Poly(ethylene glycol) brush on Li6.4La3Zr1.4Ta0.6O12 towards intimate interfacial compatibility in composite polymer electrolyte for flexible all-solid-state lithium metal batteries

Polyethylene oxide (PEO)/Li6.4La3Zr1.4Ta0.6O12 (LLZTO) composite solid electrolyte is considered as a promising electrolyte for lithium batteries. However, LLZTO nanoparticles tend to agglomerate in PEO/LLZTO composite polymer electrolyte due to interfacial incompatibility between PEO and LLZTO nanoparticles, which leads to low ionic conductivity, poor interface stability with the electrode, and inferior batteries cycling stability. In order to enhance interfacial compatibility, herein, LLZTO nanoparticles are modified through firstly surface-functionalizing by dopamine coating and then grafting poly (ethylene glycol) (PEG) brush on it via amino and epoxy reaction. As a consequence, the ionic conductivity of LLZTO/PEO composite polymer electrolyte filled with 2 wt% modified LLZTO increases up to 1.1×10−4 S cm−1, which is about twice and 20 times in comparison with LLZTO/PEO filled with 2 wt% unmodified LLZTO and PEO electrolytes, respectively. Moreover, high oxidation potential of around 4.8 V and ionic transference number of 0.34 as well as good interface stability with lithium anode are also achieved. Thus, LiFePO4||Li all-solid-state lithium metal batteries based on LLZTO/PEO composite polymer electrolyte filled with 2 wt% modified LLZTO exhibit excellent cyclic stability of 152.3 mAh g−1 with capacity retention of 90.35% at 0.5 C after 500 cycles under 60 °C.