The interface modification with polyethyleneimine enhances both ionic conductivity and interfacial compatibility of composite solid electrolyte

The composite solid electrolyte (CSE), polyethylene oxide (PEO)-Li _6.4La ₃Zr _1.4Ta _0.6O ₁₂ (LLZTO), is deemed a promising candidate for all-solid-state batteries. Nevertheless, due to the poor interfacial compatibility between LLZTO nanoparticles and PEO, achieving a homogeneous dispersion of LLZTO nanoparticles within PEO is not readily attainable. The aggregation of LLZTO within PEO leads to a decline in the ionic conductivity of the CSE and poor interface stability with the electrode, ultimately resulting in deteriorated battery cyclic performance. In this work, the interface between LLZTO and PEO is designed and comprehensively investigated. Initially, dopamine self-polymerization is employed to form a uniform coating layer on the surface of LLZTO nanoparticles. Subsequently, by utilizing the amino groups present in polyethyleneimine (PEI), which can react with the phenolic hydroxyl groups of dopamine and the ether linkages in PEO, PEI serves as a bridging agent, enhancing the interfacial compatibility between LLZTO and PEO. Here it is shown that, the ionic conductivity of the LLZTO-PEO CSE containing 40 wt% modified LLZTO increases from 6.14✕10 ⁻⁵ S cm ⁻¹ to 1.89✕10 ⁻⁴ S cm ⁻¹. Furthermore, this CSE exhibits improved thermal stability, an enlarged electrochemical window of 4.8 V, a lithium-ion transference number of 0.45, and excellent interface stability with the lithium anode. The assembled LiFePO ₄ | 40 wt% LLZTO@PDA@PEI-PEO CSE | Li all-solid-state battery demonstrates an initial discharge specific capacity of 151.8 mA h g ⁻¹ at 0.2 C, with a capacity retention of 85.8% after 200 cycles. This work provides a novel strategy for interface-modified polymer- inorganic composite solid electrolytes, which will advance the development of high-energy-density all-solid-state lithium batteries.