The limited range of electric vehicles—most of which max out at 380 miles—is one of the prevailing roadblocks of widespread EV adoption. Automotive manufacturers and researchers often look to three solutions for the range problem: energy-efficient automotive systems, improved battery recharging techniques, or higher-capacity batteries.
Range for some popular EVs currently on the market. Image used courtesy of Car and Driver
This week, General Motors (GM) invested significantly into the third solution—higher-capacity batteries—as the company’s answer to long-range EVs. While competing EV manufacturers like Tesla have aimed for higher-capacity batteries by modifying the architecture of lithium-ion batteries, GM’s solution is to move R&D away from lithium-ion altogether.
Instead, the automotive giant is opting to develop batteries with lithium-metal in the hopes of creating a higher-capacity, lower-cost battery. What are the merits of lithium-metal batteries for EVs in contrast to lithium-ion batteries? And why hasn’t this technology been picked up by manufacturers in a significant way until now?
Lithium-metal Batteries vs. Lithium-ion Batteries
Lithium-metal batteries function using similar principles to lithium-ion batteries.
In a Li-ion battery, the anode and cathode are separated by a separator “moistened” with an electrolyte to promote the movement of lithium ions between the anode and cathode. The separator isolates the anode and cathode to prevent a short circuit while allowing only Li-ons to pass through the electrolyte. This creates a functional current.
In a Li-on battery, the anode is normally made of graphite while the cathode is composed of lithium cobalt oxide.
Lithium-ion working principle. Image used courtesy of Battery University
Lithium-metal batteries work in the same fashion, but instead of using a graphite anode, they use a high-energy lithium metal.
According to researchers at Washington State University, lithium metal is considered a “dream material” for batteries because of all known solid materials, it has the highest energy density. In fact, a lithium-metal battery can store at least 33% more power per pound than Li-on batteries, yielding batteries with higher capacity and lighter weight.
Challenges for Lithium-metal Batteries
While lithium-metal sounds like a clear candidate for EV developers, concerns about the battery’s safety has been a major limitation.
When transferring lithium ions between anode and cathode, a lithium-metal battery is more prone to dendrites—solid, needle-like structures that form on lithium metal. If left unchecked, dendrites will eventually pierce through the cathode, shorting the battery and risking combustion of the battery’s electrolyte.
Dendrite formation can pierce the cathode, causing a short. Image used courtesy of MSE Supplies
Even if the battery does not catch fire, dendrites can increase self-discharge, meaning that lithium-metal batteries lose their ability to store charges for a long time. Because of these shortcomings, manufacturers have mostly given up on this battery type in favor of its more-established cousin, the lithium-ion battery.
However, with more research and investment in lithium-metal batteries in recent years, the technology seems to be making a comeback.
GM Bets on Lithium Metal
Six years ago, GM invested in a startup called SolidEnergy Systems (SES), a company researching new ways to develop and manufacture lithium-metal batteries that were actually safe to use. Now, the companies have announced a joint development agreement, part of which involves a plan to build a manufacturing prototyping line in Woburn, Massachusetts.
Prototype of GM’s lithium-metal battery. Image used courtesy of Steve Fecht and GM
While most information is still kept under wraps, both companies are bringing their own lithium metal IP to the table, with GM alone owning 49 patents and waiting on 45 pending patents. GM claims it has already developed a lithium-metal battery with a protected anode, which has completed over 150,000 test miles in a research facility.
This partnership aims to accelerate the lithium-metal R&D at both companies with the eventual hope to surface a commercial battery by 2023.
