Nathan Taylor, a post-doctoral fellow in mechanical engineering at the University of Michigan, inspects a piece of lithium metal in the Phoenix Memorial Laboratory building. (Image courtesy of Evan Dougherty, Michigan Engineering)

A rechargeable battery technology developed at the University of Michigan could double the output of today’s lithium ion cells, drastically extending electric vehicle ranges and time between cell phone charges, without taking up any added space.

By using a ceramic, solid-state electrolyte, engineers can harness the power of lithium metal batteries without the historic issues of poor durability and short-circuiting. The result is a roadmap to what could be the next generation of rechargeable batteries. In the 1980s, rechargeable lithium metal batteries that used liquid electrolytes were considered the next big thing, penetrating the market in early portable phones. But their propensity to combust when charged led engineers in different directions. The lithium atoms that shuttle between the electrodes tended to build tree-like filaments called dendrites on the electrode surfaces, eventually shorting the battery and igniting the flammable electrolyte.

The lithium ion battery, a more stable but less energy-dense technology, was introduced in 1991 and quickly became the new standard. These batteries replaced lithium metal with graphite anodes, which absorb the lithium and prevent dendrites from forming, but also come with performance costs. Graphite can hold only one lithium ion for every six carbon atoms, giving it a specific capacity of approximately 350 milliampere hours per gram (mAh/g). The lithium metal in a solid-state battery has a specific capacity of 3800 mAh/g. Current lithium ion batteries max out with a total energy density around 600 watt-hours per liter (Wh/L) at the cell level. In principal, solid-state batteries can reach 1200 Wh/L. To solve lithium metal’s combustion problem, University of Michigan engineers created a ceramic layer that stabilizes the surface, keeping dendrites from forming and preventing fires. It allows batteries to harness the benefits of lithium metal — energy density and high-conductivity — without the danger of fires or degradation over time.

In earlier solid-state electrolyte tests, lithium metal grew through the ceramic electrolyte at low charging rates, causing a short circuit, much like that in liquid cells. The researchers solved this problem with chemical and mechanical treatments that provide a pristine surface for lithium to plate evenly, effectively suppressing the formation of dendrites or filaments. Up until now, you’d have to charge a lithium metal car battery over 20 to 50 hours for full power, but with this breakthrough, the battery can be charged in 3 hours or less. This puts the batteries on par with lithium ion cells in terms of charging rates, but with additional benefits.

The charge/recharge process is what inevitably leads to the eventual death of a lithium ion battery. Repeatedly exchanging ions between the cathode and anode produces visible degradation right out of the box. In testing the ceramic electrolyte for 22 days, however, no visible degradation was observed.

Bulk solid-state electrolytes enable cells that are a drop-in replacement for current lithium ion batteries could leverage existing battery manufacturing technology. With the material performance verified, the research group has begun producing the thin solid electrolyte layers required to meet solid state capacity targets.