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

• Ti3 + self-doped Li4Ti5O12 was synthesized by a new strategy without use of any additional reducing reagents.
• The introduction of Ti3 + improved the rate capability and cycle stability of Li4Ti5O12 electrode.
• A high performance lithium-ion capacitor was fabricated by using Ti3 + self-doped Li4Ti5O12 as an insertion-type anode.

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 Ti3 + 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.

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