Operando pH Measurements Decipher H⁺/Zn²⁺ Intercalation Chemistry in High-Performance Aqueous Zn/δ-V₂O₅ Batteries

Abstract

Vanadium oxides have been recognized to be among the most promising positive electrode materials for aqueous zinc metal batteries (AZMBs). However, their underlying intercalation mechanisms are still vigorously debated. To shed light on the intercalation mechanisms, high-performance δ-V 2 O 5 is investigated as a model compound. Its structural and electrochemical behaviors in the designed cells with three different electrolytes, i.e., 3 m Zn(CF 3 SO 3 ) 2 /water, 0.01 M H 2 SO 4 /water, and 1 M Zn(CF 3 SO 3 ) 2 /acetonitrile, demonstrate that the conventional structural and elemental characterization methods cannot adequately clarify the separate roles of H + and Zn 2+ intercalations in the Zn(CF 3 SO 3 ) 2 /water electrolyte. Thus, an operando pH determination method is developed and used toward Zn/δ-V 2 O 5 AZMBs. This method indicates the intercalation of both H + and Zn 2+ into δ-V 2 O 5 and uncovers an unusual H + /Zn 2+ -exchange intercalation–deintercalation mechanism. Density functional theory calculations further reveal that the H + /Zn 2+ intercalation chemistry is a consequence of the variation of the electrochemical potential of Zn 2+ and H + during the electrochemical intercalation/release.

Electrolyte Study with in Operando pH Tracking Providing Insight into the Reaction Mechanism of Aqueous Acidic Zn//MnO2 Batteries

“…Altogether, the combination of the CV curves with the pH tracking values shows that every redox peak of the CV curve has a corresponding pH change answer (s. Figure 6). Considering the ZnSO 4 ‐containing electrolyte compositions, possible Zn 2+ intercalation would be the only chemical process that does not affect the pH of the ARZIB electrolyte (s. equation (7)) [12,48] . All other expected chemical reactions influence the pH value due to the formation/consumption of the pH‐relevant ions H + and OH − .…”

“…(2020) recently used an in operando pH measurement technique in Swagelok© three‐electrode cells to reveal the reaction mechanisms with different electrolyte compositions (Zn(CF 3 SO 3 ) 2 +water/+acetonitrile, 0.01 M H 2 SO 4 +water). Thereby, the pH curves were associated to H + /Zn 2+ (de‐)intercalation and unusual H + /Zn 2+ exchange (de‐)intercalation processes into the vanadium oxide host material [48] …”

An In Situ Artificial Cathode Electrolyte Interphase Strategy for Suppressing Cathode Dissolution in Aqueous Zinc Ion Batteries

“…This basic precipitation indicates the pH changing after the H + deinsertion/insertion process, which is consistent with other reports. [ 33,34 ] The EDS mapping images, as shown in Figure S5 of the Supporting Information, display that the O area is larger than the V area, demonstrating that this basic vanadium‐contained precipitation is not a part of the CEI layer.…”

Aqueous MnV2O6‐Zn Battery with High Operating Voltage and Energy Density

“…The high energy density and good cycling stability of the MVO:CNT cathode are among the best reported in state-of-the-art AZIBs (Figure 3f and Table S4, Supporting Information). [42] O d -Mn 3 O 4 @C (O d -MO@C), [18] Na 3 V 2 (PO 4 ) 2 O 1.6 F 1.4 (NVPOOF), [43] H-VO 2 , [44] δ-Ca 0.34 V 2 O 5 •1.16H 2 O/rGO (CVO/rGO), [45] PANI-V 2 O 5 (PANI-VO), [46] δ-Ni 0.25 V 2 O 5 •nH 2 O (NiVO), [47] NaCa 0.6 V 6 O 16 •3H 2 O (NCVO), [11] KV 3 O 8 •0.75H 2 O/CNT (KVO/CNT), [22] MnO 2 @PEDOT (MO-PDOT), [48] and PNiCo 2 O 4−x (P-NCO). [49] Cyclabilities of the pristine MVO and the MVO:CNT cathodes were also investigated through 3000 charge/discharge processes at 1000 and 2000 mA g −1 , respectively, as shown in Figure 4a and Figure S10, Supporting Information.…”

“…dQ/dV curves of d) oxidation and e) reduction for MVO and MVO:CNT at different current densities. f) Comparison of energy density and capacity retention among MVO, MVO:CNT, and reported cathode materials for aqueous Zn-ion batteries: O d -V 6 O 13 (O d -VO),[42] O d -Mn 3 O 4 @C (O d -MO@C),[18] Na 3 V 2 (PO 4 ) 2 O 1.6 F 1.4 (NVPOOF),[43] H-VO 2 ,[44] δ-Ca 0.34 V 2 O 5 •1.16H 2 O/rGO (CVO/rGO),[45] PANI-V 2 O 5 (PANI-VO),[46] δ-Ni 0.25 V 2 O 5 •nH 2 O (NiVO),[47] NaCa 0.6 V 6 O 16 •3H 2 O (NCVO),[11] KV 3 O 8 •0.75H 2 O/CNT (KVO/CNT),[22] MnO 2 @PEDOT (MO-PDOT),[48] and PNiCo 2 O 4−x (P-NCO) [49].…”