Domain Size Modulation of Clay–Nanocellulose Composites for Enhanced Na-Ion Transport

Abstract

Rechargeable batteries using alkali metal anodes garner significant interest as a transformative energy storage technology for grid and mobile applications. However, scanty resources of lithium (Li) have pushed the research focus toward the realm of abundant alkali and alkaline earth metals such as sodium (Na), potassium (K), magnesium (Mg), and aluminum (Al). Moreover, safety issues related to inflammability, dendritic growth, limited cycle life, and capacity fading in liquid electrolytes seriously hamper their extensive deployment. Here, we propose a flexible, solid-polymer-composite electrolyte thin film (thickness ≈ 20–25 μm) with enhanced sodium-ion transport characteristics based on cellulose nanocrystals (CNC) and laponite (Lap)/montmorillonite (MMT) clay, which can be mass-produced at room temperature. This composite electrolyte has important flame-retardant and mechanical properties coupled with excellent Na-ion conductivity. From a critical analysis of the preliminary results using various compositions and optimized architecture of the composite electrolyte, an ionic conductivity of the order of 10^–4 S cm^–1 at 50 °C is obtained with an enhanced stability window. In parallel, a good electrochemical response is also seen, indicating potential applications in all-solid-state batteries. Molecular dynamics simulations of randomly packed CNC and MMT composites provide ionic diffusivity using the Einstein equation, and the estimated conductivity is qualitatively aligned well with the experimental results. Overall, these nanocomposite films open game-changing perspectives for fabricating flexible power sources from abundant resources.