Construction of multiwall carbon nanotubes/biomass-derived nitrogen-doped carbon@regenerated LiFePO₄ cathode materials for lithium-ion batteries

The multiwall carbon nanotubes/nitrogen-doped carbon-coated regenerated LiFePO₄ composites (referred as MCNTs/N-DC@LFP) with the excellent lithium storage properties have been successfully designed and synthesized by combining a facile spray-drying and high-temperature calcination process. The raw materials were spent LiFePO₄, chitin and carbon nanotubes, in which the spent LiFePO₄ were recycled using a novel low-temperature freezing/thawing technology. The three-dimensional network structure from chitin-derived N-doped carbon coating and CNTs network in MCNTs/N-DC@LFP composites is capable of enhancing the electrical conductivity of the composites and providing short diffusion paths for lithium ions. Upon utilization as cathode materials in lithium-ion batteries (LIBs), the obtained MCNTs/N-DC@LFP composites displayed a 157.0 mAh g⁻¹ high initial specific discharge capacity at 0.2 C of the elevated current rate, representing high initial coulombic efficiency of 95.2%. After 500 cycles, a remarkable specific discharge capacity was observed which was 146.9 mAh g⁻¹. The electrode retains a substantial discharge capacity of 111.4 mAh g⁻¹ even when subjected to a peak current of 5 C. The superior electrochemical performances of the MCNTs/N-DC@LFP composites are mainly ascribed to advantageous combination of regenerated LiFePO₄ structure, highly conductive chitin-derived nitrogen-doped carbon coating and CNTs network with efficient electron and Li-ion transport.