Patent Application
20240178506
This application claims the benefit of priority to Japanese Patent Application No. 2022-188413 filed on Nov. 25, 2022. The entire contents of this application are hereby incorporated herein by reference.
The present disclosure relates to a battery pack.
One of the conventionally used vehicle driving power sources and the like employs a battery pack including a plurality of batteries (cells) arranged in a predetermined direction, spacers disposed between the adjacent batteries in the arrangement direction, and a restriction mechanism that applies a restriction load on the plurality of batteries and the spacers from the arrangement direction (for example, Japanese Patent Application Publication No. 2015-138753, Japanese Patent Application Publication No. 2017-107648, Japanese Patent No. 6198844, and Japanese Patent Application Publication No. 2022-013634).
For example, Japanese Patent Application Publication No. 2015-138753 discloses a battery pack including a rectangular secondary battery in which a wound electrode body with a flat shape is disposed inside a battery case so that a winding axis extends along a bottom wall, and a spacer including a pressing part that presses a center part of a wide surface of the battery case that faces a flat region of the wound electrode body, and presses an upper end part and a lower end part thereof that face curved regions. According to Japanese Patent Application Publication No. 2015-138753, the surface pressure to be applied to the center part is reduced by making the elastic coefficient of the pressing part that presses the center part relatively low, thereby homogenizing the surface pressure that acts on the wide surface of the battery case.
According to the present inventor's earnest examination, there is still room for improvement in the aforementioned art. That is to say, when the battery is charged and discharged, gas such as CO2 and CO may be generated inside the electrode body (specifically, on a surface of an electrode). In the case of the wound electrode body, however, the gas generated in the electrode body is discharged only from both ends in a winding axis direction corresponding to opening parts. Therefore, it has been turned out that if the pressing on the curved region is insufficient or, on the contrary, the pressing on the flat region is excessive, the gas generated in the electrode body is not discharged and remains in the electrode body. Meanwhile, it has been found out that if the pressing on the flat region is insufficient, the charging and discharging reaction becomes inhomogeneous. Because of these facts, particularly the battery including the wound electrode body in which the wound electrode body with a flat shape is disposed inside the battery case so that the winding axis extends along the bottom wall has a problem that, for example, repeating high-rate charging and discharging results in frequent metal precipitation (for example, Li precipitation).
The present disclosure has been made in view of the above circumstances, and a main object is to provide a battery pack in which the remaining of gas inside a wound electrode body is suppressed and the occurrence of metal precipitation is suppressed.
According to the present disclosure, a battery pack including a wound electrode body with a flat shape that includes a positive electrode and a negative electrode, a battery case that accommodates the wound electrode body, and a pressing member that presses the battery case is provided. The battery case includes a bottom wall, an upper wall, a pair of first side walls disposed so as to face each other and connecting the bottom wall and the upper wall, and a pair of second side walls disposed so as to face each other and connecting the bottom wall and the upper wall. The wound electrode body includes a flat region provided with a pair of flat outer surfaces, and a pair of curved regions provided on both ends of the flat region and each provided with a curved outer surface, and the wound electrode body is disposed inside the battery case in a manner that a winding axis is disposed along the bottom wall and each of the pair of flat outer surfaces faces the first side wall. In at least one of the pair of first side walls of the battery case here, when an entire area of parts facing the pair of curved regions is 100%, 80% or more of the area including border parts with the flat region is pressed in a band shape along the winding axis by the pressing member, when an entire area of a part facing the flat region is 100%, 20% or more and 50% or less of the area is pressed by the pressing member, and a space extending from a center part to an end part of the wound electrode body in a winding axis direction is formed between the part facing the flat region and the pressing member.
In the present disclosure, 80% or more of the area of the parts facing the curved regions of the wound electrode body including the border parts with the flat region is pressed in the band shape along the winding axis. Thus, the gas generated in the flat region does not move easily to the curved region, and the gas moves in the winding axis direction along the pressed part in the band shape and is discharged out of the electrode body easily. Therefore, the remaining of the gas in the curved region can be suppressed. In addition, when the area of the part to be pressed in the part facing the flat region is set to 50% or less and the space (part that is not pressed) extending from the center part to the end part in the winding axis direction is secured between the pressing member and the part facing the flat region, the gas moves easily in the winding axis direction in the flat region and the gas is easily guided to an opening end of the wound electrode body. Therefore, the gas generated in the flat region can be discharged smoothly out of the electrode body from the end part of the wound electrode body and the remaining of the gas in the flat region can be suppressed. In addition, when the area of the part, which is pressed, in the part facing the flat region is set to 20% or more, inhomogeneity of charging and discharging reaction due to the lack of the pressure can be suppressed. As a result, according to the above-described structure, the occurrence of metal precipitation (for example, Li precipitation) in the entire wound electrode body (curved regions and flat region) can be effectively suppressed.
The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
Preferred embodiments of a battery pack disclosed herein will be described below with reference to the drawings as appropriate. Matters other than matters particularly mentioned in the present specification and necessary for the implementation of the present disclosure (for example, the general configuration and manufacturing process of a battery that do not characterize the present disclosure) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The battery pack disclosed herein can be implemented on the basis of the disclosure of the present specification and common technical knowledge in the relevant field. Note that in the drawings below, the members and parts with the same operation are denoted by the same reference signs and the overlapping description may be omitted or simplified. Moreover, in the present specification, the notation “A to B” for a range signifies a value more than or equal to A and less than or equal to B, and is meant to encompass also the meaning of being “more than A” and “less than B”.
The restriction mechanism 300 is configured to apply a prescribed restriction load on the plurality of rectangular secondary batteries 100 and the plurality of spacers 200 from the arrangement direction X. The restriction mechanism 300 here includes a pair of end plates 310 facing each other, a pair of side plates 320 facing each other, and a plurality of screws 330. Each of the end plates 310 and the side plates 320 is preferably made of metal. However, a part made of resin may be included partially.
The pair of end plates 310 are arranged in the arrangement direction X. The pair of end plates 310 are disposed on both ends of the battery pack 500 in the arrangement direction X. The plurality of rectangular secondary batteries 100 are disposed between the pair of end plates 310 along the arrangement direction X. The plurality of spacers 200 are each disposed between the rectangular secondary batteries 100 that are adjacent in the arrangement direction X. The pair of end plates 310 hold the plurality of rectangular secondary batteries 100 and the plurality of spacers 200 therebetween in the arrangement direction X.
The pair of side plates 320 bridge over the pair of end plates 310. The pair of side plates 320 are fixed to the end plates 310 by the screws 330 so that the restriction load is for example about 3 to 15 kN and preferably about 5 to 10 kN. Thus, the restriction load is applied on the plurality of rectangular secondary batteries 100 and the plurality of spacers 200 from the arrangement direction X and accordingly, the battery pack 500 is held integrally. In this case, the side plates 320 and the plurality of screws 330 form the restriction mechanism of the rectangular secondary batteries 100. The restriction mechanism is, however, not limited to this example. In another example, the restriction mechanism 300 may alternatively include a plurality of restriction bands, bind bars, or the like instead of the side plates 320 and the plurality of screws 330.
In this case, the rectangular secondary battery 100 is a secondary battery that is capable of being charged and discharged repeatedly. Note that in the present specification, “battery” is a term that refers to a general power storage device capable of extracting electric energy, and refers to a concept that encompasses a primary battery and a secondary battery. In the present specification, “secondary battery” refers to a concept that encompasses a so-called storage battery (chemical battery) such as a lithium ion secondary battery and a nickel-hydrogen battery, and a capacitor (physical battery) such as a lithium ion capacitor and an electric double-layer capacitor.
As illustrated in
The battery case 10 is a housing that accommodates the wound electrode body 20 and the nonaqueous electrolyte solution. As illustrated in
As illustrated in
As illustrated in
The long side wall 12b is preferably horizontally long. That is to say, the length in the long side direction Y is preferably longer than the length in the up-down direction Z. The length of the long side wall 12b in the long side direction Y is preferably 200 mm or more, and the length thereof in the up-down direction Z is preferably 100 mm or more. As the distance between the center part and the end part in the long side direction Y (in other words, the length of the wound electrode body 20 in a winding axis direction) is longer, particularly gas remains easily inside the wound electrode body 20, especially at the center part in the long side direction Y. Thus, it is particularly effective to apply the art disclosed herein. In the long side wall 12b, the ratio (ratio of height/width) of the length in the up-down direction Z to the length in the long side direction Y is preferably 1/3 to 1/1 and more preferably 1/3 to 1/2.
In a plan view, the long side wall 12b is larger in area than the short side wall 12c. Although not particularly limited, in the rectangular secondary battery 100 of a high-capacity type that may be used as an on-vehicle battery or the like, the area of the long side wall 12b may be generally 10000 mm2 or more, preferably 15000 mm2 or more, more preferably 20000 mm2 or more, still more preferably 25000 mm2 or more, and particularly preferably 30000 mm2 or more. If the area of the long side wall 12b is large in this manner, particularly, the gas remains easily inside the wound electrode body 20, especially at the center part in the long side direction Y. Thus, it is particularly effective to apply the art disclosed herein. From the viewpoint of obtaining the effect of the art disclosed herein at a high level, the area of the long side wall 12b is generally 150000 mm2 or less, and preferably 100000 mm2 or less.
The sealing plate 14 is attached to the exterior body 12 so as to cover 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 is substantially rectangular in shape in a plan view. The battery case 10 is unified in a manner that the sealing plate 14 is joined (preferably, joined by welding) to a periphery of the opening 12h of the exterior body 12. The battery case 10 is hermetically sealed (closed).
As illustrated in
The nonaqueous electrolyte solution may be similar to the conventional nonaqueous electrolyte solution, without particular limitations. The nonaqueous electrolyte solution contains a nonaqueous solvent and a supporting salt (electrolyte salt). The nonaqueous electrolyte solution may additionally contain an additive as necessary. Examples of the nonaqueous solvent include carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The nonaqueous solvent preferably contains carbonates, particularly cyclic carbonates and chained carbonates. Examples of the supporting salt include fluorine-containing lithium salts such as lithium hexafluorophosphate (LiPF6).
The positive electrode terminal 30 is disposed at an end part of the sealing plate 14 on one side in the long side direction Y (left end part in
As illustrated in
A positive electrode external conductive member 32 and a negative electrode external conductive member 42, each having a plate shape, are attached to an external surface of the sealing plate 14. As illustrated in
Each of the pair of curved regions 20r includes a border part 20b (see
The wound electrode body 20 is disposed inside the battery case 10 with the winding axis WL (see
The positive electrode 22 may be similar to the conventional positive electrode, without particular limitations. As illustrated in
At one end part of the positive electrode core body 22c in the long side direction Y (left end part in
The positive electrode active material layer 22a is formed to have a band shape along a longitudinal direction of the positive electrode core body 22c as illustrated in
The positive electrode protection layer 22p is provided between the positive electrode core body 22c and the positive electrode active material layer 22a in the long side direction Y as illustrated in
The negative electrode 24 may be similar to the conventional negative electrode, without particular limitations. As illustrated in
At one end part of the negative electrode core body 24c in the long side direction Y (right end part in
The negative electrode active material layer 24a is formed to have a band shape along a longitudinal direction of the negative electrode core body 24c as illustrated in
The negative electrode active material layer 24a includes a negative electrode active material that is capable of reversibly storing and releasing the charge carriers. Examples of the negative electrode active material include a carbon material such as graphite. The negative electrode active material layer 24a may contain an optional component other than the negative electrode active material, for example, various additive components such as a binder, a thickener, or a dispersant. Examples of the binder include rubbers such as styrene butadiene rubber (SBR). Examples of the dispersant include celluloses such as carboxymethyl cellulose (CMC).
As illustrated in
As illustrated in
As illustrated in
The spacer 200 is a plate-shaped member. As described above, the spacers 200 are each disposed between the plurality of rectangular secondary batteries 100 in the arrangement direction X here. That is to say, in the arrangement direction X, the rectangular secondary batteries 100 and the spacers 200 are arranged alternately. The spacer 200 is an example of a pressing member. The pressing member is preferably the spacer that is disposed between the plurality of rectangular secondary batteries 100.
The size of the spacer 200 may be determined as appropriate depending on the size, the battery capacity (degree of expansion and shrinkage), or the like of the rectangular secondary battery 100 or the wound electrode body 20, for example. As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
The third part 230 includes a first convex part 231, a second convex part 232, and a third convex part 233 that protrude from the base part 208 to a side of the wound electrode body 20 (in the arrangement direction X) and that are integrally formed from the base part 208. The first convex part 231, the second convex part 232, and the third convex part 233 are disposed at positions that are separated from each other in the up-down direction Z. The first convex part 231, the second convex part 232, and the third convex part 233 are configured so that, when the spacer 200 is assembled to the battery pack 500, the first convex part 231, the second convex part 232, and the third convex part 233 are in contact with the long side wall 12b of the battery case 10 and press the contact parts.
In the up-down direction Z, a space S is secured between the first part 210 and the first convex part 231, between the first convex part 231 and the second convex part 232, between the second convex part 232 and the third convex part 233, and between the third convex part 233 and the second part 220. The space S is configured so that, when the spacer 200 is assembled to the battery pack 500, the spacer 200 is not in contact with the long side wall 12b of the battery case 10 and the long side wall 12b is not pressed.
As illustrated in
As illustrated in
In the long side wall 12b of the battery case 10 in the battery pack 500, when the entire area of parts facing the pair of curved regions 20r (the upper curved region 20r and the lower curved region 20r) is 100%, 80% or more of the area including parts facing the border parts 20b is pressed in a band shape along the winding axis WL by the spacer 200. In this case, a part facing the curved region 20r including the border part 20b on the upper side is pressed by the first part 210, and a part facing the curved region 20r including the border part 20b on the lower side is pressed by the second part 220. Thus, the gas generated in the flat region 20f does not easily move to the curved regions 20r, and the gas easily moves in the winding axis direction along the pressed part with a band shape and is discharged out of the electrode body easily. Therefore, the remaining of the gas in the curved regions 20r is suppressed. As a result, in the curved regions 20r, the occurrence of metal precipitation (for example, Li precipitation) can be suppressed effectively.
Note that in the present specification, as illustrated in
In the parts facing the pair of curved regions 20r, the area of parts pressed by the spacer 200 (that is, the area of the pressed parts/the area of the parts facing the pair of curved regions 20r, that is also referred to as “an area ratio Ay” below) may be 80% or more without particular limitations, and is preferably 90% or more, more preferably 95% or more, and particularly preferably 100% or more. In the present embodiment, the entire parts facing the pair of curved regions 20r are pressed by the first part 210 and the second part 220 of the spacer 200, respectively. Moreover, each of positions facing vertex parts of the pair of curved regions 20r, that is, an upper end (an end on the sealing plate 14 side) 20u and a lower end (an end on the bottom wall 12a side) 20d of the wound electrode body 20 is pressed by the spacer 200. Therefore, as shown by surface pressure measurement results to be described below, surface pressure can be effectively applied to the border part 20b in particular, and the effect of the art disclosed herein can be obtained at the high level. For example, the area ratio Ay may be 200% or less, or 150% or less.
In a preferred aspect, the area ratio Ay is more than 100%, and a part ranging from the part facing the curved region 20r to a part that does not face the curved region 20r and the flat region 20f (a part on a side opposite to the flat region 20f in the height direction Z) is pressed by the first part 210 and/or the second part 220 of the spacer 200 in a band shape along the winding axis WL. Therefore, as shown by the surface pressure measurement results to be described below, the surface pressure can be effectively applied to the border part 20b in particular, and the effect of the art disclosed herein can be obtained at the high level.
In the long side wall 12b of the battery case 10 in the battery pack 500, when the entire area of the part facing the flat region 20f is 100%, 20% to 50% of the area is pressed by the spacer 200. Moreover, between the spacer 200 and the part facing the flat region 20f, the space S extending from the center part to the end part of the wound electrode body 20 in the winding axis direction is formed. When the area of the part that is pressed is set to 50% or less and the space S (part that is not pressed) is secured between the spacer 200 and the part facing the flat region 20f, the gas moves easily to the winding axis direction in the flat region 20f and the gas is easily guided to opening ends (left and right end parts in
In addition, when the area of the part that is pressed is set to 50% or less, a degree of freedom of expansion and shrinkage of the wound electrode body 20 can be secured in the charging and discharging. Thus, when the wound electrode body 20 is expanded, unevenness of salt concentration is suppressed and resistance increase after a high-rate durability test can be suppressed. Therefore, an excellent high rate characteristic can be achieved for a long time.
Note that in the present specification, as illustrated in
In the part facing the flat region 20f, the area of a part pressed by the spacer 200 (that is, the area of the pressed part/the area of the part facing the flat region 20f, that is also referred to as “an area ratio Ax” below) may be in the range of 20% to 50% without particular limitations, and for example, the area may be 30% or more from the viewpoint of suppressing the metal precipitation at a high level. The rest of the part facing the flat region 20f is not pressed by the spacer 200 and the space S is secured between the rest and the spacer 200.
A difference (Ay-Ax) between the area ratio Ax (that is, the region pressed by the spacer 200 in the part facing the flat region 20f) and the area ratio Ay (that is, regions pressed by the spacer 200 in the parts facing the pair of curved regions 20r) is 30% or more and preferably 50% or more, and may be for example 60% or more, 70% or more, and furthermore 80% or more. Thus, the gas that is generated in the electrode body can move easily in the winding axis direction with priority, and the remaining of the gas in the curved region 20r can be suppressed at a high level. For example, the difference (Ay-Ax) may be 170% or less, 150% or less, or 100% or less.
The battery pack 500 is usable in various applications, and for example, can be suitably used as a motive power source for a motor (power source for driving) that is mounted in a vehicle such as a passenger car or a truck. The vehicle is not limited to a particular type, and may be, for example, a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), or a battery electric vehicle (BEV).
Several Examples relating to the present disclosure will be explained below, but the disclosure is not meant to be limited to these Examples.
First, a plurality of positive electrode sheets with a band shape including the positive electrode active material layer were manufactured. The positive electrode active material layer includes lithium-nickel-cobalt-manganese complex oxide (NCM) as the positive electrode active material, AB as the conductive material, and PVdF as the binder in a mass ratio of NCM:AB:PVdF=97.5:1.5:1.0. In addition, a plurality of negative electrode sheets with a band shape including the negative electrode active material layer were manufactured. The negative electrode active material layer includes graphite (C) as the negative electrode active material, CMC as the dispersant, and SBR as the binder in a mass ratio of C:CMC:SBR=98.3:0.7:1.0.
Next, the positive electrode sheet and the negative electrode sheet manufactured as above were disposed to face each other via a separator sheet and wound in a flat shape, and thus, three wound electrode bodies were manufactured. Note that the separator sheet including a heat-resistant layer containing alumina and PVdF on a surface of a base part made of PE was used. The height H (see
Next, as the nonaqueous electrolyte solution, a nonaqueous electrolyte solution in which LiPF6 was dissolved at a concentration of 1.0 mol/L in a mixed solvent including EC, EMC, and DMC in a volume ratio of EC:EMC:DMC=1:1:1 was prepared. Then, a plurality of secondary batteries with a cuboid shape were structured by accommodating each of the three wound electrode bodies manufactured as above and the nonaqueous electrolyte solution in a battery case. Note that in the external shape of the battery case, the length in the long side direction is 308.00±0.10 mm and the height is 103.00±0.08 mm. In the long side direction, each of left and right ends of the wound electrode body is 7.0 mm apart from the short side wall, an upper end of the wound electrode body is 11.0 mm apart from the sealing plate (upper wall), and a lower end of the wound electrode body is 7.0 mm apart from the bottom wall.
Then, spacers including convex parts with the shape illustrated in
In addition, in Examples 1 to 3, the spacer is provided with a pair of convex parts facing the pair of curved regions of the wound electrode body. The convex part has a band shape with a width a extending along the winding axis. The widths a in Example 1 to 3 are different from each other. The width a is the same as the width of one curved region of the wound electrode body (100%) in Example 1, the width a is 1.5 times the width of one curved region of the wound electrode body (150%) in Example 2, and the width a is 0.8 times the width of one curved region of the wound electrode body (80%) in Example 3. Thus, in Example 1, the whole (100%) of the pair of curved regions including the border parts with the flat region is pressed by the spacer. In Example 2, the part ranging from the part facing the curved region to the part that does not face the wound electrode body (the curved region and the flat region) is pressed by the spacer. In Example 3, 80% of the pair of curved regions including the border parts with the flat region is pressed by the spacer.
As illustrated in
In Comparative Example 6, although illustration is omitted, the spacer has a flat plate shape facing the part ranging from the flat region to the pair of curved regions of the wound electrode body. Thus, in Comparative Example 6, the entire area of the part facing the flat region and the parts facing the pair of curved regions is pressed.
Table 1 shows the summary of the spacers in the respective examples. In Table 1, “flat region facing part Ax (%)” represents the ratio when the entire area of the part facing the flat region (area of Hf×Ln in
Under an environment with a temperature of 25° C., the state of charge (SOC) of the secondary battery was adjusted to 20%, constant-current charging was performed for 10 minutes at a charging rate of 2 C, which was followed by the 10-minute rest, and then constant-current discharging was performed for 60 minutes at a discharging rate of 1/3 C, which was followed by the 10-minute rest, and this charging and discharging is regarded as one cycle. This cycle was repeated 50 times.
The secondary battery after the high-rate durability test was disassembled and for each of the flat region and the curved regions of the wound electrode body, whether Li precipitation occurred or not was determined with eyes. The results are shown in Table 1.
As shown in Table 1, Li precipitation was observed in the curved regions of the wound electrode body in Comparative Examples 1 to 4. It is considered that this is because the pressing on the part facing the curved region is insufficient and the gas generated in the flat region easily moves to the curved region; therefore, the moved gas is not discharged out of the electrode body and remains in the curved region. In Comparative Example 4, the Li precipitation was observed also in the flat region of the wound electrode body. It is considered that this is because the convex parts of the spacer have the regular longitudinal streak shape, so that the movement of gas in the winding axis direction (from the center part to the end part of the wound electrode body) is interrupted and the gas remains in the flat region. In Comparative Examples 5 and 6, the Li precipitation was observed in the flat region of the wound electrode body. In Comparative Example 5, it is considered that this is because the pressing on the part facing the flat region is insufficient and the inter-electrode distance increases; therefore, the charging and discharging reaction in the flat region becomes inhomogeneous. In Comparative Example 6, it is considered that since the spacer has a flat plate shape, the movement of the gas in the winding axis direction is interrupted in the flat region and the gas remains in the flat region.
On the other hand, in Examples 1 to 6, the Li precipitation was observed in neither the curved regions nor the flat region of the wound electrode body. A first possible reason is that when the gas generated in the flat region moves toward the pair of curved regions (upper end side and/or lower end side), 80% or more of the parts facing the curved regions including the border parts with the flat region is pressed in the band shape; thus, the gas cannot move to the curved regions and moves in the winding axis direction along the pressed part in the band shape and is discharged out of the electrode body. A second possible reason is that when the area of the part to be pressed in the part facing the flat region is set to 50% or less and the space (part that is not pressed) extending from the center part to the end part of the wound electrode body in the winding axis direction exists between the spacer and the part facing the flat region, the gas moves easily in the winding axis direction in the flat region. A third possible reason is that when 20% or more of the part facing the flat region is pressed, the charging and discharging reaction is homogenized in the flat region. These results indicate the significance of the art disclosed herein.
The secondary battery before and after the high-rate durability test was adjusted to have an SOC of 50%, constant-current discharging was performed for 10 seconds at 300 A, and then, the discharge resistance was measured. Next, the battery voltage ΔV dropped in 10 seconds was read and based on the battery voltage ΔV and the discharge current value, the IV resistance (10-second resistance) was calculated. By comparison of IV resistance before and after the durability test, the resistance increase rate was calculated. The results are shown in Table 1.
As shown in Table 1, in Comparative Example 6, the resistance increase due to the deterioration after the high-rate durability test was relatively large. It is considered that this is because the entire area of the part facing the flat region is pressed and thus, there is no degree of freedom with respect to the expansion and shrinkage of the electrode body in the charging and discharging and the unevenness of salt concentration occurs when the electrode body expands. On the other hand, in Examples 1 to 6, etc., the area of the part to be pressed in the part facing the flat region was set to 50% or less, so that a degree of freedom of expansion and shrinkage of the electrode body was secured and the resistance increase after the high-rate durability test was suppressed.
Here, the surface pressure of the border part when the size of the spacer was varied was checked using a surface pressure sensor. Specifically, using a surface pressure distribution measurement system manufactured by NITTA Corporation, surface pressure was measured under a condition with a restriction load of 7 kN regarding the following cases: (A) when the parts facing the pair of curved regions were not pressed by the spacer at all (Ay=0%), as described in Comparative Example 2; (B) when a half of the parts facing the pair of curved regions was pressed by the spacer (Ay=50%), as described in Comparative Example 1; (C) when the entire parts facing the pair of curved regions were pressed by the spacer (Ay=100%), as described in Example 1; and (D) when the part ranging from the parts facing the curved regions to the part that does not face the curved region and the flat region was pressed in the band shape by the spacer (Ay=150%), as described in Example 2. The results are shown in
As indicated by an arrow in
Although the preferable embodiments of the present disclosure have been described above, they are merely examples. The present disclosure can be implemented in various other modes. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. The techniques described in the scope of claims include those in which the embodiments exemplified above are variously modified and changed. For example, a part of the aforementioned embodiment can be replaced by another modified example, and the other modified example can be added to the aforementioned embodiment. Additionally, the technical feature may be deleted as appropriate unless such a feature is described as an essential element.
For example, in the aforementioned embodiment, the first part 210 and the second part 220 of the spacer 200 are substantially rectangular in shape and extend in the band shape along the long side direction Y (the winding axis direction of the wound electrode body 20) with the uniform width. However, the present disclosure is not limited to this example. In another example, the peripheral part (corner part in particular) of the long side wall 12b of the battery case 10 is more rigid than the center part and to this peripheral part, the restriction load is not applied easily. Therefore, the pressing effect is considered to be small. Thus, the first part 210 and the second part 220 of the spacer 200 may have a notch at a part facing an outer periphery, for example. In one example, the first part 210 and/or the second part 220 may have a part that extends more than or equal to the length Ln of the negative electrode active material layer 24a along the border part with the flat region and have a shape in which the part facing the outer periphery (corner part in particular) of the long side wall 12b is cut off. This shape can improve the degassing property of the curved region 20r.
As described above, the following items are given as specific aspects of the art disclosed herein.
Item 1: The battery pack including: the wound electrode body with the flat shape that includes the positive electrode and the negative electrode; the battery case that accommodates the wound electrode body; and the pressing member that presses the battery case, in which the battery case includes the bottom wall, the upper wall, the pair of first side walls disposed so as to face each other and connecting the bottom wall and the upper wall, and the pair of second side walls disposed so as to face each other and connecting the bottom wall and the upper wall, the wound electrode body includes the flat region provided with the pair of flat outer surfaces, and the pair of curved regions provided on both ends of the flat region and each provided with the curved outer surface, the wound electrode body is disposed inside the battery case in a manner that the winding axis is disposed along the bottom wall and each of the pair of flat outer surfaces faces the first side wall, and in at least one of the pair of first side walls of the battery case here, when the entire area of the parts facing the pair of curved regions is 100%, 80% or more of the area including the border parts with the flat region is pressed in the band shape along the winding axis by the pressing member, when the entire area of the part facing the flat region is 100%, 20% or more and 50% or less of the area is pressed by the pressing member, and the space extending from the center part to the end part of the wound electrode body in the winding axis direction is formed between the part facing the flat region and the pressing member.
Item 2: The battery pack according to Item 1, in which in at least one of the pair of first side walls of the battery case, each of the positions facing the vertex parts of the pair of curved regions is pressed by the pressing member.
Item 3: The battery pack according to Item 1 or 2, in which the pressing member includes the protrusion part with the dot shape or the stripe shape at the part facing the flat region, and in at least one of the pair of first side walls of the battery case, the part facing the flat region is pressed by the protrusion part.
Item 4: The battery pack according to any of Items 1 to 3, in which in at least one of the pair of first side walls of the battery case, each of the entire parts facing the pair of curved regions is pressed by the pressing member.
Item 5: The battery pack according to any one of claims 1 to 4, in which in at least one of the pair of first side walls of the battery case, when the area ratio of the region pressed by the pressing member in the part facing the flat region is Ax % and the area ratio of the regions pressed by the pressing member in the parts facing the pair of curved regions is Ay %, the difference between Ax and Ay (Ay-Ax) is 50% or more.
Item 6: The battery pack according to any one of Items 1 to 5, in which in at least one of the pair of first side walls of the battery case, the part ranging from the part facing the curved region to the part that does not face the curved region and the flat region is pressed in the band shape along the winding axis by the pressing member.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-188413 | Nov 2022 | JP | national |
