A highly efficient composite separator embedded with colloidal lanthanum oxide nanocrystals for high-temperature lithium-ion batteries

Summary Highly efficient microporous composite separator based on polyvinylidene fluoride-hexafluoro propylene (PVDF-HFP) and colloidal La 2 O 3 (C-La 2 O 3 ) is prepared for high-temperature lithium-ion batteries (LIBs) through facile slide coating technique. The presence of colloidal La 2 O 3 nanocrystals in PVDF-HFP significantly enhances the mechano-thermal stability of separator due to the robust microporous structure. Moreover, the C-La 2 O 3 nanocrystals also help in improving the conductivity of lithium ions by incorporating additional Li + conduction pathways due to the Lewis acid-base interaction between La atom and PVDF-HFP chain. The PVDF-HFP/C-La 2 O 3 separator owns minimal shrinkage of 6.2% after thermal annealing for 1 hour at 150°C. The as-developed separator exhibits high wettability and electrolyte uptake (238%) due to the robust microporous structure and low crystallinity, which leads towards high ionic conductivity (0.75 × 10 −3 S cm −1 ). The cells developed with PVDF-HFP/C-La 2 O 3 separator deliver the discharge capacity of 158.2 mAh g −1 at room temperature, 163 mAh g −1 on direct testing at 80°C, 130.9 mAh g −1 of batteries assembled with annealed separators at 150°C for 5 hours, and 140.3 mAh g −1 of annealed batteries at 150°C for 5 hours at 0.5 C after 100 cycles with a capacity retention of ≈98%. The PVDF-HFP/C-La 2 O 3 separator is a promising substitute of commercial separators with remarkable performances for high-temperature LIBs.