Understanding electrolyte salt chemistry for advanced potassium storage performances of transition‐metal sulfides

Abstract

Molybdenum disulfide/carbon nanotubes assembled by ultrathin nanosheets are synthesized to illustrate the electrolyte salt chemistry via potassium bis-(fluorosulfonyl)imide (KFSI) versus potassium hexafluorophosphate (KPF 6 ).Compared to the case of KPF 6 , the electrochemical performances using KFSI as the electrolyte salt are greatly improved: ~275 mAh g −1 after 15,000 cycles at 1 A g −1 , or ~172 mAh g −1 even at 40 A g −1 . These results represent one of the best performances for the reported anode materials. The enhanced performances could be attributed to the FSI-induced changes in the solvate structures, that is, a large solvation energy, a high lowest unoccupied molecular orbital, and a small bonding dissociation energy of S-F. In this case, a uniform and robust solid-electrolyte interphase (SEI) is produced, improving the mechanical properties and the interface integrity. Then, the uncontrollable fracture and repeated growth of SEI, which always lead to the dissolution of sulfur species and the blockage of charge transfer in the case of KPF 6 , are well inhibited. This similar enhancement works for other sulfides by KFSI, demonstrating the general importance of this electrolyte salt chemistry.

Understanding the Highly Reversible Potassium Storage of Hollow Ternary (Bi-Sb)2S3@N-C Nanocube

“…Meanwhile, the electrolyte undergoes an irreversible decomposition, which exhibits that the KFSI (PDF# 89-0215) diffraction peak at about 22.8° splits and the peak intensity of the decomposition products at 22.86° and 19.62° gradually increased. The peaks will remain stable in the subsequent charge-discharge process . Theoretically, the computed formation energy of K x (Bi-Sb) 2 S 3 decreases with small intercalation amounts of K + (0 ≤ x ≤ 1.6) and then gradually increases when the number of intercalated K + is >1.6, indicating there is a phase transition in the range of 1.5 ≤ x ≤ 2, as can be seen from Figure S10a.…”

“…The peaks will remain stable in the subsequent charge-discharge process. 57 Theoretically, the computed formation energy of K x (Bi-Sb) 2 S 3 decreases with small intercalation amounts of K + (0 ≤ x ≤ 1.6) and then gradually increases when the number of intercalated K + is >1.6, indicating there is a phase transition in the range of 1.5 ≤ x ≤ 2, as can be seen from Figure S10a. It has reported that the conversion reaction may take place simultaneously with intercalation in metal chalcogenide anodes, the former of which is kinetically dictated by the propagation along the heterointerphase rather than the diffusion of K-ions in the pristine metal chalcogenide crystals.…”

Colloidal synthesis of hexagonal CuFe(SxSe1−x)2 nanoplates with exposed highly active (220) facets for boosting overall water splitting

“…4e depicts the high-resolution Cu 2p spectrum of CuFe(S 0.8 Se 0.2 ) 2 and CuFeS 2 , with two typical peaks at 932.06 eV and 951.80 eV for pure CuFe (S 0.8 Se 0.2 ) 2 assigned to Cu 2p3/2 and Cu 2p1/2, respectively. 12 As for the Fe 2p spectrum, the peaks corresponding to Fe 2+ 2p3/2 and 2p1/2 were observed at 711.05 eV and 724.57 eV, respectively (Fig. 4f ).…”

“…In particular, ternary and quaternary transition metal chalcogenides have emerged as promising candidates due to their unique physicochemical characteristics, including improved electrical conductivity and riched redox properties over corresponding single-component materials. 11,12 For example, CuFeS 2 nanosheets synthesized by Xi's group exhibited exceptional HER electrocatalytic activity under acidic conditions with a low overpotential of 88.7 mV to achieve a current density of 10 mA cm −2 . 13 Chen et al found that the mechanically milled CuFeS 2 exhibits excellent OER performance in alkaline medium.…”

Stable Solid Electrolyte Interface Achieved by Separator Surface Modification for High-Performance Anode-free Potassium Metal Batteries

“…Potassium and sodium ion batteries are attractive because of their low redox potentials, high energy densities, and abundant resources (compared with lithium). − The design of high load and high energy density electrodes is helpful to promote their development and application. − In addition, potassium metal anodes with a lower cost, lower redox potential, and higher abundance are more likely to be used in high power grid energy storage systems. − Unfortunately, the practical application of K metal batteries (KMBs) is restricted by some complex issues. First, the higher chemical activity between K metal and electrolytes as well as the larger volume change during potassium plating/stripping will inevitably lead to the formation of an unstable solid electrolyte interface (SEI) during charge/discharge processes. − In addition, uneven deposition of potassium ions (K + ) will lead to uncontrollable K dendrite formation. , These factors inevitably lead to the low Coulombic efficiency (CE), poor cycle performance, and weak rate performance of K metal anodes …”