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Breakthrough in durable, stable, solid-state lithium batteries; good news for electric vehicles

Researchers have designed a stable lithium-metal solid-state battery that can be charged and discharged at least 10,000 times – many more cycles than previously shown – with a high current density.

Long-lasting, fast-charging batteries are essential for the expansion of the electric vehicle market, but today’s lithium-ion batteries are failing: they are too heavy, too expensive, and take too long to charge.

For decades, researchers have sought to harness the potential of solid-state lithium-metal batteries, which retain significantly more energy in the same volume and charge in a fraction of the time compared to traditional lithium-ion batteries.

“A lithium metal battery is considered the holy grail of battery chemistry because of its high capacity and energy density,” said Xin Li, associate professor of Materials Science at Harvard John A Paulson School of Engineering and Applied Science (SEAS).

“But the stability of these batteries has always been bad.” Li and his team have designed a stable lithium-metal solid-state battery that can be charged and discharged at least 10,000 times – many more cycles than previously shown – with a high current density.

The researchers combined the new design with a commercial cathode material with high energy density. This battery technology could extend the life of electric vehicles to gasoline cars – 10 to 15 years – without having to replace the battery.

With its high current density, the battery could pave the way for electric vehicles that can fully charge in 10 to 20 minutes.

“Our research shows that the solid-state battery may be fundamentally different from the commercial lithium-ion battery with liquid electrolyte,” said Li.

“By studying their fundamental thermodynamics, we can unlock superior performance and exploit their abundant capabilities.” The big challenge with lithium metal batteries has always been chemistry.

Lithium batteries move lithium ions from the cathode to the anode while charging. When the anode is made of lithium metal, needle-like structures called dendrites form on the surface.

These structures grow like roots in the electrolyte and pierce the barrier separating the anode and cathode, causing the battery to short or even catch fire.

To meet this challenge, Li and his team designed a multi-layer battery that trapped different materials with varying stability – lithium metal, graphite and electrolytes – between the anode and cathode.

This multi-layer, multi-material battery prevents the entry of lithium dendrites by stopping them completely, but by controlling and holding them.

“Our strategy to include instability to stabilize the battery feels counterintuitive, but just as an anchor can guide and control a screw that goes into a wall, our multi-layer design can guide and control dendrite growth,” said Luhan Ye, co-author of the paper and graduate student at SEAS.

“The difference is that our anchor quickly becomes too tight for the dendrite to drill through, so the dendrite’s growth is stopped,” added Li. The battery is also self-healing; due to its chemistry, it can fill in gaps created by the dendrites.

“This proof-of-concept design shows that lithium metal semiconductor batteries can compete with commercial lithium-ion batteries,” said Li. “The flexibility and versatility of our multi-layer design makes it potentially compatible with mass production procedures in the battery industry.

Scaling up to the commercial battery will not be easy and there are still some practical challenges, but we think they will be overcome.

The research is published in the journal Nature.