Boosted Li+ migration in LiPON electrolyte via introducing Ti-based bridge for solid-state thin film batteries

Abstract

Lithium phosphorous oxynitride (LiPON) has become a research hotspot in the application of all solid-state thin film batteries (TFBs). Meanwhile, the electrochemical stability and Li-ion conductivity of LiPON solid electrolyte films are the critical factors for TFBs with high energy density. In this work, we demonstrate the preparation of Ti-doped LiPON electrolyte (Ti–LiPON) with the enhanced stability and ionic conductivity via a multi-target co-sputtering method. The obtained Ti–LiPON electrolyte shows a larger electrochemical stability window (>5.5 V) and a higher ionic conductivity of 4.91✕10−6 S cm−1. Moreover, the solid-state LiCoO2/Ti–LiPON/Ni film battery (TFB) has been successfully assembled and exhibits a large specific capacity (77.08 mAh g−1 at 8 μA) and good cycle performance (67.44% of capacity maintained after 50 cycles). Meanwhile, the LED indicator can be able to light up by the LiCoO2/Ti–LiPON/Ni TFB and further confirm its great potential for practical applications. Based on the different d-orbital electronic structure of Ti, the local electron density of LiPON system obtains a great change. The existence of Ti can act as a network former in LiPON electrolyte and construct multiple Li+ transport paths with the different bridge bonding forms, further promoting the migration of Li+. Moreover, the introduced Ti can also weaken the electrostatic constraint between PO3N4− and Li+ and further provide a low Li+ migration barrier center.