Insight into Ion Diffusion Dynamics/Mechanisms and Electronic Structure of Highly Conductive Sodium-Rich Na3+ xLaxZr2- xSi2PO12 (0 ≤ x ≤ 0.5) Solid-State Electrolytes

Fei Sun; Yuxuan Xiang; Qian Sun; Guiming Zhong; Mohammad Norouzi Banis; Weihan Li; Yulong Liu; Jing Luo; Ruying Li; Riqiang Fu; Tsun-Kong Sham; Yong Yang; Xuhui Sun; Xueliang Sun

doi:10.1021/acsami.0c21882

Insight into Ion Diffusion Dynamics/Mechanisms and Electronic Structure of Highly Conductive Sodium-Rich Na_{3+ x}La_xZr_{2- x}Si₂PO₁₂ (0 ≤ x ≤ 0.5) Solid-State Electrolytes

ACS Appl Mater Interfaces. 2021 Mar 24;13(11):13132-13138. doi: 10.1021/acsami.0c21882. Epub 2021 Mar 15.

Authors

Fei Sun^{1

2}, Yuxuan Xiang³, Qian Sun², Guiming Zhong⁴, Mohammad Norouzi Banis², Weihan Li², Yulong Liu², Jing Luo², Ruying Li², Riqiang Fu⁵, Tsun-Kong Sham⁶, Yong Yang³, Xuhui Sun¹, Xueliang Sun²

Affiliations

¹ Soochow University-Western University Center for Synchrotron Radiation Research, Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou 215123, China.
² Department of Mechanical and Materials Engineering, University of Western Ontario, London, Ontario N6A 5B9, Canada.
³ State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
⁴ Xiamen Institute of Rare Earth Materials, Chinese Academy of Sciences, Xiamen 361021, China.
⁵ National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States.
⁶ Department of Chemistry, University of Western Ontario, London, Ontario N6A 5B7, Canada.

PMID: 33719407
DOI: 10.1021/acsami.0c21882

Abstract

Solid-state electrolytes (SSEs) have attracted considerable attention as an alternative for liquid electrolytes to improve safety and durability. Sodium Super Ionic CONductor (NASICON)-type SSEs, typically Na₃Zr₂Si₂PO₁₂, have shown great promise because of their high ionic conductivity and low thermal expansivity. Doping La into the NASICON structure can further elevate the ionic conductivity by an order of magnitude to several mS/cm. However, the underlying mechanism of ionic transportation enhancement has not yet been fully disclosed. Herein, we fabricate a series of Na_3+xLa_xZr_2-xSi₂PO₁₂ (0 ≤ x ≤ 0.5) SSEs. The electronic and local structures of constituent elements are studied via synchrotron-based X-ray absorption spectroscopy, and the ionic dynamics and Na-ion conduction mechanism are investigated by solid-state nuclear magnetic resonance spectroscopy. The results prove that La³⁺ ions exist in the form of phosphate impurities such as Na₃La(PO₄)₂ instead of occupying the Zr⁴⁺ site. As a result, the increased Si/P ratio in the NASICON phase, accompanied by an increase in the sodium ion occupancy, makes a major contribution to the enhancement of ionic conductivity. The spin-lattice relaxation time study confirms the accelerated Na⁺ motions in the altered NASICON phase. Modifications on the Si/P composition can be a promising strategy to enhance the ionic conductivity of NASICON.

Keywords: La doping; NASICON; NMR; XAS; diffusion mechanism; high ionic conductivity; solid-state electrolyte.