The bipolar plate, also known as the collector plate, is one of the important components of the fuel cell. It has the following functions and properties: separating fuel and oxidant, preventing gas from permeating; collecting and conducting electricity current, with high conductivity; designing and processing flow channels can evenly distribute gas to the reaction layer of the electrode for electrode reaction; can discharge heat , keep the battery temperature field uniform; corrosion resistance; shock and vibration resistance; thin thickness; light weight; at the same time, low cost, easy machining, suitable for mass production, etc.
The function of the bipolar plate (also known as the separator) is to provide a gas flow channel, prevent the hydrogen and oxygen in the cell gas chamber from mixing, and establish a current path between the series-connected cathode and anode. Maintaining a certain mechanical strength and good gas barrier effect, the thickness of the bipolar plate should be as thin as possible to reduce the conduction resistance to current and heat.
Bipolar plate materials can be roughly divided into three categories: carbon materials, metal materials and composite materials of metal and carbon.
(1) Carbon material. Carbonaceous materials include graphite, molded carbon materials, and expanded (flexible) graphite. Conventional bipolar plates use dense graphite that is machined to form gas flow channels. The graphite bipolar plate is chemically stable and has low contact resistance with the MEA.
(2) Metal materials. Metal materials such as aluminum, nickel, titanium, and stainless steel can be used to make bipolar plates. The metal bipolar plate is easy to process, can be manufactured in batches, has low cost, thin thickness, and has high volume specific power and specific energy of the battery.
(3) Composite materials. If the contacting resistance between the bipolar plate and the MEA is large, the polarization loss caused by the ohmic resistance is huge, and the operation efficiency is reduced. Among the commonly used bipolar plate materials, graphite material has the smallest contact resistance, and non-conductive oxide films are formed on the surface of stainless steel and titanium to increase the contact resistance.
Bipolar plates require proper surface treatment. The anode side of the bipolar plate has good electrical conductivity after nickel plating, and is not easily wetted by the electrolyte, which can avoid electrolyte loss. The flexible contact between the electrolyte separator and the bipolar plate outside the effective area of the electrode can effectively prevent the gas from leaking out, which is the so-called “wet sealing”. In order to reduce the corrosion of the stainless steel by molten carbonate at the “wet sealing” part, the bipolar plate frame needs to be “aluminized” to protect it.
There are several different processing methods for metal bipolar plate production, which can be made by CNC, stamping, laser, etching and other processes.
CNC machining: the processing cost is high, and some of the more precise wire grooves cannot meet the requirements;
Stamping: It is necessary to open a stamping die, and the cost is high. Once the design drawings are changed, the cost of re-opening the die is high;
Laser cutting: laser engraving cannot achieve half-engraving of bipolar plate, and the processing range is slightly single;
Bipolar plate etching: no hard tooling cost, no restrictions on design graphics, complex designs can also be processed and changed, low development costs. The etched bipolar plate has high precision, tight tolerance, full engraving, half engraving and adding LOGO will not be a problem.
KC has been engaged in metal etching for more than ten years. At present, our bipolar plate etching process has been matured and put into production. We have rich experience in metal bipolar plate etching and processing. The professional process team can assist customers in processing verification and solving design problems. It is our business philosophy to provide etching processing services and make high-quality products. For enquiries about bipolar plate etching, please contact us at [email protected]