Chemical Pre-lithiation of SiO_x Anodes with a Weakly Solvating Solution of Polycyclic Aromatic Hydrocarbons for Lithium-Ion Batteries

Silicon monoxide (SiOx, x similar to 1) has emerged as a highly promising candidate for high-energy-density lithium-ion batteries due to its high specific capacity and suitable working potential. Nevertheless, the formation of a large quantity of irreversible products, such as Li2O and lithium silicates, during the initial lithiation process results in a low initial coulombic efficiency (ICE) of SiOx, which is a significant impediment to its commercial application. To overcome this limitation, two lithium aromatic complexes, namely, lithium-naphthalene-2-methyl-tetrahydrofuran (N-LAC) and lithium-biphenyl-2-methyl-tetrahydrofuran (B-LAC), with a low redox potential are used to pre-lithiate SiOx anodes. The differences in lithiation kinetics and efficacy of the two LAC solutions are identified and assessed by scrutinizing the pre-lithiation process of SiOx materials. It is revealed that both pre-lithiation agents produce solid electrolyte interphase (SEI) films on the material surface enriched with substances such as LiF, Li2CO3, and ROCO2Li, but the LiF content in the SEI of the N-LAC pre-lithiated electrode is significantly higher. Furthermore, the surface roughness of the N-LAC pre-lithiated electrode is lower, and the horizontal distribution of mechanical properties and surface potential tend to be more homogeneous, even during cycling, at approximately the same degree of lithiation. The results indicate that the N-LAC solutions not only improve the ICE of the SiOx material but also optimize the interfacial and structural stability of the SiOx electrode. When the pre-lithiated SiOx anode is paired with lithium-rich layered oxide cathode materials, the energy density and ICE are significantly improved compared to the cell using pristine SiOx anode.