Measurements of the Fracture Energy of Lithiated Silicon Electrodes of Li-ion Batteries
We have measured the fracture energy of lithiated silicon thin-film electrodes as a function of lithium concentration. To this end, we have constructed an electrochemical cell capable of testing multiple thin-film electrodes in parallel. The stress in the electrodes is measured during electrochemical cycling by the substrate curvature technique. The electrodes are disconnected one by one after delithiating to various states of charge, i.e., to various concentrations of lithium. The electrodes are then examined by optical microscopy to determine when cracks first form. The fracture energy was determined to be Γ = 8.5 ± 4.3 J/m^2 at small concentrations of lithium (~Li0.7Si) and have bounds of Γ = 5.4 ± 2.2 J/m^2 to Γ = 6.9 ± 1.9 J/m^2 at larger concentrations of lithium (~Li2.8Si). These values indicate that the fracture energy of lithiated silicon is similar to that of pure silicon and is essentially independent of the concentration of lithium. Thus, lithiated silicon demonstrates a unique ability to flow plastically and fracture in a brittle manner.
The paper has been accepted for publication in Nano Letters and can be downloaded from: