In situ dual-interface layer enabling lower resistance of Ta-doped Li7La3Zr2O12-based thermal battery

Abstract

Application of Ta-doped Li7La3Zr2O12 (LLZTO) to thermal battery could solve overflow safety hazards caused by molten salt electrolytes. However, the capacity of large current discharge is obstructed by the large interfacial resistance originating from poor solid–solid contact between LLZTO and cathode. In this work, an in-situ dual-interface layer with favorable conductivity and multi-ionic diffusion between LLZTO and cathode is constructed by introducing connection layer in a simple way. The Ni(BrxCl2-x) layer with favorable conductivity would be established at high temperature during discharge for the reaction between the connection layer and NiCl2 cathode; the ionic (Br-,Cl-,O2–) diffusion layer with significant diffused direction among the connection layer, LLZTO layer and cathode layer occurs simultaneously at high temperature during discharge. Besides, the left connection layer with low melting point could form wettable interface as well. Consequently, the internal resistance of the single cell modified by in-situ dual-interface layer is reduced from 3.72 Ω to 1.70 Ω, accompanying with larger discharge current density (from 25 to 100 mA cm−2) and higher specific energy (from 444 to 1050 Wh kg−1) at 500 °C. Comparing with the typical discharge current of LLZTO which is less than 1 mA cm−2, this report provides a new insight to improve the interfacial resistance for the solid–solid contact at ambient temperature and the application for LLZTO on high-temperature battery.