As countries grapple to build an ex-China graphite supply chain, an unlikely contender has emerged: wood. 

While trees are probably not what one would expect to “revolutionise” the battery industry, Finnish paper and renewable products provider Stora Enso believes so. The company is developing bio-based anodes as an alternative to largely fossil-derived anodes in lithium-ion and sodium-ion batteries.

At the heart of Stora Enso’s offering is lignin – a carbon-rich polymer that makes up around 30% of all trees. Currently, lignin is produced as a by-product in the production of cellulose fibre – the material that goes into products like paper, pulp, and textiles. One of the world’s largest renewable sources of carbon, lignin is already mass-produced in Europe and typically burnt to provide energy.

Stora Enso, which has decades of experience in the forest industry, was exploring new business opportunities to adapt to changing market trends when researchers at the firm discovered lignin’s potential to be an alternative to graphite anodes. 

Using conversion technology, they were able to process lignin into hard carbon suitable as an ​​anode material for batteries, Juuso Konttinen, senior vice president and head of biomaterials growth at Stora Enso tells Kallanish in an interview.

They call this hard carbon product: Lignode.

A key advantage of lignin-derived anodes is the opportunity for localisation, Konttinen says. Currently, most global battery producers are heavily reliant on China for graphite anodes, which accounts for 80% of global natural graphite production, according to the International Energy Agency (IEA). The global graphite demand is expected to reach 18 million tonnes by 2040 in the IEA’s Net Zero Emission scenario – a fourfold increase from current levels. And China is projected to account for 93% of battery-grade supply by the end of this decade.

As a result, there has been an increasing push for alternative anode chemistries such as lithium metal anodes and high silicon anodes.

“Europe is super supply-limited on graphite, with the lion’s share coming from China,” the top executive says. “At the same time, there is a quite strong aspiration from Europe – if not to become self-sufficient – but at least build certain level of self-sufficiency in critical raw materials.”

“[Lignode] is a great opportunity to build a European anode material supply chain in conjunction with already existing pulp mills,” he adds. 

From pulp to batteries

Stora Enso calls itself one of the largest private forest owners in the world. The company extracts dry lignin from wood during cellulose fibre production and refines it into a fine carbon powder, before using it to produce electrode sheets and rolls. Stora Enso has been developing Lignode at its pilot plant in Kotka, Finland since summer 2021, enabling partners and potential customers to test the product.

Because of its amorphous structure, Lignode allows ions to enter from all directions, enabling the anode to be charged and discharged more quickly, compared to traditional graphite. In other words, Lignode-based batteries can offer faster charging, or so Stora Enso claims.  

While this open structure facilitates faster charging, a trade-off is a loss of capacity. The company is working with different partners to develop battery solutions that could potentially address the capacity issues, Konttinen notes.

“We are very confident that the product parameters are on a clear path towards what the market requires,” he says. “However, as a new product and new technology, it’s a very holistic multi-dimensional equation that you need to get right.”

This means ensuring the right lignin is being used alongside the right unit processes and parameters to reach the target specification – all the while ensuring the product remains competitive. In the next phase, Stora Enso plans to scale up the pilot to produce “bigger” volumes. 

Initially, the focus will be Europe, both for production and target markets. While stressing the company is making “good progress,” Konttinen did not disclose details of its manufacturing plans, including capacity and timeline.

Originally, the focus was only on lithium-ion batteries, which currently dominate the battery market. Lignode works “very well” with lithium-ion chemistries and the company has seen “good results,” Konttinen says. However, with sodium-ion batteries gaining momentum, these batteries have also been an additional consideration for the company.

Apart from sodium being cheaper than lithium, Konttinen explains that sodium ions are too big to enter the graphite layers, meaning, existing graphite cannot be used as anodes in sodium-ion batteries. Yet, the structure of hard carbon is compatible with sodium ions.

To this end, Stora Enso last week announced a partnership with Swedish sodium-ion battery developer Altris to adapt Lignode as an anode material in Altris’ sodium-ion battery cells. 

“At Altris, we strive to establish a local supply chain and leverage abundant and clean materials to develop sodium-ion batteries,” says Björn Mårlid, ceo of Altris. “Therefore, it’s exciting to team up with Stora Enso and take part in their establishment of a Europe-based tree-to-anode supply chain. We are looking forward to the partnership evolving over the coming years, with the aim to commercialise the world’s most sustainable battery.” 

In 2022, Stora Enso partnered with Swedish battery manufacturer Northvolt to develop the “world’s first” industrialised battery with anode sourced entirely from European raw materials. The company has also joined a project by Swedish electric vehicle brand Polestar to create a “truly climate-neutral” car by 2030.

Pulp fiction or a ‘new paradigm’?

Stora Enso is not alone in using bio-based materials in battery cells. Swedish start-up Ligna Energy is developing small batteries with lignin as an alternative to lithium or lead. New Zealand start-up CarbonScape, in which Stora Enso is also a shareholder, is piloting the use of forestry industry by-products such as wood chips to make graphite. 

In a 2022 study, researchers said lignin offers several advantages to a range of components in rechargeable batteries, including the binder, separator, and electrolyte.

“The high fraction of carbon element in the chemical structure makes lignin an ideal carbon precursor to being used in both the anode and cathode,” the researchers wrote. “As new strategies and applications are developed, more environmentally friendly and cheaper lignin-based materials will positively impact our lives, creating a new paradigm.”

While the use of bio-based materials in batteries sounds promising, a key question remains: how sustainable are they really? 

Stora Enso claims all its wood is sustainably sourced and making anodes from lignin would not require additional trees to be cut down.

“More or less all of our business is forest-based,” Konttinen says. “So it is utmost important for us that we do it in an extremely sustainable way. In the operations we run, all the wood we utilise comes from sustainably managed own or external forests.”

“Even when we use sustainably managed forests for our pulp production, lignin is a parallel product stream of a pulp mill,” he continues. “We are not using any extra new trees to make Lignode, but instead of using lignin for energy, we turn that into Lignode.”

While Stora Enso claims the product has a scalable model for commercial production, it has not disclosed production cost estimates. The same goes for other companies in the space. With batteries featuring anodes derived from lignin – or any other material sourced from trees – not yet produced at industry scale, it remains to be seen how competitive it will be against graphite. 

Although there are still many challenges to be overcome before lignin can be commercially used in batteries, important advances have been made to improve the performance of lignin-based materials. And as interest in lignin – and its ultimate potential in anodes – increases, so does the chances for it to become a feasible alternative to graphite in anode materials.