Opportunity
The development of safe, high-energy-density, and reversible electrochemical energy storage systems heavily relies on advanced solid-state electrolytes (SSEs). Current SSEs face significant challenges, including low ionic conductivity (typically below 10⁻⁵ S cm⁻¹ for solid polymer electrolytes, or SPEs) and poor interfacial contact with electrodes. Inorganic solid electrolytes (SIEs) like oxides and sulfides exhibit fast ion conduction but suffer from rigidity and brittleness, leading to inadequate electrode-electrolyte contact. SPEs, while flexible, struggle with insufficient ion dissociation and slow polymer chain dynamics, limiting their performance at room temperature. Additionally, multivalent ions (e.g., Zn²⁺, Mg²⁺, Ca²⁺) face stronger Coulombic forces than Li⁺, making their efficient transport in conventional SSEs difficult. These limitations motivate the need for a novel SSE that combines high ionic conductivity, flexibility, and electrochemical stability, particularly for zinc-ion batteries and supercapacitors.
Technology
This patent introduces a zinc-based solid-state electrolyte (ZSE) composed of a hydrated hydrogen-bonded organic-inorganic ionic co-crystal with the formula Zn(Im)₄(N)ₓ·6H₂O/yZn(N)ₓ·6H₂O, where "Im" is an imidazole ligand (e.g., imidazole, methylimidazole), "N" is an inorganic anion (e.g., ClO₄⁻, NO₃⁻, SO₄²⁻), and "y" ranges from 0 to 0.75. The key innovation lies in the co-crystal’s structure: Zn²⁺ ions coordinate with four imidazole ligands and surrounding anions to form tetrahedral units, which stack along the b-axis to create a flexible 3D hydrogen-bonded framework. Vacancies at crystal boundaries adsorb water molecules, forming rapid Zn²⁺ transport channels. This design achieves:
- High Zn²⁺ conductivity (11.2 mS cm⁻¹ at room temperature, 4 orders of magnitude higher than SPEs).
- Low activation energy (~0.12 eV) due to dynamic Zn²⁺ hopping at grain boundaries.
- Electrochemical stability (up to 2.35 V) and low-temperature operation (down to −40°C).
The electrolyte is prepared by simply mixing hydrated zinc salts (e.g., Zn(ClO₄)₂·6H₂O) with imidazole ligands at room temperature, followed by cooling. This cost-effective process avoids high-temperature sintering or complex synthesis.
Advantages
- Unprecedented ionic conductivity: 11.2 mS cm⁻¹ at 25°C, outperforming conventional SPEs and SIEs.
- High Zn²⁺ transference number (0.61), enabling efficient ion transport.
- Wide voltage window (~2.35 V) and dendrite suppression on Zn anodes.
- Flexible and stable: The hydrogen-bonded framework adapts to volume changes during cycling.
- Low-temperature performance: Operates at −40°C with retained conductivity (2.78 mS cm⁻¹).
- Scalable synthesis: Room-temperature preparation without toxic solvents.
Applications
- Rechargeable zinc-ion batteries: High-energy-density and safe alternatives to lithium-ion batteries.
- Supercapacitors: Achieve 139 Wh kg⁻¹ energy density and 82% capacity retention after 40,000 cycles.
- Zinc-air batteries: Neutral solid-state designs resist CO₂ corrosion, enabling stable operation.
- Flexible/wearable electronics: Compatible with bendable energy storage devices.
- Low-temperature energy storage: Reliable performance in subzero environments.
