Nitrogen-Doped\nHollow Carbon Nanospheres for High-Performance Li-Ion Batteries

Abstract

N-doped\ncarbon materials is of particular attraction for anodes of lithium-ion\nbatteries (LIBs) because of their high surface areas, superior electrical\nconductivity, and excellent mechanical strength, which can store energy\nby adsorption/desorption of Li⁺ at the interfaces between\nthe electrolyte and electrode. By directly carbonization of zeolitic\nimidazolate framework-8 nanospheres synthesized by an emulsion-based\ninterfacial reaction, we obtained N-doped hollow carbon nanospheres\nwith tunable shell thickness (20 nm to solid sphere) and different\nN dopant concentrations (3.9 to 21.7 at %). The optimized anode material\npossessed a shell thickness of 20 nm and contained 16.6 at % N dopants\nthat were predominately pyridinic and pyrrolic. The anode delivered\na specific capacity of 2053 mA h g^–1 at 100 mA g^–1 and 879 mA h g^–1 at 5 A g^–1 for 1000 cycles, implying a superior cycling stability. The improved\nelectrochemical performance can be ascribed to (1) the Li⁺ adsorption dominated energy storage mechanism prevents the volume\nchange of the electrode materials, (2) the hollow nanostructure assembled\nby the nanometer-sized primary particles prevents the agglomeration\nof the nanoparticles and favors for Li⁺ diffusion, (3)\nthe optimized N dopant concentration and configuration facilitate\nthe adsorption of Li⁺; and (4) the graphitic carbon nanostructure\nensures a good electrical conductivity.