Oxygen Defect Hydrated Vanadium Dioxide/Graphene as a Superior Cathode for Aqueous Zn Batteries

Abstract

Zinc ion batteries have become a new type of energy storage device because of the low cost and high safety. Among the various cathode materials, vanadium–oxygen compounds stand out due to their high theoretical capacity and variable chemistry valence state. Here, we construct a 3D spongy hydrated vanadium dioxide composite (Od-HVO/rG) with abundant oxygen vacancy defects and graphene modifications. Thanks to the stable structure and abundant active sites, Od-HVO/rG exhibits superior electrochemical properties. In aqueous electrolyte, the Od-HVO/rG cathode provides high initial charging capacity (428.6 mAh/g at 0.1 A/g), impressive rate performance (186 mAh/g even at 20 A/g), and cycling stability, which can still maintain 197.5 mAh/g after 2000 cycles at 10 A/g. Also, the superior specific energy of 245.3 Wh/kg and specific power of 14142.7 W/kg are achieved. In addition, MXene/Od-HVO/rG cathode materials are prepared and PAM/ZnSO4 hydrogel electrolytes are applied to assemble flexible soft pack quasi-solid-state zinc ion batteries, which also exhibit excellent flexibility and cycling stability (206.6 mAh/g after 2000 cycles). This work lays the foundation for advances in rechargeable aqueous zinc ion batteries, while revealing the potential for practical applications of flexible energy storage devices.

Stability Optimization Strategies of Cathode Materials for Aqueous Zinc Ion Batteries: A Mini Review

“… Structural modification and composite of cathode materials: (A) Crystal structures of bulk MoS 2 and MoS 2 /graphene; (B,C) the corresponding migration energy barriers with the variation of the MoS 2 -to-graphene distance; (D) schematic illustration of freestanding CNT/MnO 2 -PPy; (E) schematic diagram of Zn 2+ (de)intercalating mechanism in O d -HVO/rG; (F) illustration of electron/ion transport and ion diffusions across the electrodes of CNT@KMO@GC. Reproduced with permission ( Zhang et al, 2020a ; Li et al, 2021d ; Huang et al, 2021 ; Wang et al, 2021 ). …”

“…The optimization strategy of combination engineering usually includes carbon-based materials, which can improve the electron transmission efficiency and structural stability of materials ( Yang et al, 2021 ; Zeng et al, 2021 ). Hou et al synthesized a 3D reticular graphene-based hydrated vanadium dioxide composite (O d -HVO/rG) with abundant oxygen vacancies using the solvothermal method ( Huang et al, 2021 ). The research confirmed that oxygen vacancy defects can provide more active sites and promote the reversibility of the reaction, while the highly conductive and robust rG sponge can promote electron migration and reduce the accumulation of O d -HVO to improve the conductivity and structural stability, as shown in Figure 2E .…”

“…The prepared cathode has a capacity retention rate of 65.2% after 10,000 cycles at 5 Ag −1 , which is significantly higher than KMO (39.1% of the initial capacity) and CNT@ (F) illustration of electron/ion transport and ion diffusions across the electrodes of CNT@KMO@GC. Reproduced with permission (Zhang et al, 2020a;Li et al, 2021d;Huang et al, 2021;Wang et al, 2021). KMO (51.5% of initial capacity).…”

Advances of Metal Oxide Composite Cathodes for Aqueous Zinc‐Ion Batteries

“…[ 146,147 ] Hou and colleagues used a hydrothermal method to create a 3D graphene‐sponge hydrated vanadium dioxide (HVO) composite ( Figure a) after considering the earlier concern. [ 148 ] Reduced graphene (rG)‐doped HVO provides both copious oxygen vacancy defects (denoted as O d –HVO/rG) and graphene conducting channels (Figure 14b–d). The oxygen vacancies give additional active locations for zinc ion capacity storage.…”

“…Reproduced with permission. [ 148 ] Copyright 2021, American Chemical Society. The characterizations of VO 2 ·0·2H 2 O nanocuboids anchored on graphene sheets (VOG) composite: g) SEM images and h) TEM images.…”