Rechargeable batteries and battery packs

Abstract

To provide secondary batteries and battery packs that exhibit good lifespan performance and high energy density. [Solution] According to the embodiment, a secondary battery is provided comprising an electrode group having a flattened laminated structure, a liquid electrolyte at least partially held in the electrode group, and an outer casing member including a rectangular container that houses the electrode group and the electrolyte. The electrode group includes a laminate containing a positive electrode and a negative electrode, and has two pairs of end faces that intersect each other along the lamination direction of the laminate. The rectangular container has a pair of main walls that intersect the lamination direction. The thickness of the center of the electrode group in the lamination direction when it is outside the rectangular container is greater than the inner diameter in the direction intersecting the main walls of the rectangular container. At least one of the periphery thicknesses in the lamination direction at a position 10% of the length of the shortest side of the side intersecting the lamination direction of the end face, moving inward from the center of each end face, is thinner than the center thickness. The average value of the periphery thickness is greater than 95% of the center thickness.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to secondary batteries and battery packs. [Background technology]

[0002] Lithium-ion batteries, such as non-aqueous electrolyte batteries, which charge and discharge by the movement of lithium ions between the negative and positive electrodes, are being actively researched as high-energy-density batteries.

[0003] Carbon materials, silicon, silicon alloys, and various metal oxides are known as negative electrode active materials used in the negative electrodes of secondary batteries such as lithium-ion batteries. Many of these negative electrode active materials are known to exhibit volume changes with the charging and discharging of the battery. Furthermore, when carbon materials or silicon (Si)-based active materials are used, lithium dendrites are known to precipitate with repeated charging and discharging.

[0004] For batteries containing a negative electrode made of a negative electrode active material such as carbon or silicon, which exhibits large volume changes, it is preferable to restrain the battery during charging and discharging. Furthermore, it is preferable to set the dimensions of the electrode group and the inner dimensions of the outer casing member in consideration of the volume changes of the electrodes. For example, if the size of the outer casing member is left too large in relation to the increase in the volume of the electrode group, the energy density will decrease as a result.

[0005] Typical structures for electrode groups include a laminated structure composed of a laminate containing a positive electrode and a negative electrode, and a wound structure formed by winding such a laminate. On the one hand, because the wound structure includes curved surfaces on its outer surface, there tends to be a large amount of space not occupied by the electrode group within, for example, a rectangular outer container. Therefore, laminated electrode groups are more advantageous in terms of energy density than wound electrode groups. On the other hand, while the liquid electrolyte contained in the electrode group can be pushed out due to the expansion and contraction of the electrodes caused by factors such as charging and discharging, the curved surfaces of the wound structure function as walls against the interior of the electrode group, so the electrolyte inside the electrode group is not pushed out from the curved parts. Therefore, in a wound electrode group, the areas from which liquid is pushed out from the inside are basically limited to the end faces that intersect with the winding axis. In contrast, in a laminated electrode group, liquid can be pushed out from each side of the laminated electrodes, so electrolyte depletion is likely to occur. In addition, if there is a large difference between the thickness of the electrode group and the inner dimensions of the outer casing, gaps are likely to form between the stacked electrodes, which accelerates liquid depletion. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-73576 [Patent Document 2] Japanese Patent Publication No. 2023-26188 [Non-patent literature]

[0007] [Non-Patent Document 1] "Practical Aspects of Powder X-ray Radiation Analysis," First Edition (2002), edited by the X-ray Radiation Analysis Research Group of the Japan Society for Analytical Chemistry, authored by Izumi Nakai and Fujio Izumi (Asakura Shoten). [Overview of the project] [Problems that the invention aims to solve]

[0008] The objective is to provide secondary batteries and battery packs that exhibit good lifespan performance and high energy density. [Means for solving the problem]

[0009] According to the embodiment, a secondary battery is provided comprising an electrode group having a flattened stacked structure, a liquid electrolyte at least partially held in the electrode group, and an outer casing member including a rectangular container that houses the electrode group and the electrolyte. The electrode group includes a stack containing a positive electrode and a negative electrode, and has two pairs of end faces that intersect each other along the stacking direction of the stack. The rectangular container has a pair of main walls that intersect the stacking direction. The thickness of the center of the electrode group in the stacking direction when it is outside the rectangular container is greater than the inner diameter in the direction intersecting the main walls of the rectangular container. At least one of the periphery thicknesses in the stacking direction at a position 10% of the length of the shortest side of the side intersecting the stacking direction of the end face, moving inward from the center of each end face, is thinner than the center thickness. The average value of the periphery thickness is greater than 95% of the center thickness.

[0010] According to another embodiment, a battery pack comprising a secondary battery according to the above embodiment is provided. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic plan view showing an example of a secondary battery. [Figure 2] A partial unfolded perspective view of an example of a conventional electrode array. [Figure 3] A schematic diagram showing an example of a cross-section along line AA in Figure 1. [Figure 4] A partial transparency diagram conceptually representing the movement of liquid within a secondary battery, as shown in Figure 3. [Figure 5] A perspective view of an example of a conventional electrode group. [Figure 6] Partially unfolded perspective view of another example of a conventional electrode group. [Figure 7] A schematic diagram showing another example of a cross-section along the line A-A' in Figure 1. [Figure 8] Figure 7 is a partial transmission diagram conceptually representing the movement of liquid within a secondary battery. [Figure 9] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 10]A schematic cross-sectional view along the line B-B' in Figure 9. [Figure 11] A schematic perspective view showing an example of an electrode group included in a secondary battery according to this embodiment. [Figure 12] A schematic plan view showing an example of an electrode group included in a secondary battery according to this embodiment. [Figure 13] Schematic cross-sectional view along the line C-C' in Figure 12. [Figure 14] A schematic cross-sectional view illustrating an example of a conventional rechargeable battery. [Figure 15] A schematic cross-sectional view illustrating another example of a conventional rechargeable battery. [Figure 16] A schematic diagram showing an example of electrodes included in a secondary battery according to this embodiment. [Figure 17] A schematic diagram illustrating another example of electrodes included in a secondary battery according to the embodiment. [Figure 18] A schematic diagram illustrating another example of electrodes included in a secondary battery according to the embodiment. [Figure 19] A schematic diagram illustrating another example of electrodes included in a secondary battery according to the embodiment. [Figure 20] A cross-sectional view conceptually illustrating part of the manufacturing process of an example of an electrode included in a secondary battery according to the embodiment. [Figure 21] A plan view conceptually representing part of the manufacturing process of an example of an electrode group included in a secondary battery according to the embodiment. [Figure 22] A schematic cross-sectional view showing another example of the electrode group included in the secondary battery according to the embodiment. [Figure 23] A block diagram showing an example of the electrical circuit of a battery pack according to this embodiment. [Modes for carrying out the invention]

[0012] The embodiments will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each drawing is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, and ratios may differ from those of the actual device. These can be appropriately modified in accordance with the following description and known technology.

[0013] (First Embodiment) According to the first embodiment, a secondary battery is provided. The secondary battery comprises an electrode group having a flattened stacked structure, a liquid electrolyte, and an outer casing member including a rectangular container that houses the electrode group and the electrolyte. The electrode group includes a stack containing a positive electrode and a negative electrode. The electrode group has two pairs of end faces that intersect each other along the stacking direction of the stack. The liquid electrolyte, i.e., electrolyte solution, is at least partially held by the electrode group. The rectangular container has a pair of main walls that intersect the stacking direction of the stack. Let IW be the inner diameter of the rectangular container in the direction intersecting the main walls. Let T1 be the center thickness of the electrode group in the stacking direction when it is outside the rectangular container. Let T2 be the peripheral thickness of the electrode group in the stacking direction when it is outside the rectangular container, at a position 10% of the length of the shortest side among the sides that intersect the stacking direction of the end face, moving inward from the center of each end face of the electrode group. The center thickness T1 is greater than the inner diameter IW. At least one of the peripheral thicknesses T2 is thinner than the center thickness T1. Average value of surrounding thickness T2 AVE And the thickness T1 at the center of the surface is T2 AVE The relationship 0.95 × T1 is satisfied.

[0014] In this secondary battery, the dimensions of the electrode group and the outer casing are such that the central portion of the electrode group housed in the outer casing is pressed against the inner wall of the outer casing, and the thickness is thinner near at least one of the four outer sides than the central portion of the electrode group. The fact that the thickness T1 of the center surface of the electrode group when not housed in the outer casing is greater than the inner diameter IW of the rectangular container that serves as the outer casing indicates that the electrode group is squashed by the inner wall of the rectangular container within the secondary battery. In such a secondary battery, a high energy density can be obtained because the electrode group, which includes the power generation element, occupies a large proportion of the internal volume of the outer casing. Furthermore, as the battery charges and discharges, the electrode active material expands and contracts due to the insertion and removal of charge carrier ions (e.g., lithium ions), which can cause a liquid-pushing effect on the portion of the electrode group compressed by the rectangular container. However, since the thinner portion near the outer periphery of the electrode group is not compressed, the liquid is not pushed out of the electrode group, and its movement is limited to the thinner portion. Therefore, electrolyte depletion in the electrode group due to charging and discharging is suppressed, resulting in improved lifespan performance. The average value T2 of the periphery thickness is given by the value of the center thickness T1 of the main surface intersecting the end face along the stacking direction of the electrode group. AVE (T2 AVE (0.95 × T1), the outer thickness of the electrode group is not too small, so no large gap is created between the main surface of the electrode group and the inner wall of the outer casing even in the surrounding area. Not only is the proportion of the volume inside the outer casing that is occupied by the electrode group secured, but the amount of liquid that can be pushed out is reduced by minimizing the space where the liquid pushed out from the electrode group can go. Therefore, by satisfying the above dimensional relationship between the electrode group and the rectangular container, a secondary battery exhibiting good lifespan performance and high energy density can be obtained.

[0015] The secondary battery may further include a separator positioned between the positive and negative electrodes in the electrode group.

[0016] Furthermore, such a secondary battery may further include a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

[0017] The secondary battery may further include a restraining member. The restraining member restrains the secondary battery from the outside of the outer casing. Preferably, the restraining member mainly applies pressure to the central portion of the main wall of the rectangular container. The form of the restraining member is not particularly limited, and for example, a restraint device including a pair of plate-shaped pressure members and a connecting member connecting them can be used. Alternatively, for example, in applications in a battery pack containing one or more secondary batteries, the restraining member may be included as a component of the battery pack. Examples of materials that constitute the restraining member include resin and metal. In addition, the secondary battery according to the first embodiment has, for at least one state in which it is restrained by the restraining member and in which it is not restrained, the above-mentioned electrode group and the thickness relationship of the rectangular container T1 > IW, at least one T2 < T1, and T2 AVE > 0.95 × T1 can be satisfied. Also, the inner diameter IW of the rectangular container for a secondary battery constrained by a restraining member can be the same in the constrained state and in the state with the restraining member removed.

[0018] The secondary battery in question may be, for example, a lithium secondary battery. Furthermore, the secondary battery may include a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0019] Examples of a conventional secondary battery and a secondary battery according to the first embodiment will be described with reference to the drawings.

[0020] Figure 1 is a plan view of an example of a secondary battery, schematically showing the appearance of, for example, a conventional secondary battery or a secondary battery according to the first embodiment. Figure 2 is a perspective view schematically showing an example of a conventional wound electrode group. Figure 3 is an example of a schematic cross-sectional view along the line A-A' in Figure 1, showing an example of a conventional secondary battery equipped with a wound electrode group. Figure 4 is a partial transparency diagram conceptually representing the movement of liquid in the secondary battery shown in Figure 3, representing the secondary battery as seen from the same viewpoint as in Figure 1.

[0021] Figures 5 and 6 are schematic perspective views showing a conventional stacked electrode array. Figure 7 is another example of a schematic cross-sectional view along the line A-A' in Figure 1, showing an example of a conventional secondary battery equipped with a stacked electrode array. Figure 8 is a partial transmission diagram conceptually representing the movement of liquid in the secondary battery shown in Figure 7, representing the secondary battery from the same viewpoint as Figure 1.

[0022] Figure 9 is a schematic cross-section of an example of a secondary battery according to the first embodiment, and could be, for example, a cross-sectional view of the secondary battery shown in Figure 1. Figure 10 is a schematic cross-sectional view along the line B-B' in Figure 9. Figures 11 to 13 are schematic perspective views, schematic plan views, and schematic cross-sectional views, respectively, showing an example of an electrode group included in a secondary battery according to the first embodiment. Figure 13 is a cross-sectional view along the line C-C' in Figure 12. Figures 12 and 13 show the corresponding locations of the center thickness T1 and periphery thickness T2 of the electrode group.

[0023] The secondary batteries shown in the illustration are all sealed, rectangular batteries.

[0024] The secondary battery 100 includes an outer casing member 1, a group of flattened electrodes 2,200 or 210 housed within the outer casing member 1, and an electrolyte (not shown) held by the electrode group. The outer casing member 1 has a rectangular container 3 and a sealing plate 4 fixed to the opening of the rectangular container 3, for example, by welding. The rectangular container 3 may be, for example, a bottomed rectangular tubular container made of metal or an alloy.

[0025] In the illustrated example, the rectangular container 3 has a rectangular bottom wall 33 and two pairs of side walls that intersect the bottom wall 33. The bottom wall 33 is located on the opposite side of the sealing plate 4. The two pairs of side walls include a pair of main walls 31 that run along the long side of the bottom wall 33 as the first side walls, and a pair of second side walls 32 that run along the short side of the bottom wall 33. The pair of main walls 31 intersect the bottom wall 33 and the sealing plate 4. One and the other of the pair of main walls 31 face each other on the inner surface of the rectangular container 3. The pair of second side walls 32 intersect the bottom wall 33, the sealing plate 4, and the pair of main walls 31. One and the other of the pair of second side walls 32 face each other on the inner surface of the rectangular container 3. Each second side wall 32 connects one and the other of the pair of main walls 31.

[0026] The conventional wound electrode group 200 illustrated in Figure 2, the conventional laminated electrode group 210 illustrated in Figures 5 and 6, and the laminated electrode group 2 according to the first embodiment illustrated in Figures 11 to 13 all include a positive electrode 5, a negative electrode 6, and a separator 7, and include a laminate in which the positive electrode 5, negative electrode 6, and separator 7 are stacked with the separator 7 sandwiched between them. In each example, the positive electrode 5 includes a positive electrode current collector and a positive electrode active material-containing layer provided on the positive electrode current collector, and the negative electrode 6 includes a negative electrode current collector and a negative electrode active material-containing layer provided on the negative electrode current collector. The positive electrode current collector includes a positive electrode current collector tab 5a, which is the portion on which the positive electrode active material-containing layer is not provided, and the negative electrode current collector includes a negative electrode current collector tab 6a, which is the portion on which the negative electrode active material-containing layer is not provided.

[0027] The sealing plate 4 has a rectangular plate shape. The sealing plate 4 is provided with through holes, into which the positive terminal 15 and negative terminal 16 are inserted and attached to the sealing plate 4. The sealing plate 4 also has a liquid injection port 13. The sealing plate 4 may have only three through holes: the through holes for attaching the positive terminal 15 and negative terminal 16, and the liquid injection port 13. In this case, since the liquid injection port 13 also serves as a gas vent hole, there is no need to provide a separate gas vent hole. Therefore, there is an advantage in that the manufacturing process of the sealing plate 4 can be reduced. The liquid injection port 13 may also be provided on the wall of the rectangular container 3.

[0028] The electrolyte injection port 13 is also used to release gas generated inside the battery after the electrolyte has been injected through it. The electrolyte injection port 13 is sealed by a sealing lid 14. The sealing lid 14 has, for example, a disc shape. The sealing lid 14 is fixed to the surface of the sealing plate 4, for example, by welding. The sealing lid 14 is made of a metal such as aluminum or an aluminum alloy. Furthermore, the shape of the sealing lid 14 is not limited to a disc shape and can be appropriately changed according to the shape of the electrolyte injection port.

[0029] The positive terminal 15 and the negative terminal 16 may each have, for example, a plate-shaped head and a shaft extending from the head, as shown in Figure 9. The positive terminal 15 and the negative terminal 16 are fixed to the sealing plate 4 via an insulating gasket 17 and an insulating plate 18, respectively. The positive terminal 15 and the negative terminal 16 are also connected to the positive lead 25 and the negative lead 26, respectively. In detail, the insulating gasket 17 is placed in a recess on the outer surface of the sealing plate 4, and the insulating plate 18 is placed on the inner surface of the sealing plate 4. The shaft of the positive terminal 15 is inserted into the through-hole of the insulating gasket 17, the through-hole of the insulating plate 18, and the through-hole of the connecting plate of the positive lead 25, and is crimped and fixed to these components. The positive lead 25 further has a positive current collector tab 5a that extends from the connecting plate toward the electrode group and is electrically connected, for example, by welding. As a result, the positive terminal 15 is electrically connected to the positive current collector tab 5a via the positive lead 25. Similarly, the shaft portion of the negative terminal 16 is inserted into the through-hole of the insulating gasket 17, the through-hole of the insulating plate 18, and the through-hole of the connecting plate of the negative lead 26, and is crimped and fixed to these components. The negative lead 26 further has a current collector portion that extends from the connecting plate toward the electrode group and is electrically connected to the negative current collector tab 6a, for example by welding. As a result, the negative terminal 16 is electrically connected to the negative current collector tab 6a via the negative lead 26. The inside of the through-hole of the sealing plate 4 is covered by a portion of the insulating gasket 17.

[0030] The conventional secondary battery 100 shown in Figures 3 and 4 includes an electrode group 200 with a wound structure as shown in Figure 2. As shown in Figure 2, the flat electrode group 200 has a structure in which a laminate of a positive electrode 5 and a negative electrode 6 is wound in a flat shape with a separator 7 in between. The positive electrode 5 includes a strip-shaped positive electrode current collector made of, for example, metal foil, a positive electrode current collector tab 5a that is at one end parallel to the long side of the positive electrode current collector, and a positive electrode active material containing layer 5b formed on the positive electrode current collector except for the portion of the positive electrode current collector tab 5a. On the other hand, the negative electrode 6 includes a strip-shaped negative electrode current collector made of, for example, metal foil, a negative electrode current collector tab 6a that is at one end parallel to the long side of the negative electrode current collector, and a negative electrode active material containing layer 6b formed on the negative electrode current collector except for the portion of the negative electrode current collector tab 6a.

[0031] In this configuration, the positive electrode 5, separator 7, and negative electrode 6 are wound with their positions offset such that the positive electrode current collector tab 5a protrudes from the separator 7 in the direction of the winding axis of the electrode group, and the negative electrode current collector tab 6a protrudes from the separator 7 in the opposite direction. Due to this winding, as shown in Figure 2, the electrode group 200 has a spirally wound positive electrode current collector tab 5a protruding from one end face and a spirally wound negative electrode current collector tab 6a protruding from the other end face.

[0032] As shown in Figures 2 and 3, in the wound electrode group 200, two of the four flat end faces are curved surfaces formed by the main surfaces of the laminate of the positive electrode 5, negative electrode 6, and separator 7. The current collectors contained in the positive electrode 5 and negative electrode 6 are typically made of metal foil, and these current collectors are not permeable to liquid. Therefore, as shown in Figure 3, no liquid movement occurs, as indicated by arrow 90, which passes through the curved surface. As shown in Figure 4, the extrusion of electrolyte from the electrode group 200 is limited to the movement of liquid from the remaining two surfaces, namely the end face from which the positive electrode current collector tab 5a protrudes and the end face from which the negative electrode current collector tab 6a protrudes, as indicated by arrow 91.

[0033] As described above, batteries equipped with wound electrode groups experience relatively little electrolyte depletion in the electrode groups, and from that perspective, good battery life can be expected. However, the presence of curved portions of the electrode groups, which are the factor that suppresses electrolyte depletion, hinders the maximum utilization of space within the battery. Therefore, it can be said that there is a trade-off between battery life and battery capacity when using wound electrode groups.

[0034] Other conventional secondary batteries 100 shown in Figures 5 to 8 include a laminated electrode group 210. The flat electrode group 210 is a laminate having a rectangular main surface and includes a rectangular positive electrode 5, a rectangular negative electrode 6, and a separator 7 sandwiched between them. The positive electrode 5 includes a strip-shaped positive electrode current collector made of, for example, metal foil, a positive electrode current collector tab 5a which is a protruding portion on one side of the positive electrode current collector, and a positive electrode active material-containing layer formed on the positive electrode current collector except for the portion of the positive electrode current collector tab 5a. On the other hand, the negative electrode 6 includes a strip-shaped negative electrode current collector made of, for example, metal foil, a negative electrode current collector tab 6a which is a protruding portion on one side of the negative electrode current collector, and a negative electrode active material-containing layer formed on the negative electrode current collector except for the portion of the negative electrode current collector tab 6a.

[0035] The electrode group 210 may have a laminated structure, for example, as shown in Figure 5, in which multiple separators 7 are placed between alternately arranged positive electrodes 5 and negative electrodes 6. Alternatively, the electrode group 210 may have a laminated structure, as shown in Figure 6, in which a single separator 7 is folded in a zigzag pattern so as to meander between alternately arranged positive electrodes 5 and negative electrodes 6. The latter will be explained in more detail.

[0036] The stacked electrode group 2 shown in Figure 6 includes a strip-shaped separator 7 that is folded in a zigzag pattern. Strip-shaped positive electrodes 5 and negative electrodes 6 are alternately inserted into the space formed by the zigzag-folded separator 7 facing each other. Parts of the separator 7 are located on the outermost surface of the electrode group 2 on both sides in the stacking direction. The positive electrode current collector tab 5a of the positive electrode current collector and the negative electrode current collector tab 6a of the negative electrode current collector protrude from the electrode group 2 in the same direction. In the illustrated electrode group 210, in the stacking direction, the positive electrode current collector tabs 5a overlap with each other or the negative electrode current collector tabs 6a overlap, but the positive electrode current collector tab 5a and the negative electrode current collector tab 6a do not overlap. In this figure, the positive electrode 5 and negative electrode 6 are represented in a simplified manner, and detailed depictions of the active material-containing layer and the active material-carrying portion of the current collector are omitted.

[0037] Multiple positive electrode current collector tabs 5a can be joined together, for example. Similarly, multiple negative electrode current collector tabs 6a can be joined together. Multiple positive electrode current collector tabs 5a joined together can be electrically connected to the positive electrode terminal 15, for example, as shown in the example in Figure 9. Similarly, multiple negative electrode current collector tabs 6a joined together can be electrically connected to the negative electrode terminal 16, for example.

[0038] In the example shown in Figure 6, an electrode group 2 comprising two positive electrodes 5 and three negative electrodes 6 is illustrated. However, the number of positive electrodes 5 and negative electrodes 6 can be freely changed depending on the purpose and application. Furthermore, the protruding directions of the positive electrode current collector tabs 5a and negative electrode current collector tabs 6a from the electrode group 2 do not need to be the same as shown in the figure; for example, they may be in directions that form approximately 90° or approximately 180° relative to each other.

[0039] In the stacked electrode group 210, all four end faces of the rectangular shape can become liquid discharge surfaces. Therefore, as shown in Figures 7 and 8, both liquid extrusion from the long side (indicated by arrow 90) and liquid extrusion from the short side (indicated by arrow 91) can occur. While a structure in which rectangular electrodes are stacked is easy to match to the internal shape of a rectangular container and reduces dead space, such an electrode group is prone to liquid depletion. Therefore, using a conventional stacked electrode group results in a trade-off between lifespan performance and battery capacity, in the opposite sense to that of a wound electrode group.

[0040] The secondary battery 100 according to the first embodiment of the example shown in Figures 9 and 10 includes, for example, the electrode group 2 illustrated in Figures 11 to 13. Figure 10 is a cross-section of the secondary battery 100 shown in Figure 9 along the line B-B' as described above.

[0041] As shown in Figure 10, the main surface 20 of the electrode group 2 housed in the outer casing member 1 follows the pair of main walls 31 of the rectangular container 3. Here, the main walls 31 of the rectangular container 3 refer to the surfaces that intersect with the stacking direction of the electrode group 2. The main surface 20 of the electrode group 2 refers to the surfaces that intersect with the stacking direction, that is, the surfaces that intersect with the thickness direction of the flattened shape. In Figures 10 and 13, the stacking direction and thickness direction of the electrode group 2 are indicated as the first direction 10. At least one of the front and back sides of the main surface 20 of the electrode group 2 is not flat. In Figure 10, the central part of the main surface 20 on both sides is raised above the peripheral edges, but one of the main surfaces 20 on the front or back side may be flat. In each figure, the raised central part of the main surface of the electrode group 2 is exaggerated to make it visually clear that it is not flat.

[0042] The central parts of the main surfaces 20 on both the front and back sides of the flattened electrode group 2 are pressed against the inner surface of the main wall 31 of the rectangular container 3. In the illustrated example, each main wall 31 of the rectangular container 3 is pushed from the inside by the electrode group 2, causing the rectangular container 3 to deform by bulging in the thickness direction. Note that in Figure 10, the deformation of the main wall 31 of the rectangular container 3 is exaggerated to make it visually clearer.

[0043] The example of electrode group 2 in this example has a stacked structure similar to the electrode group 210 included in the conventional battery shown in Figures 5 and 6. Unlike the electrode group 210 illustrated in Figure 5, the stacked electrode group 2 described herein has a thickness in the stacking direction of the central portion of the main surface defined by two pairs of end faces that intersect each other along the stacking direction, which is thicker than the thickness in the stacking direction of the peripheral portion of the main surface. Specifically, the thickness T1 of the center of the surface in the first direction 10 and the peripheral thickness T2 are T1 > T2, and T1 > T2 AVE The relationship > 0.95 × T1 is satisfied. In addition, the thickness T1 at the center of the electrode group 2 is greater than the inner diameter IW in the direction intersecting the main wall 31 of the rectangular container 3, i.e., in the first direction 10. In the example in Figure 11, T1 > T2 is satisfied along all four end faces, but it is sufficient to satisfy T1 > T2 along one of the four end faces, and the relationship T1 ≥ T2 can be satisfied along the remaining three end faces.

[0044] The inner diameter IW of the rectangular container 3 corresponds to the distance between the inner surfaces of the main wall 31 along the inside of the bottom wall 33 on the opposite side of the opening where the sealing plate 4 is installed. As shown in the example in Figure 10, the main wall 31 of the rectangular container 3 is pushed outward from the inside by the electrode group 2, but in the part where the main wall 31 and the bottom wall 33 form a corner, the position of the corner is fixed by the bottom wall 33. Therefore, in the part along the bottom wall 33, the deformation of the main wall 31 is negligible, and the inner dimensions of the rectangular container 3 in the short side direction are kept constant.

[0045] The surface center thickness T1 is the thickness at the center 11 of the main surface 20 of the electrode group 2 when it is outside the rectangular container 3, as shown in Figure 12. The ratio of the surface center thickness T1 to the inner diameter IW of the rectangular container 3 can be within the range of 1 < T1 / IW < 1.07. In other words, the surface center thickness T1 can be as small as 1.07 times the inner diameter IW. Because the surface center thickness T1 is larger than the inner diameter IW of the rectangular container 3, the electrode group 2 is compressed when housed in the rectangular container 3. The center 11 of the main surface 20 is located at the intersection of the dashed line M that bisects the short side of the main surface 20 and the line C-C' that bisects the long side. The peripheral thickness T2 is the thickness at four locations that are 10% of the length L of the short side of the main surface 20, or 0.1L, inward from the center of the four end faces of the electrode group 2 toward the inside of the electrode group 2. In Figure 12, these four locations are indicated by points 12 that are 0.1L inward from the midpoints of the four sides. At least one of the four points 12, the peripheral thickness T2 toward the first direction 10 is thinner than the surface center thickness T1 toward the first direction 10. For example, as shown in Figure 13, the peripheral thickness T2 may be thinner than the surface center thickness T1 at two locations, and as shown in Figure 11, the peripheral thickness T2 may be thinner than the surface center thickness T1 at all four locations.

[0046] Figure 14 shows an example of a conventional secondary battery. The secondary battery 100 in the example shown in Figure 14 has an electrode group 21 whose thickness in the stacking direction, including the thickness T1 at the center of the surface, is generally smaller than the inner diameter IW of the rectangular container 3. In such a battery, the energy density is low because the volume occupied by the electrode group 21 within the rectangular container 3 is small, and gaps may be created between the electrodes when the electrodes in the electrode group 21 expand and contract during charging and discharging of the secondary battery 100. The creation of gaps within the electrode group 21 makes it easy for the electrolyte to move, and the electrolyte in the electrode group 21 is likely to deplete. Therefore, it is difficult to improve the lifespan performance of the secondary battery 100 in Figure 14.

[0047] Figure 15 shows another example of a conventional secondary battery. In the secondary battery 100 shown in Figure 15, not only is the center thickness T1 of the electrode group 22 smaller than the inner diameter IW of the rectangular container 3, but the peripheral thickness T2 is thicker than the center thickness T1 at least in two places. When the electrodes in the electrode group 22 expand and contract during charging and discharging of the secondary battery 100, the peripheral portion is pressed against the rectangular container 3, and the liquid held by the electrode group 22 can be pushed out. Since the liquid is pushed out from the part closer to the outer circumference of the electrode group 22, liquid movement to the outside of the electrode group 22 is likely to occur, and liquid depletion is likely to occur. Therefore, it is difficult to improve the lifespan performance of the secondary battery 100 in Figure 15.

[0048] In the secondary battery according to the first embodiment, as shown in some examples in Figures 9 to 13, the thickness of the electrode group 2 is made thinner near the outer edge than in the center, and the relationship between the thickness of the electrode group 2 and the inner dimensions of the rectangular container 3 is defined, thereby retaining the electrolyte in the electrode group 2 to obtain good lifespan performance, and making maximum use of the space inside the rectangular container 3 to obtain high energy density.

[0049] Some examples of electrodes that may be included in the electrode group of such a secondary battery are shown in Figures 16 to 19. Here, we do not distinguish between the positive electrode and the negative electrode. In other words, both the positive electrode and the negative electrode can have the structure shown in each figure.

[0050] The electrode 8 shown in Figures 16 and 17 includes a plate-shaped current collector 8c with a current-collecting tab 8a, and a rectangular-shaped active material-containing layer 8b provided on both the front and back surfaces of the current collector 8c, excluding the portion with the current-collecting tab 8a. In the electrode 8 illustrated in Figures 16 and 17, the thickness of the active material-containing layer 8b is thinner in the portion along one side than in the center. In the example shown in Figure 16, the current-collecting tab 8a protrudes outward in both directions from a pair of opposite ends of the active material-containing layer 8b, and the active material-containing layer 8b is thinner along one of these ends. In the example shown in Figure 17, the current-collecting tab 8a protrudes outward from an end along one side of the active material-containing layer 8b, and the active material-containing layer 8b is thinner along this end. In both figures, the active material-containing layer 8b provided on both sides of the current collector 8c is partially thinned, but the active material-containing layer 8b may also be partially thinned on only one side of the current collector 8c. Furthermore, in Figure 16, the current collection tabs 8a protruding from both sides extend along the entire length of their protruding surfaces, while in Figure 17, the current collection tab 8a protruding from one side is punched out and exists only in a part of that side. However, the form of the current collection tab 8a is not limited to the examples shown.

[0051] For example, by stacking electrodes 8, as illustrated in Figure 16 or Figure 17, together with a separator as the positive and / or negative electrodes to construct a stacked electrode group, and stacking multiple electrodes 8 in the same orientation, an electrode group can be obtained in which the peripheral thickness T2 at one of the four sides is thinner than the thickness T1 at the center of the surface. Alternatively, by stacking multiple electrodes 8 alternately in opposite orientations, an electrode group can be obtained in which the peripheral thickness T2 at two of the four sides is thinner than the thickness T1 at the center of the surface.

[0052] Similarly, the electrode 8 shown in Figures 18 and 19 includes a plate-shaped current collector 8c with a current collector tab 8a, and a rectangular active material-containing layer 8b provided on both the front and back surfaces of the current collector 8c, excluding the portion with the current collector tab 8a. However, in the electrode 8 illustrated in Figures 18 and 19, the thickness of the active material-containing layer 8b is thinner along two sides of the active material-containing layer 8b than in the central part. In Figures 18 and 19, the active material-containing layer 8b is thinner on the opposite side in addition to the side where it was thinner in Figures 16 and 17. In Figures 18 and 19 as well, the active material-containing layer 8b may be partially thinner on only one side of the current collector 8c, and the shape of the current collector tab 8a is not limited to the illustrated example. For example, by stacking electrodes 8, as illustrated in Figure 17 or Figure 18, together with a separator as the positive and / or negative electrodes to construct a stacked electrode group, and stacking multiple electrodes 8 in the same orientation, an electrode group can be obtained in which the peripheral thickness T2 at two of the four sides is thinner than the center thickness T1.

[0053] The shapes of the positive and negative electrodes included in the electrode group are not limited to the examples above. For example, in Figures 16 to 19, the portion of the current-collecting tab along the edge protruding from the end of the active material-containing layer was included in the area of ​​the periphery where the thickness was thinner than the thickness of the center, but it is also possible that only the portion corresponding to the end where the current-collecting tab does not protrude is thinner. Furthermore, the end from which the current-collecting tab protrudes is not limited to the end on the longer side.

[0054] The following provides a detailed explanation of the negative electrode, positive electrode, electrolyte, separator, outer casing, negative electrode terminal, and positive electrode terminal.

[0055] 1) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer provided on the negative electrode current collector. The negative electrode active material-containing layer may be formed on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer may optionally include a negative electrode active material and a conductive agent and a binder.

[0056] The negative electrode active material-containing layer contains a negative electrode active material. The negative electrode active material contained in the negative electrode active material-containing layer may include, for example, a carbonaceous active material, a titanium oxide, a lithium titanate, a niobium oxide, or a titanium niobium composite oxide. In particular, the titanium niobium composite oxide is a high-capacity active material and has lower electron conductivity than the carbonaceous active material. Therefore, when using the titanium niobium composite oxide as the negative electrode active material, the energy density and the effect of extending the life according to the configuration of the present application of the embodiment can be obtained, which is preferable. This titanium niobium composite oxide may include, for example, a titanium niobium composite oxide having a monoclinic crystal structure and a titanium niobium composite oxide having an orthorhombic crystal structure.

[0057] Examples of the titanium niobium composite oxide having a monoclinic crystal structure include compounds represented by Li a Ti 1-x M1 x Nb 2-y M2 y O 7-δ In the general formula Li a Ti 1-x M1 x Nb 2-y M2 y O 7-δ where the subscript a is in the range of 0 ≦ a < 5, the subscript x is in the range of 0 ≦ x < 1, the subscript y is in the range of 0 ≦ y < 1, and the subscript δ is in the range of -0.3 ≦ δ ≦ 0.3. The elements M1 and M2 are each at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The elements M1 and M2 are the same or different from each other. As the titanium niobium composite oxide, it is preferable to include the above Li a Ti 1-x M1 x Nb 2-y M2 y O 7-δ Specific examples include Li a Nb2TiO7 (0 ≦ a < 5).

[0058] The titanium niobium composite oxide may include a titanium niobium composite oxide having an orthorhombic crystal structure. Examples of the titanium niobium composite oxide having an orthorhombic crystal structure include Li 2+a Na2-b M3 c Ti 6-d-e Nb d M4 e O 14+σ Examples of the compound represented by the general formula Li 2+a Na 2-b M3 c Ti 6-d-e Nb d M4 e O 14+σ are as follows. In the general formula Li

[0059] The negative electrode active material-containing layer may contain, for example, one kind of titanium niobium composite oxide alone. Alternatively, the negative electrode active material-containing layer may contain two or more different negative electrode active materials. For example, the negative electrode active material-containing layer may contain both monoclinic titanium niobium composite oxide and orthorhombic titanium niobium composite oxide. Further, in addition to one kind of titanium niobium composite oxide or two or more kinds of titanium niobium composite oxides, the negative electrode active material-containing layer may contain one kind of other titanium-containing oxide, or may contain two or more kinds of other titanium-containing oxides. Examples of other titanium-containing oxides include lithium titanate having a ramsdellite structure (e.g., Li 2+y Ti3O7, 0 ≦ y ≦ 3), lithium titanate having a spinel structure (e.g., Li 4+x Ti5O 12 , 0 ≦ x ≦ 3), titanium dioxide (TiO2), anatase-type titanium dioxide, rutile-type titanium dioxide, niobium pentoxide (Nb2O5), and hollandite-type titanium composite oxide. The content of the titanium niobium composite oxide with respect to the total mass of the negative electrode active material in the negative electrode active material-containing layer is preferably 50% by mass or more and 100% by mass or less.

[0060] Conductive agents are added to enhance current collection performance and reduce contact resistance between the negative electrode active material and the negative electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanofibers, and carbon nanotubes. One of these may be used as a conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with a carbon coating or an electronically conductive inorganic material coating.

[0061] A binder is added to fill the gaps between dispersed negative electrode active materials and to bond the negative electrode active materials to the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber (SBR), acrylic resin, copolymers of acrylic resins, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0062] In the negative electrode active material-containing layer, it is preferable to blend the negative electrode active material, conductive agent, and binder in proportions of 70% to 96% by mass, 2% to 28% by mass, and 2% to 28% by mass, respectively. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. As a result, high current output performance can be expected. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient bonding between the negative electrode active material-containing layer and the negative electrode current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amount of conductive agent and binder to 28% by mass or less, respectively, in order to achieve high capacity.

[0063] The negative electrode current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and removed from the negative electrode active material. It is preferable that the negative electrode current collector contains aluminum. Specifically, it is preferable that the negative electrode current collector is made of aluminum or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the negative electrode current collector is preferably 5 μm to 20 μm. A negative electrode current collector with such a thickness can balance the strength of the negative electrode with weight reduction.

[0064] Furthermore, the negative electrode current collector may include portions on its surface where the negative electrode active material-containing layer is not formed. These portions can function as negative electrode current collector tabs.

[0065] The density of the negative electrode active material layer (excluding the current collector) is 1.8 g / cm³. 3 More than 2.8g / cm 3 The following is preferable. A negative electrode with a density of the negative electrode active material-containing layer within this range exhibits excellent energy density and electrolyte retention. The density of the negative electrode active material-containing layer is 2.1 g / cm³. 3 More than 2.6g / cm 3 The following is more preferable:

[0066] 2) Positive electrode The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer provided on the positive electrode current collector. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may optionally include a positive electrode active material and a conductive agent and a binder.

[0067] For example, oxides or sulfides can be used as the positive electrode active material. The positive electrode may contain one compound alone or a combination of two or more compounds as the positive electrode active material. Examples of oxides and sulfides include compounds that can insert and remove Li or Li ions.

[0068] Examples of such compounds include, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium nickel manganese composite oxide having a spinel structure (e.g., Li x Ni y Mn 2-y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≦ 1, Li x MnPO4; 0 < x ≦ 1, Li x Mn 1-y Fe y PO4; 0 < x ≦ 1, 0 < y ≦ 1, Li x CoPO4; 0 < x ≦ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included.

[0069] Among the above, examples of more preferred compounds as the positive electrode active material include lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li xCoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium nickel manganese composite oxide having a spinel structure (e.g., Li x Ni y Mn 2-y O4; 0 < x ≤ 1, 0 < y < 2), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; 0 < x ≤ 1), lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1), and lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≤ 1, Li x MnPO4; 0 < x ≤ 1, Li x Mn 1-y Fe y PO4; 0 < x ≤ 1, 0 < y ≤ 1, Li x CoPO4; 0 < x ≤ 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased. As specific examples, a positive electrode active material containing one or more selected from the group consisting of the above lithium manganese composite oxide, lithium cobalt composite oxide, lithium nickel cobalt manganese composite oxide, lithium phosphate, and lithium nickel manganese composite oxide can be mentioned.

[0070] When a room temperature molten salt is used as the electrolyte of the battery, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li x VPO4F (0 ≤ x ≤ 1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. Since these compounds have low reactivity with the room temperature molten salt, the cycle life can be improved. Details of the room temperature molten salt will be described later.

[0071] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. The positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. The positive electrode active material with a primary particle size of 1 μm or less can smoothly progress the solid-state diffusion of lithium ions.

[0072] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. The positive electrode active material having a specific surface area of 0.1 m 2 / g or more can sufficiently secure the Li ion intercalation and deintercalation sites. The positive electrode active material having a specific surface area of 10 m 2 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0073] The binder is blended to fill the gaps between the dispersed positive electrode active materials and to bind the positive electrode active material and the positive electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, styrene-butadiene rubber (SBR), polyacrylic acid compound, imide compound, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more of them may be combined and used as the binder.

[0074] Conductive agents are added to enhance current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, graphene, carbon nanofibers, and carbon nanotubes. One of these may be used as a conductive agent, or two or more may be used in combination. Conductive agents may also be omitted.

[0075] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0076] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, reducing the binder amount to 20% by mass or less reduces the amount of insulator contained in the electrode, thereby reducing internal resistance.

[0077] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0078] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0079] The positive electrode current collector preferably contains aluminum. Specific examples of preferred positive electrode current collectors include aluminum foil and aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0080] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0081] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode active material-containing layer is not formed. These portions can function as positive electrode current collector tabs.

[0082] 3) Electrolytes As the electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0083] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0084] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); and γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0085] Gel-like non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0086] Alternatively, in addition to liquid non-aqueous electrolytes and gel-type non-aqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions may be used as non-aqueous electrolytes.

[0087] Room temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as liquids at room temperature (15°C to 25°C). Room temperature molten salts include room temperature molten salts that exist as liquids on their own, room temperature molten salts that become liquid when mixed with an electrolyte salt, room temperature molten salts that become liquid when dissolved in an organic solvent, or mixtures thereof. Generally, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. Also, organic cations generally have a quaternary ammonium skeleton.

[0088] In addition, polymer solid electrolytes and inorganic solid electrolytes may be used as non-aqueous electrolytes together with the liquid electrolytes mentioned above.

[0089] Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and then solidifying it.

[0090] Inorganic solid electrolytes are solid materials that have lithium ion conductivity. Here, "having lithium ion conductivity" means that at 25°C, they have a conductivity of 1 × 10⁻⁶. -6 This refers to exhibiting a lithium ion conductivity of S / cm or higher. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows.

[0091] As an oxide-based solid electrolyte, it has a NASICON (Sodium (Na) Super Ionic Conductor) type structure, and its general formula is Li 1+x It is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. In the above general formula, Mα is one or more selected from the group consisting of, for example, titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is in the range of 0 ≤ x ≤ 2.

[0092] A specific example of a lithium phosphate solid electrolyte having a NASICON-type structure is Li 1+x Al x Ti2-x The LATP compound represented by (PO4)3 with 0.1 ≦ x ≦ 0.5; Li 1+x Al y Mβ 2-y The compound represented by (PO4)3 where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca and 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1; Li 1+x Al x Ge 2-x The compound represented by (PO4)3 with 0 ≦ x ≦ 2; and, Li 1+x Al x Zr 2-x The compound represented by (PO4)3 with 0 ≦ x ≦ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 The compound represented by where Mγ is one or more selected from the group consisting of Ti and Ge and 0 < x ≦ 2, 0 ≦ y < 3; Li 1+2x Zr 1-x Ca x Examples of the compound represented by (PO4)3 with 0 ≦ x < 1 can be given.

[0093] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, Li x PO y [[ID=-45]]N z The amorphous LIPON compound represented by with 2.6 ≦ x ≦ 3.5, 1.9 ≦ y ≦ 3.8, and 0.1 ≦ z ≦ 1.3 (for example, Li 2.9 PO 3.3 N 0.46 ); The garnet-type structure La 5+x A x La 3-x Mδ2O 12 The compound represented by where A is one or more selected from the group consisting of Ca, Sr, and Ba and Mδ is one or more selected from the group consisting of Nb and Ta and 0 ≦ x ≦ 0.5; Li3Mδ 2-x L2O 12 The compound represented by where Mδ is one or more selected from the group consisting of Nb and Ta and L may contain Zr and 0 ≦ x ≦ 0.5; Li 7-3x Al x La3Zr3O12 Compounds represented by 0 ≤ x ≤ 0.5; Li 5+x La3MCSR 2-x Zr x O 12 Represented by , where Mδ is 1 or more selected from the group consisting of Nb and Ta, and 0 ≤ x ≤ 2, it is an LLZ compound (e.g., Li7La3Zr2O 12 ); and having a perovskite-type structure La 2 / 3-x Li x Examples include compounds represented as TiO3 where 0.3 ≤ x ≤ 0.7.

[0094] One or more of the above compounds can be used as a solid electrolyte. Two or more of the above solid electrolytes may also be used.

[0095] 4) Separator The separator is formed from a porous film containing, for example, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), cellulose, or polyvinylidene fluoride (PVdF), or from a synthetic resin nonwoven fabric. From a safety standpoint, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and interrupt the electric current. Furthermore, it is preferable that inorganic oxide particles are present on one or both sides of the porous film.

[0096] 5) Exterior components The exterior components include a rectangular container. For example, a metal container, including a rectangular container made of metal, can be used as the exterior components. The exterior components may include a lid for the opening of the rectangular container, such as a metal sealing plate.

[0097] The wall thickness of the rectangular container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less. The preferred lower limit for the wall thickness is 0.1 mm.

[0098] The metal container is made from, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content is preferably 100 ppm by mass or less. Batteries equipped with such metal containers can dramatically improve long-term reliability and heat dissipation in high-temperature environments. Specific examples include exterior components including rectangular containers made of aluminum metal cans and rectangular containers made of aluminum alloy cans.

[0099] 6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the Li absorption / release potential of the negative electrode active material described above, and is also conductive. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use aluminum or an aluminum alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0100] 7) Positive terminal The positive terminal has a potential range of 3V to 4.5V relative to the oxidation-reduction potential of lithium (vs.Li / Li + The positive electrode terminal can be formed from an electrically stable and conductive material. Examples of positive electrode terminal materials include aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0101] <Manufacturing method> The secondary battery according to the first embodiment can be manufactured, for example, as follows:

[0102] Prepare a negative electrode, a positive electrode, and a separator. The negative electrode and positive electrode can be manufactured, for example, as follows.

[0103] Electrodes can be manufactured, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. The slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a composite in which the active material-containing layer and the current collector are laminated. Then, this composite is pressed. In this way, electrodes are manufactured. The size of the electrodes can be adjusted by cutting or punching as needed.

[0104] Alternatively, electrodes may be manufactured by the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, electrodes can be obtained by placing these pellets on a current collector. The size of the electrodes can be adjusted by cutting or punching them as needed.

[0105] By appropriately controlling the conditions in the above electrode fabrication method, it is possible to obtain an electrode in which the active material-containing layer is thinner on at least one side than in the central part, or to obtain an electrode in which the active material-containing layer has a uniform thickness throughout. For example, by using a slit coater to apply slurry to the current collector and adjusting the thickness of the shim to make the slit width of the slit die different at the center and the edges, the amount of slurry applied to the center and the edges of the current collector can be changed, making the coating thicker in the center. Alternatively, the distribution of pellets placed on the current collector can be increased in the center and decreased at the edges. By making the amount of slurry applied and the distribution of pellets on the current collector uniform, it is possible to form an active material-containing layer with no difference in thickness between the central and surrounding parts.

[0106] Furthermore, the thickness distribution of the active material-containing layer can also be controlled by the method of pressing the composite of the active material-containing layer and the current collector. For example, if a coating film formed from a slurry applied with a uniform amount is pressed uniformly, an electrode with a uniform thickness of the active material-containing layer can be obtained. However, if the same coating film is pressed with the pressing surface inclined, an active material-containing layer containing parts of varying thickness can be obtained. In addition, the formation of a coating film with uneven thickness may be combined with uneven pressing. For example, as illustrated in Figure 20, a thin coating film can be formed along one side of the active material-containing layer 8b, and the pressing can be performed by setting an angle in the direction of the axis of the press roll 80 so that the other side becomes thinner after pressing.

[0107] The prepared negative electrode and positive electrode are stacked in the order of separator, negative electrode, separator, positive electrode to obtain a laminate. For example, one separator can be folded into a zigzag pattern, or multiple strip-shaped separators can be used, one by one sandwiched between the positive and negative electrodes. The resulting laminate can then be subjected to a press process to obtain a flattened laminated electrode group.

[0108] To obtain an electrode group where the peripheral thickness T2 at one of the four locations near the periphery is thinner than the surface center thickness T1, for example, electrodes with a reduced thickness along one side of the active material-containing layer, as shown in Figures 16 and 17, can be used as at least one of the positive and negative electrodes, and the electrodes can be stacked with the positions of the reduced edges aligned. Alternatively, a laminate can be obtained using flat positive and negative electrodes together with a separator, and a press treatment can be performed along one side of the resulting laminate. To obtain an electrode group where the peripheral thickness T2 at two of the four locations near the periphery is thinner than the surface center thickness T1, for example, electrodes with a reduced thickness along one side of the active material-containing layer, as shown in Figures 18 and 19, can be used as at least one of the positive and negative electrodes, and the electrodes can be stacked with the positions of the reduced edges aligned. Alternatively, electrodes with a reduced thickness along one side of the active material-containing layer, as shown in Figures 16 and 17, can be used as at least one of the positive and negative electrodes, and the electrodes can be stacked with the positions of the reduced edges partially differing. Alternatively, a laminate may be obtained using flat positive and negative electrodes together with a separator, and then press-formed along two sides of the resulting laminate. Similarly, when obtaining an electrode group in which the peripheral thickness T2 at three or all of the four locations near the periphery is thinner than the thickness T1 at the center of the surface, the laminate may be constructed by appropriately adjusting the locations to be thinned and their arrangement during electrode fabrication, or press-formed along three or four sides of the laminate obtained using flat electrodes. As a specific example, as shown in Figure 21, the peripheral portion 19 can be pressed to obtain an electrode in which the peripheral thickness T2 at all four locations is thinner than the thickness T1 at the center of the surface.

[0109] Another method involves stacking an insulating member, which has a smaller surface dimension than the electrodes, on the outermost part of the electrode group. As shown in Figure 22, by providing an insulating member 9 in the center of the top surface in the stacking direction of the electrode group 2, or by providing an insulating member 9 in the center of both the top and bottom surfaces, the thickness T1 at the center of the electrode group 2 can be increased. As the insulating member 9, for example, a Kapton tape or a piece of the same material as the separator 7 can be used. For example, the thickness T1 at the center of the surface can be adjusted by stacking multiple pieces of Kapton tape or separator 7 to construct the insulating member 9.

[0110] Before inserting the electrode group into the rectangular container, weld the leads connected to the positive and negative electrode terminals on the lid of the outer casing to the current collectors of the positive and negative electrodes. For example, weld the corresponding leads to the current collector tabs. After inserting the electrode group with the welded leads into the rectangular container, weld the lid with the electrode terminals to the rectangular container. At this time, to prevent damage to the electrode group, a protective member, such as an electrode guard, may be used when inserting the electrode group into the rectangular container.

[0111] A spout for introducing liquid electrolyte is provided in either the rectangular container or the lid. The electrolyte is prepared and introduced through the spout. It is preferable to dry the outer casing before adding the electrolyte. Vacuum drying is more preferable. After introducing the electrolyte, the spout is sealed with a sealing lid and welded shut. At this time, it is necessary to ensure that no electrolyte is adhering to the spout.

[0112] The rectangular battery assembled as described above is restrained using a restraint device such as a resin or metal plate, and then charged and discharged. At this time, at least the central part of the main wall of the rectangular container is pressed down from both the front and back sides. The initial charge is performed to 100% state of charge (SOC). Specifically, the initial charge is performed to the rated charging voltage, or at a voltage 0.1 V higher than the rated charging voltage. Following the initial charge, aging is performed. Aging is performed after adjusting the battery from SOC 70% to 100% SOC, in an environment of 50°C to 80°C for 3 to 72 hours.

[0113] The electrode group can swell and expand as the liquid electrolyte seeps in. Furthermore, during charging and discharging, charge carrier ions are inserted into and removed from the negative electrode active material, causing the active material to expand and contract, which can result in the electrode group expanding. For example, when a negative electrode containing a titanium-niobium composite oxide is used as the negative electrode active material, the titanium-niobium composite oxide expands during charging. Although the titanium-niobium composite oxide itself contracts during discharge, the negative electrode as a whole remains expanded with increased distance between the active material particles. By applying constraint from the outside of the rectangular container during this expansion of the electrode group due to charging and discharging, it is possible to achieve a state where the electrode group is pressed against the inner surface of the rectangular container.

[0114] As the electrode group is compressed by the inner surface of the rectangular container, in an electrode group containing multiple electrodes where the active material-containing layer is thinned in the peripheral portion along one or more sides, the electrodes are compressed to fill the gaps between the electrodes in that peripheral portion. As a result, the overall thickness of the portion of the electrode group corresponding to the peripheral portion of the electrodes becomes thinner. Thus, the difference between the thickness T1 at the center of the surface and the peripheral thickness T2 does not depend solely on the thickness distribution of the outermost layer of the laminated structure.

[0115] By appropriately adjusting the relationship between the dimensions of the electrode group and the inner dimensions of the rectangular container when inserting the electrode group into the rectangular container, and by adjusting the charge and discharge conditions, the degree of expansion of the electrode group, and consequently the thickness T1 at the center and the thickness T2 around the edge of the surface after the electrode group is removed, can be controlled. When the distance between the thickness of the electrode group at insertion and the inner surface of the main wall of the rectangular container is small, the expanded electrode group tends to adhere closely to the inner surface of the rectangular container. However, from the viewpoint of avoiding scratching and damaging the surface with the edge of the rectangular container when inserting the electrode group, it is preferable to ensure a certain clearance. In addition, increasing the charging voltage and lowering the negative electrode potential further increases the expansion rate of the negative electrode active material, allowing the electrode group to expand more. It is known that lithium titanium oxide having a spinel structure does not expand or contract with charge and discharge, but it is preferable to use a compound that expands and contracts significantly with charge and discharge, such as the titanium niobium composite oxide mentioned above, as the negative electrode active material.

[0116] <Measurement method> The following describes various measurement methods for secondary batteries. Specifically, the methods for measuring the inner diameter IW of the prismatic container of the secondary battery, the methods for measuring the center thickness T1 and periphery thickness T2 of the electrode group, and the methods for measuring the electrode active material will be described.

[0117] The secondary batteries to be measured must be new or equivalent in condition. "New or equivalent in condition" here means a battery that maintains 95% or more of its rated capacity. Therefore, in order to determine whether the battery in question is suitable for measurement, the battery's capacity must first be checked.

[0118] (Method for measuring the inner diameter IW of a rectangular container) The inner diameter IW of a rectangular container can be measured with the electrode group still inside. First, the secondary battery is discharged. Discharged state here refers to a state in which the battery is discharged at a constant current value of 0.2C or less at a 25°C environment down to the lower discharge voltage limit. A computed tomography scan, or CT scan, is performed on the discharged battery. From the obtained imaging data, the distance between the main walls along the inside of the bottom wall of the rectangular container, located on the opposite side of the sealing plate or opening, is determined. The determined distance is recorded as the inner diameter IW of the rectangular container.

[0119] (Method for measuring the center thickness T1 and periphery thickness T2 of an electrode group) The thickness of the electrode group is measured with the electrode group removed from the rectangular container and placed outside.

[0120] As described above, the discharged battery is placed in a glove box with an inert atmosphere, for example, a glove box filled with argon gas. Next, the battery is disassembled inside the glove box, and the electrode group is removed from the outer casing. Specifically, inside the glove box, taking care not to short-circuit the positive and negative electrodes, the rectangular container and the sealing plate are separated at the welded joint. The electrode group is then pulled out together with the sealing plate.

[0121] The surface of the electrode group, removed from the outer casing, is washed with a solvent such as methyl ethyl carbonate (MEC). This washing removes any Li salts adhering to the surface of the electrode group. After that, the electrode group is dried. Alternatively, for convenience during measurement, the electrode group may be removed from the sealing plate and electrode terminals.

[0122] The thickness of the cleaned electrode group is measured with a micrometer at five locations: the center 11 of the main surface 20 and points 12 near the midpoints of the four sides, as shown in Figure 12. In this way, the thickness T1 at the center of the surface and the four perimeter thicknesses T2 are determined. The average of the four perimeter thicknesses T2 is then calculated to obtain the average value T2. AVE We seek.

[0123] (Method for measuring active material) The composition of the active material contained in the electrode can be determined by measuring as described below.

[0124] Electrodes are removed from the electrode group to obtain a sample for measurement. For example, the electrode electrically connected to the negative electrode terminal is cut out to obtain a negative electrode sample. Alternatively, the electrode electrically connected to the positive electrode terminal is cut out to obtain a positive electrode sample. The removed electrodes are washed with, for example, methyl ethyl carbonate (MEC) solvent. This washing removes Li salts adhering to the electrode surface, and then the electrodes are dried.

[0125] By using the obtained electrodes as samples and combining elemental analysis using a scanning electron microscope (SEM-EDX) equipped with an energy-dispersive X-ray analyzer, X-ray diffraction (XRD) measurement, and inductively coupled plasma (ICP) emission spectroscopy, the composition of the active material contained in the electrode, for example, the active material-containing layer, can be confirmed. SEM-EDX analysis allows us to determine the shape of the components contained in the active material-containing layer and the composition of the components contained in the active material-containing layer (each element from B to U in the periodic table). ICP measurement allows for the quantification of elements in the active material-containing layer. XRD measurement allows us to confirm the crystal structure of the material contained in the active material-containing layer.

[0126] The cross-section of the electrode extracted as described above is cut out by Ar ion milling. The cut-out cross-section is observed using a scanning electron microscope (SEM). Sample sampling is also carried out in an inert atmosphere such as argon or nitrogen, without exposure to air. Several particles are selected from the 3000x SEM image. At this time, the selection is made so that the particle size distribution of the selected particles is as broad as possible.

[0127] Next, elemental analysis is performed on each selected particle using EDX. This allows us to identify the types and amounts of elements other than Li contained in each selected particle.

[0128] Regarding Li, information about the Li content in the entire active material can be obtained by ICP emission spectroscopy. ICP emission spectroscopy is performed according to the following procedure.

[0129] From the dried electrodes, a powder sample is prepared as follows: The active material-containing layer is peeled off the current collector and ground in a mortar. The ground sample is dissolved in acid to prepare a liquid sample. Hydrochloric acid, nitric acid, sulfuric acid, or hydrogen fluoride can be used as the acid. By subjecting this liquid sample to ICP emission spectroscopy, the concentrations of elements contained in the active material being measured can be determined.

[0130] The crystal structure of the compound contained in each particle selected by SEM can be determined by XRD measurement. The XRD measurement is performed using CuKα radiation as the source in the measurement range of 2θ = 5° to 90°. This measurement allows us to obtain the X-ray diffraction pattern of the compound contained in the selected particle.

[0131] For XRD measurements, we will use the Rigaku SmartLab. The measurement conditions will be as follows: X-ray source: Cu target Output: 45kV, 200mA Solar slit: 5° for both incident and received light. Step size (2θ): 0.02deg Scan speed: 20deg / min Semiconductor detector: D / teX Ultra 250 Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm) Measurement range: 5° ≤ 2θ ≤ 90°.

[0132] If other equipment is used, measurements should be performed using standard Si powder for powder X-ray diffraction to find conditions that yield peak intensity, full width at half maximum, and diffraction angle equivalent to those obtained with the above equipment, and then the sample should be measured under those conditions.

[0133] The XRD measurement conditions should be such that an XRD pattern suitable for Rietveld analysis can be obtained. Specifically, to collect data for Rietveld analysis, the step size should be set to 1 / 3 to 1 / 5 of the minimum full width at half maximum of the diffraction peak, and the measurement time or X-ray intensity should be adjusted as appropriate so that the intensity at the peak position of the most intense reflection is 5000 cps or more.

[0134] The XRD patterns obtained as described above are analyzed using the Rietveld method. In the Rietveld method, the diffraction pattern is calculated from a pre-estimated crystal structure model. The crystal structure model is estimated here based on the analysis results from EDX and ICP. By fitting all of these calculated values ​​with the measured values, parameters related to the crystal structure (lattice constants, atomic coordinates, occupancy, etc.) can be precisely analyzed.

[0135] Rietveld analysis can be used to estimate the content of titanium niobium composite oxide, for example, when the negative electrode contains multiple active materials. A fitting parameter S is used as a measure to estimate the degree of agreement between the observed intensity and the calculated intensity in Rietveld analysis. The analysis must be performed so that S is less than 1.8. In addition, the standard deviation σj must be taken into consideration when determining the occupancy rate of each site. The fitting parameter S and standard deviation σj defined here shall be estimated using the formula described in Non-Patent Literature 1 ("Practical Aspects of Powder X-ray Analysis," edited by the X-ray Analysis Research Group of the Japan Society for Analytical Chemistry, Izumi Nakai and Fujio Izumi (Asakura Shoten)).

[0136] XRD measurements can be performed by directly attaching the electrode sample to the glass holder of a wide-angle X-ray diffractometer. In this process, it is necessary to pre-measure the XRD spectrum according to the type of metal foil used for the electrode current collector to determine where peaks originating from the current collector appear. It is also important to pre-determine the presence or absence of peaks from conductive agents and binders. If the current collector peak and the active material peak overlap, it is desirable to peel the active material-containing layer from the current collector before measurement. This is to separate the overlapping peaks when quantitatively measuring the peak intensity. Of course, if these factors are known in advance, this step can be omitted.

[0137] If the particles observed by the previous SEM-EDX measurement contain Ti, Nb, and O, and furthermore, if the previous XRD measurement yields an X-ray diffraction pattern attributed to a monoclinic type from the electrode being measured, it indicates that the active material being measured contains particles of monoclinic titanium-niobium composite oxide. If the EDX measurement reveals particles with significantly different Ti and Nb content, it is possible that multiple active materials are present. The amount of elements contained in the active material in the electrode can be determined by ICP emission spectroscopy following the procedure described above.

[0138] The content of titanium niobium composite oxide in the active material-containing layer can be estimated by the following method.

[0139] After cleaning and drying the electrodes removed from the battery using the procedure described earlier, the active material-containing layer is peeled off the current collector and ground in a mortar. The ground sample is placed on a glass sample plate and leveled so that the surface of the sample matches the surface of the glass sample plate. A Si standard sample may also be added to correct the peak position.

[0140] XRD measurements and Rietveld analysis are performed on the powder sample packed into a glass sample plate under the conditions described above. SEM-EDX measurements and ICP measurements are also performed on the powder sample using the procedure described above. Considering the results of the XRD, SEM-EDX, and ICP measurements, the types and proportions of active materials present can be estimated.

[0141] The secondary battery according to the first embodiment comprises an electrode group, a liquid electrolyte, and an outer casing member. The electrode group includes a laminate containing a positive electrode and a negative electrode, and has a flattened, wound structure with two pairs of end faces that intersect each other along the lamination direction. The outer casing member includes a rectangular container that houses the electrode group and the electrolyte. The rectangular container has a pair of main walls that intersect with the lamination direction of the electrode group. The thickness of the center surface of the electrode group outside the rectangular container is greater than the inner diameter in the direction intersecting with the main walls of the rectangular container. The periphery thickness at a position 10% inward from the center of at least one end face relative to the length of the short side is thinner than the center surface thickness, and the average value of the periphery thickness and the center surface thickness satisfy the relationship "average value of periphery thickness > 0.95 × center surface thickness". According to the above configuration, it is possible to provide a secondary battery and battery pack that exhibit good life performance and high energy density.

[0142] (Second embodiment) According to a second embodiment, a battery pack is provided. This battery pack comprises a secondary battery according to the first embodiment. This battery pack may comprise one secondary battery according to the first embodiment, or it may comprise multiple secondary batteries according to the first embodiment. Multiple secondary batteries may constitute a battery pack.

[0143] The battery pack may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) may be used as the protection circuit for the battery pack.

[0144] Furthermore, the battery pack may also be equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and / or for inputting current from an outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals.

[0145] Next, an example of such a battery pack will be explained with reference to the drawings.

[0146] Figure 23 is a block diagram showing an example of the electrical circuit of a battery pack according to this embodiment.

[0147] The illustrated battery pack 300 comprises a battery pack 23, a printed circuit board 340, and wiring 330. Although not shown, the battery pack 300 may further include a housing container and a lid capable of housing the battery pack 23, the printed circuit board 340, and the wiring 330. The housing container may be, for example, a bottomed rectangular container having a rectangular base. The lid may have, for example, a rectangular shape. The lid houses the battery pack 23, etc., by covering the housing container. The housing container and lid may be provided with openings or connection terminals for connecting to external devices, etc.

[0148] The battery pack 300 may also include one or more protective sheets housed in a container together with the battery pack 23, etc. The protective sheets are, for example, placed between the battery pack 23 and the wall of the container. The protective sheets are made of, for example, resin or rubber.

[0149] The battery pack 23 comprises multiple individual cells 100, a positive electrode lead 27, a negative electrode lead 28, and an adhesive tape 24.

[0150] At least one of the multiple single cells 100 is a secondary battery according to the first embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in the figure. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0151] For example, the negative terminal of one cell 100 can be connected to the positive terminal of an adjacent cell 100 by a busbar. In this way, multiple cell 100s can be connected in series by multiple busbars. Alternatively, for example, multiple cell 100s can be electrically connected by connecting multiple negative terminals to each other and multiple positive terminals to each other by busbars.

[0152] Each cell 100 may be restrained by a restraining member. Each cell 100 may have its own restraining member. Alternatively, a restraining member capable of restraining multiple cells 100 may be included. Furthermore, the housing may have a part that functions as a restraining member.

[0153] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, for example, protective sheets are placed on both sides of the battery pack 23, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0154] One end of the positive lead 27 is connected to the battery pack 23. One end of the positive lead 27 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 28 is connected to the battery pack 23. One end of the negative lead 28 is electrically connected to the negative terminal of one or more single cells 100.

[0155] The printed circuit board 340 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energizing, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. For example, the main surface of the printed circuit board 340 can face one side of the battery pack 23, and an insulating plate may be provided between them.

[0156] The other end 27a of the positive lead 27 is electrically connected to the positive connector 342. The other end 28a of the negative lead 28 is electrically connected to the negative connector 343.

[0157] The thermistor 345 is fixed to the printed circuit board 340. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0158] The external power supply terminal 350 is fixed to the printed circuit board 340. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0159] The protection circuit 346 is fixed to the printed circuit board 340. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 330.

[0160] The protection circuit 346 controls the charging and discharging of the multiple single cells 100. The protection circuit 346 also disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying power to external devices, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from each individual single cell 100 or battery pack 23.

[0161] An example of a detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. An example of a detection signal transmitted from an individual single cell 100 or a battery pack 23 is a signal indicating that overcharging, over-discharging, or overcurrent has been detected in a single cell 100. When detecting overcharging, etc., in an individual single cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode to be used as a reference electrode is inserted into each individual single cell 100.

[0162] Furthermore, the protection circuit 346 may be a circuit included in a device that uses the battery pack 300 as a power source (for example, an electronic device, an automobile, etc.).

[0163] Furthermore, as described above, the battery pack 300 is equipped with an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 23 to an external device and input current from an external device to the battery pack 23 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 23 is supplied to the external device through the external terminal 350. Also, when charging the battery pack 300, charging current from an external device is supplied to the battery pack 300 through the external terminal 350. When this battery pack 300 is used as an on-board battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0164] The battery pack 300 may have multiple battery packs 23. In this case, the multiple battery packs 23 may be connected in series, in parallel, or a combination of series and parallel connections. The printed circuit board 340 and wiring 330 may be omitted. In this case, the positive lead 27 and the negative lead 28 may be used as the positive terminal 352 and negative terminal 353 of the external terminal 350 for energization, respectively.

[0165] Such battery packs are used in applications where excellent cycle performance is required, for example, when drawing high currents. Specifically, these battery packs are used as power supplies for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

[0166] The battery pack according to the second embodiment includes the secondary battery according to the first embodiment. Therefore, such a battery pack can exhibit good lifespan performance and high energy density. [Examples]

[0167] Examples are described below, but the present invention is not limited to the examples listed below unless it exceeds the spirit of the invention.

[0168] (Example 1) In Example 1, an electrode group and a non-aqueous electrolyte battery equipped with the electrode group were manufactured using the following procedure.

[0169] <Fabrication of the negative electrode> As the negative electrode active material, particles of monoclinic titanium niobium composite oxide having a composition represented by the formula TiNb2O7 were prepared. Acetylene black (AB) was prepared as a conductive agent, and carboxymethylcellulose (CMC) and styrene butadiene rubber (SBR) were prepared as binders. These were mixed in pure water in a mass ratio of negative electrode active material:AB:CMC:SBR of 90:5:2.5:2.5 to obtain a slurry. This slurry was applied to both the front and back main surfaces of a strip-shaped current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. Here, an uncoated area was left on one side along the longitudinal direction of the current collector, where the slurry was not applied to both the front and back surfaces. Thus, a composite was obtained containing the current collector and a negative electrode active material-containing layer formed on both sides of the current collector. The coating amount of the negative electrode active material-containing layer per side was 75 g / m². 2The material was adjusted so that the amount of coating at both ends in the short direction of the current collector would be reduced. Next, the resulting composite was prepared so that the density of the negative electrode active material-containing layer in the center of the coating width in the short direction was 2.55 g / cm³. 3 The material was subjected to a roll press in the manner described. The resulting electrode was punched out into a strip shape, with an uncoated portion of the current collector on one side along the longitudinal direction, and the portion adjacent to the uncoated portion and the inner portion of the other side along the longitudinal direction having less coating of the negative electrode active material. This strip was then subjected to vacuum drying to obtain the negative electrode.

[0170] <Fabrication of the positive electrode> As the positive electrode active material, Formula LiNi 0.5 Co 0.2 Mn 0.3 Particles of lithium nickel cobalt manganese composite oxide represented by O2 were prepared. Acetylene black (AB) was prepared as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder. These were mixed in a mass ratio of positive electrode active material:AB:PVdF of 90:5:5 to obtain a mixture. Next, the obtained mixture was dispersed in n-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. This slurry was applied to both the front and back main surfaces of a strip-shaped current collector made of 15 μm thick aluminum foil, and the coating was dried. Here, an uncoated area was left on one side along the longitudinal direction of the current collector, where the slurry was not applied to both the front and back surfaces. Thus, a composite was obtained containing the current collector and a positive electrode active material-containing layer formed on both sides of the current collector. The coating amount per side of the positive electrode active material-containing layer was 100 g / m². 2 The composite was then adjusted so that the amount of coating at both ends in the short direction of the current collector would be reduced. Next, the density of the positive electrode active material-containing layer in the central part of the coating width in the short direction of the resulting composite was 3.05 g / cm³. 3 The electrodes were subjected to a roll press in this manner. The resulting electrodes were punched out into strips, each having an uncoated portion of the current collector along one side in the longitudinal direction, and the portion adjacent to the uncoated portion and the inner portion of the other side in the longitudinal direction having less coating of the negative electrode active material-containing layer. These strips were then subjected to vacuum drying to obtain the positive electrode.

[0171] <Manufacturing of electrode groups> A polyethylene (PE) separator with a thickness of 15 μm was prepared. Next, the prepared separator was folded in a zigzag pattern, and the separator, along with 108 negative electrodes and 107 positive electrodes, were stacked in the order of negative electrode, separator, positive electrode, and separator to obtain a laminate. Specifically, the negative and positive electrodes were alternately inserted into the space defined by the zigzag-folded separator. The orientation of the negative and positive electrodes was aligned so that the uncoated portions of the current collectors were located on the same side of the laminate. Next, this laminate was pressed. The pressing of the laminate was carried out at room temperature (25°C) by applying a load of 80 kN for 1 minute. Thus, an electrode group was manufactured.

[0172] In the resulting electrode group, the amount of coating of the active material-containing layer was adjusted to be less at the uncoated portion of the current collector of each electrode, the adjacent edge of the active material-containing layer, and the opposite edge. As a result, the thickness in the lamination direction was thinner at these locations in the laminate.

[0173] <Preparation of non-aqueous electrolytes> A non-aqueous electrolyte was prepared using the following procedure. First, propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a volume ratio of PC:DEC 1:2 to obtain a mixed solvent. Lithium hexafluoride phosphate (LiPF6) was dissolved in this mixed solvent at a concentration of 1 M to obtain a liquid non-aqueous electrolyte.

[0174] <Battery assembly> An aluminum outer casing (square container) and its lid (sealing plate) were prepared. Electrode terminals (positive and negative terminals) and electrode leads (positive and negative leads) were attached to the lid of the outer casing. The lid of the outer casing, the electrode terminals, and the electrode leads were welded together to the unpainted portion of the current collector of the manufactured electrode group. The electrode group was inserted into the outer casing, the lid was welded to the outer casing, and the assembled battery was vacuum-dried at 80°C for 10 hours. After that, electrolyte was poured in through the filling port. After pouring, the filling port was covered and welded to seal the outer casing.

[0175] <Initial charge / discharge> The assembled battery underwent charging and discharging as follows: Two 2 mm thick polytetrafluoroethylene (PTFE) plates were placed on the main surfaces of both sides of the outer casing, and a 7 mm thick aluminum plate was placed further outside each surface. The two PTFE plates were secured with screws so that the width between them was equal to the thickness of the outer casing before the electrode group was inserted, which is 22 mm, and charging and discharging was performed with the casing fastened in place.

[0176] Charging was performed in constant current constant voltage (CCCV) mode. Specifically, charging was performed with a constant current of 0.2C up to 3.0V, followed by charging with a constant voltage of 3.0V. Charging was terminated when the current reached 0.05C. Discharging was performed in constant current mode at a discharge rate of 0.2C. The discharge termination voltage was set to 1.5V. The discharge capacity at 0.2C was 30 Ah.

[0177] (Example 2) In Example 2, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the method of applying the slurry was changed so that the amount of coating was reduced only at the ends of the active material-containing layer on the uncoated side of the current collector for both the negative and positive electrodes.

[0178] (Example 3) In Example 3, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the method of applying the slurry was modified so that the amount of coating was reduced only on the ends of the active material-containing layer on the uncoated side of the current collector for both the negative and positive electrodes, and the pressing strength was varied in the short direction during roll pressing of the strip-shaped composite before punching so that the ends of the active material-containing layer on the opposite side of the uncoated area were pressed more strongly.

[0179] (Example 4) In Example 4, an active material-containing layer was formed on both the negative and positive electrodes without adjusting the amount of coating on the current collector surface. The resulting laminate, which consisted of the negative and positive electrodes stacked together with a separator, was then pressed at a position overlapping the outer circumference of the outermost negative electrode active material-containing layer, except that the pressing was performed in the same manner as in Example 1. For the outer circumference pressing, the portions overlapping by 20% each in the width and length directions of the strip-shaped negative electrode active material-containing layer were pressed from both ends in the short and long sides.

[0180] (Example 5) In Example 5, an active material-containing layer was formed on both the negative and positive electrodes without adjusting the amount of coating on the current collector surface. The resulting laminate, which consisted of the negative and positive electrodes stacked together with a separator, was pressed, and then Kapton tape was applied to both main surfaces at a position overlapping the center of the negative electrode active material-containing layer to a thickness of 100 μm. The dimensions of the Kapton tape were set to 50% of the width and length of the strip-shaped negative electrode active material-containing layer in the short and long sides directions, respectively.

[0181] (Example 6) In Example 6, an active material-containing layer was formed on the current collector surface of both the negative and positive electrodes without adjusting the coating amount. The resulting laminate, which consisted of the negative and positive electrodes stacked together with a separator, was then pressed. On both main surfaces, a separately prepared polyethylene separator piece was stacked to a thickness of 150 μm at a position overlapping the center of the negative electrode active material-containing layer. The dimensions of the polyethylene separator piece were 50% of the width and length of the strip-shaped negative electrode active material-containing layer in the short and long sides directions, respectively.

[0182] (Example 7) In Example 7, the positive electrode active material is of the formula LiNi 0.8 Co 0.1 Mn 0.1 The particles were changed to lithium nickel cobalt manganese composite oxide represented as O2, and the coating amount per side of the negative electrode active material-containing layer was increased to 86 g / m².2 A non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the number of layers for the positive electrode was changed to 102 and the number of layers for the negative electrode was changed to 103. The 0.2C discharge capacity was 33 Ah.

[0183] (Example 8) In Example 8, the positive electrode active material was changed to lithium iron phosphate particles represented by the formula LiFePO4, and the coating amount per side of the negative electrode active material-containing layer was set to 70 g / m². 2 A non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the number of layers for the positive electrode was changed to 92, the number of layers for the negative electrode was changed to 93, and the charging voltage during the initial charge and discharge was changed to 2.3V and the discharge termination voltage to 1.0V, respectively. The 0.2C discharge capacity was 25 Ah.

[0184] (Comparative Example 1) In Comparative Example 1, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the method of applying the slurry was changed so that the coating amount was increased at the end of the active material-containing layer on the uncoated side of the current collector and the opposite end of the current collector for both the negative and positive electrodes.

[0185] (Comparative Example 2) In Comparative Example 2, an active material-containing layer was formed on the current collector surface of both the negative and positive electrodes without any adjustment to change the coating amount. The resulting negative and positive electrodes were then laminated together with a separator. During pressing of the laminate, Kapton tape was applied to the outer circumference along both short and long sides of the outermost negative electrode active material-containing layer, stacking it to a thickness of 100 μm. Otherwise, a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1.

[0186] For the non-aqueous electrolyte batteries manufactured in Examples 1 to 8 and Comparative Examples 1 and 2, the surface thickness T1 of the electrode group, the peripheral thickness T2 near the midpoint of the four sides of the electrode group, and the inner diameter IW of the outer casing were measured according to the procedure described above. The average value T2 of the peripheral thickness T2 was also measured. AVG and its ratio T2 to the thickness T1 at the center of the surface AVG / T1 was calculated. The measurement and calculation results are summarized in Table 1 below. The peripheral thickness T2 along the four sides of the electrode group is expressed as T21, T22, T23, and T24, respectively. T21 and T22 indicate the thickness near the midpoint of the long side of the electrode, while the latter T22 indicates the thickness on the unpainted side of the current collector. T23 and T24 indicate the thickness near the midpoint of the short side of the electrode, respectively.

[0187] [Table 1]

[0188] <Rating> The cycle life performance of each battery manufactured in Examples 1 to 8 and Comparative Examples 1 and 2 was evaluated. Specifically, the discharge capacity retention rate was measured by performing charge-discharge cycle tests as follows.

[0189] The battery was charged to its termination voltage at a constant current of 5C in a 45°C environment. Specifically, it was first charged until it reached a termination voltage of 3.0 V. Then, the battery was charged at a constant voltage at the termination voltage. Charging was completed when the current converged to a value equivalent to 0.05C. After that, the battery was left in an open-circuit state for 30 minutes. Then, the battery was discharged at a constant current of 5C until the voltage reached 1.5 V.

[0190] The above sequence of charging, leaving the device in an open-circuit state, and discharging was defined as one charge-discharge cycle. This charge-discharge cycle was repeated 500 times. The ratio (%) of the discharge capacity at the 500th cycle to the discharge capacity obtained at the 1st cycle was calculated. The obtained ratio was used as the cycle discharge capacity retention rate (discharge capacity retention rate = {[discharge capacity at the 500th cycle] / [discharge capacity at the 1st cycle]} × 100%) and was used as an indicator of lifespan performance.

[0191] The test results are shown in Table 2 below.

[0192] [Table 2]

[0193] As shown in Table 2, each of the non-aqueous electrolyte batteries manufactured in Examples 1 to 8 exhibited high capacity retention rates and excellent lifespan performance after 500 charge-discharge cycles. Furthermore, in Examples 1 to 8, the center surface thickness T1 of the electrode group removed from the battery was greater than the inner diameter IW of the rectangular outer casing, and T2, which represents the average thickness of the outer periphery of the electrode group, was also greater. AVG 0.95 × T1 < T2 AVE It was within the range of < T1. That is, it had an array of electrodes that filled almost the entire internal volume of the rectangular container, and therefore had a high energy density.

[0194] In contrast, the non-aqueous electrolyte batteries manufactured in Comparative Examples 1 and 2 exhibited low capacity retention during charge-discharge cycles and inferior lifespan performance. In Comparative Examples 1 and 2, the thickness of the electrode group removed from the battery was greater than the inner diameter IW of the outer casing, not only in the central thickness T1 but also in the peripheral thickness T2. As a result, when the electrodes expanded, the outer periphery of the electrode group was pressed against the inner wall of the outer casing, causing the electrolyte to be pushed out of the electrode group and leading to a deterioration in performance.

[0195] A secondary battery is provided according to one or more embodiments and examples described above. The secondary battery comprises an electrode group including a positive electrode and a negative electrode, a liquid electrolyte, and an outer casing member that houses the electrode group and the electrolyte. The electrode group includes a laminate including a positive electrode and a negative electrode, and has a flattened laminated structure having two pairs of end faces that intersect each other along the lamination direction. The electrolyte is at least partially held by the electrode group. The outer casing member includes a rectangular container that houses the electrode group and the electrolyte and has a pair of main walls along the main surface of the electrode group. The thickness T1 at the center of the main surface of the electrode group in a single state outside the rectangular container is greater than the inner diameter IW in the direction intersecting the main wall of the rectangular container. At least one of the peripheral thicknesses T2 at a position 10% of the short side length from the center of the end face of the electrode group toward the inside is thinner than the thickness T1 at the center of the surface, and the average value T2 of the peripheral thicknesses T2 AVE And the thickness T1 at the center of the surface is T2 AVEThe relationship > 0.95 × T1 is satisfied. The above secondary battery can exhibit good lifespan performance and high energy density, and can provide a battery pack that exhibits good lifespan performance and high energy density.

[0196] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0197] Several embodiments of the present invention are described below. [1] A group of electrodes having a flattened laminated structure that includes a laminate containing a positive electrode and a negative electrode, and has two pairs of end faces that intersect each other along the lamination direction of the laminate, A liquid electrolyte held at least partially in the electrode group, An outer casing member including a rectangular container that houses the electrode group and the electrolyte and has a pair of main walls intersecting the stacking direction, It is equipped with, A secondary battery wherein the thickness of the electrode group located outside the rectangular container in the stacking direction is greater than the inner diameter of the rectangular container in the direction intersecting the main wall of the rectangular container, at least one of the peripheral thicknesses in the stacking direction at a position 10% of the length of the shortest side of the edge intersecting the stacking direction of the end face, moving inward from the center of each end face, is thinner than the thickness in the center of the surface T1, and the average value of the peripheral thickness is greater than 95% of the thickness in the center of the surface. [2] The secondary battery according to [1], wherein at least two of the surrounding thicknesses are thinner than the central thickness of the surface. [3] The secondary battery according to [1], wherein the entire surrounding thickness is thinner than the central thickness of the surface. [4] The secondary battery according to any one of [1] to [3], wherein the negative electrode comprises niobium oxide or titanium niobium composite oxide. [5] The titanium niobium composite oxide contains a compound represented by the general formula Li a Ti 1-x M1 x Nb 2-y M2 y O 7-δ where 0 ≦ a < 5, 0 ≦ x < 1, 0 ≦ y < 1, -0.3 ≦ δ ≦ 0.3, and the element M1 and the element M2 are each at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, and the element M1 and the element M2 are the same as or different from each other. The secondary battery according to [4]. [6] The positive electrode contains one or more selected from the group consisting of a lithium manganese composite oxide, a lithium cobalt composite oxide, a lithium nickel cobalt manganese composite oxide, a lithium phosphate, and a lithium nickel manganese composite oxide. The secondary battery according to any one of [1] to [5]. [7] The rectangular container is made of an aluminum metal can or an aluminum alloy can. The secondary battery according to any one of [1] to [6]. [8] The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer provided on the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer provided on the negative electrode current collector. The positive electrode current collector includes a positive electrode current collecting tab on which the positive electrode active material-containing layer is not provided. The negative electrode current collector includes a negative electrode current collecting tab on which the negative electrode active material-containing layer is not provided. Both the positive electrode current collecting tab and the negative electrode current collecting tab are disposed on one of the end faces. The secondary battery according to any one of [1] to [7]. [9] The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer provided on the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer provided on the negative electrode current collector. The positive electrode current collector includes a positive electrode current collecting tab on which the positive electrode active material-containing layer is not provided. The negative electrode current collector includes a negative electrode current collecting tab on which the negative electrode active material-containing layer is not provided. The secondary battery according to any one of [1] to [7], wherein the positive electrode current collecting tab and the negative electrode current collecting tab are respectively disposed on one and the other of the end faces.

[10] A battery pack comprising the secondary battery according to any one of [1] to [9].

[0198]

[11] An external terminal for energization, and a protection circuit The battery pack according to

[10] , further comprising.

[12] Comprising a plurality of the secondary batteries, The battery pack according to

[10] or

[11] , wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

Description of Symbols

[0199] 1... Outer packaging member, 2... Electrode group, 3... Square container, 4... Sealing plate, 5... Positive electrode, 5a... Positive electrode current collecting tab, 5b... Positive electrode active material-containing layer, 5c... Positive electrode current collector, 6... Negative electrode, 6a... Negative electrode current collecting tab, 6b... Negative electrode active material-containing layer, 6c... Negative electrode current collector, 7... Separator, 8... Electrode, 8a... Current collecting tab, 8b... Active material-containing layer, 8c... Current collector, 9... Insulating member, 13... Liquid injection port, 14... Sealing cap, 15... Positive electrode terminal, 16... Negative electrode terminal, 17... Insulating gasket, 18... Insulating plate, 20... Main surface, 21... Electrode group, 22... Electrode group, 23... Battery assembly, 24... Adhesive tape, 25... Positive electrode lead, 26... Negative electrode lead, 27... Positive electrode side lead, 28... Negative electrode side lead, 31... Main wall, 32... Second side wall, 33... Bottom wall, 80... Press roll, 100... Secondary battery, 200... Electrode group, 210... Electrode group, 300... Battery pack, 330... Wiring, 340... Printed wiring board, 342... Positive electrode side connector, 342a... Wiring, 343... Negative electrode side connector, 343a... Wiring, 345... Thermistor, 346... Protection circuit, 350... External terminal for energization, 352... Positive side terminal, 353... Negative side terminal, 348a... Plus side wiring, 348b... Minus side wiring.

Claims

1. A group of electrodes having a flattened laminated structure that includes a laminate containing a positive electrode and a negative electrode, and has two pairs of end faces that intersect each other along the lamination direction of the laminate, A liquid electrolyte held at least partially in the electrode group, An outer casing member including a rectangular container that houses the electrode group and the electrolyte and has a pair of main walls intersecting the stacking direction, It is equipped with, A secondary battery wherein the thickness of the electrode group located outside the rectangular container in the stacking direction is greater than the inner diameter of the rectangular container in the direction intersecting the main wall of the rectangular container, at least one of the peripheral thicknesses in the stacking direction at a position 10% of the length of the shortest side of the edge intersecting the stacking direction of the end face, moving inward from the center of each end face, is thinner than the thickness in the center of the surface, and the average value of the peripheral thickness is greater than 95% of the thickness in the center of the surface.

2. The secondary battery according to claim 1, wherein at least two of the peripheral thicknesses are thinner than the central thickness of the surface.

3. The secondary battery according to claim 1, wherein the entire surrounding thickness is thinner than the thickness at the center of the surface.

4. The secondary battery according to any one of claims 1 to 3, wherein the negative electrode comprises niobium oxide or titanium niobium composite oxide.

5. The aforementioned titanium niobium composite oxide has the general formula Li a Ti 1-x M1 x Nb 2-y M2 y O 7-δ The secondary battery according to claim 4, comprising a compound represented by , wherein 0 ≤ a < 5, 0 ≤ x < 1, 0 ≤ y < 1, -0.3 ≤ δ ≤ 0.3, and element M1 and element M2 are each at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, and element M1 and element M2 are the same or different from each other.

6. The secondary battery according to any one of claims 1 to 3, wherein the positive electrode comprises one or more selected from the group consisting of lithium manganese composite oxide, lithium cobalt composite oxide, lithium nickel cobalt manganese composite oxide, lithium phosphorus oxide, and lithium nickel manganese composite oxide.

7. The secondary battery according to any one of claims 1 to 3, wherein the rectangular container is made of an aluminum metal can or an aluminum alloy can.

8. The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer provided on the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer provided on the negative electrode current collector. The positive electrode current collector includes a positive electrode current collector tab that does not have the positive electrode active material containing layer provided. The negative electrode current collector includes a negative electrode current collector tab that does not have the negative electrode active material containing layer provided. The secondary battery according to any one of claims 1 to 3, wherein both the positive electrode current collector tab and the negative electrode current collector tab are arranged on one of the end faces.

9. The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer provided on the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer provided on the negative electrode current collector. The positive electrode current collector includes a positive electrode current collector tab that does not have the positive electrode active material containing layer provided. The negative electrode current collector includes a negative electrode current collector tab that does not have the negative electrode active material containing layer provided. The secondary battery according to any one of claims 1 to 3, wherein the positive electrode current collector tab and the negative electrode current collector tab are arranged on one of the end faces and the other, respectively.

10. A battery pack comprising a secondary battery as described in any one of claims 1 to 3.

11. External terminals for power supply, Protection circuit and The battery pack according to claim 10, further comprising the above.

12. The device comprises multiple secondary batteries, The battery pack according to claim 10, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

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