“Spike-Accessed” Polymer-Based Interphase-Engineered Surface-to-Bulk Lattice Stabilization for Ni-Rich Positive Electrodes

Abstract The practical deployment of high-voltage Ni-rich layered oxide positive electrodes is severely hindered by interfacial instability and structural degradation during deep delithiation. Here, inspired by the functional principle of surface-exposed reactive motifs in biological spike proteins, we develop a spike-accessed polysiloxane-based interphase that dynamically modulates positive electrode interfacial chemistry and stabilizes lattice integrity. This polymeric interphase is formed in situ through LiOH-initiated ring-opening polymerization of a new class of cyclic siloxane additives, which generates nucleophilic oxygen donor motifs─termed “spikes”─that preferentially coordinate with highly reactive surface Ni4+ species. Such coordination provides dynamic redox buffering, effectively suppressing parasitic interfacial reactions. Comprehensive spectroscopic and structural analyses reveal that the resulting polymer-based cathode–electrolyte interphase (CEI) not only stabilizes the surface Ni valence state but also extends redox homogeneity into the bulk lattice, thereby mitigating lattice distortion and irreversible phase transitions. Consequently, NCM811 positive electrodes incorporating the engineered CEI retain discharge capacities exceeding 100 mAh g–1 after 2,400 cycles at 5 C while exhibiting suppressed transition-metal dissolution and minimal impedance growth, even when cycled to 4.5 V. The strategy further enables stable cycling of 5.61 Ah lithium–metal (ca. 491 Wh kg–1) and 7.22 Ah anode-free (ca. 505 Wh kg–1) pouch cells. Moreover, its applicability to different cyclic siloxane precursors and Ni-rich layered oxides underscores the generality of this interphase-design principle. This work establishes a bioinspired interfacial design paradigm that integrates chemical adaptability, mechanical compliance, and redox-lattice coherence, thereby unlocking the full potential of Ni-rich positive electrodes in next-generation high-energy lithium–metal batteries.