Femtosecond laser drilled micro-hole arrays in thick and dense 2D nanomaterial electrodes toward high volumetric capacity and rate performance

Two dimensional (2D) nanomaterials have great application potential in developing the energy storage systems with high volumetric energy and power densities. However, due to the sluggish ion diffusion, achieving both high volumetric capacities and rate performance in thick and dense 2D nanomaterial electrodes is still challenging. Here, we report a femtosecond laser drilling method to introduce appropriate micro-hole arrays into the thick and dense electrodes for facilitated ion transport. These micro-hole arrays shorten ion transport paths and thus significantly reduce the ion transport resistance. More importantly, constructing micro-hole arrays with hole spacing higher than 40 μm rarely sacrifices the density of the electrode. The effectiveness of micro-hole arrays to improve capacities and rate performance of the thick and dense electrodes is evidenced by two model cases: a TiO₂-based electrode constructed with the upper-layer TiO₂-coated graphene hybrids and under-layer graphene (dTiO₂-G/G), and a graphene electrode. As presented, the micro-hole array with a hole spacing of 40 μm decreases the ionic resistance of the dTiO₂-G/G electrode, and consequently improves the volumetric capacity at 10C from 15.8 to 97 mA h cm⁻³. Such micro-hole array also improves the volumetric capacity and rate performance of the graphene electrode.