Metamorphosis of Seaweeds into Multitalented Materials for Energy Storage Applications

Abstract Transition metal ion dissolution due to hydrofluoric acid attack is a long‐standing issue in the Mn‐based spinel cathode materials of lithium‐ion batteries (LIBs). Numerous strategies have been proposed to address this issue, but only a fragmentary solution has been established. In this study, reported is a seaweed‐extracted multitalented material, namely, agar, for high‐performance LIBs comprising Mn‐based cathode materials at a practical loading density (23.1 mg cm⁻² for LiMn₂O₄ and 10.9 mg cm⁻² for LiNi_0.5Mn_1.5O₄, respectively). As a surface modifier, 3‐glycidoxypropyl trimethoxysilane (GPTMS) is employed to enable the agar to have different phase separation behaviors during the nonsolvent‐induced phase separation process, thus eventually leading to the fabrication of an outstanding separator membrane that features a well‐defined porous structure, superior mechanical robustness, high ionic conductivity, and good thermal stability. The GPTMS‐modified agar separator membrane coupled with a pure agar binder to the LiNi_0.5Mn_1.5O₄/graphite full cell leads to exceptional improvement in electrochemical performance outperforming binders and separator membrane in current commercial products even at 55 °C; this improvement is due to beneficial features such as Mn²⁺ chelation and PF₅ stabilizing capabilities. This study is believed to provide insights into the potential energy applications of natural seaweeds.