A reversible self-assembled molecular layer for lithium metal batteries with high energy/power densities at ultra-low temperatures

Abstract

Electrolytes for low temperature, high energy lithium metal batteries are expected to possess both fast Li+ transfer in the bulk electrolytes (low bulk resistance) and a fast Li+ de-solvation process at the electrode/electrolyte interface (low interfacial resistance). However, the nature of the solvent determines that the two always stand at either ends of the balance, and conventional electrolyte designs have to make a compromise to favor one at the expense of the other. Here, we address this irreconcilable dilemma using an “electric-field assisted self-assembly layer”, i.e. sodium perfluorooctanoate (NaPFO). Driven by the bias-potential, PFO anions dissolved in the electrolyte could reversibly self-assemble into a dense and ordered molecular layer at the cathode/electrolyte interface, which could protect the electrolyte from anodic degradation due to the high voltage and enable the stable cycling of LiNi0.8Mn0.1Co0.1O2 (NMC811) in ether-based electrolyte with an ultra-low freeing point. More importantly, the self-assembly of the PFO layer could aid the Li+ de-solvation behavior at the cathode/electrolyte interface, thus significantly lowering the interfacial resistance. Thus, with this reversible self-assembly layer on the cathode surface, low bulk resistance and low interfacial resistance are simultaneously achieved. Consequently, the tetrahydrofuran (THF)-based electrolyte containing NaPFO is applied to practical Li‖NMC811 pouch cells and achieves an unprecedented energy density of 122 W h kg−1 (except taps and packing foil, same hereafter) at −85 °C, the highest reported power density of 318 W kg−1 at a high current density of 4.1 mA cm−2 at −60 °C, and can be recharged with stable performance (175 W h kg−1 at 20th cycles) at −40 °C. This electric-field assisted self-assembly layer enables fine tuning of the micro-environment at the cathode–electrolyte interface, and provides a new design concept for the electrolyte of ultra-low temperature high voltage lithium-metal batteries.

Graphical abstract: A reversible self-assembled molecular layer for lithium metal batteries with high energy/power densities at ultra-low temperatures

Supplementary files

Article information

Article type
Paper
Submitted
22 Mar 2024
Accepted
20 May 2024
First published
22 May 2024

Energy Environ. Sci., 2024, Advance Article

A reversible self-assembled molecular layer for lithium metal batteries with high energy/power densities at ultra-low temperatures

W. Zhang, Y. Lu, Q. Cao, H. Liu, Q. Feng, P. Zhou, Y. Xia, W. Hou, S. Yan and K. Liu, Energy Environ. Sci., 2024, Advance Article , DOI: 10.1039/D4EE01298D

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