The research from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) describes a new way to make solid state batteries with a lithium metal anode. The research is published in Nature Materials.
“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,” Xin Li, Associate Professor of Materials Science at SEAS and senior author, said in a statement.
A significant challenge in the design of these batteries is the formation of dendrites on the surface of the anode. These structures grow into the electrolyte and pierce the barrier separating the anode and cathode, causing the battery to short or catch fire.
Dendrites form when lithium ions move from the cathode to the anode during charging, attaching to the surface of the anode in a process called plating that creates an uneven, non-homogeneous surface and allows dendrites to form. When discharged, that coating needs to be stripped from the anode and when plating is uneven, the stripping process can be slow and result in potholes that induce more uneven plating in the next charge.
In 2021, Li and his team designed a multilayer battery that sandwiched different materials of varying stabilities between the anode and cathode. This multilayer, multi-material design prevented the penetration of lithium dendrites by controlling and containing them.
In this new research, Li and his team stop dendrites from forming by using micron-sized silicon particles in the anode to constrict the lithiation reaction and facilitate homogeneous plating of a thick layer of lithium metal.
In this design, when lithium ions move from the cathode to the anode during charging, the lithiation reaction is constricted at the shallow surface and the ions attach to the surface of the silicon particle but do not penetrate further. This is markedly different from the chemistry of liquid lithium-ion batteries in which the lithium ions penetrate through deep lithiation reaction and destroy silicon particles in the anode.
In a solid state battery, the ions on the surface of the silicon are constricted and undergo the dynamic process of lithiation to form lithium metal plating around the core of silicon.
These coated particles create a homogenous surface across which the current density is evenly distributed, preventing the growth of dendrites. Because plating and stripping can happen quickly on an even surface, the battery can recharge in about 10 minutes, the team said.
The researchers built a postage stamp-sized pouch cell version of the battery that retained 80 per cent of its capacity after 6,000 cycles, outperforming other pouch cell batteries currently available. The technology has been licensed through Harvard Office of Technology Development to Adden Energy, which has scaled up the technology to build a smart phone-sized pouch cell battery.
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