Tailoring amino-functionalized cellulose separators for improved lithium-ion battery performance

Abstract

This study aims to enhance cellulose separators for energy storage, focusing on achieving high security and superior electrolyte wetting properties. Bacterial cellulose (BC) separators were initially prepared via vacuum filtration. Subsequently, carboxymethyl cellulose (CMC) underwent amino-functionalization by successfully cross-linking polyethyleneimine (PEI) using glutaraldehyde. The amino-functionalized CMC was then composited onto the BC separator. This composite separator demonstrated excellent thermal stability at 200 °C and favorable electrolyte wetting. The amino groups in PEI enhanced Li+ migration by forming hydrogen bonds with PF6− in the electrolyte. Additionally, molecular-level hydrogen bonding between amino groups on PEI and carboxyl/hydroxyl groups in CMC regulated the separator's porosity. The abundant carboxyl groups in CMC facilitated Li+ transfer, notably boosting the lithium-ion battery's electrochemical performance. After 90 charge and discharge cycles, the discharge capacity of the battery assembled with BC/CMC-PEI composite separator is 132.8 mAh/g, which is 25.1 % higher than the 106.1 mAh/g of the battery assembled with traditional PP separator. At a current density of 2C, the minimum discharge capacity of the battery assembled with the composite separator is 71.1 mAh/g, while the minimum discharge capacity of the battery assembled with the PP separator is 53.6 mAh/g. This approach using functional group modification provides a promising approach to improving the performance of lithium-ion batteries.