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Li6PS5Cl (LPSCl) argyrodites offer high room temperature ionic conductivity (>1 mS cm−1) and are among the most promising solid electrolytes. However, their chemical instability against Li metal compromises the long‐term cyclability. Using PEO‐LiTFSI as an interlayer or as a matrix for composite electrolytes is a promising strategy to address this issue. Nevertheless, the interphase of PEO‐LiTFSI and LPSCl requires further detailed investigations. This work explores the interfacial reactions between these phases using solid‐state nuclear magnetic resonance. Results show that PEO facilitates the formation of a complex with LiCl and Li3PS4 from LPSCl, resulting in an interphase material with limited local mobility, thus impeding ion transport. Although the addition of Br as a dopant can improve the ionic conductivity of LPSCl by inducing disorder and generating the Li vacancies, it makes the LPSCl more susceptible to PEO and increases the extent of the interfacial reaction. 6Li–6Li EXSY experiments demonstrate spontaneous Li‐ion exchange between the PEO and the LPSCl, yet this exchange is significantly hindered by reaction products within the PEO‐LPSCl interphase, attributable to their sluggish local dynamics. This study sheds light on the complex interfacial interaction between PEO‐LiTFSI and sulfide argyrodite, providing insights into designing solid electrolytes for the new generation of electrochemical devices. [ABSTRACT FROM AUTHOR]

Sodium–air batteries (SABs) are receiving considerable attention for the development of next generation battery alternatives due to their high theoretical energy density (up to 1105 W h kg−1). However, most of the studies on this technology are still based on organic solvents; in particular, diglyme, which is highly flammable and toxic for the unborn child. To overcome these safety issues, this research investigates the first use of a branched ether solvent 1,2,3-trimethoxypropane (TMP) as an alternative electrolyte to diglyme for SABs. Through this work, the reactivity of the central tertiary carbon in TMP towards bare sodium metal was identified, while the addition of N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][TFSI]) as a co-solvent proved to be an effective strategy to limit the reactivity. Moreover, a Na-β-alumina disk was employed for anode protection, to separate the TMP-based electrolyte from the sodium metal. The new cell design resulted in improved cell performance: discharge capacities of up to 1.92 and 2.31 mA h cm−2 were achieved for the 16.6 mol% NaTFSI in TMP and 16.6 mol% NaTFSI in TMP/[C4mpyr][TFSI] compositions, respectively. By means of SEM, Raman and 23Na NMR techniques, NaO2 cubes were identified to be the major discharge product for both electrolyte compositions. Moreover, the hybrid electrolyte was shown to hinder the formation of side-products during discharge – the ratio of NaO2 to side-products in the hybrid electrolyte was 2.4 compared with 0.8 for the TMP-based electrolyte – and a different charge mechanism for the dissolution of NaO2 cubes for each electrolyte was observed. The findings of this work demonstrate the high potential of TMP as a base solvent for SABs, and the importance of careful electrolyte composition design in order to step towards greener and less toxic batteries. [ABSTRACT FROM AUTHOR]

In this study, 6,7Li solid state nuclear magnetic resonance (ssNMR) has been used to characterize local disorder in LiNi0.5Mn1.5O4 (LNMO) spinel cathodes and to understand their implications for the phase transformation mechanism during electrochemical cycling vs. lithium. By comparing NMR spectra of LNMO samples with slightly varying transition metal stoichiometries, we demonstrate the high sensitivity of ssNMR in the indirect detection of transition metal order and its ability to identify disorder induced by stoichiometric variations. Secondly, we investigate the lithiation reaction mechanism of the non-stoichiometric transition metal-ordered LNMO spinel cathode by ex situ7Li NMR and highlight that its reaction process involves primarily two successive biphasic reactions. However, our results suggest that stoichiometrically induced transition metal disorder promotes a mixed solid solution and biphasic reaction mechanism. Besides an extended solid solution region, we evince that the biphasic reaction involves the presence of intermediate transient species that make it possible to bridge the miscibility gap between the Li1 and Li0.5 phases. These results go beyond our operando XRD results, underlining that local structural analysis by 7Li ssNMR can provide valuable additional insights into the complex reaction mechanism that are difficult to access by other techniques. [ABSTRACT FROM AUTHOR]

Model validation of a well-known class of solid polymer electrolyte (SPE) is utilized to predict the ionic structure and ion dynamics of alternative alkali metal ions, leading to advancements in Na-, K-, and Cs-based SPEs for solid-state alkali metal batteries. A comprehensive study based on molecular dynamics (MD) is conducted to simulate ion coordination and the ion transport properties of poly(ethylene oxide) (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt across various LiTFSI concentrations. Through validation of the MD simulation results with experimental techniques, we gain a deeper understanding of the ionic structure and dynamics in the PEO/LiTFSI system. This computational approach is then extended to predict ion coordination and transport properties of alternative alkali metal ions. The ionic structure in PEO/LiTFSI is significantly influenced by the LiTFSI concentration, resulting in different lithium-ion transport mechanisms for highly concentrated or diluted systems. Substituting lithium with sodium, potassium, and cesium reveals a weaker cation-PEO coordination for the larger cesium-ion. However, sodium-ion based SPEs exhibit the highest cation transport number, indicating the crucial interplay between salt dissociation and cation-PEO coordination for achieving optimal performance in alkali metal SPEs. [ABSTRACT FROM AUTHOR]

Solid state batteries are the next generation of safe energy storage devices offering high energy and power. Li7La3Zr2O12 garnets are fast Li-ion conductors and promising electrolytes to be used in solid-state batteries. However, they react with humid air to form LiOH and Li2CO3, reducing the ionic conductivity. In this work, the effect of heat treatment on local Li mobility in LLZO and the chemical evolution and phase transitions during the heating are investigated by a combination of solid state NMR, Raman, and XRD diffraction techniques. The results show that the activation energy for Li jumps obtained by variable temperature solid state NMR decreases after heat treatment at 750 °C and the Li dynamics are comparable to those of sintered pellets. Additionally, we show that the pretreatment of powders is an effective approach for obtaining garnet-rich composite electrolytes with better flexibility and garnet-polymer interphases, improving the prospects of this material towards processing. [ABSTRACT FROM AUTHOR]

High-voltage Li metal solid-state batteries are in the spotlight as high energy and power density devices for the next generation of batteries. However, the lack of robust solid-electrolyte interfaces (SEIs) and the propagation of Li dendrites still need to be addressed for practical application with extended cyclability. In the present work, high-voltage Li metal cells with LiNi0.6Mn0.2Co0.2O2 active material were assembled with a polyethylene(oxide) based electrolyte mixed with lithium bis(fluorosulfonyl)imide (LiFSI) salt. The addition of Li7La3Zr2O12 garnet to form a composite electrolyte demonstrated a beneficial effect for cell cycling stability. Inspired by the improved interface of ceramic Li7La3Zr2O12 garnet and Li metal, as well as by previous knowledge of favorable SEI forming species, various additive candidates were selected to optimize its electrolyte composition. Among them, lithium hydroxide (LiOH) is a key favorable species that shows a relevant improvement in the cyclability of the cells. X-ray photoelectron spectroscopy showed that the SEI layer is composed mainly of chemical species arising from the reduction of the Li salt, with lithium fluoride (LiF) being the main product. In addition, solid-state nuclear magnetic resonance proved that LiOH induces the cleavage of the labile S–F bond, increasing the concentration of LiF. Herein, we highlight that SEI-forming additives need to be considered for the interfacial engineering design of stable SEIs to expand the performance boundary of SSBs. [ABSTRACT FROM AUTHOR]