Ultra-low content-induced intercalation anomaly of graphite anode enables superior capacity at sub-zero temperatures

Abstract

The rapid development of energy storage devices has driven Li-ion batteries (LIBs) to strive for higher performance, better safety, and lower cost and the ability to operate over a wide range of temperatures. However, most LIBs are used only in favorable environments rather than in extreme conditions, such as in ocean exploration, tropical areas, high altitude drones, and polar expeditions. When chronically or periodically exposed to these harsh environments, conventional LIBs fail to operate due to hindered ion conductivity, interfacial issues, and sluggish desolvation of Li-ion. Additionally, graphite has been recognized as a state-of-the-art LIB negative electrode due to its mechanical stability, electrical conductivity, cost-efficiency, and abundant availability. However, the limited Li⁺ storage capacity of 372 mA h g⁻¹ via LiC₆ coordination has become a bottleneck, hindering its further application in next-generation LIBs. Herein, we reported an intercalation anomaly under ultra-low graphite content that enables the super-lithiation stage in the electrode. The ultrahigh rate capability (2200 mA h g⁻¹ at 1C and 1100 mA h g⁻¹ at 30C) in the graphite anode was achieved by reducing its amount within the electrode and adding more conductive filler to the electrode, creating a highly conductive system. When operated at −20 °C, the ultra-low graphite anode maintained 50% capacity (1100 mA h g⁻¹) at room temperature and ranked the best among LIB anodes toward commercialization. Systematic spectroscopy analysis revealed additional capacitive behavior and distinct structural evolution that led to a Li⁺ intercalation anomaly (up to LiC₂) in the ultra-low graphite content electrode, significantly enhancing its capacity beyond 372 mA h g⁻¹. Additionally, when the battery was operated at sub-zero temperatures, this unique electrode structure with a higher conductive environment helped overcome the sluggish desolvation process at the interface and slow diffusion in the bulk electrodes. This finding sheds new light on graphite chemistry and paves the way for the development of anode-less lithium-ion batteries.