Flexible Quasi‐Solid‐State Sodium‐Ion Capacitors Developed Using 2D Metal–Organic‐Framework Array as Reactor

Abstract

storage device, lithium ion batteries can provide high energy but usually suffer from a low power rate and short life span. To overcome these drawbacks, researchers propose the so-called metal-ion capacitors, or hybrid batteries, which combine a battery anode and a capacitor electrode in order to achieve tradeoff between conventional battery and supercapacitor. [6][7][8] It is expected that such hybrid system delivers a capacitor-like fast charge/ discharge rate and battery-like high capacity. Since the first introduction in 2001, great progress has been achieved in the field of hybrid lithium-ion capacitors (LICs) through better understanding of the charge storage mechanism and the development of highperformance nanostructured materials. In a LIC, the capacitive cathode is typically a carbonaceous material that enables fast charge− discharge processes, while the reported battery-type anode includes Li 4 Ti 5 O 12 , [9,10] graphite, [11] TiO 2 , [12] MnO, [13] and LiVO 3 . [14] Sodium-ion batteries are becoming one of most promising battery technologies for the foreseeable grid-scale applications, because of more earth-abundant sodium source and their similar chemistry to that of the existing lithium-ion batteries. [15][16][17][18][19][20][21][22] Despite the potential low-cost, constructing hybrid sodium ion capacitors (NICs) faces more challenge because most Na host materials have a rather sluggish kinetic due to the large Na ion sizes. Research on NICs began in early 2012, [23] and was focused on improving the power capability of the anode in order to match the fast kinetics of the capacitive cathode. Strategies to increase sodium ion (Na + ) and electron (e − ) transport kinetics of NIC electrodes reported so far include: (1) developing new electrode materials (such as 2D MXene Ti 2 C, [24] V 2 C), [25] (2) constructing more conductive electrode structures by hybridizing with carbon (such as NaTi 2 (PO 4 ) 3 /rGO, [26] C@NVP, [27] Nb 2 O 5 @C/rGO, [28] TiO 2 mesocages@rGO, [29] and (3) shortening the ion diffusion and electron transport lengths by rational designing nanostructures (such as TiO 2 nanospheres, [30] Ti(O,N) nanowires, [31] Na 2 Ti 3 O 7 nanosheets [32] ). Despite these efforts, these reported anodes of NIC still have relatively limited rate performance and especially low Na-ion storage capacity. Among other reasons, most of these electrode materials are powder samples, which require substantial amount of conductive additives (such as super P, 10-20 wt%) and binder in order to make compact films. This not only weakens the electron transport but also unable to meet the flexibility requirement.Achieving high-performance Na-ion capacitors (NICs) has the particular challenge of matching both capacity and kinetics between the anode and cathode. Here a high-power NIC full device constructed from 2D metal-organic framework (MOFs) array is reported as the reactive template. The MOF array is converted to N-doped mesoporous carbon nanosheets (mp-CNSs), which are then uniformly encapsulated with VO 2 and Na...

Mesopore‐Induced Ultrafast Na+‐Storage in T‐Nb2O5/Carbon Nanofiber Films toward Flexible High‐Power Na‐Ion Capacitors

“…For example, Dong et al developed a flexible sodium‐ion pseudocapacitor by using Na 2 Ti 3 O 7 /carbon cloth as an anode . In another recent work, a flexible NIC device was constructed from 2D metal–organic framework arrays on carbon cloth as the reactive template. Obviously, a high Na + ‐storage performance has been achieved for these flexible NICs based on the active materials, but their overall energy density based on the full device is significantly low.…”

Recent Advances of Two‐Dimensional Nanomaterials for Electrochemical Capacitors

“…Wang et al. fabricated a quasi‐solid‐state flexible SIC based on the NVP@mp‐CNS cathode and VO 2 @mp‐CNS anode (Figure a and b) . This hybrid NIC device delivered a high energy density of 161 Wh kg −1 at a power density of 240 W kg −1 (Figure c and d), with good cyclic stability (78 % retention after 2000 cycles at 1 A g −1 ; Figure e).…”

Large‐Area, Uniform, Aligned Arrays of Na3(VO)2(PO4)2F on Carbon Nanofiber for Quasi‐Solid‐State Sodium‐Ion Hybrid Capacitors

“…For example, Yamada, et al reported the prototype SIHC device by using the alluaudite Na 2 Fe 2 (SO 4 ) 3 cathode and the MXene Ti 2 C anode at a voltage of 2.4 V. Chen et al designed a stable NIHC device by coupling a Al 2 O 3 ‐coated Na 0.66 Mn 0.54 Ni 0.13 Co 0.13 O 2 cathode with a commercial CA anode in an Na+‐containing organic electrolyte. In addition, Na 0.44 MnO 2 nanorods and Na 3 V 2 (PO 4 ) 3 /N‐doped mesoporous carbon nanosheets were also utilized to construct NIHCs. The energy density of these SIHCs is obviously increased, but the corresponding power density is strongly dependent on the Na + ‐intercalation/de‐intercalation kinetics of the cathode materials.…”