Molecular Wedge Reconstructing the Solvation Structure for Low-Temperature Ah-Level Anode-Free Sodium Metal Batteries
Jiawen Huang, Xingguo An, Zhongling Cheng, Jinlong Jiang, Yun Bai, Hua-Kun Liu, Jian Peng, Minghong Wu, Shi Xue Dou, Xueliang Sun, Chao Wu
Abstract
Anode-free sodium metal batteries (AFSMBs) promise high energy density and cost-effectiveness, yet their all-climate practical implementation remains limited by sluggish low-temperature kinetics. Here, we report a molecular wedging strategy for electrolyte design to reconstruct the solvation structure, extending the wide-temperature function of high-energy-density AFSMBs and Ah-level pouch cells. The wedging effect is synergistically achieved by intermolecular interactions and steric hindrances, so that the noncoordinating and spatially bulky cosolvent “wedges” into the rigid solvation structure dominated by strongly solvating solvent, rendering both electrostatically and spatially disrupted coordination environments and local structural disordering for fast mass transport and facile charge transfer. Highly reversible Na plating/stripping with Coulombic efficiency up to 99.98% and long-term cycling stability with overpotential <30 mV are ensured across a wide temperature range from 25 °C to −40 °C. With reconciled wide-temperature kinetics and anion-dominant interfacial chemistry, the molecular-wedging electrolyte enables high-cathode-loading AFSMBs with a discharging capacity as high as 93 mAh g –1 (85% of its room-temperature theoretical capacity) and reversible cycling exceeding 205 cycles down to −40 °C. Remarkably, Ah-level C@All||Na 3 V 2 (PO 4 ) 3 anode-free pouch cells (up to 3 Ah) demonstrate stable wide-temperature operation, yielding a high energy density of 170 Wh kg –1 and a cumulative cycling capacity of 690 Ah at an ultralow temperature of −40 °C, while a 2.5 Ah C@All||NaNi 1/3 Fe 1/3 Mn 1/3 O 2 anode-free pouch cell achieves a further elevated energy density of 184 Wh kg –1 based on total cell weight within a cutoff voltage of 2.0–4.2 V.