The schematic representation shown in Scheme. 1 illustrates the process of sandwich-like MXene/AAC composite. First, a thin layer of MXene, as a flexible and conductive binder, is formed using vacuum-assisted filtration of a colloidal solution containing delaminated suspended Ti3C2T3 flakes. Then, a layer of AAC is deposited on the top of Ti3C2T3 layer. Finally, the sandwich-like MXene/AAC composite is produced by repeating the process. The procedure is much simpler than the conventional paste electrode fabrication means by mixing the Polytetrafluoroethylene (PTFE) as the binder, Acetylene black as the conductive binder and the active materials in aqueous solution, then coating the slurry onto nickel foam current collectors5, 11.
Fig.1. FESEM and TEM images of MXene/AAC: (a-i): FESEM images of MXene/AAC 2:1 (j-l): TEM images of MXene/AAC 2:1.
The morphology and microstructure of synthetic MXene/AAC 2:1 are observed by Field emission electron microscope (FESEM)(Fig.1.a-i) at different magnifications and the corresponding energy-dispersive spectrometry (EDS) mapping (Fig S1 (c)). As shown in Fig.1. (a-c), the MXene/AAC hybrids have a sandwich-like structure, where the AAC powers are evenly encapsulated in the MXene flakes, which could effectively avoid MXene flakes stacking and could improve the electrochemical property. The MXene exhibits a separately lamellar and accordion-like structure with lateral size of 0.5-2 µm and the AAC particles are relatively rigid and irregular with the size of 10 nm-1µm shown in Fig.1. (d-i), demonstrating that LiF and HCl treatment effectively removed Al ion from the lattices. The EDS mapping of C, Ti, O and N exhibited in Fig. S1(c). It is obviously observed that C and Ti are uniformly distributed as a whole, without visible boundaries. The sandwich-like structure with the encapsulation of the AAC particles and MXene flakes in the MXene/AAC hybrids is further confirm by TEM shown in Fig.1. (j-l) and Fig. S1(a-b), respectively. The Fig.S2 shows that the MXene/AAC film are flexible, freestanding and could be directly employed as electrodes for supercapacitors without the any metal current collector.