Chinese researchers have unveiled a groundbreaking water-based battery design that promises enhanced safety and energy efficiency compared to traditional lithium-ion batteries. This innovative battery boasts a lifespan of over 1,000 charge-discharge cycles, as reported in the April 23 issue of Nature Energy.

A key property of any battery is its energy density, which measures the amount of energy it holds relative to its size or weight. Lithium-ion batteries, known for their high energy density, are widely used in electric vehicles and portable electronics. However, the organic chemicals in their electrolytes pose fire and explosion risks if the system overheats. Water-based batteries, while inherently safer, typically suffer from lower energy density due to their limited voltage range.

The research team, led by Xianfeng Li from the Chinese Academy of Sciences, has significantly improved both the energy density and performance of aqueous batteries by innovating the chemistry within the water electrolyte.

Electrolyte solutions in batteries are composed of various chemicals, each influencing different performance aspects. Additives called mediators facilitate electron movement across the solution through oxidation and reduction (redox) reactions. In aqueous batteries, iodine is a common mediator, capable of transferring up to six electrons per cycle through a series of redox reactions. However, its slow reaction rates and byproduct issues typically result in low energy density.

To overcome these limitations, Li’s team developed a mixed halogen electrolyte, incorporating both iodide (I–) and bromide (Br–) ions in an acidic solution. The addition of bromine, another electron-transferring halogen, enhanced the reaction rate and minimized unwanted byproducts.

Through comprehensive electrochemical and spectroscopic analyses, the researchers demonstrated that bromide ions significantly boosted the efficiency and speed of the electron transfer process by forming a crucial intermediate in the redox reactions.

The team conducted extensive experiments to assess the impact of this “hetero-halogen” electrolyte on the performance of various common battery types with different anode materials. The new electrolyte nearly doubled the energy density compared to standard lithium-ion batteries when paired with cadmium anodes, which are commonly used in high-energy portable devices such as power tools. Additionally, vanadium systems, typically utilized in grid energy storage for power plants and renewable energy sources, exhibited prolonged lifespans, maintaining peak performance over more than 1,000 charge-discharge cycles.

In both scenarios, the researchers reported improved energy efficiencies and concluded that the aqueous hetero-halogen system would be cost-competitive with current lithium-ion technologies.

This substantial enhancement in performance is expected to pave the way for broader adoption of water-based batteries, offering a safer, high-energy-density alternative to existing battery systems.

By Impact Lab