Journal
NANO LETTERS
Volume 13, Issue 2, Pages 709-715Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl304379k
Keywords
Amorphous silicon; two-phase lithiation; amorphous-amorphous interface; lithium-ion battery; in situ transmission electron microscopy
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Funding
- NSF grant through University of Pittsburgh [CMMI 08010934, CMMI 1100205]
- Sandia National Lab support
- U.S. Department of Energy's National Nuclear Security Administration [DE-AC04-94AL85000]
- CAS project [KJCX2-YW-W26]
- 973 project [2012CB932900]
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [0928517] Funding Source: National Science Foundation
- Div Of Civil, Mechanical, & Manufact Inn
- Directorate For Engineering [1100205] Funding Source: National Science Foundation
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Lithium-ion batteries have revolutionized portable electronics and will be a key to electrifying transport vehicles and delivering renewable electricity. Amorphous silicon (a-Si) is being intensively studied as a high-capacity anode material for next-generation lithium-ion batteries. Its lithiation has been widely thought to occur through a single-phase mechanism with gentle Li profiles, thus offering a significant potential for mitigating pulverization and capacity fade. Here, we discover a surprising two-phase process of electrochemical lithiation in a-Si by using in situ transmission electron microscopy. The lithiation occurs by the movement of a sharp phase boundary between the a-Si reactant and an amorphous LixSi (a-LixSi, x similar to 2.5) product. Such a striking amorphous-amorphous interface exists until the remaining a-Si is consumed. Then a second step of lithiation sets in without a visible interface, resulting in the final product of a-LixSi (x similar to 3.75). We show that the two-phase lithiation can be the fundamental mechanism underpinning the anomalous morphological change of microfabricated a-Si electrodes, i.e., from a disk shape to a dome shape. Our results represent a significant step toward the understanding of the electrochemically driven reaction and degradation in amorphous materials, which is critical to the development of microstructurally stable electrodes for high-performance lithium-ion batteries.
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