Pseudocapacitive Graphene‐Wrapped Porous VO₂ Microspheres for Ultrastable and Ultrahigh‐Rate Sodium‐Ion Storage

Abstract

The exploration of anode materials with enhanced electronic/ ionic conductivity and structural stability is beneficial for the development of sodium-ion batteries. Herein, a simple solutionderived method is demonstrated to fabricate porous VO 2 microsphere composite with a graphene-wrapped structure (VO 2 /G). When used as the anode material for sodium-ion batteries, the VO 2 /G electrode delivers a high reversible specific capacity (373.0 mAh g À 1 ), great rate capability (138.8 mA h g À 1 at 24.0 A g À 1 , � 21 s per charge/discharge), and excellent longcycling performance (95.9 % capacity retention for 3600 cycles at 2.0 A g À 1 ). The outstanding electrochemical property of VO 2 /G is mainly attributed to its unique graphene-wrapped porous structure and the pseudocapacitive-dominated feature. In addition, the sodium-ion storage mechanism of VO 2 /G is investigated by various ex-situ characterization techniques. During the first sodiation process, the sodium-ion appears to partially reduce VO 2 /G and form metallic vanadium, sodium oxide, and amorphous sodium vanadium. This work provides new fundamental information for the design and application of vanadium oxides for energy storage system.[a] L.

Enhanced Pseudocapacitive Lithium-Ion Storage in a Coherent rGO/VO2-R Heterojunction

“…The high-resolution spectrum of V 2p (Figure b) was applied to identify the chemical state of V in the composite. The first two peaks with binding energies (BEs) of ∼524.6 and 517.2 eV with a spin–orbital split energy of 7.4 eV can be ascribed to the 2p 1/2 and 2p 3/2 core-level species of V 4+ in the VO 2 lattice . Another pair of peaks with BEs of 523.3 and 515.9 eV corresponds to the 2p 1/2 and 2p 3/2 species of the V 3+ species due to the partial reduction of V 4+ in VO 2 during the synthesis of the rGO/VO 2 -R composite in a carbothermal reduction procedure .…”

“…The first two peaks with binding energies (BEs) of ∼524.6 and 517.2 eV with a spin−orbital split energy of 7.4 eV can be ascribed to the 2p 1/2 and 2p 3/2 core-level species of V 4+ in the VO 2 lattice. 44 Another pair of peaks with BEs of 523.3 and 515.9 eV corresponds to the 2p 1/2 and 2p 3/2 species of the V 3+ species due to the partial reduction of V 4+ in VO 2 during the synthesis of the rGO/VO 2 -R composite in a carbothermal reduction procedure. 45 The deconvolution analysis of the O 1s XPS spectrum in Figure 3c reveals the presence of four oxygen species in the composite, namely, lattice O in VO 2 with a BE of ∼529.9 eV, 46 oxygen vacancies (V O ) on the surface (532 eV), 46 and C−O (530.9 eV) and C�O (533.1 eV) bonds on the rGO surface.…”

Advanced Vanadium Oxides for Sodium‐Ion Batteries

“…Then, the NaVO 2 compound further oxidize to form Na x VO 2 (with x ≈ 0.3) in the subsequent charging process. Therefore, the sodium storage mechanism of VO 2 can be expressed as: [62] When V 2 O 3 is employed as the electrode material for SIBs, the crystalline structure of V 2 O 3 remains unchanged throughout the entire charge-discharge process. This indicates that no phase transition occurs during the insertion/desertion of Na + ions into/from the V 2 O 3 crystal structure, thus confirming an intercalation reaction mechanism, which is represented as: [34] Similar to V 2 O 3 , V 3 O 7 •H 2 O exhibits an intercalation reaction mechanism in SIBs.…”

“…Therefore, the sodium storage mechanism of VO 2 can be expressed as: x Na + + x e − + VO 2 → Na x VO 2 ( x = 1) ↔ Na x VO 2 ( x = 0.3). [ 62 ] When V 2 O 3 is employed as the electrode material for SIBs, the crystalline structure of V 2 O 3 remains unchanged throughout the entire charge‐discharge process. This indicates that no phase transition occurs during the insertion/desertion of Na + ions into/from the V 2 O 3 crystal structure, thus confirming an intercalation reaction mechanism, which is represented as: x Na + + x e − + V 2 O 3 ↔ Na x V 2 O 3 .…”

A flower‐like VO2(B)/V2CTx heterojunction as high kinetic rechargeable anode for sodium‐ion batteries

“…8 Therefore, simple synthesis method, tailored nanoarchitecture design and additional surface engineering may facilitate industrialization. 9 So far, various nanostructures of VO 2 (B), such as nanorods, 10 nanoneedles, 11 nanobelts, 8 nanospheres, 12,13 nanofibers, 14 nanosheets, 15 and 3D grid structure 16 have been synthesized to obtain advanced electrochemical properties. These novel structures not only can provide adequate spaces for relieving volume deformation, but also construct rich interfaces to enhance ion transport.…”