Hwang Chihyun, Song Woo-Jin, Song Gyujin, Wu Yutong, Lee Sangyeop, Son Hye Bin, Kim Jonghak, Liu Nian, Park Soojin, Song Hyun-Kon
School of Energy & Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Korea.
School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
ACS Appl Mater Interfaces. 2020 Jul 1;12(26):29235-29241. doi: 10.1021/acsami.0c05065. Epub 2020 Jun 23.
Lithium metal has been considered as an anode material to improve energy densities of lithium chemistry-based rechargeable batteries (that is to say, lithium metal batteries or LMBs). Higher capacities and cell voltages are ensured by replacing practically used anode materials such as graphite with lithium metal. However, lithium metal as the LMB anode material has been challenged by its dendritic growth, electrolyte decomposition on its fresh surface, and its serious volumetric change. To address the problems of lithium metal anodes, herein, we guided and facilitated lithium ion transport along a spontaneously polarized and highly dielectric material. A three-dimensional web of nanodiameter fibers of ferroelectric beta-phase polyvinylidene fluoride (beta-PVDF) was loaded on a copper foil by electrospinning (PVDF#Cu). The electric field applied between the nozzle and target copper foil forced the dipoles of PVDF to be oriented centro-asymmetrically and then the beta structure induced ferroelectric polarization. Three-fold benefits of the ferroelectric nano-web architecture guaranteed the plating/stripping reversibility especially at high rates: (1) three-dimensional scaffold to accommodate the volume change of lithium metal during plating and stripping, (2) electrolyte channels between fibers to allow lithium ions to move, and (3) ferroelectrically polarized or negatively charged surface of beta-PVDF fibers to encourage lithium ion hopping along the surface. Resultantly, the beta-PVDF web architecture drove dense and integrated growth of lithium metal within its structure. The kinetic benefit expected from the ferroelectric lithium ion transport of beta-PVDF as well as the porous architecture of PVDF#Cu was realized in a cell of LFP as a cathode and lithium-plated PVDF#Cu as an anode. Excellent plating/stripping reversibility along repeated cycles was successfully demonstrated in the cell even at a high current such as 2.3 mA cm, which was not obtained by the nonferroelectric polymer layer.
锂金属一直被视为一种负极材料，用于提高基于锂化学的可充电电池（即锂金属电池或LMBs）的能量密度。用锂金属替代实际使用的负极材料（如石墨）可确保更高的容量和电池电压。然而，锂金属作为LMB负极材料面临着枝晶生长、新鲜表面上的电解质分解以及严重的体积变化等挑战。为了解决锂金属负极的问题，在此，我们引导并促进锂离子沿着一种自发极化且高介电的材料传输。通过静电纺丝将铁电β相聚偏二氟乙烯（β-PVDF）的纳米直径纤维的三维网络负载在铜箔上（PVDF#Cu）。施加在喷嘴和目标铜箔之间的电场迫使PVDF的偶极中心不对称取向，然后β结构诱导铁电极化。铁电纳米网络结构的三重优势保证了尤其在高电流密度下的镀锂/脱锂可逆性：（1）三维支架以适应锂金属在镀锂和脱锂过程中的体积变化，（2）纤维之间的电解质通道以允许锂离子移动，（3）β-PVDF纤维的铁电极化或带负电的表面以促进锂离子沿表面跳跃。结果，β-PVDF网络结构促使锂金属在其结构内致密且整合地生长。在以磷酸铁锂为正极、镀锂的PVDF#Cu为负极的电池中实现了β-PVDF铁电锂离子传输以及PVDF#Cu的多孔结构所预期的动力学优势。即使在2.3 mA cm等大电流下，该电池也成功展示了沿重复循环的优异镀锂/脱锂可逆性，这是由非铁电聚合物层无法实现的。
