TECHNICAL FIELD

The present disclosure generally pertains to an edge coating for secondary cells, and more particularly to an electrode roll and a cylindrical secondary cell comprising such and electrode roll.

BACKGROUND

In addressing climate change, there is an increasing demand for rechargeable batteries, e.g. to enable electrification of transportation and to supplement renewable energy. Such batteries typically comprise a number of cells, often referred to as secondary cells.

In battery manufacturing it is known in the art to provide an electrically conductive sheet with a coating that is rolled up into a cylinder. In so called tabless cells, the electrically conductive sheet has an uncoated edge protruding on a side of the cylinder. The edge may be folded to provide an electrical contact surface.

The stability of a battery determines the longevity of the battery and the limits of energy that the battery stores, and how fast the device can charge or supply energy. Defects in the battery may also cause complete failure of battery such as electrical short, rapid discharge, and subsequent fires.

Conventionally each of the cathode and anode electrodes uses small metallic components called "tabs" to connect to the positive and negative terminals of the battery can. Tabs are metallic components which are welded onto the electrodes. Tab manufacturing presents many challenges which may affect both the reliability and performance of the battery. The welding operation may for instance cause welding burrs to penetrate the separator layer between the positive and negative electrodes and therefore cause an internal short circuit. The charge and discharge current flow through the tabs and significantly increase the temperature of the region around the tab to a level much higher than other parts of the battery, and there is thus a need to be able to insulate the interface between the tabs and the electrodes. Large-format lithium-ion cells have a “foil-to-tab” weld to collect the foils inside a cell and join them to a tab. However, the electrode-roll may also be a part of a so-called tabless battery, or a tabless lithium-ion battery. In a tabless battery the conventional tab functionality is replaced with a conductive portion or strip that runs along the length of the electrode. In the tabless design, the maximum distance that electrons should travel is the height of the electrode rather than its length as in the case of a conventional electrode with tabs. Since the height of an electrode is only 5-20% of its length, the ohmic resistance and the heat that is generated is reduced.

Further, in the tabless design, the whole edge of the electrode is responsible for current (and heat) transfer, and the anode and cathode sheets are designed to form a rose-like form at the ends when they have been rolled up. The ends must, however be flattened to fit into the can, however separator alone might not be sufficient for insulation. During welding of aluminum disc and foils, particles can be generated and positioned between aluminum foil and separator or separator and anode, and this may cause malfunction of the electrical cell.

As the demand for rechargeable batteries increases, more and more focus is being placed on production speed. To achieve an effective production of rechargeable batteries, the design of the batteries can be optimized with fewer defects compromising the performance of the battery cell.

SUMMARY

It is in view of the above considerations and others that the embodiments of the present invention have been made. The present disclosure aims at providing highly performance secondary cells that are efficient in manufacture.

According to a first aspect, the present disclosure provides an electrode assembly for a secondary battery cell, the electrode assembly comprising: a conductive substrate; an electrode coating provided on at least one side of the conductive substrate; wherein the electrode coating is at least partially coated on the conductive substrate, whereby said conductive substrate exhibits uncoated portions and coated portions, and wherein an edge coating layer is arranged to cover at least a portion or part of interface between said uncoated conductive substrate portion and the electrode coating, wherein the edge coating layer comprises at least 55 wt-% polyvinylidene fluoride (PVDF). The interface may thus be any edge where the coating material layer of either the cathode or anode has an “open” boarder or interface to or with the conductive substrate or foil material. The foil material may be for instance copper or aluminium foil onto which the respective anode or cathode is coated.

The edge coating material must be able to withstand high voltages (“high voltage stability”), i.e. be electrically insulating as well as preferably thermally insulating.

It has surprisingly been found that an edge coating comprising PVDF has numerous advantages in that is exhibits a good stability during application of high voltages very good electric insulation, and good compatibility with inorganic material.

The edge coating layer may have a thickness in the range of 1 to 55 pm.

The electrode coating may be provided on said conductive substrate such that the uncoated conductive substrate portion is arranged along a longitudinal edge of the electrode assembly.

Alternatively, the electrode coating may be provided on said conductive substrate such that the uncoated conductive substrate portion is arranged across a width of electrode assembly, and such that the uncoated conductive substrate portion is surrounded by the electrode coating on both sides.

This coating may also be referred to as intermittent coating, which means that there is a gap of uncoated substrate between two portions of electrode coating.

According to the first aspect the edge coating layer or material further may comprise any one of a metal oxide, a metal hydroxide and a metal oxide hydroxide, or a combination thereof, in the range of 1 to 20 wt-%. In some embodiments, polymers are combined with metallic particles for coating on the top of an electrode. Thus, a coating of the current disclosure may comprise metal oxide particles, where the edge coating layer comprises at least any one of a metal oxide, a metal hydroxide and a metal oxide hydroxide, or a combination thereof. The metal may be any one of aluminium (Al), zirconium (Zr), titanium (Ti) and silicon (Si). According to one preferred alternative a metal oxide may be aluminium oxide. According to another preferred alternative a metal oxide hydroxide is aluminium hydroxide oxide (boehmite).

The edge coating layer may further comprise a polymer in the range of 1 to 20 wt-%.

Said polymer may be selected from the group consisting of poly(methyl methacrylate).

The edge coating layer may further comprise polyisobutane in a range of 0 to 45 wt-%.

According to an alternative of the first aspect, the edge coating layer may further comprise hydrogenated acrylonitrile butadiene (HNBR) rubber in a range of 0 to 45 wt-%.

According to yet an alternative of the first aspect the edge coating layer may comprise polyimide in a range of 0 to 45 wt-%.

The edge coating layer may comprise polyvinylidene fluoride in a range of 80 to 89 wt-% and any one of aluminium oxide in a range of 11 to 20 wt-%, aluminium oxide hydroxide in the range of 11 to 20 wt-%, and a polymer in a range of 11 to 20 wt-%, or a combination thereof.

According to the first aspect the edge coating layer may be arranged at an interface between a negative electrode coating and said substrate.

According to a second aspect, the present disclosure provides a secondary battery cell comprising the electrode assembly according to the first aspect.

According to a third aspect, the present disclosure provides use of a secondary battery cell according to the second aspect, in an electrical vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments disclosed herein are illustrated by way of example, and by not by way of limitation, in the figures of the accompanying drawings. Like reference numerals refer to corresponding parts throughout the drawings. Fig. 1 schematically shows a cross-sectional view of a conductive substrate material provided with a coating according to the invention.

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described more fully hereinafter. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those persons skilled in the art.

Figure 1 illustrates a first embodiment of a conductive substrate material 1 coated on at least one side thereof with an electrode coating material 2, 2’. Said electrode coating material may be one of a cathode (negative electrode) or anode (positive electrode) material 2, 2’ for a secondary battery cell. The conductive substrate material 1 may be a metal foil, such as a copper foil or aluminium foil.

The secondary battery cell may be an electrode-roll or cylindrical secondary cell, and may be for, or comprised in a vehicle battery or battery pack for propelling a vehicle. The vehicle may for example be a fully electrically propelled vehicle or a hybrid vehicle.

In a cylindrical battery cell, such as a lithium-ion cell, sheet-like anodes, separators and cathodes are sandwiched and rolled into a cylinder shaped can.

The electrode coating material 2, 2’ may be provided onto said conductive substrate material 1 such that an entire long edge portion, or longitudinal edge portion, of the conductive substrate is left uncoated.

Further, the electrode coating material may be provided onto the conductive substrate such that there is a gap of uncoated conductive substrate 4 between two portions of electrode coating 2, 2’. This is often referred to as intermittent coating.

The edge coating layer 3 may thus be applied or coated at any interface portion 5 or junction between the electrode coating, being either negative electrode or positive electrode coating, and the uncoated conducting substrate material. This means that the edge coating may be applied to at least partially cover or overlap, OL, any interface, gap or junction between a cathode layer, an anode layer and a welded tab and the conductive substrate material. This way the edge coating 3 may electrically, and thermally, insulate a gap between the coating and the substrate, or the tab and the substrate or coating.

The thickness T of the edge coating 3 is preferably lower than the pressed thickness, TS, of the cathode material layer 2, 2’, which may be in the range 55 to 85 pm. This means that the thickness T of the edge coating is preferably less than 65 pm.

The width W of the edge coating layer 3 is preferably in a range of 0.5 to 3 mm.

A width OL of the overlap/gap 5 between the cathode material coating and the insulating edge coating is preferably kept below 0.5 mm.

The edge coating may have insulation resistance higher than 1 MQ.

The edge coating layer 3 may further be applied with uniform or varying thickness. By varying thickness is for instance meant that the ends of the applied edge coating layer may be thinner than a central portion.

The edge coating preferably comprises at least one component, compound or material which exhibits a high electrical voltage stability, electrical insulation, and also thermal insulation.

By high electrical voltage stability is meant V vs Li/Li+ in the range of 2.5 to 5.

In a preferred embodiment, the edge coating layer or material comprises polyvinylidene fluoride (PVDF) or poly( 1,1 -difluoroethylene) (CAS No. 24937-79-9) having the molecular formula of -(C2H2F2)„- The edge coating preferably comprises at least 55 wt-% PVDF, or PVDF in a range of 55 to 100 wt-%, or more preferably in a range from 80 to 89 wt-%.

In alternative embodiments, the composition of the edge coating material contains or comprises polyvinylidene fluoride (PVDF) and additional compounds or materials.

It is to be understood that the edge coating may comprise PVDF and any one or a combination of these compounds and materials.

In one embodiment, the edge coating material further comprises at least one metal oxide in the range of 1 to 20 wt-%. In one embodiment the edge coating material further comprises at least one metal hydroxide in the range of 1 to 20 wt-%.

In one embodiment the edge coating material further comprises at least one oxide hydroxide metal in the range of 1 to 20 wt-%.

The metal in any one of the above-mentioned oxides, hydroxides and oxide hydroxides may be selected from the group consisting of aluminium (Al), zirconium (Zr), titanium (Ti) and silicon (Si).

In a more preferred embodiment, the metal oxide is aluminium oxide.

In one embodiment, the metal oxide hydroxide is aluminium oxide hydroxide, CAS 1318-23- 6).

In one embodiment, the edge coating material layer further comprises a polymer in a range of 1 to 20 wt-%.

The polymer may be selected from the group of consisting of poly(methyl methacrylate).

In one embodiment the edge coating material further comprises polyisobutane, CAS No. 40921-86-6, having the molecular formula C4H10. The edge coating preferably comprises polyisobutane in a range of 0 to 45 wt-%.

In an alternative embodiment the edge coating material further comprises hydrogenated acrylonitrile butadiene rubber, ASTM D1418 Designation HNBR, HSN, CAS No. 308068-83- 9 and having a chemical formula of:

The edge coating preferably comprises HNBR in a range of 0 to 5 wt-%. In yet an alternative embodiment the edge coating comprises polyimide (1,3- Isobenzofurandione, 5,5'-carbonylbis-, polymer with 2,4-diisocyanato-l- methylbenzene), CAS No. 58698-66-1, having the molecular formula: C41H22N4O11.

The edge coating preferably comprises polyimide in a range of 0 to 45 wt-%.

In yet an alternative embodiment, the edge coating layer or material comprises Polyvinyl butyral, CAS No. 915977-69-4, having the molecular formula (CsHi4O2)n. The edge coating material may comprise polyvinyl butyral in a range of 0 to 45 wt-%.

In a more preferred embodiment, the edge coating comprises polyvinylidene fluoride in a range of in a range of 80 to 89 wt-% and any one of an aluminium oxide in a range of 11 to 20 wt-%, a polymer in a range of 11 to 20 wt-%, and boehemite (aluminium oxide hydroxide) in a range of 11 to 20 wt-%, or a combination thereof.

Modifications and other variants of the described embodiments will come to mind to ones skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure.

Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, persons skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms “comprise/comprises” or “include/includes” do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a certain combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Finally, reference numerals in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Example 1, Hi -pot Test A Hi-pot (Hipot) Test was performed to evaluate the properties of the coated electrode. Hipot Test is short for high potential (high voltage) test, also known as Dielectric withstand test, which checks for good isolation, and ensures that no current will flow from on point to another. The test is a non-destructive test that determines the adequacy of electrical insulation for the normally occurring over voltage transient.

A coating of PVDF+Ceramic was tested, with a mixing ratio with ceramic of 1 :3 (or 1 :4) for PVDF +boehmite with a coating thickness of 20-40 um, such 35.5um, on one side of the electrode (1-Side), and a foil thickness of 17um. The SC was 6-10%. All voltages from 200 to 700V during 3sec >10MOhm got a pass in the test, indicating good insulation. As may be seen in Table 1 below, the coating showed good thermal stability at 250C.

Table 1