Hydroxyl Conducting Hydrogels Enable Low-Maintenance Commercially Sized Rechargeable Zn–MnO2 Batteries for Use in Solar Microgrids

Abstract

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.

Rechargeable Manganese Dioxide−Zinc Batteries: A Review Focusing on Challenges and Optimization Strategies under Alkaline and Mild Acidic Electrolyte Media

“…The MnO 2 À Zn system with gel electrolyte technology was performance tested through IEC solar off-grid protocol, in which the batteries are subjected to test under different SOC values at 40 °C. [119] The different SOC values signify the seasonal conditions. For example, high solar irradiation is expected at summer that synchronizes with high SOC battery operation.…”

“…Cho and coworkers developed a commercial MnO 2 À Zn system and the same was performance tested under solar microgrid application for the first time. [119] The well-known adverse effects, like zinc dendrite growth, ZnMn 2 O 4 formation, zincate crossover, Mn-dissolution etc., under liquid alkaline electrolytes were effectively mitigated by the introduction of gel electrolytes, and resultantly, improved reversibility has been achieved. The commercial sized prismatic cells with gel electrolyte exhibit excellent cyclibility, i. e., 100% capacity retention over more than 700 and 300 cycles for 9.5 and 19 Ah devices, respectively.…”

“…This full cell shows good cycling stability under 1 mA cm −2 charge/discharge within 0.8–1.9 V, and achieves 68.2% capacity retention over 80 cycles. Cho and coworkers developed a commercial MnO 2 −Zn system and the same was performance tested under solar microgrid application for the first time [119] . The well‐known adverse effects, like zinc dendrite growth, ZnMn 2 O 4 formation, zincate crossover, Mn‐dissolution etc., under liquid alkaline electrolytes were effectively mitigated by the introduction of gel electrolytes, and resultantly, improved reversibility has been achieved.…”

“…By contrast, the 19 Ah prismatic device with liquid electrolyte degrades within 100 cycles. The MnO 2 −Zn system with gel electrolyte technology was performance tested through IEC solar off‐grid protocol, in which the batteries are subjected to test under different SOC values at 40 °C [119] . The different SOC values signify the seasonal conditions.…”

High-Performance InZn Alloy Anodes toward Practical Aqueous Zinc Batteries

“…Zinc-based batteries (e.g., MnO 2 /zinc) have been commercialized as a primary battery and are one of the dominant technologies in the battery market. However, the rechargeability of MnO 2 /zinc , and other Zn-based batteries is significantly limited by zinc anode challenges. − The Zn dendrite issue is the most prevalent cause of cell failure for aqueous Zn batteries with a mildly acidic electrolyte. To date, various approaches, including anode structure control, surface coatings, and electrolyte additives have been developed to mitigate dendrite formation. − However, high performance at large capacities, high depth-of-discharge (DOD), and high plating current density are not common in the reported literature.…”