Patent Description:
There has been conventionally widely known an electrical storage device comprising a bottomed cylindrical outer can in which an electrode assembly is housed, and a sealing plate to which a positive electrode terminal and a negative electrode terminal are attached and that closes an opening of the outer can. For example, Patent Literature <NUM> discloses an electrical storage device comprising a positive electrode current collecting plate including a positive electrode terminal, a negative electrode current collecting plate including a negative electrode terminal, a positive electrode tab group formed by gathering positive electrode tabs, and a negative electrode tab group formed by gathering negative electrode tabs, in which the positive electrode tab group is welded to an upper surface of the positive electrode current collecting plate, and the negative electrode tab group is welded to an upper surface of the negative electrode current collecting plate. In the electrical storage device of Patent Literature <NUM>, the lengths of the tabs forming the tab group are varied depending on the stacking position, thereby suppressing a variation in the electrical resistance in the current collecting part. In the electrical storage device of Patent Literature <NUM>, each current collecting plate and the corresponding terminal are connected via an overcurrent protection circuit.

Patent Literature <NUM> discloses an electrical storage device comprising an electrode assembly consisting of two electrode groups each having a positive electrode tab group and a negative electrode tab group. Patent Literature <NUM> discloses that the tab group is welded to the current collecting plate in a state in which the tabs are gathered toward a center in the stacking direction of the electrode group, whereby a load acting on the tabs can be reduced.

A functional component comprising a current breaking mechanism for cutting off a current path when the abnormality occurs, for example, is generally provided in the electrical storage device such as a lithium ion battery. When vibration, impact or the other load is applied to such a functional component in the manufacture of the electrical storage device, for example, it is assumed that the performance of the functional component deteriorates. Meanwhile, if the manufacturing conditions are strictly regulated so that a load is not applied to the functional component, it leads to the decrease in the productivity.

An electrical storage device according to the present disclosure is defined in claim <NUM>.

According to the present disclosure, the electrical storage device can prevent a great load from being applied to the functional component comprising the current breaking mechanism or the like provided in the device while ensuring good productivity. Accordingly, vibration or impact hardly acts on the functional component in the manufacture of the electrical storage device, for example, which makes it possible to prevent performance deterioration, damage, and the like of the functional component from being caused by the vibration or the impact. The functional component can be sufficiently protected from the vibration or the impact even when special manufacturing conditions are not added in a step of assembling the electrical storage device.

Hereinafter, an example of embodiments of the present disclosure will be described in detail with reference to the drawings. In the present specification, notation of the "numerical value A to the numerical value B" means the "numerical value A or more and the numerical value B or less," unless otherwise specified.

<FIG> is a perspective view illustrating an appearance of a secondary battery <NUM>, which is an example of an embodiment, and <FIG> is a perspective view of an electrode assembly <NUM> and a sealing plate <NUM> forming the secondary battery <NUM> (a view illustrating a state in which an outer can <NUM> is removed). The secondary battery <NUM> illustrated in <FIG> comprises, as an outer body, a rectangular container including the outer can <NUM> and the sealing plate <NUM>, but the outer body is not limited thereto. Note that the electrical storage device according to the present disclosure is not limited to the secondary battery <NUM>, and may be, for example, a primary battery or a capacitor.

As illustrated in <FIG>, the secondary battery <NUM> comprises an electrode assembly <NUM>, an electrolyte, a bottomed cylindrical outer can <NUM> in which the electrode assembly <NUM> and the electrolyte are housed, and the sealing plate <NUM> to which a positive electrode terminal <NUM> and a negative electrode terminal <NUM> are attached and that closes an opening of the outer can <NUM>. The electrode assembly <NUM> has a structure in which positive electrodes <NUM> and negative electrodes <NUM> are alternately stacked with separators <NUM> each interposed therebetween (for details, see <FIG> described later). The outer can <NUM> is a metal rectangular container having a flat and substantially rectangular parallelepiped shape, which is open on one side in an axial direction, and the secondary battery <NUM> is a so-called rectangular battery. Each of the outer can <NUM> and the sealing plate <NUM> is made of a metal material containing aluminum as a main component, for example.

In the following description, the height direction of the outer can <NUM> is referred to as an "up-down direction" of the secondary battery <NUM>, the sealing plate <NUM> side is referred to as "upper," and the bottom portion side of the outer can <NUM> is referred to as "lower," for convenience of description. The direction along a longitudinal direction of the sealing plate <NUM> is referred to as a "lateral direction" of the secondary battery <NUM>.

The electrolyte may be an aqueous electrolyte, but preferably be a non-aqueous electrolyte. The non-aqueous electrolyte may be a solid electrolyte, but in the present embodiment, a non-aqueous electrolyte solution is used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent, and an electrolyte salt dissolved in the non-aqueous solvent, for example. As the non-aqueous solvent, for example, esters, ethers, nitriles, amids, or a mixed solvent containing at least two of those mentioned above may be used. The non-aqueous solvent may also contain a halogen substitute in which at least a part of hydrogens of these solvents is substituted with a halogen atom. As the electrolyte salt, for example, a lithium salt such as LiPF<NUM> is used.

A positive electrode terminal <NUM> and a negative electrode terminal <NUM> are attached to the sealing plate <NUM>, as described above. The sealing plate <NUM> has an elongated rectangular shape, and the positive electrode terminal <NUM> and the negative electrode terminal <NUM> are arranged at one end side and at the other end side in the longitudinal direction of the sealing plate <NUM>, respectively. The positive electrode terminal <NUM> and the negative electrode terminal <NUM> are external connection terminals to be electrically connected to another secondary battery <NUM> or a load, and are attached to the sealing plate <NUM> via an insulating member.

Although details will be described later, the positive electrode <NUM> includes a positive electrode tab <NUM> to be electrically connected with the positive electrode terminal <NUM>, and the negative electrode <NUM> includes a negative electrode tab <NUM> to be electrically connected with the negative electrode terminal <NUM>. The positive electrode terminal <NUM> is electrically connected with a positive electrode tab group <NUM> formed by stacking a plurality of positive electrode tabs <NUM> via a positive electrode current collecting plate <NUM>, and the negative electrode terminal <NUM> is electrically connected with a negative electrode tab group <NUM> formed by stacking a plurality of negative electrode tabs <NUM> via a negative electrode current collecting plate <NUM>.

The sealing plate <NUM> is provided with a current breaking device <NUM>, as a functional component, for cutting off a current path when the abnormality occurs in the battery. The functional component is, for example, a component functioning as a safety device or a control device of the secondary battery <NUM>. The functional component is arranged close to the positive electrode terminal <NUM> or the negative electrode terminal <NUM> on the inner surface of the sealing plate <NUM>. In the present embodiment, the current breaking device <NUM> is accompanied with and arranged inside the positive electrode terminal <NUM>.

The current breaking device <NUM> is a pressure-responsive safety device that breaks a current path in the case where the internal pressure in the outer can <NUM> increases beyond a predetermined pressure due to an abnormality occurring in the secondary battery <NUM>. For example, the current breaking device <NUM> is arranged between the positive electrode terminal <NUM> and the positive electrode current collecting plate <NUM>, and is electrically connected to the positive electrode terminal <NUM> and the positive electrode current collecting plate <NUM> in normal use. The structure of the current breaking device <NUM> is not limited to a particular structure, but as an example of the current breaking device <NUM>, there is a device including an inversion plate that is inverted in a direction away from the positive electrode current collecting plate <NUM> when the internal pressure increases, to cut off the electrical connection with the positive electrode current collecting plate <NUM> and break the current path between the positive electrode terminal <NUM> and the positive electrode current collecting plate <NUM>.

The sealing plate <NUM> is provided with a liquid injection portion <NUM> for injecting the non-aqueous electrolyte solution, and a gas discharge vent <NUM> that opens to discharge gas when an abnormality occurs in the battery. The gas discharge vent <NUM> is arranged in a center portion in the longitudinal direction of the sealing plate <NUM>, and the liquid injection portion <NUM> is arranged between the positive electrode terminal <NUM> and the gas discharge vent <NUM>.

As illustrated in <FIG>, the electrode assembly <NUM> is divided into a first electrode group 11A and a second electrode group 11B. The electrode groups 11A and 11B have the same stacking structure and dimensions, and are stacked in a thickness direction of the electrode assembly <NUM>, for example. The positive electrode tab group <NUM> consisting of a plurality of positive electrode tabs <NUM> and the negative electrode tab group <NUM> consisting of a plurality of negative electrode tabs <NUM> are formed on the upper end portion of each electrode group, and are connected to the respective current collecting plates of the sealing plate <NUM>. Outer circumferential surfaces of the electrode groups 11A and 11B are covered by the separator <NUM>, and the battery reaction occurs independently in the electrode groups 11A and 11B.

<FIG> is an exploded perspective view of the electrode assembly <NUM>. As illustrated in <FIG>, the electrode assembly <NUM> includes a plurality of positive electrodes <NUM> and a plurality of negative electrodes <NUM>. For example, in each of the electrode groups 11A and 11B forming the electrode assembly <NUM>, the number of negative electrodes <NUM> is greater than the number of positive electrodes <NUM> by one, so that the negative electrodes <NUM> are provided at both ends in the thickness direction of the electrode groups 11A and 11B. <FIG> illustrates that a plurality of separators <NUM> are arranged one by one between the positive electrodes <NUM> and the negative electrodes <NUM>, but the number of separators <NUM> included in each of the electrode groups 11A and 11B may be one. In this case, the long separator <NUM> is folded in a zigzag shape and is arranged between the positive electrodes <NUM> and the negative electrodes <NUM>.

The electrode assembly <NUM> is a stack-type electrode assembly in which a plurality of positive electrodes <NUM> and a plurality of negative electrodes <NUM> are alternately stacked, one by one, with separators each interposed therebetween. The positive electrode <NUM> includes the positive electrode tab <NUM> projecting upward, and the negative electrode <NUM> includes the negative electrode tab <NUM> projecting upward. In other words, the positive electrodes <NUM> and the negative electrodes <NUM> are stacked so that the respective tabs are directed in the same direction. The positive electrodes <NUM> and the negative electrodes <NUM> are stacked so that the positive electrode tab <NUM> and the negative electrode tab <NUM> are positioned at one end side and at the other end side in the lateral direction of the electrode assembly <NUM>, respectively, and a plurality of positive electrode tabs <NUM> are aligned in the thickness direction of the electrode assembly <NUM> and a plurality of negative electrode tabs <NUM> are aligned in the thickness direction of the electrode assembly <NUM>.

The positive electrode <NUM> has a positive electrode core <NUM> and a positive electrode mixture layer formed on a surface of the positive electrode core <NUM>. Examples of the positive electrode core <NUM> include a foil of a metal that is stable in a potential range of the positive electrode <NUM>, such as aluminum or an aluminum alloy, and a film in which such a metal is provided on the surface layer. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on each side of the positive electrode core <NUM>. The positive electrode <NUM> can be fabricated by, for example, applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like on the positive electrode core <NUM>, drying the resulting coating film, and then compressing it to form a positive electrode mixture layer on each side of the positive electrode core <NUM>.

The positive electrode <NUM> has a structure in which the positive electrode mixture layer is formed on the entire region of a portion excluding the positive electrode tab <NUM> (hereinafter, referred to as a "base portion") in the surface of the positive electrode core <NUM>. The thickness of the positive electrode core <NUM> is, for example, <NUM> to <NUM>, and preferably <NUM> to <NUM>. The base portion of the positive electrode core <NUM> has a rectangle shape in front view, and the positive electrode tab <NUM> projects from a side of the rectangle. The positive electrode core <NUM> is generally obtained by processing one sheet of metal foil to integrally form the base portion and the positive electrode tab <NUM>.

A lithium transition metal composite oxide is used as the positive electrode active material. Examples of a metal element contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. In particular, at least one of Ni, Co, and Mn is preferably contained. Suitable examples of the composite oxide include a lithium transition metal composite oxide containing Ni, Co, and Mn, and a lithium transition metal composite oxide containing Ni, Co, and Al.

Examples of the conductive agent contained in the positive electrode mixture layer can include carbon materials such as carbon black, acetylene black, Ketjenblack, and graphite. Examples of the binder contained in the positive electrode mixture layer can include fluororesin such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. Also, these resins may be used in combination with a cellulose derivative such as carboxymethyl cellulose (CMC) or a salt thereof, a polyethylene oxide (PEO), or the like.

The negative electrode <NUM> has a negative electrode core <NUM> and a negative electrode mixture layer formed on the surface of the negative electrode core <NUM>. Examples of the negative electrode core <NUM> include a foil of a metal that is stable in a potential range of the negative electrode <NUM>, such as copper, and a film in which such a metal is provided on the surface layer. The negative electrode mixture layer contains a negative electrode active material and a binder, and is preferably formed on each side of the negative electrode core. The negative electrode <NUM> can be fabricated by, for example, applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and the like on a surface of the negative electrode core <NUM>, drying the resulting coating film, and then compressing it to form a negative electrode mixture layer on each side of the negative electrode core <NUM>.

The negative electrode <NUM> has a structure in which the negative electrode mixture layer is formed on the entire region of a base portion which is a portion excluding the negative electrode tab <NUM> in the surface of the negative electrode core <NUM>. The thickness of the negative electrode core <NUM> is, for example, <NUM> to <NUM>, and preferably <NUM> to <NUM>. The base portion of the negative electrode core <NUM> has a rectangle shape in front view, and the negative electrode tab <NUM> projects from a side of the rectangle in the same manner as in the case of the positive electrode <NUM>. The negative electrode core <NUM> is generally obtained by processing one sheet of metal foil to integrally form the base portion and the negative electrode tab <NUM>.

For example, a carbon-based active material that reversibly occludes and releases lithium ions is used as the negative electrode active material. A preferable carbon-based active material is graphite including natural graphite such as flake graphite, massive graphite, and earthy graphite, and artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). As the negative electrode active material, a Si-based active material that is comprised of at least one of Si and a Si-containing compound may be used, and a carbon-based active material and a Si-based active material may be used in combination.

As the binder contained in the negative electrode mixture layer, a fluororesin, PAN, a polyimide, an acrylic resin, and a polyolefin, or the like may be used in the same manner as in the case of the positive electrode <NUM>, and a styrene-butadiene rubber (SBR) is preferably used. Preferably, the negative electrode mixture layer may further contain CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. In particular, SBR may be preferably used in combination with CMC or a salt thereof, or PAA or a salt thereof.

<FIG> is a view schematically illustrating a cross section taken along a line AA in <FIG>. Hereinafter, a configuration of the positive electrode tab group <NUM> and the negative electrode tab group <NUM> for the electrode assembly <NUM> will be described in detail with reference to <FIG> and <FIG>.

As illustrated in <FIG> and <FIG>, the electrode assembly <NUM> includes the positive electrode tab groups <NUM> each formed by stacking a plurality of positive electrode tabs <NUM> and the negative electrode tab groups <NUM> each formed by stacking a plurality of negative electrode tabs <NUM>. One positive electrode tab group <NUM> in which the plurality of positive electrode tabs <NUM> are superposed in the stacking direction of the electrodes is formed in each of the electrode groups 11A and 11B. Similarly, one negative electrode tab group <NUM> in which the plurality of negative electrode tabs <NUM> are superposed in the stacking direction of the electrodes is formed in each of the electrode groups 11A and 11B.

The positive electrode tab groups <NUM> are joined, by welding or the like, to the positive electrode current collecting plate <NUM> attached to the inner surface (lower surface) of the sealing plate <NUM>. The positive electrode current collecting plate <NUM> is a plate-shaped conductive member to be electrically connected with the positive electrode terminal <NUM> via the current breaking device <NUM>, as described above. An insulating member <NUM> is interposed between the sealing plate <NUM> and the positive electrode current collecting plate <NUM> to prevent a contact between both members. Similarly, the negative electrode tab groups <NUM> are joined, by welding or the like, to the negative electrode current collecting plate <NUM> attached to the inner surface of the sealing plate <NUM> via an insulating member.

The positive electrode tab groups <NUM> and the negative electrode tab groups <NUM> function as springs for connecting the electrode assembly <NUM> and the sealing plate <NUM>. The positive electrode tab groups <NUM> and the negative electrode tab groups <NUM> are configured to be expandable and contractible in the up-down direction, and for example, the sealing plate <NUM> is pushed back upward in the case where the sealing plate <NUM> is pressed from above to reduce spacing between the sealing plate <NUM> and the electrode assembly <NUM> (a portion other than the tab groups). That is, the positive electrode tab groups <NUM> and the negative electrode tab groups <NUM> are elastically deformed, whereby the spacing between the electrode assembly <NUM> and the sealing plate <NUM> is maintained.

The positive electrode tab groups <NUM> and the negative electrode tab groups <NUM> may have any shape such that they can function as conductive paths connecting the electrode assembly <NUM> and the corresponding terminal and as the above-described springs. In an example illustrated in <FIG> and <FIG>, the plurality of positive electrode tabs <NUM> and the plurality of negative electrode tabs <NUM> of the electrode group 11A are separately stacked in a state of being curved from outside to inside of the secondary battery <NUM>, so that each of the positive electrode tab group <NUM> and the negative electrode tab group <NUM> is formed to have a substantial U shape in sectional view. Similarly, the tab groups each having a substantial U shape in sectional view are also formed in the electrode group 11B. Note that each tab group may have a U shape formed by being curved from inside to outside of the secondary battery <NUM>. Then, the tab groups of the two stacked electrode groups as illustrated in <FIG> may be arranged so that the cross sectional shape of the tab group of one electrode group and the cross sectional shape of the tab group of the other electrode group are substantially symmetrical about a boundary between the electrode groups.

The positive electrode tab groups <NUM> may be welded to the upper surface of the positive electrode current collecting plate <NUM> which faces the sealing plate <NUM> side, but preferably are welded to the lower surface of the positive electrode current collecting plate <NUM>. When the positive electrode tab groups <NUM> are welded to the lower surface of the positive electrode current collecting plate <NUM>, the function of the spring is more easily exerted. In the present embodiment, all of the positive electrode tab groups <NUM> and the negative electrode tab groups <NUM> are welded to the lower surfaces of the respective current collecting plates, but the positive electrode tab groups <NUM> may be welded to the lower surface of the positive electrode current collecting plate <NUM> and the negative electrode tab groups <NUM> may be welded to the upper surface of the negative electrode current collecting plate <NUM>, for example.

In the secondary battery <NUM>, the spring constant of one tab group close to the functional component, of the positive electrode tab group <NUM> and the negative electrode tab group <NUM> is greater than a spring constant of the other tab group. In the present embodiment, the current breaking device <NUM> accompanied with the positive electrode terminal <NUM> is provided as the functional component, and the spring constant Kt of the positive electrode tab group <NUM> arranged close to the current breaking device <NUM> is greater than the spring constant Kb of the negative electrode tab group <NUM> that is away from the current breaking device <NUM>. That is, the positive electrode tab group <NUM> has higher rigidity than that of the negative electrode tab group <NUM>, and makes it harder to expand and contract than the negative electrode tab group <NUM>.

When the spring constants of the positive electrode tab group <NUM> and the negative electrode tab group <NUM> are set to satisfy Kt > Kb, the negative electrode tab group <NUM> is deformed more easily than the positive electrode tab group <NUM> when a force of pressing the sealing plate <NUM> from above acts or a force of raising the electrode assembly <NUM> from below acts on the positive electrode tab group <NUM> and the negative electrode tab group <NUM> in the manufacture of the secondary battery <NUM>, for example. That is, the negative electrode tab group <NUM> is preferentially deformed to absorb the force, which makes it hard to reduce the spacing between the electrode assembly <NUM> and the sealing plate <NUM> on the positive electrode terminal <NUM> side. This can prevent a contact between the electrode assembly <NUM> and the current breaking device <NUM>, which prevents a great load from being applied to the current breaking device <NUM>.

Each spring constant of the positive electrode tab group <NUM> and the negative electrode tab group <NUM> is calculated from a load applied to each tab group and a deformation amount of the tab group. A specific calculation method is as follows.

The ratio of the spring constant Kt of the positive electrode tab group <NUM> to the spring constant Kb of the negative electrode tab group <NUM> (Kt/Kb) satisfies the relationship of <NUM> ≤ Kt/Kb ≤ <NUM>. Setting Kt/Kb to <NUM> or more can easily prevent the current breaking device <NUM> from contacting the electrode assembly <NUM> when the electrode assembly <NUM> welded to the sealing plate <NUM> is inserted into the outer can <NUM> in the step of manufacturing the secondary battery <NUM>. Meanwhile, when Kt/Kb is set to <NUM> or less, it is not necessary to adopt the structure such that the rigidity of the positive electrode tab group <NUM> can be greatly increased or it is not necessary to adopt the structure such that the rigidity of the negative electrode tab group <NUM> can be greatly reduced. Therefore, the damage of the current breaking device <NUM> can be prevented efficiently.

The spring constant Kt of the positive electrode tab group <NUM> is, for example, <NUM>,<NUM> to <NUM> N/mm, preferably <NUM> to <NUM> N/mm, and more preferably <NUM> to <NUM> N/mm. On the other hand, the spring constant Kb of the negative electrode tab group <NUM> is, for example, <NUM> to <NUM> N/mm, preferably <NUM> to <NUM> N/mm, and more preferably <NUM> to <NUM> N/mm. As an example of a preferable combination of the spring constants Kt and Kb, Kt is <NUM> to <NUM> N/mm, Kb is <NUM> to <NUM> N/mm, and Kt/Kb is <NUM> to <NUM>.

The spring constants Kt and Kb of the positive electrode tab group <NUM> and the negative electrode tab group <NUM> can be changed depending on constituent materials, thicknesses and widths of the positive electrode tab <NUM> and the negative electrode tab <NUM>, and the number of stacked tabs forming the tab group. Since the constituent material and thickness of each tab are generally restricted from viewpoint of the battery performance, the width of each tab is preferably adjusted to control the spring constants Kt and Kb to be within the above-described respective ranges. When the width of the positive electrode tab <NUM> is increased and the width of the negative electrode tab <NUM> is reduced, Kt/Kb can be increased. Alternatively, the plurality of negative electrode tabs <NUM> forming the negative electrode tab group <NUM> are divided into two groups, and one group having shorter length is welded to the intermediate portion of the other group, that is, only the negative electrode tabs <NUM> in the other group are welded to the negative electrode current collecting plate <NUM>, so that the spring constant Kb of the negative electrode tab group <NUM> can be reduced.

<FIG> is a view illustrating a modified example of the electrode assembly <NUM>. As illustrated in <FIG>, the spring constant Kt can be changed also by folding back the positive electrode tab group <NUM> a plurality of times. The positive electrode tab group <NUM> is folded in a zigzag shape to form a plurality (two in an example illustrated in <FIG>) of folded-back portions, for example. The zigzag shape may be applied to only the positive electrode tab group <NUM>, only the negative electrode tab group <NUM>, or both tab groups. For example, the zigzag shape may be applied to the positive electrode tab group <NUM>, and the U shape illustrated in <FIG> may be applied to the negative electrode tab group <NUM>. The zigzag shape illustrated in <FIG> may be applied to the tab group of each electrode group even when a plurality of electrode groups are stacked as illustrated in <FIG>. At this time, as described above, the tab groups may be arranged so that the cross sectional shape of the tab group of one electrode group and the cross sectional shape of the tab group of the other electrode group are substantially symmetrical about a boundary between the electrode groups. In this way, the spring constants Kt and Kb can be changed also by designing the shape of each tab group.

In the example illustrated in <FIG>, the electrode assembly <NUM> is formed of one electrode group without being divided into a plurality of electrode groups. Meanwhile, the plurality of positive electrode tabs <NUM> may be divided into two groups at the center in the thickness direction of the electrode assembly <NUM>, so that two positive electrode tab groups <NUM> can be formed. The numbers of tab groups may be different between the positive electrode tab groups <NUM> and the negative electrode tab groups <NUM>, and for example, the number of positive electrode tab groups <NUM> and the number of negative electrode tab groups <NUM> may be one and plural, respectively, or the number of negative electrode tab groups <NUM> and the number of positive electrode tab groups <NUM> may be one and plural, respectively.

As described above, the secondary battery <NUM> in which the spring constants Kt and Kb of the positive electrode tab group <NUM> and the negative electrode tab group <NUM> satisfy the relationship of Kt > Kb, and <NUM> ≤ Kt/Kb ≤ <NUM> can prevent a great load from being applied to the current breaking device <NUM> while ensuring good productivity. The negative electrode tab group <NUM> is preferentially deformed to absorb the load even when the vibration or the impact is applied to the electrode assembly <NUM> or the sealing plate <NUM> when the electrode assembly welded to the sealing plate <NUM> is inserted into the outer can <NUM> in the step of manufacturing the secondary battery <NUM>, for example. This can prevent the current breaking device <NUM> from contacting the electrode assembly <NUM>. According to the secondary battery <NUM>, the current breaking device <NUM> can be sufficiently protected from the vibration or the impact even when special manufacturing conditions are not added in an assembling step or the like.

A design of the embodiment described above may be appropriately changed without impairing the object of the present disclosure. For example, in the above-described embodiment, the current breaking device <NUM> is illustrated as an example of the functional component, but the functional component may be a current fuse or protection circuit board for protecting a battery from overcurrent, a container (tank, capsule) configured to store agents for suppressing overheating of the battery, or the like.

The functional component may be arranged close to the negative electrode terminal <NUM>, and the same effect as the above-described configuration in which the functional component is arranged close to the positive electrode terminal <NUM> can be obtained. In this case, the spring constant Kb of the negative electrode tab group needs to be greater than the spring constant Kt of the positive electrode tab group. At this time, the ratio of the spring constant Kb of the negative electrode tab group <NUM> to the spring constant Kt of the positive electrode tab group <NUM> (Kb/Kt) satisfies the relationship of <NUM> ≤ Kb/Kt ≤ <NUM>. The spring constant Kt of the positive electrode tab group <NUM> is, for example, <NUM> to <NUM> N/mm, preferably <NUM> to <NUM> N/mm, and more preferably <NUM> to <NUM> N/mm. On the other hand, the spring constant Kb of the negative electrode tab group <NUM> is, for example, <NUM> to <NUM> N/mm, preferably <NUM> to <NUM> N/mm, and more preferably <NUM> to <NUM> N/mm. As an example of a preferable combination of the spring constants Kt and Kb, Kt is <NUM> to <NUM> N/mm, Kb is <NUM> to <NUM> N/mm, and Kb/Kt is <NUM> to <NUM>.

Claim 1:
An electrical storage device (<NUM>), comprising:
an electrode assembly (<NUM>) in which positive electrodes (<NUM>) and negative electrodes (<NUM>) are alternately stacked with separators (<NUM>) each interposed between the positive electrode (<NUM>) and the negative electrode (<NUM>);
a bottomed cylindrical outer can (<NUM>) in which the electrode assembly (<NUM>) is housed;
a sealing plate (<NUM>) to which a positive electrode terminal (<NUM>) and a negative electrode terminal (<NUM>) are attached and that closes an opening of the outer can (<NUM>); and
a functional component (<NUM>) that is arranged close to the positive electrode terminal (<NUM>) or the negative electrode terminal (<NUM>) on an inner surface of the sealing plate (<NUM>), wherein
the positive electrode (<NUM>) includes a positive electrode tab (<NUM>) to be electrically connected with the positive electrode terminal (<NUM>),
the negative electrode (<NUM>) includes a negative electrode tab (<NUM>) to be electrically connected with the negative electrode terminal (<NUM>),
the electrode assembly (<NUM>) has a positive electrode tab group (<NUM>) formed by stacking a plurality of the positive electrode tabs (<NUM>), and a negative electrode tab group (<NUM>) formed by stacking a plurality of the negative electrode tabs (<NUM>), in which each of the tab groups (<NUM>, <NUM>) functions as a spring for connecting the electrode assembly (<NUM>) and the sealing plate (<NUM>), and
a spring constant of one tab group (<NUM>, <NUM>) close to the functional component (<NUM>), of the positive electrode tab group (<NUM>) and the negative electrode tab group (<NUM>), is greater than a spring constant of the other tab group (<NUM>, <NUM>);
wherein a ratio (K/k) of a spring constant K of the one tab group (<NUM>, <NUM>) to a spring constant k of the other tab group (<NUM>, <NUM>) satisfies a relationship of <NUM> ≤ K/k ≤ <NUM>; where the spring constant is measured as indicated in the description.