A universal synthetic route to carbon nanotube/transition metal oxide nano-composites for lithium ion batteries and electrochemical capacitors

We report a simple synthetic approach to coaxially grow transition metal oxide (TMO) nanostructures on carbon nanotubes (CNT) with ready control of phase and morphology. A thin (∼4 nm) sulfonated-polystyrene (SPS) pre-coating is essential for the deposition of transition metal based materials. This layer has abundant sulfonic groups (-SO₃^-) that can effectively attract Ni²⁺, Co²⁺, Zn²⁺ ions through electrostatic interaction and induce them via hydrolysis, dehydration and recrystallization to form coaxial (NiO, Co₃O₄, NiCoO₂ and ZnCo₂O₄) shells and a nanosheet-like morphology around CNT. These structures possess a large active surface and enhanced structural robustness when used as electrode materials for lithium-ion batteries (LIBs) and electrochemical capacitors (ECs). As electrodes for LIBs, the ZnCo₂O₄@CNT material shows extremely stable cycling performance with a discharge capacity of 1068 mAh g^-1 after 100 cycles at a current density of 400 mAg^-1. For EC applications, the NiCoO₂@CNT exhibits a high capacitance of 1360 Fg^-1 at current densities of 10 Ag^-1 after 3000 cycles and an overall capacitance loss of only 1.4%. These results demonstrate the potential of such hybrid materials meeting the crucial requirements of cycling stability and high rate capability for energy conversion and storage devices.