EP-4736243-A1 - (METH)ACRYLATE POLYMERS AS ADDITIVES IN BATTERY ELECTRODES

Abstract

The present invention pertains to a binder for a secondary battery positive electrode, to a method of preparation of said electrode and to its use in a secondary battery. The invention also relates to the secondary batteries manufactured by incorporating said electrode.

Inventors

• BISO, MAURIZIO
• LIBERALE, Francesco
• DUFILS, PIERRE-EMMANUEL
• WILSON, DAVID JAMES

Assignees

• Syensqo Specialty Polymers Italy S.p.A.

Dates

Publication Date

20260506

Application Date

20240624

Claims (1)

1. Claims 1. A positive electrode-forming composition (C) for use in the preparation of electrodes for electrochemical devices, said composition (C) comprising: a) at least one positive electrode active material (AM); b) one binder (B), wherein binder (B) comprises: bi) at least one vinylidene fluoride (VDF) copolymer [polymer (F)] that comprises: (i) recurring units derived from VDF; and (ii) recurring units derived from at least one hydrophilic vinyl monomer (MA) of formula (I): - Ri , R2 and R3, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group, and - Rx is a C1-C20 hydrocarbon moiety comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester, a phosphate and an ether group, in an amount of from 0.05 to 10 % by moles of with respect to the total moles of recurring units of polymer (F); b2) at least one polymer [polymer (A)] derived from the polymerization of at least one monomer (I) and of at least one monomer (II), the said monomers corresponding to the following: - monomer (I): (meth)acrylic acid ester of formula CR 1 R 2 =C(R)-C(=O)-O-Rh wherein R means hydrogen or an alkyl group with 1 to 3 carbon atoms, R 1 and R 2 are independently selected from the group consisting of H and optionally substituted alkyl group with 1 to 5 carbon atoms, and Rh means a linear or branched alkyl residue with 1 to 30 carbon atoms, preferably with 1 to 15 carbons, more preferably with 1 to 5 carbons, optionally substituted by one or more nitrogen atom or by one or more hydroxyl, thiol or amino functional group; - monomer (II): nitrile group-containing monomer; wherein the content of monomer (II) in the polymer (A) is lower than 20 % by moles, preferably lower than 15 % by moles, over the total molar content of polymer (A); c) at least one solvent (S); and d) optionally at least one electroconductivity-imparting additive. 2. The composition (C) according to claim 1 , wherein the hydrophilic vinyl monomer (MA) is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate; hydroxyethylhexyl(meth)acrylate. 3. The composition according to any one of claims 1 or 2, wherein the active material (AM) is a composite metal chalcogenide of formula LiMCh, wherein M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr and V and Q is a chalcogen such as 0 or S. 4. The composition according to any one of claims 1 or 2 wherein the active material (AM) is selected from lithium-containing complex metal oxides of general formula (II) LiNixM 1 y M 2 zQ 2 (II) wherein M 1 and M 2 are the same or different from each other and are transition metals selected from Co, Fe, Mn, Cr and V, 0.5 < x < 1 , wherein y+z = 1-x, and Q is a chalcogen such as 0 or S. 5. The composition (C) according to any one of the preceding claims, wherein monomer (I) is selected from the group consisting of: acrylic acid ester or anhydride, methacrylic acid ester or anhydride, citraconic acid ester or anhydride, maleic acid ester or anhydride, fumaric acid ester or anhydride, itaconic acid ester or anhydride, crotonic acid ester or anhydride, ethacrylic acid ester or anhydride, methyl (meth)acrylic acid ester or anhydride, ethyl (meth)acrylic acid ester or anhydride, propyl (meth)acrylic acid ester or anhydride, isopropyl (meth)acrylic acid ester or anhydride, n-butyl (meth)acrylic acid ester or anhydride, 2-ethylhexyl (meth)acrylic acid ester or anhydride, n- hexyl (meth)acrylic acid ester or anhydride, n-octyl (meth)acrylic acid ester or anhydride; hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, hydroxyethylhexyl(meth)acrylate; Sipomer® I3.CEA (sold by Solvay), Sipomer® WAM (sold by Solvay), Sipomer® WAM II (sold by Solvay) and other urido-containing monomers;ethylene glycol alkyl ether acrylates such as di(ethylene glycol) ethyl ether acrylate (DEGEEA); glycidyl methacrylate; glycerol methacrylate; (meth) acryloyloxyalkyl succinic acid, such as (meth) acryloyloxyethyl succinic acid and (meth) acryloyloxypropyl succinic acid. 6. The composition (C) according to any one of the preceding claims, wherein monomer (I) is selected from methyl methacrylic acid ester (MMA) and n-butyl (meth)acrylic acid ester. 7. The composition (C) according to any one of the preceding claims, wherein monomer (II) is selected from acrylonitrile and methacrylonitrile. 8. The composition (C) according to any one of the preceding claims, wherein polymer (A) is a copolymer derived from the polymerization of methyl methacrylic acid ester (MMA), n-butyl acrylic acid ester (BA) and acrylonitrile (AN). 9. The composition (C) according to any one of the preceding claims, wherein polymer (A) comprises recurring units derived from methyl methacrylic acid ester (MMA) in an amount of from 10 to 45 wt%, n-butyl acrylic acid ester (BA) in an amount of from 45 to 80 wt% and acrylonitrile (AN) in an amount of from 5 to less than 20 wt%. 10. The composition (C) according to any one of the preceding claims, wherein the weight ratio of polymer (F) to polymer (A) in binder (B) is in the range of from 95:5 to 70:30, preferably 90:10. 11 . A process for the manufacture of a positive electrode [electrode (E)], said process comprising: (i) providing a metal substrate having at least one surface; (ii) providing an electrode-forming composition [composition (C)] according to any one of claims 1 to 10; (iii) applying the composition (C) provided in step (ii) onto the at least one surface of the metal substrate provided in step (i), thereby providing an assembly comprising a metal substrate coated with said composition (C) onto the at least one surface; (iv) drying the assembly provided in step (iii). 2. A positive electrode (E), which comprises: - a metal substrate having at least one surface, and - directly adhered onto at least one surface of said metal substrate, at least one layer consisting of a composition [composition (C’)] comprising: a) at least one positive electrode active material (AM); b) one binder (B), wherein binder (B) comprises: bi) at least one vinylidene fluoride (VDF) copolymer [polymer (F)] that comprises: (i) recurring units derived from VDF; and (ii) recurring units derived from at least one hydrophilic vinyl monomer (MA) of formula (I): wherein: - Ri , R2 and R3, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group, and - Rx is a C1-C20 hydrocarbon moiety comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester, a phosphate and an ether group, in an amount of from 0.05 to 10 % by moles of with respect to the total moles of recurring units of polymer (F); b2) at least one polymer [polymer (A)] derived from the polymerization of at least one monomer (I) and of at least one monomer (II), the said monomers corresponding to the following: - monomer (I): (meth)acrylic acid ester of formula CR 1 R 2 =C(R)-C(=O)-O-Rh wherein R means hydrogen or an alkyl group with 1 to 3 carbon atoms, R 1 and R 2 are independently selected from the group consisting of H and optionally substituted alkyl group with 1 to 5 carbon atoms, and Rh means a linear or branched alkyl residue with 1 to 30 carbon atoms, preferably with 1 to 15 carbons, more preferably with 1 to 5 carbons, optionally substituted by one or more nitrogen atom or by one or more hydroxyl, thiol or amino functional group; - monomer (II): nitrile group-containing monomer; wherein the content of monomer (II) in the polymer (A) is lower than 20 wt%, preferably lower than 15 wt%; c) at least one solvent (S); and d) optionally at least one electroconductivity-imparting additive. 13. An electrochemical device comprising the positive electrode (E) according to any one of claims 11 or 12. 14. The electrochemical device according claim 13 that is a lithium-ion secondary battery.

Description

(METH)ACRYLATE POLYMERS AS ADDITIVES IN BATTERY ELECTRODES Cross reference to previous applications [0001] This application claims priority to European application No. 23182277.6 filed on 29 June 2023, the whole content of this application being incorporated herein by reference for all purposes. Technical Field [0002] The present invention pertains to a binder for a secondary battery positive electrode, to a method of preparation of said electrode and to its use in a secondary battery. [0003] The invention also relates to the secondary batteries manufactured by incorporating said electrode. Background Art [0004] Electrochemical devices such as secondary batteries typically comprise a positive electrode, a negative electrode and an electrolyte. [0005] The electrodes for secondary batteries are usually produced by mixing a binder with a powdery electrode active material. [0006] It is known in the art that polyvinylidene fluoride (PVDF) is the preferred polymer to be used as binder for forming electrodes, in particular as binder in Nickel-rich cathodes production. Considering specific current cell production processes (eg. winding or lamination after winding) with pressures and stresses reached by the components, the use of more flexible additives becomes a need or, at least, a point of attention in materials choice. [0007] Electrodes flexibility is indeed of primary importance for battery makers because it allows to increase electrode density and/or loading without cracking during the standard cell production process i.e. avoiding fracture of electrode (of either the coating or the collector) during winding or during lamination after winding. Moreover, flexible electrodes allow to reach higher electrode density in the standard pressing conditions or same density with milder pressing conditions. [0008] When electrodes cannot stand bending, there is the risk of mechanical failure, cracking of the electrodes, eventual materials detachment from current collector and/or battery failure during cycling. [0009] EP 2953193 discloses that flexibility performances of Nickel-rich cathodes using PVDF homopolymer binders are improved when a nitrile group- containing acrylic polymer is added. [0010] JP2005-123047 discloses a sheet-like positive electrode binder based on polyvinylidene fluoride containing acrylonitrile-butadiene rubber, which provides improved flexibility to a lithium nickel oxide cathode. [0011 ] The solutions currently available in this field rely on the use of PVDF homopolymers-based binders, which however suffer from poor adhesion to current collectors. [0012] Modified polar PVDF polymers, such as those comprising recurring units derived from hydrophilic (meth)acrylic monomers (e.g. acrylic acid), are well known in the art. Such copolymers have been developed aiming at adding to the mechanical properties and chemical inertness of PVDF suitable adhesion towards metals, e.g. aluminium or copper. [0013] However, when modified polar PVDF polymers are used in the preparation of a slurry for forming positive electrodes with certain active materials, an important drawback is that the slurry often undergoes to a rapid viscosity increase, leading to the formation of a gel, thus preventing their use as binder for cathodes. [0014] A time dependency in the rheological properties of the composite electrode slurries is observed also in sodium-ion secondary batteries; in fact, gelation of the slurry can be initiated by the NaOH present on the material when exposed to air, with consequent dehydrofluorination with crosslinking of PVDF. Said gelation leads to inhomogeneous coatings being produced. [0015] The need for more performing polymers, which guarantee in particular better flexibility and higher adhesion to current collectors, is still felt both in research and from industrial perspectives. [0016] One way is to find a blend of polymers which therefore avoids the drawbacks of modified polar PVDF polymers in contact with certain active materials such as Nickel-rich active materials, but which at the same time guarantees the feasibility of electrodes through wet casting and high adhesions of the final product. Summary of invention [0017] It is thus an object of the invention a positive electrode-forming composition (C) for use in the preparation of electrodes for electrochemical devices, said composition (C) comprising: a) at least one positive electrode active material (AM); b) one binder (B), wherein binder (B) comprises: bi) at least one vinylidene fluoride (VDF) copolymer [polymer (F)] that comprises: (i) recurring units derived from VDF; and (ii) recurring units derived from at least one hydrophilic vinyl monomer (MA) of formula (I): wherein: - Ri , R2 and R3, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group, and - Rx is a C1-C20 hydrocarbon moiety comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, a