Title: Investigating Ternary Li–Mg–Si Zintl Phase Formation and Evolution for Si Anodes in Li-Ion Batteries with Mg(TFSI)₂ Electrolyte Additive

Abstract

Improved electrochemical performance of Si was recently reported by adding multivalent cation salts (such as Mg²⁺, Al³⁺, Ca^2+, etc.) in the electrolyte. This is achieved via the formation in an in situ manner of relatively more stable Li-M-Si ternary phases with less chemical reactivity. These phases stabilize Si anions and thus reduce side reactions with electrolytes at the surface and eventually benefit the overall electrochemistry. To understand the mechanism of ternary Zintl phase formation and its dynamics upon lithiation/delithiation, high-resolution solid-state ⁷Li and ²⁹Si nuclear magnetic resonance (NMR) are utilized to directly probe the local Li and Si environments on Si electrodes harvested from coin and pouch cells at various states of (de)lithiation. The NMR spectra along with the electrochemical characterization reveal that lithiation of Si starts from the surface Si-O layer further confirmed by ⁷Li–²⁹Si cross-polarization NMR. Lithiation progresses with heterogeneous silicon clustering with Si^-4 anions at high states of lithiation. At a fully lithiated state, the formation of overlithiated Si species is detected. At a low-voltage region (below 100 mV), direct evidence for Mg-ion insertion is found, postulated by two possible mechanisms: ion exchange with fully or overlithiated binary domains (Li_3.75+xSi) and/or a coinsertion with slightly underlithiated domainsmore » (similar to Li_3.55Si). Upon delithiation, Li extraction starts from overlithiated Si domains. No evidence is found for electrochemical Mg removal. Evidence for a lithium-deficient Li_yMg_0.1Si phase is found as a result of Li removal during charging. This investigation sheds light on the possible mechanisms of a new Si anode chemistry, which could enable the development of stable Si-based anodes for lithium-ion batteries.« less

Authors:

Li, Xiang  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-0088-7575"

Gilbert, James A. ^[1]; Trask, Stephen E.  ^[1];

• Search DOE PAGES for author "Trask, Stephen E."
• Search DOE PAGES for ORCID "0000-0002-0879-4779"

Uppuluri, Ritesh ^[1]; Lapidus, Saul H.  ^[2];

• Search DOE PAGES for author "Lapidus, Saul H."
• Search DOE PAGES for ORCID "0000-0002-7486-4325"

Cora, Saida ^[3]; Sa, Niya ^[3]; Yang, Zhenzhen ^[1]; Bloom, Ira D.  ^[1];

• Search DOE PAGES for author "Bloom, Ira D."
• Search DOE PAGES for ORCID "0000-0002-4877-473X"

Dogan, Fulya  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-7997-266X"

Vaughey, John T.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-2556-6129"

Key, Baris  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-1987-1629"

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+ Show Author Affiliations

1. Argonne National Lab. (ANL), Argonne, IL (United States)
2. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
3. Univ. of Massachusetts, Boston, MA (United States)

Publication Date:

Thu Jun 17 00:00:00 EDT 2021

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Vehicle Technologies Office

OSTI Identifier:

1831743

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Chemistry of Materials

Additional Journal Information:

Journal Volume: 33; Journal Issue: 13; Journal ID: ISSN 0897-4756

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

25 ENERGY STORAGE; Lithiation; Electrodes; Electrochemical cells; Silicon; Electrolytes