Enhanced Lithium-Ion Pathway in Gel-Polymer Electrolytes through Nanoclay-Organic Composite Design Strategy
Authors: Choi Younggyun , Park Jong Hyeok , Cho Seungho , Kim Jong Kyoung 
Published: December 2024

The relentless pursuit of high energy density stands as a critical objective in the continuous evolution of reliable and sustainable clean energy technologies. Despite notable progress in battery technology, conventional lithium-ion batteries (LIBs), predominantly utilizing graphite anodes, confront persistent challenges in meeting the rigorous standards necessary for practical applications, such as prolonged energy density for electric vehicles. In response to this limitation, researchers are exploring alternative approaches to significantly augment the energy density of LIBs. A particularly promising avenue of investigation involves the adoption of lithium metal anodes. Lithium anode offers a substantially higher theoretical specific capacity compared to graphite, rendering it an appealing candidate for enhancing overall battery energy density.

However, the incorporation of lithium metal anodes presents its own array of challenges, particularly concerning the stability of the electrolyte-electrode interface. Liquid electrolytes, although prevalent in LIBs, are susceptible to issues such as dendrite formation, jeopardizing battery safety and longevity. Among solid-state electrolytes, polymer electrolytes have emerged as a notably promising option. Specifically, gel polymer electrolytes (GPEs) have attracted considerable attention due to their distinctive blend of properties. Unlike liquid electrolytes, GPEs provide enhanced physical stability, adaptable geometry, favorable wettability, and non-flammability, inherently enhancing safety and applicability across various domains. Furthermore, GPEs exhibit flexibility and adequate ionic conductivity, facilitating lithium ion movement within the battery while minimizing internal resistance. This compatibility with electrodes further promotes efficient charge transfer and overall battery performance.

Despite the advantages of GPEs, several challenges persist. One limitation lies in their low mechanical strength, hindering the suppression of lithium dendrites and potentially compromising battery safety. Achieving ion conductivity levels comparable to liquid electrolytes necessitates ongoing research into polymer material design. In this context, our study introduces research focused on synthesizing ion-conductive polymers to construct ion-conducting channels within GPEs, thereby optimizing their composition. This refinement enhances electrolyte properties and enables swift and uniform lithium ion movement, leading to notable enhancements in cell performance.

Saponite, a two-dimensional (2D) clay, comprises a brucite-like structure within two Si-O tetrahedral structures. Saponite bears a negative surface charge owing to the substitution of trivalent ions in the tetrahedral structure, with interlayer cations intercalated for charge compensation. However, natural saponite's inherent hydrophilicity poses challenges in applications requiring organic solvents. Previous studies have demonstrated the conversion of hydrophilic clays like saponite into organophilic clays using typical cationic surfactants such as cetyltrimethylammonium bromide (CTAB). However, excessive use of cationic surfactants may inhibit the unique properties of the clay, necessitating meticulous synthetic control between clay and organic components.

Our objective is to develop a composite additive material leveraging cation exchange to intercalate organic compounds into the saponite interlayer. Through this approach, we aim to enhance not only the mechanical strength of GPEs but also their electrochemical properties, including lithium-ion transport. By controlling the interlayer of saponite material with CTAB organic molecules and adjusting the d-spacing to optimize lithium mobility, we have crafted a structure capable of uniform and rapid ion transport. This precision in interlayer control has enabled the establishment of pathways for lithium ions, resulting in elevated lithium ion transport. Furthermore, we have confirmed the role of CTA+ in effectively trapping anions in appropriate proportions. These findings elucidate the maximized cell performance achieved with minimal additive materials.