Deprotonation-Induced Strong Covalent Interfacial Bonding Stabilizes the Solid Electrolyte Interphase and Raises the Performance of Lithium-Ion Batteries

Chemically stable interfaces in electrodes are indispensable for maintaining the robust electrochemical interphase evolution to ensure long-term cycling stability of lithium-ion batteries. However, the potential impact on interfacial chemistry by residual protons in association with carboxyl and hydroxyl groups in water-soluble binders (e.g., PAA, CMC/SBR), which are inevitably introduced during the slurry-casting fabrication of electrodes, has received limited attention. Herein, we uncover that the chemically reactive protons trigger ethylene carbonate ring-opening reactions, thereby disrupting the solid electrolyte interphase (SEI) formation and stability, ultimately degrading battery performance. Building on this new insight, a chemically stable, deprotonated electrode (DE) featuring much reinforced interfaces arising from heterogeneous carbon-oxygen covalent bonds is developed, which enables stronger chemical anchoring than the hydrogen bond interactions by carboxyl and hydroxyl groups. In addition, the thus-developed oxygen-rich deprotonated interface reshapes the formation of an inner Li2O-dominated SEI. This deprotonation approach demonstrates broad compatibility with several anode active materials, including microsized SiO, Si, graphite, and their composites. For example, DEs with 86 wt·% SiO/graphite and 80 wt·% 5 μm-sized Si deliver 5.14 mAh·cm-2 over 500 cycles and 4.32 mAh·cm-2 over 200 cycles, respectively. With the new DEs, two Ah-level cells paired with LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.2 cathodes achieve the respective gravimetric energy densities of 288 Wh·kg-1 and 424 Wh·kg-1, while maintaining the capacity retention of 81% over 300 and 78% over 600 cycles. The present work reveals the deprotonation-driven interphase stability mechanism and establishes active-component regulation as a new paradigm for high-energy density lithium-ion batteries.