Development of a cellulose-based solid polymer electrolyte

 
Electrolytes play a crucial role in lithium-ion batteries by facilitating the transport of lithium ions between the anode and cathode. These electrolytes can exist in solid, gel, or liquid states, with liquid electrolytes being the most commonly used due to their higher conductivity. However, solid-state electrolytes are gaining attention as a safer alternative with longer lifespans and higher energy densities. Solid polymer electrolytes (SPEs) are particularly promising as they combine the properties of both the separator and the electrolyte. In SPEs, lithium salts are incorporated into a polymeric matrix, which prevents direct contact between the anode and cathode. These materials offer advantages such as flexibility, and thermal and mechanical stability, but their primary limitation is low ionic conductivity. To address this limitation, carboxymethyl cellulose (CMC), a derivate of cellulose, was selected due to its affordability, biocompatibility, and excellent film-forming capabilities. A key challenge in SPE development is mitigating lithium dendrite formation, which necessitates stabilizing the SPE. This study explores the rheological effects of a crosslinker on the stabilization of the CMC-based SPE by associating unpaired anions within its structure. The crosslinker used was citric acid, with concentrations between 0 and 10 wt.% based on total weight of the polymers. Additionally, the impact of a plasticizer, polyvinyl alcohol (PVA), (1:0 and 2:0.5 weight proportion of CMC/PVA), was investigated to enhance the mechanical properties of the SPE. The SPEs were also produced by incorporating varying concentrations of lithium perchlorate (0, 2.5, 5, 10 and 15 wt.%) into the CMC matrix. To better understand the interactions between different formulation variables, rotational rheology with a cone-plate setup was employed to study the stability of these formulations. The rheological characterization provided insights into how increasing lithium perchlorate concentration affects the stability of cellulose-based SPEs. The results indicate that higher lithium salt concentrations lead to formulation instability during production, highlighting the critical role of rheology in the development of solid polymer electrolytes. This work was developed within the scope of the project "NGS - New Generation Storage" [C644936001-00000045], financed by PRR - Plano de Recuperação e Resiliência under the Next Generation EU from the European Union.