Lignite-Based Hierarchical Porous C/SiOx Composites as High-Performance Anode for Potassium-Ion Batteries

Silicon oxide (SiOx, 0 < x <= 2) has been recognized as a prominent anode material in lithium-ion batteries and sodium-ion batteries due to its high theoretical capacity, suitable electrochemical potential, and earth abundance. However, it is intrinsically poor electronic conductivity and excessive volume expansion during potassiation/depotassiation process hinder its application in potassium-ion batteries. Herein, we reported a hierarchical porous C/SiOx potassium-ion batteries anode using lignite as raw material via a one-step carbonization and activation method. The amorphous C skeleton around SiOx particles can effectively buffer the volume expansion, and improve the ionic/electronic conductivity and structural integrity, achieving outstanding rate capability and cyclability. As expected, the obtained C/SiOx composite delivers a superb specific capacity of 370 mAh g(-1) at 0.1 A g(-1) after 100 cycles as well as a highly reversible capacity of 208 mAh g(-1 )after 1200 cycles at 1.0 A g(-1). Moreover, the potassium ion storage mechanism of C/SiOx electrodes was investigated by ex-situ X-ray diffraction and transmission electron microscopy, revealing the formation of reversible products of K6.8Si45.3 and K4SiO4, accompanied by generation of irreversible K2O after the first cycle. This work sheds light on designing low-cost Si-based anode materials for high-performance potassium-ion batteries and beyond.