Layered Polymer Stacking for Stable Interfaces and Dendrite Growth Inhibition in All-Solid-State Lithium Batteries

To improve the ionic conductivity and cycling stability of solid-state lithium batteries based on poly(ethylene oxide) (PEO) electrolytes, we developed a sandwich-structured composite polymer electrolyte (sandwich-CPE) PEO-TiN/PEO-LiYF 4 /PEO-TiN. The sandwich-CPE delivers a high ionic conductivity of 1.7 × 10 –4 S cm –1 at 30 °C and a wide potential window of 0 to 5.0 V (vs Li/Li + ). Adding PEO-TiN leads to the formation of Li 3 N between Li and sandwich-CPE during cycling, which effectively reduces the level of Li dendrite formation. Additionally, PEO-TiN acts as a sacrificial layer to stop the entry of Li dendrites into the interlayer PEO-LiYF 4 . Using the sandwich-CPE, LiFePO 4 retains a reversible capacity of 113.8 mA h g –1 at 30 °C after 300 cycles under 0.5 C. For high-voltage cells, LiNi 0.5 Co 0.2 Mn 0.3 O 2 retains a capacity retention of 71.4% at 45 °C after 300 cycles under 0.2 C among 3.0–4.3 V, while Li 3 V 2 (PO 4 ) 3 delivers an initial discharge capacity of 108.1 mA h g –1 at 60 °C and retains 81.6% after 500 cycles under 1 C among 2.8–4.4 V. These results demonstrate the strong electrochemical compatibility of the sandwich-CPE, enabling high reversible capacity and good cycling stability for solid-state Li batteries with different cathodes at different temperatures and current rates.