Impedance spectroscopy of porous silicon and silicon-carbon anodes produced by sintering

Dry-sintered macroporous Si electrodes for Li-ion batteries are studied for the first time using spectral impedance measurements. The spectra obtained in the lithiated and delithiated states are simulated with an equivalent electrical circuit, the parameters of which reveal the role of electrochemical processes caused by the surface layer of a solid-phase electrolyte (SEI), electric double layer, and diffusion in the solid phase of the electrode material. It is shown that the effective diffusion coefficient of Li in Si grows with increasing degree of lithiation from $D$ = 6.5 $\times$ 10$^{-12}$ to 2.6 $\times$ 10$^{-10}$ cm$^2$/s. The effect of carbonization via saccharose pyrolysis, which led to a decrease in the impedance and an increase in the diffusion coefficient of lithium to $D$ = 2.2 $\times$ 10$^{-10}$–1.7 $\times$ 10$^{-9}$ cm$^{2}$/s, is studied.