Manipulating oxygen vacancy for controlling the kinetics of Nb₂O₅-based anode in Li-ion capacitor

Introducing appropriate oxygen vacancies (OVs) improves the integral conductivity of the Nb₂O₅ anode of Li-ion capacitors (LICs). Whereas a few recent studies link the OVs level and the kinetics of Nb₂O₅, the quantitative relationship between the OVs and the performance of Nb₂O₅ remains elusive. Herein, we show that the OVs concentration in Nb₂O₅ can be quantitatively manipulated by regulating the oxygen content in niobium complex (NbL) precursors, thus controlling the kinetics of the Nb₂O₅-based anode. The OVs concentration is inversely proportional to the oxygen content in the NbL, where it facilitates the electronic transfer and the Li-ion migration of Nb₂O₅ with optimal introduction. In addition, the ligand in the NbL can also be used as a sacrificial template for creating an N-doped carbon coating wrapping Nb₂O₅ nanoparticles with OVs to further improve the electronic conductivity of the composite. This was followed by depositing the NbL nanoparticles via electrophoretic deposition for assembling binder-free electrodes. The integrated electrode-based LICs deliver 76 μWh cm⁻² at 550 μW cm⁻² and retain 94 % of the capacity after 5000 cycles. This work provides a new recognition for the design of metal oxide electrodes with fast kinetics for LICs from material modification to electrode material assembly.