Interfacial Barrier of Ion Transport in Poly(ethylene oxide)–Li₇La₃Zr₂O₁₂ Composite Electrolytes Illustrated by ⁶Li-Tracer Nuclear Magnetic Resonance Spectroscopy

Abstract

Fundamental understanding of the lithium-ion transport mechanism in polymer–inorganic composite electrolyte is crucially important for the rational design of composite electrolytes for solid-state batteries. In this work, the Li+ ion transport pathway in a model composite electrolyte of PEO containing sparsely dispersed LLZO (PEO–LLZO) was studied by an advanced characterization technique, i.e., 6Li-tracer NMR spectroscopy. By analyzing the 6Li distribution within the PEO–LLZO composite at the end of the discharge of an electrochemical cell of 6Li | PEO–LLZO | stainless steel with a fixed capacity (less than the total amount of the Li+ in the composite) at various current densities, it is found that the interfacial barrier between LLZO and PEO could cause a reduced Li+ flux through LLZO, particularly at high current densities, and therefore plays a critical role in determining the Li+ transport pathway in the composite electrolyte. This work provides an intuitive picture of Li+ ion transport in a polymer–inorganic composite electrolyte that is helpful to optimize and design better composite electrolytes.

Ion transport in composite polymer electrolytes

“…In addition, the interfacial barrier formed between active fillers and the polymer matrix affects the transport pathway of lithium ions as well. He et al 72 found that the increased current density caused a reduced lithium ion flux through the LLZO particles in the PEO-LiTFSI-LLZO (5 wt%) composite, because higher current densities enhanced the ion transport barrier between LLZO and the polymer matrix, and then confined the transfer of lithium ions from the polymer phase to LLZO. As active fillers have higher ionic conductivity than polymer matrices, there should be a great improvement in the ionic conductivity with an increase in the filler content, and the ionic conductivity is expected to be even close to that of the active fillers, when the content of active fillers is high enough.…”

“…In addition, the interfacial barrier formed between active fillers and the polymer matrix affects the transport pathway of lithium ions as well. He et al 72 found that the increased current density caused a reduced lithium ion flux through the LLZO particles in the PEO–LiTFSI–LLZO (5 wt%) composite, because higher current densities enhanced the ion transport barrier between LLZO and the polymer matrix, and then confined the transfer of lithium ions from the polymer phase to LLZO.…”

Rational Design of LLZO/Polymer Solid Electrolytes for Solid‐State Batteries

“…In conclusion, Li-ion transport channels gradually transition and modified related to the content of LLZO. Similarly, He's team [108] utilized the modified 6 Li-tracer NMR method to study the composite electrolyte's Liion transport mechanism qualitatively and quantitatively by measuring the exchange of a single equivalent 6 Li isotope at various current densities. It was displayed that the 6 Li ratio of LLZO was improved in 6 Li NMR spectra at 0.025 C; however, at the current densities were 0.1 C and 0.3 C, the 6 Li content was consistent with the original, demonstrating that the transport channel in LLZO has priority only at low current density.…”

Disentangling the Li‐Ion transport and Boundary Phase Transition Processes in Li10GeP2S12 Electrolyte by In‐Operando High‐Pressure and High‐Resolution NMR Spectroscopy

“…[19,20] Recently, 6 Litracer NMR spectroscopy was applied and demonstrated great superiority in tracking the Li-ion transport pathways in polymerceramic composite electrolytes. [21][22][23][24] It is disclosed that manipulating the transmission barrier (space charge layers) between two phases and the local electric field is highly effective for highefficiency Li-ion transport. The effect of space-charge layers on the ionic transport over the interface can also be exposed using NMR dynamics and two-dimensional NMR spectroscopy.…”