Heterovalent Doping of Amorphous Oxyhalide Solid Electrolytes for High-Performance All-Solid-State Lithium Batteries

Abstract

Oxyhalide solid-state electrolytes (SSEs) have attracted significant research interest in the field of high-energy-density all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity and good interfacial compatibility. In this work, the effects of heterovalent metal ion doping (Cs+ , Bi3+ , Hf4+ or Nb5+ ) on the properties of Li3.2TaCl5O1.6 (LTCO) were systematically investigated, with particular focus on the optimal dopants (Hf4+ and Bi3+ ) for further structural and electrochemical characterization. Results indicate that doping did not alter the amorphous nature of the electrolyte but significantly enhanced its ionic conductivity. The optimal doping concentration was found to be x=0.1, under which the Hf4+- and Bi3+-doped samples (Li3.3Ta0.9Hf0.1Cl5O1.6 and Li3.4Ta0.9Bi0.1Cl5O1.6 ) achieved conductivities of 8.48×10-3 S cm-1 and 7.42×10-3 S cm-1 , respectively, markedly higher than that of LTCO (6.85×10-3 S cm-1 ). These improvements can be attributed to the lattice distortion induced by the heterovalent ions (Hf4+ or Bi3+ ), which not only broadens the ion migration pathways but also reduces the binding energy and migration energy barrier of Li ions. ASSLBs fabricated with the optimally doped electrolytes exhibited superior cycling stability, higher discharge specific capacity, and improved coulombic efficiency. This study demonstrates that heterovalent ion doping is an effective strategy for enhancing the electrochemical performance of amorphous oxyhalide SSEs, providing new insights for their application in high-performance ASSLBs.