Extended-life SiOx/C||Ni-rich NCM batteries enabled by inner Helmholtz plane modulation with a self-assembled monolayer

Abstract

Lithium-ion batteries (LIBs) with Ni-rich cathodes and Si-based anodes hold great promise for achieving high energy densities over 350 Wh kg⁻¹. However, interfacial instability and crossover effects severely degrade their cycling life. The inner Helmholtz plane (IHP) layer, where molecules readily engage in electrochemical reactions, plays a critical role in interface chemistry. In this study, we construct a self-assembled monolayer (SAM) on LiNi_0.8Co_0.1Mn_0.1O₂ (NCM) via a facile wet chemical process to regulate the IHP layer. The ordered SAM, composed of highly fluorinated thiol molecules, drastically weakens the affinity to carbonate molecules, producing IHP layers with fewer solvent components and effectively suppresses adverse side reactions. This alternation bolsters cathodic interfacial and structural stability, further mitigating the dissolution of transition metals and their crossover effects. As a result, the SAM-modified NCM cathodes exhibit a capacity retention of 90.5 %, outperforming unmodified NCM (72.5 %) upon 150 cycles at 0.2 C. More impressively, the SAM layer improves the capacity retention of SiO_x/C||NCM full-cells from 48 % to 74 % over 500 cycles. This work provides a straightforward yet effective approach for enhancing interfacial stability in LIBs, offering valuable insights into interfacial chemistry regulation and advancing high-energy-density battery technologies.