Construction of Co–Mn Prussian Blue Analog Hollow Spheres for Efficient Aqueous Zn‐ion Batteries

Potassium-Hydrogen Hybrid Ion Alkaline Battery: A New Rechargeable Aqueous Battery Combined a K+ Storage Cathode and an Electrochemical Hydrogen Storage Anode

A rechargeable aqueous hybrid ion alkaline battery, using a proton and a potassium ion as charge carriers for the anode and cathode, respectively, is proposed in this study by using well-developed potassium nickel hexacyanoferrate as the cathode material and mesoporous carbon sheets as the anode material, respectively. The constructed battery operates in a concentrated KOH solution, in which the energy storage mechanism for potassium nickel hexacyanoferrate involves the redox reaction of Fe2+/Fe3+ associated with potassium ion insertion/extraction and the redox reaction of Ni(OH)2/NiOOH. The mechanism for the carbon anode is electrochemical hydrogen storage. The cathode made of potassium nickel hexacyanoferrate exhibits both an ultrahigh capacity of 232.7 mAh g-1 under 100 mA g-1 and a consistent performance of 214 mAh g-1 at 2000 mA g-1 (with a capacity retention of 92.8% after 200 cycles). The mesoporous carbon sheet anode exhibits a capacity of 87.6 mAh·g-1 at 100 mA g-1 with a good rate and cyclic performance. The full cell provides an operational voltage of 1.55 V, a capacity of 93.6 mAh g-1 at 100 mA g-1, and 82.4% capacity retention after 1000 cycles at 2000 mA g-1 along with a low self-discharge rate. The investigation and discussion about the energy storage mechanisms for both electrode materials are also provided.

Organic Zinc-Ion Battery: Planar, π-Conjugated Quinone-Based Polymer Endows Ultrafast Ion Diffusion Kinetics

A novel poly(phenazine-alt-pyromellitic anhydride) (PPPA) has been successfully designed and synthesized via a condensation polymerization strategy as promising cathode material in organic zinc-ion batteries. Electrochemical quartz crystal microbalance (EQCM), FTIR and XPS characterizations verify a reversible Zn²⁺ -coordination mechanism in our PPPA cathode. Intriguingly, an ultrahigh Zn²⁺ diffusion coefficient of 1.2×10^-7  cm²  s^-1 was found in this large π-conjugated system, which is the highest one among all organic cathode materials for zinc-ion batteries. Theoretical calculations reveal the extended π-conjugated plane in our PPPA sample results in a significant reduction on energy gap, effectively accelerating intramolecular electron transfer during charge/discharge process. Our finding provides insights to achieve high zinc-ion transport kinetics by a design strategy on planar polymer system.

Organic Ammonium Ion Battery: A New Strategy for a Nonmetallic Ion Energy Storage System

Nonmetallic ammonium (NH₄ ⁺ ) ion batteries are promising candidates for large-scale energy storage systems, which have the merit of low molar mass, sustainability, non-toxicity and non-dendrite. Herein, for the first time, we introduce the novel organic ammonium ion batteries (OAIBs). Significantly, a manganese-based Prussian white analogue (noted as MnHCF) as cathode exhibits a reversible capacity of 104 mAh g^-1 with 98 % retention over 100 cycles. We further demonstrate the electrochemical performance of the NH₄ ⁺ ion full cell, which delivers a reversible capacity of 45 mAh g^-1 with a broad electrochemical window. Combining ex situ XPS, ex situ XRD results and electrochemical properties, the NH₄ ⁺ ion storage mechanism of MnHCF in a non-aqueous electrolyte is clearly revealed. This work verifies the feasibility of employing NH₄ ⁺ ions as charge carriers in organic energy storage systems and provides new insights for designing organic nonmetallic ion batteries with broad electrochemical windows and high energy density.

Rationally Designed Mn2 O3 -ZnMn2 O4 Hollow Heterostructures from Metal-Organic Frameworks for Stable Zn-Ion Storage

Mn-based oxides have sparked extensive scientific interest for aqueous Zn-ion batteries due to the rich abundance, plentiful oxidation states, and high output voltage. However, the further development of Mn-based oxides is severely hindered by the rapid capacity decay during cycling. Herein, a two-step metal-organic framework (MOF)-engaged templating strategy has been developed to rationally synthesize heterostructured Mn₂ O₃ -ZnMn₂ O₄ hollow octahedrons (MO-ZMO HOs) for stable zinc ion storage. The distinctive composition and hollow heterostructure endow MO-ZMO HOs with abundant active sites, enhanced electric conductivity, and superior structural stability. By virtue of these advantages, the MO-ZMO HOs electrode shows high reversible capacity, impressive rate performance, and outstanding electrochemical stability. Furthermore, ex situ characterizations reveal that the charge storage of MO-ZMO HOs mainly originates from the highly reversible Zn²⁺ insertion/extraction reactions.