Insulating edge coating

Abstract

The disclosure provides a composition for an insulating edge coating comprising a ceramic material a polyurethane or polyurethane urea binder and an antioxidant. The disclosure also provides an edge coating of said material and an electrode comprising the edge coating.

Description

[0001] INSULATING EDGE COATING

[0002] FIELD OF THE INVENTION

[0003] The disclosure relates to a composition for an insulating edge coating for a cathode, to an electrode comprising said insulating edge coating, and to a method of forming an electrode comprising said insulating edge coating. The insulating edge coating comprises a polyurethane or polyurethane urea binder and an antioxidant.

[0004] BACKGROUND

[0005] Rechargeable or 'secondary' batteries find widespread use as electrical power supplies and energy storage systems. For example, in automobiles, battery packs formed of a plurality of battery modules, wherein each battery module includes a plurality of electrochemical cells, are provided as a means of effective storage and utilization of electric power.

[0006] Electrodes (anodes and cathodes) for cells typically comprise a current collector e.g. a conductive foil, and an active layer deposited on both sides of the current collector. For example, a cathode may comprise a positive current collector coated with a composition comprising a positive active material, a binder and optionally a conductive additive.

[0007] To maximize cell capacity per volume, positive and negative electrodes are layered alternatingly, with an insulating separator disposed between each electrode pair to form a stacked electrode assembly. In some applications, the stacked assembly is further rolled into a helical structure. Rolled electrode assemblies are typically referred to as jelly rolls, wound assemblies or cylindrical assemblies. The stacked / rolled electrode assemblies are then placed in a housing, wherein each of the electrodes in the assembly is electrically coupled to the housing.

[0008] In order to form the electrical connection, each of the electrodes in the stack comprises an electrically conductive connecting portion at the edge of the stack extending outwardly, often referred to as a tab.

[0009] If tabs of adjacent electrodes contact each other, the assembly will short circuit. In some designs, the insulating separator disposed between pairs of electrodes is extended such that is also disposed between tabs of adjacent electrodes.

[0010] Whilst this provides some protection from short circuits, separators are prone to splitting, and often swell and shrink during cell operation such that their position is subject to change. To provide further protection from short circuits, an insulating edge coating may be applied to the edge of the conductive foil. The insulating edge is typically coated on or close to the boundary of the active layer coating and the electrically connecting portion, ensuring that it stays in position during all phases of cell operation.

[0011] Insulating edge coatings known in the art often have sub-par mechanical properties leading to cracking and / or delamination during battery operation.

[0012] In addition, preparation of known insulating edge coatings comprise components that are difficult to process due to poor dispersibility in solvents.

[0013] There is therefore a need for an improved insulating edge coating composition.

[0014] SUMMARY (NB this section needs to be aligned to the claims when agreed)

[0015] The object of the present disclosure is to provide an edge coating and / or electrode comprising said edge coating that is environmentally-friendly, has excellent mechanical properties, good adhesion to the electrically connecting portion and the coated portion, and is easy to process.

[0016] According to a first aspect of the disclosure is an electrode comprising a conductive foil, an active layer and an insulating edge coating; wherein the active layer comprises an active material, a binder and optionally a conductive additive; the insulating edge coating comprises a ceramic material, a polyurethane or polyurethane urea binder and an antioxidant; and the conductive foil comprising a first region, a second region and a third region, wherein the second region is located between the first and third regions; wherein the active layer is coated on the first region; the insulating edge coating is coated on the second region and overlaps the interface between the active layer and the second region; and the third region is not coated with active layer or insulating edge coating.

[0017] While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the spirit and scope of the appended claims are covered as well.

[0018] The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The figures and Detailed Description that follow also exemplify various example embodiments. Various example embodiments may be more completely understood in consideration of the following Detailed Description.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1. Schematic drawing of an electrode comprising an active layer and an insulating edge coating according to the disclosure.

[0021] DETAILED DESCRIPTION

[0022] The disclosure relates to a composition for an insulting edge coating, and to an electrode comprising the insulating edge coating, a conductive foil and an active layer. The insulating edge coating finds use in battery assemblies comprising electrode assemblies wherein the electrodes are stacked or rolled together.

[0023] Current collector

[0024] The current collector of the disclosure is a conductive foil.

[0025] The conductive foil will now be described with reference to Figure 1.

[0026] The current collector (conductive foil (1)) of the disclosure comprises a first region (2), a second region (3) and a third region (4), wherein the second region is located between the first and third regions.

[0027] The active layer (5) is coated on the first region of the conductive foil.

[0028] The insulating edge coating (6) is coated on the second region of the conductive foil. Preferably, the insulating edge coating overlaps (7) the interface between the active layer and the second region.

[0029] The third region is not coated with an active layer or an insulating edge coating (8). The conductive foil may also comprise a corresponding a first, second and third regions with corresponding active layer and insulating edge coatings on the opposite side.

[0030] The conductive foil comprises a tab for electrically coupling the electrode to the housing of a cell. The tab may be integral i.e., the tab may be an uncoated edge region of the conductive foil.

[0031] In embodiments wherein the tab is integral, the tab comprises part of (or consists of) the third region of the conductive foil.

[0032] In an alternative embodiment, the tab is a separate metallic part affixed to the conductive foil e.g., via welding.

[0033] When the tab is affixed via welding, the insulating edge coating preferably covers the welded region between the conductive foil and the tab. In such embodiments, the welded region is located within the second or third region of the conductive foil, preferably within the second region.

[0034] Preferably, the maximum thickness of the insulating edge coating is less than the maximum thickness of the active layer coating. Preferably, the maximum thickness of the insulating edge coating is less than the maximum thickness of the active layer coating after of calendaring the active layer coating. In the context of the disclosure "thickness" refers to the thickness of a layer in the direction perpendicular to the plane of the conductive foil.

[0035] Preferably, the thickness of the insulating layer is between 5-50 pm, more preferably from 10 to 30 pm, such as from 15 to 25 pm.

[0036] Active layer

[0037] The active layer of the disclosure comprises an active material, a binder and optionally a conductive additive.

[0038] Preferably the active layer of the disclosure is positive active layer or a cathode active layer, comprising a cathode active material, a binder and optionally a conductive additive. The binder for the active layer may any suitable binder, for example the active layer binder may be a polyurethane binder according to the disclosure.

[0039] In the context of the disclosure "cathode active material" refers to any material that is suitable for use as the electrochemically active material in a cathode, and suitable for use in a cell. The term "electrochemically active material" is to be understood as an electrochemical species which can be oxidized and reduced in a system which enables a cell to produce electric energy during discharge. The role of the cathode active material is to reversibly intercalate ions (such as lithium ions) during cell charge and discharge cycles.

[0040] The cathode active material of the disclosure is an intercalation material, wherein the intercalation metal is lithium.

[0041] Preferably the cathode active material is a transition metal complex such as nickel manganese cobalt oxide (NMC) material. Even more preferably, the cathode active material is an NMC material intercalated with lithium or an "Li-NMC" material.

[0042] Exemplary cathode active materials include nickel-cobalt-manganese (NMC) composite oxides and lithium NMC (Li-NMC) composite oxides or lithium nickel cobalt manganese (NMC) oxides (LiNiixyCoxMnyO? (0<x+y<l)).

[0043] In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxides (NMC) (LibNii x-yCOxMnyAzCh (0<x+y< l)), where A is an element other than Li, Ni, Co, Mn or O and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 0.9<b< 1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr.

[0044] In preferred embodiments, the NMC cathode materials are lithium rich. As such, the cathode active material typically comprises lithium nickel cobalt manganese oxides (NMC) represented by the formula LibNii x-yCOxMnyAzCh (0<x+y< l), where A is an element other than Li, Ni, Co, Mn or O and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 1.05<b< 1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr.

[0045] In preferred embodiments, the NMC cathode materials are high in nickel. As such, the cathode active material typically comprises lithium nickel cobalt manganese oxides (NMC) represented by the formula LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, preferably 0<x+y<0.25, and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 0.9<b< 1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr. The ratio of the nickel of the high-nickel NMC material may range from 33 mol% to 98 mol %. Preferably, the ratio may range from 60 mol% to 95 mol%. Even more preferably, the ratio may range from 80 mol% to 95 mol%.

[0046] In preferred embodiments, the NMC cathode materials is defined as LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, preferably 0<x+y<0.25, and wherein 0<z<0.05, preferably 0.002 <z< 0.03, more preferably 0.001<z<0.01, and wherein 0.9<b< 1.1. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr.

[0047] Insulating edge coating

[0048] The electrode of the disclosure comprises an insulating edge coating. An insulating edge coating as referred to in the disclosure is a coating that has high electrical resistance e.g., an electrical insulator. The exact resistance of the insulating edge coating is not important, but rather its function. The function of the insulating edge coating is to prevent short circuits by preventing contact of the tab and / or uncoated region of adjacent electrodes when stacked.

[0049] The terms "edge coating", "insulating coating" and "insulating edge coating" may be used interchangeably throughout the disclosure.

[0050] The insulating edge coating of the disclosure comprises a ceramic material and a polyurethane or polyurethane urea binder.

[0051] The insulating edge coating typically comprises from 50 to 98 wt% ceramic material, preferably from 60 to 95 wt%, more preferably from 70 to 90 wt% ceramic material.

[0052] The insulating edge coating typically comprises from 2 to 50 wt% polyurethane or polyurethane urea binder, preferably from 5 to 40 wt%, more preferably from 10 to 30 wt% polyurethane or polyurethane urea binder.

[0053] The insulating edge coating typically comprises a 1-10 : 3-20 weight ratio of polyurethane or polyurethane urea binder to ceramic material, preferably 1-5 : 3-15 weight ratio, preferably a 1-3 : 4-10 weight ratio, more preferably a 1-2 : 5-9, even more preferably a 1.5 : 8.5 weight ratio of polyurethane or polyurethane urea binder to ceramic material. Preferred ranges of weight ratios of polyurethane or polyurethane urea binder to ceramic material include from 1 : 20 to 10 : 3, such as from 1 : 15 to 5 : 3, such as preferably from 1 : 10 to 3 : 4, more preferably from 1 : 9 to 2 : 5.

[0054] The properties of the insulating edge coating should be such that it remains in place and be capable of preventing short circuits, during all phases of cell production and operation.

[0055] During operation, some electrode components undergo volumetric deformation due to voltage changes or due to intercalation of charge carriers. In particular, cathode active layers, anode active layers and separators swell and contract significantly during charge / discharge.

[0056] The insulating edge coating of the disclosure is flexible and capable of mechanical deformation without damage such that it can withstand the volumetric changes of the surrounding components. The insulating edge coating of the disclosure further has good adhesion to the active layer and the conductive foil which decreases the risk of delamination during fabrication and operation. In particular, the edge coatings of the disclosure show improved adhesion at elevated temperatures, for example at temperatures of 40°C and above, 50°C and above, 60°C and above or 70°C and above.

[0057] Preferably, the insulating edge coating of the disclosure is deposited via a slot-die. Preferably, the insulating edge coating and the active layer are simultaneously deposited with respective slot-dies.

[0058] When coated simultaneously, the overlap region of the insulating edge coating and the active layer is formed as the two coatings flow on the conductive foil after deposition.

[0059] Thus, by "simultaneously" is meant that the insulating edge coating is deposited at the same time or immediately after the active layer. Typically, the insulating edge coating is simultaneously deposited via a slot die that is offset behind the deposition of the active layer, to ensure that the active layer contacts the conductive foil, and the insulating coating is deposited on the active layer.

[0060] If the coatings the coatings are deposited sequentially, the insulating edge coating is deposited after deposition of the active layer.

[0061] Ceramic material The insulating edge coating comprises a ceramic material, the function of which is provide high electrical resistance such that the insulating edge coating is an insulating layer. Examples of suitable ceramic materials are metal oxides, metal hydroxides and metal oxide hydroxides. Preferably the ceramic material comprises aluminium oxide hydroxide, such as y-aluminium oxide hydroxide also known as boehmite.

[0062] Boehmite is a cheap ceramic material that provides excellent insulating properties.

[0063] A further material that may preferably be used as the ceramic material is aluminium oxide (i.e. alumina, or AI2O3).

[0064] The ceramic material may therefore preferably be selected from the group consisting of aluminium oxide, boehmite, and mixtures thereof.

[0065] Polyurethane or polyurethane urea binder

[0066] The insulating edge coating comprises a polyurethane or polyurethane urea binder. The function of the polyurethane or polyurethane urea binder is to bind the particles of ceramic material such that a layer (edge coating) can be formed comprising said particles.

[0067] The polyurethane or polyurethane urea binder of the disclosure is environmentally benign compared to commonly used binder components, such as fluorinate PVDF or PTFE. Replacing such fluorinated binder components with a polyurethane or polyurethane urea binder reduces the environmental impact of cells. In addition, the polyurethane or polyurethane urea binder may be produced from recycled materials, further reducing the environmental impact.

[0068] The term "polyurethane binder" refers to a polyurethane-based polymer comprising urethane linkages. Typically, polyurethanes are prepared by reacting a polymeric isocyanate and a polyol (e.g. a diol) to form a urethane linkage.

[0069] The term "polyurethane urea binder" refers to a polyurethane-based polymer comprising urethane and urea linkages. Polyurethane urea are typically prepared in a reaction between polyols (e.g. diols) and diisocyanates that react to form a urethane linkage. Polyurethane ureas additionally comprise urea linkages that are often prepared by further reacting the diisocyanates with a diamine.

[0070] Preferably, the polyurethane or polyurethane urea binder binder comprises about 10-100 wt% polyurethane-based polymer, for example about 20-100 wt%, about 30-100 wt%, about 40-100 wt%, about 50-100 wt%, about 60-100 wt%, or about 70-100 wt% polyurethane-based polymer.

[0071] Even more preferably, the polyurethane or polyurethane urea binder comprises 90 wt% or more polyurethane-based polymer, for instance 95wt% or more, or 98wt% or more. In one embodiment, the polyurethane or polyurethane urea binder consists of a polyurethane- based polymer.

[0072] Preferably, the polyurethane or polyurethane urea binder comprises for instance a polyether-polyurea copolymer. Preferably, the polyurethane or polyurethane urea binder is a block-copolymer, for instance a block copolymer of polyether and polyurea.

[0073] In an embodiment, the polyurethane or polyurethane urea binder consists of a polyurethane-based polymer. That is, the polyurethane or polyurethane urea binder may comprise 100wt% polyurethane-based polymer.

[0074] The polyurethane or polyurethane urea binder may comprise 90wt% or more polyurethane-based polymer, for instance 95wt% or more, or 98wt% or more wherein the remainder is additives.

[0075] Accordingly, the polyurethane or polyurethane urea binder may comprise up to 10wt% additives, for instance 5wt% or 2wt%.

[0076] Polyurethane or polyurethane urea binders available from commercial suppliers often comprises additives. These additives may be stabilizers, residual solvent, delusterants and / or lubricants for example. An example of a residual solvent is dimethylacetamide, an example of a delusterant is titanium dioxide and an example of a lubricant is polydimethylsiloxane.

[0077] Preferably, when the polyurethane or polyurethane urea binder does not consist of a polyurethane-based polymer, polydimethylsiloxane, titanium dioxide and dimethylacetamide are not present. These additives can have a detrimental on the function of the polyurethane or polyurethane urea binder, for instance it may reduce the adhesion of the edge coating and the conductive foil.

[0078] In a preferred embodiment, the polyurethane or polyurethane urea binder comprises a polyurethane-based polymer and does not comprise at least one of polydimethylsiloxane, titanium dioxide and dimethylacetamide. For example, the polyurethane or polyurethane urea binder may comprise 90wt% or more polyurethane-based polymer, for instance 95wt% or more, or 98wt% polyurethane-based polymer and does not comprise at least one of polydimethylsiloxane, titanium dioxide and dimethylacetamide.

[0079] The polyurethane or polyurethane urea binder of the disclosure is highly elastic. Polyurethane-based block copolymers of a 'rigid' or 'hard' and a 'soft' polymer provide the excellent elastic properties. Without wishing to be bound by theory, it is considered that on stretching, the soft polymer expands and on release, springs back to its original form. The 'rigid' polymer does not expand, and therefore maintains the structural integrity of the polymer whilst the soft polymer undergoes deformation. Block copolymers of this structure are also referred to as segmented polymers or segmented copolymers.

[0080] An example of a highly elastic segmented copolymer according to the disclosure is polyether-polyurea wherein the polyether is the 'soft' component and the polyurea is the 'rigid' component.

[0081] Preferably, the segmented polyurethane-based polymer comprises a polyether and polyurea. That is, preferably the binder is a polyurethane urea binder.

[0082] Preferably, the polyurethane-based polymer consists of polyether and polyurea segments.

[0083] Preferably, the soft segment has a melting point of < 5 or 6°C.

[0084] Preferably, the polyurethane-based polymer has a number average molecular weight of 50k-1000k Da, for instance 100k-800k Da, 200k-500k Da, 200k-400k Da or 300-350k Da. The number average molecular weight can be determined via gel permeation chromatography (GPC).

[0085] For example, GPC may be performed on a Shimadzu Prominence LC system equipped with an R.I detector with a 300 mm x 75 mm, 5 pm PLgel 100 A and 300 mm x 7.5 mm, 5 pm PLgel 500 A column in series at 40 °C with a DMF eluent at 1.0 ml / min. The method can be calibrated with poly(styrene) standards with MW between 1000 and 10000.

[0086] The properties of the segmented polymer may be controlled by varying the length and / or molecular weight of the hard and soft segments, and by controlling the weight percent or concentration of the hard / soft segments in the polymer. In a conventional process of making segmented polyurethane-based polymers of polyether and polyurea, a glycol (diols of polyethers, polyesters or polycarbonates, including their copolymers or mixtures) is reacted with a diisocyanate in excess amount to form an isocyanate-terminated polyurethane or polyurethaneurea prepolymer. This prepolymer is then diluted in a solvent and chain extended with a short chain diol or diamine to grow the polymer chain length. A terminator can be used to control the molecular weight of the polymer. In this type of conventional process, the soft segment is formed during the prepolymer formation stage and the hard segment is formed during the chain extension stage. Accordingly, the formed polymer chains consist only of alternating soft segments and hard segments.

[0087] The polyurethane-based polymer of the disclosure may comprise alternating hard and soft segments.

[0088] The polyurethane-based polymer of the disclosure may consist of alternating hard and soft segments. For example, the polyurethane-based polymer of the disclosure may consist of alternating polyurea and polyether segments.

[0089] The polyurethane-based polymer may be produced by an extended glycol process and / or under-capping process as disclosed in WO 2019 / 118604 Al. Such a process allows for the formation of a polymer wherein the molecular weight of the soft segment, even with the use of lower molecular weight glycol, can be increased without reducing molecular weight of the hard segment as typically observed in conventional prepolymer production processes.

[0090] The extended glycol process comprises two step reactions to make the isocyanate- terminated prepolymer.

[0091] In the first step, excess amount of a lower molecular weight glycol (typical MW < 2500) is used to react with a diisocyanate to form a hydroxy-terminated glycol, or an extended glycol with typical MW > 2500.

[0092] This extended glycol is further reacted with excess amount of a diisocyanate in the second step reaction to produce an isocyanate-terminated prepolymer or capped glycol.

[0093] The diisocyanate used in the first step reaction to make the extended glycol can be same or different from the diisocyanate used in the second step reaction to make the capped glycol prepolymer. This capped glycol based on the extended glycol is then dissolved in a solvent and chain extended with a diamine extender and a monoamine as the terminator to form a segmented polyurethane or polyurethane urea polymer with engineered soft segment and hard segment molecular weights prior to spinning into fibres.

[0094] The molecular weight of the extended glycol and the capping ratio thereafter in making the capped glycol prepolymer should be controlled in order to provide the desired molecular weight ratio (SSMW / HSMW) of the soft segment to the hard segment and the urea hard segment weight percent (HSWT%) for the segmented polyurethane or polyurethane ureas according to the present invention.

[0095] The under-capping process comprises adding controlled amount of a second diisocyanate to an isocyanated-terminated prepolymer which is produced by reacting a glycol at a low capping ratio (typically less than 1.50) with a first diisocyanate. The first diisocyanate and the second diisocyanate can be the same or different.

[0096] The mixture including the added second diisocyanate and the capped glycol prepolymer from the first diisocyanate is dissolved into a solvent, and a diol or diamine chain extender and a monoamine terminator are then added to produce the polyurethane or polyurethaneurea polymer with engineered soft and hard segment molecular weights.

[0097] The capping ratio in making the capped glycol prepolymer and the amount of second diisocyanate added to the capped glycol should be controlled in order to provide the desired molecular weight ratio (SSMW / HSMW) of the soft segment to the hard segment and the urea hard segment weight percent (HSWT%) for the segment polyurethanes or polyurethaneureas according to the present invention.

[0098] In a preferred embodiment, the polyurethane or polyurethane urea binder comprises a polyurethane-based polymer comprising segments of polyether and polyurea, wherein the polymer is based on glycols with a number average molecular weight less than 2500 as measured by GPC. Preferably, the polymer has a molecular weight ratio of the soft segment to the hard segment larger than 12.0, and a urea hard segment weight percent less than 7.8%. The weight ratio of the soft and hard segments may be determined according to the methods outlined below.

[0099] For example, when the formed polymer chains consist only of alternating soft segments and hard segments, and the number average soft segment molecular weight and hard segment molecular weight of the polymer can be estimated mathematically as shown below:

[0100] SSMW = R X (MWgi + MWdi) / (R-l) (1)

[0101] HSI« = R x (MWex + MWdi) (2) where in equation (1) and (2), SSMW and HSMW stand for soft segment molecular weight and hard segment molecular weight, respectively; MWgl, MWdi and MWex represent the number average molecular weight of the glycol, the formula weight of the diisocyanate and the extender or their averages in the situation of mixed diisocyanates or extenders, respectively; and R in the equations is the capping ratio, the molar ratio of the diisocyanate to the glycol.

[0102] Combining equation (1) and (2) provides a correlation of the SSMW and the HSMW referred to as the segment molecular weight ratio, as shown in equation (3).

[0103] SSMW / HSMW =(l / (R-l))x(MWgi+ MWdi) / (MWex + MWdi) (3)

[0104] Based on equation (3), once the ingredient type is determined, such as poly(tetramethylene ether) glycol (PTMEG), methylene bis(4-phenylisocyanate) (MDI) and ethylenediamine (RDA), the SSMW and HSMW are dependent to each other with a function ofthe capping ratio R and the number average molecular weight of the glycol.

[0105] There are at least two ways of achieving a polymer with the preferred molecular weight distribution.

[0106] A first method comprises an extended glycol approach wherein a glycol with lower MW is extended to a higher MW before making the isocyanate-terminated prepolymer. This can be achieved by reacting excess glycol with a diisocyanate which functions as a linker connecting two or more glycol molecules. The desired molecular weight of the extended glycol is determined by the relative molar ratio (r> 1) of the glycol to the diisocyanate. The diisocyanate used for glycol extension can be the same or different from the diisocyanate used for making the prepolymer.

[0107] Extended Glycol MWegi= (r x MWgi + MWdi) / (r-l) (4) For example, to extend PTMEG from 1800 to 3500 MW with MDI, the r should be 2.2060. This extended glycol can be used for the conventional prepolymer formation and chain extension processes to provide the SSMW and HSMW following equation (1) and (2) except where the MWgishall be substituted by the extended glycol MWegi.

[0108] A second method comprises an under-capping process wherein a prepolymer is made for the desired soft segment MW and then an extra amount of diisocyanate is added into the capped glycol prepolymer prior to the chain extension step. In this process, the SSMW still follows equation (1) determined by the capping ratio R, and the HSMW is determined by the unreacted diisocyanate in the prepolymer and the extra amount of diisocyanate added into the prepolymer by equation (5). Again, the diisocyanate used to make the prepolymer and the diisocyanate added into the prepolymer for tuning the HSMW can be the same or different.

[0109] HSMW = Rx(MWex + MWdi) + K(R2 / (R-l))x(MWex, + MWxdi) (5) where K is the molar ratio of extra added diisocyanate to the original diisocyanate in making the prepolymer. The MWdi is the molecular weight of the extra added diisocyanate. In the event that the type of the extra amount of diisocyanate added before chain extension is the same as the type of the original diisocyanate used in making the prepolymer, then MWxdi is equal to MWdi.

[0110] The HSMW is very much dependent on how much extra diisocyanate is added into the prepolymer.

[0111] The weight percent of the soft segment content (SSWT%) in the polymer can be calculated by equation (6) based on the ingredient weights in making the prepolymer and the total weight of the polymer solids:

[0112] SSWT% = (WTgl + WTdi / R) X 100 I WTpolymer (6) where WTgi and WTdi are the respective weight of the glycol (or extended glycol) and the diisocyanate, R is the molar ratio of the diisocyanate to the glycol (or the extended glycol) in making the isocyanate-terminated prepolymer, and WT polymer is the total weight of the polymer solids consisting of all components in making the segmented polyurethane or polyurethane urea. Accordingly, the weight percent of the hard segment content in the polymer can be estimated by equation (7).

[0113] HSWT% 100 - SSWT% (7)

[0114] Preferably, the polyurethane-based polymer also has a number average molecular weight of 200k-500k Da, 200k-400k Da or 300k Da as measured by gel permeation chromatography.

[0115] The molecular weights referred to in this description, including the glycol molecular weight, the segmental molecular weights and the polymer molecular weight, are number average molecular weights.

[0116] In a non-limiting example, the polyurethane-based polymer may be prepared in a method comprising:

[0117] (a) adding a diisocyanate to a glycol at a capping ratio of less than 1.5 to produce an under-capped capped glycol;

[0118] (b) adding additional diisocyanate to the capped glycol; and

[0119] (c) adding a chain extender to produce the polymer with engineered hard and soft segment molecular weights; wherein the glycol is polytetramethylene ether glycol (PTMEG).

[0120] Nonlimiting examples of diisocyanates useful in the present disclosure include 4,4'- methylene bis(phenyl isocyanate) (also referred to as 4,4-diphenylmethane diisocyanate (MDI)), 2,4'- methylene bis(phenyl isocyanate, 4,4'-rnethylenebis(cyclohexyl isocyanate),

[0121] 1.4-xylenedi isocyanate, l,4-bis(isocyanatomethyl)cyclohexane, 2,6-toluenediisocyanate,

[0122] 2.4- toluenediisocyanate, and mixtures thereof. Examples of specific diisocyanates include Takenate® 500 and FORTIMOO 1,4-116XDI (Mitsui Chemicals), Mondur® MB (Bayer), Lupranate® M (BASF), and Isonate® 125 MDR (Dow Chemical), and combinations thereof. Nonlimiting examples of glycols useful according to the present invention include polyether glycols such as poly(tetramethylene ether) glycols (PTMEG), copolyether glycols such as poly(tetramethyleneether-co-ethyleneether) glycol and poly(tetramethylene ether-co-2- methyltetramethylene ether) glycol, polyester and copolyester glycols such as polycaprolactone diol and those produced by condensation polymerization of aliphatic dicarboxylic acids and diols, or their mixtures, oflow molecular weights with no-more than 12 carbon atoms in each molecule, and polycarbonate glycols produced by condensation polymerization of aliphatic diols with phosgene, dialkylcarbonates or diarylcarbonates. Examples of specific commercially available glycols are Terathane® glycols (INVISTA of Wichita, Kansas, USA), PTG-L glycols (Hodogaya Chemical Co., Ltd., Tokyo, Japan), ETERNACOLL® diols (Ube Industries, Ltd., Tokyo, Japan) and STEPANPOL® polyols (Stepan, Illinois, USA).

[0123] Nonlimiting examples of diamine chain extenders useful in making the segmented polyurethane ureas according to the present disclosure include one or more diamines selected from 1,2-ethylenediamine; 1,4-butanediamine; 1,2-butanediamine; 1,3- butanediamine; 1,3- diamino-2,2-dimethylbutane; 1,6-hexamethylenediamine; 1,12- dodecanediamine; 1,2- propanediamine; 1,3-propanediamine; 2-methyl-l,5- pentanediamine; l-amino-3,3,5-trimethyl-5-aminomethylcyclohexane; 2,4-diamino- 1 - methylcyclohexane; N-methylamino-bis(3- propylamine); 1,2-cyclohexanediamine; 1,4- cyclohexanediamine; 4,4'-methylene-bis (cyclohexylamine); isophorone diamine; 2,2- dimethyl- 1,3-propanediamine; meta-tetramethylxylenediarnine; l,3-diamino-4- methylcyclohexane; 1,3-cyclohexane-diamine; 1,1- methylene-bis(4,4'-diaminohexane); 3-aminomethyl-3,5,5-tri methylcyclohexane; l,3-pentanediamine(l,3-diaminopentane); m-xylylene diamine; and Jeffamine® (Texaco). When a segmented polyurethane with urethane hard segments is desired, the chain extender is a diol. Examples of such diols that may be used include, but are not limited to, ethylene glycol, 1,3- propanediol, 1,2- propylene glycol, 3-methyl-l,5-pentanediol, 2,2-dimethyl-l,3-trimethylene diol, 2,2,4- trimethyl-l,5-pentanediol, 2-methyl-2-ethyl-l,3-propanediol, 1,4- bis(hydroxyethoxy)benzene, and 1,4-butanediol and mixtures thereof.

[0124] Nonlimiting examples of useful chain terminators for the present disclosure include one or more monofunctional amines selected from ethylamine, propylamine, isopropylamine, n- butylamine, sec-butylamine, tert-butylamine, isobutylamine, isopentylamine, 1- hexylamine, 1-octylamine, 2-ethyl-l-hexaneamine, cyclohexylamine, N,N-diethylamine, N-ethyl-N-propylamine, N,N-diisopropylamine, N-tert-butyl-N-methylamine, N-tert-butyl- N-benzylamine, N,N-dicyclohexylamine, N-ethyl-N-isopropylamine, N-tertbutyl-N- isopropylamine, N-isopropyl-N-cyclohexylamine, N-ethyl-N-cyclohexylamine, N,Ndiethanolamine, and 2,2,6,6-tetramethylpiperidine.

[0125] A non-limiting example of the solvent used in the present disclosure is N,N- dimethylacetamide (DMAc).

[0126] In one nonlimiting embodiment, the process steps involved in making the segmented polyurethanes or polyurethane ureas of the present disclosure can be a batch process or a continuous process or their combinations. In one nonlimiting embodiment, an extended glycol is made by a batch process, which is further supplied to make the isocyanate- terminated capped glycol prepolymer and to make the polymer with chain extension and termination in a solvent by a continuous polymerization process. For another example, adding and mixing a diisocyanate to a capped glycol prepolymer in the under-capping process can be conducted in a batch process or a continuous process.

[0127] In another nonlimiting embodiment, steps involved in making an extended glycol and / or a capped glycol prepolymer are performed with heat, with or without the use of a catalyst, typically in a temperature range of 50 to 100°C.

[0128] In some nonlimiting embodiments, the process further comprises the step of extending a glycol of low molecular weight to a hydroxy-terminated polyurethane or polyurethaneurea or an extended glycol, prior to making an isocyanate-terminated or capped glycol prepolymer followed by chain extension, so that both molecular weights of the soft segment and the hard segment can be increased without limitation by the low molecular weight of the starting glycol.

[0129] In some nonlimiting embodiments, the process further comprises the step of adding an additional diisocyanate to an isocyanate-terminated or capped glycol prepolymer so that molecular weight of the hard segment is not affected by the low capping ratio prior to the addition of a chain extender.

[0130] The polyurethane or polyurethane urea binder is preferably from a recycled material, such as recycled textiles.

[0131] The polyurethane or polyurethane urea binder of the disclosure may be in fibre form, particle form, or granules.

[0132] The polyurethane or polyurethane urea binder of the disclosure is preferably in the form of a fibre.

[0133] In one embodiment, the polyurethane or polyurethane urea binder fibres are spun from a composition of the polyurethane-based polymer. The fibres may be, for example, but not limited to, dry spun, wet spun or melt spun. In one nonlimiting embodiment, the fibres are dry spun.

[0134] The polyurethane or polyurethane urea binder fibre may be a staple fibre. Preferably the length of polyurethane or polyurethane urea binder fibre is larger than the largest dimension of the ceramic material particle, more preferably more than 5 times larger

[0135] Preferably, the polyurethane or polyurethane urea binder fibre has a length of between 100-1000 pm, for instance 100-800 pm, or 200-600 pm.

[0136] Fibres of polyurethane or polyurethane urea binder according to the disclosure have an excellent elongation at break, for instance as measured with the general method of ASTM D 2731-72. In an example, three fibres, a 2-inch (5-cm) gauge length and a 0-300% elongation cycle are used for each of the measurements. The samples are cycled five times at a constant elongation rate of 50 centimeters per minute. Load power (5TP300), the stress on the polyurethane or polyurethane urea binder during the fifth cycle at 300% extension, is reported as gram-force for a given decitex. Unload power (5TM100) is the stress at an extension of 100% for the fifth unload cycle and is also reported in gram-force. Percent elongation at break is measured on a sixth extension cycle. Percent set was also measured on samples that had been subjected to five 0-300% elongation / relaxation cycles. The percent set, %SET, was then calculated as % SET = 100 x Lf - Lo / Lo where Lo and Lf are respectively the fibre length when held straight without tension before and after the five elongation / relaxation cycles.

[0137] The flatness index of stretch and recovery of the polyurethane or polyurethane urea binder fibres were determined by the ratio of 5TM100 / 5TP300, which was the ratio of the recovery power or unload power at 100% extension to the stretch power or load power at 300% extension measured in the fifth 0-300% stretch / recovery cycles.

[0138] Preferably the polyurethane or polyurethane urea binder fibre has an elongation at break of at least 300%, for example at least 400%, at least 500%, or at least 600%.

[0139] For instance, the elongation at break of the polyurethane or polyurethane urea binder fibre is from about 500% to about 800%, or from about 600% to about 700%.

[0140] Preferably, the polyurethane or polyurethane urea binder fibre has an excellent flat stretch / recovery determined by a 5TM100 / 5TP300 ratio of greater than 0.09.

[0141] Preferably, the polyurethane or polyurethane urea binder fibre has a SET% of less than 20, more preferably less than 16%. Fibres of polyether-polyurea block copolymers are commonly referred to as Spandex, Elastane or Lycra. Spandex / elastane / Lycra are exemplary polyurethane or polyurethane urea binders according to the disclosure. Spandex / elastane / Lycra typically comprises at least 85% segmented polyurethane-based polymer, and may additionally comprise pigments, stabilizers, lubricants, antioxidants, other additives and solvents.

[0142] Suitable spandex fibres are for example Arachra® from TK chemical Corp, Korea; Roica™ from Asahi Kasei, Japan; Elafit™ from Taekwang Indsutrial Co, Ltd., Korea; and creora® from Hyosung TNC, Korea.

[0143] The thickness of the polyurethane or polyurethane urea binder fibre may be from about 2 den to about 60 den, preferably from about 10 den to about 60 den, more preferably from about 20 den to about 50 den, even more preferably from about 30 den to about 50 den, most preferably from about 35 den to about 45 den. The thickness may be determined by any suitable method, for example ASTM D2591 - 07(2020).

[0144] In a further embodiment, the thickness of the polyurethane or polyurethane urea binder fibre is about 40 den.

[0145] The elastic properties of the polyurethane or polyurethane urea binder impart on the insulating edge coating excellent mechanical properties such that it can withstand deformation. Insulating edge coatings that cannot withstand deformation are prone to cracking, after which they may cease to function an insulating edge coating.

[0146] The excellent mechanical properties may also prevent damage to the insulating coating during later processing of the electrode e.g., during a calendaring step.

[0147] In addition, when the insulating edge coating has excellent mechanical properties, the insulating effect may be achieved with a thinner insulating edge coating layer, or a smaller overlapping region between the active layer and the second region of the conductive foil.

[0148] In addition, the improved mechanical properties provide increased resistance to delamination as shown in the Examples.

[0149] To deposit the insulating edge coating, an insulating edge coating slurry may first be formed.

[0150] An example method of preparing the insulating edge coating comprises the steps of; providing a polyurethane or polyurethane urea binder, a ceramic material and a solvent; combining the polyurethane or polyurethane urea binder, the ceramic material and the solvent to form an insulating edge coating slurry.

[0151] In the context of the disclosure "combining" refers to combining a polyurethane or polyurethane urea binder, a ceramic material and a solvent in any order, and in any form.

[0152] The components may be combined stepwise, or they may be combined simultaneously.

[0153] "Combining" may also comprise agitation, for example stirring, ultrasonication or shaking.

[0154] In preferred embodiments, the polyurethane or polyurethane urea binder is combined with the solvent to form a dispersion in a first step, and the ceramic material is added to the dispersion in a second step. In some embodiment, the ceramic material is added to the dispersion in batches.

[0155] In one embodiment, the solvent is an organic solvent such as N-methyl-2-pyrrolidone (NMP).

[0156] Typically, it is difficult to disperse a ceramic material in a solvent, and therefore large amount of solvent, long and high energy mixing steps and the preparation of small slurry batches is necessary.

[0157] Once deposited, the solvent is evaporated to leave a dry insulating edge coating. The drying step is slow and consumes significant energy. Providing a slurry that has a low solvent content can significantly reduce the time and energy required for the drying step.

[0158] The polyurethane or polyurethane urea binder has excellent dispersing properties compared to other 'green' binders commonly used in the art, for example, polyimide.

[0159] The excellent dispersing properties of the polyurethane or polyurethane urea binder allow for the preparation of an insulating edge coating slurry comprising a lower solvent content than other commonly used binders.

[0160] For instance, the insulating edge coating slurry of the disclosure may comprise about 50- 90 wt% solvent, for instance about 60-80 wt%, about 65-80 wt%, or about 70-73 wt % solvent. The excellent dispersing properties of the polyurethane or polyurethane urea binder eliminates the need for long mixing times in preparing the insulating edge coating slurry.

[0161] In addition, gentler mixing conditions can be employed e.g., lower shear and lower rpm reducing the energy required to prepare an insulating edge coating slurry and may allow for larger batches to be prepared.

[0162] The polyurethane or polyurethane urea binder also provides a highly homogenous insulating edge coating slurry dispersion, leading to homogeneous distribution of ceramic material in the insulating edge coating. This prevents the formation of areas with sub-par insulating properties due to the presence of too little ceramic material. In the same way, this also prevents the formation of areas of the insulating edge coating comprising too much ceramic material, which results in areas with poor mechanical properties.

[0163] The polyurethane or polyurethane urea binder also provides for excellent insulating edge coating slurry stability.

[0164] In the context of the disclosure, "stability" of a slurry can be tested by allowing the slurry to stand at room temperature and inspecting the change in visual appearance of the slurry. A gradient forming from bottom to top is an indication that the particles in the slurry are beginning to settle. Likewise, the slurry becoming translucent is an indication that the particles in the dispersion have settled.

[0165] A "stable" slurry is considered to be a slurry that remains opaque and shows no visible signs of settling after 5 hours, preferably after 10 hours, preferably after 24 hours, preferably after 48 hours.

[0166] The insulating edge coating slurry of the disclosure is stable for at least 5 hours, at least 10 hours, at least 24 hours or at least 48 hours.

[0167] The stability of the insulating edge coating slurry allows for the preparation of large batches, which can be stored between deposition runs without the need for re-mixing before deposition.

[0168] Antioxidant

[0169] The edge coating of the disclosure comprises an antioxidant, wherein the antioxidant is a compound comprising a sterically hindered amine or sterically hindered phenol group. The antioxidant of the disclosure is preferably an oligomeric or polymeric compound comprising a sterically hindered amine or sterically hindered phenol group.

[0170] For instance, in a preferred embodiment, the antioxidant is a compound with a high molecular weight. For instance, the antioxidant may have a molecular weight of 1000 g / mol or more. For example, the antioxidant may have a molecular weight of 1100 g / mol or more, 1250 g / mol or more, or 1500 g / mol or more.

[0171] A high molecular weight prevents the antioxidant from migrating out of the edge coating and into the electrolyte due to a strong interaction between the antioxidant and the polyurethane or polyurethane urea binder.

[0172] Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof.

[0173] The antioxidant of the disclosure comprises a sterically hindered amine or sterically hindered phenol. The term "sterically hindered" is given its common meaning in the art.

[0174] Steric hindrance occurs when the size of one or more substituents affect the chemical reactivity of other nearby substituents within the same molecule, for instance by making it more difficult for reactive species to approach the nearby substituent.

[0175] Sterically hindered phenols are physically shielded from the approach of reactants. Sterically hindered phenols comprise a tertiary or quaternary carbon in the ortho position(s) with respect to the phenol group. That is, when the phenol is in the 1 position, positions 2 and 6 are substituted with tertiary or quaternary carbons.

[0176] In the context of the disclosure, a secondary carbon is a carbon atom that is bonded to two other carbon atoms, a tertiary carbon is a carbon atom that is bonded to three other carbon atoms, and a quaternary carbon is a carbon atom that is bonded to four other carbon atoms.

[0177] Thus, the central carbon in a tert-butyl group bonded to a phenyl ring would be a quaternary carbon, as it is attached to the phenyl ring (1 carbon) and three other carbon atoms (namely, the three methyl groups of the tert-butyl). Similarly, sterically hindered amines are compounds in which the nitrogen atom of the amine molecule is physically shielded by neighbouring groups so that large molecules cannot easily approach and react with the nitrogen. For example, a sterically hindered amine may be a secondary amine in which the amino group is bonded to at least one secondary or tertiary carbon, or it may be a tertiary amine comprising sterically hindering substituents.

[0178] In the context of the disclosure, a secondary amine is an amine wherein the nitrogen atom is attached to two carbon atoms, and a tertiary amine is an amine wherein the nitrogen atom is bonded to three carbon atoms.

[0179] Accordingly, antioxidants according to the disclosure may comprise at least one of: a phenol comprising a tertiary or quaternary carbon in the position(s) ortho to the phenol group; a phenol comprising a long chain alkyl group (e.g. Cs-Cie), optionally containing an ether or thioether linkage (such as CFhOCs-Cie-alkyl or CFhSCs-Cie-alkyl); a secondary amine wherein the amino group is bonded to at least one tertiary carbon; a secondary amine wherein the amino group is part of a ring structure, wherein at least one ring carbon bonded to the amine group is a secondary or tertiary carbon; or a tertiary amine wherein the amino group is bonded to at least one alkyl group comprising at least 4 carbon atoms.

[0180] In some embodiments, the antioxidant is a sterically hindered phenol with a structure according to Formula (I) :

[0181] Formula (I)

[0182] In Formula (I), A represents the remainder of the antioxidant molecule. In Formula (I) at least one of F and R2denotes an alkyl or alkenyl group. Preferably both of R1and R2denote an alkyl or alkenyl group. R1and R2may be the same alkyl group, or they may be different.

[0183] To provide sufficient steric hindrance, preferably at least one of R1and R2denote an alkyl or alkenyl group comprising at least 4 carbon atoms (C4). For instance, the alkyl or alkenyl group may comprise a C4-C12 carbon chain.

[0184] The alkyl or alkenyl group may be linear, branched or in ring form.

[0185] Preferably, the alkyl group is a branched. In exemplary embodiments, R1and / or R2are branched alkyl groups independently selected from n-propyl, n-butyl, sec-butyl, isobutyl and tertbutyl.

[0186] In an exemplary embodiment, the antioxidant has a structure according to Formula (I) wherein:

[0187] R1and R2denote tert-butyl.

[0188] In some embodiments, the alkyl or alkenyl group of R1and / or R2comprises a hetero-atom containing group, for example an O, S or N-containing group may be present in the form of an amide, ketone or ester substituent may be present, or the alkyl or alkenyl group of R1and / or R2may comprise a sulphur linkage.

[0189] For instance, the phenol may contain a long chain alkyl group (e.g. Cs-Cie-alkyl), optionally containing an ether or thioether linkage at a position ortho to the phenol group. Suitable substituents include Cs-Cie-alkyl, CFhOCs-Cie-alkyl, and CFhSCs-Cie-alkyl.

[0190] The benzene ring of the sterically hindered phenol also comprises further substituents, denoted by A.

[0191] The group denoted by A must be suitable for use in an edge coating e.g. preferably it does not degrade and / or negatively interact with the other cell components during use or storage. The chemical nature of the group denoted by A is not important other than that is it compatible for use in an edge coating.

[0192] A may be bonded to the sterically hindered phenol at any vacant position on the ring. Preferably, the group denoted by A is bonded to the sterically hindered phenol in the position para to the phenol group. In some embodiments, A denotes an organic chain that is oligomeric or polymeric. Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof. Preferably the group denoted by A in such embodiments results in the antioxidant compound having a high molecular weight according to the disclosure.

[0193] In some embodiments, the antioxidant is a sterically hindered amine with a structure according to Formula (II):

[0194] Formula (II)

[0195] In Formula (II) both R4and R5denote alkyl or alkenyl groups. R4and R5may denote the same alkyl or alkenyl group, or they may denote different alkyl or alkenyl groups.

[0196] In some embodiments, R3is H. That is, the sterically hindered amine may be a secondary amine.

[0197] In some embodiments, R3also denotes an alkyl or alkenyl group. That is, the sterically hindered amine may be a tertiary amine.

[0198] In such embodiments, R3may represent an organic chain that is oligomeric or polymeric and is therefore analogous to A of Formula (I) and Formula (III). That is, the nature of the R3group in such embodiments must be suitable for use in an edge coating e.g. preferably it does not degrade and / or negatively interact with the other cell components during use or storage. The chemical nature of the group is not important in such embodiments other than that is it compatible for use in an edge coating.

[0199] Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof. Preferably the group denoted by R3in such embodiments results in the antioxidant compound having a high molecular weight according to the disclosure.

[0200] R4and / or R5are preferably alkyl or alkenyl groups comprising at least 4 carbon atoms (C4). For instance, the alkyl or alkenyl group may comprise a C4-C12 carbon chain. The alkyl or alkenyl group may be linear, branched or in ring form.

[0201] When the alkyl or alkenyl group is linear, preferably the sterically hindered amine is a tertiary amine. For instance, when R4and R5denote a linear alkyl or alkenyl group, R3is part of an alkyl or aryl ring. In some embodiments, the ring structure is aromatic and / or comprises heteroatoms. For instance, the ring may be a heterocycle comprising one, two or three heteroatoms. Preferably, the heteroatom is nitrogen.

[0202] In an exemplary embodiment, the antioxidant has a structure according to Formula (II), wherein:

[0203] R4and R5are linear C4 alkyl groups,

[0204] R3is part of an alkyl or aryl ring and wherein the compound of Formula (II) is a tertiary amine.

[0205] Preferably, when R4and / or R5are alkyl groups, the alkyl group is a branched. In exemplary embodiments, R4and / or R4are branched alkyl groups independently selected from n- propyl, n-butyl, sec-butyl, isobutyl and tertbutyl.

[0206] In some embodiments, the alkyl or alkenyl group comprises a hetero-atom containing group, for example an O or N-containing group may be present in the form of an amide, ketone or ester substituent as an example.

[0207] In some embodiments, R4and R5combine to form a ring, for instance a five, six or sevenmembered alkyl, alkenyl or aryl ring. In such embodiments, the amine may be a secondary or tertiary amine. Preferably R3is H when R4and R5combine to form a ring. That is, preferably the amine is a secondary amine when R4and R5combine to form a ring.

[0208] When R4and R5combine to form a ring, the carbon atom bonded to N in at least one of R4and R5is a secondary or tertiary carbon. Preferably, the carbon atom bonded to N in both R4and R5are tertiary carbons.

[0209] For example, if the ring is a 6-membered alkyl ring formed from R4and R5, the carbon atoms bonded to N in one or both of R4and R5may comprise an alkyl or alkenyl substituent. Preferably, the carbon atoms bonded to N in both of R4and R5comprise an alkyl or alkenyl substituent. Even more preferably, when the ring is an alkyl ring formed from R4and R5, the carbon atoms bonded to N of both of R4and R5comprise two alkyl or alkenyl substituents, wherein most preferably both comprise two alkyl substituents. Preferably the alkyl or alkenyl substituent comprises a C1-C4 carbon chain.

[0210] Preferably the alkyl substituent is branched. For instance, the alkyl substituent may be n- propyl, n-butyl, sec-butyl, isobutyl and tertbutyl.

[0211] Preferably, when R4and R5combine to form a ring, each carbon atom in R4and R5bonded to N comprises the maximum number of alkyl or alkenyl substituents. For example, when R4and R5combine to form a ring, each of the positions in R4and R5bonded to N may comprise two substituents. Alternatively, when R4and R5combine to form a ring, each of the positions in R4and R5bonded to N may comprise one substituent.

[0212] In an exemplary embodiment, the antioxidant has a structure according to Formula (II), wherein:

[0213] R4and R5combine to form a 6-membered alkyl ring, wherein both R4and R5are tertiary carbons each comprising two methyl groups (with the remaining carbon substituents being the alkylene chains that combine to form the ring).

[0214] For instance, the antioxidant may have a structure according to Formula (III) :

[0215] Formula (III)

[0216] In Formula (III), A represents the remainder of the antioxidant molecule.

[0217] As with the sterically hindered phenols with a structure according to Formula (I), the group denoted by A must be suitable for use in an edge coating e.g. preferably it does not degrade and / or negatively interact with the other cell components during use or storage. The chemical nature of the group denoted by A is not important other than that is it compatible for use in an edge coating. For instance, A may denote an organic chain that is oligomeric or polymeric. Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof. Preferably the group denoted by A in such embodiments results in the antioxidant compound having a high molecular weight according to the disclosure.

[0218] The bond between A and the sterically hindered amine may be at any vacant position on the sterically hindered amine. Preferably, the bond between A and the sterically hindered amine is at the 4-position relative to the amine group, in embodiments wherein R4and R5combine to form a 6-membered ring.

[0219] Preferably, the antioxidant comprises a plurality of sterically hindered amine and / or sterically hindered phenol groups. Taking Formula (III) as an example, the group denoted by A may therefore be an oligomeric or polymeric group that comprises a further sterically hindered amine or sterically hindered phenol group.

[0220] Surprisingly, antioxidants according to the disclosure can bind leached transition metals. Without wishing to be bound by theory, antioxidants according to the disclosure bind transition metals such as Ni, Co and Mn from the cathode active material thereby preventing leaching of the metals and breakdown of the cathode. Accordingly, providing an edge coating comprising an antioxidant provides a cell with improves electronic properties and improved thermal stability as shown in the Examples.

[0221] Typically, the binding between the antioxidant and the transition metal forms an antioxidant-transition metal complex in which the antioxidant and the transition metal are strongly bound. This is beneficial as it is less likely that the transition metal is released during battery operation. However, this also means that once a complexation occurs at a particular site, said site is no longer able to bind further transition metals. It is therefore beneficial to provide multiple binding sites per antioxidant compound to ensure that sufficient transition metals are bound.

[0222] Preferably, the antioxidant has multiple transition metal binding sites. Such antioxidants may be described as multi-faceted or multi-dentate binding sites.

[0223] In some embodiments, the antioxidant is an oligomeric or polymeric compound. An oligomeric or polymeric structure allows for the antioxidant to be securely lodged within the polyurethane or polyurethane urea binder and also have transition metal binding sites protruding into the electrolyte. This provides excellent and secure binding of leached transition metals.

[0224] In an embodiment, the antioxidant is an oligomeric or polymeric compound that is multidentate.

[0225] Exemplary antioxidants are compounds with the following structures:

[0226] Exemplary antioxidants include those sold under the registered trade names Irganox® 1098, Irganox 1726®, Chimassorb® 2020, Tinuvin® 770, Tinuvin® 622, Tinuvin® 249, however any suitable antioxidant can be used. Preferably, the edge coating comprises 0.1-10wt% antioxidant. For instance, the polyurethane or polyurethane urea binder may comprise 0.25-8wt%, 0.5-7wt% or l-5wt% antioxidant.

[0227] The antioxidant may be one compound, or it may be a mixture of different antioxidant compounds.

[0228] For instance, the antioxidant may comprise two compounds in a weight ratio of from 20:80 to 80:20, for instance 30:70 to 70:30, such as 40_60 to 60:40, such as about 50:50.

[0229] Preferably, when the antioxidant comprises a mixture of antioxidant compounds, wherein the antioxidant comprises at least 50 wt% of an antioxidant with a high molecular weight, more preferably at least 60 wt%, such as at least 70 wt% or even at least 80 wt%. That is, the antioxidant may comprise a mixture of compounds wherein at least 50 wt% is made up of a compound with a molecular weight of 1000 g / mol or more, for example 1100 g / mol or more, 1250 g / mol or more, or 1500 g / mol or more.

[0230] In some embodiments, the edge coating further comprises a secondary antioxidant compound. In the context of the disclosure, a secondary antioxidant is a compound that can regenerate the antioxidant of the disclosure.

[0231] As discussed above, upon binding a transition metal, the antioxidant of the disclosure is consumed and can no longer bind further metal ions. The role of a secondary antioxidant compound is to regenerate the antioxidant so that it can once again bind transition metals.

[0232] An example of a suitable secondary antioxidant is a phosphite compound or "phosphite antioxidant". Phosphite antioxidants are particularly effective at reviving antioxidants comprising sterically hindered phenols.

[0233] An example of a suitable secondary antioxidant is 2,2'-methylenebis (4,6-di-tert- butylphenyl) octylphosphite (CAS no. 126050-54-2).

[0234] Exemplary antioxidants are those sold under the registered trade names ADK STAB HP 10 ®, Irganox PS 800 FL®, Irfanos 126®, Irganox 1726®.

[0235] In an embodiment is an edge coating comprising: an antioxidant, wherein the antioxidant is a compound comprising a sterically hindered phenol or a sterically hindered amine; and a secondary antioxidant, wherein the secondary antioxidant is a phosphite antioxidant.

[0236] Particularly advantageous combinations of antioxidant and secondary antioxidant include:

[0237] • Irganox 1726® and Irganox 1098®;

[0238] • Irgafos 126® and Irganox 1098®; and

[0239] • Irganox PS 800 FL® and Irganox 1098.

[0240] In some embodiments, the same compound may act as a primary and secondary antioxidant. That is, in some embodiments, the antioxidant is self-regenerative. An example of such an antioxidant is the compound sold under the trade name Irganox 1726®.

[0241] By including a secondary antioxidant, improved transition metal binding may be achieved. In some instances, less of the antioxidant needs to be included in the edge coating due to the improved transition metal binding properties.

[0242] In some embodiments, the secondary antioxidant may lead to a further improved thermal stability of the edge coating.

[0243] The elastic properties of the polyurethane binder impart on the insulating edge coating excellent mechanical properties such that it can withstand deformation. Insulating edge coatings that cannot withstand deformation are prone to cracking, after which they may cease to function an insulating edge coating.

[0244] The excellent mechanical properties may also prevent damage to the insulating coating during later processing of the electrode e.g., during a calendaring step.

[0245] In addition, when the insulating edge coating has excellent mechanical properties, the insulating effect may be achieved with a thinner insulating edge coating layer, or a smaller overlapping region between the active layer and the second region of the conductive foil.

[0246] In addition, the improved mechanical properties provide increased resistance to delamination as shown in the Examples.

[0247] To deposit the insulating edge coating, an insulating edge coating slurry may first be formed. An example method of preparing the insulating edge coating comprises the steps of; providing a polyurethane binder, a ceramic material and a solvent; combining the polyurethane binder, the ceramic material and the solvent to form an insulating edge coating slurry.

[0248] In the context of the disclosure "combining" refers to combining a polyurethane binder, a ceramic material and a solvent in any order, and in any form.

[0249] The components may be combined stepwise, or they may be combined simultaneously.

[0250] "Combining" may also comprise agitation, for example stirring, ultrasonication or shaking.

[0251] In preferred embodiments, the polyurethane binder is combined with the solvent to form a dispersion in a first step, and the ceramic material is added to the dispersion in a second step. In some embodiment, the ceramic material is added to the dispersion in batches.

[0252] In one embodiment, the solvent is an organic solvent such as N-methyl-2-pyrrolidone (NMP).

[0253] Typically, it is difficult to disperse a ceramic material in a solvent, and therefore large amount of solvent, long and high energy mixing steps and the preparation of small slurry batches is necessary.

[0254] Once deposited, the solvent is evaporated to leave a dry insulating edge coating. The drying step is slow and consumes significant energy. Providing a slurry that has a low solvent content can significantly reduce the time and energy required for the drying step.

[0255] The polyurethane binder has excellent dispersing properties compared to other 'green' binders commonly used in the art, for example, polyimide.

[0256] The excellent dispersing properties of the polyurethane binder allow for the preparation of an insulating edge coating slurry comprising a lower solvent content than other commonly used binders.

[0257] For instance, the insulating edge coating slurry of the disclosure may comprise about 50- 90 wt% solvent, for instance about 60-80 wt%, about 65-80 wt%, or about 70-73 wt % solvent. The excellent dispersing properties of the polyurethane binder eliminates the need for long mixing times in preparing the insulating edge coating slurry.

[0258] In addition, gentler mixing conditions can be employed e.g., lower shear and lower rpm reducing the energy required to prepare an insulating edge coating slurry and may allow for larger batches to be prepared.

[0259] The polyurethane binder also provides a highly homogenous insulating edge coating slurry dispersion, leading to homogeneous distribution of ceramic material in the insulating edge coating. This prevents the formation of areas with sub-par insulating properties due to the presence of too little ceramic material. In the same way, this also prevents the formation of areas of the insulating edge coating comprising too much ceramic material, which results in areas with poor mechanical properties.

[0260] The polyurethane binder also provides for excellent insulating edge coating slurry stability.

[0261] In the context of the disclosure, "stability" of a slurry can be tested by allowing the slurry to stand at room temperature and inspecting the change in visual appearance of the slurry. A gradient forming from bottom to top is an indication that the particles in the slurry are beginning to settle. Likewise, the slurry becoming translucent is an indication that the particles in the dispersion have settled.

[0262] A "stable" slurry is considered to be a slurry that remains opaque and shows no visible signs of settling after 5 hours, preferably after 10 hours, preferably after 24 hours, preferably after 48 hours.

[0263] The insulating edge coating slurry of the disclosure is stable for at least 5 hours, at least 10 hours, at least 24 hours or at least 48 hours.

[0264] The stability of the insulating edge coating slurry allows for the preparation of large batches, which can be stored between deposition runs without the need for re-mixing before deposition.

[0265] CELLS

[0266] The present disclosure also relates to cells comprising the edge coating of the disclosure, for example a secondary lithium-ion cell. Such cells typically additionally comprise an anode, a separator disposed between the anode and cathode, said cathode, anode and separator forming an electrode assembly, the cell further comprising a housing for the electrode assembly. The cell will typically comprise an electrolyte to facilitate the transport of lithium ions between the composite cathode and anode. The housing is typically sealed to ensure the electrolyte is retained within the housing. Said housing usually includes terminals in electrical contact with the anode and composite cathode.

[0267] These cells may be combined to form a battery system (i.e. an array of cells).

[0268] The disclosure also relates to an electrical device comprising a cell of the disclosure. For instance, the disclosure relates to a vehicle comprising a cell (or battery system) of the disclosure. The vehicle is preferably an electric vehicle, such as a car, truck, bus, scooter, motorbike, bicycle or the like, preferably a car, truck or bus.

[0269] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0270] Examples

[0271] Example 1

[0272] Table 1

[0273] Samples 1 and 2 are a polyurethane urea binder, while Samples 3 and 4 are the same binder which additionally includes additives typically formulated with commercial polymers (stabilizers, delustrants etc.). Samples 5 and 6 were prepared using HSV900 which is an ultra-high molecular weight Ultra High Molecular Weight PVDF (Kynar® HSV900).

[0274] Table 1 shows the results of delamination testing. The data shows that edge coatings comprising polyurethane-based binders (samples 1-4) show improved resistance to delamination compared to edge coatings comprising fluorinated binders such as PVDF (samples 5 and 6). Without wishing to be bound by theory, it is considered that this is because of the improved mechanical properties such as elasticity that are imparted. Additionally, a more homogenous distribution of the ceramic material within the edge coating may also be achieved which also provides improved adhesion.

[0275] Additionally, it can be seen that samples comprising a polyurethane urea binder and no additives (sample 1 and 2) show improved resistance to delamination compared to polyurethane urea binders comprising around 2wt% additive (samples 3 and 4).

[0276] The delamination test comprises:

[0277] 1) Preparing an edge coating layer on an aluminium foil by; providing a binder, a ceramic material and a solvent; combining the binder, the ceramic material and the solvent to form an insulating edge coating slurry depositing the slurry on an aluminium foil to form an edge coating layer

[0278] 2) Storing the sample at 70°C for 7 days

[0279] 3) Visually inspecting the foil for signs of delamination

[0280] Example 2

[0281] Table 2 shows the results of thermal stability testing. Improved thermal stability can be estimated by monitoring the colour change of the binder on exposure to heat. The more yellow the binder become, the lower its thermal stability.

[0282] The thermal stability test is suitable for directly comparing the thermal stability of different edge coating compositions.

[0283] The thermal stability test comprises: 1) Preparing an edge coating layer on an aluminium foil by; providing a binder, a ceramic material, optionally an antioxidant and a solvent; combining the binder, the ceramic material, the optional antioxidant and the solvent to form an insulating edge coating slurry depositing the slurry on an aluminium foil to form an edge coating layer

[0284] 2) Storing the samples at 250°C for 10 minutes.

[0285] 3) Determining the Yellowness Index (Y-index) of the samples using a spectrodensitometer.

[0286] Table 2.

[0287] Samples A and B were prepared using a polyurethane urea binder, and Samples C and D were prepared using HSV900 as the binder (PVDF). Samples B and D comprised an antioxidant, whereas samples A and C did not.

[0288] The Y-index of the samples to evaluate the degree of yellowing after storage at 250°C for 10 minutes. A higher Y-index indicates a yellower sample.

[0289] As can be seen from Table 2, the Y-index of sample A is significantly higher than sample B, and the Y-index of sample C was significantly higher than for sample D. Accordingly, the Y-index of both polyurethane urea and PVDF-based edge coatings is improved by the incorporation of an antioxidant i.e. the degree of yellowing is drastically decreased.

[0290] This is correlated with an improved thermal stability of edge coatings comprising an antioxidant according to the disclosure.

Claims

Claims1. An electrode comprising a conductive foil, an active layer and an insulating edge coating; wherein the active layer comprises an active material, a binder and optionally a conductive additive; the insulating edge coating comprises a ceramic material, a polyurethane or polyurethane urea binder and an antioxidant; and the conductive foil comprising a first region, a second region and a third region, wherein the second region is located between the first and third regions; wherein the active layer is coated on the first region; the insulating edge coating is coated on the second region and overlaps the interface between the active layer and the second region; and the third region is not coated with active layer or insulating edge coating.

2. The electrode according to any preceding claim wherein the edge coating comprises 0.1- 10wt% antioxidant, for instance 0.25-8wt%, 0.5-7wt% or l-5wt% antioxidant.

3. The electrode according to any preceding claim wherein the antioxidant comprises a sterically hindered amine and / or phenol group.

4. The electrode according to any preceding claim wherein the antioxidant comprises a plurality of sterically hindered amine and / or phenol groups.

5. The electrode according to any preceding claim wherein the antioxidant comprises at least one of: a phenol comprising a tertiary or quaternary carbon in the position(s) ortho to the phenol group; a phenol comprising a Cs-Cie-alkyl, Cl- OCs-Cie-alkyl, and Cl- SCs-Cie-alkyl at a position ortho to the phenol group; a secondary amine wherein the amino group is bonded to at least one tertiary carbon;a secondary amine wherein the amino group is part of a ring structure, wherein at least one ring carbon bonded to the amine group is a secondary or tertiary carbon; or a tertiary amine wherein the amino group is bonded to at least one alkyl group comprising at least 4 carbon atoms.

6. The electrode according to any preceding claim wherein the antioxidant has a molecular weight of 1000 g / mol or more, for instance, 1100 g / mol or more, 1250 g / mol or more, or 1500 g / mol or more.

7. The electrode according to any preceding claim wherein the antioxidant is an oligomeric or polymeric compound.

8. The electrode according to any preceding claim wherein the polyurethane or polyurethane urea binder comprises a polyurethane-based polymer comprising segments of polyether and polyurea, wherein the polymer is based on glycols with a number average molecular weight less than 2500.

9. The electrode according to any preceding claim wherein the polyurethane or polyurethane urea binder comprises a polyurethane-based polymer that has a molecular weight ratio of the soft segment to the hard segment larger than 12.0, and a urea hard segment weight percent less than 7.8.

10. The electrode according to any preceding claim wherein the ceramic material is a metal oxide, a metal hydroxide or a metal oxide hydroxide, preferably wherein the ceramic material is aluminium oxide hydroxide, for instance y-aluminium oxide hydroxide, or aluminium oxide.

11. The electrode according to any preceding claim wherein the insulating edge coating comprises from 5 to 40 wt% polyurethane or polyurethane urea binder and from 95 to 60 wt% ceramic material.

12. An electrode assembly comprising the electrode according to any of claim 1-11 wherein the insulating edge coating is configured to prevent short circuits caused by contact between adjacent electrodes.

13. A cell comprising the electrode according to any of claims 1-11 or the electrode assembly of claim 12.

14. A battery system comprising the cell of claim 13.

15. A vehicle comprising the cell of claim 13 or the battery system of claim 14.

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