Energy storage module and manufacturing method thereof

Abstract

To provide a power storage module with a novel structure, in which the high-rate durability of a plurality of power storage devices can be leveled.SOLUTION: A power storage module 500 disclosed here includes a plurality of power storage devices 100. The power storage module 500 includes a low-temperature region A1 with relatively low temperature and a high-temperature region A2 with relatively high temperature when the power storage devices 100 are charged and discharged. A first power storage device 110 disposed in the low-temperature region A1 among the power storage devices 100 has lower viscosity in a nonaqueous electrolyte solution than a second power storage device 120 disposed in the high-temperature region A2.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an electricity storage module including a plurality of electricity storage devices and a method for manufacturing the same. [Background technology]

[0002] Conventionally, power storage modules formed by electrically connecting a plurality of power storage devices (single cells) have been widely used in vehicle driving power sources, etc. Patent Documents 1 and 2 are examples of related prior art documents.

[0003] For example, Patent Document 1 discloses an energy storage module having multiple submodules and a housing that houses the multiple submodules in predetermined positions. In Patent Document 1, each of the multiple submodules includes a cell group in which multiple energy storage devices (single cells) are arranged, and a restraining member that applies a restraining pressure in the arrangement direction to restrain the cell group. The housing includes an area that is prone to relatively low temperatures, and the submodules arranged in the area that is prone to low temperatures are configured so that the restraining pressure of the restraining member is relatively lower than that of the other submodules. Patent Document 1 describes that by reducing the restraining pressure on the energy storage devices in this area where high-rate resistance is prone to decrease (area that is prone to low temperatures), it is possible to level out the high-rate resistance (increase in resistance when high-rate charging and discharging is repeated) of the multiple energy storage devices. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-044212 [Patent Document 2] Japanese Patent Application Publication No. 2012-221816 [Patent Document 3] Japanese Patent Publication No. 2022-129682 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 above does not allow the multiple power storage devices included in one cell group to have different confinement pressures. Therefore, according to the inventors' studies, when a temperature distribution occurs within the cell group, it can be difficult to equalize the high-rate resistance of the multiple power storage devices. Furthermore, because a confinement member is required for each cell group, the confinement member becomes bulky, reducing the volumetric energy density of the entire power storage module. For example, when the power storage module is installed in a moving object such as a vehicle, the weight increases, potentially resulting in poor fuel efficiency.

[0006] The present invention has been made in consideration of the above circumstances, and its main object is to provide a new energy storage module that can equalize the high-rate resistance of multiple energy storage devices, and a method for manufacturing the same. [Means for solving the problem]

[0007] The present invention provides an electricity storage module including a plurality of electricity storage devices, each of which has an electrode body and a non-aqueous electrolyte, wherein the electricity storage module has a low-temperature region where the temperature is relatively low and a high-temperature region where the temperature is relatively high when the plurality of electricity storage devices are charged or discharged, and wherein a first electricity storage device of the plurality of electricity storage devices, which is arranged in the low-temperature region, has a lower viscosity of the non-aqueous electrolyte than a second electricity storage device arranged in the high-temperature region.

[0008] The present invention also provides a method for manufacturing an electricity storage module including a plurality of electricity storage devices, each of which has an electrode assembly and a non-aqueous electrolyte. The manufacturing method includes: a preparation step of preparing, as the plurality of electricity storage devices, a first electricity storage device having a non-aqueous electrolyte with a relatively low viscosity and a second electricity storage device having a non-aqueous electrolyte with a relatively high viscosity, a temperature distribution prediction step of predicting a temperature distribution in the electricity storage module when the plurality of electricity storage devices are charged and discharged, and a construction step of constructing the electricity storage module by arranging the first electricity storage device in a low-temperature region where the temperature is relatively low and arranging the second electricity storage device in a high-temperature region where the temperature is relatively high, based on the temperature distribution.

[0009] After extensive research, the inventors have found that electricity storage devices with low-viscosity non-aqueous electrolytes have relatively better high-rate resistance than electricity storage devices with high-viscosity non-aqueous electrolytes. Therefore, in the present invention, electricity storage devices with relatively low-viscosity non-aqueous electrolytes (high high-rate resistance) are arranged in low-temperature regions where high-rate resistance is likely to decrease. This makes it possible to equalize the high-rate resistance of multiple electricity storage devices. Ultimately, it is possible to improve the high-rate resistance of the entire electricity storage module. Furthermore, unlike the technology of Patent Document 1, this technology is not limited to the framework of a "cell group," and therefore allows for flexible adjustment of the high-rate resistance of each individual electricity storage device. Furthermore, since the number of restraining members can be reduced compared to the technology of Patent Document 1, it is possible to improve volumetric energy density and fuel efficiency.

[0010] Although not particularly related to the technology disclosed herein, Patent Document 3 describes the content ratio of a chain carboxylic acid ester in a non-aqueous electrolyte suitable for an electricity storage device. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view schematically illustrating an electricity storage module according to one embodiment. [Figure 2] FIG. 2 is a perspective view schematically showing the secondary battery of FIG. [Figure 3]FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of the electrode body of FIG. [Figure 5] FIG. 5 is a plan view schematically showing the power storage module and the cooling device of FIG. [Figure 6] FIG. 6 is a plan view schematically showing an electricity storage module according to a first modified example. [Figure 7] FIG. 7 is a plan view schematically showing an electricity storage module according to a second modified example. [Figure 8] FIG. 8 is a plan view schematically showing an electricity storage module according to a third modified example. [Figure 9] FIG. 9 is a plan view schematically showing an electricity storage module according to a fourth modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the technology disclosed herein will be described below with reference to the accompanying drawings. Matters necessary for implementing the present invention other than those specifically mentioned in this specification (for example, the general configuration and manufacturing process of an energy storage module or energy storage device that do not characterize the present invention) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The energy storage module disclosed herein can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

[0013] In the following drawings, the same reference numerals are used to designate components and parts that perform the same function, and redundant explanations may be omitted or simplified. In addition, in this specification, the expression "A to B" indicating a range means not less than A and not more than B, and also encompasses the meanings of "preferably larger than A" and "preferably smaller than B."

[0014] [Energy storage module] 1 is a perspective view schematically illustrating an energy storage module 500. Here, the energy storage module 500 includes a plurality of energy storage devices 100, a plurality of spacers 200, and a restraining mechanism 300. However, the plurality of spacers 200 and the restraining mechanism 300 are not essential and may be omitted in other embodiments.

[0015] In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the short side direction, the long side direction perpendicular to the short side direction, and the up-down direction, respectively, of the energy storage device 100. The short side direction X is also the arrangement direction of the energy storage devices 100. However, these directions are merely used for convenience of description and do not limit the installation form of the energy storage module 500 in any way.

[0016] The restraining mechanism 300 is a member that restrains the multiple power storage devices 100. In this embodiment, there is only one restraining mechanism 300. The restraining mechanism 300 is configured to apply an equal restraining pressure to all of the power storage devices 100 and the spacers 200 in the arrangement direction X. The restraining 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 understood as a housing that houses the multiple power storage devices 100. The pair of end plates 310 and the pair of side plates 320 are preferably made of metal.

[0017] The pair of end plates 310 are arranged at both ends of the energy storage module 500 in the arrangement direction X. The pair of end plates 310 sandwich the plurality of energy storage devices 100 and the plurality of spacers 200 in the arrangement direction X. 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 with a plurality of screws 330 so that the restraining load is, for example, approximately 10 to 15 kN. This allows a uniform restraining load to be applied to the plurality of energy storage devices 100 in the arrangement direction X, and the plurality of energy storage devices 100 are held together. However, the configuration of the restraining mechanism is not limited to this. The restraining mechanism 300 may include, for example, a plurality of restraining bands, bind bars, or the like, instead of the side plates 320.

[0018] Here, the spacers 200 are arranged between the plurality of power storage devices 100 in the arrangement direction X. That is, the power storage devices 100 and the spacers 200 are arranged alternately in the arrangement direction X. However, if the power storage module 500 does not include a spacer 200, the power storage devices 100 adjacent to each other in the arrangement direction X may abut (directly contact) each other. The spacers 200 preferably include a portion with a porous structure that allows a fluid (typically, a gas such as air) to pass through.

[0019] The electricity storage device 100 is a device that can be repeatedly charged and discharged. In this specification, the term "electricity storage device" is a concept that encompasses secondary batteries such as lithium ion secondary batteries and nickel-metal hydride batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors. Here, the plurality of electricity storage devices 100 are arranged between a pair of end plates 310 along an arrangement direction X (in other words, a thickness direction X of the electricity storage device 100). The plurality of electricity storage devices 100 are preferably restrained by a restraining mechanism 300. The shape, size, number, etc. of the plurality of electricity storage devices 100 are not limited to the embodiment disclosed in FIG. 1 and can be changed as appropriate.

[0020] Although not shown here, when the energy storage module 500 is in use, the multiple energy storage devices 100 are electrically connected to each other by conductive members such as bus bars. The connection method is not particularly limited, and may be, for example, series, parallel, or multi-series / multi-parallel. In a preferred embodiment, the multiple energy storage devices 100 are connected in series. This makes it possible to suitably improve the output characteristics to a level suitable for use in a mobile body such as a vehicle. Furthermore, in the case of a series connection, performance degradation of some of the energy storage devices 100 is likely to lead to performance degradation of the entire energy storage module 500. For this reason, applying the technology disclosed herein is particularly effective.

[0021] FIG. 2 is a perspective view of the electricity storage device 100. As can be seen from FIGS. 1 and 2, the plurality of electricity storage devices 100 are all flat and rectangular, and have the same shape here. The plurality of electricity storage devices 100 are arranged so that their long side walls 12b, which will be described later, are parallel to each other. Here, the plurality of electricity storage devices 100 are lined up in the arrangement direction X with the long side walls 12b facing each other via spacers 200.

[0022] Fig. 3 is a schematic longitudinal sectional view taken along line III-III in Fig. 2. As shown in Fig. 3, the electricity storage device 100 here includes a battery case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, and a non-aqueous electrolyte (not shown). The electricity storage device 100 is configured by accommodating the electrode assembly 20 and the non-aqueous electrolyte in the battery case 10 to which the positive electrode terminal 30 and the negative electrode terminal 40 are attached. The electricity storage device 100 is typically a non-aqueous electrolyte secondary battery, and is a lithium ion secondary battery in this case. When the electricity storage device 100 is a lithium ion secondary battery, it is particularly effective to apply the technology disclosed herein.

[0023] The battery case 10 is a container that accommodates the electrode assembly 20 and the nonaqueous electrolyte. As shown in FIG. 2, the battery case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The material of the battery case 10 may be the same as that conventionally used, and is not particularly limited. The battery case 10 is made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 3, the battery case 10 includes an exterior body 12 having an opening 12h and a sealing plate (lid) 14 that seals the opening 12h. As shown in FIG. 2, the exterior body 12 includes a substantially rectangular bottom wall 12a having long and short sides, a pair of long side walls 12b extending from the long side of the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the short side of the bottom wall 12a and facing each other. The long side walls 12b are flat.

[0024] The sealing plate 14 is a plate-like member. The sealing plate 14 has a substantially rectangular shape. As shown in FIG. 3 , the sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h of the exterior body 12. The battery case 10 is integrated with the exterior body 12 by joining (preferably welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12. The battery case 10 is hermetically sealed (sealed). The sealing plate 14 has a liquid filling hole 15 and two terminal holes 18 and 19. The liquid filling hole 15 is for filling the nonaqueous electrolyte after the sealing plate 14 is assembled to the exterior body 12. The liquid filling hole 15 is sealed with a sealing member 16. The terminal holes 18 and 19 penetrate the sealing plate 14 in the up-down direction Z.

[0025] The positive electrode terminal 30 is disposed at one end of the sealing plate 14 in the long side direction Y (the left end in FIGS. 2 and 3 ), and the negative electrode terminal 40 is disposed at the other end of the sealing plate 14 in the long side direction Y (the right end in FIGS. 2 and 3 ). As shown in FIG. 3 , the positive electrode terminal 30 and the negative electrode terminal 40 extend from the inside to the outside of the sealing plate 14 through the terminal lead-out holes 18 and 19, respectively. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are crimped to the peripheral portion of the sealing plate 14 surrounding the terminal lead-out holes 18 and 19 by crimping. Crimped portions 30c and 40c are formed at the ends of the positive electrode terminal 30 and the negative electrode terminal 40 on the exterior body 12 side (the lower end in FIG. 3 ). In this way, the positive electrode terminal 30 and the negative electrode terminal 40 are fixed to the sealing plate 14.

[0026] As shown in Fig. 3, the positive electrode terminal 30 is electrically connected to the positive electrode tab group 23 of the electrode assembly 20 via a positive electrode current collector 50 inside the exterior housing 12. The positive electrode terminal 30 is insulated from the sealing plate 14 by an internal insulating member 80 and a gasket 90. The negative electrode terminal 40 is electrically connected to the negative electrode tab group 25 of the electrode assembly 20 via a negative electrode current collector 60 inside the exterior housing 12. The negative electrode terminal 40 is insulated from the sealing plate 14 by the internal insulating member 80 and the gasket 90.

[0027] As shown in FIGS. 2 and 3 , a plate-shaped positive electrode external conductive member 32 and a plate-shaped negative electrode external conductive member 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 that electrically connect multiple electricity storage devices 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 an external insulating member 92. The electricity storage module 500 is connected in series, for example, by electrically connecting the positive electrode external conductive member 32 of one electricity storage device 100 and the negative electrode external conductive member 42 of the other electricity storage device 100 by a bus bar or the like, among the electricity storage devices 100 adjacent to each other in the arrangement direction X.

[0028] FIG. 4 is a schematic diagram showing the configuration of the electrode assembly 20. As shown in FIG. 4, the electrode assembly 20 has a positive electrode 22, a negative electrode 24, and a separator 26. Here, the electrode assembly 20 is a wound electrode assembly formed by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 with a strip-shaped separator 26 interposed therebetween and winding the stack around a winding axis WL. The electrode assembly 20 has a flat outer shape. Here, the electrode assembly 20 is disposed inside the exterior body 12 with the winding axis WL oriented substantially parallel to the long-side direction Y. However, in other embodiments, the electrode assembly 20 may be disposed inside the exterior body 12 with the winding axis WL oriented substantially parallel to the up-down direction Z. The electrode assembly 20 may also be a stacked electrode assembly formed by stacking a plurality of square-shaped (typically rectangular) positive electrodes and a plurality of square-shaped (typically rectangular) negative electrodes in an insulated state.

[0029] The configuration of the positive electrode 22 may be the same as that of a conventional positive electrode. Here, the positive electrode 22 has a positive electrode current collector 22c, and a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed to 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 metal foil. Here, the positive electrode current collector 22c is aluminum foil.

[0030] A plurality of positive electrode tabs 22t are provided at one end in the long side direction Y of the positive electrode current collector 22c (the left end in FIG. 4). The plurality of positive electrode tabs 22t protrude toward one side in the long side direction Y (the left side in FIG. 4). The plurality of positive electrode tabs 22t protrude further in the long side direction Y than the separator 26. In this example, the positive electrode tab 22t is part of the positive electrode current collector 22c and is made of metal foil (aluminum foil). The plurality of positive electrode tabs 22t are stacked at one end in the long side direction Y (the left end in FIG. 4) to form a positive electrode tab group 23. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collector 50.

[0031] 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 store 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 various additive components such as a binder and a conductive material.

[0032] The positive electrode protective layer 22p is provided at the boundary between the positive electrode current collector 22c and the positive electrode active material layer 22a in the long side 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 (e.g., alumina). The positive electrode protective layer 22p may contain optional components other than the inorganic filler, such as a conductive material, a binder, various additive components, etc.

[0033] The configuration of the negative electrode 24 may be the same as that of a conventional negative electrode. Here, the negative electrode 24 has a negative electrode current collector 24c and a negative electrode active material layer 24a fixed to 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, more preferably metal foil. Here, the negative electrode current collector 24c is copper foil.

[0034] A plurality of negative electrode tabs 24t are provided at one end of the negative electrode current collector 24c in the long side direction Y (the right end in FIG. 4). The plurality of negative electrode tabs 24t protrude toward one side in the long side direction Y (the right end in FIG. 4). The plurality of negative electrode tabs 24t protrude further in the long side direction Y than the separator 26. In this example, the negative electrode tab 24t is part of the negative electrode current collector 24c and is made of metal foil (copper foil). The plurality of negative electrode tabs 24t are stacked at one end in the long side direction Y (the right end in FIG. 4) to form a negative electrode tab group 25. The negative electrode tab group 25 is provided at a position symmetrical to the positive electrode tab group 23 in the long side direction Y. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collector 60.

[0035] 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 length Ln of the negative electrode active material layer 24a in the long side direction Y is preferably equal to or longer than the length Lp of the positive electrode active material layer 22a in the long side direction Y. The negative electrode active material layer 24a contains a negative electrode active material that can reversibly store and release 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 various additive components such as a binder, a thickener, and a dispersant.

[0036] The separator 26 is disposed between the positive electrode 22 and the negative electrode 24. The separator 26 is a member that insulates the positive electrode 22 from the negative electrode 24. The configuration of the separator 26 may be the same as that of a conventional separator. The length Ls of the separator 26 in the long side direction Y is preferably equal to or longer than the length Ln of the negative electrode active material layer 24a in the long side direction Y. The separator 26 is preferably a porous sheet (microporous film) made of a resin such as a polyolefin resin, such as polyethylene (PE) or polypropylene (PP). The separator 26 may have a functional layer (e.g., an adhesive layer or a heat-resistant layer) on the surface of the porous sheet.

[0037] A non-aqueous electrolyte typically contains a non-aqueous solvent and an electrolyte salt (supporting salt). Examples of non-aqueous solvents include various organic solvents commonly used in electrolytes for lithium-ion secondary batteries, such as carbonates, esters, ethers, nitriles, sulfones, and lactones. These solvents can be used alone or in combination of two or more. Mixed solvents containing two or more organic solvents are preferred, and those containing carbonates and / or esters are more preferred. For example, the non-aqueous solvent may be composed of several carbonates (the non-aqueous solvent may be a carbonate). In this specification, the term "carbonates" refers to all compounds containing at least one carbonate structure (-O-(C=O)-O-) in the molecule. The term "esters" refers to all compounds (excluding carbonates) containing at least one ester structure (-(C=O)-O-) in the molecule.

[0038] Specific examples of carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and fluoroethylene carbonate; and linear carbonates such as dimethyl carbonate (DMC, molecular weight = 90.1), diethyl carbonate (DEC, molecular weight = 118.1), ethyl methyl carbonate (EMC, molecular weight = 104.1), monofluoroethylene carbonate (MFEC), and difluoroethylene carbonate (DFEC). Note that the molecular weight is rounded to one decimal place (the same applies hereinafter).

[0039] Specific examples of esters include cyclic esters such as γ-butyrolactone and γ-valerolactone; and chain esters (typically chain carboxylic acid esters) such as methyl acetate (MA, molecular weight = 74.1), ethyl acetate (EA, molecular weight = 88.1), n-propyl acetate (molecular weight = 102.1), and n-butyl acetate (molecular weight = 116.1). Specific examples of ethers include cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and dioxane; and chain ethers such as diethyl ether (molecular weight = 74.1) and dimethoxyethane (molecular weight = 90.1).

[0040] Examples of the electrolyte salt include various lithium salts used as electrolyte salts in the electrolyte solutions of general lithium ion secondary batteries, specifically lithium hexafluorophosphate (LiPF6); lithium tetrafluoroborate (LiBF4); perfluoroalkylsulfonylimide compounds such as lithium bis(fluorosulfonyl)imide (LiFSI; LiN(SO2F)2), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; LiN(SO2CF3)2), and lithium bis(pentafluoroethanesulfonyl)imide. These can be used alone or in combination of two or more. Among these, it is preferable to use LiPF6. The electrolyte salt may consist of LiPF6.

[0041] The non-aqueous electrolyte may further contain additives as needed. Examples of additives include gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); film forming agents such as oxalato complex compounds containing boron atoms and / or phosphorus atoms; viscosity modifiers; etc. The non-aqueous electrolyte is typically liquid, but may also be gel-like.

[0042] FIG. 5 is a plan view schematically showing an electricity storage module 500 and a cooling device 400. Note that detailed illustration of the spacer 200 and the top surface of the electricity storage device 100 is omitted in FIG. 5. As shown in FIG. 5, the cooling device 400 includes an air intake port IP, an exhaust port OP, an air-cooled fan 410, a temperature sensor 420, and a control device 430. The cooling device 400 is an air-cooled type cooling device that uses air as a refrigerant. However, in other embodiments, the cooling device 400 may be a liquid-cooled type cooling device that uses a liquid refrigerant.

[0043] In this embodiment, the air intake port IP is provided on one side (front F side) in the arrangement direction X of the power storage module 500. The air exhaust port OP is provided on the other side (rear Rr side) in the arrangement direction X. The air cooling fan 410 is attached to the air intake port IP. The air cooling fan 410 is configured to send wind (air) to the air intake port IP. The configuration of the air cooling fan 410 is not limited, but may include, for example, an electric motor (not shown). Here, the temperature sensor 420 is disposed in the center of the power storage module 500 in the XY plane. The temperature sensor 420 is, for example, a thermocouple or a thermistor.

[0044] The control device 430 is electrically connected to the temperature sensor 420 and the electric motor of the air-cooling fan 410. For example, when the temperature sensor 420 detects that the temperature inside the power storage module 500 has reached a predetermined first temperature or higher, the control device 430 operates the air-cooling fan 410. As a result, low-temperature air outside the power storage module 500 is supplied into the power storage module 500 through the air intake port IP, generating an air flow AF inside the power storage module 500. The supplied air passes through the power storage module 500 while cooling the power storage device 100, and is then discharged through the air exhaust port OP. For example, when the temperature sensor 420 detects that the temperature inside the power storage module 500 has reached a predetermined second temperature or lower, the control device 430 stops the air-cooling fan 410. Using this air-cooling type cooling device 400, the power storage device 100 can be cooled at low cost.

[0045] According to the study by the present inventors, a temperature distribution occurs inside an energy storage module 500 equipped with a cooling mechanism such as the cooling device 400 during charging and discharging of a plurality of energy storage devices 100, and a low-temperature region A1 where the temperature is relatively low and a high-temperature region A2 where the temperature is relatively high may occur. Specifically, when the energy storage devices 100 generate heat as they are charged and discharged, adjacent energy storage devices 100 heat each other. As a result, a chain reaction of heat generation occurs between the energy storage devices 100 in the central portion of the arrangement direction X, and the temperature tends to become relatively high. On the other hand, the two ends of the arrangement direction X (the front portion F and the rear portion Rr in FIG. 5 ) have higher heat dissipation properties than the central portion, and thus the chain reaction of heat generation is less likely to occur. Therefore, the two ends of the arrangement direction X tend to have a relatively low temperature.

[0046] In particular, in this embodiment, the intake port IP and the air-cooling fan 410, through which the refrigerant (air) is supplied, are arranged on the front F side in the arrangement direction X, and the exhaust port OP is arranged on the rear Rr side in the arrangement direction X. For this reason, both ends in the arrangement direction X tend to have low temperatures. Therefore, the central portion in the arrangement direction X becomes a high-temperature region A2 with a relatively high temperature, and both ends in the arrangement direction X (the front F portion and the rear Rr portion in FIG. 5) tend to become low-temperature regions A1 with a relatively low temperature. In particular, the front F portion in the arrangement direction X, where the intake port IP and the air-cooling fan 410 are arranged, tends to have the lowest temperature. That is, in this embodiment, at least the front F side in the arrangement direction X tends to become a low-temperature region A1 with a relatively low temperature.

[0047] As described in, for example, Patent Document 1, when a temperature distribution occurs within the power storage module 500, variations in the high-rate resistance of the power storage device 100 may occur. Specifically, the high-rate resistance of the power storage device 100 may be reduced in the low-temperature region A1. In this case, if the charging and discharging of the entire power storage module 500 is controlled based on the high-rate resistance of the power storage device 100 in the low-temperature region A1, the high high-rate resistance of the power storage device 100 in the high-temperature region A2 cannot be fully utilized. On the other hand, if the high-rate resistance of the power storage device 100 in the high-temperature region A2 is used as the reference, a high voltage is applied to the power storage device 100 in the low-temperature region A1, which is likely to accelerate high-rate degradation. When a temperature distribution occurs within the power storage module 500, the high-rate resistance of the entire power storage module 500 may be reduced due to the influence of the high-rate resistance of the power storage device 100 in the low-temperature region A1. Furthermore, when the power storage module is installed in a moving object such as a vehicle, fuel efficiency may be reduced.

[0048] Therefore, in the technology disclosed herein, a first electricity storage device 110 and a second electricity storage device 120, each having a different viscosity of non-aqueous electrolyte, are used as the multiple electricity storage devices 100. The viscosity of the non-aqueous electrolyte in the first electricity storage device 110 is lower than that in the second electricity storage device 120. As will be described in detail later, the inventors have confirmed that the lower the viscosity of the non-aqueous electrolyte, the higher the high-rate resistance. Therefore, in this embodiment, the first electricity storage device 110, which has a relatively low viscosity of non-aqueous electrolyte (high high-rate resistance), is arranged in a low-temperature region A1, where the temperature is relatively low, in this case, at both ends in the arrangement direction X (the front portion F and the rear portion Rr in FIG. 5 ). Furthermore, the second electricity storage device 120, which has a relatively high viscosity of non-aqueous electrolyte (low high-rate resistance), is arranged in a high-temperature region A2, where the temperature is relatively high, in this case, at the center in the arrangement direction X.

[0049] With this configuration, the high-rate resistance of the multiple power storage devices 100 can be equalized to a high level. Consequently, the acceleration of degradation can be suppressed, improving the high-rate resistance of the entire power storage module 500. Furthermore, unlike the technology of Patent Document 1, there is no need to be bound by the framework of a "cell group," so the high-rate resistance of the multiple power storage devices 100 can be flexibly adjusted according to the temperature distribution within the power storage module 500. Therefore, it may be possible to equalize the high-rate resistance of the multiple power storage devices 100 with higher accuracy than with the technology of Patent Document 1. Furthermore, since the number of restraint mechanisms 300 can be reduced compared to the technology of Patent Document 1, volumetric energy density and fuel efficiency can also be improved. Additionally, the number of parts can be reduced, reducing manufacturing costs.

[0050] In this specification, the term "viscosity" refers to the viscosity measured using a commercially available rheometer at a measurement temperature of 25°C and a shear rate of 10 to 600 s -1 When there are a plurality of first electricity storage devices 110 and a plurality of second electricity storage devices 120 as in the present embodiment, it is preferable that the viscosity of the nonaqueous electrolyte in each of the plurality of first electricity storage devices 110 is lower than that of the plurality of second electricity storage devices 120.

[0051] Although not particularly limited, from the viewpoint of improving the characteristics of the electricity storage device 100 (for example, achieving a high level of balance between energy density and high-rate resistance), the viscosity of the nonaqueous electrolyte in both the first electricity storage device 110 and the second electricity storage device 120 is preferably approximately 1 to 10 mPa·s, more preferably 2 to 5 mPa·s, and for example, 2.7 to 4.2 mPa·s. In particular, by setting the viscosity to a predetermined value or less, the high-rate charge / discharge characteristics of the electricity storage module 500 can be improved.

[0052] Although it depends on the temperature distribution in the power storage module 500, in one embodiment, the viscosity of the non-aqueous electrolyte of the first power storage device 110 may be 4 mPa·s or less, 3.5 mPa·s or less, or 3 mPa·s or less. In particular, by setting the viscosity to a predetermined value or less, the high-rate charge / discharge characteristics of the first power storage device 110 can be further improved. The viscosity of the non-aqueous electrolyte of the first power storage device 110 may be, for example, 1 mPa·s or more, or 2 mPa·s or more. The viscosity of the non-aqueous electrolyte of the second power storage device 120 may be, for example, 5 mPa·s or less, 4 mPa·s or less, 3.5 mPa·s or less, or 3 mPa·s or less. In particular, by setting the viscosity to a predetermined value or less, the high-rate charge / discharge characteristics of the second power storage device 120 can be further improved. The viscosity of the non-aqueous electrolyte of the second power storage device 120 may be, for example, 2 mPa·s or more, or 3 mPa·s or more.

[0053] The difference in viscosity between the first electricity storage device 110 and the second electricity storage device 120 (i.e., (viscosity of the second electricity storage device 120) - (viscosity of the first electricity storage device 110)) is a design item that is adjusted as appropriate, for example, depending on the temperature distribution in the electricity storage module 500. For this reason, although not particularly limited, in cases where the temperature distributions of the first electricity storage device 110 and the second electricity storage device 120 differ greatly, the difference in viscosity between the first electricity storage device 110 and the second electricity storage device 120 is preferably 0.1 mPa·s or more, more preferably 0.2 mPa·s or more, and even more preferably, for example, 1 mPa·s or more. As a result, The difference in high-rate resistance becomes larger, and the effects of the technology disclosed herein can be more pronounced. Note that, when there are a plurality of first electricity storage devices 110 and a plurality of second electricity storage devices 120, the difference in viscosity can be the difference between the average viscosity of the plurality of first electricity storage devices 110 and the average viscosity of the plurality of second electricity storage devices 120.

[0054] From the viewpoints of improving ionic conductivity and reducing the viscosity of the nonaqueous electrolyte, the first electricity storage device 110 and the second electricity storage device 120 each preferably contain, as a nonaqueous solvent, both a cyclic solvent (for example, at least one of a cyclic carbonate, a cyclic ester, and a cyclic ether) and a chain solvent (for example, at least one of a chain carbonate, a chain ester, and a chain ether). In particular, the first electricity storage device 110 and the second electricity storage device 120 each more preferably contain a cyclic carbonate (for example, EC), and a chain carbonate (for example, EMC) and / or a chain ester (for example, MA). Note that the term "chain solvent" as used herein refers to a chain compound in general having a molecular structure without any rings, and is a compound other than a cyclic solvent.

[0055] In both the first electricity storage device 110 and the second electricity storage device 120, the content of the cyclic solvent (e.g., cyclic carbonate, more specifically, e.g., EC) in the entire nonaqueous solvent is preferably 60% by volume or less, more preferably 50% by volume or less, and may be, for example, 10 to 50% by volume, or 20 to 50% by volume.

[0056] According to the studies of the present inventors, the viscosity of the non-aqueous electrolyte can be adjusted relatively easily by, for example, changing the type or mixing ratio of the non-aqueous solvent, more specifically, by increasing the content ratio of the chain solvent, or by selectively adding or increasing the content ratio of a chain solvent having a smaller molecular weight and lower viscosity (e.g., MA).

[0057] In the first embodiment, the first electricity storage device 110 preferably has a higher content ratio of a chain solvent (for example, a chain carbonate, more specifically, for example, EMC) in the entire non-aqueous solvent than the second electricity storage device 120. In other words, the first electricity storage device 110 preferably has a lower content ratio of a cyclic solvent (for example, a cyclic carbonate, more specifically, for example, EC) in the entire non-aqueous solvent than the second electricity storage device 120. As will be described in detail later, this allows the viscosity of the first electricity storage device 110 to be adjusted to be lower than the viscosity of the second electricity storage device 120.

[0058] The difference in the content ratio of the chain solvent (e.g., a chain carbonate) between the first electricity storage device 110 and the second electricity storage device 120 is a design factor that is adjusted as appropriate, for example, depending on the temperature distribution in the electricity storage module 500. For this reason, although not particularly limited, when the temperature distribution between the first electricity storage device 110 and the second electricity storage device 120 is significantly different, the difference in the content ratio of the chain solvent (e.g., a chain carbonate) between the first electricity storage device 110 and the second electricity storage device 120 is preferably 5% by volume or more, more preferably 10% by volume or more, or 20% by volume or more. This increases the difference in high-rate resistance, and the effects of the technology disclosed herein can be more significantly exhibited. Note that when there are multiple first electricity storage devices 110 and multiple second electricity storage devices 120, the difference in the content ratio of the chain solvent may be the difference between the average content ratio of the multiple first electricity storage devices 110 and the average content ratio of the multiple second electricity storage devices 120.

[0059] In the first embodiment, the nonaqueous solvent of the first electricity storage device 110 essentially contains a chain solvent (for example, a chain carbonate) and may further contain a cyclic solvent (for example, a cyclic carbonate). The nonaqueous solvent of the first electricity storage device 110 may be composed of, for example, a chain carbonate, or may be composed of a chain carbonate and a cyclic carbonate. The nonaqueous solvent of the second electricity storage device 120 essentially contains a cyclic solvent (for example, a cyclic carbonate) and may further contain a chain solvent (for example, a chain carbonate). In other words, the nonaqueous solvent of the second electricity storage device 120 may or may not contain a chain solvent. The nonaqueous solvent of the second electricity storage device 120 may be composed of, for example, a cyclic carbonate, or may be composed of a chain carbonate and a cyclic carbonate.

[0060] Furthermore, in the second embodiment, when a chain solvent having a molecular weight of 90 or less is used as the low-molecular-weight chain solvent, the first electricity storage device 110 preferably has a higher content of the low-molecular-weight chain solvent in the entire nonaqueous solvent (or chain solvent) than the second electricity storage device 120. As will be described in detail later, this allows the viscosity of the first electricity storage device 110 to be adjusted to be lower than the viscosity of the second electricity storage device 120. The low-molecular-weight chain solvent preferably has a molecular weight of, for example, 50 or more, or 60 or more, and 80 or less, or 75 or less. Examples of low-molecular-weight chain solvents include low-molecular-weight chain esters such as methyl acetate (MA) and ethyl acetate; and low-molecular-weight chain ethers such as diethyl ether. Among these, low-molecular-weight chain esters are preferred, and MA is particularly preferred. That is, the first electricity storage device 110 preferably has a higher content of methyl acetate (MA) in the entire nonaqueous solvent (or chain solvent) than the second electricity storage device 120. This allows the high-rate resistance of the entire electricity storage module 500 to be improved to a higher level.

[0061] The difference in the content ratio of the low-molecular-weight chain solvent (e.g., MA) in the chain solvent between the first electricity storage device 110 and the second electricity storage device 120 is a design factor that is adjusted as appropriate, for example, depending on the temperature distribution in the electricity storage module 500. Therefore, although not particularly limited, when the temperature distribution between the first electricity storage device 110 and the second electricity storage device 120 is significantly different, the difference in the content ratio of the low-molecular-weight chain solvent (e.g., MA) in the chain solvent between the first electricity storage device 110 and the second electricity storage device 120 is preferably 10% by volume or more, and more preferably 15% by volume or more. This increases the difference in high-rate resistance, and the effects of the technology disclosed herein can be more significantly exhibited. Note that, when there are multiple first electricity storage devices 110 and multiple second electricity storage devices 120, the difference in the content ratio of the low-molecular-weight chain solvent may be the difference between the average content ratio of the multiple first electricity storage devices 110 and the average content ratio of the multiple second electricity storage devices 120.

[0062] In the second embodiment, the nonaqueous solvent of the first electricity storage device 110 essentially contains a low-molecular-weight chain solvent (for example, a low-molecular-weight chain ester, more specifically, for example, MA), and may further contain other chain solvents (for example, a chain carbonate) or cyclic solvents (for example, cyclic carbonate). The nonaqueous solvent of the first electricity storage device 110 may be composed of, for example, a low-molecular-weight chain solvent, or may be composed of a low-molecular-weight chain solvent (for example, a low-molecular-weight chain ester) and a carbonate (a chain carbonate and / or a cyclic carbonate). The nonaqueous solvent of the second electricity storage device 120 may or may not contain a low-molecular-weight chain solvent (for example, a low-molecular-weight chain ester). The nonaqueous solvent of the second electricity storage device 120 may be composed of, for example, a solvent other than a low-molecular-weight chain solvent (for example, a chain carbonate and / or a cyclic carbonate).

[0063] In the second embodiment, the content of a low-molecular-weight chain solvent (for example, a low-molecular-weight chain ester, more specifically, for example, MA) in the entire nonaqueous solvent is preferably 50% by volume or less, and may be, for example, 0 to 50% by volume, or 10 to 30% by volume, in both the first electricity storage device 110 and the second electricity storage device 120. In the second embodiment, it is more preferable that the content of the chain solvent (for example, a chain carbonate) is the same in the first electricity storage device 110 and the second electricity storage device 120.

[0064] In one embodiment, it is more preferable that the type and concentration of the electrolyte salt (or additive) be the same between the first electricity storage device 110 and the second electricity storage device 120. The concentration of the electrolyte salt is preferably approximately 0.5 to 2.0 mol / L, more preferably 1.1±0.2 mol / L (0.9 to 1.3 mol / L), and still more preferably 1.1±0.1 mol / L (1 to 1.2 mol / L). This makes it easier to equalize the battery performance, including high-rate resistance, between the first electricity storage device 110 and the second electricity storage device 120.

[0065] In one embodiment, the first electricity storage device 110 and the second electricity storage device 120 preferably have the same configuration other than the nonaqueous electrolyte, particularly the same configuration of the electrode assembly 20 (manufacturing errors and the like are acceptable). This makes it easier to equalize the battery performance other than high-rate resistance between the first electricity storage device 110 and the second electricity storage device 120. For example, the energy densities of the first electricity storage device 110 and the second electricity storage device 120 can be equalized, thereby achieving a high energy density for the electricity storage module 500 as a whole.

[0066] [Method of manufacturing energy storage modules] Next, a method for manufacturing an energy storage module 500 including a plurality of energy storage devices 100 will be described. The energy storage module 500 can be manufactured by a manufacturing method including, for example, (Step A) a preparation step of preparing a first energy storage device 110 and a second energy storage device 120; (Step B) a temperature distribution prediction step of predicting a temperature distribution in the energy storage module 500; and (Step C) a construction step of combining the first energy storage device 110 and the second energy storage device 120 to construct the energy storage module 500. The order of the (Step A) preparation step and the (Step B) temperature distribution prediction step is not particularly limited. For example, the (Step A) preparation step may be followed by the (Step B) temperature distribution prediction step, or the (Step B) preparation step may be followed by the (Step A) temperature distribution prediction step, or both steps may be performed simultaneously. The manufacturing method disclosed herein may further include other steps at any stage.

[0067] In the (Step A) preparation step, a first electricity storage device 110 having a non-aqueous electrolyte solution with a relatively low viscosity and a second electricity storage device 120 having a non-aqueous electrolyte solution with a relatively high viscosity are prepared as a plurality of electricity storage devices 100. In this embodiment, the (Step A) preparation step includes, in this order, (A-1) an electrolyte solution preparation step of preparing a non-aqueous electrolyte solution, (A-2) an accommodation step of accommodating the electrode assembly 20 and the prepared non-aqueous electrolyte solution in the battery case 10, and (A-3) a conditioning step.

[0068] In the (A-1) electrolyte solution preparation step, at least two types of nonaqueous electrolyte solutions with different viscosities are prepared. Specifically, a first electrolyte solution with a relatively low viscosity is prepared for the first electricity storage device 110, and a second electrolyte solution with a relatively high viscosity is prepared for the second electricity storage device 120. The first and second electrolyte solutions may be commercially available or may be prepared by a conventionally known method. In a preferred first embodiment, for example, first, a chain solvent (e.g., a chain carbonate, more specifically, EMC) and a cyclic solvent (e.g., a cyclic carbonate, more specifically, EC) are prepared as nonaqueous solvents. Then, by changing the mixing ratio of these solvents, two or more types of nonaqueous solvents with different chain solvent contents are prepared. Next, the above-mentioned electrolyte salt (e.g., LiPF6) is added to the prepared nonaqueous solvent, and the mixture is stirred and mixed until uniform. In this way, a first electrolytic solution for the first electricity storage device 110 and a second electrolytic solution for the second electricity storage device 120 are prepared. In a preferred second embodiment, for example, first, a low-molecular-weight chain solvent (e.g., MA) and a non-aqueous solvent other than the low-molecular-weight chain solvent (e.g., carbonates) are prepared as non-aqueous solvents. Then, by changing the mixing ratio of these solvents, two or more non-aqueous solvents with different contents of the low-molecular-weight chain solvent are prepared. Next, the above-mentioned electrolyte salt (e.g., LiPF6) is added to the prepared non-aqueous solvent, and the mixture is stirred and mixed until uniform. In this way, a first electrolytic solution for the first electricity storage device 110 and a second electrolytic solution for the second electricity storage device 120 are prepared.

[0069] In the (A-2) accommodation step, a separately prepared electrode assembly 20 is accommodated in the battery case 10 together with the first and second electrolytic solutions. In a preferred embodiment, first, the positive electrode tab group 23 of the electrode assembly 20 is joined to the positive electrode current collector 50, and the negative electrode tab group 25 of the electrode assembly 20 is joined to the negative electrode current collector 60. This integrates the sealing plate 14 and the electrode assembly 20. Next, the sealing plate 14 is placed over the opening 12h of the exterior body 12, and the electrode assembly 20 is placed inside the exterior body 12. Next, the sealing plate 14 is welded to the periphery of the opening 12h of the exterior body 12, thereby integrating the exterior body 12 and the sealing plate 14. Next, the first and second electrolytic solutions are injected into the battery case 10 through the injection hole 15 of the sealing plate 14. In this way, a battery assembly for the first power storage device 110 and a battery assembly for the second power storage device 120 are fabricated.

[0070] (A-3) In the conditioning step, the fabricated battery assembly is charged at least once. Preferably, the fabricated battery assembly is charged and discharged at least once. Charging and discharging of the battery assembly can be performed in the same manner as conventional methods. Typically, an external power source is connected between the positive electrode terminal 30 and the negative electrode terminal 40, and charging or discharging is performed until a predetermined state of charge (SOC) is reached between the terminals. Then, the battery case 10 is hermetically sealed (sealed). In this manner, a first electricity storage device 110 and a second electricity storage device 120 having different viscosities can be prepared.

[0071] (Step B) In the temperature distribution prediction step, the temperature distribution in the power storage module 500 is predicted when a plurality of power storage devices 100 are charged and discharged. That is, for example, in the embodiment shown in FIG. 5 , both ends in the arrangement direction X (particularly the front F portion in the arrangement direction X) tend to become low-temperature regions A1. However, the temperature distribution in the power storage module 500 may vary depending on the configuration of the cooling device 400 (e.g., the installation positions and number of the air intake port IP, the air exhaust port OP, and the air-cooling fan 410) and the heat dissipation path. Furthermore, for example, the range of the low-temperature region A1 (the length in the arrangement direction X) may also vary depending on, for example, the number of power storage devices 100 and the charge and discharge conditions. Therefore, it is preferable to predict the temperature distribution in the power storage module 500 during charge and discharge by a preliminary experiment or a simulation using commercially available analysis software. In particular, it is preferable to construct a power storage module for preliminary testing that simulates the power storage module 500, measure the temperature distribution, and predict the temperature distribution in the power storage module 500 based on the actual measurement.

[0072] In a preferred embodiment, first, a plurality of power storage devices for a preliminary test, which are different from the first power storage device 110 and the second power storage device 120 produced in the preparation step, are prepared, and a temperature sensor is attached to each of them. Next, a power storage module for a preliminary test simulating the power storage module 500 is assembled using the plurality of power storage devices for the preliminary test. Next, the plurality of power storage devices for the preliminary test are actually charged and discharged (preferably at a high rate), and the temperature distribution at this time is obtained. The charge and discharge conditions are preferably conditions that assume the actual use mode. Then, based on the obtained temperature distribution, the temperature distribution within the power storage module 500 is predicted, and the power storage module is divided (e.g., divided into two), for example, into a low-temperature region A1 and a high-temperature region A2.

[0073] (Step C) In the construction step, the first electricity storage device 110 and the second electricity storage device 120 are arranged based on the temperature distribution predicted in the temperature distribution prediction step to construct the electricity storage module 500. Specifically, the first electricity storage device 110, which has a non-aqueous electrolyte with a relatively low viscosity, is arranged in an area designated as the low temperature area A1, and the second electricity storage device 120, which has a non-aqueous electrolyte with a relatively high viscosity, is arranged in an area designated as the high temperature area A2. Then, the first electricity storage device 110 and the second electricity storage device 120 are restrained and held together as a unit by a restraining mechanism 300, for example, together with a plurality of spacers 200. In this manner, the electricity storage module 500 can be constructed.

[0074] [Uses of energy storage modules] The power storage module 500 can be used for a variety of purposes, but because it has excellent high-rate durability, it can be suitably used in purposes requiring high output, such as a power source (driving power source) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, and examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). Mounting the power storage module 500 on a moving object such as a vehicle can improve the fuel efficiency (electricity cost) of the moving object.

[0075] Some test examples relating to the present invention will be described below, but it is not intended that the present invention be limited to these test examples.

[0076] [Test Example I] In this test example, by varying the content ratio of the chain solvent (specifically, EMC), electricity storage devices with different viscosities of the non-aqueous electrolyte were constructed, and high-rate durability was confirmed. Specifically, first, non-aqueous electrolytes containing the non-aqueous solvents shown in Table 1 were prepared, and the viscosity was measured using a rheometer in a temperature environment of 25°C. Specifically, 1.5 mL of the non-aqueous electrolyte was placed on the plate of the rheometer, and the shear rate was set to 10 to 600 s -1The viscosity of the non-aqueous electrolyte was calculated from the change in stress (horizontal axis: shear rate, vertical axis: stress) when the values ​​were plotted (slope (shear rate / stress)). The results are shown in Table 1.

[0077] Next, electricity storage devices (lithium ion secondary batteries, Examples 1 to 4) were fabricated using the nonaqueous electrolyte solution. All of the electricity storage devices used LiPF6 as the electrolyte salt, with a molar concentration of 1 mol / L. The configurations other than the nonaqueous electrolyte solution were the same for all of the electricity storage devices. Next, in a temperature environment of 25°C, the electricity storage devices were adjusted to a state of SOC 50%, and constant current discharge was performed at 150 A for 10 seconds, and the discharge resistance was measured. Next, the battery voltage ΔV that had dropped over 10 seconds was read, and the IV resistance (initial resistance) was calculated based on the battery voltage ΔV and the discharge current value (150 A).

[0078] Next, the energy storage device was adjusted to a 50% SOC state in a 25°C temperature environment, and subjected to 1000 cycles of constant-current charging at a charge rate of 150 A for 10 seconds, followed by a 5-second pause, followed by a 10 A discharge rate for 150 seconds, followed by a 5-second pause. This cycle constituted one charge / discharge cycle, and a high-rate durability test was performed. After the high-rate durability test, the IV resistance was measured in the same manner 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. Table 1 shows relative values, with the resistance increase rate of Example 1 set to 1.00 (reference).

[0079] [Table 1]

[0080] As shown in Table 1, the viscosity of the nonaqueous electrolyte decreased with increasing chain solvent (specifically, EMC) content, i.e., the lower the cyclic solvent (specifically, EC) content. This indicates that the viscosity of the nonaqueous electrolyte can be adjusted by changing the chain solvent (specifically, EMC) content. Furthermore, the lower the viscosity of the nonaqueous electrolyte, the smaller the increase in resistance after the high-rate durability test, i.e., the higher the high-rate durability of the energy storage device. While not intended to be particularly restrictive, this result may be due to the fact that the lower the viscosity of the nonaqueous electrolyte, the better the movement (liquid flow) of the electrolyte during high-rate charge / discharge, making it less likely for the salt concentration to become uneven or more easily alleviated, resulting in less increase in resistance even with repeated high-rate charge / discharge.

[0081] Test Example II In this test example, electricity storage devices with different viscosities of non-aqueous electrolytes were constructed by varying the content ratio of low-molecular-weight chain solvent (specifically, MA), and high-rate durability was confirmed. Specifically, first, non-aqueous electrolytes containing the non-aqueous solvents shown in Table 2 were prepared, and electricity storage devices (lithium ion secondary batteries, Examples 5 and 6) were fabricated using the non-aqueous electrolytes in the same manner as in Test Example I. Then, a high-rate durability test was conducted in the same manner as in Test Example I, and the resistance increase rate was calculated. The results are shown in Table 2. Table 2 also shows Example 3 of Test Example I, and the resistance increase rate of Example 3 is expressed as a relative value when 1.00 (reference) is used.

[0082] [Table 2]

[0083] As shown in Table 2, the higher the content of the low-molecular-weight chain solvent (specifically, MA), the lower the viscosity of the non-aqueous electrolyte. Therefore, it was found that the viscosity of the non-aqueous electrolyte can be adjusted by changing the content of the low-molecular-weight chain solvent (specifically, MA). Furthermore, as in Test Example I, the lower the viscosity of the non-aqueous electrolyte, the smaller the increase in resistance after the high-rate durability test, i.e., the higher the high-rate durability. From the above, the experimental results also support the idea that electricity storage devices with low-viscosity non-aqueous electrolytes have relatively better high-rate durability than electricity storage devices with high-viscosity non-aqueous electrolytes.

[0084] Although the preferred embodiment of the present invention has been described above, the above embodiment is merely an example. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiment. For example, it is possible to replace part of the above-described embodiment with other modifications, or to add other modifications to the above-described embodiment. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0085] (1) For example, in the above-described embodiment, in the preparation step (step A), the electricity storage devices 100 are manufactured with intentionally different viscosities. More specifically, in the first embodiment, the electricity storage devices 100 are manufactured with intentionally different content ratios of the chain solvent (specifically, EMC), and in the second embodiment, the electricity storage devices 100 are manufactured with intentionally different content ratios of the low-molecular-weight chain solvent (specifically, MA). However, this is not limiting. For example, the first electricity storage device 110 and the second electricity storage device 120 may be prepared by selecting and preparing them within a predetermined range of acceptable products from a large number of electricity storage devices with varying viscosities. Furthermore, in addition to the type of solvent, the content ratio of an additive (viscosity modifier) ​​may be varied among the plurality of electricity storage devices 100, for example.

[0086] (2) For example, in the embodiment of FIG. 5 described above, both ends in the arrangement direction X (the front F portion and the rear Rr portion in FIG. 5 ) are low-temperature regions A1 where the temperature is relatively low, and the center portion in the arrangement direction X is a high-temperature region A2 where the temperature is relatively high. However, this is not limited to this. As described above, the temperature distribution in the power storage module 500 can vary depending on the configuration of the cooling device 400 (for example, the installation positions and number of the air intake port IP, the air exhaust port OP, and the air-cooling fans 410), the number of power storage devices 100, the charge / discharge conditions, etc. Furthermore, in the embodiment of FIG. 5 described above, the power storage module 500 is divided into two temperature regions, the low-temperature region A1 and the high-temperature region A2, and further, the temperature distribution is symmetrical in the arrangement direction X. However, this is not limited to this. For example, the power storage module 500 may be divided into three or more temperature regions. In this case, in the embodiment of Fig. 5, the low temperature region A1 on the rear Rr side in the arrangement direction X may be made into a medium temperature region A3, which has a temperature higher than that of the low temperature region A1 and a temperature lower than that of the high temperature region A2. Furthermore, when the cooling path and heat dissipation path are complex, the temperature distribution may be random, for example, with the low temperature region A1 and the high temperature region A2 appearing alternately. Some specific modified examples will be described below with reference to Figs. 6 to 9. Note that the cooling device is not shown in Figs. 6 to 9.

[0087] (First Modification) FIG. 6 is a plan view of a power storage module 500a according to a first modification. As described above, it is known that chain heat generation between the power storage devices 100 is likely to occur in the central portion of the arrangement direction X. For this reason, although not shown in FIG. 6, an air intake port IP and / or an air-cooling fan 410 through which a refrigerant (air) is supplied may be additionally installed in the central portion of the arrangement direction X to strongly cool the central portion. In this case, as shown in FIG. 6, the temperature distribution of the power storage module 500a is opposite to that in FIG. 5, with the central portion of the arrangement direction X becoming a low-temperature region A1 with a relatively low temperature, and both ends of the arrangement direction X (the front portion F and the rear portion Rr in FIG. 6) becoming high-temperature regions A2 with a relatively high temperature.

[0088] In such a case, as shown in FIG. 6, it is preferable to arrange a first electricity storage device 110 having a non-aqueous electrolyte solution with a relatively low viscosity (high high-rate resistance) in the center of the arrangement direction X, which is the low-temperature region A1, and arrange a second electricity storage device 120 having a non-aqueous electrolyte solution with a relatively high viscosity (low high-rate resistance) at both ends of the arrangement direction X, which are the high-temperature regions A2.

[0089] (Second and Third Modifications) Fig. 7 is a plan view of a power storage module 500b according to a second modification. Fig. 8 is a plan view of a power storage module 500c according to a third modification. For example, if the air-cooling fan 410 installed on the front F side in the arrangement direction X in Fig. 5 is powerful and has high cooling capacity, the temperature distribution in the power storage modules 500b and 500c may be such that the front F part in the arrangement direction X becomes a low-temperature region A1 where the temperature is relatively low, and the rear Rr part in the arrangement direction X becomes a high-temperature region A2 where the temperature is relatively high, as shown in Figs. 7 and 8, respectively.

[0090] In such a case, as shown in Figures 7 and 8, it is preferable to arrange the first electricity storage device 110, whose non-aqueous electrolyte has a relatively low viscosity (high high-rate resistance), in the front F part in the arrangement direction X, which is the low-temperature region A1, and to arrange the second electricity storage device 120, whose non-aqueous electrolyte has a relatively high viscosity (low high-rate resistance), in the rear Rr part in the arrangement direction X, which is the high-temperature region A2.

[0091] Furthermore, the distribution of the low temperature region A1 and the high temperature region A2 may differ depending on, for example, the number of power storage devices 100, the charge / discharge conditions, etc. Therefore, the low temperature region A1 and the high temperature region A2 may be uniformly provided in the arrangement direction X as shown in Fig. 7, or may be non-uniformly provided in the arrangement direction X as shown in Fig. 8. In other words, the number of first power storage devices 110 and the number of second power storage devices 120 included in the power storage module 500 may be the same or different.

[0092] (Fourth Modification) Fig. 9 is a plan view of a power storage module 500d according to a fourth modification. As shown in Fig. 9, the temperature distribution of the power storage module 500d is divided into more detailed sections than in Fig. 5. That is, both ends in the arrangement direction X (the front F section and the rear Rr section in Fig. 6) are low-temperature regions A1 with relatively low temperatures, the central section in the arrangement direction X is a high-temperature region A2 with relatively high temperatures, and between the low-temperature region A1 and the high-temperature region A2 is a medium-temperature region A3 with a temperature higher than the low-temperature region A1 and lower than the high-temperature region A2.

[0093] 9, it is preferable to arrange a first electricity storage device 110 having a nonaqueous electrolyte solution with a relatively low viscosity (high high-rate resistance) at both ends in the arrangement direction X, which are the low-temperature regions A1, arrange a second electricity storage device 120 having a nonaqueous electrolyte solution with a relatively high viscosity (low high-rate resistance) at the center in the arrangement direction X, which is the high-temperature region A2, and arrange a third electricity storage device 130 having a nonaqueous electrolyte solution with a lower viscosity than the second electricity storage device 120 and a higher viscosity than the first electricity storage device 110, at the medium-temperature region A3 between the low-temperature region A1 and the high-temperature region A2. In other words, it is preferable to arrange the multiple electricity storage devices 100 so that the viscosity of the nonaqueous electrolyte decreases stepwise in the order of the high-temperature region A2, the medium-temperature region A3, and the low-temperature region A1, in this case from the center toward both ends in the arrangement direction X.

[0094] 9, the inside of the power storage module 500 is divided into three temperature zones, but it is of course possible to divide it into four or more temperature zones. By dividing the inside of the power storage module 500 into smaller zones according to the temperature distribution in this way, the effects of the technology disclosed herein can be exerted to a high level, and the high-rate resistance of the entire power storage module 500 can be further improved.

[0095] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: An energy storage module including a plurality of energy storage devices, each of the plurality of energy storage devices having an electrode body and a non-aqueous electrolyte, wherein the energy storage module has a low-temperature region where the temperature is relatively low and a high-temperature region where the temperature is relatively high when the plurality of energy storage devices are charged or discharged, and wherein a first energy storage device of the plurality of energy storage devices, which is arranged in the low-temperature region, has a lower viscosity of the non-aqueous electrolyte than a second energy storage device arranged in the high-temperature region. Item 2: The energy storage module according to Item 1, wherein the energy storage module includes a medium temperature region that is higher in temperature than the low temperature region and lower in temperature than the high temperature region, and the plurality of energy storage devices are arranged such that the viscosity of the nonaqueous electrolyte solution decreases in stages in the order of the high temperature region, the medium temperature region, and the low temperature region. Item 3: The electricity storage module according to item 1 or 2, wherein the viscosity of both the first electricity storage device and the second electricity storage device is 2 mPa·s or more and 5 mPa·s or less. Item 4: The electricity storage module according to any one of Items 1 to 3, wherein the first electricity storage device has a higher content of chain solvent in the nonaqueous electrolyte than the second electricity storage device. Item 5: The electricity storage module according to item 4, wherein the content of the chain solvent in the nonaqueous electrolyte in both the first electricity storage device and the second electricity storage device is 50% by volume or less. Item 6: The electricity storage module according to any one of Items 1 to 5, wherein when the chain solvent having a molecular weight of 90 or less is a low-molecular-weight chain solvent, the first electricity storage device has a higher content of the low-molecular-weight chain solvent in the non-aqueous electrolyte solution than the second electricity storage device. Item 7: The electricity storage module according to Item 6, wherein the low-molecular-weight chain solvent is methyl acetate. Item 8: The electricity storage module according to any one of Items 1 to 7, wherein the content of the low-molecular-weight chain solvent in the non-aqueous electrolyte solution in both the first electricity storage device and the second electricity storage device is 50% by volume or less. Item 9: The power storage module according to any one of Items 1 to 8, wherein the first power storage device and the second power storage device are connected in series. Item 10: A method for manufacturing an electricity storage module comprising a plurality of electricity storage devices, each of the plurality of electricity storage devices having an electrode body and a non-aqueous electrolyte, the method including: a preparation step of preparing, as the plurality of electricity storage devices, a first electricity storage device having a non-aqueous electrolyte with a relatively low viscosity and a second electricity storage device having a non-aqueous electrolyte with a relatively high viscosity; a temperature distribution prediction step of predicting a temperature distribution in the electricity storage module when the plurality of electricity storage devices are charged and discharged; and a construction step of constructing the electricity storage module by arranging the first electricity storage device in a low-temperature region where the temperature is relatively low and arranging the second electricity storage device in a high-temperature region where the temperature is relatively high, based on the temperature distribution. [Explanation of symbols]

[0096] 10 Battery case 20 Electrode body 24 Negative electrode 100 Energy storage device 110 First electricity storage device 120 Second power storage device 130 Third Energy Storage Device 300 Restraint mechanism 400 Cooling device 410 Air-cooled fan 500 Energy Storage Module A1 Low temperature region A2 High temperature area A3 Medium temperature range

Claims

1. A power storage module including a plurality of power storage devices, Each of the plurality of electricity storage devices has an electrode body and a nonaqueous electrolyte solution, the power storage module includes a low-temperature region where the temperature is relatively low and a high-temperature region where the temperature is relatively high when the power storage devices are charged or discharged, Among the plurality of electricity storage devices, a first electricity storage device arranged in the low temperature region has a nonaqueous electrolyte solution with a lower viscosity than a second electricity storage device arranged in the high temperature region, When a chain solvent having a molecular weight of 90 or less is used as a low-molecular-weight chain solvent, the first electricity storage device has a higher content of the low-molecular-weight chain solvent in the nonaqueous electrolyte solution than the second electricity storage device; Energy storage module.

2. a medium temperature region within the power storage module, the medium temperature region having a temperature higher than that of the low temperature region and lower than that of the high temperature region; the plurality of electricity storage devices are arranged such that the viscosity of the nonaqueous electrolyte solution decreases stepwise in the order of the high temperature region, the medium temperature region, and the low temperature region; The energy storage module according to claim 1 .

3. The viscosity of each of the first electricity storage device and the second electricity storage device is 2 mPa·s or more and 5 mPa·s or less. The energy storage module according to claim 1 or 2.

4. the first electricity storage device has a higher content of a chain solvent in the nonaqueous electrolyte solution than the second electricity storage device; The energy storage module according to claim 1 or 2.

5. In both the first electricity storage device and the second electricity storage device, the content of the chain solvent in the nonaqueous electrolyte is 50% by volume or less. The energy storage module according to claim 4 .

6. The low molecular weight chain solvent is methyl acetate. The energy storage module according to claim 1 or 2.

7. In both the first electricity storage device and the second electricity storage device, the content of the low-molecular-weight chain solvent in the nonaqueous electrolyte solution is 50% by volume or less. The energy storage module according to claim 1 or 2.

8. The first power storage device and the second power storage device are connected in series. The energy storage module according to claim 1 or 2.

9. A method for manufacturing an electricity storage module including a plurality of electricity storage devices, each of the plurality of electricity storage devices having an electrode body and a nonaqueous electrolyte solution, a preparation step of preparing, as the plurality of electricity storage devices, a first electricity storage device in which the viscosity of the nonaqueous electrolyte solution is relatively low and a second electricity storage device in which the viscosity of the nonaqueous electrolyte solution is relatively high; a temperature distribution prediction step of predicting a temperature distribution in the power storage module when the plurality of power storage devices are charged and discharged; a construction step of constructing the power storage module by arranging the first power storage device in a low-temperature region having a relatively low temperature and arranging the second power storage device in a high-temperature region having a relatively high temperature based on the temperature distribution; Including, When a chain solvent having a molecular weight of 90 or less is used as a low-molecular-weight chain solvent, In the preparing step, a content ratio of the low-molecular-weight chain solvent in the nonaqueous electrolyte solution in the first electricity storage device is made higher than that in the second electricity storage device. A method for manufacturing a storage module.

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