Starch-based polymer electrolytes: A sustainable strategy for advanced rechargeable lithium batteries

Starch-based polymer electrolytes (Sb-PEs) have emerged as a promising alternative for the next generation of solid-state batteries. While the renewable origin, low cost, and biodegradability of the native starch host matrix make it an attractive option for safer energy storage, there are still critical challenges regarding the environmental and processing trade-offs associated with formulated multicomponent electrolytes. Furthermore, the high crystallinity and limited ionic conductivity (σ) of native starch hinder its direct application. This review critically examines recent advancements in the design, processing, and optimisation of Sb-PEs for use in rechargeable lithium batteries. Key aspects such as σ and the correlation between electrolyte structural characteristics and ion transport are discussed, along with major modification strategies including plasticisation, chemical derivatisation, crosslinking, polymer blending, and solid nanofiller incorporation. These approaches have been shown to reduce crystallinity and produce high σ (10^-4-10^-3 S cm^-1 at room temperature), with the highest values generally achieved in gel polymer electrolytes or highly plasticised systems. Moreover, an extended electrochemical stability window (ESW) of ~4.2 V and good chemical and electrochemical stability against Li metal have been demonstrated. This review provides a comprehensive framework for the rational development of Sb-PEs, emphasising their potential to enable low-impact energy storage technologies.