A new solid state lithium metal battery, that can be charged within a matter of minutes and can be charged and discharged at least 6 000 times, has been developed by researchers at the John A Paulson School of Engineering and Applied Sciences (SEAS) at Harvard University in the US.

The new battery falls into the category called ‘pouch batteries’, which are batteries which consist of an anode, a cathode, and between them, a separator, which prevents direct contact between the anode and cathode.

“Lithium metal anode batteries are considered the holy grail of batteries because they have ten times the capacity of commercial graphite anodes and could drastically increase the driving distance of electric vehicles,” explained project senior researcher and SEAS Materials Science Associate Professor Xin Li. “Our research is an important step toward more practical solid-state batteries for industrial and commercial applications.”

A major challenge in the design of solid-state batteries has been the formation, during charging, of structures called dendrites, on the surface of the anode. These form when, during charging, lithium ions move from the cathode to the anode. The lithium ions attach to the surface of the anode, in a phenomenon called plating. Plating results in an uneven surface on the anode, which allows these lithium dendrites to take root and develop. The dendrites grow, like roots do, into the battery electrolyte and, in time, penetrate the separator layer, triggering a short circuit, or even a fire, in the battery.

Back in 2021, Li and his research team developed an approach that controlled and contained the development of dendrites. This approach involved the use of a multilayer separator, composed of a sandwich of materials with differing stabilities, between the anode and cathode.

Their latest design stops the formation of lithium dendrites. The anode is coated with micron-sized silicon particles. During charging, when the lithium ions move from the cathode to the anode, they attach to the surface of the silicon particles and do not penetrate any deeper. The lithium-coated silicon particles form an homogenous surface, resulting in a current density that is evenly distributed across the anode surface, which prevents the development of dendrites.

“In our design, lithium metal gets wrapped around the silicon particle, like a hard chocolate shell around a hazelnut core in a chocolate truffle,” he elucidated. The result is a battery that can be recharged in as few as ten minutes. And it retained 80% of its capacity after 6 000 cycles of charging and discharging, more than any pouch battery currently on the market.