Stable Cycling of a 4 V Class Lithium Polymer Battery Enabled by In Situ Cross-Linked Ethylene Oxide/Propylene Oxide Copolymer Electrolytes with Controlled Molecular Structures

Woonghee Choi; Yongku Kang; In-Jung Kim; Byeong-Gi Seong; Woong-Ryeol Yu; Dong Wook Kim

doi:10.1021/acsami.1c07734

Stable Cycling of a 4 V Class Lithium Polymer Battery Enabled by In Situ Cross-Linked Ethylene Oxide/Propylene Oxide Copolymer Electrolytes with Controlled Molecular Structures

ACS Appl Mater Interfaces. 2021 Aug 4;13(30):35664-35676. doi: 10.1021/acsami.1c07734. Epub 2021 Jul 21.

Authors

Woonghee Choi^{1

2}, Yongku Kang¹, In-Jung Kim³, Byeong-Gi Seong^{3

4}, Woong-Ryeol Yu², Dong Wook Kim¹

Affiliations

¹ Advanced Materials Division, Korea Research Institute of Chemical Technology, Daejeon 34114, Republic of Korea.
² Department of Material Science and Engineering, Seoul National University, Seoul 08826, Republic of Korea.
³ Hannong Chemicals Inc., Gunsan 54008, Republic of Korea.
⁴ Department of Chemistry, Kunsan National University, Gunsan 54150, Republic of Korea.

PMID: 34284586
DOI: 10.1021/acsami.1c07734

Abstract

Commercial lithium-ion batteries are vulnerable to fire accidents, mainly due to volatile and flammable liquid electrolytes. Although solid polymer electrolytes (SPEs) are considered promising alternatives with antiflammability and processability for roll-to-roll mass production, several requirements have not yet been fulfilled for a viable lithium polymer battery. Such requirements include ionic conductivity, electrochemical stability, and interfacial resistance. In this work, the ionic conductivity of the SPEs is optimized by controlling the molecular weight and structural morphology of the plasticizers as well as introducing propylene oxide (PO) groups. Electrochemical stability is also enhanced using ethylene oxide (EO)/PO copolymer electrolytes, making the SPEs compatible with high-Ni LiNi_xCo_yMn_1-x-yO₂ cathodes. The in situ cross-linking method, in which a liquid precursor first wets the electrode and is then solidified by a subsequent thermal treatment, enables the SPEs to soak into the 60 μm thick electrode with a high loading density of more than 8 mg cm^-2. Thus, interfacial resistance between the SPE and the electrode is minimized. By using the in situ cross-linked EO/PO copolymer electrolytes, we successfully demonstrate a 4 V class lithium polymer battery, which performs stable cycling with a marginal capacity fading even over 100 cycles.

Keywords: 4 V class lithium polymer batteries; electrochemical stability; ethylene oxide/propylene oxide copolymer; in situ cross-linking; solid polymer electrolytes.