METHOD FOR PRODUCING AN ELECTRODE SEPARATOR WINDING, ELECTRODE SEPARATOR WINDING AND BUTTON CELL WITH SUCH A WINDING

Description

[0001] The invention described below relates to a method for producing an electrode-separator coil with the sequence first current collector / separator / second current collector / separator or second current collector / separator / first current collector / separator, an electrode-separator coil produced according to the method and a button cell with this coil.

[0002] Button cells usually have a cylindrical casing whose height is equal to or smaller than its diameter. The casing can contain very different electrochemical systems. Cells based on zinc / air, zinc / MnO2, and nickel / zinc are very common. Secondary (rechargeable) systems are also very common. Examples include nickel / metal hydride cells, nickel / cadmium cells, and lithium-ion cells.

[0003] The casing of button cells typically consists of two solid, usually metallic, parts with an electrically insulating seal between them. One of the parts is electrically connected to the positive electrode and is therefore positively polarized. The other is electrically connected to the negative electrode and is therefore negatively polarized. The seal is designed to prevent electrical contact between the oppositely polarized parts. Furthermore, it is designed to prevent the escape of liquid or moisture from or into the casing.

[0004] Lithium-ion cells can achieve very high energy densities. Lithium-ion cells sometimes contain a composite body in the form of a cell stack consisting of several individual cells. However, most cells contain a wound composite body (or wound composite body for short), which is usually a single cell in wound form.

[0005] Button cells with wound composites based on lithium-ion are described, for example, in WO 2010 / 146154 A2 and WO 2010 / 089152 A1. Wound composites are typically manufactured by spirally winding strip-shaped electrodes (abbreviated to electrode strips) and at least one strip-shaped separator (abbreviated to separator strip). The electrode strips and the at least one strip-shaped separator lie flat on top of one another in the wound composite. They are optionally connected to one another, for example, by lamination or adhesive bonding.

[0006] Typically, a wound composite body comprises the sequence positive electrode / separator / negative electrode. Wound composite bodies are often manufactured as so-called bicells with the possible sequences negative electrode / separator / positive electrode / separator / negative electrode or positive electrode / separator / negative electrode / separator / positive electrode.

[0007] The electrodes in wound composite bodies typically comprise a metallic current collector as well as electrochemically active components (often referred to as active materials) and electrochemically inactive components.

[0008] The current collectors serve to electrically contact the electrochemically active components over as large an area as possible. They typically consist of strip-shaped, flat metal substrates, such as metal foils, metal foam, or a metallized fleece.

[0009] Any material capable of absorbing and releasing lithium ions can be considered as active materials for secondary lithium-ion systems. The state of the art for the negative electrode of secondary lithium-ion systems is particularly carbon-based materials such as graphitic carbon or non-graphitic carbon materials capable of intercalating lithium. Lithium metal oxide compounds and lithium metal phosphate compounds such as LiCoO 2 and LiFePO 4 are suitable for the positive electrode of secondary lithium-ion systems.

[0010] Electrochemically inactive components include, first and foremost, electrode binders and conductive materials. Electrode binders ensure the mechanical stability of the electrodes and ensure contact between the particles of electrochemically active material and the current collector. Conductive materials such as carbon black serve to increase the electrical conductivity of the electrodes.

[0011] Tapes made of porous plastic films, such as polyolefin or polyether ketone, are particularly suitable as separators for these composites. Nonwovens and fabrics made of these materials can also be used.

[0012] To produce positive and negative electrodes for wound composite bodies, pastes comprising the respective active materials, an electrode binder, and optionally a conductive agent are typically applied in the form of thin layers to the strip-shaped current collectors, dried, and formed into the desired shape. Typically, the layers are rolled and pressed after drying. With intermittent application, the current collectors are only coated in sections. This results in strip-shaped current collectors that are divided longitudinally into ground sections covered with electrode material and sections arranged in between that are not covered with electrode material. To form individual electrode strips, the current collectors that are only coated in sections can be separated, for example, using a cutting or punching tool, in the area of ​​the sections not covered with electrode material.

[0013] It is fundamentally possible to combine positive and negative electrode strips formed in this way with each other and with one or more separator strips to form a strip-shaped single cell in a first step, for example by laminating the electrodes onto opposite sides of a separator strip, and then to process the strip-shaped single cell into a wound composite body by winding it in a second step.

[0014] However, it is often more advantageous to feed the current collectors, which are only coated in sections, together with one or more separator strips to a winding device and to produce the wound composite body directly from the individual strips in a single step. For this purpose, the strips are usually wound onto a winding mandrel or a winding core, ensuring that ground sections covered with electrode material overlap within the coil. The winding process can be interrupted when a section not covered with electrode material is reached. This section is then severed, whereby the formed wound composite body is separated from subsequent, not yet wound sections of the intermittently coated current collector. The result is a wound composite body with wound electrode strips, each of which has at least one contact section not covered with electrode material.

[0015] The contact sections serve to establish electrical contact between the electrodes and the aforementioned housing parts. Positive electrode strips are electrically connected to one of the two housing parts of a button cell mentioned above, and negative electrode strips are electrically connected to the other of the two housing parts. The housing parts of a button cell usually each have a circular base. In most cases, it is preferable to contact the contact sections with these circular bases.

[0016] From WO 2010 / 146154 A2, it is known to weld a contact strip axially aligned at an angle of 90° to the winding direction to a floating contact section of an electrode of a wound composite body and to place it flat on an end face of the wound composite body by folding it over. Corresponding procedures are described in Figures 2A to 2C and 3A and 3B of WO 2010 / 146154 A2. The conductor can then be welded to the base of a housing part, for example, as shown in Figures 1A and 1B of WO 2010 / 146154 A2. The welding process takes place after the cell has been closed, i.e., from outside the button cell housing.

[0017] Alternatively, terminal contact sections can simply be folded over and welded directly to one of the housing parts. The folded part of the contact section then forms the contact strip itself.

[0018] Problems can arise when separator tapes are in direct contact with the contact strips within the wound composite body. Since the contact strips often have sharp edges and the separator tapes are often only a few µm thick, meaning they can be easily damaged, this can lead to short circuits in extreme cases. The areas of the separator tapes that directly touch the contact strips are exposed to an increased risk in this regard and are therefore referred to below as risk areas. To counteract this risk, it has been proposed, as shown in Figures 2B and 2C of WO 2010 / 146154 A2, to adhere the contact strips with Kapton tapes. This solves the described problem, but at the same time creates a new one. It has been observed that the adhesive of the Kapton tape can have a negative impact on cell performance, presumably caused by water ingress or undesirable side reactions.

[0019] US 2006 / 0051662 A1 discloses an electrode-separator assembly that can be processed into an electrode coil. In addition to two separators, the assembly contains an anode and a cathode, each of which has longitudinal sections that are not coated with active material and in which contact strips are welded. The two separators can be reinforced with a foil in these areas.

[0020] The object of the present invention was to provide a solution to the problems mentioned.

[0021] To achieve this object, the invention proposes a method having the features recited in claim 1, an electrode separator coil having the features of claim 5, and a button cell having the features of claim 6. Further developments of the invention are the subject of subclaims.

[0022] The method according to the invention always comprises the following steps: Feeding a first band-shaped current collector, which is divided longitudinally into ground sections covered with a positive electrode material and contact sections arranged between the ground sections and not covered with the electrode material, to a winding device, feeding a second band-shaped current collector, which is divided longitudinally into ground sections covered with a negative electrode material and contact sections arranged between the ground sections and not covered with the electrode material, to the winding device, feeding two band-shaped separators to the winding device, and winding the first band-shaped current collector, the second band-shaped current collector and the separators in the winding device into a roll with the sequence first current collector / separator / second current collector / separator or second current collector / separator / first current collector / separator.

[0023] The process according to the invention does not differ from prior art processes, neither in terms of the described process steps nor in terms of the materials and objects used. For example, the materials, current collectors, and separators mentioned above are suitable as electrode materials, current collectors, and separators.

[0024] Also as known from the prior art, the invention provides for a contact strip to be welded to at least one of the contact sections for electrically contacting the current collectors, or for at least one of the contact sections to be folded over to form a contact strip for electrically contacting the current collectors. For this purpose, the procedure known from WO 2010 / 146154 A2 can be used, for example.

[0025] On the other hand, the method according to the invention is distinguished from the known prior art by that at least one of the separators is reinforced in at least one risk area in which the at least one separator within the finished electrode separator coil rests on the at least one contact section in which the contact strip is welded, or on the at least one contact section folded over to form a contact strip.

[0026] The term risk area was already explained at the beginning; this is an area of ​​the separator that is exposed to an increased risk of damage due to direct contact with a contact strip, which could result in a short circuit.

[0027] Reinforced separators in the risk area mean that the separator has a greater thickness in the risk area. This can counteract the described short-circuit risk just as effectively as with Kapton tapes. However, the associated disadvantages do not necessarily occur, as will be explained below.

[0028] Particularly preferably, the method is characterized by at least one of the two following features: The first and second current collectors are severed in the region of two contact sections, each forming a terminal contact section, and the separators are each severed, forming a terminal separator section. The electrode-separator coil is completed by winding the terminal contact sections and the terminal separator sections.

[0029] In some particularly preferred embodiments, the method is characterized by one of the following features: To form the contact strip for electrically connecting the current collectors, at least one of the terminal contact sections is folded over. The at least one contact section into which the contact strip is welded is a terminal contact section or a non-terminal contact section arranged between two ground sections.

[0030] In embodiments in which a contact strip is welded in at least one of the contact sections for electrically contacting the current collectors, it is usually preferred that the contact strip is welded at an angle of 45° to 135° to the main extension direction of the band-shaped current collector.

[0031] In embodiments in which at least one of the terminal contact sections is folded over to form a contact strip for electrically contacting the current collectors, it is usually preferred for the at least one terminal contact section to be folded over by folding along a fold line oriented at an angle of 10° to 80° to the main extension direction of the strip-shaped current collector. It then preferably comprises a folded, strip-shaped section and an unfolded section.

[0032] For clarification: The main direction of extension of the band-shaped current collector is the direction in which the current collector has its greatest extension when flatly spread out.

[0033] Preferably, both band-shaped separators are reinforced in the risk areas, not just one of the separators.

[0034] According to the invention, the reinforcements are formed by folding the separators, in particular by a Z-fold.

[0035] The electrode separator winding according to the invention always comprises a first band-shaped current collector which is divided longitudinally into at least one ground section covered with a positive electrode material and at least one contact section not covered with the electrode material, a second band-shaped current collector which is divided longitudinally into at least one ground section covered with a negative electrode material and at least one contact section not covered with the electrode material, and two band-shaped separators where the first band-shaped current collector, the second band-shaped current collector and the separators are wound into a coil with the sequence first current collector / separator / second current collector / separator or second current collector / separator / first current collector / separator, and for electrically contacting the current collectors in at least one of the contact sections a contact strip is welded or to form a contact strip for electrically contacting the current collectors at least one of the contact sections is folded over.

[0036] The electrode separator coil according to the invention can be produced according to the method described above. It is characterized in particular by the fact that at least one of the separators is reinforced by folding in at least one risk area in which the at least one separator within the electrode separator coil rests on the at least one contact section in which the contact strip is welded, or on the at least one contact section folded over to form a contact strip.

[0037] Preferred embodiments of the electrode separator winding emerge from the above description of the method according to the invention, both with regard to the materials and objects used and with regard to the different embodiments of the reinforcement.

[0038] Any button cell comprising the described electrode separator coil, in particular the electrode separator coil that can be produced according to the method according to the invention, is the subject of the present invention.

[0039] The button cell according to the invention can, for example, have a housing as in Fig. 4 WO 2010 / 089152 A1 or as in Fig. 1 of WO 2010 / 146154 A2. The housings each have circular bottoms. The described electrode separator coil is arranged in the housings such that its end faces point toward the circular bottoms, possibly even lying flat against them.

[0040] The welding of the housing parts to the contact strips can be carried out, for example, as shown in Fig. 1A and 1B of WO 2010 / 146154 A2.

[0041] The button cell is preferably sealed using a standard injection-molded or foil seal.

[0042] Further features, details, and advantages of the invention will become apparent from the claims and the abstract, both of which are incorporated by reference into the description, the following description of preferred embodiments of the invention, and the accompanying drawings. These show schematically: Figure 1 illustrates a method variant not according to the invention, in which two separators are reinforced in each risk area by attaching foils that can be welded to the separators. After the completion of the electrode-separator coil, the separators in the risk areas each touch contact sections of current collectors, in which contact strips are welded. The fixation is ensured by welding the foils to the separator; Figure 2illustrates a first embodiment of the method according to the invention, in which two separators are reinforced in each risk area by folding the separators at their ends. After completion of the electrode-separator coil, the separators in the risk areas each touch contact sections of current collectors in which contact strips are welded; Figure 3 illustrates a second embodiment of the method according to the invention, in which two separators are reinforced in each risk area by a Z-fold of the separators. After completion of the electrode-separator coil, the separators in the risk areas each touch contact sections of current collectors in which contact strips are welded; Figure 4illustrates a third embodiment of the method according to the invention, in which two separators are reinforced in each risk area by folding the separators at their ends. After completion of the electrode-separator coil, the separators in the risk areas touch contact sections of current collectors, in which the current collectors are folded over to form contact strips for electrically contacting the current collectors by folding along two fold lines each aligned at an angle of 45° to the main extension direction of the band-shaped current collectors; and Figure 5illustrates a fourth embodiment of the method according to the invention, in which two separators are reinforced in each risk area by a Z-fold of the separators. After completion of the electrode-separator coil, the separators in the risk areas touch contact sections of current collectors, in which the current collectors are folded over to form contact strips for electrically contacting the current collectors by folding along two fold lines, each aligned at an angle of 45° to the main extension direction of the band-shaped current collectors.

[0043] According to the Fig. 1In the method shown, a first band-shaped current collector 101, which is divided longitudinally into ground sections covered with a positive electrode material (sections 101a and 101c) and contact sections arranged between the ground sections and not covered with the electrode material (section 101b), a second band-shaped current collector 102, which is divided longitudinally into ground sections covered with a negative electrode material (sections 102a and 102c) and contact sections arranged between the ground sections and not covered with the electrode material (section 102b), and two band-shaped separators 103 and 104 are processed into an electrode-separator coil 100.

[0044] The two separators 103 and 104 are reinforced in the risk areas 103a and 104a (hatched representation) by foils 105 and 106. The foils 105 and 106 are welded to the separators 103 and 104. In the risk areas 103a and 104a, after completion of the electrode-separator winding, the separators 103 and 104 rest against the contact sections 101b and 102b of the current collectors 101 and 102. Contact strips 107 and 108 are welded to these contact sections 101b and 102b. As a result of the reinforcement, the short circuit risk in the risk areas 103a and 104a can be minimized.

[0045] According to the Fig. 2In the method shown, a first band-shaped current collector 101, which is divided longitudinally into ground sections covered with a positive electrode material (sections 101a and 101c) and contact sections arranged between the ground sections and not covered with the electrode material (section 101b), a second band-shaped current collector 102, which is divided longitudinally into ground sections covered with a negative electrode material (see sections 102a and 102c) and contact sections arranged between the ground sections and not covered with the electrode material (section 102b), and two band-shaped separators 103 and 104 are processed into an electrode-separator coil 100.

[0046] The two separators 103 and 104 are reinforced in the risk areas 103a and 104a (shown hatched) by foils 105 and 106. The foils 105 and 106 are simply folded sections of the separators 103 and 104 at their ends. In the risk areas 103a and 104a, after the completion of the electrode-separator winding, the separators 103 and 104 rest against the contact sections 101b and 102b of the current collectors 101 and 102. Contact strips 107 and 108 are welded into these contact sections 101b and 102b. As a result of the reinforcement, the short circuit risk in the risk areas 103a and 104a can be minimized.

[0047] According to the Fig. 3In the method shown, a first band-shaped current collector 101, which is divided longitudinally into ground sections covered with a positive electrode material (sections 101a and 101c) and contact sections arranged between the ground sections and not covered with the electrode material (section 101b), a second band-shaped current collector 102, which is divided longitudinally into ground sections covered with a negative electrode material (sections 102a and 102c) and contact sections arranged between the ground sections and not covered with the electrode material (section 102b), and two band-shaped separators 103 and 104 are processed into an electrode-separator coil 100.

[0048] The two separators 103 and 104 are reinforced in the risk areas 103a and 104a (shown hatched) by foils 105 and 106. The foils 105 and 106 are Z-folded sections of the separators 103 and 104. In the risk areas 103a and 104a, the separators 103 and 104 are located at the contact sections 101b and 102b of the current collectors after the completion of the electrode-separator winding. The contact strips 107 and 108 are welded to these contact sections 101b and 102b. As a result of the reinforcement, the short-circuit risk in the risk areas 103a and 104a can be minimized.

[0049] According to the Fig. 4In the method shown, a first band-shaped current collector 101, which is divided longitudinally into ground sections covered with a positive electrode material (section 101a and 101c) and contact sections arranged between the ground sections and not covered with the electrode material (section 101b), a second band-shaped current collector 102, which is divided longitudinally into ground sections covered with a negative electrode material (sections 102a and 102c) and contact sections arranged between the ground sections and not covered with the electrode material (section 102b), and two band-shaped separators 103 and 104 are processed into an electrode-separator coil 100.

[0050] The two separators 103 and 104 are reinforced in the risk areas 103a and 104a (shown hatched) by foils 105 and 106. The foils 105 and 106 are simply folded sections of the separators 103 and 104 at the ends. In the risk areas 103a and 104a, the separators 103 and 104 rest against the contact sections 101b and 102b of the current collectors 101 and 102 after the completion of the electrode-separator winding. In these contact sections 101b and 102b, the current collectors 101 and 102 are folded over to form contact strips 107 and 108 for electrically contacting the current collectors 101 and 102, respectively, by folding along two fold lines 109 and 110 aligned at an angle of approximately 45° to the main extension direction of the strip-shaped current collectors 101 and 102. As a result of the reinforcement, the short-circuit risk in the risk areas 103a and 104a can be minimized.

[0051] According to the Fig. 5 In the method shown, a first band-shaped current collector 101, which is divided longitudinally into ground sections covered with a positive electrode material (sections 101a and 101c) and contact sections arranged between the ground sections and not covered with the electrode material (section 101b), a second band-shaped current collector 102, which is divided longitudinally into ground sections covered with a negative electrode material (sections 102a and 102c) and contact sections arranged between the ground sections and not covered with the electrode material (section 102b), and two band-shaped separators 103 and 104 are processed into an electrode-separator coil 100.

[0052] The two separators 103 and 104 are reinforced in the risk areas 103a and 104a (shown hatched) by foils 105 and 106. The foils 105 and 106 are Z-folded sections of the separators 103 and 104. In the risk areas 103a and 104a, the separators 103 and 104 rest against the contact sections 101b and 102b of the current collectors 101 and 102 after the completion of the electrode-separator winding. In these contact sections 101b and 102b, the current collectors 101 and 102 are folded over to form contact strips 107 and 108 for electrically contacting the current collectors 101 and 102, respectively, by folding along two fold lines 109 and 110 aligned at an angle of approximately 45° to the main extension direction of the strip-shaped current collectors 101 and 102. As a result of the reinforcement, the short-circuit risk in the risk areas 103a and 104a can be minimized.

Claims

1. Method for producing an electrode-separator winding (100), comprising the steps of 1.1 feeding a first current collector in strip form (101), which is divided in the longitudinal direction into mass sections (101a and 101c) covered with a positive electrode material and, arranged between the mass sections (101a and 101c), contact sections (101b) not covered with the electrode material, to a winding device, 1.2 feeding a second current collector in strip form (102), which is divided in the longitudinal direction into mass sections (102a and 102c) covered with a negative electrode material and, arranged between the mass sections (102a and 102c), contact sections (102b) not covered with the electrode material, to the winding device, 1.3 feeding two separators in strip form (103 and 104) to the winding device, 1.4 winding up the first current collector in strip form (101), the second current collector in strip form (102) and the separators (103 and 104) in the winding device to form a winding with the sequence first current collector (101) / separator (103) / second current collector (102) / separator (104) or second current collector (102) / separator (103) / first current collector (101) / separator (104), wherein 1.5 a contact strip (107, 108) is welded on in at least one of the contact sections (101b and 102b) for the electrical contacting of the current collectors (101 and 102), or at least one of the contact sections (101b and 102b) is folded over to form a contact strip (107, 108) for the electrical contacting of the current collectors (101 and 102), characterized in that 1.6 at least one of the separators (103 and 104) is reinforced in at least one risk region (103a, 104a) in which the at least one separator (103 and 104) within the completed electrode-separator winding lies against the at least one contact section (101b and 102b) in which the contact strip (107, 108) is welded on or against the at least one contact section (101b and 102b) folded over to form a contact strip (107, 108), wherein the reinforcement is formed by a folding of the separator.

2. Method according to Claim 1, with the following additional steps 2.1 the first current collector (101) and second current collector (102) are cut through in the region of two contact sections (101b and 102b), in each case forming a contact section at the end, and the separators (103 and 104) are cut through, in each case forming a separator section at the end; 2.2 the electrode-separator winding (100) is completed by winding up the contact sections at the ends and the separator sections at the ends.

3. Method according to Claim 2, with the additional step that 3.1 to form the contact strip (107, 108) for the electrical contacting of the current collectors (101 and 102), at least one of the contact sections at the ends is folded over.

4. Method according to one of the preceding claims, with the additional step that 4.1 the reinforcements are formed by a Z-folding of the separators (103 and 104).

5. Electrode-separator winding (100), comprising 5.1 a first current collector in strip form (101), which is divided in the longitudinal direction into at least one mass section (101a and 101c) covered with a positive electrode material and at least one contact section (101b) not covered with the electrode material, 5.2 a second current collector in strip form (102), which is divided in the longitudinal direction into at least one mass section (102a and 102c) covered with a negative electrode material and at least one contact section (102b) not covered with the electrode material, 5.3 two separators in strip form (103 and 104) wherein 5.4 the first current collector in strip form (101), the second current collector in strip form (102) and the separators (103 and 104) are wound up to form a winding with the sequence first current collector (101) / separator (103) / second current collector (102) / separator (104) or second current collector (102) / separator (103) / first current collector (101) / separator (104), 5.5 a contact strip (107, 108) is welded on in at least one of the contact sections (101b and 102b) for the electrical contacting of the current collectors (101 and 102), or at least one of the contact sections (101b and 102b) is folded over to form a contact strip (107, 108) for the electrical contacting of the current collectors (101 and 102), characterized in that 5.6 at least one of the separators (103 and 104) is reinforced in at least one risk region (103a, 104a) in which the at least one separator (103 and 104) within the electrode-separator winding lies against the at least one contact section (101b and 102b) in which the contact strip (107, 108) is welded on or against the at least one contact section (101b and 102b) folded over to form a contact strip (107, 108), wherein the reinforcement is formed by a folding of the separator.

6. Button cell, comprising an electrode-separator winding (100) according to Claim 5.