Polymeric Anchor-Driven Multilinked Graphite Electrode for High-Performance Durable Anion Storage

A booming market for electric vehicle and stationary energy storage systems has contributed to explosive research efforts to realize impeccable rechargeable batteries. Lithium-ion batteries (LIBs) with high energy density and long lifespan have led the new renaissance of the rechargeable battery market for the past few decades, but their limited theoretical energy density and expensive/finite resources (e.g., lithium (Li), cobalt, nickel) call for the development of next-generation rechargeable batteries with advanced battery chemistry. Among the feasible alternatives, anion intercalation-type batteries such as dual-ion batteries (DIBs) and aluminum-ion batteries (AIBs) have emerged as promising energy storage systems utilizing the inexpensive transition metal-free host materials (e.g., graphite) and anion redox chemistry while delivering compatible energy/power density, cycle life, and safety of rechargeable batteries. Particularly, DIBs have achieved energy density close to commercialized LIBs (~250 Wh kg^-1) despite a short research history due to the high-voltage redox reaction of anions (&gt;5.0 V <i>vs.</i> Li/Li⁺). The Li-ions and counter ions (i.e., anions) in the electrolyte are simultaneously stored inside the anode and cathode host during charge-discharge, respectively, and thus shortened diffusion length of each charge-carrier ion significantly improves the rate capability of the DIBs.<br/>High-voltage anion-intercalation into the graphite cathode increases the operating voltage of batteries but entails inevitable structural deterioration (~200% of volume expansion) in repeated anion (de-)intercalation of large-radius anions (e.g., PF₆^-, FSI^-, TFSI^-) into the graphite. Analogous to high-capacity alloying-type anode (e.g., Silicon) in LIBs, such structural issues cause electrically isolated "dead" graphite, electrical contact loss between graphite particles, and the formation of unstable/thick cathode electrolyte interphase (CEI) that blocks the anion diffusion pathway, resulting in the material and/or electrode-level collapse and failure of sustainable anion storage. . Based on studies of large-volume-change materials, several material designs have been proposed to mitigate the degradation of graphite electrodes: (i) Introducing electrochemically anion-inactive inorganic coating layers (e.g., Al₂O₃) that physically encapsulate graphite; (ii) Using porous micro/nanoflake or nanoribbon morphologies to accommodate volumetric expansion during anion (de-)intercalation; (iii) To extend the interlayer spacing of graphite; (iv) Interlayer binding design directly connecting graphene layers with a carboxylic anhydride functionality. Such approaches have achieved significant improvements in battery cycle stability and rate capability. However, adding an electrochemically anion-inactive material lowers the energy density of the battery. Also, the excessively widened specific surface area of the host material causes excessive electrolyte decomposition and CEI generation. Therefore, there is a need for an effective strategy for simply mitigating graphite electrode degradation while overcoming the limitations of existing methods.<br/>Here, we report a high-performance durable graphite electrode using polymeric binders, which are essential for electrodes. A designed high-voltage polymer strongly holds the graphite integrity through the formation of a direct covalent bond with graphite. The graphite electrode with the designed binder shows remarkable rate capability and long-term performance of DIBs and dual-graphite batteries. In addition, it shows superb cell performance even when used for existing LIB graphite anodes. The binder design presented here offers guidelines for further designs of the advanced binder for carbonaceous host material with anion intercalation-type redox chemistry.