Solid Electrolyte Interface Regulated by Solvent‐in‐Water Electrolyte Enables High‐Voltage and Stable Aqueous Mg‐MnO₂ Batteries

Abstract

Mg batteries utilizing divalent Mg2+ as charge carriers have been attracting significant attention for energy storage owing to their uniqueness in terms of low cost, high safety, and high energy density. However, the short cycling life arising from the accumulation of a passivation layer on the Mg anode prohibits their further development. Here, a new strategy to suppress the accumulation of the passivation layer is presented, thus stabilizing the Mg anode by constructing a robust interfacial layer using organic solvent‐in‐water electrolytes. The organic solvents decompose on the Mg anode to form a MgO, polyether Mg enriched organic‐inorganic hybrid interfacial layer, preventing free water attack to the Mg anode. In addition, the organic solvent forms an H‐bond with H2O to suppress the water activity and therefore protecting the Mg anode. As an illustration to benefits of the solvent‐in‐water electrolytes, a Mg‐MnO2 battery that is coupled by a MnO2 cathode in Mn2+/MnO2 chemistry with the Mg anode is developed. The Mg‐MnO2 battery exhibits a well‐maintained discharge plateau at ≈2.5 V and a discharging capacity of ≈500 mAh g−1 over 1000 cycles. This result highlights the feasibility to stabilize the Mg anode by interface engineering through the solvent‐in‐water electrolyte design.

A Synergistic Strategy of Organic Molecules Introduced a High Zn2+Flux Solid Electrolyte Interphase for Stable Aqueous Zinc-Ion Batteries

“…The X-ray diffraction (XRD) results are shown in Figure d, and although SEM can observe the presence of passivated material decomposed by ClO 4 – decomposition in the aqueous electrolyte, the corresponding characteristic peaks cannot be observed due to the low content and poor crystallinity. However, the Zn sheet cycled in the hybrid electrolyte exhibited a characteristic peak of typical layered LDH at 9.6°, which may have contributed to zinc hydroxylcarbonate produced by PEG decomposition Figure e shows the Raman spectra of a postcycle Zn sheet, and the results show that peaks are attributed to ClO 4 – in both the aqueous electrolyte and the hybrid electrolyte (at 463, 630, and 934 cm –1 ), which may come from zinc hydroxylperchlorate .…”

“…However, the Zn sheet cycled in the hybrid electrolyte exhibited a characteristic peak of typical layered LDH at 9.6°, which may have contributed to zinc hydroxylcarbonate produced by PEG decomposition. 38 Figure 4e shows the Raman spectra of a postcycle Zn sheet, and the results show that peaks are attributed to ClO 4 − in both the aqueous electrolyte and the hybrid electrolyte (at 463, 630, and 934 cm −1 ), which may come from zinc hydroxylperchlorate. 39 Because of the different solvation structures of Zn 2+ in hybrid electrolyte and aqueous electrolyte, ClO 4 − will more easily enter the first solvation structure when PEG coordinates with Zn 2+ , so the composition of ClO 4 − related salts in SEI is different, resulting in a difference in the results in ClO 4 − of Raman spectra.…”

A bifunctional electrolyte for activating Mg–Li hybrid batteries

“…According to previous studies, the former has been widely identied as a good component for stable Mg stripping/plating, while the latter is a relatively poor conductor that hinders Mg 2+ diffusion. 50,51 Note that a small peak belonging to Si 0 appeared at ∼99 eV, which is attributed to the decomposition of small amounts of Mg(HMDS) 2 salt on the Mg surface with the dualsalt electrolyte (Fig. 4c).…”

A Passivation-Free Solid Electrolyte Interface Regulated by Magnesium Bromide Additive for Highly Reversible Magnesium Batteries

“…The increasing usage of electrochemical energy storage technologies in daily life drives the development of new battery systems to succeed existing Li-ion batteries. − Among these, rechargeable magnesium batteries (RMBs) using a bivalent Mg 2+ charge carrier display great potential in meeting future battery needs, due to high earth abundance (1.94% for Mg vs 0.002% for Li), high volumetric capacity (3833 mAh cm –3 for Mg vs 2062 mAh cm –3 for Li), low reduction potential (−2.4 V vs standard hydrogen electrode), low possibility of dendrite growth, and low cost. − Unlike in Li battery systems, conventional Mg battery electrolytes readily passivate on the Mg anode surface due to the spontaneous reduction of electrolyte components, resulting in low Mg-ion diffusion and high overpotential. − Constructing solid electrolyte interfaces (SEI) with high Mg conductivity and reversibility is a logical step to prevent passivation, either extrinsically − or intrinsically. − The most widely implemented strategy is the addition of inorganic chlorides (such as MgCl 2 ) in high concentrations with traditional salts. − The addition of Cl – ions forms electroactive species with Mg cations, while modifying the Mg anode surface with adsorbed chloride ions that regulate Mg diffusion. Even though this strategy is accepted as a working paradigm in Mg batteries, it is still limited by high corrosion behavior, low anodic stability, and low salt solubility in the electrolyte.…”