3D-Printed Zn-Ion Hybrid Capacitor Enabled by Universal Divalent Cation-Gelated Additive-Free Ti₃C₂ MXene Ink

The construction of aqueous Zn-ion hybrid capacitors (ZICs) reconciling high energy/power density is practically meaningful yet remains a grand challenge. Herein, a high-capacitance and long-life ZIC is demonstrated by 3D printing of a Ti₃C₂ MXene cathode, affording optimized carrier transport, facile electrolyte penetration, and ample porosity. The 3D-printable additive-free MXene ink with desirable rheological property is derived by a fast gelation process employing a trace amount of divalent cations, which overcomes the tedious post-treatments required for additive removal. The thus-fabricated 3D-printed (3DP) MXene cathode results in a dual-ion storage mechanism to synergize pseudocapacitive behavior of H⁺ and electrical double-layer capacitive behavior of Zn²⁺, which is systematically probed by a wide suite of in situ/ex situ electroanalytic characterizations. The 3DP MXene cathode accordingly exhibits a favorable areal capacitance of 1006.4 mF cm^-2 at 0.38 mA cm^-2 and excellent rate capability (184.4 F g^-1 at 10 A g^-1), outperforming the state-of-the-art ZICs. More impressively, ZIC full cells comprising a 3DP MXene cathode and a 3DP Zn anode deliver a competitive energy/power density of 0.10 mWh cm^-2/5.90 mW cm^-2 as well as an ultralong lifespan (86.5% capacity retention over 6000 cycles at 10 mA cm^-2).