An MBene-based colloidal electrolyte for high depth-of-discharge and energy-density 2 Ah-scale Zn metal batteries

Sluggish diffusion rates and exceptionally uneven distribution of Zn²⁺ at the electrode/electrolyte interface under high depth-of-discharge (DOD) severely limit the advancement of high-energy-density Zn metal batteries (ZMBs). Herein, a hydrated eutectic colloidal electrolyte based on a two-dimensional transition metal boride, Mo_4/3B₂T₂ MBene (where T represents –OH and –F), is developed. The good Zn²⁺ affinity of terminal groups of MBene promotes ion diffusion, thus resulting in a high Zn²⁺ transference number of 0.89, which significantly enhances and balances the ion concentration on the Zn anode surface, improving the Zn deposition dynamics. As a result, the Zn anode with an ultrathin thickness of 10 μm demonstrates 900 h of cyclability under an ultrahigh DOD of 90%. Additionally, the enlarged Zn‖Zn pouch cell with a scale of 10 × 10 cm² shows a stable cyclic performance for 500 h at 60% DOD, meanwhile the constructed 2 Ah four-electron Zn‖I₂ pouch battery delivers an energy density of 158.5 Wh L⁻¹ under the same conditions. This work provides new guidelines for the development of high-DOD metal anodes and high-energy-density metal batteries.