SnS2-based materials have been intensively explored as an anode for sodium-ion batteries. In the present study, hierarchical SnS2 microspheres with S vacancy have been successfully synthesized via a one-step solvothermal process, and it is found that the amount of thioacetamide in the synthetic process plays an important role in morphology and amounts of S vacancies. A series of results calculated from density functional theory has indicated that the introduction of S vacancies could effectively decrease the band gap. As a consequence, the hierarchical SnS2 microspheres exhibit an excellent sodium storage performance, and a large capacity of 486.2 mA h g–1 can be achieved after 1000 cycles at 1 A g–1.

Extensive research efforts are devoted to development of high performance all-solid-state lithium ion batteries owing to their potential in not only improving safety but also achieving high stability and high capacity. However, conventional approaches based on a fabrication of highly dense electrode and solid electrolyte layers and their close contact interface is not always applicable to high capacity alloy- and/or conversion-based active materials such as SnO2 accompanied with large volume change in charging-discharging. The present work demonstrates that SnO2-embedded nanoporous carbons without solid electrolyte inside the nanopores are a promising candidate for high capacity and stable anode material of all-solid-state battery, in which the volume change reactions are restricted in the nanopores to keep the constant electrode volume. A prototype all-solid-state full cell consisting of the SnO2-based anode and a LiNi1/3Co1/3Mn1/3O2-based cathode shows a good performance of 2040 Wh/kg at 268.6 W/kg based on the anode material weight.

An ongoing challenge for next-generation energy storage systems is to maximize the battery performance of lithium–sulfur (Li–S) systems, which exhibit high theoretical capacity and high energy density. Despite the outstanding effects observed by nanoconfinement of sulfur within conductive porous media, few studies have elucidated the ideal nanospace for the Li–S reaction because nanoscale characterization of lithiated sulfur molecules is difficult. We present direct evidence of electrochemically lithiated sulfur molecules confined inside carbon nanotubes (CNTs) using Cs-corrected high-resolution scanning transmission electron microscopy with electron energy loss spectroscopy. For a certain diameter of CNTs, short sulfur chains were stabilized inside CNTs via the charge transfer interaction, exhibiting a unique electrochemical activity and stable cycle performance compared to those of long sulfur chains. Our findings reveal that optimal CNTs have the one-dimensional channels for smooth progress of the lithiation reaction.

The conventional approach for fabricating all-solid-state batteries has required a highly dense layer of electrode and electrolyte. Their close contact interface is not suitable for alloy- or conversion-based active materials because their large volume change in lithiation/delithiation reactions causes a collapse of the contact interface or reaction limitations under mechanical constriction. In this study, we propose that a SnO2-embedded porous carbon electrode shows high cyclability and high capacity even at high constraint pressure owing to the nanopores, which work as a buffer space for the large volume change accompanied with SnO2–Sn conversion reaction and Sn–Li alloying–dealloying reaction. A detailed investigation between structural parameters of the electrode material and charge–discharge properties revealed Li ion conduction in carbon nanopores from a solid electrolyte located outside as well as the optimal conditions to yield high performance. SnO2-loading (75 wt %) in carbon nanopores, which provides the buffer space corresponding to the inevitable volume expansion by full lithiation, brought out an excellent performance at room temperature superior to that in an organic liquid electrolyte system: a high capacity of 1023 mAh/g-SnO2 at 50 mA/g, high capacity retention of 97% at 300th cycle at 300 mA/g, and high rate capability with over 75% capacity retention at 1000 against 50 mA/g, whose values are also superior to the system using the organic liquid electrolyte.

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