Electrochemical characterization of hexamethylguanidinium bis(fluorosulfonyl)imide [HMG][FSI] based electrolyte and its application in sodium metal batteries

Abstract

With the increasing energy demand for both electronic portable devices and energy storage for fluctuating renewable energy sources, there is a strong need for alternatives beyond lithium batteries. Sodium batteries have been attracting great attention recently due to the abundance and low supply cost of the raw materials. However, they require highly conductive, safe and electrochemically stable electrolytes in order to enable their practical realization. In this work we present the promising physicochemical properties of the electrolyte based on hexamethylguanidinium bis(fluorosulfonyl)imide [HMG][FSI] at a sodium concentration of 25 mol% sodium bis(fluorosulfonyl)amide (NaFSI). The liquid-state electrolyte supports stable Na plating and stripping at 1 h polarization times at 0.5 mA/cm2 current density in a Na symmetrical coin cell at 50 ℃, maintaining a low polarization potential of ≈ 45 mV throughout 160 cycles. Moreover, this electrolyte is characterized by relatively high Na-ion transference number of 0.36 ± 0.03 at 50 oC. A long cycle life of 300 cycles with 285 mAh/g is achieved in a half cell set up with hard carbon (HC). The SEI layer on the anode, which contributes to this high capacity, is investigated by X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance spectroscopy (NMR). The long-term cycling performance of Na|NaFePO4 (NFP) cell is also demonstrated with a high specific capacity of 106 mAh/g and 80% capacity retention after 110 cycles.

A Physics-based Model Assisted by Machine-Learning for Sodium-ion Batteries with both Liquid and Solid Electrolytes

“…53,54 It is also a reasonable assumption for liquid electrolytes taken from literature. 55,56 It can be shown that writing Eq. 4 for the two species and holding the electroneutrality condition reduces Eq.…”

Wide-temperature-range sodium-metal batteries: from fundamentals and obstacles to optimization

“…85,215 Compared with BLTE, ES6-BLTE has a lower desolvation energy (À157.5 kcal mol À1 ), indicating that Na + in ES6-BLTE electrolyte has a low desolvation barrier and accelerated interfacial transfer dynamics. 85,215 Notably, the desolvation energy of Na + is an important indicator for evaluating batteries, especially in LT environments. 115,130,179 Fig.…”

“…The high mechanical strength hinders the penetration of Na dendrites dramatically, thereby minimizing safety hazards. 167,179,215 Fig. 6e shows a Na|Na symmetric cell with the ES6-BLTE electrolyte tested at 0.1 mA cm À2 and 0.1 mA h cm À2 .…”

A comparison of the impact of cation chemistry in ionic liquid-based lithium battery electrolytes

“…For example, the hexamethylguanidinium FSI, [HMG][FSI], OIPC was recently used as an electrolyte and presented interesting properties when mixed with Na and Li salts. [39][40][41][42] Biernacka et al investigated the effect of different anions and salt concentrations on the physicochemical properties of [HMG][FSI] by creating mixtures of [HMG][FSI]/LiFSI and [HMG][FSI]/LiTFSI. The results showed that 50 mol% LiFSI or LiTFSI in [HMG][FSI] is liquid with glass transition temperatures at À58 1C and À50 1C, respectively, whereas, [HMG][FSI] with 10 mol% and 90 mol% of LiFSI or LiTFSI acts as quasi-solid electrolytes with melting points at 89 1C for 90 mol% LiFSI and 120 1C for 90 mol% LiTFSI.…”