Fast constructing polarity-switchable zinc-bromine microbatteries with high areal energy density.

Microbatteries (MBs) are promising candidates to provide power for various miniaturized electronic devices, yet they generally suffer from complicated fabrication procedures and low areal energy density. Besides, all cathodes of current MBs are solid state, and the trade-off between areal capacity and reaction kinetics restricts their wide applications. Here, we propose a dual-plating strategy to facilely prepare zinc-bromine MBs (Zn-Br 2 MBs) with a liquid cathode to achieve both high areal energy density and fast kinetics simultaneously. The Zn-Br 2 MBs deliver a record high areal energy density of 3.6 mWh cm -2 , almost an order of magnitude higher than available planar MBs. Meanwhile, they show a polarity-switchable feature to tolerate confusion of cathode and anode. This strategy could also be extended to other battery systems, such as Zn-I 2 and Zn-MnO 2 MBs. This work not only proposes an effective construction method for MBs but also enriches categories of microscale energy storage devices.