ELECTRODE FORMULATION FOR A LI-ION BATTERY AND METHOD FOR MANUFACTURING AN ELECTRODE WITHOUT SOLVENT
The present invention relates generally to the field of electrical energy storage in rechargeable secondary batteries of Li-ion type. More specifically, the invention relates to an electrode formulation for a Li-ion battery, comprising a binder based on a mixture of fluoropolymers. The invention also relates to a process for preparing electrodes using said formulation, by a technique of solvent-free deposition on a metal substrate. The invention relates finally to an electrode obtained by this process and also to Li-ion secondary batteries comprising at least one such electrode.
1 . A Li-ion battery electrode comprising an active filler for anode or cathode, an electronically conductive filler and a fluoropolymer binder, characterized in that said binder consists of a mixture consisting of:
a fluoropolymer A which comprises at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) having an HFP content greater than or equal to 3% by weight, and
a fluoropolymer B which comprises at least one VDF homopolymer and/or at least one VDF-HFP copolymer, said fluoropolymer B having a weight content of HFP which is at least 3% lower than the weight content of HFP of the polymer A.
2 . The electrode of claim 1 , wherein the HFP content in said at least one copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) of said fluoropolymer A is greater than or equal to 6% and less than or equal to 55% by weight.
3 . The electrode of claim 1 , wherein the fluoropolymer A consists of a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) having an HFP content of greater than or equal to 3%.
4 . The electrode of claim 1 , wherein the fluoropolymer A consists of a mixture of two or more copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), the HFP content of each copolymer being greater than or equal to 3%.
5 . The electrode of claim 1 , wherein the fluoropolymer B is a homopolymer of vinylidene fluoride.
6 . The electrode of claim 1 , wherein the fluoropolymer B consists of a VDF-HFP copolymer having an HFP content of between 1% and 10%.
7 . The electrode of claim 1 , wherein said mixture comprises:
i. a weight content of fluoropolymer A of greater than or equal to 1% and less than or equal to 20%, and
ii. a weight content of fluoropolymer B of less than or equal to 99% and greater than 80%.
8 . The electrode of claim 1 , wherein said active filler is selected from the group of lithium metal, graphite, silicon/carbon composites, silicon, graphene, fluorographites of CFx type where x is between 0 and 1 and titanates of LiTi 5 O 12 .
9 . The electrode of claim 1 , wherein said active filler is selected from the group of active materials of LiMO 2 type, LiMPO 4 type, Li 2 MPO 3 F type, Li 2 MSiO 4 type, where M is Co, Ni, Mn, Fe or a combination of these, LiMn 2 O 4 type and S 8 type.
10 . The electrode of claim 1 , wherein the conductive fillers are selected from carbon blacks, natural or synthetic graphites, carbon fibers, carbon nanotubes, metal fibers and powders, conductive metal oxides, and mixtures thereof.
11 . The electrode of claim 1 , having the following composition by weight:
50% to 99% of active filler,
0.05% to 25% of conductive filler,
0.05% to 25% of polymer binder,
0 to 5% of at least one additive selected from the list: plasticizer, ionic liquid, dispersant for the fillers, flow agent for the formulation, fibrillating agent,
the sum of all these percentages being 100%.
12 . A process for producing the Li-ion battery electrode of claim 1 , said process comprising the following steps:
mixing the active filler, the fluoropolymer binder and the electronically conductive filler by means of a process which makes it possible to obtain an electrode formulation that can be applied to a metal substrate by a solvent-free process;
depositing said electrode formulation on the metal substrate by a solvent-free process so as to obtain a Li-ion battery electrode, and
consolidating said electrode by a heat treatment and/or thermomechanical treatment.
13 . The process of claim 12 , wherein the mixing step is carried out in two stages:
mixing the electronically conductive filler and the fluoropolymer binder using a solvent-free process or by co-spraying, to obtain an intimate mixture, then
mixing the active filler with said intimate mixture using a solvent-free mixing process, to obtain an electrode formulation.
14 . The process of claim 12 , wherein said mixing step is carried out by a process selected from the group of: agitation, air-jet mixing, milling of the mixture, high-shear mixing, mixing with a V-mixer, mixing with a screw mixer, double-cone mixing, drum mixing, conical mixing, double Z-arm mixing, mixing in a fluidized bed, in a planetary mixer, extrusion, calendering, or mechanofusion.
15 . The process of claim 12 , wherein said solvent-free process is carried out by depositing the electrode formulation on the metal substrate by a process selected from the following processes: pneumatic spraying, electrostatic spraying, dipping in a fluidized powder bed, dusting, electrostatic transfer, deposition with rotary brushes, deposition with rotary metering rolls, and calendering.
16 . The process of claim 12 , wherein said solvent-free process is carried out in two steps: a first step which comprises producing a self-supporting film from the electrode formulation, and a second step in which the self-supporting film is assembled with the metal substrate.
17 . The process of claim 12 , wherein the consolidation of said electrode is carried out by at least one heat treatment selected from the group of passing through an oven, under an infrared lamp and through a calender with heated rolls.
18 . A secondary Li-ion battery comprising an anode, a cathode and a separator, wherein at least one of the anode or cathode comprises the composition of claim 1 .