Scalable Glass-Fiber-Polymer Composite Solid Electrolytes for Solid-State Sodium-Metal Batteries

In this work, we report a method for producing a thin (<50 mu m), mechanically robust, sodium-ion conducting composite solid electrolyte (CSE) by infiltrating the monomers of polyethylene glycol diacrylate (PEGDA) and polyethylene glycol (PEG) and either NaClO4 or NaFSI salt into a silica-based glass-fiber matrix, followed by an UV-initiated in situ polymerization. The glass fiber matrix provided mechanical strength to the CSE and enabled a robust, self-supporting separator. This strategy enabled the development of CSEs with high loadings of PEG as a plasticizer to enhance the ionic conductivity. The fabrication of these CSEs was done under ambient conditions, which was highly scalable and can be easily implemented in roll-to-roll processing. While NaClO4 was found to be unstable with the sodium-metal anode, the use of a NaFSI salt was found to promote stable stripping and plating in a symmetric cell, reaching current densities of as high as 0.67 mA cm-2 at 60 degrees C. The PEGDA + PEG + NaFSI separators were then used to form solid-state full cells with a cobalt-free, low-nickel layered Na2/3Ni1/3Mn2/3O2 cathode and a sodium-metal anode, achieving a full capacity utilization exhibiting 70% capacity retention after 50 cycles at a cycling rate of C/5 at 60 degrees C.

Automated summary

In this study, a method for producing a thin, mechanically robust, sodium-ion conducting composite solid electrolyte (CSE) was reported. This was achieved by infiltrating the monomers of polyethylene glycol diacrylate (PEGDA) and polyethylene glycol (PEG) and either NaClO4 or NaFSI salt into a silica-based glass-fiber matrix and initiating in situ polymerization. The fabricated CSEs showed high loadings of PEG as a plasticizer to enhance ionic conductivity, and the use of NaFSI salt promoted stable stripping and plating in a symmetric cell.