Thermoelectrochemical formation of a solid electrolyte interphase on a silicon negative electrode to enhance the durability of silicon-enriched lithium-ion batteries by compositional modification†

The SiO electrode interface is passivated with a SiO₂ layer, which hinders the deposition of an inorganic solid electrolyte interphase (SEI) due to its high surface work function and low exchange current density of electrolyte decomposition. Consequently, a thermally vulnerable, organic-based SEI formed on the SiO electrode, leading to poor cycling performance at elevated temperatures. To address this issue, the SEI formation process is thermoelectrochemically activated. Increasing the formation temperature lowers the work function by shifting the electron energy levels and increases the exchange current density for SEI formation. Higher temperatures promote the incorporation of inorganic Li₂CO₃ into the SEI film, resulting from the two-electron reduction of ethylene carbonate, and hence the thermally stable SEI film leads to stable cycleability. However, excessively high temperatures cause the SEI layer to become thick and resistive, significantly increasing the polarization of the SiO electrode, which leads to a deficient improvement of cycle performance. Therefore, moderate temperature exposure is required to convert the organic SEI into less resistive, inorganic components. The implementation of a mechanism-assisted SEI formation process in pouch cells using identical materials significantly improves the cycling performance, with a 20% enhancement by the 300^th cycle. Additionally, the thermoelectrochemical activation of SEI formation reduces cathodic side reactions on SiO electrodes, which helps in preventing coupled failure of the NCM electrode by mitigating intergranular cracking and preserving its structure.