Hollow Co3O4@N-doped carbon nanocrystals anchored on carbon nanotubes for freestanding anode with superior Li/Na storage performance

A template-free strategy is developed to construct a composite of hollow Co 3 O 4 nanocrystals with N-doped carbon and carbon nanotubes (CNTs) as freestanding anodes for Li and Na ion batteries (LIBs/NIBs) via a chemical precipitation and subsequent two-step annealing. In this composite, the N-doped carbon coated hollow Co 3 O 4 nanocrystals have a average diameter of 12 nm and are anchored tightly on highly conductive CNT substrates. Such nanocomposite possesses large specific surface area to supply ample active sites, highly conductive carbon networks to enhance electric conductivity, short ion diffusion distance to improve ion transport, and large interior space to accommodate volume expansion during repeatedly electrochemical reaction. Furthermore, kinetic analysis reveal that pseudocapacitive-controlled Li/Na storages plays a vital role. The freestanding composite as a anode for the LIBs exhibits large reversible capacity (1468 mAh g −1 after 130 cycles at 0.2 A g −1 ), superior rate performance (271 mAh g −1 at 12.5 A g −1 ) and good cyclic stability (905 mAh g −1 after 350 cycles at 1.0 A g −1 ). For the NIBs, the freestanding composite delivers attractive rate performance (104 mAh g −1 at 10 A g −1 ) and long cyclic performance (189 mAh g −1 after 400 cycles at 2.0 A g −1 ). Moreover, the assembled Li/Na full cell using the freestanding composite as anodes and LiFePO 4 (for LIBs) and Na 3 V 2 (PO 4 ) 3 (For NIBs) as the cathodes display superior electrochemical performances. Our results suggest the prepared freestanding composite has a highly promising application in high-performance LIBs/NIBs.