Manipulating Ion Concentration to Boost Two-Electron Mn4+/Mn2+ Redox Kinetics through a Colloid Electrolyte for High-Capacity Zinc Batteries

Aqueous zinc batteries (ZBs) have flourished due to their advantages of low-cost and intrinsically safe water-based electrolytes. However, in the traditional liquid electrolyte, sufficient energy density and efficiency for practical utility have not been realized yet. Here, instead of the use of a strong acid/alkali pH environment to elevate the working voltage in an aqueous solution, an ion concentration/dilution strategy is proposed to trigger the extra deposition/dissolution capacity of the Mn4+/Mn2+ redox reaction in normal Zn/MnO2 batteries. With the precipitation and release of Zn2+ ions during the discharge/charge process, the adjustment of manganese concentration is successfully realized via the reciprocal Zn/Mn ionic exchange rendered by the bentonite colloidal (Ben-colloid) electrolyte. This electrolyte also triggers a self-dissolution/deposition reaction even in the cathode-free system. Consequently, the Zn/MnO2 battery with Ben-colloid electrolyte affords up to 1.7x capacity release (480.7 mAh g(-1)) on average compared with a liquid electrolyte at 0.2 A g(-1), higher capacity retention (94.3% vs 63.6%) after 500 cycles at 1 A g(-1), and good elevated-temperature endurability (up to 80 degrees C). This work opens up a new horizon to improve the energy density of water-based metal ion batteries by the use of a functional electrolyte.

Automated summary

By using an ion concentration/dilution strategy, the capacity and efficiency of Zn/MnO2 batteries can be improved, leading to enhanced performance in terms of capacity release, cycle life, and elevated-temperature endurance.