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Eldfellite NaV(SO4)2 has been shown to be a versatile cathode insertion host for secondary Li-ion and Na-ion batteries.

Among the key components in batteries, binders play a vital role by interconnecting active materials and conductive additives and facilitating the coating of electrode materials on the desired substrates thus enabling the flexible fabrication of batteries. Further, they aid in buffering volume changes that arise in electrode materials and enhance their cycling stability. Presently, polyvinylidene fluoride-based binders are employed widely, despite their high cost, non-eco-friendliness, and energy inefficiency. Several water processable binders have been investigated as alternatives, but they suffer from various intrinsic issues. Here, we reveal the potential of several ionically conducting inorganic binders (ICIBs). These ICIBs are not only ionically conducting, but also water processable, chemically compatible, eco-friendly, low-cost, thermally stable (>1000 °C), emission-free, and importantly, safe to use. These inorganic binders outperformed standard polyvinylidene fluoride-based binders in several aspects. Surprisingly, ICIBs are absorbing the exothermic heat evolved by charged cathode materials at high temperatures, which will significantly enhance the safety of the batteries. The unique intrinsic ionic conductive properties combined with binding abilities enabled the flexible processing and functioning of solid-state batteries, otherwise challenging due to the mechanical rigidity, chemical incompatibility, and interfacial issues posed by solid electrolytes. The inorganic binders introduced here will make battery manufacturing and recycling more energy-efficient, eco-friendly, flexible, safe, and above all, cost-effective.

The Li+ transport kinetics at the solid–solid electrode|electrolyte interfaces are crucial for the stable and durable performance of solid-state batteries (SSBs). A poor interface due to mechanical problems and/or (electro-)chemical instabilities will curtail the performance of such batteries. Herein, we present a detailed study on the interfaces of a lithium–sulfur (Li–S) SSB with a Li anode, Li–garnet (LLZO) solid electrolyte (SE), and a sulfur–carbon composite as the cathode. Interlayer gels based on ionic liquids were introduced to improve the interfacial properties of the system. For Li symmetric cells, the strategy resulted in a decrease in cell resistance by about a factor of five and stable voltage profiles with low overpotentials (∼300 mV at 0.4 mA cm−2 after >450 hours). Furthermore, the LLZO SE efficiently blocked the polysulfide shuttle to the Li anode. Due to the advantageous features of the design, good electrochemical performance was obtained, where the Li–S SSB delivered an initial discharge capacity of ca. 1360 mA h gsulfur−1 and a discharge capacity of ca. 570 mA h gsulfur−1 after 100 cycles. Detailed electrochemical and compositional characterization of the interphase layers was performed at the Li anode and sulfur cathode interfaces through X-ray photoelectron spectroscopy (XPS), applying depth-profiling techniques, and scanning transmission electron microscopy (STEM). The results revealed the presence of interphase nano-layers with varying thicknesses on the LLZO surface which contained organic and inorganic species.

A rapid microwave hydrothermal process is adopted for the synthesis of titanium dioxide and reduced graphene oxide nanocomposites as high-performance anode materials for Li-ion batteries. With the assistance of hydrazine hydrate as a reducing agent, graphene oxide was reduced while TiO$_{2}$ nanoparticles were grown in situ on the nanosheets to obtain the nanocomposite material. The morphology of the nanocomposite obtained consisted of TiO$_{2}$ particles with a size of ∼100 nm, uniformly distributed on the reduced graphene oxide nanosheets. The as-prepared TiO$_{2}$–graphene nanocomposite was able to deliver a capacity of 250 mA h g−1 ± 5% at 0.2C for more than 200 cycles with remarkably stable cycle life during the Li+ insertion/extraction process. In terms of high rate capability performance, the nanocomposite delivered discharge capacity of ca. 100 mA h g−1 with >99% coulombic efficiency at C-rates of up to 20C. The enhanced electrochemical performance of the material in terms of high rate capability and cycling stability indicates that the as-developed TiO$_{2}$–rGO nanocomposites are promising electrode materials for future Li-ion batteries.

Rechargeable calcium (Ca) batteries have the prospect of high-energy and low-cost. However, the development of Ca batteries is hindered due to the lack of efficient electrolytes. Herein, we report novel calcium tetrakis(hexafluoroisopropyloxy)borate Ca[B(hfip)4]2 based electrolytes exhibiting reversible Ca deposition at room temperature, a high oxidative stability up to 4.5 V and high ionic conductivity >8 mS cm−1. This finding opens a new approach towards room-temperature rechargeable calcium batteries.

Magnesium molybdate (MgMoO4), which possesses synergistic features combining both hierarchical plate-like nanomaterials and porous architectures, has been successfully synthesized through a facile combustion synthesis at a low temperature. The hierarchical architecture is characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), scanning transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses. The as-obtained MgMoO4 nanoplates showed a porous structure with a pore-size distribution ranging from 50 to 70 nm. This porosity provides an electron transport pathway and enhanced surface reaction kinetics. The binding energies measured for Mg 2p, Mo 3d, 3p and O 1s are consistent with the literature, and with the metal ions being present as M(ii) and M(vi) states, respectively. This indicates that the oxidation states of the metal cations are as expected. The electrochemical behaviour of MgMoO4 was investigated using aqueous (NaOH) and non-aqueous solvents (NaClO4 in EC : DMC : FEC) for supercapacitor and battery applications. The sodium-ion capacitor involves ion absorption and insertion into the MgMoO4 electrodes resulting in superior power and energy densities. However, the cycling stability was found to be stable only for an aqueous system. The formation of a solid electrolyte surface layer restricted the reversible capacity of the MgMoO4 in the sodium-battery. Nevertheless, it does offer some promise as an anode material for storing energy with high rate performance and excellent capacity retention. Detailed comparative analyses of various electrolytes in storage devices such as hybrid sodium-ion capacitors and sodium-ion batteries are vital for the integration of hierarchical structured materials into practical applications. The reaction mechanisms are postulated.

Fluorinated alkoxyborate based magnesium electrolytes exhibit a high anodic stability, high ionic conductivity and high coulombic efficiency of magnesium deposition. Owing to the non-corrosive, chemically stable nature and the robust, economic synthesis, this design concept of ion conducting salts opens a promising avenue towards the realization of high-energy magnesium batteries.

The design of a suitable electrode is an essential and fundamental research challenge in the field of electrochemical energy storage because the electronic structures and morphologies determine the surface redox reactions. Calcium molybdate (CaMoO$_{4}$) was synthesized by a combustion route at 300 °C and 500 °C. We describe new findings on the behaviour of CaMoO$_{4}$ and evaluate the influence of crystallinity on energy storage performance. A wide range of characterization techniques was used to obtain detailed information about the physical and morphological characteristics of CaMoO$_{4}$. The characterization results enable the phase evolution as a function of the electrode synthesis temperature to be understood. The crystallinity of the materials was found to increase with increasing temperature but with no second phases observed. Molecular dynamics simulation of electronic structures correlated well with the experimental findings. These results show that to enable faster energy storage and release for a given surface area, amorphous CaMoO$_{4}$ is required, while larger energy storage can be obtained by using crystalline CaMoO$_{4}$. CaMoO$_{4}$ has been evaluated as a cathode material in classical lithium-ion batteries recently. However, determining the surface properties in a sodium-ion system experimentally, combined with computational modelling to understand the results has not been reported. The superior electrochemical properties of crystalline CaMoO$_{4}$ are attributed to its morphology providing enhanced Na$^{+}$ ion diffusivity and electron transport. However, the presence of carbon in amorphous CaMoO$_{4}$ resulted in excellent rate capability, suitable for supercapacitor applications.

Here we report for the first time the development of a Mg rechargeable battery using a graphene-sulfur nanocomposite as the cathode, a Mg-carbon composite as the anode and a non-nucleophilic Mg based complex in tetraglyme solvent as the electrolyte. The graphene-sulfur nanocomposites are prepared through a new pathway by the combination of thermal and chemical precipitation methods. The Mg/S cell delivers a higher reversible capacity (448 mA h g(-1)), a longer cyclability (236 mA h g(-1) at the end of the 50(th) cycle) and a better rate capability than previously described cells. The dissolution of Mg polysulfides to the anode side was studied by X-ray photoelectron spectroscopy. The use of a graphene-sulfur composite cathode electrode, with the properties of a high surface area, a porous morphology, a very good electronic conductivity and the presence of oxygen functional groups, along with a non-nucleophilic Mg electrolyte gives an improved battery performance.

Here we report on the first electrochemical fluorination exemplarily performed on perovskite type BaFeO2.5. A cell setup of the type BaFeO2.5 II La0.9Ba0.1F2.9 II MFx (with MFx being MgF2 and CeF3) was used to perform the reaction, charging the cell up to voltages of about 4 V. Formation of a compound of approximate composition BaFeO2.5F∼0.5 was observed, in agreement with diffraction studies of the independently performed chemically fluorinated compound using F2 gas, and also possessing a capacity which is close to the theoretical capacity of the material. This new method gives an alternative towards the use of highly reactive and toxic F2 gas, and provides potential in adjusting the chemical potential for oxidative chemical fluorinations.

Due to their high theoretical energy density values, Fluoride Ion Batteries (FIB) are interesting alternatives to Li-ion batteries. Recently, results have been reported on the reversible charge and discharge of such systems using a solid electrolyte, various metal fluorides as cathode materials and Ce metal as the anode. The work in the present study is focused on the development of new anode materials which do not contain Li. To facilitate cell preparation and material handling, cells were prepared in the discharged state with Bi or Cu as the cathode material and CeF3, CaF2 or MgF2 as potential anode materials. The charge and discharge mechanisms were examined by detailed ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. The best cycling performances were obtained with MgF2 but prepared in the half-discharged state (i.e. mixed with Mg), thus forming a composite that could provide better interface contacts between the different reactive phases. The results showed that apart from choosing carefully the electrode active materials, it is also important to optimise the architecture of the electrodes.

The hydrogen storage system [MgH2–2LiBH4] shows attractive properties such as favorable thermodynamics, high hydrogen capacity and reversibility. However, there exists an incubation period that amounts up to 10 hours in the dehydrogenation steps, which restricts this system as a practical material. In this study, the influences of stoichiometry and the nanoscale MgH2 were investigated for the system. Considerably shortened incubation times were achieved with deficit amounts of LiBH4 or by using nanoscale MgH2. In addition, the application of nanoscale MgH2 prevented or suppressed the formation of [B12H12]2− in the dehydrogenation, which is otherwise an issue concerning the re-cyclability.

Using liquid electrolytes could increase the efficiencies of fluoride ion batteries. Such an electrolyte should demonstrate good fluoride transfer, be soluble in common solvents, and exhibit stability against decomposition. We have developed a new electrolyte system, which is based on an ammonium bifluoride-doped polyethylene glycol matrix. This compound shows good stability to thermal decomposition up to about 340 °C. The good ionic conductivity at low concentration (0.02 M) could make this compound an appropriate electrolyte. We tested our fluoride-doped PEG matrix in test cells and the first discharge capacity was found to range around 189 mA h g−1 (with respect to the active mass of the cathode) under nonoptimized conditions. Furthermore, we also examined the impact of lithium ions that may dissolve from the anode into the electrolyte.

Rice husks, often neglected and considered as waste, contain constituents that could be of a potential use in advanced material applications. In this study, rice husks were used as a source of silicon dioxide for the synthesis of silicon nanoparticles (Si NPs) through magnesiothermic reduction process. The Si NPs were further used to prepare a binder-free composite system comprising Si NPs and graphene as an anode material for lithium ion battery system (LiBs). The composite system fabricated from rice husk-based Si NPs (RH-Si NPs) yielded an initial capacity of 1000 mA h g−1 at high applied current density of 1000 mA g−1. This study opens up the use of waste materials such as rice husk as a sustainable source of key components in advanced technology applications.

A simple strategy for the synthesis of electrolyte solutions comprised of binuclear magnesium aluminate complexes without the need for organomagnesium compounds is established. The as-prepared phenolate based electrolyte exhibits an anodic stability of up to 3.4 V, good ionic conductivity and air-stability.

A quasielastic neutron scattering study on (beta)-Mg(BH4)2 has been performed to investigate the hydrogen dynamics on the picosecond time-scale. Both vibrational and rotational motions of the [BH4](-) tetrahedra contribute to the signal at low energy transfers. A comprehensive analysis of the elastic and quasielastic incoherent structure factors allowed the separation of different parts. Below 200 K, vibrations and rotations (around the C2 or C3 symmetry axis of the [BH4](-) tetrahedra) are well separated. Above that temperature, a transition is observed in the vibrational part, and the spectral weight is shifted towards the quasielastic region. The dynamic transition is not accompanied by any structural phase change but we suggest that it is correlated with the anomalous thermal expansion that has been reported for (beta)-Mg(BH4)2 [Filinchuk, et al., Chem. Mater., 2009, 21, 925].

The effects of nanoconfinement on the dehydrogenation rate and reaction pathways of the eutectic LiBH4–Mg(BH4)2 have been comprehensively investigated. By means of thermal analysis, mass spectroscopy and solid state 11B MAS NMR, it has been revealed that the multistep thermal decomposition pattern of the binary LiBH4–Mg(BH4)2 has been altered in a two-step reaction and the desorption kinetics has also been significantly improved after infiltration. The formation of diborane and stable MnB12H12 intermediates of the bulk LiBH4–Mg(BH4)2 has been found to be inhibited by nanoconfinement.

Non-nucleophilic electrolytes with outstanding electrochemical performances for magnesium batteries have been synthesized through the reaction between a bisamide magnesium and a Lewis acid in an aprotic solvent. High anodic stability, good ionic conductivity, excellent cycling efficiency and the feasibility of the preparation make the in situ generated electrolyte very promising for the potential application in rechargeable magnesium batteries.

The previously observed intermediate from thermal decomposition of Ca(BH4)2 has been identified as a calcium borohydride borate with composition Ca3(11BD4)3(11BO3), synthesized from a double-isotope substituted sample Ca(11BD4)2. The crystal structure was determined on the basis of Synchrotron Radiation Powder X-ray Diffraction, supported by infrared spectroscopy measurements. The stability of the structure at ambient conditions is confirmed by Density Functional Theory calculations. Ca3(11BH4)3(11BO3) is the first example of a product from a borohydride oxidation containing both B–H(D) and B–O bonds and represents a novel category of compounds, being completely different from the hydroxoborate products upon borohydride hydrolysis. The result represents hence an important contribution to fundamental boron chemistry.

LiBH(4) is an effective additive in enhancing hydrogen desorption and absorption properties for the 2LiH-Mg(NH(2))(2) hydrogen storage system. The improving factors brought by LiBH(4) were studied experimentally. Although a minimum in activation energy was observed in the middle stage of hydrogen desorption for the samples with and without LiBH(4) doping, a reduction in the activation energy was manifest in the overall conversion range due to the LiBH(4) introduction. In contrast to the pure 2LiH-Mg(NH(2))(2), the system component Mg(NH(2))(2) crystallized in the presence of LiBH(4) at about 150 °C in situ from the post-milled amorphous mixture prior to hydrogen desorption. We believe the formation of the N-atom matrix by the crystalline Mg(NH(2))(2) is relevant to the subsequent dehydrogenation as it shares a similar sublattice structure with the desorption product. The formation and disappearance of Li(4)(BH(4))(NH(2))(3) in the dehydrogenation step witnessed the capturing and releasing of LiNH(2) that is generated from the dehydrogenation of 2LiH-Mg(NH(2))(2), which alters not only the kinetics but also thermodynamics in favor of an improved hydrogen sorption performance. The reaction mechanism could be further clarified by the refinement of powder neutron diffraction data of the intermediate compound Li(4)(BD(4))(NH(2))(3).

Ca(BH4)2 is a promising material for hydrogen storage due to its high gravimetric capacity and expected suitable thermodynamic properties. Experimental reports indicate a more complex reaction pathway than the previously proposed route, including formation of unknown intermediate phases. In this work, the reaction scheme of a mixture of γ- and β-Ca(BH4)2 was investigated using temperature programmed desorption and high-resolution synchrotron radiation powder X-ray diffraction. An unknown intermediate Ca–B–H-containing phase has been identified as a CaB2Hx compound where x most probably equals 2. A structure model is proposed.

We demonstrate the synthesis of LiBH(4) from LiH and AlB(2) without the use of additional additives or catalysts at 450 degrees C under hydrogen pressure of 13 bar to the following equation: 2LiH + AlB(2) + 3H(2)--2LiBH(4) + Al. By applying AlB(2) the kinetics of the formation of LiBH(4) is strongly enhanced compared to the formation from elemental boron. The formation of LiBH(4) during absorption requires the dissociation of AlB(2), i.e. a coupled reaction. The observed low absorption-pressure of 13 bar, measured during hydrogen cycling, is explained by a low stability of AlB(2), in good agreement with theoretical values. Thus starting from AlB(2) instead of B has a rather low impact on the thermodynamics, and the effect of AlB(2) on the formation of LiBH(4) is of kinetic nature facilitating the absorption by overcoming the chemical inertness of B. For desorption, the decomposition of LiBH(4) is not indispensably coupled to the immediate formation of AlB(2). LiBH(4) may decompose first into LiH and elemental B and during a slower second step AlB(2) is formed. In this case, no destabilization will be observed for desorption. However, due to similar stabilities of LiBH(4) and LiBH(4)/Al a definite answer on the desorption mechanism cannot be given and neither a coupled nor decoupled desorption can be excluded. At low hydrogen pressures the reaction of LiH and Al gives LiAl under release of hydrogen. The formation of LiAl increases the total hydrogen storage capacity, since it also contributes to the LiBH(4) formation in the absorption process.

NaAlH(4) doped with CeCl(3) was prepared by ball milling and cycled under hydrogen. As-prepared samples and cycled material were investigated by X-ray absorption spectroscopy in order to elucidate the local structure around Ce atoms in the material. It was found that, in contrast to Ti doped NaAlH(4), the oxidation state of the Ce(iii) remains constant during preparation and cycling. Moreover, there is no formation of a bimetallic entity consisting of Ce and Al which is the case in Ti doped samples. Rather, the first shell around Ce consists of a strongly distorted Cl coordination polyhedron with a coordination number considerably below that of CeCl(3). Al atoms are visible as second next neighbors, which indicates that the ball-milled sample is an intimate mixture between CeCl(x) entities and the alanate host matrix. A steady state seems to have been reached after 8 absorption cycles, and no significant changes of the local Ce coordination environment occur after the 9th desorption.

The thermal decomposition steps of Mg(BH4)2 were investigated under He flow and various hydrogen pressures up to 50 bar. In a He flow, the main decomposition of Mg(BH4)2 occurs between 250 and 410 °C until 12.2 mass% is lost, with three main peaks of hydrogen desorption. In the first decomposition step the crystalline phase of Mg(BH4)2 disappears while a small amount of Mg is detected in the XRD profile. However, the major part of the sample is in an amorphous state. After the second step, crystalline MgH2 is observed together with the Mg phase. The third step of hydrogen desorption corresponds to the decomposition of MgH2 and Mg remains the only crystalline phase observed by XRD measurement after heating to 410 °C. Further hydrogen evolution of 1.4 mass% is observed from 410 °C to 580 °C. Only after this hydrogen desorption, MgB2 appears in the XRD spectra of the sample. These results indicate that amorphous, hydrogen containing boron compounds take part as intermediates in the reaction. Under hydrogen pressure, the decomposition events of Mg(BH4)2 shift to higher temperatures in the DSC (differential scanning calorimetry) profiles: while there is only a small shift for steps 1 and 2 there is a clear separation of the succeeding reactions under a background pressure of hydrogen. These data show that the decomposition proceeds via several well defined steps. The final stable decomposition compound of Mg(BH4)2 is MgB2 under both inert and hydrogen gas atmosphere.

Mg(BH4)2 and Ca(BH4)2 with 14.9 and 11.6 mass% hydrogen, respectively, are among the most promising materials for mobile hydrogen storage, but until now very little has been known about their hydrogen desorption properties. In this work the materials have been studied by time-resolved in situ synchrotron powder X-ray diffraction, thermal desorption spectroscopy and energy dispersive X-ray spectroscopy, and details of the phase transitions and decomposition routes are reported.

Mg(BH4)2 is one of the few complex hydrides which have the potential to meet the requirements for hydrogen storage materials, because it contains 14.9 mass% H and has suitable thermodynamic properties. It has not been investigated for hydrogen storage applications yet. In this study, several ways to synthesize solvated and desolvated magnesium tetrahydroborate by wet chemical and mechanochemical methods were tested and compared. A direct synthesis by a reaction of MgH2 with aminoboranes yields magnesium tetrahydroborate quantitatively and in pure form. The method is also applicable to the synthesis of other tetrahydroborates. The products were characterized by elemental analysis, in situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermal analysis methods, such as thermogravimetric analysis (TGA-DSC) and high-pressure calorimetry under a hydrogen atmosphere (HP-DSC).