Wood, the insulator we all know, could be used to make batteries.
Swedish battery manufacturer Northvolt announced some time ago that it had signed a joint development agreement with Finnish forestry company Stora Enso to manufacture batteries using lignin-based hard carbon, sourced from renewable wood from Nordic forests.
The resulting batteries will be 100% recyclable.
Northvolt, the battery manufacturer, is a new energy company founded in 2016 by the Volkswagen Group, Siemens and other giants. It has not been around for long but has already become a star company in Europe.
In March this year, Northvolt officially announced that it would build a new super battery factory in Holstein, northern Germany, making it first outside Sweden, and two months later, Northvolt started shipping, becoming the first European company to supply power cells to car manufacturers.
This is clearly a job grab with Ningde Times, Panasonic and LG New Energy. Northvolt is reportedly planning to go public within two years and is currently valued at $12 billion. Northvolt aims to have a 25% market share in Europe by 2030, with an annual capacity of 150GWh or more deployed in Europe.
Northvolt has a greater focus on renewable energy and lower carbon emissions than traditional battery manufacturers. The partner, Stora Enso, is an integrated forest products company with a focus on forest products, paper and packaging paper.
The partnership, which aims to reduce the carbon footprint and production costs, has generated a lot of interest since it was announced.
01 、How to make batteries from wood?
New energy vehicles have suffered from high prices for raw materials for a long time.
At present, the main metal elements needed to make batteries in the electric vehicle market are lithium, cobalt and nickel. These metal elements on the one hand in the earth’s crust in limited resources, on the other hand, the mining and production cycle of these minerals is long. Combined with international factors, the prices of raw materials for batteries remain high.
This has led to tensions in the battery supply chain and rising prices for new vehicles, as in the case of the Zero T03 and smart Elite 1, which have just announced price increases due to high raw material prices.
Finding new renewable, resourceful and environmentally friendly alternatives has become a top priority for battery manufacturers.
Wood, a renewable energy source, has emerged as the best choice, and wood is the main source of lignin for the production of batteries.
Lignin is a complex group of organic polymers that are widely found in the cells of lignified plants. It is mainly located in the cell-to-cell space, the intercellular layer, which is also the site of the highest concentration of cell walls.
Lignin is particularly important in the formation of the cell wall, and its deposition – when lignified – increases the thickness of the ducts, improves their stiffness and toughness, and maintains the smooth transport of nutrient material in the ducts.
In addition, lignin enhances the mechanical support or compressive strength of the cells and promotes the formation of mechanical tissue. Lignin also enhances the adhesion of cells and is a natural and powerful adhesive.
Lignin is also found in the by-products of the paper industry. Previously, 95% of lignin was discharged directly into rivers as waste material in the form of ‘black liquor’ or concentrated and burned.
In recent years, however, several studies have shown that lignin can be used in the preparation of batteries.
Scientists in Poland and Sweden were the first to notice the oxidation of lignin in plants, combining it with a substance called polypyrrole to create multilayer polymer electrodes. The charge density of such electrodes can be comparable to or better than that of current lithium-ion batteries, up to 70-90 mAh/g.
As lignin is a by-product of the paper industry, it is cheap and widely available. Porous lignin-based carbon, prepared by simple and gentle chemical activation, has become a research hotspot in the fields of environmental purification, electrocatalysis and energy storage, especially as anode material for lithium-ion batteries.
02, What else can wood provide for batteries?
In fact, in the last decade, many scholars have applied lignin to battery preparation-related research.
For example, the use of renewable resources and paper industry waste sodium lignosulfonate – lignin modified by sulphonation into lignosulphonate – as a dopant and template, and finally the chemical oxidation of polypyrrole/graphene layered nanocomposites with a laminar structure. These composites can be assembled into supercapacitors.
Cellulose nanofibres from wood are also a good raw material for making solid electrolytes.
The electrolytes currently used in lithium batteries are commonly used because they contain volatile liquids that pose a risk of fire and may promote the formation of dendrites, which can affect the proper performance of the battery. Although some researchers have used solid electrolytes made from ceramic materials, the brittle nature of ceramic materials does not stand up well to the stresses of battery charging and discharging.
Last year, researchers at Brown University and the University of Maryland, USA, found an alternative from cellulose nanofibres in wood.
By combining copper with cellulose nanofibres, it was possible to demonstrate that the normally ion-insulating cellulose provided faster lithium ion transport in the polymer chain, the study said.
And polymer tubes made of wood combined with copper form a solid ionic conductor that is 10-100 times more conductive than other polymeric ionic conductors.
The researchers say the material is electrochemically stable and can accommodate lithium metal anodes and high-voltage cathodes, and can also be used as a binder to encapsulate ultra-thick cathodes in high-density batteries.
In addition, lignin can be used to prepare charcoal materials.
With their good electrical conductivity, charcoal materials can be used as electrode active materials in electrochemical applications such as fuel cells and have promising applications in the field of energy storage and conversion.
Industrial lignin is a low-cost and abundant source, as well as a high carbon content, making it a high-quality raw material for the preparation of carbon materials. 2021, researchers at Imperial College London, have prepared carbon from industrial waste by-product lignin to enable sodium-ion batteries to replace lithium-ion batteries.
The regulatory mechanism and natural structure of the grain pore membrane transport in trees has also given researchers innovative ideas.
In 2021, a research team from the Institute of Wood Industry, Chinese Academy of Forestry, in collaboration with several universities, achieved the first precise peeling of the thin polymeric layer (lamella) from the secondary cell wall of wood to optimise the performance of lithium metal batteries.
The separated lamella can be used as a solid electrolyte interface film to solve the problem of lithium-ion concentration regulation, which breaks the technical bottleneck limiting the life of lithium metal batteries and increasing the battery life by more than 75%.
- How far away are wooden batteries from being promoted?
Compared to traditional battery materials, the biggest advantage of wooden batteries is environmental protection.
Traditional button batteries and ordinary dry cell batteries contain mercury, and when discarded in the natural environment, the mercury will slowly seep into the groundwater and enter the human body through crops, damaging the internal organs of people.
One small button battery discarded in nature can contaminate 600,000 litres of water, the equivalent of a person’s lifetime water consumption. Rechargeable batteries also contain the harmful heavy metal cadmium, which leaches out in nature, passes through the land and water streams, and eventually harms the human body.
Wooden batteries, on the other hand, are made from raw materials that do not require the use of rare metals, which are in short supply. Organic fibres containing lignin are pure green products, non-toxic, non-hazardous and non-polluting for the natural environment.
Lignin is widely available and inexpensive. Previously the main source of lignin was the wastewater produced by the pulp and paper industry, hence the name paper black.
Pulp and paper production separates about 140 million tonnes of cellulose from plants every year, while about 50 million tonnes of lignin are obtained as a by-product. However, no more than 10% of the industrial lignin is effectively used. The remaining neglected industrial lignin is a huge “treasure” to be exploited.
Since 2015, the Stora Enso plant has reportedly been producing lignin industrially with an annual capacity of 50,000 tonnes, making Stora Enso the world’s largest producer of kraft lignin.
And the industrial roll-out of wood-based batteries is not too far away.
In 2021, Nippon Paper is collaborating with Tohoku University to create an accumulator using 3-nanometre diameter “cellulose nanofibres (CNF)” extracted from paper pulp, processed into a thin film and sandwiched by aluminium foil to form an electrode.
Nippon Paper says it plans to produce a prototype battery for small indoor drones by 2023, with the aim of using it in smartphones and small home appliances by 2030 and is also considering using it in pure electric vehicles.
As production technology advances and the performance of wooden batteries is optimised and improved, it will be possible to replace lithium-ion batteries with more environmentally friendly wooden batteries.
