JP2018190720A - Positive electrode active material for nonaqueous electrolytic secondary battery, and nonaqueous electrolytic secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a nonaqueous electrolytic secondary battery, which is superior in cycle characteristic.SOLUTION: Provided is a positive electrode active material for a nonaqueous electrolytic secondary battery, which comprises: particles of a spinel type oxide; and a coating layer. The spinel type oxide includes Li, Mn, Ni and an element M in the proportion of amounts of these substances of Li:Mn:Ni:M=t:2-x-y:x:y (0.96≤t≤1.25, 0.40≤x≤0.60 and 0≤y≤0.20). As to the positive electrode active material, a peak as assigned to a spinel type crystal structure of "Fd-3 m" structure is detected from an XRD pattern; and the element M is at least one element selected from Mg, Al, Si, Ti, Cr, Fe, Co, Cu and Zn. The coating layer includes a titanium compound. The spinel type oxide particles contain titanium at a rate of 0.4 mg or more and 9.0 mg or less per 1 min superficial area. According to semiquantitative analysis on the positive electrode active material performed by XPS, Ti/(Mn+Ni) is 0.14 or more and 9.5 or less.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

  In recent years, with the spread of small information terminals such as smartphones and tablet PCs, there is an increasing demand for small and lightweight secondary batteries having high energy density. In addition, development of a high-power secondary battery is strongly desired as a power source for electric vehicles including hybrid vehicles.

  As a secondary battery satisfying such requirements, there is a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. A lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material used as a material for the negative electrode and the positive electrode.

  Currently, research and development of such lithium ion secondary batteries are actively conducted. Among them, a lithium ion secondary battery using a lithium metal composite oxide as a positive electrode material is capable of being used as a battery having a high energy density because a voltage of 4 V class can be obtained.

Specifically, lithium cobalt composite oxide (LiCoO ₂ ) particles that are relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) particles using nickel that is cheaper than cobalt, lithium nickel cobalt manganese composite oxide ( LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) particles, lithium manganese composite oxide (LiMn ₂ O ₄ ) particles using manganese, lithium nickel manganese composite oxide (LiNi _0.5 Mn _0.5 O ₂ ) Lithium composite oxide particles such as particles have been proposed.

Among these, lithium manganese composite oxide particles having a spinel type crystal structure that can realize a secondary battery excellent in thermal stability without using cobalt with a small reserve amount, in particular, a part of manganese is made of Ni. The substituted lithium manganese nickel composite oxide (LiMn _1.5 Ni _0.5 O ₄ ) particles have a high energy density that can realize an operating voltage of 4.5 V or higher when the potential of Li ⁺ / Li is used as a reference. As recently, it has attracted attention.

  However, these positive electrode active materials having a spinel structure have a problem that the battery capacity decreases as charging and discharging are repeated, that is, there is a problem that the cycle characteristics are inferior.

  One of the causes of the decrease in the battery capacity is considered to be decomposition of the electrolyte during charging, which is a problem inherent to the high potential lithium manganese nickel composite oxide. That is, since the decomposition of the electrolytic solution is an irreversible reaction, the electrolytic solution that is a lithium ion carrier between the positive electrode and the negative electrode gradually decreases or the side reaction accompanying the decomposition of the electrolytic solution due to repeated charge and discharge. As a result, lithium ions are consumed, which does not contribute to charge / discharge. As a result, it is considered that the battery capacity decreases. Note that the decomposed electrolytic solution serves as a source of gas mainly composed of hydrogen or the like, and may cause problems such as swelling of the secondary battery.

  Further, although this is not a problem inherent to the high-potential lithium manganese nickel composite oxide, the elution of manganese into the electrolytic solution during charging / discharging is considered to be one of the causes of battery capacity reduction. In particular, when a carbon-based material is used as the negative electrode, manganese eluted from the positive electrode is deposited on the negative electrode and inhibits the battery reaction at the negative electrode.

  These phenomena such as decomposition of the electrolytic solution are all caused by side reactions occurring at the interface between the positive electrode active material and the electrolytic solution. For this reason, in order to improve the cycle of a secondary battery using a high potential lithium manganese nickel composite oxide as a positive electrode active material, it is important to control the surface state of the lithium manganese nickel composite oxide. It is done.

  For example, Patent Document 1 and Patent Document 2 report that the surface characteristics of spinel-type lithium manganese composite oxide are coated with aluminum oxide, zirconium oxide or the like using a metal alkoxide solution to improve cycle characteristics. .

However, Patent Document 1 and Patent Document 2 are limited to reporting batteries using a positive electrode active material that expresses about 4 V (Vs. Li ⁺ / Li), so that the coating layer is stable even at an operating voltage of 4.5 V or more. It is unclear whether Mn elution can be prevented, that is, whether the cycle characteristics are excellent.

  Patent Document 3 discloses that the surface of a spinel-type lithium manganese nickel-based composite oxide is coated with a metal oxide containing at least one metal element selected from Mg, Al, Ti, Zr, and Zn. ing.

  However, Patent Document 3 employs a method in which a metal oxide used for coating is dry-mixed with lithium manganese nickel-based composite oxide particles and adhered to the surface of the lithium manganese nickel-based composite oxide particles. For this reason, it is not clear whether the coating is stably present when repeated charge / discharge is performed, and the coating tends to be non-uniform, and a sufficient effect of improving cycle characteristics cannot be obtained.

Patent Document 4 discloses a non-aqueous electrolyte secondary battery having a positive electrode including positive electrode active material particles composed of a transition metal oxide exhibiting a charge / discharge potential of 4.5 V or more at a metal lithium counter electrode potential, A non-aqueous electrolyte secondary battery in which the active material has a coating layer containing LiTi ₂ O ₄ having a spinel crystal structure on the surface thereof is disclosed.

In the invention disclosed in Patent Document 4, the composition of the coating layer is not analyzed. In particular, when LiTi ₂ O ₄ is used, the theoretical oxidation number of Ti is 3.5, and is not an oxidation number that Ti can normally take. For this reason, it is not clear whether the coating layer has the target composition. In addition, the secondary battery was charged after being charged, and the discharge capacity after being stored for a predetermined period was only evaluated as a life characteristic, and the cycle characteristic was unknown.

JP 2001-043860 A JP 2014-231445 A JP 2006-036545 A JP 2006-031852 A

  Then, in view of the problem of the above-described conventional technology, an object of one aspect of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery excellent in cycle characteristics.

In order to solve the above problems, according to one aspect of the present invention,
A positive electrode active material for a non-aqueous electrolyte secondary battery having spinel oxide particles that are oxides having a spinel structure and a coating layer that covers at least part of the spinel oxide particles,
The spinel oxide is composed of lithium (Li), manganese (Mn), nickel (Ni), and element M (M), in a mass ratio of Li: Mn: Ni: M = t: 2- x-y: x: y (provided that 0.96 ≦ t ≦ 1.25, 0.40 ≦ x ≦ 0.60, 0 ≦ y ≦ 0.20), and X-ray diffraction (XRD) From the diffraction pattern obtained by the measurement, a peak attributed to the spinel crystal structure of the “Fd-3m” structure is detected,
The element M is selected from magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn). At least one element selected,
The coating layer contains a titanium compound, and contains titanium at a ratio of 0.4 mg to 9.0 mg per 1 m ² of the surface area of the spinel oxide particles,
When semi-quantitative analysis was performed by X-ray photoelectron spectroscopy, the amount of titanium (Ti) was divided by the total amount of manganese (Mn) and nickel (Ni) (Ti / (Mn + Ni)). Provides a positive electrode active material for a non-aqueous electrolyte secondary battery having a value of 0.14 or more and 9.5 or less.

  According to one embodiment of the present invention, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery excellent in cycle characteristics.

Explanatory drawing of the cross-sectional structure of the coin-type battery produced in the Example and the comparative example.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.
1. First, a configuration example of a positive electrode active material for a non-aqueous electrolyte secondary battery according to this embodiment will be described.

  The positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment includes a spinel oxide particle that is an oxide having a spinel structure, and a coating layer that covers at least a part of the spinel oxide particle. Can have.

  The spinel type oxide is composed of lithium (Li), manganese (Mn), nickel (Ni), and element M (M), and the mass ratio is Li: Mn: Ni: M = t: 2-x. -Y: x: y can be included. However, it is preferable to satisfy 0.96 ≦ t ≦ 1.25, 0.40 ≦ x ≦ 0.60, and 0 ≦ y ≦ 0.20. Moreover, it is preferable that the peak attributed to the spinel type crystal structure of a "Fd-3m" structure is detected from the diffraction pattern obtained by the X-ray diffraction (XRD) measurement of the spinel type oxide.

  The element M is magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn). It is possible to use at least one element selected from

The coating layer contains a titanium compound and can contain titanium at a ratio of 0.4 mg to 9.0 mg per 1 m ² of surface area of the spinel oxide particles.

  The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment is obtained by changing the amount of titanium (Ti) to manganese (Mn) and nickel (Ni) when semi-quantitative analysis is performed by X-ray photoelectron spectroscopy. ) And (Ti / (Mn + Ni)) divided by the total amount of substances can be 0.14 or more and 9.5 or less.

  Hereinafter, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment (hereinafter also simply referred to as “positive electrode active material”) will be specifically described.

The positive electrode active material of this embodiment can have spinel-type oxide particles and a coating layer that covers at least part of the spinel-type oxide particles. The spinel oxide particles and the coating layer will be described below.
[Spinel-type oxide particles]
The spinel-type oxide particles contain a spinel-type oxide which is an oxide having a spinel-type structure, and are preferably composed of a spinel-type oxide.

  Here, as the spinel-type oxide, lithium (Li), manganese (Mn), nickel (Ni), and element M (M) have a mass ratio (molar ratio) of Li: Mn: Ni. : M = t: 2-xy: x: y. That is, it is preferable to use a lithium manganese nickel composite oxide as the spinel type oxide.

  In the above formula representing the ratio of the amount of each element in the spinel oxide, the value of t indicating the lithium (Li) content can be 0.96 or more and 1.25 or less, and 0.98 or more. 1.20 or less is preferable, and 1.00 or more and 1.20 or less is more preferable.

  By setting the value of t to 0.96 or more, the internal resistance of the secondary battery using the positive electrode active material containing the spinel oxide can be suppressed and the output characteristics can be improved. Further, by setting the value of t to 1.25 or less, the initial discharge capacity of the secondary battery using the positive electrode active material containing the spinel oxide can be maintained high. That is, by setting the value of t within the above-described range, it is possible to improve the output characteristics and capacity characteristics of the secondary battery using the positive electrode active material containing the spinel oxide.

  Nickel (Ni) in the above-mentioned spinel type oxide is an element that contributes to higher potential and higher capacity of a secondary battery using a positive electrode active material containing the spinel type oxide.

  The value x indicating the nickel content can be 0.40 or more and 0.60 or less, preferably 0.40 or more and 0.56 or less, and more preferably 0.40 or more and 0.53 or less.

  By setting the value of x to 0.40 or more, in a secondary battery using a positive electrode active material containing the spinel oxide, the battery capacity at a voltage of 5 V can be sufficiently increased. In addition, by setting the value of x to 0.60 or less, the spinel oxide particles can be more reliably composed of a spinel structure single phase.

  Further, the spinel oxide may contain an element M as an additive element in addition to the metal element.

  Examples of the element M include magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn ) Can be used.

  The element M is appropriately selected according to the use of the secondary battery configured using the positive electrode active material and the required performance.

  Since the element M itself does not contribute to the oxidation-reduction reaction, the value of y indicating the content of the element M can be 0.20 or less, preferably 0.15 or less, and more preferably 0.10 or less. .

  Since the spinel oxide does not need to contain the element M, the lower limit value of y indicating the content of the element M can be zero.

  In the spinel oxide, it is preferable that a peak attributed to the spinel crystal structure of the “Fd-3m” structure is detected from a diffraction pattern obtained when X-ray diffraction (XRD) measurement is performed. In particular, in the spinel oxide, it is more preferable that only the peak attributed to the spinel crystal structure having the “Fd-3m” structure is detected from the diffraction pattern obtained when X-ray diffraction measurement is performed. This is because the spinel type oxide having the “Fd-3m” structure is preferable because the internal resistance can be particularly suppressed when the positive electrode active material containing the spinel type oxide is used as a secondary battery.

However, a spinel oxide such as the above-described lithium manganese nickel composite oxide cannot be obtained in a single phase, and impurities may be mixed. For example, there may be a case where a different phase such as nickel manganese composite oxide such as NiMn ₃ O ₈ or lithium nickel oxide such as Li _x Ni _1-x O ₂ is detected in the vicinity of 2θ in the range of 40 ° to 45 °. is there. Further, a peak due to the “P43 ₃ 2” structure constituted by an ordered arrangement of manganese and nickel in the spinel structure may be detected when 2θ is around 19 °.

  Even when impurities are mixed in this way, the intensity of the heterophasic peak other than the spinel structure of the “Fd-3m” structure is the peak intensity attributed to the spinel structure of the “Fd-3m” structure. It is preferable not to exceed.

  When the spinel-type oxide particles are observed with an electron microscope such as SEM or TEM, the particle size is 3.0 μm to 5.0 μm formed by agglomeration of many primary particles having a particle size of 0.1 μm to 2.0 μm. The following secondary particles, single primary particles having a particle size of 1.0 μm or more and 7.0 μm or less, or a mixture thereof are preferable. Each particle may have a space or void surrounded by one or more primary particles.

Particles of spinel-type oxide is preferably a specific surface area is less than 0.30 m ² / g or more 1.50 m ² / g, more not more than 0.50 m ² / g or more 1.50 m ² / g preferable.

Lithium ion desorption / insertion that occurs in the spinel oxide particles during charge and discharge of the secondary battery occurs on the surface of the spinel oxide particles. Further, by setting the specific surface area of the spinel oxide particles contained in the positive electrode active material to 0.30 m ² / g or more, the desorption / insertion of the lithium ions can be sufficiently promoted, and the internal resistance is sufficient. It is preferable because it can be suppressed. In addition, the electrolytic solution may be decomposed by a side reaction that occurs at the interface between the positive electrode active material and the electrolytic solution, but it can be obtained by setting the specific surface area of the spinel oxide particles to 1.50 m ² / g or less. Since it can suppress that the specific surface area of a positive electrode active material becomes large too much, the influence of the internal resistance increase by the deposit produced by the decomposition reaction which concerns can be fully suppressed.

  The specific surface area of the spinel-type oxide particles of the present embodiment can be evaluated by, for example, the BET method using nitrogen adsorption.

The volume average particle diameter of the spinel oxide particles of the present embodiment is preferably 2 μm or more and 8 μm or less, more preferably 3 μm or more and 8 μm or less, when measured with a laser light diffraction / scattering particle size distribution meter. Preferably, it is 3 μm or more and 7.5 μm or less. When the volume average particle diameter of the spinel oxide particles is 2 μm or more and 8 μm or less, the battery capacity per capacity in the secondary battery using the positive electrode active material containing the spinel oxide particles as the positive electrode is calculated. This is because it can be made sufficiently large, and excellent battery characteristics such as high safety and high output can be obtained.
[Coating layer]
The coating layer contains a compound containing titanium, that is, a titanium compound, and covers at least a part of the spinel-type oxide particles. A coating layer can also be comprised from a titanium compound.

  By disposing the coating layer, in the secondary battery including the positive electrode including the positive electrode active material of the present embodiment, elution of manganese and nickel into the electrolytic solution can be suppressed.

  The coating layer and the spinel oxide particles need not have a clear boundary line. For this reason, the coating layer is a region or region having a titanium concentration higher than that of the spinel-type oxide particles that are the material to be coated in the region on the surface side of the positive electrode active material of the present embodiment, that is, the central region. Point to. The coating layer may partially be in solid solution with the spinel oxide.

  Of the positive electrode active material of the present embodiment, the portion of the coating layer can be detected by energy dispersive X-ray analysis (EDS) attached to a transmission electron microscope (TEM) or the like. In the coating layer detected by the analysis by TEM-EDS, that is, in the region on the surface side of the positive electrode active material, the thickness of the portion where the titanium concentration is higher than that of the spinel oxide particles is preferably 1 nm or more and 10 nm or less. The thickness is more preferably 7.5 nm or less and further preferably 1 nm or more and 3 nm or less.

  This is because when the thickness of the coating layer detected by TEM-EDS is 1 nm or more, it indicates that the coating layer can be uniformly disposed on the entire surface of the spinel oxide particles. That is, it shows that the surface of the spinel oxide particles can be uniformly coated with the coating layer. Moreover, when the thickness of the coating layer detected by TEM-EDS is 10 nm or less, the coating layer is prevented from becoming an obstacle to the reaction of lithium intercalation / deintercalation to the spinel oxide, This is because the internal resistance can be reduced.

The content of titanium in the coating layer is not particularly limited, but the content is preferably adjusted according to the specific surface area of the spinel oxide particles to be coated. Specifically, for example, the coating layer preferably contains titanium at a ratio of 0.4 mg to 9.0 mg, and a ratio of 0.4 mg to 3.3 mg per 1 m ² of the surface area of the spinel oxide particles. It is more preferable to contain titanium, and it is more preferable to contain titanium at a ratio of 0.4 mg to 1.3 mg.

This is because when the titanium content per 1 m ² of the surface area (specific surface area) of the spinel oxide particles is 0.4 mg or more, the coating layer can be uniformly disposed on the entire surface of the spinel oxide particles. It is because it shows that it is.

In addition, the cycle characteristics can be improved by providing a coating layer, but the internal resistance may increase at the same time. Then, by setting the titanium content per 1 m ² of the surface area (specific surface area) of the particles of the spinel type oxide to 9.0 mg or less, the coating layer can intercalate / deintercalate lithium into the spinel type oxide. This is because it is possible to suppress an obstacle to the reaction of the reaction and to reduce the internal resistance.

The method for evaluating and calculating the titanium content in the coating layer is not particularly limited. For example, the titanium content in 1 g of the positive electrode active material is first measured by a method such as chemical analysis. For example, measurement can be performed by ICP (Inductively Coupled Plasma). Further, the specific surface area of the spinel-type oxide particles before the coating treatment with the titanium compound is measured by a BET method using nitrogen adsorption or the like. Then, by dividing the titanium content in 1 g of the positive electrode active material by the specific surface area of the spinel-type oxide particles before the coating treatment, the titanium content per 1 m ^{2 of the} surface area (specific surface area) of the spinel-type oxide particles Can be calculated.

Although the denominator differs between the titanium content in 1 g of the positive electrode active material and the specific surface area of the spinel-type oxide particles, it is not an exact value. The amount of titanium supported per 1 m ² of the surface area of the composite oxide can be used.

  When the spinel-type oxide particles before the coating treatment contain titanium, it is preferable to use the difference in titanium content before and after the coating treatment as the amount of titanium used for the coating.

  In addition, titanium of a coating layer and spinel type oxide may react, and titanium may be partially dissolved in the spinel type oxide. For example, heat treatment can be performed after the coating treatment, and titanium in the coating layer can be reacted with the spinel oxide depending on the conditions at that time.

  Since the titanium of the coating layer is dissolved in the spinel oxide, the coating layer simply prevents direct contact between the electrolyte and the spinel oxide particles, and not only reduces the chance of reaction, This has the effect of suppressing the reaction between the spinel oxide and the electrolyte that occurs at higher potential. However, with respect to the positive electrode active material, it is preferable to adjust the degree of solid solution so that the effect of improving the cycle characteristics can be sufficiently exhibited.

  The degree of solid solution with respect to the spinel oxide particles of the coating layer is determined by semi-quantitative analysis by XPS (X-ray Photoelectron Spectroscopy) of titanium (Ti), manganese (Mn) and nickel. It can be known from (Ni / Mn + Ni) (hereinafter also referred to as “coating metal surface amount”) divided by the total amount of substances (Ni).

  Since XPS can selectively obtain information on the surface of the measurement object from 1 nm to 5 nm, the composition ratio of the surface layer of the material can be known. The coated metal surface amount is preferably from 0.14 to 9.5, more preferably from 0.14 to 1.6, and even more preferably from 0.14 to 1.0. By setting the coating metal surface amount to 0.14 or more, titanium existing as a coating layer, that is, as a coating layer without diffusing to the side of the spinel-type oxide particles is sufficiently secured. This is because it means that a sufficiently uniform coating layer is formed to suppress elution into the electrolytic solution.

  In addition, the cycle characteristics can be improved by providing a coating layer, but the internal resistance may increase at the same time. And, by setting the coating metal surface amount to 9.5 or less, it is possible to reliably prevent the coating layer from obstructing the reaction of lithium intercalation / deintercalation to the spinel oxide. This is because the internal resistance can be suppressed.

A coating metal surface amount of 0.14 or more and 1.0 or less is more preferable because both high cycle characteristics and low internal resistance can be achieved.
Further, by doping Li in the coating layer, lithium ion conductivity can be imparted to the coating layer, and an increase in resistance can be suppressed. For this reason, it is preferable that a coating layer contains titanium and lithium.
The degree of Li content relative to the amount of Ti contained in the coating layer, which indicates the degree of Li doping in the coating layer, is determined by the amount of lithium (Li) by semi-quantitative analysis by X-ray photoelectron spectroscopy (XPS), titanium ( It can be known from Li / Ti divided by the amount of Ti) (hereinafter also referred to as “Li doping index of coating layer”). When semi-quantitative analysis by X-ray photoelectron spectroscopy is performed, the Li doping index of the coating layer is preferably 0.5 or more and 1.2 or less, more preferably 0.5 or more and 1.0 or less. Preferably, it is 0.8 or more and 1.0 or less. By setting the Li doping index of the coating layer to 0.5 or more, the lithium ion conductivity of the coating layer can be sufficiently increased, and an increase in resistance can be particularly suppressed. Excess lithium can be suppressed by setting the Li doping index of the coating layer to 1.2 or less. For this reason, it can suppress that excess lithium reacts with the carbon dioxide in the air, and produces | generates the foreign material layer which becomes resistance on the surface, and is preferable.
[Characteristics of positive electrode active material]
So far, the spinel oxide particles and the coating layer have been described, but the positive electrode active material of the present embodiment preferably has the following characteristics.

  The positive electrode active material of the present embodiment is preferably composed only of the above-described spinel-type oxide particles and the coating layer, but impurities may be mixed during the production. In particular, moisture and carbon are impurities that can be increased by the coating process. Since moisture and carbon may affect cycle characteristics, it is preferable that the moisture and carbon be controlled within a predetermined range.

  The positive electrode active material of the present embodiment preferably has a carbon content of 0.01% by mass or more and 0.5% by mass or less. By setting the carbon content to 0.5% by mass or less, generation of carbon dioxide due to, for example, decomposition of organic components contained in the coating layer during charging / discharging of the secondary battery using the positive electrode active material is prevented. This is because it can be sufficiently suppressed to prevent the battery from expanding. However, since carbon is mixed into the positive electrode active material of the present embodiment due to carbon dioxide in the air, it is difficult to make the carbon content less than 0.01 mass. For this reason, it is preferable that the lower limit of carbon content shall be 0.01 mass%.

  The carbon content of the positive electrode active material of this embodiment can be evaluated by, for example, an infrared absorption method.

  Moreover, it is preferable that the positive electrode active material of this embodiment has a water content (water content) of 0.01% by mass or more and 0.2% by mass or less. By setting the water content to 0.2% by mass or less, in the secondary battery using the positive electrode active material, the hydrolysis reaction of the electrolyte of the electrolytic solution can be more reliably suppressed.

  When the electrolyte of the electrolytic solution is hydrolyzed, an acidic component such as hydrogen fluoride is generated, and the acidic component reacts with the positive electrode active material to cause deterioration. However, the moisture content of the positive electrode active material of the present embodiment is preferably 0.2% by mass or less as described above, so that the hydrolysis reaction of the electrolyte of the electrolytic solution can be more reliably suppressed and the deterioration can be suppressed. .

  However, since moisture is mixed into the positive electrode active material of the present embodiment due to adsorption of moisture in the air, it is difficult to make the moisture content less than 0.01% by mass. For this reason, it is preferable that the lower limit of the moisture content is 0.01% by mass.

  The moisture content of the positive electrode active material of this embodiment can be evaluated by, for example, the Karl Fischer method with a vaporization temperature of 300 ° C.

  The positive electrode active material of the present embodiment preferably has a titanium content of 0.01% by mass or more and 1.00% by mass or less, more preferably 0.01% by mass or more and 0.50% by mass or less. More preferably, it is 0.04 mass% or more and 0.40 mass% or less.

By setting the content ratio of titanium to 0.01% by mass or more, for the amount of titanium per unit specific surface area of the spinel-type oxide particles, for example, the minimum amount in the preferred range described above can be more reliably ensured, which is preferable. . Further, it is preferable that the content ratio of titanium is 1.00% by mass or less because the amount of the titanium compound that does not contribute to the charge / discharge capacity can be minimized and the capacity with respect to the mass of the positive electrode active material can be improved.
2. Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary battery The manufacturing method of the positive electrode active material of this embodiment can have the following four processes.

First step: [Precursor crystallization step]
The precursor crystallization step can be a step of preparing a manganese nickel composite hydroxide, which is a spinel oxide precursor, by a crystallization reaction.

  Specifically, for example, a mixed aqueous solution is prepared using a water-soluble raw material so that the molar ratio of each element is Mn: Ni: M = 2−xy: x: y, and an alkali metal aqueous solution or the like. In addition, it can be reacted in a reaction tank to obtain a manganese nickel composite hydroxide.

  In addition, about x and y in the above-mentioned formula, it can be set as the suitable range similar to x and y demonstrated in the particle | grains of the spinel type oxide.

Second step: [oxidation roasting step]
The oxidation roasting step can be a step of preparing a manganese nickel composite oxide. Specifically, for example, the manganese nickel composite hydroxide obtained in the precursor crystallization process is fired at a temperature of 800 ° C. or higher and 1000 ° C. or lower in an oxygen-containing atmosphere to obtain a manganese nickel composite oxide. Can do.

Third step: [spinel-type oxide synthesis step]
In the spinel oxide synthesis step, a spinel oxide can be synthesized. Specifically, for example, the manganese nickel composite oxide obtained in the oxidative roasting step is mixed with a lithium compound and fired at a temperature of 600 ° C. or higher and 850 ° C. or lower in an oxygen-containing atmosphere. Thus, a lithium manganese nickel composite oxide can be obtained.

Fourth step: [Coating step]
The coating step can be a step of forming a coating layer on the surface of the spinel oxide particles. Specifically, for example, spinel-type oxide particles obtained in the spinel-type oxide synthesis step and a liquid coating agent are mixed, dried, and then heat-treated in an oxygen-containing atmosphere as necessary. A coating layer can be provided on the surface of the oxide particles.

Hereinafter, one configuration example of the method for producing the positive electrode active material of the present embodiment will be described more specifically.
[Precursor crystallization process]
First, a metal compound containing manganese, a metal compound containing nickel, and possibly a metal compound containing element M are dissolved in water at a predetermined ratio to prepare a mixed aqueous solution (mixed aqueous solution preparation step). The composition ratio of each metal in the mixed aqueous solution is the same as the composition ratio of the manganese nickel composite hydroxide finally obtained. Therefore, the ratio of the metal compound dissolved in water is adjusted so that the composition ratio of each metal in the mixed aqueous solution is the same as the composition ratio of each metal in the target manganese nickel composite hydroxide particles. It is preferable to prepare a mixed aqueous solution. The metal compound may be water-soluble, and sulfate is preferable from the viewpoint of cost. In addition, when a water-soluble suitable raw material is not found by the element M etc., you may add in the oxidation roasting process mentioned later or a spinel type oxide synthesis process, without adding to mixed aqueous solution.

  Next, water is put into the reaction vessel, and an appropriate amount of an alkaline substance and an ammonium ion supplier are added to prepare an initial aqueous solution (initial aqueous solution preparation step). At this time, it is preferable to prepare such that the pH value of the initial aqueous solution is 11.2 to 12.2 and the ammonia concentration is 2 g / L to 15 g / L on the basis of the liquid temperature of 25 ° C.

  When the precursor crystallization process is performed to prepare the manganese nickel composite hydroxide, impurities due to anions constituting the metal compound contained in the mixed aqueous solution used may be mixed into the manganese nickel composite hydroxide. However, it is preferable to set the pH value of the initial aqueous solution to 11.2 or more because it is possible to suppress contamination of impurities due to anions constituting the metal compound of the raw material. In addition, by setting the pH value of the initial aqueous solution to 12.2 or less, it is preferable that the obtained manganese nickel composite hydroxide particles can be prevented from being finely divided and can have an optimum size.

  In addition, it is preferable to set the ammonia concentration of the initial aqueous solution to 2 g / L or more because the manganese nickel composite hydroxide particles obtained can be easily formed into a spherical shape. And by making ammonia concentration of initial stage aqueous solution into 15 g / L or less, it prevents that the solubility of nickel which forms an ammonia complex rises too much, and aims at composition of the manganese nickel compound hydroxide obtained more certainly Since it can be set as a composition, it is preferable.

  In addition, although it does not specifically limit as an alkaline substance used when preparing initial stage aqueous solution, It should be 1 or more types selected from sodium carbonate, sodium hydrogencarbonate, potassium carbonate, sodium hydroxide, potassium hydroxide Is preferred. Since the addition amount can be easily adjusted, it is preferably added in the form of an aqueous solution.

  Further, the ammonium ion supplier is not particularly limited, but one or more selected from ammonium carbonate aqueous solution, ammonia water, ammonium chloride aqueous solution and ammonium sulfate aqueous solution can be preferably used.

  In the precursor crystallization process, the above-mentioned mixed aqueous solution can be dropped into the initial aqueous solution to obtain a reaction aqueous solution. However, the pH value and ammonia concentration of the reaction aqueous solution are also maintained within the preferred ranges described above. It is preferable to do.

  The atmosphere in the reaction vessel is preferably a non-oxidizing atmosphere, for example, an atmosphere having an oxygen concentration of 1% by volume (volume%) or less. This is because a non-oxidizing atmosphere, for example, an atmosphere having an oxygen concentration of 1% by volume or less is preferable because oxidation of raw materials and the like can be suppressed. For this reason, for example, it is possible to prevent oxidized manganese from being precipitated as fine particles.

  The temperature of the reaction vessel is preferably maintained at 40 ° C. or higher and 60 ° C. or lower, more preferably 45 ° C. or higher and 55 ° C. or lower. In addition, in order to maintain a reaction tank in the temperature range which concerns, it is preferable that the initial aqueous solution and reaction aqueous solution which are arrange | positioned in a reaction tank are also maintained in the same temperature range.

  Since the temperature of the reaction vessel naturally rises due to reaction heat and stirring energy, it is preferable to set the temperature to 40 ° C. or higher because extra energy is not consumed for cooling. Further, it is preferable to set the temperature of the reaction tank to 60 ° C. or lower because the initial aqueous solution and the amount of ammonia evaporated from the reaction aqueous solution can be suppressed, and the target ammonia concentration can be easily maintained.

  In the precursor crystallization step, the initial aqueous solution is placed in the reaction vessel and the temperature and the like are adjusted, and then the mixed aqueous solution is dropped into the reaction vessel at a constant rate to obtain a reaction aqueous solution, thereby producing manganese nickel as a precursor. Crystallization of the composite hydroxide particles can be performed (crystallization step).

  As described above, it is preferable that the pH value and the ammonia concentration of the reaction aqueous solution are in the same preferred range as described for the initial aqueous solution. For this reason, when dropping the mixed aqueous solution into the initial aqueous solution or the reaction aqueous solution, it is preferable that the ammonium ion supplier and the alkaline substance are also dropped into the initial aqueous solution or the reaction aqueous solution at a constant rate. And it is preferable to control so that pH value of reaction aqueous solution may be maintained at 11.2 or more and 12.2 or less on the basis of liquid temperature 25 degreeC, and ammonia concentration is 2 g / L or more and 15 g / L or less.

Thereafter, the slurry containing the manganese nickel composite hydroxide particles recovered from the overflow port provided in the reaction vessel is filtered and dried to obtain powdered manganese nickel composite hydroxide particles as a precursor. be able to.
[Oxidation roasting process]
In the oxidation roasting step, the manganese nickel composite hydroxide produced in the precursor crystallization step is fired in an oxygen-containing atmosphere, and then cooled to room temperature, whereby a manganese nickel composite oxide can be obtained.

  The roasting conditions in the oxidative roasting step are not particularly limited, but it is preferably fired in an oxygen-containing atmosphere, for example, in an air atmosphere, at a temperature of 800 ° C. to 1000 ° C. for 5 hours to 24 hours.

  This is because, by setting the firing temperature to 800 ° C. or higher, it is possible to suppress an excessive increase in the specific surface area of the resulting manganese nickel composite oxide. Moreover, it is because it can suppress that the specific surface area of manganese nickel complex oxide becomes too small because a calcination temperature shall be 1000 degrees C or less.

  By setting the firing time to 5 hours or longer, the temperature in the firing container can be made particularly uniform, and the reaction can be promoted uniformly, which is preferable. In addition, even when firing for longer than 24 hours, no significant change is observed in the resulting manganese nickel composite oxide. From the viewpoint of energy efficiency, the firing time is preferably 24 hours or less.

  The oxygen concentration in the oxygen-containing atmosphere during the heat treatment is preferably not less than the oxygen concentration in the air atmosphere, that is, the oxygen concentration is not less than 20% by volume. Since an oxygen atmosphere can also be used, the upper limit value of the oxygen concentration in the oxygen-containing atmosphere can be set to 100% by volume.

  For example, when the compound containing the element M cannot be coprecipitated in the precursor crystallization process, for example, the composition ratio for the compound containing the element M with respect to the manganese nickel composite hydroxide to be subjected to the oxidation roasting process It may be fired in addition to the same. It does not specifically limit as a compound containing the element M to add, For example, an oxide, a hydroxide, a carbonate, or its mixture etc. can be used.

  When mild sintering is observed in the manganese nickel composite oxide particles after the oxidation roasting step, a crushing treatment may be added.

When the crystal structure of the manganese-nickel composite oxide produced as described above is measured by XRD, it can be confirmed that it is a spinel crystal structure.
[Spinel-type oxide synthesis process]
In the spinel oxide synthesis step, first, the manganese nickel composite oxide particles obtained in the oxidation roasting step have a lithium content of 48 atomic% or more to the total number of metal atoms contained in the particles. A lithium mixture can be obtained by adding and mixing the lithium compound so as to be 5 atomic% or less (lithium mixture preparation step).

  The lithium compound to be added is not particularly limited, and for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof can be used. As the lithium compound, it is particularly preferable to use lithium hydroxide having a low melting point and high reactivity.

  Next, after the obtained lithium mixture is fired in an oxygen-containing atmosphere, it is cooled to room temperature to obtain a lithium manganese nickel composite oxide which is a spinel type oxide containing lithium (firing step).

  The baking conditions are not particularly limited, but for example, baking is preferably performed at a temperature of 600 ° C. to 850 ° C. for 5 hours to 36 hours.

  Note that the oxygen-containing atmosphere is preferably an atmosphere containing 80% by volume or more of oxygen. This is because by making the oxygen concentration in the atmosphere 80% by volume or more, the generation of oxygen defects in the obtained spinel oxide can be particularly suppressed, which is preferable. Since an oxygen atmosphere can also be used, the upper limit value of the oxygen concentration in the oxygen-containing atmosphere can be set to 100% by volume.

  And it is preferable for the firing temperature to be 600 ° C. or higher because the crystal structure of the lithium manganese nickel composite oxide can be sufficiently grown. Moreover, since it can suppress especially generation | occurrence | production of the oxygen defect in the lithium manganese nickel complex oxide by making calcination temperature into 850 degrees C or less, it is preferable.

  The firing time is preferably 5 hours or longer, because the temperature in the firing container can be made uniform and the reaction can proceed uniformly. In addition, even when firing for longer than 36 hours, no significant change is observed in the obtained lithium manganese nickel composite oxide. From the viewpoint of energy efficiency, the firing time is preferably 36 hours or less.

In addition, after a spinel type oxide synthetic | combination process, when mild sintering is seen in the spinel type oxide obtained, ie, lithium manganese nickel composite oxide, you may add a crushing process.
[Coating process]
In the coating step, first, the specific surface area of the spinel type oxide obtained in the spinel type oxide synthesis step is measured, and a liquid coating agent can be prepared according to the target titanium carrying amount of the coating layer ( Coating agent preparation step).

  The coating agent is not particularly limited as long as it contains titanium or a titanium compound. As the coating agent, for uniform coating, a titanium compound dissolved in a solvent, a low melting point titanium compound that is liquid at normal temperature or melts by low-temperature heat treatment, and the like can be preferably used.

Examples of the titanium compound include one or more selected from alkoxides such as titanium tetraisopropoxide and titanium tetrabutoxide, and chelates such as titanium acetylacetonate and tan lactate ammonium salt. In particular, a coating agent that can be easily prepared and that can suppress mixing of impurities and that is obtained by dissolving metallic titanium in a mixed aqueous solution of hydrogen peroxide and ammonia can be preferably used.
When doping the coating layer with Li, it is preferable to add a lithium compound to the coating agent. As the lithium compound, for example, one or more selected from alkoxides such as lithium ethoxide and lithium salts dissolved in a solvent can be suitably used. As described above, a coating agent in which metallic titanium is dissolved in a mixed aqueous solution of hydrogen peroxide and ammonia can be preferably used as the coating agent, and a lithium compound dissolved in such a solution can be particularly preferably used. Examples of the lithium compound that dissolves in the solution include lithium hydroxide.
In addition, since excess lithium may remain on the surface of the spinel-type oxide particles, the coating layer may be doped with Li even when a lithium compound is not added to the coating agent.

  Next, in the coating step, the lithium manganese nickel composite oxide particles and the coating agent can be mixed. A general mixer can be used for mixing (mixture preparation step).

  And it can dry after mixing (drying step), and also can heat-process as needed, and can fix a titanium compound as a coating layer (heat treatment step).

  In the drying step, drying can be performed at a temperature that can remove the solvent of the coating agent. For example, drying can be performed at 80 ° C. or more and less than 300 ° C.

  The heat treatment conditions of the heat treatment step are not particularly limited, but it is preferable to perform the heat treatment at a temperature of 300 ° C. to 600 ° C. for 1 hour to 5 hours in an oxygen-containing atmosphere, for example, an air atmosphere. After the heat treatment, it is cooled to room temperature, and a positive electrode active material that is a spinel oxide particle having a coating layer as a final product can be obtained.

  The oxygen concentration in the oxygen-containing atmosphere during the heat treatment is preferably not less than the oxygen concentration in the air atmosphere, that is, the oxygen concentration is not less than 20% by volume. This is because, by setting the oxygen-containing atmosphere during the heat treatment to be equal to or higher than the oxygen concentration of the air atmosphere, it is particularly preferable to prevent oxygen defects from occurring in the obtained positive electrode active material. Since an oxygen atmosphere can also be used, the upper limit value of the oxygen concentration in the oxygen-containing atmosphere can be set to 100% by volume.

  The firing temperature at the time of the heat treatment is preferably 300 ° C. or higher because the impurities contained in the coating agent can be particularly suppressed from remaining in the positive electrode active material. Further, it is preferable to set the firing temperature to 600 ° C. or lower because it is possible to suppress excessive diffusion of the components of the coating layer and maintain the form of the coating layer. In addition, it is preferable to select the firing temperature at the time of the heat treatment so that the thickness of the coating layer can be sufficiently maintained in accordance with the amount of titanium supported on the coating layer set as a target.

  It is preferable to set the firing time of the heat treatment to 1 hour or longer because it is possible to particularly suppress the impurities contained in the coating agent from remaining in the positive electrode active material. Moreover, even if firing for longer than 5 hours, no significant change is observed in the obtained positive electrode active material. From the viewpoint of energy efficiency, the firing time is preferably 5 hours or less.

  When mild sintering is observed in the positive electrode active material obtained after the coating step, a crushing treatment may be added.

Note that the heat treatment step may not be performed. That is, the positive electrode active material can also be manufactured by performing the mixture preparation step. This is because even if heat treatment is not performed, a coating layer can be uniformly and firmly formed on the surface of the spinel oxide particles by using a liquid coating agent. Even when the heat treatment step is not performed, it is preferable to perform drying in order to reduce or remove the solvent of the coating agent, moisture, or the like, if necessary.
3. Non-aqueous electrolyte secondary battery Next, a configuration example of the non-aqueous electrolyte secondary battery of the present embodiment will be described.

  The non-aqueous electrolyte secondary battery of the present embodiment (hereinafter also simply referred to as “secondary battery”) includes a positive electrode using the positive electrode active material described above, a negative electrode, a separator, and a non-aqueous electrolyte. It can have the composition provided.

Each member of the secondary battery of this embodiment will be described. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention can be used in various ways based on the knowledge of those skilled in the art based on the embodiments described in this specification. It can be implemented in a form that has been changed or improved. Moreover, the use of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited.
[Positive electrode]
The positive electrode is a sheet-like member, and can be formed, for example, by applying a positive electrode mixture paste containing the above-described positive electrode active material to the surface of a current collector made of, for example, an aluminum foil. The positive electrode can also be formed by molding a positive electrode mixture. In addition, a positive electrode is suitably processed according to the battery to be used. For example, a cutting process for forming an appropriate size according to a target battery, a pressure compression process using a roll press or the like for increasing the electrode density, and the like can be performed.

  The above-described positive electrode mixture paste can be formed by adding a solvent to the positive electrode mixture and kneading as necessary. The positive electrode mixture can be formed by mixing the positive electrode active material described above in a powder form, a conductive material, and a binder.

  The conductive material is added to give an appropriate conductivity to the electrode. The material of the conductive material is not particularly limited, and for example, graphite such as natural graphite, artificial graphite and expanded graphite, and carbon black materials such as acetylene black and ketjen black (registered trademark) can be used.

  The binder plays a role of holding the positive electrode active material. The binder used for such a positive electrode mixture is not particularly limited. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic. One or more selected from acids and the like can be used.

  In addition, activated carbon etc. can also be added to a positive electrode compound material. By adding activated carbon or the like to the positive electrode mixture, the electric double layer capacity of the positive electrode can be increased.

  The solvent has a function of dissolving the binder and dispersing the positive electrode active material, the conductive material, activated carbon, and the like in the binder. Although the solvent is not particularly limited, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

  Moreover, the mixing ratio of each substance in the positive electrode mixture paste is not particularly limited, and can be the same as that of the positive electrode of a general non-aqueous electrolyte secondary battery, for example. 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 binder content can be 1 part by mass or more and 20 parts by mass or less.

However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.
[Negative electrode]
The negative electrode is a sheet-like member formed by applying a negative electrode mixture paste to the surface of a metal foil current collector such as copper and drying it. Further, the negative electrode can be a sheet-like member made of a material containing lithium, such as metallic lithium.

  The negative electrode is formed by substantially the same method as the positive electrode described above, although the components constituting the negative electrode mixture paste, the composition thereof, and the current collector material are different. Done.

  The negative electrode mixture paste can be prepared by adding a suitable solvent to the negative electrode mixture in which the negative electrode active material and the binder are mixed to form a paste.

  As the negative electrode active material, for example, a material containing lithium, such as metallic lithium or a lithium alloy, or an occlusion material that can occlude and desorb lithium ions can be employed.

  The occlusion material is not particularly limited, and for example, one or more kinds selected from natural graphite, artificial graphite, a fired organic compound such as phenol resin, and a powdery carbon material such as coke can be used.

When such an occlusion material is employed as the negative electrode active material, a fluorine-containing resin such as PVDF can be used as the binder, as with the positive electrode, and as a solvent for dispersing the negative electrode active material in the binder, An organic solvent such as N-methyl-2-pyrrolidone can be used.
[Separator]
The separator is disposed so as to be sandwiched between the positive electrode and the negative electrode, and has a function of separating the positive electrode and the negative electrode and holding the electrolyte.

As a material for the separator, for example, a thin film such as polyethylene or polypropylene and a film having a large number of fine holes can be used. However, the separator is not particularly limited as long as it has the above function.
[Non-aqueous electrolyte]
The nonaqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

  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, ethyl methyl carbonate, and dipropyl carbonate; Ether compounds such as methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; phosphorus compounds such as triethyl phosphate and trioctyl phosphate alone or in combination of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof can be used.

  In addition, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like for improving battery characteristics.

  Next, an example of the arrangement and configuration of the members of the secondary battery of this embodiment will be described.

  The secondary battery of this embodiment composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above can be formed into various shapes such as a cylindrical shape and a laminated shape. In any case, the positive electrode and the negative electrode can be laminated via a separator to form an electrode body, and the obtained electrode body can be impregnated with a nonaqueous electrolytic solution. Then, connect between the positive electrode 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 collecting lead or the like, and seal the battery case. It can be set as a secondary battery.

  The secondary battery of this embodiment using the above-described positive electrode active material can be a secondary battery excellent in cycle characteristics. Moreover, the secondary battery of this embodiment has a high capacity and excellent output characteristics while having a high operating potential.

Specifically, the positive electrode active material of this embodiment is used as a positive electrode to form a 2032 type coin battery, the current density is 0.074 mA / cm ² , the battery is charged to a cut-off voltage of 5.0 V, and 1 hour The initial discharge capacity, which is the discharge capacity when discharged to a cutoff voltage of 3.0 V after the pause, is preferably 125 mAh / g or more, and more preferably 130 mAh / g or more.

  Further, in the secondary battery of this embodiment using the above-described positive electrode active material, the internal resistance of the battery is preferably 35Ω or less, and more preferably 32Ω or less.

The internal resistance of the battery can be evaluated by measuring DC-IR resistance (DC resistance). Specifically, the coin-type battery was charged to 60% of the initial discharge capacity, sandwiched for 1 minute, discharged for 10 seconds at a current density of 0.25 mA / cm ² , and then sandwiched again for 1 minute, Charge for 10 seconds at a current density of 0.25 mA / cm ² . This operation, a current density of 0.74mA ^/ cm 2, repeated under the conditions of 2.2 mA / cm ² and 3.7 mA / cm ^2, the voltage at the discharge start in the current density, voltage up discharge end Measure the difference. Next, the current density is plotted on the vertical axis, and the voltage difference measured at each current density is plotted on the horizontal axis, and the obtained linear relationship is obtained by a first-order linear approximation, and this slope is obtained as a DC-IR resistance (direct current). Resistance) and the internal resistance of the battery. The constituent members of the battery are common to all the evaluation batteries used in this paper except for the positive electrode, so the reason for the difference in internal resistance is determined by the properties of the positive electrode active material. Therefore, the internal resistance can also be called a positive electrode resistance.

  In addition, the secondary battery of the present embodiment using the above-described positive electrode active material preferably has a capacity maintenance ratio of 65% or more, and more preferably 70% or more.

The capacity maintenance rate can be evaluated by, for example, the following procedure. For example, a coin-type battery is configured in which a negative electrode is a sheet formed by applying a negative electrode mixture paste in which graphite powder and polyvinylidene fluoride are mixed to a copper foil. Then, the coin-type battery was charged to a cut-off voltage of 4.9 V at a current density of 0.25 mA / cm ² in a thermostat kept at 25 ° C., and after a one-hour pause, the cut-off voltage of 3. Conditioning is performed by repeating the cycle of discharging to 5 V for 5 cycles.

Next, a cycle in which the current density is set to 1.5 mA / cm ² in a constant temperature bath maintained at 60 ° C., the battery is charged to a cut-off voltage of 4.9 V, and is discharged to a cut-off voltage of 3.5 V after a pause of 1 hour. Is repeated 200 cycles.

  And the ratio which divided the discharge capacity obtained by the 200th cycle after conditioning by the discharge capacity obtained by the 1st cycle after conditioning can be made into a capacity maintenance rate.

  The application of the secondary battery of this embodiment is not particularly limited, and can be suitably used for applications requiring various power sources. In particular, the secondary battery of the present embodiment has the above-mentioned characteristics, so that it is always required to have high cycle characteristics and a small portable electronic device (a notebook personal computer, a mobile phone terminal, a small information terminal such as a smartphone or a tablet PC) that requires a high capacity. Etc.).

  Further, since the secondary battery of this embodiment is excellent in cycle characteristics and can be reduced in size and increased in output, it is suitable as a power source for an electric vehicle that is repeatedly charged and discharged and is restricted by a mounting space. The secondary battery of the present embodiment is suitable not only as a power source for electric vehicles driven purely by electric energy but also as a power source for so-called hybrid vehicles used in combination with combustion engines such as gasoline engines and diesel engines. Can be used.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
[Example 1]
1. Manufacture of Spinel Oxide Particles The positive electrode active material was manufactured by carrying out the following steps.
(A) Precursor crystallization step First, the temperature in the tank was set to 40 ° C. while stirring the water in a reaction tank (5 L) up to a half amount. The inside of the reaction vessel at this time was a nitrogen atmosphere having an oxygen concentration of 1% by volume or less.

  Appropriate amounts of 25% by mass aqueous sodium hydroxide and 25% by mass ammonia water are added to the water in this reaction tank so that the pH value becomes 11.5 based on the liquid temperature of 25 ° C., and the ammonia concentration becomes 5 g / L. An initial aqueous solution was prepared (initial aqueous solution preparation step).

  At the same time, manganese sulfate and nickel sulfate are dissolved in pure water so that the molar ratio of manganese to nickel is Mn: Ni = 1.50: 0.50, and a 2.0 mol / L mixed aqueous solution is obtained. Prepared (mixed aqueous solution preparation step).

  This mixed aqueous solution was dropped at a constant rate with respect to the initial aqueous solution in the reaction tank to obtain a reaction aqueous solution. At this time, 25% by mass ammonia water and 25% by mass sodium hydroxide aqueous solution were also dropped into the initial aqueous solution at a constant rate, the pH value of the reaction aqueous solution was 11.5 on the basis of the liquid temperature of 25 ° C., and the ammonia concentration was 5 g / L. Controlled to be maintained. By this operation, manganese nickel composite hydroxide particles (hereinafter referred to as “composite hydroxide particles”), which is a precursor of the spinel oxide, were crystallized (crystallization step).

Thereafter, the slurry containing the composite hydroxide particles recovered from the overflow port provided in the reaction vessel is filtered, water-soluble impurities are washed away with ion-exchanged water, and then dried to obtain powdered composite water. Oxide particles were obtained.
(B) Oxidation roasting step Using an atmosphere firing furnace (manufactured by Siliconit Co., Ltd., BM-50100M), the produced composite hydroxide particles are fired at 900 ° C. for 12 hours in an air atmosphere having an oxygen concentration of 20% by volume. After cooling to room temperature, manganese nickel composite oxide particles were obtained. Since the manganese nickel composite oxide particles were slightly sintered, they were crushed using a hammer mill (MF10, manufactured by IKA Japan Co., Ltd.).
(C) Spinel type oxide synthesis step Weigh the manganese nickel composite oxide particles so that the lithium content is 50 atomic% with respect to the total number of manganese and nickel atoms contained in the composite oxide particles. The lithium hydroxide monohydrate was added and mixed using a tumbler shaker mixer (manufactured by Dalton, T2F) to obtain a lithium mixture (lithium mixture preparation step).

The obtained lithium mixture was baked at 700 ° C. for 20 hours in an oxygen-containing atmosphere having an oxygen concentration of 90% by volume or more using an atmosphere baking furnace (manufactured by Siliconit Co., Ltd., BM-50100M), and then cooled to room temperature. (Firing step). As a result, lithium manganese nickel composite oxide particles, which are spinel oxide particles, were obtained.
2. Evaluation of Spinel Oxide Particles The following evaluations were performed on the obtained spinel oxide particles.
(A) Composition According to the analysis using an ICP emission spectroscopic analyzer (Varian, 725ES), the spinel oxide has a molar ratio of Li, Mn, and Ni: Li: Mn: Ni = 1.00: 1. It was confirmed that it was represented by 50: 0.50.
(B) Crystal structure When the crystal structure of the spinel-type oxide particles was measured using XRD (manufactured by PANALYTICAL, X'Pert, PROMRD), a peak attributed to the Fd-3m structure was detected in the diffraction pattern. The spinel crystal structure was confirmed.
(C) Specific surface area The BET specific surface area of the spinel-type oxide particles was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountech Co., Ltd., Macsorb). The result confirmed that it was 1.12 m < ² > / g.
(D) Volume average particle diameter The volume average particle diameter of the spinel oxide particles was measured using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Nikkiso Co., Ltd., Microtrac HRA). The result confirmed that it was 6.9 micrometers.
3. Manufacture of positive electrode active material The positive electrode active material was manufactured by implementing the following coating process on the particles of the spinel oxide.

The total surface area of the total weight of the lithium manganese nickel composite oxide particles, which are spinel oxide particles to be coated, was calculated from the specific surface area of the lithium manganese nickel composite oxide particles. Then, a sponge-like titanium metal weighed so that the weight of titanium per 1 m ² is 0.7 mg with respect to the total surface area is put in 83 mL of 30 mass% hydrogen peroxide water per 1 g of sponge-like titanium, While stirring, 23 mL of 2 mass 5% ammonia water was added dropwise per 1 g of sponge-like titanium to dissolve the sponge-like titanium. During dissolution, the reaction vessel was cooled with a water bath so that the temperature in the reaction vessel ranged from 20 ° C. to 25 ° C. (coating preparation step).

  Spiral titanium solution diluted with ion-exchanged water so that the titanium content per liter is 5.5 g, and 3.6 g of lithium manganese nickel composite oxide particles per 1 mL of the sponge titanium solution are rotated and revolved. It mixed with the apparatus (The Kurashiki Boseki Co., Ltd. make and model: KK-400W) (mixture preparation step).

Lithium manganese nickel composite oxide particles mixed with a sponge-like titanium solution are dried at 120 ° C. (drying step), and then using an atmosphere firing furnace (manufactured by Siliconit Co., Ltd., model: BM-50100M) under an air atmosphere, Firing was performed at 300 ° C. for 5 hours (heat treatment step). Then, it cooled to room temperature and obtained the particle | grains of the spinel type oxide which has a coating layer which is a positive electrode active material.
4). Evaluation of Positive Electrode Active Material The positive electrode active material thus obtained was evaluated as follows.
(A) Composition According to the analysis using an ICP emission spectroscopic analyzer (Varian, 725ES), this positive electrode active material contains 0.08% by mass of Ti, and is compared with the specific surface area before the coating treatment. It was found that the titanium carrying amount of the coating layer was 0.7 mg / m ² .
(B) Surface analysis The obtained positive electrode active material was measured using XPS (manufactured by ULVAC-PHI, Versa Probe II), and the obtained Mn ² P _3/2 spectrum, Ni ² P _3/2 spectrum, Ti ² It was found from the semi-quantitative value calculated from the peak area of the P _3/2 spectrum that the coated metal surface amount, Ti / (Mn + Ni) (substance amount ratio) was 0.16.
Moreover, from the semi-quantitative value calculated from the peak area of the obtained Li1S spectrum and Ti ² P _3/2 spectrum, Li / Ti (substance ratio) which is the Li doping index of the coating layer is 2.3. I understood.
In Table 2, the unit of the coating metal surface amount and the Li doping index of the coating layer is described as [mol / mol] in order to clarify that it is a substance amount ratio. Become.
(C) Carbon content When the carbon content of the obtained positive electrode active material was measured by a high frequency combustion infrared absorption method using a carbon analyzer (Model: CS-600 manufactured by LECO), 0.01 mass %.
(D) Moisture content When the moisture content of the obtained positive electrode active material was measured using a Karl Fischer moisture meter (Kyoto Denshi Kogyo Co., Ltd., model: MKC210) at a vaporization temperature of 300 ° C, 0.12 mass was obtained. %.
(E) Measurement of the thickness of the coating layer A powder sample of the positive electrode active material was embedded in a resin, and processed into a thin piece of less than 100 nm using an ion milling device (model: IB-09060 CIS manufactured by JEOL Ltd.). Next, the distribution of titanium is measured from the cross-section side with an energy dispersive X-ray spectrometer attached to a transmission electron microscope (JEOL Ltd. model: JEM-ARM 200F), and the coating layer thickness is directly obtained from the observed image. It was. The thickness of the coating layer, which is a region where the titanium concentration is locally higher than the central portion, was 2 nm.
5. Production of Secondary Battery For evaluation of the obtained positive electrode active material, a 2032 type coin battery 10 (hereinafter referred to as “coin type battery”) shown in FIG. 1 was used.

  The coin battery 10 includes a case 11 and an electrode 12 accommodated in the case 11.

  The case 11 has a positive electrode can 111 that is hollow and open at one end, and a negative electrode can 112 that is disposed in the opening of the positive electrode can 111, and the negative electrode can 112 is disposed in the opening of the positive electrode can 111. A space for accommodating the electrode 12 is formed between the negative electrode can 112 and the positive electrode can 111.

  The electrode 12 includes a positive electrode 121, a separator 122, and a negative electrode 123, which are stacked in this order. The positive electrode 121 contacts the inner surface of the positive electrode can 111, and the negative electrode 123 contacts the inner surface of the negative electrode can 112. It is accommodated in the case 11 so as to come into contact. The case 11 is provided with a gasket 113, and the gasket 113 fixes relative movement so as to maintain a non-contact state between the positive electrode can 111 and the negative electrode can 112.

  Further, the gasket 113 has a function of sealing the gap between the positive electrode can 111 and the negative electrode can 112 to block the inside and outside of the case 11 in an airtight and liquidtight manner.

  Such a coin-type battery 10 was produced as follows.

First, a slurry in which 20.0 g of the obtained positive electrode active material, 2.35 g of acetylene black and 1.18 g of polyvinylidene fluoride were dispersed in N-methyl-2-pyrrolidone (NMP) was placed on an aluminum foil at 1 cm ^2. After coating so that 5.0 mg of the positive electrode active material was present, it was dried in the air at 120 ° C. for 30 minutes to remove NMP. An aluminum foil coated with a slurry containing a positive electrode active material was cut into a strip shape having a width of 66 mm, and roll-pressed with a load of 1.2 t to produce a positive electrode. The positive electrode was punched into a circle having a diameter of 13 mm and dried in a vacuum dryer at 120 ° C. for 12 hours to produce a positive electrode 121 for the coin-type battery 10.

  Next, using the produced positive electrode 121, the coin-type battery 10 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C. At this time, the negative electrode 123 is a negative electrode in which a copper foil is coated with a lithium foil punched into a disk shape having a diameter of 14 mm or a negative electrode mixture paste that is a mixture of graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride. A sheet was used. In addition, the secondary battery using lithium foil for the negative electrode was used for evaluation of initial discharge capacity and internal resistance described later. Moreover, the secondary battery using the negative electrode sheet | seat which apply | coated the mixture of graphite powder and a polyvinylidene fluoride to the copper foil to the negative electrode was used for evaluation of the cycling characteristics mentioned later.

The separator 122 is a polyethylene porous film having a thickness of 25 μm, and the electrolyte is a 3: 7 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiPF ₆ as a supporting electrolyte (Toyama Chemical) Kogyo Co., Ltd.) was used.
6). Evaluation of Secondary Battery The initial discharge capacity, internal resistance, and cycle characteristics indicating the performance of the manufactured coin-type secondary battery were evaluated as follows.
(A) Initial discharge capacity The initial discharge capacity is the current density with respect to the positive electrode after the open circuit voltage OCV (Open Circuit Voltage) is stabilized after the coin-type battery using lithium foil as the negative electrode is manufactured and left for about 24 hours. Was evaluated by measuring the discharge capacity (initial discharge capacity) when discharged to a cut-off voltage of 3.0 V after a rest of 1 hour with 0.074 mA / cm ² . The measurement result was 140 mAh / g.
(B) Internal resistance Internal resistance was evaluated by measuring DC-IR resistance.

Specifically, the coin-type battery was charged to 60% of the initial discharge capacity, sandwiched for 1 minute, discharged for 10 seconds at a current density of 0.25 mA / cm ² , and then sandwiched again for 1 minute, The battery was charged for 10 seconds at a current density of 0.25 mA / cm ² . This operation, a current density of 0.74mA ^/ cm 2, repeated under the conditions of 2.2 mA / cm ² and 3.7 mA / cm ^2, the voltage at the discharge start in the current density, voltage up discharge end The difference was measured.

  Next, the current density is plotted on the vertical axis, and the voltage difference measured at each current density is plotted on the horizontal axis, and the obtained linear relationship is obtained by a first-order linear approximation, and this slope is determined by internal resistance (DC-IR Resistance).

The measurement result was 27.2Ω.
(C) Cycle characteristics The cycle characteristics were evaluated by measuring the capacity retention rate when 200 cycles of charge / discharge were performed.

Specifically, a coin-type battery using a negative electrode prepared using a sheet in which a mixture of graphite powder and polyvinylidene fluoride is applied to a copper foil is first subjected to a current density in a thermostatic chamber maintained at 25 ° C. Conditioning was performed by repeating the cycle of charging to 4.9 mA / cm ² to a cut-off voltage of 4.9 V, discharging to a cut-off voltage of 3.5 V after a pause of 1 hour, and 5 cycles. Next, a cycle in which a current density of 1.5 mA / cm ² is charged to a cut-off voltage of 4.9 V in a thermostatic chamber maintained at 60 ° C., and after a one-hour pause, the cycle is discharged to a cut-off voltage of 3.5 V. Was evaluated by measuring the discharge capacity of each cycle.

The capacity retention rate, which is the ratio of the discharge capacity obtained in the first cycle after conditioning of the coin-type battery of Example 1 divided by the discharge capacity obtained in the 200th cycle after conditioning, was 70%. It was.
[Example 2]
When carrying out the coating process of “3. Production of positive electrode active material”, it was carried out except that the coating agent was prepared in the coating agent preparation step with the target titanium loading of the coating layer being 1.3 mg / m ^2. Spinel oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 1. The evaluation results are shown in Tables 1 to 3.
[Example 3]
When carrying out the coating step of “3. Production of positive electrode active material”, the spinel-type oxide particles, the positive electrode active material, the positive electrode active material, under the same conditions as in Example 2 except that the heat treatment temperature in the heat treatment step was 600 ° C. And the secondary battery using this positive electrode active material was obtained. The evaluation results are shown in Tables 1 to 3.
[Example 4]
The spinel-type oxide particles, the positive electrode active material, and the positive electrode active material were used under the same conditions as in Example 2 except that the heat treatment step in the coating process of “3. Production of positive electrode active material” was not performed. A secondary battery was obtained.

That is, lithium manganese nickel composite oxide particles mixed with a sponge-like titanium solution were dried at 120 ° C. (drying step) to obtain spinel oxide particles having a coating layer as a positive electrode active material. The evaluation results are shown in Tables 1 to 3.
[Example 5]
When carrying out the coating process of “3. Production of positive electrode active material”, it was carried out except that the coating agent was prepared in the coating agent preparation step with the target titanium loading of the coating layer being 2.2 mg / m ^2. Spinel oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 1. The evaluation results are shown in Tables 1 to 3.
Since the amount of supported titanium was large and almost no Li1S spectrum was detected, in Table 2, Li / Ti (substance ratio), which is the Li doping index of the coating layer, is expressed as “−”.
[Example 6]
When carrying out the coating process of “3. Production of positive electrode active material”, it was carried out except that the coating agent was prepared in the coating agent preparation step with the target titanium loading amount of 3.3 mg / m ^2. Spinel oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 1. The evaluation results are shown in Tables 1 to 3.
Since the amount of supported titanium was large and almost no Li1S spectrum was detected, in Table 2, Li / Ti (substance ratio), which is the Li doping index of the coating layer, is expressed as “−”.
[Example 7]
When carrying out the coating process of “3. Production of positive electrode active material”, it was carried out except that the coating agent was prepared in the coating agent preparation step with the target titanium loading of the coating layer being 0.4 mg / m ^2. Spinel oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 1. The evaluation results are shown in Tables 1 to 3.
[Example 8]
In the mixed aqueous solution preparation step of (a) precursor crystallization step of “1. Production of spinel-type oxide particles”, cobalt sulfate was further added to the mixed aqueous solution in addition to manganese sulfate and nickel sulfate. At this time, a mixed aqueous solution of 2.0 mol / L was dissolved in pure water so that the molar ratio of manganese, nickel and cobalt was Mn: Ni: Co = 1.50: 0.45: 0.05. Was prepared. Except for the above points, spinel-type oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 2. The evaluation results are shown in Tables 1 to 3.
[Example 9]
In the mixed aqueous solution preparation step of (a) precursor crystallization process in “1. Production of spinel-type oxide particles”, iron sulfate was further added to the mixed aqueous solution in addition to manganese sulfate and nickel sulfate. At this time, a mixed aqueous solution of 2.0 mol / L was dissolved in pure water so that the molar ratio of manganese, nickel and iron was Mn: Ni: Fe = 1.50: 0.45: 0.05. Was prepared. Except for the above points, spinel-type oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 2. The evaluation results are shown in Tables 1 to 3.
[Example 10]
In the mixed aqueous solution preparation step of (a) precursor crystallization process in “1. Production of spinel-type oxide particles”, titanium sulfate was further added to the mixed aqueous solution in addition to manganese sulfate and nickel sulfate. At this time, a mixed aqueous solution of 2.0 mol / L was dissolved in pure water so that the molar ratio of manganese, nickel, and titanium was Mn: Ni: Ti = 1.45: 0.50: 0.05. Was prepared. Except for the above points, spinel-type oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 2. The evaluation results are shown in Tables 1 to 3.
[Example 11]
The point in which the coating agent was prepared by setting the target titanium loading of the coating layer to 4.4 mg / m ² in the coating agent preparation step when performing the coating process of “3. Production of positive electrode active material”. In addition, lithium hydroxide was added and dissolved in the coating agent so that Li / Ti (substance ratio), which is the Li doping index of the coating layer, was 0.8. Except for the above points, spinel-type oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 1. The evaluation results are shown in Tables 1 to 3.
[Example 12]
The point in which the coating agent was prepared by setting the target titanium loading of the coating layer to 8.5 mg / m ² in the coating agent preparation step when performing the coating process of “3. Production of positive electrode active material”. A point in which lithium hydroxide was added and dissolved in the coating agent so that Li / Ti (substance ratio) was 0.8. Except for the above points, spinel-type oxide particles, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 1. The evaluation results are shown in Tables 1 to 3.
[Comparative Example 1]
A spinel-type oxide particle, a positive electrode active material, and a secondary battery using the positive electrode active material were obtained under the same conditions as in Example 1 except that the coating step in Example 1 was not performed. The evaluation results are shown in Tables 1 to 3.

Since the coating step was not performed, the spinel oxide particles obtained in “1. Production of spinel oxide particles” serve as the positive electrode active material.
[Comparative Example 2]
When carrying out the coating step of “3. Production of positive electrode active material”, the spinel oxide particles, the positive electrode active material, the positive electrode active material, under the same conditions as in Example 1 except that the heat treatment temperature in the heat treatment step was 600 ° C. And the secondary battery using this positive electrode active material was obtained. The evaluation results are shown in Tables 1 to 3.

表１に示した結果によると、実施例１〜実施例１２、比較例１、比較例２において、目標組成のスピネル型酸化物の粒子が得られていることを確認できた。また、実施例１〜実施例１２、比較例１、比較例２において、Ｆｄ−３ｍ構造のスピネル型結晶構造に帰属されるピークが検出されることも確認できた。

According to the results shown in Table 1, it was confirmed that in Examples 1 to 12, Comparative Example 1, and Comparative Example 2, spinel-type oxide particles having a target composition were obtained. In addition, in Examples 1 to 12, Comparative Example 1, and Comparative Example 2, it was also confirmed that a peak attributed to the spinel crystal structure having the Fd-3m structure was detected.

Then, according to the results shown in Table 2, in Examples 1 to 12, confirmed that the titanium loading amount of the coating layer meets the 0.4 mg / ^{m 2} or more 9.0 mg / ^{m 2} or less It was. On the other hand, Comparative Example 1 was 0 because it did not have a coating layer.

  Further, in Examples 1 to 12, it was confirmed that the coated metal surface amount (Ti / (Mn + Ni)) was 0.14 or more and 9.5 or less.

  On the other hand, in Comparative Example 2, it was confirmed that the coated metal surface amount was 0.10. This is because when the coating layer was formed, the amount of titanium supported by the target coating layer was small, and heat treatment was performed at 600 ° C. in the heat treatment step of the film formation process, so that titanium diffused and turned into a spinel oxide. This is thought to be due to the progress of solid solution. For this reason, the coating layer thickness was also less than 1 nm.

  And from Table 3 which showed the evaluation result of the secondary battery, about Example 1- Example 12, it has confirmed that the capacity | capacitance maintenance factor which shows a cycle characteristic was high compared with Comparative Examples 1 and 2. This is considered to be because, in Examples 1 to 12, elution of manganese, nickel, and the like from the spinel oxide could be suppressed by arranging a coating layer that sufficiently contained titanium.

Claims (8)

A positive electrode active material for a non-aqueous electrolyte secondary battery having spinel oxide particles that are oxides having a spinel structure and a coating layer that covers at least part of the spinel oxide particles,
The spinel oxide is composed of lithium (Li), manganese (Mn), nickel (Ni), and element M (M), in a mass ratio of Li: Mn: Ni: M = t: 2- x-y: x: y (provided that 0.96 ≦ t ≦ 1.25, 0.40 ≦ x ≦ 0.60, 0 ≦ y ≦ 0.20), and X-ray diffraction (XRD) From the diffraction pattern obtained by the measurement, a peak attributed to the spinel crystal structure of the “Fd-3m” structure is detected,
The element M is selected from magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn). At least one element selected,
The coating layer contains a titanium compound, and contains titanium at a ratio of 0.4 mg to 9.0 mg per 1 m ² of the surface area of the spinel oxide particles,
When semi-quantitative analysis was performed by X-ray photoelectron spectroscopy, the amount of titanium (Ti) was divided by the total amount of manganese (Mn) and nickel (Ni) (Ti / (Mn + Ni)). Is a positive electrode active material for a non-aqueous electrolyte secondary battery having a value of 0.14 to 9.5.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the coating layer contains titanium (Ti) and lithium (Li).   When the semi-quantitative analysis by X-ray photoelectron spectroscopy is performed, the coating layer is obtained by dividing the amount of lithium (Li) by the amount of titanium (Ti) (Li / Ti) is 0.5 or more and 1 The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, which is .2 or less.   The carbon content is 0.01 mass% or more and 0.5 mass% or less, and the water content is 0.01 mass% or more and 0.2 mass% or less. The positive electrode active material for non-aqueous electrolyte secondary batteries as described.   The content rate of titanium is 0.01 mass% or more and 1.00 mass% or less, The positive electrode active material for nonaqueous electrolyte secondary batteries of any one of Claims 1-4. For a non-aqueous electrolyte secondary battery according to any one of the spinel-type specific surface area of the oxide particles 0.30 m ² / g or more 1.50 m ² / g or less claims 1 to 5 Positive electrode active material.   The thickness of the said coating layer is 1 nm or more and 10 nm or less, The positive electrode active material for nonaqueous electrolyte secondary batteries of any one of Claims 1-6.   A non-aqueous electrolyte solution comprising a positive electrode using the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, a negative electrode, a separator, and a non-aqueous electrolyte solution. Secondary battery.

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