In this critical Review we focus on the evolution of the hybrid ion capacitor (HIC) from its early embodiments to its modern form, focusing on the key outstanding scientific and technological questions that necessitate further in-depth study. It may be argued that HICs began as aqueous systems, based on a Faradaic oxide positive electrode (e.g., Co3O4, RuOx) and an activated carbon ion-adsorption negative electrode. In these early embodiments HICs were meant to compete directly with electrical double layer capacitors (EDLCs), rather than with the much higher energy secondary batteries. The HIC design then evolved to be based on a wide voltage (∼4.2 V) carbonate-based battery electrolyte, using an insertion titanium oxide compound anode (Li4Ti5O12, LixTi5O12) versus a Li ion adsorption porous carbon cathode. The modern Na and Li architectures contain a diverse range of nanostructured materials in both electrodes, including TiO2, Li7Ti5O12, Li4Ti5O12, Na6LiTi5O12, Na2Ti3O7, graphene, hard carbon, soft carbo...

Review of Hybrid Ion Capacitors: From Aqueous to Lithium to Sodium.

Advanced electrochemical energy storage devices (EESDs) that can store electrical energy efficiently while being miniature/flexible/wearable/load-bearing are much needed for various applications ranging from flexible/wearable/portable electronics to lightweight electric vehicles/aerospace equipment. Carbon-based fibers hold great promise in the development of these advanced EESDs (e.g., supercapacitors and batteries) due to their being lightweight, high electrical conductivity, excellent mechanical strength, flexibility, and tunable electrochemical performance. This review summarizes the fabrication techniques of carbon-based fibers, especially carbon nanofibers, carbon-nanotube-based fibers, and graphene-based fibers, and various strategies for improving their mechanical, electrical, and electrochemical performance. The design, assembly, and potential applications of advanced EESDs from these carbon-based fibers are highlighted. Finally, the challenges and future opportunities of carbon-based fibers for advanced EESDs are discussed.

Carbon-Based Fibers for Advanced Electrochemical Energy Storage Devices

High-efficiency energy storage technologies and devices have received considerable attention due to their ever-increasing demand. Na-related energy storage systems, sodium ion batteries (SIBs) and sodium ion capacitors (SICs), are regarded as promising candidates for large-scale energy storage because of the abundant sources and low cost of sodium. In the last decade, many efforts, including structural and compositional optimization, effective modification of available materials, and design and exploration of new materials, have been made to promote the development of Na-related energy storage systems. In this Review, the latest developments of micro/nanostructured electrode materials for advanced SIBs and SICs, especially the rational design of unique composites with high thermodynamic stabilities and fast kinetics during charge/discharge, are summarized. In addition to the recent achievements, the remaining challenges with respect to fundamental investigations and commercialized applications are discussed in detail. Finally, the prospects of sodium-based energy storage systems are also described.

Micro/Nanostructured Materials for Sodium Ion Batteries and Capacitors.

Peering into Alloy Anodes for Sodium‐Ion Batteries: Current Trends, Challenges, and Opportunities

The advancement of cost-effective electrocatalysts with high activity for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in water splitting is chief to renewable energy technology. In this work, an Fe-doped NiSe (a mixture of hexagonal NiSe and orthorhombic NiSe) nanorod/nanosheet hierarchical array on Ni foam was synthesized through a one-step solvothermal reaction, which exhibits high and stable catalytic activity for both the OER and HER in alkaline solution. The optimal Fe7.4%-NiSe only requires a small overpotential of 231 mV to drive 50 mA cm−2, and can provide a large current density of 500 mA cm−2 at an overpotential of 269 mV, and 1000 mA cm−2 at 291 mV for the OER. Moreover, it can afford 10 mA cm−2 at an overpotential of 163 mV, and 500 mA cm−2 at 296 mV toward the HER. A water electrolyzer with two Fe7.4%-NiSe electrodes only needs a low cell potential of 1.585 V to reach 10 mA cm−2, and 1.74 V to reach 100 mA cm−2 with great stability. The rich active sites and high conductivity of the Fe-doped NiSe nanorod/nanosheet hierarchical array contribute to its high catalytic performance. This work develops an alternative and simple synthetic approach for bimetal selenides with a hierarchical structure and provides an attractive low-cost electrocatalyst toward overall water splitting applications.

An Fe-doped nickel selenide nanorod/nanosheet hierarchical array for efficient overall water splitting

N-doped one-dimensional carbonaceous backbones supported MoSe2 nanosheets as superior electrodes for energy storage and conversion

Due to limited Li resources, sodium-ion batteries (NIBs) have become promising candidates for application in large-scale energy storage systems, and the development of high-performance anode materials for NIBs has become particularly urgent. Moreover, sodium-ion capacitors (NICs), which combine the characteristics of batteries and capacitors, have attracted significant research interest due to their high energy and power density. Herein, we report the design of efficient hydrothermal routes for synthesizing interlaced Sb2O3 nanosheets and Sb2S3 micro-nanospheres, grown on carbon fiber cloth, referred to as SO/CFC and SS/CFC, respectively, which were then used as flexible electrodes for NIBs and NICs devices. For NIBs applications, the SO/CFC electrodes exhibit a high stable capacity of 514 mA h g−1 after 500 cycles at 0.5 A g−1. The SS/CFC electrodes also display a stable capacity of 736 mA h g−1 after 650 cycles at 0.5 A g−1 and the high-rate capability can reach a high current density of 15 A g−1. Importantly, the flexible NIC device based on SO/CFC or SS/CFC as the anode and carbon fibers as the cathode was demonstrated, which manifests high power density and energy density, as well as significantly superior cycle stability.

High-performance sodium-ion batteries and flexible sodium-ion capacitors based on Sb2X3 (X = O, S)/carbon fiber cloth

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo2O4 porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo2O4 dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m2 g–1 with a pore size distribution of 2–10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo2O4 dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g–1 can be maintained after 180 cycles at 200 mA g–1. Even at a high current density of 2000 mA g–1, the electrode can still deliver a specific capacity...

Mengnan Zhu

Papers

N-doped one-dimensional carbonaceous backbones supported MoSe2 nanosheets as superior electrodes for energy storage and conversion

High-performance sodium-ion batteries and flexible sodium-ion capacitors based on Sb2X3 (X = O, S)/carbon fiber cloth

Uniform MnCo2O4 Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions.

TiO 2 nanorods grown on carbon fiber cloth as binder-free electrode for sodium-ion batteries and flexible sodium-ion capacitors

One-dimensional coaxial Sb and carbon fibers with enhanced electrochemical performance for sodium-ion batteries