MAS NMR and DFT study of electrochemical performance of silicon nanoparticle as anodes for Li-ion batteries

Abstract

In this work we have investigated the effect of slurry pH on the lithiation mechanism of silicon nanoparticle (SiNP) anodes in lithium-ion batteries. To this end, we have used a combination of lithium (7Li) and silicon (29Si) magic angle spinning nuclear magnetic resonance (MAS NMR), density functional theory (DFT), and electrochemical charge–discharge cycling. The NMR results show that different lithiation mechanisms are present depending on the pH. An acidic slurry facilitates the lithiation of SiNP, whereas a basic slurry oxidises the SiNP to form a shell of SiO/SiO2, which must be cracked before Si lithiation becomes relevant. In a basic slurry, the leading process during the first cycle is the reaction of Li+ and SiO/SiO2 to form lithium silicates. Consequently, this intermediate step leads to a greater capacity loss in the basic media than in the acidic one.