Enhancing Electrochemical Performance of Aluminum-Ion Batteries with Fluorinated Graphene Cathode.

In pursuit of high-performance aluminum-ion batteries, the selection of a suitable positive electrode material assumes paramount importance, and fluorinated graphene (FG) nanostructures have emerged as an exceptional candidate. In the scope of this study, a flexible tantalum foil is coated with FG to serve as the positive electrode for aluminum-ion batteries. FG positive electrode demonstrates a remarkable discharge capacity of 109 mA h g-1 at a current density of 200 mA g-1, underscoring its tremendous potential for energy storage applications. Concurrently, the FG positive electrode exhibits a discharge capacity of 101 mA h g-1 while maintaining an impressive coulombic efficiency of 95 % over 300 cycles at a current density of 200 mA g-1, which benefiting from the significant structure of FG. The results of the in-situ Raman spectroscopy signified the presence of intercalation/de-intercalation processes of AlCl4 - behavior within the FG layers.

The Reverse of Electrostatic Interaction Force for Ultrahigh-Energy Al-Ion batteries.

The two-dimensional (2D) MXenes with sufficient interlayer spacing are promising cathode materials for aluminum-ion batteries (AIBs), yet the electrostatic repulsion effect between the surface negative charges and the active anions (AlCl4 - ) hinders the intercalation of AlCl4 - and is usually ignored. Here, we propose a charge regulation strategy for MXene cathodes to overcome this challenge. By doping N and Co, the zeta potential is gradually transformed from negative (Ti3 C2 Tx ) to near-neutral (Ti3 CNTx ), and finally positive (Ti3 CNTx @Co). Therefore, the electrostatic repulsion force can be greatly weakened between Ti3 CNTx and AlCl4 - , or even formed a strong electrostatic attraction between Ti3 CNTx @Co and AlCl4 - , which can not only accommodate more AlCl4 - ions in the Ti3 CNTx @Co interlayers to increase the capacity, but also solve the stacking and expansion problems. As a result, the optimized Al-MXene battery exhibits an ultrahigh capacity of up to 240 mAh g-1 (2-4 times the capacity of graphite cathode, 60-120 mAh g-1 ) and a potential ultrahigh energy density (432 Wh kg-1 , 2-4 times the value of graphite, 110-220 Wh kg-1 ) based on the mass of cathode materials, comparable to LiFePO4 -based lithium-ion batteries (350-450 Wh kg-1 , based on the mass of LiFePO4 ).

Stable Low-Temperature Al Batteries Enabled by Integrating Polydopamine-Derived N-Doped Carbon Nanospheres With Flake Graphite.

The battery performance declines significantly in severely cold areas, especially discharge capacity and cycle life, which is the most significant pain point for new energy consumers. To address this issue and improve the low-temperature characteristic of aluminum-ion batteries, in this work, polydopamine-derived N-doped carbon nanospheres are utilized to modify the most promising graphite material. More active sites are introduced into graphite, more ion transport channels are provided, and improved ionic conductivity is achieved in a low-temperature environment. Due to the synergistic effect of the three factors, the ion diffusion resistance is significantly reduced and the diffusion coefficient of aluminum complex ions in the active material become larger at low temperatures. Therefore, the battery delivers an improved capacity retention rate from 23% to 60% at -20 °C and excellent ultra-long cycling stability over 5500 cycles at -10 °C. This provides a novel strategy for constructing low-temperature aluminum-ion batteries with high energy density, which is conducive to promoting the practicality of aluminum-ion batteries.

Molten salt electro-preparation of graphitic carbons.

Graphite has been used in a wide range of applications since the discovery due to its great chemical stability, excellent electrical conductivity, availability, and ease of processing. However, the synthesis of graphite materials still remains energy-intensive as they are usually produced through a high-temperature treatment (>3000°C). Herein, we introduce a molten salt electrochemical approach utilizing carbon dioxide (CO2) or amorphous carbons as raw precursors for graphite synthesis. With the assistance of molten salts, the processes can be conducted at moderate temperatures (700-850°C). The mechanisms of the electrochemical conversion of CO2 and amorphous carbons into graphitic materials are presented. Furthermore, the factors that affect the graphitization degree of the prepared graphitic products, such as molten salt composition, working temperature, cell voltage, additives, and electrodes, are discussed. The energy storage applications of these graphitic carbons in batteries and supercapacitors are also summarized. Moreover, the energy consumption and cost estimation of the processes are reviewed, which provides perspectives on the large-scale synthesis of graphitic carbons using this molten salt electrochemical strategy.

The Negative-Charge-Triggered "Dead Zone" between Electrode and Current Collector Realizes Ultralong Cycle Life of Aluminum-Ion Batteries.

Typically, volume expansion of the electrodes after intercalation of active ions is highly undesirable yet inetvitable, and it can significantly reduce the adhesion force between the electrodes and current collectors. Especially in aluminum-ion batteries (AIBs), the intercalation of large-sized AlCl4 - can greatly weaken this adhesion force and result in the detachment of the electrodes from the current collectors, which seems an inherent and irreconcilable problem. Here, an interesting concept, the "dead zone", is presented to overcome the above challenge. By incorporating a large number of OH- and COOH- groups onto the surface of MXene film, a rich negative-charge region is formed on its surface. When used as the current collector for AIBs, it shields a tiny area of the positive electrode (adjacent to the current collector side) from AlCl4 - intercalation due to the repulsion force, and a tiny inert layer (dead zone) at the interface of the positive electrode is formed, preventing the electrode from falling off the current collector. This helps to effectively increase the battery's cycle life to as high as 50 000 times. It is believed that the proposed concept can be an important reference for future development of current collectors in rocking chair batteries.

Electro-deoxidation behavior of solid SeO2 in a low-temperature molten salt.

In this work, a low-temperature electro-deoxidation strategy of solid SeO2 was proposed for the first time in neutral NaCl-AlCl3 molten salt. Based on thermodynamic and electrochemical means, the deoxidation of SeO2 was confirmed to be a two-step two-electron process. Besides, the electro-deoxidation products and their morphology evolution processes were revealed along with the change of potential. It is hoped that the deep understanding of preparing metal Se by direct electrolytic reduction can offer key insights into short-process and green metallurgy of other characteristic scattered metals.

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.

A Review of Integrated Systems Based on Perovskite Solar Cells and Energy Storage Units: Fundamental, Progresses, Challenges, and Perspectives.

With the remarkable progress of photovoltaic technology, next-generation perovskite solar cells (PSCs) have drawn significant attention from both industry and academic community due to sustainable energy production. The single-junction-cell power conversion efficiency (PCE) of PSCs to date has reached up to 25.2%, which is competitive to that of commercial silicon-based solar cells. Currently, solar cells are considered as the individual devices for energy conversion, while a series connection with an energy storage device would largely undermine the energy utilization efficiency and peak power output of the entire system. For substantially addressing such critical issue, advanced technology based on photovoltaic energy conversion-storage integration appears as a promising strategy to achieve the goal. However, there are still great challenges in integrating and engineering between energy harvesting and storage devices. In this review, the state-of-the-art of representative integrated energy conversion-storage systems is initially summarized. The key parameters including configuration design and integration strategies are subsequently analyzed. According to recent progress, the efforts toward addressing the current challenges and critical issues are highlighted, with expectation of achieving practical integrated energy conversion-storage systems in the future.

A cobalt-based metal-organic framework and its derived material as sulfur hosts for aluminum-sulfur batteries with the chemical anchoring effect.

With the urgent need to explore high-performance electrochemical energy storage systems, rechargeable Al-ion batteries (AIBs) have attracted attention from researchers and engineers due to their traits, such as abundance and safety. Among all the issues waiting to be solved, the development of a reliable positive electrode material with high specific capacity is an absolute priority for the commercialization of AIBs. Sulfur has a natural advantage when used as the active material, and its theoretical specific capacity is as high as 1675 mA h g-1. MOFs and MOF-derived materials have been proved to be promising hosts for Li-S batteries. Herein, we report a novel Al-S battery system employing MOF (ZIF-67) and MOF-derived materials as sulfur host materials. After being chemically combined with sulfur, the composite still maintains its unique well-defined polyhedron morphology. The voltage hysteresis phenomenon is effectively alleviated with the aid of the host matrix. DFT calculations confirm that ZIF-67 and carbonized ZIF-67-700 polyhedrons can act as an anchor point towards sulfur (S8) and polysulfides (Al2S3, Al2S6, Al2S12, and Al2S18), preventing the detrimental dissolution and shuttle effect. These findings can enlighten future researchers regarding Al-S batteries and broaden the application of MOFs in the field of electrochemical energy storage systems.

Nonaqueous Rechargeable Aluminum Batteries: Progresses, Challenges, and Perspectives.

For significantly increasing the energy densities to satisfy the growing demands, new battery materials and electrochemical chemistry beyond conventional rocking-chair based Li-ion batteries should be developed urgently. Rechargeable aluminum batteries (RABs) with the features of low cost, high safety, easy fabrication, environmental friendliness, and long cycling life have gained increasing attention. Although there are pronounced advantages of utilizing earth-abundant Al metals as negative electrodes for high energy density, such RAB technologies are still in the preliminary stage and considerable efforts will be made to further promote the fundamental and practical issues. For providing a full scope in this review, we summarize the development history of Al batteries and analyze the thermodynamics and electrode kinetics of nonaqueous RABs. The progresses on the cutting-edge of the nonaqueous RABs as well as the advanced characterizations and simulation technologies for understanding the mechanism are discussed. Furthermore, major challenges of the critical battery components and the corresponding feasible strategies toward addressing these issues are proposed, aiming to guide for promoting electrochemical performance (high voltage, high capacity, large rate capability, and long cycling life) and safety of RABs. Finally, the perspectives for the possible future efforts in this field are analyzed to thrust the progresses of the state-of-the-art RABs, with expectation of bridging the gap between laboratory exploration and practical applications.

Enhanced storage behavior of quasi-solid-state aluminum-selenium battery.

The current aluminum batteries with selenium positive electrodes have been suffering from dramatic capacity loss owing to the dissolution of Se2Cl2 products on the Se positive electrodes in the ionic liquid electrolyte. For addressing this critical issue and achieving better electrochemical performances of rechargeable aluminum-selenium batteries, here a gel-polymer electrolyte which has a stable and strongly integrated electrode/electrolyte interface was adopted. Quite intriguingly, such a gel-polymer electrolyte enables the solid-state aluminum-selenium battery to present a lower self-discharge and obvious discharging platforms. Meanwhile, the discharge capacity of the aluminum-selenium battery with a gel-polymer electrolyte is initially 386 mA h g-1 (267 mA h g-1 in ionic liquid electrolyte), which attenuates to 79 mA h g-1 (32 mA h g-1 in ionic liquid electrolyte) after 100 cycles at a current density of 200 mA g-1. The results suggest that the employment of a gel-polymer electrolyte can provide an effective route to improve the performance of aluminum-selenium batteries in the first few cycles.

Stable Interface between a NaCl-AlCl3 Melt and a Liquid Ga Negative Electrode for a Long-Life Stationary Al-Ion Energy Storage Battery.

Intermediate temperature NaCl-AlCl3-based Al-ion batteries are considered as a promising stationary energy storage system due to their low cost, high safety, etc. However, such a cheap electrolyte has a critical feature, i.e., strong corrosion, which results in the short cycle life of the conventional Al-metal anode and also limits the development of the NaCl-AlCl3-based Al-ion batteries. A noncorrosive electrolyte may be a good choice for addressing the above challenge, while it is difficult to obtain the electrolyte that has advantages of both noncorrosion and low cost. Therefore, here, we report a Ga-metal anode in the affordable NaCl-AlCl3 electrolyte for constructing a long-life stationary Al-ion energy storage system. This featured liquid metal anode shows good alloying and dealloying processes between metallic Ga and Al, as well as renders superior stability of the interface between the electrolyte and the anode (e.g., smoothly running for over 580 h at 2 mA cm-2). No-corrosion and no-pulverization problems appear in this novel liquid/liquid interface. Those advantages demonstrate that the liquid Ga-metal anode has a great promise for the improvement of the NaCl-AlCl3-based Al-ion batteries for large-scale stationary energy storage applications.

Rechargeable Nickel Telluride/Aluminum Batteries with High Capacity and Enhanced Cycling Performance.

Rechargeable aluminum-ion batteries (AIBs) possess significant advantages of high energy density, safety performance, and abundant natural resources, making them one of the desirable next-generation substitutes for lithium battery systems. However, the poor reversibility, short lifespan, and low capacity of positive materials have limited its practical applications. In comparison with semiconductors, the metallic nickel telluride (NiTe) alloy with enhanced electrical conductivity and fast electron transmission is a more favorable electrode material that could significantly decrease the kinetic barrier during battery operation for energy storage. In this paper, the NiTe nanorods prepared through a simple hydrothermal routine enable an initial reversible capacity of approximately 570 mA h g-1 (under the current density of 200 mA g-1) to be delivered on the basis of the ionic liquid electrolyte, along with the average voltage platform of about 1.30 V. Moreover, the cycling performance could be easily enhanced using a modified separator to prevent the diffusion of soluble intermediate species to the negative electrode side. At a high rate of 500 mA g-1, the NiTe nanorods could retain a specific capacity of about 307 mA h g-1 at the 100th cycle. The results have important implications for the research of transition metal tellurides as positive electrode materials for AIBs.

Sb2Se3 nanorods with N-doped reduced graphene oxide hybrids as high-capacity positive electrode materials for rechargeable aluminum batteries.

For substantially promoting the unexpected rechargeable capability induced from the dissolution of Sb2Se3 positive electrode materials in aluminum batteries, here a novel prototype of a cell assembled by a hybrid of single-crystalline Sb2Se3 nanorods and N-doped reduced graphene oxide (SNG) coupled with a modified separator has been developed. With this specific cell design, the hybrid positive electrode material exhibits a high discharge potential (∼1.8 V) with a considerably high initial discharge capacity of up to 343 mA h g-1 at a current density of 500 mA g-1. Owing to the alleviation of active material loss from the positive electrode, the cell having the modified separator exhibits much enhanced cycling stability. Besides, nitrogen-doping on the reduced graphene oxide is found to boost the active sites in SNG, and thus the cycling performance has been largely improved. The strategy used in this work offers a universal plateau for designing long-life cycle aluminum batteries.

High-efficiency transformation of amorphous carbon into graphite nanoflakes for stable aluminum-ion battery cathodes.

Highly efficient strategies for the transformation of amorphous carbon into graphite with high graphitization and crystallinity features have been significantly pursued in recent years; however, critical issues, including high processing temperature, insufficient graphitization, introduction of catalyst impurities, complicated post-purification procedures, and generation of greenhouse gas, still remain in traditional approaches. For significantly addressing these challenges, herein, a highly efficient catalyst-free, eco-friendly and low-temperature electrochemical transformation strategy was proposed for the preparation of highly graphitized porous graphite nanoflakes. Using inert SnO2 as an anode in CaCl2-LiCl molten salts, the graphitization transformation of amorphous carbon materials could be realized at 700 °C, approaching the record in high-efficiency converting amorphous carbon to graphite; moreover, systematical analysis was performed to understand the electrochemical transformation of amorphous carbon into highly graphitized graphite nanoflakes. For extending their valuable applications, the as-prepared graphite nanoflakes were further utilized as cathodes in aluminum-ion batteries, which exhibited significantly promising energy storage performance; moreover, an initial discharge capacity of 63.6 mA h g-1 at a current density of 200 mA g-1 was achieved, which eventually became 55.5 mA h g-1 with a coulombic efficiency of 95.4% after 1000 cycles; thus, these cathodes exhibited stable long-term cycling performance. The combination of low-temperature electrochemical transformation and the subsequent high-performance applications of these nanoflakes in energy storage indicates that the proposed strategy is highly efficient for the transformation and utilization of abundant amorphous carbon resources for the realization of high value-added applications.

The potential application of black and blue phosphorene as cathode materials in rechargeable aluminum batteries: a first-principles study.

Developing a suitable cathode material for rechargeable aluminum-ion batteries (AIBs) is currently recognized as a key challenge in pushing AIBs from lab-level to industrial application. Herein, detailed density functional theory (DFT) calculations are carried out to investigate the potential application of black and blue phosphorus monolayers as cathode materials for AIBs. It can be found that AlCl4- ions can strongly bind with both phosphorene allotropes, along with significant charge transfer. For black P, a semiconducting-to-metallic transition is realized in the (AlCl4)8P16 compound. Likewise, the band gap of blue P is reduced from 1.971 eV (pristine blue P) to 0.817 eV. Moreover, both phosphorene allotropes show excellent structural integrity with increased AlCl4- concentration, while delivering competitive theoretical capacities of 432.29 and 384.25 mA h g-1 for black ((AlCl4)8P16) and blue phosphorene ((AlCl4)8P18), respectively. Kinetic calculations present modest energy barriers of 0.19 and 0.39 eV for AlCl4- ions migrating on the surface of black and blue P, and an anisotropic migration nature is also found in both phosphorene allotropes. Based on our results, black and blue phosphorene show great potential as cathode materials for AIBs with robust ion-adsorption, insignificant deformation, self-improved conductivity, and fast kinetic performance.

The effect of graphitization degree of carbonaceous material on the electrochemical performance for aluminum-ion batteries.

Aluminum-ion batteries are currently regarded as the most promising energy storage batteries. The recent development of aluminum-ion batteries has been greatly promoted based on the use of graphitic carbon materials as a positive electrode. However, it remains unclear whether all carbonaceous materials can achieve excellent electrochemical behaviour similar to graphite. In this study, the correlation between the graphitization degree and capacity of a graphite electrode is systematically investigated for aluminum-ion batteries. The results show that the higher the graphitization degree, the larger the charge/discharge capacity and the better the cycling stability. Moreover, graphite nanoflakes with the highest graphitization degree deliver an initial discharge capacity of 66.5 mA h g-1 at a current density of 100 mA g-1, eventually retaining 66.3 mA h g-1 after 100 cycles with a coulombic efficiency of 96.1% and capacity retention of 99.7%, exhibiting an ultra-stable cycling performance. More importantly, it can be concluded that the discharge capacity of different kinds of graphite materials can be predicted by determining the graphitization degree.

Facile synthesis of Ni11(HPO3)8(OH)6/rGO nanorods with enhanced electrochemical performance for aluminum-ion batteries.

The electrochemical behaviors of the ultrashort nickel phosphite nanorods supported on reduced graphene oxide (Ni11(HPO3)8(OH)6/rGO nanorods), as a candidate for cathodic applications in aluminum-ion batteries, are firstly investigated. Ni11(HPO3)8(OH)6/rGO nanorods are synthesized by a facile solvothermal process. Ni11(HPO3)8(OH)6 and Ni11(HPO3)8(OH)6/rGO cathodes both possess very high initial discharge capacities of 132.4 and 182.0 mA h g-1 at a current density of 200 mA g-1, respectively. In addition, the long-term cycling stability of the Ni11(HPO3)8(OH)6/rGO cathode is further evaluated, exhibiting a discharge capacity of 49.2 mA h g-1 even over 1500 cycles. More importantly, the redox reaction mechanism of the Ni11(HPO3)8(OH)6 cathode for aluminum-ion batteries revealed that Ni11(HPO3)8(OH)6 is partially substituted with Al3+ to form AlmNin(HPO3)8(OH)6 and metallic Ni in the nanorod-like Ni11(HPO3)8(OH)6 cathodes during the discharge process. These findings are of great significance for the further development of novel materials for aluminum-ion batteries.

Ordered WO3-x nanorods: facile synthesis and their electrochemical properties for aluminum-ion batteries.

In this work, we have synthesized ordered WO3 nanorods via a facile hydrothermal process. And the series WO3-x nanorods with oxygen vacancies are obtained via a subsequent thermal reduction process. The formation mechanisms of WO3-x nanorods with different oxygen vacancies are proposed. And the electrochemical results reveal that the WO3-x nanorods exhibit the improved specific capacity due to the oxygen vacancies caused by the thermal reduction. More importantly, the reaction mechanism of the WO3-x nanorods as cathodes for aluminum-ion batteries has been proved.

Production of Ti-Fe alloys via molten oxide electrolysis at a liquid iron cathode.

This work studies the direct electrochemical preparation of Ti-Fe alloys through molten oxide electrolysis (MOE) at a liquid iron cathode. Cyclic voltammetry and potentiostatic electrolysis have been employed to study the cathodic process of titanium ions. The results show that cathodic behavior happens during the negative sweep at a potential range from -0.80 to -1.25 V (vs. QRE-Mo), corresponding to the electro-reduction of titanium ions. Importantly, Ti-Fe and titanium-rich Ti-Fe alloys have been successfully produced by galvanostatic electrolysis at different current densities of 0.15 and 0.30 A cm-2, respectively. The results show that it is feasible to directly prepare Ti-Fe alloys by the MOE method at a liquid iron cathode.