Developing cathode materials integrating good rate performance and sufficient cycle life is the key to commercialization of aqueous zinc‐ion batteries. The hyperstable Zn0.52V2O5−a⋅1.8 H2O (ZVOH) cathode with excellent rate performance has been successfully developed via an in situ self‐transformation from zinc‐rich Zn3V3O8 (ZVO) in this study. Different from the common synthetic method of additional Zn2+ pre‐insertion, ZVOH is obtained from the insertion of structural H2O and the removal of excess Zn2+ in ZVO, ensuring the lattice structure of ZVOH remains relatively intact during the phase transition and rendering good structural stabilities. The ZVOH delivers a reversible capacity of 286.2 mAh g−1 at 0.2 A g−1 and of 161.5 mAh g−1 at 20 A g−1 over 18 000 cycles with a retention of 95.4 %, demonstrating excellent rate performance and cyclic stability. We also provide new insights on the structural self‐optimization of Znx(CF3SO3)y(OH)2x−y⋅n H2O byproducts and the effect on the mobility of Zn2+ by theoretical calculations and experimental evidence.
Owing to their high aspect ratios and structures of high-mechanical-strength conductive scaffolds, carbon nanotubes (CNTs) are considered to be one of the most promising hosts for sulfur in lithium−sulfur batteries (LSBs). However, traditional CNTs with impermeable walls are not conducive to the penetration of sulfur, resulting in a large number of sulfur exposures to the electrolyte. Therefore, it is difficult to effectively limit the shuttle effect of polysulfides. Here, a kind of thin-walled porous amorphous carbon nanotube (HCNT) is adopted as the host for sulfur in LSBs. To further alleviate the shuttle effect, oxygen-containing functional groups (OCFGs) are introduced to modify HCNTs to form HOCNTs. The S/HOCNT composite with the embedded structure is successfully constructed. The S/HOCNT cathode demonstrates glorious cycling and rate performance (798.5 mAh g −1 at 0.2 C after 100 cycles and 511.6 mAh g −1 at 1 C after 500 cycles). The excellent electrochemical performance of S/HOCNT can be attributed to the embedded structure of sulfur in HOCNTs, which avoids direct contact with the electrolytes and strong bonding action of OCFGs and polysulfides, effectively limiting the shuttle effect of polysulfides.
Different from the
traditional template method, a thin amorphous
carbon nanotube was prepared by constructing a polymer/SiO2 composite, utilizing the shrinking action of sulfonated polymer
nanotubes (SPNTs) and the physical squeezing action of SiO2 on it during the pyrolysis of SPNT/SiO2. Remarkably,
the heat treatment atmosphere (N2, N2–H2, or O2) has an important effect on the surface
properties, pore structure, crystallinity, and especially the defect
sites, leading to different lithium storage performances. Particularly,
the sample calcined in N2–H2 (NHCNTs)
exhibits outstanding reversible capacity (400.6 mA h g–1 at 2 A g–1 after 200 cycles) and rate capability
(268.4 mA h g–1 at 5 A g–1 and
212.1 mA h g–1 at 10 A g–1 after
400 cycles), which are attributed to the thin-walled tubular structure
and abundant defect sites. NOCNTs can be obtained by the thermal treatment
of NCNTs (the sample of polymer pyrolysis in N2) in air,
and the oxygen content was increased. However, the destruction of
the tubular structure led to poor electrochemical properties. These
results proved the importance of the thin-walled tubular structure
to the electrochemical properties. Surely, this strategy for preparing
thin-walled carbon nanotubes can be widely extended to the preparation
of other nanomaterials with thin-walled structures.
Vanadium oxides attract increasing research interests for constructing the cathode of aqueous zinc-ion batteries (ZIBs) because of high theoretical capacity, but the low intrinsic conductivity and unstable phase changes during the charge/ discharge process pose great challenges for their adoption. In this work, V 2 O 3 @C microspheres were developed to achieve enhanced conductivity and improved stability of phase changes. Compounding vanadium oxides and conductive carbon through the in-situ carbonization led to significant improvement of the cathode materials. ZIBs prepared with V 2 O 3 @C cathodes produce a specific capacity of 420 mA h g −1 at 0.2 A g −1 . A reversible capacity of 132 mA h g −1 was achieved at 21.0 A g −1 . After 2000 cycles, the electrode could still deliver a capacity of 202 mA h g −1 at the current of 5.0 A g −1 . Besides, the energy density of batteries constructed with the thus-prepared electrodes was about 294 W h kg −1 at 148 W kg −1 power. The in-situ compounding of V 2 O 3 and carbon resulted in a microstructure that facilitated the stable phase transformation of Zn x V 2 O 5−a •nH 2 O (ZnVOH), which provided more Zn 2+ storage activity than the original phase before electrochemical activation. Moreover, the in-situ compositing strategy presents a simple route to the development of ZIB cathodes with promising performance.
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