Controlled growth and ion intercalation mechanism of monocrystalline niobium pentoxide nanotubes for advanced rechargeable aluminum-ion batteries

Enhancing the Lithium Storage Performance of the Nb2O5 Anode via Synergistic Engineering of Phase and Cu Doping

Nb2O5 has been viewed as a promising anode material for lithium-ion batteries by virtue of its appropriate redox potential and high theoretical capacity. However, it suffers from poor electric conductivity and low ion diffusivity. Herein, we demonstrate the controllable fabrication of Cu-doped Nb2O5 with orthorhombic (T-Nb2O5) and monoclinic (H-Nb2O5) phases through annealing the solvothermally presynthesized Nb2O5 precursor under different temperatures in air, and the Cu doping amount can be readily controlled by the concentration of the precursor solution, whose effect on the lithium storage behaviors of the Cu-doped Nb2O5 is thoroughly investigated. H-Nb2O5 shows obvious redox peaks (Nb5+/Nb4+ and Nb4+/Nb3+) with much higher capacity and better cycling stability than those for the widely investigated T-Nb2O5. When introducing appropriate Cu doping, the optimized H-Cu0.1-Nb2O5 electrode shows greatly enhanced conductivity and lower diffusion barrier as revealed by the theoretical calculations and electrochemical characterizations, delivering a high reversible capacity of 203.6 mAh g-1 and a high capacity retention of 140.8 mAh g-1 after 5000 cycles at 1 A g-1, with a high initial Coulombic efficiency of 91% and a high rate capacity of 144.2 mAh g-1 at 4 A g-1. As a demonstration for full-cell application, the H-Cu0.1-Nb2O5||LiFePO4 cell displays good cycling performance, exhibiting a reversible capacity of 135 mAh g-1 after 200 cycles at 0.2 A g-1. More importantly, this work offers a new synthesis protocol of the monoclinic Nb2O5 phase with high capacity retention and improved reaction kinetics.

Polyoxometalates@Metal-Organic Frameworks Derived Bimetallic Co/Mo2 C Nanoparticles Embedded in Carbon Nanotube-Interwoven Hierarchically Porous Carbon Polyhedron Composite as a High-Efficiency Electrocatalyst for Al-S Batteries

Al-S battery (ASB) is a promising energy storage device, notable for its safety, crustal abundance, and high theoretical energy density. However, its development faces challenges due to slow reaction kinetics and poor reversibility. The creation of a multifunctional cathode material that can both adsorb polysulfides and accelerate their conversion is key to advancing ASB. Herein, a composite composed of polyoxometalate nanohybridization-derived Mo2 C and N-doped carbon nanotube-interwoven polyhedrons (Co/Mo2 C@NCNHP) is proposed for the first time as an electrochemical catalyst in the sulfur cathode. This composite improves the utilization and conductivity of sulfur within the cathode. DFT calculations and experimental results indicate that Co enables the chemisorption of polysulfides while Mo2 C catalyzes the reduction reaction of long-chain polysulfides. X-ray photoelectron spectroscopy (XPS) and in situ UV analysis reveal the different intermediates of Al polysulfide species in Co/Mo2 C@NCNHP during discharging/charging. As a cathode material for ASB, Co/Mo2 C@NCNHP@S composite can deliver a discharge-charge voltage hysteresis of 0.75 V with a specific capacity of 370 mAh g-1 after 200 cycles at 1A g-1 .

High Performance and Long-cycle Life Rechargeable Aluminum Ion Battery: Recent Progress, Perspectives and Challenges

The rising energy crisis and environmental concerns caused by fossil fuels have accelerated the deployment of renewable and sustainable energy sources and storage systems. As a result of immense progress in the field, cost-effective, high-performance, and long-life rechargeable batteries are imperative to meet the current and future demands for sustainable energy sources. Currently, lithium-ion batteries are widely used, but limited lithium (Li) resources have caused price spikes, threatening progress toward cleaner energy sources. Therefore, post-Li, batteries that utilize highly abundant materials leading to cost-effective energy storage solutions while offering desirable performance characteristics are urgently needed. Aluminum-ion battery (AIB) is an attractive concept that uses highly abundant aluminum while offering a high theoretical gravimetric and volumetric capacity of 2980 mAh g^-1 and 8046 mAh cm^-3 , respectively. As a result, intensified efforts have been made in recent years to utilize numerous electrolytes, anodes, and cathode materials to improve the electrochemical performance of AIBs, and potentially create high-performance, low-cost, and safe energy storage devices. Herein, recent progress in the electrolyte, anode, and cathode active materials and their utilization in AIBs and their related characteristics are summarized. Finally, the main challenges facing AIBs along with future directions are highlighted.

Design Strategies of High-Performance Positive Materials for Nonaqueous Rechargeable Aluminum Batteries: From Crystal Control to Battery Configuration

Rechargeable aluminum batteries (RABs) have been paid considerable attention in the field of electrochemical energy storage batteries due to their advantages of low cost, good safety, high capacity, long cycle life, and good wide-temperature performance. Unlike traditional single-ion rocking chair batteries, more than two kinds of active ions are electrochemically participated in the reaction processes on the positive and negative electrodes for nonaqueous RABs, so the reaction kinetics and battery electrochemistries need to be given more comprehensive assessments. In addition, although nonaqueous RABs have made significant breakthroughs in recent years, they are still facing great challenges in insufficient reaction kinetics, low energy density, and serious capacity attenuation. Here, the research progresses of positive materials are comprehensively summarized, including carbonaceous materials, oxides, elemental S/Se/Te and chalcogenides, as well as organic materials. Later, different modification strategies are discussed to improve the reaction kinetics and battery performance, including crystal structure control, morphology and architecture regulation, as well as flexible design. Finally, in view of the current research challenges faced by nonaqueous RABs, the future development trend is proposed. More importantly, it is expected to gain key insights into the development of high-performance positive materials for nonaqueous RABs to meet practical energy storage requirements.

Reversible Al Metal Anodes Enabled by Amorphization for Aqueous Aluminum Batteries

Aqueous aluminum metal batteries (AMBs) are regarded as one of the most sustainable energy storage systems among post-lithium-ion candidates, which is attributable to their highest theoretical volumetric capacity, inherent safe operation, and low cost. Yet, the development of aqueous AMBs is plagued by the incapable aluminum plating in an aqueous solution and severe parasitic reactions, which results in the limited discharge voltage, thus making the development of aqueous AMBs unsuccessful so far. Here, we demonstrate that amorphization is an effective strategy to tackle these critical issues of a metallic Al anode by shifting the reduction potential for Al deposition. The amorphous aluminum (a-Al) interfacial layer is triggered by an in situ lithium-ion alloying/dealloying process on a metallic Al substrate with low strength. Unveiled by experimental and theoretical investigations, the amorphous structure greatly lowers the Al nucleation energy barrier, which forces the Al deposition competitive to the electron-stealing hydrogen evolution reaction (HER). Simultaneously, the inhibited HER mitigates the passivation, promoting interfacial ion transfer kinetics and enabling steady aluminum plating/stripping for 800 h in the symmetric cell. The resultant multiple full cells using Al@a-Al anodes deliver approximately a 0.6 V increase in the discharge voltage plateau compared to that of bare Al-based cells, which far outperform all reported aqueous AMBs. In both symmetric cells and full cells, the excellent electrochemical performances are achieved in a noncorrosive, low-cost, and fluorine-free Al₂(SO₄)₃ electrolyte, which is ecofriendly and can be easily adapted for sustainable large-scale applications. This work brings an intriguing picture of the design of metallic anodes for reversible and high-voltage AMBs.

Pencil-Drawing Graphite Nanosheets: A Simple and Effective Cathode for High-Capacity Aluminum Batteries

Commercial graphite, as an attractive cathode material, has been extensively applied in rechargeable aluminum batteries. However, low capacity and complex cathode preparation procedures limit its further development. Herein, graphite nanosheets as cathode of aluminum battery have been prepared by a novel pencil-drawing strategy, which shows superior capacity of 96 mAh g^-1 and excellent stability with almost 100% capacity retention after 2000 cycles at a current density of 0.5 A g^-1 . By increasing charge-discharge current density to 2 A g^-1 , the battery also exhibits a high capacity of 72 mAh g^-1 and retains 90% after 6000 cycles. Furthermore, a stage 3 anion intercalation/deintercalation mechanism has been proposed according to in situ X-ray diffraction and ex situ characterization techniques. This work provides a controllable method for developing a graphite nanosheets cathode with a simplified process and contributes to the development of other kinds of energy storage devices.

Three-Dimensional Cross-Linked Nb2O5 Polymorphs Derived from Cellulose Substances: Insights into the Mechanisms of Lithium Storage

Niobium pentoxide (Nb₂O₅)-based materials have been regarded as promising anodic materials for lithium-ion batteries due to their abundant crystalline phases and stable and safe lithium storage performances. However, there is a lack of systematic studies of the relationship among the crystal structures, electrochemical characteristics, and lithium storage mechanisms for the various Nb₂O₅ polymorphs. Herein, pure pseudohexagonal Nb₂O₅ (TT-Nb₂O₅), orthorhombic Nb₂O₅ (T-Nb₂O₅), tetragonal Nb₂O₅ (M-Nb₂O₅), and monoclinic Nb₂O₅ (H-Nb₂O₅) with three-dimensional interconnected structures are reported, which were synthesized via a hydrothermal method using the commercial filter paper as the structural template followed by specific annealing processes. Impressively, the TT- and T-Nb₂O₅ species both possess bronze-like phases with "room and pillar" structures, while M- and H-Nb₂O₅ ones are both in the Wadsley-Roth phases with crystallographic shear structures. Among the pristine Nb₂O₅ materials, H-Nb₂O₅ exhibits the highest initial specific capacity (270 mA h g^-1), while T-Nb₂O₅ performs with the lowest (197 mA h g^-1) at 0.02 A g^-1, meaning that crystallographic shear structures provide more lithium storage sites. TT-Nb₂O₅ realizes the best rate capability (207 mA h g^-1 at 0.02 A g^-1 and 103 mA h g^-1 at 4.0 A g^-1), indicating that the "room and pillar" crystal structures favor fast lithium storage. Electrochemical analyses reveal that the TT- and T-Nb₂O₅ phases with "room and pillar" crystal structures utilize a pseudocapacitive intercalation mechanism, while the M- and H-Nb₂O₅ phases with the Wadsley-Roth shear structures follow a typical battery-type intercalation mechanism. A fresh insight into the further understanding of the intercalation pseudocapacitance on the basis of the unit cells of the electrode materials and a meaningful guidance for crystalline structural design/construction of the electrode materials for the next-generation LIBs are thus provided.

Amorphous anion-rich titanium polysulfides for aluminum-ion batteries

The strong electrostatic interaction between Al³⁺ and close-packed crystalline structures, and the single-electron transfer ability of traditional cationic redox cathodes, pose challenged for the development of high-performance rechargeable aluminum batteries. Here, to break the confinement of fixed lattice spacing on the diffusion and storage of Al-ion, we developed a previously unexplored family of amorphous anion-rich titanium polysulfides (a-TiS _x , x = 2, 3, and 4) (AATPs) with a high concentration of defects and a large number of anionic redox centers. The AATP cathodes, especially a-TiS₄, achieved a high reversible capacity of 206 mAh/g with a long duration of 1000 cycles. Further, the spectroscopy and molecular dynamics simulations revealed that sulfur anions in the AATP cathodes act as the main redox centers to reach local electroneutrality. Simultaneously, titanium cations serve as the supporting frameworks, undergoing the evolution of coordination numbers in the local structure.