Robust Artificial Interphases Constructed by a Versatile Protein‐Based Binder for High‐Voltage Na‐Ion Battery Cathodes

Abstract The multiple issues of unstable electrode/electrolyte interphases, sluggish reaction kinetics, and transition‐metal (TM) dissolution have long greatly affected the rate and cycling performance of cathode materials for Na‐ion batteries. Herein, a multifunctional protein‐based binder, sericin protein/poly(acrylic acid) (SP/PAA), is developed, which shows intriguing physiochemical properties to address these issues. The highly hydrophilic nature and strong H‐bond interaction between crosslinking SP and PAA leads to a uniform coating of the binder layer, which serves as an artificial interphase on the high‐voltage Na₄Mn₂Fe(PO₄)₂P₂O₇ cathode material (NMFPP). Through systematic experiments and theoretical calculations, it is shown that the SP/PAA binder is electrochemically stable at high voltages and possesses increased ionic conductivity due to the interaction between sericin and electrolyte anion ClO₄⁻, which can provide additional sodium‐migration paths with greatly reduced energy barriers. Besides, the strong interaction force between the binder and the NMFPP can effectively protect the cathode from electrolyte corrosion, suppress Mn‐dissolution, stabilize crystal structure, and ensure electrode integrity during cycling. Benefiting from these merits, the SP/PAA‐based NMFPP electrode displays enhanced rate and cycling performance. Of note, the universality of the SP/PAA binder is further confirmed on Na₃V₂(PO₄)₂F₃. It is believed that the versatile protein‐based binder is enlightening for the development of high‐performance batteries.