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 Na₃V₂(PO₄)₃ cathode, the assembled foldable AFNBs demonstrate stable cycling performance.