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.
Nonaqueous potassium-ion batteries (KIBs) are attracting increasing attention as a potential low-cost energy-storage system due to the abundance of potassium resources. Here, cobalt hexacyanocobaltate (Co [Co(CN) ] ), a typical Prussian blue analog (PBA), is reported as an anode material for nonaqueous KIBs. The as-prepared Co [Co(CN) ] exhibits a highly reversible capacity of 324.5 mAh g at a current density of 0.1 A g , a superior rate capability (221 mAh g at 1 A g ), and a favorable long-term cycling stability (200 cycles with 82% capacity retention). Based on a series of characterizations, it is found that potassiation/depotassiation in Co [Co(CN) ] proceeds via solid-state diffusion-limited K-ion insertion/extraction process, in which both carbon- and nitrogen-coordinated cobalt are electrochemically active toward K-ion storage. Finally, the reaction pathway between potassium and Co [Co(CN) ] is proposed. The present study provides new insights on further exploration of PBAs as high-performance electrode materials for KIBs.
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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