Fundamental Insights into Electrical and Transport Properties of Chloroaluminate Ionic Liquids for Aluminum-Ion Batteries

Abstract

Around the world, there is a critical need for sustainable energy storage systems for grid-level stationary energy storage. In the search for such systems, aluminum (Al)-ion batteries have recently attracted considerable attention due to their positive attributes including low cost, high abundance of raw materials, and long cycling life. Among all, chloroaluminate ionic liquid (IL) composed of aluminum chloride (AlCl 3 ) and a Lewis basic organic chloride (XCl) is the most widely employed electrolyte system in Al-ion batteries. In many existing Al-ion battery chemistries, chloroaluminate IL simultaneously functions as a medium for ion transportation and as an electroactive anode material. To provide fundamental insights into designing better performing Al-ion batteries, herein, we performed a systematic investigation of the electrochemical and transport properties of four AlCl 3 -XCl ILs, where X is EMIM (1-ethyl-3-methylimidazolium), BMIM (1-butyl-3-methylimidazolium), TMAH (trimethylammonium), or TEAH (triethylammonium), using a combination of density functional theory calculations and experimentation. Results show that the electrochemical stability window, ion transference number, conductivity, and ionicity of Lewis acidic chloroaluminate ILs are fundamentally governed by the (i) AlCl 3 /XCl molar ratio (r), which dictates the concentration of ionic species, and (ii) XCl type, which affects the overall degree of interactions among ionic species.

Measuring and Enhancing the Ionic Conductivity of Chloroaluminate Electrolytes for Al-Ion Batteries

“…Zhu et al reported conductivities increasing from 15 to 17.5 mS cm –1 for AlCl 3 :EMIM-Cl liquid for mole ratios between 1.4:1 and 1.7:1 (LA:LB) . Conversely, Azimi et al reported conductivities decreasing from 22.6 to 14.7 mS cm –1 for LA:LB compositions between 1:1 and 2:1 with AlCl 3 :EMIM-Cl liquids . Other reports have found conductivities of 16.1, 15.5, and 9.2 mS cm –1 for AlCl 3 :EMIM-Cl liquids with a 1.5:1 mole ratio.…”

“…These electrolytes, often called chloroaluminate liquids, are formed by an acid–base reaction between a Lewis acid (LA; i.e., AlCl 3 salt) and a Lewis base (LB; e.g., Cl – -containing salt). To date, the majority of research has been done on chloroaluminate liquids made from the solid (at room temperature) salt 1-ethyl-3-methylimidazolium chloride (EMIM-Cl); − this electrolyte is commercially available . The electrochemical and rheological performance is promising, but it comes with a high economic cost of the starting material, which ultimately is not advantageous for scale-up.…”

Impact of Aluminium Electrode Potential during Charging on Aluminium‐Ion Battery Performance with TEA‐AlCl3 Electrolyte

“…Supporting Information is available from the Wiley Online Library or from the author. Additional references cited within the Supporting Information [36–38] …”

An Aluminum‐Benzo[1,2‐b:4,5‐b’]dithiophene‐4,8‐dione Organic Rechargeable Battery Featuring Low Self‐Discharge

“…The chloroaluminate IL prepared by mixing AlCl 3 and trimethylamine hydrochloride (TMAHCl) at a molar ratio of 1.8 was used as the electrolyte. Compared with the widely adopted EMImCl‐based chloroaluminate IL electrolyte, the higher anolyte capacity of the AlCl 3 ‐TMAHCl electrolyte due to the lower molar mass of TMAHCl (Supporting Information Figure S2) and the lower cost of TMAHCl further enhance the performance and sustainability of the resulting battery systems [28] . A schematic of the assembled cell and mechanism is presented in Figure 1(a).…”

“…Compared with the widely adopted EMImCl-based chloroaluminate IL electrolyte, the higher anolyte capacity of the AlCl 3 -TMAHCl electrolyte due to the lower molar mass of TMAHCl (Supporting Information Figure S2) and the lower cost of TMAHCl further enhance the performance and sustainability of the resulting battery systems. [28] A schematic of the assembled cell and mechanism is presented in Figure 1(a). During cycling, the reversible intercalation/deintercalation of AlCl 2 + was achieved at the carbonyl sites (C=O) of BDTD, contribute to the reversible capacity over cycles (Figure 1a).…”