Fluorine substitution enabling pseudocapacitive intercalation of sodium ions in niobium oxyfluoride. Issue 36 (30th August 2019)

• Record Type: Journal Article
• Authors: Wu, Yilan; Fan, Xin; Chen, Yinjuan; Gaddam, Rohit Ranganathan; Yu, Feng; Xiao, Changlong; Lin, Chunfu; Zhao, Qinglan; Sun, Xiaoming; Wang, Hongxia; Liu, Chenguang; Li, Jun; Zhao, Xiu Song
• Is Part Of: Journal of materials chemistry. Volume 7:Issue 36(2019)
• Page Start: 20813
• Page End: 20823
• Publication Date: 2019-08-30
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c9ta07320e
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : A collaborative materials engineering of an orthorhombic niobium oxyfluoride/carbon nanobelt anode provides enhanced sodium-ion storage through a combination of pseudocapacitive intercalation and conversion mechanisms. Abstract : Low electrical conductivity and sluggish charge storage kinetics are the key issues of orthorhombic niobium pentoxide (T-Nb2 O5 ) for sodium-ion batteries. Here, we report on an approach for improving the electrochemical properties of T-Nb2 O5 using fluorine substitution and carbon modification strategies. The obtained orthorhombic niobium oxyfluoride/carbon nanobelt composite (T-Nb2 O5− x F y ⊂C-NBs) displayed significantly improved electrochemical properties with sodium ion storage capacity as high as 292 mA h g −1 at 0.05 A g −1, along with an excellent cycling stability over 10 000 cycles at 1 A g −1 (0.002% capacity decay per cycle) as measured using a half cell. An intercalation-pseudocapacitance mechanism (1.0–3.0 V vs. Na/Na + ) for storing sodium ions was observed in T-Nb2 O5− x F y ⊂C-NBs, along with a conversion reaction mechanism (<0.2 V vs. Na/Na + ), leading to an improved energy storage performance and faster kinetics. Density functional theory calculations revealed that the fluorine-substituted niobium oxyfluoride possesses energetically more favourable sodiation sites and lower diffusion barriers compared to the pristine T-Nb2 O5 . Characterisation results confirmed that the self-assembled T-Nb2 O5− x F y ⊂C-NBs exhibit a hierarchical nanoarchitecture with T-Nb2 O5− x F y nanoslabs uniformly embedded in a carbon nanobelt matrix to form arrays, enabling excellent electron conductivity and electron/ion transport, as well as structural stability against cycling. Benefitting from both the compositional and structural advantages of the T-Nb2 O5− x F y ⊂C-NBs composite, a sodium-ion capacitor fabricated with T-Nb2 O5− x F y ⊂C-NBs as the anode and a commercial activated carbon as the cathode delivered energy densities of 86.8 and 32.1 W h kg −1 at power densities of ∼250 and 18 000 W kg −1, respectively.