Electrospinning Equipment: Scalable and Ultrathin Dual Entangled Network Polymer Electrolytes for Safe Solid-State Sodium Batteries

Recently, a joint team led by Prof. Zhongwei Chen from the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, published a research achievement titled "Scalable and Ultrathin Dual Entangled Network Polymer Electrolytes for Safe Solid-State Sodium Batteries" in the journal Angewandte Chemie. The team used an arrayed multi-nozzle electrospinning device combined with a swelling-hot pressing process to prepare a dual-polymer entangled network solid-state electrolyte with a thickness of only 9.7 micrometers, achieving high voltage tolerance, enhanced tensile strength, and excellent thermal stability. This achievement provides key technical support for the large-scale production and safe application of solid-state sodium metal batteries, and promotes the development of high-performance and low-cost energy storage devices.

Solid-state electrolytes are mainly divided into two categories: polymeric and inorganic. Polymeric electrolytes have advantages such as good interfacial contact, easy manufacture, and low cost. They can usually be prepared in the thickness range of 80 - 200 μm by the tape casting method. However, compared with commercial separators, their thickness is still relatively large, resulting in an increase in battery internal resistance and a decrease in energy density. Therefore, the development of ultrathin and flexible solid-state electrolytes with high ionic conductivity and low interfacial resistance is crucial for the large-scale production of solid-state sodium metal batteries (SSMBs). However, current challenges include poor processing scalability, insufficient intrinsic mechanical strength, and limited ionic transport capacity. To address this problem, the research team used two polymers, polyacrylonitrile (PAN) and poly(ether-block-amide) (Pebax), and successfully prepared an ultrathin solid-state electrolyte membrane with a thickness of only 9.7 μm and a dual-polymer entangled network structure through an improved electrospinning machine technique combined with a swelling-hot pressing process. The specific preparation process is shown in Figure 1.

This ultrathin electrolyte membrane features a rigid nanofiber backbone and soft functional polymer segments. This unique structural design endows the electrolyte with both rigid support and flexible transport channels (see Figure 1b). Specifically, the soft ether oxygen segments construct abundant hopping migration paths for sodium ions, while a large number of carbonyl and cyanogen groups induce the formation of continuous guiding channels. These characteristics work synergistically to promote the rapid transport of sodium ions, while ensuring good voltage tolerance and thermal stability (Figure 3a).

The electrolyte membrane forms a dual-polymer network by combining polyacrylonitrile (PAN) and poly(ether-block-amide) (Pebax), significantly enhancing its voltage tolerance, tensile strength, and thermal stability. This structure enables the electrolyte to exhibit a tensile strength of 12.4 MPa (Figure 2e), maintain its structural integrity without significant thermal shrinkage at 300°C (Figure 2g), and withstand an antioxidant potential of up to 5.1 V (Figure 4c).

The mechanical strength of this ultrathin dual-network polymer electrolyte membrane and the formation of a thin and dense organic-rich solid electrolyte interphase layer effectively promote the uniform deposition behavior of sodium ions. This uniform deposition pattern not only reduces the overpotential but also significantly inhibits the growth of sodium dendrites (see Figure 5a, b). Experimental results show that the symmetric cell using the PAPE electrolyte can stably cycle for more than 500 hours at a low overpotential (see Figure 4e), indicating that this electrolyte membrane has significant advantages in extending battery life and enhancing battery safety.

Solid-state batteries paired with layered oxides also exhibit excellent cycling stability and high energy density in a wide temperature range from 25°C to 65°C. This indicates that the electrolyte can not only operate efficiently at room temperature but also maintain stable performance under high-temperature conditions. In addition, the assembled pouch cells still maintain remarkable energy density after 100 cycles and have better non-flammability, providing strong support for their application in large-scale energy storage systems (see Figure 6).

In summary, this research carefully prepared an ultrathin solid-state electrolyte membrane with a thickness of only 9.7 μm and a dual-polymer entangled network structure through an arrayed multi-nozzle electrospinning device combined with a swelling-hot pressing process. The electrolyte membrane exhibits excellent voltage tolerance, enhanced tensile strength, and superior thermal stability. The soft ether oxygen segments in the multiblock copolymers complex with Na⁺ to promote the rapid hopping transport of Na⁺. Meanwhile, interconnected electronegative channels based on carbonyl and cyanogen groups serve as Na⁺ conduits to smooth ion fluctuations and accelerate Na⁺ selective conduction simultaneously. The obtained inorganic-organic composite solid electrolyte interface with the improved mechanical strength of the ultrathin solid-state electrolyte effectively suppresses Na dendrites with a low overpotential over 500 h. The solid-state cells paired with layered oxides deliver a capacity retention of over 91.1% between 25 °C and 65 °C, and assembled pouch cells exhibit impressive energy density over 100 cycles, showing great potential for the large-scale application of the ultrathin structure in SSMBs.

Article source: https://doi.org/10.1002/ange.202505938