Nonaqueous potassium ion batteries (KIBs) are one of the emerging electrochemical energy storage technologies due to the abundance of potassium resources, but the difficulties of intercalation of large size K‐ions into electrode materials hinder the development of KIBs. Here, a layered potassium vanadate K0.5V2O5 is proposed as a potential cathode material for KIBs. Despite the large size of K‐ions, the as‐fabricated material is capable of delivering a reversible capacity around 90 mAh g−1 at 10 mA g−1 in the voltage range of 1.5–3.8 V (vs K+/K), and also exhibits a fast rate capability with a capacity of 60 mAh g−1 at 200 mA g−1 and good cycling stability with 81% capacity retention after 250 cycles at 100 mA g−1. Ex situ X‐ray diffraction and X‐ray photoelectron spectroscopy reveal that the layered potassium vanadate exhibits a highly stable and reversible structure change with a transition between V4+ and V5+ upon potassiation/depotassiation. Additionally, galvanostatic intermittent titration technique results show that the kinetics of potassiation/depotassiation is mainly determined by K‐ion diffusion in the active material. The present study may open up further exploration of potassium vanadates and other layered transition metal oxides in the field of KIBs.
Potassium-ion batteries (KIBs) are promising electrochemical energy storage systems because of their low cost and high energy density. However, practical exploitation of KIBs is hampered by the lack of high-performance cathode materials. Here we report a potassium manganese hexacyanoferrate (K2Mn[Fe(CN)6]) material, with a negligible content of defects and water, for efficient high-voltage K-ion storage. When tested in combination with a K metal anode, the K2Mn[Fe(CN)6]-based electrode enables a cell specific energy of 609.7 Wh kg−1 and 80% capacity retention after 7800 cycles. Moreover, a K-ion full-cell consisting of graphite and K2Mn[Fe(CN)6] as anode and cathode active materials, respectively, demonstrates a specific energy of 331.5 Wh kg−1, remarkable rate capability, and negligible capacity decay for 300 cycles. The remarkable electrochemical energy storage performances of the K2Mn[Fe(CN)6] material are attributed to its stable frameworks that benefit from the defect-free structure.
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.
The application of a layered K0.5MnO2 cathode in potassium-ion batteries is limited by its poor cycling performance when charged above 4.0 V (vs K+/K), and the underlying mechanism for this electrochemical instability is still unclear. Here, it is discovered that ethylene carbonate (EC) will intercalate into the depotassiated K0.5MnO2, causing the exfoliation of the layered compound and the capacity decay under high charge cutoff voltage. When the carbonates are replaced with a nonflammable phosphate, the electrochemical performance of K0.5MnO2 above 4.0 V (vs K+/K) is significantly enhanced with a large reversible capacity (120 mAh g–1) and high capacity retention of 84% after 400 cycles. This phosphate-based electrolyte also demonstrates good compatibility with the commercial graphite anode, enabling the encouraging electrochemical performance of the K0.5MnO2|graphite full-cell. The present study provides new insights on further exploration of other electrolytes to advance the emerging low-cost and high-performance potassium-ion batteries.
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.
K2V3O8 undergoes a non-topotactic but reversible phase transition between monoclinic KV3O8 and tetragonal K2V3O8 during the electrochemical depotassiation–potassiation process.
Potassium-ion batteries (KIBs) are considered as low-cost electrochemical energy storage technologies because of the abundant potassium resources. However, the practical applications of KIBs are mainly hampered by the unsatisfactory electrochemical performance of anode materials which often undergo large volume variations during potassiation−depotassiation, limiting their cycling life. Here, low-cost sulfurized polyacrylonitrile (S-PAN) is reported as an attractive anode candidate for KIBs. It provides a high potassium storage capacity of 569 mAh g (S-PAN)−1 with decent rate capability and cycling stability (no capacity loss after 1500 cycles, running time ∼188 days). Detailed ex situ spectroscopic and in situ microscopic characterizations reveal that the distinguished electrochemical performance of S-PAN is attributed to the high reversibility of its covalent C−S and S−S bonds which undergo repeated cleavage-redimerization during potassiation− depotassiation concomitant with relatively small volume variation (less than 24.2%). Subsequently, a full-cell constructed by pairing high-voltage K 2 MnFe(CN) 6 cathode with high-capacity S-PAN anode demonstrates an attractive energy density (290.9 Wh kg −1 ) and long-term cycling stability (1200 cycles with 95.4% capacity retention). Given the high performance and low cost of both anode and cathode materials, it is believed that the present full-cell promises it as a competitive energy storage system for the cost-sensitive grid-scale applications
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