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.