For rechargeable battery technologies Li metal could be the ideal anode, due to its negative redox potential (-3.04 V vs. SHE), high specific capacity (3860 mAh g⁻¹), and low density (0.534 g cm⁻³) [1-4]. Recent advances show a new design concept where there are no initial active materials in the anode (no carbon, Si, or Li metals) and all the Li is coming directly from the cathode during charging. This resulted in important practical advantages such as enhanced volumetric and gravimetric energy densities, ease of manufacturing and reduced complexity/safety concerns of the recycling process (ideally Li is completely removed in the discharged state). However, the applicability of the Li-metal battery is constrained by the nonuniform lithium deposition, accompanied by dendrite growth and the formation of dead lithium fractions during long-term cycling, which lead to low Coulombic efficiencies and even cell failures [2]. Key approaches for solving these issues could be categorized as, (i) the formation of a stable solid electrolyte interface (SEI) by optimizing the electrolyte, (ii) modification of the current collector (CC) on the anode side, on which the lithium deposition/dissolution process takes place, (iii) cycling protocol modifications [3, 5]. A perfectly smooth surface of the CC will result in an evenly distributed electric field throughout the whole electrode, which ensures a homogeneous lithium deposition [2]. Furthermore, to obtain a lower overpotential and provide better-controlled reactions during the deposition/dissolution of lithium, one strategy is to increase the surface area of the substrate to lower the localized current densities [2].

This contribution will discuss various materials and their modifications e.g. smooth surfaces and porous structures, and how they benefit the lithium electrochemical deposition/dissolution. Surface morphology and roughness of the flat substrates are shown in Figure 1 a – d and porous structures in Figure 1 e– g were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Lithium electrodeposition, including the phase formation mechanism and the kinetic and thermodynamic phenomenon aspects during the initial stages of the process were studied by classical electrochemical methods and electrochemical quartz crystal microbalance (EQCM). Coulombic efficiency, cycling capabilities, and potential profiles of the materials were evaluated and reviewed (Figure 2). Moreover, the temperature effect on the above parameters in long-term cycling experiments will be discussed.

References:

[1] Cheng, Xin-Bing; Zhang, Rui; Zhao, Chen-Zi; Zhang, Qiang (2017): Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. In Chemical reviews 117 (15), pp. 10403–10473. DOI: 10.1021/acs.chemrev.7b00115.

[2] Cui, Jiecheng; Zhan, Tian-Guang; Zhang, Kang-Da; Chen, Dong (2017): The recent advances in constructing designed electrode in lithium metal batteries. In Chinese Chemical Letters 28 (12), pp. 2171–2179. DOI: 10.1016/j.cclet.2017.11.039.

[3] Hu, Zhongliang; Li, Jingying; Zhang, Xiaojing; Zhu, Yirong (2020): Strategies to Improve the Performance of Li Metal Anode for Rechargeable Batteries. In Frontiers in chemistry 8, p. 409. DOI: 10.3389/fchem.2020.00409.

[4] Xu, Wu; Wang, Jiulin; Ding, Fei; Chen, Xilin; Nasybulin, Eduard; Zhang, Yaohui; Zhang, Ji-Guang (2014): Lithium metal anodes for rechargeable batteries. In Energy Environ. Sci. 7 (2), pp. 513–537. DOI: 10.1039/C3EE40795K.

[5] Heubner, Christian, et al. "From Lithium‐Metal toward Anode‐Free Solid‐State Batteries: Current Developments, Issues, and Challenges." Advanced Functional Materials 31.51 (2021): 2106608.