Atomic-Scale Mechanisms of Li-Ion Transport Mediated by Li10GeP2S12 in Composite Solid Polyethylene Oxide Electrolytes

TL;DR

Addressing how LGPS nanoparticles mediate Li-ion transport in PEO-based composite polymer electrolytes, the paper integrates MD, experimental conductivity measurements, and DFT to map transport mechanisms across filler loadings. The study reports a volcano-like conductivity dependence on LGPS content up to $10 ext{ extperthousand}$, replicated by MD via Green-Kubo Onsager coefficients $L^{ij}$, and a second high-loading regime suggested by experiments and vacancy hopping with barriers as low as $0.37$–$0.50$ eV at the interface. DFT identifies vacancy-driven Li migration at the mPEO-TMS|LGPS interface, favored by sulfur-rich environments and hindered by Ge, indicating interfacial channels that enable low-energy transport distinct from bulk polymer or ceramic conduction. These findings provide design rules for optimizing filler loading and interfacial chemistry to maximize Li transport in solid composite polymer electrolytes for next-generation batteries.

Abstract

Polymer electrolytes incorporating Li$_{10}$GeP$_{2}$S$_{12}$ (LGPS) nanoparticles show promise for solid-state lithium batteries owing to their enhanced ionic conductivity, though the governing mechanisms remain unclear. We combine molecular dynamics (MD) simulations, experimental ionic conductivity measurements, and density functional theory (DFT) calculations to elucidate the effect of LGPS loading on polyethylene oxide (PEO) structure and Li-ion transport. MD and experimental results agree up to 10\% LGPS, showing a volcano-shaped conductivity trend driven by polymer segmental dynamics and interfacial effects. Beyond 10\%, experiments reveal additional conductivity enhancement unexplained by MD, suggesting a distinct transport regime. DFT calculations indicate that Li-ion migration at the PEO|LGPS interface proceeds via vacancy-mediated hopping, with low barriers favored by S-rich interfacial sites and hindered by Ge. These findings link interfacial chemistry and microstructure to Li-ion dynamics, offering guidelines for designing high-performance composite polymer electrolytes.

Figures (9)

• Figure 1: Visualization of the MD simulations of the composite polymer electrolyte (CPE) for different LGPS weight ratio (x%): (a) x=0%, (b) x=3.2% and (c) x=21%. Note that "Li$^{+}$ cluster" noted in the figures includes also TFSI$^{-}$ that are interacting with the Li$^{+}$ cations.
• Figure 2: Reaction of 3-[methoxy(polyethyleneoxy)$_{6-9}$ propyl] trimethoxysilane (mPEO-TMS) with Li$_{10}$GeP$_2$S$_{12}$ to form a mPEO-TMS|LGPS interface coupled together by a SiS$_3$ bond and some Li-O bonds from wrapping around the nanoparticle, while releasing 3 molecules of LiOCH$_3$. In the top reaction, the elements in bold are part of the LGPS particle.
• Figure 3: Ionic conductivity as a function of the LGPS weight ratio, with respect to the experimental composition presented in Table S2 and scaled for computational feasibility in Table 1, from MD simulations compared with experimental data (see Figure S1 for the experimental data shown in this plot as well as other data). Note that the result for 0 wt% is from Ref. kondori2023room and the 3.2% results differs slightly from that in Ref. kondori2023room due to uncertainties in measurements (see SI).
• Figure 4: (a) Diffusion coefficients of CPE components and (b) Li$^{+}$ transference number as a function of LGPS weight ratio from MD simulations.
• Figure 5: Schematic illustration of Li-ion diffusion and transport pathways in PEO/mPEO‑TMS–LGPS composite solid polymer electrolytes: (I) sparse LGPS network and (II) percolated LGPS-rich network.