Pitch-derived P-doped carbon/GeP₃ composite via ball milling towards enhanced sodium-ion storage

GeP₃ is a promising anode material for sodium ion battery due to better conductivity, relatively high theoretical capacity and improved mechanical endurance compared to phosphorus and other phosphides. However unsatisfied rate capability and cycling stability is still an annoying issue that hinders the application of GeP₃. Here, GeP₃ was hybridized with P doped carbon (PPC) derived from low-cost coal tar pitch to prepare composite electrode. Through ball-milling process, the GeP₃ and PPC was homogenously mixed and form fused, secondary particles as confirmed by electron microscope. The formation of P-C and P-O-C bond between GeP₃ and carbon matrix was evidenced by XPS, and prompted by P doping level and O content in PPC. The electrochemical performance of the composite electrodes was evaluated, demonstrated much enhanced properties compared to bare GeP₃ and also GeP₃/carbon black electrode. High reversible capacity of 781 mAh/g was achieved by GeP₃/PPC-950 at 0.05 A/g. At higher current density of 2 A/g, the capacity can maintain at 360 mAh/g, 46% of the value that obtained at 0.05 A/g. The correlation between the structure of carbon and battery performance was discussed. The improvement in battery performance can be attributed to suppressed volume expansion and good conductive network of the GeP₃/PPC composite, which affected by P doping level and O content of PPC.