HNBR cathode binder for battery cells using γ-valerolactone as processing solvent

Abstract

The present invention relates to a polymer comprising or consisting essentially of monomer units derived from 1,3-butadiene, acrylonitrile, and optionally methacrylic acid, wherein the weight content of the monomer units derived from 1,3-butadiene is at most 65 wt. % based on the total weight of the polymer. The polymer is useful for producing a cathode for a battery cell. The invention further relates to a battery cell cathode comprising the polymer, and a composition comprising the polymer and gamma-valerolactone.

Description

[Technical Field]

[0001] The present invention relates to a polymer comprising or consisting essentially of monomer units derived from 1,3-butadiene, acrylonitrile, and optionally methacrylic acid, wherein the weight content of the monomer units derived from 1,3-butadiene is at most 65 wt. % based on the total weight of the polymer. The polymer is useful for producing a cathode for a battery cell. The invention further relates to a battery cell cathode comprising the polymer, and a composition comprising the polymer and gamma-valerolactone. [Background technology]

[0002] A rechargeable battery (also known as a storage battery, secondary battery, or accumulator) is a type of electric battery that can be charged, discharged, and recharged multiple times. A battery cell contains electrodes (anode and cathode), an electrolyte, and a separator. Within the electrode, a polymer binder typically holds the active material and conductive material together. The binder must be flexible and insoluble in the electrolyte. It must have good adhesion to the current collector and be chemically and electrochemically stable. Furthermore, it must be easily applied to the electrode. N-methylpyrrolidone (NMP) is frequently used as a solvent in the fabrication of cathodes. However, NMP is toxic, and non-toxic alternatives are needed to enable the fabrication of safer and more environmentally friendly battery cells.

[0003] Polyvinylidene fluoride polymer (PVDF) is frequently used as a binder in the manufacture of cathodes. However, PVDF has several drawbacks, as fluorine can cause corrosion in rechargeable batteries and is inherently unsafe. Because fluorine can form hydrogen fluoride, precautionary safety measures are required when handling PVDF. PVDF's relatively high density adds weight to rechargeable batteries.

[0004] As a non-toxic, environmentally friendly solvent, gamma-valerolactone has been proposed as an alternative to NMP. However, PVDF is poorly soluble in gamma-valerolactone, requiring additional effort and high temperatures to prepare the cathode slurry and electrode. Such solutions of hot PVDF in gamma-valerolactone tend to form gels at room temperature after the solution is cooled.

[0005] (Non-Patent Document 1) relates to γ-valerolactone as an alternative solvent for the manufacture of electrodes for lithium ion batteries.

[0006] Patent Document 1 relates to an all-solid-state secondary battery including an anode active material layer, a solid electrolyte layer, and a cathode active material layer in this order. Among many others, γ-valerolactone is an example of a solvent for the anode active material layer having a boiling point in the range of 180 to 300°C.

[0007] Patent Document 2 relates to a porous membrane that can be used as a separator and is produced from a porous membrane-forming composition that includes a hydrophobically modified insulating fiber (A), a binder resin (B), and a solvent (S). The solvent (S) can be, among many others, γ-valerolactone.

[0008] Patent Document 3 relates to a battery including a first conductive substrate portion having a first surface and a second conductive substrate portion having a second surface opposite the first surface. Solvents useful for preparing the cathode include, among many others, γ-valerolactone.

[0009] Patent Document 4 relates to a binder composition for electrodes of lithium ion secondary batteries. Among many other organic dispersion media, γ-valerolactone is one example.

[0010] Patent Document 5 relates to a method for producing a separator for a lithium secondary battery, which includes the steps of forming a porous coating layer containing inorganic particles on at least one surface of a porous substrate, charging polymer particles to form charged polymer particles, transferring the charged polymer particles to the upper surface of the porous coating layer to form a functional coating layer, and fixing the functional coating layer by heat and pressure. The patent document also relates to a separator produced by this method and a lithium secondary battery including this separator. Examples of non-aqueous electrolytes include, among others, γ-valerolactone.

[0011] Patent Document 6 relates to additives for lithium secondary batteries. Examples of electrolytes include γ-valerolactone, among many others.

[0012] Patent Document 7 discloses a polymer and its use as a binder. The polymer contains conjugated diene monomer units (e.g., 1,3-butadiene) and / or alkylene structural units and nitrile group-containing monomer units (e.g., acrylonitrile), and optionally other repeating units (e.g., (meth)acrylic acid ester monomers such as n-butyl acrylate). The polymer is used together with PVDF as a binder.

[0013] There is a need for polymers that can be used as cathode binders and that offer advantages over prior art polymers. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Publication No. 2017-045611 [Patent Document 2] Japanese Patent Application Publication No. 2018-076417 [Patent Document 3] International Publication No. 2015073745A2 Brochure [Patent Document 4] International Publication No. 0045452A1 Brochure [Patent Document 5] International Publication No. 2014046521A1 Brochure [Patent Document 6] U.S. Patent Application Publication No. 20200194837A1 [Patent Document 7] European Patent Application Publication No. 3605675A1 [Non-patent literature]

[0015] [Non-Patent Document 1] VRRavikumar et al.,ACS Appl.Energy Mater.2021,4,1,696-703 Summary of the Invention [Problem to be solved by the invention]

[0016] The object of the present invention is to provide a battery cell and its cathode that have advantages over the prior art, particularly with regard to safety and environmental issues. The polymer must overcome the drawbacks of PVDF and be compatible with safer and more environmentally friendly solvents, particularly γ-valerolactone, to overcome the drawbacks of NMP. [Means for solving the problem]

[0017] This object has been achieved by the subject matter of the claims of this patent.

[0018] The present invention relates to polymers comprising or consisting essentially of monomer units derived from 1,3-butadiene, acrylonitrile, and optionally methacrylic acid, where the weight content of the monomer units derived from 1,3-butadiene is at most 65 wt. % based on the total weight of the polymer. Surprisingly, it has been found that such polymers have high electrochemical stability and are readily soluble in the non-toxic, environmentally friendly solvent gamma-valerolactone at room temperature. These binder solutions can be further processed at room temperature to obtain cathode slurries and cathodes that exhibit very good electrochemical performance and stability. Preferably, the slurries are LFP-based.

[0019] Aspects of the present invention relate to the use of a polymer as a binder in a battery cell cathode, a battery cell cathode comprising said polymer, and a composition comprising said polymer and gamma-valerolactone.

[0020] The polymer provides at least a suitable alternative to prior art cathode binders, overcoming the need to use polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP).

[0021] The polymers and cathode binders made from the polymers are PVDF-free, thus overcoming safety concerns and corrosion issues during manufacturing and use in battery applications.

[0022] The polymer exhibits at least the same or better binder properties compared to conventional cathode binders based on PDVF.

[0023] This polymer has a lower density and is lighter than PDVF, making it suitable for portable devices or electric vehicles that use rechargeable batteries.

[0024] When used as a cathode binder, the polymer maintains capacity retention after charging, discharging, and recharging.

[0025] For the fabrication of battery cell cathodes, the polymer can be advantageously processed using gamma-valerolactone as a solvent, eliminating the need for NMP. The binder solution of the polymer in gamma-valerolactone can be prepared at room temperature, allowing for smooth processing and preparation of the electrodes. Electrochemical evaluation of the cathodes shows high capacity and stability. DETAILED DESCRIPTION OF THE INVENTION

[0026] For a full understanding of the present invention and its advantages, reference should be made to the following detailed description. It should be understood that the various aspects and embodiments of the detailed description disclosed herein describe specific ways of making and using the invention and do not limit the scope of the invention when taken into account the claims and the detailed description. It should also be understood that features of different aspects and embodiments of the invention can be combined with features of different aspects and embodiments of the invention.

[0027] The polymer according to the invention comprises or essentially consists of monomer units derived from 1,3-butadiene, acrylonitrile and optionally methacrylic acid, in which case the weight content of monomer units derived from 1,3-butadiene is at most 65% by weight relative to the total weight of the polymer.

[0028] Surprisingly, it has been found that a maximum content of 1,3-butadiene, i.e. a minimum content of polar monomers including acrylonitrile and optionally methacrylic acid, provides good solubility in γ-valerolactone and performance as a binder in electrodes.

[0029] The term "monomer unit" refers to a structural unit derived from that monomer that is incorporated into the polymer backbone resulting from polymerizing that monomer. Those skilled in the art will recognize that polymerization changes the monomer structure, and such a change is reflected in the term "derived from." Furthermore, since the polymers according to the present invention are preferably hydrogenated, such hydrogenation can further modify the monomer unit derived from that monomer. In particular, radical polymerization of 1,3-butadiene using an appropriate catalyst results in a monomer unit still having ethylenic unsaturation that is subsequently fully or partially saturated by hydrogenation.

[0030] To be fully hydrogenated, there are <1% residual double bonds, and to be partially hydrogenated, there are <5% residual double bonds.

[0031] Preferably, the polymer is hydrogenated. Preferably, the content of residual C=C double bonds is at most 5%, more preferably at most 4%, relative to the content of C=C double bonds before hydrogenation. Preferably, the hydrogenation is carried out under conditions that do not essentially affect the acrylonitrile and any methacrylic acid present.

[0032] Preferably, the polymer has a weight content of monomer units derived from 1,3-butadiene in the range of 55 to 65% by weight, relative to the total weight of the polymer.

[0033] Preferably, the polymer has a weight content of monomer units derived from acrylonitrile of at least 25% by weight, based on the total weight of the polymer. Preferably, the polymer has a weight content of monomer units derived from acrylonitrile in the range of 30 to 45% by weight, based on the total weight of the polymer.

[0034] Preferably, the polymer has a weight content of monomer units derived from 1,3-butadiene in the range of 55 to 65% by weight and a weight content of monomer units derived from acrylonitrile in the range of 35 to 45% by weight, relative to the total weight of the polymer.

[0035] In a preferred embodiment, the polymer does not contain any monomer units derived from methacrylic acid. Preferably, the polymer consists essentially of monomer units (copolymer, bipolymer) derived from 1,3-butadiene and acrylonitrile.

[0036] In another preferred embodiment, the polymer further comprises monomer units derived from methacrylic acid. Preferably, the polymer consists essentially of monomer units derived from 1,3-butadiene, acrylonitrile and methacrylic acid (terpolymer).

[0037] Preferably, the polymer has a weight content of monomer units derived from methacrylic acid of at least 2.5% by weight, relative to the total weight of the polymer. Preferably, the polymer has a weight content of monomer units derived from methacrylic acid in the range of 2.5 to 7.5% by weight, relative to the total weight of the polymer.

[0038] Preferably, the polymer has a weight content of monomer units derived from 1,3-butadiene in the range of 55 to 65% by weight, a weight content of monomer units derived from acrylonitrile in the range of 30 to 45% by weight, and a weight content of monomer units derived from methacrylic acid in the range of 2.5 to 7.5% by weight, relative to the total weight of the polymer.

[0039] Preferably, the polymer has a Mooney viscosity (ML1+4@100°C) in the range of 45 to 100MU, more preferably 55 to 90MU, most preferably 60 to 70MU.

[0040] In a preferred embodiment, the polymer consists essentially of monomer units derived from the following monomers in the following contents relative to the total weight of the polymer: 62±2 wt. % 1,3-butadiene, 33±2 wt. % acrylonitrile, and 5±2 wt. % methacrylic acid (see Example C below).

[0041] In a preferred embodiment, the polymer consists essentially of monomer units derived from the following monomers in the following contents relative to the total weight of the polymer: 61±2 wt. % 1,3-butadiene, and 39±2 wt. % acrylonitrile (see Example E below).

[0042] In a preferred embodiment, the polymer consists essentially of monomer units derived from the following monomers in the following contents relative to the total weight of the polymer: 57±2% by weight of 1,3-butadiene, and 43±2% by weight of acrylonitrile (see Example F below).

[0043] The polymers according to the invention are related to different aspects of the invention.

[0044] A first aspect of the invention relates to the use of a polymer as a binder in a cathode of a battery cell.

[0045] A second aspect of the invention relates to a battery cell cathode comprising a polymer.

[0046] A third aspect of the present invention relates to a composition for manufacturing a cathode of a battery cell, said composition comprising: (i) a polymer; and (ii) gamma valerolactone.

[0047] The method for producing the polymer is not limited and can be any method known in the art. The method for producing the polymer can be any of solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. The method for producing the polymer can be radical polymerization or living radical polymerization.

[0048] The method for producing the hydrogenated polymer is similarly not limited. The method for producing the hydrogenated polymer can be either an oil phase hydrogenation method or an aqueous phase hydrogenation method. The homogeneous or heterogeneous hydrogenation catalyst used to produce the hydrogenated polymer can be any hydrogenation catalyst known in the art, such as a palladium-based catalyst, a ruthenium-based catalyst, a rhodium-based catalyst, or any combination thereof.

[0049] When the polymer is used as a cathode binder in a rechargeable battery, the binder holds the active material and conductive material within the cathode of the rechargeable battery. The polymer is then dissolved and / or dispersed in an organic solvent to form a binder solution, preferably gamma-valerolactone.

[0050] The polymer may be ground prior to dissolution and / or dispersion using a ball mill, sand mill, bead mill, pigment disperser, grinder, ultrasonic disperser, homogenizer, or planar mixer. Such equipment may also be used to facilitate dissolving and / or dispersing the polymer in an organic solvent to form a binder solution.

[0051] The binder solution is then preferably mixed with the active material and the conductive material to form the cathode slurry composition.

[0052] The active material may be lithium nickel manganese cobalt oxide (abbreviated as Li-NMC, LNMC, NMC, or NCM), which is a mixed metal oxide of lithium, nickel, manganese, and cobalt. The active material may be lithium iron phosphate (LFP). The active material may be lithium manganese oxide (LMO). Lithium iron phosphate (LFP) is preferred.

[0053] The conductive material can be a carbon material such as carbon black (e.g., acetylene black, furnace black), graphite (graphene), carbon fibers (carbon nanofibers, single-walled or multi-walled carbon nanotubes (CNTs), and vapor-grown carbon fibers), and carbon flakes.

[0054] The cathode slurry composition is then preferably applied to a current collector and then dried.

[0055] The cathode slurry composition can be applied to the current collector by a doctor blade, dip coating, reverse roll coating, direct roll coating, gravure coating, extrusion coating, bar coater, or brush coating. The thickness of the cathode slurry composition on the current collector after application and before drying can be appropriately set.

[0056] The current collector is a material that is electrically conductive and electrochemically durable. The current collector can be made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. The current collector can be in the form of a foil. The current collector is preferably aluminum foil because of its high electrical conductivity, electrochemical and chemical stability, and low cost.

[0057] Drying of the cathode slurry composition applied to at least one surface of the current collector is preferably accomplished by warm, hot, or low humidity air at ambient pressure; vacuum drying, drying by infrared radiation, or electron beam drying may also be used.

[0058] After drying, the cathode slurry composition applied to the current collector can be pressed with a mold press or roll press to obtain a more uniform layer of dried material.

[0059] The resulting positive electrodes, which include the polymer as a positive electrode binder, are then assembled to form a rechargeable battery.

[0060] The rechargeable battery is preferably assembled by stacking the positive electrode and the negative electrode via a separator, which may require rolling or folding the resulting stack depending on the shape of the rechargeable battery, placing the stack in a battery container, filling the battery container with an electrolyte, and then sealing the battery container.

[0061] To prevent pressure buildup and overcharging or over-discharging from occurring in the rechargeable battery, an overcurrent protection device such as a PTC device or a fuse, expanded metal (such as nickel sponge), or a lead plate may be provided as needed.

[0062] The shape of the rechargeable battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a prismatic type, a pouch type, or a flat plate type.

[0063] The negative electrode can be any known negative electrode, for example, a carbon material such as amorphous carbon, natural graphite, artificial graphite, natural graphite, mesocarbon microbeads, pitch-based carbon fiber, and silicon graphite, a conductive polymer such as polyacene or polyaniline, or a metal such as silicon, tin, zinc, manganese, titanium oxide, iron, lithium (for half-cells), and nickel, and alloys of these metals. The negative electrode is preferably graphite or silicon graphite.

[0064] The separator can be a microporous membrane or nonwoven fabric comprising a polyamide resin. The microporous membrane can be made from a polyolefin resin (polyethylene, polypropylene, polybutene, or polyvinyl chloride). Polyolefin resins are preferred because such separator membranes allow for a reduced overall separator thickness, thereby increasing the ratio of active material to conductive material in the rechargeable battery and ultimately reducing the size of the rechargeable battery.

[0065] The electrolyte is a solution in which a supporting electrolyte is dissolved in an organic solvent. The supporting electrolyte is a lithium salt such as LiPF, LiAsF, LiBF, LiSbF, LiAlCl, LiClO, CFSOLi, CFSOLi, CFCoLi, (CFCO)NLi, (CFSO)NLi, and (CFSO)NLi. LiPF is preferred because it is easily soluble in the solvent and exhibits a high degree of dissociation. The organic solvent can be a carbonate such as dimethyl carbonate (DMC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC), an ester such as γ-butyrolactone and methyl formate, an ether such as 1,2-dimethoxyethane and tetrahydrofuran, and a sulfur-containing compound such as sulfolane and dimethyl sulfoxide. [Example]

[0066] The invention is illustrated by the following non-limiting examples.

[0067] The following materials were used as provided: Monomer units acrylonitrile, methacrylic acid from Sigma-Aldrich, 1,3-butadiene from INEOS. Solution Fe(II)SO4: The premix solution contains 0.986 g Fe(II)SO4*7H2O and 2.0 g Rongalit® C in 400 g water. EDTA: complexing agent from Sigma-Aldrich. Fatty acids: CAS67701-08-8, emulsifier for polymerization. SDS: Sodium dodecyl sulfate CAS151-21-3, emulsifier for polymerization. t-DDM: Molecular weight regulator from Arlanxeo Deutschland GmbH. Akzo-Degussa's Trigonox® NT50, p-menthane hydroperoxide, is an initiator for emulsion polymerization. Diethylhydroxylamine: Polymerization terminator, CAS 3710-84-7. VWR dry monochlorobenzene (MCB). Wilkinson's catalyst from Materia Inc. and triphenylphosphine from VWR, and γ-valerolactone (GVL) from Sigma-Aldrich as hydrogenation catalysts. Solef® 5130, a polyvinylidene fluoride resin with a molecular weight of 1300 kDa; Kynar® HSV900, melt viscosity (230°C, 100s -1 ) polyvinylidene fluoride resin with a viscosity of 48 to 52.5 kilopoise, Lithium iron phosphate: active material, A8-4E from Hubei Wanrun New Energy Technology Co.,LTD. Conductive Carbon Black: Conductive material, Super C65, from Imerys Graphite & Carbon. Aluminum foil: current collector, thickness 20 μm, from China Aluminum Shanxi New Material Co. Lithium disc: anode, φ16mm, from China Energy Lithium Co., Ltd. Porous polyolefin film: as separator, 38 μm thick (Celgard® 2340), punched into φ18 mm discs, from Celgard. Electrolyte: LiPF6 (Aldrich) Electrolyte: 1M in EC / EMC mixture, 2 wt% VC, EC / EMC = 30 / 70 (v / v) Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC): organic solvents used in the electrolyte. Battery container: Coin cell: Case, 2032 type from ShanXi LiZhiYuan Battery Material Co. Overcurrent protection device: Nickel sponge: 1mm thick per layer, 4 layers per coin cell, from Changsha LiYuan New Material Co. 3M Tape: Vinyl electrical tape (17.5mm wide) from 3M China Company.

[0068] Test Method Acrylonitrile Content: The nitrogen content for the determination of the acrylonitrile content was determined according to Kjeldahl (DIN 53 625).

[0069] Solubility: The samples were dissolved according to the following procedure and their solubility was assessed using the following criteria:

[0070] The samples were placed in a given concentration in a given solvent and shaken at 150 rpm at room temperature using an IKA shaker KS4000i control. After a given time, the samples were visually evaluated. -- The sample does not dissolve. - The sample begins to dissolve, the particles expand, and most of the sample remains undissolved 0 The sample begins to dissolve, and the particles remain undissolved + Sample is mostly dissolved, with a small amount of residue or partly cloudy ++ The sample is completely dissolved and no residue is visible.

[0071] Mooney Viscosity: The Mooney viscosity (ML1+4@100°C) values ​​are determined in each case at 100°C using a shear disc viscometer according to DIN 53523 / 3 or ASTM D1646.

[0072] NMR: The microstructure and termonomer content of the individual polymers were determined using 1H NMR (instrument: Bruker DPX400 with XWIN-NMR3.1 software, measurement frequency 400 MHz, solvent CDCl3).

[0073] Discharge specific capacity evaluation method: The fabricated secondary battery was charged at 23°C at a rate of 0.1 C until the battery voltage reached 4.0 V. After 20 minutes, it was discharged at a constant current of 0.1 C at 23°C until the battery voltage reached 2.8 V. The coin-type secondary battery was then charged and discharged in constant current mode (CC mode at a rate of 0.5 C). Between each cycle, the cell rested for 5 minutes. The discharge specific capacity of the secondary battery was calculated as the average value from cycles 2 to 5.

[0074] Capacity retention evaluation method: The coin cell secondary battery was charged and discharged for 50 cycles in constant current mode (CC mode at a rate of 0.2 C). The capacity retention was determined in percentage as the ratio of the discharge specific capacity after 50 cycles to the discharge specific capacity after 2 cycles.

[0075] Preparation of inventive and comparative polymers Hydrogenated butadiene-acrylonitrile copolymers and hydrogenated butadiene-acrylonitrile-methacrylic acid terpolymers were produced according to the base formulations specified in Table 1, with all ingredients listed in parts by weight based on 100 parts by weight of the monomer mixture. Table 1 also specifies the polymerization conditions for each.

[0076] [Table 1]

[0077] The polymer was produced batchwise in a 5 L autoclave equipped with a stirrer system. Each autoclave batch contained 1.25 kg of the monomer mixture and a total of 2.1 kg of water, with EDTA used in an equimolar amount based on Fe(II). This amount of water, 1.9 kg, was initially charged to the autoclave along with an emulsifier and purged with a nitrogen stream. The destabilized monomers and tert-dodecyl mercaptan (t-DDM) as a molecular weight regulator were then added, and the reactor was closed. After the reactor contents reached temperature, the Fe(II)SO4 premix solution and para-menthane hydroperoxide (Trigonox® NT50) were added to initiate the polymerization.

[0078] The progress of the polymerization was monitored by gravimetric determination of conversion. Once the conversions reported in Table 1 were reached, the polymerization was stopped by adding an aqueous solution of diethylhydroxylamine. Unconverted monomer and other volatile components were removed by steam distillation.

[0079] The antioxidant was mixed with the polymer dispersion to adjust the solids content to 17.5 wt % and the resulting dispersion containing additional anti-aging ingredients was then coagulated by adding calcium salts or by adding acids to lower the pH, washed, dewatered and dried according to procedures known in the art.

[0080] The following hydrogenations were carried out in a 10 L high-pressure reactor under the following conditions: For this purpose, the polymer was dissolved in monochlorobenzene (MCB) at the given solids content: Solids concentration: 12-13 wt% polymer in MCB Reactor temperature: 137-140°C Reaction time: up to 4 hours Catalyst: Wilkinson catalyst, triphenylphosphine as cocatalyst Hydrogen pressure: 8.4 MPa Stirring speed: 600 rpm

[0081] The polymer solution was degassed three times with hydrogen (23°C, 2 MPa) while vigorously stirring. The reactor temperature was increased to 100°C, and the hydrogen pressure was increased to 6 MPa. A monochlorobenzene solution consisting of Wilkinson's catalyst and cocatalyst was added, the pressure was increased to 8.4 MPa, and the reactor temperature was adjusted to 137-140°C. The temperature and pressure were kept constant throughout the reaction. The progress of the reaction was monitored by measuring the residual double bond content by IR spectroscopy.

[0082] When the residual double bond content reached less than 5%, the hydrogen pressure was released to terminate the reaction.

[0083] The resulting hydrogenated polymer was separated from the solution by steam coagulation. For this, the monochlorobenzene solution was diluted to a polymer content of 7% by weight and continuously metered into a stirred glass reactor filled with water and preheated to 100°C. Simultaneously, steam at 0.5 bar was introduced into the coagulating water. The polymer, which precipitated as small pieces, was dehydrated and then dried under vacuum at 55°C.

[0084] The composition, monomer unit content, % residual double bonds, and Mooney viscosity of each hydrogenated polymer are shown in Table 2.

[0085] Spectra of the polymer before, during, and after hydrogenation were recorded on a Perkin Elmer Spectrum 100 FT-IR spectrometer. Polymer solutions in monochlorobenzene were cast onto KBr disks and dried to form films for testing. Hydrogenation conversion was determined by FT-IR analysis according to ASTM D5670-95.

[0086] Prior to hydrogenation of polymer G, a metathesis reaction was carried out to reduce the molecular weight of the nitrile rubber. Metathesis is known, for example, from WO 02 / 100941 A and WO 02 / 100905 A, and can be used to reduce molecular weight.

[0087] [Table 2]

[0088] Polymer C is a terpolymer according to the invention, while polymers E and F are copolymers (bipolymers) according to the invention. Polymers A and B are comparative because they are PVDC polymers. Furthermore, copolymers D, G, and I as well as terpolymer H are also comparative because they contain more than 65% by weight of monomer units derived from 1,3-butadiene.

[0089] The results in Table 2 show that polymers C to G maintain at least a low density compared to PVDF (polymers A and B).

[0090] The polymer samples were dissolved in gamma-valerolactone at room temperature, and their solubility was evaluated after 90 minutes. While polyvinylidene fluoride resins A and B were completely insoluble in gamma-valerolactone at room temperature, hydrogenated polymers C, E, and F readily dissolved in gamma-valerolactone at room temperature, improving the productivity of battery cells and saving energy during the preparation process. Furthermore, the solubility performance was independent of the molecular weight of the hydrogenated nitrile rubber.

[0091] [Table 3]

[0092] The results in Table 3 show that hydrogenated polymers with minimal polar monomer (acrylonitrile and optionally methacrylic acid) content are well soluble in γ-valerolactone at room temperature, whereas polyvinylidene fluoride resin is completely insoluble. Thus, the preparation of binder solutions at room temperature using the non-toxic solvent γ-valerolactone can be managed using hydrogenated polymers C, E, and F instead of the toxic battery solvent NMP.

[0093] Common methods for manufacturing coin cells Step (1) - Dissolution: A certain amount of polymer is dissolved in a solvent (γ-valerolactone) on a shaker overnight at room temperature to form a binder solution (8 wt%).

[0094] Step (2)—Preparation of cathode slurry composition: The binder solution from step 1 was mixed with the conductive material (conductive carbon black Super C65) in a Thinky mixer (milling conditions: 2000 rpm, 12 minutes, room temperature). Then, the active material (LFP, C-coating, A8-4E) and half of the solvent (γ-valerolactone) were added (milling conditions: 2000 rpm, 18 minutes, room temperature). Finally, the remaining solvent (γ-valerolactone) was added (milling conditions: 2000 rpm, 6 minutes, room temperature) to obtain the cathode slurry composition.

[0095] [Table 4]

[0096] Step (3)—Preparation of Cathode Disk: The cathode slurry composition was applied to a current collector (aluminum foil) using a bar coater at a coating speed of 4.1 mm / s to form a cathode sheet. The coater slit gap of the coater was adjusted to 250 μm to obtain the desired coating thickness.

[0097] Step (4)—Drying: The cathode sheet was dried in an oven at 120°C for 240 minutes to remove the solvent and moisture. After drying, the cathode sheet was first compressed in a hot press, and then calendered with a two-roll machine to adjust the areal density until the thickness after drying was reduced by 20%. Cathode disks (φ16 mm) were punched out from the calendered cathode sheet using a machine from Shenzhen Poxon Machinery Technology Co., Ltd., Model: PX-CP-S2. The cutting edge of the punch was sharp and free of burrs.

[0098] Step (5)—Assembling the Lithium-ion Secondary Battery: The assembly and pressing of the lithium-ion secondary battery were carried out in a glove box. The assembly included the top of the coin-type cell case (2032 type, negative electrode side), a support (two stainless steel spacers and a spring), a lithium disk (as the anode), a porous separator (Celgard 2400), a cathode disk, and the bottom of the case (positive electrode side). All components were assembled layer by layer. During the assembly process, electrolyte (140 μL of 1 M / L LiPF6 in EC / EMC = 30 / 70 (v / v) with 2 wt% VC) was dripped to completely fill the free volume of the coin-type cell. Finally, the coin-type cell case was pressed in a press in the glove box. An open-circuit voltage test was performed to confirm whether a short circuit occurred.

[0099] [Table 5]

[0100] The results in Table 5 show that the use of fluorine-free hydrogenated polymers C, E, and F allows for high specific capacity while maintaining good capacity retention using non-toxic solvents in battery processing. Therefore, by replacing the toxic battery solvent NMP with the nitrile rubber of the present invention, battery cells with high capacity and capacity retention can be obtained.

[0101] Having thus described the invention and its advantages, it is to be understood that the various aspects and embodiments of the invention disclosed herein are merely illustrative of specific ways to make and use the invention.

[0102] The various aspects and embodiments of the present invention do not limit the scope of the invention when taken into consideration with the appended claims and the above detailed description. What is desired to be protected by letter is set forth in the following claims.

Claims

1. A composition for manufacturing a cathode for a battery cell, (i) -1,3-butadiene, - Acrylonitrile, and - Optionally, methacrylic acid A polymer containing or essentially consisting of monomer units derived from, wherein the weight content of monomer units derived from 1,3-butadiene is at most 65% by weight of the total weight of the polymer, (ii) A composition comprising γ-valerolactone.

2. The composition according to claim 1, wherein the polymer is hydrogenated.

3. The composition according to claim 2, wherein the content of residual C=C double bonds is at most 5% of the content of C=C double bonds before hydrogenation.

4. The composition according to claim 1, wherein the polymer has a weight content of monomer units derived from 1,3-butadiene in the range of 55 to 65% by weight relative to the total weight of the polymer.

5. The composition according to claim 1, wherein the polymer has a weight content of at least 25% by weight of monomer units derived from acrylonitrile relative to the total weight of the polymer.

6. The composition according to claim 1, wherein the polymer has a weight content of monomer units derived from acrylonitrile in the range of 30 to 45% by weight relative to the total weight of the polymer.

7. With respect to the total weight of the aforementioned polymer, the polymer is, The weight content of monomer units derived from -1,3-butadiene is in the range of 55 to 65% by weight. - The composition according to claim 1, wherein the weight content of monomer units derived from acrylonitrile is in the range of 35 to 45% by weight.

8. The composition according to claim 1, wherein the polymer does not contain monomer units derived from methacrylic acid.

9. The composition according to claim 1, wherein the polymer has a weight content of at least 2.5% by weight of monomer units derived from methacrylic acid relative to the total weight of the polymer.

10. The composition according to claim 9, wherein the polymer has a weight content of monomer units derived from methacrylic acid in the range of 2.5 to 7.5% by weight relative to the total weight of the polymer.

11. With respect to the total weight of the aforementioned polymer, the polymer is, The weight content of monomer units derived from -1,3-butadiene is in the range of 55 to 65% by weight. - The weight content of monomer units derived from acrylonitrile is in the range of 30 to 45% by weight. - The composition according to claim 9 or 10, wherein the weight content of monomer units derived from methacrylic acid is in the range of 2.5 to 7.5% by weight.

12. The polymer essentially consists of monomer units derived from the following monomers, in the following proportions relative to the total weight of the polymer: (i) 62 ± 2% by weight of 1,3-butadiene, 33 ± 2% by weight of acrylonitrile, and 5 ± 2% by weight of methacrylic acid, (ii) 61 ± 2% by weight of 1,3-butadiene and 39 ± 2% by weight of acrylonitrile, (iii) 1,3-butadiene 57±2% by weight, and acrylonitrile 43±2% by weight, The composition according to claim 1.

13. Use of the composition according to claim 1 for manufacturing a cathode of a battery cell.

14. A cathode of a battery cell obtained from the composition described in claim 1.