Flexible Sodium‐Ion Pseudocapacitors Based on 3D Na₂Ti₃O₇ Nanosheet Arrays/Carbon Textiles Anodes

Abstract

Flexible energy storage devices are critical components for emerging flexible and wearable electronics. Improving the electrochemical performance of flexible energy storage devices depends largely on development of novel electrode architectures and new systems. Here, a new class of flexible energy storage device called flexible sodium‐ion pseudocapacitors is developed based on 3D‐flexible Na2Ti3O7 nanosheet arrays/carbon textiles (NTO/CT) as anode and flexible reduced graphene oxide film (GFs) as cathode without metal current collectors or conducting additives. The NTO/CT anode with advanced electrode architectures is fabricated by directly growing Na2Ti3O7 nanosheet arrays on carbon textiles with robust adhesion through a simple hydrothermal process. The flexible GF//NTO/CT configuration achieves a high energy density of 55 Wh kg−1 and high power density of 3000 W kg−1. Taking the fully packaged flexible sodium‐ion pseudocapacitors into consideration, the maximum practical volumetric energy density and power density reach up to 1.3 mWh cm−3 and 70 mW cm−3, respectively. In addition, the flexible GF//NTO/CT device demonstrates a stable electrochemical performances with almost 100% capacitance retention under harsh mechanical deformation.

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

“…Even at an extremely high power density of 48 kW kg −1 , the NIC can still deliver 49 W h kg −1 . Those values are much higher than those in the recently reported flexible energy storage devices, such as H-TiO 2 @MnO 2 //H-TiO 2 @C device (0.30 mW h cm −3 , 0.23 W cm −3 ), [56] Na 2 Ti 3 O 7 //rGO NIC (1.30 mW h cm −3 , 0.07 W cm −3 ), [32] T-Fe 2 O 3 /PPy//MnO 2 supercapacitor (1.30 mW h cm −3 , 0.07 W cm −3 ). [8,44] Obviously, our MOFderived carbon array-based NIC combines the advantages of Figure 5.…”

“…The energy density and power density values are calculated by integrating galvanostatic discharge curves and using the total mass of the two electrodes. The energy densities of the present quasi-solid-state NIC device are considerably higher than those values of the state-of-the-art reported NICs [23,[26][27][28][29][30][31][32][45][46][47] (Table S2, Supporting Information) and other energy storage systems such as lithium ion capacitors, [48][49][50] aqueous asymmetric SCs, [51,52] ionic liquid-based SCs, [33,53] and Ni/Fe batteries. Even at an extremely high power density of 48 kW kg −1 , the NIC can still deliver 49 W h kg −1 .…”

“…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 . 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] ). [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.…”

Understanding Fundamentals and Reaction Mechanisms of Electrode Materials for Na‐Ion Batteries

“…But early reports show quite poor cyclability. Improved cyclability is achieved based on the binder‐free Na 2 Ti 3 O 7 nanoarrays . Figure b shows the cyclability of Na 2 Ti 3 O 7 nanotube arrays.…”

Three‐Dimensional Graphene‐based N‐doped Carbon Composites as High‐Performance Anode Materials for Sodium‐ion Batteries

“…[5,6] However,o nly a few anode materials are suitable for SIB, because of larger radius of Na than Li, which would suffer from more serious volumee xpansion during the charge/discharge process and lead to more sluggish sodium kinetics, more difficult intercalation into the lattice andl ower diffusion in the electrode materials. [3,6,[8][9][10][11][12][13] However,t hese materials show al ow discharge capacityi nS IBs (approximately 350 mAh g À1 )b ecause of the poor insertion kinetics of Na ions into these nanomaterials. [3,6,[8][9][10][11][12][13] However,t hese materials show al ow discharge capacityi nS IBs (approximately 350 mAh g À1 )b ecause of the poor insertion kinetics of Na ions into these nanomaterials.…”