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

Electrodes with higher Na + storage capability and cycling stability are vital to improve the energy density and rate capability of sodium ion batteries (SIBs). Herein, we present a coral-like FeP composite with FeP nanoparticles anchored and dispersed on a nitrogen-doped three-dimensional carbon framework ( FeP@NC ). Due to the highly continuous N-doped carbon framework and a spring-buffering graphitized carbon layer around the FeP nanoparticle, the sodium ion battery with FeP@NC composite can exhibit an ultra-stable cycling performance at 10 A g -1 with a capacity retention of 82.0% in 10000 cycles. More importantly, an interesting particle refinement achieving capacity increasing mechanism during cycling has been well confirmed. Particularly, 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 extra active sites for Na + storage and contributes to a rising capacity with cycling . The capacity ascending phenomenon can also extend to lithium-ion batteries (LIBs). This paper holds a new feasibility insight mechanism of the enhanced capacity during cycling and also offers a feasible solution to design high performance anode material for SIBs/LIBs.