Pitch Carbon-coated Ultrasmall Si Nanoparticle Lithium-ion Battery Anodes Exhibiting Reduced Reactivity with Carbonate-based Electrolyte
Silicon anodes for lithium-ion batteries (LIBs) have the potential for higher energy density compared to conventionally used graphite-based LIB anodes. However, silicon anodes exhibit poor cycle and calendar lifetimes due to mechanical instabilities and high chemical and electrochemical reactivity with the carbonate-based electrolytes that are typically used in LIBs. In this work, we synthesize a pitch carbon-coated silicon nanoparticle composite active material for LIB anodes that exhibits reduced chemical reactivity with carbonate-based electrolytes compared to an uncoated silicon anode. Silicon primary particle sizes less than 10 nm diameter minimize micro-scale mechanical degradation of the anode composite, while conformal coatings of pitch carbon minimize the parasitic reactions between the silicon and the electrolyte. When matched with a high voltage NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O 2 ) cathode, the pitch carbon-coated silicon anode retains approximately 75% of its initial capacity at the end of 1000 cycles. Increasing the areal loading of the pitch carbon-coated silicon anodes to realize energy density improvements over graphite anodes results in severe mechanical degradation on the electrode level, highlighting a remaining challenge to be addressed in future work.