Predicting Degradation Mechanisms in Lithium Bistriflimide "Water-In-Salt" Electrolytes For Aqueous Batteries.

Aqueous solutions are crucial to most domains in biology and chemistry, including in energy fields such as catalysis and batteries. Water-in-salt electrolytes (WISEs), which extend the stability of aqueous electrolytes in rechargeable batteries, are one example. While the hype for WISEs is huge, commercial WISE-based rechargeable batteries are still far from reality, and there remain several fundamental knowledge gaps such as those related to their long-term reactivity and stability. Here, we propose a comprehensive approach to accelerating the study of WISE reactivity by using radiolysis to exacerbate the degradation mechanisms of concentrated LiTFSI-based aqueous solutions. We find that the nature of the degradation species depends strongly on the molality of the electrolye, with degradation routes driven by the water or the anion at low or high molalities, respectively. The main aging products are consistent with those observed by electrochemical cycling, yet radiolysis also reveals minor degradation species, providing a unique glimpse of the long-term (un)stability of these electrolytes.

Fusing Thiadiazole and Terephthalate: A Concept to Promote the Electrochemical Performance of Conjugated Dicarboxylates.

Organic electrode materials based on conjugated dicarboxylate moieties are particularly attractive to develop metal-ion organic batteries. Exhibiting good stability properties in liquid electrolytes, such organic electrode materials can reversibly store alkali metal ions (Li, Na or K) at low working potential. Although many molecular designs have been investigated in the last decade, conjugated dicarboxylates are impeded by low coulombic efficiencies, especially at the first cycle, and sluggish kinetics in most cases. Herein, a new strategy in the design of conjugated carboxylates by fusing a thiadiazole heterocycle to the terephthalate core is reported. The synthesis and electrochemical performance of dilithium-2,1,3-benzothiadiazole-4,7-dicarboxylate (Li2 -DCBTZ) as positive electrode material is investigated for the first time. Next to being a new structural design, the presence of the thiadiazole ring enables (i) a better conjugation of π-n electrons leading to a benefit in terms of rate capability, and (ii) a better stabilizing coordination network for Li ions through both oxygen and nitrogen atoms. In addition, the reduced state in Li4 -DCBTZ is stabilized due to a maintained aromaticity in the heteroaromatic core in comparison to the parent terephthalate. Theoretical calculations on the Li-ion storage mechanism and bonding character support the experimental work.

Deciphering the Thermal and Electrochemical Behaviors of Dual Redox-Active Iron Croconate Violet Coordination Complexes.

Interest in coordination compounds based on non-innocent ligands (NILs) for electrochemical energy storage has risen in the last few years. We have focused our attention on an overlooked redox active linker, croconate violet, which has not yet been addressed in this field although closely related to standard NILs such as catecholate and tetracyanoquinodimethane. Two anionic complexes consisting of Fe(II) and croconate violet (-2) with balancing potassium cations were isolated and structurally characterized. By a combination of in situ and ex situ techniques (powder and single-crystal X-ray diffraction, infrared, and 57Fe Mössbauer spectroscopies), we have shown that their dehydration occurs through complex patterns, whose reversibility depends on the initial crystal structure but that the structural rearrangements around the iron cations occur without any oxidation. While electrochemical studies performed in solution clearly show that both the organic and inorganic parts can be reversibly addressed, in the solid state, poor charge storage capacities were initially measured, mainly due to the solubilization of the solids in the electrolyte. By optimizing the formulation of the electrode and the composition of the electrolyte, a capacity of >100 mA h g-1 after 10 cycles could be achieved. This suggests that this family of redox active linkers deserves to be investigated for solid-state electrochemical energy storage, although it requires the solving of the issues related to the solubilization of the derived coordination compounds.

A tris-oxovanadium pyrogallate complex: synthesis, structure, and magnetic and electronic properties.

With the aim of identifying new cation-phenolate complexes, we herein investigated the reactivity of pyrogallol (H3pgal) with vanadium salts. A trimetallic anionic complex was identified, and found to be formed under a broad set of reaction conditions. This complex, with the formula V3O3(pgal)33-, consists of three oxovanadium(IV) units connected together by three pyrogallate ligands to afford a bowl-shaped species presenting a pseudo 3-fold symmetry axis. Its crystal structure is reported, as well as its characterisation by a broad set of techniques, including powder X-ray diffraction, thermogravimetric analysis, infrared and Raman spectroscopy, and solid state UV-visible diffuse reflectance. Its redox activity both in solution and in the solid state is described, together with its magnetic behavior. Finally, the relevance of this trimetallic unit in the field of phenolic-based biocoatings and Metal Organic Framework (MOF) synthesis is briefly discussed.

Electrochemical Assessment of Indigo Carmine Dye in Lithium Metal Polymer Technology.

Lithium metal batteries are inspiring renewed interest in the battery community because the most advanced designs of Li-ion batteries could be on the verge of reaching their theoretical specific energy density values. Among the investigated alternative technologies for electrochemical storage, the all-solid-state Li battery concept based on the implementation of dry solid polymer electrolytes appears as a mature technology not only to power full electric vehicles but also to provide solutions for stationary storage applications. With an effective marketing started in 2011, BlueSolutions keeps developing further the so-called lithium metal polymer batteries based on this technology. The present study reports the electrochemical performance of such Li metal batteries involving indigo carmine, a cheap and renewable electroactive non-soluble organic salt, at the positive electrode. Our results demonstrate that this active material was able to reversibly insert two Li at an average potential of ≈2.4 V vs. Li+/Li with however, a relatively poor stability upon cycling. Post-mortem analyses revealed the poisoning of the Li electrode by Na upon ion exchange reaction between the Na countercations of indigo carmine and the conducting salt. The use of thinner positive electrodes led to much better capacity retention while enabling the identification of two successive one-electron plateaus.

Dual Electroactivity in a Covalent Organic Network with Mechanically Interlocked Pillar[5]arenes.

The synthesis and characterization of a polyrotaxanated covalent organic network (CON) based on the association between the viologen and pillar[5]arene (P[5]OH) units are reported. The mechanical bond allows for the irreversible insertion of n-type redox centers (P[5]OH macrocycles) within a pristine structure based on p-type viologen redox centers. Both redox units are active on a narrow potential range and, in water, the presence of P[5]OH greatly increases the electroactivity of the material.

Conjugated sulfonamides as a class of organic lithium-ion positive electrodes.

The applicability of organic battery materials in conventional rocking-chair lithium (Li)-ion cells remains deeply challenged by the lack of Li-containing and air-stable organic positive electrode chemistries. Decades of experimental and theoretical research in the field has resulted in only a few recent examples of Li-reservoir materials, all of which rely on the archetypal conjugated carbonyl redox chemistry. Here we extend the chemical space of organic Li-ion positive electrode materials with a class of conjugated sulfonamides (CSAs) and show that the electron delocalization on the sulfonyl groups endows the resulting CSAs with intrinsic oxidation and hydrolysis resistance when handled in ambient air, and yet display reversible electrochemistry for charge storage. The formal redox potential of the uncovered CSA chemistries spans a wide range between 2.85 V and 3.45 V (versus Li+/Li0), finely tunable through electrostatic or inductive molecular design. This class of organic Li-ion positive electrode materials challenges the realm of the inorganic battery cathode, as this first generation of CSA chemistries already displays gravimetric energy storage metrics comparable to those of the stereotypical LiFePO4.

Preface to the Special Issue of ChemSusChem on Organic Batteries.

All about Organic: Guest Editors Philippe Poizot, Yan Yao, Jun Chen, and Ulrich S. Schubert provide their thoughts on organic batteries-the challenges they face, their advantages and disadvantages, and what needs to be done to make them a commercially viable option-in this preface to a special issue of ChemSusChem on organic batteries, with highly interesting contributions from scientists around the world.

Pairing Cross-Linked Polyviologen with Aromatic Amine Host Structure for Anion Shuttle Rechargeable Batteries.

Electroactive organic compounds could bring new chemical opportunities to further improve existing electrochemical energy-storage technologies as they can be prepared from less-limited resources and potentially at low environmental footprint. Among the current explored research fields, the anion-ion cell configuration appears poorly investigated although quite promising to promote the fabrication of molecular (metal-free) rechargeable batteries. Herein, we report the synthesis and the electrochemical behavior of both Mg/Li salts of 2,5-(dianilino)terephthalate (MgDAnT and Li2 DAnT) and cross-linked polyviologen (c-PV2+ ) that can reversibly uptake/extract anions at different working potentials, enabling the assembly of full anionic organic batteries. The reversible anion ingress in MgDAnT is however accompanied by solvent co-insertion from the electrolyte that provokes an overpotential effect during the first charge. Full anionic batteries pairing Li2 DAnT with c-PV2+ were assembled giving rise to 0.7 V as output voltage with a specific capacity of 50 mAh per gram of Li2 DAnT.

Opportunities and Challenges for Organic Electrodes in Electrochemical Energy Storage.

As the world moves toward electromobility and a concomitant decarbonization of its electrical supply, modern society is also entering a so-called fourth industrial revolution marked by a boom of electronic devices and digital technologies. Consequently, battery demand has exploded along with the need for ores and metals to fabricate them. Starting from such a critical analysis and integrating robust structural data, this review aims at pointing out there is room to promote organic-based electrochemical energy storage. Combined with recycling solutions, redox-active organic species could decrease the pressure on inorganic compounds and offer valid options in terms of environmental footprint and possible disruptive chemistries to meet the energy storage needs of both today and tomorrow. We review state-of-the-art developments in organic batteries, current challenges, and prospects, and we discuss the fundamental principles that govern the reversible chemistry of organic structures. We provide a comprehensive overview of all reported cell configurations that involve electroactive organic compounds working either in the solid state or in solution for aqueous or nonaqueous electrolytes. These configurations include alkali (Li/Na/K) and multivalent (Mg, Zn)-based electrolytes for conventional "sealed" batteries and redox-flow systems. We also highlight the most promising systems based on such various chemistries relying on appropriate metrics such as operation voltage, specific capacity, specific energy, or cycle life to assess the performances of electrodes.

Tuning the Chemistry of Organonitrogen Compounds for Promoting All-Organic Anionic Rechargeable Batteries.

The ever-increasing demand for rechargeable batteries induces significant pressure on the worldwide metal supply, depleting resources and increasing costs and environmental concerns. In this context, developing the chemistry of anion-inserting electrode organic materials could promote the fabrication of molecular (metal-free) rechargeable batteries. However, few examples have been reported because little effort has been made to develop such anionic-ion batteries. Here we show the design of two anionic host electrode materials based on the N-substituted salts of azaaromatics (zwitterions). A combination of NMR, EDS, FTIR spectroscopies coupled with thermal analyses and single-crystal XRD allowed a thorough structural and chemical characterization of the compounds. Thanks to a reversible electrochemical activity located at an average potential of 2.2 V vs. Li+ /Li, the coupling with dilithium 2,5-(dianilino)terephthalate (Li2 DAnT) as the positive electrode enabled the fabrication of the first all-organic anionic rechargeable batteries based on crystallized host electrode materials capable of delivering a specific capacity of ≈27 mAh/gelectrodes with a stable cycling over dozens of cycles (≈24 Wh/kgelectrodes ).

A H-bond stabilized quinone electrode material for Li-organic batteries: the strength of weak bonds.

Small organic materials are generally plagued by their high solubility in battery electrolytes. Finding approaches to suppress solubilization while not penalizing gravimetric capacity remains a challenge. Here we propose the concept of a hydrogen bond stabilized organic battery framework as a viable solution. This is illustrated for 2,5-diamino-1,4-benzoquinone (DABQ), an electrically neutral and low mass organic chemical, yet with unusual thermal stability and low solubility in battery electrolytes. These properties are shown to arise from hydrogen bond molecular crystal stabilization, confirmed by a suite of techniques including X-ray diffraction and infrared spectroscopy. We also establish a quantitative correlation between the electrolyte solvent polarity, molecular structure of the electrolyte and DABQ solubility - then correlate these to the cycling stability. Notably, DABQ displays a highly reversible (above 99%) sequential 2-electron electrochemical activity in the solid phase, a process rarely observed for similar small molecular battery chemistries. Taken together, these results reveal a potential new strategy towards stable and practical organic battery chemistries through intramolecular hydrogen-bonding crystal stabilization.

Raising the redox potential in carboxyphenolate-based positive organic materials via cation substitution.

Meeting the ever-growing demand for electrical storage devices requires both superior and "greener" battery technologies. Nearly 40 years after the discovery of conductive polymers, long cycling stability in lithium organic batteries has now been achieved. However, the synthesis of high-voltage lithiated organic cathode materials is rather challenging, so very few examples of all-organic lithium-ion cells currently exist. Herein, we present an inventive chemical approach leading to a significant increase of the redox potential of lithiated organic electrode materials. This is achieved by tuning the electronic effects in the redox-active organic skeleton thanks to the permanent presence of a spectator cation in the host structure exhibiting a high ionic potential (or electronegativity). Thus, substituting magnesium (2,5-dilithium-oxy)-terephthalate for lithium (2,5-dilithium-oxy)-terephthalate enables a voltage gain of nearly +800 mV. This compound being also able to act as negative electrode via the carboxylate functional groups, an all-organic symmetric lithium-ion cell exhibiting an output voltage of 2.5 V is demonstrated.

Voltage gain in lithiated enolate-based organic cathode materials by isomeric effect.

Li-ion batteries (LIBs) appear nowadays as flagship technology able to power an increasing range of applications starting from small portable electronic devices to advanced electric vehicles. Over the past two decades, the discoveries of new metal-based host structures, together with substantial technical developments, have considerably improved their electrochemical performance, particularly in terms of energy density. To further promote electrochemical storage systems while limiting the demand on metal-based raw materials, a possible parallel research to inorganic-based batteries consists in developing efficient and low-polluting organic electrode materials. For a long time, this class of redox-active materials has been disregarded mainly due to stability issues but, in recent years, progress has been made demonstrating that organics undeniably exhibit considerable assets. On the basis of our ongoing research aiming at elaborating lithiated organic cathode materials, we report herein on a chemical approach that takes advantage of the positive potential shift when switching from para to ortho-position in the dihydroxyterephthaloyl system. In practice, dilithium (2,3-dilithium-oxy)-terephthalate compound (Li4C8H2O6) was first produced through an eco-friendly synthesis scheme based on CO2 sequestration, then characterized, and finally tested electrochemically as lithiated cathode material vs. Li. This new organic salt shows promising electrochemical performance, notably fast kinetics, good cycling stability and above all an average operating potential of 2.85 V vs. Li(+)/Li(0) (i.e., +300 mV in comparison with its para-regioisomer), verifying the relevance of the followed strategy.

Electrochemical properties of crystallized dilithium squarate: insight from dispersion-corrected density functional theory.

The stacking parameters, lattice constants, and bond lengths of solvent-free dilithium squarate (Li(2)C(4)O(4)) crystals were investigated using density functional theory with and without dispersion corrections. The shortcoming of the GGA (PBE) calculation with respect to the dispersive forces appears in the form of an overestimation of the unit cell volume up to 5.8%. The original Grimme method for dispersion corrections has been tested together with modified versions of this scheme by changing the damping function. One of the modified dispersion-corrected DFT schemes, related to a rescaling of van der Waals radii, provides significant improvements for the description of intermolecular interactions in Li(2)C(4)O(4) crystals: the predicted unit cell volume lies then within 0.9% from experimental data. We applied this optimised approach to the screening of hypothetical framework structures for the delithiated (LiC(4)O(4)) and lithiated (Li(3)C(4)O(4)) phases, i.e. oxidized and reduced squarate forms. Their relative energies have been analysed in terms of dispersion and electrostatic contributions. The most stable phases among the hypothetical models for a given lithiation rate were selected in order to calculate the corresponding average voltages (either upon lithiation or delithiation of Li(2)C(4)O(4)). A first step towards energy partitioning in view of interpretating crystal phases relative stability in link with (de)-intercalation processes has been performed through the explicit evaluation of electrostatic components of lattice energy from atomic charges gained with the Atoms in Molecules (AIM) method.

High-potential reversible Li deintercalation in a substituted tetrahydroxy-p-benzoquinone dilithium salt: an experimental and theoretical study.

Efficient organic Li-ion batteries require air-stable lithiated organic structures that can reversibly deintercalate Li at sufficiently high potentials. To date, most of the cathode materials reported in the literature are typically synthesized in their fully oxidized form, which restricts the operating potential of such materials and requires use of an anode material in its lithiated state. Reduced forms of quinonic structures could represent examples of lithiated organic-based cathodes that can deintercalate Li(+) at potentials higher than 3 V thanks to substituent effects. Having previously recognized the unique electrochemical properties of the C(6)O(6)-type ring, we have now designed and then elaborated, through a simple three-step method, lithiated 3,6-dihydroxy-2,5-dimethoxy-p-benzoquinone, a new redox amphoteric system derived from the tetralithium salt of tetrahydroxy-p-benzoquinone. Electrochemical investigations revealed that such an air-stable salt can reversibly deintercalate one Li(+) ion on charging with a practical capacity of about 100 mAh g(-1) at about 3 V, albeit with a polarization effect. Better capacity retention was obtained by simply adding an adsorbing additive. A tetrahydrated form of the studied salt was also characterized by XRD and first-principles calculations. Various levels of theory were probed, including DFT with classical functionals (LDA, GGA, PBEsol, revPBE) and models for dispersion corrections to DFT. One of the modified dispersion-corrected DFT schemes, related to a rescaling of both van der Waals radii and s(6) parameter, provides significant improvements to the description of this kind of crystal over other treatments. We then applied this optimized approach to the screening of hypothetical frameworks for the delithiated phases and to search for the anhydrous structure.

Electrochemical immobilization of a benzylic film through the reduction of benzyl halide derivatives: deposition onto highly ordered pyrolytic graphite.

The reactivity of electrogenerated benzyl radicals at carbon surfaces was examined through the cathodic reduction of the corresponding bromide derivatives. 4-Nitrobenzyl bromide and benzyl bromide were reduced in N,N-dimethylformamide (DMF) on highly ordered pyrolytic graphite (HOPG) surfaces. Electroproduced films were examined using electrochemistry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Experiments show the formation of strongly adherent deposits and the occurrence of electrografting processes. They are based on radical generation and the reaction of the radical with the substrate. As expected, the thickness of the organic film increases with deposition time but the deposit displays a lower compactness than previously reported for the electroreduction of aryl diazonium salts. Interestingly for benzyl derivatives, the reduction potential required for the electrografting could be rendered much more positive by simply using an iodide-type supporting electrolyte.

Evaluation of polyketones with N-cyclic structure as electrode material for electrochemical energy storage: case of pyromellitic diimide dilithium salt.

Pyromellitic diimide dilithium salt was selected to complete our database on redox-active polyketones with a N-cyclic structure. Although never reported to date, such a lithiated salt was readily synthesized making its electrochemical evaluation in a Li battery possible. Preliminary data show that this novel material reversibly inserts two Li per formula unit at a relatively low potential giving a stable capacity value of 200 mAh g(-1).

Lithium salt of tetrahydroxybenzoquinone: toward the development of a sustainable Li-ion battery.

The use of lithiated redox organic molecules containing electrochemically active C=O functionalities, such as lithiated oxocarbon salts, is proposed. These represent alternative electrode materials to those used in current Li-ion battery technology that can be synthesized from renewable starting materials. The key material is the tetralithium salt of tetrahydroxybenzoquinone (Li(4)C(6)O(6)), which can be both reduced to Li(2)C(6)O(6) and oxidized to Li(6)C(6)O(6). In addition to being directly synthesized from tetrahydroxybenzoquinone by neutralization at room temperature, we demonstrate that this salt can readily be formed by the thermal disproportionation of Li(2)C(6)O(6) (dilithium rhodizonate phase) under an inert atmosphere. The Li(4)C(6)O(6) compound shows good electrochemical performance vs Li with a sustained reversibility of approximately 200 mAh g(-1) at an average potential of 1.8 V, allowing a Li-ion battery that cycles between Li(2)C(6)O(6) and Li(6)C(6)O(6) to be constructed.

From biomass to a renewable LixC6O6 organic electrode for sustainable Li-ion batteries.

Li-ion batteries presently operate on inorganic insertion compounds. The abundance and materials life-cycle costs of such batteries may present issues in the long term with foreseeable large-scale applications. To address the issue of sustainability of electrode materials, a radically different approach from the conventional route has been adopted to develop new organic electrode materials. The oxocarbon salt Li2C6O6 is synthesized through potentially low-cost processes free of toxic solvents and by enlisting the use of natural organic sources (CO2-harvesting entities). It contains carbonyl groups as redox centres and can electrochemically react with four Li ions per formula unit. Such battery processing comes close to both sustainable and green chemistry concepts, which are not currently present in Li-ion cell technology. The consideration of renewable resources in designing electrode materials could potentially enable the realization of green and sustainable batteries within the next decade.