(696g) Advancing Lithium-Ion Batteries: Gel Polymer Electrolytes for Safety and Scalability

The growing demand for lithium-ion batteries is fueled by the global transition to electric vehicles and renewable energy storage which necessitates the development of safer and more scalable electrolytes. Conventional liquid electrolytes, widely used in lithium-ion batteries, pose significant safety risks due to their flammability, instability, and environmental concerns associated with fluorinated components. To address these challenges, this research focuses on the development of aqueous gel electrolytes that utilize cost-effective, nonfluorinated materials sourced from domestic supply chains. This work aims to mitigate the economic and environmental concerns linked to traditional electrolyte formulations by replacing fluorinated salts such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with sustainable alternatives.

Aqueous gel polymer electrolytes, synthesized from readily available materials, exhibit electrochemical properties comparable to their fluorinated counterparts while offering additional benefits in terms of safety and scalability. Electrochemical impedance spectroscopy (EIS) measurements demonstrate high ionic conductivity, exceeding 1 mS/cm, making them a viable alternative to conventional liquid electrolytes. Furthermore, these electrolytes exhibit a broad electrochemical stability window that enables their integration with various cathode materials. However, one of the primary challenges in aqueous electrolyte systems is the reduction limit, or anode match, which must be addressed to enable compatibility with lithium metal anodes.

To overcome this limitation, a two-gel electrolyte system is introduced. A protective organic electrolyte layer is incorporated into the battery design to facilitate the formation of a robust solid electrolyte interphase (SEI) on the lithium anode. The protective layer is essential for preventing side reactions, minimizing lithium dendrite formation, and improving long-term cycling stability. The composition of this organic gel electrolyte is optimized to reduce the concentration of fluorinated components while maintaining its ability to stabilize the anode surface and enhance electrochemical performance. For both gel polymer electrolytes, the mechanical properties are investigated to ensure structural integrity during battery operation and building. Dynamic mechanical analysis (DMA) and rheological testing provide insights into the viscoelastic behavior of the gels, with an emphasis on optimizing crosslinking density to achieve an ideal balance between mechanical strength and ionic conductivity. Proper electrolyte formulation is crucial for preventing structural degradation and maintaining high performance over extended cycling periods.

To ensure accurate electrochemical stability assessments, a polymer-coated, micro-sized lithiated gold wire (Au₃Li alloy) is used as a reference electrode. Traditional reference electrodes can introduce inaccuracies due to their incompatibility with aqueous and solid electrolytes. In this study, the lithiated gold wire is cured in-situ in the gel electrolyte. This innovative approach allows for precise impedance and reference potential measurements during cyclic voltammetry (CV) experiments. By improving the accuracy of electrochemical measurements, this technique provides valuable insights into the stability and performance of the gel electrolytes under realistic operating conditions.

In addition to electrolyte development, this research also explores composite cathode fabrication using the same aqueous nonfluorinated materials. The elimination of toxic solvents and fluorinated polymer binders from the cathode formulation enhances sustainability and improves ionic pathways within the cathode. This approach effectively reduces resistance at the cathode-electrolyte interface leading to improvement of overall cell performance. This integrated strategy, which simultaneously advances electrolyte and electrode technology, contributes to the development of an economically viable and scalable lithium-ion battery system.

Full-cell testing is currently underway to evaluate the long-term performance and efficiency of the developed electrolyte system. Charge-transfer resistance, capacity retention, and overall cell stability are key parameters being monitored to assess the viability of this approach for next-generation lithium-ion batteries. Preliminary results indicate promising performance metrics, suggesting that this electrolyte system could play a crucial role in advancing the safety and scalability of lithium-ion battery technology.