Nip the Sodium Dendrites in the Bud on Planar Doped Graphene in Liquid/Gel Electrolytes

Abstract

Sodium (Na) metal is the most promising alternative anode to metallic lithium for high-energy batteries due to the low cost and high abundance of Na resources, but it suffers from severe dendritic/mossy growth at high current densities. Understanding Na nucleation/growth mechanism in different electrolyte systems is the key to tackling this issue but is complicated by the structural complexities of existing substrates for Na plating/stripping. Herein, well-defined planar doped graphene substrates are synthesized as model plating platforms to unravel a binding energy dominant Na nucleation-growth mode. The dopants (e.g., boron) in doped graphene and the regions close to the dopants possess high binding energies with Na atoms, providing abundant preferential nucleation sites and contributing to uniform Na plating/stripping. Accordingly, the boron-doped graphene regulated Na anode exhibits long-term stability at high current densities in both liquid and polymer electrolytes. The results enhance the understanding of Na nucleation/growth for stabilizing Na metal batteries.

Boosting the Reversibility of Sodium Metal Anode via Heteroatom‐Doped Hollow Carbon Fibers

“…As shown in the gray dashed circles of Figure a, benefitting from the large specific surface area, the initial nucleation overpotential was remarkably reduced from 17.4 mV on planar Cu to 7.8 mV on the pure CNF at 0.2 mA cm −2 . Moreover, the homogenous N, S co‐doping sites significantly improve the “sodiophilicity” of CNF, contributing to a further decreased overpotential of 3.2 mV, suggestive of the less energy needed to surmount the thermodynamic mismatch between Na metal and the D‐HCF electrode . The nucleation overpotentials under higher current densities were also examined.…”

“…The Raman spectra shows D and G bands centered at 1347.8 and 1586.3 cm −1 (Figure b). The higher ratio of D band over G band ( I D / I G = 1.37) confirms its low graphitization degree, and thus the high level of defects in the D‐HCF . The specific surface area of the D‐HCF was measured to be ≈1052 m 2 g −1 via the nitrogen adsorption–desorption isotherm (Figure c).…”

“…The higher ratio of D band over G band (I D /I G = 1.37) confirms its low graphitization degree, and thus the high level of defects in the D-HCF. [48,49] The specific surface area of the D-HCF was measured to be ≈1052 m 2 g −1 via the nitrogen adsorption-desorption isotherm (Figure 3c). Brunauer-Emmett-Teller analysis further demonstrated the presence of micropores and mesopores ranging from 0 to 15 nm in diameter (inset of Figure 3c).…”

“…Moreover, the homogenous N, S co-doping sites significantly improve the "sodiophilicity" of CNF, contributing to a further decreased overpotential of 3.2 mV, suggestive of the less energy needed to surmount the thermodynamic mismatch between Na metal and the D-HCF electrode. [48] The nucleation overpotentials under higher current densities were also examined. For planar Cu, it reaches 46.3, 193.7 mV at 0.5, 2.0 mA cm −2 , respectively ( Figure S5a, Supporting Information).…”

A robust, highly reversible, mixed conducting sodium metal anode

“…It should be noted that an electrode areal capacity of at least 3 mAh cm À2 is needed for actual battery operation [19]. To fulfill the requirement, 3D current collectors, such as 3D porous Cu [23,24], functional carbon materials [25][26][27] and Mxenes [28], were utilized to accommodate volume fluctuation of Na and reduce local current density to stabilize Na-metal anodes. Whereas these modified current collectors generally possess high specific surface area, which will expose more Na metal directly to the liquid organic electrolyte, they further exacerbate the side reactions in the initial stage [29].…”