JP2010146872A - Flat secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat secondary battery having improved volume efficiency. <P>SOLUTION: The lithium ion secondary battery 20 includes a positive electrode plate having a tab on one side along the longitudinal direction, a negative electrode plate having a tab on one side along the longitudinal direction, a flat wound group 3 wound around a winding core via a separator with the tabs 8 of positive and negative electrodes led-out in mutually opposite directions, a plane positive electrode collecting plate 8 which is fixed to the winding core 1 and to which the tab of the positive electrode is joined, a plane negative electrode collecting plate which is fixed to the winding core 1 on the opposite side to the positive electrode collecting plate 8 and to which the tab of the negative electrode is joined, electrolytic solution in which the wound group 3 is immersed, and a flat battery case 11 storing the members. Leg parts 14 are formed by cutting the positive and negative electrode collecting plates at one longitudinal side and fitted to the wound group 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a flat secondary battery, and more particularly to a flat secondary battery including an electrode group, an electrolytic solution, and a battery container.

  Conventionally, secondary batteries such as lithium batteries make use of the merit of high energy density, and power supplies for portable devices such as VTR cameras, notebook computers, and mobile phones, and stationary power supplies that make use of the merit of high charge acceptance. Widely used in etc. On the other hand, in the automobile industry, in order to cope with environmental problems, development of electric vehicles (PEV) using only a battery as a power source and hybrid electric vehicles (HEV) using both an internal combustion engine and a battery as power sources Has been accelerated and some have been put to practical use.

  A battery module is used as a power source for PEV and HEV. The battery module is configured by connecting a large number (for example, 40 to 100) of single cells in series or in series and parallel. A secondary battery (single cell) used in a battery module generally has a cylindrical shape (cylindrical shape), and infiltrates an electrode group and an electrode group obtained by winding a positive electrode and a negative electrode through a separator. A sealed structure is adopted in which the electrolytic solution to be stored in a cylindrical battery container.

  In this type of secondary battery, in order to improve vibration resistance, the winding center of the electrode group is not an air core, and the electrode group is wound with a positive electrode, a negative electrode, and a separator around a hollow cylindrical core. Yes. Moreover, in order to ensure a large current charging / discharging, a special device is given to the current collection structure. That is, a number of tabs are formed on one side along the longitudinal direction of the positive electrode and the negative electrode, and the positive and negative electrodes are wound through the separator with the lead-out directions of the positive and negative electrode tabs opposite to each other. A positive current collecting ring is disposed at a position opposite to the side end face, and a negative current collecting ring is disposed at a position opposite to the other side end face of the electrode group, and the tips of the positive and negative electrode tabs are arranged on the outer peripheral surface of the positive and negative current collecting rings, respectively. For example, it joins by ultrasonic welding etc. (for example, refer patent documents 1 and 2).

  By the way, when the above-described battery module is configured by using a cylindrical secondary battery as a single battery, a dead space is formed between the peripheral surfaces of each secondary battery, so that the volume efficiency (energy density) is inferior. Therefore, recently, a flat secondary battery in which a flat electrode group is made to be an electrolyte and accommodated in a flat battery container has been proposed. Compared to a cylindrical secondary battery, a flat secondary battery has a flat surface that can be stacked and disposed, so that it has excellent volume efficiency and a larger surface area than a cylindrical secondary battery of the same volume. Therefore, it has the secondary advantage of being excellent in heat dissipation performance. In such a flat secondary battery, a flat positive / negative current collecting ring is generally used.

Japanese Patent Application No. 10-119707 Japanese Patent Application No. 10-119709

  However, in the conventional flat secondary battery, since the flat positive and negative current collecting rings are respectively arranged at positions facing both side end faces of the flat electrode group, the height of the positive and negative current collecting rings is the same. The length in the direction (longitudinal direction) intersecting the core of the secondary battery is increased, and there is room for improvement in further improving the volume efficiency.

  An object of the present invention is to provide a flat secondary battery excellent in volumetric efficiency in view of the above case.

  In order to solve the above problems, the present invention provides a flat secondary battery, wherein the positive electrode having a tab on one side along the longitudinal direction and the negative electrode having a tab on one side along the longitudinal direction are the positive and negative electrodes. The flat electrode group wound around the core through a separator with the lead-out directions of the tabs opposite to each other, and a flat plate shape fixed to the core and joined to the positive electrode tab A positive electrode current collecting member, a flat plate negative electrode current collecting member fixed to the core opposite to the positive electrode current collecting member and having the negative electrode tab joined thereto, and an electrolyte solution infiltrating the electrode group; And a flat battery container that accommodates each of the above members.

  In the present invention, the positive and negative electrode current collecting members preferably have a bent portion that is cut and bent, and the bent portion is preferably fixed to the core. In this case, the core may have a flat hollow shape, and the bent portions may be formed at a plurality of locations in the direction along the longitudinal direction of the positive and negative electrode current collecting members or in the width direction intersecting the longitudinal direction. Further, the bent portion is rectangular and may be fitted to the end of the core. At this time, in consideration of vibration resistance, the core preferably has a channel-shaped reinforcing portion. The tabs of the positive and negative electrodes may be respectively joined to the surfaces of the positive and negative electrode current collector members facing the electrode group.

  In the present invention, for example, the following two aspects may be adopted: That is, the tabs on the positive and negative electrodes are separated from the tabs on one side or the other side of the core and are not cut off. A mode in which tabs existing on one side or one surface side are respectively joined to the positive and negative electrode current collecting members, and tabs on the positive and negative electrodes are tabs on one side or the other side of the core. It is possible to adopt a mode in which the tabs existing on the side or one side are overlapped and joined to the positive and negative current collecting members, respectively. In the latter aspect, it is preferable that a space for leading out the tab existing on one side or the other side of the core to the other side or one side of the core is formed. For example, the space may be formed by cutting off both end portions of the core, or may be formed by bending the positive and negative current collecting members.

  According to the present invention, a structure in which the positive and negative current collecting members are configured in a flat plate shape and fixed to the core is adopted, and a structure in which the tabs of the positive and negative electrodes are respectively joined to the flat positive and negative current collecting members is adopted. Therefore, it is possible to obtain an effect that the length in the longitudinal direction of the flat secondary battery is shortened and the volume efficiency can be improved.

  Hereinafter, an embodiment in which a flat secondary battery according to the present invention is applied to a lithium ion secondary battery will be described with reference to the drawings.

<Positive electrode plate>
A lithium transition metal oxide such as lithium manganate as a positive electrode active material, carbon powder as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed at a mass ratio of 90: 2: 8, for example. Then, a positive electrode slurry in which N-methyl-2-pyrrolidone (MNP) as a dispersion solvent is added and kneaded is prepared. The produced slurry is applied to both sides of a 20 μm thick aluminum alloy foil (positive electrode current collector) substantially uniformly and uniformly, and an uncoated portion is provided on one side along the longitudinal direction of the aluminum alloy foil. Form. In the present embodiment, the length in the width direction intersecting the longitudinal direction of the aluminum alloy foil is 86 mm, and the width of the uncoated part is 25 mm.

  Next, the aluminum alloy foil coated with the positive electrode slurry is dried and pressed. Further, the uncoated portion is cut out (cut) into a comb shape, thereby forming a hoop-shaped positive plate with the remaining portion of the cutout as a positive electrode tab (see reference numeral 2 in FIG. 3). In this embodiment, the dimensions of the positive electrode tab were set to a width (length in the longitudinal direction) of 5 mm and a length (length in a direction intersecting the longitudinal direction) of 25 mm at intervals of 30 mm in the longitudinal direction of the aluminum alloy foil.

<Negative electrode plate>
Carbon particles as a negative electrode active material and PVDF as a binder are mixed at a mass ratio of 90:10, for example, and a dispersion solvent MNP is added thereto and kneaded to prepare a negative electrode slurry. The prepared slurry is applied to both sides of a rolled copper foil (negative electrode current collector) having a thickness of 10 μm substantially uniformly and uniformly, and an uncoated portion is provided on one side along the longitudinal direction of the rolled copper foil. Form. In the present embodiment, the length in the width direction intersecting with the longitudinal direction of the rolled copper foil is 88 mm, and the width of the uncoated part is 25 mm.

  Next, as in the case of the positive electrode plate, the rolled copper foil coated with the negative electrode slurry is dried and pressed. Further, the uncoated portion is cut out (cut) into a comb shape to produce a hoop-shaped negative electrode plate with the remaining portion of the cutout as a negative electrode tab. In this embodiment, the dimension of the negative electrode tab was set to a width (length in the longitudinal direction) of 5 mm and a length (length in a direction intersecting the longitudinal direction) of 25 mm at intervals of 30 mm in the longitudinal direction of the rolled copper foil.

<Turn-up group>
As shown in FIG. 2 and FIG. 3, the positive and negative electrode plates prepared above are wound around a core 1 through a separator to produce a wound group 3. As shown in FIG. 2, the core 1 has a hollow flat shape, and no slack is produced when the positive and negative electrode plates are wound by the two channel-shaped reinforcing ribs 16 via the separator. It is reinforced (so that the shape can be maintained). For the core 1, for example, a material such as polypropylene can be selected, and glass fiber or the like may be mixed to increase the strength.

  The winding group 3 is produced using a winding machine. FIG. 2 schematically shows the main part (central part) of the winding machine. Both ends of the core 1 are attached to the rotating shaft of the winding machine (projections that engage with the recess 15 of the core 1 are formed on the rotating shaft), and then a porous polyethylene having a thickness of 25 μm. Two separators 6 are supplied from a polyethylene supply section that is wound in a hoop shape, and the front ends of the two separators 6 are fused to the flat portion of the core 1 by a heater front end (not shown) (see FIG. 2). ). After the separator 6 is fused, the winding shaft is rotated in the arrow direction (clockwise direction) in FIG. 2 by a driving force (not shown). After the two separators 6 are wound around the separator 2-3 by the winding machine, the supply and winding of the hoop-shaped negative electrode plate 5 are started from the negative electrode plate supply unit, and then the hoop-shaped from the positive electrode plate supply unit Supply and winding of the positive electrode plate 7 are started. At this time, the positive electrode tab of the positive electrode plate 7 and the negative electrode tab of the negative electrode plate 5 are wound (arranged) with the lead-out directions opposite to each other.

  When the positive electrode plate 7 having a predetermined length is wound around the core 1, the hoop-like positive electrode plate 7 is cut by a cutter (not shown), and then the negative electrode plate 5 having a predetermined length is wound around the core 1. When turned, the hoop-like negative electrode plate 5 is cut by a cutter (not shown). The two separators 6 are still wound around the peripheral core 1 for 2 to 3 times after the winding of the negative electrode plate 5 to the core 1, and are cut by a cutter (not shown) when a predetermined length is reached. . Then, as shown in FIG. 3, the winding tape 3 for preventing the unwinding of the separator 6 at the outermost peripheral portion is stuck to the central portion about one turn, and the wound group 3 is produced. Accordingly, in the winding group 3, the positive electrode plate 7 having a positive electrode tab on one side along the longitudinal direction and the negative electrode plate 5 having a negative electrode tab on one side along the longitudinal direction are opposite to each other in the direction in which the positive and negative electrode tabs are led out. As a flat shape wound around the core 1 through the separator 6. Note that a large number of substantially the same number of tabs are led out on both sides of the core 1 of the winding group 3, but in FIG. It is abbreviated.

<Secondary battery>
As shown in FIG. 1, flat positive electrode current collector plates 8 and negative electrode current collector plates are fixed to the wound group 3 at positions facing both end faces of the wound group 3 (see also FIG. 5). ). In the present embodiment, the positive electrode current collector plate 8 is disposed on the side (upper side) shown in FIG. 1, and the negative electrode current collector plate is disposed on the lower side (not shown). The positive and negative current collector plates have legs 14 formed by cutting and bending. That is, the leg portion 14 is formed by cutting out a rectangular shape so as to leave two locations along the longitudinal direction of each of the positive and negative electrode current collector plates, and bending the two notch remaining portions by about 90 °. Yes.

  The leg portions 14 are fixed so that the positive and negative electrode plates are close to the core 1 by being fitted into recesses 15 formed so as to be partitioned by reinforcing ribs 16 on the end side of the core 1. ing. As will be described later, the positive and negative electrode tabs led out from the positive and negative electrode plates are joined to the positive and negative electrode current collector plates by ultrasonic welding on the surfaces facing each other from the winding group 3. A positive electrode terminal 9 serving as an external terminal is welded to the positive electrode current collector plate. Similarly, a negative electrode terminal serving as an external terminal is also welded to the negative electrode current collector plate (see FIG. 5).

  The outer periphery of the winding group 3 is provided with an insulating coating (not shown) for ensuring insulation from the inner peripheral surface of the battery container over the entire periphery including the outer periphery of the peripheral portion of the positive and negative current collector plates. The For the insulation coating, for example, a pressure-sensitive adhesive tape in which a hexamethacrylate pressure-sensitive adhesive is applied to one surface of a polyimide base material is used, and the pressure-sensitive adhesive tape is wound around the wound group 3 one or more times.

  The wound group 3 is housed in a fixed state in a battery container 11 made of flat aluminum with a bottom. That is, the negative electrode terminal is fixed to the battery container 11 through the packing (see FIG. 5), and similarly, the aluminum alloy battery cover having the positive electrode terminal 9 fixed through the packing 10 is joined to the battery container 11 by welding. Thus, the lithium-ion secondary battery 20 having a sealed structure is produced. The battery lid includes a plug (not shown) that seals the electrolyte injection port and a cleavage valve (not shown) that cleaves at a predetermined internal pressure.

A predetermined amount of non-aqueous electrolyte (not shown) capable of infiltrating the entire wound group 3 is injected into the battery container 11 through the above-described electrolyte injection port. Examples of the non-aqueous electrolyte include lithium hexafluorophosphate (lithium hexafluoride phosphate as a lithium salt in a solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed at a ratio of 1: 1: 1. LiPF ₆₎ it can be used those were dissolved 1 mol / liter. The lithium ion secondary battery 20 of the present embodiment has a flat shape with an outer dimension excluding positive and negative terminals of 98 mm width, 105 mm length, and 24 mm thickness, and a capacity during 1C discharge is 12 Ah.

  In addition, since the lithium ion secondary battery 20 of the present embodiment is a large capacity large battery, the lithium ion secondary battery 20 is electrically operated in response to an increase in battery temperature as used in a small consumer lithium ion secondary battery. For example, there is no PTC (Positive Temperature Coefficient) element or a current interrupt mechanism that cuts the positive or negative electrical lead as the battery internal pressure increases.

  Next, the lithium ion secondary battery 20 of the Example produced according to the said embodiment is demonstrated. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

Example 1
As shown in FIG. 4, in the battery of Example 1, all the positive and negative electrode tabs located on one flat surface side of the core 1 are cut and removed, and only the positive and negative electrode tabs located on the other flat surface side are respectively positive and negative electrodes. A battery was fabricated by bonding to a current collector plate. As shown in FIG. 1, the leg portion 14 provided so as to protrude downward from the positive electrode current collector plate 8 by bending is structured to be fitted (fitted) to the concave portion 15 of the core 1. By fixing 9 to the battery container 11 via the packing 10 (the same applies to the negative electrode side), the wound group 3 could be indirectly supported and fixed, and practically sufficient vibration resistance was obtained.

(Example 2)
A battery used for power assist such as a hybrid electric vehicle is required to charge and discharge a large current up to approximately 10 C. Therefore, the battery of Example 1 has a high internal resistance, so that sufficient performance cannot be obtained. For this reason, in the battery of Example 2, as shown in FIGS. 5 to 7, a core 1a having a notch 12 at the center of both ends was used (see FIG. 6). As a result, a gap 13 (space) is formed between the core 1a and the positive electrode current collector plate 8 (see FIG. 5). The side surface side tab and the other surface side tab were overlapped and joined to the positive electrode current collector plate 8 (see FIG. 7). The same applies to the negative electrode side.

(Example 3)
In the battery of Example 3, in order to form the gap 13 between the core 1 and the positive electrode current collector plate, the positive electrode current collector plate was bent into a cross-sectional hat shape as shown in FIG. In this case, the positive electrode current collector plate 8a having a step due to the rising portion and the falling portion was used. In this case, unlike Example 2, it is not necessary to form a notch in the core. Similar to the battery of Example 2, a gap 13 is formed between the core 1 and the positive electrode current collector plate 8, so that the tab located on the one surface side of the core 1 is passed through the gap 13. It was bent to the surface portion side, and the tab on the one surface portion side and the tab on the other surface portion side were overlapped and joined to the positive electrode current collector plate 8. The same applies to the negative electrode side.

(Comparative example)
As a battery of a comparative example, a cylindrical lithium ion secondary battery having the same capacity was manufactured using the electrode of the embodiment with the structure disclosed in Patent Document 2 described above. The battery of the comparative example has a battery container with an outer dimension of 55 mm and a length of 110 mm.

(Examination and evaluation)
For the batteries of Examples and Comparative Examples, the voltage at the 10th second when discharged at 5C and 10C was measured. The measured 10 second voltage and the volume of the battery container (including the battery lid) excluding the external terminal part are shown in Table 1 below.

  The battery of Example 1 has a discharge voltage lower than that of the battery of the comparative example, and the difference at the time of 10C discharge is large. It is advantageous and can be used sufficiently particularly in applications that do not require charging / discharging with a large current. On the other hand, the batteries of Examples 2 and 3 have the same voltage as the cylindrical battery of the comparative example and are flat, and thus have a small volume.

(Effects etc.)
Next, functions and effects of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the lithium ion secondary battery 20 of the present embodiment, a structure in which a flat plate-like positive and negative electrode current collecting member is fixed to the core 1 and a structure in which positive and negative electrode tabs are respectively joined to the positive and negative electrode current collecting members are adopted. Therefore, the length in the longitudinal direction (the axial direction of the core 1) in the flat secondary battery is shortened, and the volume efficiency can be improved.

  At that time, in the battery of Example 1, a structure was adopted in which all the tabs located on the one plane part side of the core 1 were cut and removed, and the tip part of the tab located on the other plane part was joined to the current collector plate. Because it has the same current collecting ability and has the same volume efficiency as the cylindrical battery, there is no change, so it is easy to manufacture and cost-effective as a power source for applications that do not require a large current (for example, for stationary use). Is also advantageous. On the other hand, in the high-current charge / discharge application such as a hybrid electric vehicle, the embodiments shown in Examples 2 and 3 are preferable, but the tip of the tab disposed on the one surface side of the core 1 is a flat current collector plate. When joined, the current collector plate is restrained by the joined tab, so even if you try to join the tip of the tab located on the other surface side to the current collector plate, contact the ultrasonic jig to the part you want to join There is a problem that is difficult. At this time, if the tab is sufficiently long, the current collecting plate still moves to some extent even after the tip of the tab located on the one surface side of the core 1 is joined to the current collecting plate. It is easy to join the tip of the tab to the current collector.

  Moreover, in the lithium ion secondary battery 20 of this embodiment, since it is flat and the surface area of a battery container is larger than a cylindrical battery, better heat dissipation is obtained than a cylindrical battery, and it can endure a heavy load. .

  In the present embodiment, the lithium ion secondary battery 20 is exemplified, but the present invention is not limited to this, and it is awaited that the present invention can be applied to other secondary batteries such as a nickel metal hydride battery and a nickel cadmium battery. Absent. In the present embodiment, the positive terminal is disposed on the upper side, the negative terminal is disposed on the lower side, and the battery case 11 is neutral. However, the present invention is not limited thereto. That is, any of the positive and negative electrode terminals may be on the upper side (lower side), and the battery container may have either a positive or negative polarity.

  Further, in the present embodiment, the active material mixture (slurry) of the positive and negative electrode plates, the constituent material of the non-aqueous electrolyte, and the material of other constituent members are exemplified, but it goes without saying that the present invention is not limited thereto. . That is, a so-called person skilled in the art can appropriately select constituent materials and materials in the scope of the above-mentioned claims, and it is a matter of course that such a mode also belongs to the scope of the claims of the present invention.

  Furthermore, in this embodiment, although the example which forms the leg part 14 in two places along the longitudinal direction of a current collector plate was shown, this invention is not restricted to this, For example, it may be made to form three or more places. Alternatively, the leg portion may be formed on the side crossing the longitudinal direction of the current collector plate. Moreover, in this embodiment, as shown in FIG. 5, the example which provided the external terminal in the same side (right side of FIG. 5) of the battery container 11 was shown, but this invention is not limited to this, For example, a positive electrode The terminal 9 may be arranged on the right side as shown in FIG. 5 and the negative terminal may be arranged on the left side in FIG. 5 (so as to be symmetrical with the positive electrode terminal 9 with respect to the wound group 3). Furthermore, in the aspect of Example 1, the tabs cut and removed by the positive and negative electrode tabs may be different in the tabs existing on the one plane portion side and the other plane portion side of the core 1 (the opposite sides are cut and removed). You may do it.)

  The present invention aims to provide a secondary battery excellent in volumetric efficiency, and thus contributes to the manufacture and sale of flat secondary batteries, and thus has industrial applicability.

It is a front sectional view near the upper part of a lithium ion secondary battery of an embodiment to which the present invention is applicable. It is sectional drawing which shows typically the principal part of the winding machine which produces the winding group of the lithium ion secondary battery of embodiment. It is an external appearance perspective view of the winding group of the lithium ion secondary battery of embodiment produced with the winding machine. FIG. 3 is an enlarged side cross-sectional view in the vicinity of a positive electrode current collector plate of a battery of Example 1. 3 is a front sectional view of a battery of Example 2. FIG. It is an external appearance perspective view of the winding group of the battery of Example 2 produced with the winding machine. 6 is an enlarged side cross-sectional view of the vicinity of a positive electrode current collector plate of a battery of Example 2. FIG. 6 is a front sectional view of the vicinity of the upper part of the battery of Example 3. FIG.

Explanation of symbols

1, 1a Core 2 Positive electrode tab (tab)
3 Winding group (electrode group)
5 Negative electrode plate (negative electrode)
6 Separator 7 Positive electrode plate (positive electrode)
8, 8a Positive current collector (current collector)
11 Battery container 13 Crevice (space)
14 Leg (bent)
15 Recess (end)
16 Reinforcement rib (reinforcement part)
20 Lithium ion secondary battery (flat secondary battery)

Claims (11)

A positive electrode having a tab on one side along the longitudinal direction and a negative electrode having a tab on one side along the longitudinal direction are wound around the core via a separator with the lead-out directions of the tabs of the positive and negative electrodes opposite to each other. A flat electrode group,
A plate-like positive electrode current collector member fixed to the core and joined with the positive electrode tab;
A negative electrode current collecting member having a flat plate shape, which is fixed to the core opposite to the positive electrode current collecting member, and to which the tab of the negative electrode is joined;
An electrolyte solution infiltrating the electrode group;
A flat battery container for housing each member;
A flat secondary battery comprising:   2. The flat secondary battery according to claim 1, wherein the positive and negative electrode current collecting member has a bent portion cut and bent, and the bent portion is fixed to the core.   The said core is a flat hollow shape, The said bending part was formed in each of several places of the width direction which cross | intersects the longitudinal direction of the said positive / negative electrode current collection member, or a longitudinal direction. A flat secondary battery according to claim 1.   The flat secondary battery according to claim 2 or 3, wherein the bent portion has a rectangular shape and is fitted to an end portion of the core.   The flat secondary battery according to claim 4, wherein the core has a channel-shaped reinforcing portion.   3. The flat secondary battery according to claim 1, wherein the tabs of the positive and negative electrodes are respectively joined to surfaces of the positive and negative electrode current collecting members facing the electrode group.   The tabs on the positive and negative electrodes are cut and removed on one side or the other side of the core, and the tabs on the other side or one side that are not cut and removed are joined to the positive and negative current collecting members, respectively. The flat secondary battery according to any one of claims 1 to 6, wherein   The positive and negative electrode tabs are joined to the positive and negative electrode current collecting members by overlapping tabs existing on one side or the other side of the core with tabs existing on the other side or the other side of the core. The flat secondary battery according to any one of claims 1 to 6, wherein:   The flat secondary according to claim 8, wherein a space for leading a tab existing on one side or the other side of the core to the other side or one side of the core is formed. battery.   The flat secondary battery according to claim 9, wherein the space is formed by cutting out both end portions of the core.   The flat secondary battery according to claim 9, wherein the space is formed by bending the positive and negative current collecting members.

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