Pseudocapacitive TiNb2O7/reduced graphene oxide nanocomposite for high–rate lithium ion hybrid capacitors

Lithium ion hybrid capacitors (LIHCs) have a capacitor-type cathode and a battery-type anode and are a prospective energy storage device that delivers high energy/power density. However, the kinetic imbalance between the cathode and the anode is a key obstacle to their further development and application. Herein, we prepared TiNb 2 O 7 nanoparticles through a facile solvothermal method and annealing treatment. Then a homogeneous three-dimensional (3D) self-supported reduced graphene oxide (rGO)-coated TiNb 2 O 7 (TiNb 2 O 7 /rGO) nanocomposite was constructed by freeze-drying, followed by a high-temperature reduction, which demonstrates an enhanced pseudocapacitive lithium ions storage performance. Benefiting from the improved electrical conductivity , ultrashort ions diffusion paths, and 3D architecture, the TiNb 2 O 7 /rGO nanocomposite exhibits a high specific capacity of 285.0 mA h g −1 , excellent rate capability (73.6% capacity retention at 8 A g −1 ), and superior cycling stability. More importantly, quantitative kinetics analysis reflects that the capacity of TiNb 2 O 7 /rGO is mainly dominated by capacitive behavior, making it perfectly match with the capacitor-type activated carbon (AC) cathode. By using pre-lithiated TiNb 2 O 7 /rGO as anode material and AC as cathode material , a high-rate TiNb 2 O 7 /rGO//AC LIHC device can be fabricated, which delivers an ultrahigh energy density of 127 Wh kg −1 at the power density of 200 W kg −1 , a maximum power density of 10 kW kg −1 at the energy density of 56.4 Wh kg −1 , and durable service life.