NiMn Layered Double Hydroxide Nanosheets In-situ Anchored on Ti₃C₂ MXene via Chemical Bonds for Superior Supercapacitors

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Abstract

The poor conductivity, unsatisfactory stability, and severe aggregation of nanosheets have been recognized as the main reasons that limit the electrochemical performance of layered double hydroxide (LDH) materials. The present work proposes a chemical structure that consists of in situ anchoring highly dispersed NiMn-LDH nanosheets on Ti3C2 MXene sheets via chemical bonds. Negatively charged MXene sheets will provide abundant heterogeneous nucleation sites for NiMn-LDH during the in situ crystallization process, and the surface functional groups can strengthen the chemical connection between the two materials, achieving higher charge transfer and ion diffusion rates between MXene and NiMn-LDH compared with mechanical mixtures of MXene and NiMn-LDH (MM NiMn-LDH/MXene). The size of the NiMn-LDH in the NiMn-LDH/MXene hybrid composite can be ∼10 nm smaller than that of pure NiMn-LDH nanosheets (∼50 nm), which is beneficial for active site exposure and ion conduction. The optimized hybrid nanocomposite NiMn-LDH/MXene 2:1 delivers a high specific capacitance of 1575 F g–1 at 0.5 A g–1 (689 F g–1 for pristine NiMn LDH, 192 F g–1 for pristine MXene, and 731 F g–1 for MM NiMn-LDH/MXene), a superior cycling stability of 90.3% after 10 000 cycles at 5.0 A g–1, and good rate capability of 80% capacitance retention at 20 A g–1. Furthermore, the assembled asymmetric supercapacitor (ASC) with activated carbon (AC) and NiMn-LDH/MXene 2:1 exhibits excellent specific capacitance (169.8 F g–1 at 0.5 A g–1) and outstanding cycling stability (91.8% after 10 000 cycles at 2 A g–1). A higher energy density of 126 Wh kg–1 at 0.74 kW kg–1 and higher power density of 3.3 kW kg–1 at 97 Wh kg–1 can be achieved with NiMn-LDH/MXene 2:1, which provides an effective approach to design next-generation SC electrode materials exhibiting excellent rate performance and cycling stability.

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