Experimental and Computational Insights into Built-In Electric Field at Bronze TiO₂-Expanded Graphite Interface for...

Interfacial engineering offers a powerful route to enhance ion transport and electron mobility in lithium-ion batteries (LIBs) through the induction of built-in electric fields (BIEFs) at the interface, which in turn facilitates faster Li⁺ diffusion. Yet, direct experimental validation of this concept in intercalation-type materials has not been investigated. In this work, bronze titanium oxide (TiO₂ (B)) is strategically integrated with expanded graphite (EG), producing a strong interfacial BIEF driven by their distinct work functions, as confirmed by Kelvin probe force microscopy (KPFM). As a result, the TiO₂ (B)/EG electrode delivers a specific capacity of 75 mAh g^-1 at 10 A g^-1 along with 70% capacity retention after 1000 cycles at 2 A g^-1. Galvanostatic intermittent titration (GITT) and electrochemical impedance spectroscopy (EIS) measurements substantiate the reduction in charge-transfer resistance accompanied by enhanced Li⁺ diffusion. Density functional theory (DFT) calculations further verify the presence of the BIEF and clarify its role in lowering Li⁺ insertion/extraction energy barriers, thereby enabling highly reversible and stable high-rate operation. Overall, this study demonstrates that BIEF modulation can effectively address the intrinsic kinetic limitations of intercalation-type materials, offering a viable strategy for the development of next-generation high-power, fast-charging lithium-ion battery anodes.