Fluorinated block copolymers and uses thereof
阅读说明：本技术 氟化嵌段共聚物及其应用 (Fluorinated block copolymers and uses thereof ) 是由 S·卡雷拉 A·V·奥瑞尼 A·吉利姆 M·马佐拉 E·莫林那 于 2018-12-17 设计创作，主要内容包括：本发明涉及包含交替的硬嵌段和软嵌段的氟化嵌段共聚物,其中所述硬嵌段和软嵌段二者都包含偏二氟乙烯(VDF)。本发明进一步涉及所述嵌段共聚物在锂电池应用中的用途。(The present invention relates to fluorinated block copolymers comprising alternating hard and soft blocks, wherein both the hard and soft blocks comprise vinylidene fluoride (VDF). The invention further relates to the use of said block copolymer in lithium battery applications.)
1. Fluorinated block copolymer [ copolymer (F) ]b)]Which comprises the following steps:
-at least one first block consisting of a sequence of repeating units [ block (a) ], said sequence consisting of repeating units derived from 1,1-difluoroethylene (VDF), and optionally at least one monomer [ monomer (M) ] comprising at least one ethylenically unsaturated double bond and at least one functional group selected from-COOH and-OH; and
-at least one second block [ block (B) ] consisting of a sequence of repeating units consisting of repeating units derived from 1,1-difluoroethylene (VDF), at least one perhalogenated monomer [ monomer (PF) ], and optionally at least one monomer (M) as defined above,
with the proviso that at least one of the block (A) and the block (B) comprises repeating units derived from the monomer (M);
wherein the copolymer (F)b) Comprises the following steps:
-recurring units derived from said at least one monomer (PF) in a total amount based on said copolymer (F)b) From 1.5 mol.% to less than 15 mol.%; and
- -recurring units derived from the monomer (M), in a total amount based on the copolymer (F)b) From 0.05 mol.% to 2 mol.%,
the balance to make up 100% moles is from repeating units derived from VDF.
2. Copolymer (F) according to claim 1b) Wherein the copolymer (F)b) Comprising recurring units derived from said monomer (M) in an amount based on said copolymer (F)b) From 0.5 mol.% to 1.9 mol.%.
3. Copolymer (F) according to claim 1b) Which isIn (1),
the at least one monomer (PF) is selected in the group comprising, more preferably consisting of:
-C2-C8perfluoroolefins, such as notably Tetrafluoroethylene (TFE) and Hexafluoropropylene (HFP);
-chloro-and/or bromo-and/or iodo-C2-C6Fluoroolefins, such as notably Chlorotrifluoroethylene (CTFE);
-CF2＝CFOX0
wherein X0Selected from: c1-C12A perfluoroalkyl group; c1-C12Perfluorooxyalkyl groups having one or more ether groups, such as perfluoro-2-propoxy-propyl; -CF2ORf2Wherein R isf2Is C1-C6Perfluoroalkyl group such as CF3、C2F5、C3F7Or C with one or more ether groups1-C6(per) fluorooxyalkyl radicals such as
-C2F5-O-CF3；
-perfluorodioxole;
and/or
Said at least one monomer (M) is at least one (meth) acrylic monomer [ Monomer (MA) ], preferably conforming to formula (I):
wherein:
-R1、R2and R3Are identical or different from each other and are independently selected from hydrogen atoms and C1-C3A hydrocarbon group, and
-ROHis a hydrogen atom or C containing at least one hydroxyl group1-C5A hydrocarbon moiety.
4. Copolymer (F) according to claim 1 or 3b) Wherein said at least one monomer (PF) is C2-C8A perfluoroolefin; even if the temperature is too highTo more preferably HFP.
5. The copolymer (F) according to claim 4b) Wherein the copolymer (F)b) Comprising recurring units derived from HFP in an amount based on the copolymer (F)b) From 2 mol.% to less than 12 mol.%.
6. Copolymer (F) according to claim 1b) Wherein the Monomer (MA) is selected in the group comprising, preferably consisting of: acrylic Acid (AA), methacrylic acid, hydroxyethyl methacrylate, hydroxyethyl acrylate (HEA), hydroxypropyl methacrylate, hydroxypropyl acrylate (HPA), hydroxyethylhexyl methacrylate, hydroxyethylhexyl acrylate, and mixtures thereof.
7. The copolymer (F) according to claim 6b) Wherein the at least one Monomer (MA) is selected from the following:
-hydroxyethyl acrylate (HEA) having the formula:
-2-hydroxypropyl acrylate (HPA) having any of the following formulae:
-Acrylic Acid (AA) having the formula:
-and mixtures thereof.
8. Copolymer (F) according to any one of the preceding claimsb) Wherein the copolymer (F)b) Comprising one or more blocks arranged alternately(A) And one or more blocks (B).
9. Copolymer (F) according to any one of the preceding claimsb) Wherein:
one block (A) being interposed between two blocks (B) and the copolymer (F)b) Conforms to the formula: B-A-B; or
One block (B) being interposed between two blocks (A) and the copolymer (F)b) Conforms to the formula: A-B-A.
10. Copolymer (F) according to any one of the preceding claimsb) Wherein, in the step (A),
-said block (a) consists of a sequence of recurring units derived from 1,1-difluoroethylene (VDF) and a Monomer (MA) as defined in any one of claims 6 or 7; and/or
-said block (B) consists of a sequence of recurring units derived from 1,1-difluoroethylene (VDF), Hexafluoropropylene (HFP) and Monomer (MA) as defined in any one of claims 6 or 7.
11. A composition [ composition (C1)]In the form of a copolymer comprising at least one copolymer (F)b) In the form of an aqueous dispersion of primary particles of (a), the copolymer (F)b) Is according to any one of claims 1 to 10.
12. Composition according to claim 11, wherein the copolymer (F)b) Has an average primary size of less than 1 micron as measured according to ISO 13321.
13. Separator for an electrochemical cell, comprising a base layer [ layer (S) at least partially coated with a composition (C1) according to any one of claims 11 and 12C)]。
14. A method for manufacturing a separator for an electrochemical cell according to claim 13, the method comprising the steps of:
i) providing an uncoated substrate layer [ layer (L S) ];
ii) providing a composition (C1) according to any one of claims 11 and 12;
iii) applying the composition (C1) of step (ii) at least partially onto at least a part of the substrate layer (L S), thereby providing an at least partially coated substrate layer [ layer (S)C)](ii) a And
iv) drying the layer (S) of step (iii)C)。
15. An electrochemical cell, such as a secondary battery or a capacitor, comprising an at least partially coated separator according to claim 13.
Technical Field
The present invention relates to fluorinated block copolymers comprising alternating hard and soft blocks, wherein both the hard and soft blocks comprise vinylidene fluoride (VDF). The invention further relates to the use of said block copolymer in lithium battery applications.
Background
Copolymers comprising recurring units derived from vinylidene fluoride (VDF) and at least one other partially or fully fluorinated comonomer and uses thereof have been disclosed in the art.
For example, US 2004/0211943 (HITACHI powder metallurgy co., ltd. (HITACHI powered META L SCO.))28/10/2004 discloses a coating for a separator of a fuel cell, aiming at solving the problem of adhesion between a coating film obtained from a conductive coating and a base material of the separator.
However, this document does not disclose VDF-based block copolymers.
EP 2455408A (DAIKIN INDUSTRIES, <tttransition = L "&tttl <t/t &ttttd.)) discloses a process for producing a fluoropolymer block copolymer comprising reacting a fluoropolymer (a) with a radically polymerizable monomer (M) in the presence of a sulfur compound preferably the fluoropolymer (a) has the structure of a vinylidene fluoride polymer chain and the radically polymerizable monomer (M) is selected from the group consisting of a vinyl fluoride monomer, a non-fluorinated ethylenic monomer, (meth) acrylic monomer, a styrene monomer, a vinyl ether monomer and a vinyl ester monomer.
Thus, this document does not disclose VDF/HFP copolymers, wherein HFP is in a molar amount of less than 15 mol.% compared to the mol% of VDF.
In addition, this document neither suggests providing a copolymer of VDF and a (meth) acrylic monomer as the radical polymerizable monomer (M), nor discloses the molar amount in which the (meth) acrylic monomer should be used.
US 2014/0154611 (alcoma, france (ARKEMA FRANCE); monterey national institute of advanced chemistry (ECO L E natriona L E super element DE CHIMIE DE monte LL IER)) discloses a process for the preparation of fluorinated copolymers comprising the step of copolymerizing a fluorinated monomer (of the vinylidene fluoride type) with its derivative α -trifluoromethylacrylic acid in the presence of a xanthate or trithiocarbonate compound.
WO 2016/149238 (arkema (ARKEMA INC)) discloses modified fluoropolymers comprising fluoromonomer units and from 0.1 to 25 weight percent, based on the total amount of monomers, of residual functional groups derived from one or more low molecular weight polymer functional chain transfer agents. The modified fluoropolymer is believed to be useful in preparing an article selected from: an electrode, a separator for a battery or a capacitor, a porous membrane or a hollow fiber membrane; for coating at least one surface of an article; or for providing a multilayer construction, wherein the modified fluoropolymer forms a tie layer between a fluoropolymer layer and a polymer layer incompatible with the fluoropolymer.
Disclosure of Invention
The applicant believes that in the field of battery, notably lithium battery technology, the following problems have not been solved: provided is a separator comprising a coating layer which is capable of providing good and excellent adhesion to a separator base material and which, at the same time, does not show swelling due to contact with an electrolyte solvent.
Thus, the applicant faced the problem of providing a composition suitable for coating the matrix material of a separator for an electrochemical cell, which composition in this way simultaneously provides excellent adhesion to the separator matrix material and no swelling when immersed in an electrolyte solvent, thereby improving the long-term performance of the battery.
Surprisingly, the applicant has found that when a separator for an electrochemical cell is at least partially coated with a composition comprising at least one fluorinated block copolymer having a backbone comprising hard blocks alternating with soft blocks, good adhesion to the matrix material of the separator and reduced swelling are obtained at the same time.
Thus, in a first aspect, the present invention relates to a fluorinated block copolymer [ copolymer (F)b)]Which comprises the following steps:
-at least one first block consisting of a sequence of repeating units [ block (a) ], said sequence consisting of repeating units derived from 1,1-difluoroethylene (VDF), and optionally at least one monomer [ monomer (M) ] comprising at least one ethylenically unsaturated double bond and at least one functional group selected from-COOH and-OH; and
-at least one second block [ block (B) ] consisting of a sequence of repeating units consisting of repeating units derived from 1,1-difluoroethylene (VDF), at least one perhalogenated monomer [ monomer (PF) ], and optionally at least one monomer (M) as defined above,
with the proviso that at least one of the block (A) and the block (B) comprises repeating units derived from the monomer (M);
wherein the copolymer (F)b) Comprises the following steps:
-recurring units derived from said at least one monomer (PF) in a total amount based on said copolymer (F)b) From 1.5 mol.% to less than 15 mol.%; and
- -recurring units derived from the monomer (M), in a total amount based on the copolymer (F)b) From 0.05 mol.% to 2 mol.%,
the balance to make up 100% moles is from repeating units derived from VDF.
In a second aspect, the invention relates to a composition [ composition (C1)]In the form of a copolymer comprising at least one copolymer (F) as defined aboveb) In the form of an aqueous dispersion of primary particles.
Preferably, said copolymer (F) in said composition (C1)b) Has an average primary size of less than 1 micron as measured according to ISO 13321.
In a third aspect, the invention relates to a separator for an electrochemical cell, comprising a base layer [ layer (S1) ] at least partially coated with a composition (C1) as defined aboveC)]。
In a fourth aspect, the invention relates to a method for manufacturing a separator for an electrochemical cell as defined above, comprising the steps of:
i) providing an uncoated substrate layer [ layer (L S) ];
ii) providing a composition (C1) as defined above;
iii) (iii) applying the composition (C1) of step (ii) at least partially onto at least a part of the substrate layer (L S), thereby providing an at least partially coated substrate layer [ layer (S)C)](ii) a And
iv) drying the layer (S) of step (iii)C)。
In a fifth aspect, the present invention relates to an electrochemical cell, such as a secondary battery or a capacitor, comprising an at least partially coated separator as defined above.
Detailed Description
As used in this specification and the following claims:
the use of parentheses around the symbol or number of the identification formula, for example in expressions like "polymer (P)" or the like, has the purpose of only better distinguishing this symbol or number from the rest of the text, and therefore said parentheses can also be omitted;
the terms "1, 1-difluoroethylene", "1, 1-difluoroethylene" and "vinylidene fluoride" are used synonymously;
the terms "poly (1, 1-difluoroethylene)" and "polyvinylidene fluoride" are used as synonyms;
the term "separator" is intended to indicate a porous single-or multilayer polymeric material that electrically and physically separates the electrodes of opposite polarity in an electrochemical cell and is permeable to the ions flowing between them;
the expression "substrate layer" is intended to indicate a single-layer substrate consisting of a single layer or a multi-layer substrate comprising at least two mutually adjacent layers;
the expression "composite separator" is intended to indicate a separator as defined above, wherein at least one non-electroactive inorganic filler material is incorporated into the polymeric binder material;
the expression "electrochemical cell" is intended to indicate an electrochemical cell comprising a positive electrode, a negative electrode and a liquid electrolyte, wherein a single-or multilayer separator is adhered to at least one surface of one of said electrodes. Non-limiting examples of electrochemical cells include, notably, batteries, preferably secondary batteries, and electric double layer capacitors;
the expression "secondary battery" is intended to indicate a rechargeable battery. Non-limiting examples of secondary batteries include notably alkali metal or alkaline earth metal secondary batteries.
Preferably, said at least one monomer (PF) is selected in the group comprising, more preferably consisting of:
-C2-C8perfluoroolefins, such as notably Tetrafluoroethylene (TFE) and Hexafluoropropylene (HFP);
-chloro-and/or bromo-and/or iodo-C2-C6Fluoroolefins, such as notably Chlorotrifluoroethylene (CTFE);
-CF2＝CFOX0
wherein X0Selected from: c1-C12A perfluoroalkyl group; c1-C12Perfluorooxyalkyl groups having one or more ether groups, such as perfluoro-2-propoxy-propyl; -CF2ORf2Wherein R isf2Is C1-C6Perfluoroalkyl group such as CF3、C2F5、C3F7Or C with one or more ether groups1-C6(per) fluorooxyalkyl radicals such as-C2F5-O-CF3；
-perfluorodioxoles.
According to a preferred embodiment, said at least one monomer (PF) is C2-C8A perfluoroolefin; even more preferably HFP.
Preferably, the copolymer (F)b) Comprising recurring units derived from HFP in an amount based on the copolymer (F)b) From 2 mol.% to less than 12 mol.%, more preferably from 3 mol.% to about 10 mol.%.
Preferably, the copolymer (F)b) Comprising recurring units derived from monomer (M) in an amount based on the copolymer (F)b) From 0.5 mol.% to 1.9 mol.%.
Preferably, said at least one monomer (M) is at least one (meth) acrylic monomer [ Monomer (MA) ].
Preferably, the Monomer (MA) is a monomer structurally derived from acrylic acid or methacrylic acid and conforming to formula (I):
wherein:
-R1、R2and R3Are identical or different from each other and are independently selected from hydrogen atoms and C1-C3A hydrocarbon group, and
-ROHis a hydrogen atom or C containing at least one hydroxyl group1-C5A hydrocarbon moiety.
Preferably, the Monomer (MA) corresponds to formula (II):
wherein:
-R’1、R’2and R'3Is a hydrogen atom, and
-R’OHis a hydrogen atom or C containing at least one hydroxyl group1-C5A hydrocarbon moiety.
Non-limiting examples of Monomers (MA) include acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, hydroxyethylhexyl methacrylate, hydroxyethylhexyl acrylate, and mixtures thereof.
Preferably, the copolymer (F)b) Comprising recurring units derived from (MA) in an amount based on the copolymer (F)b) From 0.5 mol.% to 1.9 mol.%.
More preferably, the Monomer (MA) is selected from the following:
-hydroxyethyl acrylate (HEA) having the formula:
-2-hydroxypropyl acrylate (HPA) having any of the following formulae:
-Acrylic Acid (AA) having the formula:
-and mixtures thereof.
Even more preferably, the (meth) acrylic Monomer (MA) is Acrylic Acid (AA) or hydroxyethyl acrylate (HEA).
Preferably, the copolymer (F)b) The weight ratio between said one or more blocks (a) and said one or more blocks (B) in (a) is comprised between 20 and 50, more preferably between 25 and 45.
Advantageously, the copolymer (F)b) Comprising blocks (A) and one or more blocks (B) arranged alternately. In other words, the copolymer (F) according to the inventionb) Does not contain randomly distributed blocks (A) and/or (B).
According to an embodiment, one block (A) is interposed between two blocks (B), i.e.a copolymer (F)b) Conforms to the formula: B-A-B.
According to another embodiment, one block (B) is interposed between two blocks (A), i.e.a copolymer (F)b) Conforms to the formula: A-B-A.
According to a more preferred embodiment, both said block (a) and said block (B) comprise recurring units derived from said Monomer (MA).
Preferably, the block (a) consists of a sequence of repeating units derived from 1,1-difluoroethylene (VDF) and from a Monomer (MA).
Preferably, said block (B) consists of a sequence of repeating units derived from 1,1-difluoroethylene (VDF), Hexafluoropropylene (HFP) and Monomer (MA).
According to the invention, in the block (A) and the blockCopolymers (F) comprising the Monomers (MA) in both stages (B)b) Can advantageously be synthesized in an emulsion polymerization process comprising the steps of:
(Ia) contacting a first portion of VDF monomer with at least a first portion of monomer (M) and an aqueous medium to provide a first mixture [ mixture (Ma1) ];
(IIa) polymerizing the mixture (Ma 1);
(IIIa) reacting the polymerized mixture (Ma1) of step (II) with at least a first part of a mixture comprising VDF and monomer (PF) and
contacting with a second portion of monomer (M) to provide a second mixture [ mixture (Ma2) ];
(IVa) polymerizing said mixture (Ma2), thereby providing said copolymer (F) conforming to formula B-A-Bb)；
Or
(Ib) contacting at least a first portion of the mixture comprising VDF and monomer (PF) with at least a first portion of monomer (M) and an aqueous medium to provide a first mixture [ mixture (Mb1) ];
(IIb) polymerizing the mixture (Mb 1);
(IIIb) contacting the polymerized mixture of step (II) (Mb1) with at least a first portion of VDF monomer and with a second portion of monomer (M) to provide a second mixture [ mixture (Mb2) ];
(IVb) polymerizing said mixture (Mb2), thereby providing said copolymer (F) conforming to the formula A-B-Ab)。
The emulsion polymerization process of the present invention is preferably carried out at a polymerization pressure typically between 10 and 70 bar, preferably between 15 and 50 bar.
The polymerization temperature can be appropriately selected by those skilled in the art based on the monomers used. Preferably, the emulsion polymerization process of the present invention is carried out at a temperature of from 70 ℃ to 150 ℃.
Preferably, the VDF monomer and the monomer (PF) are fed to the reaction environment in gaseous form.
The process of the invention, notably step (Ia) and step (Ib), is advantageously carried out in the presence of at least one free-radical initiator. While the choice of free radical initiator is not particularly limited, it is understood that free radical initiators suitable for aqueous emulsion polymerization processes are selected from compounds capable of initiating and/or accelerating the polymerization process and include, but are not limited to, persulfates, such as sodium persulfate, potassium persulfate, and ammonium persulfate; organic peroxides, notably including alkyl peroxides, dialkyl peroxides (e.g., di-t-butyl peroxide-DTBP), diacyl peroxides, peroxydicarbonates (e.g., di-n-propyl peroxydicarbonate and diisopropyl peroxydicarbonate), peroxyesters (e.g., t-amyl peroxypivalate, t-butyl peroxypivalate, and disuccinic acid peroxide); and mixtures thereof.
Preferably, said step (Ia) is carried out in the presence of a chain transfer agent. Suitable chain transfer agent a suitable chain-chain transfer agent is typically of the formula Rf(I)x(Br)yWherein R isfIs a (per) fluoroalkyl or a (per) fluorochloroalkyl group containing from 1 to 8 carbon atoms, and x and y are integers between 0 and 2, where 1. ltoreq. x + y. ltoreq.2.
For the purposes of the present invention, "average primary particle size" is intended to mean the copolymer (F) derived from aqueous emulsion polymerizationb) The primary particles of (1).
Thus, the copolymer (F)b) Are intended to be distinguishable from agglomerates (i.e., aggregates of primary particles (collection)) which can be produced by such polymer/copolymer recovery and conditioning steps (e.g., subjecting the copolymer (F) tob) Is concentrated and/or coagulated and subsequently dried and homogenized to give the corresponding powder).
Therefore, the aqueous latex of the composition (C1) for coating the separator of the present invention is distinguishable from an aqueous slurry prepared by dispersing powder of a polymer or copolymer into an aqueous medium. The average particle size of the powder of the polymer or copolymer dispersed in the aqueous slurry is typically greater than 1 μm as measured according to ISO 13321.
Preferably, the copolymer (F) as defined aboveb) The average particle size of the primary particles of (A) is as determined according to ISO13321Amounts of more than 10nm, more preferably more than 15nm, even more preferably more than 20nm, and/or down to 600nm, more preferably below 400nm or below 300 nm.
Preferably, the total solids content of the composition (C1) is from 20 to 60 wt.%, more preferably from 45 to 55 wt.%, relative to the total weight of the composition (C1).
The composition (C1) may optionally comprise other than said copolymer (F)b) At least one other component than the primary particles of (a).
Preferably, the at least one optional component is selected in the group comprising: defoamers, surfactants, antimicrobials, fillers, and mixtures thereof.
Typically, when present, the amount of each of such optional components is less than 15 wt.%, preferably less than 10 wt.% or less than 7 wt.%, relative to the weight of the solids content of the latex.
The separator used in the electrochemical cell of the present invention may advantageously be an electrically insulating composite separator suitable for use in an electrochemical cell. When used in an electrochemical cell, the composite separator is generally filled with an electrolyte that advantageously allows ionic conduction within the electrochemical cell. Preferably, the electrolyte is a liquid or semi-liquid.
According to a preferred embodiment, the separator of the invention has two surfaces, at least one of which is at least partially coated with a composition [ composition (C2) ] comprising said composition (C1) as defined above and a non-electroactive inorganic filler material uniformly distributed therein.
According to another preferred embodiment, the membrane of the invention has two surfaces, at least one of which comprises
-a first layer adhered to at least one surface obtainable from a composition [ composition (C3) ], the composition comprising a binder and a non-electroactive inorganic filler material, and
-a second layer comprising a composition (C1) as defined above.
The term "non-electroactive inorganic filler material" is intended herein to mean an electrically non-conductive inorganic filler material that is suitable for making electrically insulating separators for electrochemical cells.
The non-electroactive inorganic filler material in the separator according to the invention typically has at least 0.1 × 10 as measured according to ASTM D257 at 20 ℃10ohm cm, preferably at least 0.1 × 1012Resistivity in ohm cm (p). Non-limiting examples of suitable non-electroactive inorganic filler materials include, notably, natural and synthetic silicas, zeolites, aluminas, titanias, metal carbonates, zirconias, silicon phosphates, and silicates, and the like. The non-electroactive inorganic filler material is typically in the form of particles having an average size of from 0.01 μm to 50 μm as measured according to ISO 13321. Typically, the non-electroactive inorganic filler material is present in an amount of from 10 to 90 wt.%, preferably from 50 to 88 wt.% or from 70 to 85 wt.% of the composition (C1).
The non-electroactive inorganic filler material may be uniformly dispersed in the polymer matrix of composition (C1) to form pores having an average diameter of from 0.1 μm to 5 μm. The pore volume fraction of the composite separator obtained from the process of the invention is at least 25%, preferably at least 40%. The composite separator obtained from the process of the invention has a total thickness typically comprised between 2 μm and 100 μm, preferably between 2 μm and 40 μm.
The layer (L S) may be a non-porous substrate layer or a porous substrate layer if the substrate layer is a multi-layer substrate, the outer layer of the substrate may be a non-porous substrate layer or a porous substrate layer.
This layer (L S) typically has a porosity of advantageously at least 5%, preferably at least 10%, more preferably at least 20% or at least 40% and advantageously at most 90%, preferably at most 80%.
The thickness of the layer (L S) is not particularly limited and is typically from 3 to 100 microns, preferably from 5 to 50 microns.
The layer (L S) is advantageously a fabric made of one or more sets of polymer fibers.
For the purposes of the present invention, the term "fabric" is understood to mean a planar textile structure obtainable by interlacing one or more groups of polymeric fibers (creating a plurality of pores).
The fabric may be a woven fabric made from one or more sets of polymeric fibers or a nonwoven fabric made from one or more sets of polymeric fibers.
"woven fabric" is intended to mean a planar textile structure obtainable by: two or more sets of polymer fibers are interwoven at right angles to each other, thereby providing warp yarns extending longitudinally in the fabric and weft yarns extending transversely in the fabric. "nonwoven" is intended to mean a planar textile structure obtainable by mechanically, thermally or chemically randomly interlocking or bonding one or more sets of polymeric fibers (creating a multiplicity of pores).
The fabric may be a unidirectional fabric in which a majority of the polymeric fibers extend in one direction, or a multidirectional fabric in which two or more sets of continuous fibers extend in different directions.
The layer (L S) may be made of any porous substrate or fabric commonly used for separators in electrochemical devices, including at least one material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polyethylene and polypropylene, or mixtures thereof.
Preferably, the layer (L S) is polyethylene or polypropylene.
Weight and layer (S) of coatingC) Preferably from 3:1 to 0.5:1, more preferably 2:1, 1.5:1, 1:1 or 0.75: 1.
Preferably, step (iii) is performed by a technique selected from: casting, spraying, roll coating, knife coating, slot coating, gravure coating, inkjet printing, spin coating and screen printing, brush coating, roller brushing (squeegee), foam applicator, curtain coating, vacuum coating, rotating disc spraying.
Preferably, step (iv) is carried out at a temperature of less than 55 ℃, preferably less than 40 ℃, more preferably less than 30 ℃.
If the disclosure of any patent, patent application, and publication incorporated by reference herein conflicts with the description of the present application to the extent that the terminology may become unclear, the description shall take precedence.
The present invention will now be described in more detail with reference to the following examples, which are intended to be illustrative only and not to limit the scope of the present invention.
Experimental part
Materials and methods
PVDF 75130 powder: VDF-AA and VDF-HFP-AA random copolymers containing 2.3 mol.% HFP and 0.7 mol.% AA made in suspension polymerization were obtained from Solvay specialty Polymers Italy S.p.A..
PVDF XPH 884 latex: VDF-AA and VDF-HFP-AA random copolymers containing 2.8 mol.% HFP and 0.6 mol.% AA made in emulsion polymerization were obtained from solvay specialty polymers italy limited.
Solvents and reactants were purchased and used as received.
Synthesis of Polymer 1 (conforming to the general Structure B-A-B)
The final HFP content was 2.9 mol.%.
Phase 1 (A). In a 21 liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50rpm, 13.5 liters of deionized water were introduced. 6.6g of 1, 4-diiodoperfluorobutane (C) are then added4F8I2) As a chain transfer agent. The temperature was brought to 90 ℃ and the pressure was maintained constant at 20 bar (absolute) throughout the test by feeding VDF gaseous monomer. For each 250g of polymer synthesized, over a period of 5 minutes15ml of a 100g/l aqueous Ammonium Persulfate (APS) solution were added (200ml/h) and simultaneously 50ml of an Acrylic Acid (AA) solution (50g/l of acrylic acid in water) were fed.
After 30 minutes, the APS solution was fed at a flux rate of 240ml/h for the entire duration of the run. When 700g of VDF gaseous monomer was fed, the flow of VDF was interrupted, the reactor was cooled to room temperature and the pressure dropped to 12 bar.
Phase 2 (B). The latex was maintained in the reactor and the feed of the VDF/HFP gaseous mixture monomers was changed to a molar ratio of 95:5, respectively. The temperature was brought to 90 ℃ and a pressure of 35 bar was maintained.
Then, for every 250g of polymer synthesized, 50ml of Acrylic Acid (AA) solution (50g/l of acrylic acid in water) was fed and APS solution was fed at a flux rate of 350ml/h for the entire duration of the run.
When 3150g of the mixture was fed, the feed mixture was interrupted, the reactor was cooled to room temperature, vented and the latex recovered. The final reaction time was 150 min.
The block copolymer thus obtained contained 96.5% by moles of VDF, 2.9% by moles of HFP and 0.6% by moles of Acrylic Acid (AA) monomer.
The aqueous latex thus obtained had a solids content of 21.0% by weight.
The block copolymer was dispersed in the aqueous latex as particles having an average primary size of 230nm as measured according to ISO13321 and was found to have a melting point of 158.5 ℃ and a crystallization Δ H of 37.0J/g (determined according to ASTM D3418).
The block copolymer was recovered in powder form by freeze-thawing the latex, washing the powder in deionized water (10 times × 15L), and finally drying in a vented oven overnight at 80 ℃.
Synthesis of Polymer 2 (conforming to the general Structure A-B-A)
The final HFP content was 3.4 mol.%.
Phase 1 (B). In a 21 liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50rpm, 13.5 liters of deionized water were introduced. Then 6.6g were added1, 4-diiodoperfluorobutane (C)4F8I2) As chain transfer agent the temperature was brought to 90 ℃ and the pressure was maintained constant at 35 bar (abs.) throughout the test by feeding the VDF/HFP gaseous mixture monomers separately in a molar ratio of 95: 5. for each 250g of polymer synthesized, 250ml of 100g/l Ammonium Persulphate (APS) aqueous solution were added (1L/h) over a period of 15 minutes and 50ml of Acrylic Acid (AA) solution (50g/l acrylic acid in water) were fed at the same time.
After 30 minutes, the APS solution was fed at a flux rate of 240ml/h for the entire duration of the run. While 3150g of the VDF/HFP gaseous mixture monomer was fed, the flow of the monomer mixture was interrupted, the reactor was cooled to room temperature and vented.
Phase 2 (A). The latex was maintained in the reactor, and the feed of VDF gaseous monomer was varied. The temperature was brought to 90 ℃ and the pressure was brought up to 35 bar with VDF.
For every 250g of polymer synthesized, 50ml of Acrylic Acid (AA) solution (50g/l of acrylic acid in water) was fed and APS solution was fed at a flux rate of 240ml/h for the entire duration of the run.
When 900g of VDF monomer was fed, the feed was interrupted, the reactor was cooled to room temperature, vented and the latex recovered. The final reaction time was 121 min.
The block copolymer thus obtained contained 96.0% by mole of VDF, 3.4% by mole of HFP and 0.6% by mole of Acrylic Acid (AA) monomer.
The aqueous latex thus obtained had a solids content of 22% by weight.
The block copolymer was dispersed in the aqueous latex as particles having an average primary size of 310nm as measured according to ISO13321 and was found to have a melting point of 152.1 ℃ and a crystallization Δ H of 35.1J/g (determined according to ASTM D3418).
The block copolymer was recovered in powder form by freeze-thawing the latex, washing the washed powder in deionized water (10 times × 15L), and finally drying in a vented oven overnight at 80 ℃.
Synthesis of Polymer 3 (conforming to the general Structure B-A-B)
The final HFP content was 4.7 mol.%.
Phase 1 (A). In a 21 liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50rpm, 13.5 liters of deionized water were introduced. 6.6g of 1, 4-diiodoperfluorobutane (C) are then added4F8I2) As a chain transfer agent. The temperature was brought to 90 ℃ and the pressure was maintained constant at 20 bar (absolute) throughout the test by feeding VDF gaseous monomer. For every 250g of polymer synthesized, 15ml of 100g/l Ammonium Persulfate (APS) aqueous solution were added (200ml/h) over a period of 5 minutes and 50ml of Acrylic Acid (AA) solution (50g/l of acrylic acid in water) were simultaneously fed in.
After 30 minutes, the APS solution was fed at a flux rate of 240ml/h for the entire duration of the run. When 700g of VDF gaseous monomer was fed, the flow of VDF was interrupted, the reactor was cooled to room temperature and the pressure dropped to 12 bar.
Phase 2 (B). The latex was maintained in the reactor and the feed of the VDF/HFP gaseous mixture monomers was changed to a molar ratio of 92:8, respectively. The temperature was brought to 90 ℃ and a pressure of 35 bar was maintained.
Then, for every 250g of polymer synthesized, 50ml of Acrylic Acid (AA) solution (50g/l of acrylic acid in water) was fed and APS solution was fed at a flux rate of 350ml/h for the entire duration of the run.
When 3150g of the mixture was fed, the feed mixture was interrupted, the reactor was cooled to room temperature, vented and the latex recovered. The final reaction time was 161 min.
The block copolymer thus obtained contained 94.7% by moles of VDF, 4.7% by moles of HFP and 0.6% by moles of Acrylic Acid (AA) monomer.
The aqueous latex thus obtained had a solids content of 21.2% by weight.
The block copolymer was dispersed in the aqueous latex as particles having an average primary size of 231nm as measured according to ISO13321 and was found to have a melting point of 159.2 ℃ and a crystallization Δ H of 29.9J/g (determined according to ASTM D3418).
The block copolymer was recovered in powder form by freeze-thawing the latex, washing the powder in deionized water (10 times × 15L), and finally drying in a vented oven overnight at 80 ℃.
Synthesis of Polymer 4 (conforming to the general Structure A-B-A)
The final HFP content was 4.7 mol.%.
Phase 1 (B). In a 21 liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50rpm, 13.5 liters of deionized water were introduced. 6.6g of 1, 4-diiodoperfluorobutane (C) are then added4F8I2) As chain transfer agent the temperature was brought to 90 ℃ and the pressure was maintained constant at 35 bar (abs.) throughout the test by feeding the VDF/HFP gaseous mixture monomers separately in a molar ratio of 92: 8. for each 250g of polymer synthesized, 250ml of 100g/l Ammonium Persulphate (APS) aqueous solution were added (1L/h) over a period of 15 minutes and 50ml of Acrylic Acid (AA) solution (50g/l acrylic acid in water) were fed at the same time.
After 30 minutes, the APS solution was fed at a flux rate of 240ml/h for the entire duration of the run. While 3150g of the VDF/HFP gaseous mixture monomer was fed, the flow of the monomer mixture was interrupted, the reactor was cooled to room temperature and vented.
Phase 2 (A). The latex was maintained in the reactor, and the feed of VDF gaseous monomer was varied. The temperature was brought to 90 ℃ and the pressure was brought up to 35 bar with VDF.
For every 250g of polymer synthesized, 50ml of Acrylic Acid (AA) solution (50g/l of acrylic acid in water) was fed and APS solution was fed at a flux rate of 240ml/h for the entire duration of the run.
When 900g of VDF monomer was fed, the feed was interrupted, the reactor was cooled to room temperature, vented and the latex recovered. The final reaction time was 112 min.
The block copolymer thus obtained contained 94.7% by moles of VDF, 4.7% by moles of HFP and 0.6% by moles of Acrylic Acid (AA) monomer.
The aqueous latex thus obtained had a solids content of 22% by weight.
The block copolymer was dispersed in the aqueous latex as particles having an average primary size of 304nm as measured according to ISO13321 and was found to have a melting point of 150.9 ℃ and a crystallization Δ H of 31.8J/g (determined according to ASTM D3418).
The block copolymer was recovered in powder form by freeze-thawing the latex, washing the washed powder in deionized water (10 times × 15L), and finally drying in a vented oven overnight at 80 ℃
Characterization of the polymers prepared as described above is reported in table 1 below.
TABLE 1
Comparative
MV ═ melt viscosity
η intrinsic viscosity
The results provided in table 1 show that the copolymers according to the invention comprising alternating soft and hard blocks have a lower amount of insolubles than the random copolymer used as a comparison.
Thus, the copolymers according to the invention can be advantageously used for the preparation of pastes for lithium battery applications.
No difference in Melt Viscosity (MV) values was found to negatively affect the behaviour of the copolymer in such applications.
Example 1-swelling in electrolyte
The swelling behavior was evaluated by measuring the increase in weight of the molded samples of polymer 1 and polymer 2 after immersion in the carbonate mixture.
These samples were obtained by moulding a powder obtained from coagulated latex into a stainless steel frame with a flat press. The stainless steel frame was designed to obtain 5 round samples with a diameter of 25mm and a thickness of 1.5 mm. Polymer samples were obtained by melting the polymer at a temperature 60 ℃ above the melting temperature of the polymer and then cooling at room temperature.
Round polymer samples (Φ 25 mm; 1.5mm thick) were dried overnight at 55 ℃. Their dry weight and thickness were measured and then immersed in 1:1(wt.) EC (ethylene carbonate): DMC (dimethyl carbonate). The weight of these samples was measured periodically after immersion in the swelling agent until the plateau absorbance was reached.
The plateau values for the relative weight gain are summarized in table 1 below.
Example 2 Dry adhesion to cathode
The polyolefin separator was coated with a solution of DMA, TPG and PVDF (component ratio by weight: 9/9/1) by a doctor blade. After the coating step, the membranes were dried under vacuum at 70 ℃.
The separator was thus laminated, exposing the coated surface to the cathode electrode.
The cathode composition was as follows:
2 wt.% PVDF SO L EF(Polymer Binder)
3 wt.% carbon black, super C65 (electronic conductor) from England porcelain company (IMERYS)
95 wt.% nickel manganese cobalt oxide, L & F (cathode active material).
The porosity of the cathode was 40%.
The separator was laminated to the cathode surface using a hydraulic flat press (hydraulic flat press) under the following conditions of pressure, time and temperature: 1MPa, 15min and 85 ℃.
After lamination, peel tests were applied at 180 ° and at 300mm/min following astm d903 to evaluate the adhesive strength.
The results are summarized in table 2 below.
TABLE 2
Comparative
Polymer 1 and polymer 2 show an advantageous combination of dry lamination and swelling properties relative to the two comparative examples.
Polymer 1 and polymer 2 provided a substantially higher lamination strength than the comparative examples, and a lower or comparable swell value.
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