Nanostructured all-solid-state supercapacitors based on NASICON-type Li1.4Al0.4Ti1.6(PO4)3 electrolyte

Abstract

Lithium aluminum titanium phosphate (LATP), a NASICON-type (structure of Na1 + xZr2SixP3 − xO12, 0 < x < 3) lithium ionic conductor, possesses high ionic conductivity at ambient temperature and sufficiently high electrochemical stability compared to well-established types of solid electrolytes. This ensures LATP being potentially used as solid electrolyte for all-solid-state supercapacitors. In the pure ionic conductors like LATP, the stoichiometry change under work potential for energy storage is not possible. Therefore, it is essential to produce heterophase contacts, at which the compositional changes could occur. Carbon nanotube (CNT), an excellent electronical conductor, has been consequently mixed with LATP. The all-solid-state supercapacitors with this LATP/CNT mixture have been manufactured in sandwich structure—two mixture layers separated by a pure LATP layer as separator. And the impedance behavior as well as supercapacitance dependent on various CNT weight percentages (1–7.5%) has been investigated by electrochemical impedance spectroscopy and cyclic voltammetry. The results clearly prove that electrical double layer could be formed at the heterophase contacts indicating the supercapacitance behavior of the device, especially when the high contents of CNTs are used. The capacitance of specimen without CNT shows only a value of 0.52 mF/cm3, which is strongly promoted to 11.59 mF/cm3 when CNT content increases to 7.5%.