Influence of KPF₆ and KFSI on the Performance of Anode Materials for Potassium-Ion Batteries: A Case Study of MoS₂

Abstract

Recently, nonaqueous potassium-ion batteries (KIBs) are attracting because of increasing interest due to the abundance of potassium resources, but the systematic study about the effects of electrolyte's salt on the electrochemical performance of electrode materials is still insufficient. Here, it is shown that the capacity retention and Coulombic efficiency of commercial micrometric MoS 2 can be remarkably improved by simply using potassium bis(fluorosulfonyl)imide (KFSI) over potassium hexafluorophosphate (KPF 6 ) dissolved in ethylene carbonate/diethyl carbonate as the electrolyte. By constructing various cell configurations, it is discovered that the degradation of MoS 2 ||K half-cells in KPF 6 -containing electrolyte originates from the failure of the MoS 2 electrode. The solid electrolyte interphase (SEI) layer formed on MoS 2 during cycling was systematically investigated by using a series of characterizations. It is found that a stable, protective, and KF-rich SEI layer is formed on MoS 2 in the KFSI-containing electrolyte, while an unstable, KF-deficient, and organic species-rich SEI layer is formed in the KPF 6 -containing electrolyte. Finally, the origins of such differences are discussed, which will provide new insights into further exploration of novel electrolytes for KIBs.

Densified Metallic MoS2/Graphene Enabling Fast Potassium‐Ion Storage with Superior Gravimetric and Volumetric Capacities

“…The KFSI with a better adaptability for the CTMG electrode may be attributed to that KFSI system can induce a more stable solid electrolyte interphase (SEI) compared to KPF 6 system. [ 31,34 ] As shown in Figure 4b, the rate performance of CTMG and reference electrodes is evaluated. The CTMG electrode delivers rate capacities of 511, 462, 377, 354, 327, and 234 mAh g −1 at the current densities of 0.1, 0.2, 0.5, 0.7, 1, and 2 A g −1 , respectively.…”

Optimized Kinetics Match and Charge Balance Toward Potassium Ion Hybrid Capacitors with Ultrahigh Energy and Power Densities

“…This should be ascribed to the formation of a thin, uniform, intact SEI layer induced by the KFSI-based electrolyte. [29] We further carried out in situ EIS analysis at different charge/discharge potentials to verify the formation of stable SEI layer in KFSI-based electrolyte (Figure 3). Figure 3a exhibits the galvanostatic charge-discharge (GCD) profiles of initial 2 cycles acquired from in situ EIS measurement at 20 mA g −1 .…”

KFSA/glyme electrolytes for 4 V-class K-ion batteries

“…These decomposition products would be a key component of the SEI enabling high coulombic efficiency, as reported before. [28][29][30] Fig. S9f † shows the relative atomic amount of carbon (except for sp 2 carbon), oxygen, potassium, phosphorus, nitrogen, uorine, and sulfur elements relative to that of sp 2 carbon estimated from the HAXPES data of the tested electrode in comparison to the one tested in a conventional KPF 6 /EC : DEC electrolyte.…”