Enhancing Electrochemical Performance of Cobalt- And Manganese-Free Layered Oxide Cathodes Via Polarized PVDF-HFP Reinforced Separator for Lithium-Ion Batteries

Abstract

Ultrahigh nickel-rich layered oxide cathodes are attractive for next-generation lithium-ion batteries (LIBs) owing to their high specific capacity and potential for cobalt elimination. However, conventional LiNi0.95Mn0.025Co0.025O2 (NMC95) suffers from structural degradation, Li+/Ni2+ cation mixing, oxygen release, and transition-metal dissolution, resulting in poor cycling stability and thermal safety, particularly under high-voltage operation. Moreover, cobalt’s scarcity, toxicity, and price volatility, along with Mn3+ instability from Jahn–Teller distortion and disproportionation, limit large-scale viability. Herein, we develop cobalt- and manganese-free ultrahigh-Ni-rich cathode LiNi0.95Zr0.025Mg0.025O2 (NZM95), as sustainable alternatives. Structural analysis via XRD, Rietveld refinement, and HR-TEM reveal improved crystallinity, reduced cation disorder, and enlarged interlayer spacing. Mg2+ and Zr4+ co-substitution strengthens Ni–O bonding and suppresses antisite and oxygen defects, as confirmed by synchrotron EXAFS, XPS, and wavelet transform analysis. DFT calculations and charge-density mapping indicate enhanced charge delocalization and stronger covalent bonding in NZM95, enabling robust cycling. Electrochemically, NZM95 retain ~78% capacity after 200 cycles, respectively, outperforming NMC95 (~60%). EIS and DRT analysis confirms reduced CEI growth and interfacial resistance, while DSC indicates superior thermal stability with a higher exothermic peak (~226 °C) and lower heat release. To further enhance performance, a polarized β-phase PVDF-HFP nanofiber (NF) coating is electrospun onto a polypropylene (PP) separator (NF@PP). This ferroelectric layer modulates the local solvation structure, repels electrolyte anions, and promotes Li+ aggregation, improving (de)lithiation kinetics. NZM95 paired with NF@PP delivers ~215 mAh g-1 with 86% retention over 200 cycles, surpassing PP (~206 mAh g-1, 78%). This integrated cathode–separator approach offers a scalable route toward high-energy-density, thermally stable, and long-life LIBs.