Japan’s NIMS reports highly stable cycling of nanoporous, amorphous silicon anodes for all-solid-state lithium batteries
Researchers at Japan’s National Institute for Materials Science (NIMS) have reported that nanoporous, amorphous silicon film anodes can show excellent cycling stability with extremely high lithium storage capacity: 2962 mAh g−1 and 2.19 mAh cm−2 after 100 cycles. An open-access paper on their work appears in the Nature journal Communications Chemistry.
Silicon has theoretical lithium storage gravimetric and volumetric capacities of 4,200 mAh g-1 and 2,370 mAh/cm3, respectively. These capacities are, respectively, approximately 11 and 3 times larger than those of conventional graphite anode materials. Many efforts therefore have been devoted to the application of silicon anodes to lithium-ion batteries using conventional organic liquid electrolytes to prolong the cruising distance of electric vehicles.
|Transmission electron microscopy (TEM) image of the cross-section of a nanoporous, amorphous silicon film anode. The film anode was prepared using a sputtering deposition method using a reacting gas of helium. Sakabe et al. Click to enlarge.|
However, as the batteries are charged and discharged, silicon anodes undergo enormous volume expansion and contraction. The large volume changes during charge and discharge cycles result in irreversible mechanical damage, which in turn results in a rapid capacity fading.
Furthermore, due to narrow electrochemical stability windows of the electrolytes and the anodes’ severe volume changes, the conventional liquid electrolytes decompose on the silicon anodes during every charge processes, which also leads to the capacity fading. Hence, a strong demand exists for research the appropriate approach to take measures against these issues without lowering the capacities of the anode materials: nanostructure design of silicon anodes and encapsulation of the anode-active materials have been extensively studied for the batteries using the liquid electrolytes.
The NIMS team addressed capacity fading by combining nanoporous, amorphous silicon films with an inorganic solid electrolyte. The nanoporous structure accommodates the volume change of silicon and thus limits the mechanical fracture and pulverization of the anode. The solid electrolyte used—unlike liquid electrolytes—does not decompose on the silicon anodes due to its wide electrochemical stability window. Experiments demonstrated that the capacity of the silicon material, which is practically high, only slightly decreased even after 100 charge and discharge cycles.
This study was financially supported by the New Energy and Industrial Technology Development Organization (NEDO) and the Toyota Motor Corporation for a project entitled “Applied and Practical LiB Development for Automobile and Multiple Applications (P12003).”
Junichi Sakabe, Narumi Ohta, Tsuyoshi Ohnishi, Kazutaka Mitsuishi & Kazunori Takada (2018) “Porous amorphous silicon film anodes for high-capacity and stable all-solid-state lithium batteries,” Communications Chemistry Volume 1, Article number: 24 doi: 10.1038/s42004-018-0026-y