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1. Perovskite Na-ion conductors developed from analogous Li 3x La 2/3−x TiO 3 (LLTO): chemo-mechanical and defect engineering

   https://doi.org/10.1039/d1ta04252a  

   Lin, Yu-Ying ; Gustafson, William J. ; Murray, Shannon E. ; Shoemaker, Daniel P. ; Ertekin, Elif ; Krogstad, Jessica A. ; Perry, Nicola H. ( September 2021 , Journal of Materials Chemistry A)

   Na-ion conducting solid electrolytes can enable both the enhanced safety profile of all-solid-state-batteries and the transition to an earth-abundant charge-carrier for large-scale stationary storage. In this work, we developed new perovskite-structured Na-ion conductors from the analogous fast Li-ion conducting Li 3 x La 2/3− x TiO 3 (LLTO), testing strategies of chemo-mechanical and defect engineering. Na x La 2/3−1/3 x ZrO 3 (NLZ) and Na x La 1/3−1/3 x Ba 0.5 ZrO 3 (NLBZ) were prepared using a modified Pechini method with varying initial stoichiometries and sintering temperatures. With the substitution of larger framework cations Zr 4+ and Ba 2+ on B- and A-sites respectively, NLZ and NLBZ both had larger lattice parameters compared to LLTO, in order to accommodate and potentially enhance the transport of larger Na ions. Additionally, we sought to introduce Na vacancies through (a) sub-stoichiometric Na : La ratios, (b) Na loss during sintering, and (c) donor doping with Nb. AC impedance spectroscopy and DC polarization experiments were performed on both Na 0.5 La 0.5 ZrO 3 and Na 0.25 La 0.25 Ba 0.5 ZrO 3 in controlled gas environments (variable oxygen partial pressure, humidity) at elevated temperatures to quantify the contributions of various possible charge carriers (sodium ions, holes, electrons, oxygen ions, protons). Our results showed that the lattice-enlarged NLZ and NLBZ exhibited ∼19× (conventional sintering)/49× (spark plasma sintering) and ∼7× higher Na-ion conductivities, respectively, compared to unexpanded Na 0.42 La 0.525 TiO 3 . Moreover, the Na-ion conductivity of Na 0.5 La 0.5 ZrO 3 is comparable with that of NaNbO 3 , despite having half the carrier concentration. Additionally, more than 96% of the total conductivity in dry conditions was contributed by sodium ions for both compositions, with negligible electronic conductivity and little oxygen ion conductivity. We also identified factors that limited Na-ion transport: NLZ and NLBZ were both challenging to densify using conventional sintering without the loss of Na because of its volatility. With spark plasma sintering, higher density can be achieved. In addition, the NLZ perovskite phase appeared unable to accommodate significant Na deficiency, whereas NLBZ allowed some. Density functional theory calculations supported a thermodynamic limitation to creation of Na-deficient NLZ in favor of a pyrochlore-type phase. Humid environments generated different behavior: in Na 0.25 La 0.25 Ba 0.5 ZrO 3 , incorporated protons raised total conductivity, whereas in Na 0.5 La 0.5 ZrO 3 , they lowered total conductivity. Ultimately, this systematic approach revealed both effective approaches and limitations to achieving super-ionic Na-ion conductivity, which may eventually be overcome through alternative processing routes. 

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2. Oxide Ion Conductivity, Proton Conductivity, and Phase Transitions in Perovskite-Derived Ba 3–x Sr x YGa 2 O 7.5 0 ≤ x ≤ 3 Materials

   https://doi.org/10.1021/acs.chemmater.1c04372  

   Fuller, Chloe A. ; Murrell, James Iain ; Blom, Douglas A. ; Vogt, Thomas ; Zhang, Weiguo ; Halasyamani, P. Shiv ; Evans, Ivana Radosavljevic ; Evans, John S. O. ( March 2022 , Chemistry of Materials)
3. Fast Ion Conduction and Its Origin in Li 6–x PS 5–x Br 1+x

   https://doi.org/10.1021/acs.chemmater.9b05331  

   Wang, Pengbo ; Liu, Haoyu ; Patel, Sawankumar ; Feng, Xuyong ; Chien, Po-Hsiu ; Wang, Yan ; Hu, Yan-Yan ( May 2020 , Chemistry of Materials)

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4. Studies of Functional Defects for Fast Na‐Ion Conduction in Na 3− y PS 4− x Cl x with a Combined Experimental and Computational Approach

   https://doi.org/10.1002/adfm.201807951  

   Feng, Xuyong ; Chien, Po‐Hsiu ; Zhu, Zhuoying ; Chu, Iek‐Heng ; Wang, Pengbo ; Immediato‐Scuotto, Marcello ; Arabzadeh, Hesam ; Ong, Shyue Ping ; Hu, Yan‐Yan ( January 2019 , Advanced Functional Materials)

   All‐solid‐state rechargeable sodium (Na)‐ion batteries are promising for inexpensive and high‐energy‐density large‐scale energy storage. In this contribution, new Na solid electrolytes, Na_3−yPS_4−xCl_x, are synthesized with a strategic approach, which allows maximum substitution of Cl for S (x= 0.2) without significant compromise of structural integrity or Na deficiency. A maximum conductivity of 1.96 mS cm⁻¹at 25 °C is achieved for Na_3.0PS_3.8Cl_0.2, which is two orders of magnitude higher compared with that of tetragonal Na₃PS₄(t‐Na₃PS₄). The activation energy (E_a) is determined to be 0.19 eV. Ab initio molecular dynamics simulations shed light on the merit of maximizing Cl‐doping while maintaining low Na deficiency in enhanced Na‐ion conduction. Solid‐state nuclear magnetic resonance (NMR) characterizations confirm the successful substitution of Cl for S and the resulting change of P oxidation state from 5+ to 4+, which is also verified by spin moment analysis. Ion transport pathways are determined with a tracer‐exchange NMR method. The functional detects that promote Na ‐ion transport are maximized for further improvement in ionic conductivity. Full‐cell performance is demonstrated using Na/Na_3.0PS_3.8Cl_0.2/Na₃V₂(PO₄)₃with a reversible capacity of ≈100 mAh g^‐1at room temperature.

    

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5. Charge- and Size-Selective Ion Sieving Through Ti 3 C 2 T x MXene Membranes

   https://doi.org/10.1021/acs.jpclett.5b01895  

   Ren, Chang E. ; Hatzell, Kelsey B. ; Alhabeb, Mohamed ; Ling, Zheng ; Mahmoud, Khaled A. ; Gogotsi, Yury ( October 2015 , The Journal of Physical Chemistry Letters)