Effective Coupling of Amorphous Selenium Phosphide with High-Conductivity Graphene as Resilient High-Capacity Anode for Sodium-Ion Batteries

It is of great importance to develop high-capacity electrodes for sodium-ion batteries (SIBs) using low-cost and abundant materials, so as to deliver a sustainable technology as alternative to the established lithium-ion batteries (LIBs). Here, a facile ball milling process to fabricate high-capacity SIB anode is devised, with large amount of amorphous SeP being loaded in a well-connected framework of high-conductivity crystalline graphene (HCG). The HCG substrate enables fast transportation of Na ions and electrons, while accommodating huge volumetric changes of the active anode matter of SeP. The strong glass forming ability of NaxSeP helps prevent crystallization of all stable compounds but ultrafine nanocrystals of Na2Se and Na3P. Thus, the optimized anode delivers excellent rate performance with high specific capacities being achieved (855 mAh g(-1) at 0.2 A g(-1) and 345 mAh g(-1) at 5 A g(-1)). More importantly, remarkable cycling stability is realized to maintain a steady capacity of 732 mAh g(-1) over 500 cycles, when the SeP in the SeP@HCG still remains 86% of its theoretical capacity. A high areal capacity of 2.77 mAh is achieved at a very high loading of 4.1 mg cm(-2) anode composite.