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Although the utilization of mildly acidic electrolyte can enhance the stability and reversibility of Zn anode, it is still challenging to achieve long cycling life for aqueous Zn batteries at low currents, due to the structural instability of cathode materials during the charge/discharge processes. Herein, we report a series of polypyrenes with different linking patterns and electronic structures as Cl−-hosting organic cathodes for aqueous Zn dual-ion batteries (AZDIBs). The comparative study demonstrates that the electronic structures are pivotal to the redox activity of the polypyrenes, which can be tuned by altering the linking patterns on the pyrene unit. Owing to the high surface area, the highly delocalized HOMO distribution, the high HOMO level and the narrow band gap, the polymer CLPy with 1,3,6,8-linking pattern delivers a much higher capacity of 180 mA h g−1 than the two linear counterparts (24 mA h g−1 for LPy-1 and 44 mA h g−1 for LPy-2). Impressively, CLPy exhibits ultra-stable cyclabilities with the capacity retentions of 97.4% after 800 cycles at 50 mA g−1 and 96.4% after 38 000 cycles at 3 A g−1. CLPy also shows a low self-discharge rate with around 90% capacity retention after resting for 28 days. The excellent electrochemical performance demonstrates that CLPy can be a promising cathode material for high-performance AZDIBs.

Potassium-ion batteries (KIBs) have attracted wide interests for energy storage because of the abundance of the electrode materials involved; however, their electrochemical performances are far behind what can be achieved from lithium-ion batteries (LIBs) or sodium-ion batteries (SIBs). This paper identifies key promising electrode and electrolyte materials for potassium-ion batteries, investigates the coupled electrochemical reactions in the cell, and demonstrates that the compatibility between different materials plays the most important role. K2 Mn[Fe(CN)6 ] cathode can deliver a high capacity of ∼125 mAh g-1 and exceptional cycling stability over 61,000 cycles (∼9 months) if the side reactions from the anode can be prevented. Graphite is a good anode material but is subjected to degradation in traditional carbonate electrolytes. New concentrated electrolytes are developed and evaluated. A stable KIB system is demonstrated by coupling a stable K2 Mn[Fe(CN)6 ] cathode, a pre-potassiated graphite anode with a concentrated electrolyte to achieve a high energy density of ∼260 Wh kg-1 (based on the active mass of cathode and anode) and good cycling of over 1000 cycles. This article is protected by copyright. All rights reserved.

We demonstrate a disposable aqueous primary battery chemistry that comprises environmentally benign materials of the sulfur cathode and Zn anode in a 1 M ZnCl2 aqueous electrolyte. The Zn–S battery shows a high energy density of 1083.3 Wh kg−1 for sulphur with a flat discharge voltage plateau around 0.7 V. When operating at a high mass loading of 8.3 mg cm−2 for sulfur in the cathode, the battery exhibits a very high areal capacity of 11.4 mA h cm−2 and areal energy of 7.7 mW h cm−2.

The elemental sulfur electrode with Cu2+ as the charge carrier gives a four-electron sulfur electrode reaction through the sequential conversion of S↔CuS↔Cu2 S. The Cu-S redox-ion electrode delivers a high specific capacity of 3044 mAh g-1 based on the sulfur mass or 609 mAh g-1 based on the mass of Cu2 S, the completely discharged product, and displays an unprecedently high potential of sulfur/metal sulfide reduction at 0.5 V vs. SHE. The Cu-S electrode also exhibits an extremely low extent of polarization of 0.05 V and an outstanding cycle number of 1200 cycles retaining 72 % of the initial capacity at 12.5 A g-1 . The remarkable utility of this Cu-S cathode is further demonstrated in a hybrid cell that employs an Zn metal anode and an anion-exchange membrane as the separator, which yields an average cell discharge voltage of 1.15 V, the half-cell specific energy of 547 Wh kg-1 based on the mass of the Cu2 S/carbon composite cathode, and stable cycling over 110 cycles.

Dual-ion batteries are known for anion storage in the cathode coupled to cation incorporation in the anode. We flip the sequence of the anion/cation-storage chemistries of the anode and the cathode...

We report reversible electrochemical insertion of NO3 - into manganese(II, III) oxide (Mn3 O4 ) as a cathode for aqueous dual-ion batteries. Characterization by TGA, FTIR, EDX, XANES, EXAFS, and EQCM collectively provides unequivocal evidence that reversible oxidative NO3 - insertion takes place inside Mn3 O4 . Ex situ HRTEM and corresponding EDX mapping results suggest that NO3 - insertion de-crystallizes the structure of Mn3 O4 . Kinetic studies reveal fast migration of NO3 - in the Mn3 O4 structure. This finding may open a new direction for novel low-cost aqueous dual-ion batteries.

Well-defined Na2Zn3[Fe(CN)6]2 nanocrystals (~300 nm) have been fabricated by a facile controlled crystallization method from low-cost precursors at room temperature. By employing [Fe(CN)6]3−/[Fe(CN)6]4− couples as redox centres, this material can realize a theoretical 1Na-storage capacity of 70 mAh g−1, a superior high-rate capability of 20 C and an impressive cycle life of 1000 cycles, offering a low-cost and high-performance alternative cathode for large-scale Na-ion applications. Keywords: Na-ion batteries, Prussian blue analogues, Intercalation cathode, Energy storage

Proton batteries are emerging as a promising solution for energy storage; however, their development has been hindered by the lack of suitable cathode materials. Herein, a hydrous Turnbull's blue analogue (TBA) of Ni[Fe(CN)

Aqueous batteries represent promising solutions for large-scale energy storage considering the cost, safety, and performance. Despite the tremendous efforts devoted to the metal cations as charge carriers for batteries, scarce attention has been paid to the non-metal cations such as proton or ammonium. In this study, we report that a Berlin green framework exhibits much greater structural compatibility for NH4+ (de)insertion than Na+ and K+. Ex situ structural studies reveal that the topochemistry of NH4+ in Berlin green is of nearly zero strain. The NH4+ topotactic performance gives rise to a higher operation potential and an ultralong cycling performance of 50,000 cycles with 78% capacity retention, far superior to Na+ and K+ (de)insertion. Furthermore, we propose a double-ion battery, where the Berlin green cathode hosts NH4+ and sodium titanium phosphate NaTi2(PO4)3 accommodates Na+ during operation. Such a new system exhibits promising results in capacity and cycling life. Our results point to a new ...

To fill the gap between batteries and supercapacitors requires integration of the following features in a single system: energy density well above that of supercapacitors, cycle life much longer than Li-ion batteries, and low cost. Along this line, we report a novel nonaqueous potassium-ion hybrid capacitor (KIC) that employs an anode of K2Ti6O13 (KTO) microscaffolds constructed by nanorods and a cathode of N-doped nanoporous graphenic carbon (NGC). K2Ti6O13 microscaffolds are studied for potential applications as the anode material in potassium-ion storage for the first time. This material exhibits an excellent capacity retention of 85% after 1000 cycles. In addition, the NGC//KTO KIC delivers a high energy density of 58.2 Wh kg–1 based on the active mass in both electrodes, high power density of 7200 W kg–1, and outstanding cycling stability over 5000 cycles. The usage of K ions as the anode charge carrier instead of Li ions and the amenable performance of this device suggest that hybrid capacitor devic...

Iron ion batteries using Fe2+ as a charge carrier have yet to be widely explored, and they lack high-performing Fe2+ hosting cathode materials to couple with the iron metal anode. Here, it is demonstrated that VOPO4 ∙2H2 O can reversibly host Fe2+ with a high specific capacity of 100 mAh g-1 and stable cycling performance, where 68% of the initial capacity is retained over 800 cycles. In sharp contrast, VOPO4 ∙2H2 O's capacity of hosting Zn2+ fades precipitously over tens of cycles. VOPO4 ∙2H2 O stores Fe2+ with a unique mechanism, where upon contacting the electrolyte by the VOPO4 ∙2H2 O electrode, Fe2+ ions from the electrolyte get oxidized to Fe3+ ions that are inserted and trapped in the VOPO4 ∙2H2 O structure in an electroless redox reaction. The trapped Fe3+ ions, thus, bolt the layered structure of VOPO4 ∙2H2 O, which prevents it from dissolution into the electrolyte during (de)insertion of Fe2+ . The findings offer a new strategy to use a redox-active ion charge carrier to stabilize the layered electrode materials.

The ever-increasing demand for storing renewable energy sources calls for novel battery technologies that are of sustainably low levelized energy cost. Research into battery chemistry has evolved to a stage where a plethora of choices based on earth-abundant elements can be compared during their development. One of the emerging candidates is the nonaqueous potassium-ion battery. K-ion’s unique properties as a charge carrier have aroused intense interest in exploring high-performing cathode and anode materials for this battery. Rapid progress has been made, where leading candidates of electrodes have been proposed, i.e., hard carbon as anode and Prussian white analogues as cathode. In this new battery technology’s infancy, it is our opinion that the focus should be given to potentially scalable, inexpensive electrode materials and the understanding of their cycle-life-property correlations. It may be the ultralong cycle life that differentiates potassium-ion batteries from sodium-ion batteries in the futur...

Prussian blue and its analogues have received particular attention as superior cathodes for Na-ion batteries due to their potential 2-Na storage capacity (∼170 mAh g–1) and low cost. However, most of the Prussian blue compounds obtained from the conventional synthetic routes contain large amounts of Fe(CN)6 vacancies and coordinated water molecules, which leads to the collapse of cyano-bridged framework and serious deterioration of their Na-storage ability. Herein, we propose a facile citrate-assisted controlled crystallization method to obtain low-defect Prussian blue lattice with greatly improved Na-storage capacity and cycling stability. As an example, the as-prepared Na2CoFe(CN)6 nanocrystals demonstrate a reversible 2-Na storage reaction with a high specific capacity of 150 mAh g–1 and a ∼ 90% capacity retention over 200 cycles, possibly serving as a low cost and high performance cathode for Na-ion batteries. In particular, the synthetic strategy described in this work may be extended to other coordi...

Aqueous Na-ion batteries have the competitive advantages of being low costing and possessing inherent safety, and they are particularly suitable for large-scale energy-storage applications. However, the development of this new battery system is hindered by the lack of suitable Na hosts with sufficiently high capacity and cycle life. Herein, we report vacancy-free Na2CoFe(CN)6 nanocubes synthesized by a controlled crystallization reaction and reveal their use as a new aqueous cathode with reversible Na-storage behavior. Owing to its perfect lattice framework with two redox-active sites, this material exhibits a high reversible capacity of 130 mA h g−1, a strong rate capability at 20 C, and superior cyclability with 90 % capacity retention over 800 cycles, all of which indicate that this material may possibly serve as a high-performance and long-life cathode for aqueous Na-ion batteries. Also, the synthetic strategy described in this work may be extended to a wide range of Prussian blue compounds for the fabrication of well-shaped nanocubes with few defects for energy storage, catalysis, and other applications.

Prussian blue compounds have potential advantages of high working potentials and multi-electron redox capacities as Na-ion battery cathodes; however, they suffer from their poor capacity utilization in aqueous electrolytes due to the blockage of the active lattice sites by coordinating and zeolitic water for Na insertion reaction. To overcome this problem, we synthesized low-defect Prussian blue FeFe(CN)6 nanocrystals and revealed their Na-storage performance in aqueous electrolytes. Benefitting from its suppressed lattice defects and well-defined nanocubic morphology, the as-prepared Prussian blue nanocrystals exhibit a greatly improved capacity of ~125 mAh g−1, a strong rate capability with 102 mAh g−1 at a high rate of 20C and a remarkably long cycle life with 83% capacity retention over 500 cycles, exceeding considerably the aqueous Na-storage cathodes reported so far and capably serving as a high performance cathode for aqueous Na-ion batteries. As a model compound, the superior electrochemical performance arising from the low-defect Prussian blue nanocrystals provide a new insight into the design of high capacity Na-storage host materials for large scale electric storage applications.

An aqueous rechargable Na-ion battery is developed by use of Na-deficient NaTi2(PO4)3 anode, Na-rich Na2NiFe(CN)6 cathode and aqueous Na2SO4 electrolyte. This battery system can give an average output voltage of 1.27 V, a energy density of 42.5 Wh kg−1 and can retain 88% of initial capacity for 250 cycles cycled at the 5 C rate. Moreover, this aqueous Na-ion battery has the advantages of low cost, environmentally friendliness and inherent safety, particularly attractive for grid-scale energy storage applications. Keywords: Sodium-ion battery, Aqueous electrolyte, Intercalation chemistry, NaTi2(PO4)3 anode, Na2NiFe(CN)6 cathode

Low cost and high performance Li-ion batteries have been extensively pursued for grid-scale energy storage applications; however, their development has been impeded for a long time due to the lack of qualified cathode materials with not only decent electrochemical performance but also resource abundance and low price. In this paper, we report Prussian-blue type FeFe(CN)6 nanocrystals with well-controlled lattice defects and perfect nanocubic morphology, which can exhibit a high Li-storage capacity of 160 mAh g(-1), a strong rate performance at 24 C, and a superior cycle stability with 90% capacity retention over 300 cycles. This low defect lattice and its excellent Li-insertion performance might provide a new insight into the design of advanced Li-ion battery materials and also a competitive alternative to the presently developed Li(+) insertion cathodes to develop low cost and high performance Li-ion batteries for grid-scale energy storage applications.

A Na-rich Na2CuFe(CN)6 high potential cathode is precipitated from aqueous solutions of CuCl2 and Na4Fe(CN)6 (6 h stirring, 25 h of aging).

Aqueous rechargeable sodium-ion batteries have the potential to meet growing demand for grid-scale electric energy storage because of the widespread availability and low cost of sodium resources. In this study, we synthesized a Na-rich copper hexacyanoferrate(II) Na2 CuFe(CN)6 as a high potential cathode and used NaTi2 (PO4 )3 as a Na-deficient anode to assemble an aqueous sodium ion battery. This battery works very well with a high average discharge voltage of 1.4 V, a specific energy of 48 Wh kg(-1) , and an excellent high-rate cycle stability with approximately 90 % capacity retention over 1000 cycles, achieving a new record in the electrochemical performance of aqueous Na-ion batteries. Moreover, all the anode, cathode, and electrolyte materials are low cost and naturally abundant and are affordable for widespread applications.

Current battery systems have severe cost and resource restrictions, difficultly to meet the large scale electric storage applications. Herein, we report an all-organic Na-ion battery using p-dopable polytriphenylamine as cathode and n-type redox-active poly(anthraquinonyl sulphide) as anode, excluding the use of transition-metals as in conventional electrochemical batteries. Such a Na-ion battery can work well with a voltage output of 1.8 V and realize a considerable specific energy of 92 Wh kg(-1). Due to the structural flexibility and stability of the redox-active polymers, this battery has a superior rate capability with 60% capacity released at a very high rate of 16 C (3200 mA g(-1)) and also exhibit an excellent cycling stability with 85% capacity retention after 500 cycles at 8 C rate. Most significantly, this type of all-organic batteries could be made from renewable and earth-abundant materials, thus offering a new possibility for widespread energy storage applications.

Prussian blue analogues are actively explored as low cost and high capacity cathodes for Na ion batteries; however, their applications are hindered by low capacity utilization and poor cyclability of these compounds. Here we show that this problem can be solved by controlling the purity and crystallinity of the Prussian blue lattices. As a model compound, single-crystal FeIIIFeIII(CN)6 nanoparticles are synthesized and found to have a sufficiently high capacity of 120 mA h g−1, an exceptional rate capability at 20 C and superior cyclability with 87% capacity retention over 500 cycles, showing great promise for Na ion battery applications. More significantly, these results provide a new insight into the intercalation chemistry of Prussian blue analogues and open new perspectives to develop Na storage cathodes for widespread applications of electric energy storage.