Harrison Katharine L, Goriparti Subrahmanyam, Merrill Laura C, Long Daniel Martin, Warren Benjamin, Roberts Scott A, Perdue Brian R, Casias Zachary, Cuillier Paul, Boyce Brad L, Jungjohann Katherine L
ACS Appl Mater Interfaces. 2021 Jul 14;13(27):31668-31679. doi: 10.1021/acsami.1c06488. Epub 2021 Jun 28.
Lithium-metal anodes can theoretically enable 10× higher gravimetric capacity than conventional graphite anodes. However, Li-metal anode cycling has proven difficult due to porous and dendritic morphologies, extensive parasitic solid electrolyte interphase reactions, and formation of dead Li. We systematically investigate the effects of applied interfacial pressure on Li-metal anode cycling performance and morphology in the recently developed and highly efficient 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane electrolyte. We present cycling, morphology, and impedance data at a current density of 0.5 mA/cm and a capacity of 2 mAh/cm at applied interfacial pressures of 0, 0.01, 0.1, 1, and 10 MPa. Cryo-focused ion beam milling and cryo-scanning electron microscopy imaging in cross section reveal that increasing the applied pressure during Li deposition from 0 to 10 MPa leads to greater than a fivefold reduction in thickness (and therefore volume) of the deposited Li. This suggests that pressure during cycling can have a profound impact on the practical volumetric energy density for Li-metal anodes. A "goldilocks zone" of cell performance is observed at intermediate pressures of 0.1-1 MPa. Increasing pressure from 0 to 1 MPa generally improves cell-to-cell reproducibility, cycling stability, and Coulombic efficiency. However, the highest pressure (10 MPa) results in high cell overpotential and evidence of soft short circuits, which likely result from transport limitations associated with increased pressure causing local pore closure in the separator. All cells exhibit at least some signs of cycling instability after 50 cycles when cycled to 2 mAh/cm with thin 50 μm Li counter electrodes, though instability decreases with increasing pressure. In contrast, cells cycled to only 1 mAh/cm perform well for 50 cycles, indicating that capacity plays an important role in cycling stability.
锂金属阳极理论上能够实现比传统石墨阳极高10倍的比容量。然而，由于多孔和枝晶形态、广泛的寄生固体电解质界面反应以及死锂的形成，锂金属阳极的循环已被证明很困难。我们系统地研究了在最近开发的高效4 M双（氟磺酰）亚胺锂在1,2 - 二甲氧基乙烷电解质中，施加的界面压力对锂金属阳极循环性能和形态的影响。我们给出了在0、0.01、0.1、1和10 MPa的施加界面压力下，电流密度为0.5 mA/cm²和容量为2 mAh/cm²时的循环、形态和阻抗数据。低温聚焦离子束铣削和低温扫描电子显微镜横截面成像显示，在锂沉积过程中，将施加压力从0增加到10 MPa会导致沉积锂的厚度（进而体积）减少超过五倍。这表明循环过程中的压力对锂金属阳极的实际体积能量密度可能有深远影响。在0.1 - 1 MPa的中间压力下观察到电池性能的“ Goldilocks区”。从0增加到1 MPa的压力通常会提高电池间的重现性、循环稳定性和库仑效率。然而，最高压力（10 MPa）会导致高电池过电位和软短路迹象，这可能是由于与压力增加相关的传输限制导致隔膜局部孔隙闭合所致。当使用50 μm厚的锂对电极循环到2 mAh/cm²时，所有电池在50次循环后都至少表现出一些循环不稳定性迹象，不过不稳定性会随着压力增加而降低。相比之下，循环到仅1 mAh/cm²的电池在50次循环中表现良好，这表明容量在循环稳定性中起着重要作用。
