Search

International audience; Mg 3 (BH 4) 4 (NH 2) 2 compound was synthesized through the investigation of the Mg(BH 4) 2-Mg(NH 2) 2 phase diagram; its crystal structure was solved in a tetragonal unit cell with the space group I4̅. Interestingly, Mg 3 (BH 4) 4 (NH 2) 2 has a high thermal stability with a decomposition temperature above 190°C and exhibits a high Mg 2+ ionic conductivity of 4.1 × 10 −5 S•cm −1 at 100°C with a low activation energy (0.84 eV). The reversible Mg deposition/stripping was demonstrated at 100°C when using Mg 3 (BH 4) 4 (NH 2) 2 as solid electrolyte. Thus, Mg 3 (BH 4) 4 (NH 2) 2 is a compound that could help to develop rechargeable Mg-ion solid-state batteries.

International audience; The structure of a novel compound, LiFeV2O7, has been determined from single-crystal X-ray diffraction data. The phase crystallizes in the non-centrosymmetric monoclinic Cc space group. The structure can be described as a layered type compound alternating (Li,Fe)–O sheets and V–O chains that are perpendicular to the [101] direction. Within the (Li,Fe)–O sheets, “hexagonal” holes are formed and assembled into tunnels running parallel to the [201] direction and hosting the vanadium atoms. Original (V4O14)8– strings are observed within the structure in association with well-known (V2O7)4– pyrovanadate units. Both units alternate parallel to the [−101] direction. LiFeV2O7 displays a reversible insertion–deinsertion mechanism for Li+ ions. The theoretical capacity for the insertion of one Li+ into LiFeV2O7 reaches 97 mAh/g. When the compound is cycled between 3.50 and 2.35 V versus Li+/Li, the electrochemical curve displays an initial capacity of 100 mAh/g, with 85% of this capacity retained after 60 cycles. No evidence of the formation of Fe4+ upon oxidation to a high voltage was observed. LiFeV2O7 represents the first reported phase in the Li2O–Fe2O3–V2O5 ternary diagram with electrochemical activities.

All-Solid-State Lithium Batteries (ASSLBs) are a new generation of lithium batteries that are developed to meet expectations in terms of safety, stability and high energy density. The liquid electrolyte of conventional Li-ion batteries is replaced in ASSLBs by a safer and more stable solid electrolyte (SE). ASSLBs are promising because they may enable the use of high potential materials as positive electrode and lithium metal as negative electrode. This is only possible through SE stated large electrochemical stability windows (ESW). Nevertheless, values for these electrochemical windows are very divergent in the published literature. Recently, several studies have come to specifically decry the frequent overestimation of SE electrochemical stability windows 1- 4 . Establishing a robust procedure to accurately determine SEs ESW has therefore become crucial. Our work is focused on using an original experimental set up to assess the ESW of two widely investigated NASICON-type SEs Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP). The experimental set-up provides a large contact surface between the SE and the conductive material, which maximizes the redox current signals. A combination of Potentiostatic Intermittent Titration Technique (PITT) and Electrochemical Impedance Spectroscopy (EIS) measurements allowed us to precisely determine the ESW of LATP and LAGP solid electrolytes. Using EIS and physico-chemical characterizations, we attempted to shed light on the degradation mechanisms occurring upon the solid electrolytes’ oxidation. 1 - Y. Tian et al. Energy Environ. Sci. 2017, 10, 1150. 2 - Z. Zhang et al. Energy Environ. Sci. 2018, 11, 1945-1976. 3 - F. Han et al. Adv. Energy Mater. 2016, 6(8), 1501590. 4 - T. Schwietert et al. Nature Mat. 2020, 19, 428–435.

During the last decades, lithium batteries have been developed to power a growing number of portable applications and to meet the needs of an increasingly mobile society. Their industrial and commercial application has always occurred in two successive steps of equal importance: the discovery of new electrode materials and/or electrolytes, followed by their extensive optimisation. A new generation of lithium batteries has been recently developed to meet high expectations in terms of safety, stability and capacity: All-Solid-State Lithium Batteries (ASSLB), where the conventional liquid electrolyte (LiPF6 + EC/DEC) is replaced by a safer and more stable ceramic, polymer or glass solid electrolyte (SE). ASSLB are partly developed with the prospect of using high potential materials as positive electrode and lithium metal as negative electrode. This is only possible through SE stated large electrochemical windows. Nevertheless, values for these electrochemical windows are very divergent in the literature published through the last decades. Recently, several studies have come to specifically decry the frequent overestimation of SE electrochemical stabilities 1,2. Establishing a robust procedure to determine SE real electrochemical windows has become detrimental. Our work is focused on developing a combined theoretical and experimental approach to better assess the electrochemical stability of widely used SE such as Li1.3Al0.3Ti1.7(PO4)3, Li1.5Al0.5Ti1.5(PO4)3 and LiLaTi2O6. In this presentation, we shed light on the importance of selecting the right experimental setup and explore the link between experimental and interpreted thermodynamic results. 1) Y. Tian, T. Shi, W. Richards, J. Li, J. Kim, S-H. Bo, G. Ceder. Energy Environ. Sci., 2017, 10, 1150 2)Z. Zhang, Y. Shao, B. Lotsch, Y-S. Hu, H. Li, J. Janek, L. Nazar, C-W. Nan, J. Maier, M. Armand, L. Chen. Energy Environ. Sci. 2018,11, 1945-1976.

In order to discover innovative electrode and electrolyte battery materials responding to specific needs in terms of capacity, working voltage, polarisation, alkali insertion mechanisms, it appears interesting to explore various insertion chemistries. With this in mind, our study was dedicated on the structural properties and electrochemical performances of iron vanadates positive electrode for Li batteries. More specifically, our groups focussed on the search for new stable phases in the Li2O - Fe2O3 - V2O5 ternary system with respect to several vanadates (FeVO4, NaCuFe2(VO4)3, β-Cu3Fe4(VO4)6, …), which structural and electrochemical properties upon Li insertion have been highlighted in previous work [1]. Among the Li2O - Fe2O3 - V2O5 system, this presentation is dedicated to two new compounds, which were not known from the literature. Both materials were obtained through solid synthesis routes, after optimising the annealing parameters to reach pure phases. After determination of the structure using single crystal X-Ray Diffraction, their physical and electrochemical properties were thoroughly characterized using SEM, Mossbauer spectroscopy, galvanostatic and potentiostatic cycling. Electrochemical characterizations in half cells resulted in finding the optimal voltage window to enhance the capacity retention of the material as compared to previously studied vanadates. The galvanostatic curves indicated complex mechanisms for both materials involving several monophasic and biphasic steps upon Li insertion (see figure for the structure of LiFeV2O7 viewed along the [-101] direction and its electrochemical curve in half cell). Mossbauer spectroscopy allows assessing the oxidation state of iron atoms in the structures before and upon the electrochemical processes. [1] Patoux, S., Richardson, T.J. “Lithium insertion chemistry of some iron vanadates”, Electrochemistry Communications, 9 (3), pp. 485-491 (2007). [2] Benabed, Y., Castro, L., Penin, N., Darriet, J., Dollé, M. “Synthesis, Structure, and Electrochemical Properties of LiFeV2O7”, Chemistry of Materials, 29 (21), pp. 9292-9299 (2017). Figure 1