Enhancing the Stability of Lithium Metal Batteries with the Polydopamine-Coated Insulating Scaffold
Authors: Jo Jinhyeon , Eom Kwang Sup 
Published: December 2024

Lithium metal is the most promising candidate for a high-capacity anode material in Li-ion batteries owing to its high theoretical theoretical capacity (3,860 mAh g-1) and the lowest redox potential (-3.04 V vs S.H.E.).[1] Despite these advantages, the practical application of Li metal anodes (LMAs) is hindered by a number of significant challenges. For instance, LMAs tend to form non-uniform dendrite, continuous dead Li growth, and infinite volume expansion.[2] These issues result in short circuits and continuous consumption of the active material, consequently lowering the Coulombic efficiency (CE) and cycling stability of LMAs.
Using a 3D scaffold in the anode is an effective method for to address the issue of infinite volume expansion. The porous structure of the 3D scaffold provides ample space to accommodate Li metal.[3] Among them, electrically insulating scaffolds that do not support electron transport not only promote bottom-up Li deposition behavior but also minimize side reactions between the electrolyte and the scaffold. However, a high current density can lead to the formation of dendritic Li, which can make it challenging to achieve uniform and dense lithium growth on the surface during repeated plating/stripping processes. Therefore, the use of an insulating scaffold requires the introduction of functionalized materials to suppress dendritic formation of Li metal.
Furthermore, to achieve further improvements, some studies have investigated the incorporation of polar functional groups into the insulating 3D structure.[4] Notably, these polar functional groups possess the capability to establish strong interactions with Li ions, which can facilitate the uniform distribution of these ions and prevent dendrite formation.[5] In this study, we utilized polydopamine (PDA) which contains polar functional groups such as O-H and N-H2, on a 3D insulating scaffold. These polar functional groups promote increased ionic conductivity and uniform deposition of Li ions by interacting with Li ions through Columbic forces.[6] Consequently, we expected that the advantageous properties of PDA would enhance the charge transfer reaction rate and cycling stability of LMBs.
In this study, we aimed to introduce the utilization of a 3D polytetrafluoroethylene (PTFE) scaffold coated with PDA to achieve highly stable and high-energy LMBs. The insulating nature of the PTFE scaffold is expected to facilitate the "bottom-up" formation of Li deposition, while the PDA coating attracts Li ions, enabling homogenization of the Li-ion distribution and uniform growth of Li (Figure 1a). This design aims to simultaneously achieve both high energy density and improved cyclic stability in LMB full cells using our 3D scaffold.
To elucidate the enhanced performance of the Lithium Metal Batteries (LMBs) equipped with PDA-coated 3D PTFE scaffold (PD-3P), we conducted a comparative study, including bare Cu foil and the 3D PTFE scaffold (3P) as control groups. Specifically, when tested at a high current density of 1 C with a 3.2 mAh cm-2 NCM, the PD-3P scaffold-based full cell exhibited a stable discharge capacity (Figure 1b).

References

[1] S. Li, J. Huang, Y. Cui, S. Liu, Z. Chen, W. Huang, C. Li, R. Liu, R. Fu, D. Wu, Nature Nanotechnology
2022, 17, 613.
[2] D. Lin, Y. Liu, Y. Cui, Nature Nanotechnology
2017, 12, 194.
[3] S. Park, H.-J. Jin, Y. S. Yun, Advanced Materials
2020, 32, 2002193.
[4] Q. Ran, L. Wang, L. Li, Y. Zhao, Z. Lu, S. Chen, J. Zou, P. Chen, J. Gao, X. Niu, Chemical Engineering Journal
2021, 426, 130780.
[5] T.-Z. H. Xin-Bing Cheng , Rui Zhang , Hong-Jie Peng , Chen-Zi Zhao , Jia-Qi Huang , and Qiang Zhang *, Advanced Materials
2016.
[6] Y. Wang, L. Shi, H. Zhou, Z. Wang, R. Li, J. Zhu, Z. Qiu, Y. Zhao, M. Zhang, S. Yuan, Electrochimica Acta
2018, 259, 386.

Figure 1