Electrolytes Design for Metal-based Anode Batteries

Abstract

Aqueous zinc-metal batteries (AZIBs) promise intrinsically safe, low-cost energy storage, yet their practical deployment is constrained by interfacial instabilities—hydrogen evolution, corrosion, and dendritic growth—especially under high current density, high depth-of-discharge (DOD), and sub-zero temperatures. This thesis develops an electrolyte-centric roadmap that couple’s solvation-structure regulation with interphase chemistry to stabilize Zn plating/stripping across harsh operating regimes. The approach integrates three mutually reinforcing pillars: (i) outer-solvation-shell tailoring to direct desolvation and crystal orientation, (ii) interphase engineering with multifunctional additives to build robust, ion-conductive SEIs, and (iii) radical management to arrest chemistry that triggers corrosion and gas evolution. Multiscale evidence from synchrotron probes, in-situ/operando imaging, depth-profiling spectroscopies, and simulation closes the loop between molecular design and device-level durability. First, I introduce an “outer-solvation-shell” strategy using 2-propanol in Zn(OTf)2/H2O that selectively modifies the second solvation environment of Zn²⁺ while preserving the canonical inner shell Zn(H2O)62+. EXAFS/XANES, wide-angle X-ray scattering, NMR, and molecular dynamics consistently indicate water-dominant inner coordination with 2-propanol and OTf- participating in the outer shell. Density-functional theory combined with 2D grazing-incidence XRD reveals preferential adsorption/desolvation pathways on Zn(101)/(002), enabling oriented, compact deposition with lower nucleation barriers. This manifests as markedly extended symmetric-cell lifetimes (≥3000 h at 1 mA cm-2), stable cycling under heavy load (15 mA cm-2 with ~50% DOD), broadened electrochemical stability, suppressed corrosion/HER, and robust low-temperature operation down to −40 °C. Second, I employ N, S-dual-doped graphene quantum dots (GQDs) as a multifunctional electrolyte/interphase regulator. Their heteroatom sites and surface functionalities coordinate within the solvated layer and at the metal interface to reduce interfacial resistance and homogenize nucleation. Electrochemical analyses (EIS, Coulombic efficiency) and multimodal imaging (in-situ optical/TXM, SEM/FIB-SEM) show dense, void-free deposits and smoother morphology evolution. Depth-profiling (XPS, ToF-SIMS) and diffraction (GIXRD) confirm a ZnF2-rich, mechanically resilient SEI that sustains reversibility under high-rate. Third, I identify hydroxyl radicals (•OH) as direct drivers of interfacial degradation and demonstrate that free-radical scavengers (FRS) effectively suppress radical-induced corrosion and gassing. EPR verifies radical quenching; cryo-TEM and computed laminography visualize mitigated porous by-product layers and reduced “dead-Zn”; line-scan micro-GIXRD tracks crystallographic evolution during plating/stripping. When integrated, the three pillars deliver coin cells with high-rate, long-life operation; Zn∥Zn symmetric cells sustaining up to ~1700+ h at ~45–51% DOD; high-areal-capacity cycling (≥5 mAh cm-2 at 2 C for extended cycles); and 17Ah-class Zn∥V2O5 pouch cells. The chemistry is compatible with scalable manufacturing, including dry-electrode processing using Zn powder anodes. Methodologically, the thesis leverages synchrotron metrologies (VESPERS-GIXRD, HXMA-XAFS, BMIT laminography/TXM), interfacial mechanics (electrochemical-AFM force spectroscopy), and depth-profiling (XPS, ToF-SIMS), complemented by MD/DFT, to establish causality from solvated Zn2+ structure through desolvation kinetics and interfacial reactions to macro-scale durability. Collectively, the results constitute a generalizable design playbook—outer-shell tailoring, interphase engineering, and radical management—that advances fast-charging, low-temperature, and high-DOD AZIBs toward practical, safe, and scalable energy storage.