Electric cars: Trees could be the next source of sustainable batteries

Now it also wants to make batteries for electric cars that charge in just eight minutes.

The company hired engineers to study the feasibility of using lignin, a polymer found in trees.

Depending on the species, a tree consists of about 30% lignin, and the rest is mainly cellulose.

“Lignin is the glue in trees that binds the cellulose fibers together and also makes the trees very tough,” says Lauri Lehtonen, manager of Lignode, Stora Enso’s lignin-based battery solution.

Lignin contains carbon. And carbon is an excellent material for an important battery component called the anode.

Your phone’s lithium-ion battery probably has a graphite anode. Graphite is a form of carbon with a layered structure.

Stora Enso engineers thought they could extract lignin from the waste paper pulp already produced at some of their plants and turn it into carbon material for battery anodes.

The company has partnered with Sweden’s Northvolt and plans to produce batteries from 2025.

As more and more people buy electric cars and store energy in their homes, global demand for batteries is expected to increase significantly in the coming years.

As Lehtone sees it: “The demand is extraordinary.”

In 2015, the global battery supply required a few hundred additional gigawatt hours (GWh) each year, but this number will increase to thousands of additional GWh per year by 2030 as the world moves away from fossil fuels. fossils, according to consulting firm McKinsey.

The problem is that today’s lithium-ion batteries rely heavily on environmentally damaging industrial and mining processes.

In addition, some of the materials in these batteries are toxic and difficult to recycle. Many of them are also from countries with weak human rights policies.

For example, making synthetic graphite involves heating carbon to 3000°C for weeks.

According to consulting firm Wood Mackenzie, the energy needed comes mostly from coal-fired power plants in China.

The search for sustainable and widespread battery materials continues. Some say it can be found in trees.

In general, all batteries need a cathode and an anode, which are positive and negative electrodes, respectively, between which charged particles called ions flow.

When batteries are charged, for example, lithium or sodium ions are transferred from the cathode to the anode, where they are stored like cars in a multi-story parking lot, says Jill Pestana, a scientist and engineer who specializes in batteries. He is based in California and now works as an independent consultant.

“The key feature we’re looking for in this storage structure of the material is that it can easily absorb lithium or sodium and release it without breaking down.”

When a battery is discharged to power something like an electric car, the ions return to the cathode after releasing electrons. The electrons then move along the wire in an electrical circuit, transferring energy to the car.

According to Pestan, graphite is an “amazing” material because it works so well as a reliable anode that allows such reactions to occur.

Alternatives containing lignin-derived carbon structures are being tested to adequately cope with this task.

However, several companies are exploring the potential of lignin in battery development, such as Sweden’s Bright Day Graphene, which produces graphene, another form of carbon, from lignin.

Mr Lehtonen highlights the advantages of Stora Enso’s carbon anode material, which he calls Lignode.

The company does not disclose how it converts lignin into a rigid carbon structure or what exactly that structure is.

But he says the process involves heating the lignin, albeit at temperatures lower than those required to make synthetic graphite.

According to Lehtone, the carbon structure thus obtained has an important feature: it is “amorphous” or irregular: “This actually allows for greater mobility of ions in and out.”

Stora Enso says this will help it create a lithium-ion or sodium-ion battery that can be charged in just eight minutes. Fast charging is a key goal for electric vehicle battery developers.

Separate research on lignin-derived carbon anodes by Magda Titirici and colleagues at Imperial College London in England shows that it is possible to make conductive structures with disordered carbon elements that contain oxygen-rich defects.

According to Titirici, these defects increase the reactivity of the anode with ions transferred from the cathode in sodium-ion batteries, which shortens charging times.

“This conductive structure is fantastic for batteries,” he says.

Wyatt Tenhaeff of the University of Rochester in New York state also developed lignin-derived anodes in the laboratory.

Lignin is “really cool,” he notes, because it’s a by-product that has so many potential uses.

During their experiments, he and his colleagues discovered that with the help of lignin, they could make an anode with a self-supporting structure that required neither glue nor a current collector made of copper, a common component of lithium batteries.

Although this could reduce the cost of lignin-derived carbon anodes, the expert doubts that they will be commercially competitive with graphite anodes.

“I don’t think it’s going to be a big enough change in cost or performance to replace conventional graphite.”

There is also the issue of sustainability.

Chelsea Baldino, a researcher at the International Council on Clean Transportation, says that since the lignin used to make the anode is removed as a byproduct of the papermaking process, no additional trees will be cut down to make the battery.

A spokesperson for Stora Enso confirms that all lignin used by the company is currently “by-stream of the pulping process” and that its use does not increase the number of trees felled or the volume of wood used for pulp production.

However, anyone looking to make an anode from lignin needs to be sure of the origin of that lignin so that it is sustainable, adds Pestana.

“If the pulp industry is not sustainable, then the material itself is not a sustainable by-product material,” he explains.

According to Stora Enso’s 2021 annual report, the company “knows the origin of all the wood it uses and is 100% from sustainable sources.”

Besides anodes, there is at least one other way to use lignin in batteries.

In April, an Italian research group published a paper on their efforts to develop a lignin-based electrolyte.

It’s the component that sits between the cathode and the anode: it helps ions flow between the electrodes, but also forces electrons to take any path in the electrical circuit the battery is connected to.

In other words, it prevents electrons from simply bouncing between the electrodes, which would kill your smartphone.

Polymers for electrolytes can be derived from petroleum, explains Gianmarco Griffini of the Polytechnic University of Milan.

But he adds that it would be useful to find alternative and sustainable sources instead.

The expert explains that the idea of ​​using lignin came about after he and his colleagues had experimented with using this material in solar panels with somewhat disappointing results.

“The yield achieved in solar cells is relatively limited because lignin is brown and therefore absorbs some of the light,” he explains. It doesn’t matter in batteries.

To produce anodes, lignin is treated with heat to break it down into its constituent carbons.

But Mr Griffini, a self-proclaimed “polymerist”, says he prefers to use it in polymer form.

With this in mind, his team developed a polymer gel electrolyte that facilitates the movement of ions in an experimental potassium battery. “It went really well,” he says.

The commercial viability of all these ideas has yet to be demonstrated.

However, Titirici adds, a battery could theoretically be made using lignin polymers in the electrolyte as well as lignin-derived carbons in the anode.

You can even use it to power the latest generation of cellulose-based electronics – perfect technology for your treehouse, right? Or will this go too far?