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-MnO₂ birnessite 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.

Recently, rechargeable aluminum batteries have received much attention due to their low cost, easy operation, and high safety. As the research into rechargeable aluminum batteries with a room-temperature ionic liquid electrolyte is relatively new, research efforts have focused on finding suitable electrode materials. An understanding of the environmental aspects of electrode materials is essential to make informed and conscious decisions in aluminum battery development. The purpose of this study was to evaluate and compare the relative environmental performance of electrode material candidates for rechargeable aluminum batteries with an AlCl₃/EMIMCl (1-ethyl-3-methylimidazolium chloride) room-temperature ionic liquid electrolyte. To this end, we used a lifecycle environmental screening framework to evaluate 12 candidate electrode materials. We found that all of the studied materials are associated with one or more drawbacks and therefore do not represent a “silver bullet” for the aluminum battery. Even so, some materials appeared more promising than others did. We also found that aluminum battery technology is likely to face some of the same environmental challenges as Li-ion technology but also offers an opportunity to avoid others. The insights provided here can aid aluminum battery development in an environmentally sustainable direction.

In aluminium (Al) symmetric cell, potentials during Al deposition on an Al foil at 1 mA cm⁻² were 60–70 mV higher in TEA‐AlCl₃ electrolyte compared to those measured with EMIMCl‐AlCl₃ reference. Because of higher electrochemical stability of TEA‐AlCl₃ solution, cut‐off voltage of charging step in AIB full‐cell was set to 2.45 V compared to 2.40 V for the reference cell. During long‐term cycling at 1 A g⁻¹, the specific capacity of the AIB cell employing TEA‐AlCl₃ increased from 60 to 94 mAh g⁻¹ (57 %) after 1000 cycles while that of cell with EMIMCl‐AlCl₃ was quite constant at about 60 mAh g⁻¹. This behaviour was explained by continuous decreasing in Al electrode potential at End‐of‐Charge state (EOC) during deposition reaction (charging step) in TEA‐AlCl₃ allowing an increase in graphite electrode potential and consequently in AIB cell capacity over the whole experiment. This increase in capacity was accompanied by a raise of defect sites in graphite material.

Carbon xerogels were synthesized using a soft-template route with resorcinol as the carbon source and sodium carbonate as the catalyst. The influence of the resorcinol to catalyst ratio in the range of 500–20,000 on pore structure, graphitic domains, and electronic conductivity of as-prepared carbon xerogels, as well as their performance in an aluminium ion battery (AIB), was investigated. After carbonization steps of the polymers up to 800 °C, all carbon samples exhibited similar specific volumes of micropores (0.7–0.8 cm³ g⁻¹), while samples obtained from mixtures with R/C ratios lower than 2000 led to carbon xerogels with significantly higher mesopore diameters up to 6 nm. The best results, in terms of specific surface (1000 m² g⁻¹), average pore size (6 nm) and reversible capacity in AIB cell (28 mAh g⁻¹ @ 0.1 A g⁻¹), were obtained with a carbon xerogel sample synthetized at a resorcinol to catalyst ratio of R/C = 500 (CXG₅₀₀). Though cyclic voltammograms of carbon xerogel samples did not exhibit any sharp peaks in the applied potential window, the presence of both oxidation and a quite wide reduction peak in CXG_500–2000 cyclic voltammograms indicated pseudocapacitance behaviour induced by diffusion-controlled intercalation/de-intercalation of AlCl₄⁻ ions into/from the carbon xerogel matrix. This was confirmed by shifting of the (002) peak towards lower 2θ angle values in the XRD pattern of the CXG₅₀₀ electrode after the charging step in AIB, whereas the contribution of pseudocapacitance, calculated from half-cell measurements, was limited to only 6% of overall capacitance.

Li‐free aluminum graphite dual ion batteries (AGDIB) have attracted attention due to abundant raw materials and low costs. AGDIB uses Al foils as anode material, natural graphite flakes as cathode, and AlCl ₃ /[EMIm]Cl as electrolyte. To allow future upscaling, a significant increase of the cathode loading and optimization of cathode composition are inevitable. This is systematically investigated by varying graphite loading, water‐soluble binders, such as sodium alginate and sodium carboxymethyl cellulose (CMC), as well as conductive additive content (Super C65, SC). The cathode loading was successfully increased to 10 mg cm ⁻² achieving a specific capacity of 62.2 mAh g ⁻¹ and a Coulombic efficiency of 97.5% at 1 C employing 700 kDa CMC and 5 wt% SC. At high currents, capacities fade more drastically when employing high‐loading electrodes—mainly caused by increasing anodic overpotentials and only minimally by the cathode. GITT measurements revealed increasing apparent diffusion coefficients ( D _app ) for high C‐rates indicating pseudocapacitive kinetics and highlighting high‐power capabilities of AGDIB. Binder and electrode stability in the corrosive IL electrolyte is emphasized by a long‐term cycle stability >700 cycles (1 C). The optimized cathode recipe yields ~61% gain in absolute cell capacity providing a foundation for future scale‐up of AGDIBs.

To face the upcoming demand on high-power energy storage systems, e.g, for high-dynamic grid-stabilization , stationary devices as used in photovoltaics, and mobile applications led to invention of various battery technologies like sodium-ion batteries (SIB), zinc-ion batteries (ZIB) and high-power lithium-ion batteries (LIBs). Especially the several lithium-ion battery technologies have in common that currently used raw materials like lithium-salts and heavy metals (Ni, Co, Mn) are becoming increasingly scarce and therefore expensive. Without substitution by less-critical materials the ongoing energy system transformation cannot be successfully achieved. One promising system that gained attention in the last few years is the so-called aluminum graphite dual-ion battery (AGDIB). The active electrodes are made of cheap and abundant materials like graphite as cathode material and an aluminum-foil as anode¹. During operation chloroaluminate anions from the electrolyte, which is currently based on ionic liquids like 1-ethyl-3-methylimidazoliumchloride ([EMIm]Cl) and AlCl₃ in stoichiometric ratios as well as deep-eutectic solvents based on mixtures of urea and AlCl₃, are (de)intercalated in the graphitic host-structure while on the anode metallic aluminum is electrochemically deposited and dissolved see equation (1) and (2), respectively^{2, 3}. The overall mechanism is quite comparable with Li-metal batteries, where metallic Li is reversibly dissolved and deposited. The big advantages of AGDIBs are cheap electrode materials (graphite & aluminum), electrolytes based on urea and an extraordinary high-power cell-chemistry. Recent publications showed charging rates up to 20 A g^-1 _Graphite equal to 9 kW kg^-1 _Graphite in laboratory-scaled cells. Also, the lifetime of those batteries seems to be non-competitive, cycles up to half a million were reported with negligible capacity fading or degradation effects.⁴ To develop scalable and more representative battery cells, we established the AGDIB cell chemistry in a new corrosion-stable pouch bag design. Due to the significant increased electrode surface area and overall capacity, hitherto unknown effects were observed which limited the end of lifetime (EOL) of those batteries to less than 8,000 cycles. Herein, we report on a detailed analysis of the cell failure, including several electrochemical in-situ techniques like galvanostatic intermittent titration techniques (GITT), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV).⁵ The obtained data will allow a fundamental understanding of the cell operation under low (≤ 1 C-rates) and very high C-rates ≥ 15 C, which is important for establishing a durable AGDIB with high cycling stability. References M.-C. Lin, M. Gong, B. Lu, Y. Wu, D.-Y. Wang, M. Guan, M. Angell, C. Chen, J. Yang, B.-J. Hwang and H. Dai, Nature, 520(7547), 325–328 (2015). M. L. Agiorgousis, Y.-Y. Sun and S. Zhang, ACS Energy Lett., 2(3), 689–693 (2017). M. Angell, G. Zhu, M.‐C. Lin, Y. Rong and H. Dai, Adv. Funct. Mater., 30(4), 1901928 (2020). G. A. Elia, N. A. Kyeremateng, K. Marquardt and R. Hahn, Batteries & Supercaps, 2, 83–90 (2019). M. Safari and C. Delacourt, J. Electrochem. Soc., 158(10), A1123 (2011). Figure 1