Elastomeric Core-Conductive Shell Slurry Additive Stabilizes High-Voltage NCM811 Cathodes via Mechanical-Electrical Dual Regulation

High-voltage (>4.3 V) Ni-rich layered cathodes are central to high-energy-density lithium-ion batteries, yet their practical operation is limited by coupled mechanical degradation, sluggish interfacial charge transport, and parasitic cathode-electrolyte reactions. Herein, we report a slurry-compatible strategy to construct a phase-separated mosaic-like interphase on LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes using poly(acrylonitrile-styrene-acrylate) (ASA) as a multifunctional additive. During N-methyl-2-pyrrolidone (NMP)-based slurry casting and electrode drying process, the core-shell ASA precursor undergoes structural reorganization, forming an ASA-derived interphase composed of poly (butyl acrylate) (PBA)-rich elastomeric regions and poly(styrene-co-acrylonitrile) (SAN)-rich polar/aromatic regions. The PBA-rich component buffers volume-change-induced stress and suppresses particle cracking, while the SAN-rich component contributes to Li⁺-related interfacial affinity and enhances electron conductive. This phase-separated, mosaic-like interphase promotes stress dissipation from intercalation (deintercalation), enabling simultaneous regulation of mechanical integrity, interfacial chemistry, and electrode kinetics. Consequently, the optimized cathode exhibits reduced polarization, enhanced Li⁺ diffusion, suppressed transition-metal dissolution, and stabilized electrode interphases. In practical NCM811||graphite pouch cells under 4.5 V operation, capacity retention increases from 55.2% to 78.7% after 500 cycles, increased by 43%. This strategy highlights the importance of regulating the phase organization of polymeric slurry additives, offering a practically compatible route for stabilizing high-voltage layered oxide cathodes.