Tin and its compounds hold promise for the development of high-capacity anode materials that could replace graphitic carbon used in current lithium-ion batteries. However, the introduced porosity in current electrode designs to buffer the volume changes of active materials during cycling does not afford high volumetric performance. Here, we show a strategy leveraging a sulfur sacrificial agent for controlled utility of void space in a tin oxide/graphene composite anode. In a typical synthesis using the capillary drying of graphene hydrogels, sulfur is employed with hard tin oxide nanoparticles inside the contraction hydrogels. The resultant graphene-caged tin oxide delivers an ultrahigh volumetric capacity of 2123 mAh cm^–3 together with good cycling stability. Our results suggest not only a conversion-type composite anode that allows for good electrochemical characteristics, but also a general synthetic means to engineering the packing density of graphene nanosheets for high energy storage capabilities in small volumes.

Design and construction of synthetic microbial consortia is a promising strategy to enhance the performance of bioelectrochemical systems (BESs) and to facilitate practical applications in bioenergy production. According to the design principle of “division-of-labor”, we synthesized a three-species microbial consortium for power generation, consisting of engineered Escherichia coli, Bacillus subtilis and Shewanella oneidensis. In this consortium, E. coli digested glucose to produce lactate as a carbon source and an electron donor; B. subtilis produced riboflavin as an electron shuttle; and S. oneidensis served as the exoelectrogen to generate electricity. In return, S. oneidensis oxidized lactate to acetate, which fed E. coli and B. subtilis as the carbon source. Thus, the three species formed a cross-feeding microbial consortium, which performed “better together” for power generation. As a result, glucose (11 mM, total 0.28 g) was converted to electricity for more than 15 days with high energy conversion efficiency (up to 55.7%). The microbial composition and electricity output were stable throughout the operation cycle. Furthermore, the consortium exhibited highly functional robustness to fluctuations in the initial inoculation ratio of the three strains. This system provided new insight into the rational design of more efficient, stable, and robust synthetic microbial consortia applicable in bioenergy and environmental bioremediation.

Lithium (Li) metal batteries (LMBs) are a promising candidate for next generation energy storage systems. Although significant progress has been made in extending their cycle life, their calendar life still remains a challenge. Here we demonstrate that the calendar life of LMBs strongly depends on the surface area of Li metal anodes exposed to the electrolyte and can be significantly improved by forming a stable solid electrolyte interphase (SEI) layer on the LMA surface. The stability and role of the accumulated SEI stacks are studied in their entirety in this work, beyond the conventional SEI investigations that focus on the local microscopic structure of a single SEI. Furthermore, we reveal, for the first time, the stability and reusability of this SEI during repeated lithium stripping/deposition processes using room temperature in situ electron microscopy. It is also demonstrated in this work that lithium anodes exhibit a much smaller active surface area under either fully charged or fully discharged conditions. Therefore, LMBs stored under these conditions exhibit a much longer calendar life than those stored at an intermediate state of charge. These findings reveal the most critical factors affecting the calendar life of LMBs and several approaches for improving both design and operation of these batteries to extend their calendar life have been proposed.