Understanding the Molecular Structure of the Elastic and Thermoreversible AlCl3 : Urea/Polyethylene Oxide Gel Electrolyte.

Álvaro Miguel,Pilar Tiemblo,Nuria García,Juan Maria García‐Lastra,Arghya Bhowmik,Rocco Peter Fornari,David Carrasco‐Busturia

doi:10.1002/cssc.202001557

Álvaro Miguel, Pilar Tiemblo + Show 5 more

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https://doi.org/10.1002/cssc.202001557

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Abstract

It is possible to prepare elastic and thermoreversible gel electrolytes with significant electroactivity by dissolving minimal weight fractions of ultra-high molecular weight polyethylene oxide (UHMW PEO) in an aluminum deep eutectic solvent (DES) electrolyte composed of AlCl3 and urea at a molar ratio of 1.5 : 1 (AlCl3 /urea). The experimental vibrational spectra (FTIR and Raman) provide valuable information on the structure and composition of the gel electrolyte. However, the complexity of this system requires computational simulations to help interpretation of the experimental results. This combined approach allows us to elucidate the speciation of the DES liquid electrolyte in the gel and how it interacts with the polymer chains to give rise to an elastic network that retains the electroactivity of the liquid electrolyte to a very great extent. The observed reactions occur between the ether in the polymer and both the amine groups in urea and the aluminum species. Thus, similar elastomeric gels may likely be prepared with other aluminum liquid electrolytes, making this procedure an effective way to produce families of gel aluminum electrolytes with tunable rheology and electroactivity.

Highlights

Batteries are at the heart of the present and future energy management strategy;[1] for light and portable devices, for powering electric vehicles, to store energy from renewable sources, and to optimize the electrical grid management
In a recent work,[9] we proposed a solvent-free strategy consisting of the melting while mixing of poly(ethylene oxide) (PEO) in AlCl3:urea electrolyte to prepare Polymer gel electrolytes (PGEs)
We showed how the use of ultra-high molecular weight PEO (MW > 106 g/mol) allows the preparation of gels where reasonable mechanical properties are attained while electrochemical activity is retained.[6]

Summary

Introduction

Batteries are at the heart of the present and future energy management strategy;[1] for light and portable devices, for powering electric vehicles, to store energy from renewable sources, and to optimize the electrical grid management. Lithium is the lightest metal with the lowest reduction potential (−3.045 V vs NHE), which makes it excellent for metal battery technologies, but it is relatively scarce.[2] Aluminum is the most abundant metal on earth’s crust, and its volumetric capacity of 8040 mAh cm−1 is almost four times higher than lithium (2046 mAh cm−1).[3] It dates back to 1948 when the first electroplating bath was patented It consisted of a mixture of the room temperature ionic liquid (RTIL) N-alkyl pyridinium halide and aluminum chloride with molar concentration 1 to 2.[4] More recently, deep eutectic solvents (DES) obtained from AlCl3:amide mixtures with different ratios have proved to be excellent electrolytes for aluminum secondary batteries. DES are environmentally friendly and have the same benefits as RTILs (low vapor pressure, tunability, easiness to prepare), at a much lower price.[5]

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