Effect of Pore Connectivity on Li Dendrite Propagation within LLZO Electrolytes Observed with Synchrotron X‑ray Tomography

Li₇La₃Zr₂O₁₂ (LLZO) is a garnet-type material that demonstrates promising characteristics for all-solid-state battery applications due to its high Li-ion conductivity and its compatibility with Li metal. The primary limitation of LLZO is the propensity for short-circuiting at low current densities. Microstructure features such as grain boundaries, pore character, and density all contribute to this shorting phenomenon. Toward the goal of understanding processing-structure relationships for practical design of solid electrolytes, the present study tracks structural transformations in solid electrolytes processed at three different temperatures (1050, 1100, and 1150 °C) using synchrotron X-ray tomography. A subvolume of 300 μm³ captures the heterogeneity of the solid electrolyte microstructure while minimizing the computational intensity associated with 3D reconstructions. While the porosity decreases with increasing temperature, the underlying connectivity of the pore region increases. Solid electrolytes with interconnected pores short circuit at lower critical current densities than samples with less connected pores

Scalable Manufacturing of Hybrid Solid Electrolytes with Interface Control

Hybrid solid electrolytes are promising alternatives for high energy density metallic lithium batteries. Scalable manufacturing of multi-material electrolytes with tailored transport pathways can provide an avenue toward controlling Li stripping and deposition mechanisms in all-solid-state devices. A novel roll-to-roll compatible coextrusion device is demonstrated to investigate mesostructural control during manufacturing. Solid electrolytes with 25 and 75 wt % PEO-LLZO compositions are investigated. The coextrusion head is demonstrated to effectively process multimaterial films with strict compositional gradients in a single pass. An average manufacturing variability of 5.75 ± 1.2 μm is observed in the thickness across all the electrolytes manufactured. Coextruded membranes with 1 mm stripes show the highest room temperature conductivity of 8.8 × 10–6 S cm–1 compared to the conductivity of single-material films (25 wt %, 1.2 × 10–6 S cm–1; 75 wt %, 1.8 × 10–6 S cm–1). Distribution of relaxation times and effective mean field theory calculations suggest that the interface generated between the two materials possesses high ion-conducting properties. Computational simulations are used to further substantiate the influence of macroscale interfaces on ion transport

Improving Contact Impedance via Electrochemical Pulses Applied to Lithium–Solid Electrolyte Interface in Solid-State Batteries

Stabilizing interfaces in solid-state batteries (SSBs) is crucial for development of high energy density batteries. In this work, we report a facile electrochemical protocol to improve the interfacial impedance and contact at the interface of Li | Li6.25Al0.25La3Zr2O12 (LALZO). Application of short duration, high-voltage pulses to poorly formed interfaces leads to lower contact impedance. It is found that the local high current density that results from these pulses at the vicinity of the interfacial pores can lead to a better contact between Li and LALZO because of local Joule heating, as supported by theoretical simulations. The pulse technique, which has also been applied to a Li | Li6.4La3Zr1.4Ta0.6O12 (LLZTO) | LiNi0.6Mn0.2Co0.2O2 (NMC622) cell, results in remarkable reduction of the charge-transfer resistance. Ex situ characterizations, which include X-ray photoelectron spectroscopy and scanning electron microscopy techniques, reveal that there is no detrimental effects of the pulse on cathode and solid electrolyte bulks and interfaces. This electrochemical pulse technique sheds light on a facile, nondestructive method that has the potential to significantly improve the interfacial contacts in a solid-state battery configuration