Researchers are attempting to replace the liquids usually employed in today’s lithium-ion batteries with solid materials in the quest for batteries that produce more power and function more safely. A research team from Brown University and the University of Maryland has created a novel material for use in solid-state batteries that is obtained from an unusual source: trees.
The team displays a solid ion conductor that blends copper with cellulose nanofibrils, polymer tubes produced from wood, in a study published in the journal Nature. According to the researchers, the paper-thin material possesses ion conductivity that is 10 to 100 times greater than conventional polymer ion conductors. It might be utilized as a solid battery electrolyte or as an ion-conducting binder for the cathode of an all-solid-state battery.
We demonstrated that the normally ion-insulating cellulose offers faster lithium-ion transport within the polymer chains by incorporating copper with one-dimensional cellulose nanofibrils, said Liangbing Hu, a professor. We discovered that this ion conductor had the highest ionic conductivity of any solid polymer electrolyte.
Hu’s group collaborated with Yue Qi’s lab at Brown’s School of Engineering.
Electrolytes of today’s lithium-ion batteries, which are extensively utilized in everything from cellphones to automobiles, are manufactured from lithium salt mixed in a liquid organic solvent. The electrolyte’s role is to transmit lithium ions between the cathode and anode of a battery. Liquid electrolytes are effective, although they have certain drawbacks. At high currents, small filaments of lithium metal called dendrites can develop in the electrolyte, causing short circuits. Furthermore, liquid electrolytes are manufactured using flammable and poisonous compounds that might catch fire.
Solid electrolytes can avoid dendrite penetration and may be manufactured from non-flammable materials. The majority of solid electrolytes studied thus far are ceramic materials, which are excellent at conducting ions but are also dense, stiff, and brittle. Stresses during manufacture, as well as charging and discharging, can cause fractures and breakage.
The material used in this study, on the other hand, is thin and flexible, almost like 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 microscopic structure of the copper-cellulose material to figure out why it conducts ions so efficiently. The modeling study indicated that copper improves the distance between cellulose polymer chains, which are typically densely packed bundles. The increased spacing generates ion superhighways through which lithium ions can travel relatively unhindered.
The lithium ions flow in this organic solid electrolyte by processes similar to those seen in inorganic ceramics, resulting in a record high ion conductivity.
Using natural materials will minimize the total environmental effect of battery manufacturing.
In addition to serving as a solid electrolyte, the novel material may also serve as a cathode binder in a solid-state battery. Cathodes must be significantly thicker than anodes to match their capacity. That thickness, however, can impair ion conduction, lowering efficiency. Thicker cathodes must be wrapped in an ion-conducting binder to function. Using their novel material as a binder, the researchers exhibited what they believe to be one of the thickest functioning cathodes yet recorded.
The researchers expect that the new material will be a step toward bringing solid-state battery technology to the mainstream market.