Battery pack control method and control device

Abstract

To provide a method for controlling a battery pack, capable of suppressing an increase in Δ load in a low SOC region.SOLUTION: According to the present invention, there is provided a method for controlling a battery pack that includes a plurality of rectangular secondary batteries and a porous elastic member disposed between adjacent ones of the rectangular secondary batteries in an arrangement direction. The control method includes: a normal discharge step of discharging the rectangular secondary batteries such that a charge state of the rectangular secondary batteries does not become lower than a preset lower limit charge state; and a refresh discharge step of discharging the rectangular secondary batteries until the charge state of the rectangular secondary batteries becomes lower than the lower limit charge state when the normal discharge step is not being performed.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a method and a control device for a battery pack. [Background technology]

[0002] Conventionally, battery packs formed by electrically connecting a plurality of secondary batteries (single cells) have been widely used in vehicle driving power sources and the like to achieve high output. An example of a related prior art document is Patent Document 1. Patent Document 1 discloses a battery pack including a plurality of secondary batteries arranged in a predetermined arrangement direction, a heat conduction suppressing member arranged between adjacent secondary batteries in the arrangement direction, and a restraining mechanism that restrains the plurality of secondary batteries and the heat conduction suppressing member.

[0003] In Patent Document 1, the thermal conduction suppressing member includes a porous body. The porous body has a plurality of communicating holes that communicate with the outside. For this reason, when the secondary battery expands due to, for example, charging and a load is applied, the porous body is compressed while discharging the air inside. On the other hand, when the secondary battery contracts due to, for example, discharging and the load is released, the porous body returns to its original shape by absorbing the air on the periphery and regains its elasticity. As a result, even if the secondary battery expands and contracts during use of the battery pack, a predetermined load can be stably applied to the secondary battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 061894 Summary of the Invention [Problem to be solved by the invention]

[0005] However, according to the study by the present inventors, as the charge-discharge cycle progresses, even if the SOC (State Of Charge) of the secondary battery becomes lower due to discharge, the thickness of the porous body does not return to its original elasticity. As a result, as shown in FIG. 12, the load applied to the secondary battery becomes smaller in the low SOC region, that is, in the region where the thickness of the secondary battery decreases (SOC 15% in FIG. 12), as the charge-discharge cycle progresses. This causes a problem that the difference in load between charging and discharging (Δ load, the difference in load between SOC 95% and SOC 15% in FIG. 12) becomes large. In addition, it was newly found that this makes it easier for metal Li to precipitate and the active material to deteriorate, so-called high-rate deterioration.

[0006] The present invention has been made in consideration of the above circumstances, and its main objective is to provide a control method and control device for a battery pack that can suppress an increase in Δ load in the low SOC region when charge / discharge cycles are repeated. [Means for solving the problem]

[0007] The inventors of the present invention conducted various studies and found that as the charge / discharge cycle progresses, the porous elastic member is unable to take in sufficient air even when the SOC of the secondary battery decreases, and as a result, the porous elastic member is unable to return to its original size, resulting in an increase in the load difference (Δload). This led to the creation of the present invention.

[0008] The present invention provides a method for controlling a battery pack comprising a plurality of prismatic secondary batteries arranged along a predetermined arrangement direction, a porous elastic member arranged between adjacent prismatic secondary batteries in the arrangement direction, and a restraining mechanism for restraining the plurality of prismatic secondary batteries and the porous elastic member, the porous elastic member having communication holes communicating with the outside and capable of elastic deformation. The control method includes a normal discharging process for discharging the prismatic secondary batteries so that the state of charge does not fall below a predetermined lower limit, and a refresh discharging process for discharging the prismatic secondary batteries until the state of charge becomes lower than the lower limit when the normal discharging process is not being performed.

[0009] The present invention also provides a control device for a battery pack comprising a plurality of prismatic secondary batteries arranged along a predetermined arrangement direction, a porous elastic member arranged between adjacent prismatic secondary batteries in the arrangement direction, and a restraining mechanism for restraining the plurality of prismatic secondary batteries and the porous elastic member, the porous elastic member having communication holes communicating with the outside and capable of elastic deformation. The control device includes a normal discharge control unit that performs a normal discharge process to discharge the prismatic secondary batteries so that the state of charge does not fall below a predetermined lower limit, and a refresh discharge control unit that performs a refresh discharge process to discharge the prismatic secondary batteries until the state of charge becomes lower than the lower limit when the normal discharge process is not being performed.

[0010] In the technology disclosed herein, the prismatic secondary battery is forcibly discharged until the state of charge (lower limit SOC) during normal discharge is lower than the lower limit, so that the prismatic secondary battery is refresh-discharged. In the refresh discharge, the thickness of the prismatic secondary battery can be made relatively thinner than during normal discharge, so that the porous elastic member can easily take in air. This makes it easier for the porous elastic member to return to its original size. Therefore, according to the technology disclosed herein, it is possible to suppress a decrease in the load applied to the prismatic secondary battery in the low SOC region when charge / discharge cycles are repeated, and thus suppress an increase in load fluctuation (Δload). This in turn suppresses the occurrence of high-rate degradation. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a schematic diagram of a battery pack according to an embodiment. [Diagram 2] FIG. 2 is a perspective view illustrating the secondary battery of FIG. [Diagram 3] FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a perspective view that shows a schematic view of an electrode assembly attached to a sealing plate. [Diagram 5] FIG. 5 is a perspective view that diagrammatically illustrates one electrode body. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of the electrode body. [Figure 7] FIG. 7 is a perspective view that typically illustrates the porous elastic member of FIG. [Figure 8] FIG. 8 is a functional block diagram of the control device. [Figure 9] FIG. 9 is a flowchart showing an example of a process related to refresh discharge. [Figure 10] FIG. 10 is a graph showing the relationship between the number of charge / discharge cycles and the load increase rate. [Figure 11] FIG. 11 is a graph showing the relationship between the number of charge / discharge cycles and the rate of increase in resistance. [Figure 12] FIG. 12 is a graph showing the relationship between the number of charge / discharge cycles and the load according to the conventional technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the technology disclosed herein will be described with reference to the drawings as appropriate. Matters other than those specifically mentioned in this specification that are necessary for implementing the present invention (for example, the general configuration and manufacturing process of prismatic secondary batteries and battery packs that do not characterize the present invention) can be understood as design matters for those skilled in the art based on the prior art in the field. The battery pack disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the field.

[0013] In the following drawings, the same reference numerals are used for components and parts having the same function, and duplicated explanations may be omitted or simplified. In addition, in this specification, the expression "A to B" indicating a range includes the meaning of "A or more and B or less," as well as "preferably larger than A" and "preferably smaller than B."

[0014] [Battery pack] First, a battery pack that is the subject of the control disclosed herein will be described. FIG. 1 is a perspective view that shows a battery pack 500 according to an embodiment. The battery pack 500 includes a plurality of prismatic secondary batteries 100, a plurality of porous elastic members 200, and a restraining mechanism 300. 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, long side direction perpendicular to the short side direction, and up-down direction, respectively, of the prismatic secondary battery 100. The short side direction X is also the arrangement direction of the prismatic secondary batteries 100. However, these directions are merely for convenience of description, and do not limit the installation form of the battery pack 500 in any way.

[0015] The restraining mechanism 300 is a mechanism for restraining the prismatic secondary batteries 100 and the porous elastic members 200. The restraining mechanism 300 is preferably configured to apply a prescribed restraining pressure to the plurality of prismatic secondary batteries 100 and the plurality of porous elastic members 200 from the arrangement direction X. Here, the restraining mechanism 300 is configured with a pair of end plates 310, a pair of side plates 320, and a plurality of screws 330. The pair of end plates 310 are aligned in the arrangement direction X. The pair of end plates 310 are disposed at both ends of the battery pack 500 in the arrangement direction X. The pair of end plates 310 sandwich the plurality of prismatic secondary batteries 100 and the plurality of porous elastic members 200 in the arrangement direction X.

[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 binding load is, for example, approximately 10 to 15 kN. As a result, a binding load is applied to the plurality of prismatic secondary batteries 100 and the plurality of porous elastic members 200 from the arrangement direction X, and the battery pack 500 is held together. However, the binding mechanism is not limited to this. The binding mechanism 300 may include, for example, a plurality of binding bands, bind bars, etc., instead of the side plates 320.

[0017] The prismatic secondary battery 100 is a battery that can be repeatedly charged and discharged. In this specification, the term "secondary battery" refers to any power storage device that can be repeatedly charged and discharged, and is a concept that encompasses storage batteries such as lithium ion secondary batteries and nickel hydride batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors. The shape, size, number, arrangement, etc. of the prismatic secondary batteries 100 that make up the battery pack 500 are not limited to the embodiments disclosed herein, and can be modified as appropriate.

[0018] In FIG. 1, multiple prismatic secondary batteries 100 are arranged between a pair of end plates 310 along the arrangement direction X (in other words, the thickness direction X of the prismatic secondary batteries 100). A porous elastic member 200 is arranged between adjacent prismatic secondary batteries 100 in the arrangement direction X. That is, the prismatic secondary batteries 100 and the porous elastic members 200 are arranged alternately in the arrangement direction X. However, as described in a modified example described later, another member (e.g., a heat-resistant member, etc.) may be interposed between adjacent prismatic secondary batteries 100 and porous elastic members 200 in the arrangement direction X. Here, the multiple prismatic secondary batteries 100 are connected in series. However, the method of connection of the multiple prismatic secondary batteries 100 is not limited to series, and may be, for example, parallel, multi-series, multi-parallel, etc.

[0019] FIG. 2 is a perspective view of a prismatic secondary battery 100. As shown in FIGS. 1 and 2, the prismatic secondary batteries 100 are arranged in an arrangement direction X so that the long side walls 12b described later face each other. In other words, the prismatic secondary batteries 100 are arranged in a direction in which the long side walls 12b are arranged in parallel. FIG. 3 is a schematic longitudinal sectional view taken along line III-III in FIG. 2. As shown in FIG. 3, the prismatic secondary battery 100 includes a battery case 10, an electrode assembly 20, a positive terminal 30, a negative terminal 40, a positive current collector 50, a negative current collector 60, and an electrolyte (not shown). The prismatic secondary battery 100 preferably includes a battery case 10, an electrode assembly 20, and an electrolyte. Here, the prismatic secondary battery 100 is a lithium ion secondary battery.

[0020] The battery case 10 is a housing that contains the electrode assembly 20 and the electrolyte. As shown in FIG. 1, 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 used conventionally, and is not particularly limited. The battery case 10 is preferably made of a metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 2, the battery case 10 includes an exterior body 12 having an opening 12h, and a sealing plate (lid body) 14 that seals the opening 12h. As in this embodiment, the battery case 10 preferably includes an exterior body 12 having an opening 12h, and a sealing plate 14 that seals the opening 12h.

[0021] As shown in FIG. 1, the exterior body 12 includes a bottom wall 12a, a pair of long side walls 12b extending from the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the bottom wall 12a and facing each other. The bottom wall 12a is substantially rectangular. The bottom wall 12a faces an opening 12h (see FIG. 3). The long side wall 12b is flat. As can be seen from FIG. 1, the long side wall 12b is a surface facing the porous elastic member 200. Here, the long side wall 12b is in direct contact with the porous elastic member 200. However, it may face the porous elastic member 200 via another member. 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 sides and short sides of the rectangle are rounded, a shape having a notch at the corner, and the like.

[0022] In a plan view, the area of ​​the long side wall 12b is larger than the area of ​​the short side wall 12c. Although not particularly limited, in the case of a high-capacity type used for in-vehicle use, the area of ​​the long side wall 12b is about 10,000 mm 2 It is better to have more than 15,000 mm 2 More than 20,000 mm is preferable. 2 More preferably, 25,000 mm 2 More preferably, 30,000 mm 2The above is particularly preferable. When the area of ​​the long side wall 12b is large in this way, it is particularly difficult for air to circulate through the inside of the porous elastic member 200 described below, particularly the central portion in the long side direction Y. Therefore, it is particularly effective to apply the technology disclosed herein. Moreover, from the viewpoint of exerting the effects of the technology disclosed herein at a high level, the area of ​​the long side wall 12b is set to approximately 150,000 mm 2 The following is preferred:

[0023] The long side wall 12b is preferably long horizontally. That is, the length in the long side direction Y is preferably longer than the length in the vertical direction Z. The length (width) of the long side wall 12b in the long side direction Y is preferably 200 mm or more, and the length (height) in the vertical direction Z is preferably 100 mm or more. The longer the distance from the center to the end in the long side direction Y, the more difficult it is for air to reach the center of the long side direction Y, so that it is particularly effective to apply the technology disclosed herein. The ratio (length / width ratio) of the length of the long side wall 12b in the vertical direction Z to the length in the long side direction Y is preferably 1 / 1 to 2 / 3, more preferably 2 / 3 to 1 / 3, and even more preferably 1 / 3 to 1 / 15.

[0024] The sealing plate 14 is a plate-like member extending along the XY plane in Fig. 2. The sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h of the exterior body 12. The sealing plate 14 faces the bottom wall 12a of the exterior body 12. The sealing plate 14 has a substantially rectangular shape. The battery case 10 is integrated 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).

[0025] The battery case 10 includes an exterior body 12 having an opening 12h, a pair of long side walls 12b, and a pair of short side walls 12c, and a sealing plate 14 that seals the opening 12h. The sealing plate 14 is joined to the periphery of the opening 12h of the exterior body 12, and the area of ​​the long side walls 12b is 20,000 mm 2 In the above cases, it is particularly effective to apply the technique disclosed herein.

[0026] As shown in FIG. 3, the sealing plate 14 is provided with a liquid inlet 15, a drain valve 17, and two terminal outlet holes 18 and 19. The liquid inlet 15 is for injecting an electrolyte after the sealing plate 14 is assembled to the exterior body 12. The liquid inlet 15 is sealed by a sealing member 16. The drain valve 17 is configured to break when the pressure inside the battery case 10 reaches or exceeds a predetermined value, thereby discharging gas inside the battery case 10 to the outside. The terminal outlet holes 18 and 19 penetrate the sealing plate 14 in the vertical direction Z. The terminal outlet holes 18 and 19 each have an inner diameter large enough to insert the positive electrode terminal 30 and the negative electrode terminal 40 before being attached to the sealing plate 14 (before being crimped).

[0027] The electrolyte may be the same as that used in the past, and is not particularly limited. The electrolyte is typically a non-aqueous electrolyte containing a non-aqueous solvent and a supporting salt (electrolyte salt). The electrolyte may further contain additives as necessary. The non-aqueous solvent includes, for example, carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The non-aqueous solvent preferably includes carbonates. In particular, it is preferable that the non-aqueous solvent includes a cyclic carbonate and a chain carbonate. The supporting salt is, for example, a fluorine-containing lithium salt such as lithium hexafluorophosphate (LiPF6).

[0028] 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 FIG. 2 and FIG. 3). 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 FIG. 2 and FIG. 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 pull-out holes 18 and 19, respectively. The positive electrode terminal 30 and the negative electrode terminal 40 are preferably fixed to the sealing plate 14. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are crimped to the peripheral portion surrounding the terminal pull-out holes 18 and 19 of the sealing plate 14 by crimping. The crimped portions 30c and 40c are formed at the ends of the positive electrode terminal 30 and the negative electrode terminal 40 on the side of the exterior body 12 (the lower end in FIG. 3).

[0029] As shown in Fig. 3, the positive electrode terminal 30 is electrically connected to the positive electrode 22 (see Fig. 6) of the electrode assembly 20 via a positive electrode current collector 50 inside the exterior body 12. The negative electrode terminal 40 is electrically connected to the negative electrode 24 (see Fig. 6) of the electrode assembly 20 via a negative electrode current collector 60 inside the exterior body 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 insulated from the sealing plate 14 by an internal insulating member 80 and a gasket 90.

[0030] 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 insulated from the sealing plate 14 by an external insulating member 92. As shown in FIG. 1, the positive electrode external conductive member 32 and the negative electrode external conductive member 42 are provided with bus bars that electrically connect the multiple prismatic secondary batteries 100 to each other. Here, among the adjacent prismatic secondary batteries 100, the positive electrode external conductive member 32 of one prismatic secondary battery 100 and the negative electrode external conductive member 42 of the other prismatic secondary battery 100 are electrically connected by the bus bars. As a result, the assembled battery 500 is electrically connected in series.

[0031] FIG. 4 is a perspective view that shows a schematic view of the electrode assembly group 20 attached to the sealing plate 14. The electrode assembly group 20 has a plurality of electrode assemblies here. The electrode assembly group 20 has three electrode assemblies 20a, 20b, and 20c here. However, the number of electrode assemblies arranged inside one exterior body 12 is not particularly limited, and may be one, two, or four or more. The electrode assemblies 20a, 20b, and 20c are arranged side by side in the short side direction X. The electrode assemblies 20a, 20b, and 20c here are electrically connected in parallel. The electrode assemblies 20a, 20b, and 20c each have a flattened outer shape. The electrode assemblies 20a, 20b, and 20c here are each wound electrode assemblies. The electrode assemblies 20a, 20b, and 20c are each arranged inside the exterior body 12 with the winding axis WL (see FIG. 6) oriented substantially parallel to the long side direction Y.

[0032] FIG. 5 is a perspective view showing the electrode body 20b. The configuration of the electrode body 20b may be the same as that of the conventional electrode body, and is not particularly limited. In the following, the electrode body 20b will be described in detail as an example, but the electrode bodies 20a and 20c may have a similar configuration. The electrode body 20b has a pair of curved portions (R portions) 20r and a flat portion 20f connecting the pair of curved portions 20r. One curved portion 20r (upper side of FIG. 5) faces the sealing plate 14, and the other curved portion 20r (lower side of FIG. 5) faces the bottom wall 12a of the exterior body 12. The flat portion 20f faces the long side wall 12b of the exterior body 12. In the electrode bodies 20a, 20b, and 20c adjacent to each other in the short side direction X, the flat portions 20f face each other.

[0033] FIG. 6 is a schematic diagram showing the configuration of the electrode body 20b. The electrode body 20b has a positive electrode 22, a negative electrode 24, and a separator 26. The electrode body 20b is configured 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 electrodes around a winding axis WL. The winding axis WL direction is substantially parallel to the long side direction Y here. However, in other embodiments, the winding axis WL direction may be substantially parallel to the up-down direction Z. The electrode body 20b may also be a laminated electrode body 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.

[0034] The positive electrode 22 may be the same as a conventional one, and is not particularly limited. As shown in FIG. 6, the positive electrode 22 has a positive electrode core 22c, and a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed on at least one surface of the positive electrode core 22c. However, the positive electrode protective layer 22p is not essential and can be omitted in other embodiments. The positive electrode core 22c is strip-shaped. The positive electrode core 22c is preferably made of metal, and more preferably made of metal foil. Here, the positive electrode core 22c is aluminum foil.

[0035] A plurality of positive electrode tabs 22t are provided at one end (left end in FIG. 6) in the long side direction Y of the positive electrode core 22c. The plurality of positive electrode tabs 22t protrude toward one side (left end in FIG. 6) in the long side direction Y. The plurality of positive electrode tabs 22t protrude in the long side direction Y beyond the separator 26. The positive electrode tab 22t is a part of the positive electrode core 22c here, and is made of metal foil (aluminum foil). As shown in FIG. 3 to FIG. 6, the plurality of positive electrode tabs 22t are stacked at one end (left end in FIG. 3 to FIG. 6) in the long side direction Y 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.

[0036] As shown in Fig. 6, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the positive electrode core 22c. The positive electrode active material layer 22a contains a positive electrode active material capable of reversibly absorbing and releasing charge carriers. An example of the positive electrode active material is a lithium transition metal composite oxide. The positive electrode active material layer 22a may contain any component other than the positive electrode active material, such as various additive components such as a binder and a conductive material.

[0037] As shown in Fig. 6, the positive electrode protective layer 22p is provided at the boundary between the positive electrode core 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 any component other than the inorganic filler, such as a conductive material, a binder, various additive components, etc.

[0038] The negative electrode 24 may be the same as a conventional one, and is not particularly limited. As shown in FIG. 6, the negative electrode 24 has a negative electrode core 24c and a negative electrode active material layer 24a fixed on at least one surface of the negative electrode core 24c. The negative electrode core 24c is strip-shaped. The negative electrode core 24c is preferably made of metal, and more preferably made of metal foil. Here, the negative electrode core 24c is copper foil.

[0039] A plurality of negative electrode tabs 24t are provided at one end (right end in FIG. 6) in the long side direction Y of the negative electrode core 24c. The plurality of negative electrode tabs 24t protrude toward one side (right end in FIG. 6) in the long side direction Y. The plurality of negative electrode tabs 24t protrude in the long side direction Y beyond the separator 26. The plurality of negative electrode tabs 24t protrude in the long side direction Y beyond the separator 26. The negative electrode tab 24t is a part of the negative electrode core 24c here, and is made of metal foil (copper foil). As shown in FIG. 3 to FIG. 6, the plurality of negative electrode tabs 24t are stacked at one end (right end in FIG. 3 to FIG. 6) in the long side direction Y 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.

[0040] As shown in FIG. 6, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the negative electrode core 24c. The length Ln of the negative electrode active material layer 24a in the long side direction Y is 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 capable of reversibly absorbing 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 any component other than the negative electrode active material, such as various additive components such as a binder, a thickener, a dispersant, etc.

[0041] 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 and the negative electrode 24. The electrode body 20b preferably includes the separator 26. The length Ls of the separator 26 in the long side direction Y is 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 resin porous sheet (microporous film) made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 may have a functional layer (e.g., an adhesive layer, a heat-resistant layer, etc.) on its surface.

[0042] As shown in Fig. 3, the positive electrode current collecting part 50 constitutes a conductive path that electrically connects the positive electrode tab group 23 consisting of a plurality of positive electrode tabs 22t and the positive electrode terminal 30. The positive electrode current collecting part 50 includes a positive electrode first current collecting part 51 and a positive electrode second current collecting part 52. The positive electrode first current collecting part 51 is attached to the inner surface of the sealing plate 14. The positive electrode second current collecting part 52 extends along the short side wall 12c of the exterior body 12. As shown in Figs. 3 to 5, the positive electrode second current collecting part 52 is attached to the electrode body 20b.

[0043] 3, the negative electrode current collecting part 60 constitutes a conductive path that electrically connects the negative electrode tab group 25 consisting of the multiple negative electrode tabs 24t to the negative electrode terminal 40. The negative electrode current collecting part 60 includes a negative electrode first current collecting part 61 and a negative electrode second current collecting part 62. The configurations of the negative electrode first current collecting part 61 and the negative electrode second current collecting part 62 may be the same as those of the positive electrode first current collecting part 51 and the positive electrode second current collecting part 52 of the positive electrode current collecting part 50.

[0044] As shown in FIG. 1, the porous elastic member 200 is disposed between the plurality of prismatic secondary batteries 100 in the arrangement direction X. However, the porous elastic member 200 only needs to be disposed between at least two prismatic secondary batteries 100 adjacent to each other in the arrangement direction X, and does not necessarily need to be disposed between all of the prismatic secondary batteries 100. The porous elastic member 200 is preferably disposed between 50% or more, more preferably 80% or more of the prismatic secondary batteries 100. The porous elastic member 200 may be separate from the prismatic secondary battery 100, or may be fixed to the prismatic secondary battery 100 and integrated with the prismatic secondary battery 100. The porous elastic member 200 may be sandwiched between two opposing prismatic secondary batteries 100, or may be adhered to the prismatic secondary battery 100 with an adhesive, tape, or the like. The shape, size, arrangement, and the like of the porous elastic member 200 can be appropriately determined according to, for example, the shape, size, capacity (degree of expansion / contraction), and the like of the prismatic secondary battery 100.

[0045] The porous elastic member 200 is an elastically deformable member. The porous elastic member 200 is preferably configured to be elastically deformable at least in the arrangement direction X by taking in or discharging gas. The porous elastic member 200 contracts when the prismatic secondary battery 100 is restrained in a pressurized state or when the thickness of the prismatic secondary battery 100 increases (expands) due to charging or the like, and preferably expands when the thickness of the prismatic secondary battery 100 decreases due to discharging or the like, and returns to its original thickness. Although not particularly limited, the elastic force of the porous elastic member 200 may be approximately 1 to 1000 kN / mm.

[0046] The porous elastic member 200 is a porous structure having a plurality of communicating holes that communicate with the outside. As a result, when the porous elastic member 200 contracts once and then expands again, it can draw in air from the outer periphery and move the drawn gas (air, etc.) to the inside. The porous elastic member 200 may be a three-dimensional mesh having communicating holes that communicate in a three-dimensional manner. The porosity of the porous elastic member 200 (pore volume / volume of the porous elastic member 200) is preferably 10 to 90 volume %, more preferably 20 to 80 volume %, and even more preferably 25 to 75 volume %. The porous elastic member 200 is preferably made of a resin material. Examples of the resin material include natural rubber, synthetic rubber, silicone resin, and urethane resin.

[0047] When the prismatic secondary battery 100 expands during charging or the like and its thickness in the arrangement direction X increases, the load applied to the porous elastic member 200 increases. As a result, the porous elastic member 200 is compressed while discharging the air inside. This makes it possible to prevent the application of a predetermined or excessive restraining load to the prismatic secondary battery 100. On the other hand, when the prismatic secondary battery 100 contracts during discharging or the like and its thickness in the arrangement direction X decreases, the load applied to the porous elastic member 200 decreases. As a result, the porous elastic member 200 absorbs air from the outside and returns to its original shape, and its elasticity is restored. This makes it possible to stably apply a predetermined load to the prismatic secondary battery 100.

[0048] FIG. 7 is a perspective view showing a schematic view of the porous elastic member 200. The thickness (length in the arrangement direction X) T of the porous elastic member 200 is preferably 1 to 10 mm, more preferably 1 to 8 mm, and even more preferably 3 to 5 mm, before being assembled into the battery pack 500 and compressed, for example, by the restraining mechanism 300. The thickness T of the porous elastic member 200 is preferably 2 to 9 mm, more preferably 3 to 8 mm, and even more preferably 4 to 7 mm, before being assembled into the battery pack 500 and compressed, for example, by the restraining mechanism 300. The overall length L1 in the long side direction Y of the porous elastic member 200 is preferably approximately the same (approximately ±1 cm) as the length (average length) Lp (see FIG. 6) in the long side direction Y of the positive electrode active material layer 22a. The overall length L1 may be shorter than the length Ls in the long side direction Y of the separator 26.

[0049] The porous elastic member 200 has a substantially rectangular shape in plan view. The total area of ​​the porous elastic member 200 in plan view is 10,000 mm 2 More than 15,000mm is preferable. 2 More preferably, 25,000 mm 2 More preferably, the ratio is about 50% or more. The ratio of the total area of ​​the porous elastic member 200 to the area of ​​the long side wall 12b is preferably about 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, and particularly preferably 80% or more. In such a case, air is unlikely to circulate inside the porous elastic member 200, so that it is particularly effective to apply the technology disclosed herein. Moreover, from the viewpoint of exerting the effects of the technology disclosed herein at a high level, the above-mentioned ratio of the area is preferably about 95% or less, more preferably 90% or less, and more preferably 85% or less.

[0050] In this specification, the "total area of ​​the porous elastic member 200 in plan view" refers to the area of ​​the surface (YZ plane in FIG. 7) that contacts the opposing member (here, the long side wall 12b), and for example, when the porous elastic member 200 is composed of multiple parts, it refers to the total area of ​​those parts. Also, when the porous elastic member 200 has slits, recesses, or other parts that do not contact the opposing member, it refers to the area excluding the areas of the slits, recesses, etc.

[0051] The battery pack 500 can be used for various purposes, but can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car, a truck, etc. The type of vehicle is not particularly limited, but examples thereof include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), a battery electric vehicle (BEV), etc.

[0052] [Battery assembly control device] However, according to the study by the present inventors, in the conventional technology, as the charge / discharge cycles progress, the porous elastic member 200 is unable to absorb air sufficiently, and it is difficult to return to its original size. As a result, there is a problem that the load applied to the prismatic secondary battery 100 becomes smaller in a low SOC region (for example, an SOC region of 30% or less, further an SOC region of 20% or less, and particularly an SOC region of 15% or less) when the charge / discharge is performed in the same SOC region, and the difference in load (Δload) between when the battery is charged and when the battery is discharged increases.

[0053] Furthermore, according to the study by the present inventors, it was newly found that high-rate degradation is likely to occur as a result of this. That is, a strong positive correlation was found between Δload and high-rate degradation (e.g., resistance increase). Although it is not intended to be interpreted in a particularly restrictive manner, the present inventors believe that the reason for this is as follows.

[0054] That is, in an environment where the amount of change in the arrangement direction X is limited (for example, in an embodiment where the electrode body 20b is housed in the battery case 10 as in the present embodiment, or in an embodiment where a load is applied to suppress the expansion and contraction of the electrode body 20b), when the negative electrode 24 expands due to charging, the electrolyte contained between the positive electrode 22 and the negative electrode 24 is usually pushed out. When the negative electrode 24 contracts due to discharging, the pushed-out electrolyte returns to the inside of the electrode body 20b. However, if the Δ load is large at this time, the amount of electrolyte returning to the inside of the electrode body 20b increases, and the electrolyte flows in and out more. Therefore, the electrolyte distribution cannot be made uniform by repeated charging and discharging, and unevenness (concentration gradient) in the salt concentration is likely to occur, especially in the long side direction Y (width direction) of the electrode body 20b. For example, the electrolyte flows in and out more at both ends of the long side direction Y, resulting in a low concentration of the supporting salt, while the supporting salt tends to be high in the center of the long side direction Y. It was thought that this concentration gradient would lead to variations in resistance, such that, for example, both ends in the long side direction Y would have relatively high resistance, making high-rate degradation more likely to occur.

[0055] Next, the control device 600 (see FIG. 8) will be described. The control device 600 is electrically connected to the battery pack 500 (specifically, a plurality of prismatic secondary batteries 100) and is configured to be capable of controlling charging and discharging of the battery pack 500 (or the prismatic secondary batteries 100). It is preferable that the control device 600 controls charging and discharging of the battery pack 500 (or the prismatic secondary batteries 100). The control device 600 is typically a computer or the like that is communicatively connected to the battery pack 500 via wire or wirelessly. The control device 600 is typically mounted on a product (e.g., a vehicle) together with the battery pack 500. The control device 600 may be electrically connected to, for example, an ECU (Electronic Control Unit) of the vehicle, or may be built into the ECU of the vehicle.

[0056] There is no particular limitation on the hardware configuration of the control device 600. The control device 600 includes, for example, an interface (I / F) for receiving print data from an external device such as a host computer, a central processing unit (CPU) for executing instructions of a control program, a read only memory (ROM) for storing the program executed by the CPU, a random access memory (RAM) used as a working area for expanding the program, and a storage device such as a memory for storing the above-mentioned program and various data.

[0057] The control device 600 may be a computer program that causes a CPU of a computer to operate as the control device 600. Such a computer program may be a computer-readable recording medium in which each process of the control device 600 described later is written. Examples of the recording medium include semiconductor recording media (e.g., ROM, non-volatile memory card), optical recording media (e.g., DVD, MO, MD, CD, BD), and magnetic recording media (e.g., magnetic tape, flexible disk). The computer program can be transmitted to a server computer via the recording medium or a network such as the Internet or an intranet. In this case, the server computer is also one form of the control device 600.

[0058] Fig. 8 is a functional block diagram of the control device 600. As shown in Fig. 8, the control device 600 is communicatively connected to an electrochemical measuring device 110 attached to the battery pack 500 (or the prismatic secondary battery 100) and a display screen 700. The measuring device 110 is, for example, a voltmeter or an ammeter. The display screen 700 is, for example, a monitor, a display, a touch panel, or the like.

[0059] The control device 600 of this embodiment includes a normal charge control unit 610, a normal discharge control unit 620, a total discharge amount calculation unit 630, a determination unit 640, a refresh discharge control unit 650, a notification unit 660, a storage unit 670, and an input / output unit 680. However, the total discharge amount calculation unit 630, the determination unit 640, the notification unit 660, and the storage unit 670 are not essential, and in other embodiments, some or all of them may be omitted. Each unit of the control device 600 is configured to be able to communicate with each other. Each unit of the control device 600 may be configured by software or hardware. Each unit of the control device 600 may be realized by one or more processors, or may be incorporated into a circuit.

[0060] The normal charging control unit 610 is a control unit that executes normal charging processing to charge the prismatic secondary battery 100 so as not to exceed a predetermined upper limit of the state of charge (upper limit SOC) and inputs power from the outside to the prismatic secondary battery 100. The upper limit SOC value is set in advance and stored in the storage unit 670. The upper limit SOC value is, for example, SOC 50-100%, SOC 80-100%, SOC 90-100%, etc., and from the viewpoint of achieving high capacity, is preferably SOC 90% or more, or even SOC 95% or more, and in one example, is SOC 95%.

[0061] The normal discharge control unit 620 is a control unit that executes a normal discharge process for discharging the prismatic secondary battery 100 so that the state of charge does not fall below a predetermined lower limit (lower limit SOC), and supplies (outputs) power from the prismatic secondary battery 100 to an external device (for example, a product such as a vehicle). The value of the lower limit SOC is set in advance and stored in the storage unit 670. The value of the lower limit SOC is, for example, SOC 5-40%, SOC 10-30%, SOC 10-20%, etc., and from the viewpoint of achieving high capacity, is preferably SOC 30% or less, or even SOC 20% or less, and in one example, SOC 15%.

[0062] Although this may vary depending on the battery configuration, for example, when the prismatic secondary battery 100 is a lithium ion secondary battery as in this embodiment, or particularly when the negative electrode active material is a carbon material, it is preferable that the battery voltage at the lower limit SOC is approximately 3.5 V or less (e.g., 3.0±0.3 V).

[0063] The total discharge amount calculation unit 630 is a control unit that executes a total discharge amount calculation process that calculates a total discharge amount ΣQ of the discharges performed by the normal discharge control unit 620. For example, the total discharge amount calculation unit 630 first acquires electrochemical data measured during the normal discharge process, such as data on voltage and current, from the measuring device 110 via the input / output unit 680 at predetermined intervals. The total discharge amount calculation unit 630 calculates, for example, the discharge amount Q in one normal discharge process. Note that, as an example, the total discharge amount calculation unit 630 calculates the discharge amount Q here, but in other embodiments, the total discharge amount calculation unit 630 may acquire the value of the discharge amount Q from, for example, an ECU, which is a higher-level control device.

[0064] When the discharge amount Q is not stored in the storage unit 670, the total discharge amount calculation unit 630 sets the calculated discharge amount Q as the total discharge amount ΣQ. The total discharge amount ΣQ is preferably stored in the storage unit 670. When the total discharge amount ΣQ is already stored in the storage unit 670, the total discharge amount calculation unit 630 accumulates the calculated discharge amount Q to the total discharge amount ΣQ stored in the storage unit 670 to calculate a new total discharge amount ΣQ. Then, the total discharge amount ΣQ in the storage unit 670 is updated. Note that the total discharge amount ΣQ stored in the storage unit 670 is typically reset and returned to zero when a refresh discharge process described later is performed. In this case, the total discharge amount ΣQ stored in the storage unit 670 is the sum of the discharge amounts Q since the last (most recent) refresh discharge process was performed.

[0065] The determination unit 640 is a control unit that executes a determination process to determine whether or not a refresh discharge process, which will be described later, is necessary, based on, for example, the performance status of the normal discharge process in the normal discharge control unit 620. The performance status of the normal discharge process is, for example, the number of normal discharge processes (number of discharges), the total discharge time, the total discharge amount ΣQ, etc. These pieces of information are obtained from the ECU or the measuring instrument 110 via the input / output unit 680, or are calculated based on information obtained from the measuring instrument 110, etc.

[0066] In this embodiment, the determination unit 640 is configured to determine whether or not a refresh discharge process is required based on whether or not the total discharge amount ΣQ calculated by the total discharge amount calculation unit 630 exceeds a predetermined threshold. The threshold is set in advance and stored in the storage unit 670. The threshold may be determined based on the relationship between the number of charge / discharge cycles and the Δ load, as described in the examples below. For example, the point at which the Δ load exceeds an allowable value may be set as the threshold. For this reason, although not particularly limited, in one example, the threshold of the total discharge amount ΣQ is 8 kAh.

[0067] However, the judgment unit 640 may be configured to judge that a refresh discharge process is necessary, for example, when the number of discharges since the last refresh discharge process was performed exceeds a predetermined number (threshold) or when the total discharge time since the last refresh discharge process was performed exceeds a predetermined time (threshold).

[0068] The refresh discharge control unit 650 is a control unit that executes a refresh discharge process that forcibly discharges the prismatic secondary battery 100 until the state of charge becomes lower than the lower limit SOC of the normal discharge process (until the refresh SOC is reached). In this embodiment, the refresh discharge process is executed when the normal charging control unit 610 is not executing the normal charging process and the normal discharging control unit 620 is not executing the normal discharging process. The refresh discharge control unit 650 may be configured to execute the refresh discharge process when the SOC of the prismatic secondary battery 100 is low, for example, after the normal discharging control unit 620 executes the normal discharging process or before the normal charging control unit 610 executes the normal charging process. This allows the prismatic secondary battery 100 to be efficiently discharged to the refresh SOC.

[0069] The refresh SOC value is set in advance and stored in the storage unit 670. The refresh SOC value is not particularly limited as long as it is lower than the lower limit SOC, but is preferably 5% or more lower than the lower limit SOC, more preferably 10% or more lower, and more preferably, for example, 15% or more lower. Specifically, from the viewpoint of exerting the effects of the technology disclosed herein at a high level, the refresh SOC value is preferably SOC30% or less, more preferably SOC20% or less, even more preferably SOC10% or less, particularly preferably SOC5% or less, and even more preferably SOC0% or less, and in one example, SOC0%. However, from the viewpoint of suppressing deterioration of the prismatic secondary battery 100, the refresh SOC value may be SOC0% or more, SOC1% or more, or SOC3% or more.

[0070] Although this may vary depending on the battery configuration, for example, when the prismatic secondary battery 100 is a lithium ion secondary battery as in this embodiment, particularly when the negative electrode active material is a carbon material, the battery voltage at the refresh SOC is preferably about 2.0 V or less (for example, about 2.0±0.3 V). Also, it is preferable that the difference between the battery voltage at the lower limit SOC and the battery voltage at the refresh SOC is 0.5 V or more.

[0071] In the refresh discharge process, it is preferable to maintain the refresh SOC state for a predetermined maintenance time. From the viewpoint of exerting the effects of the technology disclosed herein at a high level, the maintenance time is preferably 30 seconds or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more. Taking into consideration the convenience of the user and the deterioration state of the prismatic secondary battery 100, the maintenance time is preferably 30 minutes or less.

[0072] The refresh discharge control unit 650 is preferably configured to execute the refresh discharge process based on a user's instruction, taking into consideration the convenience of the user, etc. Also, the refresh discharge control unit 650 is preferably configured to execute the refresh discharge process periodically. In a preferred embodiment, the refresh discharge control unit 650 is configured to execute the refresh discharge process when it is determined in the determination process by the determination unit 640 that the refresh discharge process is necessary. In this embodiment, the refresh discharge control unit 650 is configured to execute the refresh discharge process when it is determined that the total discharge amount ΣQ exceeds a threshold value.

[0073] The notification unit 660 is a control unit that executes a notification process to notify the user of the charge / discharge status, etc., of the prismatic secondary battery 100 via the input / output unit 680. In a preferred embodiment, the notification unit 660 is configured to notify the user before the refresh discharge control unit 650 executes the refresh discharge process. In this embodiment, when the determination unit 640 determines that the refresh discharge process is necessary in the determination process, the notification unit 660 is configured to notify the user that the refresh discharge process is necessary. The notification unit 660 may, for example, notify the user by displaying characters, illustrations, etc. on the display screen 700, etc., or by sound, such as a warning sound or voice guidance.

[0074] The notification unit 660 is preferably configured to notify the user of the contents of the processing being performed by the control device 600, for example, that the normal charging control unit 610 is performing a normal charging process, that the normal discharging control unit 620 is performing a normal discharging process, and that the refresh discharging control unit 650 is performing a refresh discharging process. For example, by notifying that a refresh discharging process is being performed, the user can understand that the product (e.g., a vehicle) in which the battery pack 500 is mounted cannot be used normally for a predetermined period of time. The notification unit 660 may be configured to notify the user of the state of charge (SOC) of the battery pack 500 (or the prismatic secondary battery 100) by, for example, a number or an illustration.

[0075] It is preferable that the notification unit 660 is configured to display a first selection message for the user to select whether or not to perform a refresh discharge process, and a second selection message for inputting the timing (date and time, etc.) of performing a refresh discharge process, for example, when the judgment process by the judgment unit 640 judges that a refresh discharge process is necessary.

[0076] The storage unit 670 stores various parameters, such as an upper limit SOC value in a normal charging process, a lower limit SOC value in a normal discharging process, a total discharge amount ΣQ value, a threshold value in a determination process, a refresh SOC value in a refresh discharging process, etc. The storage unit 670 may further store in advance one or more charge / discharge patterns including at least a refresh discharging process. The charge / discharge patterns preferably include a first charge / discharge pattern in which only a refresh discharging process is performed, and a second charge / discharge pattern in which a normal charging process is performed in succession after the refresh discharging process, in which charging is performed until the battery is almost fully charged (for example, until SOC is 90% or more, or even until SOC is 95% or more). The storage unit 670 may further store reservation information for the refresh discharging process.

[0077] In the control device 600 as described above, the thickness of the prismatic secondary battery 100 can be made thinner during the refresh discharge process than during the normal discharge process, so that the porous elastic member 200 can easily take in air. As a result, the porous elastic member 200 can easily return to its original size (particularly the thickness in the arrangement direction X). Therefore, it is possible to suppress the load applied to the prismatic secondary battery 100 from decreasing in the low SOC region when the charge / discharge cycle is repeated, and to reduce the load fluctuation (Δload) during the SOC fluctuation. Furthermore, it is possible to suppress the increase in the unevenness (concentration gradient) of the salt concentration in the long side direction Y of the electrode body 20b, and to prevent the occurrence of high-rate degradation.

[0078] [Battery assembly control method] 9 is a flowchart showing an example of a process related to the refresh discharge of the present embodiment. In the control method disclosed herein, when the normal discharge process is executed by the normal discharge control unit 620, for example, control is performed until the refresh discharge process is executed according to the procedure shown in the flowchart of FIG.

[0079] In step S1, first, when normal discharge processing is started by normal discharge control unit 620, electrochemical data (e.g., changes in voltage, current, etc.) measured by measuring instrument 110 is input to total discharge amount calculation unit 630 via input / output unit 680. Total discharge amount calculation unit 630 calculates the discharge amount Q based on this. In one example, the discharge current value of prismatic secondary battery 100 is measured at regular intervals during normal discharge processing using an ammeter, and the discharge amount Q is calculated by integrating the discharge current value. Then, for example, when one normal discharge processing is completed and the discharge amount Q is obtained, the process proceeds to step S2.

[0080] In step S2, the total discharge amount calculation unit 630 executes a total discharge amount calculation process. The total discharge amount calculation unit 630 calculates the total discharge amount of the discharge performed in the normal discharge process. When the discharge amount Q is not stored in the storage unit 670, the total discharge amount calculation unit 630 calculates the discharge amount Q calculated in step S1 as the total discharge amount ΣQ as it is and stores it in the storage unit 670. On the other hand, when the total discharge amount ΣQ (typically the total discharge amount ΣQ of the discharge performed from the last refresh discharge process to the present) is stored in the storage unit 670, the total discharge amount calculation unit 630 calculates the total discharge amount ΣQ by adding the discharge amount Q calculated in step S1 to the total discharge amount ΣQ stored in the storage unit 670. Then, the total discharge amount ΣQ in the storage unit 670 is updated, and the process proceeds to step S3.

[0081] In step S3, the determination unit 640 executes a determination process. In this embodiment, the determination unit 640 determines whether or not a refresh discharge process is necessary based on the performance status of the normal discharge process. Specifically, the determination unit 640 determines whether or not the total discharge amount ΣQ calculated in step S2 exceeds a predetermined threshold. By appropriately setting the threshold and comparing it with the total discharge amount ΣQ, the refresh discharge process can be executed at an appropriate timing. If the determination unit 640 determines that the total discharge amount ΣQ exceeds the threshold, the determination in step S3 of FIG. 9 is YES, and the process proceeds to step S4.

[0082] On the other hand, if the determination unit 640 determines that the total discharge amount ΣQ does not exceed the threshold value, the elasticity of the porous elastic member 200 has not significantly decreased in the low SOC region. In this case, since it is not necessary to perform the refresh discharge process, the determination in step S3 in Fig. 9 is NO, and the process returns to step S1. Then, the discharge amount Q is accumulated each time the normal discharge process is performed, and the total discharge amount ΣQ is updated.

[0083] In step S4, notification unit 660 executes notification processing. More specifically, notification unit 660 notifies the user that a refresh discharge processing is required. This allows the user to recognize that a refresh discharge processing is required before the refresh discharge processing is actually performed. Notification unit 660 displays a message such as "Maintenance (refresh discharge processing) is required" on display screen 700, for example. Then, the process proceeds to step S5.

[0084] In step S5, the user selects whether or not to perform the refresh discharge process, and the timing of the refresh discharge process if the refresh discharge process is to be performed. While the refresh discharge process is being performed, the normal discharge process and normal charge process cannot be performed. In other words, the product (e.g., a vehicle) in which the assembled battery 500 is mounted cannot be used normally. Therefore, the user's convenience can be improved by deciding whether or not to perform the refresh discharge process, and the timing of the refresh discharge process if the refresh discharge process is to be performed, according to the user's convenience or schedule. However, as described in a modified example described later, in other embodiments, this step may be omitted, and the refresh discharge process may be set to be automatically performed (for example, a charge / discharge pattern may be set).

[0085] In this embodiment, the notification unit 660 displays a first selection message on the display screen 700, such as "Do you want to perform maintenance (refreshing discharge processing) now?". If the user selects "Yes" from a selection screen not shown (i.e., instructs the refreshing discharge processing), the determination in step S5 of Fig. 9 is YES, and the process proceeds to step S6. On the other hand, if it is inconvenient to perform the refreshing discharge processing now, for example, if the user plans to immediately use the battery pack 500 normally (to perform the normal discharge processing), and the user selects "No" from a selection screen not shown, the notification unit 660 further displays a second selection message on the display screen 700, such as "Do you want to make a reservation for maintenance (refreshing discharge processing)?".

[0086] When the user selects "Yes" from a selection screen (not shown) (i.e., instructs the refresh discharge process), a reservation screen for inputting reservation information for executing the refresh discharge process is displayed on the display screen 700. The reservation information includes, for example, information on the date and time when the refresh discharge process is to be started and information on the charge / discharge pattern including the refresh discharge process. The charge / discharge pattern may be selected from a plurality of charge / discharge patterns (for example, from among the above-mentioned first charge / discharge pattern and second charge / discharge pattern) stored in the storage unit 670, or may be freely set by the user. When the user inputs the date and time when the refresh discharge process is to be started and the charge / discharge pattern from the reservation screen (not shown), the reservation information for the refresh discharge process is stored in the storage unit 670. In this case, too, the determination in step S5 of FIG. 9 is YES, and the process proceeds to step S6.

[0087] On the other hand, if the user selects "No" from, for example, a selection screen (not shown) when the second selection message is displayed, the determination in step S5 in Fig. 9 is NO, and the process proceeds to step S8. In step S8, the notification unit 660 displays a warning on the display screen 700, such as "If maintenance (refresh discharge process) is not performed, the battery life may be shortened." Then, the control ends.

[0088] In step S6, the refresh discharge control unit 650 executes a refresh discharge process while neither the normal charging process nor the normal discharging process is being performed. More specifically, the refresh discharge control unit 650 forcibly discharges the prismatic secondary battery 100 to the refresh SOC. Preferably, the refresh SOC state is further maintained for a predetermined maintenance time. If "Yes" is selected in the first selection message in step S5, the refresh discharge process is executed immediately after step S5. If the prismatic secondary battery 100 is significantly dented by the refresh discharge process, the porous elastic member 200 will be more likely to absorb air. This allows the porous elastic member 200 to return to its proper shape. Then, the process proceeds to step S7.

[0089] On the other hand, if "Yes" is selected in the second selection message in step S5, the refresh discharge process is executed according to the reservation information. At this time, if the first charge / discharge pattern is selected on the reservation screen, only the refresh discharge process is executed by the refresh discharge control unit 650. On the other hand, if the second charge / discharge pattern is selected on the reservation screen, after the refresh discharge process is executed by the refresh discharge control unit 650, the normal charge control unit 610 continues to execute the normal charge process for charging to nearly full charge (for example, until the SOC is 90% or more). Then, proceed to step S7.

[0090] In step S7, the total discharge amount ΣQ stored in the storage unit 670 is erased. In other words, the total discharge amount ΣQ is reset to zero. At this time, the reservation information stored in the storage unit 670 may also be erased. Then, the control ends.

[0091] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to these examples.

[0092] In this test example, the effectiveness of the refresh discharge treatment was confirmed. Specifically, first, a porous elastic member having a communicating hole and capable of elastic deformation in the thickness direction was prepared. Next, a prismatic secondary battery (lithium ion secondary battery) and a porous elastic member were sandwiched in the arrangement direction by a pair of restraining jigs (restraining mechanism), and the thickness of the porous elastic member was restrained to 80% of the thickness before restraint, to prepare a plurality of test batteries. Note that a load cell for load measurement is installed on one of the pair of restraining jigs, and it is configured so that the load applied to the long side wall (the surface facing the porous elastic member) of the prismatic secondary battery can be measured.

[0093] [Δ Load Measurement] The transition of the difference in load (Δ load) between charging and discharging was measured as follows. First, the constructed test battery was charged and discharged multiple times in the range of SOC 15 to 95% in a temperature environment of 25°C, and the load at this time was measured with a load cell. Note that the test battery of the embodiment was subjected to a refresh discharge treatment every 50 cycles. Specifically, the prismatic secondary battery was forcibly discharged to SOC 0% to relieve the load on the porous elastic member. On the other hand, the test battery of the comparative example was not subjected to a refresh discharge treatment. Then, for each cycle, the load at SOC 15% was subtracted from the load at SOC 95% to calculate the Δ load, and the Δ load was expressed as the Δ load increase rate when the Δ load at the first cycle was set to 100%. The results are shown in FIG. 10.

[0094] FIG. 10 is a graph showing the relationship between the number of charge / discharge cycles and the load increase rate (%, relative value). In FIG. 10, an asterisk is attached to the cycle in which the refresh discharge treatment was performed in the embodiment. In the test battery of the embodiment in which the refresh discharge treatment was performed, the load at SOC 15% was high after the refresh discharge treatment, and as shown in FIG. 10, the increase in Δ load was relatively small compared to the test battery of the comparative example in which the refresh discharge treatment was not performed. This is considered to be because the refresh discharge treatment made it easier for the porous elastic member to take in air and to return to its original shape. Such a result shows the significance of the technology disclosed herein.

[0095] [Measurement of IV resistance] Two prismatic secondary batteries (Example and Comparative Example) with the same configuration were prepared, and high-rate degradation was measured as follows. First, the two prismatic secondary batteries were adjusted to a state of SOC 50%, and then constant current discharge was performed at 240A for 10 seconds, and the discharge resistance was measured. Next, the battery voltage ΔV that dropped in 10 seconds was read, and the IV resistance (initial resistance) was calculated based on the battery voltage ΔV and the discharge current value (240A).

[0096] Next, a durability test was performed in a temperature environment of 25°C. Specifically, the prismatic secondary battery was adjusted to a state of SOC 20%, and constant current charging was performed at a charge rate of 2C for 30 minutes, followed by a 10-minute pause, followed by a 180-minute constant current discharge at a discharge rate of 1 / 5C, followed by a 10-minute pause. This cycle was repeated 15 times. At this time, the prismatic secondary battery of the embodiment was subjected to a refresh discharge treatment every three cycles. Specifically, after discharge in the charge / discharge cycle, the prismatic secondary battery was forcibly discharged to SOC 0%, the load on the porous elastic member was relaxed, and the battery was returned to its original SOC and the charge / discharge cycle was resumed. On the other hand, the prismatic secondary battery of the comparative example was not subjected to a refresh discharge treatment. Then, the IV resistance was measured every five cycles 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. The results are shown in FIG. 11.

[0097] Fig. 11 is a graph showing the relationship between the number of charge / discharge cycles and the resistance increase rate (%, relative value). As shown in Fig. 11, in the prismatic secondary battery of the example which underwent the refresh discharge treatment, the resistance increase was relatively small and the high-rate degradation was suppressed compared to the prismatic secondary battery of the comparative example which did not undergo the refresh discharge treatment. The difference between the two became more significant as the number of cycles increased. Such a result shows the significance of the technology disclosed herein.

[0098] 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 field. The technology described in the claims includes various modifications and changes of the above-exemplified embodiment. For example, it is possible to replace a part of the above-mentioned embodiment with another modification, and it is also possible to add another modification to the above-mentioned embodiment. Furthermore, if a technical feature is not described as essential, it can be appropriately deleted.

[0099] (First Modification) For example, in the above embodiment, the battery packs 500 are connected in series, and the control device 600 is configured to control charging and discharging of the battery packs 500. However, this is not limited to this. For example, if the battery packs 500 are connected in parallel, the control device 600 may be configured to individually control charging and discharging of the prismatic secondary batteries 100.

[0100] (Second Modification) For example, in the above embodiment, the determination unit 640 is configured to determine whether or not a refresh discharge process is necessary based on the track record of the normal discharge process. Specifically, the determination unit 640 is configured to determine that a refresh discharge process is necessary when the total discharge amount ΣQ calculated by the total discharge amount calculation unit 630 exceeds a predetermined threshold value. However, the present invention is not limited to this. For example, the determination unit 640 may be configured to detect that a load applied to the rectangular secondary battery 100 has reached a predetermined value and determine that a refresh discharge process is necessary, or may be configured to determine that a refresh discharge process is necessary when a predetermined time has elapsed since the last refresh discharge process was performed.

[0101] (Third Modification) For example, in the embodiment of FIG. 9 described above, the flow chart includes step S5, and the refresh discharge control unit 650 is configured to execute the refresh discharge process upon receiving an instruction from the user. In other words, the user determines whether or not the refresh discharge process is required and the timing of the refresh discharge process. However, this is not limited to this. The refresh discharge control unit 650 may be configured to automatically execute the refresh discharge process, for example, based on the determination result of the determination unit 640. For example, the memory unit 670 may be configured to store in advance a procedure for when the determination unit 640 determines that the refresh discharge process is required, and to automatically execute the refresh discharge process based on this.

[0102] In one example, the refresh discharge control unit 650 may be configured to automatically execute the refresh discharge process by selecting a time period (e.g., a preset nighttime period) when the normal discharge process is rarely executed. Note that the nighttime period is preferably a late-night time period when the electricity rate is a nighttime rate. The refresh discharge control unit 650 may be configured to first execute the refresh discharge process and then execute the normal charging process when executing the normal charging process for the first time during a nighttime period after the determination unit 640 determines that the refresh discharge process is necessary. That is, the refresh discharge process may be executed in combination with the normal charging process.

[0103] (Fourth Modification) For example, in the above embodiment, the porous elastic member 200 is disposed between the adjacent prismatic secondary batteries 100 in the arrangement direction X, and both sides of the porous elastic member 200 in the arrangement direction X are in contact with the long side wall 12b of the prismatic secondary battery 100. However, other members may be interposed between the prismatic secondary battery 100 and the porous elastic member 200. Examples of other members that may be interposed between the prismatic secondary battery 100 and the porous elastic member 200 include, for example, a non-porous insulating film; a heat-resistant member containing a high melting point resin; a heat-resistant member containing a resin material and ceramic particles; and a heat insulating member containing silica aerogel or a nanoporous body mainly made of silica. The shape, size, and arrangement of the other members can be appropriately determined depending on, for example, the shape, size, and position of the gas flow path of the porous elastic member 200. The other members may be, for example, sheet-shaped, or may have the same shape as the porous elastic member 200.

[0104] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Clause 1: A method for controlling a battery pack comprising a plurality of prismatic secondary batteries arranged along a predetermined arrangement direction, a porous elastic member arranged between adjacent prismatic secondary batteries in the arrangement direction, and a restraining mechanism for restraining the plurality of prismatic secondary batteries and the porous elastic member, the porous elastic member having communication holes communicating with the outside and capable of elastic deformation, the method comprising: a normal discharging process for discharging the prismatic secondary batteries so that the state of charge does not fall below a predetermined lower limit; and a refresh discharging process for discharging the prismatic secondary batteries until the state of charge becomes lower than the lower limit state of charge when the normal discharging process is not being performed; A method for controlling a battery pack, comprising: Item 2: The control method described in Item 1, further comprising a judgment step of judging whether or not the refresh discharge step is necessary based on the actual performance of the normal discharge step, and configured to execute the refresh discharge step if it is judged in the judgment step that the refresh discharge step is necessary. Item 3: The control method described in Item 2, further comprising a total discharge amount calculation process for calculating a total amount of discharge performed in the normal discharge process, and the determination process is configured to determine whether or not the refresh discharge process is necessary based on whether or not the total discharge amount exceeds a predetermined threshold value. Item 4: The control method according to item 2 or 3, further comprising a notification step of notifying a user that the refresh discharge step is necessary when the determination step determines that the refresh discharge step is necessary. Item 5: The control method according to item 4, further comprising starting the refresh discharge process based on a user's instruction after the notification process. Item 6: The control method according to any one of items 1 to 5, wherein in the refresh discharge step, the prismatic secondary battery is discharged until the state of charge becomes 10% or less. Item 7: The control method according to any one of items 1 to 6, further comprising a normal charging step of charging the prismatic secondary battery until the charge state is 90% or more, and configured such that, when the normal charging step is performed, the refresh discharge step is first performed, and then the normal charging step is performed. Clause 8: A control device for an assembled battery comprising a plurality of prismatic secondary batteries arranged along a predetermined arrangement direction, a porous elastic member arranged between adjacent prismatic secondary batteries in the arrangement direction, and a restraint mechanism for restraining the plurality of prismatic secondary batteries and the porous elastic member, wherein the porous elastic member has a communication hole communicating with the outside and is elastically deformable, the control device for an assembled battery including: a normal discharge control unit that performs a normal discharge process to discharge the prismatic secondary batteries so that the charge state does not fall below a predetermined lower limit, and a refresh discharge control unit that performs a refresh discharge process to discharge the prismatic secondary batteries until the charge state becomes lower than the lower limit when the normal discharge process is not being performed. [Explanation of symbols]

[0105] 10 Battery case 20 Electrode group 20a, 20b, 20c electrode body 100 Prismatic secondary battery 200 Porous elastic material 300 Restraint mechanism 500 battery pack 600 Control device 610 Normal charging control unit 620 Normal discharge control unit 630 Total discharge amount calculation unit 640 Judgment section 650 Refresh discharge control section 660 Notification Department 670 Storage section

Claims

1. A plurality of rectangular secondary batteries arranged along a predetermined arrangement direction; a porous elastic member disposed between adjacent ones of the rectangular secondary batteries in the arrangement direction; a restraining mechanism that restrains the plurality of prismatic secondary batteries and the porous elastic member; Equipped with The porous elastic member has a through hole communicating with the outside and is elastically deformable, a normal discharging step of discharging the prismatic secondary battery so that the state of charge does not fall below a predetermined lower limit; a refresh discharge step of discharging the prismatic secondary battery until the state of charge becomes lower than the lower limit state of charge when the normal discharge step is not being performed; A method for controlling a battery pack, comprising:

2. a determination step of determining whether the refresh discharge step is necessary or not based on a performance status of the normal discharge step; The refresh discharge step is executed when it is determined in the determination step that the refresh discharge step is necessary. The control method according to claim 1 .

3. A total discharge amount calculation step of calculating a total discharge amount of the discharge performed in the normal discharge step, The determination step is configured to determine whether or not the refresh discharge step is required based on whether or not the total discharge amount exceeds a predetermined threshold value. The control method according to claim 2 .

4. a notification step of notifying a user that the refresh discharge step is necessary when the determination step determines that the refresh discharge step is necessary, The control method according to claim 2 or 3.

5. After the notification step, the refresh discharge step is started based on an instruction from a user. The control method according to claim 4.

6. In the refresh discharge step, the prismatic secondary battery is discharged until the state of charge becomes 10% or less. A control method according to any one of claims 1 to 3.

7. a normal charging step of charging the prismatic secondary battery until the charged state is 90% or more; When the normal charging step is performed, the refresh discharge step is first performed, and then the normal charging step is performed. A control method according to any one of claims 1 to 3.

8. A control device for a battery pack comprising: a plurality of prismatic secondary batteries arranged along a predetermined arrangement direction; a porous elastic member arranged between adjacent ones of the prismatic secondary batteries in the arrangement direction; and a restraining mechanism that restrains the plurality of prismatic secondary batteries and the porous elastic member, the porous elastic member having communication holes that communicate with the outside and being elastically deformable, a normal discharge control unit that executes a normal discharge process for discharging the prismatic secondary battery so that the charged state does not fall below a predetermined lower limit; a refresh discharge control unit that executes a refresh discharge process to discharge the prismatic secondary battery until the state of charge becomes lower than the lower limit state of charge when the normal discharge process is not being performed; A control device comprising:

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