3D printing technology
has stimulated a burgeoning interest to
fabricate customized architectures in a facile and scalable manner
targeting wide ranged energy storage applications. Nevertheless, 3D-printed
hybrid capacitor devices synergizing favorable energy/power density
have not yet been explored thus far. Herein, we demonstrate a 3D-printed
sodium-ion hybrid capacitor (SIC) based on nitrogen-doped MXene (N-Ti3C2T
x
) anode and activated carbon cathode. N-Ti3C2T
x
affording a well-defined porous structure
and uniform nitrogen doping can be obtained via a sacrificial template
method. Thus-formulated ink can be directly printed to form electrode
architecture without the request of a conventional current collector.
The 3D-printed SICs, with a large areal mass loading up to 15.2 mg
cm–2, can harvest an areal energy/power density
of 1.18 mWh cm–2/40.15 mW cm–2, outperforming the state-of-the-art 3D-printed energy storage devices.
Furthermore, our SIC also achieves a gravimetric energy/power density
of 101.6 Wh kg–1/3269 W kg–1.
This work demonstrates that the 3D printing technology is versatile
enough to construct emerging energy storage systems reconciling high
energy and power density.
The advent of bioethanol production has generated abundant lignin-derived byproducts which contain proteins and polysaccharides. These byproducts are inapplicable for direct material applications. In this study, lignin-derived byproducts were used for the first time as carbon precursors to construct an interconnected hierarchical porous nitrogen-doped carbon (HPNC) via hydrothermal treatment and activation. The obtained HPNC exhibited favorable features for supercapacitor applications, such as hierarchical bowl-like pore structures, a large specific surface area of 2218 m(2) g(-1), a high electronic conductivity of 4.8 S cm(-1), and a nitrogen doping content of 3.4%. HPNC-based supercapacitors in a 6 M KOH aqueous electrolyte exhibited high-rate performance with a high specific capacitance of 312 F g(-1) at 1 A g(-1) and 81% retention at 80 A g(-1) as well as an excellent cyclic life of 98% initial capacitance after 20 000 cycles at 10 A g(-1). Moreover, HPNC-based supercapacitors in the ionic liquid electrolyte of EMI-BF4 displayed an enhanced energy density of 44.7 Wh kg(-1) (remaining 74% of max value) at an ultrahigh power density of 73.1 kW kg(-1). The proposed strategy may facilitate lignin utilization and lead to a green bioethanol production process.
MXenes
are an emerging class of highly conductive two-dimensional
(2D) materials with electrochemical storage features. Oriented macroscopic
Ti3C2T
x
fibers can
be fabricated from a colloidal 2D nematic phase dispersion. The layered
conductive Ti3C2T
x
fibers are ideal candidates for constructing high-speed ionic transport
channels to enhance the electrochemical capacitive charge storage
performance. In this work, we assemble Ti3C2T
x
fibers with a high degree of flake
orientation by a wet spinning process with controlled spinning speeds
and morphology of the spinneret. In addition to the effects of cross-linking
of magnesium ions between Ti3C2T
x
flakes, the electronic conductivity and mechanical
strength of the as-prepared fibers have been improved to 7200 S cm–1 and 118 MPa, respectively. The oriented Ti3C2T
x
fibers present a volumetric
capacitive charge storage capability of up to 1360 F cm–3 even in a Mg-ion based neutral electrolyte, with contributions from
both nanofluidic ion transport and Mg-ion intercalation pseudocapacitance.
The oriented 2D Ti3C2T
x
driven nanofluidic channels with great electronic conductivity
and mechanical strength endows the MXene fibers with attributes for
serving as conductive ionic cables and active materials for fiber-type
capacitive electrochemical energy storage, biosensors, and potentially
biocompatible fibrillar tissues.
Functionalizing carbon cathode surfaces with oxygen functional groups is an effective way to simultaneously tailor the fundamental properties and customize the electrochemical properties of aqueous Zn‐ion hybrid capacitors. In this work, the oxygen functional groups of chemically reduced graphene oxide (rGO) are systematically regulated via a series of reductants and varied experimental conductions. Carboxyl and carbonyl have been proven to significantly enhance the aqueous electrolyte wettability, Zn‐ion chemical adsorption, and pseudocapacitive redox activity by experimental study and computational analysis. The rGO cathode produced through hydrogen peroxide assisted hydrothermal reduction exhibits a specific capacitance of 277 F g−1 in 1 m ZnSO4 after optimization of surface oxygen functional groups. In addition, a quasi‐solid‐state flexible Zn‐ion hybrid capacitor (ZHC) with a polyacrylamide gel electrolyte and a high loading mass of 5.1 mg cm−2 are assembled. The as‐prepared quasi‐solid state ZHC can offer a superior areal capacitance of 1257 mF cm−2 and distinguished areal energy density of 342 µW h cm−2. The significant enhancement of redox activity and Zn‐ion storage capability by regulating the oxygen functional groups can shed light on the promotion of electrochemical charge storage properties even beyond protic electrolyte systems.
The practical application of lithium-sulfur (Li-S) batteries is hindered by their poor cycling stabilities that primarily stem from the "shuttle" of dissolved lithium polysulfides. Here, we develop a nepenthes-like N-doped hierarchical graphene (NHG)-based separator to realize an efficient polysulfide scavenger for Li-S batteries. The 3D textural porous NHG architectures are realized by our designed biotemplating chemical vapor deposition (CVD) approach via the employment of naturally abundant diatomite as the growth substrate. Benefiting from the high surface area, devious inner-channel structure, and abundant nitrogen doping of CVD-grown NHG frameworks, the derived separator favorably synergizes bifunctionality of physical confinement and chemical immobilization toward polysulfides, accompanied by smooth lithium ion diffusions. Accordingly, the batteries with the NHG-based separator delivers an initial capacity of 868 mAh g with an average capacity decay of only 0.067% per cycle at 2 C for 800 cycles. A capacity of 805 mAh g can further be achieved at a high sulfur loading of ∼7.2 mg cm. The present study demonstrates the potential in constructing high-energy and long-life Li-S batteries upon separator modification.
Lithium–sulfur
(Li–S) batteries are recognized as
one of the most promising energy storage systems due to the high energy
density and cost effectiveness. However, their practical implementation
has still been handicapped due to notorious lithium polysulfide (LiPS)
shuttle and depressed sulfur redox kinetics. It is therefore desirable
to exploit key mediators synergizing electrical conductivity and electrocatalytic
activity for the cathode. Herein, we report the employment of atmospheric
pressure chemical vapor deposition to harness the efficient and controllable
synthesis of metallic VTe2 over particulated MgO substrates,
which has scarcely been demonstrated by conventional wet-chemical
synthetic routes thus far. The thus-derived VTe2@MgO heterostructure
as an efficient promotor enables effective regulation of LiPSs with
respect to polysulfide capture/conversion and Li2S decomposition.
As a result, a S/VTe2@MgO cathode with a sulfur loading
of 1.6 mg cm–2 harvests long-term cyclability with
a negligible capacity decay of 0.055% per cycle over 1000 cycles at
1.0 C. Even at a sulfur loading of 6.9 mg cm–2,
the cathode still delivers electrochemical performances that can rival
the state-of-the-art high-loading counterparts. Our work might offer
a feasible solution for developing heterostructured promotors with
multifunctionality and electrocatalytic activity for high-performance
Li–S batteries.
A self-supported and binder-free CoP@G/CC-S cathode affording high conductivity, a suppressed shuttle effect and favorable mechanical robustness enables high-performance flexible Li–S batteries for practical applications.
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