3D isotropic MXene films enabling minimized polarization for enhanced sodium-ion storage performance

Electrochemical sodium-ion storage has emerged as a tantalizing avenue for advanced energy storage systems. However, the pronounced polarization poses a formidable challenge for applications at high currents and low temperatures. Herein, we propose an electrode-level isotropic porosity generation route, which includes solution design and a scalable film-forming process, to fabricate a well-designed three-dimensional (3D) Ti3C2Tx film. The resulting 3D Ti3C2Tx film exhibits a distinctive isotropic architecture featuring interconnected horizontal and vertical channels. In contrast to the compact structure, the unique 3D isotropic architecture of the Ti3C2Tx film demonstrates a remarkable reduction in polarization, which is the outcome of comprehensive Na+ kinetics enhancement of the anode side. Consequently, capacity retentions exceeding 50% are achieved even at a current density of 20 A g−1 or sub-zero temperature (-20 °C). Furthermore, detailed analyses were conducted to elucidate the multifaceted effects of divergent pore structures on kinetic mechanisms, encompassing a thorough examination of distinct polarization effects. In addition, the assembly of a 3D Ti3C2Tx film//activated carbon sodium-ion hybrid capacitor demonstrates remarkable energy density and outstanding cycling stability. The electrode-level isotropic porosity generation route significantly enhances the electrochemical properties of MXene-based film, holding great potential for advancements in applications that can leverage this structural engineering.