All-Solid-State Lithium Batteries (ASSLBs) are promising since they may enable the use of high potential materials as positive electrode and lithium metal as negative electrode. This is only possible through solid electrolytes (SEs) stated large electrochemical stability window (ESW). Nevertheless, reported values for these ESWs are very divergent in the literature. Establishing a robust procedure to accurately determine SEs’ ESWs has therefore become crucial. Our work focuses on bringing together theoretical results and an original experimental set up to assess the electrochemical stability window of the two NASICON-type SEs Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP). Using first principles, we computed thermodynamic ESWs for LATP and LAGP and their decomposition products upon redox potentials. The experimental set-up consists of a sintered stack of a thin SE layer and a SE-Au composite electrode to allow a large contact surface between SE and conductive gold particles, which maximizes the redox currents. Using Potentiostatic Intermittent Titration Technique (PITT) measurements, we were able to accurately determine the ESW of LATP and LAGP solid electrolytes. They are found to be [2.65–4.6 V] and [1.85–4.9 V] for LATP and LAGP respectively. Finally, we attempted to characterize the decomposition products of both materials upon oxidation. The use of an O2 sensor coupled to the electrochemical setup enabled us to observe operando the production of O2 upon LAGP and LATP oxidations, in agreement with first-principles calculations. Transmission Electron Microscopy (TEM) allowed to observe the presence of an amorphous phase at the interface between the gold particles and LAGP after oxidation. Electrochemical Impedance Spectroscopy (EIS) measurements confirmed that the resulting phase increased the total resistance of LAGP. This work aims at providing a method for an accurate determination of ESWs, considered a key parameter to a successful material selection for ASSLBs.

Mg3(BH4)4(NH2)2 compound was synthesized through the investigation of the Mg(BH4)2-Mg(NH2)2 phase diagram; its crystal structure was solved in a tetragonal unit cell with the space group I-4. Interestingly, Mg3(BH4)4(NH2)2 has a high thermal stability with a decomposition temperature above 190°C and exhibits a high Mg 2+ ionic conductivity of 4.1x10 -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 Mg3(BH4)4(NH2)2 as solid electrolyte. Thus, Mg3(BH4)4(NH2)2 is a compound that could help to develop rechargeable Mg-ion solid-state batteries.

The structure of a novel compound, LiFeV 2 O 7 , has been determined from single-crystal X-ray diffraction data. The phase crystallizes in the noncentrosymmetric 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 (V 4 O 14 ) 8− strings are observed within the structure in association with well-known (V 2 O 7 ) 4− pyrovanadate units. Both units alternate parallel to the [−101] direction. LiFeV 2 O 7 displays a reversible insertion− deinsertion mechanism for Li + ions. The theoretical capacity for the insertion of one Li + into LiFeV 2 O 7 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 Fe 4+ upon oxidation to a high voltage was observed. LiFeV 2 O 7 represents the first reported phase in the Li 2 O−Fe 2 O 3 −V 2 O 5 ternary diagram with electrochemical activities.