Molecularly designed, dual-doped mesoporous carbon/SWCNT nanoshields for lithium battery electrode materials

Abstract

Formidable challenges facing lithium-ion rechargeable batteries, which involve performance degradations and safety failures during charge/discharge cycling, mostly arise from electrode-electrolyte interface instability. Here, as a polymeric ionic liquid (PIL)-mediated interfacial control strategy to address this long-standing issue, we demonstrate a new class of molecularly designed, ion/electron-conductive nanoshields based on single-walled carbon nanotube (SWCNT)-embedded, dual-doped mesoporous carbon (referred to as SMC) shells for electrode materials. The SMC shell is formed on cathode materials through solution deposition of the SWCNT/PIL mixture and subsequent carbonization. The PIL (denoted as PVIm[DS]) synthesized in this study consists of poly(1-vinyl-3-ethylimidazolium) cations and dodecyl sulfate counter anions, whose molecular structures are rationally designed to achieve the following multiple functions: (i) precursor for the conformal/continuous nanothickness carbon shell, (ii) dual (N and S)-doping source, (iii) porogen for the mesoporous structure, and (iv) SWCNT dispersant. Driven by such chemical/structural uniqueness, the SMC shell prevents direct exposure of cathode materials to bulk liquid electrolytes while facilitating redox reaction kinetics. As a consequence, the SMC-coated cathode materials enable significant improvements in cell performance and also thermal stability. We envision that the SMC shell can be suggested as a new concept of effective and versatile surface modification strategy for next-generation high-performance electrode materials.