Aqueous
potassium-ion batteries are long-term pursued, due to their
excellent performance and intrinsic superiority in safe, low-cost
storage for portable and grid-scale applications. However, the notorious
issues of K-ion battery chemistry are the inferior cycling stability
and poor rate performance, due to the inevitably destabilization of
the crystal structure caused by K-ions with pronouncedly large ionic
radius. Here, we resolve such issues by reconstructing commercial
vanadium oxide (α-V2O5) into the bronze
form, i.e., δ-K0.5V2O5 (KVO) nanobelts, as cathode materials with layered structure
of enlarged space and anisotropic pathways for K-ion storage. Specifically,
it can deliver a high capacity as 116 mAh g–1 at
the 1 C-rate, an outstanding rate capacity of 65 mAh g–1 at 50 C, and a robust cyclic stability with 88.2% capacity retention
after 1,000 cycles at 1 C. When coupled with organic anode in a full-cell
configuration, the KVO electrodes can output 95 mAh g–1 at 1 C and cyclic stability with 77.3% capacity retention after
20,000 cycles at 10 C. According to experimental and calculational
results, the ultradurable cyclic performance is assigned to the robust
structural reversibility of the KVO electrode, and the ultrahigh-rate
capability is attributed to the anisotropic pathways with improved
electrical conductivity in KVO nanobelts. In addition, applying a
22 M KCF3SO3 water-in-salt electrolyte can impede
the dissolving issues of the KVO electrode and further stabilize the
battery cyclic performance. Lastly, the as-designed AKIBs can operate
with superior low-temperature adaptivity even at −30 °C.
Overall, the KVO electrode can serve as a paradigm toward developing
more suitable electrode materials for high-performance AKIBs.
Revealing the structure and behavior of confined ionic liquids (ILs) is essential for their applications in green chemical processes. Here, we explore the electroconductivity (σ) and ionic correlation of imidazole ILs confined in graphene nanochannels via joint molecular dynamics simulation and theoretical analysis. The ideal and actual σ of ILs are first calculated, showing a growing tendency and up to the bulk value as the nanochannel size ranges from 1 to 10 nm. To account for the ionic correlation, the ionicity was determined by the ratio of the actual to ideal σ, reflecting the average fraction of free ions in the confined ILs. Amazingly, the ionicity of all three ILs shows an abnormal changing tendency, which first increases and reaches the maximum at 2 nm and then decreases to the bulk value. The conformational analysis, pair dissociating energy, and residence time are further obtained, proving that the abnormal enhanced ionicity should be attributed to the structure reconstruction of ILs near the graphene wall. The analytical model of ionicity herein can guide the rational design of efficient IL-based nanoporous electrodes and solid catalysts.
Nano-porous electrodes combined with ionic liquids (ILs) are widely favored to promote the energy density of supercapacitors. However, this is always accompanied by the reduced power density, especially considering the...
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