Electrode and Electrolyte Materials for Thin Film Microbatteries

O'Donoghue, Aaron

Electrode and Electrolyte Materials for Thin Film Microbatteries,

Aaron O’Donoghue, Louise McGrath, Ian Povey and James Rohan

In this work we assess the electrochemical performance of electrodeposited, binder-free V₂O₅ thin films with Li metal anodes in liquid and polymer gel electrolytes based on a pyrrolidinium based ionic liquid (C₄mpyrTFSI). Coulombic efficiencies >99%, with electrode capacities >120 mAh g^-1 are obtained in cyclic voltammetry analysis of crystalline V₂O₅ with C₄mpyr-based Ionic liquid (IL) electrolytes. A polymer gel electrolyte suited to layer by layer microbattery fabrication was synthesised and tested with the crystalline V₂O₅ and gave large electrode capacities at a relatively high rate (110 mAh g^-1 at 2 C) similar to those obtained in liquid electrolytes. Stable long-term cycling (up to 400 cycles) is obtained with Li metal anodes without capacity fade or short circuits developing in either the VC containing IL or the polymer gel analogue. In addition, no V₂O₅ deterioration is observed with the polymer gel electrolyte as the capacity recovered to ~125 mAh g^-1 after cycling at 5 C.

Furthermore, we assess surface modification of V₂O₅ by depositing 3nm Al₂O₃ via ALD which has been shown to improve the charge-discharge kinetics of oxide electrode materials. Coulombic efficiencies >99%, with peak electrode capacities >120 mAh g^-1 are obtained and long-term cycling stabilities up to 625 cycles.

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2) L. M. McGrath and J. F. Rohan, Molecules, (2020), 25. 6002, Pyrrolidinium containing ionic liquid electrolytes for Li-based batteries.

3) T. Teranishi, Y. Yoshikawa, M. Yoneda, A. Kishimoto, J. Halpin, S. O’Brien, M. Modreanu and I. M. Povey, (2018), ACS Applied Energy Materials, 1(7), pp. 3277-3282, Aluminum Interdiffusion into LiCoO2 Using Atomic Layer Deposition for High Rate Lithium Ion Batteries.

Figure 1: Charge/Discharge capacity of 3nm Al₂O₃ coated V₂O₅ vs Li foil in 1M LiPF₆ in EC:DEC (1:1)