Niobium-containing oxide powder, electrode using same, and non-aqueous electrolyte power storage device

Abstract

A niobium-containing oxide powder according to the present invention satisfies formula (I).　(I) AaTi(2-p-q-r)(MV (0.5+v)MIII (0.5-v))p(MV (0.67+w)MII (0.33-w))qMIV rNb(14-s)M1 sO(39±t) (In the formula, A is at least one element selected from the group that consists of Li and Na, M1 is selected from the group that consists of MV, (MIV (0.5+w)MVI (0.5-w)), (MVI (0.67+w)MIII (0.33-w)), and (MVI (0.75+w)MII (0.25-w)), each MII is independently at least one divalent metal element, each MIII is independently at least one trivalent metal element, each MIV is independently at least one tetravalent metal element, each MV is independently at least one pentavalent metal element, each MVI is independently at least one hexavalent metal element, 0≤a≤6, -0.05≤v≤0.05, -0.05≤w≤0.05, 0≤p<2, 0≤q<2, 0≤r<2, 0<p+q+r<2, 0≤s<14, and 0≤t≤1, provided that at least two of p, q, and r are not 0.)

Description

Niobium-containing oxide powder, electrode using the same, and non-aqueous electrolyte storage device

[0001] The present invention relates to a niobium-containing oxide powder suitable as an electrode material for electricity storage devices, an electrode using the same, and a non-aqueous electrolyte electricity storage device.

[0002] Energy storage devices for electric vehicles require high energy density to improve fuel economy and power consumption. Lithium-ion batteries, in particular, are widely used as power sources for electric vehicles and power storage. Various materials have been studied as electrode materials for lithium-ion batteries. While lithium titanate has excellent input / output characteristics, its energy density remains at 175 mAh / g, leaving challenges for further energy enhancement. Therefore, there has been a movement to use niobium-containing oxides, primarily niobium titanate, which has a high energy density of 380 mAh / g, as an alternative anode material.

[0003] Furthermore, because currently available lithium-ion batteries use electrolytes containing flammable organic solvents, they require the installation of safety devices to suppress temperature rises in the event of a short circuit, as well as short-circuit prevention structures. Under these circumstances, all-solid-state secondary batteries using inorganic solid electrolytes instead of organic electrolytes are attracting attention. Because the positive and negative electrodes and electrolytes of all-solid-state secondary batteries are all solid, they have the potential to significantly improve the safety and reliability issues associated with batteries using organic electrolytes. Furthermore, because safety devices can be simplified, high energy density is possible, making them promising for applications in electric vehicles, large-scale storage batteries, and more.

[0004] Non-Patent Documents 1 and 2 disclose porous Ti nanoparticles composed of primary particles with a particle size range of 20 to 200 nm, which are produced by a solvothermal method. ２ Nb １４ O ３９ When applied as an electrode material for a lithium ion battery using an electrolyte solution, Ti produced by a solid phase method is ２ Nb １４ O ３９ It has been reported that the rate characteristics are better than those of

[0005] Patent Document 1 describes TiNb２ O ７ and Ti ２ Nb １０ O ２９ It has been reported that when such niobium-titanium composite oxides are used as electrode materials for power storage devices, they can provide power storage devices with high capacity and excellent rate performance. ２ O ７ , TiNb １０ O ２９ have been disclosed, and have been reported to have lower capacity loss with cycling than oxides that do not contain trivalent metals.

[0006] Small 2017, 13, 1702903Journal of Colloid and Interface Science 608 (2022) 90-102

[0007] JP 2010-287496 A International Publication No. 2014 / 122376

[0008] However, the porous Ti composed of primary particles of 20 to 200 nm in Non-Patent Document 1 ２ Nb １４ O ３９ When used as a negative electrode material, it contains a large amount of conductive additive to ensure conductivity even inside the secondary particles. As a result, the ratio of active material in the negative electrode mixture becomes small, resulting in a problem of a low energy density per negative electrode. In addition, the specific surface area is very large, which causes a problem of a significant drop in initial efficiency. Furthermore, when such porous particles are applied to an all-solid-state battery, the inside of the secondary particles cannot come into contact with the solid electrolyte, making it impossible to obtain sufficient capacity. In addition, Ti prepared by a solid-phase method as shown in Non-Patent Document 1 ２ Nb １４ O ３９ When the TiNb alloy described in Patent Document 1 and Patent Document 2 is evaluated in a negative electrode having a higher ratio of active material and a lower ratio of conductive additive, the rate characteristics and cycle capacity retention rate are reduced. ２ O ７ Ya, Ti ２ Nb １０ O２９ , TiNb containing trivalent metal ２ O ７ and Ti ２ Nb １０ O ２９ Although the initial capacity of the batteries using TiNb is good, there is a problem that the capacity of the battery (battery capacity) decreases significantly with the cycle. ２ O ７ , Ti ２ Nb １０ O ２９ , TiNb containing trivalent metal ２ O ７ and Ti ２ Nb １０ O ２９ It was found that the thickness of the electrodes changes significantly during charging and discharging, resulting in a decrease in cycle life. The benefits of increasing battery capacity include improving the energy density per unit weight or unit area (unit volume), which can extend the driving range of electric vehicles and free up space for installing storage batteries.

[0009] For the reasons described above, the energy density and discharge rate characteristics, particularly the change in electrode thickness during charge and discharge, of electricity storage devices using the negative electrode active materials of Non-Patent Document 1, Non-Patent Document 2, Patent Document 1, and Patent Document 2 are not fully satisfactory, and further improvement is required.

[0010] Therefore, an object of the present invention is to provide a niobium-containing oxide powder that can be used as an electrode material for a non-aqueous electrolyte electricity storage device, and that in a liquid-based lithium-ion secondary battery, exhibits excellent discharge rate characteristics while maintaining initial discharge capacity, exhibits a small rate of change in electrode thickness during charge and discharge, and exhibits excellent initial discharge capacity and rate characteristics even in an all-solid-state battery; an electrode for an electricity storage device using the same; and an electricity storage device.

[0011] As a result of various investigations to achieve the above object, the present inventors have found that Ti ２ Nb １４ O ３９The present inventors have found that by using, as an electrode material, a niobium-containing oxide powder in which part of Ti in a niobium-containing oxide such as those described above is substituted with three or more different elements, it is possible to obtain an electricity storage device that is excellent in initial discharge capacity and discharge rate characteristics, and in particular, has a small rate of change in electrode thickness during charge and discharge, and have completed the present invention. Such an effect, in particular the effect of being able to reduce the change in electrode thickness during charge and discharge, is not described or suggested at all in the above-mentioned Non-Patent Documents 1 and 2 and Patent Documents 1 and 2. That is, the present invention relates to the following matters.

[0012] (1) A niobium-containing oxide powder satisfying the following formula (I): ａ Ti （２－ｐ－ｑ－ｒ） (M Ｖ （０．５＋ｖ） M ＩＩＩ （０．５－ｖ） ) ｐ (M Ｖ （０．６７＋ｗ） M ＩＩ （０．３３－ｗ） ) ｑ M ＩV ｒ Nb （１４－ｓ） M １ ｓ O （３９±ｔ） (I) [wherein A is at least one element selected from the group consisting of Li and Na; M １ is M Ｖ , (M ＩV （０．５＋ｗ） M ＶＩ （０．５－ｗ） ), (M ＶＩ （０．６７＋ｗ） M ＩＩＩ （０．３３－ｗ） ), and (M ＶＩ （０．７５＋ｗ） M ＩＩ （０．２５－ｗ） ), and M ＩＩ are each independently at least one divalent metal element, M ＩＩＩ are each independently at least one trivalent metal element, and M ＩV are each independently at least one tetravalent metal element; M Ｖ are each independently at least one pentavalent metal element; M ＶＩare each independently at least one hexavalent metal element, and 0≦a≦6, −0.05≦v≦0.05, −0.05≦w≦0.05, 0≦p<2, 0≦q<2, 0≦r<2, 0<p+q+r<2, 0≦s<14, 0≦t≦1, provided that at least two of p, q, and r are not 0.] (2) The niobium-containing oxide powder according to (1), characterized in that D50 of primary particles corresponding to 50% cumulative volume in a volume-based particle size distribution of the niobium-containing oxide powder measured by a laser diffraction scattering method is 0.25 μm or more and 4.5 μm or less. (3) The niobium-containing oxide powder has a specific surface area of ​​2.3 m ２ / g or more 10m ２ / g or less. (4) An electrode for a non-aqueous electrolyte electricity storage device, comprising the niobium-containing oxide powder according to any one of (1) to (3). (5) A negative electrode active material composition for a non-aqueous electrolyte electricity storage device, comprising the niobium-containing oxide powder according to any one of (1) to (3) and an inorganic solid electrolyte. (6) An electricity storage device, comprising the electrode according to (4). (7) An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, wherein the negative electrode layer is a layer comprising the negative electrode active material composition according to (5).

[0013] According to the present invention, it is possible to provide a niobium-containing oxide powder that, in a liquid-type lithium-ion secondary battery of a nonaqueous electrolyte electricity storage device, exhibits excellent discharge rate characteristics while maintaining initial discharge capacity, exhibits small changes in electrode thickness during charging and discharging, and exhibits excellent initial discharge capacity and rate characteristics even in an all-solid-state battery, as well as an electrode for an electricity storage device and an electricity storage device using the same.

[0014] [Niobium-containing oxide powder of the present invention] The niobium-containing oxide powder of the present invention is a niobium-containing oxide powder that satisfies the following general formula (I): ａ Ti （２－ｐ－ｑ－ｒ） (M Ｖ （０．５＋ｖ） M ＩＩＩ （０．５－ｖ） ) ｐ (M Ｖ （０．６７＋ｗ） M ＩＩ（０．３３－ｗ） ) ｑ M ＩＶ ｒ Nb （１４－ｓ） M １ ｓ O （３９±ｔ） (I) [wherein A is at least one element selected from the group consisting of Li and Na; M １ is M Ｖ , (M ＩV （０．５＋ｗ） M ＶＩ （０．５－ｗ） ), (M ＶＩ （０．６７＋ｗ） M ＩＩＩ （０．３３－ｗ） ), and (M ＶＩ （０．７５＋ｗ） M ＩＩ （０．２５－ｗ） ), and M ＩＩ are each independently at least one divalent metal element, M ＩＩＩ are each independently at least one trivalent metal element, and M ＩV are each independently at least one tetravalent metal element; M Ｖ are each independently at least one pentavalent metal element; M ＶＩ are each independently at least one hexavalent metal element, and 0≦a≦6, −0.05≦v≦0.05, −0.05≦w≦0.05, 0≦p<2, 0≦q<2, 0≦r<2, 0<p+q+r<2, 0≦s<14, 0≦t≦1. However, at least two of p, q, and r are not 0.] The niobium-containing oxide powder of the present invention is suitably used for electrodes of nonaqueous electrolyte electricity storage devices. That is, the niobium-containing oxide powder of the present invention is suitably used as a niobium-containing oxide powder for electrodes of nonaqueous electrolyte electricity storage devices. The nonaqueous electrolyte may be any other than an aqueous electrolyte, and is not particularly limited, but examples thereof include nonaqueous electrolytic solutions and solid electrolytes. Furthermore, the niobium-containing oxide may contain a titanium oxide phase (e.g., rutile-type TiO) derived from the synthesis raw materials in part. ２ , TiO, etc.

[0015] <Niobium-containing oxide powder represented by general formula (I)> The niobium-containing oxide powder of the present invention contains a niobium-containing oxide powder that satisfies general formula (I). The niobium-containing oxide powder represented by general formula (I) can significantly reduce the discharge rate characteristics and the rate of change in electrode thickness during charge and discharge while maintaining the initial discharge capacity in a liquid-based lithium-ion secondary battery of a nonaqueous electrolyte electricity storage device, and can also provide an all-solid-state battery with excellent initial discharge capacity and rate characteristics.

[0016] The A is preferably Li. ＩＩ are each independently preferably Mg, Ca, Cu, and Zn, more preferably Mg, Cu, and Zn, even more preferably Cu and Mg, and particularly preferably Mg.

[0017] Said M ＩＩＩ are each independently preferably Al, Ga, Fe and Cr, more preferably Al and Cr, and particularly preferably Al.

[0018] Said M ＩＶ are each independently preferably Zr, Si, Ge, and Sn, more preferably Zr and Si, and particularly preferably Si.

[0019] Said M Ｖ are each independently preferably Nb, Ta, and V, more preferably Nb and Ta, and particularly preferably Nb. ＶＩ are each independently preferably Mo or W, and particularly preferably Mo.

[0020] In general formula (I), the a is preferably 0≦a≦2, more preferably 0≦a≦0.5, and even more preferably a=0. The v is preferably −0.01≦v≦0.01, and more preferably v=0. The w is preferably −0.01≦w≦0.01, and more preferably w=0. The p is preferably 0≦p≦1, more preferably 0≦p≦0.5, even more preferably 0≦p≦0.2, still more preferably 0<p≦0.2, and particularly preferably 0.05≦p≦0.2. The q is preferably 0≦q≦1.5, more preferably 0≦q≦0.9, even more preferably 0≦q≦0.6, still more preferably 0<q≦0.6, particularly preferably 0.03≦q≦0.6, and most preferably 0.12≦q≦0.4. The r is preferably 0≦r≦1, more preferably 0≦r≦0.5, even more preferably 0≦r≦0.4, still more preferably 0≦r≦0.3, and particularly preferably 0≦r≦0.25. The s is preferably 0≦s≦7, more preferably 0≦s≦5, even more preferably 0≦s≦4, and even more preferably 0≦s≦2. The t is preferably 0≦t≦0.5, more preferably 0≦t≦0.2, and even more preferably t=0. In general formula (I), M Ｖ and M ＩＩ The ratio of Ｖ : M ＩＩ = 0.67 + w: 0.33 - w, but M Ｖ : M ＩＩ = 2 / 3 + w: 1 / 3 - w. In other words, in this case, when w = 0, M Ｖ : M ＩＩ = 2 / 3: 1 / 3 (i.e., A ａ Ti （２－ｐ－ｑ－ｒ） (M Ｖ （１／２＋ｖ） M ＩＩＩ （１／２－ｖ） ) ｐ (M Ｖ （２／３ M ＩＩ １／３） ) ｑ M ＩＶｒ Nb （１４－ｓ） M １ ｓ O （３９±ｔ） It is sufficient that at least two of p, q, and r are not 0, but it is preferable that either "p and q are not 0 and r=0", "p and r are not 0 and q=0", or "none of p, q, and r is 0".

[0021] <Potassium (K) + Iron (Fe) Content> Of the trace components contained in the niobium-containing oxide powder of the present invention, the potassium (K) + iron (Fe) content may be controlled. This is because the change rate of electrode thickness during charge and discharge can be further reduced, and rate characteristics can be further improved. The potassium (K) + iron (Fe) content is preferably 5000 ppm or less, more preferably 4000 ppm or less, and even more preferably 2500 ppm or less. As a method for controlling the potassium (K) + iron (Fe) content of the niobium-containing oxide powder of the present invention, there is a method of selecting and using raw materials having a potassium (K) + iron (Fe) content within a certain range for the niobium compound or titanium compound that is the starting material during synthesis. It is preferable that the potassium (K) + iron (Fe) component is substantially all solid-solved in the crystal structure of the niobium-containing oxide. By controlling the potassium (K) + iron (Fe) in the crystal structure of the niobium-containing oxide, structural stabilization and Li ＋ This is because it is assumed to contribute to migration.

[0022] <Containment of at least one metal element selected from the group consisting of Mo and Ce> The niobium-containing oxide powder of the present invention may contain at least one metal element selected from the group consisting of Mo and Ce. "Containing at least one metal element selected from the group consisting of Mo and Ce" means that the at least one metal element selected from the group consisting of Mo and Ce is localized and present on the surface of the niobium-containing oxide particles constituting the powder. More specifically, this means that at least one metal element selected from the group consisting of Mo and Ce is localized and present in greater amounts in the surface region than in the internal region of the niobium-containing oxide particles. Furthermore, this means that at least one metal element selected from the group consisting of Mo and Ce is detected in inductively coupled plasma atomic emission spectroscopy (ICP-AES) or X-ray fluorescence spectroscopy (XRF) of the niobium oxide powder of the present invention. The lower limit of the amount detected by inductively coupled plasma atomic emission spectroscopy is typically 0.001% by mass. Mo and Ce may both be contained on the particle surface of the niobium-containing oxide powder. From the viewpoint of improving initial discharge capacity and rate characteristics, the inclusion of Mo is preferred.

[0023] The content (mass%) of at least one metal element selected from the group consisting of Mo and Ce in the niobium-containing oxide powder of the present invention, as determined by X-ray fluorescence analysis (XRF), may be 0.01 to 2.0. When the content of at least one metal element selected from the group consisting of the metal elements Mo and Ce is within this range, a secondary battery with excellent initial discharge capacity and rate characteristics can be obtained. The content is preferably 0.01 to 1.7, and from the viewpoint of further improving rate characteristics, the content is more preferably 0.015 to 1.5, even more preferably 0.04 to 1.3, even more preferably 0.07 to 1.25, and particularly preferably 0.2 to 1.1. However, when Mo and Ce are simultaneously contained on the particle surface of the niobium-containing oxide powder, the content (mass%) refers to the total content of the two metal elements.

[0024] As an example, in a cross-sectional analysis of the niobium-containing oxide particles using a scanning transmission electron microscope, it is sufficient that at least one metal element selected from the group consisting of Mo and Ce is contained in a large amount in the so-called near-surface region from the surface of the niobium-containing oxide particles to a depth of about 20 nm as measured by energy dispersive X-ray spectroscopy. At a depth of 20 nm from the surface of the niobium-containing oxide particles, at least one metal element selected from the group consisting of Mo and Ce is detected, while at a depth of 100 nm from the surface, it is preferable that Mo and Ce are not detected. In such a state, it can be determined that at least one metal element selected from the group consisting of Mo and Ce is localized on the surface of the niobium-containing oxide particles. That is, when measured by energy dispersive X-ray spectroscopy, it means that the amount is below the amount detected by the measurement. The lower limit of the amount detected by energy dispersive X-ray spectroscopy varies depending on the element and state to be measured, but is usually 0.5 atm%. Other examples of surface analysis methods include X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). In the present invention, the form of the at least one metal element selected from the group consisting of Mo and Ce that is localized on the surface of the niobium-containing oxide particle is not particularly limited, and it is sufficient that at least one metal element selected from the group consisting of Mo element and Ce element is localized on the surface, and it may be in a metallic state or in the form of a metal compound such as a metal oxide.

[0025] The niobium-containing oxide powder of the present invention may also contain fibrous carbon such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). The fibrous carbon is preferably localized on the surface of the niobium-containing oxide powder, thereby enhancing electronic conductivity, and it is even more preferable for the powder to contain single-walled carbon nanotubes (SWCNT). The fibrous carbon content (mass%) is calculated from measurements using thermogravimetric analysis, and the content may be 0.001 to 2.0. If the fibrous carbon content is within this range, a secondary battery with excellent initial discharge capacity and rate characteristics can be obtained. The mass ratio is preferably 0.01 to 1.8, and from the viewpoint of further improving rate characteristics, it is more preferably 0.05 to 1.5, and particularly preferably 0.1 to 1.0.

[0026] <Specific Surface Area> The specific surface area of ​​the niobium-containing oxide powder of the present invention is the surface area per unit mass when nitrogen is used as an adsorption gas. The measurement method will be explained in the examples below.

[0027] The niobium-containing oxide powder of the present invention has an upper limit of a specific surface area of ​​10 m ２ / g or less, and ２ / g or less is preferable, and 6.5m ２ / g or less is more preferable, and 6m ２ On the other hand, the lower limit of the specific surface area is 1.5 m ２ / g or more, and 2.0m ２ / g or more is preferable, and 2.1m ２ / g or more is more preferable, and 2.3m ２ / g or more is more preferable, and 2.4m ２ / g or more is even more preferable, and 3.0m ２ Within this range, in a liquid lithium ion secondary battery as a nonaqueous electrolyte electricity storage device, an electricity storage device having excellent initial discharge capacity and discharge rate characteristics and a small rate of change in electrode thickness during charge and discharge can be obtained, and further, in an all-solid-state battery, an electricity storage device having excellent initial discharge capacity and rate characteristics can be obtained.

[0028] <D50> D50 of the niobium-containing oxide powder of the present invention is an index of the volume median particle size. It means the particle size at which the cumulative volume frequency calculated from the volume fraction determined by laser diffraction / scattering particle size distribution measurement reaches 50% when calculated from the smallest particle size. The measurement method will be explained in the examples below.

[0029] The niobium-containing oxide powder of the present invention may be primary particles or secondary particles formed by agglomeration of primary particles. When the primary particles made of niobium-containing oxide particles contain secondary particles formed by agglomeration, some of the secondary particles may not form secondary particles and may be in the form of primary particles themselves.

[0030] When the niobium-containing oxide powder of the present invention is a secondary particle, the lower limit of D50 of the secondary particle is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 9 μm or more, from the viewpoint of improving electrode density. Furthermore, the upper limit of D50 of the secondary particle is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 14 μm or less.

[0031] In the present invention, the D50 of the primary particles of the niobium-containing oxide powder is preferably 0.25 μm or more, more preferably 0.4 μm or more, and even more preferably 0.6 μm or more, from the viewpoints of improving the discharge rate characteristics in a liquid-based lithium-ion secondary battery of a nonaqueous electrolyte storage device, further reducing the rate of change in electrode thickness with charge and discharge, and further improving the initial discharge capacity and rate characteristics in an all-solid-state battery. The D50 of the primary particles is preferably 4.5 μm or less, more preferably 3 μm or less, even more preferably 2 μm or less, even more preferably 1.8 μm or less, and particularly preferably 1.1 μm or less. The niobium-containing oxide powder may contain primary particles having a size of less than 0.4 μm, or may contain primary particles having a size of more than 4.5 μm.

[0032] <D90> In the case of a liquid-based lithium-ion secondary battery of a nonaqueous electrolyte storage device, the D90 of the primary particles of the niobium-containing oxide powder of the present invention not only improves the discharge rate characteristics but also reduces the rate of change in electrode thickness with charge and discharge, and further improves the initial discharge capacity and rate characteristics of an all-solid-state battery. From this viewpoint, the lower limit of the D90 of the primary particles is preferably 0.8 μm or more, more preferably 1.0 μm or more, and even more preferably 1.2 μm or more. The upper limit of the D90 of the primary particles is preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 6 μm or less. The D90 of the primary particles of the niobium-containing oxide powder refers to the particle size at which the cumulative volume frequency calculated from the volume fraction determined by laser diffraction / scattering particle size distribution measurement is 90% when calculated from the smallest particle size. The measurement method will be described in the Examples below.

[0033] <D10> In a liquid-based lithium-ion secondary battery of a nonaqueous electrolyte storage device, the D10 of the primary particles of the niobium-containing oxide powder of the present invention not only improves the discharge rate characteristics, but also reduces the rate of change in electrode thickness with charge and discharge, further improves cycle characteristics, and further improves the initial discharge capacity and rate characteristics of an all-solid-state battery. From this viewpoint, the lower limit of the D10 of the primary particles is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. The upper limit of the D10 of the primary particles is preferably 0.9 μm or less, more preferably 0.8 μm or less, even more preferably 0.7 μm or less, and even more preferably 0.6 μm or less. The D10 of the primary particles of the niobium-containing oxide powder refers to the particle size at which the cumulative volume frequency calculated from the volume fraction determined by laser diffraction / scattering particle size distribution measurement is 10% from the smallest particle size. The measurement method will be described in the Examples below.

[0034] Ti ２ Nb １４ O ３９The reason why a remarkable effect was observed by using a niobium-containing oxide in which part of Ti was substituted with three or more different elements is not clear, but is thought to be as follows. ２ Nb １４ O ３９ Negative electrode active materials such as niobium-containing oxide powders exhibit capacity by absorbing and releasing lithium ions via an electrolyte solution or solid electrolyte. Therefore, the contact area between the negative electrode active material and a non-aqueous electrolyte such as an electrolyte solution or solid electrolyte, and the diffusion of lithium ions and electrons within the active material particles are very important. Furthermore, in electrodes using niobium oxide active materials with low electronic conductivity, the volume change associated with charge and discharge of the active material in the negative electrode composite layer gradually causes the contact with the conductive additive to disappear, resulting in a significant decrease in cycle performance. The niobium oxide of the present invention is thought to have improved diffusion of lithium ions and electrons within the active material particles by partially substituting three or more different elements for Ti. Furthermore, Ti, in which a portion of all cationic sites are vacant, is a material that can be used in a wide range of applications. ２ Nb １４ O ３９ It is believed that the volume change during lithium intercalation and deintercalation is alleviated by substituting elements having different ionic radii, and the volume change in the electrode mixture layer is reduced. As a result, a portion of Ti is not substituted with a different element. ２ Nb １４ O ３９ and TiNb containing a trivalent metal, which exhibits a large volume change during charging and discharging, as described in Patent Document 1. ２ O ７ and Ti ２ Nb １０ O ２９ , and Ti in which a part of Ti is replaced with two or less different elements. ２ Nb １４ O ３９ It is believed that this resulted in battery characteristics that could not be achieved with conventional methods.

[0035] [Method for producing niobium-containing oxide powder of the present invention] Hereinafter, an example of the method for producing niobium-containing oxide powder of the present invention will be described, divided into a raw material preparation step and a firing step, but the method for producing niobium-containing oxide powder of the present invention is not limited thereto.

[0036] <Raw Material Preparation Process> First, the starting materials are mixed. In particular, in the case of niobium titanium composite oxide, an oxide or salt containing Ti and Nb is used as the starting material. Furthermore, when other additive elements are added to the niobium titanium composite oxide, in addition to an oxide containing Ti and Nb, an oxide or salt containing at least one element selected from the group consisting of Zr, Si, Ge, Sn, Al, Ga, Fe, Cr, Mg, Ca, Cu, Zn, Ta, V, Li, Na, and Bi is used as the starting material, and these are mixed in a stoichiometric ratio to obtain the target composition of the present invention. The salt used is preferably a salt that decomposes at a relatively low melting point to produce an oxide, such as a hydroxide salt, carbonate salt, or nitrate salt. Furthermore, to reduce the primary particle size, it is preferable to use a powder as the starting material having an average primary particle size of 2 μm or less, preferably 0.5 μm or less.

[0037] The method for mixing the raw materials is not particularly limited, and either wet mixing or dry mixing may be used. For example, a Henschel mixer, an ultrasonic disperser, a homomixer, a mortar, a ball mill, a centrifugal ball mill, a planetary ball mill, a vibrating ball mill, an attritor-type high-speed ball mill, a bead mill, a roll mill, etc. may be used.

[0038] <Firing Step> Next, the mixture obtained above is fired. Firing is preferably carried out at a temperature range of 500°C or higher and 1200°C or lower, more preferably 700°C or higher and 1150°C or lower, and even more preferably 900°C or higher and 1150°C or lower. By setting the firing temperature to 1200°C or lower, general-purpose equipment can be used. When firing the mixture for a short period of time, it is preferable to prepare the mixed powder constituting the mixture before firing so that the D95 value in the particle size distribution curve measured with a laser diffraction / scattering particle size distribution analyzer is 5 μm or lower. Here, D95 refers to the particle size at which the cumulative volume frequency calculated by volume fraction is 95% when calculated from the smallest particle size.

[0039] The calcination method is not particularly limited as long as it is a method that can perform calcination under the above conditions. Examples of calcination methods that can be used include a fixed-bed calcination furnace, a roller hearth calcination furnace, a mesh belt calcination furnace, a fluidized bed calcination furnace, and a rotary kiln calcination furnace. However, when performing efficient calcination in a short time, a roller hearth calcination furnace, a mesh belt calcination furnace, and a rotary kiln calcination furnace are preferred. In particular, a rotary kiln calcination furnace is a particularly preferred calcination furnace for producing the niobium-containing oxide powder of the present invention because it does not require a container to store the mixture, can perform calcination while continuously adding the mixture, and can provide a uniform thermal history to the calcined material, thereby allowing for the production of a homogeneous oxide.

[0040] <Surface Treatment Step> The niobium-containing oxide obtained above may be subjected to a surface treatment. The localized presence of at least one metal element selected from the group consisting of Mo and Ce or fibrous carbon such as single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes (MWCNT) on the surface of the particles constituting the niobium-containing oxide powder of the present invention makes it possible to form a dense negative electrode layer and impart excellent rate characteristics when used as a negative electrode material for a battery. In the firing step, a surface-treated niobium-containing oxide powder of the present invention can be produced by adding a compound containing at least one metal element selected from the group consisting of Mo and Ce (hereinafter, sometimes referred to as a treating agent) or fibrous carbon. However, it is more preferable to produce a surface-treated niobium-containing oxide powder of the present invention by the following surface treatment step. In particular, by employing the following surface treatment step, it is possible to appropriately and relatively simply make the surface of the niobium-containing oxide particles have at least one metal element selected from the group consisting of Mo and Ce or fibrous carbon present.

[0041] There is no particular limitation on the method for mixing the niobium-containing oxide powder as the base material with the compound containing at least one metal element selected from the group consisting of Mo and Ce or the fibrous carbon, and either wet mixing or dry mixing can be used. However, it is preferable to uniformly disperse the compound containing at least one metal element selected from the group consisting of Mo and Ce or the fibrous carbon on the surfaces of the particles constituting the niobium-containing oxide powder as the base material, and in this respect, wet mixing is preferred.

[0042] In the wet mixing, the treatment agent and the niobium-containing oxide powder of the base material are introduced into a water or alcohol solvent and mixed in a slurry state. As the alcohol solvent, those with a boiling point of 100°C or less, such as methanol, ethanol, and isopropyl alcohol, are preferred because they are easy to remove. Furthermore, from an industrial perspective, water solvents are preferred because they are easy to recover and dispose of.

[0043] The compound (treatment agent) containing at least one metal element selected from the group consisting of Mo and Ce is not particularly limited, and examples thereof include oxides, phosphates, hydroxides, sulfates, nitrates, fluorides, chlorides, organic compounds, and metal salt compounds such as ammonium salts and phosphates. Specific examples of Mo compounds include molybdenum oxide, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum boride, molybdophosphoric acid, molybdenum disilicide, molybdenum chloride, molybdenum sulfide, molybdenum silicic acid hydrate, sodium molybdenum oxide, molybdenum carbide, molybdenum acetate dimer, lithium molybdate, sodium molybdate, potassium molybdate, calcium molybdate, magnesium molybdate, manganese molybdate, and ammonium molybdate. Among these, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum chloride, molybdenum sulfide, and lithium molybdate are preferred. Examples of Ce compounds include cerium oxide, cerium hydroxide, cerium fluoride, cerium sulfate, cerium nitrate, cerium carbonate, cerium acetate, cerium oxalate, cerium chloride, cerium boride, and cerium phosphate, and among these, cerium sulfate and its hydrates are preferred.

[0044] The amount of the compound containing at least one metal element selected from the group consisting of Mo and Ce may be any amount as long as the amount of the at least one metal element selected from the group consisting of Mo and Ce in the niobium-containing oxide falls within the range of the present invention. It is sufficient to add the compound at a rate of 0.03% by mass or more, preferably 0.05% by mass or more, relative to the niobium-containing oxide powder of the substrate. It is also sufficient to add the compound at a rate of 12% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less, relative to the niobium-containing oxide powder of the substrate. The amount of fibrous carbon added may be any amount as long as the amount of fibrous carbon in the niobium-containing oxide falls within the range of the present invention. It is also sufficient to add the compound at a rate of 0.001% by mass or more, preferably 0.05% by mass or more, relative to the niobium-containing oxide powder of the substrate. It is also sufficient to add the compound at a rate of 2% by mass or less, preferably 1.5% by mass or less, and more preferably 1% by mass or less, relative to the niobium-containing oxide powder of the substrate.

[0045] When the niobium-containing oxide powder contains at least one metal element selected from the group consisting of Mo and Ce, it is preferable to perform heat treatment after the surface treatment. The heat treatment temperature is preferably a temperature at which the at least one metal element selected from the group consisting of Mo and Ce diffuses into at least the surface region of the niobium-containing oxide particles constituting the niobium-containing oxide powder of the base material, and at which a significant decrease in the specific surface area due to sintering of the niobium-containing oxide of the base material does not occur. The upper limit of the heat treatment temperature is preferably 700°C or less, more preferably 600°C or less. The lower limit of the heat treatment temperature is preferably 300°C or more, more preferably 400°C or more. The heat treatment time is preferably 0.1 to 8 hours, more preferably 0.5 to 5 hours. The temperature and time at which the at least one metal element selected from the group consisting of Mo and Ce diffuses into at least the surface region of the niobium-containing oxide powder of the base material differ in reactivity depending on the compound containing at least one metal element selected from the group consisting of Mo and Ce, and therefore can be appropriately set. The heating method in the heat treatment is not particularly limited. Usable heat treatment furnaces include fixed-bed firing furnaces, roller hearth firing furnaces, mesh belt firing furnaces, fluidized-bed firing furnaces, and rotary kiln firing furnaces. The atmosphere during the heat treatment may be either air or an inert atmosphere such as a nitrogen atmosphere. In particular, when a metal salt compound is used for the surface treatment, air is preferred because it facilitates the removal of anionic species from the particle surface.

[0046] It is preferable to subject the heat-treated niobium-containing oxide powder obtained as described above to a crushing treatment as necessary in order to set the specific surface area within the above range. The crushing treatment can be carried out using, for example, a ball mill, and the conditions for the crushing treatment are not particularly limited as long as they are conditions that allow the specific surface area to be within the above range. In addition to the crushing treatment, classification may also be carried out.

[0047] The niobium-containing oxide powder of the present invention may be granulated and heat-treated to form a powder containing secondary particles formed by aggregation of primary particles. Any method for granulation may be used as long as secondary particles can be formed, but a spray dryer is preferred because it can process a large amount of particles.

[0048] In order to reduce the moisture content of the niobium-containing oxide powder of the present invention, dew point control may be performed during the heat treatment process. If the heat-treated powder is exposed to the atmosphere, moisture from the atmosphere will be adsorbed by the powder. Therefore, it is preferable to handle the powder in a dew point-controlled environment during cooling in the heat treatment furnace and after the heat treatment. The heat-treated powder may be classified as needed to adjust the particles to the desired maximum particle size range. When dew point control is performed during the heat treatment process, it is preferable to seal the niobium-containing oxide powder of the present invention in an aluminum-laminated bag or the like and then place it in an environment outside of dew point control. Even under dew point control, pulverization of the heat-treated niobium-containing oxide powder makes it easier for moisture to be absorbed from the crushed surfaces, increasing the moisture content of the powder. Therefore, it is preferable not to pulverize the heat treatment. Regarding heat treatment conditions, the temperature and holding time within specific ranges significantly affect the secondary particle morphology and the surface treatment process. The heat treatment temperature is preferably 450°C or higher, and preferably less than 550°C. This is because a heat treatment temperature exceeding 550°C significantly reduces the specific surface area, significantly degrading battery performance, particularly rate characteristics. The holding time is preferably 1 hour or more, because if the holding time is short, the amount of moisture contained in the powder increases and it is thought that this will also affect the state of the particle surfaces.

[0049] [Active Material] The active material of the present invention contains the niobium-containing oxide powder of the present invention. It may contain one or more substances other than the niobium-containing oxide powder of the present invention. Examples of other substances include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers), tin and tin compounds, silicon and silicon compounds, and lithium-containing metal oxides. In particular, lithium-containing metal oxides include Li ４ Ti ５ O １２ Lithium titanate containing the above as its main component is exemplified.

[0050] [Electricity Storage Device] The electricity storage device of the present invention is a device that includes an electrode containing the active substance material of the present invention and stores and releases energy by utilizing intercalation and deintercalation of lithium ions into such an electrode, and examples thereof include a hybrid capacitor and a lithium battery.

[0051] [Hybrid Capacitor] The hybrid capacitor is a device that uses, as a positive electrode, an active material that generates capacitance by physical adsorption, such as activated carbon, similar to the electrode material of an electric double layer capacitor, an active material that generates capacitance by physical adsorption and intercalation / deintercalation, such as graphite, or an active material that generates capacitance by redox, such as a conductive polymer, and uses, as a negative electrode, the active material of the present invention. The active material of the present invention is usually used in the form of an electrode sheet for the hybrid capacitor.

[0052] [Lithium Battery] The lithium battery of the present invention is a general term for lithium primary batteries and lithium secondary batteries. In this specification, the term lithium secondary battery is used as a concept that also includes so-called lithium ion secondary batteries and all-solid-state lithium ion secondary batteries.

[0053] The lithium battery is composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, or a solid electrolyte, and the active material of the present invention can be used as an electrode material. The active material of the present invention is usually used in the form of an electrode sheet for the lithium battery. This active material may be used as either a positive electrode active material or a negative electrode active material, but the following description will be given of its use as a negative electrode active material.

[0054] <Negative Electrode> The negative electrode has a negative electrode layer containing a negative electrode active material (the active material of the present invention), a conductive agent, and a binder on one or both sides of a negative electrode current collector. This negative electrode layer is usually in the form of an electrode sheet. In the case of a negative electrode current collector that is porous or the like and has pores, the negative electrode layer contains the negative electrode active material (the active material of the present invention), a conductive agent, and a binder in the pores.

[0055] The conductive agent for the negative electrode is not particularly limited as long as it is an electron-conductive material that does not undergo chemical change. Examples thereof include graphites such as natural graphite (e.g., flake graphite) and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon nanotubes such as single-walled carbon nanotubes, multi-walled carbon nanotubes (graphite layers in a multi-layered concentric cylindrical shape) (non-fishbone-shaped), cup-stacked carbon nanotubes (fishbone-shaped), nodular carbon nanofibers (non-fishbone structure), and platelet-type carbon nanofibers (playing card-shaped).

[0056] The amount of conductive agent added varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, and therefore should be optimized. However, it is preferably 0.1% to 10% by mass, and more preferably 0.5% to 5% by mass, in the negative electrode layer. At less than 0.1% by mass, the conductivity of the negative electrode layer cannot be ensured. At more than 10% by mass, the active material ratio decreases, resulting in insufficient discharge capacity of the energy storage device per unit mass and unit volume of the negative electrode layer, making it unsuitable for achieving high capacity. The conductive agent may be added during electrode preparation or by coating the active material itself with the conductive agent. This is because coating with a conductive agent such as carbon fiber can further improve the conductivity of the negative electrode layer.

[0057] Examples of the binder for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethyl cellulose (CMC).

[0058] The amount of binder added varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, and therefore should be optimized, but is preferably 0.2% by mass to 15% by mass in the negative electrode layer. From the viewpoint of enhancing binding properties and ensuring the strength of the negative electrode layer, the amount is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. From the viewpoint of preventing a decrease in the active material ratio and a decrease in the discharge capacity of the power storage device per unit mass and unit volume of the negative electrode layer, the amount is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0059] Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, baked carbon, and those whose surfaces are coated with carbon, nickel, titanium, silver, etc. The surface of these materials may be oxidized, or the surface of the negative electrode current collector may be roughened by surface treatment.

[0060] The negative electrode can be produced by uniformly mixing a negative electrode active material (including the active material of the present invention), a conductive agent, and a binder in a solvent to form a paint, which is then applied to the negative electrode current collector, dried, and compressed. In the case of a negative electrode current collector that is porous or the like and has pores, the paint is pressurized into the pores of the current collector to fill the pores, or the current collector having pores is immersed in the paint to diffuse the pores, and then the paint is dried and compressed.

[0061] As a method for uniformly mixing the negative electrode active material (the active material of the present invention), the conductive agent, and the binder in a solvent to prepare a paint, for example, a kneader of the type in which a stirring rod revolves while rotating on its axis in a kneading container such as a planetary mixer, a twin-screw extrusion kneader, a planetary stirring degassing device, a bead mill, a high-speed rotary mixer, a powder suction continuous dissolution and dispersion device, etc. Alternatively, the manufacturing process may be divided into steps depending on the solid content concentration, and these devices may be used separately.

[0062] Uniform mixing of the negative electrode active material (the active material of the present invention), conductive agent, and binder in a solvent requires optimization, as it varies depending on the specific surface area of ​​the active material, the type of conductive agent, the type of binder, and the combination thereof. However, when using a kneader such as a planetary mixer in which the stirring rod revolves while rotating within a kneading vessel, a twin-screw extrusion kneader, or a planetary stirring and degassing device, it is preferable to divide the manufacturing process into steps based on the solid content concentration, knead the mixture at a high solid content concentration, and then gradually reduce the solid content concentration to adjust the viscosity of the paint. A high solid content concentration is preferably 60% to 90% by mass. A solid content of 60% by mass or more is preferred because it provides shear force, while a solid content of 90% by mass or less is preferred because it reduces the load on the device, and 80% by mass or less is even more preferred.

[0063] The mixing procedure is not particularly limited, but examples include a method of simultaneously mixing the negative electrode active material, the conductive agent, and the binder in a solvent, a method of previously mixing the conductive agent and the binder in a solvent and then adding and mixing the negative electrode active material, a method of previously preparing a negative electrode active material slurry, a conductive agent slurry, and a binder solution and then mixing them, etc. Among these, in order to achieve uniform dispersion, a method of previously mixing the conductive agent and the binder in a solvent and then adding and mixing the negative electrode active material, and a method of previously preparing a negative electrode active material slurry, a conductive agent slurry, and a binder solution and then mixing them are preferred.

[0064] As the solvent, an organic solvent can be used, and examples of the organic solvent include aprotic organic solvents such as 1-methyl-2-pyrrolidone, dimethylacetamide, and dimethylformamide, used alone or in combination of two or more kinds, and preferably 1-methyl-2-pyrrolidone.

[0065] When an organic solvent is used as the solvent, it is preferable to dissolve the binder in the organic solvent before use.

[0066] <Positive Electrode> The positive electrode has a positive electrode layer containing a positive electrode active material, a conductive agent, and a binder on one or both sides of a positive electrode current collector.

[0067] As the positive electrode active material, a material capable of absorbing and releasing lithium is used, and examples of the active material include composite metal oxides containing cobalt, manganese, and nickel with lithium, and lithium-containing olivine-type phosphates. These positive electrode active materials can be used alone or in combination of two or more. Examples of such composite metal oxides include LiCoO ２ , LiMn ２ O ４ , LiNiO ２ , LiCo １－ｘ Ni ｘ O ２ (0.01<x<1), LiCo １／３ Ni １／３ Mn １／３ O ２ , LiNi １／２ Mn ３／２ O ４ These lithium composite oxides may be partially substituted with other elements, such as by substituting a portion of the cobalt, manganese, or nickel with at least one element such as B, Nb, Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, or La, or by substituting a portion of the O with S or F, or by coating with a compound containing these other elements. Examples of lithium-containing olivine-type phosphates include LiFePO ４ , LiCoPO ４ , LiNiPO ４ , LiMnPO ４ , LiFe １－ｘ MxPO ４ (M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, and x is 0≦x≦0.5), etc.

[0068] The conductive agent and binder for the positive electrode may be the same as those for the negative electrode. Examples of the positive electrode current collector include aluminum, stainless steel, nickel, titanium, baked carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The surface of these materials may be oxidized, or the positive electrode current collector surface may be roughened by surface treatment.

[0069] <Non-aqueous electrolyte> The non-aqueous electrolyte is a solution of an electrolyte salt dissolved in a non-aqueous solvent. There are no particular limitations on the non-aqueous electrolyte, and various types can be used.

[0070] The electrolyte salt used is one that dissolves in a non-aqueous electrolyte, such as LiPF ６ , LiBF ４ , LiPO ２ F ２ , LiN(SO ２ F) ２ , LiClO ４ Inorganic lithium salts such as LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiCF ３ SO ３ , LiC(SO ２ CF ３ ) ３ , LiPF ４ (CF ３ ) ２ , LiPF ３ (C ２ F ５ ) ３ , LiPF ３ (CF ３ ) ３ , LiPF ３ (iso-C ３ F ７ ) ３ , LiPF ５ (iso-C ３ F ７ ) and lithium salts containing chain-like fluorinated alkyl groups such as (CF ２ ) ２ (SO ２ ) ２ NLi, (CF ２ ) ３ (SO ２ ) ２Examples of the electrolyte salt include lithium salts containing a cyclic fluorinated alkylene chain, such as NLi, and lithium salts having an oxalate complex as the anion, such as lithium bis[oxalate-O,O']borate and lithium difluoro[oxalate-O,O']borate. Among these, a particularly preferred electrolyte salt is LiPF ６ , LiBF ４ , LiPO ２ F ２ , and LiN(SO ２ F) ２ and the most preferred electrolyte salt is LiPF ６ These electrolyte salts may be used singly or in combination of two or more.

[0071] The concentration of all of these electrolyte salts dissolved in the nonaqueous solvent is usually preferably 0.3 M or more, more preferably 0.5 M or more, and even more preferably 0.7 M or more. The upper limit is preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

[0072] On the other hand, examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and S═O bond-containing compounds, and the non-aqueous solvent preferably contains a cyclic carbonate. Note that the term "chain ester" is used as a concept including chain carbonates and chain carboxylic acid esters.

[0073] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans- or cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter, both are collectively referred to as "DFEC"), vinylene carbonate (VC), vinylethylene carbonate (VEC), and 4-ethynyl-1,3-dioxola Examples of suitable cyclic carbonates include one or more selected from EC, PC, 1,2-butylene carbonate, 2,3-butylene carbonate, FEC, and EEC, and more preferably from the viewpoint of improving the rate characteristics of the electricity storage device and suppressing the amount of gas generated during high-temperature operation. Furthermore, one or more cyclic carbonates having an alkylene chain selected from propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate are even more preferred.

[0074] In particular, the concentration of the total electrolyte salt is 0.5M to 2.0M, and the electrolyte salt contains at least LiPF ６ and further comprising 0.001M to 1M LiBF ４ , LiPO ２ F ２ , and LiN(SO ２ F) ２ It is preferable to use a non-aqueous electrolyte containing at least one lithium salt selected from the group consisting of LiPF ６ When the proportion of lithium salts other than the lithium salts in the non-aqueous solvent is 0.001 M or more, the effect of improving the rate characteristics of the electricity storage device and suppressing the amount of gas generation during high-temperature operation is likely to be exerted, and when the proportion is 1.0 M or less, there is little concern that the effect of improving the rate characteristics of the electricity storage device and suppressing the amount of gas generation during high-temperature operation will be reduced, which is preferable.

[0075] In order to achieve suitable physical properties, the non-aqueous solvents are preferably used in combination, such as a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate, a chain carbonate and a lactone, a combination of a cyclic carbonate, a chain carbonate and an ether, a combination of a cyclic carbonate, a chain carbonate and a chain ester, a combination of a cyclic carbonate, a chain carbonate and a nitrile, or a combination of a cyclic carbonate, a chain carbonate and an S═O bond-containing compound.

[0076] Suitable examples of the chain ester include one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate; one or more symmetric chain carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate; pivalic acid esters such as methyl pivalate, ethyl pivalate, and propyl pivalate; and one or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

[0077] <Structure of Lithium Battery> The structure of the lithium battery of the present invention is not particularly limited, and examples include a coin battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and further, a cylindrical battery or a prismatic battery having a positive electrode, a negative electrode, and a roll-shaped separator.

[0078] The separator is an insulating thin film having high ion permeability and a predetermined mechanical strength. Examples include polyethylene, polypropylene, cellulose paper, glass fiber paper, polyethylene terephthalate, and polyimide microporous membranes. Multilayer membranes made by combining two or more types of materials can also be used. The surface of these separators can also be coated with resins such as PVDF, silicone resins, and rubber-based resins, or with particles of metal oxides such as aluminum oxide, silicon dioxide, and magnesium oxide.

[0079] [Negative Electrode Active Material Composition] The negative electrode active material composition of the present invention is a negative electrode active material composition containing the niobium-containing oxide powder of the present invention and an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table. The content of the inorganic solid electrolyte is not particularly limited, but may be 1% by mass or more, preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more in the active material composition. A higher content of the inorganic solid electrolyte is preferable because it facilitates contact between the niobium-containing oxide powder and the solid electrolyte. Furthermore, since a too high content of the inorganic solid electrolyte reduces the battery capacity of the all-solid-state secondary battery, the content is preferably 70% by mass or less, and more preferably 60% by mass or less. Generally, a low content of the inorganic solid electrolyte is preferable to increase the battery capacity of the all-solid-state secondary battery. However, a low content of the inorganic solid electrolyte makes it difficult to achieve contact between the niobium-containing oxide powder and the solid electrolyte. By using the niobium-containing oxide powder used in the negative electrode active material composition of the present invention, satisfactory contact between the niobium-containing oxide powder and the solid electrolyte can be achieved even when the content of the inorganic solid electrolyte is low. The niobium-containing oxide powder and inorganic solid electrolyte of the present invention may contain one or more substances other than the inorganic solid electrolyte. Examples of the other substances include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers), tin and tin compounds, silicon and silicon compounds, and lithium-containing metal oxides. In particular, lithium-containing metal oxides include Li ４ Ti ５ O １２ Lithium titanate containing the above as its main component is exemplified.

[0080] <Periodic Table> The periodic table in this specification refers to a long-period periodic table of elements based on the provisions of IUPAC (International Union of Pure and Applied Chemistry).

[0081] <Solid Electrolyte> A solid electrolyte is a solid electrolyte capable of transferring ions therein. In particular, inorganic solid electrolytes are solid in a steady state and are not usually dissociated or liberated into cations and anions. The inorganic solid electrolyte is not particularly limited as long as it has the conductivity of metal ions belonging to Group 1 of the periodic table, and generally has almost no electronic conductivity. Representative examples of inorganic solid electrolytes include (A) sulfide inorganic solid electrolytes, (B) oxide inorganic solid electrolytes, and (C) chloride inorganic solid electrolytes. In particular, sulfide inorganic solid electrolytes are preferably used because they have high ionic conductivity and can be formed into dense compacts with few grain boundaries simply by applying pressure at room temperature.

[0082] The sulfide inorganic solid electrolyte may be amorphous glass, crystallized glass, or a crystalline material. Specific examples of the sulfide inorganic solid electrolyte include, but are not limited to, the following combinations: Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -Al ２ S ３ , Li ２ S-GeS ２ , Li ２ S-Ga ２ S ３ , Li ２ S-GeS ２ -Ga ２ S ３ , Li ２ S-GeS ２ -P ２ S ５ , Li ２ S-GeS ２ -Sb ２ S ５ , Li ２ S-GeS ２ -Al ２ S ３, Li ２ S-SiS ２ , Li ２ S-Al ２ S ３ , Li ２ S-SiS ２ -Al ２ S ３ , Li ２ S-SiS ２ -P ２ S ５ , Li １０ GeP ２ S １２ .

[0083] Among the above combinations, Li ２ S-P ２ S ５ In addition, as the sulfide inorganic solid electrolyte other than the above, Li ６ P.S. ５ Cl and Li ６ P.S. ５ Argerodite-type solid electrolytes such as Br are also suitable.

[0084] The oxide inorganic solid electrolyte preferably contains oxygen atoms, has ion conductivity of a metal belonging to Group 1 of the periodic table, and has electronic insulation properties.

[0085] Examples of oxide inorganic solid electrolytes include Lithium super ionic conductor (LISICON)-type crystalline structures. ３．５ Zn ０．２５ GeO ４ , La having a perovskite crystal structure ０．５５ Li ０．３５ TiO ３ , LiTi having a NASICON (sodium super ionic conductor) type crystal structure ２ P ３ O １２ , Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ), lithium phosphate (Li ３ P.O. ４), LiPON, in which some of the oxygen in lithium phosphate is replaced with nitrogen, Li ３ BO ３ -Li ２ SO ４ , Li ２ Alumni ２ O ３ -P ２ O ５ , Li ２ O—SiO ２ , and Li ６ BaLa ２ Ta ２ O １２ Suitable examples include:

[0086] The chloride inorganic solid electrolyte is Li ３ ScCl ６ , LiAlCl ４ , Ln １－Ｘ A Ｘ OCl １－Ｘ (wherein Ln represents any rare earth element, A represents an alkaline earth metal, and X is 0<X<1) and the like are preferred.

[0087] The volume average particle size of the inorganic solid electrolyte is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.1 μm or more, and the upper limit is preferably 100 μm or less, more preferably 50 μm or less.

[0088] Next, the present invention will be explained in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples and includes various combinations that can be easily inferred from the gist of the invention.

[0089] (Liquid-type lithium-ion secondary battery) [Example 1-1] <Material preparation step> Nb ２ O ５ (average particle size 0.2 μm), anatase type TiO ２ (Specific surface area 10m ２ / g), Al ２ O ３and MgO were weighed out and mixed in a molar ratio of 79.5:19.7:0.3:0.6, in that order. This mixed powder was subjected to a calcination treatment at 1050°C for 12 hours. Powder X-ray diffraction measurement was performed on the obtained calcined powder sample under conditions of a sampling interval of 0.01° and a scan rate of 2° / min. No peaks derived from the starting materials were observed, confirming that the reaction had proceeded completely. From the results of crystal structure analysis of the synthesized sample and X-ray fluorescence analysis (XRF) using an X-ray fluorescence analyzer (manufactured by SII Technology Inc., product name "SPS5100"), it was confirmed that the synthesized sample was the target niobium-containing oxide (Ti １．７５ Nb １４．１５ Al ０．０５ Mg ０．０５ O ３９ ) The content of potassium (K) + iron (Fe) was 48 ppm. The niobium-containing oxide of Example 1-1 corresponds to an oxide in which part of Ti was substituted with three different elements, Nb, Al, and Mg.

[0090] <Crushing Treatment Step> Zirconia beads of φ2.0 mm were added to the obtained fired powder sample, and crushing treatment was carried out using a ball mill, thereby producing the niobium-containing oxide powder according to Example 1 in which the particle size distribution of the primary particles was adjusted.

[0091] [Examples 1-2 to 1-10, Reference Example 1-1] Niobium-containing oxide powders according to Examples 1-2 to 1-10 and Reference Example 1-1 were produced in the same manner as in Example 1-1, except that the raw materials and mixing ratios in the raw material preparation step were changed to obtain the composition formula shown in Table 1. Note that as the Si source, SiO ２ As a Zr source, ZrO ２ were used, respectively.

[0092] [Comparative Example 1-1] Nb ２ O ５ and anatase type TiO ２ were weighed and mixed so as to have a molar ratio of 7:2. This mixed powder was simply subjected to a firing treatment at 1100°C for 12 hours, and a niobium-containing oxide powder according to Comparative Example 1-1 was produced in which the crushing treatment step was not carried out as in Non-Patent Document 1.

[0093] [Comparative Example 1-2] Nb ２ O ５ and anatase type TiO ２ The same procedure as in Example 1-1 was carried out except that the molar ratio of the components was changed to 1:1 and the firing temperature was changed to 1000°C, thereby producing a niobium-containing oxide powder according to Comparative Example 1-2.

[0094] [Measurement of Powder Physical Properties] Various physical properties of the niobium-containing oxide powders of the Examples, Comparative Examples, and Reference Examples were measured as follows.

[0095] <Measurement of specific surface area> The specific surface area (m ２ / g) was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountec Co., Ltd., product name "Macsorb HM model-1208"), and nitrogen gas was used as the adsorption gas. 0.5 g of the measurement sample powder was weighed out and placed in a φ12 standard cell (HM1201-031), and after degassing under vacuum at 100°C for 0.5 hours, it was measured by the BET single-point method.

[0096] <Calculation of D10, D50, and D90: Dry Laser Diffraction Scattering Method> The D50 of the niobium-containing oxide powders of each Example, Comparative Example, and Reference Example was calculated from a particle size distribution curve measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of sample was placed in a container containing 50 ml of ion-exchanged water as a measurement solvent, and the measurement solvent was added until the transmittance of the slurry fell within the appropriate range (the range displayed by the green bar on the device), and particle size distribution measurement was performed. The D10, D50, and D90 of the powder were calculated from the obtained particle size distribution curve.

[0097] [Evaluation of Battery Characteristics] Coin-type batteries were fabricated using the niobium-containing oxide powders of each of the Examples, Comparative Examples, and Reference Examples, and their battery characteristics were evaluated. The evaluation results are shown in Table 1.

[0098] <Preparation of Negative Electrode Sheet> A negative electrode sheet was prepared as follows in a room maintained at a room temperature of 25°C and a dew point of -20°C or lower. The niobium-containing oxide powder of each Example and Comparative Example was removed from an aluminum laminate bag in a room maintained at a temperature of 25°C and a dew point of -20°C or lower. A coating material was prepared by mixing the removed niobium-containing oxide powder of each Example and Comparative Example as an active material at 85% by mass, acetylene black as a conductive agent at 10% by mass, and polyvinylidene fluoride as a binder at 5% by mass. The obtained coating material was applied to aluminum foil and dried to prepare a single-sided negative electrode sheet for use in a coin battery described below.

[0099] <Preparation of Electrolyte> The electrolyte used in the battery for characteristic evaluation was prepared as follows: In an argon glove box controlled at a temperature of 25°C and a dew point of -70°C or less, a non-aqueous solvent of ethylene carbonate:dimethyl carbonate = 1:2 (volume ratio) was prepared, and LiPF6 was added as an electrolyte salt to the non-aqueous solvent. ６ was dissolved to a concentration of 1 M to prepare an electrolyte solution for a coin battery, which will be described later.

[0100] <Preparation of Coin Battery> The negative electrode single-sided sheet prepared by the method described above was punched into a circle with a diameter of 14 mm, and ２ An evaluation electrode was prepared by pressing the electrode at a pressure of 1000 kJ / cm2 and then vacuum drying at 120° C. for 5 hours. The evaluation electrode was placed opposite metallic lithium (molded into a circle with a thickness of 0.5 mm and a diameter of 16 mm) via glass filters (one each of GA-100 manufactured by ADVANTEC and GF / C manufactured by Whatman), and the nonaqueous electrolyte prepared by the method described above in <Preparation of Electrolyte> was added and sealed to prepare a 2032-type coin battery.

[0101] <Initial Battery Characteristics: Initial Discharge Capacity, Initial Efficiency> A coin battery prepared by the method described above in <Preparation of Coin Battery> was placed in a thermostatic chamber at 25°C and charged at 0.2 mA / cm in the direction in which Li was absorbed into the evaluation electrode. ２ The battery was charged to 1 V at a current density of 0.05 mA / cm ２ After constant current and constant voltage charging was performed until the current density reached 0.2 mA / cm ２The battery was subjected to constant-current discharge at a current density of 0.1 V to 2 V. The initial discharge capacity (mAh / g) was determined by dividing the obtained discharge capacity (mAh) by the mass of the niobium-containing oxide, and the initial efficiency (%) was determined by dividing the discharge capacity (mAh) by the charge capacity (mAh).

[0102] <Measurement of 10C Discharge Rate Characteristics> The battery was charged to 1 V at a current equivalent to 10C of the initial discharge capacity, and then subjected to constant-current / constant-voltage charging at 1 V until the charging current reached a current density of 0.05C. This was followed by constant-current discharging at 10C to 3 V. The 10C rate discharge rate (%) was calculated by dividing the capacity obtained from the 10C constant-current discharge by the initial discharge capacity. If the niobium-containing oxide has a high 10C rate discharge rate, improved discharge rate characteristics of the energy storage device can be expected when used as an electrode material for the energy storage device. The "C" in 1C represents the current value during charging and discharging. For example, 1C refers to the current value at which the theoretical capacity can be fully discharged (or fully charged) in 1 / 1 hour, and 0.1C refers to the current value at which the theoretical capacity can be fully discharged (or fully charged) in 1 / 0.1 hour.

[0103] <Measurement of electrode thickness change rate due to charge and discharge> A coin battery prepared by the method described above in <Preparation of coin battery> was placed in a thermostatic chamber at 25°C and charged at 0.2 mA / cm ２ The battery was charged to 0.8 V at a current density of 0.05 mA / cm. ２ After constant current and constant voltage charging was performed until the current density reached 0.2 mA / cm ２ A constant current discharge was performed by discharging the battery to 2 V at a current density of 0.2 mA / cm. ２ The battery was charged to 0.8 V at a current density of 0.05 mA / cm. ２ After constant-current and constant-voltage charging, the coin battery was disassembled, and the charged negative electrode sheet was removed and measured for thickness. The thickness of the negative electrode sheet after charging to 0.8 V was divided by the thickness of the negative electrode sheet before fabrication of the coin battery to calculate the rate of change in electrode thickness due to charge and discharge.

[0104]

[0105] <Evaluation Results> It was found that the electrodes using the niobium-containing oxide powders of Examples 1-1 to 1-10, in which part of Ti was substituted with three or more metal elements, had a significantly reduced rate of change in electrode thickness during battery charge and discharge compared to the electrodes using the niobium-containing oxide powders of Comparative Examples 1-1, 1-2, and Reference Example 1-1, in which part of Ti was not substituted with three or more metal elements. ２ Nb １０ O ２９ The thickness change rate upon charging of the electrode using the niobium-containing oxide powder of the present invention was 13.4%, and it was found that the electrode using the niobium-containing oxide powder of the present invention had a smaller thickness change rate than the electrode described in Patent Document 2. This effect is not mentioned at all in Non-Patent Documents 1, 2, Patent Documents 1, and 2.

[0106] (All-Solid State Secondary Battery) [Example 2-1] In a glove box under an argon atmosphere, the niobium-containing oxide powder of Example 1-2 and the sulfide solid electrolyte Li ６ P.S. ５ Cl powder (volume average particle size measured using a laser diffraction / scattering particle size distribution analyzer: 1 μm) and a conductive agent, niobium-containing oxide powder: Li ６ P.S. ５ The materials were weighed out so as to have a mass ratio of Cl:conductive agent = 60:40:6, and stirred and mixed in an agate mortar and a planetary ball mill to obtain a negative electrode active material composition of Example 2-1. The obtained negative electrode active material composition was pressed (360 MPa) at room temperature for 10 minutes to produce pellets (molded bodies) with a diameter of 10 mm and a thickness of approximately 0.7 mm. A pellet-shaped electrode containing this negative electrode active material composition and a pellet-shaped solid electrolyte layer (Li ２ S:P ２ S ５ A lithium-indium alloy foil was laminated in this order as a counter electrode, and the laminate was sandwiched between stainless steel current collectors to prepare an all-solid-state secondary battery.

[0107] Example 2-2 An all-solid-state secondary battery according to Example 2-2 was produced in the same manner as in Example 2-1, except that the niobium-containing oxide was changed to that of Example 1-8.

[0108] Comparative Example 2-1 A negative electrode active material composition of Comparative Example 2-1 was obtained in the same manner as in Example 2-1, except that the niobium-containing oxide of Comparative Example 1-1 was used, and then an all-solid-state secondary battery was fabricated.

[0109] The battery characteristics of the all-solid-state secondary batteries according to Example 2-1, Example 2-2, and Comparative Example 2-1 were evaluated. The evaluation results are shown in Table 2.

[0110] <Measurement of initial discharge capacity and 1C charge / discharge rate characteristics> In a thermostatic chamber at 25 ° C., the all-solid-state secondary battery prepared by the above method was charged to 0.5 V at a current equivalent to 0.05 C of the theoretical capacity of the niobium-containing oxide, with charging in the direction in which Li was absorbed into the evaluation electrode. Further, constant current / constant voltage charging was performed in which charging was performed at 0.5 V until the charging current reached a current equivalent to 0.01 C. The initial charge capacity (mAh / g) was calculated by dividing the charge capacity (mAh) by the mass of the niobium-containing oxide. Then, constant current discharge was performed in which the battery was discharged to 2 V at a current equivalent to 0.05 C. The initial discharge capacity (mAh / g) was calculated by dividing the discharge capacity (mAh) by the mass of the niobium-containing oxide. Next, the battery was charged to 0.5 V at a current equivalent to 1 C of the theoretical capacity of the niobium-containing oxide, and the 1C charge capacity was calculated. The 1C rate charge rate (%) was calculated by dividing the 1C charge capacity by the initial charge capacity. Thereafter, the battery was discharged to 2 V at a current equivalent to 1 C of the theoretical capacity of the niobium-containing oxide, and the 1 C discharge capacity was determined. The 1 C discharge capacity was divided by the initial discharge capacity to calculate the 1 C rate discharge ratio (%).

[0111]

[0112] <Evaluation Results> It was found that the electrode using the niobium-containing oxide powder of the present invention also had excellent initial discharge capacity and 1C charge / discharge rate characteristics in an all-solid-state battery.

[0113] The niobium-containing oxide powder obtained by the present invention can improve cycle capacity retention and discharge rate characteristics, making it useful as an electrode active material for lithium-ion batteries. Furthermore, since it can improve rate characteristics in all-solid-state batteries, it is also useful as an electrode active material for all-solid-state secondary batteries. Energy storage devices using this niobium-containing oxide powder as an electrode active material are useful as secondary batteries for driving or backing up various devices, such as automobiles and electronic devices, and for storing power overnight in homes and offices. Providing electrode materials for lithium-ion batteries, such as nonaqueous electrolyte secondary batteries, to society can contribute to the achievement of Goal 12 (Ensure sustainable consumption and production patterns), Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable, and modern energy for all), and Goal 11 (Make cities and human settlements inclusive, safe, resilient, and sustainable) out of the 17 Sustainable Development Goals (SDGs) established by the United Nations.

Claims

1. A niobium-containing oxide powder satisfying the following formula (I): ａ Ti （２－ｐ－ｑ－ｒ） (M Ｖ （０．５＋ｖ） M ＩＩＩ （０．５－ｖ） ) ｐ (M Ｖ （０．６７＋ｗ） M ＩＩ （０．３３－ｗ） ) ｑ M ＩＶ ｒ Nb （１４－ｓ） M １ ｓ O （３９±ｔ） (I) [wherein A is at least one element selected from the group consisting of Li and Na; M １ is M Ｖ , (M ＩV （０．５＋ｗ） M ＶＩ （０．５－ｗ） ), (M ＶＩ （０．６７＋ｗ） M ＩＩＩ （０．３３－ｗ） ), and (M ＶＩ （０．７５＋ｗ） M ＩＩ （０．２５－ｗ） ), and M ＩＩ are each independently at least one divalent metal element, M ＩＩＩ are each independently at least one trivalent metal element, and M ＩＶ are each independently at least one tetravalent metal element; M Ｖ are each independently at least one pentavalent metal element; M ＶＩ are each independently at least one hexavalent metal element, and 0≦a≦6, −0.05≦v≦0.05, −0.05≦w≦0.05, 0≦p<2, 0≦q<2, 0≦r<2, 0<p+q+r<2, 0≦s<14, 0≦t≦1, with the proviso that at least two of p, q, and r are not 0.

2. The niobium-containing oxide powder according to claim 1, characterized in that the D50 of primary particles corresponding to a volume cumulative 50% in a volume-based particle size distribution of the niobium-containing oxide powder as measured by a laser diffraction scattering method is 0.25 μm or more and 4.5 μm or less.

3. The specific surface area of ​​the niobium-containing oxide powder is 2.3 m ２ / g or more 10m ２ The niobium-containing oxide powder according to claim 1, wherein the niobium content is 1 / g or less.

4. An electrode for a non-aqueous electrolyte electricity storage device, comprising the niobium-containing oxide powder according to any one of claims 1 to 3.

5. A negative electrode active material composition for a non-aqueous electrolyte storage device, comprising the niobium-containing oxide powder according to any one of claims 1 to 3 and an inorganic solid electrolyte.

6. A non-aqueous electrolyte electricity storage device comprising the electrode according to claim 4.

7. An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, wherein the negative electrode layer is a layer containing the negative electrode active material composition according to claim 5.

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