Periodic Reporting for period 1 - WIZBAT (Low-cost and eco-friendly localized water-in-salt electrolyte-based rechargeable anode-free Zn-ion batteries)
Período documentado: 2025-01-01 hasta 2026-12-31
The transition to renewable energy sources such as wind and solar is crucial for a sustainable future. However, their intermittent nature requires efficient and safe energy storage systems. While lithium-ion batteries (LIBs) have dominated the market, their high cost, limited lithium resources, and safety concerns due to flammable electrolytes limit their suitability for large-scale grid storage.
Aqueous zinc-ion batteries (AZIBs) have emerged as a promising alternative, offering advantages such as low cost, environmental friendliness, and non-flammability. However, conventional AZIBs often use excess zinc metal anodes, which reduce energy density and mask performance issues. Anode-free zinc-ion batteries (AFZIBs) eliminate the initial zinc anode, depositing zinc in situ during charging, thereby maximizing energy density. A key challenge for AFZIBs is hydrogen evolution and side reactions in aqueous electrolytes, which degrade performance and shorten battery life.
This project aims to develop a novel localized water-in-salt electrolyte (LWiSE) to suppress hydrogen evolution and enhance the reversibility of zinc deposition. By using low-cost, eco-friendly salts and diluents, the project seeks to create high-performance AFZIBs suitable for practical applications, including large-format pouch cells under lean electrolyte conditions. The outcomes are expected to contribute to safer, more affordable, and sustainable energy storage solutions, supporting the EU’s green energy transition and reducing dependence on critical raw materials.
Aqueous zinc-ion batteries (AZIBs) have emerged as a promising alternative, offering advantages such as low cost, environmental friendliness, and non-flammability. However, conventional AZIBs often use excess zinc metal anodes, which reduce energy density and mask performance issues. Anode-free zinc-ion batteries (AFZIBs) eliminate the initial zinc anode, depositing zinc in situ during charging, thereby maximizing energy density. A key challenge for AFZIBs is hydrogen evolution and side reactions in aqueous electrolytes, which degrade performance and shorten battery life.
This project aims to develop a novel localized water-in-salt electrolyte (LWiSE) to suppress hydrogen evolution and enhance the reversibility of zinc deposition. By using low-cost, eco-friendly salts and diluents, the project seeks to create high-performance AFZIBs suitable for practical applications, including large-format pouch cells under lean electrolyte conditions. The outcomes are expected to contribute to safer, more affordable, and sustainable energy storage solutions, supporting the EU’s green energy transition and reducing dependence on critical raw materials.
The project began with the screening of potential diluents for the LWiSE formulation. Several organic solvents—diethylene carbonate (DEC), propylene carbonate (PC), ethanol, and ethylene glycol (EG)—were evaluated based on their miscibility with water and solubility with zinc salts.
DEC and PC were found to be immiscible with water, while ethanol and EG showed excellent miscibility even at high concentrations (up to 90% vol.). To maintain low cost and environmental friendliness, zinc chloride (ZnCl2) was selected as the salt. Ethanol was found to dissolve ZnCl2, which contradicts the requirement for a diluent that does not interact with the salt. In contrast, EG showed no solubility with ZnCl2, making it an ideal candidate.
Using EG as the diluent, a localized water-in-salt electrolyte was successfully prepared with 70% EG in water and 2M ZnCl2. This LWiSE was compared with a conventional aqueous electrolyte (2M ZnCl2 in water) in zinc symmetric cells. The conventional electrolyte supported only about 200 hours of stable cycling, while the LWiSE-enabled cells achieved over 400 hours, demonstrating significantly improved cycling stability and reversibility of zinc plating and stripping.
These results confirm that the LWiSE strategy effectively suppresses hydrogen evolution and side reactions, enhancing the electrochemical performance of zinc metal anodes.
DEC and PC were found to be immiscible with water, while ethanol and EG showed excellent miscibility even at high concentrations (up to 90% vol.). To maintain low cost and environmental friendliness, zinc chloride (ZnCl2) was selected as the salt. Ethanol was found to dissolve ZnCl2, which contradicts the requirement for a diluent that does not interact with the salt. In contrast, EG showed no solubility with ZnCl2, making it an ideal candidate.
Using EG as the diluent, a localized water-in-salt electrolyte was successfully prepared with 70% EG in water and 2M ZnCl2. This LWiSE was compared with a conventional aqueous electrolyte (2M ZnCl2 in water) in zinc symmetric cells. The conventional electrolyte supported only about 200 hours of stable cycling, while the LWiSE-enabled cells achieved over 400 hours, demonstrating significantly improved cycling stability and reversibility of zinc plating and stripping.
These results confirm that the LWiSE strategy effectively suppresses hydrogen evolution and side reactions, enhancing the electrochemical performance of zinc metal anodes.
The development of a low-cost, eco-friendly LWiSE using ethylene glycol as a diluent represents a significant advancement beyond current state-of-the-art electrolytes, which often rely on expensive fluorinated salts. This project demonstrates that:
• A locally concentrated electrolyte structure can be achieved without high salt concentrations, reducing cost and environmental impact.
• The LWiSE significantly improves zinc metal anode stability and cycling life, addressing a major bottleneck in AFZIB development.
• The use of ZnCl2 and EG aligns with EU priorities for sustainable and non-toxic battery materials.
These findings pave the way for the practical implementation of AFZIBs in large-scale energy storage systems. Further research will focus on optimizing electrolyte formulations, scaling up to pouch cells, and validating performance under realistic conditions.
• A locally concentrated electrolyte structure can be achieved without high salt concentrations, reducing cost and environmental impact.
• The LWiSE significantly improves zinc metal anode stability and cycling life, addressing a major bottleneck in AFZIB development.
• The use of ZnCl2 and EG aligns with EU priorities for sustainable and non-toxic battery materials.
These findings pave the way for the practical implementation of AFZIBs in large-scale energy storage systems. Further research will focus on optimizing electrolyte formulations, scaling up to pouch cells, and validating performance under realistic conditions.