Monocell stack and method for manufacturing same

Abstract

A single cell stack having a rectangular parallelepiped shape in which a plurality of rectangular single cells are stacked, the single cell stack being provided with a plurality of inter-cell members inserted between adjacent rectangular single cells. The plurality of inter-cell members are provided with: a first inter-cell member including a plate-shaped spacer that absorbs unevenness in the thickness of the plurality of rectangular single cells; and a second inter-cell member that does not include a plate-shaped spacer. The plate-shaped spacer is made of rigid plastic and has the same thickness, and the first inter-cell member and the second inter-cell member are irregularly arranged.

Description

Technical Field

[0001] The present disclosure relates to a cell stack and a method of manufacturing the same. Background Art

[0002] In conventional cell stacks, terminals are provided on the top surfaces of stacked rectangular cells. In recent years, cell stacks have also been developed in which terminals are provided on the longitudinal end surfaces of stacked rectangular cells, as disclosed in Patent Document 1.

[0003] Patent Document 1: U.S. Patent Application Publication No. 2022 / 0302533 Summary of the Invention

[0004] The stacked prismatic cells in a cell stack have a specified dimensional tolerance of ±b relative to the designed thickness a. That is, the thickness of the prismatic cells is a ± b. To compensate for this uneven thickness of the prismatic cells, inventors have previously employed methods such as selectively inserting two types of plate-like spacers of varying thickness, made of an elastic material such as an elastomer containing synthetic rubber, between all adjacent prismatic cells. However, the elastic material is expensive, and there is a problem in that the manufacturing becomes complicated due to the use of two types of plate-like spacers having different thicknesses.

[0005] The present disclosure has been made in view of such circumstances, and provides a cell stack that can be manufactured more cheaply and easily.

[0006] A single cell stack according to one embodiment of the present disclosure, It is a rectangular cell stack formed by stacking multiple square cells. It has a plurality of inter-cell members inserted between adjacent rectangular cells. The plurality of inter-cell members include: a first inter-cell member including a plate-shaped spacer for absorbing uneven thickness of the plurality of prismatic cells; and a second inter-cell member that does not include the plate-shaped spacer, The plate-like spacers are made of hard plastic and have the same thickness, The first inter-cell members and the second inter-cell members are arranged irregularly.

[0007] In the cell stack disclosed herein, the plurality of inter-cell members inserted between adjacent prismatic cells include a first inter-cell member including a plate-like spacer that absorbs thickness variations of the prismatic cells, and a second inter-cell member that does not include the plate-like spacer. The plate-like spacers are made of rigid plastic and have the same thickness. The first and second inter-cell members are arranged irregularly. Specifically, by irregularly inserting a single plate-like spacer of uniform thickness, made of inexpensive rigid plastic, between adjacent prismatic cells, thickness variations of the prismatic cells are absorbed. Consequently, a cell stack that can be manufactured more cost-effectively and easily can be provided.

[0008] The first inter-cell member and the second inter-cell member may each include a heat insulating plate having the same thickness. With this configuration, all adjacent prismatic cells can be thermally insulated from each other.

[0009] The thickness of the plate-shaped spacer may have a dimensional tolerance equal to that of the prismatic cell. According to this structure, variations in the thickness of the prismatic cell can be easily absorbed simply by inserting or not inserting the plate-shaped spacer.

[0010] A method for manufacturing a cell stack according to one embodiment of the present disclosure includes: This is a method for manufacturing a cell stack in which rectangular cells and inter-cell members are stacked in sequence to produce a cell stack having a rectangular parallelepiped shape. Each time the rectangular cells are stacked, the thickness of the rectangular cells to be stacked is measured. Determine whether the total thickness of the stacked prismatic cells and inter-cell members plus the measured thickness of the prismatic cells to be stacked exceeds a predetermined reference value; When the total thickness does not exceed the predetermined reference value, a first inter-cell member including a plate-shaped spacer for absorbing uneven thickness of the prismatic cells is inserted as the inter-cell member, and the prismatic cells to be stacked are stacked. When the total thickness exceeds the predetermined reference value, a second inter-cell member not including the plate-shaped spacer is inserted as the inter-cell member and the prismatic cells to be stacked are stacked. The plate-like spacers are made of hard plastic and have the same thickness.

[0011] In the manufacturing method of the cell stack involved in the present disclosure, each time square cells are stacked, the thickness of the square cells to be stacked is measured, and it is determined whether the total thickness obtained by adding the thickness of the already stacked square cells and the plate-like spacers to the measured thickness of the square cells to be stacked exceeds a specified reference value. Furthermore, if the total thickness does not exceed the specified reference value, the plate-like spacers are inserted and the square cells to be stacked are stacked. If the total thickness exceeds the specified reference value, the plate-like spacers are not inserted and the square cells to be stacked are stacked. Here, the plate-like spacers are made of hard plastic and have the same thickness. That is, by inserting or not inserting a plate-like spacer of the same thickness made of cheap hard plastic between adjacent square cells, the unevenness of the thickness of the square cells is absorbed. Therefore, it is possible to provide a cell stack that can be manufactured more cheaply and easily.

[0012] According to the present disclosure, it is possible to provide a cell stack that can be manufactured more cheaply and easily. The above and other objects, features and advantages of the present disclosure will be more fully understood from the detailed description and accompanying drawings given below. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a perspective view showing the cell stack according to the first embodiment. Figure 2 This is a perspective view showing the cell stack according to the first embodiment. Figure 3 This is a side view showing the cell stack according to the first embodiment. Figure 4 This is a flowchart showing the method for manufacturing the cell stack according to the first embodiment. DETAILED DESCRIPTION

[0014] Hereinafter, the specific embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the present disclosure is not limited to the following embodiments. In addition, the following description and drawings are appropriately simplified for clarity of description.

[0015] (First embodiment) <Single Cell Stack Configuration> First, refer to Figures 1 to 3 , the structure of the cell stack according to the first embodiment will be described. Figure 1 and Figure 2 Each of them is a perspective view showing the cell stack according to the first embodiment. Figure 3 This is a side view showing the cell stack according to the first embodiment.

[0016] In addition, of course, Figures 1 to 3 The right-handed XYZ orthogonal coordinates shown in FIG are for the convenience of explaining the positional relationship of the components. Figures 1 to 3 In the drawings, the positive direction of the Z axis is usually the vertical upward direction, and the XY plane is the horizontal plane, which is common among the drawings.

[0017] like Figure 1 and Figure 2 As shown in FIG. 1 , the cell stack CS according to this embodiment includes rectangular cells C1 to C6 and bus bars B1 to B5. Figure 3 As shown, the cell stack CS according to the present embodiment includes inter-cell members IC1 to IC5 , end plates EP1 and EP2 , and elastic members EM1 and EM2 .

[0018] In addition, Figure 2 In, omitted Figure 3 The inter-cell members IC1 to IC5, the end plates EP1 and EP2, and the elastic members EM1 and EM2 are shown. Figure 3 Shows the settings Figure 1 and Figure 2 The bus bars B1 to B5 are shown in the previous state.

[0019] The cell stack CS according to this embodiment is used, for example, as an on-vehicle battery. Vehicles equipped with the cell stack CS according to this embodiment are not particularly limited, but may include electric vehicles, hybrid vehicles, fuel cell vehicles, and the like that can be driven by electricity supplied from the cell stack CS.

[0020] like Figure 1 and Figure 2 As shown, the prismatic cells C1-C6 are rectangular parallelepiped cells extending in the Y-axis direction. The prismatic cells C1-C6 are stacked in the thickness direction (X-axis direction) to form a cell stack CS. The prismatic cells C1-C6 are secondary batteries such as lithium-ion batteries and nickel-metal hydride batteries.

[0021] In addition, Figure 1 and Figure 2 In FIG, the single cell stack CS is shown in a simplified manner. Figure 1 and Figure 2 The cell stack CS shown is composed of six prismatic cells C1 to C6 , but the number of prismatic cells constituting the cell stack CS is not particularly limited. Typically, the cell stack CS is composed of a larger number of prismatic cells.

[0022] like Figure 1 As shown in FIG. 1 , a positive terminal PT1 is provided on one end face (the end face on the negative side of the Y axis) in the longitudinal direction of the rectangular cell C1. Figure 1The positive terminal PT1 shown is rectangular in shape when viewed from the XZ plane and is provided so as to protrude outward from the end surface of the square cell C1. Figure 1 The positive electrode terminal PT1 shown is provided on the upper side (Z-axis positive side) of the end surface of the rectangular cell C1. The positive electrode terminal PT1 is made of a metal material such as copper having excellent electrical conductivity.

[0023] Likewise, Figure 1 As shown, a negative terminal NT2 is provided at one end face in the longitudinal direction (end face on the negative side in the Y-axis) of the square cell C2 adjacent to the square cell C1. A positive terminal PT3 is provided at one end face in the longitudinal direction (end face on the negative side in the Y-axis) of the square cell C3 adjacent to the square cell C2. A negative terminal NT4 is provided at one end face in the longitudinal direction (end face on the negative side in the Y-axis) of the square cell C4 adjacent to the square cell C3. A positive terminal PT5 is provided at one end face in the longitudinal direction (end face on the negative side in the Y-axis) of the square cell C5 adjacent to the square cell C4. A negative terminal NT6 is provided at one end face in the longitudinal direction (end face on the negative side in the Y-axis) of the square cell C6 adjacent to the square cell C5.

[0024] like Figure 1 As shown, the negative terminal NT2 of the square cell C2, the positive terminal PT3 of the square cell C3, the negative terminal NT4 of the square cell C4, the positive terminal PT5 of the square cell C5, and the negative terminal NT6 of the square cell C6 have the same shape as the positive terminal PT1 of the square cell C1 and are configured in the same manner.

[0025] And, as Figure 1 As shown, the positive terminal PT1 of the adjacent prismatic cell C1 and the negative terminal NT2 of the prismatic cell C2 are electrically connected by a plate-shaped bus bar B1. Similarly, the positive terminal PT3 of the adjacent prismatic cell C3 and the negative terminal NT4 of the prismatic cell C4 are electrically connected by a plate-shaped bus bar B3. Similarly, the positive terminal PT5 of the adjacent prismatic cell C5 and the negative terminal NT6 of the prismatic cell C6 are electrically connected by a plate-shaped bus bar B5.

[0026] On the other hand, Figure 2 As shown in FIG. 1 , a negative terminal NT1 is provided on the other end face (the end face on the positive side of the Y axis) in the longitudinal direction of the rectangular cell C1. Figure 2 The negative terminal NT1 is shown with Figure 1 The positive terminal PT1 shown is also rectangular in shape when viewed in the XZ plane and is provided so as to protrude outward from the end surface of the rectangular cell C1. Figure 2 The negative terminal NT1 is shown with Figure 1The positive terminal PT1 is similarly provided on the upper side (Z-axis positive side) of the end face of the rectangular cell C1. The negative terminal NT1 is similarly formed of a metal material such as copper having excellent conductivity.

[0027] Likewise, Figure 2 As shown, a positive terminal PT2 is provided on the other end face in the longitudinal direction (the end face on the positive direction of the Y axis) of the square cell C2 adjacent to the square cell C1. A negative terminal NT3 is provided on the other end face in the longitudinal direction (the end face on the positive direction of the Y axis) of the square cell C3 adjacent to the square cell C2. A positive terminal PT4 is provided on the other end face in the longitudinal direction (the end face on the positive direction of the Y axis) of the square cell C4 adjacent to the square cell C3. A negative terminal NT5 is provided on the other end face in the longitudinal direction (the end face on the positive direction of the Y axis) of the square cell C5 adjacent to the square cell C4. A positive terminal PT6 is provided on the other end face in the longitudinal direction (the end face on the positive direction of the Y axis) of the square cell C6 adjacent to the square cell C5.

[0028] like Figure 2 As shown, the positive terminal PT2 of the square cell C2, the negative terminal NT3 of the square cell C3, the positive terminal PT4 of the square cell C4, the negative terminal NT5 of the square cell C5, and the positive terminal PT6 of the square cell C6 have the same shape as the negative terminal NT1 of the square cell C1 and are configured in the same manner.

[0029] And, as Figure 2 As shown, the positive terminal PT2 of the adjacent prismatic cell C2 and the negative terminal NT3 of the prismatic cell C3 are electrically connected by a plate-shaped bus bar B2. Similarly, the positive terminal PT4 of the adjacent prismatic cell C4 and the negative terminal NT5 of the prismatic cell C5 are electrically connected by a plate-shaped bus bar B4. Like this, in Figure 1 and Figure 2 In the illustrated cell stack CS, rectangular cells C1 to C6 are connected in series via bus bars B1 to B5 .

[0030] also, Figure 2 The negative terminal NT1 of the illustrated rectangular cell C1 is not particularly limited, but is connected to the positive terminal of another cell stack via a bus bar (not shown), for example. Figure 2 The positive terminal PT6 of the illustrated rectangular cell C6 is not particularly limited, but is connected to the negative terminal of another cell stack via a bus bar (not shown), for example. With such a structure, for example, a plurality of cell stacks can be connected in series.

[0031] Figure 1 and Figure 2The bus bars B1 to B5 shown have the same structure, so bus bar B1 will be described. like Figure 1 As shown, the bus bar B1 is a plate-shaped member that electrically connects the positive terminal PT1 of the adjacently arranged rectangular cell C1 and the negative terminal NT2 of the rectangular cell C2. The bus bar B1 is made of a metal material such as copper having excellent electrical conductivity.

[0032] like Figure 1 As shown, busbar B1 is a plate-shaped member having a rectangular shape when viewed in the XZ plane. Busbar B1 is provided to substantially entirely cover the positive terminal PT1 of prismatic cell C1 and the negative terminal NT2 of prismatic cell C2. Busbar B1 includes a pair of welded portions WP1 and WP2, which are welded to the positive terminal PT1 of the adjacent prismatic cell C1 and the negative terminal NT2 of the adjacent prismatic cell C2, respectively.

[0033] Although not specifically limited, Figure 1 The welded portions WP1 and WP2 shown are provided at both ends in the X-axis direction on the lower side (Z-axis negative direction side) of the bus bar B1. Figure 1 Welded portions WP1 and WP2 before welding are shown. Figure 1 The welded portions WP1 and WP2 shown are countersunk and have a thinner plate thickness than other areas. Figure 1 The welded portions WP1 and WP2 shown have a circular shape when viewed in the XZ plane, and have a through hole in the center.

[0034] While the welding method is not particularly limited, for example, by irradiating the weld portion WP1 with a laser beam from the negative side in the Y-axis direction, the bus bar B1 is welded to the positive terminal PT1 of the prismatic cell C1 at the weld portion WP1. Similarly, by irradiating the weld portion WP2 with a laser beam from the negative side in the Y-axis direction, the bus bar B1 is welded to the negative terminal NT2 of the prismatic cell C2 at the weld portion WP2.

[0035] like Figure 3 As shown, the inter-cell members IC1 to IC5 are plate-shaped members inserted between adjacent rectangular cells C1 to C6. Figure 3 As shown, for example, an inter-cell member IC1 is inserted between adjacent rectangular cells C1 and C2. The inter-cell member IC1 thermally insulates the adjacent rectangular cells C1 and C2 from each other and adjusts the distance between the adjacent rectangular cells C1 and C2.

[0036] More specifically, inter-cell members IC1-IC5 are either first inter-cell members that include plate-shaped spacers to absorb the uneven thickness of prismatic cells C1-C6, or second inter-cell members that do not include plate-shaped spacers. The plate-shaped spacers are made of rigid plastic and have a uniform thickness.

[0037] The rectangular cells C1 to C6 have a predetermined dimensional tolerance of ±b with respect to the designed thickness a. That is, the thickness of the rectangular cells C1 to C6 is a±b. Each of the inter-cell members IC1 to IC5 (ie, the first inter-cell member and the second inter-cell member) may include a heat insulating plate having the same thickness.

[0038] Whether to use the first inter-cell member or the second inter-cell member as the inter-cell members IC1 to IC5 is determined when manufacturing the cell stack CS. When the rectangular cells C1 to C6 are stacked in sequence, the thickness of the rectangular cells to be stacked is measured each time the cells are stacked, and it is determined whether the total thickness obtained by adding the thickness of the already stacked rectangular cells and the inter-cell components to the measured thickness of the rectangular cells to be stacked exceeds a specified reference value.

[0039] For example, when stacking prismatic cell C3, a determination is made as to whether the total thickness (the thickness of the already stacked prismatic cells C1 and C2 and the inter-cell member IC1 plus the measured thickness of prismatic cell C3) exceeds a predetermined reference value. The reference value for the total thickness is predetermined for each of the second and subsequent prismatic cells C2 to C6 to be stacked. For example, this reference value is appropriately determined based on the designed thickness a of the prismatic cells, the dimensional tolerance ±b, the designed thickness of the heat shield, and other factors.

[0040] If the total thickness does not exceed the reference value, the first inter-cell member including the plate-like spacer is inserted as the inter-cell member IC2, and the prismatic cells C3 are stacked. On the other hand, if the total thickness exceeds the reference value, the second inter-cell member not including the plate-like spacer is inserted as the inter-cell member IC2, and the prismatic cells C3 are stacked. The same applies to the stacking of the other prismatic cells C2, C4 to C6.

[0041] As a result, in the cell stack CS according to the present embodiment, first inter-cell members including plate-like spacers and second inter-cell members not including plate-like spacers are irregularly arranged as the inter-cell members IC1 to IC5 .

[0042] Here, if the reference value of the total thickness is appropriately set so that the thickness of the plate-shaped spacer is equal to the dimensional tolerance width 2b of the rectangular battery, the thickness of the plate-shaped spacer can be made equal to the dimensional tolerance width 2b of the rectangular battery. Figure 3 The deviation of the center position of the rectangular cells C1 to C6 from the target position is less than the absolute value b of the dimensional tolerance ±b. In addition, the length of the rectangular cells C1 to C6 stacked with the inter-cell members IC1 to IC5 interposed therebetween can be brought close to the target value.

[0043] like Figure 3 As shown, end plate EP1 is positioned, via elastic member EM1, at the negative end of the stacked prismatic cells C1-C6, sandwiched between inter-cell members IC1-IC5, in the X-axis direction. End plate EP2 is positioned, via elastic member EM2, at the positive end of the stacked prismatic cells C1-C6 in the X-axis direction. In other words, end plates EP1 and EP2 press against the stacked prismatic cells C1-C6 from both ends in the stacking direction (X-axis direction), thereby constraining the stacked cells. The end plates EP1 and EP2 are made of a metal material such as aluminum.

[0044] The elastic members EM1 and EM2 are plate-shaped members made of an elastic material such as an elastomer containing synthetic rubber. Here, Figure 3 The length L of the cell stack CS shown is the distance between the inner surfaces of the end plates EP1 and EP2 and is a fixed value. Deviations in the length of the rectangular cells C1 to C6 stacked with the inter-cell members IC1 to IC5 from the target value can be absorbed by the elastic members EM1 and EM2.

[0045] As described above, in the cell stack CS according to this embodiment, uneven thicknesses among the prismatic cells C1-C6 are accommodated by randomly inserting a single type of plate-like spacer made of inexpensive hard plastic and having the same thickness between adjacent prismatic cells C1-C6. Consequently, the cell stack CS according to this embodiment can be manufactured more cost-effectively and easily compared to a cell stack in which two types of plate-like spacers made of elastic material and having different thicknesses are selectively inserted between all adjacent prismatic cells.

[0046] <Method for Manufacturing a Single Cell Stack> Next, refer to Figure 4 , a method for manufacturing the cell stack according to the first embodiment will be described. Figure 4 Flowchart showing the method for manufacturing a cell stack according to the first embodiment. Figure 3 The rectangular cell stack CS is manufactured by sequentially stacking the rectangular cell stack C1 to C6 and the inter-cell members IC1 to IC5 shown.

[0047] First, if Figure 4As shown, the thickness of the rectangular single cells to be stacked is measured (step ST1 ). Specifically, the thickness of the rectangular single cells C1 to be stacked is measured. Then, if Figure 4 As shown, if it is the first prismatic cell, the process returns to step ST1 as an exception. If it is not the first prismatic cell, the total thickness is calculated by adding the thickness of the stacked prismatic cells and the inter-cell member to the measured thickness of the prismatic cell (step ST2).

[0048] Specifically, after measuring the thickness of the first prismatic cell C1, the process returns to step ST1 to measure the thickness of the prismatic cell C2. Next, the process proceeds to step ST2 to calculate the total thickness by adding the measured thickness of the prismatic cell C2 to the thickness of the stacked prismatic cells C1.

[0049] then, Figure 4 As shown, a determination is made as to whether the total thickness exceeds a predetermined reference value (step ST3). If the total thickness does not exceed the predetermined reference value ("No" in step ST3), a first inter-cell member including a plate-shaped spacer that absorbs the uneven thickness of the prismatic cells is inserted as an inter-cell member, and the prismatic cells are stacked (step ST4). Specifically, the first inter-cell member including the plate-shaped spacer is inserted as the inter-cell member IC1, and the prismatic cells C2 are stacked. Here, the plate-shaped spacer is made of hard plastic and has a uniform thickness.

[0050] On the other hand, if the total thickness exceeds the predetermined reference value ("YES" in step ST3), a second inter-cell member not including a plate-shaped spacer is inserted as the inter-cell member, and the prismatic cells are stacked (step ST5). Specifically, a second inter-cell member not including a plate-shaped spacer is inserted as the inter-cell member IC1, and the prismatic cells C2 are stacked.

[0051] like Figure 4 As shown, after the prismatic cells are stacked in step ST4 or step ST5, if the stacked prismatic cell is not the final prismatic cell, the process returns to step ST1. On the other hand, if the stacked prismatic cell is the final prismatic cell, the process ends. Specifically, since the stacked prismatic cell C2 is not the final prismatic cell, the process returns to step ST1 to measure the thickness of the prismatic cell C3 to be stacked.

[0052] Then, if Figure 4 Specifically, the total thickness is calculated by adding the measured thickness of the rectangular cell C3 to the thickness of the already stacked rectangular cells C1 and C2 and the inter-cell member IC1 .

[0053] Then, if Figure 4 As shown, if the total thickness does not exceed the predetermined reference value ("No" in step ST3), the process proceeds to step ST4. Specifically, a first inter-cell member including a plate-like spacer is inserted as the inter-cell member IC2, and the prismatic cells C3 are stacked. On the other hand, if the total thickness exceeds the predetermined reference value ("Yes" in step ST3), the process proceeds to step ST5. Specifically, a second inter-cell member not including a plate-like spacer is inserted as the inter-cell member IC2, and the prismatic cells C3 are stacked.

[0054] And, as Figure 4 As shown, after the rectangular single cells C3 are stacked in step ST4 or step ST5 , the process returns to step ST1 to measure the thickness of the rectangular single cells C4 to be stacked. In this manner, by repeating the above-described steps ST1 to ST5 until the final prismatic cell C6 is obtained, the prismatic cells C1 to C6 and the inter-cell members IC1 to IC5 are stacked in sequence to manufacture the cell stack CS.

[0055] As described above, the stack manufacturing method of this embodiment compensates for variations in thickness among the prismatic cells by inserting or omitting a single plate-like spacer made of inexpensive hard plastic and having the same thickness between adjacent prismatic cells. Consequently, compared to methods that selectively insert two plate-like spacers made of elastic material and having different thicknesses between all adjacent prismatic cells, the stack manufacturing method of this embodiment enables more cost-effective and easier manufacturing of the cell stack.

[0056] From the disclosure described above, it is obvious that the embodiments of the present disclosure can be changed in many ways. Such changes should not be regarded as departing from the spirit and scope of the present disclosure, and all such modifications obvious to those skilled in the art are intended to be included within the scope of the claims.

Claims

1. A cell stack having a rectangular parallelepiped shape formed by stacking a plurality of square cells, wherein: It has a plurality of inter-cell members inserted between adjacent rectangular cells. The plurality of inter-cell members include: a first inter-cell member including a plate-shaped spacer for absorbing uneven thickness of the plurality of prismatic cells; and a second inter-cell member that does not include the plate-shaped spacer, The plate-like spacers are made of hard plastic and have the same thickness, The first inter-cell members and the second inter-cell members are arranged irregularly.

2. The single cell stack according to claim 1, wherein: The first inter-cell member and the second inter-cell member each include a heat insulating plate having the same thickness.

3. The single cell stack according to claim 1 or 2, wherein: The thickness of the plate-shaped spacer has a dimensional tolerance equal to that of the square battery cell.

4. A method for manufacturing a cell stack, wherein the method comprises stacking square cells and inter-cell members in sequence to produce a rectangular cell stack, wherein: Each time the rectangular cells are stacked, the thickness of the rectangular cells to be stacked is measured. Determine whether the total thickness of the stacked prismatic cells and inter-cell members plus the measured thickness of the prismatic cells to be stacked exceeds a predetermined reference value; When the total thickness does not exceed the predetermined reference value, a first inter-cell member including a plate-shaped spacer for absorbing uneven thickness of the prismatic cells is inserted as the inter-cell member, and the prismatic cells to be stacked are stacked. When the total thickness exceeds the predetermined reference value, a second inter-cell member not including the plate-shaped spacer is inserted as the inter-cell member and the prismatic cells to be stacked are stacked. The plate-like spacers are made of hard plastic and have the same thickness.

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