Architecting a Stable High-Energy Aqueous Al-Ion Battery

Recent Advances of Carbon Materials in Anodes for Aqueous Zinc Ion Batteries

Carbon-based materials have been successfully applied in the zinc ion batteries to improve the energy storage capability and durability of zinc anodes. In this review, four types of carbon materials (conventional carbons, fiber-like carbons, carbon nanotubes, graphene and other 2D carbon materials) are introduced based on the electrode preparation, physicochemical property and battery performance. Several modification strategies are also illustrated, such as heteroatom doping, hierarchical design and metal/carbon composites. Besides the discussion of existing issues of zinc anodes, the structure-performance relationships are analyzed in depth. Finally, conclusive remarks of this review are summarized and prospects of the future improvement are proposed.

Solid-Solution-Based Metal Coating Enables Highly Reversible, Dendrite-Free Aluminum Anode

Aluminum-ion batteries have attracted great interest in the grid-scale energy storage field due to their good safety, low cost and the high abundance of Al. However, Al anodes suffer from severe dendrite growth, especially at high deposition rates. Here, we report a simple strategy for constructing a highly reversible, dendrite-free, Al-based anode through directly introducing a solid-solution-based metal coating to a Zn foil substrate. Compared with Cu foil substrates and bare Al, a Zn foil substrate shows a lower nucleation barrier of Al deposition due to the intrinsic, definite solubility between Al and Zn. During Al deposition, a thin, solid-solution alloy phase is first formed on the surface of the Zn foil substrate and then guides the parallel growth of flake-like Al on Zn substrate. The well-designed, Zn-coated Al (Zn@Al) anode can effectively inhibit dendrite growth and alleviate the corrosion of the Al anode. The fabricated Zn@Al–graphite battery exhibits a high specific capacity of 80 mAh·g−1 and an ultra-long lifespan over 10,000 cycles at a high current density of 20 A·g−1 in low-cost molten salt electrolyte. This work opens a new avenue for the development of stable Al anodes and can provide insights for other metal anode protection.

Quinone Electrodes for Alkali-Acid Hybrid Batteries

Aqueous batteries are promising candidates for large-scale energy storage but face either limited energy density (lead-acid batteries), cost/resource concerns (Ni-MH batteries), or safety issues due to metal dendrite growth at high current densities (zinc batteries). We report that through designing electrochemical redox couples, quinones as intrinsic dendrite-free and sustainable anode materials demonstrate the theoretical energy density of 374 W h kg^-1 coupling with affordable Mn²⁺/MnO₂ redox reactions on the cathode side. Due to the fast K-ion diffusion in the electrolyte, low K-ion desolvation energy at the interface, and fast quinone/phenol reaction, the optimized poly(1,4-anthraquinone) in the KOH electrolyte shows specific capacities of 295 mA h g^-1 at 300 C-rate and 225 mA h g^-1 at 240 mA cm^-2. Further constructed practical aqueous batteries exhibit an output voltage of 2 V in alkali-acid hybrid electrolyte systems with exceptional electrochemical kinetics, which can release/store over 95% of the theoretical capacity in less than 40 s (25 000 mA g^-1). The scaled Ah level aqueous battery with the upgradation of interfacial chemistry on the electrode current collector exhibits an overall energy density of 92 W h kg^-1, exceeding commercial aqueous lead-acid and Ni-MH batteries. The rapid response, intrinsic dendrite-free existence, and cost efficiency of quinone electrodes provide promising application interests for regulating the output of the electricity grid generated by intermittent solar and wind energy.

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.

Achieving high-rate and durable aqueous rechargeable Zn-Ion batteries by enhancing the successive electrochemical conversion reactions

The mild electrolyte working environment of rechargeable aqueous Zn-ion batteries (AZIBs) features its promising characteristic and potential application for large-scale energy storage system. However, the poor cycling stability significantly hinders the broad application of AZIBs due to the complex electrochemical conversion reactions during charge-discharge process. Herein, we propose a strategy to improve the electrochemical performance of AZIB by enhancing the successive electrochemical conversion reactions. With a rational design of electrode, an even homogeneous electric field can be achieved in the cathode side, resulting to significantly enhanced efficiency of successive electrochemical conversion reactions. Charge storage mechanism studies reveal that the reversibility behaviors of byproducts alkaline zinc sulfate (ZHS) can dramatically determine the H⁺/Zn²⁺ de/intercalation process, and a high reversibility characteristic ensures the facilitated electrochemical kinetics. As expected, the resultant AZIB possesses outstanding electrochemical performance with a high specific capacity of 425.08 mAh⋅g^-1 at 0.1 A⋅g^-1, an excellent rate capacity of about 60% (246.6 mAh⋅g^-1 at 1 A⋅g^-1) and superior cycling stability of 93.7% after 3000 cycles (at 3 A⋅g^-1). This effective strategy and thinking proposed here may open a new avenue for the development of high-performing AZIBs.

High-Energy Batteries: Beyond Lithium-Ion and Their Long Road to Commercialisation

Rechargeable batteries of high energy density and overall performance are becoming a critically important technology in the rapidly changing society of the twenty-first century. While lithium-ion batteries have so far been the dominant choice, numerous emerging applications call for higher capacity, better safety and lower costs while maintaining sufficient cyclability. The design space for potentially better alternatives is extremely large, with numerous new chemistries and architectures being simultaneously explored. These include other insertion ions (e.g. sodium and numerous multivalent ions), conversion electrode materials (e.g. silicon, metallic anodes, halides and chalcogens) and aqueous and solid electrolytes. However, each of these potential "beyond lithium-ion" alternatives faces numerous challenges that often lead to very poor cyclability, especially at the commercial cell level, while lithium-ion batteries continue to improve in performance and decrease in cost. This review examines fundamental principles to rationalise these numerous developments, and in each case, a brief overview is given on the advantages, advances, remaining challenges preventing cell-level implementation and the state-of-the-art of the solutions to these challenges. Finally, research and development results obtained in academia are compared to emerging commercial examples, as a commentary on the current and near-future viability of these "beyond lithium-ion" alternatives.

A dual-function liquid electrolyte additive for high-energy non-aqueous lithium metal batteries

Engineering the formulation of non-aqueous liquid electrolytes is a viable strategy to produce high-energy lithium metal batteries. However, when the lithium metal anode is combined with a Ni-rich layered cathode, the (electro)chemical stability of both electrodes could be compromised. To circumvent this issue, we report a combination of aluminum ethoxide (0.4 wt.%) and fluoroethylene carbonate (5 vol.%) as additives in a conventional LiPF₆-containing carbonate-based electrolyte solution. This electrolyte formulation enables the formation of mechanically robust and ionically conductive interphases on both electrodes’ surfaces. In particular, the alumina formed at the interphases prevents the formation of dendritic structures on the lithium metal anode and mitigate the stress-induced cracking and phase transformation in the Ni-rich layered cathode. By coupling a thin (i.e., about 40 μm) lithium metal anode with a high-loading (i.e., 21.5 mg cm⁻²) LiNi_0.8Co_0.1Mn_0.1O₂-based cathode in coin cell configuration and lean electrolyte conditions, the engineered electrolyte allows a specific discharge capacity retention of 80.3% after 130 cycles at 60 mA g⁻¹ and 30 °C which results in calculated specific cell energy of about 350 Wh kg⁻¹.

Lithium metal batteries suffer from poor (electro)chemical stability of the electrodes during prolonged cycling. Here, the authors report a dual function liquid electrolyte additive to form protective interphases on both electrodes to produce lab-scale high energy lithium metal batteries.

Aluminum-copper alloy anode materials for high-energy aqueous aluminum batteries

Aqueous aluminum batteries are promising post-lithium battery technologies for large-scale energy storage applications because of the raw materials abundance, low costs, safety and high theoretical capacity. However, their development is hindered by the unsatisfactory electrochemical behaviour of the Al metal electrode due to the presence of an oxide layer and hydrogen side reaction. To circumvent these issues, we report aluminum-copper alloy lamellar heterostructures as anode active materials. These alloys improve the Al-ion electrochemical reversibility (e.g., achieving dendrite-free Al deposition during stripping/plating cycles) by using periodic galvanic couplings of alternating anodic α-aluminum and cathodic intermetallic Al2Cu nanometric lamellas. In symmetric cell configuration with a low oxygen concentration (i.e., 0.13 mg L−1) aqueous electrolyte solution, the lamella-nanostructured eutectic Al82Cu18 alloy electrode allows Al stripping/plating for 2000 h with an overpotential lower than ±53 mV. When the Al82Cu18 anode is tested in combination with an AlxMnO2 cathode material, the aqueous full cell delivers specific energy of ~670 Wh kg−1 at 100 mA g−1 and an initial discharge capacity of ~400 mAh g−1 at 500 mA g−1 with a capacity retention of 83% after 400 cycles.

Challenges and Strategies of Low-Cost Aluminum Anodes for High-Performance Al-Based Batteries

The ever-growing market of electric vehicles and the upcoming grid-scale storage systems have stimulated the fast growth of renewable energy storage technologies. Aluminum-based batteries are considered one of the most promising alternatives to complement or possibly replace the current lithium-ion batteries owing to their high specific capacity, good safety, low cost, light weight, and abundant reserves of Al. However, the anode problems in primary and secondary Al batteries, such as, self-corrosion, passive film, and volume expansion, severely limit the batteries' practical performance, thus hindering their commercialization. Herein, an overview of the currently emerged Al-based batteries is provided, that primarily focus on the recent research progress for Al anodes in both primary and rechargeable systems. The anode reaction mechanisms and problems in various Al-based batteries are discussed, and various strategies to overcome the challenges of Al anodes, including surface oxidation, self-corrosion, volume expansion, and dendrite growth, are systematically summarized. Finally, future research perspectives toward advanced Al batteries with higher performance and better safety are presented.

A stable and high-energy aqueous aluminum based battery

Aqueous aluminum ion batteries (AAIBs) have received growing attention because of their low cost, safe operation, eco-friendliness, and high theoretical capacity. However, one of the biggest challenges for AAIBs is...

Cost-Effective 1T-MoS2 Grown on Graphite Cathode Materials for High-Temperature Rechargeable Aluminum Ion Batteries and Hydrogen Evolution in Water Splitting

The high dependence on and high cost of lithium has led to a search for alternative materials. Aluminum ion batteries (AIBs) have gained interest due to their abundance, low cost, and high capacity. However, the use of the expensive 1-ethyl-3-methylimidazolium chloride (EMIC) electrolyte in AIBs curtails its wide application. Recently, high-temperature batteries have also gained much attention owing to their high demand by industries. Herein, we introduce cost-effective 1T molybdenum sulfide grown on SP-1 graphite powder (1T-MoS2/SP-1) as a cathode material for high-temperature AIBs using the AlCl3-urea eutectic electrolyte (1T-MoS2/SP-1–urea system). The AIB using the 1T-MoS2/SP-1–urea system exhibited a capacity as high as 200 mAh/g with high efficiency of 99% over 100 cycles at 60 °C when cycled at the rate of 100 mA/g. However, the AIB displayed a capacity of 105 mAh/g when cycled at room temperature. The enhanced performance of the 1T-MoS2/SP-1–urea system is attributed to reduced viscosity of the AlCl3-urea eutectic electrolyte at higher temperatures with high compatibility of 1T-MoS2 with SP-1. Moreover, the electrocatalytic lithiation of 1T-MoS2 and its effect on the hydrogen evolution reaction were also investigated. We believe that our work can act as a beacon for finding alternative, cost-effective, and high-temperature batteries.

A rechargeable aqueous manganese-ion battery based on intercalation chemistry

Aqueous rechargeable metal batteries are intrinsically safe due to the utilization of low-cost and non-flammable water-based electrolyte solutions. However, the discharge voltages of these electrochemical energy storage systems are often limited, thus, resulting in unsatisfactory energy density. Therefore, it is of paramount importance to investigate alternative aqueous metal battery systems to improve the discharge voltage. Herein, we report reversible manganese-ion intercalation chemistry in an aqueous electrolyte solution, where inorganic and organic compounds act as positive electrode active materials for Mn2+ storage when coupled with a Mn/carbon composite negative electrode. In one case, the layered Mn0.18V2O5·nH2O inorganic cathode demonstrates fast and reversible Mn2+ insertion/extraction due to the large lattice spacing, thus, enabling adequate power performances and stable cycling behavior. In the other case, the tetrachloro-1,4-benzoquinone organic cathode molecules undergo enolization during charge/discharge processes, thus, contributing to achieving a stable cell discharge plateau at about 1.37 V. Interestingly, the low redox potential of the Mn/Mn2+ redox couple vs. standard hydrogen electrode (i.e., -1.19 V) enables the production of aqueous manganese metal cells with operational voltages higher than their zinc metal counterparts.

In Situ Preparation of MXenes in Ambient-Temperature Organic Ionic Liquid Aluminum Batteries with Ultrastable Cycle Performance

A fluorine-free and water-free electrochemical preparation of MXenes is achieved in Lewis acidic molten salts at ambient temperature. In addition, the anode reaction of the MAX phase V₂AlC is studied in the organic ionic liquid aluminum battery and the extraction voltages of the metal atoms Al and V in the MAX phase V₂AlC are determined. This points out the direction for the constant-voltage electrochemical preparation of MXenes. Furthermore, the electrochemical performance of the etched V₂AlC (E-V₂AlC) in an aluminum battery is studied. The one-stop preparation-application process prevents the MXenes from contacting water and air, and the MXenes etched in the aluminum battery are more conducive to the intercalation/deintercalation of Al³⁺. Therefore, E-V₂AlC exhibits excellent electrochemical performance in an aluminum battery. Under the conditions of a voltage window of 0.01-2.3 V (V vs Al/Al³⁺) and a current density of 500 mA g^-1, the specific discharge capacity is about 100 mAh g^-1 after 6500 cycles. In addition, the energy storage mechanism and Faraday energy storage method of E-V₂AlC in an aluminum battery are studied. The diffusion coefficient D of Al³⁺ is determined by a galvanostatic intermittent titration technique. The reasons for its excellent electrochemical performance are clarified from the perspective of kinetics.

Zn Metal Anodes for Zn-Ion Batteries in Mild Aqueous Electrolytes: Challenges and Strategies

Over the past few years, rechargeable aqueous Zn-ion batteries have garnered significant interest as potential alternatives for lithium-ion batteries because of their low cost, high theoretical capacity, low redox potential, and environmentally friendliness. However, several constraints associated with Zn metal anodes, such as the growth of Zn dendrites, occurrence of side reactions, and hydrogen evolution during repeated stripping/plating processes result in poor cycling life and low Coulombic efficiency, which severely impede further advancements in this technology. Despite recent efforts and impressive breakthroughs, the origin of these fundamental obstacles remains unclear and no successful strategy that can address these issues has been developed yet to realize the practical applications of rechargeable aqueous Zn-ion batteries. In this review, we have discussed various issues associated with the use of Zn metal anodes in mildly acidic aqueous electrolytes. Various strategies, including the shielding of the Zn surface, regulating the Zn deposition behavior, creating a uniform electric field, and controlling the surface energy of Zn metal anodes to repress the growth of Zn dendrites and the occurrence of side reactions, proposed to overcome the limitations of Zn metal anodes have also been discussed. Finally, the future perspectives of Zn anodes and possible design strategies for developing highly stable Zn anodes in mildly acidic aqueous environments have been discussed.

An electrochemical study on LiMn2O4 for Al3+ ion storage in aqueous electrolytes

Herein, we report the possibility of electrochemical Al³⁺ ion insertion in LiMn₂O₄ in aqueous electrolytes. LiMn₂O₄ exhibits a discharge potential plateau of 1.5 V and a discharge capacity of 65 mA h g^-1 is achieved at a current rate of 800 mA g^-1 at the 75th cycle with the pre-addition of low-valence Mn ions in an aqueous AlCl₃ electrolyte.

Novel K2Ti8O17 Anode via Na+/Al3+ Co-Intercalation Mechanism for Rechargeable Aqueous Al-Ion Battery with Superior Rate Capability

A promising aqueous aluminum ion battery (AIB) was assembled using a novel layered K₂Ti₈O₁₇ anode against an activated carbon coated on a Ti mesh cathode in an AlCl₃-based aqueous electrolyte. The intercalation/deintercalation mechanism endowed the layered K₂Ti₈O₁₇ as a promising anode for rechargeable aqueous AIBs. NaAc was introduced into the AlCl₃ aqueous electrolyte to enhance the cycling stability of the assembled aqueous AIB. The as-designed AIB displayed a high discharge voltage near 1.6 V, and a discharge capacity of up to 189.6 mAh g⁻¹. The assembled AIB lit up a commercial light-emitting diode (LED) lasting more than one hour. Inductively coupled plasma–optical emission spectroscopy (ICP-OES), high-resolution transmission electron microscopy (HRTEM), and X-ray absorption near-edge spectroscopy (XANES) were employed to investigate the intercalation/deintercalation mechanism of Na⁺/Al³⁺ ions in the aqueous AIB. The results indicated that the layered structure facilitated the intercalation/deintercalation of Na⁺/Al³⁺ ions, thus providing a high-rate performance of the K₂Ti₈O₁₇ anode. The diffusion-controlled electrochemical characteristics and the reduction of Ti⁴⁺ species during the discharge process illustrated the intercalation/deintercalation mechanism of the K₂Ti₈O₁₇ anode. This study provides not only insight into the charge–discharge mechanism of the K₂Ti₈O₁₇ anode but also a novel strategy to design rechargeable aqueous AIBs.

Aqueous Aluminum Cells: Mechanisms of Aluminum Anode Reactions and Role of the Artificial Solid Electrolyte Interphase

Electrochemical cells with aluminum (Al) as the active material offer the benefits of high energy density, low cost, and high safety. Although several research groups have assembled rechargeable Al//M_xO_y (M = Mn, V, etc) cells with 2 m aqueous Al trifluoromethanesulfonate as an electrolyte and demonstrated the importance of the artificial solid electrolyte interphase (ASEI) on the Al anode for realizing high rechargeable capacity, the reactions of the Al anode in such cells remain underexplored. Herein, we investigate the effects of the ASEI on the charge/discharge cycling stability and activity of Al cells with the abovementioned aqueous electrolyte and reveal that this interphase provides chloride anions to induce the corrosion of Al rather than to support the transportation of Al³⁺ ions during charge/discharge. Regardless of the ASEI presence/absence, the main reactions at the Al anode during charge/discharge cycling are identified as oxidation and gas evolution, which suggests that the reduction of Al in the employed electrolyte is irreversible. The simple introduction of chloride anions (e.g., 0.15 m NaCl) into the electrolyte is shown to allow the realization of an Al//MnO₂ cell with superior performance (discharge working voltage ≈ 1.5 V and specific capacity = 250 mA h/g). Thus, the present work unveils the mechanisms of reactions occurring at the Al anode of aqueous electrolyte Al cells to support their further development.

A quinone electrode with reversible phase conversion for long-life rechargeable aqueous aluminum-metal batteries

The exploration of high-performance cathode candidates is of great significance for aqueous aluminum-metal batteries (AAMBs). Here, we, for the first time, report tetrachloro-1,4-benzoquinone (TCQ) as a superior organic AAMB cathode. Owing to its high reversible conversion between the carbonyl and hydroxyl groups, the TCQ cathode delivers a remarkable electrochemical performance.

Realizing high-power and high-capacity zinc/sodium metal anodes through interfacial chemistry regulation

Stable plating/stripping of metal electrodes under high power and high capacity remains a great challenge. Tailoring the deposition behavior on the substrate could partly resolve dendrites' formation, but it usually works only under low current densities and limited capacities. Here we turn to regulate the separator's interfacial chemistry through tin coating with decent conductivity and excellent zincophilicity. The former homogenizes the electric field distribution for smooth zinc metal on the substrate, while the latter enables the concurrent zinc deposition on the separator with a face-to-face growth. Consequently, dendrite-free zinc morphologies and superior cycling stability are achieved at simultaneous high current densities and large cycling capacities (1000 h at 5 mA/cm² for 5 mAh/cm² and 500 h at 10 mA/cm² for 10 mAh/cm²). Furthermore, the concept could be readily extended to sodium metal anodes, demonstrating the interfacial chemistry regulation of separator is a promising route to circumvent the metal anode challenges.

Proton-assisted calcium-ion storage in aromatic organic molecular crystal with coplanar stacked structure

Rechargeable calcium-ion batteries are intriguing alternatives for use as post-lithium-ion batteries. However, the high charge density of divalent Ca²⁺ establishes a strong electrostatic interaction with the hosting lattice, which results in low-capacity Ca-ion storage. The ionic radius of Ca²⁺ further leads to sluggish ionic diffusion, hindering high-rate capability performances. Here, we report 5,7,12,14-pentacenetetrone (PT) as an organic crystal electrode active material for aqueous Ca-ion storage. The weak π-π stacked layers of the PT molecules render a flexible and robust structure suitable for Ca-ion storage. In addition, the channels within the PT crystal provide efficient pathways for fast ionic diffusion. The PT anode exhibits large specific capacity (150.5 mAh g^-1 at 5 A g^-1), high-rate capability (86.1 mAh g^-1 at 100 A g^-1) and favorable low-temperature performances. A mechanistic study identifies proton-assisted uptake/removal of Ca²⁺ in PT during cycling. First principle calculations suggest that the Ca ions tend to stay in the interstitial space of the PT channels and are stabilized by carbonyls from adjacent PT molecules. Finally, pairing with a high-voltage positive electrode, a full aqueous Ca-ion cell is assembled and tested.

Development of negative electrode active materials alternative to Ca metal is essential for the progress of Ca-ion battery technology. Here, the authors disclose the proton-assisted Ca-ion storage behavior of a pentacenetetrone organic crystal reporting high-power cell performances.

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.