Search

Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid-electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology.

Mineralogy offers a large database to search for Li- or Na-based compounds having suitable structural features for acting as electrode materials, LiFePO4 being one example. Here we further explore this avenue and report on the electrochemical properties of the bloedite type compounds Na 2M(SO4)2·4H2O (M = Mg, Fe, Co, Ni, Zn) and their dehydrated phases Na2M(SO4) 2 (M = Fe, Co), whose structures have been solved via complementary synchrotron X-ray diffraction, neutron powder diffraction and transmission electron microscopy. Among these compounds, the hydrated and anhydrous iron-based phases show electrochemical activity with the reversible release/uptake of 1 Na+ or 1 Li+ at high voltages of ∼3.3 V vs. Na+/Na0 and ∼3.6 V vs. Li +/Li0, respectively. Although the reversible capacities remain lower than 100 mA h g-1, we hope this work will stress further the importance of mineralogy as a source of inspiration for designing eco-efficient electrode materials. © 2014 The Royal Society of Chemistry.

Carbon coating on battery electrode active material powders is a common practice in order to improve their electronic conductivity and the battery calendar life by limiting side reactions (i.e. active material surface degradation and electrolyte decomposition). Such a coating is currently achieved through chemical procedures involving dispersing the powder in a liquid medium with a carbon precursor followed by thermolysis at high temperatures (ca. 700 °C). This energy consuming procedure has the drawback of not being applicable to materials which may decompose or reduce under such conditions. We present herein an alternative procedure based on physical deposition of carbon, carried out at room temperature under dry conditions, hence avoiding the limitations mentioned above and being generally applicable to any electrode active material. Moreover it allows easy achievement of a homogeneous conformal coating with fine control of the coating thickness. Results on selected materials are reported to exemplify the wide application spectrum and performance improvements induced by the coating. © 2013 The Royal Society of Chemistry.

Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric transportation market provided that major scientific advances including new materials and concepts are developed. Classical positive electrodes for Li-ion technology operate mainly through an insertion-deinsertion redox process involving cationic species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich (Li 1+x Ni y Co z Mn (1-x-y-z) O 2) layered oxides that present unusual Li reactivity. In an attempt to overcome both the inherent composition and the structural complexity of this class of oxides, we have designed structurally related Li 2 Ru 1-y Sn y O 3 materials that have a single redox cation and exhibit sustainable reversible capacities as high as 230 mA h g-1. Moreover, they present good cycling behaviour with no signs of voltage decay and a small irreversible capacity. We also unambiguously show, on the basis of an arsenal of characterization techniques, that the reactivity of these high-capacity materials towards Li entails cumulative cationic (M n+ →M (n+1)+) and anionic (O2-→O2 2-) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li2 MO3 is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials. © 2013 Macmillan Publishers Limited. All rights reserved.

We report on the preparation and electrochemical characterization of Li 2M(SO 4) 2 (M = Co, Fe), where the Fe-based phase was previously unknown. Both compounds can be made at low temperatures (< 320 °C) and the Fe-based phase displays an open circuit voltage of 3.83 V vs. Li +/Li 0 for the Fe 3+/Fe 2+ redox potential. This corresponds to the highest voltage ever obtained for the Fe 3+/Fe 2+ redox couple in an iron-based, fluorine-free compound and is only matched by the triplite phase of LiFeSO 4F. While the theoretical capacity of 102 mA h g - 1 will likely limit the commercial prospects for this phase, knowledge of the structure will provide useful insight into the structural origin of these increased potentials. © 2012 Elsevier B.V. All rights reserved.

Polyanionic electrode materials offer an attractive combination of safety benefits and tunable redox potentials. Thus far, phosphate-based phases have drawn the most interest with a subsequent surge of activity focused on the newly discovered family of fluorosulfate phases. Here, we report the preparation of a new potassium-based fluorosulfate, KFeSO4F, which, with removal of K, leads to a new polymorph of FeSO4F crystallizing in the high-temperature structure of KTiOPO4. This new phase which contains large, empty channels, is capable of reversibly inserting 0.9 Li+ per unit formula and can accommodate a wide variety of alkali ions including Li+, Na+, or K+. This finding not only expands the rich crystal chemistry of the fluorosulfate family but further suggests that a similar strategy can apply to other K-based polyanionic compounds in view of stabilizing new attractive host structures for insertion reactions. © 2012 American Chemical Society.

The recent discovery of electrochemical activity at 3.6 V vs Li +/Li 0 in LiFeSO 4F has generated widespread research activity in this new family of fluorosulfate electrode materials aiming at either increasing the Fe 3+/Fe 2+ redox potential, searching for new active members, or extending this family to hydroxyl-fluorosulfates. Here we present a new low temperature single step synthesis of FeSO 4F 1-yOH y phases using FeF 3 and Fe 2(SO 4) 3•nH 2O as precursors. Using thorough chemical analytical techniques to test for F - content in conjunction with Mössbauer measurements, we demonstrate the existence of a limited solid solution (0.35 < y<1) within this system. Members pertaining to this solid solution have a redox activity ranging from 3.2 to 3.6 V vs Li +/Li 0 and show sustained reversible capacity retention of 130 mAh/g which makes them potentially interesting for Li-based polymer batteries. We demonstrate that the Li-insertion-deinsertion mechanism depends markedly on the sample F -content by using joint in situ XRD and Mössbauer spectroscopy. Moreover, we show the versatility of our synthetic approach by extending it to the elaboration of Fe 1-zM zSO 4F 1-yOH y phases with M = Ti and V. © 2012 American Chemical Society.

Li-ion batteries have empowered consumer electronics and are now seen as the best choice to propel forward the development of eco-friendly (hybrid) electric vehicles. To enhance the energy density, an intensive search has been made for new polyanionic compounds that have a higher potential for the Fe 2+/Fe 3+ redox couple. Herein we push this potential to 3.90 V in a new polyanionic material that crystallizes in the triplite structure by substituting as little as 5 atomic per cent of Mn for Fe in Li(Fe 1-δ Mn δ)SO 4 F. Not only is this the highest voltage reported so far for the Fe 2+/Fe 3+ redox couple, exceeding that of LiFePO 4 by 450 mV, but this new triplite phase is capable of reversibly releasing and reinserting 0.7-0.8 Li ions with a volume change of 0.6% (compared with 7 and 10% for LiFePO 4 and LiFeSO 4F respectively), to give a capacity of ∼125 mA h g -1. © 2011 Macmillan Publishers Limited. All rights reserved.

Searching for possible new cathode materials with the ability to outperform LiFePO 4, our group has recently discovered LiFeSO 4F, a novel metal fluorosulphate compound. Needing no further optimization, it delivers excellent reversible capacity (∼140 mAh/g) involving a 3.6 V Fe II/III redox plateau. This parent fluorosulphate phase has been synthesized by three different routes; namely ionothermal synthesis, solid-state synthesis and polyol-assisted synthesis. These low temperature synthesis routes are described focusing on synthesis of LiFeSO 4F. Furthermore, these methods were successfully employed to unravel other LiMSO 4F compounds (M =Co/Ni/Mn/Zn) as well as sodium-based metal fluorosulphate NaMSO 4F compounds (M = Fe/Co/Ni/Mn). These syntheses were realized at temperature not exceeding 300°C. We have discovered many interesting and at times intriguing structural, electrochemical and transport properties in these fluorosulphate materials. A few of these findings are illustrated to show the richness of the metal fluorosulphate chemistry. ©The Electrochemical Society.

Ionothermal synthesis has recently been used to prepare a fluorosulfate (LiFeSO4 F) capable of reversibly intercalating Li at 3.6 V vs Li, making this material a serious contender to LiFePO4 for HEV and electric vehicle applications. Although fluorosulfates are made from low cost and abundant starting materials, their synthesis is costly because of the use of ionic liquids as synthetic medium. Herein, we report a solid-state process by which LiFeSO4 F can be synthesized without the use of ionic liquids but at the expense of both longer reaction time and weakly contaminated samples. Additionally, we show how powerful Mössbauer spectroscopy can be in the optimization of the various stages of electrode preparation as shown through the synthesis of LiFeSO4 F and its implementation into an electrode. The importance of having Fe3+-free hydrated precursors to routinely obtain pure LiFeSO4 F samples is shown together with the need to optimize ballmilling conditions to preserve Fe3+-free LiFeSO 4 F composites. Samples prepared via this low temperature solid-state process show battery performances approaching those of samples prepared using ionic liquids as synthetic medium. Furthermore, this process can be extended to the synthesis of the other members of the fluorosulfates AMSO4 F family with A=Li, Na and M=Fe, Co, and Ni. © 2010 The Electrochemical Society.