전고체전지용 고체전해질 Li2ZrCl6의 Mn 치환에 따른 전기화학적 성능 변화 및 Li2ZrCl6로 표면이 공학적으로 개질된 전고체전지용 양극활물질 NCM811의 열화 억제에 관한 연구

Abstract

In the realm of solid-state batteries, challenges such as ionic conductivity of solid electrolytes and deterioration problem of cathode materials have been a persistent concern. In this study, Li2ZrCl6 and 0.05Mn-Li2ZrCl6 were synthesized through a high-energy ball-milling process. Mn substitution was confirmed via powder X-ray diffraction (XRD), Raman spectroscopy, solid-state nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) analysis. Ionic conductivity, activation energy, and resistance components after cycling were measured using electrochemical impedance spectroscopy (EIS). Ionic conductivity of Li2ZrCl6 and 0.05Mn-Li2ZrCl6 was found to be 0.4 and 0.8 mS·cm-1,respectively, at room temperature. Activation energy for the synthesized solid electrolytes Li2ZrCl6 and 0.05Mn- Li2ZrCl6 was calculated to be 0.342 and 0.326 eV. To assess the electrochemical stability of the synthesized solid electrolytes, cyclic voltammetry and galvanostatic charge/discharge at 0.1 C were performed. First-cycle discharge capacities were 171.6 and 186 mAh·g-1, respectively, with a consistent coulombic efficiency of 94.5%. Li2ZrCl6-NCM811 cathode composite was fabricated using a thinky, with the weight ratio of Li2ZrCl6 optimized from field-emission scanning electron microscopy and energy dispersive spectroscopy (FE-SEM & EDS) (x = 0, 2, 4, 8, 12 wt%). Galvanostatic charge/discharge measurements at 0.1 C was conducted to evaluate the electrochemical performance of the cathode composites. First-cycle discharge capacity for x = 0 and x = 4 were 173.1 and 190.7 mAh·g-1, respectively, with coulombic efficiencies of 75.2% and 84.6%. Capacity retention rate after 50 cycles were 74.1% and 91.3%, respectively. Li+ diffusion coefficient, assessed via galvanostatic intermittent titration technique (GITT), was determined as 1.6 and 5.16(10-9 cm2/s). Electrochemical impedance spectroscopy (EIS) measurements were performed to analyze the resistance variation after cycling, revealing total resistances of 1367.4 and 160.55 Ω, respectively.