Flexible battery

Abstract

The present invention pertains to a flexible electrode, to a process for the manufacture of said flexible electrode and to uses of said flexible electrode in electrochemical devices, in particular in secondary batteries.

Claims

1. An electrode (E) comprising: a current collector comprising, a polymer substrate and, adhered to said polymer substrate, an electrically conductive layer, wherein the electrically conductive layer is in the form of a foil, mesh, or net, and adhered to said electrically conductive layer of said current collector, at least one fluoropolymer layer comprising: at least one polymer (F), wherein polymer (F) is a fluoropolymer, at least one electro-active compound (EA), a liquid medium (L), wherein the medium (L) comprises at least one organic carbonate and, optionally, at least one ionic liquid, optionally, at least one metal salt (M), optionally, at least one conductive compound (C), and optionally, one or more additives; wherein the polymer substrate of the current collector comprises least one polymer selected from the group consisting of fluoropolymers; wherein the polymer substrate of the current collector comprises at least one polymer selected from the group consisting of partially fluorinated fluoropolymers comprising recurring units derived from: at least one per(halo)fluorinated monomer selected from the group consisting of tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE), at least one hydrogenated monomer selected from the group consisting of ethylene, propylene and isobutylene, and optionally, one or more additional monomers, in amounts of from 0.1% to 30% by moles, based on the total amount of TFE and/or CTFE and said hydrogenated monomer(s); wherein the polymer (F) is a partially fluorinated fluoropolymer comprising recurring units derived from vinylidene fluoride (VDF), at least one functional hydrogenated monomer comprising at least one carboxylic acid end group and, optionally, at least one fluorinated monomer different from VDF and wherein the functional hydrogenated monomer comprising at least one carboxylic acid end group is selected from the group consisting of (meth)acrylic monomers of formula (I): ##STR00019## wherein each of R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, is independently a hydrogen atom or a C1-C3 hydrocarbon group.

2. The electrode (E) according to claim 1, wherein the at least one metal salt (M) is present.

3. The electrode (E) according to claim 1 wherein the electrically conductive layer of the current collector comprises Carbon (C) or Silicon (Si) or at least one metal selected from the group consisting of Lithium (Li), Sodium (Na), Zinc (Zn), Magnesium (Mg), Copper (Cu), Aluminium (Al), Nickel (Ni), Titanium (Ti) and alloys thereof including, but not limited to, stainless steel.

4. The electrode (E) according to claim 1 wherein the amount of the medium (L) is at least 40% by weight based on the total weight of said medium (L) and the at least one polymer (F).

5. The electrode € according to claim 1, wherein the current collector consists of the polymer substrate and, adhered to said polymer substrate, the electrically conductive layer and the at least one fluoropolymer layer.

6. The electrode € according to claim 5, wherein the fluoropolymer layer consists of: the at least one polymer (F), the at least one compound (EA), the medium (L), optionally, the at least one salt (M), optionally, the at least one compound (C), and optionally, the one or more additives.

7. The electrode € according to claim 4, wherein the amount of medium (L) is at least 50% by weight, based on the total weight of said medium (L) and the at least one polymer (F).

8. The electrode (E) according to claim 4, wherein the amount of medium (L) is at least 60% by weight, based on the total weight of said medium (L) and the at least one polymer (F).

Description

EXAMPLE 1

(1) A pouch cell battery (34×36 mm) was manufactured by assembling the membrane as described hereinabove between the positive electrode and the negative electrode as described hereinabove.

(2) The battery was first charged at a C/20 rate, then discharged at a D/20 rate and successively run at C/10-D/10 rates.

(3) After the 4 cycles at a D/10 rate, the battery was bent on a tube of 7.5 mm external radio covering 50% of the radial surface for 30 seconds; when the applied stress was removed, the battery recovered the original planar form of the pouch cell.

(4) The battery continued to work regularly, as shown in Table 1, for 9 cycles. The battery was then again bent in the other direction. The battery continued cycling for 25 cycles, as shown in Table 1, by keeping substantially unmodified its capacity values.

(5) The average discharge capacity values of the battery so obtained are set forth in Table 1 here below:

(6) TABLE-US-00001 TABLE 1 Average Discharge Capacity Cycle No [mAh/g] [%] 1 80.2 100.0 2 72.1 89.9 3 69.7 86.9 4 69.0 86.0 5 80.1 99.9 6 79.6 99.3 9 78.2 97.5 10 77.8 97.0 12 79.3 98.9 25 72.6 90.5

EXAMPLE 2

(7) A pouch cell battery (34×36 mm) was manufactured by assembling the membrane as described hereinabove between the positive electrode and the negative electrode as described hereinabove.

(8) The battery was run at D/10 discharge rates.

(9) After 6 cycles, the battery was fixed and bent on a tube having an external diameter of 1.5 cm and then tested. The battery continued to work regularly, as shown in Table 2, for 5790 min (9 cycles) by keeping substantially unmodified its capacity values.

(10) After 14 cycles, the applied stress was removed and the battery recovered the original planar form of the pouch cell. The battery continued to work regularly.

(11) The average discharge capacity values of the battery so obtained are set forth in Table 2 here below:

(12) TABLE-US-00002 TABLE 2 Average Discharge Capacity Cycle No [mAh/g] [%] 1 99.4 100.0 3 98.9 99.5 6 94.5 95.1 7 61.7 62.1 10 66.2 66.6 14 67.5 67.9 15 82.9 83.4 18 83.9 84.4 25 83.4 83.9

COMPARATIVE EXAMPLE 1

(13) A pouch cell (36×36 mm) was manufactured by assembling the membrane as described hereinabove between a standard positive electrode (non-gel positive electrode) and a standard negative electrode (non-gel negative electrode).

(14) The non-gel electrodes were manufactured using a 12% by weight solution of polymer (F-B) in N-methyl 2-pyrrolidone (NMP).

(15) Negative electrode: graphite was added to the solution so obtained in a weight ratio of 96:4 (graphite/polymer (F-B)).

(16) Positive electrode: a composition comprising a blend of 50% by weight of C-NERGY® SUPER C65 carbon black and 50% by weight of VGCF® carbon fiber (CF) and LiFePO.sub.4 (LFP) was added to the solution so obtained in a weight ratio of 95.5:4.5 ((CF+LFP):polymer (F-B)). The CF/LFP weight ratio was 4:96.

(17) The solution mixture was screen printed onto a metal collector using a stencil screen with a thickness of 250 μm for the negative electrode and 350 μm for the positive electrode.

(18) NMP was evaporated by drying at 60° C. during one night and the electrodes so obtained were then calendered so as to provide a final thickness of 100 μm for the negative electrode and 112 μm for the positive electrode.

(19) The battery so obtained did not work. The pouch cell was sandwiched between two sheets of glass to ensure a better electrical contact between the layers but it still did not start to charge.

COMPARATIVE EXAMPLE 2

(20) The same procedure as detailed under Comparative Example 1 was followed but using a stencil screen with a thickness of 400 μm for the negative electrode. The negative electrode was dried at 50° C. for 30 min. The battery so obtained did not work.

(21) In view of the above, it has been found that the electrode of the invention successfully provides for electrochemical devices such as secondary batteries advantageously exhibiting outstanding electrochemical performances while ensuring outstanding mechanical resilience.