Hafnium‐Modified LATP NASICON Ceramics as High‐Performance Solid Electrolytes for Lithium‐Ion Batteries

ABSTRACT

Solid‐state lithium‐ion batteries (SSLIBs) are emerging as a promising next‐generation energy storage technology because they replace flammable liquid electrolytes with solid ones, improving safety and thermal stability. Among available materials, NASICON‐type LATP has received considerable attention due to its high lithium‐ion conductivity at room temperature and strong structural stability. It is well established that cation doping can enhance lithium‐ion transport, suppress titanium reduction, and stabilize the LATP framework. In this study, aliovalent tetravalent hafnium (Hf 4+ ) doping in the LATP NASICON structure, along with aluminum, is systematically investigated to improve structural stability and ionic conductivity. Hf 4+ ‐doped LATP ceramics were synthesized using a solid‐state reaction method, and the effects of doping on crystal structure, microstructure, and conductivity were examined. Structural analysis confirms that Hf 4+ is successfully incorporated into the LATP lattice without forming secondary phases, while morphological studies indicate improved grain connectivity and densification. Electrochemical impedance spectroscopy shows a clear enhancement in lithium‐ion conductivity for Hf 4+ ‐doped LATP compared to undoped and lower‐valence doped samples. This improvement is attributed to better lattice stability, reduced Ti 4+ reduction, and more efficient lithium‐ion migration pathways. These results demonstrate that Hf 4+ doping is more effective than divalent or trivalent doping strategies.