Synergistic Coupling of Ether Electrolyte and 3D Electrode Enables Titanates with Extraordinary Coulombic Efficiency and Rate Performance for Sodium‐Ion Capacitors

Abstract

Over the past few decades, electric doublelayer capacitors (EDLCs) have been one of the key components with high round trip efficiency and ultralong cycling lifetime in typical energy storage systems. [1][2][3][4][5][6] Unfortunately, EDLCs are subjected to limited energy density, which are inferior to that of secondary batteries and batterysupercapacitor hybrid devices. [7][8][9][10][11] As a well-known hybrid energy storage device, lithium-ion capacitors (LICs) consist of a capacitive electrode manifesting high rate capability and a battery-type electrode with high capacity, basically achieving both high power and energy densities. [12] In most cases, LICs employ Li + insertion anode and carbon-based capacitive cathode. [13][14][15][16] For instance, the state-ofthe-art LICs assembled with a prelithiated graphite anode and an activated carbon (AC) cathode were successfully commercialized. Nevertheless, the shortage of global lithium resources will bring great pressure on the development of sustainable electrochemical systems. Hybrid supercapacitors utilizing Na + instead of Li + are emerging as a possible substitute for addressing this issue due to the wide availability of sodium resources, low cost, and similar physiochemical properties between sodium and lithium. [17][18][19] As compared to LICs, sodium-ion capacitors (SICs) are still at their infant stage and need substantial advancement. Commercial graphite that is well employed as the Li-ion intercalation anode could not be directly used for SICs. Possible reasons are the insufficient interlayer spacing of graphite and the weakest chemical binding of Na to a given substrate, compared with the other alkali metals in the same column of the periodic table. [20] To search for potential carbon anodes, specific strategies have to be implemented, such as expanding the graphite interlayer, [21] forming house-of-cards structure, [22] and introducing defects. [23,24] While these functionalized carbon and structures demonstrate promoted sodium storage, the rate performance cannot always be guaranteed. Alternatively, layered titanates (A 2 Ti n O 2n+1 , A = Na, K, and H) represent a wide range of family with large interspacing of ≈0.7 nm for sodium storage. [8b] The Sodium-ion capacitors (SICs) have attracted increasing attention for sustainable energy utilization owing to their low cost and similar intercalation electrochemistry with lithium-ion capacitors. However, the practical application of SICs is seriously hindered by the low initial coulombic efficiency (ICE) and limited redox kinetics at the battery electrode side. Herein, taking a layered sodium titanate battery anode as an example, this study reports on the synergistic combination of ether electrolyte and binder-free array architecture to simultaneously achieve superior ICE and ultrafast Na + intercalation. The resulting Na 2 Ti 2 O 5 nanosheet array anode delivers extraordinary ICE (91%), high cycle CE (≈100%), and outstanding rate performance (66% capacity retention at 120 C). The key to the superior per...

Ionic‐Conducting and Robust Multilayered Solid Electrolyte Interphases for Greatly Improved Rate and Cycling Capabilities of Sodium Ion Full Cells

“…Moreover, the enhanced electrochemical performance was also proven to be effective even in the alloying‐type anode with large volume expansion. [ 13–21 ] The enhanced performance of bulk bismuth in an ether‐based electrolyte was first reported by Chen’s group; [ 19 ] the microsized bulk bismuth could be incorporated into a porous architecture during the cycling, which ensures continuous sodium‐ion transport and structural stability for over 2000 cycles. Motivated by an intriguing phenomenon where the SEI itself was associated with the cyclic stability, the sodium storage performances could be further enhanced by matching ether‐based electrolytes with bismuth‐based composite materials, such as Bi@C, [ 22 ] Bi/N‐C, [ 23 ] Bi/graphite, [ 24 ] and Bi/graphene.…”

Post-annealing tailored 3D cross-linked TiNb2O7 nanorod electrode: towards superior lithium storage for flexible lithium-ion capacitors

“…Flexible energy storage devices require not only high energy and power densities, but also good mechanical properties to ensure robust flexibility or bendability. As a result, a promising design principle of using binder-free electrode-based hybrid capacitors was recently proposed by our group [15,[62][63]. The direct growth of three-dimensional (3D) electrode architecture on flexible current collectors has been proven to fulfil all the electrochemical and mechanical requirements for advanced flexible LICs [64].…”

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

“…In this case, a higher ICE value of 95.4% can be achieved for MoSe 2 @HBC in the NaCF 3 SO 3 /diglyme electrolyte, which is mainly due to a very thin and stable SEI. [38] However, the specific capacity becomes relatively lower in NaCF 3 SO 3 /diglyme (e.g., 288.9 mA h g −1 at 10 A g −1 ) than in NaClO 4 /PC (e.g., 391.2 mA h g −1 at 10 A g −1 ) (Figure 4c). Considering the anode will undergo electrochemical activation before the assembly of SICs, [39] here we focus on achieving high Nastorage capacities.…”