High-performance flexible sodium-ion batteries enabled by high-voltage sodium vanadium fluorophosphate nanorod arrays

Flexible sodium-ion batteries (SIBs) have enormous potential in portable and wearable devices due to their suitability and price advantage in particular scenarios. Among the cathode materials, phosphate electrode materials have the advantage of good structural stability, high working potential and long lifespan. However, the design of flexible phosphates electrode materials is still a challenge due to hush fabrication requirements, complex reactions and absence of flexible substrates. Herein, we report the in-situ fabrication of three-dimensional sodium vanadium fluorophosphate nanorod array (PCNF@NVOPF NR) from vertically grown VO2 nanosheets on flexible porous carbon nanofibers. The PCNF@NVOPF NR as a flexible high-voltage cathode possesses long-term cycling stability (87.6% capacity retention after 4500 cycles). The nanorod arrays can ensure fast sodium reaction kinetics and low interfacial resistance. Moreover, PCNF@NVOPF//PCNF@VO2 NS@C full SIBs exhibit high energy and power density (220.5 W h kg−1 and 9400 W kg−1). This material design strategy for flexible cathode will inspire the commercialization of practical SIBs.