Aqueous zinc-ion batteries (ZIBs) have emerged as the most promising alternative energy storage system, but the development of a suitable cathode and the issues of Zn anodes have remained challenging. Herein, an effective strategy of high-capacity layered Mg0.1V2O5·H2O (MgVO) nanobelts together with a concentrated 3 M Zn­(CF3SO3)2 polyacrylamide gel electrolyte was proposed to achieve a durable and practical ZIB system. By adopting the designed concentrated gel electrolyte which not only inherits the high-voltage window and wide operating temperature of the concentrated electrolyte but also addresses the Zn dendrite formation problem, the prepared cathode exhibits an ultrahigh capacity of 470 mAh g–1 and a high rate capability of 345 mAh g–1 at 5.0 A g–1, and the assembled quasi-solid-state ZIBs achieve 95% capacity retention over 3000 cycles as well as a wide operating temperature from −30 to 80 °C, demonstrating a promising prospect for large-scale energy storage. In situ X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis (TGA) investigations also demonstrate a complex reaction mechanism for this cathode involving the (de)­insertion of Zn2+, H+, and water molecules during cycling. The water molecules will reinsert into the interlayer and act as “pillars” to stabilize the host structure when Zn2+ is fully extracted.

and cycle life. However, LIBs suffer from issues including flammability, toxicity, cost, and scarcity of Li metal. [4,5] Rechargeable batteries based on an aqueous electrolyte and earth-abundant elements are regarded as a more sustainable alternative to the current LIBs. Aqueous metal-ion batteries are inherently safe, eco-friendly, cheap, and capable of operating at large currents. [6][7][8] Aqueous zinc-ion battery (ZIB) is one of the types and offers a high theoretical capacity (820 mAh g −1 ) and a low electrochemical potential of metallic Zinc (−0.76 V vs standard hydrogen electrode), [9][10][11][12][13] but the development of highly stable cathode for ZIBs is still challenging.Prussian blue analogues (PBAs) with a formula of A x M[Fe(CN) 6 ] y •nH 2 O (0 < x < 2, 0 < y ≤ 1, A = alkaline metal, M = transition metal) have been considered as promising cathode materials for aqueous alkali metalion batteries. The capacity of PBAs can reach more than 120 mAh g −1 [14][15][16][17] and the stability is excellent, due to the presence of two redox couples and robust 3D open-framework structures allowing the insertion of a variety of alkaline ions without distortion. [18][19][20] However, PBAs only provide a relatively low specific capacity for Zn 2+ cations (typically less than 80 mAh g −1 ), and intercalation of Zn 2+ can lead to uncontrolled phase transition and consequent performance degrading. [9,21,22] Liu et al. first proposed a ZIB using a rhombohedral Zn 3 [Fe(CN) 6 ] 2 (ZnHCF) cathode, which exhibited a low capacity of 65.4 mAh g −1 with 76% capacity retention after 100 cycles. [23] A cubic structure PBA (CuHCF) was synthesized for Zn 2+ storage, and this cathode completed 100 cycles with a capacity of 56 mAh g −1 . [24] Mantia et al. suggested that the capacity decay in CuHCF can be attributed to a phase transition to a second phase which is electrochemically less active. [25,26] To reduce the influence of phase transition resulted from Zn 2+ insertion, researchers employed electrolytes with a low or even zero Zn 2+ concentration to make NiHCF//Zn, [27] CuHCF//Zn, [28] and NaFe-PB//Zn [29] hybrid-ion batteries. Nonetheless, the storage capacities of Zn 2+ in these cathodes were still low despite that the cycle life was improved by increasing the scanning voltage. [30] In this work, we introduce a high voltage aqueous PBA-Zn hybrid-ion battery with KMnHCF (K 1.6 Mn[Fe(CN) 6 ] 0.94 •0.63H 2 O) cathode, zinc foil anode, and 30 m KFSI + 1 m Zn(CF 3 SO 3 ) 2 Prussian blue analogues (PBAs), featuring an open framework for accommodating large ions and tunable valence states, have garnered wide interest in the context of aqueous zinc-ion batteries (ZIBs). However, PBAs in ZIBs currently still suffer from low capacity and poor cycling stability due to structural instability. Here a K 2 MnFe(CN) 6 cathode achieving a very stable capacity of 100 mAh g −1 is reported in a ZIB charged/discharged to 400 cycles. Interestingly, such a stable capacity is attributed to the fact that the K 2 MnFe(CN) 6 cathode is gradually t...

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Aqueous zinc hybrid capacitors are receiving intensive scientific interest for their merits of both capacitors and batteries in achieving safety, high power and energy density as well as long cycle...

A high voltage aqueous full K-ion battery exhibits an ultra-long lifespan of 30 000 cycles and a high energy density of 47.3 W h kg−1.