Sustainable upcycling of waste low-density polyethylene droppers into active materials for lithium-ion hybrid capacitors

Abstract

The accumulation of plastic waste in landfills poses significant environmental challenges, while the increasing demand for sustainable energy storage drives the need for developing low-cost, high-performance electrode materials. In this work, we have upcycled the low-density polyethylene (LDPE) waste droppers into the anode and cathode electroactive material for Li-ion hybrid capacitors (LICs). LDPE droppers are upcycled into phosphorous-doped hard carbon (LDPE-PHC) anodes and high surface area activated carbon (LDPE-HSAC) cathodes for LICs. LDPE-PHC exhibits an improved specific capacity of 388.7 mAh g-1 at 50 mA g-1, attributed to its intrinsic microporosity and pseudocapacitive Li-ion storage sites. LDPE-HSAC exhibits a specific surface area of 2085 m² g-¹ and delivers a specific capacitance of 138.8 F g-¹ at 0.1 A g-¹. The assembled dual carbon-based LIC delivers a maximum energy and power density of 123.9 Wh kg-¹ and 6 kW kg-¹, respectively, with a capacitance retention of 85.8% over 7000 cycles. Additionally, it maintains 92.5% retention after 2000 cycles at 50 °C, confirming its thermal stability. This work highlights an efficient strategy for converting waste polymer into functional carbon materials for LICs, aiming to meet and address the sustainable energy and environmental goals.