Method for making improved separator plates for electrochemical cells

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.degree. C. to carbonize and then fully graphitize the plate, wherein the finished plate has an initial threshold corrosion potential measured at 400.degree. 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.degree. F. of at least 4,000 psi, and an electrolyte take-up no greater than 5.0 percent.