Trigger a multi-electron reaction by tailoring electronic structure of VO2 toward more efficient aqueous zinc metal batteries.

VO2 (B) is recognized as a promising cathode material for aqueous zinc metal batteries (AZMBs) owing to its remarkable specific capacity and its unique, expansive tunnel structure, which facilitates the reversible insertion and extraction of Zn2+. Nonetheless, challenges such as the inherent instability of the VO2 structure, poor ion/electron transport and a limited capacity due to the low redox potential of the V3+/V4+ couple have hindered its wider application. In this study, we present a strategy to replace vanadium ions by doping Al3+ in VO2. This approach activates the multi-electron reaction (V4+/V5+), to increase the specific capacity and improve the structural stability by forming robust V5+O and Al3+O bonds. It also induces a local electric field by altering the local electron arrangement, which significantly accelerates the ion/electron transport process. As a result, Al-doped VO2 exhibits superior specific capacity, improved cycling stability, and accelerated electronic transport kinetics compared to undoped VO2. The beneficial effects of heterogeneous atomic doping observed here may provide valuable insights into the improvement electrode materials in metal-ion battery systems other than those based on Zn.

"Triple-synergistic effect" of K+ and PANI co-intercalation enabling the high-rate capability and stability of V2O5 for aqueous zinc-ion batteries.

Vanadium-based materials are widely recognized as the primary candidate cathode materials for aqueous Zn-ion batteries (AZIBs). However, slow kinetics and poor stability pose significant challenges for widespread application. Herein, to address these issues, alkali metal ions and polyaniline (PANI) are introduced into layered hydrated V2O5 (VO). Density functional theory calculations reveal that the synthesized (C6H4NH)0.27K0.24V2O5·0.92H2O (KPVO), with K+ and PANI co-intercalation, exhibits a robust interlayer structure and a continuous three-dimensional (3D) electron transfer network. These properties facilitate the reversible diffusion of Zn2+ with a low migration potential barrier and rapid response kinetics. The KPVO cathode exhibits a discharge specific capacity of 418.3 mAh/g at 100 mA/g and excellent cycling stability with 89.5 % retention after 3000 cycles at 5 A/g. This work provides a general strategy for integrating cathode materials to achieve high specific capacity and excellent kinetic performance.

Layered K0.37MnO2·0.25H2O as cathode material for potassium ion batteries.

Lithium supply shortages have prompted the search for alternatives to widespread grid system applications. Potassium-ion batteries (PIBs) have emerged to promising candidates for this purpose. Nonetheless, the large radius of K+(1.38 Å) impedes the march of satisfactory cathode materials. Here, we used solid-phase synthesis to prepare a layered K0.37MnO2·0.25H2O (KMO) cathode, comprising alternately connected MnO6octahedra with a large interlayer spacing (0.71 nm) to accommodate the migration and transport of K+ions. The cathode material achieved initial specific capacities of 102.3 and 88.1 mA h g-1at current densities of 60 mA g-1and 1 A g-1, respectively. The storage mechanism of K+ions in PIBs was demonstratedex situusing x-ray diffraction, x-ray photoelectron spectroscopy, and Raman spectroscopy measurements. Overall, our proposed KMO was confirmed as an auspicious cathode material for potential use in PIBs.

Mg2+ Ion Pre-Insertion Boosting Reaction Kinetics and Structural Stability of Ammonium Vanadates for High-Performance Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) attract much attention owing to their high safety, environmentally friendliness and low cost. However, the unsatisfactory performance of cathode materials is one of the unsolved important factors for their widespread application. Herein, we report NH4 V4 O10 nanorods with Mg2+ ion preinsertion (Mg-NHVO) as a high-performance cathode material for AZIBs. The preinserted Mg2+ ions effectively improve the reaction kinetics and structural stability of NH4 V4 O10 (NHVO), which are confirmed by electrochemical analysis and density functional theory calculations. Compared with pristine NHVO, the intrinsic conductivity of Mg-NHVO is improved by 5 times based on the test results of a single nanorod device. Besides, Mg-NHVO could maintain a high specific capacity of 152.3 mAh g-1 after 6000 cycles at the current density of 5 A g-1 , which is larger than that of NHVO (only exhibits a low specific capacity of 30.5 mAh g-1 at the same condition). Moreover, the two-phase crystal structure evolution process of Mg-NHVO in AZIBs is revealed. This work provides a simple and efficient method to improve the electrochemical performance of ammonium vanadates and enhances the understanding about the reaction mechanism of layered vanadium-based materials in AZIBs.

Water-Lubricated Aluminum Vanadate for Enhanced Rechargeable Magnesium Ion Storage.

Magnesium ion batteries (MIBs) have attracted much attention due to their low cost and high safety properties. However, the intense charge repulsion effect and sluggish diffusion dynamics of Mg2+ ions result in unsatisfactory electrochemical performance of conventional cathode materials in MIBs. This work reports water-lubricated aluminum vanadate (HAlVO) as high-performance cathode material for Mg2+ ions storage and investigates the capacity fade mechanism of water-free aluminum vanadate (AlVO). The charge density difference based on density functional theory calculation is performed to analyze the charge transfer process of water-lubricated/free aluminum vanadates (HAlVO/AlVO). The different charge transfer phenomena of two materials and the charge shielding effect of water molecule in HAlVO are revealed. Moreover, the single-phase structural evolution process and the Mg2+ ions storage mechanism of HAlVO are further investigated deeply by different in situ and ex situ characterization methods. This work proves that HAlVO is a potential candidate cathode material to satisfy the high-performance reversible Mg2+ ions storage, and the water-lubricated method is an effective strategy to improve the electrochemical performance of vanadium oxides cathode.