In Situ Optical Imaging of Sodium Electrodeposition: Effects of Fluoroethylene Carbonate

Abstract

The morphologies of sodium electrodeposits and gas evolution were studied in a system comprising a symmetrical Na/Na optical cell, a digital microscope, and an electrochemical workstation. Sodium deposition in ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) generated large volumes of gas and fragile, porous dendrites. The use of fluoroethylene carbonate (FEC) greatly reduced gassing during deposition and demonstrated superior cycling performance, impedance, and cycling efficiency when it was used as a cosolvent with DEC (1:1 vol); however, porous depositions persisted. Time of flight secondary-ion mass spectrometry revealed that the solid-electrolyte interphase formed in FEC/DEC, in contrast with the EC/DEC electrolyte, is thicker, richer in NaF, and forms a less dense polymer organic layer.

A Material Perspective of Rechargeable Metallic Lithium Anodes

“…Other conductive hosts for lithium anode. microscope (Figure 14), [24] X-ray diffraction (XRD), [65] transmission electron microscope, [16,18] and nuclear magnetic resonance (NMR) [66] have been employed to fundamentally investigate the morphology and structure of deposited lithium. b) The as-prepared Ti 3 C 2 -lithium hybrid exhibits a good flexibility, which is inherited from lithium metal.…”

Electrolytes for Batteries with Earth‐Abundant Metal Anodes

“…[21,22] To increasethe CE by creating amore stable electrolyte/electrode interface with the use of ac arbonate electrolyte, several strategies were applied. [25] As well as the FEC additive, Archer et al reported that the addition of an electro-polymerizable ionic liquid (IL) could also stabilizet he sodium-metal anode (Figure 2e and f). [23] The initial CE is also significantly enhanced by FEC addition.…”

“…As observed by Mullins et al,F EC additive can effectively reduce bubble formation and generateathicker,N aF-rich SEI layer. [25] As well as the FEC additive, Archer et al reported that the addition of an electro-polymerizable ionic liquid (IL) could also stabilizet he sodium-metal anode (Figure 2e and f). [26] They found that 1,3-diallyl imidazolium perchlorate (DAIM) and 1-allyl-3-vinylimidazolium perchlorate (AVIM) ILs could be electro-polymerized on the sodium-metal anode during discharge and form an ionic conductive protectivel ayer of about 50 nm.…”

Ion–Solvent Complexes Promote Gas Evolution from Electrolytes on a Sodium Metal Anode

“…[6] Thec ontinuous consumption of both Na and electrolyte leads to al ow Coulombic efficiencya nd short life cycle.M ore importantly,m ost organic electrolytes are easily reduced on Na, generating flammable gases.T he exothermic nature of the above reduction reactions,c ombined with flammable gas evolution, induces severe safety hazards. [7] Thei mperative for ap ractical and safe SMB is to understand the chemistry of the Na/electrolyte interplay and the mechanism of gas evolution. Currently,m ost efforts mainly focus on materials and structure design for stable Na anodes.L uo and co-workers employed porous aluminum as aN ah ost, achieving ad endrite-free Na anode with ah igh average Coulombic efficiency above 99.9 %d uring 1000 cycles.P int and colleagues described an in situ plated Na anode through the use of an anocarbon nucleation layer on aluminum current collectors,which enabled dendrite-free and highly reversible deposition.…”