Cobalt Nanoparticles Chemically Bonded to Porous Carbon Nanosheets: A Stable High-Capacity Anode for Fast-Charging Lithium-Ion Batteries.

A two-dimensional electrode architecture of ∼25 nm sized Co nanoparticles chemically bonded to ∼100 nm thick amorphous porous carbon nanosheets (Co@PCNS) through interfacial Co-C bonds is reported for the first time. This unique 2D hybrid architecture incorporating multiple Li-ion storage mechanisms exhibited outstanding specific capacity, rate performance, and cycling stabilities compared to nanostructured Co3O4 electrodes and Co-based composites reported earlier. A high discharge capacity of 900 mAh/g is achieved at a charge-discharge rate of 0.1C (50 mA/g). Even at high rates of 8C (4 A/g) and 16C (8 A/g), Co@PCNS demonstrated specific capacities of 620 and 510 mAh/g, respectively. Integrity of interfacial Co-C bonds, Co nanoparticles, and 90% of the initial capacity are preserved after 1000 charge-discharge cycles. Implementation of Co nanoparticles instead of Co3O4 restricted Li2O formation during the charge-discharge process. In situ formed Co-C bonds during the pyrolysis steps improve interfacial charge transfer, and eliminate particle agglomeration, identified as the key factors responsible for the exceptional electrochemical performance of Co@PCNS. Moreover, the nanoporous microstructure and 2D morphology of carbon nanosheets facilitate superior contact with the electrolyte solution and improved strain relaxation. This study summarizes design principles for fabricating high-performance transition-metal-based Li-ion battery hybrid anodes.