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Li–S batteries are promising alternatives due to their proven increased gravimetric capacity compared to Li–ion batteries. However, their development is hindered by many technical issues, one of the most challenging being the dissolution and shuttle of polysulfide species, which causes irreversible loss of cathode material leading to rapid capacity fading. Among the possible strategies to mitigate this effect, the choice of suitable solvents is easy to implement and has large room for improvement. To guide this quest, computationally-aided optimization is a powerful tool, provided that suitable descriptors are used to screen possible solvents. In this work, molecular dynamics simulations were performed for a typical lithium polysulfide Li2S6 dissolved in different solvents. Diffusion coefficients and their related activation energies were calculated, and thermodynamic properties like solvation energies and entropies were also evaluated. Additionally, a theoretical framework for computing the relative solubilities of lithium polysulfide is provided. For the set of solvents considered, we found that the system's viscosity appears as an important descriptor to correlate with different system properties. The donor number of the solvent also appears as a valid descriptor, for low-viscosity solvents. In general, it was found that higher viscosity solvents lead to lower diffusion rates and higher polysulfide solubility. These results suggest that the optimal choice to reduce the shuttle is a trade-off between high-viscosity solvents to reduce polysulfide diffusion and low-viscosity solvents to reduce its solubility, which could be further improved by properly tuning the donor number. [ABSTRACT FROM AUTHOR]

The study presents a hybrid hard-carbon/nanocrystalline-Bi2S3 material applicable for negative electrodes in sodium-ion batteries. Through a series of comprehensive analyzes, including electrochemical measurements, operando XRD, ex situ solid-state NMR, and high-resolution STEM imaging, the effectiveness of the HC/Bi2S3 hybrid configuration in the negative electrode function is elucidated with a focus on the underlying charge storage mechanism. Electrochemical analysis demonstrates the improved performance of the hybrid materials over the pristine HC negative electrode and highlights the robustness and stability of the HC/Bi2S3 hybrids over prolonged cycling even under high current densities. Here, the final capacities observed after 100 cycles reached a value of 252 mA h g−1, compared to 216 mA h g−1 of pristine HC. Cyclic voltammetry measurements demonstrate a complex charge storage behavior that integrates both surface and diffusion-driven processes at different potentials during reduction and oxidation. A series of phase transformations during cycling observed in operando XRD expose irreversible reactions during the initial cycle between Bi2S3 and sodium ions, such as the breakdown of the Bi2S3 nanocrystal structure. This phenomenon is further confirmed by the detection of Na2S species using ex situ solid-state NMR. High-resolution STEM imaging reveals morphological changes in Bi2S3 nanocrystals and highlights their resistance to pulverization due to their nanoscale dimensions. This work provides comprehensive insights into the electrochemical performance of the HC/Bi2S3 and sheds light on specific mechanisms and reactions occurring during cycling. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) have attracted a significant amount of interest in the past decade as a credible alternative to the lithium‐ion batteries (LIBs) widely used today. The abundance of sodium, along with the potential utilization of electrode materials without critical elements in their composition, led to the intensification of research on SIBs. Hard carbon (HC), is identified as the most suitable negative electrode for SIBs. It can be obtained by pyrolysis of eco‐friendly and renewable precursors, such as biomasses, biopolymers or synthetic polymers. Distinct HC properties can be obtained by tuning the precursors and the synthesis conditions, with a direct impact on the performance of SIBs. In this work, an in‐depth overview of how the synthesis parameters of HC affect their properties (porosity, structure, morphology, surface chemistry, and defects) is provided. Several synthesis‐property relationships are established based on a database created using extensive literature data. Moreover, HC properties are correlated with the electrochemical performance (initial Coulombic efficiency (iCE) and reversible capacity) vs. Na, in half‐cells. The Na‐ion storage mechanisms and solid electrolyte interphase (SEI) formation are discussed along with the HC performance in full‐cell devices, as well as the SIB prototypes and a short history of SIBs enterprises. [ABSTRACT FROM AUTHOR]

One of the possible solutions to circumvent the sluggish kinetics, low capacity, and poor integrity of inorganic cathodes commonly used in rechargeable aluminium batteries (RABs) is the use of redox-active polymers as cathodes. They are not only sustainable materials characterised by their structure tunability, but also exhibit a unique ion coordination redox mechanism that makes them versatile ion hosts suitable for voluminous aluminium cation complexes, as demonstrated by the poly(quinoyl) family. Recently, phenazine-based compounds have been found to have high capacity, reversibility and fast redox kinetics in aqueous electrolytes because of the presence of a C＝N double bond. Here, we present one of the first examples of a phenazine-based hybrid microporous polymer, referred to as IEP-27-SR, utilized as an organic cathode in an aluminium battery with an AlCl3/EMIMCl ionic liquid electrolyte. The preliminary redox and charge storage mechanism of IEP-27-SR was confirmed by ex situ ATR-IR and EDS analyses. The introduction of phenazine active units in a robust microporous framework resulted in a remarkable rate capability (specific capacity of 116 mA h g−1 at 0.5C with 77% capacity retention at 10C) and notable cycling stability, maintaining 75% of its initial capacity after 3440 charge–discharge cycles at 1C (127 days of continuous cycling). This superior performance compared to reported Al//n-type organic cathode RABs is attributed to the stable 3D porous microstructure and the presence of micro/mesoporosity in IEP-27-SR, which facilitates electrolyte permeability and improves kinetics. [ABSTRACT FROM AUTHOR]

Enhancing the performance of electrolytes stands as one of the key challenges for moving toward practical applications of Mg batteries. Within this work, we investigate different synthesis procedures for the state-of-the-art MgAlhfip electrolyte. The results show that the purity and electrochemical performance of MgAlhfip electrolytes depend on whether they are synthesized from organometallic or inorganic reagents. Additionally, electrolyte properties vary depending on the electrolyte preparation method, either in situ electrolyte formation or salt isolation. To improve electrolyte performance, we explore two approaches: additional salt isolation steps and the use of a scavenging additive. Salt precipitation results in a modest improvement in the coulombic efficiency of Mg plating/stripping, while a scavenging additive significantly reduces overpotentials and enhances coulombic efficiency, especially in electrolytes synthesized from inorganic reagents. Finally, investigated syntheses are evaluated in terms of their practical applicability through procedure complexity and costs of used chemicals. Based on this, we propose a synthesis procedure that strikes a balance between the electrochemical performance of Mg electrolyte and its costs. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are crystalline porous organic polymers that have recently emerged as promising electrode materials for rechargeable batteries. Herein, we present an approach to improve the electrochemical performance of an anthraquinone-based COF (DAAQ-TFP-COF) cathode material in metal anode (Li, Mg) based batteries through proper selection of the electrolyte and binder. Our results show that the combination of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in tetraethylene glycol dimethyl ether (TEGDME) as electrolyte and poly(tetrafluoroethylene) (PTFE) as binder led to the best electrochemical performance with high utilisation efficiency of the redox sites and specific capacities close to the theoretical value. Using such electrolyte and binder, cyclable symmetric cells consisting of two DAAQ-TFP-COF organic electrodes exemplify 79% capacity retention after 2000 cycles at a high current density of 500 mA h g−1. The high reversibility and stability of the COF electrode material upon cycling were confirmed by ex situ IR spectroscopy. In addition, DAAQ-TFP-COF was explored as a cathode in magnesium cells using two different Mg electrolytes; one based on MgCl2 and one containing weakly coordinating anions. Electrochemical characterisation reveals significant differences in the performance of COF in terms of achievable capacities and voltage profiles, pointing towards hindered transport. Our findings demonstrate that the appropriate choice of electrolyte and binder is crucial to maximise the performance of COF-based materials in different post-lithium-ion metal anode batteries. [ABSTRACT FROM AUTHOR]

Ca metal anode rechargeable batteries are seen as a sustainable high-energy density and high-voltage alternative to the current Li-ion battery technology due to the low redox potential of Ca metal and abundance of Ca. Electrolytes are key enablers on the path towards next-generation battery systems. Within this work, we synthesize a new calcium tetrakis(hexafluoroisopropyloxy) aluminate salt, Ca[Al(hfip)4]2, and benchmark it versus the state-of-the-art boron analogue Ca[B(hfip)4]2. The newly developed aluminate-based electrolyte exhibits improved performance in terms of conductivity, Ca plating/stripping efficiency, and oxidative stability as well as Ca battery cell performance. A marked improvement of 0.5 V higher oxidative stability can pave the path towards high-voltage Ca batteries. A critical issue of solvent quality during salt synthesis is identified as well as solvent decomposition at the Ca metal/electrolyte interface, which leads to passivation of the Ca metal anode. However, the new aluminate salt with preferable electrochemical properties over the existing boron analogue opens up a new area for future Ca battery research based on aluminium compounds. [ABSTRACT FROM AUTHOR]

Aqueous zinc-ion batteries are one of the most promising candidates for large-scale energy storage applications. Herein, we report a rationally designed triquinoxalinediol (TQD) organic cathode material for aqueous zinc-ion batteries. Integration of hydroquinone units with hexaazatriphenylene (HAT) core enabled a high theoretical capacity of 669 mA h g−1 (based on a twelve-electron exchange reaction) and a practical reversible capacity of 503 mA h g−1 at 100 mA g−1. Both values are among the highest available in the literature. The charge storage mechanism was systematically studied using ex situ FT-IR and various electrochemical measurements revealing a co-insertion mechanism involving protons and zinc cations. The TQD suffers from significant capacity fading, which was attributed to the dissolution of active material in the electrolyte. That was supported by using in situ UV-vis spectroscopy. This work adds a promising material in a rapidly expanding mosaic of pyrazine/quinone organic cathode materials. [ABSTRACT FROM AUTHOR]

Multivalent batteries are often hyped as a next‐generation high‐energy density battery technology, but in reality, both literature reports and practical research are plagued by poor reproducibility of electrochemical results. Within the present work, we take a look at the electrochemical testing of organic cathodes that can be used with a variety of mono‐ and multivalent cations and propose a cyclable symmetric cell approach, already applied to the field of lithium‐ion batteries. By using a model organic system based on poly(anthraquinonyl sulfide) (PAQS) active material, we demonstrate that the symmetric cell approach elegantly removes the limitations of multivalent metal anodes, and for the first time, reveals the full potential of organic cathodes in multivalent batteries. Furthermore, symmetric cells enable reliable EIS measurements on organic cathodes and open a pathway to optimize electrochemical/transport parameters through the design of next‐generation organic cathode materials and advanced electrode design(s). We suggest that the cyclable symmetric cell approach should be generally applicable in multivalent and all other batteries where electrochemical characterization requires the elimination of the counter electrode contribution. [ABSTRACT FROM AUTHOR]