Weldable and electrochemically stable composite of graphene and polyvinylidene fluoride as a current collector for promoting reversible lithium plating/stripping

Cu foils are physically heavy and chemically inappropriate for lithium metal rechargeable batteries with lithium-metal-free negatrode (LMFRBs). Physically light carbon-based current collectors (CBCCs) with high conductivity and strong resistance toward corrosion by air or electrolyte can replace Cu foil as a preferable deposition substrate for Li. However, welding problems, lithiation or electrolyte penetration-induced mechanical strength reduction, and lithiophobility-induced fragile SEI largely limit the application of CBCCs. In this work, we prepare lightweight graphene/polyvinylidene fluoride (PVDF) composite sheet via a coating and etching process to address the above issues. Cu tabs are bonded firmly to this CBCC with acceptable resistance, guaranteeing practical application. Tightly stacked graphene nanosheets mitigate lithiation and extra Li consumption (SEI), while PVDF as the binder reinforces the mechanical strength of CBCC by hindering the electrolyte penetration. Therefore, this composite CBCC satisfies the basic requirements i.e., sufficient conductivity and mechanical strength, and viable tab welding, needed for pouch cell application. In addition, as a film-forming polymer with a low Fermi level, PVDF helps form Li–F-rich and highly insulating SEI and suppresses electron transfer to the electrolyte, which induces uniform Li⁺ flux and alleviates electrolyte decomposition. The stable interface and robust SEI give rise to uniform and more reversible Li plating/stripping. The assembled LMFRB using this composite CBCC achieves remarkable capacity retention of 80% after ∼50 cycles with a high plating capacity of 4 mAh cm⁻².