Stabilizing the SiO Anode by a Highly Elastic Quasi-Solid Polyether-Based Electrolyte via an In Situ Fabrication

Silicon monoxide (SiO, x ≈ 1) has been a promising candidate of anode materials for next-generation lithium-ion batteries due to its high specific capacity (∼2600 mA h g^-1). However, huge volume expansion and the resultant repeated destruction of the solid electrolyte interphase (SEI) are key challenges to the practical application of the SiO anode. In this work, a highly elastic quasi-solid polymer electrolyte (QSPE) is demonstrated for batteries employing an SiO anode, which is prepared via in situ cationic ring-opening polymerization employing 1,3,5-trioxane (TXE) as the monomer, 1,3,2-dioxathiolane 2,2-dioxide (DTD) as both the initiator and film-forming additive, and fluoroethylene carbonate as the plasticizer. This TXE-based QSPE possesses excellent ionic conductvity properties, including an extremely low glass-transition temperature of -94.3 °C, a high ionic conductivity of 1.36 mS cm^-1 at 25 °C, and a high Li⁺ transference number of 0.66. The long poly-TXE skeleton endows the polymer electrolyte with a high elastic modulus of 42 MPa, helping to effectively suppress the volume expansion of the SiO anode during cycling. DTD participates in the construction of a robust SEI containing Li₂SO species, mitigating the structural collapse of SiO particles. As a result, the cyclic stability of the SiO anode has been remarkably enhanced─the Li||SiO half-battery with the in situ TXE-based QSPE achieves 81.9% capacity retention after 200 cycles at 0.5C, exhibiting significant improvement over its liquid-state counterparts and showing promising application potential.