Electrolytes and Interphases in Sodium‐Based Rechargeable Batteries: Recent Advances and Perspectives

Abstract

technologies. Unlike lithium, whose market is already very tight, sodium mineral deposits are almost infinite, evenly distributed worldwide, much easier to extract and thereby attainable at low cost. [1][2][3][4] If the realization of Na-rechargeable batteries could be practically possible, there will be nearly three orders of magnitude relaxation in the constraints on lithium-based resources, accompanied by sustainability, improved environmental benevolence, and cost reduction ( Table 1). Even more appealing is the possible use of the widely available and lighter aluminum, rather than copper, as negative current collector and hard carbon from renewable sources instead of graphite for the negative electrode. Finally, the stability of sodium-ion batteries (SIBs) in the fully discharged state would significantly enhance the safety associated with the shipment of large-format SIBs worldwide.These beneficial features of sodiumbased cells revived the research work on Na-based rechargeable batteries and accordingly captured the attention of both the academic research and industry sectors. However, similar to LIB, most of the research work in Na-based batteries have focused on the development and elaboration of negative and positive For sodium (Na)-rechargeable batteries to compete, and go beyond the currently prevailing Li-ion technologies, mastering the chemistry and accompanying phenomena is of supreme importance. Among the crucial components of the battery system, the electrolyte, which bridges the highly polarized positive and negative electrode materials, is arguably the most critical and indispensable of all. The electrolyte dictates the interfacial chemistry of the battery and the overall performance, having an influence over the practical capacity, rate capability (power), chemical/thermal stress (safety), and lifetime. In-depth knowledge of electrolyte properties provides invaluable information to improve the design, assembly, and operation of the battery. Thus, the full-scale appraisal of both tailored electrolytes and the concomitant interphases generated at the electrodes need to be prioritized. The deployment of large-format Na-based rechargeable batteries also necessitates systematic evaluation and detailed appraisal of the safety-related hazards of Na-based batteries. Hence, this review presents a comprehensive account of the progress, status, and prospect of various Na + -ion electrolytes, including solvents, salts and additives, their interphases and potential hazards.

Advances in materials for all‐climate sodium‐ion batteries

“…To lower the flammability of organic liquid electrolytes, flame‐retardant compounds have been explored as solvents, cosolvents, or additives in SIB electrolytes. Generally, flame‐retardant solvents such as organic phosphates have poor passivation ability on electrodes, resulting in continuous degradation 11 . Zeng et al 57 reported nonflammable phosphate electrolyte (0.8 m NaPF 6 in trimethyl phosphate [TMP]) incorporating 10 vol% FEC.…”

“…In principle, Na‐based electrolyte salts have better chemical and thermal stability than Li salts. As a result, less of the acidic species are formed, mitigating the exothermic acid‐base reaction with SEI component Na 2 CO 3 as well as the corrosion toward cathode materials 11 . However, due to the lower Lewis acidity, Na‐based SEI compounds, which are mainly Na 2 CO 3 , NaF, and sodium double alkyl carbonate (NEDC), turn to be more soluble compared to Li counterparties, rendering that SEI layers in SIBs more vulnerable toward elevated temperatures 52,59 .…”

“…In specific, the price of Li 2 CO 3 in 2019 is 13 000 USD per metric ton, which is only ~230 USD for Na 2 CO 3 . Moreover, Na + has smaller desolvation energy than that of Li + , indicating a lower activation barrier for Na (de)insertion and thereby faster charge/discharge characteristics, and Na electrolyte salts possess better thermal stability compared to the same Li‐salts (eg, NaPF 6 have higher stability than LiPF 6 by ≈200°C), making SIBs potentially favorable for safe ESSs 11 . Besides, the past decades have witnessed significant achievements on the understanding of Na storage mechanism and the development of high‐performance SIBs with competitive energy density, high rate capability, and excellent cycling life by designing new electrode materials and electrolytes 12‐20 .…”

Covalent Organic Frameworks for Next‐Generation Batteries

“…In addition, the reaction potential of sodium (À 2.71 V for Na/Na + ) is almost equivalent to that of lithium (À 3.04 V for Li/Li + ). [44][45][46][47][48] However, the energy density and cycle stability of SIBs are far inferior to those of LIBs. The main reason is that the radius of sodium ions is much larger than that of lithium ions, which causes large volume changes of the electrode materials during the charging and discharging process and leads to structural damage.…”

Towards standard electrolytes for sodium-ion batteries: physical properties, ion solvation and ion-pairing in alkyl carbonate solvents

“…[7][8][9] Investigations of SIB electrode materials are plentiful in the literature, [10][11][12][13][14][15] while there are much fewer electrolyte studies made, especially such that take a broader perspective. [16][17][18] SIB electrolytes more or less follow suit of LIB electrolytes. They are composed of cyclic carbonates e.g.…”