They also have good flexibility, maintaining almost the same galvanostatic charge-discharge (GCD) curves under different bending states. It is worth mentioning that these electrochemical performances are obtained without any excess of cathode or anode. Benefiting from these merits, the Zn-Br 2 MBs deliver record high areal capacity and areal energy density (2220 μAh cm − μWh cm −2) and maintain an excellent power density of 26.2 mW cm −2 (even better than most MSCs). The liquid feature of the Br 2 cathode could circumvent the trade-off between energy density and power density due to fast reaction kinetics in the liquid medium. For traditional MBs, increasing areal loading to pursue higher energy density could result in long ion transfer distance in solid active materials and lead to decreased power density. The new MB is expected to achieve high energy density and power density at the same time due to the liquid nature of the Br 2 cathode. It is worth mentioning that, to the best of our knowledge, the Zn-Br 2 system have not yet been introduced into the field of microscale energy storage, because it is hard to manipulate liquid Br 2 through previous methods. Moreover, the troublesome and time-consuming mass matching of the cathode and anode procedure could also be ingeniously avoided, because they always generate one by one ( 30). It also bypasses the challenge of precisely coat or deposit cathode and anode on different microelectrodes. The Zn-Br 2 MBs shows an electrode-less feature, and it only requires an interdigitated current collector and a redox-active electrolyte, eliminating the synthesis of active materials, which is a necessary procedure for previous MBs. Furthermore, current MBs contain an excess amount of anode (typically more than 10 times than the cathode), which results in a decreased overall performance and is not applicable in practice. Besides, current planar MBs are limited to solid cathodes and generally deliver unsatisfactory areal capacity and energy density (most are lower than 300 μAh cm −2 and 500 μWh cm −2) due to inferior power density originated from a too thick solid electrode ( 25– 28). For example, a multistep mask-assisted filtration strategy was proposed to construct a planar sodium-ion MB, which required at least six procedures ( 24), including preparation of cathode and anode active materials, and then step by step build current collector, cathode, and anode on the nylon substrate with the help of a preprepared interdigitated mask, adding the gel electrolyte for the final encapsulation. This work not only proposes an effective construction method for MBs but also enriches categories of microscale energy storage devices.Īlthough substantial progresses have been made in recent years, current planar MBs still suffer from tedious and complicated construction procedures as it is a considerable challenge to prepare and match cathode and anode at a microscale ( 15– 23). This strategy could also be extended to other battery systems, such as Zn-I 2 and Zn-MnO 2 MBs. Meanwhile, they show a polarity-switchable feature to tolerate confusion of cathode and anode. 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. 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. Besides, all cathodes of current MBs are solid state, and the trade-off between areal capacity and reaction kinetics restricts their wide applications. 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.
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