Method for manufacturing battery electrodes with improved properties

Abstract

A method for manufacturing a battery electrode using a low solution viscosity polymeric binder composition is disclosed, where the binder composition comprises a fluoropolymer.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an electrode slurry for a lithium secondary battery, a method for producing an electrode containing the same, and an electrode produced using the same. [Background technology]

[0002] The electrodes are used in energy storage devices, including but not limited to batteries, capacitors, ultracapacitors, non-aqueous secondary batteries, and the like.

[0003] Currently, there are two primary approaches to manufacturing electrodes: the "wet" approach and the "dry" approach. In the wet approach, a polymer binder in the form of a solvent solution or dispersion is blended with one or more active powdered electrode-forming materials to form a slurry dispersion or paste. This dispersion or paste is then applied to one or both sides of a conductive substrate and dried to form a cohesive composite electrode layer. The electrode layer can then be calendered. This approach is shown in U.S. Pat. Nos. 5,776,637 and 6,200,703, where a fluoropolymer binder is dissolved in NMP. In the dry approach, a polymer binder in powder form is blended with one or more active powdered electrode-forming materials, and then a solvent is added to form a slurry dispersion or paste. Subsequent application, drying, and calendering are the same as for the wet approach. An example of one embodiment of the dry approach is shown at https: / / doi.org / 10.1016 / j.powtec.2016.04.011.

[0004] WO 2018 / 174619 teaches that mixing a dispersant with a small particle size active material reduces the viscosity of the slurry, improving adhesion and therefore the solids content of the final electrode.

[0005] EP 2908370 uses very high shear forces to first fragment the polymer into low MW segments and then deagglomerate the conductive material to reduce the slurry viscosity.

[0006] U.S. Patent No. 10,573,895 teaches adding the binder solution in two stages, or using two different binders altogether: one in the first step uses the active material and carbon black for good dispersion; the other acts as a rheology modifier to prevent drag lines during pattern coating. The first electrode slurry in U.S. Patent No. 10,573,895 has the active material and uses 6-8 wt. % of the binder solution.

[0007] US Pat. No. 8,697,822 describes the polymerization of VDF in the presence of an acidic surfactant. Summary of the Invention [Problem to be solved by the invention]

[0008] Optimal slurry behavior is essential for casting good electrodes for batteries. Proper mixing and dispersion of the conductive material leads to better slurry fluidity. At the same concentration, a PVDF binder solution with a low solution viscosity has less ability to generate shear than one with a high solution viscosity. To overcome this issue, the binder solution concentration of the low solution viscosity PVDF was increased to a point higher than that possible with the high solution viscosity PVDF. This change requires less NMP to achieve comparable slurry and electrode properties. [Means for solving the problem]

[0009] It has surprisingly been found that by using a polymer binder composition with a low solution viscosity (less than 6000 cP as measured at 9% solids in NMP) at a concentration of 10% or greater, preferably 11% or greater, higher solids electrode slurries (greater than 70% solids, preferably greater than 72%, more preferably greater than 75%, and even more preferably greater than 77% solids) can be achieved. In some embodiments, the electrode slurry has a solids content of greater than 80% by weight. Advantageously, the electrode slurries of the present invention can be used to achieve a viscosity of the electrode slurry (10 s -1(measured as σ) was reduced by at least 10% and could be as much as 75% or more compared to the same slurry made from a 4% solids binder solution. When the electrode slurry was cast and dried to produce electrodes, the electrodes showed improved adhesion to conductive substrates compared to the same slurry made using a 4% solids binder solution.

[0010] By increasing the binder solution concentration, the resulting electrode has good electrode properties (retaining at least 75%, preferably at least 80% of the initial discharge capacity after 500 cycles).

[0011] Formulation with high PVDF binder concentrations (9 wt. % or more, preferably 10 wt. % or more, preferably 11 wt. % or more, up to 25%) results in improved slurry behavior, electrode adhesion, and battery performance.

[0012] The present invention relates to an improved method for manufacturing a battery electrode, comprising: (a) preparing a conductive material slurry comprising a binder and a conductive material, wherein the binder is present in a concentration of at least 9% by weight of the binder, preferably at least 10% by weight, or at least 11% by weight; (b) adding an active material to the conductive material slurry to produce an active material slurry; and (c) optionally diluting the active material slurry to produce an electrode slurry. If no additional dilution is required, the active material slurry becomes an electrode slurry. The electrode slurry is applied to an electrode substrate to form an electrode. The polymer binder is a material having a low solution viscosity, comprising a polyvinylidene fluoride fluoropolymer.

[0013] There are various methods for preparing the conductive material slurry.

[0014] One method for preparing the conductive material slurry is by preparing a high solids binder solution (at least 9% by weight, preferably at least 10% by weight, at least 11% by weight binder). The binder solution preferably consists essentially of the binder dissolved in a solvent. After the binder is dissolved in the solvent, the dried conductive material is combined with the binder solution to form the conductive material slurry.

[0015] Another method of preparing the conductive material slurry is to combine a dry form of the binder with a dry form of the conductive material to produce a dry blend, and then add a solvent to the dry blend to produce a high solids conductive material slurry. The solids content of the conductive material slurry is preferably at least 15% by weight, preferably at least 17% by weight, at least 20% by weight, or more, and may be as high as 34% by weight.

[0016] Preferably, the polymer binder composition comprises a polyvinylidene fluoride (PVDF) polymer composition. By using a low solution viscosity polymer binder composition, the applicant increased the solids content of the polymer binder composition, which in turn increased the solids content in the electrode slurry, thereby increasing the peel strength of the cathode. Electrodes fabricated using the method of the present invention have improved adhesion.

[0017] Applicants have discovered a method for improving adhesion in battery electrodes. The method of the present invention can provide better adhesion.

[0018] Preferably, the solids content of the electrode slurry is at least 75% by weight.

[0019] Aspects of the present invention

[0020] Aspect 1. A method for producing a battery electrode slurry, comprising: (a) preparing a conductive material slurry containing a binder, a conductive material, and a solvent; (b) adding an active material to the conductive material slurry to form an active material slurry; and (c) optionally diluting the active material slurry with a solvent to a final solids content; forming an electrode slurry; PVDF binder at 9% solids in NMP at 25°C for 3.36 seconds -1 and the PVDF binder concentration in the conductive material slurry is at least 9 wt. %, preferably at least 10 wt. % solids, more preferably at least 11 wt. % solids PVDF, and up to 23 wt. % solids, based on the total weight of the binder and the solvent.

[0021] Aspect 2. The step (a) of preparing a conductive material slurry comprises: (p) preparing a PVDF binder; (q) dissolving the PVDF binder in a solvent to a concentration of at least 9 wt. %, preferably at least 10 wt. % solids, more preferably at least 11 wt. % solids PVDF, and up to 23 wt. % solids, to produce a binder solution; (r) combining the binder solution with a conductive material to form a conductive material slurry; or (s) Prepare the PVDF binder dry; (t) preparing a conductive material in a dry state; (u) dry combining the PVDF binder and the conductive material to form a dry blend; (v) adding a solvent to the dry blend to dissolve the PVDF binder and form a slurry of conductive material; This includes: 2. The method of embodiment 1, wherein the ratio (by weight) of conductive material to PVDF binder is 5:1 to 1:5.

[0022] Embodiment 3. A method for manufacturing an electrode, comprising the method of embodiment 1 or 2, further comprising the steps of: (e) applying the electrode slurry to at least one surface of a conductive substrate to form an electrode; (f) evaporating the organic solvent in the electrode slurry composition to form a composite electrode layer on the conductive substrate.

[0023] Aspect 4. The method of any one of Aspects 1-3, wherein the PVDF has a solution viscosity of less than 4000 cP.

[0024] Embodiment 5. The method of any one of embodiments 1-4, wherein the PVDF is acid-functionalized.

[0025] Embodiment 6. The method of any one of embodiments 1-5, wherein the PVDF binder comprises a polyvinylidene fluoride polymer, the polyvinylidene fluoride polymer comprising at least 50% by weight vinylidene fluoride monomer, preferably at least 75% by weight vinylidene fluoride monomer.

[0026] Embodiment 7. The method of any one of embodiments 1-6, wherein the solids content of the binder is at least 10% solids, more preferably at least 11% solids PVDF, based on the amount of the binder in the solvent.

[0027] Aspect 8. The method of any one of Aspects 1 to 7, wherein the conductive material is selected from the group consisting of graphite fine powder and fiber, carbon black, thermal black, channel black, carbon fiber, carbon nanotubes, and acetylene black, and fine powder and fiber of metals such as nickel and aluminum.

[0028] Embodiment 9. The method of any one of embodiments 1 to 7, wherein the conductive material comprises carbon black.

[0029] Aspect 10. The method of any one of Aspects 1 to 9, wherein the ratio (by weight) of conductive material to binder solids is from 5:1 to 1:5, preferably from 1:3 to 3:1.

[0030] Embodiment 11. The method of any one of embodiments 1 to 10, wherein the electrode slurry has a solids content of at least 75% by weight.

[0031] Embodiment 12. The method of any one of embodiments 1 to 11, wherein the electrode slurry has a solids content of at least 80% by weight.

[0032] Aspect 13. The method of any one of Aspects 1-12, wherein the active material is selected from the group consisting of oxides, sulfides, phosphates, or hydroxides of lithium and transition metals; carbonaceous materials; and combinations thereof.

[0033] Aspect 14. The conductive material comprises carbon black, and the binder solids content is at least 10% solids, more preferably at least 11% solids, based on the amount of PVDF in the solvent; and the PVDF binder is cured at 9% solids in NMP at 25°C for 3.36 seconds. -1 4. The method of any one of aspects 1-3, wherein the PVDF has a solution viscosity of less than 4000 cP at 2000 kJ / min, and the PVDF is acid-functionalized.

[0034] Embodiment 15. An electrode formed by the method according to any one of embodiments 3 to 14.

[0035] Embodiment 16. A battery comprising an electrode produced by the method of any one of embodiments 3 to 14. DETAILED DESCRIPTION OF THE INVENTION

[0036] As used herein, copolymer refers to any polymer having two or more different monomer units, including terpolymers and those having more than three different monomer units.

[0037] Percentages used herein are percentages by weight unless otherwise specified.

[0038] All references cited in this application are incorporated herein by reference.

[0039] The solution viscosity was measured using a Brookfield DVII viscometer with an SC4-25 spindle at 3.36 seconds. -1Measured at 25°C.

[0040] Slurry viscosity was measured using a Brookfield DVIII viscometer, CP-52 spindle, 10 seconds -1 Measured at 25°C.

[0041] The weight percent of binder can be calculated as (weight of binder) / (weight of solvent and binder). The same formula can be used regardless of what additional solids are present in the solution or slurry.

[0042] Although the method of practicing the present invention will now be generally described with respect to a particular preferred embodiment thereof, namely, polyvinylidene fluoride-based polymers prepared by aqueous emulsion polymerization, the present invention will be generally described with respect to PVDF polymers.

[0043] The present invention provides a method for producing an electrode slurry composition and a method for producing an electrode comprising the electrode slurry composition.

[0044] Surprisingly, at 9% solids in NMP, the reaction time was 3.36 seconds at 25°C. -1 It has been found that the use of a polymer binder composition having a solution viscosity of less than 6000 cP, preferably less than 5000 cP, and more preferably less than 4000 cP, as measured by .DELTA.M., provides a higher solids content in the conductive material slurry and a higher solids content in the electrode slurry. A lower viscosity of the electrode slurry with an equivalent solids content can be achieved by using a higher binder solids content in preparing the conductive material slurry.

[0045] The present invention provides a method for producing an electrode slurry for a secondary battery, which includes preparing a conductive material slurry and preparing an active material slurry containing the conductive material slurry, wherein the binder concentration in the conductive material slurry is at least 9 wt %, preferably at least 10 wt %, based on the binder and solvent.

[0046] The present invention relates to an improved method for manufacturing a battery electrode, comprising: (a) providing a conductive material slurry comprising a binder and a conductive material, wherein the binder is at a concentration of at least 9% by weight, preferably at least 10% by weight, or at least 11% by weight of the binder; (b) adding an active material to the conductive material slurry to produce an active material slurry; and (c) optionally diluting the active material slurry to produce an electrode slurry. The electrode slurry is applied to an electrode substrate to form an electrode. The polymer binder is a material with a low solution viscosity comprising a polyvinylidene fluoride fluoropolymer.

[0047] The electrode active material and the conductive material are mainly used in the form of powder or paste (added to the slurry).

[0048] In one embodiment, the conductive material slurry is prepared by combining and mixing a high-solids binder solution with a conductive material. The solvent and binder are combined to form a high-binder solution such that the binder dissolves in the solvent. The weight percent of the binder is at least 9 weight percent, preferably at least 10 weight percent. After the binder dissolves, the conductive material is added and mixed to form the conductive material slurry.

[0049] Another method of preparing the conductive material slurry is to combine a dry form of the binder with a dry form of the conductive material to produce a dry blend, and then add a solvent to the dry blend to produce the conductive material slurry, the percentage of binder based on the final amount of solvent being at least 9% by weight, preferably at least 10% by weight or more.

[0050] Another method is to partially dissolve the binder, add the conductive material, and then completely dissolve the binder. Another method is to alternately combine the binder and conductive material with a solvent. Other iterations of preparing the conductive material slurry are possible. Regardless of how the conductive slurry is prepared, it must have a binder percentage of at least 9% by weight, preferably at least 10% by weight or more, based on the final amount of solvent.

[0051] The binder is PVDF with a low solution viscosity.

[0052] In a preferred embodiment, the PVDF is acid-functionalized.

[0053] By using PVDF with low solution viscosity to disperse the conductive material, less solvent (such as NMP) is required. The final electrode is preferably free of dispersants or additives, which maximizes the energy density of the resulting battery. There is no need to increase the energy input during compounding to maximize shear of the polymer or conductive material.

[0054] Low solution viscosity PVDF has a lower and upper limit of solution viscosity. At a solution concentration of 9%, 1000 cP < solution viscosity < 6000 cP (25°C, 3.36 seconds) -1 (measured at 1000 cP). Below 1000 cP, the PVDF polymer does not have sufficient adhesive properties using the method of the present invention. Above 6000 cP, the viscosity of the solution cannot be increased even by increasing the concentration to a significant level. This formulation modification can be used in any application where dispersion of a high surface area material with reduced solvent requirements is desired.

[0055] The binder solution can have a weight ratio of solvent to solids of about 95:5 to about 80:20, preferably 90:10 to 80:20.

[0056] The ratio of binder to conductive material is 5:1 to 1:5, preferably 3:1 to 1:3.

[0057] Preferably, the conductive material is carbon black.

[0058] According to one embodiment of the present invention, the solid content of the electrode slurry is greater than 71%, preferably in the range of 71-87%, preferably 72-85%.

[0059] Thus, higher solids contents can be achieved and less solvent is used in the present invention.

[0060] Here, the solid content refers to the weight ratio of the solid components in the slurry to the total weight of the slurry, which is calculated based on the actual amount of each component used as (weight of solid components) / (weight of solid components + weight of liquid components), and is measured by drying the slurry in an oven to remove all the solvent and measuring the remaining weight.

[0061] The binder solution comprises a PVDF resin that is completely soluble in a solvent (preferably NMP) at ambient temperature at a concentration of greater than 11%, preferably greater than 12%. PVDF can be dissolved at weight percents of up to 20%, preferably up to 17%.

[0062] The viscosity of the electrode slurry of the present invention was measured using a Brookfield DVIII viscometer equipped with a CP-52 spindle at 25°C and a shear rate of 10 s -1 When measured by , the viscosity is in the range of 1000 to 5000 cP, which provides optimal physical properties for the resulting electrode.

[0063] The fluoropolymer polymer binder composition is preferably an acid-functional fluoropolymer composition. PVDF is a preferred fluoropolymer.

[0064] In one embodiment of the present invention, the binder solution is greater than 10% by weight of polymer binder in a solvent, preferably greater than 11% by weight. A conductive material is added to the binder solution in a ratio of conductive material to polymer binder of 5:1 to 1:5, preferably 1:3 to 3:1, to produce a conductive material slurry. The solids content of the conductive material slurry is preferably greater than 12% by weight, preferably greater than 15% by weight, and preferably greater than 18% by weight. Active material is then added to the conductive material slurry. The addition of the active material results in a solids content of 90% or greater, producing an active material slurry. The active material slurry is then optionally diluted with a solvent to 71% to 87%, preferably 75% to 83%, until castable, to produce an electrode slurry. If the viscosity and solids level are castable, dilution of the active material slurry is not necessary. If dilution of the active material slurry is not necessary, the active material slurry and the electrode slurry are the same.

[0065] In one embodiment, the polymer has 0.05 to 2% by weight of acid monomer units and has a viscosity of 3.36 seconds at 25°C using a Brookfield DVII viscometer with an SC4-25 spindle. -1 Using PVDF acid-functionalized copolymers with low solution viscosities in NMP (<6000 cP at 9 wt%), as measured by HPLC, binder concentrations in solution can be increased to 16% or higher. Higher polymer solids concentrations (greater than 9 wt%, preferably greater than 10 wt%) impart more shear to the conductive material in the battery slurry, improving slurry behavior, improving adhesion to the current collector substrate, and enhancing the electrochemical behavior of the battery. Other similar copolymers made by suspension polymerization have solubility limits of <10%, <11%, or <12%, so they cannot be used in the same way to reduce NMP usage and improve performance.

[0066] Fluoropolymer The present invention applies to vinylidene fluoride homopolymers and copolymers having more than 50% by weight of vinylidene fluoride monomer units, preferably more than 65% by weight, more preferably more than 75% by weight, and most preferably more than 90% by weight of vinylidene fluoride monomers.

[0067] Vinylidene fluoride polymer copolymers include at least 50% by weight, preferably at least 75% by weight, more preferably at least 80% by weight, and even more preferably at least 90% by weight of vinylidene fluoride copolymerized with one or more comonomers. Examples of comonomers may be selected from the group consisting of tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, perfluorobutylethylene (PFBE), hexafluoropropene (HFP), vinyl fluoride (VF), pentafluoropropene, tetrafluoropropene, trifluoropropene, fluorinated (alkyl) vinyl ethers such as perfluoroethyl vinyl ether (PEVE), and perfluoro-2-propoxypropyl vinyl ether, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutyl vinyl ether (PBVE), long-chain perfluorovinyl ethers, and other monomers that readily copolymerize with vinylidene fluoride. , one or more partially or fully fluorinated α-olefins, such as 3,3,3-trifluoro-1-propene, 2-trifluoromethyl-3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 3,3,3,4,4-pentafluoro-1-butene, hexafluoroisobutylene (HFIB), fluorinated dioxoles, such as perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), C4 or higher partially or perfluorinated α-olefins, C3 or higher partially or perfluorinated cyclic alkenes, allyl, partially fluorinated allyl, or fluorinated allyl monomers, such as 2-hydroxyethyl allyl ether or 3-allyloxypropanediol, ethene, or propene, and combinations thereof. Other monomer units in these polymers can include any monomer containing a polymerizable C═C double bond. The additional monomers can be 2-hydroxyethyl allyl ether, 3-allyloxypropanediol, allyl monomer, ethene or propene, acrylic acid, methacrylic acid.

[0068] In one preferred embodiment, the fluoropolymer is an acid-functionalized fluoropolymer, preferably an acid-functionalized PVDF.

[0069] Methods for producing acid-functionalized fluoropolymers are known in the art. International Publication No. 2019 / 199753, International Publication No. 2016 / 149238 and US Patent No. 8,337,725 (each of which is incorporated herein by reference) provide some known methods for producing acid-functionalized fluoropolymers.

[0070] In one embodiment, up to 30 wt.%, preferably up to 25 wt.%, more preferably up to 15 wt.% of hexafluoropropene (HFP) units and 70 wt.% or more, preferably 75 wt.% or more, more preferably 85 wt.% or more of VDF units are present in the vinylidene fluoride polymer. It is desirable for the HFP units to be distributed as uniformly as possible to provide a PVDF-HFP copolymer with excellent dimensional stability in the end-use environment.

[0071] The most preferred copolymers and terpolymers of the present invention are those in which vinylidene fluoride units comprise more than 50% of the total weight of all monomer units in the polymer, preferably at least 60% by weight of the units, and more preferably more than 70 percent of the total weight. Copolymers, terpolymers, and higher polymers of vinylidene fluoride can be prepared by reacting vinylidene fluoride with one or more of the comonomers listed above.

[0072] Polymerization Process Fluoropolymers, such as polyvinylidene-based polymers, can be produced by any process known in the art using aqueous free-radical emulsion polymerization, although suspension, solution, and supercritical CO2 polymerization processes can also be used. Processes such as emulsion polymerization and suspension polymerization are preferred and are described in U.S. Pat. No. 6,187,885 and EP 0 120 524. The polymer binder is preferably produced by emulsion polymerization.

[0073] In a typical emulsion polymerization process, a reactor is charged with deionized water, a water-soluble surfactant capable of emulsifying the reaction mass during polymerization, and an optional paraffin wax antifouling agent. The mixture is stirred and deoxygenated. A predetermined amount of chain transfer agent (CTA) is then introduced into the reactor, the reactor temperature is raised to the desired level, and a monomer (e.g., vinylidene fluoride, possibly one or more comonomers) is fed into the reactor. Once the initial charge of monomer has been introduced and the pressure in the reactor has reached the desired level, an initiator is introduced to begin the polymerization reaction. The reaction temperature may vary depending on the characteristics of the initiator used, and those skilled in the art will know how to do so. Typically, the temperature is about 30°C to 150°C, preferably about 60°C to 120°C. Once the desired amount of polymer in the reactor has been reached, the monomer feed is stopped, but the initiator feed is optionally continued to consume the residual monomer. Residual gas (including unreacted monomer) is vented, and the latex is recovered from the reactor.

[0074] The surfactant used in the polymerization can be any surfactant known in the art to be useful in PVDF emulsion polymerization, including perfluorinated, partially fluorinated, and non-fluorinated surfactants. Preferably, the PVDF emulsion is fluorosurfactant-free and no fluorosurfactants are used in any part of the polymerization. Non-fluorinated surfactants useful in PVDF polymerization can be both ionic and non-ionic in nature, and include, but are not limited to, 3-allyloxy-2-hydroxy-1-propanesulfonate, polyvinylphosphonic acid, polyacrylic acid, polyvinylsulfonic acid and its salts, polyethylene glycol and / or polypropylene glycol and their block copolymers, alkyl phosphonates, and siloxane-based surfactants.

[0075] The polymerization generally results in a latex having a solids level of 10 to 60% by weight, preferably 10 to 50% by weight, and a weight average particle size of less than 500 nm, preferably less than 400 nm, more preferably less than 300 nm. The weight average particle size is generally at least 20 nm, preferably at least 50 nm.

[0076] For use in the present invention, the PVDF latex is recovered in a dry form, such as in powder or granular form.

[0077] In some embodiments, the binder is a fluoropolymer composition and has a melting point greater than 100°C, preferably greater than 145°C, preferably greater than 155°C.

[0078] Electrode Slurry The cathode electrode slurry contains a solvent, an active material, a conductive material, and a polymer binder. The active material and the conductive material are preferably in the form of dry powders.

[0079] Any suitable organic solvent capable of dissolving the polymer binder can be used. The organic solvent used to dissolve the polymer binder composition (preferably a fluoropolymer, more preferably a vinylidene fluoride polymer composition) to provide the binder solution according to the present invention can be preferably polar, and can include the following: N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone, dimethylformamide (DMF), N,N-dimethylacetamide, N,N-dimethylsulfoxide, hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, MilliporeSigma's Cyrene™, and trimethyl phosphate. These solvents can be used alone or in combination. The polymer binder composition is dissolved in the solvent to prepare the polymer binder solution.

[0080] When forming a positive electrode (cathode), the cathode active material contains a composite metal chalcogenide represented by the general formula LiMY2, where M represents at least one transition metal such as Co, Ni, Fe, Mn, Cr, or V, and Y represents a chalcogen such as O or S. Among these, it is preferable to use a lithium-based composite metal oxide represented by the general formula LiMO2 (M is the same as above). Preferred examples include LiCoO2, LiNiO2, and LiNi x Co 1-x O2 and the spinel structure LiMn2O4. Among these, the formula LiNi x Co 1-x The use of Li-Co or Li-Ni binary composite metal oxides or Li-Ni-Co ternary composite metal oxides, which are inclusively represented by O2 (0≦x≦1), is particularly preferred from the viewpoint of high charge / discharge potential and excellent cycle characteristics. Cathode active materials include, but are not limited to, LiCoO2, LiNi 1-x Co x O2, Li 1-x Ni 1-y Co y O2, LiMO2 (M = Mn, Fe), Li[Ni x Co 1-2x Mn x ]O, LiNi x Mn y Co z O2, LiM2O4 (M=Ti, V, Mn), LiM x Mn 2-x O4(M=Co 2+ , Ni 2+ , Mg 2+ , Cu 2+ , Zn 2+ , Al 3+ , Cr 3+ ), LiFePO4, LiMPO4 (M=Mn, Co, Ni) and LiNi x Co y Al z O2. Preferred cathode materials include, but are not limited to: LiCoO2, LiNi x Co 1-x O2, LiMn2O4, LiNiO2, LiFePO4, LiNi x Co y Mnz O m , LiNi x- Co y Al z O m (x+y+z=1, m is an integer representing the number of oxygen atoms in the oxide to provide an electron-balanced molecule); as well as lithium metal oxides such as lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide, and lithium manganese oxide.

[0081] As the positive electrode active material according to one embodiment of the present invention, a lithium transition metal oxide having a non-stoichiometric amount of lithium is preferably used, and an example thereof may be a mixture of one or more selected from the group consisting of: Li x CoO2(0.5 <x<1.3)、Li x NiO2(0.5 <x<1.3)、Li x MnO2(0.5 <x<1.3)、Li x Mn2O4(0.5 <x<1.3)、Li x (Ni a Co b Mn c )O2(0.5 <x<1.3、0<a<1、0<b<1、0<c<1、a+b+c=1)、Li x Ni 1-y Co y O2(0.5 <x<1.3、0<y<1)、Li x Co 1-y Mn y O2(0.5 <x<1.3、0≦y<1)、Li x Ni 1-y Mn y O2(0.5 <x<1.3、0≦y<1)、Li x (Ni a Co b Mn c )O4(0.5 <x<1.3、0<a<2、0<b<2、0<c<2、a+b+c=2)、Li x Mn 2-z Ni z O4(0.5 <x<1.3、0<z<2)、Li x Mn 2-z Coz O4 (0.5 < x < 1.3, 0 < z < 2), Li x CoPO4 (0.5 < x < 1.3), and Li x FePO4 (0.5 < x < 1.3). More preferably, Li x (Ni a Co b Mn c )O2 (0.9 < x < 1.2, 0.5 ≤ a ≤ 0.7, 0.1 ≤ b ≤ 0.3, 0.1 ≤ c ≤ 0.3, a + b + c = 1) may be present.

[0082] The conductive material is preferably used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the active material constituting the positive electrode (cathode). The conductive agent includes, but is not limited to, carbonaceous materials. For example, graphite fine powder and fibers, carbon black, SuperP (registered trademark) carbon black, C-NERGY (trademark) carbon black, ketjen black, denka black, thermal black, channel black, carbon fibers, carbon nanotubes, and acetylene black, as well as fine powders and fibers of metals such as nickel and aluminum. In the case of conductive carbon black, the primary particle size of the carbon black preferably has an average particle size (diameter) of 10 to 100 nm measured by observation with an electron microscope. The primary particles can form aggregates or agglomerates up to 100 μm. A preferred conductive material is carbon black.

[0083] The electrode slurry may optionally contain other additives. Preferably, the electrode slurry does not contain additives. Such additives are known to those skilled in the art. The binder composition of the present invention can optionally contain additives based on polymers in an amount of 0 to 15% by weight, preferably 0.1 to 10% by weight, including but not limited to: thickeners, pH adjusters, acids, rheology additives, anti-settling agents, surfactants, wetting agents, fillers, defoaming agents, and temporary adhesion promoters. Additional adhesion promoters can also be added to improve binding properties and provide irreversible connectivity.

[0084] Electrode formation The electrode slurry composition can be used to form an electrode structure. Specifically, the electrode slurry composition is applied to at least one surface, preferably both surfaces, of a conductive substrate and dried, for example, at 50 to 170°C to form a composite electrode layer. Any metal with high conductivity and no reactivity in the battery voltage range can be used as a metal current collector, which facilitates adhesion of the electrode slurry. Examples of such substrates include metal foils or wire mesh, including, but not limited to, iron, stainless steel, steel, copper, lithium, aluminum, nickel, silver, titanium, or combinations thereof. The electrode slurry coating generally has a thickness of 10 to 1000 μm, preferably 10 to 200 μm. Depending on the application, the coating can be thicker or thinner.

[0085] The components of the electrode slurry are combined in accordance with the present invention to form a homogeneous slurry. Exemplary equipment used to combine the components includes, but is not limited to, a ball mill, a magnetic stirrer, a planetary mixer, a high-speed mixer, a homogenizer, and a static mixer. Those skilled in the art can select an appropriate equipment for the purpose.

[0086] The solid content (%) of the electrode slurry is preferably in the range of 71 to 87% by weight, more preferably 75 to 85% by weight, and may be 80 to 87% by weight.

[0087] The cathode formulation of active material, conductive agent, and polymer binder can vary. Preferably, the amount of active material is about 90-99 wt. % based on total solids. The amount of conductive agent is about 0.5-5 wt. % based on total solids, and the amount of polymer binder is about 0.5-5 wt. % based on the combined weight of the active material, conductive agent, and polymer binder composition.

[0088] Purpose Electrodes formed by the methods of the present invention can be used to form electrochemical devices, including, but not limited to, batteries, capacitors, and other energy storage devices.

[0089] More specifically, a secondary battery, such as a lithium secondary battery, basically comprises a structure including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The battery of the present invention can be manufactured using conventional methods known in the art.

[0090] Lithium secondary batteries can be manufactured by interposing a porous separator between a positive electrode and a negative electrode and adding an electrolyte solution containing a dissolved lithium salt. The separator may be formed of a porous polymer film. Separators for lithium batteries are well known in the art. Separators comprise microporous membranes of polymeric materials such as PVDF, polyethylene, or polypropylene, and are typically impregnated with an electrolyte solution. In some embodiments, the separator can be extruded or cast directly onto the electrodes and is not freestanding.

[0091] The non-aqueous electrolyte impregnated in the separator may include a solution of an electrolyte such as a lithium salt dissolved in a non-aqueous solvent (organic solvent). Examples of the electrolyte include a lithium salt, and the anion of the lithium salt may be one or more selected from the group consisting of: - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , F3SO3, CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO- , (CF3SO2)2CH - , (SF3)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - Examples include LiPF6, LiAsF6, LiClO4, LiBF4, CH3SO3Li, CF3SO3Li, LiN(SO2CF3)2, LiC(SO2CF3)3, LiCl, and LiBr.

[0092] The organic solvents for such electrolytes may include, but are not limited to, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl propionate, ethyl propionate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, butyl propionate, and mixtures thereof.

[0093] In another example, a secondary battery, such as a lithium secondary battery, includes a structure including a positive electrode, a negative electrode, and a solid electrolyte disposed between the positive and negative electrodes. In this case, the solid electrolyte also replaces the porous polymer separator. The mobile ion is lithium. Examples of solid inorganic electrolytes may include lithium sulfide, lithium oxide, lithium phosphate, lithium nitrate, and lithium hydride. A solid polymer electrolyte may include particles of an inorganic electrolyte or a lithium salt. Polymers used to form the solid polymer electrolyte may include, among others, polyethylene oxide, polyvinylidene fluoride, polyethylene glycol, and polyacrylonitrile.

[0094] Furthermore, the present invention provides a method for producing an electrode, which includes applying the electrode slurry to at least one surface of an electrode current collector to form an electrode active material layer, an electrode produced by the method, and a lithium secondary battery including the electrode.

[0095] An electrode according to an embodiment of the present invention can be prepared by a conventional method known in the relevant field, for example, by applying an electrode slurry onto a current collector made of a metal material, compressing it, and drying it to form an electrode.

[0096] The lithium secondary battery according to an embodiment of the present invention may include a common lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. [Example]

[0097] Example 1: Solubility limits

[0098] The binder solubility after 96 hours of non-heat rolling is as follows:

[0099] PVDF1 is KYNAR® HSV1810 polymer, an acid-functionalized PVDF binder. The solution viscosity was measured to be 3455 cP at 9 wt % in NMP.

[0100] PVDF1 was dissolved in NMP at ambient temperature at various weight concentrations: 4%, 8%, 12%, and 16% (based on total solution weight, polymer and solvent combined). PVDF1 was completely dissolved at all concentrations. No coagulation or powder was observed in any of the samples.

[0101] Comparative PVDF2 was KF9700, an acid-functionalized PVDF polymer manufactured by suspension polymerization from Kureha. The viscosity of a 9% solution of KF9700 was measured to be 8862 cP. Comparative PVDF2 was dissolved at 4% and 8% by weight. The solubility limit of Comparative PVDF2 is 12%. Powder was clearly visible in the sample; therefore, the polymer was past saturation.

[0102] Comparative PVDF3 is Solef® 5130, an acid-functionalized PVDF polymer from Solvay made by suspension polymerization. The 9% solution viscosity of Solef® 5130 was measured to be 9470 cP. Comparative PVDF3 has a solubility limit of 11.5 wt.%.

[0103] Example 2: Wet mixing

[0104] The concentration of the PVDF1 binder solution was increased. The formulation outline for the cathodes prepared by the wet mixing method is listed in Table 1. Each row represents a separate formulation, which has the same final solids content for comparison of slurry viscosity. The binder solution was prepared by dissolving the weight percent of PVDF binder in NMP. Three different weight percent binders were prepared: 4%, 8%, and 12%. Each binder solution was then used to make a slurry formulation.

[0105] [Table 1]

[0106] The wet mix formulation was prepared using a Thinky ARE-310 mixer. After adding the PVDF1 binder solution to the carbon black, seven 6.5 mm zirconium beads were added to the Thinky's cup. The mixture was mixed three times for 2 minutes at 2000 RPM for a total of 6 minutes to produce a conductive material slurry. The active material was added with the first addition of NMP. The active material slurry was mixed twice for 1 minute at 2000 RPM. NMP was added, and the active material slurry was mixed twice for 1 minute at 2000 RPM. The remaining aliquots of NMP were added, mixing for 1 minute at 2000 RPM between each addition to produce the electrode slurry. The total mixing time for the entire formulation was 13 minutes.

[0107] Slurry viscosity was measured using a Brookfield DVIII viscometer equipped with a CP-52 spindle at 25°C for 10 seconds. -1As shown in the last row of Table 1, the higher the binder solution concentration at the start of the formulation, the lower the viscosity of the final electrode slurry at the same solids level.

[0108] The resulting electrode slurry was cast onto aluminum foil using a doctor blade. The electrode was dried in an oven at 120 °C to evaporate the NMP. The electrode was calendered and tested for physical properties such as adhesion and electrochemical performance.

[0109] Adhesion was measured using a 180° peel test according to ASTM D903.

[0110] Peel adhesion at binder solution concentrations of 4, 8, and 12% is listed in Table 2. The peel adhesion data for PVDF1 shows the effect of using binder solutions of various concentrations.

[0111] [Table 2]

[0112] Example 3: Dry mixing

[0113] [Table 3]

[0114] The dry blend formulations listed in Table 3 were prepared using a Thinky ARE-310 mixer. Dry PVDF and dry carbon black were added to the Thinky cup. The solids were mixed at 2000 RPM for two 2-minute cycles for a total of 4 minutes. NMP was added to the cup and mixed at 2000 RPM for three 4-minute cycles for a total of 12 minutes to produce the conductive material slurry. The active material was added to the cup and mixed at 2000 RPM for two 1-minute cycles. The remaining aliquots of NMP were added to the active material slurry, with 1-minute mixing at 2000 RPM between each addition. The total mixing time for the electrode slurries ranged from 18 to 30 minutes, depending on the number of NMP dilution steps. Slurries 4 and 5 were formulated with a CB / PVDF ratio of 1:1. Slurries 6 and 7 were prepared in a similar manner, except that the CB / PVDF ratio was 1:1.5.

[0115] Electrode slurry viscosity was measured at 25°C for 10 seconds on a Brookfield DVIII viscometer equipped with a CP-52 spindle. -1 The higher the concentration of the binder solution at the start of the formulation, the lower the viscosity of the final electrode slurry will be at the same solids level.

[0116] The resulting electrode slurry was cast onto aluminum foil using a doctor blade. The electrodes were dried in an oven at 120 °C to evaporate the NMP. The electrodes were calendered and tested for physical properties such as adhesion and electrochemical performance.

[0117] Adhesion was measured using a 180° peel test according to ASTM D903.

[0118] [Table 4]

[0119] Table 4 shows the trends in slurry viscosity and peeling data for two CB / PVDF ratios in the dry mixing process. These data show that increasing binder concentration decreases the viscosity of the slurry and increases peeling.

[0120] The viscosity of the electrode slurry decreased as the weight percent of binder solids in the conductive slurry increased.

[0121] As the weight percent of binder solids (based on the amount of binder relative to the total amount of binder and solvent) used in the conductive slurry increased, the peel strength increased.

[0122] Example 4: Coin cell performance Coin cell batteries with cathodes were fabricated using the method of the present invention using PVDF1. The same proportions of electrode slurry were used as in Electrode Slurry 5, but with a final solids content of 81% by weight solids (rather than 74.1%) to emphasize the effect of higher loading on battery performance. The 81% solids slurry was made using the same ratio of active materials as in Slurry 5, but with less NMP added for "NMP loading." The coin cells also contained conventional components for a graphite anode, a carbonate-based electrolyte, and a polyolefin separator.

[0123] The battery was cycled twice at 25°C at a 0.5 C rate. The electrode exhibited good initial DC resistance and capacity. The electrochemical performance after 500 cycles was good.

[0124] [Table 5]

[0125] After 500 cycles, the battery retained over 85% of its capacity, which is excellent performance. Above 80% is excellent performance.

Claims

1. A method for producing a battery electrode slurry, comprising: (a) preparing a conductive material slurry containing a binder, a conductive material, and a solvent; (b) adding an active material to the conductive material slurry to form an active material slurry; and (c) adjusting the active material slurry to a final solids content to form an electrode slurry. Including, The PVDF binder was 3.36 seconds at 25°C at 9% solids in NMP. -1 has a solution viscosity of less than 6000 cP at The method of claim 1, wherein the PVDF binder concentration in the conductive material slurry is at least 9% by weight solids PVDF and at most 23% solids, based on the total weight of the binder and the solvent.

2. The step (a) of preparing a conductive material slurry comprises: (p) providing a PVDF binder; (q) preparing a binder solution by dissolving the PVDF binder in a solvent at a concentration of at least 9% by weight solids PVDF and up to 23% solids; (r) combining the binder solution with a conductive material to form a conductive material slurry; or (s) providing a PVDF binder in a dry form; (t) providing the conductive material in a dry state; (u) dry combining the PVDF binder and the conductive material to form a dry blend; and (v) adding a solvent to the dry blend to dissolve the PVDF binder and form a slurry of conductive material; Including, 10. The method of claim 1, wherein the ratio (by weight) of conductive material to PVDF binder is 5:1 to 1:

5.

3. 10. A method for manufacturing an electrode, comprising the method of claim 1, further comprising the steps of: (e) applying the electrode slurry to at least one surface of a conductive substrate to form an electrode; (f) evaporating the organic solvent in the electrode slurry composition to form a composite electrode layer on the conductive substrate.

4. The method of any one of claims 1 to 3, wherein the PVDF has a solution viscosity of less than 4000 cP.

5. The method of any one of claims 1 to 3, wherein the PVDF is acid-functionalized.

6. The method of any one of claims 1 to 3, wherein the PVDF binder comprises a polyvinylidene fluoride polymer, the polyvinylidene fluoride polymer comprising at least 50% by weight of vinylidene fluoride monomer.

7. The method of any one of claims 1 to 3, wherein the solids content of the binder is at least 10% solids PVDF, based on the amount of the binder and the solvent.

8. 4. The method according to claim 1, wherein the conductive material is selected from the group consisting of graphite fine powder and fiber, carbon black, thermal black, channel black, carbon fiber, carbon nanotube, and acetylene black, and metal fine powder and fiber.

9. The method of any one of claims 1 to 3, wherein the conductive material comprises carbon black.

10. The method of any one of claims 1 to 3, wherein the ratio (by weight) of conductive material to binder solids is from 5:1 to 1:

5.

11. The method of any one of claims 1 to 3, wherein the solids content of the electrode slurry is at least 75% by weight.

12. The method of any one of claims 1 to 3, wherein the solids content of the electrode slurry is at least 80% by weight.

13. The method of any one of claims 1 to 3, wherein the active material is selected from the group consisting of oxides, sulfides, phosphates or hydroxides of lithium and transition metals; carbonaceous materials; and combinations thereof.

14. The conductive material includes carbon black, the solids content of the binder is at least 10% solids based on the amount of PVDF in the solvent, and the PVDF binder is cured at 25° C. for 3.36 seconds at 9% solids in NMP. -1 4. The method of claim 1, wherein the PVDF has a solution viscosity of less than 4000 cP at 2000 kJ / min and the PVDF is acid-functionalized.

15. An electrode formed by the method of claim 3.

16. A battery comprising an electrode made by the method of claim 3.

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