Rational construction of 2D/2D Ti3C2Tx/NiCo MOF heterostructure for highly efficient Li+ storage

Metal-organic framework (MOFs) have been regarded as ideal lithium-ion battery (LIB) anodes with abundant active sites, porous structure, shortened ion diffusion pathways, and adjustable component, but the MOF anodes suffer from the low electronic conductivity. Herein, we rationally design a 2D/2D Ti3C2Tx/NiCo MOF heterostructure through in-situ growth of ultrathin NiCo MOF nanosheets on the few-layer Ti3C2Tx MXene sheets. The carboxylate groups of BDC2− can form stable bond with the termination groups (e.g., -OH) on the Ti3C2Tx surface and hydroxyl groups in the lignin molecules, resulting in stable Ti3C2Tx/NiCo MOF interface and good structure stability of the 2D/2D Ti3C2Tx/NiCo MOF heterostructure. The Ti3C2Tx/NiCo MOF heterostructure could combine the advantages of 2D MXene nanosheets and 2D bimetallic MOF structure. The 2D bimetallic NiCo MOF can offer plenty of exposed active sites for Li+ intercalation, while the 3D conductive network structure based on the Ti3C2Tx can not only enhance the electronic conductivity, but also facilitate the electrode/electrolyte interface contact and promote the charge diffusion. The obtained 2D/2D Ti3C2Tx/NiCo MOF heterostructure anode demonstrates a high capacity of 637 mAh g−1 at 0.2 A g−1 after 200 cycles. Furthermore, the Li+ intercalation/extraction mechanism of the Ti3C2Tx/NiCo MOF heterostructure electrode is explored in detail.