Energy storage cell

Abstract

To reduce the reaction unevenness in a width direction of a band shaped electrode.SOLUTION: A power storage cell includes a wound electrode body and an electrode terminal. The wound electrode body includes a band shaped electrode. In a plan view, the band shaped electrode has a length direction and a width direction. The width direction is orthogonal to the length direction. The band shaped electrode includes a current collector and a mixture layer. The mixture layer includes an active material particle. The mixture layer is disposed on a surface of the current collector. In the width direction in the plan view, the band shaped electrode includes a first region, a second region, and a third region. The first region is disposed at an end part in the width direction. In the first region, the current collector is exposed. In the first region, the current collector is electrically connected to the electrode terminal. The second region and the third region are covered with the mixture layer. In the width direction, the second region is disposed between the first region and the third region. The second region has higher reaction resistance per unit area than the third region.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an energy storage cell. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2018-018680 (Patent Document 1) discloses a strip-shaped electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-018680 Summary of the Invention [Problem to be solved by the invention]

[0004] The energy storage cell includes a power generating element. The power generating element includes, for example, a wound electrode body. The wound electrode body is formed by spirally winding a strip electrode. The strip electrode has a current collecting portion. The current collecting portion is electrically connected to an electrode terminal (external terminal). For example, the current collecting portion may be disposed at the end of the strip electrode in the longitudinal direction. When the current collecting portion is disposed at the end of the strip electrode in the longitudinal direction, unevenness in the electrode reaction may occur in the longitudinal direction of the strip electrode. Hereinafter, unevenness in the electrode reaction may also be referred to as "uneven reaction." Uneven reaction may promote performance degradation.

[0005] In order to reduce the reaction unevenness in the longitudinal direction, it is conceivable to form a current collecting portion that extends continuously in the longitudinal direction at the end of the width direction of the strip electrode, but in this case, there is a possibility that the reaction unevenness in the width direction may occur.

[0006] An object of the present disclosure is to reduce reaction unevenness in the width direction of the strip electrodes. [Means for solving the problem]

[0007] 1. The energy storage cell includes a wound electrode body and an electrode terminal. The wound electrode body includes a strip electrode. In a plan view, the strip electrode has a length direction and a width direction. The width direction is perpendicular to the length direction. The wound electrode body is formed by winding the strip electrode in the length direction. The strip electrode includes a current collector and a composite layer. The composite layer includes active material particles. The composite layer is disposed on the surface of the current collector. In the width direction in a plan view, the strip electrode includes a first region, a second region, and a third region. The first region is disposed at an end in the width direction. The current collector is exposed in the first region. The current collector is electrically connected to the electrode terminal in the first region. The second region and the third region are covered by the composite layer. In the width direction, the second region is disposed between the first region and the third region. The second region has a higher reaction resistance per unit area than the third region.

[0008] The first region corresponds to the current collecting section. The second region is closer to the current collecting section (first region) than the third region. The second region tends to have a higher current density than the third region. It is thought that the electrode reaction is promoted in the second region compared to the third region, which causes the reaction to become uneven.

[0009] In the energy storage cell described in "1" above, the reaction resistance per unit area varies locally. Hereinafter, "reaction resistance per unit area" will also be referred to simply as "reaction resistance." The second region has a higher reaction resistance than the third region. That is, the electrode reaction is less likely to proceed in the second region than in the third region. Therefore, it is expected that the reaction unevenness in the width direction of the strip electrode will be reduced.

[0010] 2. The energy storage cell described in "1" above may include, for example, the following configuration: In the second region, the composite layer includes first active material particles; In the third region, the composite layer includes second active material particles; The first active material particles have a smaller BET specific surface area than the second active material particles.

[0011] It is believed that the smaller the BET specific surface area of ​​the active material particles, the smaller the reaction field (reaction area) between the active material particles and carrier ions (e.g., Li ions).It is believed that the smaller the reaction area, the greater the reaction resistance.In other words, the reaction resistance of each region can be adjusted by the BET specific surface area of ​​the active material particles.

[0012] 3. The energy storage cell described in "1" or "2" above may include, for example, the following configuration: In the second region, the composite layer includes first composite particles; In the third region, the composite layer includes second composite particles; Each of the first composite particles and the second composite particles includes active material particles and a binder. The binder covers at least a portion of the surface of the active material particles; The first composite particles have a larger mass fraction of the binder than the second composite particles.

[0013] For example, active material particles and a binder may form composite particles. The binder may inhibit ion conduction. It is believed that the reaction resistance may increase in the portion of the surface of the active material particles to which the binder is attached. The mass fraction of the binder in the composite particles is believed to correspond to the amount of binder attached and the coverage of the active material particles. It is believed that the greater the mass fraction of the binder in the composite particles, the greater the reaction resistance. In other words, the reaction resistance of each region can be adjusted by the mass fraction of the binder in the composite particles.

[0014] 4. The energy storage cell according to any one of the above items "1" to "3" may include, for example, the following configuration: In the second region, the composite layer includes a first layer and a second layer. In a cross-sectional view of the strip electrode, the first layer is disposed between the current collector and the second layer. The second layer has a smaller mass fraction of active material particles than the first layer.

[0015] A small mass fraction of the active material particles in the surface layer (second layer) of the composite layer is expected to increase the reaction resistance. The mass fraction of the active material particles in the second layer may be, for example, zero. For example, the second layer may be formed by applying a polymer solution to the surface of the first layer.

[0016] 5. The energy storage cell according to any one of the above items "1" to "4" may include, for example, the following configuration: The strip-shaped electrode has an inner circumferential surface and an outer circumferential surface. In the wound electrode body, the inner circumferential surface is disposed on the inner circumferential side. The outer circumferential surface is the surface opposite the inner circumferential surface. A first composite layer is disposed on the inner circumferential surface. A second composite layer is disposed on the outer circumferential surface. The first composite layer has a reaction resistance per unit area greater than that of the second composite layer.

[0017] In a wound electrode body, the inner peripheral surface tends to dissipate heat more slowly than the outer peripheral surface. That is, the inner peripheral surface tends to be hotter than the outer peripheral surface. The temperature difference between the inner peripheral surface and the outer peripheral surface may cause uneven reaction between the inner peripheral surface and the outer peripheral surface. The temperature difference between the inner peripheral surface and the outer peripheral surface can be reduced because the composite layer on the inner peripheral surface (first composite layer) has a higher reaction resistance than the composite layer on the outer peripheral surface (second composite layer). It is expected that the reduction in temperature difference will reduce uneven reaction between the inner peripheral surface and the outer peripheral surface.

[0018] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") will be described. However, the present embodiment does not limit the technical scope of the present disclosure. The present embodiment is illustrative in all respects. The present embodiment is non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and arbitrarily combined. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a storage cell according to this embodiment. [Figure 2] FIG. 2 is a schematic plan view showing an example of a strip-shaped electrode in this embodiment. [Figure 3] FIG. 3 is a conceptual diagram of a composite particle in this embodiment. [Figure 4] FIG. 4 is a first schematic cross-sectional view showing an example of a strip-shaped electrode in this embodiment. [Figure 5]FIG. 5 is a second schematic cross-sectional view showing an example of a strip-shaped electrode in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] <Terminology> The "reaction resistance per unit area" is measured using the following procedure. A fully discharged energy storage cell is disassembled to recover the strip electrodes, and samples of a predetermined area are cut out from each of the measurement targets (second and third regions). An evaluation cell (single cell or half cell) is fabricated. The evaluation cell includes the sample as a working electrode. The counter electrode may be, for example, Li foil. AC impedance measurement is performed. A Cole-Cole plot is created based on the measurement results. In the Cole-Cole plot, two intersections between the arc and the real axis (horizontal axis) are identified. The difference (absolute value) between the two intersections is considered to be the reaction resistance. The reaction resistance is divided by the opposing area of ​​the sample (working electrode) and the counter electrode to determine the value per unit area.

[0021] "Specific surface area" refers to the surface area per unit mass. "BET specific surface area" refers to the specific surface area measured by the gas adsorption method (BET single-point method). The adsorbate in the gas adsorption measurement is nitrogen.

[0022] "Planar view" means viewing an object from a line of sight parallel to the thickness direction of the object (e.g., a strip electrode). Planar view corresponds to a plan view. "Cross-sectional view" means viewing an object from a line of sight perpendicular to the thickness direction of the object. Cross-sectional view corresponds to a cross-sectional view.

[0023] Geometric terms (such as "parallel," "orthogonal," etc.) should not be interpreted in a strict sense. For example, "parallel" may deviate slightly from the strict meaning of "parallel." Geometric terms may include, for example, tolerances, errors, etc. in design, work, manufacturing, etc. The dimensional relationships in each drawing may not match the actual dimensional relationships. To help readers understand, the dimensional relationships (length, width, thickness, etc.) in each drawing may be changed. Furthermore, some components may be omitted.

[0024] "Electrically connected" means that two objects are electrically connected. The two objects may be directly connected. The two objects may also be connected by an electrically conductive member.

[0025] Terms expressed in the singular also refer to the plural unless otherwise specified. For example, the term "particle" refers not only to a single particle, but also to a plurality of particles (a particle group) and an aggregate of particles (powder).

[0026] For example, unless otherwise specified, a numerical range such as "m to n%" includes the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% but less than n%."

[0027] A "storage cell" refers to a cell that can be recharged. A storage cell is also called, for example, a "secondary battery." A storage cell can be any battery system. A storage cell may be, for example, a lithium ion battery. A storage cell may be any of a liquid battery, a polymer battery, and an all-solid-state battery. A storage cell can have any external shape. A storage cell may be, for example, cylindrical, prismatic, or pouch-shaped. A pouch-shaped cell refers to a form in which the exterior body is a pouch made of a metal foil laminate film. In this embodiment, a cylindrical liquid battery is described as an example.

[0028] <Energy storage cell> FIG. 1 is a schematic cross-sectional view showing an example of a storage cell according to this embodiment. The storage cell 100 is cylindrical. The storage cell 100 has a height direction (H direction) and a radial direction (R direction). The storage cell 100 includes a wound electrode assembly 50. The storage cell 100 may further include a case 30. The case 30 houses the wound electrode assembly 50. The case 30 may be made of, for example, metal. The case 30 is cylindrical. The case 30 may include, for example, a cap 31 and a can 32. The storage cell 100 includes electrode terminals. For example, the cap 31 and the can 32 may each function as an electrode terminal. That is, the cap 31 may have a polarity different from that of the can 32. When the cap 31 has a positive polarity, the can 32 has a negative polarity. When the cap 31 has a negative polarity, the can 32 has a positive polarity. For example, a gasket 33 may electrically isolate the cap 31 from the can 32 .

[0029] The wound electrode body 50 has a cylindrical or columnar outer shape. Note that, for example, when the energy storage cell 100 is rectangular or pouch-shaped, the wound electrode body 50 may be pressed in the R direction to form the wound electrode body 50 into a flat shape.

[0030] The wound electrode body 50 includes a positive electrode 51 and a negative electrode 52. Both the positive electrode 51 and the negative electrode 52 are strip-shaped electrodes. That is, the wound electrode body 50 includes strip-shaped electrodes. The wound electrode body 50 may further include a separator 53. The separator 53 is interposed between the positive electrode 51 and the negative electrode 52. The separator 53 electrically separates the positive electrode 51 from the negative electrode 52. For example, a laminate may be formed by stacking the positive electrode 51, the separator 53, and the negative electrode 52 in this order. The wound electrode body 50 can be formed by spirally winding the laminate. For example, the wound electrode body 50 may be housed in the case 30 so that the winding axis of the wound electrode body 50 is parallel to the H direction.

[0031] Separator 53 may include, for example, a porous resin film or the like. An electrolytic solution (not shown) can permeate separator 53. The electrolytic solution may include, for example, an organic solvent and a supporting electrolyte (for example, a Li salt).

[0032] The first current collecting tab 61 electrically connects the positive electrode 51 and the cap 31. The second current collecting tab 62 electrically connects the negative electrode 52 and the can 32. The energy storage cell 100 may have, for example, a "tabless structure." A tabless structure does not have a current collecting tab. In a tabless structure, a strip electrode (at least one of the positive electrode 51 and the negative electrode 52) can be directly connected to an electrode terminal.

[0033] <Strip electrode> FIG. 2 is a schematic plan view showing an example of a strip electrode in this embodiment. The strip electrode 10 in FIG. 2 may be either a positive electrode 51 or a negative electrode 52. The strip electrode 10 has a length direction (L direction) and a width direction (W direction). The W direction is perpendicular to the L direction. The strip electrode 10 is wound in the L direction to form a wound electrode body 50. The W direction of the strip electrode 10 corresponds to the H direction of the energy storage cell 100. In the strip electrode 10, the ratio of the L direction dimension to the W direction dimension may be, for example, 2 or more, 5 or more, 10 or more, or 100 or more.

[0034] The strip electrode 10 includes a current collector 11 and a composite layer 12. The current collector 11 has electrical conductivity. The current collector 11 can be a substrate of the strip electrode 10. The current collector 11 may include, for example, a metal foil. The current collector 11 may include, for example, at least one selected from the group consisting of Al, Cu, Ti, Ni, and Fe.

[0035] Composite layer 12 is disposed on the surface of current collector 11. Composite layer 12 may be disposed on only one surface of current collector 11, for example. Composite layer 12 may be disposed on both surfaces of current collector 11, for example. Composite layer 12 can be formed by coating the surface of the current collector with a composite.

[0036] The composite layer 12 contains active material particles. The composite layer 12 may further contain a binder, a conductive material, and the like. The active material particles can cause an electrode reaction (positive electrode reaction or negative electrode reaction). The active material particles can contain any component. The active material particles may contain, for example, a positive electrode active material. The positive electrode active material may contain, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. The active material particles may contain, for example, a negative electrode active material. The negative electrode active material may be, for example, graphite, soft carbon, hard carbon, Si, SiO, Si-C, a Si-based alloy, Sn, SnO, a Sn-based alloy, and Li4Ti5O. 12 It may contain at least one selected from the group consisting of: "Si-C" refers to a composite material of Si and carbon.

[0037] The binder can bind solid materials. The binder can contain any component. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide (PI), polyamideimide (PAI), and polyacrylic acid (PAA). The amount of the binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the active material particles.

[0038] The conductive material can form an electron conduction path. The conductive material can contain any component. For example, the conductive material may contain at least one material selected from the group consisting of carbon black, vapor-grown carbon fiber, carbon nanotubes, and graphene flakes. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the active material particles.

[0039] <1st area, 2nd area, 3rd area> In the W direction in a plan view (FIG. 2), the strip electrode 10 includes a first region 101, a second region 102, and a third region 103. The first region 101 is disposed at an end in the W direction. The first region 101 may be disposed at only one end in the W direction. The first region 101 may be disposed at both ends in the W direction. In the first region 101, the current collector 11 is exposed. The first region 101 may be referred to as, for example, a "non-coated portion." The first region 101 may be formed continuously over the entire area in the L direction. The first region 101 may be formed in a part of the L direction.

[0040] The first region 101 is a current collecting portion. That is, in the first region 101, the current collector 11 is electrically connected to the electrode terminal (the cap 31 or the can 32). A first current collecting tab 61 may electrically connect the current collector 11 to the cap 31 (see FIG. 1). A second current collecting tab 62 may electrically connect the current collector 11 to the can 32 (see FIG. 1). Each current collecting tab may be welded to the first region 101, for example. For example, in the case of a tabless structure, the first region 101 (current collector 11) of the wound electrode body 50 may be bent inward to form an end face (see FIG. 2). The end face may be perpendicular to the winding axis of the wound electrode body 50. The end face may be flat or curved. The end face may have an uneven surface. A current collecting plate may be welded to the end face. The end face may be in surface contact with the current collecting plate. A cap 31 or the like may be welded directly to the end face.

[0041] The second region 102 and the third region 103 are covered with the composite layer 12. The second region 102 and the third region 103 may be referred to as, for example, "coated portions." In the W direction, the second region 102 is disposed between the first region 101 and the third region 103. The second region 102 may be adjacent to the first region 101. The second region 102 may be adjacent to the third region 103.

[0042] The second region 102 has a larger reaction resistance than the third region 103. This is expected to reduce reaction unevenness in the W direction. The ratio (r2 / r3) of the reaction resistance (r2) of the second region 102 to the reaction resistance (r3) of the third region 103 may be, for example, 1.1 or more, 1.5 or more, 2 or more, 5 or more, or 10 or more. The ratio (r2 / r3) may be, for example, 10 or less, 5 or less, 2 or less, or 1.5 or less.

[0043] The second region 102 and the third region 103 may be formed, for example, by applying two types of composite materials in a stripe pattern. The dimension (W2) of the second region 102 and the dimension (W3) of the third region 103 in the W direction may satisfy the relationship of "W2 / W3 = 5 / 5 to 1 / 9" or "W2 / W3 = 3 / 7 to 1 / 9". The dimension (W1) of the first region 101 in the W direction can be set arbitrarily in accordance with, for example, the current collection structure.

[0044] <Specific surface area> The reaction resistance of each region may be adjusted, for example, by the BET specific surface area of ​​the active material particles. For example, in the second region 102, the composite layer 12 may contain first active material particles. In the third region 103, the composite layer 12 may contain second active material particles. The first active material particles may have a smaller BET specific surface area than the second active material particles. Since the BET specific surface area (S1) of the first active material particles is smaller than the BET specific surface area (S2) of the second active material particles, the second region 102 may have a larger reaction resistance than the third region 103. The chemical composition of the first active material particles may be the same as or different from that of the second active material particles.

[0045] The ratio (S1 / S2) of the BET specific surface area (S1) of the first active material particles to the BET specific surface area (S2) of the second active material particles may be, for example, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The ratio (S1 / S2) may be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. The BET specific surface area (S1) and the BET specific surface area (S2) are each independently, for example, 0.1 to 10 m 2 / g.

[0046] <Composite particles> FIG. 3 is a conceptual diagram of a composite particle in this embodiment. For example, composite particle 5 includes active material particles 1 and binder 2. Binder 2 covers at least a portion of the surface of active material particle 1. Composite particle 5 may further include a conductive material (not shown). For example, binder 2 may fix the conductive material to active material particle 1. Composite particle 5 may be formed by any particle composite process. For example, active material particles 1 and binder 2 may be mixed under conditions in which a strong shear force is applied to form composite particle 5. For example, particle composite process may be performed using a product called "Mechano Hybrid" manufactured by Nippon Coke and Engineering Co., Ltd.

[0047] For example, the reaction resistance of each region may be adjusted by the mass fraction of the binder in the composite particles. For example, in the second region 102, the composite layer 12 may contain first composite particles. In the third region 103, the composite layer 12 may contain second composite particles. The first composite particles may have a larger mass fraction of the binder than the second composite particles. The mass fraction (B1) of the binder in the first composite particles may be larger than the mass fraction (B2) of the binder in the second composite particles, so that the second region 102 may have a larger reaction resistance than the third region 103. The chemical composition of the active material particles and binder in the first composite particles may be the same as or different from that of the second composite particles.

[0048] The ratio (B1 / B2) of the mass fraction (B1) of the binder in the first composite particles to the mass fraction (B2) of the binder in the second composite particles may be, for example, 1.1 or more, 1.5 or more, 2 or more, 5 or more, or 10 or more. The ratio (B1 / B2) may be, for example, 10 or less, 5 or less, 2 or less, or 1.5 or less. The mass fraction (B1) of the binder and the mass fraction (B2) of the binder may each independently be 0.1 to 10%.

[0049] <Multilayer structure> FIG. 4 is a first schematic cross-sectional view showing an example of a strip electrode in this embodiment. The thickness direction (T direction) of the strip electrode 10 corresponds to the R direction of the energy storage cell 100. For example, in the second region 102, the composite layer 12 may have a multilayer structure, thereby adjusting the reaction resistance of each region. For example, in the second region 102, the composite layer 12 may include a first layer 12L and a second layer 12U. The first layer 12L and the second layer 12U may be referred to as a lower layer and an upper layer, for example. In the cross-sectional view ( FIG. 4 ), the first layer 12L is disposed between the current collector 11 and the second layer 12U. The second layer 12U may have a smaller mass fraction of active material particles than that of the first layer 12L. The ratio (A2 / A1) of the mass fraction (A2) of the active material particles in the second layer 12U to the mass fraction (A1) of the active material particles in the first layer 12L may be, for example, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The ratio (A2 / A1) may be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. The mass fraction (A2) of the active material particles in the second layer 12U may be, for example, zero.

[0050] The second layer 12U may contain, for example, an inorganic filler, a solid electrolyte, a gel electrolyte, a polymer, or the like. The second layer 12U may contain, for example, at least one selected from the group consisting of alumina, boehmite, titania, polyethylene (PE), PI, aramid, PVdF, PVdF-HFP, PAA, CMC, polyvinyl alcohol (PVA), and polyethylene oxide (PEO). When the second layer 12U does not contain active material particles, the second layer 12U may extend in the W direction so as to cover, for example, a portion of the surface of the current collector 11. The first layer 12L may have, for example, the same composition as the composite layer 12 in the third region 103. For example, the second layer 12U may be formed by applying a polymer solution (for example, a PVdF-HFP solution) to the surface of the second region 102 (composite layer 12).

[0051] <Gradation (composition gradient)> The composition of the composite layer 12 may change in the second region 102. For example, the composition of the composite layer 12 may change continuously or stepwise in the W direction. For example, the composition of the composite layer 12 may change so that the reaction resistance increases toward the first region 101 (current collecting portion). For example, the mass fraction of the active material particles may decrease toward the first region 101. For example, the mass fraction of the binder may increase toward the first region 101.

[0052] <Inner and outer surfaces> FIG. 5 is a second schematic cross-sectional view showing an example of a strip electrode in this embodiment. The strip electrode 10 has an inner circumferential surface P1 and an outer circumferential surface P2. In the wound electrode body 50, the inner circumferential surface P1 is disposed on the inner circumferential side. The outer circumferential surface P2 is the surface opposite the inner circumferential surface P1. A first composite material layer 12F is disposed on the inner circumferential surface P1. A second composite material layer 12B is disposed on the outer circumferential surface P2. For example, the first composite material layer 12F may have a higher reaction resistance than the second composite material layer 12B. For example, the second region 102 in the first composite material layer 12F may have a higher reaction resistance than the second region 102 in the second composite material layer 12B. For example, the third region 103 in the first composite material layer 12F may have a higher reaction resistance than the third region 103 in the second composite material layer 12B.

[0053] The reaction resistance (r B ) the reaction resistance (r F ) ratio (r F / r B ) may be, for example, 1.1 or more, 1.5 or more, 2 or more, 5 or more, or 10 or more. F / r B ) may be, for example, 10 or less, 5 or less, 2 or less, or 1.5 or less. [Explanation of symbols]

[0054] 1 active material particles, 2 binder, 5 composite particles, 10 strip electrode, 11 current collector, 12 composite layer, 12F first composite layer, 12B second composite layer, 12L first layer, 12U second layer, 30 case, 31 cap, 32 can, 33 gasket, 50 wound electrode body, 51 positive electrode, 52 negative electrode, 53 separator, 61 first current collecting tab, 62 second current collecting tab, 100 storage cell, 101 first region, 102 second region, 103 third region, P1 inner surface, P2 outer surface.

Claims

1. a wound electrode body and an electrode terminal; the wound electrode body includes a strip electrode, In a plan view, the strip-shaped electrodes have a length direction and a width direction, The width direction is perpendicular to the length direction, the strip-shaped electrode is wound in the length direction to form the wound electrode body, the strip-shaped electrode includes a current collector and a composite layer; the mixture layer contains active material particles, the composite layer is disposed on a surface of the current collector, the strip-shaped electrode includes a first region, a second region, and a third region in the width direction in the plan view; The first region is disposed at an end in the width direction, the current collector is exposed in the first region, In the first region, the current collector is electrically connected to the electrode terminal, the second region and the third region are covered with the composite layer, The second region is disposed between the first region and the third region in the width direction, and the second region has a reaction resistance per unit area greater than that of the third region; In the second region, the composite layer includes a first layer and a second layer; In a cross-sectional view of the strip-shaped electrode, the first layer is disposed between the current collector and the second layer, and the second layer has a mass fraction of the active material particles that is smaller than that of the first layer; Energy storage cell.

2. In the second region, the mixture layer includes first active material particles, In the third region, the composite layer includes second active material particles; and the first active material particles have a smaller BET specific surface area than the second active material particles; The energy storage cell according to claim 1 .

3. In the second region, the composite layer includes first composite particles, In the third region, the composite layer contains second composite particles, each of the first composite particles and the second composite particles includes the active material particles and a binder; the binder covers at least a portion of the surface of the active material particles; and the first composite particles have a greater mass fraction of the binder than the second composite particles; The energy storage cell according to claim 1 .

4. the strip electrode has an inner circumferential surface and an outer circumferential surface; In the wound electrode body, the inner circumferential surface is disposed on the inner circumferential side, the outer circumferential surface is the opposite surface of the inner circumferential surface, A first composite layer is disposed on the inner circumferential surface, A second composite layer is disposed on the outer peripheral surface, and The first composite layer has a reaction resistance per unit area that is larger than that of the second composite layer. The energy storage cell according to any one of claims 1 to 3.

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