Design of three-dimensional CNT host with a lithiophilicity gradient for high-performance lithium metal batteries

Abstract

The electrification of automobiles is being pursued to achieve a carbon-neutral society, driving the demand for the development of batteries with higher power density and energy density. Among several materials, lithium metal is the most promising next-generation anode material due to its lowest reduction potential (-3.04 VSHE) in nature and approximately 10 times higher theoretical capacity (3860 mAh g-1) than the conventional graphite cathode. However, due to the dendritic growth of lithium metal, there are challenges in commercialization arising from issues related to lifespan performance and safety. 3D scaffold structures have the advantage of suppressing dendrite growth by providing a wide surface area for lithium deposition. However, they also have disadvantages, such as reduced gravimetric and volumetric capacity due to additional volume and weight. Moreover, Li deposition mostly occurs near the surface of the 3D current collectors (top surface deposition), and hence the inner volume and surface area of the 3D current collectors cannot be fully utilized during cycling. In this study, a lithiophilicity-gradient CNT 3D scaffold (Ag@CNT_G) was fabricated. By employing a pore-forming agent (NaCl) with a CNT slurry, we maintained both volumetric and gravimetric capacities through low host weight, narrow thickness, and high porosity. The lithiophilicity gradient was implemented through a facile double-casting process, effectively inhibiting the growth of lithium dendrites by inducing internal deposition of lithium, thus enhancing cycle capability. We confirmed that Ag@CNT_G guides the lithium to deposit inside of the 3D scaffold by SEM images. In symmetric cell tests, charge transfer resistance was measured lower in Ag@CNT_G (19.5 Ω) compared to the CNT 3D scaffold. Full-cell test was conducted in the voltage range of 3.0-4.2V (vs. Li/Li+), Ag@CNT_G showed much higher cycling capability (92% capacity retention after 50 cycles) compared to Cu foil.