An aluminium battery operating with an aqueous electrolyte

α-MnO2 Cathode with Oxygen Vacancies Accelerated Affinity Electrolyte for Dual-Ion Co-Encapsulated Aqueous Aluminum Ion Batteries

Aluminum batteries (ABs) are identified as one of the most promising candidates for the next generation of large-scale energy storage elements because of their efficient three-electron reaction. Compared to ionic electrolytes, aqueous aluminum-ion batteries (AAIBs) are considered safer, less costly, and more environmentally friendly. However, considerable cycling performance is a key issue limiting the development of AAIBs. Stable, efficient, and electrolyte-friendly cathodes are most desirable for AAIBs. Herein, a rod-shaped defect-rich α-MnO2 is designed as a cathode, which is capable to deliver high performance with stable cycling for 180 cycles at 500 mA g-1 and maintains a discharge specific capacity of ≈100 mAh g-1. In addition, the infiltrability simulation is effectively utilized to corroborate the rapid electrochemical reaction brought about by the defective mechanism. With the formation of oxygen vacancies, the dual embedding of protons and metal ions is activated. This work provides a brand-new design for the development and characterization of cathodes for AAIBs.

Research Advances of Cathode Materials for Rechargeable Aluminum Batteries

Rechargeable aluminum ion batteries (AIBs) have recently gained widespread research concern as energy storage technologies because of their advantages of being safe, economical, environmentally friendly, sustainable, and displaying high performance. Nevertheless, the intense Coulombic interactions between the Al3+ ions with high charge density and the lattice of the electrode body lead to poor cathode kinetics and limited cycle life in AIBs. This paper reviews the recent advances in the cathode design of AIBs to gain a comprehensive understanding of the opportunities and challenges presented by current AIBs. In addition, the advantages, limitations, and possible solutions of each cathode material are discussed. Finally, the future development prospect of the cathode materials is presented.

Aluminum intercalation behaviours of {[Fe(Tp)(CN)3]2[M(H2O)2]} cyanido-bridged chain compounds in an ionic liquid electrolyte

As the development of aluminum-ion batteries is still in its infancy, researchers are still dedicated to exploring suitable host materials and investigating their aluminum intercalation behaviours. Here, a series of cyanido-bridged chain compounds with the formula {[FeIII(Tp)(CN)3]2[MII(H2O)2]}n (M = Ni, Co, Mn, Zn, Cu) are studied as cathode electrodes for aluminum-ion batteries with [EMIm]Cl-AlCl3 (1-ethyl-3-methylimidazolium chloride-AlCl3) ionic liquid as the electrolyte. The electrochemical properties suggested Fe3+/Fe2+ to be the redox-active couple during the aluminum intercalation and deintercalation processes of these compounds, and the observed maximum specific capacity obtained by the Fe-Co compound is 200 mA h g-1 despite the rapid specific capacity fading. To gain a deeper understanding of the capacity decay suffered by these compounds, further investigation was conducted to explore the evolution of compounds during the electrochemical measurements. It has been attributed to the following reasons: 1. thermodynamic instability results in the transformation/damage of two of the chain structures (for the Fe-Ni and Fe-Co compounds) during heat treatment on electrodes, a crucial step in electrode preparation; 2. the acidic nature of the electrolyte triggers the destruction of the chain structure, with the appearance of partial reduction of Fe3+ to Fe2+, and a new interaction of the cyano group with aluminum; 3. the high charge density of inserted Al ions makes the chain structure suffer from structural damage during both the charging and discharging processes. The progressive accumulation of trapped intercalated ions hampers their involvement in the reaction, consequently decreasing electrochemical reversibility.

Construction of V2O5@MXene Cathodes toward a High Specific Capacity Aqueous Aluminum-Ion Battery

Aqueous aluminum-ion batteries (AAIBs) are considered a strong candidate for the new generation of energy storage devices. The lack of suitable cathode materials has been a bottleneck factor hindering the future development of AAIBs. In this work, we design and construct a highly effective cathode with dual morphologies. Two-dimensional (2D) layered MXene materials possessed good conductivity and hydrophilicity, which are used as the substrates to deposit rod-shaped vanadium oxides (V2O5) to form a three-dimensional (3D) cathode. The cathode design provides a strong boost for the rapid electrochemical activities of rod-shaped V2O5 by embedding/extracting both protons (H+) and aluminum-ion (Al3+). As a result, the V2O5@MXene cathode based AAIB delivers an ultrahigh initial specific capacity of 626 mAh/g at 0.1 A/g with a stable cycle performance up to 100 cycles. This work is a breakthrough for the development of cathode materials for AAIBs.

Interleaved Electroactive Molecules into LDH Working on Both Electrodes of an Aqueous Battery-Type Device

By selecting two electroactive species immobilized in a layered double hydroxide backbone (LDH) host, one able to act as a positive electrode material and the other as a negative one, it was possible to match their capacity to design an innovative energy storage device. Each electrode material is based on electroactive species, riboflavin phosphate (RF) on one side and ferrocene carboxylate (FCm) on the other, both interleaved into a layered double hydroxide (LDH) host structure to avoid any possible molecule migration and instability. The intercalation of the electroactive guest molecules is demonstrated by X-ray diffraction with the observation of an interlayer LDH spacing of about 2 nm in each case. When successfully hosted into LDH interlayer space, the electrochemical behavior of each hybrid assembly was scrutinized separately in aqueous electrolyte to characterize the redox reaction occurring upon cycling and found to be a rapid faradic type. Both electrode materials were placed face to face to achieve a new aqueous battery (16C rate) that provides a first cycle-capacity of about 7 mAh per gram of working electrode material LDH/FCm at 10 mV/s over a voltage window of 2.2 V in 1M sodium acetate, thus validating the hybrid LDH host approach on both electrode materials even if the cyclability of the assembly has not yet been met.

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.

Advancing battery design based on environmental impacts using an aqueous Al-ion cell as a case study

The drive to decarbonise our economy needs to be built into our technology development, particularly in the energy storage industry. A method for creating performance targets for battery development based on environmental impact is presented and discussed. By taking the environmental impact assessments from existing lithium-ion battery technology—it is possible to derive energy density, cycle life and % active material targets required to achieve equal or better environmental impacts for emerging technologies to use. A parameter ‘goal space’ is presented using this technique for an aqueous aluminium-ion battery in its early development. This method is based on the main reason for battery technology advancement—the mitigation of climate change and the reduction of overall CO₂ emissions in society. By starting out with targets based on emission data, sustainability will be at the centre of battery research, as it should be.

A Review of Energy Storage Mechanisms in Aqueous Aluminium Technology

This systematic review covers the developments in aqueous aluminium energy storage technology from 2012, including primary and secondary battery applications and supercapacitors. Aluminium is an abundant material with a high theoretical volumetric energy density of –8.04 Ah cm−3. Combined with aqueous electrolytes, which have twice the ionic storage potential as non-aqueous versions, this technology has the potential to serve many energy storage needs. The charge transfer mechanisms are discussed in detail with respect to aqueous aluminium-ion secondary batteries, where most research has focused in recent years. TiO2 nanopowders have shown to be promising negative electrodes, with the potential for pseudocapacitive energy storage in aluminuim-ion cells. This review summarises the advances in Al-ion systems using aqueous electrolytes, focusing on electrochemical performance.

Rechargeable Mg-Ion Full Battery System with High Capacity and High Rate

Thanks to the low cost, free dendritic hazards, and high volumetric capacity, magnesium (Mg)-ion batteries have attracted increasing attention as alternative energy storage devices to lithium-ion batteries. Despite the successful development of electrode materials, the real-life application potential of Mg-ion full battery systems (MIFBSs) is largely hindered by the lack of suitable electrode couples and hence low diffusion kinetics, which induce low specific capacity, poor rate performance, and low working voltage. Herein, we report an aqueous rechargeable MIFBS by employing copper hexacyanoferrate (CuHCF) as the cathode and 3,4,9,10-perylene-tetracarboxylic acid diimide (PTCDI) as the anode in 1 moL L^-1 MgCl₂ electrolyte. The combination of PTCDI//CuHCF allows efficient redox and convenient intercalation/deintercalation of Mg²⁺ at the electrodes while facilitating a fast transfer of Mg²⁺ between the two electrodes. As a result, the system delivers a high capacity of ∼120.3 mAh g^-1 at a current density of 0.5 A g^-1 after 200 operation cycles with a broadened voltage range (0-1.95 V) and maintains a capacity of ∼97.8 mAh g^-1 at 2.0 A g^-1 after 1000 cycles. Even at a high current density of 5.0 A g^-1, the battery provides a steady capacity of ∼81.4 mAh g^-1 over 5000 cycles. Moreover, after being applied at 11.0 A g^-1, the system can deliver a capacity of ∼126.5 mAh g^-1 at 0.5 A g^-1. This work emphasizes the great promise of developing suitable electrode couples for aqueous MIFBSs to achieve high capacity and high rate.

High-Performance MnO2 /Al Battery with In Situ Electrochemically Reformed Alx MnO2 Nanosphere Cathode

Aqueous Al-ion battery (AAIB) is regarded as a promising candidate for large-scale energy storage systems due to its high capacity, high safety, and low cost, with MnO₂ proved to be a high-performance cathode. However, the potential commercial application of this type of battery is plagued by the frequent structural collapse of MnO₂ . Herein, an in situ, electrochemically reformed, urchin-like Al_x MnO₂ cathode is developed for water-in-salt electrolyte-based AAIBs. Benefiting from its unique α-MnO₂ coated Mn₂ AlO₄ structure, a high Al ion storage capacity is achieved together with a high discharge voltage plateau of 1.9 V by reversible MnO₂ electrolysis. Consequently, the battery exhibits a high specific capacity of 285 mAh g^-1 and a high energy density of 370 Wh kg^-1 at a high current density of 500 mA g^-1 . Improved stability with record capacity retention is also obtained at an ultrahigh current density of 5 A g^-1 after 500 cycles. Such a high-capacity and high-stability Al_x MnO₂ cathode would pave the way for in situ electrochemical transformation of cathode design and thus boost the practical application of AAIBs.

Prussian Blue Analogues in Aqueous Batteries and Desalination Batteries

In the applications of large-scale energy storage, aqueous batteries are considered as rivals for organic batteries due to their environmentally friendly and low-cost nature. However, carrier ions always exhibit huge hydrated radius in aqueous electrolyte, which brings difficulty to find suitable host materials that can achieve highly reversible insertion and extraction of cations. Owing to open three-dimensional rigid framework and facile synthesis, Prussian blue analogues (PBAs) receive the most extensive attention among various host candidates in aqueous system. Herein, a comprehensive review on recent progresses of PBAs in aqueous batteries is presented. Based on the application in different aqueous systems, the relationship between electrochemical behaviors (redox potential, capacity, cycling stability and rate performance) and structural characteristics (preparation method, structure type, particle size, morphology, crystallinity, defect, metal atom in high-spin state and chemical composition) is analyzed and summarized thoroughly. It can be concluded that the required type of PBAs is different for various carrier ions. In particular, the desalination batteries worked with the same mechanism as aqueous batteries are also discussed in detail to introduce the application of PBAs in aqueous systems comprehensively. This report can help the readers to understand the relationship between physical/chemical characteristics and electrochemical properties for PBAs and find a way to fabricate high-performance PBAs in aqueous batteries and desalination batteries.

9,10-Anthraquinone/K2CuFe(CN)6: A Highly Compatible Aqueous Aluminum-Ion Full-Battery Configuration

Temporally intermittent and spatially dispersed renewable energy sources strongly call for large-scale energy storage devices. Aqueous aluminum-ion batteries show great potential for application due to their safety and low cost. Thus far, however, the ideal full-battery configuration is beyond the scope due to shortcomings with regards to suitable anode and cathode materials. Herein, we report a pioneering aqueous aluminum-ion battery system consisting of a Prussian white cathode, 1 M Al₂(SO₄)₃ aqueous electrolyte, and an organic 9,10-anthraquinone anode. The oxidation capability of the Prussian white cathode during the first charging allows for the fabrication of the full battery without pre-inserting aluminum ions, thus making the rocking-chair-type battery feasible. Importantly, the open-framework structure of the Prussian white and distinct enolization charge storage mechanism of 9,10-anthraquinone ensure fast reaction kinetics. The full battery exhibits cycling stability with a capacity retention of 89.1% over 100 cycles at 500 mA g^-1, finishing a cycle in about 10 min. This work provides a pathway for developing rechargeable aqueous aluminum-ion batteries.

Nanomanufacturing of RGO-CNT Hybrid Film for Flexible Aqueous Al-Ion Batteries

A highly electrically conductive film-type current collector is an essential part of batteries. Apart from the metal-based current collectors, lightweight and highly conductive carbon materials such as reduced graphene oxide (RGO) and carbon nanotubes (CNTs) show great potential as current collectors. However, traditional RGO manufacturing usually requires a long time and high energy, which decreases the product yielding rate and manufacturing efficiency. Moreover, the performance of the manufactured RGO needs to be further improved. In this work, CNT and GO are evenly mixed into GO-CNT, which can be directly reduced into RGO-CNT by Joule heating at 2936 K within less than 1 min. The fabricated RGO-CNT achieves a high electrical conductivity of 2750 S cm^-1 , and realizes a 10⁶ -fold increase. The assembled flexible aqueous Al-ion battery with RGO-CNT as the current collector exhibits impressive electrochemical performance in terms of superior cycling stability and exceptional rate capability, and excellent mechanical ability regarding the tolerance to mechanical damage such as bending, folding, piercing, and cutting without detrimental consequences.

The Compensation Effect Mechanism of Fe-Ni Mixed Prussian Blue Analogues in Aqueous Rechargeable Aluminum-Ion Batteries

An aluminum-ion battery was assembled with potassium nickel hexacyanoferrate (KNHCF) as a cathode and Al foil as an anode in aqueous electrolyte for the first time, based on Al³⁺ intercalation and deintercalation. A combination of ex situ XRD, X-ray photoelectron spectroscopy (XPS), galvanostatic intermittent titration technique (GITT), and differential capacity analysis was used to unveil the crystal structure changes and the insertion/extraction mechanism of Al³⁺ . Al³⁺ could reversibly insert/extract into/from KNHCF nanoparticles through a single-phase reaction with reduction/oxidation of Fe and Ni. Over long-term cycling, it was Fe rather than Ni that contributed to more capacity owing to the dissolution of Ni from the KNHCF structure, which could be expressed as a compensation effect of mixed redox centers in KNHCF. KNHCF delivered an initial discharge capacity of 46.5 mAh g^-1 . The capacity decay could be attributed to the unstable interface between Al foil and the aqueous electrolyte owing to the catalytic activity of the Ni transferring from Ni dissolution of KNHCF to the Al foil anode, rather than KNHCF structure collapse; KNHCF maintained its 3 D framework structure for 500 cycles. This work is expected to inspire more exhaustive investigations of the mechanisms that occur in aluminum-ion batteries.

Voltage issue of aqueous rechargeable metal-ion batteries

Over the past two decades, a series of aqueous rechargeable metal-ion batteries (ARMBs) have been developed, aiming at improving safety, environmental friendliness and cost-efficiency in fields of consumer electronics, electric vehicles and grid-scale energy storage. However, the notable gap between ARMBs and their organic counterparts in energy density directly hinders their practical applications, making it difficult to replace current widely-used organic lithium-ion batteries. Basically, this huge gap in energy density originates from cell voltage, as the narrow electrochemical stability window of aqueous electrolytes substantially confines the choice of electrode materials. This review highlights various ARMBs with focuses on their voltage characteristics and strategies that can effectively raise battery voltage. It begins with the discussion on the fundamental factor that limits the voltage of ARMBs, i.e., electrochemical stability window of aqueous electrolytes, which decides the maximum-allowed potential difference between cathode and anode. The following section introduces various ARMB systems and compares their voltage characteristics in midpoint voltage and plateau voltage, in relation to respective electrode materials. Subsequently, various strategies paving the way to high-voltage ARMBs are summarized, with corresponding advancements highlighted. The final section presents potential directions for further improvements and future perspectives of this thriving field.

Electrochemical study of TiO2 in aqueous AlCl3 electrolyte via vacuum impregnation for superior high-rate electrode performance

This communication elucidates the charge storage mechanism of a TiO2 electrode in 1 mol dm− 3 AlCl3 for use in aqueous-ion batteries. Cyclic voltammetry studies suggest a surface contribution to charge storage and that cycle life can be improved by limiting the potential ≥ − 1.0 V vs SCE. In order to enhance this surface contribution, a simple vacuum impregnation technique was employed to improve electrode-electrolyte contact. This resulted in a significant improvement in the high rate performance of TiO2, where a capacity of 15 mA h g− 1 was maintained at the very high specific current of 40 A g− 1, a decrease of only 25% from when the electrode was cycled at 1 A g− 1. The vacuum impregnation process was also applied to copper-hexacyanoferrate, envisaged as a possible positive electrode, again resulting in significant improvements to high-rate performance. This demonstrates the potential for using this simple technique for improving electrode performance in other aqueous electrolyte battery systems.

The Aluminum-Ion Battery: A Sustainable and Seminal Concept?

The expansion of renewable energy and the growing number of electric vehicles and mobile devices are demanding improved and low-cost electrochemical energy storage. In order to meet the future needs for energy storage, novel material systems with high energy densities, readily available raw materials, and safety are required. Currently, lithium and lead mainly dominate the battery market, but apart from cobalt and phosphorous, lithium may show substantial supply challenges prospectively, as well. Therefore, the search for new chemistries will become increasingly important in the future, to diversify battery technologies. But which materials seem promising? Using a selection algorithm for the evaluation of suitable materials, the concept of a rechargeable, high-valent all-solid-state aluminum-ion battery appears promising, in which metallic aluminum is used as the negative electrode. On the one hand, this offers the advantage of a volumetric capacity four times higher (theoretically) compared to lithium analog. On the other hand, aluminum is the most abundant metal in the earth's crust. There is a mature industry and recycling infrastructure, making aluminum very cost efficient. This would make the aluminum-ion battery an important contribution to the energy transition process, which has already started globally. So far, it has not been possible to exploit this technological potential, as suitable positive electrodes and electrolyte materials are still lacking. The discovery of inorganic materials with high aluminum-ion mobility—usable as solid electrolytes or intercalation electrodes—is an innovative and required leap forward in the field of rechargeable high-valent ion batteries. In this review article, the constraints for a sustainable and seminal battery chemistry are described, and we present an assessment of the chemical elements in terms of negative electrodes, comprehensively motivate utilizing aluminum, categorize the aluminum battery field, critically review the existing positive electrodes and solid electrolytes, present a promising path for the accelerated development of novel materials and address problems of scientific communication in this field.

Water in Rechargeable Multivalent-Ion Batteries: An Electrochemical Pandora's Box

Multivalent-ion batteries built on water-based electrolytes represent energy storage at suitable price points, competitive performance, and enhanced safety. However, to comply with modern energy-density requirements, the battery must be reversible within an operating voltage window greater than 1.23 V or the electrochemical stability limits of free water. Taking advantage of its powerful solvation and catalytic activities, adding water to electrolyte preparations can unlock a wider gamut of liquid mixtures compared with strictly nonaqueous systems. However, a point-by-point sweep of all potential formulations is arduous and ineffective without some form of systematic rationalization. The present Review consolidates recent progress, pitfalls, limits, and insights critical to expediting aqueous electrolyte designs to boost multivalent-ion battery outputs.

Fast Microwave-Assisted Hydrothermal Synthesis of Pure Layered δ-MnO₂ for Multivalent Ion Intercalation

This work reports on the synthesis of layered manganese oxides (δ-MnO₂) and their possible application as cathode intercalation materials in Al-ion and Zn-ion batteries. By using a one-pot microwave-assisted synthesis route in 1.6 M KOH (Mn_VII:Mn_II = 0.33), a pure layered δ-MnO₂birnessite phase without any hausmannite traces was obtained after only a 14 h reaction time period at 110 °C. Attempts to enhance crystallinity level of as-prepared birnessite through increasing of reaction time up to 96 h in 1.6 M KOH failed and led to decreases in crystallinity and the emergence of an additional hausmannite phase. The influence of Mn_II:OH⁻ ratio (1:2 to 1:10) on phase crystallinity and hausmannite phase formation for 96 h reaction time was investigated as well. By increasing alkalinity of the reaction mixture up to 2.5 M KOH, a slight increase in crystallinity of birnessite phase was achieved, but hausmannite formation couldn’t be inhibited as hoped. The as-prepared layered δ-MnO₂ powder material was spray-coated on a carbon paper and tested in laboratory cells with Al or Zn as active materials. The Al-ion tests were carried out in EMIMCl/AlCl₃ while the Zn-Ion experiments were performed in water containing choline acetate (ChAcO) or a ZnSO₄ solution. Best performance in terms of capacity was yielded in the Zn-ion cell (200 mWh g⁻¹ for 20 cycles) compared to about 3 mAh g⁻¹ for the Al-ion cell. The poor activity of the latter system was attributed to low dissociation rate of tetrachloroaluminate ions (AlCl₄⁻) in the EMIMCl/AlCl₃ mixture into positive Al complexes which are needed for charge compensation of the oxide-based cathode during the discharge step.

Electrochemically Treated TiO₂ for Enhanced Performance in Aqueous Al-Ion Batteries

The potential for low cost, environmentally friendly and high rate energy storage has led to the study of anatase-TiO₂ as an electrode material in aqueous Al3+ electrolytes. This paper describes the improved performance from an electrochemically treated composite TiO₂ electrode for use in aqueous Al-ion batteries. After application of the cathodic electrochemical treatment in 1 mol/dm³ KOH, Mott⁻Schottky analysis showed the treated electrode as having an increased electron density and an altered open circuit potential, which remained stable throughout cycling. The cathodic treatment also resulted in a change in colour of TiO₂. Treated-TiO₂ demonstrated improved capacity, coulombic efficiency and stability when galvanostatically cycled in 1 mol·dm-3AlCl₃/1 mol·dm-3 KCl. A treated-TiO₂ electrode produced a capacity of 15.3 mA·h·g-1 with 99.95% coulombic efficiency at the high specific current of 10 A/g. Additionally, X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy were employed to elucidate the origin of this improved performance.