Karimi et al - Stable cycling of Si nanowire electrodes in fluorine-free cyano-based ionic liquid electrolytes enabled by vinylene carbonate as SEI-forming additive - Journal of Power Sources 558 (2023): 232621. - NANOTECHNOLOGY RESEARCH THE UNIVERSITY OF LIMERICK

Karimi et al – Stable cycling of Si nanowire electrodes in fluorine-free cyano-based ionic liquid electrolytes enabled by vinylene carbonate as SEI-forming additive – Journal of Power Sources 558 (2023): 232621.

March 22, 2023 – 11:22 am – Comments Off

Niyousha Karimi^a,b, Maider Zarrabeitia^a,b, Hugh Geaney^c, Kevin M. Ryan^c, Boyan Iliev^d, Thomas J. S. Schubert^d, Alberto Varzi^a,b and Stefano Passerini^a,b

^aHelmholtz Institute Ulm (HIU), Helmholtzstrasse 11, 89081, Ulm, Germany
^bKarlsruhe Institute of Technology (KIT), P.O. Box 3640, 76021, Karlsruhe, Germany
^cDepartment of Chemical Sciences and Bernal Institute, University of Limerick, Limerick, V94 T9PX, Ireland
^dIoLiTec-Ionic Liquids Technologies GmbH, Im Zukunftspark 9, 74076, Heilbronn, Germany
Corresponding Authors: alberto.varzi@kit.edu (A. Varzi), stefano.passerini@kit.edu (S. Passerini)

Received 4 July 2022; Received in revised form 22 December 2022; Accepted 28 December 2022
Link to Paper: https://www.sciencedirect.com/science/article/pii/S0378775322015981?via%3Dihub

^Highlights

• Cyano-based Ionic liquid (IL) electrolytes are studied with Si nanowire anodes.
• Vinylene carbonate (VC) is investigated as SEI forming additive.
• VC helps reducing IL decomposition and controlling SEI growth.
• The resulting SEI has a layered structure including inorganic and organic species.
• Si nanowire anodes deliver in such F-free electrolyte 1500 mAh g⁻¹ after 500 cycles.

^Abstract

Herein, the mixture of the fluorine-free cyano-based ionic liquid N-butyl-N-methylpyrrolidinium tricyanomethanide (Pyr₁₄TCM), lithium dicyanamide (LiDCA) (1:9 salt:IL mole ratio) and 5 wt% vinylene carbonate (VC) is proposed as an electrolyte for the stable electrochemical alloying of silicon nanowire (Si NW) anodes. Detailed electrochemical characterization of the electrolyte (long-term galvanostatic cycling and impedance tests of Si NW-Li half-cells) demonstrates a remarkable cycling performance of the Si anode delivering 1500 mAhg⁻¹ after 500 cycles with 99.5% Coulombic efficiency. The electrode/electrolyte interface is thoroughly investigated via scanning electron microscopy (SEM), energy dispersive X-ray (EDX) mapping, and X-ray photoelectron spectroscopy (XPS). The postmortem analysis reveals the key role of VC in controlling the IL decomposition, resulting in a bilayer solid electrolyte interphase (SEI) formation. The inner layer is mostly composed of graphitic carbon serving as a conductive coating for Si, and inorganic compounds such as Li₃N providing high Li-ion conductivity. The outer-layer, is rich in polymeric species ensuring the good mechanical stability and flexibility to withstand the extreme volume change of Si during de-/alloying process, thus explaining the observed prolonged cycling performance.
Keywords: Silicon anode, Fluorine-free, Ionic-liquid electrolyte, Vinylene carbonate (VC), Solid electrolyte interphase, Lithium batteries