Cation and anion (de)intercalation into MXene/Perovskite oxides for high-rate intercalation pseudocapacitance

Intercalation pseudocapacitance is the next hope for electrochemical energy storage devices to offer high energy density without sacrificing power density. Under intercalation pseudocapacitance, ions (e.g. Li⁺ into T-Nb₂O₅, but not limited to cation intercalation only) intercalate into the host materials without phase conversions and no limitations from solid-state diffusion, unlike batteries. Here, a concept of both cations and anions (de)intercalation into the hybrid electrode comprising nanocomposite (MLMO) of MXene (Ti₃C₂T_x) and perovskite oxides (LaMnO_3-δ, LMO) are demonstrated. Independently, multilayered MXene and oxygen deficient LMO show cation and anion-based intercalation pseudocapacitance, respectively. During analyzing the electrochemical process through ex situ XPS, it is observed that not only K⁺ ions but OH⁻ ions also (via formation of O²⁻) (de)intercalate into MLMO and contribute to the total charge storage. Accordingly, MLMO exhibits high capacitance retention (70.82%) even at a high current density of 30 A g⁻¹ (313.6 F g⁻¹). Next, a fast-kinetics dual-ion intercalated pseudocapacitive symmetric device with 1.6 V is fabricated which shows a high energy density of 34.1 Wh kg⁻¹ and astonishing power density of 14.51 kW kg⁻¹. This study sheds light on new dual-ion intercalation chemistry and sets a concrete path for the establishment of high energy storage devices with fast-kinetics.