Self-assembly of coatings utilizing surface charge
An apparatus and method for measuring the isoelectric pH for materials deposited on or otherwise affixed onto and in contact with an electrode surface, and a method for utilizing the isoelectric pH to form nanometer thickness, self-assembled layers on the material, are described. Forming such layers utilizing information obtained about the isoelectric pH values of the substrate and the coating is advantageous since the growth of the coating is self-limiting because once the surface charge has been neutralized there is no longer a driving force for the solid electrolyte coating thickness to increase, and uniform coatings without pinhole defects will be produced because a local driving force for assembly will exist if any bare electrode material is exposed to the solution. The present self-assembly procedure, when combined with electrodeposition, may be used to increase the coating thickness. Self-assembly, with or without additional electrodeposition, allows intimate contact between the anode, electrolyte and cathode which is required for successful application to solid-state batteries, as an example.
1. A method for producing an electrode having AlPO 4 coating material thereon, comprising the steps of:
electrodepositing a Cu 2 Sb substrate onto a current collector;
preparing a solution of precursors of the AlPO 4 coating material;
adjusting the pH of the solution to between the isoelectric pH of the substrate and the isoelectric pH of the coating material;
immersing the substrate in the solution for a time sufficient for self-assembly of the coating material onto the substrate;
whereby an electrically insulating and ionically conducting coating is formed on the substrate; and
increasing the thickness of the self-assembled AlPO 4 on the Cu 2 Sb by electrophoretic deposition of additional AlPO 4 onto the self-assembled AlPO 4 at a positive voltage relative to open circuit potential.
2. The method of claim 1 , wherein the pH of the solution is approximately the average of the isoelectric pH of the substrate and the isoelectric pH of the coating material.
3. The method of claim 1 , wherein said Cu 2 Sb is electroplated onto a copper current collector.
4. The method of claim 1 , wherein the solution of the coating material for said electrophoretic deposition is the same solution used for said self-assembly of said coating material.