The biopolymer lignin is a major component of wood and gives it its stability. As a by-product of the paper industry, it has previously been burned to generate energy. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) and Friedrich Schiller University Jena – both partners of the Center for Energy and Environmental Chemistry (CEEC) – now have a better idea: In the “ThüNaBsE” (Thuringian sodium-ion battery for scalable energy storage) project, funded by the Free State of Thuringia and the European Social Fund, the partners are developing and evaluating a novel sodium-ion battery with lignin – from the material to the 1 Ah full cell. This is intended to make an important contribution to strengthening independence from critical raw materials and to the transition to cheaper, more sustainable, and safer batteries. The project is supported by an industrial advisory board consisting mainly of regional companies. These include the Thuringian companies Mercer Rosenthal GmbH, Glatt Ingenieurtechnik GmbH, IBU-tec advanced materials AG, and EAS Batteries GmbH, as well as Petrochemical Holding GmbH from Vienna. Another goal of the project is to promote young researchers in Thuringia. For this reason, a number of young scientists who are pursuing doctorates in the fields of energy and battery research are involved in “ThüNaBsE.”

Lignin consists mainly of hydrocarbon building blocks that can be used in chemistry, for example as electrode material for batteries. The project aims to use the bio-based raw material for the negative electrode. "We want to eliminate critical metals such as lithium, cobalt, and nickel from the value chain in batteries. We also want to keep the fluorine content in electrodes and electrolytes as low as possible and test to what extent it can be completely avoided. However, the core of the project is the processing of locally available, high-quality lignin into high-performance electrodes in our sodium-ion batteries," says Dr. Lukas Medenbach, a scientist at Fraunhofer IKTS in Arnstadt, the gateway to the Thuringian Forest.

The lignin is provided by Mercer Rosenthal GmbH and thermally converted into carbon in the absence of air, which is then further processed into electrodes. "Our project partners from the Institute for Technical Chemistry and Environmental Chemistry at Friedrich Schiller University in Jena, led by Prof. Martin Oschatz, use thermal processes to convert the lignin into what is known as hard carbon. The structure of this hard carbon is very well suited for storing sodium ions in a reversible manner. Hard carbon offers high electrochemical performance, good cycle stability, and low acquisition costs, especially when it is obtained from sustainable raw materials," explains Dr. Medenbach's colleague Dr. Cornelius Dirksen. Berlin blue analogues, i.e., non-toxic iron compounds, are to be used as the material for the positive electrode. The substance, which was already used as a pigment around 200 years ago, is characterized by good raw material availability, environmental compatibility, and sodium ion storage properties.

Initial small-scale demonstration cells are currently being built and tested at the Fraunhofer IKTS battery test center in Arnstadt, at Fraunhofer IKTS in Hermsdorf, and at Friedrich Schiller University in Jena. The laboratory work is accompanied by realistic, multiphysical simulations. The results are promising: “The laboratory cell has not yet degraded significantly after 100 charge and discharge cycles. The goal is to demonstrate 200 charge and discharge cycles for the 1 Ah full cell by the end of the project,” says Dr. Medenbach.

Once fully developed, the battery could be used as stationary or mobile storage where fast charging times are not required. The lignin-based sodium-ion batteries are suitable, for example, for mobile applications with lower power requirements. Possible applications include microcars or industrial trucks such as forklifts. After the project is completed, the technology will be further scaled up and, with the involvement of an even larger consortium, the path to the next technology readiness levels will be pursued.