Solvent-free electrochemical cells with conductive pressure sensitive adhesives attaching current collectors
Provided are electrochemical cells and methods of manufacturing these cells. An electrochemical cell comprises a positive electrode and an electrolyte layer, printed over the positive electrode. In some examples, each of the positive electrode, electrolyte layer, and negative electrode comprises an ionic liquid enabling ionic transfer. The negative electrode comprises a negative active material layer (e.g., comprising zinc), printed over and directly interfacing the electrolyte layer. The negative electrode also comprises a negative current collector (e.g., copper foil) and a conductive pressure sensitive adhesive layer. The conductive pressure sensitive adhesive layer is disposed between and adhered to, directly interfaces, and provides electronic conductivity between the negative active material layer and the negative current collector. In some examples, the conductive pressure sensitive adhesive layer comprises carbon and/or metal particles (e.g., nickel, copper, indium, and/or silver). Furthermore, the conductive pressure sensitive adhesive layer may comprise an acrylic polymer, encapsulating these particles.
1 . A method of fabricating an electrochemical cell, the method comprising:
printing a positive active material layer over a positive current collector;
printing an electrolyte layer over the positive active material layer, wherein the electrolyte layer includes a room temperature ionic liquid and a polymer;
printing a negative active material layer over the electrolyte layer;
laminating a negative current collector assembly over the negative active material layer with a pressure sensitive adhesive at a temperature of less than 80° C.; and
wherein the electrochemical cell produced thereby is solvent-free so as to contain less than 2.0 wt. % of organic solvents.
2 . The method of claim 1 , wherein:
the negative current collector assembly comprises a negative current collector and a conductive adhesive layer that includes the pressure sensitive adhesive; and
after laminating, the conductive adhesive layer directly interfaces and adheres to each of the negative active material layer and the negative current collector.
3 . The method of claim 2 , wherein the conductive adhesive layer comprises a polymer base and a conductive filler.
4 . The method of claim 3 , wherein particles of the conductive filler are encapsulated by the polymer base within the conductive adhesive layer.
5 . The method of claim 3 , wherein the conductive filler in the conductive adhesive layer has a concentration of less than about 50% by volume.
6 . The method of claim 3 , wherein the polymer base is an acrylic polymer or polyisobutylene (PIB).
7 . The method of claim 3 , wherein the conductive filler comprises at least one of carbon particles, nickel particles, copper particles, silver particles, indium particles, and bismuth particles.
8 . The method of claim 2 , wherein the conductive adhesive layer has a thickness of less than 100 micrometers.
9 . The method of claim 1 , wherein laminating the negative current collector assembly over the negative active material layer forms an electrical connection between the negative current collector and the negative active material layer.
10 . The method of claim 1 , wherein:
the electrochemical cell further comprises a first packaging layer and a second packaging layer, enclosing the positive current collector, the positive active material layer, the electrolyte layer, the negative active material layer, and the negative current collector assembly;
at least one of the first packaging layer and the second packaging layer is flexible and conforms to the positive current collector, the positive active material layer, the electrolyte layer, the negative active material layer, and the negative current collector assembly; and
the at least one of the first packaging layer and the second packaging layer is polyester.
11 . The method of claim 1 , wherein the positive current collector comprises one of graphite foil, foil made from carbon nanotubes, metal-plated fibers, metal foams, screens, extended metal structures, grids, and woven metal mesh.
12 . The method of claim 1 , wherein the positive current collector comprises one of graphite foil.
13 . The method of claim 1 , wherein the negative active material layer comprises zinc.
14 . The method of claim 1 , wherein the negative current collector assembly comprises copper.
15 . The method of claim 1 , wherein each of the positive active material layer, the electrolyte layer, and the negative active material layer comprises an ionic liquid.
16 . The method of claim 1 , wherein the negative current collector assembly is a printed layer, comprising a polymer binder and a conductive additive, selected from the group consisting of silver, brass, indium, carbon, nickel, and copper.
17 . The method of claim 1 , wherein printing the negative active material layer over the electrolyte layer is performed using screen printing or stencil printing.
18 . The method of claim 1 , wherein the negative active material layer has a smaller footprint than the electrolyte layer printed over the negative active material layer.
19 . The method of claim 1 , wherein the electrochemical cell produced thereby is solvent-free so as to contain less than 0.5 wt. % of organic solvents.