Understanding Interlayer Deprotonation of Hydrogen Titanium Oxide for High-Power Electrochemical Energy Storage

Negative electrode materials that possess fast lithium insertion kinetics are in high demand for high power lithium-ion batteries and hybrid supercapacitor applications. In this work, hydrogen titanium oxides are synthesized by a proton exchange reaction with sodium titanium oxide, resulting in the H2Ti3O7 phase. We show that a gradual water release in four steps yields intermediate phases of hydrogen titanate with different degrees of interlayer protonation. In addition, a synthesis route using zinc nitrate is explored yielding H2Ti3O7 with a high rutile content. This material dehydrates already at a lower temperature, resulting in a lamellar rutile titania phase. The hydrogen titanate materials with partially protonated interlayers are tested as negative electrodes in a lithium-ion battery and hybrid supercapacitor setup, showing an improved performance compared to the fully protonated phases. The performance in half-cells reaches around 168 mAh/g, with high retention of 42 mAh/g at 10 A/g. This translates to an energy of 88 Wh/kg for a full-cell with a maximum power of 9.2 kW/kg and high cycling stability over 1000 cycles.