Enhanced ionic conductivity in a novel composite electrolyte based on Gd-doped SnO2 nanotubes for ultra-long-life all-solid-state lithium metal batteries

All-solid-state electrolytes are exceedingly attractive because of the outstanding inherent safety and energy density compared to liquid electrolytes. Whereas, it is still formidable to simultaneously design solid electrolytes with favorable electrode/electrolyte interface compatibility and high ionic conductivity in a simple and scalable manner. Hence, the oxygen-vacancy-rich Gd-doped SnO2 nanotubes (GDS NTs) are innovatively prepared and applied to the electrolyte of all-solid-state lithium metal batteries for the first time. The addition of GDS NTs can validly construct long-range continuous ion transport networks in the poly(ethylene oxide) (PEO)-based system and greatly improve the mechanical properties of the electrolyte. Compared to the PEO-based electrolyte, the composite electrolyte displays a higher lithium ion conductivity of 2.41 × 10–4 S cm−1 at 30 ℃, a higher lithium ion transference number up to 0.62 and a wider electrochemical window of 5 V at 50 ℃. In addition, the composite electrolyte manifests outstanding compatibility with high-voltage LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode, LiFePO4 cathode and lithium metal anode. The assembled Li/Li symmetric battery exhibits stable Li plating/stripping cycling performance, which can cycle steadily for 1500 h at a capacity of 0.3 mA h cm−2. And Li/LiFePO4 battery still maintains a high capacity of 131.54 mA h g−1 at 0.5C after 800 cycles, which has a superior capacity retention rate of 93.2%. The obtained novel composite electrolyte has promising application prospects in the field of all-solid-state lithium metal cells.