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This work presents a comprehensive analysis of the impact of carbon nanotubes (CNT) and carbon nanofibers (CNF) composition on the performance of nano-Si anodes in lithium-ion batteries. The nano-Si anode suffers from chemo-mechanical issues caused by its large volumetric change (e.g., 280%) during cycling. One of the promising solutions in electrode level is to establish a robust electronic conduction pathway in Si anodes by incorporating CNT and CNF with high aspect ratios. The objective of this work is to quantitatively measure the performance improvement achieved by CNT and CNF based on their compositions and analyze the improvement mechanism through electrochemical methods. The results indicate that substituting a portion of carbon black with CNT and CNF in a range of 1 – 10 wt% can enhance the capacity retention (from 44% to around 60%) and the fast-charging and fast-discharging capabilities. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analyses revealed that 5% – 10% CNT and CNF conductors effectively suppressed contact impedances growths in Si anodes. In summary, our findings highlight the importance of precise control over the composition of CNT and CNF to achieve good electrode morphology and electrochemical properties for nano-Si anodes. [ABSTRACT FROM AUTHOR]