Preparation and electrochemical performance of a porous polymer-derived silicon carbonitride anode by hydrofluoric acid etching for lithium ion batteries

Porous silicon carbonitride (SiCN) ceramics were pyrolyzed from poly(silylcarbondiimide) derivatives, followed by etching with different concentrations of HF aqueous solution (5, 10, 15 and 20 wt%). The morphologies, structures and electrochemical performances of the HF-etched SiCN materials were investigated. The results indicated that the surface of the HF-etched SiCN composites became rough and porous. SiCN-10-HF, one of four HF-etched SiCN samples, showed excellent electrochemical properties as an anode for lithium ion batteries. Charge-discharge measurements indicated that the SiCN-10-HF anode exhibited a high initial specific discharge capacity of 681 mA h g(-1) at a current density of 40 mA g(-1), which was 2.4 times that of the unetched SiCN anode. After 100 cycles, the discharge capacity of SiCN-10-HF anode delivered 229.3 mA h g(-1), which was 5.0 times that of the unetched SiCN anode (45.6 mA h g(-1)). Additionally, the SiCN-10-HF anode exhibited high rate performance. At a current density of 190 mA g(-1), the discharge capacity of the anode was 160 mA h g(-1). It was deduced that the formation of nano-sized pores or holes on the surface of the SiCN materials in the HF-etching process not only offered new channels for the intercalation of Li+ but also relieved the volume expansion during the charge and discharge process, resulting in improved capacity, stable cycling and good rate capability.