Size-dependent electrochemical properties of vertically aligned MXene electrodes for fast Li-ion storage

MXenes are attractive electrode materials for batteries and pseudocapacitors because they have higher electronic conductivity than carbons or oxides and can exhibit surface-confined redox reactions. However, restacking of 2D nanosheets may limit the ionic transport in MXene electrodes and lead to sluggish charge/discharge. To understand and control the 2D mass transport properties of Ti3C2Tx MXene, we fabricated electrodes with different diffusion lengths and nanosheet alignments (vertical and horizontal). The electrodes were made by combining electrophoretic deposition and freeze-drying of delaminated size-regulated MXenes (95 to similar to 600 nm lateral size). Their electrochemical lithiation/de-lithiation behavior was studied in a non-aqueous electrolyte. Vertically-aligned Ti3C2Tx MXene film with a thickness of 300 mu m provided faster Li+ storage than horizontally-stacked MXene film with a thickness of 10 mu m. Electrodes made of small-size flakes exhibited higher discharge capacity and capacity retention at high rates due to a shorter Li+ diffusion path. The vertically aligned MXene electrodes show high electrochemical performance and fast charge/discharge.