A Solid Electrolyte Based on Sodium-Doped Li_4-xNa_xTi₅O₁₂ with PVDF for Solid State Lithium Metal Battery

Solid-state batteries (SSBs) present a potential pathway for advancing next-generation lithium batteries, characterized by exceptional energy density and enhanced safety performance. Solid-state electrolytes have been extensively researched, yet an affordable option with outstanding electrochemical performance is still lacking. In this work, Li_4-xNa_xTi₅O₁₂ (LNTO)-based composite solid electrolytes (CSEs) were developed to enhance the interface stability and electronic insulation. The CSE is composed of Li_3.88Na_0.12Ti₅O₁₂ (LNTO3) and poly (vinylidene fluoride) (PVDF) with a proportion of 20 wt % exhibited high ionic conductivity (4.49×10⁻⁴ S cm⁻¹ at a temperature value equal to 35 °C), high ionic transfer number (equal to 0.72), low activation energy (equal to 0.192 eV), and favorable compatibility with the Li metal anode. The Li|LNTO3|LiFePO₄ cell, tested at a 0.5 C current density, demonstrated 154.5 mAh g⁻¹ of outstanding cycling stability for 200 cycles, capacity retention of 97.6 % along with a Coulombic efficiency of over 99 %, as well as a significant average specific capacity of 127.8 mAh g⁻¹ over 400 cycles at 5 C. The Li|LNTO3|LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cell could also operate over 100 cycles at 1 C. This study offers an effective method for preparing commercial CSEs for SSBs.