Waste-derived hierarchical porous carbon with tunable sp2/sp3 hybridization from pyrolyzed Poly (ethylene terephthalate)/oyster shell for high-performance lithium-ion battery anodes

Porous carbon (PC) with tunable carbon hybridization states and controllable nanostructure are critically important for high-performance energy storage. However, their synthesis often requires expensive precursors, graphitization catalysts, or complex activation processes. Herein, we report a sustainable and template-free strategy to fabricate hierarchically porous carbon (PC-x, x = 800, 900, and 1000 °C) with controllable sp 2 /sp 3 carbon ratio by utilizing waste oyster shells as a calcium source and discarded Poly (ethylene terephthalate) (PET) bottles as a low-cost terephthalic acid ligands precursor. Through a facile one-pot route, Ca-based metal-organic frameworks (Ca-MOFs) were constructed and subsequently pyrolyzed at different temperatures to obtain PC-x without any external catalyst. Mechanistic investigations suggest that elevated temperature promotes sp 3 -to-sp 2 conversion and structural ordering, thus enhancing graphitic domains and electronic conductivity. As a result, the optimized PC-900 as anode for lithium-ion batteries exhibits an exceptional specific capacity of 2057.2 mA·h·g −1 at 0.1 A·g −1 after 200 cycles, along with a rate capacity of 1381.9 mA·h·g −1 at 1.0 A·g −1 after 350 cycles and 559.2 mA·h·g −1 at 10.0 A·g −1 after 1000 cycles. Furtherly, the Li + migration kinetics, storage mechanisms and structure evolution of PC-900 are systematically analyzed. This work not only develops a sustainable strategy to convert plastic and biological waste into high-performance carbon anodes, but also establishes clear structure-property correlations between carbon hybridization, nanostructure evolution, and electrochemical performance, providing mechanistic guidance for the rational design of sustainable carbon anodes.