A k Descriptor to Design of Current Collectors for Anode‐Free Sodium Batteries

Abstract The anode‐free strategy enables exceptionally high energy density in rechargeable metal batteries, but the lack of theoretical frameworks impedes current collector design. Here, this study mathematically derives three critical parameters: dielectric coefficient ( ɛ ), ion mobility ( µ_C ), and the change of concentration ( δC_C ), and introduces a quantitative descriptor, k , which serves as a benchmark for evaluating current collector efficiency. Experimentally, a carbon nanotube (CNT)‐based current collector is fabricated with minimized ɛ , enhanced δC_C (nano/micro‐Sb particles), and µ_C (sodium carboxymethylcellulose, CMC‐Na). The optimized design achieves remarkable cycling stability‐over 24 months at 0.25 mAh cm −2 and 0.5 mA cm −2 , and 12 months even at a high areal capacity of 20 mAh cm −2 . The lowest k value aligns with half‐cell tests, validating this theory. This work establishes a quantitative framework for designing high‐efficiency anode‐free sodium battery current collectors.