High conductivity and low cost carbon composite hot pressed bipolar plate with gradient distribution of expanded graphite and polypropylene components

Abstract

(VRFB) is a leading energy storage technology due to its high safety and extended cycle life. As one of the cell stack key materials, the carbon-polymer composite hot pressed bipolar plate has a higher electric conductivity than the corresponding extruded bipolar plate because of the lower resin, which is favorable for the large scale high power density cell stack. The distribution of conductive carbon and resin significantly affects electrical conductivity, mechanical strength, and area specific resistance. Therefore, balancing these three factors has become a key research focus. This paper proposes a novel hot pressed bipolar plate with a gradient distribution of flexible conductive expanded graphite (EG) and polypropylene (PP), produced with multi-layer gradient structures via multi-pass compression molding. Replacing traditional PVDF resin with low-cost PP, the plate achieves a high electrical conductivity of 410.78 S/cm, flexural strength of 30.8 MPa, and an are specific resistance of 10.8 mΩ cm². At a current density of 200 mA/cm², the voltage and energy efficiencies of 83.07 % and 79.83 %, respectively. These findings demonstrate that multi-layer gradient structures effectively balance mechanical properties, electrical conductivity, and contact resistance at low cost, offering a new approach for bipolar plate material development.