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 in dual-ion batteries (DIBs) by allowing the anode to take in anions and a cation-deficient cathode to host cations, thus operating as a reverse dual-ion battery (RDIB). The anion-insertion anode is a nanocomposite having ferrocene encapsulated inside a microporous carbon, and the cathode is a Zn-insertion Prussian blue, Zn 3 [Fe(CN) 6 ] 2 . This unique battery configuration benefits from the usage of a 30 m ZnCl 2 "water-in-salt" electrolyte. This electrolyte minimizes the dissolution of ferrocene; it raises the cation-insertion potential in the cathode, and it depresses the anion-insertion potential in the anode, thus widening the full cell's voltage by 0.35 V compared with a dilute ZnCl 2 electrolyte. RDIBs provide a configuration-based solution to exploit the practicality of cation-deficient cathode materials in aqueous electrolytes.

The sluggish ion diffusion and electrolyte freezing with volumetric changes limit the low-T performance of rechargeable batteries. Herein, we report a high-rate aqueous proton battery (APB) operated at and below -78 o C via a 62 wt% (9.5 m) H 3 PO 4 electrolyte. The APB is a rocking-chair battery that operates with protons commuting between a Prussian blue cathode and a MoO 3 anode. At -78 o C, the APB full cells exhibit stable cycle life for 450 cycles, high round-trip efficiency of 85%, and appreciable power performance. The APB delivers 30% of its room-temperature capacity even at -88 o C. The proton storage mechanism is investigated by ex situ synchrotron XRD, XAS, and XPS. The APB pouch cells demonstrate nil capacity fading at -78 o C, which offers a safe and reliable candidate for high-latitude applications.

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 direction of expanding the battery chemistry with NH4 + as a charge carrier.

To date, tremendous efforts of the battery community are devoted to batteries that employ Li + , Na + , and K + as charge carriers and nonaqueous electrolytes. However, aqueous batteries hold great promise for stationary energy storage due to their inherent low cost and high safety. Among metal batteries that use aqueous electrolytes, zinc metal batteries are the focus of attention. In this study, iron as an anode candidate in aqueous batteries is investigated because iron is undoubtedly the most earth-abundant and cost-effective metal anode. Reversible iron plating/stripping in a FeSO 4 electrolyte is demonstrated on the anode side and reversible topotactic (de)insertion of Fe 2+ in a Prussian blue analogue cathode is showcased. Furthermore, it is revealed that LiFePO 4 can pair up with the iron metal anode in a hybrid cell, delivering stable performance as well.

Sulfur represents one of the most promising cathode materials for next-generation batteries; however, the widely observed polysulfide dissolution/shuttling phenomenon in metal-sulfur redox chemistries has severely restricted their applications. Here it is demonstrated that when pairing the sulfur electrode with the iron metal anode, the inherent insolubility of iron sulfides renders the shuttling-free nature of the Fe-S electrochemical reactions. Consequently, the sulfur electrode exhibits promising performance for Fe 2+ storage, where a high capacity of ~1050 mAh g -1 , low polarization of ~0.16 V as well as stable cycling of 150 cycles have been realized. The Fe-S redox mechanism was further revealed as an intriguing stepwise conversion of S 8 ↔ FeS 2 ↔ Fe 3 S 4 ↔ FeS, where a low volume expansion of ~32.6% and all-solid-state phase transitions facilitate the reaction reversibility. This study suggests an alternative direction to exploit sulfur electrodes in rechargeable transition metalsulfur batteries.The pressing need for renewable energy storage entails the development of cost-effective and sustainable battery technologies. [1] Along this line, batteries that employ earth-abundant elements such Recently, our group investigated a Fe-metal battery, where a Prussian blue cathode undertakes reversible Fe 2+ (de)insertion reactions. [38] In this work, we further demonstrate Fe-S battery chemistry Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))