Ultra-Thin Li Metal Anode for All-Solid-State Batteries

Abstract

All-solid-state lithium metal batteries are considered next-generation lithium-ion batteries that surpass the limits of conventional lithium-ion batteries owing to their ability to simultaneously reduce the risk of flammability and achieve high energy densities. Theoretically, a zero-excess Li configuration, in which the negative electrode comprises only a current collector, can achieve the highest energy density. However, low Coulombic efficiency and performance degradation caused by non-uniform plating are inevitable in this configuration. In contrast, thin-film Li metal anodes are advantageous owing to their potential to maintain the excess amount as low as possible and minimize the reduction in energy density. In this study, we report on the characteristics of thin-film Li metal anodes prepared by vacuum deposition in all-solid-state batteries. The thickness of the deposited Li metal anodes was 5 µm for the ultra-thin (UT-Li) and 23 µm for the thin (T-Li). The T-Li exhibited higher active Li utilization (98 %) and a more stable cycle life of over 2000 h, whereas the critical current density was high for UT-Li (2.5 mA cm⁻²). The differences in these properties can be explained by the microstructure of the vacuum-deposited Li metal anode surface and the mechanical properties of the anode. Domain size and crystal orientation are important factors, as they can be controlled by the vacuum deposition technique used in industrial production, making them useful for the practical application of Li metal anodes.