Seeding and Growing Plain Li-Metal Surfaces - New Approaches to Increase the Coulombic Efficiency of Anodeless Lithium-Metal Batteries

In the pursuit of higher energy densities, lithium-ion batteries with lithium metal anode appear as one particular promising technology. Especially the option to plate non-dendritic, superficially even Li-layers 1 directly onto the current collector of the negative electrode without the use of an anode active material (“anode-less battery design”) should enable gravimetric energy densities of up to 400 Wh/kg 2 and 1200 Wh/l 3 in future cell systems 4. In the presented work, Swagelok-cells in “anode-less” configuration, comprising a NMC 811-cathode and an ether-based electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1,2-dimethoxyethane (DME) in 1.2:3 molar ratio, 1.5 M LiFSI 2 were cycled under the application of pressure (up to 400 kPa) onto the cell stack. As the proper formation of Li-nuclei (number, morphology, etc.) and the even growth of lithium-layers onto the Cu-based anode (Figure 1) seems from great importance to plate and stripe Li-metal at high coulombic efficiencies, several charging programs with presumably Li-nucleation promoting effects were tested in a cycling experiment along 50 full cycles (Figure 2). As a promising result and as clear improvement compared to standard charging processes (e.g. 0.1 C), average coulombic efficiencies as high as 99.2 % together with low capacity fading were observed. Due to the design-related limitation of Swagelok-based cells and a noticeable diffusion of air fractions (N 2 , O 2 , H 2 O) across the PFA-seals into the cell, in a second experimental part the influence of ambient air on the cycling performance was tested under three conditions (Figure 2, left, middle and right diagram): a) Cells cycling in common (humid), laboratory air, b) under dry air (P 2 O 5 ) in sealed steel-containers and c) inside an argon filled glovebox (< 0.1 ppm H 2 O, < 0.1 ppm O 2 ). As a result, a strong sensitivity of operating Li-metal cells not solely versus traces of ambient, humid air, but also versus P 2 O 5 -dried nitrogen and oxygen was obvious. Reference s 1 Fang, C.; Lu, B.; Pawar, G.; Zhang, M.; Cheng, D.; Chen, S.; Ceja, M.; Doux, J.-M.; Musrock, H.; Cai, M.; Liaw, B.; Meng, Y. S., Pressure-tailored lithium deposition and dissolution in lithium metal batteries. Nature Energy 2021, 6, (10), 987-994. 2 Niu, C.; Liu, D.; Lochala, J. A.; Anderson, C. S.; Cao, X.; Gross, M. E.; Xu, W.; Zhang, J.-G.; Whittingham, M. S.; Xiao, J.; Liu, J., Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. Nature Energy 2021, 6, (7), 723-732. 3 Louli, A. J.; Eldesoky, A.; Weber, R.; Genovese, M.; Coon, M.; deGooyer, J.; Deng, Z.; White, R. T.; Lee, J.; Rodgers, T.; Petibon, R.; Hy, S.; Cheng, S. J. H.; Dahn, J. R., Diagnosing and correcting anode-free cell failure via electrolyte and morphological analysis. Nature Energy 2020, 5, (9), 693-702. 4 Li, Q.; Yang, Y.; Yu, X.; Li, H., A 700 W⋅h⋅kg−1 Rechargeable Pouch Type Lithium Battery. Chinese Physics Letters 2023, 40, (4), 048201. Figure 1