TY - JOUR

T1 - Solid electrolyte interface formation between lithium and PEO-based electrolyte

AU - Ushakova, Elena E.

AU - Frolov, Alexander

AU - Reveguk, Anastasia A.

AU - Usachov, Dmitry Yu

AU - Itkis, Daniil M.

AU - Yashina, Lada V.

N1 - Publisher Copyright: © 2022

PY - 2022/7/1

Y1 - 2022/7/1

N2 - One of the approaches to improve the performance and ensure safe operation of lithium-metal batteries is the use of solid polymer electrolytes (SPE) that demonstrate relatively low reactivity towards metallic lithium. However, when lithium comes into contact with SPE, a solid electrolyte interphase (SEI) film is formed at the interface, although its composition, properties, and formation mechanism have not yet been sufficiently investigated. The present paper focuses on the issue of the lithium metal - polymer electrolyte interface stability. We used cyclic voltammetry and impedance spectroscopy to show that a passivating SEI layer forms at the working electrode in contact with SPE (PEO20LiTFSI) both during the cell cycling and at an open circuit potential, with the SEI thickness increasing to a certain point depending on the temperature. The chemical reaction that corresponds to the SEI formation was studied by XPS and NEXAFS spectroscopy for model experiments, including lithium deposition on polyethylene oxide (PEO) under ultrahigh vacuum. Based on the spectroscopy data, we propose a reaction mechanism that features reductive cleavage of a PEO molecule by lithium atoms, which yields not only lithium alkoxides (ROLi) but also polyethylene fragments. Although such kind of SEI should generally reduce the ionic conductivity of SPE, it adds stability to the system at the same time.

AB - One of the approaches to improve the performance and ensure safe operation of lithium-metal batteries is the use of solid polymer electrolytes (SPE) that demonstrate relatively low reactivity towards metallic lithium. However, when lithium comes into contact with SPE, a solid electrolyte interphase (SEI) film is formed at the interface, although its composition, properties, and formation mechanism have not yet been sufficiently investigated. The present paper focuses on the issue of the lithium metal - polymer electrolyte interface stability. We used cyclic voltammetry and impedance spectroscopy to show that a passivating SEI layer forms at the working electrode in contact with SPE (PEO20LiTFSI) both during the cell cycling and at an open circuit potential, with the SEI thickness increasing to a certain point depending on the temperature. The chemical reaction that corresponds to the SEI formation was studied by XPS and NEXAFS spectroscopy for model experiments, including lithium deposition on polyethylene oxide (PEO) under ultrahigh vacuum. Based on the spectroscopy data, we propose a reaction mechanism that features reductive cleavage of a PEO molecule by lithium atoms, which yields not only lithium alkoxides (ROLi) but also polyethylene fragments. Although such kind of SEI should generally reduce the ionic conductivity of SPE, it adds stability to the system at the same time.

KW - Lithium metal

KW - Lithium metal batteries

KW - Polymer electrolyte

KW - SEI

KW - Solid electrolyte interface

KW - Solid polymer batteries

KW - STABILITY

KW - BATTERIES

KW - SURFACE

KW - POLYMER ELECTROLYTE

KW - XPS

KW - LAYER

KW - LI

KW - IN-SITU

UR - http://www.scopus.com/inward/record.url?scp=85126596651&partnerID=8YFLogxK

U2 - 10.1016/j.apsusc.2022.153014

DO - 10.1016/j.apsusc.2022.153014

M3 - Article

AN - SCOPUS:85126596651

VL - 589

JO - Applied Surface Science

JF - Applied Surface Science

SN - 0169-4332

M1 - 153014

ER -