Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 123, Issue 36, Pages 22027-22039Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.9b06011
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Funding
- Deutsche Forschungsgemeinschaft (DFG) [Schm 1569/25]
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Amorphous silicon is a high-capacity negative electrode material for use in advanced lithium-ion batteries. We investigated the mechanism of Li incorporation into and removal from this material during electrochemical lithiation and delithiation using a combination of in operando neutron reflectometry and ex situ secondary ion mass spectrometry. The results indicate that a heterogeneous lithiation mechanism is present for the first cycle and also for subsequent cycles during lithiation and delithiation, where a highly lithiated phase penetrates the silicon electrode. During the first lithiation half-cycle, a two-step process takes place, which is not present for delithiation and higher cycles. In the first step, a Li-poor phase penetrates the silicon electrode leading to about 10% of maximum capacity. Afterward, during the second step, a Li-rich phase moves into the electrode leading to complete lithiation in a slower process. The different phases are separated by a relatively sharp interface of only several nanometers. The Li-poor phase extended over the entire electrode is still present after delithiation in the form of irreversibly trapped Li.
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