Abstract
Herein, the electrochemical performance and the mechanism of potassium insertion/deinsertion in orthorhombic V2O5 nanoparticles are studied. The V2O5 electrode displays an initial potassiation/depotassiation capacity of 200 mAh g−1/217 mAh g−1 in the voltage range 1.5–4.0 V vs. K+/K at C/12 rate, suggesting fast kinetics for potassium insertion/deinsertion. However, the capacity quickly fades during cycling, reaching 54 mAh g−1 at the 31st cycle. Afterwards, the capacity slowly increases up to 80 mAh g−1 at the 200th cycle. The storage mechanism upon K ions insertion into V2O5 is elucidated. In operando synchrotron diffraction reveals that V2O5 first undergoes a solid solution to form K0.6V2O5 phase and then, upon further K ions insertion, it reveals coexistence of a solid solution and a two-phase reaction. During K ions deinsertion, the coexistence of solid solution and the two-phase reaction is identified together with an irreversible process. In operando XAS confirms the reduction/oxidation of vanadium during the K insertion/extraction with some irreversible contributions. This is consistent with the results obtained from synchrotron diffraction, ex situ Raman, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Moreover, ex situ XPS confirms the “cathode electrolyte interphase” (CEI) formation on the electrode and the decomposition of CEI film during cycling.
Highlights
Along with their rapid development in modern society, renewable energy sources, such as solar, wind, geothermal power, and biomass energy, are playing crucial roles as power supplies
Pmn21 and Pmmn belong to the orthorhombic system
Scanning electron microscopy (SEM) in Fig. 1(b) confirms that the V2O5 consists of nanoparticles, in agreement with Rietveld refinement result
Summary
Along with their rapid development in modern society, renewable energy sources, such as solar, wind, geothermal power, and biomass energy, are playing crucial roles as power supplies. K-ion in propylene carbonate (PC) displays a lower ion–solvent interaction due to a lower desolvation energy and a smaller solvated ion compared to Li- and Na-ion, resulting in fast diffusion kinetics and high rate capability [6] Another advantage is that Al can be used as the current collector in anodes for both sodium-ion batteries (SIBs) and KIBs, whereas an expensive and heavier Cu foil must be used in anodes for LIBs, due to the Li-Al alloy formation at low potential [7,8]. The Vbased oxides are very promising for the application in KIBs. For example, Clites and co-workers [12] recently reported that dKxV2O5ÁnH2O positive electrode with an interlayer spacing of 9.65 Å shows good electrochemical performance towards Kinsertion/deinsertion with an initial potassiation capacity of 268 mAh gÀ1 at C/50 and of 226 mAh gÀ1 at C/15 rate in the potential range of 2.0–4.3 V vs K+/K. The present work focuses on the investigation of the electrochemical properties of V2O5 nanoparticles in 1 M KPF6/PC and its storage mechanism during K ions insertion and extraction by in operando synchrotron diffraction and in operando XAS
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