Salt Water Makes Li-Ion Batteries Safer

So far, high-energy lithium-ion batteries were always a matter of concern on account of safety. If you wanted to remain safe from exploding batteries, an aqueous battery such as made from nickel/metal hydride would be preferable, but then it would give you lower energy.

Usually, 3-V batteries using aqueous electrolyte technologies are unable to achieve higher voltages because of the cathodic challenge. This happens as the aqueous solution degrades one end of the battery made from either lithium or graphite. One research team solved this problem by covering the graphite or lithium anode with a gel polymer electrolyte coating.

As the coating is hydrophobic, it does not allow water molecules to reach the electrode. However, when the battery charges for the first time, the coating decomposes, forming a stable layer separating the solid anode from the liquid electrolyte. The layer protects the anode from side reactions that could deactivate the anode. This allows the battery to use anode materials that are more effective, such as lithium metal or graphite, and allowing the battery reach higher energy densities and cycling abilities. The gel coating improves the safety of the battery, and is now comparable to the safety standards of non-aqueous lithium-ion batteries.

Organic solvents used in non-aqueous batteries are highly flammable. In comparison, aqueous lithium-ion batteries use water-based electrolytes that are non-flammable. Another advantage of this gel polymer coating is if this layer is damaged, the reaction with the lithiated graphite or lithium anode is very slow, preventing smoking, fire, or explosion that would normally happen if in the damaged battery the metal came into direct contact with the electrolyte.

This aqueous lithium-ion battery with the gel covering the anode has power and energy density matching its counterpart with non-aqueous electrolyte, and is suitable for commercial applications. However, the researchers intend to improve on the number of full-performance cycles the battery can complete. According to the researchers, this will reduce material expenses as far as possible. Although at present the battery is able to complete only 50-100 cycles, the team intends to increase that to 500 or more.

The researchers are also trying to manipulate the electrochemical process to allow the battery achieve 4 V on its terminals. According to the researchers, this is the first time they have been able to stabilize the reactive anodes such as lithium and graphite in aqueous media. They feel this opens a huge field of possibilities into several different topics in electrochemistry. For instance, this could cover not only lithium-ion batteries, but also lithium-sulfur, sodium-ion batteries, and other batteries using multiple ion chemistry technologies such as magnesium and zinc, and electrochemical and electroplating synthesis.

The researchers understand that interphase chemistry requires to be perfected before they can commercialize their product. They also feel that they need to work more towards scaling up the technology so that big cells can be used for testing. However, the researchers are confident they will be able to commercialize their product within the next five years, provided they are able to gather more funding.