The solid polymer electrolytes (SPEs) have been extensively studied as the prospective outlook for solid-state batteries due to safety and versatility, yet due to low ionic conductivity at room temperature (10 −3 mScm⁻¹ in pure polyethylene oxide PEO) and mechanical weakness, they cannot be put into practice. This review aims to critically analyze hydroxyapatite (HAp) as a ceramic of calcium phosphate as a functional filler in addressing these issues, and the key role of comparing the performance of synthetic sources and biowaste sources as sources. Arranged on the polymer support (PEO, poly vinylidene fluoride-co-hexafluoropropylene, poly methyl methacrylate), the review demonstrates that HAp can allow the dissociation of salts and decrease their crystallinity, as well as increase the mechanical strength, with obtaining room-temperature conductivities of 10⁻² to 1.7 mS cm⁻¹ and supplying Li⁺ transference figures between 0.2 and 0.6–0.7. In addition, mechanical parameters also increase, e.g., the tensile modulus of PEO-based systems increased to 15.8 MPa using 10 wt% HAp. There is high purity and reproducibility of synthetic HAp, with the morphologies predefined (nanowires), further facilitating cation flow (tLi-0.69). In comparison, a low-cost, low-carbon bioderived HAp using bones, shells, or eggshells can provide similar conductivity enhancement (∼0.1 mS.cm⁻¹ at 70 °C in PEO-NaTFSI) and the same improvement in mechanical reinforcement but is typically more variable due to dependency on the source of crystallinity. Such a comparative model emphasizes trade-offs between surface modification and sustainability, placing an emphasis on how future progress in the development of surface modification and dispersion shall be the central key to moving HAp-filled SPEs from lab-scale prototypes to scalable and environmentally conscious solid-state batteries. Further developments in the future remain in need of better filler dispersion, bio-sourcing, and scalable processing paths to turn HAp-reinforced SPEs into long-lasting and sustainable electrolytes that can be used in the high-performance solid-state battery.
Bappy et al. (Thu,) studied this question.