Power storage device

Abstract

This power storage device is provided with an electrode body. A first electrode plate of the electrode body comprises an elongated sheet-shaped current collector having a first main surface and a second main surface, and a first active material layer provided on the first main surface. The first main surface has at least one first uncoated portion that is partially provided along the longitudinal direction of the current collector and does not have the first active material layer. The first active material layer has at least one first region in which a length in the longitudinal direction of the current collector is 10% or less of the length in the longitudinal direction of the current collector. The first region extends along the width direction of the current collector. The mass per unit area of the first active material layer in the first region is 50% or more and less than 100% of the mass per unit area of the first active material layer surrounding the first region. The total proportion of the first region in the first active material layer is 50% or less. The first uncoated portion and the first region are spaced apart from each other.

Description

Energy storage device Cross-reference of related applications 【0001】 This disclosure claims priority with respect to Japanese Patent Application No. 2024-218913, filed with the Japan Patent Office on 13 December 2024, and the entirety of the said patent application is incorporated herein by reference. 【0002】 This disclosure relates to an energy storage device. 【0003】 Patent Document 1 proposes "an electrode plate for an energy storage device, comprising a long sheet-like current collector having a first main surface and a second main surface, and a first active material layer provided on the first main surface, wherein the first main surface has at least one first region that extends along the width direction of the current collector and in which the thickness of the first active material layer is smaller than that of the surrounding area, and the first active material layer is provided on at least a part of the first region." 【0004】 International Publication No. 2024 / 057630 【0005】 To improve the capacity of an energy storage device, it is effective to increase the mass of the active material layer per unit area of ​​the current collector in the electrodes. However, if such electrodes are wound tightly together to form the electrode body, the permeability of the electrolyte and the heat dissipation of the electrode body will decrease. When the permeability of the electrolyte in the electrode body decreases, it becomes difficult to achieve sufficient battery characteristics. Furthermore, when the heat dissipation of the electrode body decreases, the safety of the energy storage device may be compromised. 【0006】 Patent Document 1 describes a current collector on which an active material layer is provided that extends along the width direction of the current collector and is thinner than the surrounding area, with the aim of improving the permeability of the electrolyte. However, the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body are strongly affected by the uncoated portion of the current collector that does not have an active material layer. Electrode tabs for current collection are connected to the uncoated portion. The electrode tabs are covered with an insulating material. Therefore, the uncoated portion hinders the flow of the electrolyte and reduces heat dissipation. 【0007】One aspect of the present disclosure comprises an electrode body formed by winding a first electrode plate and a second electrode plate with a separator in between, and an electrolyte, wherein the first electrode plate comprises a long sheet-like current collector having a first main surface and a second main surface, and a first active material layer provided on the first main surface, the first main surface having at least one first uncoated portion that is partially provided along the longitudinal direction of the current collector and does not have the first active material layer, and the length of the first active material layer in the longitudinal direction of the current collector is as The present invention relates to an energy storage device having at least one first region that is 10% or less of the length in the longitudinal direction of the current collector, the first region extending along the width direction of the current collector, the mass per unit area of ​​the first active material layer in the first region being 50% or more and less than 100% of the mass per unit area of ​​the first active material layer surrounding the first region, the total proportion of the first region in the first active material layer being 50% or less, and the first uncoated portion and the first region being spaced apart. 【0008】 According to this disclosure, it is possible to improve sufficient electrolyte permeability and heat dissipation of the electrode while minimizing the decrease in the energy density of the electrode. Novel features of the present invention are described in the appended claims, but the present invention, in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in reference to the drawings, both in terms of structure and content. 【0009】 This is a schematic longitudinal cross-sectional view showing an example of an energy storage device according to one embodiment of the present disclosure. This is a front view (2A) showing the positional relationship between a first region and a first uncoated portion of an example of a positive electrode plate, a cross-sectional view (2B) along the line IIB-IIB in the front view, and a cross-sectional view (2C) along the line IIC-IIC in the front view. This is a front view of another example of a positive electrode plate. This is a front view of yet another example of a positive electrode plate. This is a front view of yet yet another example of a positive electrode plate. 【0010】The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. 【0011】 Furthermore, this disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises. 【0012】 The energy storage device according to this disclosure may be a battery or a capacitor. The battery may be a primary battery such as a lithium primary battery, an alkaline storage battery (such as a nickel-metal hydride battery or a nickel-cadmium battery), or a non-aqueous electrolyte secondary battery. The energy storage device according to this disclosure includes an electrode body. 【0013】 The type of energy storage device is not particularly limited, but an energy storage device to which this disclosure can be suitably applied is typically a non-aqueous electrolyte secondary battery capable of achieving high capacity. Non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries, solid-state batteries containing gel electrolytes or solid electrolytes, and the like. That is, a non-aqueous electrolyte secondary battery may be a liquid-type secondary battery containing an electrolyte, or an all-solid-state secondary battery containing a solid electrolyte. 【0014】The power storage device includes an electrode body formed by winding a first electrode plate and a second electrode plate with a separator interposed therebetween. That is, the power storage device includes a wound electrode body (electrode group). The cross-sectional shape perpendicular to the winding axis of the wound electrode body may be, for example, circular or elliptical, and the outer shape may be, for example, cylindrical, but is not limited thereto. In a lithium-ion secondary battery, one of the first electrode plate and the second electrode plate corresponds to a strip-shaped positive electrode plate and the other corresponds to a strip-shaped negative electrode plate. The separator may be composed of a porous sheet having ion permeability and insulation properties. Examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric. 【0015】 Hereinafter, the power storage device will be mainly described assuming a lithium-ion secondary battery. 【0016】 The first electrode plate includes a long sheet-shaped current collector having a first main surface and a second main surface, and a first active material layer provided on the first main surface. However, the first main surface has a first uncoated portion that does not have a first active material layer partially provided along the longitudinal direction of the current collector. The first active material layer has at least one first region in which the length in the longitudinal direction of the current collector is 10% or less of the length in the longitudinal direction of the current collector. The first region extends along the width direction of the current collector and is a region where the mass per unit area is smaller than that of the surroundings. 【0017】 The length in the longitudinal direction of the current collector of each first region may be 0.25% to 9% of the length in the longitudinal direction of the current collector. Thereby, it is possible to maintain the uniformity of the battery reaction required in the electrode body. 【0018】 However, the mass per unit area of the first region (the first active material layer in the first region) (hereinafter, also referred to as "areal density M1") needs to be 50% or more and less than 100% of the mass per unit area of the first active material layer around the first region (hereinafter, also referred to as "the first main region"). 【0019】Also, the total ratio of the first regions in the first active material layer (i.e., the ratio of the first regions in the total of the first regions and the first main region) (hereinafter, also referred to as "ratio (1 / (1 + M))") needs to be 50% or less. Note that only one first region may exist, but from the viewpoint of improving the current collection performance of a power storage device such as a lithium-ion secondary battery, it is preferable that a plurality of first regions exist. 【0020】 Since the first region is a region with relatively low capacity, it is necessary to provide the first region within a necessary and sufficient range. By setting the areal density M1 to be 50% or more of the areal density Mm1 and restricting the ratio (1 / (1 + M)) to 50% or less, it is possible to suppress a decrease in the energy density of the electrode body while improving the permeability of the electrolyte in the electrode body and the heat dissipation property of the electrode body. 【0021】 Note that, from the viewpoint of ensuring a high capacity, the area of all the first uncoated portions is sufficiently smaller than the area of the first main surface, for example, 2% or less of the area of the first main surface. Therefore, the ratio (1 / (1 + M)) can be rephrased as the ratio of the area S1 of the first main surface of the current collector on which the first region is formed to the total area S0 of the first main surface of the current collector. That is, "the area S0 of the first main surface of the current collector on which the first active material layer is formed" may be rephrased as "the total area of the first main surface of the current collector". 【0022】 The first region and the first main region may be formed by preparing two types of slurries (for the first region and for the first main region) in which an electrode binder constituting the first active material layer is dispersed in a liquid component, applying the two types of slurries to the first main surface, drying, and rolling. The slurry for the first region and the slurry for the first main region may be applied using a first device and a second device for applying them, respectively. 【0023】 The first uncoated portion may be formed by intermittently applying a slurry in which an electrode binder constituting the first active material layer is dispersed in a liquid component to the first main surface. 【0024】If the current collector is the positive electrode current collector of a lithium-ion secondary battery, the current collector may be made of aluminum foil or aluminum alloy foil. If the current collector is the negative electrode current collector of a lithium-ion secondary battery, the current collector may be made of copper foil or copper alloy foil. 【0025】 If the first active material layer provided on the first main surface is the positive electrode active material layer of a lithium-ion secondary battery, the first active material layer may include a positive electrode active material (e.g., lithium-containing transition metal oxide), a conductive agent, a binder, etc. If the first active material layer is the negative electrode active material layer of a lithium-ion secondary battery, the first active material layer may include a negative electrode active material (carbonaceous material, silicon-containing material, etc.), a binder, etc. 【0026】 The first active material layer may have at least one first region. The first region may be a low-density region with a lower density per unit volume than the first main region, or it may be a thinner region than the first main region. When a wound electrode body is fabricated using a first electrode plate having at least one first region, a low-density region or gap extending in the axial direction of the electrode body is formed at the location of the first region. The low-density region or gap improves the permeability of the electrolyte in the electrode body and also improves the heat dissipation of the electrode body. Furthermore, because the first region has lower rigidity than its surroundings, it becomes easier to bend the electrode plate when winding it, making it possible to wind it smoothly and accurately. 【0027】 Here, the first uncoated area and the first region must be separated. In other words, the first uncoated area and the first region are not continuous, and a part of the first main region is always interposed between the first uncoated area and the first region. As a result, the first region can exert its effect of improving the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body without being affected by the first uncoated area. A first electrode tab for current collection is connected to the first uncoated area, and the first electrode tab is further covered with an insulating material. Therefore, if the first uncoated area is adjacent to the first region, the flow of the electrolyte and heat dissipation from the electrode body will be hindered by the first electrode tab and the insulating material, making it difficult for the first region to fully exert the expected effect. 【0028】Furthermore, the effect of the above configuration on improving the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body increases as the area density of the first main region in the first electrode plate increases (in other words, as the energy density of the electrode body increases). Therefore, for example, if the first electrode plate is the positive electrode of a lithium-ion secondary battery or a lithium metal secondary battery, the area density of the first main region is, for example, 240 g / m². ２ The above is also acceptable, 260 g / m ２ The above is also acceptable, 280 g / m ２ Anything above that is also acceptable; for example, 240 g / m² ２ 350g / m or more ２ It may fall within the following range. 【0029】 Furthermore, the energy of the electrode body is, for example, 15 Wh or more per cell in the case of a lithium-ion secondary battery, and may be, for example, 80 Wh or more as capacity increases further. Each cell has only one electrode body. For example, a wound electrode body has a cylindrical shape, and only one electrode body is housed in a cylindrical case having an inner diameter slightly larger than the diameter of the cylinder, thus forming one cell. 【0030】 Furthermore, for example, if the first electrode plate is the positive electrode of a lithium-ion secondary battery, the thickness of the first main region (the positive electrode active material layer) may be, for example, 50 μm or more, 60 μm or more, 90 μm or more, or within the range of 50 μm to 100 μm. 【0031】 Furthermore, the effect of the above configuration on improving the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body increases with increasing number of turns in a wound electrode body. The greater the number of turns in the electrode body, the greater the length of the first electrode plate in the longitudinal direction. The length of the first electrode plate in the longitudinal direction may be, for example, 3000 mm or more. 【0032】The first region may be positioned from one end of the width direction Dw of the current collector to the midpoint of the width direction Dw. This first region is also referred to as "first region A". In this case, the length Lr1 of the first region in the width direction Dw may be 20% to 90%, 40% to 90%, 50% to 90%, 60% to 90%, or 70% to 90% of the length Lw of the width direction Dw of the current collector. The smaller the length Lr1, the higher the energy density of the electrode body can be maintained. On the other hand, the larger the length Lr1, the greater the effect of improving the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body. Also, by having the first region extend from one end of the width direction Dw of the current collector, the electrolyte and heat can be more easily released from the electrode body to the outside. If there are multiple first regions, at least one of the first regions may be first region A, or all of the first regions may be first region A. 【0033】 The first region may be arranged from one end of the width direction Dw to the other end of the width direction Dw. This first region is also referred to as "first region B". In this case, the effect exerted by this first region (the effect of improving the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body) is greatest. If there are multiple first regions, at least one of the first regions may be first region B, or all of the first regions may be first region B. Both first region A and first region B may be present in a single first electrode plate. 【0034】 The length (width) of the longitudinal Dleng of each first uncoated current collector is preferably not excessively large from the viewpoint of maintaining a high energy density of the electrode body, and is preferably in the range of 10 mm to 90 mm, and more preferably in the range of 20 mm to 60 mm. 【0035】The first unpainted portion may extend from one end of the width direction Dw to the midpoint of the width direction Dw. This first unpainted portion is also referred to as "first unpainted portion A". In this case, the length Lex of the first unpainted portion in the width direction Dw may be 50% or less, 40% or less, 30% or less, or 20% or less of the length Lw of the width direction Dw of the current collector. The smaller the length Lex, the higher the energy density of the electrode body can be maintained. On the other hand, it is preferable that the length Lex has a sufficient area to which the first electrode tab for current collection is connected. Therefore, it is preferable that the length Lex is 10% or more of the length Lw of the width direction Dw of the current collector. If there are multiple first unpainted portions, at least one of the first unpainted portions may be first unpainted portion A, or all of the first unpainted portions may be first region A. 【0036】 The first unpainted portion may extend from one end of the width direction Dw to the other end of the width direction Dw. In this case, the contact area between the current collector and the first electrode tab can be increased, thereby improving the current collection performance from the first electrode plate. This first unpainted portion is also referred to as "first unpainted portion B". If there are multiple first unpainted portions, at least one of the first unpainted portions may be first unpainted portion B, or all of the first unpainted portions may be first unpainted portion B. Both first unpainted portion A and first unpainted portion B may be present on a single first electrode plate. 【0037】 If the first region is located from one end (first end) in the width direction Dw to the midpoint of the width direction Dw and has a length of 20% to 90% of the width direction, the first uncoated portion may extend from the other end (second end) in the width direction Dw to the midpoint of the width direction Dw and have a length of 50% or less of the width direction. In this way, when the first region and the first uncoated portion extend from opposite ends in the width direction, the shape symmetry of the electrode body is increased, making it less likely for distortion to occur in the electrode body, which is advantageous in terms of battery performance. 【0038】If the first region is located from one end (first end) in the width direction Dw to the midpoint MP in the width direction Dw and has a length of 20% to 90% of the width direction, the first uncoated portion may extend from the other end (second end) in the width direction Dw to the midpoint MP in the width direction Dw. In this case, the sum of the lengths of the first region and the first uncoated portion in the width direction Dw is equal to 100% of the length of the first active material layer in the width direction Dw, and the midpoint MP in the first region and the first uncoated portion is the same point. Such a configuration can be efficiently realized by combining a first device that applies slurry from the first end to the midpoint MP and a second device that applies slurry from the second end to the midpoint MP in the process of applying the slurry that will become the first active material layer. In other words, such a configuration is industrially practical and allows the first region and the first main region to be efficiently formed along the longitudinal direction of the current collector while forming the first uncoated portion. 【0039】 In cases where there are multiple first regions and first uncoated portions, it is preferable, though not limited to, that all first regions extend from one end (first end) in the width direction Dw, and all first uncoated portions extend from the other end (second end) in the width direction Dw. 【0040】 When a first electrode tab is attached to the first unpainted portion, it is preferable that the length (width) of the first unpainted portion is greater than the length of the first electrode tab in the longitudinal direction Dleng of the current collector. Furthermore, from the viewpoint of suppressing internal short circuits, it is preferable that a part of the first electrode tab, together with at least a part of the first unpainted portion, is covered with an insulating material. In this disclosure, since the first unpainted portion is not adjacent to the first region but is spaced apart, the flow of the electrolyte and heat dissipation from the electrode body are not hindered by the first electrode tab and the insulating material. Therefore, the effects expected of the first region are fully realized. 【0041】The total proportion of the first region in the first active material layer (1 / (1+M)) should be 50% or less, but is preferably in the range of 0.1% to 10%. This allows for a very small reduction in the energy density of the electrode while sufficiently improving the permeability of the electrolyte in the electrode and the heat dissipation of the electrode. The proportion (1 / (1+M)) may also be 1% to 8%, 1% to 7%, or 1% to 5%. 【0042】 When the first active material layer has multiple first regions, the proportion of each first region in the first active material layer (the ratio of the area SN of the first main surface of the current collector on which one first region is formed to the area S0 of the first main surface of the current collector on which the first active material layer is formed) is preferably 0.1% to 2.5%. For example, when multiple first regions are provided in the first active material layer, each with a proportion of 1% to 2%, the sum of the proportions of all first regions (i.e., the proportion (1 / (1+M))) may be 50% or less, or 1% to 8%. 【0043】 As previously described, the area density M1 should be smaller than the area density Mm1 and at least 50% of the area density Mm1. However, from the viewpoint of maintaining a high energy density of the electrode body, the area density M1 is preferably at least 90% of the area density Mm1, may be at least 95%, and may be at least 96%, 97%, 98%, or 99%. Furthermore, from the viewpoint of ensuring the effect of improving the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body, the area density M1 is preferably at least 99.5% of the mass of the area density Mm1. 【0044】 The number of first regions is not particularly limited, but it is preferable to form them in multiple locations according to a ratio (1 / (1+M)). In this case, the first regions and the first main regions can be formed alternately along the longitudinal direction of the current collector. This allows for more uniform improvement of electrolyte permeability and heat dissipation within the electrode body. 【0045】From the viewpoint of maintaining a high energy density of the electrode body, the length (width) of the current collector in the longitudinal direction Dleng of the first region is preferably in the range of 10 mm to 90 mm and, more preferably, in the range of 40 mm to 75 mm per first region. 【0046】 The number of first uncoated areas may be one or more, but multiple first uncoated areas may be formed on the first main surface. A first electrode tab may be connected to each of the multiple first uncoated areas. In this case, it is preferable that the first region and the first uncoated areas are formed alternately along the longitudinal direction of the current collector. That is, it is preferable that a first region is provided between two adjacent first uncoated areas. This improves the shape balance of the electrode body, and the permeability of the electrolyte and the heat dissipation of the electrode body can be improved more uniformly within the electrode body. 【0047】 The first electrode plate may further comprise a second active material layer provided on the second main surface. The composition of the second active material layer may be the same as or different from that of the first active material layer. 【0048】 The configuration of the second main surface can be arbitrarily applied to the configuration of the first main surface. The second main surface may have the same configuration as the first main surface. 【0049】 In other words, the second main surface may have at least one second uncoated portion that does not have a second active material layer partially provided along the longitudinal direction of the current collector. The second active material layer may also have at least one second region whose length in the longitudinal direction of the current collector is 10% or less of the length in the longitudinal direction of the current collector. The second region extends along the width direction Dw of the current collector and has a smaller mass per unit area than the surrounding area. 【0050】The mass per unit area of ​​the second region (the second active material layer) (hereinafter also referred to as "area density M2") may be 50% or more and less than 100% of the mass per unit area of ​​the second active material layer surrounding the second region (hereinafter also referred to as "second main region") (hereinafter also referred to as "area density Mm2"). The total proportion of the second region in the second active material layer (i.e., the proportion of the second region in the sum of the second region and the second main region) (hereinafter also referred to as "proportion (2 / (2+M))") may be 50% or less. The second uncoated portion and the second region may be separated. 【0051】 The first region and the second region may overlap in at least a portion when viewed from the direction normal to the first main surface. Preferably, at least a portion of all of the first regions overlaps with any of the second regions when viewed from the direction normal to the first main surface. This ensures a more reliable flow path for the electrolyte in the electrode body and a heat dissipation path from the electrode body, and can significantly improve the permeability of the electrolyte in the electrode body and the heat dissipation of the electrode body. 【0052】 When viewed from the direction normal to the first main surface, all of the first regions, for example, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, may overlap with any of the second regions. In this case, the rigidity of the parts where the first and second regions are located can be reduced, making it possible to perform winding smoothly and accurately. 【0053】 The following section specifically describes the case where the first electrode plate is the positive electrode plate of a lithium-ion secondary battery. The positive electrode plate (first electrode plate) comprises a long, sheet-like current collector (positive electrode current collector) having a first main surface and a second main surface, a first active material layer (positive electrode active material layer) provided on the first main surface, and a second active material layer (positive electrode active material layer) provided on the second main surface. Since the configuration on the first main surface side and the configuration on the second main surface side are the same, the configuration on the first main surface side will be described below. 【0054】 The positive electrode active material layer is composed of a positive electrode mixture. The positive electrode mixture contains the positive electrode active material as an essential component and may contain optional components such as binders, conductive additives, and thickeners. The positive electrode active material layer may also be referred to as the positive electrode mixture layer. 【0055】The positive electrode active material layer can be obtained, for example, by applying a positive electrode slurry in which a positive electrode mixture containing particles of a positive electrode active material, a binder, a conductive assistant, etc. is dispersed in a dispersion medium onto the surface of a positive electrode current collector, drying it, and rolling the dried coating film. As the dispersion medium, N-methyl-2-pyrrolidone (NMP), cyclohexanone, alcohols, ethers, etc. are used. 【0056】 The binder may contain, for example, a fluorine-based polymer. The fluorine-based polymer can exhibit high binding force. The fluorine-based polymer is a general term for polymers having fluorine atoms (F) bonded to carbon atoms constituting the main chain. 【0057】 Examples of the conductive assistant include carbon materials such as graphite, carbon blacks such as furnace black and acetylene black, carbon fibers (carbon nanotubes (CNT), carbon fibers other than CNT), graphene, etc. 【0058】 As the positive electrode current collector, a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, punching sheet) is used. Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, titanium, etc. The thickness of the positive electrode current collector is not particularly limited, but 5 to 20 μm is preferable. 【0059】 The positive electrode active material can be a material that reversibly intercalates and deintercalates lithium ions. The positive electrode active material may be, for example, a lithium-containing transition metal oxide. The crystal structure of the lithium-containing transition metal oxide is not particularly limited, but may be, for example, a layered rock salt type. 【0060】 As the positive electrode active material, for example, a composite oxide containing lithium and transition metals such as Ni, Co, Mn, etc. may be used. Specifically, Li ａ CoO ２ 、Li ａ NiO ２ 、Li ａ MnO ２ 、Li ａ Co ｂ Ni １－ｂ O ２ 、Li ａ Co ｂ M １－ｂ Oｃ Li ａ Ni １－ｂ M ｂ O ｃ Li ａ Mn ２ O ４ Li ａ Mn ２－ｂ M ｂ O ４、 LiMPO ４、 Li ２ MPO ４ Examples include F (where M is at least one selected from the group consisting of Na, Mg, K, Ca, Rb, Sr, Sc, Y, Ti, Zr, V, Nb, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B). Here, 0 < a ≤ 1.2, 0 < b ≤ 0.9, and 2.0 ≤ c ≤ 2.3. Note that the value of a, which indicates the molar ratio of lithium, increases or decreases with charging and discharging. 【0061】 Among them, Li ａ Ni １－ｂ M ｂ O ２ Lithium nickel composite oxides represented by (M being at least one selected from the group consisting of Mn, Co, and Al, with 0 < a ≤ 1.2 and 0 < b < 0.7) are preferred. From the viewpoint of increasing capacity, it is more preferable that 0 < b < 0.2 is satisfied. From the viewpoint of crystal structure stability, Li containing Co and Al as M is preferred. ａ Ni １－ｂ Co ｄ Al ｅ O ｃ , or Li containing Co and Mn as M ａ Ni １－ｂ Co ｄ Mn ｅ O ｃ (0 < a ≤ 1.2, 0 < b < 0.2, 0 < d < 0.15, 0 < e ≤ 0.1, b = d + e) ​​is even more preferable. Also, Li ａ Ni ｂ Co （１－ｂ－ｃ） Me ｃ M d O e(wherein the formula, 0.9 < a ​​≤ 1.2, 0.3 ≤ b ≤ 0.96, 0.03 ≤ c ≤ 0.70, 1.9 ≤ e ≤ 2.1, and Me / (Ni + Co + M + Me) = d, 0 ≤ d ≤ 0.02.) is also preferred, where Me is at least one of Al and Mn, and M is at least one selected from the group consisting of Na, Mg, K, Ca, Rb, Sr, Sc, Y, Ti, Zr, V, Nb, Fe, Cu, Zn, Cr, Pb, Sb, B.) 【0062】 The average particle size d1 of the active material contained in the first region is, for example, 6.0 μm or more and 17.0 μm or less, and may be 8 μm or more, 10 μm or more, 11 μm or more, 12 μm or more, or 15 μm or more. Furthermore, from the viewpoint of improving discharge characteristics, d1 may be 30 μm or less, 25 μm or less, or 20 μm or less. d1 may be 6 ≤ d1 (μm) ≤ 30, and preferably 6 ≤ d1 (μm) ≤ 17. 【0063】 The average particle size dm1 of the active material contained in the first main region is, for example, 1.0 μm or more and 17.0 μm or less, and may be 10 μm or less, 8 μm or less, 6 μm or less, or 5 μm or less. From the viewpoint of improving charge-discharge cycle characteristics, it is preferable that dm1 be 1 μm or more, and may be 3 μm or more. dm1 may be 1 ≤ dm1 (μm) ≤ 17, and preferably 1 ≤ dm1 (μm) ≤ 10. 【0064】 The average particle size of the positive electrode active material is preferably such that d1 > d2, and the d1 / d2 ratio may be, for example, 2 or more and 6 or 3 or more and 5 or less. 【0065】 The types (composition formulas) of the positive electrode active materials contained in the first region and the first main region may be the same or different. The positive electrode active materials contained in the first region and the first main region may each independently contain multiple types of positive electrode active materials or contain a single positive electrode active material. 【0066】The median diameter (D50) in the volume-based particle size distribution may be measured by separating the positive electrode active material from the positive electrode active material layer, or it may be determined by image analysis of a cross-sectional SEM image of the positive electrode active material layer. Both methods yield approximately the same (without significant difference) median diameter (D50). 【0067】 When separating the positive electrode active material from the positive electrode active material layer, the positive electrode active material layer may be peeled off from the positive electrode, immersed in a suitable solvent to dissolve or swell components other than the active material particles, such as dispersants, and separated by centrifugation, and this process may be repeated one or more times. When the separated sample of positive electrode active material is analyzed using a laser diffraction scattering particle size distribution analyzer, the volume-based particle size distribution and median diameter can be determined. 【0068】 When performing image analysis of a cross-sectional SEM image of the positive electrode active material layer, the positive electrode active material layer and the positive electrode current collector are simultaneously cut along the width direction of the positive electrode to obtain a cross-sectional sample of the positive electrode in the thickness direction. At this time, the cross section may be processed with a cross-section polisher (CP) to obtain the cross-sectional sample. Next, the cross section of the positive electrode active material layer in the cross-sectional sample is observed using a scanning electron microscope (SEM). 【0069】 From the contour images of the active material particles in the cross-sectional SEM image, the area enclosed by the contour is determined. The diameter of a circle (equivalent circle) having the same area as the area enclosed by the contour of the active material particles is determined and taken as the particle size of each particle i. Then, the volume of a sphere having the same diameter as the equivalent circle is considered as the volume Vi of each particle i. By determining the diameter and volume of the equivalent circles for any 100 or more (preferably 1000 or more) particles, the volume-based particle size distribution and median diameter can be calculated. 【0070】 Next, the configuration of the second electrode plate can be arbitrarily applied to the configuration of the first electrode plate as described above. The second electrode plate may have the same configuration as the first electrode plate. However, the configuration of the second electrode plate is arbitrary and can have various configurations different from those of the first electrode plate. 【0071】 If the first electrode plate is the positive electrode plate of a lithium-ion secondary battery, then the second electrode plate is the negative electrode plate of the lithium-ion secondary battery. The following section will describe the negative electrode plate of a lithium-ion secondary battery. 【0072】The negative electrode plate (second electrode plate) has a long, sheet-like current collector (negative electrode current collector) having a first main surface and a second main surface, and may also include a first active material layer (negative electrode active material layer) provided on the first main surface and a second active material layer (negative electrode active material layer) provided on the second main surface. 【0073】 The negative electrode active material layer is composed of, for example, a negative electrode mixture. The negative electrode mixture contains a negative electrode active material as an essential component and may contain binders, conductive additives, thickeners, etc. as optional components. The negative electrode active material layer may also be called the negative electrode mixture layer. Alternatively, the negative electrode active material layer may be composed of at least one selected from the group consisting of lithium metal and lithium alloy. 【0074】 The negative electrode active material layer, composed of a negative electrode mixture, is obtained, for example, by dispersing a negative electrode slurry containing particles of negative electrode active material, a binder, a conductive additive, etc., in a dispersion medium, coating the surface of a negative electrode current collector with the slurry, drying it, and rolling the dried coating. Suitable dispersion media include water, N-methyl-2-pyrrolidone (NMP), cyclohexanone, alcohols, ethers, etc. 【0075】 The negative electrode active material used in the negative electrode mixture may be a material that reversibly intercepts and releases lithium ions, or an alloying material. Preferred materials for reversibly intercepting and releasing lithium ions include carbon materials, spinel-type lithium titanium oxide, and spinel-type lithium manganese oxide. Carbon materials may include graphite, easily graphitizable carbon (soft carbon), and poorly graphitizable carbon (hard carbon). Alloying materials contain a phase that reversibly forms an alloy with lithium. The phase that reversibly forms an alloy with lithium may be, for example, silicon (silicon phase). 【0076】 Examples of binders include acrylic resins and rubber-like materials such as styrene-butadiene copolymer rubber (SBR). 【0077】 Examples of conductive additives include carbon black such as furnace black and acetylene black, carbon fibers (carbon nanotubes (CNTs), carbon fibers other than CNTs), and graphene. 【0078】Examples of thickening agents include carboxymethylcellulose (CMC) and its modified forms (including salts such as sodium salts). 【0079】 Non-porous conductive substrates and porous conductive substrates are used as the negative electrode current collector. Examples of materials for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys. The thickness of the negative electrode current collector is not particularly limited, but 5 to 20 μm is desirable. 【0080】 Below, an example of an energy storage device related to this disclosure will be described in detail with reference to the drawings. The components of the energy storage device in the example described below can be the components described above. The components of the energy storage device in the example described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiments. Among the components of the energy storage device in the example described below, components that are not essential to the energy storage device related to this disclosure may be omitted. Note that the figures shown below are schematic and do not accurately reflect the actual shape and number of components. 【0081】 The energy storage device 10 of this embodiment is configured as a lithium-ion secondary battery, but is not limited to this. As shown in Figure 1, the energy storage device 10 comprises an electrode body 20, a case 40, a sealing body 50, a positive electrode tab 61, and a negative electrode tab 62. 【0082】 The electrode body 20 includes a positive electrode plate 21, a negative electrode plate 29, and a separator 31. The positive electrode plate 21, the negative electrode plate 29, and the separator 31 are all in the form of long sheets (or strips). The positive electrode plate 21 and the negative electrode plate 29 are wound in a spiral shape with the separator 31 interposed between them, so that their width directions are parallel to the winding axis. A first insulating plate 71 and a second insulating plate 72 are arranged on both sides of the electrode body 20 in the axial direction. The positive electrode plate 21 is an example of a first electrode plate, and the negative electrode plate 29 is an example of a second electrode plate. The configuration of the positive electrode plate 21 will be described in detail later. 【0083】The case 40 is configured as a bottomed cylindrical shape with an opening at one end (the upper end in Figure 1). The case 40 houses the electrode body 20 and the electrolyte (not shown). The case 40 has a stepped portion 41 formed by partially pressing the side wall of the case 40 from the outside. The stepped portion 41 may be formed annularly along the circumferential direction of the case 40 on the side wall of the case 40. In this case, the sealing body 50 can be supported on the opening side of the stepped portion 41. 【0084】 The sealing body 50 seals the opening of the case 40. An insulating gasket 81 is placed between the sealing body 50 and the case 40, thereby ensuring the airtightness of the case 40. The sealing body 50 includes a filter 51, a lower valve body 52, an insulating member 53, an upper valve body 54, and a cap 55. In the sealing body 50, these members are stacked in this order. The sealing body 50 is fitted into the opening of the case 40 such that the cap 55 is located on the outside of the case 40 and the filter 51 is located on the inside of the case 40. Each of the above-mentioned members constituting the sealing body 50 is, for example, disc-shaped or ring-shaped. Each member, except for the insulating member 53, is electrically connected to one another. 【0085】 The positive electrode tab 61 is attached to the first uncoated portion 24 (described later) of the positive electrode plate 21, and electrically connects the positive electrode plate 21 and the sealing body 50. Specifically, one end of the positive electrode tab 61 is connected to the first uncoated portion 24, and the other end is connected to the cap 55 of the sealing body 50. The positive electrode tab 61 passes through a through hole formed in the first insulating plate 71. Therefore, the cap 55 of the sealing body 50 functions as an external positive electrode terminal. Only one positive electrode tab 61 may be provided, or multiple positive electrode tabs may be provided. The positive electrode tab 61 is an example of a first electrode tab. 【0086】 The negative electrode tab 62 is attached to the negative electrode plate 29 and electrically connects the negative electrode plate 29 and the case 40. Specifically, one end of the negative electrode tab 62 is connected to the negative electrode plate 29, and the other end is connected to the inner bottom surface of the case 40. Thus, the case 40 functions as an external negative electrode terminal. Only one negative electrode tab 62 may be provided, or multiple negative electrode tabs 62 may be provided. 【0087】Next, with reference to Figure 2, the configuration of the positive electrode plate 21 will be explained in detail. 【0088】 As shown in Figure 2, the positive electrode plate 21 comprises a long, sheet-like current collector 22 having a first main surface 23 and a second main surface 25, a first active material layer (positive electrode active material layer) 27 provided on the first main surface 23, and a second active material layer (positive electrode active material layer) 28 provided on the second main surface 25. 【0089】 The current collector 22 is made of, for example, aluminum foil or aluminum alloy foil. The longitudinal direction Dleng of the current collector 22 is the left-right direction in Figure 2A, and the width direction Dw of the current collector 22 is the up-down direction in Figure 2A. The longitudinal direction Dleng of the current collector 22 coincides with the winding direction of the electrode body 20, and the width direction Dw of the current collector 22 coincides with the axial direction of the electrode body 20. 【0090】 The first active material layer 27 includes a positive electrode active material (e.g., lithium-containing transition metal oxide), a conductive agent, and a binder. The second active material layer 28 has the same composition as the first active material layer 27, for example. 【0091】 The first active material layer 27 includes a positive electrode active material (e.g., lithium-containing transition metal oxide), a conductive agent, and a binder. The second active material layer 28 has the same composition as the first active material layer 27, for example. 【0092】 The first active material layer 27 extends along the width direction Dw of the current collector 22 and has a first region R1 in which the thickness of the first active material layer 27 is smaller than that of the surrounding area (first main region Rm1). The density of the first region R1 and the first main region Rm are the same. In other words, the area density M1 of the first region R1 is smaller than the area density Mm1 of the first main region Rm. 【0093】The first region R1 is located from one end (first end) in the width direction Dw to the midpoint of the width direction Dw. The length of the first region R1 in the width direction Dw is, for example, within the range of 70% to 90% of the length of the current collector in the width direction Dw. On the other hand, the first unpainted portion 24 extends from the other end (second end) in the width direction Dw to the midpoint of the width direction Dw. The length of the first unpainted portion 24 in the width direction Dw is, for example, within the range of 5% to 30% of the length of the current collector in the width direction Dw. As described above, when the first region R1 and the first unpainted portion 24 extend from opposite ends in the width direction Dw, the shape symmetry of the electrode body is enhanced. 【0094】 The length L3 in the longitudinal direction Dleng of the current collector in each first region R1 is set to a range of, for example, 10 mm to 90 mm, taking into consideration the shape symmetry, capacitance, and flexibility of the electrode body. 【0095】 The thickness Tmin1 of the first region R1 is, for example, 95% to 99.5% of the thickness Tmax1 of the first main region Rm1. The thicknesses of the first region R1 and the first main region Rm1 may also be determined as the average value of the thicknesses at any five locations within the first region R1 and the first main region Rm1, respectively. 【0096】 The second active material layer 28 has the same configuration as the first active material layer 27. That is, the second region R2 is located from one end (first end) in the width direction Dw to the midpoint in the width direction Dw. The length of the second region R2 in the width direction Dw is, for example, within the range of 70% to 90% of the length of the current collector in the width direction Dw. On the other hand, the second uncoated portion 26 extends from the other end (second end) in the width direction Dw to the midpoint in the width direction Dw. The length of the second uncoated portion 26 in the width direction Dw is, for example, within the range of 5% to 30% of the length of the current collector in the width direction Dw. 【0097】 The thickness Tmin2 of the second region R2 is, for example, 95% to 99.5% of the thickness Tmax2 of the second main region Rm2. Alternatively, the thicknesses of the second region R2 and the second main region Rm2 may be determined as the average value of the thicknesses at any five locations within the second region R2 and the second main region Rm2, respectively. 【0098】A positive electrode tab 61, shown by a dashed line in Figure 2A, is attached to the first unpainted portion 24, for example, by welding. In the longitudinal Dleng of the current collector 22, the length L1 of the first unpainted portion 24 is greater than the length L2 of the positive electrode tab 61. The length L1 of each first unpainted portion of the current collector in the longitudinal Dleng is set to a range of, for example, 10 mm to 90 mm, depending on the length L2 of the positive electrode tab 61. 【0099】 The second region R2 is located on the back side of the first region R1. The position of the second region R2 corresponds to the position of the first region R1. In this way, the first region R1 and the second region R2, which correspond to each other, overlap each other by at least a portion (preferably 90% or more) when viewed from the direction normal to the first main surface 23. 【0100】 As shown in Figure 3, the first region R1 may be provided at multiple locations on the first main surface 23. A positive electrode tab 61 is connected to each first unpainted portion 24. In Figure 3, the first region and the first unpainted portion are formed alternately along the longitudinal direction of the current collector. Each first region R1 is positioned from one end (first end) in the width direction Dw to the midpoint in the width direction Dw. 【0101】 As shown in Figure 4, the first region R1 may be provided at multiple locations on the first main surface 23. A positive electrode tab 61 is connected to each first unpainted portion 24. In Figure 4, the first region and the first unpainted portion are formed alternately along the longitudinal direction of the current collector. The first region R1 is arranged alternately along the longitudinal direction of the current collector from one end (first end) or the other end (second end) of the width direction Dw to the midpoint of the width direction Dw. 【0102】 As shown in Figure 5, the first region may extend from one end of the width direction Dw to the other end of the width direction Dw. The first region R1 extending from one end of the width direction Dw to the other end of the width direction Dw may be provided at multiple locations on the first main surface 23. A positive electrode tab 61 is connected to each first unpainted portion 24. Multiple first regions extending from one end of the width direction Dw to the other end of the width direction Dw and multiple first unpainted portions may be formed alternately along the longitudinal direction of the current collector. 【0103】[Note] The above description of embodiments discloses the following technologies. (Technical 1) An electrode body comprising a first electrode plate and a second electrode plate wound around a separator, and an electrolyte, wherein the first electrode plate comprises a long sheet-like current collector having a first main surface and a second main surface, and a first active material layer provided on the first main surface, the first main surface having at least one first uncoated portion that does not have the first active material layer and is partially provided along the longitudinal direction of the current collector, the first active material layer having at least one first region whose length in the longitudinal direction of the current collector is 10% or less of the length in the longitudinal direction of the current collector, the first region extending along the width direction of the current collector, the mass per unit area of ​​the first active material layer in the first region being 50% or more and less than 100% of the mass per unit area of ​​the first active material layer surrounding the first region, and the total proportion of the first region in the first active material layer being 50% or less, A power storage device in which the first uncoated portion and the first region are spaced apart. (Technology 2) The power storage device according to Technology 1, wherein the first region is located from one end in the width direction to the midpoint in the width direction and has a length of 20% to 90% of the length in the width direction. (Technology 3) The power storage device according to Technology 1, wherein the first region is located from one end in the width direction to the other end in the width direction. (Technology 4) The power storage device according to any one of Technologies 1 to 3, wherein the first uncoated portion extends from one end in the width direction to the midpoint in the width direction and has a length of 50% or less of the length in the width direction. (Technology 5) The energy storage device according to any one of Techniques 1 to 4, wherein the first region is located from one end in the width direction to the midpoint in the width direction and has a length of 20% to 90% of the length in the width direction, and the first uncoated portion extends from the other end in the width direction to the midpoint in the width direction and has a length of 50% or less of the length in the width direction. (Technology 6) The energy storage device according to any one of Techniques 1 to 4, wherein the first region is located from one end in the width direction to the midpoint in the width direction and has a length of 20% to 90% of the length in the width direction, and the first uncoated portion extends from the other end in the width direction to the midpoint in the width direction.(Technology 7) The first uncoated portion is fitted with a first electrode tab, and a portion of the first electrode tab is covered with an insulating member together with at least a portion of the first uncoated portion, as described in any one of Techniques 1 to 6. (Technology 8) The total proportion of the first region in the first active material layer is 0.1% to 10%, as described in any one of Techniques 1 to 7. (Technology 9) The first active material layer has a plurality of first regions, and the proportion of the first region in the first active material layer is 0.1% to 2.5% per first region, as described in any one of Techniques 1 to 8. (Technology 10) The mass per unit area of ​​the first active material layer in the first region is 90% or more and 99.5% or less of the mass per unit area of ​​the first active material layer surrounding the first region, as described in any one of Techniques 1 to 9. (Technical 11) The first electrode plate further comprises a second active material layer provided on the second main surface, the second main surface has at least one second uncoated portion that is partially provided along the longitudinal direction of the current collector and does not have the second active material layer, the second active material layer has at least one second region whose length in the longitudinal direction of the current collector is 10% or less of the length in the longitudinal direction of the current collector, the second region extends along the width direction of the current collector, the mass per unit area of ​​the second active material layer in the second region is 50% or more and less than 100% of the mass per unit area of ​​the second active material layer around the second region, the total proportion of the second region in the second active material layer is 50% or less, and the second uncoated portion and the second region are spaced apart, the energy storage device according to any one of Technical 1 to 10. (Technical 12) The energy storage device according to Technical 11, wherein, when viewed from the direction normal to the first main surface, at least a portion of all of the first regions overlaps with any of the second regions. 【0104】 This disclosure can be used in energy storage devices such as lithium-ion secondary batteries. 【0105】Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. 【0106】 10: Energy storage device 20: Electrode body 21: Positive electrode plate (first electrode plate) 22: Current collector 23: First main surface 24: First uncoated area 25: Second main surface 26: Second uncoated area 27: First active material layer 28: Second active material layer 29: Negative electrode plate (second electrode plate) 31: Separator 40: Case 41: Stepped section 50: Sealing body 51: Filter 52: Lower valve body 53: Insulating member 54: Upper valve body 55: Cap 61: Positive electrode tab (first electrode tab) 62: Negative electrode tab 71: First insulating plate 72: Second insulating plate 81: Gasket L1: Length of the first uncoated area L2: Length of the positive electrode tab R1: First region R2: Second region Tmin1: Minimum thickness of the first active material layer Tmin2: Maximum thickness of the first active material layer Tmax1: Minimum thickness of the second active material layer Tmax2: Maximum thickness of the second active material layer

Claims

1. The electrode body comprises an electrode body formed by winding a first electrode plate and a second electrode plate with a separator in between, and an electrolyte, wherein the first electrode plate comprises a long sheet-like current collector having a first main surface and a second main surface, and a first active material layer provided on the first main surface, the first main surface has at least one first uncoated portion that does not have the first active material layer and is partially provided along the longitudinal direction of the current collector, the first active material layer has at least one first region whose length in the longitudinal direction of the current collector is 10% or less of the length in the longitudinal direction of the current collector, the first region extends along the width direction of the current collector, the mass per unit area of ​​the first active material layer in the first region is 50% or more and less than 100% of the mass per unit area of ​​the first active material layer surrounding the first region, and the total proportion of the first region in the first active material layer is 50% or less. An energy storage device in which the first uncoated portion and the first region are separated.

2. The energy storage device according to claim 1, wherein the first region is located from one end in the width direction to the midpoint in the width direction and has a length of 20% to 90% of the length in the width direction.

3. The energy storage device according to claim 1, wherein the first region is arranged from one end in the width direction to the other end in the width direction.

4. The energy storage device according to claim 1, wherein the first uncoated portion extends from one end in the width direction to the midpoint in the width direction and has a length of 50% or less of the length in the width direction.

5. The energy storage device according to claim 1, wherein the first region is located from one end in the width direction to the midpoint in the width direction and has a length of 20% to 90% of the length in the width direction, and the first uncoated portion extends from the other end in the width direction to the midpoint in the width direction and has a length of 50% or less of the length in the width direction.

6. The energy storage device according to claim 1, wherein the first region is located from one end in the width direction to the midpoint MP in the width direction and has a length of 20% to 90% of the length in the width direction, and the first uncoated portion extends from the other end in the width direction to the midpoint MP in the width direction.

7. The energy storage device according to claim 1, wherein a first electrode tab is attached to the first uncoated portion, and a portion of the first electrode tab is covered with an insulating member together with at least a portion of the first uncoated portion.

8. The energy storage device according to claim 1, wherein the total proportion of the first region in the first active material layer is 0.1% to 10%.

9. The energy storage device according to claim 1, wherein the first active material layer has a plurality of first regions, and the proportion of the first region in the first active material layer is 0.1% to 2.5% per first region.

10. The energy storage device according to claim 1, wherein the mass per unit area of ​​the first active material layer in the first region is 90% or more and 99.5% or less of the mass per unit area of ​​the first active material layer surrounding the first region.

11. The energy storage device according to claim 1, wherein the first electrode plate further comprises a second active material layer provided on the second main surface, the second main surface has at least one second uncoated portion that is partially provided along the longitudinal direction of the current collector and does not have the second active material layer, the second active material layer has at least one second region whose length in the longitudinal direction of the current collector is 10% or less of the length in the longitudinal direction of the current collector, the second region extends along the width direction of the current collector, the mass per unit area of ​​the second active material layer in the second region is 50% or more and less than 100% of the mass per unit area of ​​the second active material layer surrounding the second region, the total proportion of the second region in the second active material layer is 50% or less, and the second uncoated portion and the second region are spaced apart.

12. The energy storage device according to claim 11, wherein, when viewed from the direction normal to the first main surface, at least a portion of all of the first regions overlaps with any of the second regions.

Images