Advanced Materials for Sodium‐Ion Capacitors with Superior Energy–Power Properties: Progress and Perspectives

Abstract

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10. 1002/smll.201902843. Developing electrochemical energy storage devices with high energy-power densities, long cycling life, as well as low cost is of great significance. Sodium-ion capacitors (NICs), with Na + as carriers, are composed of a high capacity battery-type electrode and a high rate capacitive electrode. However, unlike their lithium-ion analogues, the research on NICs is still in its infancy. Rational material designs still need to be developed to meet the increasing requirements for NICs with superior energy-power performance and low cost. In the past few years, various materials have been explored to develop NICs with the merits of superior electrochemical performance, low cost, good stability, and environmental friendliness. Here, the material design strategies for sodium-ion capacitors are summarized, with focus on cathode materials, anode materials, and electrolytes. The challenges and opportunities ahead for the future research on materials for NICs are also proposed. www.advancedsciencenews.com www.small-journal.com to LICs, NICs are still in their infancy stage with many difficulties for their practical application. [23] For example, many battery-type electrode materials for lithium ion storage cannot meet the requirements of NIC devices due to the large size of Na + ions. In addition, due to the redox potential of Na/Na + is 0.3 V higher than that of Li/Li + , the working voltage ranges of NICs are expected to be a little narrower than LICs, which may influence the energy densities of NICs. Moreover, the electrolyte should provide a rapid migration process of Na + ions. Therefore, the rational material design will play crucial roles in the electrochemical performance improvement of NICs.So far, there are few papers which summarize the recent progress in NIC research area. In particular, the materials used in NICs, including anode, cathode, and electrolyte, have not been systematically reviewed. In this article, we focus on the latest advances in the cathode materials, anode materials, and electrolytes for NICs. First, we review the energy storage mechanism and demonstrate the configurations of NICs; then, we summarize the recent progress on electrode materials, including anode materials, cathode materials, as well as different electrolytes for NICs; finally, the challenges and future prospects for NIC research are proposed.

MXene‐Based Anodes for Metal‐Ion Batteries

“…Conceptually, hybrid ion capacitors (HICs) are asymmetrical supercapacitors where one electrode is that typical of a supercapacitor, storing energy through electrical double layer capacitance (EDLC), and the other is redox‐active, as in a battery. Modern HICs usually combine these electrodes using an organic electrolyte which can sustain a high voltage, giving them more similarity to Li‐ion batteries . As discussed in a review by Ding et al ., HICs presently serve to compete with ELDC supercapacitors in applications where higher specific energy takes priority over cyclability …”

“…As in MXene‐based batteries, the first charge‐discharge cycle had a very low coulombic efficiency (presumably due to SEI formation), but between the 2 nd and 100 th cycles at 0.6 A g −1 , 96 % of its capacity was retained . These, as well as other MXenes, perform well compared to a number of other anode materials – especially at high current rates – but when tested at lower power, they currently only reach half the energy density of the best carbon‐based HIC electrodes . Like batteries, these anodes could benefit from shallower gradients in their charge‐discharge curves, as this signifies an increased capacity within the voltage window available.…”

Na‐Ion Batteries—Approaching Old and New Challenges

“…[142] Other anode materials tested in NICs include TiO 2 and sodium titanates, metal oxides, alloys, and organic materials, and the results have been summarized in various extensive review works. [143][144][145][146][147][148] NIC marketability would also benefit from the custom design of electrolytes. Most of the electrolytes used in NICs are just like the ones used in NIBs, even though the operation conditions of hybrid systems are different from battery requirements.…”

“…[ 142 ] Other anode materials tested in NICs include TiO 2 and sodium titanates, metal oxides, alloys, and organic materials, and the results have been summarized in various extensive review works. [ 143–148 ]…”

In Situ Hard‐Template Synthesis of Hollow Bowl‐Like Carbon: A Potential Versatile Platform for Sodium and Zinc Ion Capacitors

“…Different from rocking-chair SIBs, sodium-ion capacitors (SICs) utilize both cations (e.g., Na + ) and anions (e.g., ClO 4 − ) to simultaneously store energy. [7][8][9][10][11] In a typical SIC, the anode involves intercalation of Na ions, while the cathode is based on the surface-driven physisorption on the porous carbon surface. That is to say, the drawback of Na + is present in only one electrode of the SIC system.…”