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Sodium ions electrolyte; quasi-solid state; Na$_2$O−B$_2$O$_3$−SiO$_2$−H$_2$O system hydrated glass; voltage window; ionic conductivity; cycle performance.

Na$_2$O−B$_2$O$_3$−SiO$_2$−H$_2$O system hydrated glass with $T_{\rm g}$ ranges from $−$10 to 150$^{\circ}$C is synthesized by aqueouschemical methods and is applied to symmetrical cells as quasi-solid electrolyte. At the temperature around $T_{\rm g}$, the solid state transforms to quasi-solid state, whose mechanical property keeps like gel electrolyte, but the conductivity leaps from $5.31 \times 10^{−6}$ S cm$^{−1}$ to $5.43 \times 10^{−3}$ S cm$^{−1}$, much higher than most of the glass–ceramic electrolytes. As most of the solvated water is evaporated, H$_2$O left in the system distributes in the intervals as hydroxyl, which is much benefit to the ions transportation, and more important is to increase the voltage window to 2.24 V and even higher. The cycle performance is also researched. After 1000 circulations, there is still 65% capacity retention and no obvious damage is discovered in the electrolyte, which means much better cycle property of the electrolyte than gel electrolyte. Other compositions in the quasi-solid system including different contents of B$_2$O$_3$, Na$_2$SO$_4$ and m in sodium silicate NaO$_2$·mSiO$_2$ are also studied. In general, quasi-solid Na$_2$O−B$_2$O$_3$−SiO$_2$−H$_2$O system owns better conductivity and cycle performance than mostglass–ceramic solid electrolyte, and it is environment-friendly, inexpensive and practical to be used as sodium ions quasi-solid electrolyte.

YINGMING ZHAO¹ FAN TONG¹ CHENYAO FAN¹ SIQI YU¹ BING HAN¹ JIAYANG GAO¹ YUNCHAO LOU¹ PENGLIN JIANG¹ ZHIYU WANG¹

1. State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China

Published

18 February 2020

Manuscript received

29 August 2019

Accepted

29 November 2019

Final version published online

18 February 2020