Wu Jing, Tian Liliang, Duan Humin, Cheng Yonghong, Shi Le
State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
ACS Appl Mater Interfaces. 2021 Oct 6;13(39):46821-46829. doi: 10.1021/acsami.1c14950. Epub 2021 Sep 22.
The practical application of lithium-/sodium-metal batteries is currently hindered by severe safety issues caused by uncontrolled continuous dendrite growth. Semiconductive nanoporous g-CN film has been demonstrated to be an effective protection layer for lithium-/sodium-metal anode, which can suppress the growth of dendrite. However, the underlying mechanism of how this semiconductive flexible thin film works to suppress dendrite growth remains unclear. In this work, we investigate the detailed working mechanism of g-CN protection layer employing both density functional theory calculations and ab initio molecular dynamics simulations. The calculation results indicate that g-CN layers show strong adhesion toward the lithium-/sodium-metal surface. When contacting with lithium/sodium metal, the intrinsic triangular nanopores of g-CN will be quickly filled with lithium/sodium atoms, turning the semiconductive g-CN into a metallic material. Lithium/sodium atoms can migrate through the triangular nanopores of stacked g-CN layers via a vacancy-mediated approach with moderate energy barriers of 0.42 and 0.61 eV, respectively. With a low current density, the newly deposited lithium/sodium atoms can permeate through the g-CN protection layers, therefore resulting in a flat electrode surface with no dendrite; with a high current density, however, the newly deposited lithium/sodium atoms cannot transport across the protection layer timely, which will result in the aggregation of lithium/sodium atoms on the surface of the g-CN protection layer.
锂/钠金属电池的实际应用目前受到不受控制的连续枝晶生长所导致的严重安全问题的阻碍。半导体纳米多孔g-CN薄膜已被证明是锂/钠金属负极的有效保护层，它可以抑制枝晶的生长。然而，这种半导体柔性薄膜如何抑制枝晶生长的潜在机制仍不清楚。在这项工作中，我们采用密度泛函理论计算和从头算分子动力学模拟来研究g-CN保护层的详细工作机制。计算结果表明，g-CN层对锂/钠金属表面表现出很强的附着力。当与锂/钠金属接触时，g-CN固有的三角形纳米孔会迅速被锂/钠原子填满，使半导体g-CN变成金属材料。锂/钠原子可以通过空位介导的方式穿过堆叠的g-CN层的三角形纳米孔，其能量势垒分别为0.42和0.61 eV。在低电流密度下，新沉积的锂/钠原子可以渗透过g-CN保护层，从而使电极表面平整无枝晶；然而，在高电流密度下，新沉积的锂/钠原子不能及时穿过保护层，这将导致锂/钠原子在g-CN保护层表面聚集。
