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In the pursuit of urgently-needed, energy dense solid-state batteries for electric vehicle and portable electronics applications, halide solid electrolytes offer a promising path forward with exceptional compatibility against high-voltage oxide electrodes, tunable ionic conductivities, and facile processing. For this family of compounds, synthesis protocols strongly affect cation site disorder and modulate Li+ mobility. In this work, we reveal the presence of a high concentration of stacking faults in the superionic conductor Li3YCl6 and demonstrate a method of controlling its Li+ conductivity by tuning the defect concentration with synthesis and heat treatments at select temperatures. Leveraging complementary insights from variable temperature synchrotron X-ray diffraction, neutron diffraction, cryogenic transmission electron microscopy, solid-state nuclear magnetic resonance, density functional theory, and electrochemical impedance spectroscopy, we identify the nature of planar defects and the role of nonstoichiometry in lowering Li+ migration barriers and increasing Li site connectivity in mechanochemically-synthesized Li3YCl6. We harness paramagnetic relaxation enhancement to enable 89Y solid-state NMR, and directly contrast the Y cation site disorder resulting from different preparation methods, demonstrating a potent tool for other researchers studying Y-containing compositions. With heat treatments at temperatures as low as 333 K (60{\deg}C), we decrease the concentration of planar defects, demonstrating a simple method for tuning the Li+ conductivity. Findings from this work are expected to be generalizable to other halide solid electrolyte candidates and provide an improved understanding of defect-enabled Li+ conduction in this class of Li-ion conductors.

In this study, the relationship between structure, cation disorder and Na-ion conduction properties is elucidated in a series of Na3−xY1−xZrxCl6 solid electrolytes.

Solid-state batteries are a promising energy storage technology that can potentially offer both improved safety and energy density. The solid electrolyte is the defining feature and plays a significant role in the electrochemical performance of a solid-state cell, especially at room temperature. Herein, we report a series of glass-ceramic, sodium-deficient chloride solid electrolytes, NaxY0.25Zr0.75Cl3.75+x (0.25  x  0.875), possessing significantly improved ionic conductivities when compared to their stoichiometric counterpart, Na2.25Y0.25Zr0.75Cl6 (x = 2.25). By tuning both the sodium molar content and the sample’s crystallinity, the composition Na0.625Y0.25Zr0.75Cl4.375 (x = 0.625) was found to exhibit the highest Na+ conductivity of 0.4 mS cm−1 at room temperature. Furthermore, the relationship between composition, structure, and conductivity for these compositions in the NaCl−YCl3−ZrCl4 system was evaluated using a combination of X-ray diffraction (XRD), solid-state nuclear magnetic resonance spectroscopy (ss-NMR), and electrochemical impedance spectroscopy (EIS) techniques. Materials characterization reveals that sodium-deficiency (i.e., lower molar % of NaCl) results in reduced crystallinity and preferred occupancy of prismatic Na local environments. These combined factors contribute to a lower activation energy for Na+ hopping, an increased ionic conductivity, and improved electrochemical performance at both higher cycling rates and at room temperature.

This reply provides updated energy consumption estimates at clearly defined separation conditions for electrochemical desalination concepts.

We conduct a techno-economic analysis of electrochemical water deionization technologies. The objective of the analysis is to compare cost, volume, and energy consumption of membrane capacitive deionization (mCDI) to intercalative deionization techniques. Here, we first explore the concept of hybrid capacitive deionization (HCDI), i.e., a cation intercalation electrode paired with an activated carbon capacitive electrode. Then we explore in detail a novel device concept, fully intercalative water deionization (IDI), which relies entirely on the cation intercalation principle. The intercalation host materials in our study are Prussian blue analogs (PBAs), e.g., NiFe(CN)6 or CuFe(CN)6, that offer ∼3–5× higher gravimetric salt removal capacities than typical activated carbon. Our analysis shows that IDI should be superior to mCDI in module cost, volume, and energy efficiency, despite a more complex module architecture. Making careful assumptions on material costs, we provide a cost breakdown for mCDI, HCDI, and IDI modules and show that IDI is the only concept that is not dominated by ion exchange membrane costs. The environmental impact of electrochemical water deionization is illustrated by estimating the carbon footprint of currently installed reverse osmosis capacity in different world regions and comparing it to the respective carbon footprint of mCDI, HCDI, and IDI at similar capacity.

Nuclear magnetic resonance (NMR) spectroscopy provides detailed insights into the working principles of ionic and mixed conductors used in rechargeable battery applications. Notably, NMR is sensitive to crystalline, disordered or even amorphous phases that arise during electrochemical cycling, and can provide atomic-level structural information, as well as insights into the dynamics of ion motion. In this talk, I will present our recent work on Li-ion conducting rocksalt halides [1] and Li-conducting polymeric ionic liquids [2]. Using a combination of synchrotron X-ray diffraction/scattering, electrochemical impedance spectroscopy (EIS), solid-state NMR, pulsed field gradient NMR (PFG-NMR), NMR relaxometry, and first principles calculations, we provide a multiscale understanding of ion diffusion processes and link these findings to local structure features, crystallinity, and materials synthesis/processing conditions. [1] Sebti, E., Evans, H., Chen, H., Richardson, P., White, K., Giovine, R., Koirala, K. P., Xu, Y., Gonzalez-Correa, E., Wang, C., Brown, C., Cheetham, A., Canepa, P., Clément, R.*, "Stacking Faults Assist Lithium-Ion Conduction in a Halide-Based Superionic Conductor", J. Am. Chem. Soc., accepted. DOI: 10.1021/jacs.1c11335. [2] Jones, S., Nguyen, H., Richardson, P., Chen, Y.-Q., Wyckoff, K., Hawker, C., Clément, R., Fredrickson, G., Segalman, R., "Design of Polymeric Zwitterionic Solid Electrolytes with Superionic Lithium Transport", ACS Cent. Sci., 8(2), 169-175 (2021). DOI: 10.1021/acscentsci.1c01260.

Rechargeable solid-state sodium-ion batteries (SSSBs) hold great promise for safer and more energy-dense energy storage. However, the poor electrochemical stability between current sulfide-based solid electrolytes and high-voltage oxide cathodes has limited their long-term cycling performance and practicality. Here, we report the discovery of the ion conductor Na3-xY1-xZrxCl6 (NYZC) that is both electrochemically stable (up to 3.8 V vs. Na/Na+) and chemically compatible with oxide cathodes. Its high ionic conductivity of 6.6 × 10−5 S cm−1 at ambient temperature, several orders of magnitude higher than oxide coatings, is attributed to abundant Na vacancies and cooperative MCl6 rotation, resulting in an extremely low interfacial impedance. A SSSB comprising a NaCrO2 + NYZC composite cathode, Na3PS4 electrolyte, and Na-Sn anode exhibits an exceptional first-cycle Coulombic efficiency of 97.1% at room temperature and can cycle over 1000 cycles with 89.3% capacity retention at 40 °C. These findings highlight the immense potential of halides for SSSB applications., Rechargeable solid-state sodium-ion batteries hold great promise for safer and more energy-dense energy storage. Here, the authors show a new sodium-based halide, Na3-xY1-xZrxCl6, for sodium-all-solid-state batteries with enhanced ionic conductivity and long-term cycling stability.

Desalination of brackish water sources is critical to addressing the growing global freshwater demand. One promising approach is electrically driven desalination using intercalation electrodes. While intercalation electrodes have been widely researched for energy storage applications, only a small subset of those materials is suitable for desalination. Here we report the synthesis, characterization, and in-device testing of three Prussian blue analogue intercalation compounds: copper, manganese, and zinc hexacyanoferrate with formulas KxM[Fe(CN)6]z·nH2O (M = Cu, Mn, Zn). The desalination performance for each of these materials against carbon electrodes is reported for Na+ intercalation and for Ca2+ intercalation using 1000 ppm NaCl and 1000 ppm CaCl2 feed solutions, respectively. While the copper and manganese analogs showed promising performance for Na+ and Ca2+ intercalation, the zinc compound was unstable and underwent rapid dissolution. Manganese hexacyanoferrate showed the best desalination performance in terms of salt removal capacities and salt removal rates with NaCl while copper hexacyanoferrate performed the best with CaCl2. The manganese analog proved to be the most stable intercalation material, retaining 83% and 72% of its salt removal capacity after 280 cycles in NaCl and CaCl2 feed solutions respectively.