Multi-physics-coupled corrosion of stainless steel positive current collectors in Li||Bi liquid metal batteries

The intrinsic three-layer liquid architecture of liquid metal batteries (LMBs) enables a simple cell configuration, high safety, low projected cost, and exceptional theoretical cycle life, making them a promising technology for grid-scale energy storage. However, under high-temperature and multi-physics operating conditions, the corrosion of the stainless steel positive current collector (PCC) by molten cathode metal and halide electrolyte limits long-term durability. A systematic evaluation of commercially available stainless steels under realistic electrochemical, thermal, and chemical conditions is therefore essential. Herein, we investigate the corrosion behaviors of four representative stainless steels (SS201, SS304, SS316, SS430) used as PCCs in Li|LiCl-LiF-LiBr|Bi liquid metal batteries through a two-stage approach combining high-temperature hanging-coupon screening and service-condition cell testing. The results reveal pronounced synergistic corrosion during battery operation, where the combined effects of molten Bi, molten salt electrolyte, and electrochemical polarization substantially accelerate PCC degradation compared to static exposure. Among the investigated materials, SS316 exhibits the highest corrosion resistance, enabling stable cycling without observable capacity decay over 100 cycles. By integrating corrosion resistance, electrochemical performance, and techno-economic considerations, this work establishes an engineering-oriented PCC selection framework and identifies SS316 as the optimal candidate for 200 Ah-scale LMBs, allowing thinner, lighter, and more cost-effective collector architectures. The elucidated corrosion mechanisms under coupled electrochemical, thermal, and flow conditions provide critical insights for the rational design of durable and commercially viable liquid metal batteries.