Foldable anode-free sodium batteries enabled by N,P-codoped carbon macroporous fibers incorporated with CoP nanoparticles.

Anode-free sodium batteries (AFNBs) are regarded as promising alternatives for next-generation energy storage systems because of their high energy density, high safety, cost-effectiveness, and simple manufacturing processes. However, their practical application is limited by a low coulombic efficiency (CE) and a short lifespan resulting from a large volume change and the growth of Na dendrites. Here, we propose a three-dimensional versatile host composed of interconnected N,P-codoped carbon macroporous fibers incorporated with CoP nanoparticles (denoted as CoP@N/P-CMFs) for selective nucleation and uniform deposition of Na. The porous skeleton reduces structural stress and inhibits dendrite growth by decreasing local current density and homogenizing Na flux. Furthermore, the sodiophilic CoP and N,P-codoped carbon reduce the energy barrier for Na nucleation, further manipulating homogeneous Na growth. Consequently, the CoP@N/P-CMFs exhibit an ultrahigh CE of more than 99.97% (10 milliamperes per square centimeter and 10 milliampere-hours per square centimeter) and dendrite-free Na deposition. When coupled with a NaV(PO) cathode, the assembled foldable AFNBs demonstrate stable cycling performance.