An “acetonitrile/water in salt” electrolyte with non-flammability, high conductivity, a high stability window and a wide applicable temperature range enables high-performance supercapacitors.
With the advantages including wide ESW, superior conductivity, low viscosity and low cost, NaClO4-based WIS electrolyte can be considered as a promising candidate for high-voltage and high-rate aqueous carbon based SCs with good safety.
Two-dimensional
(2D) Ti3C2 MXene has attracted
great attention in electrochemical energy storage devices (supercapacitors
and lithium-ion and sodium-ion batteries) due to its excellent electrical
conductivity as well as high volumetric capacity. Nevertheless, a
previous study showed that multivalent Mg2+ ions cannot
reversibly insert into MXene, resulting in a negligible capacity.
Here, we demonstrate a simple strategy to achieve high magnesium storage
capability for Ti3C2 MXene by preintercalating
a cationic surfactant, cetyltrimethylammonium bromide (CTAB). Density
functional theory simulations verify that intercalated CTA+ cations reduce the diffusion barrier of Mg2+ on the MXene
surface, resulting in the significant improvement of the reversible
insertion/deinsertion of Mg2+ ions between MXene layers.
Consequently, the MXene electrode exhibits a desirable volumetric
specific capacity of 300 mAh cm–3 at 50 mA g–1 as well as outstanding rate performance. This work
endows MXene material with an application in electrochemical energy
storage and, simultaneously, introduces magnesium battery materials
as a member.
Carbon sheets with 3D architectures, large graphitic interlayer spacing, and high electrical conductivity are highly expected to be an ideal anode material for sodium‐ion hybrid capacitors (SIHCs). Pursuing a simple synthesis methodology and advancing it from the laboratory to industry is of great importance. In this study, a new approach is presented to prepare 3D framework carbon (3DFC) with the above integrated advantages by a direct calcination of sodium citrate without aid of any additional carbon source, template, or catalyst. The first‐principle calculations verify that the large interlayer spacing and the curvature structure of 3DFC facilitate the sodium ion insertion/extraction. As a consequence, the optimal 3DFC sample exhibits high reversible capacity as well as excellent rate and cycling performance. On this basis, a dual‐carbon SIHC is fabricated by employing 3DFC as battery‐type anode and 3DFC‐derived nanoporous carbon as capacitor‐type cathode. It is able to deliver high energy‐ and power‐density feature as well as outstanding long‐term cycling stability in the potential range of 0–4.0 V. This study may open an avenue for developing high‐performance carbon electrode materials and pushes the practical applications of SIHCs a decisive step forward.
Sodium-ion hybrid capacitors (SIHCs) can potentially combine the virtues of high-energy density of batteries and high-power output as well as long cycle life of capacitors in one device.The key point of constructing a highperformance SIHC is to couple appropriate anode and cathode materials, which can well match in capacity and kinetics behavior simultaneously. In this work, a novel SIHC, coupling a titanium dioxide/carbon nanocomposite (TiO 2 /C) anode with a 3D nanoporous carbon cathode, which are both prepared from metal-organic frameworks (MOFs, MIL-125 (Ti) and ZIF-8, respectively), is designed and fabricated. The robust architecture and extrinsic pseudocapacitance of TiO 2 /C nanocomposite contribute to the excellent cyclic stability and rate capability in half-cell. Hierarchical 3D nanoporous carbon displays superior capacity and rate performance. Benefiting from the merits of structures and performances of anode and cathode materials, the as-built SIHC achieves a high energy density of 142.7 W h kg −1 and a high power output of 25 kW kg −1 within 1-4 V, as well as an outstanding life span of 10 000 cycles with over 90% of the capacity retention. The results make it competitive in high energy and power-required electricity storage applications.
The interlayer modification and the intercalation pseudocapacitance have been combined in vanadium oxide electrode for aqueous zinc-ion batteries. Intercalation pseudocapacitive hydrated vanadium oxide Mn 1.4 V 10 O 24 •12H 2 O with defective crystal structure, interlayer water, and large interlayer distance has been prepared by a spontaneous chemical synthesis method. The inserted Mn 2+ forms coordination bonds with the oxygen of the host material and strengthens the interaction between the layers, preventing damage to the structure. Combined with the experimental data and DFT calculation, it is found that Mn 2+ refines the structure stability, adjusts the electronic structure, and improves the conductivity of hydrated vanadium oxide. Also, Mn 2+ changes the migration path of Zn 2+ , reduces the migration barrier, and improves the rate performance. Therefore, Mn 2+ -inserted hydrated vanadium oxide electrode delivers a high specific capacity of 456 mAh g −1 at 0.2 A g -1 , 173 mAh g -1 at 40 A g -1 , and a capacity retention of 80% over 5000 cycles at 10 A g -1 . Furthermore, based on the calculated zinc ion mobility coefficient and Zn(H 2 O) n 2+ diffusion energy barrier, the possible migration behavior of Zn(H 2 O) n 2+ in vanadium oxide electrode has also been speculated, which will provide a new reference for understanding the migration behavior of hydrated zinc-ion.
Water-in-salt" (WIS) electrolytes with wide electrochemical stability windows (ESWs) have made a breakthrough in energy density of aqueous batteries and supercapacitors (SCs), but the sluggish ion diffusion limits their widespread application. Although the ion diffusion of WIS electrolytes can be improved by the addition of organic co-solvents, the effects of types and amounts of added organic solvents on the physicochemical properties of hybrid electrolytes are not clear. Here, the conductivity, ESW, and flammability of a series of hybrid electrolytes prepared by adding different organic solvents to a typical lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-based WIS electrolyte are systematically studied. The results show that acetonitrile (ACN) is the best one to improve ion diffusion while maintaining high-level safety and wide ESW. Furthermore, a ternary phase diagram of LiTFSI/H 2 O/ACN is drawn to comprehensively show the relationship among the conductivity, flammability, and solubility of the hybrid electrolytes. According to the guidance of this phase diagram, an optimal hybrid electrolyte (LiTFSI/H 2 O/(ACN) 3.5 ) is obtained, and the carbon-based symmetric SC using such hybrid electrolyte is able to fully work at 2.4 V with superior rate capability and excellent cycling stability over 40 000 cycles.
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