Unveiling Atom Migration Abilities Affected Anode Performance of Sodium-Ion Batteries

In sodium-ion batteries (SIBs), the low initial coulombic efficiency (ICE) is commonly induced by irreversible phase conversion and difficult desodiation, especially on transition metal compounds (TMCs). Yet the underlying physicochemical mechanism of poor reaction reversibility is still a controversial issue. Herein, by using in situ transmission electron microscopy and in situ X-ray diffraction, we demonstrate the irreversible conversion of NiCoP@C is caused by the rapid migration of P in carbon layer and preferential formation of isolated Na3P during discharge. By modifying the carbon coating layer, the migration of Ni/Co/P atoms is inhibited, thus the improvement of ICE and cycle stability is realized. The inhibiting of fast atom migration which induces component separation and rapid performance degradation might be applied to a wide range of electrode materials, and guides the development of advanced SIBs.

Automated summary

By using in situ transmission electron microscopy and in situ X-ray diffraction, it has been discovered that the irreversible conversion of NiCoP@C in sodium-ion batteries is caused by the rapid migration of P in the carbon layer and preferential formation of isolated Na3P during discharge. The modification of the carbon coating layer inhibits the migration of Ni/Co/P atoms, resulting in improved initial coulombic efficiency (ICE) and cycle stability. This inhibition of fast atom migration could be applied to various electrode materials and guide the development of advanced sodium-ion batteries.