Designing Isocyanate-Containing Elastomeric Electrolytes for Antioxidative Interphases in 4.7 V Solid-State Lithium Metal Batteries

Abstract

To facilitate the use of solid polymer electrolytes (SPEs) with high-nickel (Ni) cathodes in high-voltage lithium (Li) metal batteries (LMBs), it is crucial to address the challenges of low oxidative stability and the formation of vulnerable interphases. In this study, isocyanate groups (−N═C═O) are incorporated to develop an SPE with a bi-continuous structure, consisting of elastomeric and plastic crystal phases. This rationally designed SPE exhibits high ionic conductivity (0.9 × 10⁻³ S cm⁻¹ at 25 °C), excellent elasticity (elongation at break of 330%), and enhanced oxidative stability (over 4.8 V vs. Li/Li⁺). A full cell, incorporating this SPE with a thin Li foil of 40 µm, and a high-Ni LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode operating at 4.7 V vs. Li/Li⁺, demonstrates excellent cyclability, retaining 70% of its initial capacity after 200 cycles under a high C-rate of 1C at 25 °C. The extended cycling of isocyanate-containing SPE at 4.7 V vs. Li/Li⁺ is attributed to robust and compact inorganic-rich interphases enabled by antioxidative −N−C═O components, as well as uniform Li deposition attributed to the bi-continuous structured SPE. This study suggests that the isocyanate-containing SPE system is a promising candidate for high-voltage solid-state LMBs by constructing stable interphases.