Membrane-free lithium-ion batteries could help power grid

Problems with conventional batteries

Before lithium-ion batteries, the world has functioned mainly on lead-acid batteries used today in automobiles and smaller energy storage requirements.

However, Lead-acid batteries have a very low energy density, making them unsuitable for storing large amounts of energy. This is because as energy density drops, the infrastructure needed to store energy increases. So, the lithium-ion battery system will pack more energy in the same footprint as a lead acid system.

Another drawback of lead-acid batteries is their low electrochemical stability. Water used in these batteries has a voltage limit. Once the voltage exceeds 1.5 V, the water begins splitting into hydrogen and oxygen molecules, making it prone to explosion.

The effort is, therefore, ongoing to improve lithium-ion-based energy storage by decreasing its cost of manufacture, and this is where Cincinnati researchers have achieved a significant feat.

Membrane-free lithium-ion battery

A team of researchers led by Jimmy Jiang, an associate professor in the Department of Chemistry at the university, has now developed a new lithium-based battery that does not use a membrane separator.

According to Jiang, membranes are "super expensive" components of lithium-ion batteries, and by removing them altogether, battery costs can be drastically reduced. The team estimates cost savings of as much as 30 percent when using their design. There is another advantage, too.

In addition to being expensive, membrane separators are highly inefficient too. "They can’t separate the positive and negative sides completely, so there is always crossover," added Jiang in the press release. This issue is also now overcome in the absence of membranes.

The battery design used by the team does not use water and generates four volts of power. With water out of the setup, the risk of explosion is also reduced.

Jiang admits that the team has a long way to go but is confident that the research to improve the performance of the batteries will surely lead us into a technological revolution in the next two decades.

Jiang envisions a future where every household can be powered by renewable energy stored in batteries; some may be those designed by his team. "Batteries store renewable energy for when it’s needed, not just when it’s produced. This is crucial for getting the most out of wind and solar power."

The team's research findings were published in the journal Nature Communications.

Abstract

Lithium-based nonaqueous redox flow batteries (LRFBs) are alternative systems to conventional aqueous redox flow batteries because of their higher operating voltage and theoretical energy density. However, the use of ion-selective membranes limits the large-scale applicability of LRFBs. Here, we report high-voltage membrane-free LRFBs based on an all-organic biphasic system that uses Li metal anode and 2,4,6-tri-(1-cyclohexyloxy-4-imino-2,2,6,6-tetramethylpiperidine)-1,3,5-triazine (Tri-TEMPO), N-propyl phenothiazine (C3-PTZ), and tris(dialkylamino)cyclopropenium (CP) cathodes. Under static conditions, the Li||Tri-TEMPO, Li||C3-PTZ, and Li||CP batteries with 0.5 M redox-active material deliver capacity retentions of 98%, 98%, and 92%, respectively, for 100 cycles over ~55 days at the current density of 1 mA/cm2 and a temperature of 27 °C. Moreover, the Li||Tri-TEMPO (0.5 M) flow battery delivers an initial average cell discharge voltage of 3.45 V and an energy density of ~33 Wh/L. This flow battery also demonstrates 81% of capacity for 100 cycles over ~45 days with average Coulombic efficiency of 96% and energy efficiency of 82% at the current density of 1.5 mA/cm2 and at a temperature of 27 °C.