Equal mass, unequal impact: Particle density and bending rigidity of carbon nanotube additives govern silicon anode performance

초록

Silicon offers a much higher lithium storage capacity than graphite but suffers from severe volume expansion during cycling, which undermines electrode stability. Carbon nanotubes (CNTs) are widely employed to address this limitation, yet their coupled mechanical and electrical functions remain poorly understood. Here, we systematically compare single-walled (SWCNT) and multi-walled (MWCNT) carbon nanotubes as conductive additives in silicon nanoparticle anodes at identical loadings (0.5-5 wt%). SWCNTs are theoretically estimated to provide over 10(3) times more individual tubes per gram, forming dense percolation networks that enable rapid charge-discharge performance (2330 mAh g(-1) at 3 C, 5 wt%). MWCNTs, though fewer in number, exhibit higher bending rigidity, restricting electrode thickening to similar to 50% after 10 cycles. At CNT contents below 1 wt%, capacity retention scales with particle population, emphasizing the dominance of physical contact over intrinsic conductivity. These results decouple the roles of particle density (SWCNT) and mechanical stiffness (MWCNT), offering practical guidelines for optimizing CNT selection in cost-effective, high-energy silicon anodes.

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