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.

Surfactant flooding as a potential enhanced oil recovery technology in depleted reservoirs after water flooding has attracted extensive attention. In this study, 12 surfactants belonging to five different types of surfactants and their compounded formulations were investigated for surfactant flooding under 90−120 °C and 20 × 10 4 mg/L salinity. Two surfactant formulations obtained a stable ultralow interfacial tension (IFT) level (≤10 −3 mN/m) with crude oil after aging for 125 days. The surfactant formulations were used to further investigate the effects of the initial IFT values, the dynamic reduction rate of IFT, and the surfactant concentration and emulsification on oil recovery through core flooding experiments. The results indicated that oil recovery increased with the decrease of the initial IFT values and the increase of the dynamic reduction rate of IFT. The 10 −3 mN/m IFT level yielded an additional oil recovery of approximately 7% compared with the 10 −1 mN/m IFT level. However, under the same IFT level (10 −4 mN/m), it was not the bigger the surfactant concentration that resulted in a higher additional oil recovery. In four surfactant concentrations (0.2%, 0.5%, 1%, and 3%), the 0.5% surfactant formulation obtained the highest oil recovery of 36.65%. Further study manifested that emulsification has important effects on oil recovery. When surfactant concentrations were increased to 1% and 3%, the emulsification was too strong, which makes it more difficult to displace oil. The two selected surfactant formulations could successfully yield additional oil recovery of 20−26%, which indicates these two formulations have great potential for improving oil recovery in high temperature and high salinity oil reservoirs.

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Recently, potassium-ion batteries (PIBs) are being actively investigated. The development of PIBs calls for cathode materials with a rigid framework, reversible electrochemical reactivity, and a high amount of extractable K ions, which is extremely challenging due to the large size of potassium. Herein, a new layered compound K0.83V2O5 is reported as a potential cathode material for PIBs. It delivers an initial depotassiation capacity of 86 mAh g–1 and exhibits a reversible capacity of 90 mAh g–1 with a high redox potential of 3.5 V (vs K+/K) and a capacity retention of more than 80% after 200 cycles. Experimental investigations combined with theoretical calculation indicate that depotassiation–potassiation is accommodated by contraction–expansion of the interlayer spacing along with unpuckering–puckering of the layers. Additionally, the calculated electronic structure suggests the (semi)­metallic feature of K x V2O5 (0 < x ≤ 0.875) and K-ion transport in the material is predicted to be one-dimensional with the experimentally estimated chemical diffusion coefficient in the order of 10–15–10–12 cm2 s–1. Finally, a K-ion full cell consisting of the K0.83V2O5 cathode and a graphite anode is demonstrated to deliver an energy density of 136 Wh kg–1. This study will provide insights for further designing novel layered cathodes with high K-ion content for PIBs.

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