A study by the EHU-University of the Basque Country shows how biomass can be used as an alternative in commercial batteries, thus making them more sustainable

Dr Nekane Nieto of the EHU's Materials and Solid-State Group has proven that batteries made from biomass materials not only store sufficient energy, but can also withstand up to 1,000 charge and discharge cycles. This discovery paves the way for more environmentally friendly alternatives to traditional batteries, which are more expensive and pollute more.

Over the past few decades, sodium-ion batteries have kindled considerable interest owing to the abundance, low cost and widespread availability of sodium in the Earth’s crust. So sodium-ion batteries are a more cost-effective alternative to lithium-ion batteries (which are widely used, although they have a significant environmental impact) and are less reliant on mineral reserves. However, sodium-ion batteries pose significant challenges, such as low energy density and insufficient charge-discharge cycles.

“Almost all the batteries used in both electric vehicles and smaller devices are lithium-ion batteries. The lithium used in these batteries, as well as other materials needed to manufacture them, such as cobalt, nickel and manganese, are elements on the European Union’s list of critical materials, and efforts need to be made to reduce their use,” explained Dr Nekane Nieto. The EHU’s Materials and Solid-State Group is aiming to develop sodium-ion batteries using biomass-based materials.

Batteries consist of a cathode (the positive terminal), an anode (the negative terminal) and an electrolyte, which allows charges to move from one terminal to the other, thereby generating an electric current. The EHU group is conducting research to develop anodes based on carbons obtained from waste biomass collected in the ACBC (Autonomous Community of the Basque Country), in other words, by turning waste into materials that can be used in these batteries. “Our idea is to produce batteries that are as sustainable as possible,” said Nieto.

Button cell batteries

In this study, the team tested various types of biomass, such as coffee grounds, plant stems, shrubbery comprising invasive species, grape seeds and skins, maize cobs, and even compost made from biowaste. “But out of all of them, it was the carbons produced from sunflower seed shells that yielded the best results,” Nieto pointed out. After optimizing this anode made from sunflower seed shells, “we paired it with several different cathodes in rechargeable button-cell batteries, which contain vanadium, iron and/or titanium in their composition, elements that are not as critical and are used in smaller quantities in these materials”, she added.

With all this in mind, the group carried out a life-cycle analysis to determine which anode/cathode combination offered the best battery performance and the lowest environmental impact. “We achieved some very competitive results compared with the ones described so far. These are rechargeable batteries made from sunflower seed shells that are capable of storing a sufficient amount of energy and withstanding up to 1,000 charge and discharge cycles, with the most environmentally friendly cathode chemistry selected for each application,” said the researcher.

Nieto stressed the importance of having manufactured these batteries “using biomass materials and components that are not on the list of critical materials”. “Although it is true,” she admitted, “that our batteries are not yet competitive compared with lithium-ion ones, but can be used as a complementary system or in small devices”. They are currently working to develop larger batteries.

Nieto stressed that “we shouldn’t always focus on batteries that are already on the market. It is always possible to explore a range of approaches and improve sustainability by using waste that is currently not put to any use. It is important to bear in mind that we need to look for alternatives to lithium-ion batteries, and that, going forward, industry may be able to use different types of waste to manufacture batteries, depending on their intended application”.