Strong and Flexible PEO/Pvdf Polymer Composite Electrolyte for All Li Metal Solid-State Battery
Authors: Bera Bapi , Aaron Douglas S , Mench Matthew M 
Published: December 2024

The state-of-the-art Li-ion battery has energy density plateauing at ~300 Wh/kg [1]. Replacing the graphite-based anode with Li metal is one promising pathway to increase energy density. However, a lithium metal anode is prone to non-uniform plating/striping that leads to capacity decay and dendrite formation. Solid-state batteries (SSBs) hold great promise for next-generation energy storage systems due to their potential to address safety concerns, provide energy density, and enable the use of high-energy electrode materials such as lithium (Li) metal. Additionally, SSBs exhibit greater mechanical stability and can limit dendritic growth [2]. Furthermore, solid electrolytes show much higher thermal stability, are non-toxic, and have high energy density.

Among the various types of solid-state electrolytes, composite polymer electrolytes (CPEs) have emerged as a promising option owing to their excellent ionic conductivity, mechanical flexibility, and compatibility with Li metal electrodes. Polyethylene oxide (PEO) polymer electrolyte has very good interfacial contact between electrode and very flexible in nature [3]. But PEO by itself is unstable. A PEO composite with solid ceramic offers the potential for better stability with high conductivity as well as improved physical properties.

Our research focuses on elucidating key parameters that affect the electrochemical behavior and stability of these systems, aiming to enhance their overall performance and longevity. One of the primary factors under investigation is the composition and morphology of the composite polymer electrolyte. We explored PEO polymer and LLZTO ceramic fillers to optimize the electrolyte's mechanical strength, Li-ion conductivity, and interfacial stability with Li metal electrodes [2]. Through systematic characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and impedance spectroscopy, we gain insights into the microstructure and ion transport properties of the CPE.

The combination of PEO and Polyvinylidene fluoride (PVdF) polymer creates a remarkably robust and flexible polymer electrolyte, renowned for its exceptional mechanical and electrochemical stability. Figure 1 (a) shows the cycling profile of PEO/PVdF electrolyte at different C rates with LFP cathode and Li metal as anode. Compared to PEO membrane, the composite exhibits higher ohmic polarization. However, this composite polymer electrolyte demonstrates better stability and high-rate capability than a pure PEO membrane. At 1-C rate charging and discharging condition cell shows 99% columbic efficiency and good capacity retention. In Figure 1(b) and (c) show the SEM image of PVdF and PEO composite membrane respectively. Which shows PEO completely covers the PVdF network and helps better contact with solid electrode.

Reference:

Bapi Bera, Anirban Roy, Douglas Aaron, and Matthew M Mench, “Understanding the Transport Phenomena in Solid State Battery (SSB)”, Electrochemical Society Meeting Abstracts-241, 2022, 1, 45-45.

Yanda Fu et al., “Surface Defects Reinforced Polymer-Ceramic Interfacial Anchoring for High-Rate Flexible Solid-State Batteries”, Adv. Funct. Mater. 2023, 33, 2210845.

Sahore, Z. Du, X. C. Chen, W. B. Hawley, A. S. Westover, and N. J. Dudney, Practical considerations for testing polymer electrolytes for high-energy solid-state batteries, ACS Energy Lett. 2021, 6, 2240-2247.

Figure 1