Iron phosphate hydroxide hydrate as a novel anode material for advanced aqueous full potassium-ion batteries

Polyimide-Based Aqueous Potassium Energy Storage Systems Using Concentrated WiSE Electrolyte

Aqueous batteries are considered as promising alternative power sources due to their eco-friendly, cost-effective, and nonflammable attributes. Employing organic-based electrode materials offers further advantages toward building greener and sustainable systems, owing to their tunability and environmental friendliness. In order to enhance the energy and power densities, superconcentrated aqueous electrolytes, such as water-in-salt electrolytes (WiSE), have renewed the interest in aqueous batteries due to their enhanced stability and much wider electrochemical stability window (>1.23 V) compared with the traditional aqueous electrolytes. Here, we present a perylene diimide-based electrode material (PDI-Urea) as an appealing anode for aqueous potassium energy storage systems and investigate their electrochemical performance in three WiSE electrolytes, namely, 30 M potassium acetate, 40 M potassium formate and 30 M potassium bis(fluorosulfonyl)imide (KFSI). To explore the potential of PDI-Urea for potassium-based electrochemical energy systems, we fabricated full cell devices such as aqueous potassium dual-ion battery (APDIB) and aqueous K-ion battery (AKIB) and studied their electrochemical properties with 30 M KFSI electrolyte. The full cell K-ion battery, using a PBA cathode, exhibited excellent electrochemical performance with good rate capability and impressive capacity retention of 91% upon 1000 cycles. Further, the reaction mechanism of the electrodes is systematically analyzed using ex-situ studies.

Regulating Interlayer-Spacing of Vanadium Phosphates for High-Capacity and Long-Life Aqueous Iron-Ion Batteries

Although the research on aqueous batteries employing metal as the anode is still mainly focused on the aqueous zinc-ion battery, aqueous iron-ion batteries are considered as promising aqueous batteries owing to the lower cost, higher specific capacity, and better stability. However, the sluggish Fe2+ (de)intercalation leads to unsatisfactory specific capacity and poor electrochemical stability, which makes it difficult to find cathode materials with excellent electrochemical properties. Herein, phenylamine (PA)-intercalated VOPO4 materials with expanded interlayer spacing are synthesized and applied successfully in aqueous iron-ion batteries. Owing to enough diffusion space from the expanded interlayer, which can boost fast Fe2+ diffusion, the aqueous iron-ion battery shows a high specific capacity of 170 mAh g-1 at 0.2 A g-1 , excellent rate performance, and cycle stability (96.2% capacity retention after 2200 cycles). This work provides a new direction for cathode material design in the development of aqueous iron-ion batteries.

Dynamic Regulation Achieving High-Performance La-Containing Prussian Blue Analogues for Aqueous K+ Storage

Lanthanum (La), an "industrial aginomoto" element, exhibits that a small amount of introduction would greatly improve performance. However, La-containing Prussian blue analogues (PBAs) would be dissolved into aqueous solutions, which cannot act as a potassium-ion (K+) storage host. Here, an effective dynamic regulating strategy (chemical components and structures) is developed to overcome the high solubility of La-containing PBA in aqueous electrolytes and achieve high structural stability and superior aqueous K+ storage. For chemical component regulation, Fe3+ ions in the electrolyte fill the La3+ vacancies on the surface and the modified surface hinders the La atoms from further dissolving, and the remaining La atoms in bulk phase improve electron/ion transfer ability and amount of K+ storage. For the structure regulation, the material is transferred from the hexagon to the cubic lattice during charging-discharging procedures, achieving a highly thermodynamically optimal structure. The cathode presents ultrahigh capacities of 171, 155, 132, and 116 at current densities of 1, 2, 3, and 4 A g-1 respectively, and the capacity remains almost constant after 1000 cycles. The mechanism is revealed by experiments and density functional theory (DFT).