JP7733033B2 - Battery module and flat battery with built-in spacer - Google Patents

Description

The present invention relates to a battery module and a flat battery with a built-in spacer.

Conventionally, battery modules (battery packs) installed in vehicles and used over long periods of time have been known in which multiple flat batteries, which are flat in the expansion direction perpendicular to the battery thickness direction, are stacked in the battery thickness direction to form a battery stack, and this battery stack is compressed and rigidly restrained with restraining devices to a fixed size. This is because the stacked multiple flat batteries are compressed in the battery thickness direction for reasons such as improving the cycle characteristics of each flat battery.

As examples of batteries used in such battery modules and battery modules (battery packs) using such batteries, Patent Document 1 describes a battery comprising an electrode assembly and a battery case that houses the electrode assembly, and a battery pack in which multiple batteries are stacked and constrained to a fixed size. The battery in Patent Document 1 has an elastic spacer between the electrode assembly and the battery case to prevent uneven electrolyte concentration caused by expansion and contraction of the electrode assembly due to repeated charging and discharging.

Japanese Patent Application Laid-Open No. 2014-216086

Incidentally, some flat electrode bodies in flat batteries used in battery modules gradually increase in thickness with repeated charging and discharging. For example, this may be the case when the negative electrode active material layer of the negative electrode plate of the flat electrode body uses negative electrode active material particles made of a carbon-based negative electrode active material such as graphite or a silicon-based negative electrode active material such as silicon or silicon oxide. In this case, the repeated insertion and desorption of Li ions and other ions that accompany charging and discharging is thought to cause the active material particles to expand or crack, resulting in swelling. Furthermore, flat electrode bodies that include negative electrode plates with negative electrode active material layers made of silicon-based negative electrode active material particles are particularly prone to increasing in thickness with repeated charging and discharging.

In this way, as the electrode thickness of the flat electrode body gradually increases and the battery thickness of the flat battery in the battery thickness direction increases, the pressure applied to each flat battery in the battery module, which is constrained to a fixed size, gradually increases, and may eventually reach a state where extremely high pressure is applied.

The present invention was developed in light of this current situation, and provides a battery module that suppresses the increase in pressure applied to each flat battery in a battery module that is constrained to a fixed size, even if the electrode thickness of the flat electrode bodies of the flat batteries included in the battery module increases due to repeated charging and discharging, and a flat battery with built-in spacers used therein.

(1) One aspect of the present invention for solving the above problem is a battery module including a battery stack in which a plurality of flat batteries that are flat in an expansion direction perpendicular to the battery thickness direction are stacked in the battery thickness direction, and a restraining device that compresses the battery stack in the battery thickness direction and restrains it to a fixed size, wherein the flat batteries have flat electrode bodies that are flat in the expansion direction and whose electrode body thickness in the battery thickness direction increases with repeated charging and discharging, and a battery case that houses the flat electrode bodies, and when the surface pressure of the battery stack increases and reaches a yield surface pressure, the battery stack transitions from elastic deformation to plastic deformation, The battery module includes plate-shaped spacers that are made of plate material that subsequently transitions to elastic deformation again when the compression limit of plastic deformation is reached and the thickness after plastic deformation is reached, and that are elastically compressed in the battery thickness direction when a surface pressure less than the yield surface pressure is applied in the battery thickness direction, and that are plastically compressed in the battery thickness direction by plastic deformation when a surface pressure of the yield surface pressure is applied until the thickness after plastic deformation is reached, and the restraining device restrains the battery stack so that the surface pressure applied to the spacers exceeds the yield surface pressure as the thickness of the electrode bodies of the flat batteries increases due to repeated charging and discharging .

As mentioned above, in a battery module in which a battery stack consisting of multiple flat batteries stacked in the battery thickness direction is compressed in the battery thickness direction and restrained to a fixed size using restraining devices, if the electrode body thickness of each flat battery increases with repeated charge and discharge, the surface pressure applied to the electrode body gradually increases. Therefore, repeated charge and discharge can result in an extremely large surface pressure applied to each flat battery.
Such an extremely high surface pressure may damage the restraining device, which is undesirable because it would require the use of a high-strength or large restraining device that can withstand the high surface pressure in order to prevent the restraining device from being damaged.

In contrast, in the battery module described above, the battery stack is compressed in the battery thickness direction and restrained to a fixed size by restraining devices. However, in addition to this, this battery stack also includes spacers that undergo plastic deformation when subjected to a surface pressure of yield pressure. Therefore, as the electrode thickness of the flat electrode bodies of the flat batteries that make up the battery stack increases with repeated charging and discharging, the surface pressure applied to the spacers gradually increases, and the spacer thickness elastically decreases. However, as the electrode thickness of the flat electrode bodies further increases and the surface pressure applied to the spacers reaches the yield surface pressure, the spacers undergo plastic deformation, causing them to plastically compress in the battery thickness direction. Therefore, while the spacers are undergoing plastic deformation, their thickness gradually decreases, while the surface pressure applied to the spacers is maintained at approximately the yield surface pressure. Furthermore, if the electrode thickness of the flat electrode bodies further increases and the spacer thickness reaches the compression limit thickness for plastic compression, the spacers are again elastically compressed, and the surface pressure applied to the spacers also increases again. In this way, in the battery module described above, the spacers exhibit the above-described behavior, and therefore the surface pressure applied to the flat batteries can be reduced once the surface pressure reaches the yield surface pressure, compared to a battery module that does not have spacers that undergo plastic deformation.

Flat batteries used in battery stacks include secondary batteries such as lithium-ion secondary batteries and sodium-ion secondary batteries. The flat electrode bodies of flat batteries may be flat in the expansion direction, and may be laminated electrode bodies made by stacking sheet-shaped positive and negative electrode plates and separators, or flat, wound electrode bodies made by winding and crushing strip-shaped positive and negative electrode plates and separators. These flat electrode bodies have the characteristic of increasing in thickness with repeated charging and discharging. For example, the negative electrode active material particles contained in the negative electrode active material layer of the negative electrode plate may include negative electrode active material particles made of a carbon-based active material such as graphite, or silicon-based negative electrode active material such as silicon or silicon oxide. In addition to flat batteries containing a single flat electrode body within a battery case, flat batteries containing multiple flat electrode bodies stacked in the thickness direction within a battery case may also be used.

In addition, the restraining device that restrains the battery stack to a fixed size is a restraining body that rigidly restrains the battery stack without changing the dimension of the entire battery stack in the battery thickness direction, even if the electrode thickness of the flat electrode bodies increases and the battery thickness of the flat batteries increases, increasing the surface pressure applied to each flat battery.

A spacer that undergoes plastic deformation can be any plate material that, when compressed, increases surface pressure, transitions from elastic to plastic deformation when it reaches the yield surface pressure, and then transitions back to elastic deformation when it reaches the compression limit of plastic deformation and reaches the thickness after plastic deformation. Examples that can be used include porous metal oxides such as silica aerogel and alumina aerogel, metals with a honeycomb structure extending in the thickness direction, metal foams such as nickel foam, resin foams such as polystyrene foam, and composites of porous metal oxides such as silica aerogel and fibers (e.g., NASBIS (registered trademark) manufactured by Panasonic).

The spacers described above may be internal battery spacers, which are placed inside the flat battery case and overlap the flat electrode bodies in the battery thickness direction. They may also be external battery spacers, which are placed outside the flat battery and overlap the flat batteries in the battery thickness direction to form a battery stack.

(2) In the battery module described in (1) above, at least one of the plurality of flat batteries may be a spacer-integrated flat battery having the flat electrode body and the spacer, which is a flat plate-shaped internal battery spacer that overlaps the flat electrode body in the thickness direction of the battery.

In the above-mentioned battery module, at least one of the multiple flat batteries is a flat battery with built-in spacers. Therefore, this battery module uses flat batteries with built-in spacers that can be treated in the same way as batteries that do not contain plastically deformable spacers, resulting in a battery module with reduced surface pressure on each battery.

In a battery module, at least one of the flat batteries constituting the battery stack may be a flat battery with a built-in spacer, but it is preferable that all of the flat batteries are flat batteries with a built-in spacer.
In addition, the battery stack may have inter-battery interposing members disposed between the flat batteries stacked in the battery thickness direction to form the battery stack, or between the flat batteries and the end plates of the restraint device, for the purpose of insulating the flat batteries from each other or allowing cooling air to circulate.

(3) Furthermore, in the battery module described in (1) or (2), the battery stack may preferably have external spacers as the spacers between the flat batteries that make up the battery stack, on one side of all the flat batteries in the battery thickness direction, and on the other side of all the flat batteries in the battery thickness direction.

In the above-described battery module, the battery stack has external battery spacers located between the flat batteries, on one side of all the flat batteries in the battery thickness direction, or on the other side of all the flat batteries in the battery thickness direction, i.e., outside the flat batteries. Therefore, even though the above-described battery module uses conventional flat batteries that do not include plastically deformable spacers, the use of external battery spacers reduces the surface pressure applied to the flat batteries after the surface pressure reaches the yield surface pressure.

(4) Another solution is a flat battery that is flat in an expansion direction perpendicular to the battery thickness direction, and includes a flat electrode body whose thickness in the battery thickness direction increases with repeated charging and discharging, and a battery case that houses the flat electrode body. The flat battery case further includes an internal spacer that is flat and overlaps the flat electrode body in the battery thickness direction, and is elastically compressed in the battery thickness direction when a surface pressure less than the yield surface pressure is applied in the battery thickness direction, and is plastically compressed in the battery thickness direction by plastic deformation when a surface pressure of the yield surface pressure is applied until it reaches the thickness after plastic deformation.

The above-mentioned spacer-integrated flat battery has an internal battery spacer inside the battery case, so when a battery module is formed using these spacer-integrated flat batteries, the surface pressure applied to the flat batteries can be reduced after the surface pressure reaches the yield surface pressure, even without the need for a separate external battery spacer.

FIG. 1 is a perspective view of a battery according to an embodiment. 1 is a cross-sectional view of a battery according to an embodiment, taken along a plane along a battery width direction CH and a battery height direction DH. 2 is a cross-sectional view of the battery according to the embodiment, taken along a plane along the battery thickness direction BH and the battery height direction DH. FIG. 2 is a cross-sectional view of the battery according to the embodiment, taken along a plane along the battery thickness direction BH and the battery width direction CH. FIG. FIG. 2 is a perspective view of an electrode body according to the embodiment. FIG. 2 is a development view of an electrode assembly according to an embodiment, showing a state in which a positive electrode plate and a negative electrode plate are stacked on top of each other with a separator interposed therebetween. 10 is an explanatory diagram showing the relationship between the surface pressure FP applied to a plastic spacer and the spacer thickness T. FIG. FIG. 2 is a side view of the battery module according to the embodiment. FIG. 10 is an explanatory diagram showing how a restraint test fixture is used to investigate the change in surface pressure applied to a plastic spacer when the thickness of a test battery increases. 10 shows an example of an investigation into the relationship between the number of charge/discharge cycles of a test battery and the surface pressure applied to a plastic spacer. 10 is a cross-sectional view of a battery according to a modified embodiment, taken along a plane along the battery thickness direction BH and the battery height direction DH. FIG. FIG. 10 is a side view of a battery module according to a modified embodiment.

(Embodiment)
A battery 10 (an example of a flat battery, a flat battery with a built-in spacer) according to an embodiment of the present invention and a battery module 100 using the same will be described below with reference to FIGS. 1 to 10. In the following description, the battery thickness direction BH, battery width direction CH, and battery height direction DH of the battery 10 will be defined as the directions shown in FIG. 1. The direction perpendicular to the battery thickness direction BH, i.e., the direction including the battery width direction CH and the battery height direction DH, will be defined as the expansion direction SH. The axial direction EH, electrode body thickness direction FH, and electrode body width direction GH of the electrode assembly 30 will be defined as the directions shown in FIG. 5.

The battery 10 is a rectangular, sealed lithium-ion secondary battery that is flat in the expansion direction SH. The battery module 100 and battery 10 are installed in vehicles such as hybrid cars, plug-in hybrid cars, and electric cars, as well as in various devices.

As described below, the batteries 10 are used as a battery module 100 by stacking multiple batteries 10 and inter-battery members 130 alternately in the battery thickness direction BH to form a battery stack 120, and then restraining this battery stack 120 with restraining devices 110 (see Figure 8). Note that in Figure 8, the positive electrode terminal portion 60 and negative electrode terminal portion 70 of the batteries 10 are omitted.

This battery 10 is composed of a rectangular parallelepiped battery case 20 that is flattened in the expansion direction SH, a flat wound electrode assembly 30 (an example of a flat electrode assembly) housed within this battery case 20, and a positive electrode terminal 60 and a negative electrode terminal 70 supported by the battery case 20. A non-aqueous electrolyte 27 is held within the battery case 20. In addition, this battery 10 has a pair of plate-shaped plastic spacers 80 (an example of a spacer, an internal battery spacer) disposed between the battery case 20 and the electrode assembly 30.

Of these, the battery case 20 is made of metal (specifically, aluminum). The battery case 20 is composed of a case body 21 in the shape of a rectangular cylinder with a bottom, which has a rectangular opening 21h only on the upper side, and a rectangular plate-like lid 23 that seals the opening 21h of the case body 21 (see Figures 1 to 4). A non-returnable safety valve 23v is provided near the center of the lid 23 in its longitudinal direction (battery width direction CH, left-right direction in Figure 2).

A positive electrode terminal 60 and a negative electrode terminal 70 are fixed to the lid 23 near both ends of its longitudinal axis, extending from the inside to the outside of the battery case 20 (see Figures 1 and 2). Specifically, the aluminum positive electrode terminal member 61 and the copper negative electrode terminal member 71 are each connected to the electrode assembly 30 within the battery case 20, while penetrating the lid 23 and extending to the outside of the battery case 20. The positive electrode terminal member 61 and the negative electrode terminal member 71 are fixed to the lid 23 via resin insulating members 65, 75 that insulate them.

Next, the electrode body 30 will be described (see Figures 2 to 6). The electrode body 30 is housed in the battery case 20 with its axial direction EH aligned with the battery width direction CH, its electrode body thickness direction FH aligned with the battery thickness direction BH, and its electrode body width direction GH aligned with the battery height direction DH (see Figure 2). The electrode body 30 is a flat-wound electrode body formed by stacking a strip-shaped positive electrode plate 31 and a strip-shaped negative electrode plate 41 with a pair of strip-shaped separators 51 made of porous resin sandwiched between them (see Figure 6), winding them around the axis AX, and flattening them (see Figure 5). As will be described later, the electrode body 30 has a characteristic in which the electrode body thickness THe in the battery thickness direction BH increases with repeated charging and discharging of the battery 10.

The strip-shaped positive electrode plate 31 comprises a strip-shaped aluminum positive electrode foil 32, and a positive electrode active material layer 33 extending in the longitudinal direction (left-right direction in FIG. 6) on one side (upper side in FIG. 6) of the width direction (vertical direction in FIG. 6) of either the front or back surface of the positive electrode foil 32. This positive electrode active material layer 33 is formed from positive electrode active material particles 34, a conductive material, and a binder. In this embodiment, lithium-cobalt-nickel-manganese composite oxide is used as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVDF) as the binder.

On the other hand, the strip-shaped negative electrode plate 41 comprises a strip-shaped negative electrode foil 42 made of copper, and a strip-shaped negative electrode active material layer 43 extending in the longitudinal direction (left-right direction in FIG. 6) is formed on the other side (bottom side in FIG. 6) of the width direction (top-bottom direction in FIG. 6) of the front and back surfaces of the negative electrode foil 42. This negative electrode active material layer 43 is formed from negative electrode active material particles, a binder, and a thickener. In this embodiment, silicon oxide (SiOx) particles and graphite particles are used as the negative electrode active material particles 44, styrene butadiene rubber (SBR) is used as the binder, and carboxymethyl cellulose (CMC) is used as the thickener. In this embodiment, the weight ratio of silicon oxide (SiOx) particles to graphite particles in the negative electrode active material particles 44 is 2:8.

These negative electrode active material particles 44 expand during the charging process and contract during the discharging process. In addition, as the battery 10 is repeatedly charged and discharged, the silicon oxide particles within the negative electrode active material particles 44 gradually expand. As a result, the thickness of the negative electrode plate 41 also gradually increases.

In the electrode assembly 30, a portion of the positive electrode plate 31 protrudes in a flat spiral shape from the separator 51 toward one side EH1 in the axial direction EH (upward in FIG. 6, leftward in FIG. 2), forming the positive electrode current collector 30P of the electrode assembly 30. A positive electrode terminal member 61 is welded to this positive electrode current collector 30P. Furthermore, a portion of the negative electrode plate 41 protrudes in a flat spiral shape from the separator 51 toward the other side EH2D in the axial direction EH (downward in FIG. 6, rightward in FIG. 2), forming the negative electrode current collector 30N of the electrode assembly 30. A negative electrode terminal member 71 is welded to this negative electrode current collector 30N.

The flat laminated portion 30L is located inside (at the center) the positive electrode current collector 30P and negative electrode current collector 30N of the electrode body 30 in the axial direction EH, and is where a large number of flattened positive electrode plates 31 and negative electrode plates 41 overlap each other in the electrode body thickness direction FH (battery thickness direction BH) with separators 51 interposed between them (see Figure 5).

Next, the plastic spacers 80 will be described (see Figures 2 to 4). These plastic spacers 80 are arranged inside the battery case 20, on both sides of the electrode body 30 in the electrode body thickness direction FH. These two plastic spacers 80 are rectangular plates with a slightly larger area (larger dimensions in both the axial direction EH and the electrode body width direction GH) than the flat plate-like laminated portion 30L of the electrode body 30, and are arranged outside the flat plate-like laminated portion 30L, overlapping it. These plastic spacers 80 are made, for example, of a composite material of fiber and silica aerogel (NASBIS (trademark), manufactured by Panasonic Corporation).

This plastic spacer 80 generally has the characteristics shown in Figure 7. Assume that the spacer thickness T of the plastic spacer 80 in its free state is initially Ts. When this plastic spacer 80 is gradually compressed, it initially undergoes elastic compression, and as the surface pressure FP1 gradually increases, the spacer thickness T gradually decreases. That is, as the surface pressure FP1 increases, the spacer thickness T decreases approximately linearly. However, once the surface pressure FP1 reaches the yield surface pressure FPY (the spacer thickness T at this time is the thickness before plastic deformation Tp), the compression proceeds with almost no increase in the surface pressure FP1, and the spacer thickness T decreases rapidly. This is because the plastic spacer 80 has been plastically compressed (plastically deformed). Then, once the spacer thickness T reaches the thickness after plastic deformation Tq, the spacer thickness T gradually decreases elastically again as the surface pressure FP1 increases.

The electrolyte 27 was prepared by dissolving LiPF ₆ at a concentration of 1.0 mol/L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3.

Furthermore, as shown in FIG. 3 , the dimension of the electrode body 30 in the electrode body thickness direction FH (battery thickness direction BH) of the battery 10 is referred to as the electrode body thickness THe, and the dimension of the battery 10 in the battery thickness direction BH is referred to as the battery thickness THb. The electrode body thickness THe of the electrode body 30 gradually increases due to the expansion of the negative electrode active material particles 44 caused by repeated charging and discharging of the battery 10 described above.

This battery 10 is used as a battery module 100 (see Figure 8). This battery module 100 includes a battery stack 120 and a restraint 110. The battery stack 120 is formed by stacking multiple batteries 10 and multiple inter-battery members 130 alternately in the battery thickness direction BH (electrode body thickness direction FH). Adjacent batteries 10 are electrically connected in series by bus bars (not shown). The inter-battery members 130 are rectangular plates and are disposed between adjacent batteries 10, forming cooling paths (not shown) through which cooling air flows between the batteries 10.

Meanwhile, the restraining device 110 rigidly restrains the battery stack 120, i.e., the batteries 10 and inter-battery members 130, while compressing them in the battery thickness direction BH. This restraining device 110 has a pair of end plates 111, four fastening bolts 113, and eight nuts 115. The end plates 111 are rectangular and are arranged on both sides of the battery stack 120 (stacked batteries 10 and inter-battery members 130). The fastening bolts 113 are cylindrical and have threads on both ends 113t. They are arranged between the pair of end plates 111 and connect the end plates 111 to each other. The nuts 115 fasten the ends 113t of the fastening bolts, which are inserted into through holes (not shown) provided in the end plates 111, to the end plates 111.

When this battery module 100 is constructed, the flat laminate portion 30L and plastic spacer 80 of the electrode body 30 of each battery 10 are compressed in the electrode body thickness direction FH via the battery case 20. Even when the negative electrode active material particles 44 expand and contract as the battery 10 is charged and discharged, the battery thickness THb (dimension in the battery thickness direction BH) of the battery 10 is maintained at a fixed size, resulting in a compressed, fixed-size state.

Here, if the battery 10 does not have a plastic spacer 80, and the electrode body thickness THe of the electrode body 30 gradually increases through repeated charging and discharging of the battery 10, the battery stack 120 and the battery thickness THb of each battery 10 are maintained at a fixed size. As described above, the surface pressure FP1 applied to the battery 10 gradually increases, and may eventually become extremely large.

However, in the battery module 100 of this embodiment, a plastic spacer 80 is provided inside the battery case 20 of the battery 10, so even if the electrode body thickness THe of the electrode body 30 gradually increases, the increase in surface pressure FP1 applied to each battery 10 can be suppressed. Therefore, the change in surface pressure when this plastic spacer 80 is used and when it is not used was confirmed by the following surface pressure test using the restraint test fixture CB shown in Figure 9.

<Surface pressure test>
First, the restraint test fixture CB will be described. The restraint test fixture CB comprises a rectangular bottom plate BB, an intermediate plate MB, and an upper plate UB, as well as support bolts BT erected at the four corners of the bottom plate BB, nuts NT fastening the support bolts BT to the upper plate UB, a load cell LC disposed between the bottom plate BB and the intermediate plate MB, and a stress measuring device LA that drives the load cell LC and detects the stress acting on the load cell LC. The intermediate plate MB has through holes (not shown) drilled at its four corners, through which the support bolts BT are inserted.

The test battery CE was formed as follows. First, the portion of the belt-shaped positive electrode plate 31 provided with the positive electrode active material layer was cut into a 29 mm x 39 mm rectangular shape to prepare two rectangular positive electrode plates. The portion of the belt-shaped negative electrode plate 41 provided with the negative electrode active material layer was cut into a 30 mm x 40 mm rectangular shape to prepare three rectangular negative electrode plates. Six rectangular separators, each measuring 32 mm x 42 mm, were then cut out from the belt-shaped separator 51. The positive and negative electrode plates were then alternately stacked with the separators in between, and electrode terminals were attached to form a five-layer stacked electrode assembly. This stacked electrode assembly was inserted into an aluminum laminate film case with portions of the electrode terminals protruding to the outside, and the case was sealed to complete the test battery CE.

Using this test battery CE and restraint test fixture CB, we investigated the behavior of a plastic spacer PS cut into a 32mm x 42mm rectangle from the aforementioned plastic spacer 80. First, the test battery CE and plastic spacer PS were stacked and placed between the middle plate MB and upper plate UB of the restraint test fixture CB, and the nuts NT were tightened to apply a slight surface pressure FP that brought the test battery CE and plastic spacer PS into close contact. This compressed the test battery CE and plastic spacer PS between the middle plate MBA and upper plate UB and restrained them to a fixed size.

The test battery CE was then connected to a power source (not shown) and charged/discharged over a range of SOC 0%-100% using a charge/discharge cycle that repeated CCCV charging at a charge current of 1/3 C and CC discharging at a discharge current of 1/3 C. The number of charge/discharge cycles and the surface pressure FP applied to the plastic spacer PS, obtained by the load cell LC, were also measured.

Figure 10 shows, in a dashed line graph (with spacer), the relationship between the number of charge/discharge cycles of the test battery CE and the surface pressure FP applied to the test battery CE and plastic spacer PS, obtained in a surface pressure test using the restraint test fixture CB. The solid line graph (without spacer) also shows the relationship between the number of charge/discharge cycles of the test battery CE and the surface pressure FP applied to the test battery CE when the plastic spacer PS is removed and only the test battery CE is placed between the middle plate MB and the upper plate UB and restrained to a fixed size.

In Figure 10, the solid line for "without spacer" shows that the surface pressure FP applied to the plastic spacer PS gradually and monotonically increases as the number of charge/discharge cycles applied to the test battery CE increases. As mentioned above, charge/discharge causes the negative electrode active material particles 44 to expand, gradually increasing the thickness of the negative electrode plate 41 and, ultimately, the electrode body thickness of the stacked electrode body in the test battery CE. Meanwhile, the test battery CE is constrained to a fixed size between the intermediate plate MB and the upper plate UB. This is thought to be why the test battery CE is elastically compressed, causing the surface pressure FP applied to the test battery CE to gradually increase.

On the other hand, in Figure 10, the graph for "with spacer," shown by the dashed line, shows that at low cycle counts (specifically, when the cycle count is 19 or less), as in the graph for "without spacer," the surface pressure FP applied to the test battery CE and the plastic spacer PS gradually increases as the number of charge/discharge cycles applied to the test battery CE increases. As in the case of "without spacer" described above, the negative electrode active material particles 44 expand during charge/discharge, gradually increasing the thickness of the negative electrode plate 41 and, ultimately, the electrode body thickness of the stacked electrode assembly within the test battery CE. Meanwhile, the test battery CE and the plastic spacer PS are constrained to a fixed size between the intermediate plate MB and the upper plate UB. Therefore, the test battery CE and the plastic spacer PS are elastically compressed, presumably increasing the surface pressure FP applied to the test battery CE and the plastic spacer PS.

However, in the graph "with spacer" shown by the dashed line, once the surface pressure increased to a certain extent (specifically, when the surface pressure FP reached 1.4 MPa), the behavior was different from that of the graph "without spacer" shown by the solid line, which showed a monotonically increasing value.
First, after the surface pressure FP applied to the plastic spacer PS increased to a certain level, the surface pressure FP remained constant (1.4 MPa in this example) for a while (the plastic deformation period, specifically, the nine-cycle period from 19 to 28 cycles in which the surface pressure FP reached 1.4 MPa). This constant surface pressure FP (1.4 MPa in this example) is considered to correspond to the yield surface pressure FPY in Figure 7. In other words, during the nine-cycle plastic deformation period from 19 to 28 cycles, even though the electrode body thickness of the stacked electrode body in the test battery CE gradually increased, the plastic spacer PS was plastically compressed, and the spacer thickness T rapidly decreased from the thickness before plastic deformation Tp, so the surface pressure FP did not increase.
Furthermore, once the plastic compression stage is exceeded, that is, once the spacer thickness T reaches the thickness after plastic deformation Tq, specifically, after the number of cycles reaches 29, the surface pressure FP applied to the plastic spacer PS gradually increases again as the number of cycles increases.

Because of this behavior in the plastic spacer PS, as can be easily seen by comparing the solid and dashed lines in Figure 10, after 19 cycles, plastic compression (plastic deformation) occurs in the plastic spacer PS, causing the surface pressure FP applied to the test battery CE to be smaller in the "with spacer" case shown by the dashed line than in the "without spacer" case shown by the solid line. Furthermore, after 29 cycles, the surface pressure FP applied to the test battery CE in the "with spacer" case shown by the dashed line is consistently about 0.5 MPa smaller than in the "without spacer" case shown by the solid line.

In the battery module 100 of this embodiment, when the batteries 10 connected in series are charged and discharged, the electrode body thickness THe of the electrode body 30 of each battery 10 gradually increases due to the expansion of the negative electrode active material particles 44 (see Figure 3). Meanwhile, in the battery module 100, each battery 10 has a plastic spacer 80, similar to the plastic spacer PS described above, inside the battery case 20. Therefore, in the battery module 100 of this embodiment, the number of charge/discharge cycles and the surface pressure FP1 applied to the electrode body 30 and plastic spacer 80 behave similarly to the results of the surface pressure test described above (see the graph labeled "With spacer" in Figure 10).

That is, when the number of cycles is low, the surface pressure FP1 applied to the electrode assembly 30 and plastic spacer 80 gradually increases as the number of charge/discharge cycles applied to each battery 10 increases. Charge/discharge causes the negative electrode active material particles 44 to expand, gradually increasing the thickness of the negative electrode plate 41 and, ultimately, the electrode body thickness THe of the electrode assembly 30 in the battery 10, while the battery stack 120 including each battery 10 is constrained to a fixed size between a pair of end plates 111 of the restraining device 110. Therefore, it is believed that the plastic spacer 80 of each battery 10 is elastically compressed, causing the surface pressure FP1 applied to each plastic spacer 80 to increase.

However, for a period of time (plastic deformation period) after the stage at which the surface pressure FP1 applied to the plastic spacer 80 increases and reaches the yield surface pressure FPY of the plastic spacer 80 (the stage at which the spacer thickness T reaches the thickness before plastic deformation Tp; see Figure 7), the surface pressure FP1 does not increase even if the number of charge/discharge cycles increases, and is maintained at the yield surface pressure FPY. During this plastic deformation period, even if the electrode body thickness THe of the electrode body 30 in each battery 10 gradually increases, it is thought that the surface pressure FP1 did not increase because the plastic spacer 80 in each battery 10 was plastically compressed and the spacer thickness T decreased from the thickness before plastic deformation Tp.

After that, once the plastic compression period is over, that is, once the spacer thickness T of the plastic spacer 80 in each battery 10 reaches the thickness after plastic deformation Tq, the surface pressure FP1 applied to the electrode body 30 and plastic spacer 80 gradually increases again as the number of charge/discharge cycles increases.

Thus, similar to the graph for "with spacers" shown by the dashed line in Figure 10, due to the occurrence of plastic compression (plastic deformation) of the plastic spacers 80, the surface pressure FP1 applied to the plastic spacers 80 and, more specifically, to each battery 10 is smaller after the start of the plastic compression period than in a battery module using batteries without plastic spacers 80, which corresponds to the case for "without spacers" shown by the solid line. Furthermore, after the plastic compression period, the surface pressure FP1 applied to the batteries 10 can be consistently smaller than in a battery module using batteries without plastic spacers 80.

(Transformed form)
Next, a battery module 300 according to a modified embodiment will be described with reference to Figures 11 and 12. In the battery module 100 of the above embodiment, a battery stack 120 in which batteries 10, each having plastic spacers 80 arranged in addition to electrode bodies 30 in a battery case 20, and inter-battery members 130 are alternately stacked is restrained by a restraining device 110 (see Figure 8).

In contrast, the battery module 300 according to the modified embodiment uses batteries 210 that differ from the battery 10 in that they do not have plastic spacers, even though the electrode assembly 30 is disposed within the battery case 220 (see FIG. 11). Instead, plastic spacers 330 (same as the plastic spacers 80 in the embodiment) are used outside the battery. That is, a battery stack 320 in which batteries 210 and plastic spacers 330 outside the battery are alternately stacked is restrained by a restraining device 110 similar to that in the embodiment (see FIG. 12). As in the embodiment, adjacent batteries 210 are electrically connected in series by bus bars (not shown). The battery 210 contains the electrode assembly 30 and electrolyte 27 in a bottomed, rectangular cylindrical case body 221, and the rectangular opening 221h is sealed with a lid 223.

Even in this modified battery module 300, when the batteries 210 connected in series are charged and discharged, the electrode body thickness THe of the electrode body 30 of each battery 210 gradually increases due to the expansion of the negative electrode active material particles 44 (see Figure 11). This also gradually increases the battery thickness THb. Meanwhile, the battery module 300 has plastic spacers 330 similar to the plastic spacers PS described above between the batteries 210. Therefore, even in this modified battery module 300, the number of charge/discharge cycles and the surface pressure FP2 applied to the electrode body 30, batteries 210, and plastic spacers 330 behave similarly to the results of the surface pressure test described above (see the graph for "with spacers" in Figure 10).

That is, when the number of cycles is low, the surface pressure FP2 applied to the electrode assembly 30 and plastic spacer 330 gradually increases as the number of charge/discharge cycles applied to each battery 210 increases. Charge/discharge causes the negative electrode active material particles 44 to expand, gradually increasing the thickness of the negative electrode plate 41 and, consequently, the electrode assembly thickness THe of the electrode assembly 30 in the battery 210 and the battery thickness THb of the battery 210. Meanwhile, the battery stack 320 including each battery 210 is constrained to a fixed size between the pair of end plates 111 of the restraining device 110. Therefore, each battery 210 and plastic spacer 330 is elastically compressed, and it is believed that the surface pressure FP2 applied to each battery 210 and plastic spacer 330 increases.

However, after the surface pressure FP2 applied to each plastic spacer 330 outside the battery increases and reaches the yield surface pressure FPY of the plastic spacer 330 (after the spacer thickness T reaches the thickness before plastic deformation Tp; see Figure 7), for a certain period (the plastic deformation period), the surface pressure FP2 does not increase and is maintained at the yield surface pressure FPY even if the number of charge/discharge cycles increases. During this plastic deformation period, even if the electrode body thickness THe of the electrode body 30 in each battery 210 gradually increases, it is thought that the surface pressure FP2 did not increase because the plastic spacer 330 outside the battery was plastically compressed and the spacer thickness T decreased from the thickness before plastic deformation Tp.

After that, once the plastic compression period is over, that is, once the spacer thickness T of the plastic spacer 330 reaches the thickness after plastic deformation Tq, the surface pressure FP2 applied to the electrode body 30 and the plastic spacer 330 gradually increases again as the number of charge/discharge cycles increases.

Thus, as shown by the dashed line in Figure 10, due to the occurrence of plastic compression (plastic deformation) of the plastic spacers 330, after the start of the plastic compression period, the surface pressure FP2 applied to the plastic spacers 330 and, moreover, to each battery 210 is smaller than in a battery module using a battery stack without plastic spacers 330, which corresponds to the "no spacer" case shown by the solid line. Furthermore, after the plastic compression period, the surface pressure FP2 applied to the batteries 210 can be consistently smaller than in a battery module using batteries without plastic spacers 330.

Note that while this modified battery module 300 uses conventional batteries 210 that do not include plastically deformable spacers, the use of plastic spacers 330 allows the surface pressure FP2 applied to each battery 210 to be reduced once the surface pressure FP2 reaches the yield surface pressure FPY.

The present invention has been described above in accordance with embodiments and modified forms, but it goes without saying that the present invention is not limited to the embodiments, etc., and can be modified and applied as appropriate within the scope of the gist of the present invention.
For example, in the embodiment, an example has been shown in which a battery 10 is used in which, in addition to the electrode body 30, a pair of plastic spacers 80 are arranged on both sides of the electrode body 30 in the electrode body thickness direction FH in the battery case 20 (see FIG. 3 ). However, a battery in which a plastic spacer 80 is arranged on one side of the electrode body 30 in the electrode body thickness direction FH may also be used.

In the embodiment, all of the batteries used in the battery module 100 are batteries 10 incorporating plastic spacers 80 (see FIG. 8 ). However, only some of the batteries may be batteries 10 incorporating plastic spacers 80.
Similarly, in a modified embodiment, a battery stack 320 of a battery module 300 has multiple batteries 210 and multiple plastic spacers 330 stacked alternately (see FIG. 12 ). However, some of the multiple plastic spacers 330 may be replaced with the inter-battery members 130 used in the embodiment, thereby reducing the number of plastic spacers 330 used in the battery stack 320. Conversely, plastic spacers 330 may also be placed between the end plates 111 and the batteries 210.

10 (flat battery, flat battery with built-in spacer)
210 Battery (flat battery)
20, 220 Battery case 30 Electrode body (flat electrode body)
THe electrode body thickness 30L flat plate-shaped laminated portion 80 plastic spacer (internal spacer, spacer)
100, 300 Battery module 110 Restraint device 120, 320 Battery stack 330 Plastic spacer (outside battery spacer)
BH: Battery thickness direction BH1: One side of the battery thickness direction BH2: Other side of the battery thickness direction SH: Expansion direction EH: Axial direction EH1: One side of the axial direction EH2: Other side of the axial direction FH: Electrode body thickness direction (stacking direction)
GH Electrode body width direction FP, FP1, FP2 Surface pressure FPY Yield surface pressure T Spacer thickness Ts Initial thickness Tp Thickness before plastic deformation Tq Thickness after plastic deformation

Claims (3)

a battery stack formed by stacking a plurality of flat batteries that are flat in an expansion direction perpendicular to the battery thickness direction in the battery thickness direction;
a restraining device that compresses the battery stack in the battery thickness direction and restrains it to a fixed size,
The flat battery is
a flat electrode body that is flat in the expansion direction and whose thickness in the battery thickness direction increases with repeated charging and discharging;
a battery case that houses the flat electrode body,
The battery stack is
The battery includes a plate-like spacer that is made of a plate material that, when the surface pressure increases and reaches a yield surface pressure, transitions from elastic deformation to plastic deformation, but then transitions back to elastic deformation when the compression limit of plastic deformation is reached and the thickness after plastic deformation is reached, and is elastically compressed in the battery thickness direction when a surface pressure less than the yield surface pressure is applied in the battery thickness direction, and is plastically compressed by plastic deformation in the battery thickness direction when a surface pressure of the yield surface pressure is applied until the thickness after plastic deformation is reached ,
The restraint device is
The battery stack is constrained so that the surface pressure applied to the spacer exceeds the yield surface pressure due to an increase in the thickness of the electrode body of the flat battery caused by repeated charging and discharging.
Battery module. The battery module according to claim 1,
At least one of the plurality of flat batteries
The flat electrode body;
The battery module is a flat battery module having a flat electrode body and a flat intra-battery spacer, the spacer being a flat plate-shaped intra-battery spacer that overlaps the flat electrode body in the thickness direction of the battery. The battery module according to claim 1 or 2,
The battery stack is
A battery module having an external battery spacer, which is the spacer, at least either between the flat batteries that make up the battery stack, on one side of all the flat batteries in the battery thickness direction, or on the other side of all the flat batteries in the battery thickness direction.