JP2020057597A - Battery pack - Google Patents

Abstract

To prevent an increase in internal resistance in both high-rate cycle and low-rate cycle in a battery cell including a separator with a protrusion.SOLUTION: A battery pack, which is one example of an embodiment, is formed by stacking a plurality of nonaqueous electrolyte secondary batteries via inter-battery separators 30. The inter-battery separators include a protrusion group protruding from a body plate portion 31 in a lamination direction. In the inter-battery separators, a second region S2, a fifth region S5, and eighth region S8 overlap with a center potion in a wound axis direction of an electrode body 13 when viewed from one side in the lamination direction. The protrusion group includes a plurality of end side protrusions overlapping with all regions S1-S3 and S7-S9 of a first group G1 and a third group G3 and a plurality of center side protrusions overlapping with a fourth region S4 and a sixth region S6. Formation density of the protrusion group is lower in the fifth region S5 than the fourth region S4 and the sixth region S6.SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to a battery pack.

  In recent years, against the background of a growing environmental protection movement, development of electric vehicles (EV) and hybrid electric vehicles (HEV, PHEV) equipped with non-aqueous electrolyte secondary batteries has been actively performed. When a non-aqueous electrolyte secondary battery represented by a lithium ion battery is mounted on an EV, HEV, PHEV, or the like, a plurality of batteries are electrically connected in series or parallel to form an assembled battery and used. Is done.

  It is generally known that, when a battery pack is used, when the battery is exposed to a high temperature state due to self-heating when the battery is charged and discharged, the deterioration of the battery is promoted. For this reason, the battery may be cooled by flowing gas such as air into the groove using an inter-cell separator having ribs (projections) and gaps (grooves) between the ribs between adjacent cells. (See Patent Document 1).

Japanese Patent No. 5813656

  In a non-aqueous electrolyte secondary battery, the negative electrode active material expands due to the absorption of lithium ions by the negative electrode active material during charging, and the negative electrode plate containing the negative electrode active material expands. On the other hand, when the inter-battery separator described in Patent Literature 1 is used, the battery is pressed substantially uniformly by the protrusion of the inter-battery separator. Thereby, expansion of the electrode body is suppressed. Therefore, when the negative electrode plate expands during charging, the non-aqueous electrolyte present in the electrode body is pushed out of the electrode body. In addition, even if the negative electrode plate shrinks during discharging, the non-aqueous electrolyte existing outside the electrode body does not easily return to the electrode body, and particularly the charge / discharge current called a high rate cycle is large, and the depth of charge (SOC) fluctuates greatly. In the cycle mode in which the expansion and contraction is large, the internal resistance tends to increase.

  Further, it was also found that depending on the position of the protrusion formed on the inter-battery separator, the internal resistance may increase in a cycle mode called a low rate cycle in which the charge / discharge current is small.

  An assembled battery according to an embodiment of the present disclosure is an assembled battery in which a plurality of nonaqueous electrolyte secondary batteries are stacked with an inter-cell separator interposed therebetween, and each of the plurality of nonaqueous electrolyte secondary batteries is A positive electrode plate having a positive electrode mixture layer containing a positive electrode active material, and a wound electrode body having a negative electrode plate, a non-aqueous electrolyte, and a case accommodating the electrode body and the non-aqueous electrolyte. A flat portion having a flat outer peripheral surface and two curved surface portions having curved outer peripheral surfaces disposed at both ends in the first direction of the flat portion, and the inter-battery separator is laminated from the main body plate portion and the main body plate portion A protrusion group that projects in the direction, and when the inter-battery separator is viewed from one side in the stacking direction, a region overlapping with the positive electrode mixture layer disposed in the flat portion of the electrode body in the main body plate portion, The first side direction along the first side orthogonal to the direction and the second side parallel to the first direction The battery is divided into nine regions obtained by equally dividing into three in each of the second side directions, and the nine regions are divided into first regions from one end in the first direction to the other end of the inter-battery separator. A first group consisting of a region, a second region, and a third region; a second group consisting of a fourth region, a fifth region, and a sixth region; and a seventh group, an eighth region, and a ninth region. When divided from the third group, when viewed from one side in the stacking direction, the second region, the fifth region, and the eighth region overlap the central portion in the winding axis direction of the electrode body, and the projection group Has a plurality of end-side protrusions overlapping all the regions of the first and third groups, and a plurality of center-side protrusions overlapping the fourth region and the sixth region. In the region, the battery pack is lower than each of the fourth region and the sixth region.

  The “density of formation of the protrusion group” is defined as the area of the region when viewed from one side in the stacking direction with respect to the area of the region when viewed from one side in the stacking direction. It is the ratio of the total area.

  According to an embodiment of the present disclosure, in an assembled battery including a separator with projections, an increase in internal resistance can be suppressed in both a high-rate cycle and a low-rate cycle.

It is a perspective view of an assembled battery which is an example of an embodiment, and is a figure which omits and shows an end plate, a bind bar, and a bus bar. FIG. 2 is a sectional view of a non-aqueous electrolyte secondary battery constituting the battery pack of FIG. 1. FIG. 3 is a plan view of the nonaqueous electrolyte secondary battery in FIG. 2. FIG. 3A is a front view of an inter-battery separator incorporated in the assembled battery of the embodiment, and FIG. 2B is a cross-sectional view of a plane orthogonal to the direction of the winding axis of an electrode body stacked on the inter-battery separator via a case. FIG. 4 is a front view of an inter-cell separator incorporated in the battery pack of Reference Example 1. FIG. 5A is a front view of an inter-battery separator incorporated in the assembled battery of Example 2 and FIG. 7B is a cross-sectional view of a plane orthogonal to the winding axis direction of an electrode body stacked on the inter-battery separator via a case. . FIG. 6 is a schematic diagram showing a state in which an electrode body is divided into five along a winding axis direction in Reference Example 1. FIG. 9 is a diagram showing a cross-sectional image of one nonaqueous electrolyte secondary battery in the battery pack of Reference Example 2 on a plane orthogonal to the direction of the winding axis of the electrode body.

  As described above, when the battery is pressed substantially evenly by the protrusion of the inter-battery separator, the internal resistance tends to increase in a high-rate cycle. On the other hand, in the inter-battery separator, when the protrusion near the one curved surface portion of the flat portion of the electrode body and overlapping with the central portion in the winding axis direction is eliminated, the internal resistance increases at a low rate cycle. Was.

  The present inventor has conducted intensive studies to solve the above-described problems, and as a result, the central portion in the winding axis direction in the vicinity of one curved surface portion in the flat portion of the electrode body is pressed, and the flat portion of the electrode body is In the vicinity of the other curved surface portion, the central portion in the winding axis direction is pressed, and the central portion of the flat portion of the electrode body is hardly pressed, so that the internal resistance of both the high rate cycle and the low rate cycle is reduced. It has been found that the rise can be suppressed. More specifically, the wound electrode body has a flat portion with a flat outer peripheral surface and two curved surface portions having curved outer peripheral surfaces disposed at both ends in the first direction of the flat portion. When the inter-battery separator is viewed from one side in the stacking direction, a region overlapping with the positive electrode mixture layer disposed in the flat portion of the electrode body is defined as a first side orthogonal to the first direction in the main body plate portion of the inter-battery separator. Are divided into nine regions obtained by equally dividing into three in each of a first side direction along the second direction and a second side direction along a second side parallel to the first direction. The nine regions are divided into a first group including a first region, a second region, and a third region from one end of the inter-battery separator in the first direction to the other end, and a fourth region, a fifth region, and a sixth region. The second group of regions is divided into the third group of seventh, eighth, and ninth regions. In this case, when viewed from one side in the stacking direction, the second region, the fifth region, and the eighth region overlap the center of the electrode body in the winding axis direction. The projection group is configured to have a plurality of end-side projections overlapping all the regions of the first and third groups, and a plurality of center-side projections overlapping the fourth and sixth regions. The formation density of the projection group is set lower in the fifth region than in each of the fourth region and the sixth region. ADVANTAGE OF THE INVENTION According to the assembled battery which concerns on this indication, in the assembled battery provided with the protrusion-to-battery separator, the increase in internal resistance can be suppressed in both the high rate cycle and the low rate cycle of the battery. This will be described in detail later.

  Hereinafter, an example of an embodiment of the present disclosure will be described in detail. In the following description, specific shapes, materials, directions, numerical values, and the like are examples for facilitating understanding of the present disclosure, and can be appropriately changed according to uses, purposes, specifications, and the like. Hereinafter, a rectangular battery in which the wound electrode body 13 (FIG. 2) is housed in a battery case 100 which is a square metal case will be exemplified. The battery case is a laminate sheet including a metal layer and a resin layer. It may be a configured battery case.

  FIG. 1 is a perspective view of the battery pack 1 of the embodiment, in which an end plate, a bind bar, and a bus bar are omitted. As illustrated in FIG. 1, the assembled battery 1 is configured by stacking a plurality of nonaqueous electrolyte secondary batteries 10 as batteries, with an inter-battery separator 30 interposed therebetween. In the battery pack 1, end plates are arranged at both ends of the nonaqueous electrolyte secondary battery 10 in the stacking direction. Then, the end plates are fixed by the bind bar. Adjacent nonaqueous electrolyte secondary batteries 10 are electrically connected by a bus bar.

  FIG. 2 is a cross-sectional view of the non-aqueous electrolyte secondary battery 10, and FIG. 3 is a plan view of the non-aqueous electrolyte secondary battery 10. Hereinafter, the nonaqueous electrolyte secondary battery 10 is referred to as a battery 10. The battery 10 includes a rectangular exterior body 11 having an opening on the upper side, and a sealing plate 12 for closing the opening. The battery case 100 is constituted by the rectangular exterior body 11 and the sealing plate 12. The rectangular exterior body 11 and the sealing plate 12 are each made of metal, and are preferably made of aluminum or an aluminum alloy. The battery 10 includes a flat wound electrode body 13 in which a positive electrode plate 14 and a negative electrode plate 15 are wound via a separator (not shown), and a non-aqueous electrolyte. The electrode body 13 and the non-aqueous electrolyte are housed in the battery case 100.

The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and a mixed solvent of two or more thereof may be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of hydrogen of these solvents is substituted with a halogen atom such as fluorine. As the electrolyte salt, for example, a lithium salt such as LiPF ₆ is used.

  The positive electrode plate 14 has a metal positive electrode core, and a positive electrode mixture layer formed on both surfaces of the core, and a positive electrode core is formed at one end in the short direction along the longitudinal direction. The exposed positive electrode core exposed portion 14a is formed. Similarly, the negative electrode plate 15 has a metal negative electrode core and negative electrode mixture layers formed on both surfaces of the core, and one end in the short direction has a negative electrode along the long direction. A negative electrode core exposed portion 15a from which the core is exposed is formed. In the electrode body 13, a positive electrode core exposed portion 14a is arranged on one end side in the winding axis direction (right side in FIG. 2), and a negative electrode core exposed portion 15a is arranged on the other end side in the winding axis direction (left side in FIG. 2). In this state, the positive electrode plate 14 and the negative electrode plate 15 are wound flat. Thereby, as shown by a cross section in a plane perpendicular to the winding axis in FIG. 4B described later, the electrode body 13 has a flat portion 13b having a flat outer peripheral surface and both ends in the first direction of the flat portion 13b. The disposed outer peripheral surface has two curved surface portions 13a that are curved surfaces.

  As shown in FIG. 2, a positive electrode current collector (positive electrode tab) 16 is connected to the laminated portion of the positive electrode core exposed portion 14a, and a negative electrode current collector 18 is connected to the laminated portion of the negative electrode core exposed portion 15a. . A suitable positive electrode current collector 16 is made of aluminum or an aluminum alloy. Suitable negative electrode current collectors 18 are made of copper or a copper alloy. The positive electrode terminal 17 has a flange portion 17 a (FIG. 3) arranged outside the battery of the sealing plate 12 and an insertion portion inserted into a through hole provided in the sealing plate 12. Is electrically connected to Further, the negative electrode terminal 19 has a flange portion 19 a (FIG. 3) arranged on the outside of the battery of the sealing plate 12, and an insertion portion inserted into a through hole provided in the sealing plate 12. It is electrically connected to the body 18.

  The positive electrode terminal 17 and the positive electrode current collector 16 are fixed to the sealing plate 12 via the inner insulating member 20 and the outer insulating member 21, respectively. The inner insulating member 20 is arranged between the sealing plate 12 and the positive electrode current collector 16, and the outer insulating member 21 is arranged between the sealing plate 12 and the positive electrode terminal 17. Similarly, the negative electrode terminal 19 and the negative electrode current collector 18 are fixed to the sealing plate 12 via the inner insulating member 22 and the outer insulating member 23, respectively. The inner insulating member 22 is arranged between the sealing plate 12 and the negative electrode current collector 18, and the outer insulating member 23 is arranged between the sealing plate 12 and the negative terminal 19.

  The electrode body 13 is accommodated in the rectangular exterior body 11 in a state of being covered with the insulating sheet 24. The sealing plate 12 is welded to the opening edge of the rectangular exterior body 11 by laser welding or the like. The sealing plate 12 has an electrolyte injection hole 26. The electrolyte injection hole 26 is sealed with a sealing plug 27 after the non-aqueous electrolyte is injected into the battery case 100. The sealing plate 12 is provided with a gas discharge valve 25 for discharging gas when the pressure inside the battery becomes equal to or higher than a predetermined value.

  The batteries 10 are stacked in the thickness direction with the inter-battery separator 30 interposed therebetween to form the battery stack 2. The plurality of batteries 10 are arranged with their directions alternately changed so that the positive electrode terminals 17 and the negative electrode terminals 19 are alternately arranged in the stacking direction of the batteries 10. The plurality of batteries 10 are electrically connected in series by connecting the positive electrode terminal 17 and the negative electrode terminal 19 adjacent in the stacking direction with a bus bar (not shown).

  The inter-battery separator 30 is formed of an insulating material such as a resin, and is formed to include a substantially flat main body plate portion 31 and a frame portion 50 protruding from the periphery of the main body plate portion 31 in the thickness direction and connected thereto. You. The main body plate portion 31 is a portion disposed between the batteries 10, and has a rib group 32 (FIG. 4) including a plurality of ribs as protrusions formed on one surface in a thickness direction (stacking direction). The rib group 32 corresponds to a projection group. The plurality of ribs are used to cool the battery 10 by separating adjacent batteries 10 by a predetermined distance and flowing a gas such as air between the adjacent batteries 10 through the space between the ribs.

  A pair of end plates (not shown) are arranged at both ends in the stacking direction of the battery stack 2. The end plate is formed of a metal such as aluminum or a hard resin. From the outside of the pair of end plates in the stacking direction, a restraining force is applied in a direction to compress the battery 10 in the stacking direction. For example, a pair of end plates is fixed by a metal bind bar. In this state, the binding force can be applied to the battery stack 2 in the compression direction by shortening the distance between the pair of end plates from the length in the stacking direction of the battery stack 2 without applying the binding force. . In this state, the ribs on the surface of the inter-battery separator 30 and the surface of the adjacent battery 10 are in close contact with each other.

  As another example, on the inner surface of the battery pack case accommodating the battery pack, by making the length of the battery pack in the stacking direction smaller than the length of the battery pack before restraint, a restraining force is applied to the battery stack in the compression direction. You can also.

  In the battery stack 2, at positions corresponding to the upper side of the gas discharge valves 25 of the plurality of batteries 10, a discharge duct long in the stacking direction (shown in the drawing) for discharging the gas discharged from the gas discharge valves 25 to the outside. ) May be arranged.

  Next, the shape of the rib of the inter-cell separator 30 will be described with reference to FIG. FIG. 4 is a front view (a) of the inter-battery separator 30 of the embodiment, and a cross-sectional view (b) of a plane orthogonal to the direction of the winding axis of the electrode body 13 stacked on the inter-battery separator 30 via the battery case 100 ). In FIG. 4, the illustration of the frame portion of the inter-battery separator 30 is omitted.

  In FIG. 4, the rib group 32 is indicated by a sand portion. The rib group 32 is formed so as to protrude from one surface of the main body plate portion 31 in the stacking direction of the battery 10. In FIG. 4A, a region overlapping with the positive electrode mixture layer included in the flat portion 13b of the electrode body 13 of the battery 10 when the battery pack 1 is formed is indicated by a broken line frame α1.

  The rib group 32 includes end ribs 33, 34, 35 arranged at both ends in the vertical direction, and a plurality of central ribs 36, 37 arranged vertically at both ends in the width direction (left-right direction in FIG. 4). And Each of the ribs 33 to 37 extends in the width direction. The two end ribs 33 and 34 are longer than the other ribs 35 to 37 and have a length close to the entire length of the main body plate portion 31 in the width direction.

  The plurality of ribs 33 to 37 are arranged at predetermined intervals in the vertical direction. Thereby, the groove 40 is formed between the adjacent ribs 33 to 37. When the battery pack 1 is formed, the groove 40 forms a refrigerant flow path through which a gas such as air for cooling the battery 10 flows.

  The arrangement positions of the ribs 33 to 37 will be described in more detail. As shown in FIG. 4A, when the inter-battery separator 30 is viewed from one side in the stacking direction, a region of the main body plate portion 31 that overlaps with the positive electrode mixture layer arranged in the flat portion 13 b of the electrode body 13. (A region within the broken line frame α1 in FIG. 4A) is defined as a positive electrode mixture overlapping region. Then, the positive electrode mixture overlapping region is divided into three in the first side direction along the first side A1 orthogonal to the vertical direction and the direction of the second side A2 parallel to the vertical direction (second side direction). It is equally divided into nine areas S1, S2, S3,... S9 obtained by the division. The nine regions S1, S2, S3,..., S9 form a first group from one end (upper end in FIG. 4A) in the vertical direction of the inter-battery separator 30 to the other end (lower end in FIG. 4A). G1, a second group G2, and a third group G3. The first group G1 includes a first area S1, a second area S2, and a third area S3. The second group G2 includes a fourth area S4, a fifth area S5, and a sixth area S6. The third group G3 includes a seventh area S7, an eighth area S8, and a ninth area S9. When the battery pack 1 is viewed from one side in the stacking direction, the second region S2, the fifth region S5, and the eighth region S8 overlap the center of the electrode body 13 in the winding axis direction. In this case, the rib group 32 protruding from the main body plate portion 31 of the inter-battery separator 30 in the stacking direction has a plurality of end sides overlapping all the regions S1 to S3 and S7 to S9 of the first group G1 and the third group G3. It has ribs 33, 34, 35 and a plurality of central ribs 36, 37 overlapping the fourth region S4 and the sixth region S6. The formation density of the rib group 32 is lower in the fifth region S5 than in each of the fourth region S4 and the sixth region S6. That is, the ratio of the total area of the rib-formed portion in the fifth region S5 when viewed from one side in the stacking direction to the area of the fifth region S5 when viewed from one side in the stacking direction is equal to the ratio in the stacking direction. The ratio of the total area of the ribs formed in the fourth region S4 to the area of the fourth region S4 when viewed from one side in the stacking direction is lower than the area of the fourth region S4 when viewed from one side. Is lower than the total ratio of the area of the portion where the rib is formed in the sixth region S6. Thereby, as described later, an increase in the internal resistance of the battery 10 can be suppressed in both the high rate cycle and the low rate cycle in charging and discharging.

  The electrode body 13 has a connecting portion E at a boundary between the curved surface portion 13a and the flat portion 13b. When the battery pack 1 is viewed from one side in the stacking direction, at least some of the end ribs 33, 34, 35 of the plurality of end ribs 33, 34, 35 are in a portion overlapping the vicinity of the connection portion E in the flat portion 13b. Be placed. The end ribs 33 and 34 extend in parallel to the first side direction, and are continuous with the end ribs 33 over the first, second, and third regions S1, S2, and S3, and the seventh, eighth, and eighth ribs. End ribs 34 are provided continuously over the ninth regions S7, S8, and S9.

  It is preferable that the total length of the end ribs 33 and 34 is 50% or more of the length of the positive electrode mixture layer indicated by the broken line frame α in the first side direction.

  When the battery pack 1 is viewed from one side in the stacking direction, the total area of the rib group 32 provided in a portion overlapping the flat part 13b is the positive electrode disposed in the flat part 13b when viewed from one side in the stacking direction. Preferably, it is 40 to 60% of the area of the mixture layer.

  Hereinafter, the positive electrode plate 14, the negative electrode plate 15, and the separator constituting the electrode body 13 will be described in detail.

[Positive electrode plate]
As described above, the positive electrode plate 14 has the positive electrode core and the positive electrode mixture layers formed on both surfaces of the positive electrode core. For the positive electrode core, a metal foil or the like that is stable in the potential range of the positive electrode, such as aluminum or an aluminum alloy, can be used. The positive electrode mixture layer includes a positive electrode active material, a conductive material, a binder, and the like. The positive electrode plate 14 is formed by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and a dispersion medium on a positive electrode core, drying the coating film to remove the dispersion medium, and then compressing. Thus, it can be manufactured by forming the positive electrode mixture layer on both surfaces of the positive electrode core.

  The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, and Sn. , Ta, W and the like. One example of a suitable lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. In addition, inorganic compound particles such as aluminum oxide and lanthanoid-containing compounds may be fixed to the surface of the particles of the lithium-containing metal composite oxide.

  Examples of the conductive material contained in the positive electrode mixture layer include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer include fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[Negative electrode plate]
The negative electrode plate 15 has a negative electrode core and negative electrode mixture layers formed on both surfaces of the negative electrode core. The negative electrode mixture layer includes a negative electrode active material and a binder.

  A metal foil, such as copper or a copper alloy, which is stable in the potential range of the negative electrode can be used for the negative electrode core. The negative electrode plate 15 is formed by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, a dispersion medium, and the like on a negative electrode core, drying the coating film and removing the dispersion medium, and then compressing the negative electrode mixture. It can be manufactured by forming layers on both sides of the negative electrode core.

  The negative electrode mixture layer contains, for example, a carbon-based active material that reversibly stores and releases lithium ions as a negative electrode active material. Suitable carbon-based active materials are natural graphite such as flaky graphite, massive graphite and earthy graphite, artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Further, as the negative electrode active material, a Si-based active material composed of at least one of Si and a Si-containing compound may be used, or a carbon-based active material and a Si-based active material may be used in combination. Examples of the binder contained in the negative electrode mixture layer include styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC).

[Separator]
As the separator, a porous sheet having ion permeability and insulating properties is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. As the material of the separator, olefin resins such as polyethylene and polypropylene, cellulose, and the like are preferable. The separator may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator.

[Examples and Reference Examples]
Hereinafter, the assembled batteries of Reference Examples 1 and 2 and Examples 1 and 2 manufactured to confirm the effects obtained by the embodiment will be described.

<Reference Example 1>
[Preparation of positive electrode plate]
A lithium-containing metal composite oxide represented by LiNi _0.35 Co _0.35 Mn _0.30 O ₂ , acetylene black, and polyvinylidene fluoride (PVdF) in a solid content mass ratio of 91: 7: 2. After mixing and adding an appropriate amount of N-methyl-2-pyrrolidone (NMP), the mixture was kneaded to prepare a positive electrode mixture slurry. The positive electrode mixture slurry is applied to both surfaces of a positive electrode core made of an aluminum alloy foil having a thickness of 15 μm, and after the coating film is dried, the coating film is rolled using a compression roller and cut into a predetermined electrode size. Thus, a positive electrode plate having positive electrode mixture layers formed on both surfaces of the positive electrode core was produced. The width of the positive electrode plate was 120 mm. In the positive electrode plate, the coating width of the coating film was 104 mm, and a core exposed portion was formed on one end side in the width direction.

[Preparation of negative electrode plate]
A graphite powder, a sodium salt of carboxymethyl cellulose (CMC), and a dispersion of styrene butadiene rubber (SBR) are mixed at a solid content mass ratio of 99: 0.8: 0.2, and water is dispersed in a dispersion medium. To prepare a negative electrode mixture slurry. The negative electrode mixture slurry is applied to both surfaces of a negative electrode core body made of copper foil having a thickness of 8 μm, and after the coating film is dried, the coating film is rolled using a compression roller and cut into a predetermined electrode size. Then, a negative electrode plate having negative electrode mixture layers formed on both surfaces of the negative electrode core was produced. The width of the negative electrode plate was 122 mm. On the negative electrode plate, the coating width of the coating film was 109 mm, and a core exposed portion was formed on one end side in the width direction.

[Preparation of non-aqueous electrolyte (electrolyte solution)]
LiPF ₆ was added to a mixed solvent obtained by mixing ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) at a volume ratio of 3: 3: 4 (25 ° C., 1 atm). A non-aqueous electrolyte was prepared by adding so as to have a concentration of 15 mol / L, and further adding vinylene carbonate so as to have a concentration of 0.3% by mass.

[Production of Battery]
The positive electrode plate and the negative electrode plate are wound through a separator having a three-layer structure of polypropylene (PP), polyethylene (PE), and polypropylene (PP) and having a thickness of 20 μm, and then crushed in a radial direction to be wound. A flat electrode body of a mold was produced. At this time, the exposed portion of the core of the positive electrode plate and the exposed portion of the core of the negative electrode plate are shifted so as not to overlap with the active material layers of the electrodes facing each other, and are moved to one end side in the winding axis direction of the electrode body. The exposed core portion of the positive electrode plate was disposed, and the exposed core portion of the negative electrode plate was disposed on the other end side in the winding axis direction. A positive electrode terminal was attached to the sealing plate, and a positive electrode current collector was connected to the positive electrode terminal. Further, a negative electrode terminal was attached to the sealing plate, and a negative electrode current collector was connected to the negative electrode terminal. Then, the positive electrode current collector was welded to the exposed core of the positive electrode plate, and the negative electrode current collector was welded to the exposed core of the negative electrode plate. The electrode body was housed in a rectangular outer can, and the opening of the outer can was closed with a sealing plate. The gap between the sealing plate and the outer can was welded by, for example, laser welding. After injecting 45 g of the non-aqueous electrolyte from the electrolyte injection hole of the sealing plate, a sealing plug was attached to the injection hole to produce a prismatic battery. The external shape of the battery was 13 mm in thickness, 140 mm in width, and 65 mm in the vertical direction. The full charge capacity of the battery was 4 Ah.

[Preparation of assembled battery]
Then, by stacking a plurality of the above-described batteries via an inter-cell separator, a battery stack is formed, and end plates are arranged at both ends in the stacking direction of the battery stack, and the batteries are stacked in the stacking direction by appropriate restraining means. Pressurized. The inter-battery separator 30a shown in FIG. 5 was used for the battery stack. The inter-battery separator 30a includes a main body plate portion 31 and a plurality of ribs 60 formed to protrude from one surface of the main body plate portion 31 in the battery stacking direction. The plurality of ribs 60 extend in a direction parallel to the direction of the winding axis of the electrode body, and are arranged at predetermined intervals in a vertical direction (vertical direction in FIG. 5). The lengths of the plurality of ribs 60 are substantially the same as each other.

  In such an inter-battery separator 30a of Reference Example 1, when viewed from one side in the laminating direction, the positive electrode mixture layer disposed in the flat portion 13b (see FIG. 4) of the electrode body 13 in the main body plate portion 31 The overlapping region (the region within the broken line frame α2 in FIG. 5) is defined as the positive electrode mixture overlapping region. In the positive electrode mixture overlapping region, the ribs 60 are arranged in all of the nine regions S1 to S9 divided by equal division. Therefore, the inter-battery separator 30 has a shape having protrusions in all the regions S1 to S9.

  Further, in Reference Example 1, of the plurality of ribs 60, referring to FIG. 4, the entire length of the rib 60 located in a portion overlapping the vicinity of the connecting portion E in the flat portion 13b of the electrode body 13 (length in the horizontal direction in FIG. 5) Is 100% of the length of the positive electrode mixture layer in the first side direction (the left-right direction in FIG. 5). In the flat portion 13b of the electrode body 13, one flat portion 13b of the electrode body 13 is separated from one connecting portion E by 10 mm from the one connecting portion E toward the other connecting portion E. It refers to the area between the location.

  Further, in Reference Example 1, the total area of the plurality of ribs 60 provided in a portion overlapping the flat portion 13b when the battery pack is viewed from one side in the stacking direction is the flat portion 13b when viewed from one side in the stacking direction. This is 60% of the area of the positive electrode mixture layer disposed therein.

<Reference Example 2>
In reference example 2, although not shown, the inter-battery separator in which the ribs 60 provided in the fifth region S5 and the eighth region S8 were partially removed from the inter-battery separator 30a of reference example 1 was used.

<Example 1>
In Example 1, the inter-cell separator 30 shown in FIG. 4 was used. The rib group 32 of the inter-battery separator 30 has a plurality of end ribs 33 overlapping all the regions S1 to S3 and S7 to S9 of the first group G1 and the third group G3 on both curved surface portions 13a of the electrode body 13. 34, and a plurality of central ribs 36 and 37 overlapping the fourth region S4 and the sixth region S6 at both ends in the winding axis direction of the electrode body 13. Furthermore, the formation density of the rib group 32 is lower in the fifth region S5 than in each of the fourth region S4 and the sixth region S6. In the first embodiment, other configurations are the same as those of the first embodiment.

<Example 2>
Example 2 used the inter-battery separator 30b shown in FIG. FIG. 6 is a front view (a) of the inter-battery separator 30b incorporated in the assembled battery according to the second embodiment, and a plane orthogonal to the winding axis direction of the electrode body 13 stacked on the inter-battery separator 30b via the battery case. (B) of FIG. In the case of the second embodiment, in the inter-battery separator 30b, of the rib group 32a, the end side ribs 33a and 34a located at both ends in the vertical direction are separated from each other on both sides in the vertical direction in the winding axis direction. Be placed. Thereby, in the assembled battery including the inter-battery separator 30b, gas such as air can flow between the adjacent batteries through the gap (groove 40). In the case of the second embodiment as well, similarly to the configuration of the embodiment shown in FIG. 4, on both sides in the vertical direction of the inter-battery separator 30 b, the ends at the portions overlapping the vicinity of the connection portion E in the flat portion 13 b of the electrode body 13. It is preferable that the total of the total lengths of the side ribs 33a and 34a is 50% or more of the length in the first side direction of the positive electrode mixture layer indicated by the broken line frame α. Other configurations in the second embodiment are the same as those in the first embodiment.

[Test method]
Using the assembled batteries of Reference Examples 1 and 2 and Examples 1 and 2, a high-rate resistance evaluation test and a low-rate resistance evaluation test were performed. The high-rate resistance evaluation test was performed in a 25 ° C. environment. In the high-rate resistance evaluation test, charging and discharging of the battery were repeated in a high-rate cycle. Specifically, in the high-rate resistance evaluation test, the battery was charged at a high-rate constant current of 40 C until the battery voltage reached a predetermined voltage (CC charging), and then charged at a constant voltage until the current value attenuated to the predetermined current. (CV charging). The depth of charge (SOC) was set to 60% ± 10%. After charging, the battery was discharged at a constant current of 40 C until the battery voltage reached a predetermined voltage (CC discharge). Such a charge / discharge cycle was repeated from 1 cycle to 2000 cycles. There was no pause between charging and discharging. The internal resistance of each of the assembled batteries of Reference Examples 1 and 2 and Examples 1 and 2 subjected to the high-rate cycle in this way was measured, and the amount of increase from the initial internal resistance was detected. In Table 1 below, the column of “high-rate resistance rise” of each of Reference Examples 1 and 2 and Examples 1 and 2 indicates the ratio of the increase amount of the internal resistance value to the internal resistance value at the initial stage (high-rate resistance increase ratio). ).

  Further, the low-rate resistance evaluation test was performed in an environment of 70 ° C. In the low-rate resistance evaluation test, charging and discharging of the battery were repeated in a low-rate cycle. Specifically, in the low-rate resistance evaluation test, the battery was charged at a low-rate constant current of 20 C until the battery voltage reached a predetermined voltage (CC charging), and then charged at a constant voltage until the current value attenuated to the predetermined current. (CV charging). The charge depth (SOC) was set to 60% ± 1%. After charging, the battery was discharged at a constant current of 20 C until the battery voltage reached a predetermined voltage (CC discharge). Such a charge / discharge cycle was repeated from 1 cycle to 9000 cycles. There was no pause between charging and discharging. The internal resistance of each of the battery packs of Reference Examples 1 and 2 and Examples 1 and 2 subjected to the low rate cycle was measured, and the amount of increase from the internal resistance at the initial stage was detected. In Table 1, the ratio of the increase amount of the internal resistance value to the internal resistance value at the initial stage (low-rate resistance increase ratio) is shown in the column of “low rate resistance increase” of each of Reference Examples 1 and 2 and Examples 1 and 2. ing.

[Test results]
Here, the target value of the high rate resistance increase ratio is 3.5% or less, and the target value of the low rate resistance increase ratio is 18% or less. As shown in Table 1, in Reference Example 1, the high-rate resistance increase rate and the low-rate resistance increase rate were 6% and 18%, respectively, and the high-rate resistance increase rate was particularly high. On the other hand, in Reference Example 2, the rate of increase in high-rate resistance was 5%, which was lower than in Reference Example 1, but the rate of increase in low-rate resistance was as high as 22%. In Table 1, in the column of high-rate resistance rise or low-rate resistance rise, a value that largely deviates from the target value is indicated by “x”. Further, in Examples 1 and 2, the rate of increase in high-rate resistance was 3%, and the rate of increase in low-rate resistance was 17% and 13%, respectively. Compared with Reference Examples 1 and 2, the rate of increase in high-rate resistance was about the same as in Examples 1 and 2, and the rate of increase in low-rate resistance was lower in Example 2.

In order to analyze such test results, the present inventor disassembled the battery of Reference Example 1 immediately after the completion of the high-rate cycle test in Reference Example 1, and divided each of the five parts into the negative electrode plate. The amount of EC constituting the non-aqueous electrolyte (electrolyte solution) and the amount of LiPF ₆ as an electrolyte salt were measured. The amount per unit area of the negative electrode plate was measured. FIG. 7 is a schematic diagram showing a state in which the electrode body is divided into five along the winding axis direction in Reference Example 1. The horizontal direction in FIG. 7 matches the winding axis direction in FIG. The battery extends from one end in the winding axis direction (right end in FIG. 7) to the other end in the winding axis direction (left end in FIG. 7) in the positive electrode core exposed portion side end region (positive electrode core exposed portion side end portion). ), The inner region of the positive electrode core exposed portion (inside of the positive electrode core exposed portion), the central region, the inner region of the negative electrode core exposed portion (inside of the negative electrode core exposed portion), the end region of the negative electrode core exposed portion side (the negative electrode) (The end on the side of the core body exposed portion).

Table 2 shows the measured values of the EC amount and the LiPF ₆ amount in the five regions at the initial stage and after the deterioration of the battery. In Table 2, the end of the exposed portion of the positive electrode core is “positive electrode end”, the inside of the exposed portion of the positive electrode core is “inside the positive electrode”, the inside of the exposed portion of the negative electrode core is “inside the negative electrode”, and the end of the exposed portion of the negative electrode core is Is shown as “negative electrode end”. In Table 2, the amount of LiPF ₆ relative to the amount of EC is indicated by “LiPF ₆ amount / EC amount”.

As understood from the measurement results in Table 2, in Reference Example 1, the EC amount is substantially uniform both inside and outside in the winding axis direction of the electrode body both at the initial stage and after the deterioration. On the other hand, the amount of LiPF _{6 as} the electrolyte salt is greatly reduced at both ends in the winding axis direction of the electrode body after deterioration. In Table 2, "x" is attached to the numerical value in the column where the value has greatly decreased after deterioration. As a result, the present inventor believes that the main cause of the resistance increase in the high-rate cycle of Reference Example 1 shown in Table 1 is that the DC concentration is reduced due to the decrease in the salt concentration in the electrolyte at both ends in the winding axis direction of the electrode body. It was thought that the liquid resistance increased. In order to suppress the resistance increase, the inventor eliminates or reduces the rib in the central region (fifth region S5) in the inter-battery separator 30 as in the embodiment of FIGS. Therefore, during charging, the electrolyte easily escapes to the center of the electrode body instead of to the outside, and the electrolyte easily diffuses inside the electrode body at the time of discharging, so that the salt concentration of the electrolyte present in the electrode body is reduced and biased. We thought that it could be resolved relatively quickly, thereby suppressing the increase in resistance during high rate cycling. It is considered that such an effect can be obtained to some extent by the reference example 2.

  Furthermore, the inventor observed a cross-sectional image of a plane orthogonal to the winding axis direction of the battery 10 part of the battery pack using an X-ray CT apparatus after the charge / discharge cycle test using Reference Example 2. . FIG. 8 is a diagram showing a cross-sectional image of one battery 10 in the battery pack of Reference Example 2 on a plane orthogonal to the winding axis direction of the electrode body 13. As can be understood from the cross-sectional image shown in FIG. 8, in Reference Example 2, the dashed-dotted circle near the one curved surface side end (the right end in FIG. 8) of the flat portion of the electrode body 13. Buckling of the battery 10 occurred in a portion surrounded by β. The inventor of the present invention has identified that the pressurizing force is applied to the electrode body 13 by omitting the ribs of the flat part of the electrode body 13 near the end near one curved surface side in the inter-battery separator 30c. It was considered that this was because the gap between the electrodes in this portion was increased. The present inventor has considered that such factors cause a resistance increase in the low rate cycle of Reference Example 2 shown in Table 1. Unlike the high-rate cycle, the low-rate cycle is hardly affected by the chemical degradation of the battery, so it is considered that the buckling greatly affects the battery.

  According to the embodiment shown in FIGS. 1 to 4 described above, the rib group 32 of the inter-cell separator 30 includes all the regions of the first group G1 and the third group G3 on both the curved surface portions 13a side of the electrode body 13. A plurality of end ribs 33, 34 overlapping S1 to S3, S7 to S9; a plurality of center ribs 36, 37 overlapping the fourth region S4 and the sixth region S6 at both ends in the winding axis direction of the electrode body 13; Having. Furthermore, the formation density of the rib group 32 is lower in the fifth region S5 than in each of the fourth region S4 and the sixth region S6. Thus, it is estimated that the increase in the internal resistance of the battery 10 can be suppressed in both the high rate cycle and the low rate cycle. If the formation density of the rib group 32 is lower in the fifth region S5 than in each of the fourth region S4 and the sixth region S6, the ribs can be arranged in the fifth region S5. On the other hand, by setting the number of ribs in the fifth region S5 to 0, the increase in the internal resistance of the battery 10 can be further suppressed.

  Further, when viewed from one side in the stacking direction, at least some of the end ribs 33, 34, 35 of the plurality of end ribs 33, 34, 35 are in the flat portion 13b where buckling of the electrode body 13 is likely to occur. Since it is located in a portion overlapping the vicinity of the connecting portion E, buckling of the electrode body 13 can be further suppressed. Thereby, an increase in the internal resistance in the low rate cycle can be further suppressed.

  In the embodiment, the end side ribs 33 and 34 can be inclined with respect to the first side direction. However, extending along the first side direction is more effective from the viewpoint of suppressing an increase in internal resistance. preferable.

  Furthermore, according to the embodiment, on both sides in the up-down direction, the total length of each end-side rib 33, 34 in a portion overlapping the vicinity of the connection portion E in the flat portion 13b is the length of the positive electrode mixture layer in the first side direction. Is preferably 50% or more. According to this preferred configuration, buckling in the vicinity of the connection portion E in the flat portion 13b of the electrode body 13 can be further suppressed, so that an increase in internal resistance in a low rate cycle can be further suppressed.

  Furthermore, the total area of the rib group 32 provided in a portion overlapping the flat portion 13b when the battery pack 1 is viewed from one side in the stacking direction is arranged in the flat portion 13b when viewed from one side in the stacking direction. It is preferably 40 to 60% of the area of the positive electrode mixture layer. According to this preferred configuration, an increase in the internal resistance of the battery 10 can be suppressed more effectively in both the high rate cycle and the low rate cycle.

  REFERENCE SIGNS LIST 1 battery pack, 2 battery stack, 10 non-aqueous electrolyte secondary battery (battery), 11 prismatic outer package, 12 sealing plate, 13 electrode assembly, 13 a curved surface portion, 13 b flat portion, 14 positive electrode plate, 14 a positive electrode core exposed Part, 15 negative electrode plate, 15a negative electrode core exposed part, 16 positive electrode current collector, 17 positive electrode terminal, 18 negative electrode current collector, 19 negative electrode terminal, 20, 22 internal insulating member, 21, 23 external insulating member, 24 Insulating sheet, 25 gas discharge valve, 26 electrolyte injection hole, 27 sealing stopper, 30, 30a, 30b, 30c inter-battery separator, 31 body plate, 32, 32a rib group, 33, 33a, 34, 34a, 35 end side rib, 36, 37 center side rib, 40 groove, 50 frame part, 60 rib, 100 battery case,

Claims (4)

A plurality of non-aqueous electrolyte secondary batteries are assembled batteries configured to be stacked via an inter-cell separator,
Each of the plurality of nonaqueous electrolyte secondary batteries has a positive electrode plate having a positive electrode mixture layer containing a positive electrode active material, and a wound electrode body having a negative electrode plate, a nonaqueous electrolyte, the electrode body and the And a case for containing a non-aqueous electrolyte,
The electrode body has a flat portion having a flat outer peripheral surface, and two curved surface portions each having a curved outer peripheral surface disposed at both ends in the first direction of the flat portion,
The inter-battery separator includes a main body plate portion, and a projection group protruding from the main body plate portion in the stacking direction,
When the inter-battery separator is viewed from one side in the stacking direction, a region of the main body plate portion that overlaps with the positive electrode mixture layer disposed in the flat portion of the electrode body is orthogonal to the first direction. Dividing into nine regions obtained by equally dividing into three in each of a first side direction along the first side and a second side direction along a second side parallel to the first direction, The nine regions are a first group including a first region, a second region, and a third region from one end to the other end in the first direction of the inter-battery separator, and a fourth region, a fifth region, And a second group composed of a sixth region and a third group composed of a seventh region, an eighth region, and a ninth region. The region, the fifth region, and the eighth region overlap with the center of the electrode body in the winding axis direction. The projection group includes a plurality of end projections overlapping all the regions of the first group and the third group, and a plurality of central projections overlapping the fourth region and the sixth region, The formation density of the protrusion group is lower in the fifth region than in each of the fourth region and the sixth region.
Battery pack. When viewed from one side in the stacking direction, at least a part of the plurality of end side protrusions is in a portion of the flat portion that overlaps near a connection portion between the flat portion and the curved surface portion,
The battery pack according to claim 1. On both sides of the first direction, the total length of at least one of the plurality of end-side protrusions in a portion overlapping the vicinity of the connecting portion in the flat portion is the positive-electrode mixture layer. 50% or more of the length in the first side direction of
The battery pack according to claim 2. The total area of the protrusion group provided in a portion overlapping the flat portion when viewed from one side in the stacking direction is the positive electrode mixture disposed in the flat portion when viewed from one side in the stacking direction. 40-60% of the area of the layer,
The battery pack according to claim 1.

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