Carrageenan as a Sacrificial Binder for 5 V LiNi_0.5Mn_1.5O₄ Cathodes in Lithium‐Ion Batteries

Abstract 5 V‐class LiNi_0.5Mn_1.5O₄ (LNMO) with its spinel symmetry is a promising cathode material for lithium‐ion batteries. However, the high‐voltage operation of LNMO renders it vulnerable to interfacial degradation involving electrolyte decomposition, which hinders long‐term and high‐rate cycling. Herein, this longstanding challenge presented by LNMO is overcome by incorporating a sacrificial binder, namely, λ‐carrageenan (CRN), a sulfated polysaccharide. This binder not only uniformly covers the LNMO surface via hydrogen bonding and ion‐dipole interaction but also offers an ionically conductive cathode–electrolyte interphase layer containing LiSO_xF, a product of the electrochemical decomposition of the sulfate group. Taking advantage of these two auspicious properties, the CRN‐based electrode exhibits cycling and rate performance far superior to that of its counterparts based on the conventional poly(vinylidene difluoride) and sodium alginate binders. This study introduces a new concept, namely “sacrificial” binder, for battery electrodes known to deliver superior electrochemical performance but be adversely affected by interfacial instability.