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A key challenge for practical magnesium–sulfur (Mg–S) batteries is to overcome the sluggish conversion kinetics of sulfur cathodes, achieving a high energy density and long-lasting battery life. To address this issue, a doping strategy is demonstrated in a model Ketjenblack sulfur (KBS) cathode by introducing selenium with a high electronic conductivity. This leads to a significantly enhanced charge transfer in the resultant KBS1−xSex cathodes, giving rise to a higher S utilization and less polysulfide dissolution. Compared to the bare S cathode, the S-Se composite cathodes exhibit a higher capacity, smaller overpotentials, and improved efficiency, serving as better benchmark compounds for high-performance Mg–S batteries. First principles calculations reveal a charge transport mechanism via electron polaron diffusion in the redox end-products, that enhances the reaction kinetics. By suppressing polysulfide dissolution in the electrolyte, the use of the KBS1−xSex cathodes also enables a more uniform anode reaction, and thereby significantly extends the cyclability of the cells. To improve the performance, further efforts are made by implementing a Mo6S8 modified separator into the cell. With an optimized cathode composition of KBS0.86Se0.14, the cell applying modified separator shows an improvement of capacity retention by >50% after 200 cycles.

Emerging energy storage systems based on abundant and cost-effective materials are key to overcome the global energy and climate crisis of the 21st century. Rechargeable Magnesium Batteries (RMB), based on Earth-abundant magnesium, can provide a cheap and environmentally responsible alternative to the benchmark Li-ion technology, especially for large energy storage applications. Currently, RMB technology is the subject of intense research efforts at laboratory scale. However, these emerging approaches must be placed in a real-world perspective to ensure that they satisfy key technological requirements. In an attempt to bridge the gap between laboratory advancements and industrial development demands, herein, we report the first non-aqueous multilayer RMB pouch cell prototypes and propose a roadmap for a new advanced RMB chemistry. Through this work, we aim to show the great unrealized potential of RMBs.

Aluminum sulfur batteries with ionic liquid electrolytes are promising next-generation energy storage devices due to the high abundance of both aluminium and sulfur. However, very little understanding of the discharge mechanism is currently available, which hampers their development. Herein, a mathematical model that considers the complex electrochemical reduction of the sulfide species as well as the formation of the various polysulfides is developed to describe the discharge performance and the reversibility of Al–S cells at different current densities. The model is validated with experimental data obtained from Swagelok cells composed of Al metal anode, S@CNT cathode, and EMIMCl-AlCl3 ionic liquid electrolyte. The cells exhibited different discharge mechanisms and Al2S3 precipitation routes at the different current densities. The contact resistance between the composite electrode and the current collector was the main factor limiting the discharge performance at high current densities. The reversibility of the Al–S cells based on the formation of Al2S3 precipitates strongly depends on the operating current density. The developed model will serve as a tool for other researchers to enhance the electrochemical performance of aluminum sulfur batteries.

Magnesium–Sulfur batteries are one of most appealing options among the post-lithium battery systems due to its potentially high energy density, safe and sustainable electrode materials. The major practical challenges are originated from the soluble magnesium polysulfide intermediates and their shuttling between the electrodes, which cause high overpotentials, low sulfur utilization, and poor Coulombic efficiency. Herein, a functional Mo6S8 modified separator is designed to effectively address these issues. Both the experimental results and density functional theory calculations show that the electrochemically active Mo6S8 layer has a superior adsorption capability of polysulfides and simultaneously acts as a mediator to accelerate the polysulfide conversion kinetics. Remarkably, the magnesium–sulfur cell assembled with the functional separator delivers a high specific energy density (942.9 mA h g−1 in the 1st cycle) and can be cycled at 0.2 C for 200 cycles with a Coulombic efficiency of 96%. This work demonstrates a new design concept toward high-performance metal–sulfur batteries.

This work deals with the search of polymers apt for the preparation of solid-like chloroaluminate-based electrolytes. To accomplish this, the solubility and gelling ability of a large set of polymers in the deep eutectic solvent AlCl3:urea (uralumina) are studied, followed by the characterization of the electrochemical activity of the gels. The polymers are directly dissolved in urea:AlCl3 without auxiliary solvents following a fast and scalable gel preparation methodology previously reported for ultra-high molecular weight (UHMW) polyethylene oxide (PEO). The list of polymers studied includes diverse chemical structures, different thermal properties and different aggregation states at the mixing temperature of 70 °C, defined by the thermal stability of AlCl3:urea. To avoid a molecular weight influence on the ionogel rheological properties, polymers with molecular weight close to 100,000 g mol−1 have been chosen. The polymers considered include poly(ε-caprolactone) (PCL), poly(dimethyl siloxane) (PDMS), poly(vinyl pyrrolidone) (PVP), polyformal, thermoplastic polyurethanes, polymethacrylates, polyacetates and the elastomer SEBS. It was found that together with polyethylene oxide, only poly(ε-caprolactone) and poly(dimethyl siloxane) are soluble and produce gel electrolytes with AlCl3:urea. The solubility rules of polymers in chloroaluminates are discussed. The stripping/plating of Al and the ionic conductivity of PEO, PDMS and PCL ionogels are studied by cyclic voltammetry and impedance spectroscopy. PDMS proves to be as efficient as PEO to produce ionogels at low polymer concentration, that are also self-standing and electroactive, whereas a higher concentration of PCL is required to produce self-standing gels. The molecular structure of the ionogels and the modification of the chloroaluminate speciation is studied by vibrational spectroscopies, and supported by DFT calculations.

Stable and fast ionic conductors for magnesium cathode materials have the prospect of enabling high energy density batteries beyond current Lithium-ion technologies. So far, only a few candidate materials have been identified leading to data only being scarcely available to the community. Here, we present a systematic study, in the framework of Density Functional Theory, including the estimation of the migration barrier for 16 materials through employing Nudged Elastic Band (NEB) calculations. By introducing a path finder algorithm based on the idea of Voronoi tessellations, we show that an estimate of the transition state configuration can be extracted automatically prior to running NEB-calculations. Using geometrical descriptors in combination with a principal component analysis it is possible to further sub-group the migration paths. This approach also extends to materials which are not part of the study, making it a viable approach to more efficiently explore crystal structures with distinguishable migration characteristics.

The main advantage of Mg‐ion batteries over other metal‐ion counterparts is its ability to work with a pure metallic anode, achieving a very high specific capacity. Unfortunately, pure Mg is hard to machine due to its brittleness, making it extremely difficult to produce foils that are thin enough for practical battery applications. Alloying Mg with small amounts of doping elements can enhance its ductility. However, care should be given to ensure that the dopants do not interfere with the electrochemical process of plating and stripping of Mg from the anode during battery operation. Dopants should prefer to be in bulk or at a stacking fault rather than migrating to the surface to meet this requirement. In this work, we carried out a computational screening of 34 dopants that are reported to reduce Mg brittleness to check which of them energetically prefers to stay in bulk. We found that only 12 out of the 34 meet such a criterion. Y and Nd, two of the main dopants in the WE43 commercial alloys, are among the 12 beneficial doping elements, which presents a practical avenue for the exploration for superior Mg‐ion battery anode material.

Ultrafast, light-induced dynamics in copper–zinc–tin–sulfide (CZTS) photovoltaic nanoparticles are investigated through a combination of optical and x-ray transient absorption spectroscopy. Laser-pump, x-ray-probe spectroscopy on a colloidal CZTS nanoparticle ink yields element-specificity, which reveals a rapid photo-induced shift of electron density away from Cu-sites, affecting the molecular orbital occupation and structure of CZTS. We observe the formation of a stable charge-separated and thermally excited structure, which persists for nanoseconds and involves an increased charge density at the Zn sites. Combined with density functional theory calculations, the results provide new insight into the structural and electronic dynamics of CZTS absorbers for solar cells.

Tantalum is the only element of Group 5 in the periodic table that lacks any experimental reports on the existence of reduced crystalline oxide between the pentoxide (Ta2O5) and the dioxide (TaO2). We computationally predict the existence of a novel tantalum oxide with Ta4O9 stoichiometry, which lies at the midpoint between Ta2O5 and TaO2. The ground-state Ta4O9 structure was found through simulated annealing based on a cluster expansion model, which is trained using 186 density functional theory calculations. The newfound Ta4O9 material has space group number 10 (P2/m), and it can be viewed as an oxygen-deficient λ-Ta2O5 structure in which oxygen vacancies aggregate pair-wise in nearest-neighbor sites. Tad–Tad bonds fill the spatial void of the oxygen vacancies, keeping the system non-magnetic and non-metallic. The synthesis of the new Ta4O9 crystal is deemed feasible through a controlled reduction of λ-Ta2O5. The reported Ta4O9 has the potential to open new avenues in catalysis and resistive switching device applications where the reduced tantalum oxides are broadly employed.

Metal–air batteries have higher theoretical specific energies than existing rechargeable batteries including Li-ion batteries. Among metal–air batteries, the Na–O2 battery has gained much attention due to its low discharge/charge overpotentials (∼100 mV) at relatively high current densities (0.2 mA/cm2), high electrical energy efficiency (90%), high theoretical energy density, and low cost. However, there is no information reported regarding the effect of CO2 contamination in non-aqueous Na–air batteries. Density functional theory has, here, been applied to study the effect of low concentrations of CO2 contamination on NaO2 and Na2O2 growth/depletion reaction pathways and overpotentials. This was done on step surfaces of discharge products in non-aqueous Na–air batteries. Adsorption energies of CO2 at various nucleation sites for both step surfaces were determined, and results revealed that CO2 preferentially binds at the step valley sites of (001) NaO2 and (11⎯⎯00) Na2O2 surfaces with binding energies of −0.65 eV and −2.67 eV, respectively. CO2 blocks the step nucleation site and influences the reaction pathways and overpotentials due to carbonate formation. The discharge electrochemical overpotential increases remarkably from 0.14 V to 0.30 V and from 0.69 V to 1.26 V for NaO2 and Na2O2 surfaces, respectively. CO2 contamination is thus drastically impeding the growth/depletion mechanism pathways and increases the overpotentials of the surface reaction mechanism, hampering the performance of the battery. Avoiding CO2 contamination from intake of gas and electrolyte decomposition is thus critical in development of Na–air batteries.

The transition between Ta2O5 and TaO2 governs resistive switching in tantalum oxide-based resistive random access memory. Despite its importance, the Ta2O5–TaO2 transition is scarcely described in the literature, in part because the tantalum oxide layer in devices is amorphous, which makes it difficult to characterize. In this paper, we use first-principles calculations to construct the convex hull of the amorphous Ta2O5−x system for 0 ≤ x ≤ 1 and show that oxygen deficiency in tantalum oxide leads to phase-separation into Ta2O5 and TaO2. In addition, our work challenges the conventional interpretation of X-ray Photoelectron Spectroscopy (XPS) spectra of the Ta 4f orbitals. Specifically, we find that TaO2 exhibits both the Ta4+ peak associated with TaO2 and the Ta5+ peak normally associated with Ta2O5. While our simulated Ta2O5 peak originates from a narrow range of oxidation states, the TaO2 peak comes from disproportionated Ta atoms with Bader charges ranging from +3 to +1, the lowest of which are well below Ta atoms in crystalline TaO. Finally, we demonstrate that the XPS blueshift of around 1 eV observed experimentally in amorphous Ta2O5 with respect to crystalline Ta2O5 comes from both the presence of under-coordinated Ta atoms and longer Ta–O bond distances in the amorphous system. Our simulated XPS analysis shows that amorphous XPS spectra may be more complex than previously thought, and hence, caution should be applied when assigning XPS peaks to oxidation states.

The choice of electrolyte has a crucial influence on the performance of rechargeable magnesium batteries. In multivalent electrolytes an agglomeration of ions to pairs or bigger clusters may affect the transport in the electrolyte and the reaction at the electrodes. In this work we include the formation of clusters in our general model for magnesium batteries. In our model we consistently take into account the effect of cluster formation on transport, thermodynamics and kinetics. The model is used to analyze the effect of ion clustering in a Mg[B(hfip) 4 ] 2 \ DME electrolyte. It becomes apparent that the ion agglomeration is able to explain experimentally observed phenomena at high salt concentrations.

Intense research efforts in electrochemical energy storage are being devoted to multivalent ion technologies in order to meet the growing demands for high energy and low-cost energy storage systems. However, the development of multivalent metal (such as Mg and Ca) based battery systems is hindered by lack of suitable cathode chemistries that show well reversible multi-electron redox reactions. Cationic redox centers in the classical cathodes could only afford stepwise single electron transfer, which we believe are not ideal for multivalent ion storage. The possible local charge balance issue would set additional kinetic barrier for ion mobility. Therefore, most of the multivalent battery cathodes only exhibit slope-like voltage profiles with insertion/extraction redox of less than one electron. To address this issue, we propose to activate anionic redox chemistry enabling multi-electron transfer in insertion cathodes for high-energy multivalent batteries. Taking VS 4 as a model material, reversible two-electron redox with synergetic cationic-anionic contribution has been verified in both rechargeable Mg batteries (RMBs) and rechargeable Ca batteries (RCBs). The corresponding cells exhibit high capacities of > 300 mAh g -1 at a current density of 100 mA g -1 in both RMBs and RCBs, resulting in a high energy density of >300 Wh kg -1 for RMBs and >500 Wh kg -1 for RCBs. Mechanistic studies reveal the unique redox activity at anionic sulphides moieties and demonstrate fast Mg 2+ ion diffusion kinetics enabled by the soft structure and flexible electron configuration of VS 4 . The concept of coupling a cathode based on anionic redox reactions with a multivalent metal anode provides a general approach towards high performance multivalent batteries.

The development of automated computational tools is required to accelerate the discovery of novel battery materials. In this work, we design and implement a workflow, in the framework of Density Functional Theory, which autonomously identifies materials to be used as intercalation electrodes in batteries, based on descriptors like adsorption energies and diffusion barriers. A substantial acceleration for the calculations of the kinetic properties is obtained due to a recent implementation of the Nudged Elastic Bands (NEB) method, which takes into consideration the symmetries of the system to reduce the number of images to calculate. We have applied this workflow to discover new cathode materials for Mg batteries, where two of these materials display a threefold increase in the potential of the Chevrel phase, the state‐of‐the‐art cathode in commercial prototype Mg batteries.

Facile and reversible insertion and extraction of Li+ was recently demonstrated to be possible with a new cation-disordered rock salt (DRS) LiVO2 compound (Space Group (SG): Fm3 ̅m). Further structural analyses describing the links between the well-known layered trigonal structure of LiVO2 (space group:R3 ̅m) and DRS LiVO2 synthesized by mechanical ball milling are presented. Optimized Rietveld refinements of the X-ray diffraction patterns confirm the formation of LiVO2 in disordered rock salt phase. We observed the phase transition from the trigonal to cubic structure and the evolution of cell parameters during the ball-milling process using ex situ X-ray diffraction. The reverse phase transition from cubic to trigonal structure is achieved via thermal treatment, which was confirmed via differential scanning calorimetry and in situ X-ray diffraction experiments. The phase transition to trigonal structure suggests the metastability of the cubic structure. An exhaustive computational analysis based on a cluster expansion model trained by density functional theory calculations is conducted to confirm the metastability. The presented methods and results show that different (meta-)stable phases can be achieved depending on the synthesis method, which is an important aspect to consider in investigating the properties of the new DRS cathode materials for Li-ion batteries.

The structure of the electrolyte is crucial for the performance of rechargeable magnesium batteries. Doubly charged cations interact much stronger with both anions and solvent molecules, forming different size clusters. Here, we apply DFT calculations to investigate salt solvation by altering the first solvation shell of the magnesium‐chloride complexes in different ethereal solvents: tetrahydrofuran, monoglyme, diglyme, triglyme and tetraglyme. The analysis was performed by looking for the most stable structures, considering mono‐, di‐ and trimeric clusters of Mg x Cl y . The determination of clusters geometries, together with their energies, resulted in a comprehensive picture of the thermodynamically preferred state of the electrolyte, and allowed for a simple assessment of the electrochemical activity of the electrolyte. Our analysis shows that clustering is beneficial for desolvation of magnesium from the cluster, but causes overpotentials due to hindered electron transfer.

It is possible to prepare elastic and thermoreversible gel electrolytes with significant electroactivity by dissolving minimal weight fractions of Ultra High Molecular Weight poly(ethylene oxide) (UHMW PEO) in an aluminum deep eutectic solvent (DES) electrolyte composed of AlCl 3 and urea at a molar ratio of 1.5:1 (AlCl 3 :urea). The experimental vibrational spectra (FT-IR and Raman) provide valuable information on the structure and composition of the gel electrolyte. However, the complexity of this system requires computational simulations to help interpretation of the experimental results. This combined approach allows us to elucidate the speciation of the DES liquid electrolyte in the gel and how it interacts with the polymer chains to give rise to an elastic network that retains the electroactivity of the liquid electrolyte to a very great extent. The observed reactions occur between the ether in the polymer and both the amine groups in urea and the aluminum species. Thus, similar elastomeric gels may likely be prepared with other aluminum liquid electrolytes, making this procedure an effective way to produce families of gel aluminum electrolytes with tunable rheology and electroactivity.

The Front Cover illustrates an autonomous workflow, implemented in the framework of Density Functional Theory, designed to automatically calculate crucial properties for battery intercalation electrodes, including thermodynamic and mechanical stability, open circuit voltages (OCV), as well as kinetic barriers. Applied here to identify cathode materials for Mg‐ion batteries, this workflow enables an accelerated discovery of intercalation battery electrodes. More information can be found in the Article by J. M. Garcia‐Lastra, I. E. Castelli and co‐workers.

A key step in engineering resistive switching is the ability to control the device switching behavior. Here, we investigate the possibility to tune the resistive switching of tantalum oxide (TaOx)-based memristors from a non-switchable state to a switchable state by applying post-fabrication annealing of the devices. The switching of the devices was found to be related to: (1) the oxidation state changes in the TaOx thin film after annealing and (2) the local variations in oxygen stoichiometry in the vicinity of the interface between the TiN electrode and the TaOx active resistive layer. We further discuss the possible mechanism behind the resistive switching after annealing. This experimental approach provides a simple but powerful pathway to trigger the resistive switching in devices that do not show any resistive switching initially.