ABSTRACT Anode‐free sodium ion batteries (SIBs) promise higher energy density and lower costs, by eliminating the need for an anode host material; however, achieving efficient Na plating/stripping remains a major challenge. Here, three electrolyte classes − carbonate‐based, glyme‐based, and a localized high‐concentration electrolyte−are evaluated for Na plating/stripping on a commercial carbon‐coated aluminium current collector. Measurements across a broad temperature and current range (−30°C–+60°C, 0.25–14 mA cm −2− ) and studies on the Na growth modes by operando optical microscopy reveal the superior behavior of the glyme‐based electrolyte, including a uniform crystalline metal deposition. In anode‐free full cells with Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 as cathode, this electrolyte enables superior cycling with 75.3% capacity retention over 400 cycles at areal loadings above 3 mAh cm −2− . Projected energy densities of 290 Wh/kg and 751 Wh/l are calculated at the cell‐stack level, exceeding current LiFePO 4 ‐based Li‐ion batteries. The excellent Na plating/stripping behavior is evidenced by a particularly low initial areal capacity loss (IACL, mAh cm −2 ). The IACL parameter represents the first cycle Na inventory loss that must be compensated by the cathode. Unlike for conventional Na‐ion cells with traditional anodes, the IACL is a constant for anode‐free cells. For the given cell, the IACL amounts to only 0.14–0.16 mAh cm −2 (~5% of the 3 mAh cm −2 cathode areal capacity). This highlights the potential of anode‐free SIBs using commercially available components.
Exner et al. (2026) studied this question.