A novel array current collector design enabling high energy efficiency liquid metal batteries

•Novel array current collector configuration is designed for LMBs.•The system achieves ultra-high energy efficiency.•In-situ observation reveals the nucleation and growth process of discharge products.•More efficient contact modes and mass transfer interfaces. Liquid metal battery (LMB) is one of the most competitive large-scale energy storage technologies due to its low-cost, long-lifespan, and high-safety. However, the low energy efficiency of the battery is currently one of the major challenges hindering its application process. The problem of poor wettability of the cathode liquid alloy is exacerbated by the design of the conventional planar structure of the positive collector. And the resulting interfacial mass transfer modes are inefficient. These lead to slow electrode reaction kinetics and large internal polarization. To address this issue, a novel array current collector suitable for LMB was designed here for the first time. The unique structure of the collector greatly increases the effective reaction area at the electrolyte/cathode and the contact area of the cathode/collector, providing more efficient nucleation and growth modes of the products as well as richer ionic mass-transfer channels, thus accelerating the electrode reaction kinetics. Benefiting from the application of the array current collector, the voltage efficiency of Li||Sb-Sn LMBs with a capacity of 20 Ah at 0.5C rate is increased by 4.8 %. Meanwhile, an average voltage efficiency of ∼ 94.7 % and an average energy efficiency of ∼ 92.2 % are achieved at 0.1C, which is the highest efficiency among the most promising LMB systems known to date. These encouraging results provide new directions for the design of high-performance LMBs and further promote the practical process of LMBs.