Patent Description:
A conventional laminated battery is disclosed in Patent Literature <NUM>. The conventional laminated battery is a battery in which an electrode body is accommodated in an exterior member. The conventional laminated battery includes plural current-collecting terminals that are drawn from the electrode body to the outside of the exterior member. The plural current-collecting terminals are superimposed on each other with a thermoplastic resin being interposed between two each of the plural current-collecting terminals. A peripheral edge portion of the exterior member is closed by welding the thermoplastic resin to the peripheral edge portion of the exterior member. In this conventional laminated battery, each of the plural current-collecting terminals is drawn to the outside of the exterior member, and the plural current-collecting terminals are not connected to each other in the exterior member. In this conventional laminated battery, a space inside the exterior member can be used to enlarge the electrode body, which is advantageous for improving energy density of the battery.

The conventional laminated battery is manufactured by a heat-sealing process. In the heat-sealing process, the thermoplastic resins superimposed on each other in the peripheral edge portion of the exterior member are welded to each other by pressing a heat plate as an energy supply source against the thermoplastic resins in a superimposed direction.

Here, when the number of current collectors is increased in a battery cell that has the same structure as the conventional laminated battery, a large number of stacked resins have to be welded together during manufacturing of the battery cell. When the large number of the resins are stacked on each other, the resin at a center in a stacking direction is located far away from the energy supply source. As a result, there is a possibility that sufficient energy is not supplied to the resin located at the center, which results in insufficient welding of the resin located at the center.

The object of the present invention is to suppress insufficient welding of a resin during manufacturing of a battery cell.

The above object is achieved by the present invention as defined in independent claims. Particularly, a battery cell includes:.

In the battery cell, each of the plural stacked current collectors projects to the outside of the pouch through the opening of the pouch. The plural current collectors are connected to the electrodes with the same polarity, for example. In the pouch, the plural current collectors are not mutually connected. Thus, a space for connecting the current collectors in the pouch can be eliminated. As a result, the electrodes of the battery cell can be enlarged by using the space in the pouch. In this way, energy density of the battery cell can be increased.

The opening of the pouch is sealed by the first resin and the second resin. The first resin and the second resin are supplied with energy for welding during manufacturing of the battery cell. Each of the first resin and the second resin is a thermoplastic resin, for example. The energy supplied to the first resin and the second resin is thermal energy, for example. However, the energy for welding is not limited to the thermal energy. The energy may be vibration energy, for example. An interface between the first resin and the second resin, each of which is supplied with the vibration energy, is welded by frictional heat.

The current collectors, the first resin, and the second resin are stacked in the stacking direction. An energy supply source, such as a heat plate, is located on the outer side in the stacking direction and supplies the energy from the outer side toward the center. The energy is transferred to the second resin through the current collectors and the first resin. Due to attenuation of the energy, the energy supplied to the second resin, which is located at the center in the stacking direction, is lower than the energy supplied to the first resin, which is located on the outer side in the stacking direction.

Here, the second resin is thinner than the first resin in the stacking direction. Although the energy supplied to the second resin is low, the supply energy per unit volume to the second resin is equivalent to the supply energy per unit volume to the first resin. Since the energy commensurate with the volume is supplied to the second resin, the second resin can sufficiently be welded to the current collector or another resin. Since the energy commensurate with the volume is also supplied to the first resin, the first resin can also sufficiently be welded to the current collector or another resin. In this way, it is possible to suppress insufficient welding of the resin during manufacturing of the battery cell.

The battery cell may further include a third resin that seals the opening of the pouch, the third resin being welded to the current collector at a position between the stacked current collectors, being located between the first resin and the second resin in the stacking direction, being thinner than the first resin in the stacking direction, and being thicker than the second resin in the stacking direction.

The third resin is located between the first resin and the second resin in the stacking direction. The energy for welding is transferred in an order of the first resin, the third resin, and the second resin.

The thickness of the third resin in the stacking direction is less than the thickness of the first resin and greater than the thickness of the second resin. The supply energy per unit volume to the third resin is equivalent to the supply energy per unit volume to the second resin or the supply energy per unit volume to the first resin. Since the energy commensurate with the volume is supplied to the first resin, the second resin, and the third resin, each of the first resin, the second resin, and the third resin can stably and sufficiently be welded to the current collector or another resin.

Portions of the current collectors, to which the first resin and the second resin are welded, may be thicker than the other portions thereof in the stacking direction.

For example, the current collector that is made of metal has higher energy transfer efficiency for welding than the resin, and examples of the energy are thermal energy and vibration energy. The metallic current collector has lower specific heat than the resin. The metallic current collector has higher Young's modulus than the resin. The current collector transfers the energy for welding relatively easily. In the case where the portion of the current collector, to which the resin is welded, is thick, the thickness of the resin is reduced. As a result, attenuation of the energy is suppressed during the energy transfer for welding in the stacking direction. The suppression of the energy attenuation is advantageous for the energy supply to the second resin at the center.

The second resin may have a lower melting point than the first resin.

In the case where the second resin has the low melting point, the second resin can be welded to the current collector or another resin even with the low supply energy to the second resin. The second resin with the low melting point can suppress insufficient welding of the resin.

Further particularly, a battery cell includes:.

As described above, in the case where the second resin has the low melting point, the second resin can be welded even with the low supply energy to the second resin. Therefore, it is possible to suppress insufficient welding of the resin.

An additive may be added to the second resin. The additive may be configured to lower the melting point.

Use of the additive is effective in lowering the melting point of the resin.

Further particularly, a method of manufacturing a battery cell includes:.

When the electrode sheets are stacked during manufacturing of the battery cell, the plural current collectors, the first resin, and the second resin are stacked in the stacking direction, and the first resins and the second resins are located between the current collectors. The current collectors, the first resin, and the second resin are pressurized and heated from the outer side toward the center in the stacking direction. The thermal energy is transferred to the second resin through the current collector and the first resin.

The second resin is thinner than the first resin in the stacking direction. The thermal energy per unit volume supplied to the second resin is equivalent to the thermal energy per unit volume supplied to the first resin. The second resin can sufficiently be welded by the supplied thermal energy. The first resin can also be welded stably and sufficiently. In this way, it is possible to suppress insufficient welding of the resin during manufacturing of the battery cell.

Further particularly, a method of manufacturing the battery cell includes:.

The second resin has the lower melting point than the first resin. Even when the thermal energy supplied to the second resin is low, the second resin can sufficiently be welded by the supplied thermal energy. Meanwhile, since the high thermal energy is supplied to the first resin with the high melting point, the first resin can sufficiently be welded. In this way, it is possible to suppress insufficient welding of the resin during manufacturing of the battery cell.

The manufacturing method may further include: heating the second resin through the current collector that is in contact with the second resin during pressurizing and heating of the first resin and the second resin.

To the second resin at the center in the stacking direction, the thermal energy is supplied not only in the stacking direction, the thermal energy is supplied but also through the current collector. Therefore, the second resin at the center in the stacking direction can be welded stably and sufficiently.

According to the battery cell and the method of manufacturing the battery cell, it is possible to suppress insufficient welding of the resin during manufacturing of the battery cell.

A description will hereinafter be made on embodiments of a battery cell and a method of manufacturing a battery cell with reference to the drawings. The battery cell and the method of manufacturing a battery cell described herein are merely illustrative.

<FIG> schematically illustrates an overall structure of a battery cell <NUM>. <FIG> illustrates an electric power generating element <NUM> that is accommodated in a pouch (or a container, or a package) <NUM> of the battery cell <NUM>. The battery cell <NUM> may be a secondary battery. The battery cell <NUM> may be a lithium-ion battery, for example.

The pouch <NUM> of the battery cell <NUM> may be formed by folding a laminated material <NUM> or superimposing two laminated materials <NUM> in a bag shape. The laminated material <NUM> may have a multi-layer structure, particularly a three-layer structure in which a metal layer is sandwiched between two resin layers on both sides, for example. The metal layer may be made of aluminum or stainless steel, for example. The resin layer may be made of polypropylene (PP) or polyethylene (PE), for example.

The pouch <NUM> is sealed in a state of containing the electric power generating element <NUM> and an electrolyte. The battery cell <NUM> is a so-called pouch-type battery.

The electric power generating element <NUM> has one or more first electrode sheets <NUM> and one or more second electrode sheets <NUM>. The first electrode sheet <NUM> may be an anode sheet, for example. The second electrode sheet <NUM> may be a cathode sheet, for example. However, the first electrode sheet <NUM> may be the cathode sheet, and the second electrode sheet <NUM> may be the anode sheet. The first electrode sheets <NUM> and the second electrode sheets <NUM> are alternately superimposed on each other. Appropriate numbers of the first electrode sheets <NUM> and the second electrode sheets <NUM> can be used in the electric power generating element <NUM>. The electric power generating element <NUM> is an electrode stack. Hereinafter, a direction in which the first electrode sheets <NUM> and the second electrode sheets <NUM> are stacked may be referred to as a stacking direction.

The first electrode sheet <NUM> has a current collector <NUM> (i.e., the first electrode sheets <NUM> have current collectors <NUM>). The current collector <NUM> is a thin plate material that extends in a direction orthogonal to the stacking direction. A first end portion of the current collector <NUM>, that is, a left end portion thereof in <FIG>, projects from a first opening <NUM> of the pouch <NUM> to the outside of the pouch <NUM>.

Portions of upper and lower surfaces of the current collector <NUM>, which are located inside the pouch <NUM>, may be each coated with an active material. The active material may form a first electrode <NUM>. The current collector <NUM> is connected to the first electrode <NUM>.

The first electrode sheet <NUM> has a separator <NUM> (i.e., the first electrode sheets <NUM> have separators <NUM>). The separator <NUM> separates the first electrode <NUM> of the first electrode sheet <NUM> from a second electrode <NUM> of the second electrode sheet <NUM>. The second electrode <NUM> will be described below.

The separator <NUM> may be a porous material through which an ionic material can permeate, for example. The separator(s) <NUM> covers a surface of each of the two first electrodes <NUM> in the first electrode sheet <NUM>. An area of the separator <NUM> may be larger than an area of the first electrode sheet <NUM>.

The second electrode sheet <NUM> has a current collector <NUM> (i.e., the second electrode sheets <NUM> have current collectors <NUM>). The current collector <NUM> is a thin plate material that extends in the direction orthogonal to the stacking direction. A second end portion of the current collector <NUM>, that is, a right end portion thereof in <FIG>, projects from a second opening <NUM> of the pouch <NUM> to the outside of the pouch <NUM>.

The second opening <NUM> may be an opposite opening from the first opening <NUM> in the direction orthogonal to the stacking direction. A projecting direction of the current collector <NUM> is not limited to an opposite direction from a projecting direction of the current collector <NUM>.

Portions of upper and lower surfaces of the current collector <NUM>, which are located inside the pouch <NUM>, may be each coated with the active material. The active material may form the second electrode <NUM>. The current collector <NUM> is connected to the second electrode <NUM>.

As described above, the first electrode sheets <NUM> and the second electrode sheets <NUM> are alternately stacked on each other. In the pouch <NUM>, the first electrode sheets <NUM> and the second electrode sheets <NUM> are stacked in the stacking direction via the separators <NUM>.

The first opening <NUM> of the pouch <NUM> is sealed by a resin <NUM>. The resin <NUM> is located between the laminated material <NUM> and the current collector <NUM> and between the current collectors <NUM>.

Similarly, the second opening <NUM> is sealed by the resin <NUM>. The resin <NUM> is located between the laminated material <NUM> and the current collector <NUM> and between the current collectors <NUM>.

The plural current collectors <NUM> separately project to the outside of the pouch <NUM> without being connected to each other in the pouch <NUM>. Similarly, the plural current collectors <NUM> separately project to the outside of the pouch <NUM> without being connected to each other in the pouch <NUM>.

Since a space for connecting the current collectors <NUM> and a space for connecting the current collectors <NUM> can be eliminated in the pouch <NUM>, areas for the first electrodes <NUM> and the second electrodes <NUM> can be increased by an area of elimination. As a result, energy density of the battery cell <NUM> can be increased.

Next, a description will be made on a method of manufacturing the battery cell <NUM> with reference to <FIG> and <FIG>. A description will herein be made on the method of manufacturing the battery cell <NUM> by using welding of the resin in the first opening <NUM> as an example. The same also applied to welding of the resin in the second opening <NUM>.

First, the first electrode sheets <NUM> and the second electrode sheets <NUM> are prepared. As described above, the first electrode sheet(s) <NUM> has the current collector(s) <NUM>, the first electrode(s) <NUM>, and the separator(s) <NUM>. The second electrode sheet(s) <NUM> has the current collector(s) <NUM> and the second electrode(s) <NUM>.

The first electrode sheets <NUM> and the second electrode sheets <NUM> are alternately stacked on each other. The first electrode <NUM> and the second electrode <NUM> are superimposed on each other via the separator <NUM>. As illustrated in <FIG>, the electric power generating element <NUM> is formed which has the plural first electrode sheets <NUM> and the plural second electrode sheets <NUM> (that is, a first step).

Here, as illustrated in <FIG> and the left view of <FIG>, in or on the current collector(s) <NUM> of the first electrode sheet <NUM>, resins <NUM>, <NUM> are welded to a portion (or portions) between the first end portion(s) and the first electrode(s) <NUM> in advance. The resins <NUM>, <NUM> may be welded to the upper surface and the lower surface of the current collector <NUM>.

Each of the resins <NUM>, <NUM> extends along the surface of the current collector <NUM> in the direction orthogonal to the stacking direction. The resins <NUM>, <NUM> form the resin <NUM> that seals the first opening <NUM> of the pouch <NUM>. In the electric power generating element <NUM>, the resins <NUM>, <NUM> may be aligned in the stacking direction. Also, in or on the current collector(s) <NUM> of the second electrode sheet(s) <NUM>, the resin(s) is welded to a portion (or portions) between the second end portion and the second electrode <NUM>.

Each of the resins <NUM>, <NUM> may be a thermoplastic resin. Each of the resins <NUM>, <NUM> may be selected from cast polypropylene (CPP), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), biaxially oriented polypropylene (OPP), polyethylene terephthalate (PET), and biaxially oriented nylon (ONY), for example.

After the electric power generating element <NUM> is formed, the laminated material <NUM> is provided to cover the electric power generating element <NUM>. As illustrated in the left view of <FIG>, an edge of the laminated material <NUM> may be located at a position that corresponds to the resins <NUM>, <NUM> aligned in the stacking direction, and may be located on an outer side of the outermost current collector <NUM> in the stacking direction. In other words, in the left view of <FIG>, the edges of the laminated material <NUM> may be respectively located above the uppermost current collector <NUM> and below the lowermost current collector <NUM> in a vertical direction.

The resin <NUM> is also welded to the edge of the laminated material <NUM>. However, for example, the resin <NUM> may not be provided to the edge of the laminated material <NUM>. In this case, the laminated material <NUM> is welded to the current collector <NUM> by a resin material that is contained in the laminated material <NUM>.

Next, the resins <NUM>, <NUM> that are aligned in the stacking direction are welded to each other. Here, the resins <NUM>, <NUM> may be heat-plate welded. More specifically, as indicated by blank arrows in the left view of <FIG>, two heat plates <NUM>, <NUM>, each of which is located on the outer side of the respective laminated material <NUM>, pressurize and heat the resins <NUM>, <NUM>, which are aligned in the stacking direction, from the outer side to the center in the stacking direction (that is, a second step).

Thermal energy from the two heat plates <NUM>, <NUM> is transferred from the outer side toward the center in the stacking direction through the laminated material <NUM>, the resins <NUM>, <NUM>, and the current collectors <NUM>, and the resins <NUM>, <NUM> that are adjacent to each other in the stacking direction receive the thermal energy and are welded together. As illustrated in <FIG>, the opening (the first opening <NUM> herein) of the pouch <NUM> between the laminated material <NUM> and the current collector <NUM> and the opening thereof between the current collectors <NUM> are sealed by the welded resin <NUM> (that is, a third step).

Here, the battery cell <NUM> may have large numbers of the first electrode sheets <NUM> and the second electrode sheets <NUM>. During welding of the resins <NUM>, <NUM>, the resin <NUM> that is located at the center in the stacking direction may be away from the heat plates <NUM>, <NUM>. The thermal energy that is supplied to the resin <NUM> located at the center in the stacking direction may attenuate during the transfer through the large number of the current collectors <NUM> and the large number of the resins <NUM>, and thus may be lower than the thermal energy that is supplied to the resin <NUM> located on the outer side in the stacking direction. A reduction in the supply energy possibly results in insufficient welding of the resin <NUM>.

In this respect, particularly, not all of the resins <NUM>, <NUM> of the first electrode sheet(s) <NUM> and the resin of the second electrode sheet(s) <NUM> have the same thickness in the stacking direction. The thickness of the resin located at the center in the stacking direction, that is, a thickness T2 of the second resin <NUM> is less than the thickness of the resin located on the outer side in the stacking direction, that is, a thickness T1 of the first resin <NUM>. A volume of the second resin <NUM> is relatively small. The second resins <NUM> are welded to the upper surface and the lower surface of the current collector <NUM> that is located at the center in the stacking direction. Here, the number of the current collectors <NUM>, to which the second resins <NUM> are welded, is not limited to one. The second resins <NUM> may be welded to the plural current collectors <NUM> that are located at the center in the stacking direction. In addition, welding of the second resins <NUM> is not limited to that to both of the upper surface and the lower surface of the current collector <NUM>. The second resin <NUM> may be welded to one of the upper surface and the lower surface of each current collector <NUM>, and the first resin <NUM> may be welded to the other of the upper surface and the lower surface of each current collector <NUM>.

The supply energy per unit volume to the second resin <NUM> may be equivalent to the supply energy per unit volume to the first resin <NUM>. Even when the supply energy to the second resin <NUM> is relatively low, the second resin <NUM> ensures sufficient welding together with another resin. On the contrary, even when the supply energy to the first resin <NUM> is relatively high, the first resin <NUM> ensures stable welding with another resin without excessive melting. In this way, it is possible to suppress insufficient welding of the resins <NUM>, <NUM> during manufacturing of the battery cell <NUM>.

As illustrated in the right view of <FIG>, in regard to the resins <NUM> for sealing the first opening <NUM> and/or the second opening <NUM> of the pouch <NUM>, the manufactured battery cell <NUM> has a characteristic that a thickness (T1 + T2) in the stacking direction of the resin <NUM> located at the center in the stacking direction is less than a thickness (T1 + T1) in the stacking direction of the resin <NUM> located on the outer side in the stacking direction. The battery cell <NUM> that has this structural characteristic suppresses insufficient welding of the resins <NUM>, <NUM> during manufacturing, and thus can stabilize quality.

<FIG> illustrates a modified example related to the thickness of the resin. In or on the first electrode sheet <NUM> of <FIG>, the thickness T2 of the second resin <NUM>, which is located at the center in the stacking direction, is less than the thickness T1 of the first resin <NUM>, which is located on the outer side in the stacking direction. In addition, a thickness T3 of a third resin <NUM> that is located between the first resin <NUM> and the second resin <NUM> is less than the thickness T1 and greater than the thickness T2. That is, the thicknesses of the resins <NUM>, <NUM>, <NUM> are reduced particularly in a stepwise manner from the outer side to the center in the stacking direction.

The thermal energy for welding is transferred in an order of the first resin <NUM>, the third resin <NUM>, and the second resin <NUM>. The supply energy per unit volume to the third resin <NUM> may be equivalent to the supply energy per unit volume to the second resin <NUM> or the supply energy per unit volume to the first resin <NUM>. The first resin <NUM>, the second resin <NUM>, and the third resin <NUM> are each supplied with the energy commensurate with the volume thereof. Each of the first resin <NUM>, the second resin <NUM>, and the third resin <NUM> can be welded sufficiently with another resin.

The number of the current collectors <NUM>, to which the third resin <NUM> is welded, is appropriately set. In addition, welding of the third resin <NUM> is not limited to that to both of the upper surface and the lower surface of the current collector(s) <NUM>. The third resin <NUM> may be welded to one of the upper surface and the lower surface of the current collector <NUM>, and the first resin <NUM> or the second resin <NUM> may be welded to the other of the upper surface and the lower surface of the current collector <NUM>.

<FIG> illustrates a modified example related to the form of the resin that is welded to the current collector. In or on the first electrode sheet <NUM> (and the second electrode sheet <NUM>) illustrated in <FIG> or <FIG>, each of the resins <NUM>, <NUM> is welded to both of the surfaces of the current collector <NUM> (or the current collector <NUM>) in advance. Conversely, in or on the first electrode sheet <NUM> (and the second electrode sheet <NUM>) illustrated in <FIG>, each of a first resin <NUM> and a second resin <NUM> is welded to only one of the surfaces of the current collector <NUM> (or the current collector <NUM>) in advance. In addition, the first resin <NUM> is welded to one of the two edges of the laminated materials <NUM> in advance.

A thickness T5 of the second resin <NUM>, which is located at the center in the stacking direction, is less than a thickness T4 of the first resin <NUM>, which is located on the outer side in the stacking direction.

The resins <NUM>, <NUM> are welded to the current collector(s) <NUM> or the laminated material <NUM> instead of another resin. During welding of the resins <NUM>, <NUM>, the supply energy per unit volume to the second resin <NUM> may be equivalent to the supply energy per unit volume to the first resin <NUM>. The second resin <NUM> can sufficiently be welded to the current collector <NUM>. The first resin <NUM> can also sufficiently be welded to the current collector <NUM> or the laminated material <NUM>. In this way, it is possible to suppress insufficient welding of the resins <NUM>, <NUM> during manufacturing of the battery cell <NUM>.

<FIG> illustrates a modified example related to a melting point of the resin. The resins <NUM> to <NUM> in the battery cells <NUM> illustrated in <FIG> vary in thickness. The resins <NUM> to <NUM> may be the same type of the resin, and the resins <NUM> to <NUM> may have the same melting point.

In the battery cell <NUM> of <FIG>, resins <NUM>, <NUM> have different melting points. More specifically, the melting point of the second resin <NUM>, which is located at the center in the stacking direction, is lower than the melting point of the first resin <NUM>, which is located on the outer side in the stacking direction.

Here, the first resin <NUM> with the relatively high melting point can be selected from biaxially oriented polypropylene (OPP), polyethylene terephthalate (PET), and biaxially oriented nylon (ONY), for example. The melting point of the first resin <NUM> may be in a range of <NUM> to <NUM>, for example.

The second resin <NUM> with the relatively low melting point can be selected from cast polypropylene (CPP), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), for example. The melting point of the second resin <NUM> may be in a range <NUM> to <NUM> or <NUM> to <NUM>.

An additive may be added to the second resin <NUM> to lower the melting point. For example, any of phthalate-based additive, phosphate-based additive, fatty acid ester-based additive, polyester-based additive, epoxy-based additive, and sulfonamide-based additive may be used.

During welding of the resins <NUM>, <NUM> illustrated in a left view of <FIG>, the second resin <NUM> with the low melting point can sufficiently be welded even with the low supplied thermal energy. Meanwhile, since the high thermal energy is supplied to the first resin <NUM> with the high melting point, the first resin <NUM> can sufficiently be welded. In this way, it is possible to suppress insufficient welding of the resins <NUM>, <NUM> during manufacturing of the battery cell <NUM>.

As illustrated in a right view of <FIG>, in regard to the resins <NUM> for sealing the first opening <NUM> and/or the second opening <NUM> of the pouch <NUM>, the manufactured battery cell <NUM> has a characteristic that the melting point of the resin <NUM> located at the center in the stacking direction is lower than the melting point of the resin <NUM> located on the outer side in the stacking direction. That is, of the resins <NUM> that are welded to the current collectors <NUM> at the positions between the current collectors <NUM>, the resin <NUM> located at the center in the stacking direction contains the resin <NUM> with the low melting point. The battery cell <NUM> that has this structural characteristic suppresses insufficient welding of the resins <NUM>, <NUM> during manufacturing, and thus can stabilize the quality.

In <FIG>, the thickness T1 of the second resin <NUM> in the stacking direction may be the same as the thickness T1 of the first resin <NUM>. However, the thickness of the second resin <NUM> in the stacking direction may be less than the thickness T1 of the first resin <NUM>.

The number of the current collectors <NUM>, to which the second resin(s) <NUM> is(are) welded, is appropriately set. In addition, welding of the second resin <NUM> is not limited to that to both of the upper surface and the lower surface of the current collector <NUM>. The second resin <NUM> may be welded to one of the upper surface and the lower surface of the current collector <NUM>, and the first resin <NUM> may be welded to the other of the upper surface and the lower surface of the current collector <NUM>.

<FIG> illustrates a modified example related to a shape of the current collector. The battery cells <NUM> in <FIG> are structured such that the second resins <NUM>, <NUM>, <NUM> can sufficiently be welded even with the low supplied energy to the second resins <NUM>, <NUM>, <NUM>, each of which is located at the center in the stacking direction.

In detail, in the battery cells <NUM> illustrated in <FIG>, the second resins <NUM>, <NUM>, each of which is located at the center in the stacking direction, are thin in order to increase the supply energy per unit voltage to the second resins <NUM>, <NUM>, each of which is located at the center in the stacking direction. In the battery cell <NUM> of <FIG>, the second resin <NUM>, which is located at the center in the stacking direction, has the low melting point such that the second resin <NUM> is welded even when the energy received by the second resin <NUM> is low.

The battery cell <NUM> in <FIG> promotes energy transfer to increase an amount of the energy supplied to the second resin <NUM>, which is located at the center in the stacking direction. More specifically, the battery cell <NUM> in <FIG> uses a fact that the current collector <NUM> made of the metal has higher energy transfer efficiency than the resins <NUM>, <NUM>.

In the current collector <NUM>, thicknesses T6, T7 of portions, to each of which respective one of the resins <NUM>, <NUM> is welded, are greater than a thickness T8 of the other portions. It can be rephrased that the current collector <NUM> has one or two projections <NUM> in the portion, to which one of the resins <NUM>, <NUM> is welded. The thicknesses of the resins <NUM>, <NUM> may be reduced due to the thicknesses T6, T7 of the current collectors <NUM>.

In the battery cell <NUM> of <FIG>, the thickness T2 of the second resin <NUM>, which is located at the center in the stacking direction, is less than the thickness T1 of the first resin <NUM>, which is located on the outer side in the stacking direction. In contrast, the thickness of the second resin <NUM> may be the same as the thickness T1 of the first resin <NUM>.

During welding of the resins <NUM>, <NUM>, the thermal energy from the heat plates <NUM>, <NUM> is transferred to the second resin <NUM> through the first resin <NUM> and the current collector <NUM>. The thickness of the first resin <NUM> is reduced due to the large thickness of the current collector <NUM>. Since the current collector <NUM>, which is made of the metal, has relatively low specific heat, attenuation of the thermal energy up to reaching to the second resin <NUM> is suppressed. The second resin <NUM> can receive the sufficient thermal energy for welding. In this way, it is possible to suppress insufficient welding of the resins <NUM>, <NUM> during manufacturing of the battery cell <NUM>.

All of the current collectors <NUM> may have the single projection <NUM>, or all of the current collectors <NUM> may have the two projections <NUM>. In addition, the second resin <NUM> may be the resin with the lower melting point than the first resin <NUM>.

<FIG> illustrates a modified example of the method of manufacturing the battery cell <NUM>. More specifically, in this manufacturing method, not only the heat plates <NUM>, <NUM>, each of which is located on the outer side in the stacking direction, (that is, first heat sources <NUM>, <NUM>) but also second heat sources <NUM>, <NUM> are used during welding of the resins <NUM>, <NUM>.

The second heat sources <NUM>, <NUM> may be connected to the current collector <NUM> that is in contact with the second resins <NUM> located at the center in the stacking direction. A projection length of this current collector <NUM> may be longer than those of the other current collectors <NUM>. This current collector <NUM> may have a connection allowance for the second heat sources <NUM>, <NUM>. The number of the current collectors <NUM>, to which the second heat sources <NUM>, <NUM> are connected, is not limited to one but may be plural.

As described above, during welding of the resins <NUM>, <NUM>, the first heat sources <NUM>, <NUM> pressurize and heat the resins <NUM>, <NUM> in the stacking direction. The second heat sources <NUM>, <NUM> supply the thermal energy to the resins <NUM> through the current collector <NUM>. As indicated by blank arrows in <FIG>, the second resin <NUM> receives the thermal energy from the first heat sources <NUM>, <NUM> and the second heat sources <NUM>, <NUM>. In this way, the second resin <NUM> can sufficiently be welded. The first resin <NUM> can also sufficiently be welded.

In the modified example of <FIG>, the second resin <NUM> may be a different type of the resin from the first resin <NUM>, and the melting point thereof may be relatively low, for example. However, the second resin <NUM> may be of the same type as the first resin <NUM>.

In addition, the thickness of the second resin <NUM> may be less than or the same as the thickness of the first resin <NUM>.

Heat-plate welding is performed in the above description. However, the resins may be welded by vibration welding, ultrasonic welding, or high-frequency welding, for example. In the various welding methods, all of the above-described configurations ensure sufficient welding of the resin, which is located at the center in the stacking direction, even with the attenuation of the energy for welding.

Claim 1:
A battery cell (<NUM>) comprising:
a pouch (<NUM>) that is configured to accommodate electrodes (<NUM>);
plural current collectors (<NUM>), each of which is connected to a corresponding one of the electrodes (<NUM>) in the pouch (<NUM>), the plural current collectors (<NUM>) being stacked in a stacking direction, the plural current collectors (<NUM>) projecting to the outside of the pouch (<NUM>) through an opening (<NUM>) of the pouch (<NUM>);
a first resin (<NUM>, <NUM>, <NUM>) that is configured to seal the opening (<NUM>) of the pouch (<NUM>), the first resin (<NUM>, <NUM>, <NUM>) being welded to the current collector (<NUM>) at a position between the stacked current collectors (<NUM>); and
a second resin (<NUM>, <NUM>, <NUM>) that is configured to seal the opening (<NUM>) of the pouch (<NUM>), the second resin (<NUM>, <NUM>, <NUM>) being welded to the current collector (<NUM>) at a position between the stacked current collectors (<NUM>), and being located closer to a center in the stacking direction than the first resin (<NUM>, <NUM>, <NUM>) is to the center,
wherein the second resin (<NUM>, <NUM>, <NUM>) has a thickness (T2, T5) thinner than a thickness (T1, T4) of the first resin (<NUM>, <NUM>) in the stacking direction and/or has a lower melting point than the first resin (<NUM>).