Eco-friendly electrolyte for aqueous Li-ion batteries

Thursday, 30 April, 2020

Eco-friendly electrolyte for aqueous Li-ion batteries

Researchers at The Chinese University of Hong Kong (CUHK) have taken a critical step towards improving high-energy batteries by introducing a novel electrolyte to aqueous lithium-ion (Li-ion) batteries. The electrolyte is cheap, non-flammable, eco-friendly and less toxic than other alternatives, according to the researchers, yet creates stable voltage for common use.

Li-ion batteries are at the heart of electronic devices such as smartphones and laptops, as they are rechargeable and can provide relatively stable energy. However, they rely on toxic and flammable materials and have already raised serious safety concerns.

In contrast, aqueous Li-ion batteries are non-flammable and do not pose any significant risks of explosion due to their water-based electrolytes. However, aqueous Li-ion batteries have been suffering from low energy density due to the low battery cell voltage limited by water stability (1.23 V). Existing approaches to increase the cell voltage of aqueous batteries often involve the use of large amounts of expensive and toxic salts to stabilise water molecules, which raises the issues of cost, toxicity and environmental sustainability.

Building on their previous research into aqueous lithium-ion batteries, Professor Yi-Chun Lu and her team have introduced a ‘molecular crowding’ aqueous electrolyte using polyethylene glycol (PEG) as a stabilisation agent. PEG is water-soluble polymer that can be easily incorporated into aqueous batteries. It is also the basis of many skin creams and personal lubricants and is even used in toothpastes and as an anti-foaming agent in food and drinks.

Using this stabilisation agent, the team successfully expanded the aqueous electrolyte stability window to 3.2 V and demonstrated stable battery operation for over 300 cycles. The electrolyte also enables the use of many electrode materials that cannot be used in the conventional aqueous electrolytes.

The team’s research, published in the journal Nature Materials, thus provides a new platform for designing aqueous electrolytes with a large-voltage window and high stability for safe, low-cost and eco-friendly energy storage.

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