With the ever-growing demand for electrifying everything, we need more sustainable batteries. Li-ion devices are cost-effective but rely on lithium, graphite, and other materials, whose sourcing has significant environmental and social impacts. One potential solution is being developed where wood is used to replace these materials with a bio-based alternative. So, would wood work or is it just… deadwood…?

Are Li-ion batteries good enough?

I’ve said it before and I’ll say it again, but it feels like there’s some new, crazy energy storage breakthrough happening every week. This one might start setting off alarm bells for you when you hear that some energy storage developers are incorporating wood by-products into their battery design. It raises a lot of questions. Is that really sustainable? How well does it work? And, probably the biggest one … why? To understand the value of bio-based batteries, we should first look at why li-ion batteries are not as good as you might think as a long term solution. It will help to illustrate why these bio-based batteries may be a good indicator of where battery technology is heading.

Lithium-ion batteries are ubiquitous in today’s world. You can find them in your smartphones, cars, or even in large-scale energy storage systems. Compared to the old-fashioned lead-acid batteries, Li-ion devices recharge over 4x faster, last 10x longer1, and store up to 10x more energy per unit of volume.2 You can probably see why our electronic devices have become smaller. Also, you can now drive your EV for a long time without stopping and waste less time when charging it up.

There’s no doubt about it, lithium-ion devices make our high-tech life much easier and have opened doors for new technologies. But lithium-ion batteries are…charged…with sustainability violations. For instance, you typically get lithium by evaporating water out of massive ponds containing a salt solution, a.k.a. brine. For each ton of lithium you recover, you lose around 500,000 gallons of water.3 To put that in perspective, that would be enough to make batteries for only 0.001% of all the cellphones in the world.4 In Salar de Atacama, a salt flat hosting ca. 40% of lithium global reserves5, extraction drinks up 65% of the Chilean region’s water. That’s not the worst of it though. Refining it into battery-grade lithium carbonate contaminates the few drops of leftover water with toxic metals such as antimony and arsenic.6 Which means even less usable water for indigenous people. On top of that, the manufacture of battery-grade lithium accounts for 40% of the device’s carbon emissions.7

Lithium is not the only high-carbon ingredient of traditional batteries. As of today, the anode of lithium-ion batteries contains graphite, which is a carbon-based and carbon-intensive material. In a recent study,8 Minviro assessed the global warming impact of sourcing graphite in regions like inner Mongolia, who rely on coal-based grids. The environmental consultancy’s estimate was up to 1,000% higher compared to previous reports. Apart from releasing CO2 in the atmosphere, graphite mining and refining contaminates drinking water and crops with dust in China9, where the Chinese company, BTR, takes around 75% of natural graphite global demand.10

Aside from an unsustainable supply chain, lithium-ion batteries might also imply safety risks. Graphite-based anodes don’t like to be in the cold. To be more specific, the charge they can hold drops quickly as the temperature goes below the freezing point. If you’ve ever driven an electric car in the cold weather, like I do, you may know what I’m talking about. Previous research identified the flat orientation of graphite in the anode as the culprit of lithium-ion batteries’ rapid discharge at sub-freezing temperatures.11 High temperatures aren’t any better because they could potentially lead to the evaporation of the flammable compounds contained in the electrolyte organic solution. As a result of this thermal runaway, the battery could get damaged or catch fire. Not to exaggerate the reports of lithium-ion batteries, but it does happen.12 For instance, the batteries in the world’s largest energy storage caught fire twice in 5 months.13

That’s where the wood battery comes into the picture. And yes, I know … wood can burn too, but these might be more sustainable and less risky approaches to pursue.

Wooden batteries are electric!

As mentioned earlier, graphite is not the optimal ingredient for a battery anode. Which is why the Finnish company Stora Enso is providing the Swedish Northvolt battery manufacturer with a more sustainable raw material.14 This is called Lignode®15, as it’s made of lignin, a carbon-rich polymer which makes up 25% of wood’s structure16. Second only to cellulose, lignin is one of the most abundant renewable carbon sources on Earth.17 Stora Enso is sourcing lignin from sustainably grown forests in Nordic countries. The result of this joint effort is a 100% EU-based growable battery supply chain, where Northvolt will take care of cell design, battery assembly, and scale-up. Swapping graphite with a local bio-carbon in their battery anode, the company is aiming to reduce its production cost and carbon emissions.

That sounds great, right? But how do you turn trees into a battery anode component?

You probably know that wood is the standard feedstock for producing paper. What you might not know is that lignin is one of papermaking’s by-products. Typically, lignin ends up in an incinerator to generate energy. Instead, Stora Enso is upcycling it into a hard-carbon powder, a.k.a. char. This is a crucial step as it turns an insulator like lignin into a conductor like carbon. The charred lignin is then pressed into an electrode sheet that can be assembled with the other cell components.

But is it green? Will it mean more forests being cut down? Thanks to their circular approach, the biomaterials supplier won’t need to cut down additional trees. Apart from being more climate-friendly than graphite, the manufacture of a lignin-based anode would also be easier to scale. Just think that European producers could tap into the 17 million tonnes of lignin generated annually as a by-product of the paper industry, which are currently not being used.18 In 2021, the Finnish company launched a pilot plant to start producing their Lignode®.19 They strategically built it on the same site as their existing biorefinery, which is extracting 50,000 tonnes of lignin from pulp every year. Other than electrical mobility, their lignin-based anode is suitable for consumer electronics and grid-scale stationary energy storage.20

As claimed by Stora Enso, Lignode® would also allow faster charging compared to graphite-based anodes. As reported in their white paper21, their material has a more disordered and open structure compared to graphite, which is arranged in regularly spaced layers. This framework is more accessible by lithium ions, which speeds up the charging process.22 While they haven’t provided any evidence for that yet, their claim might be solid as wood. Previous studies showed that graphite interacts with the electrolyte solution during the charging process. This leads to the formation of a solid layer over the anode surface which slows down the movement of lithium ions, which limits the charging rate of the battery.23

For this reason, researchers have turned to bio-based carbon sources to replace graphite in the battery anode. Last year, a Japanese group harnessed a biopolymer to make a battery anode and achieved shorter charging times compared to those obtained when using graphite.24 Stora Enso also touts that Lignode® structure improves battery performance at temperatures below freezing. Once again, this seems to be plausible. As mentioned earlier, the poor low-temperature endurance of lithium-ion batteries was associated with the graphite leveled surface. Recently, Chinese scientists boosted the durability of a lithium-ion device at temperatures as low as -31°F (-35°C) by replacing its graphitic anode with one made of carbon nanospheres having a bumpy surface.25

Stora Enso isn’t alone here.26 Rather than just replacing the graphite-made anode, Ligna Energy has come up with an organic recipe for the whole battery. With lignin, water, and natural polymers as the main ingredients, their formula has a bio-based content of up to ca. 80%.27 Just like Stora Enso, this Swedish start-up is recovering lignin from paper manufacturing sidestreams. They then mix lignin with carbon through a process called dry-ball milling.28 The result of this organic cocktail is a conducting nanocomposite that’s fed to a printing press to make an anode sheet. But Ligna Energy introduced another key innovation, an electrolyte solution made of water and potassium polyacrylate,29 which is a superabsorbent polymer used for baby diapers.30 Now…I don’t know about you, but I’ve never heard of babies catching fire because of a dirty nappy, so I guess it’s safe to assume that potassium polyacrylate-based electrolytes aren’t flammable.

I know that all this sounds too good to be true (dirty diapers aside), but when presenting their creation at COP26 in 2021, Ligna Energy won the Startup 4 Climate innovation award.31 This is one of Europe’s biggest energy innovation challenges32, where green tech, energy, and climate action experts shortlist the best ideas for promoting a transition to clean power.

While Stora Enso and Ligna Energy are leading the way to try and bring wood-based batteries to market, a team of Swiss researchers printed a 100% biodegradable battery on a piece of paper.33 Wait, what? How does it even work? Scientists formulated two inks, one containing graphite for the air cathode, and a zinc-based one for the anode. They then stencil-printed one ink on the front and the other on the back of the paper strip that acted as a separator. To make this metal-air battery work, you just need to add a pinch of table salt and a couple of water drops to the paper sheet. When doing that, you create the electrolyte solution that triggers redox reactions and allows electrons to travel between the two electrodes. In their lab experiment, researchers harnessed a two-cell battery to power an LCD alarm clock.34 …typical Swiss. Anyway, that’s still just a lab experiment, but a cool example to show what’s possible.

All these inventions are electrifying, but will they perform well enough to switch off li-ion batteries for good? A low energy density might restrict their use in some applications, but we’ll get into that in a minute…

Shall we just touch wood and hope it’ll work?

Clearly, wet bio-waste sounds like a way safer and greener battery raw material compared to lithium and graphite. But are these bio-batteries worth a shot from an economic standpoint? None of the creators have disclosed any comprehensive estimates yet. However, based on one of Ligna Energy’s scientific advisors, all the materials used in their battery cost less than 1 USD$/kg. If we consider raw lignin, this quote seems to be correct. According to some estimates, recovering lignin through ultrafiltration of pulp would only cost 0.062 USD$/kg.35 However, this figure doesn’t factor in the cost of upcycling the recovered lignin into a material suitable for battery anodes, like Stora Enso’s Lignode® for instance. Just for comparison, you would need to spend 2 USD$ for making 1 Kg of synthetic battery-grade graphite.36

As any other technology, scaling up will lower production cost. The question is, when will these technologies get to the market? Obviously, it’s hard to say for printable batteries as the ink isn’t even dry … it’s still in the lab. Though, the lead researcher hopes to turn them into real products within 5 years.37

Seems optimistic to me, but how about the other two solutions? As it stands, Stora Enso Lignode® is ahead of the bio-charging race. We’ve already mentioned that the Finnish company trial line has been churning out lignin-based anode over the last year. Last October, the company went beyond that by signing a Letter of Intent with Beyonder, a Norwegian energy storage developer.38 As part of this agreement, the pair committed to optimize Lignode® properties and fast-track its scale-up. On top of that, Stora Enso can also rely on Northvolt’s existing gigafactory infrastructure in Sweden.39 Back in 2017, Stora Enso’s head of innovation predicted that their material might reach commercial production by 2027.40 And they’re still on that track. Based on their last year forecast, the company pilot plant could reach full scale by 2025.41 As for Ligna Energy, last March the start-up raised ~$1.4M.42 While there are still no clear timelines on when their grid-scale storage application will turn into a real-world use case, they’ve just released a rechargeable unit for IoT devices such as temperature and moisture sensors used in smart buildings.43

But how do they stack up against traditional devices right now? In terms of energy density, Ligna Energy battery would be able to store only 40 Wh per kg.44 When you compare it to lithium-ion batteries, that’s up to nearly 7x lower.45 To by-pass this obstacle, the start-up is focusing on stationary applications, where heavy weight is not an issue. While Stora Enso hasn’t revealed an exact figure yet, they expect a lithium-ion battery featuring their Lignode® to be less energy dense than the benchmark.46 Other than packing as much energy as possible in smaller and lighter containers, we should extend our batteries’ lifespan. But what does that mean in real life? For example, a lithium-ion battery in a typical electric car retains 80% of its charging capacity after 2,000 cycles.47 Ligna Energy heralds that their battery could push this to 5,000 cycles.48 Just like for energy density, Stora Enso hasn’t still provided a specific value but they claim that swapping the graphite anode with their Lignode® will increase lithium-ion batteries’ cycling stability.49

So obviously, with the dramatically lower energy density, this isn’t a solution for electric vehicles, but that doesn’t matter. Reusing existing waste streams for a material supply has big potential economic upsides. Just as with all of the technologies I cover on the channel, there’s no silver bullet. It’s all about picking the right tool for the right job. If these batteries are cheaper to produce and buy, they’ll find a market … most likely in stationary energy storage or small IoT style devices at first.

Using bio-based materials instead of graphite and lithium would certainly improve the sustainability and safety of our batteries. It can also help give more countries and states a supply chain they can control themselves. Stora Enso and Ligna Energy are on the right track for bringing their products to the market. However, let’s try to see…the wood for the trees…some of the claims made by these technologies are only on paper and developers will need time to iron the wooden kinks out. Regardless of how this develops, it’s this type of research and thinking that shows us where battery and energy storage are potentially heading.

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