Synthesis and Application of PVDF Compatible LLZO in Composite Solid-State Electrolytes for Lithium-Ion Batteries

Date of Award

12-2025

Degree Name

Doctor of Philosophy

Department

Mechanical and Aerospace Engineering

First Advisor

Qingliu Wu, Ph.D.

Second Advisor

Muralidhar Ghantasala, Ph.D.

Third Advisor

Wenquan Lu, Ph.D.

Fourth Advisor

Zachary Asher, Ph.D.

Keywords

Composite film fabrication, interface stability, LLZO coating, LLZO-PVDF reactivity, scalable solid-state electrolytes, solid-state electrolytes

Abstract

This dissertation presents the development, characterization and electrochemical evaluation of a novel hybrid oxide-based solid-state electrolyte (SSE) film, designated as HOx-4f, designed to address key limitations in solid-state lithium-ion battery interfaces. The HOx-4f system integrates garnet type Li7La3Zr2O12 (LLZO) ceramic electrolyte within a polymeric binder matrix, aiming to balance mechanical flexibility, ionic conductivity and interfacial compatibility with both Li metal and composite cathodes. Synthesis efforts focus on tailoring the structure and morphology of PVDF based hybrid films incorporating surface-modified LLZO particles, specifically through a 5 wt% polyvinylidene fluoride (PVDF) coating, which demonstrates enhanced stability, dispersion, compatibility and electrochemical performance.

A comprehensive suite of materials characterization techniques, including FTIR, XRD, Raman spectroscopy, NMR, TGA/DSC, SEM, TEM and EDS mapping, elucidates the structural features, phase composition, interfacial morphology and thermal stability of the HOx-4f SSE films. Particular attention is given to comparing the effects of pristine versus PVDF coated LLZO on film uniformity, agglomerations and chemical interactions within the composite matrix. Electrochemical evaluations are conducted through symmetric Li|SSE|Li cells and full cell configurations using LiFePO4 (LFP) composite cathodes. Key performance metrics such as critical current density, impedance spectra and cycling stability are examined under both dry and minimal liquid electrolyte (LE) hybrid conditions.

The hybrid HOx-4f SSE demonstrates stable plating and stripping behavior at current densities up to 0.6 mA cm-2, with high voltage stability as high as 10V for the SSE films and >7V for the quasi-SSE films. In full cell studies, LFP cathodes prepared with PVDF coated LLZO (P64) outperform those using unmodified LLZO (P63), particularly under low LE conditions. Cyclic voltammetry reveals sharper redox peaks and improved Li⁺ kinetics in the P64+LE cells, while galvanostatic cycling at 0.2C over 30 cycles shows over 95% capacity retention and stable coulombic efficiency near 100%. In contrast, P63+LE cells display gradual capacity fade and coulombic efficiency fluctuations linked to poor interfacial contact and potential soft shorting.

Overall, this work demonstrates that interfacial engineering of ceramic fillers plays a critical role in neutralizing reactivity and optimizing composite SSEs. The PVDF coated LLZO framework within HOx-4f films enables improved percolation networks, ionic transport and long-term electrochemical reversibility, offering a viable pathway toward scalable, safer and more stable solid-state battery systems.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

12-1-2027

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