ZAP // Dall-E-2
A new method for coating lithium-ion battery cathodes with graphene extends the life and performance of these widely used rechargeable batteries.
According to , this discovery could reduce dependence on cobalt, an element often used in lithium-ion batteries and which is difficult to obtain sustainably.
David Boydprincipal investigator at Caltech, has worked for the past decade on developing techniques to produce graphene, a one-atom-thick layer of carbon that is incredibly strong and conducts electricity more easily than materials such as silicon.
In 2015, Boyd and his colleagues discovered that high-quality graphene could be produced at room temperature. Before that, graphene production required extremely high temperatures, up to 1000 degrees Celsius.
After this discovery, the search for new applications for graphene began. Recently, Boyd joined Will Westa technologist at JPL, which Caltech manages for NASA.
West specializes in electrochemistry and, in particular, the development of improved battery technologies. Boyd and West set out to see if they could create an improved lithium-ion battery. Now they have shown that they do.
“Demonstrating a reliable trend in battery cell performance requires consistent materials, consistent cell assembly and careful testing under a variety of conditions,” he says. Brent Fultzprofessor of Materials Science and Applied Physics at Caltech.
“It’s fortunate that the team was able to do this work in such a reproducible way, although it took some time to be sure.”
The lithium-ion battery, first introduced on the market in 1991, revolutionized the way we use electricity in our daily lives.
From cell phones to electric vehicles, we rely on lithium-ion batteries as a relatively cheap, energy-efficient and, most importantly, energy source. rechargeable on the go.
Despite its successes, lithium-ion battery technology still has room for improvement. For example, Boyd says that “Tesla engineers want a cost-effective battery that can charge quickly and run for a longer period of time between charges. This is called load rate capacity.
West adds that “the more times a battery can be charged over its lifespan, the fewer batteries you will need to use. This is important because lithium-ion batteries use limited resources and disposing of lithium-ion cells safely and efficiently is a very difficult task.
An important feature of lithium-ion batteries is their performance after many load and use cycles.
Batteries work by creating chemical energy between the two ends of the cell — the cathode and anode — and converting it into electrical energy.
As the cathode and anode chemicals work over time, they may not fully recover to their original state.
A common problem is the dissolution of transition metals from the cathode material, which is particularly serious for cathode materials with a high manganese content, although less serious for cathode materials with a high cobalt content.
“As a result of unwanted side reactions that occur during the cycle, transition metals in the cathode gradually end up at the anode, where they become trapped and reduce the anode’s performance,” explains Boyd.
This dissolution of the transition metal is one of the reasons why expensive cathodes with cobalt are used instead of cheap cathodes with high manganese content.
Another challenge for lithium-ion batteries is the fact that they require metals that are expensive, scarce and not always mined responsibly. A significant amount of the world’s cobalt supply, in particular, is concentrated in the Democratic Republic of the Congo, and much of this cobalt is mined by so-called artisanal miners: independent workers, including children, who perform dangerous and demanding physical work for little or no pay. .
Ways have been sought to increase battery performance, reducing or eliminating the use of cobalt and avoiding TMD.
Engineers knew that carbon coatings on the cathode of a lithium-ion battery could slow or stop TMD, but it was difficult to develop a method to apply these coatings.
“Researchers have attempted to deposit graphene directly onto the cathode material, but the process conditions normally required to deposit graphene would destroy the cathode material,” explains Boyd.
“We investigated a new technique for depositing graphene onto cathode particles, called dry coating. The idea is to have a “host” substance of large particles and a “guest” substance of tiny particles.
When mixing them under certain conditions, the system can suffer a phenomenon known as “ordered mixing”, in which the guest particles uniformly coat the host particles.”
Dry coating technology has been used since the 1970s in the pharmaceutical industry to extend the shelf life of tablets by protecting them from moisture, light and air.
Dry coating the cathode with a graphene compound has proven successful in the laboratory. The graphene coating dramatically reduced TMD, simultaneously doubled battery life, and allowed batteries to operate over a slightly wider temperature range than was previously possible.
This result surprised the researchers. It was assumed that only a continuous coating could suppress TMD and that a dry coating composed of particles could not do so.
Additionally, because graphene is a form of carbon, it is widely available and environmentally friendly.
Teresa Oliveira Campos, ZAP //
