Synergistic sulfonyl–ether polyimide binders for stabilized high-loading NCM811 cathodes in high-energy lithium-ion batteries

Abstract

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes offer high-energy-density potential for lithium-ion batteries (LIBs) due to their 275 mAh g⁻¹ theoretical capacity and cost efficiency. However, the high-nickel composition under demanding loading conditions accelerates structural degradation, interfacial side reactions, and Li⁺ transport limitations, necessitating advanced binders for enhanced stability and kinetics. This work addresses these challenges through a novel polyimide binder (PI-BPADA) featuring synergistic sulfonyl and ether functionalities synthesized via conventional one-step polycondensation. Comparative studies with PI-BPDA, PI-BTDA, and commercial PVDF binders demonstrate PI-BPADA's superior performance. At 4.3 V cutoff voltage, the PI-BPADA/NCM half-cell achieves 86.4% capacity retention after 100 cycles at 0.2 C versus PVDF's 70%, alongside higher rate capacity (122 vs. 103 mAh g⁻¹ at 5 C). These advantages intensify at 4.5 V with 78.4% capacity retention (vs. 61.1%) and 144 mAh g⁻¹ discharge capacity (vs. 79 mAh g⁻¹). Mechanistically, uniform Li⁺-diffusive coatings reduce polarization, stabilize interfaces, and optimize ion transport. This molecular design strategy provides critical insights for developing high-loading, high-energy LIBs.