11.29.16

Make No Assumptions in Building a Better Battery

On the path to ultra-stable, low-cost, earth-abundant zinc-manganese oxide rechargeable batteries for the electric grid.

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A highly reversible aqueous zinc-manganese oxide battery offers a cost effective, environmental friendly alternative energy storage to help stabilize the electrical grid. In depth analysis of the structure and chemistry in zinc-manganese oxide batteries provided insights on the mechanisms that controlled the battery chemistry and allowed development of a system with longer battery lifetime.  Shown is a high resolution image of the atomic structure of the manganese oxide battery electrode material when fully discharged (left) and charged (right).  The discharged image shows that the initial pristine, well-defined nanofibers were transformed to short nanorods and nanoparticle aggregates. When recharged, the structure reverts to the crystalline manganese oxide structure.  (The spacing between the fringes in the images is about 0.3 nanometers – less than the width of a single strand of DNA, or the size of a few atoms side by side)

The Science

Ultra-low cost rechargeable batteries could store sporadic wind and other energy sources until needed. A zinc-based battery seemed promising, but it quickly failed. Scientists discovered a reversible chemical conversion reaction mechanism, similar to what powers lead-acid car batteries. They used the reaction to manipulate the chemical balance inside the battery. The modified battery could be charged and discharged over 5,000 cycles, while retaining 92 percent of its initial storage capacity.

The Impact

Large-scale energy storage for wind and other intermittent sources could make renewable energy easier to use. The research showed that rechargeable zinc-manganese oxide could be a more viable solution than today’s lithium-ion and lead-acid batteries. In addition, the zinc-based batteries use abundant, inexpensive, and environmentally friendly materials.

Summary

Zinc-manganese oxide rechargeable batteries have been studied for more than 20 years, but the batteries usually stop working after a limited number of charge-discharge cycles. Researchers at Pacific Northwest National Laboratory asked “why?” Most researchers had assumed that rechargeable zinc-based batteries work via a mechanism similar to rechargeable lithium-ion batteries. They assumed that during use the charged atoms (ions) move in and out of microscopic regions within the battery. However, they found that zinc-manganese oxide batteries have a reversible chemical reaction. In this reaction, one material is transformed into another, similar to the chemistry in lead-acid batteries. They found the manganese oxide on the positive electrode reversibly reacted with protons from the water-based electrolyte, zinc sulfate, to form manganese oxyhydroxide and zinc hydroxyl sulfate. The team made these findings using instruments at the Environmental Molecular Sciences Laboratory, a U.S. Department of Energy scientific user facility. By understanding the inner workings of the batteries, they found that an optimal concentration of manganese sulfate added to the electrolyte suppressed the manganese ion dissolution reaction and stabilized the electrode. The addition slowed the degradation of the battery during use. The result was a better battery. It has a capacity of 285 mAhg-1, a much higher energy density than what lead-acid batteries offer. It retains 92 percent of this capacity after 5,000 charge cycles. This finding opens new opportunities for the development of low-cost, high-performance rechargeable aqueous batteries to store renewable energy for later use in the electrical grid.

Contact

Jun Liu
Pacific Northwest National Laboratory
jun.liu@pnnl.gov

Funding

This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences. Characterization was performed at the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility. Work at University of Washington was sponsored by the Inamori Foundation.   

Publications

H. Pan, Y. Shao, P. Yan, Y. Cheng, K.S. Han, Z. Nie, C. Wang, J. Yang, X. Li, P. Bhattacharya, K.T. Mueller, and J. Liu, “Reversible aqueous zinc/manganese oxide energy storage from conversion reactions.” Nature Energy 1, 16039 (2016). [DOI: 10.1038/NENERGY.2016.39]

Related Links

Pacific Northwest National Laboratory news release: Unexpected Discovery Leads to a Better BatteryExternal link

Highlight Categories

Program: BER, BES, MSE

Performer/Facility: University, DOE Laboratory, SC User Facilities, BER User Facilities, EMSL

Additional: Collaborations, International Collaboration

Last modified: 12/14/2016 4:31:56 PM