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 µm), 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 °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 °C.

Facile Synthesis of O3-Type NaNi0.5Mn0.5O2 Single Crystals with Improved Performance in Sodium-Ion Batteries.

Sodium-ion batteries can be a practical alternative to lithium-ion batteries due to the relatively high abundance of sodium and the projected scarcity of lithium. Both of these factors are critical considerations for grid-scale energy storage, but the central challenge to implementing sodium layered oxides in sodium-ion batteries is their relatively poor cycle life. Single-crystal particles with micrometer size can mitigate several failure mechanisms related to sodium layered oxides and can improve performance when compared to the commonly used polycrystalline particles. This work demonstrates a novel two-step molten-salt synthesis method using sodium chloride and metal oxides to form "single crystals" of a mixed-phase, spinel/rock-salt intermediate that crystallizes as micron-sized truncated octahedra. The mixed-phase spinel/rock-salt material is effectively used as a precursor to form O3-type NaNi0.5Mn0.5O2 with large primary particles and substantially improved cycle life. This synthesis route offers the added benefit of using simple metal oxides instead of hydroxide precursors, eliminating the need for coprecipitation. Particle morphology is found to be a critical factor in mitigating the structural damages incurred during phase transformations and maintaining the electrochemical performance.