Sustainable batteries made from wood
Lignin, a polymer found in trees, could power electrical vehicles.
In order to power something, all batteries need a cathode and anode – the positive and negative electrodes, respectively, between which charged particles called ions flow. When a battery is charged, lithium or sodium ions transfer from the cathode to the anode. When the battery is discharged, the ions move back to the cathode after releasing electrons – the electrons move through the wire in an electrical circuit, transferring energy to the vehicle. What makes a battery a good one is the capacity to take in the ions and let them leave, without crumbling apart.
Graphite is perfect for this purpose. The problem is that the lithium-ion batteries we rely on today largely depend on environmentally damaging industrial processes and mining that use materials which are toxic and difficult to recycle. Making synthetic graphite, for example, involves heating carbon to temperatures of up to 3,000C (5,432F) for weeks at a time.
In the last few years there have been several researches on more sustainable batteries.
Image provided by Mikko Nikkinen | Stora Enso
A turning point seems to come from Scandinavia, more precisely from the partnership between Northvolt, a colossus in battery business, and Stora Enso, a company founded between Sweden and Finland, leading provider of cellulose and paper, that has discovered and improved the production of sustainable batteries using lignin-based hard carbon.
A team of experts has patented Lignode, a battery made of lignin, which is a polymer found in wood. Around 20-30% of trees is lignin, that glues the cellulose fibres together and also makes the trees very stiff.
Stora Enso uses lignin from sustainably managed Nordic forests, so renewable wood.
A team of experts has patented Lignode, a battery made of lignin, which is a polymer found in wood. It glues the cellulose fibres together and also makes the trees very stiff.
The process of turning lignin into a hard carbon structure involves heating the lignin, but to temperatures nowhere near as high as those required for synthetic graphite production. According to the team, one important feature of the resulting carbon structure is that it is “amorphous”, or irregular, and this allows a lot more mobility of the ions in and out.
Stora Enso claims that this will help them make a lithium ion or sodium ion battery that can be charged in as little as eight minutes. Fast charging is a key goal for developers of electric vehicle batteries.
This shows how the development of a sustainable batteries industry can have a positive impact on both society and costs.
Wyatt Tenhaeff, at the University of Rochester in New York State, has also made lignin-derived anodes in laboratory settings. Lignin could have many potential uses, he says. In experiments, he used the lignin to make an anode with a self-supporting structure, which didn’t require glue or a copper-based current collector – a common component in lithium-ion batteries. Despite the fact that this could reduce the cost of lignin-derived carbon anodes, he is sceptical that they can compete commercially with graphite anodes.
Stora Enso claims that this will help them make a lithium ion or sodium ion battery that can be charged in as little as eight minutes. Fast charging is a key goal for developers of electric vehicle batteries.
As for sustainability, Chelsea Baldino, a researcher at the International Council on Clean Transportation, says that so long as the lignin used for anode production is extracted as a byproduct from the paper-making process, then additional trees won’t be chopped down in order to make batteries. A spokesman for Stora Enso confirmed to BBC that, currently, all lignin the company uses is “a side stream of the pulping process”, and utilising it does not increase the number of trees felled or volume of wood used in pulp-making.
There is at least one other way that lignin could be used in batteries, besides anodes. In April, a research team in Italy published a paper about their efforts to develop a lignin-based electrolyte. This is the component that sits between the cathode and anode – it helps ions flow between the electrodes but also forces electrons to take the desired path through the electrical circuit to which the battery is connected.
Gianmarco Griffini at the Polytechnic University of Milan, explained that the idea of using lignin arose after he and colleagues experimented with using the material in solar panels – with slightly underwhelming results. “The efficiencies you get in solar cells are relatively limited because lignin is brown, so it actually absorbs some light,” he explains. In batteries, that doesn’t matter.
After partnering with Swedish company Northvolt, Stora Enso has announced that it plans to manufacture batteries as early as 2025. Meanwhile, other multiple firms have started to explore lignin’s potential in battery development, such as Bright Day Graphene in Sweden.
