Enhancing Structural Integrity and Interfacial Stability of High-Voltage LiMn _{1– x} Fe _x PO ₄ Cathodes via a Cyano-Rich Binder

The binder plays a critical role in determining the structural integrity and interfacial environment of high-voltage olivine-type LiMn 1– x Fe x PO 4 (LMFP) cathodes, yet the correlation between binder chemistry and electrode performance remains unclear. Herein, we elucidate this relationship by comparing three distinct binders: nonpolar poly(vinylidene fluoride) (PVDF), multifunctional acrylonitrile-based copolymer (LA133), and cyano-rich polyacrylonitrile (PAN). Density functional theory (DFT) calculations combined with experimental analysis reveal that while polar functional groups in both LA133 and PAN significantly enhance binder-particle interaction and electrode structural integrity compared to PVDF, their interfacial behaviors differ fundamentally. Although the LA133 binder promotes the formation of a kinetically favorable LiF-rich cathode electrolyte interphase, this advantage comes at the expense of severe electrolyte decomposition, leading to inferior cycling stability. In contrast, the high density of cyano groups in PAN facilitates the formation of a robust and interconnected cohesive network while maintaining intrinsic electrochemical stability. This dual functionality effectively suppresses detrimental side reactions and preserves structural integrity. Consequently, the LMFP-PAN electrode exhibits superior electrochemical performance, delivering 109.8 mAh g –1 at 10C and stable cycling performance over 250 cycles at 2C. This work highlights that synergistically optimizing binder-mediated structural integrity and interfacial chemical stability is essential for surmounting the design challenges of high-voltage cathodes.