A Coral‐Like FeP@NC Anode with Increasing Cycle Capacity for Sodium‐Ion and Lithium‐Ion Batteries Induced by Particle Refinement

We present a coral‐like FeP composite with FeP nanoparticles anchored and dispersed on a nitrogen‐doped 3D carbon framework (FeP@NC). Due to the highly continuous N‐doped carbon framework and a spring‐buffering graphitized carbon layer around the FeP nanoparticle, a sodium‐ion battery with the FeP@NC composite exhibits an ultra‐stable cycling performance at 10 A g −1 with a capacity retention of 82.0 % in 10 000 cycles. Also, particle refinement leads to a capacity increase during cycling. The FeP nanoparticles go through a refining–recombination process during the first cycle and present a global refining trend after dozens of cycles, which results in a gradually increase in graphitization degree and interface magnetization, and further provides more active sites for Na + storage and contributes to a rising capacity with cycling. The capacity ascending phenomenon can also extend to lithium‐ion batteries.