Electrolytic Reduction of Titanium Dioxide in Molten LiCl–Li2O

Meng Shi,Shelly Li,Bin Liu,Haiyan Zhao

doi:10.3390/electrochem2020016

Meng Shi, Shelly Li + Show 2 more

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https://doi.org/10.3390/electrochem2020016

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Abstract

The electrolytic reduction of TiO2 in LiCl–Li2O (1 wt.%) at 650 °C was investigated under a series of cathodic reduction potentials and applied charges to provide a mechanistic understanding of the electrochemical characteristics of the system. The optimal cathodic reduction potential was determined as being −0.3 V vs. Li/Li+. Li2TiO3 and LiTiO2 were structurally identified as intermediate and partial reduction products of the TiO2 electrolytic reduction. The reduction of LiTiO2 was extremely slow and reversible due to its high stability and the detrimental effect of Li2O accumulation within the solid particles. The most reduced product obtained in this study was LiTiO2, which was achieved when using 150% of the theoretical charge under the optimal reduction potential. The highest reduction extent obtained in this study was 25%. Based on theoretical DFT modeling, a detailed multistep reduction mechanism and scheme were proposed for TiO2 electrolytic reduction in LiCl–Li2O (1 wt.%) at 650 °C.

Highlights

Titanates and titanium metal are valuable for batteries, coatings, and structural material applications [1,2,3,4]
The most reduced product obtained in this study was LiTiO2, which was achieved when using 150% of the theoretical charge under the optimal reduction potential
Soaking is a routine step for the electrolytic reduction of metal oxides and spent oxide fuels, which allows time for the system to reach stability and for salts to diffuse into the metal oxides matrix before the lithium metal is formed [11,27,28]

Summary

Introduction

Titanates and titanium metal are valuable for batteries, coatings, and structural material applications [1,2,3,4]. Electrolytic reduction is a promising way for Ti metal and intermediates production directly from solid titanium dioxide through molten salt electrolysis. The Fray–Farthing–Chen (FFC) Cambridge and calciothermic Ono–Suzuki (OS) processes are the two most well-studied processes utilizing CaCl2 (melting point 772 ◦ C) as electrolytes for electrolytic reduction between. The FFC process presumes that TiO2 is reduced directly in CaCl2 via electrons through multiple titanate intermediates, including CaTiO3 and CaTi2 O4 , as well as titanium suboxides (TiOx , x < 2) [13,14,15,16]. Through the OS process, TiO2 is reduced using in-situ-generated calcium metal from the CaCl2 electrolyte at an overpotential when the applied potential is higher than the electrolyte decomposition potential [7,8,9,17,18]

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