Dioxolanone-Anchored Poly(allyl ether)-Based Cross-Linked Dual-Salt Polymer Electrolytes for High-Voltage Lithium Metal Batteries

Vidyanand Vijayakumar; Diddo Diddens; Andreas Heuer; Sreekumar Kurungot; Martin Winter; Jijeesh Ravi Nair

doi:10.1021/acsami.9b16348

Dioxolanone-Anchored Poly(allyl ether)-Based Cross-Linked Dual-Salt Polymer Electrolytes for High-Voltage Lithium Metal Batteries

ACS Appl Mater Interfaces. 2020 Jan 8;12(1):567-579. doi: 10.1021/acsami.9b16348. Epub 2019 Dec 26.

Authors

Vidyanand Vijayakumar^{1

2

3}, Diddo Diddens¹, Andreas Heuer^{1

4}, Sreekumar Kurungot², Martin Winter^{1

4

5}, Jijeesh Ravi Nair¹

Affiliations

¹ IEK-12, Forschungszentrum Jülich GmbH , Helmholtz Institute Münster , Corrensstraße 46 , 48149 Münster , Germany.
² Physical and Materials Chemistry Division , CSIR-National Chemical Laboratory , 411008 Pune , Maharashtra , India.
³ Academy of Scientific and Innovative Research (AcSIR) , Sector 19, Kamla Nehru Nagar , 201002 Ghaziabad , Uttar Pradesh , India.
⁴ Institute of Physical Chemistry , University of Münster , Corrensstraße 28/30 , 48149 Münster , Germany.
⁵ MEET Battery Research Center , Corrensstraße 46 , 48149 Münster , Germany.

PMID: 31825198
DOI: 10.1021/acsami.9b16348

Abstract

Novel cross-linked polymer electrolytes (XPEs) are synthesized by free-radical copolymerization induced by ultraviolet (UV)-light irradiation of a reactive solution, which is composed of a difunctional poly(ethylene glycol) diallyl ether oligomer (PEGDAE), a monofunctional reactive diluent 4-vinyl-1,3-dioxolan-2-one (VEC), and a stock solution containing lithium salt (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) in a carbonate-free nonvolatile plasticizer, poly(ethylene glycol) dimethyl ether (PEGDME). The resulting polymer matrix can be represented as a linear polyethylene chain functionalized with cyclic carbonate (dioxolanone) moieties and cross-linked by ethylene oxide units. A series of XPEs are prepared by varying the [O]/[Li] ratio (24 to 3) of the stock solution and thoroughly characterized using physicochemical (thermogravimetric analysis-mass spectrometry, differential scanning calorimetry, NMR, etc.) and electrochemical techniques. In addition, quantum chemical calculations are performed to elucidate the correlation between the electrochemical oxidation potential and the lithium ion-ethylene oxide coordination in the stock solution. Later, lithium bis(fluorosulfonyl)imide (LiFSI) salt is incorporated into the electrolyte system to produce a dual-salt XPE that exhibits improved electrochemical performance, a stable interface against lithium metal, and enhanced physical and chemical characteristics to be employed against high-voltage cathodes. The XPE membranes demonstrated excellent resistance against lithium dendrite growth even after reversibly plating and stripping lithium ions for more than 1000 h with a total capacity of 0.5 mAh cm^-2. Finally, the XPE films are assembled in a lab-scale lithium metal battery configuration by using carbon-coated LiFePO₄ (LFP) or LiNi_0.8Co_0.15Al_0.05O₂ (NCA) as a cathode and galvanostatically cycled at 20, 40, and 60 °C. Remarkably, at 20 °C, the NCA-based lithium metal cells displayed excellent cycling stability and good capacity retention (>50%) even after 1000 cycles.

Keywords: cross-linked polymer electrolyte; dual-salt electrolyte; high-voltage cathode; lithium metal battery; solvent-free photopolymerization.