Method for making improved separator plates for electrochemical cells

Claim 1

In a method for making a thin electrochemical cell separator plate the steps of: molding, to substantially the desired size of said plate, a well blended mixture of high purity graphite powder and a carbonizable thermosetting phenolic resin in a proportion 45-65 parts by weight graphite and 55-35 parts by weight resin, said molding being done at pressures and temperatures which melt and partially cure the resin and produce material flow such that a density of 97-99 percent of the maximum theoretical density is obtained, said graphite powder consisting of substantially 100% fully graphitic particles having a density of at least 2.0 gm/cc, an average aspect ratio of less than about 0.40, and a distribution of particle sizes up to a maximum of about 230 microns, with between 31 to 62 weight percent of the particles having a size less than 45 microns, and said resin having a carbon yield of at least 50%, and heat treating the molded plate to a temperature of at least 2100° C. to carbonize and then fully graphitize the plate, wherein the finished plate has an initial threshold corrosion potential measured at 400° F. of at least 1,000 millivolts, a maximum initial thru-plane electrical resistivity of 0.009 ohm-cm, an initial flexural strength measured at 400° F. of at least 4,000 psi, and an electrolyte take-up no greater than 5.0 percent.

Claim 4

The method according to claims 1 or 2 wherein the molded plate is heat treated to a temperature of 2800° C.

Claim 5

The method according to claims 1 or 2 wherein said mixture of high purity graphite powder and carbonizable thermosetting phenolic resin comprises 50-60 parts by weight graphite and 50-40 parts by weight resin, and said graphite powder in said mixture has a particle size distribution wherein 35-50 weight percent of the particles are less than 45 microns, 19-52 weight percent are between 45-100 microns, 5-30 weight percent are between 100-150 microns, less than 12 weight percent are greater than 150 microns, less than 5 weight percent are greater than 200 microns, and less than 0.5 weight percent are greater than 230 microns.