The new electrolyte eliminates the Li-ion battery short circuit

Recently, US scientists have announced that they have created a new electrolyte for Lithium batteries that promises to increase battery efficiency and improve capacity.

New electrolyte for Lithium batteries

The microscope image shows that the dendrite fibers grow long in Li-ion batteries .

According to scientists at the US Pacific Northwest National Laboratory (PNNL), the electrolyte has the ability to completely remove dendrite fibers - a thin conductive fiber often formed on the side. In Lithium batteries, battery cells reduce life expectancy and are explosive agents.

Microscopic images show that the electrolyte normally facilitates dendrite fibers to grow (Figure a) while PNNL electrolyte causes lithium to form small nodules, without causing short circuits (Figure b).

Many types of rechargeable batteries used on mobile devices now use Li-ion technology - consisting of 2 electrodes, 1 Lithium anode, 1 cathode of graphite (graphite) and chemical electrolyte. Basically, the electrolyte contains electrically charged electrons and acts as an intermediary to transmit electricity between the electrodes when the battery is connected to an electrical circuit. When discharging the battery, Lithium leaves the anode surface and clings to the cathode, whereas when charging, Lithium converts back on the anode. Over charge / discharge time, the anode surface forms dendrite fibers and these fibers will grow longer when Lithium is continuously deposited.

The dendrite fibers break down the normal charge path and create jumbled paths throughout the battery structure.Once the dendrite yarn grows long enough, penetrates the electrolyte and directly connects the cathode to the anode, the battery will be short-circuited.

As a result, self-discharge batteries cannot be controlled to reduce battery life. In addition, the dendrite fiber also makes the battery heat up, causing an exothermic reaction and exploding whether it is outside or inside the mobile device.

The dendrite yarn grows very quickly from the anode and touches the cathode.

To prevent the formation of dendrite fibers, some researchers have experimented with several solutions such as adding a coating containing carbon spheres to the battery's anode or adjusting the electrolyte formulation with some extra or even add Kevlar nanofibers to this mixture. However, dendrite fiber still grows without signs of being restricted.

The newly developed PNNL electrolyte aims to completely replace the electrolyte that is being used on Li-ion batteries because it does not facilitate dendrite fibers to form. In addition, it also increases battery capacity and performance.

Dr. Ji-Guang "Jason" Zhang from PNNL said: "Our new electrolyte helps increase 99% efficiency of Li-ion batteries and increases current density 10 times higher than previous technology. Our new range can start the process of developing more powerful and powerful next generation rechargeable batteries such as Lithium-sulfur (Li-sulfur) batteries, Lithium-gas batteries and Lithium-metal batteries. "

Based on a study showing that electrolytes containing high concentrations of salt can interfere with the formation of dendrite fibers, Dr. Zhang and colleagues used a large amount of Lithium bis (fluorosulfony) imide, a compound Organic silicon and solvent dimethoxyethaein to produce electrolyte.

To test the new mixture, the team created a circular cell cell with a diameter of less than 25 mm. When the cell is charged, instead of dendrite fibers appear and grow, the Lithium electrode produces a thin sheet of small Lithium nodules on the surface and they do not affect the electrolyte causing a short circuit.

The team then continued to experiment with cell batteries with more than 1000 charging / discharging cycles and said the cell still maintained 98.4% of its initial charge and current density of about 4 mA / cm2. When changing the current density, battery performance is also affected. Accordingly, if the density of 10 mA / cm2 is maintained, the efficiency of the battery will be approximately 97% while if the density of 0.2 mA / cm2 is kept, the battery's efficiency can reach 99.1%.

According to the researchers, these are very impressive numbers because most ordinary Li-ion batteries with Lithium poles operate at current density of less than 1 mAh / cm2 and often fail after less than 300 cycles. charge / discharge.

In addition to increasing efficiency, the new electrolyte is also thought to pave the way for a new design in battery technology - called cell batteries without anode . In other words, the electrolyte itself can play the role of an electrode. The actual design of this type of cell will certainly need to be refined but with an electrolyte operating at more than 99% efficiency, researchers are facing an opportunity to create a battery with only components. accumulate opposite charge currents without the need for a reactive coating material on the anode. Removing anode also helps reduce cost, size and improve the safety of rechargeable batteries.

Of course, the new electrolyte of PNNL still needs to undergo many tests and corrections before being commercialized. Zhang and his colleagues are continuing to expand research with many other additives to improve electrolyte to achieve 99.9% efficiency - a prerequisite for commercial production and market release.