Self‐Confinement of Na Metal Deposition in Hollow Carbon Tube Arrays for Ultrastable and High‐Power Sodium Metal Batteries

Sodium metal battery is considered as one of the most promising energy storage/conversion devices due to their high energy density, and abundant sodium reserves. However, its development is hampered by the limited metallic utilization and detrimental sodium dendrite growth ascribed to the unstable, and fragile solid electrolyte interphase (SEI). Here, the high stable and modulus SEI is constructed with a component of a thin and dense layer of high Na‐ion conductive Na2SiO3. It is in situ formed by the reaction between sodium anode and fish‐skin structure separator, which exhibits a 3D porous polyvinylidene fluoride‐based framework embedded with thin and robust vermiculite sheets. The robust interphase cannot only suppress sodium dendrite growth but also enable high energy density with small interphase‐consumed Na ions in anode‐less batteries. Accordingly, the as‐assembled NaNi1/3Fe1/3Mn1/3O2//Na cell shows 83% capacity retention after 5000 cycles at a rate of 5 °C. Moreover, the proof‐of‐concept pouch cells deliver an energy density of 205 Wh kg−1 (based on the total mass of the battery), and high safety (not catching fire after punctured) under anode‐less condition (with a low negative/positive capacity ratio of ≈2.1).

High Modulus Na₂SiO₃‐Rich Solid Electrolyte Interphase Enable Long‐Cycle and Energy‐Dense Sodium Metal Battery

Yang,

Zhang

et al. 2024

Interfacial Modulation with Phosphorylated Covalent Organic Framework Enabling Highly Durable Sodium Metal Batteries in Carbonate‐Based Electrolytes

Hou,

Xia,

Fan

et al. 2024

The practical usage of Na metal anode is severely prohibited by the instability of the natively formed solid electrolyte interface (SEI) layer and the uncontrollable Na dendrite growth, inducing short cycle life and serious safety concerns. Herein, phosphorylated covalent organic frameworks (P‐COF) is first synthesized and rationally used to construct the robust artificial interface layer for Na metal stabilization. The modified Na metal anode demonstrates high rate performance (5 mA cm−2) and ultralong cycling lifespan (1800 h) with dendrite‐free Na deposition in carbonate‐based electrolyte. And the assembled Na|Na3V2(PO4)3 (NVP) cell also reveals extraordinarily stable cycling at 5 C for 4000 cycles with a quite low decay rate of 0.002% per cycle. Moreover, the Na|NVP full cell with high areal capacity (2.0 mAh cm−2) and thin Na metal (30 µm) still demonstrates prolonged cycling over 500 cycles even under the harsh condition of a low negative‐to‐positive‐capacity (N/P) ratio of 2:3. Furthermore, the Na|NVP pouch cell with an ultrathick cathode (≈17 mg cm−2) also manifests significantly prolonged cycling performance. This work demonstrates a facile and effective strategy toward reliable Na metal batteries.

Commercial Carbon Fibers as Host for Sodium Deposition to Achieve High Volumetric Capacity

Ji,

Liu,

Wang

et al. 2024

The advancement of flexible electronic devices necessitates the utilization of electrode materials that offer robustness and high capacity. In this paper, it is revealed that commercially available carbon fibers with specific microcrystalline structures not only have high mechanical strength but also a high volumetric capacity of up to 300 mAh cm−3, surpassing conventional carbon materials. When multiple structural parameters of carbon fiber reach certain thresholds, a breakthrough in sodium storage capacity and rate performance can be achieved. This study further elucidates the mechanism whereby this specific carbon fiber primarily utilizes an all‐plateau sodium deposition mechanism, which occurs in pore‐like grain boundaries. Through in situ spectroscopy and synchrotron techniques, the reversible deposition process of metallic sodium has been revealed at different scales. Theoretical calculations and thermodynamic principles further confirm the desolvation and deposition mechanisms in carbon fibers. As a result, this research discovers the modulating effects and patterns of crystallinity, defect, and orientation of carbon materials on sodium storage sites and diffusion kinetics, thereby achieving controlled sodium storage. This work shows that commercial carbon fibers can serve as robust hosts for sodium deposition and enhances the theoretical understanding of how the microcrystalline structure of carbon materials relates to sodium storage properties.