Heterostructure‐Engineered TiO$_2$‐TiN Electrocatalyst Boosts Bidirectional Sulfur Redox Kinetics in Magnesium–Sulfur Batteries

The sluggish sulfur redox kinetics in magnesium–sulfur (Mg–S) batteries leads to low discharge voltage, poor sulfur utilization, and severe magnesium polysulfides (MgPS) shuttling, limiting their practical energy density. Herein, a heterostructure-engineered TiO$_2$-TiN electrocatalyst is rationally constructed and applied to separator modification to accelerate bidirectional sulfur conversion reactions. The TiO$_2$-TiN heterostructure induces charge redistribution, promoting electron/ion transport and providing strong chemical anchoring toward MgPS. Density functional theory calculations reveal that the heterostructure substantially lowers the energy barriers for MgPS and MgS dissociation, thereby enhancing the reversible MgPS ⇄ MgS conversion kinetics, which is corroborated by spectroscopic and electrochemical analyses. As a result, sulfur cathodes incorporated with the TiO$_2$-TiN-modified separator exhibit well-defined discharge plateaus and outstanding rate capability, delivering a high energy density of 1370 Wh kg$^{−1}$ at 0.1 C—three times higher than that of the cathode using the pristine separator. A reversible capacity of 254.8 mAh g$^{−1}$ at 1.0 C is achieved, far surpassing the pristine counterpart (38.3 mAh g$^{−1}$) and outperforming most previously reported Mg–S systems. ... mehrThis work demonstrates a viable heterostructure-based catalytic strategy to boost sulfur redox kinetics and achieve high-rate Mg–S batteries.