Lithium-ion diffusion behaviour in silicon nanoparticle/graphite blended anodes

Abstract

An attractive approach to improving lithium-ion battery graphite anode capacity is the addition of high-capacity silicon (Si) nanoparticles (NPs). However, there is currently limited understanding of the evolution of the overpotential that is generated in the new types of anodes with increasing Si content. In this work both the synergistic and antagonistic effects of Si NPs (0–15 wt-%) blended with spheronized natural graphite was investigated. The overpotential was determined by comparing the corresponding peak positions in graphite and the Si NP/graphite blends using differential capacity (dQ dV⁻¹) analysis. Li⁺-ion diffusion coefficients were calculated via the galvanostatic intermittent titration technique (GITT) at different stages of (de)lithiation, before and after low and high current rate cycling. Results show that there is a clear interplay between graphite and Si NPs in the Li⁺-ion diffusion into (lithiation) and out (delithiation) of these materials. Graphite dominates during phase transitions, while Si NPs dominate when graphite undergoes liquid-like Li⁺-ion diffusion. No change was observed in the overpotential with a Si NP content <12 wt-%, both at initial lithiation and at the end of delithiation. However, as the Si NP content increased to 15 wt-% the lithium-ion diffusion lowered, reducing the graphite-based anodes' rate capability.