Forced ion flux by multi-redox molecule to break diffusion limit and boost electrode process

Abstract

For any electrode process, the active species reaching the reaction sites of the electrode surface will ultimately become a controlling step, and this depends on the diffusion layer and its thickness. The diffusion layer, however, is not readily modified other than by introducing vigorous stirring. In lithium-ion-based energy storage, the supply of lithium ion to the reaction sites is certainly a rate-limiting step. Herein, we report an unusual type of “forced convection” by introducing a functionalized molecule in the electrode to break the traditional diffusion limit resulting in an alternative mode of mass transfer. The functionalized molecule, methylene blue phosphotungstate (MB-PW 12 ), is designed with multiple redox properties that can “adsorb” and “release” lithium ion during its redox processes. By implanting the MB-PW 12 in sulfur cathode matrix, forced lithium-ion flux can be realized, and this also favors polysulfides adsorption and catalysis, thus boosting the sulfur conversion reactions. • A mode of mass transfer is created by a designed functionalized molecule • MB-PW 12 can inhale and exhale Li + , breaking the traditional diffusion limit • Faster Li + transfer and favorable adsorption boost sulfur species conversion • Rate capability and cycling lifespan of Li-S battery are enhanced greatly The diffusion layer and its thickness will ultimately determine the electrode process. Fan et al. design a functionalized molecule MB-PW 12 with multiple redox properties and implant it into the electrode, which can inhale and exhale Li + during its redox process to form forced lithium ion flux, resulting in a type of forced convection.