📄 Our Lab Paper

Enhanced Electrochemical Performance of Vanadium Redox Flow Batteries Using Li₄Ti₅O₁₂/TiO₂ Nanocomposite-Modified Graphite Felt Electrodes

ChemElectroChem, 12 (2025) e202400477 | DOI: 10.1002/celc.202400477

Authors：Zih-Jhong Huang, Daniel Manaye Kabtamu, Aknachew Mebreku Demeku, Guan-Cheng Chen, Ning-Yih Hsu, Hung-Hsien Ku, Yao-Ming Wang, Tai-Chin Chiang, Chen-Hao Wang*

📄 Abstract

In this study, Li₄Ti₅O₁₂ (LTO) and TiO₂ nanocomposites uniformly were synthesized on the heat-treated graphite felt (HGF) through hydrothermal and heat treatment methods, denoted by LTO/TiO₂@HGF, which acts as effective electrocatalysts to enhance the electrochemical activity in vanadium redox flow battery (VRFB) systems. The cyclic voltammetry (CV) curves of the LTO/TiO₂@HGF show higher peak current densities and smaller peak separation than TiO₂@HGF, HGF, and pristine graphite felt (PGF) for catalyzing V²⁺/V³⁺ and VO₂⁺/VO²⁺, indicating superior electrochemical activity of LTO/TiO₂@HGF. The VRFB using LTO/TiO₂@HGF as the positive and negative electrodes demonstrates an energy efficiency of 82.89 % at 80 mA cm⁻². When the VRFB using LTO/TiO₂@HGF is applied at a high current density of 200 mA cm⁻², it still shows an energy efficiency of 62.22 %. However, the VRFB using PGF cannot perform any performance, and the VRFB using HGF only performs 51.94 %. This improvement can be attributed to the uniform distribution of LTO/TiO₂ nanowires on the surface of the graphite felt and the presence of oxygen vacancies on LTO/TiO₂, which increased the number of active sites for vanadium ion absorption.

🔬 Five Core Findings

Superior electrochemical activity of LTO/TiO₂@HGF: CV results show that LTO/TiO₂@HGF exhibits higher peak current densities and smaller peak separation (ΔEp) for V²⁺/V³⁺ and VO₂⁺/VO²⁺ redox couples compared to TiO₂@HGF, HGF, and PGF, indicating significantly enhanced electrochemical reversibility and reaction kinetics.

Energy efficiency of 82.89% at 80 mA cm⁻²: VRFB with LTO/TiO₂@HGF electrodes achieves 82.89% energy efficiency (EE) at 80 mA cm⁻², far superior to HGF (51.94%), while maintaining 62.22% EE at high current density of 200 mA cm⁻², demonstrating wide current-density operation potential.

Zero-strain characteristic and structural stability: Li₄Ti₅O₁₂ possesses "zero-strain" properties with minimal lattice volume change during charge/discharge, ensuring structural integrity for long-term cycling—critical for VRFB longevity requirements.

Uniform nanowire structure and oxygen vacancies increase active sites: XRD confirms LTO (JCPDS 49-0207) and TiO₂ (anatase and rutile, JCPDS 89-4920/89-4921) composite phase formation; SEM shows uniform LTO/TiO₂ nanowire growth on graphite felt fibers, enhancing specific surface area and electrolyte wettability, increasing active sites for vanadium ion adsorption.

Enhanced conductivity of biphasic composite: LTO/TiO₂ biphasic composite combines TiO₂'s higher theoretical capacity (336 mAh g⁻¹) with Li₄Ti₅O₁₂'s structural stability, while interfacial effects improve electronic and ionic conductivity, addressing the conductivity limitations of pure Li₄Ti₅O₁₂.

📊 Key Figures

Key Figure 1: Electrochemical performance of LTO/TiO₂ composite, caption embedded in image.

Key Figure 2: Structural and morphological analysis, caption embedded in image.