Strategies for Harnessing High Rate and Cycle Performance from Graphite Electrodes in Potassium-Ion Batteries

Abstract

Potassium-ion batteries (PIBs) have been lauded as the next-generation energy storage systems on account of their high voltage capabilities and low costs and the high abundance of potassium resources. However, the practical utility of PIBs has been heavily encumbered by severe K metal dendrite formation, safety issues, and insufficient electrochemical performance during operationsindeed critical issues that underpin the need for functional electrolytes with high thermal stability, robust solid− electrolyte interphase (SEI)-forming capabilities, and high electrochemical performance. In a bid to establish a knowledge framework for harnessing high rate capabilities and long cycle life from graphite negative electrodes, this study presents the physical properties and electrochemical behavior of a high K + concentration inorganic ionic liquid (IL) electrolyte, K[FSA]-Cs[FSA] (FSA − = bis(fluorosulfonyl)amide) (54:46 in mol), at an intermediate temperature of 70 °C. This IL electrolyte demonstrates an ionic conductivity of 2.54 mS cm −1 and a wide electrochemical window of 5.82 V. Charge− discharge tests performed on a graphite negative electrode manifest a high discharge capacity of 278 mAh g −1 (0.5 C) at 70 °C, a high rate capability (106 mAh g −1 at 100 C), and a long cyclability (98.7% after 450 cycles). Stable interfacial properties observed by electrochemical impedance spectroscopy during cycling are attributed to the formation of sulfide-rich all-inorganic SEI, which was examined through X-ray photoelectron spectroscopy. The performance of the IL is collated with that of an N-methyl-Npropylpyrrolidinium-based organic IL to provide insight into the synergism between the highly concentrated K + electrolyte at intermediate temperatures and the all-inorganic SEI during electrochemical operations of the graphite negative electrode.

Advances in studying interfacial reactions in rechargeable batteries by photoelectron spectroscopy

“…131,132 XPS has been found to be a valuable tool in studying both SIBs and KIBs. [133][134][135][136][137][138] Going even further into novel systems, we nd multivalent-ion batteries based on magnesium and calcium that present further unique challenges and require some unique solutions. 139,140 Fig.…”

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

“…For example, Chagas et al 148 149 reviewed IL electrolytes for sodium-ion batteries from ion conductivity thermal and cycling stability aspects and pointed out that cations including pyrrolidinium-based, quaternary ammonium, quaternary phosphonium are currently the most stable cations in IL electrolyte candidates for sodium-ion batteries. Furthermore, for potassium-ion batteries, in addition to the application of [Pyr][FSI] or [Pyr][Tf 2 N] ([Pyr] + = pyrrolidinium) summarized by Zhou et al, 35 Kaushik et al 150 applied a high-concentrated K[FSI]-Cs[FSI] electrolyte and achieved a higher rate and cycle performance from graphite electrodes than that with pyrrolidinium-based electrolytes at 70 °C. This improvement is attributed to the SEI-free design, which reduces internal resistance.…”

Amide‐Based Ionic Liquid Electrolytes for Alkali‐Metal‐Ion Rechargeable Batteries

“…In essence, the occurrence of Na metal deposition dominates over Na + ion intercalation into graphite. Recently, Kaushik et al reported that an inorganic IL K[FSA]À Cs[FSA] (x(K[FSA]) = 0.54) was successfully applied as the electrolyte in potassium-ion batteries in combination with graphite negative electrodes at 343 K. [44] The absence of organic cations facilitated stability at elevated temperatures; however, the melting point of this IL was as high as 336 K. [12b]…”