Composite Polymer Electrolyte Enabled through 2D g-C3N4 for All Solid-State Sodium-Ion Batteries
Authors: Vasudevan Sudharshan , Dwivedi Sushmita , Balaya Palani 
Published: December 2024

Coupling the advantages of sodium ion chemistry and solid-state batteries can circumvent challenges such as leakage, fire risk, cost, supply chain and better electrochemical performance compared to conventional non-aqueous Li-ion batteries. Here, the inherent low ionic conduction and poor mechanical strength of solid polymer electrolytes urges the necessity of coalescing of polymer with active or passive ceramic fillers to efficiently overcome the individual demerits by offering benefit of both counterparts. Hence, a composite polymer electrolyte through passive or functional fillers are explored due to their enhancements in the ionic conductivity, structural and electrochemical properties. It has been found that morphology, size, and shape of the fillers along with their concentration in the polymer host will have significant effect on the performance improvement of the electrolyte. Dimensional control such as aligned nanowires and two-dimensional clays have resulted in much improved ionic conductivity and battery performance. The filler addition firstly influences the crystallinity of the host and then ameliorates the mechanical strength to hinder dendrite growth and overall rigidity of the electrolyte. Furthermore, functional filler induced salt-filler interaction improves the dissociation ability, cation mobility and anion immobility. Morphology being a critical performance enabler, compared to 0D/1D/3D fillers, fillers with 2D morphology that possess abundant surfaces induce increased active interface that allows better transport network and mechanical strength.

Herein, we have attempted to develop a unique functional filler, graphitic carbon nitride, g-C3N4 layered material based composite polymer electrolyte with PEO and salt for all solid-state sodium ion battery. As a two-dimensional filler, GCN synthesis is facile and scalable by simple thermal oxidative etching. Further, the functional N groups in the abundant surface of GCN allows increased interaction with Na salt that allows better ionization and transference. The 2D filler with high active surface properties can effectively create more nonslip region under load to augment the mechanical property. Additionally, unlike other 2D materials, GCN along with its high surface, also possess numerous defect regions that prospectively provide increased ion transport network for better ion migration through the created channels and thus efficiently improving the ionic conductivity of the composite electrolyte. Therefore, a ~60% increment in ionic conductivity (~4.5 × 10-6 S/cm) was observed for PEO-GCN composite compared to pure PEO electrolyte. Also, an assembled solid state sodium metal battery with the composite polymer electrolyte delivered an impressive discharge capacity of 102 mAh/g at 0.2 C operated at 60 °C using a functional composite NVP catholyte.

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