Exploring the Impact of Mechanical Pressure on the Performance of Anode-Free Lithium Metal Cells

By A. Louli, M. Genovese, Rochelle Weber, Samuel Hames, E. Logan, J. Dahn. Journal of the Electrochemical Society, 2019

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In the pursuit of surpassing the energy density of conventional lithium ion cells, significant efforts have been made to develop lithium metal cells. However, many reports in the literature utilize Li-metal cells with significant excess lithium, resulting in a dramatically reduced practical energy density. In contrast, anode-free cells do not utilize excess lithium; instead, a lithium metal anode is formed in-situ from the stored lithium within the positive electrode during the first charge. Here, we evaluate anode-free lithium metal pouch cells (NMC532||Cu) with operando pressure measurements constrained to different stack pressures between 75–2205 kPa with two different electrolytes, 1M LiPF 6 FEC:DEC (1:2) and 1M LiPF 6 FEC:TFEC (1:2). Increasing the initial average pressure from 75–2200 kPa was found to generally improve cycle life, with the most significant benefits achieved up to 1200 kPa. Cells containing FEC:TFEC electrolyte exhibited a superior initial performance compared to FEC:DEC cells, as evidenced by cycling data and SEM analysis of the lithium morphology. Although generally beneficial, we found that the effect of increased pressure on the performance of cells with different solvent systems was not equal, indicating that the physical properties of electrolyte play an important roll in cells constrained to higher pressures between 1200–2200 kPa. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative In this present work, we study the performance of anode-free (NMC532||Cu) Li-metal pouch cells with lean liquid electrolyte ( ∼ 3 g/Ah) using two different fluorinated solvent chemistries while constrained to increasing mechanical pressures. Instead of the conven- tional carbonate solvent blend ethylene carbonate:dimethyl carbonate (EC:DEC) used in Li-ion electrolytes, we employ modified fluori- nated analogs of to increase the cycling stability of anode-free cells. in two while physically constrained to pressures between kPa, and operando pressure measurements were performed to monitor the ir- reversible expansion of the lithium metal anode during cycling. The performance of anode-free cells as a function of applied pressure were evaluated by capacity retention, polarization growth and operando pressure measurements, and the lithium morphology was evaluated with scanning electron microscopy. We show here how the performance of anode-free cells depends strongly on the applied pressure and choice of electrolyte, and how these parameters are coupled.

Subfields: Automotive Engineering, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/deba4d04e7d724174d3fec257271cacbdbc4a2bb

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