lithium (Ni, Mn, element M, Ti, and Nb) satisfy 0.005 ≦ z ≦ 0.05, 0.001 < w ≦ 0.03, (z + w) ≦ 0.06, and z > w. Also, the ratio (c) of the amount of substance of niobium in the mixture may satisfy 0.002 ≦ c ≦ 0.03.

[0152] Note that the contents (ratios) of niobium (Nb) and titanium (Ti) in the mixture are substantially maintained even in the lithium nickel manganese composite oxide. Therefore, the mixing amounts of the niobium compound and the titanium compound in the mixture preparation step (S10A) are preferably in the same range as the contents of niobium and titanium in the above-described lithium nickel manganese composite oxide.

[0153] Also, the amount of substance of titanium contained in the entire mixture in the mixture preparation step (S10B) may be the same as the amount of substance of titanium contained in the nickel manganese composite compound containing titanium. Further, when a titanium compound is further mixed in the mixture preparation step (S10B), it may be the same as the total amount of substance of titanium contained in the nickel manganese composite compound containing titanium and the titanium compound to be mixed.

[0154] Also, the amount of substance of niobium contained in the entire mixture in the mixture preparation step (S10C) may be the same as the amount of substance of niobium contained in the nickel manganese composite compound containing niobium. Further, when a niobium compound is further mixed in the mixture preparation step (S10C), it may be the same as the total amount of substance of niobium contained in the nickel manganese composite compound containing niobium and the niobium compound to be mixed.

[0155] [Firing Step (S20)] The firing step (S20) is a step of firing the mixture obtained in the mixture preparation step (S10) to obtain a lithium nickel manganese composite oxide.

[0156] When the mixture is fired, lithium in the lithium compound diffuses into the nickel manganese composite compound, so that a lithium nickel manganese 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 manganese composite compound to form a lithium nickel manganese composite oxide. The lithium compound melts at the temperature during firing and penetrates into the nickel manganese composite compound to form a lithium nickel manganese 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 penetrate into the primary particles if there are grain boundaries or the like.

[0157] The firing atmosphere is preferably an oxygen concentration of 80% by volume or more and 100% by volume or less, more preferably an oxygen concentration of 90% by volume or more and 100% by volume or less. In a lithium nickel manganese composite oxide with a high nickel ratio, so-called cation mixing occurs in which transition metal elements such as Ni are arranged at the 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 and 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 high battery capacity and thermal stability.

[0158] The firing temperature is 750 ° C or higher and 1000 ° C or lower in an oxidizing atmosphere, preferably 750 ° C or higher and 950 ° C or lower. When firing at the above temperature, melting of the lithium compound occurs, and penetration and diffusion of titanium are promoted. In addition, since the mixture contains manganese, the firing temperature can be increased. The firing temperature can be appropriately adjusted within the above range. By increasing the firing temperature, the diffusion of titanium and niobium is promoted. Furthermore, the crystallinity of the lithium nickel manganese composite oxide is increased, and the battery capacity can be further improved.

[0159] On the one hand, when the firing temperature is less than 750 °C, the diffusion of lithium, titanium, and manganese into the nickel-manganese composite compound is not sufficiently carried out, and surplus lithium or unreacted particles remain, or the crystal structure is not sufficiently formed, resulting in a problem that sufficient battery characteristics cannot be obtained. On the other hand, when the firing temperature exceeds 1000 °C, intense sintering occurs between the particles of the formed lithium nickel manganese composite oxide, and abnormal grain growth may occur. When abnormal grain growth occurs, the particles after firing become coarse. When the positive electrode active material is formed, not only does the filling property decrease, but also the reaction resistance increases due to the disorder of the crystal structure, resulting in a problem that the discharge capacity decreases.

[0160] The firing time is preferably at least 3 hours or more, more preferably 6 hours or more and 24 hours or less. When the firing time is less than 3 hours, the formation of the lithium nickel manganese composite oxide may not be sufficiently carried out. The furnace used for firing is not particularly limited as long as it can fire the titanium mixture in an oxygen stream, but it is preferable to use an electric furnace without gas generation, and either a batch type or a continuous type furnace can be used.

[0161] [4.0 g / cm 3 with the volume resistivity at compression] The lithium nickel manganese composite oxide obtained after firing 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 4.0 g / cm 5 It is preferably 1.0×10 3 Ω·cm or more and 1.0×10 4 Ω·cm or less, more preferably 2.0×10 3 Ω·cm or more and 1.0×10 4 Ω·cm or less. When the volume resistivity of the lithium nickel manganese composite oxide is within the above range, high thermal stability during short circuit can be obtained.

[0162] Note that the volume resistivity is measured, 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 compressing it into a cylindrical shape with a diameter of 20 mm to 4.0 g / cm3 After pressure molding so as to obtain the above, it can be measured and obtained by a resistivity test method using a four-probe method in accordance with JIS K 7194:1994 while under pressure.

[0163] [Calcination] Note that the firing step (S20) may further include a calcination step at a temperature lower than the firing temperature before firing at a temperature of 750°C or higher and 1000°C or lower. Calcination is preferably performed at a temperature at which the lithium compound in the mixture can melt and react with the nickel manganese composite compound. The calcination temperature can be, for example, 350°C or higher and lower than the firing temperature. Also, the lower limit of the calcination temperature is preferably 400°C or higher. By holding (calcining) the mixture within the above temperature range, the lithium compound penetrates into the nickel manganese composite compound, and the diffusion of lithium is sufficiently carried out, and a uniform lithium nickel manganese composite oxide can be obtained. For example, when using lithium hydroxide as the lithium compound, the calcination 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 or less.

[0164] [Crushing] Note that the lithium nickel manganese 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.

[0165] Also, the manufacturing method according to the present embodiment may include a water washing step (S30) and a drying step (S40) after the firing step (S20) as described below. By providing these steps, the discharge capacity can be improved, so that high thermal stability and a higher battery capacity can be achieved at the same time. Hereinafter, each step will be described.

[0166] [Water washing step (S30)] The water washing step (S30) is a step of mixing the lithium nickel manganese composite oxide obtained in the firing step (S20) with water, stirring (hereinafter referred to as "water stirring"), and then performing solid-liquid separation.

[0167] The manufacturing method according to the present embodiment includes a water washing step (S30) and a drying step (S40) described later, thereby improving the crystallinity of the positive electrode active material and the discharge capacity. Although the details are not clear, for example, when lithium in the positive electrode active material is extracted by water stirring, the disorder of the atomic arrangement is alleviated, thereby improving the crystallinity of the positive electrode active material and showing a high discharge capacity. In addition, by the water washing step (S30), the excess lithium component on the surface is dissolved and removed by water, so that the gelation of the positive electrode mixture paste during the production of the electrode plate of the secondary battery can be suppressed.

[0168] The amount of water mixed in the water washing step (S30) is preferably 50 parts by mass or more and 200 parts by mass or less with respect to 150 parts by mass of the lithium nickel manganese composite oxide. When the mixing ratio of water is 200 parts by mass or more, an excessive amount of lithium is extracted from the positive electrode active material, which may cause a decrease in battery capacity and an increase in reaction resistance. On the other hand, when the mixing ratio of water is less than 50 parts by mass, the effect of improving crystallinity and the removal of the excess lithium component become insufficient, which may cause a decrease in battery capacity and gelation of the positive electrode mixture paste. In addition, the amount of water mixed in the water washing step (S30) may be 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the lithium nickel manganese composite oxide.

[0169] The time for water washing is not particularly limited, but for example, it is about 1 minute or more and 2 hours or less, and may be 5 minutes or more and 50 minutes or less.

[0170] After the lithium nickel manganese composite oxide is water stirred, solid-liquid separation is performed to obtain the lithium nickel manganese composite oxide (precipitate). The method of solid-liquid separation is not particularly limited, and a known method can be used. For example, solid-liquid separation can be performed using one or more selected from suction filters such as Nutsche (Buchner funnel), filter presses, centrifuges, etc.

[0171] [Drying Process (S40)] The drying process (S40) is a process of drying the lithium nickel manganese composite oxide (precipitate) obtained by the above washing process (S30) to obtain a powder of the lithium metal composite oxide (dried powder).

[0172] The drying conditions are preferably heat treatment at a temperature of 100°C or higher and 250°C or lower in an oxidizing atmosphere or a vacuum atmosphere. When the drying temperature is 100°C or higher, the moisture in the precipitate can be sufficiently evaporated. Also, when the drying temperature is 250°C or lower, a compact drying device can be used, which is suitable for implementation on an industrial scale.

[0173] The atmosphere during drying is preferably an atmosphere that does not contain water vapor or carbon dioxide in order to avoid the reaction between the moisture and carbonic acid in the atmosphere and the obtained positive electrode active material. Specifically, an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is preferred. Also, from the viewpoint of being able to quickly discharge the water vapor generated by drying, it is preferable to add an exhaust mechanism to the drying device.

[0174] The drying time is not particularly limited, but in order to sufficiently evaporate the moisture of the raw material mixture, it is preferably 0.5 hours or more at the maximum temperature reached during drying. Also, the upper limit of the drying time is preferably 48 hours or less from the viewpoint of productivity.

[0175] 3. Lithium-Ion Secondary Battery The lithium-ion secondary battery (hereinafter also referred to as "secondary battery") according to this 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 this embodiment may be applied to various modified and improved forms based on the embodiments described in this specification.

[0176] [Positive Electrode] Using the above-described positive electrode active material, a positive electrode of the secondary battery is fabricated. An example of the method for manufacturing the positive electrode will be described below.

[0177] 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 mixture paste. At this time, according to the performance of the target secondary battery, the mixing ratio of each component in the positive electrode mixture paste can be appropriately adjusted. For example, when the solid content of the positive electrode mixture 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.

[0178] The obtained positive electrode mixture 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-like positive electrode. If necessary, it may be pressed by a roll press or the like to increase the electrode density. The sheet-like positive electrode obtained in this way can be cut to an appropriate size according to the target battery and used for manufacturing the battery. However, the method for manufacturing the positive electrode is not limited to the above example and may rely on other methods.

[0179] 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, etc. can be used.

[0180] 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.

[0181] 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. Also, activated carbon can be added to the positive electrode composite material to increase the electric double layer capacitance.

[0182] [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 state, 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.

[0183] 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.

[0184] [Separator] A separator is disposed between the positive electrode and the negative electrode while sandwiching the separator. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and a known one 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.

[0185] [Non-aqueous electrolyte] As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used. The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. 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 the 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.

[0186] As the organic solvent, one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, 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.

[0187] 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.

[0188] Also, as the non-aqueous electrolyte, a solid electrolyte may be used. The solid electrolyte has a property of withstanding a high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

[0189] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0190] 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.

[0191] 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.

[0192] 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. The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt).

[0193] Note that 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 high potentials, there is no gas generation or thermal runaway due to the decomposition of the electrolyte during charging as seen in non-aqueous electrolytes, 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.

[0194] [Shape and Configuration of Secondary Battery] The configuration of the secondary battery is not particularly limited, and may be composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, etc. as described above, 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 it can be made into various shapes such as cylindrical and laminated.

[0195] 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. 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 are connected using a current collecting lead or the like, and sealed in a battery case to complete the secondary battery.

[0196] Note that the secondary battery according to the present embodiment is not limited to the form using a non-aqueous electrolyte solution as the non-aqueous electrolyte. For example, a secondary battery using a solid non-aqueous electrolyte, that is, an all-solid-state battery can also be used. In the case of an all-solid-state battery, the configuration other than the positive electrode active material can be changed as needed.

[0197] 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 as compared 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 electric vehicles that are restricted in mounting space. Note that the secondary battery can be used not only as a power source for electric vehicles that are purely driven by electrical energy, but also as a power source for so-called hybrid vehicles that are used in combination with combustion engines such as gasoline engines and diesel engines.

Example

[0198] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples. The analysis method of the metal contained in the positive electrode active material and various evaluation methods of the positive electrode active material in the Examples and Comparative Examples are as follows.

[0199] (1) Analysis of composition: Measured by ICP emission spectrometry.

[0200] (2) Volume average particle size (Mv) and particle size variation index [(D90 - D10) / average volume particle size]: Measured on a volume basis using a laser diffraction / scattering particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0201] (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.

[0202] (4) Volume resistivity: 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 4.0 g / cm 3 and then measured and determined by the resistivity test method using the four-probe method in accordance with JIS K 7194:1994 in the pressurized state.

[0203] (5) Amount of eluted lithium: 2 g of the positive electrode active material was taken and put into 125 ml of pure water at room temperature stirred by a stirrer. Immediately after the active material was put in, titration was carried out using an HCl aqueous solution with a concentration of 1 mol / L. The titration was carried out using an automatic titrator COM-1750 (manufactured by Hiranuma Sangyo Co., Ltd.) under the following conditions. Endpoint detection method: Inflection point detection Detection sensitivity: 2500 Burette model number: H-1700 Burette speed: 2 Minimum drop volume: 0.013 mL The titration results were evaluated by the Warder method, lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) were calculated, and the sum of these lithium amounts was calculated as the eluted lithium.

[0204] (6) Initial discharge capacity: The initial charge capacity and the initial discharge capacity were measured by the following method. After manufacturing the coin-type battery CBA shown in Fig. 16 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 as the initial charge capacity. After a 1-hour rest, the capacity when discharging to a cut-off voltage of 3.0 V was taken as the initial discharge capacity. For the measurement of the discharge capacity, a multi-channel voltage / current generator (manufactured by Advantest Corporation, R6741A) was used.

[0205] (Manufacture of coin-type battery) 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 pressed at a pressure of 100 MPa into a disk with a diameter of 11 mm and a thickness of 100 μm to fabricate the positive electrode (evaluation electrode) PE shown in Fig. 16. After drying the fabricated positive electrode PE in a vacuum dryer at 120 °C for 12 hours, a 2032 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 at -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.

[0206] (7) Maximum oxygen generation peak temperature 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 in (5) and charged at a 0.05 C rate up to a cut-off voltage of 4.3 V (constant current - constant voltage charging). After that, the coin 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 temperature.

[0207] (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 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 0.8 mg / L. Into this reaction tank, a 2.0 M mixed aqueous solution of nickel sulfate, manganese sulfate, and cobalt sulfate formulated so that the molar ratio of nickel:manganese:cobalt was 85:10:5, a 25% by mass sodium hydroxide solution which is an alkaline solution, and 25% by mass aqueous ammonia as a complexing agent were continuously added to the reaction tank simultaneously, and crystallization was carried out by a continuous crystallization method.

[0208] 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 12.0 - 12.6 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 = 0.85:0.10:0.05.

[0209] [Mixture Preparation 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 1.01:0.973:0.022:0.005, and then thoroughly mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy E. Bachofen (WAB)) to obtain a lithium mixture.

[0210] [Firing Step] The obtained lithium mixture was held at 850 °C for 10 hours in a stream of oxygen (oxygen concentration: 90% by volume) for firing, and then crushed to obtain particles of lithium nickel manganese cobalt composite oxide (cathode active material).

[0211] [Evaluation] The production conditions of the positive electrode active material are shown in Table 1, and the results of evaluating the obtained positive electrode active material by the above evaluation method are shown in Table 2. In addition, the molar ratio of each element in the following table represents a value obtained by rounding the fourth decimal place of the measured value, and the Ti / Nb molar ratio represents a ratio calculated from the measured values of the molar ratios of Ti and Nb, rounded to the second decimal place.

[0212] (Example 2A) In the firing process, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A except that the firing temperature was 870°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0213] (Example 3A) In the firing process, a positive electrode active material was obtained and evaluated in the same manner as in Example 1A except that the firing temperature was 890°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0214] (Example 4A) In the mixture preparation process, a positive electrode active material was obtained and evaluated in the same manner as in Example 2A except that the particles of the obtained 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 1.02:0.975:0.022:0.003. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0215] (Example 5A) In the mixture preparation process, a positive electrode active material was obtained and evaluated in the same manner as in Example 2A except that niobium oxide (Nb2O5) was used as the niobium compound. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0216] (Example 6A) In the firing process, firing was carried out in an oxygen stream (oxygen concentration: 60% by volume). The following is the same as in Example 2A to obtain a positive electrode active material and evaluate it. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0217] (Comparative Example 1A) In the mixture preparation process, a titanium compound and a niobium compound were not prepared. The obtained particles of nickel manganese cobalt composite hydroxide, lithium hydroxide, and lithium hydroxide were weighed so that the molar ratio of lithium:nickel:manganese:cobalt was 1.02:0.85:0.10:0.05. A positive electrode active material was obtained and evaluated in the same manner as in Example 1A except that the firing temperature was 800 °C in the firing process. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0218] (Comparative Example 2A) In the mixture preparation process, a niobium compound was not prepared. 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 1.02:0.974:0.026. A positive electrode active material was obtained and evaluated in the same manner as in Example 1A except that the firing temperature was 830 °C in the firing process. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0219] (Comparative Example 3A) In the mixture preparation process, a titanium compound was not prepared. 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 1.02:0.99:0.010. A positive electrode active material was obtained and evaluated in the same manner as in Example 1A except that the firing temperature was 850 °C in the firing process. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0220] (Comparative Example 4A) In the mixture preparation step, the particles of nickel manganese cobalt composite hydroxide obtained, 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 1.01:0.977:0.022:0.001. 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 set to 840°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 1 and 2.

[0221]

Table 1

[0222]

Table 2

[0223] (Example 1B) [Crystallization step] A predetermined amount of pure water was placed in a reaction tank (60 L), and the temperature inside the tank was set to 49°C while stirring. At this time, N2 gas was flowed into the reaction tank so that the dissolved oxygen concentration in the reaction tank liquid was 0.8 mg / L. A 2.0 M mixed aqueous solution of nickel sulfate, manganese sulfate, cobalt sulfate, and titanium sulfate, in which the molar ratio of nickel:manganese:cobalt:titanium was 0.833:0.095:0.050:0.022, a 25% by mass sodium hydroxide solution as an alkaline solution, and 25% by mass aqueous ammonia as a complexing agent were continuously added to the reaction tank simultaneously, 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 12.0 - 12.6 and the ammonia concentration was adjusted to 10 - 14 g / L. After the reaction tank was stabilized, a slurry containing nickel manganese cobalt titanium composite hydroxide was recovered from the overflow port, and then filtration was performed to obtain a cake of nickel manganese cobalt titanium composite hydroxide. 1 L of pure water was passed through 140 g of nickel manganese cobalt titanium composite hydroxide in the filter to wash the impurities. The filtered powder was dried to obtain particles of nickel manganese cobalt titanium composite hydroxide in which the molar ratio of nickel, manganese, cobalt, and titanium was represented as Ni:Mn:Co:Ti = 0.833:0.095:0.050:0.022.

[0225] [Mixture Preparation Step] The obtained particles of nickel manganese cobalt titanium composite hydroxide, lithium hydroxide, and niobic acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + titanium):niobium was 1.01:0.995:0.005, and then thoroughly mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy E. Bachofen (WAB)) to obtain a lithium mixture.

[0226] [Firing Step] The obtained lithium mixture was held at 850°C for 10 hours in an oxygen (oxygen concentration: 90% by volume) stream for firing, and then crushed to obtain particles of lithium nickel manganese cobalt composite oxide (cathode active material).

[0227] [Evaluation] Table 3 shows the manufacturing conditions of the cathode active material, and Table 4 shows the results of evaluating the obtained cathode active material by the above evaluation method.

[0228] (Example 2B) In the firing step, a cathode active material was obtained and evaluated in the same manner as in Example 1B except that the firing temperature was 870°C. Table 3 and 4 show the manufacturing conditions and evaluation results of the cathode active material.

[0229] (Example 3B) In the firing process, a positive electrode active material was obtained and evaluated in the same manner as in Example 1B, except that the firing temperature was set to 890°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0230] (Example 4B) In the mixture preparation process, a positive electrode active material was obtained and evaluated in the same manner as in Example 2B, except that the particles of the obtained nickel manganese cobalt titanium composite hydroxide, lithium hydroxide, and niobic acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + titanium):niobium was 1.01:0.997:0.003. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0231] (Example 5B) In the mixture preparation process, a positive electrode active material was obtained and evaluated in the same manner as in Example 2B, except that niobium oxide (Nb2O5) was used as the niobium compound. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0232] (Example 6B) In the firing process, firing was carried out in an oxygen (oxygen concentration: 60% by volume) gas stream. A positive electrode active material was obtained and evaluated in the same manner as in Example 2B. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0233] (Example 1C) [Crystallization process] In the crystallization process, crystallization was carried out in the same manner as in Example 1B, except that the 2.0 M mixed aqueous solution added to the reaction tank did not contain titanium sulfate, and nickel sulfate, manganese sulfate, and cobalt sulfate were blended so that the molar ratio of nickel:manganese:cobalt was 0.85:0.10:0.05. A cake of nickel manganese cobalt composite hydroxide obtained after filtration was obtained.

[0234] [Coating process] The cake of the obtained nickel manganese cobalt composite hydroxide was dispersed in pure water, adjusted to pH 8.2 using sulfuric acid, and then niobic acid dissolved in a potassium hydroxide solution was added so that the molar ratio of nickel:manganese:cobalt:niobium was 0.847:0.098:0.050:0.005, and the nickel manganese cobalt composite hydroxide was coated with a niobium compound.

[0235] [Mixture Preparation Step] The particles of the obtained nickel manganese cobalt niobium composite hydroxide, lithium hydroxide, and titanium oxide (TiO2) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + niobium):titanium was 1.01:0.978:0.022, and then mixed in the same manner as in Example 1B to obtain a lithium mixture. [Firing Step] Firing was carried out under the same conditions as in Example 2B to obtain and evaluate a positive electrode active material. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0236] (Example 2C) In the coating step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1C, except that niobic acid dissolved in a potassium hydroxide solution was added so that the molar ratio of nickel:manganese:cobalt:niobium was 0.848:0.097:0.052:0.003. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0237] (Comparative Example 1B) In the crystallization step, an aqueous titanium sulfate solution was used. In the mixture preparation step, no niobium compound was prepared. The particles of the obtained nickel manganese cobalt composite hydroxide, lithium hydroxide, were weighed so that the molar ratio of lithium:nickel:manganese:cobalt was 1.01:0.85:0.10:0.05, and 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 800°C. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0238] (Comparative Example 2B) In the mixture preparation step, without preparing a niobium compound, the obtained particles of nickel manganese cobalt titanium composite hydroxide and lithium hydroxide were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + titanium) was 1.01:1. A positive electrode active material was obtained and evaluated in the same manner as in Example 1B except that the firing temperature was set to 830°C in the firing step. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0239] (Comparative Example 3B) In the crystallization step, without preparing an aqueous titanium sulfate solution, 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 1.01:0.990:0.010. A positive electrode active material was obtained and evaluated in the same manner as in Example 1B except that the firing temperature was set to 850°C in the firing step. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0240] (Comparative Example 4B) In the mixture preparation step, the obtained particles of nickel manganese cobalt titanium composite hydroxide, lithium hydroxide, and niobic acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + titanium):niobium was 1.01:0.999:0.001. A positive electrode active material was obtained and evaluated in the same manner as in Example 1B except that the firing temperature was set to 840°C in the firing step. The production conditions and evaluation results of the positive electrode active material are shown in Tables 3 and 4.

[0241]

Table 3

[0242]

Table 4

[0243] (Evaluation Result 1) As shown in Tables 1 to 4 and FIGS. 1 and 2, the positive electrode active material obtained in the examples had a volume resistivity of 5×10 2 Ω·cm or more and a maximum oxygen generation peak temperature of 250°C or more, had high thermal stability, and it was clear that oxygen release during overcharge was suppressed.

[0244] Also, as shown in Tables 1 to 4 and FIG. 3, in Examples 1A to 5A, 1B to 5B, 1C, and 2C baked in an atmosphere with an oxygen concentration of 80% by volume, a positive electrode active material having a high discharge capacity of 184 mAh / g or more, high thermal stability, and a high battery capacity was obtained.

[0245] FIGS. 17(A) and 18(A) are diagrams showing cross-sectional photographs of the positive electrode active material. The portions surrounded by squares in these figures show an example of the locations used for analysis. By point analysis using STEM-EDX, the concentration (atomic %) of each element in the portion surrounded by the square was analyzed. FIGS. 17(B), 17(C) and FIGS. 18(B), 18(C) are diagrams showing an example of the results of evaluating the composition of the inside of the primary particles (FIG. 17(B): Example 2A, FIG. 17(C): Example 2B) and the grain boundaries (FIG. 18(B): Example 2B, FIG. 18(B): Example 2B) in the cross-section of the positive electrode active material obtained in Examples 2A and 2B by point analysis using STEM-EDX.

[0246] As shown in FIGS. 17(B), 17(C) and FIGS. 18(B), 18(C), niobium was segregated at the grain boundaries between the primary particles in the positive electrode active material obtained in the examples. Also, as shown in Tables 2 and 4, the niobium concentration at the grain boundaries between the primary particles (grain boundary niobium concentration / intragranular niobium concentration) was 1.3 times or more with respect to the niobium concentration inside the primary particles. Regarding titanium, segregation at the grain boundaries between the primary particles was not confirmed, and the titanium concentration at the grain boundaries between the primary particles (grain boundary titanium concentration / intragranular titanium concentration) was less than 1.3 times (specifically, 0.8 times or more and 1.1 times or less) with respect to the titanium concentration inside the primary particles.

[0247] On the other hand, since the positive electrode active materials of Comparative Examples 1A and 1B do not contain titanium and niobium, the volume resistivity during compression and the maximum oxygen generation peak temperature are low, and the thermal stability is not sufficient.

[0248] Further, in the positive electrode active materials of Comparative Examples 2A, 3A, 2B, and 3B, since they contain only one of titanium or niobium, the maximum oxygen generation peak temperature and the volume resistivity during compression are slightly higher compared to Comparative Example 1, but lower compared to the Examples, and it cannot be said that the thermal stability during short circuit is sufficient.

[0249] Moreover, in the positive electrode active materials of Comparative Examples 4A and 4B, since the niobium content is 0.001 or less, the volume resistivity during compression and the maximum oxygen generation peak temperature are low, and the thermal stability is not sufficient.

[0250] Hereinafter, Examples 11A to 11C that have undergone a water washing step and a drying step will be described. [Example 11A] To 150 parts by mass of the lithium nickel manganese cobalt titanium composite oxide obtained under the same conditions as in Example 2A, 100 parts by mass of water was mixed, and after stirring with water, suction filtration was performed using a Nutsche to obtain a precipitate (water washing step). The obtained precipitate was placed in a SUS container and heated to 100 °C for 12 hours and then to 190 °C for 10 hours using a vacuum dryer, and allowed to stand and dry to obtain a positive electrode active material (drying step). The production conditions and evaluation results of the positive electrode active material are shown in Tables 5 to 7. In Tables 5 to 7, for reference, the production conditions and evaluation results of the positive electrode active materials of Example 2A and Comparative Examples 1A to 4A are also shown.

[0251]

Table 5

[0252]

Table 6

[0253]

Table 7

[0254] (Example 7B) [Crystallization Process] A predetermined amount of pure water was placed in a reaction tank (60 L), and the temperature inside the tank was set to 49 °C while stirring. At this time, N2 gas was passed through the reaction tank so that the dissolved oxygen concentration in the reaction tank liquid was 0.8 mg / L. A 2.0 M mixed aqueous solution of nickel sulfate, manganese sulfate, cobalt sulfate, and titanium sulfate, a 25% by mass sodium hydroxide solution as an alkaline solution, and 25% by mass aqueous ammonia as a complexing agent were continuously added to the reaction tank simultaneously so that the molar ratio of nickel:manganese:cobalt:titanium was 0.829:0.098:0.050:0.023, and crystallization was carried out by the continuous crystallization method.

[0255] 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 12.0 - 12.6 and the ammonia concentration was adjusted to 10 - 14 g / L. After the reaction tank was stabilized, a slurry containing nickel manganese cobalt titanium composite hydroxide was recovered from the overflow port, and then filtration was carried out to obtain a cake of nickel manganese cobalt titanium composite hydroxide. Washing of impurities was carried out by passing 1 L of pure water through 140 g of nickel manganese cobalt titanium composite hydroxide in the filter. The powder after filtration was dried to obtain particles of nickel manganese cobalt titanium composite hydroxide containing titanium in which the molar ratio of the amounts of nickel, manganese, cobalt, and titanium was represented as Ni:Mn:Co:Ti = 0.829:0.098:0.050:0.023.

[0256] [Mixture Preparation Process] The obtained particles of nickel manganese cobalt titanium composite hydroxide containing titanium, lithium hydroxide, and niobic acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + titanium):niobium was 1.01:0.995:0.005, and then sufficiently mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy E. Bachofen (WAB)) to obtain a lithium mixture.

[0257] [Firing Process] The obtained lithium mixture was held at 870 °C for 10 hours in a stream of oxygen (oxygen concentration: 90% by volume) and fired, and then crushed to obtain particles of lithium nickel manganese cobalt composite oxide (positive electrode active material).

[0258] [Evaluation] The production conditions of the positive electrode active material are shown in Table 8, and the evaluation results of the obtained positive electrode active material are shown in Tables 9 and 10. Also, the 4.0 g / cm 3 volume resistivity during compression was 3.5×10 3 (Ω·cm).

[0259] (Example 11B) 150 parts by mass of lithium nickel manganese cobalt titanium composite oxide obtained under the same conditions as in Example 7B was mixed with 100 parts by mass of water, and after stirring with water, suction filtration was performed using a Nutsche to obtain a precipitate (water washing process). The obtained precipitate was placed in a SUS container, heated to 100 °C using a vacuum dryer for 12 hours, heated to 190 °C for 10 hours, and allowed to stand and dry to obtain a positive electrode active material (drying process). The production conditions and evaluation results of the positive electrode active material are shown in Tables 8 to 10.

[0260] (Example 11C) [Crystallization Process] In the crystallization process, the crystallization process was carried out in the same manner as in Example 11B except that the 2.0 M mixed aqueous solution added to the reaction tank did not contain titanium sulfate, and nickel sulfate, manganese sulfate, and cobalt sulfate were blended so that the molar ratio of nickel:manganese:cobalt was 0.85:0.10:0.05, and a cake of nickel manganese cobalt composite hydroxide obtained after filtration was obtained.

[0261] [Coating Process] The cake of the obtained nickel-manganese-cobalt composite hydroxide was dispersed in pure water, adjusted to pH 8.2 using sulfuric acid, and then niobic acid dissolved in a potassium hydroxide solution was added so that the molar ratio of nickel:manganese:cobalt:niobium was 0.845:0.100:0.050:0.005, and the nickel-manganese-cobalt composite hydroxide was coated with a niobium compound.

[0262] [Mixture Preparation Step] The particles of the obtained nickel-manganese-cobalt-niobium composite hydroxide, lithium hydroxide, and titanium oxide (TiO2) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + niobium):titanium was 1.01:0.978:0.022, and then mixed in the same manner as in Example 1B to obtain a lithium mixture.

[0263] [Firing Step] Firing, washing with water, and drying were carried out under the same conditions as in Example 11B to obtain and evaluate a positive electrode active material. The production conditions and evaluation results of the positive electrode active material are shown in Tables 8 to 10.

[0264] (Comparative Example 5B) In the crystallization step, an aqueous titanium sulfate solution was used. In the mixture preparation step, no niobium compound was prepared. The particles of the obtained nickel-manganese-cobalt composite hydroxide, lithium hydroxide, were weighed so that the molar ratio of lithium:nickel:manganese:cobalt was 1.02:0.85:0.10:0.05, and in the firing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 7B except that the firing temperature was 800 °C. The volume resistivity when the obtained positive electrode active material was compressed to 4.0 g / cm 3 was 8.5×10 1 Ω·cm. The production conditions and evaluation results of the positive electrode active material are shown in Tables 8 and 9.

[0265] (Comparative Example 6B) In the mixture preparation step, without preparing a niobium compound, the obtained particles of nickel manganese cobalt composite hydroxide containing titanium and lithium hydroxide were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + titanium) was 1.02:1. A positive electrode active material was obtained and evaluated in the same manner as in Example 7B except that the firing temperature was 830°C in the firing step. The volume resistivity when the obtained positive electrode active material was compressed to 4.0 g / cm 3 was 2.1×10 2 Ω·cm. The production conditions and evaluation results of the positive electrode active material are shown in Tables 8 and 9.

[0266] (Comparative Example 7B) In the crystallization step, without preparing an aqueous titanium sulfate solution, 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 1.01:0.991:0.009. A positive electrode active material was obtained and evaluated in the same manner as in Example 7B except that the firing temperature was 850°C in the firing step. The volume resistivity when the obtained positive electrode active material was compressed to 4.0 g / cm 3 was 3.4×10 2 Ω·cm. The production conditions and evaluation results of the positive electrode active material are shown in Tables 8 and 9.

[0267] (Comparative Example 8B) In the mixture preparation step, the obtained particles of nickel manganese cobalt composite hydroxide containing titanium, lithium hydroxide, and niobic acid (Nb2O5·4H2O) were weighed so that the molar ratio of lithium:(nickel + manganese + cobalt + titanium):niobium was 1.01:0.999:0.001. A positive electrode active material was obtained and evaluated in the same manner as in Example 7B except that the firing temperature was 840°C in the firing step. The volume resistivity when the obtained positive electrode active material was compressed to 4.0 g / cm 3 was 3.3×10 2 Ω·cm. The production conditions and evaluation results of the positive electrode active material are shown in Tables 8 and 9.

[0268]

Table 8

[0269]

Table 9

[0270]

Table 10

[0271] (Evaluation Results 2) As shown in Table 6, 9, and FIG. 4, the cathode active materials obtained in Examples 11A to 11C have a maximum oxygen generation peak temperature of 250° C. or higher, have high thermal stability, and it is clear that oxygen release during overcharge is suppressed.

[0272] Also, as shown in Table 6, 9, and FIG. 5, Examples 11A and 11B that were washed and dried have a higher discharge capacity compared to Examples 2A and 7B that were not washed and dried, and a cathode active material with higher battery capacity was obtained along with high thermal stability.

[0273] Also, as shown in Table 7 and 10, in Examples 2A and 7B that were not washed and dried, the amount of eluted lithium exceeded 0.20% by mass, while in Examples 11A, 11B, and 11C, the amount of eluted lithium was 0.20% by mass or less, indicating that the excess lithium was reduced.

[0274] On the other hand, in the cathode active materials of Comparative Examples 1A and 5B, since they do not contain titanium and niobium, the maximum oxygen generation peak temperature was low and the thermal stability was insufficient.

[0275] Also, in the cathode active materials of Comparative Examples 4A and 8B, since the niobium content was 0.001 or less, the maximum oxygen generation peak temperature was low and the thermal stability was insufficient.

Industrial Applicability

[0276] In this embodiment, a cathode active material for a lithium-ion secondary battery having high thermal stability and excellent battery characteristics can be obtained by an industrial manufacturing 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.

[0277] In addition, the secondary battery using the cathode active material according to this embodiment is excellent in thermal stability and also excellent in terms of capacity even when compared with a battery using a conventional cathode active material of a lithium nickel-based oxide. Therefore, since it can be miniaturized, it is suitable as a power source for electric vehicles that are restricted in mounting space.

[0278] In addition, the secondary battery using the cathode active material according to this embodiment can be used not only as a power source for electric vehicles that are purely driven by electric energy, but also as a power source for so-called hybrid vehicles that are used in combination with combustion engines such as gasoline engines and diesel engines, or as a stationary battery.

[0279] 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 contents of Japanese Patent Application Nos. 2019-127259, 2019-236895, 2020-092692, 2019-127258, 2019-236896, 2020-092693, 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

[0280] CBA… Coin-type battery (for evaluation) PE… Positive electrode (electrode for evaluation) NE… Negative electrode SE… Separator GA… Gasket WW… Wave washer PC… Positive electrode can NC…Negative electrode can G…Gap

Claims

1. A method for producing a positive electrode active material for a lithium-ion secondary battery, comprising a lithium nickel manganese composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated, including at least a mixture preparation step of preparing a mixture containing a nickel manganese composite compound, a lithium compound, and optionally one or both of a titanium compound and a niobium compound, and a firing step of firing the mixture at 750° C. or higher and 1000° C. or lower to obtain the lithium nickel manganese composite oxide, wherein the nickel manganese composite compound contains nickel (Ni), manganese (Mn), and optionally at least one element M (M) selected from the group consisting of Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, titanium (Ti), and niobium (Nb), and the molar ratio of each of the elements is represented by Ni:Mn:M:Ti:Nb = (1 - x - y):x:y:z':w' (where 0.03 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, 0 ≦ z' ≦ 0.05, 0 ≦ w' ≦ 0.03), the mixture satisfies 0.005 ≦ z ≦ 0.05, 0.001 < w ≦ 0.03, (z + w) ≦ 0.06, and z > w, where z is the molar ratio of titanium and w is the molar ratio of niobium with respect to the total molar amount of nickel, manganese, element M, titanium, and niobium, at least a part of niobium in the lithium nickel manganese composite oxide segregates at grain boundaries between the primary particles, 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 manganese 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 manganese composite oxide determined by point analysis using STEM-EDX, A method for producing a positive electrode active material for a lithium-ion secondary battery.

2. A method for producing a positive electrode active material for a lithium-ion secondary battery, comprising a lithium nickel manganese composite oxide having a hexagonal layered structure and composed of secondary particles in which a plurality of primary particles are aggregated, including at least a mixture preparation step of mixing a nickel manganese composite compound, a titanium compound, a niobium compound, and a lithium compound to prepare a mixture, A firing step of firing the mixture at 750°C or higher and 1000°C or lower to obtain the lithium nickel manganese composite oxide, The nickel manganese composite compound contains nickel (Ni), manganese (Mn), and optionally at least one element M (M) selected from the group consisting of Co, V, Mg, Mo, Ca, Cr, Ta, Na, W, Fe, Zn, B, Si, P, Zr, and Al, and the molar ratio of each of the elements is represented by Ni:Mn:M = (1 - x - y):x:y (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30), In the mixture, the ratio (z) of the amount of titanium and the ratio (w) of the amount of niobium to the total amount of nickel, manganese, element M, titanium, and niobium satisfy 0.005 ≤ z ≤ 0.05, 0.001 < w ≤ 0.03, (z + w) ≤ 0.06, and z > w, At least a part of the niobium in the lithium nickel manganese composite oxide segregates at the grain boundaries between the primary particles, 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 manganese 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 manganese composite oxide determined by point analysis using STEM-EDX, A method for producing a positive electrode active material for a lithium ion secondary battery.

3. A water washing step of mixing 150 parts by weight of the lithium nickel manganese composite oxide obtained after firing with 50 parts by weight or more and 200 parts by weight or less of water, stirring, and then performing solid-liquid separation, A drying step of drying the lithium nickel manganese composite oxide after water washing, Comprising: The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or claim 2.

4. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or claim 2, wherein in the mixture, the ratio (z) of the amount of titanium and the ratio (w) of the amount of niobium to the total amount of nickel, manganese, element M, titanium, and niobium satisfy 0.005 ≤ z ≤ 0.05, 0.002 ≤ w ≤ 0.03, (z + w) ≤ 0.06, and z > w.

5. In the step of preparing the mixture, at least a nickel-manganese composite compound containing titanium, a niobium compound, and a lithium compound are mixed, The nickel-manganese composite compound containing titanium contains nickel (Ni), manganese (Mn), titanium (Ti), and optionally at least one element M selected from the group consisting of 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 Ni:Mn:M:Ti = (1 - x - y - z'):x:y:z' (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.005 ≤ z' ≤ 0.05). The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1.

6. The nickel-manganese composite compound containing titanium is obtained by crystallization. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5.

7. The nickel-manganese composite compound containing titanium is obtained by coating a nickel-manganese composite compound obtained by crystallization with a compound containing titanium. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5.

8. In the step of preparing the mixture, at least a nickel-manganese composite compound containing niobium, a lithium compound, and a titanium compound are mixed. The nickel-manganese composite compound containing niobium contains nickel (Ni), manganese (Mn), niobium (Nb), and optionally at least one element M selected from the group consisting of 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 Ni:Mn:M:Nb = (1 - x - y):x:y:w' (where 0.03 ≤ x ≤ 0.30, 0 ≤ y ≤ 0.30, 0.001 < w' ≤ 0.03). The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1.

9. The nickel-manganese composite compound containing niobium is obtained by coating a nickel-manganese composite compound obtained by crystallization with a compound containing niobium. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 8.

10. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 8, wherein the molar ratio of the elements in the nickel-manganese composite compound containing niobium is represented by Ni:Mn:M:Nb = (1−x−y):x:y:w' (where 0.03 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, 0.002 ≦ w' ≦ 0.03).

11. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 10, wherein the firing step is performed in an atmosphere having an oxygen concentration of 80% by volume or more and 100% by volume or less.

12. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 11, wherein titanium in the lithium nickel manganese composite oxide is present inside the primary particles.

13. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 12, wherein the titanium compound is titanium oxide.

14. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 13, wherein the niobium compound is niobium oxide, niobic acid, or a mixture thereof.

15. The lithium nickel manganese composite oxide obtained after firing has a volume resistivity of 5.0×10 ３ when compressed to 4.0 g / cm ２ Ω·cm or more and 1.0×10 ５ Ω·cm or less. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 14.

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