Morphology Processing by Encapsulating GeP₅ Nanoparticles into Nanofibers toward Enhanced Thermo/Electrochemical Stability

Compared with elemental phosphorus, GeP5, with much better thermostability and super higher conductivity, can exhibit a comparable capacity (>2000 mA h g–1) with a much higher first Coulombic efficiency (95%) for lithium-ion batteries. However, such high capacity is accompanied by large volume expansions, leading to fast capacity fading. To improve the cycle stability, fabricating a special nanostructure to reduce the volume stress and compositing with a carbon matrix to buffer the volume change are highly required. However, nanostructured metal phosphides were rarely reported up to now because they are difficult to be synthesized via a normal wet chemistry method or gas phosphorization because of lack of proper reactants and poor thermostability of phosphides. Herein, we successfully achieve uniform carbon-encapsulated GeP5 nanofibers (GeP5@C-NF) by processing GeP5 nanoparticles into carbon nanofibers via electrospinning. After carbon encapsulation, the thermostability of GeP5 can be greatly improved to over 600 °C for higher battery safety. Such a nanofiber structure in which nanosized GeP5 is embedded in a carbon matrix can greatly accommodate the large volume changes during lithiation and provide fast electron transportation, thus contributing to a long cycle life (>1000 mA h g–1 after 200 cycles) and high rate performance (803 mA h g–1 at 2000 mA g–1). This morphology processing technique can be easily extended to other metal phosphide anodes which are limited by a lack of appropriate synthesis methods and poor thermostability.