Slurry-induced <italic>in situ</italic> self-assembly of a conductive polymer interfacial layer for stabilizing Ni-rich layered oxide cathodes

<sec><p indent="0mm">High-nickel layered oxides are among the most promising cathodes for high-energy-density lithium-ion batteries, yet their commercialization is still limited by unstable cathode/electrolyte interfaces, sluggish interfacial charge transport, transition-metal dissolution, microcracking, and irreversible surface reconstruction under deeply delithiated states. Conventional surface coatings can mitigate these issues, but they generally require additional powder-level processing and may introduce electronically insulating barriers. Herein, we report a slurry-induced <italic>in situ</italic> self-assembly strategy to stabilize LiNi_0.83Co_0.12Mn_0.05O₂ (NCM83) cathodes by directly introducing a highly conductive n-type polymer, poly(benzodifurandione) (PBFDO), into the electrode slurry. During slurry mixing, PBFDO spontaneously assembles on the NCM83 particle surface, forming a uniform amorphous interfacial layer with a thickness of approximately <sc>2 nm</sc> without altering the bulk layered structure or requiring any extra coating step. This process-compatible design integrates naturally with conventional electrode fabrication and is therefore attractive for practical electrode manufacturing. </sec><sec> The PBFDO interfacial layer plays multiple synergistic roles. Its ultrahigh electronic conductivity <sc>(~2000 S cm^–1)</sc> improves surface electron transport and reduces electrode polarization, while its favorable Li⁺ transport characteristics promote interfacial ion migration. Meanwhile, abundant carbonyl groups in the polymer backbone provide coordination sites for surface transition-metal ions, helping to stabilize the local chemical environment and suppress metal dissolution. The flexible polymer chains further buffer mechanical stress associated with anisotropic lattice evolution and repeated volume variation during cycling. In addition, PBFDO can regulate the formation of the cathode electrolyte interphase (CEI), enabling a more uniform, compact, and LiF-rich interphase during the initial cycles. XPS, TOF-SIMS, HRTEM, EIS, chronoamperometry, and GITT analyses collectively confirm that the modified cathode exhibits reduced interfacial side reactions, lower charge-transfer resistance, more homogeneous fluorinated CEI distribution, and faster Li⁺ diffusion kinetics. </sec><sec> <italic>In situ</italic> XRD further reveals that PBFDO modification modulates the anisotropic lattice response of NCM83 during high-voltage de-lithiation. The modified cathode maintains a more reversible layered-framework evolution while alleviating excessive contraction and distortion within the transition-metal layers, thereby suppressing the formation of electrochemically inactive rock-salt phases. After long-term cycling, PB-NCM83 shows a much thinner reconstructed surface layer than pristine NCM83, confirming the effectiveness of the polymer-derived interfacial protection. As a result, PB-NCM83 delivers an initial discharge capacity of 217.2 mAh g^–1 at <sc>0.1 C,</sc> a high-rate capacity of 159.0 mAh g^–1 at <sc>5 C,</sc> and 80.0% capacity retention after 388 cycles at <sc>0.3 C.</sc> Even in graphite-based full cells with practical electrode loading, the modified cathode exhibits markedly improved rate capability, especially at <sc>4 C.</sc> This work provides a simple, scalable, and multifunctional polymer-additive strategy for interfacial engineering of Ni-rich cathodes, offering a promising route toward durable high-energy lithium-ion batteries. </sec>