We have discovered and clarified the ultrahigh glass-forming ability of the metal-organic frameworks—ZIF-62 [Zn(Im2−xbImx)].

Li2MnSiO4 has been identified recently as one of the first cathode battery materials that, at least in principle, could exchange more than 1 lithium per redox-active transition metal ion. In this article, we analyze experimentally and by computer simulations based on density functional theory (DFT) why actual experiments have not confirmed these expectations. We show that Li2MnSiO4 is unstable upon delithiation, with a strong tendency to amorphize. Detailed DFT calculations further indicate that it might be possible to obtain a stable material with a reversible exchange of more than one Li per formula unit (FU) by using an appropriate Mn/Fe mixture (solid solution) with a general formula Li2Mn x Fe1 - x SiO4.

The thermodynamic stability of Li 2 MnSiO 4 polymorphs and their electrochemical properties as electrode for Li batteries are investigated combining experimental and computational methods. Three possible Li 2 MnSiO 4 forms have been considered crystallizing in Pmnb, Pmn2 1 (β-Li 3 PO 4 derivatives) and P2 1 /n (γ-Li 3 PO 4 derivative) space groups (S.G.). We have first demonstrated that the relative stability of βand γ-Li 3 PO 4 polymorphs is well-reproduced by density functional theory (DFT) methods (LDA, GGA). For Li 2 MnSiO 4 , the Pmnb form is predicted to be 2.4 meV/f.u. and 65 meV/f.u. more stable than the Pmn2 1 and P2 1 /n forms, respectively (GGA + U results). Computational results indicate that the denser Pmn2 1 polymorph can be obtained by high pressure/high temperature treatment of the other polymorphs or their mixtures. A sample of Li 2 MnSiO 4 prepared at 900 °C consists of a mixture of polymorphs, as detected by XRD and confirmed by means of SAED and 6 Li MAS-NMR. As expected from DFT results, exposing the as-prepared Li 2 MnSiO 4 sample to high pressure/high temperature (pressure range 2-8 GPa, temperature range 600-900°C) allows to isolate the Pmn2 1 polymorph. The crystal structure has a minor impact in the average lithium intercalation voltage for the two electron process (GGA+U calculated voltages are 4.18, 4.19,and 4.08 V for Pmnb, Pmn2 1 and P2 1 /n, respectively). Major structural rearrangements are expected under lithium deinsertion from the P2 1 /n polymorph, as previously found for the β-Li 3 PO 4 derivatives, rendering any MnSiO 4 delithiated hosts prompt to transform into a more stable structure or a mixture of them.