Electrospinning Machine | High-areal-capacity Na-ion battery electrode with high energy and power densities by simultaneous electrospinning-spraying fabrication

Rechargeable batteries power everything from personal electronics to electric vehicles and play a crucial role in the transition to clean energy. However, cost remains a major obstacle in large-scale energy storage systems—especially when relying on lithium. Sodium-ion batteries (SIBs) are a promising, more abundant, and cost-effective alternative. Among existing cathode materials for SIBs, Na₂V₃(PO₄)₃ (NVP) has attracted attention due to its excellent stability and outstanding rate performance. 

But its lower energy density remains a major obstacle to widespread application. To improve energy density, researchers have explored various electrode design methods, such as increasing areal loadings, increasing active material content, and removing current collectors. Despite extensive research, no single design currently can simultaneously achieve high energy density, high power density, long-term cycling stability, and industrial scalability. These limitations stem from inherent trade-offs between the requirements. Therefore, developing a novel electrode architecture that meets all these criteria is of urgent importance. This research addresses this by proposing a new electrode architecture and manufacturing process that overcomes these limitations, representing a significant advancement not only for sodium-ion batteries but also for other secondary battery systems.

Researchers from Imperial College London, led by Mengzheng Ouyang, introduced a novel electrode preparation technique for sodium-ion batteries (SIBs)—the co-electrospinning-electrospraying (co-ESP) method. This technique simultaneously employs electrospinning and electrospraying to construct a continuous conductive network, where active particles are firmly embedded without binders. The study found that performance is superior when the active particle size exceeds the network pore size. The self-supporting Na₂V₃(PO₄)₃ (NVP) cathode fabricated this way achieved a high areal loading of 296 mg/cm² and a high active material content of 97.5 wt%, demonstrating excellent rate capability and cycling stability. The full cell exhibited an energy density of 231.6 Wh/kg and a power density of 7152.6 W/kg, ranking among the leading performances for SIBs with industrially relevant areal loadings. Pouch cell tests further validated the electrode’s scalability and commercial potential, providing critical design insights and technical support for SIB development. The related research findings were published under the title "High-areal-capacity Na-ion battery electrode with high energy and power densities by simultaneous electrospinning-spraying fabrication" in the journal Energy & Environmental Science (Impact Factor 30.8).

Fig. 1 Preparation process and 2D morphology of the co-ESP prepared NVP/C/CNTF electrode. (a) Schematic diagram of the co-ESP preparation setup. (b) Photo of the 600 cm² as-spun NVP/C-PEO/CNT-PAN electrode (top) and the calcined 20 cm co-ESP NVP/C/CNF electrode (bottom, with CNT:CNF:NVP/C weight ratio of 1:1.5:97.5). Scanning electron microscopy (SEM) images of the co-ESP electrode: (c) Original micron-sized NVP/C particles; (d) Ball-milled nano-sized NVP/C particles. Schematic diagram of the NVP/C/CNTF co-ESP electrode: (e) Composed of original micron-sized NVP/C particles; (f) Composed of ball-milled NVP/C particles.

Fig. 2 Performance of co-ESP NVP/C cathodes with different particle sizes and active material contents: (a) Schematic diagram of a sodium-ion battery half-cell; Half-cell performance of co-ESP NVP/C cathodes composed of original and ball-milled NVP/C: (b) Rate performance and (c) Cycling stability at 0.2C; Schematic diagram of the morphology and electron transport paths in NVP/C/CNTF co-ESP electrodes with (d) original NVP/C particles and (e) ball-milled NVP/C particles; Half-cell performance of co-ESP NVP/C with different active material contents: (f) Third discharge curves, (g) Rate performance, and (h) Cycling stability at 0.2C; (i) Conductivity of co-ESP NVP/C electrode compositions with different CNTF contents; (j) Composition comparison between co-ESP electrodes with 25 mg cm⁻² areal loading and state-of-the-art conventional slurry-cast NVP/C cathodes.

Fig. 3 Physical properties and 3D morphology of the co-ESP NVP/C electrode: Schematic diagram and 3D reconstruction based on micro-CT scan of the NVP/C/CNTF electrode: (a) Uncompressed state; (b) Compressed state; (c) Fine structure of a single NVP/C particle (yellow indicates cross-section); (d) Thickness of compressed and uncompressed NVP/C/CNTF electrodes at different areal loadings and conventional electrodes (including current collector); (e) Volume percentage of different components in the compressed NVP/C/CNTF electrode; (f) Summary of structural parameters obtained from X-ray computed tomography (XCT); Schematic diagram of sodium ion transport paths in the pores of (g) conventional electrode and (h) co-ESP electrode.

Fig. 4 Performance of co-ESP NVP/C cathodes with different areal loadings: (a) Rate performance and (b) Voltage curves for a cathode with 4.3 mg cm⁻² areal loading; (c) Rate performance and (d) Voltage curves for a cathode with 49.6 mg cm⁻² areal loading; (e) Cycling stability of half-cells with different areal loadings; (f) Specific discharge capacity versus areal loading and C-rate; (g) Areal capacity versus areal current; (h) Ragone plot of gravimetric energy density vs. power density, and (i) Ragone plot of areal energy density vs. areal power density, including previous sodium-ion battery half-cell data for comparison.

Fig. 5 Performance of sodium-ion battery full cells and pouch cells consisting of co-ESP NVP/C cathode and co-ESP hard carbon (HC) anode: (a) Schematic diagram of a sodium-ion battery full cell; (b) Specific discharge capacity versus areal loading and C-rate; (c) Areal capacity versus areal current; (d) Cycling stability of full cells with different areal loadings; (e) Ragone plot of gravimetric energy density vs. power density, and (f) Ragone plot of areal energy density vs. areal power density, including previous sodium-ion battery full cell data for comparison; Performance of a pouch cell with cathode loading of 100 mg cm⁻²: (g) Schematic diagram of the sodium-ion battery pouch cell; (h) Cycling performance of a pouch cell with 0.2 A h capacity and cathode loading of 100 mg cm⁻².

The co-electrospinning-electrospraying (co-ESP) sodium-ion battery (SIB) full cell using commercial particles can achieve energy density comparable to existing lithium iron phosphate (LFP)-based lithium-ion batteries (LIBs), while significantly exceeding the latter in power density. This study also demonstrates the scaling potential of the co-ESP method—using lab-scale electrospinning-electrospraying equipment, a single batch can produce 600 cm² of co-ESP sodium vanadium phosphate carbon (NVP/C) membrane (Fig. 1b). Industrial-grade electrospinning/spraying equipment could have an annual production capacity exceeding 20,000,000 m², which, calculated at a medium areal loading of 60 mg cm⁻², is equivalent to 12 GWh capacity. 

Co-ESP sodium-ion batteries may become a rational alternative for cheaper and faster-charging electric vehicles in the future. However, the current requirement for a calcination step in preparing co-ESP electrodes, which is not part of the standard process for conventional electrodes, is a major obstacle to wider application. Integrating the calcination step into the battery manufacturing process increases cost and is energy-intensive. Although studies have attempted to directly electrospin conductive fibers, the conductivity of these fibers is far insufficient for battery electrode needs. Omitting the calcination step could also significantly shorten the preparation time of co-ESP electrodes, making it shorter than that of conventional electrodes (as no separate drying process is needed). Therefore, it is necessary to explore new techniques for electrospinning conductive fibers, which will be the focus of our next phase of research.

Original link: https://doi.org/10.1039/D5EE01444A