In the frame of research on new metallic hydrides as conversion reaction materials for negative electrodes of Li-ion batteries, the MgFe₂H₆ complex hydride has been investigated in and ex situ using XRD, XAS and magnetic measurements at different states: initially ball milled complex hydride (CH), electrochemically desorbed (ED) and thermally desorbed (TD). Fe–H bonding is clearly evidenced by EXAFS in the CH sample. It is also observed that the electrochemical reaction leads to a nanocrystalline state that needs local probe analyses to be fully investigated and interpreted. From the XAS and magnetic data, the different routes (ED and TD) for dehydrogenation of the complex hydride are compared. For both electrochemically and thermally driven reactions, the hydrogen depletion from Mg₂FeH₆ hydride leads to decomposition into its constituting elements Mg and Fe. However, different Fe structures are observed: bulk α-Fe and amorphous Fe nanoparticles for TD and ED samples, respectively.

Using a new class of (BH₄)⁻ substituted argyrodite Li₆PS₅Z_0.83(BH₄)_0.17, (Z = Cl, I) solid electrolyte, Li-metal solid-state batteries operating at room temperature have been developed. The cells were made by combining the modified argyrodite with an In-Li anode and two types of cathode: an oxide, Li_xMO₂ (M = ⅓ Ni, ⅓ Mn, ⅓ Co; so called NMC) and a titanium disulfide, TiS₂. The performance of the cells was evaluated through galvanostatic cycling and Alternating Current AC electrochemical impedance measurements. Reversible capacities were observed for both cathodes for at least tens of cycles. However, the high-voltage oxide cathode cell shows lower reversible capacity and larger fading upon cycling than the sulfide one. The AC impedance measurements revealed an increasing interfacial resistance at the cathode side for the oxide cathode inducing the capacity fading. This resistance was attributed to the intrinsic poor conductivity of NMC and interfacial reactions between the oxide material and the argyrodite electrolyte. On the contrary, the low interfacial resistance of the TiS₂ cell during cycling evidences a better chemical compatibility between this active material and substituted argyrodites, allowing full cycling of the cathode material, 240 mAhg⁻¹, for at least 35 cycles with a coulombic efficiency above 97%.

Intermetallic compounds are key materials for energy transition as they form reversible hydrides that can be used for solid state hydrogen storage or as anodes in batteries. AB_y compounds (A = Rare Earth (RE); B = transition metal; 2 < y < 5) are good candidates to fulfill the required properties for practical applications. They can be described as stacking of [AB₅] and [AB₂] sub-units along the c crystallographic axis. The latter sub-unit brings a larger capacity, while the former one provides a better cycling stability. However, AB_y binaries do not show good enough properties for applications. Upon hydrogenation, they exhibit multiplateau behavior and poor reversibility, attributed to H-induced amorphization. These drawbacks can be overcome by chemical substitutions on the A and/or the B sites leading to stabilized reversible hydrides. The present work focuses on the pseudo-binary Sm₂Mn_xNi_7−x system (0 ≤ x < 0.5). The structural, thermodynamic and corrosion properties are analyzed and interpreted by means of X-ray diffraction, chemical analysis, scanning electron microscopy, thermogravimetric analysis and magnetic measurements. Unexpected cell parameter variations are reported and interpreted regarding possible formation of structural defects and uneven Mn distribution within the Ni sublattice. Reversible capacity is improved for x > 0.3 leading to larger and flatter isotherm curves, allowing for reversible capacity >1.4 wt %. Regarding corrosion, the binary compound corrodes in alkaline medium to form rare earth hydroxide and nanoporous nickel. As for the Mn-substituted compounds, a new corrosion product is formed in addition to those above mentioned, as manganese initiates a sacrificial anode mechanism taking place at the early corrosion stage.