Non-aqueous electrolytes for sodium-ion batteries

Abstract

The first review of the various electrolytes currently used and developed for sodium-ion batteries (SIBs), both in terms of materials and concepts, is presented. In contrast to the Li-ion battery (LIB), which is a mature technology for which a more or less unanimously accepted "standard electrolyte" exists: 1 M LiPF 6 in EC/DMC, the electrolyte of choice for SIBs has not yet fully conformed to a standard. This is true for both materials: salts, solvents, or additives, and concept, using the main track of organic solvents or aiming for other concepts. SIB research currently prospers, benefitting from using know-how gained from 30 years of LIB R&D. Here the currently employed electrolytes are emphasized and their effects on practical SIB performance are outlined, scrutinizing the rationale for specific choices made, salts, solvents, additives, concentrations, etc. for each specific cell set-up and usage conditions.

Ultraconcentrated Sodium Bis(fluorosulfonyl)imide-Based Electrolytes for High-Performance Sodium Metal Batteries

“…To control the Na metal electrode-electrolyte interface for high performance Na metal batteries, considerable efforts have been made to find electrolyte systems that are stable at the Na metal electrode. 20,21,[23][24][25][26] The use of linear carbonates such as dimethyl carbonate (DMC), which are widely used as electrolyte solvents in lithium batteries, is limited due to their drastic decomposition at Na metal electrodes and sodiated hard carbon anodes. 24,27 Using fluoroethylene carbonate (FEC) as an electrolyte additive for in situ formation of an artificial solid electrolyte interphase (SEI) layer could stabilize the anode-electrolyte interface ( Figure 2).…”

“…[20][21][22][23][24][25][26][27] Nevertheless, the practical application of Na metal batteries is quite challenging because the high chemical and electrochemical reactivity of Na metal electrodes with organic liquid electrolytes leads to low Coulombic efficiencies and limited cycling performance. 20,[24][25][26] Severe electrolyte decomposition at the Na metal electrode results in the formation of a resistive and non-uniform surface film, leading to dendritic Na metal growth.…”

Solvation structure in dilute to highly concentrated electrolytes for lithium-ion and sodium-ion batteries

“…the charge carrier concentration and the ion mobility are both crucial for the power rates as well as overall functionality. The standard LIB electrolyte is today based on 1.0 M LiPF6 in mixtures of organic carbonates (propylene carbonate (PC), ethylene carbonate (EC) and dimethyl carbonate (DMC)) with similar salts and solvents being investigated for SIBs [1,10]. Future LIBs/SIBs, however, will require novel electrolytes displaying i) wider electrochemical stability windows to allow cycling of high energy capacity cathodes and especially at higher voltages e.g.…”

“…The limitations with respect to stability, energy and power density needs to be addressed in order to better meet the safety, autonomy, and power standards and improvements required [1] [2]. Lithium-ion batteries (LIBs) represent one of the most promising technologies, readily used already today, but recently also the prospect of sodium-ion batteries (SIBs) has re-emerged and grown into an active research topic.…”

Alkali-Metal Insertion Processes on Nanospheric Hard Carbon Electrodes: An Electrochemical Impedance Spectroscopy Study

“…51,52 There are good empirical reasons to suspect that the dissolution of the SEI in NIBs is more of a challenge than that in LIBs. Firstly, sodium salts can have very different solubilities than their lithium analogues in the same solvent 53,54 and secondly, there is some evidence from propylene carbonate based systems (a work by Aurbach and coworkers 55 ), where sodium perchlorate in propylene carbonate is shown to produce a substantial amount of soluble decomposition products while LiClO 4 and KClO 4 do not.…”