Article Link: https://www.nature.com/articles/s41560-020-0584-y
Driven by the urgent demand for large-scale energy storage, rechargeable batteries featuring high safety, environmental friendliness, and high energy density are attracting ever-increasing attention. Aqueous rechargeable batteries based on nonflammable and low-cost water-based electrolytes, such as the Zn-MnO2 battery, have a safety advantage, offering robustness and cost advantages. Alkaline zinc–manganese batteries have long been commercialized, but their working voltage and rechargeability are still limited due to the alkaline operating condition applied in most applications. While the alkaline environment can provide stability for the use of Zn anodes, it suppresses the cathode performance due to the formation of poorly reversible intermediates. Moreover, previous studies have found that although the use of an acidic solution works well for MnO2, it introduces side reactions, such as the hydrogen evolution reaction and serious corrosion of Zn, which thus limits the stability and practicability of the batteries.
To combine the merits of operating Zn anodes in an alkaline condition and MnO2 cathodes in an acidic condition, here we demonstrate various electrolyte-decoupling strategies, including using acidic and alkaline electrolytes separated by an ion-selective membrane or a bipolar membrane or a neutral electrolyte. The decoupled Zn–MnO2 battery (DZMB) with optimized structure has an exceptionally high open-circuit voltage of 2.83 V and also demonstrates good cycling stability even in deep cycling condition. We also demonstrate the feasibility of the DZMB in integrating with a wind and photovoltaic hybrid power generating system. We further extend this electrolyte-decoupling strategy to other Zn-based aqueous batteries such as Zn–Cu and Zn–Ag batteries.
Science sometimes thrives on mistakes, which can often contain surprising discoveries. The origin of this work is no exception. It occurred unintentionally when we assembled alkaline Zn–MnO2 battery with freshly electrodeposited MnO2, which has some residual H2SO4 (from the electrodeposition bath) on the MnO2 surface. At that moment, something interesting happened. The assembled battery exhibited extra higher discharge voltage than conventional Zn–MnO2 battery, which encourages us to strip things down to basics, leading to the formation of the article. The decoupling strategy is surprising, while when we trace back to the early history of the battery, we would find that Prof. Daniell had utilized such a strategy to build the well-known Daniell battery. The Daniell battery, also known as Zn–Cu battery, consists of two different electrolytes (H2SO4 and CuSO4), enabling the smooth and steady power supply and formed the basis of electrochemical research. In this regard, we are greatly honoured to think alike with Prof. Daniell and it feels like we are talking to each other spiritually after nearly two hundred years later. However, we are also ashamed for we did not realize and utilize the decoupling strategy earlier, which is obviously proposed by Prof. Daniell. May we all stand on the shoulders of giants, stay humble, stay foolish, and try our best to broaden the boundaries of human knowledge, making the world a better place.