Positive electrode active material for lithium ion secondary battery, method for producing positive electrode active material for lithium ion secondary battery, lithium ion secondary battery

Abstract

To provide a positive electrode active material for a lithium ion secondary battery, which has a high battery capacity and can suppress the generation of gas when used in a lithium ion secondary battery.SOLUTION: A positive electrode active material for a lithium ion secondary battery includes Li composite oxide particles including Li, Ni, Mn, Zr, and an additive element M (M) in the ratio of the amount of substance, Li:Ni:Mn:Zr:M=a:b:c:d:e (0.95≤a≤1.20, 0.70≤b≤0.98, 0.01≤c≤0.20, 0.0003≤d≤0.02, 0.01≤e≤0.20, and an additive element M is one or more elements selected from Co, W, Mo, V, Mg, Ca, Al, Ti, and Ta), and the half-value width of the peak on the (003) plane calculated from an X-ray diffraction pattern of the Li composite oxide particles is 0.065° or more and 0.10°or less, and the half-value width of the peak on the (104) plane is 0.10°or more and 0.15°or less, and the moisture content is 0.01 mass% or more and 0.06 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, there is a strong demand for the development of small, lightweight secondary batteries with high energy density and durability. There is also a strong demand for high-output secondary batteries for use in power tools and electric vehicles, including hybrid cars. In addition to the above-mentioned required characteristics, there is also a growing demand for secondary batteries that are highly durable and do not deteriorate even when used repeatedly.

[0003] A lithium-ion secondary battery is a secondary battery that satisfies such requirements. A lithium-ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, etc., and a material capable of desorbing and inserting lithium is used as the active material of the negative electrode and the positive electrode. As described above, a lithium-ion secondary battery has high energy density, output characteristics, and durability.

[0004] Research and development into lithium-ion secondary batteries is currently underway in earnest. In particular, lithium-ion secondary batteries that use layered or spinel-type lithium metal composite oxides as the positive electrode material are capable of achieving a high voltage of around 4 V, and are therefore being put into practical use as batteries with high energy density.

[0005] Currently, the positive electrode materials for such lithium-ion secondary batteries include lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2), which uses nickel, which is cheaper than cobalt, and lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2), lithium manganese composite oxide (LiMn2O4), lithium nickel manganese composite oxide (LiNi 0.5 Mn 0.5 Lithium composite oxides such as CrO2 have been proposed.

[0006] However, in lithium-ion secondary batteries, gas may be generated during use due to decomposition of the electrolyte. Therefore, battery modules that can exhaust gas generated inside the battery to the outside have been studied. For example, Patent Document 1 proposes a battery module having a battery that contains battery elements such as electrodes, active material, and electrolyte inside and is sealed with a laminate film, and a case that houses the battery, wherein the case has a structure that supports the front or part of the battery, and the case has a protrusion that has a through hole that leads from its tip to the outside of the case. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2003-168410 A Summary of the Invention [Problem to be solved by the invention]

[0008] Thus, a method of providing an additional member in a battery module and discharging the gas generated inside the battery to the outside of the system has been studied. However, from the viewpoint of reducing costs and improving the stability of the battery, there has been a demand for a positive electrode active material for a lithium ion secondary battery that can suppress the generation of the gas when used in the lithium ion secondary battery.

[0009] In addition, from the viewpoint of improving the performance of lithium ion secondary batteries, there has been a demand for a positive electrode active material for lithium ion secondary batteries that can improve the battery capacity when used in the lithium ion secondary battery. Accordingly, there has been a demand for a positive electrode active material for lithium ion secondary batteries that can suppress gas generation and increase the battery capacity when used in the lithium ion secondary battery.

[0010] In view of the problems associated with the above-described conventional techniques, an object of one aspect of the present invention is to provide a positive electrode active material for a lithium ion secondary battery, which has a high battery capacity and can suppress gas generation when used in a lithium ion secondary battery. [Means for solving the problem]

[0011] In order to solve the above problem, according to one aspect of the present invention, A positive electrode active material for a lithium ion secondary battery containing lithium composite oxide particles, Further containing a lithium-zirconium composite oxide, The lithium composite oxide particles are particles of a lithium composite oxide containing lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and an additive element M (M) in a substance amount ratio of Li:Ni:Mn:Zr:M=a:b:c:d:e (wherein 0.95≦a≦1.20, 0.70≦b≦0.98, 0.01≦c≦0.20, 0.0003≦d≦0.02, 0.01≦e≦0.20, and the additive element M is one or more elements selected from Co, W, Mo, V, Mg, Ca, Al, Ti, and Ta), The half width of the peak of the (003) plane calculated from the X-ray diffraction pattern of the lithium composite oxide particles is 0.065° or more and 0.10° or less, and the half width of the peak of the (104) plane is 0.10° or more and 0.15° or less, The present invention provides a positive electrode active material for lithium ion secondary batteries, the moisture content of which is 0.01% by mass or more and 0.06% by mass or less. Effect of the Invention

[0012] According to one embodiment of the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery, which has a high battery capacity and can suppress gas generation when used in a lithium ion secondary battery. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is an explanatory diagram of a cross-sectional configuration of a coin battery produced in an experimental example. [Diagram 2] FIG. 2 is an explanatory diagram of the configuration of a laminated battery produced in an experimental example. [Diagram 3] FIG. 1 is a schematic explanatory diagram of an example of impedance evaluation measurement and an equivalent circuit used in the analysis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the form for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment, and various modifications and substitutions can be made to the following embodiment without departing from the scope of the present invention. [Positive electrode active material for lithium-ion secondary batteries] The positive electrode active material for a lithium ion secondary battery of this embodiment (hereinafter also simply referred to as "positive electrode active material") contains lithium composite oxide particles.

[0015] The lithium composite oxide particles can be lithium composite oxide particles containing lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and an additive element M (M) in a substance amount ratio of Li:Ni:Mn:Zr:M=a:b:c:d:e.

[0016] It is preferable that a, b, c, d, and e satisfy 0.95≦a≦1.20, 0.70≦b≦0.98, 0.01≦c≦0.20, 0.0003≦d≦0.02, and 0.01≦e≦0.20. The additive element M may be one or more elements selected from Co, W, Mo, V, Mg, Ca, Al, Ti, and Ta.

[0017] The lithium composite oxide particles can have a half width of the peak of the (003) plane calculated from the X-ray diffraction pattern of 0.065° to 0.10°, and the lithium composite oxide particles can have a half width of the peak of the (104) plane calculated from the X-ray diffraction pattern of 0.10° to 0.15°.

[0018] Furthermore, the positive electrode active material of this embodiment can have a moisture content of 0.01% by mass or more and 0.06% by mass or less.

[0019] The inventors of the present invention have conducted extensive research into a positive electrode active material that can increase battery capacity and suppress gas generation when used in a lithium ion secondary battery. As a result, they have found that by containing particles of a lithium composite oxide to which zirconium (Zr) has been added, and by setting the half widths of the (003) and (104) faces of the lithium composite oxide within predetermined ranges and the moisture content within predetermined ranges, the battery capacity can be increased and gas generation can be suppressed when used in a lithium ion secondary battery, and have completed the present invention.

[0020] The positive electrode active material of this embodiment can contain particles of a lithium composite oxide containing lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and an additive element M (M) in a ratio of substance amount Li:Ni:Mn:Zr:M=a:b:c:d:e as described above. The positive electrode active material of this embodiment can also be composed of particles of the lithium composite oxide.

[0021] The range of a, which indicates the lithium content of the lithium composite oxide, is preferably 0.95≦a≦1.20, and more preferably 1.00≦a≦1.10.

[0022] The range of b, which indicates the nickel content of the lithium composite oxide, is preferably 0.70≦b≦0.98, and more preferably 0.75≦b≦0.95. When the value of b is within the above range, that is, when the nickel content is high, a high battery capacity can be obtained when a positive electrode active material containing particles of the lithium composite oxide is used in a lithium ion secondary battery. In addition, the cobalt content can be reduced, so that the cost can be reduced.

[0023] The range of c, which indicates the manganese content of the lithium composite oxide, is preferably 0.01≦c≦0.20, and more preferably 0.02≦c≦0.15. When the value of c is within the above range, when a positive electrode active material containing particles of the lithium composite oxide is used in a lithium ion secondary battery, excellent durability and high battery capacity can be obtained, and further high stability can be obtained.

[0024] The range of d, which indicates the content of zirconium in the lithium composite oxide, is preferably 0.0003≦d≦0.02, and more preferably 0.0005≦d≦0.0008. When the value of d is within the above range, when a positive electrode active material containing particles of the lithium composite oxide is used in a lithium ion secondary battery, gas generation can be suppressed. This is considered to be because the structure of the lithium composite oxide is stabilized and excess lithium (eluted lithium) can be suppressed, thereby suppressing gas generation due to the reaction between the electrolyte and the excess lithium. In addition, it is considered that a stable Zr-O structure can be formed in the crystal of the lithium composite oxide, and when a positive electrode active material containing particles of the lithium composite oxide is used in a lithium ion secondary battery, cycle characteristics can be improved.

[0025] The range of e, which indicates the content of the additive element M in the lithium composite oxide, is preferably 0.01≦e≦0.20, and more preferably 0.03≦e≦0.18. By containing the element M, when a positive electrode active material containing particles of the lithium composite oxide is used in a lithium ion secondary battery, the cycle characteristics and output characteristics can be further improved.

[0026] The types of elements that can be suitably used as the additive element M have already been described, and therefore will not be described here.

[0027] In the lithium composite oxide, the sum of b, c, d, and e, which indicate the contents of nickel, manganese, zirconium, and the additive element M, is preferably 1. In other words, it is preferable that b+c+d+e=1 is satisfied.

[0028] As described above, the lithium composite oxide may contain lithium, nickel, manganese, zirconium, and an additive element M in a predetermined ratio. The specific composition is not particularly limited. For example, the lithium composite oxide may be represented by the general formula Li a Ni b Mn c Zr d M e O 2+α In the general formula, a, b, c, d, and e each preferably satisfy the above-mentioned range. In addition, in 2+α indicating the oxygen content, α preferably satisfies, for example, -0.2≦α≦0.2.

[0029] The lithium composite oxide contained in the positive electrode active material of this embodiment preferably has a half-width of the peak of the (003) plane calculated from the X-ray diffraction pattern of 0.065° or more and 0.10° or less, and more preferably 0.066° or more and 0.095° or less.

[0030] When the half-width of the peak of the (003) plane is within the above range, it means that the lithium composite oxide has high crystallinity, and excess lithium (eluted lithium) can be suppressed, and gas generation due to the reaction between the electrolyte and the excess lithium can be suppressed. In addition, by increasing the crystallinity of the lithium composite oxide, the structure is stabilized even when lithium is inserted and removed, so that the cycle characteristics can be improved when a positive electrode active material containing the lithium composite oxide particles for a lithium ion secondary battery is used.

[0031] Furthermore, the half-width of the peak of the (104) plane calculated from the X-ray diffraction pattern of the lithium composite oxide particles contained in the positive electrode active material of this embodiment is preferably 0.10° or more and 0.15° or less, and more preferably 0.105° or more and 0.145° or less.

[0032] When the half-width of the peak of the (104) plane is within the above range, it means that the lithium composite oxide particles have high crystallinity. Therefore, the structure is stable even when lithium is inserted and extracted, so that the cycle characteristics can be improved when the lithium composite oxide particles are used as a positive electrode active material for a lithium ion secondary battery.

[0033] The lithium composite oxide particles contained in the positive electrode active material of this embodiment can have secondary particles formed by agglomeration of primary particles. The lithium composite oxide particles can also be composed of secondary particles formed by agglomeration of primary particles. The average particle diameter D50 of the secondary particles is preferably 10 μm or more and 20 μm or less, and more preferably 10.5 μm or more and 14.5 μm or less. By setting the average particle diameter D50 of the secondary particles of the lithium composite oxide particles in the above range, when the positive electrode active material of this embodiment is used in the positive electrode of a lithium ion secondary battery, the output characteristics and battery capacity can be particularly improved, and further, high filling properties in the positive electrode can be achieved at the same time. Specifically, by setting the average particle diameter D50 of the secondary particles to 10 μm or more, the filling properties in the positive electrode can be improved. In addition, by setting the average particle diameter of the secondary particles to 20 μm or less, the output characteristics and battery capacity can be particularly improved.

[0034] In this specification, the average particle size refers to the particle size at an integrated value of 50% in the particle size distribution determined by a laser diffraction / scattering method.

[0035] In addition, the lithium composite oxide contained in the positive electrode active material of this embodiment has a specific surface area of ​​0.2 m2 or less as measured by the BET method. 2 / g or more 0.8m 2 It is preferable that the molecular weight is not more than 1 / g.

[0036] By setting the specific surface area of ​​the positive electrode active material of this embodiment within the above range, output characteristics and stability can be particularly improved, which is preferable.

[0037] Specifically, the specific surface area is 0.8 m 2 By making the specific surface area 0.8 m or less, the packing density can be increased when preparing a positive electrode, and the energy density as a positive electrode active material can be increased. 2 / g or less, the amount of excess lithium present on the particle surface can be suppressed, and the reaction between the electrolyte and the excess lithium can be suppressed. This makes it possible to significantly reduce the generation of various gases such as carbon dioxide, hydrogen carbonate, and CO gas during charge / discharge reactions, and suppress cell expansion, etc. Furthermore, because the amount of excess lithium can be suppressed, the slurry containing the positive electrode active material is less likely to gel when the electrode plate is made, which is an advantage in that defects in the manufacture of the positive electrode are reduced, i.e., an advantage in the production process of improving the yield. In addition, the specific surface area is 0.2 m 2 / g or more, the contact area with the electrolyte can be increased and the positive electrode resistance can be suppressed, thereby particularly improving the output characteristics.

[0038] The positive electrode active material of this embodiment may further contain a lithium-zirconium composite oxide. The lithium-zirconia composite oxide is an oxide containing lithium and zirconia, such as Li2ZrO3.

[0039] According to the study by the inventors of the present invention, the positive electrode active material of this embodiment contains a lithium-zirconium composite oxide, and therefore the amount of excess lithium can be particularly suppressed, and when used in a lithium ion secondary battery, the reaction between the electrolyte and the excess lithium can be suppressed. Therefore, the generation of various gases such as carbon dioxide gas, hydrogen carbonate gas, and CO gas during charge and discharge reactions can be further significantly reduced, and cell expansion can be suppressed.

[0040] In addition, by suppressing the amount of excess lithium, the slurry containing the positive electrode active material is less likely to gel when the electrode plate is produced, which has the advantage of reducing defects when manufacturing the positive electrode, i.e., an advantage in terms of the production process of improving yield.

[0041] The content of the lithium-zirconium composite oxide in the positive electrode active material of this embodiment may be extremely small, and may not be fully detected by analysis using a general powder X-ray diffraction device. For this reason, it is preferable to perform the analysis using a diffraction pattern measured using a high-brightness synchrotron radiation or the like as a light source.

[0042] In the positive electrode active material of this embodiment, the amount of eluted lithium determined by the Warder method is preferably 0.05% by mass or more and 0.10% by mass or less, and more preferably 0.055% by mass or more and 0.09% by mass or less. The amount of eluted lithium is determined by the Wader method as described above. Specifically, for example, the amount of lithium is calculated by adding pure water to the positive electrode active material, stirring for a certain period of time, and then performing neutralization titration on the filtrate obtained by filtration. The compound state of the eluted lithium can be evaluated from the neutralization point that appears by adding hydrochloric acid while measuring the pH of the filtrate, and the amount of eluted lithium can be calculated.

[0043] The amount of eluted lithium indicates the ratio of the excess lithium attached to the surface of the lithium composite oxide particles of the positive electrode active material of this embodiment to the positive electrode active material. As described above, by making the amount 0.10 mass% or less, when the positive electrode active material of this embodiment is used in a lithium ion secondary battery, the reaction between the electrolyte and the excess lithium can be suppressed. Therefore, the generation of various gases such as carbon dioxide gas, hydrogen carbonate gas, and CO gas during the charge and discharge reaction can be further significantly reduced, and the expansion of the cell can be suppressed.

[0044] In addition, by keeping the amount of eluted lithium to 0.10 mass % or less, the slurry containing the positive electrode active material is less likely to gel when the electrode plate is produced, which has the advantage of reducing defects when manufacturing the positive electrode, i.e., an advantage in terms of the production process of improving yield.

[0045] However, in the positive electrode active material of this embodiment, if the amount of eluted lithium is excessively reduced, the content of lithium inside the particles may decrease, and the battery characteristics may deteriorate. Therefore, the amount of eluted lithium in the positive electrode active material of this embodiment is preferably 0.05 mass% or more.

[0046] The moisture content of the positive electrode active material of this embodiment is not particularly limited, but is preferably 0.01% by mass or more and 0.06% by mass or less, and more preferably 0.01% by mass or more and 0.05% by mass or less. When the moisture content of the positive electrode active material of this embodiment is 0.06% by mass or less, it is possible to particularly suppress the reaction of gas components containing carbon and sulfur in the atmosphere with excess lithium, etc., to form lithium compounds on the surface of particles. Therefore, when used in a lithium ion secondary battery, it is possible to reduce the generation of gas and suppress the expansion of the cell, etc.

[0047] In addition, by setting the moisture content within the above range, the slurry containing the positive electrode active material is less likely to gel when preparing the electrode plate, which has the advantage of reducing defects when manufacturing the positive electrode, i.e., the advantage in terms of the production process of improving the yield.

[0048] Furthermore, by setting the moisture content within the above range, the battery capacity of a lithium ion secondary battery using the positive electrode active material can be increased. The moisture contained in the positive electrode active material may react with a non-aqueous electrolyte to generate hydrofluoric acid, etc. The hydrofluoric acid, etc. generated by such a side reaction may further react with the positive electrode active material, causing a decrease in battery capacity. In contrast, by setting the moisture content of the positive electrode active material to 0.06 mass% or less, the occurrence of the above side reaction can be prevented and the irreversible capacity can be suppressed, thereby increasing the battery capacity of the lithium ion secondary battery.

[0049] However, in the positive electrode active material of this embodiment, it may be difficult to reduce the moisture content excessively, and therefore the moisture content of the positive electrode active material of this embodiment is preferably 0.01 mass % or more.

[0050] The moisture content was measured at a vaporization temperature of 300° C. using a Karl Fischer moisture meter.

[0051] According to the positive electrode active material of the present embodiment described above, as described above, the lithium composite oxide particles to which zirconium (Zr) is added are contained, and the half width of the (003) plane and the (104) plane of the lithium composite oxide particles are within a predetermined range, and the moisture content is within a predetermined range. Therefore, when the positive electrode active material of the present embodiment is used in a lithium ion secondary battery, the battery capacity can be increased and gas generation can be suppressed. [Method of manufacturing positive electrode active material for lithium ion secondary batteries] Next, a configuration example of the method for producing a positive electrode active material for a lithium ion secondary battery according to this embodiment (hereinafter, also simply referred to as a "method for producing a positive electrode active material") will be described.

[0052] According to the method for producing a positive electrode active material of this embodiment, the positive electrode active material already described can be produced, and therefore some of the matters already described will not be described again.

[0053] The method for producing a positive electrode active material for a lithium ion secondary battery according to the present embodiment can include the following steps. A mixing step of mixing a nickel-manganese composite compound containing nickel, manganese and an additive element M, a lithium compound and a zirconium compound to prepare a raw material mixture. A firing step of firing the raw material mixture at a temperature of 750°C or higher and 900°C or lower in an oxygen-containing atmosphere having an oxygen concentration of 50% by volume or higher and lower than 80% by volume. The raw material mixture prepared in the mixing step can contain lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and an additive element M (M) in a ratio of substance amount Li:Ni:Mn:Zr:M=a:b:c:d:e. Note that a, b, c, d, and e are preferably 0.95≦a≦1.20, 0.70≦b≦0.98, 0.01≦c≦0.20, 0.0003≦d≦0.02, and 0.01≦e≦0.20. The additive element M can be one or more elements selected from Co, W, Mo, V, Mg, Ca, Al, Ti, and Ta.

[0054] Each step will be described in detail below.

[0055] (A) Mixing process In the mixing step, the nickel-manganese composite compound, the lithium compound, and the zirconium compound are mixed together to obtain a raw material mixture.

[0056] The nickel-manganese composite compound is not particularly limited as long as it contains nickel, manganese, and an additive element M, but for example, one or more selected from nickel-manganese composite oxide and nickel-manganese composite hydroxide can be suitably used. The nickel-manganese composite hydroxide can be prepared by a crystallization reaction or the like. The nickel-manganese composite oxide can be obtained by oxidative roasting of the nickel-manganese composite hydroxide.

[0057] Since the nickel manganese composite compound serves as a supply source of nickel, manganese, and the additive element M, it is preferable that nickel (Ni), manganese (Mn), and the additive element M (M) are contained in a ratio of Ni:Mn:M=b:c:e in terms of substance amount in accordance with the target composition of the raw material mixture. The ranges of b, c, and e can be the same as those explained for the lithium composite oxide in the positive electrode active material, so that the explanation will be omitted here.

[0058] For example, when nickel manganese composite oxide is used as the nickel manganese composite compound, Ni b´ Mn c´ M e´ O 1+β In addition, when a nickel manganese composite hydroxide is used as the nickel manganese composite compound, the nickel manganese composite oxide represented by the formula: b´ Mn c´ M e´ (OH) 2+γ It is preferable to use a nickel manganese composite hydroxide represented by the following formula. In the above chemical formula, b', c', and e' satisfy the relationship b':c':e'=b:c:e with the already-mentioned b, c, and e, and it is preferable to satisfy b'+c'+e'=1. In addition, it is preferable that β and γ satisfy -0.2≦β≦0.2 and -0.2≦γ≦0.2, respectively.

[0059] The lithium compound is not particularly limited, and may be, for example, one or more compounds selected from lithium carbonate, lithium hydroxide, etc. Lithium hydroxide may contain water of hydration, and may be used as it is, but it is preferable to roast it in advance to reduce the amount of water of hydration.

[0060] As the zirconium compound, zirconium oxide (zirconia) or the like can be used. By adding zirconium as a zirconium compound, rather than adding it in advance to the nickel-manganese composite compound, it is possible to generate a lithium-zirconium composite oxide, although in a very small amount. Furthermore, by containing the lithium-zirconium composite oxide, it is possible to particularly suppress the amount of eluted lithium in the positive electrode active material obtained by the manufacturing method for the positive electrode active material of this embodiment.

[0061] It is preferable to adjust the particle size and the like of the nickel-manganese composite compound, the lithium compound, and the zirconium compound in advance so that a desired lithium composite oxide can be obtained after the firing step.

[0062] For example, the average particle size of the zirconium compound particles is preferably 0.5 μm or more and 5.0 μm or less, and more preferably 0.5 μm or more and 2.0 μm or less, because according to the studies of the inventors of the present invention, by adjusting the average particle size of the zirconium compound to be within the above range, the uniformity of the distribution of zirconium in the obtained positive electrode active material can be particularly improved.

[0063] A general mixer can be used to mix the nickel manganese composite compound, the lithium compound, and the zirconium compound, and for example, one or more types selected from a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, etc. The mixing conditions in the mixing step are not particularly limited, but it is preferable to select conditions such that the raw material components are sufficiently mixed to the extent that the shells of the raw material particles, etc., of the nickel manganese composite compound, etc. are not destroyed.

[0064] It is preferable that the raw material mixture is thoroughly mixed in a mixing step before being subjected to the firing step. If the mixing is insufficient, the Li / Me ratio varies between individual particles, and problems such as insufficient battery characteristics may occur. Note that Li / Me refers to the ratio of the number of atoms of lithium (Li) and metals other than lithium (Me) contained in the raw material mixture.

[0065] The nickel manganese composite compound, the lithium compound, and the zirconium compound are preferably weighed and mixed so that the raw material mixture after mixing contains lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and the additive element M (M) in a ratio of substance amounts of Li:Ni:Mn:Zr:M=a:b:c:d:e. The preferred ranges of a, b, c, d, and e in the formula can be the same as those explained for the lithium composite oxide in the positive electrode active material, so the explanation will be omitted here.

[0066] This is because the content ratio of each metal hardly changes before and after the firing step, and therefore it is preferable to mix the metals so that the content ratio of each metal in the raw material mixture is the same as the intended content ratio of each metal in the positive electrode active material obtained by the manufacturing method for a positive electrode active material of this embodiment. (B) Firing process In the firing step, the raw material mixture obtained in the mixing step is fired in an oxygen-containing atmosphere having an oxygen concentration of 50% by volume or more and less than 80% by volume at a temperature of 750° C. or more and 900° C. or less, to obtain a lithium composite oxide.

[0067] When the raw material mixture is fired in the firing step, lithium in the lithium compound and zirconium in the zirconium compound are diffused into the particles of the nickel-manganese composite hydroxide, forming a lithium composite oxide made up of particles with a polycrystalline structure.

[0068] In the firing step, as described above, the raw material mixture is preferably fired in an oxygen-containing atmosphere having an oxygen concentration of 50% by volume or more and less than 80% by volume, and more preferably fired in an oxygen-containing atmosphere having an oxygen concentration of 55% by volume or more and less than 80% by volume. The remaining components other than oxygen in the firing step are not particularly limited, but are preferably inert gases such as nitrogen and rare gases.

[0069] According to the investigations of the present inventors, the oxygen concentration in the calcination step affects the crystallinity of the obtained lithium composite oxide, etc. By setting the oxygen concentration in the calcination step within the above range, the crystallinity can be sufficiently improved, and the half-width of the peaks of the (003) plane and (104) plane calculated from the X-ray diffraction pattern of the obtained lithium composite oxide particles can be set within a desired range.

[0070] In the firing step, the raw material mixture is preferably fired at 750° C. or more and 900° C. or less, and more preferably fired at 780° C. or more and 870° C. or less, as described above.

[0071] By setting the firing temperature at 750° C. or higher, lithium and zirconium can be sufficiently diffused into the particles of the nickel-manganese composite compound, and therefore, for example, excess lithium and unreacted particles can be prevented from remaining, and a lithium composite oxide having a desired composition and a regular crystal structure can be obtained, and when a positive electrode active material containing such lithium composite oxide particles is used in a lithium ion secondary battery, desired battery characteristics can be obtained.

[0072] In addition, by setting the firing temperature to 900° C. or less, sintering between particles of the formed lithium composite oxide can be suppressed, and abnormal grain growth can also be prevented. If abnormal grain growth occurs, the particles after firing may become coarse and unable to maintain their particle shape, and when a positive electrode is formed, the specific surface area decreases and the resistance of the positive electrode increases, which may result in a decrease in battery capacity.

[0073] The firing time is preferably 3 hours or more, and more preferably 6 hours or more and 24 hours or less, because by setting the firing time to 3 hours or more, the production of the lithium composite oxide can be sufficiently promoted.

[0074] In the firing step, it is preferable to perform calcination at a temperature lower than the firing temperature, 105°C to less than 780°C, at which the lithium compound and the particles of the nickel-manganese composite compound can react, before firing at a temperature of 750°C to 900°C, which is the firing temperature. The calcination temperature is more preferably 400°C to 700°C. By maintaining the raw material mixture at such a temperature and calcining, lithium and zirconium are sufficiently diffused into the particles of the nickel-manganese composite compound, and a particularly uniform lithium composite oxide can be obtained. For example, when lithium hydroxide is used as the lithium compound, it is preferable to perform calcination by maintaining a temperature of 400°C to 550°C for about 1 hour to 10 hours.

[0075] The furnace used for firing in the firing step is not particularly limited, and may be any furnace capable of firing the raw material mixture in a gas atmosphere having a predetermined oxygen concentration or in a gas flow having a predetermined oxygen concentration. An electric furnace that does not generate gas is preferable, and either a batch type or a continuous type furnace may be used.

[0076] The lithium composite oxide particles obtained by calcination may have coarse particles formed due to weak sintering or aggregation, although sintering between particles is suppressed. In such a case, it is preferable to adjust the particle size distribution by eliminating the sintering or aggregation by crushing.

[0077] The lithium composite oxide particles obtained after the firing can be used as the positive electrode active material of this embodiment.

[0078] The method for producing a positive electrode active material according to the present embodiment is not limited to the steps described above, and may further include any optional steps.

[0079] For example, the method may include a crystallization step of preparing a nickel-manganese composite hydroxide, which is a type of nickel-manganese composite compound, by a crystallization method and an oxidizing roasting step of oxidizing and roasting the nickel-manganese composite hydroxide obtained in the crystallization step. (C) Crystallization process The crystallization process can include a crystallization step of crystallizing particles of nickel-manganese composite hydroxide containing nickel, manganese, and the additive element M.

[0080] The specific procedure of the crystallization step is not particularly limited, but for example, a mixed aqueous solution containing nickel (Ni), manganese (Mn), and an additive element M can be mixed with an alkaline aqueous solution to crystallize nickel-manganese composite hydroxide particles. Specifically, for example, it is preferable to carry out the crystallization step according to the following procedure.

[0081] First, water is poured into the reaction tank and controlled to a predetermined atmosphere and temperature. During the crystallization step, the atmosphere in the reaction tank is not particularly limited, but can be, for example, an inert atmosphere such as a nitrogen atmosphere. In addition to the inert gas, an oxygen-containing gas such as air can also be supplied to adjust the dissolved oxygen concentration of the solution in the reaction tank. In addition to water, an alkaline aqueous solution or a complexing agent, which will be described later, can also be added to the reaction tank to form an initial aqueous solution.

[0082] Then, in the reaction tank, a mixed aqueous solution containing at least nickel, manganese, and the additive element M and an alkaline aqueous solution are added to prepare a reaction aqueous solution. Next, the reaction aqueous solution is stirred at a constant speed to control the pH, thereby coprecipitating and crystallizing particles of nickel-manganese composite hydroxide in the reaction tank. It is also possible to supply a mixed aqueous solution containing some of the metals and an aqueous solution containing the remaining metals, instead of a mixed aqueous solution containing nickel, manganese, and the additive element M. Specifically, for example, a mixed aqueous solution containing nickel and manganese and an aqueous solution containing the additive element M may be supplied. Alternatively, aqueous solutions of each metal may be prepared separately, and the aqueous solutions containing each metal may be supplied to the reaction tank.

[0083] A mixed aqueous solution containing nickel, manganese, and the additive element M can be prepared by adding salts of each metal to water, which is a solvent. The type of salt is not particularly limited, and for example, one or more types of salts selected from sulfates, nitrates, and chlorides can be used as salts of nickel and manganese. The types of salts of each metal may be different, but it is preferable to use the same type of salt from the viewpoint of preventing the inclusion of impurities.

[0084] Furthermore, as the salt containing the additive element M, for example, one or more selected from cobalt sulfate, cobalt chloride, titanium sulfate, tungsten oxide, molybdenum oxide, molybdenum sulfide, vanadium pentoxide, calcium chloride, aluminum sulfate, sodium aluminate, magnesium sulfate, magnesium chloride, magnesium carbonate, etc. can be used.

[0085] The alkaline aqueous solution can be prepared by adding an alkaline component to water, which is a solvent. The type of alkaline component is not particularly limited, but for example, one or more types selected from sodium hydroxide, potassium hydroxide, sodium carbonate, etc. can be used.

[0086] The composition of the metal elements contained in the mixed aqueous solution is almost the same as the composition of the metal elements contained in the obtained nickel-manganese composite hydroxide. Therefore, it is preferable to adjust the composition of the metal elements in the mixed aqueous solution so that it is the same as the composition of the metal elements in the target nickel-manganese composite hydroxide.

[0087] In the crystallization step, any component other than the aqueous solution containing the metal component (mixed aqueous solution) and the aqueous alkali solution can be added to the aqueous reaction solution.

[0088] For example, a complexing agent may be added to the aqueous reaction solution together with the aqueous alkaline solution.

[0089] The complexing agent is not particularly limited, and may be any agent capable of forming a complex by bonding with nickel ions or other metal ions in an aqueous solution. An example of the complexing agent is an ammonium ion donor. The ammonium ion donor is not particularly limited, and may be one or more selected from ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.

[0090] The temperature and pH of the aqueous reaction solution in the crystallization step are not particularly limited, but for example, when no complexing agent is used, the temperature of the aqueous reaction solution is preferably in the range of more than 60° C. to 80° C., and the pH at the temperature of the aqueous reaction solution is preferably 10 to 12. In this specification, the pH of the aqueous reaction solution means the pH at the temperature of the aqueous reaction solution, unless otherwise specified.

[0091] In the crystallization step, when a complexing agent is not used, the pH of the reaction aqueous solution is set to 12 or less, which can prevent the nickel-manganese composite hydroxide particles from becoming fine particles and improves filterability. In addition, spherical particles can be obtained more reliably.

[0092] Furthermore, by setting the pH of the reaction aqueous solution to 10 or more, the production rate of nickel-manganese composite hydroxide particles can be increased and some components such as Ni can be prevented from remaining in the filtrate, etc. Therefore, nickel-manganese composite hydroxide particles having the target composition can be obtained more reliably.

[0093] In the crystallization process, when a complexing agent is not used, the solubility of Ni increases by setting the temperature of the reaction aqueous solution to above 60°C, which more reliably prevents the amount of Ni precipitate from deviating from the target composition and thus preventing coprecipitation.

[0094] In addition, by setting the temperature of the aqueous reaction solution at 80° C. or less, the amount of water evaporation can be suppressed, and therefore the slurry concentration can be prevented from becoming high. By preventing the slurry concentration from becoming high, it is possible to suppress the unintended precipitation of crystals such as sodium sulfate in the aqueous reaction solution, which would otherwise cause the impurity concentration to become high.

[0095] On the other hand, when an ammonium ion donor such as ammonia is used as a complexing agent, the solubility of Ni increases, so the pH of the reaction aqueous solution in the crystallization step is preferably 10 to 13. In this case, the temperature of the reaction aqueous solution is preferably 30° C. to 60° C.

[0096] When an ammonium ion donor is added to the reaction aqueous solution as a complexing agent, the ammonia concentration in the reaction aqueous solution in the reaction tank is preferably maintained within a certain range of 3 g / L or more and 25 g / L or less.

[0097] By setting the ammonia concentration in the reaction aqueous solution to 3 g / L or more, the solubility of metal ions can be kept particularly constant, and therefore primary particles of nickel-manganese composite hydroxide with a regular shape and particle size can be formed. As a result, the spread of the particle size distribution of the obtained nickel-manganese composite hydroxide particles can be suppressed.

[0098] Furthermore, by setting the ammonia concentration in the reaction aqueous solution to 25 g / L or less, the solubility of metal ions can be prevented from becoming excessively high, and the amount of metal ions remaining in the reaction aqueous solution can be suppressed, so that nickel-manganese composite hydroxide particles having the target composition can be obtained more reliably.

[0099] In addition, since fluctuations in ammonia concentration may cause fluctuations in the solubility of metal ions and may result in failure to form uniform hydroxide particles, it is preferable to maintain the ammonia concentration within a certain range. For example, during the crystallization process, it is preferable to maintain the ammonia concentration at a desired concentration with the upper and lower limits within about 5 g / L.

[0100] After the steady state is reached, the precipitate is collected, filtered, and washed with water to obtain nickel-manganese composite hydroxide particles. Alternatively, the mixed aqueous solution, the alkaline aqueous solution, and optionally an aqueous solution containing an ammonium ion donor may be continuously supplied to the reaction tank, and the precipitate is allowed to overflow from the reaction tank, collected, filtered, and washed with water to obtain nickel-manganese composite hydroxide particles.

[0101] In order to optimize the crystallization conditions and facilitate control of the composition ratio, the additive element M can also be added by coating the surfaces of the nickel-manganese composite hydroxide particles with the additive element M. In this case, the crystallization process can further include a coating step of coating the surfaces of the obtained nickel-manganese composite hydroxide particles with the additive element M.

[0102] In the coating step, the method for coating the surface of the nickel-manganese composite hydroxide particles with the additive element M is not particularly limited, and for example, various known methods can be used.

[0103] For example, nickel manganese composite hydroxide particles are dispersed in pure water to form a slurry. A solution containing an additive element M in an amount corresponding to the target coating amount is mixed with this slurry, and an acid is dropped to adjust the pH value to a predetermined value. The acid used in this case is not particularly limited, but it is preferable to use one or more types selected from sulfuric acid, hydrochloric acid, nitric acid, and the like.

[0104] After adjusting the pH value, the mixture is mixed for a predetermined period of time, and then filtered and dried to obtain a nickel-manganese composite hydroxide coated with the additive element M.

[0105] The method for coating the surface of the nickel-manganese composite hydroxide particles with the additive element M is not limited to the above method. For example, a method of drying a solution containing a compound of the additive element M and a solution containing the nickel-manganese composite hydroxide particles by spray drying, a method of impregnating the nickel-manganese composite hydroxide particles with a solution containing a compound of the additive element M, etc. can also be used.

[0106] The nickel-manganese composite hydroxide particles to be subjected to the coating step may have a part of the additive element M added in advance, or may not contain the additive element M. When a part of the additive element M is added in advance, as described above, for example, when performing crystallization, an aqueous solution containing the additive element M may be added to the mixed aqueous solution. When the nickel-manganese composite hydroxide particles thus contain a part of the additive element M, it is preferable to adjust the amount of the additive element M added in the coating step so as to obtain a target composition. (D) Oxidation roasting process When the oxidizing roasting step is carried out, the nickel-manganese composite hydroxide obtained in the crystallization step is calcined in an oxygen-containing atmosphere, and then cooled to room temperature to obtain a nickel-manganese composite oxide. In the oxidizing roasting step, the nickel-manganese composite hydroxide is calcined to reduce moisture, and at least a portion of it can be converted into a nickel-manganese composite oxide as described above. However, in the oxidizing roasting step, it is not necessary to completely convert the nickel-manganese composite hydroxide into a nickel-manganese composite oxide, and the nickel-manganese composite oxide referred to here may contain, for example, a nickel-manganese composite hydroxide or an intermediate thereof.

[0107] The roasting conditions in the oxidation roasting step are not particularly limited, but it is preferable to roast in an oxygen-containing atmosphere, for example, in an air atmosphere, at a temperature of 350° C. to 1000° C. for 5 hours to 24 hours.

[0108] This is because a firing temperature of 350° C. or higher is preferable because it can prevent the specific surface area of ​​the resulting nickel-manganese composite oxide from becoming excessively large, and a firing temperature of 1000° C. or lower is preferable because it can prevent the specific surface area of ​​the nickel-manganese composite oxide from becoming excessively small.

[0109] By setting the calcination time to 5 hours or more, the temperature in the calcination vessel can be particularly uniform, and the reaction can proceed uniformly, which is preferable. Furthermore, even if the calcination is performed for a time longer than 24 hours, no significant change is observed in the obtained nickel-manganese composite oxide, so from the viewpoint of energy efficiency, the calcination time is preferably set to 24 hours or less.

[0110] The oxygen concentration in the oxygen-containing atmosphere during the heat treatment is not particularly limited, but for example, the oxygen concentration is preferably 20% by volume or more. Since the oxygen atmosphere can be used, the upper limit of the oxygen concentration of the oxygen-containing atmosphere can be 100% by volume. [Lithium-ion secondary battery] The lithium ion secondary battery (hereinafter also referred to as "secondary battery") of this embodiment can have a positive electrode containing the above-mentioned positive electrode active material.

[0111] Hereinafter, an example of the configuration of the secondary battery of this embodiment will be described for each component. The secondary battery of this embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of the same components as a general lithium-ion secondary battery. Note that the embodiment described below is merely an example, and the lithium-ion secondary battery of this embodiment can be embodied in various forms that have been modified and improved based on the knowledge of those skilled in the art, including the following embodiment. In addition, the secondary battery is not particularly limited in its use. (positive electrode) The positive electrode of the secondary battery of this embodiment can contain the positive electrode active material described above.

[0112] An example of a method for manufacturing a positive electrode is described below. First, the positive electrode active material (powder), conductive material, and binder are mixed to prepare a positive electrode mixture, and activated carbon and a solvent for viscosity adjustment, etc. are added as necessary, and the mixture is kneaded to prepare a positive electrode mixture paste.

[0113] The mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium ion secondary battery, and can be adjusted depending on the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium ion secondary battery, and for example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 mass%, the positive electrode active material can be contained in a ratio of 60 mass% to 95 mass%, the conductive material can be contained in a ratio of 1 mass% to 20 mass%, and the binder can be contained in a ratio of 1 mass% to 20 mass%.

[0114] The obtained positive electrode composite paste is applied to the surface of a current collector made of, for example, aluminum foil, and dried to remove the solvent, thereby producing a sheet-like positive electrode. If necessary, pressure can be applied by a roll press or the like to increase the electrode density. The sheet-like positive electrode thus obtained can be cut to an appropriate size according to the desired battery and used for the production of the battery.

[0115] As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and Ketjen Black (registered trademark) can be used.

[0116] The binder serves to bind the active material particles together, and may be, for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, etc.

[0117] If necessary, a solvent for dispersing the positive electrode active material, conductive material, etc. and dissolving the binder can be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can also be added to the positive electrode mixture to increase the electric double layer capacity.

[0118] The method for producing the positive electrode is not limited to the above-mentioned example, and other methods may be used. For example, the positive electrode may be produced by pressing a positive electrode mixture and then drying it in a vacuum atmosphere. (Negative electrode) The negative electrode may be made of metallic lithium, a lithium alloy, etc. Alternatively, the negative electrode may be made by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, adding an appropriate solvent to make a paste-like negative electrode mixture, applying the paste to the surface of a metal foil current collector such as copper, drying it, and compressing it to increase the electrode density as necessary.

[0119] As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powder of carbon material such as coke can be used. In this case, as with the positive electrode, fluorine-containing resin such as PVDF can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders. (Separator) A separator may be sandwiched between the positive electrode and the negative electrode as necessary. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and a known separator may be used, such as a thin membrane made of polyethylene or polypropylene having many minute pores. (Non-aqueous electrolyte) As the non-aqueous electrolyte, for example, a non-aqueous electrolytic solution can be used.

[0120] As the non-aqueous electrolyte, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. Alternatively, as the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an ionic liquid can be used. Note that the ionic liquid refers to a salt that is composed of cations and anions other than lithium ions and is liquid even at room temperature.

[0121] The organic solvent may be one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. Two or more of these organic solvents may be used in combination.

[0122] The supporting salt may be LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, or a composite salt thereof. Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

[0123] The non-aqueous electrolyte may be a solid electrolyte. The solid electrolyte has a property of being able to withstand high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

[0124] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0125] The oxide-based solid electrolyte is not particularly limited, and for example, an oxide-based solid electrolyte containing oxygen (O) and having lithium ion conductivity and electronic insulation can be suitably used. Examples of the oxide-based solid electrolyte include lithium phosphate (Li3PO4), Li3PO4N X , LiBON X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≦X≦1), Li 1+X Al X Ge 2-X (PO4)3(0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≦X≦2 / 3), Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 S 0.6 P 0.4 One or more types selected from O4, etc. can be used.

[0126] The sulfide-based solid electrolyte is not particularly limited, and for example, one containing sulfur (S) and having lithium ion conductivity and electronic insulation can be suitably used. For example, the sulfide-based solid electrolyte can be one or more selected from Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, etc.

[0127] As the inorganic solid electrolyte, materials other than those mentioned above may be used, for example, Li3N, LiI, Li3N-LiI-LiOH, etc. may be used.

[0128] The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity, and examples of the organic solid electrolyte that can be used include polyethylene oxide, polypropylene oxide, copolymers thereof, etc. The organic solid electrolyte may also contain a supporting salt (lithium salt). (Shape and structure of secondary battery) The lithium ion secondary battery of the present embodiment described above can be made into various shapes such as a cylindrical shape, a laminated shape, etc. Regardless of the shape, if the secondary battery of the present embodiment uses a non-aqueous electrolyte solution as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte solution, and the positive electrode current collector and the positive electrode terminal connected to the outside, and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and the battery case is sealed to form a structure.

[0129] As described above, the secondary battery of the present embodiment is not limited to a form using a non-aqueous electrolyte solution as a non-aqueous electrolyte, and may be, for example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery. When making an all-solid-state battery, the configuration other than the positive electrode active material may be changed as necessary.

[0130] In the secondary battery of this embodiment, gas generation can be suppressed and the battery has excellent storage stability. Therefore, the secondary battery of this embodiment can be particularly preferably used for batteries that are easily affected by gas generation, such as laminated type batteries. In addition, the secondary battery of this embodiment can be preferably used for batteries other than laminated type batteries, since gas generation can be suppressed and the battery characteristics can be stabilized.

[0131] The secondary battery of the present embodiment can be used for various purposes, but since it can be a high-capacity, high-output secondary battery, it is suitable, for example, as a power source for small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity, and is also suitable as a power source for electric automobiles that require high output.

[0132] In addition, the secondary battery of this embodiment can be made compact and have high output, making it suitable as a power source for electric vehicles that are limited in installation space. The secondary battery of this embodiment can be used not only as a power source for electric vehicles that are driven purely by electrical energy, but also as a power source for so-called hybrid vehicles that are used in conjunction with combustion engines such as gasoline engines and diesel engines. EXAMPLES

[0133] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0134] In the following experimental examples, unless otherwise specified, the nickel-manganese composite compound and the positive electrode active material were prepared using respective samples of special grade reagents manufactured by Wako Pure Chemical Industries, Ltd.

[0135] First, the evaluation methods of the positive electrode active materials and secondary batteries obtained in the following experimental examples will be described. (Evaluation of Positive Electrode Active Material) The obtained positive electrode active material was evaluated as follows.

[0136] (a) Composition The composition of the positive electrode active material was evaluated by analysis using an ICP emission spectrometer (VARIAN, 725ES). In the following experimental examples, the positive electrode active material may contain lithium-zirconium composite oxide as a different phase, but the content is extremely small and the material is almost composed of lithium composite oxide, so the composition of the positive electrode active material obtained can be considered to be the composition of lithium composite oxide. For the same reason, the average particle size and specific surface area described below can also be evaluated for the positive electrode active material and used as the evaluation results for the lithium composite oxide particles.

[0137] (b) FWHM of the (003) plane peak, FWHM of the (104) plane peak, and confirmation of heterogeneous phases An X-ray diffractometer (BRUKER, D8 DISCOVER) was used with monochromated CuKα1 as the X-ray source, and the half-width of the peak of the (003) plane near 2θ=18° and the half-width of the peak of the (104) plane near 2θ=44° were determined from the obtained XRD pattern.

[0138] In addition, phase identification was performed on the obtained XRD pattern to confirm whether or not a different phase such as a lithium-zirconium composite oxide was included in addition to the lithium composite oxide. When a different phase was confirmed, phase identification was performed to confirm the composition of the different phase.

[0139] (c) Average particle size The average particle size D50 of the lithium composite oxide particles was measured using a laser light diffraction scattering type particle size analyzer (manufactured by Nikkiso Co., Ltd., model: Microtrack HRA).

[0140] (d) Amount of dissolved lithium The amount of eluted lithium was evaluated by the Warder method, which is one of the neutralization titration methods. From the evaluation results, the amounts of lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) were calculated, and the sum of these lithium amounts was taken as the amount of eluted lithium.

[0141] Specifically, pure water was added to the obtained positive electrode active material and stirred, and then the filtrate was filtered and the pH of the filtrate was measured while hydrochloric acid was added. The state of the lithium compound eluted from the neutralization point that appeared was evaluated and calculated.

[0142] The titration was performed up to the second neutralization point. The amount of lithium in the filtrate was calculated from the amount of hydrochloric acid dropped up to the second neutralization point and the concentration of hydrochloric acid, with the alkali content neutralized by hydrochloric acid up to the second neutralization point being the amount of lithium (Li) derived from lithium hydroxide (LiOH) and lithium carbonate (Li2CO3).

[0143] The calculated amount of lithium in the filtrate was then divided by the amount of the sample of the positive electrode active material used in preparing the filtrate, and the amount of eluted lithium was calculated by converting the unit into % by mass.

[0144] (e) Moisture content The moisture content of the obtained positive electrode active material was measured at a vaporization temperature of 300° C. using a Karl Fischer moisture meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., model: CA-200).

[0145] (f) Specific surface area The specific surface area of ​​the lithium composite oxide particles was measured using a flow type gas adsorption specific surface area measuring device (Multisorb, manufactured by Yuasa Ionics Co., Ltd.). (Evaluation of battery characteristics) The charge capacity, discharge capacity, efficiency, and positive electrode resistance were evaluated using the coin-type battery shown in Figure 1, which was fabricated in the following experimental example. In addition, the cycle characteristics, positive electrode resistance after cycling, and storage gas amount were evaluated using the laminate-type battery shown in Figure 2. (a) Charge capacity, discharge capacity, efficiency The coin-type batteries prepared in each experiment were left for about 12 hours after preparation, and after the open circuit voltage (OCV) had stabilized, the current density to the positive electrode was increased to 0.1 mA / cm 2 The capacity when the battery was charged to a cut-off voltage of 4.3 V was defined as the charge capacity. After charging, the battery was allowed to rest for 1 hour, and then the capacity when the battery was discharged to a cut-off voltage of 3.0 V was defined as the discharge capacity.

[0146] The efficiency, which is the ratio of the discharge capacity to the charge capacity, was calculated. (b) Positive electrode resistance After measuring the charge and discharge capacity in (a), the coin-type battery was charged at a constant current / constant voltage (CCCV) at a rate of 0.2C up to 4.1V (SOC 80%), and the resistance of the charged battery was measured by the AC impedance method. A frequency response analyzer and a potentiogalvanostat (manufactured by Solartron) were used for the measurement, and a Nyquist plot was obtained as shown in Figure 3(A). The plot is expressed as the sum of the characteristic curves showing the solution resistance, the negative electrode resistance and capacity, and the positive electrode resistance and capacity, so a fitting calculation was performed using the equivalent circuit shown in Figure 3(B) to calculate the positive electrode resistance. (c) Cycle characteristics The cycle characteristics were evaluated by measuring the capacity retention rate after 500 charge / discharge cycles. Specifically, the laminated battery was placed in a thermostatic chamber maintained at 25°C and charged at a current density of 0.3 mA / cm. 2 The battery was conditioned by charging it to a cut-off voltage of 4.2 V, resting for 10 minutes, and discharging it to a cut-off voltage of 2.5 V for 5 cycles. After that, the battery was placed in a thermostatic chamber maintained at 45°C and discharged at a current density of 2.0 mA / cm. 2 The battery was charged to a cut-off voltage of 4.2 V, rested for 10 minutes, and then discharged to a cut-off voltage of 2.5 V. This cycle was repeated 500 times, and the capacity retention rate, which is the ratio of the discharge capacity at the 500th cycle after conditioning to the discharge capacity at the 1st cycle, was calculated and evaluated. The evaluation results are shown in the column for capacity retention rate after 500 cycles in Table 2. (d) Positive electrode resistance after cycling After 500 cycles of charge and discharge in the cycle characteristic evaluation of (c), constant current constant voltage (CCCV) charging was performed and the charge capacity was measured. Then, using the measured charge capacity as a reference, charging was performed at a rate of 0.2C to SOC80%, and the resistance value was measured by the AC impedance method as in the case of (b) positive electrode resistance. In this case, too, fitting calculations were performed using an equivalent circuit from the Nyquist plot obtained after the measurement to calculate the positive electrode resistance value after the cycle. The evaluation results are shown in the column for SOC80% after cycle in Table 2. (e) Amount of stored gas After preparing the laminated battery, place the laminated battery in a thermostatic chamber maintained at 25°C and apply a current density of 0.3 mA / cm 2 The battery was conditioned by charging it to a cut-off voltage of 4.2 V, resting for 10 minutes, and discharging it to a cut-off voltage of 2.5 V for 5 cycles. The gas generated during this process was allowed to escape from the laminated battery. The volume of the laminated battery was measured by the Archimedes method (as an evaluation standard for the amount of stored gas).

[0147] Next, the charge / discharge capacity was measured, and based on this value, the battery was charged at a constant current and constant voltage (CCCV) up to 4.2 V at a temperature of 25° C. so that the depth of charge (SOC) was 100%.

[0148] After charging, the battery was stored in a thermostatic chamber set at 60°C for 7 days, and after 7 days, it was discharged to 2.5 V. The volume of the laminated battery after discharge was measured using the Archimedes method, and the amount of gas generated in the cell was evaluated from the difference between this volume and the volume of the laminated battery measured after conditioning (the evaluation standard for the amount of stored gas).

[0149] The amount of gas stored in Experimental Example 3 was set to 1.00, and the results are shown as relative percentages.

[0150] The manufacturing conditions and evaluation results of the positive electrode active material and the like in each experiment will be described below. Experimental Examples 1 and 2 are working examples, and Experimental Examples 3 and 4 are comparative examples. [Experimental Example 1] (1) Manufacturing of nickel-manganese composite compounds (Crystallization process) First, water was poured halfway into a reaction tank (60 L) and the temperature inside the tank was set to 49°C while stirring. At this time, nitrogen gas (N2) and air (Air) were supplied into the reaction tank, and the N2 / Air flow rate was adjusted so that the dissolved oxygen concentration in the reaction tank liquid was 1.5 mg / L or more and 2.5 mg / L or less.

[0151] Appropriate amounts of 25% by mass sodium hydroxide aqueous solution, which is an alkaline aqueous solution, and 25% by mass ammonia water, which is a complexing agent, were added to the water in the reaction tank to prepare an initial aqueous solution with a pH value of 12.4 at a liquid temperature of 49°C and an ammonia concentration of 12 g / L.

[0152] At the same time, nickel sulfate, manganese sulfate, and cobalt sulfate were dissolved in pure water so that the mass ratio of nickel, manganese, and cobalt was Ni:Mn:Co=85.0:10.0:5.0, to prepare a mixed aqueous solution with a metal component concentration of 2.0 mol / L.

[0153] This mixed aqueous solution was added dropwise at a constant rate to the initial aqueous solution in the reaction tank to obtain a reaction aqueous solution. At this time, a 25% by mass aqueous solution of sodium hydroxide, which is an alkaline aqueous solution, and a 25% by mass aqueous ammonia, which is a complexing agent, were also added dropwise at a constant rate to the initial aqueous solution to control the pH value of the reaction aqueous solution to be 12.4 or more and 12.5 or less at a liquid temperature of 49°C, and the ammonia concentration to be maintained at 12.0 g / L. Through this operation, nickel manganese composite hydroxide particles were crystallized (crystallization step).

[0154] Thereafter, the slurry containing the nickel-manganese composite hydroxide particles was collected from an overflow port provided in the reaction tank, filtered, and water-soluble impurities were removed by washing with ion-exchanged water, followed by drying. (Oxidation roasting process) The obtained nickel-manganese composite hydroxide particles were subjected to oxidative roasting in an air stream (oxygen concentration: 21% by volume) at 500° C. for 5 hours, thereby obtaining nickel-manganese composite oxide particles. (2) Manufacturing of positive electrode active material (Mixing process) The obtained nickel manganese composite oxide particles, lithium hydroxide having an average particle size of 25 μm, which is a lithium compound, and zirconium oxide having an average particle size of 1.5 μm were thoroughly mixed using a shaker mixer (Willi & Bachofen (WAB), model: TURBULA Type T2C) to prepare a raw material mixture. At this time, each raw material was weighed and mixed so that the ratio of the number of atoms of lithium (Li) and metal other than lithium (Me) contained in the obtained raw material mixture, Li / Me, was 1.015, and the ratio of the number of atoms of zirconium to the total number of atoms of the metal components in the nickel manganese composite oxide particles and the zirconium in the zirconium oxide was 0.30 at.%. (Firing process) The raw material mixture obtained in the mixing step was fired at 820° C. for 12 hours in an oxygen-containing atmosphere having an oxygen concentration of 75% by volume, the remainder being nitrogen.

[0155] The obtained fired product was pulverized using a pin mill at a strength sufficient to maintain the secondary particle shape.

[0156] By the above procedure, a positive electrode active material made of lithium composite oxide particles (lithium composite oxide powder) was obtained.

[0157] The composition and the presence of different phases in the obtained positive electrode active material were confirmed. The positive electrode active material obtained in this experiment was found to have the general formula: Li 1.015 Ni 0.8485 Mn 0.0985 Zr 0.003 Co 0.05 It was confirmed that the active material contained a lithium composite oxide represented by the formula: Li2ZrO3. From the XRD pattern of this active material, it was confirmed that the active material contained a very small amount of lithium-zirconium composite oxide, Li2ZrO3, as a heterophase.

[0158] Other evaluation results are shown in Table 1. (3) Preparation of secondary batteries A coin-type battery having the structure shown in FIG. 1 or a laminate-type battery having the structure shown in FIG. 2 was fabricated according to the following procedure, and the batteries were evaluated as described above. (Coin cell battery) As shown in FIG. 1, a coin battery 10 is composed of a case 11 and an electrode 12 housed within this case 11.

[0159] Case 11 has a hollow positive electrode can 111 with one end open, and a negative electrode can 112 placed in the opening of positive electrode can 111, and is configured so that when negative electrode can 112 is placed in the opening of positive electrode can 111, a space for accommodating electrode 12 is formed between negative electrode can 112 and positive electrode can 111.

[0160] Electrode 12 consists of a positive electrode 121, a separator 122, and a negative electrode 123, which are stacked in this order and are housed in case 11 so that positive electrode 121 contacts the inner surface of positive electrode can 111 and negative electrode 123 contacts the inner surface of negative electrode can 112.

[0161] Case 11 is provided with gasket 113, which restricts relative movement between positive electrode can 111 and negative electrode can 112 and fixes them in place so as to maintain a non-contact state between them, i.e., an electrically insulated state. Gasket 113 also has the function of sealing the gap between positive electrode can 111 and negative electrode can 112 to provide an airtight and liquidtight barrier between the inside of case 11 and the outside.

[0162] This coin-type battery 10 was fabricated as follows: First, 52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) resin were mixed and pelletized to a diameter of 11 mm and a weight of about 75 mg to fabricate the positive electrode 121, which was then dried in a vacuum dryer at 100° C. for 12 hours.

[0163] Using the positive electrode 121, the negative electrode 123, the separator 122 and the electrolyte, a coin-type battery 10 was fabricated in a glove box in an Ar atmosphere with a dew point controlled at -60°C.

[0164] For the negative electrode 123, lithium metal punched into a disk shape with a diameter of 13 mm was used.

[0165] A polyethylene porous film having a thickness of 25 μm was used for the separator 122. A mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1, with 1M LiClO4 as the supporting electrolyte, was used for the electrolyte.

[0166] The evaluation results are shown in Table 2. (Laminated battery) 2, the laminated battery 20 has a structure in which a laminate of a positive electrode film 21, a separator 22, and a negative electrode film 23 is impregnated with an electrolyte solution and sealed with a laminate 24. A positive electrode tab 25 is connected to the positive electrode film 21, and a negative electrode tab 26 is connected to the negative electrode film 23. The positive electrode tab 25 and the negative electrode tab 26 are exposed to the outside of the laminate 24.

[0167] 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) to form a slurry, which was then spread to a thickness of 1 cm on an Al foil. 2 The positive electrode active material was applied so that 7.0 mg of the positive electrode active material was present per unit area. Next, the slurry containing the positive electrode active material was applied to the Al foil, and dried in the air at 120 ° C for 30 minutes to remove the NMP. The Al foil to which the positive electrode active material was applied was cut into a strip shape with a width of 66 mm, and roll pressed with a load of 1.2 t to prepare a positive electrode film. The positive electrode film was then cut into a rectangle of 50 mm × 30 mm, and dried in a vacuum dryer at 120 ° C for 12 hours to be used as the positive electrode film 21 of the laminated battery 20.

[0168] In addition, a negative electrode film 23 was prepared by applying a negative electrode composite paste, which was a mixture of graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride, to a copper foil. A polyethylene porous film with a thickness of 20 μm was used for the separator 22, and a 3:7 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiPF6 as the supporting electrolyte (manufactured by Ube Industries, Ltd.) was used for the electrolyte.

[0169] In a dry room controlled at a dew point of −60° C., the laminate of the positive electrode film 21 , separator 22 and negative electrode film 23 was impregnated with an electrolyte solution and sealed with a laminate 24 to prepare a laminate type battery 20 .

[0170] Two laminated batteries were fabricated, one for evaluating cycle characteristics and the other for evaluating the amount of stored gas. The evaluation results are shown in Table 2. [Experimental Example 2] A positive electrode active material was produced and evaluated in the same manner as in Experimental Example 1, except that an oxygen-containing atmosphere with an oxygen concentration of 55% by volume and the remainder being nitrogen was used in the firing process. A secondary battery was then produced and evaluated using the positive electrode active material.

[0171] The composition and the presence of different phases in the obtained positive electrode active material were confirmed. The positive electrode active material obtained in this experiment was found to have the general formula: Li 1.015 Ni 0.8485 Mn 0.0985 Zr 0.003 Co 0.05 It was confirmed that the material contained a lithium composite oxide represented by the formula O2. It was also confirmed that the material contained a very small amount of a lithium-zirconium composite oxide, Li2ZrO3, as a different phase.

[0172] Particle observation by SEM confirmed that the lithium composite oxide particles were composed of secondary particles formed by aggregation of primary particles.

[0173] Other evaluation results are shown in Tables 1 and 2. Moreover, FIG. 6 shows an SEM image of the lithium composite oxide particles contained in the obtained positive electrode active material. [Experimental Example 3] A positive electrode active material was produced and evaluated in the same manner as in Experimental Example 1, except that zirconium oxide was not added in the mixing step when producing the positive electrode active material. Further, a secondary battery was produced and evaluated using the positive electrode active material.

[0174] The composition and the presence of different phases in the obtained positive electrode active material were confirmed. The positive electrode active material obtained in this experiment was found to have the general formula: Li 1.015 Ni0.8500 Mn 0.1000 Co 0.05 It was confirmed that the material consisted of a lithium composite oxide represented by O2 and did not contain any other phases.

[0175] Other evaluation results are shown in Tables 1 and 2. [Experimental Example 4] A positive electrode active material was produced and evaluated in the same manner as in Experimental Example 1, except that an oxygen-containing atmosphere with an oxygen concentration of 45% by volume and the remainder being nitrogen was used in the firing process. A secondary battery was then produced and evaluated using the positive electrode active material.

[0176] The composition and the presence of different phases in the obtained positive electrode active material were confirmed. The positive electrode active material obtained in this experiment was found to have the general formula: Li 1.015 Ni 0.8485 Mn 0.0985 Zr 0.003 Co 0.05 It was confirmed that the material contained a lithium composite oxide represented by the formula O2. It was also confirmed that the material contained a very small amount of a lithium-zirconium composite oxide, Li2ZrO3, as a different phase.

[0177] Particle observation by SEM confirmed that the lithium composite oxide particles were composed of secondary particles formed by aggregation of primary particles.

[0178] Other evaluation results are shown in Tables 1 and 2.

[0179] [Table 1]

[0180] [Table 2] From the results shown in Tables 1 and 2, it was confirmed that the positive electrode active materials in Experimental Examples 1 and 2, which contain lithium composite oxide particles containing a predetermined amount of Zr, have half-widths of the peaks of the (003) plane and the (104) plane calculated from the X-ray diffraction pattern of the lithium composite oxide within predetermined ranges, and have moisture contents within predetermined ranges, have high battery capacities and can suppress gas generation.

Claims

1. A positive electrode active material for a lithium ion secondary battery containing lithium composite oxide particles, Further containing a lithium-zirconium composite oxide, The lithium composite oxide particles are particles of a lithium composite oxide containing lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr), and an additive element M (M) in a substance amount ratio of Li:Ni:Mn:Zr:M=a:b:c:d:e (wherein 0.95≦a≦1.20, 0.70≦b≦0.98, 0.01≦c≦0.20, 0.0003≦d≦0.02, and 0.01≦e≦0.20, and the additive element M is one or more elements selected from Co, W, Mo, V, Mg, Ca, Al, Ti, and Ta), the half width of the peak of the (003) plane calculated from the X-ray diffraction pattern of the lithium composite oxide particle is 0.065° or more and 0.10° or less, and the half width of the peak of the (104) plane is 0.10° or more and 0.15° or less; A positive electrode active material for a lithium ion secondary battery, the moisture content of which is 0.01% by mass or more and 0.06% by mass or less.

2. 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the amount of eluted lithium determined by the Warder method is 0.05% by mass or more and 0.10% by mass or less.

3. a mixing step of mixing a nickel-manganese composite compound containing nickel, manganese and an additive element M with a lithium compound and a zirconium compound to prepare a raw material mixture containing lithium (Li), nickel (Ni), manganese (Mn), zirconium (Zr) and the additive element M (M) in a substance amount ratio of Li:Ni:Mn:Zr:M=a:b:c:d:e (wherein 0.95≦a≦1.20, 0.70≦b≦0.98, 0.01≦c≦0.20, 0.0003≦d≦0.02, 0.01≦e≦0.20, and the additive element M is one or more elements selected from Co, W, Mo, V, Mg, Ca, Al, Ti, and Ta); A firing step of firing the raw material mixture at a temperature of 750° C. or higher and 900° C. or lower in an oxygen-containing atmosphere having an oxygen concentration of 50% by volume or higher and lower than 80% by volume, The method for producing a positive electrode active material for a lithium ion secondary battery, wherein the positive electrode active material for a lithium ion secondary battery obtained after the calcination step contains a lithium-zirconium composite oxide.

4. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 3, further comprising an oxidation roasting step of calcining a nickel-manganese composite hydroxide in an oxygen-containing atmosphere to obtain the nickel-manganese composite compound.

5. A lithium ion secondary battery having a positive electrode comprising the positive electrode active material for lithium ion secondary batteries according to claim 1 or 2.

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