Stable Sodium‐Metal Batteries in Carbonate Electrolytes Achieved by Bifunctional, Sustainable Separators with Tailored Alignment

Abstract

Sodium (Na) is the most appealing alternative to lithium as an anode material for cost‐effective, high‐energy‐density energy‐storage systems by virtue of its high theoretical capacity and abundance as a resource. However, the uncontrolled growth of Na dendrites and the limited cell cycle life impede the large‐scale practical implementation of Na‐metal batteries (SMBs) in commonly used and low‐cost carbonate electrolytes. Herein, the employment of a novel bifunctional electrospun nanofibrous separator comprising well‐ordered, uniaxially aligned arrays, and abundant sodiophilic functional groups is presented for SMBs. By tailoring the alignment degree, this unique separator integrates with the merits of serving as highly aligned ion‐redistributors to self‐orientate/homogenize the flux of Na‐ions from a chemical molecule level and physically suppressing Na dendrite puncture at a mechanical structure level. Remarkably, unprecedented long‐term cycling performances at high current densities (≥1000 h at 1 and 3 mA cm−2, ≥700 h at 5 mA cm−2) of symmetric cells are achieved in additive‐free carbonate electrolytes. Moreover, the corresponding sodium–organic battery demonstrates a high energy density and prolonged cyclability over 1000 cycles. This work opens up a new and facile avenue for the development of stable, low‐cost, and safe‐credible SMBs, which could be readily extended to other alkali‐metal batteries.

Enabling Further Organic Electrolyte Infiltration of Cellulose-Based Separators via Defect-Rich Polypyrrole Modification for High Sodium Ion Transport in Sodium Metal Batteries

“…Increasing the electrolyte affinity of the separator facilitates the extension of the ion transport channels, thereby homogenizing the ion flux and reducing the resistive overpotential. 38,39 The electrolyte wettability of PPY-H@ FIBER separators, unmodified FIBER separators, and commercial PP separators was measured by contact angle tests in the electrolyte (i.e., 1.0 M NaClO 4 in propylene carbonate). As shown in Figure 2e, the PPY-H@FIBER separator exhibits a smaller contact angle (∼36.5°) than that of the FIBER separator (∼41.6°) and the PP separator (∼62.7°), indicating that the modification promotes the wettability of the separator.…”

Multifunctionalized Safe Separator Toward Practical Sodium‐Metal Batteries with High‐Performance under High Mass Loading

“…[ 40 ] Notably, our full SMBs with the designed NZSP@PP separators exhibit much better cycling performance than those of reported values in literatures, such as s‐2D mesoporous polydopamine‐graphene‐coated PP separator (500 cycles at 2 C), and 1 m NaPF 6 in fluoroethylence carbonate/propylene carbonate/1,1,2,2‐tetrafluoroethyl 2,2,3,3‐tetrafluoropropyl ether+ perfluoro‐2‐methyl‐3‐pentanone electrolyte (1000 cycles at 0.5 C) (Figure 4d and Table S2, Supporting Information). [ 25,33,34,37,38,56–61 ]…”

“…[40] Notably, our full SMBs with the designed NZSP@PP separators exhibit much better cycling performance than those of reported values in literatures, such as s-2D mesoporous polydopamine-graphenecoated PP separator (500 cycles at 2 C), and 1 m NaPF 6 in fluoroethylence carbonate/propylene carbonate/1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether+ perfluoro-2-methyl-3-pentanone electrolyte (1000 cycles at 0.5 C) (Figure 4d and Table S2, Supporting Information). [25,33,34,37,38,[56][57][58][59][60][61] In order to evaluate the practicability of NZSP@PP separator, we also tested the performance of full SMB with a high NVP loading of 10.7 mg cm −2 . The full cell could still deliver a high capacity of 107.4 mAh g −1 and 200 stable cycles with a capacity retention of 96.4% at 0.5 C (Figure 4e; Figure S19, Supporting Information).…”

Multifunctional Electrolyte Additives for Better Metal Batteries

“…[ 94 ] To solve these problems, various strategies have been explored, such as modifying the deposition substrate, [ 95,96 ] using solid‐state electrolytes, [ 97,98 ] constructing the interface layer, and optimizing electrolytes. [ 99–101 ] Among the reported strategies, optimizing electrolytes with additives is considered to be the most economical and practical approach to address the inherent drawbacks of SMBs due to their simple operation, rich chemistry, and high compatibility with battery fabrication. [ 102 ] In this section, we will summarize the effect of multifunctional electrolyte additives on high‐performance SMBs, mainly including the effective mechanism for stable Na anode, synchronous effect on both anode and cathode, and enhancing the overall performance of SMBs.…”