Designing Architectured Siloxane Molecules for High-Voltage Lithium Batteries

The development of high-voltage lithium-ion batteries (HV-LIBs) is limited by the chemical instability of electrolytes, which suffer from rapid degradation of the cathode–electrolyte interphase (CEI) at operating voltages above 4.5 V. Here, we describe molecular design of an architectured siloxane molecule, as the co-solvent, trimethoxylsiloxane propoxyl carbonate (TSPC) with an umbrella-inspired architecture that integrates three synergistic structural motifs: a high-polarity carbonate “hook” for strong coordination with Li⁺ and efficient ionic transport; a low-polarity extended alkyl “shaft” that sterically shields extensive coordination with carbonate solvents; and a siloxane “canopy” that imparts high-voltage resilience by promoting the formation of robust Si─O─enriched interphases. This multifunctional design effectively stabilizes the electrolyte–electrode interphase and suppresses parasitic side reactions, enabling stable cycling of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode with 82.7% capacity retention for 300 cycles (4.7 V) and excellent rate performance showing 138.7 mA h g⁻¹ capacity at 10 C. A 6-Ah Si/C||NCM811 pouch cell retained 86.7% capacity after 500 cycles at 1 C (4.4 V). The rationally architectured siloxane molecule and the interphase regulation are compatible with a broad range of cathode chemistries, providing a general molecular design guideline for stabilizing electrode-electrolyte interphases in LIBs and related batteries operated at elevated voltages.