Electrode, battery, and method for manufacturing electrode

Abstract

According to an embodiment, provided is an electrode including a current collector and an active material-containing layer formed on at least one surface of the current collector. The active material-containing layer includes an active material containing a niobium-containing oxide. Furthermore, the active material-containing layer has a moisture content of 250 to 660 mass ppm, inclusive.

Description

Electrode, battery, and method for manufacturing an electrode

[0001] Embodiments of the present invention relate to electrodes, batteries, and methods for manufacturing electrodes.

[0002] If moisture is introduced into a non-aqueous electrolyte battery, hydrogen will be generated through electrolysis, raising concerns that the battery may swell. Electrodes fabricated by coating with water as the dispersion medium have a high moisture content, so it is necessary to control the residual moisture level. Methods for controlling the residual moisture level, such as adjusting the drying conditions during coating or performing drying after coating, are being considered.

[0003] Japanese Patent No. 6253106 Japanese Patent Publication No. 2015-173034

[0004] The objective is to provide an electrode with low resistance and suppressed volume increase due to storage, a battery equipped with this electrode, and a method for manufacturing the electrode.

[0005] According to the embodiment, an electrode is provided that includes a current collector and an active material-containing layer formed on at least one surface of the current collector. The active material-containing layer contains an active material including a niobium-containing oxide, and has a water content of 250 ppm by mass or more and 660 ppm by mass or less.

[0006] According to another embodiment, a battery comprising the above-mentioned electrodes is provided.

[0007] In yet another embodiment, a battery pack comprising the above-mentioned battery is provided.

[0008] According to another embodiment, a method for manufacturing an electrode is provided, which includes the steps of: preparing a structure in which an active material-containing layer is formed on at least one surface of a current collector by applying a slurry containing an active material containing a niobium-containing oxide to at least one surface of a current collector and drying it; pressing the structure; cutting the structure to obtain one or more electrodes to be processed; and drying the one or more electrodes to be processed so that the moisture content of the active material-containing layer of the one or more electrodes to be processed is 250 ppm by mass or more and 660 ppm by mass or less.

[0009] FIG. 1 is a partially cutaway plan view schematically showing an example of the electrode according to the embodiment. FIG. 2 is a partially cutaway perspective view of an example of the battery according to the embodiment. FIG. 3 is an enlarged cross-sectional view of part A in FIG. 2. An exploded perspective view of another example of the battery according to the embodiment. A partially developed perspective view of the electrode group used in the battery shown in FIG. 4. FIG. 6 is an exploded perspective view of an example of the battery pack according to the embodiment. FIG. 7 is a block diagram showing an electric circuit of the battery pack shown in FIG. 6. Embodiment

[0010] Hereinafter, embodiments will be described with reference to the drawings. Note that common configurations are denoted by the same reference numerals throughout the embodiments, and duplicate descriptions are omitted. Each drawing is a schematic diagram for facilitating the description and understanding of the embodiments, and the shapes, dimensions, ratios and the like may differ from the actual device, but these can be appropriately modified in design in consideration of the following description and known techniques.

[0011] (First Embodiment) The electrode according to the first embodiment includes a current collector and an active material-containing layer formed on at least one surface of the current collector. The active material-containing layer contains an active material including a niobium-containing oxide. The water content of the active material-containing layer is 250 mass ppm or more and 660 mass ppm or less.

[0012] When using an active material containing a niobium-containing oxide, it is possible to use a solvent containing water as the solvent for dispersing the active material in the slurry. When a solvent containing water is used, it is desirable to use an aqueous binder as the binder. Under such circumstances, water tends to be mixed into electrodes using an active material containing a niobium-containing oxide. If water is present inside the battery, there is a risk that hydrogen will be generated by electrolysis and the battery will swell. If an attempt is made to completely dry the electrode to avoid this, drying at a high temperature under reduced pressure is required to shorten the production tact time. However, if the drying temperature is too high, deterioration of the binder may be accelerated, leading to an increase in resistance. In addition, if the drying speed is too fast, the binder will float up together with the solvent, which may cause uneven distribution of the binder and increase the electrode thickness.

[0013] The present inventors have found that by setting the moisture content of the active material-containing layer of an electrode using an active material containing a niobium-containing oxide to 250 mass ppm or more and 660 mass ppm or less, gas generation due to electrolysis (for example, reductive decomposition) of moisture can be suppressed while suppressing deterioration and uneven distribution of the binder and an increase in electrode thickness. As a result, an electrode capable of suppressing an increase in resistance and an increase in volume during storage is realized. The moisture content is more preferably 250 mass ppm or more and 400 mass ppm or less.

[0014] The electrode according to the embodiment may be a battery electrode. Examples of batteries that can include such an electrode include secondary batteries such as lithium ion secondary batteries. The secondary batteries include non-aqueous electrolyte secondary batteries containing a non-aqueous electrolyte. The electrode is desirably, for example, a negative electrode for a battery.

[0015] Hereinafter, the current collector and the active material-containing layer will be described.

[0016] As the current collector, a non-porous sheet such as a foil or a porous sheet can be used. Examples of the material of the current collector include at least one metal selected from the group consisting of copper, nickel, stainless steel, aluminum, and aluminum alloys. The aluminum alloy desirably contains at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Various shapes can be used for the negative electrode current collector depending on the application of the battery.

[0017] The active material-containing layer contains an active material including a niobium-containing oxide. The active material-containing layer may contain at least one of a binder and a conductive agent.

[0018] The niobium-containing oxide has a Li deintercalation potential on the nobler side than that of a graphite negative electrode. Examples of the niobium-containing oxide include niobium oxides, niobium-titanium-containing oxides, niobium-tungsten-containing oxides, and niobium-titanium-molybdenum-containing oxides. The type of the niobium-containing oxide used can be one type or two or more types.

[0019] Examples of niobium oxides include Nb ２ O ５ is included.

[0020] Examples of niobium-titanium-containing oxides include monoclinic niobium-titanium-containing oxide, Ti₂Nb₂O₉, Ti₂Nb 10 O 29 , TiNb 14 O 37 , TiNb 24 O 62 , and substituted niobium-titanium composite oxides in which at least a part of Nb and / or Ti is substituted with a different element. Examples of the substituting element include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, Al and the like. The substituted niobium-titanium composite oxide may contain one type of substituting element, or may contain two or more types of substituting elements.

[0021] Examples of the monoclinic niobium-titanium oxide include Li a Ti 1-x M1 x Nb 2-y M2 y O 7+δ A compound represented by the formula is mentioned. Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. Each subscript in the composition formula satisfies 0≦a≦5, 0≦x<1, 0≦y<2, and -0.3≦δ≦0.3. Specific examples of the monoclinic niobium-titanium oxide include Li a Nb₂TiO₇ (0≦a≦5).

[0022] As another example of the monoclinic niobium-titanium oxide, Li a Ti 1-x M3 x+y Nb 2-y O 7-δ The compound represented by these is mentioned. Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula satisfies 0≦a≦5, 0≦x<1, 0≦y<2, and -0.3≦δ≦0.3.

[0023] Among the above active materials, one may be contained in the electrode as an active material, or two or more may be contained in the electrode as active materials.

[0024] In the active material-containing layer, the proportion of the active material is preferably 75% by mass or more and 96% by mass or less.

[0025] The binder can fill the gaps between the active materials and bond the active materials to the current collector. The binder preferably includes an aqueous binder. An example of an aqueous binder is one that has affinity for an aqueous solvent. Another example of an aqueous binder is one that can be dispersed or dissolved in an aqueous solvent. The aqueous solvent may be water alone or a polar solvent containing water. Examples of aqueous binders include carboxymethyl cellulose (CMC), salts of CMC, and styrene-butadiene rubber. Examples of CMC salts include sodium salt and potassium salt. One of these may be used as a binder, or two or more may be used in combination.

[0026] The binder may include a binder other than a water-based binder (referred to as a secondary binder). Examples of secondary binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorinated rubber. One or more types of secondary binders may be used.

[0027] In the active material-containing layer, the proportion of the binder is preferably 1% by mass or more and 5% by mass or less.

[0028] The conductive agent may, for example, have the form of particles or fibers. A mixture of a particulate conductive agent and a fibrous conductive agent may also be used as the conductive agent. The average particle size of the conductive agent particles is preferably 20 nm or more and 100 nm or less. In the active material-containing layer, the proportion of the conductive agent is preferably, for example, 3% by mass or more and 20% by mass or less.

[0029] The density of the active material-containing layer is 2.0 g / cm³. 3 3.0g / cm or more 3 The following is preferable:

[0030] The electrodes are preferably single-leaf type electrodes. Single-leaf type electrodes, also called single-leaf type electrodes, have a structure (shape) that forms an electrode group by being stacked with the other electrode, rather than by being wound up. Single-leaf type electrodes are not limited to the structure shown in Figure 1. Single-leaf type electrodes can have a current collector and an active material-containing layer, and can have a structure without a current collector tab.

[0031] When the electrode is rectangular in shape, excluding the current collection tab and terminals, it is desirable that the length of the shorter side be in the range of 85 mm to 95 mm, and the length of the longer side be in the range of 274 mm to 909 mm.

[0032] The electrode thickness should preferably be 140 μm or less. The lower limit for the electrode thickness should preferably be 100 μm.

[0033] Next, a specific example of the electrode according to the first embodiment will be described with reference to the drawings.

[0034] Figure 1 is a schematic cutaway plan view showing an example of an electrode according to the embodiment. The direction parallel to the thickness direction of the electrode is defined as the z-axis direction. The extension direction of the current collector tab is defined as the y-axis direction. The direction that intersects approximately perpendicularly with the extension direction of the current collector tab is defined as the x-axis direction.

[0035] The electrode 1 shown in Figure 1 comprises a current collector 1a and an active material-containing layer 1b provided on the surface (xy plane) of the current collector 1a. The active material-containing layer 1b is supported on the main surface (xy plane) of the current collector 1a.

[0036] Furthermore, the current collector 1a includes a portion of its surface where the active material-containing layer 1b is not provided. The center of one side of the current collector 1a parallel to the x-axis direction protrudes in the y-axis direction, and this portion acts as, for example, a current-collecting tab 1c. In the illustrated example, the current-collecting tab 1c is a narrow portion in which the width in the x-axis direction is narrower than the length of one side of the active material-containing layer 1b parallel to the x-axis direction. The width of the current-collecting tab 1c in the x-axis direction may be narrower than the width of the active material-containing layer 1b in the x-axis direction, or it may be the same as the width of the active material-containing layer 1b in the x-axis direction. Instead of the current-collecting tab 1c which is part of the current collector 1a, a separate conductive member may be electrically connected to the electrode 1 and used as an electrode current-collecting tab.

[0037] The electrode 1 in the structure shown in Figure 1 has a rectangular shape excluding the current-collecting tab 1c. If L1 is the width parallel to the extension direction (y-axis direction) of the current-collecting tab 1c, and L2 is the width in the direction approximately perpendicular to the extension direction (x-axis direction), it is desirable that L1 be between 274 mm and 909 mm, and L2 be between 85 mm and 95 mm.

[0038] The method for manufacturing the electrode of the first embodiment is described below.

[0039] The electrode manufacturing method of the first embodiment includes the steps of: creating a structure in which an active material-containing layer is formed on at least one surface of a current collector by applying a slurry containing an active material containing a niobium-containing oxide to at least one surface of a current collector and drying it; pressing the structure; cutting the structure to obtain one or more electrodes to be processed; and drying the one or more electrodes to be processed so that the moisture content of the active material-containing layer of the one or more electrodes to be processed is 250 ppm by mass or more and 660 ppm by mass or less. The details of each step will be described below.

[0040] <Preparation of the structure> The slurry is prepared, for example, by adding a binder and, if necessary, a conductive agent to an active material containing a niobium-containing oxide, and stirring these in the presence of a solvent such as water. The obtained slurry is applied to one or both sides of the current collector. The applied slurry is dried. This gives a structure in which an active material-containing layer is formed on at least one side of the current collector. The structure may be of a shape and size that allows for obtaining one or more electrodes to be treated by cutting. Specifically, the structure may have a strip shape or a reel shape.

[0041] The drying process should be sufficient to prevent defects such as the structure adhering to the press equipment during the subsequent pressing process.

[0042] <Pressing> The pressing method is not particularly limited and may be either a flat plate press or a roll press.

[0043] <Cutting> Cutting is performed using a die, such as a Thomson blade. Cutting is also called punching.

[0044] The electrode to be processed obtained by cutting is preferably a single-leaf electrode. A single-leaf electrode, also called a single-leaf electrode, has a structure (shape) that forms an electrode group by being stacked with another electrode, rather than by being wound up. The single-leaf electrode is not limited to the structure shown in Figure 1. The single-leaf electrode can have a current collector and an active material-containing layer, and can have a structure without a current collector tab.

[0045] <Drying> Dry one or more electrodes to be treated. If there are multiple electrodes to be treated, it is desirable to dry them in a stacked state in the direction of their thickness. In the stack, adjacent electrodes may be in contact with each other.

[0046] It is desirable to reduce the thickness of the electrode after drying to 140 μm or less. This makes it easier to reduce the moisture content of the electrode after drying. When drying multiple electrodes stacked in the thickness direction, reducing the thickness of each electrode to 140 μm or less promotes moisture release from the electrodes, thereby suppressing an increase in electrode thickness due to drying. It is desirable to set the lower limit of electrode thickness to 100 μm.

[0047] The drying oven can be a single oven or a continuous oven divided by partitions. A continuous oven divided by partitions is preferable because it allows for quick switching of ambient temperatures. It is desirable to include a vacuum pump in the drying oven to reduce the pressure inside.

[0048] The drying process should ideally consist of three drying steps, from the first to the third. Each step will be explained below.

[0049] <First Drying Process> It is desirable to carry out this process at a first temperature of 100°C to 130°C under normal pressure. Normal pressure is also called atmospheric pressure. The first drying process is also called the electrode preheating process.

[0050] When the first drying process is carried out in an atmospheric pressure environment, the temperature distribution tends to become more uniform due to air convection. A uniform temperature distribution helps to suppress uneven drying of the electrode being treated, thereby preventing wrinkles from forming on the electrode.

[0051] Setting the first temperature to 100°C or higher contributes to keeping the electrode's moisture content within the range of 250 ppm by mass to 660 ppm by mass through short-time drying. However, if the first temperature is too high, the drying process will proceed rapidly, potentially causing the binder to float to the surface along with the solvent (such as water), resulting in a thicker electrode. Furthermore, uneven distribution of the binder or deterioration of the binder may be accelerated. Uneven distribution and deterioration of the binder can lead to an increase in the electrode's resistance. By setting the first temperature to 100°C to 130°C, it is possible to keep the electrode's moisture content within the desired range through short-time drying while suppressing changes in electrode thickness, uneven distribution of the binder, and deterioration of the binder.

[0052] <Second Drying Process> It is desirable to carry out the drying process at a second temperature higher than the first temperature under atmospheric pressure. The second drying process is also called the atmospheric pressure heating process.

[0053] By raising the temperature at atmospheric pressure, air convection can be utilized, making it easier to achieve a uniform temperature distribution. Higher uniformity in temperature distribution suppresses the formation of wrinkles caused by uneven drying of the electrode being treated. However, when raising the temperature in a reduced-pressure atmosphere, the temperature rise is solely due to heat conduction from the heater or the container in contact with the electrode, which tends to result in an uneven temperature distribution.

[0054] The second temperature is preferably in the range of 130°C to 150°C. Setting the second temperature above 130°C contributes to bringing the moisture content of the electrode within the range of 250 ppm to 660 ppm by mass through short drying times. However, if the second temperature is too high, the drying will proceed rapidly, which may accelerate the increase in electrode thickness, uneven distribution of the binder, or degradation of the binder. By setting the first temperature between 130°C and 150°C, it is possible to bring the moisture content of the electrode within the desired range through short drying times while suppressing changes in electrode thickness, uneven distribution of the binder, and degradation of the binder.

[0055] The drying time in the second drying process should preferably be between one and two hours. This allows for efficient and reliable control of the electrode's moisture content within the desired range.

[0056] <Third Drying Step> This step is preferably carried out in a vacuum of 0.1 Pa to 100 Pa at a temperature of 130°C to 150°C. The third drying step is also called the reduced-pressure drying step.

[0057] The transition from the second drying process to the third drying process is made possible by changing the drying atmosphere from atmospheric pressure to a reduced pressure atmosphere. The temperature may be maintained at the second temperature, but it can be increased or decreased from the second temperature as long as it is within the range of 130°C to 150°C. Therefore, the drying process may include a drying process carried out under different conditions from the first, second, and third drying processes.

[0058] By reducing the vacuum level to 100 Pa or less, moisture can be more easily removed from the electrodes. By maintaining a vacuum level between 0.1 Pa and 100 Pa, it is possible to promote moisture release from the electrodes while reducing the time and cost required for vacuuming.

[0059] The third temperature is preferably in the range of 130°C to 150°C. Setting the third temperature above 130°C contributes to bringing the moisture content of the electrode within the range of 250 ppm to 660 ppm by mass with short drying time. However, if the third temperature is too high, drying will proceed rapidly, which may accelerate the increase in electrode thickness, uneven distribution of the binder, or degradation of the binder. By setting the third temperature between 130°C and 150°C, it is possible to bring the moisture content of the electrode within the desired range with short drying time while suppressing changes in electrode thickness, uneven distribution of the binder, and degradation of the binder.

[0060] The drying time for the third drying step should preferably be between 8 and 12 hours. This allows for efficient and reliable control of the electrode's moisture content within the desired range.

[0061] By performing the first to third drying steps, it is possible to suppress wrinkle formation on the electrode, changes in electrode thickness, uneven distribution of the binder, and deterioration of the binder, while drying in a short time to achieve a moisture content of 250 ppm by mass or more and 660 ppm by mass or less in the active material-containing layer of the electrode.

[0062] Subsequently, other processes such as welding of current collection tabs or terminals may be performed. Alternatively, aging treatment may be performed between processes (for example, between the pressing process and the cutting process). Furthermore, if it is possible to keep the moisture content between 250 ppm and 660 ppm by mass, the process may be omitted. In this way, the electrode of the embodiment can be manufactured.

[0063] In the electrode according to this embodiment, the electrode thickness, moisture content, and active material composition can be confirmed by the following method.

[0064] When analyzing electrodes incorporated into a battery, remove the electrodes using the following procedure.

[0065] First, prepare the battery to be measured. The battery to be measured must have a discharge capacity of 80% or more of its rated capacity. In other words, batteries that have deteriorated excessively will not be measured.

[0066] Next, discharge the prepared battery until the open-circuit voltage is between 1.5V and 2.0V. Then, transfer the discharged battery to a glove box filled with argon, where the dew point of the internal atmosphere is -70°C. Cut open the battery inside the glove box. Remove the electrode group from the opened battery. If the removed electrode group includes positive and negative leads, carefully cut the positive and negative leads, taking care not to short-circuit them.

[0067] Next, the electrode assembly is disassembled into a positive electrode, a negative electrode, and a separator. For example, the positive electrode is selected as the electrode to be measured. The resulting electrode is then washed using ethyl methyl carbonate as the solvent. In this washing process, the disassembled components are completely immersed in the ethyl methyl carbonate solvent and left in that state for 60 minutes.

[0068] After cleaning, the electrodes are subjected to vacuum drying. Vacuum drying is performed in a 25°C environment by reducing the pressure from atmospheric pressure to -97 kPa or higher and maintaining that state for 10 minutes. The electrodes thus removed after disassembly, cleaning, and vacuum drying are to be used for the following measurements.

[0069] <Measurement of electrode thickness> For an electrode with a current-collecting tab as illustrated in Figure 1, the thickness is measured using a micrometer with a measurement area of ​​5 mm in diameter. The thickness is measured at five points: the four corners and the center of the electrode, and the average value is taken as the measured value.

[0070] <Measurement of moisture content> Use a Karl Fischer moisture meter. Heat to 140°C to generate moisture, then detect the moisture for 5 minutes or more. The obtained value will be taken as the moisture content.

[0071] <Measurement of Active Material Composition> The composition of the electrode active material can be determined by measuring the surface of the electrode using X-ray fluorescence (XRF).

[0072] The electrode of the first embodiment described above comprises an active material containing a niobium-containing oxide and an active material-containing layer with a moisture content of 250 ppm by mass or more and 660 ppm by mass or less. According to the electrode of the first embodiment, an electrode with low resistance and suppressed volume increase due to storage can be realized.

[0073] (Second Embodiment) The battery according to the second embodiment comprises the electrodes of the embodiment. The battery comprises the electrodes and electrolyte according to the first embodiment. The battery may comprise a positive electrode and a negative electrode. The battery may include the electrodes according to the first embodiment as the negative electrode.

[0074] The battery may further include a separator positioned between the positive and negative electrodes. The positive electrode, negative electrode, and separator can constitute an electrode group. The electrolyte can be held within the electrode group.

[0075] Furthermore, such a battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0076] Furthermore, such a battery may further comprise a positive terminal electrically connected to the positive electrode and a negative terminal electrically connected to the negative electrode. Each electrode terminal may be connected, for example, to a current-collecting tab of the electrode in question. At least a portion of the positive terminal and at least a portion of the negative terminal may extend outside the housing member.

[0077] The battery in question may be a secondary battery, such as a lithium-ion secondary battery. Furthermore, the secondary battery may include, for example, a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0078] The positive electrode, electrolyte, separator, casing, positive electrode terminal, and negative electrode terminal of a battery using the electrode of the embodiment as the negative electrode will be described in detail below.

[0079] <Positive Electrode> The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer (positive electrode composite layer) supported on one side or both sides of the positive electrode current collector, which contains positive electrode active material. If the positive electrode current collector has, for example, a sheet shape, the positive electrode active material-containing layer may be supported on at least one main surface of the positive electrode current collector.

[0080] An example of a positive electrode active material is lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0<x≦1, 0<y<1, 0<z<1, y+z<1), Li x M ｙ O ２ (0 < x ≤ 1, 0 < y ≤ 1, M is for example Mn), Li ｘ M ２ｙ O ４ (0 < x ≤ 1, 0 < y ≤ 1, M is, for example, Mn), lithium phosphate oxide having an olivine structure (e.g., Li x M ｙ PO ４ (M is at least one element selected from Mn, Ni, Co, Fe, 0 < x ≤ 1.1, 0.8 ≤ y ≤ 1.1), Li ｘ FePO ４ (0<x≦1.1), Li ｘ Fe １－ｙ Mn ｙ PO ４ (0<x≦1.1, 0≦y≦1), Li ｘ CoPO ４ (0<x≦1.1), Li ｘ MnPO ４ (0 < x ≤ 1.1), lithium nickel cobalt composite oxide (e.g., LixNi 1-a Co aO2, 0 < x ≤ 1, 0 < a ≤ 1), lithium cobalt composite oxide (e.g., Li x CoO2, 0 < x ≤ 1), lithium manganese cobalt composite oxide (e.g., Li x Mn 1-a Co a O2, 0 < x ≤ 1, 0 < a < 1), spinel-type lithium manganese nickel composite oxide (e.g., Li x Mn 2-a Ni a O4, 0 < x ≤ 1, 0 < a < 2), fluorinated iron sulfate (e.g., Li) having a tabolite structure ｘ M ｙ SO ４ F (0 < x ≤ 1, 0 < y ≤ 1, M is at least one of Fe or Mn), Li ｘ Fe １－ａ Mn a SO ４ This includes F (0 < x ≤ 1, 0 < a ≤ 1), etc. The type of positive electrode active material can be one or more types.

[0081] The positive electrode active material-containing layer may contain substances other than the positive electrode active material, such as conductive agents and binders. Conductive agents can enhance current collection performance and reduce contact resistance between the active material and the current collector. Preferably, the conductive agent contains a carbon material. Examples of carbon materials include acetylene black, Ketjen black, furnace black, graphite, carbon nanotubes, and carbon nanofibers. The active material-containing layer may contain one or more of the above carbon materials.

[0082] The conductive agent may have the form of particles or fibers, for example. The average particle size of the conductive agent particles is preferably 20 nm to 100 nm. In the positive electrode active material-containing layer, the proportion of the conductive agent is preferably 3% to 20% by mass.

[0083] Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or fluorinated rubber. One or more types of binders may be used. Preferably, the proportion of the binder in the positive electrode active material-containing layer is 1% by mass or more and 1.8% by mass or less.

[0084] The density of the positive electrode active material-containing layer is 3.2 g / cm³. 3 3.8g / cm or more 3 The following is preferable:

[0085] For the positive electrode current collector, for example, metal foil or alloy foil can be used. Examples of metal foil include aluminum foil, stainless steel foil, and nickel foil. Examples of alloy foil include aluminum alloy, copper alloy, and nickel alloy.

[0086] The positive electrode is prepared, for example, by the following method: A slurry is prepared by kneading the positive electrode active material, conductive agent, and binder with a solvent (e.g., N-methylpyrrolidone (NMP)). The obtained slurry is applied to a positive electrode current collector, dried, and then pressed to obtain the positive electrode.

[0087] <Separator> A material having electrical insulating properties can be used for the separator. While not particularly limited as long as it has insulating properties, for example, a porous film or nonwoven fabric can be used as the separator. Examples of materials constituting the separator include polyolefin, cellulose, polyethylene terephthalate, and vinylon. The separator material may be one type, or two or more types may be used in combination.

[0088] The thickness of the separator can be between 5 μm and 20 μm.

[0089] <Electrode Group> The electrode group preferably has a stacked structure in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators in between. Alternatively, the electrode group may have other structures such as a wound type.

[0090] <Electrolytes> Examples of electrolytes include non-aqueous electrolytes. Non-aqueous electrolytes include liquid non-aqueous electrolytes containing a non-aqueous solvent and an electrolyte salt (solute), and gel-like non-aqueous electrolytes formed by compounding a liquid non-aqueous electrolyte with a polymer material.

[0091] Examples of electrolyte salts include lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium hexalithium antimonate (LiSbF6), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3; commonly known as LiTFS), and lithium bistrifluoromethanesulfonylamide {Li(CF3SO2)2N}. Examples of lithium salts include {LiTFSI}, bispentafluoroethanesulfonylamide lithium {Li(C2F5SO2)2N; commonly known as LiBETI}, bisoxalatoborate lithium {LiB(C2O4)2; commonly known as LiBOB}, and difluoro(trifluoro-2-oxide-2-trifluoro-methylpropionato(2-)-0,0)borate lithium {LiBF2OCCOOC(CF3)2; commonly known as LiBF2(HHIB)}. These electrolyte salts may be used individually or in combination of two or more. Examples of desirable electrolytes include LiPF6, LiBF4, LiB(C2O4)2 (commonly known as LiBOB), LiF2BC2O4), LiBF2(OCOOC(CF3)2) (commonly known as LiBF2(HHIB)), and LiPO2F2.

[0092] The electrolyte salt concentration is preferably within the range of 0.5 M to 3 M. This improves performance when high load currents are applied.

[0093] Examples of non-aqueous solvents are not limited to propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane, acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and dipropyl carbonate (DPC). These solvents may be used individually or in combination of two or more. When combining two or more solvents, it is preferable to select solvents with a dielectric constant of 20 or higher.

[0094] Non-aqueous electrolytes may contain compounds as additives. Examples of compounds are not particularly limited, but include vinylene carbonate (VC), fluorovinylene carbonate, methylvinylene carbonate, fluoromethylvinylene carbonate, ethylvinylene carbonate, propylvinylene carbonate, butylvinylene carbonate, dimethylvinylene carbonate, diethylvinylene carbonate, dipropylvinylene carbonate, vinylene acetate (VA), vinylene butyrate, vinylene hexanate, vinylene crotonate, catechol carbonate, propane sultone, butane sultone, and the like. The number of additives can be one or more.

[0095] <Exterior Components> The exterior components may be formed from laminate film or made of a metal container. The thickness of the laminate film and the metal container may be 0.5 mm or less. Alternatively, resin containers made of polyolefin resin, polyvinyl chloride resin, polystyrene resin, acrylic resin, phenolic resin, polyphenylene resin, fluororesin, etc., may be used as exterior components. When a metal container is used, the lid may be integrated with the container or be a separate component.

[0096] Examples of exterior component shapes include flat (thin), rectangular, cylindrical, coin-shaped, button-shaped, sheet-shaped, and laminated types. These exterior components can be used for small batteries mounted in portable electronic devices, as well as for large batteries mounted in two-wheeled or four-wheeled vehicles.

[0097] Examples of laminate films include multilayer films comprising resin layers and metal layers placed between the resin layers. For weight reduction, aluminum foil or aluminum alloy foil is preferred for the metal layers. The resin layers can be films made from polymer materials such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The laminate film can be sealed by heat fusion and molded into the shape of an exterior component.

[0098] Metal containers are made from aluminum or aluminum alloys. Aluminum alloys containing elements such as magnesium, zinc, and silicon are preferred. When aluminum or aluminum alloys contain transition metals such as iron, copper, nickel, and chromium, their content is preferably 100 ppm by mass or less.

[0099] <Positive Terminal> A positive terminal can act as a conductor for electrons to move between the positive electrode and an external circuit by being electrically connected to a portion of the positive electrode. The positive terminal can be connected, for example, to a positive current collector, particularly a positive current collector tab. Alternatively, the positive terminal can be connected to a positive current collector tab via, for example, a positive lead.

[0100] The positive terminal should, for example, have a voltage of 3.0V to 4.5V relative to the Li oxidation-reduction reaction potential (vs. Li / Li). + It is preferable that the positive electrode terminal is formed from a material that is electrically stable and conductive in the range of potentials. It is preferable that the positive electrode terminal is formed from aluminum, or from an aluminum alloy containing one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si.

[0101] The positive terminal is preferably made of a material with high electrical conductivity. When connected to a positive current collector, it is preferable that the positive terminal is made of the same material as the current collector. Using the same material can reduce the contact resistance between the positive terminal and the positive current collector. Similarly, it is preferable that the positive lead is made of the same material as the positive terminal and the positive current collector.

[0102] <Negative Terminal> A negative terminal can act as a conductor for electrons to move between the negative electrode and an external circuit by being electrically connected to a portion of the negative electrode. The negative terminal can be connected, for example, to a negative current collector, particularly a negative current collector tab. Alternatively, the negative terminal can be connected to a negative current collector tab via, for example, a negative lead.

[0103] The negative terminal should have a voltage of 0.4V to 3.0V relative to the Li oxidation-reduction reaction potential (vs. Li / Li). + It is preferable that the negative electrode terminal is formed from a material that is electrically stable and conductive at the potential of ).

[0104] The negative electrode terminal is preferably made of a material with high electrical conductivity. When connected to a negative electrode current collector, it is preferable that the negative electrode terminal is made of the same material as the current collector. Using the same material can reduce the contact resistance between the negative electrode terminal and the negative electrode current collector. Similarly, it is preferable that the negative electrode lead is made of the same material as the negative electrode terminal and the negative electrode current collector.

[0105] The battery of the embodiment will be described in detail with reference to Figures 2 to 5.

[0106] Figures 2 and 3 show an example of a secondary battery 1 using a laminate film outer casing as the container.

[0107] The secondary battery 100 shown in Figures 2 and 3 comprises an electrode group 2 shown in Figures 2 and 3, an outer casing member 3 shown in Figure 2, and an electrolyte (not shown). The electrode group 2 and the electrolyte are housed within the outer casing member 3. The electrolyte is held within the electrode group 2.

[0108] The exterior component 3 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0109] As shown in Figure 3, electrode group 2 is a stacked electrode group. The stacked electrode group 2 has a structure in which negative electrodes 4 and positive electrodes 6 are stacked alternately with a separator 5 interposed between them.

[0110] The electrode group 2 includes a plurality of negative electrodes 4. Each of the plurality of negative electrodes 4 comprises a negative electrode current collector 4a and a negative electrode active material-containing layer 4b supported on both sides of the negative electrode current collector 4a. The electrode group 2 also includes a plurality of positive electrodes 6. Each of the plurality of positive electrodes 6 comprises a positive electrode current collector 6a and a positive electrode active material-containing layer 6b supported on both sides of the positive electrode current collector 6a.

[0111] Each negative electrode 4's negative electrode current collector 4a includes a portion 4c on one side where the negative electrode active material-containing layer 4b is not supported on any surface. This portion 4c functions as a negative electrode current collector tab. As shown in Figure 3, the portion 4c that functions as a negative electrode current collector tab does not overlap with the positive electrode 6. Furthermore, multiple negative electrode current collector tabs (portions 4c) are electrically connected to a strip-shaped negative electrode terminal 7. The tip of the strip-shaped negative electrode terminal 7 is extended to the outside of the outer casing member 3.

[0112] Although not shown in the diagram, the positive electrode current collector 6a of each positive electrode 6 includes a portion on one side where the positive electrode active material-containing layer 6b is not supported on any surface. This portion functions as a positive electrode current collector tab. The positive electrode current collector tab, like the negative electrode current collector tab (part 4c), does not overlap with the negative electrode 4. The positive electrode current collector tab is located on the opposite side of the electrode group 2 from the negative electrode current collector tab (part 4c). The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 8. The tip of the strip-shaped positive electrode terminal 8 is located on the opposite side from the negative electrode terminal 7 and is extended to the outside of the outer casing member 3.

[0113] Figure 4 is an exploded perspective view of an example of a non-aqueous electrolyte battery according to an embodiment. The battery shown in Figure 4 is a sealed, rectangular non-aqueous electrolyte battery. The non-aqueous electrolyte battery shown in Figure 4 comprises an outer casing 11, a lid 12, a positive electrode external terminal 13, a negative electrode external terminal 14, and an electrode group 2. The outer casing is composed of the outer casing 11 and the lid 12. The outer casing 11 has a bottomed rectangular tube shape and is made of a metal such as aluminum, aluminum alloy, iron, or stainless steel. The bottom surface of the outer casing 11 is defined by a long side parallel to the winding axis direction 19 of the electrode group 2 and a short side perpendicular or approximately perpendicular to the long side. In Figure 4, the x-axis direction is parallel to the winding axis direction 19. The y-axis direction is perpendicular to the winding axis direction 19 and parallel to the short side of the outer casing 11. The z-axis direction is parallel to the height direction of the outer casing 11.

[0114] Figure 5 is a partially unfolded perspective view of the electrode group used in the non-aqueous electrolyte battery shown in Figure 4. As shown in Figure 5, the flat electrode group 2 has a positive electrode 6 and a negative electrode 4 wound in a flat shape with a separator 5 between them. The positive electrode 6 includes a strip-shaped positive electrode current collector made of, for example, metal foil, a positive electrode current collector tab 6c that is one end parallel to the long side of the positive electrode current collector, and a positive electrode material layer (positive electrode active material containing layer) 6b formed on the positive electrode current collector, except for the portion of the positive electrode current collector tab 6c. On the other hand, the negative electrode 4 includes a strip-shaped negative electrode current collector made of, for example, metal foil, a negative electrode current collector tab 4c that is one end parallel to the long side of the negative electrode current collector, and a negative electrode material layer (negative electrode active material containing layer) 4b formed on the negative electrode current collector, except for the portion of the negative electrode current collector tab 4c.

[0115] In this configuration, the positive electrode 6, separator 5, and negative electrode 4 are wound with their positions offset such that the positive electrode current collector tab 6c protrudes from the separator 5 in the winding axis direction 19 of the electrode group, and the negative electrode current collector tab 4c protrudes from the separator 5 in the opposite direction. Due to this winding, as shown in Figure 4, the electrode group 2 has the positive electrode current collector tab 6c, wound in a spiral pattern, protruding from one end face, and the negative electrode current collector tab 4c, wound in a spiral pattern, protruding from the other end face. A non-aqueous electrolyte (not shown) is impregnated into the electrode group 2.

[0116] As shown in Figure 1, the positive electrode current collector tab 6c and the negative electrode current collector tab 4c are each divided into two bundles near the winding center of the electrode group. The conductive clamping member 15 has first and second clamping portions 15a and 15b that are roughly U-shaped, and a connecting portion 15c that electrically connects the first clamping portion 15a and the second clamping portion 15b. In each case, one bundle of the positive and negative electrode current collector tabs 6c and 4c is clamped by the first clamping portion 15a, and the other bundle is clamped by the second clamping portion 15b.

[0117] The positive lead 16 has a roughly rectangular support plate 16a, a through hole 16b opened in the support plate 16a, and strip-shaped current collectors 16c and 16d that branch out from the support plate 16a and extend downward. On the other hand, the negative lead 17 has a roughly rectangular support plate 17a, a through hole 17b opened in the support plate 17a, and strip-shaped current collectors 17c and 17d that branch out from the support plate 17a and extend downward.

[0118] The positive electrode lead 16 sandwiches a clamping member 15 between the current collecting portions 16c and 16d. The current collecting portion 16c is positioned on the first clamping portion 15a of the clamping member 15. The current collecting portion 16d is positioned on the second clamping portion 15b. The current collecting portions 16c and 16d, the first and second clamping portions 15a and 15b, and the positive electrode current collecting tab 6c are joined together, for example, by ultrasonic welding. As a result, the positive electrode 6 of the electrode group 2 and the positive electrode lead 16 are electrically connected via the positive electrode current collecting tab 6c.

[0119] The negative electrode lead 17 has a clamping member 15 sandwiched between the current collecting portions 17c and 17d. The current collecting portion 17c is positioned on the first clamping portion 15a of the clamping member 15. On the other hand, the current collecting portion 17d is positioned on the second clamping portion 15b. The current collecting portions 17c and 17d, the first and second clamping portions 15a and 15b, and the negative electrode current collecting tab 4c are joined together, for example, by ultrasonic welding. As a result, the negative electrode 4 of the electrode group 2 and the negative electrode lead 17 are electrically connected via the negative electrode current collecting tab 4c.

[0120] The material of the positive and negative electrode leads 16, 17 and the clamping member 15 is not specifically designated, but it is desirable that they be made of the same material as the positive and negative electrode external terminals 13, 14. For example, aluminum or an aluminum alloy may be used for the positive electrode external terminal 13, and aluminum, an aluminum alloy, copper, nickel, or nickel-plated iron may be used for the negative electrode external terminal 14. For example, if the material of the external terminal is aluminum or an aluminum alloy, it is preferable that the material of the leads be aluminum or an aluminum alloy. Also, if the external terminal is copper, it is desirable that the material of the leads be copper or the like.

[0121] The rectangular plate-shaped lid 12 is seam-welded to the opening of the outer can 11, for example, by laser. The lid 12 is made of a metal such as aluminum, aluminum alloy, iron, or stainless steel. It is preferable that the lid 12 and the outer can 11 are made of the same type of metal. The positive external terminal 13 is electrically connected to the support plate 16a of the positive lead 16, and the negative external terminal 14 is electrically connected to the support plate 17a of the negative lead 17. An insulating gasket 18 is placed between the positive and negative external terminals 13, 14 and the lid 12, electrically insulating the positive and negative external terminals 13, 14 from the lid 12. It is preferable that the insulating gasket 12 is a molded resin product.

[0122] Although the battery shown in Figure 4 uses a wound electrode group in which a separator is wound together with the positive and negative electrodes, a stacked electrode group in which the positive and negative electrodes are alternately stacked with a separator in between may also be used. Alternatively, the electrode group may have other structures.

[0123] The battery according to the second embodiment includes the electrodes according to the first embodiment. Therefore, this battery has low resistance and can suppress volume increase during storage.

[0124] (Third Embodiment) According to the third embodiment, a battery pack is provided. This battery pack comprises the battery according to the second embodiment.

[0125] The battery pack according to the third embodiment may comprise one or more of the batteries (single cells) according to the second embodiment described above. Multiple batteries that may be included in such a battery pack can be electrically connected to each other in series or parallel to form a battery pack. Such a battery pack may include multiple battery packs.

[0126] Next, an example of a battery pack according to the third embodiment will be described with reference to the drawings.

[0127] Figure 6 is an exploded perspective view of an example battery pack according to the embodiment. Figure 7 is a block diagram showing the electrical circuit of the battery pack in Figure 6.

[0128] The battery pack 20 shown in Figures 6 and 7 comprises a plurality of individual cells 21. Each individual cell 21 may be a flat-type battery, as is one example according to this embodiment.

[0129] Multiple individual cells 21 are stacked so that their outwardly extending negative terminals 51 and positive terminals 61 are aligned in the same direction, and then fastened together with adhesive tape 22 to form a battery pack 23. These individual cells 21 are electrically connected in series with each other, as shown in Figure 7.

[0130] The printed circuit board 24 is positioned opposite the side from which the negative terminal 51 and positive terminal 61 of the single cell 21 extend. As shown in Figure 7, the printed circuit board 24 is equipped with a thermistor 25, a protection circuit 26, and terminals 27 for supplying power to external devices. An insulating plate (not shown) is attached to the side of the printed circuit board 24 that faces the battery pack 23 to avoid unnecessary connections with the wiring of the battery pack 23.

[0131] The positive lead 28 is connected to the positive terminal 61 located at the bottom layer of the battery pack 23, and its tip is inserted into the positive connector 29 of the printed circuit board 24 for electrical connection. The negative lead 30 is connected to the negative terminal 51 located at the top layer of the battery pack 23, and its tip is inserted into the negative connector 31 of the printed circuit board 24 for electrical connection. These connectors 29 and 31 are connected to the protection circuit 26 through wiring 32 and 33 formed on the printed circuit board 24.

[0132] The thermistor 25 detects the temperature of the individual cell 21, and the detection signal is transmitted to the protection circuit 26. The protection circuit 26 can shut off the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the terminal 27 for supplying power to external devices under predetermined conditions. An example of a predetermined condition is when the temperature detected by the thermistor 25 exceeds a predetermined temperature. Another example of a predetermined condition is when overcharging, over-discharging, overcurrent, etc., of the individual cell 21 is detected. This detection of overcharging, etc., is performed for individual cell 21 or for the entire battery pack 23. When detecting individual cell 21, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each individual cell 21. In the battery pack 20 of Figures 6 and 7, wiring 35 for voltage detection is connected to each individual cell 21. Detection signals are transmitted to the protection circuit 26 through these wirings 35.

[0133] Protective sheets 36 made of rubber or resin are placed on three sides of the battery pack 23, excluding the side from which the positive terminal 61 and negative terminal 51 protrude.

[0134] The battery pack 23 is housed in a storage container 37 together with each protective sheet 36 and the printed circuit board 24. Specifically, the protective sheets 36 are placed on both inner surfaces in the long direction and on each inner surface in the short direction of the storage container 37, and the printed circuit board 24 is placed on the inner surface opposite to the short direction. The battery pack 23 is located in the space enclosed by the protective sheets 36 and the printed circuit board 24. The lid 38 is attached to the top surface of the storage container 37.

[0135] Alternatively, heat-shrinkable tape may be used instead of adhesive tape 22 to secure the battery pack 23. In this case, protective sheets are placed on both sides of the battery pack, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to secure the battery pack.

[0136] Figures 6 and 7 show a configuration in which the single cells 21 are connected in series, but they may be connected in parallel to increase the battery capacity. Furthermore, assembled battery packs can also be connected in series and / or in parallel.

[0137] Furthermore, the configuration of the battery pack can be appropriately modified depending on the application. Preferably, the battery pack is designed for applications where good cycle performance is desired when drawing high current. Specific applications include power supplies for digital cameras, and in-vehicle use in two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, and electric assist bicycles. Such a battery pack is particularly suitable for in-vehicle use.

[0138] The battery pack according to this embodiment comprises the battery according to this embodiment. Therefore, such a battery pack has low resistance and can suppress volume increase during storage.

[0139] Examples are described below, but the present invention is not limited to the examples listed below unless it exceeds the spirit of the invention.

[0140] (Example 1) [Preparation of the negative electrode] As the active material, particles of monoclinic niobium titanium oxide having a composition represented by the formula TiNb2O7 were prepared. Acetylene black was prepared as a conductive agent, and carboxymethylcellulose and styrene butadiene rubber were prepared as binders. These were mixed in pure water in a mass percentage ratio of active material:acetylene black:carboxymethylcellulose:styrene butadiene rubber of 90:5:2.5:2.5 to obtain a slurry. This slurry was applied to both sides of a current collector made of strip-shaped aluminum foil with a thickness of 12 μm, excluding one side, and the coating was dried at 120°C for 180 seconds. Thus, a reel-shaped structure with an active material-containing layer formed on both sides of the current collector was obtained. The side of the current collector that was not coated with slurry functions as a negative electrode current collector tab.

[0141] A reel-shaped structure was pressed. Next, a single-wafer negative electrode (electrode to be processed) was punched out from the reel-shaped structure using a die-cutting machine with a Thomson blade. The single-wafer negative electrode had the structure shown in Figure 1.

[0142] A negative electrode preheating process was performed as the first drying step for the single-wafer negative electrode. The negative electrode preheating process was carried out at 110°C for 2 hours at atmospheric pressure. Next, as the second drying step, a negative electrode atmospheric pressure heating process was carried out at 130°C for 1 hour at atmospheric pressure. After that, while maintaining the temperature of 130°C, the pressure was reduced from atmospheric pressure to 100 Pa. Drying was carried out at 130°C for 8 hours in a vacuum atmosphere of 100 Pa (also called the third drying step or negative electrode reduced pressure drying step). In this way, a negative electrode with a thickness of 120 μm after drying was manufactured. The moisture content of the negative electrode was measured using the method described above, and the results are shown in Table 2. [Preparation of the positive electrode] Particles of lithium cobalt oxide (LiCoO2) were prepared as the positive electrode active material. Acetylene black was prepared as a conductive agent, and PVdF was prepared as a binder. These were dispersed in N-methyl-2-pyrrolidone (NMP) such that the mass percentage of active material:acetylene black:PVdF was 90:5:5 to obtain a slurry. This slurry was applied to both sides of a current collector made of 12 μm aluminum foil, excluding one side, and the coating was dried at 100°C for 240 seconds. Thus, a laminate was obtained in which an active material-containing layer was formed on both sides of the current collector (excluding one side). The one side of the current collector that was not coated with slurry functions as a positive electrode current collector tab. Next, the obtained laminate was subjected to a press to obtain a positive electrode roll. A single-wafer positive electrode was produced from the obtained positive electrode roll using a die-cutting machine with a Thomson blade.

[0143] Using the positive electrode, negative electrode, and polyethylene separator prepared as described above, a stacked electrode array was created.

[0144] [Preparation of Non-Aqueous Electrolyte] A non-aqueous solvent was prepared by mixing propylene carbonate (PC) and diethyl carbonate (DEC) in a 1:1 volume ratio. Lithium hexafluoride phosphate (LiPF6) was dissolved in the obtained non-aqueous solvent at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0145] [Battery Assembly] The electrode group, which was molded into a flat shape as described above, was placed in a pack made of laminate film and vacuum dried. The laminate film used was a 0.1 mm thick laminate film with polypropylene layers formed on both sides of a 40 μm thick aluminum foil. The above electrolyte solution was poured in. After pouring, the laminate was heat-sealed under reduced pressure to manufacture a non-aqueous electrolyte battery.

[0146] (Example 2) A non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the negative electrode preheating step (first drying step), the negative electrode atmospheric pressure heating step (second drying step), and the negative electrode reduced pressure drying step (third drying step) were carried out as described below.

[0147] The negative electrode preheating process was carried out at atmospheric pressure at 130°C for 2 hours. Next, the negative electrode atmospheric pressure heating process was carried out at atmospheric pressure at 145°C for 1 hour. After that, while maintaining the temperature of 145°C, the pressure was reduced from atmospheric pressure to 100 Pa. Drying was carried out at 145°C for 8 hours in a 100 Pa vacuum atmosphere as the negative electrode vacuum drying process. The negative electrode thickness and moisture content after drying were measured using the method described above, and the results are shown in Table 2.

[0148] (Example 3) A non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the negative electrode preheating step (first drying step), the negative electrode atmospheric pressure heating step (second drying step), and the negative electrode reduced pressure drying step (third drying step) were carried out as described below.

[0149] The negative electrode preheating process was carried out at atmospheric pressure at 110°C for 2 hours. Next, the negative electrode atmospheric pressure heating process was carried out at atmospheric pressure at 145°C for 1 hour. After that, the temperature was lowered to 130°C, and the pressure was reduced from atmospheric pressure to 100 Pa. Drying was carried out at 130°C for 8 hours in a 100 Pa vacuum atmosphere as the negative electrode vacuum drying process. The negative electrode thickness and moisture content after drying were measured using the method described above, and the results are shown in Table 2.

[0150] (Example 4) A non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the negative electrode preheating step (first drying step), the negative electrode atmospheric pressure heating step (second drying step), and the negative electrode reduced pressure drying step (third drying step) were carried out as described below.

[0151] The negative electrode preheating process was carried out at atmospheric pressure at 110°C for 2 hours. Next, the negative electrode atmospheric pressure heating process was carried out at atmospheric pressure at 130°C for 1 hour. After that, the temperature was raised to 145°C, and the pressure was reduced from atmospheric pressure to 100 Pa. Drying was carried out at 145°C for 8 hours in a 100 Pa vacuum atmosphere as the negative electrode vacuum drying process. The negative electrode thickness and moisture content after drying were measured using the method described above, and the results are shown in Table 2.

[0152] (Comparative Examples 1 to 4) Non-aqueous electrolyte batteries were manufactured in the same manner as in Example 1, except that the negative electrode preheating process, the negative electrode atmospheric pressure heating process, and the negative electrode reduced pressure drying process were carried out under the conditions shown in Table 1.

[0153] (Comparative Example 5) A non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the negative electrode was prepared using the method described below.

[0154] Graphite powder and polyvinylidene fluoride (PVdF) were mixed in a mass ratio of 90:10, and the resulting mixture was kneaded in the presence of an organic solvent (N-methylpyrrolidone) to prepare a slurry. The obtained slurry was applied to both sides of a 12 μm thick strip of copper foil, excluding one edge, dried, and pressed to obtain a strip-shaped structure in which an active material-containing layer was formed on both sides (excluding one edge) of the current collector. The one edge of the current collector that was not coated with slurry functions as a negative electrode current collector tab.

[0155] A strip-shaped structure was pressed. Next, a single-wafer negative electrode (electrode to be processed) was punched out from the strip-shaped structure using a die-cutting machine with a Thomson blade. The single-wafer negative electrode had the structure shown in Figure 1.

[0156] A negative electrode preheating process was performed on a single-wafer negative electrode. The negative electrode preheating process was carried out at 110°C for 2 hours at atmospheric pressure. Next, a negative electrode atmospheric pressure heating process was carried out at 130°C for 1 hour at atmospheric pressure. After that, while maintaining the temperature of 130°C, the pressure was reduced from atmospheric pressure to 100 Pa. Drying was carried out at 130°C for 8 hours in a vacuum atmosphere of 100 Pa (negative electrode vacuum drying process). The thickness and moisture content of the negative electrode fabricated in this way were measured using the method described above, and the results are shown in Table 2.

[0157] (Comparative Example 6) In the negative electrode fabrication of Example 1, after pressing the reel-shaped structure, a drying process was carried out without cutting. The drying process was carried out under the same conditions as in Example 1. A non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that the negative electrode fabricated in this way was used.

[0158] For each of the examples and comparative examples, the change in thickness before and after drying during anode manufacturing was measured. The anode thickness was measured using the method described above for the anode after the cutting (punching) process and before the anode preheating process. The anode thickness before drying was set to 100%, and the change in anode thickness after drying (%) is shown in Table 2 as the change in anode thickness before and after drying.

[0159] For each of the example and comparative example batteries, charging was performed at 25°C with a current of 1C until the state of charge (SOC) reached 50%. The battery voltage at this time was measured and defined as voltage A. Next, the battery, which had been charged to 50% SOC, was discharged at a current of 10C for 0.2 seconds. The battery voltage after discharge was measured and defined as voltage B. Then, the battery resistance was calculated from the difference between voltage A after charging and voltage B after discharge. Table 2 shows the results of the battery resistances of the other examples, with the battery resistance of Example 1 set to 1.00.

[0160] For each of the example and comparative example batteries, the charge state (SOC) was charged to 100% at a current of 1C in an environment of 25°C. Then, using Archimedes' principle, which states that an object in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces, the volume of the battery was measured from the buoyancy when the cell was submerged in water. The volume of the battery was similarly measured after being stored at 72°C for 120 hours in the same charged state, and the increase in battery volume after storage was obtained. The increase in battery volume after storage for Example 1 is set to 1.00, and the results of the increase in battery volume after storage for the other examples are shown in Table 2.

[0161]

[0162]

[0163] As is clear from Tables 1 and 2, the electrodes of Examples 1 to 4 exhibit small changes in thickness before and after drying, low resistance, and minimal increase in battery volume when stored in a high-temperature environment.

[0164] In contrast, the electrodes of Comparative Examples 1 and 2 had a high moisture content due to insufficient drying, resulting in a large change in thickness after drying, and consequently, increased battery resistance and increased battery volume after storage. In Comparative Example 3, the binder deteriorated due to high temperatures during drying, resulting in increased battery resistance. In Comparative Example 4, the electrode was not completely dried due to its thickness, resulting in a high moisture content, a large change in thickness after drying, and consequently, increased battery resistance and increased battery volume after storage. The electrode of Comparative Example 5, being a graphite negative electrode, is more susceptible to the reductive decomposition reaction of water than the electrodes of the Examples. Therefore, although the moisture content of the active material-containing layer was 300 ppm by mass, the battery resistance and increased battery volume after storage were significant. Furthermore, the electrode of Comparative Example 6 was dried while still in its reel shape, making it difficult for moisture to escape, resulting in increased battery resistance and increased battery volume after storage.

[0165] The electrodes according to the one or more embodiments and examples described above include an active material containing a niobium-containing oxide and an active material-containing layer with a moisture content of 250 ppm by mass or more and 660 ppm by mass or less. With these electrodes, it is possible to realize electrodes with low resistance and suppressed volume increase during storage.

[0166] The invention according to the embodiment is described below.

[0167] <1> An electrode comprising a current collector and an active material-containing layer formed on at least one surface of the current collector, the active material containing an active material comprising a niobium-containing oxide and having a moisture content of 250 ppm by mass or more and 660 ppm by mass or less.

[0168] <2> The electrode according to <1>, wherein the niobium-containing oxide includes a monoclinic niobium-titanium-containing oxide.

[0169] <3> An electrode as described in <1> or <2>, having a thickness of 140 μm or less.

[0170] <4> A battery comprising an electrode group including a positive electrode and a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is the electrode described in any one of <1> to <3>.

[0171] <5> The battery according to <4>, wherein the electrode group further comprises a separator, and the positive electrode and the negative electrode are stacked on top of each other via the separator.

[0172] <6> A method for manufacturing an electrode, comprising the steps of: preparing a structure in which an active material-containing layer is formed on at least one surface of a current collector by applying a slurry containing an active material containing a niobium-containing oxide to at least one surface of the current collector and drying it; pressing the structure; cutting the structure to obtain one or more electrodes to be processed; and drying the one or more electrodes to be processed to make the moisture content of the active material-containing layer of the one or more electrodes to be processed 250 ppm by mass or more and 660 ppm by mass or less.

[0173] <7> The method for manufacturing electrodes according to <6>, wherein drying of the one or more electrodes to be processed includes a first drying step performed at a first temperature of 100°C to 130°C at atmospheric pressure, a second drying step performed at a second temperature higher than the first temperature at atmospheric pressure, and a third drying step performed at a temperature of 130°C to 150°C in a vacuum of 0.1 Pa to 100 Pa.

[0174] <8> The method for manufacturing an electrode according to <6> or <7>, wherein the second temperature in the second drying step is in the range of 130°C to 150°C, and the drying time in the second drying step is 1 hour to 2 hours.

[0175] <9> The method for manufacturing an electrode according to any one of <6> to <8>, wherein the drying time of the third drying step is 8 hours or more and 12 hours or less.

[0176] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. An electrode comprising a current collector and an active material-containing layer formed on at least one surface of the current collector, the active material containing a niobium-containing oxide and having a moisture content of 250 ppm by mass or more and 660 ppm by mass or less.

2. The electrode according to claim 1, wherein the niobium-containing oxide includes a monoclinic niobium-titanium-containing oxide.

3. The electrode according to claim 1, wherein the thickness is 140 μm or less.

4. A battery comprising an electrode group including a positive electrode and a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is the electrode described in any one of claims 1 to 3.

5. The battery according to claim 4, wherein the electrode group further comprises a separator, and the positive electrode and the negative electrode are stacked on top of each other via the separator.

6. A method for manufacturing an electrode, comprising the steps of: preparing a structure in which an active material-containing layer is formed on at least one surface of a current collector by applying a slurry containing an active material containing a niobium-containing oxide to at least one surface of the current collector and drying it; pressing the structure; cutting the structure to obtain one or more electrodes to be processed; and drying the one or more electrodes to be processed to make the moisture content of the active material-containing layer of the one or more electrodes to be processed 250 ppm by mass or more and 660 ppm by mass or less.

7. The method for manufacturing an electrode according to claim 6, wherein drying of the one or more electrodes to be processed includes a first drying step performed at a first temperature of 100°C to 130°C at atmospheric pressure, a second drying step performed at a second temperature higher than the first temperature at atmospheric pressure, and a third drying step performed at a temperature of 130°C to 150°C in a vacuum of 0.1 Pa to 100 Pa.

8. The method for manufacturing an electrode according to claim 7, wherein the second temperature in the second drying step is in the range of 130°C to 150°C, and the drying time in the second drying step is 1 hour to 2 hours.

9. The method for manufacturing an electrode according to claim 7, wherein the drying time of the third drying step is 8 hours or more and 12 hours or less.

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