Fast Li + Conduction Mechanism and Interfacial Chemistry of a NASICON/Polymer Composite Electrolyte

The unclear Li + local environment and Li + conduction mechanism in solid polymer electrolytes, especially in a ceramic/polymer composite electrolyte, hinder the design and development of a new composite electrolyte. Moreover, both the low room-temperature Li + conductivity and large interfacial resistance with a metallic lithium anode of a polymer membrane limit its application below a relatively high temperature. Here we have identified the Li + distribution and Li + transport mechanism in a composite polymer electrolyte by investigating a new solid poly(ethylene oxide) (PEO)-based NASICON–LiZr 2 (PO 4 ) 3 composite with 7 Li relaxation time and 6 Li → 7 Li trace-exchange NMR measurements. The Li + population of the two local environments in the composite electrolytes depends on the Li-salt concentration and the amount of ceramic filler. A composite electrolyte with a [EO]/[Li + ] ratio n = 10 and 25 wt % LZP filler has a high Li + conductivity of 1.2 × 10 –4 S cm –1 at 30 °C and a low activation energy owing to the additional Li + in the mobile A2 environment. Moreover, an in situ formed solid electrolyte interphase layer from the reaction between LiZr 2 (PO 4 ) 3 and a metallic lithium anode stabilized the Li/composite-electrolyte interface and reduced the interfacial resistance, which provided a symmetric Li/Li cell and all-solid-state Li/LiFePO 4 and Li/LiNi 0.8 Co 0.1 Mn 0.1 O 2 cells a good cycling performance at 40 °C.