Composition for secondary battery electrodes
The present invention pertains to electrode-forming compositions, to the use of said electrode-forming compositions in a process for the manufacture of electrodes, to said electrodes and to electrochemical devices such as secondary batteries comprising said electrodes.
1. An electrode-forming composition (C) comprising:
a. at least one vinylidene fluoride (VDF) copolymer [polymer (A)] that comprises:
(i) recurring units derived from vinylidene fluoride (VDF);
(ii) recurring units derived from at least one hydroxyl group-containing vinyl monomer (HA);
(iii) recurring units derived from at least one carboxyl group-containing vinyl monomer (CA);
wherein a total amount of recurring units derived from monomer (HA) and recurring units derived from monomer (CA) in said polymer (A) is of at most 1.5% by moles, with respect to a total moles of recurring units of polymer (A); and wherein a fraction of at least 40% of recurring units derived from monomer (HA) and a fraction of at least 40% of recurring units derived from monomer (CA) are randomly distributed into said polymer (A);
b. at least one electro-active material (AM); and
c. at least one solvent(S).
2. The electrode-forming composition (C) according to claim 1 wherein the hydroxyl group-containing vinyl monomer (HA) is a compound of formula (I):
wherein:
R 1 , R 2 and R 3 , equal to or different from each other, are independently selected from a hydrogen atom, a halogen atom, and a C 1 -C 3 hydrocarbon group and R OH is a C 2 -C 10 hydrocarbon chain moiety comprising at least one hydroxyl group and optionally containing in the chain one or more oxygen atoms, carbonyl groups or carboxy groups.
3. The electrode-forming composition (C) according to claim 2 wherein monomer (HA) is a compound of formula (Ia):
wherein
R 1 , R 2 and R 3 , equal to or different from each other, are independently selected from a hydrogen atom and a C 1 -C 3 hydrocarbon group and R′ OH is a C 1 -C 5 hydrocarbon moiety comprising at least one hydroxyl group.
4. The electrode-forming composition (C) according to claim 3 wherein monomer (HA) of formula (Ia) is selected from the group consisting of
hydroxyethyl(meth)acrylate (HEA),
2-hydroxypropyl acrylate (HPA),
hydroxyethylhexyl(meth)acrylate,
and mixtures thereof.
5. The electrode-forming composition (C) according to claim 1 wherein the carboxyl group-containing vinyl monomer (CA) is a compound of formula (II):
wherein:
R 1 , R 2 and R 3 , equal to or different from each other, are independently selected from a hydrogen atom and a C 1 -C 3 hydrocarbon group and R H is a C 1 -C 10 hydrocarbon chain moiety comprising at least one carboxyl group.
6. The electrode-forming composition (C) according to claim 5 wherein monomer (CA) is a compound of formula (IIa):
wherein
R 1 , R 2 and R 3 , equal to or different from each other, are independently selected from a hydrogen atom and a C 1 -C 3 hydrocarbon group and R′ H is a hydrogen or C 1 -C 5 hydrocarbon moiety comprising at least one carboxyl group.
7. The electrode-forming composition (C) according to claim 6 wherein monomer (CA) of formula (IIa) is selected from the group consisting of acrylic acid (AA), (meth)acrylic acid and mixtures thereof.
8. The electrode-forming composition (C) according to claim 1 wherein a molar ratio between monomer (HA) and monomer (CA) in polymer (A) is in the range from 20:1 to 1:20.
9. The electrode-forming composition (C) according to claim 1 which further comprises recurring units derived from one or more fluorinated comonomers (CF) different from VDF.
10. The electrode-forming composition (C) according claim 1 comprising:
from 0.5% by weight to 10% by weight of polymer (A); and
from 80% by weight to 99% by weight, of the at least one electro active material (AM), wherein all percentages being weight percentages with respect to a total solid content of composition (C).
11. The electrode-forming composition (C) according to claim 1 further comprising at least one acid donor.
12. The electrode-forming composition (C) according to claim 1 wherein the composition is a positive electrode forming composition, wherein said at least one electro-active material (AM) is selected from lithium-containing complex metal oxides of general formula (III)
LiNi x M1 y M2 z Y 2 (III)
wherein M1 and M2 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 Y denotes a chalcogen.
13. A process for the manufacture of an electrode, said process comprising:
(i) providing a metal substrate having at least one surface;
(ii) providing an electrode-forming composition (C) according to claim 1 ;
(iii) applying the composition (C) provided in (ii) onto the at least one surface of the metal substrate provided in (i), thereby providing an assembly comprising a metal substrate coated with said composition (C) onto the at least one surface; and
(iv) drying the assembly provided in (iii).
14. An electrode obtained by the process according to claim 13 said electrode comprising:
a metal substrate, and
directly adhered onto at least one surface of said metal substrate, at least one layer consisting of a composition comprising:
(a) at least one vinylidene fluoride (VDF) copolymer [polymer (A)] that comprises:
(i) recurring units derived from vinylidene fluoride (VDF);
(ii) recurring units derived from at least one hydroxyl group-containing vinyl monomer (HA);
(iii) recurring units derived from at least one carboxyl group-containing vinyl monomer (CA);
wherein a total amount of recurring units derived from monomer (HA) and recurring units derived from monomer (CA) in said polymer (A) is of at most 10.0% by moles, with respect to a total moles of recurring units of polymer (A); and
wherein a fraction of at least 40% of recurring units derived from monomer (HA) and a fraction of at least 40% of recurring units derived from monomer (CA) are randomly distributed into said polymer (A); and
(b) at least one electro-active material (AM).
15. An electrochemical device comprising at least one electrode according to claim 14 .
16. The electrochemical device according to claim 15 , said electrochemical device being a secondary battery comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode.