Application for the porous structure of cellulose separators: Ionic conduction path in lithium-ion battery

In lithium-ion batteries, separator is an important component as its porous structure is the ionic conduction path. Renewable biomacromolecule cellulose separators have pores that can be modified, and the modification has the potential to affect ion conduction. In this work, functionalized separators based on cellulose are prepared, which can affect the conduction behavior of ions. The cellulose separators TF4030 are firstly Atomic Layer Deposition (ALD) treated to get a silica reinforcement coating layer on the cellulose fibers; then, the ALD layer is further chemically modified to graft specific boron-containing groups -NH-B(OH)2 and form a functional structure on the surface of cellulose fibers. The conduction of lithium-ions is promoted due to the widely distributed electron-deficient boronic groups in the pores of the separator, reflected as the increased lithium-ion transference number of 0.48. Proved by Density Functional Theory (DFT) Calculations, the essential reason for this phenomenon is that the binding of electron-deficient boron groups and anions weakens the conduction of anions as well as the binding of electron-deficient boron groups and solvents influences the desolvation of lithium-ions in electrolytes. As a result, batteries assembled with functionalized cellulose separators have better battery performances, including cycle stability and capacity retention at high current rates.