Centrifugal-Gravity-Enforced Deposition of MXene Electrodes for High-Performance and Ultrastable Microsupercapacitors

Two-dimensional (2D) transition metal carbides, known as MXenes, have captured much attention for their excellent electrical conductivity and electrochemical capability. However, the susceptibility of MXenes to oxidation, particularly Ti3C2Tx transforming into titanium dioxide upon exposure to ambient air, hinders their utilization for extended operational life cycles. This work introduces a simple and straightforward method for producing ultrathin MXene electrode films tailored for energy storage applications, employing centrifugal-gravity force. Our approach significantly suppresses the oxidation phenomenon that arises in MXene materials and also effectively prevents the recrystallization of potentially residual LiF during the film formation. Additionally, the utilization of this MXene electrode in an all-solid-state microsupercapacitor (MSC) with an interdigitated pattern demonstrates an exceptionally improved and stable electrochemical performance. This includes a high volumetric capacitance of approximately 467 F cm-3, an energy density of around 65 mWh cm-3, and impressive long-term cycle stability, retaining about 94% capacity after 10 000 cycles. Moreover, a downsized MSC device exhibits remarkable mechanical durability, retaining over 98% capacity even when folded and sustaining stability over extended periods. Therefore, we believe that this study provides valuable insights for advancing highly integrated energy storage devices, ensuring exceptional electrochemical efficiency and prolonged functionality in diverse environments, whether ambient or humid.

L. M. A carbon nanotube reinforced functionalized styrene–maleic anhydride copolymer as an advanced electrode material for efficient energy storage applications

In the wake of the global energy crisis, innovative materials are being developed to alleviate the energy shortage by utilizing the available sources sustainably.

CoNi2 S4 Nanoparticle/Carbon Nanotube Sponge Cathode with Ultrahigh Capacitance for Highly Compressible Asymmetric Supercapacitor

Compared with other flexible energy-storage devices, the design and construction of the compressible energy-storage devices face more difficulty because they must accommodate large strain and shape deformations. In the present work, CoNi₂ S₄ nanoparticles/3D porous carbon nanotube (CNT) sponge cathode with highly compressible property and excellent capacitance is prepared by electrodepositing CoNi₂ S₄ on CNT sponge, in which CoNi₂ S₄ nanoparticles with size among 10-15 nm are uniformly anchored on CNT, causing the cathode to show a high compression property and gives high specific capacitance of 1530 F g^-1 . Meanwhile, Fe₂ O₃ /CNT sponge anode with specific capacitance of 460 F g^-1 in a prolonged voltage window is also prepared by electrodepositing Fe₂ O₃ nanosheets on CNT sponge. An asymmetric supercapacitor (CoNi₂ S₄ /CNT//Fe₂ O₃ /CNT) is assembled by using CoNi₂ S₄ /CNT sponge as positive electrode and Fe₂ O₃ /CNT sponge as negative electrode in 2 m KOH solution. It exhibits excellent energy density of up to 50 Wh kg^-1 at a power density of 847 W kg^-1 and excellent cycling stability at high compression. Even at a strain of 85%, about 75% of the initial capacitance is retained after 10 000 consecutive cycles. The CoNi₂ S₄ /CNT//Fe₂ O₃ /CNT device is a promising candidate for flexible energy devices due to its excellent compressibility and high energy density.

Design of aqueous redox-enhanced electrochemical capacitors with high specific energies and slow self-discharge

Electrochemical double-layer capacitors exhibit high power and long cycle life but have low specific energy compared with batteries, limiting applications. Redox-enhanced capacitors increase specific energy by using redox-active electrolytes that are oxidized at the positive electrode and reduced at the negative electrode during charging. Here we report characteristics of several redox electrolytes to illustrate operational/self-discharge mechanisms and the design rules for high performance. We discover a methyl viologen (MV)/bromide electrolyte that delivers a high specific energy of ∼14 Wh kg(-1) based on the mass of electrodes and electrolyte, without the use of an ion-selective membrane separator. Substituting heptyl viologen for MV increases stability, with no degradation over 20,000 cycles. Self-discharge is low, due to adsorption of the redox couples in the charged state to the activated carbon, and comparable to cells with inert electrolyte. An electrochemical model reproduces experiments and predicts that 30-50 Wh kg(-1) is possible with optimization.

Structural optimization of 3D porous electrodes for high-rate performance lithium ion batteries

Much progress has recently been made in the development of active materials, electrode morphologies and electrolytes for lithium ion batteries. Well-defined studies on size effects of the three-dimensional (3D) electrode architecture, however, remain to be rare due to the lack of suitable material platforms where the critical length scales (such as pore size and thickness of the active material) can be freely and deterministically adjusted over a wide range without affecting the overall 3D morphology of the electrode. Here, we report on a systematic study on length scale effects on the electrochemical performance of model 3D np-Au/TiO2 core/shell electrodes. Bulk nanoporous gold provides deterministic control over the pore size and is used as a monolithic metallic scaffold and current collector. Extremely uniform and conformal TiO2 films of controlled thickness were deposited on the current collector by employing atomic layer deposition (ALD). Our experiments demonstrate profound performance improvements by matching the Li(+) diffusivity in the electrolyte and the solid state through adjusting pore size and thickness of the active coating which, for 200 μm thick porous electrodes, requires the presence of 100 nm pores. Decreasing the thickness of the TiO2 coating generally improves the power performance of the electrode by reducing the Li(+) diffusion pathway, enhancing the Li(+) solid solubility, and minimizing the voltage drop across the electrode/electrolyte interface. With the use of the optimized electrode morphology, supercapacitor-like power performance with lithium-ion-battery energy densities was realized. Our results provide the much-needed fundamental insight for the rational design of the 3D architecture of lithium ion battery electrodes with improved power performance.