COMPOSITE SEPARATOR AND ELECTROCHEMICAL CELL, COMPREHENSIVE OF THIS

Abstract

Separator (12) for an electrochemical cell (10) that cycles lithium ions, wherein the separator (12) comprises: a microporous layer (28) with a first side (30) and an opposing second side (32), and one or more fire-retardant layers (34, 36) arranged on at least one of the first side (30) or the second side (32) of the microporous layer (28), wherein the one or more fire-retardant layers (34, 36) comprise cross-linked cyclopolyphosphazene particles, wherein the cross-linked cyclopolyphosphazene particles are formed by a nucleophilic polycondensation polymerization reaction between a cyclophosphazene and a comonomer, where cyclophosphazene is an organophosphorus compound with the following chemical formula: where X 1 , X 2 , X 3 , X 4 , X 5 , and X 6Each is a halid, and wherein the comonomer comprises 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-(9-fluorenylidene)diphenol, phenolphthalein, oxyresveratrol, resveratrol, dopamine, 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein or a combination thereof.

Description

INTRODUCTION

[0001] The present disclosure relates generally to electrochemical cells operated with lithium ions, and in particular to separators for electrochemical cells operated with lithium ions, wherein the separators have fire-retardant properties.

[0002] Such separators are known, for example, from CN 109 980 162 A. Another separator is described in the article by Fu, W.; Xu, R.; Zhang, X.; Tian, ​​Z.; Huang, H.; Xie, J.; Lei, C.: Enhanced wettability and electrochemical performance of separators for lithium-ion batteries by coating core-shell structured silicapoly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) particles. In: Journal of Power Sources, Vol. 436, 2019, 226839, pp. 1-6.

[0003] Electrochemical cells of secondary lithium batteries generally comprise a negative electrode and a positive electrode separated by a porous separator. The negative and positive electrodes, as well as the porous separator, are infiltrated with a liquid electrolyte, which acts as a medium for the conduction of lithium ions between the negative and positive electrodes during the discharge and recharge of the electrochemical cell. The porous separators of lithium batteries are generally made of ionically conductive and electrically insulating polymers and often take the form of a thin membrane or film.

[0004] Manufacturing defects, aging, and / or certain conditions of improper use can impair the thermal stability of secondary lithium batteries. Certain conditions that increase the internal temperature of lithium batteries can trigger undesirable events and / or chemical reactions within the batteries, which can lead to further undesirable heat generation. Since components of lithium batteries and / or their environment can be flammable, it may be desirable to incorporate materials into the internal components of such batteries that can effectively inhibit the propagation of combustion chain reactions. SUMMARY

[0005] To solve this problem, a separator with the features of claim 1, an electrochemical cell with the features of claim 4, and a method for producing a composite separator with the features of claim 8 are provided. Advantageous embodiments of the invention can be found in the dependent claims, the description, and the accompanying drawings.

[0006] Specifically, the present disclosure relates to a separator for an electrochemical cell that cycles lithium ions. The separator according to the invention comprises a microporous layer and one or more flame-retardant layers. The microporous layer has a first side and an opposing second side. The one or more flame-retardant layers are arranged on at least one of the first side or the second side of the microporous layer. The one or more flame-retardant layers comprise cross-linked cyclopolyphosphazene particles.

[0007] The cross-linked cyclopolyphosphazene particles are formed by a nucleophilic polycondensation polymerization reaction between a cyclophosphazene and a comonomer.

[0008] Cyclophosphazene is an organophosphorus compound with the following chemical formula: where X 1 , X 2 , X 3 , X 4 , X 5 and X 6 Each one is a halid.

[0009] The comonomer comprises 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-(9-fluorenylidene)diphenol, phenolphthalein, oxyresveratrol, resveratrol, dopamine, 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein or a combination thereof.

[0010] The cross-linked cyclopolyphosphazene particles can be spherical particles with a mean particle diameter of approximately 50 nanometers or greater than or equal to approximately 2 micrometers.

[0011] The cross-linked cyclopolyphosphazene particles can be tubular particles with a width greater than or equal to about 50 nanometers to less than or equal to about 200 nanometers and a length greater than or equal to about 500 nanometers to less than or equal to about 2 micrometers.

[0012] The one or more fire-retardant layers may also contain particles of a ceramic material. This ceramic material may include aluminum oxide, silicon dioxide, a dehydrated zeolite, a lithiated zeolite, or a combination thereof.

[0013] The particles of the ceramic material can have a mean particle diameter of approximately 50 nanometers or greater than or equal to approximately 5 micrometers.

[0014] The one or more fire-retardant layers may also include a binder.

[0015] The microporous layer may contain a polyolefin.

[0016] Each of the one or more fire-retardant layers can have a thickness of approximately 1 micrometer or greater than or equal to approximately 30 micrometers.

[0017] The cross-linked cyclopolyphosphazene particles can constitute, by mass, more than or equal to approximately 1% to less than or equal to approximately 80% of the one or more flame-retardant layers.

[0018] An electrochemical cell that cycles lithium ions is also disclosed. The electrochemical cell according to the invention comprises a negative electrode, a positive electrode spaced apart from the negative electrode, and a composite separator arranged between the negative and positive electrodes. The positive electrode comprises a transition metal oxide that can be subjected to reversible intercalation of lithium ions. The composite separator comprises a microporous layer with a first side and an opposing second side, and one or more flame-retardant layers arranged on at least one of the first or second sides of the microporous layer. The microporous layer comprises a polyolefin. The one or more flame-retardant layers comprise cross-linked cyclopolyphosphazene particles.The cross-linked cyclopolyphosphazene particles are formed by a nucleophilic polycondensation polymerization reaction between a cyclophosphazene and a comonomer.

[0019] Cyclophosphazene is an organophosphorus compound with the following chemical formula: where X 1 , X 2 , X 3 , X 4 , X 5 and X 6 Each of these components is a halide. The comonomer comprises 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-(9-fluorenylidene)diphenol, phenolphthalein, oxyresveratrol, resveratrol, dopamine, 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein, or a combination thereof.

[0020] The one or more fire-retardant layers may also contain particles of a ceramic material. This ceramic material may include aluminum oxide, silicon dioxide, a dehydrated zeolite, a lithiated zeolite, or a combination thereof.

[0021] The electrochemical cell may further comprise a liquid electrolyte that infiltrates the pores of the composite separator and establishes a lithium ion transport pathway between the negative and positive electrodes. The liquid electrolyte may comprise a lithium salt dissolved in a non-aqueous organic solvent. The non-aqueous organic solvent may comprise an organic carbonate, an aliphatic carboxylic acid ester, or a combination thereof.

[0022] The cross-linked cyclopolyphosphazene particles can exhibit a solubility of less than or equal to approximately 1% by mass in the non-aqueous organic solvent.

[0023] A process for producing a composite separator for an electrochemical cell that cycles lithium ions is disclosed. In the process according to the invention, a precursor mixture is prepared. The precursor mixture comprises a cyclophosphazene, a comonomer, an organic solvent, and a tertiary amine catalyst. The cyclophosphazene has the chemical formula (-N=P(-X)2-)3, where X is a halogen, and the comonomer comprises 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-(9-fluorenylidene)diphenol, phenolphthalein, oxyresveratrol, resveratrol, dopamine, 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein, or a combination thereof. The preparation of the precursor mixture initiates a nucleophilic polycondensation polymerization reaction between the cyclophosphazene and the comonomer, forming cross-linked cyclopolyphosphazene particles.The cross-linked cyclopolyphosphazene particles are dispersed in a solvent to form a slurry. The slurry is deposited onto at least one of the first or opposite second sides of a microporous polyolefin layer. The solvent is then removed from the slurry to form one or more flame-retardant layers arranged on at least one of the first or second sides of the microporous polyolefin layer.

[0024] Further areas of application will become apparent from the present description. The description and specific examples in this summary serve only for illustration and are not intended to limit the scope of protection of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein serve only to illustrate selected embodiments and not all possible embodiments, and are not intended to limit the scope of protection of the present disclosure. Fig. Figure 1 is a schematic side cross-sectional view of an electrochemical cell that cycles lithium ions, wherein the electrochemical cell comprises a compound separator positioned between a negative electrode and a positive electrode, and a liquid electrolyte infiltrating the pores of the compound separator. Fig. Figure 2 is a schematic representation of a cross-linked cyclopolyphosphazene macromolecule with several interconnected cyclophosphazene monomers bridged by organic comonomers. Fig. Figure 3 is a scanning electron micrograph of spherical particles of a cross-linked cyclopolyphosphazene. Fig. Figure 4 is a scanning electron micrograph of tubular particles of a cross-linked cyclopolyphosphazene. Fig. Figure 5 is a schematic side cross-sectional view of the composite separator of Fig. 1, wherein the composite separator comprises first and second flame-retardant layers arranged on opposite first and second sides of a microporous layer, and wherein each of the first and second flame-retardant layers comprises a mixture of cross-linked cyclopolyphosphazene particles and ceramic material particles. Fig. Figure 6 shows diagrams of capacity conservation (%) versus cycle count for an electrochemical cell comprising a composite separator with a mixture of cross-linked cyclopolyphosphazene particles and lithium-ion exchanged zeolite particles deposited on opposite first and second sides of a polymer membrane (solid line), and an electrochemical cell comprising a separator with lithium-ion exchanged zeolite particles deposited on opposite first and second sides of a polymer membrane (dashed line). Fig. Figure 7 shows Nyquist diagrams of -Im (Z) / Ohm versus Re (Z) / Ohm for an electrochemical cell comprising a composite separator with a mixture of cross-linked cyclopolyphosphazene particles and lithium ion-exchanged zeolite particles deposited on opposite first and second sides of a polymer membrane (solid line), and an electrochemical cell comprising a separator with lithium ion-exchanged zeolite particles deposited on opposite first and second sides of a polymer membrane (dashed line).

[0026] The corresponding reference symbols designate the relevant parts in the different views of the drawings. DETAILED DESCRIPTION

[0027] Since exemplary embodiments are provided, this is a careful disclosure that conveys the full scope to those skilled in the art. Numerous specific details are listed, such as examples of specific compositions, components, devices, and processes, to provide a comprehensive understanding of the embodiments of the present disclosure. It is obvious to those skilled in the art that specific details need not be used, that exemplary embodiments can be implemented in many different forms, and that none of them should be designed in such a way as to limit the scope of protection of the disclosure. In some exemplary embodiments, known processes, known device structures, and known technologies are not described in detail.

[0028] The terminology used herein serves only to describe exemplary embodiments and is not to be understood as restrictive. As used herein, the singular forms "a," "an," and "the" can also include the plural forms unless the context clearly indicates otherwise. The terms "includes," "comprehensive," "contain," and "exhibit" are inclusive and therefore specify the presence of specified features, elements, compositions, steps, integers, processes, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, processes, elements, components, and / or groups thereof.Although the open terms "comprises," "comprising," "including," and "having" are to be understood as non-restrictive terms used to describe and claim various embodiments set forth herein, in certain aspects these terms can alternatively be understood as more restrictive and limiting terms, such as "consisting of" or "essentially consisting of." Therefore, for each given embodiment that specifies compositions, materials, components, elements, ingredients, features, integers, operations, and / or process steps, the present disclosure expressly includes embodiments that consist of or essentially consist of such specified compositions, materials, components, elements, ingredients, features, integers, operations, and / or process steps.In the case of "consisting of", the alternative embodiment excludes all additional compositions, materials, components, elements, ingredients, features, integers, operations and / or process steps, whereas in the case of "essentially consisting of", all additional compositions, materials, components, elements, ingredients, features, integers, operations and / or process steps that significantly affect the basic and novel properties are excluded from such an embodiment, but all compositions, materials, components, elements, ingredients, features, integers, operations and / or process steps that do not significantly affect the basic and novel properties may be included in the embodiment.

[0029] All procedures, processes, and operations described herein are not to be interpreted as necessarily having to be carried out in the order explained or illustrated, unless they are expressly designated as the order of execution. It is also understood that additional or alternative steps may be applied unless otherwise specified.

[0030] When a component, element, or layer is described as being "on" or "interacting" with another element or layer, or as being "connected" or "coupled" with it, it may be directly on or interacting with, connected, or coupled to that other component, element, or layer, or there may be intervening elements or layers. Conversely, when an element is described as being "directly on" or "directly interacting with" another element or layer, or as being "directly connected" or "directly coupled" to it, there must be no intervening elements or layers. Other words used to describe the relationship between elements should be interpreted similarly (e.g.,“Between” as opposed to “directly between”, “neighboring” or “adjacent” as opposed to “directly adjacent” or “directly bordering”, etc.). As used herein, the term “and / or” includes combinations of one or more of the related listed items.

[0031] Although the terms "first," "second," "third," etc., may be used herein to describe different steps, elements, components, areas, layers, and / or sections, these steps, elements, components, areas, layers, and / or sections should not be restricted by these terms unless otherwise specified. These terms should only be used to distinguish one step, element, component, area, layer, or section from another. Terms such as "first," "second," and other numerical terms, when used herein, do not imply any sequence or order unless the context clearly indicates otherwise.Thus, one could refer to a first step, a first element, a first component, a first area, a first layer or a first section, which will be discussed below, as a second step, second element, second component, second area, second layer or second section, without deviating from the principles of the exemplary embodiments.

[0032] Spatially or temporally relative terms such as "before," "after," "inner," "outer," "below," "under," "lower," "above," "upper," and the like may be used herein for the sake of simplicity to describe the relationship of one element or feature to one or more other elements or features, as illustrated in the figures. Spatially or temporally relative terms may be intended to include, in addition to the orientation shown in the figures, different orientations of the device or system in use or operation.

[0033] Throughout this entire disclosure, numerical values ​​represent approximate measures or limits for ranges and include minor deviations from the stated values ​​and embodiments that approximate the stated value, as well as those that exactly approximate the stated value. Unlike the working examples at the end of the detailed description, all numerical values ​​of parameters (e.g., of quantities or conditions) in this patent specification, including the claims in the appendix, are to be understood as being modified in all cases by the term "approximately," regardless of whether "approximately" actually precedes the numerical value or not. "Approximately" means that the stated numerical value permits a slight inaccuracy (with some approximation to the accuracy of the value, approximately, or quite close to the value, almost).If the imprecision indicated by "approximately" is not otherwise understood in engineering with this ordinary meaning, then "approximately," as used herein, denotes at least variations that may arise from ordinary procedures for measuring and using such parameters. For example, "approximately" may encompass a deviation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and, in certain aspects, optionally less than or equal to 0.1%.

[0034] Furthermore, the disclosure of ranges includes the disclosure of all values ​​and further subdivided ranges within the entire range, including the endpoints and the subranges specified for the ranges.

[0035] As used herein, the terms “composition” and “material” are used interchangeably to refer generally to a substance containing at least the preferred chemical constituents, elements, or compounds, but which may also contain additional elements, compounds, or substances, including trace impurities, unless otherwise specified. An “X-based” composition or “X-based” material generally refers to compositions or materials in which “X” is the largest single constituent of the composition or material by weight percent (%). This may include compositions or materials with a weight percentage of X greater than 50% as well as compositions or materials with a weight percentage of X less than 50%, as long as X is the largest single constituent of the composition or material by weight.

[0036] The term "battery" refers to a device containing several interconnected electrochemical cells (battery cells) arranged in series and / or parallel, and may refer to battery cells grouped together in the form of battery modules and / or battery packs.

[0037] Exemplary embodiments will now be described in more detail with reference to the attached drawings.

[0038] The composite separators disclosed herein are formulated for use in electrochemical cells that cycle lithium ions to help prevent or inhibit the propagation of combustion chain reactions with the electrochemical cells. The composite separators comprise a microporous layer and one or more flame-retardant layers arranged on at least one of a first side or an opposite second side of the microporous layer. The one or more flame-retardant layers comprise cross-linked cyclopolyphosphazene particles. The cross-linked cyclopolyphosphazene particles can effectively quench, suppress, and / or terminate combustion chain reactions when exposed to thermal runaway temperatures.

[0039] Fig. Figure 1 shows a schematic side cross-sectional view of an electrochemical cell 10 that cycles lithium ions. The electrochemical cell 10 can be combined with one or more additional electrochemical cells to form a secondary lithium battery, such as a lithium-ion battery or a lithium-metal battery. The electrochemical cell 10 includes a composite separator 12 arranged between a positive electrode 14 and a negative electrode 16. The composite separator 12 is infiltrated with a liquid electrolyte 18, which provides a medium for the conduction of lithium ions between the positive electrode 14 and the negative electrode 16. The positive electrode 14 is arranged on a main surface of a positive electrode current collector 20, and the negative electrode 16 is arranged on a main surface of a negative electrode current collector 22.In practice, the positive and negative electrode current collectors 20, 22 can be electrically connected to a power source or load 24 via an external circuit 26.

[0040] The composite separator 12 physically and electrically isolates the positive electrode 14 and the negative electrode 16 from each other while simultaneously allowing lithium ions to pass through. As in Fig. 1 and Fig. As shown in Figure 2, the composite separator 12 comprises a microporous layer 28 with a first side 30 and an opposing second side 32, as well as at least one flame-retardant layer arranged on the first side 30 and / or the second side 32 of the microporous layer 28. The first side 30 of the microporous layer 28 faces the positive electrode 14, and the second side 32 of the microporous layer 28 faces the negative electrode 16. The Fig. 1 and Fig. The composite separator 12 shown in Figure 2 comprises a first fire-retardant layer 34 arranged on the first side 30 of the microporous layer 28, and a second fire-retardant layer 36 arranged on the second side 32 of the porous microporous layer 28. The first fire-retardant layer 34 can be arranged directly on a surface of the microporous layer 28 defined by its first side 30, and the second fire-retardant layer 36 can be arranged directly on a surface of the microporous layer 28 defined by its second side 32.

[0041] The microporous layer 28 has an open microporous structure and can comprise one or more ionically conductive and electrically insulating polymers. The microporous layer 28 can be in the form of a continuous membrane or film, or it can be a discontinuous nonwoven material, such as a fabricated sheet, web, or mat of oriented or randomly oriented fibers. Examples of ionically conductive and electrically insulating polymers include polyolefins, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and / or polyvinyl chloride (PVC). The microporous layer 28 can comprise a single polymer or a combination of polymers. In some aspects, the porous substrate 28 can comprise a laminate of one or more polymers, such as a laminate of PE, PE, and / or PET.The microporous layer 28 can have a thickness of greater than or equal to about 100 nanometers or about 5 micrometers to less than or equal to about 30 micrometers or about 20 micrometers, and a porosity of greater than or equal to 25% to less than or equal to 75%.

[0042] The flame-retardant layers 34, 36 are configured to provide the composite separator 12 with mechanical integrity and thermal stability at high temperatures (e.g., temperatures greater than or equal to about 150 °C) and to help prevent or inhibit the propagation of combustion chain reactions within the electrochemical cell 10 during a thermal runaway event. The flame-retardant layers 34, 36 can have a thickness of greater than or equal to about 1 micrometer to less than or equal to about 30 micrometers and a porosity of greater than or equal to about 20% to less than or equal to about 80%.

[0043] The flame-retardant layers 34, 36 may include, consist substantially of, or be composed of cross-linked cyclopolyphosphazene particles. The cross-linked cyclopolyphosphazene particles are configured to extinguish, suppress, and / or terminate combustion chain reactions that may occur in the electrochemical cell 10 during a thermal runaway event. Without being bound to the theory, it is assumed that if the cross-linked cyclopolyphosphazene particles are exposed to relatively high temperatures (e.g., temperatures above approximately 150°C), they may thermally decompose and generate gaseous chemical compounds or species that effectively suppress, eliminate, or disrupt free radical-induced combustion chain reactions occurring within the electrochemical cell 10.

[0044] The cross-linked cyclopolyphosphazene particles are formulated to be essentially chemically unreactive and insoluble (or exhibit very low solubility) in the liquid electrolyte 18. For example, the cross-linked cyclopolyphosphazene particles may exhibit a solubility of less than or equal to approximately 1 wt% in the one or more non-aqueous organic solvents (e.g., in the one or more organic carbonates and / or aliphatic carboxylic esters) contained in the liquid electrolyte 18. Without being bound by theory, it is assumed that the low solubility of the cross-linked cyclopolyphosphazene particles in the liquid electrolyte 18 may allow the cross-linked cyclopolyphosphazene particles to be introduced into the electrochemical cell 10 without affecting the performance or cycle life of the electrochemical cell 10.

[0045] The cross-linked cyclopolyphosphazene particles can be formed by a nucleophilic polycondensation polymerization reaction between a cyclophosphazene and a comonomer. The polymerization reaction can be carried out by preparing a precursor mixture comprising the cyclophosphazene, the comonomer, an organic solvent, and optionally a catalyst.

[0046] Cyclophosphazene can be an organophosphorus compound with a 6-membered ring consisting of alternating phosphorus and nitrogen atoms, interspersed with alternating single and double bonds. For example, cyclophosphazene could be an organophosphorus compound with the following chemical formula: where X 1 , X 2 , X 3 , X 4 , X 5 , and X 6 Each is a halide, e.g., F, Cl, Br, and / or I.

[0047] The comonomer can be a polyfunctional organic nucleophilic compound. For example, the comonomer can be a phenol (a chemical compound with two or more phenol groups, -C6H4OH) or an aniline (a chemical compound with two or more aniline groups, -C6H4NH2). Examples of phenols include 4,4'-(hexafluoroisopropylidene)diphenol (BPAF or bisphenol AF); 4,4'-sulfonyldiphenol (BPS or bisphenol S); 4,4'-(9-fluorenylidene)diphenol (BPFL or bisphenol FL); phenolphthalein; oxyresveratrol; resveratrol; dopamine; and combinations thereof. Examples of anilines include 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein, or combinations thereof.

[0048] The organic solvent may be a polar aprotic solvent. Examples of polar aprotic solvents are acetone, acetonitrile, tetrahydrofuran (THF), and combinations thereof.

[0049] The catalyst can include a Lewis base (an acid acceptor) that can react with and / or absorb acidic species (e.g., HCl, HF, HBr, and / or HI) that are formed as byproducts of the polymerization reaction. The catalyst can effectively increase the polymerization rate. For example, the catalyst can include a tertiary amine: NRR'R'', where R, R', and R'' are each individually alkyl or aryl groups. Examples of alkyl groups are methyl groups (-CH3) and ethyl groups (-CH2CH3). Examples of alkyl groups are phenyl groups (-C6H5) and benzyl groups (-C6H5CH2). Examples of tertiary amines are triethylamine (TEA) and trimethylamine. The catalyst can have a pKa value of approximately 9.5 or greater than or equal to approximately 10.

[0050] During the polymerization reaction, the cyclophosphazene and the comonomer can be covalently bonded to each other to form highly cross-linked cyclopolyphosphazene macromolecules. In these cross-linked macromolecules, the cyclophosphazene monomers can be linked or bridged by the comonomers. As in Fig. As shown in Figure 2, a cross-linked cyclopolyphosphazene macromolecule 100 can comprise a network of cyclophosphazene monomers bridged by comonomers (R), where X is a halide, e.g., F, Cl, Br, or I. Each of the cyclophosphazene monomers comprises a 6-membered ring of alternating phosphorus (P) and nitrogen (N) atoms with alternating single and double bonds intervening. At least one phosphorus atom in each cyclophosphazene monomer is linked to another cyclophosphazene monomer by a comonomer R. Phosphorus atoms in the cyclophosphazene monomers that are not linked to another cyclophosphazene monomer (i.e., by a comonomer R) may be linked to a halide or a comonomer R.

[0051] In some aspects, such as in Fig. As shown in Figure 3, the cross-linked cyclopolyphosphazene particles can exist in the form of spherical particles. In some aspects, such as in Fig. As shown in Figure 4, the cross-linked cyclopolyphosphazene particles can have the shape of tubular particles. The physical shape of the cross-linked cyclopolyphosphazene particles can depend on the reaction conditions of the polymerization. Without being bound to theory, it is assumed, for example, that if the precursor mixture is stirred or agitated during the polymerization reaction and / or throughout the entire polymerization reaction, the resulting cross-linked cyclopolyphosphazene particles will aggregate into spherical particles. If, on the other hand, the precursor mixture is left undisturbed during the polymerization reaction without stirring or other agitation, the resulting cross-linked cyclopolyphosphazene particles have the shape of tubular particles. If the precursor mixture is not stirred or agitated, it is assumed that the acidic species (e.g.,HCl, HF, HBr, and / or HI), which are formed as byproducts of the polymerization reaction, react with the basic catalyst to form needle-shaped salt crystals (e.g., triethylamine hydrochloride crystals). In this case, the needle-shaped salt crystals can serve as a template for the cross-linked cyclopolyphosphazene particles, leading to the formation of cross-linked tubular cyclopolyphosphazene particles. As another example, the concentration of cyclophosphazene, the comonomer, and / or the catalyst in the precursor mixture can affect the resulting shape of the cross-linked cyclopolyphosphazene particles.Without wishing to be bound to the theory, it is assumed that the preparation of a precursor mixture with a relatively high concentration of the cyclophosphazene, the comonomer and / or the catalyst can promote the precipitation of needle-shaped salt crystals from the precursor mixture during the polymerization reaction and the formation of cross-linked tubular cyclopolyphosphazene particles.

[0052] When the cross-linked cyclopolyphosphazene particles are in the form of spherical particles, they can have mean particle diameters ranging from approximately 50 nanometers to approximately 2 micrometers. In some cases, they can also be spherical particles with mean particle diameters ranging from approximately 400 nanometers to approximately 800 nanometers. When the cross-linked cyclopolyphosphazene particles are in the form of tubular particles, they can have a width ranging from approximately 50 nanometers to approximately 200 nanometers and a length ranging from approximately 500 nanometers to approximately 2 micrometers.

[0053] After the formation of the cross-linked cyclopolyphosphazene particles, they can be separated from the organic solvent, catalyst, and reaction byproducts by filtration. The cross-linked cyclopolyphosphazene particles can then be dried to remove any remaining solvent.

[0054] The cross-linked cyclopolyphosphazene particles can constitute, based on mass, more than or equal to about 1%, optionally about 30% or optionally about 50% to less than or equal to about 80% or optionally about 60% of the fire-retardant layers 34, 36.

[0055] The fire-retardant layers 34, 36 can optionally contain particles of a porous ceramic material. The porous ceramic material can impart high mechanical strength and thermal stability to the fire-retardant layers 34, 36. The porous ceramic material can comprise an inorganic material that exhibits high mechanical strength and thermal stability and is chemically inert with other components of the electrochemical cell 10 (e.g., the positive and negative electrodes 14, 16 and the electrolyte 18). In some aspects, the porous ceramic material can be aluminum oxide (Al₂O₃). 3The ceramic material may consist essentially of silicon dioxide (SiO2) and / or a dehydrated natural or synthetic zeolite. Zeolites are porous crystalline aluminosilicate materials comprising a three-dimensional framework of tetrahedral AlO2 and SiO2 units and cations outside the framework. Each AlO2 unit introduces a negative charge into the framework, which is balanced by the cations outside the framework. The cations outside the framework may be organic or inorganic. In some cases, the ceramic material may comprise a lithiated zeolite with a three-dimensional framework of tetrahedral AlO2 and SiO2 units and lithium cations (Li+) outside the framework. If the ceramic material consists of a zeolite, the zeolite may be essentially free of the following cations outside the framework: Na+ and H+.The particles of the ceramic material can have mean particle diameters ranging from approximately 50 nanometers to approximately 5 micrometers.

[0056] When present in the fire-retardant layers 34, 36, the ceramic material particles can constitute, by mass, more than or equal to approximately 5%, optionally approximately 20%, or optionally approximately 30% to less than or equal to approximately 99%, optionally approximately 80%, or optionally approximately 50% of the fire-retardant layers 34, 36. When present in the fire-retardant layers 34, 36, the mass ratio of the ceramic material particles to the crosslinked cyclopolyphosphazene particles in the fire-retardant layers 34, 36 can range from approximately 1:99 to approximately 99:1. In some aspects, the mass ratio of the ceramic material particles to the crosslinked cyclopolyphosphazene particles in the fire-retardant layers 34, 36 can range from approximately 40:60 to approximately 60:40.

[0057] The flame-retardant layers 34, 36 may optionally contain a binder. The binder can provide cohesion between the components of the flame-retardant layers 34, 36 (e.g., the cross-linked cyclopolyphosphazenes and the optional ceramic particles) and help the flame-retardant layers 34, 36 adhere to the first and second sides 30, 32 of the microporous layer 28, respectively. The binder may consist of a polymeric material, e.g., polyvinylidene fluoride (PVdF), polyvinylpyrrolidone (PVP), ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid, SOTERAS™ CCS two-component binder, or a combination thereof. When the binder is present in the fire-retardant layers 34, 36, it can constitute, in relation to mass, more than or equal to about 1% or about 2% to less than or equal to about 10% or about 5% of the fire-retardant layers 34, 36.In some aspects, the binder can constitute about 3% of the fire-retardant layers 34, 36 by mass.

[0058] Referring now to Fig. 5 the first fire-retardant layer 34 can comprise a mixture of cross-linked cyclopolyphosphazene particles 38 and particles of ceramic material 40 arranged on the first side 30 of the microporous layer 28, and the second fire-retardant layer 36 can comprise a mixture of cross-linked cyclopolyphosphazene particles 38 and particles of ceramic material 40 arranged on the second side 32 of the microporous layer 28.

[0059] The positive electrode 14 is porous and can comprise one or more electrochemically active positive electrode materials capable of undergoing a reversible redox reaction with lithium, e.g., a material that can be subjected to sufficient intercalation and deintercalation, alloying and dealloying, or coating and peeling processes. In one form, the positive electrode 14 can consist of an intercalation host material that enables the reversible incorporation or intercalation of lithium ions. In this case, the intercalation host material of the positive electrode 12 can comprise a layered oxide represented by the formula LiMeO2, an olivine-type oxide of the formula LiMePO4, a spinel-type oxide of the formula LiMe2O4, a tavorite represented by one of the formulas LiMeSO4F and / or LiMePO4, or a combination thereof, where Me is a transition metal (e.g., Co, Ni, Mn, Fe, Al, V, or a combination thereof).In another form, the positive electrode 14 can comprise a conversion material containing a component capable of undergoing a reversible electrochemical reaction with lithium, whereby the component undergoes a phase change or a change in crystal structure accompanied by a change in oxidation state. In this case, the conversion material of the positive electrode 14 can include sulfur, selenium, tellurium, iodine, a halide (e.g., a fluoride or chloride), sulfide, selenide, telluride, iodide, phosphide, nitride, oxide, oxysulfide, oxyfluoride, sulfur fluoride, sulfur oxyfluoride, or a lithium and / or metal compound thereof. Examples of metals that can be included in the conversion material of the positive electrode 14 are iron, manganese, nickel, copper, and cobalt.The electrochemically active positive electrode material of the positive electrode 14 can be mixed with a polymer binder to provide structural integrity to the positive electrode 14. Examples of polymer binders include polyvinylidene fluoride (PVdF), ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid, and mixtures thereof. The positive electrode 14 can optionally contain particles of an electrically conductive material, which may, for example, comprise very fine particles of carbon black with a large surface area.

[0060] The negative electrode 16 is spaced from the positive electrode 14 by the composite separator 12. The negative electrode 16 can be porous or non-porous. In some aspects, the negative electrode 16 can comprise, consist substantially of, or be composed of lithium (Li) metal. For example, in some aspects, the negative electrode 16 can comprise more than 97 wt% lithium or more than 99 wt% lithium and be substantially free of elements or compounds that undergo a reversible redox reaction with lithium during operation of the electrochemical cell 10. In other aspects, the negative electrode 16 can comprise an electrochemically active negative electrode material that can undergo reversible incorporation or intercalation of lithium ions or that can react with lithium to form a lithium-containing intermetallic compound.The electrochemically active negative electrode material of the negative electrode 16 can comprise a silicon-based material, a carbon-based material (e.g., graphite, activated carbon, carbon black, and / or graphene), tin oxide, aluminum, indium, zinc, germanium, titanium oxide, and / or lithium titanate. The electrochemically active negative electrode material of the negative electrode 16 can be mixed with the same polymeric binder(s) and / or the same electrically conductive material particles as that of the positive electrode 14.

[0061] The liquid electrolyte 18 infiltrates the pores of the compound separator 12 and the positive electrode 14 and is in physical and ionic contact with the negative electrode 16. In cases where the negative electrode 16 is porous, the electrolyte 18 can infiltrate the pores of the compound separator 12, the positive electrode 14, and the negative electrode 16. The electrolyte 18 is formulated to facilitate the transport of lithium ions between the positive electrode 14 and the negative electrode 16 during the cycling of the electrochemical cell 10. The liquid electrolyte 18 can be in solution form and may comprise one or more lithium salts dissolved in a non-aqueous aprotic organic solvent or a mixture of non-aqueous aprotic organic solvents.Examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClQ4), lithium tetrachloroaluminate (LiA1Cl4), lithium iodide (Lil), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalato)borate (LiB(C2O4)2) (LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4)), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethane)sulfonylimide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) (LiSFI), and combinations thereof. Examples of non-aqueous aprotic organic solvents include organic carbonates, e.g. B. cyclic carbonates (e.g. ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC)), linear carbonates (e.g. dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC)), aliphatic carboxylic acid esters (e.g., methyl formate, methyl acetate, methyl propionate), γ-lactones (e.g.γ-Butyrolactone, γ-Valerolactone), chain-structured ethers (e.g., 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (e.g., tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane), sulfur compounds (e.g., sulfolane) and combinations thereof.

[0062] The positive and negative electrode current collectors 20, 22 can be in the form of thin and flexible porous or non-porous electrically conductive metal substrates. Each of the positive and negative electrode current collectors 20, 22 can consist of a metal capable of collecting free electrons and reversibly conducting them to and from their respective electrodes 14, 16. The term "metal," as used here in reference to the positive and negative electrode current collectors 20, 22, can refer to a pure elemental metal or to a combination (e.g., an alloy) of an elemental metal and one or more other metallic or non-metallic elements. For example, the positive and negative electrode current collectors 20, 22 can include or consist of a transition metal. Thus, the positive electrode current collector 20 can be aluminum (Al), nickel (Ni), or an iron alloy (Fe) (e.g.,The electrodes (stainless steel) and the negative electrode current collector (22) may be made of copper (Cu), nickel (Ni), an iron alloy (Fe) (e.g., stainless steel), or titanium (Ti). Of course, other electrically conductive metals can also be used.

[0063] The composite separator 12 can be produced by depositing the crosslinked cyclopolyphosphazenes onto the first side 30 and / or the second side 32 of the microporous layer 28 to form the flame-retardant layers 34, 36. The crosslinked cyclopolyphosphazenes can be deposited onto the first side 30 and / or the second side 32 of the microporous layer 28 as a slurry. The slurry can contain the crosslinked cyclopolyphosphazenes, a solvent, and optionally a binder. The crosslinked cyclopolyphosphazenes and the optional binder can be suspended in the solvent. In cases where the flame-retardant layers 34, 36 comprise a ceramic material, the slurry can include particles of the ceramic material.

[0064] The solvent can be aqueous (e.g., water) or non-aqueous (e.g., an organic solvent). Examples of non-aqueous organic solvents include N-methyl-2-pyrrolidone (NMP). The binder can be a polymeric material, such as polyvinylidene fluoride (PVdF), polyvinylpyrrolidone (PVP), ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid, SOTERAS™ CCS two-component binder, or a combination thereof. After the slurry has been applied to the first side 30 and / or the second side 32 of the microporous layer 28, the solvent can be removed from the slurry, e.g., by... B. by evaporation to form the first and second flame-retardant layer 34, 36 on the first side 30 and / or the second side 32 of the microporous layer 28.For example, the solvent can be removed from the slurry by heating under vacuum at a temperature greater than or equal to approximately 50°C to less than or equal to approximately 80°C for more than or equal to approximately 2 hours to less than or equal to approximately 48 hours. TRY

[0065] Composite separators with first and second flame-retardant layers arranged on their opposite first and second sides were manufactured, installed in electrochemical cells, and the electrochemical stability and performance of the electrochemical cells was evaluated.

[0066] Composite separators enclosing cross-linked cyclopolyphosphazene particles were fabricated by depositing a mixture of cross-linked cyclopolyphosphazene (PZS) and lithium-ion-exchanged zeolite (LiZ) particles onto opposing first and second sides of polymer membranes. The flame-retardant layers enclosing the PZS and LiZ particles were applied to the first and second sides of the polymer membranes to a thickness of approximately 10 micrometers. The polymer membranes were made of a PP / PE / PP laminate and were approximately 20 micrometers thick. The PZS particles had a mean particle diameter in the range of 400 to 800 nanometers and constituted approximately 55% of the first and second flame-retardant layers by mass.The LiZ particles were of the Y-(FAU) zeolite scaffold type, had a mean particle diameter in the range of 50 nanometers to 5 micrometers and, in terms of mass, made up about 42% of the first and second flame-retardant layers.

[0067] For comparison, composite separators were fabricated without PZS particles but with LiZ particles applied to the first and second sides of the polymer membranes. The LiZ particles were applied to the first and second sides of the polymer membranes with a thickness of approximately 10 micrometers.

[0068] The PZS-LiZ separators and the LiZ separators were integrated into electrochemical cells with lithium metal anodes (30 µm Li-foil), NMC622 cathodes (3.75 mAh / cm²), and an FEC / DMC + LiPF6 liquid electrolyte (30 µl). Each PZS-LiZ separator contained approximately 0.65 milligrams of PZS particles.

[0069] The electrochemical cycling behavior of cells with PZS-LiZ separators and cells with LiZ separators was evaluated by galvanostatic charge-discharge cycles. The areal capacity (mAh / cm²) of the electrochemical cells in the prepared state was measured while the cells were cycled between voltages of 3 V and 4.3 V at a charge / discharge rate of C / 10 for the first two cycles, followed by a charge at a charge / discharge rate of C / 5 and a discharge at a discharge rate of C / 2 for a further 80–90 cycles. Fig. Figure 6 shows graphs of capacity retention (%) 200 versus cycle count 210 for one of the cells with a PZS-LiZ separator (solid line) and one of the cells with a LiZ separator (dashed line). The area capacity measurements indicate that the cells with the PZS-LiZ separators exhibit essentially the same area capacity as the cells with the LiZ separators, at least during the first 70 cycles. This suggests that the addition of the PZS particles has no negative impact on cycle life.

[0070] Impedance measurements were performed on the cells with the PZS-LiZ separators and the LiZ separators using electrochemical impedance spectroscopy. Fig.Figure 7 shows Nyquist plots of -Im(Z) / Ω 300 versus Re(Z) / Ω 310 for one of the cells with a PZS-LiZ separator (solid line) and one of the cells with a LiZ separator (dashed line). The impedance measurements indicate that the addition of the PZS particles has no negative effect on the cell impedance. In other words, the cells with the PZS-LiZ separators and the cells with the LiZ separators exhibited essentially the same cell impedance.

[0071] The electrochemical stability of the cells with PZS-LiZ separators and LiZ separators was evaluated using cyclic voltammetry. The cyclic voltammetry measurements indicate that the addition of PZS particles does not negatively affect the electrochemical stability of the cells with PZS-LiZ separators compared to the cells with LiZ separators.

[0072] The foregoing description of the embodiments is provided for illustrative and descriptive purposes only. It makes no claim to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not restricted to that embodiment, but are optionally interchangeable and may be used in a selected embodiment even if they are not specifically shown or described.

Claims

[1] Separator (12) for an electrochemical cell (10) that cycles lithium ions, wherein the separator (12) comprises: a microporous layer (28) with a first side (30) and an opposite second side (32), and one or more fire-retardant layers (34, 36) arranged on at least one of the first side (30) or the second side (32) of the microporous layer (28), wherein the one or more fire-retardant layers (34, 36) comprise cross-linked cyclopolyphosphazene particles, wherein the cross-linked cyclopolyphosphazene particles are formed by a nucleophilic polycondensation polymerization reaction between a cyclophosphazene and a comonomer, where cyclophosphazene is an organophosphorus compound with the following chemical formula: where X 1 , X 2 , X 3 , X 4 , X 5 , and X 6Each is a halid, and wherein the comonomer comprises 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-(9-fluorenylidene)diphenol, phenolphthalein, oxyresveratrol, resveratrol, dopamine, 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein or a combination thereof. [2] Separator (12) according to claim 1, wherein the cross-linked cyclopolyphosphazene particles are: (i) spherical particles with a mean particle diameter greater than or equal to about 50 nanometers to less than or equal to about 2 micrometers, or (ii) tubular particles having a width greater than or equal to about 50 nanometers to less than or equal to about 200 nanometers and a length greater than or equal to about 500 nanometers to less than or equal to about 2 micrometers. [3] Separator (12) according to claim 1, wherein the one or more flame-retardant layers (34, 36) further comprise particles of a ceramic material (40), and wherein the ceramic material comprises aluminium oxide, silicon oxide, a dehydrated zeolite, a lithiated zeolite or a combination thereof, and wherein the particles of the ceramic material (40) have a mean particle diameter of greater than or equal to about 50 nanometers to less than or equal to about 5 micrometers. [4] Electrochemical cell (10) that cycles lithium ions, the electrochemical cell comprising: a negative electrode (16); a positive electrode (14) spaced apart from the negative electrode (16), wherein the positive electrode (14) comprises a transition metal oxide that can be subjected to reversible intercalation of lithium ions; and a composite separator (12) arranged in a sandwich-like manner between the negative electrode (16) and the positive electrode (14), the composite separator (12) comprising: a microporous layer (28) with a first side (30) and an opposing second side (32), wherein the microporous layer (28) comprises a polyolefin, and one or more fire-retardant layers (34, 36) arranged on at least one of the first side (30) or the second side (32) of the microporous layer (28), wherein the one or more fire-retardant layers (34, 36) comprise cross-linked cyclopolyphosphazene particles, wherein the cross-linked cyclopolyphosphazene particles are formed by a nucleophilic polycondensation polymerization reaction between a cyclophosphazene and a comonomer, where cyclophosphazene is an organophosphorus compound with the following chemical formula: where X 1 , X2 , X 3 , X 4 , X 5 , and X 6 Each is a halid, and wherein the comonomer comprises 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-(9-fluorenylidene)diphenol, phenolphthalein, oxyresveratrol, resveratrol, dopamine, 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein or a combination thereof. [5] Electrochemical cell (10) according to claim 4, wherein the one or more flame-retardant layers (34, 36) further comprise particles of a ceramic material (40) and wherein the ceramic material comprises aluminium oxide, silicon dioxide, a dehydrated zeolite, a lithiated zeolite or a combination thereof. [6] Electrochemical cell (10) according to claim 4, further comprising: a liquid electrolyte (18) which penetrates the pores of the composite separator (12) and establishes a lithium ion transport pathway between the negative electrode (16) and the positive electrode (14), wherein the liquid electrolyte (18) comprises a lithium salt dissolved in a non-aqueous organic solvent and wherein the non-aqueous organic solvent comprises an organic carbonate, an aliphatic carboxylic ester or a combination thereof. [7] Electrochemical cell (10) according to claim 6, wherein the cross-linked cyclopolyphosphazene particles have a solubility of less than or equal to about 1% in the non-aqueous organic solvent, based on mass. [8] Method for producing a composite separator (12) for an electrochemical cell (10) that cycles lithium ions, the method comprising: Preparation of a precursor mixture comprising a cyclophosphazene, a comonomer, an organic solvent, and a tertiary amine catalyst to initiate a nucleophilic polycondensation polymerization reaction between the cyclophosphazene and the comonomer to form cross-linked cyclopolyphosphazene particles, wherein the cyclopolyphosphazene has the chemical formula (-N=P(-X) 2 -) 3 comprising, wherein X is a halogen, the comonomer comprising 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-(9-fluorenylidene)diphenol, phenolphthalein, oxyresveratrol, resveratrol, dopamine, 4,4'-(hexafluoroisopropylidene)dianiline, 4,4'-sulfonyldianiline, 4,4'-(9-fluorenylidene)dianiline, anilinephthalein or a combination thereof; Dispersing the cross-linked cyclopolyphosphazene particles in a solvent to form a slurry; Deposition of the slurry onto at least one of a first side (30) or an opposing second side (32) of a microporous polyolefin layer (28); and Removing the solvent from the slurry to form one or more flame-retardant layers (34, 36) arranged on at least one of the first side (30) or the second side (32) of the microporous polyolefin layer (28).

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