Lithium-Ion Accelerated Regulators by Locally-Zwitterionic Covalent Organic Framework Nanosheets

Abstract

Rational regulation of the Li-ion (Li⁺) migration behaviors and charge distribution at the electrolyte–electrode interface is of great significance in pursuit of high-performance lithium metal battery (LMB) chemistry. Herein, unique locally-zwitterionic covalent organic framework nanosheets (ziCOFNs) are developed as Li⁺ accelerated regulators, whose functions include not only kinetics-boosted Li⁺ migration but also induces uniform charge distribution in LMBs. The zwitterions act as “dissociation enhancers” to trigger efficient Li⁺ desolvation, while the abundant ─COO⁻ units within the nanopores favor rapid Li⁺ diffusion. In addition, the ordered ionic skeleton dynamically homogenizes the interfacial charge, thereby inhibiting Li dendrite growth and stabilizing the Li-interface chemistry. When implemented as a functional interlayer in the cell configuration, ziCOFNs display ultrahigh transfer number (0.84) and ionic conductivity beyond 4.5 mS cm⁻¹. With such a layer, stable Li plating/stripping (over 6500 h) at 3 mA cm⁻² in symmetric cells, and superior long-term cycle performance in high-loading LiFePO₄ (9.4 mg cm⁻²) full cells are achieved. Detailed experimental characterizations combined with theoretical calculations elucidate the mechanism of the zwitterionic framework tuning Li⁺ migration behaviors. This work is anticipated to shed fresh light on the exploration of zwitterionic crystalline materials in next-generation LMBs.