Compositions, methods, and cells for metal-ion batteries

Abstract

Methods and compositions are disclosed for electrodes suitable for active metal-ion batteries. Suitable active metals for such batteries include alkali metals, alkaline earth metals, Zn, Al, Fe, V, Mn, and Cr In some embodiments, the active metal is lithium. The electrodes are formed from a slurry of electrode active material dispersed in 1,3 -propanediol (PDO), cast onto a conductive substrate to form an electrode coating, which is dried and densified to form the active electrode. The slurry includes some combination of a water-soluble polymer dissolved in the PDO and hydrophobic polymer nanoparticles. The hydrophobic polymer nanoparticles can be formed in PDO solution by miniemulsion polymerization.

Description

Attorney Docket No.: 105131-101COMPOSITIONS, METHODS, AND CELLS FOR METAL-ION BATTERIESCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 643,431, filed May 7, 2024, the disclosure of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to compositions, methods, and cells for metal-ion batteries. The disclosure relates particularly to compositions incorporating polymer binders, and to solvents useful as reaction and suspension media for emulsion polymerization synthesis of such binders for battery electrodes. The disclosure includes but is not limited to lithium-ion battery applications.BACKGROUND

[0003] During the manufacture of electrodes for a metal-ion battery it is common for a slurry of electrode active material in a solvent to be deposited as a coating on an electrically conductive substrate. The slurry typically includes a small amount of one or more polymeric binders, which may be dissolved in the solvent, or dispersed as particles. The coating is then dried to remove solvent and densified to form a positive or negative electrode. The polymeric binder provides control over the coating process (e.g. through viscosity modulation) and also helps to bind the final product as a functional electrode.

[0004] For lithium-ion batteries, a commonly used binder is polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP) is commonly used as a solvent for its ability to dissolve PVDF. Although N-methyl-2-pyrrolidone (NMP) is used in large quantities in electrode manufacturing, safety and exposure controls are not generally well addressed, and little research has been conducted on the health and environmental effects of exposure of NMP. Moreover, NMP is a well-known teratogen, and there is considerable motivation in the battery industry to move away from NMP based processes toward safer, water-based solvents. But, to date, technical issues with using water-based solvents have yet to be overcome. Such technical issues 131257365.1Attorney Docket No.: 105131-101may be solvable through use of an alternative solvent with chemical and physical properties similar to NMP but a superior safety profile. The use of such an alternative solvent with a physicochemical profile similar to NMP requires little change in battery production infrastructure, but provides a significant improvement in safety and in recyclability.SUMMARY

[0005] 1,3-propanediol (PDO) is generally considered safe. The FDA approves PDO for use in foods; it is widely used in body soaps and shampoos, and it has no determined toxicity to humans. There is a desire in the battery industry to move away from NMP based processes toward water-based solvents; however this poses a technical challenge even though there are obvious safety improvements when considering water as the primary solvent. It is hypothesized that many of the issues observed with water-based electrode slurry approaches may be solvable with PDO while still addressing the safety issues associated with NMP use.

[0006] The use of water-soluble polymeric binders allows batteries to be recycled more safely and efficiently with aqueous solutions. And, because many common water-soluble polymeric binders are also soluble in PDO, they may be used in the processes disclosed in the present application.

[0007] In addition to simple cost per mass savings, the incorporation of PDO into a typical electrode slurry manufacturing process would be straightforward. Chemical properties in terms of boiling point, flash point, viscosity, and corrosivity are all similar if not better for manufacturing than NMP, so little would change in terms of infrastructure when adopting PDO technology.

[0008] Because PDO can dissolve many polymers that are also water-soluble, it can allow for the use of binders that are typically only achieved in water-based electrodes (polyacrylic acid (PAA), some cellulosics, and polyvinyl pyrrolidones (PVP) for example). PDO cannot dissolve PVDF, so a new polymer replacement is needed for battery electrode binders. Potential PVDF replacements include water soluble polymers (WaSPs) which are also soluble in PDO, including PAA, PVP, and certain chemically modified cellulose derivatives, including carboxymethycellulose (CMC) and hydroxypropylcellulose (HPC). By replacing the NMP / PVDF combination binder package with PDO / WaSP, the safety of producing electrode slurries can be greatly enhanced, and battery materials can be more efficiently recycled using 231257365.1Attorney Docket No.: 105131-101aqueous solutions. The use of PDO / WaSP further avoids the difficulty which arises in waterbased approaches of drying the electrode to remove water. Another issue which arises with water-based processes is that certain battery materials are incompatible with water (high-nickel lithium nickel manganese cobalt oxide (NMC), lithium-rich layered oxide materials, and pre-lithiated negative electrode materials). Moreover, water retained in the positive electrode can lead to aluminum corrosion which in turn can rapidly degrade battery performance. And, although battery products made with water-based PVDF suspensions have historically been attempted, it is not expected that any such products will be successful in replacing current state of the art solvent-based electrodes. Disclosed herein are methods based on chemical properties, cost, and safety that will lead to performance parameters similar to NMP based electrodes but with the enhanced safety and recyclability of water-based binder approaches. In an embodiment, a solvent selected for this use is PDO, which has similar physicochemical properties as NMP, and which allows for significant flexibility in the choice of polymeric binders.

[0009] PDO based approaches also allow the in-situ incorporation of nanoparticles of a hydrophobic polymer binder. Such incorporation may be performed by miniemulsion polymerization in PDO solvent using monomers of hydrophobic polymers. Such a hydrophobic polymer binder can include a styrene based rubber, a thermoplastic fluoropolymer, a PDO-insoluble acrylate polymer, and combinations thereof.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 shows the core features of preparing an electrode by the methods of the current application.

[0011] Fig. 2 provides more details of the various options for preparing an electrode by the methods of the current application.

[0012] Fig. 3 displays a lithium-ion battery with electrodes constructed according to methods of the current application.DETAILED DESCRIPTION

[0013] Definitions.331257365.1Attorney Docket No.: 105131-101

[0014] As defined herein, “acrylates” include acrylic acid, and the salts, esters, and conjugate bases of acrylic acid.

[0015] A “polyacrylate” is a polymer synthesized from acrylate monomers

[0016] A “polyacrylate copolymer” is a polymer synthesized from at least two different types of monomers, at least one of which is an acrylate.

[0017] As a liquid for preparing a slurry of electrode active materials for manufacturing an electrode, PDO has similar processing properties to NMP but is safer, more environmentally friendly, and can provide electrodes that are more amenable to recycling using aqueous solutions. Consequently, replacing NMP with PDO as a liquid for electrode manufacturing allows for direct implementation of standard electrode production processes. Because electrode manufacturing processes using PDO are essentially identical to NMP based processes, replacing NMP with PDO improves safety while enabling similar levels of control over electrode processing parameters.

[0018] Figs. 1 and 2 provide an overview of a manufacturing process for an active metal electrode according to methods disclosed in the present application. As shown in Fig. 1, an electrode slurry is prepared in PDO solution 110. The slurry is cast onto a conductive substrate to form a composite coating 120. The composite coating is dried 130 and densified 140 to form a compact composite coating. In some embodiments, densification can be performed by a calendaring process.

[0019] The electrode slurry has particulates disposed therein including an electrode active material and a conductive additive. The electrode active material can include an intercalating compound for an active metal ion, an accepting compound for the active metal ion, or a conversion-type compound. For some embodiments, the conductive additive comprises a form of carbon. Suitable forms of carbon include but are not limited to carbon black, graphite, graphene, carbon nanotubes, and amorphous carbon, wherein amorphous carbon includes hard carbon and soft carbon.

[0020] As indicated in Figs. 1 and 2, in some embodiments, a water soluble polymer (WaSP) binder composition can be dissolved in the PDO solution. For some embodiments, the WaSP binder composition can include a water-soluble polymer selected from the group consisting of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), chemically modified cellulose, and combinations thereof. For some embodiments, the chemically modified cellulose can be one or 431257365.1Attorney Docket No.: 105131-101more of hydroxy ethyl cellulose (HEC), hydroxypropyl cellulose (HPC), and carboxymethyl cellulose (CMC). For some embodiments, the WaSP composition can be a copolymer. For some embodiments, the WaSP is an acrylate copolymer.

[0021] As further indicated in Figs. 1 and 2, preparing the electrode slurry 110 can include mixing into the slurry hydrophobic polymer binder nanoparticles (NPs). For some embodiments, the hydrophobic polymer binder NPs includes a polymer selected from the group consisting of a styrene based rubber, a thermoplastic fluoropolymer, a PDO-insoluble acrylate polymer, and combinations thereof.

[0022] According to some embodiments, a WaSP binder composition is dissolved in the PDO solution and the electrode slurry includes hydrophobic polymer binder NPs.

[0023] In some embodiments, as indicated in Fig. 2, the hydrophobic polymer binder NPs can be prepared by a miniemulsion polymerization process of 1) mixing hydrophobic monomers, a hydrophobic solvent, a surfactant, and a free radical initiator in PDO, and emulsifying the mixture by an emulsification process to form a miniemulsion 150, and 2) polymerizing the monomers to form hydrophobic polymer binder NPs in PDO 160.

[0024] In order to obtain a miniemulsion, the emulsification process 150 can include ultrasonication, high pressure homogenization, or other process suitable to obtain nanometer sized droplets (nanodroplets). The miniemulsion thus formed has a continuous phase of PDO, and a discontinuous phase of emulsion nanodroplets of the hydrophobic solvent dispersed in the continuous phase. The emulsion droplets are stabilized by the surfactant. In an embodiment, the emulsion droplets have diameters of about 20 nm to about 500 nm, 20 nm to about 300 nm, or 20 nm to about 200 nm. The hydrophobic monomers dissolve primarily in the discontinuous oil phase. The hydrophobic monomers are monomers suitable for free-radical polymerization, and can include but are not limited to one or more monomers selected from the group consisting of styrene, butadiene, isoprene, one or more acrylates soluble in the discontinuous phase, hexafluoropropylene, and vinylidene fluoride.

[0025] In an embodiment, the initiator is soluble in the continuous phase and insoluble in the discontinuous phase. In an alternative embodiment, the initiator is soluble in the discontinuous phase and insoluble in the continuous phase.

[0026] For some embodiments, polymerizing the polymerizable mixture includes agitating and / or heating the polymerizable mixture. For some embodiments, the polymer binder531257365.1Attorney Docket No.: 105131-101nanoparticles formed from polymerizing the monomers can have a particle size between about 20 nm to about 500 nm, 20 nm to about 300 nm, or 20 nm to about 200 nm.

[0027] For miniemulsion polymerization the small size of the nanodroplets allows nucleation and polymerization to proceed directly in the nanodroplets, so that the dimensions of the nanoparticles mirror the dimensions of the nanodroplets. In contrast, emulsion droplets for conventional emulsion polymerization are much larger than the nanodroplets of miniemulsion polymerization, with a surface to volume ratio which is too small to allow significant initiation at the surface of the droplets. In contrast to the mechanism of miniemulsion polymerization, the primary polymerization mechanism for conventional emulsion polymerization involves nucleation in the continuous (generally aqueous) phase, followed by polymerization within monomer-swollen polymer particles.

[0028] For some embodiments shown in Fig. 2, the WaSP binder can be formed by mixing a high molecular weight WaSP and a low molecular weight WaSP, the low molecular weight WaSP having a lower average molecular weight than the high molecular weight WaSP. For some embodiments, the low molecular weight WaSP can have a molecular weight of 1 kDa to 300 kDa, and the high molecular weight WaSP can have a molecular weight of 300 kDa to 1000 kDa. According to some embodiments the high molecular weight WaSP and the low molecular weight WaSP can have the same chemical composition. According to other embodiments, the high molecular weight WaSP and the low molecular weight WaSP can have different chemical compositions. For some embodiments, the high molecular weight WaSP and the low molecular weight WaSP are separately selected from the group consisting of a water-soluble polyacrylate and a chemically modified cellulose. For some embodiments, the water soluble polyacrylate can be polyacrylic acid. For some embodiments, the chemically modified cellulose can be hydroxypropylcellulose.

[0029] According to some embodiments, the WaSP binder composition can form cross-links which stabilize the composite coating on the conductive substrate. Such cross-links can in some embodiments be formed from reactive groups on WaSPs which have the same chemical composition. For other embodiments, the cross-links can be formed from reactive groups on WaSPs having different chemical compositions but similar molecular weights. For some embodiments the cross-links can be formed from reactive groups on WaSPs having different chemical compositions and different average molecular weights. For some embodiments, the 631257365.1Attorney Docket No.: 105131-101cross-links can involve the reaction of a carboxylic acid group with a hydroxyl group to form an ester. For some embodiments, such esterifications can involve reactions between hydroxyl groups on a chemically modified cellulose and carboxyl groups on polyacrylic acid or an acrylate copolymer formed from monomers including acrylic acid. For some embodiments the esterifications can involve reactions between a chemically modified cellulose and polyacrylic acid or an acrylate copolymer. For some embodiments, the esterifications can involve reactions between hydroxypropylcellulose (HPC) and polyacrylic acid (PAA).

[0030] According to some embodiments, the active metal for the active metal electrode is selected from the group consisting of an alkali metal, an alkaline earth metal, Zn, Al, Fe, V, Mn, and Cr. For some embodiments, the water-soluble polymer binder includes a polymer selected from the group consisting of polyvinylpyrrolidone, water-soluble polyacrylates, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and combinations thereof. For some embodiments, the water-soluble polyacrylate is polyacrylic acid. For some embodiments, the water-soluble polyacrylate is a polyacrylate copolymer.

[0031] For some embodiments, the water-soluble polymer binder is between about 0.1% and about 5% by weight of the dry electrode coating, and the hydrophobic polymer binder is about 0.1% and about 5% by weight of the dry electrode coating. For some embodiments, the water-soluble polymer binder is between about 0.5% and about 1.5% by weight of the dry electrode coating, and the hydrophobic polymer binder is about 2% and about 4% by weight of the dry electrode coating.

[0032] As shown in one embodiment in Fig. 3, the electrodes of the current application are configured for use in an active metal -ion cell 200 having a negative electrode 210 and a positive electrode 220. For the embodiment shown in Fig. 3 the active metal is Li. However, the core features apply equally well to other active metal ion cells, as an artisan of average skill would readily understand. Such active metals include Zn, Al, Fe, V, Mn, and Cr. During discharge, the negative electrode 210 is configured to act as an, anode, releasing an electron into an external circuit 270 and a lithium ion into the electrolyte 230. Lithium ions (Li+) and counterions (typically PFe’) in the electrolyte pass through the separator 240, so as to maintain charge neutrality. The positive electrode 220, which functions as a cathode during discharge, accepts the electron through the external circuit 270 and incorporates Li+into its structural framework.731257365.1Attorney Docket No.: 105131-101

[0033] According to embodiments of the present disclosure, the negative electrode comprises a conductive substrate coated with a negative electrode coating 250 formed from a PDO slurry as embodied in Fig. 1, the negative electrode coating 250 having an electrode active material configured for release of active metal ions during discharge (exemplified in Fig. 3 by lithium ions). For some such embodiments, the electrode active material is a carbon material. Suitable carbon materials can include carbon black, graphite, graphene, carbon nanotubes, and amorphous carbon, wherein amorphous carbon includes hard carbon and soft carbon. For other embodiments, the electrode active material is a conversion-type compound or an intercalation material for active metal ions.

[0034] According to embodiments of the present disclosure, the positive electrode comprises a conductive substrate coated with a positive electrode coating 260 formed from a PDO slurry as embodied in Fig. 1, the positive electrode coating 260 having an electrode active material configured for accept active metal ions during discharge. For some such embodiments, the electrode active material can be a conversion-type compound or an intercalation material.

[0035] While the active metal exemplified in Fig. 3 is lithium, other suitable active metals can include alkali metals, alkaline earth metals, Zn, Al, Fe, V, Mn, and Cr.

[0036] For some embodiments of the cell of Fig. 3, the PDO slurry forming each electrode coating comprises a lithiated electrode active material, a conductive additive, a water soluble polymer binder dissolved in a PDO solvent, and a HF nanoparticle binder suspended in a PDO solvent.

[0037] For some embodiments, the active metal-ion cell is one of a plurality of active metal-ion cells in an active metal-ion battery pack.Examples

[0038] Miniemulsions for mini emulsion polymerization are characterized by having a discontinuous oil phase of a hydrophobic solvent nanodroplets emulsified in a continuous phase of PDO. In contrast to the droplets in conventional emulsion polymerization, the nanodroplets in miniemulsions are very small, in the size range of about 20 nm to about 500 nm in diameter. In order to form such small particles, methods such as sonification or high pressure homogenization are typically required.

[0039] For some embodiments, the HF solvent forming the oil phase is hexadecane. For some embodiments, the HF solvent is cyclohexane, octane, or other short chain alkane.831257365.1Attorney Docket No.: 105131-101

[0040] The disclosed miniemulsions share features with oil in water miniemulsions, with the role of the water phase being taken by PDO. The droplets are stabilized by surfactant. Dissolved within the droplets are hydrophobic monomers polymerizable to form hydrophobic binder polymers. Polymerization is initiated by a free radical forming initiator, which in some embodiments is soluble in the PDO phase, but not in the oil phase. According to some embodiments, the initiator is also a surfactant stabilizing the droplets. For some embodiments the initiator is PEGA200, a poly(ethylene glycol)-azo-initiator which is soluble in PDO, and also functions as a surfactant.

[0041] In the presence of free-radical forming initiator, agitation, and heat, polymerization occurs, and micelles stabilize the polymer nanoparticles formed.

[0042] For some embodiments, the oil phase can be removed following polymerization by physical or chemical processes. If the oil phase has a lower boiling point than the PDO phase (-214 °C), then separation can be by distillation. Nanoparticle suspensions of polymer binders in PDO can be readily incorporated as a co-binder along with a solubilized polymer binder in PDO as part of an electrode slurry.

[0043] In some embodiments the solubilized polymer in PDO is also water-soluble. For such embodiments, the water- solubility of the binder can simplify recycling methods. An analogy can be drawn between forming an electrode with a water-based slurry of carboxymethylcellulose and styrene-butadiene rubber and forming one according to the present disclosure with a PDO based slurry having a dissolved WaSP binder and nanoparticles of a hydrophobic polymer binder. As with water-based anodes, electrode formation with such a PDO based slurry allows for a higher degree of control over the electrode coating. For example, one can vary the amount of discrete versus solubilized binder to tune rheology and coating performance of the electrode slurry.

[0044] Utilizing both a solubilized and an emulsified hydrophobic polymer binder in PDO allows for the benefits of viscosity modification from the solubilized binder and improved adhesion and flexibility of the electrode from the point-to-point connections established by the emulsified hydrophobic polymer binder. The point-to-point binding mechanism may also enhance ionic conductivity at the electrode level, because the binding mechanism between particles can be achieved with less surface area than the solubilized binder. The point-to-point binding mechanism enables sufficient binding function but blocks less of the surface area compared to the soluble binder that typically insulates particles. Assuming the hydrophobic 931257365.1Attorney Docket No.: 105131-101binder particles are homogeneously mixed throughout the electrode microstructure, it can also allow for high coating thicknesses to be achieved due to the good cohesion between cathode particles from the point-to-point binding mechanism.

[0045] The following example assumes use of PVP in place of PVDF to act as an analogous bridge since PDO and NMP both dissolve PVP:

[0046] PDO and NMP can both be used to dissolve PVP polymer to make binder solution as a comparative example. The main difference, other than health / safety / cost, is processability. PVP carries a higher viscosity in PDO than in NMP. By simple high shear overhead mixing, PVP can be easily dissolved in PDO and used as a direct binder replacement. With higher relative viscosity by simply changing solvent, less polymer can be used in order to achieve higher viscosity slurries, which in turn leads to lower necessary solids content for stable slurries. This higher relative viscosity compared to NMP provides greater control over the coating parameters and rheological properties of the slurry when fabricating electrodes. For example, simply switching from NMP / PVP to PDO / PVP allows for lower coat weights by decreasing solids content, and the slurry remains stable due to its higher viscosity. Such lower coat weights benefit high power applications. For higher energy applications, thicker active material coat weights can be obtained at lower overall polymer content and higher solids content due to the higher viscosity of the PDO.

[0047] Moreover, PDO, unlike NMP, is a safe chemical. Unlike NMP, which can cause reproductive harm, PDO does not negatively interact with the human body and naturally decomposes quickly. PDO is FDA approved for food consumption. PDO is cost effective, equal to or better than NMP, due to its wide-spread use in large industries like food, pharma, and cosmetics. PDO has a higher flash point than NMP making it less flammable. PDO is more soluble in water than NMP, so in the event of excess water from electrode powder sources, gelation is less likely. PDO enables more control over solids content for certain electrode materials due to gelation prevention and design flexibility from higher viscosity than NMP.

[0048] To date, most of the industry -based focus on improved methods to reduce dependence on NMP has been directed to making water-based PVDF suspensions work by adding pH / base inhibitors to the water-based PVDF binder package. This approach yields improvement in electrochemical data in the laboratory but has not been commercially accepted. Modifying pH as a requirement for slurry manufacturing presents a large risk, as it makes the process even more 1031257365.1Attorney Docket No.: 105131-101difficult to control. Mistakes in pH management at the production level could lead to large scrap rates. Utilizing PDO represents a lower risk in scrap rate, because PDO does not require pH modification and is stable in basic solutions. No gelations have been observed in laboratory testing even in the presence of moisture and high nickel content, high surface area NMC.

[0049] Other solvents can be used in place of PDO; however, such solvents may either be less effective at dissolving specific binders or have high toxicity or boiling points, making them less desirable in manufacturing. The present application discloses a direct replacement of NMP with PDO in processing, and implements new binder materials suitable for use in PDO.

[0050] Finally, this technology and approach can be used specifically to prevent issues associated with materials which experience gelation from residual water. By using PDO, and ensuring low water content throughout the process, one can achieve similar or better water contents compared to NMP based processes. Also, PDO is less likely to gel with water than NMP in a slurry, which can allow increased slurry stability times for difficult electrode slurries. For example, suppose an NMC powder was not properly baked and had high water content. If added to NMP, gel formation is likely, especially in the presence of PVDF and high residual lithium sources (lithium hydroxide and lithium carbonate) from the NMC surface. If instead, PDO is used, it will not gel with the small amount of water added by the NMC nor with the residual lithium sources leached from the NMC. Moreover, other polymers (for example PVP) used with PDO binder package are also soluble in water, and their presence would also hamper a phase change of the binder and hence prevent gelation.

[0051] We have compared slurries made with NMP / PVDF and PDO / HPC. For the same 96:2:2 formula of NMC811 (single crystal high surface area): binder : carbon black, we observed slurry gelation of the NMP / PVDF case but not the PDO / HPC case even though both slurries were mixed with double planetary centrifugal mixing at 3500 rpm. Both slurries became very warm during a high solids content mixing step prior to serial dilution to final target solids, but only the NMP / PVDF slurry gelled. The NMP / PVDF slurry became very thick and resistant to flow even when diluted to 65% solids, whereas the PDO / HPC slurry at 65% solids easily coated onto aluminum foil. The gelation of the NMP / PVDF slurry likely reflects dehydrofluorination of the PVDF in the presence of dissolved residual lithium sources (lithium hydroxide and lithium carbonate) in trace amounts of water in the NMP that raises the pH. When PVDF is exposed to highly basic pH, and the slurry is heated (in this case due to friction during mixing) a local 1131257365.1Attorney Docket No.: 105131-101reaction at the PVDF can occur in which HF is ejected. The leftover PVDF chains can become chemically crosslinked, and the HF can lead to undesired consequences in slurry coating such as aluminum foil etching and poor electrochemical performance. A cellulose or PAA based binder used with PDO will not experience such gelation as cellulose and PAA are more stable in a highly basic environments. PAA will react with hydroxide to form a salt, but the polymer backbone will remain intact. Hydroxy and carboxyl groups on cellulose will also respond in a similar way in highly basic pH’s, but the overall cellulose structure is robust.

[0052] In addition to PVP, other polymer binders include PAA, polymethyl methacrylate (PMMA), polymethacrylic acid (PMA), and some cellulosic derivatives. In some embodiments, PVDF is used in the emulsion polymerization to generate a suspension of PVDF nanoparticles in PDO.

[0053] Mini emulsion polymerization of hydrophobic polymer binders can be performed with PDO as a solvent to form nanoparticles. There are three main types of polymers that may be synthesized in propanediol as the main solvent: Styrene-rubber based (SBR for example), Vinylidene fluoride based (PVDF for example), and poly acrylates, including polyacrylate copolymers.

[0054] Polystyrene synthesis in miniemulsions of hexadecane and glycol utilizing specific free radical initiators that are soluble in glycol solutions has been demonstrated, but not soluble in the oil phase. Styrene monomer was soluble in the hydrophobic nanodroplets, but not soluble in the continuous polar phase (glycol). Specific surfactants allowed for stabilized micelle formation, and an equilibration size of monomer in oil droplets was achieved with stirring. The particle size was dependent on the amount of surfactant used: increasing surfactant led to decreasing particle size. Appropriate surfactant-particle size trending was demonstrated with Lutensol AT50 emulsifier / surfactant and PEGA200 initiator. The PEGA200 initiator was a poly(ethylene glycol)-azo-initiator which is soluble in glycol solutions.

[0055] According to some embodiments of the present application, PEGA200 can also be used as an initiator for polymerization in PDO miniemulsions.

[0056] PVP is also a suitable surfactant in emulsion polymerizations. According to Khromiak et.al. “PVP can serve as an emulsifier in the processes of emulsion polymerization and also be an effective polymer matrix, which actively participates directly in the polymerization process”. Without wishing to be bound by theory, PVP is a protective colloid in embodiments of the 1231257365.1Attorney Docket No.: 105131-101present disclosure, not just an emulsifier. PVP can also be left within the binder and applied in the battery slurry mixing.

[0057] According to some embodiments of the present application, reactive polymer emulsifiers can be used as initiators and emulsifiers. Although PEGA200 and other polymeric initiators would be incorporated into the polymer structure of the miniemulsion particles, they do not serve as true emulsifiers / stabilizers. Reactive polymer emulsifiers / surfactants contain three components according to Heming et.al., US 7,199,195: “a hydrophilic moiety, a hydrophobic moiety, and a moiety that possesses reactive or cross-linking ability with respect to a monomer”, and “the cross-linking moieties enable the surfactant to become reacted with or bound to the monomer... while the colloid stabilizing moieties of the surfactant provide surface active properties.” Reactive emulsifiers have a polymerizable reactive group, either anionic, cationic, or non-ionic.

[0058] Anionic groups can include sulfate or sulfonate head groups. An example is sodium dodecyl allyl sulfosuccinate. A cationic example is alkyl maleate trimethylamine ethyl bromide. Non-ionic example includes functionalized poly(ethylene oxide)-poly(butylenes oxidejcopolymer. Reactive groups generally include allyics, acrylamides, methacrylates, styrenics (includes substituted styrenes), and maleates.

[0059] Other additives can be included, including buffers, plasticizers, and thickening agents. pH can be important for stabilization of colloids, and typically holding between pH of 6-8 is desirable, especially for polyacrylate based polymer emulsions. High or low pH can lead to unstable colloid situations and agglomerations / precipitations of synthesized polymer particles.

[0060] Based on these considerations, a synthesis plan can generate a directly useable polymer emulsion for a binder in an electrode based on propanediol. For this plan, PDO can provide the main dispersal solvent. Hydrophobes can be chosen for the discontinuous oil phase that are effective in forming stable droplets in PDO, but have a lower boiling point than hexadecane (< 286.9°C) so that they can be evaporated in electrode slurry drying during electrode fabrication or during binder purification step. The oil phase can utilize hexadecane. In some embodiments, the hexadecane is removed with purification techniques prior to using the end product binder in an electrode slurry mix. Monomers can be selected based on the desired polymer content. Initiators are chosen that are either oil or propanediol soluble.1331257365.1Attorney Docket No.: 105131-101

[0061] All components are selected based on an understanding that they will be incorporated directly into the polymer structure and have electrochemical compatibility in the battery environment. In the case of PEGA initiators, the polyethylene glycol) chains that are incorporated are crosslinked sufficiently to prevent electrolyte breakdown in the final battery.

[0062] Surfactants / emulsifiers are chosen that are efficient and stable in continuous phase. For some embodiments, reactive polymer emulsifiers are used, because they can covalently bond to the surface to the synthesized polymer nanoparticles. The use of such reactive polymer emulsifiers ensure that there are no free floating ‘contaminant’ monomers in the continuous phase that could be a problem for battery slurry and battery operation. Further, the reactive polymer emulsifiers that are covalently bonded to the surface of the synthesized polymer nanoparticles can be selected based on a final embodiment in which water-soluble functional groups are present, including but not limited to hydroxyl and carboxyl groups, which would aid in the water-based recycling of scrap or reclaimed electrodes

[0063] An optional crosslinker can be chosen that can be added to further crosslink the poly(ethylene glycol) chains in the PEGA initiator to prevent decomposition in the electrolyte. However, such cross-linkers may not be necessary depending on the natural crosslink density and desired electrolyte uptake of the final polymer binder. Optional chain transfer agents in the form of mercaptans can be included to assist in controlling the polymer molecular weight and distribution.

[0064] According to some embodiments, polymer nanoparticles are synthesized while ensuring that there are very little to no leftover components in the continuous phase that could lead to parasitic side reactions. The final synthesized product can be readily used as a co-binder in the electrode without significant further modifications (like rinsing, separations, purification, etc.) Each component has a purpose, being incorporated into the polymer by design in order to withstand the slurry making process as well as battery / electrochemical environment (e.g. some additives for the emulsion polymerization process are not very stable in slurry mixing or could have side reactions if left behind in the electrode).General Miniemnlsion Polymerization Process Parameters:

[0065] Initiator: PEGA200 is a good choice for some embodiments. Other initiators could include higher molecular weight PEGA, e.g. PEGA2000 and PEGA20000, and sulfonated forms,1431257365.1Attorney Docket No.: 105131-101e g. PEGAS200. PEGA200 is chosen because it is soluble only in PDO, and is not soluble in the oil phase (cyclohexane for example). Use of other initiators that are soluble in both phases will cause agglomeration.

[0066] Surfactant / Emul sifier: Lutensol AT50 can be used for emulsification in PDO. Lutensol AT50 is a type of non-ionic alcohol ethoxylate. Although incorporation of Lutensol AT50 is optional in some embodiments, it aids in micelle formation and stabilization as well as helps control particle size. Other alcohol ethoxylates may be useful as well. The Lutensol AT line includes varying degrees of ethoxylate content: AT 11, 18, 25 , 50, and 80. According to the manufacturer’s specifications, AT 25 and 50 may have a good balance between polyglycol content and are used for surface-active applications, such as the present application. These surfactants would be left behind in the binder after synthesis, but could be statically adhered to the surface of the polymer nanoparticles. However, they may not be electrochemically stable, so a glycol crosslinker may be required to create covalent bonding at the surface, or there would need to be a replacement with a reactive polymer emulsifier. In one embodiment, Lutensol AT50 and PEGA200 could be crosslinked with the same polyglycol crosslinking additive. That crosslinking additive would have to be oil soluble, be present inside the micelle, and generate crosslinks within the PEGA initiator structure and at the surface interface with the glycol portion of the Lutensol emulsifier.

[0067] Hydrophobe (Oil Solvent): Hexadecane provides excellent properties for miniemulsion polymerization. However, because of its high boiling point, it may not be ideal for removal after synthesis. Cyclohexane may be an appropriate low boiling point substitute, having a boiling point of 80.74C. Cyclohexane is generally safe, having only minor health related effects in the acute exposure range. However, over long periods of time, exposure may have adverse health effects. Cyclohexane has a very low flash point at -20C, so flammability is a concern in a production setting. However, with proper ventilation, if concentrations in evaporation streams are kept low, the risks of flammability are low.

[0068] Hexadecane is present in jet fuel, and may have similar toxicity to cyclohexane. The main advantage is that the flash point is a much safer 135 °C, however the boiling point is 287 °C, so it would certainly be left behind and is unstable in battery applications or need to be removed during a purification stage. According to Steel et. al., cyclohexane and hexadecane were measured spectroscopically in mixtures with water to determine the interfacial properties1531257365.1Attorney Docket No.: 105131-101between polar and non-polar phases. The conclusion was that they were similar in terms of measured transition between polar to non-polar phase, so it is believed that cyclohexane could generate similar boundary conditions for droplet formation compared to hexadecane. Although PDO is less polar than water, the difference in polarity between PDO and hexadecane is high enough that it can still generate miniemulsions.

[0069] Monomers : The monomers chosen will depends on the desired polymer structure.Typically for the propanediol based emulsion polymerization, the monomers should be oil soluble, and not soluble, or poorly soluble, in the polar phase. However, for the case of gas phase with 1,1 -di fluoroethylene (VDF) in PVDF synthesis, or HFP (hexafluoropropene) in PHFP synthesis, this consideration is not relevant.

[0070] Reaction Temperature : The reaction temperature can be in the range of about 50 °C to about 200 °C, or 50 °C to about 100 °C. Notably it can be higher in PDO systems than in water systems due to not being limited by the boiling point of water (PDO b.p. -214 °C). The reaction temperature is largely determined by the initiator used.

[0071] Reaction Time : The appropriate reaction time will depend on factors including monomer selection, initiator selection, desired molecular weight, and reaction temperature. In some embodiments, the reaction time will be between 480 and 840 minutes.

[0072] Chain Transfer Agents : n-dodecyl mercaptan or tert-dodecyl mercaptan provide good choices for some embodiments.

[0073] Optional Crosslinkers for Oil Soluble Monomers : DVB is useful in acrylate polymers or in styrene-butadiene rubbers.

[0074] Optional Crosslinkers for Polar Phase / Propanediol Soluble Monomers and VDF Polymerizations: N-(hvdroxvmethvl acrylamide works well in aqueous solution and should work in PDO solution, although it is less soluble in PDO than in water. Ethylene glycol dimethacrylate (EGDMA) can be used at low concentrations and should be PDO soluble. For ethylene, it could actually be di, tri, tetra, - ethylene. Another potential crosslinker is poly(ethylene glycol) dimethacrylate with MW between about 200 and about 20,000. Specific molecular weights can be 200, 400, 1000, 4000, 10000, or 20000 Da. Ethylene glycol diglicidyl ether (EGDGE) can also aid in crosslinking PEO chains.Synthetic procedures:

[0075] Styrene-SBR Miniemulsion Polymerization:1631257365.1Attorney Docket No.: 105131-101(1) add Propanediol and Lutensol AT50, at a 0.3-2 wt% concentration, to dispersed (oil) phase. The dispersed phase includes an oil-soluble initiator and hexadecane (or cyclohexane), plus distilled styrene monomer and an optional transfer agent selected from n-DM or t-DM. Suitable oil-soluble initiators include V59 (2,2’-azobis(2-methylbutyronitrile)), LPO (lauroyl peroxide), and KPS (potassium persulfate);(2) obtain miniemulsion of styrene by high agitation, stirring 2000 rpm for 1 hour;(3) with a sonifi er, sonicate at 80-100% power for 1-3 minutes;(4) during this homogenization process, cool with an ice bath to prevent any thermal initiation;(5) condense butadiene monomer in a cooled and pressurizable reaction vessel;(6) add the precursor styrene miniemulsion to frozen butadiene;(7) seal the vessel, and homogenize with vigorous stirring, 2000 rpm for 30 min- 1 hr; (8) polymerize at a temperature dependent on the initiator used, for example, v59 would be 72 °C, for up to 14 hours.

[0076] For a crosslinking reactive emulsifier option, one moiety could be based on styrene or substituted styrenes. The rest of the reactive emulsifier copolymer would include PVP, and a methylmethacrylate or other oil-soluble moiety. Further, a PDO-soluble initiator can be used in place of an oil-soluble initiator with similar effect.

[0077] Fluorinated Polymer (PVDF and PHFP) Synthesis in 1,3-propanediol:(1) Fill the reaction vessel under vacuum with the following:Initiator: PEGA200, V50 or VA-044 from Wako Chemical, ammonium persulfate (APS), potassium persulfate (KPS),Surfactant: a reactive emulsifier based on VDF, PVP, and HFP; other surfactants that have good solubility in propanediol could be used, especially Lutensol AT50,Solvent, propanediol,(2) Cool the vessel, for example with an acetone / liquid nitrogen bath;(3) Transfer VDF or HFP (hexafluoropropene) gas to the reaction vessel;(4) Warm the vessel to room temperature;1731257365.1Attorney Docket No.: 105131-101(5) Stir and gradually heat to 70 °C (Note: if using propanediol and PEGA200, this initiator could be added during or just after this step instead of in step 2, to prevent premature initiation);(6) Stop the reaction by quenching with an ice bath after certain time; and(7) Purge the unreacted monomer and dispense a dispersion of fluorinated polymer (PVDF or PHFP) in propanediol.

[0078] Acrylate Copolymer Synthesis in E3-propanediol:(1) add the following to a pressurizable polymerization reactor:Initiator: PEGA200, or any other poly(ethylene glycol)-azo-initiator that performs as an interfacial active initiator and is soluble in PDO,Surfactant: optional, but could be selected from any number of propanediol soluble surfactants, including Lutensol AT50, or could also add a crosslinking reactive emulsifier based on the moieties of methacrylate, PVP, and methacrylic acid,Hydrophobe, cyclohexane, or other low boiling point hydrophobic solvent, Monomers', oil soluble monomers can include styrene, methylmethacrylate (MMA) or other acrylate monomers, depending on the desired copolymer composition,Optional chain transfer agents, mercaptans, such as n-DM or t-DM (2) increase the temperature to 70 °C with high speed stirring, up to 2000 rpm, or, in an embodiment, could employ an temperature controlled jacket to prevent accidental heating while stirring in step 1 additions;(3) After 480-780 minutes, quench reaction by lowering in temperature, e.g. in an ice bath, taking care not to crash out the particles and cause unwanted agglomeration,(4) Adjust the pH as needed,(5) Remove unreacted monomers and hydrophobe by distillation.

[0079] For acrylate copolymers, it may be unnecessary to add a crosslinker for the initiator PEO chains. When using methyl methacrylate, butyl acrylate, and acrylic acid in the presence of an unsaturated polyester resin, a hybrid system can be s obtained with “internal domains of polyester resin in an acrylic matrix”. This situation can provide a more heavily crosslinked1831257365.1Attorney Docket No.: 105131-101polymer system in which any PEO chain presence left over from the initiators would likely be negligible.

[0080] Although the invention has been described and illustrated with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.31257365.1

Claims

Attorney Docket No.: 105131-101What is claimed is:

1. A mixture configured to form an emulsion upon undergoing an emulsification process, the emulsion comprising:a continuous phase comprising 1,3- propanediol;a discontinuous phase comprising nanometer-sized emulsion droplets of a hydrophobic solvent dispersed in the continuous phase, the discontinuous phase including one or more monomers dissolved therein, the one or more monomers suitable for forming a hydrophobic polymer binder by free-radical polymerization;a surfactant for stabilizing the nanometer-sized emulsion droplets;an initiator, soluble in the continuous phase, but insoluble in the discontinuous phase; wherein the monomers are selected from the group consisting of styrene, butadiene, isoprene, one or more acrylates soluble in the discontinuous phase, hexafluoropropylene, and vinylidene fluoride.

2. The mixture of claim 1, wherein a polymer binder is dissolved in the continuous phase.

3. The mixture of claim 2, wherein the polymer binder is a water soluble polymer binder.

4. The mixture of claim 3, wherein the water soluble polymer binder is selected from the group consisting of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), chemically modified cellulose, and combinations thereof.

5. An electrode slurry, comprising:a 1,3 -propanediol (PDO) solution of a water-soluble polymer binder;an electrode active material, wherein the electrode active material includes an intercalating compound for an active metal ion, an accepting compound for the active metal ion, or a conversiontype compound;a conductive additive,wherein the active metal ion is an ion of an active metal selected from the group consisting of an alkali metal, an alkaline earth metal, Zn, Al, Fe, V, Mn, and Cr,2031257365.1Attorney Docket No.: 105131-101wherein the water-soluble polymer binder includes a polymer selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid, chemically modified cellulose, and combinations thereof.

6. The electrode slurry of claim 5, further including a hydrophobic polymer binder dispersed as nanoparticle in the PDO solution.

7. The electrode slurry of claim 6, wherein the hydrophobic polymer binder includes a polymer selected from the group consisting of a styrene based rubber, a thermoplastic fluoropolymer, a PDO-insoluble acrylate polymer, and combinations thereof.

8. The electrode slurry of claim any one of claims 5 to 7, wherein the conductive additive comprises carbon.

9. The electrode slurry of any one of claims 5 to 8, wherein the water-soluble polymer binder comprises a low molecular weight polymer and a high molecular weight polymer, the low molecular weight polymer having a molecular weight lower than a molecular weight of the high molecular weight polymer.

10. The electrode slurry of claim 9, wherein the low molecular weight polymer and the high molecular weight polymer have the same chemical composition.

11. The electrode slurry of claim 9, wherein each of the low molecular weight polymer and the high molecular weight polymer are separately selected from the group consisting of polyacrylic acid and hydroxyproplycellulose.

12. A method for forming an electrode coating, the method comprising:mixing an electrode active material, a conductive additive, and a water-soluble polymer binder dissolved in a PDO solvent to obtain an electrode slurry, wherein the electrode active2131257365.1Attorney Docket No.: 105131-101material includes an intercalating compound for an active metal ion, an accepting compound for the active metal ion, or a conversion-type compound;casting the electrode slurry onto a conductive substrate to form a slurry-coated conductive substrate;drying the slurry-coated conductive substrate by evaporation of the PDO solvent; and densifying the dried slurry-coated conductive substrate to form the electrode coating.

13. The method of claim 12, further comprisingpreparing a hydrophobic polymer binder suspension comprising a hydrophobic polymer binder suspended as nanoparticles in 1,3 -propanediol (PDO); andmixing the hydrophobic polymer binder suspension with the electrode active material, the conductive additive, and the water-soluble polymer binder dissolved in a PDO solvent to obtain the electrode slurry.

14. The method of claim 13, wherein the hydrophobic polymer binder is selected from the group consisting of a styrene based rubber, a thermoplastic fluoropolymer, a 1,3- propanediol insoluble acrylate polymer, and combinations thereof.

15. The method of any one of claims 12 to 14, wherein the water-soluble polymer binder is selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid, water- soluble acrylic ester / acrylate polymers, chemically modified cellulose, and combinations thereof.

16. The method of claim 15, wherein the chemically modified cellulose is selected from the group consisting of hydroxy ethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and combinations thereof.

17. The method of any one of claims 13 or 14, wherein preparing the hydrophobic polymer binder suspension comprises:mixing a free radical initiator, hydrophobic polymer monomers, PDO, a hydrophobic solvent, and a surfactant to obtain a polymerizable mixture, the hydrophobic solvent being 2231257365.1Attorney Docket No.: 105131-101insoluble in PDO, and the hydrophobic polymer monomers being soluble in the hydrophobic solvent;emulsifying the polymerizable mixture to form a miniemulsion having emulsion droplets with diameters in the range of about 20 to about 200 nm;polymerizing the polymerizable mixture.

18. The method of claim 17, wherein polymerizing the polymerizable mixture includes agitating and heating the polymerizable mixture.

19. The method of any one of claims 13, 14, 17, or 18, whereinthe water-soluble polymer binder is between about 0.1 wt. % and about 5 wt. % of the electrode coating, andthe hydrophobic polymer binder is about 0.1 wt. % and about 5 wt. % of the electrode coating.

20. The method of any one of claims 13, 14, 17, or 18, whereinthe water-soluble polymer binder is between about 0.5% and about 1.5% of the electrode coating, andthe hydrophobic polymer binder is about 2-4% of the electrode coating.

21. An active metal-ion cell, comprising:a positive electrode, the positive electrode having a first electrode coating formed from a propanediol (PDO) slurry coated on a conductive substrate according to the method of any one of claims 12 to 20;a negative electrode;a separator interposed between the positive and negative electrodes; andan electrolyte in physical contact with each of the positive electrode, the negative electrode, and the separator, wherein the active metal-ion cell incorporates an active metal selected from the group consisting of an alkali metal, an alkaline earth metal, Zn, Al, Fe, V, Mn, and Cr.

22. An active metal-ion cell, comprising:2331257365.1Attorney Docket No.: 105131-101a positive electrode,a negative electrode, the negative electrode having an electrode coating formed from a propanediol (PDO) slurry coated on a conductive substrate according to the method of any one of claims 12 to 20;a separator interposed between the positive and negative electrodes; andan electrolyte in physical contact with each of the positive electrode, the negative electrode, and the separator, wherein the active metal-ion cell incorporates an active metal selected from the group consisting of an alkali metal, an alkaline earth metal, Zn, Al, Fe, V, Mn, and Cr.

23. The metal-ion cell of any one of claim 21 or claim 22, wherein the active metal is lithium, and wherein the PDO slurry comprises a lithiated electrode active material, a conductive additive, a water soluble polymer binder dissolved in a PDO solvent, and an emulsion second binder suspended in a PDO solvent.

24. The active metal-ion cell of any one of claims 21 to 23, wherein the active metal-ion cell is one of a plurality of active metal-ion cells in an active metal-ion battery pack.2431257365.1

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