In next-generation batteries, a substance generated from trees could potentially replace liquid electrolytes.
Researchers are aiming to replace the liquids frequently utilized in today’s lithium ion batteries with solid materials in order to create batteries that deliver more power and run more safely. Now, a team of scientists from Brown University and the University of Maryland has found a new material for solid-state batteries that comes from an odd source: trees.
The scientists demonstrated a solid ion conductor that mixes copper with cellulose nanofibrils, which are polymer tubes generated from wood, in a study published in the journal Nature. The researchers claim that the paper-thin material has a 10 to 100-fold higher ion conductivity than existing polymer ion conductors. It could serve as a solid battery electrolyte or an ion-conducting binder for an all-solid-state battery’s cathode.
“We demonstrated that the normally ion-insulating cellulose offers a faster lithium-ion transport within the polymer chains by incorporating copper with one-dimensional cellulose nanofibrils,” said Liangbing Hu, a professor at the University of Maryland’s Department of Materials Science and Engineering. “We discovered that this ion conductor has the highest ionic conductivity of any solid polymer electrolyte.”
Hu’s lab collaborated with Yue Qi’s lab at Brown University’s School of Engineering on the project.
Electrolytes manufactured from lithium salt mixed in a liquid organic solvent are utilized in today’s lithium-ion batteries, which are used in everything from cellphones to automobiles. The electrolyte’s job is to transport lithium ions between the cathode and anode of a battery. Liquid electrolytes are effective, although they do have certain drawbacks. Dendrites, or small filaments of lithium metal, can form in the electrolyte at high currents, causing short circuits. Liquid electrolytes are also manufactured with flammable and poisonous compounds that can ignite.
Solid electrolytes, which can be constructed from non-flammable materials, have the ability to inhibit dendrite penetration. So far, the majority of solid electrolytes studied have been ceramic materials, which are good at conducting ions but thick, inflexible, and brittle. Cracks and breaks can occur as a result of stresses encountered during manufacture, as well as charging and discharging.
The material used in this study, on the other hand, is thin and flexible, similar to a sheet of paper. Its ion conductivity is comparable to that of ceramics.
Qi and Qisheng Wu, a senior research associate at Brown, used computer simulations of the copper-cellulose material’s tiny structure to figure out why it can conduct ions so well. Copper increases the distance between cellulose polymer chains, which are generally closely packed bundles, according to the modeling study. The increased spacing acts as ion superhighways, allowing lithium ions to pass through relatively unhindered.
“The lithium ions travel in this organic solid electrolyte via methods similar to those seen in inorganic ceramics,” Qi explained, “allowing the record high ion conductivity.” “Using natural materials will lessen the total environmental impact of battery manufacturing.”
In addition to serving as a solid electrolyte, the novel material can also serve as a solid-state battery’s cathode binder. Cathodes must be significantly thicker to match the capacity of anodes. However, such thickness can obstruct ion conduction, lowering efficiency. Thicker cathodes must be enclosed in an ion-conducting binder to function. The researchers demonstrated what they believe to be one of the thickest functional cathodes yet reported using their new material as a binder.