![]() ![]() We used a three-dimensional (3D) network of graphene as the cathode to promote charge capacity, along with pure Al as the anode. When batteries are allowed to discharge, Al (anode) will be oxidized but the carbon (cathode) reduced. Rather, the Al mono-complex will adsorb on positively charged carbon surfaces. On the carbon side, no new products will form. As a result, electrons from Al will jump over to the Al duo-complex and reduce it to a mono-complex, depositing fresh Al (0) over the Al electrode. When this electrolyte is placed inside an Al-ion battery, the Al electrode will be biased negatively and carbon electrode positively for charging. ![]() Three major ions have been reported in this electrolyte, i.e., Al mono-complex (AlCl 4 −), Al duo-complex (Al 2Cl 7 −), and the organic cation (EMI +) 5, 15. Preparation of the electrolyte is straightforward: mixing imidazolium chloride (EMI +Cl −) (solid) and anhydrous powder of AlCl 3 produces an ionic liquid (eutectic mixture). Instead, the metal ions exist as anions or as negatively charged metal complexes. Different from metal salts in water, cations here do not have any metal element therefore, they don’t directly participate in redox reactions. We show that the byproducts formed during charging/discharging can be used to calibrate and challenge conventional understanding in the bulk.Īl-ion batteries earned their fame by using an organic cation-based electrolyte 1, 5, similar to those cases in lithium 13 and lithium-ion batteries 14. Most importantly, acceleration of the charge transfer reaction enabled the discovery of many intermediates inside the EDLs, expanding our understanding of the role that EDLs play in rechargeable batteries. We gained multiple technological and scientific advances including the ultrafast charging rate, high capacity, and 500% higher specific capacity under high-rate conditions. As a result, the sites for Al (0) deposition are no longer assisted by surface defects only. In this study, we demonstrate that charge transfer through the interface between Al electrode and the organic electrolyte can be effectively accelerated. It is even less known about how to regulate EDLs in order to facilitate a quick reaction at the interface. It is currently not clear how EDLs participate in the reduction of negatively charged ions. Current research treats EDLs as stable nanostructures 12. It has been generally accepted that thin, in the range of a few nanometers, EDLs exist at the interface between electrolyte and a metal electrode. For instance, this will eliminate the clear boundary between a supercapacitor and a battery, making the device both high capacity and high rate and it will provide a deeper understanding of the electric double layers (EDLs). If the limitation in charge transfer is removed, we can then expect much bigger impacts than mere savings in time. From a chemistry standpoint, metal ions in state-of-the-art Al-ion batteries exist as anionic complexes the rate of reduction for these large negatively charged ions is much slower than the reduction rate of metal salts in water. Physics considerations suggest that faster charging requires a larger current injection but a larger current will result in larger drop in resistance ( iR) at the interface. Rarely has attention been paid at the intrinsic barrier for charge transfer through the interface between the electrolyte and the electrode. As such, long lasting performance with several tens of thousands of reversible charging and discharging has been demonstrated 1.Ĭan we further reduce the charging time from minutes to fractions of a second while keeping most of the capacity? We have seen great works from different research groups, where they focused on getting a higher specific capacity 1, 4, 5, synthesizing a new carbon electrode to promote adsorption 4, 6, 7, 8, 9, or finding an affordable organic electrolyte 10, 11. In addition, a stable Al electrode-electrolyte interface removes the complexity from an interphase layer that is commonly seen in lithium or lithium-ion systems 2, 3. The adoption of a pure Al as the electrode provides significant merits such as low cost, nonflammability, and high capacity. Over the past five years, it has quickly captured the fame of exceptional rate in both charging and discharging. A typical example can be found in a non-lithium platform, i.e., Al-ion batteries 1. For energy storage platforms that rely on reversible redox reactions, the reduction in charging time from hours to minutes has already become a reality. Fast charging is the key feature for portable electronics and electric vehicles which has ignited vigorous research activities. ![]()
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