Building a flexible and applicable sodium ion full battery based on self-supporting large-scale CNT films intertwined with ultra-long cycling NiCo2S4

Abstract

The major difficulties for the development of flexible energy storage batteries lie in the scalable manufacture of high-performance flexible electrodes with bending tolerance. In the present study, large-scale CNT films are prepared by a continuous production method and used to fabricate a self-supported flexible high-capacity conversion anode with ultra-long cycling life by the in situ growth of NiCo₂S₄ nanosheets tightly anchored on the CNTs. The CNTs produced via such a scalable method have interconnected porous channels, providing a large contact area between the active materials and electrolyte facilitating the electrochemical conversion reaction of NiCo₂S₄. An ultra-high rate capability is achieved in terms of a capacity of 280 mA h g⁻¹ at 20 A g⁻¹. The interlaced construction of NiCo₂S₄ nanosheets with CNTs and firm anchoring on the CNT film result in a remarkable ultra-long cyclability of the NiCo₂S₄/CNT electrode with a capacity retention rate of 96% after 7500 cycles. A flexible full battery device is further established with the NiCo₂S₄/CNT anode and Na₃V₂(PO₄)₃/CNT cathode with the sealed package of PDMS, exhibiting good cycling stability and mechanical durability under different bending states. The present work highlights a scalable flexible battery electrode material, and demonstrates its potential applications in flexible Na-ion batteries.