Abstract:

Li metal batteries (LMBs) have attracted worldwide attention in recent years with a focus on the extremely high theoretical energy density of 3580 Wh·kg^-1 (Li-O₂) and 2600 Wh·kg^-1 (Li-S), which benefit from the highest specific capacity (3860 mAh·g^-1) and the lowest negative potential (-3.04 V) of Li metal anodes. However, further development and practical applications are hindered by the formation of Li dendrites and a large volume expansion, which not only lowers the coulombic efficiency but also leads to many security risks, such as internal short circuits, fires, and even explosions. In this study, we selected a low-cost and commercial carbon fiber cloth (CC) as a 3D framework for accommodating Li metal and relieving the volume expansion during the Li plating/stripping process. In addition, lithiophilic SnS₂ nano-sheet arrays were grown on the surface of carbon fiber cloth via a one-step method. The SnS₂ arrays can be partially converted to Li-Sn alloy and Li₂S components during the Li plating process. The as-formed Li-Sn alloy can provide reversible sites for further Li deposition and improve the electrochemical kinetics process. As a typical component of the solid electrolyte interface (SEI), Li₂S can promote Li⁺ migration at SEI and ensure a homogeneous distribution of Li⁺-flux near the electrode surface, thereby reducing the overpotential of Li deposition and suppressing the formation and growth of Li dendrites. Meanwhile, the 3D carbon skeleton can also reduce the local current density of the electrode because of its high specific surface area to ensure uniform Li deposition. Benefiting from the design of the combination bulk and the surface, the composite SnS₂@carbon fiber cloth (SnS₂@CC) demonstrated excellent prospects for practical applications. Upon pairing with Li foils, the SnS₂@CC electrode displayed stable cycling performance with improved coulombic efficiency (> 98%) over 100 cycles at 1.0 mA·cm^-2/5.0 mAh·cm^-2. After loading 10 mAh·cm^-2 Li metal, the composite Li metal anode could run over 400 h with a low overpotential of 60 mV at a current density of 1.0 mA·cm^-2, even when the current density was increased to 2.0 mA·cm^-2; additionally, a low overpotential of 85 mV could also be maintained over 350 h, manifesting one of the most stable composite Li metal anodes to date. Moreover, when the composite Li metal anode was assembled with a LiFePO₄ cathode, the full cells exhibited a high initial specific discharge capacity of 160.6 mAh·g^-1 and high cycling stability. At a rate of 2.0C, the cell showed a high capacity retention of 80.6% after 500 cycles.We believe that the lithiophilic SnS₂@CC composite electrode offers a simple and effective strategy to suppress dendritic Li growth and relieve the volume change during the charging/discharging process.

Key words: Composite Li anode, Current collector, Lithium dendrite, Carbon fiber cloth, Li alloy