Developing high capacity and stable cathodes is a key to successful commercialization of aqueous Zn‐ion batteries (ZIBs). Pure layered V2O5 has a high theoretical capacity (585 mAh g−1), but it suffers severe capacity decay. Pre‐inserting cations into V2O5 can substantially stabilize the performance, but at an expense of lowered capacity. Here we show that an atomic layer deposition derived V2O5 can be an excellent ZIB cathode with high capacity and exceptional cycle stability at once. We report a rapid in situ on‐site transformation of V2O5 atomic layers into Zn3V2O7(OH)2⋅2 H2O (ZVO) nanoflake clusters, also a known Zn‐ion and proton intercalatable material. High concentration of reactive sites, strong bonding to the conductive substrate, nanosized thickness and binder‐free composition facilitate ionic transport and promote the best utilization of the active material. We also provide new insights into the V2O5‐dissolution mechanisms for different Zn‐salt aqueous electrolytes and their implications to the cycle stability.
The cathode is a critical component for aqueous Zn-ion batteries (ZIBs) to achieve high capacity and long stability. In this work, we demonstrate a dissolution-free, low-Zn-preinserted bilayer-structured V 2 O 5 xerogel cathode, Zn 0.1 V 2 O 5 •nH 2 O (ZnVO), with excellent capacity and stability using a low-cost ZnSO 4 electrolyte. Its discharge capacity reaches 463 mAh g −1 at 0.2 A g −1 and 240 mAh g −1 at 10 A g −1 , while 93% and 88% of its capacity are retained at 0.2 A g −1 for 200 cycles and at 10 A g −1 for 20 000 cycles, respectively. We then show that the outstanding performance of ZnVO is derived from the enlarged gallery spacing by the solvent water intercalation and the water stable V 2 O 5 bilayer structure. We further unveil via ab initio molecular dynamics that H + is largely originated from the dissociation of the gallery water, while OH − moves out of the gallery to form Zn 4 (SO 4 )(OH) 6 •5H 2 O with ZnSO 4 electrolyte on the surface of ZnVO; the intercalated Zn 2+ forms aquo complex [Zn(H 2 O) 6 ] 2+ with the gallery water. Our theoretical analysis also suggests that the gallery water and solvent water in the electrolyte are statistically the same and functionally equivalent. Overall, this study shows the promise of ZnVO as a practical cathode for ZIBs and offers fundamental insights into the roles of gallery water, solvent water, bilayer V 2 O 5 structure, and dual Zn 2+ /H + intercalation mechanisms in achieving high capacity and long stability. KEYWORDS: cathode, ab initio molecular dynamics, gallery water, bilayer V 2 O 5 structure, hybrid H + /Zn 2+ intercalation
The predictive self‐assembly of tunable nanostructures is of great utility for broad nanomaterial investigations and applications. The use of equilibrium‐based approaches however prevents independent feature size control. Kinetic‐controlled methods such as persistent micelle templates (PMTs) overcome this limitation and maintain constant pore size by imposing a large thermodynamic barrier to chain exchange. Thus, the wall thickness is independently adjusted via addition of material precursors to PMTs. Prior PMT demonstrations added water‐reactive material precursors directly to aqueous micelle solutions. That approach depletes the thermodynamic barrier to chain exchange and thus limits the amount of material added under PMT‐control. Here, an ex situ hydrolysis method is developed for TiO2 that mitigates this depletion of water and nearly decouples materials chemistry from micelle control. This enables the widest reported PMT range (M:T = 1.6–4.0), spanning the gamut from sparse walls to nearly isolated pores with ≈2 Å precision adjustment. This high‐resolution nanomaterial series exhibits monotonic trends where PMT confinement within increasing wall‐thickness leads to larger crystallites and an increasing extent of lithiation, reaching Li0.66TiO2. The increasing extent of lithiation with increasing anatase crystallite dimensions is attributed to the size‐dependent strain mismatch of anatase and bronze polymorph mixtures.
Developing high capacity and stable cathodes is a key to successful commercialization of aqueous Zn‐ion batteries (ZIBs). Pure layered V2O5 has a high theoretical capacity (585 mAh g−1), but it suffers severe capacity decay. Pre‐inserting cations into V2O5 can substantially stabilize the performance, but at an expense of lowered capacity. Here we show that an atomic layer deposition derived V2O5 can be an excellent ZIB cathode with high capacity and exceptional cycle stability at once. We report a rapid in situ on‐site transformation of V2O5 atomic layers into Zn3V2O7(OH)2⋅2 H2O (ZVO) nanoflake clusters, also a known Zn‐ion and proton intercalatable material. High concentration of reactive sites, strong bonding to the conductive substrate, nanosized thickness and binder‐free composition facilitate ionic transport and promote the best utilization of the active material. We also provide new insights into the V2O5‐dissolution mechanisms for different Zn‐salt aqueous electrolytes and their implications to the cycle stability.
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