Dissimilar Electrolyte Decouples Zn and MnO₂ Redox Chemistry Enabling Dual-Electrode-Free Lean-Electrolyte Batteries

Dual-electrode-free Zn-MnO₂ batteries offer exceptionally high theoretical energy density (616 mAh g^-1 at 2 V) and simplified manufacturing, yet their practical use is hampered by low Coulombic efficiency (CE) and unstable cycling, arising from the intrinsic incompatibility of Zn and MnO₂ redox chemistries. Previous studies employing preloaded Zn and excess electrolyte obscure this incompatibility. Herein, we design a dissimilar electrolyte architecture to decouple Zn plating-stripping from MnO₂ deposition-dissolution, fundamentally addressing their incompatibility. The architecture integrates two distinct gels, wherein a self-assembled nanometer-thin water layer functions as a "soft wall" for selective ion transport due to binding energy differences at the gel/water interface. Further, the screening effect induced by the discrepancy in ionic conductivity across the junction is investigated for the first time, offering new insights into ion transport in heterogeneous electrolytes. This strategy enables a dual-electrode-free lean-electrolyte Zn-MnO₂ cell with areal and volumetric energy densities of 3.1 mWh cm^-2 and 25.8 Wh L^-1, and a power density of 24.1 mW cm^-2 at 2 mAh cm^-2. The cell also achieves an average CE of 91% at 1mAh cm^-2 cycling. Moreover, the dual-electrode-free configuration readily integrates with diverse current collectors, extending the concept to flexible and stretchable batteries for wearable electronics, soft robotics, and beyond.