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Boron nitride coating increases the lifespan of solid-state lithium batteries

American scientists have developed a technique to make solid state lithium batteries last longer. The researchers have developed a special nanocoating to prevent the electrolyte from being attacked by the energy-dense lithium.

The scientists at Columbia University School of Engineering explain that they developed a boron nitride coating as an interface to protect the solid electrolyte of lithium metal batteries from lithium metal. This should ultimately lead to solid state batteries with a relatively high energy density, long service life and high safety. The researchers see this as an important type of battery for the 'next generation of energy storage', for example with electric cars.

Lithium metal as a replacement for the graphite used in the anodes of lithium-ion batteries can provide nearly ten times the energy charge, but lithium metal can be deposited around the anode during the charging process in a cell. This process is called lithium plating. This eventually leads to problems, because dendrites are often formed during this process. These are crystal structures that grow between the anode and cathode and can cause short circuits and heat development, which can even cause a fire.

The scientists say they are able to limit this risk by first using solid ceramic electrolyte, because it is naturally better at limiting the formation of dendrites than the liquid electrolyte in lithium-ion batteries. In addition, this solid electrolyte is not naturally flammable, which makes it a lot safer than the flammable electrolyte in lithium-ion batteries.

Then there is the problem of instability by the lithium, in the form of corrosion. In order to make the unstable solid electrolytes useful for everyday applications, a stable interface must be used that is not only electronically insulating but can also continue to conduct the lithium ions. In addition, the interface must be very thin so as not to limit the energy capacity of the batteries.

According to the researchers, a nanocoating of boron nitride of 5 to 10nm is the solution. This is the very thin protective layer that electrically separates the lithium metal and the ion-conducting solid electrolyte. According to the scientists, boron nitride was chosen as a protective layer because it is chemically and mechanically stable with lithium metal. The boron nitride is deliberately designed with intrinsic bumps to allow the passage of lithium ions. The researchers describe it as a 'bulletproof vest' that allows a long life of lithium metal batteries.

The researchers see lithium metal as indispensable for increasing the energy density in batteries. They are currently extending their method to a wide category of unstable solid electrolytes to further optimize the interface. The scientists expect that with their method solid state batteries with high performance and long life can be made.

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