Currently cation doping is common for improving ionic conductivity of metal oxide-based lithium-ion conductors. In this work, anions (nitrogen ions) have been doped to perovskite Li3xLa2/3?-?xTiO3 (LLTO) nanofibers by heat treatment in the ammonia-containing atmosphere, and substituted for oxygen anions partially in the perovskite structure. Density-functional theory (DFT) calculations reveal that nitrogen doping weakens the bonding of Li ions on the A sites in the perovskite ABO3 structure and allows for larger lattice distortion, reducing the activation energy for Li-ion hopping in both forward and backward jumping directions. Experimental results have also confirmed that nitrogen doping has improved ionic conductivity of LLTO. Nitrogen-doped LLTO nanofibers have been incorporated with a poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) polymer to form a solid-state composite electrolyte, which exhibits ionic conductivity of 3.8 × 10-4 S?cm-1 at room temperature and an electrochemical stability window of up to 4.9 V vs. Li/Li+. The all-solid-state Li metal|composite electrolyte|LiFePO4 lithium batteries, which employ nitrogen-doped LLTO nanofibers, show better rate capability and cycling stability at room temperature than the counterparts with pristine LLTO nanofibers.
Published: December 3, 2021
Citation
Yang H., K. Tay, Y. Xu, B. Rajbanshi, S. Kasani, J. Bright, and J. Boryczka, et al. 2021.Nitrogen-Doped Lithium Lanthanum Titanate Nanofiber-Polymer Composite Electrolytes for All-Solid-State Lithium Batteries.Nature Communications 168, no. 11:Art. No. 110507.PNNL-SA-162349.doi:10.1149/1945-7111/ac30ad