High Areal Capacity Porous Sn-Au Alloys with Long Cycle Life for Li-ion Microbatteries
Sai Gourang Patnaik, Ankita Jadon, Chau Cam Hoang Tran, Alain Estève, Daniel Guay & David Pech
Scientific Reports volume 10, Article number: 10405 (2020) Cite this article

Long-term stability is one of the most desired functionalities of energy storage microdevices for wearable electronics, wireless sensor networks and the upcoming Internet of Things. Although Li-ion microbatteries have become the dominant energy-storage technology for on-chip electronics, the extension of lifetime of these components remains a fundamental hurdle to overcome. Here, we develop an ultra-stable porous anode based on SnAu alloys able to withstand a high specific capacity exceeding 100 μAh cm?2 at 3?C rate for more than 6000 cycles of charge/discharge. Also, this new anode material exhibits low potential (0.2?V versus lithium) and one of the highest specific capacity ever reported at low C-rates (7.3 mAh cm?2 at 0.1?C). We show that the outstanding cyclability is the result of a combination of many factors, including limited volume expansion, as supported by density functional theory calculations. This finding opens new opportunities in design of long-lasting integrated energy storage for self-powered microsystems.

With ultrahigh speed rate and low latency of 5?G mobile networks in the upcoming years, the emergence of the Internet of Things (IoT) is set to revolutionize all aspects of our lives1,2. This trendy concept describes a network of connected objects able to collect data, interact with the environment and communicate wirelessly over the internet for a plethora of applications such as healthcare, self-driving vehicles, environmental monitoring and smart manufacturing. The integration of self-powered micrometric sensors will rely on efficient microscale energy storage units3 to interface with various types of energy harvesters, which are intermittent by nature. The inherent requirement is to enable monitoring by a remote sensor without further maintenance. Microbatteries with high areal capacity and ultralong life cycle are thus quintessential in such a scenario for realizing “fit and forget” type solutions. Moreover, microbatteries will be confined in an embedded microsystem with limited space available. The size and the compactness being critical, it is imperative to consider their properties normalized to the surface area. This calls for utilization of innovative materials with high volumetric capacity coupled with exploitive architectures, which are easy to realize and compatible with microsystem fabrication technologies, providing robust stability in limited footprint area. Furthermore, pricey electrode materials can be used in miniaturized devices, where cost is mainly determined by the microfabrication process and not by the minute amount of active materials involved.

Alloy anodes are promising candidates as negative electrodes in Li and post Li-ion chemistries due to their high specific capacity4,5,6,7,8,9. Especially, Sn and their oxides have extremely high volumetric capacity (7200 mAh cm?3 for Sn, i.e. even higher than metallic Li) and hence apt for utilization in microbatteries requiring high energy density per footprint area. However, Sn anodes suffer from a variety of issues like volume expansion (up to 360%), related continuous solid electrolyte interface (SEI) formation and capacity fading10,11. Such issues are magnified in context of microbatteries, where there are not many amenities for structural engineering due to limited space. Nevertheless, there have been several efforts to utilize Sn-based materials in microbatteries – through alloying with other metal12,13,14 constructing porous 3D architectures15,16,17,18,19,20,21 making homogenous/ordered carbon composites22,23,24,25,26 etc. However, most of them failed to achieve long cyclability and high rate capability. In the cases where high rate was demonstrated, the charge-discharge profile was more capacitive than battery-like24.


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