Seeding and Growing Plain Li-Metal Surfaces - New Approaches to Increase the Coulombic Efficiency of Anodeless Lithium-Metal Batteries
Authors: Lieb Luca , Furtmair Michael , Hawe Philipp , Wolters Anika , Thannhuber Markus , Ruhl Günther , Sternad Michael 
Published: August 2024

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 (N2, O2, H2O) 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 (P2O5) in sealed steel-containers and c) inside an argon filled glovebox (< 0.1 ppm H2O, < 0.1 ppm O2). As a result, a strong sensitivity of operating Li-metal cells not solely versus traces of ambient, humid air, but also versus P2O5-dried nitrogen and oxygen was obvious.

Reference
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Figure 1