RESUMO
Zinc (Zn)-anode batteries, although safe and non-flammable, are precluded from promising applications because of their low voltage (<2 V) and poor rechargeability. Here, we report the fabrication of rechargeable membrane-less Zn-anode batteries with high voltage properties (2.5 to 3.4 V) achieved through coupling cathodes and Zn-anodes in gelled concentrated acid and alkaline solutions separated by a gelled buffer interlayer containing the working ions. The concentrated gelled buffer interlayers perform dual functions of regulating the pH of the system and acting as the source and sink of the working ions. With this strategy we show low-cost membrane-less 2.5 to 3.4 V Zn-manganese dioxide (MnO2) batteries capable of cycling 10-100% of 617 mA h g-1-MnO2 and 20-30% of 820 mA h g-1-Zn and demonstrate their application in electric vehicles. This strategy is then applied to other oxide-based cathode systems like Cu2O and V2O5, where voltages of 2 to 3 V are obtained in membrane-less batteries.
RESUMO
Zinc (Zn)-manganese dioxide (MnO2) rechargeable batteries have attracted research interest because of high specific theoretical capacity as well as being environmentally friendly, intrinsically safe and low-cost. Liquid electrolytes, such as potassium hydroxide, are historically used in these batteries; however, many failure mechanisms of the Zn-MnO2 battery chemistry result from the use of liquid electrolytes, including the formation of electrochemically inert phases such as hetaerolite (ZnMn2O4) and the promotion of shape change of the Zn electrode. This manuscript reports on the fundamental and commercial results of gel electrolytes for use in rechargeable Zn-MnO2 batteries as an alternative to liquid electrolytes. The manuscript also reports on novel properties of the gelled electrolyte such as limiting the overdischarge of Zn anodes, which is a problem in liquid electrolyte, and finally its use in solar microgrid applications, which is a first in academic literature. Potentiostatic and galvanostatic tests with the optimized gel electrolyte showed higher capacity retention compared to the tests with the liquid electrolyte, suggesting that gel electrolyte helps reduce Mn3+ dissolution and zincate ion migration from the Zn anode, improving reversibility. Cycling tests for commercially sized prismatic cells showed the gel electrolyte had exceptional cycle life, showing 100% capacity retention for >700 cycles at 9.5 Ah and for >300 cycles at 19 Ah, while the 19 Ah prismatic cell with a liquid electrolyte showed discharge capacity degradation at 100th cycle. We also performed overdischarge protection tests, in which a commercialized prismatic cell with the gel electrolyte was discharged to 0 V and achieved stable discharge capacities, while the liquid electrolyte cell showed discharge capacity fade in the first few cycles. Finally, the gel electrolyte batteries were tested under IEC solar off-grid protocol. It was noted that the gelled Zn-MnO2 batteries outperformed the Pb-acid batteries. Additionally, a designed system nameplated at 2 kWh with a 12 V system with 72 prismatic cells was tested with the same protocol, and it has entered its third year of cycling. This suggests that Zn-MnO2 rechargeable batteries with the gel electrolyte will be an ideal candidate for solar microgrid systems and grid storage in general.
