Trivalent Ti self-doped Li₄Ti₅O₁₂: A high performance anode material for lithium-ion capacitors

To enhance kinetics of lithium insertion/extraction of anode materials for hybrid lithium-ion capacitors (hybrid LICs), we develop a new applicable strategy toward the synthesis of trivalent Ti self-doped Li₄Ti₅O₁₂ nanoparticles. Starting with Ti₂O₃, we show that subsequent solid state reaction with Li₂CO₃ leads to the formation of trivalent Ti self-doped Li₄Ti₅O₁₂. The presence of trivalent Ti gives rise to high electric conductivity and the nanostructure reduces the transport path lengths of lithium-ions and electrons, permitting fast kinetics for both transported lithium-ions and electrons, thus enabling high-power performance. A high performance hybrid LIC is fabricated by using Ti^{3 +} self-doped Li₄Ti₅O₁₂ as an insertion-type anode and activated carbon derived from outer peanut shell as cathode, which delivers high energy density (67 Wh kg^{- 1}), high power density (8000 W kg^{- 1}). Additionally, the device still retains about 79% of its original capacity even after 5000 cycles at 0.5 A g^{- 1}.