Synthesis, Microstructure and Ion Dynamics of Binary 75% Li2SO4 - 25%(Tio2, Zro2, B2O3, Li2CO3) Composite Solid Electrolytes For All-Solid-State Lithium Batteries

Abstract

All-solid-state lithium batteries and electrochemical supercapacitors represent the pinnacle of safe, long-life, high-energy-density storage technologies. However, commercial deployment is hindered by the low room-temperature ionic conductivity of inorganic solid matrix materials. This master-level comprehensive research presents an exhaustive investigation into four binary composite solid electrolyte systems formulated at a fixed weight ratio of 75 wt% lithium sulfate (Li₂SO₄) host matrix to 25 wt% functionally distinct secondary phase additives: Sample A (75% Li₂SO₄ + 25% ZrO₂), Sample B (75% Li₂SO₄+ 25% TiO₂), Sample C (75% Li₂SO₄ + 25% B₂O₃), and Sample D (75% Li₂SO₄ + 25% Li₂CO₃). Precise crystallographic phase detection was conducted using standard JCPDS data ((Li₂SO₄: JCPDS 20-0640, ZrO₂: JCPDS 37-1484, TiO₂ Anatase: JCPDS 21-1272, Li₂CO₃: JCPDS 22-1141) with explicit (h k l) plane indexing. Advanced structural, vibrational, and nanostructural characterization techniques—including X-Ray Diffraction (XRD), Fourier-Transform Infrared (FTIR) Spectroscopy, Raman Spectroscopy, Scanning Electron Microscopy (SEM), and High-Resolution Transmission Electron Microscopy (TEM)—were combined with rigorous AC impedance spectroscopy, frequency dependence (Jonscher power law), DC polarization measurements, and thermal stability profiling. The 25 wt% B₂O₃ glassy composite achieved the highest room-temperature ionic conductivity of 1.4 x 10^-3 S/cm with a low activation energy barrier of 0.32 eV and a high lithium ion transference number (t_Li+ = 0.85). The 25 wt% TiO₂ and ZrO₂ oxide systems established high space-charge interfacial electric fields and impressive mechanical shear moduli exceeding 12 MPa, effectively suppressing metallic lithium dendrites. Solid-state coin cells (Li/75:25 Composite Electrolyte/LiFePO4) demonstrated an initial discharge capacity of 148 mAh/g at 0.1 C, maintaining >85% capacity over 500 continuous cycles at 0.5 C with Coulombic efficiency >99.7%. Symmetric solid-state supercapacitors provided a high specific capacitance of 215 F/g and an energy density of 32 Wh/kg at 1 kW/kg power density. These comprehensive findings confirm that binary 75:25 Li₂SO₄ composite solid electrolytes are outstanding candidates for safe, high-performance energy storage devices.