Heat-regulating effects of inert salts on magnesiothermic reduction preparation of silicon nanopowder for lithium storage

Silicon is one of the most promising anode candidates for next-generation Li-ion batteries. Inert salt, acting as heat absorbent in magnesiothermic reduction, is playing a crucial role in scaled and economic derivation of Si from SiO 2 . Herein, the regulating effects of KCl and NaCl as heat absorbent on particle size, morphology and especially electrochemical behavior of obtained silicon are comparatively investigated. Although NaCl assists to get ultrafine nm-Si (~ 12.7 nm), inexpungible SiO x is accompanied, leading to lower reversible capacity (only 496.9 mAh g −1 ) and first coulombic efficiency (~ 48.7%). Comparatively, superior heat regulation of KCl facilitates to form uniform and well-crystalized Si nanoparticles (nano-Si KCl ) with vital size domain (~ 54.6 nm) and reduced surface energy restrains redundant SiO x formation, thus obtaining improved reversible capacity (2201 mAh g −1 ) and cycling stability. After further carbon coating on nano-Si KCl , an excellent capacity retention of 89.4% over 300 cycles can be obtained by nano-Si KCl @C composite.