Adhesive for electrode primer in lithium ion batteries

Abstract

The disclosed technology relates to a coating primer for electrochemical devices, such as lithium ion batteries, including electrodes (both anode and cathode) prepared with a polymer binder functionalized with a leaving group that acts as a mechanical kill switch.

Description

Docket No. 4851TITLEADHESIVE FOR ELECTRODE PRIMER IN LITHIUM ION BATTERIES BACKGROUND OF THE INVENTION

[0001] The disclosed technology relates to a polymeric binder for current collector primer for electrochemical devices, such as lithium ion batteries, including electrodes (both anode and cathode) prepared with a polymer binder functionalized with a leaving group that acts as a mechanical kill switch.

[0002] The demand for high energy density batteries is increasing. Lithium- ion batteries are one of the most promising battery types currently used.

[0003] Lithium-ion batteries are generally composed of an anode, made of a carbon material or a lithium-metal alloy, a cathode, made of a lithium-metal oxide, and an electrolyte in which a lithium salt is dissolved in an organic solvent. Polyacrylic acid (PAA) polymer is commonly used to coat a layer of primer on the current collector. It has excellent electrochemical stability, film formation and lithium ion conductivity. The polymer is formulated into an aqueous slurry with conductive carbon, neutralizer and additives, coated on the Al or Cu current collector and dried. Despite some of the beneficial properties of PAA, there is a need to improve flexibility of the binder, and provide additional properties to improve battery performance and safety.

[0004] Safety of lithium-ion batteries is an important issue. Thermal runaway is an issue of safety in lithium-ion batteries. Thermal runaway occurs when a chain of exothermic reactions within the battery is touched off causing a sharp rise in the internal battery temperature leading to the destabilization of the inner structures of the battery, which eventually leads to the failure of the battery.

[0005] There are methods to prevent thermal runaway, such as various cooling systems employed to prevent thermal conditions from rising to the point of a runaway event. Likewise, various extinguishing possibilities have been explored for mitigation of combustion events that propagate thermal runaway conditions.

[0006] There is a need for a battery having built-in prevention mechanisms to improve the safety of electrochemical devices.SUMMARY OF THE INVENTION

[0007] In one embodiment, the disclosed technology, solves the problem of thermal runaway events in electrochemical cells, by providing an electrochemical cell having electrodes prepared with a polymer binder having temperature sensitive leaving groups. The disclosed technology improves the coating firm properties and battery safety.Docket No. 4851

[0008] The technology provides a method of separating two adhered surfaces in a system in situ. The method includes 1) binding the two adhered surfaces with a polymer binder of a (meth)acrylic acid or ester polymer functionalized with a thermally degradable leaving group, and 2) raising the temperature of the system greater than a thermal degradation temperature of the leaving group. Upon leaving, the leaving group can form a gas at the thermal degradation temperature that expands and thereby mechanically separates the adhered surfaces. The leaving group can be, for example, a tert-but oxy carbonyl (Boc) group.

[0009] In a particular embodiment, the technology provides a method of preventing thermal runaway in an electrochemical device involving preparing the electrochemical device with the polymer binder as set forth above. The leaving group in the polymer can have a thermal degradation temperature of 120°C or greater such that when the electrochemical device is operated to a temperature of 120°C or greater, the leaving group forms a gas that expands and thereby mechanically separates the surfaces of the electrochemical device, thereby breaking the electrochemical circuit.

[0010] The technology also provides an electrochemical device that includes electrodes, both anode and cathode, a separator disposed between the anode and cathode electrodes, an electrolyte in ionic contact with the electrodes and separator, and a polymer binder of a (meth)acrylic acid or ester polymer functionalized with a leaving group.

[0011] Another aspect of the technology includes a coating primer composition for surfaces in an electrochemical cell. The primer composition includes a slurry of a solvent, conductive carbon, and the polymer binder. The slurry can be employed on electrodes as well as separators in the electrochemical cell.DETAILED DESCRIPTION OF THE INVENTION

[0012] Various preferred features and embodiments will be described below by way of non-limiting illustration.

[0013] Polymers are derived from the successive “linking” of monomers in a polymerization reaction. By linking, it means that the monomers become bonded together. The linking of monomers requires alteration of the chemical structures of the monomers for the purpose of freeing a bond the monomers can use to link by.

[0014] For example, the chemical structure of ethylene monomer is two CH2 units connected by a double bond;H2C^CH2Docket No. 4851When ethylene monomers are polymerized, or linked, the double bond is opened and becomes free to bond with another ethylene monomer;or otherwise represented as a repeating unit;

[0015] As can be seen, the repeating polyethylene unit is different from the starting ethylene monomer in that the double bond of the ethylene monomer has been opened. Although the polyethylene repeat unit is altered from the ethylene monomer from which it was derived, it is a common practice in the art of polymer plastics to refer to the repeating units of the polymer by the same name as the monomer. So, ethylene monomer refers both to CH2=CH2 and the polymerized repeat unit -[CH2-CH2]n-, where n is the number of repeat units in the polymer. Likewise, ethylene units or blocks of ethylene in the polymer means units or blocks derived from ethylene monomer. Similarly, styrene units or blocks of styrene in the polymer means units or blocks derived from styrene monomer, and so on for other types of monomers.

[0016] Those of ordinary skill in the art recognize that the polymerized monomer will be of altered chemical structure, but understand the relation between the repeat unit and the monomer from which the repeat unit was derived. Thus, as used in the description below and in the claims, monomer will refer both to a repeat unit of a polymer derived from the monomer, as well as the stand-alone monomer itself.

[0017] The disclosed technology provides an in situ method of separating two adhered surfaces in a system where the system is subject to a pre-determined thermal event. The method involves binding the surfaces of the system with a polymer binder that is functionalized with a thermally degradable leaving group. Once the temperature of the system is raised to the thermal degradation temperature or greater, the leaving group forms a gas that expands and thereby mechanically separates the adhered surfaces.

[0018] The method can find particular use in an electrochemical cell in which the polymer binder can be used to bind together materials, such as carbonaceousDocket No. 4851 materials of an electrode in the electrochemical cell. Electrochemical cells can include, for example, a lithium-ion battery.

[0019] The method can include, for example, preventing thermal runaway in an electrochemical device. The method would include preparing the electrochemical device with a polymer binder of a (meth)acrylic acid or ester polymer functionalized with a leaving group having a predetermined thermal degradation temperature, then operating the electrochemical device up to or greater then the thermal degredation temperature. Once the thermal degradation temperature is achieved, the leaving group will form a gas that expands and thereby mechanically separates the surfaces of the electrochemical device and breaks the circuit.

[0020] The method calls for a polymer binder composition.

[0021] The polymer binder encompasses a (meth)acrylic acid or ester polymer functionalized with a leaving group. In the context of this technology, the prefix “(meth) in "(meth)acrylic acid or ester " includes (meth)acrylic acids as well as (meth)acrylic acid esters, otherwise known as "acrylate" or "methacrylate" polymers, for example polymerized from monomers of Formula I:Formula Iwhere R is H or CH3, and R’ is H+, Na+, Li+, K+, Vi Mg2+, Vi Ca2+or a Cl to Cl 8 hydrocarbyl or mono-alcohol group.

[0022] Exemplary component (meth)acrylic acid or ester monomers from which the (meth)acrylic acid or ester polymer may be prepared, include, but are not limited to, methyl acrylic acid or methyl acrylate, methyl methacrylic acid or methyl methacrylate, ethyl acrylic acid or ethyl acrylate, ethyl methacrylic acid or methacrylate, hydroxyethyl acrylic acid or hydroxyethyl acrylate, hydroxyethyl acrylic acid or hydroxy ethyl methacrylate, n-propyl acrylic acid or n-propyl acrylate, n-propyl methacrylic acid or n-propyl methacrylate, isopropyl acrylic acid or isopropyl acrylate, isopropyl methacrylic acid or methacrylate, hydroxypropyl acrylic acid or hydroxypropyl acrylate, hydroxypropyl methacrylic acid or methacrylate, n-butyl acrylic acid or n-butyl acrylate, n-butyl methacrylic acid or n-butyl methacrylate, isobutyl acrylic acid or isobutyl acrylate,Docket No. 4851 isobutyl methacrylic acid or isobutyl methacrylate, tert-butyl acrylic acid or tertbutyl acrylate, tert-butyl methacrylic acid or tert-butyl methacrylate, secbutyl acrylic acid or secbutyl acrylate, sec-butyl methacrylic acid or sec-butyl methacrylate, hydroxybutyl acrylic acid or hydroxybutyl acrylate, hydroxybutyl methacrylic acid or hydroxybutyl methacrylate, n-pentyl acrylic acid or n-pentyl acrylate, n-pentyl methacrylic acid or n-pentyl methacrylate, neopentyl acrylic acid or neopentyl acrylate, neopentyl methacrylic acid or neopentyl methacrylate, cyclohexyl acrylic acid or cyclohexyl acrylate, cyclohexyl methacrylic acid or cyclohexyl methacrylate, 2-hexyl acrylic acid or 2-hexyl acrylate, 2-hexyl methacrylic acid or 2-hexyl methacrylate, 2-ethylhexyl acrylic acid or 2-hexyl acrylate, 2- ethylhexyl methylacrylic acid or 2-ethylhexyl methacrylate, n-octyl acrylic acid or n-octyl acrylate, n-octyl methacrylic acid or n-octyl methacrylate, isooctyl acrylic acid or isooctyl acrylate, isooctyl methacrylic acid or isooctyl methacrylate, decyl acrylic acid or decyl acrylate, decyl methacrylic acid or decyl methacrylate, isodecyl acrylic acid or isodecyl acrylate, isodecyl methacrylic acid or isodecyl methacrylate, dodecyl acrylic acid or dodecyl acrylate, dodecyl methacrylic acid or dodecyl methacrylate, 2-propylheptyl acrylic acid or 2-propylheptyl acrylate and 2-propylheptyl methacrylic acid or 2-propylheptyl methacrylate, lauryl acrylic acid or lauryl acrylate, lauryl methacrylic acid or lauryl methacrylate, cetyl acrylic acid or cetyl acrylate, cetyl methacrylic acid or cetyl methacrylate, stearyl acrylic acid or stearyl acrylate, stearyl methacrylic acid or stearyl methacrylate, behenyl acrylic acid or behenyl acrylate, behenyl methacrylic acid or behenyl methacrylate, melissyl acrylic acid or melissyl acrylate, melissyl methacrylic acid or melissyl methacrylate, hydroxy isobutyl acrylic acid or hydroxy isobutyl acrylate, hydroxy isobutyl methacrylic acid or hydroxy isobutyl methacrylate, hydroxy tertbutyl acrylic acid or hydroxy tertbutyl acrylate, hydroxy tertbutyl methacrylic acid or hydroxy tertbutyl methacrylate, and mixtures thereof.

[0023] The (meth)acrylic acid or ester polymer may also include comonomers, such as, for example, ethylene, propylene, butadiene, neoprene, chlorprene, acrylonitrile, methacrylonitrile, carboxymethyl cellulose salt, acrylamide, 2- acrylamido-2-methyl propane sulfonic acid and it’s salts, styrene, other (meth)acrylic acid co-monomers, fumaric acid and esters thereof, itaconic acid and esters thereof, maleic acid and esters thereof, adipic acid and esters thereof, malic acid and esters thereof, poly ethylene glycol (meth)acrylates, and mixtures thereof.Docket No. 4851

[0024] Depending on the requirements of the system, the (meth)acrylic acid or ester polymer can have a number average molecular weight (Mn) of from about 2,000 to 2,500,000 daltons, or from 10,000 to 2,250,000 daltons, or even from 50,000 or 100,000 to 2,000,000 daltons, or from 200,000 to 1,500,000 or even 250,000 to 1,000,000 daltons.

[0025] The (meth)acrylic acid or ester polymer will be functionalized with a leaving group. The leaving group can be chosen such that the group deprotects from the polymer at elevated temperatures, such as, for example, greater than 75 or 80°C, or greater than 90°C or greater than 100°C, or greater than 110°C or 120°C, even at greater than 130°C, or even at greater than 140°C or 150°C.

[0026] An example leaving group includes a Zc / V-butyloxycarbonyl (“Boc”) leaving group. Other leaving groups include, for example, benzyl carbonate (“Cbz”), 9-fluorenylmethyl carbonate (Fmoc), ethyl carbonate, methyl carbonate, tert-butyl ether, ethyl group, and isopropyl group.

[0027] Greater than about 0.01 mole percent of the monomers of the polymer can be functionalized with the leaving group, or greater than 0.05 mol%, or even greater than 0.1mole% or greater than 0.15 mole%, or between 0.01 and 10 mol%, or even between 0.05 and 8 mol% of the monomers in the polymer can be functionalized with the leaving group, or from 0.1 to 6 mol% or 0.15 to 4 mol%.

[0028] The polymer binder can be made as a solution polymer or as an emulsion. Conventional emulsifiers can be used to form the emulsion of the monomers and to stabilize growing latex particles of the polymer binder. Typical anionic emulsifiers include alkali or ammonium alkyl sulfates, alkyl sulfonates, salts of fatty acids, esters of sulfosuccinic acid salts, alkyl diphenylether disulfonates, and the like, and mixtures thereof. Typical nonionic emulsifiers include polyethers, e.g., ethylene oxide and propylene oxide condensates, including straight and branched chain alkyl and alkylaryl polyethylene glycol and polypropylene glycol ethers and thioethers, alkyl phenoxypoly(ethyleneoxy) ethanols having alkyl groups containing from about 7 to about 18 carbon atoms and having from about 4 to about 100 ethyleneoxy units, and polyoxy-alkylene derivatives of hexitol, including sorbi- tans, sorbides, mannitans, and mannides; and the like, and mixtures thereof. Preferred surfactants include phosphate ester, sodium lauryl sulfate; benzene 1, 1’- oxybis-, tetrapropylene derivatives, sulfonate; sodium dioctyl sulphosuccinate; and dodecylbenzene sulfonate. Surfactants approved for food contact are preferred for heat seal applications involving food contact and are listed in 21 CFRDocket No. 4851§ 177.1010 Subpart B. Co-surfactants typically are employed in the compositions of the present invention at levels of about 0 wt. % to about 3 wt. %.

[0029] The emulsion polymerization can be carried out in a conventional manner using well-known additives and ingredients, such as emulsifiers, free radical polymerization initiators, and the like, and mixtures thereof. Either thermal or redox initiation processes may be used. The reaction temperature typically is maintained at a temperature lower than about 100° C. throughout the course of the reaction. In one embodiment, a reaction temperature between about 25° C. and 95° C. is used. For the purpose of adjusting pH at the outset of the emulsion polymerization pH control agents and buffers typically are added. The initial reactor pH will normally be within the range of about 0 to about 12, or about 1 to about 11, or about 3 to about 10. However, other pH values may be obtained in particular applications using pH control agents and buffers well known to those skilled in the art. Non-limiting examples of suitable pH control agents include but are not limited to ammonium and alkali metal hydroxides (such as sodium hydroxide, lithium hydroxide, potassium hydroxide, etc), and mixtures thereof, and the like. Non-limiting examples of suitable buffers include ammonium carbonate, sodium carbonate, sodium bicarbonate, and mixtures thereof, and the like. pH may be adjusted if desired at the end of the polymerization process according to the desired application.

[0030] The present disclosure is also directed to the use of the above-described binder as a primer in an electrochemical cell. The binder may be used, for example, on separators or electrodes in, for example but without limitation, fuel cells, batteries, and / or capacitors.

[0031] A coating primer composition for surfaces in an electrochemical cell can include a slurry of a solvent, conductive carbon, and the polymer binder.

[0032] Suitable solvents for the slurry include, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, any one thereof or a mixture of two or more thereof.

[0033] Examples of conductive carbon include, but are not limited to, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers.

[0034] Likewise, the present disclosure is directed to a battery comprising the presently disclosed polymer binder. In one embodiment, the battery may be a lithium ion battery.Docket No. 4851

[0035] The present disclosure is also directed to an electrochemical cell comprising the presently disclosed polymer binder in at least one electrode or in both cathode and anode. The electrochemical cell may further comprise at least one electrolyte. Additionally, the cathodes and anodes may be any suitable cathode and / or anode as would be known to a person of ordinary skill in the field. The electrolyte may be in the form of a gel and / or liquid.

[0036] The amount of each chemical component described is presented exclusive of any solvent or diluent, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, by-products, derivatives, and other such materials which are normally understood to be present in the commercial grade.

[0037] As used herein, the term "hydrocarbyl substituent" or "hydrocarbyl group" is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include:

[0038] hydrocarbon substituents, that is, aliphatic (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic-, aliphatic-, and alicy- clic-substituted aromatic substituents, as well as cyclic substituents wherein the ring is completed through another portion of the molecule (e.g., two substituents together form a ring);

[0039] substituted hydrocarbon substituents, that is, substituents containing nonhydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and sulfoxy);

[0040] hetero substituents, that is, substituents which, while having a predominantly hydrocarbon character, in the context of this invention, contain other than carbon in a ring or chain otherwise composed of carbon atoms and encompass substituents as pyridyl, furyl, thienyl and imidazolyl. Heteroatoms include sulfur, oxygen, and nitrogen. In general, no more than two, or no more than one, nonhydrocarbon substituent will be present for every ten carbon atoms in the hydrocarbyl group; alternatively, there may be no non-hydrocarbon substituents in the hydrocarbyl group.Docket No. 4851

[0041] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present invention; the present invention encompasses the composition prepared by admixing the components described above.EXAMPLES

[0042] Example 1 - Control Solution Polymer - A polymeric solution was prepared through a solution polymerization process in water, ran in a 3 liter, 4-neck, spherical reactor fitted with half-moon blade agitator, temperature probe, condenser, and feed ports. The reaction was carried out as a semi-batch process, where all the monomer was contained in an agitated pre-mix vessel and fed to the reactor over 120 minutes. The polymerization was performed in a hood with the reactor placed in a heating mantel with a controlled temperature. A slight nitrogen purge was applied throughout the reaction.

[0043] The pre-mix content was prepared by adding 439.8 grams of acrylic acid to the pre-mix vessel. The reactor content was prepared by adding 1197 grams of demineralized (DM) water to the reactor. The reactor content was heated to 95°C. After the temperature stabilized, a solution of 1.7 grams of ammonium persulfate and 39 grams of DM water was added to the reactor. The acrylic acid pre-mix feed was added to the reactor over 120 minutes at a constant rate. After the completion of the acrylic acid feed, a solution of .5 grams of ammonium persulfate and 9 grams of DM water was added to the reaction mass and allowed to react for 30 minutes. Another identical ammonium persulfate solution was added and allowed to complete the reaction over 60 minutes. The reaction was cooled to 40°C. The reaction mass pH was adjusted to 2.5 by adding 25 grams of a 50% aqueous solution of sodium hydroxide. Reaction polymer solids content was adjusted to 25% by adding 33 grams of DM water. The reaction product was then filtered through a 150-micron nylon mesh filter and collected.

[0044] Solution polymer pH was measured with a Mettler Toledo SevenExcel- lence Multiparameter instrument fitted with an InLab Power Pro electrode. TotalDocket No. 4851 solids content was measured with a CEM Smart 6 microwave / infrared instrument and viscosity was measured with a Brookfield Synchro-Lectric LVT viscometer.

[0045] The characterization of solution polymer example 1 is illustrated in table 1.Example 1 polymer Prop- ,, .Value erty pH 2.5Total Solids 25.0 %Viscosity 800 cpsTable 1 : Example 1 properties

[0046] Example 2 - A solution polymer was prepared and characterized the same way as described in Example 1, where pre-mix content was prepared with 437.6 grams of acrylic acid and 2.2 grams of Boc-HEMA monomer. The initial ammonium persulfate solution was prepared by adding 5.5 grams of ammonium persulfate and 39 grams of DM water. The reaction temperature was set at 85°C.

[0047] The characterization of solution polymer example 2 is illustrated in table2.Example 2 polymer Prop- ,, .Value erty pH 2.51Total Solids 25.0 %Viscosity 255 cpsTable 2: Example 2 properties

[0048] Example 3 - A solution polymer was prepared and characterized the same way as described in Example 2, where pre-mix content was prepared with 428.8 grams of acrylic acid and 11 grams of Boc-HEMA monomer.

[0049] The characterization of solution polymer example 3 is illustrated in table3.Example 3 polymer Prop- ,, .Value erty pH 2.50Total Solids 26.56 %Viscosity 360 cpsTable 3: Example 3 properties

[0050] Example 4 - A solution polymer was prepared and characterized the same way as described in Example 2, where pre-mix content was prepared with 417.8 grams of acrylic acid and 22 grams of Boc-HEMA monomer.Docket No. 4851

[0051] The characterization of solution polymer example 4 is illustrated in table4.Example 4 polymer Prop- ,, .Value erty pH 2.51Total Solids 23.31 %Viscosity 1400 cpsTable 4: Example 4 properties

[0052] Example 5 - A solution polymer was prepared and characterized the same way as described in Example 2, where pre-mix content was prepared with 324.8 grams of acrylic acid and 26.3 grams of Boc-HEMA monomer. The reactor content was prepared by adding 1324 grams of DM water to the reactor.

[0053] The characterization of solution polymer example 5 is illustrated in table5.Example 5 polymer Prop- ,, .Value erty pH 2.40Total Solids 19.29 %Viscosity 160 cpsTable 5: Example 5 properties

[0054] Example 6

[0055] A solution polymer was prepared and characterized the same way as described in Example 5, where pre-mix content was prepared with 316 grams of acrylic acid and 35.1 grams of Boc-HEMA monomer.

[0056] The characterization of solution polymer example 6 is illustrated in table6.Example 6 polymer Prop-Value erty pH 2.48Total Solids 18.69 %Viscosity 420 cpsTable 6: Example 6 properties

[0057] Example 7

[0058] A polymeric latex was prepared through an emulsion polymerization process ran in a 3 liter, 4-neck, spherical reactor fitted with half-moon blade agitator, temperature probe, condenser, and feed ports. The monomer was contained separately in a pre-mixed emulsion vessel and gradually metered to the reactor overDocket No. 4851180 minutes to reach a steady and controlled reaction rate. Reaction was carried out as a semi-batch reaction. The polymerization was performed in a hood with the reactor submerged in a water bath with controlled temperature. A slight nitrogen purge was applied throughout the reaction.

[0059] The pre-emulsion content was prepared by mixing 274 grams demineralized (DM) water, 25.81 grams of a 45% aqueous solution of Calfax DB45 surfactant from Pilot Chemical, and subsequently adding the monomers under agitation: 9.77 grams acrylic acid, 58.6 grams Acrylonitrile and 908.37 grams n-butyl acrylate. The reactor content was prepared by mixing 308 grams of DM water with 1.19 grams of a 45% aqueous solution of Calfax DB45 and 2.67 grams of ammonium carbonate. The reactor content was heated to 82°C. After the temperature stabilized, a solution consisting of 4.4 grams ammonium persulfate and 15 grams DM water was added to the reactor. The pre-emulsion feed into the reactor was started and continued for 30 minutes at a constant rate. When 14.6% of the pre- emulsion was consumed, the feed rate was increased, and the pre-emulsion was fed at a constant rate for 150 minutes. At the completion of the pre-emulsion feed a solution of .71 grams of ammonium persulfate and 15 grams of DM water was added to the reaction mass. Another identical ammonium persulfate solution was added after 60 minutes, and the reaction proceeds for 120 minutes. The reactor was then cooled to 57°C and a redox initiator was added consisting of 22.7 grams DM water, 2.48 grams of a 70% aqueous solution of t-butyl hydroperoxide, and .54 grams of a 45% aqueous solution of Calfax DB45, followed by an aqueous solution consisting of 72 grams DM water, 3.37 grams of sodium formaldehyde sulfoxylate and .54 grams of a 45% aqueous solution of Calfax DB45. 60 minutes after the redox initiator addition, 25.5 grams of DM water was added to the reactor and the reactor was cooled to 40°C, and the reaction product was filtered through a 150-micron nylon mesh filter.

[0060] Latex pH was measured with a Mettler Toledo SevenExcellence Multiparameter instrument fitted with an InLab Power Pro electrode. Total solids content was measured with a CEM Smart 6 microwave / infrared instrument, viscosity was measured with a Brookfield Synchro-Lectric LVT viscometer, and particle size was measured with a Nicomp 380 Submicron Particle Sizer. TGA analysis was performed using a TA Instruments legacy Discovery TGA.

[0061] The characterization of solution polymer example 7 is illustrated in table 7.Docket No. 4851Example 7 Latex Property Value pH 3.5Total Solids 55%Viscosity 100 cpsParticle size 300 nmTGA Wt. Loss @ 150°C 0%Table 7: Example 7 latex properties

[0062] Example 8

[0063] A polymeric latex was prepared through an emulsion polymerization process ran in a 3 liter, 4-neck, spherical reactor fitted with half-moon blade agitator, temperature probe, condenser, and feed ports. The monomer was contained separately in a pre-mixed emulsion vessel and gradually metered to the reactor over 180 minutes to reach a steady and controlled reaction rate. Reaction was carried out as a semi-batch reaction. The polymerization was performed in a hood with the reactor submerged in a water bath with controlled temperature. A slight nitrogen purge was applied throughout the reaction.

[0064] The pre-emulsion was prepared by mixing 280 grams of DM water, 3.4 grams of Calfax 16L35 surfactant from Pilot Chemical, 6 grams of hydroxy ethyl acrylate, 202 grams of Boc-HEMA monomer and 14 grams of ethyl acrylate while mixing under agitation. The reactor content was prepared by mixing 202 grams of DM Water and 1.7 grams of Calfax 16L35 under agitation. The reactor content was heated to 80°C. After the temperature stabilized a solution of 10 grams of water and .5 grams of ammonium persulfate were added to the reactor. The preemulsion was fed at a constant rate for 180 minutes. After completion of the preemulsion feed a solution of 10 grams of DM water and .3 grams of ammonium persulfate was added to the reaction mass and the reaction is allowed to proceed for 60 minutes. The reaction was then cooled to 57°C and a redox initiator was added consisting of 2.8 grams of DM water,.1 grams of sodium lauryl sulfate and 1.1 grams of tBHP followed by the addition of a solution containing 7.3 grams of DM water and .2 grams of sodium formaldehyde sulfoxylate. A 10% solution of lithium hydroxide was then added to adjust the pH. The reactor was then cooled to 40°C, and the reaction product was filtered through a 150-micron nylon mesh filter.

[0065] The characterization of solution polymer example 8 is illustrated in table 8.Docket No. 4851Example 8 Latex Property Value pH 8.4Total Solids 27%Viscosity 15 cpsParticle size 118 nmTGA Wt. Loss @ 150°C 40%Table 8: Example 8 latex properties

[0066] Example 9

[0067] A polymeric latex was prepared through an emulsion polymerization process ran in a 3 liter, 4-neck, spherical reactor fitted with half-moon blade agitator, temperature probe, condenser, and feed ports. The monomer was contained separately in a pre-mixed emulsion vessel and gradually metered to the reactor over 180 minutes to reach a steady and controlled reaction rate. Reaction was carried out as a semi-batch reaction. The polymerization was performed in a hood with the reactor submerged in a water bath with controlled temperature. A slight nitrogen purge was applied throughout the reaction.

[0068] The pre-emulsion was prepared by mixing 222 grams of DM water, 0.27 grams of ammonium carbonate, 3.8 grams of Sodium lauryl sulfate, 2.9 grams of Abex VA-50 from Syensqo, 62 grams of n-butyl acrylate, 449 grams of Boc- HEMA monomer and 9.9 grams of methyl methacrylate, 27 grams of a 50% solution of acrylamide and .3 grams of methacrylic acid while mixing under agitation. The reactor content was prepared by mixing 858 grams of DM water and .3 grams sodium lauryl sulfate under agitation. The reactor content was heated to 80°C. After the temperature stabilized 5% of the pre-emulsion was added to the reactor along with a solution of 20 grams of water and 2 grams of ammonium persulfate. After a 15 -minute hold the pre-emulsion was fed at a constant rate for 180 minutes. 30 minutes after the pre-emulsion feed started a solution of 81 grams of DM water and .7 grams of ammonium persulfate were metered to the reaction mass at a constant rate for 210 minutes. After completion of the pre-emulsion feed and the metered initiator feed the reaction was held at 80°C for 60 minutes. The reaction was then cooled to 57°C and a redox initiator was added consisting of 20 grams of DM water, .2 grams of sodium lauryl sulfate and 1.1 grams of tBHP followed by the addition of a solution containing 27 grams of DM water and .95 grams of erythorbic acid. A 10% solution of lithium hydroxide was then added to adjust the pH. The reactor was then cooled to 40°C, and the reaction product was filtered through a 150-micron nylon mesh filter.deDocket No. 4851

[0069] The characterization of solution polymer example 9 is illustrated in table9. Example 9 Latex Property Value pH 8.1Total Solids 28%Viscosity 6 cpsParticle size 258 nmTGA Wt. Loss @ 150°CTable 9: Example 9 latex properties

[0070] Each of the documents referred to above is incorporated herein by reference. The mention of any document is not an admission that such document qualifies as prior art or constitutes the general knowledge of the skilled person in any jurisdiction. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as modified by the word "about." It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements. As used herein, the expression "consisting essentially of" permits the inclusion of substances that do not materially affect the basic and novel characteristics of the composition under consideration.

Claims

1. Docket No. 4851What is claimed is:

1. A method of separating two adhered surfaces in a system in situ comprising 1) binding the surfaces with a polymer binder comprising a (meth)acrylic acid or ester polymer functionalized with a thermally degradable leaving group, and 2) raising the temperature of the system greater than a thermal degradation temperature of the leaving group, wherein the leaving group forms a gas at the thermal degradation temperature that expands and thereby mechanically separates the adhered surfaces.

2. The method of claim 1, wherein the leaving group comprises an organic group having a thermal degradation temperature of 80°C or greater.

3. The method of any preceding claim, wherein the leaving group comprises a tert-butoxycarbonyl (Boc) group.

4. The method of any preceding claim, wherein the (meth)acrylic acid or ester polymer comprises a polymer polymerized from monomers of Formula I:Formula Iwhere R is H or CH3, and R’ is H+, Na+, Li+, K+, Vi Mg2+, Vi Ca2+or a Cl to C18 hydrocarbyl or mono-alcohol group.

5. The method of claim 7, wherein the (meth)acrylic acid or ester polymer further comprises a polymer polymerized from co-monomers.

6. The method of any preceding claim, wherein greater than about 0.01 mole percent of the monomers of the polymer can be functionalized with the leaving group.

7. The method of any preceding claim, wherein the (meth)acrylic acid or ester polymer comprises a hydroxy ethyl methacrylate (“HEMA”) polymer.

8. An electrochemical device comprising: a. an anode electrode;Docket No. 4851 b. a cathode electrode; c. a separator, disposed between said anode electrode and said cathode electrode; d. an electrolyte in ionic contact with said anode electrode, said cathode electrode, and said separator; and e. a polymer binder comprising a (meth)acrylic acid or ester polymer functionalized with a leaving group.

9. The electrochemical device of claim 6, wherein the leaving group comprises an organic group that deprotects from the polymer backbone at temperatures of greater than 120°C.

10. The electrochemical device of any preceding claim, wherein the leaving group comprises a tert-but oxy carbonyl (Boc) group.

11. The electrochemical device of any preceding claim, wherein the (meth)acrylic acid or ester polymer of (e) comprises a hydroxyethyl methacrylate (“HEMA”) polymer.

12. A method of preventing thermal runaway in an electrochemical device comprising preparing the electrochemical device with a polymer binder comprising a (meth)acrylic acid or ester polymer functionalized with a leaving group, wherein the leaving group has a thermal degradation temperature of 120°C or greater, and operating the electrochemical device to a temperature of 120°C or greater wherein the leaving group forms a gas that expands and thereby mechanically separates the surfaces of the electrochemical device and breaks the circuit.

13. The method of claim 5, wherein the leaving group comprises a tertbutoxycarbonyl (Boc) group.

14. The method of claim 5, wherein the (meth)acrylic acid or ester of (e) comprises a hydroxy ethyl methacrylate (“HEMA”) polymer.

15. A coating primer composition for surfaces in an electrochemical cell comprising a slurry of a solvent, conductive carbon, and a polymer binder comprising a (meth)acrylic acid or ester polymer functionalized with a thermally degradable leaving group.Docket No. 485116. An electrode coated with the coating primer composition of claim 16.

17. An electrochemical cell separator coated with the primer composition of claim 16.

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