Battery pack

Abstract

To provide a battery pack excellent in high-rate resistance.SOLUTION: A battery pack includes three or more prismatic secondary batteries 100 arranged along a stacking direction X. The three or more prismatic secondary batteries 100 include: two first prismatic secondary batteries 110 disposed at both ends in the stacking direction X, respectively; and one or two or more second prismatic secondary batteries 120 disposed between the two first prismatic secondary batteries 110. The mass of a non-aqueous electrolyte solution in each of the two first prismatic secondary batteries 110 is larger than the mass of the non-aqueous electrolyte solution in the second prismatic secondary battery 120.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a battery pack.

Background Art

[0002] Conventionally, for power sources for vehicle drive and the like, battery packs formed by electrically connecting a plurality of secondary batteries (single cells) have been widely used. As related prior art documents, Patent Documents 1 to 3 can be cited.

[0003] For example, Patent Document 1 discloses a battery pack including three or more alkaline storage batteries arranged along the stacking direction. Patent Document 1 describes that the amount of electrolyte in the alkaline storage battery located at the central portion in the stacking direction is 5 to 30 mass% more than the amount of electrolyte in the alkaline storage batteries located at both ends in the stacking direction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a battery pack mounted on a vehicle or the like, relatively excellent high-rate tolerance is required as compared with, for example, a battery pack for a power storage / backup system as described in Patent Document 1.

[0006] The present invention has been made in view of the above circumstances, and its main object is to provide a battery pack having excellent high-rate tolerance.

Means for Solving the Problems

[0007] According to the present invention, a battery pack including three or more rectangular secondary batteries arranged along the stacking direction is disclosed. The rectangular secondary battery includes an electrode body and a non-aqueous electrolyte. The electrode body is a flat wound electrode body formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state with a strip-shaped separator interposed therebetween. The three or more rectangular secondary batteries are composed of two first rectangular secondary batteries respectively arranged at both ends in the stacking direction and one or two or more second rectangular secondary batteries arranged between the two first rectangular secondary batteries, and the mass of the non-aqueous electrolyte in the two first rectangular secondary batteries is respectively larger than the mass of the non-aqueous electrolyte in the second rectangular secondary battery (however, the mass of the non-aqueous electrolyte in the second rectangular secondary battery means the arithmetic average of the masses of the non-aqueous electrolyte in two or more second rectangular secondary batteries when there are two or more second rectangular secondary batteries).

[0008] According to the present invention, a battery pack with excellent high-rate tolerance can be realized.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the assembled battery disclosed herein will be described with reference to the drawings as appropriate. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention (for example, the general configurations and manufacturing processes of assembled batteries and prismatic secondary batteries that do not characterize the present invention) can be grasped as design matters for those skilled in the art based on the prior art in the relevant field. The assembled battery disclosed herein can be implemented based on the content disclosed in this specification and the common general knowledge in the relevant field.

[0011] In the following drawings, members and parts having the same function are denoted by the same reference numerals, and redundant descriptions may be omitted or simplified. Also, the notation "A to B" indicating a range in this specification includes the meaning of "not less than A and not more than B", as well as the meaning of "preferably greater than A" and "preferably less than B".

[0012] FIG. 1 is a perspective view schematically showing an assembled battery 500 according to an embodiment. The assembled battery 500 includes three or more prismatic secondary batteries 100 arranged along a predetermined stacking direction X. The assembled battery 500 further includes a restraint mechanism 300 here. However, the restraint mechanism 300 is not essential and can be omitted in other embodiments. Also, other members such as spacers may be interposed between adjacent prismatic secondary batteries 100 in the stacking direction X.

[0013] In the following description, the reference numerals L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, upper, and lower, respectively, and the reference numerals X, Y, and Z in the drawings represent the thickness direction, the width direction orthogonal to the thickness direction, and the height direction orthogonal to the thickness direction and the width direction of the prismatic secondary battery 100, respectively. The thickness direction X is also the stacking direction of the prismatic secondary batteries 100. However, these are merely directions for convenience of explanation and do not limit the installation form of the assembled battery 500 in any way.

[0014] The restraint mechanism 300 is a member that restrains a plurality of rectangular secondary batteries 100. The restraint mechanism 300 is configured to apply a prescribed restraint pressure to the plurality of rectangular secondary batteries 100 in the stacking direction X. Here, the restraint mechanism 300 includes a pair of end plates 310, a pair of side plates 320, and a plurality of screws 330. The pair of end plates 310 and the pair of side plates 320 can also be regarded as a box body that houses the plurality of rectangular secondary batteries 100. The pair of end plates 310 and the pair of side plates 320 are preferably made of metal. However, a part of the pair of end plates 310 and / or the pair of side plates 320 may be made of resin.

[0015] The pair of end plates 310 are respectively arranged at both ends of the plurality of rectangular secondary batteries 100 in the stacking direction X. The pair of end plates 310 sandwich the plurality of rectangular secondary batteries 100 in the stacking direction X. Note that an insulating sheet or the like may be arranged between the rectangular secondary battery 100 and the end plate 310.

[0016] The pair of side plates 320 bridge the pair of end plates 310. The pair of side plates 320 are fixed to the end plates 310 by a plurality of screws 330 so that the restraint load is approximately 10 to 15 kN, for example. Thereby, a restraint load is applied to the plurality of rectangular secondary batteries 100 from the stacking direction X, and the assembled battery 500 is integrally held. However, the configuration of the restraint mechanism is not limited to this. The restraint mechanism 300 may include, for example, a plurality of restraint bands or binding bars instead of the side plates 320. Also, in other embodiments, for example, the rectangular secondary batteries 100 may be stacked in a box body without using the restraint mechanism 300.

[0017] The rectangular secondary battery 100 is a battery that can be repeatedly charged and discharged. Note that in this specification, the term "secondary battery" refers to a general term for devices that can be repeatedly charged and discharged, and includes capacitors such as lithium-ion capacitors in addition to so-called storage batteries such as lithium-ion secondary batteries and nickel-metal hydride batteries.

[0018] Three or more rectangular secondary batteries 100 are arranged side by side along the stacking direction X (the thickness direction X of the rectangular secondary battery 100) between a pair of end plates 310. It is preferable that the plurality of rectangular secondary batteries 100 are constrained by a constraint mechanism 300. Note that the shape, size, number, arrangement, etc. of the plurality of rectangular secondary batteries 100 are not limited to the embodiments disclosed in FIG. 1 and can be changed as appropriate.

[0019] Although not shown in FIG. 1, when the assembled battery 500 is used, a plurality of rectangular secondary batteries 100 are electrically connected by a conductive member such as a bus bar. The connection method is not particularly limited, and may be, for example, series, parallel, or multi-series multi-parallel. In a preferred embodiment, a plurality of rectangular secondary batteries 100 are connected in series. Thereby, for example, the output characteristics can be preferably improved to a level suitable for use in a vehicle or the like. Also, in the case of series connection, deterioration of the performance of some of the rectangular secondary batteries 100 (for example, deterioration of the high-rate characteristics) is likely to lead to deterioration of the performance of the entire assembled battery 500. Therefore, it is particularly effective to apply the technology disclosed herein.

[0020] FIG. 2 is a perspective view of the rectangular secondary battery 100. As can be seen from FIGS. 1 and 2, the plurality of rectangular secondary batteries 100 are all flat rectangular shapes and are of the same shape here. The plurality of rectangular secondary batteries 100 are arranged such that the long side walls 12b described later are parallel to each other. The plurality of rectangular secondary batteries 100 are arranged such that the long side walls 12b face each other here.

[0021] Although not particularly limited, the battery capacity of the rectangular secondary battery 100 (typically, a value calculated from the theoretical capacity of the active material) is preferably 50 Ah or more, more preferably 100 Ah or more, and even more preferably 150 Ah or more, 200 Ah or more, for example. As will be described in detail later, when the battery capacity is a predetermined value or more, the amount of heat generated during charge and discharge increases, and the temperature of the rectangular secondary battery 100 (the second rectangular secondary battery 120 described later) tends to be high at the central portion in the stacking direction X of the battery pack 500. As a result, the temperature difference of the rectangular secondary battery 100 tends to be large between the central portion and the end portion in the stacking direction X of the battery pack 500. Therefore, it is particularly effective to apply the technology disclosed herein. From the viewpoint of exhibiting the technology disclosed herein at a high level, the battery capacity of the rectangular secondary battery 100 is preferably 500 Ah or less.

[0022] FIG. 3 is a schematic longitudinal sectional view taken along line III-III of FIG. 2. As shown in FIG. 3, the rectangular secondary battery 100 here includes a battery case 10, an electrode body 20, a positive electrode terminal 30, a negative electrode terminal 40, and a non-aqueous electrolyte 70. The rectangular secondary battery 100 is configured by housing the electrode body 20 and the non-aqueous electrolyte 70 in a battery case 10 to which the positive electrode terminal 30 and the negative electrode terminal 40 are attached. The rectangular secondary battery 100 is typically a non-aqueous electrolyte secondary battery, and here is a lithium-ion secondary battery. When the rectangular secondary battery 100 is a lithium-ion secondary battery, it is particularly effective to apply the technology disclosed herein.

[0023] The battery case 10 is a housing that houses the electrode body 20 and the non-aqueous electrolyte 70. As shown in FIG. 2, the battery case 10 has an outer shape of a flat and bottomed rectangular parallelepiped (rectangular). The material of the battery case 10 may be the same as those conventionally used, and is not particularly limited. The battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, aluminum alloy, iron, iron alloy, or the like. As shown in FIG. 3, the battery case 10 here includes an outer package 12 and a sealing plate (lid body) 14.

[0024] As shown in FIG. 2, the outer package 12 includes a substantially rectangular bottom wall 12a having a long side and a short side, a pair of long side walls 12b extending from the long side of the bottom wall 12a and facing each other, a pair of short side walls 12c extending from the short side of the bottom wall 12a and facing each other, and an opening 12h (see FIG. 3) facing the bottom wall 12a. The long side walls 12b are flat. The area of the long side walls 12b is larger than the area of the short side walls 12c. In this specification, the term "substantially rectangular" includes, in addition to a perfect rectangular shape (rectangular shape), for example, a shape in which the corners connecting the long side and the short side of the rectangular shape are R-shaped, a shape having a notch at the corner, and the like.

[0025] The sealing plate 14 is a plate-like member that seals the opening 12h of the outer package 12. As shown in FIG. 3, the sealing plate 14 is attached to the outer package 12 so as to close the opening 12h. The sealing plate 14 faces the bottom wall 12a of the outer package 12. The sealing plate 14 is substantially rectangular. The battery case 10 is integrated by joining (preferably, welding) the sealing plate 14 to the periphery of the opening 12h of the outer package 12. The battery case 10 is hermetically sealed. The sealing plate 14 is provided with a liquid injection hole 15 and two terminal lead-out holes 18 and 19. The liquid injection hole 15 is for injecting a non-aqueous electrolyte 70 into the battery case 10 after the sealing plate 14 is assembled to the outer package 12. The liquid injection hole 15 is sealed by a sealing member 16. The terminal lead-out holes 18 and 19 penetrate the sealing plate 14 in the height direction Z.

[0026] The positive electrode terminal 30 is disposed at one end (the left end in FIGS. 2 and 3) in the width direction Y of the sealing plate 14. The negative electrode terminal 40 is disposed at the other end (the right end in FIGS. 2 and 3) in the width direction Y of the sealing plate 14. As shown in FIG. 3, the positive electrode terminal 30 and the negative electrode terminal 40 respectively extend from the inside to the outside of the sealing plate 14 through the terminal lead-out holes 18 and 19. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are caulked to the peripheral portion surrounding the terminal lead-out holes 18 and 19 of the sealing plate 14 by caulking. Caulking portions 30c and 40c are formed at the ends (the lower ends in FIG. 3) on the side of the outer package 12 of the positive electrode terminal 30 and the negative electrode terminal 40. Thereby, the positive electrode terminal 30 and the negative electrode terminal 40 are fixed to the sealing plate 14.

[0027] As shown in FIG. 3, inside the outer package 12, the positive electrode terminal 30 is electrically connected to the positive electrode tab group 23 of the electrode body 20 via the positive electrode current collecting member 50. The positive electrode terminal 30 is insulated from the sealing plate 14 by the internal insulating member 80 and the gasket 90. Inside the outer package 12, the negative electrode terminal 40 is electrically connected to the negative electrode tab group 25 of the electrode body 20 via the negative electrode current collecting member 60. The negative electrode terminal 40 is insulated from the sealing plate 14 by the internal insulating member 80 and the gasket 90.

[0028] As shown in FIGS. 2 and 3, plate-shaped positive electrode external conductive members 32 and negative electrode external conductive members 42 are attached to the outer surface of the sealing plate 14. The positive electrode external conductive member 32 is electrically connected to the positive electrode terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative electrode terminal 40. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are members to which conductive members such as bus bars for electrically connecting a plurality of rectangular secondary batteries 100 to each other are attached. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are insulated from the sealing plate 14 by the external insulating member 92. The assembled battery 500 is, for example, serially connected by electrically connecting the positive electrode external conductive member 32 of one rectangular secondary battery 100 and the negative electrode external conductive member 42 of the other rectangular secondary battery 100 among the adjacent rectangular secondary batteries 100 in the stacking direction X via a conductive member.

[0029] FIG. 4 is a schematic diagram showing the configuration of the electrode body 20. As shown in FIG. 4, the electrode body 20 includes a positive electrode 22, a negative electrode 24, and a separator 26. The electrode body 20 is a wound electrode body in which a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 are laminated and wound in an insulated state via a strip-shaped separator 26. The electrode body 20 has a flat outer shape. Since the electrode body 20 is a wound electrode body, the volumetric energy density can be improved. Further, in the wound electrode body, since only both ends in the winding axis WL direction are open, the non-aqueous electrolyte 70 is supplied into the electrode body only from these both ends. For this reason, the liquid circulation property is likely to deteriorate during high-rate charge and discharge, and it is particularly effective to apply the technology disclosed herein.

[0030] As shown in FIG. 3, the electrode body 20 is disposed inside the battery case 10 in a direction in which the winding axis WL (see FIG. 4) is substantially parallel to the width direction Y here. The winding axis WL direction is the same as the width direction Y of the rectangular secondary battery 100 here. Note that the configuration of the electrode body 20 may be the same as that of the conventional one, and there is no particular limitation. Further, the number of electrode bodies 20 disposed inside one battery case 10 is not particularly limited, and may be one or a plurality. When the number of electrode bodies 20 disposed inside one battery case 10 is a plurality (for example, two to three), the rectangular secondary battery 100 is likely to generate heat during charge and discharge, and particularly at the central portion in the stacking direction X of the assembled battery 500, the temperature of the rectangular secondary battery 100 (the second rectangular secondary battery 120 described later) tends to be high. Therefore, it is particularly effective to apply the technology disclosed herein.

[0031] The height H (see FIG. 3) of the electrode body 20 is preferably 120 mm or less, more preferably 60 to 120 mm, still more preferably 80 to 110 mm, and particularly preferably 90 to 105 mm. Note that in this specification, the "height H of the electrode body 20" refers to the length in a direction perpendicular to the winding axis WL direction of the electrode body 20 and perpendicular to the thickness direction X of the electrode body 20. The height H is the length in the height direction Z here.

[0032] The configuration of the positive electrode 22 may be the same as that of the prior art. Here, the positive electrode 22 has a positive electrode current collector 22c, a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed on at least one surface of the positive electrode current collector 22c. However, the positive electrode protective layer 22p is not essential and can be omitted in other embodiments. The positive electrode current collector 22c is strip-shaped. The positive electrode current collector 22c is preferably made of metal, and more preferably made of a metal foil. Here, the positive electrode current collector 22c is an aluminum foil.

[0033] A plurality of positive electrode tabs 22t are provided at one end in the width direction Y (the left end in FIG. 4) of the positive electrode current collector 22c. The plurality of positive electrode tabs 22t are convex and protrude toward one side in the width direction Y (the left side in FIG. 4). The plurality of positive electrode tabs 22t protrude in the width direction Y more than the separator 26. Here, the positive electrode tab 22t is a part of the positive electrode current collector 22c and is made of a metal foil (aluminum foil). The plurality of positive electrode tabs 22t are laminated at one end in the width direction Y (the left end in FIG. 4) to form a positive electrode tab group 23 (see FIG. 3). The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collecting member 50.

[0034] The positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material that can reversibly occlude and release charge carriers. Examples of the positive electrode active material include lithium transition metal composite oxides. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a binder, a conductive material, various additives, etc.

[0035] The positive electrode protective layer 22p is provided at the boundary portion between the positive electrode current collector 22c and the positive electrode active material layer 22a in the width direction Y. The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (for example, alumina). The positive electrode protective layer 22p may contain optional components other than the inorganic filler, such as a conductive material, a binder, various additives, etc.

[0036] The configuration of the negative electrode 24 may be the same as that of the conventional one. Here, the negative electrode 24 has a negative electrode current collector 24c and a negative electrode active material layer 24a fixed on at least one surface of the negative electrode current collector 24c. The negative electrode current collector 24c is strip-shaped. The negative electrode current collector 24c is preferably made of metal, and more preferably made of a metal foil. Here, the negative electrode current collector 24c is a copper foil.

[0037] A plurality of negative electrode tabs 24t are provided at one end (the right end in FIG. 4) in the width direction Y of the negative electrode current collector 24c. The plurality of negative electrode tabs 24t project toward one side in the width direction Y (the right side in FIG. 4). The plurality of negative electrode tabs 24t are convex and project in the width direction Y more than the separator 26. Here, the negative electrode tab 24t is a part of the negative electrode current collector 24c and is made of a metal foil (copper foil). The plurality of negative electrode tabs 24t are laminated at one end (the right end in FIG. 4) in the width direction Y to form a negative electrode tab group 25 (see FIG. 3). The negative electrode tab group 25 is provided at a position symmetric to the positive electrode tab group 23 in the width direction Y. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collecting member 60.

[0038] The negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material capable of reversibly occluding and releasing charge carriers. Examples of the negative electrode active material include carbon materials such as graphite. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a binder, a thickener, a dispersant, and various additives.

[0039] The length Ln in the width direction Y (average length in the winding axis WL direction) of the negative electrode active material layer 24a is preferably the same as or longer than the length Lp in the width direction Y (average length in the winding axis WL direction) of the positive electrode active material layer 22a. In some embodiments, the length Ln of the negative electrode active material layer 24a is preferably 15 cm or more, and more preferably 20 cm or more. When the length Ln of the negative electrode active material layer 24a is equal to or greater than a predetermined value, the rectangular secondary battery 100 tends to generate heat during charge and discharge, and particularly at the central portion in the stacking direction X of the battery pack 500, the temperature of the rectangular secondary battery 100 (the second rectangular secondary battery 120 described later) tends to increase. Therefore, it is particularly effective to apply the technology disclosed herein. The length Ln of the negative electrode active material layer 24a may be generally 45 cm or less, for example, 40 cm or less.

[0040] In some embodiments, the length Ln of the negative electrode active material layer 24a is preferably longer than the height H of the electrode body 20. That is, the ratio (Ln / H) of the length Ln of the negative electrode active material layer 24a to the height H of the electrode body 20 is preferably greater than 1. Thereby, the energy density can be improved better. Also, when the energy density is high, the amount of heat generated by the rectangular secondary battery 100 increases, and particularly at the central portion in the stacking direction X of the battery pack 500, the temperature of the rectangular secondary battery 100 (the second rectangular secondary battery 120 described later) tends to increase. Therefore, it is particularly effective to apply the technology disclosed herein. The above ratio (Ln / H) is more preferably 2 or more, and even more preferably 2.5 or more.

[0041] The separator 26 is a member disposed between the positive electrode 22 and the negative electrode 24 and insulating the positive electrode 22 and the negative electrode 24. The configuration of the separator 26 may be the same as that of the prior art. The length Ls in the width direction Y (average length in the winding axis WL direction) of the separator 26 is preferably the same as or longer than the length Ln of the negative electrode active material layer 24a. As the separator 26, for example, a porous sheet (micro-porous membrane) made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable. The separator 26 may be provided with a functional layer (for example, an adhesive layer or a heat-resistant layer, etc.) on the surface of the porous sheet.

[0042] The configuration of the non-aqueous electrolyte 70 may be the same as that of the conventional one. The non-aqueous electrolyte 70 typically contains a non-aqueous solvent and an electrolyte salt (supporting salt). Examples of the non-aqueous solvent include various organic solvents used in the electrolytes of typical lithium-ion secondary batteries, specifically, carbonates, esters, ethers, nitriles, sulfones, lactones, and the like. These can be used alone or in combination of two or more. Among them, it is preferable to contain carbonates, and more preferably, it consists of carbonates (the non-aqueous solvent is carbonates). In this specification, "carbonates" refers to all compounds containing at least one carbonate structure (-O-CO-O-) in the molecule.

[0043] Specific examples of carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), fluoroethylene carbonate; chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC). Among them, from the viewpoints of improving ionic conductivity and reducing the viscosity of the non-aqueous electrolyte 70, etc., it is preferable that the non-aqueous solvent contains both a cyclic carbonate (e.g., EC) and a chain carbonate (e.g., DMC and / or EMC). Also, the proportion of the cyclic solvent (e.g., cyclic carbonate) in the whole non-aqueous solvent is preferably 50% by volume or less, for example, 10 - 50% by volume, 20 - 30% by volume.

[0044] As the electrolyte salt, for example, various lithium salts used as electrolyte salts in the electrolytes of common lithium-ion secondary batteries can be mentioned. Specifically, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), etc. can be mentioned. These can be used alone or in combination of two or more. The concentration of the electrolyte salt is preferably 0.5 to 1.5 mol / L, and more preferably 0.7 to 1.3 mol / L. Further, the non-aqueous electrolyte 70 may further contain an additive as necessary. Examples of the additive include gas generators such as biphenyl (BP) and cyclohexylbenzene (CHB); film-forming agents such as oxalato complex compounds containing a boron atom and / or a phosphorus atom.

[0045] Although not particularly limited, as shown in FIG. 3, in the rectangular secondary battery 100, it is preferable that an excess non-aqueous electrolyte 70 exists between the exterior body 12 and the electrode body 20. The presence of the excess non-aqueous electrolyte 70 can prevent liquid depletion inside the electrode body 20.

[0046] In some embodiments, the mass of the non-aqueous electrolyte 70 contained in the rectangular secondary battery 100 is preferably such that the mass of the non-aqueous electrolyte 70 per unit battery capacity represented by the following formula: mass of non-aqueous electrolyte 70÷battery capacity; is 1.6 g / Ah or more, and more preferably 1.7 g / Ah or more. Although details will be described later, according to the study by the present inventor, the higher the mass of the non-aqueous electrolyte 70, the more likely the high-rate resistance is to decrease. Therefore, it is effective to apply the technology disclosed herein. The mass of the non-aqueous electrolyte 70 per unit battery capacity is preferably 2.5 g / Ah or less.

[0047] FIG. 5 is a plan view schematically showing the assembled battery 500. In FIG. 5, three or more rectangular secondary batteries 100 of the assembled battery 500 are composed of two first rectangular secondary batteries 110 respectively arranged at both ends in the stacking direction X of the assembled battery 500, and one or two or more second rectangular secondary batteries 120 arranged between the two first rectangular secondary batteries 110. The second rectangular secondary battery 120 is located at the central part in the stacking direction X of the assembled battery 500.

[0048] According to the findings of the present inventors, when the assembled battery 500 is charged, the rectangular secondary battery 100 generates heat due to Joule heat (Q = I 2 R). Since the central portion in the stacking direction X of the assembled battery 500 is sandwiched by at least two first rectangular secondary batteries 110, the heat dissipation property is relatively low. Therefore, when the rectangular secondary battery 100 generates heat, the temperature of the second rectangular secondary battery 120 located at the central portion in the stacking direction X tends to be relatively high. The temperature of the second rectangular secondary battery 120 can be, for example, 50°C or higher. On the other hand, both ends (the foremost F and the rearmost Rr in FIG. 5) in the stacking direction X of the assembled battery 500 have higher heat dissipation properties than the central portion. Therefore, the first rectangular secondary batteries 110 located at both ends in the stacking direction X are relatively unlikely to have a high temperature. In the assembled battery 500, the temperature difference between the first rectangular secondary battery 110 and the second rectangular secondary battery 120 can be about 5 to 30°C, for example, 10°C or higher.

[0049] And according to the study of the present inventors, when such a temperature distribution occurs in the assembled battery 500, variations may occur in the high-rate tolerance of the rectangular secondary battery 100. Specifically, the high-rate tolerance of the second rectangular secondary battery 120 located at the central portion in the stacking direction X (where the temperature tends to be high) may be relatively low. In this case, if the charging and discharging of the entire assembled battery 500 are controlled based on the high-rate tolerance of the second rectangular secondary battery 120, the high high-rate tolerance of the first rectangular secondary battery 110 cannot be fully utilized. On the other hand, if the high-rate tolerance of the first rectangular secondary battery 110 is used as a reference, a high voltage is applied to the second rectangular secondary battery 120 and high-rate deterioration is likely to occur.

[0050] Therefore, in the technology disclosed herein, the mass of the non-aqueous electrolyte 70 in the two first rectangular secondary batteries 110 disposed at both ends in the stacking direction X (locations with high heat dissipation and low temperature rise) is made larger than the mass of the non-aqueous electrolyte 70 in the second rectangular secondary battery 120 disposed at the central portion in the stacking direction X (locations with low heat dissipation and high temperature rise). Note that the "mass of the non-aqueous electrolyte 70 in the second rectangular secondary battery 120" is the arithmetic mean of the masses of the non-aqueous electrolyte 70 in two or more second rectangular secondary batteries 120 when there are two or more second rectangular secondary batteries 120. It is more preferable that the mass of the non-aqueous electrolyte 70 in each of the two first rectangular secondary batteries 110 is larger than the mass of the non-aqueous electrolyte 70 in each (before arithmetic averaging) second rectangular secondary battery 120.

[0051] Although it will be described in detail later, as a result of the intensive studies by the present inventor, it has been confirmed that the greater the mass of the non-aqueous electrolyte 70 present in the battery case 10, the more likely high-rate degradation occurs, that is, the lower the high-rate tolerance. Therefore, in the technology disclosed herein, the first rectangular secondary battery 110 with a relatively large mass of the non-aqueous electrolyte 70 (low high-rate tolerance) is disposed at both ends in the stacking direction X, and the second rectangular secondary battery 120 with a relatively small mass of the non-aqueous electrolyte 70 (low high-rate tolerance) is disposed at the central portion in the stacking direction X. According to such a configuration, the high-rate tolerance of the plurality of rectangular secondary batteries 100 can be equalized. As a result, high-rate degradation can be suppressed and the high-rate tolerance of the entire assembled battery 500 can be improved.

[0052] Although not intended to be construed as particularly limited, in the rectangular secondary battery 100 including the electrode body 20, as a factor for the high-rate tolerance to decrease as the mass of the non-aqueous electrolyte 70 increases, the present inventor is considering the influence of salt concentration unevenness during high-rate charging. FIGS. 6(A) to (D) are schematic diagrams for explaining the mechanism of salt concentration unevenness and represent the interface between the positive electrode 22 and the negative electrode 24. A non-aqueous electrolyte 70 is interposed between the positive electrode 22 and the negative electrode 24.

[0053] Fig. 6(A) is a schematic diagram before high-rate charging. As shown in Fig. 6(B), when the prismatic secondary battery 100 is high-rate charged, charge carriers (here Li + ) are released from the positive electrode 22 (specifically, the positive electrode active material) into the non-aqueous electrolyte 70. Also, charge carriers (here Li + ) are occluded from the non-aqueous electrolyte 70 into the negative electrode 24 (specifically, the negative electrode active material). At this time, near the interface between the negative electrode 24 and the non-aqueous electrolyte 70, the transport of Li + cannot catch up with the occlusion rate of Li + , and the concentration of Li + per unit volume in the non-aqueous electrolyte 70 can decrease. And, as shown in Fig. 6(C), when Li + is occluded in the negative electrode 24 by high-rate charging, the negative electrode 24 (for example, the negative electrode active material layer 24a) expands. As a result, a liquid with a low Li + concentration near the negative electrode 24 can be discharged from the inside of the electrode body 20. According to the study by the present inventor, the larger the mass of the non-aqueous electrolyte 70, the larger the discharge amount of the liquid with a low Li + concentration from the electrode body 20.

[0054] Next, as shown in Fig. 6(D), when the prismatic secondary battery 100 is discharged, this time the negative electrode 24 (for example, the negative electrode active material layer 24a) contracts. As a result, the liquid with a low Li + concentration discharged from the electrode body 20 can be sucked into the inside of the electrode body 20 from the ends in the width direction Y (the width direction of the electrode body 20). As a result, as shown in Fig. 6(D), in the width direction Y, the distribution of the Li + concentration becomes convex, that is, high at the central part in the width direction Y and low at both ends. As a result, the resistance can become relatively large at both ends in the width direction Y (the locations marked with circles in Fig. 6(D)).

[0055] By repeating the charge and discharge as described above, Li can be deposited at locations with high resistance (both ends in the width direction Y of the electrode body 20). According to the study by the present inventor, the Li deposition at both ends in this width direction Y is correlated with the mass of the non-aqueous electrolyte 70, and specifically, the larger the mass of the non-aqueous electrolyte 70, the more the deposition. Therefore, it is considered that the higher the mass of the non-aqueous electrolyte 70, the lower the high-rate tolerance.

[0056] In some embodiments, the non-aqueous electrolyte 70 in the two first rectangular secondary batteries 110 is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and may be, for example, 5% by mass or more, than the non-aqueous electrolyte 70 in the second rectangular secondary battery 120. The difference in the mass of the non-aqueous electrolyte 70 between the first rectangular secondary battery 110 and the second rectangular secondary battery 120 may vary depending on, for example, the number of the rectangular secondary batteries 100 (the length in the stacking direction X of the battery pack 500), but is generally 50% by mass or less, and may be, for example, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 6% by mass or less.

[0057] In some embodiments, when there are two or more second rectangular secondary batteries 120, the variation in the mass of the non-aqueous electrolyte 70 in the two or more second rectangular secondary batteries 120 is preferably within ±5%, and more preferably within ±1%.

[0058] Note that the mass of the non-aqueous electrolyte 70 in each rectangular secondary battery 100 (the first rectangular secondary battery 110 to the second rectangular secondary battery 120) can be calculated, for example, by disassembling the rectangular secondary battery 100 and adding up the mass of the non-aqueous electrolyte 70 impregnated in the electrode body 20 and the like and the mass of the excess non-aqueous electrolyte 70 present between the exterior body 12 and the electrode body 20. Also, regarding the magnitude relationship of the mass of the non-aqueous electrolyte 70 in the first rectangular secondary battery 110 and the second rectangular secondary battery, more simply, it can also be grasped by comparing the mass of the excess non-aqueous electrolyte 70 present between the exterior body 12 and the electrode body 20 (outside the electrode body). The mass of the excess non-aqueous electrolyte 70 can be detected and calculated, for example, by non-destructively detecting the height of its liquid level by X-ray inspection.

[0059] Although not particularly limited, it is preferable that the first rectangular secondary battery 110 and the second rectangular secondary battery 120 have the same type and composition of electrolyte salt. The first rectangular secondary battery 110 and the second rectangular secondary battery 120 may each have an electrolyte salt made of LiPF6. It is preferable that the concentrations of the electrolyte salts in the first rectangular secondary battery 110 and the second rectangular secondary battery 120 are substantially the same (allowing a tolerance of about ±0.05%).

[0060] Although not particularly limited, it is more preferable that the first rectangular secondary battery 110 and the second rectangular secondary battery 120 have the same type and composition of non-aqueous solvent. Thereby, it becomes easier to equalize battery performances other than high-rate tolerance between the first rectangular secondary battery 110 and the second rectangular secondary battery 120. The first rectangular secondary battery 110 and the second rectangular secondary battery 120 may have a non-aqueous solvent made of carbonates. Among them, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferable.

[0061] Although not particularly limited, it is preferable that the first rectangular secondary battery 110 and the second rectangular secondary battery 120 have the same configuration other than the non-aqueous electrolyte, particularly the configuration of the electrode body 20 (manufacturing errors, etc. are allowable). Thereby, for example, the energy densities of the first rectangular secondary battery 110 and the second rectangular secondary battery 120 can be equalized, and a high energy density can be achieved for the entire assembled battery 500.

[0062] In some embodiments, it is preferable that the IV resistance of each of the two first rectangular secondary batteries 110 is higher than the IV resistance of the second rectangular secondary battery 120. Thereby, the effects of the technology disclosed herein can be exerted at a high level. Note that the "IV resistance in the second rectangular secondary battery 120" means the arithmetic average of the IV resistances in two or more second rectangular secondary batteries 120 when there are two or more second rectangular secondary batteries 120. Further, the "IV resistance" is a resistance value obtained by dividing the voltage drop amount ΔV in the range of 0.1 to 10 seconds by the current value I when the charge state of the rectangular secondary battery 100 is adjusted to 50% at 25°C and a constant current discharge is performed for 10 seconds. At this time, the constant current value is preferably a high rate of 1C or more. Note that 1C means a current value that can charge the battery capacity (Ah) in 1 hour.

[0063] It is preferable that the IV resistance of each of the two first rectangular secondary batteries 110 is 5% or more higher than the IV resistance of the second rectangular secondary battery 120, more preferably 8% or more higher, and still more preferably 10% or more higher. The difference in the IV resistance between the first rectangular secondary battery 110 and the second rectangular secondary battery 120 may be, for example, 20% or less, 15% or less.

[0064] The battery pack 500 can be used for various applications. Since it has excellent high-rate tolerance, it can be suitably used as a power source (driving power source) for a motor mounted on a vehicle that requires high output, such as a vehicle such as a passenger car or a truck. The type of the vehicle is not particularly limited, and examples thereof include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0065] Hereinafter, some examples related to the technology disclosed herein will be described, but the present invention is not intended to be limited to such examples.

[0066] <Test Example I: Evaluating the Influence of Heat Dissipation on High-Rate Tolerance> In this test example, two rectangular secondary batteries (Example 1 and Example 2) with the same configuration were prepared. Heat insulation materials (ceramic fibers) with different thicknesses were respectively attached to a pair of long side walls of the two rectangular secondary batteries to evaluate the influence of heat dissipation. As the electrolyte of the rectangular secondary battery, a mixture of EC, DMC, and EMC in a volume ratio of EC:DMC:EMC = 30:40:30 was used, and LiPF6 as an electrolyte salt was contained at a concentration of 1.1 mol / L. Also, the two rectangular secondary batteries had the same mass of the non-aqueous electrolyte and the same configuration (such as the electrode body, etc.) other than the non-aqueous electrolyte.

[0067] Next, in a temperature environment of 25°C, the rectangular secondary battery was adjusted to a state of SOC 50%, and a constant current discharge was performed at I = 240 A (1.2C) for 10 seconds, and the discharge resistance was measured. Then, the voltage drop ΔV that dropped between 0.1 and 10 seconds was read, and the IV resistance (initial resistance) was calculated by dividing the voltage drop ΔV by the discharge current value (240 A) according to the following formula: R = ΔV / I.

[0068] Next, in a temperature environment of 25°C, the rectangular secondary battery was adjusted to a state of SOC 15%, and after constant current charging at a charging rate of 1C for 600 seconds, constant current discharging at a discharging rate of 0.25C for 2400 seconds was taken as one cycle, and this was repeated 144 cycles to conduct a high-rate durability test. Then, after the high-rate durability test, the IV resistance was measured in the same way as the initial resistance, and the resistance increase rate (%) was calculated from the ratio of the IV resistance after the durability test to the initial resistance (IV resistance after the durability test / initial resistance). The results are shown in Table 1.

[0069]

Table 1

[0070] As shown in Table 1, in Example 1 with a thick heat insulation material, due to the low heat dissipation during high-rate charging, the rise in battery temperature was more significant compared to Example 2 with a thin heat insulation material. Example 1 with a large rise in this battery temperature had a large resistance increase rate and relatively low high-rate tolerance.

[0071] <Test Example II: Evaluating the Influence of the Amount of Electrolyte on High-Rate Tolerance> In this test example, as shown in Table 2, two prismatic secondary batteries (Example 3 and Example 4) with different masses of non-aqueous electrolyte only compared to Example 2 were further prepared, and the influence of the amount of electrolyte was evaluated in the same manner as in Example 2. Table 2 shows the relative values when the amount of electrolyte in Example 2 was set as 100 (reference). The results of the resistance increase rate are shown in Table 2.

[0072]

Table 2

[0073] As shown in Table 2, the prismatic secondary battery with a larger amount of electrolyte had a larger resistance increase rate (high-rate degradation) after high-rate charge and discharge, that is, the high-rate tolerance was lower. As described above, from the results of Test Examples I and II, by arranging the prismatic secondary battery with a relatively large amount of electrolyte at a location with high heat dissipation (both ends in the stacking direction) and arranging the prismatic secondary battery with a relatively small amount of electrolyte at a location with low heat dissipation (the central part in the stacking direction), it was also verified from the experimental results that the high-rate tolerance of a plurality of prismatic secondary batteries can be equalized.

[0074] As described above, the preferred embodiments of the present invention have been described, but the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the content disclosed in this specification and common general knowledge in the art. The technology described in the claims includes various modifications and changes of the above-exemplified embodiments.

[0075] As described above, specific aspects of the technology disclosed here include those described in the following items. Item 1: A battery pack comprising three or more rectangular secondary batteries arranged along a stacking direction, wherein each of the rectangular secondary batteries includes an electrode body and a non-aqueous electrolyte; the electrode body is a flat wound electrode body formed by stacking and winding a strip-shaped positive electrode and a strip-shaped negative electrode with a strip-shaped separator therebetween in an insulated state; the three or more rectangular secondary batteries are composed of two first rectangular secondary batteries respectively arranged at both ends in the stacking direction and one or two or more second rectangular secondary batteries arranged between the two first rectangular secondary batteries; and the mass of the non-aqueous electrolyte in each of the two first rectangular secondary batteries is greater than the mass of the non-aqueous electrolyte in the second rectangular secondary battery (however, when there are two or more second rectangular secondary batteries, the mass of the non-aqueous electrolyte in the second rectangular secondary battery refers to the arithmetic mean of the masses of the non-aqueous electrolytes in the two or more second rectangular secondary batteries). Battery pack. Item 2: The battery pack according to Item 1, wherein the non-aqueous electrolyte in each of the two first rectangular secondary batteries is 3% by mass or more greater than the non-aqueous electrolyte in the second rectangular secondary battery. Item 3: The negative electrode includes a negative electrode current collector and a negative electrode active material layer fixed to the negative electrode current collector. When the length in a direction perpendicular to the winding axis direction of the wound electrode body and perpendicular to the thickness direction of the wound electrode body is defined as the height of the wound electrode body, the length of the negative electrode active material layer in the winding axis direction is longer than the height of the wound electrode body. The battery pack according to Item 1 or 2. Item 4: The negative electrode includes a negative electrode current collector and a negative electrode active material layer fixed to the negative electrode current collector, and the length of the negative electrode active material layer in the winding axis direction of the wound electrode body is 15 cm or more. The battery pack according to Item 1 or 2. Item 5: When the state of charge of the above rectangular secondary battery is adjusted to 50% at 25°C and a constant current discharge is performed for 10 seconds, when the resistance value obtained by dividing the voltage drop amount ΔV in the range of 0.1 to 10 seconds by the current value I is defined as the IV resistance, the IV resistances of the two above first rectangular secondary batteries are each higher than the IV resistance of the above second rectangular secondary battery (however, the IV resistance of the above second rectangular secondary battery, when there are two or more second rectangular secondary batteries, refers to the arithmetic mean of the IV resistances of the two or more second rectangular secondary batteries), the assembled battery according to Item 1 or 2. Item 6: The IV resistances of the two above first rectangular secondary batteries are each 10% or more higher than the IV resistance of the above second rectangular secondary battery, the assembled battery according to Item 5.

Explanation of symbols

[0076] 10 Battery case 20 Electrode body 24 Negative electrode 24a Negative electrode active material layer 24c Negative electrode current collector 70 Non-aqueous electrolyte 100 Rectangular secondary battery 110 First rectangular secondary battery 120 Second rectangular secondary battery 300 Restraint mechanism 500 Assembled battery X Thickness direction (lamination direction) Y Width direction (winding axis direction)

Claims

1. A battery pack comprising three or more rectangular secondary batteries arranged along the stacking direction, wherein the rectangular secondary battery includes an electrode body and a non-aqueous electrolyte, the electrode body is a flat wound electrode body formed by laminating and winding a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state with a strip-shaped separator interposed therebetween, the three or more rectangular secondary batteries are composed of two first rectangular secondary batteries respectively arranged at both ends in the stacking direction and one or two or more second rectangular secondary batteries arranged between the two first rectangular secondary batteries, the mass of the non-aqueous electrolyte in each of the two first rectangular secondary batteries is greater than the mass of the non-aqueous electrolyte in the second rectangular secondary battery (however, the mass of the non-aqueous electrolyte in the second rectangular secondary battery, when there are two or more second rectangular secondary batteries, refers to the arithmetic mean of the masses of the non-aqueous electrolyte in the two or more second rectangular secondary batteries), a battery pack.

2. The non-aqueous electrolyte in each of the two first rectangular secondary batteries is 3% by mass or more more than the non-aqueous electrolyte in the second rectangular secondary battery, The battery pack according to Claim 1.

3. The negative electrode includes a negative electrode current collector and a negative electrode active material layer fixed to the negative electrode current collector, when the length in a direction perpendicular to the winding axis direction of the wound electrode body and perpendicular to the thickness direction of the wound electrode body is defined as the height of the wound electrode body, the length of the negative electrode active material layer in the winding axis direction is longer than the height of the wound electrode body, The battery pack according to Claim 1 or 2.

4. The negative electrode includes a negative electrode current collector and a negative electrode active material layer fixed to the negative electrode current collector, the length of the negative electrode active material layer in the winding axis direction of the wound electrode body is 15 cm or more, The battery pack according to Claim 1 or 2.

5. At 25°C, when the charge state of the rectangular secondary battery is adjusted to 50% and a constant current discharge is performed for 10 seconds, when the resistance value obtained by dividing the voltage drop amount ΔV in 0.1 to 10 seconds by the current value I is defined as the IV resistance, the IV resistances of the two first rectangular secondary batteries are respectively higher than the IV resistance of the second rectangular secondary battery (however, the IV resistance in the second rectangular secondary battery, when there are two or more second rectangular secondary batteries, refers to the arithmetic mean of the IV resistances in the two or more second rectangular secondary batteries), The battery pack according to Claim 1 or 2.

6. The IV resistance of each of the two first rectangular secondary batteries is 10% or more higher than the IV resistance of the second rectangular secondary battery. The assembled battery according to claim 5.

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