High‐Rate Aqueous Aluminum‐Ion Batteries Enabled by Lewis‐Acid Chloride Electrolyte Additives and BiOI Cathodes

Molybdenum trioxide (MoO3) is a promising positive electrode material for aqueous aluminum-ion batteries (AAIBs) due to its high theoretical capacity. However, MoO3 faces several challenges in an aqueous electrolyte, such as easy dissolution of reaction products, volume expansion, and low conductivity, which severely limit its application in aqueous batteries. In this work, we effectively increased the overall conductivity of the electrode by in situ growing MoO3 on the Mo2C MXene layer. MXene can effectively inhibit the dissolution and structural loss of MoO3 reaction products. Additionally, the coordination effect of Mo2C and MoO3 achieves a stable near-surface reaction on the MXene laminates, resulting in the Mo2C/MoO3 composite exhibiting excellent aluminum storage properties (123.5 mAh/g after 200 cycles at 0.4 A/g). The energy storage mechanism of H+/Al3+ co-insertion/extraction was elucidated through ex situ characterization, and the promotion effect of Mo2C on MoO3 reaction kinetics was verified by density functional theory (DFT) calculations. This work provides new insights into improving the stability of AAIBs cathodes and extends the application of Mo-based MXene in aqueous batteries.

Aqueous aluminum ion system: A future of sustainable energy storage device

The increasing utilization of renewable energy sources, including wind and solar power, has created new demands for safe, low-cost, and reliable electrochemical energy storage (EES). Existing EES systems, primarily based on lithium (Li)-ion batteries, face challenges, including the scarcity of Li reserves and safety concerns. Consequently, the development of "beyond Li" batteries has become a research hotspot. Among these, rechargeable aqueous aluminum-ion batteries (AAIBs) have garnered significant attention because of their notable advantages. These include the intrinsic safety provided by aqueous electrolytes, the abundance of aluminum (Al) resources (constituting 8.23 wt% of the Earth's crust), the low cost of Al metal, and its well-established industry. Specifically, employing Al metal as the battery anode theoretically offers a substantial gravimetric capacity of 2980 mAh g−1 and a volumetric capacity of 8046 mAh cm−3. However, the development of Al metal anodes in aqueous electrolytes is hindered by several issues, including surface passivating films that obstruct charge/ion transport, the highly negative deposition potential of Al ions, which induces hydrogen evolution reaction (HER), poor reversibility of Al stripping/plating (ASP), low battery voltage plateaus, and poor cycle stability, all of which diminish the attractiveness of aqueous aluminum metal batteries (AAMBs). This thesis aims to alleviate these key challenges of Al anodes through anode engineering strategies, such as amorphization, composite heterometallic structures, and coating with transition metal disulfides (TMDs). These approaches aim to alleviate passivation, enhance the ASP reversibility, and suppress side reactions like HER and corrosion, thereby improving the voltage plateau, specific capacity, and cycle stability of AAMBs. The first project employs an amorphization approach to alter the potential of Al plating. An amorphous Al (aAl) interface is generated on Al substrates via Li-ion alloying/dealloying. Experimental and theoretical studies reveal that the amorphous structure significantly reduces the nucleation barrier for Al, promoting Al plating in competition with HER. Additionally, it mitigates passivation and enhances interfacial ion transport kinetics. This electrode achieves stable ASP for 800 hours in symmetric cells. Compared to bare Al-based cells, full cells using an aAl anode exhibit a voltage plateau increase of 0.6 V. The second project involves the introduction of secondary metals to composite with Al. Tin (Sn) is chosen as the secondary metal because of its suitable standard electrode potential, work function, and Al compatibility, which aids in Al plating and improves the reversibility of the anode. The Sn–Al laminate (Sn@Al), prepared via iterative folding/rolling procedures, efficiently enhances ASP and minimizes resistance. The Sn@Al electrode exhibits long-lasting cycling for more than 900 hours in symmetric cells and shows outstanding performance when paired with AlxMnO2 or Prussian blue analog cathodes. To improve the performance of the Sn@Al, a polymer layer is utilized to effectively inhibit corrosion. The third project investigates Al anodes coated with four types of TMDs. The results indicate that TiS2 and NbS2 exhibit electrochemical activity in aqueous aluminum sulfate electrolyte, while MoS2 and ReS2 show negligible activity. AAIBs with Al anodes coated with all four TMDs demonstrate higher capacities compared to uncoated Al anodes. This enhancement may arise from two distinct mechanisms. TiS2 and NbS2 could potentially intercalate and de-intercalate Al ions and/or protons, while MoS2 and ReS2 mainly function as protective coatings. These findings reveal the feasibility of using TMD-coated Al as anodes for AAIBs. These findings provide valuable insights into the rational design of Al anodes, advancing the development of high-performance AAIBs for sustainable energy storage applications.

The advantages of aluminum-ion batteries in the area of power source systems are: inexpensive manufacture, high capacity, and absolute security. However, due to the limitations of cathode materials, the capacity and durability of aluminum-ion batteries ought to be further advanced. Herein, we synthesized a nitrogen-doped tubular carbon material as a potential cathode to achieve advanced aqueous aluminum-ion batteries. Nitrogen-doped tubular carbon materials own an abundant space (367.6 m2 g-1) for electrochemical behavior, with an aperture primarily concentrated around 2.34 nm. They also exhibit a remarkable service lifespan, retaining a specific capacity of 78.4 mAh g-1 at 50 mA g-1 after 300 cycles. Additionally, from 2 to 300 cycles, the material achieves an appreciable reversibility (coulombic efficiency CE: 99.7%) demonstrating its excellent reversibility. The tubular structural material possesses a distinctive hollow architecture that mitigates volumetric expansion during charging and discharging, thereby preventing structural failure. This material offers several advantages, including a straightforward synthesis method, high yield, and ease of mass production, making it highly significant for the research and development of future aluminum-ion batteries.

Ocean‐like free water in conventional aqueous electrolytes limits operating voltage and induces parasitic reactions in rechargeable Zn metal batteries (AZMBs). Herein, a hydrated salt electrolyte (HSE), which suppresses the presence of free water and triggers an unsaturated hydration structure (Zn(H2O)n2+, n < 6), is proposed to circumvent the parasitic reactions occurring on the zinc anode and cathode and elevate the decomposition voltage (to ≈2.55 V vs Zn2+/Zn). In a full cell with a transition metal oxide cathode, the parasitic reactions of dissolution and diffusion of discharge products are inhibited, and high discharge capacity retention above 80% at 500 mA g‐1 and super‐stable Coulombic efficiency (average value ≈99.97%) are delivered. Moreover, when applied in a high‐voltage AZMB with zinc hexacyanoferrate cathode, the full cell yields an average output voltage above 1.8 V together with a 132.3 Wh kg‐1 energy density at 10 mA g‐1 and 1.78 V output voltage combining high energy density and power density (88.5 Wh kg‐1/106.2 W kg‐1). The exceptional electrochemical performance of HSE indicates rosy prospects for the prevention of parasitic reactions in AZMBs, a key step on the road to further commercialization of AZMBs.

Organic materials demonstrate significant potential as electrodes for aqueous batteries, owing to their high theoretical capacity, structurally tunable frameworks, and sustainable material accessibility. Small‐molecule organic electrode materials enable better active‐site accessibility but remain challenged by the dissolution in aqueous electrolytes, which deteriorates cycling stability, and poor conductivity due to limited conjugation. Here, we designed an organic small‐molecule cathode material (DPPZ‐CN) featuring functional pyridine, pyrazine, and cyano groups. Its highly conjugated fused N‐heteroaromatic structure provides strong intermolecular interactions and high reactivity, resulting in improved stability, capacity, and conductivity. The electron‐withdrawing cyano group further modulates electron delocalization and molecular orbitals, enhancing electronic conductivity and operating voltage. Through combined theoretical and experimental studies, including operando synchrotron FT‐IR, in situ Raman, ex situ XPS, and 1H NMR, we demonstrate that DPPZ‐CN facilitates efficient dual‐cation storage (Al3+/H+), thereby reducing Al3+ cation repulsion and induced structural distortion. As a result, the Al//DPPZ‐CN battery exhibits outstanding capacity, a well‐defined voltage plateau, and an extended lifespan in organic aluminum batteries with aqueous and seawater electrolytes, highlighting its potential for operation in challenging environments.

Aqueous zinc metal batteries are an attractive candidate for next-generation energy storage, yet their application is still impeded by uncontrollable zinc dendrite growth, anode corrosion, and parasitic hydrogen evolution side reaction. Benefiting from its corrosion-resisting property and low desolvation energy barrier for hydrated Zn2+ ions, ZnF2 emerges as a promising protective material for zinc anodes. However, the migration kinetics of Zn2+ in ZnF2 is insufficient, thereby causing severe interfacial polarization and uneven Zn deposition. Herein, we develop an oxygen plasma-engineered ZnF2 interlayer (ZnO/ZnF2) on the zinc anode utilizing the built-in electric field to accelerate the transfer kinetics of Zn2+. Both experimental and theoretical findings reveal that the formation of ZnO/ZnF2 heterojunction can also raise the energy barrier for hydrogen evolution, inhibit side reactions, homogenize the electric field, and promote uniform Zn2+ plating. Remarkably, the symmetric cell based on ZnO/ZnF2@Zn demonstrates exceptional cycling stability up to 2000 and 550 h at 1 and 20 mA cm−2, respectively. When paired with an NH4V4O10 (NVO) cathode, the ZnO/ZnF2@ZnǁNVO full cell achieves a notable specific capacity of 280.9 mAh g−1 and maintains 85% of its initial capacity after 1000 cycles even under a high current density of 3 A g−1, highlighting the efficacy of plasma-engineering strategy in developing advanced zinc metal batteries.

Towards reusable 3D-printed graphite framework for zinc anode in aqueous zinc battery

Aqueous aluminum-ion batteries have garnered significant attention owing to the abundance of aluminum resources, high theoretical specific capacity, and excellent safety. However, challenges such as electrolyte-induced water decomposition, aluminum anode corrosion, and electrode material compatibility continue to constrain their performance. In this study, we restructured the solvation environment using the chelating reagent Bis(2-methoxyethyl)amine (BMEA), achieving an expanded electrochemical window of 2.2V and mitigating hydrogen evolution side reactions. Advanced atom probe tomography analysis confirmed that BMEA actively participates in the formation of the solid-electrolyte interphase (SEI), effectively preventing aluminum surface corrosion and extending the cycle life of the aluminum anode. Employed as a BMEA-containing electrolyte in aluminum-organic batteries, the resulting Al||Tetrachloro-1,4-benzoquinone (TCB) battery delivered a high capacity of 218.0mAhg-1 and demonstrated stable cycling over 300 cycles. This study highlights the potential of chelating agents as additives in advancing high-performance aluminum batteries.

In this work, a series of Li2MnO3 samples are synthesized by hydrothermal method, towards understanding the proton substitution, the crystallite morphology and electrochemical properties as a function of precursor concentration, reaction time and temperature. The stoichiometry of Li:Mn ratio and the proton substitution of as-synthesized Li2−xHxMnO3 samples are dependent on the hydrothermal conditions. In sample 180C12h, a maximum charge capacity reaches to 470 mAh g−1, corresponding to the almost total removal of Li out of Li[Li1/3Mn2/3]O2, and maximum discharge capacity 256.4 mAh g−1 is obtained. The remained crystal structure of Li2MnO3 is unstable after more Li+ are extracted, which results in less Li+ to be reinserted and poor cycleability demonstrated. When the sample is charged to lower cut-off voltage 4.5 V, an increased discharge capacity and well cycleability are appeared. For improving the discharge capacity and cycleability, the nanocomposites of Li2−xHxMnO3 treated by LiMnO2 are synthesized by two steps hydrothermal methods. The nanocomposite presents very well electrochemical performance at the cut-off voltage of 2.0–4.4 V than that in pure Li2−xHxMnO3 and LiMnO2. The nanocomposite with weight ratio (Li2–xHxMnO3: LiMnO2) of 1.40:1 presents the discharge capacity of 230 mAh g−1 at the 20th and of 220 mAh g−1 at the 40th cycle.

Conjugated polyaniline as “conveyor” in tungstate boosting cation storage for high-performance aqueous batteries

Polyoxometalate oxate solution: An electrolyte additive to sustainably improve the anodes electrode of aqueous Zn ion batteries

The positive electrodes of nickel metal hydride (NiMH) batteries were doped with Al to improve the discharge capacity of NiMH batteries and its effects on the electrode performance were studied. Al-doped α-Ni(OH)2 electrodes were prepared by co-precipitation method. The characteristics of the positive electrode in KOH solution were investigated with charge/discharge cycles. The elution of doped Al into the electrolyte was observed as the number of charge/discharge cycles increased, which was confirmed by the ICP-AES analysis of the electrolyte after repeated charge/discharge cycles. This subsequently led to the decrease in the discharge capacity. However, it was found that the addition of Al ions into the electrolyte stabilized α-Ni(OH)2 and resulted in the increased discharge capacity.

Predominant intercalation of H+ enables ultrahigh rate capability of oxygen deficient MoO3 for aqueous Al-ion batteries

The aqueous iron ion batteries (AIIBs) are an attractive option for large-scale energy storage applications. However, the inadequate plating and stripping of Fe2+ ions underscore the need to explore more suitable cathode materials. Herein, we optimize the structure of tunnel-like VO2 nanosheets by introducing Mn2+ ion intercalation as a cathode material to enhance their performance in AIIBs. Mn2+ serves as a stabilizing pillar for VO2, which brings some oxygen vacancies to provide extra electrochemically active sites, and accelerates the reversible (de)insertion of Fe2+ ions. In addition, the density functional theory (DFT) calculations show that the introduction of Mn2+ reduces the band gap of VO2 and also decreases the electrostatic interaction between Fe2+ and VO2. Consequently, the VO2 with interlayer Mn2+ pillars (5% MVO) electrodes exhibit a remarkable capacity of 284.32 mAh g-1 at a current density of 0.1 A g-1 and demonstrate excellent cycle life, maintaining 81.7% of their capacity at 1.0 A g-1 after 600 cycles. Therefore, these results offer a promising choice for the cathode material to achieve outstanding electrochemical performance in AIIBs.