Pitch Carbon‐coated Ultrasmall Si Nanoparticle Lithium‐ion Battery Anodes Exhibiting Reduced Reactivity with Carbonate‐based Electrolyte

Abstract 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 ≈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.