Pseudocapacitive Na-Ion Storage Boosts High Rate and Areal Capacity of Self-Branched 2D Layered Metal Chalcogenide Nanoarrays

The abundant reserve and low cost of sodium have provoked tremendous evolution of Na-ion batteries (SIBs) in the past few years, but their performances are still limited by either the specific capacity or rate capability. Attempts to pursue high rate ability with maintained high capacity in a single electrode remains even more challenging. Here, an elaborate self-branched 2D SnS₂ (B-SnS₂) nanoarray electrode is designed by a facile hot bath method for Na storage. This interesting electrode exhibits areal reversible capacity of ca. 3.7 mAh cm^–2 (900 mAh g^–1) and rate capability of 1.6 mAh cm^–2 (400 mAh g^–1) at 40 mA cm^–2 (10 A g^–1). Improved extrinsic pseudocapacitive contribution is demonstrated as the origin of fast kinetics of an alloying-based SnS₂ electrode. Sodiation dynamics analysis based on first-principles calculations, ex-situ HRTEM, in situ impedance, and in situ Raman technologies verify the S-edge effect on the fast Na⁺ migration and reversible and sensitive structure evolution during high-rate charge/discharge. The excellent alloying-based pseudocapacitance and unsaturated edge effect enabled by self-branched surface nanoengineering could be a promising strategy for promoting development of SIBs with both high capacity and high rate response.