JP2020102431A - Positive electrode active material for lithium ion secondary battery and production method thereof, and lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material capable of obtaining a lithium ion secondary battery where high battery capacity and low positive electrode resistance are compatible with low conductivity.SOLUTION: A positive electrode active material for lithium ion secondary battery contains a lithium-nickel-manganese composite oxide composed of secondary particles agglutinating multiple primary particles, where the lithium-nickel-manganese composite oxide contains lithium nickel, manganese, boron, and titanium, and an element M arbitrarily, the mass ratio of respective elements is Li:Ni:Mn:M1:B:Ti=e:(1-a-b-c-d):a:b:c:d (where, 0.05≤a≤0.60, 0≤b≤0.60, 0.001≤c≤0.03, 0.001≤d≤0.05, and 0.95≤e≤1.20, the element M1 is represented by at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Cr, Zr and Ta, and at least part of boron is segregated to at least one of the surface of the primary particles or the grain boundary.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery.

In recent years, with the spread of portable electronic devices such as mobile phones and notebook computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density and durability has been strongly desired. Further, development of a high output secondary battery as a battery for electric vehicles such as electric tools and hybrid vehicles is strongly desired.

There is a lithium ion secondary battery as a non-aqueous electrolyte secondary battery that satisfies such requirements. The lithium ion secondary battery is composed of a negative electrode, a positive electrode, a non-aqueous electrolyte, etc., and a material capable of desorbing and inserting lithium is used as an active material of the negative electrode and the positive electrode.

Regarding lithium-ion secondary batteries, research and development are currently being actively conducted. Among them, lithium-ion secondary batteries using a lithium metal composite oxide having a layered or spinel type crystal structure as a positive electrode material are Since a high voltage of 4 V class can be obtained, it is being put to practical use as a battery having a high energy density.

As a positive electrode active material of a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize at present, lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, Lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _{0. 5} Mn _0.5 O ₂ ) and other lithium metal composite oxides have been proposed.

By the way, since a lithium ion secondary battery uses a non-aqueous electrolyte as a battery material, high thermal stability is required. For example, when a short circuit occurs inside the lithium ion secondary battery, heat is generated due to a sudden current, and thus higher thermal stability is required. It is considered effective to reduce the conductivity of the positive electrode active material as one of methods for suppressing a rapid current due to a short circuit.

For example, in Patent Document 1, a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium nickel manganese composite oxide composed of secondary particles obtained by aggregating a plurality of primary particles, wherein the lithium nickel manganese composite oxide is , general formula _{(1): Li d Ni 1} -a-b-c Mn a M b Nb c O 2 + γ ( the general formula (1), M is, Co, W, Mo, V , Mg, Ca, Al , Ti, Cr, Zr, and Ta, and at least one element selected from 0.05≦a≦0.60, 0≦b≦0.60, 0.0003≦c≦0.03, 0. 95≦d≦1.20, 0≦γ≦0.5), at least a part of niobium is solid-dissolved in the primary particles, and the average niobium concentration in the primary particles is Then, an active material for a non-aqueous electrolyte secondary battery in which the maximum niobium concentration in the primary particles is 1 to 3 times is proposed. According to Patent Document 1, a secondary battery using this positive electrode active material can achieve both high energy density and output characteristics and thermal stability at the time of short circuit due to low conductivity.

International Publication No. 2018/043669 JP, 2008-017729, A Patent No. 4807467 JP, 2006-147499, A JP, 2007-265784, A JP, 2008-257902, A JP 2008-198364 A JP, 2004-325278, A JP, 2013-239434, A

However, in general, the higher the conductivity of the positive electrode active material, the better the battery characteristics such as battery capacity (charge/discharge capacity) and output characteristics tend to be. Therefore, it is difficult to achieve both high battery characteristics and low conductivity. .. Further, the positive electrode active material described in Patent Document 1 has been proposed to reduce the conductivity by containing niobium in a specific form, but since niobium is expensive, there is a problem in terms of cost. ..

The present invention has been made in view of these circumstances, and an object thereof is to provide a positive electrode active material capable of achieving both high battery capacity and output characteristics in a secondary battery and low conductivity at low cost. .. Another object of the present invention is to provide a method capable of easily producing such a positive electrode active material in industrial scale production.

By the way, several techniques for adding various metal elements to a lithium metal composite oxide have been proposed for the purpose of obtaining a positive electrode active material having high battery characteristics. For example, Patent Documents 2 to 7 propose techniques for adding titanium to a lithium metal composite oxide. According to Patent Documents 2 to 6, the positive electrode active material made of a lithium nickel cobalt titanium composite oxide has good thermal stability and a high battery capacity.

Also, some techniques for adding boron to the lithium metal composite oxide have been proposed. For example, Patent Document 8 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery having at least a layered crystal structure lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is particles and There has been proposed a positive electrode active material for a non-aqueous electrolyte secondary battery, which has lithium borate on at least the surface of the particles. According to Patent Document 7, this positive electrode active material is said to have excellent thermal stability.

Further, for example, Patent Document 9, the general formula _{Li a Ni 1-x-y} Co x M1 y W z M 2 wO 2 (1.0 ≦ a ≦ 1.5,0 ≦ x ≦ 0.5,0 ≦y≦0.5, 0.002≦z≦0.03, 0≦w≦0.02, 0≦x+y≦0.7, M1 is at least one selected from the group consisting of Mn and Al, and M2 is A non-aqueous electrolyte containing a lithium-transition metal composite oxide represented by at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, and Mo, and a boron compound containing at least a boron element and an oxygen element. A positive electrode composition for a secondary battery has been proposed. According to Patent Document 8, this positive electrode composition can improve output characteristics and cycle characteristics.

However, the above Patent Documents 2 to 9 do not describe any influence on the conductivity of the positive electrode active material when titanium or boron is added to the lithium nickel manganese composite oxide. Furthermore, these patent documents do not describe at all the effect of adding titanium and boron in combination.

A first aspect of the present invention includes a lithium nickel manganese composite oxide composed of secondary particles obtained by aggregating a plurality of primary particles, wherein the lithium nickel manganese composite oxide includes lithium, nickel, manganese, boron, and titanium. , And optionally containing the element M1, and the material amount ratio of each element is Li:Ni:Mn:M1:B:Ti=e:(1-a-b-c-d):a:b:c: d (however, 0.05≦a≦0.60, 0≦b≦0.60, 0.001≦c≦0.03, 0.001≦d≦0.05, 0.95≦e≦1. 20 and the element M1 is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Cr, Zr, and Ta.), and at least a part of boron is included. Provided is a positive electrode active material for a lithium ion secondary battery, which is segregated on at least one of the surface of primary particles and a grain boundary.

Further, in cross-sectional SEM observation in the secondary particles, it is preferable that voids exist in the secondary particles and that the void ratio in the secondary particles be 0.2% or more and 10% or less. The volume average particle size MV is preferably 5 μm or more and 30 μm or less. In addition, the electric conductivity when compressed at 4.0 g/cm ³ obtained by measurement of dust resistance is in the range of 1.0×10 ⁻⁶ S/cm or more and 4.0×10 ⁻³ S/cm or less. It is preferable.

A second aspect of the present invention is a method for producing a positive electrode active material for a lithium-ion secondary battery, which comprises a lithium nickel manganese composite oxide composed of secondary particles in which a plurality of primary particles are aggregated, and comprises the following steps: The method includes: a mixing step including at least one of (1-a), (1-b), and (1-c); and a step (2), wherein the lithium nickel manganese composite oxide is at least A material amount ratio (Li/Me) of lithium and a metal element Me other than lithium is 0.95 or more and 1.20 or less, including lithium, nickel, manganese, boron, and titanium, and at least a part of boron Is segregated on at least one of the surface and the grain boundary of the primary particle, the method for producing a positive electrode active material for a lithium ion secondary battery.
Step (1-a): nickel and manganese, and optionally an element M2, and the material ratio of each element is Ni:Mn:M2=(1-ab'):a:b' (however, , 0.05≦a≦0.60, 0≦b′≦0.60, and M2 is selected from Ti, Co, W, Mo, V, Mg, Ca, Al, Cr, Zr, and Ta. A nickel manganese composite compound represented by the formula (1), a boron compound, a titanium compound, and a lithium compound to obtain a lithium mixture;
Step (1-b): The surface is coated with a titanium compound, and nickel, manganese, and optionally the element M2 are contained, and the substance amount ratio of each element is Ni:Mn:M2=(1-a -B'): a:b' (where 0.05≤a≤0.60, 0≤b'≤0.60, and M2 is Ti, Co, W, Mo, V, Mg, Ca, A mixing step of mixing a nickel-manganese composite compound represented by Al, Cr, Zr, and Ta), a boron compound, and a lithium compound to obtain a lithium mixture. Step (1-c): Nickel, manganese, and titanium, and optionally the element M1, and the substance ratio of each element is Ni:Mn:M1:Ti=(1-a-b-d):a. :B:d (where 0.05≦a≦0.60, 0≦b≦0.60, 0.001≦d≦0.05, and M1 is Co, W, Mo, V, Mg, A nickel-manganese composite compound represented by the formula: at least one element selected from Ca, Al, Cr, Zr, and Ta, a boron compound, and a lithium compound are mixed to obtain a lithium mixture. Process;
Step (2): firing step of firing the lithium mixture at 750° C. or higher and 1000° C. or lower in an oxidizing atmosphere to obtain a lithium nickel manganese composite oxide;
In the mixing step, the lithium mixture contains titanium in an amount of 0.1 atomic% or more and 5 atomic% or less and boron in an amount of 0.1 atomic% or more and 3 atomic% or less with respect to the total amount of the metal element Me excluding lithium. Including.

Further, the following step (1-1) may be provided before the mixing step, and the average particle diameter of the boron compound in the mixing step may be 1 μm or more and 1 mm or less.
Step (1-1): A crystallization step of obtaining a nickel-manganese composite compound by crystallization.

Further, the boron compound in the mixing step may be at least one of boric acid, boron oxide, lithium borate, and ammonium borate.

Further, before the mixing step, the following steps (1-1) and (1-2) are provided, and in the mixing step, the boron compound may be mixed while being impregnated with the nickel-manganese composite compound. ..
(1-1) A crystallization step of obtaining a nickel-manganese composite compound by crystallization;
(1-2) A solution containing at least one of boric acid and borate is added to a slurry obtained by mixing the nickel-manganese composite compound and water to impregnate the nickel-manganese composite compound with boron. Boron impregnation process.

Further, the following step (1-3) may be provided before the mixing step.
(1-3) A heat treatment step of heat treating the nickel-manganese composite compound at a temperature of 105° C. or higher and 700° C. or lower.

According to a third aspect of the present invention, there is provided a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte solution, the positive electrode containing the positive electrode active material described above.

INDUSTRIAL APPLICABILITY The positive electrode active material for a lithium ion secondary battery of the present invention can achieve both high battery capacity and output characteristics and low conductivity in a secondary battery at low cost. Further, the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention can easily produce such a positive electrode active material in industrial scale production, and thus can be said to have an extremely high industrial value. ..

FIG. 1 is a graph showing the electric conductivity and the positive electrode resistance of the positive electrode active materials obtained in Example 2 and Comparative Examples 1, 2, and 3. FIG. 2 is a diagram showing an example of the method for producing the positive electrode active material of the present embodiment. FIG. 3 is a diagram showing an example of the method for producing the positive electrode active material of the present embodiment. FIG. 4 is a diagram showing an example of the method for producing the positive electrode active material of the present embodiment. FIG. 5(A) and FIG. 5(B) are diagrams showing an example of a method for producing a nickel-manganese composite compound according to this embodiment. FIG. 6 is a diagram showing an example of the mixing step (S1) according to the present embodiment. FIG. 7 is a schematic sectional view of a coin-type battery used for battery evaluation. FIG. 8 is a diagram showing an example of an equivalent circuit used for impedance evaluation and a Nyquist plot. FIG. 9 is a view showing an SEM image of the positive electrode active material (cross section) obtained in Example 2. FIG. 10 is a view showing an SEM image of the positive electrode active material (cross section) obtained in Comparative Example 2. FIG. 11 is a graph showing the conductivity and the positive electrode resistance of the positive electrode active materials obtained in Examples 1 to 3 and Comparative Examples 2 and 4. FIG. 12 is a graph showing the electric conductivity and the positive electrode resistance of the positive electrode active materials obtained in Examples 2, 4 to 5 and Comparative Examples 3 and 5.

Hereinafter, the present embodiment will be described with reference to a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery using the positive electrode active material.

1. Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for lithium ion secondary battery according to the present embodiment (hereinafter, also referred to as “positive electrode active material”) is composed of secondary particles obtained by aggregating a plurality of primary particles. Including lithium nickel manganese composite oxide. The lithium nickel manganese composite oxide contains lithium, nickel, manganese, boron, and titanium, and optionally the element M1, and the material amount ratio (molar ratio) of each element is Li:Ni:Mn:M1:B:. Ti=e:(1-a-b-c-d):a:b:c:d (where 0.05≤a≤0.60, 0≤b≤0.60, 0.001≤c≤ 0.03, 0.001≦d≦0.05, 0.95≦e≦1.20, and the element M is Co, W, Mo, V, Mg, Ca, Al, Cr, Zr, and Ta. Which is at least one element selected from the above).

Further, at least part of boron contained in the lithium nickel manganese composite oxide segregates on at least one of the surface of primary particles and the grain boundary. At least a part of boron contained in the lithium nickel manganese composite oxide may exist in a state in which it can be removed by washing with water, as described later.

As a result of intensive studies by the present inventors, the present invention provides a positive electrode active material obtained by adding a specific amount of titanium (Ti) and boron (B) in the production process of a lithium nickel manganese composite oxide. It has been completed by finding that it is possible to realize both high battery capacity and output characteristics and low conductivity.

In the lithium ion secondary battery, when the positive electrode and the negative electrode are short-circuited, a current rapidly flows and a large amount of heat is generated, so that the positive electrode active material is decomposed, and a chain of further heat generation may occur. Here, when the positive electrode active material with reduced conductivity is used for the positive electrode of the secondary battery, like the positive electrode active material according to the present embodiment, it is possible to suppress a rapid increase in current caused by a short circuit, The thermal stability at the time of short circuit can be further improved. The thermal stability at the time of short circuit can be evaluated by, for example, a nail penetration test or a foreign matter short circuit test.

Further, the positive electrode active material according to the present embodiment has a high battery capacity and a low positive electrode resistance in a secondary battery, although it has low conductivity. When the positive electrode resistance is low, the voltage lost in the battery decreases, the voltage actually applied to the load side becomes relatively high, and high output can be obtained.

Hereinafter, the relationship between the addition of titanium (Ti) and boron (B) and the conductivity and the battery characteristics (eg, positive electrode resistance) in the lithium nickel manganese composite oxide will be described with reference to FIG. Note that FIG. 1 is created based on the evaluation results of the positive electrode active material and the secondary battery obtained in Examples and Comparative Examples described later.

FIG. 1 shows a lithium nickel manganese composite oxide in Comparative Example 1 in which titanium and boron were not added, Comparative Example 2 in which titanium was added alone (Ti: 2.3 atomic %), and Comparative Example 3 in which boron was added alone. (B: 0.5 atom %), and a graph showing conductivity and positive electrode resistance of Example 2 in which the same amounts of titanium and boron were added as Comparative Examples 2 and 3 (conductivity: left axis, bar graph). , Positive resistance: right axis, line graph).

As shown in FIG. 1, as compared with the case where titanium is added alone (Comparative Example 2) and the case where titanium and boron are not added (Comparative Example 1), the conductivity is reduced and the positive electrode resistance is also reduced. .. On the other hand, when boron is added alone (Comparative Example 3), as compared with the case where titanium and boron are not added (Comparative Example 1), the positive electrode resistance is reduced, but the conductivity is increased and the thermal stability during short circuit Is expected to get worse. However, when both titanium and boron are added (Example 2), not only the positive electrode resistance is reduced as compared with the cases where titanium and boron are added alone (Comparative Examples 2 and 3), but the conductivity is It was shown that the conductivity was further reduced as compared with the case where titanium was added alone (Comparative Example 2).

From the above, it is clear that, in the lithium nickel manganese composite oxide, by adding titanium and boron in combination, it is possible to achieve both high battery characteristics and low conductivity at a high level. Hereinafter, the configuration of the positive electrode active material according to this embodiment will be described in detail.

[Lithium nickel manganese composite oxide]
The lithium nickel manganese composite oxide contained in the positive electrode active material according to the present embodiment is composed of secondary particles obtained by aggregating a plurality of primary particles. The lithium nickel manganese composite oxide contains lithium, nickel, manganese, boron, and titanium, and optionally the element M, and the substance ratio (molar ratio) of each element is Li:Ni:Mn:M1:. B:Ti=e:(1-a-b-c-d):a:b:c:d (where 0.05≦a≦0.60, 0≦b≦0.60, 0.001≦ c≦0.03, 0.001≦d≦0.05, 0.95≦e≦1.20, and the element M1 is Co, W, Mo, V, Mg, Ca, Al, Cr, Zr and It is at least one element selected from Ta). The substance amount ratio of each element can be measured by quantitative analysis by inductively coupled plasma (ICP) emission spectrometry. Hereinafter, each element will be described.

(lithium)
In the above ratio, e indicating the content of lithium (Li) is a substance amount ratio (Li/Me) of Li and a metal element Me other than lithium (that is, Ni, Mn, M1, Ti, and B). Corresponding to. The range of e is 0.95≦e≦1.20, and may be 1.00≦e≦1.05. The value of e may exceed 1.

(manganese)
In the above ratio, the range of a showing the content of manganese (Mn) is 0.05≦a≦0.60, preferably 0.05≦a≦0.50, and more preferably 0.05. <a≦0.35, and more preferably 0.05≦a≦0.25. When a is in the above range, the thermal stability is excellent. In addition, in the firing step (S3) described below, by including manganese, the firing temperature can be increased and the dispersion of boron and titanium can be promoted.

(Element M1)
The element M1 is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, and Ta. In the above ratio, the range of b showing the content of the element M1 is 0≦b≦0.60. When b exceeds 0, thermal stability, storage characteristics, battery characteristics, etc. can be improved. For example, when the element M1 contains Co, the battery capacity and output characteristics are excellent. In the above ratio, when the content of Co contained in the element M1 is b1, it is preferably 0.01≦b1≦0.50, and more preferably 0.01≦b1≦0.40.

(Boron)
In the above ratio, the range of c showing the content of boron (B) is 0.001≦c≦0.030, preferably 0.001≦c≦0.025, and more preferably 0.003. ≦c≦0.020. As described above, in the case where boron is contained in the above range in addition to titanium, the conductivity of the lithium nickel manganese composite oxide can be significantly reduced and high battery characteristics (battery capacity, positive electrode resistance) can be obtained. .. On the other hand, when the value of c exceeds 0.03, the positive electrode resistance increases and sufficient battery capacity and output characteristics cannot be obtained.

Further, at least a part of boron segregates on at least one of the surface of the primary particle and the grain boundary. The presence of boron can be confirmed, for example, by EDX measurement using a scanning transmission electron microscope (S-TEM) and performing line analysis/area analysis of the composition of the cross section of the primary particles.

(Titanium)
In the above ratio, the range of d indicating the content of titanium (Ti) is 0.001≦d≦0.05, may be 0.001≦d≦0.04, and 0.005≦d It may be ≦0.035. As described above, when titanium is contained in the above range in addition to boron, the conductivity of the lithium nickel manganese composite oxide can be significantly reduced and high battery characteristics (battery capacity, positive electrode resistance) can be obtained. ..

At least a part of titanium may be present on at least one of the surface and the grain boundary of the primary particles, as in the case of boron.

(nickel)
In the above ratio, the range of (1-a-bcd) showing the content of nickel (Ni) is a value that varies depending on the content of other metal elements other than lithium, and preferably 0<( 1−a−b−c)≦0.948, and more preferably 0.3≦(1−a−b−c)≦0.948. The value of (1-a-b-c-d) may be 0.5 or more, or may be 0.6 or more, from the viewpoint of improving the battery capacity (charge/discharge capacity).

Incidentally, the lithium-nickel-manganese composite oxide, for example, the general formula _{(1): Li e Ni 1} -a-b-c-d Mn a M1 b B c Ti d O ₂ (the above general formula (1), 0 0.05≦a≦0.60, 0≦b≦0.60, 0.001≦c≦0.03, 0.001≦d≦0.05, 0.95≦e≦1.20, and M1 Is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Cr, Zr, and Ta.). The preferable range of each element in the general formula (1) is the same as the above substance amount ratio. In addition, the lithium nickel manganese composite oxide preferably has a layered crystal structure.

[Porosity]
The lithium nickel manganese composite oxide may have voids in the secondary particles. The voids can be confirmed by observing the cross section inside the secondary particles with a scanning electron microscope (SEM). The porosity in the secondary particles is preferably 0.2% or more and 10% or less, more preferably 0.2% or more and 5% or less. The porosity can be set within the above range, for example, by appropriately adjusting the addition amount of the boron compound in the production method described later.

The porosity in the secondary particles can be measured, for example, by the following method. First, after embedding a plurality of lithium nickel manganese composite oxides in a resin or the like and making it possible to observe the cross-section of secondary particles by cross section polisher processing or the like, an image is acquired by a scanning electron microscope (SEM). Then, randomly select 20 cross sections of secondary particles having a volume average particle size (MV) of 50% or more from the acquired image, and calculate the porosity (%) of each cross section from the following formula. Then, the average value is calculated as the porosity of the cross section of the secondary particles.
Formula: Porosity=[(void area in secondary particles)/(cross-sectional area of secondary particles)×100]
However, the void area in the secondary particles (in the cross section) and the cross-sectional area of the secondary particles in the above formula are determined using image analysis software (ImageJ or the like).

FIG. 9 is a diagram showing an example of a cross section of the lithium nickel manganese composite oxide 10 according to the present embodiment. As shown in FIG. 9, it is preferable that the voids G exist relatively uniformly in the cross section of the secondary particles. In the production method described below, it is considered that voids are formed due to the addition of the boron compound, and the presence of the voids uniformly in the secondary particles means that the boron compound is uniformly diffused throughout the secondary particles. Indirectly.

It should be noted that the size of voids in the secondary particles is determined by observing particles having a secondary particle diameter within the volume average particle diameter MV±4 μm in the cross-sectional observation of the secondary particles (per one ) A value obtained by dividing the longest diameter (average) of the voids by the secondary particle diameter is about 0.005 or more and 0.050 or less.

[Volume average particle size MV]
The volume average particle size MV of the positive electrode active material is preferably 5 μm or more and 40 μm or less, more preferably 10 μm or more and 25 μm or less. When the volume average particle size MV is in the above range, when the positive electrode active material is used for the positive electrode of the secondary battery, it is possible to achieve both high output characteristics and battery capacity and high filling property in the positive electrode. If the average particle size of the secondary particles is less than 5 μm, high filling properties for the positive electrode may not be obtained, and if the average particle size exceeds 30 μm, high output characteristics and battery capacity may not be obtained. The average particle size can be obtained from, for example, a volume integrated value measured by a laser light diffraction/scattering particle size distribution meter.

[conductivity]
The positive electrode active material preferably has a conductivity of 1.0×10 ⁻⁶ S/cm or more and 4.0×10 ⁻³ S/cm or less, which is determined by measurement of dust resistance. Usually, the higher the conductivity of the positive electrode active material, the lower the resistance in the electrochemical reaction is considered to be an excellent active material.However, considering the thermal stability during a short circuit, the conductivity is reasonably low, so that a short circuit occurs. It is possible to suppress the sudden generation of current. Therefore, when the conductivity of the positive electrode active material is within the above range, high thermal stability at the time of short circuit can be obtained. Further, the conductivity may be 1.0×10 ⁻⁵ S/cm or more and 3.0×10 ⁻³ S/cm or less from the viewpoint of achieving both battery characteristics and thermal stability at the time of short circuit, It may be 1.0×10 ⁻⁴ S/cm or more and 2.0×10 ⁻³ S/cm or less. The conductivity 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, press-molding it into a cylindrical shape having a diameter of 20 mm to be 4.0 g/cc, and then applying pressure. In this state, the volume resistivity measured by the resistivity test method by the 4-probe method according to JIS K 7194:1994 can be converted and obtained.

The lithium nickel manganese composite oxide may contain a small amount of the above-mentioned metal elements (Li, Ni, Mn, M1, B, Ti) and elements other than oxygen within a range that does not impair the effects of the present invention. The lithium nickel manganese composite oxide contained in the positive electrode active material may contain a small amount of single primary particles in addition to the secondary particles. Further, the positive electrode active material may contain a compound other than the above lithium nickel manganese composite oxide.

2. Method for Manufacturing Positive Electrode Active Material for Lithium Ion Secondary Battery FIGS. 2 to 4 show an example of a method for manufacturing a positive electrode active material for a lithium ion secondary battery (hereinafter, referred to as “positive electrode active material”) according to the present embodiment. It is a figure.

The method for producing a positive electrode active material according to this embodiment includes a mixing step (S1) and a firing step (S2). Further, the mixing step (S1) includes at least one of the following steps (1-a), (1-b) and (1-c).

The method for producing a positive electrode active material according to this embodiment may include the following step (1-a) and step (2), for example, as shown in FIG. 2.
Step (1-a): Mixing step (S1-a) in which a nickel-manganese composite compound, a boron compound, a titanium compound, and a lithium compound are mixed to obtain a lithium mixture;
Step (2): A firing step (S2) of firing the lithium mixture at 750° C. or higher and 1000° C. or lower in an oxidizing atmosphere to obtain a lithium nickel manganese composite oxide.

Further, the method for manufacturing the positive electrode active material according to the present embodiment may include the following step (1-b) and step (2), for example, as shown in FIG. 3.
Step (1-b): A nickel-manganese composite compound coated with a titanium compound, a boron compound, a titanium compound, and a lithium compound are mixed to obtain a lithium mixture, a mixing step (S1-a);
Step (2): A firing step (S2) of firing the lithium mixture at 750° C. or higher and 1000° C. or lower in an oxidizing atmosphere to obtain a lithium nickel manganese composite oxide.

Further, the method for producing a positive electrode active material according to this embodiment may include the following step (1-c) and step (2), for example, as shown in FIG. 4.
(1-c) Mixing step (S2) of mixing a nickel-manganese composite compound containing nickel, manganese, and titanium, a boron compound, and a lithium compound to obtain a lithium mixture.
(2) A firing step (S2) of firing the lithium mixture at 750° C. or higher and 1000° C. or lower in an oxidizing atmosphere to obtain a lithium nickel manganese composite oxide.

The method for producing a positive electrode active material according to the present embodiment, in any case including a nickel-manganese composite compound, a lithium compound, a specific amount of boron, and titanium, by firing a lithium mixture by firing Obtainable. Further, by this manufacturing method, the positive electrode active material containing the lithium nickel manganese composite oxide described above can be easily obtained on an industrial scale.

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

[Crystallization Step (S1-1)]
In the method for producing a positive electrode active material according to the present embodiment, as shown in FIG. 5(A), before the mixing step (S1), a crystallization step (S1-1) of obtaining a nickel-manganese composite compound by crystallization is performed. It is preferable to provide. Hereinafter, the crystallization step (S1-1) will be described.

The crystallization step (S1-1) is a step of obtaining the nickel-manganese composite compound (nickel-manganese composite hydroxide) used in the mixing step (S1) by crystallization. The crystallization step (S1-1) can be performed by a conventionally known method. For example, when a nickel-manganese composite compound containing titanium used in the mixing step (S2) is obtained, it is described in Patent Documents 4 to 6. Crystallization methods can be used. Hereinafter, with respect to the crystallization step (S1-1), the case of obtaining the nickel-manganese composite compound (nickel, manganese, optionally containing the element M2) used in the mixing steps (S1-a) and (S1-b) will be taken as an example. explain.

First, in a reaction tank, a mixed aqueous solution containing nickel and manganese is stirred at a constant rate while a neutralizing agent is added to neutralize the pH to control the nickel-manganese composite hydroxide ( Nickel manganese composite compound) is produced by co-precipitation.

As the mixed aqueous solution containing nickel and manganese, for example, a sulfate solution, a nitrate solution, or a chloride solution of nickel and manganese can be used. Further, the mixed aqueous solution may contain the element M2. The composition of the metal element contained in the mixed aqueous solution is almost the same as the composition of the metal element contained in the obtained nickel manganese composite hydroxide. Therefore, the composition of the metal element of the mixed aqueous solution can be adjusted so as to be the same as the intended composition of the metal element of the nickel-manganese composite hydroxide. As the neutralizing agent, an alkaline aqueous solution can be used, and for example, sodium hydroxide, potassium hydroxide or the like can be used.

Further, it is preferable to add the complexing agent to the mixed aqueous solution together with the neutralizing agent. The complexing agent is not particularly limited as long as it is capable of forming a complex by binding with nickel ions or other metal ions in an aqueous solution in the reaction tank (hereinafter referred to as “reaction aqueous solution”), and known ones It can be used, for example, an ammonium ion donor can be used. The ammonium ion supplier is not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride or the like can be used. By adding a complexing agent, the solubility of metal ions in the reaction aqueous solution can be adjusted.

In the crystallization step (S1-1), when the complexing agent is not used, the temperature of the reaction aqueous solution is preferably such that the temperature (liquid temperature) exceeds 60° C. and 80° C. or less, and The pH of the aqueous reaction solution at temperature is preferably 10 or more and 12 or less (25° C. standard). When the pH of the reaction aqueous solution exceeds 12, the resulting composite hydroxide particles become fine particles, the filterability deteriorates, and spherical particles may not be obtained. On the other hand, when the pH of the reaction aqueous solution is less than 10, the production rate of the composite hydroxide particles is remarkably slowed, Ni remains in the filtrate, and the Ni precipitation amount deviates from the target composition, and the composite ratio of the target ratio is increased. Hydroxide may not be obtained.

Further, when the temperature of the reaction aqueous solution exceeds 60° C., the phenomenon that the solubility of Ni increases, the amount of Ni precipitation deviates from the target composition, and coprecipitation does not occur can be avoided. On the other hand, when the temperature of the reaction aqueous solution exceeds 80° C., the slurry concentration (reaction aqueous solution concentration) increases due to a large amount of water vaporization, the Ni solubility decreases, and crystals such as sodium sulfate are generated in the filtrate. However, there is a possibility that the charge/discharge capacity of the positive electrode active material may decrease, such as the impurity concentration increasing.

In the crystallization step (S1-1), when an ammonium ion donor (complexing agent) is used, 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 more and 13 or less (25° C. standard).

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, and thus primary particles of a complex hydroxide having a regular shape and particle size may not be formed. Further, since gel-like nuclei are likely to be formed, the particle size distribution of the obtained composite hydroxide particles is likely to broaden. On the other hand, when the ammonia concentration exceeds 25 g/L, the solubility of metal ions becomes too large, the amount of metal ions remaining in the reaction aqueous solution increases, and the composition of the obtained composite hydroxide particles tends to shift. .. If the ammonia concentration changes, the solubility of metal ions also changes and uniform hydroxide particles are not formed. Therefore, it is preferable to keep the value at a constant value. For example, the ammonia concentration is preferably maintained at a desired concentration by setting the upper limit and the lower limit to about 5 g/L.

In the crystallization step (S1-1), a batch crystallization method or a continuous crystallization method may be used. For example, in the case of a batch-wise crystallization method, the composite hydroxide particles can be obtained by collecting the precipitate after the reaction aqueous solution in the reaction tank has reached a steady state, filtering and washing with water. In the case of the continuous crystallization method, a mixed aqueous solution and an alkaline aqueous solution, and in some cases, an aqueous solution containing an ammonium ion supplier is continuously supplied to overflow the reaction tank to collect a precipitate, which is filtered and washed with water to form a composite. Hydroxide particles can be obtained.

When the nickel-manganese composite hydroxide contains the element M2, the method of blending the element M is not particularly limited, and a known method can be used. For example, from the viewpoint of improving productivity, nickel, A preferred method is to add an aqueous solution containing the element M2 to a mixed aqueous solution containing manganese to coprecipitate a nickel-manganese composite hydroxide containing the element M2.

Examples of the aqueous solution containing the element M2 include cobalt sulfate, sodium tungstate, tungsten oxide, molybdenum oxide, molybdenum sulfide, vanadium pentoxide, magnesium sulfate, magnesium chloride, calcium chloride, aluminum sulfate, sodium aluminate, titanium sulfate, and peroxo. An aqueous solution containing ammonium titanate, potassium titanium oxalate, zirconium hydroxide, zirconium sulfate, chromium chloride, sodium tantalate, tantalic acid or the like can be used.

From the viewpoint of optimizing the crystallization conditions and facilitating the control of the composition ratio, after obtaining the nickel-manganese composite hydroxide by crystallization, the element M2 is further added to the obtained nickel-manganese composite hydroxide. A step of coating may be provided. The method of coating the element M2 is not particularly limited, and a known method can be used.

Hereinafter, an example of a coating method of the element M2 will be described. First, the nickel-manganese composite hydroxide obtained by crystallization is dispersed in pure water to form a slurry. Next, a solution containing the element M2, which is in proportion to the target coating amount, is mixed with this slurry, and an acid is added dropwise to adjust the pH to a predetermined value. Examples of the acid include sulfuric acid, hydrochloric acid, nitric acid and the like. Next, the slurry is mixed for a predetermined time, and then the slurry is filtered and dried to obtain a nickel manganese composite hydroxide coated with the element M2. Other coating methods include a spray-drying method in which a solution containing a compound containing the element M2 is sprayed on a nickel manganese composite hydroxide and then dried, and a solution containing a compound containing the element M2 is nickel manganese composite hydroxide. Examples include a method of impregnating an object.

[Heat treatment step (S1-3)]
Further, in the method for manufacturing the positive electrode active material according to the present embodiment, as shown in FIG. 5B, the nickel-manganese composite compound is heat-treated at a temperature of 105° C. or higher and 700° C. or lower before the mixing step (S1). A heat treatment step (S1-3) may be provided.

The heat treatment step (S1-3) is a step of removing at least a part of water contained in the nickel-manganese composite compound by heat treatment. By performing the heat treatment step (S1-3), it is possible to prevent the Li/Me of the positive electrode active material obtained in the firing step (S3) from varying.

The nickel-manganese composite compound after the heat treatment step (S1-3) is, for example, a nickel-manganese composite oxide obtained by converting at least a part of the nickel-manganese composite hydroxide obtained in the crystallization step (S1-1) into an oxide. And may be composed of a nickel-manganese composite oxide in which the entire nickel-manganese composite hydroxide is converted into an oxide.

From the viewpoint of further reducing the variation in Li/Me, the heat treatment preferably oxidizes the nickel-manganese complex hydroxide sufficiently to convert it into the nickel-manganese complex oxide. Note that it is not necessary to convert all the hydroxides in the nickel-manganese composite compound to oxides, as long as water can be removed to the extent that there is no variation in Li/Me of the positive electrode active material. Further, when the heat treatment step (S1-3) is performed, in the mixing step (S1), the nickel-manganese composite hydroxide is heat-treated before adjusting the lithium mixture, and then the nickel-manganese composite compound (water Oxides and/or oxides), lithium compounds, boron compounds and optionally titanium compounds can be mixed to prepare a lithium mixture. When the nickel-manganese composite compound covers the element M1 or M2, the nickel-manganese composite hydroxide may be heat-treated after coating the compound containing the element M1 or M2 with the nickel-manganese composite hydroxide. Alternatively, a compound containing the element M1 or M2 may be coated.

The temperature of the heat treatment is, for example, 105° C. or higher and 700° C. or lower. When the nickel-manganese composite compound is heated at 105° C. or higher, at least part of residual water can be removed. If the temperature of the heat treatment is less than 105°C, it takes a long time to remove the residual water, which is industrially unsuitable. On the other hand, if the heat treatment temperature exceeds 800° C., the particles converted into the nickel-manganese composite oxide may sinter and aggregate. For example, when most of the nickel-manganese composite hydroxide is converted to the nickel-manganese composite oxide, the heat treatment temperature is preferably 350°C or higher and 700°C or lower.

The atmosphere in which the heat treatment is performed is not particularly limited, and for example, it is preferable to perform the heat treatment in an air stream from the viewpoint of easy operation. The heat treatment time is not particularly limited and can be, for example, 1 hour or more. When the heat treatment time is less than 1 hour, the residual water content in the composite hydroxide particles may not be sufficiently removed. The heat treatment time is preferably 5 hours or more and 15 hours or less. Further, the equipment used for the heat treatment is not particularly limited as long as it can heat the composite hydroxide particles in an air stream, and for example, a blower dryer, an electric furnace that does not generate gas can be preferably used. ..

In FIG. 5(B), the nickel-manganese composite compound (hydroxide) after the crystallization step (S1-1) is heat-treated, but it was obtained by a step other than the crystallization step (S1-1). You may heat-process a nickel manganese compound compound. Even in this case, the above-described effect can be obtained by removing at least a part of the water content in the nickel-manganese composite compound.
[Mixing step (S1-a)]
The method for manufacturing the positive electrode active material according to the present embodiment includes, for example, as shown in FIG. 2, a mixing step (S1-a) and a firing step (S2). As shown in FIG. 2, the mixing step (S1-a) is a step of mixing a nickel-manganese composite compound, a boron compound, a titanium compound, and a lithium compound to obtain a lithium mixture.

The obtained lithium mixture contains 0.1 atom% or more and 5 atom% or less of titanium, and contains boron in an amount of 0.1% or less with respect to the total amount of the metal elements Me (Ni, Mn, M2, B, Ti) excluding lithium. Included at 1 atom% or more and 3 atom% or less. Hereinafter, each component contained in the lithium mixture will be described.

(Nickel-manganese composite compound)
The nickel-manganese composite compound contains nickel, manganese, and optionally the element M2, and the substance ratio (molar ratio) of each element is Ni:Mn:M2=(1-ab'):a:b. '(However, 0.05≦a≦0.60, 0≦b′≦0.60, and M2 is Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, and Ta. Which is at least one element selected from the above).

The element M2 may or may not include titanium (Ti). When the nickel-manganese composite compound contains titanium as the element M2, the amount of titanium contained in the lithium mixture is the sum of the amount of titanium contained as M2 and the amount of titanium added as the titanium compound. .. From the viewpoint of productivity, it is preferable that M2 does not contain titanium and titanium is added as a titanium compound.

Further, since the content (composition) of the metal (Ni, Mn, M2) in the nickel-manganese composite compound is almost maintained even in the lithium-nickel-manganese metal composite oxide, the content of each metal (Ni, Mn, M2). Is preferably in the same range as the content of each metal in the above-mentioned lithium nickel manganese metal composite oxide except for titanium. The nickel-manganese composite compound can be obtained by the crystallization step (S1-1), but may be obtained by another method.

(Boron compound)
The boron compound is a compound containing boron, and is preferably at least one of boric acid, boron oxide, lithium borate, and ammonium borate. In addition, 1 type may be used for a boron compound and 2 or more types may be used for it.

Further, the boron compound may be mixed in a solid phase (powder). When the boron compound is mixed in the form of powder, the average particle size of the boron compound is preferably 1 μm or more and 1 mm or less, more preferably 1 μm or more and 700 μm or less. As the particle size of the boron compound is smaller within the above range, the conductivity of the obtained positive electrode active material tends to decrease and the battery characteristics tend to improve. The average particle size of boron can be obtained from, for example, a volume integrated value measured by a laser light diffraction/scattering particle size distribution meter.

Further, as shown in FIG. 6, the boron compound may be mixed while being impregnated with the nickel-manganese composite compound. In this case, it is preferable to include a crystallization step (S1-1) and a boron impregnation step (S1-2) before the mixing step (S1).

In the boron impregnation step (S1-2), a solution containing at least one of boric acid and a boron salt is added to a slurry obtained by mixing the nickel-manganese composite compound and water, and boron is added to the nickel-manganese composite compound. Is a step of impregnating. In this case, the boron compound is mixed with other components in a state of being attached to the surface or the inside of the nickel-manganese composite compound.

The boron compound is used in a lithium mixture obtained after the mixing, and the boron (B) is 0.1 atom% or more and 3 atom% or more with respect to the total amount of the metal elements Me (Ni, Mn, Ti, B, M2) excluding lithium. Below, preferably 0.1 at% or more and 2.5 at% or less, more preferably 0.1 at% or more and 2.0 at% or less are mixed.

(Titanium compound)
The titanium compound is a compound containing titanium, and for example, titanium oxide, titanium sulfate, titanium tetrabromide, titanium tetrachloride, titanium silicide or the like can be used. Among these, titanium oxide is preferable from the viewpoint of easy availability and avoiding inclusion of impurities in the lithium metal composite oxide. In addition, a titanium compound may use 1 type and may use 2 or more types.

The titanium compound contains titanium (Ti) in an amount of 0.1 atom% or more and 5 atom% or less, preferably 0.1% or less, based on the total amount of metal elements (Ni, Mn, Ti, B, M2) excluding lithium in the lithium mixture. It is mixed so as to be 1 atom% or more and 4 atom% or less, more preferably 0.5 atom% or more and 3.5 atom% or less.

(Lithium compound)
The lithium compound is not particularly limited, and a known compound containing lithium can be used. As the lithium compound, for example, lithium carbonate, lithium hydroxide, lithium nitrate, or a mixture thereof is used. Among these, lithium carbonate, lithium hydroxide, or a mixture thereof is preferable from the viewpoint of being less affected by residual impurities and dissolving at the firing temperature.

The lithium compound is mixed so that Li/Me in the lithium mixture is 0.95 or more and 1.20 or less. That is, Li/Me in the lithium mixture is mixed so as to be the same as Li/Me in the obtained positive electrode active material. This is because the molar ratio of Li/Me and each metal element does not change before and after the firing step (step S3). Therefore, in this mixing step (step S12), Li/Me of the lithium mixture is equal to Li/Me of the positive electrode active material. This is because it becomes Me.

(Mixing method)
The method of mixing the nickel-manganese composite compound, the boron compound, the titanium compound, and the lithium compound is not particularly limited, and the compounds such as nickel-manganese composite hydroxide are sufficiently mixed as long as the skeleton such as nickel-manganese composite hydroxide is not destroyed. Just do it. As a mixing method, for example, a general mixer can be used, and for example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender or the like can be used. It is preferable that the lithium mixture is thoroughly mixed before the firing step (S3) described below. If the mixing is not sufficient, Li/Me may vary among individual particles of the positive electrode active material, and problems such as insufficient battery characteristics may occur.

[Mixing step (S1-b)]
The method for manufacturing the positive electrode active material according to the present embodiment includes, for example, as shown in FIG. 3, a mixing step (S1-b) and a firing step (S2). As shown in FIG. 3, the mixing step (S1-c) is a step of mixing a nickel-manganese composite compound coated with a titanium compound, a boron compound, and a lithium compound to obtain a lithium mixture.

Further, as shown in FIG. 3, a step (S1-4) of coating the surface of the nickel-manganese composite compound with a titanium compound may be provided before the mixing step (S1-b). The coating method of the titanium compound is not particularly limited and a known method can be used, for example, the method described in JP-A-2008-198364 can be used.

An example of a titanium compound coating method will be described below. First, the nickel-manganese composite hydroxide obtained by crystallization is dispersed in pure water to form a slurry. Next, a titanium salt aqueous solution and an alkaline aqueous solution are added to this slurry to adjust the pH to 8 to 11. Then, the slurry is filtered, washed with water, and dried to obtain a nickel-manganese composite hydroxide whose surface is coated with a titanium compound. Further, as the titanium salt aqueous solution, a titanyl sulfate aqueous solution can be used.

The obtained lithium mixture contains 0.1 atomic% or more and 5 atomic% or less of titanium, and has a boron content of 0.1% or less with respect to the total amount of the metal elements Me (Ni, Mn, M1, B, Ti) excluding lithium. Included at 1 atom% or more and 3 atom% or less.

The mixing step (S1-b) differs from the mixing step (S1-a) in that the nickel-manganese composite compound coated with a titanium compound is used and that the titanium compound (powder) may not be mixed. Since the boron compound, the lithium compound, and the mixing method are the same as those in the mixing step (S1-a), the description thereof will be omitted.

[Mixing step (S1-c)]
The method for manufacturing the positive electrode active material according to the present embodiment includes, for example, as shown in FIG. 4, a mixing step (S1-c) and a firing step (S2). As shown in FIG. 4, the mixing step (S1-c) is a step of mixing a nickel-manganese composite compound containing titanium (Ti), a boron compound, and a lithium compound to obtain a lithium mixture.

The obtained lithium mixture contains 0.1 atomic% or more and 5 atomic% or less of titanium, and has a boron content of 0.1% or less with respect to the total amount of the metal elements Me (Ni, Mn, M1, B, Ti) excluding lithium. Included at 1 atom% or more and 3 atom% or less.

The mixing step (S1-c) differs from the mixing step (S1) in that the nickel-manganese composite compound contains titanium (Ti) as an essential component and that the titanium compound may not be mixed. Hereinafter, each component contained in the lithium mixture will be described. Since the boron compound, the lithium compound, and the mixing method are the same as those in the mixing step (S1), the description thereof will be omitted.

(Nickel-manganese composite compound)
The nickel-manganese composite compound contains nickel, manganese, and titanium, and optionally the element M1, and the substance ratio of each element is Ni:Mn:M1:Ti=(1-a-b-d):a: b: d (however, 0.05≦a≦0.60, 0≦b≦0.60, 0.001≦d≦0.05, and M1 is Co, W, Mo, V, Mg, Ca , At least one element selected from Al, Cr, Zr, and Ta).

Since the content (composition) of the metal (Ni, Mn, M1, Ti) in the nickel-manganese composite compound is almost maintained even in the lithium-nickel-manganese composite oxide, the content of each metal (Ni, Mn, M1, Ti) is included. The amount is preferably in the same range as the content of each metal in the lithium nickel manganese composite oxide described above. The nickel-manganese composite compound can be obtained by the crystallization step (S1-1), but may be obtained by another method.

The mixing step (1S) may include any one of the above mixing steps (1-a), (1-b), and (1-c), and each step may be performed alone. However, the steps may be combined. In any case, the contents of titanium and boron in the lithium mixture are mixed so as to fall within the above specified range.

The mixing step (1S) is, for example, a combination of the mixing steps (1-a) and (1-b), a nickel-manganese composite compound coated with a titanium compound, a titanium compound (powder), a boron compound, and a lithium compound. You may mix and. The mixing step (1S) is a nickel-manganese composite containing titanium obtained by adding titanium in the crystallization step by combining the mixing step (1-a) and the mixing step (1-c). You may mix a compound, a titanium compound (powder), a boron compound, and a lithium compound. In the mixing step (1S), the nickel-manganese composite compound containing titanium obtained by adding titanium in the crystallization step by combining the mixing steps (1-b) and (1-c) is used. After coating with the compound, the boron compound and the lithium compound may be mixed. In addition, the mixing step (1S) includes, for example, titanium obtained by adding titanium in the crystallization step by combining the mixing steps (1-a), (1-b), and (1-c). The nickel-manganese composite compound containing may be coated with a titanium compound, and then the titanium compound (powder), the boron compound, and the lithium compound may be mixed.

[Firing step (S2)]
The firing step (S2) is a step of firing the lithium mixture obtained in the mixing step (S1) at 750° C. or higher and 1000° C. or lower in an oxidizing atmosphere. When the lithium 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 of firing and penetrates into the nickel-manganese composite compound to form a lithium-nickel-manganese composite oxide. At this time, it is considered that the boron and titanium contained in the lithium mixture also penetrate into the inside of the secondary particles together with the molten lithium compound, and penetrate into the primary particles if there is a crystal grain boundary or the like.

The firing temperature is 750°C or higher and 1000°C or lower, and preferably 750°C or higher and 950°C or lower. In the case of firing at the above temperature, melting of the lithium compound occurs, and penetration and diffusion of boron and titanium are promoted. In addition, the lithium mixture can increase the firing temperature by containing manganese. When the firing temperature is high, the diffusion of boron and titanium is promoted, and the crystallinity of the lithium nickel manganese composite oxide is increased, so that the output characteristics and the battery capacity can be further improved.

On the other hand, when the firing temperature is lower than 750° C., diffusion of lithium, boron, and titanium into the nickel-manganese composite compound is not sufficiently performed, excess lithium and unreacted particles remain, and the crystal structure is sufficiently adjusted. There may be a problem that sufficient battery characteristics cannot be obtained due to disappearance. Further, when the firing temperature exceeds 1000° C., vigorous sintering may occur between the formed particles of the lithium nickel manganese composite oxide and abnormal grain growth may occur. When abnormal grain growth occurs, the grains after firing become coarse and the grain morphology cannot be maintained. As a result, the specific surface area of the obtained positive electrode active material decreases, which causes problems such as an increase in resistance of the positive electrode and a decrease in battery capacity.

The atmosphere during firing is an oxidizing atmosphere. Here, the oxidizing atmosphere means an atmosphere having an oxygen concentration of 3 to 100% by volume. The calcination is preferably performed in an air atmosphere or an oxygen stream. When the oxygen concentration of the firing atmosphere is less than 3% by volume, the lithium nickel manganese composite oxide may not be sufficiently oxidized and may not be sufficiently crystalline. Further, considering the battery characteristics, it is more preferable that the firing is performed in an oxygen stream. Further, the furnace used for firing is not particularly limited, as long as it can fire the lithium mixture in the air or an oxygen stream, it is preferable to use an electric furnace that does not generate gas, batch type or continuous type Any of the furnaces can be used.

The firing time is preferably at least 3 hours or more, more preferably 6 hours or more and 24 hours or less. If the firing time is less than 3 hours, the lithium nickel manganese composite oxide may not be sufficiently produced.

[Calcination]
The firing step (S2) may further include a step of calcination at a temperature lower than the firing temperature before firing at a temperature of 750° C. or higher and 1000° C. or lower. The calcination is preferably performed at a temperature at which the lithium compound and the boron compound in the lithium mixture melt and can react with the nickel-manganese composite compound. The calcination temperature can be, for example, 350° C. or higher and lower than the firing temperature. Further, the lower limit of the calcination temperature is preferably 400° C. or higher. By holding (calcining) the lithium mixture in the above temperature range, lithium, boron and titanium are sufficiently diffused, and a uniform lithium nickel manganese composite oxide can be obtained. For example, when lithium hydroxide is used as the lithium compound, calcination is preferably carried out by holding the temperature at 400° C. or higher and 550° C. or lower for about 1 hour to about 10 hours.

[Crush]
In the lithium nickel manganese composite oxide obtained after the firing step (S2), sintering between particles is suppressed, but coarse particles may be formed due to weak sintering or aggregation. In such a case, the particle size distribution can be adjusted by eliminating the above-mentioned sintering and aggregation by crushing.

3. Lithium Ion Secondary Battery The lithium ion secondary battery according to the present embodiment (hereinafter, also referred to as “secondary battery”) includes a positive electrode including the positive electrode active material described above, 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. In addition, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. The secondary battery may be a secondary battery that charges and discharges by desorption and insertion of lithium ions, and may be, for example, a non-aqueous electrolyte secondary battery or an all-solid lithium secondary battery. It may be. The embodiments described below are merely examples, and the secondary battery according to the present embodiment is applied to various modified and improved embodiments based on the embodiments described in the present specification. May be.

[Components]
(Positive electrode)
First, the positive electrode active material 100, the conductive material, and the binder described above are mixed, and activated carbon or a solvent for the purpose of adjusting the viscosity is added if necessary, and the mixture is kneaded to prepare a positive electrode mixture paste. .. At that time, the respective mixing ratios in the positive electrode mixture paste can be appropriately adjusted according to the intended performance of the secondary battery. 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 is 60 parts by mass or more and 95 parts by mass or less, and the content of the conductive material is 1 part by mass or more and 20 parts by mass or less. The content of the binder may be 1 part by mass or more and 20 parts by mass or less.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, or the like) or a carbon black-based material such as acetylene black or Ketjen black can be used.

The binder plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin and polyacryl. Acids can be used.

If necessary, the positive electrode active material, the conductive material and the activated carbon may be dispersed and a solvent that dissolves the binder may be added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. Activated carbon may be added to the positive electrode mixture to increase the electric double layer capacity.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of aluminum foil, for example, and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. In this way, a sheet-shaped positive electrode can be manufactured. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for the production of the battery. The method for producing the positive electrode is not limited to the above method and may be another method.

(Negative electrode)
You may use metallic lithium, a lithium alloy, etc. as a negative electrode. In addition, as a negative electrode, a negative electrode active material capable of absorbing and desorbing lithium ions is mixed with a binder, and a suitable solvent is added to form a paste-like negative electrode mixture, which is used as a surface of a metal foil current collector such as copper. It is also possible to use a product formed by applying it to, drying it, and, if necessary, compressing it to increase the electrode density.

As the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite or phenol resin, or a powdery body of a carbon material such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder as in the positive electrode, and a solvent for dispersing these active materials and the binder can be an organic material such as N-methyl-2-pyrrolidone. A solvent can be used.

(Separator)
If necessary, a separator may be sandwiched between the positive electrode and the negative electrode. The separator is for separating the positive electrode and the negative electrode and holding the electrolyte, and a thin film such as polyethylene or polypropylene, which has a large number of minute holes, can be used.

(Non-aqueous electrolyte)
A non-aqueous electrolyte solution can be used as the non-aqueous electrolyte. As the non-aqueous electrolyte solution, for example, a lithium salt as a supporting salt dissolved in an organic solvent may be used. Further, as the non-aqueous electrolyte solution, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid refers to a salt that is composed of cations and anions other than lithium ions and that is liquid at room temperature.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran and 2- One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone or in combination of two or more. Can be used.

As the supporting _{salt, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiN (CF 3 SO 2) 2, and the like can be used those composite salt. Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

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

Examples of the inorganic solid electrolyte include oxide solid electrolytes and sulfide solid electrolytes.

The oxide-based solid electrolyte is not particularly limited, and any oxide-containing solid electrolyte containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. The oxide-based solid electrolyte, for example, lithium phosphate _{(Li 3 PO 4), Li} 3 PO 4 N X, LiBO 2 N X, LiNbO 3, LiTaO 3, Li 2 SiO 3, Li 4 SiO 4 -Li 3 _{PO 4, Li 4 SiO 4 -Li} 3 VO 4, Li 2 O-B 2 O 3 -P 2 O 5, Li 2 O-SiO 2, Li 2 O-B 2 O 3 -ZnO, Li 1 + X Al X Ti _{2-X (PO 4) 3} (0 ≦ X ≦ 1), Li 1 + X Al X Ge 2-X (PO 4) 3 (0 ≦ X ≦ 1), LiTi 2 (PO 4) 3, Li 3X La 2 / _3-X TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6. P _0.4 O ₄ and the like.

The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur (S) and has lithium ion conductivity and electronic insulation. The sulfide-based solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 _{S-B 2 S 3, Li} 3 PO 4 -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O _{5, LiI-Li 3 PO 4} -P 2 S 5 , and the like.

As the inorganic solid electrolyte, those other than the above may be used, and for example, Li ₃ N, LiI, Li ₃ N-LiI-LiOH, or the like may be used.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof, or the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When the solid electrolyte is used, the solid electrolyte may be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Battery shape and configuration)
The structure of the secondary battery is not particularly limited, and may be composed of a positive electrode, a negative electrode, a separator, a nonaqueous electrolyte, etc. as described above, or may be composed of a positive electrode, a negative electrode, a solid electrolyte, etc. The shape of the secondary battery is not particularly limited, and various shapes such as a cylindrical shape and a laminated shape can be used.

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 the non-aqueous electrolyte solution to collect the positive electrode. The secondary battery is connected between the current collector and the positive electrode terminal that communicates with the outside, and between the negative electrode current collector and the negative electrode terminal that communicates with the outside using a current collection lead, etc., and then sealed in the battery case. To complete.

(Characteristics of secondary battery)
The secondary battery according to the present embodiment can achieve both high battery capacity and low positive electrode resistance, and thermal stability at the time of short circuit due to decrease in conductivity. The secondary battery according to the present embodiment is suitable as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that always require a high capacity. In addition, the lithium-ion secondary battery according to the present embodiment is twice as good as a battery using a conventional lithium cobalt-based oxide or lithium nickel-based oxide as a positive electrode active material, and is excellent in thermal stability at the time of short circuit. Furthermore, it is excellent in terms of output characteristics and battery capacity. Therefore, the secondary battery according to the present embodiment is capable of downsizing and high output, and is a so-called hybrid vehicle that is used in combination with a power source for an electric vehicle that is restricted in mounting space and a combustion engine such as a gasoline engine or a diesel engine. It can also be suitably used as a power supply for the.

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. In addition, the analysis method of the metal contained in the positive electrode active material and the various evaluation methods of the positive electrode active material in Examples and Comparative Examples are as follows.
(1) Analysis of composition: Measured by ICP emission spectrometry.
(2) Volume average particle size MV: Measured with a laser diffraction/scattering particle size distribution measuring device (Microtrack HRA manufactured by Nikkiso Co., Ltd.).
(4) Morphological observation, porosity: A positive electrode active material was embedded in a resin and the like, and a cross section of the secondary particles was made possible by cross-section polisher processing and the like, and then observed by a scanning electron microscope (SEM). Next, from the SEM image, 20 cross sections of secondary particles having a volume average particle size (MV) of 50% or more are randomly selected, and image analysis software (ImageJ or the like) is used for each cross section of the secondary particles. Then, the average value of the porosity was calculated from the following formula.
Formula: [(void area inside secondary particle)/(cross-sectional area of secondary particle) x 100] (%)
(5) Conductivity: 5 g of the positive electrode active material was pressure-molded into a cylinder having a diameter of 20 mm so as to have a pressure of 4.0 g/cc, and then the pressure was measured by a four-point probe method according to JIS K 7194:1994. It was determined by converting the volume resistivity measured by the resistivity test method.

(Battery production)
52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm, and the positive electrode shown in FIG. An evaluation electrode) PE was produced. After drying the produced positive electrode PE in a vacuum dryer at 120° C. for 12 hours, a 2032 type coin battery CBA was produced using this positive electrode PE in a glove box in an Ar atmosphere whose dew point was controlled at −80° C. .. Lithium (Li) metal having a diameter of 17 mm and a thickness of 1 mm was used for the negative electrode NE, and the electrolyte solution was an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (1M LiClO ₄ as a supporting electrolyte). Toyama Pharmaceutical Co., Ltd.) was used. A 25-μm-thick polyethylene porous film was used as the separator SE. In addition, the coin-type battery CBA was assembled into a coin-type battery by arranging the gasket GA and the wave washer WW, and using the positive electrode can PC and the negative electrode can NC. Table 2 shows the measurement results of the initial charge/discharge capacity and the positive electrode resistance value of the obtained positive electrode active material.
(7) Initial charge capacity:
After the coin-type battery CBA shown in FIG. 7 was produced and left for about 24 hours, the open circuit voltage OCV (open circuit voltage) was stabilized, and then the current density to the positive electrode was set to 0.1 mA/cm ² and the cut-off voltage was 4. The initial charge capacity was obtained by charging to 3 V, and the capacity at the time of discharging to a cutoff voltage of 3.0 V after a pause of 1 hour was taken as the initial discharge capacity. A multi-channel voltage/current generator (R6741A manufactured by Advantest Corporation) was used for measuring the charge/discharge capacity.
(8) Positive electrode resistance (reaction resistance):
For the positive electrode resistance, a coin-type battery whose temperature was adjusted to the measurement temperature was charged at a charging potential of 4.1 V, and the resistance value was measured by the AC impedance method. For the measurement, a frequency response analyzer and a potentiogalvanostat (Solartron, 1255B) were used to create the Nyquist plot shown in FIG. 8 (top), and the fitting calculation was performed using the equivalent circuit shown in FIG. 8 (bottom). Then, the value of the positive electrode resistance (reaction resistance) was calculated.

(Example 1)
(Crystallization process)
A predetermined amount of pure water was put into a reaction tank (60 L), and the temperature inside the tank was set to 45° C. with stirring. At this time, N ₂ gas was flowed into the reaction tank so that the concentration of dissolved oxygen in the reaction tank liquid was 1.5 mg/L. A 2.0 M mixed aqueous solution of nickel sulfate, manganese sulfate, and cobalt sulfate and 25 mass% hydroxylation that is an alkaline solution were used in this reaction tank so that the molar ratio of nickel:manganese:cobalt was 85:10:5. A sodium solution and 25 mass% aqueous ammonia as a complexing agent were continuously and simultaneously added to the reaction tank. At this time, the flow rate was controlled so that the residence time of the mixed aqueous solution was 8 hours, the pH in the reaction tank was adjusted to 12.0 to 12.8, and the ammonia concentration was adjusted to 12 to 13 g/L. After the reaction tank was stabilized, a slurry containing nickel-cobalt-manganese composite hydroxide was recovered from the overflow port and then filtered to obtain a cake of nickel-cobalt-manganese composite hydroxide (crystallization step). Impurities were washed by passing 1 L of pure water through 140 g of nickel cobalt manganese composite hydroxide in the filtered Denver. The powder after filtration was dried to obtain a nickel-cobalt-manganese composite hydroxide represented by Ni _0.85 Co _0.10 Mn _0.05 (OH) _2+α (0≦α≦0.4).

(Mixing process)
The obtained nickel-cobalt-manganese composite hydroxide, lithium hydroxide, boric acid (H ₃ BO ₃ , average particle size 500 μm), and titanium compound (TiO ₂ ) were mixed with a shaker mixer device (Willy E. Bakofen). (WAB) TURBULA Type T2C) was thoroughly mixed to obtain a lithium mixture. In the lithium mixture, each component is such that titanium is 2.3 atom% and boron is 0.3 atom% with respect to the total amount of metal elements Me (Ni, Mn, Co, B, Ti) other than lithium. And were mixed so that the molar ratio (Li/Me) of lithium (Li) and the metal element Me other than Li was 1.01.

(Firing process)
The obtained lithium mixture was held in an oxygen stream at 800° C. for 10 hours for firing, and then crushed to obtain a positive electrode active material made of a lithium nickel cobalt manganese composite oxide.

The production conditions of the obtained positive electrode active material are shown in Table 1, and the evaluation results (composition, volume average particle size MV, porosity, conductivity, battery characteristics) are shown in Table 2.

(Example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that boric acid was weighed so that boron was 0.5 atomic %. The manufacturing conditions and evaluation results are shown in Tables 1 and 2. A cross-sectional SEM image of the obtained positive electrode active material is shown in FIG.

(Example 3)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that boric acid was weighed so that boron was 1.0 atomic %. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 4)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that boric acid was weighed so that titanium was 1.2 at %. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 5)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the titanium compound was weighed so that titanium was 3.3 atomic %, and the firing temperature was 830° C. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 6)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the firing temperature was 830°C. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 7)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the firing temperature was 850°C. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 8)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the average particle size of boric acid was 100 μm. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 9)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the average particle size of boric acid was 50 μm. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 10)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the average particle size of boric acid was 10 μm. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Example 11)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that boron oxide (average particle size 500 μm) was used as the boron compound. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Comparative Example 1)
In the mixing step, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that boric acid and the titanium compound were not mixed. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Comparative example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that boric acid was not mixed and the firing temperature was 830°C. The manufacturing conditions and evaluation results are shown in Tables 1 and 2. A cross-sectional SEM image of the obtained positive electrode active material is shown in FIG.

(Comparative example 3)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the titanium compound was not mixed and the firing temperature was 830°C. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Comparative Example 4)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that boric acid was weighed so that boron was 5 atomic %, and the firing temperature was 830° C. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Comparative example 5)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the titanium compound was weighed so that titanium was 10 atomic %, and the firing temperature was 830° C. The manufacturing conditions and evaluation results are shown in Tables 1 and 2.

(Evaluation results)
As shown in Table 1 and Table 2, in the positive electrode active materials of Examples containing titanium and boron in specific amounts, the conductivity was in the range of 4.0×10 ⁻³ S/cm or less, and the positive electrode resistance was also It is lower than those of Comparative Examples 1 to 3 in which titanium and/or boron is not added. In addition, the positive electrode active materials of Examples maintain the same charge capacity as Comparative Example 1 containing no titanium and boron.

Further, FIG. 11 is a graph showing the conductivity and the positive electrode resistance of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 2 and 4 manufactured under the same conditions except for the amount of boron added. As shown in FIG. 11 and Table 2, in the positive electrode active material of Comparative Example 4 in which the amount of boron added exceeded 3 atomic %, the positive electrode resistance was significantly increased and the charging capacity was also decreased.

Further, FIG. 12 is a graph showing the conductivity and the positive electrode resistance of the positive electrode active materials of Examples 2, 4, 5 and Comparative Examples 3, 5 manufactured under substantially the same conditions except for the amount of titanium added. .. As shown in FIG. 12 and Table 2, in the positive electrode active material of Comparative Example 5 in which the amount of titanium added exceeded 5 atomic %, it was shown that the positive electrode resistance was significantly increased and the charge capacity was also decreased.

Further, FIG. 9 is a view showing a SEM cross section of the positive electrode active material of Example 2. As shown in FIG. 9, in the positive electrode active material of the example, a plurality of voids G are observed inside the secondary particles of the lithium nickel manganese composite oxide 10. In addition, as shown in Table 2, it was confirmed that the ratio of the void G tends to increase according to the amount of boron added.

In the present embodiment, a positive electrode active material for a lithium ion secondary battery that achieves both high output characteristics, energy density, and short circuit safety can be obtained by an industrial manufacturing method. The lithium-ion secondary battery is suitable as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that always require a high capacity.

In addition, the secondary battery of the present embodiment is excellent in safety even when compared with a battery using a conventional lithium cobalt-based oxide or lithium nickel-based oxide positive electrode active material, and further has output characteristics and capacity. Is excellent in terms of. Therefore, it is possible to reduce the size and increase the output, and thus it is suitable as a power source for an electric vehicle that is restricted in mounting space.

Further, the positive electrode active material of the present embodiment and the secondary battery using the same are not only a power source for an electric vehicle driven purely by electric energy but also a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine. It can also be used as a power source.

Note that the technical scope of the present invention is not limited to the modes 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-described embodiments and the like can be appropriately combined. Moreover, as long as it is permitted by law, the contents of all the documents cited in this specification are incorporated and made a part of the description of the text.

CBA... coin type battery (for evaluation)
PE... Positive electrode (evaluation electrode)
NE... Negative electrode SE... Separator GA... Gasket WW... Wave washer PC... Positive electrode can NC... Negative electrode can G... Void 10... Lithium nickel manganese composite oxide

Claims (10)

Including a lithium nickel manganese composite oxide composed of secondary particles in which a plurality of primary particles are aggregated,
The lithium nickel manganese composite oxide contains lithium, nickel, manganese, boron, and titanium, and optionally the element M1, and the material amount ratio of each element is Li:Ni:Mn:M1:B:Ti=e. :(1-a-b-c-d):a:b:c:d (where 0.05≤a≤0.60, 0≤b≤0.60, 0.001≤c≤0.03 , 0.001≦d≦0.05, 0.95≦e≦1.20, and the element M1 is selected from Co, W, Mo, V, Mg, Ca, Al, Cr, Zr, and Ta. Is at least one element),
At least a portion of the boron is segregated on at least one of the surface and grain boundaries of the primary particles,
Positive electrode active material for lithium-ion secondary batteries. The lithium according to claim 1, wherein voids are present in the secondary particles and a porosity in the secondary particles is 0.2% or more and 10% or less in a cross-sectional SEM observation in the secondary particles. Positive electrode active material for ion secondary batteries. The positive electrode active material for a lithium ion secondary battery according to claim 1, which has a volume average particle diameter MV of 5 μm or more and 30 μm or less. The electric conductivity when compressed at 4.0 g/cm ³ obtained by powder dust resistance measurement is in the range of 1.0×10 ⁻⁶ S/cm or more and 4.0×10 ⁻³ S/cm or less. Item 4. The positive electrode active material for a lithium ion secondary battery according to any one of Items 1 to 3. A method for producing a positive electrode active material for a lithium ion secondary battery, which comprises a lithium nickel manganese composite oxide composed of secondary particles in which a plurality of primary particles are aggregated,
A mixing step including at least one of the following steps (1-a), (1-b) and (1-c), and step (2),
The lithium nickel manganese composite oxide contains at least lithium, nickel, manganese, boron, and titanium, and the substance amount ratio (Li/Me) of lithium to a metal element Me other than lithium is 0.95 or more 1 20 or less, and at least a part of the boron segregates on at least one of the surface and the grain boundary of the primary particles,
A method for producing a positive electrode active material for a lithium ion secondary battery.
Step (1-a): nickel and manganese, and optionally an element M2, and the material ratio of each element is Ni:Mn:M2=(1-ab'):a:b' (however, , 0.05≦a≦0.60, 0≦b′≦0.60, and M2 is selected from Ti, Co, W, Mo, V, Mg, Ca, Al, Cr, Zr, and Ta. A nickel manganese composite compound represented by the formula (1), a boron compound, a titanium compound, and a lithium compound to obtain a lithium mixture;
Step (1-b): The surface is coated with a titanium compound, and nickel, manganese, and optionally the element M2 are contained, and the substance amount ratio of each element is Ni:Mn:M2=(1-a -B'): a:b' (where 0.05≤a≤0.60, 0≤b'≤0.60, and M2 is Ti, Co, W, Mo, V, Mg, Ca, A mixing step of mixing a nickel-manganese composite compound represented by Al, Cr, Zr, and Ta), a boron compound, and a lithium compound to obtain a lithium mixture. Step (1-c): Nickel, manganese, and titanium, and optionally the element M1, and the substance ratio of each element is Ni:Mn:M1:Ti=(1-a-b-d):a. :B:d (where 0.05≦a≦0.60, 0≦b≦0.60, 0.001≦d≦0.05, and M1 is Co, W, Mo, V, Mg, A nickel-manganese composite compound represented by the formula: at least one element selected from Ca, Al, Cr, Zr, and Ta, a boron compound, and a lithium compound are mixed to obtain a lithium mixture. Process;
Step (2): a step of firing the lithium mixture in an oxidizing atmosphere at 750° C. or higher and 1000° C. or lower to obtain a lithium nickel manganese composite oxide;
In the mixing step, the lithium mixture contains titanium in an amount of 0.1 atomic% or more and 5 atomic% or less and boron in an amount of 0.1 atomic% or more and 3 atomic% with respect to the total amount of the metal elements Me excluding lithium. Included below. Before the mixing step, the following step (1-1) is provided, and the average particle size of the boron compound in the mixing step is 1 μm or more and 1 mm or less.
The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5.
Step (1-1): A crystallization step of obtaining the nickel-manganese composite compound by crystallization. The positive electrode active material for a lithium ion secondary battery according to claim 5 or 6, wherein the boron compound in the mixing step is at least one of boric acid, boron oxide, lithium borate, and ammonium borate. Production method. Before the mixing step, the following steps (1-1) and (1-2) are provided, and in the mixing step, the boron compound is mixed in a state of being impregnated with the nickel-manganese composite compound. Will be
The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5.
(1-1) A crystallization step of obtaining the nickel-manganese composite compound by crystallization;
(1-2) A solution containing at least one of boric acid and borate is added to a slurry obtained by mixing the nickel-manganese composite compound and water to impregnate the nickel-manganese composite compound with boron. Boron impregnation step. Before the mixing step, the following steps (1-3) are provided:
The manufacturing method of the positive electrode active material for positive electrode active materials for lithium ion secondary batteries as described in any one of Claims 5-8.
(1-3) A heat treatment step of heat treating the nickel-manganese composite compound at a temperature of 105° C. or higher and 700° C. or lower. A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution, and the positive electrode contains the positive electrode active material according to any one of claims 1 to 4.