Cobalt Ion-Stabilized VO2 for Aqueous Ammonium Ion Hybrid Supercapacitors

Aqueous ammonium ion hybrid supercapacitor (A-HSC) is an efficient energy storage device based on nonmetallic ion carriers (NH4+), which combines advantages such as low cost, safety, and sustainability. However, unstable electrode structures are prone to structural collapse in aqueous electrolytes, leading to fast capacitance decay, especially in host materials represented by vanadium-based oxidation. Here, the Co2+ preintercalation strategy is used to stabilize the VO2 tunnel structure and improve the electrochemical stability of the fast NH4+ storage process. In addition, the understanding of the NH4+ storage mechanism has been deepened through ex situ structural characterization and electrochemical analysis. The results indicate that Co2+ preintercalation effectively enhances the conductivity and structural stability of VO2, and inhibits the dissolution of V in aqueous electrolytes. In addition, the charge storage mechanisms of NH4+ intercalation/deintercalation and the reversible formation/fracture of hydrogen bonds were revealed.

Metal-Free Eutectic Electrolyte with Weak Hydrogen Bonds for High-Rate and Ultra-Stable Ammonium-Ion Batteries

As the need for sustainable battery chemistry grows, non-metallic ammonium ion (NH4 + ) batteries are receiving considerable attention because of their unique properties, such as low cost, nontoxicity, and environmental sustainability. In this study, the solvation interactions between NH4 + and solvents are elucidated and design principles for NH4 + weakly solvated electrolytes are proposed. Given that hydrogen bond interactions dominate the solvation of NH4 + and solvents, the strength of the solvent's electrostatic potential directly determines the strength of its solvating power. As a proof of concept, succinonitrile with relatively weak electronegativity is selected to construct a metal-free eutectic electrolyte (MEE). As expected, this MEE is able to significantly broaden the electrochemical stability window and reduce the solvent binding energy in the solvation shell, which leads to a lower desolvation energy barrier and a fast charge transfer process. As a result, the as-constructed NH4 -ion batteries exhibit superior reversible rate capability (energy density of 65 Wh kg-1 total active mass at 600 W kg-1 ) and unprecedent long-term cycling performance (retention of 90.2% after 1000 cycles at 1.0 A g-1 ). The proposed methodology for constructing weakly hydrogen bonded electrolytes will provide guidelines for implementing high-rate and ultra-stable NH4 + -based energy storage systems.

Oxygen Vacancy-Enriched Bi2SeO5 Nanosheets with Dual Mechanism for Ammonium-Ion Batteries

Ammonium ions feature a light molar mass and small hydrated radius, and the interesting interaction between NH4+ and host materials has attracted widespread attention in aqueous energy storage, while few studies focus on high-performance NH4+ storage anodes. Herein, we present a high-performance inset-type anode for aqueous ammonium-ion batteries (AIBs) based on Bi2SeO5 nanosheets. A reversible NH4+/H+ co-intercalation/deintercalation accompanied by hydrogen bond formation/breaking and a conversion reaction mechanism in layered Bi2SeO5 is proposed according to ex situ characterizations. Accordingly, the optimized Bi2SeO5 anode has a high reversible capacity of 341.03 mAh g-1 at 0.3 A g-1 in 1 M NH4Cl electrolyte and an impressive capacity retention of 86.7% after 7000 cycles at 3 A g-1, which is related to the existence of oxygen vacancies that enhance ion/electron transfer and promote the formation of hydrogen bonds between NH4+ and the host material. When the rocking-chair ammonium-ion battery is assembled using a MnO2 cathode, the device delivers an ultrahigh capacity of 140.73 mAh g-1 at 0.15 A g-1 and energy density of 207.13 Wh kg-1 at the power density of 2985.07 W kg-1. This work provides a promising strategy for designing high-performance anodes for next-generation AIBs.

A Short-Range Ordered α-MoO3 with Modulated Interlayer Structure via Hydrogen Bond Chemistry for NH4 + Storage

The layered orthorhombic molybdenum trioxide (α-MoO3 ) is a promising host material for NH4 + storage. But its electrochemical performances are still unsatisfactory due to the absence of fundamental understanding on the relationship between structure and property. Herein, NH4 + storage properties of α-MoO3 are elaborately studied. Electrochemistry together with ex situ physical characterizations uncover that irreversible H+ /NH4 + co-intercalation in the initial cycle confines the electrochemically reactive domain to the near surface of α-MoO3 thus resulting in a low reversible NH4 + storage capacity. This issue can be resolved by decreasing ion diffusion pathway to construct short-range ordered α-MoO3 (SMO), which improves the specific capacity to 185 mAh g-1 . SMO suffers from dissolution issue. In view of this the interlayer structure of SMO is reconstructed via hydrogen bond chemistry to reinforce the structural stability and it is discovered that the hydrogen bond network only with moderate intensity endows SMO with both high capacity and ability against dissolution. This work presents a new avenue to improve the NH4 + storage properties of α-MoO3 and highlights the important role of hydrogen bond intensity in optimizing electrochemical properties.

Initiating Hexagonal MoO3 for Superb-Stable and Fast NH4 + Storage Based on Hydrogen Bond Chemistry

Nonmetallic ammonium (NH₄ ⁺ ) ions are applied as charge carriers for aqueous batteries, where hexagonal MoO₃ is initially investigated as an anode candidate for NH₄ ⁺ storage. From experimental and first-principle calculated results, the battery chemistry proceeds with reversible building-breaking behaviors of hydrogen bonds between NH₄ ⁺ and tunneled MoO₃ electrode frameworks, where the ammoniation/deammoniation mechanism is dominated by nondiffusion-controlled pseudocapacitive behavior. Outstanding electrochemical performance of MoO₃ for NH₄ ⁺ storage is delivered with 115 mAh g^-1 at 1 C and can retain 32 mAh g^-1 at 150 C. Furthermore, it remarkably exhibits ultralong and stable cyclic performance up to 100 000 cycle with 94% capacity retention and high power density of 4170 W kg^-1 at 150 C. When coupled with CuFe prussian blue analogous (PBA) cathode, the full ammonium battery can deliver decent energy density 21.3 Wh kg^-1 and the resultant flexible ammonium batteries at device level are also pioneeringly developed for potential realistic applications.