Patent Description:
<CIT> discloses a secondary battery that includes an electrode assembly and a case. The electrode assembly includes a plurality of electrodes and a separator provided between adjacent electrodes, and the case houses the electrode assembly and an electrolytic solution. The separator is formed in a zigzag shape.

<CIT> discloses a separation layer of a lithium polymer secondary battery and a lithium polymer secondary battery. Provided is the separation layer of the lithium polymer secondary battery comprising a desorption prevention member formed on a foldable area of the separation layer between electrode panels to prevent ceramic coating being desorbed.

<CIT> discloses a stacked secondary battery having an electrode body in which at least one positive and at least one negative plate are stacked, with a multilayered separator interposed, said separator including two porous layers of different materials; and an outer packaging case housing an insulating holder and an electrolyte together, said insulating holder housing the electrode body and being formed of overlapping sheets comprises an insulating material. The outer packaging case has a bottom surface, a plurality of side walls that are provided standing upright from the bottom surface, and an opening that is opposite from the bottom surface. In at least one separator, a section that is exposed from end surfaces of active material mixture layers and metal foil-comprising core bodies of the positive plate and the negative plate is in contact with the vicinity of a bottom line of a valley section that is formed from the sheet.

In the secondary battery described in <CIT>, since the electrolytic solution is released from the negative electrode during the charging/discharging or the like, it is concerned that the negative electrode may become short of the electrolytic solution.

It is an object of the present disclosure to provide a power storage cell capable of preventing the negative electrode from becoming short of an electrolytic solution.

It is the object of the present invention to provide a power storage cell as defined in appended claim <NUM>.

Embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding members are denoted by the same reference numerals.

<FIG> is a perspective view schematically illustrating a power storage cell <NUM> according to an embodiment of the present disclosure. <FIG> is a cross-sectional view of the power storage cell <NUM> illustrated in <FIG>.

As illustrated in <FIG> and <FIG>, the power storage cell <NUM> includes an electrode assembly <NUM>, a cell case <NUM>, an electrolytic solution (not illustrated), a pair of external terminals <NUM>, a pair of connecting members <NUM>, and an insulating member <NUM>.

<FIG> is a cross-sectional view of the electrode assembly <NUM>. As illustrated in <FIG>, the electrode assembly <NUM> includes a plurality of electrodes <NUM> and <NUM>, a separator <NUM>, and an insulating film <NUM> (see <FIG>).

As illustrated in <FIG>, the plurality of electrodes <NUM> and <NUM> are arranged side by side in one direction (the lateral direction in <FIG>). The plurality of electrodes <NUM> and <NUM> include a plurality of positive electrodes <NUM> and a plurality of negative electrodes <NUM>.

Each positive electrode <NUM> is formed in a rectangular shape elongated in a width direction (a direction orthogonal to both the one direction and the vertical direction). Each positive electrode <NUM> includes a positive electrode collector foil <NUM> and a positive electrode active material layer <NUM> provided on both surfaces of the positive electrode collector foil <NUM>. As illustrated in <FIG> and <FIG>, the positive electrode collector foil <NUM> includes a positive electrode tab 112p on which the positive electrode active material layer <NUM> is not provided. The positive electrode tab 112p protrudes toward one side of the width direction (a direction orthogonal to the paper surface of <FIG>).

Each negative electrode <NUM> is formed in a rectangular shape elongated in the width direction. Each negative electrode <NUM> includes a negative electrode collector foil <NUM> and a negative electrode active material layer <NUM> provided on both surfaces of the negative electrode collector foil <NUM>. As illustrated in <FIG> and <FIG>, the negative electrode collector foil <NUM> includes a negative electrode tab 122n on which the negative electrode active material layer <NUM> is not provided. The negative electrode tab 122n protrudes toward the other side of the width direction.

The separator <NUM> insulates the positive electrode <NUM> and the negative electrode <NUM> from each other. The separator <NUM> is made of an insulating material, and has minute voids that allow ions to pass through. As illustrated in <FIG>, the separator <NUM> is formed in a zigzag shape.

As illustrated in <FIG>, the separator <NUM> includes a separator body <NUM> and a side covering portion <NUM>.

The separator body <NUM> has a rectangular shape before being formed in a zigzag shape. The separator body <NUM> is formed in a zigzag shape and is arranged between the electrodes <NUM> and <NUM>. The separator body <NUM> includes a plurality of intervening portions 132a, a plurality of upper folded portions 132b, a plurality of lower folded portions 132c, and an outermost covering portion 132d.

Each intervening portion 132a is interposed between a pair of electrodes <NUM> and <NUM> adjacent to each other in the one direction. In other words, each intervening portion 132a functions to insulate the positive electrode <NUM> and the negative electrode <NUM> from each other. Each intervening portion 132a is formed in a rectangular shape.

Each upper folded portion 132b connects an upper end of one intervening portion 132a of the plurality of intervening portions 132a to an upper end of another intervening portion 132a of the plurality of intervening portions 132a which is adjacent to the one intervening portion 132a on one side of the one direction. In the present embodiment, the upper folded portion 132b is disposed above the positive electrode <NUM>.

Each lower folded portion 132c connects a lower end of one intervening portion 132a of the plurality of intervening portions 132a to a lower end of another intervening portion 132a of the plurality of intervening portions 132a which is adjacent to the one intervening portion 132a on the other side of the one direction. In the present embodiment, the lower folded portion 132c is disposed below the negative electrode <NUM>. In other words, the negative electrode <NUM> is disposed above the lower folded portion 132c. The porosity of the lower folded portion 132c is smaller than the porosity of the intervening portion 132a. For example, the porosity of the lower folded portion 132c is <NUM>% to <NUM>%, and the porosity of the intervening portion 132a is <NUM>% to <NUM>%. The porosity is measured by, for example, mercury porosimetry.

In the present embodiment, the lower folded portion 132c is provided with a void filling material <NUM> that fills voids in the separator <NUM>. The void filling material <NUM> preferably has a property of repelling an electrolytic solution (liquid repellency). Examples of the void filling material <NUM> include polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), and polyimide. In <FIG>, the void filling material <NUM> is indicated by dots. The dimension of the void filling material <NUM> in the vertical direction is preferably set to <NUM> or more.

The void filling material <NUM> may be provided on the lower folded portion 132c by applying the void filling material <NUM> in advance according to a gravure coating (intermittent coating) method to a portion of the separator body <NUM> which becomes the lower folded portion 132c after the separator body <NUM> is formed in a zigzag shape, and then drying the same. Alternatively, the void filling material <NUM> may be provided on the lower folded portion 132c by immersing each lower folded portion 132c in a container containing the void filling material <NUM> after the separator body <NUM> is formed in a zigzag shape, and then drying the same.

The outermost covering portion 132d collectively covers each upper folded portion 132b and each lower folded portion 132c. More specifically, the outermost covering portion 132d collectively covers all of the electrodes <NUM> and <NUM>, all of the intervening portions 132a, all of the upper folded portions 132b and all of the lower folded portions 132c while being wound around a central axis parallel to the width direction. A terminal end 132e (see <FIG> and <FIG>) of the outermost covering portion 132d is configured not to overlap with the positive electrode active material layer <NUM> and the negative electrode active material layer <NUM> in the one direction. In the present embodiment, the terminal end 132e of the outermost covering portion 132d is provided below each of the electrodes <NUM> and <NUM>.

The side covering portion <NUM> faces both ends of the plurality of electrodes <NUM> and <NUM> in the width direction. In <FIG>, the side covering portion <NUM> is indicated by a two-dot chain line. The side covering portion <NUM> is connected to the lower folded portion 132c. As illustrated in <FIG>, in the present embodiment, the side covering portion <NUM> protrudes in a direction orthogonal to a longitudinal direction of the separator body <NUM> from an end of the separator body <NUM> in the longitudinal direction. The side covering portion <NUM> is connected to all the lower folded portions 132c arranged side by side in the one direction. The side covering portion <NUM> and the lower folded portion 132c form a storage space S (see <FIG>) for storing the electrolytic solution below the negative electrode <NUM>. The side covering portion <NUM> is provided with a void filling material that fills voids in the separator <NUM>.

The insulating film <NUM> collectively covers the peripheral surface and bottom surface of the plurality of electrodes <NUM> and <NUM> and the separator <NUM>. In <FIG>, the insulating film <NUM> is indicated by dots.

The cell case <NUM> houses the electrode assembly <NUM>. The cell case <NUM> contains an electrolytic solution (not illustrated). The cell case <NUM> is sealed. The cell case <NUM> includes a case body <NUM> and a lid <NUM>.

The case body <NUM> has an opening that opens upward. The case body <NUM> is made of a metal such as aluminum. As illustrated in <FIG>, the case body <NUM> includes a bottom wall <NUM> and a peripheral wall <NUM>. The bottom wall <NUM> is formed in a rectangular flat plate shape. The peripheral wall <NUM> rises from the bottom wall <NUM>. The peripheral wall <NUM> is formed in a quadrangular cylindrical shape. The length of the peripheral wall <NUM> in the width direction is longer than the length of the peripheral wall <NUM> in the thickness direction. The length of the peripheral wall <NUM> in the height direction is longer than the length of the peripheral wall <NUM> in the thickness direction.

The lid <NUM> closes the opening of the case body <NUM>. The lid <NUM> is connected to the opening by welding or the like. The lid <NUM> is formed in a flat plate shape. The lid <NUM> is made of a metal such as aluminum. The lid <NUM> includes a pressure release valve <NUM> and a sealing member <NUM>.

The pressure release valve <NUM> is formed at a central portion of the lid <NUM>. The pressure release valve <NUM> is configured to break when the internal pressure of the cell case <NUM> becomes equal to or higher than a predetermined pressure. When the pressure release valve <NUM> is broken, the gas in the cell case <NUM> is released to the outside of the cell case <NUM> through the pressure release valve <NUM>, which reduces the internal pressure of the cell case <NUM>.

The sealing member <NUM> seals a liquid injection port h formed in the lid <NUM>. The liquid injection port h is a through hole for injecting an electrolytic solution into the cell case <NUM> in the manufacturing process of the power storage cell <NUM>. After the electrolytic solution is injected into the case body <NUM> through the liquid injection port h, the liquid injection port h is sealed by the sealing member <NUM>.

The pair of external terminals <NUM> is fixed to the cell case <NUM>. One of the pair of external terminals <NUM> is a positive external terminal, and the other is a negative external terminal. Each external terminal <NUM> is fixed to an upper surface of the lid <NUM> via an upper insulating portion <NUM> which will be described later. Each external terminal <NUM> is made of a metal such as aluminum. Each external terminal <NUM> is formed, for example, in a rectangular parallelepiped shape. A bus bar (not illustrated) is connected to each external terminal <NUM> by welding or the like.

The pair of connecting members <NUM> connects a plurality of electrode tabs 112p and a plurality of electrode tabs 122n to the pair of external terminals <NUM>, respectively. More specifically, one of the pair of connecting members <NUM> connects the plurality of positive electrode tabs 112p to the positive external terminal <NUM>, and the other connecting member <NUM> connects the plurality of negative electrode tabs 122n to the negative external terminal <NUM>. Since the pair of connecting members <NUM> have substantially the same structure, only one connecting member <NUM> will be described below.

The connecting member <NUM> includes a collector tab <NUM>, a subtab <NUM>, and a connecting pin <NUM>.

The collector tab <NUM> has a side portion <NUM> and an upper portion <NUM>. The side portion <NUM> is arranged on a side surface of the electrode assembly <NUM> in the width direction. The upper portion <NUM> is arranged on an upper surface of the electrode assembly <NUM>. The upper portion <NUM> extends inward in the width direction from an upper end of the side portion <NUM>.

The subtab <NUM> connects the plurality of positive electrode tabs 112p to the collector tab <NUM>. One end <NUM> of the subtab <NUM> is connected to the plurality of positive electrode tabs 112p by welding or the like, and the other end <NUM> of the subtab <NUM> is connected to the side portion <NUM> of the collector tab <NUM> by welding or the like.

The connecting pin <NUM> connects the collector tab <NUM> to the external terminal <NUM>. The connecting pin <NUM> connects the upper portion <NUM> to the external terminal <NUM>. Specifically, the lower end of the connecting pin <NUM> is inserted into a through hole provided on the upper portion <NUM> and is connected to the upper portion <NUM> by welding or the like, and the upper end of the connecting pin <NUM> is inserted into a through hole provided on the external terminal <NUM> and is connected to the external terminal <NUM> by welding, caulking or the like.

The insulating member <NUM> insulates the cell case <NUM> and the connecting member <NUM> from each other. The insulating member <NUM> includes an upper insulating portion <NUM>, a lower insulating portion <NUM>, an insulator <NUM>, and an insulating plate <NUM>.

The upper insulating portion <NUM> is fixed to the upper surface of the lid <NUM>. The upper insulating portion <NUM> is disposed between the lid <NUM> and the external terminal <NUM>. The upper insulating portion <NUM> is provided with an insertion hole through which the connecting pin <NUM> is inserted.

The lower insulating portion <NUM> is fixed to the lower surface of the lid <NUM>. The lower insulating portion <NUM> is disposed between the lid <NUM>, and the upper portion <NUM> and a lower portion of the connecting pin <NUM>. The lower insulating portion <NUM> is provided with an insertion hole through which the connecting pin <NUM> is inserted.

The insulator <NUM> is disposed between the connecting pin <NUM> and the lid <NUM>. The insulator <NUM> is formed in a cylindrical shape, and is configured to surround the connecting pin <NUM>.

The insulating plate <NUM> is fixed to the lower surface of the upper portion <NUM>. The insulating plate <NUM> is disposed on the electrode assembly <NUM>. A through hole is formed in a portion of the insulating plate <NUM> located below the pressure release valve <NUM> and a portion of the insulating plate <NUM> located below the liquid injection port h.

Next, a process of manufacturing the power storage cell <NUM> will be described with reference to <FIG>.

First, while the separator body <NUM> is being formed in a zigzag shape, each electrode <NUM> and each electrode <NUM> are alternately disposed between a pair of intervening portions 132a. After winding the outermost covering portion 132d of the separator body <NUM>, the side covering portion <NUM> is bent against the separator body <NUM> and connected to the lower folded portion 132c.

Next, as illustrated in <FIG>, one end <NUM> of the subtab <NUM> is connected to the plurality of electrode tabs 112p and 122n by welding or the like. Then, as indicated by an arrow in <FIG>, the end <NUM> and the plurality of electrode tabs 112p and 122n are bent in such a manner that the end <NUM> of the subtab <NUM> is in contact with the side portion <NUM> of the collector tab <NUM>.

Subsequently, as illustrated in <FIG>, after the peripheral surface and bottom surface of the plurality of electrodes <NUM>, <NUM> and the separator <NUM> are collectively covered with the insulating film <NUM>, the electrode assembly <NUM> is inserted into the case body <NUM>. Then, the lid <NUM> is welded to the case body <NUM> to close the opening.

Thereafter, the electrolytic solution is supplied into the cell case <NUM> through the liquid injection port h, and the liquid injection port h is sealed with the sealing member <NUM>.

As described above, in the electrode assembly <NUM> of the present embodiment, since the negative electrode <NUM> is disposed above the lower folded portion 132c, and the porosity of the lower folded portion 132c is smaller than the porosity of the intervening portion 132a, the electrolytic solution released from the negative electrode <NUM> during the charging/discharging or the like is effectively held by the lower folded portion 132c. Accordingly, the negative electrode <NUM> absorbs the electrolytic solution again, which thereby prevents the negative electrode <NUM> from becoming short of the electrolytic solution.

Further, since the separator <NUM> includes the side covering portion <NUM> which forms the storage space S together with the lower folded portion 132c, it is more reliable to prevent the negative electrode <NUM> from becoming short of the electrolytic solution. Furthermore, since the side covering portion <NUM> prevents misalignment between the lower folded portions 132c, which in turn prevents misalignment between the intervening portions 132a, and thereby it is not necessary to provide a dedicated member (such as a tape) for fixing the separator <NUM>.

As illustrated in <FIG>, the electrode assembly <NUM> may further include a liquid holding member <NUM> configured to hold an electrolytic solution. The liquid holding member <NUM> is different from the separator <NUM>. The liquid holding member <NUM> is made of a porous material. The liquid holding member <NUM> is provided at an end portion of the plurality of electrodes <NUM> and <NUM> and the separator <NUM> in the width direction. The liquid holding member <NUM> may be provided at an upper end portion or a lower end portion of the plurality of electrodes <NUM> and <NUM> and the separator <NUM>.

It will be appreciated by those skilled in the art that the exemplary embodiments described above are specific examples.

In the electrode assembly of the power storage cell of the present invention, since the negative electrode is disposed above the lower folded portion and the porosity of the lower folded portion is smaller than the porosity of the intervening portion, the electrolytic solution released from the negative electrode during the charging/discharging or the like is effectively held by the lower folded portion. Accordingly, the negative electrode absorbs the electrolytic solution again, which thereby prevents the negative electrode from becoming short of the electrolytic solution.

Also, since the storage space for storing the electrolytic solution is formed by the lower folded portion and the side covering portion, it is more reliable to prevent the negative electrode from becoming short of the electrolytic solution. Furthermore, since the side covering portion prevents misalignment between the lower folded portions, which in turn prevents misalignment between the intervening portions, and thereby, it is not necessary to provide a dedicated member (such as a tape) for fixing the separator.

In the power storage cell, the lower folded portion may be provided with a void filling material that fills voids in the separator.

Accordingly, the electrolytic solution is more reliably held by the lower folded portion.

The power storage cell may further comprise: a liquid holding member which is different from the separator and is configured to hold an electrolytic solution, wherein the liquid holding member is provided on at least one of an end of the separator in the vertical direction and an end of the separator in the width direction orthogonal to both the one direction and the vertical direction.

Accordingly, since the electrolytic solution released from the negative electrode is held by the liquid holding member, the negative electrode absorbs the electrolytic solution again, which thereby prevents the negative electrode from becoming short of the electrolytic solution.

Claim 1:
A power storage cell (<NUM>) comprising:
an electrode assembly (<NUM>);
a cell case (<NUM>) that houses the electrode assembly; and
an electrolytic solution contained in the cell case,
wherein the electrode assembly (<NUM>) includes:
a plurality of electrodes (<NUM>, <NUM>) arranged side by side in one direction; and
a separator (<NUM>) formed in a zigzag shape and configured to insulate the plurality of electrodes from each other,
the separator includes:
a plurality of intervening portions (132a), each of which is interposed between a pair of electrodes adjacent to each other in the one direction;
an upper folded portion (132b) which connects an upper end of one intervening portion of the plurality of intervening portions and an upper end of another intervening portion of the plurality of intervening portions which is adjacent to the one intervening portion on one side of the one direction; and
a lower folded portion (132c) which connects a lower end of the one intervening portion of the plurality of intervening portions and a lower end of another intervening portion of the plurality of intervening portions which is adjacent to the one intervening portion on the other side of the one direction,
the plurality of electrodes include a plurality of positive electrodes (<NUM>) and a plurality of negative electrodes (<NUM>),
the negative electrode is disposed above the lower folded portion (132c), and
the porosity of the lower folded portion (132c) is smaller than that of the intervening portion (132a),
characterized in that:
the separator further includes a side covering portion (<NUM>) which faces both ends of the plurality of electrodes in a width direction orthogonal to both the one direction and a vertical direction and is connected to the lower folded portion,
the side covering portion and the lower folded portion form a storage space (S) for storing the electrolytic solution below the negative electrode, and
the side covering portion (<NUM>) is provided with a void filling material that fills voids in the separator.