Nanocomposite with Fast Li⁺ Ion Conductivity: A Solvent-Free Polymer Electrolyte Reinforced with Decorated Fe₃O₄ Nanoparticles

Polyethylene oxide (PEO)-based structures integrated with filler nanoparticles are known as a potential promising electrolyte applicable for developing all-solid-state lithium secondary batteries for solving the challenging obstacle of low ionic conductivity. In this direction, for the first time, this research investigated resorcinol formaldehyde@Fe 3 O 4 core–shell structures decorated by Ni nanoparticles, which were efficiently synthesized using a feasible method (indicated as NiNP@RF@Fe 3 O 4 ). The favorable characteristics of the PEO-based polymeric films embedded with NiNP@RF@Fe 3 O 4 particulate fillers were explored using appropriate analytical tools. It is observed that the polymeric electrolyte filled with the nanoparticles represented a rougher surface with more pores, greater ion pair dissociation, fewer crystalline domains, and superior thermal stability than the unfilled electrolyte. In addition, the introduction of filler particles into the polymeric membrane resulted in an increment of the ionic conductivity from 0.021 to 1.02 mS·cm –1 at an ambient temperature. Also, it led to a drop in the activation energy from 62.18 to 13.05 kJ·mol –1 . The filler-filled polymer electrolyte revealed a steady platform up to 5.5 V with a high ion transference number of 0.4. In a Li/LCO half-cell, the designed polymer electrolyte showed reversible Li + /Li in the cyclic voltammetry test after five cycles. More importantly, the prepared coin cell exhibited a discharge capacity of 136 mA·h·g –1 at 0.5 C after 100 cycles and retained 96% of the initial discharge capacity. The results of this investigation suggested that a polymer electrolyte filled with the synthesized NiNP@RF@Fe 3 O 4 additive could be a promising candidate toward engineering high-efficient solid lithium-ion batteries.