Tianjin University Laboratory proposes a design for a stable, high-energy zinc-manganese battery

The global demand for rechargeable batteries has grown exponentially over the past decade or so, as they are needed to power an increasing number of portable electronic devices such as smartphones, laptops, tablets, smartwatches and fitness trackers. To work more efficiently, rechargeable batteries should have a high energy density while also being safe, stable and environmentally friendly.

Although lithium-ion batteries are one of the most widely used rechargeable energy storage systems, they contain volatile organic electrolytes, which greatly reduces their safety.

The most promising alternatives to lithium batteries are batteries based on non-flammable and low-cost water-based electrolytes, such as lead-acid batteries and zinc-manganese batteries. These batteries have many advantages, including greater safety and lower production costs. However, so far, their performance, operating voltage and rechargeability have certain limitations compared to lithium batteries

Researchers from the Key Laboratory of Advanced Ceramics and Processing Technology of the Ministry of Education and the Key Laboratory of Composite Materials and Functional Materials of Tianjin University recently proposed a new design strategy to improve the performance of zinc-manganese oxide (Zn-MnO2) batteries. The method they proposed in a paper published in the journal Nature Energy is to decouple the electrolyte inside the battery to achieve optimal redox chemistry on the zinc and manganese dioxide electrodes.

Professor Zhong, one of the researchers, said: "Our paper was completed accidentally when we assembled an alkaline zinc-manganese battery with freshly electrodeposited MnO2, and there was some residual H2SO4 on the surface of the MnO2. The assembled battery showed a higher discharge voltage than conventional Zn-MnO2 batteries, which encouraged us to strip things down to the basics and lay the foundation for our research."

Zhong's team found that their decoupled electrolyte strategy allowed for better performance in Zn-MnO2 batteries with an open circuit voltage of 2.83 V. This is quite promising considering that more traditional Zn-MnO2 batteries typically have a voltage of 1.5 V.

The battery made using their electrolytic decoupling strategy showed only a 2% drop in capacity after 200 hours of continuous use and charging. In addition, the battery still maintained 100% of its capacity at various discharge current densities. Notably, the researchers demonstrated that the battery made using their method can also be integrated with wind and photovoltaic hybrid systems, which further improves the sustainability of the battery.

"The electrolytic decoupling strategy aims to achieve the optimal redox chemistry of both the zinc and manganese dioxide electrodes simultaneously," explained Professor Zhong. "Decoupling the operating conditions of the MnO2 cathode and Zn anode allows the acidic MnO2 and alkaline Zn redox reactions to proceed simultaneously within a single cell. The resulting DZMB battery has a higher operating voltage and longer cycle life than conventional alkaline zinc-manganese batteries."

In the future, the new design strategy proposed by Professor Zhong and his colleagues could be used to produce new Zn-MnO2 batteries that are low-cost and safe, but at the same time have extremely high open-circuit voltage and longer cycle life. Notably, the same strategy could also be used to improve the performance of other zinc-based aqueous batteries, including those containing zinc-copper and zinc-silver combinations.

Professor Zhong said: "Since the cost and performance of current state-of-the-art ion-selective membranes are still unsatisfactory, our future research will focus on decoupled designs that do not use such membranes.