Abstract: Electrolytic manganese dioxide is one of the promising cathode candidates for electrochemical energy storage devices due to its high redox capacity and ease of synthesis. Yet, high‐loading MnO2 often suffers from sluggish reaction kinetics, especially in non‐aqueous electrolytes. The non‐uniform deposition of MnO2 on a porous current collectors also makes it difficult to fully utilize the active materials at high mass loading. Here, a 3D printed graded graphene aerogel (3D GA) that contains sparsely separated exterior ligaments is developed to create large open channels for mass transport as well as densely arranged interior ligaments providing large ion‐accessible active surface. The unique structural design homogenizes the thickness of electro deposited MnO2 even at an ultrahigh mass loading of ≈70 mg cm−2. The electrode achieves a remarkable volumetric capacity of 29.1 mA h cm−3 in the non‐aqueous electrolyte. A Li‐ion hybrid capacitor device assembled with a graded 3D GA/MnO2 cathode and graded 3D GA/VOx anode exhibits a wide voltage window of 0–4 V and a superior volumetric energy density of 20.2 W h L−1. The findings offer guidance on 3D printed electrode design for supporting ultrahigh loading of active materials and developments of high energy density energy storage devices.

Electrolytic MnO2 batteries store charges via the Mn2+/MnO2 two-electron transfer process with higher capacity and voltage than conventional one-electron (Zn2+ or H+) intercalation reactions. Yet, the opposite effect of interfacial H+ on the dissolution/deposition processes and the role of interfacial H2O are rarely discussed. Here we introduce tetrafluoroborate (BF4-) into the sulfate-based electrolyte to regulate interfacial H+ and H2O activity. First, BF4- hydrolysis increases the electrolyte’s acidity, promoting MnO2 dissolution. Second, BF4- forms H-bond networks with interfacial H2O that assist H+ diffusion while retaining a sufficient H2O supply to facilitate MnO2 deposition. As a result, the cathode-free Zn//MnO2 electrolytic cell achieves a high platform of ∼1.92 V and energy efficiency of ∼84.23%. Significantly, the cell delivers 1000 cycles at 1 C with ∼100% Coulombic efficiency and a high energy efficiency retention of 93.65%. Our findings disclose a new strategy to promote Mn2+/MnO2 platform voltage and energy efficiency.