Figure 2: Decomposition mechanism of FSI⁻ and TFSI⁻ anions on bare and cPAN-coated Li₁₃Si₄ surface.

Ball and stick models of the (a) FSI⁻ anion (b) decomposed FSI²⁻ radical di-anion, (c) TFSI⁻ anion and (d) decomposed TFSI²⁻ di-anion. DFT simulations of the (e) intact PYR₁₃⁺/FSI⁻ pair on bare Li₁₃Si₄, (f) decomposed PYR₁₃⁺/FSI⁻ pair on bare Li₁₃Si₄, (g) intact PYR₁₃⁺/TFSI⁻ pair on bare Li₁₃Si₄ and (h) decomposed PYR₁₃⁺/TFSI⁻ pair on bare Li₁₃Si₄. In (e–h) excess electrons on FSI⁻ or TFSI⁻ are not added explicitly but come from Li₁₃Si₄. Ball and stick model of the (i) cPAN coating Li₁₃Si₄. DFT simulation of the (j) spontaneous decomposition of FSI⁻ anion on cPAN-coated Li₁₃Si₄, (k) intact TFSI⁻ anion on cPAN-coated Li₁₃Si₄ and (l) decomposed TFSI⁻ anion on cPAN-coated Li₁₃Si₄. Li, Si, C, O, N, S and F atoms are depicted as silver, green, grey, red, blue, yellow and purple spheres, respectively. The PYR₁₃⁺ cation is shown as a grey line diagram in the background of (e–h). All panels are optimized geometries except (f,h) which are AIMD snapshots at T=350 K.