The use of aqueous electrolytes as suitable electrolytes for supercapacitors (SCs) largely depends on maintaining a wide operating cell voltage window while ensuring good rate capabilities, thereby achieving high energy and power densities over many cycles. Electrolyte engineering with anion- and/or solvent-rich solvation structures has been recently explored in batteries of any type to enhance the interphase stability at high voltages, typically by the formation of a SEI. This approach has been less explored in SCs to not only extend the range of operational voltage but also balance the inherently distinct electrochemical stability of cations and anions with carbon electrodes. Herein, we prepared electrolytes composed of two ionic liquids with a common cation (e.g., EMIMTFSI and EMIMBF<inf>4</inf>) in solvent mixtures of H<inf>2</inf>O, DMSO and CH<inf>3</inf>CN. We found that the electrolyte with the richest solvation structure (i.e., with many and diverse anions that surrounded the cation) was the most effective at widening the cell voltage at which the electrolyte is capable of operating (e.g., up to 2.2 V). Interestingly, this extremely rich solvation structure also exhibited the best transport properties for different ions that, ultimately, were responsible for an excellent maintenance of the energy density at high power densities., This work was supported by MCIN/AEI/10.13039/501100011033 (TED2021-130372B-C42, TED2021-131812B-I00 and PID2021-123648OB-I00), by “ERDF A way of making Europe” (PID2021-123648OB-I00) and by “European Union Next Generation EU/PRTR” (TED2021-130372B-C42 and TED2021-131812B-I00). Authors also acknowledge the Severo Ochoa Centres of Excellence Program through Grant CEX2024-001445-S. L. G.-A. acknowledges the grant PRE2019-090008 funded by MCIN/AEI/10.13039/501100011033 and “ESF Investing in your future”. P. G.-B. acknowledges the grant PRE2022-101750 funded by MCIN/AEI/10.13039/501100011033 and ESF+. X. L. also acknowledges the National Natural Science Foundation of China (22393961). J. M. V.-L., S. C., and R. M. M.-C. also thank C3UPO for HPC support. The Servicio Interdepartmental de Investigación (SIdI) of the Universidad Autónoma de Madrid and the Thermal Analysis Unit at the Instituto de Ciencia de Materiales de Madrid (ICMM) are acknowledged for helpful assistance with FTIR and NMR spectroscopies and DSC studies, respectively., Data for this article, including data presented in gures and tables have been included as part of the SI. Experimental procedures, tables with different data (physicochemical properties, NMR chemical shis, etc.), NMR, ATR and NIR spectra, RDFs from MD simulations, and electrochemical results (CVs, GCDs, Nyquist plots, etc.). See DOI: https://doi.org/10.1039/d5ta04796j., Peer reviewed