Gallium doped NASICON type LiTi2(PO4)3 thin-film grown on graphite anode as solid electrolyte for all solid state lithium batteries

Abstract

Gallium-doped LiTi2(PO4)3 (LGTP) film has been successfully in-situ fabricated on graphite substrate by hydrothermal method. The effects of Ga addition amount on LGTP crystal structure, as well as its ionic conductivity have been investigated. LGTP exhibits improved conductivity compared with LTP, and this improvement could be attributed to the formation of denser layer, higher lithium ion concentration in NASICON structure, and probable establishment of zig-zag pathways for faster lithium ion conduction. The highest total conductivity (2.1 × 10−5 S cm−1) and lowest activation energy (0.29 eV) are achieved by LGTP-Ga-20mM with Ga addition of 20 mM. Interestingly, after annealing treatment to LGTP-Ga-20mM at 800 °C, it exhibits total conductivity of 2.3 × 10−4 S cm−1, which is applicable for the all solid state lithium batteries (ASSLBs). The cell Li/LGTP-Ga-20mM/graphite exhibited initial charge capacity of 339.2 mAh g−1 and discharge capacity of 272.5 mAh g−1, with coulombic efficiency of 80.3%. After 30 cycles at 0.5C, it still has capacity retention of 85.2%. So it proves the feasibility of application of LGTP & graphite in ASSLBs. Moreover, it has been found the plasma surface treatment is favorable for the full coverage of the LGTP layer on graphite and formation of dense film layer.