Solvation-engineered Li/arene complexes for controlled mild prelithiation of SiO anodes

The practical application of high-capacity SiO anode is hindered by its low initial Coulombic efficiency (ICE). Chemical prelithiation, employing Li/arene complex (LAC) solutions, offers a promising avenue to mitigate active lithium loss and enhance ICE. However, the complex solvation environment in LAC solution easily leads to uncontrolled, aggressive prelithiation, resulting in SiO particle fracture and excessive SEI formation. To address this, we developed a standardized protocol for quantifying prelithiation degree by monitoring the open-circuit potential of Li||SiO cells. Using Li-2-methylbiphenyl-cyclic ether LAC solution system as a demonstration of this method, we identified a Li-2-methylbiphenyl-tetrahydropyran (LBP) solution with appropriate solvation power and prelithiation kinetics. Combining various characterizations and calculations, it is revealed that weak solvation in LBP solution presents loose Li + -solvent coordination, ensures reasonable desolvation of Li + ions, facilitates controlled mild prelithiation of SiO to form a radially uniform Li x Si distribution, and thus effectively preserving SiO structural integrity and achieving high ICE. Consequently, the full cell demonstrates a significant improvement in capacity retention after 130 cycles from 22.04% to 70.74%. This work provides a universal criterion for evaluating prelithiation degree and offers valuable insights into the kinetic mechanisms governing prelithiation in high-capacity SiO-based anodes.