Rhizosphere Microenvironment-Induced Transformation of Lithium Cobalt Oxide Triggers Singlet Oxygen and Plant Injury

Lithium cobalt oxide (LCO), a layered lithium-ion battery cathode material, undergoes pronounced chemical and structural reprogramming at the plant interface. Here we show that root-associated conditions convert LCO nanosheets into a high-aspect-ratio needle-like state while preserving the layered oxide framework, consistent with interfacial reconstruction rather than bulk collapse. The transformed material becomes oxidizing under rhizosphere-relevant mild acidity and produces singlet oxygen as the dominant reactive species. Kinetic analysis, pharmacological perturbation, and genetic evidence further show that this early material-derived oxidative input is followed by apoplastic RBOH-dependent ROS production in the plant. These results define a coupled injury mechanism in which rhizosphere-driven transformation creates the initial oxidizing state and the plant amplifies it through its own ROS machinery. LCO phytotoxicity therefore arises from interfacial chemical evolution, rather than from pristine material identity or ion release alone.