Materials Science

A Battery for Twos

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Science  22 Nov 2013:
Vol. 342, Issue 6161, pp. 911
DOI: 10.1126/science.342.6161.911-b

In theory, Mg batteries can obtain higher energy density and specific energy than Li-based ones, because of the divalent nature of the Mg ion. They may also prove safer than those that rely on Li metal. However, it has been a challenge to find materials that can allow for the fast and reversible insertion of Mg2+. Wang et al. explore materials from the Prussian Blue family, which have an open framework and a crystal structure similar to those of ABX3 perovskites. For their materials, the B sites were occupied with either Ni2+ at the N-coordinated sites or Fe3+ at the C-coordinated sites, linked together with cyano (CN) groups, which increase the separation distance between the Ni and Fe ions to allow for cation insertion. Nickel hexacyanoferrate was synthesized as nanoparticles and combined with a C cloth as the working electrode. Over 2000 cycles, they were able to reversibly insert and remove Mg2+, Ca2+, Sr2+, and Ba2+, when using the appropriate electrolyte. The specific capacity tended to decrease with cycling, but that was probably due to the dissolution of Ni2+ into the electrolyte; the capacity loss was eliminated by dissolving Ni2+ into the electrolyte before cycling. Changes in the hysteresis seen with increasing charge/discharge rates suggest that there might be a rate-limiting dehydration step during the insertion process.

Nano Lett. 10.1021/nl403669a (2013).

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