Soft X-ray Li-K and Si-L _2,3 emission spectra of crystalline and amorphous lithium silicides Li ₁₃ Si ₄ and Li ₁₅ Si ₄ forming upon electrochemical lithiation of silicon anode in lithium-ion batteries (LIBs) have been investigated theoretically. It is shown that shape and energy position of X-ray emission bands can be used for determination of the chemical structure and composition of the electrochemically lithiated silicon, while the intensities of Li-K and Si-L _2,3 bands provide information on Li concentration. It is demonstrated that theoretical methods of soft X-ray emission spectroscopy (XES) can be used as a powerful tool for the detailed analysis of the electronic and structural properties of Li-Si alloys in LIBs.