Titanium-containing oxide powder, a negative electrode active material composition using the same, and all-solid-state secondary battery

Abstract

A titanium-containing oxide powder which is mainly composed of a titanium-containing oxide represented by Li4Ti5O12 or Ti1-X / 2Nb2O7-X (wherein 0 ≤ X < 2), and which is characterized by containing particles of the titanium-containing oxide and a solvation ionic liquid that is composed of an Li salt and an organic solvent.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material composition using titanium-containing oxide powder and a all-solid-state secondary battery.

Background Art

[0002] In recent years, power storage devices, particularly lithium batteries, are widely used for small electronic devices such as mobile phones and notebook computers, electric vehicles, and power storage. In this specification, the term "lithium battery" is used as a concept including so-called lithium ion secondary batteries.

[0003] Currently commercially available lithium batteries mainly consist of a positive electrode and a negative electrode containing a material capable of occluding and releasing lithium, and a non-aqueous electrolyte composed of a lithium salt and a non-aqueous solvent. As the non-aqueous solvent, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC) are used. Since such a lithium battery uses an electrolyte containing a flammable organic solvent, it is likely to cause liquid leakage and may catch fire during a short circuit, so a safety device for suppressing the temperature rise during a short circuit or a structure for preventing a short circuit is required. Under such circumstances, all-solid-state secondary batteries using inorganic solid electrolytes have attracted attention. Since all-solid-state secondary batteries are composed entirely of a positive electrode, a negative electrode, and an electrolyte, there is a possibility of greatly improving the safety and reliability, which are problems of batteries using organic electrolytes. In addition, since the safety device can be simplified, the energy density can be increased, and thus application to electric vehicles and large-scale storage batteries is expected.

[0004] Unlike conventional lithium-ion secondary batteries that use an electrolyte, in all-solid-state secondary batteries, it is extremely important to form and continuously maintain a good solid-solid interface in order to achieve excellent ionic conductivity and long-term cycle characteristics. Lithium titanate is attracting attention as a way to maintain a good interface between the active material and the solid electrolyte. Because lithium titanate undergoes very little volume change during charging and discharging, it is expected that the interface between the active material and the solid electrolyte will be maintained for a long period of time during charging and discharging. Furthermore, lithium titanate is attracting attention because of its high safety due to its high reaction potential and the absence of lithium electrodeposition concerns. Patent Document 1 discloses an electrode using lithium titanate with a specific BET specific surface area and solid electrolyte particles smaller than the average particle size of lithium titanate, and reports that the contact between lithium titanate and solid electrolyte particles is better than conventional methods. Patent Document 2 discloses a solid-state battery using an electrode active material layer containing an active material, a sulfide solid electrolyte, and a solvated ionic liquid, and discloses that the ionic conductivity of the active material layer made using silicon, a conductive additive, and composition A (a composition obtained by mixing a sulfide solid electrolyte and a solvated ionic liquid in a specific ratio) is improved. Furthermore, in order to further increase the energy density, there is a movement to utilize niobium-titanium composite oxides, mainly niobium titanate represented by the general formula TiNb2O7, which has a high energy density of 380 mAh / g, as a negative electrode active material. Patent document 3 describes sulfide solid electrolytes and D 50 (μm) / BET(m 2 The general formula Ti ( / g) is between 0.005 and 5.0. 1±α Nb 2±β O 7±γ An electrode mixture containing the above is disclosed. According to Patent Document 3, it is disclosed that when applied as an electrode mixture for a solid-state battery, excellent charge and discharge efficiency can be obtained. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-243644 [Patent Document 2] Japanese Patent Publication No. 2019-121455 [Patent Document 3] International Publication No. 2021 / 049665 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0006] Although using the electrode described in Patent Document 1 resulted in improved contact between the lithium titanate powder and the solid electrolyte powder, improving the battery characteristics of the all-solid-state secondary battery, further improvement in charge rate characteristics was necessary. In particular, when lithium titanate particles with a relatively small average particle size and a large specific surface area were used, a decrease in battery characteristics was observed even with the configuration described in Patent Document 1. This is thought to be because a side reaction occurred between the active site on the lithium titanate surface and the solid electrolyte, creating a high-resistance layer. Also, regarding the relationship between BET specific surface area and D in Patent Document 3... 50 Although improvements in the battery characteristics of an all-solid-state secondary battery were observed by using an electrode mixture consisting of a titanium-niobium composite oxide and a sulfide solid electrolyte with a predetermined ratio, further improvements were needed regarding the charge rate characteristics. This is thought to be because, similar to lithium titanate, side reactions occurred between the active sites on the surface of the titanium-niobium composite oxide and the solid electrolyte, resulting in the formation of a high-resistance layer. To address the above problem, the present invention provides a titanium-containing oxide powder, a negative electrode active material composition, and an all-solid-state secondary battery that can form a negative electrode layer with excellent battery characteristics, particularly charge rate characteristics, in an all-solid-state battery by pre-treating the active sites on the surface of the titanium-containing oxide to effectively suppress the reaction with the solid electrolyte. [Means for solving the problem]

[0007] As a result of repeated studies to suppress side reactions between the active sites on the surface of a titanium-containing oxide and a solid electrolyte when using a titanium-containing oxide powder with high reactivity and a relatively large specific surface area, the inventors have found that by complexing a solvation ionic liquid composed of particles of a titanium-containing oxide, a Li salt, and an organic solvent, the active sites on the surface of the titanium-containing oxide can be inactivated, and the reaction with the solid electrolyte can be effectively suppressed, thus completing the present invention. By using a negative electrode active material composition containing the titanium-containing oxide powder and the solid electrolyte in a all-solid-state secondary battery, the initial discharge capacity can be increased and the charge rate characteristics can be improved. Although Patent Document 2 discloses that a solvation ionic liquid is contained in the negative electrode binder layer, it does not describe anything about suppressing the reaction between the titanium-containing oxide and the solid electrolyte at all. Further, when using graphite or silicon described in Patent Document 2 with a low reaction potential, reduction decomposition of the solvation ionic liquid occurs, and the excellent battery characteristics found in the present invention cannot be obtained. Furthermore, when using a composition in which a sulfide inorganic solid electrolyte and a solvation ionic liquid are premixed as described in Patent Document 2, even when a titanium-containing oxide is used as the negative electrode active material, the active sites on the surface of the titanium-containing oxide cannot be completely inactivated, and the excellent battery characteristics found in the present invention cannot be obtained.

[0008] The present invention relates to a titanium-containing oxide powder suitable as a negative electrode material for an all-solid-state secondary battery, a negative electrode active material composition using the titanium-containing oxide powder, and an all-solid-state secondary battery.

[0009] That is, the present invention provides the following (1) to (14).

[0010] (1) Li4Ti5O 12 or Ti 1-X / 2 Nb2O 7-X (0 ≦ X < 2), which is a titanium-containing oxide powder mainly composed of a titanium-containing oxide represented by The titanium-containing oxide powder contains particles of a titanium-containing oxide and a solvation ionic liquid. The titanium-containing oxide powder is characterized by comprising a Li salt and an organic solvent in the solvated ionic liquid.

[0011] (2) The titanium-containing oxide powder according to (1), wherein the volume-based particle size distribution of the titanium-containing oxide powder by laser diffraction scattering method has a D50 of 0.5 μm or more for primary particles corresponding to a volume accumulation of 50%.

[0012] (3) The specific surface area of ​​the titanium-containing oxide powder is 1 m² 2 / g or more 10m 2 Titanium-containing oxide powder as described in (1) or (2), which is less than or equal to / g.

[0013] (4) The titanium-containing oxide powder according to any one of (1) to (3) wherein Al is present on the particle surface of the titanium-containing oxide powder.

[0014] (5) The titanium-containing oxide powder according to any one of (1) to (4), wherein the Li salt is at least one Li salt selected from LiPF6, LiBF4, LiN(SO2F)2, LiN(SO2CF3)2, and LiN(SO2C2F5)2.

[0015] (6) The titanium-containing oxide powder according to any one of (1) to (4), wherein the Li salt is at least two Li salts selected from LiPF6, LiBF4, LiN(SO2F)2, LiN(SO2CF3)2, and LiN(SO2C2F5)2.

[0016] (7) The titanium-containing oxide powder according to any one of (1) to (4), wherein the Li salt comprises at least one Li salt selected from LiPF6, LiBF4, LiN(SO2F)2, LiN(SO2CF3)2, and LiN(SO2C2F5)2, and further comprises at least one Li salt selected from Li salts having an oxalic acid skeleton, Li salts having a phosphate skeleton, and Li salts having an S=O group.

[0017] (8) The titanium-containing oxide powder according to any one of (1) to (7), wherein the organic solvent is an ether compound.

[0018] (9) The titanium-containing oxide powder according to any one of (1) to (8), wherein the molar ratio of the Li salt to the organic solvent is 0.3 or more and 2.5 or less.

[0019] (10) The titanium-containing oxide powder according to any one of (1) to (9), wherein the ratio of the solvated ionic liquid to the titanium-containing oxide powder is 0.1% by mass or more and 30% by mass or less.

[0020] (11) A negative electrode active material composition comprising titanium-containing oxide powder and an inorganic solid electrolyte having conductivity of metal ions belonging to Group 1 of the periodic table, wherein the titanium-containing oxide powder comprises the titanium-containing oxide powder described in any one of (1) to (10).

[0021] (12) The negative electrode active material composition according to (11), wherein the inorganic solid electrolyte is a sulfide inorganic solid electrolyte.

[0022] (13) The negative electrode active material composition according to (11) or (12), wherein the content of the inorganic solid electrolyte is 1% by mass or more and 50% by mass or less in the active material composition.

[0023] (14) 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 described in any one of (11) to (13). [Effects of the Invention]

[0024] According to the present invention, side reactions between titanium-containing oxides and solid electrolytes can be effectively suppressed, resulting in a negative electrode active material composition and an all-solid-state secondary battery with excellent initial discharge capacity and charge rate characteristics. [Modes for carrying out the invention]

[0025] The present invention relates to a titanium-containing oxide powder suitable as a negative electrode material for an all-solid-state secondary battery, a negative electrode active material composition using the titanium-containing oxide powder, and an all-solid-state secondary battery.

[0026] [Titanium-containing oxide powder of the present invention] Li4Ti5O 12 or action 1-X / 2 Nb2O 7-X A titanium-containing oxide powder whose main component is a titanium-containing oxide represented by (0≦X<2), wherein the titanium-containing oxide powder contains titanium-containing oxide particles and a solvated ionic liquid consisting of a Li salt and an organic solvent.

[0027] [Li4Ti5O 12 [Lithium titanate powder, which is the main component of this substance] The lithium titanate powder of the present invention is Li4Ti5O 12 The main component is Li4Ti5O, within the range in which the effects of the present invention can be obtained. 12 It may contain crystalline and / or amorphous components other than Li4Ti5O. The main component is the diffraction peak measured by X-ray diffraction, which is Li4Ti5O. 12 This means that the proportion of the main peak intensity is 90% or more. The lithium titanate powder of the present invention is Li4Ti5O 12 The intensity ratio of the main peak is preferably 92% or higher, and more preferably 95% or higher. Li4Ti5O 12 Other components include the sum of the intensity of the main peak due to the crystalline component and the maximum intensity of the halo pattern due to the amorphous component. In particular, the lithium titanate powder of the present invention, depending on the raw materials and synthesis conditions during its synthesis, can be anatase-type titanium dioxide, rutile-type titanium dioxide, and lithium titanate with a different chemical formula, such as Li2TiO2. 3、 Li 0.6 Ti 3.4 O 8、 The lithium titanate powder of the present invention may contain the above-mentioned crystalline components. 12 Other crystalline components, especially Li 0.6 Ti3.4 The lower the proportion of O8 generation, the better the charging characteristics and charge / discharge capacity of the energy storage device. Among the diffraction peaks measured by X-ray diffraction, Li4Ti5O 12 When the intensity of the main peak of is set to 100, it is particularly preferable that the sum of the intensity of the main peak of anatase-type titanium dioxide, the intensity of the main peak of rutile-type titanium dioxide, and the intensity corresponding to the main peak of Li2TiO3 calculated by multiplying the peak intensity corresponding to the (-133) plane of Li2TiO3 by 100 / 80 is 5 or less. Here, Li4Ti5O 12 The main peak is Li4Ti5O in PDF card 00-049-0207 of ICDD (PDF2010). 12 This peak corresponds to the diffraction peak attributed to the (111) plane (2θ=18.33). The main peak of anatase-type titanium dioxide corresponds to the diffraction peak attributed to the (101) plane (2θ=25.42) in PDF card 01-070-6826. The main peak of rutile-type titanium dioxide corresponds to the diffraction peak attributed to the (110) plane (2θ=27.44) in PDF card 01-070-7347. The peak corresponding to the (-133) plane of Li2TiO3 corresponds to the diffraction peak attributed to the (-133) plane (2θ=43.58) of Li2TiO3 in PDF card 00-033-0831. Li 0.6 Ti 3.4 The main peak of O8 corresponds to the diffraction peak attributed to the (101) plane (2θ=19.98) in PDF card 01-070-2732. "ICDD" stands for International Centre for Diffraction Data, and "PDF" stands for Powder Diffraction File.

[0028] [General formula Ti 1-x / 2 Nb2O 7-x (Niobium titanium composite oxide powder represented by 0 ≤ X < 2) The niobium titanium composite oxide powder of the present invention has the general formula Ti 1-x / 2 Nb2O7-x It contains a niobium-titanium composite oxide represented by (0 ≦ X < 2). Specific examples of the compound include TiNb2O7, which is a niobium-titanium composite oxide capable of occluding and releasing Li ions and Na ions. TiNb2O7 is excellent in initial discharge capacity and is preferably contained in the niobium-titanium composite oxide powder. The niobium-titanium composite oxide may partially contain a titanium oxide phase (such as rutile-type TiO2, TiO, etc.) derived from the synthesis raw materials. In the case of the niobium-titanium composite oxide, the ratio of the number of moles of Nb to the number of moles of Ti (Nb / Ti ratio) is preferably in the range of 1.5 to 2.5, and more preferably in the range of 1.8 to 2.0. In this range, the electron conductivity of the niobium-titanium composite oxide is improved and the rate characteristics are excellent.

[0029] Regarding the niobium-titanium composite oxide of the present invention, there is no limitation on the crystal system, but it is generally monoclinic. In the case of the monoclinic type, the aspect ratio tends to be large, but from the viewpoint of electrode density, it is preferably in the range of 1.0 to 4.0.

[0030] <Solvated ionic liquid> Li4Ti5O of the present invention 12 or Ti 1-x / 2 Nb2O 7-x The titanium-containing oxide powder mainly composed of a titanium-containing oxide represented by (0 ≦ X < 2) is characterized by containing particles of the titanium-containing oxide constituting the titanium-containing oxide powder and a solvated ionic liquid. The solvated ionic liquid of the present invention is composed of a Li salt and an organic solvent, inactivates the active sites on the surface of the titanium-containing oxide particles, and effectively suppresses the reaction with the solid electrolyte. The solvated ionic liquid may be liquid at -30°C.

[0031] As the first Li salt contained in the solvated ionic liquid of the present invention, one selected from the group consisting of LiPF6, LiBF4, LiN(SO2F)2 [LFSI], LiN(SO2CF3)2 [LTFSI], and LiN(SO2C2F5)2 is preferable, or two or more kinds may be combined. Among them, it is preferable to use LTFSI and LFSI.

[0032] Furthermore, the solvated ionic liquid of the present invention preferably contains a second Li salt to further enhance the charge rate characteristics. The second Li salt is more preferably one or more Li salts selected from the group consisting of Li salts having an oxalic acid skeleton, Li salts having a phosphate skeleton, and Li salts having an S=O group (excluding LTFSI and LFSI). The solvated ionic liquid of the present invention may contain both the first Li salt and the second Li salt.

[0033] Suitable Li salts having an oxalic acid skeleton included in the solvated ionic liquid of the present invention include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoro(oxalato)phosphate (LiTFOP), and lithium difluorobis(oxalato)phosphate (LiDFOP), with LiBOB, LiDFOB, and LiDFOP being particularly preferred.

[0034] Suitable examples of Li salts having a phosphate skeleton and Li salts having an S=O group included in the solvated ionic liquid of the present invention include lithium difluorophosphate (LPF), lithium fluorophosphate (Li2PO3F), lithium fluorosulfate (FSO3Li), lithium methyl sulfate (LMS), lithium ethyl sulfate (LES), lithium 2,2,2-trifluoroethyl sulfate (LFES), lithium trifluoro((methanesulfonyl)oxy)borate (LiTFMSB), and lithium pentafluoro((methanesulfonyl)oxy)phosphate (LiPFMSP). Among these, LPF, LMS, LES, FSO3Li, and LiTFMSB are preferred, and LMS and LES are even more preferred.

[0035] When the first Li salt and the second Li salt are included, it is preferable that the molar ratio of the first Li salt to the second Li salt is 99.5:0.5 to 80:20, as this can further improve the charge rate characteristics. It is even more preferable that the molar ratio of the first Li salt to the second Li salt is 99.3:0.7 to 85:15, even more preferable that it is 99:1 to 90:10, and particularly preferable that it is 99:1 to 97:3.

[0036] <organic solvents> Suitable organic solvents for the solvated ionic liquid of the present invention include cyclic carbonates, lactones, and chain ether compounds. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and vinylethylene carbonate (VEC), while an example of a lactone is gamma-butyl lactone (GBL). The chain ether compound is preferably a chain ether compound having two or more carbon atoms and a methoxy group, more preferably a chain ether compound having two or more methoxy groups, and even more preferably a chain ether compound containing four or more carbon atoms, ten or more hydrogen atoms, and two or more oxygen atoms. Specific examples of linear ether compounds include one or more selected from alkylene glycol dimethyl ether and dimethoxyethane. In addition, triethylene glycol groups and tetraethylene glycol groups are preferred as alkylene glycol groups in alkylene glycol dimethyl ether. Particularly preferred examples of chain-like ether compounds include one or more selected from triethylene glycol dimethyl ether (same as triglyme), tetraethylene glycol dimethyl ether (same as tetraglyme TetraG), and dimethoxyethane.

[0037] <[Li salt / organic solvent] molar ratio> In the solvated ionic liquid of the present invention, since the organic solvent needs to be completely coordinated with the Li salt, the molar ratio of the total Li salt to the organic solvent [total Li salt / organic solvent] is preferably 0.3 or more and 2.5 or less. A molar ratio of 0.3 or more is desirable because it prevents an excess of organic solvent relative to lithium, thus preventing a decrease in charge rate characteristics. When the organic solvent is dimethoxyethane, the molar ratio is preferably 0.4 or more and more preferably 0.5 or more. Furthermore, the upper limit is preferably 1.8 or less and more preferably 1.5 or less. When the organic solvent is an alkylene glycol dimethyl ether such as triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether, the molar ratio is preferably 0.7 or higher, more preferably 0.75 or higher. Furthermore, the upper limit is preferably 2.2 or lower, more preferably 2.0 or lower.

[0038] In the titanium oxide powder of the present invention, the content of the solvated ionic liquid may be 0.05% by mass or more and 30% by mass or less, based on 100% by mass of the titanium oxide. If the content is 0.05% by mass or more, the active sites on the particle surface of the titanium oxide can be deactivated, and the rate characteristics can be appropriately improved. If the content is 30% by mass or less, the shape of the powder can be maintained even if the solvated ionic liquid is included. The content is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 3% by mass or more, and particularly preferably 5% by mass or more, based on 100% by mass of the titanium oxide. Furthermore, the upper limit is preferably 27% by mass or less, and more preferably 25% by mass or less.

[0039] <Specific surface area> The specific surface area of ​​the titanium-containing oxide powder of the present invention refers to the adsorption area per unit mass when nitrogen is used as the adsorption gas. The measurement method will be explained in the examples described later.

[0040] In the titanium-containing oxide, which is the main component of the titanium-containing oxide powder of the present invention, the specific surface area is 1 m². 2 / g or more 10m 2If it is below / g, a titanium-containing oxide powder excellent in initial discharge capacity and charge rate characteristics can be obtained. Preferably, 2m 2 / g or more and 9m 2 / g or less, more preferably 4m 2 / g or more and 8.5m 2 / g or less.

[0041] <Content of Al> Since the titanium-containing oxide powder of the present invention can further enhance the charge rate characteristics, Al may be contained on the surface of titanium-containing oxide particles which are the main component of the titanium-containing oxide. Containing Al means that Al is detected by a known analyzer such as X-ray fluorescence analysis (XRF) or inductively coupled plasma atomic emission spectrometry (ICP-AES) of the titanium-containing oxide powder of the present invention. The lower limit of the detection amount by inductively coupled plasma atomic emission spectrometry is usually 0.001% by mass.

[0042] <Content ratio of Al> When Al is contained on the surface of titanium-containing oxide particles, the content ratio of Al in the titanium-containing oxide powder determined by X-ray fluorescence analysis (XRF) in the titanium-containing oxide powder is 0.01% by mass or more and 5% by mass or less in terms of the content of Al. If the content ratio of Al is within this range, a titanium-containing oxide powder for the negative electrode of an all-solid-state secondary battery excellent in charge rate characteristics can be obtained. The content ratio of Al is preferably 0.01% by mass or more and 2% by mass or less, more preferably 0.01% by mass or more and 0.8% by mass or less, still more preferably 0.1% by mass or more and 0.6% by mass or less, and even more preferably 0.1% by mass or more and 0.4% by mass or less. The content ratio represents the ratio of the mass of Al contained to the mass of the entire titanium-containing oxide powder.

[0043] Furthermore, in the titanium-containing oxide powder of the present invention, it is sufficient that Al is present on the surface of the titanium-containing oxide particles constituting the titanium-containing oxide powder, and it is preferable that more Al is contained on the surface than inside the primary particles of the titanium-containing oxide contained in the titanium-containing oxide powder. Specifically, in cross-sectional analysis of the primary particles of the titanium-containing oxide using a scanning transmission electron microscope, if the atomic concentration of Al at a depth of 1 nm from the surface of the primary particles of the titanium-containing oxide, measured by energy-dispersive X-ray spectroscopy, is C1 (atm%) and the atomic concentration of Al at a depth of 100 nm from the surface of the primary particles of the titanium-containing oxide is C2 (atm%), then it is preferable that the following formula (I) is satisfied, and it is more preferable that the following formula (II) is satisfied. C1>C2 (I) C1 / C2≧5 (II)

[0044] In titanium-containing oxide powder, it is preferable that no Al is detected at a depth of 100 nm from the surface of the primary titanium-containing oxide particles, which are the main component of the titanium-containing oxide powder, as measured by energy-dispersive X-ray spectroscopy in cross-sectional analysis of the primary titanium-containing oxide particles using a scanning transmission electron microscope. It is preferable that Al is fixed to the surface of the primary particles in a chemically bonded state. When Al is present in this state, a dense negative electrode layer with few voids can be obtained, resulting in an all-solid-state secondary battery with excellent initial discharge capacity and charge rate characteristics. The lower limit of the detection amount in measurement by energy-dispersive X-ray spectroscopy varies depending on the element and state being measured, but is usually 0.5 atm%. Therefore, Al may be detected in a range of 0.5 atm% or less at a depth of about 100 nm.

[0045] <d50> In the present invention, D50 of the titanium-containing oxide powder refers to the particle size at which the cumulative volume frequency calculated using the volume fraction determined by laser diffraction / scattering particle size distribution measurement, which is an indicator of the median volume particle size, accumulates to 50% when calculated from the smallest particle size. The measurement method will be explained in the examples described later.

[0046] In the titanium-containing oxide powder of the present invention, the primary particle D50 is 0.5 μm or larger, preferably 0.55 μm or larger, and more preferably 0.6 μm or larger, from the viewpoint of initial discharge capacity, charge rate characteristics, and improvement of the density of the negative electrode layer. It is also 5 μm or smaller, preferably 4.5 μm or smaller, and more preferably 4 μm or smaller. Furthermore, the titanium-containing oxide powder may contain a cumulative volume frequency of primary particles with a primary particle diameter of less than 0.5 μm in the range of 10% to 50%, a cumulative volume frequency of primary particles with a primary particle diameter of less than 0.55 μm in the range of 10% to 55%, and a cumulative volume frequency of primary particles with a primary particle diameter of less than 0.6 μm in the range of 10% to 60%. Furthermore, the cumulative volume frequency of primary particles larger than 5 μm may be included in the range of 50% to 90%, the cumulative volume frequency of primary particles larger than 4.5 μm may be included in the range of 45% to 90%, and the cumulative volume frequency of primary particles larger than 4 μm may be included in the range of 40% to 90%.

[0047] [Li4Ti5O of ​​the present invention] 12 [Method for producing lithium titanate powder with as the main component] Below, an example of a method for producing lithium titanate powder according to the present invention will be described, divided into a raw material preparation step, a calcination step, a surface treatment step, and a mixing step with a solvated ionic liquid. However, the method for producing lithium titanate powder according to the present invention is not limited thereto.

[0048] <Preparation process of raw materials> The lithium titanate powder of the present invention consists of a titanium raw material and a lithium raw material. As the titanium raw material, titanium compounds such as anatase-type titanium dioxide and rutile-type titanium dioxide are used. It is preferable that the raw material reacts easily with the lithium raw material in a short time, and from this viewpoint, anatase-type titanium dioxide is preferred. In order to sufficiently react the raw materials with short firing time, the D50 of the titanium raw material is preferably 5 μm or less.

[0049] Lithium compounds such as lithium hydroxide monohydrate, lithium oxide, lithium bicarbonate, and lithium carbonate are used as lithium raw materials.

[0050] Furthermore, the charging ratio of titanium and lithium raw materials should be such that the atomic ratio of Li to Ti (Li / Ti) is 0.81 or higher, and preferably 0.83 or higher. This is because a low charging ratio may promote the generation of specific impurity phases in the lithium titanate powder obtained after firing, which could adversely affect battery characteristics.

[0051] In the present invention, when firing a mixture consisting of the above raw materials in a short time, it is preferable to prepare the mixed powder constituting the mixture before firing so that D95 in the particle size distribution curve measured by a laser diffraction / scattering particle size distribution analyzer is 5 μm or less. Here, D95 is the particle size at which the cumulative volume frequency calculated by volume fraction, when accumulated from the smallest particle size, accounts for 95%.

[0052] The following methods can be used to prepare the mixture. The first method involves mixing the raw materials and then grinding them simultaneously. The second method involves grinding each raw material until the D95 is 5 μm or less, and then mixing them, or mixing them while lightly grinding them. The third method involves producing powders consisting of fine particles from each raw material by methods such as crystallization, classifying them as needed, and then mixing them, or mixing them while lightly grinding them. Among these, the first method, in which the raw materials are mixed and ground simultaneously, is industrially advantageous because it involves fewer steps. A conductive agent may also be added at the same time.

[0053] In any of the first to third methods, there are no particular restrictions on the method of mixing the raw materials; either wet mixing or dry mixing is acceptable. For example, a Henschel mixer, ultrasonic dispersion device, homomixer, mortar and pestle, ball mill, centrifugal ball mill, planetary ball mill, vibrating ball mill, Attritor-type high-speed ball mill, bead mill, roll mill, etc., can be used.

[0054] If the mixture obtained by any of the first to third methods is a mixed powder, it can be used as is for the next firing step. If the mixture is a mixed slurry consisting of mixed powder, the mixed slurry can be dried using a rotary evaporator or the like before being used for the next firing step. If the firing is performed using a rotary kiln, the mixed slurry can be placed directly into the furnace.

[0055] <Firing Process> Next, the resulting mixture is calcined. From the viewpoint of reducing the proportion of specific impurity phases, increasing the crystallinity of lithium titanate, and increasing the crystallite size and primary particle size of the powder, the maximum calcination temperature is 800°C or higher, preferably 810°C or higher. From the viewpoint of increasing the specific surface area of ​​the powder obtained by calcination and reducing the amount of impurities originating from the furnace tube, the maximum calcination temperature is 1100°C or lower, preferably 1000°C or lower, and more preferably 960°C or lower. Similarly, from the above two viewpoints, the holding time at the maximum calcination temperature is 2 minutes to 60 minutes, preferably 5 minutes to 45 minutes, and more preferably 5 minutes to 35 minutes. When the maximum calcination temperature is high, it is preferable to select a shorter holding time. During the heating process of calcination, from the viewpoint of increasing the crystallite size obtained by calcination, it is good practice to shorten the residence time at 700°C to 800°C, preferably within 15 minutes.

[0056] The firing method is not particularly limited as long as it can be fired under the aforementioned conditions. Usable firing methods include fixed-bed furnaces, roller hearth furnaces, mesh belt furnaces, fluidized-bed furnaces, and rotary kilns. However, for efficient firing in a short time, roller hearth furnaces, mesh belt furnaces, and rotary kilns are preferred. When using a roller hearth furnace or a mesh belt furnace in which the mixture is placed in a sagger for firing, it is preferable to place a small amount of mixture in the sagger in order to ensure uniformity of the temperature distribution of the mixture during firing and to maintain consistent quality of the resulting lithium titanate powder.

[0057] A rotary kiln-type firing furnace is particularly preferred for producing the lithium titanate powder of the present invention because it does not require a container for holding the mixture, allows for continuous loading of the mixture during firing, and provides a uniform thermal history to the fired material, resulting in a homogeneous lithium titanate powder.

[0058] The atmosphere during firing is not particularly limited, regardless of the type of firing furnace, as long as it is an atmosphere that can remove the detached moisture and carbon dioxide. Usually, an air atmosphere using compressed air is used, but an oxygen, nitrogen, or hydrogen atmosphere is also acceptable.

[0059] Although the lithium titanate powder after calcination shows slight aggregation, it does not require grinding that would destroy the particles. Therefore, after calcination, it is sufficient to perform crushing or classification to break down the aggregation as needed. If only crushing to break down the aggregation is performed without grinding, the high crystallinity of the lithium titanate powder after calcination is maintained.

[0060] The lithium titanate powder obtained through the above process, before surface treatment (hereinafter sometimes referred to as the base lithium titanate powder; also hereinafter sometimes referred to as the base lithium titanate particles), is mixed with a treatment agent and preferably heat-treated.

[0061] <Surface treatment process> The lithium titanate powder of the present invention may be a lithium titanate powder containing Al, and the inclusion of Al can provide superior charge rate characteristics when applied as a negative electrode material for all-solid-state secondary batteries. The lithium titanate powder of the present invention can be produced by adding an Al-containing compound (hereinafter sometimes referred to as a treatment agent) in the firing process, but more preferably, the lithium titanate powder of the present invention can be produced by a surface treatment process such as the following.

[0062] Compounds containing Al (treatment agents) are not particularly limited, but examples include aluminum oxides, hydroxides, sulfate compounds, nitrate compounds, fluorides, organic compounds, and metal salt compounds containing aluminum. Specifically, examples of Al-containing compounds include aluminum acetate, aluminum fluoride, or aluminum sulfate.

[0063] The amount of Al-containing compound (treatment agent) to be added can be any amount as long as the Al content in the lithium titanate powder falls within the range described above, but it should be added in a proportion of 0.1% by mass or more relative to the base lithium titanate powder. Alternatively, it may be added in a proportion of 12% by mass or less relative to the base lithium titanate powder, preferably 10% by mass or less, and more preferably 8% by mass or less.

[0064] There are no particular restrictions on the method of mixing the lithium titanate powder base material with the Al-containing compound; either wet mixing or dry mixing can be used. However, it is preferable to uniformly disperse the Al-containing compound on the surface of the lithium titanate particles of the base material, and in this respect, wet mixing is preferred.

[0065] For dry mixing, for example, a paint mixer, Henschel mixer, ultrasonic dispersion device, homomixer, mortar and pestle, ball mill, centrifugal ball mill, planetary ball mill, vibrating ball mill, Attritor-type high-speed ball mill, bead mill, roll mill, etc. can be used.

[0066] For wet mixing, the treatment agent and the lithium titanate powder base material are added to water or an alcohol solvent and mixed in a slurry state. As for the alcohol solvent, methanol, ethanol, isopropyl alcohol, etc., which have a boiling point of 100°C or less are preferred because they are easy to remove. Furthermore, from an industrial standpoint, water is preferred because it is easy to recover and dispose of.

[0067] Regarding the amount of solvent, any amount that sufficiently wets the lithium titanate particles of the treatment agent and the substrate is acceptable. However, it is sufficient that the lithium titanate particles of the treatment agent and the substrate are uniformly dispersed in the solvent. For this reason, it is preferable that the amount of solvent dissolved in the solvent is 50% or more of the total amount of treatment agent added to the solvent. Since the amount of treatment agent dissolved in the solvent increases with temperature, it is preferable to mix the lithium titanate powder of the substrate and the treatment agent in the solvent while heating. Furthermore, heating also reduces the amount of solvent, so mixing while heating is an industrially suitable method. The mixing temperature is preferably 40°C to 100°C, and more preferably 60°C to 100°C.

[0068] In the case of wet mixing, depending on the heat treatment method, it is preferable to remove the solvent before the heat treatment performed after the mixing process. The solvent is preferably removed by evaporation to dryness. Methods for evaporation to dryness include heating and evaporating the slurry while stirring with a stirring blade, using a drying device that allows drying while stirring, such as a conical dryer, and using a spray dryer. If the heat treatment is performed using a rotary kiln, the mixed raw materials can be supplied to the furnace as a slurry.

[0069] It is preferable to perform a heat treatment after mixing the lithium titanate powder base material with the treatment agent. The heat treatment temperature should be such that Al diffuses into at least the surface region of the lithium titanate particles of the base material, without causing a significant reduction in the specific surface area due to sintering of the lithium titanate particles of the base material. The upper limit of the heat treatment temperature should be 700°C or lower, preferably 600°C or lower. The lower limit of the heat treatment temperature should be 300°C or higher, preferably 400°C or higher. The heat treatment time should be 0.1 hours to 8 hours, preferably 0.5 hours to 5 hours. The temperature and time at which Al diffuses into at least the surface region of the lithium titanate particles of the base material should be set appropriately, as the reactivity differs depending on the Al-containing compound.

[0070] The heating method used in heat treatment is not particularly limited. Suitable heat treatment furnaces include fixed-bed furnaces, roller hearth furnaces, mesh belt furnaces, fluidized-bed furnaces, and rotary kilns. The atmosphere during heat treatment can be either air or an inert atmosphere such as nitrogen.

[0071] The lithium titanate powder obtained after heat treatment as described above shows slight aggregation, but does not require grinding that would destroy the particles. Therefore, after heat treatment, it is sufficient to perform crushing or classification to break down the aggregation as needed.

[0072] The lithium titanate powder of the present invention may be mixed with a treatment agent in a surface treatment process, then granulated and heat-treated to produce a powder containing secondary particles formed by the aggregation of primary particles. Granulation can be performed by any method that produces secondary particles, but a spray dryer is preferred because it can process large quantities.

[0073] <Mixing process with solvated ionic liquid> The mixing with the solvated ionic liquid is not particularly limited. For example, preferred methods include adding a specific proportion of the solvated ionic liquid to the lithium titanate powder and mixing it using a planetary mill or the like, or adding a specific proportion of the solvated ionic liquid to a slurry containing lithium titanate powder and a dispersion medium, mixing it, and then distilling off the dispersion medium to compound the solvated ionic liquid with the lithium titanate powder.

[0074] After mixing the lithium titanate powder with the solvated ionic liquid, heat treatment may be performed. The upper limit of the heat treatment temperature should be 300°C or less, preferably 250°C or less. The lower limit of the heat treatment temperature should be 80°C or higher, preferably 100°C or higher. The heat treatment time should be 0.1 hours to 8 hours, preferably 0.5 hours to 5 hours. The temperature and time should be appropriately set depending on the type of solvated ionic liquid.

[0075] The lithium titanate mixed with the solvated ionic liquid obtained in this invention has solid properties that allow it to maintain its shape.

[0076] [General formula of the present invention] 1-x / 2 Nb2O 7-x [Method for producing niobium titanium composite oxide powder represented by (0≦X<2)] Below, an example of a method for producing the niobium-titanium composite oxide powder of the present invention will be described, divided into a raw material preparation step, a calcination step, a surface treatment step, and a mixing step with a solvated ionic liquid. However, the method for producing the niobium-titanium composite oxide powder of the present invention is not limited thereto.

[0077] <Preparation process of raw materials> First, the starting materials are mixed. In particular, in the case of niobium-titanium composite oxides, oxides or salts containing Ti and Nb are used as starting materials. Furthermore, when other additive elements are included in the niobium-titanium composite oxide, the salt used as the starting material is preferably a salt that decomposes at a relatively low melting point to produce oxides, such as a hydroxide salt, carbonate, or nitrate salt. In addition, in order to allow sufficient elemental diffusion to proceed in the calcination process described later, it is preferable to use a powder with an average particle size of 2 μm or less, preferably an average particle size of 0.5 μm or less, as the starting material.

[0078] There are no particular restrictions on the method of mixing the raw materials; either wet or dry mixing is acceptable. For example, a Henschel mixer, ultrasonic dispersion device, homomixer, mortar and pestle, ball mill, centrifugal ball mill, planetary ball mill, vibrating ball mill, Attritor-type high-speed ball mill, bead mill, roll mill, etc., can be used.

[0079] <Firing Process> Next, the mixture obtained above is calcined. The calcination is carried out at a temperature range of 500 to 1200°C, more preferably in the range of 700 to 1000°C. By performing the calcination at a temperature of 1000°C or lower, general-purpose equipment can be used. When calcining the mixture in a short time, it is preferable to prepare the mixed powder constituting the mixture before calcination so that the D95 in the particle size distribution curve measured by a laser diffraction / scattering particle size distribution analyzer is 5 μm or less. Here, D95 is the particle size at which the cumulative volume frequency calculated by volume fraction, when accumulated from the smallest particle size, accounts for 95%.

[0080] The firing method is not particularly limited as long as it can be fired under the aforementioned conditions. Usable firing methods include fixed-bed firing furnaces, roller hearth firing furnaces, mesh belt firing furnaces, fluidized bed firing furnaces, and rotary kiln firing furnaces. However, for efficient firing in a short time, roller hearth firing furnaces, mesh belt firing furnaces, and rotary kiln firing furnaces are preferred. In particular, rotary kiln firing furnaces are especially preferred for producing the niobium titanium composite oxide powder of the present invention because they do not require a container to hold the mixture, allow for continuous feeding of the mixture during firing, and provide a uniform thermal history to the fired material, resulting in a homogeneous oxide.

[0081] <Surface treatment process> The niobium titanium composite oxide powder of the present invention is the aforementioned Li4Ti5O 12 It can be manufactured using the same method as the surface treatment step in the manufacturing method for lithium titanate powder, which has as its main component.

[0082] <Mixing process with solvated ionic liquid> The niobium titanium composite oxide powder of the present invention is the aforementioned Li4Ti5O 12 It can be manufactured by the same method as the mixing step with the solvated ionic liquid in the method for producing lithium titanate powder, which has as its main component.

[0083] The niobium titanium composite oxide obtained in this invention, when mixed with the solvated ionic liquid, has solid properties that allow it to maintain its shape.

[0084] <Periodic table> The periodic table of this invention refers to the long-period periodic table of elements as defined by IUPAC (International Union of Pure and Applied Chemistry).

[0085] [Inorganic solid electrolyte] Inorganic solid electrolytes are solid electrolytes that are inorganic, and a solid electrolyte is a solid electrolyte that can move ions within itself. Since inorganic solid electrolytes are solid in a steady state, they do not usually dissociate or become liberated into cations and anions. Inorganic solid electrolytes are not particularly limited as long as they have conductivity to metal ions belonging to Group 1 of the periodic table, and generally have little to no electronic conductivity.

[0086] In the present invention, the inorganic solid electrolyte has conductivity of metal ions belonging to Group 1 of the periodic table. Typical examples of inorganic solid electrolytes include (A) sulfide inorganic solid electrolytes and (B) oxide inorganic solid electrolytes. In the present invention, sulfide inorganic solid electrolytes are preferably used because they have high ionic conductivity and a dense molded body with few grain boundaries can be formed by pressurization at room temperature alone.

[0087] (A) Sulfide inorganic solid electrolyte The sulfide inorganic solid electrolyte is preferably one that contains a sulfur atom (S), has conductivity of a metal ion belonging to Group 1 of the periodic table, and is also an electronic insulator. The sulfide inorganic solid electrolyte can be produced by reacting a metal sulfide belonging to Group 1 of the periodic table with at least one sulfide represented by the following general formula (III), and two or more sulfides represented by general formula (III) may be used in combination.

[0088] M x S y (III) (M represents one of P, Si, Ge, B, Al, Ga, or Sb, and x and y represent the numbers that give the stoichiometric ratio, depending on the type of M.)

[0089] The metal sulfide belonging to Group 1 of the periodic table is any of lithium sulfide, sodium sulfide, or potassium sulfide, with lithium sulfide or sodium sulfide being more preferred, and lithium sulfide being even more preferred.

[0090] The sulfide represented by general formula (III) is preferably one of P2S5, SiS2, GeS2, B2S3, Al2S3, Ga2S3, or Sb2S5, with P2S5 being particularly preferred.

[0091] The composition ratio of each element in the sulfide inorganic solid electrolyte produced as described above can be controlled by adjusting the blending amounts of the metal sulfides belonging to Group 1 of the periodic table, the sulfides represented by the general formula (III), and elemental sulfur.

[0092] The sulfide inorganic solid electrolyte of the present invention may be amorphous glass, crystallized glass, or a crystalline material.

[0093] The following combinations are preferred as sulfide inorganic solid electrolytes, but are not particularly limited. Li2S-P2S5, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S -GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li 10 GeP2S 12 .

[0094] Among the aforementioned combinations, LPS glass and LPS glass ceramics manufactured using a combination of Li2S-P2S5 are preferred.

[0095] The mixing ratio of the metal sulfide belonging to Group 1 of the periodic table and the sulfide represented by the general formula (III) is not particularly limited as long as it can be used as a solid electrolyte, but it is preferably 50:50 to 90:10 (molar ratio). If the molar ratio of the metal sulfide is 50 or more and 90 or less, the ionic conductivity can be sufficiently increased. The mixing ratio (molar ratio) is more preferably 60:40 to 80:20, and even more preferably 70:30 to 80:20.

[0096] The sulfide inorganic solid electrolyte may contain, in addition to metal sulfides belonging to Group 1 of the periodic table and sulfides represented by the general formula (III), at least one lithium halide selected from LiI, LiBr, LiCl, and LiF, or a Li salt such as lithium oxide or lithium phosphate, in order to increase ionic conductivity. However, the mixing ratio of the sulfide inorganic solid electrolyte and these Li salts is preferably 60:40 to 95:5 (molar ratio), and more preferably 80:20 to 95:5.

[0097] In addition to the above, other suitable sulfide inorganic solid electrolytes include algerodite-type solid electrolytes such as Li6PS5Cl and Li6PS5Br.

[0098] The methods for producing the sulfide inorganic solid electrolyte mentioned above include, but are not particularly limited to, solid-phase methods, sol-gel methods, mechanical milling methods, solution methods, and melt-quenching methods.

[0099] (B) Oxide inorganic solid electrolyte

[0100] The oxide inorganic solid electrolyte is preferably one that contains oxygen atoms, has metal ion conductivity belonging to Group 1 of the periodic table, and also has electronic insulating properties.

[0101] Examples of oxide inorganic solid electrolytes include Li, which has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 La, which has a perovskite crystal structure, is GeO4. 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li7La3Zr2O has a garnet-type crystal structure. 12 (LLZ), lithium phosphate (Li3PO4), LiPON (Lithium Phosphate with some of the oxygen replaced by nitrogen), Li3BO3-Li2SO4, Li2O-B2O3-P2O5, Li2O-SiO2, and Li6BaLa2Ta2O 12 These are some examples of preferred materials.

[0102] The volume-average particle size of the inorganic solid electrolyte is not particularly limited, but it should be 0.01 μm or larger, and preferably 0.1 μm or larger. The upper limit should be 100 μm or less, and preferably 50 μm or less. The volume-average particle size of the inorganic solid electrolyte can be measured using a laser diffraction / scattering particle size distribution analyzer.

[0103] <Negative electrode active material composition> The amount of inorganic solid electrolyte mixed in is not particularly limited, but it should be 1% by mass or more, preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more in the active material composition. A higher amount of inorganic solid electrolyte is preferable because it makes it easier to obtain contact between the titanium-containing oxide powder and the solid electrolyte. However, if the amount of inorganic solid electrolyte is too high, the battery capacity of the all-solid-state secondary battery will decrease, so it should be 70% by mass or less, and preferably 50% by mass or less. Normally, a lower amount of inorganic solid electrolyte is preferable to increase the battery capacity of the all-solid-state secondary battery, but if the amount is too low, it becomes difficult to obtain contact between the titanium-containing oxide powder and the solid electrolyte. By using the titanium-containing oxide powder used in the negative electrode active material composition of the present invention, satisfactory contact between the titanium-containing oxide powder and the solid electrolyte can be obtained even when the amount of inorganic solid electrolyte is low.

[0104] [Other contents] The negative electrode active material composition of the present invention may also contain a conductive agent and a binder, in addition to the titanium-containing oxide powder and the inorganic solid electrolyte.

[0105] The conductive agent for the negative electrode is not particularly limited as long as it is an electron-conducting material that does not undergo chemical changes. Examples include graphites such as natural graphite (flaky graphite, etc.) and artificial graphite; carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; single-phase carbon nanotubes, multi-walled carbon nanotubes (multi-walled concentric cylindrical graphite layer) (non-fishbone-shaped); cup-type carbon nanotubes (fishbone-shaped); segmented carbon nanofibers (non-fishbone structure); platelet-type carbon nanofibers (playing card-shaped); and other carbon nanotubes. Furthermore, graphites, carbon blacks, and carbon nanotubes may be mixed as appropriate. While not particularly limited, the specific surface area of ​​the carbon black is preferably 30 m². 2 / g~3000m 2 / g, and more preferably 50m 2 / g~2000m 2 The specific surface area of ​​graphites is preferably 30 m². 2 / g~600m 2 / g, and more preferably 50m 2 / g~500m 2 The ratio is / g. The aspect ratio of the carbon nanotubes is 2 to 150, preferably 2 to 100, and more preferably 2 to 50.

[0106] The amount of conductive agent to be added should be optimized as it varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents. However, it is sufficient for the negative electrode active material composition to contain 0.1% to 10% by mass, preferably 0.5% to 5% by mass. By setting the amount in the range of 0.1% to 10% by mass, the active material ratio can be made sufficient, thereby increasing the conductivity of the negative electrode layer while ensuring sufficient initial discharge capacity of the energy storage device per unit mass and unit volume of the negative electrode layer.

[0107] Examples of binders for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethylcellulose (CMC). While not particularly limited, the molecular weight of polyvinylidene fluoride is between 20,000 and 1,000,000. From the viewpoint of further improving the binding properties of the negative electrode layer, it is preferable that the molecular weight be 25,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more. From the viewpoint of further improving conductivity without hindering contact between the active material and the conductive agent, it is preferable that the molecular weight be 500,000 or less. In particular, the specific surface area of ​​the active material is 10 m². 2 If the amount is greater than or equal to 1g, the molecular weight is preferably 100,000 or more.

[0108] The amount of binder added should be optimized as it varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, but it is sufficient if it is included in the negative electrode active material composition at a concentration of 0.2% to 15% by mass. From the viewpoint of improving binding properties and ensuring the strength of the negative electrode layer, it is preferable to have 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 not reducing the active material ratio and thus reducing the initial discharge capacity of the energy storage device per unit mass and unit volume of the negative electrode layer, it is preferable to have 10% by mass or less, and even more preferably 5% by mass or less.

[0109] [Method for preparing a negative electrode active material composition] The method for producing the negative electrode active material composition of the present invention is not particularly limited, but preferred methods include adding a specific proportion of the inorganic solid electrolyte powder to the titanium-containing oxide powder and mixing them using a mixer, stirrer, disperser, etc., or adding the titanium-containing oxide powder to a slurry containing a solid electrolyte.

[0110] The negative electrode active material composition of the present invention can be used as the negative electrode of an all-solid-state secondary battery. In this case, it is preferable to form a press-molded body by press molding of the negative electrode active material composition of the present invention. The conditions for press molding are not particularly limited, but the molding temperature may be 15°C to 200°C, preferably 25°C to 150°C, and the molding pressure may be 180 MPa to 1080 MPa, preferably 300 MPa to 800 MPa. The negative electrode active material composition of the present invention can form a dense molded body with few voids, and therefore a dense negative electrode layer with few voids can be formed. The molded body obtained using the negative electrode active material composition of the present invention has a filling rate of 72.5% to 100%, preferably 73.5% to 100%.

[0111] [All-solid-state secondary battery] The all-solid-state secondary battery of the present invention is composed of a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive and negative electrodes, but the Li4Ti5O 12 or action 1-x / 2 Nb2O 7-x A negative electrode active material composition containing a titanium-containing oxide powder, mainly composed of a titanium-containing oxide represented by (x=0~2), and an inorganic solid electrolyte having conductivity of metal ions belonging to Group 1 of the periodic table, is used in the negative electrode layer. The method for producing the negative electrode layer is not particularly limited, and suitable examples include a method of pressurizing the negative electrode active material composition, or a method of adding the negative electrode active material composition to a solvent to make a slurry, then applying this negative electrode active material composition to a current collector, drying, and pressurizing it.

[0112] Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, calcined carbon, or materials coated with carbon, nickel, titanium, or silver on their surfaces. The surfaces of these materials may also be oxidized, and surface treatment may be used to create irregularities on the surface of the negative electrode current collector. Examples of the negative electrode current collector form include sheets, nets, foils, films, punched materials, laths, porous materials, foams, fiber bundles, and molded nonwoven fabrics. Porous aluminum is preferred as the form of the negative electrode current collector. The porosity of the porous aluminum is 80% or more and 95% or less, preferably 85% or more and 90% or less.

[0113] As long as the negative electrode layer contains the negative electrode active material composition of the present invention, the components such as the positive electrode layer and the solid electrolyte layer can be used without any particular limitations. For example, as a positive electrode active material used in the positive electrode layer of an all-solid-state secondary battery, a composite metal oxide containing one or more elements selected from the group consisting of cobalt, manganese, and nickel, along with lithium, is used. These positive electrode active materials can be used individually or in combination of two or more elements. Examples of such lithium composite metal oxides include LiCoO2 and LiCo 1-x M x O2 (where M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, 0.001 ≤ x ≤ 0.05), LiMn2O4, LiNiO2, LiCo 1-x Ni x O2(0.01 <x<1)、LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiLiLi 0.5 Mn 0.3 Co 0.2 O2, LiLiLi 0.8 Mn 0.1 Co 0.1 O2, LiLiLi 0.8 Co 0.15 Al 0.05 Solid solutions of O2, Li2MnO3 and LiMO2 (where M is a transition metal such as Co, Ni, Mn, or Fe), and LiNi 1 / 2 Mn 3 / 2 One or more selected from O4 are preferably mentioned, and two or more are more preferable. Also, they may be used in combination such as LiCoO2 and LiMn2O4, LiCoO2 and LiNiO2, LiMn2O4 and LiNiO2.

[0114] Furthermore, as the positive electrode active material, a lithium-containing olivine-type phosphate can also be used. Particularly, a lithium-containing olivine-type phosphate containing at least one or more selected from iron, cobalt, nickel and manganese is preferable. Specific examples thereof include LiFePO4, LiCoPO4, LiNiPO4, LiMnPO4 and the like. Some of these lithium-containing olivine-type phosphates may be substituted with other elements, and a part of iron, cobalt, nickel, manganese can be substituted with one or more elements selected from the group consisting of Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr, or they can also be coated with a compound or a carbon material containing these other elements. Among these, LiFePO4 or LiMnPO4 is preferable. Also, the lithium-containing olivine-type phosphate can be used, for example, by mixing it with the above-mentioned positive electrode active material.

[0115] The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. For example, graphite such as natural graphite (scaly graphite etc.), artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and the like can be mentioned. Also, graphite and carbon black may be appropriately mixed and used. The addition amount of the conductive agent to the positive electrode active material composition is preferably 1 to 10% by mass, and particularly preferably 2 to 5% by mass.

[0116] The positive electrode active material composition contains at least the positive electrode active material and a solid electrolyte, and may optionally contain a conductive agent such as acetylene black or carbon black, and a binder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), carboxymethylcellulose (CMC), or ethylene propylene diene polymer. The method for producing the positive electrode is not particularly limited, and suitable examples include a method of pressurizing the powder of the positive electrode active material composition, or a method of adding the powder of the positive electrode active material composition to a solvent to make a slurry, and then applying this positive electrode active material composition to an aluminum foil or stainless steel lath plate of a current collector, followed by drying and pressurizing.

[0117] The surface of the positive electrode active material may be coated with another metal oxide. Examples of surface coating agents include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specifically, Li4Ti5O 12 Examples include Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, B2O3, etc.

[0118] The solid electrolyte layer is located between the positive and negative electrodes, and its thickness is not particularly limited but may be between 1 μm and 100 μm. The constituent material of the solid electrolyte layer can be the aforementioned sulfide inorganic solid electrolyte or oxide inorganic solid electrolyte, and may differ from the solid electrolyte used in the electrodes. The solid electrolyte layer may also contain a binder such as butadiene rubber or butyl rubber.

[0119] There are no particular limitations on the structure of all-solid-state rechargeable batteries; coin-type batteries, cylindrical batteries, prismatic batteries, laminated batteries, etc., can be used. [Examples]

[0120] (Lithium titanate)

[0121] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples and encompasses various combinations that can be easily inferred from the spirit of the invention. [Manufacturing Example 1] <Raw material preparation process> Li₂CO₃ (average particle size 4.6 μm) and anatase-type TiO₂ (specific surface area 10 m²) are used so that the atomic ratio of Li to Ti (Li / Ti) is 0.83. 2 A raw material mixture slurry was prepared by weighing the raw material powder (by g) and adding deionized water to the mixture so that the solid content concentration of the slurry was 41% by mass, and then stirring. This raw material mixture slurry was then wet-mixed and pulverized using a bead mill (Willi E. Bakkofen, model: Dynomill KD-20BC, agitator material: polyurethane, vessel inner surface material: zirconia). Zirconia beads (outer diameter: 0.65 mm) were packed into the vessel at 80% by volume, and the process was carried out with an agitator peripheral speed of 13 m / s and a slurry feed rate of 55 kg / hr, while controlling the internal pressure of the vessel to 0.02 to 0.03 MPa.

[0122] <Firing Process> The obtained mixed slurry was introduced into the furnace core from the raw material supply side of a rotary kiln-type firing furnace (furnace core length: 4 m, furnace core diameter: 30 cm, external heating type) equipped with an anti-adhesion mechanism, dried in a nitrogen atmosphere, and fired. At this time, the tilt angle of the furnace core from the horizontal direction was 2.5 degrees, the rotation speed of the furnace core was 20 rpm, and the flow rate of nitrogen introduced into the furnace core from the calcined material recovery side was 20 L / min. The heating temperature of the furnace core was set to 600°C on the raw material supply side, 840°C in the center, and 840°C on the calcined material recovery side, and the holding time of the calcined material at 840°C was 30 minutes.

[0123] <Post-processing steps> The calcined material recovered from the calcined material recovery side of the furnace tube was crushed using a hammer mill (Dalton, AIIW-5 model) under the following conditions: screen opening: 0.5 mm, rotation speed: 8,000 rpm, and powder feed rate: 25 kg / hr.

[0124] <Granulation process> To the crushed calcined powder, ion-exchanged water was added and stirred to achieve a solid content concentration of 30% by mass, and a mixed slurry was prepared. This mixed slurry was sprayed and dried using a spray dryer (L-8i, manufactured by Okawara Chemical Machinery Co., Ltd.) at an atomizer rotation speed of 25,000 rpm and a drying temperature of 250°C, and then granulated. Next, the powder that passed through the sieve was placed in an alumina sagger and heat-treated at 500°C for 1 hour in a mesh belt conveying continuous furnace equipped with a recovery box at the outlet side, where the temperature was controlled at 25°C and the dew point was below -20°C. The heat-treated powder was cooled in the recovery box, classified using a sieve (screen opening: 53 μm), and the powder that passed through the sieve was collected in an aluminum laminate bag, sealed, and then removed from the recovery box to produce lithium titanate powder.

[0125] <Preparation of solvated ionic liquids> A solvated ionic liquid (LTFSI-TetraG) was obtained by mixing 1 mole of tetraglyme (TetraG) with 1 mole of LiN(SO2CF3)2 (LTFSI) and stirring thoroughly. <Mixing process> The solvated ionic liquid prepared above was added at a concentration of 25% by mass relative to 100% by mass of the synthesized lithium titanate powder, mixed, and thoroughly stirred to prepare lithium titanate powder surface-treated with the solvated ionic liquid of Example 1.

[0126] [Manufacturing Examples 1-12] As shown in Tables 1 and 2, the product was manufactured in the same manner as in Manufacturing Example 1. In Manufacturing Example 4, surface treatment with a solvated ionic liquid was followed by heat treatment, and in Manufacturing Example 4, 1.6% by mass of aluminum sulfate 16-hydrate (Al2(SO4)3·16H2O) was added to the calcined powder obtained by crushing as a treatment agent during the preparation of the mixed slurry in the granulation process. Furthermore, in Production Example 7, no treatment with solvated ionic liquid was performed, and in Production Examples 8 to 12, two types of Li salts were used to obtain the solvated ionic liquid, with their amounts (molar ratio) as shown in Table 2.

[0127] [Measurement of Al content] The Al content in the lithium titanate powder of manufacturing example 4 was measured as follows.

[0128] <X-ray fluorescence analysis (XRF): Identification of Al> The amount of Al contained in the lithium titanate powder of each example and comparative example was quantitatively analyzed using an X-ray fluorescence spectrometer (manufactured by SII Technology Co., Ltd., product name "SPS5100").

[0129] [Measurement of powder properties] The various physical properties of the lithium titanate powder used in each manufacturing example were measured as follows.

[0130] <Measurement of specific surface area> The specific surface area (m²) of the lithium titanate powder used in each manufacturing example. 2 The specific surface area ( / g) was measured using a fully automated BET specific surface area analyzer (Mountec Co., Ltd., product name "Macsorb HM model-1208"), with nitrogen gas used as the adsorption gas. 0.5g of the sample powder was weighed, placed in a φ12 standard cell (HM1201-031), degassed under vacuum at 100°C for 0.5 hours, and then measured using the BET single-point method.

[0131] <Calculation of D50 of primary particles: Dry laser diffraction scattering method> The D50 of the lithium titanate powder used in each manufacturing example was calculated from the particle size distribution curve measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of the sample was placed in a container containing 50 ml of deionized water as the measurement solvent. The container was shaken by hand until the powder was visibly and uniformly dispersed in the solvent, and then the container was placed in the measurement cell for measurement. For the crushing process, ultrasound (30 W, 3 s) was applied using an ultrasonic device in the instrument. Further measurement of the particle size distribution was performed by adding more measurement solvent until the slurry transmittance was within the appropriate range (indicated by the green bar on the instrument). The D50 of the crushed mixed powder was calculated from the obtained particle size distribution curve.

[0132] [Table 1]

[0133] [Table 2]

[0134] [Example 1] [Preparation of the negative electrode active material composition] In a glove box under an argon atmosphere, lithium titanate powder from Production Example 1 and sulfide inorganic solid electrolyte powder having the composition Li6PS5Cl (volume-average particle size measured using a laser diffraction / scattering particle size distribution analyzer: 6 μm) were weighed in a mass ratio of lithium titanate:Li6PS5Cl = 60:40 and mixed in an agate mortar. Next, zirconia balls (3 mm in diameter, 20 g) were placed in an 80 mL zirconia pot, and the mixed powder was added. Then, this pot was set in a planetary ball mill and stirred at a rotation speed of 200 rpm for 15 minutes to obtain the negative electrode active material composition of Example 1. [Examples 2-14, Comparative Examples 1-4] The negative electrode active material compositions described in Tables 3 to 6 below were prepared in the same manner as in Example 1, except that lithium titanate powder produced by the methods described in Tables 1 and 2 was used.

[0135] [Evaluation of battery characteristics] All-solid-state secondary batteries were fabricated using pellets of the negative electrode active material composition from each example, and their battery characteristics were evaluated. The evaluation results are shown in Tables 3 to 6.

[0136] [Synthesis of sulfide inorganic solid electrolytes] In a glove box under an argon atmosphere, lithium sulfide (Li2S) and phosphorus pentasulfide (P2S5) were weighed in a molar ratio of Li2S:P2S5 = 75:25, and mixed in an agate mortar to obtain the raw material composition. Next, zirconia balls (3 mm in diameter, 160 g) and 2 g of the obtained raw material composition were placed in an 80 mL zirconia pot, and the container was sealed under an argon atmosphere. This pot was set in a planetary ball mill and mechanical milling was performed at a rotation speed of 510 rpm for 16 hours to obtain yellow powder sulfide inorganic solid electrolyte (LPS glass). 80 mg of the obtained LPS glass was placed over an area of ​​0.785 cm². 2 A pellet-shaped solid electrolyte layer was obtained by pressing it at a pressure of 360 MPa using a pellet molding machine having a molding section.

[0137] [Fabrication of all-solid-state secondary batteries] A solid-state secondary battery was fabricated by laminating pellets of the negative electrode active material composition of each embodiment, the pelletized solid electrolyte layer, and a lithium indium alloy foil as a counter electrode in this order, and then sandwiching the laminate between stainless steel current collectors.

[0138] <Measurement of initial discharge capacity and charge rate characteristics> In a constant temperature bath at 25°C, the coin-type battery prepared using the method described above was charged to 0.5V with a current equivalent to 0.05C of the theoretical capacity of lithium titanate, with the direction in which Li is absorbed into the evaluation electrode considered as charging. Then, constant current constant voltage charging was performed until the charging current at 0.5V was equivalent to 0.01C, followed by constant current discharge to 2V with a current equivalent to 0.05C. The initial discharge capacity (mAh / g) was calculated by dividing the discharge capacity (mAh) by the mass of lithium titanate. Next, the 0.4C charge capacity was determined by charging to 0.5V with a current equivalent to 0.4C of the theoretical capacity of lithium titanate, and then discharging to 2V with a current of 0.05C. The rate characteristic (%) was calculated by dividing this 0.4C charge capacity by the initial discharge capacity. The initial discharge capacity and charge rate characteristics were examined relative to the values ​​of Comparative Example 1, which were set to 100%. The evaluation results are shown in Tables 2 and 3. The "C" in 1C represents the current value used during charging and discharging. For example, 1C refers to the current value that can completely discharge (or fully charge) the theoretical capacity in 1 / 1 hour, while 0.1C refers to the current value that can completely discharge (or fully charge) the theoretical capacity in 1 / 0.1 hour.

[0139] [Table 3] [Table 4]

[0140] Tables 3 and 4 above show that Examples 1 to 6 of the all-solid-state secondary battery using the negative electrode active material composition of the present invention exhibit excellent initial discharge capacity and further enhance the charge rate characteristics.

[0141] Furthermore, when a composition was used in which the same sulfide inorganic solid electrolyte and the same solvated ionic liquid as in Example 1 were pre-mixed in the same proportions, as described in Patent Document 2, and the mass ratio of lithium titanate:Li6PS5Cl = 60:40 was used, the ionic conductivity of the mixture increased, and the charge rate characteristics improved (charge rate characteristics 127.5%), but it was inferior to the case where lithium titanate powder of Example 1 was used, and the initial discharge capacity decreased (94%) compared to Comparative Example 1. This result is thought to be due to a side reaction occurring between the solid electrolyte and the ionic liquid, which caused the initial characteristics to decrease compared to Comparative Example 1, where the ionic liquid was not mixed. Also, when using the composition described in Patent Document 2, it is not possible to completely inactivate the active site on the surface of the lithium titanate, which is thought to be why the improvement in rate characteristics was inferior to that of Example 1.

[0142] <Battery characteristics test at 45°C> The evaluation was carried out in the same manner as in Example 1, except that the temperature inside the constant temperature bath was set to 45°C. To determine the charge rate characteristics at high temperatures, the lithium titanate was charged to 0.5V with a current equivalent to 0.2C of its theoretical capacity, and then discharged to 2V with a current of 0.05C to determine the 0.2C charge capacity. The charge rate characteristics (%) were calculated by dividing this 0.2C charge capacity by the initial discharge capacity. The evaluation results are shown in Tables 5 and 6.

[0143] [Table 5]

[0144] [Table 6]

[0145] Tables 5 and 6 above show that Examples 7 to 14 of the all-solid-state secondary battery using the negative electrode active material composition of the present invention exhibit excellent initial discharge capacity even at 45°C, and that the charge rate characteristics can be further improved.

[0146] Furthermore, when the lithium titanate:Li6PS5Cl ratio was 90:10, the lithium titanate produced in Manufacturing Example 7 did not charge at 45°C and did not function as a battery. On the other hand, the lithium titanate produced in Manufacturing Example 1 had an initial discharge capacity of 227.4% and a charge rate characteristic of 348.4% compared to Comparative Example 4 (when lithium titanate:Li6PS5Cl = 80:20). These results show that by using the lithium titanate of the present invention, high battery characteristics could be maintained even when the ratio of solid electrolyte in the mixture was very small.

[0147] (Niobium titanate) <Raw material preparation process> Nb2O5 (average particle size 0.2 μm) and anatase-type TiO2 (specific surface area 10 m2 / g) were weighed in a molar ratio of 1:1 and mixed. This mixed powder was heat-treated at 1000°C for 5 hours. Powder X-ray diffraction measurements were performed on the resulting calcined powder sample under conditions of a sampling interval of 0.01° and a scan speed of 2° / min. Crystal structure analysis results by the Rietveld method confirmed that the synthesized sample was the target titanium-containing oxide, niobium titanate (TiNb2O7: Titanium niobium oxide, ICDD (PDF2010) PDF card 01-077-1374).

[0148] Niobium titanate (hereinafter referred to as TNO) was prepared by using the calcined powder obtained above as the base material and surface-treating it with a solvated ionic liquid using the same solvated ionic liquid and mixing process as in Production Example 1.

[0149] The evaluation was carried out in the same manner as in Example 7, except that the TNO was surface-treated with the solvated ionic liquid prepared above. The initial discharge capacity of the TNO surface-treated with the solvated ionic liquid was 144.6% of that of the untreated TNO, indicating an improvement in initial characteristics. Furthermore, while the untreated TNO could not be charged at 0.2C, charging became possible after surface treatment with the solvated ionic liquid.

[0150] Based on the above results, the negative electrode active material composition of the present invention effectively suppresses side reactions between the active site on the titanium-containing oxide surface and the solid electrolyte, thereby exhibiting excellent battery characteristics.

Claims

1. Li ４ Ti ５ O １２ Or Ti １-Ｘ／２ Nb ２ O ７-Ｘ A titanium-containing oxide powder whose main component is a titanium-containing oxide represented by (0 ≤ X < 2), The titanium-containing oxide powder contains titanium-containing oxide particles and a solvated ionic liquid. The solvated ionic liquid consists of a Li salt and an organic solvent. The aforementioned titanium-containing oxide powder is a solvated ionic liquid treated powder obtained by surface treatment with a solvated ionic liquid. A titanium-containing oxide powder characterized in that the D50 of primary particles corresponding to 50% of the volume cumulative particle size distribution of the titanium-containing oxide powder as measured by laser diffraction scattering is 0.5 μm or larger.

2. The specific surface area of ​​the titanium-containing oxide powder is 1 m². ２ / g or more 10m ２ The titanium-containing oxide powder according to claim 1, wherein the amount is less than or equal to / g.

3. The titanium-containing oxide powder according to claim 1 or 2, wherein Al is present on the particle surface of the titanium-containing oxide powder.

4. wherein the Li salt is LiPF ６ , LiBF ４ , LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ), ２ , and LiN(SO ２ C ２ F ５ ), ２ The titanium-containing oxide powder according to any one of claims 1 to 3, which is at least one Li salt selected from the group consisting of

5. The Li salt is LiPF ６ LiBF ４ , LiN (SO ２ F) ２ , LiN (SO ２ CF ３ ) ２ , and LiN(SO ２ C ２ F ５ ) ２ The titanium-containing oxide powder according to any one of claims 1 to 3, which is at least two or more Li salts selected from the group consisting of the following.

6. The Li salt is LiPF ６ LiBF ４ , LiN (SO ２ F) ２ , LiN (SO ２ CF ３ ) ２ , and LiN(SO ２ C ２ F ５ ) ２ A titanium-containing oxide powder according to any one of claims 1 to 3, comprising at least one Li salt selected from the group consisting of Li salts having an oxalic acid skeleton, Li salts having a phosphate skeleton, and Li salts having an S=O group.

7. The titanium-containing oxide powder according to any one of claims 1 to 6, wherein the organic solvent is an ether compound.

8. The titanium-containing oxide powder according to any one of claims 1 to 7, wherein the molar ratio of the Li salt to the organic solvent is 0.3 or more and 2.5 or less.

9. The titanium-containing oxide powder according to any one of claims 1 to 8, wherein the ratio of the solvated ionic liquid to the titanium-containing oxide powder is 0.1% by mass or more and 30% by mass or less.

10. A negative electrode active material composition comprising a titanium-containing oxide powder according to any one of claims 1 to 9 and an inorganic solid electrolyte having conductivity of metal ions belonging to Group 1 of the periodic table.

11. The negative electrode active material composition according to claim 10, wherein the inorganic solid electrolyte is a sulfide inorganic solid electrolyte.

12. The negative electrode active material composition according to claim 10 or 11, wherein the content of the inorganic solid electrolyte in the negative electrode active material composition is 1% by mass or more and 50% by mass or less.

13. 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 described in any one of claims 10 to 12.

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