Electrochemical performance enhancement mechanism of CTMS modulating on LLZTO/PEO composite solid electrolyte interface

Abstract

With the rapid development of solid state battery technology, composite electrolytes, as a key material for enhancing battery performance, face poor interfacial compatibility issues between inorganic fillers and the polymer matrix, which becomes a bottleneck restricting the improvement of electrochemical properties of the electrolyte. To address the issues of low ionic transport efficiency and the growth of lithium dendrites, which are triggered by the poor interfacial compatibility, this paper introduces the silane coupling agent (3-chloropropyl) trimethoxysilane (CTMS) into the PEO-LLZTO composite solid electrolytes to bridge the inorganic filler and polymer matrix through an in-situ coupling reaction, thereby enhancing the performance of the composite electrolyte. Its ionic conductivity is 1.84 × 10⁻³ S/cm at 60°C, and the stability to lithium anode is improved, with a polarization voltage of only 0.017 V and ultra-long lithium symmetrical battery constant current cycle exceeding 1670 h. The assembled full battery exhibited excellent rate performance and cycle stability at 60°C under 0.2 C, its specific capacity remains 138.52 mAh/g after 135 cycles. The mechanism of CTMS enhancing electrolyte properties was investigated by density functional theory (DFT). The adsorption energy, differential charge density, and ELF are calculated to analyze the interaction between the electrolyte components. DFT calculation results suggest that O-Si-O bonds are readily formed at the LLZTO/PEO interface upon the addition of CTMS. More importantly, CTMS modifies the charge distribution of the space charge layer at this interface, effectively facilitating the migration of lithium ions, thereby optimizing the ionic transport properties at the interface. Both experimental and DFT results indicate that CTMS forms a strong chemical bond between the inorganic and polymer segments, which creates a rapid transport channel for lithium ions and reduces the migration of the lithium salt anion group, thereby improving the electrochemical performance of the electrolyte.