From monoanhydride to dianhydride: molecular engineering of electrolytes for chemomechanically stable NCM613||Si/C batteries.

High-energy LiNi0.6Co0.1Mn0.3O2 (NCM613) ||silicon/carbon (Si/C) full cells undergo pronounced interfacial chemomechanical degradation under high-voltage and high-temperature conditions, as repeated Si volume fluctuation, electrolyte decomposition, and transition-metal (TM) dissolution accelerate cell failure. Although monoanhydride additives such as succinic anhydride (SA) can scavenge acidic impurities, their limited reactive sites and insufficient structural adaptability restrict long-term interphase stabilization. To address these limitations, 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) is introduced as a multifunctional electrolyte additive, extending additive design from monoanhydride to dianhydride. Relative to SA, the dual-anhydride framework of HPMDA provides four carbonyl-active sites, enabling enhanced H2O/HF scavenging and more effective regulation of Li+ solvation, while the cyclohexane backbone imparts conformational flexibility for mechanically compliant interphases. HPMDA regulates the electrolyte solvation structure toward an aggregate-rich configuration and facilitates the preferential decomposition of fluoroethylene carbonate (FEC), thereby promoting the formation of thin and uniform solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers that accommodate Si volume fluctuation and suppress cathode corrosion. Consequently, the coupled chemical-mechanical degradation is markedly suppressed, leading to improved cycling stability of NCM613||Si/C full cells, with capacity retentions of 80% after 400 cycles at 45 °C, 82% after 200 cycles at 55 °C, and 80% after 300 cycles at 4.6 V. These results reveal the structure-function relationship underlying the transition from monoanhydride to dianhydride additives and provide a molecular basis for electrolyte design that couples bulk chemistry, solvation structure, and interphase mechanics.