SnO₂-Embedded Nanoporous Carbon Electrode with a Reaction-Buffer Space for Stable All-Solid-State Li Ion Batteries

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.