NaV1.25Ti0.75O4 Engineered by an Element Regulation Strategy as a Low-Potential and Pseudocapacitive Anode for Li-Ion Capacitors

Searching for a high-power anode material with a low but safe insertion potential is an efficient method for achieving a high-performance Li-ion capacitor (LIC). In this study, we first introduce NaV1.25Ti0.75O4 as a favorable anode for high-performance LIC devices. A series of porous carbon-coated NaV1–xTi1+xO4 (NV1–xT1+x@C) are prepared by a modified two-step solid-state method. Relying on regulating the V/Ti ratio, the average potential can decrease from 0.67 V (NV0.75T1.25@C) to 0.56 V (NV1.25T0.75@C). NV1.25T0.75@C exhibits a high capacity of 379.8 mAh g–1, an excellent rate capability, and a remarkable cyclic stability. Through kinetic analysis, it is proven to possess a fast pseudocapacitive property. The Li+ storage mechanism of NV1.25T0.75@C has been systematically investigated by in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), and ex situ high-resolution transmission electron microscopy (HRTEM) techniques. Solid-solution insertion-type reaction and 3.5 electron transfer reaction can be found in the Li+ storage process of NV1.25T0.75@C. Through density functional theory (DFT) calculations, an open and large channel with a low Li+ diffusion energy barrier can be found. When employing this low-potential NV1.25T0.75@C as the anode and AC-80F as the cathode, such an LIC full cell can demonstrate a high energy density of ∼107.3 Wh kg–1 at 190 W kg–1, a maximum power density of 15.2 kW kg–1, and a long cycle life of over 3000 cycles. These results indicate that NV1.25T0.75@C can serve as a new promising anode and provides a novel element regulation strategy for achieving low-potential as well as high-power anode materials for LICs.