Journal
NANO LETTERS
Volume 11, Issue 9, Pages 3991-3997Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl2024118
Keywords
Germanium nanowire; sponge; pore memory effect; reversible volume change; lithium ion battery; in situ TEM
Categories
Funding
- Sandia National Laboratories (SNL)
- Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center (EFRC)
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DESC0001160]
- LDRD
- NEES center
- CINT
- Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration [DE-AC04-94AL85000]
- NSF [CMMI-0758554, 1100205, DMR-1008104]
- AFOSR [FA9550-08-1-0325]
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1100205] Funding Source: National Science Foundation
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [0758554] Funding Source: National Science Foundation
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Retaining the high energy density of rechargeable lithium ion batteries depends critically on the cycle stability of microstructures in electrode materials. We report the reversible formation of nanoporosity in individual germanium nanowires during lithiation-delithiation cycling by in situ transmission electron microscopy. Upon lithium insertion, the initial crystalline Ge underwent a two-step phase transformation process: forming the intermediate amorphous LixGe and final crystalline Li15Ge4 phases. Nanopores developed only during delithiation, involving the aggregation of vacancies produced by lithium extraction, similar to the formation of porous metals in dealloying. A delithiation front was observed to separate a dense nanowire segment of crystalline Li15Ge4 with a porous spongelike segment composed of interconnected ligaments of amorphous Ge. This front sweeps along the wire with a logarithmic time law. Intriguingly, the porous nanowires exhibited fast lithiation/delithiation rates and excellent mechanical robustness, attributed to the high rate of lithium diffusion and the porous network structure for facile stress relaxation, respectively. These results suggest that Ge, which can develop a reversible nanoporous network structure, is a promising anode material for lithium ion batteries with superior energy capacity, rate performance, and cycle stability.
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