Metal composite sintered plate and lithium-ion battery

Abstract

To provide a lithium-ion battery that is less susceptible to deterioration in a high-temperature and vibration environment, and to provide a negative electrode material suitable for constituting such a lithium-ion battery.SOLUTION: The present invention relates to a sintered plate used as an electrode for a lithium-ion battery, the sintered plate being a metal composite plate containing lithium titanate particles and metal particles dispersed among the lithium titanate particles. The present invention also relates to a lithium-ion battery including a positive electrode containing a lithium composite oxide, a negative electrode containing the metal composite sintered plate, and a separator disposed between the positive electrode and the negative electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a metal composite sintered plate and a lithium ion battery. [Background technology]

[0002] Lithium-ion batteries using lithium-titanium composite oxide as the negative electrode active material are known. For example, Patent Document 1 (JP 2007-87909 A) discloses that a negative electrode of a lithium-ion battery is constructed by coating a metal foil serving as a negative electrode current collector with a slurry containing a negative electrode active material, a negative electrode conductive agent, and a binder. Examples of negative electrode conductive agents that can be used to improve current collection performance and reduce contact resistance with the current collector include acetylene black, carbon black, and graphite.

[0003] Patent Document 2 (JP 2019-96599 A) discloses a lithium-ion battery having a negative electrode that is a lithium titanate sintered plate. The lithium titanate sintered plate disclosed in Patent Document 2 is characterized by the shape of the sintered plate, such as the particle size of the primary particles, porosity, pore shape and distribution, etc. It is disclosed that the sintered plate in Patent Document 2 has a structure in which primary particles of lithium titanate, which is the negative electrode active material, are bonded together, and does not contain auxiliary components such as binders. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-87909 [Patent Document 2] Japanese Patent Application Publication No. 2019-96599 Summary of the Invention [Problem to be solved by the invention]

[0005] The range of applications for lithium-ion batteries continues to expand, and there is a demand for lithium-ion batteries that can be used for long periods of time even under high-temperature, high-load environments where continuous vibration occurs. To meet these needs, batteries that do not deteriorate easily under high-temperature and vibration environments are desired.

[0006] In view of this situation, one of the objects of the invention according to the present disclosure is to provide a lithium ion battery that is less susceptible to deterioration in high-temperature and vibration environments, and to provide an electrode material suitable for constituting such a lithium ion battery. [Means for solving the problem]

[0007] A metal composite sintered plate according to the present disclosure is a sintered plate used as an electrode for a lithium ion battery, and contains lithium titanate particles and metal particles dispersed among the lithium titanate particles. [Effects of the Invention]

[0008] The metal composite sintered plate provides a lithium ion battery that is less susceptible to deterioration in high temperature and vibration environments. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a lithium-ion battery according to the present disclosure. [Figure 2] FIG. 2 is a scanning electron microscope image showing a cross section of a sintered metal composite plate according to the present disclosure. [Figure 3] FIG. 3 is a scanning electron microscope image showing a cross section of a sintered metal composite plate according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Outline of implementation] First, embodiments of the present disclosure will be described. A metal composite sintered plate according to the present disclosure is a sintered plate used as an electrode for a lithium ion battery, and contains lithium titanate particles and metal particles dispersed among the lithium titanate particles.

[0011] Aiming to further improve the performance of lithium-ion batteries, research into the elements that make up batteries is ongoing. Electrodes for lithium-ion batteries that use lithium titanate (LTO) as the active material are known. So-called coated electrodes are known, which are obtained by coating and drying a slurry containing LTO, a conductive additive, and a binder on a metal foil (see, for example, Patent Document 1). Because coated electrodes contain an organic binder, there is a possibility that the binder will decompose at high temperatures, resulting in electrode deterioration. Also known are electrodes that use a sintered plate made by sintering LTO particles (see, for example, Patent Document 2). Because electrodes made of a sintered plate do not contain organic compounds, they have higher durability at high temperatures than coated electrodes.

[0012] The inventors conducted extensive research to develop a lithium-ion battery that would not deteriorate even in high-temperature, vibration-filled environments. They discovered that by using a sintered LTO electrode and a metal composite sintered plate in which metal particles are dispersed among the LTO particles, a lithium-ion battery with excellent durability and little loss in battery capacity could be realized, even after being placed in high-temperature, vibration-filled conditions. Without being bound by any particular theory, it is believed that the presence of metal particles, which are softer than LTO particles, in the sintered plate acts as a cushion, suppressing micro-fractures in the electrode, thereby improving durability against vibration.

[0013] In the metal composite sintered plate, the content of the metal particles relative to the total of the lithium titanate particles and the metal particles may be 5% by volume or more and 40% by volume or less, which allows the effects of containing the metal particles to be obtained and also prevents a decrease in capacity due to isolation of the active material and an increase in production costs.

[0014] In the metal composite sintered plate, the metal particles may be one or more types of metal particles selected from the group consisting of Ag, Pt, Al, and Au, which can reliably achieve the effects of the present disclosure.

[0015] In the metal composite sintered plate, the metal particles may have an aspect ratio of 1.1 or more. When the metal composite sintered plate contains metal particles with an aspect ratio of 1.1 or more, the effects of the present disclosure can be reliably obtained.

[0016] In the metal composite sintered plate, the ratio of the longitudinal length (L2) of the lithium titanate particles to the longitudinal length (L1) of the metal particles may satisfy L2 / L1 ≥ 1.1. When the size ratio of the lithium titanate particles to the metal particles is within this range, the effects of the present disclosure can be reliably obtained.

[0017] In the metal composite sintered plate, the electrode may be a negative electrode. Lithium ion batteries using an LTO sintered plate as a negative electrode are well known, and a lithium ion battery can be stably and reliably constructed using the sintered plate according to the present disclosure.

[0018] The lithium-ion battery according to the present disclosure may include a positive electrode containing a lithium composite oxide, a negative electrode containing the metal composite sintered plate, and a separator disposed between the positive electrode and the negative electrode. Furthermore, in the lithium-ion battery, the positive electrode, the negative electrode, and the separator may be an integrated sintered plate that is integrally sintered as a whole. A lithium-ion battery having such a configuration exhibits little deterioration in high-temperature and vibration environments and can be suitably used in high-temperature and vibration environments, such as in tires.

[0019] [Specific examples of embodiments] Specific embodiments of the metal composite sintered plate and lithium ion battery according to the present disclosure will be described with reference to the drawings.

[0020] (Metal composite sintered plate) The metal composite sintered plate according to the present disclosure is used as an electrode for a lithium-ion battery. The metal composite sintered plate according to the present disclosure contains lithium titanate particles and metal particles dispersed among the lithium titanate particles.

[0021] The thickness of the metal composite sintered plate according to the present disclosure is not particularly limited, but may be, for example, 30 to 500 μm, preferably 50 μm to 350 μm. The metal composite sintered plate according to the present disclosure can be used as an anode or cathode in a lithium-ion battery, and is preferably used as an anode. The metal composite sintered plate according to the present disclosure may be used in combination with other electrode components (positive or negative electrode, separator) of a lithium-ion battery, or may be formed into an integrated sintered body with the other components. That is, the metal composite sintered plate according to the present disclosure may be part of an integrated sintered plate in which a positive electrode, a negative electrode, and a separator are sintered together. Even when formed as an integrated sintered plate, deterioration of the electrode containing metal particles is suppressed, making it possible to obtain an electrode with excellent durability in high-temperature and vibration environments. The sintered plate according to the present disclosure may include only one layer in a lithium-ion battery, or multiple sintered plates. When a plurality of metal composite sintered plates are included, the electrode of the lithium ion battery is typically a multilayer laminated electrode in which a plurality of positive electrode layers and a plurality of negative electrode layers are laminated with separators interposed therebetween. The metal composite sintered plate according to the present disclosure may be provided as a negative electrode layer in the multilayer laminated electrode.

[0022] In the metal composite sintered plate according to the present disclosure, lithium titanate particles (LTO particles) have a structure in which multiple primary particles are bonded together. The primary particle size, which is the average particle size of the multiple primary particles, is not particularly limited and may be, for example, 10 μm or less, preferably 5 μm or less. Here, the "primary particle size" of the LTO particles is a value measured by image analysis of a scanning electron microscope (SEM) image of the cross section of the sintered plate. For example, the sintered plate is processed using a cross-section polisher (CP) to expose the polished cross section. This polished cross section is observed by SEM at a predetermined magnification (e.g., 1000x) and a predetermined field of view (e.g., 125 μm × 125 μm). The field of view is set so that 20 or more primary particles are present within the field of view, and the diameters of the circumscribed circles drawn for all primary particles in the obtained SEM image are determined, and the average of these diameters is taken as the primary particle size.

[0023] The LTO particles may have a flat shape with different longitudinal and lateral lengths. The longitudinal length (L1) of the LTO particles is not particularly limited, but may be, for example, 0.5 μm to 10 μm, and preferably 0.5 μm to 5 μm. When the length is within these ranges, a negative electrode for a lithium ion battery having excellent lithium ion conductivity and electron conductivity can be suitably formed.

[0024] Lithium titanate Li4Ti5O that forms LTO particles 12 Lithium-ion-oxide (LTO) is typically known to have a spinel structure, but can also adopt other structures during charging and discharging. For example, LiTiO 12 (spinel structure) and Li7Ti5O 12 The reaction proceeds in the coexistence of two phases, i.e., a spinel phase (rock salt structure). Therefore, LTO is not limited to a spinel structure. Part of LTO may be substituted with other elements. Examples of other elements include Nb, Ta, W, Al, and Mg.

[0025] The metal composite sintered plate according to the present disclosure contains metal particles in addition to LTO particles. The metal particles are dispersed among the lithium titanate particles. In the metal composite sintered plate, the metal particles may be uniformly dispersed in the thickness direction and the surface direction, or the concentration of the metal particles may be uneven. Preferably, the metal particles are uniformly dispersed in the metal composite sintered plate.

[0026] The shape of the metal particles is not particularly limited, and may be spherical, oval, flat, rod-like, irregularly shaped, or the like. The metal particles preferably have an aspect ratio of 1.1 or more, more preferably 5 or more. A method for measuring the aspect ratio of metal particles is described in detail in the Examples. A lithium ion battery equipped with a metal composite sintered plate containing metal particles with an aspect ratio of 1.1 or more exhibits less decrease in battery capacity even under high temperature and vibration environments, and provides a lithium ion battery with excellent durability.

[0027] The content of metal particles in the metal composite sintered plate according to the present disclosure is not particularly limited, but is preferably 5% to 40% by volume of the total of the lithium titanate particles and the metal particles. When the metal particles are contained at 5% by volume or more, the effects of the present disclosure due to the inclusion of metal particles become clear. When the content of metal particles is 40% by volume or less, it is possible to suppress a decrease in capacity due to isolation of the active material and an increase in manufacturing costs.

[0028] In the metal composite sintered plate according to the present disclosure, the ratio of the size of the LTO particles to the size of the metal particles is not particularly limited, but it is preferable that the longitudinal length (L2) of the metal particles relative to the longitudinal length (L1) of the LTO particles satisfies L2 / L1≧1.1. In other words, it is preferable that the LTO particles have a shorter longitudinal length than the metal particles. The method for measuring the particle size ratio of the LTO particles to the metal particles is described in detail in the Examples.

[0029] When the metal particles are flat (aspect ratio of 5 or more), the longitudinal length (L2) of the metal particles may be, for example, 0.5 μm to 20 μm, and preferably 0.5 μm to 10 μm. When the metal particles are spherical or ellipsoidal (aspect ratio of 1 to 2), the longitudinal length (L2) of the metal particles may be, for example, 0.3 μm to 20 μm, and preferably 3 μm to 5 μm.

[0030] The metal particles are not particularly limited as long as they can achieve the effects of the present disclosure, but may contain silver (Ag), platinum (Pt), aluminum (Al), gold (Au), or palladium (Pd). The metal particles are preferably particles made of one or more metals selected from the group consisting of Ag, Pt, Al, Au, and Pd.

[0031] The metal composite sintered plate according to the present disclosure may contain pores. When the metal composite sintered plate contains pores, particularly open pores, and the metal composite sintered plate is incorporated into a battery as a negative electrode plate, the electrolyte can penetrate into the sintered plate, improving lithium ion conductivity. The porosity is not particularly limited, but may be, for example, 10 to 60%.

[0032] FIG. 2 shows an example of a scanning electron microscope image of a cross section of a metal composite sintered plate according to the present disclosure. In FIG. 2, the gray areas are LTO particles. Particle m shown in white is a metal particle. In the example shown in FIG. 2, the aspect ratio of particle m is 5, and the particle size ratio between the LTO particle and the metal particle is 5. FIG. 3 shows an example of a scanning electron microscope image of a cross section of a metal composite sintered plate according to the present disclosure. In FIG. 3, the light gray areas are metal particles, and the darker gray areas are LTO particles. One of the LTO particles is shown surrounded by a dotted line.

[0033] (Lithium-ion battery) The lithium ion battery according to the present disclosure may be in any form, and may be, for example, a small coin-type battery or a pouch-type battery. FIG. 1 is a schematic cross-sectional view showing the structure of a coin-type lithium ion battery, which is an example of the lithium ion battery according to the present disclosure. Note that FIG. 1 shows the actual configuration with some parts enlarged, emphasized, and omitted for ease of understanding. The configuration shown in FIG. 1 does not necessarily reflect the actual dimensions.

[0034] Referring to FIG. 1 , a lithium-ion battery 10 includes a positive electrode layer 12, a negative electrode layer 13, a separator 14, an electrolyte 19, and an exterior body 20. The positive electrode layer 12 is formed of a sintered body containing lithium cobalt oxide. The negative electrode layer 13 is formed of a metal composite sintered plate according to the present disclosure. The separator 14 is made of resin or ceramic and is interposed between the positive electrode layer 12 and the negative electrode layer 13. The electrolyte 19 is impregnated into the positive electrode layer 12, the negative electrode layer 13, and the separator 14.

[0035] The exterior housing 20 has a sealed space, and the positive electrode layer 12, the negative electrode layer 13, the separator 14, and the electrolyte solution 19 are accommodated within this sealed space. The positive electrode 12 and the negative electrode 13 are separately formed sintered plates, with the separator 14 interposed between the positive electrode 12 and the negative electrode 13. In another embodiment, the positive electrode layer 12, the separator 14, and the negative electrode layer 13 may form a single integrated sintered plate as a whole. That is, the positive electrode layer 12, the separator 14, and the negative electrode layer 13 may be bonded to one another. Note that "forming a single integrated sintered plate" means that the three layers of the positive electrode layer 12, the separator 14, and the negative electrode layer 13 are connected and bonded to one another without relying on other bonding methods such as adhesives. In yet another embodiment, the positive electrode layer 12 and the separator 14 may form a single integrated sintered plate, and the negative electrode layer 13 may be a sintered plate formed separately from the single integrated sintered plate.

[0036] The exterior body 20 includes a positive electrode can 21, a negative electrode can 22, and a gasket 23. The positive electrode can 21 and the negative electrode can 22 are crimped together via the gasket 23 to form a sealed space. The positive electrode can 21 and the negative electrode can 22 may be made of a metal such as stainless steel. The gasket 23 may be an annular member made of an insulating resin such as polypropylene, polytetrafluoroethylene, or PFA resin, and is not particularly limited. The specific dimensions of the exterior body 20 are not particularly limited, but, as an example, it is preferable that the diameter is 25 mm or less and the thickness is 6 mm or less.

[0037] Referring to FIG. 1 , a lithium-ion battery 10 includes a positive electrode current collector 15 and a negative electrode current collector 17. The positive electrode current collector 15 and the negative electrode current collector 17 are preferably, but not limited to, metal foils such as copper foil or aluminum foil. The positive electrode current collector 15 is preferably disposed between the positive electrode layer 12 and the positive electrode can 21. The negative electrode current collector 17 is preferably disposed between the negative electrode layer 13 and the negative electrode can 22. A positive electrode-side carbon layer 16 is preferably disposed between the positive electrode layer 12 and the positive electrode current collector 15 to reduce contact resistance. Similarly, a negative electrode-side carbon layer 18 is preferably disposed between the negative electrode layer 13 and the negative electrode current collector 17 to reduce contact resistance. Both the positive electrode-side carbon layer 16 and the negative electrode-side carbon layer 18 are preferably composed of conductive carbon. The carbon layers can be formed, for example, by applying a conductive carbon paste to the surface of a metal foil current collector using screen printing or the like.

[0038] The thickness of the positive electrode layer 12 is preferably 30 to 500 μm, more preferably 40 to 400 μm, and even more preferably 50 to 300 μm. The positive electrode layer 12 may have a porosity of, for example, 10 to 60%, more preferably 20 to 55%, and even more preferably 30 to 50%.

[0039] The thickness of the negative electrode layer 13 is preferably 30 to 500 μm, more preferably 40 to 400 μm, and even more preferably 50 to 350 μm. The negative electrode layer 13 is made of a metal composite sintered plate according to the present disclosure.

[0040] The separator 14 is a resin separator, specifically, for example, a cellulose porous monolayer membrane. The resin separator is not limited to a cellulose porous monolayer membrane, and may be a monolayer separator formed of a resin. Examples of resins that can be used include polyimide and polyester (e.g., polyethylene terephthalate (PET)). The thickness of the separator is, for example, 15 μm or more, preferably 18 μm or more, and more preferably 20 μm or more. The thickness of the separator is, for example, 31 μm or less, preferably 28 μm or less, and more preferably 26 μm or less. By making the separator thicker, even if lithium dendrites (tree-like crystals of lithium) precipitate, it is possible to prevent short-circuiting between the positive electrode and the negative electrode due to lithium dendrites. Furthermore, by making the separator thinner, it is possible to facilitate permeation of the electrolyte and lithium ions, thereby reducing the internal resistance of the battery.

[0041] Next, the configuration of the lithium ion battery according to the present disclosure other than the metal composite sintered plate, that is, the more specific configuration of the positive electrode layer, the current collector layer, the separator, and the electrolyte will be described.

[0042] (positive electrode layer) The positive electrode layer can be composed of a thin plate-shaped ceramic sintered body containing a lithium composite oxide. Preferably, the positive electrode layer is composed substantially only of the lithium composite oxide. Gold (Au) or the like may be sputtered onto the positive electrode layer as a current collecting aid.

[0043] The positive electrode layer preferably has a structure in which a plurality of (i.e., a large number of) primary particles are bonded together. The primary particles are composed of a lithium composite oxide having a layered rock salt structure. The lithium composite oxide is a composite oxide of lithium and a transition metal element M (general formula: Li pIn MO₂ (where 0.05 < p < 1.10), part of it is substituted by a substituted metal element which is another metal element. The transition metal element M includes, for example, one or more selected from cobalt (Co), nickel (Ni), and manganese (Mn). The transition metal element M is the main one among the metals other than lithium contained in the lithium composite oxide, and hereinafter, it is referred to as the "main transition metal element".

[0044] Examples of the composite oxide of lithium and the transition metal element M include, for example, lithium cobaltate (Li p CoO₂ (where 1 ≤ p ≤ 1.1), lithium nickelate (LiNiO₂), lithium manganate (Li₂MnO₃), lithium nickel manganate (Li p (Ni 0.5 ,Mn 0.5 )O₂), solid solution represented by the general formula: Li p (Co x ,Ni y ,Mn z )O₂ (where 0.97 ≤ p ≤ 1.07, x + y + z = 1), Li p (Co x ,Ni y ,Al z )O₂ (where 0.97 ≤ p ≤ 1.07, x + y + z = 1, 0 < x ≤ 0.25, 0.6 ≤ y ≤ 0.9 and 0 < z ≤ 0.1), or a solid solution of Li₂MnO₃ and LiMO₂ (where M is a transition metal such as Co, Ni, etc.). Particularly preferably, the lithium composite oxide is lithium cobaltate Li p CoO₂ (where 1 ≤ p ≤ 1.1), for example, LiCoO₂ (sometimes referred to as LCO).

[0045] The transition metal element M may be one or more of elements such as magnesium (Mg), aluminum (Al), silicon (Si), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), strontium (Sr), yttrium (Y), zirconia (Zr), niobium (Nb), molybdenum (Mo), silver (Ag), tin (Sn), antimony (Sb), tellurium (Te), barium (Ba), and bismuth (Bi). Titanium (Ti) or niobium (Nb) is preferred.

[0046] The layered rock salt structure is a crystalline structure in which lithium layers and transition metal layers other than lithium are alternately stacked with oxygen layers sandwiched between them. That is, the layered rock salt structure is a crystalline structure in which metal ion layers other than lithium and lithium-only layers are alternately stacked with oxide ions interposed between them. Typically, it is an α-NaFeO2 type structure, i.e., a structure in which transition metals and lithium are regularly arranged along the

[0111] axis of a cubic rock salt type structure.

[0047] (current collector layer) The current collector layer is, for example, a layer of metal foil made of a metal such as aluminum. A conductive carbon layer may be provided in contact with the current collector layer and laminated on the upper surface of the metal foil serving as the current collector. In other words, the main surface of the current collector facing the positive electrode layer or the negative electrode layer may be coated with a conductive carbon layer. The metal foil may be formed of various metals other than aluminum (e.g., copper, nickel, silver, gold, chromium, iron, tin, lead, tungsten, molybdenum, titanium, zinc, or alloys containing these). The current collector layer does not necessarily have a conductive carbon layer. The positive electrode current collector layer and the negative electrode current collector layer may have the same configuration or different configurations.

[0048] (separator) The separator may be a ceramic separator or a resin separator, or may be a laminate of two or more layers of ceramic and resin. It may also be a microporous membrane made of ceramic alone. When the separator is a ceramic separator, it may be, for example, at least one selected from MgO, Al2O3, ZrO, SiC, Si3N4, AlN, and cogeneration light. Preferably, it may be at least one selected from MgO, Al2O3, and ZrO2.

[0049] When the separator is a ceramic separator, it has the advantage of being excellent in heat resistance and being able to be manufactured as a single integrated sintered body together with the positive electrode layer and the negative electrode layer. The thickness of the ceramic separator is preferably 3 to 40 μm, more preferably 5 to 35 μm, and even more preferably 10 to 30 μm. The porosity of the ceramic separator is preferably 30 to 85%, more preferably 40 to 80%.

[0050] (electrolyte) The lithium ion battery contains an electrolyte. The electrolyte is not particularly limited, and any electrolyte known for use in lithium ion batteries can be used. For example, the solvent can be one or a combination of two or more selected from ethylene carbonate (EC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and γ-butyrolactone (GBL). The electrolyte dissolved in the solvent can be, for example, a lithium salt compound such as lithium hexafluorophosphate (LiPF6) or lithium fluoroborate (LiBF4). The electrolyte 22 may further contain at least one additive selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinylethylene carbonate (VEC), and lithium difluoro(oxalato)borate (LiDFOB).

[0051] The concentration of the electrolyte in the electrolytic solution is preferably 0.5 to 4.0 mol / L, more preferably 0.6 to 3.0 mol / L, even more preferably 0.7 to 2.5 mol / L, and particularly preferably 0.8 to 2.0 mol / L.

[0052] In addition to an electrolytic solution, a solid electrolyte or a polymer electrolyte can also be used as the electrolyte. In this case, as with an electrolytic solution, it is preferable that the electrolyte is impregnated at least into the pores of the separator. The impregnation method is not particularly limited, but examples include a method in which the electrolyte is melted and infiltrated into the pores of the separator, and a method in which a powder compact of the electrolyte is pressed against the separator.

[0053] (Manufacturing method) The method for producing the metal composite sintered plate and lithium ion battery according to the present disclosure is not particularly limited, but they can be produced, for example, by the following method.

[0054] (Method for manufacturing metal composite sintered plates) The metal composite sintered plate according to the present disclosure can be manufactured through (a) preparing a metal composite LTO green sheet and (b) firing the metal composite LTO green sheet.

[0055] (a) Preparation of metal composite LTO green sheets Lithium titanate (LTO) raw powder and metal powder are prepared. The LTO raw powder may be commercially available or newly synthesized. For example, a powder obtained by hydrolyzing a mixture of titanium tetraisopropoxyalcohol and isopropoxylithium may be used, or a mixture containing lithium carbonate, titania, etc. may be sintered. The volumetric D50 particle size of the LTO raw powder is not particularly limited, but may be, for example, 0.05 to 5.0 μm, preferably 0.1 to 2.0 μm. The LTO raw powder may be pulverized to the desired particle size using, for example, a pot mill, a bead mill, or a jet mill. Larger particle sizes of LTO raw powder tend to result in larger pores in the sintered plate. Commercially available metal powders can be used as is, or after pretreatment as necessary. Examples of pretreatment for metal powders include dispersion, washing, and pulverization. The LTO raw powder and metal powder are mixed with a dispersion medium and various additives (binders, plasticizers, dispersants, etc.) to form a slurry. The slurry is preferably stirred under reduced pressure to degas and the viscosity is adjusted to 4000 to 10000 cP. The obtained slurry is formed into a sheet to obtain a metal composite LTO green sheet. The sheet formation is performed, for example, by applying the slurry to a resin film such as PET using a doctor blade method. The thickness of the metal composite LTO green sheet can be appropriately set taking into account the thickness after firing. The metal composite LTO green sheet may be a single layer, or, for example, 2 to 30 green sheets may be stacked and pressure-bonded to form an integrated sheet. The single-layer or multiple-layer pressure-bonded green sheet can be cut to the desired shape.

[0056] (b) Firing of metal composite LTO green sheets The metal composite LTO green sheet is placed on a setter. The setter is made of ceramic, preferably zirconia or magnesia. The setter is preferably embossed. The green sheet placed on the setter is then placed in a sheath. The sheath is also made of ceramic, preferably alumina. After optional degreasing, the green sheet is fired to obtain a metal composite LTO sintered plate. Firing can be performed at 600 to 900°C for 0.1 to 50 hours, preferably 700 to 800°C for 0.1 to 20 hours. The heating rate during firing can be 100 to 3000°C / h, preferably 200 to 2500°C / h. The heating rate may be constant throughout the heating process, or it may not be constant. For example, the heating rate may be changed depending on the temperature range and elapsed time.

[0057] The metal composite LTO green sheet may be laminated with a separately prepared LCO green sheet or separator green sheet, and then compressed and integrated, followed by sintering. In this case, an integrated sintered plate-type electrode is obtained, in which the positive electrode, negative electrode, and separator are integrated.

[0058] (Lithium-ion battery manufacturing method) The method for producing a lithium ion battery according to the present disclosure can be appropriately selected depending on the form of the lithium ion battery and is not particularly limited. A lithium ion battery can be obtained by combining the metal composite sintered plate obtained by the above-mentioned production method as a negative electrode, a positive electrode, a separator, and further a negative electrode current collector and a positive electrode current collector, and housing the resulting package, and then sealing the package with an electrolyte.

[0059] [Example] The lithium-ion battery according to the present disclosure will be described in more detail below with reference to examples and comparative examples. Samples 1 to 14 are examples of the lithium-ion battery according to the present disclosure. Sample 15 is a comparative example that is outside the scope of the lithium-ion battery according to the present disclosure.

[0060] [Sample production] [Sample 1] A metal composite LTO sintered plate and a lithium ion battery were produced according to the methods described in (1) to (3) below.

[0061] (1) Preparation of metal composite LTO sintered plate (1a) Preparation of metal composite LTO green sheets 100 parts by weight of LTO raw material powder (manufactured by Shinko Chemical Industry Co., Ltd.), 143 parts by weight of a dispersion medium (xylene:butanol = 1:1), 18 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 4.5 parts by weight of a plasticizer (product number G-260, manufactured by Sekisui Chemical Co., Ltd.), 4 parts by weight of a dispersant (product number SC0505K, manufactured by NOF Corporation), and metal powder (Al flat particles 1 in Table 1) were mixed. The metal powder and LTO raw material powder were mixed so that the volume ratio of metal powder:LTO was 20:80. The resulting mixture was then stirred to degas and adjusted to a viscosity of 4000 cP to prepare an LTO slurry. The viscosity was measured using a Brookfield LVT viscometer. The LTO slurry was then applied to a PET film by doctor blade to form a metal composite LTO green sheet, which was then dried to a thickness of 76 μm per layer to produce a battery with a positive / negative active material capacity ratio (C / A) of 1.1. (1b) Fabrication of metal composite LTO sintered plate Five of the resulting metal composite LTO green sheets were stacked in order, and the resulting laminate was pressed using hot isostatic pressing (WIP) at 14.5 MPa for 5 minutes to bond the green sheets together. The bonded laminate was then punched into a 16.5 mm diameter disk using a punching die. The resulting disk-shaped laminate was degreased at 350°C for 5 hours, then heated to 800°C at a rate of 300°C / h and held there for 1 hour. The resulting disk-shaped laminate was then cooled to obtain a metal composite LTO sintered plate.

[0062] (2) Preparation of LiCoO2 sintered plate (2a) Preparation of LiCoO2 green sheets First, Co3O4 powder (manufactured by Coremax) and Li2CO3 powder (manufactured by Honjo Chemical Co., Ltd.) were mixed so that the Li / Co molar ratio was 1.02, and then the mixture was heated to 780 °C for 5 hours. The resulting powder was then pulverized in a pot mill to a volumetric D50 particle size of 0.7 μm to obtain LiCoO2 powder. 100 parts by weight of this LiCoO2 powder was mixed with 137 parts by weight of a dispersion medium (xylene:butanol = 1:1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 3 parts by weight of a plasticizer (product number G-260, manufactured by Sekisui Chemical Co., Ltd.), and 4.5 parts by weight of a dispersant (product number SC0505K, manufactured by NOF Corporation). The resulting mixture was stirred under reduced pressure to degas and the viscosity was adjusted to 4000 cP to prepare a LiCoO2 slurry. The viscosity was measured using a Brookfield LVT viscometer. The slurry thus prepared was formed into a sheet on a PET film by the doctor blade method to form a LiCoO2 green sheet, the thickness of which was adjusted to 50 μm after firing. (2b) Preparation of LiCoO2 sintered plate Five of the resulting green sheets were stacked in order, and the resulting laminate was pressed by hot isostatic pressing (WIP) at 14.5 MPa for 5 minutes to bond the green sheets together. The bonded laminate was then punched into a disk with a diameter of 16.5 mm using a punching die. The resulting disk-shaped laminate was degreased at 350°C for 5 hours, then heated to 800°C at a rate of 300°C / h and held there for 1 hour. After cooling, a LiCoO2 sintered plate was obtained.

[0063] (3) Fabrication of lithium-ion batteries A stack was fabricated by sequentially stacking a LiCoO2 sintered plate (positive electrode), a separator, and a metal composite LTO sintered plate (negative electrode). This stack was then immersed in an electrolyte solution to fabricate a coin-type battery. The electrolyte solution was a 1.5 mol / L solution of LiBF4 dissolved in an organic solvent containing ethylene carbonate (EC) and gamma-butyrolactone (GBL) in a volume ratio of 1:3. A 25 μm-thick cellulose porous monolayer membrane (manufactured by Nippon Kodoshi Kogyo Co., Ltd.) was used as the separator.

[0064] [Sample 2] In (1a) above, a metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium-ion battery were produced in the same manner as Sample 1, except that metal powder (Al flat particles 1 in Table 1) was mixed so that the volume ratio of metal powder to LTO was 5:95.

[0065] [Sample 3] In the above (1a), a metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium-ion battery were produced in the same manner as Sample 1, except that in step (1a), metal powder (Al flat particles 1 in Table 1) was mixed so that the volume ratio of metal powder to LTO was 10:90.

[0066] [Sample 4] In the above (1a), a metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium-ion battery were produced in the same manner as Sample 1, except that in step (1a), metal powder (Al flat particles 1 in Table 1) was mixed so that the volume ratio of metal powder to LTO was 40:60.

[0067] [Sample 5] In (1a) above, a metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium-ion battery were produced in the same manner as Sample 1, except that metal powder (Al flat particles 1 in Table 1) was mixed in a volume ratio of metal powder:LTO = 50:50.

[0068] [Sample 6] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium-ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to Ag flat particles shown in Table 1. Cross-sectional SEM images of the metal composite LTO sintered plate of Sample 6 are shown in Figures 2 and 3.

[0069] [Sample 7] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to the Pt flat particles shown in Table 1.

[0070] [Sample 8] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to the Au flat particles shown in Table 1.

[0071] [Sample 9] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to Al flat particles 2 shown in Table 1.

[0072] [Sample 10] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to Al oval spherical particles shown in Table 1.

[0073] [Sample 11] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to the Al spherical particles shown in Table 1.

[0074] [Sample 12] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to Al flat particles 3 shown in Table 1.

[0075] [Sample 13] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to Al flat particles 4 shown in Table 1.

[0076] [Sample 14] A metal composite LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery were produced in the same manner as Sample 1, except that the metal powder used in (1a) above was changed to Al flat particles 5 shown in Table 1.

[0077] [Sample 15] An LTO sintered plate, a LiCoO2 sintered plate, and a lithium ion battery containing no metal powder were fabricated in the same manner as Sample 1, except that no metal powder was added in (1a) above.

[0078] [Analysis and Evaluation] The metal composite LTO sintered plates and lithium ion batteries obtained as Samples 1 to 15 were analyzed and evaluated by the following methods.

[0079] [Aspect ratio of metal particles] The metal composite LTO sintered plates of Samples 1 to 14 were subjected to CP polishing (JEOL Ltd., IB-15000CP), and the cross sections of the obtained sintered plates were observed with an SEM (JEOL Ltd., JSM6390LA) in a field of view where 20 or more metal particles were present. Next, 20 metal particles were randomly selected from the SEM image, and the lengths of the metal particles in the longitudinal and lateral directions were measured. The aspect ratio of the metal particles was determined by dividing the "average length in the longitudinal direction" by the "average length in the lateral direction."

[0080] [Ratio of particle size between metal particles and LTO particles] The metal composite LTO sintered plates of Samples 1 to 14 were subjected to CP polishing (JEOL Ltd., IB-15000CP), and the cross sections of the obtained sintered plates were observed using an SEM (JEOL Ltd., JSM6390LA) in a field of view where 20 or more metal particles were present. Next, 20 LTO particles and 20 metal particles were randomly selected from the SEM image, and the longitudinal lengths of the LTO particles and metal particles were measured. The particle size ratio of the metal particles to the LTO particles was determined by dividing the "average longitudinal length of the metal particles" by the "average longitudinal length of the LTO particles."

[0081] Table 1 shows the longitudinal length, lateral length, aspect ratio of the metal particles, and particle size ratio of the metal particles to the LTO particles for the metal particles and LTO particles used in Samples 1 to 15. Table 1 also shows the longitudinal length, lateral length, aspect ratio of the metal particles, and particle size ratio of the metal particles to the LTO particles for the metal particles and LTO particles before firing.

[0082] [Table 1]

[0083] [Battery capacity after high load conditions (durability evaluation against high temperatures and vibration)] The lithium ion batteries of Samples 1 to 15 were evaluated for durability against vibration at high temperatures according to the following procedure. At room temperature and without vibration, the battery to be evaluated was CV charged to 2.7 V (cutoff current was 0.02 C) and CC discharged at 0.02 C. The capacity at this time was taken as the initial discharge capacity (C0). After CV charging (cutoff current was set to 0.02 C) again to 2.7 V, the battery was subjected to vibration at 70° C. The vibration conditions were as follows. Total amplitude: 1.6mm Frequency cycle: 100 cycles, each consisting of (a) a linear sweep from 10 Hz to 880 Hz for 10 seconds, (b) a hold at 880 Hz for 5 seconds, (c) a linear sweep from 880 Hz to 10 Hz for 10 seconds, (d) a hold at 10 Hz for 5 seconds. Vibration direction: Vibration is applied perpendicular to the circular surface of the battery After the vibration at high temperature was stopped, the battery was CV charged to 2.7 V (cutoff current: 0.02 C) at room temperature without vibration, and then CC discharged at 0.02 C. The capacity at this time was defined as the post-load discharge capacity (C1). The "post-load discharge capacity (C1)" was divided by the "initial discharge capacity (C0)" to obtain the capacity retention rate (%) after high load conditions.

[0084] Table 2 summarizes the metal particle content (volume %), type of metal particles, aspect ratio of metal particles, particle size ratio of metal particles to LTO particles, and battery capacity retention rate (%) after high load for samples 1 to 15. Table 2 also shows the aspect ratio of metal particles, particle size ratio of metal particles to LTO particles, and longitudinal and lateral lengths of metal particles in the metal composite sintered plate after sintering. The aspect ratio of the metal particles has changed from before sintering.

[0085] [Table 2]

[0086] Referring to Table 2, the lithium ion batteries of Samples 1 to 14 (Examples 1 to 14) all had a capacity retention rate of 90% or more after vibration at 70°C. In contrast, Sample 15 (Comparative Example 1), in which the LTO sintered plate did not contain metal particles, had a capacity retention rate of 80% after vibration at 70°C. Referring to Samples 1, 2, 3, 4, and 5, the capacity retention rate was 90% or more when the metal composite amount was 5% by volume or more and 50% by volume or less, and the capacity retention rate was 95% or more when the metal particles were 5% by volume or more and 40% by volume or less. Referring to Samples 1, 6, 7, and 8, the capacity retention rate was 95% or more when the metal particles were Al, Ag, Pt, or Au. Referring to Samples 1, 9, 10, and 11, the capacity retention rate was 90% or more when the aspect ratio of the metal particles was 1 to 10, and the higher the aspect ratio, the higher the capacity retention rate. With reference to Samples 1, 12, 13, and 14, the capacity retention rate was 90% or higher in all particle size ratios between metal particles and LTO particles from 0.9 to 10, and the capacity retention rate was higher when the particle size ratio was larger.

[0087] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present disclosure is defined not by the above description but by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0088] 10 lithium ion battery, 12 positive electrode layer, 13 negative electrode layer, 14 separator, 15 positive electrode current collector, 16 positive electrode side carbon layer, 17 negative electrode current collector, 18 negative electrode side carbon layer, 19 electrolyte, 20 exterior body, 21 positive electrode can, 22 negative electrode can, 23 gasket

Claims

1. A sintered plate used as an electrode for a lithium ion battery, The lithium titanate particles are dispersed among the lithium titanate particles. Metal composite sintered plate.

2. In the metal composite sintered plate, the content of the metal particles relative to the total of the lithium titanate particles and the metal particles is 5% by volume or more and 40% by volume or less; The metal composite sintered plate according to claim 1.

3. The metal particles are particles of one or more types of metal selected from the group consisting of Ag, Pt, Al, and Au. The metal composite sintered plate according to claim 1 or 2.

4. The aspect ratio of the metal particles is 1.1 or more. The metal composite sintered plate according to claim 1 or 2.

5. The longitudinal length (L １ ) relative to the longitudinal length (L ２ ) but L ２ / L １ ≧1.1, The metal composite sintered plate according to claim 1 or 2.

6. The metal composite sintered plate according to claim 1 or 2, wherein the electrode is a negative electrode.

7. a positive electrode containing a lithium composite oxide; A negative electrode comprising the metal composite sintered plate according to claim 1 or 2; a separator disposed between the positive electrode and the negative electrode.

8. The positive electrode, the negative electrode, and the separator are integrally sintered to form an integrated sintered plate. The lithium ion battery of claim 7.

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