Polymer-based solid-state electrolytes are shown to be highly promising for realizing low-cost, high-capacity, and safe Li batteries. One major challenge for polymer solid-state batteries is the relatively high operating temperature (60-80°C), which means operating such batteries will require significant ramp up time due to heating. On the other hand, as polymer electrolytes are poor thermal conductors, thermal variation across the polymer electrolyte can lead to nonuniformity in ionic conductivity. This can be highly detrimental to lithium deposition and may result in dendrite formation. Here, a polyethylene oxide-based electrolyte with improved thermal responses is developed by incorporating 2D boron nitride (BN) nanoflakes. The results show that the BN additive also enhances ionic and mechanical properties of the electrolyte. More uniform Li stripping/deposition and reversible cathode reactions are achieved, which in turn enable all-solid-state lithium-sulfur cells with superior performances.

The bond valence technique has been applied on reverse Monte Carlo produced structural models of Agbased superionic glasses and crystals. The results for the ͑AgI͒ 0.75 -͑Ag 2 MoO 4 ͒ 0.25 and ͑AgI͒ 0.6 -͑Ag 2 O-2B 2 O 3 ͒ 0.4 glasses show the importance of including Ag sites with a high oxide coordination for the long-range mobility. The majority of the Ag ϩ ions belonging to the long-range conduction pathways is coordinated to both O and I Ϫ , and the pathways including only iodide coordinated sites are restricted to very local regions of a few Å. The most important finding of the present study is that the ionic conductivity as well as its activation energy can be determined directly from the ''pathway volume'' ͑i.e., the volume fraction of the percolating pathway cluster͒ of the structural models. The conductivity pathway volume relation is found to hold for glassy and crystalline conductors ͑including their temperature dependencies͒, whose conductivities differ by more than 11 orders of magnitude.

Two modifications of elemental tin exhibiting fundamentally different bonding exist, the semimetallic a form and the metallic p form. In the 4th main group of the periodic table, this dimorphism constitutes a stage between non-and semimetallic elements (C, Si, Ge) on the one hand and metallic lead on the other. In the inorganic chemistry of tin, Zintl phases and cluster anions with homonuclear Sn-Sn bonds reveal a continuous transition from metallic to covalent bonding."] The structural investigations of organopolystannanes[zal carried out so far have shown a relationship between these compounds and alkanes; the structure of a distannene has also been described."'] Further linking of Sn centers, beyond that studied so far, should build a bridge between the organic and inorganic chemistry of tin. With this goal in mind, we allowed the 1,n-diiodo compounds ZL3l to react with Ph,SnLi 1 [reaction (a)]. This chain-lengthening reaction is more complicated than the stoichiometry would at first lead one to expect. Variation of the molar ratio of the starting materials as well as of the solvent and the concentration (Table 114]) made it possible to isolate the tri-(3a), tetra-(3b), penta-(3c), and hexastannane (3d). The solutions of the iodine components react as equilibrium mixtures of different 1 ,n-diiodopolystannanes; only when nonpolar toluene is used in excess relative to added T H F is 3d obtained in good yield. X-ray structure analyse~'~' of 3a-d revealed the molecular conformations, bond angles, and Sn-Sn distances shown in Figure 1. Bulky, electron-rich substituents on the Sn-Sn units generally effect an increase of the Sn-Sn bond 1ength.l'"' This is confirmed by the series of tBu-substituted compounds investigated here. The central bond in 3d same is true for tBu-substituted p o l y~i l a n e s . [~"~~~ In all compounds 3 as well as in I f t B~~S n ) 4 I [~~l the Sn, unit exhibits the trans conformation. Intermolecular interactions are not present in the crystal. The polystannanes 3 are relatively soluble in CDCI,; in the Il9Sn-NMR spectra, two (3a,b) or three (3c,d) major signals are surrounded by numerous well-resolved coupling satellites. Plotting of 1J(119Sn-119Sn) versus d(Sn-Sn) (eight independent pairs of values) reveals a correlation that shows opposite signs for couplings via short (positive) or long (negative) bonds (change in sign at about 285 pm); data measured earlier by us (13 pairs of v a i~e s [~"~~~~) and data from the literature (15 pairs of values[*l) fit this relation (Fig. 2). A linear relationship[*"' between 'J( 1'9Sn-"9Sn) and the "nonbonding" distance d(Sn-. -Sn) was confirmed; in this case, too, the series 3a to 3d reveals a change in the sign of the coupling constants (at about 500 pm; 513 pm and -92 Hz for the central bonds in 3d).The UV spectra (Fig. 3) exhibit strong absorption maxima with marked redshift with increasing chain length."'1 Parallels exist with conjugated polyenes, except that the HOMO in Sn, chains is determined by o Sn-Sn bonds. The HOMOILUMO energy difference decre...

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Oxides. -Bond valence sums for the ion positions in single-crystal structure data of the garnet-like fast lithium ion conductors Li5La3M2O12 (M: Nb, Ta) exhibit unusually large deviations from the ideal valences. The structure model can be significantly improved by optimizing the light atoms (oxygen and lithium) positions using a bond valence mismatch minimization procedure in the previously suggested space group I213 or its centrosymmetric counterpart Ia3. Possible pathways for lithium ion migration in Li5La3M2O12 are identified by a bond valence analysis. Li-bond valence mismatch isosurface models for Li + ion transport pathways are found to be nearly the same in both compounds. The characteristic feature of the three-dimensional Li + ion pathway network is a nonplanar square of partially occupied Li sites. -(THANGADURAI*, V.; ADAMS, S.; WEPPNER, W.; Chem.