Nanostructured block copolymer electrolytes have the potential to enable solid-state batteries with lithium metal anodes. We present complete continuum characterization of ion transport in a lamellar polystyrene-b-poly(ethylene oxide) copolymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte as a function of salt concentration. Electrochemical measurements are used to determine the Stefan-Maxwell salt diffusion coefficients [Formula: see text], [Formula: see text], and [Formula: see text]. Individual self-diffusion coefficients of the lithium- and TFSI-containing species were measured by pulsed-field gradient NMR (PFG-NMR). The NMR data indicate that salt diffusion is locally anisotropic, and this enables determination of a diffusion coefficient parallel to the lamellae, D, and a diffusion coefficient through defects in the lamellae, D. We quantify anisotropic diffusion by defining an NMR morphology factor and demonstrate that it is correlated to defect density seen by transmission electron microscopy. We find agreement between the electrochemically determined Stefan-Maxwell diffusion coefficients and the diffusion coefficient D determined by PFG-NMR. Our work indicates that the performance of nanostructured block copolymer electrolytes in batteries is strongly influenced by ion transport through defects.

Alanates have recently attracted attention as new anodic materials for lithium ion batteries. The electrochemical activity of sodium alanate has been already reported and the conversion mechanism explained. Through a complex conversion reaction, this compound is able to develop almost all the theoretical capacity, achieving more than 1700 mAh/g upon first discharge with an efficiency of 70%. Nevertheless alanate undergoes to capacity fade in few cycles. This is mainly due to the severe structural reorganization following the conversion reaction, that results in electrode pulverization and loss of electric contact. Here, we present a nanocomposite material consisting of NaAlH4 confined in the nanoporous of a carbon matrix able to mitigate the effect of volume expansion and improve the cyclability. Specifically, the nanocomposite has been studied in terms of structure, morphology and hydrogen content by the means of Infrared Spectroscopy, solid state NMR, electronic microscopy and thermal analysis. Finally, its performance in lithium cells is presented.

Sodium alanate has proven to be a feasible candidate for electrochemical applications. Within a lithium cell, NaAlH 4 closely approaches its theoretical capacity of 1985 mAhg −1 upon the first discharge. Despite its high specific capacity, NaAlH 4 suffers from poor cycle efficiency, mostly due to the severe volume expansion following the conversion reaction and resulting in damage to electrode mechanical integrity with loss of electrical contact. Synthesis of an appropriate composite alanate/carbon by high energy ball milling demonstrates an ability to mitigate these deleterious effects, whereby large improvements in terms of electrochemical reversibility can be achieved. In order to highlight the effects of mechanochemical treatment on the electrochemical properties of NaAlH 4 , new insights on such NaAlH 4 /C composites are reported. Solid state NMR has been used to study the impact of ball milling on the NaAlH 4 crystal structure, while, the hydrogen content and associated desorption properties have been evaluated by thermal programmed desorption measurements. Also, electrochemical features have been analyzed via the combined application of potentiodynamic cycling with galvanostatic acceleration and electrochemical impedance spectroscopy measurements. Finally, new evidence concerning the reversibility of the conversion processes has been obtained by ex-situ NMR measurements on cycled electrodes.