Coupled Biphasic NaMnO ₂ Cathode and Ti ₃ C ₂ MXene Anode with Complementary Charge-Storage Kinetics for Aqueous and Non-aqueous Sodium-Ion Hybrid Energy Storage

A metallic sodium-free hybrid electrochemical system has been developed by coupling a biphasic birnessite-type NaMnO2 cathode with a multilayer Ti3C2Tx MXene anode, exhibiting complementary and cooperative electrochemical behavior. The orthorhombic/monoclinic NaMnO2 structure enables stable Na+ intercalation/deintercalation, while Ti3C2Tx provides fast, surface-driven pseudocapacitive charge storage with favorable interfacial kinetics. This combination offers kinetic complementarity between diffusion-controlled and surface-dominated processes, leading to efficient charge balancing and enhanced rate performance. Assembled coin cell devices exhibit outstanding rate capability and cycling stability in both aqueous (Na2SO4) and non-aqueous (NaPF6 in EC/DMC) electrolytes with a higher voltage window for enhancing energy density. Energy and power densities reach 90 and 610 W/kg in the aqueous system, and 360 and 970 W/kg in the organic one, with 97 and 88% capacity retention after 1000 cycles, respectively. The demonstrated universality of this electrode pairing establishes a versatile, safe, and sustainable strategy for high-performance sodium-ion energy storage beyond metallic sodium systems.