Method and apparatus for annealing exposed metal edge margins of battery electrodes

Abstract

A method of annealing exposed metal edge margins of a coated battery electrode strip to relieve stress and reduce wrinkles includes applying a magnetic field to the exposed metal edge margins through a porous magnetic shield. The magnetic field induces an eddy current that heats the exposed metal edge margin to an annealing temperature while the magnetic shield blocks the magnetic field from approaching the coating to protect it from overheating. An apparatus for annealing exposed metal edge margins of a coated battery electrode strip includes a magnetic field source and a porous magnetic shield. In an alternative embodiment, the apparatus includes a laser for heating the exposed metal edge margin without overheating the coating.

Description

[0001] introduction

[0002] The information provided in this section is for the purpose of generally presenting the background of the present disclosure. To the extent described in this section, the work of the presently named inventors, and aspects that may not qualify as prior art at the time of filing, are neither explicitly nor implicitly admitted to be prior art to the present disclosure. Technical Field

[0003] The present disclosure relates to the manufacture of battery electrodes, and more particularly to methods and apparatus for annealing exposed metal edges of battery electrodes. Background Art

[0004] It is common practice in manufacturing battery electrodes to anneal the uncoated edges of the electrode strips prior to calendaring the electrode coating. This annealing can remove residual stresses and / or help prevent edge wrinkling. Typical annealing temperatures are between 200 and 300°C. A problem with currently available annealing techniques is the potential for inadvertent heating of the coated sections of the electrode, which can have a negative impact on battery cell performance. This is particularly true in cases where the melting point of the binder used for the coating is below the annealing temperature, which is often the case. Summary of the invention

[0005] Generally speaking, embodiments of the present disclosure provide methods of annealing the exposed edge margins of electrode strips after the electrode strips have been coated with electrode materials, and preferably after those coatings have been calendered.

[0006] According to a first embodiment of the present disclosure, a magnetic field is applied to the exposed metal edge margin of a coated battery electrode strip through a perforated magnetic shield to induce eddy currents in the metal edge margin to heat the exposed metal edge margin to a desired annealing temperature range. The perforated shield blocks the application of the magnetic field close enough to the edge of the coating material to avoid exceeding a temperature that is harmful to the coating on the electrode strip. The electrode strip is preferably moved past a magnetic field source and a perforated shield, and the source and shield are spaced and positioned so that heating of the exposed edge margin does not excessively heat the coating material on the substrate.

[0007] The present disclosure provides the following technical solutions:

[0008] 1. A method of annealing the exposed metal edge margin of a coated battery electrode strip to relieve stress and reduce wrinkling, the method comprising:

[0009] A magnetic field is applied to the exposed metal edge margin of the coated battery electrode strip through a perforated magnetic shield to induce eddy currents in the exposed metal edge margin to heat the exposed metal edge margin to a desired annealing temperature, the perforated magnetic shield blocking the application of the magnetic field close enough to the edge of the coating on the electrode strip to reach a temperature that is harmful to the coating.

[0010] 2. The method according to technical solution 1, wherein the step of applying a magnetic field to the exposed metal edge margin of the coated battery electrode strip through a perforated magnetic shield includes moving the exposed metal edge margin of the coated battery electrode strip through the magnetic field.

[0011] 3. The method according to technical solution 1, wherein the step of applying a magnetic field to the exposed metal edge margin of the coated battery electrode strip through a perforated magnetic shield, wherein the magnetic field is applied using an electromagnetic coil.

[0012] 4. The method according to technical solution 3, wherein the step of applying a magnetic field to the exposed metal edge margin of the coated battery electrode strip through a perforated magnetic shield includes moving the exposed metal edge margin of the coated battery electrode strip through the magnetic field.

[0013] 5. The method according to technical solution 1, wherein the perforated magnetic shield comprises multiple layers of material.

[0014] 6. The method according to technical solution 1, wherein the perforated magnetic shield includes at least one of copper, silver, brass, titanium, tungsten and lead.

[0015] 7. The method according to technical solution 1, wherein the perforated magnetic shield comprises at least one of steel and stainless steel.

[0016] 8. The method according to technical solution 1, wherein the perforated magnetic shielding member comprises at least one of a ferromagnetic alloy, a Permalloy, or a high-permeability magnetic alloy.

[0017] 9. The method according to technical solution 1, wherein the porous magnetic shielding member comprises a metal mesh.

[0018] 10. The method according to technical solution 1, wherein the porous magnetic shielding member comprises metal foam.

[0019] 11. A method according to technical solution 1, wherein the perforated magnetic shield has an inner side oriented toward the electrode coating and an outer side oriented toward the edge of the exposed metal edge margin, and wherein the inner side of the hole has a straight edge extending parallel to the edge of the electrode coating.

[0020] 12. The method according to technical solution 11, wherein the hole widens toward the outside of the perforated magnetic shield.

[0021] 13. The method according to technical solution 1, wherein, during the application of the magnetic field, the electrode strip moves in a direction parallel to the edge of the strip.

[0022] 14. An apparatus for annealing exposed metal edge margins of coated battery electrode strips to relieve stress and reduce wrinkling, the apparatus comprising:

[0023] A magnetic field source, and a perforated magnetic shield disposed between the magnetic field source and the exposed metal edge remainder of the coated battery electrode strip, the magnetic shield allowing a magnetic field to pass through the holes to apply the magnetic field to the exposed metal edge remainder of the coated battery electrode strip, thereby inducing eddy currents in the exposed metal edge remainder to heat the exposed metal edge remainder to a desired annealing temperature and blocking the application of a magnetic field close enough to a coating on the battery electrode strip to cause the coating to reach a temperature that is harmful to the coating.

[0024] 15. An apparatus for annealing exposed metal edge margins of coated battery electrode strips according to technical solution 14, wherein the magnetic field source is an electromagnetic coil.

[0025] 16. An apparatus for annealing exposed metal edge margins of coated battery electrode strips according to technical solution 15, wherein the perforated magnetic shield comprises multiple layers of material.

[0026] 17. An apparatus for annealing exposed metal edge margins of coated battery electrode strips according to technical solution 16, wherein the perforated magnetic shield comprises at least one of copper, silver, brass, titanium, tungsten and lead.

[0027] 18. An apparatus for annealing the exposed metal edge margin of a coated battery electrode strip according to Technical Solution 16, wherein the perforated magnetic shield has an inner side oriented toward the coating of the strip battery electrode strip, and an outer side oriented toward the edge of the exposed metal edge margin, and wherein the inner side of the hole has a straight edge extending parallel to the edge of the coating on the battery electrode strip.

[0028] 19. An apparatus for annealing exposed metal edge margins of coated battery electrode strips according to solution 18, wherein the holes in the magnetic shield widen toward the outside of the perforated magnetic shield.

[0029] 20. A method of annealing the exposed metal edge margin of a coated battery electrode strip to relieve stress and reduce wrinkling, the method comprising:

[0030] The laser is applied to the exposed metal edge margin of the coated battery electrode strip at a location sufficient to heat the exposed metal edge margin to a desired annealing temperature, but sufficiently spaced from the edge of the coating on the electrode strip so that the coating does not reach a temperature that is detrimental to the coating.

[0031] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings.The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0033] Figure 1 is a side elevation view showing an electromagnet applying a magnetic field to the exposed metal edge margin of a battery electrode;

[0034] Figure 2 is a top view of a battery electrode strip showing the exposed metal edge margin and a layer of rolled electrode material;

[0035] Figure 3 is a side elevation view showing an electromagnet applying a magnetic field through a shield to an exposed metal edge margin of a battery electrode;

[0036] Figure 4 is a top plan view of a battery electrode strip showing an exposed metal edge margin with a magnetic field application area, and a layer of calendared electrode material;

[0037] Figure 5A is a top plan view of a magnetic shield having a circular hole;

[0038] Figure 5B is a top plan view of a magnetic shield having a semicircular or "D" shaped aperture;

[0039] Figure 5C is a top plan view of a magnetic shield having a rectangular hole;

[0040] Figure 5D is a top plan view of a magnetic shield having a trapezoidal hole that is wider at one side than the other;

[0041] Figure 6 is a side elevation view showing an electromagnet applying a magnetic field through a shield to the top and bottom surfaces of an exposed metal edge margin of a battery electrode;

[0042] Fig. 7A is an enlarged view of the electrode material applied to the surface of the battery electrode;

[0043] Figure 7B is an enlarged view of electrode material applied to the surface of a battery electrode after exposure to a substrate temperature of 220°C;

[0044] Figure 7C is an enlarged view of electrode material applied to a battery electrode surface after exposure to a substrate temperature of 300°C; and

[0045] Figure 8 is a schematic diagram of an alternative embodiment of the present disclosure.

[0046] In the drawings, reference numerals may be repeated to identify similar and / or identical elements. DETAILED DESCRIPTION

[0047] Embodiments of the present disclosure provide methods of annealing the exposed edge margins of battery electrode strips after the battery electrode strips have been coated with electrode materials, and preferably before those coatings have been calendered.

[0048] During the battery manufacturing process, electrodes are prepared by coating a metal strip substrate. Typically, copper foil is used for the negative electrode of the anode, and aluminum is used for the positive electrode of the cathode (because aluminum is more easily oxidized than copper). The substrate, which is usually in the form of a continuous metal strip, is coated with anode and cathode materials on one or both sides, respectively, and the coated substrate is calendered to reduce the porosity of the electrode, which generally improves particle contact and thus increases the energy density of the battery. Calendering can also affect the pore structure and therefore also the wettability of the electrode. Finally, calendering can help ensure a uniform coating on the electrode.

[0049] The electrode coating is typically not applied all the way to the edge of the substrate, leaving exposed metal edge margins. These exposed metal edge margins are typically annealed in some processes to relieve stress in the material and help reduce wrinkling of these metal edge margins.

[0050] According to a first embodiment of the present disclosure, a magnetic field is applied to the exposed metal edge margin of the coated battery electrode strip through a perforated magnetic shield to induce eddy currents in the metal edge margin, thereby heating the exposed metal edge margin to a desired annealing temperature (typically in the range of 200-300° C.). The perforated shield blocks the application of a magnetic field close enough to the edge of the coating material on the substrate to heat the substrate near the coating to a temperature that is harmful to the coating material. For example, some adhesives commonly used in battery electrodes have a melting point at 165° C., and when these adhesives are used, exceeding this temperature may be harmful to the electrode material.

[0051] like Figure 1-2 As shown, the electrode strip 20 comprises a continuous metal strip substrate 22 (typically copper or aluminum) coated on each side with a layer of electrode material 24 and 26. Typically, the coating does not extend all the way to the edge of the substrate 22, but terminates at edge 28, leaving an exposed metal edge margin 30. This exposed metal edge margin 30 is typically annealed after the electrode material layer has been calendered to remove residual stresses and reduce wrinkling of the exposed metal edge margin.

[0052] Likewise Figure 1 As shown, a magnetic field 32 can be applied to the exposed metal edge remainder 30 of the electrode strip 20. The magnetic field 32 can be applied, for example, using an electromagnetic coil 34. The magnetic field 32 induces eddy currents in the exposed metal edge remainder 30, which heat the exposed metal edge remainder. This induction heating can heat the exposed metal edge remainder 30 to a desired annealing temperature (typically 200-300° C.). However, this heating can also reach the edges 28 of the electrode material layers 24 and 26 on the substrate 22 and potentially adversely affect the electrode material.

[0053] like Figure 3 and Figure 4 As shown, according to the principles of the present disclosure, a magnetic shield 36 having holes 38 can be inserted between a magnetic field source and the exposed metal edge margin 30 of the electrode strip 20 to control a location 40 where the magnetic field 32 induces heating in the edge margin. By sufficiently spacing the location 40 from the edge 28 and controlling the application time, the temperature adjacent to the layers 24 and 26 can be maintained below a temperature that would adversely affect the materials in the layers.

[0054] like Figures 5A-5D As shown, the shield 36 has at least one hole 38 to allow magnetic flux (represented by magnetic field lines 32) to pass through. The hole 38 can have a shape that controls the amount and location of the magnetic field applied to the exposed metal edge margin 30. Figure 5A As shown, the hole 38 may be circular. Figure 5B As shown, the hole 38 can have a semicircular or "D" shape with straight sides that can be oriented parallel to the edge 28. Figure 5C As shown, the aperture 38 may have a rectangular shape (square as shown) with straight sides that may be oriented parallel to the edge 28. Figure 5D As shown, the hole 38 can have a trapezoidal shape with straight sides that can be oriented parallel to the edge 28 and that widen toward the edge of the exposed metal edge margin 30 so that relatively more energy is transferred to the substrate 22 closer to the edge of the exposed metal edge margin and relatively less energy is transferred to the substrate adjacent to the edge 28.

[0055] The size and shape of the apertures 38 can be designed to transfer energy to the exposed metal edge margin to achieve the desired temperature distribution. This shape will depend on the nature of the applied magnetic field, the internal resistance and thermal conductivity of the substrate material, and the duration of exposure. In embodiments where the electrode material moves relative to the magnetic field source and shield, the speed of movement is also a factor.

[0056] The shield 36 may be made of one or more magnetic shielding materials, including at least one of copper, silver, brass, ferromagnetic alloys, steel, stainless steel, permalloy, mu metal, aluminum, titanium, tungsten, and lead, or any non-ferromagnetic material. The shield may include multiple layers of material, either layers of the same material or layers of different materials. At least some of the shielding material may be in the form of a mesh or a metal foam.

[0057] like Figure 6 As shown, a magnetic field 32 may be applied to both sides of the exposed metal edge margin 30 using two opposing electromagnetic coils 34, each with its own shield 36, to control the amount and location of energy applied to the exposed metal edge margin.

[0058] The disclosed method may be incorporated into a continuous manufacturing process wherein the electrode strip 20 is supported on non-magnetic and non-magnetic conductive rollers 42 and transported past one or more electromagnetic coils 34 and shields 36 (at Figure 2 and 4 The rollers 42 support the strip 20 and help maintain a fixed distance between the surface of the exposed metal edge margin 30 and the electromagnetic coils 34 and their corresponding shields 36.

[0059] This arrangement also allows for rapid conversion to other electrode types, as the electromagnetic coils can be standardized to provide a sufficiently strong magnetic field to adequately heat all types of electrodes being produced, and adapted to the specific electrode being produced by simply changing the shield. For example, anode electrodes typically have a copper substrate, and cathode electrodes typically have an aluminum substrate. Copper has a greater thermal conductivity than aluminum, and therefore a different shield with different holes can be used on a copper electrode than on an aluminum electrode in order to achieve satisfactory heating of the exposed metal edge margin without adversely affecting coatings already applied to these substrates.

[0060] According to another embodiment of the present disclosure, a system for annealing exposed metal edge margins of an electrode is provided. Figure 3 and 6As shown, the system includes a variable magnetic field source (such as an electromagnetic coil 34), and a magnetic shield 36 having an aperture 38 disposed between the magnetic field source and the exposed metal edge remainder of the electrode. The shield 36 and aperture 38 are preferably configured to apply a magnetic field to the exposed metal edge remainder to heat a substantial portion of the exposed metal edge remainder to an annealing temperature while maintaining a temperature of the substrate adjacent the electrode material sufficiently low to minimize or avoid any deleterious temperature effects. The strip 20 may pass through the magnetic field source and the shield on rollers that support and hold the strip at a fixed distance from the shield and magnetic field source.

[0061] According to another embodiment of the present disclosure, Figure 8 Generally indicated at 50, a laser 52 may be provided to heat and thereby anneal the exposed metal edge margin 30 of the electrode strip 20. The laser 52 may be mounted on a translation or orientation system 54 so that the laser may be directed to a specific portion of the exposed metal edge margin. A thermal sensor such as an infrared thermal sensor 56 may scan the exposed metal edge margin 30 to determine its temperature. A controller 58 may be provided to control the position, power and / or duration of application of the laser 52 in response to the temperature measured by the sensor 56. In this way, the electrode coatings 24 and 26 may be protected from overheating damage. Such thermal measurements may be applied to other embodiments of the present disclosure, and parameters such as electromagnetic positioning, power and frequency, as well as shield position and opening size and travel speed of the strip may be controlled to prevent overheating of the electrode material.

[0062] The foregoing description is merely illustrative in nature and is in no way intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be so limited, because after studying the drawings, the specification and the appended claims, other modifications will become apparent. It should be understood that one or more steps in the method can be performed in different orders (or simultaneously) without changing the principles of the present disclosure. In addition, although each embodiment is described above as having certain features, any one or more of those features described with respect to any embodiment of the present disclosure can be implemented in the features of any other embodiment and / or combined with the features of any other embodiment, even if the combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and the replacement of one or more embodiments with each other is still within the scope of the present disclosure.

[0063] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaged," "coupled," "adjacent," "next to," "on top of," "above," "below," and "disposed." Unless explicitly described as "direct," when describing a relationship between a first and a second element in the above disclosure, the relationship can be a direct relationship in which there are no other intervening elements between the first and second elements, but can also be an indirect relationship in which there are one or more intervening elements (spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be interpreted to mean a logical (A or B or C) using a non-exclusive logical "or," and should not be interpreted to mean "at least one of A, at least one of B, and at least one of C."

Claims

1. A method of annealing the exposed metal edge margin of a coated battery electrode strip to relieve stress and reduce wrinkling, the method comprising: A magnetic field is applied to the exposed metal edge margin of the coated battery electrode strip through a perforated magnetic shield to induce eddy currents in the exposed metal edge margin to heat the exposed metal edge margin to a desired annealing temperature, the perforated magnetic shield blocking the application of the magnetic field close enough to the edge of the coating on the electrode strip to reach a temperature that is harmful to the coating.

2. The method according to claim 1, wherein: The step of applying a magnetic field to the exposed metallic edge remainder of the coated battery electrode strip through the perforated magnetic shield includes moving the exposed metallic edge remainder of the coated battery electrode strip through the magnetic field.

3. The method according to claim 1, wherein: The step of applying a magnetic field to the exposed metal edge margin of the coated battery electrode strip through a perforated magnetic shield, wherein the magnetic field is applied with an electromagnetic coil.

4. The method according to claim 3, wherein: The step of applying a magnetic field to the exposed metallic edge remainder of the coated battery electrode strip through the perforated magnetic shield includes moving the exposed metallic edge remainder of the coated battery electrode strip through the magnetic field.

5. The method according to claim 1, wherein: The perforated magnetic shield includes multiple layers of material.

6. The method according to claim 1, wherein: The perforated magnetic shield includes at least one of copper, silver, brass, titanium, tungsten, and lead.

7. The method according to claim 1, wherein: The perforated magnetic shield includes at least one of steel and stainless steel.

8. The method according to claim 1, wherein: The perforated magnetic shielding member includes at least one of ferromagnetic alloy, permalloy or highly permeable magnetic alloy.

9. The method according to claim 1, wherein: The perforated magnetic shield comprises a metal mesh.

10. The method according to claim 1, wherein: The porous magnetic shield includes a metal foam.

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