JP7280232B2 - secondary battery - Google Patents

Description

The present invention relates to secondary batteries.

A secondary battery is known that includes an electrode body in which an electrode sheet and a separator are wound. The electrode body is produced by laminating a long positive electrode sheet having a positive electrode active material layer and a long negative electrode sheet having a negative electrode active material layer with a separator interposed therebetween, and winding the laminate from one end. formed. In the case of the wound electrode body, when the electrolytic solution is permeated into the electrode body in the manufacturing process of the secondary battery, it is difficult for the electrolytic solution to permeate the central part of the electrode body. It takes a relatively long time.

For example, if the liquid permeability of the separator that constitutes the electrode body is low, the liquid pourability for evenly spreading the electrolytic solution over the electrode body is reduced. For example, it has been proposed that one end of a separator is joined in order to suppress the discharge and absorption of the electrolytic solution due to the contraction and expansion of the active material (see, for example, Patent Document 1). According to this configuration, the shortage of the electrolytic solution with which the active material layer is impregnated is suppressed, so it is possible to suppress an increase in the internal resistance due to the shortage of the electrolytic solution.

JP 2014-154484 A

Not only the secondary battery in which one end of the separator is joined, but also the material, thickness, etc. of the separator may reduce the liquid pourability of the electrode assembly. In addition, not only the separator but also the wettability of the active material with respect to the electrolytic solution may reduce the liquid pourability of the electrode assembly. If the injectability deteriorates, it takes longer for the electrolyte to permeate the electrode body, which not only lowers production efficiency, but also causes the electrolyte to drain out of the electrode body due to expansion and contraction associated with the battery reaction of the active material. It becomes difficult to return to the back, and there is a possibility that the shortage of the electrolyte solution will occur.

A secondary battery for solving the above problems is a battery comprising an electrode body in which an electrode sheet having an active material layer and a separator are alternately laminated and wound, and an electrolytic solution, wherein the electrode sheet and the A retention layer that retains a portion of the electrolyte is provided between the separator and the retention layer, and the retention layer extends from one end of the active material layer along the direction perpendicular to the winding direction to the center. a plurality of first linear portions extending toward each other and arranged with passages for the electrolyte to flow through; and the other end portion of the active material layer positioned opposite to the one end portion. and a plurality of second linear portions extending toward the center from the first linear portion and arranged with passages for the electrolytic solution to pass through. A region without the holding layer is provided between the end of the first linear portion and the end of the second linear portion and is spaced apart from the ends of the two linear portions on the central side. be provided.

According to the above configuration, when the electrolytic solution is injected into the secondary battery, the electrolytic solution is provided between the passages provided between the plurality of first linear portions and the second linear portions that constitute the holding layer . It moves to the central region of the active material layer through which the electrolyte solution does not easily permeate. Therefore, it is possible to improve the electrolyte pourability. Furthermore, even when the battery is in use, the electrolytic solution discharged to the outside of the electrode body quickly moves to the central region through the passage, so that the shortage of the electrolytic solution impregnated in the active material layer can be suppressed. Therefore, an increase in the internal resistance of the secondary battery can be suppressed.

In the secondary battery, the width of the passage provided between the first linear portions and the passage provided between the second linear portions narrows from the end of the electrode sheet toward the center. may be arranged as follows.

According to the above configuration, the width of the passage becomes smaller from the end of the active material layer toward the central region. Therefore, it is possible to prevent the electrolyte from remaining in the middle of the passage and allow the electrolyte to reach the central region, thereby improving the injectability.

In the secondary battery, the electrode body has a flattened shape and includes a first region having a large curvature and a second region adjacent to the first region. The linear portion may be wholly included in either the first region or the second region.

According to the above configuration, the entirety of the first linear portion and the second linear portion is included in either the first region or the second region. Therefore, it is possible to prevent the first linear portion and the second linear portion from interfering with the flow of the electrolytic solution due to straddling the first region and the second region.
In the above secondary battery, one of the electrode sheets is housed in a separator to which at least one of the ends in the longitudinal direction is joined, and the other electrode sheet has the first linear portion and the second linear portion. may be provided.

According to the above configuration, the entirety of the first linear portion and the second linear portion is included in either the first region or the second region. Therefore, it is possible to prevent the first linear portion and the second linear portion from interfering with the flow of the electrolytic solution due to straddling the first region and the second region.

In the above secondary battery, the first linear portion and the second linear portion may contain an absorbent polymer that absorbs the electrolytic solution.
According to the above configuration, the retaining layer containing the absorbent polymer retains the electrolytic solution between the electrode sheet and the separator. Therefore, it is possible to suppress an increase in internal resistance due to the presence of the retention layer .

In the above secondary battery, it is preferable that the holding layer includes an adhesive material that adheres the electrode sheet and the separator.
According to the above configuration, the retention layer can have both the function of retaining the electrolytic solution and the function of adhering the electrode sheet and the separator.

ADVANTAGE OF THE INVENTION According to this invention, the injection property of the electrolyte solution of a secondary battery can be improved.

1 is a perspective view of a secondary battery according to a first embodiment; FIG. FIG. 3 is an exploded view of the electrode assembly of the lithium-ion secondary battery of the same embodiment; The figure which shows typically the side surface of the electrode body of the same embodiment. Sectional drawing of the electrode body before winding in the same embodiment. The front view which shows the principal part of the positive electrode sheet in the same embodiment. The figure which expanded the principal part of the positive electrode sheet in the same embodiment. The front view which shows the principal part of the positive electrode sheet of a modification. The front view which shows the principal part of the positive electrode sheet in a comparative example. 4 is a table showing evaluation results of secondary batteries in Examples and Comparative Examples;

A secondary battery will be described with reference to FIGS. 1 to 6. FIG. In this embodiment, the secondary battery will be described as a lithium ion secondary battery.
As shown in FIG. 1, the secondary battery 11 includes a case body 12 having an opening and a lid 13 that seals the opening of the case body 12 . The lid portion 13 is provided with a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging. The cover portion 13 is formed with an injection port 13A for injecting an electrolytic solution. An electrode body 16 and an electrolytic solution are accommodated in the accommodation space formed by the case main body 12 and the lid portion 13 . The electrode body 16 has a positive electrode current collecting part 17 which is an end located on one side (left side in FIG. 1) and a positive electrode current collecting part 17 located on the other side (right side in FIG. 1) when housed in the case body 12. A negative electrode current collecting portion 18 is provided as an end portion for connecting the electrodes. The positive current collecting portion 17 is connected to the positive external terminal 14 via the connecting member 171 , and the negative current collecting portion 18 is electrically connected to the negative external terminal 15 via the connecting member 181 .

As shown in FIG. 2, the electrode assembly 16 is produced by laminating a long positive electrode sheet 20, a separator 40, a long negative electrode sheet 30, and a separator 41 in this order, and then winding and pressing the laminated body from one end. formed by The electrode body 16 has a flat shape. The laminate before winding is laminated so that the longitudinal directions of the positive electrode sheet 20 and the negative electrode sheet 30 are aligned. The winding direction 101 is the longitudinal direction of the positive electrode sheet 20 and the negative electrode sheet 30 in which the sheets are wound around the central axis 100 of the electrode body 16 .

The positive electrode sheet 20 includes a positive electrode current collector 21 and positive electrode active material layers 22 provided on both sides of the positive electrode current collector 21 . An uncoated portion 23 in which the positive electrode current collector 21 is exposed without forming the positive electrode active material layer 22 is provided along the longitudinal direction at one end portion of the positive electrode sheet 20 in the lateral direction. At least part of the uncoated portion 23 is positioned outside the separators 40 and 41 .

The negative electrode sheet 30 includes a negative electrode current collector 31 and negative electrode active material layers 32 provided on both sides of the negative electrode current collector 31 . Of the ends of the negative electrode sheet 30 in the lateral direction, the other end opposite to the uncoated portion 23 of the positive electrode sheet 20 has the negative electrode current collector 31 without the negative electrode active material layer 32 formed thereon. An exposed uncoated portion 33 is provided. At least part of the uncoated portion 33 is positioned outside the separator 40 . The uncoated portions 23 of the positive electrode sheet 20 are pressed against each other to form the positive current collector 17 . The uncoated portions 33 of the negative electrode sheet 30 are pressed against each other to form the negative electrode collector portion 18 .

Next, the material for the positive electrode will be described. Metal foil such as aluminum foil is used for the positive electrode current collector 21 . As the positive electrode active material contained in the positive electrode mixture, one or more of various materials known to be usable as positive electrode active materials for lithium ion secondary batteries can be used. Preferred examples include layered and spinel-based lithium composite metal oxides (e.g., LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO ₄ ). is mentioned. Examples of the conductive material include carbon black such as acetylene black and ketjen black, and other powdery carbon materials (graphite, etc.). Examples of binders include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE).

Next, the material for the negative electrode will be described. The negative electrode current collector 31 is made of metal foil such as copper or nickel. As the negative electrode active material contained in the negative electrode mixture, one or more of various materials known to be usable as negative electrode active materials for lithium ion secondary batteries can be used. Examples thereof include carbon materials such as graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and carbon nanotubes. Among them, graphite-based materials such as natural graphite and artificial graphite (especially natural graphite) can be preferably used because of their excellent conductivity and high energy density.

Moreover, the negative electrode mixture may contain additives such as a conductive agent and a binder in addition to the negative electrode active material. As the binder, the same binder as that used for the positive electrode can be used. In addition, a thickener, a dispersant, a conductive material, and the like can be used as appropriate. For example, carboxymethyl cellulose (CMC) and methyl cellulose (MC) can be used as thickeners.

Separators 40 and 41 have porous layers made of resin. The porous layer is, for example, a single-layer structure composed of porous polyethylene, porous polyolefin, porous polyvinyl chloride, or the like, or a laminated structure composed of a plurality of materials. The porous layer may also contain a filler for the purpose of improving strength.

A retention layer is interposed between the separator 40 and the positive electrode sheet 20 . The holding layer joins the separator 40 and the positive electrode sheet 20 and is made of a holding material capable of holding the electrolytic solution in the holding layer . For example, at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyacrylate, polytetrafluoroethylene (PTFE), and the like can be used as the holding material . In addition, low density polyethylene (LDPE), polypropylene (PP), poly-α-olefin such as polybutene-1, polyacrylic acid ester, ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer Copolymers (EMA), ethylene-ethyl acrylate copolymers (EEA), ethylene-butyl acrylate copolymers (EBA), ethylene-methyl methacrylate copolymers (EMMA), ionomer resins, and the like. In addition, each resin described above, styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, ethylene-propylene rubber, etc., which exhibits adhesiveness at room temperature, is used as a core, and the melting point and softening point are 60 ° C. or higher and 120 ° C. C. or less, and a resin having a core-shell structure in which the shell is a resin may be included as the adhesive resin. In this case, various acrylic resins, polyurethanes, and the like can be used for the shell. Further, as the adhesive resin, one-liquid type polyurethane, epoxy resin, or the like, which exhibits adhesiveness within the range of 60° C. or more and 120° C. or less, can also be used. As the adhesive resin, one of the above-exemplified resins may be used alone, or two or more thereof may be used in combination.

The electrolytic solution is a composition containing a supporting salt in a non-aqueous solvent. Here, as the non-aqueous solvent, one or more of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and the like are used. can be used. Support salts include _{LiPF 6} , LiBF ₄ , LiClO 4 , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiI 1 or 2 or more lithium compounds (lithium salts) selected from the above can be used.

FIG. 3 schematically shows a side view of the electrode body 16. As shown in FIG. The electrode body 16 has a first portion 16A in which the wound positive electrode sheet 20 and the negative electrode sheet 30 have a large curvature, and a second portion 16B that is substantially flat and has a smaller curvature than the first portion 16A. The second portion 16B is sandwiched between the pair of first portions 16A. The electrode body 16 may be accommodated in the case main body 12 so that the first portion 16A is located on the upper side and the lower side along the vertical direction as illustrated in FIG. , may be accommodated in the case body 12 so as to be positioned on the left side and the right side.

FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. The negative electrode sheet 30 is sandwiched between separators 40 and 41 . One ends 40A and 41A of the separators 40 and 41 protruding from the negative electrode sheet 30 are joined to each other. The method of joining the ends 40A and 41A is not particularly limited, but at least one of various joining methods such as adhesion using an adhesive, heat welding, vibration welding that welds by applying ultrasonic waves, and laser welding that irradiates laser light. You can use one. Moreover, the ends 40B and 41B of the separators 40 and 41 on the side of the uncoated portion 33 of the negative electrode sheet 30 do not protrude outside the uncoated portion 33 . These other ends 40B and 41B are joined together. At least one of the various methods described above can be used as the joining method. In addition, the ends of the separators 40 and 41 that are parallel to the lateral direction and that are at the winding start position and at the winding end position in the longitudinal direction (winding direction 101) are It may or may not be joined.

A holding layer 50 is provided between the positive electrode active material layer 22 and the separator 40 of the positive electrode sheet 20 and on the surface of the positive electrode sheet 20 opposite to the separator 40 side. Specifically, of the positive electrode sheet 20, the holding layer 50 is provided on the joint surface 24A on the side of the separator 40 and the joint surface 24B on the opposite side. The holding layer 50 adheres the positive electrode sheet 20 and the separators 40 and 41 and enhances the liquid injection property to the electrode body 16 . The retention layer 50 is not applied over the entire area of the positive electrode active material layer 22 but is provided partially. That is, of the joint surfaces 24A and 24B of the positive electrode sheet 20 on the separator 40 side, in the central region including the midpoint between the end of the positive electrode active material layer 22 on the uncoated portion 23 side and the opposite end, No retaining layer 50 is provided. In addition, retaining layers 50 are provided on both sides of the central region. In FIG. 4, the holding layer 50 is provided on the joint surfaces 24A and 24B of the positive electrode sheet 20 on the separator 40 side, but the holding layer 50 is provided only on the joint surface 24A or only the joint surface 24B of the positive electrode sheet 20. may 2, for the sake of convenience, illustration of the holding layer 50 on the joint surface 24B side of the positive electrode sheet 20 is omitted. Further, each layer shown in FIG. 4 shows its thickness for convenience, and the thickness ratio of each layer is not limited to the thickness ratio shown in FIG.

FIG. 5 is a front view showing part of the positive electrode sheet 20. FIG. The positive electrode sheet 20 has a first region 20R positioned in the first region 16R having a large curvature in the state of the electrode body 16, and a second region 20F positioned in the second region 16F that is flat in the state of the electrode body 16. including. On the joint surface 24A of the positive electrode sheet 20 and on the positive electrode active material layer 22, with the central region 22C of the positive electrode active material layer 22 interposed therebetween, a holding layer 50 including a plurality of first linear portions 51 and a plurality of second linear portions 51 are formed. A holding layer 50 consisting of two linear portions 52 is provided. The retention layer 50 is not provided in the central region 22C. The central region 22C is a region including an intermediate point between the end 22A of the positive electrode active material layer 22 on the uncoated portion 23 side and the end 22B on the opposite side. The holding layer 50 on the joint surface 24A and the holding layer 50 on the joint surface 24B have the same structure.

The first linear portion 51 and the second linear portion 52 are provided so as to be entirely included in either the first region 20R or the second region 20F. The first linear portion 51 positioned in the second region 20</b>F linearly extends from the end portion 22</b>A of the positive electrode active material layer 22 toward the central region 22</b>C of the positive electrode active material layer 22 . The first linear portions 51 define passages 25 through which the electrolytic solution passes between adjacent first linear portions 51 . Further, the first linear portions 51 extend from the end portion 22A of the positive electrode active material layer 22 toward the central region 22C so that the width of the passage 25 between the adjacent first linear portions 51 becomes smaller. ing. That is, the cross-sectional area of the passage 25 decreases from the end portion 22A of the positive electrode active material layer 22 toward the central region 22C.

As with the first linear portions 51 , the second linear portions 52 linearly extend from the end portions 22</b>B of the positive electrode active material layer 22 toward the central region 22</b>C of the positive electrode sheet 20 in the lateral direction. The second linear portions 52 define passages 25 between them through which the electrolyte passes. The second linear portions 52 extend from the end portion 22B of the positive electrode active material layer 22 toward the central region 22C so that the width of the passage 25 between the adjacent second linear portions 52 becomes smaller. .

That is, the first linear portion 51 and the second linear portion 52 radially extend from the central region 22C toward the end portions 22A and 22B in the second region 20F. The width of the passage 25 is several millimeters to several tens of millimeters, and is determined according to the viscosity and surface tension of the electrolyte.

In addition, the adhesive between the positive electrode active material layer 22 and the separator 40 does not directly contribute to the battery reaction, so it increases the internal resistance of the battery, although the effect is smaller than that of the decrease in liquid pourability. Since the retention layer 50 of the present embodiment retains the electrolyte, it is possible to suppress an increase in internal resistance more than a normal adhesive. By reducing the amount, the increase in internal resistance is suppressed. In addition, in the second region 20F, the center region 22C is particularly difficult to be injected with the electrolytic solution. On the other hand, since the region close to the first region 20R is located at the end of the electrode body 16, it is easier to retain the electrolytic solution than the central region 22C. Therefore, in the positive electrode active material layer 22, regions 22D and 22E located at the ends in the parallel direction where the first linear portions 51 are arranged, 22D and 22D located at the ends in the parallel direction where the second linear portions 52 are arranged, and By not applying the holding material to 22E, an increase in internal resistance caused by the application of the holding material is suppressed. Furthermore, the holding material is not provided in the region 22F between the two regions 22D and adjacent to the central region 22C, and in the region 22F between the two regions 22E and adjacent to the central region 22C. suppressing the rise.

The first linear portion 51 and the second linear portion 52 located in the first region 20R also extend from the ends 22A and 22B of the positive electrode active material layer 22 toward the central region 22C, similarly to the second region 20F. out. The retention layer 50 is not provided in the central region 22C. The plurality of first linear portions 51 and the plurality of second linear portions 52 define the passage 25 . The first region 20R occupies a smaller area within the positive electrode sheet 20 than the second region 20F. In order to provide a predetermined number of the first linear portions 51 and the second linear portions 52 in the limited space of the first region 20R, the first linear portions 51 and the second linear portions 52 in the first region 20R may be different from the extending direction of the first linear portion 51 and the second linear portion 52 in the second region 20F. For example, as shown in FIG. 5 , the first linear portions 51 and the second linear portions 52 in the first region 20R may be parallel or substantially parallel to the lateral direction of the positive electrode sheet 20 . A region without the retention layer 50 may also be provided in the first region 20R.

When the first linear portion 51 and the second linear portion 52 are arranged across the first region 20R and the second region 20F, the passage 25 is provided along the curved surfaces of the positive electrode sheet 20 and the separator 40. As a result, the positive electrode active material layer 22 and the separator 40 press and shrink. As described above, the entirety of the first linear portion 51 and the second linear portion 52 are located in either the first region 20R or the second region 20F so as not to impede the flow of the electrolytic solution as much as possible. can do.

Although it depends on the overall width of the positive electrode active material layer 22, the width L2 of the holding layer 50 should be larger than the width L1 of the central region 22C in order to reliably guide the electrolytic solution to the middle point of the positive electrode active material layer 22. do it. The width L1 of the central region 22C is preferably 1 cm or more and 2 cm or less. If the width is too narrow, the additive in the electrolytic solution cannot be diffused in the central portion and is concentrated, resulting in uneven concentration of the additive in the entire electrode plate, which is not preferable. Further, when the width of the entire positive electrode active material layer 22 is relatively small, the width L2 of the retention layer 50 may be smaller than the width L1 of the central region 22C.

(action)
Next, the operation of this embodiment will be described together with its manufacturing method.
In the manufacturing process of the secondary battery 11, first, a positive electrode sheet 20 provided with a positive electrode active material layer 22 and a negative electrode sheet 30 provided with a negative electrode active material layer 32 are prepared, and the negative electrode sheet 30 is sandwiched between separators 40 and 41. . Then, both ends parallel to the longitudinal direction and both ends parallel to the lateral direction of the separators 40 and 41 are joined by a joining method such as adhesion with an adhesive or heat welding. Next, the positive electrode sheet 20 and the negative electrode sheet 30 sandwiched between the separators 40 and 41 are laminated. Further, winding is started from one end of the laminate in the winding direction 101 and is wound until the other end is finished. Then, pressing force is applied to the wound body to form the flat electrode body 16 , and connecting members 171 and 181 are connected to the positive electrode current collector 17 and the negative electrode current collector 18 that are the ends of the electrode body 16 . Furthermore, the electrode body 16 to which the connecting members 171 and 181 are connected is housed in the case main body 12 , and the opening of the case main body 12 is sealed with the lid portion 13 . Further, the electrolytic solution is injected into the case main body 12 from the injection port 13A provided in the lid portion 13 . The separators 40 and 41 suppress the ingress and egress of the electrolytic solution, but the electrolytic solution can permeate through the separators 40 and 41 , and the electrolytic solution permeates the negative electrode active material layer 32 through the separators 40 and 41 . Also, the electrolyte penetrates into the positive electrode active material layer 22 through the gaps between the ends of the separators 40 and 41 and the ends of the positive electrode sheet 20 .

When the ends of the separators 40 and 41 sandwiching the negative electrode sheet 30 are joined so that the separators 40 and 41 form a bag shape, the electrode assembly is more compact than the electrode assembly in which the ends of the separators 40 and 41 are not joined. The liquid permeability of the electrolyte in 16 is lowered. However, since the passages 25 defined by the first linear portions 51 and the second linear portions 52 are provided in the positive electrode active material layer 22 of the positive electrode sheet 20, the electrolytic solution flows into the positive electrode active material layer by capillary action. 22 toward the central region 22C.

On the other hand, when a passage is provided from one end portion 22A of the positive electrode active material layer 22 to the other end portion 22B, the electrolytic solution flowing from the end portion 22A and the electrolytic solution flowing from the end portion 22B are The collision occurs at the center of the material layer 22 . Then, the amount of the electrolytic solution locally increases at the location of collision, and concentration unevenness of the additive contained in the electrolytic solution occurs within the positive electrode active material layer 22 . In contrast, in the present embodiment, since the retention layer 50 is not provided in the central region 22C, it is possible to suppress concentration unevenness of the additive in the electrolytic solution.

FIG. 6 is an enlarged view of a region of the positive electrode sheet 20 where the first linear portions 51 are provided. The passage 25 provided between the first linear portions 51 has a smaller cross-sectional area toward the central region 22C. Since the flow rate of the electrolytic solution is ensured at each cross section of the passage 25, the flow velocity 102 increases toward the central region 22C. That is, since the momentum of the electrolytic solution increases toward the central region 22C of the passage 25, even if the central region 22C is distant from the end portion 22A of the positive electrode active material layer 22 serving as the inlet of the electrolytic solution, the electrolytic solution will flow through the central region. reach up to 22C. Similarly, the passage 25 provided between the second linear portions 52 also has a smaller cross-sectional area from the end portion 22B toward the central region 22C. Therefore, the electrolytic solution flows from the end portion 22B of the positive electrode active material layer 22 to the central region 22C. Therefore, the injectability of the electrolyte into the electrode body 16 is enhanced. When the electrolyte pours into the electrode body 16 in this way, the time required for impregnating the entire electrode body 16 with the electrolyte can be shortened, resulting in an increase in production efficiency.

Next, the operation of the secondary battery 11 during use will be described. In the negative electrode sheet 30, the negative electrode active material expands and contracts due to the insertion and extraction of lithium ions into and from the negative electrode active material. When the negative electrode active material contracts, the electrolyte is discharged from the negative electrode active material, and when the negative electrode active material expands, the electrolyte is absorbed into the negative electrode active material. In a conventional secondary battery, the electrolytic solution discharged from the negative electrode active material layer 32 tends to be difficult to return to the negative electrode active material layer 32, especially when charging and discharging are repeated at a high rate. In this embodiment, since the ends of the separators 40 and 41 sandwiching the negative electrode sheet 30 are joined together, it is possible to suppress the amount of electrolytic solution impregnated in the negative electrode sheet 30 from being discharged to the outside of the separators 40 and 41. . Therefore, when the negative electrode active material expands, it can quickly absorb the electrolyte existing inside the separators 40 and 41 .

Further, the electrolyte solution is held in the holding layer 50 provided in the positive electrode active material layer 22 . Therefore, the electrolyte contained in the holding layer 50 also contributes to the battery reaction. Therefore, as compared with the case where the positive electrode sheet 20 and the separators 40 and 41 are adhered with an adhesive layer that does not absorb the electrolytic solution, the liquid injection property can be improved, and the shortage of the electrolytic solution in the positive electrode active material layer 22 can be suppressed. In addition, the application amount of the holding material is reduced by providing the holding material in a linear shape. An increase in the internal resistance of the secondary battery 11 during use can be suppressed from both the structure of the passage 25 and the amount of application of the holding material .

Furthermore, the electrolytic solution discharged to the outside of the electrode body 16 through the end of the positive electrode sheet 20 due to the battery reaction moves rapidly to the central region 22C through the passage 25 when reabsorbed by the electrode body 16. As a result, liquid return during use of the battery is enhanced. Therefore, battery characteristics such as internal resistance can be improved.

Effects of the above embodiment will be described.
(1) When the electrolyte is injected into the secondary battery 11, the electrolyte is injected between the passage 25 provided between the plurality of first linear portions 51 constituting the holding layer 50 and the second linear portions 52. It moves to the central region 22C, through which the electrolyte hardly permeates, through the passage 25 provided in the . Therefore, it is possible to improve the electrolyte pourability. Further, after the battery is started to be used, the electrolytic solution discharged to the outside of the electrode body 16 due to the battery reaction moves quickly to the central region 22C through the passage 25, so that the electrolytic solution impregnated in the positive electrode active material layer 22 Shortage of liquid can be suppressed. Therefore, an increase in the internal resistance of the secondary battery 11 can be suppressed.

(2) The width of the passage 25 decreases from the end of the positive electrode active material layer 22 toward the central region 22C. Therefore, it is possible to prevent the electrolyte from staying in the middle of the passage 25 and allow the electrolyte to reach the central region 22C, so that the electrolyte injection performance can be improved.

(3) The first linear portion 51 and the second linear portion 52 are wholly included in either the first region 20R or the second region 20F. Therefore, it is possible to prevent the first linear portion 51 and the second linear portion 52 from straddling the first region 20R and the second region 20F from impeding the flow of the electrolytic solution.

(4) By housing the negative electrode sheet 30 in the separators 40 and 41 whose ends are joined, the state in which the entire negative electrode active material layer 32 is sufficiently impregnated with the electrolyte even during high-rate charging/discharging can be maintained. can be maintained. Therefore, it is possible to suppress an increase in internal resistance particularly during high-rate charging and discharging.

(5) The retention layer 50 containing the absorbent polymer retains the electrolyte between the positive electrode sheet 20 and the separators 40 and 41 . Therefore, it is possible to suppress an increase in internal resistance due to the presence of the retention layer 50 .

(6) Since the retaining layer 50 contains an adhesive material that bonds the electrode sheet and the separator, it can have both the function of retaining the electrolytic solution and the function of bonding the electrode sheet and the separator. Therefore, it is possible to reduce the content of materials that do not directly contribute to the battery reaction, thereby suppressing an increase in internal resistance.

Each of the above embodiments can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
(Modification 1) In the above-described embodiment, the first linear portion 51 and the second linear portion 52 are arranged in the winding direction 101 of the negative electrode sheet 30 and in the direction intersecting the transverse direction perpendicular to the winding direction 101. procrastinate. Alternatively, as shown in FIG. 7, the first linear portion 51 and the second linear portion 52 may extend in a direction intersecting the lateral direction orthogonal to the winding direction 101 of the negative electrode sheet 30. good. Even in this case, the first linear portions 51 define the passages 25 between adjacent first linear portions 51 . In addition, the second linear portions 52 define passages 25 between adjacent second linear portions 52 .

- In the above-described embodiment, the regions 22D to 22F of the positive electrode active material layer 22 are regions in which the retention layer 50 is not provided. Alternatively, the retention layer 50 may be provided in at least one of the regions 22D-22F. Also in this aspect, the holding layer 50 is preferably provided with linear holding materials and defining the passages 25 therebetween, similarly to the first linear portion 51 and the second linear portion 52 .

- In the above-described embodiment, the holding layer 50 has both the function of holding the electrolytic solution and the function of bonding the electrode sheet and the separator. Alternatively, the holding layer 50 may have only the function of holding the electrolytic solution, and an adhesive for bonding the positive electrode sheet 20 and the separator 40 may be provided separately from the holding layer 50 .

- In the said embodiment, the secondary battery 11 was used as the lithium ion secondary battery. Alternatively, the secondary battery 11 may be a nickel-hydrogen secondary battery or the like. A nickel-hydrogen secondary battery includes a positive electrode containing nickel oxide, a negative electrode containing a hydrogen-absorbing alloy, an electrolytic solution made of an alkaline aqueous solution, and a separator. The negative electrode expands and contracts due to absorption and desorption of hydrogen in the hydrogen storage alloy. Also in this aspect, it is preferable to sandwich the negative electrode sheet between a pair of separators and to join the both ends. A retention layer is provided between the positive electrode sheet and the separator.

- In the above embodiment, the width of the passage 25 is made smaller toward the central region 22C. Alternatively, the width of the passageway 25 may be constant. Also, the widths of the plurality of passages 25 may be varied according to the easiness of permeation of the electrolytic solution.

- Although the retention layer 50 is provided on the positive electrode sheet 20 in the above embodiment, it may be provided on the separator 40 .
- In the present invention, at least the ends 40A and 41A or the ends 40B and 41B need only be joined. If at least one of the ends is joined, the electrolyte flows into and out of the negative electrode sheet 30 less than in the electrode assembly 16 including the separators 40 and 41 whose ends are not joined, and the flow of the electrolyte into the negative electrode sheet 30 is reduced. Deviation of density distribution can be reduced. Even in these embodiments, since good liquid injection properties between the positive electrode sheet 20 and the separator 40 can be maintained, it is possible to improve the production efficiency in the manufacturing process and prevent shortage of the electrolyte when the battery is in use.

- In the above embodiment, the holding layer 50 is provided between the positive electrode sheet 20 and the separator 40 . Alternatively or additionally, a retention layer 50 may be interposed between the negative electrode sheet 30 and the separator 40 .

(Example)
Examples that are examples of the above embodiment will be specifically described below. For the sake of convenience, the configuration of the secondary battery will be described using the reference numerals of the above embodiments, but these examples do not limit the present invention.

(Example 1)
<Preparation of positive electrode sheet>
LiNiO ₂ as a lithium composite metal oxide as a positive electrode active material, acetylene black (AB) as a conductive material, and PVDF as a binder were mixed with an NMP (N-methyl-2-pyrrolidone) solution and kneaded. The ratio of the positive electrode active material to the total mass of the solid content of the positive electrode mixture was set to 90% by mass or more. Then, the positive electrode sheet 20 was produced by coating the kneaded positive electrode mixture on both sides of an elongated aluminum foil (positive electrode current collector) and drying it. After drying the positive electrode mixture, the positive electrode active material layer 22 was pressed.

Also, a holding material was prepared by dissolving PVDF in NMP. The positive electrode sheet 20 is divided into a first region 20R having a large curvature when used as the electrode body 16, and a second region 20F adjacent to the first region 20R or sandwiched between the first regions 20R. On 20F, the holding material was linearly applied by a gravure roll to form nine first linear portions 51 and nine second linear portions 52 . The width of the first linear portion 51 and the second linear portion 52 is 40 mm to 50 mm, and the height (thickness) is approximately 2 μm. The width of the passage 25 formed between the first linear portion 51 and the second linear portion 52 is set to 5 mm at the end of the positive electrode active material layer serving as the entrance of the electrolytic solution, and as shown in FIG. Made the width of the passage narrower as it went towards the area. Also, three first linear portions 51 and three second linear portions 52 are formed in the first region 20R.

<Production of negative electrode sheet>
Natural graphite powder as a negative electrode active material, SBR, and CMC were dispersed in water and kneaded. The ratio of the negative electrode active material to the entire mass of the negative electrode mixture was set to 98% by mass or more. The negative electrode sheet 30 was produced by applying this negative electrode mixture to both sides of a long copper foil and drying it. After drying the negative electrode mixture, the negative electrode active material layer 32 was pressed.

<Preparation of separator>
Separators 40 and 41 made of porous polyolefin were prepared. The negative electrode sheet 30 was sandwiched between a pair of separators 40 and 41, and both longitudinal ends of the separators 40 and 41 were joined by heat welding.

<Lithium ion secondary battery>
The positive electrode sheet 20 prepared as described above and the negative electrode sheet 30 sandwiched between the separators 40 and 41 are laminated, the laminated body is wound, and the wound body is pressed from the side to form a flat electrode body 16. made.

The electrolytic solution used was a mixed solvent containing EC, EMC, and DMC at a volume ratio of 3:3:4, and containing LiPF ₆ as a supporting salt at a concentration of about 1.1 mol/L. The wound electrode body 16 was housed in the case main body 12 , and the opening of the case main body 12 was sealed with the lid portion 13 . Furthermore, the electrolytic solution was injected from the injection port 13A formed in the lid portion 13 .

After that, under a temperature condition of 20° C., an operation of charging at a constant current and constant voltage to 4.1 V at a charging rate of 0.1 C and an operation of discharging at a constant current and constant voltage to 3.0 V at a discharge rate of 0.1 C were performed three times. A secondary battery 11 was obtained by repeating the conditioning treatment several times.

(Example 2)
A secondary battery 11 was produced in the same manner as in Example 1, except that the width of the passage 25 was 8 mm, which was larger than that in Example 1.

(Example 3)
Like the positive electrode sheet 20 of Modified Example 1 shown in FIG. A secondary battery 11 was produced in the same manner as in 1.

(Example 4)
A secondary battery 11 was fabricated in the same manner as in Example 1, except that the ends of the separators 40 and 41 were joined so as not to be closed.

(Comparative example 1)
As shown in FIG. 8 , the retention layer 50 was formed by coating the entire surface of the positive electrode active material layer 22 with the retention material without linearly providing the retention material on the positive electrode active material layer 22 . A secondary battery 11 was fabricated in the same manner as in Example 1 except for the above.

(Comparative example 2)
The ends of the separators 40 and 41 were joined so as not to be closed, and a holding material was applied to the entire surface of the positive electrode active material layer 22 . A secondary battery 11 was fabricated in the same manner as in Example 1 except for the above.

If a layer having an adhesive function is not provided between the positive electrode sheet 20 and the separator 40, a gap may occur between the positive electrode sheet 20 and the separator 40 during use of the battery. Therefore, it is necessary to provide a layer having an adhesive function between the positive electrode sheet 20 and the separator 40. For comparison with Examples 1 to 4, samples of Reference Examples 1 and 2 below were prepared. .

(Reference example 1)
The configuration was such that the ends of the separators 40 and 41 were not joined and the holding layer 50 was not provided between the positive electrode active material layer 22 and the separators 40 and 41 . A secondary battery 11 was fabricated in the same manner as in Example 1 except for the above.

(Reference example 2)
A configuration was adopted in which the holding layer 50 was not provided between the positive electrode active material layer 22 and the separators 40 and 41 . A secondary battery 11 was fabricated in the same manner as in Example 1 except for the above.

<Pourability before battery use>
At the time of manufacture of the battery, the impregnation state of the electrolyte solution was examined after a predetermined time had passed since the electrolyte solution was poured into the case body. Whether or not the impregnation into the electrode body was completed was determined by dismantling the battery after a predetermined period of time had passed since the injection of the electrolyte, and determining whether or not the positive electrode sheet and the negative electrode plate sheet were entirely wet with the electrolyte. The results are shown in the table of FIG. "○" indicates that the entire positive electrode sheet is impregnated with the electrolytic solution, "Δ" indicates that the electrolytic solution is impregnated up to the central region 22C but not the entire positive electrode sheet, and the central region 22C is also impregnated with the electrolytic solution. If not, it was marked with "x".

<Increase in initial resistance due to retention layer >
The initial resistance of the secondary battery was measured before use. Specifically, the resistance was measured by discharging at 1 C for 10 seconds in an environment of 25° C. and SOC 60%. The results are shown in the table of FIG. Based on the initial resistance value of Reference Example 1, the case where the resistance increase amount was within 5% was indicated as "◎", the case where it exceeded 5% and within 10% was indicated as "◯", and the case where it exceeded 10% was indicated as "x". .

<High rate characteristics>
The secondary batteries 11 after the conditioning treatment of Examples 1 to 4, Comparative Examples 1 and 2, and Reference Examples 1 and 2 were charged to an SOC of 60%. Then, under an environmental temperature of 25° C., each battery was discharged at 30 C for 10 seconds and then rested for 10 seconds. It was then charged at 7.5C for 40 seconds and then rested for 10 seconds. This charging/discharging was regarded as one cycle, and 2000 cycles were carried out. Then, the current-voltage characteristics (IV characteristics) of the secondary battery after 2000 cycles were measured. When the resistance value (IV characteristic) was less than 1.3 times the IV characteristic before the charge/discharge cycle, it was evaluated as "O", and when it was 1.3 times or more, it was evaluated as "X".

<Evaluation>
In Examples 1 to 4, the liquid pourability was "○" or "Δ", and the increase in initial resistance due to the retention layer was also small with "○" or "⊚", all of which were good. Comparative Examples 1 and 2, in which the retention layer 50 was applied over the entire surface, were inferior to the examples in which the retention layer 50 was partially applied, and the initial resistance was increased, so that the desired initial voltage could not be obtained. It should be noted that the evaluation “◯ to ◎” regarding the initial resistance of Example 2 indicates that some of the samples prepared as Example 2 were “◯” and the rest were “◎”.

Examples 1 to 3, Comparative Example 1, and Reference Example 2, in which both ends of the separators 40 and 41 were joined, had good high rate characteristics. In Example 4, Comparative Example 2, and Reference Example 1, in which both ends of the separators 40 and 41 were not joined, the high rate characteristics were not good.

DESCRIPTION OF SYMBOLS 11... Secondary battery 16... Electrode body 20... Positive electrode sheet 30... Negative electrode sheet 40, 41... Separator 50... Holding layer

Claims (6)

A battery comprising an electrode body and an electrolytic solution in which an electrode sheet having an active material layer and a separator are alternately laminated and wound,
A retaining layer for retaining a portion of the electrolyte is provided between the electrode sheet and the separator,
The holding layer extends from one end of the active material layer along a direction orthogonal to the winding direction toward the center and is arranged with a passage for the electrolyte to pass through. A first linear portion extends toward the center from the other end of the active material layer located opposite to the one end, and is arranged with a passage for the electrolytic solution to pass through each other. and a plurality of second linear portions,
A secondary battery, wherein a region without the holding layer is provided between the center-side end of the first linear portion and the center-side end of the second linear portion. The passages provided between the first linear portions and the passages provided between the second linear portions are arranged such that their widths become narrower from the ends of the electrode sheet toward the center. The secondary battery according to claim 1. The electrode body has a flat shape and includes a first region having a large curvature and a second region adjacent to the first region,
The secondary battery according to claim 1 or 2, wherein the first linear portion and the second linear portion are entirely included in either the first region or the second region. One of the electrode sheets is housed in a separator to which at least one of longitudinal ends is joined,
The secondary battery according to any one of claims 1 to 3, wherein the other electrode sheet comprises the first linear portion and the second linear portion. The secondary battery according to any one of claims 1 to 4, wherein the first linear portion and the second linear portion each contain an absorbent polymer that absorbs the electrolytic solution. The secondary battery according to any one of claims 1 to 5, wherein the holding layer includes an adhesive material that adheres the electrode sheet and the separator.

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