A new NASICON lithium ion-conducting glass-ceramic of the Li1 + xCrx(GeyTi1 − y)2 − x(PO4)3 system

Abstract

We propose a new lithium ion-conducting glass-ceramic based on the Li1+xCrx(GeyTi1−y)2−x(PO4)3 (LCGTP) system. A specific composition (x=y=0.4) of this system was synthesized by the melt-quenching method, followed by crystallization. The crystallization behavior of the precursor glass was examined by differential scanning calorimetry(DSC) and infrared spectroscopy (IR). The main results indicate that the LCGTP precursor glass presents homogeneous nucleation and considerable glass stability, which allows solid electrolytes to be obtained by the glass-ceramic route. After heat treatment, this glass crystallizes in a NASICON LiTi2(PO4)3-type phase, demonstrating that the proposed system can accommodate Cr, Ti and Ge in an octahedral site. Different heat treatment temperatures were employed to obtain these glass-ceramics. Ionic conductivity was measured by electrochemical impedance spectroscopy (EIS). The sample heat-treated at 900°C for 12h showed the highest ionic conductivity at room temperature (6.6×10−5Ω−1cm−1). This specific glass-ceramic presented a remarkably low activation energy (0.274eV) related to grain contribution, which culminated in a grain conductivity of 8.5×10−4Ω−1cm−1 at room temperature. In addition, a correlation was found between the cell volume and the activation energy for lithium conduction. The samples' microstructures were examined by scanning electron microscopy (SEM) and were also correlated to their ionic conductivity. This set of results suggests that the proposed system is promising for the development of fast lithium ion-conducting glass-ceramics with further compositional optimization.