Mechanistic Insight into the Electrochemical Performance of Zn/VO₂ Batteries with an Aqueous ZnSO₄ Electrolyte

Abstract

Zn-H 2 O fuel cells, [8] etc.), rechargeable aqueous Zn-ion batteries (ZIBs) with a mild electrolyte are particularly attractive as zinc is more compatible with water than alkaline metals, Zn-ions are divalent, and the production and recycling of these batteries is relatively simple. [9][10][11][12] A variety of manganese dioxide (MnO 2 ) polymorphs (α-, β-, γ-, δ-, and amorphous) have been investigated as cathodes materials for ZIBs. [10,11,[13][14][15][16][17][18][19] Several studies have demonstrated that the storage capacity of MnO 2 in a neutral or mildly acidic aqueous electrolyte is partly induced by a reversible Zn 2+ insertion/extraction reaction and partly by the reversible H + insertion/extraction. [10,11,19] This process is governed by the reversible phase transition of the MnO 2 polymorphs from a tunneled to layered structure, driven by the electrochemical reaction. During this phase transition, even though the crystalline structure is maintained, Mn 3+ in the tunnel chains are reduced to soluble Mn 2+ leading to a capacity fading, a short cycle life and low Coulombic efficiency of aqueous Zn/MnO 2 batteries. [17,20] To prevent this dissolution of Mn ions, alternative electrolytes were identified, for example, Zhang et al., found that by using a Zn(CF 3 SO 3 ) 2 aqueous electrolyte, Mn-ion dissolution was suppressed and a high capacity retention with a ZnMn 2 O 4 cathode was achieved. [21] Alternatively by using a MnSO 4 additive to a mild ZnSO 4 aqueous electrolyte, Pan et al. reported that the Mn 2+ dissolution in the aqueous Zn/MnO 2 electrolyte was inhibited. [11] Though research into MnO 2 cathodes for aqueous ZIBs has gained momentum, it is of great importance to develop alternative high capacity cathode materials for ZIBs that are stable in an aqueous electrolyte.Very recently, vanadium oxide and its related compounds have been reported as cathodes for ZIBs, showing higher energy densities and better capacity retention compared to MnO 2 cathodes. Senguttuvan et al. reported the reversible Zn 2+ insertion/extraction process in a V 2 O 5 cathode for a nonaqueous ZIBs. [22] Kundu et al. developed a highly stable vanadium bronze (Zn 0.25 V 2 O 5 ·nH 2 O) cathode for aqueous ZIBs, which displayed a high energy density and capacity retention through a reversible Zn 2+ (de)intercalation process. [12] In addition, LiV 3 O 8 , [23] H 2 V 3 O 8 , [24] and V 2 S [25] cathodes exhibit good capacity reversibility and power density for aqueous ZIBs. Although Oberholzer et al. [26] observed a proton intercalation Rechargeable aqueous zinc-ion batteries (ZIBs) are promising for cheap stationary energy storage. Challenges for Zn-ion insertion hosts are the large structural changes of the host structure upon Zn-ion insertion and the divalent Zn-ion transport, challenging cycle life and power density respectively. Here a new mechanism is demonstrated for the VO 2 cathode toward proton insertion accompanied by Zn-ion storage through the reversible deposition of Zn 4 (OH) 6 SO 4 ·5H 2 O on the cathode surface, sup...

Conversion Synthesis of Self‐Standing Potassium Zinc Hexacyanoferrate Arrays as Cathodes for High‐Voltage Flexible Aqueous Rechargeable Sodium‐Ion Batteries

“…To explore the electrochemical kinetics of the CC@KZHCF electrode, the relationship between the scan rates ( v ) and the corresponding peak current densities ( i ) is displayed in Figure d. The slopes ( b , where a b value of 0.5 implies a diffusion‐controlled process, whereas 1.0 indicates a surface‐controlled process) of the corresponding log( v )–log( i ) plots for peak 1 and peak 2 are 0.74 and 0.72, respectively, which demonstrates that the insertion/extraction processes of Na + are a combination of diffusion‐controlled and surface‐controlled . In addition, the capacitive contribution ratios of CC@KZHCF at various scan rates from 1 to 5 mV s −1 are 77.9%, 78.9%, 81.0%, 84.6%, and 89.3% (Figure S7, Supporting Information), respectively, indicating that the capacitive contribution plays an important role in the rate performance .…”

Phosphorus‐Functionalized Fe2VO4/Nitrogen‐Doped Carbon Mesoporous Nanowires with Exceptional Lithium Storage Performance

“…The Fe 2p spectrum presented in Figure S9A can be assigned to the Fe 3+ 2p 3/2 (713.3 eV), Fe 2+ 2p 3/2 (710.8 eV), Fe 3+ 2p 1/2 (727.2 eV), Fe 2+ 2p 1/2 (724.2 eV), and their satellite peaks, respectively . The V 2p spectrum is divided into V 4+ 2p 3/2 (516.7 eV), V 4+ 2p 1/2 (523.9 eV), V 3+ 2p 3/2 (515.4 eV), V 3+ 2p 1/2 (522.5 eV), respectively (Figure S9B) . It is interesting that the peak intensities of Fe 3+ decreased after P‐doping, which is consistent with the previous report .…”

Binding Zinc Ions by Carboxyl Groups from Adjacent Molecules toward Long‐Life Aqueous Zinc–Organic Batteries

“…[ 2–7 ] Among them, aqueous zinc batteries have aroused extensive interest and attention, which benefits from many advantages of zinc anode, including high theoretical capacity (820 mAh g −1 ), appropriate redox potential (−0.762 V vs the standard hydrogen electrode (SHE)), and intrinsic safety in aqueous system. [ 8–20 ] Inspired by conventional Li + storage reaction, intercalation reaction of transition metal oxides are employed to storage Zn 2+ in the mild aqueous solution. For example, Zn 0.25 V 2 O 5 · n H 2 O, [ 9 ] Prussian blue analogue, [ 15 ] VO 2 , [ 17 ] MnO 2 , [ 18 ] Zn 3 V 2 O 7 (OH) 2 ·2H 2 O, [ 19 ] CuV 2 O 6 [ 20 ] have been used as cathodes for zinc batteries.…”

“…[ 8–20 ] Inspired by conventional Li + storage reaction, intercalation reaction of transition metal oxides are employed to storage Zn 2+ in the mild aqueous solution. For example, Zn 0.25 V 2 O 5 · n H 2 O, [ 9 ] Prussian blue analogue, [ 15 ] VO 2 , [ 17 ] MnO 2 , [ 18 ] Zn 3 V 2 O 7 (OH) 2 ·2H 2 O, [ 19 ] CuV 2 O 6 [ 20 ] have been used as cathodes for zinc batteries. However, the hydrated Zn 2+ and H + usually result in large volumetric change and serious structural collapse of these inorganic compounds with the insertion of a large amount of hydrated Zn 2+ , [ 21–25 ] showing significant capacity fading and limited cycle life.…”