Theoretically, transition metal oxide/carbon nanofibril aerogels are promising candidates for lithium-ion battery anode materials as they combine the high stability and electrical conductivity of the carbon matrix and the high theoretical specific capacity of transition metal oxide (TMO). However, challenges still exist to embed TMO nanoparticles into thin carbon nanofibril absolutely and tightly, limiting further improvements in electrochemical performances of the composites. Herein, necklace-like Fe3O4/carbon nanofibril aerogel (Fe3O4/CNF) was constructed by crosslinking alginate with Fe3+, followed by carbonization of the obtained ferric alginate aerogel. Based on an "egg-box" helical structure resulting from strong coordination between the Fe3+ and the carboxylate groups of alginate, three-dimensional interconnected carbon aerogel was facilely fabricated with Fe3O4 nanoparticles (similar to 11 nm in diameter) firmly embedded in ultrafine carbon nanofibrils (similar to 18 nm in diameter), exhibiting a special necklace-like structure. Consequently, the composite exhibits a high reversible capacity and stability of 1176 mAh g(-1) over 200 cycles at 1 A g(-1) and a high rate performance of 615 mAh g(-1) at 4 A g(-1). These Fe3O4/CNF aerogels may have potential applications for enhanced lithium storage of electrochemical devices. (C) 2020 Elsevier Inc. All rights reserved.